Original Text © Astro, Ltd., 2011.
1
1. INTRODUCTION
Recently, erbiumdoped fiber (EDF) ring lasers with multiwavelength operation have much consider able interest in the wavelengthdivisionmultiplexing (WDM) communication systems and fiberoptics sen sor applications. However, the maximum number of lasing wavelength only could reach two or three because of the homogeneous broadening characteris tic of EDF [1–3]. Hence, to overcome the limitation of primarily homogeneous broadening of EDF at room temperature, several methods have been studied and investigated [1–6]. Using an independent gain segment was the most straightforward method to for each wavelength, where EDF ring lasers may be achieved by pumping with appropriate wavelength multiplexing and demultiplexing [4, 7], However, most of the approaches resulted in inhomogeneity in a single EDF, when various elements such as acousto optic frequency shifters, comb or interferometer fil ters, array waveguide grating (AWG), nonlinear soli ton, highbirefringence fiber loop mirror, intracavity loss optimization and Sagnac loop reflectors were used inside gain cavity [2, 8–18]. To enhance the stability of the multiwavelength EDF lasers, many different techniques of reducing mode competition, such as cooling the EDF at 77 K, introducing active overlap ping linear cavities, using the polarization hole burn ing principle, and using Fabry–Perot laser diode (FP LD) with Sagnac loop, have been investigated [5, 19–
1 The article is published in the original.
21]. In addition, using selfinjected FPLD and satu rableabsorber filter (SAF) could achieve the broad band and singlelongitudinalmode (SLM) operation [22–25].
In this study, a stable and tunable dualwavelength EDF dualring laser is proposed and experimentally investigated. Here, two tunable filters are used inside the dualring gain cavity to generate dualwavelength lasing. And, due to the gain competition of the EDF gain cavity, the modespacing (Δλs) of lasing dual wavelength will be limited at different operating wave lengths. Hence, the minimum and maximum mode spacing in the proposed EDF laser scheme are obtained at 0.75 and 15.35 nm, respectively, in Cband operation. Moreover, the stability performances of fiber laser have also been demonstrated and analyzed.
2. EXPERIMENT AND DISCUSSIONS Figure 1 shows the experimental setup of proposed tunable dualwavelength EDF dualring laser config uration. The proposed fiber laser scheme was con structed by an erbiumdoped fiber amplifier (EDFA), two 1 × 2 optical couplers (OCPs), two polarization controllers (PCs), and two tunable bandpass filters (TBFs). The EDFA consisted of a 10 m long EDF, two optical isolators (OISs), a 1550/980 nm WDM cou pler (WCP) and a 980 nm pumping laser diode with 76.4 mW output power to serve as a gain medium. In the experiment, we used two 1 × 2 OCPs to produce dualring scheme and two TBFs were utilized inside
OPTICS
Simple ErbiumDoped DualRing Fiber Laser Configuration
for Stable and Tunable Dualwavelength Output
1C. H. Yeha, *, C. W. Chowb, B. C. Chengc, J. H. Chend, and K. H. Chene
a Information and Communications Research Laboratories, Industrial Technology Research Institute (ITRI), Hsinchu 31040, Taiwan
b Department of Photonics and Institute of ElectroOptical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
c Department of Physics, Fu Jen Catholic University, New Taipei 24205, Taiwan d Department of Photonics, Feng Chia University, Taichung 40724, Taiwan e Department of Electrical Engineering, Feng Chia University, Taichung 40724, Taiwan
*email: yeh1974@gmail.com, depew@itri.org.tw
Received March 12, 2011; in final form, March 21, 2011; published online August 3, 2011
Abstract—We propose and experimentally investigate a stable and tunable dualwavelength erbiumdoped fiber (EDF) dualring laser scheme. Here, two tunable bandpass filters (TBFs) are used inside the dualring gain cavity to generate dualwavelength lasing. And, due to the gain competition of the EDF gain cavity, the modespacing (Δλs) of lasing dualwavelength will be limited at different operating wavelengths. Hence, the minimum and maximum modespacing in the proposed EDF laser scheme are 0.75 and 15.35 nm in Cband range. Besides, the output performances of proposed fiber laser have also been studied and analyzed. DOI: 10.1134/S1054660X11170300
the gain cavity to generate dualwavelength output. The wavelength tuning ranges and 3 dB bandwidths of two TBFs were both 35 nm (1525 to 1560 nm) and 0.4 nm. Besides, the two PCs were used to adjust the properly polarization status and obtain maximum out put power of lasing dualwavelength. In the measure ment, we used an optical spectrum analyzer (OSA) with a 0.05 nm resolution to measure the lasing dual wavelength.
