Generation and optimum control of picosecond optical pulses fromgain-switched semiconductor lasers

The generation of picosecond pulses from gain-switched semiconductor laser diodes is studied. Theoretically, common-rate equations are used to give pulse width and amplitude as a function of external parameters. The numerical predictions are compared with experimental results. It is found that optimum conditions can be achieved by an appropriate choice of the bias current     

Stable optical picosecond pulses from actively mode-lockedtwin-section diode lasers

Stable, repetitive pulses with durations as short as 8 ps and peak powers in excess of 400 mW are generated with actively mode-locked twin-section semiconductor lasers operating at 0.898 μm with a locking range of ±1 MHz around 496 MHz     

Generation of short optical pulses in semiconductor lasers by combined dc and microwave current injection

We report picosecond pulse generation in low threshold buried optical guide lasers using combined direct and microwave current excitation. The pulse widths were obtained as a function of direct current for several levels of RF excitation using lasers 125 and 380 μm long. The pulses have a Gaussian shape with full widths at half maximum intensity ranging from 19 to 57 ps. The pulse widths were obtained from the second harmonic autocorrelation. The experimental results are in reasonable agreement with the theory of short pulse formation in sinusoidally modulated lasers. The pulse width decreases with increasing dc and microwave current, and decreasing laser length. The shortest pulses were obtained with a 125μm long laser using 0.25 W RF at 1 GHz and 35 mA de bias. Multiple pulses are emitted at high dc excitation levels. Using the above laser at the indicated current levels the emission consists of a burst of ∼10 pulses which are separated by 30 ps, and has an approximately exponentially decaying amplitude. Saturable absorption was introduced in the lasers by degradation and results in shortening the pulses. A comparison is made of the pulse widths obtained for sinusoidal microwave current modulation and for pulsed excitation where the excitation is obtained from a step recovery diode. Reduced pulse widths are obtained for short current pulse excitation.     

Self-coupled phenomena of semiconductor lasers caused by an optical fiber

Output intensity noise spectra of semiconductor lasers coupled to optical fibers with end-butt joints are measured to show periodic peaks with a fundamental frequency decided only by the fiber length. The frequency is found to coincide with the reciprocal of the roundtrip time of the light beam in the optical fibers.     

Millimeter wave narrowband optical fiber links using externalcavity semiconductor lasers

We present the theoretical analysis and the experimental implementation of a narrowband millimeter wave optical fiber communication system using an external cavity semiconductor laser. We derive analytic expressions and present experimental data for the modulation response, relative intensity noise, carrier-to-noise ratio, and harmonic distortion for a semiconductor laser in an external cavity operating as a transmitter in the millimeter wave frequency range. We present a system implementation of this capable of transmitting 40-Mbt/s digital data at a 35-GHz subcarrier frequency with bit-error rates below 10^-9 over a 6.3-km-long optical fiber link     

Measurement of very-high-speed photodetectors with picosecond InGaAsP film lasers

The impulse responses of very-high-speed photodiodes are determined using 5?15 ps pulses from optically pumped ultrashort-cavity film lasers operating between wavelengths of 1.15 ?m and 1.54 ?m. The measured response time (FWHM) for a back-illuminated InGaAs/InP punch-through PIN photodiode is 30 Ps.     

电脉冲调制下半导体激光器保真输出研究

从速率方程组出发,对电调制方式下由多脉冲现象引起的脉冲畸变现象进行了讨论,并提出通过改变调制条件来实现光脉冲保真输出的方案。     

光纤耦合光双稳半导体激光器的研究

介绍一种紧凑的、能以较低输入光功率工作的光学双稳器件,由光电检测器、光纤定向耦合器和半导体激光二极管组合而成的。描述了工作原理,解释所观测到的一些效应,例如滞后回线、微分增益以及记忆功能。     

Investigation of polarization dispersion in long lengths of single-mode fiber using multilongitudinal mode lasers

We have used multilongitudinal mode lasers to investigate the polarization properties of long lengths of single-mode fiber cable. We find that the individual longitudinal modes are >99-percent polarized after propagation through 54.6 km of cabled fiber; however, the different longitudinal modes have different states of polarization at the output. This difference is caused by polarization dispersion, and we estimate a propagation delay difference for the two principal states of polarization to be 0.42 ps in the 54.6 km of cabled fiber.     

Generation of self-sustained optical pulses from transients inexternal cavity, semiconductor lasers

A novel technique to achieve self-sustained picosecond optical pulse-train generation at Gbit/s rates is presented. The technique relies on the nature of external cavity laser-switching transients and injection-locking. Preliminary experimental results confirm the practicality of the proposed technique     

Propagation of short pulses in an active nonlinear two-core optical fiber

The switching dynamics of short pulses in an active nonlinear two-core fiber coupler is investigated theoretically. The analysis takes into account the effects of coupling-coefficient dispersion, gain bandwidth, and gain saturation. In particular, we demonstrate that the pulse breakup effect due to coupling-coefficient dispersion can be suppressed by limiting the bandwidth of the linear gain, whether gain saturation is considered or not.     

