Patent Description:
This section introduces aspects that may help facilitate a better understanding of the disclosure.

A fiber-optic system typically employs an optical transmitter at one end of a fiber and an optical receiver at the other end of the fiber. Some fiber-optic systems operate by transmitting in one direction on one fiber and in the opposite direction on another fiber to achieve full duplex (FDX) operation. An FDX system can be implemented using optical transceivers, with an optical transceiver being an electro-optical subsystem that includes a respective optical transmitter and a respective optical receiver, typically integrated in a manner that supports the intended function. The telecom industry and its suppliers develop, manufacture, sell, and use a large variety of optical transceivers for many different applications.

<CIT> discloses a method and an apparatus to control an optical receiver using Bit Error Rate (BER). The apparatus comprises a transmitter with Forward Error Correction encoding (FEC) and a receiver system including a FEC decoder and a controller. The transmitter accepts a feedback signal in order to vary the output power. Depending on the BER calculated by the FEC decoder, the controller transmits the feedback signal to the transmitter.

<CIT> discloses an optical transmission system comprising an optical transmitter, an optical receiver and a BER estimator. The BER estimator provides the BER to the optical transmitter and/or the optical receiver in order to optimize the performance of the transmission system by adjusting transmission characteristics such as output power level.

<CIT> discloses an optical transmission system comprising a dispersion compensating device. In one embodiment, the optical transmission system comprises two transmission/reception terminal nodes linked by a transmission line. The destination terminal node measures a transmission dispersion and transmits it to the source terminal node. In another embodiment, the optical transmission system comprises a receiver transmitting wavelength control information relative to a target dispersion to a transmitter. The receiver also comprises a performance acquiring unit measuring BER, Q-value information and transmits this performance information through an Optical Supervisor Channel light or in a main signal light to a wavelength control unit located in the source node.

Disclosed herein are various embodiments of an optical transceiver capable of optimizing the performance of the corresponding optical channel by dynamically adjusting the optical power of the output signal in response to the FEC-performance data received from the corresponding remote transceiver. In an example embodiment, the FEC-performance data can be exchanged by the two optical transceivers using a dedicated field in the overhead of the transmitted data frames. The power-adjustment process is configured to be relatively slow to prevent the occurrence of transients on other optical channels and ensure stable operation of the corresponding WDM system as a whole, while different transceivers thereof are allowed to adjust their respective output powers in an autonomous way and independent of each other. The performance optimization can be directed at meeting a predefined performance target specified by the system designer or operator while driving the operating point away from conditions under which nonlinear optical effects may become relatively prominent.

According to an example embodiment, provided is an apparatus comprising an optical data receiver, an optical data transmitter, and an electronic controller connected therebetween, the optical data receiver including a photodetector configured to detect an optical input signal carrying a first data frame, the optical data transmitter including a laser configured to generate a carrier wavelength for an optical output signal; wherein the optical data receiver comprises a frame decoder configured to read a first value of a measure of transmission quality from the first data frame, the measure of transmission quality representing an error rate at which an FEC code used at a remote receiver encounters errors in data transmitted using the optical output signal; and wherein the electronic controller is configured to change an optical output power of the laser in response to the first value of the measure of transmission quality provided thereto by the frame decoder.

According to another example embodiment, provided is an apparatus comprising an optical data receiver, an optical data transmitter, and an electronic controller connected therebetween, the optical data receiver including a photodetector configured to detect an optical input signal carrying a first data frame, the optical data transmitter including a laser configured to generate a carrier wavelength for an optical output signal carrying a second data frame; wherein the optical data receiver comprises a frame decoder configured to count a number of errors corrected in the first data frame using an FEC data block thereof; wherein the electronic controller is configured to compute a first value of a measure of transmission quality using the number of errors counted by the frame decoder; and wherein the optical data transmitter comprises a frame generator configured to write the first value of the measure of transmission quality into the second data frame.

According to yet another example embodiment, provided is a communication method carried out at an optical transceiver, the method comprising the steps of: receiving an optical input signal carrying a first data frame; decoding the first data frame to read a first value of a measure of transmission quality from the first data frame, the measure of transmission quality representing an error rate at which an FEC code used at a remote receiver encounters errors in data received from the optical transceiver; and changing an optical output power of a laser in response to the first value of the measure of transmission quality, the laser being configured to generate a carrier wavelength for an optical output signal directed to the remote receiver.

Other aspects, features, and benefits of various disclosed embodiments will become more fully apparent, by way of example, from the following detailed description and the accompanying drawings, in which:.

<FIG> shows a block diagram of an optical communication system <NUM> according to an embodiment. System <NUM> comprises wavelength-division-multiplexing (WDM) transceivers <NUM>W and <NUM>E connected using a fiber-optic link <NUM>. For illustration purposes and to simplify the description, WDM transceivers <NUM>W and <NUM>E are referred-to herein as being located at the West and East ends, respectively, of link <NUM>. This notation should not be interpreted to imply any preference or limitation with respect to the geo-positioning of system <NUM>.

In some embodiments, system <NUM> complies with the ITU-T G. <NUM> Recommendation.

In an example embodiment, link <NUM> can be implemented using two or more optical fibers, e.g., including fibers <NUM>W and <NUM>E, with at least one fiber per propagation direction. As indicated in <FIG>, fiber <NUM>W is configured to transmit Eastward-propagating optical signals, whereas fiber <NUM>E is configured to transmit Westward-propagating optical signals. In addition, link <NUM> typically has optical amplifiers <NUM>W and <NUM>E. Each of optical amplifiers <NUM>W is connected between two respective sections of fiber <NUM>W. Each of optical amplifiers <NUM>E is similarly connected between two respective sections of fiber <NUM>E.

In some embodiments, link <NUM> may comprise an undersea cable system that includes, inter alia, submersible optical repeaters, each including at least one optical amplifier <NUM>E and at least one optical amplifier <NUM>W. Link <NUM> may also incorporate additional optical elements (not explicitly shown in <FIG>), such as optical splitters, combiners, couplers, switches, etc., as known in the pertinent art.

In an example embodiment, an optical amplifier <NUM> can be implemented as known in the pertinent art, e.g., using an erbium-doped fiber, a gain-flattening filter, and one or more laser-diode pumps. The number of optical amplifiers <NUM> used in optical link <NUM> depends on the particular embodiment and may be in the range, e.g., from <NUM> to -<NUM>. A typical length of the span of fiber <NUM>W or <NUM>E between two adjacent optical amplifiers <NUM> may range from -<NUM> to -<NUM>.

