Abstract: An optical amplifier which includes an elongated slab of solid state lasing material, such as a rare earth doped yttrium-aluminum-garnet (YAG). In order to provide a relatively increased absorption length and thus a higher overall efficiency, the optical amplifier in accordance with the present invention incorporates end pumping in which the pumped light is coaligned with the amplified light resulting in relatively longer absorption lengths and higher overall efficiencies. The coaligned pumped sources are directed to lateral faces of the slab which include windows, formed from an insulating coating such as an anti-reflection coating, at the pump wavelength. In order to cause internal reflection of the pump beam along the lasing axis, the end faces are formed at about a 45.degree. angle relative to the longitudinal axis which causes the pumped light to be reflected within the slab co-axially with a amplified light.

Abstract: An optical amplifier system includes a fiber amplifier doped with rare earth dopant provided in its fiber core. A plurality of fiber lasers have their light outputs optically coupled together for launching into the fiber amplifier for optically pumping the amplifier. Each of the fiber lasers have a rare earth dopant provided in its fiber core for stimulated lasing emission with the rare earth dopant of the fiber amplifier being different from the rear earth dopant of the fiber lasers. A reflector may be provided in each of the coupling fibers for reflecting a portion of the respective light outputs back into the fiber lasers to control their wavelength of operation, the wavelength of operation of the reflectors chosen to be within a high absorption region of the absorption band of the fiber amplifier. Where the pump source is a semiconductor laser source, the source may include a flared gain section to increase the output intensity of the light output of the source.

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: A Raman amplifier is provided that includes at least a portion of optical fiber in which an optical signal travels. The optical fiber portion may encompass all or part of the optical transmission path of an optical communication system. A pump energy unit is provided that includes first and second pump sources providing pump power at first and second wavelengths, respectively. The first and second wavelengths generate first and second overlapping gain profiles in the optical fiber portion. An optical circulator has a first port receiving the pump power, a second port providing the pump power to the optical fiber and receiving the optical signal, and a third port transmitting the optical signal received from the second port. As a result of this arrangement, a Raman amplifier is provided in which the bandwidth is substantially increased over the bandwidth that can be achieved by the previously mentioned Raman amplifier.

Abstract: This invention describes new developments in Sagnac Raman amplifiers and cascade lasers to improve their performance. The Raman amplifier bandwidth is broadened by using a broadband pump or by combining a cladding-pumped fiber laser with the Sagnac Raman cavity. The broader bandwidth is also obtained by eliminating the need for polarization controllers in the Sagnac cavity by using an all polarization maintaining configuration, or at least using loop mirrors that maintain polarization. The polarization maintaining cavities have the added benefit of being environmentally stable and appropriate for turn-key operation. The noise arising from sources such as double Rayleigh scattering is reduced by using the Sagnac cavity in combination with a polarization diversity pumping scheme, where the pump is split along two axes of the fiber. This also leads to gain for the signal that is independent of the signal polarization.

Abstract: A wideband optical amplifier employs split-band architecture in which an optical signal passes through a common amplification stage and is then split to pass through parallel gain stages, each of which may be optimized for a particular band being traversed. A broadband grating reflector is used after the input gain section to reflect the signals of one of the bands so that they again will pass through the common input gain section before passing through gain section of the split structure dedicated to their particular wavelength. Meanwhile, the other signals pass through the reflector and move on through the gain section pertinent to their wavelength.

Abstract: Generally speaking, in accordance with the invention, an optical transmission modulation apparatus is provided for modulating light transmitted through the apparatus. The apparatus comprises a metal film having a periodic array of subwavelength-diameter holes provided therein, and a supporting layer. At least a portion of the supporting layer has a selectively variable refractive index, the selectively variable refractive index portion being substantially adjacent to the metal film such that the metal film and the supporting layer form a perforated metal film unit. Selective variation of the refractive index of the selectively variable refractive index portion modulates the intensity of the light transmitted through the perforated metal film unit without substantially changing the direction of the light. Flat panel displays, spatial light modulators and tunable optical filters based on the optical transmission control apparatus are also provided.

Abstract: The subject matter is directed to a parallel array of optical amplifiers and is also directed to equally sharing the optical power supplied by a plurality of optical pumps among the array of optical amplifiers such that if one of the pumps fails the power outputted by the remaining pumps is still equally shared among the array of optical amplifiers.

