We propose a 128-channel SiN-Si dual-layer optical phased array (OPA) chip based on SOI substrate. It combines the low loss characteristics of SiN with the excellent modulation characteristics of Si. Compared with a Si single-layer OPA chip, it avoids the problem of high waveguide loss in the case of high input optical power due to the strong nonlinear absorption effect of Si. Therefore, our double-layer OPA has lower overall waveguide loss and can achieve high output power, which is conducive to long-distance detection. When it works, the beam is emitted from the end faces of its waveguides, with a radiation efficiency over 94%. Since the center spacing of the waveguides in the antenna area is close to the sub-micron scale, a large scanning range of 100.4° is achieved.
We propose an optical beam scanner based on an on-chip 1×100 micro-ring optical switch array. By adopting a combination of optical switch array and lens system, it can achieve beam steering. It uses a simple control circuit to achieve fast beam scanning. The simulation shows that its emission efficiency exceeds 95%, which is conducive to long distance scanning and detection. All the components of this scanner can be fabricated on SOI substrate except for the optical lens, so its cost is low and the overall size of the device can be greatly reduced .In addition, since there are no moving parts in our scanner, it has advantages in performance and service life compared with mechanical optical beam steering devices. These advantages make our scanner is promising in light detection and ranging (LiDAR) field and free space optical communication field.
Si-based photonic integrated circuit is developing rapidly and has been widely used, such as optical communication, optical neural network, lidar and so on. However, Si has strong optical nonlinear effects, which limits the maximum transmitting optical power. It needs numbers of semiconductor optical amplifiers to expand the scale of the photonic integrated circuit because of the limited input optical power, which increases the complexity and cost of the Si-based photonic integrated circuits. Therefore, with much lower the waveguide loss and optical nonlinear effects than Si, SiN waveguide is able to transmit higher optical power and has received a lot of research. In this paper, a grating coupler based on SiN-Si dual-layer structure is proposed. It is composed of a layer of Si grating above the SiN waveguide layer. In the case of coupling from grating coupler to single-mode fiber, the minimum coupling loss is about -1.07 dB at 1563.5 nm, and the 1 dB bandwidth is over 100 nm. As to coupling from single-mode fiber to grating coupler, the minimum coupling loss is about -2.53 dB at 1553.4 nm, and the 1 dB bandwidth is about 65 nm. With the proposed grating coupler, it is able to effectively reduce the coupling loss between the single-mode fiber and the chip, increase the working bandwidth, and achieve higher input power. It is very helpful to reduce the complexity and cost of Si-based photonic integrated circuits, because of the reduced requirements for the number of semiconductor optical amplifiers. This will be useful in Si-SiN hybrid integration and SiN-based photonic integrated circuits.
We propose and numerically investigate a double-cladded athermal waveguide structure aiming at broadband low anomalous dispersion operation. Single-crystal aluminum nitride (AlN) is the core of the waveguide, cladding with silicon oxide (SiO2) and titanium dioxide (TiO2). TiO2 with a negative thermo-optic coefficient (TOC) is used to realize material thermal compensation for AlN. By optimizing the waveguide structure parameters, it shows a near-zero broadband effective TOC, ±4×10-6 /K over a 1770-nm bandwidth from 1830 to 3600 nm. Besides, it also has low anomalous dispersion, from -20 to 20 ps/nm/km in the same wavelength range. Different with the conventional strip waveguide, the waveguide is a double cladded structure, which is easy to fabricate in practice. Furthermore, this structure will not damage the single crystal state of aluminum nitride, maintaining its original excellent optical properties.
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