In some embodiments, link <NUM> may not have any optical amplifiers <NUM> therein.

In an example embodiment, WDM transceivers <NUM>W and <NUM>E are configured to use carrier wavelengths λ<NUM>-λN arranged on a frequency (wavelength) grid, such as a frequency grid that complies with the ITU-T G. <NUM> Recommendation. The frequency grid used in system <NUM> can be defined, e.g., in the frequency range from about <NUM> THz to about <NUM> THz, with a <NUM>, <NUM>, <NUM>, or <NUM>-GHz spacing of the channels therein. While typically defined in frequency units, the parameters of the grid can equivalently be expressed in wavelength units. For example, in the wavelength range from about <NUM> to about <NUM>, the <NUM>-GHz spacing between the centers of neighboring WDM channels is equivalent to approximately <NUM> spacing. In alternative embodiments, other suitable frequency grids (e.g., flexible or having other spacing grids) can also be used.

In some embodiments, the set of carrier wavelengths used for generating Eastward-propagating optical WDM signals may be different from the set of carrier wavelengths used for generating Westward-propagating optical WDM signals.

In some embodiments, system <NUM> can be configured to transport polarization-division-multiplexed (PDM) signals, wherein each of the two orthogonal polarizations of each optical WDM channel can be used to carry a different respective data stream.

In an example embodiment, WDM transceiver <NUM>W comprises N individual-channel transceivers <NUM>1W-<NUM>NW, where the number N is an integer greater than one. Each of transceivers <NUM>1W-<NUM>NW comprises a respective optical transmitter (not explicitly shown in <FIG>; see <FIG>) configured to generate a respective WDM component of the Eastward-propagating optical WDM signal using a different respective carrier wavelength (e.g., one of wavelengths λ<NUM>-λN, as indicated in <FIG>). A multiplexer/demultiplexer (MUX/DMUX) <NUM>W operates to combine these WDM components, thereby generating the corresponding Eastward-propagating optical WDM signal that is applied to fiber <NUM>W for transmission to WDM transceiver <NUM>E. Along the propagation path, this WDM signal is amplified using optical amplifiers <NUM>W.

Each of transceivers <NUM>1W-<NUM>NW further comprises a respective optical receiver (not explicitly shown in <FIG>; see <FIG>) configured to detect and decode a respective WDM component of the Westward-propagating optical WDM signal received by way of fiber <NUM>E from WDM transceiver <NUM>E. Along the propagation path, the Westward-propagating optical WDM signal is amplified using optical amplifiers <NUM>E. MUX/DMUX <NUM>W operates to separate the WDM components of the received Westward-propagating optical WDM signal, thereby generating optical input signals for the optical receivers of the individual-channel transceivers <NUM>1W-<NUM>NW.

In an example embodiment, MUX/DMUX <NUM>W can be implemented as known in the pertinent art, e.g., using one or more of the following: (i) a wavelength-selective optical filter; (ii) a wavelength-selective switch; (iii) a diffraction grating; (iv) an array of micro-mirrors; (v) a MEMS device; and (vi) an LCoS filter or modulator. Herein, the acronym "MEMS" refers to micro-electro-mechanical systems; and the acronym "LCoS" refers to liquid crystal on silicon.

In an example embodiment, WDM transceiver <NUM>E is constructed using components similar to those of WDM transceiver <NUM>W and configured to operate in a similar manner. A description of WDM transceiver <NUM>E can therefore be obtained from the above description of WDM transceiver <NUM>W, e.g., by interchanging the subscripts E and W.

Descriptions of the example structure and operation of an individual-channel transceiver <NUM> are given below in reference to <FIG>. In the embodiment shown in <FIG>, each of WDM transceivers <NUM>W and <NUM>E comprises a respective plurality of such nominally identical transceivers <NUM>. A person of ordinary skill in the art will understand that other suitable compositions of WDM transceivers <NUM>W and <NUM>E may also be used in some alternative embodiments.

<FIG> shows a block diagram of an optical transceiver <NUM> that can be used in system <NUM> (<FIG>) according to an embodiment. Transceiver <NUM> comprises an optical transmitter <NUM>, an electronic controller <NUM>, and an optical receiver <NUM> interconnected as indicated in <FIG>. Transmitter <NUM> is configured to generate a modulated optical signal <NUM> having encoded thereon client data <NUM>. Modulated optical signal <NUM> is applied to MUX/DMUX <NUM> for coupling into link <NUM> (see <FIG>) as a component of the corresponding output WDM signal. Receiver <NUM> is configured to receive a modulated optical signal <NUM> having encoded thereon client data <NUM>. Modulated optical signal <NUM> is applied to receiver <NUM> by MUX/DMUX <NUM> in response to receiving the corresponding input WDM signal from link <NUM> (see <FIG>).

Transmitter <NUM> comprises a transmitter optical front end (Tx OFE) <NUM> interfaced with a digital transmit chain <NUM>. In operation, digital transmit chain <NUM> generates an electrical output signal <NUM> configured to drive OFE <NUM> in a manner that causes the resulting modulated optical signal <NUM> to carry, inter alia, client data <NUM>. OFE <NUM> comprises a laser <NUM> configured to generate an optical carrier wave for the modulated optical signal <NUM>, the generated optical carrier wave having one of wavelengths λ<NUM>-λN (see <FIG>). The optical output power of laser <NUM> can be changed using a control signal <NUM> generated by controller <NUM>, e.g., as described further below.

In an example embodiment, OFE <NUM> may include (i) an optical modulator (not explicitly shown in <FIG>) configured to generate the modulated optical signal <NUM> by modulating the optical carrier wave generated by laser <NUM> and (ii) a driver circuit (not explicitly shown in <FIG>) configured to electrically drive the optical modulator in response to electrical signal <NUM>. Depending on the embodiment, the optical modulator used in OFE <NUM> can be implemented using one or more optical IQ modulators, Mach-Zehnder modulators, amplitude modulators, phase modulators, and/or intensity modulators. In some embodiments, laser <NUM> can be a directly modulated laser, e.g., a laser diode configured to generate the modulated optical signal <NUM> in response to modulated electrical currents directly applied thereto by the corresponding driver circuit. Driver circuits for electrically driving the various optical modulators and/or directly modulated lasers that may be used in various embodiments of OFE <NUM> for the above-described purposes are known to those skilled in the pertinent art.

