JP7305354B2 - laser power controller - Google Patents

Description

In fiber optic communication systems, being able to control the output power of a transmitting laser diode is important for many reasons. First, the average and peak power of the laser must not exceed certain limits to avoid damage. Second, the different power levels corresponding to the binary (or other radix) data values are such that the modulation index (or extinction ratio, defined as must be set to be within One difficulty in dealing with any control system is that laser characteristics can vary significantly with temperature, aging, and even deviations from an ideal linear response; ' and 'low' drive current levels are not sufficient.

There are numerous techniques in the prior art describing methods aimed at estimating the instantaneous values of minimum and maximum transmitted optical power and compensating for changes in device characteristics. The limited bandwidth of monitor diodes and their associated circuitry limits their effectiveness in large part. Others require specific patterns to be present in the data stream or intentionally inserted into the data stream in some defined way.

Monitoring transmitted output power is even more difficult in optical communication links, which transmit data in a series of discrete bursts, because the simple average value of optical power can vary greatly over time. Yes, and because the instantaneous levels are not stable enough for most methods described in the prior art to arrive at good estimates of minimum and maximum levels. Temperature-related effects are likely to be even more severe, because the transmit laser diode may be off for long periods of time before being activated for a data burst, thus This is because it can be cooled to ambient temperature before warming up.

Therefore, it is desirable to be able to sense substantially continuously the minimum and maximum light outputs corresponding to logic '1' and logic '0' during data bursts. Further, it would be desirable to be able to perform such measurements using a transmit power monitor function with only a modest bandwidth and by a means that does not disturb the transmitted data payload or degrade the noise performance of the received signal. Such an approach is proposed in US Pat.

British Patent No. 2541291 (British Patent Application No. 1611938.0)

However, the method described above has the advantage of having only one data point per data burst, but is therefore susceptible to noise, as it can unacceptably affect the calculation of the required laser current value. Cheap. It is an object of the present invention to achieve improved, accurate and stable control of laser power in burst mode optical communication systems by using additional measurements of light level during each data burst.

According to a first aspect, there is provided a system for transmitting information in a fiber optic communication system contained in at least two consecutive bursts of data transmitted in sequence . The system selects a data input value during a data transmission period during a defined burst period and selects a logic high value and a logic low value during an extended period during said defined burst period and immediately following said data transmission period. , such that for said sequence of at least two data bursts, at least one data burst is a logic low value burst and at least one data burst is a logic high value burst. a selection circuit configured to select one of a value, a logic high value or a logic low value; and a data input value, logic high value or logic low value selected by said selection circuit during said defined burst period. a drive circuit configured to provide a current corresponding to one of the values or a zero value to a laser diode such that the laser diode provides a light output; and configured to provide a corresponding sensor module output, said sensor module output providing an electrical output proportional to the light output of said laser diode corresponding to said logic high value and said logic low value in said sequence of bursts. an optical sensor module configured to provide an output corresponding to an average value of said sensor module output only during said data transmission period in said sequence of bursts; and an optical signal output power level of said laser diode. receiving a desired value and receiving an output from the light sensor module proportional to the light output of the laser diode corresponding to the logic high value and the logic low value; and receiving the data in the sequence of bursts. configured to receive said output corresponding to an average value of said sensor module outputs only during a transmission period, and to provide a control value to said drive circuit using those outputs from said photosensor module and said desired value; and a controller.

The optical sensor module may comprise a photodiode output power detector.
The photosensor module may comprise a photosensor and a transimpedance amplifier, the transimpedance amplifier configured to provide the sensor module output.

The control value comprises an average power of the optical output of the laser diode, a power of the optical output of the laser diode representing a logic high, a power of the optical output of the laser diode representing a logic low, and a modulation of the optical output of the laser diode. It may be configured to control at least one of the indices.

The current may include a steady component and a variable component.
The drive circuit may be configured to set the current provided to the laser diode according to a combination of a bias control value and a modulation control value.
The control value may be configured to control the drive circuit to set at least one of a bias current and a modulation current provided to the laser diode.

The drive circuit may comprise a bias circuit configured to provide a bias current to the laser diode.
The drive circuit may comprise a modulation circuit configured to provide a modulated current to the laser diode.
The drive circuit may be configured to set the current provided to the laser diode according to a combination of an average value and a modulation value.

The burst period may be gated by a burst enable signal.
The control value may control the drive circuit to provide the desired logic high and logic low optical output power levels.
The extension period may be longer than the settling time of the sensor module output.

