Jan Radil

High-definition multimedia for multiparty low-latency interactive communication

We describe a high-quality collaborative environment that uses High-Definition (HD) video to achieve near realistic perception of a remote site. The capture part, consisting of a HD camera, Centaurus HD-SDI capture card, and UltraGrid software, produces a 1.5 Gbps UDP data stream of uncompressed HD video that is transferred over a 10GE network interface to the high-speed IP network. The HD video stream displaying uses either a software-based solution with color depth down-sampling and field de-interlacing, or another Centaurus card. Data distribution to individual participants of the videoconference is achieved using a user-controlled UDP packet reflector based on the Active Element idea. The viability of this system has been demonstrated at the iGrid 2005 conference for a three-way high quality videoconference among sites in the Czech Republic, Louisiana, and California.

Large signal model of TDM-pumped Raman fiber amplifier

In this letter, we study spectral optical signal-to-noise ratio (OSNR) profile of a wide-band Raman fiber amplifier (RFA)with time-division-multiplexed (TDM) pumping. We derive a comprehensive large-signal numerical model which incorporates time variation effects and the downstream propagation of signals, upstream propagation of pumps, and downstream and upstream propagation of amplified spontaneous emission spectral components. We present results for a four-wavelength-pumped discrete RFA with TDM and continuous-wave pumping. Improvement in OSNR flatness of 0.9 dB due to TDM pumping is demonstrated.

Channel addition-removal response in all-optical gain-clamped lumped Raman fiber amplifier

Application of all-optical gain-clamped (AOGC) lumped Raman fiber amplifier (RFA) for protection of surviving channels in multiwavelength networks is investigated experimentally and theoretically. Channel addition-removal was simulated by transmitting signals of two lasers through a counterdirectionally pumped RFA consisting of 16 km of dispersion compensating fiber. Light of one of the lasers was square-wave modulated at 500 Hz; power fluctuations of the other laser caused by cross-gain modulation of the RFA were monitored at the output of the amplifier with a digital oscilloscope. An all-optical feedback loop was implemented in the form of a ring laser. Theoretical analysis of the AOGC lumped RFA is based on numerical solution of coupled propagation equations for forward and backward-propagating pumps, signals, and spectral components of amplified spontaneous emission powers.

All optical two-way time transfer in strongly heterogeneous networks

We experimentally compared different options for interconnection of remote places in precise time transmission infrastructures. We aimed at lines with bidirectional single path amplification, as they provide the best results in term of time uncertainty. For links with high reflections and without accessible midpoints, the distributed Raman amplification has been tested. In case of dark channels with fibre based “last miles”, the Raman amplification in the last miles only has been verified. According to author’s knowledge, this is the first time when the distributed amplification is used for modulated precise time transmission over fiber. For reference, the traditional lumped EDFAs suitable for transmission links or dark channels with accessible mid-point have been compared.

Surviving-Channel-Power Transients in Second-Order Pumped Lumped Raman Fiber Amplifier: Experimentation and Modeling

In this paper, the effect of addition and/or dropping of wavelength-division-multiplexed channels in an all- optical gain-clamped (AOGC) second-order (SO) pumped lumped Raman fiber amplifier (LRFA) has been investigated experimentally and analyzed by numerical simulation. Channel addition/ removal was simulated by transmitting ten signals through a counter-directionally pumped LRFA consisting of a 16-km-long dispersion-compensating fiber. The light from eight lasers was square-wave modulated at 500 Hz; power transients of the surviving channels caused by cross-gain modulation of the LRFA were monitored at the output of the amplifier. All-optical feedback loop was implemented in the form of a ring laser. Gain-clamping properties of the SO-pumped LRFA are compared with those of the first-order pumped LRFA having the same ON/OFF Raman gain. Theoretical analysis of the AOGC LRFA was based on numerical solution of coupled propagation equations for the backward propagating pump, signals, and both forward and backward propagating spectral components of amplified spontaneous emission powers.

