Nec Corporation

Naoki Shimosaka

Kazuhisa Kaede

Takahiro Shiozawa

Katsumi Emura

The method and apparatus for time-division multiplexing/demultiplexing of signals multiplexes input signals, and a predetermined frame synchronization pattern signal to thereby generate the first time-division multiplexed signals, then multiplexes each of the first time-division multiplexed signals to thereby generate the second time-division multiplexed signal. After receiving from a transmission line, the time-division multiplexed signal is demultiplexed to thereby generate a predetermined number of first time-division demultiplexed signals, then each of the first time-division demultiplexed signals is demultiplexed to generate the second time-division demultiplexed signals, and the orders of the second time-division demultiplexed signals are permuted until the same signal as a predetermined frame synchronization pattern signal is obtained from the second time-division demultiplexed signal corresponding to the predetermined frame synchronization pattern signal of the second time-division demultiplexed signals.

Method and apparatus for time-division multiplexing and demultiplexing

For supply to a time division multiplexer for multiplexing a predetermined number of digital multiplexer input signals bit by bit into a multiplexed signal in which a long pathological pattern is suppressed and which is supplied preferably to an optical network. A parallel scrambler subjects a plurality of digital video signals to scrambling of a prescribed number of scrambling stages with the prescribed number selected greater than the predetermined number. Produced by the scrambler, scrambled signals, equal in number to the digital video signals, are used in the digital multiplexer input signals preferably with an inverter used to invert one of the scrambled signals so that the predetermined number is equal to one plus the plurality.

TD multiplexing digital video signals with scramble of scrambling stages

An apparatus for controlling an acousto-optic filter includes a high-frequency oscillator, a beam intensity detector, a first and a second oscillator, and a first and a second controller. The high-frequency oscillator drives the acousto-optic filter and the frequency of the driving signal is finely modulated by oscillation frequency f.sub.0 of the first oscillator. The detector detects an output signal beam intensity of the acousto-optic filter. An output of the detector is synchronously detected at the frequency f.sub.0 and the frequency of the driving signal is controlled by the first controller so that the resultant detected output becomes zero. Similarly, the amplitude of the driving signal is finely modulated by the oscillation frequency f.sub.1 of the second oscillator. The output of the detector is synchronously detected at the frequency f.sub.1 and the amplitude of the driving signal is controlled by the second controller so that the resultant detected output becomes zero. The frequency f.sub.0 of the first oscillator is different from that f.sub.1 of the second oscillator. Thus, the transmittivity can be maximized and stable filter operation can be realized. The apparatus may further include another variable high-frequency oscillator or a variable low-frequency oscillator which supplies to the acousto-optic filter two or more high-frequency signals for varying transmission bandwidth of the acousto-optic filter.

Method and apparatus for controlling acousto-optic filter

When a data transmission request is received in a node apparatus in an optical LAN system, the node apparatus receives a light of a wavelength assigned to a destinated node apparatus. Where the received light is not a modulated light, the received light will be modulated by a transmitting data, and where the received light is a modulated light, the received light is passed through the transmitting node apparatus without a further modulation.

Optical local area network system and node apparatus used in the same

Reference signals having a predetermined frequency interval are produced in use of a wavelength tunable laser device and an optical resonator. Plural laser devices are controlled to radiate light outputs with oscillation frequency separation. The light outputs and a frequency swept light output of the wavelength tunable laser device are combined, and then converted to beat signals. The reference signals and the beat signals are compared to detect time differences of signal occurrance timings. The plural laser devices are driven with the oscillation frequency separation, such that the time differences become a predetermined value. Where a beat pulse is not produced due to a fault in at least one laser device among the plural laser devices, a dummy pulse is produced to produce signal of the time differences. The laser device of the fault may be driven with an injecting current varying in a predetermined range to produce a beat pulse.

Method and apparatus for stabilizing oscillation frequency separation

There are disclosed a method and apparatus for stabilizing an oscillation frequency separation among a plurality of laser devices wherein a plurality of laser devices are controlled to radiate output lights each having a predetermined frequency so that a frequency separation is stabilized. Reference pulses are produced in an optical resonator which has periodic resonant frequencies and receives a frequency sweep signal, and beat signals are produced in accordance with the combination of the frequency sweep signal and oscillation frequencies of the plurality of laser devices. The reference signals and beat signals thus produced are processed to produce error signals which are time differences between the producing times of the both signals. The plurality of laser devices are controlled to be driven such that the error signals become a predetermined value.

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Tokyo, Japan

Naoki Shimosaka