|HAI LALA MADIU ANNAT

US009784995B2

(12) United States Patent (10) Patent No.: US 9 ,784,995 B2

Hauenschild et al. (45) Date of Patent: Oct. 10, 2017
(54) MULTI- SEGMENT RING MODULATOR 2005/0206479 Al * 9/2005 Nguyen ....... ...…... H03H3333/ 0072
/186
(71) Applicant: RANOVUS INC ., Ottawa (CA ) 2007/ 0052498 A1 * 3/ 2007 Pan ............ HO3H 3 /0077
@ 333 / 186
(72 ) Inventors: Juergen Hauenschild , Bochum (DE ); 2011/0058765 Al 3/ 2011 Xu
David John Nicholson , Ottawa (CA ); 2013/0251300 A1* 9/2013 Suzuki .. ... ... G02F 1/3132
Dylan Logan , Ottawa (CA ) 385/ 2
2014 /0321848 A1* 10 /2014 Sekiguchi ............ GO2F 1/0123
398 /38
(73 ) Assignee: RANOVUS INC ., Ottawa, Ontario 2015/0261061 Al* 9/2015 Akiyama ................ GO2F 1/225
(CA ) 385 /2
(Continued )
Notice: Subject to any disclaimer, the term of this
(* ) Ž
patent is extended or adjusted under 35
U .S .C . 154 (b ) by 0 days. OTHER PUBLICATIONS
(21) Appl. No.: 14 /976 , 290 Hai, Mohammed Shafiqul, et al., " A Low -voltage PAM -4 SOI
Ring-based Modulator” , OFC2015 , TuB3.3 .,pp. 194 - 195 , IEEE ,
(22 ) Filed : Dec . 21, 2015 Published Oct. 12 , 2014 .
(Continued )
(65 ) Prior Publication Data
US 2017 /0176779 A1 Jun . 22 , 2017 Primary Examiner — Tina Wong
(74 ) Attorney, Agent, or Firm — Perry + Currier, Inc .
(51 ) Int. Cl.
GO2F 1/035 ( 2006 .01) (57 ) ABSTRACT
GO2F 1 /01 ( 2006 . 01) A device that includes a multi -segment ring modulator is
(52 ) U . S . CI. provided . In particular, the device comprises: an optical
CPC ............ G02F 1/0121 (2013 .01); GO2F 1/011 waveguide; an optical ring modulator optically coupled to
(2013 .01); GO2F 1/ 0147 (2013 .01 ); GO2F the optical waveguide ; a first voltage control device along a
2201/06 (2013 .01) first segment of the optical ring modulator ; a second voltage
(58 ) Field of Classification Search control device along a second segment of the optical ring
None modulator ; a first driver device configured to control the first
See application file for complete search history. voltage control device to a first voltage and a second voltage ;
and , a second driver device configured to control the second
(56 ) References Cited voltage control device to a third voltage and a fourth voltage .
In particular implementations, a ratio of a length of the first
U . S. PATENT DOCUMENTS segment to a length of the second segment can be one or
5,475,704 A * 12/1995 Lomashevich .... GO2B 6/37212004 more of about 2 : 1 and greater than 1 : 1 , and non -linear driver
/ 21 devices can be used .
7 ,733 ,558 B2 * 6 / 2010 Arai ................... GO2B 26 / 0841
359 / 198 .1 12 Claims, 4 Drawing Sheets

Device
101

185

Laser
144
103 105
Driver Driver
Device V3 Device
111 - 1 110
-2 V4 111-2

Controller V1= V3
V2 = V4
120 V1 # V2

Interface Memory
124 122
126
 US 9 , 784 ,995 B2
Page 2

(56 ) References Cited

U . S . PATENT DOCUMENTS
2015/0316794 A1* 11/2015 Hayakawa ........... H04B 10/501
385 /2
2016 /0103382 A1 4 /2016 Liboiron -Ladouceur et al.
2016 /0156149 A1 * 6 / 2016 Takabayashi ........... HO1S 5 /142
372 /6
OTHER PUBLICATIONS
Karimelahi, Samira, et al., “ PAM -N signaling by coupling modu
lation in a ring resonator” , Optics Letters/, vol. 40 , No. 3 , Feb . 1,
2015, pp . 332 -335 . Published Feb . 1 , 2015 .
Wu, Xiaotie , et al., “ A 20Gb / s NRZ / PAM - 4 IV Transmitter in 40nm
CMOS Driving a Si- Photonic Modulator in 0 . 13um CMOS” ,
ISSCC 2013 , Session 7, Optical Transceivers and Silicon Photonics,
7 .7 , 2013 IEEE International Solid - State Circuits Conference . Pub
lished Feb . 17 , 2013 .
Extended European Search Report dated May 4 , 2017 for European
Patent Application No. 16205882.0 .
* cited by examiner
U.S.Pater
atent Oct. 10 , 2017 Sheet 1 of 4 US 9 ,784 ,995 B2

195

VDrive Dev114ice
V4
111
2
-

wy

un
site
p Aft aruh
Device 101
found M

inistry Juni
Arse

DriverDevice 1
-
111 . . . . . . . . . .
V3V4V1
=V2
V1= V2
+
Memory 122 126

Contrle 120

103 Interface 124

185
Laser
Laser 144 1
.
Fig
 atent Oct. 10 , 2017 Sheet 2 of 4 US 9,784,995 B2

one
The + A

Input wavelength .

: .

.
.
.

11 1
.

-
. --"--
.

I: - *
.
..
Care.com.ai
.
....
3 . . . . . . . . - v . . . . - . . -

- ; .
[dBm]POpotwicearl 6 10 - - - - -- -- -Romero 6-
---10
'
one .
on
. . . . . . . . v . . . .. . . . . ... . . ..
- 100 Lil/ . . . . . .. . . . . . . .. . . . ..

t
ap
HiiVini
. . . . . .
.. . ... ... . . . .. .... .

8 and - 00 - V1,V3
s
p ;. . . . . . . . . . . . .. . . . . . .
- 01 - - V1,V4
- - 10 . . V2,V3
-54 ... ......... .. . . . . .. . . . . . . . . . . . . . . . . . . . v . . . . . . . .. - :11. - V2 . 14
1544 . 1 1544 .2 1544. 3 1544 . 4 1544 .5
Fig. 2 Wavelength [nm ]
 atent Oct. 10 , 2017 Sheet 3 of 4 US 9 ,784 ,995 B2

395

DriveV3rDevice
V4
311
-
2 . . . . . . . . . . . . .

antin
AUME
Attes

305 AswathyAUX
Device 301 sh

ne scayaAnh| ANA

Driver Device 1
-
311 V1
V4
#
V3=V1Control"V2V4er
7 Memory
322 326

320
303 Interface 324

385
Laser 344 3
.
Fig
U .S. Patent atent Oct. 10 , 2017 Sheet 4 of 4 US 9 ,784 ,995 B2

495

DriverDevice V6
411
-
3
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

V4
V3 DriverDevice 2
-
411

3
-
410
2
-
410
et

iste
405 mu

Device
.

