- Email: [email protected]
Electrically tunable Brillouin fiber laser based on a metal-coated single-mode optical fiber
RINP 554
No. of Pages 2, Model 5G
11 February 2017 Results in Physics xxx (2017) xxx–xxx 1
Contents lists available at ScienceDirect
Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics
2
Microarticle
6 4 7 5
Electrically tunable Brillouin fiber laser based on a metal-coated single-mode optical fiber
8
S.M. Popov a, Y.K. Chamorovski a, V.A. Isaev a, P. Mégret b, I.O. Zolotovskii d, A.A. Fotiadi b,c,d,⇑
9 10 11 12
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a
Institute of Radio Engineering and Electronics (Fryazino Branch) Russian Academy of Science, Vvedenskogo Sq. 1, 141190 Fryazino, Moscow Region, Russian Federation Electromagnetism and Telecommunication Department, University of Mons, 31 Boulvard Dolez, Mons 7000, Belgium c Ioffe Physico-Technical Institute of the Russian Academy of Sciences, 26 Polytekhnicheskaya Street, St. Petersburg 194021, Russian Federation d Ulyanovsk State University, 42 Leo Tolstoy Street, Ulyanovsk 432970, Russian Federation b
a r t i c l e
i n f o
Article history: Received 21 December 2016 Accepted 23 January 2017 Available online xxxx Keywords: Brillouin fiber laser Metal-coated optical fiber Laser tuning Fiber sensors
a b s t r a c t We explore tunability of the Brillouin fiber laser employing Joule heating. For this purpose, 10-m-length of a metal-coated single-mode optical cavity fiber has been directly included into an electrical circuit, like a conductor wire. With the current up to 3.5 A the laser tuning is demonstrated over a spectrum range of 400 MHz. The observed laser line broadening up to 2 MHz is explained by frequency drift and mode-hoping in the laser caused by thermal noise. Ó 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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Single longitudinal-mode fiber lasers with a narrow linewidth are demanded for many potential applications in coherent optical communications, distributed sensing and microwave photonics. Stimulated Brillouin scattering is a well-known universal way to organize narrow-band lasing in fiber configurations enabling a variety of the performance characteristics [1–5]. Single-mode Brillouin fiber lasers based on a short fiber ring cavity exhibit low threshold, high spectral purity and low intensity noise [1–4]. In this paper, we present a tunable Brillouin fiber laser pumped by a frequency-stabilized laser diode. Controlling the temperature of the fiber through Joule heating, the Brillouin frequency shift can be changed by current. The lasing frequency follows the Brillouin frequency shift change and, thus, can be tuned. The experimental configuration of the laser is shown in Fig. 1a. The 1550 nm light from a 100 kHz linewidth laser diode is amplified up to the power of 150 mW by an erbium-doped fiber amplifier. The amplified light is injected into the Brillouin laser cavity through a circulator to operate as the Brillouin pump. The cavity comprises an optical circulator and 10-m-length of the metalcoated single-mode optical fiber [6]. Lasing occurs in the cavity when the injected power exceeds the threshold (90 mW). The residual pump and laser light come out from the 5% ends (Out 1 and 2, respectively) of a 95/5 coupler and could be combined in ⇑ Corresponding
author at: Electromagnetism and Telecommunication Department, University of Mons, 31 Boulvard Dolez, Mons 7000, Belgium. E-mail address: [email protected] (A.A. Fotiadi).
the 50/50 coupler for monitoring of laser spectrum by 20-GHz radio-frequency spectrum analyzer. A polarization controller provides adjustment of the light polarization state inside the cavity. Due to the circulator directionality, the pump light passes through the cavity with only one round trip and does not resonate in the cavity. The Stokes light circulates in the cavity and gets the resonance for efficient lasing. To tune the lasing frequency, the metal-coated single-mode fiber (SMF) is included directly into a Joule electrical circuit for heating employing the fiber copper coating as a conductor wire (the fiber coils are electrically isolated). Due to heating, the Brillouin gain spectrum is shifted leading to a change of the laser frequency. The fiber used in the experiment has been manufactured in IRE (step-index difference 0.005, core/cladding diameters 9/200 lm, thickness of the copper coating 21.5 lm) and tested for operation at temperatures up to 900 °C. Before the experiment, we have measured the Brillouin frequency shift (Fig. 1b) in the fiber with BOTDA (OZ-optics, Inc.). At 20 °C it is 10,802 MHz GHz and exhibits a linear increase with the temperature demonstrating a slope of 1.3 MHz/°C that is slightly higher than for SMF-28 Corning fiber. Fig. 2 shows the features of laser operation. The Brillouin lasing threshold is achieved at pump power of 100 mW. At the pump power of 150 mW the output power is 20 mW. At this pump level the laser could be stabilized for operation with a linewidth <100 kHz. However, for this purpose the laser configuration has to be stabilized thermally providing fluctuations of the fiber
http://dx.doi.org/10.1016/j.rinp.2017.01.034 2211-3797/Ó 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: Popov SM et al. Electrically tunable Brillouin fiber laser based on a metal-coated single-mode optical fiber. Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.01.034
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RINP 554
No. of Pages 2, Model 5G
11 February 2017 S.M. Popov et al. / Results in Physics xxx (2017) xxx–xxx
a
b
optical circulator
DFB laser
EDFA Out 1
Current source
Brillouin
Pump metal-coated fiber
detector 50/50 Out 2 5/95 coupler coupler
RF Analyzer
Brillouin frequency shift, MHz
2
300
200
100
polarization controller
0
0
50
100 150 200 250 o Temperature, C
300
Fig. 1. Experimental configuration of the Brillouin laser (a) and the temperature dependence of the Brillouin frequency shift (b).
