Abstract: Provided are light sources and methods of controlling them, and devices and methods for use in measurement applications, particularly in metrology, for example in a lithographic apparatus. The methods and devices provide mechanisms for detection and/or correction of variations in the light source, in particular stochastic variations. Feedback or feedforward approaches can be used for the correction of the source and/or the metrology outputs. An exemplary method of controlling the spectral output of a light source which emits a time-varying spectrum of light includes the steps of: determining at least one characteristic of the spectrum of light emitted from the light source; and using said determined characteristic to control the spectral output.

Abstract: A measurement apparatus includes: a light source unit configured to generate optical signals of, from among n+1 frequencies (n is an integer of 3 or larger) at a predetermined frequency interval, n frequencies except for a target frequency, and output the generated optical signals to an optical transmission path that is a measurement target; an optical power measurement device configured to measure of an optical signal of the target frequency output from the optical transmission path and generated in the optical transmission path as a result of four-wave-mixing of the optical signals of the n frequencies; and a processor configured to determine a power spectrum density of non-linear interference noise that occurs in the optical transmission path, by multiplying the power of the optical signal of the target frequency by an adjustment value.

Abstract: A microcomputer 202 is coupled to a SFP module 101 via control signal lines 112 to 114. The microcomputer 202 monitors control signals transmitted on the control signal lines 112 to 114, and acquires, based on the result of monitoring, the condition of the SFP module 101 from a ROM 151 at a timing when a protocol chip 102 is not accessing the SFP module 101.

Abstract: A communication device is provided that estimates one or more disturbance values associated with one or more components of the communication device, and adjusts the communication device to change a received power of the output signal. The communication device includes a transmitter having a seed laser configured to provide an amount of bandwidth for an output signal, an Erbium-doped fiber amplifier (EDFA) configured to increase an amplitude of the output signal, and a single mode variable optical attenuator (SMVOA) configured to decrease the amplitude of the output signal.

Abstract: Example fiber amplifiers and gain adjustment methods for the fiber amplifiers are described. One example fiber amplifier includes a first power amplifier, a wavelength level adjuster, and a controller, where the first power amplifier and the wavelength level adjuster are sequentially connected. The controller includes a first input end and a control output end. The first input end is configured to receive an input optical signal of the fiber amplifier, and the control output end is configured to output a first amplification control signal to the first power amplifier, and output an adjustment control signal to the wavelength level adjuster. The wavelength level adjuster is configured to perform power adjustment on each wavelength based on the adjustment control signal.

Abstract: Embodiments of the present disclosure disclose an optoelectronic oscillator including an optical chip and a microwave chip. The optical chip is implemented by fabricating different optoelectronic devices on an integrated optical substrate, comprising: a laser assembly; a mode selection device coupled to the laser assembly, and configured to receive the laser and perform mode selection; an optical delay module coupled to the mode selection device; and a detector coupled to the optical delay module. The microwave chip is a microwave integrated circuit formed by fabricating microwave elements on a semiconductor substrate, comprising: a microwave processing circuit configured to receive microwave signal and perform signal processing; a coupler coupled to the microwave processing circuit, and configured to provide a part of the microwave signal to a phase shifter and output the other part thereof; and a phase shifter configured to feed the phase-shifted microwave signal to the laser assembly.

Abstract: Systems and methods of undersea optical communication are provided. An undersea optical amplifier assembly can include a water-tight housing and a photonic integrated circuit disposed within the housing. The photonic integrated circuit includes a plurality of optical fiber inputs, each configured to receive an end of a respective optical fiber of a first fiber optic cable bundle, and a plurality of optical fiber outputs. Each optical fiber output corresponds to a respective optical fiber input to form a fiber optic input-output pair, and is configured to receive an end of a respective optical fiber of a second fiber optic cable bundle. The photonic integrated circuit includes an optical amplifier optically coupled to each respective fiber optic input-output pair. The housing includes a first water-tight access port configured to receive the first fiber optic cable bundle, and a second water-tight access port configured to receive a second fiber optic cable bundle.

