OFC '98 Technical Digest Tuesday Afternoon 0 45

TuH5 3:15pm

Net gain of 27 dB with a 8.6-cm-long Er/Ybdoped glass-planar-amplifier

D. Barbier, P. Bruno, C. Cassagnettes, M. Trouillon, R.L. Hyde, A. Kevorkian, J.M.P. Delavaux,* GeeO, 46 avenue Fklix Viallet, 38 031 Grenoble cedex, France; E-mail: Denis. Barbier@in pg. fr

In our previous work we have shown the efficiency of our ion-exchange technology in producing waveguide amplifiers in erbiumlytterbium (Erl Yb) co-doped phosphate glass,' as well as in producing lossless splitters and lossless wavelength combiner m o d ~ l e s . ~ , ~ These components were developed for applications around 1534 nm, near the gain peak of our Er-doped glass. In order to increase the available gain near the 1550-nm wavelength window, we have followed two new approaches in the real- ization of the waveguide amplifiers. The first one was to increase the length of the amplifier and the second to increase the mode confinement in the guide at both pump and signal wavelengths.

In this paper we report the gain performances at both 1534 and 1548 nm wavelengths and we discuss the respective advantages of these new waveguide amplifiers.

In a 2 weight% erbium and 4 weight% ytterbium-doped phosphate glass, we have made series of 86- or 55-mm-long channel waveguides, by a two-step ion-exchange process. The waveguides, buried 4.5 p m be- neath the glass surface, propagate light in a single-mode operation at 1534 nm and slightly bimodal operation at 980 nm. Their TE, lle mode sizes were, in the horizontal and vertical directions, @h1540 = 7.3 pm, @v1540 = 6.4 pm, @h,,o = 5.6 pm, = 5.3 p m for the longer guides, and @h1540 = 5.5 pm, @v1540 = 3.5 pm, = 4.7 pm, @v980 = 2.7 pm for the shorter ones. We have measured fiber-to-fiber insertion losses of 3.2 dB at 1340 nm for the former guide and 1 dB for the later, which has both of its ends tapered to match the mode size of the mono- mode fiber used. We have estimated, for the shorter waveguides, that the fiber-to-guide coupling losses, were <0.25 dB and the propagation losses were about 0.1 dB/cm.

For the gain and noise figure characterization of our waveguide amplifiers we have used a single 980-nm pump laser diode, spliced to a fiber multiplexer. 180 mW of pump power were available at the output of the multiplexer. Two temperature-stabilized distributed feedback (DFB) lasers were alternatively used to measure the amplifier performances at both 1534- and 1548-nm wavelengths. The output power of these signal lasers was adjusted with an erbium-doped fiber amplifier and a variable attenuator installed between the DFB and the multiplexer. We have used micropositioner devices to align input and output fibers with our waveguides. The output fiber is directly connected to the optical spec- trum analyzer (OSA), used to measure gain and noise figure.

In order to compare the behavior of the long standard waveguide with the short confined one, we have plotted on Fig. 1 the net gain and

at the two above wavelengths. We have obtained higher gain with the longest amplifier: 18 dB at 1534 nm and 9 dB at 1548 nm, instead of 16 dB and 7.5 dB with the shortesl one. It is clear that the short waveguide amplifier required much less pump power to reach its saturation regime. For example a 10-dB gain is achieved with only 70 mW of pump power for the short amplifier, instead of 110 mW for the longer one. This is due

noise figure evolutions versus input pump power for the two waveguides

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TuH5 waveguide amplifiers.

Fig. 1. Gain and noise figure vs. pump powter for 5.5- and 8.6-cm-long

to the better mode confinement that we have achieved in these new types of waveguides. Indeed, this high confinement helps us to reach the infinite pump power conditions we have described in a previous paper: with less pump power. A similar noise figure of about 3.5 dB is obtained for these two waveguide amplifiers.

To check the maximum achievable gain we have characterized the longer waveguide in a double-pass configuration. We have used for this experiment an optical circulator and a Faraday rotator mirror. Figure 2 shows the gain and noise figure evolution with pump power for the two wavelengths. Due to back reflection at the waveguidelfiber interfaces, the system starts lasing, which clamps the maximum 1534-nm gain at 27 dB and the maximum 1548-nm gain at 11 dB.

To analyze the saturation behavior of our amplifiers, we have plot- ted in Fig. 3 the gain and noise figure evolutions with signal output power for the short amplifier. Deep saturation occurs around 11 dBm for the two wavelengths.

