Wavelength division multiplexing technique for grating panel-based fiber optic sensor

An optical fiber sensor system with multichannel fiber Bragg gratings (FBGs) is proposed. The gratings are designed and fabricated by phase sampling technique within strongly chirped phase masks. The sensing application can be realized at multiple points through wavelength division multiplexing (WDM) technique. It means that the different point can be monitored by different gratings, which occupies different wavelength region, according to the central pitch and chirp coefficient of phase masks. The heating position with high resolution can be analyzed through three corresponding channel shifts in the multichannel profile. In our experiment, the two multichannel gratings with channel spacing of 0.8 and 1.6 nm, respectively, are fabricated and used to sensing in two points. At last, the 400 μm accuracy of localizing the heating position is achieved.

We report on the use of a frequency-rnodulated continuous wave (FMCW) technique for multiplexing fiber Bragg grating (FBG) sensors. This technique is based on the modulation of light intensity from a broadband source by a linear swept-frequency RF carrier. Signals from the FBG sensors located at different positions in an array are separated in frequency-domainand demodulated using a tunable optical filter. The potential and limitation of the technique are discussed. A 3-sensor FMCWmultiplexed FBG array of parallel topology and a 6-sensor hybrid FMCWIWDM system were experimentally demonstratedwith -30 dB crosstalk between sensors and 2 tc resolution in terms ofroot-mean-square strain value.Keywords: optical fiber sensors, fiber Bragg grating sensors, frequency-modulated continuous wave, strain measurements. 1. Introduction Fiber Bragg gratings (FBGs) have been identified as an enabling technology for a variety of applications from aerospace, marine, to civil engineering structural monitoring, from medical, nuclear power industry, to electrical power industry[1]. In many applications such as condition monitoring of civil structures such as highways, bridges and buildings. FBG sensorsneed to be multiplexed in order to achieve quasi-distributed measurement and to reduce cost per sensing point to compete withconventional electrical or optical sensors.The most popular technique for multiplexing FBG sensors is the wavelength division multiplexing (WDM) technique[2,3]. The maximum sensor number that can be multiplexed using the WDM technique is determined by the ratio ofthe sourcespectral width over the spacing between the Bragg wavelengths of the FBGs. For applications requiring a larger multiplexinggain, a combination ofthe WDM and time-division multiplexing (TDM) techniques [3] may be used.A TDM system employs a pulsed or gated CW source to illuminate gratings in sequence as the pulse travels along thefiber, the reflected signals from the gratings are separated in time domain [4]. The physical separation between the gratings isdetermined by the input pulse width. A fast time-gated photodetector can be used to select the signal from an individual grating

Measurement device independent quantum key distribution (MDI QKD) has attracted growing attention for its immunity to attacks at the measurement unit, but its unique structure limits the secret key rate. Utilizing the wavelength division multiplexing (WDM) technique and reducing error rates are effective strategies for enhancing the secret key rate. Reducing error rates often requires active feedback control of wavelengths using precise external references. However, for a multiwavelength laser, employing multiple references to stabilize each wavelength output places stringent demands on these references and significantly increases system complexity. Here, we demonstrate a stable, wavelength-tunable multiwavelength laser with an output wavelength ranging from 1270 to 1610 nm. Through precise temperature control and stable drive current, we passively lock the laser wavelength, achieving remarkable wavelength stability. This significantly reduce the error rate, leading to an almost doubling of the secret key rate compared to previous experiments. Furthermore, the exceptional wavelength stability offered by our multiwavelength laser, combined with the WDM technique, has further boosted the secret key rate of MDI QKD. With a wide wavelength tuning range of 5.1 nm, our multiwavelength laser facilitates flexible operation across multiple dense wavelength division multiplexing channels. Coupled with high wavelength stability and multiple wavelength outputs simultaneously, this laser offers a promising solution for a high-rate MDI QKD system.

