Silicon nitride (Si(3)N(4)) thin film optical waveguides with propagation losses of less than 0.1 dB/cm for the TE(0) mode at lambda(0) = 6328 A have been successfully grown by low-pressure chemical vapor deposition. Silicon wafers 5 cm in diameter were used as substrates, and the Si(3)N(4) was separated from the substrate by a steamoxide SiO(2) buffer layer. Propagation losses are examined for the various waveguide modes, and their dependence on waveguide parameters and wavelength are discussed and compared with exact calculations. Leakage into the silicon substrate is shown to be a major loss mechanism, especially at longer wavelengths and for higher mode numbers.

Silicon nitride films on silicon for optical waveguides

This paper presents a selective review of planar guided-wave acoustooptics, including some of the most recent results. The emphasis is on those aspects which relate to wide-band multichannel optical communications and real-time signal processing. First to be discussed are the analytical and numerical techniques required for the treatment of a Bragg modulator which uses a single aperture SAW transducer. The frequency responses generated for Y -cut LiNbO_3 waveguides using a digital computer serve as the basic data for the design of such a basic modulator. Next the key device parameters relevant to modulation and signal processing are discussed. The design parameters and procedures for wide-band Bragg modulators and deflectors are then established. Finally, some potential applications of such wide-band modulators and deflectors in optical communications and RF signal processing together with the best measured performance figures are described.

Guided-wave acoustooptic Bragg modulators for wide-band integrated optic communications and signal processing (Invited Paper)

A wide-band real-time spectrum analyzer is examined as a viable integrated optical circuit for processing electronic signals. The spectrum analyzer includes a Luneburg beam expansion lens system, a surface elastooptic Bragg spatial modulator, reflectors, a Luneburg Fourier-transform lens, and a waveguide coupled photodetector array, all formed on thermally grown SiO 2 on Si as the substrate. A distributed-feedback (GaAl)As laser with hybrid coupling is included as the carrier for the optical Fourier transform. The developmental status of this integrated-optical spectrum analyzer and its essential design considerations are delineated.

An integrated-optical approach to the Fourier transform

The dispersion characteristics and radiation loss characteristics of ARROW (antiresonant reflecting optical waveguide), a novel single-mode slab waveguide, are analyzed in detail. The mechanism by which the waveguide produces a large amount of light radiation from the waveguide core to the semiconductor substrate is explained and some approximate formulas of propagation characteristics are obtained, which are useful for the design of ARROW. Two novel integrated structures of ARROW and photodetector are proposed to realize high coupling efficiency from waveguide to photodetector, small device size, and easy fabrication process. In these structures, an antireflecting (AR) layer is introduced to greatly enhance coupling efficiency. Their performance is discussed compared with the conventional waveguide structure. It is shown theoretically and experimentally that a high coupling efficiency (>90%) is achievable with short detector length in the ARROW structures.

High efficiency light coupling from antiresonant reflecting optical waveguide to integrated photodetector using an antireflecting layer

Direct coupling of light from fibers supported in preferentially etched grooves on a silicon surface to channel waveguides formed in the same grooves is demonstrated. Criteria are presented for choosing a groove geometry that matches the center of the fiber to the center of the waveguide and thereby yielding optimum coupling. Channel waveguide tapering and integration of detectors into the channel waveguide termination are demonstrated. A general configuration allowing CCD time multiplexing is introduced.

Optical coupling from fibers to channel waveguides formed on silicon.

We consider device design, fabrication, and operation of integrated optical photodiode arrays in which p-i-n junction photodiodes are formed in silicon. A SiO2 layer on silicon serves as the effective substrate for a KPR waveguide. Light is coupled from the waveguide at the detector region either through the evanescent field or by multiple refraction into the detector. The waveguide–photodiode structure is designed so that nearly 100% of the incident optical energy can be absorbed in the photodiode junction depletion region. A device quantum efficiency of 80% is measured compared to a theoretical value of 93%.

Integrated optical silicon photodiode array

The fabrication of optical waveguide couplers involving tapered layers of is discussed. Details of the SiO2 photolithographic fabrication processing sequence are presented. This process utilizes carefully controlled etchant undercutting and has been found to be quite reproducible. It has allowed fabrication of tapers having changes in SiO2 thickness of 1.0 μm over lengths of 55–75 μm. Results are presented which demonstrate taper transverse uniformity for distances of over 600 μm. The smoothness and gradual nature of the tapers are apparent in scanning electron microscope pictures of a taper cross section.

Fabrication of optical waveguide taper couplers utilizing SiO 2

Applications of integrated optical devices to optical communications or signal processing often involve light beam deflection or spatial Fourier transformation performed by optical waveguide lenses. In each of these processes information carried by the light beam can be converted to an electrical signal through use of a detector array. By integrating a detector array into an optical waveguide structure, optical scattering which would occur in coupling light out of the waveguide and into a detector array is eliminated so that the primary limitation on information capacity is the detector array resolution. We consider herein such an integrated optical waveguide detector array which uses silicon as the substrate. The use of silicon allows fabrication of CCD array scanning structures or other array addressing circuitry, signal enhancement circuitry, and signal processing circuitry on the same substrate as the optical waveguide. A silicon substrate is also advantageous for optical waveguide formation in that the thermallygrown Si02 layer which supports the thin-film optical waveguide has a low refractive index and a very smooth surface for waveguide deposition. Also, Si is well-suited for the formation of three-dimensional channel waveguides by preferential etching.

http://ieeexplore.ieee.org/iel5/9941/31745/01478317.pdf

C. L. Chen

Papers

Integrated optical silicon photodiode array

Fabrication of optical waveguide taper couplers utilizing SiO 2

Integrated optical silicon photodiode array

Integrated optical silicon photodiode array