Patent Application
20150110143
Fiber-optic communication networks serve a key demand of the information age by providing high-speed data between network nodes. Fiber-optic communication networks include an aggregation of interconnected fiber-optic links. Simply stated, a fiber-optic link involves an optical signal source that emits an optical signal into an optical fiber, the optical signal carrying information. Due to principles of internal reflection, the optical signal propagates through the optical fiber until it is eventually received into an optical signal receiver. If the fiber-optic link is bi-directional, information may be optically communicated in reverse typically using a separate optical fiber.
Fiber-optic links are used in a wide variety of applications, each requiring different lengths of fiber-optic links. For instance, relatively short fiber-optic links may be used to communicate information between a computer and its proximate peripherals, or between a local video source (such as a DVD or DVR) and a television. On the opposite extreme, however, fiber-optic links may extend hundreds or even thousands of kilometers when the information is to be communicated between two network nodes.
Long-haul and ultra-long-haul optics refers to the transmission of light signals over long fiber-optic links on the order of hundreds or thousands of kilometers. Typically, long-haul optics involves the transmission of optical signals on separate channels over a single optical fiber, each channel corresponding to a distinct wavelength of light using principles of Wavelength Division Multiplexing (WDM) or Dense WDM (DWDM).
Transmission of optical signals over such long distances using WDM or DWDM presents enormous technical challenges, especially at high bit rates in the gigabits per second per channel range. Significant time and resources may be required for any improvement in the art of high speed long-haul and ultra-long-haul optical communication. Each improvement can represent a significant advance since such improvements often lead to the more widespread availability of communications throughout the globe. Thus, such advances may potentially accelerate humankind's ability to collaborate, learn, do business, and the like, with geographical location becoming less and less relevant.
At least one embodiment described herein relates to an assembly that includes a laser diode and an electrical current supply circuit (e.g., a driver circuit). The driver circuit operates such that the assembly has an adjustable impedance. As an example only, the impedance of the assembly may be adjusted such that its impedance is more closely matched with a supply impedance. For instance, in the case of a long haul repeater, the repeater impedance may be more closely matched with the line impedance used to deliver power to the optical repeater.
Rather than rely on a variable resistor to provide variable impedance, the driver circuit operates to alternate between a first operational phase and a second operational phase when a voltage is applied between a first supply node and a second supply node. In the first operation phase, current is at least dominantly supplied through the laser diode using a first current path being from the first supply node, directly or indirectly, to the laser diode. The first current path continues from the laser diode, directly or indirectly, to the second supply node. In the second operational phase, current is at least dominantly supplied through the laser diode using a recirculating second current path. The current through the laser diode increases during the first operational phase, and decays during the second operational phase.
For a given applied voltage level between the first and second supply nodes, the duty cycle of the first and second operational phases may be adjusted so that the current through the laser diode is approximately a target current. In some embodiments, a current preservation mechanism, such as an inductor, may be placed in an overlapping portion of the first and second current paths so as to have more refined control over the current through the laser diode.
The principles described herein permit for impedance control to be accomplished at greater efficiency. This is an important advantage when delivering electrical power to remote locations. For instance, suppose that the assembly was in a submarine optical repeater. Such a repeater may be many kilometers away from where power is initially provided. Accordingly, electricity within the repeater itself is at a premium. The improved efficiencies allows the repeater to be powered using less power and/or allows that power to be directed towards other purposes, such as providing Raman amplification to the repeater, to thereby improve the bandwidth of the repeater.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In order to describe the manner in which the above-recited and other advantages and features can be obtained, a more particular description of various embodiments will be rendered by reference to the appended drawings. Understanding that these drawings depict only sample embodiments and are not therefore to be considered to be limiting of the scope of the invention, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
In accordance with embodiments described herein, an assembly is described that includes a laser diode and a driver circuit that operates to give the assembly an adjustable impedance. The driver circuit adjusts impedance by repeatedly alternating between two operational phases. In one operational phase (called a “first” operational phase), current is primarily or fully supplied through the laser diode using a first current path being from the first supply node, to the laser diode, and into the second supply node. In the other operational phase (called a “second” operational phase), current is supplied through the laser diode using a recirculating second current path.
