Horizontal Slot Research Articles

Silicon Nitride Horizontal Air-Slot Microdisk Resonators With a Nanocrystal Si Emitting Layer

Silicon nitride (SiN) microdisk resonators with a 40-nm horizontal air slot and a nanocrystal Si (nc-Si) emitting top layer are investigated. The whole structure is fabricated using only a single deposition and lithography step, with the light-emitting layer self-aligned to excite the slot-mode within the air slot. The nc-si are excited via top-pumping using a UV laser diode, and the visible light emission from nc-Si is coupled into the whispering gallery mode (WGM) with the light concentrated in the air slot. The WGM resonances are observed via side-photoluminescence setup using a Si charge-coupled device. The feasibility of applying this structure as a biosensor is demonstrated, with an estimated surface sensitivity of 2.8 nm/nm.

CMOS compatible horizontal nanoplasmonic slot waveguides TE-pass polarizer on silicon-on-insulator platform

An ultra-compact broadband TE-pass polarizer was proposed and demonstrated on the silicon-on-insulator (SOI) platform, using the horizontal nanoplasmonic slot waveguide (HNSW). Detailed design principle was presented, taking advantage of the distinct confinement region of the TE and TM modes in the HNSW. TM mode cut-off could be achieved when waveguide width was below 210 nm. Proof-of-concept devices were subsequently fabricated in a CMOS-compatible process. The optimized device had an active region length of 1 μm, three orders of magnitude smaller than similar device previously demonstrated on the SOI platform. More than 16 dB polarization extinction ratio was achieved across 80 nm wavelength range, with a relatively low insertion loss of 2.2dB. The compact device size and excellent broadband performance could provide a simple yet satisfactory solution to the polarization dependent performance drawback of the silicon photonics devices on the SOI platform.

Efficient perfectly vertical fiber-to-chip grating coupler for silicon horizontal multiple slot waveguides

Horizontal multiple slot waveguides of polysilicon and silicon nanocrystalline oxide were grating coupled to a surface normal fiber array. Measurements yielded a coupling efficiency of 60% per grating. The fabrication-tolerant, four-stage grating design was genetically evolved from a random seed without starting from first-principle design. Theoretical coupling efficiency was 68% and was re-designed to 63% after accommodating all sources of fabrication error. To our knowledge, this is the first implementation of a purely polysilicon and silicon nanocrystalline oxide slot waveguide platform.

Horizontal slot waveguide channel for enhanced Raman scattering

Herein we characterize and experimentally demonstrate a new type of a horizontal slot waveguide structure for remarkably enhanced Raman scattering detection in nanometer-scale void channels. As the measurement sensitivity is one of the key limiting factors in nanofluidic detection, it is essential to search advanced solutions for such detection. Combining an all dielectric resonance waveguide grating and a surface enhanced Raman scattering (SERS) substrate in a close proximity it is possible to create high electromagnetic field energy hot zones within an adjustable slot region. This results in a strong enhancement in Raman scattering. We show the theoretical principles and demonstrate, with rhodamine 6G molecules, an approximately 20-fold enhancement compared to a conventional SERS substrate within the corresponding slot arrangement. We foresee potential applications for the proposed approach in the fields of medical, biological and chemical sensing, where the high detection sensitivity is essential due to integration with nanofluidic devices.

Er-doped light emitting slot waveguides monolithically integrated in a silicon photonic chip

An integrated erbium-based light emitting diode has been realized in a waveguide configuration allowing 1.54 μm light signal routing in silicon photonic circuits. This injection device is based on an asymmetric horizontal slot waveguide where the active slot material is Er3+ in SiO2 or Er3+ in Si-rich oxide. The active horizontal slot waveguide allows optical confinement, guiding and lateral extraction of the light for on-chip distribution. Light is then coupled through a taper section to a passive Si waveguide terminated by a grating which extracts (or inserts) the light signal for measuring purposes. We measured an optical power density in the range of tens of μW/cm2 which follows a super-linear dependence on injected current density. When the device is biased at high current density, upon a voltage pulse (pump signal), free-carrier and space charge absorption losses become large, attenuating a probe signal by more than 60 dB/cm and thus behaving conceptually as an electro-optical modulator. The integrated device reported here is the first example, still to be optimized, of a fundamental block to realize an integrated silicon photonic circuit with monolithic integration of the light emitter.

