high-efficiency L-band erbium-doped fiber laser
3.4 Results and discussions
Several pumping schemes have been investigated in order to construct low-noise and high-gain L-band EDFA as the gain medium, and a 980nm (forward)/1480nm
is effective for improving the noise characteristics, while the backward pumping at 1480nm benefits from a better quantum conversion efficiency and gain coefficient [15].
With such a simplified EDFA, a extremely high PCE of 37% with a wavelength dependent gain deviation of 6 dB is achieved according to chapter 2.
Figure 3.3 illustrates the output laser wavelength, power, and corresponding quantum efficiency as a function of the output coupling ratio detuned by the TROC.
As a result, the wavelength of the EDFL with maximum output power can be linearly tunable from 1567 nm to 1612 nm as the output coupling ratio of the TROC detunes from 95% to 5 %, while the output power of the EDFL is monotonically decreasing from 90 mW to 7 mW, as shown in Fig. 3.3.
Fig. 3.3 The trend of lasing wavelength, output power, and quantum efficiency with detuning output coupling ratio.
It is seen that higher output coupling ratios as well as intra-cavity losses result in the EDFL lasing at shorter wavelengths. The lasing spectra of the EDFL at wavelengths corresponding to maximum output power also corroborates the maximum tuning range up to 45 nm (see Fig. 3.4).
1565 1570 1575 1580 1585 1590 1595 1600 1605 1610 1615 -40
-20 0 20
Rout = 5%
Power (dBm)
Wavelength (nm) Rout = 95%
Δλ = 0.3 nm
Fig.3.4 The lasing spectra of L-band EDFL with detuning output coupling ratio.
Previously, a similar simulating result concerning with the cavity-loss dependent tuning range of L-band EDFL system was proposed, which described a increasing sensitivity of the EDFL output power and bandwidth at lower intra-cavity losses. As the cavity-loss increases, the maximum output power and the wavelength tuning range are concurrently reduced [16]. By using the TROC based coupling ratio detuning technique, our experimental results not only correlate well with the theoretical observation, but also demonstrate the coupling-ratio dependent peak EDFL wavelength shifting phenomenon. These results sophisticate the operation of a widely tunable L-band EDFL since the minimizing in intra-cavity loss may achieve an extremely large tuning range at a scarification on output power of the EDFL, as shown in Fig. 3.4.
Nonetheless, an accurate and repeatable wavelength selection is easily achieved with precise control on the output coupling ratio. In experiment, a minimum wavelength tuning resolution of 0.3 nm can be obtained under a change in coupling ratio of 0.6%, corresponding to tuning slope of 0.5 nm/%. On the other hand, the theoretical simulation also interpreted that the maximum tuning range of the L-band EDFL is
and stable output power associated with a maximum quantum efficiency of up to 42%
is obtained at an output coupling ratio of 0.9, as shown in Fig. 3.3. Even at a low-output and wide-band tunable condition with coupling ratio of only 10 %, the corresponding quantum efficiency of 8% can be still comparable with previous results [16, 17].
Each output channel exhibits the power of greater than 18.4 dBm and the maximum of 19.6 dBm at output coupling ratio of 90% is observed under the pumping power of 217.5 mW, as shown in Fig. 3.5. Such a deviation of 1.2 dB is already smaller than the best value of 1.5 dB in previous reports [9]. Moreover, a highly stable output with power variation of 0.036mW (0.04%) is obtained during a monitoring interval over 10 min, as shown in the right inset of Fig. 3.6.
1570 1580 1590 1600 1610
18.0 18.5 19.0 19.5 20.0
Power (dBm)
Wavelength (nm)
ΔP < 1.2 dB
Fig. 3.5 Wavelength dependent output power at 90% output coupling ratio.
0 100 200 300 400 500 600 89.0
89.5 90.0
Power (mW)
Time (s)
ΔP/P = 0.04%
Fig. 3.6 Power stability of the L-band EDFL measured within 10 minutes.
