Frequency stabilisation of semiconductor lasers for heterodyne-type optical communication systems

In the somewhat distant future, heterodyne-type optical communications will appear, increasing channel capacity and repeater separation. At present, the greatest difficulty is the frequency drift of lasers. The letter describes an a.f.c. (automatic frequency control) experiment using a Peltier cooling element; it is shown that the frequency fluctuation can be reduced to below 10 MHz.     

Design theory of electrically frequency-controlled narrow-linewidth semiconductor lasers for coherent optical communication systems

We describe a design rule for the automatic frequency control of semiconductor lasers by electrical feedback for coherent optical communications. The linewidth achieved by the feedback control is not a good measure for evaluating the system performance, but the bandwidth of the feedback loop is the most important parameter. For example, a 500-MHz loop bandwidth is required for a heterodyne DPSK system when the free-running linewidth of the laser is 10 MHz.     

光通信系统中新型可调谐半导体激光器的设计

为了适应当前光通信系统对波长可调谐激光器的需求,提出用游标效应来实现波长可调谐的激光器,设计了一种功率稳定且频率可调的三段式开槽法布里-珀罗结构可调谐半导体激光器,给出了系统结构的设计原理,并进行了理论分析和实验验证。取得了三段式开槽法布里-珀罗结构可调谐半导体激光器激射谱叠加图数据,利用光纤延迟自外差法测量激光器线宽,对比了3种不同激光器的线宽测量曲线。结果表明,基于游标效应设计的新型开槽法布里-珀罗可调谐半导体激光器波长调谐机制简单方便,且具有很好的单模性和信道切换能力。该研究在未来的光通信领域中具有一定的应用价值和实际意义。     

Frequency stabilization of gas lasers

The state of the art in the field of frequency stabilization of gas lasers is surveyed. A brief discussion of the methods employed to determine the frequency stability of lasers is followed by a listing of the principle causes of frequency instability. The close relationship existing between the control system design and the laser environment is pointed out. Stabilization techniques based on the use of atomic resonance and on the use of interferometers are discussed in detail. Many of these techniques are capable of achieving long-term frequency stabilities of one part in 10⁹or better, which appears to be entirely adequate for most systems applications.     

Single-mode stabilization by traps in semiconductor lasers

Recently it has been observed that certain single-transverse-mode semiconductor lasers continue to emit light predominantly in a particular longitudinal mode even after the optical gain peak has shifted by one or more mode spacings due to changes in bias current or temperature [1], [2]. The purpose of this paper is to show that this type of mode stabilization can be caused by the saturable optical absorption resulting from deep-level states or traps, which have been observed in AlGaAs laser structures [3]-[7]. The mode-selection mechanism is due to the spatial variation in the optical loss created by the standing-wave pattern of the single predominant mode. This loss pattern results in a lower average loss for the creating mode and a higher loss for all other modes. It is possible that laser devices with greatly improved single-mode stability can be made by introducing traps of the proper type and density during fabrication.     

Performance characteristics of 1.5-µm external cavity semiconductor lasers for coherent optical communication

The performance characteristics of 1.5-μm external cavity semiconductor lasers have been investigated. Measurements of phase, frequency, and amplitude stability are presented together with the power and threshold characteristics. Amplitude shift keyed coherent receiver sensitivity measurements gave a receiver sensitivity of -55.7 dBm at 150 Mbit/s equivalent to 137 photon/bit as compared to previous amplitude shift keying results of 520 photon/bit and the shot-noise limit of 36 photon/bit.     

Reliability of semiconductor lasers used in current communication systems and sensing equipment

The degradation mechanisms that had occurred – but that have now been largely suppressed or eliminated – in established consumer equipment and optical communication systems have also become problems in current optical fiber communication systems. This is due to the requirements of recently developed communication systems for semiconductor lasers, which operate at higher performance levels under severe environmental conditions. In addition, semiconductor lasers have now become important optical sources in new application fields such as sensing equipment, and these new applications have in turn brought new reliability problems to semiconductor lasers. In this paper, the degradation modes and reliability of semiconductor lasers are reviewed and discussed in association with recently developed optical sensing equipment and communication systems.     