Abstract: An optical amplifier uses a gain medium pumped with pump energy of a first wavelength that oscillates through the gain medium. In one embodiment, the pumping is essentially a cavity resonator that is coupled to either end of the gain medium such that oscillating pump energy passes through the gain medium as it reflects back and forth between the ends of the cavity. Highly reflective gratings may be used to maintain the oscillation of the pump energy, and a pump energy source, such as pumped doped optical fiber, is coupled to at least one of the gratings. In another embodiment, the pump source consists of multiple reflectors used at each end, and independent pump sources each having a slightly different wavelength within the absorption spectrum of the amplifier are coupled together, such that two pump wavelengths are simultaneously oscillated through the gain medium.

Abstract: A dual-band optical amplifier uses a single pump source, such as a YAG solid-state laser emitting a pump light at a wavelength of 1047 nm, to provide amplification in both the 1550 nm and 1310 nm bands which are commonly encountered in the optical telecommunications environment. The pump light is fed into a fiber doped with praseodymium fluoride having Pr atoms in a +3 ionization state. These ions exhibit a ground state absorption that includes the 1047 nm wavelength. The same pump light is also coupled to a separate amplification fiber doped with trivalent erbium ions and ytterbium. This combination of ions also can be pumped to a metastable excited state by a 1047 nm wavelength source. Accordingly, when photon emission is generated, there is signal amplification in both fibers results.

Abstract: An apparatus for maintaining an electromagnetic beam, namely a laser beam, aimed at a particular point in space and aligned with a unique propagation path. The apparatus includes one or more adjustable beam steerers located in the propagation path, and first and second spaced apart beam position detectors arranged in the beam path. The beam steerer(s) are preferably adjustable along at least two orthogonal axes of rotation for controlling the propagation direction of the beam. Error signals from the position sensors are fed into a beam steerer controller connected to the beam steerer(s) for electro-mechanically adjusting the beam steerer. The method of the invention involves fixing the propagation path on an angularly adjustable beam steering surface so that the propagation path at a different unique point in space, such as a target, can be controlled by adjusting the angular orientation of that beam steerer.

Abstract: An efficient, powerful and reliable system for amplifying optical pulses. Seed-pulses are generated by a seed-pulse source and are transmitted to an optical amplifier for amplification. The power for the amplification is provided by a Q-switched, diode-pumped, intracavity-doubled pump laser.

Abstract: Two approaches are provided for achieving an optical amplifier system capable of producing high peak power, high energy pulse outputs while suppressing scattering noise. The first approach relates to an optical amplifier system which has at least one laser diode pulsed or cw pumped double clad fiber amplifier utilized for receiving a high frequency modulated injected signal pulse of short duration from the laser diode, via the fiber core, for amplification by coupling pump light into the inner cladding of the fiber. The average signal power is sufficient to saturate the gain of the fiber so as to minimize significant onset and buildup of forward and backward scattering noise. The duty cycle of the injected signal source pulse is chosen to allow adequate gain recovery in the fiber amplifier between pulses.

Abstract: An apparatus for pumping an optical gain medium, such as a fiber gain medium, comprises a pump source having a plurality of different spatially separate or multiple wavelengths or wavelength bands which are all coupled into the fiber gain medium and provide at least one or more wavelengths to fall within the absorption band of fiber gain medium producing gain despite wavelength shifts in the pump source multiple wavelengths due to changes in the operating temperature of the pump source. At least one or more of the pump wavelengths will overlap the gain spectrum of the fiber gain medium sufficiently to continually provide high input power for pumping of the fiber gain medium.

Abstract: An optical fiber amplifier is pumped by a fiber pump laser which has a pair of separate active media within a common resonator. The fiber gain section of the amplifier is also located within the resonator.

Abstract: A WDM communication system utilizes a pump-mediated gain-shaped fiber amplifier having a predetermined nominal signal gain bandwidth and is pumped by a plurality of laser pump sources having different wavelength outputs with their outputs combined to provide a scaled power output of a weighted average of their wavelengths for launching into at least one end of the fiber amplifier. The weighted average of the output wavelengths of the individual sources is varied to produced a modified weighted average that broadens the predetermined nominal signal gain bandwidth. The wavelength weighted average of the combined pump sources may be modified by changing the operation of at least one of the pump laser sources, e.g., by changing the power level or the temperature level of one or more of the individual pump sources or by terminating the operation of one or of the individual pump sources.

