Photocurrent sensing for feedback control

Abstract

An electroabsorption modulated laser can include a first diode and a second diode. The first diode can be operable to receive a first voltage and generate a first output. The second diode can be coupled to the first diode and can be operable to receive a second voltage. The second diode can use the first output and the second voltage to generate a photocurrent.

Description

Cross-references to related applications

[0001] This U.S. patent application claims priority to U.S. Provisional Patent Application No. 63 / 593,704, filed October 27, 2023, entitled “PHOTOCURRENT SENSING FOR FEEDBACK CONTROL,” and U.S. Provisional Patent Application No. 63 / 556,396, filed February 21, 2024, entitled “PHOTOCURRENT SENSING FOR FEEDBACK CONTROL,” the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0002] This disclosure relates to optical data transmission, and more specifically, to using photocurrent sensing to optimize the performance of optical data transmission. Background Technology

[0003] Unless otherwise indicated herein, the material described herein is not prior art to the claims of this application and is not considered prior art by virtue of its inclusion in this section.

[0004] Optical transceivers for data center applications in the prior art can operate at symbol rates exceeding 56 gigabits per second. One way to transmit optical signals at this speed can involve using high-speed electronic circuitry to drive the modulator terminals of a high-speed electro-optical device called an electro-absorption modulated laser (EML), thereby converting the electrical signal into an electrical signal carried by the laser. The EML can include a distributed feedback laser that can feed the electro-absorption (EA) modulator. The EA modulator can take the form of a PIN diode, whose absorption characteristics can depend on the voltage applied to the terminals of the EA modulator. In some instances, the output of the EML may suffer degradation in certain environments. Degradation can cause the generated optical signal to have increased noise levels, which can lead to data loss in some instances. For example, existing systems may rely on lookup tables to adjust the operation of the EML to accommodate changes in operating temperature. While these types of approaches may be beneficial in certain use cases, they may not address issues such as poor factory calibration or system / component degradation over time. In addition, the use of lookup tables may require additional calibration steps when connecting the optical cable to the optical receiver of the optical transceiver.

[0005] The subject matter claimed in this disclosure is not limited to implementations that address any shortcomings or operate only in environments such as those described above. Rather, this background is provided merely to illustrate an example technical field in which some of the implementations described in this disclosure can be practiced. Summary of the Invention

[0006] In an example embodiment, the electroabsorption modulated laser (EML) may include a first diode and a second diode. The first diode is operable to receive a first voltage and generate a first output. The second diode may be coupled to the first diode and is operable to receive a second voltage. The second diode may use the first output and the second voltage to generate a photocurrent.

[0007] In another embodiment, an apparatus may include an EML and sensing circuitry. The EML may include a first diode and a second diode. The first diode is operable to receive a first voltage and generate a first output. The second diode may be coupled to the first diode and is operable to receive a second voltage. The second diode may use the first output and the second voltage to generate a photocurrent. In response to the sensing circuitry determining that the photocurrent exceeds a threshold, the sensing circuitry may cause an adjustment to the second voltage, such that the output from the EML may be adjusted.

[0008] In another embodiment, a method may include obtaining a first voltage at a first diode. The method may also include generating a first output in response to the first voltage using the first diode. The method may further include obtaining a second voltage at a second diode. The method may also include generating a photocurrent using the second diode. The photocurrent may be generated using the second diode in response to the first output and the second voltage.

