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Field-Programmable Silicon Temporal Cloak

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Field-Programmable Silicon Temporal Cloak ARTICLE https://doi.org/10.1038/s41467-019-10521-5 OPEN Field-programmable silicon temporal cloak Feng Zhou1, Siqi Yan1, Hailong Zhou1, Xu Wang1, Huaqing Qiu2, Jianji Dong 1, Linjie Zhou3, Yunhong Ding 2, Cheng-Wei Qiu 4,5 & Xinliang Zhang1 Temporal cloaks have aroused tremendous research interest in both optical physics and optical communications, unfolding a distinct approach to conceal temporal events from an interrogating optical field. The state-of-the-art temporal cloaks exhibit picosecond-scale and static cloaking window, owing to significantly limited periodicity and aperture of time lens. 1234567890():,; Here we demonstrate a field-programmable silicon temporal cloak for hiding nanosecond- level events, enabled by an integrated silicon microring and a broadband optical frequency comb. With dynamic control of the driving electrical signals on the microring, our cloaking windows could be stretched and switched in real time from 0.449 ns to 3.365 ns. Such a field-programmable temporal cloak may exhibit practically meaningful potentials in secure communication, data compression, and information protection in dynamically varying events. 1 Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, 430074 Wuhan, China. 2 Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens, Lyngby, Denmark. 3 State Key Laboratory of Advanced Optical Communication Systems and Networks, Depart of Electronic Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. 4 Department of Electrical and Computer Engineering, National University of Singapore, Engineering Drive 3, Singapore 117583, Singapore. 5 NUS Suzhou Research Institute (NUSRI), Suzhou Industrial Park, Suzhou 215123, China. Correspondence and requests for materials should be addressed to J.D. (email: [email protected]) or to C.-W.Q. (email: [email protected])ortoX.Z.(email:[email protected]) NATURE COMMUNICATIONS | (2019) 10:2726 | https://doi.org/10.1038/s41467-019-10521-5 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-019-10521-5 ince the breakthrough concept of temporal cloak was pro- may make its applications, such as secure communication and Sposed by McCall et al. at the first time1, a great deal of data compression, more practical and closer to our daily life. attention was paid to new methodology and experimental verification of temporal cloaks2–13. Particularly, the concept of temporal cloak first came true with an experiment by Gaeta Results et al.14, and later Weiner et al. facilitated temporal cloak into Operation principle. Time-lens is a core of temporal cloak, more practical applications at telecommunication data rate with which determines the capacity of cloaking window at the event superior cloak efficiency15. Temporal cloak, derived from spatial plane. To intuitionally understand the cloaking window, the cloaking due to the space-time duality16,17, does not create a void probe light waveform at the event plane is illustrated in Fig. 1a. to conceal spatial objects18–20, but open and suture a time gap to The zero-intensity regions represent the time gaps as the cloaking hide events in time-domain. To create a time gap as the cloaking windows23. Within these time slots, any temporal events will be window, a time lens with quadratic phase profile is required to concealed and not appear to the observer. In the traditional bend the light along the time and a dispersive medium is used to temporal cloaking systems shown in Fig. 1a, the open windows converge the light beam to a time spot14,15,21. The suture of the can only last for <200 ps14,15,21,24 because of the limited aperture time gap is implemented by an opposite dispersive medium. A lot of time-lens. Besides, the open windows are periodic, which of temporal cloak approaches were proposed theoretically and means all events in the cloaking windows are concealed peri- confirmed to be feasible in experiments. However, the existing odically without flexibility. cloaking experiments exhibited only a fixed and small cloaking Figure 1b shows the probe light waveform at the event plane in window with picosecond-level due to the periodicity and aperture our cloaking scheme, featuring a large cloaking window (~3 ns) limit of time lens. In early years, the time lens was created by a and the cloaking window can be field-programmable. The large pair of split time lens employing four-wave mixing in a highly- cloaking window makes it possible to conceal optical packets with nonlinear fiber (HNLF)14, suffering from strong pump con- nanosecond-level events, and the controllable cloak windows sumption and low energy efficiency. Afterwards, the time lens was allow for real-time