The tuning range and resolution of lasing wavelength was mainly determined by the gain profile of the EDF since dynamic range on the coupling ratio of the TROC is nearly 100% in our case. The EDFL is unable to operate in the C-band with insufficient gain as the design of the specific EDF which benefits from a better transition of the power from C-band to L-band. Note that the lasing linewidth of the EDFL output can be further narrowing from 0.05 nm to 0.02 nm by simply inserting an tiny air-gap between the FC/PC connectors of fiber patch cord, which functions as a intra-cavity Fabry-Perot filter in the cost-effective L-band EDFL system, as shown in Fig. 3.7. The measured linewidth maybe somewhat limited by the commercial optical spectrum analyzer (Ando AQ6317B). Figure 3.8 shows the variation of 3-dB spectral linewidth when the spacing of air-gap is detuned, and the inset is the scheme of air-gap.
Such a system benefits from not only the simplified wavelength tuning technique but also the cost-effective solution to the full L-band fiber laser systems.
1605.3 1605.4 1605.5 1605.6 0.0
0.2 0.4 0.6 0.8 1.0
Power (.a.u.)
Wavelength (nm)
Fig. 3.7 The lasing linewidth without (hollow circle) or with (solid square) an air-gap inserting between FC/PC fiber connectors.
2 4 6 8 10
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Δλ (nm)
Air-gap spacing (mm)
Fig 3.8 The variation of the 3-dB spectral linewidth when the spacing of air-gap is detuned.
3.5 Conclusions
We have experimentally investigated and demonstrated an output-coupling-ratio controlled, full long-wavelength-band erbium-doped fiber ring laser by using a bi-directionally dual-wavelength pumped EDFA in close-loop with a tunable ratio optical coupler. The L-band EDFL is wavelength-tunable from 1567 nm to 1612 nm
at a maximum quantum efficiency of 42%, respectively with ultra-high power conversion efficiency of 37%, comparable gain of 34 dB, and maximum output power of up to 91mW. The minimum wavelength tuning resolution of 0.3 nm is achieved under the maximum wavelength tuning range of up to 45 nm covering whole L-band, while a low channel power variation of <1.2dB and a stable output with 0.04% power fluctuation is observed.
3.6. APPENDIX A
In this appendix we show the derivation of Eq. (14) from Eq. (13). Let us consider two positive functions y(λ) and w(λ) and let us suppose that we intend to solve
max [ ( )λ y λ +Aw( )] 0.λ = (A1) From Eq. (13), the quantities appearing in Eq. (Al) can be identified as
[ ]
Since the laser can operate only if the gain at complete inversion exp[g(λ)L] is greater that the cavity loss ΓTOT(λ), then y(λ) is a positive function.
Condition (Al) is equivalent to the following set of relations:
( ) ( ) 0,
where the primes indicate derivation with respect to λ.
Equation (A2) indicates that, for a given wavelength λ, the laser reaches the oscillation threshold. In fact, with y(λ) + Aw(λ) being the net gain coefficient, Eq.
(A2) has to be null. Equation (A3) and inequality (A4) serve to yield the wavelength A that maximizes the gain.
From Eq. (A2) we get A = - y(λ)/w(λ) and hence, bymaking use of Eq. (A3),
where we used relations (A2), (A4), and (A5).
This result proves that we can find the maximum in Eq. (Al), i.e., in Eq. (13), by maximizing y(λ)/w(λ), or, equivalently, by minimizing A = - y(λ)/w(λ) as in Eq. (14).
3.7 References
[1] Y. Sun, J. W. Shlhoff, A. K. Srivastava, J. L. Zyskind, T. A. Strasser, J. R.
Pedrazzani, C. Wolf, J. Zhou, J. B.Judkins, R. P. Espindola, and A. M.
Vengasarkar, “80nm ultra-wideband erbium-doped silica fibre amplifier,”
Electron. Lett., vol. 33, 1965-1967 (1997).
[2] S. M. Zhang, Y. F. Lu, X. F. Yang, F. J. Dong, H. J. Wang, and X. Dong,
“Wavelength tunable linear cavity cladding pump Er3+/Yb3+ co-doped fiber laser operating in L-band,” Opt. and Quantum Electron., vol. 37, 417-424 (2005).
