InP-In1-xGaxAsyP1-yembedded mesa stripe lasers

A laser structure was fabricated using two-step liquid-phase epitaxy, employing the melt-back technique. The fabrication and properties of this structure are described in detail. Good linearity of the power output up to power levels of 20 mW was obtained. The threshold current density at 300 K is 9-12 kA/cm². This high value is mainly due to Zn-diffusion from the third to the buffer layer during the second growth step of the fabrication process. The external differential quantum efficiency is 30-35 percent under pulsed operation at 25°C. The pulsed threshold current has an exponential behavior with temperature whereT_{0} = 60degC. The far-field beam divergences in the directions parallel and perpendicular to the junction plane are12-15degand35-40deg, respectively. Transverse mode stabilization was improved with this laser structure.     

Efficient luminescence band created in (Al, Ga)As multilayers by athermal laser processing

A new luminescence band is observed in (Al, Ga)As three-layer structures which were subjected to well-controlled CW Krion laser irradiation at power densities of 0.55 MW/cm². The new band is shifted by 90 meV to lower energies with respect to the band-to-band recombination. The total photoluminescence efficiency at room temperature can be improved by as much as 80 percent. Measurements of the luminescence at 0.8 μm and of the infrared (IR) power emitted at 3.1 μm have been performed during processing. Maximum temperature rises of320-350degC for the laser heated zone have been evaluated from these measurements. The well-defined laser threshold power, necessary to create the new luminescence centers, does not depend on the substrate temperature in the range of20-250degC. It does increase linearly with decreasing laser photon energy.     

Low-threshold distributed feedback lasers fabricated on material grown completely by LP-MOCVD

GaInAsP-InP distributed feedback (DFB) lasers emitting at 1.57 μm have been fabricated on material grown completely by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The CW threshold current of 60 mA and an output power of 6 mW per facet at room temperature have been obtained. The lasing wavelength λLunder CW operation showed a temperature coefficient (d_{lambdaL}/dT) of 0.9 Å/°C for this DFB laser over the range of10-90degC. A stable single longitudinal mode was maintained under high speed pulse modulation up to 500 ps, and sinusoidal modulation at 1 Ghz.     

An Experimental 50 Mb/s Fiber Optic PCM Repeater

An experimental repeater for amplification and regeneration of 50 Mb/s fiber-optical pulses has been built and tested. For the receiver either Si p-i-n or avalanche photodiodes are used in conjunction with a high impedance FET input amplifier. The high voltage for the avalanche photodiode is generated internally and controlled by the received signal. This AGC circuit is capable of compensating for temperature changes of the avalanche gain over the range of-40 - +60degC. The optical transmitter consists of either a GaAs light emitting diode or a GaA1As laser diode coupled to optical fibers and directly modulated by a current driver with 30 percent electrical efficiency. For 10^-9error rate, the required average optical signal power for a pseudorandom signal is p-i-n diode: -41.5 dBm; avalanche diode: -56.6 dBm. The optical output power into a fiber with 1 percent index difference is LED: -17 dBm; GaAlAs laser: 0 dBm. The repeater power requirement is about 2 W.     

A laser-pumped temperature sensor using the fluorescent decay time of alexandrite

In this work a simple intensity-independent fiber-optic temperature sensor using alexandrite crystal was constructed. The sensor uses the change in the characteristics of the fluorescence of the material to sense the parameter required and operates using light from an electrooptically modulated He-Ne laser at 633 nm. Microprocessor control and signal processing is used to achieve an accuracy ofsim pm1degC with a 3-s response.     

Interferometric measurement of the elongation of a pulsed diode laser

An interferometric technique was developed for detecting fast displacements of small areas in beam direction by less thanlambda/8. It utilizes a modified Michelson interferometer and a He-Ne laser light source. The technique was applied to measure the temporal and spatial evolution of the thermal mirror deformation of a GaAs-Ga1-xAlxAs single heterostructure laser diode. A small spot on the facet of the laser diode formed one mirror of the interferometer. The other mirror was moved linearly with time by applying a ramp voltage to a piezoelectric transducer. The diode was pulsed during this motion. The local elongation of the laser diode was evaluated from the interferometer output signal. The measured elongation of the active region at a time 1 μs after a 150-ns pulse with current density 48 000 A/cm²was between 4 and 20 nm, indicating a temperature rise of2-11degC. The smallest elongations detected were in the range of 0.5-1 nm. The measured values are in substantial agreement with theoretical expectations from thermal model calculations.     