The current through the laser diode increases during the first operational phase, and decays during the second operational phase. For a given applied voltage level between the first and second supply nodes, the duty cycle of the first and second operational phases may be adjusted so that the current through the laser diode is approximately a target current. A current preservation mechanism, such as an inductor, may be placed in an overlapping portion of the first and second current paths so as to have more refined control over the current through the laser diode.
The principles described herein permit for impedance control to be accomplished at greater efficiency. Impedance matching and efficient power delivery are important advantages when considering delivering electrical power to remote locations.
For instance, suppose that the assembly was in a submarine optical repeater. In that case, the power is delivered over a long electrical conductor that is perhaps tens, hundreds, or even thousands of kilometers in length. Thus, the impedance of the power delivery cable may vary greatly as the precise distance (and thus impedance) of the electrical conductor might not be predetermined By allowing the assembly to have an adjustable impedance, the impedance of the assembly may be made to more closely match the impedance of the electrical conductor, whatever the impedance of the electrical conductor might be.
Furthermore, electricity within the repeater itself is at a premium given the electrical losses that occur over the long stretch of the electrical conductor. The improved efficiencies allows the repeater to be powered using less power and/or allows that power to be directed towards other purposes, such as providing Raman amplification to the repeater, to thereby improve the bandwidth of the repeater.
The driver 120 provides current to the laser diode during operation when a voltage (hereinafter referred to as “VS”) is applied between a first supply node 121 and a second supply node 122 of the driver 120. Element 130 permits the voltage VS to be maintained by preventing the supply nodes 121 and 122 from being shorted to each other. The amount of current that is to flow through the laser diode should also be relatively stable. An example of a rated current that might flow through a laser diode is, for example, 400 mA (or 0.4 amps). However, the principles described herein are not limited to the desired amount of current to flow through the laser diode 110. In general, the rated current to flow through laser diode will be referenced herein as “I”.
The voltage VS that is applied across the supply nodes 121 and 122 may be very different than the voltage drop across the laser diode (V). During operation, the driver 120 repeatedly alternates between a first operational phase 131 and a second operational phase 132. These operational phases 131 are illustrated abstractly in
During the first operational phase, current is at least dominantly supplied through the laser diode using a first current path 151 being from the first supply node 121, directly or indirectly, to the laser diode 110, the first current path 151 continuing from the laser diode 110, directly or indirectly, to the second supply node 122. In this first operational phase 131, the current through the laser diode 110 increases. In this description and in the claims, current is “at least dominantly supplied” through a component along a current path when the current that travels along the entire current path either entirely passes through the component, or at least the majority of the current that passes through the component is current that travels along the entire current path. Here, however, it is preferred that during the first operational phase 131, the current passing through the laser diode 110 is entirely supplied along the first current path 151.
During the second operational phase 132, current is at least dominantly supplied through the laser diode using a recirculating current path 152. In this recirculating current path 152, the current flows in a recirculating motion through the laser diode 110 and clockwise as illustrated by the dotted recirculation arrow 152. The first current path 151 and the second current path 152 overlap somewhat to define an overlapping portion 153 (see the more thick-lined portion of the assembly 100 labeled as 152). The laser diode 110 resides within the overlapping portion 153 so that the laser diode 110 receives current along the first current path 151 when the driver 120 is operating in the first operational phase 131, and receives current along the second current path 152 when the driver 120 is operating in the second operational phase 132. Since most (or all) of the current is supplied by a power source in the first operational phase 131, and most (or all) of the current is merely recirculating in the second operational phase 132, the current passing through the laser diode 110 increases during the first operational phase 131, and decays during the second operational phase 132.
Although there are no circuit elements (other than the laser diode 110) illustrated as being within the current paths 151 or 152, there may be other circuit elements within one or both of the current paths. For instance, a current momentum preservation mechanism 133 is only abstractly represented in
During the first operational phase 131, the current through the laser diode 110 will increase from slightly below the target current to slightly above the target current, at which point the driver 120 switches to the second operational phase 132. During the second operational phase 132, the current through the laser diode 110 will decay from slightly above the target current to slightly below the target current, at which point the driver 120 switches to the first operational phase 131. This process repeats. Thus, so long the driver 120 repeatedly switches between the first and second operational phases 131 and 132 at a high enough frequency, the current through the laser diode 110 will hover closely around a target current.
