Substrate Lens Research Articles

Numerical study of terahertz circular polarized substrate lens dipole antennas for polarization sensitive detectors

Wide band circular polarized (CP) antennas behind extended hemispherical lenses suitable for polarization sensitive THz detector and wireless communication have been designed and characterized using numerical simulation. Two novel, compact and CP dipole antennas are designed and studied for this purpose. CP property of planar antennas is achieved by geometrical modifications of antennas without any complicated feeding structure. Due to compact dimensions, wideband performance and CP behavior, these designs have applications in circular dichroism (CD) spectroscopy and terahertz detectors. This numerical study deals with polarization diversity with substrate lens, effect of off axis displacement on CP behavior of lens antenna which determines number of pixels for any application, far field patterns variation due to lens's internal reflection, directivity variation attributed to internal reflection and losses. Radiation efficiency variation of antenna by antenna dimensions is also studied carefully to design appropriate lens from application's point of view. Off axis performance of antenna on hemisphere lens is also studied and redesigning of antenna by some geometric modification has been carried out to improve far field patterns.

Dielectric Rod Waveguide Antenna as THz Emitter for Photomixing Devices

We propose a dielectric rod waveguide antenna (DRW) integrated with a photomixer as a THz emitter. This represents a different approach as opposed to the classical solution of a substrate lens. Main goals are an inexpensive alternative to substrate lenses, reduction of both reflections on the semiconductor-air interface and scattering of terahertz-generated power into the substrate. A radiation pattern measured at 137 GHz is shown as a proof-of-concept. In order to increase radiated power, the improvement of the rod antenna is discussed. Finally, as an application example, evanescent coupling of the DRW into a high index whispering gallery mode resonator is shown.

2508 Press Molding of Si-HDPE Hybrid Lens Substrate for Infrared Optical Applications

A hybrid Si-HDPE substrate was developed as an alternative to infrared (IR) lens material in 7.5 to 14μm wavelength using high-precision molding press. HDPE was heated to melt state and pressed onto a Si wafer. Hybrid Si-HDPE with the thin laminated polymer improved IR characteristics of Si. The hybrid substrate then used as an IR lens for night vision camera and the images captured shows similarity to Si filtered images. These results show that hybrid Si-HDPE provide an effective solution for inexpensive IR lens with easy fabrication. Micro dimples can be precisely formed on HDPE for night vision systems lens.

Colloidal quantum dot solar cells on curved and flexible substrates

Colloidal quantum dots (CQDs) are semiconductor nanocrystals synthesized with, processed in, and deposited from the solution phase, potentially enabling low-cost, facile manufacture of solar cells. Unfortunately, CQD solar cell reports, until now, have only explored batch-processing methods—such as spin-coating—that offer limited capacity for scaling. Spray-coating could offer a means of producing uniform colloidal quantum dot films that yield high-quality devices. Here, we explore the versatility of the spray-coating method by producing CQD solar cells in a variety of previously unexplored substrate arrangements. The potential transferability of the spray-coating method to a roll-to-roll manufacturing process was tested by spray-coating the CQD active layer onto six substrates mounted on a rapidly rotating drum, yielding devices with an average power conversion efficiency of 6.7%. We further tested the manufacturability of the process by endeavoring to spray onto flexible substrates, only to find that spraying while the substrate was flexed was crucial to achieving champion performance of 7.2% without compromise to open-circuit voltage. Having deposited onto a substrate with one axis of curvature, we then built our CQD solar cells onto a spherical lens substrate having two axes of curvature resulting in a 5% efficient device. These results show that CQDs deposited using our spraying method can be integrated to large-area manufacturing processes and can be used to make solar cells on unconventional shapes.

A 0.54 THz Signal Generator in 40 nm Bulk CMOS With 22 GHz Tuning Range and Integrated Planar Antenna

This work presents the design and measurements of a 0.54 THz signal generator implemented in a 40 nm bulk CMOS technology. An LC-VCO operating at 180 GHz is connected to a nonlinear buffer, which is designed to generate the wanted third harmonic at 540 GHz. The third harmonic is coupled via a transformer to the output. The developed techniques are implemented on two different chips: one with a probe pad for on-wafer measurements and one with an on-chip planar dipole. The measured peak output power using a WR-1.5 probe is -31 dBm at 543 GHz, for 16.8 mW of dc power consumption. By changing value of the parasitic I-MOS varactors of the LC-VCO (“parasitic tuning”), the output frequency can be tuned from 561.5 to 539.6 GHz, resulting in a 21.9 GHz tuning range, which is the highest reported so far for CMOS THz oscillators. The 3-dB output bandwidth is 5.5 GHz. The 540 GHz signal generator with on-chip antenna is used for THz imaging without the use of substrate or focusing lenses, demonstrating some of the capabilities of CMOS for low-cost, mass-produced THz imagers.

