JP2019145785A - Laser power controller - Google Patents

Abstract

To achieve a stable control of a laser output in a burst mode optical communication system.SOLUTION: A system for transmitting a sequence of at least two data bursts in an optical fiber communications system includes: a selection circuit configured to select a data input value during a data transmission period during a defined burst period and select one of a logical high value and a logical low value during the burst period and during an extension period immediately following the data transmission period; a drive circuit configured to drive a laser diode with a current that corresponds to one of a data input value, a logical high value, or a logical low value selected by the selection circuit, or a zero value otherwise; an optical sensor module corresponding to the optical output of the laser diode; and a controller configured to provide control values for the laser drive circuit corresponding to an optical sensor module output.SELECTED DRAWING: Figure 8

Description

  In an optical fiber communication system, it is important for many reasons that the output power of the transmitting laser diode can be controlled. First, the laser average and peak power should not exceed certain limits to avoid damage. Secondly, the different power levels corresponding to binary (or other radix) data values have a modulation index (or defined as extinction ratio) that can be used to ensure reliable reception at the end of the link. Must be set to be inside. One difficulty in dealing with any control system is that laser characteristics can change significantly with temperature and with age, and even with deviations from the ideal linear response. ”And“ low ”drive current levels, the conventional factory setup is not sufficient.

  There are a number of techniques in the prior art that describe methods aimed at estimating instantaneous values of minimum and maximum transmitted light output and compensating for changes in device characteristics. Due to the limited bandwidth of monitor diodes and associated circuitry, their effectiveness is largely limited. Others exist in the data stream or require a specific pattern to be intentionally inserted into the data stream in some defined way.

  Monitoring the transmitted output power is even more difficult with optical communication links that transmit data in a series of discrete bursts, because the simple average value of the optical output can vary significantly over time. And because the instantaneous level is not sufficiently stable for most methods described in the prior art to reach a reasonable estimate of the minimum and maximum levels. Temperature related effects are likely to be more severe because the transmit laser diode may be off for an extended period of time before being activated for a data burst, and therefore during the data burst. This is because it can be cooled to the ambient temperature before the temperature rises.

  Therefore, it is desirable to be able to detect the minimum and maximum light outputs corresponding to logic “1” and logic “0” almost continuously during a data burst. Furthermore, it is desirable to be able to perform such measurements by means that use the transmit power monitoring function with only a moderate bandwidth, and that do not disturb the transmit data payload and do not degrade the noise performance of the received signal. Such an approach is proposed in US Pat.

British Patent No. 2541291 (UK Patent Application No. 161198.0)

  However, the method described above has the advantage that there is only one data point per data burst, and is therefore susceptible to noise because it can have an unacceptable effect on 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 a burst mode optical communication system by using further measurements of the light level during each data burst.

  According to a first aspect, a system is provided for transmitting a sequence of at least two data bursts in an optical fiber communication system. The system selects a data input value during a data transmission period during a specified burst period and a logic high value and a logic low value during an extension period during the specified burst period and immediately after the data transmission period. For the sequence of at least two data bursts, the data input such that at least one data burst is a logical low value burst and at least one data burst is a logical 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, a logic high value or a logic low selected by the selection circuit during the specified burst period A current corresponding to one of the values or a zero value so that the laser diode provides a light output. A drive circuit configured to provide the current to a laser diode; and a sensor module output corresponding to the light output of the laser diode, the logic high value and the logic low value corresponding to the sequence of bursts An output configured to provide an output of the sensor module that provides an electrical output proportional to the optical output of the laser diode, and further corresponding to an average value of the sensor module output only during the data transmission period during the sequence of bursts An optical sensor module configured to provide an optical signal output power level of the laser diode, and a light output of the laser diode corresponding to the logic high value and the logic low value. Receive proportional output from the photosensor module And receiving the output corresponding to an average value of the sensor module outputs only during the data transmission period during the sequence of bursts, and using the outputs from the photosensor module and the desired value, And a controller configured to provide a control value to the drive circuit.

