Femtosecond (fs) laser writing has become an effective way to process any type of transparent optical material, such as silica optical fibers [
Journal of the European Optical Society-Rapid Publications, Volume. 19, Issue 1, 2022015(2023)
Wavelength-switchable L-band fiber laser assisted by random reflectors
A wavelength-switchable L-band erbium-doped fiber laser (EDFL) assisted by an artificially controlled backscattering (ACB) fiber reflector is here presented. This random reflector was inscribed by femtosecond (fs) laser direct writing on the axial axis of a multimode fiber with 50 μm core and 125 μm cladding with a length of 17 mm. This microstructure was placed inside a surgical syringe to be positioned in the center of a high-precision rotation mount to accurately control its angle of rotation. Only by rotating this mount, three different output spectra were obtained: a single wavelength lasing centered at 1574.75 nm, a dual wavelength lasing centered at 1574.75 nm and 1575.75 nm, and a single wavelength lasing centered at 1575.5 nm. All of them showed an optical signal-to-noise ratio (OSNR) of around 60 dB when pumped at 300 mW.
1 Introduction
Femtosecond (fs) laser writing has become an effective way to process any type of transparent optical material, such as silica optical fibers [
In addition to the above, these fiber-optic microstructures also have interesting applications in areas such as fiber-optic lasers [
In this work, an artificially controlled backscattering (ACB) fiber reflector inscribed by fs laser direct-write technique is used into an L-band erbium doped fiber laser (EDFL). This random reflector was inscribed on the axial axis of a 50/125 multimode fiber (MMF), with a length of 17 mm, and located into a high-precision rotation mount to control its angle of twist rotation. Only by rotating in a range of 8° the MMF sample where the RFG was inscribed, this wavelength-switchable EDFL can be switched among three different lasing spectra: a single wavelength lasing centered at 1574.75 nm, a dual wavelength lasing centered at 1574.75 nm and 1575.75 nm, or a single wavelength lasing centered at 1575.5 nm. An OSNR of 60 dB and 58 dB were measured for single and dual-wavelength operation respectively, when pumped at 300 mW.
2 Fabrication and characterization process
An ACB multimode fiber reflector was inscribed by using ultrafast laser writing, performed by a Cazadero fiber laser (Calmar Laser) that delivers 370 fs laser pulses at a central wavelength of 1030 nm. It is worth noting that, as presented in [
Figure 1.Backscattered optical power as a function of fiber length for the MMF-RFG, located about 1.88 m from the connector of the OBR (a) and reflected power as a function of the wavelength for the MMF-RFG reflector (b).
3 Experimental setup
Figure 2.Schematic diagram of the experimental L-band linear-cavity fiber laser setup; (a) pump laser; (b) wavelength-division multiplexer; (c) erbium-doped fiber; (d) fiber optic circulator; (e) optical coupler; (f) optical spectrum analyzer; (g) high-precision rotation mount where the MMF-RFG was rotated; (h) photograph of the inscribed MMF-RFG located into a syringe.
4 Results and discussion
Figure 3.Relationship between the output-power levels versus 976-nm pump power when (a) single-wavelength operation centered at 1574.75 nm (blue line) or at 1575.75 nm (red line) and (b) dual-wavelength operation were obtained.
Figure 4.Output spectra of the linear-cavity fiber laser with a MMF-RFG reflector pumped by a 976-nm laser, when (a) a single wavelength lasing centered at 1574.75 nm, (b) a dual wavelength lasing centered at 1574.75 nm and 1575.75 nm, and (c) a single wavelength lasing centered at 1575.5 nm are obtained. (d) Electric beat with a tunable laser source (TLS) of the single-wavelength lasing emission when pumped at 300 mW.
Such multimode lasers are usually more unstable that single mode ones in their output power levels. However, in this case, an output power level variation of 0.28 dB, with a confidence level (CL) of 95% was measured at room temperature. Measured data was stored each 10 s for 1 h, when single wavelength lasing pumped at 300 mW with a FWHM of 28.05 pm was obtained. The central emission wavelength of this laser showed a variation of 23 pm during the same period but with a CL of 100%.
5 Conclusions
In this work, a new wavelength-switchable L-band erbium-doped fiber laser is proposed and experimentally characterized. The laser is assisted by an artificially controlled backscattering fiber reflector, inscribed by femtosecond laser writing. This reflector is a random fiber grating that was written on the axial axis of a 50/125 multimode fiber with a length of 17 mm. This quasi-distributed fiber reflector was placed inside a surgical syringe to be positioned in the center of a high-precision rotation mount to precisely control its angle of rotation. Only by rotating this mount, three different output spectra were obtained: a single wavelength lasing centered at 1574.75 nm, a dual wavelength lasing centered at 1574.75 nm and 1575.75 nm, and a single wavelength lasing centered at 1575.5 nm. All of them showed an optical signal-to-noise ratio of 60 dB when pumped at 300 mW.
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R.A. Perez-Herrera, P. Roldan-Varona, A. Sanchez-Gonzalez, L. Rodriguez-Cobo, J.M. Lopez-Higuera, M. Lopez-Amo. Wavelength-switchable L-band fiber laser assisted by random reflectors[J]. Journal of the European Optical Society-Rapid Publications, 2023, 19(1): 2022015
Category: Research Articles
Received: Oct. 18, 2022
Accepted: Dec. 5, 2022
Published Online: Aug. 1, 2023
The Author Email: Perez-Herrera R.A. (rosa.perez@unavarra.es)