Microdisks provide strong light confinement for erbium-doped silicon lasers
It has been a long-standing goal to create efficient light sources that are compatible with complementary metal-oxide semiconductor (CMOS) technology. One approach is to implant rare-earth ions in silicon or silica. Erbium, for example, emits at 1.55 µm, which makes it an obvious choice when designing lasers for fibre-based applications. However, erbium ions tend to cluster, putting a limit on their concentration and, as a result, on the conditions required for lasing. High-quality optical resonators can make up for this. T. J. Kippenberg and colleagues have now shown how it is possible to fabricate the required resonators without the drawbacks inherent to earlier approaches1.
In previous devices, the necessary light confinement was provided by either toroid microcavities or microspheres. Their fabrication, however, is not well-suited for use in combination with ion implantation: high-power lasers are needed to melt the silicon and this makes it difficult to control the distribution of the ions. Microdisks do not require such heavy-handed processing, just wet etching.
Kippenberg et al. created 1-µm-thick silica disks with a radius of 60 µm, attached to a silicon substrate by a narrow silicon post. The team point out that the acid etch is critical as it creates slanting sides on the structure that help to confine light efficiently. On exciting the rare-earth ions with an external laser, the microdisks lase at a wavelength of 1.55 µm and a threshold power of 43 µW. As all the techniques used to create the device are CMOS-compatible, this work opens the door to optoelectronics components on a silicon chip.
Kippenberg, T. J., Kalkman, J., Polman, A. & Vahala, K. J. Demonstration of an erbium-doped microdisk laser on a silicon chip. Phys. Rev. A 74, 051802 10.1103/PhysRevA.74.051802 (2006).
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Gevaux, D. Disks set to shine. Nature Photon (2006). https://doi.org/10.1038/nphoton.2006.67