An optical microphone having enhanced sensitivity only along a specified axis and free from the effect of ambient noises. Movement of the mechanical steering input device causes movement of the mechanical linkage, which in turn causes rotation of the steering shaft. A reference detector measures the intensity of the reference beam for compensating the effects of temperature and light source variations on the system signals. The sample-receiving cavity has a volume of less than 1. Since the write errors of the flash memory can be remedied, the service life of the semiconductor disk can be increased.