Abstract: A method of inducing light losses at a parasitic wavelength in a fiber laser system includes providing a wavelength discriminator (WD) spaced from and between feeding and process fibers or from the end output of the feeding fiber so as to induce losses of light at parasitic wavelength. The device implementing the disclosed method is configured with a laser source, the delivery fiber and WD spaced at a distance between the surface to be treated and the end of the delivery fiber, wherein the WD receives the parasitic light over free space and is configured as a dichroic filter inducing losses to the light at the parasitic wavelength.

Abstract: This application discloses an optical amplifier apparatus including a first amplifier unit and a hybrid filter unit. The first amplifier unit is configured to receive a first beam including signal light and first monitoring light. The first amplifier unit is further configured to amplify the first beam to obtain a second beam. The hybrid filter unit is configured to: receive the second beam output by the first amplifier unit, and separate the first monitoring light and the signal light from the second beam. The hybrid filter unit is further configured to: transmit the first monitoring light in the second beam to a monitoring light detection apparatus of a first station through a first output port. The hybrid filter unit is further configured to: perform gain flattening filtering processing on the signal light in the second beam to obtain filtered signal light, and output the filtered signal light.

Abstract: A method is provided for determining the gain spectrum of an optical amplifier such as an erbium doped optical amplifier (EDFA). In accordance with the method, an optical amplifier such as an EDFA that is to accommodate a specified number of channels at different optical wavelengths is provided. A subset of the specified number of channels at which gain is to be measured is selected. The number of channels in the subset is determined based at least in part on a number of samples required by the Nyquist sampling theorem to reconstruct the gain spectrum. A gain value for each channel in the selected subset of channels is measured for a probe signal that does not perturb the gain spectrum of the EDFA by more than a prescribed amount. The gain spectrum for the EDFA is constructed from the measured gain values.

Abstract: The invention relates to a method for producing a reference frequency ?f. According to the invention, the use of a first optical resonator (3a; 24) and of a second optical resonator (25) is provided, wherein the first resonator (3a; 24) has a first resonator mode having a first frequency f1 and the second resonator (25) has a second resonator mode having a second frequency f2, wherein the frequencies of the two resonator modes are functions of an operating parameter BP and assume the values f1 and f2 at a specified value BP0 of the operating parameter such that f1(BP0)=f1 and f2(BP0)=f2 apply, wherein the resonators (3a; 24, 25) are designed in such a way that the respective first derivatives of the frequencies f1(BP), f2(BP) with respect to BP or at least respective difference quotients around BP0 correspond within a deviation of at most ±0.

Abstract: Embodiments of the disclosure relate to reducing out-of-channel noise in a wireless distribution system (WDS). A digital filter in a remote unit is configured to suppress out-of-channel noise in a downlink digital communications signal based on at least one filter configuration parameter received from a control circuit. The control circuit is configured to determine the filter configuration parameter based on physical characteristics of the downlink digital communications signal. By suppressing the out-of-channel noise of the downlink digital communications signal, it is possible to provide a downlink RF communications signal communicated from the remote unit that complies with a spectrum emission mask (SEM).

Abstract: The present invention achieves a fiber laser having a high reflection resistance. A length of an optical fiber MMF is set so that a condition is satisfied at each point on an individual optical path of a fiber laser (FL2), the condition being that a difference between time at which a power of a forward Stokes beam (SF) is at a maximum value and time at which a power of a backward Stokes beam (SB) is at a maximum value is greater than a sum of a half width at half maximum of the power of the forward Stokes beam (SF) and a half width at half maximum of the power of the backward Stokes beam (SB).

Abstract: The invention comprises a multilevel optical signal system comprising two or more light source branches and an optical power-combiner, wherein each branch comprising a light source, an optical modulator and an electrical driver for the modulator, wherein each electrical driver is configured for being driven by electrical signals to drive the modulator to modulate the light generated by the light source into a corresponding 2-level data signal such that the respective 2-level data signals differs in power level.

Abstract: A multi-stage optical amplifier has an input port for receiving an optical signal and a relatively short erbium doped optical fiber is coupled to the input port. Complex costly pump feedback is not required as a constant non-varying saturation pump is configured to provide non varying output power pump light of a predetermined wavelength suitable for excitation and full saturation of the erbium ions such that a full population inversion occurs. The length of the short erbium doped fiber and rare earth doping concentration of the erbium doped fiber is such that when pumped by said pump provides amplification of the optical signal of less than 15 dB. Locating a gain flattening filter after the short erbium doped optical fiber provides a relatively flat amplified output signal. Multi-stages of similar short erbium doped fibers pumped and saturated by the same pump signal economically provide increased amplification of the signal and filters after each state flatten the gain.

