# Cavity Wavelength on Erbium-Doped Fiber Ring Laser Depending on Fabry-Perot Etalon Steering Angle
## 3 Experimental Results
Conversely, it is important to note that the dual-wavelength laser tuning would be suboptimal when utilizing the architecture situated on the left side of \[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]8 Since more light is transmitted through the LC-FP, this may result in different beam paths at the LC-FP with equal transmitted and reflected power. This reaction creates additional interference that is different from the interference of the LC-FP filter itself, which will affect the wavelength and power changes of the dual-wavelength laser. The steering angles in Figure 7a,b are counterclockwise and clockwise, both from 4\({}^{\circ}\) to 18\({}^{\circ}\), with no wavelength shift from 0\({}^{\circ}\) to 4\({}^{\circ}\), and the wavelength shift begins at 5\({}^{\circ}\), owing to sufficient optical path difference. The laser wavelength tuning presented in Figure 7a ranges from 1557.67 nm to 1543.81 nm at the longer wavelength and from 1540.1 nm to 1526.24 nm at the shorter wavelength, as illustrated in Figure 8a. In Figure 7b, the tuning at the longer wavelength spans from 1557.07 nm to 1543.32 nm, while the shorter wavelength ranges from 1539.4 nm to 1525.85 nm, as depicted in Figure 8b. The spacing between the dual wavelengths is consistently maintained at approximately 17.5 nm, with an overall tuning range for the dual-wavelength laser of about 14 nm. On average, the wavelength of the laser shifts by approximately 0.1 nm for each 1\({}^{\circ}\) change in the steering angle, which is consistent with the findings of the single-wavelength laser configuration. \[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]9 **(a)** Dual-wavelength laser tuning results are based on the architecture shown on the right side of Figure 1, utilizing the counterclockwise change in the steering angle of the LC-FP. **(b)** Dual-wavelength laser tuning results are based on the architecture shown on the right side of Figure 1, utilizing the clockwise change in the steering angle of the LC-FP. Figure 9 presents the measurements of wavelength per minute and power variation corresponding to the dual-wavelength laser results illustrated in Figure 7, utilizing the configuration depicted on the right side of Figure 1.0 Specifically, Figure 9a depicts a counter-clockwise steering angle setting, wherein the wavelengths of the sampled dual-wavelength lasers are recorded at 1553.92 nm and 1536.34 nm. In contrast, Figure 9b illustrates a clockwise steering angle setting, with the recorded wavelengths of the sampled dual-wavelength lasers at 1543.79 nm and 1526.32 nm. The measurement selection encompasses both the long and short-wavelength regions of the laser's tuning range. Notably, the maximum change in wavelength position is approximately 0.1 nm, while the maximum difference in peak laser levels is about 3 dB. Moreover, as illustrated in Figures 3, 6 and 9, it is evident that the standard deviation of power at longer wavelengths is generally greater than that at shorter wavelengths. This phenomenon can be attributed to the fact that the gain provided by the EDFA is larger around 1530 nm, and thus the power at short wavelengths may be more stable. Figure 1.1 (**a,b**) are the values of the laser wavelengths at different steering angles corresponding to the spectra in Figure 7a,b in sequence. The purple bar corresponds to longer wavelengths; the blue bar corresponds to shorter wavelengths. Figure 1.2 (**a**) The wavelength and power stability measurements for 1553.92 nm and 1536.34 nm laser wavelengths are set up for Figure 7a measurements. (**b**) The wavelength and power stability measurements for 1543.79 nm and 1526.32 nm laser wavelengths are set up for Figure 7b measurements. The square symbols denote wavelengths, whereas the diamond symbols represent power. Brown symbols correspond to longer wavelengths, and blue symbols signify shorter wavelengths.