Frantisek Hanacek

OPTICAL FIBER SENSOR BASED ON REDISTRIBUTION OF POWER AMONG SEVERAL GUIDED MODES

Optical fiber sensors are suitable for measuring almost all magnitudes these days. This article describes one new possible area of optical fiber sensors. These sensors use for their function fundamentals of redistribution of power inside optical fiber. This principle should allow constructing a very sensitive optical fiber sensor. We designed novel optical fiber that affords utilizing of optical fiber for telecommunications and measurement at the same time. This fiber is designed to work on two wavelengths. This fiber works on telecommunication wavelength of 1550 nm in single mode regime and works on measurement wavelength of 850 nm in quasi-single mode regime. The refractive index profiles of real fabricated optical fiber samples and their development are shown in this article as well. All fiber samples were made thanks to grant cooperation with Academy of Science of the Czech Republic. The aim of this article is that brings new approach to utilization of optical fiber as a sensor based on redistribution of optical power among several guided modes and to show novel optical fiber structure design that agrees with conditions for such operations.

Passive fiber ring as a device for effective refractive index measurement

Fiber optic rings are used for synchronization of modes and optical pulses shaping in fiber lasers. The resulting pulses are characterized by stable amplitude and reduced chirp. The length of fiber ring is chosen so as to avoid loss of laser light coherence. New application of optical fiber loops is their inclusion in the closed loop during their excitation by laser light modulated by low-frequency signal and middle frequency signal. If loop also includes amplifying fiber which covers losses incurred by couplers will thus be possible evaluated a signal delay in long loop and thus measure the length of fiber. Reverse task is possibility to measure n1eff if we know the length of SM fiber loop. This type of designed fiber optic oscillator consists of single-mode optical fiber SM28e in lengths of order of kilometers. This fiber is connected in a series with erbium doped fiber that covers loop losses. Loop, which acts as an oscillator is excited by DFB lasers both at a wavelength of 1550 nm and at wavelength of 1310 nm. The paper will demonstrated the comparison between active and passive fiber loops and their influence to accuracy of effective refractive index measurement.

The design of equipment for optical power measurement in FSO link beam cross-section

The free space optical links have found their major application in todays technological society. The demand for quality broadband is a must for all types of end users in these times. Because of the large jamming from wireless radio networks in non-licensed ISM bands, the free space optical links provide bridging of some densely populated urban areas. Their advantage is the high transmission rate for relatively long distances. However, the disadvantage is the dependence of free space optical links on atmospheric influences. Aired collimated optical beam passes through the atmospheric transmission environment and by its influence cause the deformation of the optical beam. Authors team decided to construct a special measuring device for measurement of optical power in FSO link beam cross-section. The equipment is mobile and can be rearranged and adjust according to the given location and placement of the FSO link at any time. The article describes the individual structural elements of the measuring equipment, its controlling and application for evaluation and adjustment of measuring steps. The graphs from optical power measurements in the beam cross-section of professional FSO links are presented at the end.

The optical intensity distribution in the far field

This article describes an intensity distribution of optical beam in the far field. In free space communication laser transmitters, optical lenses and other components are used. When an optical beam impacts optical lens, the diffraction can appear at the edge of lens. A laser transmitted optical beam whose intensity distribution was Gaussian. This beam was aimed at the circular apertures of different diameters. These circular apertures represented transmitting lens. We could use circular apertures instead of lenses, because we obtained the same effects of diffraction. The optical beam passed by aperture and optical intensity distribution was observed at the screen, which was placed in the far field.

Measurement of the spectral characteristics of telecommunication fiber emitted at high temperatures

The fiber optic sensors have a great possibilities thanks to its sizes, features and usage possibilities in measurement engineering. Optical fiber is mostly used as a medium for the transfer of information, but if we consider an optical fiber as a sensor then the other usage can be found for example in medicine or biology. If the optical fiber is heated by sufficiently high temperature, the light signal starts to be emitted in the internal structure. This signal has a spectral characteristic, which can be used for evaluation of temperature thanks to quality analysis. The article will describe the evaluation of spectral characteristics for utilizationof optical fiber as fiber optic sensor for very high temperatures.

Passive fiber rings as a basic part of fiber optic sensors

The article deals with topics about fiber optic loop, evaluation of the signals delay in the loop and in case of the first designed arrangement measurement of the fiber length. The second task is to detect the effective refractive index n1eff of the fiber core at the given length of loop. Authors team gradually discusses how configurations for the tasks are created. From configuration designs is possible to build up optical fiber sensor.

Changes in optical spectrum of photonic fiber with two counter propagating laser beams

Photonic fiber with single mode couplers or splitters at each fiber end can be used as a sensitive structure for fiber sensing applications. The sensitive structure is created with two DFB lasers at λ = 1550 nm. Each laser is connected to opposite sides of photonic fiber provided with SM couplers. One DFB laser is isolated and its light goes through variable attenuation. Isolation is necessary for DFB laser stability. The second laser is DFB or F-P laser without any isolator. Its radiation is driven as with driven current so with DFB laser passing through photonic fiber. Small changes of DFB laser light passing through photonic fiber activate large changes in FP laser radiation. Temperature and pressure actuating on photonic fiber are examples of effects that are able to change properties of passing laser light. These changes can be measured with the help of photo detector at the second arm of SM couplers. Changes in optical spectra of F-P and DFB laser under temperature and pressure are the results.

From university to company: education of optical communications in cooperation with industry at Technical University of Ostrava

Paper deals with cooperation between companies and university, especially with interactions companies and students, companies and pedagogues. At present it is possible to observe insufficient level of practical skills and knowledge among students and their pedagogues, there is no articulation for companies’ demands. We try to solve this situation with the help of pilot compartment. Its main task is to associate university teachers, graduate students and companies‘ specialists. Within the scope activities of the compartment is to prepare one or two day’s long special courses. Their mass point is focused to practical training; prepare conditions for trainee-ships dedicated to teachers and students on one side and special courses for technicians, dealers and companies’ management on the other. The main goal of this compartment is an interconnection between university education and requirements out coming from praxis. There are many ways of how to fulfill such cooperation.