Application Cases

Experiment Name: Application of Power Amplifier in Fiber-Optic Acousto-Optic Frequency Shifting Experiments Using Piezoelectric Ceramics

Research Direction: Acousto-optic effect in optical fibers

Experimental Content:
A high-frequency, high-voltage signal is used to drive a piezoelectric ceramic to vibrate an optical fiber, generating acoustic waves. This, in turn, induces the Doppler effect on light, producing frequency-shifted components.

Test Objective:
Utilize the amplifier to amplify the driving voltage, achieving high-efficiency vibration of the piezoelectric ceramic. The significantly increased driving voltage enhances the vibration intensity of the piezoelectric ceramic sheet. The intensified acousto-optic interaction generates effective acoustic wave transmission and Doppler frequency shift in the optical fiber.

Testing Equipment:
Piezoelectric ceramic, coupler, fiber Bragg grating, PZT, ATA-2022H high-voltage amplifier, etc.

Experimental Procedure:
Heterodyne coherent detection technology is based on the mixing of the probe beam and the local oscillator beam on the photosensitive surface of the detector. Optical heterodyne coherent detection can respond to the amplitude, frequency, and phase information of light waves, making it suitable for detecting weak signals. A method to achieve low-frequency shifts was proposed using the acousto-optic Doppler effect during the mode conversion process in optical fibers, and it was applied to vibration detection.

An optical fiber mode conversion frequency shifter (MCFS) was fabricated using a mode-selective coupler (MSC) and an acoustically induced fiber grating (AIFG). The basic principle is that during the conversion of the LP11 core mode to the fundamental mode in the optical fiber, a Doppler frequency shift is generated due to the acousto-optic effect, directly yielding a low-frequency shift component in the range of 500 kHz to 1 MHz. Based on this MCFS, two heterodyne coherent detection schemes were proposed, enabling coherent detection and demodulation of optical information. In the experiment, the ATA-2022H power amplifier was used to amplify the signal for the PZT. It effectively drove the high-frequency PZT with an amplification factor of 25, achieving a voltage of up to 100 V and a driving frequency of up to 5 MHz. This effectively drove the PZT to generate high-efficiency vibrations, thereby enabling acoustic wave transmission on the optical fiber and producing effective fiber bending and the Doppler effect on the light wave.

Test Results:
In the all-fiber FBG heterodyne coherent detection experiment, the MSC was used as the device for generating core modes. The reason is that the all-fiber MSC not only efficiently converts the fundamental mode beam into a higher-order core mode beam but also uses the two output ports (SMF and FMF) to eliminate SSBI (signal-signal beat interference), greatly improving the performance of heterodyne coherent detection.

In the experiment, the beam from the SMF output port of the MSC is called the probe beam, and the beam from the FMF output port of the MSC is called the local oscillator beam, which outputs the LP11 core mode. The acousto-optic effect in the optical fiber generates micro-bending, forming a dynamic long-period grating. While the LP11 core mode is converted back to the fundamental mode in the AIFG, the acousto-optic Doppler effect also imposes a Doppler frequency shift on the converted fundamental mode. The amount of frequency shift depends on the frequency of the acoustic wave applied to the optical fiber. The experimental diagram shows an all-fiber heterodyne coherent detection scheme based on MCFS and AIFG. The SMF output port of the MSC and the FMF output port of the AIFG are connected via a 3 dB single-mode fiber coupler, combining the beams into one that is sent to an optical oscilloscope and a spectrum analyzer for signal measurement.

Specifications of ATA-2022B Power Amplifier: