Abstract
We present experimental results of a low-emission self-mixing interferometer that uses a coupled interferometric effect to improve the signal produced by a vibrating target. This method is intended to be useful in applications where the target is prone to be damaged by high-intensity laser sources. The beam of a Fabry-Perot laser diode is split and ∼21% of the original emission is used to measure the harmonic micro-displacements of the target using the self-mixing effect. A portion of the residual beam, which also carries the interferometric information related to the target displacement, is reinjected back into the laser cavity by means of a fixed reflector, causing a second interferometric phenomenon that improves the signal-to-noise ratio of the measurement by up to ∼13 dB. A theoretical description of the phenomena is also proposed. Further, we apply this technique to the two most common self-mixing sensing schemes: internal photodiode and junction voltage. The reported results show good agreement with theory and prove the capability of the method to enhance the SNR in SMI schemes.
Highlights
Interferometers based on the well-known self-mixing effect are nowadays widely employed in applications for sensing variables such as displacement [1,2,3], distance [4,5], vibration [6], and velocity [4]
We present experimental results of a low-emission self-mixing interferometer that uses a coupled interferometric effect to improve the signal produced by a vibrating target
In 1968, Rudd [11] measured the Doppler shift occurring in the light-wave of a He-Ne laser focused onto a rotating mirror, reporting that the small portion of the light reinjected into the laser cavity after interacting with the moving object causes a modulation in the optical output power (OOP) equivalent to the Doppler frequency
Summary
Interferometers based on the well-known self-mixing effect are nowadays widely employed in applications for sensing variables such as displacement [1,2,3], distance [4,5], vibration [6], and velocity [4]. The resulting low-intensity beam was used to measure the harmonic motion induced to a target by a piezo-electric actuator; as explained before, as far as the back-reflected light reaching the laser cavity after a round-trip is limited by the very nature of the system, the SNR of the SMI signal was compromised to some extent. We overcome this issue by using the residual part of the original beam as a signal amplifier through a novel coupled interferometric effect.
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