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In this paper the comparative study of spectral transmission characteristics of tilted Bragg gratings made using uniform phase mask and chirped phase mask are presented. Results are focused on low tilt angles with special interest on cladding modes behavior. The spectral characteristic shape for simultaneously tilted and chirped Bragg gratings poin...
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... spectral ch and excitation hen tilted fibe n both figures The arrow in F cal sensitivity Position indicated by the arrow shows disappearing of comb-like shape of this part of spectral transmission characteristics. Characteristic point (marked by an arrow) moves to the longer-wavelength side with increasing of ambient refractive index (Table 1). This phenomenon can be applied for practical implementation of short range value refractometer. ...
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Citations
... Over the past decades, many techniques have been proposed for SRS suppression, such as the application of large-mode-area (LMA) fibers, spectrally selective fibers, long-period fiber gratings (LPFGs) and chirped tilted fiber Bragg gratings (CTFBGs) [8][9][10]. Due to the continuous broadband spectral profile, better stability, and convenient adjustable wavelength range, CTFBG is considered a comparatively suitable components for SRS suppression in high power fiber laser systems. ...
CTFBGs with different center wavelengths are cascaded to broad the bandwidth to 20 nm (FWHM). The homemade duplexed CTFBG assists a 20.88 kW output of single fiber laser system with 18.6 dB of SRS suppression.
... Many recent techniques have been explored for SRS suppression over the past decades among which include the large-mode-area (LMA) fibers, spectrally selective fibers, long-period fiber gratings (LPFGs), and chirped tilted fiber Bragg gratings (CTFBGs) [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The LMA fibers cannot unlimitedly expand the core areas which may in turn lower the thermally induced modal instability (TMI) threshold [26,27]. ...
... CTFBGs utilized as broadband spectral filters have been extensively studied since 2017 [17][18][19][20][21][22][23][24][25], when the first research effort in suppressing SRS for fiber lasers was conducted by integrating a CTFBG into a 20-W continuous-wave (cw) fiber laser [20]. Shortly after, CTFBGs were reported with power handling capability up to a few hundred watts [20,21]. ...
In this paper, we present experimental studies on newly developed multiplexed chirped tilted fiber Bragg gratings (MCTFBGs) for stimulated Raman scattering (SRS) suppression for high-power fiber laser systems. The MCTFBG device is composed of five continuous segments of chirped tilted fiber Bragg gratings (CTFBGs), which are inscribed into the large-mode-area (LMA, 25/400μm) fibers. The SRS suppression capability of the MCTFBG device has been successfully demonstrated with a master oscillator power amplification (MOPA) fiber laser system at the output level of 3.4 KW. The experimental observation thus indicates the MCTFBG’s excellent SRS suppression capability at a very high power level (∼15 dB under >3 kW) and high thermal handling capacity (∼1.48℃/kw). Our work thus provides a key development of essential fiber grating components that can effectively suppress the SRS suppression at a very high power level.
... Moreover, with a chirped mask, the discrete resonances will overlap each other and lead to a continuous spectral profile in transmission over a wide band of wavelength, which provides good potential for wideband rejection filters. Among the reported CTFBG-based band-rejection filters [7][8][9][10][11], a relatively new report has combined the chirped fiber Bragg gratings (CFBGs) with TFBGs to fabricate a tunable broadband rejection filter in single-mode fibers (SMF-28), and good filtering functions over a large range of bandwidths (more than 100 nm), together with a low insertion loss (less than 1 dB), and a negligible backreflection (lower than −20 dB) was achieved [11]. ...
We demonstrate here the inscription of chirped and tilted fiber Bragg gratings (CTFBGs), to the best of our knowledge, for the first time in hydrogen-loaded large-mode-area (LMA) double-cladding fibers using UV pulses and linearly chirped phase masks. High reflectivity wideband adjustable band-rejection filters are achieved in fibers like LMA-GDF-10/130-M and PS-GDF-20/400-M, with a wavelength coverage of more than 10 nm and suppression ratio around 20 dB. The spectrum and temperature properties are investigated. Experimental results indicate that CTFBGs could be used in double-cladding fiber systems with a smoothly varying attenuation spectrum and a low insertion loss, which is significant for further power scaling in a high-power fiber system.
... Before the grating inscription, optical fiber was hydrogenated at room temperature under the pressure of 110 bars for ten days. Tilt angle θ was obtained by rotating the phase mask against the optical fiber and laser beam 19 . Transmission spectrum of resulted TFBG with θ=3.5° tilt angle is presented in Fig. 1. ...
In this paper, the concept and experimental characterization of tilted fiber Bragg grating (TFBG) based sensor for temperature and liquid level measurement are presented. It is shown that, when liquid level increases the peak amplitudes of cladding modes linearly decreases (in dB). In turn, changes in temperature causes a shift of the TFBG transmission spectrum, which can be accurately measured by monitoring the Bragg wavelength corresponding to the liquid level independent core mode. The main advantages of proposed sensor are simple design as well as linear
responses to liquid level and temperature.
... The liquid level was adjusted by injecting liquid into the container, and controlled by either directly reading the scale and or by calculating, based on the volume of injected fluid. TFBG with θ = 3.5°tilt angle and 10 mm length was written in a single-mode optical fiber (SMF-28) using phase mask technique with frequency doubled CW Ar ion laser operating at 244 nm [21]. Prior to the grating inscription, the optical fiber was hydrogen-loaded for enhancing photosensitivity. ...
