Optical Fiber Path Research Articles

A high resolution and large range fiber Bragg grating temperature sensor with vortex beams

The vortex beam owns helical phase factor, orbital angular momentum, and hollow structure of intensity distribution. It is widely applied in information coding, optical manipulation and optical sensing. This paper attempts to design a fiber Bragg temperature sensor based on vortex light, including an orbital angular momentum (OAM) beam transmitted by fiber Bragg grating (FBG), an optical fiber path used to eliminate errors, and a Gaussian beam, which is used to interfere with FBG transmission light. The interference pattern of a Gaussian beam and an OAM beam rotates with the changes of phase difference between the two beams. When the temperature changes, FBG is affected by the thermal optical effect and thermal expansion effect, and the central wavelength of the reflected spectrum will shift. Based on the relationship between wavelength shift and temperature change, temperature measurement in a large range can be realized. Additionally, the Filter is placed behind the FBG, and the transmission light (λ=1.466μm) with less reflection is selected to interfere with the Gaussian light, with the change of phase of transmission light, the rotation of the interference pattern will change accordingly. The temperature change corresponding to the 2π rotation of the interference pattern can be obtained, thus temperature measurement with high resolution can be realized. The simulation results show that when the temperature range is 27 °C–427 °C, the sensitivity of this sensor is 14.42 pm/°C. On the basis of the rotation of the interference pattern, when the rotation angle of the temperature-induced interference pattern change within 2π the temperature sensitivity is 1.529 rad/°C, based on the angular resolution of CCD, the theoretical resolution of temperature measurement is 6.3e−7 °C. Similar to the cursor effect, the main ruler measures a wide range of temperature changes according to wavelength drift, and the cursor is a high-resolution measurement of temperature according to the rotation angle of the interference pattern.

Adjustable testing setup for a single-loop optoelectronic oscillator with an electrical bandpass filter

In this paper we present a novel method to measure the free spectral range (FSR) and side-mode suppression ratio (SMSR) of an optoelectronic oscillator (OEO) by adjusting the optical fiber length using an optical path selector and signal source analyzer. We have designed a setup for a single-loop OEO operating around 5 GHz and 10 GHz that features electrical bandpass filters for side-mode suppression. The proposed approach makes it possible to evaluate the FSR and SMSR of OEOs with different optical fiber paths without requiring the changing of fiber spools or optical connectors. This approach could be useful for testbeds that investigate the implementation of an OEO in a 5G radio access network.

Extrinsic Fabry-Perot interferometric cavity-based fiber-optic spectrum equalization filter for the Gaussian spectrum of superluminescent diodes.

To flatten the Gaussian spectrum of superluminescent diodes (SLDs), a fiber-optic spectrum equalization filter based on an extrinsic Fabry-Perot interferometric (EFPI) cavity is proposed. By the proper usage of a low-finesse EFPI cavity and the delicate design of a splitting and recombining fiber-optic path, the Gaussian spectrum of an SLD can be effectively flattened, which is verified by a numerical simulation and an experiment. An SLD with a center wavelength of 1568 nm and a 3-dB spectral width of 98 nm is spectrum-equalized to obtain a spectrum flatness of 0.27 dB in the wavelength range 1544.8-1605.6 nm. When the SLD is with a max power of 3.38 mW, the output power after the fiber-optic spectrum equalization filter can reach 178.06 μW.

Non-contact all-fiber optic laser Doppler accelerometer.

A non-contact all-fiber optic acceleration measurement system has been proposed in this work. Using a fiber delay line in the fiber-optic path, the difference between two Doppler shifted frequencies of a laser beam corresponding to two different velocities of a moving object with a fixed time delay was measured and used for acceleration extraction. By performing acceleration measurements for a piezoelectric ceramic oscillator driven by an open-loop piezo controller at different voltages, a measurement error of better than -3.766% and nonlinearity degree of 0.314% were achieved.

Nonzero-drift differential all-fiber-optic heterodyne Doppler measurement system

To eliminate the serious detrimental effects caused by frequency drifts of acousto-optic frequency shifters (AOFSs) in conventional all-fiber-optic heterodyne Doppler measurement systems, a differential all-fiber-optic heterodyne configuration is proposed. By delicate arrangement of the fiber-optic path and using only one AOFS, zero drift, which commonly occurs in conventional systems, is eliminated. Based on the proposed configuration, a differential all-fiber-optic heterodyne Doppler measurement system has been built. Using a piezoelectric ceramic oscillator as the moving object, it has been verified that the proposed system is able to eliminate zero drift, and the displacement and velocity measurement accuracies reach 0.775 μm and 0.009 mm / s, respectively. It has been shown that the differential all-fiber-optic heterodyne Doppler measurement system can achieve good performance in both displacement and velocity measurements, even in a harsh environment with drastic temperature variation.

