The use of plastic optical fibers as sensors represents advantages due to the malleability of the material and the number of modulations it allows, in addition, it's a flexibility and low-cost material. Currently, optical couplers have also been developed in plastic fiber optics, due to their main use in telecommunications, and prices are increasingly affordable. In addition, the use of technologies in optics and photonics are more accepted in areas such as medicine, industry, beauty, sensors, and more. (1) In this work, a force sensor is achieved, based on beam modulation, made of a 2x2 (50:50) coupler of 1mm diameter Plastic Optical Fiber (POF), with a 10 cm POF joined to the output to generate a loop. This section was polished in D, V and cylindrical shapes, at 30% and 50% polished depth, using a visible spectrum, in 632.8 nm of an He-Ne laser source. The spectral response is obtained in a force range of 0-500 N which is gradually applied to the fiber polished section. A linear sensitivity of force-beam modulation is obtained.
We have investigated ultrashort parabolic pulse formation via passive nonlinear reshaping in normal dispersive optical fibers at 1550 nm. It was investigated parabolic pulse formation in the transient-state regime and in the steady-state regime. Numerical simulations have been made based on generalized nonlinear Schrödinger equation taking into account high-order dispersion terms and high order nonlinear terms. It was examined the applicability of different commercially available fibers for parabolic pulse formation at 1550 nm. It was found that small amount of positive second-order dispersion and quite sufficient third-order dispersion can restrict strongly the formation of parabolic pulses at 1550 nm. The most suitable fiber for pulse reshaping has been found.
Microstructured fibers have recently become popular due to their numerous applications for fiber lasers,1 super-continuum generationi2 and pulse reshaping.3 One of the most important properties of such fibers that is taken into account is its dispersion. Fine tuning of the dispersion (i.e. dispersion management) is one of the crucial peculiarities of the photonic crystal fibers (PCFs)4 that are particular case of the microstructured fibers.
During last years, there have been presented various designs of the PCFs possessing specially-designed dispersion shapes. 5-7 However, no universal technique exists which would allow tuning the PCF dispersion without using optimization methods.
In our work, we investigate the sensitivity of the PCF dispersion as respect to variation of its basic parameters. This knowledge allows fine-tuning the position of local maximum of the PCF dispersion while maintaining other properties unchanged.
The work is organized as follows. In the first section we discuss the dispersion computation method that is suitable for the global sensitivity analysis. The second section presents the global sensitivity analysis for this specific case. We also discuss there possible selection of the variable parameters.
We present the fabrication and characterization of a mechanically induced long period grating (MLPG) using a grating period of 400 μm and 1m of NZ-DSF. Pressure is gradually applied up to 120 Lb at different angles like 0, 30, 45 and 60 degrees. An attenuation band is observed centered at a wavelength around 1064nm using a fiber position of 30 degrees with respect to the grating´s metal plate and a maximum pressure of 145 Lb. The loss band presents a maximum depth of 22dB and a bandwidth of approximately 10nm. Torsion and curvature characterizations did not change the output spectrum of the optical grating. However, temperature characterization depicted a small shifting which could be insignificant for some applications. Still, there is 16dB attenuation as temperature increases in a range from room temperature up to 450°C. These preliminary studies show that this 1064 nm centered wavelength MILPG might be used in a low linear dynamic range with temperature (75-300)°C as a temperature sensor.
We present the results from the fabrication and characterization of mechanically induced long period fiber gratings in
polarization maintaining photonic crystal fiber (PM-PCF). A supercontinuum source in the range of 600nm - 1700nm is
used. This source is generated using a micro-chip laser at 1064nm and a single mode fiber. A long-period grating is
induced over 40mm long unjacketed PCF using a V-grooved aluminum plate. External pressure is gradually applied with
a metal screw and a torque meter and a loss dip with resonance wavelength is observed. Low insertion losses are
depicted from (1-3) dBm with a bandwidth of about 30nm and a loss dip around 15dBm. Sensitivity for this preliminary
work is found at 27 dB/Lb. Several applications are potentially possible with the optimization of the transmission
spectrum controlled by applied pressure.
Here we propose a simple design for a solid-core photonic crystal fiber made of silica by keeping the golden ratio
(1.618) between pitch and air hole diameter Λ /d in a subset of six rings of air-holes with hexagonal arrangement. In the
case when we have a pitch equal to one micron (Λ =1 μm), we need air-holes diameters d=0.618 μm in order to obtain
the golden ratio parameter (Λ/d=1.618), and achieve two zero dispersion wavelength (ZDW) points at 725 nm and 1055
nm; this gives us the possibility to use this fiber in supercontinuum generation using a laser emission close to that points.
We analyzed a series of fibers using this relation and show the possibilities of tunable ZDW in a wide range of
wavelengths from 725 nm to 2000 nm with low losses and small effective area. In agreement with the ZDW point
needed, the geometry of the structure can be modified to the point of having only three rings of air holes that surround
the solid core with low losses and good confinement mode. The design proposed here is analyzed using the finite
element method (FEM) with perfectly matched layers (PML), including the material dispersion directly into the model
applying the Sellmeier’s equation.
The supercontinuum (SC) generated by pumping in anomalous dispersion is sensitive to the input pulse fluctuations and pump laser’s shot noises and does not possess a single-pulse waveform, so the incident pulse becomes a noise-like train of spikes. A simple method of creating pulsed lasers with either pulse-maintaining ultrabroad SC or specially shaped pulse waveforms can be implemented using all-normal-dispersion microstructured optical fibers (ANDi-MOFs). An ANDi-MOF with a simple topology and dispersion profile maximum at 800 nm was designed using the effective index method. Its properties and suitability were characterized via numerical simulation of femtosecond parabolic pulse formation and generation of an octave-spanning pulse-maintaining SC using a generalized propagation equation. The designed ANDi-MOF is suitable for resolving both problems and allows some detuning of the pulse’s wavelength around 800 nm. However, a better choice for SC generation is pumping at or near the wavelength where the third-order dispersion becomes zero. This configuration benefits from the absence of pulse break-up under large pulse energies, which appears otherwise. The fiber can provide a low-cost method for developing supercontinuum sources and a solution to the problems of parabolic waveform formation to meet the needs of optical signal processing and pulse amplification and compression.