The duty cycle D1 of the first operational cycle 131 will depend on the supply voltage VS supplied across the supply nodes 121 and 122 approximately according the following equation 1:
D1=V/VS (1)
For instance, suppose that the diode voltage is 2.5 volts, and the diode current is 0.4 amps (resulting in a power of 1 watt). If the voltage supply VS were 10 volts, the duty cycle of the first operational phase would be 25% (or 2.5 volts/10 volts). If the voltage supply VS were 5 volts, the duty cycle of the first operational phase would be 50% (or 5 volts/10 volts). Thus, the driver 120 is operational for a wide variety of supply voltages VS. In one embodiment, the duty cycle D2 of the second operational phase is merely the unitary complement of the duty cycle D1 of the first operational phase. In other words, the sum of the first and second duty cycles (D1+D2) is equal to unity (1). However, the principles of the present invention do not preclude the use of further operational phases.
The assembly 100 allows the power in the system to be efficiently used. For instance, assuming 100 percent efficiency, the power supplied through the laser diode 110 should be the same as the power supplied by the voltage source, regardless of the current supplied by the voltage source. Thus, suppose that the current supplied through the 2.5 volt laser diode was 0.4 amps (for 1 watt of total power). The power supplied by a 10 volt supply voltage should be 0.1 amps (10 volts×0.1 amps=1 watt). Likewise, the power supplied by a 5 volt supply voltage should be 0.2 amps (5 volts×0.2 volts=1 watt). Though the assembly allows for improved power efficiency, the efficiency still may fall short of 100 percent. But approximately speaking, by adjusting the duty cycle D1, the power supplied by the driver 120 remains the same while adjusting the current. This has the effect of adjusting the impedance of the assembly 100.
This assembly may be especially useful in cases where there is significant source impedance, as might be the case, for example, should the power be supplied remotely to the assembly 100. For instance, perhaps a line conductor (e.g., a power cable) of several hundred kilometres is providing power from a terrestrial location to a laser driver assembly (perhaps within a submarine repeater) that is operating in a submarine environment.
The maximum power theorem states that the source and load impedance have to be the same to achieve maximum power transfer. In the context of powering a repeater, the power cable impedance (i.e., the source impedance in a repeater environment) is relatively fixed at approximately 1 Ω/km. Accordingly, the principles described herein allow the assembly impedance (i.e., the repeater impedance) to be adjusted thereby allowing a match between source and load impedances in a submarine environment, regardless of what the actual voltage levels are that are received at the repeater. The efficient use of power at the assembly 100, the ability to do adjust the impedance of the assembly 100, and along with the tremendous cost of supplying power over remote distances, make the assembly particularly advantageous in powering remotely located assemblies, such as an assembly in a submarine or remotely located terrestrial repeater.
A controller 141 control a duty cycle of the first and second operational phases so as to control an amount of current flowing through the laser diode 110. In embodiments in which the voltage supply VS, the efficiency of the driver 120, and the efficiency of the laser diode 110 are relatively stable, the duty cycle D1 of the first operational phase (and hence the duty cycle D2 of the second operational phase) may also be relatively constant. In this case, perhaps the controller affixes the duty cycle D1 of the first operational phase based on a configuration setting. However, to afford flexibility, the controller 141 may control the duty cycle based on a measured light output of the laser diode 110. Thus, if the voltage supply VS, the efficiency of the driver 120, and/or the efficiency of the laser diode 110 were to change over time, the controller 141 would respond with an appropriate adjustment to the duty cycle D1.
In
In addition to the controller 210, each assembly 221, 222, 223 may have their own controller, as described in
Alternatively or in addition, the controller 210 may communicate with each assembly's controller to indirectly control the duty cycle of each driver. For instance, if the measured light from the assembly 221 were to decline, the controller 210 might respond by instructing the assemblies 222 and/or 223 to increase their light output. In the case of a configuration setting affixing the duty cycle, the controller 210 may change that configuration setting for the assemblies 222 and/or 223. In the case of a controller for each assembly, dynamically adjusting the duty cycle based on measured light output, the controller 210 may instruct the assembly-specific controller(s) to change the desired light output for that assembly. Thus, should an assembly and/or diode fail, the controller 210 may encourage a relatively stable light output by adjusting the intensity of light output for the other laser diodes. By providing multiple levels of redundancy, the reliability of the environment 200 is quite strong. For instance, each of the assemblies 221, 222 and 223 may have multiple controllers (see controller 140 of
An inductor 333 is placed in the overlapping portion of the current paths, and represents an example of the current momentum preservation mechanism 133 of
As illustrated the inductor 333 (the solid-lined box) may be placed between the first supply node 321 and the laser diode 310 in the first current path 351, but still in the overlapping portion. Alternatively or addition, an inductor 333′ (the dashed-lined box) may be placed between the second supply node 322 and the laser diode 311 in the first current path 351, but still in the overlapping portion.
