Yb-doped strictly all-fiber laser actively Q-switched by intermodal acousto-optic modulation

We show an actively Q-switched ytterbium-doped strictly all-fiber laser. Cavity loss modulation is achieved in a tapered optical fiber by core-to-cladding mode-coupling induced by travelling flexural acoustic waves. When the acoustical signal is switched-off, the optical power losses within the cavity are reduced, and then a laser pulse is emitted. Trains of Q-switched pulses were successfully obtained at repetition rates in the range 1–10 kHz, with pump powers between 59 and 88 mW, at the optical wavelength of 1064.1 nm. Best results were for laser pulses of 118 mW peak power, 1.8 μs of time width, with a pump power of 79 mW, at 7 kHz repetition rate.     

Mode-locked all-fiber ring laser based on broad bandwidth in-fiber acousto-optic modulator

Active mode-locking of long-cavity all-fiber ring laser based on broad bandwidth in-fiber acousto-optic modulator (AOM) is reported. The proposed AOM combines the advantages of intermodal coupling induced by standing flexural acoustic waves in a double-ended tapered fiber. We focus our attention on the effects of large tapered transitions to improve the bandwidth modulation. Our approach permits the implementation of broad modulation bandwidth (13 nm), high modulation depth (50 %), and low optical loss (1.1 dB) in an 80-μm configuration. The effects of the AOM in the laser performance are also investigated. Transform-limit optical pulses of 25 ps temporal width and 2.7 W peak power were obtained at 2.46 MHz repetition rate.     

Proposal and design of an in-fiber all-optical fractional integrator

We theoretically and numerically demonstrate that a single fiber Bragg grating – conveniently apodized and of uniform period – operated in reflection can perform an arbitrary-order fractional integration of an input optical waveform. Analytical expressions were found relating the fractional integration order with the apodization profile of the fiber Bragg grating. This simple device shows a good accuracy calculating the fractional time integral of the complex field of arbitrary input optical waveforms.     

Experimental study of an all-fiber laser actively mode-locked by standing-wave acousto-optic modulation

We report an experimental study of an actively mode-locked erbium-doped all-fiber laser, based on a standing-wave acoustically-induced superlattice modulation. Our experiments involve the characterization of the laser as a function of the active fiber length, and with different types of delay line fibers. The effect of the modulation on the laser performance was also investigated. Narrower pulses were obtained at higher modulation depths, normal dispersion, and shorter lengths of active fiber. Optical pulses of 160 mW peak power and 630 ps temporal width were obtained at 9 MHz repetition rate.     

Actively mode-locked fiber ring laser by intermodal acousto-optic modulation

We report an actively mode-locked fiber ring laser. A simple and low-insertion-loss acousto-optic modulator driven by standing flexural waves, which couples core-to-cladding modes in a standard single-mode optical fiber, is used as an active mechanism for mode locking. Among the remarkable features of the modulator, we mention its high modulation depth (72%), broad bandwidth (187 GHz), easy tunability in the optical wavelength, and low insertion losses (0.7 dB). The narrowest optical pulses obtained were of 95 ps time width, 21 mW peak power, repetition rate of 4.758 MHz, and 110 mW of pump power.     

Mechanochemical Reactions in Fe2O3–M (M: Al, Ti)

The production of metal–ceramic nanodispersion by mechanical milling of powders through the displacement reaction Fe₂O₃+M→Fe+M-oxide (with M: Al, Ti) was studied. The reaction progress with milling time was followed by recording the temperature and pressure during the process. The samples were characterized by X-ray diffraction and Mössbauer spectroscopy at the intermediate and final stages. In both cases self-sustained reactions were observed with different activation times. The results confirm that mechanical work at room temperature yields the reduction of hematite by Ti and Al. The final oxides were identified as Ti₂O₃ and Al₂O₃, respectively. The dependence of the intermediate and final stages on the milling conditions and the starting composition will be discussed.     

Experimental study of an actively mode-locked fiber ring laser based on in-fiber amplitude modulation

We report an experimental study of an actively mode-locked fiber ring laser based on the development of an efficient in-fiber amplitude modulator. Intermodal coupling induced by standing flexural acoustic waves permits the implementation of broad bandwidth (1.5 nm), high modulation depth (72%), low-insertion-loss (0.75 dB), in-fiber amplitude modulators, operating in the MHz frequency range. The experimental characterization of the laser as a function of the radio frequency voltage that controls the modulator, the length of the active fiber, and the optical bandwidth of an intracavity filter implemented with a fiber Bragg grating has led to an improved performance of the Erbium-doped fiber laser: optical pulses of 34-ps temporal width, 1.4-W peak power, and 4.75-MHz repetition rate.     

All-optical ultrafast fractional differentiator

In this work we present a technique for the implementation of an ultrafast all-optical temporal differentiator. A photonic Mach–Zehnder interferometer can provide the required spectral response for fractional differentiation within certain fractional order extent. This device shows a good accuracy calculating the fractional time derivatives of the complex field of an arbitrary input optical waveform. Analytical expressions were found relating the photonic Mach–Zehnder parameters and the required spectral characteristics of the differentiator for integer and fractional operation. The introduced concept is supported by numerical simulations.     

Distortion in optical pulse equalization through phase modulation and dispersive transmission

By combining phase modulation and dispersive transmission we propose an adjustable optical device to compress a time-varying input signal for producing ultrashort light pulses of high optical power. The relationship between the required properties of the input signal and the device parameters to get well-conformed sharp pulses with large energy concentration was established. High-order aberrations effects of the electro-optical modulator acting as the time lens of the employed setup are also considered. We found a mathematical analogy between the output signal of the analyzed device and the signal which would be obtained by using an equivalent first-order dispersive line. Some numerical simulations are shown which illustrate the feasibility of the method.