Ultra-compact optical 90° hybrid based on a wedge-shaped 2 × 4 MMI coupler and a 2 × 2 MMI coupler in silicon-on-insulator

Abstract

We propose an ultra-compact optical 90° hybrid with the smallest length of 107μm, consisting of a wedge-shaped 2 × 4 MMI coupler connected with a 2 × 2 MMI coupler using silicon nanowaveguide technology. Neither cascaded phase shifters nor waveguide crossings are attached to the proposed 90° hybrid in coherent receiving system. The proposed device is demonstrated on silicon-on-insulator (SOI) with 220nm thick top-silicon layer and 2μm thick buried oxide layer. A high performance of the proposed 90° hybrid is exhibited experimentally with a high extinction ratio larger than 20dB, an excess loss mostly less than 0.5dB, a common mode rejection ratio better than -20dB and phase deviation within the range of 5° over C-band spectral range.

Compact and low loss 90° optical hybrid on a silicon-on-insulator platform

“…We implemented two kinds of test structures to characterize different performance metrics of the 90º optical hybrid. One kind of test structure has a Mach-Zehnder (MZ) delay interferometer with a length difference of 126 µm before the 90º optical hybrid used to extract phase error [14,15]. The four outputs of the 90º optical hybrid are connected directly to grating couplers.…”

“…There are two major types of 90° optical hybrids: Type-I is based on several discrete components such as 1x2 couplers, 2x2 couplers and phase shifters [8][9][10][11]; Type-II is based on a single device such as a 4x4 multimode interference (MMI) coupler [12,13]. There are designs constructed by 2x4 MMI couplers followed by 2x2 MMI couplers [14][15][16], which can be regarded as a derivative of Type-II hybrid.…”

“…Type-II hybrids are generally the solution of choice in high-index-contrast platforms like deeply-etched indium phosphide (InP) [13,14,20] and silicon-on-insulator [12,15,21] because they are fully passive and require no active control loop to stabilize the 90° phase relation. However, governed by the self-imaging theory [22][23][24], to realize optimum self-imaging, 90° optical hybrids based on 4x4 MMI couplers or 2x4 MMI couplers usually have a length of hundreds of micrometers.…”

硅基光电子学的最新进展

“…MMI 耦 合 器 是 基 于 自 映 像 效 应 (Self-Image Effects)原理完成 90°光混频功能, 光进入多模波导后 被分裂为许多模式, 各模式之间相互干涉传播, 在特 [120,121] 、2×2 MMI 耦合器组合 [122,123] 和 2×4 MMI 耦 合器组合 [124][125][126] . 其中 4×4 MMI 耦合和 2×2 MMI 耦 合器组合存在波导交叉的现象, 带来交叉损耗和信 号间的干扰, 影响传输信号的质量, 普通矩形 2×4 MMI 耦合器组合 [124,125] 调制器的性能好坏时, 一般要考虑以下几种参数: 调 制深度, 也叫消光比, 是关于最大传输光强度与最小 传输光强度的比例.…”

A novel polarization converter and filter based on MMI couplers in silicon-on-insulator

“…It is noted that the difficulty for polarizationdivision multiplexing (PDM) signal processing is mainly due to the polarization sensitivity induced by the silicon nanoscale devices [2]. Mode conversion provides a method to overcome this problem by converting TM polarized light to TE polarized light since many devices for TE polarized light has been demonstrated in optical transmission system such as hybrids [3]. An optical filter is also needed to eliminate the noise and increase the optical signal to noise ratio (OSNR) in optical transmission.…”