47
401 be

f
*
**

Mightyuture . . . . . . . . . . . . . . . . .

DriverDevice 1
-
411
V5
=
V3
V1
420440
V2
=
V4
V6V1V2
# -

-
Memory422 426

Contrle Interface
-

403 424

485
LSoiugrhcte 444 4
.
Fig
 US 9,784 ,995 B2
MULTI- SEGMENT RING MODULATOR PAM -8 modulation . In other words, for each additional
voltage control device added along an additional segment of
The specification relates generally to telecommunication the optical ring modulator, an additional bit can be added to
devices , and specifically to a device that includes a multi the modulation scheme. Use of such devices can hence
segment ring modulator . 5 generally eliminate a need for a PAM encoder in optical
transmission devices in optical communication systems.
BACKGROUND In this specification , elements may be described as “ con
Modulating optical signals for PAM -N (pulse amplitude for ” suchto functions
figured ” perform one or more functions or " configured
. In general, an element that is configured
modulation to “ N ” levels) is generally performed using 10 toto perform or configured for performing a function is
se
Mach -Zehnder (MZ) modulators with multi-segment phase enabled to perform the function ,or is suitable for performing
shifters , or MZ -ring hybrid modulators . Such MZ modula the function , or is adapted to perform the function , or is
tors are large (about 1 mm ) compared to other optical operable to perform the function , or is otherwise capable of
devices in high density photonic integrated circuits (PICs ),
resulting in PICs of lower density. While
While MZMZ assisted ring 1515 performing
assisted ring P the function .
modulators are about an order ofmagnitude smaller (phase tionFurthermorecertain
, as will become apparent, in this specifica
elements may be described as connected physi
shifter length of 340 um ), they are still large compared to
other optical device in high density PICs . While some MZ cally, electronically, or any combination thereof, according
coupled ring modulator designs have been demonstrated to context. In general, components that are electrically
they have relatively slow speeds (e . g . about 120 Mb / s. 20 connected are configured to communicate (that is, they are
Alternatively, single electrode modulators can be driven to capable of communicating) by way of electric signals .
different voltage levels using linear drivers,but these drivers According to context, two components that are physically
require high power dissipation to achieve linear perfor- coupled and/or physically connected may behave as a single
mance . element. In some cases, physically connected elements may
25 be integrally formed , e .g ., part of a single - piece article that
SUMMARY may share structures and materials . In other cases, physi
cally connected elements may comprise discrete compo
The present specification provides a device that includes nents that may be fastened together in any fashion . Physical
an optical ring modulator on an optical waveguide (and/or
optical bus ) with at least two voltage control devices ( each 30 connections
components
may also include a combination of discrete
fastened together, and components fashioned as
of which can include, but is not limited to , electrode pairs )
along respective segments of the optical ring modulator, a single It is
piece .
understood that for the purpose of this specification ,
which are independently controlled using respective driver
devices. For example , each voltage control device can of X , Y and Z ” can beoneconstrued
language of “ at least of X , Y, and Z ” and “ one or more
comprise a diode, which can be driven in reverse bias so it 35 011 combination of two or moreas items X only , Y only , Z only,
acts as a capacitor to generate an electrical field across the orXYZany, XY X , Y , and Z (e . g .,
, YZ, XZ , and the like ). Similar logic can be
ring and thereby change respective optical properties of a
respective segment, which in turn shifts the resonance applied for two or more items in any occurrence of at least
properties of the optical ring modulator. Each voltage con - one . . . ” and “ one or more . . . ” language .
trol device is controlled by a respective driver device to two 40 An aspect of the specification provides a device compris
different voltage values. The resonance shift provided by ing : an optical waveguide ; an optical ring modulator opti
each segment is generally proportional to its length . A length cally coupled to the optical waveguide ; a first voltage
of a segment of first voltage control device can be longer control device along a first segment of the optical ring
than a segment of a second voltage control device (e. g . in a modulator; a second voltage control device along a second
ratio of about 2 : 1 , which can be adjusted to adjust the degree 45 segment of the optical ring modulator ; a first driver device
of resonance shift; either way, the ratio of the lengths of the configured to control the first voltage control device to a first
segments of the two voltage control devices is greater than voltage and a second voltage ; and , a second driver device
1 : 1 ); in these implementations, the respective two voltages configured to control the second voltage control device to a
to which each voltage control device are driven can be the third voltage and a fourth voltage .
same ( e . g . each voltage control device can be driven with 50 ratio of the first segment, where the first voltage control
identical voltage levels ), and hence non -linear driver devices device is located , to the second segment, where the second
can be used . However , when the lengths are about the same, voltage control device is located can be about 2 : 1 , the first
the voltages to which each voltage control device are driven voltage being about equal to the third voltage , and the
are different, and linear drive devices can be used ; however second voltage being about equal to the fourth voltage .
this implementation can have generally higher power dissi- 55 A ratio of the first segment, where the first voltage control
pation as compared to the greater than 1 : 1 case , where device is located , to the second segment, where the second
non - linear drivers can be used . Either way, amplitude of an voltage control device is located , can be one or more of
optical signal on the optical waveguide can be modulated by greater than 1 : 1 and about 2 : 1 , the first voltage being about
the optical ring modulator to four different amplitudes to equal to the third voltage , and the second voltage being
encode data therein to achieve PAM -4 modulation . In other 60 about equal to the fourth voltage . Each of the first driver
words , four different voltage conditions can be applied to the device and the second driver device can comprise a respec
optical ring modulator resulting in four different amplitude tive non -linear driver device .
modulation conditions. Adding a third voltage control A ratio of the first segment, where the first voltage control
device along a third segment of the optical ring modulator, device is located , to the second segment, where the second
and a corresponding third driver device , results in an optical 65 voltage control device is located can be about 1 :1 , wherein
signal on the optical waveguide being modulated to eight at least one of: the third voltage is different from the first
different amplitudes to encode data therein to achieve voltage ; and the fourth voltage is different from the second
 US 9,784 ,995 B2
voltage . The third voltage can be about the same as the first synchronized and phase aligned NRZ electrical signals into
voltage, and fourth voltage can be different from the second a PAM4 optical signal which can generally eliminate a need
voltage . for a PAM4 encoder at device 101. Furthermore, in some
Each of the first voltage control device and the first implementations, each of first driver device 111- 1 and sec
voltage control device can comprise a respective diode, a 5 ond driver device 111- 2 can comprise a non -linear driver
