S. T. Eng

Solving the Schrodinger equation in arbitrary quantum-well potential profiles using the transfer matrix method

A simple, accurate, and fast algorithm for solving the one-dimensional time-independent Schrodinger equation is presented. The algorithm is based on the transfer matrix method. This makes it possible to calculate all bound and quasi-bound energy levels and the corresponding wave functions for an arbitrarily shaped potential profile. The results of calculations are compared with those obtained by other authors for various types of problems. A central part of this study deals with solving the Schrodinger equation in quantum-well structures. The results show that the transfer matrix method is as accurate as other methods, but it is easier to implement and, hence, is superior for calculations on small computer, such as a PC. >

Tunable superlattice p-i-n photodetectors: characteristics, theory, and application

Extended measurements and theory on the recently developed monolithic wavelength demultiplexer consisting of voltage-tunable superlattice p-i-n photodetectors in a waveguide confirmation are discussed. It is shown that the device is able to demultiplex and detect two optical signals with a wavelength separation of 20 nm directly into different electrical channels at a data rate of 1 Gb/s and with a crosstalk attenuation varying between 20 and 28 dB, depending on the polarization. The minimum acceptable crosstalk attenuation at a data rate of 100 Mb/s is determined to be 10 dB. The feasibility of using the device as a polarization angle sensor for linearly polarized light is also demonstrated. A theory for the emission of photogenerated carriers out of the quantum wells is included, since this is potentially a speed limiting mechanism in these detectors. It is shown that a theory of thermally assisted tunneling by polar optical phonon interaction is able to predict emission times consistent with the observed temporal response. >

Generation of single‐mode picosecond pulses by injection locking of an AlGaAs semiconductor laser

We report on the generation of picosecond single‐mode optical pulses with 1‐GHz repetition rate. Single‐mode operation is obtained by injection locking a modulated multimode buried optical guide laser with a single‐mode channel substrate planar master laser. The power ratio of the dominant mode to the total emitted power is improved from less than 0.07 without to more than 0.9 with injection locking. Detection is performed with an autocorrelator using second‐harmonic generation in a nonlinear crystal. A pulsewidth of 58 ps is obtained assuming a Gaussian pulse shape. Moreover, the substructure of spikes caused by multimode operation is strongly suppressed when the laser is injection locked.

Photodetection properties of semiconductor laser diode detectors

Several commercial GaAlAs and InGaAsP injection lasers have been investigated with respect to their photodetection properties. The responsivity of the laser diode detectors is in the 0.15-0.25 A/W range and the dark current ranges from 5 nA to 500 nA at 3-V reverse bias. The high frequency performance of a laser diode detector strongly depends on the laser structure. The bandwidth is determined by the capacitance of the lasers and ranges from 70 MHz to 1.3 GHz. The structure showing the fastest response was the TJS laser due to its low junction capacitance.

High‐speed dual‐wavelength demultiplexing and detection in a monolithic superlattice p‐i‐n waveguide detector array

We demonstrate high-speed (1 Gbit/s) dual-wavelength demultiplexing and detection in a monolithic linear array of superlattice p-i-n photodetectors in a waveguide configuration. A crosstalk attenuation of 28 dB was achieved between two digital transmission channels with an interchannel wavelength spacing of 30 nm. The device performance is a result of an enhanced electroabsorption due to the quantum-confined Stark effect in the superlattice p-i-n diodes.

Generation of tunable single-mode picosecond pulses from an AlGaAs semiconductor laser with grating feedback

Widely tunable single‐mode picosecond pulses have been obtained from a buried optical guide AlGaAs semiconductor laser operated with external grating feedback. Intensity autocorrelation measurements show single‐mode 30‐ps pulses. A tuning range of 20 nm, corresponding to more than 70 different laser frequencies, was easily achieved.

Temperature and pressure dependence of NH 3 and C 2 H 4 absorption cross sections at CO 2 laser wavelengths

Absorption cross sections at CO(2) laser wavelengths have been measured for ethylene and ammonia. The dependence of the cross sections on pressure and temperature have been investigated for pressures and temperatures normally occurring in the atmosphere. The changes in cross section are, e.g., 5% for ethylene at the P(14) 00 degrees 1-10 degrees 0 line and 10% for ammonia at the R(8) 00 degrees 1-10 degrees 0 line for a temperature change of 30 K. A comparison with theoretical calculations is made for ammonia.

Differential reflectance of natural and man-made materials at CO 2 laser wavelengths

The differential reflectance of several naturally occurring and man-made materials at CO(2) laser wavelengths is determined. The computer-controlled measurement system has two CO(2) lasers and determines the differential reflectance of each material by measuring the ratio of the reflected signals at two wavelengths simultaneously. These results can be used to improve the accuracy of air pollution measurement systems which derive their return signals from topographic targets.

In situ characterization of laser diodes from wide-band electrical noise measurements

The wide-band electrical noise characteristics of 0.8-, 1.3-, and 1.5-μm laser diodes have been studied theoretically and for the first time also experimentally. The electrical noise is related to the optical intensity noise behavior, and can therefore be used for in situ measurements and characterization of laser diodes. Since the measurements are performed without any optical components, undesired optical feedback is eliminated. The results show that several important laser parameters and characteristics can be extracted from purely electrical noise measurements. Among these are the relaxation frequency, the threshold current, the emission linewidth, optical feedback properties, and longitudinal mode hopping behavior. Good agreement between the noise theory and the electrical noise measurements has been obtained. An expression for obtaining both the spectral linewidth and lineshape from electrical noise measurements is also derived.

Air pollution monitoring with a computer-controlled CO2-laser long-path absorption system

A CO2-laser long-path absorption system has been developed. It is highly automated with computer-controlled laser-line selection and real-time data processing. The system has been used to monitor ethylene and vinyl chloride concentrations over a petrochemical factory area. The ethylene concentrations ranged from below 0.02 ppm to 45 ppm. The vinyl chloride concentrations were less than 0.05 ppm. Different path lengths from 20 m to 2800 m were used. The minimum detectable ethylene concentration was typically 15 ppm m.