Description:
TECHNOLOGY AREA(S): Materials
OBJECTIVE: Develop functional photonic devices and circuits which exploit non-linear morphological and nanostructure compositions that are complementary metal–oxide–semiconductor (CMOS) compatible.
DESCRIPTION: There is a critical DoD need to consider miniaturization and CMOS compatibility of on-chip tunable and non-linear photonic components and devices. Traditionally, the diffraction limit of light has limited the miniaturization and high-density integration of photonic circuits and devices. One solution has been to exploit surface plasmon polaritons (SPPs), which are bound waves at the interface between a metal and a dielectric. SPPs supporting structures include metal-insulator-metal (MIM) waveguides, insulator-metal-insulator (IMI) waveguides and dielectric loaded surface plasmon polaritons waveguides have been suggested and demonstrated [1]. Because the energy mostly propagates in the low loss dielectric layer, the latter have much longer propagation lengths than MIM waveguides. However, to broaden nanoscale photonic functionality, MIM structures can confine light to deep subwavelength scales (e.g. < 0.05 of a wavelength) enhancing non-linear effects. In addition, recent developments in subwavelength antennas and meta-atoms, suggests that the dynamics and coupling between two or more subwavelength shaped structures can provide further functionality. The propagation length of MIM structures varies from several micrometers to several tens of micrometers, which is adequate for many for nano-photonic applications. Passive photonic circuits elements such directional couplers (DC) and Mach–Zehnder interferometers (MZIs) based on MIM structures have been proposed and demonstrated. These devices can provide components for signal processing, but an all-optical circuit requires active devices. SPP’s in reduced sized structures containing non-linear optical materials can provide modulating capabilities [2]. Control over the plasmon characteristics relies on the design of the nanostructures’ composition and morphology. Prior research includes optical bistability and variable transmission responses under different incident intensities [3], demonstrating all-optical approaches to control light with light. The wavelength of electromagnetic radiation used in photonic components, devices and circuits, and hence photonic device size, is approximately one hundred times larger than typical electronic components. The use of high index dielectrics will only shrink the optical wavelength in proportion to the refractive index of refraction. Plasmonics, i.e. a collective oscillation of electrons at the surface of a conducting material, oscillate at optical frequencies and propagate along and are tightly confined to the surface with dimensions comparable to electronic circuits. Transverse decay lengths are on the order of the skin depth, 10 nm. Plasmonic structures and devices are lossy but only need to carry information a few centimeters across a chip or a few microns within a device to be effective in fusing electronics with photonics. Light at optical frequencies can be focused to a spot size of only 5 nm through the use of surface plasmons. This tight confinement of electromagnetic waves provides device opportunities and high intensities facilitate non-linear effects that may have low switching threshold energies and fast response times. Non-linear effects can be exploited for frequency conversion, parametric effects as well as simple harmonic generation. These properties are governed by the subwavelength features in plasmonic components and devices, and provide a means to control light with light [4].
PHASE I: Demonstrate the feasibility of non-linear, plasmonic-based devices which provide some specific functionality like frequency conversion at high data rates. Ideally they should have low loss, support small (e.g. less than 1 µm2) footprints and be compatible with CMOS electronic devices at the chip level for control and tunability. Suggested devices include, but are not limited to, all-optical switch, modulators, optical limiter, frequency up-conversion, frequency down-conversion, self focusing, self phase modulation, and Raman scattering. To support scalability requirements of next generation signal processing architectures, the modulators should occupy a small footprint (target is ≤ 2 µm2) have low insertion loss characteristics (<5dB), while providing efficient performance. Phase I deliverables will include a final report, which includes a detailed analysis of the compatibility of the proposed devices, and predicted performance for Phase II. For this topic, DARPA will accept proposals for work and cost up to $225,000 for Phase I. The preferred structure is a $175,000, 12-month base period, and a $50,000, 4-month option period. Alternative structures may be accepted if sufficient rationale is provided.
PHASE II: Finalize the device and material parameters from Phase I. Conduct basic experimental observation of the expected performance of the plasmonic device and its application. Design and fabricate a prototype, ultra-compact plasmonic device. Phase II deliverables will include a final report, which includes designs, fabrication process, and experiment results.
PHASE III: Possible applications for this technology span both the military and commercial arenas. The rapid increase in the clock speed of computers has slowed in recent years due to the interconnect bottlenecks on the chip itself. A plasmonic architecture is expected to alleviate the problems associated with the large size of present day optical components. In the near term, for applications not requiring an entire plasmonic ensemble of active and passive circuitry with sources, detectors, and devices, we recognize that individual advances in plasmonic devices will help to couple photonics to the broader field of nanotechnology.
REFERENCES:
1: R. Zia et al, "Plasmonics: the next chip-scale technology," Materials Today, Vol.9, Issue 7-8 (2006)
2: C. Min et al, "All-Optical Switching in Subwavelength metallic grating structure containing non-linear optical materials," Opt. Letters, Vol. 33, No.8 (2008)
3: H. Ming et al, "Optical bistability in subwavelength metallic grating coated by non-linear material," Opt Express, Vol 15, No. 19 (2007)
4: M. Kauranen et al, "Non-linear plasmonics," Nature Photonics, No. 6 (2012)
KEYWORDS: Plasmonics, Non-linear Devices, Parametric Processes, Plasmonic Devices
