Tilted Fiber Bragg Grating Research Articles

Generation of leaky mode resonance by metallic oxide nanocoating in tilted fiber-optic gratings.

This work investigates the excitation of dense comb-like enhanced leaky mode resonance (eLMR) in tilted fiber Bragg grating (TFBG) integrated with indium tin oxide (ITO) nanocoating. The ITO overlay leads to a large reduction in mode loss and a great increase of propagation length for s-polarized leaky modes, which means the leaky modes become guided. The guidance of leaky modes enhances significantly the interaction with the core guided mode, which leads to the generation of strong dense comb-like eLMR. The results show that the ultra-narrow eLMR bands present promising sensing performance with an extended measurement range and provide advantages of high Q measurement over the case of surface plasmon resonance (SPR) and lossy mode resonance (LMR). The similarities and differences between the eLMR and SPR and LMR are also discussed. This study offers new opportunities to develop eLMR-based multifunctional fiber-optic devices with high performance.

Inscription of superimposed tilted fiber Bragg gratings

This study focuses on the tilted fiber Bragg gratings. The paper describes the method of their inscription into optical fiber using the Talbot interferometer and KrF excimer laser system. The method allows precise selection of the resonant wavelengths and tilt angles of the created structures in a wide range of values. In course of the study, an original method was proposed for inscription of a superposition comprising two structures being identical in parameters but having the opposite tilt angles of grating strokes relative to the optical fiber cross-section. The described method makes it possible to compensate the decrease in the reflective efficiency of fiber Bragg gratings with an increase in their tilt angle.

Multimodal plasmonic optical fiber grating aptasensor.

Tilted fiber Bragg gratings (TFBGs) are now a well-established technology in the scientific literature, bringing numerous advantages, especially for biodetection. Significant sensitivity improvements are achieved by exciting plasmon waves on their metal-coated surface. Nowadays, a large part of advances in this topic relies on new strategies aimed at providing sensitivity enhancements. In this work, TFBGs are produced in both single-mode and multimode telecommunication-grade optical fibers, and their relative performances are evaluated for refractometry and biosensing purposes. TFBGs are biofunctionalized with aptamers oriented against HER2 (Human Epidermal Growth Factor Receptor-2), a relevant protein biomarker for breast cancer diagnosis. In vitro assays confirm that the sensing performances of TFBGs in multimode fiber are higher or identical to those of their counterparts in single-mode fiber, respectively, when bulk refractometry or surface biosensing is considered. These observations are confirmed by numerical simulations. TFBGs in multimode fiber bring valuable practical assets, featuring a reduced spectral bandwidth for improved multiplexing possibilities enabling the detection of several biomarkers.

An Integrated Biological Analysis and Flow Rate Sensing for the Real-Time Detection of Carcinogen in Water Based on Co2+-Doped Optical Fibers

The multi-parameter measurement has significant meaning for biosensor to enhance their practical sensing performance. For the biological detection, simultaneous measurement of biological molecule and flow rate could improve the accuracy and sensitivity of sensors significantly. In this paper, an integrated biological analysis and flow rate sensing based on Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> doped tilted fiber Bragg gratings has been proposed and experimentally demonstrated for real-time the detection of the Benzo[a]pyrene molecules. A tilted fiber Bragg grating with a tilted angle of 8° was inscribed into a Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> doped fiber. The flow rate and Benzo[a]pyrene molecules can be measured simultaneously by interrogating the resonance wavelength of core mode and wavelength interval between the core mode and cladding mode according to the heat exchange and evanescent field of the cladding mode, respectively. Experimental results show that the real-time measurement sensitivities of 12 pm/pM and -0.13 nm(μL/s) for the Benzo[a]pyrene detection and flow rate were achieved, respectively. Thus the technique appears to have potential applications in chemistry, medicine, and biology.

Triple-order Orbital-angular-momentum modes generation based on single tilted fiber Bragg grating in a few-mode ring-core fiber

Abstract Orbital-angular-momentum (OAM) modes generation using tilted fiber Bragg grating (TFBG) in a few-mode ring-core fiber (FM-RCF) is proposed and demonstrated. Theoretical and experimental investigations reveal that OAM beams can be switched among three topological charges (±1, ±2, and ±3) at different corresponding oscillation wavelengths by single TFBG. In this work, OAM beams with linear polarization are produced by combining four degenerated vector modes. We firstly use TFBG to directly generate OAM beams with three different topological charges in FM-RCF, which provides an increased stability and compatibility for the manipulation and control of the OAM beams states in optical fibers.

