Relationship between rheological manufacturing process and optical performance of optical fiber coupler

Through theoretical analysis and experiments, the viscoelastic mechanical model of optical fiber coupler in the process of fused biconical taper was established, and the numerical analysis in non-uniform temperature field was made. The results show that the rheological parameters, such as drawing speed and fused temperature, have a tremendous influence on stress distribution and performance of optical fiber coupler, especially the influence of fused temperature. The change of fused temperature by 5℃ can lead to the change of the maximum stress by 30% and stress difference by 20% in the same cross section. The change of temperature gradient by 3% can result in the change of stress difference by 90%. In the present condition of rheological technology, rheological defects such as crystallizations and microcracks are easy to generate in the optical fiber coupler.

Experimental measurement and numerical analysis of fused taper shape for optical fiber coupler

To find out the effect of the shape of fused taper region on the optical fiber coupler, the fiber couplers were fabricated at different drawing speeds with a six-axes fiber coupler machine. The results, which were obtained from the shape of fused taper region measured with microscope, show that there is a close correlation between the cone angle and optical performance of fiber coupler. High-performance fiber coupler cannot be obtained until rheological shape is controlled accurately. The numerical analysis model, which was built based on generalized Maxwell viscoelastic theory, is resolved with ANSYS software. The calculated results accord with the experimental data. It can apply a theoretic basis for forecasting the shape of fiber coupler fabricated under the conditions of different technological parameters.

Novel manufacturing method of optical fiber coupler

Based on the coupling mode theory that the coupling ratio of fiber coupler changes periodically with center distance of two optical fibers, a novel manufacturing method of optical fiber couplers was developed with fused biconical taper experimental system. Its fabrication process is that the fiber is fused but not stretched when light begins to split, and the reduction of diameter of fiber is dependent on the rheological characteristic of the fused fiberglass. The performance of the coupler was tested. The results show that the performance of the novel optical fiber coupler meets the performance expectations, and its diameter of coupling region (about 30μm) is twice as long as that of classical fused biconical taper coupler (about 16μm), so the default, that is, the device is easy to fracture, is restrained and the reliability is greatly improved.

Towards an optical coupler using fine-wire:a study of the photovoltaic effect of a heterojunction formed in a single fine-wire of tungsten oxides

Nanodevices using the photovoltaic effect of a single nanowire have attracted growing interest. In this paper, we consider potential applications of the photovoltaic effect to optical signal coupling and optical power transmission, and report on the realization of a heterojunction formed between WO2 and WO3 in a fine-wire having a diameter on the micrometer scale. Using a laser beam of 514.5 nm as a signal source, the WO2-WO3 heterojunction yields a maximum output power of up to 37.4 pico watt per heterojunction. Fast responses （less than a second） of both photovoltaic voltage and current are also observed. In addition, we demonstrate that it is a simple and effective way to adapt a commercial Raman spectrometer for the combined functions of fabrication, material characterization and photovottaic measurement of an optical signal coupler and optical power transmitter based on a fine-wire. Our results show an attractive perspective of developing nanowire or fine-wire elements for coupling optical signals into and for powering a nanoelectronic or nano-optoelectronic integrated circuit that works under the condition of preventing it from directly electrically connecting with the optical coupler.

Ultrashort optical pulse shaper based on complex-modulated long-period-grating coupler

In this paper,we present a novel ultrashort pulse shaper based on complex-modulated long-period-grating coupler（CM-LPGC）.Temporal rectangular waveform with 2-ps full width at half maximum（FWHM） is obtained by transforming the input Gaussian pulse.Tolerances of the CM-LPGC-based shaper to various non-ideal excitation conditions and fabricating errors are investigated.Results confirm that CM-LPGC is stable and suitable for optical pulse shaping operation.

Numerical Analyses Optical Solitons in Dual Core Couplers with Kerr Law Nonlinearity

In this paper, we present the results of numerical analysis of optical solitons in dual core couplers. We studied the optical couplers as an application for the non-linear Schrödinger equation in the case of Kerr law for non-linear and clarify the exact solution in this case. Then we have provided a numerical study of the effect of changing the constants in the form of the three types of solitons: bright soliton and dark solitons and singular soliton.

Effect of technological parameters on optical performance of fiber coupler

To find out the influence of technological parameters on optical performance of fused optical fiber device, the fiber coupler was served as subject investigated by using the fused biconical taper machining as experimental setup. Fused fiber coupler's optical performances such as insertion loss, excess loss, directivity and uniformity were tested with the optical test system that was constituted of tunable laser and optical spectrum analyzer. Especially the relationship between optical performance and drawing speed was investigated. The experimental results show that the optical performance is closely related to process conditions. At fused temperature of 1 200 ℃, there exists a drawing speed of 150 μms, which makes the device's performance optimum. Out of this speed region, the optical performance drops quickly. At drawing speed of 200 μms, the excess loss is relatively small when the fused temperature is above 1 200 ℃. So the technological parameters have close relationship with optical performance of the coupler, and the good performance coupler can't get until the drawing speed and fused temperature match accurately.

