Formula for two-carrier intermodulation distortion in wavelengthconverted subcarrier multiplexed signals via cross gain modulation

We present, for the first time to our knowledge, closed expression for the computation of the harmonic and intermodulation distortions that appear on a wavelength converted two-tone subcarrier modulation (SCM) signal via cross gain modulation     

Linearity and third-order intermodulation distortion in DFBsemiconductor lasers

This paper presents a systematic investigation of the third-order intermodulation distortion characteristics in distributed feedback (DFB) semiconductor lasers. The influence of several nonlinearities, such as longitudinal spatial hole burning, gain compression, and relaxation oscillation, is considered. Detailed analysis shows that it is possible to make different nonlinearities cancel one another to give a low intermodulation distortion by choosing the appropriate DFB structure and beat conditions. Specifically, conditions for cancellation between spatial hole burning and gain compression nonlinearities are introduced     

A novel frequency-independent third-order intermodulation distortion cancellation technique for BJT amplifiers

Second-harmonic control is implemented in a balanced common-emitter configuration to facilitate frequency-independent third-order intermodulation distortion cancellation. Moreover, this circuit configuration facilitates a simultaneous match for either power and linearity or noise and linearity. Experiments demonstrated an improvement of over 15 dB in the output third-order intercept point while maintaining freedom in the choice of load and source impedance.     

Nonlinear distortion performance of semiconductor laser diodes influenced by coherent reflected waves

The influence of the coherent reflected waves on the non-linear distortion performance of semiconductor laser diodes excited by an arbitrary number of input sinusoids with arbitrary amplitudes is analyzed by using the modified simple nonlinear rate equations. The special case of relatively small input amplitudes is considered, and closed-form expressions for the amplitudes of the resulting harmonics and intermodulation products of any order, as well as the differential gain, are obtained.     

Detailed dynamic model for semiconductor optical amplifiers andtheir crosstalk and intermodulation distortion

An advanced dynamic model for multisection semiconductor optical amplifiers is presented. It accounts for the carrier and field distributions in the longitudinal direction as well as for the facet reflectivities. The model can handle arbitrary time-varying input signals and current modulations. The model is used to assess intermodulation distortion and crosstalk. Cascaded amplifiers are considered, and the crosstalk and intermodulation distortion due to cascaded amplifiers are found to accumulate by adding together in amplitude; this may limit the number or cascaded amplifiers in multichannel systems. Carrier-induced nonlinearities depend strongly on facet reflectivities; for 25 dB of single-pass gain, a reflectivity of 5×10^-4 will result in 3 dB excess distortion. Reduction of intermodulation distortion by use of multisection amplifiers is found to be possible only for small channel separations (<300 MHz). Simulations of 11-channel amplification showed a reduction of 13 dB in intermodulation distortion when random-phase optical carriers are applied     

一种半导体二级管激光稳定控制方法

为了解决电流和温度变化对小功率半导体激光二极管工作性能的影响,提出了一种激光稳定控制方法。通过设计恒流电路稳定激光管工作电流,双层温度控制电路稳定激光管工作温度,使半导体激光二极菅工作在稳定电流、温度的环境下。结果表明：激光管工作稳定,工作电流波动范围在μA量级,工作温度波动范围在10^-2℃量级,达到了设计的要求。     

Temperature stabilization in semiconductor laser diodes

Active layer temperature stabilization in semiconductor lasers is treated theoretically. Laser diodes are assumed to be mounted on a submount which is in contact with a heat sink block. The active layer temperature fluctuation signal is fed back to a Peltier device, an injection current, or a resistor layer in the chip. Active layer temperature stability and conditions required for the control circuit are analyzed theoretically and numerically.     

窄线宽半导体激光器件

分布反馈半导体激光器的线宽一般较大,难以满足光纤传感等领域的要求。根据C.H. Henry于1982年提出的半导体激光器的线宽理论,通过适当设计DFB半导体激光器的腔长、耦合系数、微分增益、光限制因子,能有效地减小激光器的线宽。同时,空间烧孔现象也可限制DFB半导体激光器的线宽,为此需要合理设计光栅结构。在此基础上,DFB激光器的线宽能达到几十千赫兹的量级。此外,采用DBR结构或者外腔结构,也可以获得相当窄的线宽。     

Effect of gain coupling on the intermodulation distortion in DFB laser

The effect of increasing gain coupling on the intermodulation distortion is investigated. It is shown that only in the absence of other sources of distortion, gain coupling improves intermodulation distortion. Otherwise, it may reduce or increase distortion depending on the operating frequency.     

The modelling of semiconductor laser diodes

This paper presents a number of models for semiconductor laser diodes. The models are divided into different categories, according to the independent variables they include. The use of these different models is critically investigated and the advantages of these models are compared and discussed. A number of models are elaborated into mathematical detail and some examples are discussed.     