Figure 2 presents the gain spectrum of EDFA used in the measurement, when the injected power of probe wavelength was –20 dBm the wavelength range of 1524 to 1568 nm. We could also observe the gain value of >20 dB in the operating wavelength bandwidth. Thus, to realize the output characteristic of lasing dualwavelength in the proposed fiber laser, first we fixed the passband of TBF2 at the wavelength of 1560.35 nm (λ2). Then, we varied and tuned the pass band of TBF1 from 1560.35 nm to the shorter wave lengths gradually in order to generate different mode spacing (Δλ) of lasing dualwavelength. Hence, Fig. 3 shows the output spectra of lasing dualwavelength in the proposed fiber laser while the TBF1 is tuned to shorter wavelengths. When the TBF1 is tuned to 1551.45 nm, we can observe the first dualwavelength lasing at 1551.45 and 1560.35 nm (modespacing Δλs= 8.9 nm) with –15.1 and –17.2 dBm peak pow ers, respectively, as shown in Fig. 3. And then, when the passband of TBF1 was shifted to shorter wave lengths, the lasing wavelength (λ1) via a TBF1 only could be generated at the wavelength λ1 of 1551.75, 1540.05, 1536.35, and 1532.25 nm with the peak power of ⎯49.6, –60.8, –62.7, and –68.6 dBm, respectively. At this time, the peak power of fixed wavelength λ2 was both kept at –12.9 dBm. As illus
trated in Fig. 3, we can obtain the measured power variations (ΔPs) of five dualwavelengths, which are 1.7, 36.7, 48.1, 49.8, and 55.7 dB, respectively, increasing fast while the TBF1 is tuned to shorter wavelengths. And the corresponding modespacing of the five lasing dualwavelengths are 8.9, 8.7, 20.3, 24.0, and 28.1 nm, respectively. As mentioned before, we know that the lasing dualwavelength cannot be selected and tuned arbitrarily via the two TBFs. This is because the gain competition, of Er+ in the proposed laser scheme.
In the measurement, we could fix the TBF2 at dif ferent passbands in the effectively gain range of EDFA used to generate λ2, and then we varied the TBF1 to produce properly λ1 for dualwavelength lasing of the proposed EDF laser. And, the tuning step of TBF2 was 2 nm from 1538.35 to 1556.35 nm. Besides, we defined the modespacing (Δλs), which was equal to (λ1 – λ2), and the measured power difference (ΔP) of dualwave length must be less than 2.2 dB in the measurement. Therefore, Fig. 4 shows the different modespacing of lasing dualwavelength, having the ΔP within 2.1 dB, when the wavelength λ2 is placed at the wavelength range of 1538.35 to 1560.35 nm with 2 nm tuning step. In Fig. 4, we can observe the maximum and minimum modespacing are 15.35 and 0.75 nm when the λ2 are both kept at 1550.35 nm. Moreover, when the wave length λ2 is set at 1538.35, 1546.35, 1558.35, and 1560.35 nm, respectively, only we can get a set of dual wavelength lasing, as seen in Fig. 4. In addition, Fig. 5 also presents the output spectra of related dualwave lengths in accordance with the measured results of Fig. 4. PC PC TBF 2 TBF 1 OCP Output OIS WCP EDF OIS 980 nm LD
Fig. 1. Experimental setup of proposed EDF dualring
laser configuration. 23 21 19 17 15 1515 1525 1535 1545 1555 1565 1575 Wavelength, nm Pin = −20 dBm
Fig. 2. Measured gain spectrum of EDFA used in the mea
surement when the injected power of probe wavelength was –20 dBm the wavelength range of 1524 to 1568 nm.
