Low-loss Polymer Research Articles

Silicon-free, low-loss and high contrast polymer multimode waveguides

The fabrication and characterization of SU-8 multimode optical waveguides on fused quartz and silicon oxide substrates were successfully realized and analyzed. Optical losses for the transverse electric (TE) mode polarization of 0.58 dB cm−1 and 1.44 dB cm−1 and transverse magnetic (TM) mode polarization of 0.73 dB cm−1 and 1.16 dB cm−1 were measured for SU-8 waveguides on fused quartz and silicon oxide substrates, respectively. The fabrication process for SU-8 waveguides on quartz developed herein could be applied for SU-8 optical integrated devices on other substrate materials.

Broad- and Narrow-Line Terahertz Filtering in Frequency-Selective Surfaces Patterned on Thin Low-Loss Polymer Substrates

A new class of frequency-selective surface filters (FSS) for terahertz (THz) applications is proposed and investigated both numerically and experimentally. A periodic FSS array of cross-shaped apertures is patterned on aluminum, deposited on thin foils of the low-loss cyclo-olefin polymer Zeonor. Apart from the fundamental filtering response of the FSS elements, we also observe very narrow-linewidth peaks with high transmittance, associated with guided-mode resonances in the dielectric substrate. The effect of the filter's geometrical parameters on its performance is systematically studied via finite-element method simulation and confirmed by time-domain spectroscopy characterization of the fabricated samples. Finally, thanks to the flexibility of the employed substrates, THz-FSS filters are also characterized in bent configuration, revealing a robust response in terms of the fundamental FSS passband filter and a high sensitivity of the GMR peaks. These features can be exploited in the design of novel THz filters or sensors.

Electrical properties of polyetherimide thin films: Non-parametric dielectric response analysis with distribution of relaxation times.

High temperature polymeric materials for electrical insulation and energy storage are needed for transformational power applications such as pulsed-power and hybrid electrical vehicles. One of the candidate materials has been polyetherimide, an amorphous thermoplastic with a glass transition over 200 °C. Here, the dielectric studies on the material are reported by taking into account the polarization and conduction processes in the polyetherimide. The dielectric data were analyzed with the distribution of relaxation times approach with Debye expression as the kernel in the inversion algorithm, the results then created the relaxation map for polyetherimide. The method satisfies the Kramers-Kronig relationships, so the ohmic conductivity and permittivity at high frequencies could be estimated from the experimental data even if there exists significant measurement error. The data were compared to the published results on polyetherimide in the literature. The materials is a low loss polymer with negligible ohmic losses below 200 °C. The estimated fragility of the polyetherimide was high about 284 from the resolved relaxation map using the Vogel-Fulcher-Tammann-Hesse expression. Polyetherimide is a good dielectric for advanced energy storage and electrical insulation technologies up to 200 °C.

Glass Interposer Electromagnetic Bandgap Structure for Efficient Suppression of Power/Ground Noise Coupling

In this paper, we propose glass interposer electromagnetic bandgap (EBG) structure to efficiently suppress power/ground noise coupling. We designed, fabricated, measured, and analyzed a glass interposer EBG structure for the first time. Glass interposer EBG structure test vehicles were fabricated using a thin-glass substrate, low-loss polymer layers, and periodic metal patches with through glass vias (TGVs) in glass interposer power distribution network. Using the dispersion characteristics, we thoroughly analyzed and derived f L and f U of the glass interposer EBG structure. We experimentally verified that the proposed glass interposer EBG structure achieved power/ground noise suppression (below –40 dB) between f L of 5.8 GHz and f U of 9.6 GHz. Derived f L and f U based on dispersion analysis, full three-dimensional electromagnetic (3-D-EM) simulation and measurement achieved good correlation. In the glass interposer EBG structure, tapered structure of the TGV and thickness of the low-loss polymer used for metal-layers lamination affected the noise suppression bandgap significantly. The effectiveness of the proposed glass interposer EBG structure on suppression of the power/ground noise propagation and coupling to high-speed TGV channel was verified with 3-D-EM simulation. As a result, the proposed glass interposer EBG structure successfully and efficiently suppressed the power/ground noise propagation and improved eye-diagram of the high-speed TGV channel.

