Abstract: Optical equipment and methods for manufacturing optical equipment that allow equipment to be fabricated using fiber pigtails of various lengths are provided. An equipment housing may be used that has fiber channels. Optical components fibers of various lengths may be spliced together during manufacturing. The lengths of fiber may be routed through the fiber channels. Different paths may be taken through the channels to accommodate different fiber lengths. The equipment housing may include electronics boards for electrical components and an optical tray for mounting optical components with fibers. The fiber channels may be formed as part of the optical tray.

Abstract: Optical amplifiers are provided for use in fiber-optic communications networks. 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 in a given amplifier may be controlled by a control unit. Taps may be used to monitor the power of optical signals being amplified by the amplifier. The tapped optical signals may be spectrally-filtered. The control unit may calculate the appropriate pump power for the pumps to supply to the fiber coils based on the measured spectrally-filtered optical signals. The gain of the amplifier may be maintained at a desired level using feedback control techniques. The gain spectrum of the amplifier need not be flat. A combination of feed-forward and feedback techniques may be used to calculate the pump power to be supplied by the pumps.

Abstract: Spectral tilt controllers are provided for optical amplifiers and other optical network equipment used in fiber-optic communications links in fiber-optic networks. The tilt controllers may be used to adjust the gain or output power spectrum of an optical amplifier or to modify the optical data signal spectrum in other optical network equipment. Tilt controllers may use mechanical actuators to position a filter element substrate relative to an optical beam. Dielectric filters or other filter arrangements having various different spectral tilt characteristics may be implemented on the same substrate. Spectral tilt and average spectral attenuation values may be adjusted using the tilt controllers if desired.

Abstract: Optical amplifier equipment for operation in fiber-optic communications networks is provided. The optical amplifier equipment may include one or more gain, stages based on rare-earth-doped fiber or Raman-pumped fiber. The gain stages may be optically pumped using diode lasers. Optical monitors may be used to measure optical signals in the optical amplifier equipment. Input signals and output signals may be measured. A control unit may adjust the pump powers in the gain stages based on the measured optical signals to suppress gain transients. An optical delay line may be used to provide additional time for the control unit to process the optical signals before adjusting the pump powers. A midstage module including dispersion-compensating fiber may be installed in the optical amplifier equipment. The control unit may automatically detect the amount of optical delay associated with the installed module and may control the pump powers accordingly during transient control operations.

Abstract: Optical amplifiers are provided in which optical gain is produced by Raman pumping fiber. The Raman-pumped fiber may be a span of transmission fiber or a coil of fiber in a discrete amplifier. Raman pump light may be provided using laser diodes operating at different wavelengths. The Raman pump light that is produced by the laser diodes may be modulated to reduce pump interactions in the fiber. Raman pump light may be modulated by directly modulating the laser diodes or by using optical components that modulate constant power pump light from the laser diodes.

Abstract: Novel optical amplifier designs are disclosed. The optical amplifier generally comprises an amplification section having an anti-reflection coating on a first end face and a reflector optically coupled to a second end face. The amplification section of the amplifier interacts with the input and reflected optical signals to produce an amplified optical signal. The amplification section may include rare earth doped glass amplifiers (e.g., erbium-doped amplifiers), rare earth doped waveguide amplifiers (e.g. erbium-doped waveguide amplifiers), polymer amplifiers or parametric amplifiers. The amplifier may include a waveguide structure proximate the amplification section to confine optical signals within the amplification section and/or guide signals into and out of the amplifier. The amplifier may be combined with optical components for coupling signals between optical fibers and the amplifier. The waveguide may have a modified “V” shape where the “V” with at two legs.

Abstract: Distributed Raman amplifier systems are provided in which gain transients are controlled. Signal taps may be used to monitor optical signal powers at network nodes. A telemetry channel may be used to share information between nodes. Information on the output power of a given node may be passed to a subsequent node using the telemetry channel. The subsequent node may use feed-forward and feedback control schemes to control Raman gain transients in the preceding transmission fiber span based on the output power information received over the telemetry channel.

Abstract: Circuitry for generating AC signals is provided. The circuitry may be used to produce AC drive signals for microelectromechanical systems (MEMS) devices such as MEMS devices used in fiber-optic communications network equipment. The circuitry may include an amplitude controller for producing a DC voltage, a waveform generator for producing an AC waveform having an amplitude proportional to the DC voltage, and a transformer for boosting the AC waveform to produce the AC drive signals.

