Broadband GHz frequency characterizations of Permalloy nanorods’ array

The radio frequency characteristics of Permalloy nanorods’ array have been examined by coplanar waveguide (CPW) cell. The Permalloy nanorods’ array was grown in anodic aluminum oxide porous templates with a diameter of 20 nm. As the Permalloy nanorods’ array was placed on CPW, the characteristic impedances of the CPW were changed from 50 to at 1 GHz. The magnitude of inductance was decreased from 3 GHz and the capacitance was increased up to twice in comparison with that of CPW. The signal attenuations were abruptly increased over 1 GHz. The propagation wavelengths due to the insertion of Permalloy nanorods’ array were decreased about 30% at 1 GHz in comparison with that of CPW without magnetic materials.     

A Broadband CPW-to-Microstrip Modes Coupling Technique

A broadband vertical transition from coplanar waveguide (CPW)-to-microstrip modes is presented. The transition has a double resonance and can be tuned for very wide-band operation. The CPW-to-microstrip modes coupling technique is useful for the vertical integration of multi-layer millimeter-wave circuits, packaging and antenna feeding networks. A vertical transition has been fabricated on 100 m silicon substrate for operation at W-band frequencies and shows less than 0.3 dB of insertion loss and better than 12 dB of return loss from 75 to 110 GHz. A 94 GHz CPW-fed microstrip antenna showing a 10-dB bandwidth of about 30 % has been built using the same transition technique.     

Widely tunable electrooptic pulse-pattern generation and its application to on-wafer large-signal characterization of ultra high-speed electronic devices

A pulse-rate-tunable, electrooptic pulse-pattern generator and a wideband high-efficiency optical-to-electrical (OE) conversion stimulus probe have been developed. Sinusoidal electrooptic amplitude/phase modulation and chirp compensation were used to provide picosecond pulsation, and the relationship between pulse-rate tunability and the extinction ratio has been studied analytically and experimentally. Return-to-zero (RZ) pylse patterns of 10–72 Gb s^–1 have been generated by using LiNbO₃ amplitude/phase modulators with a bandwidth of 18 GHz, a single dispersion shifted fibre, and a time-division multiplexer. A 1.55 m waveguide p-i-n photodiode yielded high responsivity (0.75 A W^–1) and a saturation peak voltage of 200 mV at the probe tip. The measured effective 3 dB bandwidth exceeds 50 GHz, which is currently limited by the frequency dispersion of the coplaner waveguide (CPW) used in the probe. Use of this generator and probe, in combination with electrooptic sampling, for on-wafer characterization of a broadband distributed amplifier revealed the amplifier's saturation characteristics and waveform distortion under actual operating conditions with a 64 Gb s^–1, 120 mV per probe, RZ pulse-pattern input.     

Dual-band microwave duplexer based on spiral resonators (SR) and complementary split ring resonators (CSRR)

In this work, a microstrip dual-band microwave duplexer implemented by means of a pair of dual-band branch-line hybrid couplers and a pair of dual-band band-stop filters is presented. The hybrid couplers are implemented by using complementary split ring resonators (CSRRs), etched in the ground plane, while the band-stop filters are made of spiral resonators (SRs) coupled to the host line. The measured duplexer characteristics are good and the device is compact by virtue of the small electrical size of the employed resonant elements. From this paper, it is clear that CSRRs and SRs are useful particles for the design of dual-band microwave systems requiring various microwave components.     

Coplanar Waveguide Characterization with Thick Metal Coating

Coplanar waveguides (CPW) used in microwave integrated circuits are significantly dispersive. An analytical approximation to the frequency dependence of both _eff and _c of CPW with finite metallisation thickness and conductivity is discussed. The effect of increasing loss tangent on dielectric constant is also presented.     

A propagating beam analysis of optical waveguide couplers

We study the mode coupling among the local normal modes of couplers formed from planar parabolic graded-index tapered optical waveguides with the propagating beam method. Our results indicate that couplers whose radiia (z) depend on axial length as \Lambda /2$$ " align="middle" border="0"> , have many desirable properties not possessed by other couplers.     

