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Erbium-doped materials have been investigated for generating and amplifying light in low-power chip-scale optical networks on silicon, but several effects limit their performance in dense microphotonic applications. Stoichiometric ionic crystals are a potential alternative that achieve an Er 3+ density 100× greater. We report the growth, processing, material characterization, and optical properties of single-crystal Er 2 O 3 epitaxially grown on silicon. A peak Er 3+ resonant absorption of 364 dB/cm at 1535 nm with minimal background loss places a high limit on potential gain. Using high-quality microdisk resonators, we conduct thorough C/L-band radiative efficiency and lifetime measurements and observe strong upconverted luminescence near 550 and 670 nm.

Cavity polaritons around two Er 3+ optical transitions are observed in microdisk resonators fabricated from epitaxial Er 2 O 3 on Si͑111͒. Using a pump-probe method, spectral anticrossings and linewidth averaging of the polariton modes are measured in the cavity transmission and luminescence at temperatures above 361 K. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3109791͔On-chip optical interconnects with wavelength division multiplexing are being pursued as a low-power low-latency high-bandwidth alternative to metal interconnects.1 Significant research has focused on integrating optical gain material into the Si platform, with III-V wafer bonding to Si being the most successful candidate to date.2 In addition there is a long history of efforts to incorporate Er 3+ into Si material systems for light emission and optical gain. Erbium-doped fibers are the dominant amplifiers for telecommunications because of their high quantum efficiency and because the shielded Er 3+ 4f transition wavelengths are largely insensitive to temperature and the host matrix.3 However, the small gain coefficient of Er 3+ -doped materials is insufficient for dense microphotonic applications. 4 To compensate for erbium's small emission cross section, stoichiometric erbium compounds are potential alternatives that achieve Er 3+ densities 100 times greater than erbium's solubility limit in doped materials.5-8 The high density and weak inhomogeneous broadening of stoichiometric erbium crystals can intrinsically produce large dispersive resonances in the refractive index and vacuum-Rabi splitting of optical cavity modes. 9Rabi splitting and the associated cavity-polariton modes can be described as a consequence of linear dispersion or as nonperturbative coupling between the dipole͑s͒ and an optical cavity, while perturbative coupling to a single ion produces Purcell-enhanced emission.10 For rare-earth emitters, cavity polaritons have been observed around a single Er 3+ transition in an oxidized polycrystalline erbium layer, 11 but the effect was quenched at T տ 40 K. 12 We have previously shown that atomic layer epitaxy produces high quality single-crystal Er 2 O 3 films on silicon and offers the prospect of electrical injection through precisely controlled heterostructures.8 In this letter, we describe the spectroscopy of small mode-volume Er 2 O 3 microdisk resonators formed from this material, and we analyze the properties of high temperature ͑T Ͼ 361 K͒ cavity polaritons formed between the cavity's whispering-gallery modes ͑WGMs͒ and two Er 3+ transitions in the 1500 nm band.Analyzing the polariton response involves continuously tuning a cavity mode across the Er 3+ transitions. As a mode is shifted through an optical transition, the resonances anticross ͑i.e., the vacuum-Rabi splitting͒ and produce symmetric hybrid modes ͑i.e., the cavity polaritons͒, which appear in both the cavity transmission and photoluminescence ͑PL͒. In terms of cavity quantum electrodynamics ͑cQED͒, the fundamental quantity for cavity polaritons is the Ra...

We demonstrate a wavelength monitor and a two-wavelength detector based on two single-quantum-well absorbers that sample a standing wave created by a distributed Bragg reflector. As a wavelength monitor, our device is power independent over a 15 dB range. Wavelength discrimination is linear over a 12 nm range.

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