Design of highly-nonlinear horizontal slot waveguide with low and flat dispersion

We present an optimum design of highly-nonlinear horizontal slot waveguides consisting of silicon and silicon nanocrystals with flat dispersion characteristics. Results from numerical simulations show that the nonlinear coefficient of 6600W−1m−1 at 1550-nm wavelength and the dispersion values between −150 and 150ps/nm/km in the S, C, and L bands can be achieved. In addition, when we limit the operating bandwidth to C-band, the most tolerant slot height is 20nm for the 10nm fabrication errors of waveguide width and high-index region height.

Polarization splitter using horizontal slot waveguide

In this paper a compact and efficient polarization splitter using horizontal slotted waveguides is presented. The splitter is designed by finite-difference-time-domain simulation and realized experimentally. The splitter is built by using a direction coupler consisting of two horizontal slotted waveguides and achieves a high extinction ratio of 14.1 and 16.8 dB for cross and through ports. The optimal coupling length is found to be 15 µm. The device exhibits a good response of extinction ratio across C + L broadband. The splitter obtained is readily used for a polarization diversity circuit, particularly for platforms with horizontal slot waveguides.

Toward a 1.54 $\mu$m Electrically Driven Erbium-Doped Silicon Slot Waveguide and Optical Amplifier

In this paper, we report on the first attempt to design, fabricate, and test an on-chip optical amplifier which works at 1540 nm and can be electrically driven. It is based on an asymmetric silicon slot waveguide which embeds the active material. This is based on erbium-doped silicon rich silicon oxide. We describe the horizontal asymmetric slot waveguide design which allows us to get a high field confinement in a nanometer thick active layer. In addition, we detail the complex process needed to fabricate the structure. The waveguides have been characterized both electrically as well as optically. Electroluminescence can be excited by hot carrier injection, due to impact excitation of the Er ions. Propagation losses have been measured and high values have been found due to processing defects. Pump and probe measurements show a voltage dependent strong attenuation of the probe signal due to free carrier accumulation and absorption in the slot waveguide region. At the maximum electrical pumping level, electroluminescence signal is in the range of tens of μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the overall loss of the device is only -6 dB. Despite not demonstrating optical amplification, this study shines some light on the path to achieve an all-silicon electrically driven optical amplifier.

Comparison of Functional Recovery of Manual Dexterity after Unilateral Spinal Cord Lesion or Motor Cortex Lesion in Adult Macaque Monkeys

In relation to mechanisms involved in functional recovery of manual dexterity from cervical cord injury or from motor cortical injury, our goal was to determine whether the movements that characterize post-lesion functional recovery are comparable to original movement patterns or do monkeys adopt distinct strategies to compensate the deficits depending on the type of lesion? To this aim, data derived from earlier studies, using a skilled finger task (the modified Brinkman board from which pellets are retrieved from vertical or horizontal slots), in spinal cord and motor cortex injured monkeys were analyzed and compared. Twelve adult macaque monkeys were subjected to a hemi-section of the cervical cord (n = 6) or to a unilateral excitotoxic lesion of the hand representation in the primary motor cortex (n = 6). In addition, in each subgroup, one half of monkeys (n = 3) were treated for 30 days with a function blocking antibody against the neurite growth inhibitory protein Nogo-A, while the other half (n = 3) represented control animals. The motor deficits, and the extent and time course of functional recovery were assessed. For some of the parameters investigated (wrist angle for horizontal slots and movement types distribution for vertical slots after cervical injury; movement types distribution for horizontal slots after motor cortex lesion), post-lesion restoration of the original movement patterns (“true” recovery) led to a quantitatively better functional recovery. In the motor cortex lesion groups, pharmacological reversible inactivation experiments showed that the peri-lesion territory of the primary motor cortex or re-arranged, spared domain of the lesion zone, played a major role in the functional recovery, together with the ipsilesional intact premotor cortex.