Low-loss plastic molded optical multifiber connector for ribbon-to-single fiber fan-out

This paper describes a newly developed low-loss demountable multifiber connector for ribbon-to-single optical fiber fan-out. The connector plugs contain special gathering parts that make a high-density arrangement for monocoated optical fibers. Using a multi-V-grooved mold, the optical fibers are accurately positioned and then a plastic formation process is adopted to form the plug. Plugs are precisely aligned by using two pins. An average connecting loss of 0.07 dB has been achieved in the stationary mode distribution with index matching. The change in connecting loss did not exceed ± 0.03 dB when the connector was subjected to heat cycles in a temperature range of-30-+60degC.     

The dielectric properties of brine in sea ice at microwave frequencies

The dc conductivity and complex dielectric constant at frequencies of 7.50, 9, 11, 30, and 40 GHz of 16 samples of sea water brine in equilibrium with sea ice with freezing temperatures ranging from -2.8degC to-25.0degC have been measured. The data is analyzed to yield parameters occurring in a Debye relaxation equation so that the dielectric constant of brine may be calculated throughout the microwave region of the electromagnetic spectrum.     

The liquid-phase epitaxial growth of low net donor concentration (5 × 1014-5 × 1015/cm3) GaSb for detector applications in the 1.3 - 1.6 µm region

We report on the liquid-phase epitaxial (LPE) growth of low doped n-GaSb for long wavelength photodiodes. Very low net donor concentration epilayers (5 times 10^{14}-5 times 10^{15}/cm³) were grown both from undoped Ga rich solutions in the300-375degC range and by compensation using Ga-rich solutions atsim500degC with intentionally added Te. The preparation of Au-GaSb Schottky diodes forC-Vprofiling is also discussed.     

Dielectric properties of snow in the 3 to 37 GHz range

Microwave dielectric measurements of dry and wet snow were made at nine frequencies betweeo 3 and 18 GHz, and at 37 GHz, using two free-space transmission systems. The measurements were conducted during the winters of 1982 and 1983. The following parametric ranges were covered: 1) liquid water content, 0 to 12.3 percent by volume; 2) snow density, 0.09 to 0.42 g cm^-3; 3) temperature, 0 to-5 degC and-15degC (scattering-loss measurements); and 4) crystal size, 0.5 to 1.5 mm. The experimental data indicate that the dielectric behavior of wet snow closely follows the dispersion behavior of water. For dry snow, volume scattering is the dominant loss mechanism at 37 GHz. The applicability of several empirical and theoretical mixing models was evaluated using the experimental data. Both the Debye-like semi-empirical model and the theoretical Polder-Van Santen mixing model were found to describe adequately the dielectric behavior of wet snow. However, the Polder-Van Santen model provided a good fit to the measured values of the real and imaginary parts of wet snow only when the shapes of the water inclusions in snow were assumed to be both nonsymmetrical and dependent upon snow water content. The shape variation predicted by the model is consistent with the variation suggested by the physical mechanisms governing the distribution of liquid water in wet snow.     

Polarization-maintaining optical fibers used for a laser diode redundancy system in a submarine optical repeater

Polarization-maintaining optical fibers are developed for installation in a submarine optical repeater. These fibers preserve the polarization of light emitted from laser diodes (LD's) to a single-mode fiber through a light-switching coupler. Crosstalk of less than -30 dB in a 1-m length of these optical fibers, called PANDA optical fibers, is achieved with a bending radius greater than 10 mm, twists of less than 60 turns, and tension of less than 3 kg, and ambient temperatures of-20-80degC. The mechanical strength of these fibers is the same as that of single-mode fibers.     