respective junction of the respective diode located along a device which can operate at speeds greater and/ or power
respective segment of the optical ring modulator. dissipation lower than linear driver devices; hence, device
Each of the first voltage control device and the first 101 can provide PAM4 encoding without a PAM4 encoder,
voltage control device can comprise a respective diode , each and utilize non -linear drivers.
of the first driver device and the second driver device 10 First voltage control device 110 - 1 and second voltage
configured to operate the respective diode in a reverse bias control device 110 - 2 will hereafter be referred to , collec
tively , voltage control devices 110 and , generically , as a
mode.
The device can further comprise : further comprising: one voltage control device 110 ; and first driver device 111 - 1 and
or more further voltage control devices along respective second driver device 111-2 will hereafter be referred to ,
further segments of the optical ring modulator; and, one or 15 collectively , driver devices 111 and , generically, as a driver
more
m further driver devices each configured to control a device 111 .
respective further voltage control device to two respective For clarity , in FIG . 1 and through -out the present speci
voltages . fication , solid lines connecting components depict links
The device can further comprise a controller in commu and/or optical waveguides that include flow of optical sig
nication with the first driver device and the second driver 20 nals there between , while stippled lines connecting compo
device , the controller configured to : convert data to be nents depict links that include flow electrical data and /or
transmitted along the opticalwaveguide into a pulse ampli electrical signals there between . Hence, driver devices 111
tude modulation (PAM ) compatible format; and control each are electrically connected to respective voltage control
of the first driver device and the second driver device to in devices 110 , and ring 105 is optically coupled to optical
turn control a respective voltage control device to modulate 25 waveguide 103 over which optical data signals are carried .
an optical signal on the optical waveguide to encode the data As depicted , device 101 further comprises a controller
therein . 120 , in communication with driver devices 111 , a memory
The device can further comprise a heater configured to 122 and an interface 124 each interconnected with controller
maintain a given temperature of the optical ring modulator. 120 . In particular, memory 122 stores an application 126 ,
The device can further comprise a laser configured to 30 which , when processed by controller 120 , enables controller
provide an optical signal along the optical waveguide , the to control driver devices 111 to in turn control voltage
optical signal modulated by the optical ring modulator. control devices 110 .
While ring 105 is depicted as circular, it is appreciated
BRIEF DESCRIPTIONS OF THE DRAWINGS that ring 105 can be elliptical and/or racetrack shaped and /or
35 vary from a circular shape, as long as ring 105 is closed and
For a better understanding of the various implementations is coupled to optical waveguide 103 ; while not depicted,
described herein and to show more clearly how they may be coupling devices can be located at an interface of ring 105
carried into effect, reference will now be made , by way of and optical waveguide 103 to facilitate coupling thereof.
example only , to the accompanying drawings in which : Furthermore , while also while not depicted , ring 105 can be
FIG . 1 depicts a schematic diagram of a device that 40 coupled to one or more additional optical waveguides and /or
includes a two-segment optical ring modulator of different optical buses, including , but not limited to , one or more drop
lengths, according to non - limiting implementations . ports . In addition , optical waveguide 103 can comprise an
FIG . 2 depicts resonance properties of the device of FIG . optical bus which can be used to convey more than one
1 under four different voltage driving conditions, according optical signal; indeed , optical waveguide 103 can be inter
to non -limiting implementations . 45 changeably referred to as an optical bus.
FIG . 3 depicts a schematic diagram of a device that while not depicted device 101 further comprises a heater
includes a two-segment optical ring modulator of similar configured to maintain a given temperature of ring 105 ; the
lengths, according to non -limiting implementations. heater can be controlled by controller 120; for example , the
FIG . 4 depicts a schematic diagram of a device that heater can about parallel to ring 105 , but can be located on
includes a three-segment optical ring modulator of different 50 either side of a plane defined by ring 105 .
lengths, according to non -limiting implementations . Indeed , voltage control devices 110 are appreciated to be
depicted schematically as along a respect segment of ring
DETAILED DESCRIPTION 105 , with a portion of each voltage control device 110
located inside and outside ofring 105 ; however, in practise ,
FIG . 1 depicts a device 101 comprising: an optical wave - 55 voltage control device 110 can comprise electrodes " above "
guide 103 ; an optical ring modulator 105 optically coupled and “ below ” ring 105 (e.g . out of and into the page of FIG .
to optical waveguide 103; a first voltage control device 1 ), which are controlled by controller 120 .
110 - 1 along a first segment of optical ring modulator 105 ; a In particular, each voltage control device 110 can com
second voltage control device 110 - 2 along a second segment prise a respective diode , and specifically a PN -diode , a
of optical ring modulator 105 ; a first driver device 111 - 1 60 respective junction of each respective diode located along a
configured to control first voltage control device 110 - 1 to a respective segment of optical ring modulator 105 . In these
first voltage V1 and a second voltage V2 ; and, a second implementations, each of first driver device 111 - 1 and sec
driver device 111 -2 configured to control second voltage ond driver device 111 -2 can be configured to operate the
control device 110 - 2 to a third voltage V3 and a fourth respective diode , such that a change in voltage modifies a
voltage V4. Optical ring modulator 105 will hereafter be 65 charge carrier density and /or refractive index of a respective
interchangeably referred to as ring 105 . In general, as segment of ring 105 . For example , each of first driver device
described in detail below , device 101 can convert two 111 - 1 and second driver device 111 - 2 can be configured to
 US 9 ,784 ,995 B2
5
operate a respective diode in either a forward bias (and /or a respective segment of ring 105, to modulate the given
injection )mode or a reverse bias ( and/or depletion )mode . In optical signal being conveyed along optical waveguide 103
particular implementations, however, each of first driver based , for example, on input received from interface 124 .
device 111 - 1 and second driver device 111 - 2 can be config - Hence , a modulated optical signal produced by ring 105 has
ured to operate a respective diode in a reverse bias mode . 5 data encoded therein , and can be conveyed through an
Hence , in yet further implementations, each voltage control optical telecommunication network . Such data can include,
device 110 can comprise a capacitor, with a respective
segment of ring 105 located between electrodes and/or but is not limited to , voice, audio , video , images, web data ,
browser data, and the like .
“ plates ” of the capacitor. Either way , voltage control device
110 can apply electric field across a respective segment of 10 dataIn toparticular , controller 120 can be configured to : convert
be transmitted along optical waveguide 103 into a
ring 105 to change physical and/or optical properties pulsed modulate amplitude (PAM ) compatible format ; and
