Mid-IR plasmonic laser antenna

The purpose of this research work is to design and fabricate suitable antenna structures to concentrate incident mid-IR illumination to a sub- wavelength region with significant field enhancement, which may find application in infrared near field microscopy and chemical analysis. The antenna is fabricated on the facet of a QCL. A scanning near field setup based on an atomic force microscope is constructed to characterize the field distribution around the antenna structure.

Nanfang Yu, Ertugrul Cubukcu, Mikhail Belkin, and Laurent Diehl in collaboration with Ken Crozier (Harvard)

Small divergence semiconductor lasers by plasmonic collimation

Surface plasmons offer the exciting possibility of improving the functionality of optical devices through the subwavelength manipulation of light. We show that surface plasmons can be used to shape the beams of edge-emitting semiconductor lasers and greatly reduce their large intrinsic beam divergence. Using quantum cascade lasers as a model system, we show that by defining subwavelength apertures and metallic gratings on their facet, a small beam divergence angle can be achieved in directions both perpendicular and parallel to the laser waveguide layers. Divergence angles as small as a few degrees are obtained, representing a reduction in beam spread by more than one order of magnitude compared with the original lasers used. Despite having a patterned facet, our collimated lasers do not suffer significant reductions in output power. Plasmonic collimation provides a means of efficiently coupling the output of a variety of lasers into optical fibres and waveguides, or to collimate them for applications such as free-space communications, ranging, and remote sensing.

Nanfang Yu, Romain Blanchard and Christian Pflügl

Fiber Based Remote Sensing

We have developed a fabrication method to make fiber based remote sensors that can identify chemicals present in a sample. These sensors consist of an array of metallic nanorods (optical antennas) integrated on the facet of an optical fiber. Light coupled into the fiber interacts with the antennas, exciting their Surface Plasmon Resonances and generating strong electric fields between the rods. Molecules (from the sample) that interact with these strong fields produce detectable signals at their characteristic Raman wavelengths. Some of these signals are coupled into the fiber and are detected with a spectrometer.

Jenny Smythe in collaboration with the group of G.M. Whitesides (Harvard)

Active optical antenna

A compact source with sub-wavelength spatial resolution provides distinct advantages in a number of applications (microscopy, spectroscopy, optical data storage, lithography and laser processing). Limitations on throughput of near-field scanning optical microscopy (NSOM) fibers have led to work on very-small aperture lasers (VSAL), where a sub-wavelength aperture is placed on the facet of a diode laser. In recent years, much attention has been given to optical antennas, in particular due to their ability to couple light very efficiently to sub-wavelength dimensions. In this work, we implement optical antennas on the facet of a laser, thereby creating a new plasmonic device, termed an active optical antenna.

Ertugrul Cubukcu in collaboration with Ken Crozier (Harvard)

Engineering of Nanowire Surface Plasmon Resonances

Nanowires of noble metals have found applications in many fields, such as surface enhanced Raman scattering, and in optoelectronic circuits as waveguides to propagate light below the diffraction limit. Different applications, however, require nanowires with different surface plasmon resonance. In this project, we are exploring how the surface plasmon resonance of metallic nanowires can be tuned by appropriate design of their cross-sectional geometry.

Jiming Bao in collaboration with George M. Whitesides (Harvard)