Abstract: A multi-stage optical amplifier has an input port for receiving an optical signal and a relatively short erbium doped optical fiber is coupled to the input port. Complex costly pump feedback is not required as a constant non-varying saturation pump is configured to provide non varying output power pump light of a predetermined wavelength suitable for excitation and full saturation of the erbium ions such that a full population inversion occurs. The length of the short erbium doped fiber and rare earth doping concentration of the erbium doped fiber is such that when pumped by said pump provides amplification of the optical signal of less than 15 dB. Locating a gain flattening filter after the short erbium doped optical fiber provides a relatively flat amplified output signal. Multi-stages of similar short erbium doped fibers pumped and saturated by the same pump signal economically provide increased amplification of the signal and filters after each state flatten the gain.

Abstract: A pluggable electric connector can communicate a communication data signal and a control signal with an optical communication device. An optical signal output unit is configured to be capable of selectively output a wavelength of an optical signal. An optical power adjustment unit can adjust optical power of the optical signal. A pluggable optical receptor can output the optical signal to an optical fiber. A control unit controls a wavelength change operation according to the control signal. The control unit, according to a wavelength change command, commands the optical power adjustment unit to block output of the optical signal, commands the light signal output unit to change the wavelength of the optical signal after the optical signal is blocked, and commands the light signal output unit and the optical power adjustment unit to output the optical signal after the wavelength change operation.

Abstract: The present disclosure relates to the field of communications technologies, and in particular, to an optical add/drop multiplexer, such that the optical add/drop multiplexer can ensure proper processing of light in two directions. The optical add/drop multiplexer can complete an extraction of a signal in one direction using one microring resonant cavity and two optical circulators, and if a wavelength of a signal in the other direction is the same as a resonant wavelength of the microring resonant cavity, the signal may reenter an optical network after passing through two microring resonant cavities and one optical circulator, and is not affected. Therefore, proper processing of optical signals in the two directions is ensured, and the optical signals in the two directions do not interfere with each other.

Abstract: A bidirectional optical amplifier amplifies optical signals having signal wavelength and signal power input from two directions. The amplifier is arranged so that two counter-propagating signals pass through a first pumped rare earth doped pre-amplifier before passing through other amplifiers downstream. Optical circulators route the two counter propagating signals so that they both pass through in a counter-propagating manner through subsequent pumped rare earth doped amplifiers downstream.

Abstract: A method for optical network termination (ONT) configuration is provided. The method includes: obtaining, by an optical line terminal (OLT), service types supported by an ONT and management methods available for each of the service types; and negotiating, by the OLT, with the ONT according to the management methods available for each of the service types, so as to determine a management method to be adopted for each of the service types, and configuring the ONT according to the determined management method.

Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for optical communications. One optical amplifier includes an input port; a bar-cross switch optically coupled to the input port; a first gain stage optically coupled between first port of the bar-cross switch and to an output port; and a secondary gain stage optically coupled between a second port and a third port of the bar-cross switch, wherein in a bar-state of the bar-cross switch the secondary gain stage is bypassed and in a cross-state, the secondary gain stage and the first gain stage are applied to an input light beam.

Abstract: Thermal processing is performed by transmission of mid infra-red laser light through a substrate such as a semiconductor substrate with a limited mid infra-red transmission range. The laser light is generated by a rare-earth-doped fiber laser and is directed through the substrate such that the transmitted power is capable of altering a target material at a back side region of the substrate, for example, on or spaced from the substrate. The substrate may be sufficiently transparent to allow the transmitted mid infra-red laser light to alter the target material without altering the material of the substrate. In one example, the rare-earth-doped fiber laser is a high average power thulium fiber laser operating in a continuous wave (CW) mode and in a 2 ?m spectral region.

