Single-frequency lasers based on Er3+-doped or Er3+/Yb3+ co-doped gain fibers mainly work in the 1.5 μm band (C-band: 1530-1565 nm) and part of the L-band (1565-1625 nm). Its wavelength is in the C window of optical fiber communication, which makes the 1.5 μm band single-frequency fiber laser with narrow linewidth and low noise characteristics very important in coherent optical communication. It is used in high-resolution sensing, optical frequency domain reflectometer , laser radar and other fields also have a wide range of applications.
The eye-safe L-band single-frequency fiber laser can be used in high-resolution molecular spectroscopy, lidar, high-performance pump source of Tm3+ doped laser and nonlinear frequency conversion and other fields.
(1) 1.5 μm band CW single-frequency fiber laser
In terms of continuous single-frequency laser output with a wavelength of about 1.6 μm, the MOPA structure can be used to amplify the 1.6 μm single-frequency fiber laser seed source. Field area Er3+/Yb3+ co-doped polarization-maintaining double-clad fiber obtained a 1603 nm continuous single-frequency laser output with a power of 15 W, a linewidth of 4.5 kHz, and a polarization extinction ratio greater than 23 dB.
In terms of high-power continuous single-frequency laser output, in 2016, the MOPA structure can be used to amplify the single-frequency fiber laser seed source. Doped double-clad fiber, a 1560 nm continuous single-frequency laser output with a power of 207 W and a slope efficiency of 50.5% was obtained. This is the highest power of the single-frequency laser based on the MOPA structure in the 1.5 μm band that has been reported so far. The experimental schematic diagram and power curve diagram are shown in Figure 4 and Figure 5, respectively.
Schematic diagram of high power single frequency Er3+/Yb3+ co-doped fiber amplifier
Output power curve of high power EYDFA pumped at 940 nm
In terms of single-frequency laser noise suppression, the MOPA structure composed of two-stage fiber amplifiers can be used to amplify the single-frequency fiber laser seed source that has been suppressed by intensity noise, and a low-noise 1550 with a power of 23 W and a linewidth of less than 1.7 kHz can be achieved. nm continuous single-frequency laser output, its relative intensity noise in the 0.1-50 MHz frequency band is as low as -150 dB/Hz@0.5 mW, which is close to the limit of quantum noise.