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

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

The current may include a stationary component and a variable component.
The drive circuit may be configured to set the current supplied to the laser diode in accordance with 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 applied 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 modulation current to the laser diode.
The drive circuit may be configured to set the current supplied 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 circuit may alternately select one of the logic high value and the logic low value for each successive extension period.
The selection circuit may select the logic high value or the logic low value for each successive extension period according to a predetermined sequence.
The selection circuit may select the logic low value immediately after an extended period in which the logic high value is selected.
The selection circuit may have a selector switch function.
The bandwidth of the selection circuit may be configured to be switchable between the data input, the logic high value, and the logic low value in a time significantly shorter than the time of the extension period.

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

The system may comprise substantially digital circuitry.
The control value for the drive circuit may be calculated by a digital calculation function.
The system may comprise substantially analog circuitry.

  According to a second aspect, a method is provided for transmitting a sequence of at least two data bursts in an optical fiber communication system. The method selects a data input value during a data transmission period during a specified burst period and a logic high value and a logic low value during an extension period during the specified burst period and immediately after the data transmission period. For the sequence of at least two data bursts, the data input value, logic, so that at least one data burst is a logic low value burst and at least one data burst is a logic high value burst. Selecting one of a high value or a logic low value and a current corresponding to a data input value, one of a logic high value or a logic low value selected during the specified burst period, or a zero value Applying a current to the laser diode such that the laser diode provides optical output; and Providing 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, Providing an output corresponding to an average value of the output corresponding to the optical output of the laser diode only during the data transmission period, and receiving a desired value for the optical signal output power level of the laser diode; Using the output corresponding to the light output of the laser diode and the desired value to provide a control value to the drive circuit.

  The method includes: an average power of an optical output of the laser diode; an optical output power of the laser diode representing a logical high; an optical output power of the laser diode representing a logical low; and a modulation index of the optical output of the laser diode. The method may further include applying the control value to control at least one of the following.

The current may include a stationary component and a variable component.
The method may further include setting the current supplied to the laser diode in response 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.
Supplying the current may further include supplying a bias current to the laser diode.
Supplying the current may further include supplying a modulation 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 include applying the control value to convey a desired logic high and logic low optical output power level.
The extension period may be longer than a settling time for providing the output.

Selecting one of a data input value, a logic high value, or a logic low value may include alternately selecting the logic high value and the logic low value for each successive extension period.
Selecting one of the data input value, the logic high value, or the logic low value includes selecting the logic high value or the logic low value for each successive extension period according to a predetermined sequence. But you can.
Selecting one of a data input value, a logic high value, or a logic low value may include selecting the logic low value immediately after an extended period in which the logic high value is 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 within a time significantly shorter than the time of the extension period, and the data input value, the logic high value, and the logic low value May include switching between.
Using the output corresponding to the light output of the laser diode and the desired value for supplying a control value to the drive circuit is an average value, a high value, respectively, from the photosensor module scaled by a factor. And providing a control value based on the combination of the low value.

  According to a third aspect, a system is provided for transmitting a sequence of at least two data bursts in an optical fiber communication system. The system selects a data input value during a data transmission period during a specified burst period and a logic high value and a logic low value during an extension period during the specified burst period and immediately after the data transmission period. For the sequence of at least two data bursts, the data input such that at least one data burst is a logical low value burst and at least one data burst is a logical high value burst. Means for selecting one of a value, a logic high value or a logic low value, and a data input value, a logic high value or a logic low value selected by said means for selecting during said prescribed burst period Current corresponding to one or a zero value before the laser diode provides the light output. Means for providing current to the laser diode, and sensor module output corresponding to the light output of the laser diode, the light 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 sensor module output only during the data transmission period during the sequence of bursts, the sensor module output being configured to provide an electrical output proportional to Means for providing a sensor module output; and receiving a desired value for the optical signal output power level of the laser diode; and the optical output power level of the laser diode corresponding to the logic high value and the logic low value. Proportional output of the optical sensor module And receiving the output corresponding to the average value of the sensor module output only during the data transmission period in the sequence of bursts, and using those outputs from the photosensor module and the desired value And control means configured to provide a control value to the means for providing the current to the laser diode.

The means for providing the 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 being configured to provide the sensor module output.

