Abstract: The invention is directed to an optical fiber amplifier having a switchable or interchangeable fiber module for varying the effective length of an amplification fiber. An optical fiber amplifier for wavelength-division multiplex (WDM) signals comprises an interchangeable fiber module (FM) in the basic amplifier module (VM) for matching the gain to different input levels for optimum noise behavior. The change in amplification is based on the variation of the length of the amplification fibers (EDF1, EDF2).

Abstract: Three Mach-Zehnder interferometers 141 to 143 are connected in a series between an optical input terminal and an optical output terminal in an optical filter. Each interferometer is composed of two optical paths optical coupled at both ends by optical couplers. Only one interferometer has same optical path lengths between optical couplers. Heaters are disposed on each optical paths to allow the slope of transmission loss to change through the adjustment of the phase shift between those respective optical paths.

Abstract: On a second thermo-module there are disposed a prism, an optical filter, and a sub-mount, via a base respectively. On the front side of the sub-mount, there are disposed a first photodetector and a second photodetector. The optical filter is structured with a crystal member that satisfies a condition that &agr;+(1/n0)×(&Dgr;n/&Dgr;T) becomes not more than 3.5, where &agr; is a coefficient of linear expansion, n0 is a refractive index at a normal temperature, and &Dgr;n is a change of a refractive index corresponding to a temperature variation &Dgr;T.

Abstract: A wideband optical amplifier for amplifying an input optical signal of known wavelength in one of at least two bands of wavelength has a significantly small number of optical components and thus is low cost. The wideband optical amplifier includes: a first set of a first optical coupler, a first pump light source, and a first erbium doped optical fiber (EDF) which is excited by the first pump light source; an optical switch for changing an output signal of the first set; and a second set of a second optical coupler, a second pump light source, and a second EDF which is excited by the second pump light source. The first set amplifies a first band of optical signal while a series connection of the first set and the second set amplifies a second band of optical signal. In another aspect, a wideband variable wavelength optical source is achieved by utilizing the wideband optical amplifier described above within a closed loop.

Abstract: Optical amplifiers and other optical network equipment is provided for use in fiber-optic communications networks. The equipment may include dynamic spectral filters and optical channel monitors. Temperature controllers may be used to control the temperatures of the dynamic spectral filters, optical channel monitors, and other components such as erbium-doped fiber coils in optical gain stages. Control units in the equipment may provide alarms based on status information and data from the dynamic spectral filters, optical channel monitors, temperature sensors, and other components.

Abstract: The invention relates to a method and to an arrangement for estimating total noise power (k·P&lgr;) at a specified point in a WDM-system which includes a predetermined number of amplifiers (51), and which is designed to transmit data in channels at mutually different signal wavelengths within a specific wavelength region. The method comprises the steps of: measuring total optical power (Pouttot) at said specific point. Filtering wavelength power (P&lgr;) out from the total optical power (Pouttot) at a given measuring wavelength (&lgr;m) within the transmitted wavelength range but outside the signal wavelength. The wavelength power (P&lgr;) is multiplied by a constant (k) which gives the total noise power (k·P&lgr;) at said specified point.

Abstract: A particular signal from a legacy photonic source may have a distribution of wavelengths in a particular signal that is excessively broad for modern, narrowband equipment. In order to provide a drop-in apparatus for integrating modern narrowband signal carrying and handling devices with legacy equipment as either sender or receiver, various implementations of a data stabilizer are provided. Data stabilizers may rely on information transfer mechanisms, signal directors, wavelength shifters, cross-gain modulation, cross-phase modulation, and four-wave mixers. Moreover, data stabilizers may be implemented directly as multiplexers, or integrated into systems using conventional multiplexers.

Abstract: An optical amplifier waveguide provides variable amplification gain to a broad wavelength input signal. The degree of amplification is proportional to the length of the transmission of the input signal along the amplification waveguide. The amplification waveguide means further comprises a series of output wavelength couplers, which are preferably fiber gratings, placed along the length of the amplification waveguide for coupling a predetermined amplified signal from the amplification waveguide to the output fiber. Additionally, the optical amplifier waveguide of the present invention may include a plurality of noise wavelength coupling means, which are preferably fiber gratings, for coupling unwanted noise from the amplification waveguide means to a noise dissipation means.

Abstract: A multi-mode gain fiber is provided which affords substantial improvements in the maximum pulse energy, peak power handling capabilities, average output power, and/or pumping efficiency of fiber amplifier and laser sources while maintaining good beam quality (comparable to that of a conventional single-mode fiber source). These benefits are realized by coiling the multimode gain fiber to induce significant bend loss for all but the lowest-order mode(s).