Structure analysis of optical fiber coupler with infrared spectrometry

To obtain excellent performance optical fiber couplers, the structural difference of SiO2 in couplers with different manufacturing techniques was investigated. With 740-FT-IR infrared spectrometric analyzer, the infrared absorption spectrum of SiO2 in couplers at different drawing velocities was measured, and two characteristic peaks in the wavenumber range of 6502000 cm-1 were observed. One characteristic peak is at about 943 cm-1, which is （attributed） to Si—O—Si bond asymmetric stretching vibration, the other is at about 773 cm-1, which is attributed to （Si—O—Si） bond symmetric stretching vibration. From the infrared spectrum, it is found that the intensity and wavenumber of the characteristic peaks are related to the manufacturing technique of couplers. The characteristic peak at （about） 943 cm-1 becomes steeper when increasing the drawing velocity. At the drawing velocity of 150 μm/s, the distance between the two characteristic peaks is maximum, and then the optical fiber coupler has excellent performance, indicating that the performance of the optical fiber coupler has a close relationship with the wavenumber of the two characteristic peaks.

Low Cost Acrylic-Based 1×2 Asymmetric Plastic Optical Fiber Coupler for Optical Code Generating Devices

An optical code generating device has been developed based on a 1×2 asymmetric plastic optical fiber （POF） coupler. The code generating device provides a unique series of output power which are successively used as an optical code in a portable optical access-card system. The device utilizing a tap-off ratio （TOFR） technique based on a simple variation of the tap width of an asymmetric Y-branch splitter, allows various ratios of optical power to be generated. The POF coupler has been fabricated using low cost acrylic material and computer numerical control （CNC） machining technique. The simulated and fabricated results show the same linear characteristics between the TOFR and the tap width. The fabricated device enables a variation of the TOFR from 10% up to 50% for a tap width of 500 um to 1 mm.

硫族化合物非晶态薄膜波导optical-stopping效应研究

本文通过实验对As2S8这种硫系非晶态材料的光学截止(optical-stopping)现象进行研究,报告了硫系非晶态As2S8薄膜波导的制备工艺,以及实验光路和光学截止现象的过程。并且结合了其它一些有关硫系非晶态半导体中的光诱起现象的报道,提出了以微结构变动为前提、结合半导体能级理论的电子抽运模型,对实验现象进行了解释。

Transmittance investigation on capacitive mesh on thick dielectric substrates as output windows for optically pumped terahertz lasers

This paper reports that an output window for optically pumped terahertz （THz） laser has been fabricated by depositing a capacitive nickel-mesh on a thick high-resistivity silicon substrate （approximating to 5 mm thick）. Unlike the conventional process of depositing a gold film approximating to 100 nm on negative photoresist using electron-beam evaporation, a nickel film approximating to 1.5 μm thick is directly deposited on the clean surface of dielectric substrate using magnetron sputtering and then a positive photoresist is spun onto the nickel metal surface at 6000 r for 60 s. A transmittance spectrum of the output window in a certain frequency range （say, from zero to 1 THz） has been obtained by using THz time domain spectroscopy. Moreover a transmittance spectrum simulated numerically has also been estimated with respect to the output window using the transmission-line model （TLM） containing attenuation component from dielectric substrate. The simulation results show that the TLM can explain well the experimental curve in a certain frequency range from zero to 1 THz. Thus it is demonstrated that the improved optical component can be efficiently used as both output coupler and output window for optically pumped THz lasers.

Research on Multi-System Ultra-High Speed Optical Signal Access System

In view of the small transmission capacity and single signal modulation format of the existing optical transmission system, this paper proposes an ultra-high-speed optical signal access scheme based on NEL0670, which can realize the transmission of 100 G DP-QPSK, 200 G DP-16QAM and 400 G DP-16QAM signals, and realize flexible and intelligent reception of multi-system optical signals.

