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Single-Frequency ytterbium-doped fiber laser with 26 nm tuning range
Optics Express, Vol. 15, Issue 8, pp. 4617-4622 (2007)
http://dx.doi.org/10.1364/OE.15.004617
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– Abstract
1. Introduction
2. Experimental setup
3. Experimental results
4. Conclusion
– References and links
– Abstract
1. Introduction
2. Experimental setup
3. Experimental results
4. Conclusion
– References and links
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Abstract
A core-pumped ytterbium-doped fiber laser is presented, tunable over 26 nm from 1017 nm to 1043 nm. A diffraction grating pair in Littman-Littrow configuration in the unidirectional ring-cavity provides the wavelength adjustment. The laser resonator with a free spectral range of 260 MHz supported stable single frequency operation with a maximum linear polarized output power of 31 mW.
© 2007 Optical Society of America
1. Introduction
Broadly tunable single-frequency lasers are versatile tools for many applications, including gas-sensing, bio-medical technology and metrology. One category of those systems are formed by vibronic solid-state lasers with the titanium doped sapphire laser as its most prominent representative. However, for efficient operation, these laser crystals have to be
integrated in sophisticated resonator designs. Another drawback is their required pump source, which is either a gas laser or a frequency-doubled solid state laser. A second group of tunable laser systems is represented by laser diodes operated in an external cavity. However, here the facets of the semiconductor chip have to be antireflection coated with a highly complex technique in order to achieve reflection coefficient values of 10-4 to 10-5. Only with these ultra-low values, lasing of the solitary diode chip or a coherence collapse during operation in an external cavity can be avoided.
Rare earth doped fiber lasers are an attractive alternative to these laser systems. Especially ytterbium doped fiber lasers with their broad gain bandwidth of 100 nm around 1 μm are promising light sources, which can be directly pumped by laser diodes and efficiently be further amplified in fiber amplifiers [1,2,3,4]. However, single-frequency operation in combination with a large tuning range has only been demonstrated at telecom wavelength so far [5], whereas in the 1 μm range only 20.4 nm with small output power were reported [6].
H. M. Pask, R. J. Carman, D. C. Hanna, A. C. Tropper, C. J. Mackechnie, P. R. Barber, and J. M. Dawes, “Ytterbium-Doped Silica Fiber Lasers: Versatile Sources for 1-1.2 μm Region,” IEEE J. Sel. Top. Quantum Electron. 1, 2–13 (1995). [CrossRef]
M. Auerbach, P. Adel, D. Wandt, C. Fallnich, S. Unger, S. Jetschke, and H. R. Müller, “10 W widely tunable narrow linewidth double-clad fiber ring laser,” Opt. Express 10, 139–144 (2002). [PubMed]
S. Huang, G. Qin, A. Shirakawa, M. Musha, and K. Ueda, “Single frequency 1083 nm ytterbium doped fiber master oscillator power amplifier laser,” Opt. Express 13, 7113–7117 (2005). [CrossRef] [PubMed]
M. Ibsen, S. Y. Set, G. S. Goh, and K. Kikuchi, “Broad-Band Continuously Tunable All-Fiber DFB Lasers,” IEEE Phot. Tech. Lett. 14, 21–23 (2002). [CrossRef]
In this paper, we present an ytterbium-doped fiber laser providing single-frequency operation as well as a tuning range of 26 nm. We have combined a large free spectral range resonator with a widely tunable small linewidth grating spectral filter, resulting in a stable and tunable single frequency laser.
2. Experimental setup
The setup of the unidirectional ring-cavity is shown in Fig. 1. The polarization maintaining ytterbium-doped single-clad fiber (INO Yb500) had a length of 25 cm with a nominal pump light absorption of 490 dB/m. FC/APC connectors were attached at the fiber ends to avoid Fresnel back-reflections. The fiber had a core diameter of 5.4 μm and cutoff wavelength of 900 nm which ensured single transverse mode operation of the laser. An optical isolator ensured unidirectional operation of the laser, preventing spatial hole burning which could result in multi longitudinal mode operation, lowering the laser performance [7].