In an example embodiment, digital transmit chain <NUM> comprises a plurality of processing modules, only one of which, i.e., a frame generator <NUM>, is explicitly shown in <FIG> for clarity. Additional processing modules (not explicitly shown in <FIG>) that can be used in digital transmit chain <NUM> are known to persons skilled in the pertinent art and may be implemented using digital circuits conventionally used for these purposes.

In an example embodiment, frame generator <NUM> is configured to perform at least some of the following:.

<FIG> explicitly shows only two processing sub-modules (see reference numerals <NUM> and <NUM> in <FIG>) of frame generator <NUM>, which correspond to the above-listed processing step (D). For example, sub-module <NUM> is configured to insert the OTU overhead into the appropriate fields of the corresponding ODU. Sub-module <NUM> is configured to apply an FEC code to the (entire) ODU to generate the corresponding FEC data block, which is then appended to the ODU, thereby extending the latter to form the OTU (also see <FIG>). A person of ordinary skill in the art will understand how to make and use other constituent sub-modules of frame generator <NUM>, e.g., those corresponding to the above-listed processing steps (A)-(C).

Digital transmit chain <NUM> typically comprises additional modules (not explicitly shown in <FIG>) that are known to persons skilled in the pertinent art and conventionally used in such digital transmit chains.

Receiver <NUM> comprises a receiver optical front end (Rx OFE) <NUM> interfaced with a digital receive chain <NUM>. OFE <NUM> comprises a photodetector (PD) <NUM> and operates to convert the received modulated optical signal <NUM> into a corresponding electrical signal <NUM>. Digital receive chain <NUM> then processes electrical signal <NUM> to recover client data <NUM> encoded in the received modulated optical signal <NUM>.

In some embodiments, OFE <NUM> is an optical demodulator that can be configured as known in the pertinent art for coherent (e.g., intradyne or homodyne) detection of signal <NUM>. In such embodiments, OFE <NUM> may also include: (i) an optical local-oscillator (LO) source; and (ii) an optical hybrid configured to optically mix signal <NUM> and the LO signal generated by the optical LO source. In such embodiments, photodetector <NUM> is configured to convert the optical interference signals generated by the optical hybrid into the corresponding sub-signals of electrical signal <NUM>.

In some other embodiments, OFE <NUM> is an optical demodulator that can be configured for direct (e.g., square law, intensity) detection of signal <NUM>. In such embodiments, photodetector <NUM> is configured to generate electrical signal <NUM> to be proportional to the intensity (optical power, squared amplitude of the electric field) of signal <NUM>.

In an example embodiment, digital receive chain <NUM> comprises a plurality of processing modules, only one of which, i.e., a frame decoder <NUM>, is explicitly shown in <FIG> for clarity. Additional processing modules (not explicitly shown in <FIG>) that can be used in digital receive chain <NUM> are known to persons skilled in the pertinent art and may be implemented using digital circuits conventionally used for these purposes.

In an example embodiment, frame decoder <NUM> is configured to perform at least some of the following:.

<FIG> explicitly shows only two processing sub-modules (see reference numerals <NUM> and <NUM> in <FIG>) of frame decoder <NUM>, which correspond to the above-listed processing steps (F) and (G). For example, sub-module <NUM> is configured to count the number of errors that have been corrected in the (entire) OTU using the FEC data block thereof and provide the resulting error count, by way of a control signal <NUM>, to controller <NUM>. Sub-module <NUM> is configured to extract information from at least some fields of the OTU overhead and provide the extracted information, by way of a control signal <NUM>, to controller <NUM>. A person of ordinary skill in the art will understand how to make and use other constituent sub-modules of frame decoder <NUM>, e.g., those corresponding to the processing steps (E) and (H)-(J).

Controller <NUM> operates to generate control signal <NUM> for laser <NUM> in response to control signal <NUM> received from frame decoder <NUM>. Controller <NUM> further operates to generate a control signal <NUM> in response to control signal <NUM>. Frame generator <NUM> then operates to insert at least some of the information received by way of control signal <NUM> into the OTU overhead of the outgoing data frame. Example operating methods that can be implemented in controller <NUM> for these and other purposes are described in more detail below in reference to <FIG>.

<FIG> pictorially show a frame structure that can be used in system <NUM> (<FIG>) and by transceiver <NUM> (<FIG>) according to an example embodiment. The shown frame structure complies with the above-cited ITU-T G. <NUM> Recommendation. A person of ordinary skill in the art will understand that other suitable frame structures may similarly be used in alternative embodiments of system <NUM>.

<FIG> pictorially shows an optical data unit ODUk that can be generated by frame generator <NUM> using the above-listed processing steps (A)-(C). The data of optical data unit ODUk are organized in <NUM> columns and four rows, with each position containing one byte of data.

<FIG> pictorially shows an optical transport unit OTUk that can be generated by frame generator <NUM> using the above-listed processing step (D). The frame structure of optical transport unit OTUk is based on the frame structure of optical data unit ODUk which is extended to contain <NUM> additional columns for an OTUk FEC data block <NUM>. An OTU overhead OTU OH is located in row <NUM>, columns <NUM> to <NUM>, of optical data unit ODUk. The overhead bytes in row <NUM>, columns <NUM> to <NUM>, of OTU overhead OTU OH are used for the frame-alignment overhead, which is labeled in <FIG> as FA OH. The overhead bytes in row <NUM>, columns <NUM> to <NUM>, of OTU overhead OTU OH are used for the OTUk-specific overhead, which is labeled in <FIG> as OTUk OH.

In various embodiments, the FEC code used for generating the OTUk FEC data block <NUM> can be an FEC code specified in the above-cited ITU-T G. <NUM> Recommendation or any other suitable (e.g., proprietary) FEC code.

<FIG> pictorially shows a more-detailed (expanded) view of the OTU overhead OTU OH. Columns <NUM> to <NUM> of OTU OH are configured to carry a frame alignment signal FAS. Column <NUM> of OTU OH is configured to carry a multi-frame alignment signal MFAS. Columns <NUM> to <NUM> of OTU OH are configured to carry an overhead corresponding to the general communication channel GCC0. Columns <NUM> and <NUM> of OTU OH are configured to carry an overhead RES, which is reserved for proprietary use and future standardization. A more-detailed description of the various bytes of the OTU overhead OTU OH shown in <FIG> can be found, e.g., in the above-cited ITU-T G. <NUM> Recommendation.

In an example embodiment, at least one byte (e.g., column <NUM>) of overhead RES can be used to carry a binary value that represents the error count determined by frame decoder <NUM> at the above-listed processing step (F). The manner in which this binary value can be computed and used by controller <NUM> is described in more detail below in reference to <FIG>.

