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Tunable Semiconductor Laser with Two Acousto-Optic Filters in the External Cavity

We demonstrate a semiconductor laser with a linear external resonator containing an injection semiconductor optical amplifier (SOA) of the 840 nm range as an active element and two acousto-optic tunable filters (AOTFs) with a quasi-collinear interaction of light and acoustic waves. Studies have shown that an optical scheme of a semiconductor laser with an external linear resonator containing two AOTFs that compensate for the Doppler shift of the optical frequency can significantly narrow the optical spectrum in both the stationary mode of operation and in the wavelength sweep mode in comparison with a scheme without the Doppler shift compensation [1–2]. In the stationary mode of operation, the laser linewidth reaches 25 MHz (FWHM) with a zero mismatch between the frequencies of the AOTF control signals (Figure 1). It is almost three orders of magnitude less than that with a single AOTF configuration. In the wavelength sweep mode, the laser emission line is broadened, but does not exceed 0.022 nm (8.8 GHz) at the maximum wavelength tuning speed of the AOTF − 10000 nm/sec. The study shows the feasibility of the tunable semiconductor laser as a commercial device, with the following technical parameters: output optical power of 3 mW; wavelength tuning range of 815875 nm; maximum sweep speed of 10000 nm/sec; instantaneous spectral width when tuning of <0.025 nm; excess of a maximum of the spectral line over a superluminescent background of >40 dB (Figure 2). Such devices are of practical interest for optical coherence tomography (OCT), spectroscopy, optical metrology.