Optical disk memory, optical fiber communication systems, and photolithography are examples of success in photonics. In the case of optical disk memory, storage and readout of the pit size smaller than λ/NA are not possible, where λ and NA are the wavelength of the incident light and a numerical aperture of the focusing lens, respectively. Shorter-wavelength lasers have been intensively developed in order to decrease the diffraction-limited pit size, i.e., the major efforts of increasing storage density have been how to use the shorter-wavelength light for storage and readout. However, the upper limit of the storage density to be realized by using visible light is several 10 Gb/in.2, while the value to be required in the year 2010 is 1 Tb/in.2. Semiconductor lasers, optical waveguides, and optical switching devices have to confine the light in their bodies for effective operations. In the case of a semiconductor laser, its active layer has to be larger than the diffraction-limited volumes, i.e., λ3, for this confinement. In the case of an optical fiber, its core diameter has to be larger than λ. These examples mean that the sizes of photonic devices cannot be smaller than the wavelength of light, which is the diffraction-limited size of the photonic device. However, sizes of photonic switching devices for the optical fiber communication system in the year 2015 must become smaller than the diffraction-limited ones. The most narrow linewidth of the pattern fabricated by photolithography is also limited by diffraction. Progress in decreasing the patterned size has been the result of the effort of using shorter-wavelength light for decreasing the diffraction-limited value. However, further shortening of the wavelength requires gigantic and expensive light sources, which can prohibit developing practical microfabrication systems. For the visible light sources, the 30–70-nm linewidth for 64–256 GbDRAMs is far beyond the diffraction limit. To summarize, the society of the twenty-first century requires a novel optical technology in order to realize measurement, fabrication, control, and function with the size of several tens of nanometers. However, such miniaturization of optical technology is not possible as long as the conventional propagating light is used. This is the bottleneck imposed by light diffraction. One must go beyond the diffraction limit in order to open a new field of optical technology; this field is called as “nanophotonics.”
Optical disk memory, optical fiber communication systems, and photolithography are examples of success in photonics. In the case of optical disk memory, storage and readout of the pit size smaller than λ/NA are not possible, where λ and NA are the wavelength of the incident light and a numerical aperture of the focusing lens, respectively. Shorter-wavelength lasers have been intensively developed in order to decrease the diffraction-limited pit size, i.e., the major efforts of increasing storage density have been how to use the shorter-wavelength light for storage and readout. However, the upper limit of the storage density to be realized by using visible light is several 10 Gb/in.2, while the value to be required in the year 2010 is 1 Tb/in.2. Semiconductor lasers, optical waveguides, and optical switching devices have to confine the light in their bodies for effective operations. In the case of a semiconductor laser, its active layer has to be larger than the diffraction-limited volumes, i.e., λ3, for this confinement. In the case of an optical fiber, its core diameter has to be larger than λ. These examples mean that the sizes of photonic devices cannot be smaller than the wavelength of light, which is the diffraction-limited size of the photonic device. However, sizes of photonic switching devices for the optical fiber communication system in the year 2015 must become smaller than the diffraction-limited ones. The most narrow linewidth of the pattern fabricated by photolithography is also limited by diffraction. Progress in decreasing the patterned size has been the result of the effort of using shorter-wavelength light for decreasing the diffraction-limited value. However, further shortening of the wavelength requires gigantic and expensive light sources, which can prohibit developing practical microfabrication systems. For the visible light sources, the 30–70-nm linewidth for 64–256 GbDRAMs is far beyond the diffraction limit. To summarize, the society of the twenty-first century requires a novel optical technology in order to realize measurement, fabrication, control, and function with the size of several tens of nanometers. However, such miniaturization of optical technology is not possible as long as the conventional propagating light is used. This is the bottleneck imposed by light diffraction. One must go beyond the diffraction limit in order to open a new field of optical technology; this field is called as “nanophotonics.”
