Bidirectional Couplers Research Articles

HIFU Power Monitoring Using Combined Instantaneous Current and Voltage Measurement.

During high-intensity focused ultrasound (HIFU) therapy, it is important that the electrical power delivered to the transducer is monitored to avoid underexposure or overexposure, ensure patient safety, and to protect the transducer itself. Due to ease of measurement, the transducer's potential difference may be as an indicator of power delivery. However, even when a transducer's complex impedance is well characterized at small amplitudes and matching networks are used, voltage-only (VO) monitoring cannot account for the presence of drive waveform distortion, changes to the acoustic path, or damage to the transducer. In this study, combined current and voltage (CCV) is proposed as a magnetic resonance imaging (MRI)-compatible, miniature alternative to bidirectional power couplers, which is compatible with switched amplifiers. For CCV power measurement, current probe data were multiplied by the voltage waveform and integrated in the frequency domain. Transducer efficiency was taken into account to predict acoustic power. The technique was validated with a radiation force balance (RFB). When using a typical HIFU transducer and amplifier, VO predictions and acoustic power had a maximum difference of 20%. However, under the same conditions, CCV only had a maximum difference of 5%. The technique was applied to several lesioning experiments and it was shown that when VO was used as a control between two amplifiers, there was up to a 38% difference in lesion area. This greatly reduced to a maximum of 5% once CCV was used instead. These results demonstrate that CCV can accurately predict real-time electrical power delivery, leading to safer HIFU treatments.

Mid-plane PAM launcher study for KSTAR LHCD system

A prototype of a midplane passive active multijunction (PAM) antenna was fabricated for the lower hybrid current drive system of KSTAR. The antenna includes a PAM launcher, bidirectional couplers, power dividing components, and two RF windows. The RF characteristics of each component, such as the splitting ratio, phase shift, transmission, and reflection, were measured using a network analyzer. A taper adapter and matched load, which can be inserted into the active waveguide of the PAM mouth, were designed and fabricated for the phase shift and power coupling measurement. The maximum error and the standard deviation of measured phase shifts between adjacent active waveguides of the PAM were 6.5° and 2.28°, respectively. The design improvement of the mid-plane PAM launcher is suggested. Multiple round trips of the reflected field in a multijunction provides the advantage of lowering the reflection but, at the same time, it causes the deterioration of directivity and an increase of the electric field in the waveguide. Adding a hybrid splitter at the end of the multijunction structure reduces the reflection by redirecting the reflection to plasma as in multijunction, however, contrary to the multijunction, it does not switch the toroidal direction of phase progression and thus improves the antenna directivity. The directivity of the hybrid PAM increases by more than 10% and the reflection decreases to 1/3–1/100 in comparison with the prototype PAM.

Analysis and optimisation of bidirectional optical couplers in PCBs

Integrated optical waveguides on board level gain more interest with growing bandwidth. Due to limited space on board level, a new approach is to use bidirectional optical transmission on one single waveguide, to save space. As manufacturing technique we used an ion exchange process, as this has proven to be highly scalable and can be easily integrated into current PCB manufacturing processes. We developed an optical coupler for application in bidirectional optical transmission paths on a single waveguide. Due to the highly multimodal character of the structure, we applied ray tracing techniques to analyse the optical properties. By such means efficiency calculations as well as a transient analysis were possible. We determined important parameters of the structure for optimisation of the coupling efficiency.

Load Modulation Measurements of X-Band Outphasing Power Amplifiers

This paper presents an in-depth investigation of both isolated and non-isolated outphasing power amplifiers, with and without supply modulation. X-band GaN MMIC power amplifiers with 70% power-added efficiency and 2.7 W output power at 10.1 GHz are configured in hybrid outphasing circuits with several combiners that include bi-directional couplers, enabling calibrated measurements of internal load modulation. It is experimentally demonstrated that the load modulation critically depends on the power balance of the two internal MMIC PAs. Despite the additional loss in the combiner, peak total efficiencies greater than 47% are achieved by full outphasing PAs with more than 3.7 W of output power. A comparison between several outphasing configurations quantifies the improvement in efficiency for both isolated and non-isolated outphasing PAs with supply modulation.

Flip-chip optical couplers with scalable I/O count for silicon photonics

A scalable and tolerant optical interfacing method based on flip-chip bonding is developed for silicon photonics packaging. Bidirectional optical couplers between multiple silicon-on-insulator waveguides and single-mode polymer waveguides are designed and fabricated. Successful operation is verified experimentally in the 1530-1570 nm spectral window. At the wavelength of 1570 nm, the coupling loss is as low as 0.8 dB for both polarization states and the planar misalignment loss is less than 0.6 dB for TE and 0.3 dB for TM polarization in a lateral silicon-polymer waveguide offset range of ± 2 µm. The coupling loss does not exhibit any temperature dependence up to the highest measurement point of 70°C.

Dual-wavelength first-order optical differentiators based on bidirectional fiber couplers

We simulated a novel dual-wavelength first-order optical differentiator based on a bidirectional fused-fiber coupler. Conventional optical directional couplers act as ultrafast optical differentiators that provide operability at multi-wavelength regions owing to the sinusoidal variations of their transfer functions in the frequency domain. In this study, a dual-wavelength optical differentiator that operates at both 1310 nm and 1550 nm was designed with a fused-fiber coupler under specific conditions. The proposed device has the potential to be used as an ultrafast optical differentiator that provides unparalleled performance with advantages such as wide bandwidth, ease of fabrication, and multi-wavelength operation.

