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We demonstrate the highest, to the best of our knowledge, capacity obtained for an OM4 fiber reaching 1.6 Tb/s for 3.5 km of OM4 fiber. The result is obtained using a highly selective modal multiplexer exciting the LP01 mode and a state-of-the-art coherent transmission setup operating in the C-band. The results indicate that there is no need to replace legacy optical fibers to increase their capacity, which may be an extremely important factor when considering the costs of upgrading existing networks.

We report for the first time, the fast inscription of high-quality Bragg gratings in highly birefringent microstructured polymer optical fibers by the phase mask method using 248-nm UV radiation. The fibers birefringence is created through a special design of the structure of holes through the fiber. A Bragg grating in these type of fibers allows the creation of two reflection peaks, where the peak separation is related to the phase birefringence.

In this study, an innovative method is presented for preparing optical fibers for application in fiber optic sensors operating in harsh environments. It is shown, how to attach a metal-coated fiber electrolytically to a metal sensing element, as well as an electroless method for depositing a nickel protective layer on optical fibers. Additionally, the results of the reliability tests of these methods are presented. It is also shown, that by depositing an additional nickel protective layer, it is possible to slow down the oxidation process of the copper coating. Analysis of the conducted experiments allows us to predict, that the connection method investigated and the method of protecting the fiber are robust and may find application in industrial optical sensors.

Sensors based on fiber optics are irreplaceable wherever immunity to strong electro-magnetic fields or safe operation in explosive atmospheres is needed. Furthermore, it is often essential to be able to monitor high temperatures of over 500°C in such environments (e.g. in cooling systems or equipment monitoring in power plants). In order to meet this demand, we have designed and manufactured a fiber optic sensor with which temperatures up to 900°C can be measured. The sensor utilizes multi-core fibers which are recognized as the dedicated medium for telecommunication or shape sensing, but as we show may be also deployed advantageously in new types of fiber optic temperature sensors. The sensor presented in this paper is based on a dual-core microstructured fiber Michelson interferometer. The fiber is characterized by strongly coupled cores, hence it acts as an all-fiber coupler, but with an outer diameter significantly wider than a standard fused biconical taper coupler, which significantly increases the coupling region’s mechanical reliability. Owing to the proposed interferometer imbalance, effective operation and high-sensitivity can be achieved. The presented sensor is designed to be used at high temperatures as a result of the developed low temperature chemical process of metal (copper or gold) coating. The hermetic metal coating can be applied directly to the silica cladding of the fiber or the fiber component. This operation significantly reduces the degradation of sensors due to hydrolysis in uncontrolled atmospheres and high temperatures.

Fiber optic sensors (FOS) are insensitive to external EM fields and are intrinsically safe (as no electrical power is needed at the sensing point), so the measurement can be performed in areas where standard electronic devices cannot easily be applied. What is more, due to the very low silica fiber attenuation the measurement point can be located kilometers away from a light source and detector, which makes the sensors independent of a local power source. Furthermore the FOS are small so they can be used for sensing in mechanical mechanisms where there is not much free space. They can also be easily integrated with the structure of different materials for military applications (e.g. in tanks and airplanes). In this work we propose an intrinsically safe temperature sensor based on fiber optic technology. The presented sensor is entirely passive and benefits from all of the advantages mentioned above, which allows it to be applied in the most demanding environments. The construction of the presented sensor is based on a dedicated microstructured optical fiber which allows both the range and sensitivity of the sensor to be adjusted to a specific application.

An novel low-temperature method was used to enhance the corrosion resistance of copper or gold-coated optical fibers. A characterization of the elaborated materials and reports on selected studies such as cyclic temperature tests together with tensile tests is presented. Gold-coated optical fibers are proposed as a component of optical fiber sensors working in oxidizing atmospheres under temperatures exceeding ~900 °C.

