Optically addressed spatial light modulators by MBE-grown nipi MQW structures.

Promising approaches for achieving optically addressed spatial light modulators (O-SLMs) are investigated based on combining nipi and multiple quantum well structures. Theoretical aspects of photooptic effects achievable in such structures are treated. Test structures are grown by molecular beam epitaxy using two material systems, (In,Ga)As/GaAs and (Al,Ga)As/GaAs. Experiments show large optically controlled modulation of the absorption coefficient in the quantum well layers ( approximately 10(4) cm(-1)), a log power dependence on the control signal, millisecond and shorter time response, and generally predictable behavior. The results are encouraging for several different O-SLM device structures proposed.

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.

Ethylene mass flow measurements with an automatic CO(2) laser long-path absorption system.

A computer controlled CO(2) laser long-path absorption system has been used in a field experiment to measure the total emission of ethylene from a petrochemical factory. The ethylene concentration was measured along eight measurement paths at different elevations. Simultaneously meteorological data were collected. From these data we have calculated the mass flow from the factory. The result of the calculations agree well with the value estimated at the factory using conventional methods.

Optical fiber communication experiment at 5 Gbit/sec.

A Gbit/sec optical fiber communication experiment was performed. The maximum speed was 3 Gbit/sec with a BH laser and 5 Gbits/sec with a TJS laser. A 500-m single-mode fiber was used, and the power was coupled by mounting the laser butt-end to the fiber, giving a minimum loss of 10 dB. The receiver employed a Si-avalanche photodiode with an impulse-response width of 210 psec (FWHM) and a 10-Gbit/sec and gate built from GaAs MESFETs. Bit-error-rate measurement values of <10(-9) prove the feasibility of optical fiber transmission at 5 Gbit/sec.

Air pollution monitoring with a Q-switched CO(2)-laser lidar using heterodyne detection.

A differential absorption lidar (DIAL) using a Q-switched CO(2) laser and a heterodyne receiver has been developed. The DIAL system is highly automated with computer-controlled laser-line selection and signal processing. The transmitter operates at a pulse-repetition frequency of 20 kHz and has an average output power of 1.8 W. A wideband HgCdTe detector is used together with a high speed adding buffer to detect the return signals. The system has been used in a field experiment to monitor ethylene emission from a petrochemical factory.

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.

Gigahertz analog modulation and differential delay of GaAIAs lasers: temperature and current behavior.

Gigahertz analog modulation characteristics of broad-area commercially available GaAlAs lasers have been investigated as a function of temperature and current in the vicinity of the upper frequency limit, where the resonance phenomena occur. The optimum temperature for small-signal amplitude modulation was found to be around -15 degrees C for our particular broad-stripe geometry double-heterostructure laser. The Q was found to increase by a factor of 2 and the bandwidth by about 2%; the external quantum efficiency was maximized in this range. The optimum dc current bias was about 2% above the threshold current. Differential delays have also been measured down to a few picosecond accuracy by a unique phase-angle measurement method using a vector voltmeter. Some of the temperature effects observed may be related to mode changes and multimode and superradiance behavior.

Theory of optical heterodyne detection using the pyroelectric effect.

Up to this time, thermal detectors have been limited to a minimum detectable power of 10(-10) W Hz(-(1/2)) at very low frequencies. It is shown theoretically in this paper that by using the pyroelectric effect in a heterodyne detection mode of operation, a factor of 10(7) improvement is possible in the minimum detectable power and that 1-GHz frequencies are attainable with sacrifice in sensitivity. The detector is quantum and temperature noise limited for large local oscillator power. These theoretical limits in the minimum detectable power do not seem to be practically attainable at present. The room temperature pyroelectric detector in the heterodyne mode of operation described in the paper would be very useful for special communication and ir radar applications.