2-μm fiber lasers have become a research topic with an increased emphasis due to a variety of applications including eye-safe LIDAR, spectroscopy, remote sensing, and mid-infrared (mid-IR) frequency generation. We review our latest development on various 2-μm fiber laser sources, including single-frequency fiber lasers, Q-switched fiber lasers, mode-locked fiber lasers, and mid-IR supercontinuum fiber sources. All these fiber laser sources are based on thulium and holmium ions using our proprietary glass fiber technology. Potential applications of these fiber laser sources for sensing are also briefly discussed.
We demonstrate a single-frequency gain-switched Ho-doped fiber laser based on heavily doped silicate glass fiber
fabricated in house. A Q-switched Tm-doped fiber laser at 1.95μm was used to gain-switch the Ho-doped fiber laser via in-band pumping. Output power of the single-frequency gain-switched pulses has been amplified in a cladding-pumped Tm-Ho-codoped fiber amplifier with 1.2m active fiber pumped at 803nm. Two different nonlinear effects, i.e.,
modulation instability and stimulated Brillouin scattering, could be seen in the 10μm-core fiber amplifier when the
peak power exceeds 3kW. The single-frequency gain-switched fiber laser was operated at 2.05μm, a popular laser
wavelength for Doppler lidar application. This is the first demonstration of this kind of fiber laser.
Mode-locked fiber lasers based on Tm-doped and Tm-Ho-codoped silicate fibers have been studied. The first modelocked
fiber laser oscillator beyond 2 μm was demonstrated. The first mode-locked 2μm fiber laser with ~GHz repetition
rate was demonstrated. The broadest spectrum (50nm FWHM) was obtained from dispersion managed 2μm mode-locked
fiber laser. Various operation regimes of mode-locked thulium fiber lasers are presented, as well as all-fiber 2μm pulse
amplifiers.
30ns, 3μJ Q-switched pulse laser with the repetition rate of 10 kHz at 1950 nm was amplified with a 50cm long piece of
thulium(Tm)-doped silicate fiber, and 300μJ pulses with the pulse width of 20 ns were obtained. The heavily Tm-doped
silicate fiber has the cladding-pump absorption of 22dB/m at 793nm and the fiber maintains solid single-mode operation
at 1950nm. To further increase output pulse energy, the Q-switched seed was pre-amplified to 20 μJ with core-pumping
at 1567 nm. The power amplifier features of a 55cm long piece of Tm-doped silicate fiber with 21μm core. ~600μJ
pulses with peak power up to 28 kW have been achieved. The ASE was suppressed 40dB below the laser pulses due to
the short highly Tm-doped silicate fiber. Mode-locked pulses with the pulse energy of 0.3 nJ and the spectral width of 14
nm were amplified with a 30cm long Tm-fiber with 10 μm core, pulses with 16kW peak power as well as 20nJ pulses
were achieved. With another Tm-doped silicate fiber (22μm core), 36nJ pulses with 1.1ps pulse width were obtained in
all-fiber configuration. The high peak power pulses at 2 μm reported here should be useful for mid-IR generation.
A high-spectral-flatness mid-infrared supercontinuum fiber source is presented. It generates highly stable single-mode
broadband beam with a FWHM bandwidth of ~600nm and a 20dB-down spectra spanning from 1.8μm up to ~ 2.7μm.
The supercontinuum pulses are emitted from a single-mode fiber with ~15kW peak power and >20GW/cm2 laser peak
intensity. This compact fiber source, in combination with a commercial mid-infrared optical spectrum analyzer
(Yokogawa), offers a powerful tool for mid-infrared component characterization with high spectral resolution.
Mid-infrared fiber laser sources have attracted a lot of interest in space and defense applications. We review our latest
developments of various fiber laser sources operating near 2μm based on Tm3+ and Ho3+ ions, which include singlefrequency
CW laser sources, Q-switched laser sources, mode-locked laser sources. Potential applications of these fiber
laser sources are also briefly discussed.
We generated 2 nJ, ~690 fs pulses with 10 MHz repetition rate from a linear cavity mode-locked Er3+-doped fiber laser with a fiber taper embedded in carbon nanotubes (CNTs)/polymer composite. Evanescent
field out of the taper section can interact with CNTs to see saturation of absorption. With the fiber based
saturable absorber this laser has simple and robust all-fiber configuration comparing to traditional linear
cavity mode-locked lasers with semiconductor saturable absorbers. In addition, we have demonstrated a
mode-locked ring laser, with a similar saturable absorber, by using an ion-exchanged Er3+-Yb3+-codoped
planar waveguide as the gain medium.
In this paper, we propose and experimentally demonstrate a pressure sensor based on birefringent single mode
fiber FP cavity using optical heterodyne. The proof of concept device consists of a light source, a polarizer controller,
a modulator, a RF generator, a single mode fiber Fabry-Perot cavity, a strain inspector, an erbium doped fiber amplifier,
a filter, a polarizer, an optical spectrum analyzer, and a digital communication analyzer. The dynamic range of the
proposed sensor is explored. The results demonstrate the new concept of fiber pressure sensors and the technical
feasibility for pressure measurements.
In this paper, we propose a novel passively mode-locked waveguide laser using carbon nanotubes saturable
absorber integrated with gain medium, in which the carbon nanotubes saturable absorber is directly sprayed on the
Er-Yb doped phosphate glass waveguide, a ring cavity is chosen. The mode-locking mechanism is the interaction
between the evanescent field of guiding mode and the carbon nanotubes. An elementary research on the proposed
passively mode-locked waveguide laser is presented.
Sophisticated modulation formats like phase shift keying (PSK) as discussed for high-speed fiber-optic transmission systems operating at 40 Gbit/s and beyond, cause new challenges for clock recovery. Whereas conventional return-to-zero on-off keyed (RZ-OOK) modulated signals provide proper clock tones which can be used to recover the clock signal, the additional phase modulation (RZ-PSK) changes the spectral composition of the signal and weakens or suppresses the clock tones. This effect is bit pattern dependent as can be seen from a simple example: If all the pulses in an RZ-PSK signal are in phase, the result is equivalent to an ordinary RZ on-off-keying (OOK) signal with a strong carrier and clock tones. If the pulses in a sequence oscillate in phase by &pgr;, the result is equivalent to the well-known carrier-suppressed return-to-zero signal (CS-RZ) where the carrier is suppressed and where clock tones are differently spaced compared to RZ-OOK. In this paper we present results of the simulation of the different cases taking into account realistic bit sequences and analyze the results with special emphasis on the influence the effect has on clock recovery.
We report on an experimental study of waveguide lasers in Er/Yb-codoped phosphate glass. The waveguides serving as laser cavities were fabricated by electric field assisted silver-film ion exchange technology. Threshold power, slope efficiency, and output power were measured from these lasers and compared to previously reported data. We also report on waveguide DBR-lasers using photowritten gratings in a hybrid glass.
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