[3] T. A. Haddud, M. H. Al-Mansoori, A. K. Zamzuri, S. Shaharudin, M. K.
Abdullah, and M. A. Mahdi, “24-Line of Brillouin-Erbium Fiber Laser Utilizng Fabry-Perot Cavity in L-band,” Microwave Opt. Techno. Lett., vol. 45, 165-167
[4] S. W. Harun, and H. Ahmad, “Multiwavelength Laser Comb in L-band Region with Dual-Cavity Brillouin/Erbium Fiber Laser,” Jpn. J. Appl. Phy., vol. 41, L1234-L1236 (2002).
[5] Q. H. Mao, and W. Y. Lit, “Optical Bistability in an L-Band Dual-Wavelength Erbium-Doped Fiber Laser with Overlapping cavities,” IEEE Photon. Technol.
Lett., vol. 14, 1252-1254 (2002).
[6] H. Chen, M. Leblanc, G. W. Schinn, “Gain enhanced L-band optical fiber amplifiers and tunable fiber lasers with erbium-doped fibers,” Opt. Commun., vol.
216, 119-125 (2003).
[7] Q. H. Mao, and W. Y. Lit, “Widely tunable L-band erbium-doped fiber laser with fiber Bragg gratings based on optical bistability,” App. Phys. Lett., vol. 82, 1335-1337 (2003).
[8] X. H. Feng, Y. G. Liu, S. H. Yuan, G. Y. Kai, W. G. Zhang, and X. Y. Dong,
“L-Band switchable dual-wavelength erbium-doped fiber laser based on a multimode fiber Bragg grating,” Opt. Express, vol. 12, 3834-3839 (2004).
[9] M. Melo, O. Frazao, A. L. J. Teixeira, L. A. Gomes, J. R. Ferreira da rocha, and H. M. Salgado, “Tunable L-band erbium-doped fibre ring laser by means of induced cavity loss using a fibre taper,” Appl. Phys. B, vol. 77, 139-142 (2003).
[10] J. Lee, U. C. Ryu, S. J. Ahn, and N. Park, “Enhancement of Power Conversion Efficency for an L-band EDFA with a Secondary Pumping Effect in the Unpumped EDF Section,” IEEE Photon. Technol. Lett., vol. 11, 42-44 (1999).
[11] P. Franco, M. Midrio, and A. Tozzato, “Characterization and optimization criteria for filterless erbium-doped fiber lasers,” J. Opt. Soc. Am. B, vol.11, 1090-1097 (1994).
[12] E. Desurvire and J. R. Simpson, “Amplification of spontaneous emission in erbium-doped single-mode fibers,” IEEE J. Lightwave Technol., vol. 7, 835 (1989).
[13] A. E. Siegman, “An Introduction to Lasers and Masers(McGraw-Hill, New York, 1971)”.
[14] C. R. Giles and D. DiGiovanni, “Spectral dependence of gain and noise in erbium doped fiber amplifiers,” IEEE Photon. Technol. Lett., vol. 2, 797 (1990).
[15] H. Ono, M. Yamada, T. Kanamori, S. Sudo, and Y. Ohishi, “1.58-μm Band Gain-Flattened Erbium-Doped Fiber Amplifier for WDM Transmission Systems,” J. Lightwave Technol., vol. 17, 490-496 (1999).
[16] X. Y. Dong, P. Shum, N. Q. Ngo, H. Y. Tam, X. Y. Dong, “Output Power Characteristics of Tunable Erbium-Doped Fiber Ring Lasers,” J. Lightwave Technol., vol. 23, 1334-1341 (2005).
[17] S. Q. Yang, C. L. Zhao, H. Y. Meng, L. Ding, X. O. Dong, S. H. Yuan, G. Y.
Kai, and Q. D. Zhao, “Wavelength tunable erbium-doped fiber ring laser operating in L-band,” Opt. and Quantum Electron., vol. 35, 69-73 (2003).