Today, there is no doubt that optical networks are the solution to the explosion of Internet traffic that two decades ago we only dreamed about. They offer high capacity with the use of Wavelength Division Multiplexing (WDM) techniques among others. However, this increase of available capacity can be betrayed by the high quantity of information that can be lost when a failure occurs because not only one, but several channels will then be interrupted. Efficient fault detection and location mechanisms are therefore needed. Our challenge is to identify and locate failures (single or multiple) at the physical layer of an optical network in the presence of some lost and/or false alarms. After briefly introducing optical networks and the multiplexing techniques that can be used, we study the most common components and their most usual failures. We propose a classification of all the network components based on their behaviour when failures occur. This classification gives an abstract model of the optical network, which is appropriate for developing algorithms to locate faulty elements. Two algorithms that solve the fault location problem are proposed. Both algorithms cope with existence of false and missing alarms when locating single and multiple failures. The problem of locating multiple failures already in the absence of false or missing alarms, has been shown to be NP-complete. The first algorithm, which is called Alarm Filtering Algorithm (AFA) is based on the combination of two approaches: forward and backward. The forward approach returns for each network element, their domain, which is the set of network elements that will send an alarm when the considered element fails. The backward approach returns the set of elements that are directly related to the received alarms. In this approach, the alarms that are considered to provide redundant information, are discarded. The combination of the results given by both approaches allows the location of multiple failures, given an allowed number of false and missing alarms. However, this algorithm does not minimize the complexity when new alarms are received. Hence, a second algorithm, which is called Fault Location Algorithm (FLA), is proposed. The FLA concentrates the complexity in ,a pre-computation phase, so that when new alarms are received, the result of the algorithm is rapidly displayed. The FLA algorithm is based on the construction of a binary tree that realizes a non linear error correcting code. The FLA has also been extended to locate soft failures in addition to hard failures. Hard failures are unexpected failures, whereas soft failures are progressive failures due to equipment aging, misalignments or external factors such as temperature or pressure. Both algorithms are compared on some simulated networks using different network topologies and failure cases. The comparison has also be done on the basis of their worst case complexity. Some conclusions indication with which settings each algorithm perform the best, were obtained.

To solve the explosively growth of the Internet demands, metropolitan area networks (MAN) use SONET to provide huge bandwidth. However, the SONET network is suitable for constant bit rate (CBR) traffic. Therefore, it cannot effectively handle the burst-natured metropolitan area networks traffic. This paper proposed a novel MAN network architecture and protocol by using the wavelength division multiplexing (WDM) technique to efficiently share the network bandwidth among every network nodes. The proposed novel network architecture adopts carrier sense multiple access with carrier preemption (CSMA/CP) that is a media access control (MAC) protocol to handle the variable size IP packet transport on WDM MAN ring network. This paper also shows the simulation results to verify the proposed MAC protocol is able to take more efficiently utilization and lower packet latency. Further developments are proposed to improve the efficiency and add new capabilities such as QoS.

Fiber Bragg grating (FBG) sensors were used to measure the torsional strain distribution in a second-generation (rare-earth) Ba2Cu3Oy high-temperature superconducting sample tape (SST) at 77 K. Two SST samples were prepared. A slit was fabricated in each sample to allow an optical fiber to be embedded. In the first sample, a 10-mm-long single grating element was inserted into the slit. In the second sample, three grating elements of 10-mm length each were put into the slit. These grating elements were fabricated along a single-mode fiber and could be addressed individually using the wavelength division multiplexing (WDM) technique. Finally, the samples were recoated with a primary and secondary coating to form an embedded sensing system. When the high-temperature superconducting (HTS) tape is subjected to torsion, there is a strain induced in the FBG sensor, which varies the grating period accordingly. It was interrogated using a tunable laser in a WDM scheme. Based on the wavelength shift and the photoelastic properties of the FBG sensor embedded to the HTS tape, the torsional deformation of the HTS tape can be obtained. In this paper, the design and technology requirements to embed the single and WDM FBG sensors into the coated conductors are presented. Initial experiments to measure the torsional strain distribution at 77 K are reported.

The technical advances in wavelength division multiplexing (WDM) techniques has made possible the introduction of optical technology into the path layer of the transport network. Besides the significant improvement in the transmission capacity, WDM technology allows the accomplishment of routing and switching functions directly in the optical domain. Thus Optical Cross-Connects (OXCs) can be realized with a throughput of a few hundreds of Gbit/s, so removing the bottleneck placed by electronic technology. The transport network node can be designed as an OXC interfacing a Digital Cross-Connect (DXC). Multi-Gigabit signals are directly routed in the optical network layer by the OXCs, while the DXCs provide demultiplexing to lower digital hierarchies and routing at the electrical level. The optical path layer can be designed so as to be transparent to the signal transmission format and speed. The aim of this paper is to assess the feasibility of transmitting sub-carrier multiplexed CATV channels in this optical path layer, by analysing the performance of the following transmission path: the CATV channels are generated in a production center, cross a geographical area through a transport network and an optical ring of a regional network, down to the access network and then to the customer.