Ultra-low noise optical injection locking amplifier with AOM-based coherent detection scheme

A novel optical injection locking amplifier with acousto-optic modulator based phase modulation and a coherent detection scheme for optical frequency transfer applications is experimentally demonstrated in this study. A commercial distributed feedback diode laser is injection-locked to the resonant frequency of the optical signal with an optical fiber path length of hundreds of kilometers. This provides approximately 59 dB gain and ensures that the input carrier frequency fractional stability can be as good as 10−20 at 1000 s. The amplifier was tested for the transfer of a commercial narrow-linewidth laser in a 180 km fiber link to a remote site with only a single amplification step. The transferred frequency at the remote end reached 10−20 at 20000 s, which is suitable for optical frequency distribution and remote comparison between optical atomic clocks.

Cost Effective Wide Area Measurement Systems for Smart Power Network

Due to the large number of applications of wide area monitoring systems (WAMSs), many power utilities are implementing phasor measurement units (PMUs)-based WAMS replacing the conventional supervisory control and data acquisition system. The biggest challenge in implementing the technology is the cost of WAMS. Many researchers are trying to minimize the cost of WAMS by making the system observable with optimal placement of PMU. Along with the cost of PMU, the cost of communication infrastructure (CI) is dominating the cost of WAMS. Hence, it is necessary to optimize the communication path link and also to find out the optimal location of phasor data concentrator (PDC). In this paper, an optimization model to find the optimal placement of PMU, optimal location of PDC, and their CI is developed. For this, both independent and simultaneous optimization carried out by using differential evolution algorithm. The multi-objective differential evolution is used for simultaneous optimization. The presence of conventional flow measurement device and its effect on overall cost of WAMS with and without considering presence of optical fiber is presented. The method is implemented with different ( $N-1$ ) contingency considerations. Also, the results with the presence of pre-existing PMUs and optical fiber paths are provided.

Single-branch Er:fiber frequency comb for precision optical metrology with 10^−18 fractional instability

The comparison of optical atomic clocks with frequency instabilities reaching 1 part in 1016 at 1 s will enable more stringent tests of fundamental physics. These comparisons, mediated by optical frequency combs, require optical synthesis and measurement with a performance better than, or comparable to, the best optical clocks. Fiber-based mode-locked lasers have shown great potential for compact, robust, and efficient optical clockwork but typically require multiple amplifier and fiber optic paths that limit the achievable fractional frequency stability near 1 part in 1016 at 1 s. Here we describe an erbium-fiber laser frequency comb that overcomes these conventional challenges by ensuring that all critical fiber paths are common mode and within the servo-controlled feedback loop. Using this architecture, we demonstrate a fractional optical measurement uncertainty below 1×10−19 and fractional frequency instabilities less than 3×10−18 at 1 s and 1×10−19 at 1000 s.

Ghost Imaging for Online Angiography

Ghost imaging (GI) has characteristics that make it promising for applications in life sciences and other fields, such as its high sensitivity and strong anti-interference compared with traditional imaging. This paper presents a new approach for online angiography using GI. Two signals are correlation-calculated to detect the object image: one of them is the random light field generated by a computer, and the other enters the optical fiber path after being transmitted to the detected object via a modulator. A new approach for the real-time imaging of intravascular flow, vascular wall structures, and components of atherosclerotic plaque is proposed, which has the advantages of a high sensitivity and anti-interference.

Testing of Piezo-Actuated Glass Micro-Membranes by Optical Low-Coherence Reflectometry.

