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The bending losses in rectangular dielectric waveguides deposited on a chemical mechanical polished (CMP) surface above the metal interconnect/interlayer dielectric stack of a processed Si wafer are modeled and estimated. CMP efficiently removes local topography and microroughness, but leaves long-range surface profile undulations due to variations in the metal pattern density. These surface undulations are then transferred to the waveguides deposited on this surface. A beam propagation method (BPM) waveguide simulation program and an equation for bending loss developed by Marcuse have been used to examine the bending losses seen by waveguides deposited on such a surface. In order to simplify the simulation of the bending losses of the waveguides, the undulations are modeled as a series of arcs, which is shown to be a good approximation. It was determined that under typical conditions, the bending losses may be ignored as they are less than 0.1 dB/cm, which is below the range of typical propagation losses for a straight guide.

Two-dimensional optical data links can be used in applications where it is necessary to have high density high throughput interconnections. Verticalcavity surface emitting lasers (VCSELs) are a promising low cost optical interconnection technology and can easily be fabricated in two- dimensional arrays.

The effects of nonuniform current injection along the length of a semiconductor laser are investigated using multiple segmented stripe contact lasers. The results of the experiments are analyzed with a model for which the carrier concentration, gain, and photon density are functions of position. From the model, it was determined that nonuniform current injection caused large variations in the optical field within the laser, and the field produced a redistribution of electrical carriers in the active region. The nonlinearities in the light versus current measurements were explained by the redistribution of carriers as the optical field changed.

Calculations of threshold current densities for lead-tin telluride double-heterojunction (DH) laser diodes are presented, in which the spatial distribution of the injected minority carriers and the critical level of minority carrier injection necessary for population inversion are considered. Excellent agreement between the predictions of this model and experimental data is obtained, which suggests that credible predictions of high-temperature performance can be made. The need to inject a critical level of minority carriers is shown to be the principal contribution to the threshold current density except at very low temperature and to lead to a rapid increase in threshold with increasing temperature. It is found experimentally that below 40 K the threshold no longer decreases with temperature; two possible explanations for this behavior are suggested.

Coupling coefficient calculations of the type originally published for gallium arsenide distributed feedback (DFB) lasers are here extended to the lead-tin telluride based family of devices. Specific calculations of the coupling coefficient as a function of active region and grating dimensions are presented for PbTe/Pb 1-x Sn x Te/PbTe devices, x = 0.13 and x = 0.18 , at 8 K and 77 K, and the implications of the results for device design and fabrication are discussed.

Distributed feedback (DFB) pulsed laser operation has been demonstrated in stripe geometry Pb 1-x Sn x Te double-heterostructures grown by liquid-phase epitaxy. The grating structure of 0.79 μm periodicity operates in first order near 780cm-1(12.8 μm) and was fabricated prior to the liquid-phase epitaxial growth using holographic exposure techniques. These DFB lasers had moderate thresholds, 3.6 kA/cm2, and the output power versus current curves exhibited a sharp turn-on free of kinks. Clean, single-mode emission spectra, continuously tunable over a range in excess of 20 cm-1, centered about 780 cm-1(12.8 μm), and at an average rate of 1.2 cm-1. K-1from 9 to 26 K, were observed. While weaker modes could at times be seen in the spectrum, substantially single-mode operation was obtained over the entire operating range and to over 10 times threshold. These observations have been shown to be in good agreement with published lead-salt parameter values and DFB theory, and significantly increase the attractiveness of the DFB structure for tunable lead-salt laser diodes.

A new calculation of radiative minority carrier lifetime in PbSnTe is presented which yields lifetimes an order of magnitude greater than previously accepted values. These results are used in combination with recent measurements of minority carrier lifetime and interface recombination velocity in PbSnTe double heterojunction laser structures to calculate DH laser thresholds. It is demonstrated that radiative recombination is a relatively inefficient process in present PbSnTe lasers, and that when this inefficiency is taken into account the magnitude of the experimentally observed threshold and its variation with active region width and temperature can be accurately predicted, even at low temperatures where all previous models have failed.