b 15
Out 2 Out 1
Power, a.u.
Output power, mW
20
10 10810
5
10815 10820 Laser frequency shift
10825
0 0
20
40 60 80 100 120 140 Pump power, mW
Laser frequency shift, MHz
a
400 300 200 100 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Current, A
Fig. 2. Laser power characteristics (a) and laser frequency tuning (b), RF laser spectrum at 1 A (offset).
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temperature less than 0.05 °C. Such stabilization is beyond the scope of this paper. Without thermal stabilization the singlefrequency laser operation exhibits frequency drift and continuous mode-hopping caused by a thermal noise perturbating the cavity fiber optical length. However, significant part of the laser power is concentrated in a narrow spectrum peaks with a linewidth less than 2 MHz that is much narrower than the cavity FSR 18 MHz. Offset of Fig. 2a shows a typical RF spectra recorded with an average time 0.2 s. This feature indicates existence of a frequency stabilization mechanism that probably involves thermal-optical properties of the circulator responsible for the main optical losses (>10%) in the cavity. Fig. 2b shows the results of the laser frequency tuning. The frequency changes are not linear with the current: the curve demonstrates slope of 45 MHz/A and 135 MHz/A at low and high current, respectively. The total laser frequency shift 400 MHz is achieved at the current of 3.5 A. According to Fig. 1b, the temperature of the fiber in this regime is 350 °C. In conclusion, we have demonstrated an electrically tunable Brillouin fiber laser. With control of the current flowing through the fiber, the lasing frequency can be tuned up to 400 MHz. Over the whole tuning spectrum range the laser is able to operate with the linewidth of 2 MHz. Further improvements of the laser performance require precise thermal stabilization of the laser cavity that is rather difficult technically for the considered configuration. However, even with the reported features, the laser could be a
simple, compact, and cost effective solution for many practical applications.
112
Acknowledgement
114
The authors thank IRE staff for manufacturing of the metal-coated fiber. The work was supported by IAP program VII/35 of the Belgian Science Policy, Ministry of Education and Science of Russian Federation (14.Z50.31.0015) and Russian Fund of Fundamental Research (16-32-60109 mol_a_dk, 14-29-08195, and 16-42732135 R-OFIM).
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References
121
[1] Wu Zh, Zhan L, Shen Q, Liu J, Hu X, Xiao P. Ultrafine optical-frequency tunable Brillouin fiber laser based on fiber strain. Opt Lett 2011;36:3837. [2] Spirin VV, Mégret P, Fotiadi AA. Passively stabilized doubly-resonant Brillouin fiber lasers. In: Paul MCh, editor. Fiber laser. INTECH; 2016. [3] Spirin VV, López-Mercado CA, Kinet D, Mégret P, Zolotovskiy IO, Fotiadi AA. A single-longitudinal-mode Brillouin fiber laser passively stabilized at the pump resonance frequency with a dynamic population inversion grating. Laser Phys Lett 2013;10:015102. [4] Spirin VV, Kellerman J, Swart PL, Fotiadi AA. Intensity noise in SBS with injection locking generation of Stokes seed signal. Opt Exp 2006;14(18):8328–35. [5] Grukh DA, Kurkov AS, Razdobreev IM, Fotiadi AA. Self-Q-switched ytterbiumdoped cladding-pumped fibre laser. Quant Electron 2002;32(11):1017. [6] Popov SM, Voloshin VV, Vorobyov IL, Ivanov GA, Kolosovskii AO, Isaev VA, Chamorovskii YK. Optical loss of metal coated optical fibers at temperatures up to 800 °C. Opt Memory Neural Networks 2012;21:45–51.