Temporal coherence properties of picosecond pulses generated by GaAlAs semiconductor lasers for directly modulated and frequency stabilized optical communication systems

The temporal coherence properties of picosecond pulses from GaAlAs semiconductor lasers have been studied by measuring first- and second-order autocorrelation functions with a Michelson interferometer. The time-bandwidth product and chirp have been evaluated for several different laser structures and frequency stabilization schemes. Time-bandwidth products from 1.2 for a CSP laser to 3.6 for a TJS laser were obtained with operating conditions representative of high-speed communication systems. Computer simulations based on the rate equations have been used to model the temporal coherence during the pulse and they show good agreement with our measurements. The results show that it is important to select the appropriate laser structure and stabilization scheme in applications where the temporal coherence is significant for system performance.     

Generation of single-longitudinal-mode gigabit-rate optical pulses from semiconductor lasers through harmonic-frequency sinusoidal modulation

Generation of optical pulses at gigabit rates from semiconductor lasers by means of harmonic-frequency sinusoidal injection current modulation has been demonstrated for the first time. It was confirmed that these optical pulses consisted of one longitudinal oscillating mode because of the presence of a `self-optical injection-locking effect?.     

Wavelength switching of picosecond pulses in a self-seededFabry-Perot semiconductor laser with external fiber Bragg gratingcavities by optical injection

All-optical wavelength switching of single-mode picosecond pulses was demonstrated in an optically gain-switched Fabry-Perot semiconductor laser with self-seeding from two uniform fiber Bragg gratings (FBGs) or a linearly chirped FBG by injecting optical pulse trains with a peak power of ~1.0 mW at GHz repetition rates. Sidemode suppression ratio (SMSR) better than 17 dB was achieved in both wavelengths in the former case. Wavelength switching among three successive laser cavity modes was achieved in the latter case. A SMSR better than 15 dB was obtained at all three wavelengths. This laser has potential applications in remote optically controlled fiber sensors, such as temperature sensors     

Direct streak-camera observation of picosecond gain-switched optical pulses from a 1.5 ?m semiconductor laser

For the first time a streak camera has been used to observe picosecond pulses generated at 1.5 ?m wavelength by an injection laser without the use of frequency-doubling techniques in the detection system. Gain-switched pulses of 11 ps halfwidth have been observed, and hitherto unmeasured pulse delay data have been obtained. The observed pulse widths are believed to be the shortest yet generated using 1.5 ?m diode lasers.     

Generation and wavelength switching of picosecond pulses by optically modulating a semiconductor optical amplifier in a fiber laser with optical delay line

A novel actively mode-locked fiber laser having a semiconductor optical amplifier playing the roles of both a gain element and an optically controlled mode-locker and eight cascaded fiber Bragg gratings playing the role of the wavelength selecting element is proposed and demonstrated. Stable amplitude equalized pulse trains with a pulsewidth about 43 ps at 2.5 GHz have been obtained by injecting optical control signals into the laser. Wavelength switching among eight wavelengths is achieved by merely tuning an intracavity optical delay line. This all-optical generation and wavelength-switching scheme should be useful in applications where picosecond pulse trains at high repetition rates are desired.     

Influence of probe depletion and cross-gain modulation on four-wavemixing of picosecond optical pulses in semiconductor optical amplifiers

The influence of probe depletion (PD) and cross-gain modulation (XGM) on four-wave mixing (FWM) of picosecond optical pulses in semiconductor optical amplifiers has been investigated numerically. The effects of PD and XGM become more significant for shorter input pulsewidth, higher pulse energy and smaller pump-probe frequency detuning. Results indicate that if the effects of PD and XGM are neglected the FWM efficiency can be seriously overestimated     

由输出光脉冲选择半导体激光器泵浦电流

从实践的需要出发,用速率方程组探讨了如何选择半导体激光器的泵浦电流以产生预先设定的光脉冲,并以高斯、整形等形状的光脉冲为例,推导了所需泵浦电流的解析表达式。     

Generation of complex microwave and millimeter-wave pulses using dispersion and Kerr effect in optical fiber systems

We study a new method to synthesize high-frequency complex microwave and millimeter-wave pulses using dispersion, Kerr effect, and group velocity delay in optical fiber systems. The profile of the generated pulses can be controlled by changing the parameters of the optical system. Nonlinear propagation effect in fibers can be used to generate electrical pulses with an extremely broad spread spectrum. Soliton trapping can be used to generate electrical pulses with a controllable frequency. Implicit results are given when dispersion or nonlinear effect can be neglected. Generation of electrical pulses with a controllable microwave frequency is demonstrated experimentally using a Mach-Zehnder interferometer and a chirped fiber Bragg grating.     

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.