A switch (also called herein a “first” switch) is positioned in the first current path 351, but not in the overlapping portion. For instance, as illustrated, the first switch 361 (the solid-lined box) may be placed between the first supply node 321 and the laser diode 310 in the first current path 351, but not in the overlapping portion. Alternatively, the first switch 361′ (the dashed-lined box) may be placed between the second supply node 322 and the laser diode 310 in the first current path 351, but not in the overlapping portion. The first switch 361 (and/or switch 361′) is closed during the first operational phase 131 allowing current to flow along the first current path 351, and is open during the second operational phase 132, preventing or inhibiting current from flowing from the voltage supply 323.
The assembly 300 also includes a component 362 that is positioned in the second current path 352, but not in the overlapping portion. The component 362 allows current to recirculate during the second operational phase 132, but prevents or inhibits current from flowing through the component 362 during the first operational phase 131.
In a synchronous example, the component 362 is a second switch that is opened during the first operational phase 131, but closed during the second operational phase. Such a configuration may achieve power efficiencies as high as 95 percent or even higher. Alternatively, in an asynchronous embodiment, the component 362 may be another diode that allows current to flow upwards in
In operation, during the first operational phase 131, the switch 361 is closed, and the component 362 does not allow significant current to flow (either because it is an open switch in the synchronous embodiment, or a reverse-biased diode in the asynchronous embodiment). Thus, in the first operational phase 131, current is supplied to the laser diode 310 from the voltage source 323 along the first current path 351. During the second operational phase 132, the switch 361 is open, but the component 362 does allow current to flow upwards (either because it is a closed switch, or because it is a forward-biased diode). Thus, the current flows along the recirculating current path 352 during the second operational phase 132.
First, an initial voltage is applied between the first and second supply nodes (e.g., supply nodes 121 and 122) of the driver circuit (act 401). Note that in order to provide a particular supply voltage to the driver circuit remotely, since there will be voltage loss in the line conductor (e.g., the power cable), a much higher voltage may have to be applied to the line conductor in order to account for such line losses. A parameter of the system is then measured (act 402). The applied voltage is then adjusted (act 403) and the parameter re-measured (act 402) until the parameter achieves its desired range. This repeating is represented by arrow 404. As described above, such adjustment of the applied voltage to the assembly 100 will cause a corresponding change to the duty cycle of the first operational phase 131 of the assembly 100, thereby adjusting the impedance of the assembly. Thus, the applied voltage may be adjusted in order to achieve the desired assembly impedance. In one embodiment, the applied voltage is adjusted until 70, 80, 90, or 95 percent impedance matching between the source (e.g., the power cable) and the load (e.g., the repeater) is achieved.
In the optical communications system 700, information is communicated between terminals 701 and 702 via the use of optical signals. For purposes of convention used within this application, optical signals travelling from the terminal 701 to terminal 702 will be referred to as being “eastern”, whereas optical signals traveling from the terminal 702 to the terminal 701 will be referred to as being “western”. The terms “eastern” and “western” are simply terms of art used to allow for easy distinction between the two optical signals traveling in opposite directions. The use of the terms “eastern” and “western” does not imply any actual geographical relation of components in
In one embodiment, the optical signals are Wavelength Division Multiplexed (WDM) and potentially Dense Wavelength Division Multiplexed (DWDM). In WDM or DWDM, information is communicated over each of multiple distinct optical channels called hereinafter “optical wavelength channels”. Each optical wavelength channel is allocated a particular frequency for optical communication. Signals that fall within the particular frequency will be referred to as respective optical wavelength signals. Accordingly, in order to communicate using WDM or DWDM optical signals, the terminal 701 may have “n” optical transmitters 711 (including optical transmitters 711(1) through 711(n), where n is a positive integer), each optical transmitter for transmitting over a corresponding eastern optical wavelength channel. Likewise, the terminal 702 may have “n” optical transmitters 721 including optical transmitters 721(1) through 721(n), each also for transmitting over a corresponding western optical wavelength channel. The principles described herein are not limited, however, to communications in which the number of eastern optical wavelength channels is the same as the number of western optical wavelength channels. Furthermore, the principles described herein are not limited to the precise structure of the each of the optical transmitters. However, lasers are an appropriate optical transmitter for transmitting at a particular frequency. That said, the optical transmitters may each even be multiple laser transmitters, and may be tunable within a frequency range.
