Numerical investigation of ultrahigh frequency polarizationself-modulation in semiconductor lasers

Numerical simulations performed show that polarization self-modulation in suitably designed semiconductor lasers into the tens of GHz frequency region should be possible. The calculations are based on a simple model developed to describe polarization self-modulation in a ring laser cavity with a traveling-wave semiconductor laser amplifier as the gain medium. A set of difference-differential equations is derived and numerically solved. Periodic oscillations in the two polarization modes are obtained as previously reported experimentally. An examination of the various parameters and their roles in maintaining this instability is also conducted. The results indicate that, in an appropriately designed semiconductor laser with a monolithically integrated intracavity TE-TM mode converter, ultrahigh frequency polarization self-modulation to at least 50 GHz should be possible     

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.     

光电反馈主动锁模

本文报道采用光电反馈法实现半导体激光器的主动锁模。在反馈环大增益工作状态下,得到了宽度为17.7ps、重复频率为926MHz、峰值功率为80mW的超短脉冲输出。     

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     

染料碰撞脉冲锁模的理论研究

提出染料碰撞脉冲锁模新理论,它的物理图象清晰,能较好地说明锁模脉冲的性质,特别在频率方面。     

Dressed resonance frequency for semiconductor lasers

General formulas are given for the instantaneous or dressed resonance frequency and damping parameter of semiconductor lasers. Calculations of the excursion of the resonance frequency during direct current modulation are presented     

Realization of ultrahigh coherence in semiconductor lasers bynegative electrical feedback

To be useful, an ultrahigh-coherence semiconductor laser source requires high frequency stability, narrow linewidth, the capability of frequency tracking to a master laser, and stable frequency tuning. Negative electrical feedback is proposed to meet these four requirements simultaneously. Although the degree of frequency fluctuation that can be reduced by negative electrical feedback is limited by the noise contained in the feedback signal, theoretical calculations show that the fluctuations can be lower than the quantum noise limit. Experimental results obtained recently by the author are reviewed     

Gigabit pulse position bistability in semiconductor lasers

The paper briefly reviews the major forms of optical bistability in active optical devices compatible for use in gigabit optical communication systems, and reports an entirely new optical bistability for the first time. Unlike previous devices, the two bistable states of the optical device are each a series of picosecond optical pulses at 1 GHz or greater repetition rates, and are distinguished by a half period temporal shift between their temporal positions in relation to a clock pulse. The bistable device is based on a gain switched semiconductor laser. Theoretical studies suggest 100-ps switching speeds might be achieved, and experimental results are reported indicating optically triggered switching times of 500 ps.     

Model for return-beam-induced noise generation in GaAlAs semiconductor lasers

The nature of the output intensity fluctuation noise generated when semiconductor lasers are irradiated by their own output beam are described. A possible explanation of their generation mechanism is presented utilising a simple rate equation model with an additional term accounting for the multiple reflections of the laser beam.     

Kinetics of picosecond pulse generation in semiconductor lasers with bimolecular recombination at high current injection

The kinetics of generating ultrashort light pulses by gain switching unbiased semiconductor lasers emitting relaxation oscillations is theoretically modeled and described using phase portraits. Biomolecular recombination processes and realistic injection current pulse shapes are incorporated in the model. Approximate analytical solutions of the rate equations are derived for high current injection. Laser pulse widths, pulse peak power, electrical to optical pulse delay times, and time difference to subsequent relaxation oscillations are computed. Their dependence on injection current to threshold current density ratio (J/J_{t}) and on material and laser design parameters is explicitly derived and is in good agreement with experiment. In particular the remarkable observation that the laser pulse width is broadly independent of the injection current rise and fall time can thus be understood.     

