Optik 124 (2013) 3671–3673 Contents lists available at SciVerse ScienceDirect Optik jou rn al homepage: www.elsevier.de/ijleo A low loss mechanical splice for gas sensing using Hollow-Core Photonic Crystal Fibre Ravi Dhawan ∗ , Mohd. Mansoor Khan, Nishtha Panwar, Umesh Tiwari, Randhir Bhatnagar, S.C. Jain Central Scientific Instruments Organization, Chandigarh 160 030, India 1 a r t i c l e i n f o Article history: Received 28 June 2012 Accepted 10 November 2012 Keywords: Butt-coupling Gas sensing Hollow-Core Photonic Crystal Fibre Spectroscopy a b s t r a c t In this paper, a low loss mechanical splice for Hollow-Core Photonic Crystal Fibre (HC-PCF) based multi- gas sensing system is introduced. Compared with the recent micro-structured optical fibre gas cells, the proposed HC-PCF gas cell has relatively simpler construction. The gas cell is composed of HC-PCF of 50 cm length and core diameter is 10 ± 1 m. The HC-PCF is connected to the single mode fibre (SMF) and multi mode fibre (MMF) via FC-APC connector. This creates a longitudinal gap between the two fibres which acts as a channel of gas diffusion in HC-PCF. The hollow-core and the capillaries in the cladding of HC-PCF act as gas channels. A measurement system for low gas concentrations based on this approach is also proposed. © 2012 Elsevier GmbH. All rights reserved. 1. Introduction Gas detection and measurement system plays an important role in the fields of safety [1]. It is extremely useful in variety of envi- ronmental and industrial [2], scientific and domestic applications. The gases like methane in mines are toxic to human health in the form of an atmospheric pollutant. Besides the systems which provide a detection signal, it is required to obtain accurate real- time measurements of the concentration of a particular gas, often in a mixture of other gases. For the given purpose there are various types of gas sensors available like catalytic gas sensors, electro- chemical detectors, capacitive gas sensors etc. But these sensors have various disadvantages like catalytic gas sensors get poisoned due to contamination, electrochemical gas sensors are unsuitable for dry environment and operate in narrow range of pressures, etc. [3]. So, optical fibres offer the great advantages over con- ventional gas sensing due to their high sensitivity, fast response, freedom from electromagnetic influence, immunity to combustion and explosion, have the access to hazardous site and are unsuscep- tible to poisoning [4]. Recently in the field of spectroscopy, HC-PCF based gas sensors have a key role as they itself act as compact gas cells [5–10]. Due to their advanced properties which cannot be achieved with ∗ Corresponding author at: Photonics Division, Central Scientific Instruments Organization, Sector-30, Chandigarh 160 030, India. Tel.: +91 7814833273/172 2651746x234; fax: +91 172 2659951/2657082/2657267. E-mail address: ravidhawan273@gmail.com (R. Dhawan). 1 Council for Scientific and Industrial Research, New Delhi. conventional optical fibres, HC-PCFs have attracted various researchers. HC-PCFs guide the light through the core, surrounded by the microstructure cladding formed by the periodic arrange- ment of the holes in silica. Unlike the conventional fibres, the light is trapped inside the hollow core of PCF by the photonic bandgap effect due to the micro-structured cladding [11]. In HC-PCFs, 94–95% of the light is confined within the core and the air filling fraction inside the core is greater than 90%. When filled with the gas, strong interaction between the propagating light and the gas takes place. Therefore they are widely used in the high sensitive gas sensors as they provide long interaction path lengths and are insensitive to bending [10]. Of late many approaches have been investigated for the HC-PCF based gas cell. One is the fibre fusion technique where the ends of SMF or MMF and HC-PCF are spliced and air holes are drilled on the surface of the HC-PCF by using femtosecond laser pulses [12]. These holes act as a passage for the gas diffusion in and out of HC- PCF. But the disadvantage of this process is it leads to the collapse of air holes and losses increases. Moreover, expensive instruments are needed for drilling the holes and splicing. Multiple coupling of HC-PCFs of small lengths is another approach which creates a multiple entry points for the gases to diffuse through the fibres [13]. Advantage of this technique is that diffusion time gets lowered. But the perfect condition of multiple coupling of gaps needs vigilance on lateral and longitudinal gap misalignments. Another technique is the anti-reflection coated windows which suffer from high losses [8]. A low-loss mechanical splice between the conventional solid- core fibre and the HC-PCF to make HC-PCFs more applicable in field 0030-4026/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ijleo.2012.11.016