After a fiber Bragg grating (FBG) is fabricated, the reflection spectrum of the FBG is generally not tunable without mechanical deformation or temperature adjustment. Here we present a microcavity-coupled FBG with both a tunable reflection lineshape and dispersion using electromagnetically induced transparency. The Fano interference of light in the FBG and the microcavity allows for dramatic modification of the reflection spectrum. The phase of the reflected spectrum is continuously tunable between 0 and 2π to produce various Fano lineshapes. The dispersion of the output light is adjustable from normal dispersion to abnormal dispersion, consequently providing an adjustable speed of light. Additionally, it allows the FBG to switch from a notch filter to a bandpass filter at the resonant wavelength, which is not possible in a conventional uniform FBG.
After a fiber Bragg grating (FBG) is fabricated, the reflection spectrum of the FBG is generally not tunable without mechanical deformation or temperature adjustment. Here we present a microcavity-coupled FBG with both a tunable reflection lineshape and dispersion using electromagnetically induced transparency. The Fano interference of light in the FBG and the microcavity allows for dramatic modification of the reflection spectrum. The phase of the reflected spectrum is continuously tunable between 0 and 2π to produce various Fano lineshapes. The dispersion of the output light is adjustable from normal dispersion to abnormal dispersion, consequently providing an adjustable speed of light. Additionally, it allows the FBG to switch from a notch filter to a bandpass filter at the resonant wavelength, which is not possible in a conventional uniform FBG.
We proposed and experimentally demonstrated an extremely simple and feasible slow-light technique to achieve tunable optical delay by using the Er/Yb codoped fiber Bragg grating (FBG). The signal light experiences strong dispersion when it is launched into the reflection edge of FBG, and the group delay value is determined by the signal wavelength and the pump power. In the experiment, a controllable delay of 0.9 ns can be obtained through changing the 980 nm pump power. The group velocity can be slowed down to 5.6x10(7) m/s, which is 19% of the speed of light in free space. It provides a very simple approach to control the light group delay, which is likely to have important implications for practical applications.
This study demonstrates the generation of a tunable all-fiber Fano resonance comb by incorporating a 10° tilted fiber Bragg grating (TFBG) into an all-fiber Mach–Zehnder interferometer (MZI). The TFBG generates the discrete state that couples with the continuum state of the MZI to produce all-fiber Fano resonance comb spanning an 80 nm spectral range. This system exhibits precise tunability, enabling continuous transitions among asymmetric Fano line shape, symmetric electromagnetically induced transparency, and electromagnetically induced absorption line shapes. The results also demonstrate that key spectral parameters, including the Fano parameter q , slope rate, and extinction ratio, exhibit periodic variation. The proposed approach offers a robust, low-loss, and scalable solution for multi-Fano resonance generation and holds promise for applications of high-sensitivity sensing and optical switching.
Abstract A novel all-optical scheme for fast modulation of Fano-like resonance using Er/Yb doped fiber (EYDF) is proposed and demonstrated experimentally. In the integrated system, an apodized fiber Bragg grating (AFBG) is inserted into one arm of the fiber Mach–Zehnder interferometer (MZI), and the asymmetric Fano-like resonances is generated by the interference between the MZI mode and AFBG mode. In addition, a section of EYDF is inserted into the other arm of the MZI to control the phase difference between the two arms of the MZI. By adjusting the power of optical pump applied to the EYDF, the transmission spectrum lineshapes of the integrated device can be effectively modulated into asymmetric Fano-like resonances, symmetric transmission dip or electromagnetically induced transparency-like resonances, which has a fast response speed. The proposed all-optical Fano-like modulation scheme is simple in structure, and has advantages of remote control and long-term stability, providing potential applications in the fields of fast and slow light, optical filters and fiber sensing.
We achieve Fano-like resonances in an all-in-fiber structure embedded with an in-line Mach-Zehnder interferometer (MZI). A fiber Bragg grating is inserted into MZI's one arm to form a resonance, which functions as the discrete state of the Fano-like resonance to couple with the continuum propagating mode of MZI in the fiber core. A theoretical model predicts the controllable resonance lineshape by changing the phase difference between the MZI's two interference pathways. Fano-like resonances with an extinction ratio over 20 dB are experimentally observed, which are reliably tuned into Lorentzian and electromagnetically induced transparency-like resonances by versatile methods. The realization of Fano-like resonances with broad tunability in this all-in-fiber structure holds potentials in fiber-based applications of sensing, signal processing and nonlinear optics.
We report a graphene-assisted all-optical control of a fiber Bragg grating (FBG), which enables in-fiber optical bistability and switching. With an optical pump, a micro-FBG wrapped by graphene evolves into chirped and phase-shifted FBGs, whose characteristic wavelengths and bandwidths could be controlled by the pump power. Optical bistability and multistability are achieved in the controlled FBG based on a shifted Bragg reflection or Fabry-Perot-type resonance, which allow the implementation of optical switching with an extinction ratio exceeding 20 dB and a response time in tens of milliseconds.
Here, an all-optical switch is modeled in the form of fiber Bragg grating (FBG) based on electromagnetically induced transparency (EIT) phenomena dealing with a three-level EIT silicon (Si) nanocrystalline medium. The EIT consists of two fields, namely a strong control and weak probe fields that interact with the medium. Fast-optical switching of the probe is achieved by applying a pulsed control field, which relies on both steady-state and transient density matrices. The effects of four significant parameters of interest, i.e., Rabi frequency of the control field, EIT nanocrystal density, FBG length, and spontaneous decay rate, have been extensively investigated to optimize the probe transmission. Subsequently, the time-dependent density matrix is solved to obtain the response time of the FBG-EIT switch. Eventually, FBG is modeled such that low index layers contain EIT material and the high index layers do not. The FBG-EIT switch satisfies the criteria of maximum transmission and minimum rise time to give out the optimal operational condition. Despite the optical switching is in OFF mode at Ωc=0 THz demonstrating a high FBG reflectance, the reflectance suddenly vanishes at a certain Ω c s to satisfy the equivalence of low and high refractive indices (switching ON). Therefore, a fast-optical switch is envisaged operating as large as 100 GHz in theory. The future applications of the FBG- EIT include the fast Q-switching of fiber lasers, ultra-fast modulation, optical quantum communication, and high speed optical processing and computation.