CC BY
5*
ALT'23
The 30th International Conference on Advanced Laser Technologies
LS-I-4
Laser and sensor systems based on FBG arrays fs-inscribed in passive and active multicore fibers
A.A. Wolf, A.G. Kuznetsov, A.V. Dostovalov, S.A. Babin*
Institute of Automation andElectrometry SB RAS, Novosibirsk 630090, Russia
Multicore fibers (MCFs) offer the involvement of multiple cores in optical signal generation, transmission and processing. Developments in this direction resulted in fiber-optic communication systems with increased capacity via spatial division multiplexing [1], an opportunity to use passive MCFs for multi-parameter sensing systems is also started to be explored [2]. Active MCFs also represent an attractive gain medium as an alternative to large-mode area (LMA) singlemode fibers for the development of compact laser systems with high-power output obtained by coherent combining of beams generated in individual cores [3], but they still have some lacks especially in terms of performance. The performance of MCF laser and sensor systems may be greatly improved with the use of in-fiber elements such as fiber Bragg gratings (FBGs) selectively inscribed in different cores. For that a point-by-point (PbP) femtosecond (fs) pulse inscription technology is the most promising for fabrication in passive and active MCFs the FBG arrays of arbitrary shape. Here we review our recent results on the PbP fs inscription of regular and random FBG arrays in active and passive MCFs and implementation of such structures in the advanced laser and sensor systems.
In passive 7-core MCFs, we fabricated 3D FBG arrays by the PbP fs inscription through polyimide protective coating. It is enough to involve in the array 3 side cores and central core for precise 2D and 3D fiber shape reconstruction with accuracy as high as ~ 1% [2,4] at curvature radii variation in the range from 2.6 mm to 500 mm. The temperature resistance of both the inscribed FBG structures and the protective coating, along with the high mechanical strength of the polyimide, makes it possible to use the sensor in harsh environments or in medical and composite material applications. Further, FBGs selectively inscribed in side cores of 7-core passive MCF were used as complex reflector of a MCF Raman laser with pumping and output coupling through the central core, which is able to generate singlemode output with narrow spectrum [6]. The narrowing occurs due to the suppression of nonlinear effects in the large effective area of 7-core fiber cavity and due to the interference of signals reflected from FBGs in different cores, which have sufficient optical coupling.
In active MCFs, we first studied an LD-pumped 4-core Yb-doped fiber with FBGs fs-inscribed in each core, where the core crosstalk is induced via strong bending, and have observed the fiber output power concentration in one core [5] that is different from the single-core out-coupling in 7-core fiber Raman laser [4]. We also perform similar study of an LD-pumped 7-core Yb-doped fiber with 3D FBG array [6]. Femtosecond inscription of highly-reflective FBGs in each core of 7-core Yb-doped fiber enables efficient (~70%) 1064-nm lasing in robust all-fiber scheme with ~33 W power, nearly the same for uncoupled and coupled cores. However, output spectrum is quite different: without coupling, 7 individual lines corresponding to the in-core FBG reflection spectra sum up into broad (>0.22 nm) total spectrum, whereas the multiline spectrum collapses into single narrow line at strong coupling. The developed model shows that the coupled-core laser generates coherent superposition of supermodes at the wavelength corresponding to the geometric mean of individual FBG spectra, whereas the generated laser line broadens with power (0.04-0.12nm) like single-core mode of 7-times larger effective area.
The details of these studies and potential application of devices will be presented at the conference. This work is supported by Russian Science Foundation (№21-72-30024).
[1] D. J. Richardson, J. M. Fini, & L. Nelson, Space-division multiplexing in optical fibres, Nature Photonics, vol. 7, pp. 354-362 (2013).
[2] K. Bronnikov, A. Wolf, S. Yakushin, A. Dostovalov, O. Egorova, S. Zhuravlev, S. Semjonov, S. Wabnitz, and S. Babin, Durable shape sensor based on FBG array inscribed in polyimide-coated multicore optical fiber, Opt. Express, vol. 27, pp. 38421-38434 (2019).
[3] C. Jaregui, J. Limpert, & A. Tunnermann, High-power fibre lasers, Nature Photonics, vol. 7, pp. 861-867 (2013).
[4] A. Wolf, A. Dostovalov, K. Bronnikov, M. Skvortsov, S. Wabnitz, and S. Babin, Advances in femtosecond direct writing of fiber Bragg gratings in multicore fibers: technology, sensor and laser applications, Opto-Electronic Advances, vol. 5, 210055 (2022).
[5] A. A. Wolf, M. I. Skvortsov, I. A. Lobach, A. V. Dostovalov, and S. A. Babin, Bending induced output power concentration in a core of a 4-core Yb-doped fiber laser, Opt. Exp., vol. 30, pp. 7580-7590 (2022).
[6] A. G. Kuznetsov, A. A. Wolf, A. V. Dostovalov, E. V. Podivilov, S.A. Babin. Spectrum collapse in a 7-core Yb-doped fiber laser with an array of fs-inscribed fiber Bragg gratings. Opt. Lett. (2023), in press.
