Integrated electroabsorption-modulated DFB laser by using an improved butt-joint method

An improved butt coupling method is used to fabricate an electroabsorption modulator (EAM) monolithically integrated with a distributed feedback (DFB) laser. The obtained electroabsorption-modulated laser (EML) chip with the traditional shallow ridge exhibits very low threshold current of 12 mA, output power of more than 8 mW, and static extinction ratio of -7 dB at the applied bias voltage from 0.5 to -2.0 V.     

用于10Gb/s传输系统的电吸收调制器与分布反馈激光器集成光源

采用超低压(22×１０^２Pa)选择区域生长(selective area growth, SAG)金属有机化学气相沉积(metal-organic chemical vapor deposition, MOCVD)技术成功制备了应变型InGaAsP/InGaAsP电吸收调制器(electroabsorption modulator, EAM)与分布反馈激光器(distribute feedback laser, DFB)单片集成光源的新型光电器件.实验结果表明，采用该技术制备的集成器件表现出了良好的性能：激射阈值为19 mA，出光功率接近7 mW，边模抑制比(side-mode suppression ratio, SMSR)大于40 dB，将该集成器件出射光耦合进普通单模光纤后进行测量，获得了16 dB的消光比，器件3 dB响应带宽达到了10 GHz以上.将该集成器件完全封装后成功进行了10 Gb/s非归零码(non-return zero, NRZ)的传输实验：在误码率为10^-10的传输条件下于普通单模光纤中传输了53.3 km，色散代价小于1.5 dB，动态消光比大于8 dB，且眼图清晰张开. 关键词： 超低压 选择区域生长 集成光电子器件 10 Gb/s     

Study of Internal Wavelength Locker Integrated 10 Gbps Electro-Absorption Modulated Laser Modules in Metro DWDM Applications

Several different divergences are tested in the several internal wavelength locker schemes for 10 Gbps electro-absorption modulated laser (EML) module. A 10 Gbps EML module with a simple and robust internal wavelength locker for metro dense WDM application is successfully demonstrated. The wavelength aging over 2000 h is done at elevated temperature of 70°C. The average wavelength drift of 10 modules is measured to be ± 5 pm. These modules can be successfully applied to the 10 Gbps DWDM systems with 50 GHz channel spacing.     

Analysis of the photon–photon resonance influence on the direct modulation bandwidth of dual-longitudinal-mode distributed feedback lasers

The paper explores the possibilities to extend the direct modulation bandwidth in dual-longitudinal-mode distributed feedback lasers by exploiting the photon–photon resonance induced by the interaction of the two modes in the laser cavity. The effects on the direct amplitude modulation and on the direct modulation of the difference frequency between the two modes are analyzed using simulation and experimental results. When the photon–photon resonance, which occurs at the difference frequency between the two modes, is properly placed at a higher frequency than the carrier-photon resonance, the small-signal amplitude modulation (AM) bandwidth of the laser can be significantly increased. However, both simulations and experiments point out that a high small-signal AM bandwidth does not lead to a high large-signal AM bandwidth if the small-signal modulation response has significant variations across the modulation bandwidth. The paper shows that a high large-signal AM bandwidth is obtained when the two modes are significantly unbalanced, whereas a high-bandwidth difference frequency modulation can be best detected when the two modes are balanced and the DC bias is properly chosen.     

Monolithic integration of electroabsorption modulator and DFB laser for 10-Gb/s transmission

A strained InGaAsP-InP multiple-quantum-well DFB laser monolithically integrated with electroabsorption modulator by ultra-low-pressure (22 mbar) selective-area-growth is presented. The integrated chip exhibits superior characteristics, such as low threshold current of 19 mA, single-mode operation around 1550 nm range with side-mode suppression ratio over 40 dB, and larger than 16 dB extinction ratio when coupled into a single-mode fiber. More than 10 GHz modulation bandwidth is also achieved. After packaged in a compact module, the device successfully performs 10-Gb/s NRZ transmission experiments through 53.3 km of standard fiber with 8.7 dB dynamic extinction ratio. A receiver sensitivity of −18.9 dBm at bit-error-rate of 10⁻¹⁰ is confirmed.     

