Gordon B. Morrison

Monolithically integrated active components: a quantum-well intermixing approach

As the demand for bandwidth increases, the communications industry is faced with a paradigm shift. Photonic integration is a key technology that will facilitate this shift. Monolithic integration allows for the realization of highly functional optical components, called photonic integrated circuits. Herein, we discuss the advantages and potential applications of photonic integration, and after a brief overview of various integration techniques, provide a detailed look at our work using a novel quantum well intermixing processing platform.

Design and demonstration of novel QW intermixing scheme for the integration of UTC-type photodiodes with QW-based components

We present the design and demonstration of unitraveling carrier (UTC) photodiodes fabricated using a novel quantum-well (QW) intermixing and metal-organic chemical vapor deposition (MOCVD) regrowth fabrication platform. The photodiodes discussed here were realized on the same chip as high gain centered QW active regions, intermixed passive centered well waveguides, and low optical confinement offset QW active regions regrown over intermixed wells. This demonstration lifts previous constraints imposed on high functionality photonic circuits, which forced a common waveguide architecture in the detector, laser, and amplifier by validating a platform suited for the monolithic integration of UTC photodiodes into photonic integrated circuits comprised of widely tunable high gain laser diodes, high efficiency modulators, and low optical confinement high saturation power semiconductor optical amplifiers. In this manuscript we focus on the design and performance of UTC photodiodes fabricated on intermixed QWs using this novel scheme. The photodiodes exhibit /spl sim/90% internal quantum efficiency, excellent photocurrent handling capabilities, and minimal response roll-off over the 20 GHz of our testing capability. The 40 Gb/s operation was achieved with the demonstration of open eye diagrams.

Photocurrent spectroscopy for quantum-well intermixed photonic integrated circuit design

Photocurrent spectroscopy is used to characterize band edges in quantum-well intermixed InGaAsP material lattice matched to InP. The band edge absorption data is used as a design tool to predict the dc performance of electroabsorption modulators, and is shown to agree well with data obtained from actual devices. In addition, we demonstrate the presence of an exciton peak in InGaAsP quantum wells, and present its evolution as a function of quantum-well intermixing and reverse bias voltage.

Bonding-Induced Strain Effects in InP DFB Components Soldered p-Side-Up on AlN Substrates

Bonding-induced strain is shown to have significant impact on the performance of distributed feedback (DFB) lasers mounted p-side up on AlN carriers using AuSn solder. Degree of polarization (DOP) of photoluminescence was used to estimate top-side longitudinal strain profiles in InP chips soldered to AlN carriers. Asymmetric strain profiles were revealed, the orientation of which are shown to be dependent on bonding tool coplanarity. Solder profiles measured on the same chips by scanning electron microscopy (SEM) were found to be nonuniform. Finite-element method (FEM) simulations were used to confirm that the asymmetric strain profiles resulted from solder nonuniformity caused by the bonding process. The FEM simulations were extended to analyze the effects of various bonding parameters on the top-side longitudinal strain profiles in InP chips, and suggestions are made for minimizing strain variations. The measured strains were included in a DFB laser model, and are shown to cause changes in slope efficiency and threshold current. These changes in slope efficiency and threshold current with bonding compare well with data collected from a large ensemble of DFB laser devices measured before and after the mounting process.

Photocurrent spectroscopy analysis of widely tunable negative-chirp quantum-well intermixed laser-modulator transmitters

High-speed laser-modulator transmitters fabricated using InGaAsP quantum-well intermixing exhibit negative chirp over a wavelength range of more than 30nm. Photocurrent spectroscopy is used to examine the multiple band edges in these devices. An exciton peak is found in the photocurrent data, and the evolution of the band edge as a function of quantum-well intermixing and applied bias voltage is revealed. The photocurrent data are then exploited to verify and explain the negative chirp characteristics of the wavelength-agile transmitters.

Component development for RF photonic systems

Freedom Photonics has demonstrated a semiconductor modulator with 1.2V static Vπ and >20 GHz bandwidth, and photodetectors that operate linearly up to 100mA photocurrent and with a bandwidth exceeding 20 GHz. These components will form the basis for high performance RF photonic links with low noise figure, high SFDR and realistic operating optical power in the 100s mW range.

Optical synthesis using Kerr frequency combs

An InP-based photonic integrated circuit was demonstrated for offset locking an on-chip broadly tunable laser to a heterogeneously integrated optical frequency comb oscillator based on a crystalline whispering gallery mode resonator. Optical tuning within 60nm band is demonstrated. The locked laser has excellent spectral purity, sub-kHz linewidth, and good frequency stability.

New semiconductor laser technology for gas sensing applications in the 1650nm range

Atmospheric methane (CH4) is the second most important anthropogenic greenhouse gas with approximately 25 times the radiative forcing of carbon dioxide (CO2) per molecule. CH4 also contributes to pollution in the lower atmosphere through chemical reactions leading to ozone production. Recent developments of LIDAR measurement technology for CH4 have been previously reported by Goddard Space Flight Center (GSFC). In this paper, we report on a novel, high-performance tunable semiconductor laser technology developed by Freedom Photonics for the 1650nm wavelength range operation, and for LIDAR detection of CH4. Devices described are monolithic, with simple control, and compatible with low-cost fabrication techniques. We present 3 different types of tunable lasers implemented for this application.

Monolithic Tunable Interferometric Transmitter (TunIT) in Indium Phosphide

Tunable chip-scale optical transmitter devices have revolutionized the pluggable module telecom market, by enabling excellent performance with great cost and size reduction. In this paper, we report on a novel patented tunable transmitter device, based on a dual-output tunable laser, and a pair of modulators, which are interferometrically combined (Tunable Interferometric Transmitter, TunIT). The dual-output laser is based on a Y-branch device architecture, and it utilizes high-reflectivity coating on the back facet. This device exhibits 50-nm tuning range and >40-dB side mode suppression ratio, as well as allows for chirp control. Transmission experiments at 10 Gbps through 75 km of SMF-28 fiber validate its performance. A tunable optical subassembly module with the TunIT device has also been demonstrated.

Microtune - a simple monolithic widely tunable laser: Design, Fabrication, and Characterization

The design and simulation of a novel compact tunable laser is presented. Preliminary results match theoretical predictions. A tuning range greater than 30 nm with >30dB SMSR has been demonstrated.