To realize the relationship of pumping power of 980 nm laser diode and output power of dualwave length in the proposed EDF laser, we set the two lasing
wavelengths at 1556.35 (λ1) and 1547.40 nm (λ2) with ⎯10.0 and –10.4 dBm peak powers initially, when the pumping power was 76.4 mW. And so, Fig. 6 shows the different pumping power versus two output powers of dualwavelength. The threshold pumping power was around 29.8 mW for the proposed dualwavelength fiber laser, as shown in Fig. 6. We can also obtain the power difference of dualwavelength between 0.03 and 1.46 dB under the pumping power of 29.8 to 76.4 mW. Finally, we investigated and experimentally dis cussed the stability performances of output wavelength and power in the proposed dualwavelength EDF ring laser. In this experiment, we also set the lasing dual wavelength at 1556.35 (λ1) and 1547.40 nm (λ2) with ⎯10.0 and –10.4 dBm peak powers initially, when the pumping power was operated at 76.4 mW. First, we can observe the maximum wavelength variation and power fluctuation of dualwavelength are 0 nm and 1.5 dB after 30 min shortterm observation time, as shown in Fig. 7a. Besides, Fig. 7b also shows the corresponding modespacing (Δλs) and power difference (ΔP) of dualwavelength in the observation time of 30 min. And, the measured Δλs is no change keeping at 8.75 nm and the ΔP is between 0.3 and 2.1 dB under the observingtime. 0 −10 −20 −30 −40 −50 −60 −70 1530 1540 1550 1560 1570 Wavelength, nm Power, dBm
Fig. 3. Output spectra of lasing dualwavelength in the proposed fiber laser while the passband of TBF2 at the wavelength of
1560.35 nm and the TBF1 is tuned to shorter wavelengths.
12 8 4 0 −4 −8 −12 −16 −20 1536 1542 1548 1554 1560 Fixed wavelength λ2, nm Mode spacing Δλs, nm (Varying λ1)
Fig. 4. Measured different modespacing of lasing dual
wavelength, having the ΔP within 2.1 dB, when the wave
length λ2 is placed at the wavelength range of 1538.35 to
3. CONCLUSIONS
We have proposed and experimentally investigated a stable and tunable dualwavelength EDF dualring laser source. Here, two TBFs were used inside the dualring gain cavity to produce dualwavelength las
ing. Furthermore, due to the gain competition of the EDF gain cavity, the modespacing (Δλs) of dual wavelength could be limited at different wavelength locations. And, the minimum and maximum mode spacing in the proposed laser scheme are 0.75 and 0 −20 −40 −60 −80 1550 1555 1560 1565 15701 2 3 4 Samp le Wavelength, nm Power, dBm
Fig. 5. Output spectra of related dualwavelengths in accordance with the measured results of Fig. 4.
0 −10 −20 −30 −40 −50 −60 −70 30 40 50 60 70 80 2.0 1.5 1.0 0.5 0 −0.5 −1.0 λ1 λ2 ΔP Pumping power, mW Power difference, dB Output power, dBm Mode spacing 8.95 nm
Fig. 6. Measured different pumping power versus two output powers of dualwavelength at the wavelengths of 1556.35 (λ1) and
15.35 nm in Cband operation. The power difference (ΔP) of dualwavelength could be kept within 2.2 dB in the entire tuning steps. Besides, the output stabili ties of proposed EDF ring laser have also been studied and analyzed.
