JINU PAUL | Indian Institute of Technology Kharagpur (original) (raw)

Papers by JINU PAUL

Optical Devices for Fiber Communication IV, 2003

ABSTRACT Fiber Bragg gratings (FBGs) are widely used in optical communication and sensing applica... more ABSTRACT Fiber Bragg gratings (FBGs) are widely used in optical communication and sensing applications. The accuracy and stability of the center wavelength of the FBG is affected by the fluctuations of the ambient conditions, especially the temperature. The center wavelength shift can be reduced either by using a temperature compensating package or by keeping the FBG in an athermal environment. A novel coating design is proposed for achieving passive athermalisation of FBGs. The FBG is coated at different locations with materials having different coefficient of thermal expansion and stiffness. The differential thermal expansion gives rise to an effective strain at the FBG which can compensate the wavelength shift due to temperature change. Theoretical analysis of the proposed model has been carried out and the effect of coating length and thickness is analyzed. It is proved theoretically that almost zero wavelength shifts can be achieved by optimizing the design of the coating.

Reliability of Optical Fiber Components, Devices, Systems, and Networks II, 2004

ABSTRACT Polymeric coatings are often used to develop various thermally tunable FBG based devices... more ABSTRACT Polymeric coatings are often used to develop various thermally tunable FBG based devices. Coatings on FBGs can be intended for protection, improvement of thermal sensitivities, special spectral shaping etc., and the quality of the coating on the FBG deserves special attention. For example, the adhesion of the polymeric coatings to the silica based optical fiber plays an important role in the wavelength response characteristics of fiber Bragg gratings during thermal tuning. In this paper, we theoretically investigate the effect of adhesion and the non-uniformity of the coating thickness on the thermal tuning process of FBGs. Experiments were done to qualitatively analyze the influence of adhesion. However practically it is very difficult to quantify the percentage adhesion and quality of coatings for experimental verification. Therefore a methodology based on finite element analysis has been utilized for theoretical investigation of the effect of adhesion of polymeric coating on the performance of FBG based thermally tuned devices. Three-dimensional finite element simulations were carried out. Spring elements are used to inter connect the nodes of the meshed models of optical fiber and coating. The effect of adhesion is studied as a function of spring stiffness. The effect of non-uniformity in the coating thickness in the circumferential direction was also studied.

Industrial and Highway Sensors Technology, 2004

ABSTRACT Bragg grating devices are widely used in the field of optical sensing and communication.... more ABSTRACT Bragg grating devices are widely used in the field of optical sensing and communication. Thermally tunable devices utilize the effect of temperature on the wavelength response characteristics of the fiber Bragg grating. But the low sensitivity of a Bragg grating device to temperature limits its usage to many applications. The wavelength sensitivity of a bare FBG is only 1.3 nm for a temperature change of 100°C. In order to enhance the temperature sensitivity of a fiber Bragg grating, we propose modification of the cladding of the FBG through etching and put another coating layer outside the cladding. The cladding is etched to a certain depth around the grating and the etched portion is coated with a suitable polymer. Theoretical analysis has been done to find the relationship between the wavelength shifts and the etching depths and coating thickness of the polymer. A finite element model of the cladding etched FBG coated with polymer has also been developed and the wavelength shift due to thermal expansion is analyzed under various etching depths and coating thickness. The high thermal expansion coefficient of the polymer enables to enhance the thermal sensitivity by improving the wavelength shift due to thermal expansion. Also the polymer coating on the etched fiber reduces the susceptibility of fracture and improves the reliability. It is found that that temperature sensitivity increases with increase in etching depth. But there is maximum limit to which the cladding can be etched without affecting the performance. Also it is found that increasing the coating thickness of the polymer increases the wavelength shift due to temperature change.

Optical Communications and Networks - Proceedings of the First International Conference on ICOCN 2002, 2002

Sensor Review, 2004

Abstract: Polymeric coatings and packaging are often used to enhance the temperature sensitivity ... more Abstract: Polymeric coatings and packaging are often used to enhance the temperature sensitivity of fiber Bragg grating temperature sensors. The high thermal expansion coefficient of the polymer enhances the thermal sensitivity by improving the wavelength ...

Eighth International Symposium on Laser Metrology, 2005

ABSTRACT Wavelength tuning of fiber Bragg gratings (FBGs) by virtue of a lateral or transverse lo... more ABSTRACT Wavelength tuning of fiber Bragg gratings (FBGs) by virtue of a lateral or transverse load is attractive for a variety of applications in the field of optical sensing. The wavelength response characteristic of the FBG upon application of a transverse load is highly dependent on the pressurizing media and the contact conditions. In this paper, we evaluate the effect of contact friction and contact angle of the pressurizing media on the lateral pressure tuning of FBGs. Our results showed that pressurizing media with a lower value of stiffness is favorable for greater contact areas and for distributing the lateral load. Thus, the sensing load becomes more hydrostatic in nature, which enhances the lateral pressure sensitivity and tuning range while reducing birefringence. Also, a higher contact friction is favorable for effective transfer of the load through the contact area and improved sensitivities accordingly. The present study is thus useful in better utilization of lateral pressure tuning of FBGs for sensing applications.

