Abstract: A data communication apparatus which improves security against eavesdropping is provided for secret communication using Y-00 protocol. A multi-level code generation section 111 generates, based on key information 11, a multi-level code sequence 12 in which signal in which a signal level changes so as to be approximately random numbers. A multi-level processing section 112 combines information data 10 and the multi-level code sequence 12, and generates a multi-level signal 13 having a plurality of levels each corresponding to the combination of the information data 10 and the multi-level code sequence 12. A delayed wave generation section 113 generates, based on a delay profile 19, a delayed wave of the multi-level signal 13, combines the generated delayed wave and the multi-level signal 13, and outputs a multipath signal 20. A modulator section 114 modulates the multipath signal 20 in a predetermined modulation method, and outputs a modulated signal 14.

Abstract: A data transmitting apparatus which improves security against eavesdropping is provided for secret communication using Y-00 protocol. The multi-level code generation section 111 generates, based on key information 11, a multi-level code sequence 12 in which a signal level changes so as to be approximately random numbers. The multi-level processing section 112 generates a multi-level signal 13 having a level which corresponds to a combination between information data 10 and the multi-level code sequence 12. The error signal generation section 113 generates an error signal 21 which changes randomly. The accumulation section 114 accumulates the error signal 21, and outputs an accumulated error signal 22. The adding section 116 adds the accumulated error signal 22 to the multi-level signal 13, and outputs a variable multi-level signal 23. The modulator section 117 modulates the variable multi-level signal 23, and outputs a modulated signal 14.

Abstract: An object of this invention is to provide a modulator, an optical transmitter and an optical transfer device which can modulate a channel signal while suppressing residual AM signals regardless of the frequency of a channel signal and suppressing deterioration of the channel signal due to impossibility of giving a sufficient FM demodulation amplitude.

Abstract: A data communication apparatus which improves security against eavesdropping is provided for secret communication using Y-00 protocol. A multi-level code generation section 111 generates, based on key information 11, a multi-level code sequence 12 in which a signal level changes so as to be approximately random numbers. A level conversion section 113 irreversibly converts the multi-level code sequence 12 such that a converted multi-level code sequence 19 does not constitute a mapping of the multi-level code sequence 12. A multi-level processing section 112 generates a multi-level signal 13 having a plurality of levels each corresponding to a combination between the information data 10 and the multi-level code sequence 12. A modulator section 114 modulates a multi-level signal 14 in a predetermined modulation method and outputs a modulated signal 15.

Abstract: The present invention provides a wideband modulated signal generating device capable of realizing an always stable operation and obtaining an intended wideband modulated signal in spite of a shift in the optimal bias voltage due to DC drift occurring in an optical intensity modulation section. In the wideband modulated signal generating device, a DC power supply control section 50 controls a first DC power supply 51 and a second DC power supply 52 for applying first and second bias voltages to an optical intensity modulation section 30 based on a signal level detected by a level detecting section 70, and controls a third DC power supply 53 for applying a third bias voltage to an optical intensity modulation section 30 based on a distortion level detected by a distortion level detecting section 81, thus compensating for a shift in the optimal bias voltage occurring due to DC drift.

Abstract: An optical SSB-SC modulation section 13 subjects an optical signal fa outputted from an optical source 11 to an optical SSB-SC modulation based on the amplitude of an external electric signal fc to thereby output an optical intensity-modulated signal. An optical phase modulation section 14 subjects the optical signal fa to an optical phase modulation based on the amplitude levels of the first to nth external electric signals having frequencies f1 to fn to thereby output the resultant signal as an optical phase-modulated signal. An optical combining section 15 combines together the optical intensity-modulated signal and the optical phase-modulated signal. An optical detecting section 16 performs an optical homodyne detection through a squared detection of the optical intensity-modulated signal and the optical phase-modulated signal combined together to thereby produce a wideband modulated signal, being the difference beat signal between the two optical signals.

Abstract: The present invention provides an optical transmission device 100 capable of solving the problem of an unnecessary residual sideband components to thereby obtain a high-quality optical intensity-modulated signal in a case where an SSB optical modulation section 20 has wavelength dependence and a manufacturing error. In the optical transmission device 100, where the SSB optical modulation section 20 cannot evenly branch the intensity of the optical carrier into two routes of optical waveguide, the amplitude adjusting section 62 adjusts the amplitude of an electric signal that changes the refractive index of the SSB optical modulation section 20 so that the unnecessary sideband component of the optical intensity-modulated signal outputted from the SSB optical modulation section 20 disappears.

Abstract: An optical composite module whose optical axis can be easily adjusted, which is small-sized and has an advantage in ease of mountability. A convergent rod lens 2 with a band-pass optical filter 5 (BPF) bonded to an end thereof, and a double-core glass tube 3 housing an input optical fiber 1a and an output optical fiber 1b are secured. The double-core glass tube 3 has an outer diameter coinciding with that of the convergent rod lens 2. The center line between the input optical fiber 1a and the output optical fiber 1b coincides with an optical axis of the convergent rod lens Light with wavelength &lgr;4 output from the input optical fiber 1a passes through the BPF 5, and is received by a light-receiving element 7 and converted into an electric signal. Light with other wavelengths output from the input optical fiber 1a is reflected by the BPF 5, and coupled into the output optical fiber 1b.