Periodic Reporting for period 1 - ChirLog (Chirality based all-optical logic gates)
Reporting period: 2022-07-01 to 2024-06-30
Currently, the optical processing based on optical fibre networks mostly supports the capability of ∼hundreds of Tbits/s. However, the signal conversions of optical-to-electrical and then electrical-to-optical in the fibre communication are limited by the conversion operation bandwidth and communication rates. Further, with the ever-growing demand for carrying and processing data in a fast and efficient way, all-optical computing and processing become a promising candidate for the next generation computing and processing applications, due to many advantages (such as high-speed and parallel data processing), compared with their electronic counterparts. Optical computing and processing can avoid low-efficiency and low-speed opto-electronic signal conversion thanks to their fully reconfigurable ability and multi-function programmability. Indeed, all-optical logic gates are indispensable for optical computing and have been demonstrated to perform all-optical arithmetic binary calculations including addition and multiplication. Current all-optical logic gates mainly use linear and nonlinear optical effects. With the linear optical approaches, common logic gates (e.g. AND, OR, NAND, NOR, XOR, and XNOR) have been demonstrated in various optical structures such as nanowire networks, photonic crystals, plasmonic waveguides and metasurfaces, etc. As many different particles (e.g. electrons, molecules), photons process an intrinsic degree of freedom, chirality. Optical chirality, regarding left-handed and right-handed circularly polarized light, has attracted huge interest for fundamental research (e.g. to study the symmetry of single molecules or carbon nanotubes (my host group work) and applications (e.g. quantum technology, sensing and imaging). However, optical chirality-based computing and processing still remain largely elusive. In this project, we construct a universal ultrafast computing approach with the optical chirality and demonstrate their unique performance advantages, such as atomically thin footprint, multiple gates simultaneous operation in a single device, and broken bandwidth limitations, which is fundamentally different from the conventional optical gates. It suggests that optical chirality could provide a powerful degree of freedom for future optical computing and is promising for quantum computing. After published, this work was picked up by more than 20 news outlets such as ‘EurekAlert’ entitled ’New optical computing approach offers ultrafast processing’; ‘NewScientist’ entitled ‘Light-based computer could outpace traditional electrical chip designs’; ’SciTechDaily’ entitled ‘One Million Times Faster Than Current Technology: New Optical Computing Approach Offers Ultrafast Processing; ‘PhysicsWorld’ entitled ‘Chiral logic gates make ultrafast processors’, which points out that our devices that work using circularly polarized light are a million times faster than current technologies; etc. The journal ‘IEEE Spectrum’ in the reports ‘These Optical Gates Offer Electronic Access Ultrafast optical computing interfaces with traditional circuits’ highlighted that our work reveals a new and promising interface between optical computing and conventional electronic computing. The ‘Semiconductor Engineering’ recommended our work and select it into “Semiconductor Engineering’s library 10 new technical papers of October of 2022. Later on, invited by the editor Professor Lesley Cohen, we wrote a perspective paper entitled ‘Prospect of optical chirality logic computing’ for the journal Applied Physics Letters.
There are three objectives for this project. OBJECTIVE 1: Experimental construction of various chirality logic gates with nonlinear optical processes in monolayer 2D materials. We have demonstrated all-optical chirality logic gates (XNOR, NOR, AND, XOR, OR, and NAND) and a half adder in atomically thin monolayer MoS2 and bulk silica crystal with typical nonlinear optical processes such as second harmonic generation (SHG), sum-frequency generation (SFG), and four-wave mixing (FWM). This underlines the universal applicability of the chirality logic gate concept with different materials (i.e. monolayer and bulk materials) and nonlinear optical processes. Moreover, we demonstrate the reconfiguration of chirality logic gates by taking advantage of the fact that the optical chirality can be flexibly changed with linear optical components, including ultrathin on-chip devices. We also discuss the strategies to reduce the energy consumption (i.e. boosting the nonlinear optical conversion efficiency) and large-scale integration applications via optical fibres and silicon waveguides. OBJECTIVE 2: Simultaneous construction of multiple (>3) ultrafast (at ~ tens of femtoseconds) chirality logic gates in parallel via phase-matching-free nonlinear optics. We demonstrated the simultaneous construction and operation of four chirality logic gates (e.g. Buffer, XNOR, NOT, and NOR) in parallel by simultaneously recording SHG, SFG, and FWM due to the broadband feature of phase matching–free nonlinear optics in the MoS2 monolayer. This shows a fundamentally different logic computing scheme compared to conventional electronic and optical logic gates, which show only one logic operation capability in a single device. We also demonstrated simultaneous multiple chirality logic gates at different input frequency, indicating the frequency-independent nature of our approach. It is beneficial for constructing logic circuits. OBJECTIVE 3: Demonstration of electrically configurable chirality logic gates. We demonstrate the electrical control of the chirality logic gates in a gated MoS2 monolayer device based on the electrically controllable exciton oscillator strength, which directly affects the nonlinear optical signals. The electrical modulation of chirality logic gates sheds light on the interfacing between electrical and optical computing toward next-generation mixed and hybrid computing.
By exploiting the light chirality for the first time, we reported all-optical logic gates via the symmetry enabled chiral selection rule, which offer a completely new strategy for next-generation optical computing. First, it is a significant conceptual advance, indicating a new degree of freedom for computing. We utilized the light chirality for computing via symmetry enabled chiral selection rule, and constructured ultrafast (~<100fs), all-optical logic gates (XNOR, NOR, AND, XOR, OR, and NAND) and a half adder. This concept is fundamentally different from the previously reported optical computing strategies (e.g. intensity, polarization, phase), presenting a new physical approach, which represents a universality of the operation concept. We demonstrated the viability of the concept in the bulk silica crystals and atomically thin semiconductors, via different nonlinear optical processes (e.g. SHG, SFG, and FWM). This is the very universality of the operation concept in the selection of materials and optical processes. Secondly, it holds a great technological capability, showing high-performance. We realize multiple chirality logic gates for simultaneous operation in a single device, in striking contrast to the conventional optical and electrical logic devices that typically perform one logic operation per device. Our results open a new way for multi-functional logic circuits and networks. It provides a unique electro-optical computing interface: Traditionally, the connection between electronic and optical/photonic computing has mainly been realized through slow and inefficient optical-to-electrical and electrical-to-optical conversion. We demonstrate electrical control of the chirality optical gates, realizing an exciting prospect for first and direct interconnection between electrical and optical computing. We firmly believe that our work will initiate a new field of chirality computing and represents a significant breakthrough.