A novel speckle-based sensing technique for cost-effective heart-rate monitoring is demonstrated. This technique detects periodical changes in the spatial distribution of energy on the speckle pattern at the output of a Step-Index Polymer Optical Fiber (SI-POF) lead by using a low-cost webcam. The scheme operates in reflective configuration thus performing a centralized interrogation unit scheme. The prototype has been integrated into a mattress and its functionality has been tested with 5 different patients lying on the mattress in different positions without direct contact with the fiber sensing lead.
KEYWORDS: Radio over Fiber, Radio optics, Phase only filters, Optical fibers, Energy efficiency, Photovoltaics, Solar cells, Antennas, Wavelength division multiplexing, Solar energy
Future high capacity of the 5th Generation radio environment will boost transport networks to be adapted. The high bandwidth, together with stringent delay and jitter requirements, make dedicated optical connectivity a preferred solution for fronthaul. Those Radio Access Networks apart from higher capacity and lower latency should have higher energy efficiency. In order to cover this aspect, power over fiber has been pointed out as a key technology for that purpose having in mind that control plane will be centralized on future Cloud RAN and that sometimes Remote Radio Heads should be deployed in places lacking external power supply in order to fulfill the desired coverage. In this paper, different scenarios on potential demanding environments of power over fiber on Radio over Fiber systems such as automotive, in-house and remote mobile fronthaul will be discussed. Some tests on power over fiber systems based on different optical fibers are provided.
A novel speckle-based method for sensing frequency vibration is demonstrated in a reflective configuration. By
employing a visible dual-wavelength approach it is also possible to determine the relative spatial location of the
vibrations along a plastic optical fiber lead of 8 m in a distributed scheme.
Small-cell and cloud-RAN systems along with the use of the millimeter-wave band have been considered as promising solutions to meet the capacity demand of the future wireless access networks. Radio over Multimode fibers (RoMMF) can play a role in the integrated optical-wireless access systems for next-generation wireless communications, mainly in within-building environments. The numerical results show the effectiveness of MMF to transmit at 60 GHz band with 7- GHz bandwidth for different link lengths and refractive index profiles under restricted mode launching and using narrow linewidth sources. The integration with optically powered remote antenna units is also proposed based on the large core effective area of MMF. Temperature impairments and graded index plastic optical fiber transmission are also discussed.
In this work, we explore the variation of power losses of PMMA-core plastic optical fiber through tensile tests. Experimental results of received optical power during elastic and plastic deformation process demonstrate the feasibility of POFs as simple intensity-based fiber-optic sensors for Structural Health Monitoring applications beyond complex schemes. A theoretical approach of the POF behavior versus strain is also provided.
In this work a self-referencing intensity-based fiber-optic sensor using virtual instrumentation is presented. The use of
virtual delay lines along with novel self-referencing techniques minimizing resolution and using a single frequency
avoids all-optical or electrical-based delay lines approaches at reception. This solution preserves the self-referencing and
performance characteristics of the proposed optical sensing topology, and leads to a more compact solution with higher
flexibility for the multiple interrogation of remote sensing points. Results are presented for a displacement sensor
demonstrating the concept feasibility.
In this work, different non-contact fiber-optic pyrometers have been developed for measuring localized temperatures on
material removal area during mechanizing processes. Designs are developed for adaptation to the harsh measuring
conditions on specific cutting tool machinery and using commercial optoelectronics and fiber-optic components for
resolution enhancement. A 0.1 dB/°C sensitivity at 300 °C is obtained, and calibration curves at 1100 nm, 1300 nm, 1550
nm and 1610 nm are reported. Different reception circuits are used for testing resolution limits, higher bandwidths imply
greater noise and worst results as expected.
Arbitrary operating conditions, such as the temperature dependence in the fiber link impose a challenge for the extension of radio-over-multimode fiber techniques. Temperature impairment characterization is analyzed over the broadband transmission bands that can be present in the frequency response of multimode fiber (MMF) supporting multiple-GHz carriers delivering schemes. Experimental results show that these transmission bands are dramatically influenced by the hysteresis of heating and cooling temperature cycles, respectively. The influence of the MMF graded index exponent tolerance on frequency response at higher bands is also analyzed. And this variation can be directly attributed to environmental temperature changes that could affect the MMF link. Additionally, selective mode-launching schemes combined with the use of narrow line-width optical sources are experimentally demonstrated to enable broadband transmission, not only at short but also at middle-reach distances over MMFs.
