Abstract: An optical transmission apparatus communicable with a plurality of subscriber including a delay measuring part for detecting a response delay time from each subscriber based on reception timing of the delay measurement response optical packet, a detection part for detecting a received optical level of the delay measurement response optical packet received by the reception part and a state determination part for determining quality of an optical transmission state between the optical transmission apparatus and each subscriber based on the received optical level of the delay measurement response optical packet of each of the plurality of subscribers.

Abstract: An image encodes processing parameters for a set of images. A wireless communication device optically receives and processes the received image to generate first image data. The image data represents the processing parameters. The wireless communication device processes the first image data to obtain the processing parameters. The wireless communication device then optically receives the set of images. The set of images encode second image data. The wireless communication device processes the optically received set of images based on the processing parameters to obtain second image data.

Abstract: An optical wavelength multiplexing system includes transmission-side and reception-side optical wavelength multiplexers, and terminal devices, which are connected to each other by optical fiber cables. Optical wavelength converters in the transmission-side optical wavelength multiplexers are connected to ports respectively. The optical wavelength converter converts an input optical signal into an arbitrary preset wavelength to generate a converted optical signal. The port has a predetermined wavelength preset therein. Each optical power level of input converted optical signals is compared with each optical power level of optical signals of respective wavelengths set in the ports. When a difference is detected in the comparison result, it is determined that an optical wavelength converter is incorrectly connected to the port.

Abstract: Disclosed are a system and a method for controlling multicast data. The system may comprise: a plurality of transceivers, each of which comprises a laser configured to generate an optical carrier, the generated optical carrier being modulated by electrical downstream p-t-p data so as to generate optical downstream p-t-p IRZ signal; a PM configured to modulate the generated optical downstream p-t-p IRZ signal by electrical multicast data so as to generate orthogonally modulated signal; and a DI configured to demodulate the orthogonally modulated data and has a frequency response peak or dip in response to the demodulating, wherein an offset of a laser center wavelength of the laser from the frequency response peak or dip is adjustable so as to selectively enable or disable the multicast data.

Abstract: A testing input module for testing an in-service WDM system is provided. The testing input module includes a first light source configured to emit a first light signal to one or more empty channels of the in-service WDM system; and a tunable second light source configured to emit a second light signal to test the one or more empty channels. The testing input module also includes a first switch module configured to: receive from the first light source and output the first light signal during a first time interval; and receive from the second light source and output the second light signal during a second time interval. The second time interval is a duration wherein a channel power monitoring function of the in-service WDM system is not triggered.

Abstract: A communication system including: a transmission apparatus configured to modulate a first light by using a first signal to be transferred and a second signal having a frequency different from a frequency of the first signal so as to generate a first optical signal, modulate a second light by using a third signal to be transferred and a fourth signal having a frequency different from a frequency of the third signal so as to generate a second optical signal, polarization-multiplex the first optical signal and the second optical signal, and transmit a polarization-multiplexed optical signal in which the first optical signal and the second optical signal are polarization-multiplexed, each of the first light and the second light being polarized; and a measuring apparatus configured to measure powers of the second signal and the fourth signal which are included in the polarization-multiplexed optical signal transmitted from the transmission apparatus.

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: In particular embodiments, providing signal reachability information to a network includes establishing signal reachability information at a network node of the network. The signal reachability information describes attributes that affect reachability of an optical signal. The signal reachability information is inserted into an advertisement, and the advertisement is sent to network nodes of the network.

Abstract: A modular development platform is described which enables creation of reliable, compact, physically robust and power efficient embedded device prototypes. The platform consists of a base module which holds the processor and one or more peripheral modules each having a peripheral device and an interface element. The modules can be electrically and physically connected together. The base module communicates with peripheral modules using packets of data with an addressing portion which identifies the peripheral module that is the intended recipient of the data packet.

Abstract: Dual laser-power-level control and calibration system for burst-mode and continuous-mode transmitter. A first signal path receives a transmit signal that also drives the transmit laser, and a second signal path receives the output of a monitor diode. The first and second signal paths include filtering so that the two signal paths have a similar frequency response. The upper and lower excursions in both signal paths are compared, and the power levels of the optical transmitter are adjusted based on those comparisons. Embodiments with one control loop and two control loops are disclosed.