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Please cite this article in press as: Popov SM et al. Electrically tunable Brillouin fiber laser based on a metal-coated single-mode optical fiber. Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.01.034
113
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137
No. of Pages 2, Model 5G
11 February 2017 Results in Physics xxx (2017) xxx–xxx 1
Contents lists available at ScienceDirect
Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics
2
Microarticle
6 4 7 5
Electrically tunable Brillouin fiber laser based on a metal-coated single-mode optical fiber
8
S.M. Popov a, Y.K. Chamorovski a, V.A. Isaev a, P. Mégret b, I.O. Zolotovskii d, A.A. Fotiadi b,c,d,⇑
9 10 11 12
13 1 2 5 6 16 17 18 19 20 21 22 23 24 25
a
Institute of Radio Engineering and Electronics (Fryazino Branch) Russian Academy of Science, Vvedenskogo Sq. 1, 141190 Fryazino, Moscow Region, Russian Federation Electromagnetism and Telecommunication Department, University of Mons, 31 Boulvard Dolez, Mons 7000, Belgium c Ioffe Physico-Technical Institute of the Russian Academy of Sciences, 26 Polytekhnicheskaya Street, St. Petersburg 194021, Russian Federation d Ulyanovsk State University, 42 Leo Tolstoy Street, Ulyanovsk 432970, Russian Federation b
a r t i c l e
i n f o
Article history: Received 21 December 2016 Accepted 23 January 2017 Available online xxxx Keywords: Brillouin fiber laser Metal-coated optical fiber Laser tuning Fiber sensors
a b s t r a c t We explore tunability of the Brillouin fiber laser employing Joule heating. For this purpose, 10-m-length of a metal-coated single-mode optical cavity fiber has been directly included into an electrical circuit, like a conductor wire. With the current up to 3.5 A the laser tuning is demonstrated over a spectrum range of 400 MHz. The observed laser line broadening up to 2 MHz is explained by frequency drift and mode-hoping in the laser caused by thermal noise. Ó 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
27 28 29 30 31 32 33
34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58
Single longitudinal-mode fiber lasers with a narrow linewidth are demanded for many potential applications in coherent optical communications, distributed sensing and microwave photonics. Stimulated Brillouin scattering is a well-known universal way to organize narrow-band lasing in fiber configurations enabling a variety of the performance characteristics [1–5]. Single-mode Brillouin fiber lasers based on a short fiber ring cavity exhibit low threshold, high spectral purity and low intensity noise [1–4]. In this paper, we present a tunable Brillouin fiber laser pumped by a frequency-stabilized laser diode. Controlling the temperature of the fiber through Joule heating, the Brillouin frequency shift can be changed by current. The lasing frequency follows the Brillouin frequency shift change and, thus, can be tuned. The experimental configuration of the laser is shown in Fig. 1a. The 1550 nm light from a 100 kHz linewidth laser diode is amplified up to the power of 150 mW by an erbium-doped fiber amplifier. The amplified light is injected into the Brillouin laser cavity through a circulator to operate as the Brillouin pump. The cavity comprises an optical circulator and 10-m-length of the metalcoated single-mode optical fiber [6]. Lasing occurs in the cavity when the injected power exceeds the threshold (90 mW). The residual pump and laser light come out from the 5% ends (Out 1 and 2, respectively) of a 95/5 coupler and could be combined in ⇑ Corresponding
author at: Electromagnetism and Telecommunication Department, University of Mons, 31 Boulvard Dolez, Mons 7000, Belgium. E-mail address: [email protected] (A.A. Fotiadi).
the 50/50 coupler for monitoring of laser spectrum by 20-GHz radio-frequency spectrum analyzer. A polarization controller provides adjustment of the light polarization state inside the cavity. Due to the circulator directionality, the pump light passes through the cavity with only one round trip and does not resonate in the cavity. The Stokes light circulates in the cavity and gets the resonance for efficient lasing. To tune the lasing frequency, the metal-coated single-mode fiber (SMF) is included directly into a Joule electrical circuit for heating employing the fiber copper coating as a conductor wire (the fiber coils are electrically isolated). Due to heating, the Brillouin gain spectrum is shifted leading to a change of the laser frequency. The fiber used in the experiment has been manufactured in IRE (step-index difference 0.005, core/cladding diameters 9/200 lm, thickness of the copper coating 21.5 lm) and tested for operation at temperatures up to 900 °C. Before the experiment, we have measured the Brillouin frequency shift (Fig. 1b) in the fiber with BOTDA (OZ-optics, Inc.). At 20 °C it is 10,802 MHz GHz and exhibits a linear increase with the temperature demonstrating a slope of 1.3 MHz/°C that is slightly higher than for SMF-28 Corning fiber. Fig. 2 shows the features of laser operation. The Brillouin lasing threshold is achieved at pump power of 100 mW. At the pump power of 150 mW the output power is 20 mW. At this pump level the laser could be stabilized for operation with a linewidth <100 kHz. However, for this purpose the laser configuration has to be stabilized thermally providing fluctuations of the fiber
http://dx.doi.org/10.1016/j.rinp.2017.01.034 2211-3797/Ó 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: Popov SM et al. Electrically tunable Brillouin fiber laser based on a metal-coated single-mode optical fiber. Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.01.034
59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85
RINP 554
No. of Pages 2, Model 5G
11 February 2017 S.M. Popov et al. / Results in Physics xxx (2017) xxx–xxx
a
b
optical circulator
DFB laser
EDFA Out 1
Current source
Brillouin
Pump metal-coated fiber
detector 50/50 Out 2 5/95 coupler coupler
RF Analyzer
Brillouin frequency shift, MHz
2
300
200
100
polarization controller
0
0
50
100 150 200 250 o Temperature, C
300
Fig. 1. Experimental configuration of the Brillouin laser (a) and the temperature dependence of the Brillouin frequency shift (b).
