Kwang Yong Jeong

Low threshold current single-cell hexapole mode photonic crystal laser

The authors report an electrically driven, hexapole mode, single-cell photonic crystal laser operating at 1537.8nm. Electrical current is supplied through a submicrometer-sized current post beneath the cavity center. This wavelength-scale single-cell photonic crystal laser operates in a single mode with threshold current of ∼100μA at room temperature. Operation in the hexapole mode is confirmed by the near-field profile, far-field polarization, and the finite-difference time-domain computation based on the fabricated cavity structure.

Electrically driven nanobeam laser

The realization of lasers as small as possible has been one of the long-standing goals of the laser physics and quantum optics communities. Among multitudes of recent small cavities, the one-dimensional nanobeam cavity has been actively investigated as one of the most attractive candidates for effective photon confinement thanks to its simple geometry. However, the current injection into the ultra-small nano-resonator without critically degrading the quality factor remains still unanswered. Here we report an electrically driven, one-dimensional, photonic-well, single-mode, room-temperature nanobeam laser whose footprint approaches the smallest possible value. The small physical volume of ~4.6 × 0.61 × 0.28 μm3 (~8.2(λ n−1)3) was realized through the introduction of a Gaussian-like photonic well made of only 11 air holes. In addition, a low threshold current of ~5 μA was observed from a three-cell nanobeam cavity at room temperature. The simple one-dimensional waveguide nature of the nanobeam enables straightforward integration with other photonic applications such as photonic integrated circuits and quantum information devices.

A double-strip plasmonic waveguide coupled to an electrically driven nanowire LED.

We demonstrate the efficient integration of an electrically driven nanowire (NW) light source with a double-strip plasmonic waveguide. A top-down-fabricated GaAs NW light-emitting diode (LED) is placed between two straight gold strip waveguides with the gap distance decreasing to 30 nm at the end of the waveguide and operated by current injection through the p-contact electrode acting as a plasmonic waveguide. Measurements of polarization-resolved images and spectra show that the light emission from the NW LED was coupled to a plasmonic waveguide mode, propagated through the waveguide, and was focused onto a subwavelength-sized spot of surface plasmon polaritons at the tapered end of the waveguide. Numerical simulation agreed well with these experimental results, confirming that a symmetric plasmonic waveguide mode was excited on the top surface of the waveguide. Our demonstration of a plasmonic waveguide coupled to an electrically driven NW LED represents important progress toward further miniaturization and practical implementation of ultracompact photonic integrated circuits.

Modal Characteristics in a Single-Nanowire Cavity with a Triangular Cross Section

In this study, the modal characteristics of a single-GaN nanowire cavity with a triangular cross section surrounded by air or located on a silicon dioxide substrate have been analyzed. Two transverse resonant modes, transverse electric-like and transverse magnetic-like modes, are dominantly excited for nanowire cavities that have a small cross-sectional size of <300 nm and length of 10 microm. Using the three-dimensional finite-difference time-domain simulation method, quality factors, confinement factors, single-mode conditions, and far-field emission patterns are investigated for a nanowire cavity as a function of one length of the triangular cross section. The results of these simulations provide information that will be vital for the design and development of efficient nanowire lasers and light sources in ultracompact nanophotonic integrated circuits.

Ultrasmall square-lattice zero-cell photonic crystal laser

We report room-temperature lasing action in an optically pumped heterogeneous square-lattice zero-cell photonic crystal cavity. Photoluminescence spectroscopy exhibits lasing at 1511 nm with a low lasing threshold of ~130 muW. We compute an ultrasmall mode volume of 0.017 mum3 ~ 1.7 (lambda/2nslab)3 using 3D-FDTD simulation.

