Optical bistability in semiconductor lasers under intermodal lightinjection

Optical bistability in semiconductor lasers under intermodal light injection is predicted using small-signal analysis. The optical bistability is a special case of sidemode injection locking and originates from the strong gain nonlinearity introduced by external light injection. The theory can be applied to the optical bistability under both intramodal and intermodal light injection. And the difference of the optical bistabilities between intermodal and intramodal light injection is discussed. Expression for the bistable loop width is presented. Optical frequency-bistability and power-bistability in semiconductor lasers can be realized by intermodal light injection, which imply that a small (a few GHz) change of the injected light frequency or a small (several μW) change of the injected light power will induce a large (up to THz) change of the laser emitting frequency. Besides, hybrid optical bistability can be achieved by varying the bias current (only a few mA) of the laser. Dynamic properties, such as turn-on and turn-off delay and carrier overshoot during switching are discussed and some consideration of the practical aspects of the optical switching is presented     

Theoretical analysis of polarization bistability in vertical cavitysurface emitting semiconductor lasers

The polarization bistability of vertical cavity surface emitting lasers under external optical injection is analyzed theoretically. It is found that on the condition where the optical gain is blue-shifted relative to the cavity mode, the bistable characteristics of VCSEL's can be improved significantly: (1) low optical power of the external injection light is required, (2) the influence of self-heating effects is minimized, and (3) wide bistable hysteresis loop width can be maintained. Furthermore, it is also shown that the reflectivity of Bragg reflectors should also be optimized to improve the performance of VCSEL's as bistable switches     

Picosecond pulse generation in semiconductor lasers using resonance oscillation

Narrow pulses below 100 ps (f.w.h.m.) have been generated by applying 100 or 300 ps current pulses to a wide-stripe double heterostructure laser. The modulation current was increased to minimise the pulse width.     

Minimizing pattern effects in semiconductor lasers at high rate pulse modulation

This paper deals with analytical and experimental work related to modulation of a semiconductor laser used in high bit rate communication. The approach is based upon minimizing the charge storage effect by a proper choice of the area of the modulating pulses and the bias current. The concept of using additional current pulses to probe for variations in electron density between pulses is investigated. The primary limitation on bit rate is found to be the ability to generate laser drive pulses free of ringing or similar transients. This and the 300 ps pulsewidth, an experimental constraint, limit the bit rate to about 1 Gbit/s. However, by using this approach it appears that bit rates considerably higher than 2 Gbits/s could be reached with sufficiently accurate control of drive pulse shape. It is found that the laser bias and the current pulse area had to be controlled within 1 percent and 10 percent, respectively.     

用半导体激光器实现50KV脉冲波形安全测量方法的研究

一种可确保人身和设备安全的高压脉冲波形的测量方法。它由发送电路将被测电压或电流之实时值转换成串行数字信号，再用它调制半导体激光器发出的光，其湛我穿过100mm以上变压器油和10mm厚玻璃板，送给接收电路。后者将串行数字信号转换成模拟信号，然后送给示波器，即可观察到被测高压脉冲电路电压或电流的波形。所述方法新颖实用，具有参考价值。     

Optical bistability in semiconductor periodic structures

A theoretical demonstration of optical bistability in periodic layered media, particularly in long-period GaAs/AlAs superlattices is presented. The proposed structure consists of a periodic multilayer system, as opposed to previously demonstrated nonlinear bistable devices which employed Fabry-Perot etalons. The optical resonance effect which is essential for bistable devices is, in this case, induced by a refractive index modulation. The nonlinear active medium is distributed in the whole structure rather than placed between the two mirrors of a Fabry-Perot cavity. It is shown by a complete calculation of wave propagation in the periodic nonlinear medium that a multiple valued feature appears in the structure's nonlinear reflectivity spectrum. The input/output characteristics of the structure exhibit bistable hysteresis similar to that of a nonlinear Fabry-Perot etalon     

Suppression of multiple pulse formation in external-cavitymode-locked semiconductor lasers using intrawaveguide saturableabsorbers

Imperfect antireflection coatings in external-cavity mode-locked semiconductor lasers can cause multiple output pulse generation. The incorporation of an intrawaveguide saturable absorber segment into the laser suppresses this problem. Single pulse outputs of less than 2.8 ps and 0.7 pJ of energy are obtained using such devices with both quantum well and bulk active regions     

Condition for short pulse generation in ultrahigh frequency mode-locking of semiconductor lasers

It is shown that although it is possible to obtain mode-locking without self-pulsation when certain criteria are satisfied, the shortest pulses are almost always generated at or close to the onset of self-pulsation. Thus, the amplitude of the optical pulse train is modulated by the (relatively) low-frequency envelop of a few gigahertz under this condition. This observation was obtained by simultaneously measuring the pulsewidth using an autocorrelator and monitoring the optical intensity using a high-speed photodiode and a microwave spectrum analyzer. It is concluded that while it is possible to generate picosecond optical pulses in ultrahigh-frequency mode-locking of quantum-well lasers, very short pulses ( to 1 ps) are almost always accompanied by self-pulsation which is manifested as low-frequency (gigahertz) envelope modulation of the optical pulse train.<>     