We investigate the influence of air holes on phase sensitivity in microstructured optical fibers to longitudinal strain. According to the numerical simulations performed, large air holes in close proximity to a fiber core introduce significant compression stress to the core, which results in an increase in the effective refractive index sensitivity to longitudinal strain. The theoretical investigation is verified by an experiment performed on four fibers drawn from the same preform and differentiated by air hole diameter. We show that introducing properly designed air holes can lead to a considerable increase in normalized effective refractive index sensitivity to axial strain from −0.21 e−1 (for traditional single mode fiber) to −0.14 e−1.

This paper focuses on the utilization of crosstalk phenomenon to construct an innovative strain sensor. In our experiments, we take advantage of special fiber design and technology of fiber post-processing in order to receive strain sensing areas. We present results, which indicate possibility of achieving strain sensitivity at level of several me/nm with negligible temperature cross-sensitivity at the same time. Furthermore after coating the sensor with the developed copper and gold coatings, it can be easily applied in extremely high temperature (e.g. 500–800 °C) and/or aggressive media applications.

We present the novel 7-core and 19-core hole-assisted fibers designed to satisfy the most demanding requirements of the ITU-T G.657.B3 recommendation for bend-insensitive fibers. The fibers are compatible with standard single-mode fibers with regard to modal properties, dispersion characteristics, and transmission loss. The fibers presented exhibit no crosstalk and it is possible to use them together with other multiplexing methods like CWDM or DWDM. Dedicated fanin/ fan-outs have been created in order to make immediate use in industry possible. The hole-assisted 19-core fiber with single-mode cores is being presented for the very first time.

In presented work, we examined the structures of dual-core fibers paying special attention to the possibility of using them for sensing. In the hole-assisted fiber structure, the character of propagation in the cores was changed fluently, by post-processing the fiber, i.e. tapering with collapsing the holes. Fiber post-processing changed the conditions for supermodes interference and thus the different scale of power transfer between cores was observed. In the paper we investigated the influence of the taper parameters (taper waist, length and ratio) on the properties of the fiber. We have also studied the behaviour of the transmitted signal, while putting post-processed segment of fiber into different external conditions. Presented research shows a great potential of using modified hole-assisted fibers as sensing elements.

In this work we present an innovative method of enhancing optical fibers’ resistance to extremely high temperatures by deposition of a multilayer metal coating on the fibers’ surface. Such multilayer coating is necessary because of the silica degradation at elevated temperatures. Despite the fact that copper coated fibers work well at temperatures up to 400°C, at higher temperatures copper oxidizes and can no longer protect the fiber. To hold back the copper oxidation and silica degradation processes we developed a dedicated multilayer coating which allows fibers to operate at temperatures up to 700°C. The optimal protective layer has been chosen after numerous high-temperature tests, where copper plates coated with different kinds of coatings were evaluated. What is more, we present results of the high-temperature reliability tests of copper coated fibers protected with our multilayer coating. Performed tests proved that our solution significantly improved optical fibers’ reliability to both: elevated temperatures and rapid changes of temperature. Furthermore the developed metal coatings allow fibers’ to be electrolytically bonded to other metal elements (e.g. sensor transducers) what makes them great candidates for harsh environment fiber optic sensor applications.

The use of optical elements and other photonic components makes it possible to overcome telecommunication satellite’s bottleneck problems such as size and weight reduction. Despite the unquestionable potential of such elements, nowadays they are not widely used in systems operating in space. This is due to many factors, including the fact that space radiation has disruptive influence on optical fibre. Namely it introduces additional radiation induced attenuation (RIA) that significantly lowers efficiency of optical fibre based systems. However, there is a possibility to produce radiation-hardened (rad-hard) components. One of them is seven core erbium-doped active fibre (MC-EDF) for fibre amplifiers in satellites that we have been developing. In this paper we present a detailed description of seven core structure design as well as experimental results. We report that average gain of 20 dB in C-band with noise figure of 5.8 dB was obtained. We also confirmed that low crosstalk value for a multicore fibre amplifier based on our fibre can be achieved.

