Long-span optical FSK heterodyne single-filter detection transmission experiment using a phase-tunable DFB laser diode

High receiver sensitivity (?51.9 dBm) and long span (243 km) transmission expriments have been achieved with a 140 Mbit/s optical FSK heterodyne single-filter detection system, using a phase-tunable DFB laser diode as a transmitter. This has enabled direct FSK modulation without waveform distortion. Also, a 280 Mbit/s 204 km transmission experiment has been carried out successfully.     

Multiple bistability and multistability in a fabry-perot laser diode amplifier

The experimental observation of multiple bistability is reported, for the first time, in a semiconductor laser system using a laser diode amplifier with a long Fabry-Perot cavity. The condition for realization of multistability in a laser diode amplifier is also studied theoretically in connection with the gain saturation through the rate equation analysis.     

InAs量子点双区共腔双稳激光器

本文介绍了一种新型的双区结构的InAs量子点激光器,实现了波长1.24μm室温连续激射,同时在对可饱和吸收区施加反向偏压或开路的条件下观察到了明显的光学双稳现象,其回滞宽度优于已知所报道的结果。此外,还发现减小反向偏压或增大吸收区长度能有效增加回滞宽度。应用一个改进的阈值电流模型,揭示了可饱和吸收区内量子点吸收和电吸收两种机制对光学双稳的影响,并对所观察到的实验结果进行了解释。     

Optical bistability in a two-section InAs quantum-dot laser

Room temperature,continuous-wave bistable operation is achieved in two-section 1.24μm InAs quantum-dot (QD) lasers with integrated intracavity QD saturable absorbers(SA).It is found that the hysteresis width is narrowed with increasing reverse bias voltage,and broadened with increasing length of saturable absorber.This can be explained by the competition between QD absorption and electroabsorption in the SA section.In addition,a larger hysteresis width is realized than other reports so far,which can be a...     

DFB激光器阵列与MMI耦合器、SOA的单片集成

采用变脊宽原理和对接生长技术,设计并制作了4通道分布反馈(DFB)激光器阵列与多模干涉(MMI)耦合器、半导体光放 大器(SOA)的单片集成器件。在25℃的测试温度下,激光器的阈值电 流约55~60mA;当激光器注入150mA、SOA 注入50mA电流时,各通道的出光功率保持在2mW以上,出射波长 处于1550nm波段,边模抑制比(SMSR)大于33 d B,4通道可实现单独或同时工作。     

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。     

Optical spectral bistability in a semiconductor fiber ring laserthrough gain saturation in an SOA

We demonstrate the operation of optical bistability in a widely tunable semiconductor fiber ring laser, using a semiconductor optical amplifier (SOA). The laser can be operated in two bistable states: the spectrum of the first state has one main lasing peak with very narrow linewidth, and the second state has simultaneous oscillation of two main peaks at different wavelengths. The two bistable states can be switched to each other using either electrical or optical methods. We further explain the bistable operation using the theory of two-mode competition through gain saturation in the SOA     

Optical bistability and nonlinear resonance in a resonant-type semiconductor laser amplifier

We report here on the first observation of hysteresis in the asymmetrical tuning curve of a semiconductor laser operating as a resonant-type amplifier. This bistable amplification resulting from a nonlinear resonance phenomenon is caused by the dependence of the refractive index on the injected carrier density.     

Intensity noise suppression in fibre DFB laser using gain saturated SOA

Experimental results of a simple, all-optical technique to reduce low-frequency intensity noise in an Er-Yb codoped fibre distributed feedback (DFB) laser are reported. This method utilises the gain dynamics of a saturated semiconductor optical amplifier (SOA) to produce a reduction of 30 dB in the relaxation oscillation noise component of the fibre laser.     

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.     

Design and performance of a broad-band optical diode to enforce one-direction traveling-wave operation of a ring laser

The principles for designing an intracavity "optical diode" for operation over a broad wavelength range are discussed. This is a device for enforcing one-direction traveling-wave operation of a ring laser. Test results in four dyes spanning the visible spectrum for two diode designs are given. The design with the broadest range, based on SF-2 glass as the Faraday rotator material, has given stable one-direction single-frequency operation from 425 to 810 nm.     