A Novel Reflective Surface With Polarization Rotation Characteristic

A reflective surface with polarization rotation property is proposed in this letter. The primary function of the surface is to reflect the linearly polarized incident wave with 90° polarization rotation. The fractional bandwidth reaches up to 9.5%, with copolarization reflection coefficient better than -10 dB at normal incidence. Stable frequency responses in the passband have been obtained with oblique incidence for TE polarization. The periodic element of the proposed surface consists of a dual-mode substrate integrated waveguide (SIW) cavity resonator with horizontal and vertical slots on the same side. A parametric study of its frequency responses has been done with full-wave simulation. To verify the design method, a prototype designed at 35 GHz is fabricated and measured. The measured results are in good agreement with the numerical simulations.

Heat Transfer Due to Natural Convection in a Periodically Heated Slot

Heat transfer resulting from the natural convection in a fluid layer contained in an infinite horizontal slot bounded by solid walls and subject to a spatially periodic heating at the lower wall has been investigated. The heating produces sinusoidal temperature variations along one horizontal direction characterized by the wave number α with the amplitude expressed in terms of a suitably defined Rayleigh number Rap. The maximum heat transfer takes place for the heating with the wave numbers α = 0(1) as this leads to the most intense convection. The intensity of convection decreases proportionally to α when α→0, resulting in the temperature field being dominated by periodic conduction with the average Nusselt number decreasing proportionally to α2. When α→∞, the convection is confined to a thin layer adjacent to the lower wall with its intensity decreasing proportionally to α−3. The temperature field above the convection layer looses dependence on the horizontal direction. The bulk of the fluid sees the thin convective layer as a “hot wall.” The heat transfer between the walls becomes dominated by conduction driven by a uniform vertical temperature gradient which decreases proportionally to the intensity of convection resulting in the average Nusselt number decreasing as α−3. It is shown that processes described above occur for Prandtl numbers 0.001 &lt; Pr &lt; 10 considered in this study.

Sensing performance of plasma-enhanced chemical vapor deposition SiC-SiO2-SiC horizontal slot waveguides

We have studied, for the first time, the sensing capabilities of plasma-enhanced chemical vapor deposition (PECVD) SiC-SiO2-SiC horizontal slot waveguides. Optical propagation losses were measured to be 23.9 dB?cm for the quasi-transverse magnetic mode. To assess the potential of this device as a sensor, we simulated the confinement factor in the slot. This simulation revealed that SiC-based slot waveguides can be used, advantangeously, for sensing as the confinement strongly varies with the refractive index of the slot material. A confinement factor change of 0.15?refractive index units was measured for different slot materials

Low TPA and free-carrier effects in silicon nanocrystal-based horizontal slot waveguides

We present the characterization of the ultrafast nonlinear dynamics of a CMOS-compatible horizontal-slot waveguide with silicon nanocrystals. Results are compared to strip silicon waveguides, and modeled with nonlinear split-step calculations. The extracted parameters show that the slot waveguide has weaker carrier effects and better nonlinear figure-of-merit than the strip waveguides.

Efficient and broadband polarization rotator using horizontal slot waveguide for silicon photonics

We report an efficient and low-loss polarization rotator based on mode evolution using horizontal slot waveguide. The device is fabricated using complementary metal–oxide–semiconductor compatible processes, which allows monolithic integration with active drive electronics and other photonic components. A rotator fabricated with 100 μm transition length provides a high extinction ratio &amp;gt;14 dB for both transverse-magnetic (TM)-transverse-electric (TE) and TE-TM rotation. The excess loss of the device is &amp;lt;1 dB for both rotations as etching of the bottom Si waveguide is prevented. The device also exhibits a uniform rotation response over C+L band wavelength range of 1530-1600 nm.

