Laser Doppler vibrometry (LDV) is a non-contact vibration measurement technique based on the Doppler effect of the reflected laser beam. Thanks to its feature of high resolution and flexibility, LDV has been used in many different fields today. The miniaturization of the LDV systems is one important development direction for the current LDV systems that can enable many new applications. In this paper, we will review the state-of-the-art method on LDV miniaturization. Systems based on three miniaturization techniques will be discussed: photonic integrated circuit (PIC), self-mixing, and micro-electrochemical systems (MEMS). We will explain the basics of these techniques and summarize the reported miniaturized LDV systems. The advantages and disadvantages of these techniques will also be compared and discussed.

Non-contact detection of photoacoustic signals is important for various applications, particularly in medical sensing and imaging, where contact methods can be uncomfortable or risky for the patient. Techniques using optical detection of vibrations, such as laser doppler vibrometers (LDVs), have been proven to be a key component for enabling non-contact photoacoustic sensing. However, most LDV systems rely on fiber-based or free-space optics, which can be unwieldy and expensive, especially for multiple location sensing. In this work, we present a compact, photonic integrated circuit (PIC)-based homodyne LDV system for the detection of photoacoustic signals. The system is fabricated on a silicon-on-insulator platform, which has the potential to be low-cost in case of medium or large volume production. To generate the photoacoustic signals, we used a 532 nm pulsed laser directed towards a target embedded in a silicone phantom designed to mimic the acoustic properties of human tissue. The target consists of an ink-solution-filled channel, which absorbs the excitation light and generates acoustical signals within the phantom through the photoacoustic effect. After performing a series of measurements with different ink concentrations, we found a good correlation between the photoacoustic signals detected by the on-chip detectors and the absorption of the target. Our system was able to detect ink solutions with absorption values as low as 5 cm −1 , an order of magnitude lower than the typical absorption of whole blood at 532 nm. These results demonstrate that PIC-based LDVs can be used to realize compact and low-cost non-contact detection for photoacoustic biomedical sensing applications.

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In this paper, we introduce a novel method to realize a multi-beam optical frequency shifting component for photonic integrated circuits, utilizing an array of parallel optical modulators and a free-propagation region (FPR), such as a slab waveguide-based star coupler. This component generates multiple optical beams with different frequency shifts, making it suitable for various systems, such as multi-beam laser Doppler vibrometry (LDV). We thoroughly elaborate on the working principle of the component through theoretical analysis and demonstrate that by applying periodic wave-like modulation in the modulator array, the discrete harmonic content of the light can be selectively directed to different outputs based on the delay between consecutive modulators. A design comprising a 16-element modulator array and 5 outputs will be presented. Simulations show that this design can generate and collect 5 different harmonics (−2, −1, 0, +1, +2) in the different outputs with a side band suppression ratio of 20 dB to 30 dB for each output. Our proposed design is just one possibility and the component can be modified and optimized for specific applications.