|
In physics, a high contrast grating is a single layer near-wavelength grating physical structure where the grating material has a large contrast in index of refraction with its surroundings. The term near-wavelength refers to the grating period, which has a value between one optical wavelength in the grating material and that in its surrounding materials. The high contrast gratings have many distinct attributes that are not found in conventional gratings. These features include broadband ultra-high reflectivity, broadband ultra-high transmission, and very high quality factor resonance, for optical beam surface-normal or in oblique incidence to the grating surface. The high reflectivity grating can be ultrathin, only <0.15 optical wavelength. The reflection and transmission phase of the optical beam through the high contrast grating can be engineered to cover a full 2π range while maintaining a high reflection or transmission coefficient. == History == The concept of high contrast grating took off with a report on a broadband high reflectivity reflector for surface-normal incident light (the ratio between the wavelength bandwidth with a reflectivity larger than 0.99 and the central wavelength is greater than 30%) in 2004 by Constance J. Chang-Hasnain et al.,〔C. F. R. Mateus, M. C. Y. Huang, Y. Deng, A. R. Neureuther, and C. J. Chang-Hasnain, “Ultra-broadband mirror using low index cladded subwavelength grating”, IEEE Photon. Technol. Lett. 16, 518-520 (2004).〕〔C. J. Chang-Hasnain, C. F. R. Mateus, and M. C. Y. Huang, “Ultra broadband mirror using subwavelength grating,” U.S. Patent 7,304,781 (Dec. 4, 2007).〕 which was demonstrated experimentally in the same year.〔C. F. R. Mateus, M. C. Y. Huang, L. Chen, and C. J. Chang-Hasnain and Y. Suzuki, “Broadband mirror (1.12-1.62 um) using single-layer sub-wavelength grating”, IEEE Photon. Technol. Lett. 16, 1676-1678 (2004).〕 The key idea is to have the high-refractive-index material all surrounded by low-refractive-index material. They are subsequently applied as a highly reflective mirror in vertical-cavity surface-emitting lasers,〔M. C. Y. Huang, Y. Zhou, and C. J. Chang-Hasnain, “A surface-emitting laser incorporating a high index-contrast subwavelength grating,” Nat.Photonics 1(2), 119–122 (2007).〕 as well as monolithic, continuously wavelength tunable vertical-cavity surface-emitting lasers.〔M. C. Y. Huang, Y. Zhou, and C. J. Chang-Hasnain, “A nanoelectromechanical tunable laser,” Nat. Photonics 2, 180–184 (2008).〕 The properties of high contrast grating are rapidly explored since then. The following lists some relevant examples: In 2008, a single layer of high contrast grating was demonstrated as a high quality factor cavity.〔Y. Zhou, M. Moewe, J. Kern, M. C. Y. Huang, and C. J. Chang-Hasnain,“Surface-normal emission of a high-Q resonator using a subwavelength high-contrast grating,” Opt. Express 16(22), 17282–17287 (2008).〕 In 2009, hollow-core waveguides using high contrast grating were proposed,〔Y. Zhou, V. Karagodsky, B. Pesala, F. G. Sedgwick, and C. J. ChangHasnain, “A novel ultra-low loss hollow-core waveguide using subwavelength high-contrast gratings,” Opt. Express 17(3), 1508–1517 (2009).〕 followed by experimentally demonstration in 2012.〔W. Yang, J. Ferrara, K. Grutter, A. Yeh, C. Chase, Y. Yue, A. E. Willner, M. C. Wu, and C. J. Chang-Hasnain, ”Low loss hollow-core waveguide on a silicon substrate,” Nanophotonics 1(1), 23–29 (2012).〕 This experiment is the first demonstration to show a high contrast grating reflecting optical beam propagating in the direction parallel to the gratings, which is a major distinction from photonic crystal or distributed Bragg reflector. In 2010, planar, single-layer lenses and focusing reflectors with high focusing power using a high contrast grating with spatially varying grating dimensions were proposed and demonstrated.〔F. Lu, F. G. Sedgwick, V. Karagodsky, C. Chase, and C. J. Chang-Hasnain,“Planar high-numerical-aperture low-loss focusing reflectors and lenses using subwavelength high contrast gratings,” Opt. Express 18, 12606–12614 (2010).〕〔D. Fattal, J. Li, Z. Peng, M. Fiorentino, and R. G. Beausolei, “Flat dielectric grating reflectors with focusing abilities,” Nat. Photonics 4(7), 466–470 (2010).〕 Some literatures quote the high contrast gratings as photonic crystal slabs or photonic crystal membranes.〔X. Letartre, J. Mouette, J. L. Leclercq, P. R. Romeo, C. Seassal, and P. Viktorovitch, “Switching devices with spatial and spectral resolution combining photonic crystal and MOEMS structures,” IEEE J. Lightwave Technol. 21, 1691-1699 (2003).〕〔C. Sciancalepore, B.B. Bakir, X. Letartre, J. Harduin, N. Olivier, C. Seassal, J. Fedeli, P. Viktorovitch, “CMOS-compatible ultra-compact 1.55- μ m emitting VCSELs using double photonic crystal mirrors”, IEEE Photon. Technol. Lett. 24, 455-457 (2012).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「high contrast grating」の詳細全文を読む スポンサード リンク
|