Theory, Design, and Operation of Large-Orbit High-Harmonic Gyroklystron Amplifiers

The high-harmonic gyroklystron is a compact RF amplifier which relies on the synchronous interaction between large-orbit axis-encircling electrons and high-order azimuthal cylindrical cavity TEn11 modes. Because of this unique structure, it offers the promise of moderate- to high-millimeter-wave output power. Experimental results for a fifth-harmonic two-cavity device are compared to both small-signal analytic theory and large-signal numerical calculations which assess gain, bandwidth, sensitivity to longitudinal velocity spread, self-oscillation, and saturation characteristics. Principal theoretical results include the transition to infinite gain as the start-oscillation current threshold is reached as well as the demonstration of the insensitivity of the small-signal gain to parallel velocity spread. The required high-energy rotating electron beam is provided through gyroresonant RF acceleration. To date, over 20 dB of small-signal gain has been achieved at 11.3 GHz in a 1.3-kG magnetic field. The design of a four-cavity configuration is also presented along with simulation of its gain, bandwidth, amplitude modulation (AM) and phase modulation (PM) sensitivity, dependence upon guiding-center spread, and large-signal saturation characteristics. This device has been constructed and initial tests have yielded a gain of 30 dB. Gain in excess of 50 dB is predicted.     

Thermal analysis of GaN-based laser diode mini-array

Thermal characteristics of multiple laser stripes integrated into one chip is investigated theoretically in this paper. The temperature pattern of the laser diode mini-array packaged in a TO-can is analyzed and optimized to achieve a uniform temperature distribution among the laser stripes and along the cavity direction. The temperature among the laser stripes varies by more than 5 K if the stripes are equally arranged, and can be reduced to less than 0.4 K if proper arrangement is designed. For conventional submount structure, the temperature variation along the cavity direction is as high as 7 K, while for an optimized trapezoid submount structure, the temperature varies only within 0.5 K.     

Distributed feedback lasers: An overview

Distributed feedback (DFB) lasers were considered promising light-source candidates for coherent optical transmissions over a long-distance. In this paper, the development history of distributed feedback laser diodes (DFB-LDs) is briefly described, followed by a review of the theoretical analysis of DFB structures. Different DFB structures are investigated theoretically, with their performances compared in terms of threshold gain, spectral linewidth, stability, and external differential quantum efficiency. The analysis reveals the need for further improvement of DFB structures and further investigations into other characteristics of DFB-LDs before the DFB-LD can be used more efficiently for coherent optical transmissions.     

Experimental and Theoretical Study of High Temperature-Stability and Low-Chirp 1.55 µm Semiconductor Laser with an External Fiber Grating

An experimental and theoretical study of the effect of temperature on the static and dynamic characteristics of packaged external fiber grating semiconductor lasers (FGL) is reported on. Operating in single frequency mode, the laser exhibits high output power (> 8 mW), high temperature stability of operating frequency (-3.4 GHz/K), and low static chirp (-60 MHz/mA). The observed hysteresis in wavelength versus temperature dependence is explained in the frame of a time-domain FGL model accounting for asymmetric nonlinear gain. The laser has low dynamic chirp (~16 MHz/mA) under 2.5 GB/s direct modulation, which is the key factor determining low penalty transmission over 312 km of SSM fiber. Dense WDM transmission performed at 2.6 Gbit/s over 117 km of SSM fiber shows that an FGL-based transmitter is a factor of 7 more tolerant to temperature variations than externally modulated DFB lasers.     

