R.J. Bailey

40-Gbit/s all-optical circulating shift register with an inverter.

We report what is believed to be the first demonstration of an all-optical circulating shift register using an ultrafast nonlinear interferometer with a polarization-insensitive semiconductor optical amplifier as the nonlinear switching element. The device operates at 40 Gbits/s, to our knowledge the highest speed demonstrated to date. Also, the demonstration proves the cascadability of the ultrafast nonlinear interferometric switch.

AlGaAs-InGaAs slab-coupled optical waveguide lasers

The slab-coupled optical waveguide laser (SCOWL) concept, recently proposed and demonstrated, is extended to the AlGaAs-InGaAs-GaAs material system. Both 980- and 915-nm SCOWL devices feature a nearly circular large-diameter single-spatial mode that can be butt coupled with high efficiency to a single-mode fiber. Single-ended continuous-wave output powers of greater than 1 W have been obtained at 980 nm.

Slab-coupled 1.3-μm semiconductor laser with single-spatial large-diameter mode

A high brightness semiconductor diode laser structure, which utilizes a slab-coupled optical waveguide region to achieve several potentially important advances in performance, is proposed and experimentally demonstrated using a simple rib waveguide in an InGaAsP-InP quantum-well structure operating at 1.3-/spl mu/m wavelength. These lasers operate in a large low-aspect-ratio lowest-order spatial mode, which can be butt coupled to a single-mode fiber with high coupling efficiency.

1.5-μm tapered-gain-region lasers with high-CW output powers

High-power diode lasers consisting of a a tapered region have waveguide section coupled to fabricated in 1.5-/spl mu/m InGaAsP-InP multiple-quantum-well material. Self-focusing at high current densities and high intensity input into the taper section has been identified as a fundamental problem in these devices that has to be dealt with. To date, continuous-wave output powers of >1 W with /spl ap/80% of the power in the near-diffraction-limited central lobe of the far field have been obtained through a judicious choice of device parameters.

Monolithic two‐dimensional surface‐emitting arrays of GaAs/AlGaAs diode lasers

Monolithic two‐dimensional arrays with light emission normal to the surface have been obtained by fabricating edge‐emitting quantum well GaAs/AlGaAs lasers with deflecting mirrors adjacent to both laser facets. The facets and mirrors were formed by ion beam assisted etching. Proton bombardment between adjoining lasers was used to prevent lasing in the transverse direction. At the highest pulsed current used in these experiments, 10.5 A, the power output of a 22‐element array was 1.6 W, which corresponds to a power density of 160 W cm−2. At this level, the power output was still linear with current.

Diffraction-limited 1.3-μm-wavelength tapered-gain-region lasers with >1-W CW output power

Diode lasers have been fabricated in InGaAsP-InP multiple-quantum-well material grown by atmospheric-pressure organometallic vapor-phase epitaxy with an active optical cavity consisting of a ridge-waveguide region coupled to a tapered gain region. Over 1 W of CW output power was obtained with 85% of the power in the central lobe of a diffraction-limited far-field radiation pattern.

Monolithic two‐dimensional surface‐emitting strained‐layer InGaAs/AlGaAs and AlInGaAs/AlGaAs diode laser arrays with over 50% differential quantum efficiencies

Monolithic two‐dimensional surface‐emitting arrays of strained‐layer InGaAs/AlGaAs and AlInGaAs/AlGaAs diode lasers have been fabricated and operated pulsed with low‐threshold current densities and differential quantum efficiencies greater than 50%. The InGaAs/AlGaAs arrays emit at 1.03 μm, while the AlInGaAs/AlGaAs arrays emit at 0.815 μm. Thus, it should be possible to fabricate monolithic arrays with comparable performance over a wide wavelength range. The individual lasers of the arrays are horizontal folded‐cavity devices with two 45° internal reflectors and two top‐surface facets. The design is simple to implement using optical pattern‐generator masks, optical projection printing, and chlorine ion‐beam‐assisted etching in key fabrication steps.

Monolithic two-dimensional GaAs/AlGaAs laser arrays fabricated by chlorine ion-beam-assisted micromachining

Chlorine ion-beam-assisted etching (IBAE) has been used to micromachine laser facets and deflecting mirrors for monolithic two-dimensional GaAs/AIGaAs laser arrays. Three laser cavity/deflector designs have been successfully implemented. The first utilizes a parabolic deflecting mirror to directly focus the laser radiation; the second consists of a folded cavity with a vertical facet, a top surface facet, and an internal 45° reflector; and the third has a folded cavity with an internal Al0.2Ga0.8As/Al0.8Ga0.2As dielectric mirror stack and a top surface facet formed in a single etch step with two internal 45° reflectors. The parabolic deflecting mirrors are currently modeled forf- 0.8 collection efficiency, making the first design attractive in incoherent arrays for high-power applications such as pumping Nd:YAG lasers. The other two structures are of interest for incoherent or coherent arrays used in high- and medium-power applications, since the top surface facets can easily be antireflection coated. The design with a dielectric mirror stack is particularly simple to fabricate.

Hybrid approach to two‐dimensional surface‐emitting diode laser arrays

A new hybrid structure for two‐dimensional surface‐emitting diode laser arrays has been demonstrated. Each hybrid array consists of linear arrays of GaAs/AlGaAs lasers, with conventional cleaved end facets, that are mounted in grooves etched in a Si substrate. The etched grooves have flat bottoms and 45° sidewalls that are coated with a highly reflecting Cr/Au layer. A hybrid array with three 4‐mm‐wide GaAs/AlGaAs linear laser arrays has been fabricated and tested. Approximately 10 W of peak power perpendicular to the array surface was obtained from each of the linear arrays for 11–12 A of pulsed current per array. The measured differential quantum efficiencies were 65–70%, indicating that the 45° metallized sidewalls deflect by 90° essentially all of the light emitted from the laser facets. The new approach allows for the use of integral Si heat sinks and should prove useful for fabricating large, high‐power, two‐dimensional laser arrays in any material system.

High-power 1.3-μm InGaAsP-InP amplifiers with tapered gain regions

Tapered structures fabricated in InGaAsP-InP 1.3-/spl mu/m quantum-well material have been evaluated as high-gain high-saturation-power amplifiers. The devices, which had a 1-mm-long ridge-waveguide input gain section followed by a 2-mm-long tapered section, demonstrated an unsaturated gain of 26 dB at 2.0 A and about 30 dB at 2.8 A. Saturated output power at 2.8 A was >750 mW. At 2.0-A drive current and /spl ap/10-mW input power, the relative intensity noise of the amplified signal was /spl les/-160 dB/Hz at frequencies /spl ges/2 GHz.