The past decade has seen an explosion of development in new devices, modalities, and architectures for advanced sensing, computation, and communication. This growth has been driven by the massive investments of large consumer-tech companies in data-hungry domains of customer interest. As these companies develop their products and seek a competitive edge, technologies which can provide advantage across application areas by making computation cheaper, or sensors more knowledgeable, or communication faster, are attracting more interest in and outside academia. Photonics, or the study of how to manipulate light, is a broad-based platform that inherently delivers on these promises. Although photonics has been a part of daily life since the invention of the laser, modern needs and aspirational designs which meet those needs far exceed the capabilities of the platforms which have traditionally constituted the photonics toolkit.\nThere are two specific areas where standard photonic materials are lacking - support for visible wavelengths and functionality for quantum optics. Currently, there are many implementations of systems which use visible light or quantum optics on the tabletop, but the drive to scale these technologies and deliver them to the consumer encounters a roadblock in their size and cost. Visible light sensors, for instance, could greatly benefit from conversion into an integrated photonics platform, where the optical components are printed onto a small substrate. However, the standard materials used for such systems (silicon and indium phosphide) absorb visible light, and other materials (like silicon nitride) do not have the attributes required for advanced functionality. More compellingly, there exist very few material platforms which can host the quantum defects required for next-generation technologies like quantum computation or secure communication.\nThe past decade has seen extensive research into an emerging material platform which can deliver on the ability to bring integrated visible photonics and quantum optics to the same chip - diamond. With a broad transparency region (from UV to the far infrared) and high refractive index, diamond makes an excellent material for run-of-the-mill photonic devices. More importantly, it harbors atom-like defects in its crystal lattice - the nitrogen-vacancy, silicon-vacancy, and germanium-vacancy centers, among many more - which provide a direct interface between the photons circulating within the diamond device and the quantum world. Taken together, these simple properties of diamond constitute a powerful approach towards implementation of advanced quantum technologies, such as repeaters for secure quantum communication or even, one day, computers.\nBefore that future arrives, diamond's capability must first be developed. Diamond has only been available in significant quantities for research use for about a decade, and as such, the processing technologies which are taken for granted in silicon or silicon nitride-based work must be redeveloped. Within the context of photonic devices, we discuss different fabrication strategies and their implications for device design. For visible light devices especially, we investigate methods to reduce sidewall roughness for etched structures.\nInterfacing with diamond photonic structures also brings its own unique set of challenges due to its high refractive index and very small material footprint. To this end, we develop a method termed "loaded tapered-fiber coupling" to optically access large, free-standing diamond devices. For size-limited diamond resonators and waveguides, we also develop auxiliary optical waveguides to act as spot-converters for visible wavelengths, an improvement on previous techniques for telecom-range wavelengths.\nFinally, by synthesizing these improvements in fabrication, we embark on a set of experiments in diamond microresonators. Nonlinear optics is an excellent testbed for such improvements, both for diamond's superlative properties in that regard and their high sensitivity to improvements in fabrication. First, we look at a process known as Raman lasing by constructing long path-length resonators.This technique involves the shifting of an input photon by 40 THz via the interaction with the diamond's crystal lattice.The first demonstration in a diamond integrated device was shown with a pump wavelength of 1600 nm, with an output that was tuned over 100 nm and a low threshold. Leveraging the developments in visible photonics for diamond, a second Raman laser was demonstrated, this time at near-visible (720 nm) wavelengths.This too had a Stokes output which was tunable to over 100 nm and a very low threshold. Raman-specific effects such as polarization conversion were also investigated.\nA cousin to the Raman effect, the Kerr nonlinearity plays a key role in so-called microresonator (or Kerr) frequency combs. We survey the possibilities and difficulties in implementation for a diamond platform, highlighting the competition between the Kerr and Raman nonlinearities. Although the outlook for a technologically relevant Kerr comb in diamond is ultimately pessimistic, avenues for improvement are highlighted. Namely, we investigate via simulation a related class of effects, known as supercontinuum generation.Taking advantage of subtleties of the Raman process in diamond, we can find a preferred geometry which enables generation of a broadband light spectrum natively in diamond.\nFinally, we look at alternative applications of diamond, particularly in high-power systems. Due to its excellent thermal conductivity and power-handling capacity, optics fashioned purely out of diamond can show significant advantages compared to other materials. We end with a discussion of the design principles and results stemming from this work.
