Analysis of the carrier-induced FM response of DFB lasers:theoretical and experimental case studies

A comprehensive analysis of the carrier-induced FM response of DFB lasers is given. Experimentally it is found that the FM response can sometimes vary strongly from chip to chip. In a number of cases anomalies either as a function of frequency or as a function of bias are observed. Theoretically, a dynamic model which includes spectral as well as longitudinal spatial hole burning is presented. The main feature of the model is that local variations of the Bragg wavelength caused by hole burning are rigorously and self-consistently taken into account. By comparing the experimental results with theoretical calculations, it is shown that in DFB lasers, spatial hole burning is an important phenomenon. The model confirms that the dynamic (FM) behavior can vary from DFB chip to DFB chip. The model shows that spatial hole burning is indeed the dominant factor which induces the anomalies that are found experimentally in the FM response     

Characteristics of the optical-frequency conversion in asemiconductor laser

A small signal analysis is presented for optical-frequency conversion using nearly degenerated four-wave mixing (FWM) in a semiconductor laser. The nearly degenerate FWM is mainly introduced by the carrier beating at the detuning frequency of the pump and the probe waves. Generally speaking, the influence of the nonlinear gain saturation on the frequency conversion efficiency is very small compared with that of the carrier density beating. However, the conversion efficiency is damped by the nonlinear gain saturation at higher bias current. The frequency conversion efficiency and the probe transmissivity are almost symmetrical with respect to the zero detuning frequency. The bandwidth of the converted signal is governed by the relaxation resonance frequency of the laser. A definition of the conversion. The theoretical results agree with experiments     

On the thermal FM response of a semiconductor laser diode

The letter proposes a simplified transfer function for the thermal FM response of a semiconductor laser diode, derived from an approximate thermal model of the laser chip. Based on this, the dip in the overall FM response is analyzed theoretically. Experimental data on the FM response of DFB laser diodes are in excellent agreement with the proposed theory     

Effect of nonuniform laser FM response on the performance ofmultichannel heterodyne FSK systems using optical amplifiers

A theoretical analysis is provided to evaluate the performance of optical frequency division multiplexed systems taking into considerations the combined effect of receiver noise, laser phase noise and nonuniform FM response characteristic of a practical DFB laser. To overcome the effect of nonuniform frequency modulation characteristic of semiconductor lasers, two different linecoding schemes are used for the laser driving signal. The crosstalk penalty due to the combined effect of nonuniform FM response and phase noise of lasers is evaluated. The improvement in receiver sensitivity due to optical preamplifier is also estimated. The computed results show that the performance of the system is highly degraded due to the effect of laser nonuniform fm response and can be reduced substantially by using linecoding. Further, there is considerable improvement in receiver sensitivity due to the use of an optical preamplifier in the absence of phase noise. In the presence of phase noise there is a reduction in receiver sensitivity     

不对称干涉自相关测量超短激光脉冲啁啾方向

提出了测量超短激光脉冲混合啁啾方向的方法。这种方法是基于混合啁啾方向随干涉自相关(IAC)信号不对称性及超短激光脉冲光谱不对称性的变化而变化。据此,得到用(IAC)包络差值信号及超短激光脉冲光谱判断线性啁啾与平方啁啾的方向。采用IAC二次谐波检测系统对加浓染料激光器输出的脉冲进行了测量,获得了被测超短激光脉冲的线性啁啾值及平方啁啾值的正与负。从而实现了对超短激光脉冲混合啁啾方向的测量。     

Measurement of charge-carrier behaviour in PIN diodes using a laser technique

A measurement system for the determination of charge-carrier densities in operating power devices is described. The system is computer-controlled and uses the free carrier absorption at 3.39 μm wavelength to deduce charge densities as a function of space and time. Measurements of carrier distribution in PIN power diodes have enabled derivation of the ambipolar diffusion length, the carrier lifetime and the carrier mobility.     

Measurement of a modulated DFB laser spectrum using gated delayedself-homodyne technique

The mixing of a modulated DFB laser with a CW local oscillator can be achieved with a single laser by using a gated modulation technique combined with an appropriate optical delay. Frequency chirp measurements up to ±22 GHz are demonstrated using this technique     

FM response of InGaAsP buried heterostructure distributed feedbacklasers and their applications in incoherent FSK systems

Measurements are reported of the frequency modulation (FM) response of InGaAsP buried heterostructure distributed feedback (DFB) lasers and the system performance of a 1.7-Gb/s and 622-Mb/s incoherent frequency-shift-keyingn (FSK) system using these lasers. The measured lasers include 1.55-μm conventional DFB lasers and quarter-wave shifted DFB lasers. The thermal dips in the FM response of quarter-wave shifted DFB lasers usually occur at the lower frequencies, compared with that of conventional (250-μm-long) DFB lasers. A receiver sensitivity of -32.5 dBm (-39.5 dBm) for a 1.7-GB/s (622-Mb/s) incoherent frequency-shift-keying (FSK) system was achieved using a quarter-wave shifted DFB laser     

Thermal and free carrier concentration mapping during ESD event in smart Power ESD protection devices using an improved laser interferometric technique

Spatial distribution of temperature and free-carrier concentration during high-current stress is studied in smart power electrostatic discharge (ESD) protection devices using a backside laser interferometric technique. The method is based on detecting changes in the refractive index of silicon due to thermo-optical and plasma-optical effects. We use a modified version of a heterodyne interferometer, where the reference beam is reflected from an external mirror outside the sample chip, which allows one to perform measurements without any restriction to the size of the scanning area. We have found two pronounced heat dissipating regions due to a vertical and a lateral current flow path in the device. In addition, two regions with increased current density due to carrier injection related to the two current paths have been found. These temperature and carrier concentration distributions found by the experiment agree very well with the results of 2D device simulation.     

