We propose and demonstrate a temperature immune biosensor based on two concatenated LPGs incorporating a suitable
inter-grating-space (IGS). Compensating the thermal induced phase changes in the grating region by use of an
appropriate length of the IGS the temperature insensitivity has been achieved. Using standard telecommunication grade
single-mode fibers we show that a length ratio of ~8.2 is sufficient to realize the proposed temperature insensitivity. The
resulting sensor shows a refractive index sensitivity of 423.28 nm/RIU displaying the capability of detecting an index
variation of 2.36 × 10-<sup>6</sup> RIU in the bio-samples. The sensor can also be applied as a temperature insensitive WMD
channel isolation filter in the optical communication systems, removing the necessity of any external thermal insulation
In this paper we report on fabrication and characterization of a refractive index sensor based on two concatenated double resonanced long period fiber gratings (LPFGs) with an inter grating space in between them. The inter grating space provides a temperature dependent extra phase difference between the core mode and the participating cladding modes, making the sensor similar to a Mach-Zehnder interferometer with its arms phase shifted. We demonstrate that by adjusting the inter grating space the thermally induced phase difference in the LPG region can be compensated, producing temperature insensitive resonance wavelengths. The interferometer is highly stable over a wide range of temperatures (20-100 °C). The measured refractive index sensitivity for aqueous solutions (1.333-1.393) is 2583.3 nm/RIU, which is highly desirable for precision sensing of biological samples.
In this paper, we develop a novel structure and approach of a pure surface Plasmon Polariton (SPP) sensor with fiber Bragg gratings (FBG) in gold coated specially designed H-cross-section fiber. We evaluate its potential for biological sensing applications of the surrounding refractive index (SRI). Pure SPP has almost all its field concentration at the metal-dielectric interfaces and hence, it is highly sensitive to changes in the sensed medium refractive index. This scheme represents an “in-line” optical fiber SPP sensor scheme. Also, it provides larger and more flexible sensing area along its flat side. Simulation results show that the gold layer thickness essentially influences the sensitivity, and the shape of the reflection spectrum. Increasing the gold layer thickness decreases its sensitivity and broadens the spectrum, increasing the FWHM bandwidth. Results show a maximum sensitivity of 230 nm/RIU and maximum figure of merit; defined as the ratio of sensitivity to FWHM bandwidth of the reflection spectrum; of 10952 RIU<sup>-1</sup> (Sensitivity = 230 nm/RIU and FWHM = 2.1 x 10<sup>-5</sup> μm) with gold thickness of 10 nm. In conclusion, the proposed sensor is highly sensitive and free from any moving parts and can be used as bio-chemical sensor.
A novel, highly sensitive refractive index sensor based on the modal interference in a microtapered telecom grade SMF
is presented. The considered structure consists of a uniformly thinned region in between the tapered regions where the
original core is virtually absent and the modes are supported by the cladding-ambient region index difference. The core
mode evolution within the tapered region and its coupling to the cladding modes has been obtained using the localnormal-
mode-matching. The proposed device has extremely high sensitivity ~ 2.6 μm/RIU for biological samples (n<sub>se</sub> ~
1.33) and hence should be useful for precision bio/chemical sensing applications.
We present a novel highly sensitive biochemical sensor based on a Bragg grating written in the cladding region of a
submicron planar Si/SiO<sub>2</sub> waveguide. Owing to the high refractive index contrast at the Si/SiO<sub>2</sub> boundary the TM modal
power is relatively high in low refractive index sensing region, leading to higher sensitivity in this configuration .
Waveguide parameters have been optimized to obtain maximum modal power in the sensing region (<i>P<sub>Se</sub></i>) and an
optimum core width corresponding to maximum sensitivity is found to exist while operating in TM mode configuration,
as has been shown in Fig. 1. It has been found that operating in TM mode configuration at optimum core width the
structure exhibits extremely high sensitivity, ~ 5×10<sup>-6</sup> RIU - 1.35×10<sup>-6</sup> RIU for the ambient refractive indices between
1.33 - 1.63. Such high sensitivities are typically attainable for Surface Plasmon Polariton (SPP) based biosensors and is
much higher than any non SPP based sensors. Being free from any metallic layer or bulky prism the structure is easy to
realize. Owing to its simple structure and small dimensions the proposed sensor can be integrated with planar lightwave
circuits and could be used in handy lab-on-a-chip devices. The device may find application in highly sensitive
biological/chemical sensing areas in civil and defense sectors where analyzing the samples at the point of need is
required rather than sending it to some centralized laboratory.