The transmission of information as optical signals encoded on light waves traveling through optical fibers and optical networks is increasingly moving to shorter and shorter distance scales. In the near future, optical networking is poised to supersede conventional transmission over electric wires and electronic networks for computer-to-computer communications, chip-to-chip communications, and even on-chip communications. The ever-increasing demand for faster and more reliable devices to process the optical signals offers new opportunities in developing all-optical signal processing systems (systems in which one optical signal controls another, thereby adding "intelligence" to the optical networks). All-optical switches, two-state and many-state all-optical memories, all-optical limiters, all-optical discriminators and all-optical transistors are only a few of the many devices proposed during the last two decades. The "all-optical" label is commonly used to distinguish the devices that do not involve dissipative electronic transport and require essentially no electrical communication of information. The all-optical transistor action was first observed in the context of optical bistability [1] and consists in a strong differential gain regime, in which, for small variations in the input intensity, the output intensity has a very strong variation. This analog operation is for all-optical input what transistor action is for electrical inputs.
Ever since superconducting nanowire single-photon detectors (SNSPDs or SSPDs) were demonstrated, they have attracted a considerable attention due to the detectors’ promising performance that includes high detection efficiency (DE), low dark count rate (DCR), broadband sensitivity, and low timing jitter. The system detection efficiency (SDE) has been improved to be over 90% with a wavelength of 1550 nm in a fiber-coupled system by embedding the SNSPD in optical cavities. However, the implementation of optical cavity usually reduces the bandwidth of SNSPDs. As a result, there are some recent works on increasing the bandwidth of SNSPD. Furthermore, the size of the active area of meandered nanowires has to be compatible with the core size of an optical fiber such that good optical coupling can be achieved; this setup requires a long nanowire with a large kinetic inductance, thus resulting in a small counting rate and a large timing jitter, particularly for multi-mode fiber-coupled devices. Nevertheless, a particularly impressive waveguide-coupled SNSPD has been developed in recent years. By placing an SNSPD atop an optical waveguide that has been fabricated on various substrate materials, photons propagating in the waveguide have been found to be evanescently absorbed by nanowires that are only a few tens of microns long. The on-chip DE of this device has been estimated to be over 90%, thus indicating that it has both high absorptance and high intrinsic DE. If the waveguide and the nanowire are correctly dimensioned, the absorptance of this device can reach over 90% for a wavelength range of more than 700 nm. Furthermore, the length of the nanowire is shorter than that of the fiber-coupled SNSPD, thus leading to a higher count rate and lower timing jitter (~18 ps). However, unsatisfactory coupling losses between the optical fiber and the waveguide in such devices can decrease its SDE (~10%), thus limiting its applicability to quantum photonic integrated circuits (QPIC). Recently, we proposed a type of SNSPD that was coupled with microfibers (MFs), and simulations for this SNSPD indicated that its absorption would be as high as 90%. Microfibers and nanofibers, tapered adiabatically from standard fibers, with diameters close to or smaller than the wavelength of the guided light were demonstrated to have low transmittance losses by Tong et al. in 2003. MFs have been shown to have many interesting properties, such as strong evanescent fields, tight optical confinement, wideband abilities, and small masses; these properties are appealing for applications such as optical sensing and coupling. MFs also provide seamless connections with high transmittance from standard fibers; therefore, MF-coupled SNSPDs can achieve both high SDEs and wideband compatibility. We proposed and demonstrated the MF-coupled SNSPDs successfully. The simulation results indicate that with optimal device structure, the optical absorption with efficiency < 90% can be realized over a wavelength range of 350 nm to 2150 nm. The fabricated MF-coupled SNSPD, shows unparalleled broadband system detection efficiencies (SDEs) of more than 50% from 630 nm to 1500 nm. The SDEs reach 66% at 785 nm and 45% at 1550 nm. These results pave the way for ultra-broadband weak light detection with quantum-limit sensitivity.