Angle-resolved and polarization-dependent investigation of cross-shaped frequency-selective surface terahertz filters

The spectral response of a terahertz (THz) filter is investigated in detail for different angles of incidence and polarization of the incoming THz wave. The filter is fabricated by patterning an aluminum frequency-selective surface of cross-shaped apertures on a thin foil of the low-loss cyclo-olefin polymer Zeonor. Two different types of resonances are observed, namely, a broadline resonance stemming from the transmittance of the slot apertures and a series of narrowline guided-mode resonances, with the latter being investigated by employing the grating theory. Numerical simulations of the filter transmittance based on the finite-element method agree with experimental measurements by means of THz time domain spectroscopy (THz-TDS). The results reveal extensive possibilities for tuning the guided-mode resonances by mechanically adjusting the incidence or polarization angle, while the fundamental broadline resonance is not significantly affected. Such filters are envisaged as functional elements in emerging THz systems for filtering or sensing applications.

50th Anniversary Perspective: Dielectric Phenomena in Polymers and Multilayered Dielectric Films

High dielectric constant and low dielectric loss are desirable electrical properties for next-generation polymer dielectrics that show promise for applications in pulsed power, power electronics, and printable electronics. Unfortunately, the dielectric constant of polymers is often limited to 2–5, much lower than that of inorganic dielectrics, because of the nature of hydrocarbon covalent bonds for electronic and atomic polarizations. It is essential to understand the fundamental physics of different types of polarization and the associated loss mechanisms in polymers. In this Perspective, we discuss the characteristics of each polarization and explain how to enhance the polarization using rational molecular designs without causing significant dielectric losses. Among various approaches for high dielectric constant and low loss polymers, the multilayer film technology is of particular interest because a multilayer film is a unique one-dimensional system with tailored material choices, layer thicknesses, a...

Periodical Elements as Low-Cost Building Blocks for Tunable Terahertz Filters

Periodical elements made by stacking thin layers of the cyclo-olefin polymer Zeonor, separated by spacers made of bi-adhesive tape, are used as building blocks for realizing tunable terahertz (THz) filters. The basic block is a Bragg reflector whose bandgap can be controlled by changing the geometrical features of the periodical elements. By combining two of these Bragg building blocks, separated by a void defect cavity, a tunable bandpass filter is obtained. The thickness of the defect cavity is mechanically tuned by means of a translation stage. The resulting filter are mechanically stable and they show both high transmittance and narrow linewidths, owing to the selected THz low-loss polymer.

Three-dimensional patterning in polymer optical waveguides using focused ion beam milling

Waveguide (WG) photonic-bridge taper modules are designed for symmetric planar coupling between silicon WGs and single-mode fibers (SMFs) to minimize photonic chip and packaging footprint requirements with improving broadband functionality. Micromachined fabrication and evaluation of polymer WG tapers utilizing high-resolution focused ion beam (FIB) milling is performed and presented. Polymer etch rates utilizing the FIB and optimal methods for milling polymer tapers are identified for three-dimensional patterning. Polymer WG tapers with low sidewall roughness are manufactured utilizing FIB milling and optically tested for fabrication loss. FIB platforms utilize a focused beam of ions (Ga+) to etch submicron patterns into substrates. Fabricating low-loss polymer WG taper prototypes with the FIB before moving on to mass-production techniques provides theoretical understanding of the polymer taper and its feasibility for connectorization devices between silicon WGs and SMFs.

Discontinuous Tapered Surface Plasmon Polariton Waveguides with Gap.