We present a tilted fiber Bragg grating (TFBG)-based fiber optic sensor for the simultaneous measurement of liquid level and temperature. Due to different responses of cladding modes and core mode in TFBG spectrum to liquid level and temperature changes, both values can be measured independently. The examined 3.5° TFBG exhibits linear liquid level, as well as temperature, responses and sensitivities of-0.456 ± 0.009 dB/mm and 11.4 ± 0.2 pm/°C, respectively. In addition, greater sensor applicability is proposed for liquids having lower refractive indexes using TFBG with greater tilt angle. The presented system is capable of being applied in chemical, food, and automotive industries as well as, thanks to its all-fiber structure, in potentially hazardous environments where the immunity to electromagnetic fields or/and electric isolation is required.
... Therefore, a chirped and tilted FBG (CTFBG) provides good potential for broadband-rejection filters. However, in all CTFBG based band-rejection filters reported so far, the effective bandwidth tuning range is limited to several tens of nanometer [17][18][19][20]. Designing band-rejection filters with better quality (broadband tuning and spectral trimming ability to hundreds of nanometers) and lower cost (based on well-established grating fabrication techniques) encourages further research in this field. ...
Broadband-trimming band-rejection filters based on chirped and tilted fiber Bragg gratings (CTFBG) are proposed and experimentally demonstrated. The flexible chirp-rate and wide tilt-angle provide the gratings with broadband filtering functions over a large range of bandwidth (from 10 nm to 150 nm), together with a low transmission loss (less than 1 dB) and a negligible back-reflection (lower than 20 dB). The slope profile of CTFBG in transmission can be easily tailored by adjusting the tilt angle, grating irradiation time and chirp rate-grating factor, and it is insensitive to polarization of launch condition. Furthermore, by coating the CTFBG with a suitable polymer (whose refractive index is close to that of the cladding glass), the cladding modes no longer form weakly discrete resonances and leave a smoothly varying attenuation spectrum for high-quality band rejection filters, edge filters and gain equalizers.
... Therefore, a chirped and tilted FBG (CTFBG) provides good potential for broadband-rejection filters. However, in all CTFBG based band-rejection filters reported so far, the effective bandwidth tuning range is limited to several tens of nanometer [17][18][19][20]. Designing band-rejection filters with better quality (broadband tuning and spectral trimming ability to hundreds of nanometers) and lower cost (based on well-established grating fabrication techniques) encourages further research in this field. ...
Wideband-adjustable band-rejection filters based on chirped and tilted fiber Bragg gratings (CTFBG) are proposed and experimentally demonstrated. The flexible chirp-rate and wide tilt-angle provide the gratings with broadband filtering functions over a large range of bandwidths (from 10 nm to 150 nm), together with a low insertion loss (less than 1dB) and a negligible back-reflection (lower than −20 dB). The slope profile of CTFBG in transmission can be easily tailored by adjusting the tilt angle, grating irradiation time and chirp rate-grating factor, and it is insensitive to the polarization state of the input light, as well as to temperature, axial strain and surrounding refractive index. Furthermore, by coating the CTFBG with a suitable polymer (whose refractive index is close to that of the cladding glass), the cladding modes no longer form weakly discrete resonances and leave a smoothly varying attenuation spectrum for high-quality band-rejection filters, edge filters and gain equalizers.
The average power of diode-pumped fiber lasers has been developed deeply into the kW regime in the past years. However, stimulated Raman scattering (SRS) is still a major factor limiting the further power scaling. Here, we have demonstrated the mitigation of SRS in kilowatt-level diode-pumped fiber amplifiers using a chirped and tilted fiber Bragg grating (CTFBG) for the first time. The CTFBG is designed and inscribed in large-mode-area (LMA) fibers, matching with the operating wavelength of the fiber amplifier. With the CTFBG inserted between the seed laser and the amplifier stage, an SRS suppression ratio of is achieved in spectrum at the maximum output laser power of 2.35 kW, and there is no reduction in laser slope efficiency and degradation in beam quality. This work proves the feasibility and practicability of CTFBGs for SRS suppression in high-power fiber lasers, which is very useful for the further power scaling.
The average power of fiber lasers has been scaled deeply into the kW regime in the past years. However, stimulated Raman scattering (SRS) is still a major factor limiting further power scaling. Here, we have demonstrated for the first time, to the best of our knowledge, the suppression of SRS in a half 10 kW tandem pumping fiber amplifier using chirped and tilted fiber Bragg gratings (CTFBGs). With specially self-designed and manufactured CTFBGs inserted between the seed laser and the amplifier stage, a maximum SRS suppression ratio of >15 dB in spectrum is observed with no reduction in laser efficiency. With one CTFBG, the effective output power is improved to 3.9 kW with a beam quality M ² factor of ∼1.7 from <3.5 kWwith an M ² factor of >2; with two CTFBGs, the effective laser power reaches 4.2 kW with an increasing ratio of 20% and an M ² factor of ∼1.8, and further power improvement is limited by the power and performance of the 1018 nm pump sources. This work provides an effective SRS suppression method for high-power all-fiber lasers, which is useful for further power scaling of these systems.