[0009] The objectives and advantages of the embodiments will be realized and achieved, at least by means of the elements, features, and combinations particularly pointed out in the claims. The foregoing general description and the following detailed description are given by way of example and are illustrative of the claimed invention, not limiting. Attached Figure Description

[0010] The example implementation will be described and illustrated with additional features and details using the accompanying drawings, in which:

[0011] Figure 1A and Figure 1B An example electroabsorption modulated laser device and an example implementation of the electroabsorption modulated laser device are shown;

[0012] Figure 2 It shows including Figure 1A An example system of an electroabsorption modulated laser device;

[0013] Figure 3A and Figure 3BThe graphs show example responses of an electroabsorption modulated laser device to various input voltages;

[0014] Figure 4A It shows including Figure 2 An example configuration of the optical transceiver for the sensing circuit shown;

[0015] Figure 4B It shows including Figure 2 Another example configuration of the optical transceiver for the sensing circuit shown;

[0016] Figure 5 An example configuration of a distributed amplifier system is shown;

[0017] Figure 6 A flowchart illustrating an example method for photocurrent sensing for feedback control is shown; and

[0018] Figure 7 The formulas described in this disclosure are shown. Detailed Implementation

[0019] Electroabsorption modulated lasers (EMLs) naturally generate a photocurrent during operation, and accordingly produce a nonlinear transfer function associated with the applied modulation voltage. In many existing systems and devices, the photocurrent is neglected. Furthermore, many existing systems and devices utilize monitoring photodiodes to sense the power of distributed feedback (DFB) lasers.

[0020] This disclosure addresses these and other limitations by monitoring the photocurrent generated by the modulator in the EML within the transceiver and / or utilizing the photocurrent as feedback within the transceiver. The photocurrent can be used for at least: monitoring the power of the DFB laser in the transceiver, improving the quality of the optical signal output from the transceiver, adjusting the modulator in the EML to improve the modulation amplitude and / or extinction ratio, and / or for alignment purposes of optical components in the transceiver.

[0021] Figure 1A An example electro-absorption modulated laser (EML) device 100 according to at least one embodiment of the present disclosure is shown. The EML device 100 may include a first diode 104, a second diode 108, and a ground 110. Figure 1B An EML device 100 implemented in example system 120 is shown. System 120 may include transceiver 150, EML device 100 (e.g., with...), Figure 1A (The same or similar EML device as EML device 100) and housing 112.

[0022] The operation of the EML device 100 can be based on a first voltage 102 driving the first diode 104 and a second voltage 106 applied to the second diode 108. In some instances, the first voltage 102 may be a laser bias voltage, and the second voltage 106 may be a modulation voltage. In some instances, a change in the second voltage 106 may alter the strength of the electric field generated within the second diode 108. In response to the change in the electric field within the second diode 108, the absorption coefficient of the second diode 108 may change, which may alter the amount of laser energy passing through the second diode 108 and exiting the EML device 100.

[0023] In some instances, the second diode 108 may be a photodiode or a PIN photodiode. In some instances, when the second voltage 106 is negative and then applied to the second diode 108, a change in the absorption coefficient of the second diode can be achieved. In some embodiments, some results of applying the second voltage 106 to the second diode 108 may be as follows: Figure 3A and Figure 3B As shown.

[0024] During operation, the first voltage 102 can be maintained at a substantially constant value, while the second voltage 106 can vary. Variations in the second voltage 106 may cause coded data transmission in the output of the EML device 100. For example... Figure 1B As shown, the output of EML device 100 can be received by optical fiber 140. It should be noted that the first diode 104 and the second diode 108 are shown sharing a ground 112, because this configuration indicates that EML device 100 is designed such that the first diode 104 and the second diode 108 are integrated into a single chip. Other configurations are also contemplated (e.g., where the first diode 104 and the second diode 108 are on separate chips), where a first ground can be associated with the first diode 104 and a second ground can be associated with the second diode 108.

[0025] In some instances, the first diode 104 may be a laser diode, and the second diode 108 may be an electro-absorption (EA) modulator. The first diode 104 may be a distributed feedback (DFB) laser, or various other laser diodes (e.g., an EA modulator with an external laser, a distributed Bragg reflector (DBR) laser, etc.). Alternatively or additionally, the second diode 108 may be a PIN diode.

