Design of DFB lasers for high-power single-mode operation

The longitudinal-mode behaviour above threshold for DFB lasers has been analysed taking into account spatial hole burning along the laser axis. As a result, the single-longitudinal-mode operating condition up to high optical output power has been made clear.     

1.5 ?m phase-shifted DFB lasers for single-mode operation

Fabrication and single-mode laser oscillation were demonstrated for modified DFB lasers where the phase of the corrugations was shifted at the centre by a quarter guided-wavelength and which, in principle, provided a resonance at the Bragg wavelength and stable single-mode oscillation. Phase-shifted corrugations were fabricated using electron-beam lithography.     

端面反射率对半导体激光器单模工作性能的影响

本文利用半导体激光器多模速率方程组的隐式解析解，从理论上了端面反射率对半导体激光器单模工作性能的影响，结果表明，在相同的输出功率下，端面反射率越低，单模工作性能越差，与Ｅｔｔｅｎｂｅｒｇ等人通过实验研究所得的结论相同。     

High-power single-mode operation in DFB and FP lasers usingdiffused quantum-well structure

Distributed feedback (DFB) and Fabry-Perot (FP) semiconductor lasers with step and periodic interdiffusion quantum-well structures are proposed for high-power single-longitudinal-mode operation. It is shown that the phase-adjustment region formed by the diffusion step (i.e., step change in optical gain and refractive index) counteracts the influence of spatial hole burning, especially for DFB lasers with large coupling-length products biased at high injection current. Furthermore, it is found that with careful design of the diffusion grating (i.e., grating period and amount of diffusion extent) of FP lasers, side-mode suppression ratio can be enhanced and threshold current density can be minimized to a satisfied level     

High-temperature single-mode operation of 1.3-μm strained MQWgain-coupled DFB lasers

Single-mode and high-power operation at temperatures up to 120°C has been achieved in 1.3-μm strained MQW gain-coupled DFB lasers. A stable lasing wavelength is maintained due to a large modal facet loss difference of the two Bragg modes, which is provided by the gain-coupling effect. A very low temperature dependence of the threshold current has been obtained by detuning the lasing wavelength to the long wavelength side of the material gain peak at room temperature, which effectively compensates the waveguide loss at higher temperatures. An infinite characteristic temperature T_o can be realized at certain ranges of temperature depending on the detuning value     

Enhanced single-mode operation in multisection DFB lasers with bothlocalized and distributed phase shift

Multisection distributed feedback lasers with both localized (λ/8 phase shift) and distributed phase shift (produced by a phase-adjustment region) are investigated theoretically. It is shown that such a mixed phase shift, combined with a stronger coupling coefficient in the center of the cavity, may enlarge the threshold gain margin as well as the output optical power, enhance the intra cavity field flatness and produce an effective index profile leading to a low sensitivity to spatial-hole burning (SHB) (with respect to conventional λ/4 phase-shifted DFB lasers). As a consequence, the side-mode suppression ratio (SMSR) is improved and single-mode operation up to high bias currents is maintained     

高速宽温度范围无致冷DFB半导体激光器

报道了一种高性能的1.3μm波长的应变多量子阱分布反馈半导体激光器,它具有高的直接调制速率、宽的无致冷工作温度范围以及可靠性能好的特点.通过对激光器有源区、波导层以及DFB光栅结构的综合优化,所制作的激光器具有低的阈值电流以及高的量子效率,其室温直接调制速率达到16GHz,能实现-40℃～85℃范围内无致冷工作,其中值寿命超过200万小时.     

Improvement of single-mode gain margin in gain-coupled DFB lasers

Using the Bloch-wave analysis, this paper investigates the effect of the gain grating on the single-mode condition in DFB lasers. Various factors affecting the threshold gain of gain-coupled DFB lasers are analyzed in some detail. It is shown for the first time that unequal section lengths in the gain grating can have a significant effect on the single-mode gain margin of gain-coupled DFB lasers, especially when the linewidth enhancement factor α_M is large, because the long and shortwavelength Bloch waves are in phase and in antiphase with the index grating of DFB lasers, respectively     

The effect of facet mirror reflectivity on the spectrum of single-mode CW constricted double-heterojunction diode lasers

In this paper we show that the spectral mode content of mode-stabilized constricted douhle-heterojunction lasers can be altered by changes in facet reflectivity. If the facet reflectivity is substantially reduced below the nominal value of 30 percent, then the lasers will exhibit multilongitudinal mode operation. Nearly planar-geometry lasers that show instabilities can be made to operate in a stable single mode by increasing the facet reflectivity to values above 50 percent.     

Design of asymmetric quarter-wave-shifted DFB semiconductor lasers

Quarter-wave-shifted distributed-feedback (QWS-DFB) semiconductor lasers with asymmetric structure are theoretically analysed in terms of wavelength selectivity, differential efficiency, linewidth and sensitivity to external optical feedback. The analysis is used to design narrow-linewidth lasers with low sensitivity to optical feedback for coherent transmission.     

