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Interferometric optical systems have been proposed for implementing dual-parameter optical sensors. For this type of sensors, the sensitivity matrix equation is generally used to determine the parameters to be measured based on the sensitivity of each parameter to one particular feature of the output reflective spectrum of the interferometric system. One of the disadvantages of this method is that the measurement ranges will be very short if the sensitivities are not linear or if these present cross-sensitivity. In this work, a multiple regression model for the simultaneous detection of refractive index and temperature based on an interferometric optical sensor is proposed. Here, the mathematical model is a weighted sum of features used to estimate the values of two response variables. These features are functions of an initial set of 27 explanatory variables whose values were extracted of the output reflective spectrum of the interferometric system. Besides, in order to sustenance the model application, the sensor was modeled and experimentally carried out. Three cases were studied: the estimation of temperature at different refractive indices, the estimation of temperature when refractive index is equal to one, and the estimation of refractive index at different temperatures. For each one of these cases, an optimal basis of functions was founded with the algorithm proposed and used to estimate the values of the response variables. Besides, a technique to reduce the initial set of variables was implemented. Finally, for the experimental data, For each one of these cases, an optimal basis of functions was founded with the algorithm 1 proposed and used to estimate the values of the response variables.

A homemade interferometer based on a non-ideal beam splitter and an only one home mirror is presented. Its interference pattern presented dark and bright rings when the mirror was tilted.

In this letter, an enhanced thermally tunable filter design based on a stack of three layers and a long external sleeve at the tip of a single mode fiber is presented. Here, two of these layers and the sleeve are thermo-sensitive. Moreover, it is shown that by using the sleeve with a large length compared with the thicknesses of the layers, the thermal tuning mechanism can be considerably enhanced. Furthermore, the mathematical model of the enhanced filter is presented and it is experimentally supported. Finally, a tunable single-wavelength erbium doped fiber laser based on this filter was implemented. This laser can be tuned ~19 nm by applying a temperature change of just 2.7°C achieving a resolution of 6.89 nm/°C.

In this paper, we present a hybrid semiconductor structure for biosensing applications that features the co-integration of nanoelectromechanical systems with the well-known metal oxide semiconductor technology. The proposed structure features an MOSFET as a readout element, and a doubly clamped beam that is isolated from the substrate by a thin air gap, as well as by a tunnel oxide layer. The beam structure is functionalised by a thin layer of biotargets, and the main aim is to detect a particular set of biomolecules, such as enzymes, bacteria, viruses, and DNA/RNA chains, among others. In here, a three-dimensional finite element analysis is performed in order to study the behaviour of the functionalised, doubly clamped beam. Preliminary results for the fabrication and characterisation processes show good agreement between the simulated and measured characteristics.

This work presents a novel methodology to implement a fuzzy inference system (FIS) to overcome the measurement ambiguity that is typically observed in interferometric sensors. This ambiguity occurs when the measurand is determined by tracing the wavelength position of a peak or dip of a spectral fringe. Consequently, the sensor measurement range is typically limited to the equivalent of 1 free spectral range (FSR). Here, it is demonstrated that by using the proposed methodology, the measurement range of this type of sensor can be widened several times by overcoming the ambiguity over some FSR periods. Furthermore, in order to support the viability of the methodology, it was applied to a couple of temperature interferometric sensors. Finally, experimental results demonstrated that it was possible to quintuple the measurement range of one of the tested sensors with a mean absolute error of MAE = 0.0045 °C, while for the second sensor, the measurement range was doubled with an MAE = 0.0073 °C.

A simple and low cost curve tracer which can build by students in their houses is presented. It is based on a microcontroller development board, a PC computer program, and a few generic electronic components.

In this letter, a tunable filter design based on polymer and silicon layers is presented. It is shown that by taking advantage of the different thermal properties of these materials, the overall spectral and tuning characteristics can be controlled by selecting the thickness of these layers. Moreover, a mathematical model to simulate the reflectivity spectrum and the tuning behavior due to the temperature of the filter is presented. Finally, two filters were fabricated and their experimental behavior is well described by our mathematical approximation model.

