Generation of a variable carrier frequency for laser doppler vibrometers based on an optical phase-locked loop

State of the Art/Motivation

• Variable offset frequency cannot be achieved in the employment of conventional acoustooptic devices (e.g. Bragg cells). And the limited highest frequency of acoustooptic devices impose restrictions on its widespread application.
• Given the limitation of the relation between the carrier frequency and vibration frequency, conventional LDVs with acoustooptic devices are hardly applied for different measurements with a relatively large variation of vibration frequency.
• Disadvantages of conventional LDV in volume and price are against the portable tendency for instrument
• The feasibility and design criteria of employment of OPLL have been proofed preliminarily. The result has indicated the advantages of LDVs with a structure of OPLL in the generation of a variable carrier frequency and its alluring prospects.

Objects

• Investigation of the relation on the parameter of OPLL and LDV properties and building a relevant mathematical model as well as find an optimal solution with minimum noise.
• Establishment of experimental platform and realization of the variable carrier frequency generation.

Methods

• Variable carrier frequency generation in MHz with two diode lasers via frequency-offset-lock in a heterodyne optical phase-lock loop (OPLL).
• Building a mathematical model to explore the effect of the parameter in OPLL for LDV properties.
• Based on the change rule of LDV parameters (e.g. PSD of photocurrent) making decisions on the structure and devices of OPLL.
• Setting up an experimental platform for generation of the variable carrier frequency.