The effect of a gradual reduction of the fiber diameter on the acousto-optic (AO) interaction is reported. The experimental and theoretical study of the intermodal coupling induced by a flexural acoustic wave in a biconical tapered fiber shows that it is possible to shape the transmission spectrum, for example, substantially broadening the bandwidth of the resonant couplings. The geometry of the taper transitions can be regarded as an extra degree of freedom to design the AO devices. Optical bandwidths above 45 nm are reported in a tapered fiber with a gradual reduction of the fiber down to 70 μm diameter. The effect of including long taper transition is also reported in a double-tapered structure. A flat attenuation response is reported with 3-dB stopband bandwidth of 34 nm.
We theoretically demonstrate by using fractional calculus tools the linking between the instantaneous phase profile of a
given temporal optical pulse and its photonics semi-differintegration, i.e. a 0.5th-order differentiation/integration. In both
cases, the signal's temporal phase can be retrieved by simple dividing two temporal intensity profiles, namely the
intensities of the input and output pulses of a spectrally-shifted 0.5th-order differentiator/integrator. In both cases, we
obtained simple analytical expressions for the instantaneous frequency profile. We numerically prove the viability of
these proposals.
The development of efficient in-fiber amplitude modulators that operate in the MHz frequency range has enabled some
recent advances in actively mode-locked all-fiber lasers. Our approach is based on the excitation of a standing acoustic
wave along the fiber, which modulates the coupling between modes at twice the frequency of the acoustic wave. Among
the remarkable features of these in-fiber modulators, we mention the high peak power damage, high modulation depth,
broad bandwidth, easy tunability in optical wavelength and low insertion losses. The in-fiber modulation is crucial for
the implementation of all-fiber compact and robust lasers. The experimental characterization of different cavity
configurations as a function of the radio frequency voltage that controls the modulator, the length of the active fiber, the
overall dispersion of the cavity, etc., has led to an improved operation of the lasers: output optical pulses of 34 ps
temporal width, 1.4 W peak power and 4.7 MHz repetition rate, at the emission wavelength of erbium.
Here we numerically demonstrated that the phase profile of a given temporal optical pulse can be retrieved by photonic
semi-differintegration, where by semi-differintegration we mean either a 0.5th-order differentiation or integration. In
both cases, the signal's temporal phase can be obtained by simple dividing two temporal intensity profiles, namely the
intensities of the input and output pulses of a spectrally-shifted semi-differintegral. In both cases, we obtained simple
analytical expressions for the phase profile. We numerically prove the viability of these proposals.
In this work we describe the development of a compact all-fiber pulsed light source composed by a fiber-Bragg-grating-based
distributed-feedback fiber laser. We demonstrate that the temporal and spectral characteristics of this fiber laser are suitable as light
source for Brillouin back-scattering sensors. Using a 10 km fiber spool, we have measured the Stokes and anti-Stokes processes at
different pump powers and they were clearly discernible around the central (Rayleigh backscattering) peak at the appropriate
wavelength shift (88 pm at room temperature). Our results indicate that this compact all-fiber source is a good alternative for Brillouin
sensor applications.
We study the wavelength-division multiplexing implementation of the recently proposed temporal Fresnel transform encoding technique, in order to evaluate its potential application for secure data transmission in short-haul fiber optic links. The different signal broadenings produced by each stage of the encoding process are analyzed in a dual time-frequency domain by using the Wigner distribution function. Furthermore, the robustness of the proposed method is illustrated by comparing the signal-to-noise ratio between the input and the decrypted signals obtained by varying typical parameters of the encryption-decryption setup. Numerical simulations revealed good system performance. Finally, we consider experimental feasibility with current photonic technology.
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