James O'Callaghan

Discretely Tunable Semiconductor Lasers Suitable for Photonic Integration

A sequence of partially reflective slots etched into an active ridge waveguide of a 1.5 mum laser structure is found to provide sufficient reflection for lasing. Mirrors based on these reflectors have strong spectral dependence. Two such active mirrors together with an active central section are combined in a Vernier configuration to demonstrate a tunable laser exhibiting 11 discrete modes over a 30 nm tuning range with mode spacing around 400 GHz and side-mode suppression ratio larger than 30 dB. The individual modes can be continuously tuned by up to 1.1 nm by carrier injection and by over 2 nm using thermal effects. These mirrors are suitable as a platform for integration of other optical functions with the laser. This is demonstrated by monolithically integrating a semiconductor optical amplifier with the laser resulting in a maximum channel power of 14.2 dBm from the discrete modes.

Integrable Slotted Single-Mode Lasers

A single-mode laser structure based on slots suitable for monolithic photonic integration is presented. The laser can be fabricated by photolithography without any regrowth steps. Stable single-mode performance with a sidemode suppression ratio up to 50 dB at twice threshold has been demonstrated for the fabricated lasers.

Integration of AlInGaAs-MQW Fabry–Pérot Lasers With Emission at Two Wavelength Ranges via Quantum-Well Intermixing

We demonstrate ridge waveguide lasers based on AlInGaAs multiple quantum wells emitting at 1434 and 1541 nm on the same laser bar using quantum-well intermixing with dielectric capping layers. The internal quantum efficiencies are measured to be 61% and 72% and the internal losses are 49 and 23 cm-1 for lasers with intermixing promoted and inhibited, respectively. The characteristic temperatures are found to be approximately 50 K for lasers emitting around 1433 nm and 75 K for those emitting around 1541 nm.

Focusing properties of high brightness gain tailored broad-area semiconductor lasers

In this letter, we present a simple broad-area semiconductor laser using a current spreading layer to modify the transverse gain profile. The device exhibits excellent spatial coherence to total output powers of 2.5 W under pulsed operation. Devices have been focused down to a spot size of approximately 5 /spl mu/m full-width at half-maximum at 2.5 W, with the beam profile and position remaining stable over the entire range of operation. Under continuous-wave operation, thermal effects reduce spatial coherence, leading to a significantly increased spot size and loss of beam stability. This work demonstrates the advantages of modifying the transverse gain profile, and how it can be used to produce high brightness devices required for single-mode fiber coupling.

Transfer Printing of AlGaInAs/InP Etched Facet Lasers to Si Substrates

InP-etched facet ridge lasers emitting in the optical C-band are heterogeneously integrated on Si substrates by microtransfer printing for the first time. 500 μm × 60 μm laser coupons are fabricated with a highly dense pitch on the native InP substrate. The laser epitaxial structure contains a 1-μm-thick InGaAs sacrificial layer. A resist anchoring system is used to restrain the devices while they are released by selectively etching the InGaAs layer with FeCl3:H2O (1:2) at 8 °C. Efficient thermal sinking is achieved by evaporating Ti-Au on the Si target substrate and annealing the printed devices at 300 °C. This integration strategy is particularly relevant for lasers being butt coupled to polymer or silicon-on-insulator (SOI) waveguides.

Spatial coherence and thermal lensing in broad-area semiconductor lasers

Injection profiled broad-area edge-emitting semiconductor lasers demonstrate single transverse mode operation and near-diffraction-limited beam output when driven by pulsed pump current. Thermal effects arising from CW operation induce filamentary dynamics, thus degrading the beam. Transition from the stable nonthermal to the unstable CW regime is analyzed experimentally and numerically, and techniques to improve beam quality in the thermal regime, based on feedback or thermal profiling, are proposed.

Monolithic Integration of Single Facet Slotted Laser, SOA, and MMI Coupler

We demonstrate a monolithically photonic integrated circuit (PIC) comprising a single facet slotted laser (SFSL), a semiconductor optical amplifier (SOA), and a 1 × 2 multimode interference (MMI) coupler. The integrated SFSL generates a tunable single longitudinal mode output, and utilizes a simplified fabrication process for the PIC when compared with distributed feedback or distributed Bragg reflector lasers by eliminating the epitaxial regrowth as well as the ebeam or holographically generated gratings. The integration technique is implemented by biasing the MMIs to transparency, which makes the fabrication comparable the standard ridge waveguide laser. The demonstrated PIC can be used as a 1 × 2 splitter or by integrating with other waveguide devices, such as laser, modulators, or SOAs, to realize different functionality.

Multiple coherent outputs from single growth monolithically integrated injection locked tunable lasers

We present a photonic integrated circuit (PIC) designed to create multiple coherent optical signals for the generation of coherent modulation formats, such as DPSK. A Multimode Interference Coupler (MMI) is monolithically integrated with single facet Slotted Fabry Perot (SFP) lasers at its input and output arms. In this work we show that light from a master SFP laser can be used to injection lock both output slave SFPs for use in the generation of coherent optical channels.

Compact Electroabsorption Modulators for Photonic Integrated Circuits, Using an Isolated Pedestal Contact Scheme

We demonstrate a shallow ridge waveguide, lumped element electroabsorption modulator (EAM) based on AlInGaAs multiple quantum wells, operating with input powers up to 8 dBm. The device was isolated between two DC controlled sections, using angled etched slots in the waveguide, minimizing optical feedback, while also providing 40-KΩ resistance between devices. The EAM uses a planar isolated pedestal contact with a benzocyclobutene bridge, allowing for a small contact footprint of just 0.024 mm2, while being suitable for flip-chip packaging. The parasitic capacitance was measured to be 19.6 fF, and the EAM has a f3dB bandwidth of 42 GHz.

Quantum well intermixing in AlInGaAs MQW structures through impurity-free vacancy method

We report on quantum well intermixing of AlInGaAs-MQWs using the impurity-free vacancy diffusion method with dielectric capping layers which has potential for realization of photonic integrated circuits. The extent of the bandgap shifts with respect to different dielectric capping layers and alloy temperatures are investigated. The intermixing inhibitor and promoter are then integrated using combination of SiO2 and SiNx dielectric capping layers which shows a differential photoluminescence wavelength more than 110 nm. Based on this developed intermixing technique, we have fabricated AlInGaAs-InP based material stripe lasers emitting at two different wavelength ranges centered at 1519 nm and 1393 nm respectively. Characterizations including the current-voltage and electroluminescence measurements show that the integration of two-bandgaps can be achieved and furthermore a differential wavelength in lasing spectra up to 120 nm is demonstrated.