For the 8.6-cm-long waveguide, we have compared its gain satura- tion behavior when pumped with a single 180-mW 980-laser diode or with two 120-mW 980-laser diodes. Figure 4 shows the gains measured in both cases at the two wavelengths. Deep saturation of 11 dBm, similar to that of the 5.5-cm-long amplifier, is observed with the single pump configuration. But deep saturation above 14 dBm is reached with the double pump configuration. This shows that power booster applications can be investigated with these ion-exchanged glalss waveguide amplifiers.

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TuH5 Fig. 2. 8.6-cm-long waveguide.

Double-pass gain and noise figure vs. pump power for the

46 a Tuesdav Afternoon OFC '98 Technical Digest

Pump power = 18OmW Pump power wavelength 980m

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TuH5 Fig. 3. Saturation behavior of the long amplifier.

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TuH5 Fig. 4. 8.6-cm-long waveguide.

Single- and double-pump 5.5-cm saturation behavior of the

It is clear from these results that net gain above 30 dB can be reached with 15-cm-long ion-exchanged phosphate-glass waveguide amplifiers, used in single-pass configuration. But this will require high pump power, which is not desirable. We have demonstrated here that similar gain will be obtained with shorter waveguides and much lower pump power if the mode confinement of these waveguides is high enough. This opens the way toward low-cost, high-gain, compact, Er-doped-glass ion-exchanged waveguide- amplifiers for 1.55-pm telecommunication applications.

The authors thank K. Ogawa for his support. *Lucent Technologzes, Mountain Avenue, Murray Hill, New Jersey 07974- 0636 1. J.M.P. Delavaux, S. Granlund, 0. Mizuhara, L.D. Tzeng, D. Barbier,

M. Rattay, F. Saint Andreand, A. Kevorkian, IEEE Photon. Technol. Lett. 9, (1997). D. Barbier, M. Rattay, N. Krebs, M. Trouillon, F. Saint Andri., G. Clauss, J.M.P. Delavaux, presented at ECI0'97, Stockholm, Swe- den, April 2-4, 1997. D. Barbier, M. Rattay, F. Saint Andre, G. Clauss, M. Trouillon, A. Kevorkian, J.M.P. Delavaux, E. Murphy, IEEE Photon. Technol. Lett. 9, (1997). D. Barbier, in Optical Amnplifitrs and their Applications, Vol. XVI of OSA Trends in Optics and Photonics Series (Optical Society of America, Washington, D.C., 1997).

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TuH6 3:30pm

10.6 W continuous wave power from InGaAs/AIGaAs (915 nm) laser diodes

X. He, S. Srinivasan, M. Ung, R. Patel, Opt0 Power Corporation, 3321 E. Global Loop, Tucson, Arizona 85706

High-power continuous wave (cw) InGaAdAlGaAs laser diodes have been the efficient pumping source for fiber lasers. We report 10.6 W cw power from a 100-pm-wide InGaAslAlGaAs quantum well laser diode. Power conversion efficiencies as high as 59% have been achieved for a 2-mm cavity-length diode. These devices also demonstrate a unique resistance to thermal damage.

The laser structures consist of an InGaAs quantum well active region between AlGaAs confinement layers. 100-pm-wide stripe diode lasers were prepared and bonded p-side down on a conduction-cooled heat sink.

Figure 1 shows the cw light-current (L-I) and efficiency-current (qw-I) characteristics of an InGaAslAlGaAs laser diode (cavity length 4 mm) measured at 4 "C heat sink temperature. 10.64 W cw power from front facet has been measured. The device exhibits no degradation at this power level, however, measurement was interrupted to avoid damage to the device. This power is 1.3 W higher than the best published data (9.3 W) for InGaAslAlGaAs laser diodes with nonabsorbing mirrors' and about 30% higher than the best data (8.1 W) for Al-free InGaAs laser diodes.' This laser diode not only shows high power capability, but also reveal high efficiency. It achieves more than 50% power conversion efficiency between 3-7 amp driving currents. The L-I characteristics shown in Fig. 1 also indicate that the maximum power of the diode is limited by cooling efficiency. If superior heat sinks such as, diamond heat sink as in Ref. 2, were used, higher power is conceivable.

The laser structure used for this work shows low loss and high efficiency. Figure 2 shows the L-I and qw-I characteristics of the laser diode with 2-mm cavity length measured at heat sink temperature of 5 "C. As high as 59% power conversion efficiency has been achieved for

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TuH6 Fig. 1. Continuous wave light-current (L-I) and efficiency-current (qw-I) characteristics of an InGaAs/AlGaAs laser diode (cavity length 4 mm) measured at 4 "C heat sink temperature.