Frequency separation locking and synchronization for FDM opticalsources using widely frequency tunable laser diodes

A laser diode (LD) frequency separation locking method (called the reference pulse method) is proposed. This method has advantageous features for frequency division multiplexing (FDM) networks from the viewpoint of frequency separation stability with a strict frequency separation standard, modulation format independence, controllability over a large number of LDs, and frequency synchronization capability. Frequency locking experiments, using four and ten controlled LDs, confirmed that the control system using the method can stabilize frequency spacing for more than 100 LDs. The frequency fluctuation is suppressed to less than 10 MHz. Frequency synchronization, utilizing the reference pulse method, is proposed and demonstrated experimentally for two controlled LD groups, each consisting of three LDs. Frequency discrepancy between two LD groups was only 2.7% of the frequency separation. Required frequency-swept light power and controlled LD power at the detector input for frequency synchronization indicate that more than 50000 LD groups within a 10 km area, each having 100 LDs, can be synchronized simultaneously     

从CLEO''''98看半导体激光器的最新进展

根据ＣＬＥＯ’９８ 会议报道的有关内容,综述了半导体激光器的发展状况。重点叙述了大功率ＬＤ、可见光ＬＤ、中红外ＬＤ 及垂直腔面发射半导体激光器（ＶＣＳＥＬ） 的最新研究进展     

窄线宽可调谐外腔半导体激光器阵列

介绍一种半导体激光器(LDs)阵列的外腔可调谐系统。腔体是Littrow结构,2个透镜将光栅选取的锁模光信号形成颠倒阵列像反馈回各个LD中。系统容易调整,对中心波长810nm、输出功率20W的单排24管LDs阵列,在光学元件参数均非最佳的情况下,获得线宽0．5nm(230GHz)、可调范围近30nm和输出功率为LDs阵列自由运行时的60％。实验结果表明,阵列中单个LD接收到的锁模信号并不必是自己发出的光,而可以来自阵列中其它LDs;此外,只要阵列中部分LDs获得锁模信号,即可达到全阵列锁模的目的。     

半导体激光器辐照损伤效应实验研究进展

半导体激光器(LD)工作在空间辐射或核辐射环境中时,会受到辐照损伤的影响而导致器件性能退化。文章回顾了不同时期研制的LD(从早期的GaAs LD到量子阱LD和量子点LD)在辐照效应实验方面的研究进展,梳理了国际上开展不同辐射粒子或射线(质子、中子、电子、伽马射线)诱发LD辐射敏感参数退化的实验规律,分析总结了当前LD辐照效应实验方法研究中亟待解决的关键技术问题,为今后深入开展LD的辐照效应实验方法、退化规律、损伤机理及抗辐射加固技术研究提供理论指导和实验技术支持。     

GaInAsP/InP lasers with monolithically integrated monitoring photodiodes fabricated by inclined reactive ion etching

Monolithic fabrication of a GaInAsP/InP laser (LD) with a monitoring photodiode (PD) is described. LDs and PDs have etched facets fabricated by inclined reactive ion etching (RIE). The etched LD facing facet PD is perpendicular to the junction plane and the etched PD facet facing LD is inclined by 55 degrees to the plane by the 'windward-leeward effect' of the inclined RIE. Therefore, coupling efficiencies between LDs and PDs are uniform because the multireflection effect of double mirrors does not exist for the LD-PD devices with inclined PD facets. Typical CW threshold current ranges from 20 to 30 mA and light output power from a single facet exceeds 15 mW at 25 degrees C. A PD can detect about 2% of the light beam emitted from an LD facing it.<>     

642-nm AlGaInP laser diodes with a triple tensile strain barriercladding layer

For the first time, tensile strain barrier cladding (TSBC) layers were used in AlGaInP laser diodes (LDs). It was found that the TSBC layers can provide a better optical confinement and a better carrier confinement. AlGaInP LDs with and without the TSBC layers were both fabricated. It was found that the 48-mA threshold current of the 5 μm×800 μm gain-guided triple TSBC AlGaInP LD is lower than the 56-mA threshold current of the conventional AlGaInP LD with the same physical size. The characteristic temperature T₀ of the triple TSBC AlGaInP LD (i.e., 117 K) is also higher than the conventional AlGaInP LD (i.e., 99 K)     

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.     

