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 paper, different optical configurations, simple and compound, based on ring resonators and using liquid crystals as
the tuning or controlling block, are reported. Specific attention is given to their application as tunable filters and
wavelength switches, in this last case as part of complex matrix fabrics for all optical switching. Simulations of
integrated optics ring resonators are developed using <i>FullWave by R-Soft</i>. In the compound configurations that use serial
micro ring resonators it is implemented a 3 port reconfigurable demultiplexer in a compact cross-grid configuration.
Theoretical 10 nm tuning is reported on SOI substrate with nematic liquid crystals. Optimization of the critical coupling
condition by changing the evanescent coupling length is also reported. Theoretical analysis is presented to identify and
emphasize the design parameters of each configuration as regards its application of interest. The reported structures can
be developed in integrated optic technologies; all designs corresponds to state of the art integrated optics technology. A
revision of photonics circuits with equivalent components already developed is reported.
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.
In this paper, the dispersive properties of the optical ring resonator (RR) with an internal Sagnac (SG) loop filter are studied for chromatic dispersion managing in digital transmission systems over amplified single-mode fiber (SMF) spans in DWDM backbone networks. Design issues for the architecture as regards quadratic dispersion and magnitude distortion are provided. The RR+SG compound filter provides frequency tunability of the dispersion peaks by adjusting a coupling coefficient of an optical coupler, with no need for using integrated thermo-optic nor current-injection based phase shifters. The configuration can be employed as an additional structure for a general RR-based design and synthesis architecture, allowing bandwidth increase of dispersion compensators. The performance of a compound filter consisting of a two RR in series stage and a RR+SG filter has been simulated over a 200 km amplified SMF span model, obtaining a power penalty enhancement >3 dB for a 5 Gb/s NRZ transmission with a bit error rate (BER) of 10<sup>-9</sup>. Comparative simulations with regards to a dispersion compensating fiber span show that the compound filter is a much more compact and effective solution for existing multi-channel SMF backbone links operating at high bit rates.
In this paper, different optical configurations based on ring resonators and a reflective section in the feedback path, are proposed in order to show the feasibility of their applications in different fields. Additionally, the use of optical amplification in some of the configurations offers the possibility of improving the device insensibility to fabrication tolerances and gives flexibility to the designs. In the compounds configurations that use reflective elements in the ring resonators, such as Sagnac configurations and Bragg Gratings, tuning is achieved by changing the coupling ratio of a coupler apart from conventional tuning by changing the equivalent loop length, using temperature or injection current. Applications as tunable filters in DWDM networks and lasers will be discussed. The reported structures can be integrated in InP or silicon technology, because photonics circuits with equivalent components have already been developed. Some of them are a monolithically integrated Sagnac interferometer for an all-optical controlled-NOT gate. Integrated optic devices have higher free spectral ranges, thus complying with applied standards on DWDM networking. Theoretical analysis is presented to identify and emphasize the design parameters of each configuration as regards its application of interest. Measurements on fibre optic prototypes for showing the principle of operation and validating the theoretical models are reported in .
A Radio-Frequency (RF) Ring Resonator (RR) Fibre-Optic sensor (FOS) configuration is theoretically analyzed and a specific example to show the principle of operation is reported: an intensity-encoded fiber-optic sensor prototype based on the optical losses due to fibre curvature. The proposed configuration can be used for self-referencing purposes and to improve sensitivity as regards the measurand in any intensity fibre-optic sensor. Light intensity fluctuations to be measured are converted to ring resonator losses that produce high amplitude variations of the transfer function of the ring resonator. The use of an Erbium-Doped Waveguide Amplifier (EDWA) offers the theoretical possibility of increasing sensitivities to the greatest extent previously reported. A proper selection of the ring resonator point of operation is achieved using an optical attenuator, a variable coupling ratio coupler and an EDWA if needed. Modulation of the optical carrier by a RF signal allows overcoming possible instabilities due to environmental perturbations and simplifying the detection electronics. Two self-reference techniques to overcome unwanted source and local intensity fluctuations are developed. Both self-referencing techniques avoid possible intensity fluctuations because of long leads perturbations, in case of remote operation. Temperature effect on the measurements is also discussed.
A theoretical and experimental study of a Radio-Frequency (RF) Ring Resonator (RR) configuration for self-referencing and improving the sensitivity of fibre-optic intensity sensors (FOS) is reported. An experimental set-up directly applying this scheme to a multimode (MM) fibre strain sensor is shown and discussed, and a generic calibration using a single-mode (MM) optical attenuator has also been reported in order to show the principle of operation and to validate the theoretical expressions. The separation between lead and transducer losses in the FOS is solved by converting light intensity fluctuations to be measured into ring resonator losses that produce high amplitude variations in the proximity of the RR resonance frequencies. Modulation of the optical carrier by a RF signal allows using cheap sources and simplifying the detection electronics.
A theoretical and experimental study of radio-frequency ring resonators (RR) for referencing and improving the sensitivity of fiber-optic intensity sensors (FOS) is reported. The separation between lead and transducer losses in the FOS is solved by converting the light intensity fluctuations to be measured into RR losses that produce high amplitude variations in the proximity of the RR resonance frequencies. Two different self-referencing techniques are developed. Via the definition of the measurement parameter RM, sensor linearity and sensitivity are analyzed. A calibration using an optical attenuator is reported to validate the model.