平面传播宽光谱–窄带通滤波片的优化设计与研究

Optimal Design and Investigation for the Traveling-in-Plane Filters Having Both Wide-Spectrum Region and Narrow-Band Passing

摘要: 光通信领域中随着光芯片研究与应用的迅猛发展，光学窄带滤波在其中愈发重要。传统的干涉滤波片是通过高低折射率材料层的对称性交替结构形成，通过逐层镀膜来实现，而其操作方式是：被滤波的光波垂直穿过滤波片平面。然而，对于平面内传播的导波而言，多层干涉滤波片需要垂直插入波导通道中，从而各层的1/4波长光学厚度给设计与加工都带来更大难度。对此，本文针对红外光区域设计了氮化硅为芯和氧化硅为包层的单模波导结构，并分别作为高低折射率层设计了截止型干涉滤光片，进而设定了截止点方向相反的两个截止滤光片，最后还将其与多层干涉滤波片结构复合在一起形成复合型窄带滤光片。研究中，利用传输矩阵法对窄带滤波片的带通性能进行了系统性数值模拟，对带通信号半高宽、自由光谱区域和透射率性能进行分析，并利用TFCalc软件对器件性能进行了优化。结果表明：优化的窄带滤波片较传统结构有着更加优越的滤波性能；复合型干涉滤光片有着更加出色的滤波和截止性能，实现了≤ 1.0 nm半高宽带通峰值和≥ 150 nm单侧自由光谱区；单侧截止斜度达到≤ 0.01 nm，达到了实际通信系统的要求。

Abstract: In the field of optical communications, with the booming development and applications of integrated photonic circuits, the optical narrow band-passing filtering function is paramount important. The traditional narrow-band filter is formed by symmetric alternating high-/low-index layers and its operating form is that the filtered beam normally passes through the filter plate. Nevertheless, for a guided-wave traveling in a plane film, the multiple high-/low-index layers need to be vertically inserted a waveguide channel, so the λ/4 optical thickness of each layer leads to the bigger difficulty in fabrication. To overcome such a problem, in the infrared (IR) area this work designs a Si₃N₄-core/SiO₂ clad single-mode SiN waveguide, then uses Si₃N₄-layer SiO₂-layer as high-(H) and Low-index (L) layers, respectively, to form two cutoff filters having the inverse cutoff-points, and finally combines with multilayer interference structure to create a hybrid narrow-band filter. In study, with transfer matrix model, the band-passing performance of filter is systematically numerical simulated, and then the full width at half-maximum (FWHM), free spectral region (FSR) and transmittance are analyzed, and are further optimized by TFCalc software. Results: the optimal narrow-band filter has better filtering property than the traditional ones; the hybrid filter has the excellent performance in both filtering and cut-off, illustratively, a ≤ 1.0 nm FWHM and a ≥ 150 nm FSR, and ≤ 0.01 nm single-side slope are implemented, so meeting the requirements of industrial systems.