Abstract: The fiber amplifier of this invention includes: a first rare earth element doped fiber; a second rare earth element doped fiber; and a pump light source for generating pump light for exciting the first rare earth element doped fiber and the second rare earth element doped fiber, the fiber amplifier receiving analog signal light and amplifying the analog signal light, wherein the fiber amplifier further includes a directional transmitter disposed between the first rare earth element doped fiber and the second rare earth element doped fiber, and a transmittance of the directional transmitter for at least light having the same wavelength as the signal light propagating from the first rare earth element doped fiber to the second rare earth element doped fiber is larger than a transmittance of the directional transmitter for the light propagating from the second rare earth element doped fiber to the first rare earth element doped fiber.

Abstract: A first pumping beam at a wavelength of 1210 nm emitted from a first pumping source is focused by a first lens system on an optical fiber. A second pumping beam at a wavelength of 650 nm emitted from a second pumping source passes through a coupler and a second lens system and arrives at the optical fiber to be incident thereon. Tm ions with which a core portion of the optical fiber is doped sequentially experience a ground-state level absorption transition upon absorption of the first pumping beam, an excited-state level absorption transition to an upper laser level upon absorption of the second pumping beam, and a radiative transition from the upper laser level to a ground-state level, thereby emitting light at a wavelength of 460 to 500 nm. The light at a wavelength of 460 to 500 nm emitted from the Tm ions is resonated by a resonator consisting of an incident mirror and an emitting mirror and outputted as a laser beam.

Abstract: The erbium-doped fiber amplifier comprises: a first erbium-doped optical fiber pumped by 0.98 .mu.m band light and amplifying the signal light; a first pump light source for producing the 0.98 .mu.m band light; a first optical coupler for coupling the 0.98 .mu.m band light with the signal light at an input portion of the first optical fiber; a second erbium-doped optical fiber pumped by 1.48 .mu.m band light and amplifying the signal light; a second pump light source for producing the 1.48 .mu.m band light; and a second optical coupler for coupling the 1.48 .mu.m band light with the signal light at an output portion of the second optical fiber; wherein a pump light isolator is installed between the first optical fiber and the second optical fiber for blocking the passing of the 1.48 .mu.m band light from the second optical fiber to the first optical fiber while allowing the passing of the signal light.

Abstract: The optical fiber amplifier includes a rare earth doped optical fiber and a pumping light source for outputting pumping light for pumping the rare earth doped optical fiber, the optical fiber amplifier optically amplifying signal light received at an input end and outputting the amplified signal light from an output end, wherein the optical fiber amplifier further includes an optical fiber resonator for laser-oscillating a portion of light of spontaneous emission generated in the rare earth doped optical fiber, which has a wavelength shorter than the wavelength of the signal light, thereby to keep a gain substantially fixed independent of a variation in the wavelength of the signal light.

Abstract: The optical fiber amplifier of the invention includes: a rare earth element doped optical fiber, and a pump light generator for optically pumping the rare earth element doped optical fiber. The optical fiber amplifier further includes a reflector for selectively reflecting an optical signal input from an input end of the rare earth element doped optical fiber to the input end, so as to give a gain to the optical signal.

Abstract: An optical fiber amplifier for optically amplifying a plurality of signals having different wavelengths includes a series of rare earth doped optical fibers and at least one pump light source generating pump light for exciting the series of rare earth doped optical fibers. A first signal among the plurality of signals propagates through a part of the series of rare earth doped optical fibers, and a second signal among the plurality of signals propagates through all of the series of rare earth doped optical fibers.

Abstract: The optical signal amplification apparatus of this invention includes a plurality of optical fiber amplifiers connected in series, each optical fiber amplifier including: an optical fiber doped with rare earth ions; and a pumping light source for emitting pumping light for exciting the optical fiber, wherein the power of signal light input into each optical fiber amplifier is set so that the value of a distortion component of the signal light output from the optical fiber amplifier is equal to the value of a distortion component of the signal light input into the optical fiber amplifier and that the distortion component of the signal light output from the optical fiber amplifier increases when the power of the signal light input into the optical fiber amplifier increases. An optical fiber transmission system including the optical signal amplification device is also provided.

Abstract: An analog transmission system for transmitting a multi-channel analog signal including plural carrier signals having different frequencies, comprises: a laser unit responsive to the multi-channel analog signal for emitting laser light signal intensity-modulated by the multi-channel analog signal, the laser unit having an oscillation wavelength W1; an optical fiber amplifier for amplifying the laser light signal with a peak gain at a wavelength W2; an optical fiber for transmitting the amplified laser light; and an optical receiver for receiving the transmitted laser light and for converting the received laser light into an electric signal as an output. In this system, a total distortion characteristic of the laser unit is compensated by distortions developed in the optical fiber amplifier.