The selection circuitry may alternately select one of the logic high value and the logic low value for successive extended periods of time.
The selection circuitry may select the logic high value or the logic low value for each successive extended period of time according to a predetermined sequence.
The selection circuit may select the logic low value immediately after an extended period of time during which the logic high value was selected.
The selection circuit may have a selector switch function.
A bandwidth of the selection circuit may be configured to switch between the data input, the logic high value and the logic low value in a time significantly less than the time of the extended period.

The control value of the drive circuit may be based on a combination of average, high and low values from the light sensor module each scaled by a factor.

The system may comprise circuits that are primarily digital in function .
The control values for the drive circuit may be calculated by a digital computing function.
The system may comprise circuits that are primarily analog in function .

According to a second aspect, a method is provided for transmitting information in a fiber optic communication system contained in at least two consecutive bursts of data transmitted in sequence . The method selects a data input value during a data transmission period in a prescribed burst period and selects a logic high value and a logic low value during an extended period during said prescribed burst period and immediately following said data transmission period. to select one of the data input values, logic selecting one of a high value or a logic low value; and a current corresponding to the selected data input value, the one of the logic high value or logic low value, or a zero value during the defined burst period. providing said current to a laser diode such that said laser diode provides a light output; and an output corresponding to said light output of said laser diode, said logic high value and said logic in said sequence of bursts. providing an electrical output proportional to the optical output of the laser diode corresponding to a low value and corresponding to an average value of the output corresponding to the optical output of the laser diode only during the data transmission period in the sequence of bursts. providing an output; receiving a desired value for an optical signal output power level of said laser diode; and controlling a drive circuit using said output and said desired value corresponding to the optical output of said laser diode. providing a value.

The method comprises: average power of the optical output of the laser diode; optical output power of the laser diode representing a logic high; optical output power of the laser diode representing a logic low; and modulation index of the optical output of the laser diode. applying the control value to control at least one of

The current may include a steady component and a variable component.
The method may further comprise setting the current supplied to the laser diode according to a combination of a bias control value and a modulation control value.
Setting the current supplied to the laser diode may include setting at least one of a bias current and a modulation current supplied to the laser diode based on the bias control value and the modulation control value. good.
Providing the current may further comprise providing a bias current to the laser diode.
Providing the current may further comprise providing a modulated current to the laser diode.

Setting the current supplied to the laser diode may include setting the current according to a combination of an average value and a modulation value.
The burst period may be gated by a burst enable signal.
The method may further comprise applying the control value to convey desired logic high and logic low optical output power levels.
The extended period of time may be longer than the settling time to provide the output.

Selecting one of a data input value, a logic high value or a logic low value may comprise alternately selecting said logic high value and said logic low value for successive extended periods of time.
Selecting one of a data input value, a logic high value or a logic low value includes selecting said logic high value or said logic low value for each successive extended period of time according to a predetermined sequence. It's okay.
Selecting one of a data input value, a logic high value or a logic low value may include selecting said logic low value immediately after an extended period of time during which said logic high value was selected.

Selecting one of the data input value, the logic high value or the logic low value may include selecting using a selector switch function.
Selecting one of a data input value, a logic high value or a logic low value is performed within a time period substantially less than the extended period of time. may include switching between
Using said output corresponding to the light output of said laser diode and said desired value for supplying a control value to said drive circuit is an average value, a high value respectively from said light sensor module scaled by a factor. and providing a control value based on a combination of the row values.

According to a third aspect, there is provided a system for transmitting information in a fiber optic communication system contained in at least two consecutive bursts of data transmitted in sequence . The system selects a data input value during a data transmission period during a defined burst period and selects a logic high value and a logic low value during an extended period during said defined burst period and immediately following said data transmission period. , such that for said sequence of at least two data bursts, at least one data burst is a logic low value burst and at least one data burst is a logic high value burst. means for selecting one of a value, a logic high value or a logic low value; and a data input value, logic high value or logic low value selected by said means for selecting during said defined burst period. means for providing a laser diode with a current corresponding to one or a zero value of said laser diode such that said laser diode provides a light output; and a sensor module output corresponding to said light output of said laser diode. is configured to provide the sensor module output that provides an electrical output proportional to the optical output of the laser diode corresponding to the logic high value and the logic low value in the sequence of bursts; means for providing said sensor module output for providing an output corresponding to an average value of said sensor module output only during said data transmission periods in said sequence; receiving values from the optical sensor module proportional to the optical output power level of the laser diode corresponding to the logic high value and the logic low value; and the data in the sequence of bursts. means for receiving said output corresponding to an average value of said sensor module output only during a transmission period and using those outputs from said photosensor module and said desired value to apply said current to a laser diode; and control means configured to provide a control value.

The means for providing a sensor module output may comprise a photodiode output power detector.
The means for providing the sensor module output may comprise an optical sensor and a transimpedance amplifier, the transimpedance amplifier configured to provide the sensor module output.

