F. J. Leonberger

High‐speed InP optoelectronic switch

The successful fabrication and demonstration of an InP optoelectronic switch is reported. The results obtained suggest that this device may be better suited for high‐speed analog signal processing applications than previously reported Si and GaAs switches. In experiments using cw mode‐locked lasers, the switches have exhibited an on‐state impedance of 45 Ω for 40pJ of incident laser energy and an inherent rise time of 30 psec. In addition, the switches have been used to generate a train of 70‐psec‐wide pulses at a 900‐MHz repetition rate, and to sample a 68.9‐MHz sine wave at 275 MS/sec with an accuracy to 0.2 dB (98%) and an on‐off ratio of 40 dB.

Photodeposition of Ti and application to direct writing of Ti:LiNbO3 waveguides

An ultraviolet laser photodeposition process based on the photolysis of TiCl4 has been developed. The photochemistry of this new metal‐halide system has been shown to involve a surface‐catalyzed reaction confined to adsorbed molecular layers. By using this process, Ti films have been deposited on LiNbO3 to form, after diffusion, 4‐μm‐wide single‐mode channel waveguides of comparable quality to conventionally fabricated Ti‐indiffused guides. The technique introduces new design flexibility into waveguide fabrication, permitting controlled gradations in the diffused index change and the lateral width along the guide.

Picosecond InP optoelectronic switches

Proton bombardment is used to increase the response speed of InP optoelectronic switches. Photoconductivity measurements indicate response times following bombardment of <100 ps, with the electron mobility estimated to be ⩾600 cm2/Vs. This mobility is over an order of magnitude larger than that observed in similar high‐resistivity devices of comparable speed fabricated in germanium or silicon‐on‐sapphire.

Integrated optical temperature sensor

An integrated optical temperature sensor requiring no electrical connection and consisting of a parallel array of unequal arm‐length waveguide interferometers in LiNbO3 has been designed and the key components have been demonstrated. The optical transmission of each interferometer varies sinusoidally with temperature with a period inversely proportional to the path length difference between the two arms. This device has a projected range and resolution of ≳700 °C and 2×10−3 °C, respectively, and would be particularly useful in applications requiring immunity to electrical noise.

GaAs p+n−n+ directional‐coupler switch

GaAs p+n−n+ electro‐optic directional‐coupler switches have been successfully fabricated and evaluated at 1.06 μm for use as components in integrated optical circuits. The devices were fabricated from a pair of closely spaced low‐loss [α≈1 cm−1 (4.3 dB/cm) at 1.06 μm] single‐mode p+n−n+ channel‐stop strip guides. They are operable both as passive directional couplers and as electro‐optic switches. The couplers have exhibited 98% power transfer and have an attenuation only about 0.1 dB/cm greater than that of a single guide having the same dimensions as one of the coupled guides. The switch performance was found to depend on the crystallographic direction chosen for light propagation. All devices were in the {100} plane, and 17‐dB (98%) power isolation in both the switched and unswitched states with constant total power output (≲0.2‐dB variation) was achieved for propagation along a [011] direction. These switches were 7.2 mm long, and had an optimum switching voltage of 43 V and a calculated power‐bandwid...

Low‐loss GaAs p+n−n+ three‐dimensional optical waveguides

Two types of low‐loss single‐mode p+n−n+ GaAs three‐dimensional waveguides have been successfully fabricated and their attenuation coefficients measured. The devices are an optical stripline and a new device, the channel‐stop strip guide. The channel‐stop strip guides have losses of 0.8 cm−1 at 1.06 μm and 1.1 cm−1 at 0.920 μm; the losses for the optical striplines are 1.2 cm−1 at 1.06 μm and 1.7 cm−1 at 0.920 μm. A first‐order loss calculation has yielded attenuation coefficients within 25% of these measured values. Both structures have an n+ substrate, an n− epitaxial layer for guiding, and p+ regions to laterally confine the light. The p+ regions have a uniform concentration and are formed by multiple‐energy Be+‐ion implantation; the p+n− junctions show sharp high‐voltage breakdowns at average electric fields in the n− layer of 1.5×105 V/cm.

GaAs directional‐coupler switch with stepped Δβ reversal

A GaAs electro‐optic waveguide switch in which the power isolation in both switch states can be electrically optimized has been demonstrated. The devices exhibit up to 25‐dB power isolation in both states, with total power output constant to within ⩽0.3 dB. The device is formed on one chip and consists of two equal‐length directional‐coupler switches in series separated by a 25‐μm gap. This structure permits the sign of Δβ, the electro‐optically induced propagation constant difference between the guides, to be reversed midway along the device length. The loss associated with propagation across the waveguide gap is small (⩽0.2 dB), suggesting that similar gaps could be used to electrically isolate waveguide devices on a common substrate in future GaAs‐based integrated optical circuits.

Uniform‐carrier‐concentration p‐type layers in GaAs produced by beryllium ion implantation

Multiple‐energy Be+ ion implantation has been used to create uniform‐carrier‐concentration p‐type layers (≳1.5 μm thick) in GaAs. The implanted samples were annealed at 900 °C using pyrolytic Si3N4 as an encapsulant. High activation of the implanted Be was observed. On samples with implanted hole concentrations of 2×1018/cm3, the measured carrier concentration as a function of depth is in good agreement with that expected from LSS range theory. For higher doses, diffusion of the implanted Be was observed. p+n−n+ junctions formed by implantation into undoped epitaxial material have low leakage currents and sharp breakdowns at average electric fields in the n− region of 1.5×105 V/cm.

High‐speed ultraviolet and x‐ray‐sensitive InP photoconductive detectors

The performance of iron‐doped InP photoconductive detectors in the optical and x‐ray spectral regions is compared. The detectors show uniform, high cw quantum efficiency from 900 to 200 nm. Pulse response times at 193 nm are laser source limited to ⩽12 ns. The response to ∼9‐keV‐fast x‐ray pulses indicates device rise times <90 ps.

Broadband guided‐wave optical frequency translator using an electro‐optical Bragg array

We describe a new type of optical frequency translator which utilizes Bragg diffraction from a traveling index wave produced by an interdigitated electrode grating on a LiNbO3 surface waveguide. The grating is driven by a three‐phase electrical signal that results in a unidirectional wave with a fixed Bragg angle determined by the electrode spacing. The diffraction thus produces a single‐sideband suppressed carrier optical output. Measurements at 10 and 100 MHz have yielded greater than 90% carrier‐to‐sideband conversion efficiency with over 100:1 suppression of the carrier and unwanted sideband. The device should be operable from arbitrarily low frequencies up to several gigahertz.