M. D. Divino

Narrowband grating resonator filters in InGaAsP/InP waveguides

We report the first demonstration of efficient narrowband optical wavelength filters using InGaAsP/InP passive waveguide grating resonators. Filter bandwidths as narrow as 1 A, centered about λ=1.55 μm with excess resonator loss as low as 1 dB, have been achieved.

Balanced bridge modulator switch using Ti‐diffused LiNbO3 strip waveguides

An experimental integrated optical version of the Mach‐Zehnder interferometer switch, analogous to the microwave balanced bridge, is reported. The bridge is formed by 3‐μm‐wide Ti‐diffused strip waveguides in LiNbO3 and the switch utilizes electro‐optical tuning to achieve 3‐dB operation of the directional couplers. The switching voltage required to switch between the states, corresponding to a π phase shift in one arm, equals 14.8 V. The cross talk between channels that corresponds to the extinction ratio when operated as an on‐off modulator is −21.6 dB.

Quantum well waveguide intensity modulator at visible wavelengths using CdZnTe/ZnTe quantum wells

We demonstrate the first waveguide intensity modulator for visible wavelengths based on the quantum‐confined Stark effect. The active waveguide core is composed of 58 Cd0.42Zn0.58Te/ZnTe quantum wells surrounded by Cd0.12Zn0.88Te cladding layers. We obtain ≳10 dB modulation depth at 640 nm with 4 V bias in a 500‐μm‐long waveguide.

Large blueshifting of InGaAs/InP quantum‐well band gaps by ion implantation

We demonstrate that phosphorous ion implantation in InGaAs/InP quantum wells can be used to produce large (from 1550 to 1200 nm) blueshifts of the band edge. This reproducible technique of lateral band‐gap control can be used in quantum‐well photonic integrated circuits to produce regions of low‐loss waveguide, e.g., for interconnects or large passive cavities. Phosphorous implants with subsequent p‐type InP regrowth produces blueshifted quantum‐well diodes with good reverse‐bias characteristics and low‐loss p‐i(multiple quantum well)‐n waveguides.

Multi‐gigahertz‐bandwidth intensity modulators using tunable‐electron‐density multiple quantum well waveguides

We report the first measurement of modulation bandwidth in electron transfer quantum well modulators. A device with 1 pF capacitance provides ≳10 dB optical modulation depth at 1.537 μm wavelength with a 3 dB electrical bandwidth of 5.7 GHz. Optical pump‐probe measurements indicate that the fundamental response time is determined by the voltage‐dependent speed of carrier escape from the well.

InGaAsP/InP waveguide grating filters for λ=1.5 μm

We report the first demonstration of InGaAsP/InP passive waveguide reflection grating filters. Waveguide filters with ∼1.5‐μm center wavelength, peak reflectivity >99%, and spectral bandwidths (full width at half‐maximum) as narrow as 6 A and as broad as 130 A have been achieved.

Integrated-optic polarization controller with unlimited transformation range

We demonstrate a novel waveguide polarization controller that allows endless transformations from any varying general input polarization state into any varying general output state. The electro‐optic controller is implemented in lithium niobate and produces adjustable elliptical birefringence of constant total phase retardation via three independent drive voltages. We show that it allows fast and reset‐free automatic polarization control using an entirely analog feedback circuit that derives its error signal from the intensity in the prescribed output polarization.

InGaAs/InP multiple quantum well tunable Bragg reflector

We demonstrate a voltage‐tunable distributed Bragg reflector grown by chemical beam epitaxy that utilizes 31 periods of alternating InGaAs/InP multiple quantum well and bulk InP quarter‐wave layers. We obtain a differential change in transmission of 14% at 1570 nm wavelength for an applied field of 2.25×104 V/cm. We find good agreement between the experimental results and transmission spectra calculated using the optical transmission matrix method.

Mirror-folded polarization-independent wavelength filter

A 1.55- mu m polarization-independent optical bandpass filter with a 3-dB bandwidth of 6 AA and a tuning range of at least 100 AA is demonstrated. The photonic circuit of the filter consists of a waveguide TE-TM mode splitter, two parallel electrooptic TE-to-TM, TM-to-TE mode converters as the wavelength selective element, and a reflective mirror at the far end of the crystal. The circuit can be viewed as a mirror-folded version of the polarization-independent filter. It is shown that by passing the light two times through the narrowband mode converters, the filter bandwidth can be reduced by about a factor of two compared to a conventional single-pass filter of the same length. A novel tunable mode converter structure is also demonstrated that allows coherent in-phase mode conversion during the two passes through the mirror-folded filter.<<ETX>>

High-contrast electron-transfer GaAs-AlGaAs multiple-quantum-well waveguide modulator

The development of a GaAs-AlGaAs multiple quantum well electron transfer waveguide modulator is reported. On-off ratios as high as 75:1 are obtained at 864.5 nm of an applied voltage of -5 to 10 V. It is shown that the wavelength and voltage characteristics of the device can be successfully interpreted in terms of the calculated energy band diagram.<<ETX>>