Silicon photonics and Optical interconnection

In the 21st century, with the continuous development of modern society, more and more data information are required to be processed and transmitted. Due to the physical nature, the photon is more suitable to transmit and process information with unique characteristics, including bosonic nature, wide bandwidth and high-data-rate density, low transmission loss, low power consumption, and simple system design. On the one hand, as a carrier of information, photons show great potential in interconnection even in very short distance; on the other hand, it is expected that photons (or light wave) can employed with non-von-Neumann architecture to complete identification tasks and solve optimization problems with high operation speed and energy efficiency. Optoelectronic devices based on silicon substrate are expected to integrate both photonic and electronic devices on the same chip. Thus, it is possible to achieve information transmission and processing as well as new functionalities with high-speed, large capacity, low power consumption on chip.

We are dedicated to implement optoelectronic devices with micro/nano-structure, including the light emitter, transmission line, passive devices, modulator and photonic integrated circuit on silicon platform. We are focused on the new materials, new structures, new mechanism and new breakthrough in science and technology, and try to explore highly integrated and low-powered optoelectronic devices with novel functionality and application, e.g. optical interconnect, optical processing, classical and quantum optical computing, et.al.

Research Topic

- Universal linear transformation and application on optical computing

- Integrated orbital angular momentum (OAM) devices

- Photonic integrated circuit and devices

Representative Result

Universal linear optical operations on discrete phase-coherent spatial modes

(1) Taking inspirations from the conjugate pair of OAM state, i.e., angle state, the concept of the physically realizable quasi-angle state with high dimensionality is developed. Based on quasi-angle state, a method for high dimensional matrix transformation is proposed, in which any linear operator can be decomposed into just two processes, namely beam splitting and recombining(Phys. Rev. A 95 (3): 33827, (2017), also Highlighted as the Editor’s Suggestion). Recently, we have demonstrated the unitary transformation matrix with dimensionalities ranging from 7 to 24 with corresponding fidelities from 95.1% to 82.1% as well as a  non-unitary matrix for the tomography of a 4-level quantum system a fidelity of 94.9%. (J. Opt. 21, 104003, (2019), special issue of “Twisted Waves and Fields”).

(2)  A simple and flexible scheme for high-dimensional linear quantum operations is demonstrated. The quantum Fourier transformation (QFT) and quantum state tomography (QST) via symmetric informationally complete positive operator-valued measures (SIC POVMs) are implemented with dimensionality of 15. According to the experimental results, the matrix fidelity of QFT is 0.85, while the statistical fidelity of SIC POVMs and fidelity of QST are around 0.97 and up to 0.853, respectively. The dimensionality of 15 is the highest dimension reported to the best of our knowledge. We believe that our approach has the potential for further exploration of high-dimensional spatial entanglement provided by spontaneous parametric down conversion in nonlinear crystals. Furthermore, the architecture to realize Shor’s algorithm with our setup is also proposed. (Physical Review Applied, 14(2), 024027, (2020))

Integrated orbital angular momentum (OAM) emitter

(1) Integrated orbital angular momentum (OAM) encoder/decoder: Orbital angular momentum (OAM) of beams on chip is proposed for wireless optical interconnects and a full scheme of encoding and decoding of OAM is demonstrated with numerical simulation. With proposed structure, beams with OAM order of -3 to 4 is generated and four orders of them (0~3) are used encoding and decoding data so that the increased data density of two folds is achieved. According to such results, we believe that if OAM as an additional dimension is utilized in wireless optical interconnects, the data density can be increased significantly since the adopted orders of OAM could be infinite in principle. Moreover, such improvement could be easily applied to the existing optical interconnects without any more complex technology (Optics Express, 20(24), pp. 26986-26995, (2012)).

(2) Integrated “Cobweb” and “Cogwheel” emitter with a wide switching range of OAM Modes: An integrated "cobweb" emitter with a wide switching range of OAM modes is demonstrated. The independence of the micro-ring cavity and the gratings unit provides the flexibility to design the device and optimize the performance. Specifically, the dynamic switching of 9 OAM modes (l = ?4~4) with azimuthal polarization has been demonstrated with electrically controlled thermo-optical effect (Scientific Reports 6: 22512, (2016)). Moreover, the superposition of optical vortex beams is also demonstrated with a variable amplitude splitter and an orbital angular momentum emitter. With fixed wavelength and power of incident beam, the OAM flux of the radiated optical superimposed vortex beam can be dynamically tuned. The experimental results confirm the tunability of superimposed vortex beams with topological charge of l=-5~5. (Scientific Reports 5, 10958, (2015)).  