b 15
Out 2 Out 1
Power, a.u.
Output power, mW
20
10 10810
5
10815 10820 Laser frequency shift
10825
0 0
20
40 60 80 100 120 140 Pump power, mW
Laser frequency shift, MHz
a
400 300 200 100 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Current, A
Fig. 2. Laser power characteristics (a) and laser frequency tuning (b), RF laser spectrum at 1 A (offset).
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temperature less than 0.05 °C. Such stabilization is beyond the scope of this paper. Without thermal stabilization the singlefrequency laser operation exhibits frequency drift and continuous mode-hopping caused by a thermal noise perturbating the cavity fiber optical length. However, significant part of the laser power is concentrated in a narrow spectrum peaks with a linewidth less than 2 MHz that is much narrower than the cavity FSR 18 MHz. Offset of Fig. 2a shows a typical RF spectra recorded with an average time 0.2 s. This feature indicates existence of a frequency stabilization mechanism that probably involves thermal-optical properties of the circulator responsible for the main optical losses (>10%) in the cavity. Fig. 2b shows the results of the laser frequency tuning. The frequency changes are not linear with the current: the curve demonstrates slope of 45 MHz/A and 135 MHz/A at low and high current, respectively. The total laser frequency shift 400 MHz is achieved at the current of 3.5 A. According to Fig. 1b, the temperature of the fiber in this regime is 350 °C. In conclusion, we have demonstrated an electrically tunable Brillouin fiber laser. With control of the current flowing through the fiber, the lasing frequency can be tuned up to 400 MHz. Over the whole tuning spectrum range the laser is able to operate with the linewidth of 2 MHz. Further improvements of the laser performance require precise thermal stabilization of the laser cavity that is rather difficult technically for the considered configuration. However, even with the reported features, the laser could be a
simple, compact, and cost effective solution for many practical applications.
112
Acknowledgement
114
The authors thank IRE staff for manufacturing of the metal-coated fiber. The work was supported by IAP program VII/35 of the Belgian Science Policy, Ministry of Education and Science of Russian Federation (14.Z50.31.0015) and Russian Fund of Fundamental Research (16-32-60109 mol_a_dk, 14-29-08195, and 16-42732135 R-OFIM).
115
References
121
[1] Wu Zh, Zhan L, Shen Q, Liu J, Hu X, Xiao P. Ultrafine optical-frequency tunable Brillouin fiber laser based on fiber strain. Opt Lett 2011;36:3837. [2] Spirin VV, Mégret P, Fotiadi AA. Passively stabilized doubly-resonant Brillouin fiber lasers. In: Paul MCh, editor. Fiber laser. INTECH; 2016. [3] Spirin VV, López-Mercado CA, Kinet D, Mégret P, Zolotovskiy IO, Fotiadi AA. A single-longitudinal-mode Brillouin fiber laser passively stabilized at the pump resonance frequency with a dynamic population inversion grating. Laser Phys Lett 2013;10:015102. [4] Spirin VV, Kellerman J, Swart PL, Fotiadi AA. Intensity noise in SBS with injection locking generation of Stokes seed signal. Opt Exp 2006;14(18):8328–35. [5] Grukh DA, Kurkov AS, Razdobreev IM, Fotiadi AA. Self-Q-switched ytterbiumdoped cladding-pumped fibre laser. Quant Electron 2002;32(11):1017. [6] Popov SM, Voloshin VV, Vorobyov IL, Ivanov GA, Kolosovskii AO, Isaev VA, Chamorovskii YK. Optical loss of metal coated optical fibers at temperatures up to 800 °C. Opt Memory Neural Networks 2012;21:45–51.
122 123 124 125 126 127 128 129 130 131 132 133 134 135 136
Please cite this article in press as: Popov SM et al. Electrically tunable Brillouin fiber laser based on a metal-coated single-mode optical fiber. Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.01.034
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