大功率半导体激光器的可靠性研究

文中介绍了半导体激光器寿命测试的理论依据,给出寿命测试的数学模型,据此对InGaAsP/GaAs有源区无铝的808nm大功率半导体激光器进行高温恒流加速老化实验,得到器件在高温下的寿命,利用外推公式推算出激光器在室温条件下工作的寿命可超过30000小时。讨论了实验中出现的灾变退化,提出了防止灾变退化的几种方法。     

DFB laser intermodulation distortion analysis taking longitudinalelectrical field distribution into account

DFB laser intermodulation distortion were theoretically analyzed, taking longitudinal electrical field distribution in the laser cavity into account. The modulation distortion mechanism caused by longitudinal electrical field nonuniformity along the laser cavity was theoretically clarified. Furthermore, theoretical law distortion yields, which are decided by the uncontrollable grating phases at cleaved facets, were calculated for devices with various κL values and facet reflectivities, in order to obtain desirable design for the lasers used for subcarrier multiplexing     

Third-order intermodulation distortion in microwave amplifier

Third-order intermodulation distortions of a microwave GaAs f.e.t. amplifier are analysed using a simple nonlinear model for the device. If the amplifier has strong feedback at low frequencies, the second-order interactions may dominate and degrade the third-order distortions. Solutions are presented to eliminate this distortion degradation. The analysis is very well substantiated by measurements.     

High light output-power single-longitudinal-mode semiconductor laser diodes

Issues related to realizing high light output-power single-longitudinal-mode InGaAsP/InP DFB LD's have been studied experimentally and theoretically. Asymmetry in the reflections as the front and rear facets of DFB cavity has been found to result in enhanced single-longitudinal-mode selectivity and higher light output power from the front facet. Single-longitudinal-mode CW light output power as high as 103 mW has been obtained in a 1.3-µm DFB-DC-PBH LD with facet reflectivities of 2 and 80-90 percent. Low internal quantum efficiency is pointed out to bean important problem for 1.5-µLD's.     

High light output-power single-longitudinal-mode semiconductor laser diodes

Issues related to realizing high light output-power single-longitudinal-mode InGaAsP/InP DFB LD's have been studied experimentally and theoretically. Asymmetry in the reflections as the front and rear facets of DFB cavity has been found to result in enhanced single-longitudinal-mode selectivity and higher light output power from the front facet. Single-longitudinal-mode CW light output power as high as 103 mW has been obtained in a 1.3-μm DFB-DC-PBH LD with facet reflectivities of 2 and 80-90 percent. Low internal quantum efficiency is pointed out to be an important problem for 1.5-μm LD's.     

Spatial separation of the third-order intermodulation for amplifier linearization

A quadrature balanced structure is presented for linearizing amplifiers. It works by routing the most annoying distortion component (the third-order intermodulation) to a port, while routing the useful information signals to a distinct port. This arrangement is not prone to oscillations as the negative feedback method is. It also has advantages over predistortion and feedforward linearization methods, as it is simpler and needs no adjustments. Theoretically, third-order intermodulation products would be totally eliminated when using the proposed arrangement. In practice, it was observed that, even with non-perfectly balanced amplifiers, the third-order intermodulation level was reduced up to 17?dB. The fifth-order intermodulation components were not reduced.     

Harmonic and intermodulation generation in quantum-well diodes

A Fourier-series model describing the current-voltage characteristic of a quantum-well diode (QWD) is presented. Using this model, closed-form expressions are obtained for the harmonic and intermodulation performance of a QWD excited by a multisinusoidal voltage superimposed on a dc voltage.     

Multichannel intermodulation distortion in high-speed GaInAsP lasers

We present an experimental study of intermodulation distortion (IMD) in high-speed, long-wavelength GaInAsP lasers modulated up to 8 GHz. It is found that three-tone distortion products are the dominant contribution to IMD interference when the number of subcarriers is large. These distortion data are used with a simple theory to predict accurately the measured signal/noise ratio for each channel of a multichannel subcarrier system.     

Origins of intermodulation distortion in transferred-electron amplifiers

Computer simulations and experiments on cathode-notch transferred-electron amplifiers have been carried out to relate one source of intermodulation distortion to the shape of the velocity-field characteristic of GaAs. Other sources of nonlinearity are caused by signal-dependent phase relationships between current and voltage when space-charge propagation effects are important.     

Third-order intermodulation distortion in coherent subcarrier-multiplexed systems

Distortion due to third-order intermodulation products in coherent optical subcarrier-multiplexed communication systems is investigated. It is shown that intermodulation distortion limits both the number of data channels and the maximum obtainable carrier-to-noise ratio. Analysis is restricted to systems operating over one octave. Experimental results on the optimal phase modulation (PM) index based on the number and frequency allocation of the microwave channels are discussed. The conditions for optimal performance with respect to channel number and phase modulation index are given.<>