Abstract: An optical line terminal (OLT) includes an optical receiving assembly and a processor (4). A current mirror (1), a current-voltage conversion circuit (2) and a switching circuit (3) are connected in sequence between the optical receiving assembly and the processor (4). An energy storage circuit connected to ground is connected between the switching circuit (3) and the processor (4). The optical receiving assembly generates a response current according to the optical signal received. The current mirror (1) processes the current and then transmits it to the current-voltage conversion circuit (2). The conversion circuit (2) converts the current into a voltage signal and transmits the voltage signal to the switching circuit (3). The switching circuit (3) transmits the voltage signal outputted by the conversion circuit (2) to the energy storage circuit. The voltage signal is sampled and held by the energy storage circuit and then outputted to the processor (4).

Abstract: An optoelectronic transceiver includes an optoelectronic transmitter, an optoelectronic receiver, memory, and an interface. The memory is configured to store digital values representative of operating conditions of the optoelectronic transceiver. The interface is configured to receive from a host a request for data associated with a particular memory address, and respond to the host with a specific digital value of the digital values. The specific digital value is associated with the particular memory address received form the host. The optoelectronic transceiver may further include comparison logic configured to compare the digital values with limit values to generate flag values, wherein the flag values are stored as digital values in the memory.

Abstract: A transponder having a dynamic remapping circuit remaps a value of decision threshold voltage Vdtc and a value of optical power RXP to a reference voltage Vref to minimize the bit error rate BER of a communication system. The dynamic remapping circuit implements a bilinear mapping of Vdtc and RXP to Vref with three bilinear remapping constants “a”, “b”, and “c” selected to align a remapped value of Vdtc_opt to a selected Vdtc normalization value, Vdtc_norm. A transponder in accord with an embodiment of the invention prevents BER from exceeding a threshold value of BER whether RXP or OSNR, or both, remain constant, change continuously, or change intermittently. Constants “a”, “b”, and “c” are related to parameters resulting from mathematically fitting a line to data comprising Vdtc_opt versus RXP. Another embodiment comprises a method for dynamically optimizing Vdtc and RXP to Vref in a transponder with a bilinear remapping circuit.

Abstract: Apparatus, systems and methods for separating a selected optical signal wavelength component from a plurality of optical signal wavelength components of an aggregate optical signal, and for passing the selected optical signal wavelength component while suppressing the remaining wavelength components are provided. Generally, the apparatus provides an optical signal wavelength selective element enabling output of a selectable optical signal wavelength component. The system contains a fiber optic cable carrying an optical signal, an optical signal measurement apparatus to measure optical signal characteristics, and an optical wavelength selector to pass the selected optical signal wavelength component to the optical signal measurement apparatus.

Abstract: The disclosure relates to optical fiber transmission systems, and in particular, pertains to the transceiver cards in an optical fiber transport system. In particular the disclosure teaches an improved transceiver card architecture that allows high density, flexibility and interchangeability of functionality.

Abstract: Monolithic single and/or dual detector structures are fabricated on the emitting surface of a VCSEL and/or on a lens or glass substrate configured to be positioned along the axis of emission of an optical light source. Each monolithic detector structure includes one or two PIN detectors fabricated from amorphous silicon germanium with carbon doping or amorphous germanium with hydrogen doping. The monolithic detectors may additionally include various metallization layers, buffer layers, and/or anti-reflective coatings. The monolithic detectors can be grown on 1550 NM VCSELs used in optical transmitters, including lasers with managed chirp and TOSA modules, to reduce power and real estate requirements of the optical transmitters, enabling the optical transmitters to be implemented in long-reach SFP+ transceivers.

Abstract: A channel alignment system in an optical communication network includes logic to sample power of a quadrature amplitude modulation (QAM) channel at a component downstream from a QAM modulator. The system determines if the sampled channel power has a sufficient level. The system signals power control logic of the QAM modulator to adjust a gain of the sampled channel.

Abstract: Provided is an automatic optical power control method for an optical line terminal (OLT) of a passive optical network (PON). The automatic optical power control method includes at the OLT, measuring an allowable range of the optical power allowing a normal network operation on the PON, at the OLT, setting an optimum optical signal level within the measured allowable range of the optical power, and at the OLT, adjusting a power level of a transmitter to the set optimum optical signal level. Accordingly, an appropriate power level can be selected depending on an optical distribution network (ODN) structure to drive the transmitter. Also, when the entire optical network units are deactivated, a laser of the transmitter is turned off to thereby minimize unnecessary power consumption at the OLT.

