Here we describe the fabrication and testing of a hollow prism and its application in a spectrograph. A hollow prism with a grating (GRISM) is used as a tunable spectrograph.
A Mueller-Stokes analysis of the polarization characteristics of a photonic crystal fiber (PCF) with a mechanically induced long-period fiber grating (MLPFG) is presented. Results show that the diattenuation and the polarizance parameters, and the anisotropic degree of depolarization, increase greatly with the LPFG in the PCF. The depolarization index, the Q (M) depolarization scalar metric, the theorem of Gil-Bernabeu, and the degree of polarization, provide consistent results that indicate the existence and the increasing of depolarization effects due to the presence of the LPFG in the PCF. Finally, the polarization dependent loss also increases when the LPFG is present in the fiber for a wavelength illumination centered at 1064 nm. As a conclusion, the PCF with LPFG cannot be described by the Jones matricial formulism. One important result we have found here is that the PCF we employed has an intrinsic anisotropic degree of depolarization.
A simple experimental setup for measuring the cleave angle of optical fiber facets by using a plano-convex cylindrical lens is presented. In this method, a laser beam is coupled to the perpendicularly cleaved input fiber facet and propagates up to the output end, where the fiber facet is cleaved at a certain angle. The divergent beam emerges from the output end fiber at an angle determined by the cleave angle and impinges at the cylindrical lens through a very narrow slit. The slit is placed in contact with the vertex of the convex side of the cylindrical lens and parallel to its axis. The slit-lens assembly is moved perpendicular to the optical axis of the lens so that the marginal rays of the incident beam pass through the slit. Using the output angles from marginal rays of the refracted beam by the cylindrical lens, it is possible to calculate the output angle of the principal ray and, by measuring this angle, the cleave angle can be estimated.
Photonic crystal optical fibers have much more degrees of freedom concerning the geometries and index contrasts than
step-index fibers; therefore, the theoretical analysis of their performance is usually based on the finite element method.
In this work, taking advantage of the similarities observed for twisted single-mode fibers: standard (SMF-28 and SMF-
28e) and hexagonal photonic fibers, we propose that in regard with polarization performance, photonic fibers can be
described using a simpler model based on classical polarization optics. The main advantages of the matrix model we
propose lie in its accuracy and generality: for each one of the selected wavelengths and input states of polarization, it
allows a precise prediction of the output polarization state. The comparison of the experimental results measured for
standard and photonic fibers with the theoretical model predictions indicates that in both cases, twist induced
birefringence is produced not only by the medium's photoelasticity, but also by the waveguide (cladding/core structure
and asymmetry) modification. In addition, for the photonic fiber, the non-symmetrical response to right and left twist
allowed the identification of an initial twist as part of the residual elliptical birefringence.
A wavelength-switchable erbium-doped fiber ring laser is demonstrated and reported. The erbium-doped fiber net gain
of the fiber laser is modified by controlled heating of a Long Period Fiber Grating (LPFG) inserted into the laser cavity.
The rejection band of the LPFG is altered in the resonant wavelength and loss according to the exposed temperature and
consequently, the operating wavelength of the fiber laser can be switched from a single wavelength operation at 1563 nm
to a simultaneous operation at 1527 and 1563 nm. The laser system can be used as a temperature fiber sensor as well.
In the modeling of supercontinuum generation in photonic crystal fibers by ultrashort pulses, the knowledge of the
higher-order dispersion terms of the fiber are necessary to achieve a good approximation between the simulated and
experimental spectra. However, these parameters are usually not provided by the manufacturer. In this work, we present
the numerical estimation of the higher-order dispersion terms for a nonlinear photonic crystal fiber with hexagonal holes.
For the simulation, we chose a commercial fiber with a high nonlinear response (Blazephotonics NL-2.4-8). The fiber
was designed with a small core diameter of 2.4 μm and a triangular pattern of air holes in the cladding with a pitch of
2.9 μm. Through the free software, MIT Photonic Bands, the structure of the fiber was modeled and the effective
refractive index, as well as the dispersion terms curves are estimated. From our results, the zero-dispersion wavelength of
the fiber resulted to be of 800 nm and at this wavelength, the higher-order dispersion terms were: β2=0, β3=0.05 ps3/km,
β4=-7.03×10-5 ps4/km, β5=1.4×10-7 ps5/km, β6=-4.163×10-10 ps6/km, β7=1.118×10-12 ps7/km. The zero-dispersion
wavelength and the dispersion slope estimated at this wavelength agree with the values reported by the manufacturer.