The control values are the average power of the optical output of the laser diode, the optical output power of the laser diode representing a logic high, the optical output power of the laser diode representing a logic low, and the modulation index of the optical output of the laser diode. may be configured to control at least one of the

The current may include a steady component and a variable component.
The means for providing the current to the laser diode may be configured to set the current provided to the laser diode in response to a combination of a bias control value and a modulation control value.
The means for applying the current to the laser diode may comprise means for setting at least one of a bias current and a modulation current applied to the laser diode based on the control value.

The means for applying a current to the laser diode may comprise means for applying a bias current to the laser diode.
The means for applying a current to the laser diode may comprise means for applying a modulated current to the laser diode.
The means for applying said current to a laser diode may comprise means for setting said current applied to said laser diode in response to a combination of an average value and a modulation value.

The burst period may be gated by a burst enable signal.
The control means may comprise means for using the control values to control the means for providing current to provide desired logic high and logic low optical output power levels.
The extended period of time may be longer than the settling time of the means for providing the sensor module output.

The means for selecting may be configured to alternately select one of the logic high value and the logic low value for successive extended periods of time.
The means for selecting may be arranged to select the logic high value or the logic low value for each successive extended period of time according to a predetermined sequence.
The means for selecting may be configured to select the logic low value immediately after an extended period of time during which the logic high value was selected.
The means for selecting may be arranged to select based on a selector switch function.

The bandwidth of the means for selecting is such that the means for selecting switches between the data input, the logic high value and the logic low value in a time significantly less than the time of the extended period of time. It may be configured as follows.
The control means may be configured to generate a control value based on a combination of average, high and low values from the means for providing the photosensor module output each scaled by a factor.

The invention will now be described, by way of example only, with reference to the accompanying drawings.

1 shows a typical configuration for a transmitter in a burst mode fiber optic link with unidirectional modulated current. Figure 2 shows a typical configuration for a transmitter in a burst mode fiber optic link with bidirectional modulated current. Figure 2 shows the output characteristics of a laser diode and the effect of temperature. We show the limitations of the conventional estimation method when there is curvature in the laser characteristics. Figure 2 shows the structure of a typical data burst with typical allowable laser turn-off times; FIG. 2 shows a burst mode optical signal with high and low reference levels embedded within a valid data packet; FIG. Fig. 3 shows a burst mode optical signal with a low reference level embedded within the valid data burst period; Fig. 3 shows a burst mode optical signal with a high reference level embedded within the valid data burst period; Fig. 3 shows an embodiment of the invention using unidirectional modulated current; Fig. 3 shows an embodiment of the invention using bi-directional modulated current; Fig. 4 shows a further embodiment of the means for sensing the reference level; Fig. 4 shows a further embodiment of the means for obtaining the gated average value from the input;

The description should not be construed in a limiting sense, but is merely meant to illustrate the general principles of embodiments of the invention. For example, operations illustrated as being performed using digital signals and circuits may be accomplished using substantially analog signals and circuits.

Figures 1a and 1b show a typical configuration in a transmitter suitable for optical communication systems. The laser diode 101 is supplied by a drive circuit with a current having a constant component and a variable component. This current may be in the form of a smaller steady-state bias current 115 with modulation current 116 cut off by switching function 110 to indicate a logic low level in modulation data input 107 . Alternatively, in the form of average current 125 with bidirectional modulated currents 126, 127 adding and subtracting currents after selection by switch 120 to produce maximum and minimum values in light output under control of input data stream 107. may be These currents are converted by digital-to-analog converters (DAC) 111, 112 for unidirectional modulated currents or by digital-to-analog converters (DAC) 121, 122 for bidirectional modulated currents. As may be provided, these DACs have current outputs controlled by respective digital values 113, 114 or 123, 124 set by controller functions 117 or 128, respectively.

When operating in burst mode, these currents may be gated in a manner corresponding to active transmission periods in data bursts by a further signal or signals 108 corresponding to the specified length of the transmission burst. .

The light output of laser diode 101 is sensed by a light sensor, such as monitor photodiode 102, to produce a current proportional to the sensed light level. The current may be sensed directly or, more generally, converted to voltage 105 by a transimpedance amplifier 103 . The combination of monitor photodiode 102 and transimpedance amplifier 103 typically has a bandwidth substantially less than the main data channel bandwidth. This monitored value 105 may be converted to digital form 106 by an analog-to-digital converter 104 and these data are used by a controller 117 or 128 to calculate and set the laser diode current level according to some algorithm. may therefore be used. Monitor diode 102 and its associated amplifier 103 typically have a signal bandwidth much less than the bandwidth of the data transmitted by laser 101, and this limitation of monitor channel bandwidth means that it is the maximum of the transmitted optical signal. and limit the observability of minimum peak and trough values, which is very important in the implementation of any transmitted light level control scheme.

