Nanotechnology/Nano-optics

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Nanophotonics and nanooptics

With the increasing demand for smaller, faster, and more highly integrated optical and electronic devices; as well as extremely sensitive detectors for biomedical and environmental applications; a field called nano-optics or nano-photonics is emerging - studying the many promising optical properties of nanostructures.

Like nanotechnology itself, it is a rapidly evolving and changing field – but because of strong research activity in optical communication and related devices, combined with the intensive work on nanotechnology, nano-optics appears to be a field with a promising future.

Nanophotonics is seen as a crucial technology for extending Moore's Law into the next few decades. In the past few years nanophotonics researchers worldwide have developed, On Chip Silicon Lasers, Gigahertz Silicon Electro Optic Switches, and Low Loss Highly Integratable Compact Nanowires (With waveguides of 100’s of nanometers' width).

Nanophotonics is mainly expected to play a complementary role to micro/nano electronics on chip and extend the capacity of telecommunication networks into the Terabit/s regime. One of the major emphasis’s in the last few years has been developing on-chip interconnects to break the bottle neck for higher data rates within integrated chips.

In conjugation with Nanofluidics, Nanophotonics is also finding applications in biomedical sensors, Medical diagnosis, etc.

Nanophotonic components such as Microcavities with ultra high life time of trapped photons are expected to find applications in fundamental experimental physics such as gravitational wave detection.

Intel, IBM, Lucent, and Luxtera have highly functional and well funded nanophotonic research groups. A number of universities in: US, UK, Japan, Italy, China, Belgium, etc. have been actively pursuing nanophotonics. Apart from a growing number of hits on the word in publication databases like "Web of Science", which shows it is already getting increased attention, it is also increasingly mentioned in the aims of the funding agencies, which will surely add to the activity in the field as increased economical support becomes available.

Electrooptic modulators

Electro-optic modulators are devices used to modulate, or modify a beam of light. Currently they are mainly used in the information technology and telecommunications industries (e.g. fiber-optic cables). EOM’s have good potential in nanophotonics. Nanoscale optical communication devices will have increased speed and efficiency, once they can be engineered and used. Nano-size electrooptic modulators will be an integral part of a nanoscale communications network.

Photodetector

Photodetectors respond to radiant energy. They are basically sensors of light or other electromagnetic energy. A sensor is a electronic device that converts one type of energy to another for various reasons. Nanoscale size photodetectors will be an integral part of a theoretical nanoscale optical information network.

Electrooptic switches

Electrooptic switches change signals in optical fibers to electrical signals. Typically semiconductor-based, their function depends on the change of refractive index with electric field. This feature makes them high-speed devices with low power consumption. Neither the electro-optic nor thermo-optic optical switches can match the insertion loss, back reflection, and long-term stability of opto-mechanical optical switches. The latest technology combines all-optical switches that can cross-connect fibers without translating the signal into the electrical domain. This greatly increases switching speed, allowing today's telcos and networks to increase data rates. However, this technology is only now in development, and deployed systems cost much more than systems that use traditional opto-mechanical switches.

Photonic crystals

"Photonic crystals are composed of periodic dielectric or metallo-dielectric nanostructures that are designed to affect the propagation of electromagnetic waves (EM) in the same way as the periodic potential in a semiconductor crystal affects the electron motion by defining allowed and forbidden electronic energy bands. Simply put, photonic crystals contain regularly repeating internal regions of high and low dielectric constant." Photonic crystals are used to modify or control the flow of light. Photonic crystals may have a novel use in optical data transmission but are not extremely prominent. They may be used to filter for interference in a fiber optic cable, or increase the quality of the transmission. In addition, they can be used to divide different wavelengths of light. Photonic crystals can already be manufactured at close to the nanoscale.

Sensors

Nanotechnology creates many new, interesting fields and applications for photonic sensors. Existing uses, like digital cameras, can be enhanced because more ‘pixels’ can be placed on a sensor than with existing technology. In addition, sensors can be fabricated on the nano-scale so that they will be of higher quality, and possibly defect free. The end result would be that photos would be larger, and more accurate. As part of a communication network, photonic sensors will be used to convert optical data (photons) into electricity (electrons). Nanoscale photonic sensors will be more efficient and basically receive similar advantages to other materials constructed under the nanoscale.

Multiplexers

A multiplexer is a device for converting many data streams into one single data stream, which is then divided into the separate data streams on the other side with a demultiplexer. The main benefit is cost savings, since only one physical link will be needed, instead of many physical links. In nano-optics, multiplexers will have many applications. They can be used as part of a communication network, as well as utilized on a smaller scale for various modern scientific instruments.

Vanadium dioxide

Vanadium dioxide has the interesting property of changing from a transparent state to a reflective, mirror-like state in less than 100 femtoseconds (1/10 of a trillionth of a second). Vanderbilt University discovered the transition at 68 degrees celsius. The temperature that the transition happens can be changed by adding small amounts of impurities, and it is possible to lower the temperature by as much as 35 degrees celsius. However, there is a size limit, the change will not occur in particles that are smaller than 20 atoms across, or 10 nanometers. This property has many applications. Possibilities are a 'solar shade' window that changes from letting light in, to reflecting light back automatically when the temperature starts rising. Also, nanosensors could be created which could measure the temperature at different locations in human cells. However, most importantly, this transition can be utilized in creating an 'ultrafast' optical switch which could be used in communications or computing. Currently, researchers are seeing if they can put a layer of vanadium dioxide nanoparticles on the end of an optical fiber to create a very high speed link.

Quantum dots

Quantum dots have several applications. One of the first applications found was their ability to emit very specific wavelengths of light. This is different from other light emitting bulbs since quantum dots could be tuned across the visible and ultraviolet spectrums very precisely. Researchers have found that if they put about 2,000 quantum dots together, they would have a finely tuned LED. Researchers have tried for an extremely long time to get these dots to emit light. In the 1990’s someone was able to get a dark red light. Since then other researchers have been able to tune the dots to a higher frequency, thus gaining blue and green light. The applications for this would be beneficial so that we could make full color screens and monitors.

Resources

• Near and far field - near and far field radiation can to some extent be compared to listening to a walkmans earphones; the one carrying the earphones can hear the sound perfectly even though the bass sound wavelength is much larger than the earphone. If you are not wearing the earphones, the high frequency sounds will be much higher than the bass. The bass can only be heard in the near field.
• plasmonics
• Rochester Nano Optics

Bibliography

• Lucas Novotny and Bert Hect, Principles of Nano-Optics, Cambridge University Press (2006).