Coherent light generators – Particular resonant cavity – Distributed feedback
Reexamination Certificate
2000-06-23
2002-12-10
Davie, James (Department: 2828)
Coherent light generators
Particular resonant cavity
Distributed feedback
C372S045013
Reexamination Certificate
active
06493371
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a vertical cavity apparatus, and more particularly to a vertical cavity apparatus with at least one tunnel junction.
2. Description of Related Art
Continued advances in long-distance, fiber-optic communications depend on high-quality laser sources. Since optical fibers exhibit lowest attenuation and dispersion at the wavelengths of 1.3 &mgr;m and 1.55 &mgr;m, suitable sources should emit at these relatively long wavelengths in single-mode operation.
Traditionally, long-wavelength distributed feedback (DFB) lasers are employed in fiber-optic communications systems for their single longitudinal and transverse mode characteristics. However, fabricating DFB lasers involves very complicated and low-yield processes. Furthermore, the DFB laser performance is very sensitive to the surrounding temperature change. Thus, complicated electronics are needed in the transmitter to control the operating environment. These disadvantages render the DFB laser a very expensive light source and severely limit its application in the fiber-optic communications field.
Vertical Cavity Surface Emitting Lasers (VCSELs) emitting in the 1.3 &mgr;m and 1.55 &mgr;m ranges have been visualized as promising candidates for replacing DFBs in telecommunications applications. Due to their extremely short cavity length (on the order of one lasing wavelength), VCSELs are intrinsically single longitudinal mode devices. This eliminates the need for complicated processing steps that are required for fabricating DFB lasers. Furthermore, VCSELs have the advantage of wafer-scale fabrication and testing due to their surface-normal topology.
Unfortunately, VCSELs suffer material limitations that are negligible in the case of short-wavelength VCSELs but drastically affect the performance of long-wavelength VCSELs. The small available refractive index difference An between reflective layers of the Distributed Bragg Reflectors(DBRs) requires that a large number of layers with high composition and thickness precision be used to achieve sufficient reflectivity. Another object of the present invention is to reduce loss in a vertical cavity apparatus. Due to the small &Dgr;n the relatively thick DBR's result in high diffraction losses. Furthermore, high free-carrier absorption loss limits the maximum achievable reflectivity and the high non-radiative recombination rate increases the electrical current for reaching the lasing threshold.
These problems have restricted prior art fabrication efforts to non-wafer-scale, complicated and low-yield processes such as wafer fusion described by D. I. Babic et al., “Room-Temperature Continuous-Wave Operation of 1.54 &mgr;m Vertical-Cavity-Lasers”, IEEE Photonics Technology Letters, Vol. 7, No. 11, 1995, pp. 1225-1227 and Y. Ohiso et al., “1-55 &mgr;m Vertical-Cavity Surface-Emitting Lasers with Wafer-Fused InGaAsP/InP-GaAs/AlAs DBRs”, Electronics Letters, Vol. 32, No. 16, 1996, pp. 1483-1484. Alternatively, long-wavelength VCSELs have also been manufactured by evaporation of dielectric mirrors as described by S. Uchiyama et al., “Low Threshold Room Temperature Continuous Wave Operation of 1.3 &mgr;m GaInAsP/InP Strained Layer Multiquantum Well Surface Emitting Laser”, Electronics Letters, Vol. 32, No. 11, 1996, pp. 1011-13; M. A. Fisher et al., “Pulsed Electrical Operation of 1.5 &mgr;m Vertical-Cavity-Surface-Emitting Lasers”, IEEE Photonics Technology Letters, Vol. 7, No. 6, 1995, pp. 608-610 and T. Tadokoro et al., “Room Temperature Pulsed Operation of 1.5 &mgr;m GaInAsP/InP Vertical-Cavity Surface-Emitting Lasers”, IEEE Photonics Technology Letters, Vol. 4, No. 5, 1992, pp. 409-411.
Unfortunately, these methods do not allow one to efficiently grow long-wavelength VCSELs.