Analysis and design of highly broad-band,planar evanescent couplers

It is shown that by taking advantage of the maximum in the spectral dependence of the coupling coefficient, very broad-band symmetric and asymmetric single-mode planar couplers can be designed. The symmetric coupler allows at least 95.6% coupling between the two cores over the wavelength range 1.3–1.58 m, while the asymmetric coupler can act as a 3 dB splitter with only ±1.6% variation in the splitting ratio over the wavelength range 1.3–1.67 m. In both cases, the design includes the curved input-output arms, and the estimated bend loss is approximately 0.1 dB.     

带状注行波管E面和H面宽带耦合器

设计和分析了应用于W波段带状注行波管的E面多孔输入输出耦合器和H面多孔输入输出耦合器。研究表明,采用多孔耦合,不仅可以实现电磁场与电子注的汇聚和分离,还可以实现极宽工作带宽。HFSS仿真分析结果表明:E面多孔定向耦合器1dB相对带宽达43GHz,且隔离度优于20dB的相对带宽达到40GHz;H面定向耦合器在E面耦合器的10个耦合孔数的基础上,通过增加2个耦合孔数,1dB相对带宽提升到30GHz,且隔离度大于15dB的相对带宽达到32GHz。两种新型耦合器在极宽的工作带宽内实现低反射、高隔离的性能。与E面耦合器相比,H面耦合器易于加工和利于与周期永久磁体的封装集成。     

Ultra‐broadband nanophotonic beamsplitter using an anisotropic sub‐wavelength metamaterial

Nanophotonic beamsplitters are fundamental building blocks in integrated optics, with applications ranging from high speed telecom receivers to biological sensors and quantum splitters. While high‐performance multiport beamsplitters have been demonstrated in several material platforms using multimode interference couplers, their operation bandwidth remains fundamentally limited. Here, we leverage the inherent anisotropy and dispersion of a sub‐wavelength structured photonic metamaterial to demonstrate ultra‐broadband integrated beamsplitting. Our device, which is three times more compact than its conventional counterpart, can achieve high‐performance operation over an unprecedented 500 nm design bandwidth exceeding all optical communication bands combined, and making it one of the most broadband silicon photonics components reported to date. Our demonstration paves the way toward nanophotonic waveguide components with ultra‐broadband operation for next generation integrated photonic systems.

     

Wavelength-agile H2O absorption spectrometer for thermometry of general combustion gases

Using a novel Fourier-domain mode-locking (FDML) laser scanning 1330-1380 nm, we have developed a gas thermometer based on absorption spectroscopy that is appropriate for combustion gases at essentially arbitrary conditions. The path-integrated measurements are particularly useful in homogeneous environments, and here we present measurements in a controlled piston engine and a shock tube. Engine measurements demonstrate a RMS temperature precision of ±3% at 1500 K and 200 kHz bandwidth; the precision is improved dramatically by averaging. Initial shock tube measurements place the absolute accuracy of the thermometer within ∼2% to 1000 K. The sensor performs best when significant H₂O vapor is present, but requires only at 300 K, at 1000 K, or at 3000 K for 2% accurate thermometry, assuming a 4 kHz measurement bandwidth (200 kHz scans with 50 averages). The sensor also provides H₂O mole fraction and shows potential for monitoring gas pressure based on the broadening of spectral features. To aid in designing other sensors based on high-temperature, high-pressure H₂O absorption spectroscopy, a database of measured spectra is included.     

Microwave and millimeter-wave losses in conventional optoelectronic devices

In this paper, microwave characteristics of conventional optoelectronic devices, with emphasis on devices with microstrip (MS) and coplanar waveguide (CPW) electrode structures, are obtained. This analysis is essential for any improvement in the structure of the conventional optoelectronic devices so as to obtain a high performance. Microwave loss is one of the important bandwidth limitation factors in microwave and millimeter-wave (mmW) optical devices. Different sources of loss including ohmic, dielectric and radiating loss in MS and CPW of conventional optical devices are analyzed and compared. The results show that the total microwave loss increases with frequency in conventional MS and CPW waveguides. Also, in traveling-wave optoelectronic devices, the bandwidth is limited in the optical part by effects such as the carrier transit time effect and in the microwave part by factors such as length of the devices in active and non-active sections. In addition, validation of the results in the paper is performed with published theoretical and/or measurement results.     

