Abstract: A wavelength demultiplexer is equipped with a spectroscopic means (which separates light that is input from multiple input light paths, and outputs the light to multiple output light paths) and a light path switching device (a device that switches the light paths that are input to the spectroscopic means, with the switching being performed by an external operation), and the light path switching device may be a device that distributes the input from one input port to multiple output ports. The light path switching device and the spectroscopic means are polarization-independent, with the input light paths, the output light paths, and the light paths between the light path switching device and the spectroscopic means being polarization-maintaining light paths, so the relative polarization configuration is the same for the input light and the output light.

Abstract: A wavelength demultiplexer is equipped with a spectroscopic means (which separates light that is input from multiple input light paths, and outputs the light to multiple output light paths) and a light path switching device (a device that switches the light paths that are input to the spectroscopic means, with the switching being performed by an external operation), and the light path switching device may be a device that distributes the input from one input port to multiple output ports. The light path switching device and the spectroscopic means are polarization-independent, with the input light paths, the output light paths, and the light paths between the light path switching device and the spectroscopic means being polarization-maintaining light paths, so the relative polarization configuration is the same for the input light and the output light.

Abstract: An optical access system is provided that enables subscriber terminals or termination devices to be interconnected via dedicated lines as needed, with respect to subscriber terminals or termination devices participating in an optical network. The optical network is a network connecting a plurality of accommodating stations, and in this network, the accommodating stations have a plurality of optical line termination devices and optical path selection means, the subscriber side optical terminals or optical line termination devices are connected in single star optical paths, and the optical line termination devices in the accommodating stations are connected with the above mentioned optical terminals or optical line termination devices via the optical path selection means.

Abstract: An optical access system is provided that enables subscriber terminals or termination devices to be interconnected via dedicated lines as needed, with respect to subscriber terminals or termination devices participating in an optical network. The optical network is a network connecting a plurality of accommodating stations, and in this network, the accommodating stations have a plurality of optical line termination devices and optical path selection means, the subscriber side optical terminals or optical line termination devices are connected in single star optical paths, and the optical line termination devices in the accommodating stations are connected with the above mentioned optical terminals or optical line termination devices via the optical path selection means.

Abstract: A method for transmitting high-frequency signals in an optical communication system includes combining an optical signal, the first optical local component from a local light source and the second optical local component from the local light source having a predetermined frequency differential from the first optical local component, selecting the first high-frequency signal which consists of two predetermined electrical components from plural electrical components obtained by the optical frequency mixing process, and mixing the two selected electrical components included in the first high-frequency signal.

Abstract: A method for transmitting high-frequency signals in an optical communication system includes combining an optical signal, the first optical local component from a local light source and the second optical local component from the local light source having a predetermined frequency differential from the first optical local component, selecting the first high-frequency signal which consists of two predetermined electrical components from plural electrical components obtained by the optical frequency mixing process, and mixing the two selected electrical components included in the first high-frequency signal.

Abstract: A method for transmitting high-frequency signals in an optical communication system includes combining an optical signal, the first optical local component from a local light source and the second optical local component from the local light source having a predetermined frequency differential from the first optical local component, selecting the first high-frequency signal which consists of two predetermined electrical components from plural electrical components obtained by the optical frequency mixing process, and mixing the two selected electrical components included in the first high-frequency signal.

Abstract: A method of evaluating free-space optical propagation characteristics includes emitting a plurality of laser beams from a corresponding plurality of laser sources, receiving laser beams at different target points, and measuring the time-based spatial fluctuations between the laser beams thus received. The respective distances from the laser sources to each target point are used to normalize the time-based spatial fluctuations. The difference between the normalized spatial positions of the laser beams at the target points is derived and used to obtain the frequency spectrum of time-based fluctuations of the spatial positions.

Abstract: A modulated optical signal processing method and apparatus optically convert an optical signal to an intermediate frequency band that simplifies electrical processing after optical detection, thereby increasing the optical reception sensitivity. Either single-mode light is modulated with a first radio wave overlaid with data, or a modulated optical signal is directly generated, and the optical carrier and optical sideband contained in that modulated optical signal are transmitted, the transmitted optical carrier and optical sideband are input and the input optical carrier and optical sideband are mixed with a radio wave of a predetermined frequency and a combination of an adjacent optical carrier and optical sideband that are closer together than the frequency of the first radiofrequency electrical signal is optically selected from among a frequency-converted or frequency-unconverted optical carrier and optical sideband thus obtained and an electrical signal is detected from this selected optical signal.

Abstract: A method for transmitting high-frequency signals in an optical communication system includes combining an optical signal, the first optical local component from a local light source and the second optical local component from the local light source having a predetermined frequency differential from the first optical local component, selecting the first high-frequency signal which consists of two predetermined electrical components from plural electrical components obtained by the optical frequency mixing process, and mixing the two selected electrical components included in the first high-frequency signal.