In this paper we present the idea and test results of an all-fiber unbalanced Mach-Zehnder interferometer for fiber Bragg grating shift demodulation. The interferometer design allows to monitor Bragg wavelength changes (caused by temperature or strain variations) as changes of intensity on the output detector. Furthermore the construction is cost-effective and based on simple optoelectronic components, which makes the solution attractive for application as a low cost fiber Bragg grating interrogator.

The paper reports on the metal (Cu, Ni, Au)-coated fibers annealed under concentrated solar radiation in ammonia and N 2 /H 2 atmospheres at temperatures up to 580 °C. Tensile strength of the annealed fiber components was studied from the point of view of their possible application as a fiber optic sensors in urea chemical synthesis process control.

An optical fiber CO 2 gas sensor is reported in this work. Sensor is based on the change of absorption of a selected dye dissolved in an organically modified silica coating of an optical fiber. CO 2 in the atmosphere decreases the pH of the deposited active layer, which eventually leads to the change of the fiber transmittance. Elaborated sensor exhibits high sensitivity, short response time and good stability, which makes it suitable for potential industrial, agricultural and household use. Described method can also be used for sensing other gases in sensor matrices.

In this work we present a nanocrystalline monoclinic ZrO2 with large free volumen open towards the nanocrystals surface dedicated for optical oxygen sensors. Nanoporous zirconia nanopowder was fabricated in hydrothermal microwave-driven process followed by annealing at 800°C. Metal-coated optical fibers are proposed as a light carrier when the working temperature exceeds 500°C. The obtained results may also find application in luminescent fiber optic oxygen sensors. Publisher PDF

In this work we present an innovative method of connecting metal coated optical fibers with metal surfaces. The process is based on electrolytic reaction between copper and allows to obtain a robustand inflexible connection. Furthermore reliability tests of such fiber to metal joints have been performed, with the results of mechanical strength and temperature resistance tests presented. Additionally, as accelerated oxidation of copper at elevated temperatures is a major concern in long term temperature stability of the connection, we propose a method of slowing down the oxidation process with chemical nickel coating. Analysis of the obtained results allows us to predict that the investigated connection may find applications in various industrial optical sensors with special focus on harsh environments.

The paper presents a new solution of flowmeter to measure the flowing medium velocity using fiber sensing methods. A Mach-Zehnder interferometer is implemented for the detection of vortices [1] [2]. The measurement of flow is based on the vortex frequency detection of a vibrating diaphragm placed in an optimized measuring chamber. The stress of the vibrating diaphragm is measured with use of a Mach-Zehnder (MZ) fiber interferometer whose fiber arms are fixed with the diaphragm. This solution allows for measuring flow of liquids, gases and vapors in the temperature range of -200°C to +550°C and pressures up to 300 bar.

In this work we present a novel highly Ge doped microstructured fiber design dedicated for fiber Bragg grating (FBG) inscription and longitudinal strain sensing. Three series of the reported fiber differentiated by air-hole diameters were drawn and presented. After numerical analysis of the propagation conditions (with effective refractive index, loss and mode area calculated) in the real structures, the fibers were subjected to femtosecond FBG inscription. We show the resulting typical FBG spectra, as well as measure the longitudinal strain sensitivity of the fabricated samples and its dependence on the microstructure geometry. An increase of approx. 4% in the Bragg wavelength strain sensitivity was noticed for an increase of the large air-hole diameter of approx. 10%.