In this work, we have applied optical low-coherence reflectometry (OLCR), implemented with infra-red light propagating in fiberoptic paths, to perform static and dynamic analyses on piezo-actuated glass micro-membranes. The actuator was fabricated by means of thin-film piezoelectric MEMS technology and was employed for modifying the micro-membrane curvature, in view of its application in micro-optic devices, such as variable focus micro-lenses. We are here showing that OLCR incorporating a near-infrared superluminescent light emitting diode as the read-out source is suitable for measuring various parameters such as the micro-membrane optical path-length, the membrane displacement as a function of the applied voltage (yielding the piezo-actuator hysteresis) as well as the resonance curve of the fundamental vibration mode. The use of an optical source with short coherence-time allows performing interferometric measurements without spurious resonance effects due to multiple parallel interfaces of highly planar slabs, furthermore selecting the plane/layer to be monitored. We demonstrate that the same compact and flexible setup can be successfully employed to perform spot optical measurements for static and dynamic characterization of piezo-MEMS in real time.

Ghost imaging for online angiography

Ghost imaging (GI) has characteristics that make it promising for applications in life sciences and other fields, such as its high sensitivity and strong anti-interference compared with traditional imaging.This paper presents a new approach for online angiography using GI.Two signals are correlation-calculated to detect the object image:one of them is the random light field generated by a computer, and the other enters the optical fiber path after being transmitted to the detected object via a modulator.A new approach for the real-time imaging of intravascular flow, vascular wall structures, and components of atherosclerotic plaque is proposed, which has the advantages of a high sensitivity and anti-interference.

Automated numerical calculation of Sagnac correction for photonic paths

Relativistic effects must be taken into account for highly accurate time and frequency transfers. The most important is the Sagnac correction which is also source of non-reciprocity in various directions of any transfer in relation with the Earth rotation. In this case, not all important parameters as exact trajectory of the optical fibre path (leased fibres) are known with sufficient precision thus it is necessary to estimate lower and upper bounds of computed corrections. The presented approach deals with uncertainty in knowledge of detailed fibre paths, and also with complex paths with loops. We made the whole process of calculation of the Sagnac correction fully automated.

A novel phase-sensitive scanning near-field optical microscope**Project supported by the National Natural Science Foundation of China (Grant Nos. 61177089, 61227014, and 60978047).

Phase is one of the most important parameters of electromagnetic waves. It is the phase distribution that determines the propagation, reflection, refraction, focusing, divergence, and coupling features of light, and further affects the intensity distribution. In recent years, the designs of surface plasmon polariton (SPP) devices have mostly been based on the phase modulation and manipulation. Here we demonstrate a phase sensitive multi-parameter heterodyne scanning near-field optical microscope (SNOM) with an aperture probe in the visible range, with which the near field optical phase and amplitude distributions can be simultaneously obtained. A novel architecture combining a spatial optical path and a fiber optical path is employed for stability and flexibility. Two kinds of typical nano-photonic devices are tested with the system. With the phase-sensitive SNOM, the phase and amplitude distributions of any nano-optical field and localized field generated with any SPP nano-structures and irregular phase modulation surfaces can be investigated. The phase distribution and the interference pattern will help us to gain a better understanding of how light interacts with SPP structures and how SPP waves generate, localize, convert, and propagate on an SPP surface. This will be a significant guidance on SPP nano-structure design and optimization.

Four-path multiple ∞-shaped fiber protection mechanism for cable television networks

Traditional cable television (CATV) network configuration is mainly a branch topology. When fibers break, there are always disconnections of CATV and Internet access. Meanwhile, network service providers usually cannot be instantly informed of network breakage; network problems are noticed only after the users call for services. Network breakage location detection and repair are, in general, costly and time-consuming. This paper proposes a new framework to protect CATV fiber optic networks, where a HUB with multiple optical protection switching (OPS) is constructed between the head end and the fiber nodes. The first layer ranging from the head end to the HUB forms a 1+1 protection path ring structure. The second layer ranging from the HUB to the fiber nodes forms multiple 1+1 protection path ring structures. The framework can form a four fiber optic path protection architecture with multiple ∞-shapes between the head end and the fiber nodes. When the CATV network system experiences a malfunction, such as fiber optic cable breakage or poor signal quality, OPS can immediately switch the fiber transmission path in order to maintain uninterrupted CATV network traffic. After simulation tests on fiber path switching time automatic protection switching, frame loss, packet jitter, latency, bit errors, and system traffic flow monitoring by manually switching OPS and pulling broken fiber optic cable, results show that the fiber path protection switching mechanism can react immediately, and test data results show that network traffic is unaffected, so the proposed framework can effectively enhance the survivability and quality of service of CATV network systems.

