We demonstrate a compactly integrated polarization beam splitter (PBS) with high polarization extinction ratios greater than 20 dB over the full C-band wavelength range based on a simple bridged silicon nanowaveguide directional coupler. The PBS device is designed via three dimensional finite-difference time-domain (3D-FDTD) simulation, and fabricated experimentally. The optimum dimension of the bridge waveguide is determined to be 7.5-μm-long and 500 nm-wide for 250-nm thick silicon core. At the 1,550-nm wavelength, the measured polarization extinction ratios (PERs) of the PBS device are 22.5 dB and 22.9 dB for TE and TM polarization modes, respectively, and its corresponding insertion losses (ILs) are about 2.1 dB and 1.8 dB, both PERs and ILs within the maximum error range of ± 2.0 dB.

We demonstrate an integrated polarization beam splitter (PBS) of a simple and compact device geometry with high polarization extinction ratios (PERs). A silicon PBS based on a three-waveguide directional coupler is numerically simulated for optimum device parameters, and fabricated experimentally. The measured PER values of the fabricated PBSs are 40.74 dB and 39.01 dB for transverse electric and transverse magnetic modes, respectively, and their corresponding insertion losses are 0.35 dB on average for a coupler length of about 29.4 μm.

We propose and experimentally demonstrate an ultracompact transverse magnetic (TM) mode pass filter based on a rectangularly-shaped one-dimensional (1-D) photonic crystal silicon waveguide with an extremely high polarization extinction ratio (PER) of >30 dB and a low insertion loss (IL) of ~1 dB. The device structure of the TM mode-pass filter is numerically simulated using a three-dimensional (3-D) finite difference time domain (FDTD) method. The proposed device supports its fundamental TM mode only, whereas the transverse electric (TE) mode is reflected by the 1-D photonic crystals (PhCs). The measured PER of the fabricated TM mode-pass filter is ~34 dB, and the IL is about 1 dB. The entire device length is about 4 μm. Our simulation results predict that the device bandwidth of 30 dB PER is about 200 nm.

We report a simple method of measuring the absolute values of the phase refractive index of an optical material of a flat plate shape over a wide spectral range at a single measurement run. A white-light interferometric technique with angle rotation of the optical plate sample located in one of the interfer ometer arms was used in this method. The validity of this method was proved by measuring the absolute phase refractive indices of flat plate samples of fused silica and BK7, and by comparing them with calculated values from their well-known Sellmeier dispersion formulas. The accuracy of this refractive index measurement method was within 0.002, which can be further improved by enhancing the angle measurement accuracy of the angle rotating stage used in this method.

All-optical set-reset flip-flop operations of conventional circular cylindrical-shaped 1.55-μm wavelength single-mode vertical-cavity surface-emitting lasers (VCSELs) have been demonstrated at a switching frequency of 1 GHz based on polarization bistability observed via injection current variation. The energy of set and reset pulses was lower than 4.5 fJ at a bias current of the VCSEL of 4 mA. Polarization bistable VCSELs will be useful for high-speed optical signal processing applications.

Comparative Study of Uniform and Nonuniform Grating Couplers for Optimized Fiber Coupling to Silicon Waveguides Grating couplers;Integrated optics devices; We have investigated the ultimate limits of nonuniform grating couplers (NGCs) for optimized fiber coupling to silicon waveguides, compared to uniform grating couplers (UGCs). Simple grating coupler schemes, which can be fabricated in etching steps of the conventional complementary metal-oxide semiconductor (CMOS) process on silicon-on-insulator (SOI) wafers without forming any additional overlay structure, have been simulated numerically and demonstrated experimentally. Optimum values of the grating period, fill factor, and groove number for ultimate coupling efficiency of the NGCs are determined from finite-difference time-domain (FDTD) simulation, and confirmed with experimentally demonstrated devices by comparison to those for the UGCs. Our simulated results indicate that maximum coupling efficiency of NGCs is possible when the minimum pattern size is below 50 nm, but the experimental value for the maximum coupling efficiency is limited by the attainable fabrication tolerance in a practical device process.