Wavelength-scale photonic-crystal laser formed by electron-beam-induced nano-block deposition

A wavelength-scale cavity is generated by printing a carbonaceous nano-block on a photonic-crystal waveguide. The nanometer-size carbonaceous block is grown at a pre-determined region by the electron-beam-induced deposition method. The wavelength-scale photonic-crystal cavity operates as a single mode laser, near 1550 nm with threshold of approximately 100 microW at room temperature. Finite-difference time-domain computations show that a high-quality-factor cavity mode is defined around the nano-block with resonant wavelength slightly longer than the dispersion-edge of the photonic-crystal waveguide. Measured near-field images exhibit photon distribution well-localized in the proximity of the printed nano-block. Linearly-polarized emission along the vertical direction is also observed.

Switching of Photonic Crystal Lasers by Graphene

Unique features of graphene have motivated the development of graphene-integrated photonic devices. In particular, the electrical tunability of graphene loss enables high-speed modulation of light and tuning of cavity resonances in graphene-integrated waveguides and cavities. However, efficient control of light emission such as lasing, using graphene, remains a challenge. In this work, we demonstrate on/off switching of single- and double-cavity photonic crystal lasers by electrical gating of a monolayer graphene sheet on top of photonic crystal cavities. The optical loss of graphene was controlled by varying the gate voltage Vg, with the ion gel atop the graphene sheet. First, the fundamental properties of graphene were investigated through the transmittance measurement and numerical simulations. Next, optically pumped lasing was demonstrated for a graphene-integrated single photonic crystal cavity at Vg below -0.6 V, exhibiting a low lasing threshold of ∼480 μW, whereas lasing was not observed at Vg above -0.6 V owing to the intrinsic optical loss of graphene. Changing quality factor of the graphene-integrated photonic crystal cavity enables or disables the lasing operation. Moreover, in the double-cavity photonic crystal lasers with graphene, switching of individual cavities with separate graphene sheets was achieved, and these two lasing actions were controlled independently despite the close distance of ∼2.2 μm between adjacent cavities. We believe that our simple and practical approach for switching in graphene-integrated active photonic devices will pave the way toward designing high-contrast and ultracompact photonic integrated circuits.

Low-threshold photonic-band-edge laser using iron-nail-shaped rod array

We report the experimental demonstration of an optically pumped rod-type photonic-crystal band-edge laser. Lasing operation was achieved with a low threshold of ~90 μW and a peak wavelength of 1451.5 nm at room temperature.

Resonant light scattering from a single dielectric nano-antenna formed by electron beam-induced deposition

Dielectric nano-antennas are promising elements in nanophotonics due to their low material loss and strong leaky-mode optical resonances. In particular, light scattering can be easily manipulated using dielectric nano-antennas. To take full advantage of dielectric nano-antennas and explore their new optical applications, it is necessary to fabricate three-dimensional nano-structures under arbitrary conditions such as in non-planar substrates. Here, we demonstrate full-visible-range resonant light scattering from a single dielectric optical nano-rod antenna. The nano-rod antenna was formed by electron beam-induced deposition (EBID), a promising three-dimensional nanofabrication technique with a high spatial resolution. The nano-rods consist of amorphous alloys of C and O, with a width of 180 nm on average and a length of 4.5 μm. Polarization-resolved dark-field scattering measurements show that both transverse-electric and transverse-magnetic mode resonances cover the full visible range as the height of the nano-rod antenna varies from 90 to 280 nm. Numerical simulations successfully reproduce the measured scattering features and characterize the modal properties, using the critical points dispersive dielectric constant of the EBID carbonaceous material. Our deep understanding of resonant light scattering in the EBID dielectric nano-antenna will be useful for near-field measurement or for the implementation of three-dimensional nanophotonic devices.

Polarization-resolved far-field measurement of single-cell photonic crystal lasing modes

This paper reports the unambiguous identification of lasing modes observed in a single-cell photonic crystal cavity using a solid angle scanning system. The polarization-resolved far-field measurements showed distinctive features of each mode and distinguished it from the other modes in contrast to conventional optical characterization methods. Monopole, quadrupole, and hexapole lasing modes were observed and identified, showing good agreement with numerical simulations. Our understanding of the lasing modes will be useful for determining practical applications as promising light sources in ultracompact photonic integrated circuits.