<FIG> graphically illustrates example performance characteristics of system <NUM> according to an embodiment. More specifically, a curve <NUM> in the graph of <FIG> represents an example dependence of the quality factor Q<NUM> measured at the optical receiver <NUM> of a transceiver <NUM> located at one (e.g., West) end of link <NUM> as a function of output optical power of laser <NUM> of the corresponding transceiver <NUM> located at the other (e.g., East) end of link <NUM>. Curve <NUM> has a maximum at the output power PNL. At the optical power levels that are below PNL, the quality factor Q<NUM> generally increases with an increase of the laser output power. At the optical power levels that are above PNL, the quality factor Q<NUM> generally decreases with an increase of the laser output power, primarily due to the increasing detrimental contributions of nonlinear optical effects in link <NUM>.

Target characteristics of a transmitter/receiver pair that communicate with one another over link <NUM> can be specified using a range of the quality-factor values located between Q<NUM>L and Q<NUM>U, where Q<NUM>L is the lower limit of the range, and Q<NUM>U is the upper limit of the range. Typically, the values of Q<NUM>L and Q<NUM>U are the design and/or configuration parameters of system <NUM> that may be selected and/or specified by the system operator based on the intended use of the system. Once selected, the values of Q<NUM>L and Q<NUM>U can be stored in controller <NUM> for further use in the pertinent algorithms and/or protocols employed, e.g., for configuring transceiver <NUM> for optimal performance as described in reference to <FIG>.

In some embodiments, the values of Q<NUM>L and Q<NUM>U can be made applicable to multiple carrier wavelengths (optical WDM channels). In some embodiments, a different respective pair of Q<NUM>L and Q<NUM>U can be specified for each carrier wavelength (e.g., managed on a per-channel basis). In some embodiments, the Q<NUM>L and/or Q<NUM>U values can be made dependent on some other system-configuration parameters, such as the modulation format, the type of the used FEC code, the FEC-code rate, etc..

A person of ordinary skill in the art will understand that the use of the quality factor Q<NUM> represents only one of many possible ways of specifying and/or attaining a desired (e.g., optimal) configuration of system <NUM>. For example, in an alternative embodiment, the optical signal-to-noise ratio (OSNR) or the bit error rate (BER) can similarly be used. In some embodiments, other suitable measures of transmission quality can alternatively be used.

The BER is the most-direct indicator of the transmission quality. For example, due to the adverse effects of noise, nonlinearities, and dispersion, the waveforms of optical signals coupled into fibers typically become distorted when those optical signals arrive at the remote end of the fiber-optic link, such as link <NUM>. As a result, bit errors are typically present when the receiver converts the optical signals into the corresponding electrical signals and then decodes the latter. A greater number of pre-FEC bit errors is therefore an indication of the poorer transmission quality, and vice versa. The quality factor Q<NUM> and BER have a one-to-one correspondence that can be expressed, e.g., as follows:
(<NUM>).

The OSNR is the ratio of the signal power to the noise power within a valid bandwidth. At power levels below PNL (see <FIG>), the changes of the OSNR and of the Q value expressed in decibel are approximately linearly proportional to one another. Eq. (<NUM>) gives the expression that can be used to convert the quality factor Q<NUM> into the Q value expressed in decibel, e.g., for relating the latter to the OSNR:
(<NUM>).

In an example embodiment, Eqs. (<NUM>)-(<NUM>) can be used to program controller <NUM> to interconvert various possible quantitative measures of the end-to-end transmission performance of a wavelength channel in system <NUM>.

As used herein below, the term "measure of transmission quality" should be construed to cover each and any of: (i) the quality factor Q<NUM>; (ii) the Q value expressed in decibel; (iii) the BER, e.g., expressed as the number of FEC-code-corrected errors per data frame; and (iv) the OSNR. These quantities can be inter-converted, e.g., in the above-explained manner. Furthermore, the term "measure of transmission quality" should also be construed to cover any other value or quantity that can be unambiguously mapped onto any one of those parameters. One or more of such "measures of transmission quality" (e.g., one per carrier wavelength, per transmission direction) can be used to configure and operate various embodiments of system <NUM>, e.g., as further explained below.

<FIG> shows a flowchart of a communication method <NUM> that can be used in transceiver <NUM> (<FIG>) according to an embodiment. For illustration purposes and without any implied limitations, method <NUM> is described in reference to the frame format shown in <FIG>. A person of ordinary skill in the art will understand that other suitable frame formats may similarly be used.

At step <NUM> of method <NUM>, receiver <NUM> (<FIG>) operates to receive an optical input signal <NUM> carrying a first data frame transmitted by the corresponding remote transceiver <NUM> (also see <FIG>).

At step <NUM>, frame decoder <NUM> of receiver <NUM> processes the first frame to recover the corresponding client data <NUM> encoded therein. This processing includes using the operative FEC code and the FEC data block <NUM> (see <FIG>) of the first data frame to correct errors (if any) in the first data frame. This processing further includes reading information from the various overhead fields, such as the fields of OTU OH (<FIG>).

At step <NUM>, sub-module <NUM> of frame decoder <NUM> counts the number of errors that have been corrected using the FEC code at step <NUM>. Frame decoder <NUM> then provides the FEC error count, by way of control signal <NUM>, to controller <NUM>.

At step <NUM>, controller <NUM> generates control signal <NUM> in response to the control signal <NUM> of step <NUM>. More specifically, controller <NUM> generates control signal <NUM> in a manner that causes this control signal to carry a measure of transmission quality corresponding to the FEC error count of step <NUM>. As already indicated above, the measure of transmission quality may be any one of the quality factor Q<NUM>, the Q value expressed in decibel, the BER, the OSNR, or any other suitable quantity.

For example, in an embodiment in which such measure of transmission quality is not the same as BER, controller <NUM> may be configured to: (i) convert the FEC error count of step <NUM> into the corresponding BER value, e.g., as known in the art; and (ii) convert the latter BER value into the corresponding measure of transmission quality, e.g., as explained above in reference to <FIG> and/or Eqs. (<NUM>)-(<NUM>).

At step <NUM>, frame generator <NUM> of transmitter <NUM> generates a second data frame using the corresponding client data <NUM> and the measure of transmission quality provided thereto by control signal <NUM> generated at step <NUM>. For example, step <NUM> may include a sub-step of writing the provided measure of transmission quality into the designated field of OTU OH, such as the overhead RES (see <FIG>) of the second data frame, said writing being performed using sub-module <NUM> of frame generator <NUM>. Step <NUM> may also include a sub-step of generating the FEC data block <NUM> (see <FIG>) for the second data frame using the operative FEC code.