FIG. 2 is a diagram showing the characteristics of a typical laser diode, such as those used in optical communication systems. The current through the laser diode is modulated such that the minimum current exceeds the threshold 203 for the laser 101 and the maximum current is below the device manufacturer's rating when used to generate a modulated optical signal. be. A simple linear model 201 is sufficient when the laser diode is cold or the current level is relatively low. However, as the laser diode heats up, or as its characteristics age, the threshold current changes (204) and the relationship between current and light output may exhibit a more curved shape 202. FIG. Therefore, maintaining the desired light output and desired depth of modulation during operation over the life of the system is not straightforward.

In a given practical system, the maximum current can be set such that the average operating power of the laser is set at a specified level with respect to the signal level required to establish reliable communication. An important parameter in such systems is the ratio of maximum to minimum optical power, commonly called extinction ratio (ER), which affects the signal-to-noise level of the receiver. ER is a function of minimum and maximum laser diode current values and is sometimes expressed as a simple linear relationship, although in practice this is not an exact representation.

FIG. 3 shows the minimum laser drive current level 305 and maximum laser drive current level 306 required to produce the specified minimum optical power level 301 and maximum optical power level 302 at the average optical power 303 of a laser diode at elevated temperature. This indicates that it is not suitable as a basis for accurate estimation and therefore as a method for maintaining the desired ER. The drive current 304 corresponding to the monitored average light output does not average the actual minimum current level 305 and maximum current level 306 .

If the system operates with a continuous data stream, the laser can reach a steady state temperature, which is relatively easy to monitor. In addition, it is sufficient to collect data from the monitor diode system and measure peak and trough optical data levels by some kind of averaging of the measurements to provide reliable estimates of ER and average optical power. I have time Systems for this purpose are known in the prior art (e.g. Smith et al, Electronics Letter Vol 14, 1978, and similar derivatives), often using slow modulation of the absolute drive current level. .

Figure 4 shows the general form of an optical signal intended to transmit data bursts in a system conforming to specifications for burst mode operation (e.g. standard ITU-T Recommendation G.984.2). ing. The bias current to the laser is gated by burst enable signal 108 before data signal 107 is used to modulate the laser output. In such standards, the duration T1 of data burst 403 is precisely defined, typically on the order of hundreds of nanoseconds. Note that at the end of the data burst, the logic value can be in a high state (logic high value) or low state (logic low value). Such standards also typically define T2 as the time interval 404 within which the laser power must return to zero. Considering the bandwidth of practical bias control systems, this interval is on the order of 10 ns (12.8 ns is the defined value in the given example).

In such burst mode systems, the problem of controlling average power and ER is difficult to solve. Before the burst begins, the laser is relatively cold. As soon as the data packet is sent, the laser begins to heat up and continues to heat up during normal bursts. It is a requirement of the standard that the system is operable after, for example, five short training bursts or less, during which the operating parameters of the system should be controlled. A means for establishing operating parameters in time is disclosed in GB 2535553B, in which to determine an estimate of the slope efficiency of a laser at the beginning of a series of data bursts: , a trial burst of defined amplitude is output. Maintaining operating conditions after operation of such a start-up system by only monitoring the average optical power output, firstly due to intermittent bursts of optical power and secondly to a well-defined average value. It is generally not satisfactory because of its reliance on having data content in each burst. This latter requirement requires that the number of data 0 and 1 values in a burst be substantially equal, which may not be guaranteed.

A further need remains to provide a means for precisely controlling the ER of the laser output after the first training burst in which the laser has warmed up to a substantially elevated average temperature. Peak and trough measurements are subject to the same monitor channel bandwidth limitations as for continuous mode systems, but the intermittent nature of the signal further complicates the requirements and makes the task more difficult.

In one embodiment of the present invention, a means for quickly and accurately estimating instantaneous values of light output representing data '1' values and/or data '0' values, or other values as may be defined. is provided, along with means for estimating the average value of the light output only during the data content period of each data burst, all of said means operating in a manner that does not require modification of the data content of said burst. This estimate can be used to calculate the required value of drive current to provide a desired output level, as well as changes in laser characteristics due to short-term heating and/or long-term aging. Further means are provided by which these levels can be maintained. The current can take the form of a smaller bias current and a unidirectional modulation current, or an average current and a bidirectional modulation current, depending on the system.

