N. Bar-Chaim

Direct amplitude modulation of short‐cavity GaAs lasers up to X‐band frequencies

Experimental and theoretical studies indicate that a high‐frequency laser with bandwidths up to X‐band frequencies (≳10 GHz) should be one having a short cavity with a window structure, and preferably operating at low temperatures. These designs would accomplish the task of shortening the photon lifetime, increasing the intrinsic optical gain, and increasing the internal photon density without inflicting mirror damage. A modulation bandwidth of >8 GHz has been achieved using a 120‐μm laser without any special window structure at room temperature.

Ultralow‐threshold graded‐index separate‐confinement single quantum well buried heterostructure (Al,Ga)As lasers with high reflectivity coatings

Unlike conventional semiconductor lasers, single quantum well lasers with high reflectively coatings have dramatically reduced threshold currents as a result of the smaller volume of the (active) quantum well region. A cw threshold current of 0.95 mA was obtained for a buried graded‐index separate‐confinement heterostructure single quantum well laser with facet reflectivities of ∼70%, a cavity length of 250 μm, and an active region stripe width of 1 μm.

Enhancement of modulation bandwidth in InGaAs strained‐layer single quantum well lasers

It is shown that the unique properties of strained‐layer quantum well lasers can be identified by measuring the relaxation oscillation frequency as a function of optical gain. These measurements are insensitive to effects due to nonradiative recombinations and leakage currents, which can mask the beneficial effects in terms of a lower threshold current due to a reduced hole mass in strained quantum wells. The conclusion, both theoretically and experimentally, is that strained‐layer quantum well lasers have a higher differential gain but saturate at a lower gain level as compared to regular quantum well lasers. As a consequence, for a strained single quantum well, slightly higher relaxation oscillation frequency results, but only for certain limited ranges of device parameters. A multiple strained‐layer quantum well can in theory take better advantage of the higher differential gain.

AlGaAs lasers with micro-cleaved mirrors suitable for monolithic integration

A technique has been developed for cleaving the mirrors of AlGaAs lasers without cleaving the substrate. Micro‐cleaving involves cleaving a suspended heterostructure cantilever by ultrasonic vibrations. Lasers with microcleaved mirrors have threshold currents and quantum efficiencies identical to those of similar devices with conventionally cleaved mirrors.

A monolithic integration of GaAs/GaAlAs bipolar transistor and heterostructure laser

A GaAlAs double-heterostructure laser has been monolithically integrated with a heterojunction bipolar transistor on a GaAs substrate. Integration is achieved by means of a mutually compatible structure formed by Be ion implantation. Typical pulsed threshold currents for the laser are 60 mA, and the transistors have a typical common-emitter current gain of 900.

High-speed digital modulation of ultralow threshold (<1 mA) GaAs single quantum well lasers without bias

GaAlAs buried heterostructure lasers with submilliampere threshold current fabricated from single quantum well wafers can be driven directly with logic level signals without any current bias. The switch‐on delay was measured to be <50 ps and no relaxation oscillation ringing was observed. These lasers permit fully on‐off multigigabit digital switching while at the same time obviating the need for bias monitoring and feedback control.

A monolithically integrated optical repeater

A monolithically integrated optical repeater has been fabricated on a single‐crystal semi‐insulating GaAs substrate. The repeater consists of an optical detector, an electronic amplifier, and a double heterostructure crowding effect laser. The repeater makes use of three metal semiconductor field effect transistors, one of which is used as the optical detector. With light from an external GaAlAs laser incident on the detector, an overall optical power gain of 10 dB from both laser facets was obtained.

11‐GHz direct modulation bandwidth GaAlAs window laser on semi‐insulating substrate operating at room temperature

We have demonstrated a direct modulation bandwidth of up to 11 GHz in a window GaAlAs buried heterostructure laser fabricated on a semi-insulating substrate, operating at room temperature.

High-power microwave photodiode for improving performance of rf fiber optic links

The rf performance of fiber optic links is often limited by the maximum optical power rating of the photodiode receiver, particularly in short distance, point to point applications where the received power can be rather high. Required attenuation of the optical power can significantly compromise performance parameters such as the gain, noise, and dynamic range of the link, as well as adding extra cost and complexity in installing and maintaining the link. This paper presents results from the development of a high speed InGaAs photodiode (16 GHz) which can operate at a dc photocurrent as high as 15 mA, or 20 mW of received optical power.

Monolithic optoelectronic integration of a GaAlAs laser, a field‐effect transistor, and a photodiode

A low threshold buried heterostructure laser, a metal-semiconductor field-effect transistor, and a p-i-n photodiode have been integrated on a semi-insulating GaAs substrate. The circuit was operated as a rudimentary optical repeater. The gain bandwidth product of the repeater was measured to be 178 MHz.