Single longitudinal mode control of semiconductor lasers by rectangular conical diffractor system for wavelength-division-multiplexing transmission

A new external feedback system named the rectangular conical diffractor (RCD), which is composed of a diffraction grating and a mirror, is designed. This system has advantages for wavelength-division-multiplexing transmission systems. By using this system in both single and multimode semiconductor lasers: 1) the oscillation wavelength of a semiconductor laser can be selected freely; 2) some semiconductor lasers oscillate at different wavelengths from one another simultaneously, and no interference exists between the oscillation wavelengths under the condition that each semiconductor laser is operated independently; and 3) the selected wavelength is stable against temperature variation of the lasers.     

Active mode-locking of an external cavity GaInAsP laserincorporating a fibre-grating reflector

Active mode-locking of a GaInAsP semiconductor diode amplifier, coupled to an external cavity incorporating an optical fibre grating as a bandwidth limiting and wavelength selective mirror, is reported. The grating defined the central emission wavelength to the 1.53 μm region where mode-locked pulses having durations of less than 10 ps were generated at a repetition rate of 648 MHz     

Design and performance of a complex-coupled DFB laser with sampled grating

A complex-coupled DFB laser with sampled grating has been designed and fabricated. The method uses the + 1 st order reflection of the sampled grating for laser single-mode operation. The typical threshold current of the sampled grating based DFB laser is 25 mA, and the optical output is about 10 mW at the injected current of 100 mA. The lasing wavelength of the device is 1.5385μm, which is the +1 st order wavelength of the sampled grating.     

Broadly wavelength-tunable external cavity, mid-infrared quantumcascade lasers

Wavelength tuning over 120 nm for a grating-coupled 5.1-μm quantum-cascade type-I laser was studied for temperature from 80 to 243 K (-30°C). Both the Littman-Metcalf and first-order grating direct feedback cavity configurations were used with similar tuning results. The goal is to achieve broad tunability, and the result is a combined grating and temperature tuning of 245 nm, from 5.040 to 5.285 μm. The laser was designed for predominantly single-mode or at most, two-longitudinal mode operation. The instrument-limited laser linewidth was less than the cavity longitudinal mode spacing. Stepping-motor control of the grating allowed 0.4-GHz wavelength increments (35 pm) to be realized with high reproducibility. A current-induced wavelength shift of ~2-3 GHz was observed, corresponding to an effective refractive index change of ~10^-3. Analysis indicates that single-mode, continuously tunable operation is feasible with a more optimal device and cavity     

Novel micromirror for vertical optical path conversion formed insilica-based PLC using wettability control of resin

A novel technique has been developed for fabricating a micromirror in a single-mode silica-based planar lightwave circuit (PLC), in which the flat slope for the mirror is made of resin by utilizing wettability control and the surface tension effect. It was shown that the mirror could be designed by numerical calculation based on the equation of Young and Laplace for a liquid surface. A controllable mirror angle range from 30 to 60° was achieved experimentally by changing the position of the boundary line between high and low wettability regions using oblique evaporation. The characteristics of a fabricated 45° mirror installed in a silica-based PLC were evaluated by coupling it vertically to a single-mode fiber. The obtained coupling losses between waveguides and a fiber were 0.60-1.15 dB for mirrors with widths of more than 200 μm, and 0.92 1.62 dB for 190 μm wide mirrors, at a wavelength of 1.55 μm. The experimental minimum losses of 0.6 and 0.92 dB coincided with the calculated values     

Low-loss single-mode GaAs/AlGaAs miniature optical waveguides withstraight and bending structures

Low-loss single-mode GaAs/AlGaAs miniature optical waveguides fabricated for use in monolithically integrated optical circuits are discussed. The propagation characteristics of these waveguides with straight and S-bending structures have been investigated at wavelengths of 1.30 and 1.55 μm. The lowest propagation losses are estimated to be 0.58 dB/cm and 0.69 dB/cm at wavelengths of 1.30 and 1.55 μm, respectively. The total loss of an S-bending waveguide with a curvature radius of 2 mm and with a lateral displacement of 200 μm was 0.61 dB and 0.46 dB at wavelengths of 1.30 and 1.55 μm. The fabricated single-mode strip-loaded waveguides proved to be suitable for application of the semiconductor waveguide into monolithically integrated optical circuits     

Laser-to-fiber coupling scheme by utilizing a lensed fiberintegrated with a long-period fiber grating

