A diffusion-current theory based on the superposition theorem of constant-current sources is applied to analyzing nerve
impulses transmitting through arrayed neurons laterally coupled via excitatory and inhibitory lateral connection paths.
Nonlinear dynamic responses to density-modulated impulses are simulated for simple point stimulus. Responses to
spatially distributed stimulus are also simulated to show that the arrayed neurons not only enhance contours of objects to
be detected but also exhibit some illusions.
This paper describes a new approach to realize a bidirectional repeater suitable for sensor networks with absolute time synchronization, and discuss propagation delay measurements of an experimental bidirectional repeatered system. A time-shared quasi-bidirectional linear repeater, that enables to the direction of signal flow to be changed. It uses a unidirectional EDFA, an optical router module composed of magneto-optic components and a delay fiber. The repeater has realized identical propagation delay for both directions of signal flows and attained multipath interference free amplification of optical packet signals for absolute time synchronization and sensing. A 50.078 km bidirectional repeatered line varied its propagation delays by 1.2 ns for both directions of signal flow with laboratory temperature change. Nevertheless, the experimental setup has not detected the propagation delay difference between both directions of signal flows that exceeded +/- 30 ps. This means that highly accurate absolute time synchronization will be feasible using bidirectional transmission system equipped with the time-shared quasi-bidirectional linear repeaters.
A method for testing distributed amplifiers is presented; the multipath interference (MPI) is detected as a beat spectrum between the multipath signal and the direct signal using a binary frequency shifted keying (FSK) test signal. The lightwave source is composed of a DFB-LD that is directly modulated by a pulse stream passing through
an equalizer, and emits the FSK signal of the frequency deviation of about 430MHz at repetition rate of 80-100 kHz. The receiver consists of a photo-diode and an electrical spectrum analyzer (ESA). The base-band power spectrum peak appeared at the frequency of the FSK frequency deviation can be converted to amount of MPI using a calibration chart. The test method has improved the minimum detectable MPI as low as -70 dB, compared to that of -50 dB of the conventional test method. The detailed design and performance of the proposed method are discussed, including the MPI simulator for
calibration procedure, computer simulations for evaluating the error caused by the FSK repetition rate and the fiber length under test and experiments on singlemode fibers and distributed Raman amplifier.
We propose a new approach to realize a bidirectional linear repeater suitable for future optical internet networks and fault location in repeater chain with OTDR. The proposed approach is the linear repeater of simple configuration whose directionality is rearranged dynamically by electrical control signal. The repeater is composed of a magneto-optical switch, a circulator, a dynamically gain stabilized unidirectional EDFA, and control circuits.
The repeater directionality is rearranged as fast as 0.1ms by an electrical control pulse.
It is experimentally confirmed that OTDR with the directionality switchable repeater is feasible for repeater chain.
The detailed design and performance of the repeater are also discussed, including the multi-pass interference (MPI) which may arise in the proposed repeater, the effect of the MPI on SNR degradation of the repeater chain and the feed-forward EDFA gain control circuit.
Highly selective tunable receiver has been studied experimentally for optical packet dense WDM systems. Performance evaluation of the receiver using new test methods confirms the feasibility of ultra-dense WDM spaced by several GHz. The receiver consists of a fiber loop which contains fiber delay line, tunable optical band-pass filters, an erbium-doped fiber amplifier and an optical switch, an optical switch at the receiver input port, and a photodiode followed by a switch at the fiber loop oputput port. Target packets are selected from input optical packet WDM signals by time and wavelength windows realized by the optical switches, and the tunable filters, respectively. Wavelength selectively enhancement is attained by the target packet multiple circulation in the loop. Optical packet ultra dense WDM test signal was generated by multiplexing 8 optical packets, where channel spacing ranged as narrow as from 0.62GHz to 3.62GHz in 500MHz step. The receiver fiber loop employed tunable disk filters, a gain stabilized EDFA, low PDL isolators and a magneto-opticla switch to realize high selectivity, high stability and low noise. The receiver has demultiplexed the target optical packets from optical packet ultra-dense WDM spaced by 1.1GHz, attaining high SNR and stable operation.
We propose a scheme for reduction of cross-talk arising form stop-band rejection limitation of optical band-pas filters in a wavelength-division multiplexing receiver. Experiment confirms high selectivity of the receiver and reveals feasibility of optical packet ultra dense WDM systems spaced by several GHz.
The receiver consists of optical switches at input and output ports of a fiber loop, which contains fiber delay line, tunable optical band-pass filters, an erbium-doped fiber amplifier, and an optical switch.
Target packet is selected from input optical packet WDM signals by time and wavelength windows realized by the optical switches at the input and output ports of the fiber loop, and the tunable filters in the loss compensated fiber loop, respectively.
The selectivity is measured by using pulsed lightwave sweep frequency, which contains 7 frequencies in 500MHz step. The results show 11dB suppression for signals 2 GH apart from the target channel after 10 circulation, and 12dB suppression for signals 1.5 GHz apart from the target channel after 18 circulation.
Details of the receiver configuration, pulsed lightwave sweep frequency generator and experimental results are discussed.
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