Abstract
A five-wavelength-switchable thulium-doped fiber laser with a fiber Bragg grating (FBG)-based five-channel transmitting Fabry-Pérot (F-P) filter and a multi-coupler based triple-ring cavity (CTRC) filter, is experimentally proposed. For the first time, a multi-channel F-P filter and specially-designed coupler-based compound cavity filter were combined to realize multi-wavelength-switchable operation, with single-longitudinal-mode (SLM) lasing for each wavelength channel in a 2 µm band fiber laser. The theoretical analysis of the CTRC filter and the principle for achieving SLM operation by corporately using the F-P filter and CTRC filter were presented in detail. The experimental results demonstrated the good performance of the proposed filters. Five lasing wavelengths (1941.13 nm, 1941.22 nm, 1941.30 nm, 1941.39 nm, and 1941.47 nm) were obtained with good switchability, and each operated in a stable SLM state. The OSNR of each lasing wavelength was higher than 50 dB, and the linewidths of all obtained wavelengths were less than 8 kHz.
Highlights
SINGLE-longitudinal-mode (SLM) fiber lasers have drawn intense research interest because they provide a narrowlinewidth, low relative intensity noise, and high beam quality output
According to the total cavity length, the SLM fiber laser configurations can be classified into the short-cavity structure, which includes distributed feedback (DFB) lasers[5] and distributed Bragg reflection (DBR) fiber lasers[6], and long-cavity structures with proper mode selection mechanisms [7]
The experimental results given below prove the good mode selection ability of the proposed coupler based triple-ring cavity (CTRC) filter
Summary
SINGLE-longitudinal-mode (SLM) fiber lasers have drawn intense research interest because they provide a narrowlinewidth, low relative intensity noise, and high beam quality output. DFB and DBR lasers provide compactness structure and robust SLM operation; they suffer from relatively low laser efficiencies due to the short length of the gain fiber When it comes to laser flexibility and tunability, long-cavity lasers embedded mode selectors are the laser of choice over any other short-cavity lasers. Thulium-doped fiber lasers offer a broad emission range (1660–2200 nm), which falls in the eye-safe spectral region and covers the atmospheric transparency window where the permissible power transmission for light in free space can be several orders of magnitude higher than other wavelength bands With these advanced features, a 2 μm SLM fiber laser can be adapted for use in free-space optical communications and laser weapon manufacturing [23]. We present the laser linewidth at each obtained wavelength that was measured by the in-house constructed linewidth measurement system based on the laser phase noise demodulation method
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