In this work, a waveband tunable and switchable multi-line ring-cavity fiber laser is presented. Here, the losses of the cavity are controlled by means of a variable optical attenuator (VOA) and a thermal sensitive interferometric filter, which was formed by a stack of 3 layers at the tip of an optical fiber and a long thermal sensitive sleeve. Thus, the laser can emit single–, dual–, triple–, quadruple–, quintuple–and sextuple–wavelength emissions which can be switched by adjusting the VOA. Moreover, the laser waveband can be tuned by varying the temperature of the filter. Here, it is shown that with this setup a waveband tuning resolution of ∼ 1.37 nm ∘ C−1 within the range from 1527.52 to 1534.40 nm can be achieved.

In this work, a novel tailored algorithm to enhance the overall sensitivity of gas concentration sensors based on the Direct Absorption Tunable Laser Absorption Spectroscopy (DA-ATLAS) method is presented. By using this algorithm, the sensor sensitivity can be custom-designed to be quasi constant over a much larger dynamic range compared with that obtained by typical methods based on a single statistics feature of the sensor signal output (peak amplitude, area under the curve, mean or RMS). Additionally, it is shown that with our algorithm, an optimal function can be tailored to get a quasi linear relationship between the concentration and some specific statistics features over a wider dynamic range. In order to test the viability of our algorithm, a basic C 2 H 2 sensor based on DA-ATLAS was implemented, and its experimental measurements support the simulated results provided by our algorithm.

In this work, lateral force sensing detection based on an all fiber intrinsic Fabry–Perot interferometer (IFPI) is presented. The IFPI generates several high-order reflected modes in conventional single-mode fiber (SMF), these modes were affected by lateral force distributed over a short section of SMF. Here, we analyze a fiber optic detection system based on intensity modulation reflection signal. The force is applied from 17 to 89 lbsf, over a SMF section and excitation of high-order modes is analyzed. The system presents good sensitivity around 0.1 dB/lbf and linear response in forward and backward direction. This system presents good mechanical strength, flexibility, and temperature-phase independent properties.

In this letter, a temperature sensor based on a fiber ring laser is presented. A fiber Bragg grating was used as a sensor head, and a Mach–Zehnder interferometer (MZI) was utilized as a wavelength selective filter to enhance the temperature sensing capability. The MZI was achieved by splicing a piece of photonic crystal fiber between two segments of single-mode fiber. Moreover, it is shown that when the laser emission wavelength is shifted as the temperature is varied, achieving a temperature sensitivity of 18.8 pm/°C at 1550 nm, within the temperature range from 20 °C to 90 °C.

An all-fiber Fabry–Perot (FP) interferometer is proposed and validated by the arc splicing technique. By using conventional fiber and special hollow-core photonic crystal fiber, several FP cavities were formed at the conventional fiber tip using arc discharges. As a result of the interaction between these cavities, modified FP principle operation was obtained; and temperature, refractive index, and load analyses validated this operation modification. In addition, this all-fiber interferometer presents good resolution and sensitivity in each parameter examined. The structure offers compactness, robustness, high repeatability, and stability measurement.

In this letter, a torsion sensing arrangement based on a three beam path Mach–Zehnder interferometer (MZI) is presented. The MZI with three beam paths was fabricated by fusion splicing a piece of double ytterbium-doped double-cladding photonic crystal fiber (Yb-d-DPCF) between two segments of single mode fiber (SMF). Moreover, in our sensing arrangement the Yb-d-DPCF segment is acting both as the MZI as the gain medium. Here, a spectral MZI fringe shifting is induced by applying torsion over the Yb-d-DPCF. By this setup, a torsion sensitivity of 0.001 nm/° was achieved. Finally, it is shown that the sensing arrangement is compact and robust. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1857–1860, 2015

A highly sensitive curvature and displacement sensing arrangement based on an all optical fiber micro Fabry–Perot Interferometer (MFPI) is presented. Here, the MFPI spectral fringes contrast is decreased due to curvature effects occurring within a segment of single mode fiber (SMF). Therefore by detecting optical power variations, at certain wavelengths, it was possible to determine curvature and displacement changes. For this setup the achieved curvature sensitivity was 0.3 dB/m−1 and the curvature resolution was 31.5×10−3 m−1. Finally some experimental results are provided to support the viability of this low cost sensing arrangement.