We present the calculations of the higher order dispersion coefficients in a photonic crystal fiber. The dispersion
coefficient is obtained from the calculated effective index of the fiber structure by double differentiation with respect to
the wavelength (or frequency), or from the integral formula used to calculate the group index. Although both approaches
are equivalent we show that they lead to totally dissimilar results, like different zero dispersion wavelength and hence the
higher-order dispersion coefficients are different. In fact, the way in which the higher-order dispersion coefficients are
calculated will affect the prediction of the dynamics of the supercontinuum generation. This effect will be discussed in
this work.
Here we report on the first CENAM realization of the phase-shift method for chromatic dispersion measurements in
mono-mode phase-shifted optical fibers used for the telecommunications C-band (1 550 nm). This chromatic dispersion
measurement and calibration capability development at CENAM will provide the Mexican telecommunications industry
with a formally established SI units traceability source, thus promoting this rapidly growing and high impact economic
sector competitiveness in Mexico. We also identified a 40 MHz modulation frequency, a 2.5 nm wavelength step and the
1 535 nm to 1 570 nm wavelength scanning range, as the optimum experimental parameters that have to be set in order
to obtain experimental data which numerical Sellmeier polynomials fittings produce representative determinations for
the group delay and the chromatic dispersion. We also obtained 1 549.388 nm ± 0.098 nm, (k=1), for the zero dispersion
wavelength, and 0.719 7 ps-nm-2 ± 0.005 5 ps·nm-2, (k=1), for the zero dispersion slope of the tested optical fiber.
A numerical study of the effects of tapering a hollow-core photonic bandgap fiber (HC-PBGF) on the spatial
parameters: effective area, nonlinear parameter and dispersion parameter is presented. The taper on the fiber is
modeled by scaling the cross section of the original fiber geometry. Both the air and the silica contribution to the
effective area and the nonlinear parameter are shown. The obtained results show a blueshift of the transmission
band and of the zero-dispersion wavelength. By tapering the fiber 30%, the transmission band and the zerodispersion
wavelength blueshift around 300 nm and 320 nm, respectively. HC-PBGFs have made possible the
study of nonlinear optical effects and by tapering the fiber, such nonlinear phenomena can be made stronger.
We present the fabrication and characterization of a micro-displacement sensor using Mach-Zehnder
interferometer in conventional optical fiber SMF28-e. The Mach-Zehnder interferometer uses a
configuration of two long-period gratings (LPG) in series mechanically induced. The Mach-Zehnder
interferometers were made to operate in the region of 1300 nm. As a result the interferometers were
obtained with transmission bands with a bandwidth of 2 nm, extinction ratio of 12 dB and insertion loss of
2 to 3 dB. The characterization of the interferometer was found to be measured displacements up to 500
μm with a resolution of 7 microns, which envisions potential applications of micro-displacement sensor in
the measurement of micro-deformations.
We present a new computational scheme to design supercontinuum spectra "à la carte" by means of Genetic Algorithms.
Due to the potentially large amount of computations required by this strategy, the deployment of these heuristic
algorithms is performed using distributed computing in the form of a Grid platform. The optimization procedure is
automated within the Grid platform and permits escalation to large computational Grids. Some examples of designed
supercontinua are given and potential applications for the design of future photonic devices are briefly described.
We present the temperature response of a mechanically-induced long-period fiber grating (MLPFG) made in photonic
crystal fiber (PCF) with and without the coating polymer. In both cases, we found a wavelength shift to shorter
wavelengths and a critical decrease of the attenuation peaks. A maximum wavelength shift of 6 nm at 1060 nm was
obtained when the temperature changed from 20 to 80 °C in PCF without the polymer. Whereas, the depth of the
attenuation peaks were dramatically reduced from 12 to almost 2 dB at 1060 nm when the temperature increase from 20
to 100 °C in both experiments. These results are important to consider when MLPFG are applied in a medium with room
temperature variation.
An analytic method based on Mueller matrix formalism and the Poincaré sphere is used to evaluate the birefringence
dispersion in hexagonal photonic fibers with circular air-holes when the hexagonal symmetry is modified. This
evaluation has been performed in the wavelength range from 1520 to 1570 nm, using monochromatic signals.