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

The current may include a stationary component and a variable component.
The means for supplying the current to the laser diode may be configured to set the current applied to the laser diode in accordance with a combination of a bias control value and a modulation control value.
The means for supplying 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 providing the current to the laser diode may comprise means for providing a bias current to the laser diode.
The means for providing the current to the laser diode may comprise means for providing a modulation current to the laser diode.
The means for supplying the current to the laser diode may comprise means for setting the current applied to the laser diode in accordance with 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 value to control the means for providing the current 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 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 each successive extension period.
The means for selecting may be configured to select the logic high value or the logic low value for each successive extension period according to a predetermined sequence.
The means for selecting may be configured to select the logic low value immediately after an extended period in which the logic high value is selected.
The means for selecting may be configured 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 at a time significantly shorter than the time of the extension period. It may be configured as follows.
The control means may be configured to generate a control value based on a combination of an average value, a high value, and a low value from the means for providing the light sensor module output, each scaled by a factor.

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

1 illustrates an exemplary configuration for a transmitter in a burst mode optical fiber link using a unidirectional modulation current. Figure 2 shows an exemplary configuration for a transmitter in a burst mode fiber optic link using bidirectional modulation current. The output characteristics of the laser diode and the influence of temperature are shown. The limitation of the conventional estimation method when there is a curvature in the laser characteristics is shown. Figure 2 shows a structure of a typical data burst with a typical allowable laser turn-off time. Fig. 4 shows a burst mode optical signal having high and low reference levels embedded in a valid data packet. Fig. 5 illustrates a burst mode optical signal having a low reference level embedded within a valid data burst period. Fig. 5 illustrates a burst mode optical signal having a high reference level embedded within a valid data burst period. 1 illustrates one embodiment of the present invention using a unidirectional modulation current. 1 shows an embodiment of the present invention using a bidirectional modulation current. Fig. 4 shows a further embodiment of a means for sensing a reference level. Fig. 4 shows a further embodiment of means for obtaining a gate average value from an input.

  The description is not to be construed in a limiting sense, but is merely for the purpose of illustrating the general principles of embodiments of the present invention. For example, operations described as being performed using digital signals and digital circuits can be accomplished using substantially analog signals and analog circuits.

  1a and 1b show a typical configuration in a transmitter suitable for an optical communication system. A current having a steady component and a variable component is supplied to the laser diode 101 by a drive circuit. This current may be in the form of a smaller steady-state bias current 115 having a modulation current 116 that is disconnected by the switching function 110 to indicate a logic low level in the modulation data input 107. Alternatively, a form of average current 125 having bi-directional modulation currents 126, 127 that add and subtract current after selection by switch 120 to produce maximum and minimum values in the optical output under control of input data stream 107. It may be. These currents are supplied by digital-to-analog converters (DACs) 111 and 112 in the case of unidirectional modulation currents, or by digital-to-analog converters (DACs) 121 and 122 in the case of bidirectional modulation currents. These DACs may have a current output controlled by each digital value 113, 114 or 123, 124 set by a controller function 117 or 128, respectively.

  When operating in burst mode, these currents may be gated in a manner corresponding to the active transmission period in the data burst by means of an additional signal or signals 108 corresponding to a defined length of the transmission burst. .

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

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

  In a given practical system, the maximum current can be set so that the average operating power of the laser is set to 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 light output, usually called the extinction ratio (ER), which affects the signal-to-noise level of the receiver. ER is a function of the minimum and maximum laser diode current values and may be expressed as a simple linear relationship, but in practice this is not an accurate representation.

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

  When 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 the peak and trough optical data levels by averaging some kind of measurement to provide a reliable estimate of the ER and average optical power. Have a good time. Systems for this purpose are known in the prior art that often use slow modulation of absolute drive current levels (eg, Smith et al, Electronics Letter Vol 14, 1978, and similar derivative devices). .

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

  In such burst mode systems, the problem of controlling average power and ER is difficult to solve. The laser is relatively cold before the burst begins. As soon as the data packet is transmitted, the laser begins to warm up and continues to warm during normal bursts. For example, it is a requirement of the standard that the system is operable after 5 short training bursts, during which the operating parameters of the system should be controlled. A means for establishing operating parameters in a timely manner is disclosed in GB 2535553 (GB 2535553B), where an estimate of the slope efficiency of the laser at the start of a series of data bursts is determined. A defined amplitude trial burst is output. Maintaining operating conditions after operation of such a start-up system only by monitoring the average optical power, secondly because of intermittent bursts of optical power, secondly with a well-defined average value. It is generally not satisfactory because of the dependence on having data content in each burst it has. This latter requirement requires that the number of data 0 and 1 values in the burst be substantially equal, which may not be guaranteed.

