Optical transmission device and system

An optical transmission system for converting an electrical signal into an optical signal directly intensity-modulated by the electrical signal and then bilaterally transmitting the optical signal, comprising:

• a first device operable to transmit a first electrical signal,
• a second device operable to transmit a second electrical signal, and
• an optical transmission path operable to interconnect said first device and said second device,
• said first device including:
• an oscillator operable to output an additional signal with a frequency which is lower than a half of a lowest frequency of frequency bands allotted for transmission of the first and second electrical signals,
• a first multiplexing portion operable to multiplex the first electrical signal and the additional signal outputted from said oscillator,
• a first DC current source operable to output a DC bias current,
• a first semiconductor laser operable to output an optical signal directly intensity-modulated by a signal obtained by mixing by said first multiplexing portion and the DC bias current outputted by said first DC current source, and
• a first optical-electrical converting portion operable to convert an optical signal transmitted from said second device into an electrical signal;
• said second device including:
• a second optical-electrical converting portion operable to convert an optical signal transmitted from said first device into an electrical signal,
• a band separating portion operable to separate the electrical signal obtained by converting by said second optical-electrical converting portion into the first electrical signal and the additional signal outputted from said oscillator,
• a second multiplexing portion operable to multiplex the additional signal obtained by separating by said band separating portion and the second electrical signal,
• a second DC current source operable to output a DC bias current, and
• a second semiconductor laser operable to output an optical signal directly intensity-modulated by a signal obtained by mixing a signal obtained by said second multiplexing portion and the DC bias current outputted by said second DC current source;
• and
• said optical transmission path including:
• a first optical fiber operable to transmit the optical signal outputted from said first semiconductor laser to said second device, and
• a second optical fiber operable to transmit the optical signal outputted from said second semiconductor laser to said first device.

An optical transmission system, comprising a main station and a plurality of sub-stations, for converting an electrical signal into an optical signal directly intensity-modulated by the electrical signal and then transmitting the optical signal from the plurality of sub-stations to the main station,

• said plurality of sub-stations comprise first to n-th (where n is an arbitrary even number not less than 2) sub-stations in a wavelength order of optical signals emitted from each station, and each of a 2k-th (where k=1, 2, . . . , n/2) sub-station among the plurality of sub-stations comprises:
• an oscillator operable to output an additional signal,
• a multiplexing portion operable to multiplex an electrical signal to be transmitted by the sub-station and the additional signal outputted from said oscillator,
• a DC current source operable to output a DC bias current, and
• a semiconductor laser operable to output an optical signal directly intensity-modulated by a signal obtained by mixing a signal obtained by said multiplexing portion and the DC bias current outputted from said DC current source;
• and
• each of 2k-1-th sub-stations comprises:
• a DC current source operable to output a DC bias current, and
• a semiconductor laser operable to output an optical signal directly intensity-modulated by a signal obtained by mixing the electrical signal to be transmitted by the sub-station and the DC bias current outputted from said DC current source.

An optical transmission system, comprising a main station and a plurality of sub-stations, for converting an electrical signal into an optical signal directly intensity-modulated by the electrical signal and then transmitting the optical signal from the plurality of sub-stations to the main station,

• said plurality of sub-stations comprise first to n-th (where n is an arbitrary odd number not less than 3) sub-stations in a wavelength order of optical signals emitted from each station, and each of a 2k-th (where k=1, 2, . . . , (n−1)/2) sub-station among the plurality of the sub-stations comprises:
• an oscillator operable to output an additional signal,
• a multiplexing portion operable to multiplex an electrical signal to be transmitted by the sub-station and the additional signal outputted from said oscillator,
• a DC current source operable to output a DC bias current, and
• a semiconductor laser operable to output an optical signal directly intensity-modulated by a signal obtained by mixing a signal obtained by said multiplexing portion and the DC bias current outputted from said DC current source;
• and
• each of a 2k-1-th sub-station comprises:
• a DC current source operable to for output a DC bias current, and
• a semiconductor laser operable to output an optical signal directly intensity-modulated by a signal obtained by mixing the electrical signal to be transmitted by the sub-station and the DC bias current outputted from said DC current source.

An optical transmission system, comprising a main station and a plurality of sub-stations, for converting an electrical signal into an optical signal directly intensity-modulated by the electrical signal and then transmitting the optical signal from the plurality of sub-stations to the main station,

• each of said plurality of sub-stations comprising:
• an oscillator operable to output an additional signal,
• a multiplexing portion operable to multiplex an electrical signal to be transmitted by the sub-station and the additional signal outputted from said oscillator,
• a DC current source operable to output a DC bias current, and
• a semiconductor laser operable to output an optical signal directly intensity modulated by a signal obtained by mixing a signal obtained by said multiplexing portion and the DC bias current outputted from said DC current source, wherein
• said oscillator is operable to output the additional signal with a frequency which is higher than a frequency corresponding to a widest bandwidth of a frequency band allotted to the electrical signal to be transmitted and lower than a half of a lowest frequency of a frequency band allotted to the electrical signal to be transmitted.