Abstract: Optical network for signal transfer from a central station to subscriber stations. The signal to be distributed is split in at least two stages, with the signal being amplified by optical amplifiers. The Erbium Doped Fiber Amplifiers (EDFAs) to be used for this purpose are fed by an optical supply signal. By building up the supply signal from various signals with wavelengths lying closely together, Stimulated Brillouin Scattering (SBS) is avoided. As a result, by utilising centrally supplied EDPAs more splitting stages may be applied, as a result of which many more subscribers may be reached from one signal source than before. The subscribers may utilize inexpensive, low-sensitivity receivers. The optical network is particularly suited to form, in conjunction with a conventional non-optical (twisted-pair) network, a hybrid bi-directional transmission system.

Abstract: An optical amplifier for a high power, solid state laser which includes a slab of a solid state laser material, for example, yttrium-aluminum-garnet (YAG) crystal. One or more diode arrays may be vertically stacked and configured to provide generally uniform energy distribution in the crystal in a vertical direction. By maintaining a relatively uniform energy distribution in the crystal in a vertical direction, thermal and stress aberrations of the resulting laser beam are minimized.

Abstract: Arrangements for high output power laser sources and optical fiber amplifiers are disclosed. In one arrangement, an optical fiber section which is doped with erbium, is coupled with one or two mirror elements, such as fiber Bragg gratings, to form a DBR or DFB fiber laser. The optical fiber section receives energy at one end from a pumping laser and lases at one or more selected wavelengths. This output light, along with energy from the pumping laser, is transmitted through the second end of the optical fiber section to an erbium-doped fiber amplifier, which boosts the laser output even higher. The gain of the optical fiber section may be further increased by co-doping the section with erbium and ytterbium. With co-doped optical fiber sections, high power output fiber optical amplifiers and laser sources, in the form of DBR and DFB fiber lasers, which can accept the pumping energies of a plurality of pumping lasers, can be created with properly selected WDM coupler and WDM coupler/isolator devices.

Abstract: A diode laser excitation sold-state laser amplifier capable of withstanding a mechanical disturbance, is easily fabricated and adjusted, can stably generate a high-efficiency high-quality laser beam and easily realize a large output. A diode laser excitation solid-state laser using this amplifier, including: a solid-state laser rod extending along the optical axis of a laser beam and including an active medium therein; two side plates for supporting both ends of the solid-state laser rod respectively; a flow tube provided to enclose the solid-state laser rod and containing a cooling medium; a plurality of excitation modules each having a flat substrate, with a hole formed at the center thereof through which the solid-state laser rod is passed, and at least one excitation light source, for providing excitation light from the lateral of the solid-state laser rod; and connecting and fixing means and for connecting a plurality of the excitation modules to each other and fixing them to the side plates.

Abstract: In a light amplifier device having a rare-earth element doped optical fiber to which an input light signal and an exciting light are applied, an exciting-light emitting part generates the exciting light. A variable attenuator which attenuates the exciting light applied. A driving part which supplies a driving current to the exciting light part. A monitor part monitors the input light signal. A light-emitting part generates a light in a wavelength band which includes a wavelength of the input light signal. A control part for controlling either the attenuator or driving part, when the monitor part detects a change in the input light signal, so that the light generated by the light-emitting part is applied to the rare-earth element doped optical fiber.

Abstract: A system and method are disclosed for adjusting the gain profile of an optical amplifier including a pump laser and an active gain element by selectively controlling the electron populations of at least one Stark sublevel of the electronic energy levels of the optical amplifier's active gain element. By dynamically controlling the electron populations of selected Stark sublevels the gain profile of the active gain element can be flattened. In a first method for controlling electron populations two-photon transitions are initiated between a pair of Stark sublevels of the same energy manifold of the active gain element. Two-photon transitions are stimulated by two additional pump lasers operating at wavelengths whose difference approximates the energy difference in the pair of Stark sublevels between which electrons are to be moved.

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 amplifying optical fiber (111) whose wavelength dependency of gain is approximated by a second-order function of wavelength in which the coefficient of square term of wavelength is a negative value and an amplifying optical fiber (112) whose wavelength dependency of gain is approximated by a second-order function of wavelength in which the coefficient of square term of wavelength is a positive value are cascaded to each other. The amplifying optical fiber (112) is realized as the kind and amount of co-dopant element are appropriately selected. To these amplifying optical fibers, pumping light is supplied by way of fiber type couplers (123, 132) after the light intensities of the pumping light output from pumping light sources (121, 131) are adjusted by light intensity adjusting devices (122, 132).

