Hong Wu Li

Via-Hole Less Broadband Grounded Coplanar to Coupled Microstrip Transition for up to 40 GHz

A broadband via-hole less transition from a conductor-backed coplanar waveguide (CBCPW) to a parallel coupled microstrip line (CMS) via microstrip section (MS) is reported in this paper that is realized on a MCL FX-2 substrate (100 μm thick). This transition should find a wide variety of applications due to its demonstrated broadband (from 4.5 GHz up to 39.5 GHz) behavior, ease of fabrication, and low manufacturing cost. In addition, utilization of the MS section between the CBCPW and CMS sections allows putting ground electrode in a different plane than the signal electrodes. This exibility made possible by electromagnetic field coupling between the bottom and top ground planes simplifies the transition manufacturing and facilitates the characterization of optical components driven with CMS line using coplanar probes.

An ultra-wideband dielectric material characterization method using grounded coplanar waveguide and genetic algorithm optimization

An ultra-wideband complex permittivity extraction method is reported here using numerical fitting of scattering parameters to measured results. A grounded coplanar waveguide transmission line is realized on an unknown dielectric material, whose dielectric constant and loss tangent are extracted by the best fitting of the simulated magnitude, |S21|, and phase, ϕ21, of forward scattering parameter using an electromagnetic full-wave simulator (high frequency structure simulator) to the measured results. The genetic algorithm is employed for optimum rapid extraction, where errors between the numerically simulated and measured S21 (|S21| and ϕ21) are minimized in an iterative manner. As long as the convergence criterion is not satisfied, modifications to dielectric properties are made with this genetic algorithm implemented in Matlab. Feasibility of this extraction technique is validated on benzocyclobutane polymer from 10 MHz to 40 GHz.

Leaky waveguide deflector for 40 GS/s and 6 bits all-optical analog-to-digital converters

Abstract Analog-to-digital converters (ADC) are an important part of realizing direct digital receivers in future communication systems, where broad bandwidth, high effective number of bits, and low DC power consumption are an important requirement of achieving it at microwave frequencies. Due to a number of physical limitations of electrical ADC, design of an all-optical analog-to-digital converter (AOADC) is pursued and presented here based on highly stable mode-locked laser based clock signal pulses for optical sampling, and a combination of leaky waveguide optical deflector using electro-optical (EO) polymers and stationary optical windows followed with high-speed photodetectors as optical quantizer. The reported principle of the AOADC is to convert a broadband RF signal into a spatially sampled light using optical deflection angle variation before quantizing it using either binary or Gray coded optical windows. The design and modeling of an AOADC working up to 20 GHz RF frequencies (with Nyquist sampling rate of over 40 GS/s) and for providing a resolution of better than 6 bits with under 4W of power consumption. Performance is currently limited by both optical and microwave attenuation in the available EO polymers.

Coplanar-microstrip transitions for ultra-wideband communications

Nowadays optics is penetrating into the broadband access networks, so the data transmission bit-rate can be guaranteed regardless the distance between the subscriber and the central office. Many laboratories are working on the radio over fiber technology in the home networks. For home network applications, one must use low-cost and broadband modulators to transcribe the electrical signal into optical signal. The electrooptic polymers on which very active research is being carried out have the required properties for realizing this kind of modulators. Their realization needs a certain number of delicate manufacturing steps, therefore, a rigorous study of the component must be made before the realization of the modulators. The optimization of the modulator optical structure must be made first, from the properties of polymers at one’s disposal and the technological constraints, in order to obtain a single mode guide with minimum losses. Then, optimization of the driving electrode, inseparable step from the optical study, should be carried out. In electro-optic modulators based on polymer, the chromophore molecules responsible for the electro-optic effect are oriented perpendicularly to the substrate as they are generally poled by Corona effect or with contact electrodes. Consequently, a microstrip line is suitable to apply the driving signal to induce the electro-optic effect. Before packaging the final component, it is necessary to assess its performances directly on wafer by use of a probe station, usually equipped with probes compatible with coplanar lines GSG (Ground-Signal-Ground) insuring an easy electrical contact. So, a transition between coplanar and microstrip lines (CPW-MS) is indispensable to characterize the components on wafer. This transition must satisfy at least these three criteria: ultra-wideband, easy to realize and low-cost. One solution is to physically connect the coplanar ground planes to the bottom ground plane of the microstrip line through a via-hole, which would make the component more expensive without eliminating all parasitic resonance (Haydl, 2002). It is in this context that we conducted a comprehensive study of via-free transitions between coplanar and microstrip lines, in order to make easy and simple the characterization of components driven by microstrip line with CPW (Coplanar waveguide) probes. These transitions may be also employed in all microwave circuits driven by microstrip lines.

