Miloslav Filka

Φ-OTDR signal amplification

Phase-sensitive optical time-domain reectometry (Φ-OTDR) seems to be the most appropriate solution for acoustic vibration along standard optical fiber detection. In general the sensing system measures phase changes of the received Rayleigh back-scattered signal in the fiber. Since the back-scattered signal intensity is decreased about tens of decibels in comparison to the forward propagating pulse power level, the received signal power level is very low. That is why the main limiting parameter of the system is the power level of the back-scattered signal, which limits maximum achievable distance. For long reach sensing it is necessary to create high power optical pulses with short time-duration. Direct pulse amplification by erbium doped fiber amplifier (EDFA) is an issue because of the pulses low repetition rate. We have designed and verified a simple method using a holding beam for amplifying of pulses with low repetition rate by standard telecommunication EDFA booster instead of deployment of an expensive optical shutter. A second CW laser with a different wavelength for EDFA stabilization is used in our setup. Because a pulse losses its energy during propagation in the fiber and with longer distances by 1st order Raman amplifier (RA). In telecommunications this amplifier is used to compensate for fiber losses. The second setup uses remote amplification by remotely pumped erbium doped fiber (EDF) placed after a few tens of kilometers of sensing fiber. A pump laser is placed in the transmitter part of the system from where EDF is pumped. In this paper, we present an overview of few techniques for Φ-ODTR signals amplification and their verification by measurement.

The influence of binary modulations in passive optical network based on WDM

In this paper, a performance analysis of binary modulation formats in passive optical networks based on wavelength division multiplexing (WDM-PON) has been carried out. WDM-PON offers much higher transmission capacity and longer transmission distance than current PONs using separate wavelengths for each end unit and arrayed waveguide gratings for signal division. Nonlinearities and dispersion effects may affect a performance of transmission system and certain modulation formats can improve a quality of signal so the influence of current modulation formats on the performance of WDM-PON is tested.

Simultaneous transmission of distributed sensors and data signals

Nowadays, fiber-optic sensors are widely used in many areas of an industry. To confirm increasing interest in these sensors we performed a short survey of market analysis not only for recent years but also market prediction for a near future. We performed also a short survey of current trends in fiber-optic sensors based on latest published results. For special applications we designed two possible setups of simultaneous transmission of data and sensor signals in the same fibers. By measurement we have verified suitability of interferometric methods for sensor applications if fibers with active data transmissions are used. For back-scattered based sensors a high-power optical signal is necessary hence a measurement of dependence of pulse duration on intensity of the Brillouin peaks was performed.

Transmission convergence layer in XG-PON

The article deals with the Transmission Convergence Layer in 10 Gigabit passive optical networks. There is a description of conditions, under which the Optical Network Units (ONU) pass through, when is activated. Additionally, this article focuses on the processes of connecting ONUs to the Passive Optical Networks (PONs). The simulations demonstrate that as the number of simultaneous connections to ONU increase, longer wait time for each additional connection becomes. This also solves the collision conditions, that might arise in communication and the Equalization Delay (EqD). Finally, the article deals with the influence of a refractive index on timing relationships. The speed up of the frame transfer between Optical Line Terminal (OLT) and ONUs has been proven.

The Design of Optical Routes Applications

Contemporary optical fibers can deal with almost all of the unfavorable effects which are known these days. They have sufficiently low specific slump, they can handle a slump caused by OH-ions, they can restrain the multimode effect and finally they can compensate a chromatic dispersion. But there is one problem, which the present science can’t solve and this problem is the Polarization Mode Dispersion (PMD). This effect is a restricting factor of high-speed long-distance optical routes. The capacity increase of the existing optical routes is more often realized by multiplexing methods. Using more wavelengths makes multiplication of the optical fiber transfer rate possible. It evokes not only the advancement of fiber letting (known as “Dark Fiber” service), but more often also a single wavelength letting.

Multimedia communication transmission in medicine

The authors deal with transmitting, archiving, and sharing medical data between various modalities. The emphasis is on PACS, transmission media ( in this case the Metropolitan Academic Computer Network in Brno, Czech Republic) and interconnection of various types of hospitals and medical institutions.

The influence of digital modulations on 320 Gbit/s OTDM

In this article the optical time division multiplexing technique for high speed point-to-point optical networks is discussed. We performed test of influence of selected types modulation formats in the optical time division multiplexing simulation model with a distance of 30 km. Additionally, this paper focuses on maximum bandwidth usage, improvement of bit error rate and the another goal is to achieve the maximal transmission distance by using of special compensation optical fiber. Optimal length of compensation optical fiber was found and used during simulations. We demonstrated positive influence compensation optical fiber on bit error rate. For comparison of modulation formats such as return-to-zero, non-return-tozero, chirped-return-to-zero, carrier-suppressed-return-to-zero, and m-ary quadrature amplitude modulation were tested. Our results confirm that it is possible to achieve better bit error rate for selected modulation formats.

Transmitting Conditions of Cable Tree

Research and development of Spectrum Administration for metallic access networks analyzed possibilities of matrix representation for transmission circumstances. Some interesting remarks were gained as a side output of this work.