# Cavity Wavelength on Erbium-Doped Fiber Ring Laser Depending on Fabry-Perot Etalon Steering Angle
## 3 Experimental Results
Figure 4: **(a)** The direction of the steering angle is counterclockwise, as determined by the laser tuning results of the steering angle variation associated with the left-side structure depicted in Figure 1. **(b)** The direction of the steering angle is clockwise, following the laser tuning results of the steering angle variation related to the left-side structure illustrated in \[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]0 **(c)** The steering angle direction is counterclockwise, based on the laser tuning results of the steering angle variation associated with the right-side structure presented in \[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]1 **(d)** The direction of the steering angle is clockwise, as indicated by the laser tuning results of the steering angle variation pertinent to the right-side structure shown in \[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]2  
\[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]3 _Cont._  
Figure 6 shows the measurement of laser wavelength position and laser peak power per minute by changing the steering angle of the LC-FP to adjust the laser wavelength. Figure 6a,b show the counterclockwise and clockwise steering angle changes, respectively, using the left architecture of \[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]4 Figure 6c,d show the counterclockwise and clockwise steering angle changes, respectively, using the right side of \[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]5 The sampling wavelengths are 1537 nm and 1532 nm, one at the short wavelength and the other near the middle of the wavelength tuning range. Since the steering angle of the LC-FP at the long wavelengths is small, it is not meaningful to observe it as a sampling location, as Figure 3b shows the results when the steering angle is 0\({}^{\circ}\). Among them, the maximum wavelength fluctuation value is about 0.32 nm, and the maximum difference in values corresponding to the laser peak is about 4 dB. \[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]6 (**a–d**) are the values of the laser wavelengths at different steering angles corresponding to the spectra in Figure 4a–d in sequence. \[2 ndcos\theta=(\text{m}-1/2)\cdot\lambda \tag{1}\]7 (**a–d**) Stability measurements of wavelength and power for laser wavelengths of 1537 nm and 1532 nm; the sampling obtained using the architectural settings correspond sequentially to Figure 4a–d. The square symbols denote wavelengths, whereas the diamond symbols represent power. Brown symbols correspond to longer wavelengths, and blue symbols signify shorter wavelengths. Figure 7 illustrates the results obtained from employing the architecture depicted on the right side of Figure 1, specifically by adjusting the steering angle of the LC-FP device to facilitate dual-wavelength laser tuning. The primary distinction is that the collimator utilized in the previous single-wavelength laser configuration possesses a narrower spectral range, limited to around 1550 nm. To achieve effective dual-wavelength laser operation, it is imperative to utilize a collimator with a broader wavelength range, thereby permitting the transmission of light across the spectrum from 1500 nm to 1600 nm. Given that the spacing between the two segments of LC-FP glass is fixed, the free spectral range (FSR) can be expressed as FSR(v) = c/2 nd, where v represents the frequency and c denotes the speed of light. Consequently, the spacing between the two wavelengths of the dual-wavelength laser is also inherently fixed at approximately 17.5 nm, necessitating the implementation of a wide-band collimator. Furthermore, the broadband collimator has a lower optical loss, which enables the beam transmitting through the LC-FP to be increased to achieve an optical signal-to-noise ratio of more than 50 dB.