O.P. Kowalski

A UNIVERSAL DAMAGE INDUCED TECHNIQUE FOR QUANTUM WELL INTERMIXING

We report a novel technique for quantum well intermixing which is simple, reliable and low cost, and appears universally applicable to a wide range of material systems. The technique involves the deposition of a thin layer of sputtered SiO2 and a subsequent high temperature anneal. The deposition process appears to generate point defects at the sample surface, leading to an enhanced intermixing rate and a commensurate reduction in the required anneal temperature. Using appropriate masking it is possible to completely suppress the intermixing process, enabling large differential band gap shifts (over 100 meV) to be obtained across a single wafer.

Monolithic integration via a universal damage enhanced quantum-well intermixing technique

A novel technique for quantum-well intermixing is demonstrated, which has proven a reliable means for obtaining postgrowth shifts in the band edge of a wide range of III-V material systems. The technique relies upon the generation of point defects via plasma induced damage during the deposition of sputtered SiO/sub 2/, and provides a simple and reliable process for the fabrication of both wavelength tuned lasers and monolithically integrated devices. Wavelength tuned broad area oxide stripe lasers are demonstrated in InGaAs-InAlGaAs, InGaAs-InGaAsP, and GaInP-AlGaInP quantum well systems, and it is shown that low absorption losses are obtained after intermixing. Oxide stripe lasers with integrated slab waveguides have also enabled the production of a narrow single lobed far field (3/spl deg/) pattern in both InGaAs-InAlGaAs, and GaInP-AlGaInP devices. Extended cavity ridge waveguide lasers operating at 1.5 /spl mu/m are demonstrated with low loss (/spl alpha/=4.1 cm/sup -1/) waveguides, and it is shown that this loss is limited only by free carrier absorption in waveguide cladding layers. In addition, the operation of intermixed multimode interference couplers is demonstrated, where four GaAs-AlGaAs laser amplifiers are monolithically integrated to produce high output powers of 180 mW in a single fundamental mode. The results illustrate that the technique can routinely be used to fabricate low-loss optical interconnects and offers a very promising route toward photonic integration.

Quantum well intermixing in material systems for 1.5 μm (invited)

Precise control over local optical and electrical characteristics across a semiconductor wafer is a fundamental requirement for the fabrication of photonic integrated circuits. Quantum well intermixing is one approach, where the band gap of a quantum well structure is modified by intermixing the well and barrier layers. Here we report recent progress in the development of intermixing techniques for long wavelength applications, discussing two basic techniques. The first is a class of laser disordering techniques which take place in the solid state. The second is a novel intermixing technique involving plasma induced damage. Both techniques enable large band gap shifts to be achieved in standard GaInAsP multiple quantum well laser structures. The potential of both techniques for photonic integration is further demonstrated by the fabrication and characterisation of extended cavity lasers.

Monolithically integrated fabrication of 2/spl times/2 and 4/spl times/4 crosspoint switches using quantum well intermixing

We report the fabrication of 2/spl times/2 and 4/spl times/4 crosspoint switches, in which semiconductor optical amplifiers, electro-absorption modulators, and passive waveguides were monolithically integrated on one chip, using sputtered SiO/sub 2/ for quantum well intermixing. The static performance of the 2/spl times/2 switches was assessed, with the extinction ratio of the modulator being 25 dB for a reverse bias of 2 V, and inter-channel crosstalk being better than -23 dB. The gain of the amplifiers is about 8 dB.

Fabrication of 2 x 2 crosspoint switches using a sputtered SiO 2 intermixing technique

We report the fabrication of a 2/spl times/2 crosspoint switch, which monolithically integrates passive waveguides and electroabsorption modulators on one chip, using the sputtered SiO/sub 2/ technique for quantum-well intermixing. The static performance of the modulators has been tested, and a modulation depth of 25 dB has been obtained at a wavelength of 1.55 /spl mu/m for an applied bias of 2 V.

Three band-gap QW intermixing in InP/InGaAs/InGaAsP system for monolithically integrated optical switch

We have demonstrated that independent control of three band-gaps across an InP-InGaAs-InGaAsP QW wafer can be achieved by a two-stage sputtered silica intermixing processes. This will be used for optimisation of the performance of optical switches which consist of passive components, modulators and amplifiers.

Benefits of quantum well intermixing in high power diode lasers

Quantum well intermixing (QWI) can bring considerable benefits to the reliability and performance of high power laser diodes by intermixing the facet regions of the device to increase the band-gap and hence eliminate absorption, avoiding catastrophic optical damage (COD). The non-absorbing mirror (NAM) regions of the laser cavity can be up to ~20% of the cavity length, giving an additional benefit on cleave tolerances, to fabricate very large element arrays of high power, individually addressable, single mode lasers. As a consequence, large arrays of single mode lasers can bring additional benefits for packaging in terms of hybrization and integration into an optics system. Our QWI techniques have been applied to a range of material systems, including GaAs/AlGaAs, (Al)GaAsP/AlGaAs and InGaAs/GaAs.

High-Performance Red Lasers With Low Beam Divergence

We report the design and fabrication of high-performance 650-nm lasers using a novel wafer structure that offers substantially independent control of the vertical far field and of the optical confinement factor. By incorporating a graded V-shaped layer into the epitaxial structure, a low divergence can be realized while retaining high optical overlap with the quantum wells and, therefore, a low threshold current. Broad-area lasers (BALs) were fabricated for a range of designs, and close agreement was obtained between the modeling and the experiment.

Theoretical and experimental study of improved catastrophic optical damage performance in 830nm high power lasers with non-absorbing mirrors

We carry out a systematic theoretical and experimental study on the improvement in catastrophic optical damage of 830 nm lasers with non-absorbing mirrors. We find a three-fold increase in COD optical power level compared to conventional lasers

Ultra-fine pitch individually addressable visible laser arrays for high speed digital printing applications

An individually addressable visible semiconductor laser diode array with a 20 μm pitch is demonstrated that is highly suited for deployment in next-generation digital print systems. The array, operating at 660 nm, comprises 22 single mode lasers fabricated on a single GaInP/AlGaInP/GaAs substrate. The laser array is flip-chip bonded onto a patterned ceramic submount that enables the individual elements to be driven independently and is integrated into a 26-pin butterfly package. Arrays tested CW exhibit low threshold current (<20 mA per emitter), up to 50 mW output power per channel with a high slope efficiency (0.9 W/A) and a high characteristic temperature of over 100 K.