We investigate characteristics of discontinuous tapered surface plasmon polariton waveguides with a gap (DTG-SPPWs) to control a guided surface plasmon polariton (SPP) at a telecommunication wavelength of 1.55 μm. The DTG-SPPWs are composed of an input 2 μm-wide and 10 μm-long reverse tapered IMI-W (RT-IMI-W) and a 10 μm-long tapered and output 2 μm-wide IMI-W (T-IMI-W) with the 8 μm-long gap. The width and length of the tapered regions in the RT-IMI-W and the T-IMI-W were varied from 2 to 10 μm and 1 to 8 μm, respectively. Gold is used as the metal in the insulator-metal-insulator waveguides (IMI-Ws). The thickness of the gold strips is fixed with 20 nm. A low-loss polymer is used for the 30 μm-thick upper and lower cladding layers. The coupling losses of the DTG-SPPWs are less than 0.055 dB with an 8 μm-long gap and various taper widths up to 10 μm. The normalized transmissions (NTs) of the DTG-SPPWs are less than about -0.060 dB with various taper widths up to 10 μm. The NTs of the DTG-SPPWs are less than about -0.069 dB with various taper lengths up to 8 μm. The maximum NT of about -0.042 dB was obtained using the 6 μm-wide taper width and the 3 μm-long taper length in the DTG-SPPW. The DTG-SPPWs have potential as a new plasmonic modulation device via control of the guided SPP through interaction with an applied force in the gap.

Measurements of the Complex Permittivity of Low Loss Polymers at Frequency Range From 5 GHz to 50 GHz

Complex permittivity of Polytetrafluoroethylene (PTFE), Polypropylene (PP), Polyethylene (PE) and cross-linked Polystyrene (Rexolite), has been measured at frequency range from 5 GHz to 50 GHz. Measurements have been performed in two cylindrical cavities employing several quasi $\text{TE}_{0 \mathrm{mn}}$ modes excited in samples under test. Measurement uncertainties for the real part of permittivity were $\pm$ 0.5% while for the imaginary part of permittivity in the range from $\pm$ 8% for the lowest loss materials to $\pm$ 3% for Rexolite. It has been confirmed that the real part of permittivity of all measured polymers is constant in the microwave frequency spectrum to within measurement uncertainties, while the dielectric loss tangent values vary with frequency

Adaptive Broadband Radar Absorber Based on Tunable Graphene

An innovative broadband adaptive absorber, providing a reflection coefficient lower than $-10\,{\rm dB}$ in the frequency range from 7 to 22 GHz, is proposed. The new absorber is a two-period dielectric Salisbury, in which the outer lossy sheet is made of a graphene monolayer, and the inner one consists of a tunable graphene/dielectric laminate (GL). The two dielectric spacers are made of a commercial low-loss polymer. The total thickness is $\sim 6\,{\rm mm}$ . The adaptive broadband response of the absorber is achieved tuning the effective sheet resistance of the GL through an applied electrostatic field bias. The sensitivity analysis of the reflection coefficient of the absorber illuminated by a plane wave with normal incidence is carried out with respect to the spacer thickness and the graphene carrier charge mobility. By applying a dc-voltage source always below 15 V, the minimum reflection coefficient of the adaptive absorber is centered around 14 GHz, and it is characterized by a bandwidth at $-10\,{\rm dB}$ of $\sim 15\,{\rm GHz}$ .

Bandwidth enhancement of microstripline-to-waveguide transitions for broadband E-band module applications

In this work, a broadband microstripline-to-waveguide (MSL-to-WG) transition has been presented for E-band module applications. In order to extend its bandwidth (BW), extended ground (eGND) planes and patch-type probe are designed and their dimension and structure are optimized. Compared to the ordinary transition using a simple electric probe (S-probe), the optimized eGND plane on the dielectric substrate and triple-patch probe enhance the operational BW of 56.4 and 71.7%, respectively. The designed transition on the low-loss liquid crystal polymer (LCP) dielectric substrate was fabricated. Its measured operational BW for the reflection loss (S11) below −10 dB is over 28 GHz at all test frequencies from 67 to 95 GHz. The measured insertion loss of the fabricated transition can be analyzed as −1.45 and −1.59 dB per a transition at 70 and 80 GHz, respectively, considering the loss contribution of the cable adapter and waveguide transition. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1398–1401, 2016

BROADBAND TRANSITION FROM MICROSTRIP LINE TO WAVEGUIDE USING A RADIAL PROBE AND EXTENDED GND PLANES FOR MILLIMETER-WAVE APPLICATIONS

