Short wavelength (/spl lambda//spl sim/4.3 /spl mu/m) high-performance continuous-wave quantum-cascade lasers

We report continuous-wave (CW) operation of a 4.3-/spl mu/m quantum-cascade laser from 80 K to 313 K. For a high-reflectivity-coated 11-/spl mu/m-wide and 4-mm-long laser, CW output powers of 1.34 W at 80 K and 26 mW at 313 K are achieved. At 298 K, the CW threshold current density of 1.5 kA/cm/sup 2/ is observed with a CW output power of 166 mW and maximum wall-plug efficiency of 1.47%. The CW emission wavelength varies from 4.15 /spl mu/m at 80 K to 4.34 /spl mu/m at 298 K, corresponding to a temperature-tuning rate of 0.87 nm/K. The beam full-width at half-maximum values for the parallel and the perpendicular far-field patterns are 26/spl deg/ and 49/spl deg/ in CW mode, respectively.     

Improved GaAs-based quantum cascade laser (/spl lambda//spl sim/11 /spl mu/m) using high-reflectivity metal facet coating

By applying a high-reflectivity metal coating to the rear facet of a GaAs-based quantum cascade laser operating at /spl lambda//spl sim/11.5 /spl mu/m, the threshold current has been reduced by 11% at 260 K and pulsed operation of the epilayer-up mounted device was extended from 283 to 294 K.     

Resonant-phonon terahertz quantum-cascade laser operating at 2.1 THz (/spl lambda//spl sime/141 /spl mu/m)

The development of quantum-cascade lasers (QCLs) at 2.1 THz (/spl lambda//spl sime/141 /spl mu/m), which is the longest wavelength QCL to date without the assistance of magnetic fields, is reported. This laser uses a structure based on resonant-phonon depopulation, and a metal-metal waveguide to obtain high modal confinement with low waveguide losses. Lasing was observed up to a heatsink temperature of 72 K in pulsed mode and 40 K in continuous-wave (CW) mode, and 1.2 mW of power was obtained in CW mode at 17 K.     

Design of a MEMS-based microchemical oxygen-iodine laser (/spl mu/COIL) system

A design of a microelectromechanical systems (MEMS)-based microscale chemical-oxygen iodine laser (/spl mu/COIL) system is presented. A mathematical model of the /spl mu/COIL system, based upon existing macroscale models of the COIL system and related microscale technologies, is formulated and used to predict system performance. The new /spl mu/COIL concept is comprised of an array of cocurrent gas- and liquid-flow singlet-oxygen generators, which supply a supersonic slit nozzle for Iodine dissociation and excitation, a segment of a macroscale optical cavity, and a /spl mu/-scale pressure-recovery system to maintain low-pressure operation. Reactor, nozzle, optical cavity, and pressure recovery system models are developed individually and integrated into a model of the overall system. The resulting model of the /spl mu/COIL system is employed to determine the optimal reagent throughputs, reactor dimensions, and operating pressures to maximize output energy density, defined as the output power divided by the total system and reagent weight for a 100 s operating time. Detailed simulation results corresponding to an optimal energy density of 24.6 kJ/kg are presented, in conjunction with energy density values obtained over the entire parameter space studied. Consideration is given to the design of a realizable, integrated /spl mu/COIL system, for minimum (7.1 kW) and high-power (/spl sim/100 kW) systems. Results of the study suggest that the /spl mu/COIL system could be a superior alternative to existing COIL devices, via reduced system volume and weight and improved reliability and safety.     

A two-step laterally tapered 1.55-/spl mu/m SSC DFB laser fabricated by using a nonselective grating process

We demonstrate a two-step laterally tapered 1.55-/spl mu/m spot size converter distributed feedback laser diode (SSC DFB LD) having a planar buried heterostructure-type active waveguide and a ridge-type passive waveguide fabricated by using a nonselective grating process. Unlike conventional SSC DFB LDs, where a selective grating is employed, this SSC DFB LD employed a nonselective grating over the entire device region in order to make its fabrication much simpler than that of the conventional SSC DFB LDs. The two-step laterally tapered SSC is effective in removing an unwanted wavelength peak originating from the SSC section having a multiquantum well and a grating under it. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far field pattern in horizontal and vertical directions of 13.4/spl deg/ and 19.5/spl deg/, respectively.     

Antimonide semiconductor saturable absorber for passive mode locking of a 1.5-/spl mu/m Er : Yb : glass laser at 10 GHz

We demonstrate the first antimonide (AlGaAsSb) semiconductor saturable absorber mirror (SESAM) for stable passive mode locking of an Er : Yb : glass laser at 10 GHz and a center wavelength of 1535 nm generating 4.7-ps pulses. The nearly resonant SESAM is InP-based, grown by metal-organic vapor phase epitaxy and optimized for high pulse repetition rates. We fully characterized the linear and nonlinear optical parameters: The saturation fluence is 80 /spl mu/J/cm/sup 2/, the modulation depth is 0.4% and the nonsaturable losses are 0.35%. A 1/e decay time of 95 ps is achieved after wet chemical etching of the 10-nm InP cap on top of the absorber.     

Re-investigation of optically pumped hydrazine far-infrared laser around 11 /spl mu/m from the 10HP and 10P bands of a pulsed CO/sub 2/ laser: new lines and assignments

A high-peak-power (several hundreds of watts) pulsed CO/sub 2/ laser, recently developed in our laboratory, has been used for exciting optically pumped far-infrared laser transitions of N/sub 2/H/sub 4/. A systematic search for N/sub 2/H/sub 4/ absorption coincidences with 10P and 10HP CO/sub 2/ laser emissions has led to the observation of 27 new far-infrared laser lines, excited by 18 different absorption transitions. All of these new lines have been characterized in wavelength, offset, relative polarization, optimum operation pressure and intensity. Using the LaseRitz program, ten of these lines were assigned, corresponding to five laser systems. For other two laser systems possible J and K quantum numbers of the energy levels involved in the laser transitions were given.     

Reduced linewidth re-broadening by suppressing longitudinal spatial hole burning in high-power 1.55-/spl mu/m continuous-wave distributed-feedback (CW-DFB) laser diodes

For the first time, the impact of longitudinal photon density distribution and longitudinal carrier density distribution on the spectral linewidth re-broadening effect in single-electrode 1.55-/spl mu/m distributed feedback (DFB) laser diodes (LDs) is investigated experimentally in details. By optimizing the front-to-rear facet power ratio, the nonuniformity of the photon density distribution along the laser cavity is reduced, hence reducing the degree of longitudinal spatial hole burning (SHB). Using this optimized value of front-to-rear facet power ratio, the degree of longitudinal SHB can be further reduced through reduction of the nonuniformity of the longitudinal carrier density distribution by increasing the cavity length. As a result, the local stimulated emission is reduced, hence reducing linewidth re-broadening caused by longitudinal SHB. The outcomes of this analysis is being used fruitfully to design high-power 1.55-/spl mu/m DFB LDs exhibiting very narrow spectral linewidth of approximately 1.3 MHz at an output power of 175 mW under continuous-wave operation.     

Wide-temperature-range operation of 1.3-/spl mu/m beam expander-integrated laser diodes grown by in-plane thickness control MOVPE using a silicon shadow mask

A new fabrication method of high-quality thickness-tapered semiconductor waveguides is proposed based on controlling in-plane thickness during MOVPE by using a comb-shaped silicon shadow mask. It was used to fabricate a 1.3-/spl mu/m-wavelength narrow-beam (less than 13/spl deg/) InGaAsP-InP laser diode, which achieved high-power (over 20 mW) operation up to 85.