Analysis of a distributed fiber-optic temperature sensor using single-photon detectors

We demonstrate a high-accuracy distributed fiber-optic temperature sensor using superconducting nanowire single-photon detectors and single-photon counting techniques. Our demonstration uses inexpensive single-mode fiber at standard telecommunications wavelengths as the sensing fiber, which enables extremely low-loss experiments and compatibility with existing fiber networks. We show that the uncertainty of the temperature measurement decreases with longer integration periods, but is ultimately limited by the calibration uncertainty. Temperature uncertainty on the order of 3 K is possible with spatial resolution of the order of 1 cm and integration period as small as 60 seconds. Also, we show that the measurement is subject to systematic uncertainties, such as polarization fading, which can be reduced with a polarization diversity receiver

All-optical wavelength-tunable narrow-linewidth fiber laser

Parameter regulations of narrow-linewidth fiber lasers in frequency domain has drawn considerable interests for widespread applications in the light quantum computing, precise coherent detection, and generation of micro-waves. All-optical methods provide compact, precise and fast accesses to achieving these lasers with wavelength-tunability. Here, the optical-thermal effects of graphene is utilized to precisely control operations of free-running lasers with a tuning speed of 140 MHz/ms. Assisted by the single-longitude-mode operation and linewidth suppression of stimulated Brillouin backscattering, we obtain an optical-controllable ~750 Hz fiber laser with a wavelength-tuning range of 3.7 nm

Multiwavelength operation of erbium-doped fiber lasers by periodic filtering and phase modulation

This paper explains the principles behind multiwavelength operation of an erbium-doped fiber laser (EDFL) under the combined effect of cavity phase modulation and periodic wavelength filtering. A mathematical model is developed to simulate the behaviour of the multiwavelength EDFL, both in time and frequency domains. The effects of various parameters such as pump power, filter channel spacing, modulation index and frequency are observed and explained. An all-fiber EDFL was constructed, using a piezo-transducer-based phase modulator and a Sagnac loop periodic filter, to validate the theoretical results. The effects of pump power, modulation frequency and modulation index were monitored experimentally, justifying the theoretical explanation. The multiwavelength EDFL has several potential applications in fiber sensing due to its flexible all-fiber design

Investigation of Broadband S-Band to L-Band Erbium-Doped Fiber Amplifier (EDFA) Module

This chapter presents three sections that describe the broadband S-band to L-band erbium-doped fiber amplifier modules. In the first section, an S-band gain-clamped erbium-doped fiber amplifier (EDFA) module, employing a fiber Bragg grating (FBG) to act as a reflected element for generating a saturated tone injected into the EDFA module by using forward optical feedback method, is proposed. Moreover, the output performance of the gain and noise figure (NF) in the proposed gain-clamped S-band EDFA has been discussed in the wavelength range of 1478–1520 nm. In the second section, we demonstrate experimentally a gain-flattened two-stage erbium-based fiber amplifier (EBFA) module, which is composed of by an erbium-doped waveguide amplifier (EDWA) and a C-band EDFA in serial structure. In an operation range of 1528–1562 nm, the entire gain is larger than 35 dB and the observed NF is between 5.5 and 6.7 dB. Moreover, ±1.1 dB maximum gain variation is also obtained for the input signal power of -25 dBm. Hence, the proposed fiber amplifier not only enhances the gain but also achieves the flatness in the wavelength region. In the final section, a broadband hybrid two-stage fiber amplifier, which is composed by a C-band EDFA and a C-band semiconductor optical amplifier (SOA) in serial scheme, is investigated experimentally. Here, we only use a 3 m long erbium-doped fiber (EDF) serving as a preamplifier to increase the gain and reduce the noise figure. Therefore, the proposed hybrid amplifier achieves a 110 nm effectively amplification of 1500–1610 nm (from S- to L-band). In addition, the output performance of gain and NF in the proposed fiber amplifier has also been discussed

Single-Longitudinal-Mode Brillouin/Erbium Fiber Laser with High Linewidth-Reduction Ratio

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Performance Analysis of WDM Network Based On EDFA Amplifier with Different Pumping Techniques

A key mechanism for Wavelength Division Multiplexing (WDM) implementation in optical network systems is gain flatness of Erbium-Doped Fiber Amplifier (EDFA). The main intention of this paper is to correct the non-uniformity in the gain for every single channel so that the amplitude gain of the Wavelength Division Multiplexing (WDM) arrangement can be equalized.The software used in this paper is Optisystem 13 so as to accomplish gain flatness of EDFA. The gains are flattened inside 27dB from 1546nm to 1568nm group of wavelength with noise figure < 14dB and we have also seen the effect of various pumping techniques on gain and noise figure. A WDM system arrangement that includes an EDFA is modeled and obtained maximum uniformed gains