A broadband microstrip line-to-waveguide (MSL-to-WG) transition is developed for E-band applications. In order to achieve a sufficient and broadband coupling between the microstrip line (MSL) and waveguide (WG), a radial electric probe at the end of the MSL and extended ground (GND) planes on the dielectric substrate are proposed. Results are compared against a simple transition (S-Tr) with a straight electric probe. For the case of operational bandwidth (BW) for an input return loss (S11) below −20 dB, the proposed transitions using the radial probe and extended GND planes show the BW enhancement of 33.8% and 61.9%, respectively, compared to the S-Tr. The proposed and simple transitions were fabricated on a low-loss liquid crystal polymer (LCP) dielectric substrate. The measured bandwidth (BW) for S11 below −10 dB of the proposed transition is over 28 GHz, which is satisfied at all test frequencies from 67 to 95 GHz. Its measured insertion loss can be analyzed as −1.33 and −1.41 dB per transition at 70 and 80 GHz, respectively, considering the loss contribution of the cable adapter and waveguide transition.

Gapped Surface Plasmon Polariton Waveguides for Plasmonic Signal Modulation Applications.

We investigate the characteristics of gapped surface plasmon polariton waveguides (G-SPPWs) to control a guided SPP through interaction with an applied force in the gap at a telecommunication wavelength of 1.55 μm. Gold is used as the metal in the insulator-metal-insulator waveguides (IMI-Ws). A low-loss polymer is used for the 30-μm-thick upper and lower cladding layers. The excited input SPPs propagate, jump over gaps with low coupling losses, and propagate again, even though there is a lengthy 12-μm-long gap in the G-SPPWs. The coupling loss is less than 0.05 dB for G-SPPWs with a gap up to 8-μm long, various widths up to 8 μm, and various thicknesses up to 50 nm. The normalized transmissions of the 2-μm-wide and 20-nm-thick G-SPPWs are less than -0.06 dB with various gap lengths up to 8 μm. The normalized transmissions of the 2-μm-long and 20-nm-thick G-SPPWs are less than -0.05 dB with various widths up to 8 μm. The normalized transmissions of the G-SPPWs that are 2-μm-wide and 2-μm-long are less than -0.27 dB for various thicknesses up to 50 nm. The maximum normalized transmission of -0.041 dB is obtained using the 2-μm-long, 2-μm-wide and 20-nm-thick G-SPPW. G-SPPWs have potential as a new plasmonic modulation device via control of the guided SPP through interaction with an applied force in the gap.

Core/Shell Iron/Oxide Nanoparticles for Improving the Magneto‐Dielectric Properties of Polymer Composites

A simple method to obtain high magnetic permeability (μr), high dielectric permittivity (ϵr), and low loss polymer composites with core/shell iron/metal oxide particles is developed. Magnetic iron (Fe0) particles with protective SiO2 shells are synthesized in aqueous environment at room temperature. The shells provide electrical insulting layers which decrease energy loss and also prevent the possibility of μr decrease due to Fe0 oxidation. Furthermore, Fe0 particles could also be coated with TiO2 shells which allow ϵr to be tuned. The ϵr and μr of the resulting polydimethylsiloxane composites are optimized for core‐shell particle doping. The value of ϵr is up to 9.8 and most importantly, the μ is close to 2 at 1 GHz with 43 wt% doping of core‐shell particles. The dielectric loss of the composites is less than 0.02.

G-s0 mode converter with lateral gold mirrors for nano-plasmonic integrated circuits.

We propose a waveguide-typed plasmonic mode converter with lateral gold mirrors (LGMs) at a wavelength of 1.55 μm. The 17.5 μm-long gap-s0 mode converter (G-s0 MC) is composed of an input 4.5 μm-wide insulator-metal-insulator-metal-insulator waveguide (IMIMI-W) and an output 2.0 μm-wide metal-insulator-metal waveguide (MIM-W) with LGMs connected by a laterally tapered (LT) IMIMI-W with LGMs. The strip thicknesses of the IMIMI-Ws and MIM-W are 20 nm and 50 nm, respectively. The 12.0 μm-long LGMs with 1.5 μm thickness are located beside the LT-IMIMI-W and MIM-W. All metals in the IMIMI-Ws, MIM-W, and LGMs are designed with gold. A low-loss polymer is used for the 30 μm-thick upper and lower cladding layers. The thickness of the central insulator in both the IMIMI-Ws and MIM-W was designed to be 500 nm. The input Ss0 mode with the size of -5.9 μm x 4.8 μm is converted to the output G-s0 mode with the size of 1.1 μm x 0.5 μm. The total loss of the G-s0 MC, including conversion loss, is -6.96 dB in simulation. The proposed G-s0 MC may be potentially useful for bridging micro- to nano-plasmonic integrated circuits.

