Determination of the delay time and feedback strength of a semiconductor laser with optical feedback from time series of radiation intensity

A method for estimating the delay time and feedback of a single-mode semiconductor laser from time series of fluctuations of the laser radiation intensity is proposed. The method is based on searching the nearest neighbors of state vectors chosen in time series in a definite way and is resistant to high noise levels. The efficiency of the method is demonstrated by an example of time series of Lang–Kobayashi equations.     

Phase effects in a semiconductor laser with diffraction extraction of radiation

Phase effects arising in a semiconductor laser with diffraction extraction of radiation and a distributed Bragg reflector on the substrate side are taken into account exactly quantitatively and the possibilities of using these effects in lasers is analyzed. It is shown that the phase effects studied can be used to increase the laser efficiency substantially. Pis’ma Zh. Tekh. Fiz. 23, 7–11 (September 26, 1997)     

Modulation of the polarization of semiconductor laser radiation at constant output power

The degree of polarization of “doubly”-modulated (by the pump current and the optical confinement factor) laser radiation is analyzed by applying a method of analyzing the stability of the solutions of systems of Lyapunov differential equations to a system of rate equations. An analysis of the system of rate equations yielded its eigenvalues, also called stability coefficients, which are the characteristic time for a transition of the system from one state to another. The behavior of a doubly modulated laser was modeled mathematically and it was demonstrated that the polarization of the laser output radiation can be controlled with almost constant output power. Pis’ma Zh. Tekh. Fiz. 24, 84–90 (August 26, 1998)     

High-power semiconductor radiation sources based on 100-W diode laser bars for pumping solid-state lasers

High-power semiconductor radiation sources with a total optical output power of up to 5 kW and a power density of 400 W/cm² have been developed, representing a vertical stack of quasi-continuous pulsed (500 μs) 100-W diode laser bars. Based on such sources, a solid-state laser with an output radiation energy of up to 150 mJ has been created, which is intended for information systems, laser radars, spectrum analyzers, etc.     

Statistics of intensity of backscattered semiconductor laser radiation in single-mode optic fiber

We have studied the statistics of the intensity of backscattered radiation of a semiconductor laser in single-mode optic fiber as a function of the probing laser pulse duration and coherence time. It is shown that, at a given radiation source coherence time, the intensity distribution function varies, depending on the pulse duration, from nearly exponential to nearly Gaussian. The exponential statistics provides a better sensitivity for a coherent reflectometer with direct detection. Using the calculated distribution function, it is possible to qualitatively determine the degree of deterioration of the reflectometer sensitivity with respect to external factors during increasing probing pulse duration or decreasing laser coherence time. These data provide criteria for the optimum choice of a radiation source for the coherent fiber-optic reflectometer.     

All-optical time-division demultiplexer using semiconductor switching

An all-optical time-division demultiplexer system is proposed that employs semiconductor switching. The technique can be applied through the use of input infrared signals of wavelengths ≥1 μm. The device is simple to construct and has a potential capacity of 1 Tbit/s, with cross talk between channels of only approximately -13 to -17 dB at operating wavelengths between 1 and 15 μm, respectively. The optimum characteristics and the operational parameters are also presented.     

Small-signal-equivalent circuits for a semiconductor laser

Passive electrical circuits whose voltage and current equations are exactly equivalent to the small-signal rate equations of a semiconductor laser are derived to model an electrically modulated laser (verified to be the same as that given in the literature), an optically modulated laser (i.e., a laser used as an optical amplifier), and a multimode laser. These circuits offer a fast and efficient simulation tool with little computational complexity in which the small-signal assumption (i.e., small modulation range) is neither violated nor insufficient for the simulation.     

Polarization rotation in asymmetric semiconductor quantum dots

Rotation of input polarization arising due to the recombination of electrons from the 1s-excitonic state to the hybrid valence band states have been theoretically examined in asymmetric semiconductor quantum dots. The Jones matrix calculations suggest that the polarization rotation directly depends on the asymmetry of the quantum dot and strength of hh–lh coupling. The results advocate the suitability of quantum dots as polarizing devices.     

InP based semiconductor structures for radiation detection

We report the preparation of semi-insulating InP single crystals of p-type conductivity and intentionally undoped p-type epitaxial layers for radiation detection. We focus on (i) the growth of InP single crystals doped with copper by the Czochralski technique and their subsequent temperature annealing to convert them to a semi-insulating (SI) state of p-type conductivity, and (ii) the growth of thick (>10 μm) p-type InP layers by liquid phase epitaxy with an admixture of Pr and Dy. Grown layers and single crystals were examined by low-temperature photoluminescence spectroscopy, capacitance-voltage and temperature dependent Hall measurements. An efficient purification due to rare earth (RE) admixture has been observed and layers grown with the addition of Pr and Dy exhibit the change of electrical conductivity from n to p at certain RE concentration in the melt. Dominant acceptors responsible for conductivity conversion have been identified. Three types of detection structures exploiting the Schottky or Schottky like contacts on pure and SI p-type InP or exploiting the p–n junction were designed.     

