Enhanced self-mixing interferometry based on volume Bragg gratings and laser diodes emitting at 405-nm wavelengths.

Self-mixing interferometry (SMI) represents a robust, self-aligned technique for metrology applications. Recently, it has been shown that the detection of the frequency-modulated (FM) signal enhances the conventional SMI signal based on the amplitude modulation. Here, an all-optical, simple and effective alternative approach to detect the FM self-mixing signal is presented. We demonstrate the enhanced self-mixing approach using a laser diode emitting at 405 nm and a volume Bragg grating (VBG) to map frequency to intensity modulations for further optical detection. Our approach overcomes the spectral range limitation of the edge filtering approach based on molecular absorption filters, since the VBGs can be fabricated at any spectral range.