In this paper, we propose an improved method of phase generated carrier (PGC) combined with 3×3 coupler to extend dynamic range and compensate low-frequency drift of modulation depth. The small amplitude signal(≤10-2 rad) is figured out by the PGC method to keep the minimum phase resolution and the large amplitude signal(≥10rad) can be calculated by the 3×3 fixed phase difference algorithm to extend the maximum amplitude of the dynamic range. We can get the same result to the signal with the normal amplitude(10-2 rad≤D≤10rad) by any two kinds of methods. Furthermore, the modulation carrier wave amplitude and frequency information can be monitored by the 3×3 auxiliary algorithm to compensate low-frequency drift of modulation depth and keep the system stability as a feedback. According to the result, the interferometer is able to resolve 2.0 ×10-5 rad/√Hz with a dynamic range of 182.2dB@10Hz frequency and 2Mbps sample rates.
In this paper, we present an improved fixed phased demodulation method combined with phase generated carrier (PGC) and ellipse fitting algorithm (EFA) to enhance the phase resolution and suppress the total harmonic distortion (THD) caused by the laser intensity disturbance (LID) of modulation phase. We make the subtraction operation to the outputs of the two 1×2 couplers to get the differential signals without DC offset, which is used to achieve the fixed phase demodulation. The EFA is applied to construct the standard quadrature signals with the two signals. The last output is utilized to finish the small amplitude (<2π rad) demodulation in PGC method, which can increase the phase resolution. The distortion signals caused by the LID effect can be eliminated by the EFA. According to the result, the phase error of the EFA is 0.03rad, the amplitude error is 5% and the phase resolution of system is 2.0×10-6rad/√Hz@1kHz (-106.3dB) with the THD is 5%.
A method of simultaneous evaluation for two branches of a multi-functional integrated optic chip (MFIOC) with a dual channel system is proposed. The difference between the two branches of the MFIOC can be tested simultaneously with a high precision. In the system, the chip is used as a 1×2 splitter and its two branches are combined by a 2×2 coupler. The characteristic peaks of the two branches are distinguished by selecting proper length of the extended fibers which connected to each polarization-maintaining (PM) pigtails. Temperature responses of the two branches of the MFIOC are experimented. Results show that the dual channel system can simultaneously measure the characteristics of the two branches of MFIOC with resolution of over -85 dB and dynamic range of 85dB.
This paper focus on the strain characteristic of the fiber-optic flexural disk accelerometer based on the multilayer sensing fiber coils. The strain state is analyzed in theory, and by using the simulation software, we built the simulation model and obtain the strain distribution of the multilayer sensing fiber coils in different bonding position of the flexural disk. The strain theoretical model agrees well with the strain distribution obtained by the simulation model. According to the results, a flexural disk accelerometer is produced. Experiment results show that the phase sensitivity is 6814rad/g, which is equivalent to the acceleration sensitivity of 15ng/Hz1/2.
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