  After the first training burst when the laser has warmed to a substantially elevated average temperature, there remains a further need to provide a means for accurately controlling the ER of the laser power. Peak and trough measurements are subject to the same monitor channel bandwidth limitations as in a continuous mode system, but the intermittent nature of the signal complicates the requirements and makes the task more difficult.

  In one embodiment of the invention, means for quickly and accurately estimating the value of data “1” and / or the instantaneous value of the light output representing the value of data “0”, or other values as may be defined. And means for estimating the average value of the optical output only during the data content period of each data burst, all of which operate in a manner that does not require modification of the data content of the burst. The estimated value can be used to calculate the required drive current to provide the desired output level, and can be subject to changes in laser characteristics due to short-term heating and / or long-term aging. A further means is provided that can maintain these levels. Depending on the system, 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.

  Note that in FIG. 4, the time to turn off the laser after a burst of data may not be a constant duration, but is likely to depend on the logical 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. high. This turn-on and turn-off time is usually determined by the response time of internal circuitry that maintains the bias current 115 (or average current 125), which is typically designed to respond at the same rate as laser data modulation. Not. However, the bandwidth of the modulation circuit 110 or 120 in response to the modulated data signal 107 is necessarily very fast to switch the laser current at the data symbol rate. Thus, rather than using a bias current (or average current) control to turn off from a “high” state, the modulator circuit 110 or 120 is used to initially very quickly, typically dozens of laser outputs. It can be reduced to a “low” state in about a picosecond. Once the laser power is in the “low” state, the task of turning off to complete quenching becomes much easier. Furthermore, it is difficult to ensure that the bias current 115 (or average current 125) responds to the burst enable signal 108 or substantially equivalent signal at a time interval substantially shorter than the interval 404 required by the standard. Not a task. This approach makes available a time interval that is not very long but is still longer than the transient settling time typical of such monitor channel circuits. With this knowledge, it is possible to take advantage of the above time available at a specified turn-off interval 404 to perform useful measurements on general optical “high” and “low” power levels. is there.

  Simultaneously with the measurement of optical “high” and “low” values during a short extension of a data burst, it is also possible to collect useful information about the current state of the average optical power during transmission of the data content of the burst The average output of the monitor photodiode circuit 105 is acquired during the data period in the burst and outside any settling time required by the monitor circuit. Gate control for such averaging is easily derived from the burst enable signal 108 in several combinations of the data input 107 and other internal logic signals.

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

  A time interval is first defined to provide a framework for the modification, which is substantially shorter than the laser turn-off time 404 allowed by the transmission standard, but more than the settling time of the monitor channel output 105. While satisfying the condition that it is long enough to be substantially long, the bias current control circuit provides enough time remaining in period 404 to completely quench the laser. A feature of the present invention is the replacement of the raw data signal 107 with a modified form of the laser modulation signal 501 where the known logical value at the end of each burst is retained for an extended period T3,502. At the same time, the bias current 115 (or average current 125) to the laser is applied to the burst enable signal so that the bias (or average) and modulation circuitry remain active for a specified period after the data for that burst is complete. Controlled by a modified version of (Laser Current Enable Control Signal 506).

  The logical value of this extension of the data burst may be timed to alternate between “1” shown at 503 in FIG. 5 and “0” shown at 504 in FIG. Alternatively, the logical value of this extension of the data burst may be set to “0” for several consecutive data bursts, as shown in FIG. Alternatively, the logical value of this extension of the data burst may be set to “1” for several consecutive data bursts, as shown in FIG. The duration of this logical value holding period 502 is made sufficiently long so that the monitor channel output 105 can settle to a substantially accurate measurement result. When the logical value held at the end of the data burst is “1”, the laser modulation current 115 (or 125 for bidirectional modulation current) is transferred to the data modulation circuit 110 (or both) at the end of this extended period 502. In the case of directionally modulated current, it is returned to “0” by the command edge 505 of the laser current enable control signal 506 to 120). In this way, the laser current is reduced substantially towards its extinction state by the wide bandwidth modulation circuit function, typically in tens of picoseconds, rather than by a much slower bias current control. As soon as this state is reached, bias current 115 (or average current 125) and modulation current 116 (or 126 and 127 in the case of bi-directional modulation) are turned off by laser current control signal 506 and the laser's The total current decays to zero before the end of the time allowed by the relevant standard. Thus, by these or substantially similar means, the monitor output 105 can be driven to a logic high “1” and logic low without significant limitations resulting from specific data patterns and / or run lengths as is often the case in the prior art. During both “0” data states, a substantially accurate estimate of the proper general light output can be provided.

