Introduction
There has been considerable research effort in semiconductor lasers toward control of the optical mode. The goals of this control are wavelength tunability and profile selectivity. One of the techniques that was used successfully in edge emitting semiconductor lasers is the cleaved-coupled-cavity structure. In this device, two independent cavities are fabricated in close proximity to one another. Various geometric configurations including axial and transverse coupling have been used [1]-[6]. Typically the second cavity is passive, and acts as a source of frequency selective absorption. Using these techniques, previous work has shown single longitudinal mode operation from a cavity that would by itself lase in many modes [3], [4]. In addition, the coupled cavity has been used to tune the emission wavelength of the device [4], [5].
In VCSELs, the mirrors are grown epitaxially on the substrate instead of cleaving the facets. The analogue of the coupled-cavity structure for surface-emitting devices is one with a second cavity grown in addition to the first. This is known as a composite-resonator vertical-cavity laser (CRVCL) [7]-[16].
Device Structure
Figure 1: Sample CRVCL device structure.
The device structure shown in Figure 1 is a CRVCL with two active cavities. The top cavity is defined using ion implantation and the bottom cavity is defined using selective oxidation. The double mesa structure allows for independent electrical contact to each cavity. Recent work in our group has focused on the output and spectral characteristics of this device.
The middle DBR region has a reflectivity of 85-90%, which implies that an optical field circulating in one cavity can be partially transmitted to the other cavity. Although the two cavities may be identical, this coupling between the cavities causes a longitudinal mode splitting. Previous work has shown that the splitting is inversely proportional to the number of middle DBR layer pairs, and can easily be varied from 2-25nm. A transmission electron micrograph (TEM) image of an unprocessed CRVCL appears below in Figure 2 [16]. The TEM image was taken by D. Mathes and R. Hull, University of Virginia.
Figure 2: TEM image of CRVCL with 11.5 middle DBR layer pairs.
Current and future work on CRVCLs to include:
- modeling of dc and spectral characteristics
- high speed electrical and optical modulation
- fabrication of novel device structures
References
Legend:
- JQE = IEEE Journal of Quantum Electronics
- APL = Applied Physics Letters
- PTL = IEEE Photonics Technology Letters
[1] Y. Suematsu, M. Yamada, and K. Hayashi, JQE QE-11 457 (1975).
[2] J. L. Merz, R. A. Logan, and M. Sergent, JQE QE-15 72 (1979).
[3] L. A. Coldren, B. I. Miller, K. Iga, and J. A. Rentchler, APL 38 315 (1981).
[4] W. T. Tsang, N. A. Olsson, and R. A. Logan, APL 42 650 (1983).
[5] J. Salzman, R. Lang, and A. Yariv, APL 47 195 (1985).
[6] W. T. Tsang, Semiconductors and Semimetals 22 Part B 257 (1993).
[7] A. J. Fischer, K. D. Choquette, W. W. Chow, A. A. Allerman, and K. M. Geib, APL 76 1975 (2000).
[8] A. J. Fischer, K. D. Choquette, W. W. Chow, A. A. Allerman, D. K. Serkland, and K. M. Geib, APL 79 4079 (2001).
[9] A. J. Fischer, K. D. Choquette, W. W. Chow, A. A. Allerman, and K. M. Geib, APL 77 3319 (2000).
[10] A. J. Fischer, K. D. Choquette, W. W. Chow, H. Q. Hou, and K. M. Geib, APL 75 3020 (1999).
[11] M. Brunner, K. Gulden, M. Moser, J. F. Carlin, R. P. Stanley, and M. Ilegems, PTL 12 1316 (2000).
[12] J. F. Carlin, R. P. Stanley, P. Pellandini, U. Oesterle, and M. Ilegems, APL 75 908 (1999).
[13] P. Pellandini, R. P. Stanley, R. Houdre, U. Oesterle, M. Ilegems, and C. Weisbuch, APL 71 864 (1997).
[14] P. Michler, M. Hilpert, and G. Reiner, APL 70 2073 (1997).
[15] R. P. Stanley, R. Houdre, U. Oesterle, M. Ilegems, and C. Weisbush, APL 65 2093 (1994)
[16] D. M. Grasso, K. D. Choquette, D. T. Mathes, R. Hull, A. J. Fischer, W. W. Chow, K. M. Geib, and A. A. Allerman, CLEO ‘02 Tech. Digest p468.