Raimundo Garcia-Olcina

Transverse Strain Measurements Using the Birefringence Effect in Fiber Bragg Gratings

Birefringence in fiber Bragg gratings (FBGs) leads to polarization-dependent properties such as polarization-dependent loss (PDL). Although this property is not desired for telecommunications applications, we demonstrate that the PDL generated by uniform FBGs written into standard single-mode fiber can be advantageously used for transverse strain measurements, which is not directly possible through amplitude spectral measurements.

Influence of the Grating Parameters on the Polarization Properties of Fiber Bragg Gratings

Due to the lateral inscription process, photo-induced birefringence is present in fiber Bragg gratings (FBGs) written into photosensitive single mode fiber. The birefringence value is generally too small to be perceived in the grating spectral response but it can lead to significant polarization dependent loss (PDL) and differential group delay (DGD) evolutions. In this paper, we first theoretically analyze the evolution with wavelength of PDL and DGD as a function of the grating parameters and the birefringence value. We demonstrate that the PDL and DGD evolutions with wavelength can be strongly enhanced by a modification of the grating parameters. Simulations carried out using the coupled mode theory and the Jones formalism are then confirmed by experiments conducted on FBGs written into photosensitive single mode fiber. Our work brings a complete characterization of polarization related phenomena in FBGs and presents a great interest for the evaluation of system performances and the design of gratings for specific applications, either for telecommunications or sensing purposes. In addition, based on the comparison between experimental and simulated evolutions, we are able to verify that the birefringence value is strongly dependent on the fluence of the laser used for the grating inscription.

Continuous tuning of photonic transversal filter based on the modification of tapped weights

We propose and experimentally demonstrate a novel technique to tune the microwave photonic filter which is based on the sinusoidal modulation superimposed to the envelope of the filter coefficients. This configuration overcomes the use of tunable optical sources and optical dispersive devices. To the best of our knowledge, these are the first experimental results where the resonances of the cited filters are shifted by changing the weight of the optical taps

Transverse force sensor exploiting the birefringence effect in uniform fibre Bragg gratings

Birefringence in fiber Bragg gratings (FBGs) can result from two distinct effects that combine with the intrinsic fiber birefringence: the birefringence induced by the UV photo-writing and the birefringence due to a transversal load. In both cases, it leads to polarization dependent loss (PDL) and differential group delay (DGD) inside gratings. Although these parameters are not desired for optical telecommunications applications, we demonstrate here that they can be advantageously used to obtain temperature-insensitive transverse strain measurements with uniform FBGs written into standard single mode fiber, which is not possible through conventional amplitude spectral measurements. Simulated results obtained by means of the coupled mode theory and the Jones formalism as well as experimental results measured by means of a tunable laser source and a polarimeter are presented.

Amplified CWDM self-referencing sensor network based on phase-shifted FBGs in transmissive configuration

A new amplified CWDM (Coarse Wavelength Division Multiplexing) self-referencing sensor network using phase-shifted fiber Bragg gratings (PS-FBGs) is experimentally demonstrated in this work. The network uses the PS-FBGs to address intensity sensors in a transmissive configuration, obtaining simultaneously in reflection a wavelength encoded reference signal. In order to enable the remote operation of the sensors, we have introduced optical amplification at the interrogation header of the network, using highly doped erbium fiber.

Effect of group velocity dispersion on all-optical encoded labels in optical packet networks

This paper describes the chromatic dispersion effect over the optical en/decoding process in coherent Direct Sequence (DS) systems and its respective verification by simulation and experimentally. The en/decoders are based on Super Structured Fiber Bragg Gratings (SSFBG) with 63 chips and binary optical phase codification with chip rates of 104 Gchip/s and 174 Gchip/s. This type of optical codification has been proposed for head processing in all optical Photonic Label Switching (PLS) networks.

Experimental demonstration of the continuous tuning of microwave photonic filters by sinusoidal modulation of the filter coefficients

We show the results of a technique to tune continuously the resonances of the microwave photonic filters are shifted by changing the weight of the optical taps. It improves the performance of the cited filters.

Relationship Between Chromatic Dispersion and Differential Group Delay in Weakly Birefringent Fiber Gratings

The presence of weak birefringence in fiber gratings slightly affects their amplitude response. In this case, we report that the wavelength dependencies of chromatic dispersion and differential group delay (DGD) are linked by the birefringence value. This relationship is used to analyze the grating DGD and exploited to get the grating birefringence. Experimental results are finally reported in good agreement with the theory.

Experimental demonstration of the reduction of PDL and DGD in Fibre Bragg Gratings by using a twisted-fibre for the inscription

We experimentally report the possibility to reduce PDL and DGD in fibre Bragg gratings by inducing polarization mode coupling. This is obtained by using a twisted-fibre for the inscription.

Determination of the fiber birefringence induced by transversal loads by means of fiber Bragg gratings

The application of transversal strain on an optical fiber leads to an asymmetry of the fiber section that locally induces fiber birefringence. In this paper, we show that it is possible to use FBG as a probe to obtain the amount of this induced birefringence. We describe two techniques able to get the birefringence value. They are both based on differential group delay (DGD) measurement. The first technique makes use of the comparison between the measurement and the simulation of the wavelength dependency of grating DGD. Considering that all grating parameters are known, we adjust the birefringence value to obtain the best fit between experiment and simulation. For the second technique, we first demonstrate that the wavelength dependencies of chromatic dispersion (CD) and DGD parameters differ in their amplitude by a quantity proportional to the birefringence. We exploit this relationship to get the birefringence value by separately measuring the DGD and CD spectral evolutions. The birefringence value is adjusted to obtain the best fit between the two measurements. These two techniques are discussed and experimental results are finally reported.