Phase noise and linewidth in an InGaAsP DFB laser

Measurements and calculations of interferometrically demodulated phase noise in an InGaAsP DFB laser are reported. The results led to a novel method of laser linewidth measurement. The effect of this noise on a DPSK coherent system is considered.     

基于CPM-FBG的单频窄线宽DFB光纤激光器

利用电弧放电对光纤Bragg光栅(FBG)折射率的调制作用,提出了基于折射率周期调制(CPM)FBG的单频窄线宽分布反馈(DFB)光纤激光器方案。建立了CPM-FBG的数学模型并进行了仿真,验证了CPM-FBG的相移光栅特性;在掺铒光纤(EDF)上制作出CPM-FBG,形成了DFB单频窄线宽光纤激光器,激光器阈值功率为25.4mW,3dB线宽为805Hz,边摸抑制比大于48.8dB。     

氧化锌单晶DFB半导体激光器的设计与分析

基于严格耦合波理论(RCWA)和介质平板波导理论,针对光通信中的1550 nm波长,设计了一种基于氧化锌(ZnO)单晶的分布反馈式(DFB)半导体激光器的光栅结构,分析了二维电场模式图以及激射波长线宽图,得到了光栅结构的变化对其单纵模传输的影响。仿真结果表明,当光栅的周期为489 nm,占空比为50%,光栅深度为400 nm时,全局电场能量达到了8.3×107 J,光谱线宽小于0.1 。该激光器具有很好的窄线宽输出以及波长选择特性。理论分析与仿真结果基本一致为后期进行该器件的制备提供了较好的参考。     

1.55 mu m tunable DFB laser with narrow linewidth and high power

Wavelength tunability over 5 AA at narrow linewidths (less than 10 MHz) and high-output powers (over 15 mW/front facet) is demonstrated in long-cavity multielectrode distributed-feedback (DFB) lasers for coherent optical transmission systems.<>     

浅析元件参数对外腔半导体激光器输出谱宽影响

半导体抽运碱金属蒸气激光器（DPAL）需大功率窄线宽泵浦源,但市售半导体激光器输出线宽远远大于碱金属原子吸收谱宽,难以实现有效泵浦,因此需采用Littrow 外腔法压窄半导体激光器输出谱宽。Littrow 外腔系统中元件参数的选择直接影响大功率半导体激光器输出谱宽。为此文中沿入射光线方向构建外腔压窄模型,利用球面镜替代柱面镜,分析了微柱透镜阵列、光学系统和光栅元件对外腔输出谱宽的影响,模拟结果为微柱透镜阵列焦距越小、光栅刻线越密、球面镜焦距越大,外腔输出谱宽越窄,实验结果符合理论模型。     

用于Rb蒸气激光泵浦的可调谐窄线宽半导体激光器

由于Rb蒸气的吸收峰随缓冲气体气压存在漂移,利用体布拉格光栅(VBG)实现线宽压窄的同时,实现泵浦半导体激光器中心波长的可调谐也是十分必要的。本文采用国内封装的半导体激光阵列(LDA),利用VBG的温度特性,实现了线宽不大于0.3nm的同时,激光器中心波长从779.89nm到780.35nm可调谐。该激光器可以通过叠阵方式用于Rb蒸气的泵浦和激励。     

A tunable distributed amplification DFB laser diode (TDA-DFB-LD)

A novel wavelength-tunable distributed amplification distributed feedback laser diode (TDA-DFB-LD) is proposed and fabricated. The proposed structure provides synchronous change between the longitudinal mode and the Bragg wavelength in tuning; thereby continuous wavelength tuning can be realized with single control-current. Moreover, extended tuning is also possible with two control-currents. A continuous tuning range of 2.9 nm and an extended discrete tuning range of 15 nm are experimentally obtained with a 1.55-μm TDA-DFB-LD     

Comparison of DFB laser linewidth measurement techniques results from COST 215 round robin

An interlaboratory comparison on four different linewidth measurement techniques is performed for twelve DFB lasers from various manufacturers. The measured linewidths agree very well for the lasers that have a flat frequency noise spectrum. Differences of more than a factor of 2 in measured linewidth for some of the other lasers can be explained by an increased level of the low frequency noise spectrum recognised by a Michelson interferometer. The conclusion is made that the application of the laser determines what is the best definition of linewidth and which is the best method for its measurement.<>     

Analysis of quarter-wave-shifted DFB laser

Wavelength selectivity of a quarter-wave-shifted DFB laser is analysed taking into account the effect of a mirror facet at the end of the corrugation. The structure with no reflection is found to be the most promising. The effect of a cleaved facet at an end is not serious as long as KL is as large as 3?5.     