Constantly refined technology of manufacturing increasingly complex photonic crystal fibers (PCF) leads to new optical fiber sensor concepts. The ways of enhancing the influence of external factors (such as hydrostatic pressure, temperature, acceleration) on the fiber propagating conditions are commonly investigated in literature. On the other hand longitudinal strain analysis, due to the calculation difficulties caused by the three dimensional computation, are somehow neglected. In this paper we show results of such a 3D numerical simulation and report methods of tuning the fiber strain sensitivity by changing the fiber microstructure and core doping level. Furthermore our approach allows to control whether the modes’ effective refractive index is increasing or decreasing with strain, with the possibility of achieving zero strain sensitivity with specific fiber geometries. The presented numerical analysis is compared with experimental results of the fabricated fibers characterization. Basing on the aforementioned methodology we propose a novel dual-core fiber design with significantly increased sensitivity to longitudinal strain for optical fiber sensor applications. Furthermore the reported fiber satisfies all conditions necessary for commercial applications like good mode matching with standard single-mode fiber, low confinement loss and ease of manufacturing with the stack-and-draw technique. Such fiber may serve as an integrated Mach-Zehnder interferometer when highly coherent source is used. With the optimization of single mode transmission to 850 nm, we propose a VCSEL source to be used in order to achieve a low-cost, reliable and compact strain sensing transducer.

Microstructured optical fibers (MOF) sometimes also referred to as photonic crystal fibers (PCF) have been a subject of extensive research for over a decade. This is mainly due to the fact that by changing the microstructure geometry (e.g. distribution and size of the air-holes) fiber properties can be significantly modified to better fit specific applications. In this manuscript we present a novel fiber design with three large air-holes neighboring the core and report on how the air-hole diameter influences the effective refractive index strain sensitivity. As direct measurement of the effective refractive index change may be complex and challenging, we propose to use fiber Bragg gratings (FBG) in our sensing set up. The Bragg wavelength is a function of the effective refractive index, hence the external strain changes can be monitored through the Bragg wavelength shift with a simple optical spectrometer. Furthermore we also include an analysis of the fibers temperature sensitivity.

In this work we would like to present the results of low loss coupling of a novel soft glass fiber for super continuum generation with standard single mode fiber by a filament splicing method. For our experiment we used an all solid soft glass microstructured fiber (MSF) made from a composition of F2 lead-silicate glass and NC21 borosilicate glass. The structure and material properties of the fiber were optimized to achieve all normal dispersion (ND) flattened around 1560 nm, which offers two general advantages for supercontinuum generation. The ND supercontinuum avoids soliton dynamics, hence it is less sensitive to pump laser shot noise and has larger degree of coherence than supercontinuum in the anomalous dispersion range. Furthermore flattening around 1560 nm indicates optimal supercontinuum pump wavelength, which is readily available from erbium doped femtosecond fiber lasers. Using Vytran splicing station (GPX3400) we were able to achieve repeatable splice loss between a standard fused-silica single mode fiber (SMF28) and the low-melting-temperature soft glass MSF as low as 2.12 dB @1310 nm and 1.94 dB @ 1550 nm. The developed very low loss splicing technology together with the above mentioned all solid soft glass MSF advantages give very promising perspectives for commercial applications.

Phase sensitivities of temperature, longitudinal strain or pressure, are very important fiber features in sensing and telecommunication applications. The most common ways to modify such sensitivities are to change the material properties (by adjusting the core doping level) or employ microstructured fibers (which properties strongly depend on the cross-section geometry). We decided to investigate strain sensitivity influenced by effective mode field area and mode field diameter as clear consequence of fiber cross-section geometry. In this paper we present the results of a three dimensional numerical analysis of the correlation between the fiber mode field diameter and its longitudinal strain sensitivity. Both conventional and microstructured (commercially available and custom designed) fibers are investigated. Furthermore we compare the theoretical results with experimental data. To measure fiber sensitivity we developed a dedicated all-fiber Mach-Zehnder interferometer which enables the measurement of strain induced phase changes in various fiber types (including conventional and microstructured fibers). As a conclusion of our work we present relationship between strain sensitivity and MFD .