G. P. Agrawal and M. Lax, “Analytic evaluation of interference effects on laser output in a Fabry-Perot resonator,” J. Opt. Soc. Am. 71, 515–519 (1981). [CrossRef]
Fig. 1. Setup of the unidirectional ring cavity. HWP: zero order half wave plate, FR: Faraday rotator, DC: dichroic mirror; the arrow inside the active fiber indicates the operation direction of the laser.
A telecom grade laser diode emitting 425 mW of polarized light at 976 nm was used as a pump source. The pump light was delivered to the active fiber contra-directional to the laser operating direction through the output port of the laser. Pump light and laser signal were separated externally by a dichroic mirror.
Single frequency operation of a laser can be achieved, if all other longitudinal modes of the laser are sufficiently suppressed. In our case, this was given by the combination of a relatively large free spectral range (FSR) of the laser cavity and a small bandwidth spectral filter. Our laser cavity had an optical path length of 1.15 m, corresponding to a FSR of 260 MHz. The spectral filter was assembled by a combination of two gratings with 1200 lines/mm in Littrow-Littman configuration [8]. The incidence angle on the Littman grating was 80°. The resolution was further increased by using a telescope with cylindrical
lenses with a magnification ratio of 1 to 13. This arrangement was placed inside a sigma branch, built up with the optical isolator. The laser was tunable by rotation of the Littrow grating, either by using a motorized rotation axis or a piezo-actor for fine-tuning.
D. Wandt, M. Laschek, A. Tünnermann, and H. Welling, “Continuously tunable external-cavity diode laser with a double-grating arrangement,” Opt. Lett. 15, 390–392 (1997) [CrossRef]
To adjust the polarization between the polarization maintaining fiber and the residual resonator half wave plates were placed in front of and behind the fiber (HWP1 and HPW2 respectively). The output coupling ratio could be adjusted with HWP2 and the polarization beam splitter cube ensured linear polarized operation of the laser.
The linewidth of the grating arrangement, crucial for the single frequency operation of the system, was measured with a fiber-coupled Nd:YAG nonplanar ring oscillator (NPRO). With a linewidth of some kHz, the signal of this laser can be regarded as a delta peak, compared to the transmission linewidth of the grating pair [9]. This laser was tunable for some GHz by changing the temperature of the crystal. A scanning Fabry-Perot cavity with 2 GHz free spectral range was used to record the relative frequency while tuning the NPRO over the transmission spectrum of the grating arrangement. A linewidth of 1.8 GHz (FWHM) at 1064 nm and a maximum transmission of 20 % was measured (Fig. 2). At 1030 nm a linewidth of 1.87 GHz results [10].
T. J. Kane, A. C. Nilsson, and R. L. Byer, “Frequency stability and offset locking of a laser-diode-pumped Nd:YAG monolithic nonplanar ring oscillator,” Opt. Lett. 12, 175–177 (1987). [CrossRef] [PubMed]
I. Shoshan and U. P. Oppenheim, “The use of a diffraction grating as a beam expander in a dye laser cavity,” Opt. Commun. 25, 375–378 (1978). [CrossRef]
For a detuning of the filter by one FSR of the laser, the transmission reduced by 10 %. These extra losses prevented the laser from running on more than one mode, if the filter was adjusted properly.
3. Experimental results
The power spectra for different wavelengths are shown left in Fig. 3. The laser was tunable from 1020 nm to 1040 nm with only 2.5 % amplified spontaneous emission (ASE).
Fig. 3. Left: Spectra of the oscillator at different wavelengths (0.2 nm resolution of the spectrum analyzer) . Right: Output power and fraction of power within the linewidth of the laser versus wavelength.
The whole tuning range spanned from 1017 nm to 1043 nm and the output power changed due to the gain profile of the active medium with a maximum output power of 31 mW at 1030 nm. Less than 0.5 % of additional power was outside the linewidth of the laser as shown in the right graph in Fig. 3.
The combination of the 260 MHz FSR and the small spectral filter led to a stable single frequency operation of the laser, if the grating filter transmission maximum coincided with a resonator mode. The spectral behavior of the laser was measured with a scanning Fabry-Perot cavity with a free spectral range of 2 GHz and a finesse of 400 at the central laser wavelength of 1030 nm. A typical Fabry-Perot measurement is shown in the left part of Fig. 4, verifying that there was no oscillating second mode present. The measured linewidth was 5 MHz, limited by the resolution of the Fabry-Perot cavity.
