Quantum-dot lasers provide high performance near 1.15 microns

Abstract

Monomode laser diodes in the wavelength range around 1.15μm are of particular interest for applications such as sensing (of moisture, for example) and for frequency doubling into parts of the spectrum that are currently largely inaccessible. Coherent green and yellow light from frequency-doubled lasers would be very useful for gas sensing and other industrial instrumentation, as well as biomedical and fluorescence applications. An essential prerequisite for efficient frequency conversion, however, is single-frequency laser light, such as could be provided by distributed feedback (DFB) laser diodes. One particular challenge at the range around 1.15μm is to produce a gain medium with high internal efficiency. For broad area lasers, good results have recently been achieved using quantum dots (QDs) or high strained InGaAs quantumwells (QWs).1 In general, devices that use QDs can provide a variety of advantages compared to conventional QW-based devices.2 DFB devices are ideally suited to provide longitudinal and transverse single-mode emission at a precise wavelengthwith an extremely narrow linewidth. They guarantee high output power andmode-hop-free tunability. Our DFB concept shown in Figure 1 is based on an overgrowth-free technology, which can easily be adapted to a variety of independent epitaxial designs. Based on this approach, we are manufacturing DFB laser diodes from 760nm up to 2800nm.3, 4 Device fabrication makes use of a GaAs-based laser structure grown by molecular beam epitaxy with an undoped active region consisting of self-organized InGaAs/GaAs QD layers. The spectral gain properties of this underlying QD active region allow us to make DFB lasers with emission spanning a broad wavelength range. We fabricated a ridge waveguide structure using photolithography and an electron-cyclotron-resonance asFigure 1. Schematic of a laterally-coupled distributed-feedback (DFB) laser with a metal grating structure and an active region incorporating quantum dots (QDs).