Abstract: The conversion efficiency of a cascaded Raman laser (CRL) can be significantly improved if it comprises one or more of the below recited design features. The CRL comprises an intracavity section between an input section and an output section. The CRL is adapted for receiving pump radiation of wavelength .lambda..sub.p, and for emitting output radiation of wavelength .lambda..sub.n >.lambda..sub.p, and each of the input section and output section comprises fiber Bragg gratings of center wavelengths .lambda..sub.1, .lambda..sub.2 . . . .lambda..sub.n, where n.gtoreq.2 and .lambda..sub.1 <.lambda..sub.2 < . . . .lambda..sub.n-1. Among the efficiency-increasing features is ordering of the fiber Bragg gratings such that in the input section and the output section the gratings of center wavelengths .lambda..sub.1 . . . .lambda..sub.n and .lambda..sub.1 . . . .lambda..sub.

Abstract: An efficient, powerful and reliable system for amplifying optical pulses. Seed-pulses are generated by a seed-pulse source and are transmitted to an optical amplifier for amplification. The power for the amplification is provided by a Q-switched, diode-pumped, intracavity-doubled pump laser.

Abstract: A distributed gain medium, such as an optical fiber, is configured as a Sagnac interferometer or loop mirror, and this mirror is used as at least one of the two reflectors in the amplifier or laser. The distributed gain medium produces optical signal gain through nonlinear polarization, that may cascade through several orders. The Sagnac interferometer or loop mirror defines two optical paths that will support both common mode and difference mode optical signals. Pump fluctuations resulting from higher cascade orders are at least partially rejected through the difference mode signal path, thereby reducing the overall effect of pump fluctuation. The result is a broadband optical resonator, suitable for use at a variety of different wavelengths, including 1.3 .mu.m and 1.55 .mu.m wavelengths. Amplifiers based on this technology are "four-level," providing a pass through signal even when the pump laser is not functioning.

Abstract: An amplifier method and apparatus for use with optic systems utilizing a fiber optic circulator to direct input signals to a splitter that splits the copropagating pump light and input signals into two equal parts for simultaneous introduction into the two opposite ends of the active gain fiber. Half of the pump light and half of the signal are propagating through the active fiber in a clockwise and counterclockwise direction at the same time. This bidirectional propagation results in a more uniform excitation along the entire length of the active fiber, providing uniform stimulation of photon emission at both ends, causing significantly reduced noise and higher gain of the signal. Two half-amplified signals are combined and supplied to the circulator that provides the amplified output signal without any residual pumping light at the input or the output port of the circulator.

Abstract: An explosively pumped laser module has a concentrically-arranged laser rod and surrounding sleeve of explosive material with an annular gas chamber formed between the explosive sleeve and laser rod. An explosive initiation assembly surrounds the explosive sleeve with a plurality of detonator points or pads positioned symmetrically about the explosive sleeve. The assembly is connected to a central firing device or detonator via equal length pathways between each detonator point and the central firing device, so that the explosive is simultaneously detonated at a plurality of different points.

Abstract: The invention provides an optical transmission method and apparatus suitable for use with a terminal station apparatus for an optical communication system for a very long distance of up to several thousands kilometers across an ocean as well as an optical amplification method and apparatus suitable for use with a repeater for an optical communication system. The methods and apparatus are improved in that the excessive loss in an optical amplifier and the variation of the branching ratio are suppressed to suppress the variation of the gain to suppress the polarization dependency of the loss or the gain on a transmission line of the optical communication system. The optical transmission apparatus comprises a depolarized light source for outputting depolarized light, and an external modulator for modulating light from the depolarized light source.

Abstract: A second optical branching coupler and a second light sensor are additionally provided at the output side of the optical amplifier, in addition to a first optical branching filter for branching part of the light outputted from the optical amplifier and a first light sensor for measurement of the level of the branching light. Provided between the first light sensor and the second light sensor is a band-pass filter which allows passage of only light with specific wavelengths, for measurement of the level of the light with specific wavelengths. The difference between the levels of the outputted light measured by the first light sensor and the light with specific wavelengths measured by the second light sensor is calculated by a subtracting process to control the gain of the optical amplifier on the basis of the result of the subtracting process. The band-pass filter is provided for removal of amplified spontaneous emission from the optical output.