In this work an Intrinsic Fabry-Perot Interferometer (IFPI) based on an air-microcavity is presented. Here the air microcavity, with silica walls, is formed at a segment of a hollow core photonic crystal fiber (HCPCF), which is fusion spliced with a single mode fiber (SMF). Moreover, the spectral response of the IFPI is experimentally characterized and some results are provided. Finally, the viability to use the IFPI to implement a simple, compact size, and low cost refractive index sensor is briefly analyzed.

In this paper we present an analytical methodology to evaluate the response of a gas sensor based on correlation spectroscopy using a Fabry-Perot Interferometer (FPI). Here we consider a FPI which is illuminated with a converging beam from a black-body source. It is shown that the optimal FPI cavity length and reflectivity can be easily determined. We designed and tested three different gas sensors (CO, CO2, and CH4) using this methodology. Our numerical results are fully supported by experimental measurements.

In this work experimental measurements showing formation of dark periodic lattices in negative nonlinear liquid medium are reported. These lattices were formed by the propagation of periodic patterns through a nonlinear liquid media. These periodic patterns were induced by interference of three plane waves. Here three interesting cases showing the evolution of bright into dark periodic lattices are reported. In the first case periodic lattices formed by dark spots were observed. In the second case a periodic lattice formed by a set of stripes was observed. Finally in the third case a periodic lattice showing a combination of stripes and dark spots is reported.

In this work a refractive index sensor based on a combination of the non-dispersive sensing (NDS) and the Tunable Laser Spectroscopy (TLS) principles is presented. Here, in order to have one reference and one measurement channel a single-beam dual-path configuration is used for implementing the NDS principle. These channels are monitored with a couple of identical optical detectors which are correlated to calculate the overall sensor response, called here the depth of modulation. It is shown that this is useful to minimize drifting errors due to source power variations. Furthermore, a comprehensive analysis of a refractive index sensing setup, based on an intrinsic micro Fabry-Perot Interferometer (FPI) is described. Here, the changes over the FPI pattern as the exit refractive index is varied are analytically modelled by using the characteristic matrix method. Additionally, our simulated results are supported by experimental measurements which are also provided. Finally it is shown that by using this principle a simple refractive index sensor with a resolution in the order of 2.15 × 10(-4) RIU can be implemented by using a couple of standard and low cost photodetectors.

We present the fabrication and characterization of a mechanically induced long period grating (MLPG) using a grating period of 400 μm and 1m of NZ-DSF. Pressure is gradually applied up to 120 Lb at different angles like 0, 30, 45 and 60 degrees. An attenuation band is observed centered at a wavelength around 1064nm using a fiber position of 30 degrees with respect to the grating´s metal plate and a maximum pressure of 145 Lb. The loss band presents a maximum depth of 22dB and a bandwidth of approximately 10nm. Torsion and curvature characterizations did not change the output spectrum of the optical grating. However, temperature characterization depicted a small shifting which could be insignificant for some applications. Still, there is 16dB attenuation as temperature increases in a range from room temperature up to 450°C. These preliminary studies show that this 1064 nm centered wavelength MILPG might be used in a low linear dynamic range with temperature (75-300)°C as a temperature sensor.

In this work, a refractive index sensor setup based on a biconically tapered fiber (BTF) concatenated to an intrinsic all-fiber micro Fabry-Perot interferometer (MFPI) is presented. Here, the power of the MFPI spectral fringes decreases as the refractive index interacts with theevanescent field of the BTF segment. Furthermore, it is demonstrated that the RI sensitivity can be enhanced by bending the BTF segment.Finally, it is shown that by using this sensing arrangement, at ~1.53 µm wavelength, it is possible to detect refractive index changeswithin the measurement range of 1.3 to 1.7 RIU, with a sensitivity of 39.92 dB/RIU and a RI resolution of 2.5 x 10􀀀^-3 RIU with a curvature of C = 18.02 m^-􀀀1.

