Er-Doped Sol-Gel Microlaser

In our lab, we developed Erbium-doped microtoroid lasers on a chip by use of a sol-gel surface-functionalization technique. These microlasers can be fabricated in parallel and have characteristics that are easily controllable using wafer-scale processing methods. In addition to being integrable with other optical or electronic components, these microchip lasers are directly coupled to optical fiber using fiber tapers.

Silica toroid-shaped microresonators supported by a circular silicon pillar were first fabricated upon a silicon wafer containing a 2 m layer of thermal silica (SiO2). A thin Erbium doped sol gel silica film was subsequently deposited on the toroid resonator by the dip-coating method. Microtoroids were then irradiated with a CO2 laser in order to reflow and selectively densify the sol-gel films.

Like all whispering-gallery type microresonators, microtoroids feature optical modes that are confined near the resonator periphery, which makes ultra-low threshold microlasers possible. In addition, the thickness of the microtoroid is generally much smaller than the microtoroid diameter. Thus these structures support fewer azimuthal modes than other geometries, such as microspheres. This facilitates single-mode operation in the microtoroids. Typical laser spectra and a light output versus pump power showing a threshold pump power of 34 W are presented in figure 2.

Additionally, multple forms of sol-gel microlasers have been fabricated.  One method is using Er-doped sol-gel, to form an Er-doped sol-gel microlaser entirely from sol-gel, by spincoating Er-doped solgel onto Si wafers, lithographically defining the solgel, etching the silicon to form sol-gel microdisks, then reflowing the solgel using a CO2 laser to form a microtoroid.  Additionally, sol-gel Raman lasers have been demonstrated using un-doped solgel.

More information can be found in the following papers:

L. Yang, T. Carmon, B. K. Min, S. M. Spillane, and K. J. Vahala
“Erbium-doped and Raman microlasers on a silicon chip fabricated by the sol-gel process”
Applied Physics Letters, Volume 86, 091114, February 2005.

Lan Yang, Deniz Armani and Kerry Vahala
"Fiber-coupled Erbium Microlasers on a chip"
Applied Physics Letters, vol. 83, No. 5, 825-826, August 2003.

Deniz Armani, Tobias Kippenberg, Sean Spillane and Kerry Vahala
"Ultra-high-Q toroid microcavity on a chip"
Nature, vol. 421, pp. 925-929, 27 February 2003.

er fig 1 copy04

Figure 1: Illustration showing a micro-chip laser consisting of an Erbium-doped sol-gel thin film applied to a microtoroid. Also shown is a fiber taper used for both pump coupling and laser emission extraction. The inset is a photomicrograph top view of an Erbium microtoroid laser coupled by a fiber taper.

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Figure 2: Emission spectrum of a microtoroid laser with approximate diameter of 80 micron.