An optical coupling scheme between a laser diode and a single-mode fiber utilizing a lensed fiber integrated with a long-period fiber grating is experimentally demonstrated and qualitatively analyzed. A long working distance of 110 μm and a coupling of 35% are obtained for a laser diode with an ellipticity of 2.5. The longitudinal and transverse tolerances at 1-dB excess loss are 26 and 2.5 μm, respectively     

A study of wet oxidized AlxGa1-xAs forintegrated optics

An investigation of wet oxidized Al_xGa_1-xAs layers in integrated optical applications is reported. Refractive index and thickness shrinkage of wet oxidized Al_xGa_1-xAs layers are measured using spectroscopic ellipsometry. A Cauchy fit to the refractive index is found in the wavelength range between 0.3 and 1.6 μm. The refractive index at 1.55 μm is found to be 1.66±0.01 with little dispersion around 1.55 μm. Very low loss single-mode waveguides with metal electrodes showing very low polarization dependence of loss coefficient are fabricated using wet oxidized Al_xGa_1-xAs layers as upper cladding. Optical polarization splitters are also designed and fabricated from the same type of waveguides taking advantage of increased birefringence. Designs utilizing wet oxidized Al_xGa_1-xAs are compared with conventional designs using only compound semiconductor heterostructures     

复增益耦合型取样光栅DFB激光器的设计制作与性能

A complex-coupled DFB Laser with sampled grating has been designed and fabricated. The key concepts of the approach are to utilize the +1st order reflection of the sampled grating for laser single mode operation, and use a conventional holographic exposure combined with the usual photolithography to fabricate the sampled grating. The typical threshold current of the sampled grating based DFB laser is 25mA, and the optical output is about 10mW at the injected current of 100mA. The lasing wavelength of the device is 1.5385μm, which is the +1st order wavelength of the sampled grating.     

A fiber lens with a long working distance for integrated couplingbetween laser diodes and single-mode fibers

A new scheme is proposed for lensed fibers with a long working distance, as used in the coupling between laser diodes and single-mode fibers. The scheme consists of the combination of a hemispherically-ended coreless-fiber tip and an expanded-core fiber. The working distance is measured as 169 μm with a relatively low coupling-loss of 4.2 dB at a wavelength of 1.49 μm. Tolerances for a 1-dB loss increment for axial-, lateral-, and angular-misalignment are 35, 2.6 μm, and 0.8 degrees, respectively. The new configuration is suitable for alignment-free coupling between arrayed laser diodes and an array of single-mode fibers     

基于液晶/聚合物光栅选频的高效率有机半导体激光器

报道了一种基于液晶/聚合物光栅选频的高效率有机半导体激光器的制备方法。首先在一片玻璃基板上旋涂有机半导体荧光薄膜MEH-PPV作为增益介质,然后在其上通过光场中的定域光聚合制备液晶/聚合物光栅,形成分布式反馈(DFB)有机半导体激光器。激光出射阈值0.32μJ/pulse,斜率转化效率高达7.8%,呈现良好的s偏振特性。采集了激光束的光斑,轮廓清晰,呈现扇形结构。通过改变光栅周期,实现了53.4nm激光出射范围。本工作为新型有机激光器的制备提供了有益的指导和借鉴意义。     

Low threshold InGaAs/GaAs 45° folded cavity surface-emittinglaser grown on structured substrates

A novel folded cavity surface-emitting laser structure integrating a horizontal cavity InGaAs/GaAs laser grown on a structured substrate with a high reflectivity Bragg reflector has been fabricated. Devices with threshold currents of 8 mA and CW wall plug efficiencies at 5% at 6 mW output power have been demonstrated at a wavelength of 0.99 μm. By combining a cleaved uncoated mirror with the 45° deflecting mirror the authors have obtained threshold current as low as 5 mA for a device 450 μm long     

A scheme of picosecond pulse shaping using gain saturationcharacteristics of semiconductor laser amplifiers

To obtain high power, well shaped picosecond pulses from gain-switched semiconductor lasers, the use of dynamic gain saturation characteristics of semiconductor laser amplifiers was investigated theoretically and experimentally. A configuration of a reflected-wave amplifier (RWA) with single-side external coupling is introduced for pulse shaping, which is found to be suitable for enhancing dynamic gain saturation. By a combination of a distributed feedback laser oscillator at 1.3 μm in wavelength and a reflected-wave amplifier of 400 μm cavity length with asymmetric facet reflectivities of 0.01% and 30%, single-mode optical pulses with almost no tailing, full width at half maximum of 15 ps, and peak power exceeding 50 mW were obtained without pulse broadening, despite the considerable tail structure of the incident pulse     