Exploring Strategies for High Dielectric Constant and Low Loss Polymer Dielectrics.

Polymer dielectrics having high dielectric constant, high temperature capability, and low loss are attractive for a broad range of applications such as film capacitors, gate dielectrics, artificial muscles, and electrocaloric cooling. Unfortunately, it is generally observed that higher polarization or dielectric constant tends to cause significantly enhanced dielectric loss. It is therefore highly desired that the fundamental physics of all types of polarization and loss mechanisms be thoroughly understood for dielectric polymers. In this Perspective, we intend to explore advantages and disadvantages for different types of polarization. Among a number of approaches, dipolar polarization is promising for high dielectric constant and low loss polymer dielectrics, if the dipolar relaxation peak can be pushed to above the gigahertz range. In particular, dipolar glass, paraelectric, and relaxor ferroelectric polymers are discussed for the dipolar polarization approach.

Thermally Stable, Low Loss Optical Silicones: A Key Enabler for Electro-Optical Printed Circuit Boards

We report the development and characterization of a low loss polymer waveguide material with a polysiloxane backbone for enabling the new generation electrooptical printed circuit boards (PCBs). The polymer was designed to have low optical loss of <;0.05 dB/cm at 850 nm and low residual stress to withstand the harsh reliability requirements during PCB integration. The thermomechanical properties of the polymer were tuned to exhibit a residual stress of ~1 MPa over a temperature range of 25 °C to 200 °C in ambient air. Multimode polymer waveguides were fabricated using the polysiloxane polymer and embedded in a six-layer PCB architecture that was subjected to lamination, through-hole via drilling, plating, and IPC shock test (immersion) in solder bath at 288 °C. Eight channels of multimode polymer waveguide spirals of length 1.2 m were fabricated and the insertion loss measured after waveguide fabrication, lamination, and solder reflow. The deviation in insertion loss as a function of the PCB fabrication process was less than 3% with final insertion loss after solder reflow being 0.052 +/- 0.002 dB/cm. This finding presents an optical waveguide material which when embedded in a PCB fabricated using an industry standard process meets reliability requirements while maintaining optical performance.

Polymer waveguide Bragg grating Fabry–Perot filter using a nanoimprinting technique

A narrow band waveguide Fabry–Perot filter at 1550 nm, which is composed of two polymer waveguide Bragg gratings as reflectors, is presented. By using conventional lithography, a low-loss polymer channel waveguide was fabricated, and the submicron Bragg grating structure was transferred onto the waveguide surface using a nanoimprinting technique. The transmission spectrum of the device was measured, and the results show that there is a very narrow transmission peak, with a 3 dB bandwidth of 0.011 nm in the 0.38 nm rejection band of the waveguide Bragg grating. A quality factor of Q ≈ 1.41 × 105 is achieved. The insertion loss and the extinction ratio of the Fabry–Perot filter are about −12.5 dB and 17 dB, respectively. In addition, the measured transmission spectrum is in excellent accordance with the numerical simulation.

Curing kinetics of step-index and graded-index single mode polymer self-written waveguides

A low-loss polymer medium to interconnect 2 single mode optical fibers is developed and characterized. It consists of a so-called self-written waveguide (SWW) formed by illuminating a photosensitive polymerization mix with light emanating from the fiber, after which the exposed part polymerizes. Depending on the material system used, this waveguide can have a step index or graded refractive index profile. The fabrication process and its effect on the waveguide performance are explained using an empirical model and afterwards experimentally verified. This approach enables easy process monitoring and optimization, effectively resulting in total insertion losses below 0.3 dB for a single mode fiber-SWW-fiber transition at 1550 nm.