High-modulus low-linear-expansion-coefficient loose-jacket optical fibers

Optical fibers loosely jacketed with high-modulus low-linear-expansion-coefficient polymers have been proposed, and the mechanical, thermal, and optical properties have been investigated. The loose-jacket tube is made of highly oriented polyoxymethylene (POM), which is produced by tensile-drawing the isotropic POM tube with dielectric heating. The oriented POM exhibits Young's moduli 20-40 GPa and linear expansion coefficients of the order of10^{-5}-10^{-6}degC^-1. Owing to the low linear expansion coefficients of the material, the oriented POM loose-jacket optical fiber has no low-temperature excess losses, which is due to fiber bends caused by thermal contraction of the loose tube, in the-60-80degC temperature range.     

Quantum-well heterostructure lasers

The various features peculiar to the operation of quantum-well semiconductor lasers are described and illustrated with data on single- and multiple-quantum-well AlxGa1-xAs-GaAs heterostructures grown by metalorganic chemical vapor deposition (MO-CVD). Photo-pumped and p-n diode lasers (injection lasers) are described that are capable of continuous room temperature (CW 300 K) operation. The basic problems of carrier collection, thermalization, and quantum-well band filling are considered and have made clear the limits on single quantum-well laser operation and how these can be overcome with multiple quantum-well active regions. The idea that the steplike density-of-states of a quantum-well heterostructure can improve the operation of a semiconductor laser is shown to be valid. Also, it is shown that phonon participation in the operation of a quantum-well laser, which was not anticipated, is a major (even dominant) effect, with perhaps the phonon emission itself in the compact active region being stimulated. Besides the obvious freedom that quantum-well layers offer in how the active region of a semiconductor laser can be designed, quantum-well lasers are shown to exhibit a lesser sensitivity of the threshold current density on temperature, which is explained in terms of the step-like density-of-states and the disturbed electron and phonon distributions in the quantum-well active regions. Values as high assim437degC have been obtained for T0in the usual expressionJ_{th}(T) = J_{th}(0) exp (T/T_{0}). Since photopumped multiple-quantum-well MO-CVD AlxGa1-xAs-GaAs heterostructures have operated as CW 300 K lasers with only 5-10 mW of photoexcitation (uncorrected for focusing and window losses,lambda sim 5145Å), it is suggested that quantum-well laser diodes can be made that will operate at ∼1 mA or even less excitation.     

Static characteristics of 1.5 - 1.6 µm GaInAsP/InP buried heterostructure butt-jointed built-in integrated lasers

Lasing characteristics of GaInAsP/InP buried heterostructure butt-jointed built-in distributed Bragg reflector integrated lasers (BH-BJB-DBR lasers) intended for dynamic single mode operation in the wavelength range of1.5-1.6 mum are given. In the first section, the coupling property between the active region and the butt-jointed external waveguide region is calculated to show the possibility of large fabrication tolerance. A coupling coefficient of more than 95 percent is estimated. Secondly, the GaInAsP/InP integrated lasers were fabricated and tested in the view of the static characteristics and the axial mode selection property. Lateral mode control was achieved by the use of a buried heterostructure, so that the axial and lateral modes were maintained to a fixed single mode. The lasers thus fabricated were operated in CW conditions at room temperature with a threshold current of about 100 mA. Single longitudinal mode operation was observed with a temperature dependence of about 0.13 nm/deg with the temperature range of more than50-65degC at around 0°C. Differential quantum efficiency as high as 13 percent/ facet was obtained for the laser with power output of more than 5 mW/facet. The output spectrum below threshold indicated the strong wavelength selectivity of the DBR region, and the net gain difference between the main DBR mode and the adjacent submode was measured to be about 6 cm^-1. No appreciable degradation and change of characteristics have been observed even after CW operation of more than 9770 h at 20°C.     