We study the nonlinear processes involved in the generation of broadband spectra with selectable spectral width. The continuum spectra were generated in short piece of SMF-28 fiber as nonlinear media pumped by a microchip laser at 1064 nm. Bending effects in the spectra were observed through wrapping the fibers on a cylindrical tube. We show that the spectral characteristics directly depend on the properties of the nonlinear medium, the excited nonlinear effects, and the location of the wrapped section which can produce a filtering effect on the SC spectrum. Finally, the main advantages of the proposed scheme are to obtain an adjustable bandwidth for a supercontinuum source through an easy and flexible control, and to provide a low-cost configuration in which photonic crystal fibers are not used.

In this work a hybrid gas sensor based on a tunable fiber laser and a correlation spectroscopy technique is presented. The laser is tuned by varying the temperature of a bulk silicon wafer of 85 μ m thickness and, once the desired wavelength is reached the line, is locked by keeping fixed its temperature. According to experimental results the wafer temperature variation was in the order of 0.02 K, which induced an estimated wavelength deviation of 0.12 pm, which satisfies the high wavelength position accuracy required for gas sensing applications. Additionally, it is shown that errors due to laser intensity fluctuations can be minimized by implementing a simple dual path correlation spectroscopy stage. As a proof of the suitability of our tunable fiber laser for gas sensing applications, a C2H2 sensor was implemented. By using a 10 cm gas cell at atmospheric pressure, it was possible to detect concentrations from 0 to 20% with a sensitivity of 521 ppm and sub-minute time response. Moreover, the experimental measurements and simulated results have a high level of agreement. Finally, it is important to point out that, by using doped fiber with different characteristics, other wavelength emissions can be generated.

We show the sensing of load by means mechanically induced long-period fiber grating (MLPFG) made by applying pressure by means a screw to a pair of grooved plates over single-mode fiber. We used a torquemeter in order to obtain precision in the adjustment screw and thus establish an equilibrium pressure applied to a specific region of the optical fiber to form the long-period grating mechanically induced fiber. The increase the torque to screw, the resonance wavelength of MLPFG increases its depth over 16 dB. We use a detector to observe the changes amplitude according to the fiber pressure.

We present the results from the fabrication and characterization of mechanically induced long period fiber gratings in polarization maintaining photonic crystal fiber (PM-PCF). A supercontinuum source in the range of 600nm - 1700nm is used. This source is generated using a micro-chip laser at 1064nm and a single mode fiber. A long-period grating is induced over 40mm long unjacketed PCF using a V-grooved aluminum plate. External pressure is gradually applied with a metal screw and a torque meter and a loss dip with resonance wavelength is observed. Low insertion losses are depicted from (1-3) dBm with a bandwidth of about 30nm and a loss dip around 15dBm. Sensitivity for this preliminary work is found at 27 dB/Lb. Several applications are potentially possible with the optimization of the transmission spectrum controlled by applied pressure.

In this work the interaction between modulation instability (MI) and stimulated Raman Scattering (SRS) in conventional short fibers (8m) to supercontinuum generation is reported. Here we used short length optical fibers pumped with a microchip laser emitting a pulsed signal at 1064 nm wavelength and 700ps. Moreover was obtained a detailed analysis of spectral evolution of pulses propagated through the fiber. Hence MI is observed as first nonlinear effect unchaining more of those until reach a 293 nm wide spectrum. A comparative analysis was done between 1060XP and SM28 short section optic fibers showing important SRS gaining differences, achieving on SMF28 fiber a higher gain on anti-Stokes wavelength. On the other side was achieved a higher broadening spectral on 1060XP fiber than the one generated on communications optical.