The huge potential of optical networks for satisfying the skyrocketing needs of broadband telecommunication services while meeting rigid quality of service requirements has long been acknowledged. However, although fiber has become the medium of choice in telecommunication networks, its vast resources are severely under-used, due to the much slower electronics that are interfaced with the optical medium. For instance, transceivers operate at speeds that are several orders of magnitude below the actual usable capacity of the fiber (several Gbps versus hundreds of Gbps). In order to achieve higher rates, Wavelength Division Multiplexing (WDM) techniques have been widely suggested. The concept behind WDM is to partition the optical spectrum into multiple non-overlapping wavelength channels, each modulated at electronic speed. WDM networks offer potential advantages, including higher aggregate bandwidth per fiber, new flexibility for automated network management and control, noise immunity, transparency to different data formats and protocols, low bit-error rates, and better network configurability and survivability-all leading to more cost-effective networks.

Coherent wavelength division multiplexing (WDM) transmission technique has been penetrated into the intra-data-center interconnection (Intra-DCI), due to its capability of high receiver sensitivity and efficient impairment mitigation. Here, we experimentally present a coherent WDM transmission of 40-channel 60 GBaud dual-polarization 16-level quadrature amplitude modulation (DP-16QAM) signals covering the extended C-band over 500 m homemade nested anti-resonant nodeless fiber (NANF) for high-capacity Intra-DCI. We also propose to utilize a simplified Volterra nonlinear equalizer (S-VNE) to mitigate the transmission nonlinearities originating from the transmistter hardware, resulting in 17.2% and 23% computational complextity reduction in terms of additions and multiplications with almost negligible performance penalty, in comparison with conventional VNE. As a result, the bit-error ratio (BER) of all 40 WDM channels can be lower than the 7% hard-decision forward error correction (HD-FEC) threshold of BER = 4.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . We experimentally realize a net bit-rate of 448.6 Gbit/s per wavelength and a total transmission capacity of 17.9 Tbit/s.

In general, OAM can be regarded as an additional degree of freedom of a light beam or even of a single photon, to be added to the standard ones ordinarily exploited in current photonic technologies. In many respects OAM resembles polarization, with which it shares many features. However, while polarization is characterized by two orthogonal basis states, OAM is defined in an unbounded space (a Hilbert space in the case of photons). Therefore, it is in principle possible to encode a much larger amount of information in the OAM space than in the polarization space, e.g., achieving a greater channel capacity. This property makes OAM highly attractive for future optical communication systems. Specifically, OAM states could be used as a different dimension to create an additional set of data carriers in a Space Division Multiplexing (SDM) system. Moreover, OAM multiplexing does not rely on the wavelength or polarization, indicating that OAM could be used in addition to Wavelength Division Multiplexing (WDM) and Polarization Division Multiplexing (PDM) techniques to boost system capacity. This paper will discuss the potential applications of OAM of light in optical communication systems, and highlight recent advances in CMOS-compatible silicon photonic integrated device technology for OAM generation, manipulation, and (de)multiplexing.

As the wavelength division multiplexing (WDM) technique is established as a standard for optical communication system upgrade, Raman amplifiers based on silica fibers has been intensively studied for their flexible gainband control and potential as an alternative to rare earth doped fiber amplifiers. Raman amplifiers showed large gain (/spl sim/30 dB) at the 1st Stokes shift with the pump power of 300 mW and wide bandwidth over 90 nm by using cascaded pumps of different wavelengths. Recently low loss and high Ge doped silica fiber has been developed to reduce the pumping power. The evolution of 1st and 2nd Stokes shift, however, has not been rigorously analyzed including the effects of GeO/sub 2/ both on the gain and Rayleigh scattering loss. In the study, we obtained the amplified gain and optimum length of Raman medium for various germanium concentrations using Raman frequency modeling whose governing equations are given.

