A new demodulation technique for optical fiber interferometric sensors with[3×3]directional couplers

Optical fiber interferometric sensors based on [3×3] couplers have been used in many fields. A new technique is proposed to demodulate output signals of this kind of sensors. The technique recovers the signal of interest by fitting coefficients of elliptic （Lissajous） curves between each fiber pair. Different from other approaches, this technique eliminates the dependence on the idealization of [3×3] coupler, provides enhanced tolerance to the variance of photoelectric converters, and is anti-polarization in a certain extent. The main algorithm has been successfully demonstrated both by numerical simulation and experimental result.

Asymmetric directional couplers based on silicon nanophotonic waveguides and applications

Directional couplers （DCs） have been playing an important role as a basic element for realizing power exchange. Previously most work was focused on symmetric DCs and little work was reported for asymmetric directional couplers （ADCs）. In recently years, silicon nanophotonie waveguides with ultra-high index contrast and ultra-small cross section have been developed very well and it has been shown that ADCs based on silicon-oninsulator （SOI） nanophotonic waveguides have some unique ability for polarization-selective coupling as well as mode-selective coupling, which are respectively very important for polarization-related systems and mode-division-mulitplexing systems. In this paper, a review is given for the recent progresses on silicon-based ADCs and the applications for power splitting, polarization beam splitting, as well as mode conversion/（de）multiplexing.

Analysis of Nonlinear Directional Couplers

1 IntroductionSince the coupled-mode theory in cylindrical optical-fiber systems was proposed in 1972, the optical coupling between parallel optical waveguides has been a matter of scientific concern. Two-core fiber couplers, especially, have been studied extensively since the success of producing a two-core fiber functioning as a directional coupler in 1980. The wavelength and polarization selectivity of two-core fibers can find many applications. The nonlinear properties of the two-core fiber coupler ...

Investigation on the multi-hole directional coupler for power measurement of the J-TEXT ECRH system

Power measurement is necessary for an electron cyclotron resonance heating(ECRH)system.The directional coupler method has been put forward to monitor high-power microwave from gyrotrons in real time.A multi-hole directional coupler has been designed and manufactured for the 105 GHz/500 kW ECRH system on the J-TEXT tokamak.During the design process,we established the relationships between hole parameters and coupling characteristics based on the multi-hole coupling method and small-hole coupling theory.High-power tests have been carried out.The results indicated the reasonability of the theoretical design and practicality of the fabricated directional coupler.Sources of test errors have been discussed in detail,and the influences of spurious modes on the directional couplers have been emphatically analyzed.

Design of a High Power Directional Coupler with High Directivity Used in the LHCD Launcher for EAST

A high power waveguide directional coupler was designed to measure the transmitted power and reflected power in the 4.6 GHz LHCD （lower hybrid current drive） launcher for the EAST tokamak. The design principle of the coupler is assessed. Further analysis is performed by CST （computer simulating test） and Ansoft HFSS （high frequency structure simulator） software and the optimal structural parameter is obtained. In addition, finite element code ANSYS is used to determine the temperature distribution in the coupler conductively cooled by forced water. The test results of a directional coupler manufactured according to the design are close to what is expected.

Fabrication of Polymer Nonlinear Directional Coupler by Photo-bleaching

The preparation of a nonlinear directional coupler in polymer PMMA/DR1 film by photobleaching is studied. We find it easier to obtain a required coupling length by controlling photo bleaching time than by controlling the dimension of the coupler. The transmittance of each arm is measured when the pulse input light energy changes in our experiment. The experimental results show that the coupling length will change with the intensity of input light due to optical nonlinearities of the polymer PMMA/DR1 at 1 064 nm.

Nonideal effects in quantum field-effect directional coupler

The nonideal effects in a quantum field-effect directional coupler where two quantum wires are coupled through a finite potential barrier are studied by adopting the lattice Green function method. The results show that the electron energy distribution, asymmetric geometry and finite temperature all have obvious influence on the electron transfer of the coupler. Only for the electrons with energies in a certain region, can the complete periodic transfer between two quantum wires take place. The conductance of these electrons as a function of the barrier length and potential height exhibits a fine periodic or quasi-periodic pattern. For the electrons with energies beyond the region, however, the complete periodic transfer does not hold any more since many irregular oscillations are superimposed on the conductance profile. In addition, the finite temperature and asymmetric geometry both can reduce the electron transfer efficiency.

Analysis and Design of a 3 dB Tunable Lumped-Element Directional Coupler

An analysis of a 3 dB lumped-element directional coupler （LEDC） based on arbitrary terminal impedance is described numerically. To solve the conflicted requirement for broad bandwidth and small size in LEDC, a new structure of coupler is introduced, which can significantly improve bandwidth and whose size is only 3 cm×4 cm on the conditions of the frequency domain of 410 MHz to 490 MHz. The measure results are in good agreement with simulations despite the unexpected resistor loss.

