A Seven Bit Silicon Optical True Time Delay Line for Ka-Band Phased Array Antenna

Abstract

A seven-bit optical true time delay unit with a delay tuning increment of 1.42 ps was designed and fabricated on silicon photonics platform, which can be utilized in Ka-band phased array antenna systems. The delay unit consists of eight thermo-optical switches and seven waveguide delay lines with different lengths. By manipulating the states of the thermo-optical switches, 128 stages of discrete time delays varying from 0 to 191.37 ps has been obtained with low average power consumption of 178.77 mW. Besides, the integrated delay unit was fabricated on the silicon-on-insulator chip that has a very compact footprint of 7.4 mm × 1.8 mm. In addition, as the waveguide delay dependence on the modulation frequency is very limited and can be neglected, the proposed delay unit should process a large bandwidth that allows it to be utilized in microwave applications with abundant bandwidth.

A Tunable Optical Delay Line Based on Cascaded Silicon Nitride Microrings for Ka-Band Beamforming

“…Compared to Ref [5], much larger delay tuning range is achieved in our work with larger bandwidth, and cascaded MRRs are relative simple and easy to fabricate compared to waveguide Bragg gratings. Compared to Ref [9], larger delay tuning range is achieved in this work, although the bandwidth of switchable waveguides should be much larger than cascaded MRRs, only discrete delay can be switched, which will limit the beam direction resolution.…”

“…The beam squint can be effectively avoided by replacing the electrical phase shifters with microwave photonics optical delay lines (ODLs), which have lower transmission loss, larger bandwidth, and immunity to electromagnetic interference [2], [3]. With the development of integrated microwave photonics, a variety of integrated ODLs have been proposed, such as photonic crystal waveguides [4], waveguide Bragg gratings [5], [6], optical switchable waveguides [7]- [9] and microring resonators (MRRs) [10]- [22]. Among them, the ODL structures based on optical switchable waveguides and tunable MRRs are relative simple and easy to fabricate.…”

“…And both of them can be easily realized on the CMOS compatible platforms such as the silicon on insulator (SOI) and silicon nitride (Si 3 N 4 ). In our previous work [9], we have realized a seven-bit ODL based on the optical switchable SOI waveguides, which is suitable for Ka-band beamforming. And the proposed ODL was designed with a delay increment of 1.42 ps.…”

Microwave Photonic Array Radars

“…The chip has a size of 4.5 cm × 8.5 cm, but the time delay can reach 2.35 ns. Similarly, using thermo-optical switches and silicon delay lines, a 7-bit true time delay was achieved on a 7.4 mm × 1.8 mm chip, which could produce a maximum delay of 191.37 ps [78]. In addition to the thermo-optical switches, MEMS-based switches can also be integrated on a chip [79], [80].…”

“…20 shows the state-of-the-art of the integrated optical true time delays. It should be noted that the bandwidth of the optical true time delay line itself, no matter based on dispersive waveguide [113], [114] or waveguide with different length [78], [109]- [113], can be extremely high, since it is essentially frequency insensitive. When it is co-integrated with other electrooptic devices to realize a phased array radar, the upper limit of the operation bandwidth is finally determined by the electrooptic devices, e. g., the EOM or PD, which is typically lower than 40 GHz.…”