Application Cases

Experimental Name: Structural Parameter Optimization of Silicon-based Silica Optical Waveguide Resonator Cavities for Angular Velocity Sensing Applications

Experimental Content: This chapter proposes a novel double-loop crossed optical waveguide resonator structure. This configuration effectively enhances the quality factor of the resonator by increasing its cavity length within the limited chip space.

Test Equipment: Power amplifier, tunable laser, signal generator, polarization controller, photodetector, oscilloscope, etc.

Figure 1: Silica Optical Waveguide Resonator Test System

Experimental Process:

Figure 2: Resonance Spectrum of the Optical Waveguide Resonator with 4.4μm Spacing

The optical waveguide resonator with 4.4μm spacing was placed in a temperature-controlled chamber. The temperature was adjusted to bring the resonator's resonant frequency close to the laser's central frequency. After stabilization, the resonance spectrum of the optical waveguide resonator was obtained, as shown in Figure 2. Parameters such as the quality factor, resonance depth, and full width at half maximum (FWHM) of the resonator can be calculated from the measured spectrum. The triangular wave in the figure represents the laser's frequency sweep signal at 10 Hz, generated by the signal generator and amplified to an amplitude of 59.6V by the high-voltage amplifier. Resonance peaks of the optical waveguide resonator can be observed during the rising edge of the triangular sweep signal. Lorentzian fitting of this resonance peak yields a temporal FWHM of 0.0012s, corresponding to a sweep voltage difference of 1.49V. Given the laser's frequency modulation coefficient of 15 MHz/V, the FWHM of the resonator is calculated to be 22.35 MHz. The quality factor can be derived from the FWHM, and the resonance depth can be obtained from the ratio of the light intensity at resonance to the off-resonance intensity. The measured quality factor for this optical waveguide resonator is 8.66×10⁶, with a resonance depth of 99.9%.

Experimental Results:

Figure 3: Comparison of Simulation and Measured Results for the Optical Waveguide Resonator (a) Relationship between FWHM and Spacing, (b) Relationship between Resonance Depth and Spacing

Optical waveguide resonators with different spacings were tested for their resonance spectra, and the results are shown in Figure 3. It can be seen that the simulation results agree well with the measured results. The FWHM of the resonator gradually decreases with increasing spacing, and the measured results show the same trend as the simulated values; the resonance depth first increases and then decreases with increasing spacing, and the measured results follow this pattern as well. Furthermore, at the 4.4μm spacing, the resonator is in a critical coupling state, showing good consistency with the simulation.

The test results of the resonators demonstrate the reliability of the design method proposed earlier. Among this batch of silica optical waveguide resonators, the one with 5.2μm spacing achieved the highest quality factor of 1.02×10⁷; the one with 4.4μm spacing achieved the highest resonance depth of 99.9% and a Q-factor of 8.66×10⁶.

However, Figure 3 also shows certain errors between the simulated and actual measured values. Based on analysis of the test results, this paper suggests that potential causes for the errors may include: measurement inaccuracies in the actual transmission loss of the optical waveguides, spacing errors introduced by the fabrication process, and measurement errors in the spectral FWHM due to the laser linewidth, among other factors.

Power Amplifier Recommendation: ATA-1200C Broadband Amplifier

Figure: ATA-1200C Broadband Amplifier Specifications and Parameters

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