基于多芯片封装的半导体激光器热特性

设计了一种由12只单条形芯片分为2组以从高到低阶梯排列的百瓦级半导体激光器结构。针对其在稳态工作条件下的热特性利用ANSYS软件进行了模拟分析,通过改变Cu热沉的宽度、间距和高度差,得到了最高和最低Cu热沉封装的芯片有源区温度及两者温度差值的变化规律。最后设计了一种较为理想的百W级半导体激光器的散热结构。     

X~Ku波段宽带驱动放大器设计

基于SiC衬底的0.25 μm GaN HEMT工艺,设计了一款X~Ku波段宽带1 W驱动放大器单片微波集成电路。设计使用了一种有源器件的大信号输出阻抗的等效RC模型验证了GaN HEMT工艺模型的准确性,并获得了不同尺寸的GaN HEMT的大信号输出阻抗。第一级管芯采用负反馈结构,降低匹配网络的Q值,通过带通匹配网络拓扑,实现了宽带匹配。测试结果表明,在28 V的工作电压下,8~18 GHz的频率内驱动放大器实现了输出功率大于30 dBm,功率附加效率大于21%,功率增益大于15 dB。芯片尺寸为:2.20 mm×1.45 mm。该芯片电路具有频带宽、效率高、尺寸小的特点,主要用于毫米波收发组件、无线通讯等领域,具有广泛的应用前景。     

激光线宽对单次通过PPMgO:LN晶体倍频效率的影响

通过单次穿过PPMgO:LN晶体产生了2.06 W的780 nm可调谐的连续倍频光. 采用1560 nm的分布反馈式(DFB)半导体激光器、光栅外腔半导体激光器(ECDL)和分布反馈式掺铒光纤激光器(DFB-EDFL)分别作为掺铒光纤放大器(EDFA)的注入光源, 所用的EDFA具有保持窄线宽的功能, 因此可以忽略它对基波线宽的展宽. 研究了激光线宽对单次通过PPMgO:LN 晶体的倍频效率的影响. 控制三台激光器各自注入EDFA的功率一致, 同时也保持EDFA 的输出功率. 在基波功率为12.42 W 时, 使用DFB半导体激光器注入EDFA时得到了1.36 W的780 nm倍频光输出, 转换效率为11.0%; 使用ECDL作为种子源时得到了1.78 W 的780 nm倍频光输出, 转换效率为14.3%; 使用DFB-EDFL作为种子源时得到了2.06 W的780 nm倍频光输出, 转换效率为16.6%. 测得三台种子激光器的线宽分别为1.2 MHz (DFB), 200 kHz (ECDL)和600 Hz (DFB-EDFL). 线宽越窄, 倍频效率越高, 实验结果与理论分析一致.     

Demonstration of a portable near-infrared CH4 detection sensor based on tunable diode laser absorption spectroscopy

A portable near-infrared (NIR) CH₄ detection sensor based on a distributed feedback (DFB) laser modulated at 1.654 μm is experimentally demonstrated. Intelligent temperature controller with an accuracy of −0.07 to +0.09 °C as well as a scan and modulation module generating saw-wave and cosine-wave signals are developed to drive the DFB laser, and a cost effective lock-in amplifier used to extract the second harmonic signal is integrated. Thorough experiments are carried out to obtain detection performances, including detection range, accuracy, stability and the minimum detection limit (MDL). Measurement results show that the absolute detection error relative to the standard value is less than 7% within the range of 0–100%, and the MDL is estimated to be about 11 ppm under an absorption length of 0.2 m and a noise level of 2 mV_pp. Twenty-four hours monitoring on two gas samples (0.1% and 20%) indicates that the absolute errors are less than 7% and 2.5%, respectively, suggesting good long term stability. The sensor reveals competitive characteristics compared with other reported portable or handheld sensors. The developed sensor can also be used for the detection of other gases by adopting other DFB lasers with different center-wavelength using the same hardware and slightly modified software.     

Characterization of 1550 nm sub-picoseconds optical pulse using a gain-switching distributed feedback laser with CW-mode external-injection and pulse-mode self-injection

In this paper, we experimentally demonstrated the 1550 nm short optical pulses generation using a TO-packaged gain-switching distributed feedback (DFB) semiconductor laser driving by 2.5 GHz radio frequency (RF) signals and combining with optical injection techniques. The characteristics of the generated optical pulse by the proposed CW-mode external-injection and pulse-mode self-injection schemes are characterized in the side mode suppression ratio (SMSR), spectrum line-width, pulse-width and root-meansquare (RMS) jitter. In the CW-mode external-injection case, the SMSR of 35.5 dB, line-width of 0.235 nm, pulse-width of 47.69 ps, and RMS jitter of 1.4 ps are obtained when the optical injection ratio of 5 dB. In the pulse-mode self-injection, however, the SMSR of 61.2 dB, spectrum line-width of 0.189 nm, pulse-width of 58.46 ps, and RMS jitter of 1 ps are achieved and its overall performances are better than CW-mode externalinjection one.     

