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Light detection and ranging (LiDAR) is an important technique for three-dimensional environment reconstruction that is useful for self-driving car, robotic vehicle, agriculture detection and blind guidance. Beam steering in the current LiDAR is accomplished by a mechanical spinning architecture, which is heavy, slow and expensive. Micro-electrical-mechanical system (MEMS) built mirror is an alternative solution to reduce size and cost. However, the mechanical beam steering in both techniques cause reliability issues in long-term precise beam positioning that limit the broad application of the LiDAR.
Optical phased arrayed (OPA) comprise periodic placed emitters with coherent light output by using Silicon photonics. The beam steering in the OPA is accomplished by the interference of coherent light that has no moving parts. Each emitter is modulated and delayed by a pre-determined phase that cause the maximum light intensity has an angle to the emitter plane. This angle is determined by the phase difference in each emitter. Therefore, the beam steering is implemented and controlled by the phase adopted. However, according to the interference theory, second and high-order maximum, the side-lobes, appear at different angles that confuse the LiDAR system by multiple positioning at the same time. In addition, to implement wide angle beam steering, the large amounts of arrayed emitters should be applied. To keep coherent, multiple -3dB light coupling structure were applied. The wide distributed and non-uniform light output between emitters cause the beam steering disturbed.
In this work, instead of wide angle beam steering, we design a linear optical phased array (LOPA) with limited number and closed-distance emitters for small angle beam steering. Practical-wise, multiple LOPA modules could be integrated to implement wide angle beam steering. Finite-element method was used to simulate the 1550 nm beam steering behavior in LOPA. With proper and minimal phase delayed, the intensity of the side-lobes was largely suppressed to the primary light. With proper tuning on the sensitivity of the receiver, the high-order disturbance in the LOPA for LiDAR could be eliminated.
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