Abstract: Assemblies having a first optical circulator, a pumping laser, a rare-earth doped fiber and a first coupler are described. The first coupler has a first fiber connected to the optical circulator, a second fiber connected to said pumping laser, and a third fiber connected to one end of the rare-earth doped fiber which is operated as a fiber amplifier. The coupler blocks the pumping laser light from the first fiber and reflects the light into the third fiber. The coupler further transmits the input signals from the first fiber into the third fiber. This arrangement allows the rare-earth doped fiber to amplify the input signals from the energy of the pumping laser light. By changing the elements connected to the second end of the rare-earth doped fiber, optical fiber amplifier assemblies in which the message signals are amplified by passing through the rare-earth doped fiber twice, by pumping the rare-earth doped fiber with two pumping lasers, or both, are provided for.

Abstract: An optical amplifier of the type including an inlet for a light signal to be amplified and an outlet for an amplified light signal that has been amplified by means of an amplifying waveguide that is controlled by regulation light coming from a pumping diode; the amplifier comprising: an optical circulator having an inlet port receiving the light signal to be amplified, an outlet port delivering the amplified light signal, and two intermediate ports, the first of the intermediate ports being connected to the amplifying waveguide; and regulation means having an inlet connected to the second of the intermediate ports and an outlet connected to the pumping diode, whereby the amplifying waveguide has equalized gain for all of the carrier waves constituting the amplified light signal.

Abstract: The present invention relates to a laser amplification system (1). The system (1) is constituted by a laser light source (2) for providing a main laser beam (LB); a laser light amplifier (3) for amplifying the main laser beam (LB) and apparatus for supplying a bleed laser beam (BO) to the laser radiation amplifier (3). The bleed laser beam (BO) is amplified by the laser radiation amplifier (3) at least when the main laser beam (LB) has a low or zero power valve substantially to prevent super-radiance.

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: A laser has a resonant cavity defined by a pair of mirrors butted to respective ends of a fluorozirconate optical fiber. The fiber has a numerical aperture of 0.205 and an LP.sub.11 mode cut-off of about 2.0 .mu.m. The fibre is co-doped with thulium ions to a concentration of about 0.1%, and with terbium ions to a concentration of about 1%. An optical pump source provides a pump signal at 775 nm which excites the thulium ions into the .sup.1 G.sub.4 energy level to provide lasing at about 475 nm. The pump source is preferably a high power semiconductor laser.

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: An optical amplification system capable of operating without being affected by the waveform of the incoming optical signal is provided for amplifying the optical signal in its optical waveguide by the effect of stimulated emission of a fluorescent substance induced by pumped light. According to a first aspect of the invention, an optical amplification system turns on its pumping source 8 when there is an optical signal s1 in the optical waveguide 5 whereas the pumping source 8 is kept off as long as no optical signal s1 is found in the optical waveguide 5 so that, when the pumping source 8 is turned on, pumped light from the pumping source 8 is fed to the optical waveguide 5 with a delay of time relative to the incoming optical signal s1.

Abstract: A pulse compression device is disclosed for generating ultra short pulses in the femtosecond range In the device an input soliton is subjected to pulse width compression by propagation in a rare-earth doped optical fiber having a gradually diminishing group velocity dispersion from an input end to an output end. The pulse compression is produced by the diminishing dispersion value of the optical fiber as well as by adiabatic narrowing generated by a pumping light coupled, through an optical coupler, to the optical fiber by increasing the energy of the input soliton propagating in the optical fiber. By adjusting the light power of the pumping light, the pulse width of the soliton can be freely controlled.

Abstract: Stability of a pump laser for activating an erbium amplifier is enhanced by a grating which results in laser operation in the coherence collapse regime.

Abstract: The invention provides an optical transmission method and apparatus suitable for use with a terminal station apparatus for an optical communication system for a very long distance of up to several thousands kilometers across an ocean as well as an optical amplification method and apparatus suitable for use with a repeater for an optical communication system. The methods and apparatus are improved in that the excessive loss in an optical amplifier and the variation of the branching ratio are suppressed to suppress the variation of the gain to suppress the polarization dependency of the loss or the gain on a transmission line of the optical communication system. The optical transmission apparatus comprises a depolarized light source for outputting depolarized light, and an external modulator for modulating light from the depolarized light source.

Abstract: Plural planar optical devices are simultaneously pumped by a single pumping source. Various arrangements for accomplishing such pumping are disclosed. By utilizing these arrangements, the topology and routing of integrated arrays including optical devices are simplified.

