Overview of course Capabilities of photonic crystals Applications MW 3:10 - 4:25 PMFeatheringill 300 Professor Sharon Weiss

What is a photonic crystal?  Structure for which refractive index is a periodic function in space 1-D photonic crystal 2-D photonic crystal 3-D photonic crystal y x z y x y

What is a photonic crystal?  Propagation of light over a particular wavelength range is forbidden (called photonic band gap – PBG) Wavelength (nm) Reflectance (%) PBG  a/ 2  c PBG

How do you make a photonic crystal? Photoresist patterning Exposure by electron- beam or stepper Pattern transfer by reactive ion etch Wet chemistry (opals) Molecular beam epitaxy or thin film deposition (multilayer films)  Lithography (top down)  Chemistry (bottom up)

How do you make a photonic crystal?  Lithography (top down)  Chemistry (bottom up) Blanco et al., Nature 405, 437(2000) Grüning et al., Appl. Phys. Lett. 68, 747(1996) 1.5  m

Emergence of the field Seminal papers (theory) First expt. PBG demonstration

Size scales Wavelength range of photonic band gap directly related to feature size of photonic crystal Refractive index periodicityPhotonic band gap wavelength 1 millimeter 1 micron 0.5 micron 0.1 micron THz Mid IR Near IR Visible

Preview: photonic crystal geometries and potential applications Bragg mirrors Microcavities 1-D PBG waveguides Omnidirectional mirrors 2-D PBG waveguides Add/drop filters Lasers Superprism Fiber Artificial opals 3-D PBG woodpile structure

Bragg mirrors Earliest example of photonic crystal Initial applications include mirrors for VCSELs (vertical cavity surface emitting lasers) Consists of alternating quarter wavelength optical thickness high and low refractive index materials Wavelength (nm) Reflectance (%) PBG

Effect of Photonic Crystal Composition Stopband width increases as index ratio of n H /n L increases

Omnidirectional Mirrors A. Bruyant et al., Appl. Phys. Lett. 82, 3227 (2003) Completely reflect light for all angles of incidence and all polarizations

Omniguide – Commercial Company Light guided in air core of hollow tube Confinement based on multilayer films that constitute the cladding Y. Fink et al., J. Lightwave Technology 17, 2039 (1999)

Microcavities Defect layer breaks periodicity of dielectric function and introduces allowed mode into PBG Wavelength (nm) Reflectance (%)

1-D Photonic Crystal Waveguides Feature size of 100 nm achieved by x-ray lithography Light guided near 1.5  m Missing hole in center enables resonance wavelength Changing length of defect tunes resonance wavelength J. S. Foresi et al., Nature 390, 143 (1997)

2-D PBG Waveguides Silicon waveguides fabricated by a combination of lithography and electrochemistry 2  m F. Muller et al., J. Porous Materials 7, 201 (2000) M. Loncar et al., Appl. Phys. Lett. 77, 1937 (2000)

Fabrication of 2-D Photonic Crystal Oxidation Reactive ion etching (CF 3 and O 2 ) KOH etching Buffered HF crystalline silicon oxide photoresist Lithography Spin photoresist Electrochemical etching

Add/Drop Filters Theoretically investigated, preliminary experiments Design of missing holes and enlarged holes allow for light to selectively exit waveguide H. Takano et al., Appl. Phys. Lett. 86, (2005) Y. Akahane et al., Appl. Phys. Lett. 82, 1341 (2003)

Photonic Crystal Lasers Incorporation of 2-D photonic crystal with light emitting semiconductor quantum well provides confinement and gain necessary for lasing O. Painter et al., Science 284, 1819 (1999)

Superprism Effect Light path shows a extremely wide swing with a slight change of incident light angle Based on highly anisotropic dispersion by photonic band (negative refraction) T. Sato et al., Phys. Rev. B 58, R10096 (1998)

Photonic Crystal Fiber Light guided in air core instead of traditional high refractive index core Allows for lower losses 2-D PBG confines light in fiber Currently 1.2dB/km (traditional fiber 0.15dB/km) R. F. Cregan et al., Science 285, 1537 (1999) P. J. Roberts et al., Opt. Express 13, 236 (2004)

Artificial Opals Chemical synthesis using chemical vapor deposition and wet etch to form air spheres surrounded by silicon shells Complete photonic band gap observed in near-IR Easier to achieve smaller dimensions with bottom-up technology Blanco et al., Nature 405, 437(2000) 1.5  m

Woodpile Structure: 3-D PBG Extremely complicated high tech lithography used to achieve 3-D PBG –Series of deposition, patterning, etching, and planarization steps Light confined in all three dimensions S. Y. Lin et al., Nature 394, 251 (1998)