Study on Sensitivity Characteristics of Laser Microphone Using Self-Coupling Effect Depending on Oscillation Mode of Laser Diode

Abstract

We investigated the relationships of the sensitivity of laser microphones to the oscillation mode of LDs using two types of them. A VCSEL has a side mode power ratio that ranges from 12 to 66 %, and for DFB-LD the side mode power ratio that is less than 5 %. The sensitivity is affected by the side modes and decrease more greatly with an increase of the side mode power ratio. When it exceeds 50%, the sensitivity of the laser microphone decreases greatly. Although the sensitivity of a laser microphone using VCSEL is 1.87 mV/Pa at most, the one using DFB-LD is 2.12 mV/Pa. We conclude that, the side oscillation mode negatively affects to the sensitivity, which increases with an LD that has a lower side mode and higher laser power. Therefore, DFB-LD is suitable for laser microphones.