Abstract: Methods and systems for controlling power fluctuations in a network including a plurality of nodes are disclosed. A node in the network may be configured to modify power levels in accordance with either an active state or an inactive state. The node may transition to an inactive state in response to a power change that exceeds a power change threshold. The role of the node in controlling the power fluctuation in the network is reduced in the inactive state.

Abstract: An optical node may include a plurality of optical input components operable to receive a plurality of signals communicated in an optical network and a plurality of optical output components operable to transmit a plurality of signals to be communicated in the optical network.

Abstract: The present invention provides apparatus for self-phase modulation noise calculation, apparatus for self-phase modulation noise elimination and optical coherent receiver. The apparatus for calculation comprises: a signal receiver to receive an input signal; a calculator connected to the signal receiver to calculate a self-phase modulation noise at the current instant by using the signal powers of an input signal waveform at the current instant and at several sampling instants adjacent to the current instant. The embodiments of the present invention calculates the self-phase modulation noise at a certain instant by using the signal powers at a plurality of digital sampling periods before and after this instant, and when the apparatus is used to calculate the self-phase modulation noise of each of the sub-spans in an optical fiber transmission link, in case that the calculation precision is ensured, the granularity of the sub-spans may be reduced, thereby lowering the complexity of the calculation.

Abstract: Described is a method for controlling the wavelength of a laser in a wavelength division multiplexed (WDM) system. The method includes generating broadband light having a dithered optical power and a wavelength spectrum that includes a plurality of WDM wavelengths. The broadband light is spectrally filtered to generate a spectrally-sliced optical signal having a wavelength spectrum that includes one of the WDM wavelengths. The spectrally-sliced optical signal is injected into a laser and a dithered optical power of the laser is determined. A parameter of the laser is controlled in response to the determination of the dithered optical power to thereby align a wavelength of the laser to the wavelength spectrum of the spectrally-sliced optical signal.

Abstract: An optical access network (5) comprises optical network units (10) connected to a node (40). A monitoring unit (35) determines information indicative of energy consumption at the optical network unit (10) over a period of time. An optical network unit (10) can operate in operating states/modes which differ in their energy consumption. Monitoring unit (35) can determine the information by determining a time that an optical network unit spends in the different operating states/modes. Monitoring unit (35) can use a state machine (31) at the node (40) which represents the optical network unit (10). An optical network unit (10) can locally record time spent in states/modes and forward this to the monitoring unit (35). An optical network unit (10) can locally monitor energy consumption and forward this to the monitoring unit (35). An operational parameters of the access network (5) can be modified based on the information determined by the monitoring unit (35).

Abstract: The present disclosure relates to a high-speed and/or power-saving bi-directional transceiver. The transceiver generally includes a (burst) laser driver; an output power monitoring and indicating circuit; control logic (e.g., a microcontroller unit); bi-directional optics; a photodiode bias control circuit; a limiting amplifier; and a receiver optical power monitoring circuit. Optionally, the present transceiver includes a small form factor pluggable (SFP+) connector housing. In addition, the power-saving bi-directional transceiver generally includes a transmitter (TX) energy-saving circuit, a TX burst holding circuit, a receiver (RX) energy-saving circuit, a RX continuous holding circuit and the control logic.

Abstract: A method performed in an optical line terminal (OLT) in a passive optical network (PON) for detecting a rogue optical network unit (ONU) operating among a plurality of ONUs in the PON. The OLT receives a plurality of bursts of light from a plurality of ONUs, each burst being separated from other bursts by an inter-burst gap containing a minimum dark interval during which the OLT expects to receive no optical power. The OLT measures the received optical power during one or more of the minimum dark intervals of the inter-burst gaps and determines whether the inter-burst gaps were anomalous. In response to determining that an inter-burst gap was anomalous, the OLT increments an anomaly count that indicates a rogue ONU has been detected when the anomaly count exceeds an anomaly count threshold. When the anomaly count is exceeded, the OLT declares an alarm associated with the presence of a rogue ONU, and may also initiate rogue isolation diagnostics.

