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A novel intersection waveguide-type polarization splitter based on total reflection using the birefringence of the GaInAsP/InP superlattice waveguide is proposed and analyzed in this paper. The semivectorial finite difference beam propagation method (FD-BPM) (which handles both TE and TM modes) is used in the analysis. The waveguide structure including the GaInAsP/InP superlattice is designed; and it is shown that, although with a superlattice core the refractive index for the TM mode is reduced by approximately 0.4 percent, there is no change for the TE mode. Based on this result, the optimal structural parameters such as superlattice layer number, rib height (h), intersecting angle (θ), and port separation length (Lsp) are investigated using a 1.55μm wavelength. It is found that the TE and TM modes can be separated with an insertion loss of less than 0.4 dB for both modes and a crosstalk of less than −35 dB using an intersecting angle of 5° and a device length of approximately 0.9 mm. It is shown that compared to conventional devices, the device length in the proposed device structure can be reduced by using total reflection. The wavelength dependence of the device is also analyzed.

In this paper, the aims of our study are to analyze the gain of semiconductor optical amplifiers with tensile strained multiple quantum wells and to examine the structure for polarization-insensitive characteristics for the purpose of showing the design guidelines. Since lasers with conventional lattice-matched multiple quantum wells have large optical confinement coefficient and large gain coefficient for TE mode, they are not polarization insensitive. Since the modal gain is the product of the optical confinement coefficient and the gain coefficient, the elimination of polarization sensitivity requires increasing the gain coefficient for the TM mode by applying the tensile strain to the well layer in order to compensate for the difference in the optical confinement factor. Assuming a multiple quantum well structure, the analysis obtains the strain distribution over the structure and an envelope function of the wave function and calculates the gain using a density matrix method by electron relaxation effect. It includes the band mixing effect of valence bands. As a result, a structure with little modal gain difference over a wide range at 1.55-μm wavelength has been designed. Also, as a result of examining the effect of deviation from the designed values, it has been found that the variation in the material composition (amount of strain) has a larger effect on the modal gain difference than the variation in the quantum well thickness.

Three-dimensional (3-D) analysis of an intersec-tional optical switch is performed using the finite difference beam propagation method (FD-BPM), and design guidelines are obtained from this analysis. The operating characteristics of the switch are evaluated by extinction ratio and power attenuation in two output ports. The optimal structure parameters, such as normalized frequency (V), waveguide relative refractive index difference (Δω), and intersecting angle (θ), are obtained for 1.55 μm wavelength operation. Wideband operation in the 1.3 to 1.6 μm wavelength range is discussed taking into account the wavelength dispersion of materials. It is found that to achieve an extinction ratio that is better than 20 dB, a refractive index variation of 0.5 percent is enough for single-wavelength operation; however, a refractive index variation larger than 0.7 percent is required at the longer-wavelength side for wideband operation. Finally, the results of 2-D and 3-D analyses are compared and good agreement is obtained with an error of about 1 dB.

This paper proposes an optical filter consisting of GaInAsP/InP waveguides whose performance is examined analytically. This filter is composed of a vertical three- or four-waveguide directional coupler. Based on an eigenmode analytical method, a compact and demultiplexing device is realized. The propagation characteristics of such devices are calculated as being expressed in terms of the superposition of the eigenmodes. A design criterion for both a demultiplexer and bandpass filter is presented. The demultiplexing of the two wavelengths of 1.545 and 1.585 μm with a crosstalk level better than -23 dB at a coupling length 265 μm is demonstrated. Also, with a multiple quantum well waveguide, a value of 6.9 nm for the -15 dB bandwidth at a coupling length 972 μm is obtained. Furthermore, the demultiplexing of the three wavelengths of 1.51, 1.545, and 1.60 μm is found to be possible in a four-guide coupler structure (coupling length 942 μm) with MQW waveguides.

This paper reports a gain analysis of a quantum well laser with multiple quantum well with different well thickness. Since quantum energy levels corresponding to each well appear in a quantum well with different well thickness, it is possible to control to a certain extent the energy distribution of the electrons. This characteristic is used advantageously to control the gain profile of a quantum well laser. In this case, the individual quantum well structures are different and are mutually coupled. Also, since the quantum levels of the second- and higher-order are used, the analysis must be carried out rigorously taking into account the wave nature of the electrons. The laser theory based on the electron relaxation phenomenon has been developed with the wave nature of the electrons considered so that the gain equation is derived. As an example, a structural design has been carried out for low current operation of the oscillation wavelength switch and for flattening the gain profile. Excellent numerical results were obtained. A possibility for new applications of the quantum effect devices is expected.