Abstract: In an optical transmission system for transmitting a video signal by transmitting a laser light modulated with a video signal, through an optical fiber; and for receiving and photoelectrically converting the received laser light, a pilot signal is added to the video signal by a summing amplifier. A frequency of the pilot signal is smaller than a band width of the laser light, so that peak level of interference noise developed by multi-reflection at both ends of the optical fiber is decreased considerably.

Abstract: The optical fiber is doped at the core thereof with Tm ions and Nd ions. When light at a wavelength in a 800-nm band for exciting the Nd ions, is incident upon the optical fiber through an incident portion thereof, the Nd ions emit light at a wavelength in the vicinity of 1,012 .mu.m. Through three excitations by absorption of light emitted from the Nd ions and/or energy transfer from the Nd ions, the Tm ions experience three excitation transitions and reach a third high energy level through first and second high energy levels. Thereafter, the Tm ions experience a radiative transition from the third high energy level, thereby to emit blue light at a wavelength of 480 nm.

Abstract: The effective rate of deactivation from the terminal state to the ground state of a rare earth ion doped optical material in a four-level amplifying or lasing scheme may be increased greatly by doping the optical material with two rare earth ions, an activator and a deactivator. Energy transfer occurs between the terminal state in the activator ion and the deactivator ion. The transition from the deactivator to the ground state occurs via phonon emission. By increasing the deactivation rate, the efficiency of the laser and the amplifier is increased.

Abstract: A core of a fluorozirconate optical fiber is doped with rare earth ions, namely trivalent Dy ions. The Dy ion makes an absorption transition with excitation light generated by an 800 nm semiconductor laser module. Then the Dy ion undergoes transitions, namely a nonradiative transition involving phonon emission, a transition to a metastable excited level, and a radiative transition wherein radiation corresponding to the 1.28 .mu.m to 1.35 .mu.m range occurs, thereafter returning to its ground state level. The Dy ion having an electrovalence of three can be pumped with a high-output 800 nm semiconductor laser module and is not subject to saturation at a lower energy level of population inversion. Using an optical fiber of the invention, a higher gain is obtained in the region of 1.3 .mu.m telecommunications window.

Abstract: Ultrashort optical pulses of a high peak output are generated by gain-switching of a semiconductor laser possessing a current non-injection region with short current pulses. By coupling this semiconductor laser to a wavelength conversion element, a second harmonic wave is generated, and ultrashort optical pulses of a short wavelength and a high peak output are generated.

Abstract: A speed control apparatus is provided for controlling a speed of a movable equipment in such a way that the speed of the movable equipment is detected, calculates a deviation value between a detected speed of the movable equipment and a speed instruction signal, and controls the speed of the movable equipment based on the deviation value. The speed control equipment detects harmonic wave components included in the detected speed and reduces the harmonic wave components from the speed instruction signal so as to control the speed of the movable equipment.

Abstract: By using a polarization controller, a semiconductor laser apparatus oscillating in the transverse magnetic mode in mode-locked state is realized, and a short optical pulse is generated. By coupling this mode-locked semiconductor laser to a wavelength conversion element, a second harmonic wave is generated, and an even shorter optical pulse is obtained at a higher power.

Abstract: A semiconductor laser device of a new monolithic structure has a long transparent optical waveguide used as a passive cavity directly coupled with an active cavity possessing a gain in the direction of the optical axis of the active cavity on a compound semiconductor substrate. The device is intended to satisfy all of four characteristics, which are;(1) stable single longitudinal mode oscillation;(2) narrow spectral linewidth;(3) suppression of wavelength chirping due to current modulation; and(4) low noiseand to be applied as a light source for optical fiber communication, optical information processing or the like.

Abstract: Disclosed is an optical integrated circuit for heterodyne detection. The optical integrated circuit comprises: a semiconductor substrate; an active region of a semiconductor laser; two optical waveguides; a photo detector; and an optical coupler composed of the waveguides. The emission of light from the active region of the semiconductor laser is synthesized as local oscillation light with the transmission light. The synthesized light travels through the optical coupler and is detected by the photo detector.

Abstract: A semiconductor laser device of a new monolithic structure has a long transparent optical waveguide used as a passive cavity directly coupled with an active cavity possessing a gain in the direction of the optical axis of the active cavity on a compound semiconductor substrate. The device is intended to satisfy all four characteristics, which are;(1) stable single longitudinal mode oscillation;(2) narrow spectral linewidth;(3) suppression of wavelength chirping due to current modulation; and(4) low noiseand to be applied as a light source for optical fiber communication, optical information processing or the like.