thereof, and hence change a resonance condition of ring 105 . control each of first driver device 111 - 1 and second driver
For example, in general, a resonance and/or reference device 111- 2 to in turn control a respective voltage control
frequency of an optical ring resonator can be coarsely
controlled by controlling a diameter and / or circumference 15 device 110 to modulate an optical signal on optical wave
and/ or a refractive index of an optical ring resonator ( e. g . guide 103 to encode the data therein .
during fabrication thereof) and /or finely controlled by con For example, laser 144 can comprise a distributed Bragg
trolling the temperature of the optical ring resonator. As reflector laser, an external cavity laser and the like config
such , the heater can be used to tune the refractive index of ured to output optical signals ( e .g . light ) of a plurality of
a portion of ring 105 to coarsely control a reference reso - 20 different wavelengths (and/or frequencies ), for example with
nance frequency, while each voltage control device 110 is a frequency constant spacing, into optical waveguide 103 ;
used to change the refractive index of a respective segment ring 105 can hence be configured to resonate at a given
of ring 105 to modulate the reference resonance frequency wavelength of the plurality of different wavelengths such
which in turn causes optical signals on optical waveguide that an optical signal of the given wavelengths is modulated
103 to be modulated , as described in further detail below . 25 by ring 105 to produce a modulated optical signal .
Each driver device 111 is configured to control a respec - In general, the modulated optical signal is conveyed out
tive voltage control device 110 to one of two respective of device 101 on output waveguide 103 at output 195 , for
voltages (voltages V1, V2 for voltage control device 110 - 1 , example to a fiber optic, which in turn conveys the modu
and voltages V3, V4 for voltage control device 110 - 2 ), such lated optical signal through an optical telecommunication
that the voltages are applied across a respective segment of 30 network to a receiver, where the modulated optical signal is
ring 105 . Each driver device 111 can comprise a non -linear received and demodulated to retrieve data encoded therein .
driver device or a linear driver device. When a ratio of the Hence , device 101 can generally comprise a transmitter in
first segment (along which the voltage control device 110 - 1 an optical telecommunications system configured to gener
is located ) to the second segment (along which second ate and transmit a modulated optical signal at a given optical
voltage control device 110 - 2 is located ) is greater than 1 : 1 35 frequency (and a given data rate ), the modulated optical
( for example, as depicted , about 2 : 1 ) , each of first driver signal having data encoded therein . As such , an optical
device 111- 1 and second driver device 111 -2 can comprises wavelength and/ or optical frequency provided by laser 144
a respective non - linear driver device . Application of volt - can comprise a given carrier optical wavelength and/ or a
ages V1, V2, V3, V4 are described in further detail below . given carrier optical frequency including , but not limited to ,
However, when a ratio of the first segment (along which 40 an optical frequency used in optical telecommunications in
the voltage control device 110 - 1 is located ) to the second a range of about 184 .5 - 238 THz (and corresponding wave
segment (along which second voltage control device 110 - 2 lengths ); however other optical frequencies ( and/ or wave
is located ) is about 1: 1 (e .g . see FIG . 3 ), each of first driver lengths ) are within the scope of present implementations.
device 111 - 1 and second driver device 111 - 2 can comprise a While not depicted , device 101 can be further configured
respective linear driver device . While such an implementa - 45 to optically interface with an optical fiber (e . g . at output
tion can comprise an adaption of a single diode modulator 195 ), and device 101 can hence transmit the modulated
that also uses a linear driver device , such implementations optical signal through the optical fiber, which can be hun
are generally slower than implementations where non -linear dreds of kilometers long (or more ). Device 101 can hence
driver devices are used . Hence , alternatively , when a ratio of comprise a modulating optical signal generator including ,
the first segment to the second segment is about 1 : 1 , each of 50 but not limited to , one or more lasers , including laser 144
first driver device 111- 1 and second driver device 111 - 2 can which can be internal or external ( as depicted ) to device 101 ,
comprise a respective non -linear driver device but operated one more light emitting diodes (LEDs ), and the like, as well
voltages in about a 2 : 1 ratio , which can be challenging to as one or more interfaces ( such as interface 124 ) to data
implement ( e.g . non - linear driver devices operated with generating devices, including , but not limited to , servers,
different amplitudes). 55 personal computers, laptops, mobile devices and the like,
In particular, in some implementations, each driver device and the like.
111 can comprise a non -linear CMOS (complementary It should be emphasized , however, that the structure of
metal- oxide -semiconductor ) driver device . device 101 in FIG . 1 is purely an example, and contemplates
As depicted , device 101 further comprises a laser 144 , and a device that can be used for optical data communications.
optical waveguide 103 is configured to receive optical 60 In particular, at least optical waveguide 103 and ring 105 can
signals from laser 144 at an optical input 185 thereof, the be formed from a photonic integrated circuit (PIC ) ; indeed ,
optical waveguide 103 further configured to convey the any components of device 101 that convey and /or interact
optical signals to an optical output 195 . In general, ring 105 with optical signals can be formed from a PIC . In particular
modulates the optical signals, and in particular optical non -limiting implementations , components of device 101
signals of a given frequency and / or a given wavelength . 65 that convey and / or interact with optical signals can be
Controller 120 is generally configured to control driver formed from a silicon based PIC , however other materials
devices 111 to , in turn , apply voltages V1, V2, V3, V4 along are within the scope of present implementations.
 US 9, 784,995 B2
Controller 120 can comprise a processor and /or a plurality In other words, in FIG . 1 , a ratio of a first segment, along
of processors, including but not limited to one or more which first voltage control device 110 - 2 is located , to the
central processors (CPUs) and /or one or more processing second segment, along which second voltage controldevice
units ; either way, controller 120 comprises a hardware 110 -2 is located , is about 2 : 1, a first voltage V1 is about
element and /or a hardware processor. Indeed , in some imple - 5 equal to third voltage V3 , and second voltage V2 is about
mentations, controller 120 can comprise an ASIC (applica equal to fourth voltage V4 .
tion -specific integrated circuit ) and /or an FPGA ( field -pro In other words , it is assumed in the following discussion
grammable gate array ) specifically configured to implement that voltage V1 is about equal to voltage V3, and that voltage
the functionality of controller 120 . Hence , controller 120 is V2 is about equal to voltage V4 . Furthermore , it is assumed
not necessarily a generic computing device and /or a generic V4 is a less than voltage V3 .
processor and /or a generic component of computing con
troller 120 , but a device specifically configured to imple It can be further assumed that each driver device 111
ment specific functionality ; such specific functionality comprises a non -linear driver device . Indeed , in implemen
