Monolithic mode-locked lasers with deeply dry etched Bragg mirror

Research output: Contribution to conferencePosterResearch


Background: Semiconductor mode-locked lasers are attractive as components in futureultra high-speed telecommunication systems (160-640Gb/s); as picosecond pulse sources,clock-recovery devices and for demultiplexing in Optical Time Division Multiplexing(OTDM) systems. We have recently designed, fabricated and characterized monolithicmode-locked lasers with record-low timing instabilities (jitter) and high optical power1.However, these lasers were of the Fabry-Pérot type and the optical spectrum is influencedby the biasing of the gain and absorber sections and also by the carrier dynamics in thegain section, such as self-phase modulation. The solution to this problem is to integratethe laser with a wavelength selective Bragg grating. Another advantage of the gratingshould be lower noise. Deep Reactive Ion Etching (RIE) of the grating is a key for lowcostmass production of these lasers, making it possible to buy epitaxial wafers fromphotonic foundries as in the microelectronic industry.Design: The reflectivity spectrum from the total grating is calculated by matrixmultiplication of the individual periodic grating elements. The period of the grating,given by the mean effective index of the low and high index regions (etched andunetched), is 240 nm for a 1st order grating and 480 nm for the 2nd order.Fabrication: The mask for the grating is formed by a combination of E-beam writing andUV-lithography. The resist pattern is transferred to a 100 nm SiO2-film, with a CHF3(Freon) based dry etch. The SiO2-film functions as a mask in the subsequent RIE of thesemiconductor (InP). We are now optimizing the semiconductor RIE to achieve 2 µmdeep waveguides and gratings with smooth vertical sidewalls and smooth bottom surface.This optimization involves optimizing the reaction chamber parameters: CH4/H2 gasmixture, gas flow, chamber pressure and the power supplied to the plasma2.Figure 1: SEM micrograph of a deeply etched 2nd order grating and waveguidein InP. 1K. yvind et al, Phot. Technology Letters 16, 975-977 (2004)2Y. Feurprier et al., J. Vac. Sci. A 16(3), 1552-1559 (1998)
Original languageEnglish
Publication date2005
Publication statusPublished - 2005
EventNanoDay DTU - Kgs. Lyngby, Denmark
Duration: 6 Dec 2005 → …


ConferenceNanoDay DTU
CityKgs. Lyngby
Period06/12/2005 → …


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