step 1: measuring a frequency shift coefficient α caused by a power variation of an optical signal output by a laser;

step 2: setting power of the optical signal output by the laser to A_i, and acquiring an error signal slope k_i of an error signal generated by a lock-in amplifier when the power of the optical signal output by the laser is A_i;

step 3: changing the power A_i of the optical signal output by the laser and repeating the step 2 until a first plurality of sets of the power of the optical signal output by laser and the corresponding error signal slopes (A_i, k_i) are acquired, wherein i is a power sequence number;

and then, performing fitting to obtain a relationship coefficient β between the error signal slope k_i and the power A_i of the optical signal output by the laser;

step 4: calculating a preset reference voltage V_offset of a proportional integral differential amplifier by the following formula:

wherein n is an exponential parameter, and A₀ is power of the optical signal output by the laser set during actual working;

step 5: setting a reference voltage of the proportional integral differential amplifier to the preset reference voltage V_offset, and testing a corrected frequency shift coefficient α′ caused by the variation in the power of the optical signal output by the laser, wherein the corrected frequency shift coefficient α′ is calculated based on the following formula:

αδf_L/δA, wherein δf_L is a maximum variation in a locking frequency of the laser within a fluctuation range of the power of the optical signal output by the laser after the preset reference voltage V_offset is set, and δA is a power variation; and

step 6: optimizing the preset reference voltage V_offset, comprising changing the reference voltage of the proportional integral differential amplifier within a preset fluctuation range, and

until a minimum corrected frequency shift coefficient α′ caused by the power variation of the optical signal output by the laser is tested and the reference voltage of the proportional integral differential amplifier corresponding to the minimum corrected frequency shift coefficient α′ is an optimal reference voltage, ending suppression of the frequency shift coefficient α caused by the power variation of the optical signal output by the laser, wherein the frequency shift coefficient α is measured based on the following steps: setting the reference voltage of the proportional integral differential amplifier to 0 V by a voltage setting point of the proportional integral differential amplifier, locking a laser frequency, changing power A of the optical signal output by the laser, measuring the locking frequency f of the laser, acquiring a second plurality of sets of the power of the optical signal output by the laser and the corresponding locking frequencies of the laser, and then performing a first linear fit by a first linear function formula f=αA to obtain the frequency shift coefficient α caused by the power variation of the optical signal output by the laser.