At step <NUM>, sub-module <NUM> of frame decoder <NUM> reads the measure of transmission quality from the designated field of OTU OH, such as the overhead RES (see <FIG>) of the first data frame. Frame decoder <NUM> then provides this measure of transmission quality, by way of control signal <NUM>, to controller <NUM>.

At step <NUM>, controller <NUM> generates control signal <NUM> in response to the control signal <NUM> of step <NUM>. More specifically, controller <NUM> operates to generate control signal <NUM> that is configured to cause laser <NUM> of transmitter <NUM> to set (e.g., change) its optical output power based on the measure of transmission quality provided at step <NUM>. Example embodiments of the sub-step of setting the optical output power of laser <NUM> that can be used to implement step <NUM> are described below in reference to <FIG>.

At step <NUM>, transmitter <NUM> uses the optical power set at step <NUM> to generate an optical output signal <NUM> carrying the second data frame generated at step <NUM>. Transmitter <NUM> then operates to transmit the optical output signal <NUM> generated in this manner to the corresponding remote transceiver <NUM> (also see <FIG>).

<FIG> shows a flowchart of a control method <NUM> that can be used in transceiver <NUM> (<FIG>) according to an embodiment. For illustration purposes and without any implied limitations, method <NUM> is described in reference to an embodiment in which the measure of transmission quality is the quality factor Q<NUM>. Based on the provided description, a person of ordinary skill in the art will be able to make and use other embodiments, in which the measure of transmission quality is different from the quality factor Q<NUM>. Method <NUM> can be used in conjunction with method <NUM>.

Method <NUM> is generally directed at setting the output optical power of laser <NUM> in the local transmitter <NUM> such that (i) the output optical power is smaller than PNL and (ii) the corresponding remote receiver <NUM> is placed into an operating regime characterized by the quality factor Q<NUM> whose value is between the values of Q<NUM>L and Q<NUM>U (also see <FIG>). As already indicated above, the values of Q<NUM>L and Q<NUM>U are the design and/or configuration parameters and, as such, have fixed values for the purposes of method <NUM>. The threshold power PNL is a system characteristic that can be determined within method <NUM>, e.g., by appropriately analyzing the history of its execution generated and stored in the memory as explained in more detail below.

Method <NUM> starts at step <NUM> during which the corresponding transceiver <NUM> is turned on, booted up, and brought online.

Step <NUM> is configured to direct the processing of method <NUM> along two different processing paths depending on the encountered situation. More specifically, for the first install of transceiver <NUM>, the processing of method <NUM> is directed to step <NUM>. Otherwise, the processing of method <NUM> is directed to step <NUM>. In the latter case, step <NUM> is performed after the completion of step <NUM>.

An example embodiment of step <NUM> is described in reference to <FIG>.

<FIG> shows a flowchart of step <NUM> according to an embodiment. During the power-adjustment process of step <NUM>, controller <NUM> may store the history of its execution in a memory. In an example embodiment, each entry in the history may include the optical output power of laser <NUM> and the resulting value of the quality factor Q<NUM> obtained at the remote receiver <NUM> and communicated back to controller <NUM>, e.g., using method <NUM> (<FIG>). The stored history can be used, e.g., to determine if an optimum configuration has been passed or missed during the power-adjustment process of step <NUM>.

Sub-step <NUM> is configured to direct the processing of step <NUM> along two different processing paths depending on whether or not the overhead of the incoming data frame contains a quality-factor (QF) value. If the corresponding remote receiver <NUM> has included a QF value in the frame overhead, then the processing of step <NUM> is directed to sub-step <NUM>. Otherwise, the processing of step <NUM> is directed to sub-step <NUM>.

Sub-steps <NUM>, <NUM>, and <NUM> are configured to direct the processing of step <NUM> along different processing paths depending on (i) the result of the comparison of the received QF value with the values of Q<NUM>L and Q<NUM>U and (ii) the result of the comparison of the corresponding output optical power of laser <NUM> with the threshold power PNL.

If the received QF value is greater than Q<NUM>U, then the processing of step <NUM> is directed to sub-step <NUM>. Otherwise, the processing of step <NUM> is directed to sub-step <NUM>.

If the received QF value is smaller than Q<NUM>L, and if the corresponding output optical power of laser <NUM> is greater than the threshold power PNL, then the processing of step <NUM> is directed to sub-step <NUM>.

If the received QF value is smaller than Q<NUM>L, and if the corresponding output optical power of laser <NUM> is smaller than the threshold power PNL, then the processing of step <NUM> is directed to sub-step <NUM>.

If the received QF value is between the values of Q<NUM>L and Q<NUM>U, then the processing of step <NUM> is directed to sub-step <NUM>.

At sub-step <NUM>, controller <NUM> concludes that the output optical power of laser <NUM> is at an acceptable level, and proceeds to generate control signal <NUM> such that the output optical power of laser <NUM> remains unchanged.

An example embodiment of sub-step <NUM> is described in reference to <FIG>.

<FIG> shows a flowchart of sub-step <NUM> according to an embodiment.

At sub-step <NUM> of sub-step <NUM>, it is determined whether or not the output optical power of laser <NUM> is set to Pref. If yes, then the processing of sub-step <NUM> is terminated. Otherwise, the processing of sub-step <NUM> is directed to sub-step <NUM>.

In an example embodiment, Pref is a fixed reference power. The value of Pref is a design parameter that defines the maximum power to be used while a QF value is not yet delivered from the corresponding remote transceiver <NUM> on the received data frame(s).

At sub-step <NUM>, it is determined whether or not the output optical power of laser <NUM> is set to a last valid value of the output optical power. If yes, then the processing of sub-step <NUM> is terminated. Otherwise, the processing of sub-step <NUM> is directed to sub-step <NUM>.

In an example embodiment, the term "last valid value" refers to a recent output optical power that resulted in a QF value within the target range, i.e., between the values of Q<NUM>L and Q<NUM>U. A last valid value is typically stored in the memory of controller <NUM> and can be retrieved therefrom.

At sub-step <NUM>, controller <NUM> operates to generate control signal <NUM> such that the output optical power of laser <NUM> is increased by a relatively small increment. In an example embodiment, the increment can be determined as a fixed percentage of the difference between Pref and the present output optical power of laser <NUM>. After the execution of sub-step <NUM>, the processing of sub-step <NUM> is terminated.