Trichromatic Optical Fiber Radiation Thermometer

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Real-Time 4-Mode MDM Transmission Using Commercial 400G OTN Transceivers and All-Fiber Mode Multiplexers

Weakly-coupled mode division multiplexing(MDM)technique is considered a promising candidate to enhance the capacity of an optical transmission system,in which mode multiplexers/demultiplexers(MMUX/MDEMUX)with low insertion loss and modal crosstalk are the key components.In this paper,a low-modal-crosstalk 4-mode MMUX/MDEMUX for the weakly-coupled triple-ring-core few-mode fiber(TRC-FMF)is designed and fabricated with side-polishing processing.The measurement results show that a pair of MMUX/MDEMUX and 25 km weakly-coupled TRC-FMF MDM link achieve low modal crosstalk of lower than−17.5 dB and insertion loss of lower than 11.56 dB for all the four modes.Based on the TRC-FMF and all-fiber MMUX/MDEMUX,an experiment for 25 km real-time 4-mode 3-λwavelength division multiplexing(WDM)-MDM transmission is conducted using commercial 400G optical transport network(OTN)transceivers.The experimental results prove weakly-coupled MDM techniques facilitate a smooth upgrade of the optical transmission system.

Experimental demonstration of single-mode fiber coupling using adaptive fiber coupler

Coupling plane wave into a single-mode fiber （SMF） with high and steady coupling efficiency is crucial for fiber- based free-space laser systems, where random angular jitters are the main influencing factors of fiber coupling. In this paper, we verified a new adaptive-optic device named adaptive fiber coupler （AFC） which could compensate angular jitters and improve the SMF coupling efficiency in some degree. Experiments of SMF coupling under the angular jitter situation using AFC have been achieved. Stochastic parallel gradient descent （SPGD） algorithm is employed as the control strategy, of which the iteration rate is 625 Hz. In closed loop, the coupling efficiency keeps above 65% when angular errors are below 80/3tad. The compensation bandwidth is 35 Hz at sine-jitter of 15 ~rad amplitude with average coupling efficiency of above 60%. Also, experiments with simulated turbulence have been studied. The average coupling efficiency increases from 31.97% in open loop to 61.33% in closed loop, and mean square error （MSE） of coupling efficiency drops from 7.43% to 1.75%.

CMOS compatible highly efficient grating couplers with a stair-step blaze profile

A novel grating coupler with a stair-step blaze profile is proposed. The coupler is a CMOS process compatible device and can be used for light coupling in optical communication. The blaze profile can be optimized to obtain a high efficiency of 66.7% for the out-of-plane coupling at the centre wavelength of 1595 nm with a 1 dB bandwidth of 41 nm. Five key parameters of the stair-step blaze grating and their effects on the coupling are discussed for the application in L band telecommunication.

High-Speed Mach-Zehnder-OTDR Distributed Optical Fiber Vibration Sensor Using Medium-Coherence Laser

This article presents a high-speed distributed vibration sensing based on Mach-Zehnder-OTDR （optical time-domain reflectometry）. Ultra-weak fiber Bragg gratings （UWFBG）, whose backward light intensity is 2-4 orders of magnitude higher than that of Rayleigh scattering, are used as the reflection markers. A medium-coherence laser can substitute conventional narrow bandwidth source to achieve an excellent performance of distributed vibration sensing since our unbalanced interferometer matches the interval of UWFBGs. The 3 m of spatial resolution of coherent detection and multiple simultaneous vibration sources locating can be realized based on OTDR. The enhanced signal to noise ratio （SNR） enables fast detection of distributed vibration without averaging. The fastest vibration of 25 kHz and the slowest vibration of 10Hz can be detected with our system successfully, and the linearity is 0.9896 with a maximum deviation of 3.46nε.

Single-side-band optical modulation in SCM systems for high-speed optical transmission

In order to decrease dispersion penalty and increase the optical bandwidth efficiency,an optical single-side-band modulation(SSBM) scheme in sub-carrier multiplexing(SCM) is proposed.The principle of the SSBM is analytically presented,and a configuration for generating optical SSB signal is proposed using a balanced Mach-Zehnder electro-optic modulator.

Integrated model optocouplers

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High efficiency grating couplers based on shared process with CMOS MOSFETs

Grating couplers are widely investigated as coupling interfaces between silicon-on-insulator waveguides and optical fibers.In this work,a high-efficiency and complementary metal-oxide-semiconductor（CMOS） process compatible grating coupler is proposed.The poly-Si layer used as a gate in the CMOS metal-oxide-semiconductor field effect transistor（MOSFET） is combined with a normal fully etched grating coupler,which greatly enhances its coupling efficiency.With optimal structure parameters,a coupling efficiency can reach as high as ～ 70% at a wavelength of 1550 nm as indicated by simulation.From the angle of fabrication,all masks and etching steps are shared between MOSFETs and grating couplers,thereby making the high performance grating couplers easily integrated with CMOS circuits.Fabrication errors such as alignment shift are also simulated,showing that the device is quite tolerant in fabrication.