## 3 Experimental Steps and Results  
A schematic and a photograph of the tunable dispersion compensator are shown in Figure 3. This device includes a fiber circulator, a fiber collimator, a half-wave plate, two blazed gratings with identical parameters (40 mm \(\times\) 40 mm, 1740 gr/mm, diffraction wavelength of 1060 nm, diffraction efficiency of 86% at 1053 nm, a Littrow angle of 67.2\({}^{\circ}\), and Au coating), and a two-dimensional electric adjusting mirror mount. The relevant parameters were estimated based on the grating parameters used in the experiment, including size, diffraction efficiency, wavelength, linear density, and spot size of incident light. We think these parameters have good reference value. Thus, in the tuning process, more accurate small-scale adjustment was required. The electric adjusting mirror mount was produced by New Focus. The Type 8742 is a four-axis open-loop intelligent motion controller/driver that serves as a compact and cost-effective solution for driving New Focus open-loop picomotor products. It is a single-box solution that can be computer-controlled using the Newport Motion Control Language (NMCL) command set via USB and Ethernet com  
Figure 2: Schematic of compensation device. munication interfaces. An oscilloscope with a bandwidth of 30 GHz (Agilent, DSO93004 L) and a high-speed photodetector with a bandwidth of 45 GHz (Newport, 1014) were used to collect the nanosecond pulses in the time domain. The injecting spectrum was applied with a two-stage phase modulation (3 GHz and 20 GHz) and a 3 dB bandwidth of 0.3 nm. After the input pulse light was transmitted through the optical fiber, it entered the circulator 1 port and was output from the circulator 2 port into the optical fiber collimator. Subsequently, after collimation and expansion, the beam passed through a half-wave plate and was incident on grating 1. The diffraction efficiency of the grating is closely related to the polarization state of the incident light. Therefore, it was necessary to rotate the wave plate and adjust the polarization state of the incident light to achieve the highest diffraction efficiency of the grating and reduce the system loss. Next, the light beam was diffracted by grating 1 and transmitted over a certain distance in space to grating 2. Thereafter, it was diffracted by grating 2 for a second time, became a parallel light beam, reached the plane mirror, was reflected by it, returned to the collimator, was coupled into the optical fiber by the collimator, and re-entered port 2 of the circulator. Finally, the output from port 3 of the circulator entered the next section of the fiber for further transmission. The angle of incidence can be altered by adjusting the two-dimensional direction of the plane mirror to tune the grating's dispersion. The overall insertion loss of the system was approximately 5 dB, mainly originating from the annular insertion loss and coupling. If a low insertion loss circulator is used and the coupling is finely tuned, the system insertion loss can be further reduced. In the experiment, in order to avoid the introduction of additional FM-AM by PMD, a single polarization fiber was used as the transmission fiber. In the ICF driver, for accurate synchronization, the length of the transmission optical fiber used for each channel is usually different, ranging from 50 to 200 m. In addition, the seed spectral width of the front-end system should be adjustable within 0.1\(\sim\)0.3 nm and the central wavelength is required to be adjustable within 1053.0 \(\pm\) 0.5 nm; this necessitates that the compensation system should be tunable and also possess a certain tolerance for the tuning of the signal spectral width and central wavelength. Figure 3: _Cont._  
First, we roughly scanned the relationship between the FM-AM depth and the motor operating state, including the direction and steps of the motor. The diagram of the motor scan is shown in Figure 4, where step 1 and step 2 represent the two dimensions of the motor, respectively.