Determining the minimum number of arrayed waveguides and the optimal orientation angle of slab for the design of arrayed waveguide gratings
Introduction
Wavelength-division multiplexing (WDM) technique is considered as a promising solution to meet the demand of tremendous information transmission in the current telecommunication network because it expands the network’s capacity and also offers flexibility for the construction of novel network architectures [1], [2]. Arrayed waveguide gratings (AWGs), which are also known as Dragone–Smit router or PHASAR, are key devices in WDM systems in which they can serve as multiplexers, demultiplexers and wavelength routers [3], [4], [5]. AWGs have been developed commercially using various types of materials such as SiO2/Si, InP and polymer [6], [7], [8]. We present here an optimal design of a 16 × 16 AWG demultiplexer based on the silica-based (GeO2:SiO2) sol–gel process which is considered as a flexible and low-cost method for fabricating integrated optical devices with highly tailor-able properties [9]. The design and fabrication issues of AWG components, especially crosstalk, insertion loss and non-uniformity of the transmission spectrum are of great importance. In this paper, firstly, we describe the schematic layout of the AWG and the primary consideration in searching for suitable parameter values of the sol–gel film. Secondly, a simple criterion for determining the minimum number of arrayed waveguides is presented using the design theory of the AWG and Fraunhofer diffraction. In addition, some parameters such as the waveguide separation and the orientation angle of the slab waveguide are chosen to optimize the AWG structure to satisfy the performance specifications and to meet the fabrication conditions in our laboratory. Finally, simulation results of the designed AWG using the beam propagation method (BPM) confirmed the effectiveness of selected parameters such as the number of arrayed waveguides on the performance of the AWG.
Section snippets
Structure design
Fig. 1 shows the schematic layout of an N×N AWG multiplexer. It consists of plural input/output waveguides (i.e., I/O channels), two slab waveguides (i.e., free propagation region (FPR)) and a phase-array of multiple channel waveguides with a constant optical path difference of ΔL between adjacent arrayed waveguides. The locations of the input/output waveguides, concave slab waveguides and arrayed waveguides are based on a Rowland-circle construction. A WDM signal launched into one of the input
Results and discussion
A 16 × 16 AWG is designed with a wavelength channel spacing of Δλ=0.8 nm. Table 1 shows the values of the parameters used in the simulation by using the BPM. Fig. 7 shows the transmission spectral response of the designed AWG for the TM mode. It can be seen that the spectral response of the AWG meets the required specifications such that the crosstalk of adjacent channels is well below −30 dB, the insertion loss is less than 3 dB without including the absorption loss of the sol–gel material which
Conclusion
We have presented a criterion for determining the minimum number of arrayed waveguides in the design of AWG by the analysis of Fraunhofer diffraction of the Gaussian mode in the slab waveguide. And the optimal orientation angle θC of the AWG has been obtained by trading off the minimum bent losses of the arrayed waveguides and that of the I/O channel waveguides in our design process. As a sample, a 16 × 16 AWG based on the silica-based sol–gel material has been optimally designed with this method
Acknowledgements
The authors acknowledge the support of the ONFIG Program of A*STAR of Singapore. One of the authors (Jun Zhou) also acknowledge the partial support from the TWAS under the Research Grant Agreement No. 01-137 RG/PHYS/AS, and the ICTP Programme for TRIL, Trieste, Italy.
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