For automatic service composition, a planning based framework MOCIS is proposed. Planning is based on two major
techniques, service reasoning and constraint satisfaction. Constraint satisfaction can be divided into quality constraint
satisfaction and quantity constraint satisfaction. Contrary to traditional methods realizing upon techniques by interleaving
activity, message and provider, the novelty of the framework is dividing these concerns into three layers, with activity
layer majoring service reasoning, message layer for quality constraint and provider layer for quantity constraint. The
layered architecture makes automatic web service composition possible for activity tree that abstract BPEL list and
concrete BPEL list are achieved automatically with each layer, and users can selection proper abstract BPEL or BPEL to
satisfy their request. And E-traveling composition cases have been tested, demonstrating that complex service can be
achieved through three layers compositing automatically.
The multimode devices, which are also polarization-sensitive, have been widely used in modern optical communication
system. In some cases, the modal properties, including the modal propagation constants and the modal fields of every
order, must be given for the device design. The scalar finite difference beam propagation method (FD-BPM) is extended
to solve this polarization-related problem. The different finite difference schemes corresponding to different polarized
directions, which satisfy different boundary continual conditions, are formulized and the alternate directions implicit
(ADI) FD-BPM were used to deal with the three dimensional (3D) waveguide. The guided modal properties of a 3D rib
waveguide including the propagation constants and modal field distributions up to ten ranks were obtained and illustrated
as an example.
The development and application of single-photon detectors are introduced. The operating principles of photomultiplier
tube (PMT), avalanche photodiode (APD) and superconducting,
single-photon detector (SSPD) are expounded. The characteristic, advantages and disadvantages of them are discussed. Then give a view for the perspective and the development of these devices. In the above types of single-photon detectors, the PMT can't detect photon in
near-infrared while the APD has great advantage on it, so it is the most preponderant detector in the single-photon detection. The capability of SSPD are excelled the former single-photon detectors, besides, it can detect the arriving time and energy of the photon, so it has great potential in the astronomical observation and the high-speed quantum communication and so on.
Proc. SPIE. 7055, Infrared Systems and Photoelectronic Technology III
KEYWORDS: Avalanche photodetectors, Signal to noise ratio, Control systems, Avalanche photodiodes, Signal detection, Interference (communication), Temperature metrology, Analog electronics, Sensors, Mathematics
According to the randomness of multiplication of the carrier for the avalanche photodiode (APD), a mathematic model of
the false alarm ratio (FAR) and the multiplication factor of APD were established based on the statistics. Through
monitoring FAR for avalanche noise, the curve between bias voltage and temperature characteristic and the temperature
coefficient of breakdown voltage have been obtained. The experiment shows that false alarm method not only can gain
the breakdown voltage of APD in different temperature accurately, but also can determine the degree of avalanche
breakdown. The temperature compensating circuit designed for the bias of APD can guarantee the normal operating of APD in a large variation of temperature, it is suitable for the photoelectric system that the high-frequency continuous signal detect.
The multimode interference (MMI) couplers, which operate at 1.55 microns in deep rib InGaAsP/ InP waveguide with
large lateral confinement and tunable power splitting ratios, are of high interest in integrated optics. The gold contacts
are applied on the top of waveguides where tuning is desired and the plasma effect will lead to negative refractive index
change. The three-dimensional (3D) finite difference beam propagation method (FD-BPM) is used to model the tunable
MMI couplers. The length of a 2×2 overlap-MMI is determined by FD-BPM, so the longitudinal position of tuning spots
is obtained. The position of gold contacts with two types, the edge-pads or center-pad, are also determined. In our design,
the length of MMI is 180 microns. If the width of pads is 50 micros and the refractive index is tuned from 0 to -0.027,
the power ratio is tuned from50:50 to maximums 88.5:11.4. For deep rib structure, the effective index (EI) method can
not be used to simplify the 3D waveguide to plane waveguide because its lower precision, and then the direct 3D FD-BPM
simulation is necessary for the design of 3D MMI couplers.
A passive polarization beam splitter in silicon-on-insulator (SOI) waveguides, which consists of two 3-dB multimode interference (MMI) couplers and two Mach-Zehnder interferometer (MZI) arms with the same length but different rib widths, has been proposed recently and a numerical method of design is needed because the analytical solution for this 3-dimensional (3D) SOI waveguides is difficult to achieve. The scalar finite difference beam propagation method (FD-BPM) is used to design the 3-dB MMI couplers and the positions of the input or output waveguides and the length of multimode waveguide are determined. In our design, the length of MMI couplers is 1228 micron when the width of rib is 36 micron. The propagation constants of TE-polarized and TM-polarized mode supported by 3D rib waveguides on SOI are calculated by the Semi-vector FD-BPM which is polarization related. From these data obtained for different rib widths (from 2.0 micron to 4.0 micron), the appropriate length of MZI arms is selected. In our example, the widths of two arms are 3.4 micron and 2.0 micron respectively and the length of arms is 1506 micron. The TE-polarized light and TM-polarized light are input to the splitter separately and the Semi-vector FD-BPM is used to check the design.