[0026] like Figure 1BAs shown, system 120 may be a transceiver 150 that may include EML device 100. In some instances, transceiver 150 may include housing 112, which may include one or more ports configured to couple optical cable 140 to transceiver 150. In some instances, transceiver 150 may be an optical transceiver, and / or housing may include multiple ports such that multiple optical cables can be coupled to transceiver 150. Optical cable 140 may include a clamp disposed at its end for coupling to housing 112 of transceiver 150. Other methods of coupling optical cable 140 to transceiver 150 may be utilized. In some instances, transceiver 150 may include circuitry configured to send data to and / or receive data from second diode 108 from a server or other computing device that may be used to drive changes in second voltage 106.

[0027] In some instances, the output from EML device 100 and / or transceiver 150 may be an optical signal, and the optical signal may include an optical waveform. In some instances, the photocurrent associated with EML device 100 may be proportional to the optical waveform from EML device 100. In such instances, the photocurrent may be used to provide feedback to adjust the optical waveform, thereby improving the quality of the optical waveform compared to not performing photocurrent-based adjustments. In these and other embodiments, a temperature lookup table may be used to determine the temperature and the curve associated with EML device 100 (e.g., as described herein). Figure 3A and Figure 3B The curve shown represents a change in the optical waveform, which improves the optical waveform.

[0028] Modifications, additions, or omissions may be made to the EML device 100 without departing from the scope of this disclosure. For example, the naming of different elements in the manner described is intended to aid in the illustration of the concepts described herein, and not to limit them. Furthermore, the EML device 100 may include any number of other elements, or may be implemented in a system or context other than that described. For example, Figure 1A and Figure 1B Any component can be divided into additional components, or can be combined into fewer components.

[0029] Figure 2 The illustration shows at least one embodiment of the present disclosure, including... Figure 1A An example system 200 of the EML device 100. System 200 may include, as per the description of... Figure 1B The transceiver 150 and computing device 204 are described. Alternatively or additionally, the transceiver 150 may include components that can interact with... Figure 1A and Figure 1B EML device 100 is similar to EML device 100. Figure 2As shown, the EML device 100 may include a sensing circuit 202.

[0030] In some instances, the sensing circuit 202 can be configured to monitor the output generated by the second diode 108, which can be correlated with the performance of the EML device 100. In some instances, as described herein, the output of the second diode 108 can be a photocurrent. Figure 2 As shown, transceiver 150 can be electrically coupled to computing device 204, which can be external to transceiver 150. In some instances, computing device 204 can be responsible for generating or at least contribute to generating the second voltage 106. In some instances, computing device 204 can be a data center server and / or other computing device that can be cabled to a high-speed data network.

[0031] In some instances, the sensing circuit 202 may include one or more processors configured to monitor changes in photocurrent. Changes in photocurrent from the second diode 108 detected by the sensing circuit 202 can be used to adjust the operation of the EML device 100. For example, the sensing circuit 202 may be configured to adjust the output from the EML device 100 when a reading detected by the sensing circuit 202 indicates that the EML device 100 is operating outside a predetermined range. Alternatively or additionally, the sensing circuit 202 may be configured to delay any adjustment to the output of the EML device 100 to confirm that any change in the output may not be transient in nature. Alternatively or additionally, in some instances, the output from the EML device 100 may be fed into a closed-loop feedback control scheme. In some instances, the sensing circuit 202 may be on a separate die from the EML device 100. Alternatively or additionally, the sensing circuit 202 may be implemented on the same die as the EML device 100.

[0032] Modifications, additions, or omissions may be made to the EML device 100 without departing from the scope of this disclosure. For example, the naming of different elements in the manner described is intended to aid in the illustration of the concepts described herein, and not to limit them. Furthermore, the EML device 100 may include any number of other elements, or may be implemented in a system or context other than that described. For example, Figure 1A and Figure 1B Any component can be divided into additional components, or can be combined into fewer components.