Assuming that the imaginary part of the propagation constant of leaky modes is much smaller that its real part, we
describe a procedure for the calculation of the effective refractive index of multilayer optical fibers. In our method
there is no need to look for roots in the complex plane, since the differential equations for the transverse modal
distribution are expressed in terms of the absolute value of the propagation constant.
A three-wavelength ytterbium-doped fiber laser based on a long period grating induced mechanically in a twisted holey
fiber is proposed and demonstrated. The long period grating is inserted into the laser cavity to introduce inhomogeneous
loss in order to obtain up to three output laser wavelengths at room temperature. The lasing wavelengths are localized at
1081.5 nm, 1090.5 nm, and 1100.7 nm with an average wavelength separation of 9.6 nm which can be slightly modified
by changing the twist rate of the holey fiber into the laser cavity.
We demonstrate the minimization of background loss for arc-induced long-period fiber gratings in standard fiber by Taguchi's optimization method. We use Taguchi's method to determine the optimum values for parameters like electric-arc power, arc duration, and tensile strain applied over the fiber during the inscription process. With these optimal parameters, we minimize the background loss resulting from the geometrical deformations of the fiber. The experimental results show that background loss can be reduced from more than 1 dB to less than 0.3 dB at rejection bands with isolation >15 dB.
A method for tuning the transmission characteristics of arc-induced long-period fiber gratings by local heating is
presented. A traveling burner, produced by the combustion of a mixture of oxygen and butane, locally heats the longperiod
grating producing a wavelength shift of the resonant peaks. We have found that the resonant wavelengths are
blue-shifted during the first 7 round trips of the flame, but when heating process continues the notches shifts toward
longer wavelengths. A fine and long range tuning of the resonant wavelengths up to 120 nm can be achieved without
substantial degradation on the grating characteristics. The process is repeatable and only takes a few minutes.
We propose a temperature sensor based on dispersion shifted long period fiber grating (LPFG) fabricated with the
fattening method, using electric arc discharges from a commercial fusion splicer machine. The fattened LPFG are
centered at 1524 and 1550 nm, respectively. A temperature characterization in terms of the transmitted spectrum is
realized with a pumped Er+3 doped fiber as the light source. The less than 3 mm in length fattened LPFG reached a
sensitivity of 72 pm/°C between a temperature range of (25-500°C). Temperature stability was observed among the
temperature range of (25-200°C), result in agreement with our previous studies. From up to 200°C sensing is observed
as temperature increases. To apply this LPFG as a temperature sensor, sensing was measured as voltage signal outputs
with repeatable results. This sensor is a high temperature resistant device because non deterioration of its properties was
observed, and can find useful applications when temperature stability may be needed or the sensing requirements are
desirable.
An optical pumping device consisting of pigtailed diode lasers and a paraboloidal mirror is presented. The pigtailed diode lasers are mounted on a circular plate in radial position in front of the mirror, and the reflected beams are then launched into a 200-µm-diam undoped silica fiber with silicone cladding, with up to 75% coupling efficiency. The implementation of the device is simple and can be used to scale the power in fiber laser systems.
Ytterbium absorbs at 915 and 976nm. It also emits at 976nm and from 1060nm to even 1150nm, showing a quantum
efficiency of up to 86%. In this experimental work, our novel inner cavity structures were firstly characterized and
studied as free-running lasers from the 4% Fresnel reflection from the flat-cleaved fiber facets. The available pump
source, a commercially available laser diode, had a maximum power of 0.5W at 915nm from which a coupled power
(into the inner cladding) of 1W was reached; fiber laser efficiency reached, in our best case, 55% with respect to
launched pump power. For the second part of the work, polarization controlled Yb-doped fiber laser cavities were
studied by way of inserting a polarized beam splitter and a &lgr;/4 wave-plate into de cavity. From this, 177mW of single
polarization output were obtained by rotating the wave-plate until the maximum points were identified on a wave-plate
angle vs. output power plot. The maximum output power was 200mW from 60° to 90° aprox. Now, based on the data
obtained, one can claim that at least 40% of the maximum output power available from the laser was linearly polarized.
Finally, a 600 lines/mm bulk grating was employed in order to obtain laser tuning results on a traditional way. i.e. by
reflecting lasing into the cavity and selecting output from the close end. The tuning range was measured to be from
1088nm up to 1097nm. All these results and possible applications will be discussed in detail.
In this work, we propose a set of photonics devices that can be employed as part of optical communications systems.