Photonic crystal fibers (PCF), sometimes also referred to as microstructured fibers (MSF), have been a subject of extensive research for over a decade. This is mainly due to the fact that by changing the geometry and distribution of the air holes the fiber properties can be significantly modified and tailored to specific applications. In this paper we present the results of a numerical analysis of the influence of the air-hole distribution on the sensitivity of the propagated modes’ effective refractive index to externally applied longitudinal strain. We propose an optimal strain sensitive fiber design, with a number of fibers drawn and experimentally evaluated to confirm the theoretical results. Furthermore as the direct measurement of the effective refractive index change may be complex and challenging in field environment, we propose to use fiber Bragg gratings (FBG) in our sensing set-up. As the Bragg wavelength is a function of the effective refractive index, the external strain changes can be monitored through the Bragg wavelength shift with a simple optical spectrometer. Moreover, since the PCF is also optimized for low-loss splicing with standard single mode fiber, our novel sensor head can be used with standard off-the-shelf components in complex multiplexed sensing arrays, with the measured signal transmitted to and from the sensor head by standard telecom fibers, which significantly reduces costs.

In this Letter, we present the technology of fiber Bragg grating (FBG) inscription in highly birefringent (HB) few-mode microstructured fibers (MSFs) with two different (nanosecond and femtosecond) lasers in a Talbot interferometer setup. The spectral characteristics of FBGs written in the core region of the investigated fiber, with particular modes represented by dual peaks, are presented and discussed. Furthermore, we calculate the fundamental fiber parameters (mode effective refractive index and phase modal birefringence) from the spectral characteristics and show very good agreement with the performed numerical fiber characterization. We expect the results of our experiments to be very useful in future development of FBG sensors based on novel HB MSFs, with enhanced strain sensitivity of higher-order modes.

Sensitivity of optical fibers to the temperature, longitudinal strain or pressure, is a very important feature in many applications, such as sensors or telecommunication. The most common way to modify (depending on application - either mitigate or strengthen,) this sensitivity is changing the fiber material properties by appropriate glass doping or by employing appropriate microstructure in the fiber. In some cases the precise adjustment of a doping level and sophisticated design of air-holes arrangement is needed to obtain required features of the fiber. In this paper, for the first time, to the best of our knowledge, we report the investigation of the mode area and geometry influence on the fiber temperature and mechanical sensitivities. To do so, we engaged a dedicated all-fiber interferometer which enables the measurement of the temperature and longitudinal strain sensitivities of different fiber types, including conventional and microstructured fibers with different core diameters.

Fiber Bragg gratings (FBG) are one of the most successful fiber optic technologies with very interesting perspectives for application in fiber optic sensing. It has been already reported that the possibility of its fabrication in novel microstructured fibers (MSF), creating a unique 3D structure, can significantly improve their performance and sensing properties. In this paper we present the results of FBG inscription in a dual-mode highly birefringent (HB) MSF with enhanced polarimetric strain sensitivity of the second order mode, as its mode maxima are closer to the cladding air-holes, where the strain distribution during fiber elongation is the highest. We perform an analysis and comparison of the FBG reflection and transmission characteristics, showing the effects of power coupling to cladding radiation modes. Furthermore we present the results of temperature and longitudinal strain sensitivities of the particular modes visible in the grating reflection spectrum followed by conclusions with reference to our previously reported results of polarimetric strain and temperature measurements of a similar fiber design.

Numerical Aperture (NA) is one of the fundamental properties of optical fibres. It determines the ability of efficient light coupling into the fibre and low loss splicing with other fibres. NA is essential when novel fibres are manufactured. Moreover, dispersive behaviour of geometrical guiding mechanisms, existing in microstructured fibres, is completely different comparing with material guiding mechanisms of classical fibres. Therefore we constructed measurement system, for characterization the dispersive properties of NA of specialty microstructured fibres in broad wavelength range. Additionally, presented setup can be applied for measurements refractive index of different materials (including highly absorbing) filling the holes of microstructured fibre in broad wavelength range.