includes controlling driver devices 111 to modulate an tationswhich described herein where a ratio of a first segment,
optical signal on optical waveguide 103 according to a 15 along first voltage control device 110 -2 is located , to
the second segment, along which second voltage control
PAM - N protocol, as described in further detail below . For device 110 - 2 is located , is one or more of about 2 : 1 and
example , controller 120 can specifically comprise an engine
configured to modulate an optical signal on optical wave greater driver
than 1 : 1, each of first driver device 111 - 1 and second
device 111 - 2 can comprises a respective non - linear
guide 103 according to a PAM - N protocol. 20 driver device . Such non -linear driver devices are fast com
Memory 122 can comprise a non - volatile storage unit pared to linear driver devices and as each non -linear driver
( e.g . Erasable Electronic Programmable Read Only Memory device is controlled to only two given voltages, the effect of
(“ EEPROM ” ), Flash Memory ) and a volatile storage unit their non - linear response is minimized . The driving voltage
( e .g . random access memory (“ RAM ” ) . Programming conditions for each of the two output voltage are determined ,
instructions that implement the functional teachings of con - 25 and then each driver device 111 is changed between the two
troller 120 and / or device 101 as described herein are typi- output voltages .
cally maintained , persistently , in memory 122 and used by It is yet further assumed in the following discussion that
controller 120 which makes appropriate utilization of vola the heater has been controlled to a given value such that an
tile storage during the execution of such programming optical signal of a given wavelength is being modulated by
instructions. Those skilled in the art recognize that memory 30 ring 105 ; in particular, it is assumed that a wavelength of
122 is an example of computer readable media that can store about 1544 .22 nm is being modulated by ring 105 , and
programming instructions executable on controller 120 . heater is controlled accordingly such a minimum of a
Furthermore , memory 122 is also an example of a memory resonance curve of ring 105 is adjacent about 1544. 22 nm
unit and/ or memory module and /or a non - volatile memory. (for example see FIG . 2 ). In particular , wavelength 1544 .22
In particular, memory 122 stores application 126 that 35 nm is located on a blue-side of a minimum of a resonance
when processed by controller 120 enables controller 120 to curve of ring 105 . However, other wavelengths are within
modulate an optical signal on optical waveguide 103 accord - the scope of present implementations.
ing to a PAM - N protocol by controlling driver devices 111 . Attention is next directed to TABLE 1, below , in which a
Interface 124 can comprise any wired and/or wireless driving scheme for device 101 is provided , which can be
interface configured to receive data used to modulate optical 40 stored atmemory 122 , for example in application 126 and/or
signals. As such , interface 124 is configured to correspond as a lookup table which can be processed by controller 120 ,
with communication architecture that is used to implement and the like . Furthermore , while TABLE 1 is provided in
one or more communication links used to receive data , rows and columns, such a format is shown for simplicity ,
including but not limited to any suitable combination of, and TABLE 1 can be in any suitable format.
cables , serial cables, USB (universal serial bus) cables, and 45
wireless links (including, but not limited to , WLAN (wire TABLE 1
less local area network ) links, WiFi links, WiMax links,
cell-phone links, BluetoothTM links , NFC (near field com Voltage Control Device 111 -1 Voltage Control Device 111- 2
munication ) links , packet based links, the Internet, analog Data (Most Significant Bit ) (Least Significant Bit )
networks, access points , and the like , and /or a combination ) . 50 00 V1 V3
However , interface 124 is generally non -limiting and any 01
10
V1
V2
V4
V3
interface used in optical telecommunication devices and /or 11 V4
optical telecommunication transmitters is within the scope
of present implementations .
Operation of device 101 will now be described in more 55 For example, when voltage V1, and voltage V3 are
detail. applied to each of respective segments of voltage control
It is further appreciated that, in FIG . 1 , length of a devices 110 - 1 , 110 - 2 , by respective driver devices 111 - 1 ,
segment of ring 105 along which first voltage device 111 - 1 111 - 2 , it is assumed that a corresponding amplitude modu
is located is about twice a respective length of a segment of lation of the optical signal on optical waveguide 103 corre
ring 105 along which second voltage device 111 - 2 is located . 60 sponds to an encoding of “ 00” . Similarly, when voltage V1,
For example, first voltage device 111 - 1 is located along and voltage V4 are applied to each of respective segments of
about half of ring 105 , while second voltage device 111 - 2 is voltage control devices 110 - 1 , 110 - 2 , by respective driver
located along about a quarter of ring 105 , with the remaining devices 111 - 1, 111 -2 , it is assumed that a corresponding
quarter comprising a coupling region of ring 105 to optical amplitude modulation of the optical signal on optical wave
waveguide 103 , which can include a point coupler ( e . g . not 65 guide 103 corresponds to an encoding of “ 01” . Similarly ,
an MZI (Mach - Zehnder interferometer ) coupler as in the when voltage V2 , and voltage V3 are applied to each of
prior art ). respective segments of voltage control devices 110 -1 , 110 -2 ,
 US 9,784,995 B2
10
by respective driver devices 111 - 1 , 111 -2 , it is assumed that than the length of segment of ring 105 along which second
a corresponding amplitude modulation of the optical signal voltage control device 110 - 2 is located , first voltage control
on optical waveguide 103 corresponds to an encoding of device 110 - 1 will have a larger effect on shifting the reso
“ 10 ” . And finally , when voltage V2, and voltage V4 are nance of ring 105 as compared to second voltage control
applied to each of respective segments of voltage control 5 device 110 - 2 , for similar applied voltages ; accordingly ,
devices 110 - 1 , 110 - 2 , by respective driver devices 111 - 1 , second voltage control device 110 -2 will hence have a
111 - 2 , it is assumed that a corresponding amplitude modu comparatively smaller effect on shifting the resonance of
lation of the optical signal on optical waveguide 103 corre ring 105 than first voltage control device 110 - 1 for similar
sponds to an encoding of “ 11” . applied voltages . This changing shift in resonance is
In other words , as there are two segments of different 10 reflected in FIG . 2 , and further the shifts in resonance , and
lengths on ring 105 that can be tuned differently using two corresponding changes in amplitude of an optical signal of
respective “high ” and “ low " voltages , four different ampli- the input wavelength , due to second voltage control device
tude modulations of the given wavelength of the optical 110 - 2 (which has a smaller effect), can correspond to a least
signal on optical waveguide 103 can occur. In particular, significant bit of data encoding , and corresponding changes
when the two segments are of different lengths ( e . g . a ratio 15 in amplitude of an optical signal of the input wavelength ,
of their lengths is greater than 1: 1 and /or about 2 : 1 ) the high due to first voltage control device 110- 1 (which has a larger
and low voltages can be the same, and/ or about the same, for effect), can correspond to a most significant bit of data
the two diodes and /or voltage control devices 110 , and encoding .
non - linear drivers can be used . Hence , the optical signal of the input wavelength can be
