Tunable semiconductor laser with two acousto-optic tunable filters in its external cavity

• Published in: Quantum electronics (Woodbury, N.Y.) Vol. 50; no. 2; pp. 136 - 140
• Main Authors: Magdich, L.N., Chamorovskiy, A.Yu, Shidlovsky, V.R., Shramenko, M.V., Yakubovich, S.D.
• Format: Journal Article
• Language: English
• Published: Bristol Kvantovaya Elektronika, Turpion Ltd and IOP Publishing 01.02.2020; IOP Publishing
• Subjects: acousto-optic filter; Acousto-optics; Amplification; AMPLIFIERS; Automatic control; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COHERENCE LENGTH; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; DOPPLER EFFECT; EMISSION; Emissions control; FILTERS; Frequency shift; Gain; GHZ RANGE; INTERACTIONS; LASERS; LINE WIDTHS; MHZ RANGE; Near infrared radiation; Optical Coherence Tomography; Optics; Radio frequency; Semiconductor lasers; semiconductor optical amplifier; Semiconductor optical amplifiers; SIGNALS; SPECTROSCOPY; STABILIZATION; Tunable filters; tunable laser; Tunable lasers; Tuning; Wave filters; WAVELENGTHS
• ISSN: 1063-7818; 1468-4799
• DOI: 10.1070/QEL17180

We report a laser with a linear external cavity containing a near-IR injection semiconductor optical amplifier as a gain element and two acousto-optic tunable filters (AOTFs) with quasi-collinear interaction of acoustic and light waves. At identical frequencies of RF signals that control the filters and ensure compensation for the Doppler frequency shift of light passing through the AOTFs, the steady-state laser emission linewidth can be reduced to about 25 MHz, which is almost three orders of magnitude smaller than that in the case of one filter (20 GHz). The position of the emission line, which remains narrow, slowly fluctuates within a spectral range about 3 GHz wide, which seems to be due to the large length of the external cavity and insufficient thermal stabilization of its components. This does not prevent us from obtaining light with a large coherence length. In emission wavelength sweep mode, the instantaneous emission linewidth increases with tuning rate, reaching 0.022 nm (8.8 GHz) at the highest tuning rate: 104 nm s−1. In the case of automatic control over the output optical power at a level of 3 mW, the tuning range is 815 - 875 nm. Such instruments are of practical interest for optical coherence tomography, spectroscopy, optical metrology, and other application areas.