Implementing UMS to Improve Efficiency of Optical Fiber Path Testing

Implementing UMS to Improve Efficiency of Optical Fiber Path Testing

Business Continuity and Security in Datacenter Interconnection

Large enterprises are increasingly running applications that demand the storage and real time transfer of massive amounts of data. Such applications require high bandwidth and low latency in order to meet current operational business needs and disaster recovery time objectives. Critical enterprise data is synchronously mirrored between two geographically diverse datacenters, typically at least 60 to 100 kilometers apart, to ensure that no data will be lost if disaster should strike. This paper will explore complementary technologies to Dense Wave Division Multiplexing (DWDM) in order to address current datacenter challenges specific to business continuity and security in light of the potential for equipment failure, fiber cuts, floods, fire, or massive power grid blackouts, as well as denial of service and terrorist attacks. These include intrusion detection on the optical fiber path, line speed encryption, and multiple mechanisms to address the potential for major outages. The combination of these technologies mitigates the risks present to critical datacenter infrastructure. © 2012 Alcatel-Lucent.

Positioning of Embedded Optical Fibres Sensors for the Monitoring of Buckling in Stiffened Composite Panels

A numerical/experimental study on the monitoring of the skin buckling phenomenon in stiffened composite panels by embedding optical fibres is presented in this paper. A numerical procedure has been introduced able to provide the most efficient embedded optical fibre path (with minimum length) fulfilling the grating sensors locations and directions requirements whilst satisfying specific embedding/integrity constraints for the optical fibre. The developed numerical procedure has been applied to a stiffened composite panel under compression load. The best location and direction of the grating sensors and the optimal optical fibre path for the monitoring of the skin buckling phenomenon have been found by performing respectively non-linear FEM analyses and optimization analyses. The procedure has been validated by means of an experimental testing activity on a stiffened panel instrumented with embedded optical fibres and back-to-back strain gauges which have been positioned according to the numerically estimated grating sensors locations and directions.

Integrated Near-Infrared Dual-Modality Imaging With Common Path Fiber Optic System

A simple configuration of combining two imaging modalities for diagnostic endoscopy is experimentally demonstrated. It is based on a near-infrared optical imaging system by using a common fiber optic path, where the probing arm provides both the sample and the reference paths. This feature allows integrating the optical coherence tomography and the confocal optical microscopy with simply inserting a directional optical coupler at the receiver's measurement part. The coupler divides the two different imaging modalities for separately measuring optical signals from the specimen without employing additional instrumentation except for a 3-dB loss of received power in return. Furthermore, the acquired tomography signal is related to the confocal point spread function of the scanning optical probe in the imaging system. As a result, the surface and cross-sectional images of a biological tissue (kidney with a tumor) sample were successfully obtained and registered using the proposed combined imaging scheme incorporating different measurement systems.

基于白光干涉的光缆无损伤识别方法

A method of the lossless identification for fiber cable based on white-light interference is studied. When the two ends of fiber-optic are connected,the light-wave is coupled into two beams of light with the same light intensity and transmit in the opposite directions.Detector receives signals generated by the other side.The two optical fibers side by side with the force of outside and the optical fiber path changes are analyzed. The output signals on some conditions are simulated and verified by experiment.The impact signal,the sinusoidal signal with a known frequency and the music signals are used as the divided external signal source, and the output signal is observed.By analyzing the spectral,and comparing with the input signal,this method of the lossless identification system is proved feasible.

Development of FBG Sensing System for Outdoor Temperature Environment

We have experimentally designed a practical pass-through type FBG temperature sensor. The objective of this study is to design and built a prototype outdoor fibre Bragg grating (FBG) temperature sensor system. Its performance is evaluated at different times of the day. In order to reduce the optical losses of the FBG system, the shortest optical fiber path used to connect the FBG system is 55.5m. It has a total connector loss 4.0dB and fibre loss of 0.3dB thus giving a total loss of the system as 4.3dB. The FBG sensor system is connected to the tunable laser source (TLS) and optical spectrum analyzer (OSA). The TLS is used to provide a broadband light source via a fibre optic cable of wavelength 1550nm. The OSA is used to display the transmission and reflection spectrum to give the Bragg wavelength _B, bandwidth and power dip. The output spectrum can be obtained through direct connection to the FBG. Result of transmission and reflection spectrum show the sensitivity which is calculated from the slope of the graph. The FBG temperature sensor system has an average sensitivity of 9.1 pm (°C)-1 based on the transmission spectrum. It has an average sensitivity of 10.6 pm (°C)-1 based on the reflection spectrum.