Design of a compact polarization beam splitter based on a deformed photonic crystal directional coupler

In this paper a compact polarization beam splitter based on a deformed photonic crystal directional coupler is designed and simulated. The transverse-electric （TE） guided mode and transverse-magnetic （TM） guided mode are split due to different guiding mechanisms. The effect of the shape deformation of the air holes on the coupler is studied. It discovered that the coupling strength of the coupled waveguldes is strongly enhanced by introducing elliptical airholes, which reduce the device length to less than 18.Sttm. A finite-difference tlme-domain simulation is performed to evaluate the performance of the device, and the extinction ratios for both TE and TM polarized light are higher than 20 dB.

An Ultra-Compact Broadband Polarizing Beam Splitter Utilizing Hybrid Plasmonic Waveguide

Polarizing beam splitter has rather significant applications in polarization diversity circuits and polarization multiplexing systems.In this paper,we present an asymmetric polarizing beam splitter utilizing hybrid plasmonic waveguide.The special hybrid structure with a hybrid waveguide and a dielectric waveguide can limit the energy of TE and TM modes to a different layer.Therefore,we can achieve beam splitting by adjusting the corresponding parameters of the two waveguides.First,we studied the influences of different structure parameters on the real part of the effective mode refractive index of the two waveguides,and obtained a set of parameters that satisfy the condition of strong coupling of TM mode and weak coupling of TE mode.Then,the performance of our proposed polarizing beam splitter is evaluated numerically.The length of the coupling section is only 4.1μm,and the propagation loss of TM and TE modes is 0.0025 d B/μm and 0.0031 d B/μm respectively.Additionally,the extinction ratios of TM and TE modes are 10.62 d B and 12.55 d B,respectively.Particularly,the proposed device has excellent wavelength insensitivity.Over the entire C-band,the fluctuation of the whole normalized output power is less than 0.03.In short,our proposed asymmetric polarizing beam splitter features ultra-compactness,low propagation loss,and broad bandwidth,which would provide promising applications in polarization multiplexing system and polarization diversity circuits relevant to optical interconnection.

Highly sensitive and fast response strain sensor based on evanescently coupled micro/nanofibers

Flexible strain sensors play an important role in electronic skins,wearable medical devices,and advanced robots.Herein,a highly sensitive and fast response optical strain sensor with two evanescently coupled optical micro/nanofibers(MNFs)embedded in a polydimethylsiloxane(PDMS)film is proposed.The strain sensor exhibits a gauge factor as high as 64.5 for strain≤0.5%and a strain resolution of 0.0012%which corresponds to elongation of 120 nm on a 1 cm long device.As a proof-of-concept,highly sensitive fingertip pulse measurement is realized.The properties of fast temporal frequency response up to 30 kHz and a pressure sensitivity of 102 kPa^(−1) enable the sensor for sound detection.Such versatile sensor could be of great use in physiological signal monitoring,voice recognition and micro-displacement detection.

Switching Dynamic Analysis for Twin-Core Fibre Coupler Using Supermode Theory

Characteristics of optical switching in a twin-core fibre coupler are numerically analysed under short pulse input by using supermode theory. The dynamic nonlinear coupled superlnode equations are derived, The numerical results show that the input pulse width determines the power transfer and the pulse temporal profile in the output ports. The optimal switching characteristics can be obtained by selecting an appropriate initial pulse width. In addition, the switching characteristic curves are insensitive to the input pulse shape for either fundamental soliton pulse or Gaussian pulse input, but sensitive to pulse sharpness. A reduced switching power and a sharper switching transition can be obtained by using the sharp super-Gaussian pulse.

Duplexer Design for Full-Duplex Based Wireless Communications

The full-duplex(FD) based wireless communication devices,which are capable of concurrently transmitting and receiving signals with a single frequency band,suffer from a severe self-interference(SI) due to the large power difference between the devices' own transmission and the useful signal comes from the remote transmitters. To enable the practical FD devices to be implementable,the SI power must be sufficiently suppressed to the level of background noise power,making the received signal-to-interference-plus-noise ratio(SINR) satisfy the decoding requirement. In this paper,the design and implementation of the duplexer for facilitating SI cancellation in FD based wireless communications are investigated,with a new type of duplexer(i.e. an improved directional coupler) designed for improving the spatial suppression of the SI power. Furthermore,the practical circuit boards are designed and verified for the proposed prototype,showing that the spatial suppression capability may be up to 36 d B(i.e. much higher than that attainable in the commonly designed ferrite circulator) by using the proposed design.

Ultra-wideband optical diode based on photonic crystal 90° bend and directional coupler

We propose an ultra-wideband optical diode device based on two-dimensional square-lattice photonic crystals. For the device, the odd mode is completely transmitted in one direction and converted to the fundamental even mode, but completely reflected in the other direction. The operation bandwidth of the device is preserved within a rather wide range of frequencies, which is over 6.5% of the central frequency. A directional coupler and 90° bend are utilized as the composite function device with mode filter and mode converter. It is possible that the photonic crystal device can help to construct on-chip optical logical devices and benefit greatly to the optical systems with multiple spatial modes.

Optimization Design and Application of S-Band 3dB Directional Coupler

The application of the 3dB directional coupler is very extensive,such as the phase shifter,the attenuator and the RF pulse compressor etc.The performance of the 3dB directional coupler is very important for these components. Optimization design has been done using the HFSS code.The new phase shifter prototype using the new optimization results has been tested.The tested results are in agreement with the measured ones.