Nanophotonics describes optical science and technology at the nanoscale that offers challenging opportunities for studying fundamental processes of interaction between the radiation eld and the matter on a scale much smaller than the wavelength of radiation. The use of such conned interaction to spatially localized processes offers exciting opportunities to chemists. Nanophotonics is considered to be of immense technological signicance. The evolution and development of the nanophotonics technology with the increased need for an internetworking broadband communication had lead to the development of more sophisticated optical networks. Those networks are now interconnected CONTENTS Summary ........................................................................................................................................ 21 2.1 Introduction ..........................................................................................................................22 2.2 Nanometer Connement and Fabrication of Matter ......................................................22 2.3 Application of Computational Intelligence in Photonics Technology .........................23
T hink about coherent systems, and odds are that the first example to cross your mind will be a laser: a device that emits monochromatic light homogenized so that the photons propagate with their phase in lockstep. The well-defined wavefront of the laser beam makes it possible to focus the light to spot sizes on the order of the wavelength of the light without the aberrations usually observed with the random wavefront of incoherent light. The well-defined phase also provides a medium capable of storing and carrying information more efficiently than the intensity-modulated signals typical of incoherent sources. These useful properties of coherence have made lasers almost ubiquitous in science and technology, and that “almost” is shrinking by the day.
In general, coherence comes about when individual components of a system act in unison, either in phase or with a fixed phase difference between the components. More accurately, the system can be described as a local oscillator whose wavefunction contains phase and amplitude terms that define how the system evolves in space and time. The collection of articles in this special issue describes the recent progress and developments of coherence in optical, atomic, and semiconductor systems, and how manipulating that coherence may lead to useful applications and to experimental systems for studying the elements of quantum mechanics.
Since the first demonstration of the laser in 1960, progress in improving the extent of the spatial and temporal coherence of laser light has been steady. Psaltis (p. [1359][1]) reviews developments in optical coherence and highlights examples of the key role coherence has played in applications in imaging, communication, and information processing and storage. Just as lasers revolutionized the field of optics, many researchers have high expectations that other coherent systems will provide similar advances in their respective fields. Exploiting the fundamental tenet of quantum mechanics whereby particles have the properties of waves, Kasevich (p. [1363][2]) reviews coherence effects in collections of cold atoms and describes how the shorter wavelengths associated with atoms and the recent accessibility of bright coherent atom sources may lead to precision measurements beyond anything currently available to the optical regime. For integration and potential applications, the ideal system would be based in semiconductors. Snoke (p. [1368][3]) describes recent work toward the formation of coherent semiconductor systems.
With coherence in the atomic and optical systems generally comprising macroscopic systems, Mabuchi and Doherty (p. [1372][4]) look at coherence effects at the quantum limit, probing the interactions between single atoms and single photons confined to high-quality cavities. In addition to providing invaluable information on the limits of quantum mechanics, such effects might also shed new light on information science in the quantum regime.
The section opens with a pair of News features by staff writers Charles Seife and Robert Service. Seife presents a smattering of common applications that scientists and engineers have found for coherent waves, whether in light, sound, or subatomic particles. Service describes efforts to create new coherent sources of the type of radiation known as “hard” x-rays—a long-sought range of high frequencies with enormous potential for scientific research, technology, and medicine.
[1]: /lookup/doi/10.1126/science.1078823
[2]: /lookup/doi/10.1126/science.1079430
[3]: /lookup/doi/10.1126/science.1078082
[4]: /lookup/doi/10.1126/science.1078446