Smart Medical and Biomedical Sensor Technology II, 2004

Grip strength is an easy measure of skeletal muscle function as well as a powerful predictor of d... more Grip strength is an easy measure of skeletal muscle function as well as a powerful predictor of disability, morbidity and mortality. In order to measure the grip strength, a novel fiber optic approach is proposed and demonstrated. Strain dependent wavelength response of fiber Bragg gratings (FBGs) has been utilized to obtain the strength of individual fingers. Five FBGs are written at different center wavelengths on a single photosensitive fiber. Each FBG is used to get the response from each individual finger. The fiber containing the gratings is attached to a suitable grip holder, which can effectively transfer the grip force to the FBGs. An additional reference FBG is also provided to make the device temperature insensitive. Experimental results show that the wavelength shifts of the order of 0.2-0.5 nm can be achieved for individual fingers. The device is calibrated in terms of load to convert the wavelength shift to the strength of the grip. The time dependent wavelength fluctuations was also studied and presented in this paper.

Optical Engineering, 2004

ABSTRACT Lateral-pressure tuning of a coaxially embedded fiber Bragg grating in a cylindrical pol... more ABSTRACT Lateral-pressure tuning of a coaxially embedded fiber Bragg grating in a cylindrical polymeric package is demonstrated. The polymeric coating, having very low stiffness and high Poisson's ratio, enables effective transfer of the applied radial load to the axial direction. Such a transfer enhances the tuning range and reduces birefringence. A tuning range more than 1 nm, with negligible bandpass broadening and peak splitting, could be demonstrated. A lateral pressure sensitivity of 0.3 nm/(N/mm), which is almost 7 times as high as that of bare FBG, could be obtained. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

Small, 2010

The fabrication and characterization of nanostructured fibrous gold mats having high specific sur... more The fabrication and characterization of nanostructured fibrous gold mats having high specific surface areas is reported. Freestanding porous films of 6-20-μm thickness and density 0.43 ± 0.02 g cm(3) are prepared using e-beam evaporation of gold on an electrospun nanoporous polymer template and subsequent removal of the template polymer in a suitable solvent. Structural characterization using electron microscopy techniques shows a nanofiber diameter in the range of 300-6000 nm, and the size of the nanochannels on the fiber surface is ≈200-350 nm. Such surface structuring is achieved through fast evaporation of organic solvent and phase separation of polymers during the electrospinning process. The wedge thickness varies from a few nanometers to a few tens of nanometers. The freestanding films possess good mechanical integrity and robustness. The calculated Young&amp;amp;amp;amp;amp;amp;amp;amp;#39;s modulus based on the slope in the elastic region is ≈114 MPa and gives an ultimate breaking strength of 0.7-0.8 MPa at a percentage elongation of 1.5-2.0%. X-ray diffraction and transmission electron microscopy measurements demonstrate the formation of polycrystalline gold nanostructures. Electrical characterization performed on these gold nanotubes reveals pure metallic behavior. Raman spectroscopic characterization of the fibrous membrane is performed using crystal violet (CV) adsorbed on it. Well-defined spectral peaks are obtainable at concentrations as low as 10(-7) M of CV, which did not give spectral signals at this low concentration on its own.

Carbon, 2011

The fabrication and characterization of ultrathin composite films of surfactant-wrapped graphene ... more The fabrication and characterization of ultrathin composite films of surfactant-wrapped graphene nanoflakes and poly(vinyl chloride) is described. Free-standing composite thin films were prepared by a simple solution blending, drop casting and annealing route. A significant enhancement in the mechanical properties of pure poly(vinyl chloride) films was obtained with a 2wt.% loading of graphene, such as a 58% increase in Young’s

Carbon, 2009

ABSTRACT A simple and effective method for the preparation of a few layered graphene nanoflakes d... more ABSTRACT A simple and effective method for the preparation of a few layered graphene nanoflakes directly from graphite has been successfully demonstrated. Mild ultrasonication of highly ordered pyrolytic graphite, in presence of a cationic surfactant cetyltrimethylammonium bromide and acetic acid yielded graphene nanoflakes, which formed a stable colloidal suspension in organic solvent such as N,N-dimethyl formamide. Scanning and transmission electron microscopic analyses showed that the dispersed phase consist of mainly few layered graphene nanoflakes. Average thickness of the flakes was found to be ∼1.18 nm. Energy dispersive X-ray analysis indicated the absence of graphene oxide. Field emission measurements for the nanoflakes showed a turn on voltage of 7.5 V/μm and emission current densities of 0.15 mA/cm2.

Applied Physics Letters, 2006

[Applied Physics Letters 89, 184101 (2006)]. J. Paul, S. Sindhu, MH Nurmawati, S. Valiyaveettil. ... more [Applied Physics Letters 89, 184101 (2006)]. J. Paul, S. Sindhu, MH Nurmawati, S. Valiyaveettil. Abstract. ... Sci., Part B: Polym. Phys. 41, 520 (2003). KPRyan, M.Cadek, A.Drury, M.Ruether, WJBlau, and JNColeman, Fullerenes, Nanotubes, Carbon Nanostruct. 13, 431 (2005). ...