Geometrical shaping of non-adiabatic single tapers is used to modify the filtering characteristics. The fiber tapers are shaped by successive tapering. The taper shaping produces deeper rejection bands. As an application of the shaped tapers, fluidic temperature sensing cells were fabricated. In a first case, the wavelength shift of a single rejection band was monitored, showing a nonlinear response and low sensitivity to temperature changes. In a second case, a shaped taper fluidic cell containing two rejection bands was used, and the wavelength shift of the half intensity points of the transmission band (between the rejection bands) was taken as a measure of the temperature change. In this case, the fluidic cell showed a linear sensitivity of 481.9 pm/°C in a temperature range of 25°C-60°C.
A new and simple method for measuring the refractive index of liquid substances is presented. In this method, a laser beam impinges transversely on a glass tube (cylindrical cell) filled with the liquid to be measured. The laser beam incident on the cylindrical cell is deviated when it propagates through the wall of the cell and the liquid contained in it. By measuring the deviation of the principal ray of the laser beam when it emerges from the cylindrical cell, we can determine the refractive index of the liquid. To show the feasibility of the method, we measured the refractive index of pure water with a He-Ne laser.
A phase recovery procedure from several interferograms acquired in highly noisy environments as severe vibrations is
described. This procedure may be implemented when phase shifting techniques may not be applicable due to the high
error in the phase shift due to the vibrations. The phase differences among successive interferograms may contain nonlinear
terms that could lead a sign changes in the supposed constants shift terms among acquired images. This can not be
handled correctly with algorithms that corrects small nonlinearities in the phase shifts due to moderate disturbances
during the phase shifting process. In most interferometric configurations for phase measurements the main effect of
vibrations is to introduce a misalignment in the interferometric setup. Then, the phase differences between each
interferogram may contain piston, tilt, and defocus errors. We observed that the tilt term is often the most dominant of the phase differences terms. In such cases, cosine of the phase differences among interferograms may be recovered. This cosine may be processed with Fourier methods in order to recover the phase differences. Once the phase differences are available the phase encoded in the interferograms may be determined. The proposed algorithm is tested in real interferograms.
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.
A new technique for the phase gradient estimation encoded in a single interferogram is proposed. The gradient is
calculated numerically solving a differential equation obtained from the interferogram's derivatives in orthogonal
directions. The phase gradient is assumed to vary almost linearly among adjacent pixels in a small window. A
regularized term is aggregated to the differential equation which enables us to find the solution for the phase derivatives
adjusting a plane in a minimization process. Both phase derivatives terms are obtained simultaneously from a set of
linear equations that results from the minimization process. The algorithm requires a small initial region with the phase,
the phase derivatives, and the sine of the phase already estimated. The calculated values of the sine of the phase from the
initial region are used as a regularized term to solve the differential equation. The phase derivatives solution is then
propagated from the initial region until the whole interferogram field is processed. Each value of the sine of the phase
found is aggregated in the regularized term which makes the solution stable. The initial region may be easily found
applying a band pass filter in the frequency domain as done with the Fourier method. The phase of the interferogram is
calculated with a least square method using the information of the phase derivatives found with the proposed technique.
The feasibility of the described approach for phase gradient reconstruction is tested in simulated and experimental data.
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.
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.
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.
The classical method for wavefront retrieval from Hartmann test data by integration of the transverse aberrations using a linear approximation between the sampled points: In this work we report a method using splines that produces a more precise wavefront shape.