Scribd
Upload
32 views1 page

314

This document provides a schematic of a tunable parametric oscillator. It consists of a laser medium pumped by a laser, with a nonlinear crystal and mirrors. By rotating the nonlinear crystal, which has a dielectric constant dependent on propagation direction, the matching condition for propagation constants can be satisfied at different frequencies, allowing tuning over a wide range. Common crystals like BBO in China can be tuned over a factor of 7 in wavelength when pumped by the third or fourth harmonic of a Nd:YAG laser. The document then briefly discusses optical fiber amplifiers, noting their importance for long-distance communication via optical fibers. Erbium-doped fiber amplifiers pumped by diode lasers are now standard components for signal amplification.

Uploaded by

Nurul Fahmi Arief
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
32 views1 page

314

This document provides a schematic of a tunable parametric oscillator. It consists of a laser medium pumped by a laser, with a nonlinear crystal and mirrors. By rotating the nonlinear crystal, which has a dielectric constant dependent on propagation direction, the matching condition for propagation constants can be satisfied at different frequencies, allowing tuning over a wide range. Common crystals like BBO in China can be tuned over a factor of 7 in wavelength when pumped by the third or fourth harmonic of a Nd:YAG laser. The document then briefly discusses optical fiber amplifiers, noting their importance for long-distance communication via optical fibers. Erbium-doped fiber amplifiers pumped by diode lasers are now standard components for signal amplification.

Uploaded by

Nurul Fahmi Arief
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 1

-"Es?

314
Laser

Lasers
Focusing

oscillator

f-lA
1I

lens

I
Fig.12.23
o1,
@2.

Laser medium

ll \/ \t
u

\t /\ ] 1lw{}*,1{
t

l\

W2-Nonlinear crystal

R, loo"'
R, = 100% R.,-070

R, (high but R, (high but Rr=


oEo

<l)
<I)

Schematic representation of a funeable pararnetric oscrllator. Rr, R:, and Rr are the reflectivities of the mirrors at frequencies

(,:

respectively.

as in our classical studies of Chapter 1) conditions. then there is a parametric

interaction between the waves. The power at rrl and a-l2 builds up from the general noise background at the expense of pump po\rier. Thus, we have output at all three fiequencies. But why is this set-up tuneable? Because of the particular properties of the chosen non-linear medium. It is a crystal in which the dielectric constant is dependent on the direction of propagation. By rotating the crystal, the matching condition for the propagation consrants is satistled at another set of frequencies, o, and roi, still obeving @3 : rlt, 1rr . The crystal used most often is bariurn borate (BBO). produced abundantly in the People's Republic of China. It rnav be used in a pulsed paramerric oscillator, pumped by either the third harmonic (355 nm) or by the tburth hannonic (266nm) of the l.066pm radiation fiom a Nd3*:YAG laser. The runing range for either pump u'avelengths is remarkablv large as shown in Fig. 12.24. Remember. for a dye laser with a given dye. we might have a tuning range in the vicinity of l0%, but noi.v we have a device rvhich can tune lvavelength bv a factor of 7 between the highest and the lowest wavelengths. The price we pay for it is the necessity to use an additional resonator with a piece (in practice usually fwo pieces) of crystal in it.

12.10 Optical fibre amplifiers


It is quite obvious that amplifiers can be built on the same principles as oscillators. but usually there is less need for them. A field, horvever, in which amplihers have crucial importance is long-distance communications. One might be able to span the oceans of the world by opticai fibres r.vithout
ifthe signals propagating in the fibres could be amplified. The idea of using fibre amplifiers is just about as old as the oldest laser. There were experiments in the early 1960s rvith fibres doped with Nd. Population inversion could be achieved by pumping it r,,'ith a flash-lamp, which then served to amplif' a signal. This idea was resunected in the middle 1980s, using another rare-earth element, erbium, as the dopant. Today, erbium doped fibre amplifiers (acronym EDFA) pumped by diode lasers are standard components in an optical
the need to regenerate the signal in repeaters,

You might also like