The development of flat acoustic lenses for different applications such as biomedical engineering is a topic of great interest. Flat lenses like Fresnel Zone Plates (FZPs) are capable of focusing energy beams without the need of concave or convex geometries, which are more difficult to manufacture. One of the possible applications of these type of lenses is tumor ablation through High Intensity Focused Ultrasound (HIFU) therapies with real time Magnetic Resonance Imaging (MRI) monitoring. In order to be MRI compatible, the FZP material cannot have electromagnetic interaction. In this work, a Phase-Reversal FZP (PR-FZP) made of Polylactic Acid (PLA) manufactured with a commercial 3D printer is proposed as a better, more efficient and MRI compatible alternative to conventional Soret FZPs. Phase-Reversal lenses, unlike traditional FZPs, take advantage of all the incident energy by adding phase compensation regions instead of pressure blocking regions. The manufactured PR-FZP achieves 21.9 dB of focal gain, which increases the gain compared to a Soret FZP of its same size by a factor of 4.0 dB. Both numerical and experimental results are presented, demonstrating the improved focusing capabilities of these types of lenses.

/pdf/acoustic-focusing-enhancement-in-fresnel-zone-plate-lenses-2d7qsm8xjn.pdf

Acoustic Focusing Enhancement In Fresnel Zone Plate Lenses.

We present a design of an ultra-fast in-line graphene optical modulator on a silicon waveguide with a bandwidth exceeding 100 GHz, very small power consumption below 15 fJ/bit, and insertion loss of 1.5 dB. This is achieved by utilizing the transverse-electric-mode silicon slot to tailor the overlap of graphene electrodes, thus significantly reducing the capacitance of the device while maintaining a low insertion loss and using conservative estimates of the graphene resistance. Our design is substantiated by comprehensive finite-element-method simulations and RC circuit characterization, as well as fabrication feasibility discussion.

/pdf/ultra-high-speed-graphene-optical-modulator-design-based-on-51n6k563ak.pdf

Ultra-high-speed graphene optical modulator design based on tight field confinement in a slot waveguide

In this paper, we experimentally demonstrate an ultra-broadband high-performance polarization beam splitter (PBS) based on silicon-on-insulator (SOI) platform. The proposed device is based on a directional coupler consisting of a 70-nm taper-etched waveguide and a slot waveguide with a compact coupling length of 11 microns, the structure of which is suitable for a commercial two-step fabrication process. Benefiting from the preferences of coupling TM mode to slot waveguide and restricting TE mode in taper-etched waveguide, the polarization extinction ratios (PER) for TE and TM polarizations can reach as high as 30 dB and 40 dB at 1550 nm based on experimental results, respectively; besides, an ultra-wide operation bandwidth with PER >20 dB is achieved as ~175 nm from 1450 nm to 1625 nm (covering S, C and L bands), or the bandwidth with PER >25 dB is over ~120 nm from 1462 nm to 1582 nm, which is the largest operation bandwidth to the best of our knowledge. At last, the insertion losses (IL) are −0.17 dB and −0.22 dB for TE and TM polarizations at 1550 nm, respectively.

Compact polarization beam splitter with a high extinction ratio over S + C + L band

http://xrm.phys.northwestern.edu/research/pdf_papers/2011/mayer_ultramic_2011.pdf

Multilayer Fresnel zone plate for soft X-ray microscopy resolves sub-39 nm structures

Silicon photonics, which is compatible with standard CMOS technology, is the most promising platform for large-scale photonic integration. The rapid growth of data volume demands larger link capacity and higher integration density of photonic integrated circuits. Multiplexing technology is an effective approach to enhance the capacity of on-chip optical interconnects. This review provides an introduction to the silicon on-chip multiplexing devices using plasmonics and subwavelength grating (SWG). To expand the data transmission capacity, one solution is introducing wavelength-division-multiplexing structures where diplexer and triplexer are fundamental elements. Another is adopting polarization-division-multiplexing (PDM) technology. Polarizer, polarization beam splitter, polarization rotator, polarization beam splitter-rotator, and polarization-independent directional coupler are all essential components for integrated PDM scheme. By using plasmonics and SWG, the mode profile distribution, refractive index, birefringence, and dispersion can all be manipulated, which enables compact devices with high performance.

