Noise caused by semiconductor lasers in high-speed fiber-opticlinks

Theoretical and experimental results are presented for the signal-to-noise (S/N) ratio caused by mode partition noise, intensity noise, and reflection-induced noise in optical data links. Under given conditions an additional noise source with a S /N ratio of 20 dB will cause a power penalty of 1 dB in order to maintain a 10^-9 bit error rate. From numerical simulations the authors predict the maximum allowable dispersion in the presence of mode partition noise to be approximately 40% of a clock period. This figure is almost independent of bit rate and laser structure and agrees well with the measurements and with results of other workers. Numerical simulations of a buried-heterostructure and a TJS laser were carried out at four bit rates from 565 Mbit/s to 4.5 Gbit/s and the measurements were done at 2.2 Gbit/s using a TJS laser     

The high-speed limit of FM response in semiconductor lasers

The high-speed frequency modulation (FM) response has been investigated through rate equation analysis. The intrinsic limit of FM response has been found to be given by the product of FM efficiency, η_FM, and the FM bandwidth, B. This relation shows that a wide FM bandwidth means a small FM efficiency. Although the FM efficiency changes with the differential gain or the nonlinear gain coefficient, η_FMB is almost constant. The value of η _FMB was about 5 GHz²/mA for 1.5-μm InGaAsP/InP lasers with 300-μm cavity length. This limit has been confirmed experimentally     

Reduction of optical phase noise in semiconductor lasers

There are several applications of highly coherent semiconductor lasers, especially in coherent optical-fibre communications systems and optical-fibre sensors. Optical phase noise is extremely important in these applications. Here we report preliminary results from a simple technique whereby phase noise in semiconductor lasers may be reduced. Initial results demonstrate a phase-noise reduction of typically 20 dB. Developments of the technique should permit reduction towards the shot noise limit.     

Reduction of dynamic linewidth in single-frequency semiconductor lasers

Carrier density oscillations and frequency chirping of pulse code modulated single frequency semiconductor lasers are shown to be greatly reduced by use of a small current step in the leading edge of the drive pulse. For a 100 km single mode fibre link the dispersion power penalty at 1.55 ?m resulting from dynamic line broadening is predicted to be reduced from 3.7 to 1.0 dB by use of the modified current pulse.     

Longitudinal mode spectrum of semiconductor lasers under high-speed modulation

Experimental observations of the lasing spectrum of a single-mode semiconductor laser under continuous microwave modulation reveal that the lasing spectrum is apparently locked to a single-longitudinal mode for optical modulation depths up to ∼ 80 percent, beyond which the lasing spectrum breaks into multimode oscillation. The width of the envelope of the multimode spectrum increases very rapidly with further increase in modulation depth. These results are satisfactorily explained by a theoretical treatment which gives simple analytic results for the time evolution of the individual longitudinal modes. It also yields considerable insight into spectral dynamics, and enables one to predict the dynamic lasing spectrum of a laser from its CW lasing spectra at various output powers. The results can also be used to predict the amount of spectral envelope broadening under single or pseudo-random pulse modulation.     

Approaching intraband relaxation rates in the high-speed modulation of semiconductor lasers

This paper uses a nonequilibrium semiconductor laser model to investigate high-modulation bandwidth operation in semiconductor lasers. In particular, limitations to /spl gsim/100GHz modulation response, which approaches the carrier-phonon scattering rate, are analyzed. It is found that plasma heating leads to a dynamic carrier population bottleneck, which limits scaling of modulation bandwidth. An optical injection scheme is proposed to verify this phenomenon experimentally.     

Stable single-longitudinal-mode operation under high-speed direct modulation in cleaved-coupled-cavity GaInAsP semiconductor lasers

We describe a new self-aligned coupled-cavity laser formed by a simple variation of the usual cleaving procedures. Such cleaved-coupled-cavity (CCC or C3) lasers were highly single-longitudinal-moded with spectral and stability as good as those obtained from frequency-selective feedback lasers such as distributed feedback and distributed Bragg reflector lasers under high-speed direct modulation.     

Generation and detection of high-speed pulses of mid-infraredradiation with intersubband semiconductor lasers and detectors

Semiconductor lasers and detectors based on intersubband electron transitions are used to generate and measure high-speed pulses of mid-infrared radiation. In particular, we use a commercial comb generator to gain-switch a state-of-the-art 8-μm quantum cascade laser mounted in a high-speed package. The output pulses of this device are then detected with a small-area quantum-well infrared photodetector, also packaged for high-speed operation. Pulse widths shorter than 90 ps are directly measured with this system. Accounting for the finite response time of the detection electronics, a deconvolved duration of approximately 45 ps is extrapolated     

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.     

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     

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 。     

Advanced semiconductor lasers

Recent research activities in the field of advanced semiconductor lasers are reviewed with emphasis on highly stable single-wavelength lasers and surface-emitting (SE) lasers for wideband lightwave communication systems and optical parallel information processing. The operational characteristics of DSM (dynamic single-mode) lasers are summarized and requirements for high-performance operation as light sources for high-speed transmission or coherent communications are described. A type of DSM laser called the distributed-reflector (DR) laser is described as an advanced DSM laser which enables high efficiency, high power, and narrow linewidth operations. Specific features and the potential of SE lasers are summarized. Research activities and remaining problems to be solved for a breakthrough in optical parallel information processing are presented. The potential of multidimensional quantum-well structures, such as QW lasers and quantum-box lasers, is discussed in terms of superior characteristics in both stationary and dynamic operations. The present fabrication technologies for realizing high-performance lasers based on multidimensional QW structures are also presented     

Generation of single-longitudinal-mode subnanosecond light pulses by high-speed current modulation of monolithic two-section semiconductor lasers

The spectral behaviour of monolithic two-section GaInAsP/InP lasers is studied. Single-longitudinal-mode light pulses of less than 750 ps length are produced by driving the long section of the laser only or by prebiasing the long cavity and modulating the short section with a current pulse of 1 ns halfwidth. The wavelength of the output light can be changed by varying the operation temperature or the prebias level.     

Density-matrix theory of semiconductor lasers with relaxation broadening model-gain and gain-suppression in semiconductor lasers

The density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments. The dipole moment is given theoretically by thek . pmethod and is calculated for various semiconductor materials. As a result, gain and gain-suppression for a variety of crystals covering wide wavelength region are calculated. It is found that the linear gain is larger for longer wavelength lasers and that the gain-suppression is much larger for longer wavelength lasers, which results in that single-mode operation is more stable in long-wavelength lasers than in shorter-wavelength lasers, in good agreement with the experiments.     

Q-switching of semiconductor lasers

A scheme forQ-switching semiconductor lasers is proposed and analyzed. The method is based upon electrooptic switching of the Bragg reflectivity of the grating reflectors forming the cavity of the semiconductor laser. The basic configuration, the operating principles, and the dynamic behavior of these lasers are described. Although the maximum initial inversion in this laser system is limited to a rather low value, the peak output power is found to be higher than the value usually obtained in a CW GaAs double-heterostructure (DH) laser by two orders of magnitude. A pulsewidth shorter than 100 ps is shown to be obtainable.