Kaname Jinguji

Silica-based single-mode waveguides on silicon and their application to guided-wave optical interferometers

Low-loss silica-based single-mode waveguides and directional couplers are fabricated on silicon substrates. Their application to Mach-Zehnder interferometer type guided-wave devices is demonstrated. Optical switches or tunable optical couplers are fabricated using the thermooptic effect. Asymmetrical Mach-Zehnder interferometers are successfully applied to multi/demultiplexers for optical FDM transmission systems. >

Synthesis of coherent two-port lattice-form optical delay-line circuit

A method is presented for synthesizing a coherent two-port lattice-form optical delay-line circuit that is composed of optical delay lines, directional couplers, and phase shifters. The two bases of the method are the use of a unimodulus para-unitary matrix as a transfer matrix and the division of the transfer matrix into basic component transfer matrices. We succeeded in obtaining a set of recurrent equations with which to calculate circuit parameters to use for designing an optical delay-line circuit with a desired cross-port (through-port) transfer function. In the developed method, it is shown that two-port optical delay-line circuits can have the same transmission characteristics as finite impulse response digital filters with complex expansion coefficients. Three synthesis examples for optical frequency filters are described: a linear-phase Chebyshev filter, a multi-channel selector, and a group-delay dispersion equalizer. It is confirmed that transmission characteristics with a maximum transmittance of 100% can be always synthesized. The allowable parameter error for the synthesized linear-phase Chebyshev filter is also discussed. >

Optical half-band filters

This paper proposes two kinds of novel 2/spl times/2 circuit configuration for finite-impulse response (FIR) half-band filters. These configurations can be transformed into each other by a symmetric transformation and their power transmittance is identical. The configurations have only about half the elements of conventional FIR lattice-form filters. We derive a design algorithm for achieving desired power transmittance spectra. We also describe 2/spl times/2 circuit configurations for infinite-impulse response (IIR) half-band filters. These configurations are designed to realize arbitrary-order IIR half-band filter characteristics by extending the conventional half-band circuit configuration used in millimeter-wave devices. We discuss their filter characteristics and confirm that they have a power half-band property. We demonstrate design examples including FIR maximally flat half-band filters, an FIR Chebyshev half-band filter, and an IIR elliptic half-band filter.

Birefringence control of silica waveguides on Si and its application to a polarization-beam splitter/switch

A novel polarization-beam splitter/switch with a Mach-Zehnder interferometer configuration was fabricated using a silica-based planar lightwave circuit (PLC) on a silicon substrate. The polarization-beam splitter/switch was realized by accurately controlling the waveguide birefringence and the phase state by laser trimming two kinds of stress-applying amorphous silicon film with widths of 50 /spl mu/m and 95 /spl mu/m. Fiber-waveguide-fiber insertion loss of 0.5 dB and crosstalk attenuations of over 25.6 dB were attained. >

Synthesis of coherent two-port optical delay-line circuit with ring waveguides

A method has already been reported by the author and others for synthesizing coherent two-port lattice-form optical delay-line circuits which have the same filter characteristics as finite impulse response (FIR) digital filters. This paper proposes a two-port circuit configuration with ring waveguides which can realize the same filter characteristics as infinite impulse response (IIR) digital filters. It also describes a synthesis method for realizing arbitrary IIR filter characteristics with the circuit configuration. This method is based on scattering matrix factorization. Some synthesis examples are demonstrated including an elliptic filter, a Butterworth filter, an optical filter with maximally flat group-delay characteristics, a group-delay dispersion equalizer, and a multichannel selector.

Two-port optical wavelength circuits composed of cascaded Mach-Zehnder interferometers with point-symmetrical configurations

Wavelength circuit characteristics are investigated systematically for a family of two-port optical wavelength circuits composed of cascaded Mach-Zehnder interferometers (MZIs) with point-symmetrical configurations. A novel design method is presented for flattening their cross-port passbands (through-port stopbands). The design principle is based on a consideration of the general relations between wavelength circuit characteristics and circuit configuration symmetries. It is shown that the role of this novel design method is complementary to that of the conventional flattening method which is used for simple wavelength-insensitive couplers (WINCs) with a single-stage MZI configuration. Various optical wavelength circuits are designed by using both the novel and conventional design principles, including fixed and tunable WINCs, a wavelength-insensitive switch (WINS), and a wavelength multi/demultiplexer with a flattened passband and stopband. Measurement results are provided for some of the designed optical circuits which were fabricated using silica-on-silicon planar lightwave circuits (PLCs).

Wavelength characteristics of (2*2) optical channel-type directional couplers with symmetric or nonsymmetric coupling structures

The wavelength dependence of waveguide-type directional couplers is investigated with respect to waveguide pattern symmetry in the coupling region. A rough approximation of the dependence is determined based on simplified transfer matrix multiplications, followed by a more detailed computer calculation using the beam propagation method (BPM). Wavelength-flattened coupling characteristics over a wide range, for example, from 1.33-1.55 mu m, are predicted for several types of directional coupler with waveguide width asymmetry or a tapered width structure in the coupling region. >

Silica-based waveguide-type wavelength-insensitive couplers (WINC's) with series-tapered coupling structure

The authors propose new wavelength-insensitive directional couplers (WINCs) with series-tapered waveguides in the coupling region. The wavelength-insensitive characteristics are investigated with respect to the geometric symmetry of the series-tapered coupling structure. An approximate analysis of three types of WINC is made using simple transmission matrix multiplication. These new WINCs were fabricated based on silica-based planar lightwave circuits (PLCs) on silicon substrates. The experimental results for the wavelength-insensitive responses of the series-tapered coupler, which was designed in detail with the beam propagation method (BPM), are in good agreement with the calculated results. The novel wavelength-insensitive characteristics of these couplers are also demonstrated for the first time. >

Synthesis of One-Input M-Output Optical FIR Lattice Circuits

This paper presents a one-input M-output (1 x M)configuration and a synthesis algorithm for realizing an optical finite impulse response (FIR) lattice filter having M output channels (M ges 2). The circuit configuration has a multilayer structure consisting of multiple Mach-Zehnder interferometers with delay time differences of zero or Deltatau. It is a natural extension of the conventional two-port optical FIR lattice circuit (M = 2) . The proposed synthesis algorithm is based on factorizations of the paraunitary total transfer matrix. It realizes output responses having highest orders equal to the number of stages for all output channels. It is shown that such a synthesis algorithm maximizes the degrees of freedom for designing output responses. Two kinds of five-channel interleave filters are demonstrated as synthesized examples: one has a flat group delay response while the other has an inclined group delay response.

Design and Fabrication of Silica-Based Waveguide-Type (3?3) Directional Couplers with Two Identical Outer Waveguides

We analytically and experimentally demonstrate the design and fabrication of silica-based waveguide-type (3×3) directional couplers with emphasis on the wavelength-flattened responses of the couplers when the center guide is excited. Complete optical power transfer from the center guide to the two outer guides, which corresponds to a 0.5:0:0.5 splitting ratio (3 dB coupler), is attained with slightly wider outer guides. Wavelength-flattened splitting ratios of 0.33:0.34:0.33 (5 dB coupler) or 0.1:0.8:0.1 (10 dB coupler) over a wide range from 1.3 µm to 1.55 µm are obtained with larger differences between the widths of the center and two outer guides. When the light is launched into one of the outer guides, complete power transfer is always obtained for the outer-to-outer path but not for the outer-to-center path, reflecting the waveguide symmetry of (3×3) structures. These experimental results are in good agreement with results calculated using the beam propagation method (BPM).