These devices consist of an isolator, a circulator, a multiplexer and a pump concentrator, and are based on the
functionality of an optical paraboloidal mirror. The devices were first studied using software for optical modeling and
then were experimentally tested. For the cases of the isolator and the circulator, we obtained numerically roughly 50 dB
of isolation. Furthermore, we proposed a simple and a novel multi channel multiplexing device, and finally, we asses the
alternative and elegant way of the combination of high power multimode diode laser to increase the power capability of
diode laser systems that are commonly used in high power fiber laser. In all the cases, the design showed the advantage
of the easiness of alignment and the simplicity to implement.
A very simple and cost-effective technique for wavelength tuning a fiber laser using multimode interference effects is
demonstrated. The tuning mechanism relies on the self-imaging effect which occurs in multimode waveguides. The
tuning mechanism consists of a section of multimode fiber (MMF) spliced to a single mode fiber (SMF), with a
broadband mirror located at the other end of the MMF. The signal coming out of the SMF will be imaged within the
MMF at a very specific location. Therefore, if the length of the MMF is slightly shorter than this length, the image will
be formed in free space. By placing the mirror at this position, the light is reflected back through the MMF and SMF.
Since the self-imaging is wavelength dependent, the position of the re-imaging point will depend on the wavelength, and
the laser wavelength can then be tuned by varying the distance between the MMF facet and the broadband mirror. To
obtain a stable system and easy to align mechanism an integrated fiber gripper was fabricated on silicon wafer. This
novel tuning device was incorporated into a double-clad Ytterbium-doped fiber laser (DCYDF), and the tuning
characteristics were evaluated by varying the distance between the broadband mirror and the output facet of the MMF.
The mirror was moved in 25 microns steps, and the optical power and spectrum measured at every step. A tunability of
12.24 nm was measured with this implementation, and the laser system was shown to be very robust and highly stable.
We believe that further improvement in our system will lead to a wider tuning range.
A birefringence compensation method for a mechanically induced tunable long period holey fiber grating is proposed.
With this method the tunable long period holey fiber grating becomes polarization-insensitive. A device with such
characteristics is desirable in applications where filter tunability is used to reject (or simply attenuate) non desired optical
bands. Characterizations with polarized and nonpolarized light are presented and the potential applications are discussed
as well.
We present a novel approach for the combination of high power multimode diode lasers. The design considered to ensemble several pigtail multimode diode lasers in a radial position on a circular thin disk (the lid) which has a hole-concentrator at the center point. The reflect mirror which is in charge of concentrating the beams at one point and overlapping them without mutual spatial interference is a paraboloidal mirror which is sprayed by a silver thin reflectance film and it is physically covered by the lid. We simulate this device by using commercial software for optical design and we will show the complete analysis of the ray traces as well as the coupling efficiency of the system.
We present a fast and efficient numerical model for Yb3+-doped fiber lasers based on shooting method. The algorithm is based on the assumption of a starting value for the slope efficiency and the evaluation of the pump power threshold. The starting value of slope efficiency is related to initial conditions through the boundary conditions, and it is subsequently optimized by iteration. The method ensures a fast and efficient convergence of the solution of the coupled first-order differential equations that describes the evolution of pump and signal powers in a Yb3+-doped fiber laser. The results of the numerical solution are compared with experimental and published data giving a good agreement.
We present all-fiber double-clad Yb3+-doped fiber laser capable to switch between three different wavelengths. The fiber laser device consists of an array of three fiber Bragg gratings at 1064, 1080, and 1096 nm, spliced to one end of the double-clad Ytterbium-doped fiber, thus forming three laser cavities that share the same gain medium. The selection of a specific wavelength is realized by induced bend loss in the sections between gratings, thus allowing the control of the feedback at each specific wavelength. The device can operate separately at 1064, 1084 and at 1096 nm, with slope efficiencies at these three wavelengths of the order of 48% with respect to the launched pump power.
A novel design in the inner cladding of a cladding-pumped ytterbium-doped fiber is presented. The fiber includes a modification of the inner cladding by the insertion of four D-shaped holes distributed around the core in a square configuration. This novel fiber structure makes the device efficient in absorbing the pump power while keeping the overall circular structure. As a result, up to 5 W of single mode at 1095 nm from a 7 W of absorbed pump power was achieved; the slope efficiency was 60% wrt. launched pump power and the beam quality was measured to be 1.2 implying that our laser has a diffraction limited output beam.
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