基于连通器原理的小探头光纤液位传感器研究

介绍了以汞包层光波导为传感探头的光纤液位传感器的原理及信号处理,其工作原理是利用连通器将液位的变化转变为汞包层光波导包层长度的变化。理论分析和实验表明,当光波导直径和光波长一定时,光功率衰减随汞包层光波导长度增加作线性增加。通过对汞包层光波导引起光功率衰减的检测,探头结构的优化设计以及探测器件的选型,可以获得实时性很强的高精度液位测量。实验测得10m液位的最大测量误差为5．2mm,理论分析的相对测量精度可达0．02％。该液位传感器的研制对于油库等易燃、易爆环境中的液位测量具有重要意义。     

Splitting-on-demand optical power splitters using multimode interference (MMI) waveguide with programmed modulations

Reconfigurable multi-channel optical power splitter is proposed and its optical properties are calculated. The device can dynamically reconfigure the number of splitting channels by providing programmed refractive index modulations on a multimode interference (MMI) waveguide. A reconfigurable 3-channel optical power splitter is designed to work as 1 × 1, 1 × 2 or 1 × 3 optical power splitter depending on the state of the heat electrodes using thermo-optic modulation, and the input light can be distributed to three output channels with sequential orders. The device can work in the whole C-band (1530-1565 nm) with extinction ratio better than −29.0 dB, excess loss better than −0.45 dB, imbalance better than 0.08 dB and polarization dependent loss (PDL) better than 0.14 dB. The design conception is scalable to a multi-channel splitting-on-demand optical power splitter which can divide input light to 1, 2, …, N output channels equally by using the 3-channel reconfigurable optical power splitter as a building block.     

A liquid lens-based broadband variable fiber optical attenuator

To the best of our knowledge, proposed is the first variable fiber optical attenuator (VFOA) using an electronically controlled variable focus liquid lens. The approach uses the changes in the radius of curvature of the liquid lens edge to enable an electronically controlled optical wedge that produces a varying beam tilt angle. In effect, changing beam tilt within a single mode fiber (SMF) lens free space coupling assembly leads to a polarization independent broadband VFOA design. The demonstrated VFOA experiment shows broadband operation over the 1530-1560 nm C-Band with a 40 dB dynamic range, <0.5 dB resolution, 0.3 dB polarization dependant loss, 4.3 dB fiber-to-fiber optical loss, 3 dB optical bandwidth from 1510 nm to 1700 nm, and switching time of <100 ms. Applications for this VFOA include use in hand held test and measurement equipment.     

Bit-rate adaptive optical performance monitoring method for fiber communication systems

A novel bit-rate adaptive method, by varying the optical sampling rates alternatively, is proposed in this paper for optical performance monitoring. Firstly, the theoretical model and the differential software-synchronized algorithm are developed. Then, the results verify that different channel bit-rate can be estimated with high precision irrespective of the modulation formats and signal distortion caused by chromatic dispersion and nonlinearity along the fiber link. Employing the proposed bit-rate adaptive method, the eye diagrams and Q values of 10 Gbit/s, 40 Gbit/s and even higher bit-rate signal can be monitored by a single optical performance monitoring system without any prior knowledge about bit-rate or signal period. The method we propose in this paper has the advantage that different channel bit-rates can be adaptively estimated and the differential software-synchronized algorithm is much simpler.     

Agile lensing-based non-contact liquid level optical sensor for extreme environments

To the best of the author's knowledge, demonstrated is the first opto-fluidic technology- based sensor for detection of liquid levels. An opto-fluidic Electronically Controlled Variable Focus Lens (ECVFL) is used to change the spatial intensity profile of the low power optical beam falling on the liquid surface. By observing, tuning and measuring the liquid surface reflected intensity profile to reach its smallest size, the liquid level is determined through a beam spot size versus ECVFL focal length calibration table. Using a 50 μW 632.8 nm laser wavelength liquid illuminating beam, a proof-of-concept sensor is tested using engine oil, vegetable oil, and detergent fluid with measured liquid levels over a 75 cm range. This non-contact Radio Frequency (RF) modulation-free sensor is particularly suited for hazardous fluids in window-accessed sealed containers including liquid carrying vessels in Electromagnetic Interference (EMI) rich environments.     

A 1 × 4 polarization and wavelength independent optical power splitter based on a novel wide-angle low-loss Y-junction

A 1 × 4 polarization and wavelength independent optical power splitter is reported. This device is based on a novel wide-angle low-loss Y-junction structure which can give a theoretical TE junction excess loss of 0.26 dB at a branching angle of 16°. To the best of our knowledge, it is so far the lowest reported loss at such a large angle. The detailed design of the device and its fabrication are described. Our experimental results show the measured TE excess loss to be 1.2 dB and TM excess loss 1.8 dB for the whole splitter over the wavelength between 1.47 μm and 1.57 μm.     

