Phase quadrature four-wavelength demodulation system and method of optical fiber f-p cavity sensor

A phase quadrature four-wavelength demodulation method of an optical fiber F-P cavity sensor, wherein a change of to-be-measured external environment is detected by using a phase quadrature four-wavelength demodulation system of an optical fiber F-P cavity sensor, wherein the phase quadrature four-wavelength demodulation system comprises a flat amplified spontaneous emission (ASE) broadband light source, an optical fiber circulator, a dense wavelength division multiplexer, a photoelectric detector, and a data acquisition processing unit, wherein the flat ASE broadband light source is connected to the optical fiber circulator, the optical fiber circulator is connected to the dense wavelength division multiplexer, the dense wavelength division multiplexer is connected to the photoelectric detector, and the photoelectric detector is connected to the data acquisition processing unit;

• and
• the optical fiber circulator is configured to transmit an optical signal, wherein the optical signal from the flat ASE broadband light source enters the optical fiber F-P cavity sensor via the optical fiber circulator;
• the optical fiber F-P cavity sensor is configured to generate reflected light, wherein the reflected light generated by the optical fiber F-P cavity sensor is input to the dense wavelength division multiplexer via the optical fiber circulator;
• the dense wavelength division multiplexer is configured to decompose the received reflected light into four beams of narrowband light of different wavelengths and input the four beams of narrowband light of different wavelengths to the photoelectric detector;
• the photoelectric detector is configured to perform a photoelectric conversion on the four beams of narrowband light of different wavelengths and input the photoelectrically converted four beams of narrowband light of different wavelengths to the data acquisition processing unit;
• and the data acquisition processing unit is configured to demodulate the photoelectrically converted four beams of narrowband light of different wavelengths to obtain a cavity length change amount of the optical fiber F-P cavity sensor, wherein the cavity length change amount is used for reflecting a change of to-be-measured external environment;
• and
• the method comprises:
• acquiring an interference spectrum of the optical fiber F-P cavity sensor;
• calculating an initial cavity length L of the optical fiber F-P cavity sensor according to the interference spectrum;
• in a case where a light source enters the optical fiber F-P cavity sensor and the optical fiber F-P cavity sensor generates reflected light, decomposing the reflected light into four beams of narrowband light, and performing a photoelectric conversion on the four beams of narrowband light to determine wavelengths of the photoelectrically converted four beams of narrowband light;
• calculating phases corresponding to the wavelengths of the four beams of narrowband light according to the initial cavity length L of the optical fiber F-P cavity sensor and the wavelengths of the photoelectrically converted four beams of narrowband light;
• calculating light intensities corresponding to the wavelengths of the four beams of narrowband light according to the phases corresponding to the wavelengths of the four beams of narrowband light;
• and
• calculating the cavity length change amount of the optical fiber F-P cavity sensor according to the light intensities corresponding to the wavelengths of the four beams of narrowband light;
• wherein a formula of the cavity length change amount of the optical fiber F-P cavity sensor is as follows:
• {
• ϕ
• i
• =
• tan
• -
• 1
• [
• I
• 4
• -
• I
• 2
• I
• 1
• -
• I
• 3
• ]
• ±
• m
• ⁢
• π
• L
• d
• =
• λ
• i
• ⁢
• ϕ
• i
• 4
• ⁢
• n
• ⁢
• π
• L
• d
• =
• L
• +
• Δ
• ⁢
• L
• wherein i=1, 2, 3, 4;
• ϕi is a phase corresponding to an ith narrowband optical wavelength;
• λi is the ith narrowband optical wavelength;
• I1, I2, I3, and I4 are light intensities corresponding to wavelengths of the four beams of narrowband light of different wavelengths, respectively;
• m is an integer;
• n is a refractive index of air in a cavity of the optical fiber F-P cavity sensor:
• Ld is a real-time cavity length of the optical fiber F-P cavity sensor:
• L represents an initial cavity length of the optical fiber F-P cavity sensor;
• and ΔL is the cavity length change amount of the optical fiber F-P cavity sensor.