Dobryna Zalvidea

Effective length of short Fabry-Perot cavity formed by uniform fiber Bragg gratings

In this paper, we describe the properties of Fabry-Perot fiber cavity formed by two fiber Bragg gratings in terms of the grating effective length. We show that the grating effective length is determined by the group delay of the grating, which depends on its diffraction efficiency and physical length. We present a simple analytical formula for calculation of the effective length of the uniform fiber Bragg grating and the frequency separation between consecutive resonances of a Fabry-Perot cavity. Experimental results on the cavity transmission spectra for different values of the gratings reflectivity support the presented theory.

Q-switched all-fiber laser based on magnetostriction modulation of a Bragg grating

We report an actively Q-switched all-fiber laser based on magnetostriction modulation of a Bragg grating. The laser employs a pair of Bragg gratings as reflective mirrors, one of which is bonded to a magnetostrictive element. Lengthening of the magnetostrictive element when a magnetic field is applied shifts the Bragg wavelength of the grating, allowing control of the Q-factor of the cavity and, thus, performing active Q-switching. The magnetostrictive modulator is small, compact and requires less than 300 mW electrical drive power. Using erbium-doped fiber and a maximum pump power of 120 mW, Q-switch pulses of more than 1 W peak power were obtained, with a pulse repetition rate that can be continuously varied from 1 Hz to 125 kHz.

Multimodal optical workstation for simultaneous linear, nonlinear microscopy and nanomanipulation: Upgrading a commercial confocal inverted microscope

In this work we propose and build a multimodal optical workstation that extends a commercially available confocal microscope (Nikon Confocal C1-Si) to include nonlinear/multiphoton microscopy and optical manipulation/stimulation tools such as nanosurgery. The setup allows both subsystems (confocal and nonlinear) to work independently and simultaneously. The workstation enables, for instance, nanosurgery along with simultaneous confocal and brightfield imaging. The nonlinear microscopy capabilities are added around the commercial confocal microscope by exploiting all the flexibility offered by this microscope and without need for any mechanical or electronic modification of the confocal microscope systems. As an example, the standard differential interference contrast condenser and diascopic detector in the confocal microscope are readily used as a forward detection mount for second harmonic generation imaging. The various capabilities of this workstation, as applied directly to biology, are demonstrated using the model organism Caenorhabditis elegans.

Simultaneous Switching of the

We report a pulsed erbium-doped fiber laser with simultaneous switching of the laser cavity Q-value and generation wavelength. The laser generates a train of short pulses with adjacent pulses alternately being on one of two fixed wavelengths. This regime is realized at periodical modulation of physical length of overwritten fiber Bragg gratings composing the laser cavity

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We report for the first time the use of two photon fluorescence as detection method of affinity binding reactions. We use a resonant grating waveguide structure as platform enhancement for detecting the interaction between fluorescent labeled Boldenone, a non-natural androgenic hormone, and a specific anti-anabolic antibody. We were able to detect a surface coverage of approximately 0.7 ng/mm(2).

-Value and Operation Wavelength in an Erbium-Doped Fiber Laser

Because of its polarization sensitivity, SHG microscopy can provide information about the orientation and degree of structural organization inside biological samples. To fully exploit the above potential, the state of the polarization at the sample plane needs to be known. In this work we present starch granules as a reliable probe for the polarization state of the excitation beam at the sample plane of a high resolution multiphoton microscope. Polarization dependent SHG series of images demonstrated the radial distribution of SHG active molecules inside starch granules. This allowed the granule to exhibit symmetrical SHG emission regions. The pattern rotates along with the rotation of a λ/2 waveplate and thus, can demonstrate the polarization at the sample plane. Maximum signal in the forward detected geometry appears when imaging starch granules exactly at the hemisphere plane. Symmetric SHG regions rotating with the incoming linear polarization were also recorded in the backward detected geometry. A portion of the backwards detected SHG signal, which corresponds to two rotating equator arcs, does not overlap with the forward SHG signal. Importantly, polarization measurements, performed either in the forward or the backwards directions, have demonstrated the suitability and flexibility of this technique for both detection schemes. As result, observation of the starch signal allowed us to know the polarization of our SHG microscope. Furthermore, by coding this information in an angular representation, we corrected the input values in a theoretical model that predicts the average orientation of SHG active molecules. This has allowed us to map the mean orientation of SHG active molecules in body walls muscle of Caenorhabditis elegans, with pixel resolution.

Nonlinear immunofluorescent assay for androgenic hormones based on resonant structures

We report a high efficiency and high repetition rate acoustic-induced Q-switched Er-doped-fiber laser. Two fiber Bragg gratings were used as cavity mirrors, whilst the active Q-Switching was performed by temporally controlling the Q-cavity factor by coupling light from the core mode to cladding modes using flexural acoustic waves. The acousto-optic attenuator was implemented by applying a RF signal to a piezoelectric disc and using an aluminum horn to focus the acoustic wave in a tapered fiber. The RF signal that drives the piezoelectric disc was amplitude modulated with a rectangular wave of variable frequency and duty cycle. Q-switched laser pulses of ~ 1 W peak power, 0.1 - 2 μs pulse width and continuously variable frequency up to 100 kHz, were obtained. The laser efficiency of energy conversion was as high as 20%.

Starch granules as a probe for the polarization at the sample plane of a high resolution multiphoton microscope.

All-fibre lasers are important in the development of telecommunication systems. The modulation techniques based on all-fibre components permit to obtain new compact and robust laser configurations. Interesting results on new Q-switching and lambda-switching techniques have been obtained. Q-switched distributed feedback fibre-lasers exhibit a narrow bandwidth below 0.4 pm and peak powers the order of 300 mW.

High-efficiency acoustic-induced Q-switched erbium-doped fiber laser

We report an experimental study of the response of a hydrogen sensor based on a palladium-coated tapered optical fiber, at different temperatures in the range [-30, 80]°C. The main features of the sensors response have been correlated with the pressure-composition isotherms of the Pd-H system and its phase transitions. Moreover, heating of the palladium layer optically with an auxiliary laser diode, allows improving the sensor’s time response at low temperatures.

All-fibre lasers: active Q-switching techniques

We present a novel configuration of a fiber-optic hydrogen sensor suitable for wavelength multiplexing. It is based on a palladium-coated tapered fiber and a fiber Bragg grating. This scheme allows sensors multiplexing, which increases the capability to implement multipoint sensor networks for volumetric detection. Moreover, the sensitivity of the sensor is enhanced since light interacts twice with the palladium layer.