{"id":3432,"date":"2011-07-07T15:50:42","date_gmt":"2011-07-07T15:50:42","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/?p=3432"},"modified":"2011-07-19T21:01:58","modified_gmt":"2011-07-19T21:01:58","slug":"nonlinear-optics-in-cmos-photonics-2","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/nonlinear-optics-in-cmos-photonics-2\/","title":{"rendered":"Nonlinear Optics in CMOS photonics"},"content":{"rendered":"
\"Figure<\/a>

Figure 1: (a) Through transmission of 40 \u00b5m radius ring with 200 nm coupling gap for four different in-waveguide input powers. (b) Measured through transmissions (circles) on resonance normalized to off-resonance transmission, and fits (lines) for 20 \u00b5m rings, and (c) for 40 \u00b5m rings with various coupling gaps g; along with the gap, the fitted \u03b2 is labeled for each sample.<\/p><\/div>\n

Nonlinear optics comprises a rich body of physics that could enable a number of interesting functionalities in integrated silicon photonics [1<\/a>] <\/sup>. We are currently interested in the phenomenon of two-photon absorption (TPA) as a means to achieving sub-bandgap photodetection in silicon. Though TPA is a relatively weak absorption mechanism in crystalline silicon, the fact that absorbed power scales quadratically with intensity implies that its strength can be increased for device applications by concentrating a large amount of light energy in a small mode-volume resonator, for example in photonic crystal microcavities [2<\/a>] <\/sup> [3<\/a>] <\/sup>.<\/p>\n

Further enhancement of TPA may be expected when polycrystalline Si is used instead of crystalline Si as the detector material, due to a larger TPA coefficient (\u03b2) resulting from mid-gap electronic states at grain boundaries. Though \u03b2 has been fairly well characterized for crystalline Si [4<\/a>] <\/sup>, an understanding of two-photon absorption in the polycrystalline phase is lacking. We have therefore measured \u03b2 in polycrystalline Si waveguide devices by monitoring the peak through transmission dip in ring resonator devices as a function of input power and fitting the results to a model with \u03b2 as a fitting parameter; data from such measurements are shown in Figure 1. These measurements indicate \u03b2 = 310 \u00b1 70 cm\/GW, a value over two orders of magnitude larger than that in crystalline Si at 1550 nm and on the same order of magnitude as the value observed in amorphous silicon [5<\/a>] <\/sup>. As polysilicon is widely available in advanced CMOS processes, these results suggest that high-density, integrated devices utilizing nonlinear absorption at relatively low powers should be achievable.<\/p>\n<\/div>

  1. J. Leuthold, C. Koos, and W. Freude, \u201cNonlinear silicon photonics.\u201d Nature Photonics<\/em>, vol. 4, pp. 535-544, July 2010. [↩<\/a>]<\/li>
  2. J. Bravo-Abad, E.P. Ippen, and M. Soljacic. \u201cUltrafast photodetection in an all-silicon chip enabled by two-photon absorption.\u201d Appl. Phys. Lett., <\/em>vol. 94, no. 241103, pp. 1-3, June 2009. [↩<\/a>]<\/li>
  3. T. Tanabe, H. Sumikura, H. Taniyama, A. Shinya, and M. Notomi. \u201cAll-silicon sub-Gb\/s telecom detector with low dark current and high quantum efficiency on chip,\u201d Appl. Phys. Lett.,<\/em> vol. 96, no. 101103, pp. 1-3, March 2010. [↩<\/a>]<\/li>
  4. M. Dinu, F. Quochi, and H. Garcia. \u201cThird-order nonlinearities in silicon at telecom wavelengths,\u201d Appl. Phys. Lett., <\/em>vol. 82, pp. 2954-2956, May 2003. [↩<\/a>]<\/li>
  5. K. Ikeda,Y. Shen and Y. Fainman. \u201cEnhanced optical nonlinearity in amorphous silicon and its application to waveguide devices,\u201d Opt. Express, vol. 15, 17761-17771, December 2003. [↩<\/a>]<\/li><\/ol>","protected":false},"excerpt":{"rendered":"

    Nonlinear optics comprises a rich body of physics that could enable a number of interesting functionalities in integrated silicon photonics…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[5532],"tags":[4224,6249,63],"_links":{"self":[{"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/posts\/3432"}],"collection":[{"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/comments?post=3432"}],"version-history":[{"count":6,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/posts\/3432\/revisions"}],"predecessor-version":[{"id":4215,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/posts\/3432\/revisions\/4215"}],"wp:attachment":[{"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/media?parent=3432"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/categories?post=3432"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/wp-json\/wp\/v2\/tags?post=3432"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}