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

Abstract

We report a vertical chirped grating coupler with high coupling efficiency (CE) fabricated on lithium niobate on insulator (LNOI). According to finite difference time domain simulations, loss in a uniform grating in LNOI comes from downward diffracted light, internal reflections, and mode mismatch between the single-mode fiber and the out-coupled light from the grating. A chirped grating coupler, whose parameters were optimized to reduce the mode mismatch loss and internal reflections, was fabricated with integrated waveguides through a single etch-step and exhibited insertion losses as low as 3.6 dB, 1.9 dB lower than a uniform grating fabricated in the same process. The demonstrated grating features high CE, ease of manufacturing, and the ability to vertically couple light—a fundamental characteristic required to facilitate the integration of on-chip laser sources and detectors.

Microdisk lasers on an erbium-doped lithium-niobite chip

“…Subsequently, Cai's group [19] designed an electro-optic modulator on the basis of a silicon-LN hybrid integrated platform, with a modulation bandwidth of more than 70 GHz and a modulation rate of 112 Gbit/s. To achieve high-efficiency coupling between off-chip and on-chip LNOI devices, grating couplers [20,21] and tapered waveguides or tapered fibers were introduced into the system, and coupling efficiency up to 73.8% [22,23] was reported. Generally, an integrated optical system includes light sources, detectors, and devices with transmission and control functions.…”

Rejuvenating a Versatile Photonic Material: Thin‐Film Lithium Niobate

“…In general, further improvement in terms of fiber-to-chip interface coupling, [92][93][94][95][96][97][98][99] careful consideration of electrical, RF, and optical packaging, and thermal/temporal reliability and stability studies are expected to be achieved soon for commercialization of fully-packaged TFLN devices. Heterogeneous integration of active elements such as lasers, amplifiers, and photodetecotrs along with various TFLN components on single photonic chip is another front which is expected to attract extensive research for a host of applications such as optical communication transceivers, high-performance computation, analog, digital, and quantum communication links, and LiDAR systems.…”

“…In recent years, based on this rapidly-growing technology, a plethora of ultracompact integrated photonic devices and circuits, such as microdisk [59][60][61][62] and microring [46,[63][64][65][66] resonators, EO modulators, [67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85] acousto-optic modulators, [86][87][88][89] photodetector, [90] integrated single-photon detector, [91] grating couplers, [92][93][94][95][96] fiber-to-chip edge couplers, [97][98][99] wavelength Figure 2. Summary of the steps for fabrication of TFLN on Si wafers.…”

Efficient light coupling between an ultra-low loss lithium niobate waveguide and an adiabatically tapered single mode optical fiber

“…Generally, grating couplers, considered to be an important coupling method, have the advantage of high alignment tolerance. However, large insertion losses hinder its further practical application [28,31]. The end-face coupling on a hybrid silicon nitride/LN platform suffers from large coupling loss (> 6 dB/facet) due to the serious mode mismatch between the optical fiber and microscale LN waveguide [27].…”