Note in FIG. 4 that the time to turn off the laser after a burst of data may not be a constant duration, but likely depends on the logic value present at the end of the data transmission period 401. The process of turning off the laser bias current (or average current) from the high state 405 at the end of the data transmission period can be significantly longer than the time to turn off the laser bias current from the low state 406 at the end of the data transmission period. expensive. This turn-on and turn-off time is typically determined by the response time of the internal circuitry that maintains the bias current 115 (or average current 125), which is typically designed to respond at the same speed as the laser's data modulation. not However, the bandwidth of modulation circuit 110 or 120 in response to modulated data signal 107 is necessarily very fast to switch laser current at the data symbol rate. Therefore, rather than using bias current (or average current) control to turn off from a "high" state, modulation circuit 110 or 120 is used to first ramp the laser output very rapidly, typically several tens of It can be reduced to the "low" state in times on the order of picoseconds. The task of turning off to complete extinction becomes much easier once the laser output is in the above "low" state. Furthermore, it is difficult to ensure that the bias current 115 (or average current 125) responds to the burst enable signal 108, or a substantially equivalent signal, in time intervals substantially shorter than the interval 404 required by the standard. not a simple task. This approach makes available a time interval that is not very long but still longer than the transient settling time typical of such monitor channel circuits. With this knowledge, it is possible to take advantage of the time available in the specified turn-off interval 404 to make useful measurements of general optical "high" and "low" output levels. be.

Along with measuring the optical "high" and "low" values during the short extension of the data burst, it is also possible to gather useful information about the current average optical power during the transmission of the data content of the burst. , the average output of the monitor photodiode circuit 105 is obtained during the data period in the burst and also outside any settling time required by the monitor circuit. The gating control for such averaging is readily derived from burst enable signal 108 in some combination of data input 107 and other internal logic signals.

FIG. 5 shows the light levels associated with a burst mode system with clever modifications to the transmitted signal to facilitate high and low level measurements. Such modifications are made so that they do not affect normal transmission of data in burst packets and do not violate specifications set by the relevant transmission standards.

A time interval is first defined to provide a framework for the above modifications, which is substantially less than the laser turn-off time 404 allowed by the transmission standard, but less than the monitor channel output 105 settling time. It provides sufficient time remaining within period 404 for the bias current control circuit to completely extinguish the laser while satisfying the condition of being long enough to be substantially long. A feature of the present invention is to replace the raw data signal 107 with a modified form of the laser modulated signal 501, with a known logic value at the end of each burst held for an extended period of time T3,502. At the same time, the bias current 115 (or average current 125) to the laser is adjusted by the burst enable signal so that the bias (or average) and modulation circuits remain active for a defined period of time after the data for that burst has ended. (laser current enable control signal 506).

The logic value of this extended portion of the data burst may be timed to alternate between a "1" indicated at 503 in FIG. 5 and a "0" indicated at 504 in FIG. Alternatively, the logic value of this extended portion of the data burst may be set to '0' for several consecutive data bursts, as shown in FIG. Alternatively, the logical value of this extended portion of the data burst may be set to '1' for several consecutive data bursts, as shown in FIG. The duration of this logic hold period 502 is made long enough to allow the monitor channel output 105 to settle to a substantially accurate measurement result. If the logic value held at the end of the data burst is a "1", the laser modulating current 115 (or 125 for bidirectional modulating current) is applied to the data modulating circuit 110 (or both) at the end of this extended period 502. Returned to '0' by the command edge 505 of the laser current enable control signal 506 to 120) for directionally modulated current. In this way, the laser current is substantially reduced toward its extinction state by the wide bandwidth modulation circuit function, typically in tens of picoseconds, rather than by much slower bias current control. Upon reaching this state, bias current 115 (or average current 125) and modulation current 116 (or 126 and 127 for bi-directional modulation) are turned off by laser current control signal 506 and the laser The total current decays to zero before the end of the time allowed by the relevant standard. Thus, by these or substantially similar means, monitor output 105 can be a logic high "1" and a logic low without significant limitations resulting from particular data patterns and/or run lengths as is often the case in the prior art. During both "0" data states, it can provide a substantially accurate estimate of the proper and typical light output.

During data burst periods, the data input 107 and burst enable signal 108 in combination with other internal signals are used to be active for a period entirely within the data transmission period, typically for most of said data transmission period. It provides a gating signal 508 that is active and is used to enable the averaging function to calculate an average value from the monitor channel output 105 . The gating signal 508 is configured to become active only after the expected settling time of the monitor channel output resulting from the start of the data burst and resulting from the limited bandwidth of the monitor channel. This requirement for delay from the start of the burst enable signal is typically on the order of a few data symbol periods. The averaging function, in one embodiment, keeps the average value at the end of the burst and scales it somewhat proportionally with the new input signal during the next burst to create a rolling average rather than an estimate based on a single burst. to use the retained mean value.

