The invention discloses an ultra narrow linewidth
low noise high power single frequency
fiber laser which comprises a single mode
semiconductor laser pumped source, a polarization-maintaining
wavelength division
multiplexing device, a
coupling output polarization maintaining
fiber raster, a high reflection polarization maintaining
fiber raster, a wave plate, a high
gain fiber, a low reflection narrow linewidth fiber
grating, a dichroscope, a
heat sink, a sealed
air chamber and a fiber clamp and polarization maintaining fiber
isolator. A common end of the polarization-maintaining
wavelength division
multiplexing device connects with the
coupling output polarization maintaining fiber raster. The
coupling output polarization maintaining fiber raster and the high reflection polarization maintaining fiber raster are etched on a same polarization maintaining fiber or respectively etched on two strips of polarization maintaining fibers with consistent fast and slow shaft directions in connection, the high reflection polarization maintaining fiber raster connects with the high
gain fiber through the wave plate, the high
gain fiber connects with the low reflection narrow linewidth fiber
grating, and the dichroscope in order. According to the invention, a folding composite chamber and a double virtual annular chamber are constructed in a short straight chamber structure, and a single frequency
fiber laser with ultra narrow linewidth and polarization-maintaining output is generated.