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Transcript of Photonic Crystals
Photonic Crystals are periodic optical nanostructures that are designed to affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons. Photonic crystals occur in nature and in various forms have been studied scientifically for the last 100 years.
Wikipedia ContinuedPhotonic crystals are composed of periodic dielectric or metallo-dielectric nanostructures that affect the propagation of electromagnetic waves (EM) in the same way as the periodic potential in a crystal affects the electron motion by defining allowed and forbidden electronic energy bands. Photonic crystals contain regularly repeating internal regions of high and low dielectric constant. Photons (as waves) propagate through this structure - or not - depending on their wavelength. Wavelengths of light that are allowed to travel are known as modes, and groups of allowed modes form bands. Disallowed bands of wavelengths are called photonic band gaps. This gives rise to distinct optical phenomena such as inhibition of spontaneous emission, high-reflecting omni-directional mirrors and low-loss-waveguides, amongst others.Since the basic physical phenomenon is based on diffraction, the periodicity of the photonic crystal structure has to be of the same length-scale as half the wavelength of the EM waves i.e. ~350nm (blue) to 700nm (red) for photonic crystals operating in the visible part of the spectrum - the repeating regions of high and low dielectric constants have to be of this dimension. This makes the fabrication of optical photonic crystals cumbersome and complex.
A New Frontier in Modern Optics
NASA Jet Propulsion Laboratory
California Institute of Technology
If only were possible to make materials in which electromagnetically waves cannot propagate at certain frequencies, all kinds of almost-magical things would happen
Sir John Maddox, Nature (1990)
I would like to begin my talk with a quote of the Nature magazine editor, published few few years after the theoretical prediction of photonic crystals, as a part of a rather pessimistic paper regarding the possibility of creating such crystals. Fortunately, over the past 15 years, this pessimism has been proven wrong, and in this talk I will like present some of the almost-magical word of photonic crystals.
Two Fundamental Optical PrinciplesLocalization of Light
S. John, Phys. Rev. Lett. 58,2486 (1987)Inhibition of Spontaneous Emission
E. Yablonovitch, Phys. Rev. Lett. 58 2059 (1987)
Photonic crystals: periodic dielectric structures.interact resonantly with radiation with wavelengths comparable to the periodicity length of the dielectric lattice. dispersion relation strongly depends on frequency and propagation direction may present complete band gaps Photonic Band Gap (PBG) materials. Guide and confine light without losses Novel environment for quantum mechanical light-matter interaction A rich variety of micro- and nano-photonics devices Photonic crystals are periodic dielectric structures. Their interact resonantly with radiation with wavelengths comparable to the periodicity length of the dielectric lattice. The dispersion relation of the light propagating through PC is strongly depending on the frequency and propagation direction. If there band gaps are present in the photonic band structure, then they are simply called PBG materials.The simplest example is a Bragg stack of dielectric planes, which presents spectral range over which the transmission of light is strongly suppressed. In quantum optics we are mostly interested in the density of states of the photonic reservoir associated with the PC, which is presented here, with the gap characterized by the absence of elmgn modes, and the band edge frequencies. We note the fast variations with the frequency of the PDOS in the spectral range surrounding the band edge freq. (in this low-dimensional system, the PDOS is actually divergent at the BEFs, a square root divergence).
A whole new research field was created with the invention of photonic crystals. These are artificial periodic structures that have the ability of inhibiting the linear propagation of light in all directions.
Photonic crystals were originally proposed as means to realize two fundamental optical principles:the localization and trapping of light in a bulk material and the complete inhibition of spontaneous emission over a broad frequency range.
Photonic crystals not only have the ability to guide and confine light but also provide a novel environment for quantum mechanical light-matter interaction , which make make them suitable for a series of revolutionazing applications.
Photonic Crystals History
1987: Prediction of photonic crystals
S. John, Phys. Rev. Lett. 58,2486 (1987), Strong localization of photons
in certain dielectric superlattices
E. Yablonovitch, Phys. Rev. Lett. 58 2059 (1987), Inhibited spontaneous
emission in solid state physics and electronics
1990: Computational demonstration of photonic crystal
K. M. Ho, C. T Chan, and C. M. Soukoulis, Phys. Rev. Lett. 65, 3152 (1990)
1991: Experimental demonstration of microwave photonic crystals
E. Yablonovitch, T. J. Mitter, K. M. Leung, Phys. Rev. Lett. 67, 2295 (1991)
1995: Large scale 2D photonic crystals in Visible
U. Gruning, V. Lehman, C.M. Englehardt, Appl. Phys. Lett. 66 (1995)
1998: Small scale photonic crystals in near Visible; Large scale
1999: First photonic crystal based optical devices (lasers, waveguides)
Photonic crystals were introduced independently and simultaneously in 1987 by two researchers, each following different paths. Sajeev john was formulating an answer to the question whether andreson localization of electrons in a disordered solid can be extended to photons in a strongly scattering medium, and predicted that localized stated of the electromagnetic field can be created in a periodic dielectric medium. At the same time, yablo was trying to address the possibility of suppressing the unwanted spontaneous emission affecting the semiconductor lasers, and predicted that a 3d periodic dielectric can produce a forbidden gap in the electromagnetic spectrum where.
As a consequence of the unique properties of photonic crystals, they attracted wordwide attention of physicist, chemists or engineers such that the field of photonic crydtal is in continue expansion, with the number of publishe papars doublig every two years.
Photonic Crystals- Semiconductors of Light
Periodic array of atoms
Atomic length scales
Control electron flow
1950s electronic revolution
Periodic variation of dielectric
Length scale ~
Control e.m. wave propagation
New frontier in modern optics
Photonic crystals may be regarded as semicondutors of light. Rather than a periodic array of atoms which scatter and modify the energy-momentum of electrons, PC consinsists of a periodic dielectric structure having spatially periodic constant, with a periodicity of the order of the wavelength of light. They are artificial structures that control the flow of light, and are expected to lead to a new photonic era, similar to the electronic revolution produced by the semicondutors.
Natural Photonic Crystals:
Structural Colours through Photonic Crystals
Periodic structure striking colour effect even in the absence of pigments
In recent years, scientists have discovered that the iridescence of various colorful creatures, from beetles to birds to butterflies, is often due to microscopic structures known as photonic crystals. Unlike pigments, which absorb or reflect certain frequencies of light as a result of their chemical composition, the way that photonic crystals reflect light is a function of their physical structure. That is, a material containing a periodic array of holes or bumps of a certain size may reflect blue light, for example, and absorb other colors even though the crystal material itself is entirely colorless. Because a crystal array looks slightly different from different angles (unlike pigments, which are the same from any angle), photonic crystals can lead to shifting shades of iridescent color that may help some animals attract mates or establish territories.
Artificial Photonic Crystals
Requirement: overlapping of frequency gaps along different directionsHigh ratio of dielectric indicesSame average optical path in different mediaDielectric networks should be connected
J. Wijnhoven & W. Vos, Science (1998)
S. Lin et al., Nature (1998)
Inverted OpalsOn the experimental front, an extremely large number of methods create 3D photonic crystal structures have been investigated. From micro-lithography to self assembly of artificial opals and laser lattices that provide the seed on which the periodic structure will grow. I present here some of the earliest structures produced with the periodicity on the micrometer length scale.The current experimental effort is directed at decreasing the disorder present in the structures, increasing their scalability and, in the mean time, there is a continuous search for designing new structures wit