From these measurements obtained from multiple data bursts, the analog values representing optical "0", optical "1" and optical average can be converted to digital form and these values combined in a simple A simple algorithm can be used to determine the general extinction ratio and average optical power in an advantageous manner that minimizes susceptibility to noise and error. The algorithm also uses modulation current 116 (or 126 and 127 for bi-directional modulation) and bias current 115 (or corresponding average current 125) such that the ER and average power match the desired target values for the system. can determine the necessary adjustments to

FIG. 8 shows a configuration according to one embodiment of the invention. A bias current 115 is set by a current output digital-to-analog converter (DAC) 111 and a modulation current 116 is similarly set by another DAC 112 . The control digital values for those DACs are determined by a digital computation function 826, which inputs digital inputs corresponding to the system feedback value and the desired average power 131 and modulation depth 132 (or ER). and get from. The modulation circuit 110 is not directly controlled by the incoming data input 107, but can switch its input between the data input 107 and a logic "1" or a logic "0" by a selection circuit, such as a selector switch function 813. can. When burst enable signal 108 is asserted to indicate the start of a data burst, logic control function 811 sets the modulation input path using selector 813 to pass input data directly to modulation circuit 110 . A modulated optical signal is generated by a laser 101 and a band-limited monitor signal 105 is generated by a monitor diode 102 and its associated amplifier 103 . This monitor signal 105 is directly converted to a digital value 821 by an analog-to-digital converter (ADC) 820 . During the data transmission portion of the data burst, this output 821 can be used, but it will be of limited value due to the bandwidth limitations of this channel. At the end of the data payload, burst enable signal 108 marks the end of this transmission period.

In conventional systems, deasserting burst enable signal 108 completely disables modulation current 116 and bias current 115 . According to this embodiment of the invention, control logic 811 holds the bias current and modulation current on for a predetermined delay time. An additional burst status signal 810 can change logic values as needed with each data burst, effectively designating the burst as "high" or "low." As an exemplary implementation, if the burst is designated as "high", then during postponing the end of the burst, the modulation input selector 813 outputs a logic "1" 503 so that the optical output is held at a high level 302. is set to This modulation optical value is long enough for the monitor channel to make accurate measurements despite the limited bandwidth of the monitor, but the time to completely extinguish the laser within the time 404 allowed by the transmission standard. is held for a sufficiently short period 502 as . The monitor channel output 105 is converted to digital form 821 and then passed through a logic gate 822 enabled by the burst state signal 810 to a first register 824 at the appropriate time. This register then provides the measured optical “high” value to calculation function 826 .

At the end of this extension period 503, the modulation selector leaves a logic "1" selected or is set to a logic "0", removing the laser modulation current 116 using the normal modulation circuit 110 and reduces the light output very rapidly. At the same instant 505, control logic 811 commands bias current DAC 111 and modulation current DAC 112 to stop output current, so that laser 101 is completely extinguished within time period 404 as required by the relevant communication standard. do.

At the end of the data payload, the modulation selector 813 is set to a logic "0" 504 and the laser output goes to a low level 301 if the burst is designated as "low" by the burst status signal 810. FIG. Even if the last symbol of the burst data payload required a logic '1' at the end of the burst, the transition to logic '0' can be made very fast by using a conventional modulation circuit 110 . Again, this modulation optical value is long enough for the monitor channel to make accurate measurements despite its limited bandwidth, but the time to completely extinguish the laser within the time 404 allowed by the transmission standard. is held for a sufficiently short period 502 as . The monitor channel output 105 is converted to digital form 821 and then passed to a second register 825 via a logic gate 823 enabled by the logic complement of the burst state signal 810 at the appropriate time. This register then provides the measured optical “low” value to calculation function 826 .

One convenient configuration would be to alternately designate bursts as "high" and "low." However, the invention is also useful if estimates of certain levels need to be obtained sooner than others, or if other requirements of the system need to be taken into account, e.g. Some other sequence of "high" and "low" states may be used in more critical cases.

Also during each data burst, the output 105 of the monitor diode 102 and associated circuitry 103 is passed to an averaging function 804 that operates only when commanded by the gating signal 508 . This averaging function provides an average of the signal presented at its input over the period enabled by the gate signal 508 and holds the result when the gate signal indicates that averaging should stop. be able to. Note that the end of gating signal 508 ensures that the averaging function does not consider setting the laser output to a “high” or “low” state during the extended period of data burst 504 . Said averaging function may take into account each previous calculation of the average value, optimizing response time and noise immunity as is commonly done by those skilled in the art when using such functions. A defined weighting or decay rate can be used. The output 805 of the averaging function 804 is passed to ADC 806 and converted to digital form and passed to register 807 after each data burst. The timing of this conversion to digital form can be conveniently synchronized through the use of control signal 801 . The output of said register 807 is also passed to computational function 826 .

