Nanophotonics
Encyclopedia
Nanophotonics or Nano-optics is the study of the behavior of light
on the nanometer scale. It is considered as a branch of optical engineering
which deals with optics
, or the interaction of light with particles or substances, at deeply subwavelength length scales. Technologies in the realm of nano-optics include near-field scanning optical microscopy (NSOM), photoassisted scanning tunnelling microscopy, and surface plasmon optics.
Traditional microscopy makes use of diffractive elements to focus light tightly in order to increase resolution. But because of the diffraction limit (also known as the Rayleigh Criterion), propagating light may be focused to a spot with a minimum diameter of roughly half the wavelength of the light. Thus, even with diffraction-limited confocal microscopy, the maximum resolution obtainable is on the order of a couple of hundred nanometers.
The scientific and industrial communities are becoming more interested in the characterization of materials and phenomena on the scale of a few nanometers, so alternative techniques must be utilized. Scanning Probe Microscopy (SPM) makes use of a “probe”, (usually either a tiny aperture or super-sharp tip), which either locally excites a sample or transmits local information from a sample to be collected and analyzed. The ability to fabricate devices in nanoscale that has been developed recently provided the catalyst for this area of study.
The study of nanophotonics involves two broad themes 1) studying the novel properties of light at the nanometer scale 2) enabling highly power efficient devices for engineering applications.
The study has the potential to revolutionize the telecommunications industry by providing low power, high speed, interference-free devices such as electrooptic and all-optical switches on a chip.
The interaction of light with these nanoscale features leads to confinement of the electromagnetic field
to the surface or tip of the nanostructure resulting in a region referred to as the optical near field
. This effect is to some extent analogous to a lightning rod, where the field concentrates at the tip. In this region, the field may need to adjust to the topography of the nanostructure (see boundary conditions of Maxwell's equations
). This means that the electromagnetic field will be dependent on the size and shape of the nanostructure that the light is interacting with.
This optical near field can also be described as a surface bound optical oscillation which can vary on length scale of tens or hundreds of nanometers – a length scale smaller than the wavelength of the incoming light. This can provide higher spatial resolution beyond the limitations imposed by the law of diffraction
in conventional far-field microscopy. The technique derived from this effect is known as near-field microscopy, and opens up many new possibilities for imaging and spectroscopy on the nanoscale. A novel embodiment which has picometer resolution in the vertical plane above the waveguide surface is dual polarisation interferometry
.
Novel optical properties of materials can result from their extremely small size. A typical example of this type of effect is the color change associated with colloidal gold
. In contrast to bulk gold, known for its yellow color, gold particles of 10 to 100 nm in size exhibit a rich red color. The critical size where these and related effects take place are correlated with the mean free path of the conduction electrons of the metal.
In addition to these extrinsic size effects that determine a material's optical response to incoming light, the intrinsic properties of the material can change. These size effects occur as particles become even smaller. At this stage some of the intrinsic electronic properties of the medium itself change. One example of this phenomenon is in semiconductor nanostructures where the extremely small particle size confines the quantum mechanical wavefunction
, leading to discrete optical transitions, e.g., fluorescence colors that depend on the size of the particle. The changing bandgap of the semiconductor is the reason for this color change. This effect, however, since not directly correlated with optical wavelength, is not unanimously included when referring to nano-optics.
In March 2010, S. Assefa et al. of IBM
reported invention of ultra fast and noise free nanophotonic avalanche photodetectors which are poised to bring about the exaflop light circuit era. "We are now working on integrating all of our devices onto a microprocessor alongside transistors". "The Avalanche Photodetector achievement, which is the last in a series of prior reports from IBM Research, is the last piece of the puzzle that completes the development of the “nanophotonics toolbox” of devices necessary to build the on-chip interconnects". "With optical communications embedded into the processor chips, the prospect of building power-efficient computer systems with performance at the Exaflop level might not be a very distant future.”
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
on the nanometer scale. It is considered as a branch of optical engineering
Optical engineering
Optical engineering is the field of study that focuses on applications of optics. Optical engineers design components of optical instruments such as lenses, microscopes, telescopes, and other equipment that utilizes the properties of light. Other devices include optical sensors and measurement...
which deals with optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
, or the interaction of light with particles or substances, at deeply subwavelength length scales. Technologies in the realm of nano-optics include near-field scanning optical microscopy (NSOM), photoassisted scanning tunnelling microscopy, and surface plasmon optics.
Traditional microscopy makes use of diffractive elements to focus light tightly in order to increase resolution. But because of the diffraction limit (also known as the Rayleigh Criterion), propagating light may be focused to a spot with a minimum diameter of roughly half the wavelength of the light. Thus, even with diffraction-limited confocal microscopy, the maximum resolution obtainable is on the order of a couple of hundred nanometers.
The scientific and industrial communities are becoming more interested in the characterization of materials and phenomena on the scale of a few nanometers, so alternative techniques must be utilized. Scanning Probe Microscopy (SPM) makes use of a “probe”, (usually either a tiny aperture or super-sharp tip), which either locally excites a sample or transmits local information from a sample to be collected and analyzed. The ability to fabricate devices in nanoscale that has been developed recently provided the catalyst for this area of study.
The study of nanophotonics involves two broad themes 1) studying the novel properties of light at the nanometer scale 2) enabling highly power efficient devices for engineering applications.
The study has the potential to revolutionize the telecommunications industry by providing low power, high speed, interference-free devices such as electrooptic and all-optical switches on a chip.
