Abstract: A rare earth element doped fiber forming an optical amplifier is pumped with a plurality of pumping lights to prevent drop of the inversion population ratio in the length direction of the rare earth element doped fiber.

Abstract: An apparatus has first and second light sources, a plurality of filters, and an optical switch. The light sources output a light beam having a spectrum determined by a gain band thereof. The plurality of filters each have a reflection band included in the gain band. The optical switch selectively couples the filters to the light source. The first and second light sources provide pumping light to a single transmission line. The first and second filters are configured so as to not reflect signal light to be amplified.

Abstract: Multi-wavelength light is inputted to an erbium-doped fiber as an optical amplification medium. Pump light is supplied to this erbium-doped fiber. When a transition from a state signal light on the short wavelength area in the multi-wavelength is input in the erbium-doped fiber to a state the signal light is not input, the output power of signal light on the long wavelength area in the multi-wavelength light can vary. The wavelength of pump light is selected in such a way that the output power of the signal light on the long wavelength area can not be negative when the power varies.

Abstract: A signal light passes through an isolator, and is coupled by a coupler with a pump light from a pump light source. Then, the signal light passes through an ASE reflection filter, is amplified by an EDF, and is transmitted from an isolator. At this time, an ASE light having a predetermined wavelength among ASE lights that occur within the EDF and proceed to the ASE reflection filter is reflected and again input to the EDF. By setting the predetermined wavelength to a wavelength on the short wavelength side of an amplification band of the EDF, gain deviation occurring on the long wavelength side of the amplification band can be cancelled.

Abstract: An optical amplification device which includes first and second optical amplifiers, and a controller. The first optical amplifier receives a light and amplifies the received light. The second optical amplifier receives the light amplified by the first optical amplifier, and amplifies the received light. When a level of the light received by the first optical amplifier changes by &Dgr;, the controller controls a level of the light received by the second optical amplifier to change by approximately −&Dgr;. In various embodiments, the controller causes the sum of the gains of the first and second optical amplifiers to be constant. In other embodiments, the optical amplification device includes first and second optical amplifier and a gain adjustor. The gain adjustor detects a deviation in gain of the first optical amplifier from a target gain, and adjusts the gain of the second optical amplifier to compensate for the detected deviation.

Abstract: An optical amplification device which includes first and second optical amplifiers, and a controller. The first optical amplifier receives a light and amplifies the received light. The second optical amplifier receives the light amplified by the first optical amplifier, and amplifies the received light. When a level of the light received by the first optical amplifier changes by &Dgr;, the controller controls a level of the light received by the second optical amplifier to change by approximately −&Dgr;. In various embodiments, the controller causes the sum of the gains of the first and second optical amplifiers to be constant. In other embodiments, the optical amplification device includes first and second optical amplifier and a gain adjustor. The gain adjustor detects a deviation in gain of the first optical amplifier from a target gain, and adjusts the gain of the second optical amplifier to compensate for the detected deviation.

Abstract: Wavelength multiplexed light is amplified by first and second EDFs. Gains of the first and the second EDFs are respectively held to be predetermined values by first and second AGC circuits. Between the first and the second EDFs, a variable attenuator is arranged. A loss in the variable attenuator is controlled by an ALC circuit so that output power is held to be a predetermined value instructed by a supervisory control signal. Respective time constants of the first and the second AGC circuits are sufficiently short in comparison with the response times of the first and the second EDFs. The time constant of the ALC circuit is sufficiently long in comparison with the time period required to transmit the supervisory control signal to each optical node.

Abstract: Method and apparatus using four wave mixing (FWM) for wavelength conversion. An optical waveguide doped with a rare earth element is pumped so that an input optical signal is amplified as the input optical signal travels through the optical waveguide. The optical waveguide is provided with at least one light which, together with the input optical signal, causes four wave mixing (FWM) to occur in the optical waveguide. The FWM causes a converted optical signal to be produced in the optical waveguide and having a wavelength different from the input optical signal. If the input optical signal is modulated by a transmission signal, then the converted optical signal will also be modulated by the transmission signal. The optical waveguide can be, for example, an erbium doped optical fiber operating as an erbium doped fiber amplifier (EDFA). Therefore, an EDFA can be used for both amplification and wavelength conversion.

Abstract: An apparatus has first and second light sources, a plurality of filters, and an optical switch. The light sources output a light beam having a spectrum determined by a gain band thereof. The plurality of filters each have a reflection band included in the gain band. The optical switch selectively couples the filters to the light source. The first and second light sources provide pumping light to a single transmission line. The first and second filters are configured so as to not reflect signal light to be amplified.

Abstract: Multi-wavelength light is inputted to an erbium-doped fiber as an optical amplification medium. Pump light is supplied to this erbium-doped fiber. When a transition from a state signal light on the short wavelength area in the multi-wavelength is input in the erbium-doped fiber to a state the signal light is not input, the output power of signal light on the long wavelength area in the multi-wavelength light can vary. The wavelength of pump light is selected in such a way that the output power of the signal light on the long wavelength area can not be negative when the power varies.