<FIG> shows a flowchart of sub-step <NUM> according to an embodiment. The power adjustment process corresponding to sub-step <NUM> is generally directed at gradually shifting the operating point along curve <NUM> toward a portion <NUM> of the curve located between the values of Q<NUM>L and Q<NUM>U at the power levels that are below the threshold power PNL (see <FIG>). As used herein the term "gradually" refers to relatively small incremental changes that do not perturb too much the operation of other transceivers <NUM> transmitting in the same direction through link <NUM> on other carrier wavelengths. A person of ordinary skill in the art will understand that gradual changes are typically needed to maintain the overall operating stability of the corresponding WDM transceiver <NUM> in which individual transceivers <NUM> are configured for independent power adjustment using methods <NUM> and <NUM>.

At sub-step <NUM> of sub-step <NUM>, controller <NUM> operates to generate control signal <NUM> such that the output optical power of laser <NUM> is decreased by a relatively small increment. In an example embodiment, the increment value can be a fixed parameter.

At sub-step <NUM>, it is determined whether or not the overhead of the incoming data frame contains a QF value corresponding to the decreased output optical power that was set at sub-step <NUM>. If the corresponding remote receiver <NUM> has included such a QF value in the frame overhead, then the processing of sub-step <NUM> is directed to sub-step <NUM>. Otherwise, the processing of sub-step <NUM> is directed to sub-step <NUM>, a copy of which is incorporated into the processing flow as shown in <FIG> (also see <FIG>).

At sub-step <NUM>, the QF value is read from the overhead of the received data frame. Controller <NUM> then generates a corresponding entry for the history stored in the memory. This entry contains (i) the QF value read from the overhead of the received data frame and (ii) the corresponding output optical power of laser <NUM> that was set at sub-step <NUM>.

At sub-step <NUM>, it is determined whether or not the output optical power of laser <NUM> that was set at sub-step <NUM> is below the threshold power PNL. If yes, then the processing of sub-step <NUM> is terminated. Otherwise, the processing of sub-step <NUM> is returned back to sub-step <NUM>.

<FIG> shows a flowchart of sub-step <NUM> according to an embodiment. The power adjustment process corresponding to sub-step <NUM> has a similar purpose to that of sub-step <NUM>. However, the staring point on curve <NUM> for sub-step <NUM> is different from the staring point on curve <NUM> for sub-step <NUM> due to a different processing path through sub-steps <NUM>, <NUM>, and <NUM>. As a result, the execution of sub-step <NUM> may cause the output optical power of laser <NUM> to decrease or increase, whereas the execution of sub-step <NUM> causes the output optical power of laser <NUM> only to decrease.

At sub-step <NUM> of sub-step <NUM>, the QF value is read from the overhead of the received data frame.

At sub-step <NUM>, controller <NUM> uses the QF value of step <NUM> to determine a next possible value NewP of the output optical power of laser <NUM>. In an example embodiment, this next possible value can be a power that shifts the operating point along curve <NUM> (<FIG>) by a power increment needed to place the operating point within portion <NUM> of curve <NUM> (see <FIG>). Controller <NUM> may need to access the history stored in its memory to make this determination of the next possible value of the output optical power of laser <NUM>.

Sub-step <NUM> serves as a check against unacceptably large changes of the output optical power of laser <NUM>. As already explained above in reference to <FIG> the changes of the output optical power of laser <NUM> need to be gradual keep the corresponding perturbations for other transceivers <NUM> at a safe level. As such, at sub-step <NUM>, controller <NUM> operates to (i) determine the power increment ΔP that is needed to reach the possible value of the output power computed at step <NUM> and (ii) compare ΔP with a fixed threshold value MaxStep. The fixed threshold value MaxStep is an algorithm parameter that is judged to guarantee the "gradual" pace of the power changes.

If it is determined at sub-step <NUM> that ΔP > MaxStep, then the processing of sub-step <NUM> is directed to sub-step <NUM>. Otherwise, the processing of sub-step <NUM> is directed to sub-step <NUM>.

At sub-step <NUM>, the next possible value NewP computed at step <NUM> is replaced by a different value of NewP that is computed by applying the increment MaxStep to the present output power instead of the power increment ΔP, which was judged at sub-step <NUM> to be too large.

At sub-step <NUM>, controller <NUM> operates to generate control signal <NUM> such that the output optical power of laser <NUM> is changed to NewP. Depending on the result of sub-step <NUM>, the value of NewP can be the value computed at sub-step <NUM> or the value computed at sub-step <NUM>.

<FIG> shows a flowchart of step <NUM> according to an embodiment. As shown, step <NUM> is implemented by modifying sub-step <NUM> shown in <FIG>, with the modification being the replacement of sub-step <NUM> by sub-step <NUM>. As such, for the description of sub-steps <NUM> and <NUM> of step <NUM>, the reader is referred to the description of <FIG>. An example embodiment of sub-step <NUM> is described in reference to <FIG>.

<FIG> shows a flowchart of sub-step <NUM> according to an embodiment. The processing flow of sub-step <NUM> incorporates two copies of sub-step <NUM> and a copy of sub-step <NUM>. For the description of the latter two, the reader is referred to the description of <FIG>, respectively.

At sub-step <NUM>, it is determined whether or not the overhead of a first received data frame contains a QF value. If the corresponding remote receiver <NUM> has included such a QF value in the frame overhead, then the processing of sub-step <NUM> is directed to sub-step <NUM>. Otherwise, the processing of sub-step <NUM> is directed to a first copy of sub-step <NUM>.

At sub-step <NUM>, the QF value is read from the overhead of the first received data frame. Controller <NUM> then generates a corresponding entry for the history stored in the memory. This entry contains (i) the QF value read from the overhead of the first received data frame and (ii) the corresponding output optical power of laser <NUM>.

At sub-step <NUM>, controller <NUM> operates to generate control signal <NUM> such that the output optical power of laser <NUM> is increased by a relatively small increment. In an example embodiment, the increment can be smaller than MaxStep (see <FIG>).

At sub-step <NUM>, it is determined whether or not the overhead of a second received data frame contains a QF value. If the corresponding remote receiver <NUM> has included such a QF value in the frame overhead, then the processing of sub-step <NUM> is directed to sub-step <NUM>. Otherwise, the processing of sub-step <NUM> is directed to a second copy of sub-step <NUM>.

At sub-step <NUM>, the QF value is read from the overhead of the second received data frame. Controller <NUM> then generates a corresponding entry for the history stored in the memory. This entry contains (i) the QF value read from the overhead of the second received data frame and (ii) the corresponding increased output optical power of laser <NUM> that was set at sub-step <NUM>.