For example , attention is next directed to FIG . 2 , which 20 amplitude modulated according to a PAM - 4 scheme using
depicts four different resonance curves in terms of transmit device 101 (e .g . PAM -N where N = 2 * and x = 2 ).
ted optical power (y - axis ), in decibels , of ring 105 as a In other words, device 101 can convert two synchronized
function of wavelength (x -axis ). Also depicted in FIG . 2 is and phase aligned NRZ electrical signals into a PAM4
a reference wavelength of 1544 . 22 nm of the optical signal optical signal which can generally eliminate a need for a
on optical waveguide 103 that is to be modulated . 25 PAM4 encoder . In implementations where each voltage
Further depicted is a legend which indicates which pairs control device 110 comprises a respective diode , one NRZ
voltages V1, V2, V3 , V4 are being applied to ring 105 by signal can be applied to the small diode (Least Significant
voltage control devices 110 for each curve , relative to Bit — LSB ) at ring 105 and the second NRZ signal can be
TABLE 1 . As depicted , it is assumed that: each voltage V1, applied to the large diode (Most Significant Bit - MSB ) at
V3 is about the same; each voltage V2 , V4 is about the same; 30 ring 105 . Voltage across each respective diode creates an
and that voltages V1, V3 are greater than voltages V2 , V4 . electrical field that causes the optical resonance frequency
It is furthermore assumed that each voltage control device and /or optical resonance wavelength of ring 105 to shift. The
110 comprises a respective diode operated in a reverse bias shift is proportional to a size and /or length of a respective
mode by a respective non - linear driver device ( e.g . a respec - diode and/or a segment of ring 105 along which a respective
tive driver device 111 ) ; depletion of each respective diode 35 diode is located .
causes a resonance position of ring 105 to shift to larger As depicted the large diode (first voltage control device
wavelengths. In other words, changing a respective voltage 110 - 1 ) that is about twice a size of the small diode (second
of a respective diode from voltage V1, V3 to voltage V2, V4 voltage control device 110 -2 ); hence , the large diode ( first
causes the resonance curve in FIG . 2 to shift towards a voltage control device 110- 1 ) will generate about twice the
higher wavelength (e. g. a red -shift occurs in the resonance). 40 resonance shift for the same applied voltage as the small
Furthermore , each curve is labelled according to data diode ( second voltage control device 110 - 2 ). Given the
represented by each set of voltage conditions, such that: nature of resonant ring modulators, the equally spaced
curve 00 corresponds to an amplitude modulation corre - resonance shift will lead to unequally spaced optical modu
sponding to data “ 00 " when voltages V1, V3 are applied to lation amplitude levels. Hence, in practise , the ratio of the
respective segment; curve 01 corresponds to an amplitude 45 length of the larger diode to the length of the smaller diode
modulation corresponding to data “ 01” when voltages V1, is generally adjusted to be different from 2 :1 , to adjust
V4 are applied to respective segments; curve 10 corresponds separation between optical modulation amplitude levels.
to an amplitude modulation corresponding to data “ 10 ” Furthermore , the position of the optical modulation
when voltages V2 , V3 are applied to respective segments ; amplitude levels generally depends on the position of the
and curve 11 corresponds to an amplitude modulation cor- 50 input wavelength relative to the resonance locations each
responding to data “ 11 ” when voltages V2, V4 are applied curve 00 , curve 01 , curve 10 , curve 11 so thermal tuning of
to respective segments. the resonance location can be used optimize the resulting
It is apparent that with each successive voltage condition , PAM4 response . For example , the heater of device 101 is
a minimum of the resonance curves shift towards longer used to position an initial resonance of ring 105 such that the
wavelengths, such that a position of the inputwavelength on 55 input wavelength is at a given location relative to each curve
each successive curve 00 , curve 01, curve 10 , curve 11 shifts 00 , curve 01, curve 10 , curve 11 . For example, the heater of
to a higher transmission optical power. In other words, device 101 can be calibrated and /or designed and /or provi
amplitude of an optical signal of the input wavelength will sioned to modulate one or more given input wavelength and
have lower amplitude when voltages V1, V3 are applied to a look -up table , and the like, can be stored at memory 122
ring 105 , then when voltages V2 , V4 are applied to ring 105 . 60 to provide heater parameters to which the heater of device
Furthermore, the amplitude of each curve 00 , curve 01, 101 is controlled to modulate the one or more given input
curve 10 , curve 11 at the input wavelength corresponds to an wavelengths .
opticalmodulation amplitude level of the input wavelength In general, the position ofthe input wavelength relative to
as each pair of voltages (V1, V3 ), (V1, V4 ), (V2, V3 ), (V3 , the resonance wavelength of each of curve 00 , curve 01,
V4 ) are applied to ring 105 . 65 curve 10 , curve 11 can be selected to maximize separation
Furthermore , as the length of segment of ring 105 along between optical modulation amplitude levels, though input
which first voltage control device 110 - 1 is located is longer wavelength can also be at a position relative to the resonance
 US 9, 784,995 B2
11 12
wavelength of each of curve 00 , curve 01, curve 10 , curve voltage control device 310 - 1 along a first segment of optical
11 where less than maximize separation between optical ring modulator 305 ; a second voltage control device 310 - 2
modulation amplitude levels occurs . For example , the posi- along a second segment of optical ring modulator 305 ; a first
tion of the input wavelength relative to the resonance driver device 311 - 1 configured to control first voltage con
wavelength of each of curve 00 , curve 01, curve 10 , curve 5 trol device 310 - 1 to a first voltage V1 and a second voltage
11 be selected such that separation between optical modu - V2 ; and , a second driver device 311 - 2 configured to control
lation amplitude levels is about evenly spaced on a log -scale . second voltage control device 310 -2 to a third voltage V3
However, such shifts in amplitude need not be exactly and a fourth voltage V4 . Optical ring modulator 305 will
evenly spaced . For example as depicted in FIG . 2 , for the hereafter be interchangeably referred to as ring 305 . First
inputwavelength , where transmission is at about 51. 5 dB for 10 voltage control device 310 - 1 and second voltage control
curve “ 00 ” , about - 48. 5 dB for curve “ 01” , about - 46 dB for device 310 - 2 will hereafter be referred to , collectively ,
curve “ 10 ” , and about - 44 dB for curve “ 11 ” . voltage control devices 310 and , generically , as a voltage
In any event, by simultaneously applying synchronous control device 310 ; and first driver device 311 - 1 and second
and phase aligned digital signals to the diodes a multi -level driver device 311 - 2 will hereafter be referred to , collectively,
optical signal can be generated . In other words, device 101 , 15 driver devices 311 and, generically, as a driver device 311 .
as well as converting electrical signals into optical signal, Device 101 further comprises a controller 320 , a memory
can also act as a digital to analogue converter (DAC ) . 322 and an interface 324 , memory storing application 326 ,
As described above , device 101 can be used in optical a laser 344 , an input 385 and an output 395 .
transmission system applications . In particular, PAM - 4 is a However, in contrast to device 101 , in device 301, a ratio
modulation technique that doubles spectral density through 20 of the first segment, along which first voltage control device
multi- level coding . Two bits are transmitted in the same time 310 - 1 is located , to the second segment, along which second
