Graphene-based fine-tunable optical delay line for optical beamforming in phased-array antennas

Abstract

The design of an integrated graphene-based fine-tunable optical delay line on silicon nitride for optical beamforming in phased-array antennas is reported. A high value of the optical delay time (τ_g=920 ps) together with a compact footprint (4.15 mm²) and optical loss <27 dB make this device particularly suitable for highly efficient steering in active phased-array antennas. The delay line includes two graphene-based Mach-Zehnder interferometer switches and two vertically stacked microring resonators between which a graphene capacitor is placed. The tuning range is obtained by varying the value of the voltage applied to the graphene electrodes, which controls the optical path of the light propagation and therefore the delay time. The graphene provides a faster reconfigurable time and low values of energy dissipation. Such significant advantages, together with a negligible beam-squint effect, allow us to overcome the limitations of conventional RF beamformers. A highly efficient fine-tunable optical delay line for the beamsteering of 20 radiating elements up to ±20° in the azimuth direction of a tile in a phased-array antenna of an X-band synthetic aperture radar has been designed.

Integrated Microwave Photonics for Wideband Signal Processing

“…It should be noted that a considerable delay of 627 ps can be achieved in the over-coupling condition while maintaining the optical loss less than 25 dB. Optical delay lines can also be realized via adopting a series of Mach Zehnder Interferometer (MZI) or microring resonator-based optical switches, thus generating a tunable time delay controlled by the optical path change [45][46][47][48]. In [48], for example, a delay element based on microring resonators in combination with graphene-based Mach-Zehnder interferometer switches is reported on a silicon nitride platform, demonstrating an optical delay up to 920 ps with optical loss less than 27 dB.…”

“…Optical delay lines can also be realized via adopting a series of Mach Zehnder Interferometer (MZI) or microring resonator-based optical switches, thus generating a tunable time delay controlled by the optical path change [45][46][47][48]. In [48], for example, a delay element based on microring resonators in combination with graphene-based Mach-Zehnder interferometer switches is reported on a silicon nitride platform, demonstrating an optical delay up to 920 ps with optical loss less than 27 dB. Additionally, optical delay lines based on photonic crystal (PhC) waveguides [49,50], which allow flexible dispersion control, offer an attractive solution to support the realization of an on-chip signal processor.…”

Design of an ultra-compact graphene-based integrated microphotonic tunable delay line

“…Typical requirements for optical delay lines used in Synthetic Aperture Radar (SAR) systems for Earth observation applications are a broad bandwidth (B ⩾ 1 GHz), wide and continuous delay tunability (delay range in the order of hundreds of picoseconds), fast reconfigurability, and low power consumption [6].…”

“…However, electro-optic approach is typically affected by high values of absorption loss that could be limited only with optimized design and manufacturing technique. Recently, optical delay lines based on the electro-optic tuning realized with a graphene structure have been proposed [6,[22][23][24]. The great interest in graphene is due to its unique optical properties and several graphene-based optical devices have been exploited for several applications, such as antennas [25], optical modulators [26][27][28], photodetectors [29,30] and optical sensors [31].…”

Performance evaluation of optical beamforming-based wideband antenna array (Invited Paper)

“…Thanks to the intrinsic advantage of large instantaneous bandwidth brought by optical technologies, broadband and large-range true time delay (TTD) can be easily implemented in the optical domain [8][9][10][11][12] . Thus, complex waveforms with larger instantaneous bandwidth can be applied, which enables distinctive features such as better resolution for ranging [13] , larger suppression of grating lobes [14,15] , and higher speed in wireless communications [16,17] .…”