switching off, switching on, and stretching the created by temporal Talbot effect employing phase modulator cloaking window freely. The field-programmable temporal cloak (PM) and chirped fiber grating15,21. Unfortunately, a PM could enables to share some public data to the user (at the state of cloak only provide very limited aperture of time lens when driven by a off) but conceal other private data (at the state of cloak on, gray sinusoidal voltage22. Even the PM was optimized by chirped labels) in real time, similar to a hardware of data protection. component and cascaded structure, the maximum continuously However, the traditional temporal cloaking systems were unable cloaking windows was 196 ps, far from nanosecond-level. A large to do so. cloaking window has been pursued all along since it represents Figure 1c describes the schematic of the proposed field- the hidden capacity available in a time slot for secure commu- programmable silicon temporal cloak, and the bottom insets nications. For some specific scenario of secure communication, show the waveforms and spectra of the light transmission, data protection is an important secure device, allowing for electrical control signal and event at different locations in the sharing some public data to the user but concealing other private cloaking system. A continuous wave (CW) light (Fig. 1d) is firstly data in real time. Thus, it is very important to make cloaking converted into a broadband flat optical frequency comb source window field-programmable (i.e., the cloaking window can be via an optical frequency comb generator (Fig. 1e, green), then switched off, switched on, or stretched freely, similar to the launched into the ET-MRR. The ET-MRR acts as a swept- concept of field programmable gate arrays in digital circuits) since frequency filter when driven by an electrical split sawtooth different types of optical packets can be hidden at any time slots waveform (Fig. 1f, green curve within gray label). The ET-MRR is with the cloaking system. However, all state-of-the-art cloaking fabricated on a commercial silicon-on-insulator (SOI) wafer systems so far featured periodical cloaking windows without field- consisting of a ring waveguide and two straight waveguides. The programmability. microscope images of the fabricated ET-MRR and the zoom-in In this paper, we demonstrate a field-programmable silicon ring region is shown in the top inset. The details of ET-MRR temporal cloak with a record cloaking window at the nanose- fabrication can be found in Methods section for device cond-level, benefiting from a unique electrically controllable fabrication. The detailed scheme and the whole micrograph of silicon-based time lens. The superior time lens consists of an the ET-MRR can be found in Supplementary Note 1. The output optical frequency comb and an electrically tuned microring wavelength dependent on time is a split sawtooth function resonator (ET-MRR) acting as a scanning filter, whose output (Fig. 1g, pink) curve within gray label since the output wavelength wavelength is proportional to the applied voltage. The electrically of optical frequency comb source is continuously scanned by the controllable time lens is enabled by applying an electrical split swept-frequency filter. Then, the electrically controllable time lens sawtooth signal on the ET-MRR and disabled by applying a direct is created. The detailed principle of the electrically controllable current (DC) electrical signal. This electrically controllable time lens can be found in Supplementary Note 2. silicon-based time lens has distinct advantages of field- While the cloak is set to cloak on (i.e., the ET-MRR is driven by programmable cloaking window, moderate power consumption a split sawtooth waveform, gray labels), the light then passes and compact photonic integration. To break the periodicity of the through a dispersion element, such as a spool of single mode fiber cloaking window, we demonstrate, for the first time, a field- (SMF), where the shorter wavelength light propagates faster than programmable silicon temporal cloak with potential applications the longer wavelength light. Thus, the dispersion effect makes in data protection, enabling to share some public data to the user energy of longer wavelengths and shorter wavelengths converge but conceal other private data in real time. In addition, we obtain into temporal pulses and leave a time gap, which is shown in a record cloaking window of up to 3.365 ns, which is 17 times Fig. 1h (blue curve within gray label), and the cloaking window larger than the longest time window reported so far21. Further- (or time gap) is opened. Any event during this time gap will not more, we succeed in concealing pseudorandom dark return-to- be perceived
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