Author Affiliations
1State Key Laboratory of Advanced Optical Communication Systems and Networks, Shanghai Jiao Tong University, Shanghai 200240, China2SJTU-Pinghu Institute of Intelligent Optoelectronics, Pinghu 314200, Zhejiang, Chinashow less
Fig. 1. Structure of optical beamforming network (OBFN). (a) Three microring resonators (MRR) basic delay unit; (b) 1×N binary tree OBFN chip
Fig. 2. Simulated delay spectra of MRR at various coupling coefficients
Fig. 3. Simulated delay results of OBFN. (a) Delay spectra of the longest path in different stages of OBFNs with each BDU continuously tuned to 5 ps; (b) delay bandwidth of the longest path in different stages of OBFNs with one MRR continuously tuned in each stage
Fig. 4. Pictures of chip before and after packaging. (a) Microscopy image of BDU chip; (b) cross section of Si3N4 waveguide; (c) microscopy image of 1×8 OBFN chip; (b) picture of packaged chip with optical and electrical connections
Fig. 5. Schematic of experimental setup for optical and microwave measurement
Fig. 6. Flowchart of optical and microwave group delay calibration
Fig. 7. Optical calibration of MRRs. (a) Measured thermal efficiency of MRR phase shifter (MRR PS); (b) simulated transmission spectra of an MRR at various coupling coefficients; (c) MSE of optical transmission as a function of MZI PS power for K=1 state calibration; (d) measured optical transmission of a BDU at the shortest and the longest delay states
Fig. 8. Optical characterization for MRR resonance alignment. (a) Process of MRR resonance alignment; (b) power relationship between MZI phase shifter and microring phase shifter for resonance alignment
Fig. 9. Measured delay spectra of a continuously tuned MRR at different coupling coefficients
Fig. 10. Experimental results of microwave delay characterization. (a) Microwave delay spectra of optical characterization results, where MRRs are affected by thermal crosstalk; (b) measured microwave delay spectra of path 7 as MRRs are digitally tuned from K=0 state to K=1 state one by one, where MRR states are optimized to eliminate the effect of thermal crosstalk; (c) microwave delay spectra of three continuously tuned MRRs at various delay increments; (d) delay fluctuation of three continuously tuned MRRs over the frequency of 08 GHz at various delay increments
Content | This work | OBFN[10] | OTTDL[19] | OBFN[23] | OTTDL[24] | OBFN[31] |
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Material platform | Si3N4 | Si3N4 | Si3N4 | SOI | SOI | Si3N4 | Input×output | 1×8 | 1×4 | 1×1 | 1×4 | 1×1 | 1×8 | Bandwidth /GHz | 8 | 6.3 | 9 | 2 | 16 | 2.5 | MRR number | 36 | 8 | 4 | 5 | 4 | 12 | Delay range /ps | 0560 | 8.7208.7 | 0209.4 | 36200 | 0160 | 1801200 | Delay fluctuation /ps | 11.2 | 16 | 8.5 | | 6.2 | 100 | Automatic calibration | Yes | No | No | Yes | No | No |
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Table 1. Comparison of several integrated OBFNs and optical true time delay lines based on cascaded MRRs