A simple expression for estimating attenuation by fog at millimeter wavelengths

At millimeter wavelengths, fog attenuation is a function of the fog density, extent, index of refraction of the fog medium, and wavelength. The attenuation is usually determined by first estimating the index of refraction of water for the wavelength and temperature of interest and then calculating the attenuation using the Rayleigh approximation. In this communication fog attenuation is computed for a large set of wavelengths and indices of refraction. A regression analysis of the attenuation is then conducted as a function of wavelength and temperature. It is shown that an almost perfect fit can be obtained with a four-term regression on wavelength and temperature for the ranges of 3 mm <lambda < 3cm and-8degC< T < 25degC, respectively 5666. This expression produces a normalized fog attenuation; the total attenuation is easily computed by multiplying the normalized attenuation by the fog density and extent. If fog density data are not available, a formula for estimating the density from fog visibility is given.     

An experimental evaluation of multiplate antenna properties

A large steerable-beam antenna can be built by using a number of independent reflectors that redirect energy from a desired direction to a focus. An experimental program of measurement has determined the radiation pattern, the efficiency, and the relative change of gain and antenna temperature vs. beam angle of a test section of a multiplate antenna. The effect of the interstices in the reflecting surface produced grating lobes of approximately -20 dB and an additional temperature component that varied from20degK-65degK depending on the beam angle.     

Evaluation of InGaAsP laser material by optical pumping

A novel technique based on optical pumping has been developed to evaluate InGaAsP laser material before it is processed into electrical devices. By pumping unprocessed InGaAsP chips with cleaved mirrors with a 1.06 μm wavelength Nd:YAG laser and detecting the light emitted by the quaternary active layer, various properties such as laser threshold, wavelength, and differential quantum efficiency can be determined. This technique provides a method for screening InGaAsP laser material prior to time-consuming processing. The technique is also applicable to partially processed laser chips, and hence, the effect of each processing step can be evaluated. We find that threshold pumping intensities andT_{0} (sim60degC), the parameter characterizing the temperature variation of threshold, are virtually the same for chips without and with a p-n junction or alloyed contact.     

Gain and carrier lifetime measurements in AlGaAs single quantum well lasers

We have measured the optical gain and carrier lifetime (τ) at threshold in AlGaAs single quantum well lasers in the temperature range10-70degC. The small shift of the spectral position of the gain peak with increasing injection is evidence for the two-dimensional-like density of states in a quantum well. The net gainGis found to vary linearly with the currentI. The observed slow decrease ofdG/dIand τ with increasing temperature suggests the absence of a large temperature-dependent nonradiative carrier loss or optical absorbtion loss in these lasers. This is also supported by the observed low temperature dependence of the external differential quantum efficiency.     

Temperature dependent phase-matched nonlinear optical devices using CdSe and ZnGeP2

Temperature tuning and stability of nonlinear optical devices employing CdSe and ZnGeP2are considered for the first time. From the measured refractive index data at room temperature and the corresponding appropriate temperature derivatives, Sellmeier coefficients are found for the evaluation of refractive indexes both below and above room temperature. These can be used to calculate phase-matching angles at different temperatures. We have evaluated temperature stability of phase-matching angles in tunable parametric oscillators and down-converters and also in up-converter operations which have been reported at room temperature. Temperature characteristics have been worked out for tunable generation of radiation near the 16 μm region in CdSe and the type II second-harmonic generation has been found to be possible for temperaturesgsim275degC in ZnGeP2because of its positive temperature coefficient in birefringence.     

Loss increase for optical fibers exposed to hydrogen atmosphere

Loss spectrum changes for optical fibers exposed to a hydrogen atmosphere in the15-200degC temperature range are measured. Loss increase due to molecular hydrogen dissolved into fibers is investigated from the loss peak at 1.24 μm, and that due to hydroxyl group formation from the loss peak at 1.41 μm. The loss increase due to molecular hydrogen is fully explained by physical solubility theory and diffusion equation. The empirical formula for time, temperature, and hydrogen-pressure dependences of the loss increase due to hydroxyl group formation is evaluated from the experimental results. The loss increase at 1.3- and 1.5-μm wavelength band at room temperature are estimated.