  During the data burst period, the burst enable signal 108 combined with the data input 107 and other internal signals is used to be fully active for a period within the data transmission period, typically during most of the data transmission period. An active gate signal 508 is provided, which is used to enable the averaging function to calculate an average value from the monitor channel output 105. The gate signal 508 is configured to be 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, maintains an average value at the end of a burst and is somewhat proportional to the new input signal during the next burst to create a rolling average rather than an estimate based on a single burst. Thus, the retained average value can be used.

  From these measurements taken from multiple data bursts, analog values representing optical “0”, optical “1” and optical averages can be converted to digital form and combined with these values. Can be used to determine the general extinction ratio and average optical power in an advantageous manner that minimizes susceptibility to noise and errors. The algorithm also modifies the modulation current 116 (or 126 and 127 in the case of bi-directional modulation) and bias current 115 (or corresponding average current 125) so that the ER and average power match the desired target value of the system. Necessary adjustments to can be determined.

  FIG. 8 shows a configuration according to an embodiment of the present invention. The bias current 115 is set by a current output digital-to-analog converter (DAC) 111, and the modulation current 116 is similarly set by other DACs 112. The control digital values for those DACs are determined by a digital calculation function 826 that inputs the digital feedback 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 logic “1” or logic “0” by a selection circuit, eg, selector switch function 813. it can. When the burst enable signal 108 is asserted to indicate the start of a data burst, the logic control function 811 sets the modulation input path using the selector 813 and passes the input data directly to the modulation circuit 110. The modulated optical signal is generated by the laser 101, and the monitor signal 105 band-limited by the monitor diode 102 and the associated amplifier 103 is generated. This monitor signal 105 is directly converted to a digital value 821 by an analog-to-digital converter (ADC) 820. This output 821 can be used during the data transmission portion of the data burst, but it will be of a limited value due to bandwidth limitations of this channel. At the end of the data payload, the burst enable signal 108 indicates 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 takes a predetermined postponement time and keeps the bias current and modulation current on. An additional burst status signal 810 can change the logical value 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”, during postponement of the end of the burst, the modulation input selector 813 may have a logic “1” 503 so that the optical output is held at the high level 302. 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. For a sufficiently short period 502. Monitor channel output 105 is converted to digital form 821 and then passed to first register 824 at the appropriate time via logic gate 822 enabled by burst status signal 810. This register then provides the measured optical “high” value to the calculation function 826.

  At the end of this extension period 503, the modulation selector is either left with logic “1” selected or set to logic “0” to remove the laser modulation current 116 using the normal modulation circuit 110, which Reduces the light output very rapidly. At the same instant 505, the control logic 811 commands the bias current DAC 111 and modulation current DAC 112 to stop the output current so that the laser 101 is completely extinguished within the period 404 required by the relevant communication standard. To do.

  If the burst is designated as “low” by the burst status signal 810, the modulation selector 813 is set to logic “0” 504 at the end of the data payload, and the laser output goes to a low level 301. Even if the last symbol of the burst data payload requires a logic “1” at the end of the burst, the transition to logic “0” can be made very fast using the normal 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 quench the laser within the time 404 allowed by the transmission standard. For a sufficiently short period 502. Monitor channel output 105 is converted to digital form 821 and then passed to second register 825 at the appropriate time via logic gate 823 enabled by the logical complement of burst status signal 810. This register then provides the measured optical “low” value to the calculation function 826.

  One convenient configuration would be to alternately designate bursts as “high” and “low”. However, the present invention can also be used when an estimate of one level needs to be acquired earlier than other levels, or when other requirements of the system need to be taken into account, eg noise at any level. In more important cases, any other sequence of “high” and “low” states may be used.

