光栅周期包含的Bragg层数对Bragg型凹面衍射光栅的影响

单个衍射光栅周期所包含的Bragg周期层数是连续Bragg齿型凹面衍射光栅的主要参数之一,该参数可改变光栅齿结构,对凹面衍射光栅的分辨力.自由光谱范围及衍射效率有重要影响.本文通过理论分析与仿真模拟,对比了4种不同层数的Bragg型凹面衍射光栅的特性参数.研究结果表明:在衍射光栅尺寸不变的情况下,改变单个光栅周期包含的Bragg周期层数不会显著提高器件主衍射级次的分辨力;单个光栅周期包含的Bragg周期层数与光栅可衍射的级次数成正相关.单周期层数的Bragg凹面衍射光栅的主衍射级次效率最高,其可衍射的级次数最少,且其他衍射级次分散的能量最少;增加单个光栅周期所包含的Bragg周期层数会降低主衍射级次的自由光谱范围.该研究对于设计低插损、高分辨率、宽工作波段的波分复用器或光栅光谱仪具有重要的指导意义.

Effects of Bragg periods per grating period on performance of Bragg concave diffraction grating

Concave diffraction gratings (CDGs) have the advantages of being compact, time reliability, cost effective, and channel spacing accuracy. These devices can be used in the wavelength division multiplexing (WDM) systems and micro-spectrometer devices. However, comparing with arrayed waveguides gratings (AWGs), the development of traditional CDGs is far from satisfactory. Because the traditional CDGs need deeply etched facets and perfect grating profiles to reduce the insertion losses, which will increase the difficulty in etching process. In order to solve this problem, Bragg reflectors based CDGs (Bragg-CDGs) are proposed. This structure can greatly reduce the insertion loss, and reduce the difficulty in etching process. The performance of the Bragg-CDG is determined by both the reflection condition of the Bragg reflectors and the diffraction condition of the CDG. With the Bragg reflection condition determined, the diffraction condition of Bragg-CDG will have a major influence on the performance of device. For successive strips based Bragg-CDG, the number of Bragg periods per diffraction grating period is an important parameter of Bragg-CDG. The diffraction condition of concave gratings is closely related to this parameter. This parameter has an effect on the performance of Bragg-CDG, specially termed resolution, the free spectrum range, and the diffraction efficiency. The effect of the number of Bragg periods per diffraction grating period on the Bragg diffraction grating is studied by theoretical analysis. In addition, four Bragg-CDGs with different numbers of Bragg periods are studied using the finite-difference time domain method. The results show that with sizes of diffraction gratings fixed, the resolution of Bragg-CDG does not have a significant improvement by changing the number of Bragg periods per diffraction grating period; the total number of diffraction orders is proportional to the number of Bragg periods per diffraction grating period. The Bragg-CDG with a single Bragg period per grating period has a maximum diffraction efficiency, since it has the minimal number of diffraction orders; in addition, with the increase of the number of Bragg periods per diffraction grating period, the free spectrum range of the main diffraction order gradually decreases. This research can contribute to the development of the demultiplexer with the low insertion loss, the high resolution, and the wide operating waveband.