Abstract: A robust broadband ASE (amplified spontaneous emission) fiber light source device outputs a light beam which is little affected by temperature and radiation. The light source device is a single-pass backward or double-pass backward architecture, and has a coolerless pump laser and temperature compensated bandpass reflector. The light source device may have a high pass filtering element disposed between the wavelength division multiplexer thereof and the optical isolator thereof, so as to compensate the effect of the temperature to the mean wavelength of the light beam. The specific band of the temperature compensated bandpass reflector which reflects the light beam, and the band which the high pass filtering element transmits the light beam are within the band which the ASE unit amplifies the light beam, and the high pass filtering element mainly absorbs the light beam outside the specific band.

Abstract: A burst-mode optical amplification apparatus and method is provided. The burst-mode optical amplification apparatus includes a gain saturation signal generator configured to generate a gain saturation signal for gain stabilization based on an incoming input optical signal; a wavelength multiplexer configured to wavelength multiplex the incoming input optical signal and the gain saturation signal; and an optical amplifier configured to amplify both the wavelength-multiplexed input optical signal and the wavelength-multiplexed gain saturation signal. The apparatus may further include a time delay module configured to synchronize the input optical signal and the gain saturation signal by delaying the transmission time of the input optical signal, taking into consideration the processing time needed by the gain saturation signal generator to generate the gain saturation signal.

Abstract: This disclosure provides several mechanisms for adapting transmit power spectral density (PSD). A communications device may adapt the power spectrum utilized at the transmitter based, at least in part, on the channel conditions or PSD constraints associated with the communications medium between the transmitter and a receiver device. Additionally, the transmit PSD may be adapted based, at least in part, on a total power capability associated with a transmitter. Power is allocated to improve throughput and utilization of the communications channel. A transmission profile may be selected based, at least in part, on the notch depth. The transmission profile may be associated with symbol timing parameters. The communications device may maintain a plurality of selectable pulse shapes that are optimized for different notch depths.

Abstract: An optical circuit can include a bidirectional amplifier connected so as to amplify source light prior to emission through an output device such as a telescope as well as amplification of reflected light received by the telescope. Such an optical circuit can be used in laser doppler velocimeter applications as well as other applications. The optical circuit can also include passive splitters or active switches to provide for advantageous multiplexing.

Abstract: Methods and systems for current amplification to improve optical amplifier performance may include equalizing a current level indicative of input optical power to an optical amplifier with a current level indicative of an output optical power level of the optical amplifier. In this manner, a first bandwidth of an input log amp may be matched with a second bandwidth of an output log amp in a gain control loop circuit to improve overall transient gain accuracy of the optical amplifier, irrespective of the input optical power. In this manner, the optical amplifier may be enabled to operate at a defined gain level even in the presence of transients in the input signal.

Abstract: Laser-induced damage in an optical material can be mitigated by creating conditions at which light absorption is minimized. Specifically, electrons populating defect energy levels of a band gap in an optical material can be promoted to the conduction band—a process commonly referred to as bleaching. Such bleaching can be accomplished using a predetermined wavelength that ensures minimum energy deposition into the material, ideally promoting electron to just inside the conduction band. In some cases phonon (i.e. thermal) excitation can also be used to achieve higher depopulation rates. In one embodiment, a bleaching light beam having a wavelength longer than that of the laser beam can be combined with the laser beam to depopulate the defect energy levels in the band gap. The bleaching light beam can be propagated in the same direction or intersect the laser beam.

Abstract: A multi-core amplification optical fiber includes a plurality of rare-earth-doped core portions and a cladding portion positioned at an outer periphery of the core portions and having refractive index lower than those of the core portions. When a doping concentration of the rare-earth of each of the core portions is 250 ppm to 2000 ppm, a relative refractive index difference of each of the core portions relative to the cladding portion is 0.5% to 2% at a wavelength of 1550 nm, and a core diameter of each of the core portions is 1 ?m to 5 ?m, a separation distance between each of the core portions and adjacent one of the core portions is set at equal to or larger than 30 ?m and at equal to or smaller than 60 ?m so that a light-crosstalk between the adjacent core portions is equal to or lower than ?30 dB.

Abstract: The present invention greatly reduces the likelihood that fiber fusion will occur. A laser apparatus comprises an excitation light source and an optical amplifier unit, which optically amplifies by receiving excitation light that is output from the excitation light source and that transits an optical fiber. A monitor unit monitors the power level of the excitation light transmitted from the excitation light source to the optical amplifier unit side via the optical fiber.