The calculation function 826 then obtains estimates for the optical "high" value, the optical "low" value and the optical average value, and also obtains the required target value inputs for the average value 131 and ER132. , to obtain a new bias current control value 113 and a new modulation current value 114 using simple calculations. The calculation uses several scaling factors ranging from '0' to '1' for each input to the calculation, depending on the achieved signal quality obtained from each channel in the actual application. , optical "high", optical "low" and optical average. The calculations are performed such that the error between the calculated ER and mean values and the corresponding required ER and mean values is minimized to negligible or acceptable levels. This process requires several iterations of "high" and "low" bursts and several averaging operations, and the exact convergence speed of the system depends on the inputs and other system variables in a particular application. Depends on the scaling factor chosen.

The numerical values of these scaling factors may be fixed or variable. For example, coefficients may be determined during manufacturing and testing and stored in the system. Alternatively, the user can determine the numerical values of the coefficients during testing or as a result of monitoring extended operation, optimize the values from these monitoring, and store them in the system. As another alternative, a controller function may be built with the ability to change the coefficients while the system is using other performance information or adaptively starting from defined starting values. .

FIG. 9 shows an arrangement according to a second embodiment of the invention. In this configuration, the calculation function 826 obtains estimates for the optical "high" value, the optical "low" value and the optical average value, as well as the required target value inputs for the average value 131 and ER132. , and a new average current control value 123 and a new bidirectional modulation current value 124 are obtained using simple calculations. The calculation likewise uses several scaling factors ranging from '0' to '1' for each input to the calculation, depending on the achieved signal quality obtained from each channel in the actual application. can be used to consider an optical "high", an optical "low" and an optical average. The calculations are performed such that the error between the calculated ER and mean values and the corresponding required ER and mean values is minimized to negligible or acceptable levels. This process requires several iterations of "high" and "low" bursts and several averaging operations, and the exact convergence speed of the system depends on the inputs and other system variables in a particular application. Depends on the scaling factor chosen.

The numerical values of these scaling factors may be fixed or variable. For example, coefficients may be determined during manufacturing and testing and stored in the system. Alternatively, the user can determine the numerical values of the coefficients during testing or as a result of monitoring extended operation, optimize the values from these monitoring, and store them in the system. As another alternative, a controller function may be built with the ability to change the coefficients while the system is using other performance information or adaptively starting from defined starting values. .

FIG. 10 shows an embodiment of a configuration that can be used within a system to provide digital information regarding optical "high" and optical "low" level estimates without conventional ADC functionality. Analog input 1007 is compared to some desired reference value 1003 in comparator 1004 . The output of the comparator may be gated with a select signal 1008 in some logic function 1005 such that a counter 1006 is incremented or decremented when an enable sampling clock signal 1009 is present. By these means the digital output 1010 scales according to the sign of the difference between the input signal 1007 and the reference value 1003 . When this value 1010 is used in some closed-loop system, such as the system presented herein, the value of the input signal 1007 tends to approach and equal the reference value 1003 . It is convenient to use a DAC 1002 to convert a reference in digital form 1001 to an analog reference 1003 .

FIG. 11 shows one embodiment of a simple means of obtaining the gated average value from the analog input signal 1101 . The analog input signal 1101 is passed through switching function 1107 to an analog integrator comprising amplifier 1103 , resistor 1105 and capacitor 1104 under the control of gate signal 803 . While switch 1107 is closed, output 1102 of integrating amplifier 1103 rises or falls depending on the instantaneous sign and magnitude of input signal 1101 . When switch 1107 is opened under the control of gate signal 803, the integration and averaging operations stop and the value is held. Output value drift is due to electrical imperfections in the components used. It is desirable to have some damping function for the averaging operation. A simple and convenient method illustrated is to connect a resistor 1106 across a capacitance 1104 with a switch 1108 that allows the output to decay at a rate set by the relative values of these components. be.

Over many data bursts, the system will adjust the current to minimize the error, so the laser will operate at substantially the desired average optical power and substantially the desired ER.

Although the invention has been described with reference to specific examples and possible embodiments thereof, these should not be construed as limiting the scope of the invention in any way. Many other possible embodiments, modifications and improvements can be incorporated into or with the present invention without departing from the scope and spirit of the invention as set forth in the claims. is clear.

