Tuning Optimization of Ring Resonator Delays for Integrated Optical Beam Forming Networks

Abstract

Comprehensive tuning optimization of an integrated optical ring resonator (ORR) based 1 × 4 optical beam forming network (OBFN) for W-band millimeter wave (mmW) phased arrays is reported. The OBFN chip is implemented using a ultralow loss silicon nitride technology and a two stage binary tree topology. The delay responses of a single-and multiORR delay line were carefully measured, and the results agree well with a lossless theoretical model. Tuning of an ORR was calibrated and verification experiments were performed to verify the tuning accuracy. A flattened delay response for a 3-ORR delay line was achieved, demonstrating a bandwidth of 6 GHz and dynamic tuning range of 209 ps, which corresponds to a phase shift of 33.4π for an 80-GHz signal. A larger bandwidth can be achieved by reducing the dynamic tuning range. The result is promising for high data rate mmW communications with beamforming. Index Terms-Microwave photonics, millimeter wave communication, optical ring resonators, phased arrays, photonic integrated circuits, true time delays.

Wideband Beam Steering Concept for Terahertz Time-Domain Spectroscopy: Theoretical Considerations

“…They have been used as optical switches [ 24 ], filters [ 25 ], modulators [ 26 ], and ODUs in photonic beam steering networks [ 14 , 15 , 16 ]. For applications that require wideband operation, ORRs with slightly different resonant frequencies have been cascaded to achieve a flat group delay response within a couple of GHz [ 16 ]. The ORR has a group delay characteristic that is periodic in frequency with an FSR that is determined by the optical perimeter of the ring.…”

“…The emitted beam can be steered by adjusting the time delays between the optical signals at the photonic terahertz emitters. This concept is known from photonic communications and is commonly referred to as photonic true time delay beam steering [ 12 , 13 , 14 , 15 , 16 ]. The delays introduced in the infrared domain are translated directly to the terahertz domain.…”

“…Most prominently, integrated optical ring resonators (ORRs) have been proposed by Meijerink et al [ 14 ] and successfully implemented by Zhuang et al [ 15 ] as variable optical delay units (ODUs) for X-band communications. More recently, ORRs have been demonstrated for photonic beam steering for W-band communications by Liu et al [ 16 ]. The group delay response of ORRs is intrinsically narrowband and periodic in the frequency domain.…”

“…The group delay response of ORRs is intrinsically narrowband and periodic in the frequency domain. Although bandwidths of a few GHz have been reported by cascading several rings [ 16 ], this is still orders of magnitude too small for THz TDS.…”

Wideband Integrated Optical Delay Line Based on a Continuously Tunable Mach–Zehnder Interferometer

“…The ring delay line considered for the comparison has a single ring resonator equipped with a tunable coupler that allows to control the amount of optical power K coupled in and out of the resonant cavity. Also for this structure the normalized group delay as function of frequency and coupling coefficient K can be analytically calculated [22]. The comparison is done through normalized quantities and hence the actual unbalance of the Mach-Zehnder and length of the ring do not play a role and results can be applied to delay lines of any length.…”