We report a normal-incident quantum well infrared photodetector ͑QWIP͒ strongly coupled with surface plasmon modes. A periodic hole array perforated in gold film was integrated with In 0.53 Ga 0.47 As/ InP QWIP to convert normal-incident electromagnetic waves into surface plasmon waves, and to excite the intersubband transition of carriers in the quantum wells. The peak responsivity of the photodetector at ϳ8 m was ϳ7 A/ W at the bias of 0.7 V at 78 K with the peak detectivity as high as ϳ7.4ϫ 10 10 cm Hz 1/2 / W. The full width at half maximum of the response spectrum was only ϳ0.84 m due to a narrow plasmonic resonance.Since Ebbesen et al. 1 found the extraordinary optical transmission of periodic metal nanohole arrays by surface plasmons, properties of surface plasmons have attracted a lot of research interests and been applied into many applications. 2 For example, surface plasmons have been used to improve the efficiency of optoelectronic devices such as solar cells, 3 light emitters, 4 semiconductor lasers, 5 and photodetectors. 6 Recently, periodic metal hole arrays have been applied to quantum dot infrared photodetectors to enhance the efficiency. 7,8 However, as far as we know, there is still no experimental study on applying surface plasmons to enhance the sensitivity of quantum well infrared photodetector ͑QWIP͒. Unlike quantum dot infrared photodetectors, QWIP is only sensitive to the electromagnetic ͑EM͒ waves which have electric field component normal to the quantum wells surface ͑TM mode͒. 9 In the mid and long-infrared wavelengths, where most QWIP devices are operational, the penetration depth of surface plasmons in metals is greatly reduced. Therefore, it yields a low optical loss, and surface plasmon waves have a long propagation length. 10 Surface plasmon supports TM mode and requires the electric field being normal to the surface because of the generation of surface charge. 11 In addition, a carefully designed plasmonic array forms standing waves and produces a cavity effect, which leads to an enhanced transverse plasmonic mode. Therefore, if properly coupled, surface plasmons can resonate with electron intersubband transitions, and efficiently excite carriers in the QWs to generate a strong photocurrent.To simulate the surface plasmon waves and electric field component distribution we used three-dimensional finitedifference time-domain methods. The simulated structure is shown in Fig. 1͑a͒, where the source is a normally incident plane wave. After optimizing the electric field intensity distribution at the wavelength of ϳ8 m, where our QWIP device works, we selected the diameter of the holes d as 1.4 m, the lattice constant of the array a as 2.9 m, and the thickness of Au layer t as 40 nm. The Au layer perforated with holes array is on top of In 0.53 Ga 0.47 As/ InP semiconductor layers. Figure 1͑b͒ shows the simulated spectrum of ͉E z ͉ 2 averaged across the whole quantum well active region between 140 and 584.8 nm below the Au/Semiconductor interface ͓the exact structure is shown in Fig. 2͑...

We present spatial mapping of optical force generated near the hot spot of a metal-dielectric-metal bowtie nanoantenna at a wavelength of 1550 nm. Maxwell's stress tensor method has been used to simulate the optical force and it agrees well with the experimental data. This method could potentially produce field intensity and optical force mapping simultaneously with a high spatial resolution. Detailed mapping of the optical force is crucial for understanding and designing plasmonic-based optical trapping for emerging applications such as chip-scale biosensing and optomechanical switching.

Optical nanoantennas are capable of enhancing the near-field intensity and confining optical energy within a small spot size. We report a novel metal-dielectric-metal coupled-nanorods antenna integrated on the facet of a quantum-cascade laser. Finite-difference time-domain simulations showed that, for dielectric thicknesses in the range from 10 to 30 nm, peak optical intensity at the top of the antenna gap is 4000 times greater than the incident field intensity. This is 4 times higher enhancement compared to a coupled metal antenna. The antenna is fabricated using focused ion-beam milling and measured using modified scanning probe microscopy. Such a device has potential applications in building mid-IR biosensors.

