Application Cases

Experiment Title: Exploration of PMN-PT Transparent Ceramics in the Field of Electro-Optic Modulation

Testing Purpose:

PMN-PT transparent ceramics possess excellent electro-optic properties, but due to the difficulty in preparing highly transparent ceramics, their application research in the field of optical communications is limited. To explore their potential applications in optical communications, we designed an electro-optic modulation system based on PMN-PT transparent electro-optic ceramics with a Sm doping content of 0.5% mol. Figure 1(a) shows the schematic diagram of the signal transmission device. From left to right, the setup includes a 632nm He-Ne laser, a polarizer, the transparent electro-optic ceramic, an analyzer, a silicon photodetector, and a subsequent two-stage amplification circuit. A signal generator is used to produce the initial signal, while an oscilloscope allows for a direct observation of the transmitted and received signals. A LabVIEW program compiled in-house is used on the computer end to display the signals on the screen.

Testing Equipment:

High Voltage Amplifier, Signal Generator, Oscilloscope, He-Ne Laser, Polarizer, Electro-Optic Ceramic, Computer, etc.

Experiment Process:

Figure 1: (a) Schematic Diagram of the Electro-Optic Switching Principle (b) Variation of Light Intensity with Electric Field

Figure 1(a) illustrates the principle of the electro-optic switch. As shown, when the electro-optic material is placed between two mutually perpendicular polarizers, no laser light can pass through the analyzer in the absence of an electric field since the polarizer and analyzer are perpendicular to each other. However, when an electric field is applied to the electro-optic material, the polarization state of the light passing through the material is rotated due to the electro-optic effect, allowing some light to pass through the analyzer. The intensity of the transmitted light can be controlled by the magnitude of the applied electric field. When the applied voltage is at the half-wave voltage, the phase difference between the o-light and e-light reaches 180 degrees, causing the polarization state of the light to rotate by 90 degrees. At this point, the polarization direction of the light transmitted through the transparent ceramic is parallel to the analyzer, and the light intensity reaches its peak, as shown in Figure 1(b).

As shown in Figure 2, a high voltage amplifier can be used to apply the signal voltage across the material. Utilizing the electro-optic effect of the material, modulation of electrical signals into optical signals can be achieved. At the demodulation end, a photoelectric conversion module is used to demodulate the optical signal back into an electrical signal, which is then sent to the computer via a serial port for signal reconstruction and display. Currently, both digital and analog signal transmission have been realized.

Figure 2: Schematic Diagram of the Electro-Optic Modulation System Principle

In the signal demodulation part of the experiment, to reduce the modulation voltage and enhance the sensitivity of the receiving end, a two-stage amplification circuit was employed, as shown in Figure 3. A T-network proportional operational amplifier circuit combined with an inverting proportional amplifier circuit was used to achieve a gain of 100 times under small signal conditions. Additionally, an add-subtract operational circuit was added at the backend to enable signal bias adjustment. This allows for arbitrary threshold adjustment and minimizes the impact of ambient light intensity. Through this amplification circuit, electro-optic information modulation under low voltage conditions was achieved, with the modulation voltage kept within 0.5kV/cm. Further improvements in sensitivity and control of ambient light intensity could potentially lower the electric field even more. In this study, due to experimental conditions, only an electric field of 0.5kV/cm was used for audio signal modulation.

Figure 3: Circuit Diagram of the Signal Receiving End Amplification Circuit

Experimental Results:

The actual optical path and signal comparison for analog signal transmission are shown in Figure 4. A mobile phone Bluetooth connection was used as the signal input end to load the analog signal onto the ceramic plate. After modulating the electrical signal into an optical signal via the electro-optic effect, the original and modulated signals were collected. As shown in Figure 4(b), the waveform of the original audio signal and the modulated laser signal are essentially identical, indicating that the audio information modulated by the PMN-PT transparent electro-optic ceramic maintains good fidelity.

Figure 4: (a) Schematic Diagram of the Actual Optical Path and Circuit for Electro-Optic Modulation of Audio Information (b) Comparison of Original and Received Audio Signals

High Voltage Amplifier Recommendation: ATA-7030

Figure: Specifications of the ATA-7030 High Voltage Amplifier

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