A traveling-wave stripline dipole antenna on a substrate lens at terahertz frequency

In this paper, a study of a stripline dipole antenna on a substrate lens used as a photoconductive detector in a terahertz system is presented. The traveling-wave behavior of the stripline dipole and the influence of the substrate lens are investigated over a broad frequency range up to 5.0 THz. The numerical results show that the lens shape represented by the ratio of the extension length to the lens radius plays an important role in maximizing the antenna gain and radiation spectral bandwidth. The gain response exhibited an increased level of sensitivity to the lens shape as the lens size increased, and this is particularly important in optimizing large substrate lenses. Improvements in the gain level over the entire frequency range of interest were observed as the lens diameter increased. This study provides helpful guidelines in choosing and optimizing a substrate lens designed for a terahertz photoconductive antenna, which is particularly useful for specific applications requiring a miniaturized photoconductive antenna design.

Fabrication of hybrid structures using UV roll-typed liquid transfer imprint lithography for large areas

Recently, nanoscale and micro-scale hybrid structures have become the focus of significant research interest due to their potential for use in anti-reflection films, anti-fingerprint films, solar cells, nanofluidic and microfluidic channels, and some functional optical films. Moreover, the nanopatterning lithography systems using roll-typed stamps have become increasingly appealing technologies for undertaking mass production and for continuous fabrication of hybrid patterns on large area substrates. In this study, we propose a roll-typed liquid transfer imprint lithography (R-LTIL) system and process for fabrication of nanoscale and microscale hybrid patterns on flat and micro lens substrates. Using the proposed system, nanoscale patterns that are 350nm hole and 250nm in height are flawlessly transferred to 6in. Si wafer and microscale lens substrates.

W-Band Mutlilayer Perforated Dielectric Substrate Lens

W-band planar perforated dielectric substrate lens antenna is designed and implemented. The lens utilizes a perforated dielectric multilayer substrate that converts spherical wavefront into planar wavefront. The dielectric perforation is performed with air holes, and each hole has a uniform diameter through all layers for simplicity. The transmission coefficient phase is controlled locally. The lens is designed at 94 GHz and composed of 29 × 29 elements that cover an area of 58×58 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The lens is center-fed by a WR-10 rectangular waveguide located at 44.5 mm from the lens making an aperture angle of 42 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> . Two lenses are investigated, a single-layer lens and a six-layers lens. The six-layers lens provides 30 dB gain, which is 1.7 dB higher than the gain provided by the single-layer lens at 94 GHz. The numerical and measured results are found to be in good agreement.

Fabrication of Thin-Film Fresnel Optics by Combining Diamond Turning and Photolithographic Processes

A novel fabrication process is proposed for manufacturing thin-film metal Fresnel lenses for X-ray applications. This process combines diamond turning technology and photolithographic processes. To prevent thin-film lens substrates from deflection during diamond turning, films were prepared on single crystalline silicon wafers by electrolytic plating. After the Fresnel lens structure is generated on the metal thin films by diamond turning, the silicon substrate was then removed selectively by reactive ion etching. Experimental results demonstrated that the proposed hybrid fabrication process achieves submicron form accuracy and nanometer surface roughness.

Fully Integrated ASK Receiver MMIC for Terahertz Communications at 300 GHz

An ASK receiver MMIC operating at 300 GHz for future terahertz communications is presented. In the receiver IC, we fully integrated all necessary components-a receiving dipole antenna, high gain RF amplifier, envelop detector for demodulating ASK signal and output differential data amplifier-in a 1000×2500 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area. A silicon lens was used to compensate for the small gain of the on-chip antenna. To ensure reliable and stable operation, we designed the MMIC with a thin-film microstrip line, which is expected to suppress crosstalk between the on-chip antenna and the RF amplifier through the substrate and silicon lens. The packaged receiver module with the silicon lens is expected to provide approximately 24-dBi beam directivity. Measured RF and baseband bandwidths are around 30 and 15 GHz, respectively, when a single bias of 3.3 V and total current of around 86 mA are applied. With the receiver module, simple wireless data transmission was conducted for up to 24 Gbps in the 300-GHz band. At 12.5 Gbps, error-free data transmission (bit error rate <; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> ) over 0.3 m was achieved with the transmission power of - 16-dBm and a 25-dBi transmitting antenna. With -10-dBm transmission power, measured Q-factors of the received eye patterns were larger than 6 for up to 20 Gbps, which implies that the bit error rate will be less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> .