Claims (22)

1. A system for transmitting information in a fiber optic communication system contained in at least two consecutive bursts of data transmitted in sequence, comprising :
Selecting a data input value during a data transmission period in a defined burst period and selecting one of a logic high value and a logic low value during an extended period during said defined burst period and immediately following said data transmission period. a data input value, a logic high value such that for said sequence of at least two data bursts, at least one data burst is a logic low value burst and at least one data burst is a logic high value burst a selection circuit configured to select one of a value or a logic low value;
a current corresponding to one of a data input value, a logic high value, a logic low value, or a zero value selected by the selection circuit during the defined burst period, such that the laser diode provides light output; a drive circuit configured to provide said current to the laser diode;
a sensor module output corresponding to the light output of said laser diode, said sensor module output providing an electrical output proportional to said light output of said laser diode corresponding to said logic high value and said logic low value in said sequence of bursts. and further configured to provide an output corresponding to an average value of the sensor module output only during the data transmission period in the sequence of bursts;
receiving a desired value for the optical signal output power level of the laser diode and an output from the optical sensor module proportional to the optical output of the laser diode corresponding to the logic high value and the logic low value; and a controller configured to receive said output corresponding to an average value of said sensor module output only during said data transmission period in said sequence of bursts, said light being each value scaled by a factor. said controller configured to provide a control value to said drive circuit using a combination of average, high and low values of outputs from sensor modules and said desired value;
system including. 2. The system of claim 1, wherein the optical sensor module comprises a photodiode output power detector. 2. The system of claim 1 , wherein the optical sensor module comprises an optical sensor and a transimpedance amplifier, the transimpedance amplifier configured to provide the sensor module output. The control value comprises an average power of the optical output of the laser diode, a power of the optical output of the laser diode representing a logic high, a power of the optical output of the laser diode representing a logic low, and a modulation of the optical output of the laser diode. A system according to any one of claims 1 to 3, arranged to control at least one of the indices. The system of any one of claims 1-4, wherein the current comprises a steady component and a variable component. 6. The drive circuit according to claim 1, wherein said drive circuit is configured to set said current applied to said laser diode according to a combination of a bias control value and a modulation control value. system. 7. The system of Claim 6, wherein the control value is configured to control the drive circuit to set at least one of a bias current and a modulation current provided to the laser diode. The system of any one of claims 1-5, wherein the drive circuit comprises a bias circuit configured to provide a bias current to the laser diode. The system of any one of claims 1-5, wherein the drive circuit comprises a modulation circuit configured to provide a modulated current to the laser diode. A system according to any one of claims 1 to 5, wherein the drive circuit is arranged to set the current applied to the laser diode according to a combination of average and modulation values. The system of any one of claims 1-10, wherein the burst period is gated by a burst enable signal. The system of any one of claims 1-11, wherein the control value controls a driver circuit to provide desired logic high and logic low optical output power levels. The system of any one of claims 1-12, wherein the extended period of time is longer than the settling time of the sensor module output. 14. The system of any one of claims 1-13, wherein the selection circuit alternately selects one of the logic high value and the logic low value for successive extended periods of time. The system of any one of claims 1-13, wherein the selection circuit selects the logic high value or the logic low value for each successive extended period of time according to a predetermined sequence. The system of any one of claims 1-13, wherein the selection circuit selects the logic low value immediately after an extended period of time during which the logic high value was selected. The system according to any one of claims 1 to 16, wherein said selection circuit comprises a selector switch function. The bandwidth of the selection circuit is configured to be switchable between the data input value, the logic high value and the logic low value in a time significantly less than the time of the extended period of time. 18. The system according to any one of 17. A system according to any one of claims 1 to 18, comprising circuits whose functions are predominantly digital . The system according to any one of claims 1 to 19, wherein said control values for said drive circuit are calculated by a digital computing function. A system according to any one of claims 1 to 18, comprising circuits which are predominantly analog in function . A method for transmitting information in a fiber optic communication system contained in at least two consecutive bursts of data transmitted in sequence, comprising :
Selecting a data input value during a data transmission period in a defined burst period and selecting one of a logic high value and a logic low value during an extended period during said defined burst period and immediately following said data transmission period. Then, for said sequence of at least two data bursts, the data input value, the logic high value or the logic selecting one of the rho values;
a current corresponding to one of a data input value, a logic high value, a logic low value, or a zero value selected during said defined burst period, said current such that said laser diode provides light output; feeding a laser diode;
providing an electrical output corresponding to the optical output of the laser diode, the electrical output being proportional to the optical output of the laser diode corresponding to the logic high value and the logic low value in the sequence of bursts; providing an output corresponding to an average value of the output corresponding to the light output of the laser diode only during the data transmission periods in the sequence;
receiving a desired value for an optical signal output power level of the laser diode;
combining the average, high and low values of the output corresponding to the optical output of the laser diode, each value scaled by a factor, and the desired value for the optical signal output power level of the laser diode; using the determined value to provide a control value for controlling the current applied to the laser diode;
method including.

Images