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A micrometre-scale Raman silicon laser with a microwatt threshold

Abstract

The application of novel technologies to silicon electronics has been intensively studied with a view to overcoming the physical limitations of Moore’s law, that is, the observation that the number of components on integrated chips tends to double every two years. For example, silicon devices have enormous potential for photonic integrated circuits on chips compatible with complementary metal–oxide–semiconductor devices, with various key elements having been demonstrated in the past decade1,2,3,4,5,6. In particular, a focus on the exploitation of the Raman effect has added active optical functionality to pure silicon7,8,9,10, culminating in the realization of a continuous-wave all-silicon laser11. This achievement is an important step towards silicon photonics, but the desired miniaturization to micrometre dimensions and the reduction of the threshold for laser action to microwatt powers have yet to be achieved: such lasers remain limited to centimetre-sized cavities with thresholds higher than 20 milliwatts12, even with the assistance of reverse-biased p–i–n diodes. Here we demonstrate a continuous-wave Raman silicon laser using a photonic-crystal, high-quality-factor nanocavity without any p–i–n diodes, yielding a device with a cavity size of less than 10 micrometres and an unprecedentedly low lasing threshold of 1 microwatt. Our nanocavity design exploits the principle that the strength of light–matter interactions is proportional to the ratio of quality factor to the cavity volume and allows drastic enhancement of the Raman gain beyond that predicted theoretically13,14. Such a device may make it possible to construct practical silicon lasers and amplifiers for large-scale integration in photonic circuits.

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Figure 1: Structure of Raman silicon laser based on a heterostructure nanocavity.
Figure 2: Configuration of nanocavity Raman silicon laser.
Figure 3: Optical measurements on fabricated nanocavities.
Figure 4: Continuous-wave operation of fabricated nanocavity Raman silicon laser.

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Acknowledgements

We especially thank H. Takano for a preliminary calculation done before the start of this project. We thank K. Ishizaki and K. Kitamura for assistance in device fabrication, Y. Tanaka for assistance with finite-difference time-domain calculations, A. Oskooi and H. Ishihara for comments, and Y. Sakamoto for software assistance. Y.T. is supported by the NanoSquare programme, Funds for the Development of Human Resources in Science and Technology, commissioned by MEXT. This work was supported by JST, PRESTO, the NanoSquare programme and MEXT KAKENHI (grant numbers 23104721 and 21104512). The spectral measurements were partly supported by JSPS KAKENHI (grant number 23686015) and the Asahi Grass Foundation. The device fabrication was greatly supported by JSPS KAKENHI (grant number 20226002), the Ministry of Economy, Trade and Industry (METI) through its ‘Future Pioneering Projects’, and the CPHoST programme.

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Contributions

Y.T. designed the project, designed the original device, fabricated the samples, performed the measurements and wrote the paper. S.N. organized the contribution to the project from Kyoto University, where the fundamental studies to realize high-Q/V nanocavities and the initial investigation into Raman lasers was performed. S.N. also contributed greatly to writing the paper. Y.I. analytically determined the optimum crystalline direction for lasing and contributed to writing Supplementary Information, sections A and B. M.C. established the method to tune the nanocavity mode spacing, T.A. contributed to the theoretical analysis and R.T. contributed to the development of the measurement system.

Corresponding authors

Correspondence to Yasushi Takahashi or Susumu Noda.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text and Data parts A-F, which include a Supplementary Discussion and Equations, Supplementary Figures 1-6 and additional references. (PDF 445 kb)

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Takahashi, Y., Inui, Y., Chihara, M. et al. A micrometre-scale Raman silicon laser with a microwatt threshold. Nature 498, 470–474 (2013). https://doi.org/10.1038/nature12237

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