[0033] Figure 3A and Figure 3BGraphs 300a and 300b are shown illustrating example responses of an EML device according to at least one embodiment of the present disclosure to various input voltages. Graphs 300a and 300b may represent the performance of an EML device that may include components such as a DFB laser and a PIN diode. Although EML devices can take many forms, as described herein, graphs 300a and 300b may be associated with a particular implementation. It should be understood that this particular implementation should not be construed as limiting the scope of other devices described herein.

[0034] Figure 3A Figure 300a shows the electroabsorption (EA) modulator in an EML device (e.g., Figure 1A Applying a negative voltage to the second diode (108) can reduce the output power of the EML device. The curve depicted in Figure 300a can be defined by the output power of the laser diode and the characteristics of the EA modulator. The voltage applied to the laser diode can define the magnitude of the original output of the EML device when no voltage is applied to the EA modulator. This original output can define the extinction ratio associated with the EML device, which can include the ratio of the maximum optical power to the minimum optical power of the EML device. In instances where the EML device can be used in high-speed optical communication systems, a high extinction ratio may be valuable because it can increase the possible variation in the laser output as a function of the modulation bias. However, the power output of the laser diode can be limited to a point where the desired extinction ratio can be achieved to avoid unwanted power consumption and / or heat buildup within the associated optical transceiver (which may include the EML device).

[0035] The bias voltage can be modulated so that the EML device operates in the portion of the curve where changes in the modulated voltage can cause relatively large changes in the EML device output. In this configuration, signal modulations can be differentiated from each other, and / or the possibility of signal corruption can be reduced. For devices with, such as Figure 3A The EML device with the output response shown can promote modulation maximization in the modulation bias by values ​​in the range of approximately -2.5V to -2.25V, because this part of the curve can have the steepest slope.

[0036] In some instances, algorithms can be used to adjust the modulation bias voltage to track the slope associated with the photocurrent (e.g., Figure 3AThe performance of the curve (slope in the equation). For example, the modulation bias voltage may change by a certain amount (dV), and a corresponding current change (dI) can be detected. The ratio of the current change to the voltage change (e.g., dI / dV) can then be calculated. The result of this ratio can be used to determine at least one additional change in the modulation bias voltage. For example, in an instance where the ratio is positive, the modulation bias voltage may not be changed. In an instance where the ratio is negative, the sign (e.g., positive or negative) of the modulation bias voltage may be reversed. In these and other embodiments, the algorithm may be executed at a slower rate than the symbol rate in the transmitted data, and / or at a faster rate than the rate at which the temperature in the system may drift.

[0037] Figure 3B Graph 300b illustrates another EML device in which a smaller negative voltage can be used to establish operation within the region of the graph where output power variation is maximized. As shown in Graph 300b, a reverse voltage between -1.0V and -0.5V can be used to operate the EML device in a state where small changes in the modulation bias voltage can cause a discernible change in the optical output power of the EML device. Alternatively or additionally, Graph 300b can illustrate how the EML device can generate a photocurrent proportional to the laser intensity. An approximate optical power output can be determined by monitoring the photocurrent generated by the EA modulator. By monitoring the photocurrent, the operation of the EML device can be adjusted to keep it operating within a desired operating window. For example, in an instance where the manufacturer wants the EML device to have a constant output power of approximately 0.9mW, a controller can be used to adjust the modulation bias voltage until a photocurrent of approximately 14mA can be detected. In some instances, under normal operating conditions, a modulation bias voltage of -0.75V can achieve a photocurrent of approximately 14mA. However, temperature variations and / or (e.g., due to component aging of the EML device) EML device degradation may necessitate adjusting the modulation bias of the EML device to achieve the desired operating state (e.g., approximately 14mA in this example). In some instances, using photocurrent-based feedback control can reduce and / or eliminate the need for time-consuming calibration of individual optical transceivers prior to sale or installation.

