Dual-Polarization Distributed Feedback Fiber Laser Sensor Based on Femtosecond Laser-Inscribed In-Fiber Stressors for Simultaneous Strain and Temperature Measurements

Abstract

We propose and experimentally demonstrate a novel dual-polarization distributed feedback fiber laser (DFB-FL) sensor based on femtosecond laser-inscribed in-fiber stressors. The resonant cavity of the DFB-FL sensor consists of a phase-shifted fiber Bragg grating (PS-FBG) in the fiber core of a section of heavily erbium-doped fiber (EDF), together with two stressors in the fiber cladding around the PS-FBG. The PS-FBG was fabricated by means of a scanning UV laser beam and shielded phase mask technique. The two in-fiber stressors, i.e. a sawtooth stressor and a straight stressor, were directly inscribed at two orthogonal planes in the EDF cladding using a near-infrared femtosecond laser. The two stressors could precisely adjust the fiber birefringence in the laser cavity, and hence the DFB-FL sensor can operate in two polarization modes. Moreover, simultaneous measurement of axial strain and temperature was demonstrated by detecting the polarization beat frequency νB and lasing wavelength λ of the dualpolarization DFB-FL sensor. Experimental results exhibit strain sensitivities of 34.5 kHz/µε, 1.25 pm/µε and temperature sensitivities of 684.6 kHz/°C, 11.5 pm/°C, respectively. As such, the proposed dualpolarization DFB-FL sensor could be used for simultaneous strain and temperature measurements, and hence is promising for application in many areas, such as smart structures and intelligent robotics.

2 μm Passively Mode-Locked Thulium-doped Fiber Lasers with Ta2AlC-deposited Tapered, Side- polished and D-shaped Fibers

“…It was observed from the XRD pattern that a distinct prominent peak at 2θ = 39.07° together with a few sharp peaks was detected at 2θ = 12.92, 25 70.61, and 73.96 °. These peaks were assigned to the (1 0 3), (0 0 2), (0 0 4), (1 0 0), (1 0 1), (1 0 2), (1 0 4), (1 0 5), (1 0 6), (0 0 8), (1 0 7), (1 1 0), (1 1 2), (1 1 4), (1 0 9), (2 0 1) and (2 0 3) planes of the Ta 2 AlC MAX Phase, respectively.…”

“…The discovery of optical bers by Charles Kao and George A. Hockam in 1966 gave the inroads for optical ampli er development with a wavelength range of 1.46 µm to 1.53 µm 1,2 , 1.53 µm to 1.565 µm 3,4 and 1.565 µm to 1.625 µm [5][6][7][8][9][10] . Consequently, the development of laser con guration such as pulsed 11,12 , dual and multiwavelength [13][14][15][16][17][18][19][20][21][22] , and optical sensors [23][24][25] has been the focus of many research laboratories. There have been numerous activities on pulsed laser operating at wavelengths 1 µm and 1.5 µm, of interest will be to generate short pulses in the 2 µm wavelength region for several applications such as in spectroscopy 26 , gas detection 27 , laser ablation 28 , long-range light detection and ranging (LIDAR) 29 , plastic and glass processing 30 as well as in the medical eld 31 .…”

Extremely Efficient DFB Lasers with Flat-Top Intra-Cavity Power Distribution in Highly Erbium-Doped Fibers

“…The distributed feedback (DFB) fiber laser consists of a Bragg grating with a π-phase shift (PPS) written in an active fiber [ 1 ] and exhibits higher-order mode suppression as well as stable single-frequency operation [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Such π-phase-shifted gratings, initially used for DFBs in semiconductors [ 34 ], have also been implemented in erbium-doped fiber (EDF) DFB lasers [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]; however, the efficiency is still limited, whilst highly efficient unidirectional EDF-DFB lasers around 1.55 μm are of great importance for sensor technology, metrology, and spectroscopy amongst other applications [ 10 , 11 , 12 , 13 , 14 ].…”

“…Moreover, DFB fiber lasers formed in co-doped fibers reveal much higher frequency noise [ 14 ]. Therefore, an alternative is the use of EDFs with high-concentration in the core to increase the gain [ 22 , 23 , 24 , 25 , 26 , 27 ]. Nevertheless, the efficiency and unidirectionality of highly EDF-DFB lasers are still restricted due to the use of conventional designs as follows.…”

2 μm passively mode-locked thulium-doped fiber lasers with Ta2AlC-deposited tapered and side-polished fibers

“…The discovery of optical fibers by Charles Kao and George A. Hockam in 1966 gave the inroads for optical amplifier development with a wavelength range of 1.46–1.53 µm 1 , 2 , 1.53–1.565 µm 3 , 4 and 1.565–1.625 µm 5 – 10 . Consequently, the development of laser configuration such as pulsed 11 , 12 , dual and multiwavelength 13 – 22 , and optical sensors 23 – 25 has been the focus of many research laboratories. Although there have been numerous works on pulsed lasers operating at wavelengths of 1 μm and 1.5 μm, there is an increasing interest to generate short pulses in the 2 μm wavelength region for several applications such as in spectroscopy 26 , gas detection 27 , laser ablation 28 , light detection and ranging (LIDAR) for remote sensing 29 , plastic and glass processing 30 as well as in the medical field 31 .…”