Quantum-limited FM-spectroscopy with a lead-salt diode laser

Ultrasensitive absorption spectroscopy of NO₂ was performed with a tunable lead-salt diode laser (TDL) using a single-tone high-frequency modulation (FM) technique. With a detection bandwidth of 200 kHz, an optical density of 2.7 × 10^–5 was detectable at SNR of 1. The detectable optical density could be further improved by reducing the detection bandwidth in agreement with the f relationship, reaching 2.5 × 10^–6 at a detection bandwidth of 1.56 kHz. Normalized to 1 Hz bandwidth, the demonstrated performance would then correspond to a detectable optical density of 5.9 × 10^–8. This detection limit agrees well with the calculated quantum limited performance based on the measured laser power, modulation index, noise figure of the electronic components, and other parameters of the apparatus. These measurements and calculations show that by implementation of the FM technique, the sensitivity of the present TDL absorption spectrometers (TDLAS) can be improved by at least a factor of 10 and possibly even of 100. Such a sensitivity improvement would greatly extend the applicability of TDLAS for trace gas analysis, especially in atmospheric monitoring.     

Development of the SRAO 1024-Channel Digital Auto-Correlator

We developed a 1024-channel digital auto-correlation spectrometer for the Seoul Radio Astronomy Observatory (hereafter the SRAO-1KACS). The SRAO-1KACS has two main modules: the IF-to-baseband converter (IFBC) module and the 1024-channel auto-correlator (1KACR) module. The input frequency range of the IFBC module is from 1.5 to 1.55 GHz with a dynamic range of –4 +3 dBm. The 1KACR module performs calculations of auto-correlation coefficients by the accumulation and modulo-2-counting method in 3-level configuration. The system is controlled by a Linux-based personal computer. The SRAO-1KACS provides 3 different observational modes: 50, 25, and 12.5 MHz bandwidth modes. The channel losses are 20%, 12%, and 8% for each bandwidth mode, respectively. Various tests were executed including lab tests and astronomical tests. Lab tests were performed for a 1.5625MHz sinusoidal wave input and for a white noise source. We also executed astronomical tests in 12CO J=1–0 emission line at 115.2712 GHz, which showed that SRAO-1KACS can be used at astronomical observatories.     

Optimal design of broadband long period grating-based LP01↔LP02 mode converters for dispersion compensation

Dispersion compensation with higher order mode is emerging as a promising technique that can provide full dispersion and dispersion slope compensation for a long distance high bit rate system. Long period grating-based LP₀₁LP₀₂ mode converters are designed in the wavelength region of 1550 nm for this purpose. The simulated mode converters have large bandwidth with conversion efficiencies of over 99% and the estimated figure of merit is 309 ps/(nm dB). The negative dispersion of –124 ps/(nm km) is obtained over a bandwidth (@20 dB) of 58 nm with relative dispersion slope of 0.008/nm.     

Analyze and calculation of coupling coefficient based on evanescence field for plasmonic directional coupler structure

We obtain the calculation of coupling coefficient of plasmonic directional coupler made up of two monolayer waveguides separated in the range of 200 nm for TM mode and we assume each waveguides acts as a perturbation to other waveguide but does not affect the waveguide mode. We simulation the transfer distance respect to normalized frequency in two directions, x and z, values transfer distance a limitation of a bandwidth is suitable for designing of integrated optical circuits and construction of couplers and switches.     

Optimization of the operational bandwidth in air-core photonic bandgap fibers for IR transmission

We determine the optimal inner glass ring thickness in infrared air-core photonic bandgap fibers (PBGFs) with 19-cell and 7-cell cores. For PBGFs with a 19-cell core, we find that an inner ring thickness of , where Λ is pitch, yields the widest operational bandwidth, which is nearly 6%. The operational bandwidth increases as the refractive index decreases from 2.8 to 2.0. For PBGFs with a 7-cell core, one needs to draw fiber with a ring thickness of less than to achieve a comparable operational bandwidth.     

