12 / CLE0'99 / MONDAY MORNING wide broad stripe laser diode, generated 3.3 W in a single pass configuration and 3.0 W as a tunable fiber laser. An electrical-to-optical power conversion efficiency of 34% was measured. This work was supported by the Office of Naval Research. The authors thank David Mehuys of SDL Inc. for providing the broad stripe laser diode. *Sandia National Laboratories, Combustion Research Facility, Livermore, California 945510969 USA 1. H. Po, et al., Electron. Lett. 29, 1500 (1993). 2. J.D. Minelly, et al., IEEE Photon. Tech. Lett. 5,301 (1993). 3. M. Muendel, et al., Conference on Lasers and Electro-optics, CPD30-2, 1997. 4. H. Zellmer, et al., Optics Lett. 20, 578 (1995). 5. V. Gapontsev, et al., CLEO, Anaheim, June 1996, paper CTuU3. 6. S.V. Chernikov, et al., Electr. Lett. 33, 787 (1997). 7. M. Muendel, et al., Conference on Lasers and Electro-Optics, CPD30-2, 1997. 8. J.P. Koplow, etal., IEEE Photon. Technology Lett. 10,793 (1998). 9. S. O'Brien, et al., Electron. Lett. 33, 1869 (1997).
DBGs
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Mid-stage filters. The configurations are (a) 01, (b) WBBG, 1 0 1 (c) WBBG 2 OIs, (d) DBGs, OC. CMCZ Fig. 2.
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Experimental investigation of erbiumdoped fiber amplifier gain equalization schemes using short-period Bragg gratings
Martin Rochette,* Sophie LaRochelle, Martin Guy,** Jocelyn Lauton,** Franqois Trepanier,** COPL, Lava1 University, Department of Electrical and Computer Engineering, Quebec, Canada, GlK 7P4; E-mail:
[email protected] Gain equalization has become a necessity for in-line Erbium-doped fiber amplifiers (EDFAs) in long-haul Wavelength Division Multiplexing (WDM) systems. In this paper, we use spectrally designed Bragg gratings in the midstage section of a dual-stage amplifier to perform gain equalization. These gratings are easily fabricated using a previously described writing technique with a chirped phase mask.' The dual-stage amplifier used in the experiment is presented in Fig. 1. Various filters [Figs. 2(a) to 2(d)] types are inserted in the mid-stage section to compare flatness and noise-figure performances: (a) an optical isolator (01) as the non-equalized reference, (b) an optical isolator followed by a spectrally designed WideBand Bragg Grating (WBBG), (c) a WBBG with an optical isolator on input and output
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CMCZ Fig. 1.
stage filter.
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Dual-stage amplifier with mid-
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Electrically tunable efficient broadband long-period fiber grating filter
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Bragg gratings. Add/drop functions could also be implemented at port 2 of the optical circulator. Such DBGs scheme results in a multifunction amplifier.2 Finally, noise-figure penaltyis below the -CO. 15dB error margin in both the DBGs and WBBG, 2 01s experiments. In conclusion, the results presented in this paper clearly demonstrate that short-period Bragg gratings can provide an effective way to achieve gain equalization of optical amplifiers for WDM systems. *Workperformed while at I N 0 **INO, 369 Franquet, Sainte-Foy, Qutbec GIP 4N8; E-mail:
[email protected] 1. M. Guy, J. Lauzon, D. Asselin, M. Pelletier, P. Verville, Technical digest ECOC'97, Edinburgh, UK, 1997. 2. M. Rochette, M. Guy, J. Lauzon, S. LaRochelle, F. Trepanier, Technical digest ICAPT'98, Ottawa, Canada, 1998.
CMCZ Fig. 3. Gain of the different amplifier
configurations. filter ports and (d) an optical circulator (OC) with a cascade of Discrete Bragg Gratings (DBGs) in port 2. The interest with mid-stage filtering is that the losses incurred by this process are partially compensated by amplification in stage 2. As expected, the non-equalized amplifier configuration displays a non-uniform gain with the highest maximumvalue (28.4 dB) and the lowest noise-figure. Because the introduction of a midstage filter partially attenuates the signal, there will be a noise-figure penalty when the gain is equalized by filtering the midstage signal. The use of a WBBG greatly improves the gain flatness but decreases the gain level to 22.4 dB. Also, maximum noise-figure penalty is 0.85 dB since back-propagating ASE from stage 2 is reflected by the WBBG and reamplified by stage 2. Gain and noise-figure are further improved by adding an optical isolator that blocks the back-propagating ASE therefore avoiding double amplification of noise. Both WBBG configurations give gain excursion better than 50.3 dB. One of the main advantages of WBBGs is that the equalizing filter does not have to be replaced when a channel density increase is considered. Regarding the output gain and flatness, the DBG filters give the best performances. All the ASE from stage 1 is rejected at port 2 with the exception of ASE reflected by the gratings. Also, backpropagating ASE from stage 2 is eliminated by the optical circulator. More energy from stage 2 is then available for amplification of the signals. An advantage of using an optical circulator is the opportunity to compensate for dispersion by chirping the discrete
Benjamin J. Eggleton, Anatoli A. Abramov, John A. Rogers, Roland0 P. Espindola, Arturo Hale, Robert S. Windeler, Thomas A. Strasser, Bell Laboratories, Lucent Technologies, 700 Mountain Avenue, Murray Hill, New Jersey 07974 USA; E-mail:
[email protected] Tunable filters based on long-period fiber gratings (LPGs) are of great interest particularly in the area of fiber communications as they can provide active gain flattening in optical networks.' Tuning of LPGs can be achieved using temperature, in which shifts of 3-1 1 nm per 100°C change in temperature, have been demonstrated in conventional communication fibers.1.2 Recently, Costantini et al. demonstrated temperature tuning of an LPG with an electrical tuning efficiency of 16 nm/W by passing current through a thin film of metal deposited onto the fiber surface.2 The temperature sensitivity of LPGs can be dramatically enhanced by incorporating into the fiber, special polymers, which exhibit high temperature sensitivity;3 temperature tuning by as much as 50 nm by heating the fiber in the range of 2O-8O0C, with a conventional oven was recently dem~nstrated.~ In this paper, we present a new type ofthe tunable filter based on a metal coated LPG written in a specially-developed fiber containing air regions inside the cladding. The air regions are filled with polymers with high temperature sensitivity resulting in broadband tuning range and high electrical heating efficiency. These new structures are attractive because they are practically insensitive to the variations of the refractive index of the surroundings, and thus can be coated by metal with no measurable changes in the transmission spectrum. The temperature dependence of the peak wavelength (A,) of an LPG is given by,
