Low-loss chip-scale programmable silicon photonic processor

Chip-scale programmable optical signal processors are often used to flexibly manipulate the optical signals for satisfying the demands in various applications,such as lidar,radar,and artificial intelligence.Silicon photonics has unique advantages of ultra-high integration density as well as CMOS compatibility,and thus makes it possible to develop large-scale programmable optical signal processors.The challenge is the high silicon waveguides propagation losses and the high calibration complexity for all tuning elements due to the random phase errors.In this paper,we propose and demonstrate a programmable silicon photonic processor for the first time by introducing low-loss multimode photonic waveguide spirals and low-random-phase-error Mach-Zehnder switches.The present chip-scale programmable silicon photonic processor comprises a 1×4 variable power splitter based on cascaded Mach-Zehnder couplers(MZCs),four Ge/Si photodetectors,four channels of thermally-tunable optical delaylines.Each channel consists of a continuously-tuning phase shifter based on a waveguide spiral with a micro-heater and a digitally-tuning delayline realized with cascaded waveguide-spiral delaylines and MZSs for 5.68 ps time-delay step.Particularly,these waveguide spirals used here are designed to be as wide as 2μm,enabling an ultralow propagation loss of 0.28 dB/cm.Meanwhile,these MZCs and MZSs are designed with 2-μm-wide arm waveguides,and thus the random phase errors in the MZC/MZS arms are negligible,in which case the calibration for these MZSs/MZCs becomes easy and furthermore the power consumption for compensating the phase errors can be reduced greatly.Finally,this programmable silicon photonic processor is demonstrated successfully to verify a number of distinctively different functionalities,including tunable time-delay,microwave photonic beamforming,arbitrary optical signal filtering,and arbitrary waveform generation.

Reconfigurable multichannel amplitude equalizer based on cascaded silicon photonic microrings

A compact on-chip reconfigurable multichannel amplitude equalizer based on cascaded elliptical microrings is proposed and demonstrated experimentally.With the optimized structure of the elliptical microring with adiabatically varied radii/widths,the average excess loss for each channel in the initialized state is measured to be less than 0.5 d B,while the attenuation dynamic range can be over 20 d B.Flexible tunability through the overlapping of the resonance peaks of adjacent wavelength-channels enables even higher attenuation dynamic ranges up to50 d B.Leveraging the thermo-optic effect and fine wavelength-tuning linearity,precise tuning of the resonance peak can be implemented,enabling dynamic power equalization of each wavelength-channel in wavelengthdivision-multiplexing(WDM)systems and optical frequency combs.The proposed architecture exhibits excellent scalability,which can facilitate the development of long-haul optical transport networks and high-capacity neuromorphic computing systems,while improving the overall performance of optical signals in WDM-related systems.

Wavelength-selective 2 × 2 optical switch based on a Ge2Sb2Te5-assisted microring

A novel wavelength-selective 2×2 optical switch based on a Ge2Sb2Te5(GST)-assisted microring-resonator(MRR)is proposed.The present GST-assisted MRR consists of two access optical waveguides and an MRR coupled with a bent GST-loaded silicon photonic waveguide.The 2×2 optical switch is switched ON or OFF by modifying the GST state to be crystalline or amorphous.In particular,the microring waveguide and the bent GST-loaded waveguide are designed to satisfy the phase-matching condition when the GST is crystalline.As a result,the MRR becomes highly lossy and the resonance peak is depressed significantly.On the other hand,when it is off,there is little coupling due to the significant phase mismatching.Consequently,one has a low-loss transmission at the drop port for the resonance wavelength.In this paper,the simulation using the three-dimensional finite-difference method shows that the extinction ratio of the designed photonic switch is^20 d B at the resonance wavelength,while the excess losses at the through port and drop port are 0.9 d B and 2 d B.In particular,the resonance wavelength changes little between the ON and OFF states,which makes it suitable for multichannel wavelength-division-multiplexing systems.