We use integrated Aluminum Nitride (AlN) piezoelectric actuator, which control is significantly faster, bi-directional, minimizes crosstalk, operates at ultra-low power, and exhibits a flat response up to MHz frequencies. The fabrication is compatible with standard silicon semiconductor and MEMS foundry processing.
Low-loss silicon nitride photonic integrated circuits
We engineer chip-based self-injection locked laser, which allows to use compact and cost-effective commercially mature semiconductor laser diodes. We are then able to significantly reduces the laser linewidth up to 1 kHz.
Presently, all commercially mature solutions of LiDAR are based on the time-of-flight detection method. In time-of-flight LiDAR, a laser pulse is modulated and send out to an object via a scanning mirror. From the time, which the signal takes to return, the distance is inferred (time-of-flight, TOF). A key advantage of time-of-flight is the cost of the lasers, which can be very cheap as the temporal coherence of the laser source is not required to be high. A different approach is based on coherent LiDAR (also known as frequency modulated continuous wave, FMCW, LiDAR) that is an optical analog to the coherent acoustic echolocation strategies used by bats or dolphins. It uses chirped signals to instantaneously determine both distance and velocity of an object. The method is based on homodyne detection, i.e. beating the back-reflected signal with a local oscillator derived from the same laser source and maps time-to-frequency. Critically, if the object moves the return signal frequency will experience also a Doppler shift. Hence, it can also directly measure the relative object speed by virtue of the Doppler effect.
Why FMCW LiDAR?
- Long range distance ranging. Many time-of-flight LiDAR solutions have limitation due to eye-safe power limits. FMCW can increase the photon flux and achieves a 10-100X increase in sensitivity enabling ranging out to beyond 200 m even to low reflectivity objects.
- Directly measures velocity for every pixel simplifying image classification. Objects can be identified faster, because no frame-to-frame analysis or image recognition is required.
- Immunity to interference. Coherent LiDAR rejects all light that is not an exact copy of the transmitted wavelength sweep.
- Reduced peak power and large dynamic range removing concerns about eye safety
- Insensitivity to sunlight glare
- Coherent LiDAR is monostatic, implying that the transmit and receive paths are the same, thus, always aligned.
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This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101035029.