[Komori, Smith, Fujimoto, Saito]

When the OMC REFL PD signal was observed without injecting the sub-laser light, the fringe amplitude was approximately 4 counts. After injecting the sub-laser light, the fringe amplitude increased to approximately 180 counts, corresponding to an SNR of about 45. As in the previous measurement (klog:37138), the LO frequency was frequency-modulated with a coefficient of ±15 MHz/V. As the external signal for the frequency modulation, a 300 Hz, 800 mVpp triangular or sinusoidal waveform generated by a function generator was applied, and scans of SRX and SRY were performed to acquire data. In addition, to obtain data with a higher sampling frequency, the channel "K1:IOP-OMC0_MADC0_TP_CH12" was used to monitor the OMC REFL PD signal, and the channel "K1:IOP-LSC0_MADC0_TP_CH22" was used to monitor the external signal used for frequency modulation. An attempt was made to determine the lengths of SRX and SRY from these data using curve fitting. However, the fitting procedure developed previously (klog:37145) depended strongly on the initial fitting parameters and did not produce reliable results. Therefore, the fitting method will be improved so that stable fitting can be achieved.
 

• First, the OMC REFL PD signal was observed without injecting the sub-laser light, and the fringe amplitude was found to be approximately 4 counts. Next, the sub-laser light was injected and the sub-laser PZT was driven, resulting in a fringe amplitude of approximately 180 counts. Therefore, the SNR was approximately 45. Since the signal amplitude was sufficiently large, attention was shifted to the PLL system. The beat signal amplitude was approximately 5 dBm, which was considered sufficient, and measurements proceeded to scanning SRX.
   
• As in the previous measurement (klog:37138), the LO frequency was frequency-modulated with a coefficient of ±15 MHz/V. A 300 Hz, 800 mVpp triangular waveform generated by a function generator was applied as the external signal for the frequency modulation. In addition, to obtain data with a higher sampling frequency, the channel "K1:IOP-OMC0_MADC0_TP_CH12" was used to monitor the OMC REFL PD signal, and the channel "K1:IOP-LSC0_MADC0_TP_CH22" was used to monitor the external signal for frequency modulation. The signals from these two channels were recorded, and after changing the external modulation signal from a triangular wave to a sinusoidal wave, another set of data was acquired.
   
• After acquiring the SRX scan data, measurements proceeded to SRY scanning. As in the SRX measurements, data were acquired both when the external signal for frequency modulation was a triangular waveform and when it was a sinusoidal waveform (Fig. 1). An attempt was then made to determine the lengths of SRX and SRY from these data using curve fitting. However, the fitting method developed previously (klog:37145) depended strongly on the initial fitting parameters and did not provide satisfactory results. Therefore, the fitting procedure will be improved to achieve more reliable and stable fitting results.