We discuss the theoretical aspects of core-to-core power transfer in multicore fibers relying on supermode theory. Based on a dual core fiber model, we investigate the consequences of this approach, such as the influence of initial excitation conditions on cross talk. Supermode interpretation of power coupling proves to be intuitive and thus may lead to new concepts of multicore fiber-based devices. As a conclusion, we propose a definition of a uniform cross talk parameter that describes multicore fiber design.

In this paper we present the experimental comparison of mechanical and temperature sensitivities of Mach-Zehnder interferometer with replaceable FC connectorized sensing fibre arm, such as: off-the-shelf endlessly single mode microstructured fibre (MSF) or standard telecom single mode fibre. Experimental results clearly show reduced crosssensitivity to temperature of studied MSF compared with standard doped core fibre. Additionally, microstructured fibre Mach-Zehnder interferometer with standard FC receptacles allows using different fibres as sensors with the same device. Moreover, investigated interferometer consumes in total extremely low electric power (< 20 mW) and VCSEL as the light source.

In this paper we present the results of theoretical characterization of a few-mode birefringent microstructured fiber dedicated for fiber Bragg grating (FBG) inscription. The spectral characteristics of FBGs written (with a nanosecond and femtosecond laser Talbot interferometer setups) in the core region of the investigated fiber are presented and discussed. We compare the experimental results of the polarimetric strain sensitivity with our previously reported data, outlining perspectives for developing a highly sensitive (with strain sensitivity of second order mode two orders of magnitude higher in comparison to fundamental mode), temperature independent, FBG based strain transducer.

The possibility of manufacturing highly birefringent (HB) microstructured optical fibers (MOF) made these fiber types very attractive for use in sensing applications. In contrary to traditional optical fibre sensors, properly designed MOF based components do not need temperature compensation as their birefringence remains insensitive to temperature changes. Furthermore the polarimetric strain sensitivity can significantly increase (even two orders of magnitude according to our previously reported results) for higher order modes, as their mode maxima get closer to the holey region of the fiber, hence are subjected to higher strain distribution. In this paper we present the results of numerical modeling of the propagation conditions in the HB dual-mode MOF including effective refractive index, confinement losses and birefringence calculations. Furthermore we show and discuss the spectral characteristics of fiber Bragg grating (FBG) structures written in the dedicated fiber with two technologies (with a nanosecond and femtosecond UV laser sources). A comparison of the theoretical and experimental values of effective refractive index and birefringence of the fundamental and second order modes is also included. We show the preliminary results of the fabricated structures strain response measurements and discuss ideas of increasing the structures strain sensitivity.

Microstructured fibres (MSFs) reveal unique properties including endlessly single-mode operation from ultraviolet to infrared wavelengths, very high birefringence or nonlinearity, very large or very small effective mode field area, and many others. The size, shape and the location of the air holes allow for tailoring MSF parameters in a very wide range, way beyond the classical fibres, what opens up the possibilities for various applications. Due to their advantages MSFs obtain growing attention for their perspectives in sensing applications. Different MSF sensors have already been investigated, including interferometric transducers for diverse physical parameters. Until now, there have not been any publications reporting on the sensing applications of MSF Mach-Zehnder interferometers, targeting the mechanical measurements of vibrations, dynamic or static pressure, strain, bending and lateral force. Moreover, a critical feature opening the prospective of optical fibre transducer to successfully accomplish a particular sensing task remains its cross-sensitivity to temperature. Studied MSF is made of pure silica glass in the entire cross-section with a hexagonal structure of the holes. Consequently, there is no thermal stress induced by the difference in thermal expansion coefficients between the doped core region and the pure silica glass cladding, in contrast to standard fibres. In this paper we present the experimental comparison of mechanical and temperature sensitivities of Mach- Zehnder interferometer with replaceable FC connectorized sensing fibre arm, such as: off-the-shelf endlessly single mode MSF or standard telecom single mode fibre. Experimental results clearly show very low cross-sensitivity to temperature of studied MSF compared with standard fibre. Additionally, microstructured fibre Mach-Zehnder interferometer with standard FC receptacles allows using different fibres as sensors with the same device. Moreover, investigated interferometer consumes in total extremely low electric power (< 20 mW) due to the implementation of exceptionally effective data analysis electronics and VCSEL as the light source.

