Self-aligned non-dispersive external cavity tunable laser

Christophe Moser,Frank Havermeyer,Lawrence Ho

doi:10.1364/oe.16.016691

Abstract

We are reporting on a novel self-aligned non-dispersive external cavity laser (ECL) based on thick volume holographic gratings (VHG). The ECL is tunable and operates with single mode and broad area multimode laser diodes. We experimentally demonstrate tunable single frequency operation at 405 nm and 785 nm. The tunable ECL concept is also experimentally tested with high power broad area laser diodes near 780 nm. The passive alignment feature of the cavity is expected to reduce the assembly cost of tunable ECLs.

Highlights

State-of-the-art Littrow and Littman external cavity lasers (ECL) use an angularly dispersive surface diffraction grating as the frequency selective element and a rotation scheme to provide wavelength tuning [1,2,3]
To experimentally test the concept of this ECL architecture based on a polarizing beamsplitter, the following components are positioned according to Fig.4(a): a volume holographic gratings (VHG) with one grating wave-vector recorded with 40% efficiency and 4 mm length, a 4 mm focal length single element lens, a 3 x 3 mm polarizing beam-splitter, a quarter wave plate at 405 nm and a 2 x 2 mm mirror to simulate a reflective liquid crystal (LC) cell with no
We have experimentally demonstrated a self-aligned tunable External Cavity Laser based on volume holographic reflection gratings

Summary

Introduction

State-of-the-art Littrow and Littman external cavity lasers (ECL) use an angularly dispersive surface diffraction grating as the frequency selective element and a rotation scheme to provide wavelength tuning [1,2,3]. - The spectral resolution of a dispersive ECL (eq 1) is dependent on the collimated beam diameter It results from the divergence of a diffraction limited collimated beam and the angular dispersion of the grating illuminated. - In contrast, the spectral resolution of a non-dispersive ECL (eq 2) is independent of the collimated beam diameter This is because the reflective VHG is not dispersive and the laser diode emission area forms a spatial filter. The impact of a small collimated beam is a reduced effective coupling efficiency in the laser diode This can be alleviated by increasing the diffraction efficiency of the VHG

Passively aligned ECLs with volume holographic grating

Summary and conclusion