Abstract: The present invention relates to a laser apparatus using optical fibers for stable laser welding and a laser welding method using same. Hybrid ring mode-shaped laser beams, in which a central beam using fiber laser is positioned at the center of outer beams using diode laser, are used to perform welding by irradiating a to-be-welded portion of an object with the outer beams, the central beam, and the outer beams in this order. Thus, since the welding is performed using the central beam as a heat source in a state in which the to-be-welded portion of the object has been heated with a sufficient amount of heat input, the temperature gradient of the to-be-welded portion is low and solidification cracking does not occur. Also, problems such as spatter and voids can be minimized, and the laser welding is stable, and thus a quality of welding that is uniform and stable overall can be obtained.

Abstract: Disclosed is a fiber laser to which an isolation technique for preventing damage to a pump light source is applied. The fiber laser, which includes a fiber laser cavity that includes a gain medium, and a pump light source that supplies pump light to the fiber laser cavity, comprises an isolator that is formed in an inline shape between the pump light source and the fiber laser cavity in order to prevent damage to the pump light source which is caused by the ray reflected from the output terminal of the fiber laser.

Abstract: An optical DPSK signal demodulator includes a signal separator that separates an optical signal into an input optical signal and an output optical signal in a signal optical path. First and second reflectors are provided at a predetermined interval and reflect the optical signals with a predetermined time delay to have substantially the same intensity. A phase shifter is provided between the first and second reflectors and configured to allow the optical signals reflected from the first and second reflectors to have a phase difference.

Abstract: A wavelength division multiplexed-passive optical network includes an optical line terminal for generating downstream optical signals of discrete wavelengths and for receiving upstream optical signals of discrete wavelengths, a remote node, coupled to the optical line terminal, a wavelength division unit settled to reflect a predetermined wavelength, and a plurality of optical network units. Each optical network unit has an optical source which is oscillated in a multi-mode and is self-injection locked by the predetermined wavelength provided thereto, thereby to generate the upstream optical signal in a single mode to be provided to the remote node.

Abstract: An optical DPSK signal demodulator includes a signal separator that separates an optical signal into an input optical signal and an output optical signal in a signal optical path. First and second reflectors are provided at a predetermined interval and reflect the optical signals with a predetermined time delay to have substantially the same intensity. A phase shifter is provided between the first and second reflectors and configured to allow the optical signals reflected from the first and second reflectors to have a phase difference.

Abstract: A wavelength division multiplexed-passive optical network includes an optical line terminal for generating downstream optical signals of discrete wavelengths and for receiving upstream optical signals of discrete wavelengths, a remote node, coupled to the optical line terminal, a wavelength division unit settled to reflect a predetermined wavelength, and a plurality of optical network units. Each optical network unit has an optical source which is oscillated in a multi-mode and is self-injection locked by the predetermined wavelength provided thereto, thereby to generate the upstream optical signal in a single mode to be provided to the remote node.