We present a multicore fiber dedicated for next generation transmission systems. To overcome the issue of multicore fibers' integration with existing transmission systems, the fiber is designed in such a way that the transmission parameters for each core (i.e., chromatic dispersion, attenuation, bending loss, etc.) are in total accordance with the obligatory standards for telecommunication single core fibers (i.e., ITU-T G.652 and G.657). We show the results of numerical investigations and measurements carried out for the fabricated fiber, which confirm low core-to-core crosstalk and compatibility with standard single-core single-mode transmission links making the fiber ready for implementation in the near future.

In this Letter we present, for the first time to our knowledge, the results of fiber Bragg grating (FBG) inscription in a novel microstructured multicore fiber characterized by seven single-mode isolated cores. A clear Bragg reflection peak can be observed in all of the 7 cores after one inscription process with a KrF nanosecond laser in a Talbot interferometer set up. We furthermore perform a numerical analysis of the effective refractive indices of the particular modes and compare it with the FBG inscription results. An experimental analysis of the strain and temperature sensitivities of all of the Bragg peaks is also included.

We present the results of theoretical and experimental characterization of a designed and manufactured dual-mode highly birefringent microstructured fiber. We also demonstrate the measured values of polarimetric temperature and strain sensitivity of both the fundamental and second order modes. As the mode field of the second order mode has a strong interaction with the fiber air holes, we observed a significant (over two orders of magnitude) increase in the polarimetric strain sensitivity of this mode in comparison to the fundamental mode. The enhanced strain sensitivity together with the low temperature sensitivity makes our fiber very attractive for application as extremely sensitive temperature independent strain transducers.

In this paper we discuss optical fiber sensors protected by metal coatings and their industrial applications. In particular, we focus on gold-coated temperature sensor for application in temperature up to 900°C based on dual-core fiber.

Summary form only given. Fibre sensitivity to the temperature, longitudinal strain or pressure, is a very important fibre feature in many applications, such as sensing application or telecommunication. The most common way to modify (either mitigate or strengthen, depending on application) this sensitivity is to change the material properties by doping or to employ microstructured fibres. In some cases the precise adjustment of a doping level and sophisticated design of air-hole arrangement is needed to obtain required features of a fibre, for example to increase sensitivity to the hydrostatic pressure and avoid cross-sensitivity to the temperature [1].In this paper we investigate, for the first time to the best of our knowledge, the influence of the mode field diameter (MFD) on the fibre sensitivity. To do so, we engage a dedicated all-fibre interferometer [2] which enables the measurement of the sensitivity of different types of fibres (including conventional and microstructured fibres with different core diameters) to the different factors (e.g. temperature, longitudinal strain or pressure). To calculate fibre sensitivity we used the formula [3]: l dφ Sp= L dp, (1) where L is the fibre length which is exposed to the factor X, dij is the phase change caused by the this factor and dX is the factor change. Results of measurements of the fibre sensitivity to the longitudinal strain (SI) for different fibres as well as images of these fibres are demonstrated in Fig. 1. The strain sensitivity calculated with the use of Eq. (1) clearly depends on the MFD, which is evidenced in Table 1.The larger is the MFD, the more sensitive is the fibre to the longitudinal strain. We have kind of relation in measurements also observed the same of the temperature sensitivity. In addition to the measurement results we present in the paper the complex analysis of this phenomenon and we discuss its consequences and possibilities of application .