Abstract: A digital apparatus comprising a fast Fourier transform (FFT) module configured to transform a time domain optical signal into a frequency domain optical signal, a circular shifter coupled to the FFT module and configured to provide coarse frequency offset compensation to the frequency domain optical signal based on an estimated frequency offset; and a frequency offset estimation module coupled to the circular shifter and configured to provide the estimated frequency offset based on a power spectrum of the frequency domain optical signal or a data block header autocorrelation of the time domain optical signal.

Abstract: An optical system includes an optical integrator, a readout mechanism, and an optical thresholder. The optical integrator is configured to perform temporal integration of an optical input signal having a first wavelength received at an input. The readout mechanism is coupled to the optical integrator and provides optical signals having a second wavelength to the optical integrator for measuring a state of the optical integrator. The optical thresholder is coupled to an output of the optical integrator and is configured to receive a signal representing a temporal integration of the optical input signal from the optical integrator and produce an optical signal identifying if an amplitude of the signal representing the temporal integration of the optical input signal is above or below a threshold value.

Abstract: The embodiments of the present invention relate to communications technology, and disclose an optical power measurement method, an Optical Line Terminal (OLT), and an Optical Network Unit (ONU). The method includes: generating a Physical Layer Operation Administration Maintenance (PLOAM) message that includes an identifier of at least one ONU to be measured and information about a time bucket that is allocated to the ONU to be measured and is used for sending upstream optical signals; sending the PLOAM message to the multiple ONUs; receiving the upstream optical signals that are sent, in the allocated time bucket, by the ONU to be measured; and detecting the received upstream optical signals, and determining the optical power of the upstream optical signals. The present invention avoid waste of bandwidth caused in the prior art when the DBA is required to allocate bandwidth to the ONU to be measured for the purpose of detecting the optical power.

Abstract: An optical transmitting and receiving apparatus 1 has a transmitting circuit unit 20 including a light emitting element 2 and a driving circuit 3 which drives the light emitting element 2, a receiving circuit unit 30 including a light receiving element 5 and amplification circuit 6 which amplifies a signal received from the light receiving element 5, a judging unit 8 which judges an abnormality or failure of either or both of the transmitting circuit unit 20 and the receiving circuit unit 30 based on a measured data value provided from the transmitting circuit unit 20 and/or the receiving circuit unit 30, and a measured value storing unit 9 which stores the measure data value in the case that the judging unit 8 judges the abnormality or failure occurs in the transmitting circuit unit 20 and/or the receiving circuit unit 30.

Abstract: In a passive optical network, an upstream transmission rate from an ONT to an OLT can be optimized by matching a transmission scheme for a channel to the upstream transmission characteristics of the channel. An FEC coding can be made channel dependent so that channels with low error rates can use minimal protection, and therefore minimal overhead, while channels with high input bit error rates can use the level of FEC coding required to produce a desired output bit error rate.

Abstract: A general object of the present invention is to provide an optical communication system in which an optical transmission power of an optical communication apparatus is controlled to be a required minimum power that apparatuses of all subscribers in the optical communication system meet a prescribed error rate. An optical line terminating apparatus (OLT) transmits data to multiple optical network apparatuses (ONUs) at an optical intensity calculated based on information acquired from the multiple ONUs, which is related to optical intensities of signals that the multiple ONUs receive from the OLT, the optical intensity being calculated so that a minimum optical intensity of the optical intensities of the signals is greater than a predetermined value.

Abstract: The present invention relates to a light source and detecting device thereof includes: a housing; a printed circuit board; an optical fiber connector; a laser diode; a laser driving module; a light coupling device; a light detecting module; an analog-to-digital converter; a micro controlling device; a stroke switch and a displaying device; when the stroke switch is pressed, the light detecting module is activated according to a determination made by the micro controlling device then a light signal coupled by the light coupling device is detected by the light detecting module, then the signal is displayed on the displaying device after being converted by the analog-to-digital converter or the laser diode is driven by the laser driving module and a laser source is therefore emitted.