As for the eastern channel for optical transmission in the eastern direction, the terminal 701 multiplexes each of the eastern optical wavelength signals from the optical transmitters 711 into a single eastern optical signal using optical multiplexer 712, which may then be optically amplified by an optional eastern optical amplifier 713 prior to being transmitted onto a first fiber link 714(1).
There are a total of “m” repeaters (labeled 715 for the eastern repeaters and 725 for the western repeaters) and “m+1” optical fiber links (labeled 714 for the eastern fiber links and 724 for the western fiber links) between the terminals 701 and 702 in each of the eastern and western channels. However, there is no requirement for the number of repeaters in each of the eastern and western channels to be equal. In a repeatered optical communication system, “m” would be one or greater. Each of the repeaters, if present, may consume electrical power to thereby amplify the optical signals.
The eastern optical signal from the final optical fiber link 714(m+1) is then optionally amplified at the terminal 702 by the optional optical amplifier 716. The eastern optical signal is then demultiplexed into the various wavelength optical wavelength channels using optical demultiplexer 717. The various optical wavelength channels may then be received and processed by corresponding optical receivers 718 including receivers 718(1) through 718(n).
As for the western channel for optical transmission in the western direction, the terminal 702 multiplexes each of the western optical wavelength signals from the optical transmitters 721 (including optical transmitters 721(1) through 721(n)) into a single western optical signal using the optical multiplexer 722. The multiplexed optical signal may then be optically amplified by an optional western optical amplifier 723 prior to being transmitted onto a first fiber link 724(m+1). If the western optical channel is symmetric with the eastern optical channel, there are once again “m” repeaters 725 (labeled 725(1) through 725(m)), and “m+1” optical fiber links 724 (labeled 724(1) through 724(m+1)).
The western optical signal from the final optical fiber link 724(1) is then optionally amplified at the terminal 701 by the optional optical amplifier 726. The western optical signal is then demultiplexed using optical demultiplexer 727, whereupon the individual wavelength division optical channels are received and processed by the receivers 728 (including receivers 728(1) through 728(n)). Terminals 701 and/or 702 do not require all the elements shown in optical communication system 700. For example, optical amplifiers 713, 716, 723, and/or 726 might not be used in some configurations. Furthermore, if present, each of the corresponding optical amplifiers 713, 716, 723 and/or 726 may be a combination of multiple optical amplifiers if desired.
Often, the optical path length between repeaters is approximately the same. The distance between repeaters will depend on the total terminal-to-terminal optical path distance, the data rate, the quality of the optical fiber, the loss-characteristics of the fiber, the number of repeaters (if any), the amount of electrical power deliverable to each repeater (if there are repeaters), and so forth. However, a typical optical path length between repeaters (or from terminal to terminal in an unrepeatered system) for high-quality single mode fiber might be about 50 kilometers, and in practice may range from 30 kilometers or less to 100 kilometers or more. That said, the principles described herein are not limited to any particular optical path distances between repeaters, nor are they limited to repeater systems in which the optical path distances are the same from one repeatered segment to the next.
The optical communications system 700 is represented in simplified form for purpose of illustration and example only. The principles described herein may extend to much more complex optical communications systems. The principles described herein may apply to optical communication systems in which there are multiple fiber pairs, each for communicating multiplexed WDM optical signals. Furthermore, the principles described herein also apply to optical communications in which there are one or more branching nodes that split one or more fiber pairs and/or optical wavelength channels in one direction, and one or more fiber pairs and/or optical wavelength channels in another direction.
Accordingly, the principles described herein provide for an assembly that drives a laser diode efficiently while providing for the adjustment of the impedance of the assembly. Although not limited to a repeatered environment, the assembly may be included within a submarine or terrestrial repeater, and permit customized impedance matching appropriate for the optical system.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
The present application claims priority under 35 U.S.C. 119(e) to U.S. provisional application Ser. No. 61/780,534 filed Mar. 13, 2013, which provisional patent application is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61780534 | Mar 2013 | US |