Performance of linecoded optical heterodyne FSK systems withnonuniform laser FM response

A simple theoretical analysis for evaluating the performance of linecoded optical frequency shift keying (FSK) systems is presented. It accounts for the combined effects of laser phase noise, receiver noise, and nonuniform BM response of distributed feedback lasers. A close form expression for the random frequency noise due to the combined effect of laser nonuniform FM response and phase noise is developed. The analysis is carried out for three different linecoding schemes, i.e., alternate mark inversion, Miller code or delay modulation, and Manchester coding, to investigate the efficacy of the line coding schemes in counteracting the effect of nonflat FM response. Theoretical and simulation results show that the sensitivities of linecoded FSK systems are within 0.7 and 0.4 dB for single-branch and dual-branch detection, respectively, at a bit error probability of 10^-9 relative to the random non-return to zero FSK with flat FM response     

Frequency stabilization of the FM laser

A technique for the frequency stabilization of an FM laser is discussed. This technique employs a stabilization discriminant derived from a residual variation of the phase and amplitude of the small FM laser beat note at the modulation frequency, as the frequency of the FM carrier moves across the Doppler gain profile. A first-order analysis describes the dependence of that stabilization discriminant on δ, the mode coupling coefficient produced by the internal KDP phase modulator, and Γ, the resulting FM modulation index. Experimentally, a 50-mW He-Ne FM laser was frequency stabilized to better than one part in 10⁸on a long-term basis. In addition, the beat note at the modulation frequency was suppressed by 40 dB from its free-running value.     

Analysis of delay-and-multiply optical FSK receivers withline-coding and non-flat laser FM response

We present a theoretical analysis of the performance of coherent optical FSK systems when the driving laser signal is AMI or Manchester (biphase) line-coded to counteract the nonideal FM characteristic of the transmit laser diode, and the received signal is heterodyned and detected by a delay-and-multiply demodulator. The analysis takes into account IF filtering by assuming linear filtering of the noisy signal phase, accounting, for small linewidths, for laser phase noise in a straightforward and accurate manner. A simple equivalent baseband model of the system is derived for performance evaluation, applicable to both cases of large demodulator delay and when the delay tends to zero (ideal discriminator). Noise statistics include the clicks due to both signal and phase noise. The problem of performance evaluation is reduced to a classical intersymbol interference problem which is solved by mead of the method of Gauss quadrature rules. The analysis accurately predicts the effectiveness of AMI and Manchester line coding, depending on several system parameters such as linewidth, modulation index, IF bandwidth and laser FM response, and can be easily extended to other line coding techniques     

FM response of narrow-linewidth, multielectrode λ/4 shiftDFB laser

Flat FM response from 100 kHz to 15 GHz was achieved in a multielectrode distributed-feedback (DFB) laser. A λ/4-shifted corrugation and a 1200-μm-long cavity were very effective not only in reducing the linewidth to less than 1 MHz, but also in making FM response flat by selective current injection     

Proposal of novel gain-levered MQW DFB laser with high andred-shifted FM response

A gain-levered multiple quantum well (MQW) distributed feedback (DFB) laser with high FM efficiency is discussed. The device consists of three sections with different bandgap energy. It can be fabricated by a selective area metalorganic vapor phase epitaxy (MOVPE) growth technique. Numerical analysis shows that a flat, red-shifted, and high FM efficiency of above 1 GHz/mA at 20-mW output power can be realized using the gain levering scheme     

利用PSD传感器元件测量湍流密度场

描述了一种利用激光、PSD(position sensitive detector)元件及计算机数据采集系统测量湍流场气体密度及其脉动统计平均值的方法;并在流场是轴对称统计定常的假设条件下,建立了测量数据处理的数学模型。用这种测量技术可以定量地获得湍流场内部的统计平均特性。     

Effects of intraband crosstalk on incoherent light using SOA-based noise suppression technique

We investigate the effects of intraband crosstalk on the intensity noise suppression of spectrum-sliced incoherent light sources using semiconductor optical amplifiers (SOAs). Both Q-factor and electrical spectrum measurements clearly show that intraband crosstalk deteriorates the SOA-based noise suppression by breaking the correlation between optical frequency components of light.     

Controlled bistable operation of an FM mode-locked Nd:YAG laser

It is well known that there are two possible phase positions for the pulse in a mode-locked laser with an internal phase modulator. By using a modulator cut in the form of a Brewster angle prism, it becomes possible to operate an Nd:YAG laser stably in either position at will. The angular beam deflection is slightly different for the two modes and, hence, by mirror adjustment one mode or the other can be selected. A simple analysis is presented to estimate the magnitude of this effect in rough agreement with experimental observations.     

Intensity modulation technique using a directly frequency-modulatedsemiconductor laser and an interferometer

Harmonic distortion in semiconductor laser direct frequency modulation is described with the aid of a nonlinear differential equation for the photon density including gain damping. Curves are presented showing the fundamental, second-order harmonic and third-order harmonic FM responses. It is found that systems using a frequency-modulated laser and an interferometer would exhibit lower distortion levels than those using direct intensity modulation of the laser diode     

Spectral properties of the coherence collapsed state of asemiconductor laser with delayed optical feedback

A theoretical analysis of the coherence collapsed state for a single-mode semiconductor laser with a moderate amount of delayed optical feedback that is operating well above threshold is presented. Both phase fluctuations and the amplitude fluctuations satisfy a bivariate Gaussian distribution. The autocorrelation properties are determined self-consistently from the rate equations. The asymmetry of the optical power spectrum is discussed