Carl M. Verber

Self-timed integrated-optical serial-to-parallel converter for 100 Gbit/s time demultiplexing

We describe a novel all-optical serial-to-parallel (S/P) converter using surface-emitted second harmonic generation (SHG). This passive self-timing integrated-optical device is designed to demultiplex optical signals at rates exceeding 100 Gb/s. The results of a proof-of-concept demonstration are presented.<<ETX>>

Simple technique to reveal a slow nonlinear mechanism in a z-scanlike n 2 measurement

We report a simple technique to determine whether the nonlinear mechanism that dominates the results of a z-scan n2 measurement is slower than the duration of the exciting pulse. In this technique, the temporal waveform of the beam transmitted through an aperture is observed, instead of total energy per pulse as in a normal z-scan measurement. Using a doubled Nd:YAG laser, we observed a slow response in index change in the absorptive material methyl nitroaniline, whereas CS2 showed fast response compared with the laser pulse width of 65 ns.

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.

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.

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.

Stochastic mode-locking theory for external-cavity semiconductor lasers

A stochastic mode-locking model is developed to study the effect of intrinsic spontaneous emission noise and carrier shot noise on the process of active mode locking in external-cavity semiconductor lasers. The model includes the nonlinear carrier dynamics, the population pulsation, and the gain saturation and is sufficiently flexible to account for coupling of multiple harmonic field components. Through numerical simulation, the model can generate statistical fluctuations in the mode-locked output and provide a basis for investigating the fundamental constraints on the pulse-to-pulse stability of a mode-locked semiconductor laser device.

Computer modeling of the effects of apertures in the Fourier-transform plane of Fourier-transform imaging systems.

Two computer models are presented that can be used to determine the image formed by a 4-∱ Fourier imaging system with an aperture in the Fourier-transform plane of the system. These models were designed to aid in the selection of system parameters in a Fourier-transform hologram recording system (namely, object size, feature ratio, focal length, and storage area) required to obtain a retransformed image of a given quality. The results of the simulations are verified in the laboratory.

Adaptive optical interconnection

We explore the ability of a double phase-conjugate mirror to compensate for thermal, vibrational, and other environmental fluctuations. This property lends itself to the establishment and maintenance of bidirectional optical interconnections. We further introduce a bidirectional interconnection scheme that utilizes two wavelengths.

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.