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Applied Physics Express

Group velocity control by gain-assisted fibre Mach-Zehnder interferometers

Lirun Gao, Li Zhan, Wenyan Zhang, Tianhao Xian

Published Aug 1, 2019• 2 citations
Publisher

Abstract

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.

DOI
10.7567/1882-0786/ab37a2

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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.
We propose and experimentally demonstrate the propagation of slow/fast light in an erbium-doped fiber (EDF) using mutually modulated cross-gain modulation. The group velocity of the light signal can be manipulated by the effect of gain cross-saturation modulation by a saturating light at an arbitrary wavelength in the gain bandwidth of the EDF. The ultraslow propagation with a small group velocity of 5.6 × 10⁻³c (c is the light speed in free space) and superluminal propagation with a negative group velocity of -1.1 × 10⁻³c has been observed under different modulation phases.
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.
We demonstrate a method to achieve an extremely wide and flexible external control of the group velocity of signals as they propagate along an optical fiber. This control is achieved by means of the gain and loss mechanisms of stimulated Brillouin scattering in the fiber itself. Our experiments show that group velocities below 71000km∕s on one hand, well exceeding the speed of light in vacuum on the other hand and even negative group velocities can readily be obtained with a simple benchtop experimental setup. We believe that the fact that slow and fast light can be achieved in a standard single-mode fiber, in normal environmental conditions and using off-the-shelf instrumentation, is very promising for a future use in real applications.
We demonstrate a method to achieve an extremely wide and flexible external control of the group velocity of signals as they propagate along an optical fibre. This control is achieved by means of the gain and loss mechanisms of stimulated Brillouin scattering in the fibre itself. Our experiments show that group velocities below 71,000 km/s on one hand, well exceeding the speed of light in vacuum on the other hand and even negative group velocities can readily be obtained with a simple benchtop experimental setup. Advanced schemes can be realized thanks to the extremely flexible possibility to shape the gain spectrum to make it optimized for applications. Ultra wide bandwidth, delaying with flat amplitude response and lower distortion were successfully demonstrated this way.
Recently, researches about the controllable group velocity of light propagation had made many progresses. And several experiments had demonstrated the signal evolution of slow and fast light. In this letter, the authors described a simple experiment for the tracing of light signals in an erbium-doped optical fiber at the optical communication wavelength firstly. We have, directly, observed the evolution of slow and fast signals with different waveforms that travel in an erbium-doped fiber amplifier. Through tracing the signal evolution, when slow light (Vg<;<;c) or fast light (Vg<;0) was got in it, we concluded that asymmetrical absorption and amplification on the periodical signal could account for the generation of slow and fast light in an erbium-doped fiber amplifier easily.