Polarization dynamics and non-equilibrium switching processes in ferroelectrics

Time- and temperature-dependent effects are critical for the operation of non-volatile memories based on ferroelectrics. In this paper, we assume a domain nucleation process of the polarization reversal and we discuss the polarization dynamics in the framework of a non-equilibrium statistical model. This approach yields analytical expressions which can be used to explain a wide range of time- and temperature-dependent effects in ferroelectrics. Domain wall velocity derived in this work is consistent with a domain wall creep behavior in ferroelectrics. In the limiting case of para-electric equilibrium, the model yields the well-known Curie law. We also present experimental P-E loops data obtained for soft ferroelectrics at various temperatures. The experimental coercive fields at various temperatures are well predicted by the coercive field formula derived in our theory.     

Memory switching in amorphous Ge---Se---Tl chalcogenide semiconductor films

The switching effects in amorphous GeSe₂, GeSe₄, GeSe₂Tl and GeSe₄Tl thin films have been investigated. The observed switching phenimenon for these compositions was of the memory type. The threshold switching voltage was found to increase linearly with increasing film thickness (80–740 nm), while it decreased exponentially with increasing temperature (T < T_g).

The effect of adding thallium to both amorphous GeSe₂ and amorphous GeSe₄ results in decreasing the values of the threshold electric field, the activation energy of switching, as well as the thermal activation energy of conduction. The results obtained are explained in accordance with the electrothermal model of breakdown.     

Unipolar semiconductor laser for the terahertz frequency range

In this paper a new design is proposed for a unipolar semiconductor laser with longitudinal transport of electrons and a stepped variation in the thickness of quantum wells, in which population inversion is obtained, and as a result the electrons of the first subband in the narrow part of the well, with injection into the wide part, preferentially populate its second subband. Deceased Pis’ma Zh. Tekh. Fiz. 23, 90–94 (February 26, 1997)     

Kinoform-only Gaussian-to-rectangle beam shaper for a semiconductor laser

A kinoform that shapes the divergent beam from a semiconductor laser without using any other optical components was designed and fabricated. The kinoform-only concept means that the kinoform must perform both the actual beam shaping as well as focusing the divergent laser beam, correcting for the astigmatism of the laser, and correcting for the spherical aberration of the laser exit window. A rectangular beam of dimensions 1000 μm × 300 μm is formed 42 mm behind the kinoform. Of the total output from the laser, some 50% is incident upon the kinoform, of which ~50% will appear in the rectangular beam. The intensity uniformity error within the rectangle increases from the design value of 8% to 38% because of sensitivity to fabrication errors. The kinoform-only design for beam-shaping applications requires high manufacturing accuracy but is attractive because a system using such a component is easily mounted and aligned and, with the use of kinoform-replication techniques, can be mass produced at low cost.     

Far infrared radiation generated during femtosecond laser excitation of a semiconductor surface in magnetic field

The effect of a magnetic field on the generation of electromagnetic radiation pulses in the terahertz frequency range from a semiconductor surface excited by an ultrashort laser pulse is considered within the framework of a hydrodynamic model. The appearance of a photocurrent component in the Hall direction leads to elliptic polarization of the microwave radiation and to a severalfold increase in the generation efficiency. This is consistent with the results of Monte Carlo modeling of a self-consistent field and photogenerated carrier dynamics.     

Cycle time estimation for semiconductor final testing processes with Weibull-distributed waiting time

Accurate cycle time is an essential planning basis required for many production applications, especially on due date commitments, performance metrics analysing, capacity planning, and scheduling. The re-entrant final testing process is the final stage of the complicated semiconductor manufacturing process. To enhance the ability of quick responses and to achieve better on-time delivery in final testing factories, it is essential to develop an accurate cycle time estimation method. In this paper, we provide a statistical approach to calculate the cycle time for multi-layer semiconductor final testing involving the sum of multiple Weibull-distributed waiting times. In addition, percentiles of the cycle time are obtained which are useful to industrial practitioners for due date commitments satisfying the targeted on-time delivery rate. To demonstrate the applicability of the proposed cycle time estimation model, a real example in a semiconductor final testing factory which is located on the Science-based Industrial Park in Hsinchu, Taiwan, is presented.     

大功率半导体激光器全固态风冷散热系统

设计并制作了一种全固态大功率半导体激光阵列恒温散热系统。它利用半导体制冷器对大功率半导体激光阵列吸热,然后经由风冷散热。经测试,单bar激光阵列连续输出功率达到15.28W,双 bar 阵列输出达 27.8W 时,全部达到风冷散热控温精度±0.1 ;当环境温度达到 45 时,仍然能够保证激光阵列的正常使用。     

Improving the radiation resistance of semiconductor detectors of radioactive radiation

The possibility of using semiconductor detectors not containing potential barriers (p-n junctions) to measure the intensity radioactive radiation fluxes causing degradation of the electric parameters of detector material is theoretically substantiated. The assumptions are confirmed by experimental results.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 61–63, January, 1994.