Fig. 4. Left: Fabry-Perot measurement of the laser at 1030 nm. The inset shows one peak in detail. Right: Temperature dependence of the frequency of the laser.
To evaluate the thermal influence on the laser frequency, the easily accessible part of the fiber, being about one half of the total length, was positioned on a temperature controlled base plate. As shown in the right part of Fig. 4., the laser can be tuned over the free spectral range of the resonator and than exhibited a mode hop. Taking into account that only one half of the fiber was temperature controlled, the laser frequency showed a temperature dependency of 600 MHz/K corresponding to 2.4 MHz/(K*mm) or 0.4 K temperature change for a frequency change of one FSR.
This unusual small dependency of the laser against temperature-changes is a result of the short fiber length and the large FSR of the laser and strongly contributes to its stable single frequency operation. If the gratings are adjusted in between two mode hops, the laser showed no multimode instabilities as observed and described elsewhere [11,12]. On the other hand, if the gratings were adjusted to a mode hopping position, the laser showed mode hopping between the two adjacent modes or operated on both modes.
F. Fontana, M. Begotti, E. M. Pessina, and L. A. Lugiato, “Maxwell-Bloch modelocking instabilities in erbium-doped fiber lasers,“ Opt. Commun. 114, 89–94 (1995). [CrossRef]
T. Voigt, M. O. Lenz, F. Mitschke, E. Roldan, and G. J. de Valcárcel, “Experimental investigation of Risken-Nummendal-Graham-Haken laser instability in fiber ring lasers,” Appl. Phys. B 79, 175–183 (2004). [CrossRef]
In order to characterize the long term frequency drift of the laser, the Nd: YAG nonplanar ring oscillator was additionally complied to the scanning Fabry-Perot cavity as a comparably stable frequency reference (drift about 120 MHz in 3000 s) [13]. The Fabry-Perot trace was evaluated and the difference in the peak positions of the two lasers was measured every two seconds. As the laser was not completely stabilized, the laser frequency showed a long term drift up to 500 MHz over one hour, depending on the ambient conditions in the laboratory. Therefore mode hops were observed in the long term measurement of the frequency (Fig. 5, left).
P. Burdack, M. Tröbs, M. Hunnekuhl, C. Fallnich, and I. Freitag, “Modulation free sub-Doppler laser frequency stabilization to molecular iodine with a common-path, two-color interferometer,” Opt. Express 12, 644–650 (2004). [CrossRef] [PubMed]
Fig. 5. Long term measurements of the frequency drift. Left: Frequency drift at 1030 nm with modehops. Right: Modehop free operation of the laser at different wavelength over a time periode of 10 h.
However, the laser operated single frequency over a time period of 10 h in thermally steady ambient conditions. The frequency change versus time apparent in the right part of Fig. 5, was most likely caused by a small change of the laboratory temperature during the measurements, which was in the range of 0.1 K and caused a small change of the length of the resonator due to the thermal expansion of the base plate. As no stabilized frequency reference was used for the measurement, a drift of the measurement equipment can not be excluded as well.
By using the piezo actor a fine tuning has been achieved. This is shown in Fig. 6 where the piezo was operated with a triangular shaped voltage with a period of 45 s. Mode hopping occurred only between adjacent longitudinal modes resulting in a stepwise tuning process.
Fig. 6. Fine tuning characteristics. Left: Modehops measured with a 2 GHz Fabry-Perot cavity. Right: Frequency response of the laser at a slow triangular shaped fine tuning process.
The combination of the frequency tuning due to the fiber temperature and the tuning using the grating would lead to a mode hop free tuning range beyond the free spectral range of the resonator, if these two mechanisms are synchronized. To demonstrate this modehop free tuning behavior, the grating was adjusted manually during temperature tuning of the laser. This led to a large modehop free tuning over 1600 MHz as shown in Fig. 7.
Fig. 7. Modehop free tuning by synchronization of temperature tuning and grating rotation. Displayed is the actual frequency of the laser and the temperature of the temperature controlled fiber part versus time.