Femtosecond Laser Inscribed Tilted Gratings for Leaky Mode Excitation in Optical Fibers

We consider the excitation of leaky mode resonances (LMRs) in an optical fiber that originate from light coupling initiated by small angle (<21°) tilted fiber Bragg gratings (TFBGs), through sub-micrometric grating inscription using a femtosecond laser. The femtosecond laser inscription triggers the interaction between the fiber's guided mode and backward coupling to the LMRs, a process that requires tight control of the grating period, reflection angle, order and the strength of the modified refractive index. The TFBG itself exhibits very low spectral polarization dependence, whereas the LMRs display strong polarization dependence in specific wavelength ranges, allowing for easy mode selection and opening avenues for various applications related to sensing and optical filtering. The tailored-for-LMR-generation optical filters were characterized for torsion, temperature and strain, exhibiting a very large negative strain sensitivity of –2 pm/μϵ and a temperature sensitivity of 14.73 pm/°C that when compared with the grating response led to an exceptionally large strain response and remarkably well-behaved conversion matrix for the separation of strain and temperature in a single measurement. The LMR also proves to be insensitive to bend. The nature of LMRs is considered and confirmed by measuring their radiation field using an infrared camera, simulating their resonance wavelength using a finite element method and by experimentally observing their behavior, while changing the ambient refractive index.

Hybrid tilted fiber gratings-based surface plasmon resonance sensor and its application for hemoglobin detection

We proposed a hybrid tilted fiber gratings (polarizing grating and tilted fiber Bragg grating)-based surface plasmon resonance (SPR) sensor. The hybrid tilted fiber grating, consisting of a polarizing grating and tilted fiber Bragg grating (TFBG), is fabricated in a single-mode fiber in series by using a UV-inscription technique, in which the TFBG could generate a dense cladding mode resonance to excite SPR and the polarizing grating could filter out the S-polarization cladding mode of the TFBG. Such proposed hybrid tilted fiber gratings could greatly simplify the interrogation system of the TFBG-based SPR sensor. The experiment results showed that the hybrid tilted fiber gratings-based SPR sensor has the refractive index sensitivity of 522.8 nm/RIU. Finally, by using the proposed sensor, we have achieved the hemoglobin concentration detection within a sensing range from 0.1 mg/mL to 1.0 mg/mL and the sensitivity of 8.144 nm/(mg/mL).

Cortisol in-fiber ultrasensitive plasmonic immunosensing

Cortisol is a stress biomarker whose chronic elevated levels are associated with higher risk of metabolic syndromes, anxiety, and cardiovascular diseases, among other medical conditions. A new immunosensor based on plasmonic tilted fiber Bragg grating (TFBG) has been developed and tested for rapid and ultrasensitive cortisol detection. The gold coated TFBG was characterized to surrounding refractive index (SRI) changes and functionalized with anti-cortisol antibodies via cysteamine. The functionalization was monitored, allowing to verify the SRI alteration at the fiber surface by the respective molecular adhesion. In this work, an alternative method to the monitoring of the most sensitive surface plasmon resonance mode was explored, based on tracking the local maximum of the plasmonic signature of the lower envelope of the spectra. With this interrogation method, the sensor achieved a sensitivity to cortisol detection of 0.275 ± 0.028 nm/ng.mL−1, for the detection range of 0.1-10 ng/mL, with a total wavelength shift of around 3 nm, which is higher several orders of magnitude than the usually reported TFBG plasmonic immunosensors. The proposed biosensor provides a rapid, highly sensitive, label-free, low-volume consumption method for cortisol detection, with a working range suitable to monitor different biological samples.

Interrogation system of signals from rotation sensors using tilted fiber Bragg gratings

The paper herein is concerned with the system of interrogating the signals, entering from rotation sensors. The systems for analyzing the sensors thereof most often require capacity’s reference mea...

基于倾斜FBG的光纤受激布里渊散射抑制

基于倾斜FBG的光纤受激布里渊散射抑制

基于倾斜光纤Bragg光栅的受激布里渊散射滤波器

基于倾斜光纤Bragg光栅的受激布里渊散射滤波器

Bragg reflection and conversion between helical Bloch modes in chiral three-core photonic crystal fiber

Optical fiber modes carrying orbital angular momentum (OAM) have many applications, for example in mode-division-multiplexing for optical communications. The natural guided modes of N -fold rotationally symmetric optical fibers, such as most photonic crystal fibers, are helical Bloch modes (HBMs). HBMs consist of a superposition of azimuthal harmonics (order m ) of order $\ell _{\rm{A}}^{(m)} = \ell _{\rm{A}}^{(0)} + mN$ . When such fibers are twisted, these modes become circularly and azimuthally birefringent, that is to say HBMs with equal and opposite values of $\ell _{\rm{A}}^{(0)}$ and spin s are non-degenerate. In this article we report the use of Bragg mirrors to reflect and convert HBMs in a twisted three-core photonic crystal fiber, and show that by writing a tilted fiber Bragg grating (FBG), reflection between HBMs of different orders becomes possible, with high wavelength-selectivity. We measure the near-field phase and amplitude distribution of the reflected HBMs interferometrically, and demonstrate good agreement with theory. This new type of FBG has potential applications in fiber lasers, sensing, quantum optics, and in any situation where creation, conversion, and reflection of OAM-carrying modes is required.