Optical Simulation Study on the Effect of Diffusing Substrate and Pillow Lenses on the Outcoupling Efficiency of Organic Light Emitting Diodes

The effect of diffusing substrate and pillow lenses on the outcoupling efficiency of organic light-emitting diodes (OLEDs) was studied by optical simulation based on the point-dipole model. The diffusing substrate included Mie scatterers by which the condition of total internal reflection could be broken. The finite-difference time-domain method was used to obtain the intensity distribution on the transparent electrode of an OLED, which was used as a light source to carry out a ray-tracing simulation of the OLED and the diffusing substrate. It was found that the outcoupling efficiency of the OLED was sensitive to the thickness of organic layers and could be increased by 21.0% by adopting a diffusing substrate in which Mie scatterers whose radius was 2.0 μm were included at the density of 10 7 mm -3 and by 65.5% by forming one pillow lens with the radius of 2 mm on the front surface of the glass substrate. This study revealed that the outcoupling efficiency could be improved by adopting diffusing substrate and pillow lenses along with the optimization of the thickness of each layer in the OLED.

EFFECTS OF ANTENNA DESIGN PARAMETERS ON THE CHARACTERISTICS OF A TERAHERTZ COPLANAR STRIPLINE DIPOLE ANTENNA

This paper presents the antenna design parameter dependency on the impedance and radiation characteristics of a terahertz coplanar stripline dipole antenna. The antenna response is numerically investigated by applying a semi-inflnite substrate and by generating a constant voltage source to drive a signal on the antenna. In this way, we can analyze the antenna characteristics without the photoconductive material response and the substrate lens geometrical efiects. Further, we explain the mechanism underlying the preferable uses of several millimeter length DC bias striplines in a typical THz coplanar stripline dipole antenna design. The antenna, consisting of a center dipole connected to long bias striplines, has a traveling wave characteristic supporting an attenuated current, rather than a resonant characteristic supporting a standing wave of current. The traveling wave behavior produces stable antenna input impedances and minimal changes in the antenna radiation patterns. We also found that the length of the center dipole has a prominent efiect on the antenna gain response.

A 15–50-GHz Quasi-Optical Scalar Network Analyzer Scalable to Terahertz Frequencies

A 15-50-GHz two-port quasi-optical scalar network analyzer consisting of a transmitter and receiver built in a planar technology is presented. The network analyzer is based on a Schottky-diode multiplier and mixer integrated inside a planar antenna and fed differentially by a coplanar waveguide transmission line. The antenna is placed on an extended hemispherical high-resistivity silicon substrate lens. The local oscillator signal is swept from 3 to 5 GHz and high-order harmonic mixing in both the up- and down-conversion mode is used to realize the RF bandwidth. The network analyzer has a dynamic range of >;50 dB in a 1-kHz bandwidth, and was successfully used to measure frequency-selective surfaces with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =20, 30, and 40 GHz and a second-order bandpass response. Furthermore, the system was built with circuits and components for easy scaling to millimeter-wave frequencies, which is the primary motivation for this work.

Numerical Study of Self-Complementary Antenna Characteristics on Substrate Lenses at Terahertz Frequency

This paper presents a numerical study of self-complementary antennas on substrate lenses made of high-permittivity dielectric material. Bowtie, logarithmically periodic, and logarithmic spiral antennas with the same outer and inner dimensions were selected for study, and their overall performances were compared in the terahertz band at frequencies up to 5.0 THz. The resonance and radiation characteristics of the three antennas were investigated in terms of input impedance, directivity, and radiation efficiency, using a full electromagnetic simulator. This study provides useful guidelines and partially solves the difficult problems of choosing the proper feed and optimizing the lens structure for a THz broadband integrated lens antenna.