A compact high temperature fiber sensor where the sensor head consists of a short fattened long period fiber grating (F-LPFG) of at least 2 mm in length and background loss of −5 dBm is reported. On purpose two different F-LPFGs were used to measure temperature variations, taking advantage of their broad spectrum and the slope characteristics of the erbium light source. This approach affected the spectrum gain as the linear band shifting took place. The measured sensitivity of the long period fiber gratings were about 72 pm/°C in a range from 25 to 500 °C. Here, the temperature rate of the experiment was 0.17 °C/s and the temperature response time was within 3 s. Moreover, temperature changes were detected with an InGaAs photodetector, where a sensitivity of 0.05 mV/°C was achieved.

In this work a very simple continuously tunable laser based on an erbium ring cavity and a silicon wafer is presented. This laser can be tuned with very fine steps, which is a compulsory characteristic for gas sensing applications. Moreover the laser is free of mode hopping within a spectral range sufficiently wide to match one of the ro-vibrational lines of a target molecule. Here the proposed laser reached, at ∼1530 nm, a continuous tuning range of around 950 pm (>100 GHz) before mode hopping occurred, when a silicon wafer of 355 μm thickness was used. Additionally, the laser can be finely tuned with small tuning steps of

In this letter, a switchable ytterbium doped double cladding photonic crystal fiber (Yb-doped-DCPCF) laser based on a three optical path Mach-Zehnder interferometer (MZI) is presented. Here, the MZI with three-beam path was achieved by fusion splicing a segment of an Yb-doped-DCPCF between two pieces of single mode fibers. Moreover, in the proposed laser arrangement, the Yb-doped-DCPCF segment is acting simultaneously as the MZI and also as the gain medium. This laser can be switched to emit a single or double line by controlling the polarization state and it operates within the range from 1028 to 1033 nm. In addition, the laser emission has a linewidth of 0.07 nm and a single-mode suppression ratio of 40 dB. Finally, it is shown that the fiber laser arrangement is compact and robust and that requires a relativity simple fabrication procedure.

Research nonlinear optical properties of the materials for the fabrication of opto-electronic devices have growth in the last years. Ionics liquids present nonlinear optical properties. In this work we present the results of nonlinear optical properties of four ionic liquids of 1-methylpyrrolidine family, analyzed using a z-scan technique. The results show the difference obtained using or not a chooper for measuring the nonlinearity and the photoinduced lens. Ionic liquids have a negative nonlinearity (self-defocusing) of thermal origin.

Supercontinuum generation is being widely studied due to its applications in communications, medicine and metrology. Usually, special fibers, such as photonic crystal fibers and dispersion-shifted fiber, have been utilized. However, there is few information about the potential use of standard fiber with this purpose, which shows some advantages: low cost and availability. In this work, the influence of losses due to induced macrobends on the supercontinuum generation using standard fiber was studied. The losses were introduced by wrapping 30 m in length of standard fiber on cylinders with different diameter, a nanosecond microchip laser and 1064 nm of wavelength were employed. The continuum was recorded at the fiber output by using an optical spectrum analyzer and its dynamics was analyzed by tuning the launched power. In a first stage, the fiber was used without bends generating strong firs-order Raman Stokes and a supercontinuum spectrum of 636 nm. When the fiber was wrapped in a cylinder of 0.9 cm of diameter to induce macrobends, the Raman Stokes of high order were attenuated and the output spectrum was reduced to 240 nm. Also, a peak pulse was observed, around 1030 nm, that means new frequencies were generated in the near infrared region. Thus, induced macrobends affect the supercontinuum broadening.

In the paper, we investigate in details switching ON and switching OFF dynamics of the wideband optical filter on the basis of nonlinear photonic crystal which possess all-optical bistability properties. The all-optical flip-flop using ultra-short pulses with duration lower than 200 fs have been demonstrated in such filters.

This article presents the fabrication of Long Period Gratings in Optical Fiber (LPFGs) applied to the sensing loops. In implementing the manufacturing method used a commercial splicer fiber optic (FiTel S-175), capable of being programmed to a short section of standard optical fiber (SMF28) is taken at intervals between shots in a range from 400µm to of 650µm. The LPFGs Being able to obtain through attenuation bands above 20 dB, while the wavelength of central attenuation is close to 1550nm. We shows the experimental scheme to measure curvatures with diameters ranging between 12 and 13.1cm, having a linear variation of peak output cut at the LPFGs with tuning of 17nm.

