In data transmission systems there are applications where lateral coupling light is requested. Fluorescent optical fibers radiate light as a response to incident illumination along the side. Because of photosensitivity along the side, the plastic photo-luminescent fiber is considered a flexible coupling alternative of the light, instead of discrete position coupler or tap. Fluorescent optical fibers have been investigated for data transmission applications. With commercially available fluorescent fiber for the optical bus system and smartphone based data transmission (ASK modulation) the data rates up to 500Mbit/s are feasible, by selecting the right parameters such as short fluorescence lifetime, spectral region of the fibers correlated with light sources and photodetectors and in-fiber low spectral attenuation. The application is useful in automotive applications for data transmission and distributed sensing.
Fluorescent optical fibers employ the luminescence property of fluorescent dyes in order to radiate light as a response to incident illumination. When multiple dyes are used to dope the fiber, fluorescence results from the energy transfer between the donor and acceptor dyes and the reabsorption process.<p> </p> In this work we propose a high-resolution distributed optical sensor for position monitoring developed around a yellow fluorescent fiber. Immunity vs. ambient light variations is achieved by employing the spectral behavior of the donoracceptor energy transfer mechanism and the reabsorption process. This consists in a red shift of the fiber emission peaks vs. distance. <p> </p>Extensive experimentation with the laboratory proof of principle validates the proposed solution. Measurements carried out in laboratory environment under ambient illumination show that the wavelength of the emission peaks is insensitive to the intensity of the incident light, but is dependent on the variation of the ambient light color. Accordingly, rather than monitoring the wavelengths of the emission peaks, the proposed positions sensor evaluates the spectral spacing between the peaks. This provides an accurate estimate of the distance between the fiber end and the incident light application point. The proposed sensor exhibits a monotonous decrease of the spectral spacing vs. distance, which is indeed insensitive to limited variation of the ambient light.
Active integrated multicore waveguide structures (AIMWS) with high refractive index contrast values and controlled local composition can be fabricated inside a bulk doped glass as a result of recent developments in high repetition femtosecond laser writing. The modeling of these structures presents some distinct characteristics when compared to that of corresponding multicore fiber structures. In this paper we present a study of the influence of two of these features in the signal amplification: the glass homogeneous doping and the existence of a zone of depressed refractive index. In order to do that, we use a home-made computer code that solves the optical power propagation equations of the structure supermodes coupled to the rate equations of the active ions.
The optimized geometry based on high-order active microring resonators (MRR) geometry is proposed. The solution possesses both the filtering and amplifying functions for the signal at around 1534nm (pump 976 nm). The cross-grid resonator with laterally, series-coupled triple-microrings, having 15.35μm radius, in a co-propagation topology between signal and pump, is the structure under analysis (commonly termed an add-drop filter).
A detailed model of the performance of a highly Yb<sup>3+</sup>/Er<sup>3+</sup>-codoped phosphate glass add-drop filter, which combines the propagation at resonance of both pump and signal powers inside the microring resonator with their interaction with the dopant ions, is used to analyze the requirements for gain/oscillation in these structures. Special attention is paid to the influence of additional coupling losses and asymmetry between the input/output couplers. It is concluded that, due to small signal gain saturation and the limited range of pump amplitude coupling coefficients, asymmetry does not greatly influence gain/oscillation requirements through the pump intensity build-up inside the ring. Asymmetry effect on small signal intensity transfer rate and threshold gain instead allows a significant lightening of the demanding doping ions concentrations requirements to achieve oscillation.
An analytic model of the scattering response of a highly Yb<sup>3+</sup>/Er<sup>3+</sup>-codoped phosphate glass microring resonator matrix is considered to obtain the transfer functions of an M x N cross-grid microring resonator structure. Then a detailed model is used to calculate the pump and signal propagation, including a microscopic statistical formalism to describe the high-concentration induced energy-transfer mechanisms and passive and active features are combined to realistically simulate the performance as a wavelength-selective amplifier or laser. This analysis allows the optimization of these structures for telecom or sensing applications.
In this work the analytical model of the scattering response of a highly Yb<sup>3+/</sup>Er<sup>3+-</sup>codoped phosphate glass microring
resonator array is developed. The microscopic statistical formalism is used to simulate its performance as a wavelengthselective
amplifier. The performance of the integrated add-drop filter was investigated based on the signal transfer
functions for Through and Drop ports, correlated the with gain coefficient and its dependence on pump power, signal
power and Yb<sup>3+/</sup>Er<sup>3+-</sup> dopants concentration. In consequence, microring arrays with gain operating in the near infrared
spectral range and, in particular, in the 1.5-mm wavelength band (emission band of Er-doped fiber amplifiers and lasers,
already used in several bio/chemical sensing tasks) are highly attractive.
In this paper a simple theoretical model is presented where the energy conservation principle is used. The model is based
on semi-analytical equations describing the behaviour of an erbium-doped photonic crystal fibre (PCF) inside a ring
laser. These semi-analytical equations allow the characterisation of the erbium-doped PCF. Spectral absorption and
emission coefficients can be determined through the measurement of the gain in the PCF as a function of pump power
attenuation for several fibre lengths by means of a linear fitting. These coefficients are proportional to the erbium
concentration and to the corresponding absorption or emission cross section. So if the concentration is known the erbium
cross sections can be immediately determined.
The model was successfully checked by means of two different home-made erbium doped PCFs. Once the fibres were
characterised the values of the spectral absorption and emission coefficients were used to simulate the behaviour of a
back propagating ring laser made of each fibre. Passive losses of the components in the cavity were previously
calibrated. A good agreement was found between simulated and experimental values of efficiency, pump power
threshold and output laser power for a wide set of experimental situations (several values of the input pump power,
output coupling factor, laser wavelength and fibre length).
An erbium-doped photonic crystal fiber laser has been designed, constructed and characterized in order to examine the
feasibility of this kind of devices for secure communications applications based on two identical chaotic lasers. Inclusion
of a tailored photonic crystal fiber as active medium improves considerably the security of the device because it allows
customization of the mode transversal profile, very influential on the laser dynamics and virtually impossible to be
cloned by undesired listeners. The laser design has been facilitated by the combination of characterization procedures
and models developed by us, which allow prediction of the most suitable laser features (losses, length of active fiber,
etc.) to a given purpose (in our case, a laser that emits chaotically for a wide assortment of pump modulation conditions).
The chaotic signals obtained have been characterized by means of topological analysis techniques. The underlying
chaotic attractors found present topological structures belonging to classes of which very scarce experimental results
have been reported. This fact is interesting from the point of view of the study of nonlinear systems and, besides, it is
promising for secure communications: the stranger the signals, the more difficult for an eavesdropper to synthesize
another system with similar dynamics.
We report on a comparison of characterization techniques for high concentration erbium-doped photonic crystal fibres
(PCFs). A highly erbium-doped-silica PCF was fabricated and an amplifier based on the PCF was built. Then,
measurements on the amplifier output optical powers were carried out. To model the amplifier, three different
formalisms were assumed for the Er<sup>3+</sup>-ion upconversion mechanism and the numerical results were fitted to the
experimental ones. The sets of best-fit parameters are compared and the use of these techniques for active PCF
characterisation is discussed.
A characterisation technique for packaged Er/Yb-codoped waveguides based on the analysis of laser transient behaviour is studied. A ring laser configuration was used and measurements on the evolution of laser output power during transient regime were carried out. An approximate analytical method was developed for the analysis of this behaviour. A good agreement is obtained for the relevant damped oscillation parameters. The use of this technique for active waveguides characterisation is discussed.