The theoretical gain of strained-layer semiconductor lasers is analyzed in the large strain regime based on the density-matrix method, taking into account the modification of both the valence bands and the transition dipole moments. The wave functions for the valence-band states for an arbitrary wave vector at the Gamma point in the presence of stain are derived from diagonalization of the strain Hamiltonian using the original wave functions obtained from the k-p method. These wave functions are then used to obtain the dipole moment matrix elements at the band edges, which are found to be independent of the wave vector. >

Using a mode-matching technique, a modular microwave equivalent circuit incorporating both guided and continuum spectra has been developed to model open guided-wave integrated optical components accurately with limited computational effort. The accuracy of the analysis is verified by comparison with other methods of analysis, and by experiments performed on GaAs homojunction rib waveguides, directional couplers, and three-guide couplers. The limitations of approximate theories for the analysis of coupled structures are also identified. >

The semiconductor stimulated gain saturation model of Zee has been extended using reasonable approximations to obtain an analytical solution for the gain saturation process in PbSnTe and to determine the limit to single mode power directly from the gain expression, the intraband relaxation time, and device and material parameters. The theoretical results are compared with experimental observations for single transverse mode cavity narrow stripe buried heterostructure PbSnTe lasers. Those results are interpreted in terms of an intraband relaxation time on the order of 2 \times 10^{-12} s in the temperature range 20-80 K.

Coupling between two uncoupled waveguides in proximity can be affected by introducing a third waveguide between them. One advantage of this scheme is that it can eliminate the need for bends. Another advantage is the resulting improvement in the shape of the transfer characteristic. Improved sampling and tunable filter operation of this new structure are also shown. An analysis of a uniform filter structure is presented. The "sidelobe" analysis of Alferness is adapted to the present case and tapers are investigated for further sidelobe suppression.

The use of the grating-coupled emission concept with lead-tin telluride double-heterojunction diode lasers is analyzed theoretically. The GCE configuration is shown to be attractive for producing small divergence-angle emission from fixed-wavelength lead-salt devices, but to be of more limited interest for use with tunable lasers because of the small critical angle characteristic of the PbTe-air interface and because of the variation of the angle of emission with wavelength. The device structure studied is one incorporating a reflecting contact in close proximity to the grating, a feature which leads to resonant enhancement or reduction of the emission, depending upon the wavelength and the device dimensions.

An analysis of rib dielectric waveguides based on a mode matching technique is presented. When the constituent slab guides support only one guided mode, it is shown that the cutoff condition for the higher order modes is the same as the result of the effective dielectric constant method. However, when the rib region is thick enough to support two guided slab modes, the cutoff conditions are significantly different. For this case universal design curves are produced and plotted. The results are also compared with another theory that exists to analyze such structures.

A tunable, narrow-band thin-film filter consisting of two uniform grating filter sections separated by a phase-shift section is proposed, and the theoretically predicted performance of these new components is verified experimentally. A straightforward method of calculating the reflection spectrum of these structures is also presented; the technique is particularly well suited to accounting for the effects of parasitics in practical structures. Finally, a qualitative model useful for intuitive analysis of these filters and their spectra is described.

An exact transient solution is presented for the spatial and temporal variation of the injected minority carrier distribution and for the total number of injected minority carriers in a double heterojunction device, e.g., a light-emitting diode (LED) or diode laser, in the presence of interface recombination centers at the heterojunction boundaries, with finite minority carrier lifetime in the center region, and for current pulse excitation. The solution for the model assumed is completely general and can be applied to any material or dimensional situation; for purposes of illustration, numerical results appropriate for typical III-V or Pb-salt heterostructures are presented. It is shown that for the total number of injected minority carriers, an effective minority carrier lifetime can, in certain cases, be defined which is a function of the interfacial recombination centers, the minority carrier lifetime, and the middle or "active" region width. The practical implications of this and other results for device performance and analysis are discussed.

An analysis of the sensitivity of InGaAs/InP bipolar heterojunction phototransistors (HJPT's) used in pulse code modulated optical communications systems is presented. The minimum detectable power of an HJPT biased at the optimum level is found to increase linearly with bit rate B while because of the fixed transconductance of the FET amplifier, the minimum detectable power of a p-i-n FET increases as B^{3/2} . It is shown that HJPT's can thus have higher sensitivity than p-i-n FET detectors, particularly at high bit rates, and can have comparable sensitivity to APD-FET detectors.