This paper develops a fiber optical sensor network based on OADM (optical add-drop multiplexer) devices with a bus
configuration. Unlike conventional bus sensor networks which need optical couplers to include the sensors, the proposed network uses OADM to incorporate the sensors to the network. These devices make it possible to increase the number of sensors in bus networks in comparison with those that have optical couplers, wherein the transmitted signal into the spine of the bus decreases because of the insertion loss and also because of the coupling ratio. In this work, different intensity sensors have been efficiently employed because the proposed configuration addresses the two main concerns of intensity sensors: on the one hand, each sensor is associated with a different wavelength directly offered by each OADM; and on the other hand, a reference wavelength is included in order to distinguish between power variations induced by the transducer or to detect a fiber failure.
This work proposes and demonstrates a 200 km long distance fiber ring laser for multiplexing arrays of FBGs. Unlike
previous long distance reported fiber lasers, the system in based on a ring cavity which involves that the amplified
transmitted signal travels in a different fiber than the signal reflected by the FBGs. This fact helps to avoid the most
limiting factors when the distance between the sensor and the processing unit needs to be increased. To our knowledge,
this is the longest reported fiber laser system with remote sensing capability; it is also able to multiplex 7 fiber Bragg
gratings, while previous ultra-long systems only multiplex up to 4. In addition, due to the mode operation of the system,
it is a low noise configuration, thus the OSNR of all the sensors is high enough to interrogate them 200 km away from
the monitoring station.
KEYWORDS: Fiber Bragg gratings, Sensors, Fiber lasers, Tunable lasers, Remote sensing, Raman spectroscopy, Signal to noise ratio, Signal detection, Single mode fibers, Sensing systems
We propose and demonstrate the feasibility of a novel Fiber Bragg Grating interrogation technique for remote sensing
based on the use of a hybrid Raman-Brillouin fiber laser configuration. The laser comprises 100 km of standard singlemode
fiber (SMF) in a linear cavity configuration with four Fiber Bragg Gratings (FBGs) arranged in series. The FBGs
are used both for the sensing function and for the selection of the lasing wavelengths. A wavelength-swept laser pumps
Brillouin gain in the fiber cavity, which is previously set just under lasing threshold by the Raman gain. Furthermore, the
sensor signal is detected in the radio frequency domain instead of the optical domain so as to avoid signal to noise ratio
limitations produced by Rayleigh scattering. Experimental results demonstrate that the shift of the Bragg wavelength of
the FBG sensors can be precisely measured with good signal to noise ration when the FBG are used for temperature
sensing.
In this work, a novel single-longitudinal-mode (SLM) four-wavelength laser configuration for sensing applications in
L-band is proposed and experimentally demonstrated. This spectral region presents some advantages for the detection of
dangerous gases. The sensor system presented here is based on ring resonators, and employs fiber Bragg gratings to
select the operation wavelengths. The stable SLM operation is guaranteed when all the lasing channels present similar
output powers. It is also experimentally demonstrated that when a SLM behavior is achieved, lower output power
fluctuations are obtained.
This paper describes the development of a hybrid multiplexing network for optical fiber sensors using a multiwavelength
lasing long-range structure and the simultaneous utilization of an OTDR on the same network to interrogate
displacement sensors based on microbenders. With this design, simultaneous interrogation of displacement and
temperature was carried out 50 km away from the system header.
We propose a hybrid network that combine point and distributed Brillouin sensors in an architecture that also deploys
remote distributed Raman amplification to extend the sensing range. A 46-km proof-of-concept network is
experimentally demonstrated integrating point vibration sensors based on fiber-optic tapers, with distributed temperature
sensing along the network bus. The sensor network with a double-bus topology offers a higher optical signal to noise
ratio and dynamic range than a single-bus for intensity point multiplexed sensors. In this network, we include low-cost
intensity sensors that are able to measure vibrations in the 0.01 to 50 Hz frequency range, which are important in the
monitoring of large infrastructures such as pipelines.
An experimental comparison of the stability performance of two different optical multiwavelength lasers is shown based
on erbium highly doped fiber amplification. The two laser structures compared were: a star configuration using a 2x4
coupler to extract the signal from the ring to 4 FBGs and a structure with 4 active ring resonators that use both the same
pump laser. Both lasers use Fiber Bragg gratings (FBG) to select the operation wavelengths within the resonant ring
cavity.
The stability of this new laser is compared with the achieved by a single ring configuration. The improvement of both
stabilities depending on the time and temperature for the new structure was experimentally demonstrated.
The utilization of the new configuration for multiplexing optical fiber sensors has also been carried out. The sensors
provide amplitude modulation in response to the curvature introduced by a temperature-sensitive element. Each sensor is
identified by a different wavelength generated by each FBG. The signal generated by the grating firstly is used as
reference signal ant secondly is launched towards the sensors and the transmitted signal is measured. The sensors show a
stable and linear response when measurements are carried out using simultaneously all the outputs of the structure for
transmitting the multiple wavelengths to the sensors and utilizing the serial referencing output of the laser.
This paper shows a long-distance remote sensing system using a multiwavelength Raman laser. The sensor network is
based on a 50 km of standard single-mode fiber (SMF) and is composed by a simple cavity based on a loop mirror and
four Fiber Bragg Gratings (FBGs) arranged in a star configuration. FBGs are used for both the sensing function and the
selection of the lasing wavelengths. The system is designed to be inherently resilient to fiber failures. The
multiwavelength laser has been characterized for temperature measurements showing a good stability performance.
This paper presents the application of a new erbium-doped fiber ring laser configuration for the multiplexing
of intensity sensors. The proposed scheme exploits two separated branches to generate simultaneous emission
at four different wavelengths. Fiber Bragg gratings are used to select the operating wavelengths within the
erbium-doped fiber ring. The first branch presents a serial configuration to generate the reference lasers. The
second branch exploits a tree configuration and includes the optical intensity temperature sensors. A comparison
between both branches of the same setup is carried out, and their temperature and time stability is shown by
varying the erbium doped fiber.
In this work, we present and experimentally demonstrate a switchable Erbium-doped fiber laser for remote sensing
applications. The laser uses four Fiber Bragg Gratings (FBGs) for wavelength selection and for temperature sensing and
a 2x4 optical switch. By adjusting the switch combinations, the laser can be switched among the four different
wavelength lasing configurations. Stable one- and two- wavelength oscillations were achieved based on the use of this
device. An output power instability analysis with the temperature for two different multi-wavelength configurations, one
of them using the 2x4 optical switch and the other using a 1x4 coupler, was performed, for a cavity length of 50 km. A
comparison between the performances of these topologies is carried out, and their temperature sensitivity and
stabilization time are shown.
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