Fariba Hatami

Deterministic Coupling of a Single Nitrogen Vacancy Center to a Photonic Crystal Cavity

We describe and experimentally demonstrate a technique for deterministic, large coupling between a photonic crystal (PC) nanocavity and single photon emitters. The technique is based on in situ scanning of a PC cavity over a sample and allows the precise positioning of the cavity over a desired emitter with nanoscale resolution. The power of the technique is demonstrated by coupling the PC nanocavity to a single nitrogen vacancy (NV) center in diamond, an emitter system that provides optically accessible electron and nuclear spin qubits.

Biomedical terahertz imaging with a quantum cascade laser

We present biomedical imaging using a single frequency terahertz imaging system based on a low threshold quantum cascade laser emitting at 3.7THz (λ=81μm). With a peak output power of 4mW, coherent terahertz radiation and detection provide a relatively large dynamic range and high spatial resolution. We study image contrast based on water/fat content ratios in different tissues. Terahertz transmission imaging demonstrates a distinct anatomy in a rat brain slice. We also demonstrate malignant tissue contrast in an image of a mouse liver with developed tumors, indicating potential use of terahertz imaging for probing cancerous tissues.

Second harmonic generation in gallium phosphide photonic crystal nanocavities with ultralow continuous wave pump power

We demonstrate second harmonic generation in photonic crystal nanocavities fabricated in the semiconductor gallium phosphide. We observe second harmonic radiation at 750 nm with input powers of only nanowatts coupled to the cavity and conversion effciency P(out)/P(2)(in,coupled)=430%/W. The large electronic band gap of GaP minimizes absorption loss, allowing effcient conversion. Our results are promising for integrated, low-power light sources and on-chip reduction of input power in other nonlinear processes.

Controlling the spontaneous emission rate of monolayer MoS2 in a photonic crystal nanocavity

We report on controlling the spontaneous emission (SE) rate of a molybdenum disulfide (MoS2) monolayer coupled with a planar photonic crystal (PPC) nanocavity. Spatially resolved photoluminescence (PL) mapping shows strong variations of emission when the MoS2 monolayer is on the PPC cavity, on the PPC lattice, on the air gap, and on the unpatterned gallium phosphide substrate. Polarization dependences of the cavity-coupled MoS2 emission show a more than 5 times stronger extracted PL intensity than the un-coupled emission, which indicates an underlying cavity mode Purcell enhancement of the MoS2 SE rate exceeding a factor of 70.

Control of two-dimensional excitonic light emission via photonic crystal

Monolayers of transition metal dichalcogenides (TMDCs) have emerged as new optoelectronic materials in the two dimensional (2D) limit, exhibiting rich spin-valley interplays, tunable excitonic effects, and strong light–matter interactions. An essential yet undeveloped ingredient for many photonic applications is the manipulation of its light emission. Here we demonstrate the control of excitonic light emission from monolayer tungsten diselenide (WSe2) in an integrated photonic structure, achieved by transferring one monolayer onto a photonic crystal (PhC) with a cavity. In addition to the observation of an effectively coupled cavity-mode emission, the suspension effects on PhC not only result in a greatly enhanced (~60 times) photoluminescence but also strongly pattern the emission in the subwavelength spatial scale, contrasting on and off the holes. Such an effect leads to a significant diffraction grating effect, which allows us to redistribute the emitted photons both polarly and azimuthally in the far field through designing PhC structures, as revealed by momentum-resolved microscopy. A 2D optical antenna is thus constructed. Our work suggests a new way of manipulating photons in hybrid 2D photonics, important for future energy efficient optoelectronics and 2D nano-lasers.

A high-resolution spectrometer based on a compact planar two dimensional photonic crystal cavity array

We demonstrate a compact spectrometer based on an array of high-quality-factor photonic crystal nanocavities, coupled via a planar two-dimensional waveguide. This architecture enables spectral analysis of incident light with resolution as high as the bandwidth of the cavity mode–0.3 nm at 840 nm for our device. The design is easily extended to the visible and deep-infrared spectral ranges. The two-dimensional cavity array can be mated to commercial two-dimensional optical detector arrays, creating a compact and high-resolution spectrometer suitable for a range of applications including materials and chemical analysis.

Red light-emitting diodes based on InP∕GaP quantum dots

The growth, fabrication, and device characterization of InP quantum-dot light-emitting diodes based on GaP are described and discussed. The diode structures are grown on gallium phosphide substrates using gas-source molecular-beam epitaxy and the active region of the diode consists of self-assembled InP quantum dots embedded in a GaP matrix. Red electroluminescence originating from direct band-gap emission from the InP quantum dots is observed at low temperatures.With increasing temperature, however, the emission line shifts to the longer wavelength. The emission light is measured to above room temperature.

Radiative recombination from InP quantum dots on (100) GaP

We describe the growth and optical emission from strained InP quantum dots grown on GaP using gas-source molecular beam epitaxy. Self-organized island formation takes place for InP coverage greater than 1.8 monolayers on the (100) GaP surface. Intense photoluminescence from the dots is peaked at about 2.0 eV, blueshifted by 0.6 eV from the band gap of bulk InP due to strain, quantum size effects, and possibly Ga interdiffusion.

Nanocavity Integrated van der Waals Heterostructure Light-Emitting Tunneling Diode

Developing a nanoscale, integrable, and electrically pumped single mode light source is an essential step toward on-chip optical information technologies and sensors. Here, we demonstrate nanocavity enhanced electroluminescence in van der Waals heterostructures (vdWhs) at room temperature. The vertically assembled light-emitting device uses graphene/boron nitride as top and bottom tunneling contacts and monolayer WSe2 as an active light emitter. By integrating a photonic crystal cavity on top of the vdWh, we observe the electroluminescence is locally enhanced (>4 times) by the nanocavity. The emission at the cavity resonance is single mode and highly linearly polarized (84%) along the cavity mode. By applying voltage pulses, we demonstrate direct modulation of this single mode electroluminescence at a speed of ∼1 MHz, which is faster than most of the planar optoelectronics based on transition metal chalcogenides (TMDCs). Our work shows that cavity integrated vdWhs present a promising nanoscale optoelectronic platform.

Lithographic positioning of fluorescent molecules on high-Q photonic crystal cavities

Photoluminescent molecules are coupled to high quality photonic crystal nanocavities. The cavities are fabricated in a gallium phosphide membrane and show resonances from 735 to 860 nm with quality factors up to 12 000. The molecules, which are dispersed in a thin polymer film deposited on top of the cavities, can be selectively positioned onto the location of the cavity by using a lithographic technique, which is easily scalable to arrays of cavities.