1. Single and dual wavelength Er:Yb double clad fiber lasers
B. Ibarra-Escamilla, M. Durán-Sánchez, R. Álvarez-Tamayo, and E. A. Kuzin
Instituto Nacional de Astrofísica, Óptica y Electrónica MEX
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

2. Outline Introduction Conclusions Q-Switching Technique
Q-Switched Fiber Laser Configurations
Conclusions
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

3. Outline Introduction Conclusions Q-Switching Technique
Q-Switched Fiber Laser Configurations
Conclusions
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

4. Introduction
Fiber lasers are attractive because the beam quality, systems compactness and quantum efficiency.
Q-switching and mode-locking are the two main techniques enabling pulsed lasers.
With mode-locking technique it is possible to generate pulsed lasers with typical duration ranging from tens of ps to fs.
With Q-switched fiber lasers it is possible to generate pulsed lasers in the range of ns.
Considering double clad fibers it is possible to get very efficient high power and high energy short pulse generation.
The development of new fiber laser systems is of great interest for specific applications especially for eye-safe atmospheric transmission in free space optical communication and active remote sensing, medical, sensing and spectroscopy.
Our main motivation for our work is its potential application for tunable sources with mW output power for spectroscopy and THz applications.
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

5. Outline Introduction Conclusions Q-Switching Technique
Q-Switched Fiber Laser Configurations
Conclusions
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

6. Q-Switching Technique
Q-switched is an effective method to obtain giant short pulses from a laser.
In a Q-switching operation, the cavity loss kept at high level until the pumped gain medium has stored a certain amount of energy.
The cavity loss is then quickly reduced to a small value, which allows the intense stimulated laser radiation to establish quickly in the cavity.
A short optical pulse is finally released and its energy can be in the mJ to J range.
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

7. The most common type is an acousto-optic modulator (AOM).
A Q-Switch is a device which can be quickly switched between states from high to very low losses.
The most common type is an acousto-optic modulator (AOM).
Both output pulse energy and pulse duration depend on the cavity loss and the energy stored in the gain medium that is related to the pump power and the repetition rate.
The pulse duration achieved with Q-switching is typically in the ns range (corresponding to several cavity round trips).
The pulse repetition rate is usually in the range from 100s of Hz to 100s of kHz.
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

8. Outline Introduction Conclusions Q-Switching Technique
Q-Switched Fiber Laser Configurations
Conclusions
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

9. Double-clad Er-Yb doped high power fiber laser
DM2
Output f1
DM3 f2 f4
Pump Laser
PM-Er:Yb Fiber DG
l/2 P f3
DM1
B. Ibarra-Escamilla, et al., “Wavelength tunable double-clad Er:Yb doped high power fiber laser”, Laser Physics 21 (11) (2011)
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

10. L = 2.5 m
L = 3.6 m
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

11. Actively Q-Switch Er/Yb fiber laser
7.5o
The length of the resonator is ~5 m.
The gain medium is 3 m.
The size of the AOM crystal is 3 mm.
The effective diameter is 1.5 mm for the AO crystal.
The distance between the front surface of the L3 and the DM2 is 230 mm.
L1 18 mm and L2 8 mm focal length.
DM1 & DM2 have high transmission at 1064 nm and high reflection at 1550 nm.
Sagnac loop mirror (~100% reflection mirror).
The 3 dB coupler is the output laser.
Both ends of the AOM are antireflection coated at 1550 nm.
A. González-García, et al. “High efficiency, actively Q-switched Er/Yb fiber laser”, Optics and Laser Technology 48 (2013)
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

12. Average output power (W)
Pump Power (W)
Pump power against average output power for 3 m Er/Yb double-clad fiber laser at repetition rate of 120 kHz.
Variation of the output power and pulse duration with repetition rate
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

13. Pump power Pp = 8.1 W
The pulse duration of the Q-switched laser is 34 ns. The pulse profile is asymmetric with a sharp rising edge and a slow falling edge as well as a long decaying tail.
Scope trace of the pulse train from Q-switched fiber laser operating at 120 kHz.
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