At sub-step <NUM>, controller <NUM> uses the history entries stored in the memory at sub-steps <NUM> and <NUM> to compute the QF slope S as follows:
(<NUM>) where (QF<NUM>, P<NUM>) is the history entry stored in the memory at sub-step <NUM>; and (QF<NUM>, P<NUM>) is the history entry stored in the memory at sub-step <NUM>.

At sub-step <NUM>, controller <NUM> determines the sign of the QF slope S computed at sub-step <NUM>. If the sign of S is negative, then the processing of sub-step <NUM> is directed to sub-step <NUM>, a copy of which is incorporated into the processing flow of sub-step <NUM>. Otherwise, the copy of sub-step <NUM> is bypassed, and the processing of sub-step <NUM> is terminated as indicated in <FIG>.

According to an example embodiment disclosed above, e.g., in the summary section and/or in reference to any one or any combination of some or all of <FIG>, provided is an apparatus (e.g., <NUM>, <FIG>; <NUM>, <FIG>) comprising an optical data receiver (e.g., <NUM>, <FIG>), an optical data transmitter (e.g., <NUM>, <FIG>), and an electronic controller (e.g., <NUM>, <FIG>) connected therebetween, the optical data receiver including a photodetector (e.g., <NUM>, <FIG>) configured to detect an optical input signal (e.g., <NUM>, <FIG>) carrying a first data frame, the optical data transmitter including a laser (e.g., <NUM>, <FIG>) configured to generate a carrier wavelength for an optical output signal (e.g., <NUM>, <FIG>); wherein the optical data receiver comprises a frame decoder (e.g., <NUM>, <FIG>) configured to read a first value of a measure of transmission quality from an overhead (e.g., OTUk OH, <FIG>) of the first data frame, the measure of transmission quality representing an error rate at which an FEC code used at a remote receiver encounters errors in data transmitted using the optical output signal; and wherein the electronic controller is configured to change an optical output power of the laser (e.g., using <NUM>, <FIG>) in response to the first value of the measure of transmission quality provided thereto (e.g., by way of <NUM>, <FIG>) by the frame decoder.

In some embodiments of the above apparatus, the measure of transmission quality is one of: (i) a quality factor Q<NUM> corresponding to the error rate (e.g., Eq. (<NUM>)); (ii) a Q value derived from the quality factor Q<NUM> and expressed in decibel (e.g., Eq. (<NUM>)); (iii) a number of errors per data frame corrected by the FEC code; and (iv) an optical signal-to-noise ratio corresponding to the quality factor Q<NUM>.

In some embodiments of any of the above apparatus, the frame decoder is further configured to count (e.g., at <NUM>, <FIG>) a number of errors corrected in the first data frame using an FEC data block (e.g., <NUM>, <FIG>) thereof; wherein the electronic controller is configured to compute a second value of the measure of transmission quality using the number of errors counted by the frame decoder; wherein the optical data transmitter comprises a frame generator (e.g., <NUM>, <FIG>) configured to write (e.g., using <NUM> and <NUM>, <FIG>) the second value of the measure of transmission quality into an overhead (e.g., OTUk OH, <FIG>) of a second data frame; and wherein the optical data transmitter is configured to cause the optical output signal to carry the second data frame.

In some embodiments of any of the above apparatus, the frame generator is further configured to include an FEC data block (e.g., <NUM>, <FIG>) into the second data frame, the FEC data block of the second data frame being computed using the overhead of the second data frame and a payload of the second data frame, the overhead being configured to carry one or more values of the measure of transmission quality.

In some embodiments of any of the above apparatus, the apparatus further comprises a plurality of optical data transmitters (e.g., <NUM>1W-<NUM>NW, <FIG>), each configured to use a different respective carrier wavelength (e.g., λ<NUM>-λN, <FIG>), the optical data transmitter being one of the plurality.

In some embodiments of any of the above apparatus, the apparatus further comprises a plurality of optical data receivers (e.g., <NUM>1W-<NUM>NW, <FIG>), each configured to receive a different respective carrier wavelength (e.g., λ<NUM>-λN, <FIG>), the optical data receiver being one of the plurality.

In some embodiments of any of the above apparatus, the electronic controller is configured to change the optical output power of the laser (e.g., using <NUM>, <FIG>) to cause a value of the measure of transmission quality from an overhead of another data frame received by the optical data receiver from the remote receiver at a later time to be within a predetermined fixed range of values (e.g., between Q<NUM>L and Q<NUM>U, <FIG>).

In some embodiments of any of the above apparatus, the electronic controller is configured to dynamically change the optical output power of the laser (e.g., using <NUM>, <FIG>) in response to a sequence of values of the measure of transmission quality, each of said values being read from an overhead of a different respective data frame carried by the optical input signal.

In some embodiments of any of the above apparatus, the first data frame comprises an optical transport unit (e.g., OTUk, <FIG>) generated in accordance with an ITU-T G. <NUM> Recommendation.

In some embodiments of any of the above apparatus, the electronic controller is configured to change the optical output power of the laser by an increment determined in response to the first value of the measure of transmission quality, the increment being smaller than or equal to a predetermined fixed value (e.g., MaxStep, <FIG>).

In some embodiments of any of the above apparatus, the electronic controller is configured to store therein a history of power changes, each entry in the history including a respective optical output power of the laser and a corresponding value of the measure of transmission quality received from the remote receiver.

According to another example embodiment disclosed above, e.g., in the summary section and/or in reference to any one or any combination of some or all of <FIG>, provided is an apparatus (e.g., <NUM>, <FIG>; <NUM>, <FIG>) comprising an optical data receiver (e.g., <NUM>, <FIG>), an optical data transmitter (e.g., <NUM>, <FIG>), and an electronic controller (e.g., <NUM>, <FIG>) connected therebetween, the optical data receiver including a photodetector (e.g., <NUM>, <FIG>) configured to detect an optical input signal (e.g., <NUM>, <FIG>) carrying a first data frame, the optical data transmitter including a laser (e.g., <NUM>, <FIG>) configured to generate a carrier wavelength for an optical output signal (e.g., <NUM>, <FIG>) carrying a second data frame; wherein the optical data receiver comprises a frame decoder (e.g., <NUM>, <FIG>) configured to count (e.g., at <NUM>, <FIG>) a number of errors corrected in the first data frame using an FEC data block (e.g., <NUM>, <FIG>) thereof; wherein the electronic controller is configured to compute a first value of a measure of transmission quality using the number of errors counted by the frame decoder; and wherein the optical data transmitter comprises a frame generator (e.g., <NUM>, <FIG>) configured to write (e.g., using <NUM> and <NUM>, <FIG>) the first value of the measure of transmission quality into an overhead (e.g., OTUk OH, <FIG>) of the second data frame.