An optical power-equalized amplifier with a wide dynamic range

An optical power equalization amplifier with a wide dynamic range is proposed and demonstrated with no electronic control. It shows constant and equalized outputs when a power difference between input channels and a total input power are changed. It has more than a 15 dB dynamic range for input signals between −30 dBm and −5 dBm. The structure of this amplifier can be more promising when it is applied to a planar waveguide device.     

Modulation instability in silicon optical waveguide considering linear loss

Taking into account the linear loss of silicon-on-insulator (SOI) waveguide, modulation instability (MI) induced by combined effects of self-phase modulation and waveguide dispersions is investigated. The impacts of various parameters to gain spectra of MI are analyzed theoretically, and direct numerical simulation of nonlinear Schroedinger equation is performed as well. Results show that strong MI takes place even in the existence of low light power. The linear loss of waveguide obviously impacts gain spectra of MI, even within ultra-short propagation distance. The peak gain frequency and bandwidth of gain spectra decrease to 41.683% and 41.6879% of their maximum at propagation distance z = 5 mm, respectively.     

10 Gb/s TDM passive optical networks using four wavelengths multiplexed channels

We propose a new architecture for 10 Gb/s upstream traffic in TDM-PON using externally injection-locked Fabry-Perot laser diodes (FP-LDs) in each optical network unit (ONU). Four directly modulated 2.5 Gb/s FP-LDs were injection-locked by continuous wave (CW) carriers distributed from the optical line terminal (OLT). Hence, a total of 10 Gb/s upstream traffic can be achieved. Experimental results show negligible power penalty at a transmission of 25 km standard single mode fiber (SMF) without dispersion compensation. The performance of the injection-locked FP-LD is also studied.     

Analysis and optimization of an InGaAsP/InP waveguide variable optical attenuator

An InGaAsP/InP waveguide variable optical attenuator (VOA) is proposed in this paper. The device consists of straight input and output waveguides and an S-bend waveguide. An electrode is deposited on a portion of the waveguide to form an active region so that its refractive index can be modified by a current injection, resulting in the variation of the transmitted optical power. The beam propagation method is employed in the numerical simulation and the device structure is optimized using a genetic algorithm. The optimized VOA has a low excess loss (<1 dB) and a large dynamic range of about 40 dB.     

Polymer waveguide thermo-optic switches with −70 dB optical crosstalk

To reduce the crosstalk of the polymer waveguide optical switches, waveguide attenuators are integrated with the switch on the same substrate. The switch and attenuator shares a single connected electrode which is controlled by a single current source. Due to the simple structure of the integrated attenuator, the device length is reduced to 10 mm so as to provide low insertion loss of 0.8 and 1.1 dB for 1300 and 1550 nm, respectively. Further radiation of the remained optical signal on the switch-off branch is induced by the integrated attenuator so that the switching crosstalk is reduced to −70 dB with an applied electrical power of 200 mW. The low crosstalk is maintained for the environmental temperature range of −10 to 55 °C.     

Continuously wavelength-spacing-tunable and idler-output multiwavelength fiber optical parametric oscillator

We demonstrate a continuously wavelength-spacing-tunable and high-power multiwavelength fiber optical parametric oscillator based on the multiwavelength idler-output technique. The laser cavity for multiwavelength idler outputs is constructed by a pumped highly-nonlinear dispersion-shifted fiber as parametric gain medium, two highly-reflective chirped fiber Bragg gratings (CFBGs) and a superimposed CFBG as comb-like filter. At a pump power of 1.1 W, the idler output of 10 wavelengths around 1.56 μm is achieved with a wavelength spacing of 0.39 nm. The wavelength spacing can be continuously tuned from 0.39 to 1.0 nm by utilizing a cantilever beam-based chirp tuning method to change the FSR of the superimposed CFBG. Our experimental results show that the designed multiwavelength idler-output scheme can significantly increase the multiwavelength output power with a total output power of 98 mW and each idler-channel power of 16.3 mW.     

Waveguide properties and optical switching of prism-coupled Au:SiO2 nanocomposite films

In this study, we present theoretical and experimental analyses on the waveguide mode properties of prism-coupled Au:SiO₂ nanocomposite films with the near infrared laser of 1550 nm wavelength where the optical absorption diminished enough for the generation of guided mode. The evolution of guided mode in the nanocomposite waveguide and its propagation properties were also evaluated. As an effective way of utilizing the surface plasmon resonance properties for the application to optical switching devices, we employed an attenuated total internal reflection type optical switch geometry and tested its effectiveness for the absorptive opto-functional materials system using a cross-modulation technique with 532-nm pump and 1550-nm probe beams. The index change probe beam experiences was found to be purely refractive in nature and negative in sign, presumably due to the photo-thermal effect induced in the nanocomposite film by the irradiation of pump beam.     