This continuous tuning range can be further increased by a more sophisticated synchronization technique.
4. Conclusion
In conclusion, a single-mode, single-frequency fiber laser with a maximum linear polarized output power of 31 mW and less than 0.5 % of additional power in the ASE has been demonstrated. This makes the laser an ideal source as a master oscillator for power scaling approaches as well as for all kind of measurements requiring single-frequency operation. The tuning range of 26 nm is the widest tuning range demonstrated for a single-frequency ytterbium-doped fiber laser to the best of our knowledge. Stable single frequency operation was achieved over 10 h. Additionally, the feasibility of a mode hop free tuning in the GHz range was shown.
References and links
H. M. Pask, R. J. Carman, D. C. Hanna, A. C. Tropper, C. J. Mackechnie, P. R. Barber, and J. M. Dawes, “Ytterbium-Doped Silica Fiber Lasers: Versatile Sources for 1-1.2 μm Region,” IEEE J. Sel. Top. Quantum Electron. 1, 2–13 (1995). [CrossRef] | |
D. C. Hanna, R. M. Percival, I. R. Perry, R. G. Smart, P. J. Suni, and A. C. Tropper, “Yb-doped monomode fiber laser: a broadly tunable operation from 1.010 μm to 1.162 μm and three level operation at 974 nm,” J. Mod. Opt. 37, 329–331 (1987). | |
M. Auerbach, P. Adel, D. Wandt, C. Fallnich, S. Unger, S. Jetschke, and H. R. Müller, “10 W widely tunable narrow linewidth double-clad fiber ring laser,” Opt. Express 10, 139–144 (2002). [PubMed] | |
S. Huang, G. Qin, A. Shirakawa, M. Musha, and K. Ueda, “Single frequency 1083 nm ytterbium doped fiber master oscillator power amplifier laser,” Opt. Express 13, 7113–7117 (2005). [CrossRef] [PubMed] | |
M. Ibsen, S. Y. Set, G. S. Goh, and K. Kikuchi, “Broad-Band Continuously Tunable All-Fiber DFB Lasers,” IEEE Phot. Tech. Lett. 14, 21–23 (2002). [CrossRef] | |
A. Wang, L. Feng, J. Huang, C. Gu, X. Lu, H. Ming, and J. Xie, “Tunable single-frequency ytterbium-doped fiber DBR laser,” Chin. J. Quantum Electron. 22, 607–611 (2005) | |
G. P. Agrawal and M. Lax, “Analytic evaluation of interference effects on laser output in a Fabry-Perot resonator,” J. Opt. Soc. Am. 71, 515–519 (1981). [CrossRef] | |
D. Wandt, M. Laschek, A. Tünnermann, and H. Welling, “Continuously tunable external-cavity diode laser with a double-grating arrangement,” Opt. Lett. 15, 390–392 (1997) [CrossRef] | |
T. J. Kane, A. C. Nilsson, and R. L. Byer, “Frequency stability and offset locking of a laser-diode-pumped Nd:YAG monolithic nonplanar ring oscillator,” Opt. Lett. 12, 175–177 (1987). [CrossRef] [PubMed] | |
I. Shoshan and U. P. Oppenheim, “The use of a diffraction grating as a beam expander in a dye laser cavity,” Opt. Commun. 25, 375–378 (1978). [CrossRef] | |
F. Fontana, M. Begotti, E. M. Pessina, and L. A. Lugiato, “Maxwell-Bloch modelocking instabilities in erbium-doped fiber lasers,“ Opt. Commun. 114, 89–94 (1995). [CrossRef] | |
T. Voigt, M. O. Lenz, F. Mitschke, E. Roldan, and G. J. de Valcárcel, “Experimental investigation of Risken-Nummendal-Graham-Haken laser instability in fiber ring lasers,” Appl. Phys. B 79, 175–183 (2004). [CrossRef] | |
P. Burdack, M. Tröbs, M. Hunnekuhl, C. Fallnich, and I. Freitag, “Modulation free sub-Doppler laser frequency stabilization to molecular iodine with a common-path, two-color interferometer,” Opt. Express 12, 644–650 (2004). [CrossRef] [PubMed] |
