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Time cloak based on slow/fast light effects in fiber Mach-Zehnder interferometers

Li Zhan, Lirun Gao, Wenyan Zhang, Chao Li, Tianhao Xian

Published Feb 22, 2018• 3 citations
Publisher

Abstract

Restricted to picosecond scale time gaps, the previous reported temporal cloaking schemes are hardly possible for practical applications. In this paper, we report a nanosecond scale temporal cloaking regime based on the fast/slow light effect in unbalanced fiber Mach-Zehnder interferometers. By exerting a radio frequency modulation onto the probe light, we broke through the gap time limit. A time gap up to 5.3ns was created and experimentally observed. The modulation signal in the time gap was concealed efficiently. Realizing nanosecond time gaps is critical for potential applications of temporal cloaking, such as secure communication and signal processing. This solution may push this fascinating idea into reality

DOI
10.1117/12.2299198

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Restricted to picosecond scale time gaps, the previous reported temporal cloaking schemes are hardly possible for practical applications. In this paper, we report a nanosecond scale temporal cloaking regime based on the fast/slow light effect in unbalanced fiber Mach-Zehnder interferometers. By exerting a radio frequency modulation onto the probe light, we broke through the gap time limit. A time gap up to 5.3ns was created and experimentally observed. The modulation signal in the time gap was concealed efficiently. Realizing nanosecond time gaps is critical for potential applications of temporal cloaking, such as secure communication and signal processing. This solution may push this fascinating idea into reality
A temporal cloak scheme based on tunable optical delay and advance is theoretically proposed. An input optical signal is divided into two parts, and the front part is advanced while the rear part is delayed. A temporal gap which contains negligible optical energy is opened to hide events from observers, which can be closed by doing the inverse process. Different from the previous schemes that use continuous wave light, we use an optical data stream as the probe beam. Simulations have been done to investigate performance of the temporal cloak. The developed scheme can be applied in fiber-optical signal processing and secure communications.
We demonstrate the possibility of creating a time gap in the slow light based on spectral hole burning in a four-level Doppler broadened sodium atomic system. A time gap is also observed between the slow and the fast light in the hole burning region and near the burnt hole region, respectively. A cloaking time gap is attained in microseconds and no distortion is observed in the transmitted pulse. The width of the time gap is observed to vary with the inverse Doppler effect in this system. Our results may provide a way to create multiple time gaps for a temporal cloak.
We report the group velocity control of light in optical fiber by gain-imbedded unbalanced fiber Mach–Zehnder interferometer. Slow and fast light effects were observed at the frequencies near the minimum of the transmission spectrum. Controllable group velocity between 0.719 c to 0.620 c ( c is the light speed in a vacuum) was obtained via the cross-intensity modulation effect, by changing the gain index in the long arm. With the power compensation provided by the introduced Erbium doped fiber, this proposal offers a simple and operable solution to realize lossless slow and fast light propagation in optical fiber.
Recent research has revealed a significant ability to manipulate and control a light beam to hide events in time-domain. Achieving highly functional temporal cloaking, which open up and subsequently close intensity gaps in the probe beam to conceal events from the observer with satisfied performances, are still difficult in optical fiber communication. Here, we propose and experimentally demonstrate a temporal cloak system based on ultra-short-pulse generation and time-domain fraunhofer diffraction. We succeed in hiding 83 percent of the whole time axis and cloak pseudorandom dark return-to-zero data bitrate at 10 Gbit/s. The four states of temporal cloaking and condition of cloaking off have been investigated in this paper.
We propose and demonstrate a method for manipulation of group velocity from slow-to-fast light (SFL) in a two-beam Mach–Zehnder interferometer in radio frequency (RF) regime. The subluminal, superluminal, and tunneling propagation regimes occur in a narrow frequency band around the resonance frequency of the interferometer where destructive interference occurs. Importantly, the group velocity at the resonance frequency can be controlled by simply adjusting the transmission magnitude of the signals from the two beams, without changing the length of the interferometer. Models that fully describe the SFL effects in the microwave interferometer system are developed and closed-form expressions for the prediction of group delays at the resonance frequency are obtained. The simple and effective method is verified through numerical calculations and experimental measurements. We also demonstrate that the proposed method applies to a microwave cavity interferometer. A proof-of-concept experiment is performed using a custom open-ended coaxial cable resonator (OE-CCR). Positive and negative group delays are experimentally measured when the resonator is set at different coupling states.
An analytical approach is reported that describes previously observed fast-light regimes in linear and passive Mach-Zehnder interferometers (MZI) where the optical path difference is due to a different length of the branches. Approximate expressions are developed for the transmission coefficient and group delay spectral functions valid for frequencies close to the transmission minima ${\ensuremath{\omega}}_{\mathrm{min}}$, where these regimes occur. It is found that the group delay at ${\ensuremath{\omega}}_{\mathrm{min}}$ verifies a simple scaling law. We demonstrate that slow light cannot arise in this system, and that tunneling and superluminal regimes appear only for low-loss devices, where the attenuation drives the change in the propagation regimes. The propagation of a sinusoidally modulated pulse train through the MZI is described, and relevant figures of merit, which are intrinsic to the system and universal for any operative spectral range, are determined. The theoretical approach is illustrated by simulations of a silicon-based interferometer designed for advancing pulses at 1.55 \ensuremath{\mu}m. Also, previously reported experimental results in the radiofrequency range are interpreted in the framework of the model.