Silicon On-Chip PDM and WDM Technologies Via Plasmonics and Subwavelength Grating

A soft x-ray microscope based on a phase-reversal zone plate was constructed and tested using high harmonic radiation as a coherent light source. The 61st harmonic centered at 13.3 nm was optimized in spectral sharpness and intensity by controlling the incident laser energy and chirp. A phase-reversal zone plate made of polymethyl methacrylate more than doubled the first-order efficiency. The nano patterns, imaged on an x-ray CCD with a magnification of 650, showed that the measured resolution of the microscope was better than 100 nm.

Soft x-ray microscope constructed with a PMMA phase-reversal zone plate

An integrated polarization rotator is demonstrated experimentally by forming a strip waveguide with an asymmetric trench on a silicon-on-insulator wafer. The trench is located asymmetrically in the strip waveguide. It induces the evolution of an orthogonal polarization mode upon a linearly polarized beam input, and thus causes polarization rotation. The device is fabricated using a conventional complementary metal oxide semiconductor process with a single dry etching step. The fabricated device shows a maximum transverse electric (TE)-to-transverse magnetic (TM) polarization conversion efficiency of 21.3 dB and an insertion loss of −0.95 dB at a 1550 nm wavelength with a device length of 67 μm. The device exhibits a polarization conversion efficiency and insertion loss of 21.1 dB and −2.12 dB, respectively, for the TM-to-TE polarization conversion. The optimum parameters for the waveguide size and trench size are investigated by performing numerical simulations, and by demonstrating experimental fabrication and measurement.

https://iopscience.iop.org/article/10.1088/2040-8978/18/9/095801/pdf

Demonstration of integrated polarization rotator based on an asymmetric silicon waveguide with a trench

A table-top soft x-ray microscope, adopting a phase-reversal zone plate (PRZP) made of PMMA and high harmonic x-ray source, was constructed. The PMMA PRZP showed enhanced imaging efficiency compared to a metallic Fresnel zone plate.

Table-top soft x-ray microscope adopting a PMMA phase-reversal zone plate

Fresnel zone plates (FZPs) for soft X-ray microscopy with an energy range of 284 eV to 540 eV are designed and fabricated in a simple method. An adequate aspect ratio of the resist mold for electroplating was obtained by the proximity effect correction technology for an incident electron beam on a single thick layer resist. Without additional complicated reactive ion etching, a sufficient electro plating mold for nickel structures was fabricated. The overall fabrication procedures which involve a mix-and-match overlay technique for electron beam lithography and an optic exposure system that centers the membrane on the nanostructures, and hybrid silicon etching technology in junction with deep anisotropy and a KOH wet method in order to release the backside Si substrates of the Si3N4 membranes with no deformation of FZPs are introduced. High quality nanostructures with minimum outermost zone widths of 50 nm and diameters of 120 microm were fabricated with simplified fabrication process and with cost-effective.

A simplified fabrication process of Fresnel zone plates with controlling proximity effect correction.

We present an experimental and numerical study of spectral profiles of effective group indices of hydrogenated amorphous silicon (a-Si:H) waveguides and of their chromatic-dispersion effect on the four-wave-mixing (FWM) signal generation. The a-Si:H waveguides of 220-nm thickness and three different widths of 400, 450 and 500 nm were fabricated by using the conventional CMOS device processes on a $2-{\mu}m$ thick $SiO_2$ bottom layer deposited on 8-inch Si wafers. Mach-Zehnder interferometers (MZIs) were formed with the a-Si:H waveguides, and used for precise measurement of the effective group indices and thus for determination of the spectral profile of the waveguides' chromatic dispersion. The wavelength ranges for the FWM-signal generation were about 45, 75 and 55 nm for the 400-, 450- and 500-nm-wide waveguides, respectively, at the pump wavelength of 1532 nm. A widest wavelength range for the efficient FWM process was observed with the 450-nm-wide waveguide having a zero-dispersion near the pump wavelength.

/pdf/evaluation-of-chromatic-dispersion-dependent-four-wave-3g7gyyh4u8.pdf

Sang Chul Jeon

Papers

Soft x-ray microscope constructed with a PMMA phase-reversal zone plate

Demonstration of integrated polarization rotator based on an asymmetric silicon waveguide with a trench

Table-top soft x-ray microscope adopting a PMMA phase-reversal zone plate

A simplified fabrication process of Fresnel zone plates with controlling proximity effect correction.

Evaluation of Chromatic-Dispersion-Dependent Four-Wave-Mixing Efficiency in Hydrogenated Amorphous Silicon Waveguides