KEYWORDS: Silica, Temperature metrology, Microwave radiation, Radio over Fiber, Multimode fibers, Modulation, Optical fibers, Telecommunications, Signal attenuation, Fiber characterization
An emerging theme in next-generation access research includes seamless wireline-wireless convergence addressed by
Radio-over-Fiber (RoF) technologies. Optical cabling solutions offer the possibility for semi-transparent transport
through the access network microwave to mm-wave radio carriers commonly employed for creating high-capacity
picocell wireless networks, attending present demands from the wireless technologies, with portable/mobile devices
converging with photonics. Advanced RoF techniques can efficiently generate and transport such carriers, and deliver
them to simplified antenna stations or radio access points (RAPs). Thus, they can convey high data rates in
comprehensive modulation formats on multiple-GHz carriers in MMF networks.
Selective mode-launching schemes combined with the use of narrow linewidth optical sources are experimentally
demonstrated to enable broadband RF, microwave and mm-wave transmission in short- and middle-reach distances over
silica-based multimode optical fibers (MMFs); and are reviewed in this paper. However, arbitrary operating conditions,
such as the temperature dependence in the fiber link, impose a great challenge for the extension of the RoMMF
technology. Temperature impairment characterization is analyzed over the broadband transmission bands that are
present, under certain operating link conditions, in the frequency response performance of MMF to support multiple GHz
carrier delivering schemes, thus contributing to fault link prevention.
A novel self-referencing parameter for electro-optical WDM networks in reflective configuration for remote fiber-optic
intensity sensors is reported and experimentally tested. In this configuration electrical delay lines are deployed at the
processing unit, instead of long delay fiber coils in each measuring point; providing a more compact sensor-head and an
easy-reconfigurable operation point. The measurement parameter is defined as the ratio between voltage values at the
reception stage for different electrical phase-shifts and it is analyzed following the Z-transform formalism.
Measurements validating the theoretical model are reported and self-referencing and crosstalk properties of the network
are analyzed.
A short review of self-reference techniques for remote fiber-optic intensity sensors and possible integration in multiplexing sensor networks is reported. Special focus is given to developments on radio-frequency (RF) source modulation techniques in interferometric configurations operating under incoherent regime. Experimental results on ring resonator (RR) configurations in transmission and reflection modes are included. Sensitivity, optimum insertion losses and robustness to intensity error fluctuations are reported. Sensors are interrogated at two sub carrier frequencies having a high rejection of interference from laser source intensity fluctuations and loss in the fiber lead. Dependence on source coherence is also analysed.
Scalable self-referencing sensor networks with low insertion losses implemented in Coarse Wavelength Division Multiplexing (CWDM) technology are reported. The possibility of remote self-referenced measurements using a full-duplex fiber down-lead tenths of kilometers long with no need for optical amplification is also described. Fiber Bragg gratings (FBG) are used in the reflection configuration, thus increasing the sensitivity of the optical transducers. Low-cost off-the-shelf devices in CWDM and DWDM technology can be used to implement and scale the network.
Applications to specific photonic sensors are also envisaged and these techniques can be used in networks of microfiber loop resonators, being the microfiber loop the sensing element itself.
A Variable Optical Attenuator (VOA) based on a Polymer-Dispersed Liquid Crystal (PDLC) Cell is presented. The VOA's developed prototype has been successfully tested at 660nm, 850nm and 1300nm. This ability makes it strongly recommended for networks using Perfluorinated Gradual Index Polymer Optical Fiber (PF GI-POF) technology. The prototype has revealed a better than 12dBs dynamic range and losses of <1.2dB. In addition, the VOA presents a very low power consumption and non-dependendence with polarization. In order to avoid the dependence with temperature, an electrooptical feedback is incorporated to the device, by means of a microcontroller system. Electrically controllable intermediate transmission levels can be selected this way. The response time is in the milisecond range. The present feedback prototype, developed with POF technology, includes lenses, PDLC, 1x2 POF couplers and fotodiodes in the optical part, and a microcontroller system where the feedback processing is carried out. No polarizers are required so that optical losses are minimal. Polymer-Dispersed Liquid Crystals are formed by microdroplets of liquid crystal embedded in a flexible matrix, and sandwiched between transparent electrodes. This structure scatters strongly the light. When an AC electrical field is applied to the film the material becomes transparent. A largest dynamic range could be achieved designing conveniently the radius of the microdroplets. No-dependence with polarization, high transmittance when activated, and large dynamic range within a wide range of optical wavelengths make PDLC the most appropriate liquid crystal technology for VOAs fabrication.
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