period as a single bit in a NRZ based system . So , for a voltage control device 310 - 2 is located , is about 1 : 1, the first
symbol rate of 28 Gbaud , 56 Gb /s is transmitted with voltage V1, the second voltage V2, the third voltage V3 and
PAM - 4 . Optical fibers used in optical transmission have the fourth voltage V3 all being different from one another. In
limited bandwidth , so PAM - 4 allows the transmission capac - 25 particular, the first voltage V1 can be about the same as the
ity of the fiber to be doubled thereby reducing system cost. third voltage V3 (for example for a depletion modulator),
Hence device 101 configured to PAM -4 optical modulation and the second voltage V2 is different than the fourth voltage
can be used for Datacom applications within data centers V4 . In some implementations, however, the first voltage V1
and between data centers and in short reach telecommuni - can be different from the third voltage V3 , and the second
cation networks ( including , but not limited to ( access and 30 voltage V2 can be about the same as the fourth voltage V4 .
metro telecommunication networks). In other words, at least one the following conditions apply :
Furthermore , a size of a PIC of device 101 can be smaller the third voltage V3 is different from the first voltage V1;
than a PIC of prior art devices. For example , a radius of a and the fourth voltage V4 is different from the second
ring modulator is about 23 um , as compared to 1 mm long voltage V2. Each of the voltages V1, V2, V3, V4 are selected
Mach Zehnder ("MZ" ) modulators with multi-segment 35 to effect good separation between the transmission curves of
phase shifters and MZ assisted ring modulators of a length ring 305 for each pair of voltages applied to ring 305 .Hence ,
of about 340 um . Hence the present device can be more four different voltage conditions are applied to ring 305 , as
compact than such prior art devices. The present device can in device 101 to control the transmission curve of ring 305 .
also be faster than the prior art devices, for example 28 In other words, as the modulation effect of each voltage
Gbaud as compared to 120 Mb/s of some prior art devices . 40 control device 310 will be about the same due their similar
In addition , relative to a single diode ring modulator with length and /or size, at least one of the respective “ high ” and
a single linear (analogue ) driver, a product cost can be “ low ” voltages of each voltage control device 310 are
reduced (about 5 % at product level) and power dissipation different to effect four different voltage conditions are
can be lower (about 10 % reduction at product level) as applied to ring 305 , as in device 101, which again causes
non - linear CMOS drivers can be used in place of analogue 45 separation of the transmission curves of ring 305 . As such ,
SiGe drivers . linear driver devices can be used to more precisely control
Persons skilled in the art will appreciate that there are yet the voltages. This can lead to slower operation than device
more alternative implementations and modifications pos- 101 , as linear driver devices tend to be slower than non
sible . For example , the ratio of the size of voltage controls linear driver devices , otherwise, operation of device 301 is
devices 110 ( e . g . two diodes ) can deviate from 2 : 1 . Rather 50 similar to device 101. Furthermore , the power dissipation of
than targeting a ratio in resonance shift between the MSB device 301 can be higher than device 101 to achieve good
and LSB , the voltage control device /diode sizes can be separation between the transmission curves.
selected designed to produce target optical output levels In yet further implementations, modulation of device 101
after modulation , which takes into account a non - linear can be extended to higher order modulation , including, but
optical transfer function of the ring , a modulator driver 55 not limited to , PAM - 8 modulation , by using three or more
waveform and noise performance , including noise contrib - voltage control devices and/ or diodes where , approximately ,
uted by downstream optical amplifiers, and non- ideal the largest voltage control device /diode is twice the size of
responses of downstream linear channels (optical detectors a middle - sized voltage control device/diode, which in turn is
plus transimpedance amplifiers). twice the size of the smallest voltage control device / diode .
Indeed , in particular implementations the ratio of the 60 In other words, device 101 can be modified to include : one
voltage control device /diode sizes can be about 1 :1 . For or more further voltage control devices 110 (i.e. in addition
example , attention is next directed to FIG . 3 which depicts to voltage control devices 110 - 1 , 110 - 2 ) along respective
a device 301 that is substantially similar to device 101, with further segments of optical ring modulator 105 ; and , one or
like elements having like numbers , however in a “ 300 ” more further driver devices 111 i.e . in addition to driver
series rather than a “ 100 ” series. Hence , device 301 com - 65 devices 111 - 1, 111 - 2) each configured to control a respective
prises an optical waveguide 303 ; an optical ring modulator further voltage control device 110 to two respective volt
305 optically coupled to optical waveguide 303; a first ages .
 US 9, 784,995 B2
13 14
For example , attention is next directed to FIG . 4 which In any event, described herein is a device that includes at
depicts a device 401 that is substantially similar to device least two voltage control devices and/ or diodes along an
101, with like elements having like numbers, however in a optical ring modulator; when diodes of different lengths
" 400 ” series rather than a “ 100 ” series. Hence , device 401 and /or sizes are used , the diodes can be operated in a reverse
comprises an optical waveguide 403 ; an optical ring modu - 5 bias (e . g . depletion ) mode to provide high speed perfor
lator 405 optically coupled to optical waveguide 403 ; a first mance . Such a device can used for PAM - N modulation , and
voltage control device 410 - 1 along a first segment of optical can have reduced physical size ( and/ or higher density ),
ring modulatorsoomentofanticol
405 ; a second voltage
ring
control deviceE . 410fint-2 tosimplified
moduloton
coupling, and high speed operation as compared
prior art devices .
along a second segment of optical ring modulator 405 ; a first
driver device 411 - 1 configured to control first voltage con 10 implementations
Those skilled in the art will appreciate that in some
, the functionality of devices 101, 301, 401
trol device 410 - 1 to a first voltage V1 and a second voltage can be implemented using pre - programmed hardware or
V2 , and , a second driver device 411 - 2 configured to control
firmware elements ( e. g ., application specific integrated cir
second voltage control device 410 - 2 to a third voltage V3 cuits (ASICs), electrically erasable programmable read -only
and a fourth voltage V4. Optical ring modulator 405 will 15 memories (EEPROMs), etc.), or other related components .
hereafter be interchangeably referred to as ring 405 . Device In other implementations , the functionality of computing
101 further comprises a controller 420 , a memory 422 and devices 101, 301, 401 can be achieved using a computing
an interface 424 , memory storing application 426 , a laser apparatus that has access to a code memory (not shown )
444, an input 485 and an output 495 . which stores computer-readable program code for operation
However , in contrast to device 101, device 401 further 20 of the computing apparatus. The computer -readable pro
comprises : a third voltage control410 - 3 device along a third gram code could be stored on a computer readable storage
segment of optical ring modulator 405 ; and, a third driver medium which is fixed , tangible and readable directly by