Ultra-short DBR fiber laser with high-temperature resistance using tilted fiber Bragg grating output coupler.

We demonstrate a high-temperature resistant distributed Bragg reflector (DBR) fiber laser that is highly compact with an entire cavity length of 12 mm. A partial-reflection tilted fiber Bragg grating (PR-TFBG) is used as the laser output coupler whose reflectivity can be adjusted by changing the TFBG tilt angle. The laser cavity consists of two strong gratings including the PR-TFBG and a high-reflection fiber Bragg grating (HR-FBG), which is directly fabricated in an Er-doped fiber using a femtosecond laser and a phase mask. The thermal stability of the PR-TFBG and HR-FBG is experimentally investigated. After an annealing process, their remained gratings are stable at high temperatures and strong enough for laser oscillation. The laser is also annealed before its stability is tested. The results show that the laser can stably operate in single longitudinal mode with a signal-to-noise ratio better than 65 dB over the temperature range from room temperature to 550°C.

Through-the-coating writing of tilted fiber Bragg gratings with the phase mask technique.

Tilted fiber Bragg gratings are inscribed in non-photosensitized single mode fibers through the polyimide coating using a femtosecond infrared laser and a phase mask. The inscription technique used is based on simultaneously translating the fiber along its axis and the focusing cylindrical lens in the orthogonal direction by means of piezoelectric actuators. The grating plane tilt angles up to 10.3° are achieved with a 1.07 µm-pitch phase mask. The cladding modes reach ∼5 dB in strength in transmission despite the presence of the polyimide coating. The effectiveness of the fabricated tilted fiber Bragg gratings for refractive index sensing through the polyimide coating is also demonstrated. Additionally, we show that the classical approach for the inscription of tilted Bragg gratings, which is based on simply tilting the fiber with respect to the interference fringes, cannot be used in tight focusing geometries that are necessary for through-the-coating inscription.

40 GHz-rate all-optical cross-modulation of core-guided near infrared light in single mode fiber by surface plasmons on gold-coated tilted fiber Bragg gratings

All-optical control of Surface Plasmon Polaritons (SPPs) can switch light with high speed and a large signal to noise ratio. We demonstrate 25 ps-time scale switching of continuous wave light by pump pulses copropagating in the same single mode fiber at different wavelengths near 1550 nm. The switching is due to hot carriers from the SPPs in a 45 nm-thin gold coating on the fiber cladding. The SPPs are generated by pump pulses coupled from the core to cladding modes by a tilted fiber Bragg grating (TFBG). Hot carriers modify the complex permittivity of the metal coating on a time scale of the order of picoseconds and hence the cladding mode resonance wavelengths of the TFBG. A probe light signal copropagating in the same fiber can therefore be modulated by the transmission resonance shifts. With 25 ps pulses at 1540.4 nm and 1 MHz and 50 mW average power, the modulation depth of a CW probe at 1543.4 nm copropagating in the core reached 4.5% ± 1% with a pulse width broadened to 56 ps. Under these conditions, the pump power density was 0.147 GW/cm2 in the metal layer, for a conversion efficiency as high as 30% ± 7% per GW/cm2. Since many other plasmonic and nonlinear active materials can be deposited on fiber claddings, we believe that this very simple all-fiber configuration to perform all-optical switching of core-guided light in single mode fibers by plasmon-modulated resonances has strong potential applications in studies of light-matter interactions over fast and ultrafast time scales.

Gas/liquid detection system based on intra-cavity absorption spectroscopy and tilted fiber Bragg grating

Abstract A gas/liquid detection system is developed based on the intra-cavity absorption spectroscopy (ICAS) and a tilted fiber Bragg grating (TFBG). Multiple gases such as acetylene, carbon monoxide and ammonia gas with absorption lines within C-band can be detected using the proposed scheme. The wavelength sweeping range can be controlled to obtain a specific number of absorption lines to meet the requirements on different measurement accuracy. In this work, a TFBG structure is introduced into the ICAS technique to realize the sensing of liquid refractive index. The TFBG works around the wavelength of 1550 nm, which allows a long-distance signal transmission and a flexible system adjustment. The proposed system has been applied to detect the concentration of acetylene with an absolute error of less than 46 ppm. In addition, a set of glycerol-water solutions with refractive indices from 1.3959 to 1.4430 have been measured using the proposed scheme with a sensitivity of 528.2 nm/RIU.

