1530-437X (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2017.2701402, IEEE Sensors Journal > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract—A method of fabrication of a reflection type long period fiber grating (LPFG) operating near turn around point has been presented along with theoretical details. We have shown that, removal of multiple resonant bands due to unwanted phase shift introduced after cleaving the grating at an arbitrary location can be accomplished by tailoring the phase matching curve of the cladding mode. This also allows us to enhance the sensitivity of the sensor. The grating can be cleaved at any arbitrary location within the grating structure. Therefore, the probe type sensor head can be made considerably small. We have presented performance characteristics in detail. The sensitivity of the device has been found to be ~1300 nm/RIU and is superior to majority of the reflection type LPFG sensors where mostly lower order cladding modes were considered. Index Terms— Optical fiber sensor, Long period fiber grating, phase shifted grating I. INTRODUCTION ong period fiber grating (LPFG), owing to inherent interaction of its cladding modes with the surrounding medium, has played a major role in refractive index sensing since it was introduced to the research community [1,2]. One of the main constraints of LPFG based RI sensor was its very low sensitivity around 1.333 which initially limited the use of LPFG sensors in chemical and biological sensing applications where the measurements were required in aqueous solutions. However, things have dramatically changed over the last decade and a number of methods have been proposed to enhance the sensitivity of the LPFG sensors around 1.333. Sensitivity of LPFG could be enhanced by designing the same near the turn around point (TAP) or the so called dispersion turn around point (DTP) [3]. The state of the art on the TAP has been discussed in detail in one of our recent work [4]. There are other ways to enhance the sensitivity either by Manuscript submitted on November 21, 2016; This work was supported by the Network Project under Grant ESC-102 and Grant ESC-110 through the CSIR India, under the 12th five year plan. Tanoy Kumar Dey, Palas Biswas, Nandini Basumallick, Sankhyabrata Bandyopadhyay and Somnath Bandyopadhyay are with the Fiber Optics and Photonics Division, Council of Scientific and Industrial Research-Central Glass and Ceramic Research Institute, Kolkata 700032, India. (e-mail: tanoykumardey@gmail.com;palas@cgcri.res.in;nandini_b@cgcri.res.in;sankh ya.brata@gmail.com;somnath@cgcri.res.in). exploiting the mode transition (MT) [5-8] phenomenon or by designing specialty LPFG structure [9]. Sensitivity has been enhanced further by designing LPFGs working both around DTP and at MT [10,11]. It has also been successfully demonstrated that by measuring refractive index (RI) changes induced by a chemical and/or a biochemical interaction with a sensing layer deposited on LPFG, the sensors are able to allow quantitative measurement of the investigated analyte and also are able to provide ample information about the dynamic interactions taking place around the surface [12-15]. It is worth mentioning that all these sensors mentioned above, have been developed using LPFGs in transmission configuration. However, LPFGs in reflective configuration are more desirable in many applications where there is a requirement of a small sensor head that can be used to measure low volumes of samples. The LPFGs can easily be configured for use in reflection configuration by cleaving the fiber after the grating region and putting a reflective coating at the end of the fiber. The immediate consequence is however, generation of multiple interference fringes that overlap the LPFG attenuation bands [16]. This problem has been alleviated either by precisely cleaving at the end of the LPFG [17] or polishing after cleaving the optical fiber [18]. Another technique is to cleave the fiber about 20-25 mm away from the grating end and to deposit silver coating at the end as well as on the extended part of the fiber to absorb the back reflected cladding modes to obtain a single attenuation band in the reflection [19,20]. In this process however, the basic requirement of reducing the length of the sensing probe is compromised because of the additional length of the fiber at the end of the LPFG. Enhancement of sensitivity of the LPFG in reflection mode is another important issue. So far in reflection configuration sensitivity has successfully been enhanced by deposition of overlay layer [17] and by significantly reducing the cladding diameter [20]. In this paper we report design methodology and performance characteristics of an LPFG in reflection configuration where the cladding mode of our interest (LP 0,11 ) is designed to work near TAP. In our proposition, locating an LPFG cladding mode near TAP and removal of multiple resonant bands those arise due to unavoidable phase shift introduced in the LPFG structure after cleaving, have been done concurrently by tailoring the phase matching curve Realization of Long Period Fiber Grating In Reflection Mode Operating Near Turn Around Point Tanoy Kumar Dey, Palas Biswas, Member, IEEE, Nandini Basumallick, Member, IEEE, Sankhyabrata Bandyopadhyay, Student Member, IEEE and Somnath Bandyopadhyay, Member, IEEE L