Abstract: An optical device including an optical amplifier to amplify optical signals received through an optical input, and to supply the amplified optical signals from an optical output, and an optical filter component to compensate for variations in the gain spectrum of the optical amplifier that occur as a function of wavelength and operating temperature. The optical filter component includes a first optical filter having an athermalized transmission spectrum and a second optical filter having a transmission (of insertion loss) spectrum that varies as a function of operating temperature.

Abstract: An optical amplifier to reduce signal loss by reducing crosstalk, and method therefor. A demultiplexer isolates an optical signal into a first wavelength band and a second wavelength band. The first and second wavelength bands are separately amplified in first and second optical amplifiers, respectfully, first and second optical amplifies each including cutoff filters to cutoff the wavelength band not corresponding to the particular amplifier. Optical receiving elements monitor light input to the first and second optical amplifiers and receive crosstalk signals on an output side.

Abstract: In the optical amplifier an optical divider based on long wavelength (or short wavelength) transmission type dielectric multi-layer filter divides input signal light according to wavelengths, and amplifying sections disposed in parallel and having different respective wavelength amplification regions respectively amplify light signals emitted from the optical divider, and an optical combiner based on long wavelength (or short wavelength) transmission type dielectric multi-layer filter combines light signals output from the respective amplifying sections. In another configuration of the optical amplifier, input signal light is divided using an optical divider based on a dielectric multi-layer filter of a long wavelength (or short wavelength) transmission type, and output signals from the divider are filtered using an optical filter connected in series to a short wavelength (or long wavelength) amplifier generating a loss in the long wavelength (or short wavelength) region of the light signals.

Abstract: An optical fiber transmission link with reduced channel depletion due to stimulated Raman scattering is formed by including a high pass optical filter in the transmission fiber. The filter may comprise one or more discrete components, or may be formed as a “distributed” filter along the length of the optical fiber. The cut-off frequency for the high pass optical filter is selected to be immediately below the frequency of the input channel to be transmitted. When used in an arrangement with multiple input channels, the cut-off frequency is controlled to be immediately below the lowest input channel frequency.

Abstract: A method and apparatus to amplify an optical signal is described. A first filter splits an optical signal into a first and second parts. A first raman amplifier amplifies the first part. A second raman amplifier amplifies the second part. A combiner combines the amplified first and second parts.

Abstract: A calibrated dynamic spectral filter is provided. Test and programming equipment may be used to characterize the spectral performance of the dynamic filter during manufacturing. The performance measurements may be used to generate calibration data. The calibration data may be stored in memory in the dynamic filter by the test and programming equipment. The calibration data may be used to calibrate the operation of the dynamic filter when the dynamic filter is used in optical equipment such as in an optical amplifier in a fiber-optic communications network.

Abstract: Compound gain flattening filters of optical amplification include a series of filter components with spectral responses that are combined to approach a target loss spectrum. Small variations in the central wavelengths of the component responses can produce large errors in the combined response of the compound gain flattening filter. However, the components can be divided into sub-components with balanced central wavelength deviations to achieve the desired response goals despite exhibiting otherwise detrimental wavelength deviations.

Abstract: An approach for minimizing four-wave mixing (FWM) cross-talk (XT) in a WDM (wavelength division multiplexing) optical communication system is disclosed. An Erbium doped Fiber Amplifier (EDFA) includes a pre-amplifier that receives an input optical signal and outputs an amplified input optical signal. The pre-amplifier includes the following components: a first active fiber that carries WDM signals corresponding to a particular operating band (e.g., L-band); a co-propagating pump laser that induces high inversion in a portion of the first active fiber; a filter that is coupled to the first active fiber and slightly inverts the gain tilt of the WDM signals and suppresses the amplified spontaneous emission (ASE) lights accumulated at wavelengths shorter than the signal bandwidth; a second active fiber that is coupled to the filter; and a counter-propagating pump laser that induces high inversion in a portion of the second active fiber. An optical unit (e.g.

Abstract: Disclosed is a fiber optic filter that includes a central core, a ring core concentric with the central core, an inner cladding region of refractive index ni between the central and ring cores, and a cladding layer of refractive index nc surrounding the ring core. The maximum refractive index n1 of the central core and the maximum refractive index n2 of the ring core are greater than nc and ni. The propagation constants of one core mode and one ring mode are different at wavelengths except for at least one wavelength &lgr;0 whereby power transfers between the two cores at &lgr;0. At least a portion of the fiber optic filter fiber is wound around a reel to subject it to a continuous curvature, the radius of which determines the amplitude of the attenuation. Such fibers are useful in fiber amplifiers in which the central core contains active dopant ions.