Noise and distortion characteristics of semiconductor lasers in optical fiber communication systems

The distortion and noise characteristics of semiconductor lasers in connection with optical fibers are reviewed. In particular, the intrinsic distortions and noise of semiconductor lasers together with the partition noise are discussed followed by a discussion on the influence of reflections. Modal noise phenomena due to the interference pattern at the endface of optical fibers are treated with respect to noise and distortions. Finally, the influence of polarization coupling in single-mode fibers on the resulting transmission behavior is discussed.     

Recent advances in long-wavelength semiconductor lasers for opticalfiber communication

A brief history of the semiconductor laser and a short tutorial on its basic operating principles are given. Some key criteria for semiconductor lasers to be used in advanced systems are discussed. Various advanced laser structures (including single-frequency, high-speed and wavelength tunable lasers, laser transmitter optoelectronic integrated circuits, and coherent receiver photonic integrated circuits) are presented together with their performance characteristics     

半导体激光器稳频技术

窄线宽稳频激光器在精密干涉测量、光学频率标准、激光通信、激光陀螺、激光雷达、基本物理常数测量和冷原子系统等研究领域有着广泛的应用。自由运转的半导体激光器每天的频率漂移量可以达到GHz,因此研究半导体激光器的稳频具有十分重要的意义。以780 nm的半导体激光器稳频为例,介绍了目前广泛使用的各种半导体激光稳频技术的基本原理及试验方案,如消多普勒饱和吸收光谱稳频技术、消多普勒双色谱稳频技术、调制转移谱稳频技术、调频光谱稳频技术和频率-电压转换稳频技术,并对各种稳频方法的性能和特点进行了分析。     

Frequency halving in harmonically-driven mode-locked semiconductor lasers

Frequency halving in mode-locked external-cavity semiconductor lasers driven at the second harmonic of the external cavity resonance frequency is reported. It is shown that frequency halving occurs when the drive frequency is tuned only slightly above the second harmonic of the external cavity resonance frequency.<>     

Frequency offset locking of AlGaAs semiconductor lasers

Frequency offset locking was proposed as a reliable electrical negative feedback technique for tracking and sweeping of a semiconductor laser frequency. A frequency stabilized laser was used as a master laser, whose residual frequency fluctuations were 140 (kHz) at the integration time (τ) of 100 msleq tau leq 100s. A digital phase comparator of a large dynamic range of2pi times 2^{11}(rad) was employed in the feedback loop to reduce the phase fluctuations of the beat signal between the master and slave lasers. Performances of frequency tracking and sweeping of the slave laser were quantitatively evaluated, and the results are: residual frequency fluctuations of the beat signal were reduced as low as 11 (Hz) attau = 100s, which meant that the residual frequency fluctuations of the slave laser were almost equal to those of the master laser, i.e., the slave laser frequency tracked accurately to the master laser frequency. Both the capture range and lock range of the beat frequency were 1.22 GHz. Frequency tunable range of the slave laser was 36.6 GHz under the condition of frequency offset locking, in which the slave laser frequency fluctuations were maintained as low as the one given above.     

