3. Tunable Laser
Definition:
“A laser that can change its frequency over a given range.”
A tunable laser is a laser whose wavelength of action can be
altered in a skillful mode.
Tunable laser can also be defined as:
“Any form of laser; e.g., a dye laser, having an output that can be
adjusted over a wide range of wavelengths, typically 70 nm
wide.”
6. Tunable Laser Optics
Broadly tunable lasers continue to have an enormous impact
in many diverse fields of science and technology.
From a renaissance in spectroscopy to laser guide stars and
laser cooling, the nexus is the tunable laser.
It offers a transparent and comprehensive treatment of the
physics
7. History
• The first true broadly tunable laser was the dye laser in 1966.
• The first narrow-line width tunable laser is introduced in 1972, allowing
tuning over a range of tens to hundreds of nanometers.
• The most common tunable solid-state laser is Titanium-doped sapphire laser,
capable of laser operation from 670 nm to 1,100 nm wavelength.
• Typically these laser systems incorporate a Lyot filter into the laser cavity, which
is rotated to tune the laser.
• Other tuning techniques involve diffraction gratings, prisms, etalons, and
combinations of these.
• Multiple principal arrangements in several configurations as described
by Duarte are used in diode, dye, gas, and other tunable lasers.
9. Types and categories of Tunable
Lasers
Following are the types of tunable laser among those of
solid, liquid and of gas state.
Carbon dioxide laser
Dye laser (Liquid and solid state laser)
Crystal and diode laser (Semiconductor)
Free electron laser
10. solid-state bulk laser
• A few solid-state bulk laser in particular titanium–
sapphire lasers and Cr:ZnSe and Cr:ZnS lasers allow
tuning over hundreds of nanometers in the near- and
mid-infrared spectral region.
• In general, transition-metal doped gain media offer
larger tuning ranges than rare-earth-doped gain
media, since the electrons involved in such media
interact more strongly with the host lattice; see the
article on vibrosnic lasers.
• Output powers can be hundreds or even thousands of
milliwatts.
11. Dye lasers
• Dye lasers also allow for broadband tunability.
Different dyes can cover very broad wavelength
ranges, e.g. throughout the visible region. There
are narrow-linewidth dye laser
systems (continuous-wave or pulsed) for use
in laser spectroscopy, and also mode-locked dye
lasers generating femtosecond pulses.
• Some free electron lasers can cover enormously
broad wavelength ranges, and often in extreme
spectral regions.
12. Types of tenability
Single line tuning:
• All lasers can emit light in line width of
the laser transition having a narrowing
1,064 nm wavelength.
• For example:
• Nd: YAG laser has a line width of
approximately 120 GHz, or 0.45 nm.
• Tuning of the laser output across this
range can be achieved by placing
wavelength-selective optical elements
i.e etalon into the laser's optical cavity
to provide selection of a
particular longitudinal mode of the
cavity.
13. Multi-line tuning
Most laser gain media have a number of transition wavelengths
on which laser operation can be achieved. For example, as well
as the principal 1,064 nm output line, Nd:YAG has weaker
transitions at wavelengths of 1,052 nm, 1,074 nm, 1,112 nm,
1,319 nm, and a number of other lines.
Usually, these lines do not operate unless the gain of the
strongest transition is suppressed; e.g., by use of wavelength-
selective dielectric laser. If a dispersive element prism
introduced into the optical cavity, tilting of the cavity's mirrors
can cause tuning of the laser as it "hops" between different laser
lines. Such schemes are common in argon-ion lasers allowing
tuning of the laser to a number of lines from
the ultraviolet and blue through to green wavelengths.
14. For some lasers the laser's cavity length can be modified
and can be continuously tuned over a significant
wavelength range.
Distributed feedback (DFB) semiconductor
lasers and vertical cavity surface emitting
lasers (VCSELs) use periodic distributed Bragg
reflector (DBR) structures to form the mirrors of the
optical cavity.
If the temperature of the laser is changed, the index
change of the DBR structure causes a shift in its peak
reflective wavelength and the wavelength of the laser.
Narrowband tuning
15. SIMULATING LASER TUNING
With the software RP Fiber Power one can simulate the tuning behavior of
broadband laser, taking into account ASE, limitations of bandpass filters,
etc. Use that to find out the requirements on the laser tuner.
