Study Of Heterodyne Interferometry Used In Phonoic Crystal Detection

Phononic crystals have the character of modulation of the sound wave, which other acoustic materials can not have.For example: the band gap of phononic crystals makes it widely used in reducing the vibration, noise; In addition,the introduction of defect states in photonic crystals can achieve the acoustic structure of the local role, as a resonant cavity acoustic waveguide, so that in communications, sensing, biological detection and other fields it has potential applications. Therefore, the measurement of it's vibrational properties is of great practical significance.The subject uses optical heterodyne interferometry measurement technology as the leading test method, uses piezoelectric film incentive crystals to inspire the phononic crystals ,then it detects the surface vibration and turns it in the form of optical signals. The signal processing system is based on the automatic gain control circuit which is mainly formed by controllable gain amplifier CLC522AJP and gain phase detector AD8302;We use phase detector SYPD-2+ and VCO ZX95-148 to build the Phase-locked loops,the mixer used ZX05-1-S+.The system has successfully realized the testing of phononic crystal vibration ,and solved the problem caused by inequality bench,which realized that when the optical signal change in the range 0-25dB, the amplified signal will not change .System tests results show that the AGC and PLL-based optical heterodyne measurement technique has high accuracy, high sensitivity, high signal to noise ratio and high stability characteristics.It can detecte the magnitude and phase frequency characteristics . Compared with the traditional impedance analysis using network analyzer, it has realized measurement of line , for the phononic crystals and other forms vibration's online detection,it is important and real-time detection method.