Abstract: A signal light passes through an isolator, and is coupled by a coupler with a pump light from a pump light source. Then, the signal light passes through an ASE reflection filter, is amplified by an EDF, and is transmitted from an isolator. At this time, an ASE light having a predetermined wavelength among ASE lights that occur within the EDF and proceed to the ASE reflection filter is reflected and again input to the EDF. By setting the predetermined wavelength to a wavelength on the short wavelength side of an amplification band of the EDF, gain deviation occurring on the long wavelength side of the amplification band can be cancelled.

Abstract: A light source apparatus suitable for use for evaluation of an optical device and for production of pump light for an optical amplifier. The apparatus includes a light emitting element having a gain band and a band reflection filter optically connected to the light emitting element. The light emitting element outputs a light beam having a spectrum which is determined by the gain band. The filter produces, from the light beam outputted from the light emitting element, a transmission beam and a reflection beam which returns to the light emitting element. The filter has a reflection band included in the gain band of the light emitting element and narrower than the gain band, and the transmission beam of the filter has a maximum power higher than the maximum power of the light beam to be outputted from the light emitting element. With the construction, pump light having a maximum power higher than the maximum power of the light to be outputted from the light emitting element can be obtained.

Abstract: A rare earth element doped fiber forming an optical amplifier is pumped with a plurality of pumping lights to prevent drop of the inversion population ratio in the length direction of the rare earth element doped fiber.

Abstract: An optical amplification device which includes first and second optical amplifiers, and a controller. The first optical amplifier receives a light and amplifies the received light. The second optical amplifier receives the light amplified by the first optical amplifier, and amplifies the received light. When a level of the light received by the first optical amplifier changes by &Dgr;, the controller controls a level of the light received by the second optical amplifier to change by approximately −&Dgr;. In various embodiments, the controller causes the sum of the gains of the first and second optical amplifiers to be constant. In other embodiments, the optical amplification device includes first and second optical amplifier and a gain adjustor. The gain adjustor detects a deviation in gain of the first optical amplifier from a target gain, and adjusts the gain of the second optical amplifier to compensate for the detected deviation.

Abstract: Disclosed herein is an optical amplifier reduced in gain deviation. The optical amplifier includes a nonsilica fiber doped with a rare earth, and a fiber holder in which the nonsilica fiber is inserted and fixed. The fiber holder is optically arranged so that signal light to be amplified propagates in the nonsilica fiber. The nonsilica fiber is pumped so that the nonsilica fiber provides a gain band including the wavelength of the signal light. Opposite ends of the fiber holder are hermetically sealed to thereby easily cut off the nonsilica fiber from the outside air, so that the nonsilica fiber is stabilized physically or chemically. A fluoride glass fiber is suitable for the nonsilica fiber to reduce the gain deviation in a 1.55 &mgr;m band.

Abstract: An optical amplifying fiber including a core doped with a rare earth element and having a first refractive index, a cladding surrounding the core and having a second refractive index smaller than the first refractive index, and a fiber grating formed in the core for transmitting signal light having a first wavelength and pump light having a second wavelength and removing amplified spontaneous emission. The fiber grating is preferably positioned upstream of a middle point of the entire length of the optical amplifying fiber in terms of a propagation direction of signal light.

Abstract: An optical amplifier amplifies a wavelength-division-multiplexed optical input signal composed of optical signals having different wavelengths such that the output level of each of the optical signal is always optimized and such that the difference between the gains of the amplifier on the optical signals is minimized when the number of optical signals is two. The output level of the amplifier is controlled according to the number of the optical signals, to optimize the output level of each of the optical signals.

Abstract: An optical amplifying fiber including a center core region doped with erbium, aluminum, and phosphor, and a ring region doped with erbium and aluminum, the ring region being radially spaced a given distance from the center core region.

Abstract: Disclosed is an optical amplifier for collectively amplifying optical signals having multiplexed wavelengths. The optical amplifier enables a gain control in a range as wide as 1 dBm or larger, and employs a fiber that is doped with a rare-earth metal, such as erbium. The erbium-doped fiber in cross section is formed of a plurality of glass materials that are doped with erbium, and excitation light wavelength bands relative to the erbium-doped fiber are provided in a number equivalent to the count of the glass materials.

Abstract: An optical fiber having a core for propagating light, where the core includes first, second and third regions. The first, second and third regions are concentrically arranged with the second region around the first region and the third region around the second region. The third region includes a dopant for increasing the refractive index of the third region. The first region includes a first dopant for providing an amplification band and a second dopant for expanding the amplification band. The second region has an impurity concentration which is lower than the concentration of the dopant in the third region and is lower than the concentrations of the first and second dopants in the first region. Upon production of the fiber, the second region acts as a barrier to prevent diffusion of dopants. As a result, the amplification band can be effectively expanded. Various other arrangements of core and clad regions and dopants are provided.