Abstract: Known optical amplifiers, which are used in a light transmission path to amplify the light signals to be transmitted, have the disadvantage that the semiconductor lasers, used as pump lasers therein, are very sensitive to feedback.According to the invention, the operating current of such pump lasers (4) is modulated at a high frequency, which causes the pump laser to operate in a multi-mode, thereby making it insensitive to feedback. For example, the operating current is DC, on which AC is superimposed.In the event the optical amplifier has two pump lasers, their operating current is also modulated. Both pump lasers are then advantageously alternately switched on and off at a sufficiently high switching frequency, which also prevents reciprocal interference.

Abstract: The present invention is directed at an all-fiber amplifier and laser which use an active multimode graded index fiber. In the amplifier, the active fiber is a multimode graded-index fiber having an axis and a length L. The length L is longer than the distance an input beam (from an input fiber) requires to relax into a stationary state of propagation along the axis of the active fiber. The active fiber is optically connected to an input and output fibers such that the input beam couples to the active fiber at a certain distance from the axis and that the axis of the output fiber coincides with the axis of active fiber. In a laser configuration, the active fiber has a complex gradient parameter g described by the gradient function:g=g.sub.r -ig.sub.i =.omega./n.sub.0wherein .omega. is the amplification gradient and equals (2n.sub.0 (n.sub.0 -n.sub.cl)).sup.1/2. The parameter g depends upon a propagation distance z and is described by the periodic function:g.sup.2 (z)=g.sup.2 (1+4h cos 2g.sub.r z), h<1g.

Abstract: A fiber optical source of stimulated optical radiation comprises an optical fiber which includes a core doped with laser material having optical gain in two wavelength regions, the fiber additionally including a material in optical communication with said laser material in such a manner as to absorb radiation emitted from said laser material within one of said wavelength regions.

Abstract: In a of modulating a feedback signal in an optical amplifier, employing a laser diode LD, which can directly amplify an optical signal, the amplified optical signal is modulated by the feedback signal SV which is controlled in such a way as to compensate for the saturation characteristics of the laser diode LD to correctly modulate the feedback signal even if the laser diode is nearly saturated due to aging or fluctuations in temperature.

Abstract: An optical modulating and amplifying apparatus includes an optical amplifier and a modulator. In the apparatus, an input optical signal and an excited light are combined with each other to produce an output light signal. The excited light from a laser diode is sensed by a photodiode. The sense signal includes a bias and an amplitude to be respectively detected by a mean value sensor and a modulation signal sensor. A modulation degree of the excited light is computed by a divider. A control signal to develop a predetermined modulation degree is delivered from a control signal generator to a variable gain amplifier. In response to the control signal, the amplifier controls the amplitude of the oscillation signal from an oscillator. A laser diode driver adds a bias to the oscillation signal to drive the laser diode. The modulation degree is kept unchanged regardless of variation in an output level of the excited light so as to achieve the modulation with a high signal-to-noise ratio.

Abstract: A sub-nanosecond pulse operated semiconductor laser amplifier which admits light input for a time interval after the commencement of the electrical pulse. The duration of the said time interval is shorter than that of the said electrical pulse. Amplified light output reaches a peak value after the termination of the said electrical pulse. The pulsed operation can be repeated a few billion times per second. Applications in a fiber-optics communication system, a bar code scanner, and in a super speed camera are described.

Abstract: A control circuit for reducing the output of an optical amplifier when reflected light associated with the output of the amplifier temporarily increases. An erbium-added optical fiber amplifies an input optical signal. Two optical detectors respectively detect the amplified optical signal and the reflected light. When a reflected light monitor signal does not exceed the level of a threshold signal, an output control circuit controls the intensity of an exciting light source in accordance with the an output light monitor signal. However, when the former exceeds the latter, the output control circuit reduces the output power of the optical signal. At this instant, the threshold level is lowered. As soon as the reflected light monitor signal becomes lower than the lowered threshold, an inverting amplifier causes the monitor signal to be restored to the original level.

Abstract: An optical fibre for use in fibre lasers has the lasing additive eg Er.sup.3+, concentrated in center of the core. Preferably the core has an inner region which contains the additive and an outer region which is dopant free. The concentration of the dopant reduces the pump threshold for a laser and improves the gain performance for a given pump power. The fibre is conveniently made in MCVD. The use of Al.sub.2 O.sub.3 in the inner zone appears to reduce loss of dopant during tube collapse.