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     

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?.     

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     

Measurement of dispersion using short lengths of an optical fiber and picosecond pulses from semiconductor film lasers

Group velocity dispersion spectra have been determined for 7.8-m lengths of a single-mode optical fiber. The dispersion spectra are derived from measurement of the transit delay time of picosecond pulses (4-10 ps) from optically pumped ultrashort cavity semiconductor film lasers. The delay time spectra have been measured to 1 ps precision over the range from 1.11 to 1.53 μm for single-mode step-index and quadruple-clad fibers. This is the highest temporal resolution achieved for any pulse delay measurement in optical fibers. The resulting dispersion spectra are in good agreement with measurements made for the same fibers by other techniques.     

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.     

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。     

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 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.     

Generation of picosecond optical pulses with highly RF modulated AlGaAs DH laser

AlGaAs DH lasers with strong RF modulation superimposed on the relatively low dc bias below the oscillation threshold were demonstrated to be feasible for generation of a train of approximately 30 ps optical pulses at a repetitive frequency of sub-GHz range. The pulse envelope width was measured by three different methods: a fast response photodetector, the second-harmonic generation (SHG) correlation method, and an ultrafast streak camera. The results of the SHG correlation and the streak camera agreed fairly well. In order to explain the generation mechanism and the characteristics of these ultrashort optical pulses in a highly RF modulated semiconductor diode laser, the rate equation analysis was performed and the results were generally in good agreement with the experiment. Furthermore, from the computer simulation for the analysis of the SHG correlation traces, it was inferred that an individual ultrashort optical pulse has internal substructures made of fluctuating fields whose spike widths were of the order of subpicoseconds, due to the randomness of the phases among lasing modes.     

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     

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     

Second-harmonic generation by picosecond optical pulses

The generation of second-harmonic radiation in a non-linear dielectric by an arbitrary broad-band optical signal is analyzed and application of the theory is made to harmonic generation by a short pulse. The spectrum and time dependence of the harmonic radiation is calculated in terms of the corresponding quantities for the fundamental pulse. Several types of pulses, including a frequency-swept pulse, are treated. Experimental results on the second-harmonic spectrum are presented and compared with the theory, as are previously reported results on the time dependence.     

Generation and emission of high-power ultrabroadband picosecond pulses

The generation and emission of high-power ultrabroadband electromagnetic pulses are studied. The possibility of high-voltage (about 100 kV) bipolar voltage pulses with a duration of about 200 ps is demonstrated. The electromagnetic pulses with a FWHM of less than 100 ps, an effective potential of up to 400 kV, and a repetition rate of 100 Hz are generated using the 16-element antenna array.     

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。     

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 of arbitrary optical waveforms by Fourier synthesisusing three continuous-wave semiconductor lasers

Arbitrary optical waveforms have been successfully generated by Fourier synthesis using three independent continuous-wave semiconductor lasers. The lasers were phase-locked to each other using a nonlinear phase-locking scheme. By controlling their amplitude and phase, triangular and trapezoidal waveforms as well as ordinary pulses have been generated     

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.     

Coherent optical pumping of semiconductor lasers

The influence of coherent optical pumping in semiconductor lasers is investigated theoretically. In particular the mathematical conditions under which an optically pumped system behaves like an electrically (incoherently) pumped system are derived. We show that it is practically impossible to reach the interesting regime where coherent effects are important because of the inherent constraints to absorb photons at the pump frequency and to reach threshold gain at the lasing frequency. The effects of changing the temperature and of reduced dimensionality are discussed     

Sampling pulses with semiconductor optical amplifiers

We demonstrate three techniques to measure the instantaneous frequency and intensity of optical pulses using semiconductor optical amplifiers (SOAs). Four-wave mixing, gain-saturation, and interferometric switching through a nonlinear optical loop mirror are three mechanisms by which sampling is done. We have experimentally measured the intensity and chirp profiles of pulses with energies as low as 10 fJ. Since the nonlinearity in the SOA is relatively slow, these measurement techniques are most appropriate for picosecond pulses often found in telecommunication applications. The temporal resolution of these methods are limited by timing jitter, which was ≈0.5 ps for the mode-locked laser diodes we used in our experiments, and by the width of the switching window     

Characteristics of optical phase conjugation of picosecond pulsesin semiconductor optical amplifiers

Nondegenerate four-wave mixing (FWM) of picosecond optical pulses in semiconductor optical amplifiers is investigated theoretically, taking into account various carrier processes, probe depletion, and cross-gain modulation effects. Analytical solutions for greatly simplified coupled-wave mixing equations are obtained from which conditions where probe depletion and cross-gain modulation effects cannot be neglected are found. On the other hand, the frequency detuning dependence of optimum input pump pulse energy and shaping of output conjugate pulses are observed from numerical simulations. In particular, calculations show that the frequency symmetry of conjugate and probe pulses with respect to the pump pulse does not hold for optical pulse FWM. Two-photon absorption and ultrafast nonlinear refraction effects are shown to decrease the FWM conversion efficiency