Abstract: Multiwavelength Raman pumps for Raman amplifiers are provided. The multiwavelength Raman pumps may be based on semiconductor devices that have multiple source regions, each of which handles pump light at a different wavelength. An optical coupler such as a lens and isolator arrangement or an integral fiber lens may be used to couple pump light from the multiwavelength Raman pump into a fiber. A depolarizer may be used to depolarize the Raman pump light provided by the Raman pump. Gratings may be used to define the lasing wavelengths for the Raman pump. A number of tunable sources may be used on the semiconductor device. A fiber Bragg grating may be used to form an external cavity or coupled cavity arrangement for the semiconductor device.

Abstract: A method and apparatus for shutting off a source of optical power to an optical fiber in the event of a cut in the fiber are disclosed. Embodiments of the invention are particularly suited in fiber optic communications systems that use Raman pumps for signal amplification. Optical power from the pump to a fiber is shut off in response to a change in a supervisor signal provided to a first end of the fiber. The supervisor signal is generally operated in an “always-on” mode to provide for fail-safe operation. The apparatus generally comprises a controller coupled to the source of optical power and means for coupling a supervisor signal, which has been provided to a first end of the fiber, to the controller. The method and/or apparatus may be incorporated into an optical communications system having an optical fiber and two or more hubs coupled to the fiber.

Abstract: Optical amplifiers and methods for manufacturing optical amplifiers are provided that allow amplifiers to be fabricated to match design expectations. Optical amplifiers may be manufactured by assembling passive optical components in the amplifier before assembling active optical components such as doped fiber coils. Passive losses may then be characterized and used to calculate the lengths of the fibers that should be used in the amplifier gain stages. Following corrections to the nominal doped-fiber lengths based on the measured passive losses, the passive and active components of the amplifier may be assembled and characterized. Final corrections may be made to the amplifier assembly based on these characterizations. For example, the lengths of one or more of the doped fibers may be adjusted. If desired, such length adjustments may be made to fiber coils in the mid-stage portion of the amplifier, so that the impact on the operating characteristics of the amplifier are minimized.

Abstract: Raman fiber amplifiers are provided in which multiple pump wavelengths are used. A Raman fiber amplifier may be used to amplify optical signal channels over a range of wavelengths. Some of the pump wavelengths may be selected to create Raman gain in this range. Other pump wavelengths may be selected to create Raman loss in this range. Different pump powers may be used at each pump wavelength.

Abstract: Optical amplifiers are provided that have dispersion-compensating fiber that is pumped with an optical source to produce Raman gain. Removable modules of dispersion-compensating fiber, which may be separate from the Raman-pumped dispersion-compensating fiber, may be used to adjust the amount of dispersion compensation provided by a given amplifier. The Raman pump may be formed using fiber-Bragg-grating-stabilized diode lasers or other suitable pump sources. Two cross-polarized diode lasers may be used for the Raman pump to reduce the dependence of the Raman gain on the polarization of the pump. If desired, the dispersion-compensating fiber may be Raman pumped using a two-pass configuration in which pump light reflects off of a reflector to produce additional gain. The reflector may be a Faraday rotator to minimize polarization-dependent pump effects.

Abstract: An optical amplifier control system provides real-time control of an optical amplifier in response to an analog signal having a large dynamic range. The optical amplifier control system uses a non-linear analog-to-digital converter, such as a logarithmic-scale analog-to-digital converter to achieve low relative quantization error. The amplifier control system may also use multiple analog-to-digital converters.

Abstract: Optical amplifiers are provided that use a hybrid transient control scheme. Optical taps may be used to tap the main fiber path through the amplifier before and after the gain stage. The gain stage may be provided by 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 controller. The controller may calculate the appropriate power to be applied by the pumps based on the measured input and output signal powers of the amplifier. The control process implemented by the controller may be based on a combination of feedback and feed-forward control techniques.

Abstract: Amplifiers having multiple gain stages are provided. Some of the gain stages provide gain in a first wavelength band and some of the gain stages provide gain in a second wavelength band. The gain stages that provide gain in the first band are interleaved with the gain stages that provide gain in the second band. The gain stages may be based on rare-earth-doped fiber amplifiers, Raman-pumped fiber amplifiers, or other suitable optical amplifiers. Gain stages may be used that include parallel amplifier branches. Each of the parallel branches may handle a separate wavelength range.

Abstract: Optical amplifiers with variable optical attenuators that are adjusted using a sublinear control scheme are provided. Instead of increasing the attenuation of the optical attenuator by Y dBs for each desired Y dBs in decreased optical amplifier gain, the attenuation of the variable optical attenuator is increased by less than Y dBs. This sublinear control scheme improves the noise figure performance of the optical amplifier at the expense of increased gain ripple. The overall performance of the optical amplifier may be improved, particularly in conditions in which the attenuations produced by the variable optical attenuator are relatively large.

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.