Abstract: An optical amplifier device intended for WDM light signals comprises a preamplifier (3) and a power amplifier (11) of the optical fiber amplifier type, which are connected in series and have gain curves dependent on the wavelength. A controllable attenuator (5) is connected between the amplifiers (3 and 11) and is controlled by a control device (7). The signal input to the preamplifier (3) has a low power and is amplified to provide an output signal where the signals of the input channels have been amplified with different gains. The input signal of the power amplifier (11) then has a larger power resulting in a gain characteristic different from that of the preamplifier (3). By adapting the attenuation of the attenuator (5) for variations in the input signal the gain characteristic of the power amplifier (11) can be set so that the signal output from the amplifier device has a spectral dependence that is the same as the original spectral dependence obtained without variations.

Abstract: A device for equalizing the gain-wavelength characteristics of an optical repeater used in a long distance optical transmission system, wherein the gain-wavelength characteristics are equalized by one optical filter having asymmetrical loss-wavelength characteristics in a desired wavelength range order to flatten the gain-wavelength characteristics curve over a wide wavelength range. Since such a device can equalize the gain by one optical filter, adjustment the would normally be required between plural optical filters is unnecessary, so that it is simple and cost effective.

Abstract: An optical amplifier includes first, second and third amplifier stages, a first equalizer coupled between the first and second amplifier stages, a second equalizer coupled between the second and third amplifier stages, and a third equalizer coupled between an amplifier output and the third amplifier stage. The first stage includes a length of first erbium doped fiber coupled between an input and the first equalizer. The second stage includes a second erbium doped fiber coupled between the first equalizer and the second equalizer. The third stage includes a third erbium doped fiber coupled between the second equalizer and the third equalizer.

Abstract: The present invention effectively compensates gain wavelength dependency of optical amplifiers by a simple method. That is, a value smaller than the minimum value of gain, in the range of usage wavelengths, of gain wavelength dependency data of the optical amplifiers is predetermined as a reference gain value. A loss wavelength characteristic which counterbalances the gain greater than the reference gain value is provided as an ideal loss wavelength characteristic which completely compensates the gain wavelength dependency.

Abstract: In an optical gain equalizer according to the present invention, a plurality of etalon filters 1 and one ore more fiber gratings 2 or dielectric multilayer filters 3 are arranged in line, and a beam of light externally applied is passed through the etalon filters 1 and the fiber gratings 2 or dielectric multilayer filters 3 and outputted to the outside, and the etalon filters 1 have sinusoidal wave loss characteristic of the same amplitude and period as those of the term obtained by Fourier series expansion of the loss wavelength characteristic for gain flattening, and the one or more fiber gratings 2 or dielectric multilayer filters 3 compensate the ripple component remaining as the difference between the loss wavelength characteristic for gain flattening and the loss wavelength characteristic owing to the etalon filters 1. An optical amplifying device 14 is constituted by combining an optical amplifier 5 with the optical gain equalizer 4.

Abstract: An all fiber optical filter is formed by stretching an optical fiber. The all fiber filter includes a core, an inner cladding and an outer cladding. A core index of refraction is greater than an outer cladding index of refraction. The outer cladding index of refraction is greater than an inner cladding index of refraction. The all fiber optical filter attenuates a portion of an optical signal by transferring optical energy from the core to the outer cladding by evanescent coupling. The all fiber optical filter has a compact structure, which prevents bending and provides stable temperature performance. The all fiber optical filter is preferably used in Wavelength Division Multiplexing (WDM) systems for gain flattening of gain responses from Erbium Doped Fiber Amplifiers (EDFAs). Alternatively, the all fiber optical filter is used in other applications where optical filtering or attenuation is needed.

Abstract: The present invention relates to an apparatus and a method for a Non-Reciprocal Optical Wavelength Filter (NRWF) suitable for bidirectional optical transmissions, communications, and amplifiers.

Abstract: The present invention relates to an apparatus for generating a control signal for at least one periodic filter arranged to filter the optical profile of a signal, at least one of the phase and the amplitude of the filter being tunable, the apparatus comprising an optical waveguide for receiving a portion of said signal, optical filtering means connected to said waveguide for filtering the received portion, and arranged to act as a first and second periodic filter, each having substantially the same period as the filter to be controlled, the phase between the periods of the first and second filters being a non-integer of &pgr;, and optical power measuring means arranged to measure the optical power of the signal transmitted by said optical filtering means. A method is also described for determining such a control signal. Such periodic filters can be used to flatten the gain profile of an optical amplifier.

