## 3 Experimental Results  
Figure 2a plots standard a single optical resonance (blue scattered line), its IQ curve (black scattered line), its fitting IQ curve (red solid line), and its replotted resonance (magenta solid line). An MBR with a diameter of 220 \(\upmu\)m and a wall thickness of 17 \(\upmu\)m was excited with 1550 nm tunable laser via a tapered fiber whose diameter was about 2.5 \(\upmu\)m. The IQ curve has two peaks that sit symmetrically centered on the optical resonance. The intracavity Q (\(q_{0}=1.20\times 10^{6}\)), external cavity Q (\(q_{\rm e}=1.14\times 10^{6}\)), total Q (\(q_{\rm a}=(q_{0}{}^{-1}+q_{\rm e}{}^{-1})^{-1}=5.84\times 10^{5}\)) and resonant frequency (\(f_{\rm a}=1.94\times 10^{14}\) Hz) can be obtained by fitting the IQ curve with a single resonance IQ expression. Total Q (\(q_{\rm b}=5.84\times 10^{5}\)) and resonant frequency (\(f_{\rm b}=1.94\times 10^{14}\) Hz) can also be obtained by fitting the transmitted spectrum directly. The results agree with each other and prove that the IQ curve can be used to analyze the spectrum. Figure 2b plots an asymmetrical spectrum (black scattered line) and its fitting resonances (overlapping, red solid line; coupled, yellow dashed line). An MBR with a diameter of 276 \(\upmu\)m and a wall thickness of 4 \(\upmu\)m was excited with an 850 nm tunable laser via a tapered fiber whose diameter was about 2.5 \(\upmu\)m. However, direct fitting of the spectrum via a two-resonance expression did not derive unique fitting parameters. Figure 2b gives the fitted spectrum with the two group parameters. The two groups' different parameters listed in Table 1, however, provided an excellent fitting. The coefficient of determination parameters (COD, R-Square) were both above 0.980. Thus, we used the OD-PDH technique to analyze the resonance. Figure 2c plots the spectrum (blue scattered line) in Figure 2b and its IQ curve (black scattered line), fitting curve of the two resonances in Figure 2b and its replotted IQ curve (overlapping, red solid line; coupled, yellow dashed line). We used the fitted parameters from Figure 2b to replot the IQ curve. The CODs of the overlapping and coupled replotted IQ curves were 0.981 and 0.937, respectively. Clearly, the overlapping replotted IQ curves agree with the experimental spectrum. This proves that the IQ curve can discriminate asymmetrical resonance. Figure 2d plots the spectrum (blue scattered line) in Figure 2b and its IQ curve (black scattered line), fitted IQ curve and its replotted two resonances (overlapping, red solid line; couple, yellow dashed line). To verify that the IQ fitting is valid, we used the two-resonant IQ expression to fit the IQ curve. The IQ curve could be well fitted by the two groups' different parameters listed in Table 1 (CODs \(>\) 0.996). Then, we used the fitting parameters to replot the resonances. The COD of the overlapping replotted resonance was 0.968, while the COD of the coupled parameters was only 0.790. Similarly, the overlapped replotted curve better agrees with the experimental spectrum. These fitting and replotting curves prove the IQ  
Figure 1: Setup schematic of the orthogonal demodulated Pound-Drever-Hall technique system. TL, tunable laser; PC, polarization controller; PM, phase electro-optical modulator; MBR, micro-bubble resonator; PD, photoelectric detector; DAQ, data acquisition card; IQ, I-term and Q-term signal; HFSG, high frequency function signal generator; PS, pressure sensor; SP, syringe pump; DS, detection signal; LS, local oscillation signal. IQ DC, IQ demodulation circuit. The inset (**a**) illustrates the IQ demodulation circuit detail. The inset (**b**) provides an image of the MBR. curve can confirm that the overlapping parameters are the correct results. To prove that the spectrum in Figure 2b contains the two resonances, we injected air into the MBR to execute pressure tuning. Figure 2e,f shows the resonance (blue scattered line) gradually separating and eventually becoming two resonances, and its IQ curves (black scattered line).