In some embodiments of any of the above apparatus, the measure of transmission quality is one of: (i) a quality factor Q<NUM> corresponding to the number of errors (e.g., Eq. (<NUM>)); (ii) a Q value derived from quality factor Q<NUM> and expressed in decibel (e.g., Eq. (<NUM>)); (iii) the number of errors; and (iv) an optical signal-to-noise ratio corresponding to the quality factor Q<NUM>.

In some embodiments of any of the above apparatus, the frame decoder is configured to read a second value of the measure of transmission quality from an overhead (e.g., OTUk OH, <FIG>) of the first data frame; and wherein the electronic controller is configured to change an optical output power of the laser (e.g., using <NUM>, <FIG>) in response to the second value of the measure of transmission quality provided thereto (e.g., by way of <NUM>, <FIG>) by the frame decoder.

According to another example embodiment disclosed above, e.g., in the summary section and/or in reference to any one or any combination of some or all of <FIG>, provided is a communication method (e.g., <NUM>, <FIG>) that can be carried out at an optical transceiver (e.g., <NUM>, <FIG>), the method comprising the steps of: receiving (e.g., <NUM>, <FIG>) an optical input signal carrying a first data frame; decoding (e.g., <NUM>, <FIG>) the first data frame to read (e.g., <NUM>, <FIG>) a first value of a measure of transmission quality from an overhead (e.g., OTUk OH, <FIG>) of the first data frame, the measure of transmission quality representing an error rate at which an FEC code used at a remote receiver encounters errors in data received from the optical transceiver; and changing (e.g., <NUM>, <FIG>) an optical output power of a laser (e.g., <NUM>, <FIG>) in response to the first value of the measure of transmission quality, the laser being configured to generate a carrier wavelength for an optical output signal directed to the remote receiver.

In some embodiments of the above method, the method further comprises the steps of: counting (e.g., <NUM>, <FIG>) a number of errors corrected in the first data frame using an FEC data block (e.g., <NUM>, <FIG>) thereof; computing (e.g., <NUM>, <FIG>) a second value of the measure of transmission quality using the number of errors; writing (e.g., <NUM>, <FIG>) the second value of the measure of transmission quality into an overhead (e.g., OTUk OH, <FIG>) of a second data frame; and transmitting (e.g., <NUM>, <FIG>) the optical output signal to the remote receiver, the optical output signal being configured to carry the second data frame.

In some embodiments of any of the above methods, the method further comprises the step of including an FEC data block (e.g., <NUM>, <FIG>) into the second data frame, the FEC data block of the second data frame being computed using the overhead of the second data frame and a payload of the second data frame, the overhead being configured to carry one or more values of the measure of transmission quality.

While this disclosure includes references to illustrative embodiments, this specification is not intended to be construed in a limiting sense. Various modifications of the described embodiments, as well as other embodiments within the scope of the disclosure, which are apparent to persons skilled in the art to which the disclosure pertains are deemed to lie within the principle and scope of the disclosure, e.g., as expressed in the following claims.

It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this disclosure may be made by those skilled in the art without departing from the scope of the disclosure, e.g., as expressed in the following claims.

Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Unless otherwise specified herein, the use of the ordinal adjectives "first," "second," "third," etc., to refer to an object of a plurality of like objects merely indicates that different instances of such like objects are being referred to, and is not intended to imply that the like objects so referred-to have to be in a corresponding order or sequence, either temporally, spatially, in ranking, or in any other manner.

Also for purposes of this description, the terms "couple," "coupling," "coupled," "connect," "connecting," or "connected" refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms "directly coupled," "directly connected," etc., imply the absence of such additional elements.

As used herein in reference to an element and a standard, the term compatible means that the element communicates with other elements in a manner wholly or partially specified by the standard, and would be recognized by other elements as sufficiently capable of communicating with the other elements in the manner specified by the standard. The compatible element does not need to operate internally in a manner specified by the standard.

The described embodiments are to be considered in all respects as only illustrative and not restrictive. In particular, the scope of the disclosure is indicated by the appended claims rather than by the description and figures herein. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

A person of ordinary skill in the art would readily recognize that steps of various above-described methods can be performed by programmed computers. Herein, some embodiments are intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions where said instructions perform some or all of the steps of methods described herein. The program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks or tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover computers programmed to perform said steps of methods described herein.

The functions of the various elements shown in the figures, including any functional blocks labeled as "processors" and/or "controllers," may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. Moreover, explicit use of the term "processor" or "controller" should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), and non volatile storage.

As used in this application, the term "circuitry" may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry); (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and/or digital hardware circuit(s) with software/firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions); and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. " This definition of circuitry applies to all uses of this term in this application, including in any claims.

Claim 1:
An apparatus comprising an optical data transmitter (<NUM>) and an electronic controller (<NUM>), the optical data transmitter including a laser (<NUM>) configured to generate a carrier wavelength for an optical output signal (<NUM>) sent to a remote receiver through a span of optical fibers;
wherein the apparatus is configured to read a first value of a measure of transmission quality, the measure of transmission quality representing an error rate at which an FEC code used at the remote receiver encounters errors in data transmitted using the optical output signal; and
wherein the electronic controller is configured to change an optical output power of the laser in response to the first value of the measure of transmission quality,
characterized in that the apparatus further comprises an optical data receiver (<NUM>), the optical data receiver (<NUM>) including a photodetector (<NUM>) configured to detect an optical input signal (<NUM>) carrying a first data frame,
wherein the optical data receiver (<NUM>) comprises a frame decoder (<NUM>) configured to read the first value of the measure of transmission quality from the first data frame,
wherein the first value of the measure of transmission quality is provided to the electronic controller (<NUM>) by the frame decoder (<NUM>), wherein the controller is connected between the optical data receiver (<NUM>) and the optical data transmitter (<NUM>),
wherein the frame decoder is further configured to count a number of errors corrected in the first data frame using an FEC data block (<NUM>) thereof;
wherein the electronic controller is configured to compute a second value of the measure of transmission quality using the number of errors counted by the frame decoder;
wherein the optical data transmitter comprises a frame generator (<NUM>) configured to write the second value of the measure of transmission quality into a second data frame; and
wherein the optical data transmitter is configured to cause the optical output signal to carry the second data frame to the remote receiver through the span of optical fibers.