The hydrodynamic characteristics of a single suspended row of half pipes under regular waves

In this paper, the hydrodynamic performance of a new type breakwater is studied using physical models. The breakwater consists of one row of half pipes suspended on supporting piles. The transmission, the reflection, and the wave energy dissipation coefficients are presented for different wave and structure parameters. The results indicate that the performance of the proposed breakwater becomes efficient when: (1) the half pipes are horizontal; (2) the diameter of the half pipes is increased; (3) the breakwater inclination angle is 45°; (4) the breakwater draft is greater than the half of the water depth; and (5) the wavelength is more than two times the water depth. In addition, the proposed breakwater type gives high performance when compared with the other similar breakwater systems, e.g. suspended vertical or horizontal pipes and slots, by about 5%–40%.

Photonic crystal horizontally slotted nanobeam cavity for silicon-based nanolasers

We theoretically propose and investigate a TM-polarized one-dimensional photonic crystal nanocavity with a horizontal SiO2 slot on a suspended silicon nanobeam via the three-dimensional finite-element method. The ultrahigh quality factor and ultrasmall effective mode volume of 1.5×10(7) and 0.176 half-wavelength cubic of the horizontally SiO2-slotted nanocavity show strong possibilities for realizing an erbium-doped SiO2 nanolaser. This horizontal SiO2 slot structure can be precisely formed via the sputtering process and further transformed into an air slot via selective wet etching for optical index and biomolecule sensing.

Design for broadband high-efficiency grating couplers

In this Letter, we propose general optimization methods to design broadband high-efficiency grating couplers for planar waveguides. We attribute the coupling bandwidth to the mismatch of effective indices between the diffracted beam and the actual grating structure around the operation wavelength for fiber to waveguide excitation. The coupling bandwidth formula is deduced. A simple parameter-separate optimization procedure is proposed for general layered grating couplers for high coupling efficiency. Using our principle, we optimized a grating coupler for a horizontal slot waveguide operating at wavelength 1.55 μm for TM polarization. The grating coupler has 1 dB bandwidth of 60 nm and coupling efficiency of 65% with incident light from single-mode optical fiber (SMF) at 8°.

Proposal of an Ultra-Compact Branch-Type PlasmonicPolarization Beam Splitter (PBS)

Branch-type polarization beam splitter (PBS) has not been received much attention recently due to its relatively long device-length (~100s µm). In this paper, we proposed a novel design based on the horizontal nanoplasmonic slot waveguide to address this problem. A detailed design principle and procedures to optimize the device parameters are clearly illustrated. Comprehensive numerical analysis is performed to investigate the performance of the devices using the finite-difference time-domain (FDTD) methods. By carefully designing the widths of the branches, we shows that more than 15dB extinction ratio can be achieved, using only 1μm active device length. Proof-of-concept devices are subsequently fabricated in a CMOS-compatible process and characterized, producing results that agree well with the numerical simulation.

Wideband electromagnetically coupled coaxial probe fed slot loaded stacked patch antenna

A wideband U-slot loaded rectangular patch stacked with horizontal slot loaded rectangular patch antenna is presented in this paper. The resonating behavior of antenna depends on slot width, slot length of side arm and base arm of U-slot. Similarly, it depends on separation between the two patches. Optimization of these parameters gives impedance Bandwidth of 54.6%.

Nanoplasmonic power splitters based on the horizontal nanoplasmonic slot waveguide

Ultracompact power splitters based on the horizontal nanoplasmonic slot waveguide (Cu/SiO2/Si/SiO2/Cu, whose propagation loss is measured to be ∼0.36 dB/μm at 1550 nm for waveguide with ∼47-nm-wide Si core and ∼26-nm surrounding SiO2) are designed, simulated, and fabricated using the standard complementary metal-oxide-semiconductor technology. The 1 × 2 Y-splitters with the opening angle of 60°, 120°, and 180° are measured to have the excess losses of ∼1.4, ∼1.7, and ∼3.2 dB, compared with the theoretical values of ∼1.4, ∼1.5, and ∼1.8 dB, respectively. The 1 × 3 cross-splitter delivers normalized output powers of ∼ −7.6, ∼ −4.2, and ∼ −7.2 dB at the left, middle, and right output ports, respectively, compared with the theoretical value of ∼ −6.6 dB. Reasons of the discrepancy between the experimental and theoretical results are discussed, and approaches to further reduce the excess loss are then proposed.