Abstract: Devices and methods for lessening a thermal dependence of gain profile of an optical amplifier are disclosed. An optical beam is split in two sub-beams with a thermally variable power splitting ratio. One sub-beam travels a longer optical path length than the other. When the two sub-beams are recombined, they interfere with each other, causing the throughput to be wavelength dependent. An amplitude of this wavelength dependence is thermally variable due to the thermally variable power splitting ratio. The thermally variable power splitting ratio and the optical path length difference are selected so as to offset a thermal variation of a spectral gain profile of an optical amplifier.

Abstract: A method includes transmitting a first set of transmission signals over an operating frequency band. The method includes detecting if a second set of transmission signals are transmitted adjacent the operating frequency band and reducing power to a subset of the first set of transmission signals when the second set of transmission signals are detected.

Abstract: An optical transmission device includes a first power monitor to monitor a first signal into which second signals with respectively different wavelengths are multiplexed so as to measure received power of the first signal; an amplifier to amplify the first signal, to generate a third signal; a driver to drive the amplifier; a demultiplexer to separate the third signal into fourth signals with the different respectively wavelengths; second power monitors each to monitor each of the fourth signals so as to measure received power of each of the fourth signals; a memory to store therein data related to gain in the amplifier, the data corresponding to each of wavelengths of the second signals, with respect to parameters which are the received power measured by the first power monitor and driving condition; and a processor to calculate power of each of the second signals.

Abstract: The invention relates to an optical amplifier system for amplifying laser pulses, including a solid amplifying medium capable of receiving a beam of laser pulses to be amplified and generating a beam of amplified laser pulses, and a means of reducing the energy stored in said optical amplifying medium by means of optical pumping. According to the invention, said reducing means includes a continuous resonant cavity and a first optical separation means capable of sepaarating continuous resonant cavity into a common portion and a low arm, the common portion including an optical amplifying medium and the loss arm inlcuding an optical loss means, said optical separation means being capable of selectively directing a beam of pulses outside the optical path of said loss arm of the continuous resonant cavity, and of directing a continuous bean toward said loss arm of the continuous resonant cavity.

Abstract: An optical amplifier with improved transient performance has two amplifier stages and a gain flattening filter-inserted between the amplifier stages. A control unit generates a pump control signal for a common pump source pumping both amplifier stages. The pump control signal has a feed-forward component and a feedback component. After a drop of channels the feed-forward control circuit is responsible for the transient performance and fast gain stabilization. The characteristic of the gain flattening filter is taken into account in calculating an optimum feed-forward control signal.

Abstract: Techniques, devices and systems that stabilize an RF oscillator by using an optical resonator that is stabilized relative to a master RF oscillator with acceptable frequency stability performance. In the examples described, the optical resonator is stabilized relative to the master RF oscillator by using a frequency stability indicator based on two different optical modes of the optical resonator. The RF oscillator to be stabilized is then locked to the stabilized optical resonator to achieve the acceptable RF stability in the RF oscillator.

Abstract: The present invention discloses a multi-wavelength light source apparatus. The multi-wavelength light source apparatus includes: a pump light source, configured to provide pump light; an erbium-doped optical fiber, configured to absorb energy of the pump light and emit wide-spectrum laser light; and an optical fiber, configured to filter the wide-spectrum laser light and output a multi-wavelength optical signal in a free spectral range of the optical filter, where the multi-wavelength optical signal is incident on the erbium-doped optical fiber, and the erbium-doped optical fiber is further configured to re-amplify and output the incident multi-wavelength optical signal. In the multi-wavelength light source apparatus in the embodiments of the present invention, a wavelength of output light can be selected, spectral energy of the output light is concentrated, and power of the output light is high.

Abstract: A wavelength-tunable laser system includes an optical fiber collimator array having at least two ports, an optical amplifier connected to one port of an optical fiber, an optical coupler for coupling light incident from the optical amplifier and transmitting the coupled light to another port, a diffraction grating plate for guiding each wavelength component of light incident from the optical fiber collimator array in a different direction, and an Opto-Very Large Scale Integration (Opto-VLSI) processor.

Abstract: Provided is a laser oscillation apparatus capable of stabilizing resonance even when finesse of an optical resonator is increased and generating stronger laser light than that of a traditional apparatus by accumulating laser light in the optical resonator.