Components of a nanophotonic system
- Waveguides
- Couplers
- Fiber to waveguide couplers
- Optical switchOptical switchIn telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits to be selectively switched from one circuit to another....
es - photo detectors/solar cells
- Electro-optic modulatorElectro-optic modulatorElectro-optic modulator is an optical device in which a signal-controlled element displaying electro-optic effect is used to modulate a beam of light. The modulation may be imposed on the phase, frequency, amplitude, or polarization of the modulated beam...
s - Wavelength division multiplexorsWavelength-division multiplexingIn fiber-optic communications, wavelength-division multiplexing is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light...
- Amplifiers
- Lasers
- Isolators
- Optical circulators
- Saturable absorbersSaturable absorptionSaturable absorption is a property of materials where the absorption of light decreases with increasing light intensity. Most materials show some saturable absorption, but often only at very high optical intensities ....
In detail
The term typically refers to phenomena of ultraviolet, visible and near IR light, with a wavelength of approximately 300 to 1200 nanometers.The interaction of light with these nanoscale features leads to confinement of the electromagnetic field
Electromagnetic field
An electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...
to the surface or tip of the nanostructure resulting in a region referred to as the optical near field
Near field
Near field may refer to:*Near-field , an algebraic structure*Near and far field, parts of an electromagnetic field*Near field communication, a set of short-range wireless technologies, typically requiring a distance of 4 cm or less...
. This effect is to some extent analogous to a lightning rod, where the field concentrates at the tip. In this region, the field may need to adjust to the topography of the nanostructure (see boundary conditions of Maxwell's equations
Maxwell's equations
Maxwell's equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics, classical optics, and electric circuits. These fields in turn underlie modern electrical and communications technologies.Maxwell's equations...
). This means that the electromagnetic field will be dependent on the size and shape of the nanostructure that the light is interacting with.
This optical near field can also be described as a surface bound optical oscillation which can vary on length scale of tens or hundreds of nanometers – a length scale smaller than the wavelength of the incoming light. This can provide higher spatial resolution beyond the limitations imposed by the law of diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
in conventional far-field microscopy. The technique derived from this effect is known as near-field microscopy, and opens up many new possibilities for imaging and spectroscopy on the nanoscale. A novel embodiment which has picometer resolution in the vertical plane above the waveguide surface is dual polarisation interferometry
Dual Polarisation Interferometry
Dual polarization interferometry is an analytical technique that can probe molecular scale layers adsorbed to the surface of a waveguide by using the evanescent wave of a laser beam confined to the waveguide...
.
Novel optical properties of materials can result from their extremely small size. A typical example of this type of effect is the color change associated with colloidal gold
Colloidal gold
Colloidal gold is a suspension of sub-micrometre-sized particles of gold in a fluid — usually water. The liquid is usually either an intense red colour , or a dirty yellowish colour ....
. In contrast to bulk gold, known for its yellow color, gold particles of 10 to 100 nm in size exhibit a rich red color. The critical size where these and related effects take place are correlated with the mean free path of the conduction electrons of the metal.
In addition to these extrinsic size effects that determine a material's optical response to incoming light, the intrinsic properties of the material can change. These size effects occur as particles become even smaller. At this stage some of the intrinsic electronic properties of the medium itself change. One example of this phenomenon is in semiconductor nanostructures where the extremely small particle size confines the quantum mechanical wavefunction
Wavefunction
Not to be confused with the related concept of the Wave equationA wave function or wavefunction is a probability amplitude in quantum mechanics describing the quantum state of a particle and how it behaves. Typically, its values are complex numbers and, for a single particle, it is a function of...
, leading to discrete optical transitions, e.g., fluorescence colors that depend on the size of the particle. The changing bandgap of the semiconductor is the reason for this color change. This effect, however, since not directly correlated with optical wavelength, is not unanimously included when referring to nano-optics.
In March 2010, S. Assefa et al. of IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
reported invention of ultra fast and noise free nanophotonic avalanche photodetectors which are poised to bring about the exaflop light circuit era. "We are now working on integrating all of our devices onto a microprocessor alongside transistors". "The Avalanche Photodetector achievement, which is the last in a series of prior reports from IBM Research, is the last piece of the puzzle that completes the development of the “nanophotonics toolbox” of devices necessary to build the on-chip interconnects". "With optical communications embedded into the processor chips, the prospect of building power-efficient computer systems with performance at the Exaflop level might not be a very distant future.”
External links
- ePIXnet Nanostructuring Platform for Photonic Integration
- Optically induced mass transport in near fields
- “Photonics Breakthrough for Silicon Chips: Light can exert enough force to flip switches on a silicon chip,” by Hong X. Tang, IEEE Spectrum, October 2009
- NCN Nanophotonics Tutorials
- Online course on Nanophotonics
- NCN Nanophotonics: Tutorials Suite of tutorials
- NCN Nanophotonics: Simulation Tools for Education and Research Suite of simulation tools
- Nanophotonics, nano-optics and nanospectroscopy A. J. Meixner (Ed.) Thematic Series in the Open AccessOpen accessOpen access refers to unrestricted access via the Internet to articles published in scholarly journals, and also increasingly to book chapters or monographs....
Beilstein Journal of Nanotechnology
Photonics journals
- Journal of Nanophotonics
- Electro Optics
- Laser Focus WorldLaser Focus WorldLaser Focus World is a monthly magazine published by PennWell Corporation covering laser, photonics and optoelectronics technologies, applications, and markets...
- Nature Photonics
- Nature Nanotechnology
- Optics & Photonics Focus
- Photonics news
- Photonics SpectraPhotonics SpectraPhotonics Spectra is a monthly business-to-business magazine published for the engineers, scientists and end users who develop, commercialize and buy photonic products...