  Also, during each data burst, the output 105 of the monitor diode 102 and associated circuit 103 is passed to an averaging function 804 that operates only when commanded by the gate 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 retains the result when the gate signal indicates that averaging should be stopped be able to. Note that the end of the gating signal 508 ensures that the averaging function does not consider setting the laser power to a “high” or “low” state during the extension of the data burst 504. The averaging function may take into account each calculation of previous average values and optimize response time and noise immunity as is done in a general manner by those skilled in the art when using such functions The weighting or attenuation rate defined to do so can be used. The output 805 of the averaging function 804 is passed to the ADC 806, converted to digital form after each data burst, and passed to the register 807. The timing of conversion to the digital format can be easily synchronized by using the control signal 801. The output of the register 807 is also passed to the calculation function 826.

  The calculation function 826 then obtains estimates for the optical “high” value, the optical “low” value, and the optical average value, and obtains the desired target value inputs for the average value 131 and the ER 132. Using a simple calculation, a new bias current control value 113 and a new modulation current value 114 are obtained. 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 can be considered. The calculation is performed such that the error between the calculated ER value and average value and the corresponding required ER value and average value is minimized to a negligible or acceptable level. This process requires several iterations of “high” and “low” bursts and several average operations, and the exact convergence speed of the system is limited to the input and other system variables in a particular application. Depends on the scaling factor selected.

  These scaling factor values may be fixed or variable. For example, the coefficients may be determined at the time of manufacturing and testing and stored in the system. Alternatively, the user can determine the numerical values of the coefficients during the test or as a result of monitoring the extension action, optimize the values from these monitors and store them in the system. As another alternative, a controller function may be built that has the ability to change the coefficients while the system uses other performance information or is used adaptively starting from a defined starting value. .

  FIG. 9 shows a configuration according to the second embodiment of the present 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 necessary target value inputs for the average value 131 and the ER 132. And a new average current control value 123 and a new bi-directional modulated current value 124 are obtained using simple calculations. The calculation is similarly a number of 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 account for optical “high”, optical “low” and optical averages. The calculation is performed such that the error between the calculated ER value and average value and the corresponding required ER value and average value is minimized to a negligible or acceptable level. This process requires several iterations of “high” and “low” bursts and several average operations, and the exact convergence speed of the system is limited to the input and other system variables in a particular application. Depends on the scaling factor selected.

  These scaling factor values may be fixed or variable. For example, the coefficients may be determined at the time of manufacturing and testing and stored in the system. Alternatively, the user can determine the numerical values of the coefficients during the test or as a result of monitoring the extension action, optimize the values from these monitors and store them in the system. As another alternative, a controller function may be built that has the ability to change the coefficients while the system uses other performance information or is used adaptively starting from a defined starting value. .

  FIG. 10 illustrates an embodiment of a configuration that can be used in the system to provide digital information regarding the estimation of optical “high” and optical “low” levels without using conventional ADC functions. The analog input 1007 is compared with a desired reference value 1003 in a comparator 1004. The output of the comparator may be gated with a select signal 1008 in some logic function 1005 so that the counter 1006 is incremented or decremented when the enable sampling clock signal 1009 is present. By these means, the digital output 1010 increases or decreases according to the sign of the difference between the input signal 1007 and the reference value 1003. If this value 1010 is used in any closed loop system, such as the system presented herein, the value of the input signal 1007 tends to be close to the reference value 1003 and equal. It is convenient to use the DAC 1002 to convert a digital format 1001 standard to an analog standard 1003.

  FIG. 11 shows an embodiment of a simple means for obtaining the gate average value from the analog input signal 1101. The analog input signal 1101 is passed to an analog integrator including an amplifier 1103, a resistor 1105, and a capacitor 1104 through a switching function 1107 under the control of a 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 the switch 1107 is opened under the control of the gate signal 803, the integration and averaging operations are stopped and the value is held. Output value drift is due to electrical imperfections in the components used. It is desirable to have some attenuation function for the averaging operation. The simple and convenient method shown is to connect a resistor 1106 across the capacitance 1104 with a switch 1108 that allows the output to decay at a rate set by the relative values of these components. is there.

  Over a large number of data bursts, the system adjusts the current so that the error is minimized, so that the laser operates at substantially the desired average light output and substantially the desired ER.