Wide range tunable laterally coupled distributed-feedback lasers based on InGaAs-GaAs quantum dots

The authors have investigated tunable distributed feedback (DFB) lasers based on InGaAs quantum dots grown by molecular beam epitaxy. Two-section tunable DFB lasers were fabricated by patterning laterally gain coupling binary superimposed gratings perpendicular to the ridge waveguide. Side-mode suppression ratios of up to 40 dB have been achieved. The tuning range covers 30 nm.     

Single-longitudinal-mode operation of DFB lasers in gain-switchedoperating conditions

Single-longitudinal-mode operation under a gain-switched condition, generating 20 ps optical pulses, has been attained in DFB lasers emitting at 1.3 μm wavelength. It has been clarified that Δλ, which is the difference between the DFB wavelength and the gain peak wavelength, plays an important role in stable single-mode operation. The optimum range of Δλ wave found to be in the range from -15 nm to 0 nm     

Fresnel analysis of effective mirror reflectivity in folded-cavityin-plane surface-emitting lasers

Inside-cavity diffraction loss resulting from unguided regions and 45° internal total reflection mirror(s) is an important issue for fabricating folded-cavity in-plane surface-emitting lasers. A Fresnel plane-wave decomposition method was applied to analyze this problem. The effective reflectivity of an angle-etched mirror was calculated for deviation of the etched angle and different lengths of the unguided region. The results offer design criteria for fabricating folded-cavity surface-emitting lasers as well as other devices with angle-etched facet(s) for surface normal light coupling     

Simultaneous dual-wavelength operation in cascaded stronglygain-coupled DFB lasers

Using cascaded strongly gain-coupled (SGC) DFB lasers, simultaneous dual-wavelength operation can be obtained with better than a 40-dB side-mode suppression ratio (SMSR) under simple operating conditions at various temperatures. Dual-wavelength operation with various spacing can be achieved by grating fabrication and by simply activating the lasing section of the cascaded SGC DFB lasers. The lasing wavelengths can be tuned within several nanometers by base temperature variation and their spacing can be fine tuned by individual injection current     

Analysis of reflectivity for a beveled corner mirror insemiconductor ring lasers

A semiconductor ring laser is expected to be used as a tiny ring laser gyro with low power consumption, which is suitable for mobile systems. However, its corner mirrors may be beveled due to its fabrication processes. Therefore, in this paper, reflectivities of beveled corner mirrors in the semiconductor ring laser are examined. In the analysis here, a guided fundamental mode is expanded into plane waves, and thus vertical confinement of the guided mode is completely incorporated. It is revealed that there is an optimum guiding layer thickness of approximately 0.3 μm to minimize mirror losses in the beveled mirrors. Also, facet reflectivities of equilateral n-polygon shaped ring lasers with beveled mirrors are studied, and it is found that a large n leads to a low threshold current     

Influence of mirror reflectivity on laser performance ofvery-low-threshold vertical-cavity surface-emitting lasers

The influeuce of mirror reflectivity on laser performance of InGaAs-GaAs vertical-cavity surface-emitting lasers fabricated by selective oxidation is investigated by the stepwise change of the number of pairs in top mirror stack after device fabrication. Devices with 18-pair stacks in the top mirror, which is the optimized number of pairs in this structure, show an output power over 1.9 mW and a slope efficiency of 55% while maintaining a low threshold current of 212 μA. The analysis of the threshold current and differential efficiency related to mirror reflectivity shows an internal quantum efficiency of 95%, an internal round-trip loss of 0.072, and a transparency current density of 71 A/cm²     

Experimental and theoretical characterization of the mode profile of single-mode DFB fiber lasers

The characterization of the spatial mode profile of distributed feedback fiber lasers (DFB-FLs) is discussed. A new approximate solution for the mode profile of single longitudinal mode DFB-FLs with nonuniform phase and grating profiles is derived. An enhanced high resolution heat perturbation method for mode shape characterization is described. Experimental mode shape profiles are compared with theoretical predictions with good agreement.     

Optimum operation of DFB lasers under chirped pulse transmission

Theoretical calculations together with measurements of the chirping characteristics of DFB lasers have revealed the existence of optimum bias condition for longer transmission distance. Ultimate transmission distances in connection with fibre loss and dispersion are estimated for 1.3 and 1.5 ?m transmission on the basis of experimental device characteristics.     

Wide temperature operation of 40-Gb/s 1550-nm electroabsorption modulated lasers

Electroabsorption modulated lasers (EMLs) exploiting the quantum confined Stark effect need thermoelectric coolers to achieve stable output power levels and dynamic extinction ratios. Temperature-independent operation is reported between 20/spl deg/C and 70/spl deg/C for InGaAlAs-InP-based monolithically integrated 1550-nm EMLs exploiting a shared active area at 40 Gb/s by actively controlling the electroabsorption modulator bias voltage. Dynamic extinction ratios of at least 8 dB and fiber-coupled mean modulated optical power of at least 0.85 mW are obtained over the mentioned temperature range.     

High-efficiency operation of phase-adjusted DFB laser by asymmetric structure

Differential efficiency has been increased by 50% in a phase-adjusted DFB laser by the introduction of an asymmetric structure. The problem of mode degeneracy in DFB lasers has been resolved without penalty on efficiency and output power.