Thermal interaction in a distributed-feedback laser diode (DFB LD) array module

The thermal interaction in a four-element distributed-feedback laser diode (LD) array module is investigated. When the injection current of each element was 200 mA, the interactive temperature rise of an element at one end was 6.6 degrees C. At the same time, temperature rise of the mounting structure (submount, header, and heatsink) was 4.9 degrees C, or about 75% of the interactive temperature rise of the element. According to two-dimensional thermal analysis, the temperature rise of the mounting structure accounts for 98% of the interactive temperature rise of the element. These experimental and analytical results show that the temperature rise in the mounting structure is the main cause of the interactive temperature rise of this module. Stabilization of the submount temperature instead of the heatsink temperature reduced the interactive temperature rise due to the three neighboring elements to 1/3 of that achieved by conventional heatsink temperature stabilization. The thermal analysis also showed that a thicker submount further reduces the thermal interaction in an LD array module.<>     

Resonant optical amplification in a laser diode: theory andexperiment

Resonant optical amplification is studied both theoretically and experimentally. Coupled rate equations for the signal field and the spontaneous emission field, valid for input signals with bit rates up to 10 Gb/s are derived. A special weighing procedure based on a dwell-time analysis is used to account for bistable filter operation. The measured amplification characteristics of a λ/4 DFB laser injected with a 2.5 Gb/s signal show good agreement with theory     

Wavelength conversion for frequency-modulated light using opticalmodulation to oscillation frequency of a DFB laser diode

A technique for wavelength conversion for frequency-modulated (FM) light is described. It utilizes the light-injection-induced frequency shift of a distributed-feedback (DFB) laser diode and the frequency-modulated-to-intensity-modulated (FM-IM) conversion function of the Mach-Zehnder (M-Z) optical filter. Input FM light is converted into IM light by the M-Z filter. The IM light is injected into the DFB-LD oscillating at another wavelength, modulating its oscillation frequency. The output from the DFB-LD has an FM signal identical to the input FM light. Thus, wavelength conversion for FM light is achieved. The characteristics of the frequency shift induced by this optical injection were experimentally studied using a λ/4 phase-shift DFB-LD. A wavelength conversion experiment was performed. In the experimental demonstration, FM light at 1.534 μm was converted into FM light at 1.550 μm     

Optical tristability in two-section laser diode

Optical tristability in the current/light output characteristics of a two-section laser diode is observed. Three stable optical outputs are obtained at the same current. Two different types of tristability are observed by controlling injection conditions. The tristability is caused by a cavity structure having a saturable absorber and a complex resonance cavity.<>     

室温HgCdTe双光子光学双稳性及不稳定性

1.HgCdTe的带隙可以通过改变组分和工作温度来改变,因此在半导体光学双稳性的研究中它是一种具有吸引力的材料.A.Miller等人曾报道了分别用30ns脉宽和1.75μs脉宽的CO_2激光脉冲在组分配比参数为x=0.23的HgCdTe中实现的光学双稳现象.由于HgCdTe的载流子复合寿命约为90ns,用30ns的窄脉冲较难实现双稳性;而用1.75μs的脉冲,在10.6μm的红外光作用下有可能引起较大的温度变化,从而导致带隙的较大改变.我们采用脉宽介于两者之间时100ns CO_2激光脉冲射入HgCdTe标准具,实现了室温双光子光学双稳性.在x=0.223和x=0.234两种样品中观察到明显的开关转换.开启时间约为10ns,开启功率密度为400kW/cm~2.当入射功率密度达到500kW/cm~2时,两种样品都观察到了输出光强的不稳定现象.     

On the thermal contribution to the FM response of DFB lasers:theory and experiment

Laser diodes exhibiting a dip-free FM response will be key devices for future coherent FSK systems. We studied (both theoretically and experimentally) the thermal contribution to the FM response of a laser. It turns out that the agreement is good enough to validate the Fourier transform approach. This enables us to propose schemes to reduce the thermal FM response: decrease the heat generated in the laser and/or its thermal resistance by episide-down mounting     

Optical transmitter module with hybrid integration of DFB laser diode and proton-exchanged LiNbO3 modulator chip

In this work, a hybrid integrated optical transmitter module was designed and fabricated. A proton-exchanged Mach–Zehnder lithium niobate (LiNbO₃) modulator chip was chosen to enhance the output extinction ratio. A fiber was used to adjust the rotation of the polarization direction caused by the optical isolator. The whole optical path structure, including the laser chip, lens, fiber, and modulator chip, was simulated to achieve high optical output efficiency. After a series of process improvements, a module with an output extinction ratio of 34 dB and a bandwidth of 20.5 GHz (from 2 GHz) was obtained. The optical output efficiency of the whole module reached approximately 21%. The link performance of the module was also measured.     

Costas loop self-homodyne experiment for a diode laser receiver

An optical Costas loop self-homodyne experiment with semiconductor lasers at 0.82 ?m is reported. Phase synchronisation and signal demodulation for suppressed-carrier phase-shift keying modulation at 40 Mbit/s are demonstrated.     

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