William S. C. Chang

The Gate-Controlled Photodiode For Optical Matrix Multiplication Applications

A new semiconductor device -- the gate-controlled photodiode (GCPD) is presented here. Its photocurrent is dependent on the product of the light intensity and the gate voltage. Its potential applications in optical matrix multiplication is discussed.

Techniques For Fabricating High Index Overlay Films On LiNbO 3

We report here three different techniques for making high-refractive-index transparent films on LiNbO3 in the form of either planar or two-dimensional structures. Such techniques should be very useful for making a number of integrated optical components on LiNbO3.

Design Considerations For Mode Extinction Modulators In LiNb0 3 Waveguides

Many types of electro-optic modulators have been considered for IOC applications. The mode extinction modulator is particularly interesting in that its operation is based on the composition of several physical mechanisms. These include coupling between guided modes, radiation to substrate modes, and voltage dependent propagation losses. Therefore, in addition to possessing the desired properties of high frequency response, low operating voltage, high efficiency, large packing density, and simplicity in fabrication, the modulators transfer curve can be altered to optimize a particular curve shape. This is accomplished by adjusting certain physical parameters in the waveguide structure or modulator electrodes. For example, a large linear dynamic range can be achieved by the proper choice of physical parameters. Optimization for high efficiency, linearity, and modulation depth will be reported along with design parameters and trade-offs. In addition, a technique for creating an optical bias will be discussed which allows operating point selection.

Chirped Grating Lenses In Ti-Indiffused LiNbO3 Optical Waveguides

Chirped grating lenses have been successfully designed, fabricated and evaluated for the first time on Ti-indiffused LiNbO3 waveguides. The design procedure, the expected and measured performances, the materials and fabrication processes developed, and the performance limitations imposed by the waveguide parameter and by the fabrication tolerances will be presented.

Electro-Optic Mode Extinction Modulator Using Weakly Guided Channel Waveguide

Electro-optic modulators have been constructed which provide high efficiency modulation of channel guided waves in LiNb03 with a capability of large dynamic range, good linearity, and high packing density for use in large modulator arrays. Modulation of an input guided wave has been observed by creating a variable index gradient with an E-field generated by surface electrodes. The dominant modulation mechanism is determined by the degree of light energy confinement in the interaction region. Both an imaging or gradient effect and a guided mode effect are possible. Modulation efficiencies of greater than 0.95 have been achieved with a 1 mm interaction length and an E-field strength of 4 x 10-6 v/m. Linearity of about 1% has been demonstrated. Design considerations and experimental performance data are presented.

The State Of Art Of Chirp Grating Lenses On LiNbO3

Chirp gratings lens is the key technology for the next generation of integrated optical signal processing devices. These lenses have been made on LiNbO3 substrate by various fabrication processes. This paper will report the current status of this technology development.

Effect Of Asymmetry On Extinction Coefficient Of Crossing Channel LiNbO3 Waveguide Switches

In this paper we will show theoretically and experimentally that the mode conversion in converging and diverging channels caused by the asymmetry produced in the fabrication processes is limiting the extinction ratio of single mode crossing channel switches. Degradation of the extinction ratio is caused primarily by asymmetry in the transition regions of the switches.

Optical Waveguides And Electro-Optical Devices In Heterojunction And Quantum Well Structures Of III-V Compound Semiconductors A Review

Important properties of heterojunction and quantum well structures and how these structures have been used for optical waveguides and guided wave intensity and phase modulation (switching) are reviewed in this paper. Further investigations necessary to obtain large bandwidth, low insertion loss and efficient modulation are discussed.

Electro-Optical Properties Of III-V Compound Semiconductors For Spatial Light Modulation Applications

Electroabsorption and electrorefraction properties of bulk and multiple quantum well structures made fr III-V compound semiconductor materials are discussed in this paper. The large electroabsorption that has already been observed is suitable for spatial light modulation. The potential advantages for using these structures for spatial light modulation include high speed of response and monolithic integration with detectors and electronic devices on the same chip. Variations of the electro-optical properties such as absorption wavelength birefringence. nonlinearity and speed of response as a function of structural

N×M Planar Optical Waveguide Switch For Computer Communications

A new scheme for a NxM electro-optical switching network in a planar LiNbO3 optical waveguide for computer communications has been demonstrated and will be reported here. Experimental data and analysis will be presented to show its performance characteristics, such as the maximum number of communications channels, the on/off difference (i.e. signal-to-noise ratio) and the switching voltage, as affected by the inplane scattering noise in the waveguide, the lens performance, switching electrode design, and detectors.