Abstract: The optoelectronic transceiver includes an optoelectronic transmitter, an optoelectronic receiver, memory, and an interface. The memory is configured to store digital values representative of operating conditions of the optoelectronic transceiver. The interface is configured to receive from a host a request for data associated with a particular memory address, and respond to the host with a specific digital value of the digital values. The specific digital value is associated with the particular memory address received form the host. The optoelectronic transceiver may further include comparison logic configured to compare the digital values with limit values to generate flag values, wherein the flag values are stored as digital values in the memory.

Abstract: Provided is a waveform reconstruction device capable of easily reconstructing an accurate time waveform of an optical signal without using an ultrafast time gate or a reference light source.

Abstract: A received optical signal is coherently demodulated and converted into electrical complex samples, which are dispersion compensated in a compensation filter. A control circuit calculates comparison values from corrected samples and an estimated error value. A plurality of compensation functions is applied according to a predetermined dispersion range and after a second iteration, the compensation filter is set to an optimum compensation function.

Abstract: Systems and methods for performing closed-loop diagnostics in optical transceiver. The TOSA of an optical receiver includes a primary transmit module and a secondary receiver module. The transmit module transmits a data signal to a ROSA of another optical transceiver. The ROSA has a secondary transmit module that can transmit a diagnostic data signal back to the secondary receiver module of the TOSA. The TOSA can use the diagnostic data received from the ROSA to automatically adjust itself and perform closed-loop feedback functions. The closed loop diagnostics can be implemented in a network where one transceiver may be connected with more than one other transceiver in a multi-node configuration.

Abstract: According to an aspect of an embodiment, a signal detector device includes a first monitor unit, a second monitor unit, and a discrimination unit, wherein the discriminator unit discriminates whether an inputted light includes a signal light on the bases of the first monitor unit for monitoring an intensity of the inputted light and the second monitor unit for monitoring an alternating current component intensity of the inputted light.

Abstract: A circuit controlling the gain of an amplifier in an optical transmitter used for optical communication, including a detection circuit for measuring the power of the RF input to a laser; a gain controller or controlling a gain of an amplifier, and a switch connected to the gain controller, wherein the gain controller is adapted, in response to an activation of a switch, to: (i) automatically vary gain of the amplifier, and (ii) set the gain of the amplifier at a level corresponding to a reduction in the noise and/or distortion associated with the transmitter.

Abstract: A WDM signal monitoring system includes a measuring unit that measures power levels in a plurality of predetermined wavelength bands about a wavelength division multiplex signal, a waveform determination unit that determines an approximate waveform of each channel from each bit rate and modulation system of a plurality of channels which forms a wavelength division multiplex signal, and an approximation unit that determines a power level and a wavelength of each channel by approximating the power level in a plurality of wavelength bands which the measuring unit measured with the approximate waveform of each channel which the waveform determination unit determined.

Abstract: An optical signal monitoring system includes a bit rate information collecting unit and a monitoring unit. The bit rate information collecting unit gets bit rate information indicating a bit rate of an optical signal passing through an optical communication path. The monitoring unit extracts a monitoring optical signal from the optical communication path. When the bit rate information is not able to get, the monitoring optical signal is judged to be a noise. This system can make a sharp distinction between a broad optical signal whose bit rate is over 40 Gbit/sec and the ASE noise. Further, this system can correct optical signals dependently to those bit rates.

Abstract: A system, apparatus and method are described for deployment of a control loop between optical or electro-optical modules and a multiplexing module to provide a desired power profile of banded optical channel groups. The power output characteristics of the optical or electro-optical modules, the properties of the transmission paths of the banded optical channel groups, and other factors may be analyzed to allow the control loop to achieve the desired power profile on the banded optical channel groups. The control loop may adjust the output power on the optical or electro-optical modules so that the banded optical channel groups are delivered to an optical component, such as an optical multiplexer or photo-detector, having a particular optical power profile.

Abstract: A wavelength division multiplex optical ring network comprises optical fibre (1-4) arranged in a ring configuration and a plurality of doped fibre optical amplifiers (17-20) arranged in the ring. The spectral response in the ring is configured such in use amplified spontaneous emission (ASE) noise circulates around the ring in a lasing mode to clamp the gain of each doped fibre optical amplifier. Each optical amplifier (17-20) includes respective control means (28) which in use control the optical amplifier to produce a substantially constant output power or to maintain a substantially constant pump power. In the event of loss of the lasing peak, detection means switches the doped fibre optical amplifiers to a different mode of gain control, for example, a mode to produce constant gain at the value before the loss of the lasing peak. Optionally, after a predetermined delay, the optical amplifiers may revert to constant output power or pump power mode.

