J. A. Alvarez-Chavez

Polymer optical fiber moisture sensor based on evanescent-wave scattering to measure humidity in oil-paper insulation in electrical apparatus

An optical fiber moisture sensor is prepared by coating a 1 mm polymer optical fiber with a film 30 micron thick of Polyvinyl Acetate PVA. We have experimentally studied how the light transmission characteristics of such coated optical fiber changes as a function of moisture conditions within an oil-paper insulation, to which the coating is exposed. An optical fiber moisture sensor that can be used to sense moisture present in liquid transformer oil and composite paper insulation in a wide range of concentrations is characterized. The resulting optical fiber sensor can be used for on-line measurements in electrical apparatus that use oil-paper insulation under large electrical field gradients. A light guide such as an optical polymer fiber operating in the 400 nm to 970 nm wavelength range is embedded in a body of paper insulation material immersed in oil, with the free ends of the fiber extending to or beyond the edges of the structure so that radiation such as light can be directed through one end of the carrier, and measured at the other end thereof, to monitor and detect the presence of moisture in the interior of the structure. Under normal operating conditions of power transformers the moisture concentration in the oil is in the range of 10 to 100 ppm and 0.5 to 5% in paper for a temperature range of 0 to 100degC. In order to compensate for the oil optical properties, an additional optical polymer fiber in contact with the transformer oil is used as a cero reference outside of the paper structure, since amount of moisture in oil is at least 200 times smaller than the moisture in the paper.

Optimum peak pulse investigation for OTDR instrumentation

This work presents an experimental study of the optimal peak-power pulse for testing telecommunications fibers. Using a Q-switched fiber laser at 1060 nm, we obtained 100-ns pulses at a 10-kHz repetition rate with an average power of 60 mW corresponding to a 60-W peak power. With these pulses, we generated up to fifth-order Stokes within the fiber, with wavelengths on the third window of telecommunications. We demonstrate that the power exceeding the optimum peak power does not increase the penetration length of OTDR systems because of the pump depletion. The shape of the Stokes-shifted pulses attained at the end of the test fiber is similar to the pulse shape from a Q-switched fiber laser, also showing the possibility to produce suitable peak powers and pulse shapes for OTDR applications at different wavelengths.

Threshold and maximum power evolution of stimulated Brillouin scattering and Rayleigh backscattering in a single mode fiber segment

The behavior of stimulated Brillouin scattering (SBS) and Rayleigh backscattering phenomena, which limit the forward transmission power in modern, ultra-long haul optical communication systems such as dense wavelength division multiplexing systems is analyzed via simulation and experimental investigation of threshold and maximum power. Evolution of SBS, Rayleigh scattering and forward powers are experimentally investigated with a 25 km segment of single mode fiber. Also, a simple algorithm to predict the generation of SBS is proposed where two criteria of power thresholds was used for comparison with experimental data.

Temperature sensing through long period fiber gratings mechanically induced on tapered optical fibers

In this work the feasibility of employing two well-known techniques already used on designing optical fiber sensors is explored. The first technique employed involves monomode tapered fibers, which were fabricated using a taper machine designed, built, and implemented in our laboratory. This implementation greatly reduced the costs and fabrication time allowing us to produce the desired taper length and transmission conditions. The second technique used fiber Bragg gratings, which we decided to have mechanically induced and for that reason we devised and produced our own mechanical gratings with the help of a computer numerical control tool. This grating had to be fabricated with aluminum to withstand temperatures of up to 600°C. When light traveling through an optical fiber reaches a taper it couples into the cladding layer and comes back into the core when the taper ends. In the same manner, when the light encounters gratings in the fiber, it couples to the cladding modes, and when the gratings end, the light couples back into the core. For our experimentation, the tapering machine was programmed to fabricate single-mode tapers with 3 cm length, and the mechanically induced gratings characteristics were 5 cm length, and had a period of 500 μm and depth of the period of 300 μm. For the conducting tests, the tapered fiber is positioned in between two aluminum slabs, one grooved and the other plane. These two blocks accomplish the mechanically induced long period grating (LPG); the gratings on the grooved plaque are imprinted on the taper forming the period gratings. An optical spectrum analyzer is used to observe the changes on the transmission spectrum as the temperature varies from 20°C to 600°C. The resultant attenuation peak wavelength in the transmission spectrum shifts up to 8 nm, which is a higher shift compared to what has been reported using nontapered fibers. As the temperature increases there is no longer a shift, but there is significant power loss. Such a characteristic can be used as well for sensing applications.

