Sensitivity optimization with cladding-etched long period fiber gratings at the dispersion turning point

Abstract

This work presents a refractive index sensor based on a long period fiber grating (LPFG) made in a reduced cladding fiber whose low order cladding modes have the turning point at large wavelengths. The combination of these parameters results in an improved sensitivity of 8734 nm/refractive index unit (RIU) for the LP_0,3 mode in the 1400-1650 wavelength range. This value is similar to that obtained with thin-film coated LPFGs, which permits to avoid the coating deposition step. The numerical simulations are in agreement with the experimental results.

Enzyme-functionalized thin-cladding long-period fiber grating in transition mode at dispersion turning point for sugar-level and glucose detection

“…This is a maximum recorded total-peak separation of ∼460 nm which is 23% improvement compared to ∼374 nm earlier reported for light cladding-etched dual-peak LPFG. 30 Although, an RI sensitivity of ∼8734 nm∕RIU, 31 which is much higher than ours, has been achieved on a thin-cladding dual-peak LPFG, the grating fiber was etched off from original 80 μm to only 35 μm, undoubtedly reducing the mechanical strength of the grating and increasing its fragility, thus limiting its applicability. Raw sugar (turbinado sugar) has been known to contain several useful nutrients (100 g of turbinado sugar contains-100 mg potassium, 85 mg calcium, 23 mg magnesium, 3.9 mg phosphorous, and 1.3 mg iron) and less calories, and therefore is healthier than white sugar.…”

Increasing the Sensitivity of an Optic Level Sensor With a Wavelength and Phase Sensitive Single-Mode Multimode Single-Mode Fiber Structure

“…In the level sensor the surrounding medium refractive index increases when the device is immersed in liquid and, similarly to the phenomenon observed in [20], the difference between the effective indices of modes guided in the fiber increases, something that can be observed in Fig. 3 of [21]. Focusing on constructive interference, this phenomenon occurs if the difference between the phases of modes is a multiple of 2π.…”

Monitoring the Etching Process in LPFGs towards Development of Highly Sensitive Sensors

“…According to [5,6] this band is present for a cladding diameter of 30 µm. LP0,2, the last band that can be monitored, could be observed with a higher etching.…”

“…Long period fiber gratings (LPFG) can be used as highly sensitive detectors by application of three different phenomena: the mode transition [1,2], the dispersion turning point (DTP) [3], and the reduction of the cladding diameter [4,5]. It has been theoretically analyzed that a sensitivity in the water region of up to 143,000 nm/refractive index unit (nm/RIU) can be attained by considering the wavelength shift of both attenuation bands in DTP mode [6].…”

“…Here focus is centered in the combination of the DTP and the cladding diameter reduction, which is simpler to control and permits to obtain sensitivities of 8000 nm/RIU by considering the wavelength shift of both attenuation bands [5]. The attenuation bands in LPFGs are created by coupling the core mode to a specific cladding mode.…”