Abstract: An algorithm is disclosed for performing alien-wavelength channel balancing on channels between optical network elements within an optic-fiber communications system. The algorithm determines initial values of various optimization parameters for each of the channels, such as the input launch power and operating conditions of optical amplifiers in the optical path, and calculates an initial total optimization offset for the channels based on the initial values of the optimization parameters for each of the channels. The algorithm then adjusts the optimization parameters to new values and calculates a new total optimization offset based on the new optimization parameter values. The algorithm repeats this process until the relative channel launch powers and optical amplifiers are optimized.

Abstract: The subject matter disclosed herein relates to determining a photosensor operating point.

Abstract: The present invention provides methods and systems for efficiently computing optimal optical launch powers for meshed optical networks. The present invention can be utilized to find optimal launch powers for multiple wavelengths in a meshed dense-wave division multiplexed (DWDM) system. Generally, the present invention ensures Q exceeds a threshold for OSNR, and then the launch powers are optimized based on nonlinear penalties. If Q is below the threshold, DWDM equipment changes/additions are incorporated to provide adequate OSNR. The present invention provides a computationally efficient mechanism to optimize launch powers in 10 Gb/s, 40 Gb/s, 100 Gb/s, etc. highly-meshed optical networks.

Abstract: An optical transceiver stores an output A/D value which is A/D-converted from reference voltage in an EEPROM as correction data in preparing the optical transceiver. The optical transceiver, receiving a request for outputting a monitored value from an external device connected therewith, calculates a variation based on difference between the output A/D value which is A/D-converted from the reference voltage at the timing when the request for outputting the monitored value is received and the correction data stored in the EEPROM. Then, the optical transceiver uses the calculated variation to convert current of light-input power which is input thereinto into voltage, amplify the voltage, and A/D-convert the voltage to thereby correct the output A/D value. The optical transceiver outputs the corrected A/D value to the connected external device as the monitored value.

Abstract: An algorithm is disclosed for performing channel balancing on channels between optical network elements within an optic-fiber communications system. The algorithm groups at least a portion of the channels into channel pairs, differentially adjusts the transmitter output power level of each of the channel pairs until the bit error ratio (BER) of at least one channel in each of the channel pairs exceeds a threshold, and records a respective power margin for each of the channels as the difference between the initial and final power levels. From the recorded power margins, a mean power margin is determined that is used to shift the transmitter output power level of each of the channels.

Abstract: A signal strength corresponding to an incoming optical burst from each of a plurality of optical nodes is measured. The measurements can be performed at system start-up, configuration/installation of the optical nodes and/or at certain intervals of operation of the optical nodes. Signal strength information for the optical nodes based on the measurements is stored in memory. When scheduling the optical nodes for transmission, a preferred transmission order is determined in response to the stored signal strength information. In an embodiment, the preferred order is determined to reduce differences in signal strength levels between consecutive optical bursts.

Abstract: When a neighbor ONU receives a signal with light intensity high enough to secure communication between an OLT and a remote ONU, the light intensity may be excessively high to damage a receiver of the neighbor ONU. In order to avoid such a problem, each ONU is notified of a downstream signal transmission plan (downstream light intensity map) prior to transmission of a downstream signal. Each ONU receives the downstream light intensity map (light intensity transmission schedule of downstream signal) in advance. Thus, the neighbor ONU can block or attenuate an optical signal addressed to the remote ONU, and the remote ONU can determine normal operation even when the remote ONU cannot receive a signal addressed to the neighbor ONU. Thus, the remote ONU can be prevented from issuing a wrong error signal.

Abstract: Methods and apparatus for control of variable optical attenuators are described. A method for control of a variable optical attenuator located in an optical link comprising a plurality of optical attenuators. The method comprises determining that an initial calibration step of a variable optical attenuator has been completed, and transmitting a signal indicative of the variable optical attenuator having completed the initial calibration step for receipt by a downstream variable optical attenuator. A method of controlling a variable optical attenuator comprises receiving a signal indicative of an upstream variable optical attenuator having completed an initial calibration step, and initiating calibration of the variable optical attenuator in response to receipt of said signal.