Rare-earth-doped fiber designs for superluminescent sources

Abstract. The use of rare-earth-doped fiber section working in amplified spontaneous emission regime for different emission wavelengths is analyzed theoretically. From simulation results, the design of all-fiber superluminescent sources employing different rare earths as dopants for new optical windows and different applications is proposed. Results on different pump and signal powers in forward and backward propagation direction with respect to fiber length are presented.

Implantable blood pressure sensor for analyzing elasticity in arteries

MEMS technology could be an option for the development of a pressure sensor which allows the monitoring of several electronic signals in humans. In this work, a comparison is made between the typical elasticity curves of several arteries in the human body and the elasticity obtained for MEMS silicon microstructures such as membranes and cantilevers employing Finite Element analysis tools. The purpose is to identify which types of microstructures are mechanically compatible with human arteries. The goal is to integrate a blood pressure sensor which can be implanted in proximity with an artery. The expected benefits for this type of sensor are mainly to reduce the problems associated with the use of bulk devices through the day and during several days. Such a sensor could give precise blood pressure readings in a continuous or periodic form, i.e. information that is especially important for some critical cases of hypertension patients.

Three-wavelength switching in a cladding-pumped ytterbium-doped fiber laser

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 Survey on Quality of Service in the Voice Over IP Technology

In Mexico, the society in general lacks the habit and ethics of properly disposing garbage or in taking care of the environment. This paper focuses on analyzing and disposing garbage in an automated way. The present study also seeks to create and promote care for the planet. The minicomputer (GreenScanProcess) is an automated system whose process is based on an algorithm that stands out for its functionality. GreenScanProcess has sensors that allow the analysis and scanning of garbage. It also measures the weight and humidity of the garbage. The minicomputer also examines the garbage to know its composition. Likewise, GreenScanProcess takes the garbage to the container according to the garbage. The benefits obtained when conducting the research were: environmental, economic, technological, and educational.

2-um optical time domain reflectometry measurements from novel Al-, Ge-, CaAlSi- doped and standard single-mode fibers

The development of novel Al-, Ge- doped and un-doped standard single mode fibers for future optical communication at 2μm requires the integration of, among other pieces of equipment, an optical time domain reflectometry (OTDR) technique for precise spectral attenuation characterization, including the well-known cut-back method. The integration of a state of the art OTDR at 2μm could provide valuable attenuation information from the aforementioned novel fibers. The proposed setup consists of a 1.7 mW, 1960nm pump source, a 30 dB gain Thulium doped fibre amplifier at 2μm, an 0.8mm focal length lens with a 0.5 NA, a 30 MHz acusto-optic modulator, a 3.1 focal length lens with a 0.68NA, an optical circulator at 2μm, an InGaAs photodetector for 1.2 nm-2.6 nm range, a voltage amplifier and an oscilloscope. The propagated pulse rate is 50 KHz, with 500 ns, 200 ns, 100 ns and 50 ns pulse widths. Attenuation versus novel fibers types for lengths ranging from 400- to 1000- meter samples were obtained using the proposed setup.

Short range, >100Kbits/s, visible light communication protocol design for high-gamma smartphones

High gamma smartphones based on Android operating system support the development of third-party applications. This kind of devices include subsystems such as sensors and actuators which can be used for diverse purposes. One example is the implementation of short range visible light communication (VLC) channels where the built-in light-emitting diode (LED) is the transmitter, and the complementary metal-oxide semiconductor (CMOS) camera works as the receiver. A major challenge for this communication channel is the modulation bandwidth of the light source which is limited to a few MHz, and the availability of a line-of-sight. The camera shutter is limited to a few frames per second (30 or 60 fps) for a few bits per second transmission, but the Rolling Shutter effect could allow the enhancement of the bit rate. In this work, we propose a VLC protocol design for the use of the built-in camera and the flash LED in order to implement a short range VLC channel, for high gamma mobile-to-mobile devices based on Android. The design is based on On-Off Keying (OOK) modulation for initially transmitting a few bits. Based on the rolling shutter effect in the CMOS image sensor, bright and dark fringes can be observed within each received frame, and the data can then be retrieved. Furthermore, two thresholding schemes for high fluctuation and large extinction ratio (ER) variations in each frame, are explored. Full protocol design and short range (5 cm), >100 kbits/s, VLC demonstration and image processing results will be included in the presentation.