Leaky mode transition and enhanced resonance in tilted fiber Bragg grating

Leaky mode resonance in tilted fiber Bragg grating (TFBG) has been widely underestimated and ignored. Herein, we theoretically demonstrate that the leaky mode resonance can be greatly enhanced, and it presents a highly sensitive property by virtue of its mode transition. The leaky mode transition consists of five stages from the cladding guided mode to radiationlike and guidedlike leaky modes for both p- and s-polarized modes of bare TFBG. However, the graphene induces only one transition for the s-polarized guidedlike leaky mode, which, in turn, leads to an insensitive wavelength shift. The resonance amplitude depends on the imaginary part of the effective refractive index. Consequently, the enhanced leaky mode resonance (eLMR) in the s-polarized state is obtained and presents higher sensitivity than the widespread surface plasmon resonance (SPR). Furthermore, a general empirical rule associated with the refractive index of nanometer materials for exciting the eLMR in TFBG is obtained (the SPR is also discussed for comparison). The results obtained in this work have shed contemporary light on the undervalued leaky mode resonance, which is of great interest and importance to the development of novel multimodal and multifunctional eLMR-based TFBG devices, such as tunable lasers, optical modulators, and sensors.

Simultaneous excitation of leaky mode resonance and surface plasmon resonance in tilted fiber Bragg grating

This paper presents the first work that theoretically demonstrates simultaneous excitation of both enhanced leaky mode resonance (eLMR) and surface plasmon resonance in ultra-thin Au film coated tilted fiber Bragg grating. The mechanism is discussed by investigating the influence of Au film on mode characteristics of leaky modes and guided modes. A stable transmission spectrum that is only composed of strong dense comb-like eLMR in a wide window is realized. The eLMR excited by metal film exhibits insensitive response to external perturbation, which makes it ideal for tunable devices like optical filters and fiber lasers.

Leaky Mode Combs in Tilted Fiber Bragg Grating

Leaky modes in tilted fiber Bragg grating (TFBG) present attractive properties but it has been generally underestimated and ignored. Herein, we systematically investigate the enhancement mechanism and the sensing performance of the enhanced leaky mode resonance (eLMR) combs in `dielectric graphene' integrated TFBG in theory. The investigation is conducted using the Fresnel reflection theory and the effective refractive index method. The graphene induces a highly polarization-dependent influence on the internal reflection and mode coupling of the TFBG, resulting in the s-polarized cladding guided mode being highly lossy and the leaky modes becoming guided. This is verified by the propagation length and extinction ratio. The p-/s-polarized coupling coefficient κ with the core guided mode presents a sudden large increase at the position where the mode transition occurs from the cladding guided modes to the leaky modes in both bare and coated TFBG. But the s-polarized κ is further increased by the graphene. Therefore, the mode coupling associated with the s-polarized guided leaky modes is greatly enhanced whereas it is efficiently suppressed for the lossy cladding guided modes, leading to the eLMR combs in the TFBG. It is found that the sensing performance of the eLMR combs appears a quasi-periodic property, evidenced by two groups of amplitude evolution with the surrounding refractive index (SRI). By choosing the optimal eLMR combs, a quasi-continuous SRI sensing is realized. The results demonstrate that the eLMR combs present highly sensitive performance with the average sensitivity up to 5180.4 dB/RIU and 12227.8 dB/RIU for these two groups respectively. Moreover, the eLMR combs present several advantages including insensitive wavelength shift, high figure of merit and wide application fields. This research extends our knowledge and will serve as a base for future studies on the leaky mode resonance.

Simultaneous measurement of refractive index and temperature using a hybrid-grating sensor

A hybrid-grating-based optical fiber sensor for simultaneously measuring the refractive index (RI) and temperature is proposed. The sensor is fabricated by inscribing a long period grating (LPG) and tilted fiber Bragg grating (TFBG) in the same region of an optical fiber in sequence. The hybrid grating takes advantage of both LPG’s high temperature sensitivity and TFBG’s high RI sensitivity, with consideration of the temperature-insensitive characteristic of wavelength difference between the cladding mode wavelength and core mode wavelength of TFBG. Experiments prove the ability of the sensor to measure the RI and temperature simultaneously. The sensitivities are 606.82 nm/RIU and 268.79 pm °C−1, respectively.