We study nonlinear optical properties of 1-buthyl-3-methylimidazolium tetrafluoroborate [BMIM][BF 4 ]), 1-ethyl-3-methylimidazolium Bis((trifluoromethyl)sulfonyl)imide ([EMIM][TF 2 N]), 1-ethyl-3-methylimidazolium trifluoroacetate ([EMIM][CF 3 COO]), 1-buthyl-3-ethylimidazoliumtrifluoroacetate ([BMIM][CF 3 COO]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF 4 ]) and 1-buthyl-3-methylimidazolium Bis((trifluoromethyl)sulfonyl)imide ([BMIM][TF 2 N]). We determinated the focal length photo-induced lens using z-scan technique by adjusting the characteristic curves of nonlinear refraction index. This indicated the presence of thermal and electronic effects.

We present an experimental study of light polarization on solid core microstructured optical fibers type (Large Mode Area) LMA-16, LMA-20 and LMA-25. These fibers were partially filled with one micron diameter polyethylene spheres or carbon nanotubes diluted in distilled H 2 O by capillarity. Polarization characterization was realized on these Photonic Crystal fibers with air filled holes and partially particle filled holes using a He-Ne 633nm central wavelength laser at 10mW. The achieved results were compared using graphical data of every test collected at different exposition dates where the fiber was exposed to particle sedimentation. Results depicted that short time sedimentation of these particles does not change the light polarization leaving from the fiber except for the phase of the beam. On the other hand, longer time particle exposition visibly changes the light phase measured at the end of the photonic crystal fiber with repeatable results.

We prepare optrodes of fiber optic plastic with sol-gel technique. Suitable concentration of carbone nanotubes (CNTs), phenol red, bromophenol blue and cresol red, design optrodes with fiber optic plastic. The surface charge of silica and the refractive index, which play an important roll on the fiber, modifies the conditions of light propagation into the plastic optical fiber. We use the transmittance to measure the pH of a solution or fluid in a range between 3 and 9.

We propose the fabrication and characterization to bending and temperature of a long period fiber grating with the alternative electric arc method known as fattening. This is the enlargement of the fiber structure by means of arc discharges from a commercial splicing machine. The fiber structure consists of 4 layers of glass of different refractive index. The resulting device is a reject band filter with an attenuation band around 1400nm. It has a bandwidth of 162nm with a depth around 26.9 dB. Test to bending depict changes in band depth up to -10dB between radii values of 4-7cm with a shifting span of 16.8nm. Temperature characterizations are made with bending and straight fiber over a hot surface. Interesting achievements can take advantage as optical sensors with different characteristics. Optimization in the fabrication process can be achieved to lower the insertion losses so better sensors can be applied for industry and commercial applications.

In this work an investigation into the viability of a dual gas sensor based on correlation spectroscopy using a single Fabry-Perot Interferometer (FPI) is presented. Here, based on sensor response simulations, it is demonstrated that the commonly considered undesirable effect due to multiple internal reflections of the FPI's mirror substrate can be used to increase the sensing capability of the system. Usually designers tend to minimize these reflections to improve the FPI transmission spectrum. However we let them to occur in order to used them as a part of the modulation system of the sensor which allows us to detect two gases simultaneously using a single FPI.

We propose a temperature sensor based on dispersion shifted long period fiber grating (LPFG) fabricated with the fattening method, using electric arc discharges from a commercial fusion splicer machine. The fattened LPFG are centered at 1524 and 1550 nm, respectively. A temperature characterization in terms of the transmitted spectrum is realized with a pumped Er+3 doped fiber as the light source. The less than 3 mm in length fattened LPFG reached a sensitivity of 72 pm/°C between a temperature range of (25-500°C). Temperature stability was observed among the temperature range of (25-200°C), result in agreement with our previous studies. From up to 200°C sensing is observed as temperature increases. To apply this LPFG as a temperature sensor, sensing was measured as voltage signal outputs with repeatable results. This sensor is a high temperature resistant device because non deterioration of its properties was observed, and can find useful applications when temperature stability may be needed or the sensing requirements are desirable.

