V. Jayaraman, J.C. Geske, M.H. Mac Dougal,
T.D. Lowes, F.H.Peters, D. R. VanDeusen,
T.C. Goodnough, T.T. Char, S.P. Kilcoyne,
and D.J. Welch
In the last year, Gore Photonics has reported a 1300 nm VCSEL structure that is driven with a monolithically integrated electrically pumped short-wavelength VCSEL optical pump [1]. This structure has recently led to 2 mW room temperature CW single-mode power, modulation up to 7.0 Gbit/sec, and 300 microwatts of power at 80ºC. Figure 1 shows the epitaxial structure, which is assembled through two wafer bonding steps. Although the structure is optically pumped, the wafer scale nature of the pump integration leads to a structure that retains many of the promised cost advantages of VCSELs.
Figure 1. Epitaxial structure of optically pumped 1300 nm VCSEL.
Optical pumping of VCSELs has been recognized by a number of workers in the field as an approach that results in high single-transverse-mode powers for both long and short-wavelength VCSELs [2,3]. The advantages of optical pumping include an optical cavity free of absorbing dopants, de-coupling of optical and electrical design, and eliminating the need to drive current across a wafer fused interface. Using an edge- emitting diode laser, we have observed up to 10 mW of room-temperature CW power in a 1300 nm VCSEL. This is an order of magnitude higher power than obtained with direct electrical pumping. For datacom applications, however, where low cost is a key requirement, using an edge-emitting diode laser or solid state laser as a pump is not practical. Making a practical device requires using a short-wavelength VCSEL as an optical pump. This limits the available pump power, but still allows CW single-mode powers of approximately 2 mW at room temperature, and nearly 700 microwatts at 70ºC.
Figure 2 shows our latest CW results in an integrated VCSEL pumping VCSEL device. Single-mode output powers range from 1.7 mW at room temperature, to 300 microwatts at 80C. (Other single-mode devices have shown up to 2.2 mW of RTCW single-mode power.) Figure 3 shows a beam profile scan from similar devices, with a full angle beam divergence in air of 9 degrees. Early butt-coupling experiments with these devices have generated 80% coupling efficiency with no intervening optical components.
Figure 2. Recent single-mode L-I results over temperature, using integrated structure of Fig. 1.
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| 1300 nm VCSEL 9º Circular Divergence Angle | 1300 nm Edge-Emitter 30º ´ 40º Divergence Angle |
Figure 3. VCSEL beam divergence compared to commercial edge-emitter
The robust single-mode performance of these devices can be maintained over a very wide operating range of temperatures. Figure 4 shows spectra from the device of Figure 2, over the telecom temperature range of -40 to +85ºC. From -40 to +80ºC, these devices maintain >45 dB suppression of the adjacent transverse mode, even at currents close to roll-over.
Figure 4.
Current efforts at Gore Photonics are directed at addressing the reliability and manufacturability issues that must be tackled before commercialization. This work is proceeding on many fronts, including developing packaged single-mode parts, developing wafer bonding over full 2 inch wafers, performing modulation experiments, and understanding the many factors that affect device reliability. Our hope is that this work, coupled with continuing performance improvements, will make long-wavelength VCSELs a key part of emerging fiber-optic communication systems.
1. V. Jayaraman, J.C Geske, M.H MacDougal, F.H.Peters, T.D. Lowes, T.T Char, D.R. VanDeusen, T.C. Goodnough, M.H. Donhowe, S.P. Kilcoyne, and D. J. Welch, “Long-wavelength vertical cavity laser research at Gore”, SPIE Photonics West, San Jose, CA January 1999.
2. A. Keating, A. Black, A. Karim, Y.J. chiu, P. Abraham, C. Harder, E. Hu, J. Bowers, “High Temperature, Optically Pumped, 1.55 um VCSEL Operating at 6 Gb/s”, accepted for presentation at the 57th Device Research conference, Santa Barbara, June 28th-30th, Optoelectronics Devices, SessionVII.B
3. M. Kuznetsov, F. Hakimi, R. Sprague, and A. Mooradian, High-Power (>0.5 W CW) Diode- Pumped Vertical External Cavity Surface-Emitting Semiconductor Lasers with Circular TEM00 Beams, IEEE Photon. Tech. Lett. Vol. 9, No. 8, August 1997, pp. 1063-1065.
Manufacturing of Oxide VCSEL at Hewlett Packard