Figure 1: Setup of a tunable solid-state bulk laser, realized e.g. with a
Ti:sapphire laser crystal
16. Wavelength-swept Lasers
• There are certain Juniper lasers which are
optimized such that the output wavelength can
be periodically and rapidly swept through a
substantial range.
19. Widely tunable lasers
A typical laser diode. When mounted with external optics these
lasers can be tuned mainly in the red and near infrared.
Sample Grating Distributed Bragg Reflector lasers (SG-DBR)
have a much larger tunable range, by the use of vernier
tunable Bragg mirrors and a phase section, a single mode output
range of >50 nm can be selected. Other technologies to achieve
wide tuning ranges for DWDM-systems are:
20. • External cavity lasers using a MEMS structure for tuning the cavity
length, such as devices commercialized by Iolon.
• External cavity lasers using multiple-prism grating arrangements for
wide-range tunability.
• DFB laser arrays based on several thermal tuned DFB lasers: Coarse
tuning is achieved by selecting the correct laser bar. Fine tuning is
then done thermally, such as devices commercialized by Santur
Corporation.
• Tunable VCSEL: One of the two mirror stacks is movable. To
achieve sufficient output power out of a VCSEL structure, lasers in
the 1,550 nm domain are usually either optically pumped or have an
additional optical amplifier built into the device.
As of December 2008 there is no widely tunable VCSEL commercially
available any more for DWDM-system application.
It is claimed that the first infrared laser with a tunability of more than
one octave was a germanium crystal laser.
21. The prism pair spatially disperses the different wavelength components,
so that the movable slit can be used to shift the wavelength away from that
of maximum gain.
Other types of lasers offer tuning ranges spanning a few nanometers to
some tens of nanometers:
• Rare-earth-doped fiber lasers, e.g. based on ytterbium, can often be tuned
over tens of nanometers, sometimes even more than 100 nm. Most Raman
fiber lasers also have the potential for wideband tuning.
• Some rare-earth-doped laser crystals, often doped with ytterbium, also
allow for substantial tuning ranges of bulk lasers. Examples
are tungstates, vanadates, Yb:BOYS, and Yb:CALGO.
• Color center lasers rely on broadband gain from certain lattice defects in a
crystal, which can be generated e.g. with gamma irradiation. They are not
widely used, however.
• Most laser diodes can be tuned over a few nanometers (often by varying
the junction temperature), but some special types such as external-cavity
diode lasers and distributed Bragg reflector lasers can be tuned over
40 nm and more.
22. Quantum cascade lasers
• Quantum cascade lasers are also broadly tunable mid-infrared laser sources.
• Some fine tuning, often continuously without mode hops, is possible for other lasers:
• Some compact solid-state bulk lasers such as nonplanar ring oscillators (NPROs,
MISERs) allow continuous tuning within their free spectral range of several
gigahertz. Tuning may be accomplished by applying stress to the laser crystal via a
piezo, or by varying the crystal temperature.
• Similar fine tuning is possible with some single-frequency laser diodes, e.g. by
varying the drive current.
• For wideband tuning in various spectral regions, optical parametric oscillators (OPOs)
can be used. These are actually not lasers, but OPO sources are nevertheless
sometimes included with the term tunable laser sources.
23. Applications of Tunable
Lasers
• Wavelength-tunable laser sources have many applications,
some examples of which are:
• In laser absorption spectroscopy, a wavelength-tunable
laser with narrow optical bandwidth used for recording
absorption spectra with very high frequency resolution.
• In a LIDAR system, it may be tuned to a wavelength
which is specific to a certain substance to be monitored.
• Tuning to atomic resonances is also used in laser isotope
separation. The laser is then tuned to a particular isotope in
order to ionize these atoms and subsequently deflect them
with an electric field.
• A tunable laser can be used for device characterization, e.g.
of photonic integrated circuits.
24. • In optical fiber communications with wavelength division
multiplexing, a tunable laser can serve as a spare in the case that one
of the fixed-wavelength lasers for the particular channels fails. Even
though the cost for a tunable laser is higher, its use can be
economical as a single spare laser can work on any transmission
channel where it is needed. As the cost of tunable lasers is no longer
much higher than for non-tunable ones, tunable lasers are now often
even used throughout.