In this work we present the formation of dark photonic lattices in negative nonlinear medium. Bright periodic lattices are generated by interference technique and propagated through 1 cm of length of nonlinear medium (R6G with acetone). The dependence with the laser (Ar) power and the geometry selected are showed. Three very interesting cases were obtained: two dimensional dark photonic lattices (2D), one dimensional dark photonic lattices, and (1D), and 2D and 1D combination effects. Our experimental results are accord with numerical simulations.

Auto-diffraction and nonlinear properties of organic material is presented. Develop of rings by 4-(4-pentenyloxy)benzonitrile after being irradiated by a laser beam while the power is increased and nonlinear refraction index measured by Z-scan technique was investigated.

A compact and all-fiber erbium-doped tunable fiber laser is presented. This can provide an optical power in excess of +3.85 dBm with a tunability of 17 nm within the region of 1558.33-1575.32 nm. The tuning mechanism is based on the multimode interference effect.

A gas sensor design based on cross correlation spectroscopy using a FPI with long cavity length (>500 µm) as a modulator and with a pyroelectric detector is presented. This technique can be suitable to detect molecules with very well defined ro-vibrational lines such as CO, CO2 and CH4. To induce modulation one mirror of the FPI is scan over lambda/2, this will shift the spectral FPI transmission fringe pattern producing the cross correlation principle. In this design the FPI is illuminated with a converging beam and it is placed just in front of the pyroelectric detector, this configuration can be useful if the FPI and the detector are integrated within a MEMS. Furthermore here the FPI scan is driven using a triangular waveform. Therefore in this work we will analyze the effects of illuminate the FPI with a converging beam and their consequences in the overall sensor response. Moreover we will review some possible effects in the sensor response for driving the FPI mirror scan with a triangular waveform. This issue can be very important since it can change the harmonic composition of the modulated signal and consequently the overall sensor response since the pyroelectric detector responsivity is frequency dependant. Finally, simulation results and experimental measurements are provided.

Several designs of infrared sensors use a Fabry-Perot interferometer (FPI) to modulate the incident light. In this work we analyze the particular case where the FPI fringes are matched with very well defined rovibrational absorption lines of a target molecule such as CO(2), CO, N(2)O, or CH(4). In this kind of sensor, modulation is induced by scanning the FPI cavity length over one half of the reference wavelength. Here we present an analytical method based on the Fourier transform, which simplifies the procedure to determine the sensor response. Furthermore, this method provides a simple solution to finding the optimal FPI cavity length and mirror reflectivity. It is shown that FPI mirrors with surprisingly low reflectivity (50%) are generally the optimum choice for target gases at atmospheric pressure. Finally, experimental measurements and simulation results are presented.

In this letter, the effects of bending losses for the development of tunable supercontinuum sources are numerically and experimentally analyzed. Here, the proposed supercontinuum source is based on a very short length segment of standard single-mode fiber (SMF-28) which was used as a nonlinear medium and it was pumped by a microchip Q-switch laser at 1064 nm. In the experimental setup, a section of the optical fiber was wrapped around a mandrel in order to induce bending losses. In addition, by changing the fiber wrapping settings of the SMF-28 the SC source spectrum was filtered at some wavelengths due to mechanical stress. Hence, the source bandwidth can be increased or decreased by selecting the fiber length and by modifying the wrapping settings. Furthermore, in this work it is described as a numerical analysis which helps to support our experimental results. This numerical analysis was based on the fourth-order Runge–Kutta in the interaction picture method and the beam propagation method.

A gas sensor based on correlation spectroscopy using a FPI with long cavity length (>500 µm) as a modulator is presented. Eventually the FPI and the optical detector will be integrated within a MEMS structure.