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Mode-Locked Laser Diode Laser With Integrated External Cavity

IP.com Disclosure Number: IPCOM000034941D
Original Publication Date: 1989-May-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Jaeckel, H: AUTHOR [+4]

Abstract

Semiconductor mode-locked lasers are of interest as sources of picosecond optical pulses. Gain and absorption sections inside the laser must be modulated at a rate corresponding to the time it takes for a pulse to make a round trip inside the entire laser cavity. The modulation rate can be reduced by increasing the actual length of the laser cavity but this leads to high laser threshold currents. Described herein is a low threshold current mode-locked semiconductor laser having a separate gain section (GS) and an absorption section (AS), these being connected by long low-loss waveguide sections (LLWSs). The ordinarily very large absorption in the unpumped laser regions at the lasing wavelength is reduced by using channeled substrate effects.

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Mode-Locked Laser Diode Laser With Integrated External Cavity

Semiconductor mode-locked lasers are of interest as sources of picosecond optical pulses. Gain and absorption sections inside the laser must be modulated at a rate corresponding to the time it takes for a pulse to make a round trip inside the entire laser cavity. The modulation rate can be reduced by increasing the actual length of the laser cavity but this leads to high laser threshold currents. Described herein is a low threshold current mode-locked semiconductor laser having a separate gain section (GS) and an absorption section (AS), these being connected by long low-loss waveguide sections (LLWSs). The ordinarily very large absorption in the unpumped laser regions at the lasing wavelength is reduced by using channeled substrate effects. The absorption is reduced by 1-2 orders of magnitude if the bandgap in the LLWS is increased by 20-40 meV compared to the rest of the laser. GaAs quantum wells (QW) grown by molecular beam epitaxy (MBE) on ridged substrates are thicker on a narrow ridge (NR) than on a wide ridge (WR) because of surface diffusion of Ga during growth, and consequently have smaller effective bandgaps. This effect is used in the design of the mode-locked laser. A GaAs (100) substrate is patterned with a ridge in the (011) direction, the ridge width varying between NR and WR sections, as shown in the figure. During the subsequent MBE growth of the layers forming the laser structure, a L...