Beam aperture modifier and beam deflector using gradient-index photonic crystals

We designed and simulated a beam aperture modifier and a beam deflector using two-dimensional parabolic gradient-index (GRIN) photonic crystals (PCs). The GRIN PCs are composed of dielectric columns with graded radii along the direction transverse to propagation. Both finite-difference time-domain methods and gradient optics analytical solutions were used to characterize the change in beam width and propagation direction. Multifunctional GRIN PCs combining both beam aperture modification and beam deflection were also designed and simulated. These GRIN PC based designs can be used as optical connectors and bidirectional waveguide couplers in applications such as miniaturized photonic integrated circuits.

Numerical Investigation of a Bidirectional Wave Coupler Based on Plasmonic Bragg Gratings in the Near Infrared Domain

In this paper, we present a theoretical discussion of the design of bidirectional wave couplers based on plasmonic Bragg gratings in the near infrared domain. A key feature in the design of the plasmonic Bragg gratings is the dependence of the effective refractive index on the thickness of the dielectric layer. These gratings, which function as band rejection filters, enable directional coupling of different SPP modes. By placing two gratings with different band gaps on opposite sides of a subwavelength metallic slit, a bidirectional plasmonic surface wave coupler can be realized. Two-dimensional (2-D) FDTD simulations were performed to elucidate the properties of the device, and were found to agree well with the theoretical predictions. Finally, the wave confinement properties of the plasmonic Bragg gratings are studied further by introducing the equivalent 1-D photonic crystal band structures.

A new type of slotted waveguide and moving couplers for shielded microwave transfer

AbstractWe present a novel small coaxial broadband slotted waveguide that can be used where size is a critical factor. We further present adapted directional and bidirectional wave couplers that can be introduced into the waveguide to launch and detect signals. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 42–44, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11121

A homodyne multiport network analyzer forS-parameter measurements of microwaveN-port circuits/systems

A homodyne multiport network analyzer is proposed for the characterization of N-port microwave devices, circuits, and systems. The single six-port junction used as a wave correlator is operated as a two-channel wave receiver. The use of an additional test set, which comprises two switching matrices and N bidirectional couplers, allows the measurements of complete S-parameter matrices of N-port devices. By comparison to existing network analyzers, the proposed system is homodyne in the sense that it does not require any frequency down-conversion to determine the phase information, and uses only one single six-port junction to obtain complex S-parameter measurements from only scalar measurements. A detailed description of the proposed system is presented. Two- and three-port structures are measured, and the results are compared to the data obtained by a two-port commercial network analyzer. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 63–67, 2000.

Fused taper infrared optical fiber couplers in chalcogenide glass

We have fabricated low loss, high coupling ratio bidirectional optical couplers for infrared light using multimode step-index chalcogenide fiber. Using a fusion technique similar to that commonly employed with silica fibers, we have found a temperature regime where fusion can occur while interdiffusion of the core and cladding materials will not. The resultant device has a roughly 3:1 coupling ratio, less than 0.3 dB of excess insertion loss, and preserves the guided modes of the fiber intact.

High-frequency narrow-band single-mode fiber-optic transversal filters

A cascade synthesis procedure for constructing high frequency narrow-band (or high quality factor) single-mode optical fiber transversal filters using j \times j (j \geq 2) bidirectional couplers is reported. Design and analysis of the cascade filters are described. Experimental results of many fabricated cascade filters with tap numbers up to 256 and the first-order passband frequencies up to 3.25 GHz are consistent with the mathematical analysis.

1.3 μm/1.5 μm bidirectional WDM optical-fibre transmission system experiment at 144 Mbit/s

Results are reported of a 1.3 μm/1.5 μm bidirectional WDM transmission system experiment operating at 144 Mbit/s over 58 km of cabled single-mode fibre. Regenerators used Bell Laboratories-developed 1.3 and 1.5 μm InGaAsP semiconductor lasers, InGaAs PIN diodes, microwave monolithic amplifiers and optical bidirectional couplers.

Wideband, Bidirectional Lightguide Communication With an Optically Powered Audio Channel

The feasibility of bidirectional speech-television communication over a single-strand lightguide, with emergency optical powering of the remote station telephone, has been demonstrated. The remote circuits drew ∼250 μA at 0.9 volt from a double-heterostructure photovoltaic detector at 0.65 mW of received optical power; the detector low-pass response into 50 ohms was down 6 dB at 60 MHz. The optical packages featured GRIN-lens bidirectional couplers and, at the remote station, a low-threshold-current, buried-heterostructure laser.

Binary phase gratings for couplers used in fiber-optic communications

Abstract Star couplers and bidirectional couplers for use in fiber optic networks have been constructed using binary phase transmission gratings. The principles of operation and the performance of these devices are discussed. Experimental results are shown which agree with the theoretical predictions to an accuracy of 0.5 dB.

Angle selective fiber coupler

Angle selective input coupling through the side of a slightly tapered section of Corning highly multimode fiber has been experimentally demonstrated for the first time. This coupling technique allows the possibility of fabricating bidirectional (duplex) couplers for systems employing single strands of multimode, low loss fiber.