Nanofiller based spin-on materials for negligible reflection of silicon photonic external coupling

Abstract

Optical out coupling is one of the key research items of silicon photonic packaging. It is necessary to realize robust, high-bandwidth, low-power optical data communication system in an economical way. Because material interfaces are always involved for the coupling, the reflection loss at the interface often occupies a major part of loss. Here we report on an ideal anti-reflection coating method for use with silicon nanophotonics devices. Because the refractive index of silicon is large at about 3.5, the optical reflection at the silicon waveguide boundary is large. We describe a set of nanoparticle-based spin-on materials having indices of 1.8 and 1.2. The former material is suitable for a single layer antireflection coating on a silicon surface and realizes a first order thin reflection suppression which allows large bandwidth and large angle tolerance. The latter material is for coating of the fiber or polymer interface. We studied the feasibility of uniform coating over microlens structures. High index material is also photo patternable, which is desirable for silicon chip integration. IntroductionSignificant progress has been made in silicon nanophotonics technology. New opportunities are being brought to datacom, telecom, and high performance computing by this technology [1][2][3][4][5][6][7][8][9][10]. However, the large scale commercialization of silicon photonics still requires more cost effective optical inputs and output methods. Although there are several potential methods to realize these couplings, the methods have to satisfy the condition of spectral wide band, optical low loss, mechanical reliability, and cost efficiency.There are several approaches that enable the optical coupling between optical waveguides on a silicon photonics chip and an external single mode (SM) optical cable. Current approaches to interfacing silicon nanophotonic waveguides to standard single-mode fibers often use specialized equipment and show significant cost as well as scalability questions [11][12][13][14][15].