半导体激光器加速寿命测试系统研制

介绍了半导体激光器(LD)加速寿命测试的理论依据,给出了寿命测试的数学模型,并据此研制了新型LD寿命测试系统。该系统在密封抽真空充氮环境下,通过采集恒功工作LD的工作电流随时间变化的信息及所处环境的温度,绘制出LD的老化曲线,即恒功条件下的“I-t曲线”,然后推断LD的使用寿命。     

Dry-etched 650 nm AlGaInP visible-light laser diodes with operatingtime of over 3000 h

The authors have achieved CW operation of 650 nm GaInP/AlGaInP index waveguide-type visible-light laser diodes (LDs) with dry-etched mesa stripes fabricated by Cl₂ reactive ion beam etching. The threshold current of 47 mA and slope efficiency of 0.40 W/A are almost the same as those of a wet-etched LD fabricated from the same wafer (L=500 μm). The cross-sectional scanning electron microscope view of the buried mesa stripe shows that the dry-etched LD has a symmetric mesa shape resulting in a small focusing spot and stable mode operation. The wet-etched mesa, however, is asymmetric because a 6° misoriented substrate is used for this wavelength operation. An aging test with light output power of 3 mW at 50°C has revealed that these LDs have an operating time of over 3000 h, which represents a sufficient reliability for conventional uses     

Integrated AlGaAs two-beam LD-PD array fabricated by reactive ion beam etching

Monolitically integrated AlGaAs two-beam laser diode (LD)- photodiode (PD) arrays are described. LDs and PDs have etched facets fabricated by reactive ion beam etching (RIBE). LDs in the array exhibit threshold currents as low as 18 mA and external quantum efficiencies of more than 30% per facet. A PD can detect more than 20% of a light beam emitted from an LD facing it. Crosstalk between the two LD-PD columns (separated by 50 ?m), on the other hand, is suppressed to less than ?20 dB by an AlGaAs optical barrier (5 ?m thick) fabricated between them.     

Fabrication of room temperature continuous-wave operation GaN-based ultraviolet laser diodes

Two kinds of continuous-wave GaN-based ultraviolet laser diodes (LDs) operated at room temperature and with different emission wavelengths are demonstrated.The LDs epitaxial layers are grown on GaN substrate by metalorganic chemical vapor deposition,with a 10×600 μm2 ridge waveguide structure.The electrical and optical characteristics of the ultraviolet LDs are investigated under direct-current injection at room temperature. The stimulated emission peak wavelength of first LD is 392.9 nm,the threshold current density and voltage is 1.5 kA/cm² and 5.0 V,respectively.The output light power is 80 mW under the 4.0 kA/cm² injection current density. The stimulated emission peak wavelength of second LD is 381.9 nm,the threshold current density the voltage is 2.8 kA/cm² and 5.5 V,respectively.The output light power is 14 mW under a 4.0 kA/cm² injection current density.     

Large-signal spurious-free dynamic range due to static and dynamicclipping in direct and external modulation systems

Large-signal spurious-free dynamic range (SFDR) is useful in an optical system with a high intensity noise level, which can be due to optical reflections or optical beat interference, and with large modulating signals to achieve sufficient carrier-to-noise ratio (CNR). A closed-form analysis on large-signal SFDR due to static and dynamic clipping for direct and external modulation systems is presented in this paper. The analysis can be applied to laser diodes (LDs) and external modulators with arbitrary transfer functions. We have used the analysis to predict the theoretical upper-bound for large-signal SFDR due to static clipping in an ideal LD and external modulators with various linearization techniques. We have also used the analysis to predict the dynamic-clipping-induced nonlinear distortions (NLDs) in a weakly clipped LD, and confirm that dynamic clipping is more important to consider than static clipping when weak LD clipping takes place. Large-signal SFDRs in practical LDs and external modulators were also compared. The validity of our analysis is confirmed through computer simulation and actual measurement of clipping-induced NLDs in a typical CATV-quality DFB LD     

Failure analysis of InGaAs/GaAs strained-Layer quantum-well lasers using a digital OBIC monitor

The mechanisms that cause the sudden failure of InGaAs/GaAs strained-layer quantum-well lasers (LD) are analyzed by monitoring an optical beam-induced current (OBIC). Statistically, the LDs that suddenly fail have different n-OBIC/sub ridge/ intensity profiles (p-n junction OBIC under the ridge normalized by that under the electrode) from LDs with conventional catastrophic optical damage. It appears that dislocations are generated in the vicinity of an antireflection (AR) facet and extend to the AR facet, and meltdown finally occurs there. The suppression of dislocation generation around the AR facet is important in regards to preventing sudden failure.     