OCIS Codes
(140.3510) Lasers and laser optics : Lasers, fiber
(140.3570) Lasers and laser optics : Lasers, single-mode
(140.3600) Lasers and laser optics : Lasers, tunable
ToC Category:
Lasers and Laser Optics
History
Original Manuscript: February 15, 2007
Revised Manuscript: March 28, 2007
Manuscript Accepted: March 28, 2007
Published: April 3, 2007
Citation
Martin Engelbrecht, Axel Ruehl, Dieter Wandt, and Dietmar Kracht, "Single-Frequency ytterbium-doped fiber laser with 26 nm tuning range," Opt. Express 15, 4617-4622 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-8-4617
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References
- H. M. Pask, R. J. Carman, D. C. Hanna, A. C. Tropper, C. J. Mackechnie, P. R. Barber, and J. M. Dawes, "Ytterbium-Doped Silica Fiber Lasers: Versatile Sources for 1-1.2 µm Region," IEEE J. Sel. Top. Quantum Electron. 1, 2-13 (1995). [CrossRef]
- D. C. Hanna, R. M. Percival, I. R. Perry, R. G. Smart, P. J. Suni, and A. C. Tropper, "Yb-doped monomode fiber laser: a broadly tunable operation from 1.010 µm to 1.162 µm and three level operation at 974 nm," J. Mod. Opt. 37, 329-331 (1987).
- M. Auerbach, P. Adel, D. Wandt, C. Fallnich, S. Unger, S. Jetschke, and H. R. Müller, "10 W widely tunable narrow linewidth double-clad fiber ring laser," Opt. Express 10, 139-144 (2002). [PubMed]
- S. Huang, G. Qin, A. Shirakawa, M. Musha, and K. Ueda, "Single frequency 1083 nm ytterbium doped fiber master oscillator power amplifier laser," Opt. Express 13, 7113-7117 (2005). [CrossRef] [PubMed]
- M. Ibsen, S. Y. Set, G. S. Goh, and K. Kikuchi, "Broad-Band Continuously Tunable All-Fiber DFB Lasers," IEEE Phot. Tech. Lett. 14, 21-23 (2002). [CrossRef]
- A. Wang, L. Feng, J. Huang, C. Gu, X. Lu, H. Ming, and J. Xie, "Tunable single-frequency ytterbium-doped fiber DBR laser," Chin. J. Quantum Electron. 22, 607-611 (2005)
- G. P. Agrawal, and M. Lax, "Analytic evaluation of interference effects on laser output in a Fabry-Perot resonator," J. Opt. Soc. Am. 71, 515-519 (1981). [CrossRef]
- D. Wandt, M. Laschek, A. Tünnermann, and H. Welling, "Continuously tunable external-cavity diode laser with a double-grating arrangement," Opt. Lett. 15, 390-392 (1997) [CrossRef]
- T. J. Kane, A. C. Nilsson, and R. L. Byer, "Frequency stability and offset locking of a laser-diode-pumped Nd:YAG monolithic nonplanar ring oscillator," Opt. Lett. 12, 175-177 (1987). [CrossRef] [PubMed]
- I. Shoshan, and U. P. Oppenheim, "The use of a diffraction grating as a beam expander in a dye laser cavity," Opt. Commun. 25, 375-378 (1978). [CrossRef]
- F. Fontana, M. Begotti, E. M. Pessina, and L. A. Lugiato, "Maxwell-Bloch modelocking instabilities in erbium-doped fiber lasers," Opt. Commun. 114, 89-94 (1995). [CrossRef]
- T. Voigt, M. O. Lenz, F. Mitschke, E. Roldan, and G. J. de Valcárcel, "Experimental investigation of Risken-Nummendal-Graham-Haken laser instability in fiber ring lasers," Appl. Phys. B 79, 175-183 (2004). [CrossRef]
- P. Burdack, M. Tröbs, M. Hunnekuhl, C. Fallnich, and I. Freitag, "Modulation free sub-Doppler laser frequency stabilization to molecular iodine with a common-path, two-color interferometer," Opt. Express 12, 644-650 (2004). [CrossRef] [PubMed]
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