device 411 - 3 configured to control third voltage control these components , ( e .g ., removable diskette , CD -ROM ,
device 410 - 1 to a fifth voltage V5 and a sixth voltage V6 . ROM , fixed disk , USB drive ). Furthermore , it is appreciated
First voltage control device 410 - 1 , second voltage control 25 that the computer - readable program can be stored as a
device 410- 2 , and third voltage control device 410 - 3 will computer program product comprising a computer usable
hereafter be referred to , collectively , voltage control devices medium . Further, a persistent storage device can comprise
410 and , generically , as a voltage control device 410 ; and the computer readable program code. It is yet further appre
first driver device 411 - 1 , and third driver device 411 - 3 will ciated that the computer -readable program code and /or
hereafter be referred to , collectively , driver devices 411 and , 30 computer usable medium can comprise a non - transitory
generically , as a driver device 411 . computer-readable program code and /or non -transitory
Voltage V5 can be about equal to voltages V1, V3, and computer usable medium . Alternatively , the computer -read
voltage V6 can be about equal to voltages V2, V4 . Further , able program code could be stored remotely but transmit
a ratio of a length of a first segment, along which first table to these components via a modem or other interface
voltage control device 410 - 1 is located , to a length of a 35 device connected to a network ( including , without limita
second segment, along which second voltage control device tion , the Internet ) over a transmission medium . The trans
410 - 2 is located , can be about 2 : 1 ; and a ratio of a length of mission medium can be either a non -mobile medium (e . g .,
the second segment, along which second voltage control optical and / or digital and / or analog communications lines )
device 410 - 2 is located , to a length of a third segment, along or a mobile medium ( e.g ., radio - frequency (RF) ,microwave ,
which third voltage control device 410 - 3 is located , can also 40 infrared , free - space optical or other transmission schemes )
be about 2 : 1 . For example, voltage control devices 410 can or a combination thereof.
be along about three quarters of a diameter of ring 405 , and Persons skilled in the art will appreciate that there are yet
the three quarters segmented accordingly with respect to the more alternative implementations and modifications pos
aforementioned ratios. However, the aforementioned ratios sible, and that the above examples are only illustrations of
can also deviate from 2 : 1 , to obtain desired separation of 45 one or more implementations. The scope, therefore , is only
transmission curves of ring 405. to be limited by the claims appended hereto .
In any event, as each of three voltage control devices 410 What is claimed is:
is controlled independently to one of two voltages, 3 bits can 1 . A device comprising:
be encoded in modulation of an optical signalbeing trans an optical waveguide;
mitted over optical waveguide 403: 000 , 001, 010 , 011, 100 , 50 an optical ring modulator optically coupled to the optical
101, 110 , 111 , with encoding of the least significant bit waveguide ;
occurring using third voltage control device 410 -3 (i.e. the a first voltage control device along a first segment of the
smallest of the three voltage control devices 410 ), encoding optical ring modulator ;
of the most significant bit occurring using first voltage aa ser
second voltage control device along a second segment
control device 410 - 1 (i.e. the largest of the three voltage 55 of the optical ring modulator;
control devices 410 ), and encoding of the middle bit occur a first driver device configured to control the first voltage
ring using second voltage controldevice 410 -2 (i.e . of a size control device to a first voltage and a second voltage to
in -between the other two voltage control devices 410 ) . control a resonance of the optical ring modulator
Furthermore , each driver device 411 can comprise a according to a most significant bit of data encoding ;
non - linear driver device , as in device 101. Otherwise, opera - 60 and ,
tion of device 401 is similar to device 101, however PAM -8 a second driver device configured to control the second
encoding occurs (e.g . PAM -N where N = 2 * and x = 3 ). voltage control device to a third voltage and a fourth
The concept can be extended to PAM - 16 , by using four voltage to control the resonance of the optical ring
voltage controlmodulators, to PAM - 32 using five voltage modulator according to least significant bit of data
control modulators. Indeed , any PAM - N encoding scheme 65 encoding.
can be used where N = 2 * and x = a number of voltage control 2 . The device of claim 1 , wherein a ratio of respective
modulators. lengths of the first segment, where the first voltage control
 US 9 ,784,995 B2
15 16
device is located , to the second segment, where the second 8 . The device of claim 1, wherein each of the first voltage
voltage control device is located is about 2 : 1 , the first control device and the second voltage control device com
voltage being about equal to the third voltage , and the prise a respective diode, each of the first driver device and
second voltage being about equal to the fourth voltage . the second driver device configured to operate the respective
3 . The device of claim 1 , wherein a ratio of respective 5 diode in a reverse bias mode.
lengths of the first segment, where the first voltage control 9. The device of claim 1, further comprising : one or more
device is located , to the second segment, where the second further voltage control devices along respective further
voltage control device is located , is one or more of greater segments of the optical ring modulator ; and , one or more
than 1 : 1 and about 2 : 1 , the first voltage being about equal to further driver devices each configured to control a respective
the third voltage , and the second voltage being about equal 10 further voltage control device to two respective voltages to
to the fourth voltage . control the resonance of the optical ring modulator accord
4 . The device of claim 3 , wherein each of the first driver ing to further significant bits of data encoding.
device and the second driver device comprises a respective 10 . The device of claim 1 , further comprising a controller
non - linear driver device . in communication with the first driver device and the second
respective 1515
5 . The device of claim 1 , wherein a ratio of respective driver device , the controller configured to : convert data to be
lengths of the first segment, where the first voltage control transmitted along the optical waveguide into a pulse ampli
device is located , to the second segment, where the second tude modulation (PAM ) compatible format; and control each
voltage control device is located is about 1 : 1 , wherein at of the first driver device and the second driver device to in
least one of: the third voltage is different from the first turn control a respective voltage control device to modulate
nd 20 an optical signal on the opticalwaveguide to encode the data
voltage ; and the fourth voltage is different from the second 20 therein
voltage . .
6 . The device of claim 5 , the third voltage is about the 11 . The device of claim 1 , further comprising a heater
same as the first voltage , and the fourth voltage is different configured to maintain a given temperature of the optical
from the second voltage . ring modulator.
7 . The device of claim 1, wherein each of the first voltage 25 configured
12 . The device of claim 1, further comprising a laser
to provide an optical signal along the optical
control device and the second voltage control device com
prise a respective diode, a respective junction of the respec modulator. the optical signal modulated by the optical ring
waveguide ,
tive diode located along a respective segment of the optical
ring modulator. * * * * *