In the work, we have presented the technique based on the graphics processing unit accelerated finite-difference time-domain (FDTD) method for characterization of a single-mode photonic crystal fiber (PCF) with an arbitrary refractive index profile. In contrast to other numerical methods, the FDTD allows studying the mode propagation along the fiber. Particularly, we have focused attention on the method details that allowed us to reduce dramatically the computation time. It has been demonstrated that the accuracy of dispersion obtained by the FDTD method is comparable to the one provided by the finite elements method while possessing lower computation time. The method has been used to determine the fundamental mode cut-off of all-normal dispersion PCF and to find fiber losses beyond this wavelength.
In the work, we have presented the technique based on the FDTD method for the dispersion computation of a single-mode ber with an arbitrary refractive index pro le. In contrast to other numerical methods the FDTD allows studying the beam propagation along the ber taking into account material dispersion and the nonlinearity. Particularly, we have concentrated attention on the method details that allowed us to reduce dramatically the computation time and achieve the accuracy close to the one provided by the nite elements method.
We have designed an all-normal dispersion photonic crystal fiber optimized for pumping at 800 nm with initial pulses which are typical for conventional Ti:Sapphire lasers. Parabolic pulse formation and supercontinuum generation in this fiber is analyzed both in time and frequency domains.
Photonic crystal (PhC) waveguides are the prospective structures for high-speed optical micro-devices. Possessing high-effective light localization, such waveguides allow introducing active materials making additional all-optical signal control possible. The most effective from the technological point of view is embedding the PhC filters with characteristics close to the ones of the background PhC (i.e. with the same refractive index, PhC period, etc.). As has been shown in previous papers,1, 2 such filters possess spectral characteristics that allow using them for processing the ultra-short pulses in case of either passive (implemented with linear materials) of active (with nonlinear materials) devices. Moreover, from the technological point of view such PhC waveguides with filters can be easily integrated into the electronic circuit which reduces costs and production time.
Unfortunately, optical losses and back reflection from such a filters makes them unsuitable for high-speed integrated optical circuits.
In this work we propose analysing both density of modes (DOM) and the transmission spectra to optimize the parameters of the PhC filters made of linear or nonlinear material.
Proposed characteristics have been first introduced to optimize the PhC filters used for wavelength division demultiplexing.3 However, since waveguiding properties have not been taken into account, the photonic density of states maps as well as transmittance maps can be applied with high accuracy to a bulk PhC but not to confined PhC filter. Taking into account waveguiding properties provides great enhancement to the precision of characterization of the confined PhC filters.
We propose a new design method for the photonic crystal (PhC) wideband passive optical filters. For this, we join the PhC spectral analysis with investigation of guiding properties of the PhC-waveguides and filters. The method allows improvement of the characteristics of the demultiplexers presented in earlier works, which has been designed by means of photonic band gap maps analysis.
Generation and applications of the optical pulses with a parabolic intensity profile has developed into the area of
dynamic research activity over recent years. Parabolic pulses can propagate remaining their parabolic profile.
Particularly these pulses resist to the deleterious effect of the optical wave breaking. They are of great interest for a
number of applications including the high power pulse generation, and all optical signal processing. Alternative methods
of generating parabolic pulses are of especial interest in the context of non-amplification usage, such as optical
telecommunications. It is found that Gaussian waveforms provide best quasi-parabolic pulses among others and within
shortest distance. There is a range of soliton numbers where the shape of quasi-parabolic pulse is closest to parabolic
one.
We have investigated a nonlinear pulse reshaping towards parabolic pulses in the passive normal dispersive optical
fibers. We have found that pulses with parabolic intensity profile, parabolic spectrum and linear chirp can be obtained
due to the passive nonlinear reshaping at the propagation distance exceeding a few dispersion lengths. These pulses
preserve parabolic profile during subsequent pulse propagation in a fiber. We have examined the influence of initial
pulse parameters and fiber parameters on the resulted pulse shape.
In the paper, we investigated the bistable properties of the wideband optical filter on the basis of nonlinear 2D
photonic crystal. All-optical flip-flop phenomena have been discovered in such filters which allows switching with
ultra-short pulses. Particularly, the attention in this work is paid to the filter characteristics stability as respect
to radiation parameters variation as well as to production defects.
We propose a new method for mass production of the photonic crystal devices on the basis of widely-known and well-developed technology such as micristructured optical fibers. In this paper, we investigate the optical properties of side-excited microstructured fiber and discuss the conditions for utilization such a structure as planar photonic crystal device, namely, the high-quality resonance filter.
In the present paper the modified effective-index model of photonic-crystal waveguide is proved and presented. This model allows to reduce the three-dimensional numerical analysis to the two-dimensional consideration of the waveguiding due to representing of the waveguide as its step-index analog with the cladding region described by the effective refractive index of two-dimensional photonic crystal (PC) and the effective core size. The effective core size allowing equivalent description of waveguiding properties in the PC waveguide using the modified effective-index model and its numerical approximation are numerically defined. The obtained data have been used for numerical investigation of waveguide couplers formed by tapered photonic crystal fiber (PCF). It was shown that the couplers have smaller loss in comparison with couplers made by tapered step-index fiber.
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