(3) Plasmonic vortex: As a fundamental tool for light-matter interactions, plasmonic vortex (PV) is extremely attractive due to its unique near field properties. However, it is hard to dynamically and continuously tune the orbital angular momentum (OAM) carried by PVs and the properties of fractional PVs are still not well investigated. We have proposed a novel method of utilizing the propagation induced radial phase gradient of incident Laguerre-Gaussian (LG) beam to sculpture PVs from integer to fractional OAM dynamically. Furthermore, a series of plasmonic devices are proposed to generate multi-patterned and two-dimensional optical lattice with helicity or not. With the compactness and flexible tunability, we believe that this work would facilitate the utilization of optical lattice in various on-chip applications (Scientific Reports 6: 36269, (2016), Optics Letters 41 (7), 1478-1481, (2016)). Recently, based on phase modulated metallic nano-slits array, an angular momentum (AM) beam splitter has been demonstrated to distinguish both spin and orbital components carried by light beam. Experimentally, the extinction ratio for spin AM beam splitting is larger than 10 and the spatial interval of adjacent orbital AM modes is more than 1.1 μm. We believe that our proposed device would be great potential to achieve highly compact photonic integrated circuit with plasmonic wave. (ACS Photonics, 2020, 7(1): 212-220) 

Integrated optoelectronic device

(1) Integrated silicon modulator based on microring array assisted MZI: A silicon modulator with microring array assisted Mach-Zehnder interferometer (MZI) is experimentally demonstrated on silicon-on-insulator (SOI) wafer through CMOS-compatible process. The footprint of the whole modulator is about 600 μm2. With forward-biased current-driven p-n junction, the voltage length product is measured as low as VπL < 6.63 × 10-3 V・cm while the 3-dB modulation bandwidth is ~ 2GHz. Furthermore, the impact of ambient temperature is minified with the help of MZI. Within temperature range of 10 ~ 70oC, the maximum divergence of modulation curve is less than ~ 3 dB (Optics Express, 22 (9):10550-10558, (2014)).

(2) All silicon photonic integrated circuits based on silicon light source and slot waveguide operating at 1064 nm: Silicon slot waveguides operating at a wavelength of high silicon absorption are fabricated on SOI wafers. The measured transmission loss coefficient is as low as 6 ~ 8 dB/cm at 1064 nm which the bending loss of slot waveguides is measured as 4.1 ~ 4.6 dB/180o with a bending radius of 15 μm. We believe that this work could pave the way to achieve all silicon photonic integrated circuits (PICs), which are very promising for future on-chip chemical/biological analysis. (IEEE Photonics Technology Letters 28(1): 19-22, (2016), Optics Communications 359: 129?134, (2016)，Optics Communications , 306, pp131?134, (2013), Optics Communications, 306: 131?134, (2013)). For the silicon light source, plasmonic enhancement of amorphous-silicon-nitride (?-SiNx) light emission with single-layer gold (Au) waveguides was experimentally demonstrated through time-resolved photoluminescence measurement. The maximum Purcell factor value of ~3 is achieved with identified plasmonic resonance of the Au waveguide at ~530 nm. (This work was selected as “10 Breakthroughs of China Optics in 2013”)

(3) Microwave photonic filter based on integrated optical processor: Tunable and reconfigurable microwave photonic filters have been proposed and experimentally demonstrated on silicon-on-insulator substrate. For bandpass filter, the operating frequency and -3-dB bandwidth can be tuned from 18 to 40 GHz and from 5 to 15 GHz, respectively (IEEE Photonics Technology Letters, 24(17):1502-1505, (2012)). To our knowledge, it is the first on-chip demonstration of tunable and reconfigurable microwave photonic filters. Furthermore, bandstop filter has also been demonstrated. (IEEE Journal of Lightwave Technology 31(23):3668-3675, (2013))

(4) Integrated photonic reservoir computing based on hierarchical time-multiplexing structure: A micro-ring array (MRA) is employed as a typical time delay implementation of reservoir computing (RC). At the output port of the MRA, a secondary time-multiplexing is achieved by multi-mode interference (MMI) splitter and delay line array. Simulation results indicate that error rate of 0.5% and 2.7% are achieved for signal classification and chaotic time series prediction, respectively, while the sample rate is as high as 1.3Gbps (Optics Express 22(25): 31356-31370, (2014)).