Abstract: A high power laser optical amplifier system for material processing comprises multiple stage fiber amplifiers with rejection of propagating ASE buildup in and between the amplifier stages as well as elimination of SBS noise providing output powers in the range of about 10 &mgr;J to about 100 &mgr;J or more. The system is driven with a time varying drive signal from a modulated semiconductor laser signal source to produce an optical output allowing modification of the material while controlling its thermal sensitivity by varying pulse shapes or pulse widths supplied at a desire repetition rate via modulation of a semiconductor laser signal source to the system to precisely control the applied power application of the beam relative to the thermal sensitivity of the material to be processed. The high power fiber amplifier system has particular utility in high power applications requiring process treatment of surfaces, such as polymeric, organic, ceramic and metal surfaces, e.g.

Abstract: A multi-amplification path optical amplifier including a first amplification path for propagating and amplifying a first in-band optical communication signal, including a spectrally selective filter for substantially blocking the propagation and amplification of an out-of-band optical communication signal along the first amplification path, and a second amplification path for propagating and amplifying a second in-band optical communication signal, including a spectrally selective filter for substantially blocking the propagation and amplification of an out-of-band optical communication signal along the second amplification path, wherein the location. If the spectrally selective filters in each respective amplification path is selected so that a target noise figure performance and a target output power performance can be obtained from the device. The spectrally selective insertion losses suppress crosstalk or optical leakage that gives rise to multipath interference, return loss, and self oscillation.

Abstract: Optical amplifiers are provided for use in fiber-optic communications networks. An optical amplifier may be controlled to prevent gain transients. The optical amplifier may use a spectrally-filtered input power tap to monitor input power. Amplifier gain may be controlled based on the monitored spectrally-filtered input power. Gain may be provided using one or more rare-earth-doped fiber coils such as erbium-doped fiber coils. The coils may be pumped by laser diodes or other suitable pumps. The optical output power of the pumps may be controlled by a control unit. The control unit may calculate the appropriate pump power for the pumps to supply to the fiber coils based on the measured spectrally-filtered input power of the amplifier. The output power of the amplifier may also be measured. A combination of feed-forward and feedback techniques may be used to calculate the pump power to be supplied by the pumps.

Abstract: The invention is directed to a multistage optical amplifier having a gain stage between two gain flattening filters. According to illustrative embodiments, a gain flattened optical amplifier system comprises a plurality of optical gain stages and a plurality of gain flattening filter stages arranged serially in an alternating manner.

Abstract: Disclosed is a fiber optic filter that includes a central core, a ring core concentric with the central core, an inner cladding region of refractive index ni between the central and ring cores, and a cladding layer of refractive index nc surrounding the ring core. The maximum refractive index n1 of the central core and the maximum refractive index n2 of the ring core are greater than nc and ni. The propagation constants of one core mode and one ring mode are different at wavelengths except for at least one wavelength &lgr;O whereby power transfers between the two cores at &lgr;O. At least a portion of the fiber optic filter fiber is wound around a reel to subject it to a continuous curvature, the radius of which determines the amplitude of the attenuation. Such fibers are useful in fiber amplifiers in which the central core contains active dopant ions.

Abstract: An optical fiber amplifier of the erbium type is intended to amplify light signals within a wavelength band, e.g. in the range of 1540-1555 nm. The active optical fiber receives light signals to be amplified and pump light of a first pump wavelength from a pump source. A gain flattening filter is connected in the active optical fiber length. A noise filter is also connected in the active optical fiber, not more closer to the output end of the active fiber than the gain flattening filter. The noise filter blocks light waves having wavelengths around the ASE gain peak and the gain filter attenuates wavelengths within the useful signal band in order to produce a flat gain curve. The introduction of the noise filter increases the total amplification of the amplifier.

Abstract: An object is to provide a low cost optical amplifier having a simple construction where gain equalization of wavelength division multiplexed signal light, and the suppression of noise light is realized by a single optical device, and to provide a wavelength division multiplexed light transmission system using such an amplifier. Accordingly, the optical amplifier of the present invention is constructed by providing for a conventional optical amplifier incorporating an EDF, an excitation light source and a multiplexer, an optical filter having a periodic loss-wavelength characteristic with respect to a gain wavelength characteristic of the EDF. The optical filter has the characteristic that a spacing (FSR) corresponding to one period of a loss-wavelength characteristic corresponds to a gain peak wavelength difference of the EDF, and a maximum loss wavelength approximately coincides with a gain peak wavelength on a long wavelength side of the EDF.

Abstract: A fiber filter for use in an optical amplifier communication system is in the form of an optical fiber connected between a laser pump module and an amplifier. In one preferred embodiment, the optical fiber is configured to have a predetermined loop diameter to attenuate light in the signal band of the amplifier. The cutoff wavelength, the diameter of the loop, and the number of loops may also be selected to attenuate the signal light sufficiently in the signal band of the amplifier.