# US 4,397,042 A · Optical modulation/demodulation system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,397,042 A - Document ID: US4397042A - Status: Granted - Kind: A - Application number: 06/285,749 - Filed: 1981-07-22 - Granted: 1983-08-02 - Earliest claimed: 1981-07-22 - Assignees: Sumitomo Electric Industries, Ltd. - Inventors: Koichi Tsujii; Yasuo Itai - Web page: https://patentgrep.com/patent/US4397042A ## CPC - H04B 10/508: Pulse generation, e.g. generation of solitons - H04L 25/49: using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels {; Baseband coding techniques specific to data transmission systems (spectral shaping H04L25/03828)} - H04L 25/4923: {using ternary codes (H04L25/4927 takes precedence)} - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract An optical modulation/demodulation system comprising a transmitting side circuit which is capable of detecting the leading or the falling edge of a timing pulse, converting the leading and falling detection pulse signal into the pulse of either positive or negative polarity in response to the level of the electric-input signal data, in the case of synchronous systems. The transmitting side circuit in asynchronous systems is capable of generating pulses in response to the leading and falling edge of an electric input signal data, by converting the leading and falling pulse into the one of either positive or negative polarity, overlapping these positive or negative polarity signals on a ready-for-sending signal of a predetermined to be used as an input signal for a light-emitting element. ## Claims ### Claim 1 A synchronous type optical modulation-demodulation system connected by an optical fiber cable, comprising: a transmitting circuit having a leading edge and falling edge detection circuit for outputting pulses in response to a leading edge and falling edge of a timing pulse, a positive or negative polarity pulse generating circuit for generating positive or negative polarity pulse signals from the output pulses from said leading edge and falling edge detection circuit in such a manner that said positive polarity pulse signals and negative polarity pulse signals are respectively a number of an integer multiple of two in response to two levels of "0" and "1" of an input data signal, a light emitting element driving circuit for inputting and superimposing said positive polarity and negative polarity pulse signals and a signal having a predetermined flat level made from a ready-for sending signal and for outputting a driving signal, a light emitting element whose light intensity is modulated by said driving signal so as to output a carrier signal when said output signal from said light emitting element driving circuit is only at the predetermined flat level and so as to output a stronger light signal when said output signal is higher than said flat level signal and so as to output a weaker light signal when said output signal is lower than said flat level signal, optical coupling means for guiding output light signals of said light emitting element into an optical fiber cable, a receiving circuit having a light receiving element for converting the light signal transmitted through said optical fiber cable into an electric signal, a gain variable amplifying circuit for amplifying said electric signal to obtain an output signal of a predetermined level and whose gain is controlled to obtain said level, an averaging circuit for averaging the output signal from said gain variable amplifying circuit to obtain a predetermined flat level signal, a pair of binary circuits for inputting the output signal of said gain variable amplifying circuit and the output signal of flat level from said averaging circuit and for outputting individually binary signals when the former is higher or lower than the latter, a flip-flop circuit for inputting the binary signals from each binary circuit at the set and reset terminals of said flip-flop circuit and for outputting a receiving data signal, and a flip-flop circuit for inputting the binary signals from said pair of binary circuits and for outputting a receiving timing pulse. ### Claim 2 (depends on 1) A synchronous type optical modulation-demodulation system as claimed in claim 1, wherein the leading edge of the received data from the flip-flop circuit which outputs received data coincides with the leading edge of the receiving timing pulse from the flip-flop circuit which outputs the receiving timing pulse. ### Claim 3 An asynchronous optical modulation-demodulation system connected by an optical fiber cable, comprising: a transmitting circuit having a leading and falling edge detection circuit for outputting pulses in response to a leading edge and falling edge of an electric input data signal, a positive and negative polarity pulse generating circuit for generating a positive or negative polarity pulse signal in response to the output signal from said leading and falling edge detection circuit respectively, a light emitting element driving circuit for inputting and superposing said positive and negative polarity pulse signals and a signal having a predetermined flat level made from a ready-for-sending signal and for outputting a driving signal, a light emitting element whose light intensity is modulated by said driving signal so as to output a carrier signal when said output signal from said light emitting element driving circuit is only at the predetermined flat level, and for outputting a stronger light signal when said output signal is higher than said flat level and for outputting a weaker light signal when said output signal is lower than said flat level, optical coupling means for guiding the output light data signal of said light emitting element into an optical fiber cable, a receiving circuit having a light receiving element for converting the light data signal transmitted through said optical fiber cable into an electric data signal, a gain variable amplifying circuit for amplifying said electric data signal to obtain a predetermined output level and whose gain is controlled to obtain said level, an averaging circuit for averaging the output signal from said gain variable amplifying circuit to obtain a predetermined flat level signal, a pair of binary circuits for inputting the output signal of said gain variable amplifying circuit and said flat level signal from said averaging circuit and for outputting individually binary signals when the former is higher or lower than the latter, and a flip-flop circuit for inputting the binary signal at the set and reset terminals of said flip-flop circuit and for outputting a receiving data signal. ### Claim 4 (depends on 1) An asynchronous type modulation-demodulation system as claimed in claim 1 wherein, when a signal is inputted into the light emitting element driving circuit at a predetermined level in response to the ready-for-sending signal, the leading and the falling wave forms are made to be of a gradual curve.