REFERENCES
1. J. N. Maran, S. LaRochelle, and P. Besnard, Opt. Lett. 28, 2082 (2003).
2. G. Das and J. Lit, IEEE Photonics Technol. Lett. 16, 60 (2004).
3. C. S. Kim, F. Farokhrooz, and J. Kang, Opt. Lett. 29, 1677 (2004).
4. T. Miyazaki, N. Edagawa, S. Yamamoto, and S. Alciba, IEEE Photonics Technol. Lett. 9, 910 (1997).
5. Y. G. Liu, X. Feng, and S. Yuan, Opt. Express 12, 2056 (2004).
6. M. Z. Zulkifli. N. A. Hassan, N. A. Awang. Z. A. Ghani, S. W. Harun, and H. Ahmad, Laser Phys. Lett. 7, 673 (2010).
7. P. S. André, R. N. Nogueira, A. L. J. Teixeira, M. J. N. Li ma, J. F. da Rocha, and J. L. Pinto, Laser Phys. Lett. 1, 613 (2004).
8. A. Bellmare, M. Karasek, M. Rochette, and S. LaRo chelle, J. Lightwave Technol. 18, 825 (2000).
9. J. Vasseur, M. Hanna, J. Dudley, and J. Goedgebuer, IEEE Photonics Technol. Lett. 16, 1816 (2004). 10. A. P. Luo, Z. C. Luo, and W. C. Xu, Laser Phys. 20,
1814 (2010).
11. M. R. A. Moghaddam, S. W. Harun, S. Shahi, K. S. Lim, and H. Ahmad, Laser Phys. 20, 516 (2010).
12. A. W. AlAlimi, M. H. AlMansoori, A. F. Abas, M. A. Mahdi, M. Ajiya, and F. R. Mahamd Adikan, Laser Phys. 20, 2001 (2010).
13. H. B. Sun, X. M. Liu, Y. K. Gong, X. H. Li, and L. R. Wang, Laser Phys. 20, 522 (2010).
14. A. A. Latif, M. Z. Zulkifli, N. A. Awang, S. W. Harun, and H. Ahmad, Laser Phys. 20, 2006 (2010).
15. A. A. Latif, M. Z. Zulkifli, N. A. Hassan, S. W. Harun, Z. A. Ghani, and H. Ahmad, Laser Phys. Lett. 7, 597 (2010).
16. H. Ahmad, M. Z. Zulkifli, A. A. Latif, and S. W. Harun, Laser Phys. Lett. 7, 164 (2010).
17. W. C. Chen, Z. C. Luo, and W. C. Xu, Laser Phys. Lett. 6, 816 (2009).
18. A. W. AlAlimi, M. H. AlMansoori, A. F. Abas, M. A. Mahdi, and M. Ajiya, Laser Phys. Lett. 6, 727 (2009).
19. S. Yamashita and K. Hotate, Electron. Lett. 32, 1298 (1996).
20. Q. H. Mao and J. Lit, J. Lightwave Technol. 21, 160 (2003).
21. C.H. Yeh, F.Y. Shih, C.T. Chen, C.N. Lee, and S. Chi, Laser Phys. Lett. 5, 210 (2008).
22. Q. Wang and Q. X. Yu, Laser Phys. Lett. 6, 607 (2009). 23. C. H. Yeh, F. Y Shih, C. H. Wang, C. W Chow, and
S. Chi, Laser Phys. Lett. 5, 821 (2008).
24. A. W. AlAlimi, M. H. AlMansoori, A. F. Abas, M. A. Mahdi, F. R. M. Adikan, and M. Ajiya, Laser Phys. 19, 1850 (2009).
25. C. H. Yeh and C. W. Chow, Laser Phys. Lett. 7, 158 (2010). 1558 1556 1554 1552 1550 1548 1546 9 8 7 6 5 0 6 12 18 24 30 10 −8 −9 −10 −11 −12 2.8 2.1 1.4 0.7 0 Time, min Δλ , nm Wavelength, nm Δ P , dB Output power, dBm Pumping power: 76.4 mW λ1 λ2 P1 P2
Fig. 7. (a) Output wavelength variation and power fluctua
tion of dualwavelength after 30 min shortterm observa
tion time when the dualwavelength is set at 1556.35 (λ1)
and 1547.40 nm (λ2) with –10.0 and –10.4 dBm peak
powers initially and the pumping power was operated at
76.4 mW. (b) The corresponding modespacing (Δλs) and
power difference (ΔP) of dualwavelength in the observa
tion time. (a)