A reliable, continuous method of monitoring splanchnic organ oxygen saturation could allow for the early detection of malperfusion, and may prevent the onset of multiple organ failure. Current monitoring techniques have not been widely accepted in critical care monitoring. As a preliminary to developing a continuous indwelling device, this study evaluates a new handheld fiber optic photoplethysmographic (PPG) sensor for estimating the blood oxygen saturation (SpO(2)) of splanchnic organs during surgery. A fiber optic splanchnic PPG sensor, instrumentation system and virtual instrument were developed to facilitate PPG and SpO(2) measurement from splanchnic organs. Following Local Research Ethics Committee approval, the sensor was evaluated on seventeen ASA 1 and 2 patients undergoing open laparotomy. PPG signals were obtained from the large bowel, small bowel, liver and stomach. Simultaneous PPG signals from the finger were also obtained using an identical fiber optic sensor. Good quality PPG signals with high signal-to-noise (SNR) ratios were obtained from all splanchnic sites under investigation. Analysis of the ac and dc amplitudes of the red and infrared PPG signals showed there to be a statistically significant difference between PPG signals obtained from splanchnic organs with those obtained from the finger (using fiber optic sensors). Estimated SpO(2) values from the splanchnic organs show good agreement with those obtained from the finger using both a fiber optic sensor and a commercial device. Furthermore, the results of a Bland and Altman analysis indicate that fiber optic splanchnic pulse oximetry, particularly of the bowel, may provide a suitable method for monitoring splanchnic organ perfusion. The evaluation of a new fiber optic sensor on anaesthetized patients undergoing laparotomy demonstrated that good quality PPG signals and SpO(2) estimates can be obtained from splanchnic organs. Such a sensor may provide a useful tool for the intraoperative assessment of splanchnic perfusion.

Evolution of the optical fiber systems is currently seeing the general acceptance of wavelength division multiplexing (WDM) as the best mechanisms in increasing the transmission capacity of fiber optics. However, there are problems associated with WDM technique such as wavelength drifts, wavelength inventory and management and stringent demultiplexing requirements that tend to either limit the system's performance or increase the cost. Also, it is difficult to construct a WDM system for a dynamic set of multiple users because of the significant amount of coordination among the nodes required for successful operation. Optical Code Division Multiplexing (OCDM) provides some solutions to the problems. This simple technique operates on a single broadband light source, thus alleviating the problems and cost of handling multiple lasers as in WDM systems. This paper elaborates the working principle of the OCDM technique and provides some proofs on its viability.

The purpose of this paper is to review the application of various fiber-optic and optical sensor technologies in structural health monitoring (SHM) for detecting and measuring mechanical strains and stresses. As is known, fiber optic sensors have low operating costs and small dimensions compared with traditional sensors based on electrical and thermal effects, therefore, they are gradually becoming one of the most promising areas of development of sensor technologies for monitoring structural systems. This paper presents the basic operating principles of several widely used fiber optic sensor types (e.g., based on the Fabry-Perot interferometer, Bragg diffraction, reflectometry, etc.), and describes the experience of using fiber optic sensors in monitoring various physical parameters and demonstrates the possibilities of using fiber optic sensors in structural systems such as bridges, overpasses, tunnels, buildings, etc. It is shown that two types of sensors have found the greatest application for measuring and detecting mechanical deformations in building structures: sensors based on fiber Bragg gratings, as well as optical reflectometry methods (primarily Brillouin reflectometry). Thus, the specified types of sensors are the most promising and effective in the context of SHM technologies.

The ever increasing demand for higher data rates and minimum latency has resulted in a widespread growth of optical fiber communication over the last decade. Dense Wavelength Division Multiplexing (DWDM) technique is one of the most important techniques used to establish a long-distance link with higher data rate transmission. However, when the requirement is to transmit the data inside a metropolitan (shorter range) city, DWDM has certain limitations like wideband change, more power consumption, and high-cost factor for lower channels. CWDM (Coarse Wavelength Division Multiplexing) can easily overcome these disadvantages. In this paper, the performance of 8 channel optical transmission link for Coarse Wavelength Division Multiplexing based optical network has been analyzed and compared. Here we’ve compared the performances in terms of Q-factor (Quality factor), BER (Bit Error Rate), and eye height in the eye diagram. For experimental setup and simulation, Optisystem-18 software is used.KeywordsCWDMBitrateAPD photodetectorLow pass filterQ-factor