外腔半导体激光器单频输出的长期稳定

一、引言 由于光纤通讯、光纤传感、检测二光谱分析、频标、光陀螺等领域的需要；单频半导体激光器的研究近年来受到广泛重视并得到迅速发展，由于采用了长外腔选模技术，已实现了线宽小于100 kHz的单频输出~[1-3]。而频率长期稳定工作则刚刚开始~[4]。通常认为，造成半导体激光器输出频率漂移及跳模的原因是管芯温度和注入电流的波动，因此稳频工作     

Effects of TE-TM mode kinks on the performance of semiconductor lasers in lightwave communication systems

Effects of kinks in 1.3-μm InGaAsP etch-mesa-buried-heterostructure lasers on their performance in lightwave communications systems are studied through bit-error rate measurements. These kinks are due to the onset of TM modes in the light emission. Noise associated with kinks is observed when the lasers are operated above the kink region. This noise associated with kinks leads to a noise floor in the bit-error rate curves. The magnitude of the noise associated with these kinks is deduced by fitting the experimental bit-error-rate curves using computer simulations.     

Frequency-locked 1.3- and 1.5-μm semiconductor lasers forlightwave systems applications

A simple technique for frequency-locking 1.3- and 1.5-μm lasers to an excited-state atomic transition of noble gases using the optogalvanic effect is described. Many of the atomic transitions useful for these spectral regions are tabulated. The performance of frequency-locked lasers under direct frequency modulation is analyzed. It is shown that neither the frequency stability nor the receiver sensitivity shows any serious degradation when a frequency-locked laser is used in a frequency shift keying (FSK) transmission experiment     

Long-cavity, multi-electrode DFB lasers for coherent FSK systems

The fabrication and performance characteristics of 1 mm long three-electrode distributed feedback lasers is reported. CW linewidth of 500 kHz has been obtained. The frequency modulation characteristics of these devices exhibit no thermally induced dip and the magnitude of FM is large enough for practical coherent system application.<>     

Frequency stabilization of He-Ne lasers by saturated absorption

The performances of He-Ne lasers stabilized by saturated absorption in methane at 3.39 μm and iodine at 633 nm have been compared from the point of view of their use as optical frequency standards. Both lasers have shown a frequency stability comparable with the cesium-beam frequency standard and a reproducibility much better than the krypton-lamp length standard.     

Reliability of semiconductor lasers for undersea optical transmission systems

The reliability of laser diodes developed for undersea optical transmission systems is analyzed. Up to 1000 device samples of two types (DC-PBH and VSB) are used. An aging test with constant light power operation of 5 mW is carried out at 10, 50, and 70°C for 10 000 h. The median lifetime at 10°C is conservatively estimated to be1.6 times 10^{6}hours. Failure rate at 10°C is estimated at 250 FIT's at 25 years of service for the wear-out failure mode and at less than 50 FIT's for the random failure mode with a sufficient margin. Furthermore, it is determined that reliability can be further improved by selection of long-life lasers through an additional third step screening aging.     

Reliability of semiconductor lasers for undersea optical transmission systems

The reliability of laser diodes developed for undersea optical transmission systems is analyzed. Up to 1000 device samples of two types (DC-PBH and VSB) are used. An aging test with constant light power operation of 5 mW is carried out at 10, 50, and 70°C for 10 000 h. The median lifetime at 10°C is conservatively estimated to be 1.6 × 10⁶hours. Failure rate at 10°C is estimated at 250 FIT's at 25 years of service for the wear-out failure mode and at less than 50 FIT's for the random failure mode with a sufficient margin. Furthermore, it is determined that reliability can be further improved by selection of long-life lasers through an additional third step screening aging.     

可调谐半导体激光器的精密控制系统设计

为了满足高精密测量领域对半导体激光器高稳定度的要求,设计了一种高稳定度、低噪声的半导体激光器控制系统。该控制系统由电流驱动和温度控制两部分组成,电流控制部分采用负反馈控制保持电流稳定,温度控制部分采用高度集成的MAX1978作为主控芯片,驱动半导体制冷器进行温度补偿。经过实验验证,电流在200mA范围内连续可调,电流控制精度高达1A,在3kHz~100kHz带宽内交流噪声有效值小于300nA,长期温度漂移小于2m℃。结果表明,该系统可用于驱动分布式反馈外腔半导体激光器和分布式布喇格反射半导体激光器。