David I. Forsyth

Dual temperature and strain measurement with the combined fluorescence lifetime and Bragg wavelength shift approach in doped optical fiber

We have constructed fiber-optic sensors to measure temperature and strain by combining the properties of fiber Bragg gratings with the fluorescent lifetimes of various doped fibers. Sensors have been made with the fiber Bragg grating written directly into the doped fiber to ensure the collocation of the strain and temperature measurement points. Results are compared with those obtained previously from a Bragg grating written into standard photosensitive fiber spliced to doped fiber. Standard deviation errors of 7 microepsilon and 0.8 degrees C have been obtained for strain and temperature ranges of up to 1860 microepsilon and 120 degrees C, respectively.

All-incoherent wavelength conversion in highly nonlinear fiber using four-wave mixing

Abstract. This work describes efficient and polarization insensitive, all-incoherent four-wave mixing wavelength conversion achieved within a short length of highly nonlinear fiber medium, created by using both spectrally sliced pump and probe channels from a single-amplified spontaneous emission source coupled to two narrowband Fiber Bragg grating (FBG) filters. This simple and cost-effective scheme is capable of generating a down-converted probe channel across a 17.2-nm wavelength span, while still maintaining a high conversion efficiency of around −22  dB and an optical-signal-to-noise ratio of ∼21  dB. The effects of pump power, FBG detuning, and polarization are also reported.

Dual Measurement of Strain and Temperature Using the Combination of Er3+ -Doped Fibre Fluorescence Lifetime and a Fibre Bragg Grating

Fibre optic sensing devices have been produced for the dual measurement of strain and temperature using the combined properties of fibre Bragg gratings and the fluorescence lifetime of erbium-doped fibre. Two different sensors were constructed with the fibre Bragg grating written in normal fibre and also written directly in the Er3+-doped fibre. Results obtained indicate that this technique can be used to measure strains and temperatures with accuracies of approximately 1.2°C and 20.4 με

Quantifying system performance improvements in a high-density spectrum-sliced channel running at 10 Gb∕s using semiconductor optical amplifier gain compression nonlinearities

Abstract. We report on the use of semiconductor optical amplifier (SOA) gain compression for achieving intensity noise reduction in light from an incoherent broadband source, running at high data rate of 10  Gb/s in a narrow spectrum-sliced high-intensity channel of 20 GHz (∼0.16  nm) bandwidth, in order to improve quality of performance in future spectrum-sliced systems. Data have been collected on the performance of a single SOA as noise reducer at various input powers and biases. Improvements of ∼20  dB in the relative intensity noise, together with commensurate improvements in both signal-to-noise ratio and quality factor, have been achieved at a nominal 0 dBm of power inserted into the SOA at 0.15 A bias. The overall results obtained herein give designers a knowledge of the best SOA operating conditions required, particularly in terms of bias and input power, in order to achieve a desired intensity noise reduction, and thus an overall system performance improvement, while still obtaining some signal gain from the SOA as well.

Modeling of semiconductor optical amplifier gain characteristics for amplification and switching

Semiconductor optical amplifier (SOA) technology has been exposed to the world due to its commercial values and future potential in fiber optic communication systems. The basic concept of the SOA is very similar to that of a laser diode operated around threshold bias, except that the SOA has an internal anti-reflection coating to reduce its reflectivity to nearly zero. Commonly, a SOA is used as an amplifier in communication networks to regenerate the optical signal at different points in the communications link by operating as a booster amplifier, in-line amplifier or as a preamplifier. Besides amplification, SOAs can also be used as multi-functional elements in future all-optical switching, regeneration, and wavelength conversion schemes.

Modelling strain dependence of fluorescence from doped optical fibres: application to neodymium

At the present time there is much interest in sensors for the simultaneous measurement of temperature and strain. To engineer strain or temperature sensors, based on the fluorescence lifetime or fluorescence intensity ratio techniques, with desirable characteristics requires detailed understanding of the physical origin of the strain dependency of these fluorescence effects. It has been suggested that the cause is slight shifts in the energy levels, since some of the important levels in rare-earth-doped crystals shift when subjected to considerable pressure. However, recent theoretical work analysing the two techniques, and outlined in the next section, does not support this idea. Instead, in that work, it was proposed that this sensitivity is due to a volumetric distortion of the energy transfer rates between the dopant ions. In this model an applied strain results in a slight decrease in concentration. To explore this latter idea, strain and temperature dependencies of Nd/sup 3+/-doped optical fibres of various concentrations have been analysed using this model. Existing data have been supplemented by new measurements, giving the sensitivities for the two techniques at a number of dopant concentrations.

Combined fluorescence decay time and fiber Bragg grating temperature and strain sensing

Bragg grating-based sensor devices are popular as they are relatively simple to fabricate and use, but the need for compensation for temperature effects is of particular importance for accurate and reliable measurement of other parameters. Equally, the use of rare-earth-doped fiber has revolutionized many aspects of both communications and sensor systems and recent research has produced fluorescence decay-time and intensity ratio transducer devices which yield reproducible and accurate temperature measurement. This work reports on research carried out on sensor devices using co-located Bragg gratings and fluorescence decay-time sensors, using both separate optical fibers (plain and rare-earth-doped silica respectively) or with the Bragg grating actually written into the fluorescent fiber. The sensor system thus created is simple and effective with a single optical source used to excite both the fluorescence emission (which provides decay time information) and to enable the measure-induced Bragg grating wavelength shift to be determined. With such systems under test, satisfactory strain and temperature resolutions have been achieved. Applications include temperature compensated structural monitoring and monitoring of temperature in structures where the sensors are exposed to strain.

Four-wave mixing analyses for future ultrafast wavelength conversion at 0.64 Tb/s in a semiconductor optical amplifier

Abstract. This paper describes numerical and analytical analyses relating to the use of nonlinear four-wave mixing in a semiconductor optical amplifier medium for anticipated wavelength conversion at ultrahigh data rates of 320 and 640  Gb/s. The proposed system guidelines and design show that a maximum wavelength shift of 30 nm can be achieved at 640  Gb/s, while still maintaining an acceptable bit error rate. In addition, the impact of the pump–probe ratio and semiconductor optical amplifier bias current are investigated and the results are reported.

Tm/ho co-doped optical fibre sensor - : strain and temperature characteristics of a sensor probe

The temperature characteristics and strain effects in a thulium/holmium co-doped optical fibre sensor are investigated for application to optical fibre thermometer schemes. Results show a high temperature sensitivity between 200°C and 700°C and a strain sensitivity similar to other doped fibres.