We propose a plasmo-thermomechanical mid-infrared detector operating at 4.3 μm wavelength. The design utilizes an array of the bimetallic fishbone nanowires that are suspended 50 nm above a 1.5 μm × 0.3 μm silicon nitride waveguide to create a leaky wave radiation. Moreover, the thermo-mechanically actuated nanowire will induce evanescent wave modulation that can be detected by the leaky wave or transmitted power of the waveguide. The antenna has a strip length of 1.77 μm and can yield an absorption coefficient of 42.4% with a period of 3.1 μm. Six unit cells are connected by a nanowire, and the fishbone-like nanowires are clamped at the two ends, leaving the center free to bend. The mid-infrared energy is absorbed by the resonant metallic antennas, resulting in a temperature increment. The mismatch of the thermal expansion coefficients of the bimetallic materials, gold and nickel, actuates the nanowire, and thus changes the gap between the nanowire and the waveguide. The deformation of the nanowire modulates the waveguide evanescent field, and hence alternates the transmitted power as well as the leak wave power. With a normal incident power of 4 μW/μm2 , the temperature in the center of the nanobridge can be increased over 135 K above the ambient temperature, leading to an elevation of 23.5 nm in the center and thus weakening the evanescent modulation strength. The difference of S21 caused by the gap change is 0.106. This methodology can be applied in other spectrums and the fabrication progress will be reported later.
Plasmonic nanostructures are highly used for sensing purposes since they support plasmonic modes
which make them highly sensitive to the refractive index change of their surrounding medium.
Therefore, they can also be used to detect changes in optical properties of ultrathin layer films in a
multilayer plasmonic structure. Here, we investigate the changes in optical properties of ultrathin
films of macro structures consisting of STT-RAM layers. Among the highest sensitive plasmonic
structures, nanohole array has attracted many research interest because of its ease of fabrication,
small footprint, and simplified optical alignment. Hence it is more suitable for defect detection in
STT-RAM geometries. Moreover, the periodic nanohole pattern in the nanohole array structure
makes it possible to couple the light to the surface plasmon polariton (SPP) mode supported by the
structure. To assess the radiation damages and defects in STT-RAM cells we have designed a
multilayer nanohole array based on the layers used in STT-RAM structure, consisting 4nm-
Ta/1.5nm-CoFeB/2nm-MgO/1.5nm-CoFeB/4nm-Ta layers, all on a 300nm silver layer on top of a
PEC boundary. The nanoholes go through all the layers and become closed by the PEC boundary on
one side. The dimensions of the designed nanoholes are 313nm depth, 350nm diameter, and 700nm
period. Here, we consider the normal incidence of light and investigate zeroth-order reflection
coefficient to observe the resonance. Our simulation results show that a 10% change in refractive
index of the 2nm-thick MgO layer leads to about 122GHz shift in SPP resonance in reflection
We numerically investigated optical properties, including evanescent intensity ratio (EIR), effective refractive index (Neff), dispersion coefficient (D), and mode area (Aeff) of the silicon nitride trench waveguides fabricated by using conventional lithography. The waveguides are etched 3 μm deep with potassium hydroxide for triangle and trapezoidal waveguides, which is then followed by 3 μm thermal oxidation and 725 nm silicon nitride deposition. The waveguide with 725 nm thickness has an EIR peak of 0.025 when its bottom width Wbtm equals 0.65 μm. A thinner waveguide has higher evanescent intensity ratio, which can be used in sensing applications. The locations of EIR peaks correspond to the quasi-TM and TE mode boundary. Narrower waveguides mainly support quasi-TM modes, whereas wider waveguides can support only TE modes. As the waveguide width increases, higher orders of TE modes emerge. In addition, a boundary of TE single mode and multimode can also be linearly curve fitted, according to the starting points of TE higher modes, in order to provide the single mode condition of the waveguide. The waveguide dispersion can be engineered to be in the anomalous region while at the same time remain close to zero. The waveguide with 725 nm thickness and 0.2 μm bottom width has its anomalous dispersion region between the wavelength of 1356 nm and 1462 nm. The mode area decreases with increasing waveguide width. This is the first time we have studied the mode properties of trench waveguides systematically. The waveguide will find more applications in sensing and nonlinear fields with the help of this mode analysis.
