CMOS-Compatible Vertical Grating Coupler With Quasi Mach–Zehnder Characteristics

Abstract

A vertical grating coupler on silicon-on-insulator substrates has been designed and demonstrated. The light from a vertical fiber can be coupled in and split equally into two arms with the fiber placed in the grating center. An optical combiner is used to collect the transmission from the two arms. The measured peak coupling efficiency is 37%. Our device can also function like a Mach-Zehnder interferometer. In a device with an arm difference of 30 µm, the normalized transmission spectra of 20-nm free spectral range and more than 12-dB extinction ratio at 1567 nm are obtained.

Highly efficient vertical fiber interfacing grating coupler with bilayer anti-reflection cladding and backside metal mirror

“…To measure the in-plane coupling, up-reflection and substrate leakage, four power monitors were utilized in the different directions. In order to increase the coupling efficiency, the grating groove depth and the grating periods number is chosen to be 70nm and 20 respectively, which is already demonstrated by our prior work [21] . Besides, the Si 3 N 4 /SiO 2 top claddings are inserted to this design as well.…”

“…These techniques, however, need extra etching or high-precision lithography steps, which increase the fabrication cost drastically and impair the fabrication error tolerance. In order to avoid the relatively complicated design or implementation steps, grating coupler which enables vertical to in-plane bidirectional optical transmission [21] [22] is believed to be a good approach. However, parasitic upwards reflection leads to return loss and harmful interference in fiber, which limits both the coupling efficiency and its application.…”

Monolithic Integrated Silicon Photonic Interconnect With Perfectly Vertical Coupling Optical Interface

“…The optical components were carefully designed and their functions were simulated and verified by 3-D finite difference time domain (FDTD) method. As a key component, the bidirectional grating is designed to be a uniform grating coupler for perfectly vertical coupling with optimal geometrical parameters of 580 nm grating period, 70 nm etch depth, filling factor of 47%, and 22 periods [26]. The final design are verified by 3-D FDTD simulation, in which a Gaussian source with 1/e full width of 10.4 m was employed to represent the fiber launch mode and the background index was set to be 1.46 so as to simulate the effect of the oxide cladding layer.…”

“…In our prior work, we demonstrated a perfectly vertical grating coupler with quasi Mach-Zehnder characteristics on silicon-on-insulator (SOI) substrate [26]. In this paper, we proposed and demonstrated a monolithic integrated photonic interconnect based on such configuration.…”

Low-loss chirped grating for vertical light coupling in lithium niobate on insulator

“…Grating couplers (GC), considered to be the mainstream approach of all light coupling methods, have the advantage of high alignment tolerance and the ability to couple light to/from the chip at arbitrary locations, hence facilitating dense integration of optical components [8,9]. In addition, GC can be used as key components of optical circuits, such as a beam splitter [10]. Reports of GC fabricated on LNOI so far either have low CE [11,12] or require additional layers and a more complicated fabrication process to attain high CE [13].…”