Extremely narrow spectral linewidth and low chirping of theMQW-DFB-PPIBH laser diode

The low threshold current of 9 mA, the high side-mode suppression ratio of more than 45 dB, the extremely narrow spectral linewidth of 1.1 MHz, and the low chirping of 2.8 Å at -20 dB at 2 Gb/s nonreturn to zero (NRZ) modulation have been achieved in the multiple quantum well (MQW) distributed feedback (DFB) p-substrate partially inverted buried heterostructure (PPIBH) laser diode. The spectral linewidth of 1.1 MHz is the narrowest value among 300-μm-length solitary laser diodes. These results suggest that the MQW-DFB laser diodes are a promising light source for longer distance and higher bit-rate optical communication systems and coherent optical communication systems     

Experimental determination of parasitic optical feedback by diode laser linewidth measurements

Proposes a novel method for the characterisation of parasitic optical feedback by measuring the diode laser linewidth change with injection current. Results were obtained with a MCRW (metal-clad ridge-waveguide) laser and reflections from an optical isolator. A feedback signal 67 dB below the laser output was definitely measured.<>     

1064-nm DFB laser diode modules applicable to seeder for pulse-on-demand fiber laser systems

Semiconductor DFB (Distributed feedback) laser diodes with an operating wavelength of 1064 nm, which is suitable for pulse-on-demand fiber laser, have been developed. The stable performance of CW and nanosecond/picosecond pulsed operation is reviewed. By applying gain-switching operation with a simple direct modulation technique, 50-ps pulse generation with a stable spectral single-mode property was obtained. For the efficient amplification of the obtained 50-ps pulse, a monolithic semiconductor optical amplifier (SOA) was integrated into the DFB lasers. An improved peak power of 300 mW at 50-ps pulse was observed with limited optical noise injection when the synchronous modulation technique of the DFB and the SOA was employed. Short cavity lasers showed a high-frequency response compared to the original DFB lasers and achieved a short pulse width of 13 ps by standard gain-switched operation.     

Tunable DFB lasers with ultra-narrow spectral linewidth

A spectral linewidth of less than 98 kHz was achieved in three-section corrugation-pitch-modulated multiquantum-well distributed feedback (CPM-MQW-DFB) lasers over a tuning range of 1.3 nm, while maintaining a constant output power of 10 mW.<>     

Nonlinear distortions and compensations of DFB laser diode inAM-VSB lightwave CATV applications

The nonlinear distortions of a directly modulated laser diode applied to AM-VSB lightwave CATV systems are studied from the viewpoint of rate equations. A simple method for calculating composite second-order distortion (CSO) is proposed, which is called the quasidynamic approach. The contribution to nonlinearity from fiber dispersion and laser chirping is also discussed. The dependences on the variations of parameters of rate equations are investigated to determine the dominant factor for CSO degradation. This approach explains quite well the experimental results and suggests a method for constructing a predistortion circuit with at least 10 dB improvement     

Correlation of relative intensity noise with linewidth floors in narrow linewidth DFB lasers

The relative intensity noise of narrow linewidth DFB lasers in the vicinity of linewidth floors is measured. A strong correlation between linewidth rebroadening and a corresponding increase in the relative intensity noise for frequencies below 3 GHz is observed for devices with mode suppression ratios in excess of 35 dB.<>     

Linearization of DFB laser diode by external light-injected cross-gain modulation for radio-over-fiber link

A novel linearization technique of distributed-feedback laser diode in analog optical transmitter for radio-over-fiber (RoF) link was proposed. The proposed scheme was based on a light-injection technique using cross-gain modulation effect. According to the proposed idea, a linearized RoF transmitter module was implemented and evaluated. The enhanced performance of carrier-to-noise ratio and spurious-free dynamic range were experimentally demonstrated in a wide range of radio-frequency (RF) applications. The experimental results show that the proposed scheme can be applicable for broadband RF optical transmission applications.     

Self-injection locking of DFB laser diode with Brillouin amplification in optical fibre feedback

A novel optical injection-locking configuration utilising Brillouin amplification in optical fibre feedback is reported. The proposed structure exhibits properties inherent in two phenomena, self-injection locking and injection-locking in master-slave configuration at the same time. Significant narrowing of the locked DFB laser linewidth was recorded. The configuration provides intensity-stable Stokes generation without a high-frequency external modulator and generator.     

Stability of two modes in DFB laser diode under high data rate modulation

Using a DFB-LD with two longitudinal modes in the 1.55 ?m region, the mode stability was examined experimentally. It is found that these modes are very stable under direct modulation at least up to around 300 Mbit/s and there is no power penalty due to mode partition noise in 97 km single-mode-fibre transmission at 280 Mbit/s.     

Mode instability and linewidth rebroadening in DFB lasers

Results of a detailed linewidth theory for DFB lasers are presented. The authors show that the fluctuations in the longitudinal distributions of photon and carrier densities can have significant effect on the linewidth. A new type of linewidth rebroadening is identified, which is attributed to model instability. This may explain the rebroadening observed in cases with high sidemode suppression.<>     

Detailed investigation on reliability of wavelength-monitor-integrated fixed and tunable DFB laser diode modules

A highly reliable integration of a wavelength monitor (WM) in an industry standard 14-pin butterfly package has been successfully achieved by using soldering and YAG welding techniques. Mechanical integrity and endurance tests for fixed and tunable distributed-feedback (DFB) laser diode modules (LDMs) were performed according to an extended Telcordia GR-468-CORE in order to appreciate the fixtures of the WM part composed of a prism, a Fabry-Pe/spl acute/rot etalon, power, and WM photodiodes. Wavelength and a fiber output power were evaluated as a function of duration time for each test. Incident light angles change against an etalon and an optical coupling deviates due to the separation between a laser diode part and a WM part for tunable DFB LDMs. The two occurrences have a profound influence on wavelength drifts. It was found that the wavelength drifts were less than /spl plusmn/5 pm under mechanical and thermal stresses for both types of DFB LDMs. It was also confirmed that the coated and mounted etalon itself was also highly reliable under thermal stresses. These results show that the WM-integrated fixed and tunable DFB LDMs were fully applicable to next-generation dense-wavelength-division-multiplexing (DWDM) systems of 50- and 25-GHz channel spacing.