  Although the present invention has been described with reference to specific examples and possible embodiments thereof, these should in no way be construed as limiting the scope of the invention. Many other possible embodiments, modifications and improvements can be incorporated into the present invention or can be incorporated with the present invention without departing from the scope and spirit of the claimed invention. Is clear.

Claims (22)

A system for transmitting a sequence of at least two data bursts in a fiber optic communication system, comprising:
Select the data input value during the data transmission period in the specified burst period, and select one of the logic high value and the logic low value during the specified burst period and during the extension period immediately after the data transmission period For the sequence of at least two data bursts, the data input value, the logic high value, such that 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 or a logic low value selected by the selection circuit during the specified burst period, or a zero value, such that the laser diode provides an optical output. A drive circuit configured to provide a current to the laser diode;
Sensor module output corresponding to the light output of the laser diode, the sensor module output providing an electrical output proportional to the light output of the laser diode corresponding to the logic high value and the logic low value in the sequence of bursts An optical sensor module configured to provide an output corresponding to an average value of the sensor module output only during the data transmission period during the sequence of bursts; and
Receiving a desired value for the optical signal output power level of the laser diode and receiving an output from the photosensor 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 the output corresponding to an average value of the sensor module output only during the data transmission period during the sequence of bursts, wherein each value is scaled by a factor. The controller configured to provide a control value to the drive circuit using an average value of output from the sensor module, a high value and a low value, and a combination of the desired value;
Including system.   The system of claim 1, wherein the photosensor module comprises a photodiode output power detector.   The system according to claim 1 or 2, wherein the photosensor module comprises a photosensor and a transimpedance amplifier, the transimpedance amplifier being configured to provide the sensor module output.   The control values are: average power of the laser diode light output, power of the laser diode light output representing a logic high, power of the laser diode light output representing a logic low, and modulation of the laser diode light output. 4. A system according to any one of claims 1 to 3, configured to control at least one of the indices.   The system according to claim 1, wherein the current includes a stationary component and a variable component.   The said drive circuit is comprised so that the said electric current provided to the said laser diode may be set according to the combination of a bias control value and a modulation | alteration control value. system.   The system according to 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 applied to the laser diode.   The system of claim 1, wherein the drive circuit comprises a bias circuit configured to provide a bias current to the laser diode.   The system according to claim 1, wherein the drive circuit comprises a modulation circuit configured to provide a modulation current to the laser diode.   The system according to claim 1, wherein the driving circuit is configured to set the current to be supplied to the laser diode according to a combination of an average value and a modulation value.   11. A system according to any one of the preceding claims, wherein the burst period is gated by a burst enable signal.   12. A system according to any one of the preceding claims, wherein the control value controls the drive circuit to provide the desired logic high and logic low optical output power levels.   The system according to claim 1, wherein the extension period is longer than a settling time of the sensor module output.   The system according to claim 1, wherein the selection circuit alternately selects one of the logic high value and the logic low value for each successive extension period.   The system according to claim 1, wherein the selection circuit selects the logic high value or the logic low value for each successive extension period according to a predetermined sequence.   The system according to claim 1, wherein the selection circuit selects the logic low value immediately after an extended period in which the logic high value is selected.   The system according to claim 1, wherein the selection circuit has 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 shorter than the time of the extension period. The system according to any one of 17.   19. A system according to any one of the preceding claims comprising substantially digital circuitry.   20. A system according to any one of the preceding claims, wherein the control value for the drive circuit is calculated by a digital calculation function.   19. A system according to any one of the preceding claims, comprising substantially analog circuitry. A method for transmitting a sequence of at least two data bursts in a fiber optic communication system, comprising:
Select the data input value during the data transmission period in the specified burst period, and select one of the logic high value and the logic low value during the specified burst period and during the extension period immediately after the data transmission period And, for the 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, so that the data input value, logic high value or logic Selecting one of the low values;
A current corresponding to one of a data input value, a logic high value or a logic low value selected during the defined burst period, or a zero value, such that the laser diode provides an optical output. Giving to the laser diode,
An 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 period in sequence;
Receiving a desired value for the optical signal output power level of the laser diode;
Combining the desired values for 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 optical signal output power level of the laser diode, and combinations thereof Providing a control value for controlling the current applied to the laser diode using the measured value;
Including methods.