1.65µm long range distributed testing of optical fibres using a compact Q-switched fibre laser

A simple Q-switched Erbium-doped fibre laser operating at 1.5µm forms the basis of a high peak power pulsed source at 1.65µm. Applications include monitoring of active telecommunication links, loss measurement at 1.65µm and distributed temperature sensing

Validity of cognitive assessments via telecommunication links

The use of telecommunication links in health care provision is a rapidly growing field. However, there is concern that as technology advances, teleconsultation will be seen as the method of choice without adequate research as to its efficacy. Preliminary evidence suggests that cognitive assessment of adult psychiatric patients could be reliably carried out using videoconferencing equipment, and this study was designed to investigate the use of videoconferencing for the cognitive assessment of individuals with a history of alcohol abuse. Twenty seven participants were given a range of cognitive assessments, each with two equivalent forms. One of the forms was given via the telelink, the other face-to-face. All participants were assessed using both mediums and the order of presentation of the forms was counterbalanced across participants. Participant satisfaction with teleconsultations was also assessed. There was no significant difference in the majority of assessment outcome measures via telelink in comparison with face-to-face assessment. The majority of participants rated the teleconsultation positively, although some complained about the poor sound quality. The results are discussed with reference to the future developments and limitations of telecommunication links in a rural health care setting

Climate changing in microwave telecommunication links (sleet)

Rec. ITU-R P.530-12 provides an internationally recognised prediction model for the fading due to wet snow (sleet) on horizontal, terrestrial microwave links. An important parameter in this model is the altitude difference between the link and the melting layer.  This is the layer near the zero-degree isotherm (ZDI) where falling ice begins to melt into rain. Melting ice particles produce a specific attenuation up to four times that of the associated rain rate. This work will examine NOAA NCEP/NCAR Reanalysis 1 data to identify trends in the ZDI height o. ZDI height is shown to have increased by approximately 10 m per year over the last 30 years in part of Europe as it shows some decrease in other parts of the world approximately 5 m a year. This has led to a slow decrease in the incidence of fading due to wet ice over southern Europe but isolated large increases in regions where the air temperature near the ground was close to zero during winter. The annual distribution of ZDI heights relative to the annual mean are calculated and compared to models in Rec. ITU-R P.530-12 as the theory for attenuation provided and plot of the mean ZDI Height will be compared with Rec. ITU-R 840-4

PHASAR-based PICs for WDM-applications

Wavelength multiplexers, demultiplexers and routers based on optical phased arrays play a key role in multi-wavelength telecommunication links and networks. Photonic integration of PHASARS with active components will provide the functionality required in tomorrows multi-wavelength network

High stability radio links

Radio telecommunication links are used for communication with deep space probes. These links consist of sinusoidal carrier signals at radio frequencies (RF) modulated with information sent between the spacecraft and the earth. This carrier signal is a very pure and stable sinusoid, typically derived from an atomic frequency standard whose frequency and phase are used to measure the radial velocity of the probe and from this and other data types derive its trajectory. This same observable can be used to search for space-time distortions cased by low frequency (0.1 to 100 MHz) gravitation radiation. How such a system works, what its sensitivity limitations are, and what potential future improvements can be made are discussed

Equilibrium and nonequilibrium solitons in a lossy split-step system with lumped amplification

We propose a more realistic version of the recently introduced split-step model (SSM), which consists of periodically alternating dispersive and nonlinear segments, by adding uniformly distributed loss and lumped gain to it. In the case when the loss is exactly balanced by gain, a family of stable equilibrium solitons (ESs) is found. Unless the system's period L is very small, saturation is observed in the dependence of the amplitude of the established ES vs. that of the initial pulse. Stable nonequilibrium solitons (NESs) are found in the case when the gain slightly exceeds (by up to 3%) the value necessary to balance the loss. The existence of NESs is possible as the excessive energy pump is offset by permanent radiation loss, which is confirmed by computation of the corresponding Poynting vector. Unlike ESs that form a continuous family of solutions, NES is an isolated solution, which disappears in the limit of small L, i.e., it cannot be found in the overpumped nonlinear Schroedinger equation. Interactions between ESs turn out to be essentially the same as in SSM without loss and gain, while interactions between NESs are different: two NESs perturb each other by the radiation jets emanating from them, even if they are separated by a large distance. Moving NESs survive collisions, changing their velocities.Comment: a latex text file and seven jpg figure files. Physics Letter A, in pres

Distributed optical fibre sensing at 1.65µm using a Q-switched fibre laser

It is becoming increasingly vital to monitor telecommunication links during operation and installation process. By using a high peak power source and the optical time domain reflectometry (OTDR) technique operating at the wavelength region of 1.6µm, it is possible to monitor conventional C-band Erbium-doped fibre amplifier (EDFA) systems whilst transmitting data, and to characterise losses at the higher wavelengths of extended bandwidth systems designed around the L-band EDFA systems. We describe a compact design based on Raman shifting the output of an Erbium-doped Q-switched fibre laser operating at 1.5µm for obtaining a pulsed source at 1.6µm. This source was used for an OTDR measurement and also as a source for a 1.65µm Raman-based distributed temperature sensor, in contrast to distributed temperature sensors normally operating at 1.5µm. OTDR measurements at 1.65µm provide more accurate determination of macro and micro-bend losses than at 1.5µm as such losses increase with wavelength. The temperature measurement extracted from the anti-Stokes Raman signal at 1.5µm was made over a sensing range of 10.1km, with a spatial resolution of 10m and temperature resolution of 4°C

Birefringence and polarisation mode-dispersion in spun single-mode fibres

A theoretical and experimental analysis of the polarization properties of twisted single-mode fibers is presented. It is shown that whereas a conventionally twisted fiber possesses considerable optical rotation, a fiber which has a permanent twist imparted by spinning the preform during fiber drawing exhibits almost no polarization anisotropy. It is thus possible to virtually eliminate the commonly observed fiber linear birefringence. As a consequence, fibers made in this way are ideally suited for use in the Faraday-effect current transducer. It is further shown that a permanent twist of a few turns/meter effectively eliminates polarization mode-dispersion. The technique therefore appears attractive for enhancing the bandwidth of very long unrepeatered telecommunication links

Noise considerations in twin-core channel equalisers

Fibre optic channel equalisers are devices of prime importance in multi-channel telecommunication links and networks. They are used to compensate for the channel power imbalances accumulated along amplified long links and stabilise the channel optical powers. In multi-stage amplified optical links, channel power imbalances occur as a result two factors. Firstly, the emission and absorption cross-section variations across the erbium-doped fibre amplifier (EDFA) bandwidth result in channels experiencing different gains and acquiring unequal output power. Secondly, the output power imbalances are further deteriorated by the fact that the Er3+ transition is predominantly homogeneously broadened at room temperature. Therefore, the strongest signal (channel) saturates the gain medium and compresses the gain uniformly at the expense of the power of the weaker signals