In this Letter, we present a single-exposure deep-UV projection lithography at 254-nm wavelength that produces nanopatterns in a scalable area with a feature size of 80 nm. In this method, a macroscopic lens projects a pixelated optical mask on a monolayer of hexagonally arranged microspheres that reside on the Fourier plane and image the mask's pattern into a photoresist film. Our macroscopic lens shrinks the size of the mask by providing an imaging magnification of ∼1.86×10(4), while enhancing the exposure power. On the other hand, microsphere lens produces a sub-diffraction limit focal point-a so-called photonic nanojet-based on the near-surface focusing effect, which ensures an excellent patterning accuracy against the presence of surface roughness. Ray-optics simulation is utilized to design the bulk optics part of the lithography system, while a wave-optics simulation is implemented to simulate the optical properties of the exposed regions beneath the microspheres. We characterize the lithography performance in terms of the proximity effect, lens aberration, and interference effect due to refractive index mismatch between photoresist and substrate.

Abstract-Exploiting optical nano-antennas to boost the near-field confinement within a small volume can increase the limit of molecular detection by an order of magnitude. We present a novel antenna design based on Au-SiO 2 -Au single nanorod integrated on the facet of a quantum cascade laser operating in the midinfrared region of the optical spectrum. Finite-difference time-domain simulations showed that for sandwiched dielectric thicknesses within the range of 20-30 nm, peak optical intensity at the top of the antenna ends is 500 times greater than the incident field intensity. The device was fabricated using focused ion beam milling. Apertureless midinfrared near-field scanning optical microscopy showed that the device can generate a spatially confined spot within a nanometric size about 12 times smaller than the operating wavelength. Such high intensity, hot spot locations can be used in increasing photon interaction with bio-molecules for sensing applications.Index Terms-Bio-sensing, field enhancement, near-field scanning microscopy, plasmonic antenna, quantum cascade laser (QCL).

Remarkable progress has been made in the fabrication and characterization of optical antennas that are integrated with optoelectronic devices. Herein, we describe the fundamental reasons for and experimental evidence of the dramatic improvements that can be achieved by enhancing the light-matter interaction via an optical antenna in both photon-emitting and -detecting devices. In addition, integration of optical antennas with optoelectronic devices can lead to the realization of highly compact multifunctional platforms for future integrated photonics, such as low-cost lab-on-chip systems. In this review paper, we further focus on the effect of optical antennas on the detectivity of infrared photodetectors. One particular finding is that the antenna can have a dual effect on the specific detectivity, while it can elevate light absorption efficiency of sub-wavelength detectors, it can potentially increase the noise of the detectors due to the enhanced spontaneous emission rate. In particular, we predict that the detectivity of interband photon detectors can be negatively affected by the presence of optical antennas across a wide wavelength region covering visible to long wavelength infrared bands. In contrast, the detectivity of intersubband detectors could be generally improved with a properly designed optical antenna.

We introduce optomechanical nanoantennae, which show dramatic changes in scattering properties by minuscule changes in geometry. These structures are very compact, with a volume 500 times smaller than free-space optical wavelength volume. This deep subwavelength geometry leads to high speed and low switching power. The bandwidth of the device is about 4.4 GHz, with a switching energy of only 35 pJ. Such antenna structures could lead to compact and high-speed all-optical nanoswitches.

We report a type of infrared switchable plasmonic quantum cascade laser, in which far field light in the midwave infrared (MWIR, 6.1 μm) is modulated by a near field interaction of light in the telecommunications wavelength (1.55 μm). To achieve this all-optical switch, we used cross-polarized bowtie antennas and a centrally located germanium nanoslab. The bowtie antenna squeezes the short wavelength light into the gap region, where the germanium is placed. The perturbation of refractive index of the germanium due to the free carrier absorption produced by short wavelength light changes the optical response of the antenna and the entire laser intensity at 6.1 μm significantly. This device shows a viable method to modulate the far field of a laser through a near field interaction.