Optimized design of a new three branch optical waveguide

A new type of 1 × 3 Y-branch optical waveguide structure with a cone transitional section is introduced in this paper. The symmetrical branch ratio of the 1 × 3 Y branch optical waveguide is obtained by changing the width of this waveguide. The loss and the uniformity are obtained by using the finite difference beam propagation methods, and their values are 0.2 dB and 0.05 dB, respectively. Therefore, it provides some experimental basis for production of three branch optical waveguide.     

Short-length and broadband mismatched optical couplers with tapered Hamming function for C- and L-band

Mismatched optical couplers with variable widths of waveguide tapered by Hamming function are numerically investigated in the demand of short-length, broadband, and low crosstalk. We used global search algorithm and beam propagation method to seek optimal structure parameters of coupling waveguide. The coupler length is 3.6 mm within the C+L-band (1.53-1.61 μm) for variable widths of waveguide at crosstalk level of −35 dB. Comparison with constant width of waveguide, the constant width of waveguide has a coupler length of 4.4 mm and can only achieve −20 dB of crosstalk within the C-band (1.53-1.565 μm). Obviously, the waveguide with variable widths has the advantage over constant width for the demand of short-length, bandwidth, and low-crosstalk.     

Stable multiwavelength fiber ring laser with equalized power spectrum based on a semiconductor optical amplifier

We experimentally demonstrated a new structure of a multiwavelength semiconductor optical amplifier (SOA) ring laser based on a fiber Sagnac loop filter that can generate up to 25 stable output lasing wavelengths at room temperature. By varying the length of a polarization-maintaining (PM) fiber within the Sagnac loop filter, the wavelength spacing between the output lasing wavelengths can be changed to a desired value. By tuning a polarization controller (PC) within the Sagnac loop filter, stable multiwavelength 1550-nm operation with up to 17 lasing lines within 3 dB power level variation and with a wavelength spacing of ∼0.8 nm was achieved. The optical signal-to-noise ratios (OSNRs) of all the lasing wavelengths are greater than 40 dB.     

A polymeric optical switch array based on arrayed waveguide grating structure

A novel 1 × N optical switch array based on arrayed waveguide grating (AWG) structure is presented in this paper. The device is designed for polymeric materials with a large negative thermooptic (TO) coefficient, which is employed to change the imaging effect and to realize optical switching. When input wavelength is located in a special waveband, the optical signal will image at different output channel as temperature changes. The two-dimensional finite difference beam propagation method (FD-BPM) has been used to simulate a 1 × 9 optical switch array. The insertion loss of this switch array is below 1.37 dB and the extinction ratio is better than 31 dB at 1550 nm, when the coupling and propagation loss is neglected. The optimum design and the simulation results show that this structure could be a multiple wavelengths switching at the same time.     

The thermo-optical variable optical attenuator based on SOI

A thermo-optical variable optical attenuator was studied based on silicon on insulator (SOI) substrate waveguide. It is composed by the single-mode waveguide, taper waveguide, multi-mode waveguide, and inclined electrode. By adjusting the applied voltage on the inclined electrode it can achieve continuously variable attenuation of the output light. The results we studied show that when the applied voltage is about 4.7 V (the corresponding power is 233 mW), the variation of the waveguide's core temperature is about 33 °C, the refractive index changes more than 5.0 × 10⁻³ and the attenuation will reach 35 dB, and the response time is only 35 μs.     

Optically controllable variable fiber optical attenuator integrated in conventional optical fiber

New type of optically controllable variable fiber optical attenuator based on thermo-optical effect in liquid cladding of optical fiber is described. The thermo-optical effect in liquid cladding optical fiber causes refractive index contrast changes in core–cladding interface, what enables to change the propagating optical signal power with temperature. The temperature change is achieved by fiber based heating element using laser radiation. Attenuation up to −12 dB was achieved in static dependence and dynamic response confirmed rise time up to 24 ms.     

An ultra-short double-wavelength optical power splitter for two waveguides operation based on photonic crystal multimode interference

In this paper, we design an ultra-short 1 × 2 1310/1550 nm double-waveguide optical power splitter based on photonic crystal multimode interference. The device can be used to divide the input beam equally for both 1310 nm and 1550 nm at the same time. The total multimode waveguide length of this device is only about 13 μm, which is one 210th of the conventional dielectric counterparts reported. On the basis of the guided-mode propagation analysis method, the self-imaging effect is discussed for the case of symmetric incidence. The finite-difference time-domain method is used to simulate the propagation of the beam in the multimode interference. The results show that the repetitive appearances of single image and twofold image of the input field occur alternatively in this device.