J. M. Lazaro

Methane detection at 1670-nm band using a hollow-core photonic bandgap fiber and a multiline algorithm

The long interaction pathlengths provided by hollow-core photonic bandgap fibers (HC-PBFs) are especially advantageous for the detection of weakly absorbing gases such as methane (CH(4)). In this paper, we demonstrate methane sensing with a 1670-nm band HC-PBF. A multiline algorithm is used to fit the R(6) manifold (near 1645 nm) and, in this way, to measure the gas concentration. With this method, a minimum detectivity of 10 ppmv for the system configuration was estimated.

Gas Sensor Based on Photonic Crystal Fibres in the 2ν3 and ν2 + 2ν3 Vibrational Bands of Methane

In this work, methane detection is performed on the 2ν3 and ν2 + 2ν3 absorption bands in the Near-Infrared (NIR) wavelength region using an all-fibre optical sensor. Hollow-core photonic bandgap fibres (HC-PBFs) are employed as gas cells due to their compactness, good integrability in optical systems and feasibility of long interaction lengths with gases. Sensing in the 2ν3 band of methane is demonstrated to achieve a detection limit one order of magnitude better than that of the ν2 + 2ν3 band. Finally, the filling time of a HC-PBF is demonstrated to be dependent on the fibre length and geometry.

Multi-Line Fit Model for the Detection of Methane at ν2 + 2ν3 Band using Hollow-Core Photonic Bandgap Fibres

Hollow-core photonic bandgap fibres (HC-PBFs) have emerged as a novel technology in the field of gas sensing. The long interaction pathlengths achievable with these fibres are especially advantageous for the detection of weakly absorbing gases. In this work, we demonstrate the good performance of a HC-PBF in the detection of the ν2 + 2ν3 band of methane, at 1.3 μm. The Q-branch manifold, at 1331.55 nm, is targeted for concentration monitoring purposes. A computationally optimized multi-line model is used to fit the Q-branch. Using this model, a detection limit of 98 ppmv (parts per million by volume) is estimated.

Fabrication of FBGs With an Arbitrary Spectrum

A fiber Bragg grating (FBG) with an arbitrary spectrum can be obtained as the addition of the contribution of some concatenated subFBGs written without phase jumps using the same phase mask. An adaptive filter is used to obtain the parameters of the different subFBGs required to reproduce the desired response.

Methane sensing using multiple-coupling gaps in hollow-core photonic bandgap fibers

Gas detection and gas sensing based on hollow core photonic bandgap fiber (HC-PBF) is a very promising technique due to the long interaction light-gas lengths that are achievable. However, long path-lengths also imply higher gas filling times of the hollow fiber and higher response times of the detection systems what can constitute a serious practical inconvenience. In this paper, the high sensitivity is maintained but the sensor response time is reduced by using multiple-coupling fiber gaps. The results and conclusions extracted from a systematic experimental study (comparing the spectra and filling time of different HC-PBF lengths and different number of coupling gaps) are presented and discussed. Finally, the maximum number of gaps allowed in the system is modelled.

Bragg Gratings Written in Tapered Solid-Core Photonic Crystal Fibers

Fiber Bragg gratings are very useful in many applications. This is why a higher control of their properties is desirable. Therefore, a grating preprocessing technique, based on the dependence of the index guided photonic crystal fiber (IG-PCF) properties on their structural parameters, is proposed allowing a higher control of the Bragg wavelength. Using the proper combination of thermo-mechanical IG-PCFs tapering and ultraviolet photoinscription methods, it is possible to develop new optical fiber devices. Their effectiveness is demonstrated by comparison with the results on single-mode fiber. Finally, to demonstrate the feasibility of the technique, a wideband chirped Bragg grating is fabricated.

Angle transducer based on fiber Bragg gratings able for tunnel auscultation

In this paper an angle transducer based on Fiber Bragg Grating (FBG) is presented. Two gratings are glued to a metallic platen, one in each side. It is insensitive to temperature changes, given that the temperature shifts affect equally to both FBG. When the platen is uniformly bent an uniform strain appears in both sides of the platen. It depends on the bend angle and the platen length and thickness. The transducer has been designed to be used in the auscultation of tunnels during their construction process and during their live time. The transducer design and its characterization are presented.

High Temperature Long Period Grating Thermo-Mechanically Written

An optical fiber transducer able to work in high temperature environments is experimentally demonstrated in the laboratory. It is based on a permanent long period grating (LPG) written using a new technique based on a thermo-mechanical approach. Device precision was experimentally checked by means of repetitive thermal cycles between 25 and 950 °C. In addition device stability was assured by maintaining the temperature in steady state at 800 °C during 23 hours.

Effective Index and Mode Width Sensitivities to Opto-Geometrical Parameters on Index-Guided Photonic Crystal Fibers

The effective index and fundamental mode width behavior on modified total internal reflection (MTIR) photonic crystal fibers is studied in a wide normalized frequency (Lambda/lambda) area. The sensitivities to the structural and opto-geometrical parameters are obtained and the higher sensitivity region is clearly identified. The fabrication tolerance expression is also shown. Conclusions from this letter will be useful for designing and fabrication processes, also for using MTIR fibers on optical devices such sensors.

Experimental characterization of the spectral effective index dependence of index-guided photonic crystal fibers

The effective index of index-guided photonic crystal fibers (IG-PCFs) is experimentally obtained as a function of the wavelength by writing fiber Bragg gratings (FBG) in the fibers. The results are found to be in good agreement with theoretical simulations and are also discussed and compared with measurements on standard telecommunication fibers. Differences between the fibers were observed both in the Bragg grating inscription process and in the evolution of the fiber effective index value with the wavelength, which depends on the fiber cladding microstructure. Index evolution slopes of ?2.029 ? 10?5 nm?1, ?2.044 ? 10?5 nm?1 and ?1.388 ? 10?5 nm?1 were measured for two IG-PCFs and the standard fiber, respectively.