Tunneling in GaAs, at an n+/p+ junction, is well known (see, for example, N. Holonyak, Jr. and I. A. Lesk, Proc. IRE 48, 1405, 1960), and is generally of interest for its negative resistance. Tunneling in GaAs can be enhanced with an InGaAs transition region (see, for example, T. A. Richard, E. I. Chen, A. R. Sugg. G. E. Hofler, and N. Holonyak, Jr., Appl. Phys. Lett. 63, 3613, 1993), and besides its negative resistance behavior, can be used in reverse bias as a form of “ohmic” contact. This allows, for example, the reversal of the doping sequence of an Al sub x Ga sub 1-x As-GaAs quantum well heterostructure laser (n forward arrow p to p forward arrow n) grown on an n-type GaAs substrate. See, for example, A. R. Sugg, E. I. Chen, T. A. Richard, S. A. Maranowski, and N. Holonyak, Jr., Appl. Phys. Lett. 62, 2510 (1993) or the cascading of absorbing regions to produce higher efficiency solar cells (see for example D. L. Miller, S. W. Zehr and J. S. Harris Jr, Journ. App. Phys., 53(1), pp 744-748, (1982) and P. Basmaji, M. Guittard, A. Rudra, J. F. Carlin and P. Gibart, Journ. Appl,. Phys., 62(5), pp 2103-2106, (1987)).
Use of tunnel junctions in order to increase the optical round-trip gain in the cavity and increase differential efficiency is shown in “Room-temperature, electrically-pumped, multiple-active region VCSELs with high differential efficiency at 1.55 &mgr;m”, Kim, J. K.; Hall, E.; Sjolund, O.; Coldren, L. A.; Dept. Electr. & Comput. Eng., California Univ., Santa Barbara, Calif., 1999 IEEE LEOS Annual Meeting Conference Proceedings, 12
th
Annual Meeting San Francisco, Calif., Nov. 8-11, 1999 and in “CW room temperature operation of a diode cascade quantum well VCSEL”, Knodl, T.; Jager, R.; Grabherr, M.; King, R.; Kicherer, M.; Miller, M.; Mederer, F.; Ebeling, K. J.; Dept. of Optoelectron., Ulm Univ., Germany, 1999 IEEE LEOS Annual Meeting Conference Proceedings, 12
th
Annual Meeting San Francisco, Calif., Nov. 8-1 1999. The concept has also been demonstrated in edge emitting laser where several active layers have been stacked to produce high power lasers (see for example J. C. Garcia, E. Rosencher, P. Collot, N. Laurent, J. L. Guyaux, E. Chirlias and J. Nagle, PT1.15, Xth international MBE conference on Molecular Beam Epitaxy, Cannes (France), 1998; Patent 5212706, Issued May 18, 1993. “Laser diode assembly with tunnel junctions and providing multiple beams”, J. Faquir, C. Storrs.
A tunnel contact junction can be used in a light emitting semiconductor device as a hole source and makes possible lateral bias currents (electron current) to drive a quantum well heterostructure (QWH) laser without the compromise of the low mobility and large resistive voltage drop of lateral conduction in thin p-type layers. This is particularly valuable in QWH laser structures employing upper and/or lower native oxide confining layers (see, for example, M. Dallesasse, N. Holonyak Jr., A. R. Sugg, T. A. Richard, and N. El Zein, Appl. Phys. Lett 57 2844, 1990; A. R. Sugg, E. I. Chen, T. A. Richard, N. Holonyak, Jr., and K. C. Hsieh, Appl. Phys. Lett. 62, 1259, 1993: U.S. Pat. No. 5,936,266, N. Holonyak, J. J. Wierer. P. W. Evans) that require lateral bias currents (see, for example, P. W. Evans, N. Holonyak, Jr., S. A. Maranowski, M. J. Ries, and E. I. Chen, Appl. Phys. Lett. 67, 3168, 1995), or in devices such as a vertical cavity surface emitting laser (VCSEL) where lateral hole currents have been employed (see, for example, D. L. Huffker, D. G. Deppe, and K. Kumar, Appl. Phys. Lett. 65, 97, 1994). Hole conduction along a layer introduces a large device series resistance, because of the low hole mobility, and increases threshold voltages and device heating. A tunnel contact junction on the p side of an oxide confined QWH can be used to replace lateral hole excitation currents. The hole injection is supported by a lateral electron current, thus providing lower voltage drop and less series resistance. This minimizes the amount of p-type material and, to the extent possible, employ only n-type layers (electron conduction) to carry the device current. In addition to electrical and thermal performance advantages from reducing the amount of lossier p-type material, an optical advantage can also accrue since p-type material of the s
Boucart Julien
Chang-Hasnain Constance
Jansen Michael
Nabiev Rashit
Yuen Wupen
Bandwidth9 Inc.
Davie James
Davis Paul
Heller Ehrman White & McAuliffe
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