Ultrashort pulse generation by intracavity spectral shaping andphase compensation of external-cavity modelocked semiconductor lasers

Intracavity spectral shaping and external chirp compensation techniques were employed to generate nearly transform-limited optical pulses with a temporal duration of 250 fs from an external-cavity modelocked semiconductor laser. It was also demonstrated that intracavity spectral shaping techniques can be used for artificially tailoring the chirp of the output pulses     

Single-mode characteristics of short coupled-cavity semiconductor lasers

The characteristics of single-longitudinal-mode selection in short coupled-cavity (SCC) semiconductor lasers with a plane reflector are analyzed theoretically. It is found that the power ratio of the main mode to other side modes can be increased significantly by reducing the reflectivity of a laser diode facet adjacent to the external mirror. Based on the theoretical results, a new type of SCC laser is developed; single-longitudinal-mode output with 35-40 dB side mode suppression ratio is obtained under CW and 150 MHz modulation conditions.     

An experimental and numerical study of Q-switched mode-locking in monolithic semiconductor diode lasers

We present experimental results of Q-switched mode-locking (QML) of a monolithic two-section semiconductor laser. We demonstrate tuning of the Q-switched envelope repetition rate with pumping current over the range of 0.4 to 1.6 GHz. Detailed numerical modeling is used to study a range of similar devices and to investigate the mechanisms and conditions for QML to occur. We also discuss design conditions for increasing the tuning up to 4 GHz.     

Stretched-pulse additive pulse mode-locking in fiber ring lasers:theory and experiment

Stretched-pulse additive pulse mode-locking uses segments of fiber of large positive and large negative group velocity dispersion (GVD) in the cavity. The changes in pulse width per pass due to the varying GVD can be an order of magnitude or more. A theory is developed based on the master equation that covers this case of large pulse changes in one transit. The general predictions of the theory are verified by experimental results     

Circuit models for frequency modulation response of semiconductor lasers

The authors describe a new circuit modelling technique for the directly frequency-modulated CSP semiconductor laser. In particular, this model accounts not only for the carrier density but also the temperature effects. Predictions from this model are compared with other published results of sinusoidal frequency modulation in the range DC-3 GHz and show good agreement.<>     

Simple picosecond pulse generation scheme for injection lasers

A simple scheme is reported for generating picosecond optical pulses from injection lasers based on short electrical pulse excitation. An integrated step recovery diode impulse-train generator (`comb? generator) which gives 50 ps 25 V electrical pulses at 200 to 500 MHz rates is used to drive the injection lasers. Optical pulses as short as 40 ps are generated by the corresponding electrical drive pulses.     

Synchronous mode-locking in passively mode-locked semiconductor laser diodes using optical short pulses repeated at subharmonics of the cavity round-trip frequency

Synchronous mode-locking was achieved in passively mode-locked semiconductor lasers using optical pulses with repetition rates at subharmonics of the cavity round-trip frequency. Stable and continuous mode-locked pulses at 8.5 GHz were generated when the repetition rate of the control optical pulses was 4.25 GHz (2nd subharmonic). The timing jitter of the mode-locked pulses was reduced to 1 ps. The relationship between repetition rates of the control pulses and the realization of stable and continuous mode-locking was examined.     

负频反馈半导体激光器的量子噪声

相干光通信系统和相干光学测量对LD的噪声特性要求十分严格,因此LD的噪声及其抑制一直是近年来人们十分关注的问题.为了抑制LD的量子噪声,已采用了几种方法,但这又带来了机械稳定性的问题.最近报道了用NFFB抑制LD的线宽和FM噪声,对此也已有了理论解释但是在的分析中未引入反馈项,相当于开环的情况;的分析中则将反馈项引到了相位方程中,这是不符合客观情况的.本文给出的模型不仅解释了FM噪声的抑制,而且也解释了AM噪声的增大.得到的线宽与实验     

Broadband semiconductor saturable absorber mirrors in the1.55-μm wavelength range for pulse generation in fiber lasers

Broadband low-loss semiconductor saturable absorber mirrors (SESAMs) in the 1.55-μm wavelength range were monolithically grown by solid source molecular beam epitaxy using a Burstein-Moss blue-shifted Ga_0.47In_0.53As-InP distributed Bragg reflector. Absorbers with fast and slow temporal responses were used to start up and to stabilize a stretched pulse mode-locked fiber laser. Reliable operation at a fundamental repetition rate was obtained without multiple pulse break-up with pulse energy of over 250 pJ