Characterization of small-signal intensity modulation of single-mode fiber grating Fabry-Perot laser source

A comprehensive study on the small-signal intensity modulation (IM) characteristics of a fiber grating Fabry-Perot (FGFP) laser is numerically investigated. The effect of external optical feedback (OFB), temperature, injection current, cavity volume, nonlinear gain compression factor, and fiber grating (FG) parameters on IM characteristics are presented. The temperature dependence (TD) of IM is calculated according to the TD of laser cavity parameters instead of using the well-known Parkove relationship. It has been shown that the optimum external fiber length (L _ext) is 3.1 cm. The optimum range of working temperature for FGFP laser is between 23 to 27 °C. We also show that by increasing the laser injection current from 10 to 60 mA, the IM peak amplitude decreased from 6.3 to 0.2 dB and the relaxation-oscillation frequency (ROF) is shifted from 1.2 GHz towards higher frequency of 5.48 GHz. In addition, the AR coating reflectivity and gain compression factor have no significant effect on the IM. The study indicates that a stable operation and excellent modulation characteristic can be obtained after optimization process.     

Wavelength stabilized 980 nm uncooled pump laser modules for erbium-doped fiber amplifiers

We review the development of wavelength stabilized 980 nm pump laser modules without active temperature stabilization for applications in erbium-doped fiber amplifiers. Operation over a wide temperature range with an output power exceeding 400 mW at an ambient temperature of 70°C is demonstrated. The overall reliability of uncooled modules is estimated to be well below 500 FIT at all operating conditions. Such devices are made possible by continuous development and steady improvement of the pump laser chip, the optimization of the fiber Bragg grating stabilization scheme, careful design of the module package, and extended reliability analysis on the basis of stress tests as well as field data.     

High peak power optical pulses generated with a monolithic master-oscillator power amplifier

We present results on a monolithic semiconductor-based master-oscillator power amplifier (MOPA) combining a distributed-feedback (DFB) laser and a tapered amplifier on a single chip. The MOPA reaches an output power of almost 12 W at an emission wavelength around 1064 nm in continuous-wave operation. Pulses with a length of around 100 ps can be obtained either by injecting nanosecond current pulses into the tapered amplifier alone or into both the DFB laser and the tapered amplifier. In the latter case, pulses with a width of 84 ps, a peak power of 42 W, and a spectral width of 160 pm are generated.     

Gigahertz modulation of GaAs-based bipolar cascade vertical cavity surface-emitting lasers

The high-frequency modulation characteristics of GaAs-based bipolar cascade vertical cavity surface-emitting lasers operating at 980 nm with GaAs tunnel junctions and p-doped Al0.98Ga0.02As oxide apertures have been measured. We achieve -3 dB laser output modulations of 6.5 GHz for two-stage and 9.4 GHz for three-stage devices in response to small-signal current injection at an operating temperature of -50 degrees C.     

Linewidth narrowing and polarization control of erbium-doped fiber laser by self-injection locking

A novel and simple self-injection locking (SIL) configuration of distributed feedback (DFB) fiber laser is presented. By injecting the feedback light into the cavity of the fiber laser, it can realize that the line-width can be narrowed by half compared with the same system without SIL. Meanwhile the stable single-polarization lasing is achieved and the degree of polarization is improved from 0.165 to 0.989. Then the self-pulsation behavior of the DFB fiber laser is investigated in the injection-locked and unlocked system respectively and the output power fluctuation is reduced from about 4 to 0.1 dBm by injection locking. And the power output characteristics of the DFB fiber laser are also researched by changing the pump current. With increasing the pump current from 30 to 275 mA, the output power of the DFB fiber laser increases linearly and the injection-locked output increases slightly more quickly than the unlocked output. The results have a great potential application in optical communication and high sensitive fiber sensors.