多功能半导体激光医疗仪电源的研制

根据“多功能半导体激光医疗仪”整机的要求,采用同一电源对667nm和808nm半导体激光器实施供电。为避免电源在开、关机时对半导体激光管产生浪涌冲击,电源在设计中采用了适当的逻辑功能。并可保证对667nm激光器供电时,即使打开808nm激光器供电开关,也不对808nm半导体激光器供电,反之亦然。电源设有手动、计算机两种控制方法,及恒定功率、电流两种工作方式。     

Optical retiming regenerator using 1.5 mu m wavelength multielectrode DFB LDs

An optical retiming regenerator is demonstrated using two 1.5 mu m wavelength multielectrode (ME) DFB LDs at 200 Mbit/s. The regenerator consists of an injection-locked self-pulsating ME DFB LD for timing recovery and a bistable ME DFB LD for retimed regeneration.<>     

半导体激光的多光束耦合、整形及反馈隔离

本文给出一种实现半导体激光的多光束藕合及整形的新方法——界面耦合法,具有结构简单、实现光束耦合数目多及同时实现多光束的整形的特点。本文还结合半导体激光的反馈噪声,分析了常用的偏振隔离系统并给出了实用的设计、加工和装配要求,对实际工作具有指导意义。     

Lightwave synthesizer with lock-in-detected frequency references

The authors describe a lightwave synthesizer system based on the lock-in detected frequency references such as atomic or molecular spectra. This system uses two semiconductor laser diodes (LDs); one is a frequency-tunable master LD, and the other is a frequency-modulated tracking LD, used for stabilizing and tuning the master LD. The lightwave-frequency tuning of the master LD is controlled by a microwave synthesizer. This yields the same frequency stability and accuracy as the lock-in-detected frequency reference at anywhere in the tuning range. By using the 1535.39-nm absorption line of acetylene (C₂ H₂) gas as the reference, tuning range of over 13 GHz with an absolute frequency stability of better than 10 MHz is demonstrated from distributed-Bragg-reflector LD     

Noise Characteristics of a Wavelength-Locked Fabry–Perot Laser Diode

We derived a theoretical model of a wavelength-locked Fabry–Perot laser diode (F-P LD) to a sliced spectrum of externally injected amplified spontaneous emission (ASE) from wave equations. The model explains the dynamics of the wavelength-locked F-P LD. Using this model, we investigated the noise characteristics of a wavelength-locked F-P LD with respect to the various parameters, such as, the injected ASE power, the bias current of F-P LD, and the wavelength detuning. We also investigated intensity noise increment by spectral filtering in optical access networks based on wavelength-locked F-P LDs.      

Modified Face-Down Bonding of Ridge-Waveguide Lasers Using Hard Solder

A modified face-down bonding technique of ridge-waveguide laser diodes (LDs) using 80Au20Sn solder has been performed. For ease of manufacturability, a bonding window with good bonding integrity and improved optical performance was determined. Metallographical investigation showed that the solder joint comprised of a layer of delta phase compound near the solder/heatsink interface, a layer of (Au,Ni)Sn intermetallic compound (IMC) at the solder/heatsink interface, and zeta' phase Au/Sn compound at the center of the solder joint. The delta phase shifted to the interfaces after reflow was postulated by its lower surface tension than zeta' phase Au/Sn compound. Good bonding integrity was observed with LD residues still adhering onto the bond pad after die shear testing. Scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) analyses of the fracture surface showed that the fracture occurred within the LD, at the GaAs/SiN interface. LDs bonded with this modified bonding process achieved an optical improvement of 2.5-3X compared to the unbonded LDs due to its good thermal management. These bonded LDs further exhibited good long-term reliability with no significant degradation in optical performance and no significant microstructure evolution in the solder joint after 500 thermal cycling test.     

A compact tunable narrow-band LD based on emission through thesubstrate and an external abnormal-reflection mirror

Due to the high beam divergence of standard laser diodes (LDs), these are not suitable for wavelength-selective feedback without extra optical elements. This letter reports on first prototypes of compact tunable LDs with wavelength-selective feedback via a so-called abnormal reflecting mirror of a low divergent beam coming from a special LD, emitting through the substrate. With this setup, tunable narrow-band (<0.7 nm) lasing is observed showing good temperature stability. Tuning over a range of 5 nm at a maximum power of 0.2 W was demonstrated