Richard P. Kenan

Self-guiding multimode interference threshold switch.

We propose a new passive optical thresholding device that combines the principles of multimode interference (MMI) with self-guiding. The multimode region is composed of a nonlinear optical material that will support a self-guided beam (i.e., a material with a positive Kerr nonlinearity). The device operates by switching between the MMI mode of operation and the self-guiding mode of operation, depending on the input light intensity. We describe the basic principles of a self-guiding MMI device, simulate the device, and discuss design issues associated with these optically controlled optical switches.

Two-photon absorption-induced self-phase modulation in GaAs-AlGaAs waveguides for surface-emitted second-harmonic generation.

Performance-limiting asymmetric distortion is observed in the spectra of fundamental pulses transmitted through GaAs-Al(0.9)Ga(0.1)As multilayer waveguides designed for surface-emitted second-harmonic generation. This behavior is attributed to refractive-index changes resulting from the accumulation of free carriers created by two-photon absorption in the GaAs layers. Numerical simulations of the intensity-dependent spectra by use of the separately measured two-photon absorption coefficient are shown to be in good agreement with the observed spectra.

Rectangular characteristic gratings for waveguide input and output coupling.

Normal-incidence planar-optical waveguide-imbedded phase gratings of finite aperture width and length are analyzed with Svidzinskiis (Sov. J. Quantum Electron. 10, 1103 (1980)] two-dimensional Braggdiffraction theory. Svidzinskiis characteristic-grating equations are adapted for the rectangulargrating case, and an overlap integral is used to extend the theory to account for the mode structure of the waveguide. The combined theory is used to optimize the throughput of a system composed of an input grating coupler, a waveguide, and an output grating coupler for both the highly multimode (thickwaveguide) and the few-mode (thin-waveguide) cases.

Soluble saturable refractive-index nonlinearity model

Abstract TE modes of an optically linear planar waveguide on a thick nonlinear substrate are described for a model substrate refractive index or dielectric permittivity of the form ϵ= ϵ s + ϵ sat u(2+u) (1+u) 2 , where u= α|E| 2 2ϵ sat , which displays saturation at high guided-wave powers, yet for which wave equation integration and power integrals are elementary. The parameter γ= ϵ sat (ϵ f –ϵ s ) where ϵf is the guiding-layer permittivity, determines the guided-wave behavior. For γ 1, power limiting and interface guiding are observed, similar to the Kerr model except for the saturation effect.

160-Gb/s optically time-division multiplexed link with all-optical demultiplexing

An ultrafast single-wavelength optically time-division multiplexed (OTDM) link is described. The link exploits a unique integrated, all-optical serial-to-parallel (S/P) converter based on second-harmonic generation that demultiplexes multiple high-speed optical channels with a single operation. The link is composed of five major components: (1) a high-repetition-rate picosecond-pulse source; (2) a planar waveguide multiplexer that incorporates electroabsorption modulators with integral spot-size converters (SSCs); (3) a dispersion-managed (DM) short-pulse fiber channel; (4) a quasi-phase-matched, resonant-cavity-enhanced AlGaAs waveguide designed for surface-emitted second-harmonic generation (SESHG); and (5) a 775-nm receiver optimized for return-to-zero (RZ) operation. We describe our recent advances with resonant cavity enhancement of the all-optical demultiplexer and the first bit error rate (BER) measurements for this demultiplexing scheme.

Design and performance of an integrated optical digital correlator

We describe an integrated optical correlator capable of performing ordinary binary or bipolar correlations. The device consists of two surface-acoustic-wave (SAW) transducers and an electrooptic spatial light modulator in a planar Ti in-diffused LiNbO 3 waveguide. It is designed to correlate a 32-bit word at a 32-Mbit/s data rate.

MODIFIED INTEGRATED OPTIC FRESNAL LENS FOR WAVEGUIDE-TO-FIBER COUPLING

The traditional design procedure for the waveguide Fresnel lens was carried over from those of bulk optics and micro-optics. In this design it is assumed that the lens thickness is negligibly small with respect to the focal length. This criterion does not hold for many integrated optic devices, in particular those with small mode-index modulations and long wavelengths. Under these conditions, the focal properties of the lens become unpredictable and the lens efficiency is reduced, both of which severely limit the usefulness of the lens as a waveguide-to-fiber coupler. To correct for this shortcoming, the standard Fresnel lens design procedure was modified to acocunt for the thickness of the lens explicitly. Both the standard and the modified Fresnel lens designs are outlined. A comparison of the limitations of the two lenses predicts better performance for the modified Fresnel lens. This is supported through computersimulation results for a pair of test lenses.

Four-wave theory of electrooptic gratings with a simple expansion for use in design.

A four-wave theory of phase gratings electrooptically induced in dielectric waveguides is analyzed and solutions to the coupled-wave equation are derived for incidence at the first Bragg angle. These solutions are compared with the solutions for the two-wave theory of Kogelnik, and expansions for the differences are obtained in reciprocal powers of the Nath parameter rho. The leading terms in the expansion can be used to estimate the errors committed in designs using the simpler two-wave theory.

Influence of grating shapes on beam profiles for right-angle guided-wave diffraction

We present simulation results on the influence of grating shapes on diffracted beam profiles for right-angle diffraction. The first-order two-dimensional coupled-mode equations are solved numerically by using the finite-difference method for As(2)S(3) waveguide surface-relief gratings on titanium-indiffused planar waveguides. The simulation results show that square or rectangular gratings result in a distorted profile for the diffracted beam and that truncated grating shapes significantly improve the output beam quality.

Integrated optical architectures for tapped delay lines

An integrated optics (IO) device that is an implementation of an IO tapped delay line is discussed. It is capable of performing discrete convolution of an optical pulse sequence with a preset digital function. Several architectures for the device are presented. A systematic realization of the preset function samples that permits efficient utilization of all the input light power and maximization of the output signal-to-noise ratio (SNR) for the device is discussed. A detailed analysis of what determines the number of preset samples that can be realized and how to realize them on a LiNbO/sub 3/ crystal is given. Two digital filter design examples are presented, and the quantization error effects on their performance are examined. The same architectures are shown to implement digital-to-analog (D/A) conversion and systolic multiplication of a Toeplitz matrix with a vector having the form of optical pulses. >