Modeling,design, growth and characterization of red wavelength range microcavity emitters for plastic optic fiber applications

Resonant cavity light emitting diodes (RC-LEDs) and vertical cavity surface emitting lasers (VCSELs) for the red wavelength range are presented in the paper. A wide variety of simulation tools were employed in the device design and optimization and the good agreement between simulations and measurements enabled effective device development. Our red wavelength range RC-LEDs were mainly intended for short-haul communication systems based on polymethyl methacrylate plastic optical fiber and were optimized accordingly. They are achieving, under different structure and working regime variants, high output power (15 mW), high external efficiency (9.5%), record small-signal modulation bandwidth (f _-3dB up to 350 MHz), error-free back-to-back transmission rates beyond 622 Mbits/s, adjustable far-field pattern and good POF coupling efficiency with reasonably wide tolerances and without using auxiliary optics. In view of the possible use of graded-index POFs, free-space transmission and other high bandwidth or high spectral purity applications, VCSELs in the red wavelength range were also realized. They have achieved sub-milliamp room-temperature (RT) continuous-wave (CW) lasing for an 8 m diameter emission window and exhibited an external quantum efficiency of 6.65% for 10 m devices in RT CW operation. The VCSEL structures were far from optimal – not even incorporating all the RC-LED structure refinements – and significant improvement in performance characteristics are predicted for the optimized layer structure.     

180–425 GHz low noise SIS waveguide receivers employing tuned Nb/AIOx/Nb tunnel junctions

We report recent results on a 20% reduced height 270–425 GHz SIS waveguide receiver employing a 0.49 µm² Nb/AlO _x /Nb tunnel junction. A 50% operating bandwidth is achieved by using a RF compensated junction mounted in a two-tuner reduced height waveguide mixer block. The junction uses an end-loaded tuning stub with two quarter-wave transformer sections. We demonstrate that the receiver can be tuned to give 0–2 dB of conversion gain and 50–80% quantum efficiency over parts of it's operating range. The measured instantaneous bandwidth of the receiver is 25 GHz which ensures virtually perfect double sideband mixer response. Best noise temperatures are typically obtained with a mixer conversion loss of 0.5 to 1.5 dB giving uncorrected receiver and mixer noise temperatures of 50K and 42K respectively at 300 and 400 GHz. The measured double sideband receiver noise temperature is less than 100K from 270 GHz to 425 GHz with a best value of 48K at 376 GHz, within a factor of five of the quantum limit. The 270–425 GHz receiver has a full 1 GHz IF passband and has been successfully installed at the Caltech Submillimeter Observatory in Hawaii. Preliminary tests of a similar junction design in a full height 230 GHz mixer block indicate large conversion gain and receiver noise temperatures below 50K DSB from 200–300 GHz. Best operation is again achieved with the mixer tuned for 0.5–1.5 dB conversion loss which at 258 GHz resulted in receiver and mixer noise temperature of 34K and 27K respectively.     

High-Speed Coplanar Waveguide Based Submount for 40 Gbit/s Electroabsorption Modulator

A high-speed submount has been designed and fabricated for 40 Gb/s electroabsorption (EA) modulators. The submount contains a coplanar waveguide (CPW) for microwave signal feeding and a Ta₂N thin-film resistor for impedance matching. The CPW transmission line is designed to ensure low microwave loss and reflection, and Ti/Cu/Ni/Au metal is adopted for electrode fabrication to guarantee good contact with the Ta₂N thin-film. The typical reflection coefficient of fabricated submount is estimated to be lower than−21 dB up to 40 GHz. As a demonstration, a high-speed EA modulator was chip-level packaged using the high-speed submount, and the measured small-signal modulation bandwidth was over 40 GHz.     

A proposed ultra low-noise optical receiver for 1.55 μm applications

A high-sensitivity optical receiver based on InP/InGaAs superlattice avalanche photodiode (SL-APD) followed by an InGaAs MESFET transimpedance pre-amplifier has been proposed for operation in 1.55 m wavelength region. The proposed optical receiver may be realised in the hybrid integrated circuit form. The low excess-noise factor of the SL-APD significantly reduces the value of minimum detectable optical power and improves the sensitivity of the over all receiver. The proposed receiver has been analysed theoretically. The results of computation show that the device has a high transimpedance gain (60 dB-ohm) with a bandwidth of 11 GHz for a photodetector capacitance of 110 fF. The sensitivity of the receiver has been found to be (–27.3d Bm) at operating bit rate of 15 Gb/s for a bit-error-rate of 10^–9. The performance of the receiver can be optimised in respect of transimpedance gain, bandwidth and sensitivity by following guidelines provided in this paper. The proposed photoreceiver outperforms the existing receivers based on p-i-n/FET or conventional APD/FET photoreceivers.