Severino Muñoz-Aguirre

Fiber Laser Thermally Tunable by a Filter Composed of Two Sagnac Interferometers

Many applications, such as fiber Bragg grating characterization, wavelength division multiplexing, etc. require tunable laser sources with one emission line in a certain wavelength range. Generally, such sources are laser systems combined with tunable filters. In this work an all-fiber laser tunable by a filter composed of two Sagnac interferometers in series is described. The filter loops were constructed of high birefringence fibers (HiBiFi) and the filter was thermally tunable with a single transmission maximum in the Erbium gain spectrum. The results showed that for interferometers with 14 cm HiBiFi length a bandwidth reduction of the transmission peak, a single-line laser emission, a tuning sensitivity of approx. -0.8 nm/degC and a spectral full-width at half-maximum bandwidth of 0.03 nm in the range of 1538-1580 nm were obtained.

Development and implementation of a system to measure the response of quartz crystal resonator based gas sensors using a field-programmable gate array

The development of gas sensors based on quartz crystal resonators requires the use of a frequency counter to measure the sensor response. However, commercial frequency counters have at most two channels, and in odour sensory systems (electronic noses), arrays of at least eight sensors are used. Furthermore, it is also desirable that the signal processing and data analysis stage can be included in the same system. A field-programmable gate array (FPGA) can provide a solution to these kinds of problems. This work involves the development of a system to measure the response of quartz crystal resonators, which is implemented using a high resolution frequency counter using an FPGA capable of processing and storing the data in 32-bit registers. Data transfer and acquisition were performed using a microcontroller. The virtual instrumentation software LabVIEW was used for the sensor response display and data storage in a computer. A frequency range from 0 Hz to 100 MHz with a resolution and stability of 1 Hz was achieved using a timebase of 1 s. Tests were performed using gas sensors to obtain real data. The system was escalated to four channels, verifying that it behaves in a correct and stable way.

Thermally Tunable All-Fiber Filter Based on Two Series Connected Sagnac Interferometers With Different Loop Lengths

In this paper, the characterization of a thermally tunable fiber optic filter is presented. It consists of two Sagnac interferometers (SIs) connected in series. Each SI contains a high-birefringence fiber (HiBiFi) segment with different length in the loop, which generates a reduction in the bandwidth of the filter transmission peak. In a previous work, a filter composed by two SIs with equal HiBiFi segments connected in series was reported. An experimental bandwidth reduction of approximately 31%, compared with a filter composed by a single SI was obtained. Using the configuration proposed in the present work, a reduction of approximately 52% in the range of 1533 to 1586 nm and a sensitivity of -1.27 nm/degC was obtained.

Optical system based on a CCD camera for ethanol detection

This work reports the optimization of an optical system used to detect and quantify volatile organic compounds (VOC). The sensor consisted of a polydimethylsiloxane (PDMS) sensing film deposited on a glass substrate by the spin-coating technique. The PDMS has the property of swelling and/or changing its refractive index when it interacts with molecules of VOC in vapor phase. In order to measure the PDMS swelling, a charge-coupled device (CCD) camera was employed to evaluate the interference fringe shift in a Pohl interferometric arrangement. With this approach, it is possible to use each pixel of the CCD camera as a single photodetector in the arrangement. Similarly, different computer algorithms were developed in order to acquire and process the obtained data. The improvements in the system allowed the acquisition and plot of 1 datum per second. The steady-state responses of the PDMS sensors in the presence of ethanol vapor were analyzed. The obtained results showed that noise level was reduced approximately three times after performing data processing.

Multipoint sensor based on fiber Bragg gratings

In some control and industrial measurement systems of physical variables (pressure, temperature, flow, etc) it is necessary one system and one sensor to control each process. On the other hand, there are systems such as PLC (Programmable Logic Control), which can process several signals simultaneously. However it is still necessary to use one sensor for each variable. Therefore, in the present work the use of a multipoint sensor to solve such problem has been proposed. The sensor consists of an optical fiber laser with two Fabry-Perot cavities constructed using fiber Bragg gratings (FBG). In the same system is possible to measure changes in two variables by detecting the intermodal separation frequency of each cavity and evaluate their amplitudes. The intermodal separation frequency depends on each cavity length. The sensor signals are monitored through an oscilloscope or a PCI card and after that acquired by PC, where they are analyzed and displayed. Results of the evaluation of the intermodal frequency separation peak amplitude behavior with FBG stretching are presented.

Simulator of an Adaptive Optics System Using Matlab

This article describes a program developed in Matlab that simulates an Adaptive Optics system, which allows observing a graphically simulated wavefront to understand the main concepts of an Adaptive Optics system and the constraints that have to be presented in classical control algorithms. The program is based on: (a) Simulation of a wavefront Shack-Hartmann sensor as a detection system and the wavefront reconstruction using Zernike polynomials from the slopes of the wavefront and (b) Simulation of a deformable mirror as the wavefront correction. This was characterized using the so called influence functions and Zernike polynomials. The voltage vector needed for the deformation that adopts the correction mirror wavefront was also calculated. Our results were corroborated graphically by the reconstruction of the wavefront and the deformation of the deformable mirror.

Analysis of an Optical Fiber Coherent System Immune to Polarization Fluctuations Using Adaptive Detection

The light polarization fluctuations strongly affect the performance of coherent optical communication systems due to the fact that to recover the information contained in the phase of the signal beam, it is necessary to have interference with a reference beam. In the present work, a simple system based on the use of an optical fiber interferometer and two adaptive photodetectors, which is immune to polarization fluctuations provoked by the fiber in both signal and reference beams, is theoretically analyzed. In such study, two models of the optical fiber, the first with just one linear retarder and another more complex with an additional circular retarder, were used. The results for linearly polarized light in the Y axis direction showed that digital signal transmission received by the adaptive system is immune to polarization fluctuations (in both signal and reference beams) in a wide range of ellipticity and rotation variations. In particular, if TTL logic is used, a maximum fluctuation of 60% with respect to the maximum of the output signal would be allowed to transmit the information correctly, in this case, ellipticity and rotation variations could be up to ±30°.

Development of a System to Detect Ethanol Vapor Using a CCD Camera in an Interferometer

The response of a polydimethylsiloxane sensor was measured using an interferometer and a CCD camera. The advantage is to have a great amount of sensors. From ethanol responses was found that the system works appropriately.

Automation of a dynamic system to measure response of quartz crystal microbalance gas sensors

In the present work, automation of a dynamic system to measure response of gas sensors based on quartz crystal microbalance (QCM) is presented. Automation was used to study transient response, which is necessary for sensor characterization. A valves system, which controls the gas flow towards the sensor, was implemented to generate the step function. The system was fully automated by using a PIC16F877 microcontroller. Results of sensor response measurements are presented.

Automatization of a Water Flow Laser Sensor Based on Bragg Gratings

The operation of a water-flow sensor based on two FBG laser was automatized using a PIC16F877 microcontroller. The results for optical power related to water-flow agreed with those for digitalized amounts within a 7.5% error.