Abstract: The present invention addresses the need for optical transmission systems, apparatuses, and methods having increased flexibility and reliability. Optical systems of the present invention are configured to provide alarms, provision, and/or perform protection switching, if the number of corrected errors exceeds a threshold criteria. Various system parameters, in addition to protection thresholds, can be adjusted based on the relationship between the number of one errors, zero errors, and/or total errors being corrected in the system.

Abstract: The present invention provides a method of monitoring a transmission fiber including the steps of transmitting a monitor signal on the transmission fiber in a direction opposite to the propagation of traffic signals on the transmission fiber, at an optical amplifier connected to the transmission fiber detecting the monitor signal and automatically shutting down the optical amplifier in response to a predetermined change in the detected monitor signal. The invention facilitates a faster shut down of amplifiers when a fault occurs than is currently available because it shuts down the amplifier feeding directly into the area of broken fiber first rather than last as in conventional communication systems.

Abstract: For achieving a transmission light source having different transmission properties or characteristics, i.e., the a parameters, depending upon application thereof, in a light emission element of semiconductor EA modulator integrated type being constructed with a light emission portion for lasing with a single vertical mode and a plurality of EA modulators, wherein an absorption edge wavelength under the condition of applying no bias thereto, in the semiconductor multiple-quantum-well structure owned by the modulator which is near to an emission side of the light emission portion, is to be equal or longer than the absorption edge wavelength owned by the modulator positioned far from the emission side of the light emission portion.

Abstract: A wireless optical communication system can reduce the power consumption needed for light emission by a controlled node and suppress a modulated signal component, other than the modulated signal of input data for transmission, in the modulated signal components carried by the light output of the controlled node. The controlled node includes a transmission device for transmitting input data for transmission by an infrared ray amplitude-modulated by a modulated signal of a first frequency band and a light emission control device for suspending the light emission by the transmission device for a predetermined period based on a data amount of the input data for transmission. The light emission circuit generates a light emission control signal and the transmission device stops or starts the light emission based on the light emission control signal so that the modulated signal component in the second frequency band other than the first frequency band does not exceed a maximum allowable value.

Abstract: An optical transmitter circuit including a light receiving element, such as a photodiode, which monitors the optical output of a light emitting element such as a semiconductor laser. A current-voltage converting circuit supplies a drive current from a drive circuit to the light emitting element and converts the output voltage of the light receiving element into voltage. An APC amplifier compares the converted output signals and a reference signal, and a hold circuit holds the output signal of the APC amplifier and uses the output signal as a current control signal of the drive circuit. A “1” continuous signal detecting circuit detects the continuation of “1” in a specified number of bits in the input data (DATA) and updates the hold value in the hold circuit.

Abstract: A compact wavelength division demultiplexer device comprises two cascaded interferometers the wedge angle of whose mirrors are orthogonal to each other, i.e., the two interferometers are oriented such that the dispersion of light with wavelength from the second interferometer is orthogonal to the dispersion of light with wavelength from the first interferometer. The incoming beam of laser light carrying n sub-bands of m information channels is collimated and applied to the first interferometer whose free spectral range is determined by the total bandwidth required by the n×m channels and whose finesse is determined by the resolution needed to spatially separate each of the n sub-bands from one another. The light leaving the first interferometer enters the second interferometer whose wedge angle is at 90 degrees to the plane of the wedge angle of the first interferometer.