Single-quantum-well strained-layer InGaAs-InGaAsP lasers for the wavelength range from 1.43 to 1.55 mu m

Strained-layer single-quantum-well InGaAs-InGaAsP lasers have been fabricated using a novel self-aligned-contact ridge guide structure. The lasers operate with index-guided fundamental transverse mode. The laser cavity length and mirror reflectivities were chosen to achieve laser oscillation in the wavelength range from 1.43 to 1.55 mu m. It is shown that a fiber amplifier pump laser at 1.47 mu m wavelength and a transmission source laser at 1.55 mu m wavelength can be fabricated from a single wafer grown by metalorganic vapor phase epitaxy (MOVPE).<>     

Single mode multiple-element laser array with grating filter

A 1.5-μm wavelength grating filter laser array (GFA) structure which consists of a positive-index-guided multiple-element array region and a laterally unguided grating filter region is proposed and theoretically analyzed for realizing in-phase supermode and simultaneous single-longitudinal-mode operation. A five-element GaInAsP/InP GFA with a lasing wavelength of ~1.5 μm was fabricated and its single-longitudinal-mode/in-phase supermode operation was demonstrated up to four times the threshold current     

Low-loss substrate-removed (SURE) optical waveguides in GaAs-AlGaAsepitaxial layers embedded in organic polymers

Low-loss single-mode semiconductor rib optical waveguides fabricated in GaAs-AlGaAs epitaxial layers are removed from GaAs substrates and bonded to transfer substrates using a benzocyclobutene organic polymer. Optical quality facets were obtained by cleaving through the transfer substrate. An average propagation loss of 0.39 and 0.48 dB/cm at 1.55 μm wavelength for TE and TM polarizations, respectively, were measured. This was on average 0.05 dB/cm greater than control guides fabricated in GaAs-AlGaAs epilayers on GaAs substrates with air as the top cladding. This demonstrates the feasibility of a process enabling semiconductor polymer integration and processing both sides of an epitaxial layer     

Intermodal tuning characteristics of an InGaAsP laser with opticalfeedback from an external-grating reflector

A report is presented on the spectral characteristics of one-side antireflection coated 1.3-μm InGaAsP lasers exposed to strong feedback from an external grating, when the center wavelength of reflection of the grating is tuned continuously from one solitary laser longitudinal mode to the adjacent lower frequency mode. The effect of different residual reflectivities of the coated facet on the tuning characteristics of the laser was investigated experimentally. Bistability in the tuning characteristic is explained using a graphical representation of operating conditions. The stability of single-mode oscillation is found to depend on the offset between the resonance frequency of the solitary laser and the frequency of maximum reflection from the grating. An offset between the oscillation frequency of the laser and the frequency of maximum reflection from the grating is shown to occur     

Multi-oxide layer structure for single-mode operation invertical-cavity surface-emitting lasers

We propose a novel vertical-cavity surface emitting laser (VCSEL) with Al(Ga)As multi-oxide layer (MOX) structure for the purpose of enlarging window aperture maintaining single transverse mode operation. We have fabricated an InGaAs-GaAs VCSEL with the proposed MOX structure formed on GaAs (311)B substrate. We have performed a numerical simulation to investigate single-mode behavior of the proposed structure and showed a possibility of single-mode VCSEL's with a large active area. We have fabricated an 11-μm current aperture 960-nm wavelength VCSEL with this MOX structure. The threshold current and voltage were 1.0 mA and 2.0 V, respectively, which are comparable to those of conventional oxide VCSELs. In 8-μm aperture, single-mode operation was maintained with a driving current up to four times the threshold     

Semiconductor laser with external resonant grating mirror

A resonant grating composed of an ion exchanged slab waveguide on a glass substrate with a corrugation grating at its surface is shown to perform as a wavelength selective external mirror of a semiconductor laser. Preliminary wavelength tuning is demonstrated.     

Forced pump oscillation at anti-Stokes wavelength of coupled Raman fibre laser resonators

Multi-watt oscillation of a Yb/sup 3+/-doped silica fibre pump laser is demonstrated at two wavelengths when pump-coupled Raman fibre laser resonators are constructed using fibre end reflection and a dielectric mirror, which are common to both the pump and Raman fibre lasers. Using an off-resonant Bragg grating to force the initial oscillation of the Raman fibre laser, pump emission at the anti-Stokes wavelength is demonstrated.