High-performance ultra-compact polarization splitterrotators based on dual-etching and tapered asymmetrical directional coupler

High-performance ultra-compact polarization splitter-rotators(PSRs)are designed and experimentally demonstrated,using dual etching and a tapered asymmetrical directional coupler.First,two novel PSRs are designed with nanowire and subwavelength grating cross-port waveguides and verified in simulations.Then,one of the two PSRs is fabricated.Experiment results reveal that the extinction ratio is higher than 28 dB or 32 dB at 1550 nm for the launched fundamental transverse magnetic or the transverse electric modes,while the corresponding insertion loss and polarization conversion loss are 0.33 dB and 0.18 dB,respectively.

RF design and test of a high-directivity high-power waveguide directional coupler for the HEPS

Purpose A novel high-directivity high-power waveguide directional coupler(DC)working at 2998.8 MHz is developed for the High Energy Photon Source.It can help the phase control system to obtain a very accurate microwave signal,which is very important to minimize the beam emittance.Methods The novel reversely placed T-type coupling piece helps to obtain a high directivity.The N-type high-vacuum feedthroughs for vacuum sealing instead of the traditional ceramic plate is beneficial to holding a higher peak power.The simulation and the high-power commissioning are accomplished in the Institute of High Energy Physics(IHEP),while the fabrication and the low-power test are conducted in cooperation with the manufacturer.Results Both the single-coupler and the dual-coupler DCs are developed with a directivity of more than 35 dB while keeping the coupling factor within 60±0.5 dB.Finally,69.4%of all the fifty-two mass produced DCs have got a directivity of more than 40 dB.Conclusion:The mature manufacturing process for mass production is obtained.The novel high-directivity high-power waveguide DC can be mass produced with an actually internationally leading performance.

Development of a 500-MHz waveguide directional coupler with high directivity for HEPS

Purpose In order to achieve a high-precision measurement of the incident and the reflected power,a WR1800 rectangular waveguide directional coupler with high directivity and high power level has been in-house developed.Multiple couplers will be installed in the 500-MHz high-power radio-frequency transmission lines delivering 200-kW continuous-wave power for the High Energy Photon Source(HEPS).Methods The directional coupler adopts the design scheme of primary and secondary transmission lines and coaxial coupling-head structure.The shape and dimensional parameters of the coupling head were carefully optimized by using microwave simulation codes.An optimum directivity of 64 dB was achieved in simulations.Results and conclusions A prototype coupler was subsequently manufactured,and its directivity was measured to be 48.2 dB following a rigorous calibration procedure,largely exceeding the design goal and the commercial product.The coupler was then connected to an existing 500-MHz klystron system,and a high-power test with short-circuit termination was conducted.The high directivity of the coupler was confirmed up to 200 kW.During the 6 hours of power aging with continuous-wave 200 kW in a standing-wave setup,no performance degradation was observed on the coupler.The coupler temperature was measured to be 20◦C above the ambient environment.The design requirements were comfortably fulfilled.These constitute thefirst in-house development of a large-size waveguide directional coupler with high directivity and high power level for HEPS.The design,fabrication,and performance tests of the directional coupler are presented.

Local Discontinuous Galerkin Methods for the 2D Simulation of Quantum Transport Phenomena on Quantum Directional Coupler

In this paper,we present local discontinuous Galerkin methods(LDG)to simulate an important application of the 2D stationary Schrödinger equation called quantum transport phenomena on a typical quantum directional coupler,which frequency change mainly reflects in y-direction.We present the minimal dissipation LDG(MD-LDG)method with polynomial basis functions for the 2D stationary Schrödinger equation which can describe quantum transport phenomena.We also give the MDLDG method with polynomial basis functions in x-direction and exponential basis functions in y-direction for the 2D stationary Schrödinger equation to reduce the computational cost.The numerical results are shown to demonstrate the accuracy and capability of these methods.

A mechanical reliability study of 3-dB waveguide hybrid couplers in submillimeter and terahertz bands

This paper presents a mechanical reliability study of 3-dB waveguide hybrid couplers in submillimeter and terahertz bands.To show the necessity of improving the mechanical properties of the coupler’s branch in submillimeter and terahertz bands,a comprehensive study regarding the displacement of hybrid branch variation with varying width-length ratio and height-length ratio has been completed.In addition,a modified 3-dB waveguide hybrid coupler is designed and presented.Compared with the traditional branch structure,the proposed hybrid consists of a modified middle branch with circular cutouts at the top and bottom on both sides instead of the traditional rectangle branch,which increases the branch size and improves its mechanical reliability while achieving the same performance.Simulation results show that the deformation of the modified hybrid branch is 22%less than those of other traditional structure designs under the same stress.In practice,a vibration experiment is set up to verify the mechanical reliability of hybrid couplers.Measurement results show that the experiment deteriorates the coupling performance.Experimental results verify that the performance of the novel structure coupler is better than that of a traditional structure branch hybrid coupler under the same electrical properties.