All-fiber single-frequency DFB laser

All-fiber single-frequency DFB laser

Optical path design

The central wavelength of a conventional DFB fiber laser is 1550.16nm, and the side-to-side rejection ratio is greater than 40dB. Given that the 20dB linewidth of a DFB fiber laser is 69.8kHz, it can be known that its 3dB linewidth is 3.49kHz.

Optical path description

1. Single-frequency laser system

The optical route is composed of passive optical components such as a 976 nm pumped laser, π -phase shift grating, erbium-doped fiber, and wavelength division multiplexer. The working principle is that the pump light generated by the 976 nm pumped laser is output through the pump protector and divided into two paths. 20% of the pump light passes through the 980nm end of the 1550/980nm wavelength division multiplexer and enters the π -phase shift grating. The output seed source laser is connected to the 1550 nm end of the 1550/980nm WDM after passing through a fiber isolator. 80% of the pump light is coupled through a 1550/980 nm wavelength division multiplexer into a 2 m erbium-doped gain fiber EDF for energy exchange, achieving laser power amplification.

Finally, the laser output is achieved through an ISO. The output laser is respectively connected to the spectrometer (OSA) and the optical power meter (PM) for monitoring the laser output spectrum and laser power. All the components of the entire system’s optical path are connected by a fiber optic fusion splicer, achieving a fully optical fiber system structure with a cavity length of approximately 10 meters. The loop of the line width measurement system is composed of the following devices: two 3 dB optical fiber couplers, a 50 km SM-28e single-mode optical fiber delay line, a 40 MHz acouste-optic modulator, as well as a photodetector and a spectrum analyzer.

2. Device parameters:

EDF: The operating wavelength is in the C band, the numerical aperture is 0.23, the absorption peak is 1532 nm, the typical value is 33 dB/m, and the welding loss is 0.2 dB.

Pump protector: It can provide pump protection in the 800 to 2000 nm band, with a central wavelength of 976 nm and a power handling capacity of 1 W.

Optical fiber coupler: It realizes the distribution or combination of optical signal power. 1*2 optical fiber coupler, with a splitting ratio of 20:80%, a working wavelength of 976nm, and single-mode.

Wavelength division multiplexer: It realizes the combination and division of two optical signals of different wavelengths, 980/1550 nm WDM. The fiber at the pump end is Hi1060, and the fiber at the common end and signal end is SMF-28e.

Optical fiber isolator: Prevents the light source from being adversely affected by backward-reflected light, with a working wavelength of 1550nm, bipolar isolator, and a maximum optical power of 1W.