Arrayed Waveguide Grating Employing Integrated Waveguide Turning Mirror

Optical Wavelength Multi/Demultiplexer is one of the key components for DWDM (Dense Wavelength Division Multiplexing) system. Several options are available for realizing the multi /demultiplexing function, such as the MDTFF (Multiple Dielectric Thin Film Filter), FBG (Fiber Bragg Grating) and AWG (Arrayed Waveguide Grating),etc. Among these options, AWG, with its outstanding performances in this regard, takes an essential part. Especially when dealing with large channel number requirement, AWG shows obvious advantages. Silicon, which bears excellent optical properties, is not only the basic material for IC (Integrated Circuit) and MEMS (Micro-Electro-Mechanical-System), it is also one of the important materials for integrated optics. This article is just about the union of the above-said, and that is, the research on Arrayed Waveguide Gratings based on SOI material.Bent waveguide is an indispensable unit of structure used in PLC (Planar Lightwave Circuit). Especially in the design of AWG, the arrayed waveguide part is almost inevitably composed by bent waveguides. However, because of the large bent radius, the size of SOI-based AWG is difficult to minimize. In this article, we adopted the IWTM (Integrated Waveguide Turning Mirror) in to the structure of the AWG and substitute the original bent waveguides array with a structure of straight waveguides integrated with IWTM. Thus the chip size of the device is successfully reduced.At the beginning of this article, some characteristics of SOI-based ridge waveguide are summarized, including the single-mode condition, calculation of the effective index, bending loss, waveguide-waveguide coupling loss, waveguide-fiber coupling loss, polarization dependence, etc. Meanwhile, some traits concerning the SOI-based IWTM, such as the structure, the loss origins, the polarization dependent reflection, are concluded.We based our design of IWTM-AWG on traditional AWG design procedure. But particularly, we made exquisite rearrangement for the arrayed waveguides part. This new configuration can not only realize the same length difference between adjacentarrayed waveguides, it also preserved the symmetric structure of the traditional AWG without any disturbance on the waveguides. Calculations and analysis concerning loss, cross-talk and polarization dependence are also presented to discuss the impact this new configuration has on the performance of the IWTM-AWG. Photo masks are designed with full consideration for the fabrication tricks. What's more is that we used the Matlab programming method to write the photo masks which greatly reduces the odds of drawing mistakes.Based on the hands-on study of the experiments processes, we optimized the parameters used in fabrication. With respects to these efforts, we are finally able to present the first SOI-based IWTM-AWG with obvious demultiplexing function. Test results show that the on-chip loss of the IWTM-AWG is less than lOdB, with a cross talk level around -23dB and a 3dB-bandwidth of 0.25nm. The channel spacing is 1.58nm and the PDCW (Polarization Dependent Wavelength Shift) is 0.068nm while the PDL (Polarization Dependent Loss) is negligible. Comparison result shows that the chip size of the IWTM-AWG is obviously reduced. Related paper is published by the IEEE-Photonics Technology Letters.We are still trying to improve the device performances. Chips with smaller sizes and better performances are expected to be achieved in future endeavors.