Design and Fabrication of O-band Silicon-based Silicon Dioxide Dense Wavelength-division Multiplexing AWG
The O-band wavelength division multiplexer is a key component for high-speed interconnection in data centers.Thin film filters and array waveguide gratings are two commonly used technical solutions.The silica based array waveguide grating wavelength division multiplexer has the advantages of low loss and integration,becoming the main technology of data center wavelength division technology.This article adopts a silica based optical waveguide material with a relative refractive index difference of 0.75％.Based on the diffraction equation,an O-band 48 channel,120 GHz channel spacing flat top dense wavelength division multiplexing array waveguide grating chip is designed,with a single-mode waveguide cross-section of 6 μm×6 μm.Using the beam propagation method,the effective refractive index of the flat waveguide at the center wavelength was calculated to be 1.456 4,the effective refractive index of the array waveguide was 1.454 4,the group refractive index was 1.474 7,and the spacing between the array waveguides was selected to be 8 μm.The output waveguide spacing is 26 μm.The diffraction order is 31,and the difference in length between adjacent array waveguides is 27.708 μm.The focal length of Rowland circle is 14 256.97 μm.The number of waveguide arrays is 401,and the designed chip size is 4.4 cmX 3 cm.The AWG preparation adopts a planar optical path integration process,and the silicon substrate undergoes silicon thermal oxidation at 1 050 ℃ to form 20 μm-thick SiO2 lower cladding,followed by growth of 6 μm GeO2-SiO2 core layer using Plasma Enhanced Chemical Vapor Deposition(PECVD)technology.Using contact exposure lithography technology and inductively coupled plasma etching technology to achieve good pattern transfer.Subsequently,20 μm boron phosphorus silicate glass undercladding is formed through PECVD,which the refractive index is consistent with that of the lower layer SiO2.The wafer is cut and polished to an angle of 8° on the end face to reduce return loss.Place the AWG chip on an alloy material rack and cut a slot at a specific part of the AWG input Rowland circle.The input and output waveguides are coupled with the fiber array respectively.Adjust the metal screw on the alloy rack to ensure that the central wavelength is at the International Telecommunication Union(ITU)wavelength.The metal screw contracts or extends with temperature changes,pushing the input Rowland circle up and down to compensate for the drift of the AWG chip's response spectrum wavelength due to temperature,stable response spectrum was achieved within the temperature range of-5 ℃ to 65 ℃.Using an O-band tunable laser,polarization controller,and power detector,the output spectrum of the packaged AWG module was tested.The insertion loss was between-5.31 dB and-6.59 dB,with a channel spacing of 120 GHz.The 1 dB and 3 dB bandwidths were 0.41 nm and 0.55 nm,respectively.Adjacent crosstalk and non-adjacent crosstalk were 29.4 dB and 29.2 dB,respectively,and polarization related loss was less than 0.67 dB.Using a temperature controller to change the ambient temperature of the AWG module,within the temperature range of-5 ℃ to 65 ℃,the center wavelength drift was reduced from 7 pm/℃ to 0.6 pm/℃,demonstrating good temperature stability.Using an error code analyzer,lithium niobate modulator,and sampling oscilloscope,high-speed signal transmission was carried out for two modulation methods of Non Return to Zero(NRZ)and 4 Pulse Amplitude Modulation(PAM-4)signals in the AWG module.The results showed that the modulation transmission eye diagrams of 26.56 Gbps non zero and 53.12 Gbps 4-level signals were clear,with extinction ratios greater than 5.5 dB and 3.6 dB,respectively,and the total transmission capacity of 48 channels reached 2.4 Tbps.
Arrayed waveguide gratingsDense wavelength division multiplexingData centerSilica-based waveguideNon return to zero modulation4 pulse amplitude modulation
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