• In optical frequency metrology, it is often necessary to stabilize the
wavelength of a laser to a certain reference standard (e.g.
a multipass gas cell or an optical reference cavity). This can be
accomplished e.g. with an electronic feedback system, which
automatically adjusts the laser wavelength.
• Some interferometers and fiber-optic sensors profit from a
wavelength-tunable laser source, e.g. if this makes it possible to
remove an ambiguity or to avoid mechanical scanning of an optical
path length.
25. Suppliers
The RP Photonics Buyer's Guide contains 84 suppliers for tunable lasers. Among
them:
RPMC Lasers
RPMC Lasers offers a tunable DPSS laser that uses an Optical
Parametric Oscillator (OPO) to produce tunable wavelengths in 410 –
2300 nm range. Its advanced laser design results in a compact, user-
friendly turnkey system that requires little maintenance. It integrates all
laser electronics into the housing and there are no chillers or bulky
power supplies needed.
26. APE
The tunable picosecond laser source pico Emerald emits ultrashort pulses
with a duration of 2 picoseconds (other durations possible). A wavelength
scan / sweep function for fast spectra acquisition over certain specific
wavelengths is included.
28. Laser Quantum
• Many of Laser Quantum’s ultrafast lasers can be tuned to different
wavelengths for various scientific applications, ranging from
720 nm – 930 nm to meet the specific needs of the application.
Products include the taccor tune with touch-screen beam control,
and the helixx with a unique 250 MHz repetition rate.
29. NKT Photonics
The SuperK EXTREME supercontinuum white light lasers are
broadband like a lamp and bright as a laser. They deliver high brightness
diffraction limited light in the entire 400–2400 nm region and by adding
one of our computer-controlled filters, the SuperK VARIA, the SuperK
can be converted into an ultra-tunable laser with up to 16 simultaneous
lines, providing a continuous tunable output from 400 to 840 nm.
Our SuperK lasers lasers are maintenance free and the fully fiber
monolithic architecture ensures excellent reliability and a lifetime of
thousands of hours.
30. TOPTICA photonics
TOPTICA offers various tunable diode laser systems. The
combined spectral coverage is from 190 nm to 3500 nm, powers up
to 4 W (TA), mode-hop-free tuning up to 110 nm (CTL).
31. Applications
• Extremely widely in spectral resolution When coupled to
the right filter
• In basic absorptionand photoluminescence study.
• For solar cells characterization in a light beam induced
current (LBIC) experiment
• For the characterization of gold nanoparticles and single-
walled carbon nanotube thermopile.
• Tunable sources were recently used for the development
of hyper spectral imaging
• As a powerful tool
for reflection and transmission spectroscopy, photobiology
detector calibration, hyper spectral imaging and steady-state
pump probe experiment.
32. • Broadly tunable lasers continue to have a tremendous impact in many and diverse
fields of science and technology. From a renaissance in laser spectroscopy to Bose-
Einstein condensation, the one nexus is the tunable laser. Tunable Laser
Applications describes the physics and architectures of widely applied tunable
laser sources. Fully updated and ex
Dense wavelength division multiplexing networks: principles and applications
(published paper)
Abstract:
• The very broad bandwidth of low-loss optical transmission in a single-mode fiber
and the recent improvements in single-frequency tunable lasers have stimulated
significant advances in dense wavelength division multiplexed optical networks.
This technology, including wavelength-sensitive optical switching and routing
elements and passive optical elements, has made it possible to consider the use of
wavelength as another dimension, in addition to time and space, in network and
switch design. The independence of optical signals at different wavelengths makes
this a natural choice for multiple-access networks, for applications which benefit
from shared transmission media, and for networks in which very large throughputs
are required. Recent progress in multiwavelength networks are reviewed, some of
the limitations which affect the performance of such networks are discussed, and
examples of several network and switch proposals based on these ideas are
presented. Discussed also are critical technologies that are essential to progress in
this field.
33. Tunable Lasers for DIAL
Applications (published paper)
• The development of the DIAL technique has been
limited by the availability of suitable tunablelaser
sources. This review describes the four types of
tunable laser that are most widelyused in DIAL
applications. These are dye lasers, tunable solid state
lasers, line tunable carbondioxide lasers and optical
parametric oscillators.
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