Picosecond pulse generation in CW semiconductor lasers using anovel regenerative gain-switching technique

The authors demonstrate a technique for regeneratively gain-switching semiconductor laser diodes to generate picosecond pulses with tunable repetition rates. The technique is applied to several semiconductor laser diodes, and pulse widths of the order of 35 ps and tuning of the repetition rate from ~200-500 MHz were obtained in preliminary experiments. With further refinements, such as the use of higher bandwidth diode lasers (including surface emitting lasers), special saturable absorbers (e.g. a dual segment laser with one segment biased below transparency) and broadband RF harmonic generators (including step recovery diodes, nonlinear transmission lines, and pulse forming networks), pulse widths as short as ~10 ps are anticipated     

啁啾超高斯脉冲半导体激光器频谱的补偿修正研究

利用一段色散位移光纤(DSF)对半导体激光器产生的皮秒啁啾超高斯脉冲的频谱补偿修正,获得了较好的修正结果。适当的压缩脉冲频谱可以减小码间干扰,防止频谱因过度展宽而导致信号脉冲失真,从而在一定程度上有利于超高斯脉冲的稳定传输,提高光纤系统的传输距离。研究时,采用对称分步傅里叶法(SSFM),数值模拟了初始啁啾为-3,初始脉宽为10ps,峰值功率为30W的啁啾超高斯脉冲,在DSF中传输时消啁啾的频谱演变过程。模拟结果表明,利用长度为0.5m的DSF可以在最大程度上消除该初始脉冲的“红移”啁啾。     

Pitchfork bifurcation polarisation bistability in vertical-cavitysurface-emitting lasers

Pitchfork bifurcation polarisation bistability has been observed experimentally in a vertical-cavity surface-emitting laser for the first time. All-optical flipflop operation has been successfully demonstrated by injecting the trigger light inputs having the two orthogonal polarisations     

Mode-switching in semiconductor lasers

In this paper, we experimentally analyze the modal dynamics of quantum-well semiconductor lasers. Modal switching is the dominant feature for semiconductor lasers that exhibit two or several active longitudinal modes in their time-averaged optical spectrum. In quantum-well lasers, these dynamics involve a periodic switching among several longitudinal modes, which follows a well-determined sequence from the bluest to the reddest mode in the optical spectrum. This feature is radically different from the well-known noise-driven mode-hopping occurring in bulk lasers which involves only two main modes. We analyze the differences in modal dynamics for these two kinds of laser by comparing the modal switching statistics and by studying the effects of noise and modulation in the pumping current.     

分别限制异质结半导体激光器

研制成功分别限制异质结(SCH)激光器在2.5～3倍阈值时,单向输出峰值功率为8～13W,垂直于结平面方向和平行于结平面方向的全宽度半功率束发散为θ垂=15°～22°,θ平=14～18°.     

Heavily-doped semiconductor lasers

A theoretical study of the effect of heavily doping the active layer of a semiconductor laser shows that the minority carrier density required to reach inversion decreases with increasing doping. Unfortunately, the minority carrier lifetime also decreases since there is a component of the recombination rate that is proportional to the doping density. It is found that for a dopant with a recombination rate coefficientK_{B}, 5E-10cm³/s (Zn in GaAs), the inversion current density has a local minimum at zero doping, but decreases again for n-type doping above1E18/cm, and is one third of the zero value at4E18/cm. The value of KBfor other dopants and materials is unknown; however, for a dopant with a coefficient smaller than5E-11, the inversion current would be less than one tenth the zero value at4E18n-type, and would also decrease with the addition of p-type dopant. These results indicate that by heavily doping the active layer with the proper dopant, one might obtain both faster response and a lower threshold current, particularly with n-type dopants.     

半导体微腔激光器

文章简要叙述了微腔激光器的基本工作原理。采用先进的ＬＰＥ及反应离子刻蚀等微细加工技术制作了盘型－ 图钉式微腔结构,测得其有源区的光荧光谱的半宽度为０ ．０３２ ｅＶ,波长为８１５ ．３３ ｎｍ 。     

Triggerable semiconductor lasers

A triggerable semiconductor laser emits light in very short (0.1 ns) intense (0.1 W) pulses with a few nanosecond periods when biased a fraction of a milliampere above a threshold current. Single uniform lightwave pulses can be triggered by fractional milliampere current pulses up to several nanoseconds in duration. This behavior was first seen in computer simulations of devices with a high electron-trap density (other causes are possible). Devices exhibiting this behavior have been found among the population of AlGaAs stripe lasers made by deep proton bombardment. A simple lightwave pulse regenerator has been built by adding a photodiode with less than unity gain. This circuit emits lightwave pulses with 6 pJ energy, less than 0.2 ns in duration, and with an amplitude that is up to 15 times larger than the input pulse.     

波长(频率)可调谐半导体激光器

波长或频率可调谐的半导体激光器在光通信等实际应用领域中有着重要而广泛的应用。文章立足于实际应用,从谐振腔的结构出发,以调谐机理为研究对象,对可调谐半导体激光器进行了分类研究,并对它们的调谐特性做了总结