Tzong Yow Tsai

Co2+:ZnS and Co2+:ZnSe saturable absorber Q switches

The materials, Co2+:ZnS and Co2+:ZnSe, serving as Q switches with an Er3+: glass laser at 1.54 μm have been demonstrated and analyzed. The output pulses were typically 15–65 ns in duration and of 1–4 mJ depending on the doping concentration and the crystal quality. The ground-state absorption cross section of Co:ZnS has been determined to be 7.7×10−19 cm2 and 7.6×10−19 cm2 for Co:ZnSe, by bleaching experiments.

Q-switched 2-µm lasers by use of a Cr 2+ :ZnSe saturable absorber

Flash-lamp-pumped Ho:YAG (2090-nm) and Tm:YAG (2017-nm) lasers were, for the first time to our knowledge, passively Q switched by use of a Cr2+:ZnSe saturable absorber. A Q-switched Ho laser with 1.3-mJ pulse energy and ∼90-ns pulse duration and a Q-switched Tm laser with ∼3.2-mJ pulse energy and 90-ns pulse duration were demonstrated. Compared with the free-running output energies at the Q-switching threshold pump levels, the Q-switching efficiencies were approximately 5% for the Ho:YAG laser and 16% for the Tm:YAG laser.

Passively Q-switched erbium all-fiber lasers by use of thulium-doped saturable-absorber fibers

We demonstrate all-fiber passively Q-switched erbium lasers at 1570 nm using Tm(3+)-doped saturable-absorber fibers. The absorption cross section of a Tm(3+)-doped fiber at 1570 nm was measured in a bleaching experiment to be about 1.44 x 10(-20) cm(2). With a thulium-doped fiber, sequential pulses with a pulse energy of 9 microJ and a pulse duration of about 420 ns were stably produced at repetition rates in the range 0.1 to 2 kHz. The maximum pulse repetition rate was 6 kHz, limited by the maximum pump power of a 980-nm laser diode, about 230 mW.

A saturable absorber Q-switched all-fiber ring laser.

We propose a simple design of a saturable absorber Q-switched all-fiber ring laser. By locating a saturable absorber fiber in the intensity-enhanced section of a ring resonator, the laser is passively Q-switched. A set of location-dependent rate equations is established for Q-switching modeling. The design has been numerically and experimentally demonstrated using Er(3+)-doped fiber at the emission wavelength of 1550 nm. A single-mode Q-switched pulse with pulse energy of 0.37 microJ and pulse duration of 218 ns was achieved with 980-nm pump power near 7 mW.

All-fiber passively Q -switched erbium laser using mismatch of mode field areas and a saturable-amplifier pump switch

We propose and demonstrate an all-fiber self-Q-switched erbium laser system that is saturable-absorber Q switched by the mismatch of the mode-field areas in the resonator and stabilized with a saturable-amplifier pump switch. Sequential pulses with a pulse energy of 8-6 microJ and a pulse duration of 80-320 ns, corresponding to a pulse repetition rate of 0.25-1 kHz, were obtained using a cw 980 nm laser-diode pump. A peak pulse power of near 100 W was achieved.

Saturable absorber Q- and gain-switched all-Yb3+ all-fiber laser at 976 and 1064 nm.

We demonstrate a novel passively pulsed all-Yb3+ all-fiber laser pumped by a continuous-wave 915-nm pump laser diode. The laser was saturable absorber Q-switched at 976 nm and gain-switched at 1064 nm, using the method of mode-field-area mismatch. With a pump power of 
105 mW, the laser iteratively produced a 976-nm pulse with an energy of 2.8 μJ and a duration of 280 ns, followed by a 1064-nm pulse with 1.1 μJ and a 430-ns duration at a repetition rate of 9 kHz. A set of rate equations was established to simulate the self-balancing mechanism and the correlation between the Q- and gain-switched photon numbers and the populations of the gain and absorber fibers.

A novel ultracompact two-mode-interference wavelength division multiplexer for 1.5-/spl mu/m operation

A novel ultracompact 2/spl times/2 wavelength division multiplexer (WDM) for 1.55-/spl mu/m operation based on highly dispersive two-mode interference (TMI) was designed, theoretically modeled, and verified using a finite-difference-time-domain (FDTD) method. A two-moded waveguide assisted with a dispersive tooth-shaped grating provided a mode-dependent reflection band of central wavelength at 1.55 /spl mu/m. The wavelengths of 1538 and 1572 nm that were at the band edges and had the lowest reflection losses and relatively high dispersion were selected for wavelength multiplexing. The result showed that the wavelengths were separated by grating dispersion in a coupler length of 75 /spl mu/m which was much shorter than the required length of 1.1 mm in a regular TMI multiplexer of no grating. Insertion loss of about 1.7 dB and channel contrast of about 12 dB were achieved.

Characteristics of Co2+:ZnS saturable absorber Q-switched neodymium lasers at 1.3 μm

Passively Q-switched neodymium lasers, Nd:YAG, Nd:YALO, and Nd:BEL, at 1.3 μm using the saturable absorber Co:ZnS were characterized. The best performance, about ∼0.35 mJ pulse energy and 300 ns pulse duration, was obtained using the Nd:BEL laser. In a Co:ZnS Q-switched Nd:YAG laser, sequential dual-wavelength Q-switched pulses at 1319 and 1338 nm were observed. The time separation between the output pulses was about 2–10 μs. Theoretical analysis is presented including analysis of the dual-mode Q-switched laser operation.

A novel wavelength-division multiplexer using grating-assisted two-mode interference

A novel design of wavelength-division multiplexer based on two-mode interference assisted by a highly dispersive grating structure is two-dimensionally simulated and analyzed using finite-difference time-domain method. We show that the designed grating waveguide provides a mode-dependent reflection spectrum which can be used to modify the beat lengths of the two selected wavelengths 1342 and 1560 nm, so that they can be divided in a very short distance about 48 /spl mu/m. Simulation results show that contrasts /spl sim/12 dB and insertion losses about 2 dB could be achieved.

A self-Q-switched all-fiber erbium laser at 1530 nm using an auxiliary 1570-nm erbium laser.

We demonstrate a self-Q-switched, all-fiber, tunable, erbium laser at 1530 nm with high pulse repetition rates of 0.9-10 kHz. Through the use of an auxiliary 10-mW, 1570 nm laser that shortened the relaxation time of erbium, sequentially Q-switched pulses with pulse energies between 4 and 6 microJ and pulse widths of 40 ns were steadily achieved. A peak pulse power of 165 W was obtained.