We propose electronically controlled optical tweezing based on space-time-wavelength mapping technology. By using time-domain modulation, the location and the polarity of force hot-spots created by Lorentz force (gradient force) can be controlled. In this preliminary study we use 150 fs optical pulses that are dispersed in time and space to achieve a focused elliptical beam that is ~20 μm long and ~2 μm wide. We use an electro-optic modulator to modulate power spectral distribution of the femtosecond beam after temporal dispersion and hence change the intensity gradient along the beam at the focal spot. We present a theoretical model, and simulation results from a proposed experimental setup. The results show that we can achieve ±200 pN forces on nano objects (~100 nm) without mechanical beam steering. The intensity of wavelengths along the spectrum can be manipulated by using different RF waveforms to create a desired intensity gradient profile at the focal plane. By choosing the appropriate RF waveform it is possible to create force fields for cell stretching and compression as well as multiple hot spots for attractive or repulsive forces. 2D space-time-wavelength mapping can also be utilized to create tunable 2D force field distribution.
We demonstrate the fabrication of a highly nonlinear sub-micron silicon nitride trench waveguide coated with gold nanoparticles for plasmonic enhancement. The average enhancement effect is evaluated by measuring the spectral broadening effect caused by self-phase-modulation. The nonlinear refractive index n2 was measured to be 7.0917×10-19 m2/W for a waveguide whose Wopen is 5 μm. Several waveguides at different locations on one wafer were measured in order to take the randomness of the nanoparticle distribution into consideration. The largest enhancement is measured to be as high as 10 times. Fabrication of this waveguide started with a MEMS grade photomask. By using conventional optical lithography, the wide linewidth was transferred to a <100> wafer. Then the wafer was etched anisotropically by potassium hydroxide (KOH) to engrave trapezoidal trenches with an angle of 54.7º. Side wall roughness was mitigated by KOH etching and thermal oxidation that was used to generate a buffer layer for silicon nitride waveguide. The guiding material silicon nitride was then deposited by low pressure chemical vapor deposition. The waveguide was then patterned with a chemical template, with 20 nm gold particles being chemically attached to the functionalized poly(methyl methacrylate) domains. Since the particles attached only to the PMMA domains, they were confined to localized regions, therefore forcing the nanoparticles into clusters of various numbers and geometries. Experiments reveal that the waveguide has negligible nonlinear absorption loss, and its nonlinear refractive index can be greatly enhanced by gold nano clusters. The silicon nitride trench waveguide has large nonlinear refractive index, rendering itself promising for nonlinear applications.
Directive optical leaky wave antennas (OLWAs) with tunable radiation pattern are promising integrated optical modulation and scanning devices. OLWAs fabricated using CMOS-compatible semiconductor planar waveguide technology have the potential of providing high directivity with electrical tunability for modulation and switching capabilities. We experimentally demonstrate directive radiation from a silicon nitride (Si3N4) waveguide-based OLWA. The OLWA design comprises 50 crystalline Si perturbations buried inside the waveguide, with a period of 1 μm, each with a length of 260 nm and a height of 150 nm, leading to a directive radiation pattern at telecom wavelengths. The measured far-field radiation pattern at the wavelength of 1540 nm is very directive, with the maximum intensity at the angle of 84.4° relative to the waveguide axis and a half-power beam width around 6.2°, which is consistent with our theoretical predictions. The use of semiconductor perturbations facilitates electronic radiation control thanks to the refractive index variation induced by a carrier density change in the perturbations. To assess the electrical modulation capability, we study carrier injection and depletion in Si perturbations, and investigate the Franz-Keldysh effect in germanium as an alternative way. We theoretically show that the silicon wire modulator has a -3 dB modulation bandwidth of 75 GHz with refractive index change of 3×10-4 in depletion mode, and 350 MHz bandwidth with refractive index change of 1.5×10-2 in injection mode. The Franz-Keldysh effect has the potential to generate very fast modulation in radiation control at telecom wavelengths.