Abstract: Disclosed herein are methods, structures and systems for few-mode fiber (FMF) transmission including an optical amplifier exhibiting modal gain control suitable for such transmission in which higher order modes are amplified. An exemplary evaluation system is described and results presented.

Abstract: An optical amplifier includes: a rare-earth doped fiber configured to amplify signal light to thereby produce a amplified signal light; a gain control circuit configured to control an optical gain of the rare-earth doped fiber; a photodetector configured to detect intensities of different wavelength of light obtained from the amplified signal light; and an abnormality detection circuit configured to detect an abnormality of the signal light in accordance with a ratio or a difference between the intensities of the different wavelength.

Abstract: An optical amplifying apparatus that amplifies a wavelength-division multiplexed (WDM) optical signal includes an input section, a laser light source, a double-clad optical fiber, a gain equalizer, and a residual pump light attenuating section that attenuates a residual pump light outputted from the double-clad optical fiber. The residual pump light attenuating section is disposed such that the residual pump light of the laser light is incident on the residual pump light attenuating section before being incident on an isolator.

Abstract: An optical-limiter is disclosed herein. In an embodiment, the optical limiter comprises chemically functionalized graphene substantially spaced apart as single sheets in a substantially transparent liquid cell or solid thin film. A method of fabricating an optical response material is also disclosed.

Abstract: An apparatus includes: an optical amplifier configured to perform optical amplification for gain by controlling so as to be a target gain; a correction power calculator configured to calculate, in response to amplified spontaneous emission light input to the optical amplifier, correction power corresponding to an amount of gain depression in a bandwidth in which spectral hole-burning occurs in the optical amplifier; and a gain controller configured to calculate, using the correction power calculated in the correction power calculator, a gain for controlling the optical amplification performed in the optical amplifier and perform, using the calculated gain, a control operation so that the gain of the optical amplification becomes the target gain.

Abstract: The invention is directed to a system and method of regulating a slicer for a communication receiver. A zero-crossing accumulator receives a slicer output from the slicer and accordingly determines a zero-crossing length of the slicer output. A threshold decision unit regulates at least one threshold value of the slicer according to the zero-crossing length.

Abstract: An optical signal amplifier for use in optical networks operating in a ring configuration comprising a first doped optical fiber loop pumped by a first laser and a second optical fiber loop pumped by a second laser.

Abstract: A control method of a semiconductor optical amplifier includes: controlling a driving current of the semiconductor optical amplifier in a region where a light output intensity decreases in accordance with increasing of the driving current, a drive current in the region being higher than a drive current in a region where a light output intensity increases in accordance with increasing of the driving current.

Abstract: An optical amplifier module includes a first optical amplifier to amplify main signal light to be supplied to a dispersion compensation fiber (DCF), a second optical amplifier to amplify the main signal light supplied from the DCF, a generating part to generate monitoring light having a wavelength longer than a wavelength of the main signal light, a multiplexing part to multiplex the monitoring light generated by the generating part and the main signal light to be supplied to the DCF, a demultiplexing part to demultiplex the monitoring light from the main signal light supplied from the DCF, and a detection part to detect a light intensity of the monitoring light demultiplexed by the demultiplexing part.

Abstract: A system and method for Raman amplification of optical signals in a wavelength division multiplexing (WDM) optical transmission system includes transmitting optical signals within a transmission band via an optical waveguide between a transmitter and a receiver, Raman-amplifying the optical signals with at least one pump so as to distort an amplification profile of the Raman amplification within the transmission band, and rectifying the distorted amplification profile so as to compensate for the distortion.

Abstract: A fiber optical device 1A includes an amplification optical fiber 10, a seed light source 15 for supplying pulse seed light to the optical fiber 10, excitation light sources 21 to 25 for supplying excitation light, a bleaching light source 40 for supplying bleaching light for reducing a light transmission loss caused by photodarkening, and a control device 50 that controls the operations of individual portions. The control device 50 divides a period between a first output light pulse and a succeeding second output light pulse into a first period which includes a time point immediately after the output of the first output light pulse and during which the population inversion is unsaturated, and a second period which includes a time point immediately before the output of the second output light pulse, and, to the optical fiber 10, supplies the bleaching light in the first period and supplies the excitation light in the second period.