Linear-cavity tunable fibre lasers employing an Opto-VLSI processor and a MEMS-based device

This thesis proposes and demonstrates experimentally two novel linear-cavity tunable fibre lasers employing an erbium-doped fibre (EDF) in conjunction with an Opto- VLSI processor and a MEMS-based device for wavelength selection. The Opto-VLSI processor and the MEMS-based device along with an optical collimator, a Bragg grating plate and an optical lens, enable the realisation of an optical filter for continuous tuning of wavelengths over the amplified spontaneous emission (ASE) range of the EDF. We also propose the use of a section of un-pumped EDF as a saturable absorber (SA), which suppresses noise spikes caused by the high optical pumping power. Experimental results show that by optimising a length of the SA a single wavelength, high power laser signal can be achieved. In addition, we experimentally demonstrate that the performance of the proposed linear-cavity tunable fibre lasers is better than that of ring-cavity tunable laser counterparts. Specifically, we show that linear-cavity based tunable fibre lasers can achieve higher output power, a larger side mode rejection ratio (SMRR) and narrower laser linewidth than ring-cavity tunable fibre lasers

Fiber amplifiers, directly modulated transmitters and a ring network structure for optical communications

The three technologies that are considered the key elements in building a metropolitan area optical network are studied in this thesis. They are optical amplification, high-speed low cost transmitters and ring network structures. These studies concentrate on cost reduction of these three technologies thus enabling the use of optical networks in small customer base metropolitan areas. The research on optical amplification concentrated first on the solution doping process, at present the most used method for producing erbium doped fiber. It was found that separationing the soot growth and the sintering improved the uniformity of the porous layer. This made the homogeneity of the doping concentration in the fiber core better. The effects of index profile variations that arise from the non-ideal solution doping process were also simulated. In the search for a better doping method a new nanoparticle glass-forming process, the direct nanoparticle deposition, was developed. In this process the doping is done simultaneously with glass formation. Utilizing this new process it was possible to improve the uniformity of the doping resulting in higher usable doping levels and shorter erbium doped fiber lengths in the amplifiers. There were fewer limitations in the amplifier caused by optical non-linearities and polarization mode dispersion since shorter fiber lengths were needed. The double cladding fiber, which avoids the costly coupling of the pump laser into a single mode waveguide, was also studied. This pumping scheme was found to improve the inversion uniformity in the erbium doped fiber core thereby enhancing the power conversion efficiency for the long wavelength band amplifier. In characterizing the erbium doped fiber amplifier the gain and noise figure was measured with a temporal filter setup. It was made of simple, low cost components but yielded accurate measurements since the noise originating from the amplified spontaneous emission was measured at the signal wavelength. In the study of fiber amplifier controlling schemes the input power of the fiber amplifier was successfully used to regulate the pump laser. This feed-forward control scheme provides a simple, low cost control and managment system for the erbium doped fiber amplifier in metropolitan area network applications that require flexible adding and dropping of wavelength channels. The transmitter research focused on the DFB laser due to its simplicity and low cost structure. A solid state Fabry-Perot etalon made from double polished silicon chip was used as a frequency discriminator in the chirp analyser developed for the DFB lasers. This wavelength discriminator did not require repeated calibration or active stabilisation and was controled electrically enabling automatic measurements. The silicon Fabry-Perot etalon was also used for simultaneous spectral filtering and wavelength control of the laser. The usable dispersion limited transmission length was increased when the filter was used in conjunction with the directly modulated distributed feedback laser transmitter. The combination of spatial multiplexing and dense wavelength division multiplexing in ring topology was investigated in the course of the research on the ring network as the feeder part of the metropolitan network. A new way to organize different wavelengths and fibers was developed. This ring network structure was simulated and an experimental ring network built. The results of the studies demonstrated that the same limitations effecting uni-directional ring structures also are the main limitations on the scalability of the spatial and wavelength division multiplexed ring networks based on bi-directional transmission when the node spacing is short. The developed ring network structure demonstrated major cost reductions when compared with the heavy use of wavelength division multiplexing. The node structure was also greatly simplified resulting in less need for different wavelength transmitters in each node. Furthermore the node generated only minor losses for the passing signals thus reducing the need for optical amplification.reviewe