14. Tunable Q-Switch Er/Yb fiber laser with FBG
Both ends of the AOM are antireflection coated at 1550 nm.
The FBG, was placed on a 2×10 cm plate, and was adjusted with a micrometric screw.
DM1 & DM2 have high transmission at 1064 nm and high reflection at 1550 nm.
Fiber Bragg grating (~100% reflection mirror at nm).
The 3 dB coupler is the output laser.
The length of the resonator is ~8 m.
The gain medium is 3 m.
A. González-García, et al. “Compact wavelength-tunable actively Q-switched fiber laser in CW and pulsed operation based on a fiber Bragg grating”, Laser Physics 25 (2015)
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15. Compression
Stretch
Compression
Stretch
Tuning of cw fiber laser for compression/stretch (the tuning was ~12 nm), bandwidth line ~0.17 nm.
Tuning of the pulsed fiber laser for compression/stretch (the tuning was ~12 nm), bandwidth line ~0.47 nm.
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

16. Pulse duration of 420 ns. Average optical power of 1.03 W.
Characteristic of the train of pulses for the laser emitting at nm (120 kHz).
Pulse duration of 420 ns. Average optical power of 1.03 W.
Characteristic of the average power and pulse duration as a function of pump power at 120 kHz.
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

17. Tunable Q-Switch Er/Yb fiber laser with PM-FBG
Pump laser
DM1
1064/1550nm
Er/Yb 3m
SMF 1m
90/10
Coupler PC
PM-FBG 1549nm
DM2
1064/1550 nm
AOM
OSA
Oscilloscope
Photodetector L1 L2 L3
976nm
Monochromador
M. Durán-Sánchez, et al., “Tunable dual-wavelength actively Q-Switched Er/Yb double-clad fiber laser”, Laser Physics Letters 11 (2014)
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

18. 2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

19. 2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

20. Tunable Q-Switch Er/Yb fiber laser with FOLM
50/50 coupler
FBG 1538nm
OSA
Oscilloscope
Photodetector
976nm
AOM
Er/Yb 3m
FBG nm
Combiner RF
Hi-Bi Fiber
Peltier
Temperature controller X
M. Durán-Sánchez, et al., “Actively Q-switched dual-wavelength laser with double-cladding Er/Yb-doped fiber using a Hi-Bi Sagnac interferometer”, Laser Physics Letters 12 (2015)
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

21. Temperature increase
R.I. Álvarez-Tamayo, et al., “Theoretical and experimental analysis of tunable Sagnac Hi-Bi loop filter for dual-wavelength laser application,” Applied Optics, 50 (3) (2011).
M. Durán-Sánchez, et al., “Fine adjustment of cavity loss by Sagnac loop for a dual wavelength generation,” Laser Physics, 20 (5) (2010).
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

22. 2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

23. Dual Q-Switch Er/Yb fiber ring laser
Experimental setup for actively Q-switched dual wavelength ring cavity fiber laser.
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

24. Spectrum measurements for dual-wavelength actively Q-switched laser operation, (a) Different generated wavelengths separation tuning with fixed repetition rate, (b) Generated laser lines with wavelength separation of 1 nm and repetition rate variations.
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

25. Q-switched dual wavelength operation with wavelength separations of 1 nm and 4 nm on repetition rate variations, (a) pulse duration and pulse energy, (b) pulses peak power .
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

26. Outline Introduction Conclusions Q-Switching Technique
Q-Switched Fiber Laser Configurations
Conclusions
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016

27. Conclusions
We used an Er/Yb co-doped, double-clad, single-mode fiber as again medium an AOM as Q-switch to setup a compact Q-switched fiber laser. We present six configurations:
For the second configuration we demonstrated a double-clad Er:Yb wavelength-tunable fiber laser. With this configuration we can tune the wavelength from 1535 to 1567 nm using a diffraction grating.
For the first configuration the average output power of the laser was 4.0 W at maximum pump power of 8.1 W, with a pulse duration of 34 ns.
For the third configuration the average output power of the laser was 1.03 W at maximum pump power of 8.62 W, with a pulse duration of 420 ns. The operational wavelength of the laser cavity can be tuned using a FBG.
For the fourth configuration double or single wavelength operation is determined by the adjustment of the PC. The laser operate at repetition rate from 30 to 110 kHz with pulse durations of 280 ns and pulse energy near 0.5 mJ.
For the fifth configuration single- and dual-wavelength laser operation is achieved adjusting the internal cavity losses by Hi-Bi fiber loop temperature variations. The minimum pulse duration was 280 ns and the maximum pulse energy was 1.75 mJ.
For the sixth configuration we present a ring cavity dual wavelength actively Q-switched fiber laser based in the use of fiber Bragg gratings for wavelengths selection.
2nd Global Optometrist Meeting and Trade Fair on Laser Technology, July 28-29, 2016