Application Cases

Experiment Title: Fabrication and Sensing Characteristics of Sensors Based on Microring Resonators

Testing Purpose:Based on the optimized device structure and parameters from simulations, this study investigates the rational processing sequence and parameters for the microfabrication of electric field sensors based on electro-optic polymers and silicon microring resonators. A direct current (DC) electric field sensing experimental platform is established to test and analyze the sensing characteristics of the DC electric field sensor through experiments.

Testing Equipment: High Voltage Amplifier, Arbitrary Function Generator, Sensor, Spectrometer, Polarization Controller, etc.

Experiment Process:

Figure 1: Schematic Diagram of the Testing System Structure

An experimental platform for sensing, as shown in Figure 1, was set up. According to the nature of the equipment, the platform can be divided into optical and electrical parts. The optical part uses a C-band broadband light source (center wavelength of 1535nm-1560nm) connected to a polarization controller via a single-mode fiber. The fundamental mode polarization state light, after passing through the polarization controller, is vertically coupled into the chip's input end through a tapered single-mode lensed fiber and then coupled into the ring waveguide via a straight waveguide to produce resonance. The output end of the straight waveguide is coupled out through a tapered single-mode lensed fiber and connected to a spectral analyzer to display and store the output optical signal of the chip. The electrical part, on the other hand, uses a high voltage amplifier to amplify the low voltage signal from the arbitrary function generator to produce the high voltage required for creating a strong electric field.

Figure 2: Sensor Output Response Spectrum as a Function of Electric Field Amplitude

An arbitrary function generator produces a DC signal, which is amplified by the high voltage amplifier and applied to the parallel plate electrodes to generate a uniform DC electric field. Different DC electric fields are applied, and the output optical signal of the sensor is recorded by the spectrometer. The transmission spectrum of the electric field sensor under different DC electric fields is shown in Figure 2.

Experimental Results:

The test results indicate that the free spectral range of the output spectrum of the microring sensor with a radius of 10μm is 8.16nm, the quality factor is 6276, and the extinction ratio is 8.05dB. However, according to the simulation results in Section 3.2.1, when the microring resonator has a radius of 10μm, the ideal free spectral range is 9nm, and the quality factor is 9200, which is significantly different from the data obtained in the actual experiment. The reason for this discrepancy may be that the cladding of the electro-optic polymer film affects the light wave transmission, leading to increased propagation loss. Additionally, technical issues in the microfabrication process of the waveguide can also affect waveguide transmission.

Furthermore, it can be seen from Figure 2 that when the electric field amplitude changes, the sensor's resonance wavelength shifts significantly towards longer wavelengths. This can be explained by the fact that under the influence of the electric field, the refractive index of the electro-optic polymer increases, leading to an increase in the effective refractive index of the waveguide and a rightward shift in the microring resonance wavelength. Under the same constant temperature and humidity experimental conditions, a microring resonator without an electro-optic polymer cladding was tested, and no resonance wavelength shift was observed when the applied electric field amplitude was changed. Therefore, this variable is only related to the electro-optic polymer.

High Voltage Amplifier Recommendation: ATA-7050

Figure: Specifications of the ATA-7050 High Voltage Amplifier

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