Tunable Plasmonics for Ultrafast Switching at Telecom Wavelengths

Today's communication networks need to be supported by an ultra-broadband optical backbone in order to respond to the enormous demand for data exchange. Without the use of photonic components, the "magic" of being 24/7connected on a global scale just by using our portable devices would be impossible.

Recently, a new branch of science, called plasmonics, has gained great momentum in the scientific community, since it brings the promise to be complementary to photonics. For instance, in the realm of plasmonics, devices can function on a nanometric scale (1 nanometer [nm] = a billionth of a meter), with consequent advantages in terms of versatility, scalability, and reduced power consumption.

The proposed project "Tunable plasmonics for Ultrafast Switching at Telecom Wavelengths" is focused on novel materials for plasmonic applications (namely titanium nitride -TiN; and aluminum doped zinc oxide - AZO).
Besides solving fundamental issues typical of plasmonic devices such as poor transparency and low damage threshold, these two materials unable the possibility to engineer the light-matter interaction at will. This can be achieved either by changing the fabrication procedure or in a more dynamic fashion by means of an external excitation such as a laser beam or an applied voltage.

The core active material at the center of this project is a new kind of AZO developed inside the collaborative effort between Heriot-Watt University in UK, and the Birck Nanotechnology Center in USA. This "special" AZO is grown by unconventional methods and it exhibits ultrafast optical response (i.e. after the material properties are altered by an optical pulse, it restores its original behavior on a time scale shorter than 1 ps = 1/1000000000000 sec).

One fundamental goal of this project is gaining a deep knowledge of the physical mechanism behind the ultra-fast behavior of AZO (still not fully understood) and use this knowledge to further optimize the material for application in ultra-fast photonics. In addition to this, in order to properly evaluate the potentials of both AZO and TiN in the real world, this project includes the fabrication and testing of an optical modulator prototype (the modulator being the most fundamental building block for encoding information). This device will be interfaced with the external world with input/output TiN-based plasmonic waveguides and will exploit AZO as active core material for performing the ultra-fast signal encoding. Numerical simulations foresee outstanding performances in terms of compactness, reduced power consumption, and ultra-fast operational speed.

The present project will definitely benefit the semiconductor and the photonic industry in the UK, and consolidate the collaborative bridge between world-class Universities located in UK and North America.

The possibility to have materials, such as AZO, capable of largely altering their dielectric permittivity on a sub-picosecond time scale, is the missing ingredient to investigate and develop many fundamental systems in quantum optics, analogue gravity, and terahertz science. In fact, the photon acceleration associated to a sudden and large change in the material refractive index can be used for the generation of entangled photon-pairs, to model the evolution of an expanding universe, or to design efficient THz sources and detectors. The beneficiaries of this knowhow will not be just scientists but also many middle size high-tech companies focused on the previously listed technologies and whose revenue is predicted to explode in the years to come.
In addition to this, other transparent conducting oxides have been largely used by the electronic industries to produce touch and flexible screens, and transparent electrodes for photovoltaic cells. A complete control over the peculiar properties of AZO thin films will make this material very profitable for commercial use since it can be used to enhance the efficiency of all these systems. Many semiconductor companies have already expressed their interest in the full development of the present project, and a partnership has been established with a Scottish semiconductor company, which is willing to provide a generous contribution in terms of material supply and services.

With regards to TiN instead, a full development of the nano-fabrication processes at the base of this material could enable disruptive technologies such as Heat Assisted Magnetic Recording (HAMR) and efficient thermo-photovoltaic. Both these applications could potentially trigger societal changes. While the former brings the promise to increase orders of magnitude the actual data storage capability, the latter could enhance the typical efficiency of photovoltaic modules up to 90%. Both these two applications have been extensively studied from a theoretical point of view but their implementation has been elusive because of the lack of materials with the proper conductivity and thermal resistance.

The proposed project will be carried on in collaboration with prestigious research partners in USA who are world leader in the design and fabrication of novel nano-photonic devices. This collaboration will permanently establish fundamental knowhow and facilities in UK labs for the fabrication and testing of nanophotonics devices, thus drastically straighten the partnership with existent collaborators and promote new ones with other national and international top groups.