Sensitivity improvement of broadband electro-optic polymer-based optical phase modulator using 1D and 2D photonic crystal structures

This Letter introduces the design and simulation of a microstrip-line-based electro-optic (EO) polymer optical phase modulator (PM) that is further enhanced by the addition of photonic crystal (PhC) structures that are in close proximity to the optical core. The slow-wave PhC structure is designed for two different material configurations and placed in the modulator as a superstrate to the optical core; simulation results are depicted for both 1D and 2D PhC structures. The PM characteristics are modeled using a combination of the finite element method and the optical beam propagation method in both the RF and optical domains, respectively. The phase-shift simulation results show a factor of 1.7 increase in an effective EO coefficient (120 pm/V) while maintaining a broadband bandwidth of 40 GHz.

Design and realization of high-performance microwave and millimeter wave band-pass filters on thin polymer films

During the last decade, we observed an explosion of wireless communications and multimedia services. The rapid growth of data exchanged, through information and communication networks, requires the development of components and devices with higher performance and improved functionality, while satisfying the constraints of weight, size, power consumption and cost. Microwave filters are essential components in various electronic systems, including cellular radio, radars and satellite communications. They are indispensable to detect weak signal buried in noise and improve radars sensitivity. They are also very useful to improve spectrum efficiency in software radio technology. In microwave communication systems, band-pass filters are usually used in both receivers and transmitters. So they are requested to meet the following electronic requirements: low insertion loss, high frequency selectivity, phase linearity and no harmonic response. Band-pass filters structures are widely reported in the literature. However these studies were conducted in the most cases on thick commercial substrates [1-3]. To date, very few studies have focused on filters on thin films whereas the low thickness of the substrate facilitates the coupling between the circuits on the surface and the lower ground plane [4] which allows having a high selectivity filter. This paper reports the design and manufacturing of microstrip band-pass filters with good performance in terms of both insertion loss and selectivity.The proof of concept is carried out on thin BCB polymer (70 μm) film very used in microelectronics thanks to its low loss tangent (tan δ = 0.0025). The studied filters are constituted of two resonators and they combine the compactness of microstrip resonators and the connection facility of coplanar pads due to microstrip-grounded coplanar waveguide transitions integrated with the filters. The filters structures, that will be presented,have the following performance:. 6% bandwidth and -1.6 dB insertion losses at central frequency of 15 GHz, 4.5% bandwidth and -1.7 dB insertion losses at central frequency of 20 GHz, 5.5% bandwidth and -1.5 dB insertion loss at central frequency of 25 GHz, 8% bandwidth and -1.1 dB insertion loss atcentral frequency of 35 GHz, 4.8% bandwidth and -1.4 dB insertion losses at central frequency of 45 GHz. The filters on thin polymer film have the advantage of being low cost and very easy to fabricate.

Coplanar waveguide to microstrip transition in thin polymer film for characterization and packaging of microwave photonic components

We report in this paper two types of broadband transitions between microstrip and coplanar lines on thin benzocyclobutene (BCB) polymer substrate. They are both via-free, using electromagnetic coupling between the bottom and top ground planes, which simplifies the manufacturing of components driven by microstrip electrodes. In the first ones, the bottom ground is not patterned, which makes them particularly suitable to on-wafer measurement of components under development with coplanar probes. An ultra-broad bandwidth of 68 GHz (from 1 GHz to 69 GHz) was achieved with 20-pm BCB. In the second ones, intended for connectorizing components on thin substrate with coplanar connectors, the bottom ground is patterned to match the narrow center conductor (54 μm) on thin substrate to the wide center conductor (127 μm) of the connector with a tapered section, achieving to a experimental bandwidth 13 GHz for the moment.