Terahertz current oscillations in a gated two-dimensional electron gas with antenna integrated at the channel ends

We studied terahertz current oscillations induced by a frequency-tunable radiation source in a AlGaAs/InGaAs/AlGaAs heterostructure field effect transistor channel. A planar antenna was integrated on-chip, and a substrate lens was used for broadband coupling of free-space radiation at 0.18–0.72 THz to the channel ends. Through spectral analysis of the detection signal, we identified two different mixing mechanisms: one related to channel current oscillations and the other to modulation of the gate-to-channel potential. Depending on gate bias and radiation frequency, the two mechanisms either compete or cooperate, leading to responsivity up to 300 V/W and noise equivalent power of 1 nW/Hz0.5

Fabrication and Characterization of Quasi-Optical Terahertz Nanorectifiers with Integrated Antennas

We are developing microelectronic terahertz rectifiers by scaling down the dimensions of GaAs Schottky diodes and field-effect transistors to the sub-micron range, and by investigating the effect of on-chip parasitic capacitances on the square-law power detection signal. For broadband operation at THz frequencies the terahertz oscillating signal is fed to the device by integrated lithographic planar antennas, suitably coupled to a silicon substrate lens. Such room-temperature THz detectors can be fabricated in arrays and naturally provide picosecond response time, suitable for detection of coherent THz radiation produced by single electron bunches in accelerators.

Gain Measurement of Embedded On-Chip Antennas in mmW/THz Range

A method for gain measurement of embedded on-chip antennas in mmW/THz range is presented. In this method, the radiation pattern is first measured in a quasi-optical configuration using a power detector. Subsequently, the radiated power is estimated from the integration over the radiation pattern. Finally, the antenna gain is obtained from measurement of a two-antenna system. The experimental results of applying this method on an on-chip planar dipole with substrate lens are demonstrated, and verified against simulation. A radiated power of around 40 μW and measured gain of 17 dB are reported at 180 GHz for this antenna structure.

Full-Wavelength Dipole Antenna on a Hybrid GaAs Membrane and Si Lens for a Terahertz Photomixer

A full-wavelength dipole antenna on a GaAs membrane, covered with a silicon lens to improve the output power of a terahertz (THz) photomixer, is proposed. A full-wavelength dipole antenna supported by a GaAs membrane structure has been proven to achieve both high input resistance and high radiation efficiency for improved overall efficiency. However, the antenna has insufficient directivity. An extended hemispherical lens was introduced in front of the antenna in a non-contact configuration and coupled to the antenna radiation to achieve high directivity by beam collimation. This approach greatly enhances the antenna directivity while avoiding an inherent obstacle of the input resistance reduction caused by the high permittivity lens substrate. The resulting antenna after optimization had a 3818-Ω input resistance and a 71.2% radiation efficiency, corresponding to approximately 57% total efficiency at the 1.07-THz resonance frequency. The total efficiency of this structure is approximately 6.8 times that of a full-wavelength dipole antenna with the same hemisphere lens size while exhibiting slightly lower directivity.

FULL-WAVELENGTH DIPOLE ANTENNA ON A GAAS MEMBRANE COVERED BY A FREQUENCY SELECTIVE SURFACE FOR A TERAHERTZ PHOTOMIXER

An antenna consisting of a full-wavelength dipole on a GaAs membrane covered by a frequency selective surface is proposed for improved output power from photomixers used as terahertz (THz) sources. The antenna structure reduces the vertical dimension of a typical photomixer antenna using a substrate lens while still exhibiting high total e-ciency and high directivity. The resulting antenna after optimization produced an input resistance of 3870› and a radiation e-ciency of 60%, corresponding to a total e-ciency, i.e., the e-ciency of the antenna in THz wave radiation, of approximately 48.3% and a maximum directivity of 20.2dBi at the resonance frequency of 1.03THz. The proposed antenna is expected to be a promising alternativeTHz photomixer design.

Fabrication of Thin-Film Fresnel Optics by Combining Diamond Turning and MEMS Techniques

A novel fabrication process was proposed for manufacturing thin-film metal Fresnel lenses for X-ray applications, which combines MEMS technologies and diamond turning technology. To prevent thin-film lens substrates from deflection during diamond turning, the thin films were prepared on single crystalline silicon wafers by electrolytic plating. After the Fresnel lens structure has been generated on the metal thin films by diamond turning, the backside supporting silicon substrate was selectively removed by reactive ion etching. Experimental results demonstrated that submicron level form accuracy and nanometer level surface roughness could be achieved by the proposed hybrid fabrication process.