In order to verify the effectiveness of the proposed method, the intrinsic frequency of the novel polarization maintaining interference fiber optical gyroscope (PM-IFOG) was measured. A square-wave voltage was applied to the phase modulator of the IOC. Tuning the frequency of the square wave, the delay time of the sensing coil for light wave after doubling is ~6.21 μs, as shown in

Figure 3, which proved that the light waves traveled twice in the PM coil with the fiber length of 600 m and the coil diameter of 70 mm. To further prove its effectiveness, an experimental setup was established, as shown in

Figure 4. Two FPCSs (Thorlabs) were added in a conventional PM-IFOG. Both the optical system and the data sampling system were fixed on the experimental platform. The PM-IFOG before and after improvement were used to detect the earth’s rotation angular rate at the same place, respectively. Before doubling the optical path, the PM-IFOG, the length of whose PMFC is 600 m, were put on the experimental platform with the sensing axis straight up and straight down, respectively. The corresponding input regular rates were positive and negative and equal to the component of the earth’s rotate rate. As we know, the averaged output angular rates of earth’s rotation are 15°/h and −15°/h. It is well known that the theoretical value of positive and negative (Hangzhou, China) where the experiments were carried out lies at a latitude of ~

${30}^{\xb0}\mathrm{N}$, so the actual value of positive and negative angular rate of earth’s rotation in the experiments were supposed to be 7.5°/h and −7.5°/h. The output data, D

_{1}, with the input regular rate of 7.5°/h and D

_{2} with the input regular rate of −7.5°/h of PM-IFOG at the two conditions, were collected in real-time and then saved to the PC. The scale factor can be calculated as K = (D

_{1} − D

_{2})/15°/h. The experimental result data divided by K on the two conditions are shown in

Figure 5a. After doubling the optical path, the same experiments were done and the processed experimental results are shown as

Figure 5b. The positive and negative angular rate value of the normal PM-IFOG before doubling were 7.4895°/h and −7.5105°/h, while the averaged output of IFOG after doubling became 7.51258°/h and −7.48744°/h accordingly. From the insets of

Figure 5a,b, we can see the signal-to-noise ratio (SNR) improved greatly after doubling the light path. The Allan errors of the experimental results were analyzed and shown in

Figure 6.

Based on the noise analysis theory for gyroscopes, angle random walk (ARW) appears where the slope of Allan error curve is −0.5 and bias stability is thought to be the minimum value of the curve where the slope is 0 divided by 0.664 [

34]. The values of ARW and bias stability of the IFOGs before and after doubling were calculated according to the method mentioned above and are shown in

Table 1. It was obvious that the ARW, after doubling the light path, was relatively smaller than conventional PM-IFOG, which means a higher SNR. Meanwhile, compared with the conventional PM-IFOG, the positive and negative sensitivity of PM-IFOG after doubling the light path was promoted to be 2.002 and 1.740 times, according to the promotion of bias stability. In addition, the bias stability with the positive earth rotate angular rate after doubling was 0.0091°/h. Compared to Ref. [

32], we have achieved high precision gyro prototype with miniaturization.

The demonstrations before and after doubling were placed on a motor-driven turntable with the rotation rates of −3°/s and 3°/s, respectively. The scaling factor experimental results are shown in

Figure 7a,b, respectively. Before doubling, the scaling factor k1 with the rotate rate from −3°/s to 3°/s was 3.79312 × 10

^{8}/(°/s), but after doubling, the scaling factor k2 was 7.65452 × 10

^{8}/(°/s). The doubling factor was k2/k1 = 2.018. Compared to the expected value 2, the experimental doubling factor was 1% larger. This may lead by the pigtails of the two FPCSs, each of whose length is ~1.5 m.