10 Gb/s and 40 Gb/s Multi-Wavelength Conversion Based on Nonlinear Effects in HNLF

We present experimental results and numerical simulations of multi-wavelength conversion of 10 Gb/s NRZ signals based on 2-pumps four-wave mixing, 10 Gb/s and 40 Gb/s RZ signals derived from supercontinuum (SC) generated in highly nonlinear fibre (HNLF). High quality SC with bandwidth exceeding 50 nm was generated when the HNLF was pumped with 25 dBm average power. Sliced SC can be used as a source for all-optical multicasting

Experimental comparison of all-optical methods of chromatic dispersion compensation in long haul transmission at speeds of 10 Gbit/s

Feature Issue on Transmission in Optically Transparent Core NetworksDifferent techniques and scenarios of all-optical chromatic are compared experimentally. Chromatic dispersion was compensated both conventionally by dispersion compensating fibers and unconventionally using both channelized and broadband fiber Bragg gratings and Gires-Tournois etalons. Results are compared experimentally at a transmission speed of 10 Gbit/s. Emphasis was also given to tunability and broadband characteristics of elements.

Analysis of channel addition/removal response in all-optical gain-clamped cascade of lumped Raman fiber amplifiers

The effect of addition and/or dropping of wavelength-multiplexed channels in a network comprising three concatenated lumped Raman fiber amplifiers (LRFAs) have been analyzed by numerical simulation and verified experimentally. The first LRFA in the cascade is gain clamped using a ring-laser configuration, and the lasing power propagates through the cascade. A large-signal numerical model that incorporates time variation effects and the downstream propagation of signal, upstream propagation of pumps, and downstream and upstream propagation of amplified spontaneous emission spectral components has been used for the theoretical analysis. The LRFAs consist of 16 km of dispersion-compensating fiber counterdirectionally pumped at 1455 nm by a Raman fiber laser. Channel addition/removal is simulated by propagating through the cascade of LRFAs optical power from two laser diodes. One of them is square-wave modulated at 500 Hz, and power fluctuations of the second continuous-wave signal caused by the cross-gain saturation effect in LRFAs are monitored.

Optimization of NRZ Data Transmission at 10 Gbit/s over G.652 Without In-Line DFAs

Performance limits of NRZ data transmission at 10 Gbit/s over standard single mode fiber (SSMF, G.652) without the deployment of in-line erbium-doped fiber amplifiers (EDFAs) are evaluated by means of numerical simulation. The fiber system was modeled using the standard split-step Fourier algorithm for the solution of nonlinear Schroedinger equation. The effect of group velocity dispersion (GVD) compensation scheme, degree of GVD compensation of the SSMF, and input optical powers to SSMF and to the dispersion compensating fiber (DCF) have been investigated with the aim to maximize the distance between transmitter and receiver. We have found that a post-compensation scheme performs better than the pre-compensation scheme and that, by careful selection of input powers and degree of GVD compensation, it should be possible to keep the bit-error-ratio (BER) below 10 upper index = 15 for an SSMF length of 270 km.

Simultaneous transmission of the high-power phase sensitive OTDR, 100Gbps dual polarisation QPSK, accurate time/frequency, and their mutual interferences

Currently, fibre networks are only way how to satisfy the ever growing needs for more bandwidth. Thanks to that the optical fibre can be found almost anywhere and new applications and services can be transmitted through the networks. Accurate time transfer, ultra-stable frequency transfer and fibre-optic sensors networks have been rather common. High speed data transmission, time and frequency transmission, and fibre-optic sensors must share the common fibre-optic infrastructure because it would not be economically feasible to build separate fibre networks for long distances. Each system has individual transmission requirements and is prone to another type of interference. Data transmission systems based on DP-QPSK or DP-xQAM use digital signal processing for signal recovering but it cannot fully compensate signal degradation due to polarization dependent loss and nonlinear effects which are the most dominant sources of signal degradation. Accurate time signals are slow and often OOK modulated, therefore may experience the degrading effect of chromatic dispersion. Ultra-stable frequency signals are not modulated at all information transmitted is the frequency of photons and such signals are continuous wave, but they suffer from phase noise also environmentally introduced, e.g. by vibrations. For phase sensitive OTDR sensor systems the high power pulses are necessary to use which may cause interference with other signals. For this reason, parallel and simultaneous transmission in DWDM spectral grids of standard data, time, frequency, and sensing signals is rather new and unexplored area of research.