Nec Corporation

Akihiro Kanazawa

Makoto Shibutani

Morihisa Momona

Toshiharu Yasugi

An error correcting decoder for decoding a plurality of block units of data, the data being encoded with a plurality of parameters, comprising a plurality of error correcting decoding circuits for inputting and outputting the block units of data and for performing error correction decoding for the block units of data on the basis of the plurality of parameters, a selection circuit for selecting one of the block units from an output of the plurality of error correction decoding circuits on the basis of the encoding parameters of the selected block, a delay circuit for adding delay to the output of the plurality of the plurality of error correction decoding circuits wherein the delay equalizes a time between the inputted plurality of block units of data and outputted plurality of the selected block units and a multiplexing circuit for outputting a multiplexed signal from a plurality of the selected block units in the same order as that of the inputted plurality of block units of data.

Error correcting decoder

It is the object of the invention to provide a sub-carrier multiplexed optical signal transmission system employing super wide-band frequency modulation scheme, in which the SNR of a sub-carrier of a higher sub-carrier frequency is not decreased. The intensity of a sub-carrier of a higher sub-carrier frequency is increased by a pre-emphasizer, and modulated in a FM modulator. Then, a super wide-band FM signal is obtained. The super wide-band FM signal is supplied to the transmitter laser diode, and intensely modulated to obtain an optical signal. The optical signal is transmitted through an optical fiber, supplied to an optical receiver and converted into an electrical signal. The super wide-band FM signal thus obtained is demodulated by a FM demodulator. The sub-carrier multiplexed signal is supplied to a de-emphasizer having an inverse characteristic of that of the pre-emphasizer, wherein the signal supplied thereto recovers its original frequency spectrum.

Method for sub-carrier multiplexed optical signal transmission and

The subcarrier frequency multiplexed optical transmission system disclosed is one in which a plurality of analog subcarrier signals and at least one digital subcarrier signal is optically transmitted by frequency multiplexing. The system includes an amplitude limiter, a filter, a multiplexer and a semiconductor laser. Portions of the analog subcarrier signals which are lower in level than the threshold value of the semiconductor laser are eliminated by the amplitude limiter, and further impulse distortions generated due to clipping in the frequency band of the digital subcarrier signal are eliminated by the filter. Then, the analog and digital subcarrier signals are frequency multiplexed to be inputted to the semiconductor laser. The system enables to reduce the transmission quality deterioration of digital subcarrier signal caused by clipping.

Growing community of inventors

Tokyo, Japan

Akihiro Kanazawa