[0038] In some instances, the EA modulator may have a modulation transfer function, which can be a nonlinear function of the modulation voltage (also known as the EA voltage) associated with the EA modulator. As described, when a changing signal is applied to the EA modulator, the change in the EA modulator's absorption may cause modulation of the optical power output of the EML device, as in... Figure 3A and Figure 3BThe curves are shown in graphs 300a and 300b, respectively. The average value of the signal applied to the EA modulator terminals can be set by referencing the measured photocurrent value from the EA modulator to optimize the optical modulation amplitude (OMA). OMA can be... Figure 7 Mathematical calculations are performed using formulas 702, 704, and 706.

[0039] Formula 704 can convert P from Formula 702 av Defined as the laser power output (P) when the EA modulator is fully engaged. on ) and laser power output (P) when the EA modulator is not powered. off The average value of ). Formula 706 can be used to calculate r from Formula 702. e Defined as P on and P off The ratio. Figure 3B The photocurrent output shown in graph 300b can be obtained by... Figure 7 Formula 708 is used for management.

[0040] In formula 708, R esp P can represent the responsivity of an EA modulator. in It can be the optical power at the input of the EA modulator, and T(V) bias ) can represent the nonlinear transmission of the EA modulator.

[0041] In these and other embodiments, Figure 3A and Figure 3B The changes in the curves shown can be used for predictive maintenance in systems that include EML devices. For example, as the curve changes (which may be due to thermal drift and / or electronic aging), the response of the corresponding EML device may also change. Based on the changes in the EML device (e.g., according to changes in the monitoring curve), alternative routes in the system can be used to avoid deteriorating / already deteriorated EML devices, and EML devices can be replaced. In some instances, deteriorated EML devices can be replaced before failure, which can improve the performance of systems that include multiple EML devices because the workload can be shifted from deteriorated EML devices to non-deteriorated EML devices, and deteriorated EML devices can be replaced.

[0042] Figure 4A The illustration shows at least one embodiment of the present disclosure, including... Figure 2 The illustrated example configuration of the optical transceiver 400 for the sensing circuit is shown. Specifically, the modulation voltage (e.g., Figure 1AThe second voltage 106 in the data voltage 404 can be represented by the bias voltage 402 and the data voltage 404. The bias voltage 402 can be set to a value that allows the EA modulator to operate within a range suitable for providing a strong response to modulation in the data voltage 404 (e.g., as per the relevant information). Figure 3A and Figure 3B (as described). In the accompanying Figure 3A and Figure 3B The considerations for setting the bias voltage 402 are discussed in more detail in the text. The data voltage 404 can be encoded using the optical transceiver 400 to include digital data communications received from a computing device or server.

[0043] Optical transceiver 400 illustrates how a bias voltage 402 is converted from a digital signal to an analog signal via DAC 406. The bias voltage 402 can be a negative voltage, which can be routed through sensor resistor 408 and / or bias choke 410 before being combined with data voltage 404 at junction 412. The combination of bias voltage 402 and data voltage 404 can be received at modulator 414, within which an electric field is generated that modulates the output of light generated by laser diode 416, and can subsequently be received at optical fiber 417.

[0044] A bias voltage 402 and / or a data voltage 404 are applied to the modulator 414, which increases photon absorption through the modulator 414. The absorption of photons by the modulator 414 causes it to generate a photocurrent that flows back through a contact 412, a bias choke 410, and / or a sensor resistor 408. In some embodiments, a polarization capacitor 418, which may be located in front of the driver 420 and / or the DAC 422 (which can handle the data voltage 404), can prevent the photocurrent from flowing back towards the input line of the data voltage 404. The bias choke 410 may take the form of an inductor configured to filter out high-frequency modulation caused by the modulation of the encoded data introduced by the modulation in the data voltage 404. In this arrangement, the photocurrent arriving at and flowing through the sensor resistor 408 can be a steady current representing the average photon absorption occurring at the modulator 414. The current sensor 424 is operable to measure the photocurrent flowing through the sensor resistor 408. In some instances, the current measurement result can be received at a signal processor 426, which can be responsible for monitoring the photocurrent and / or modifying the operation of the bias generator 428 and / or driver 420. Since the signal processor 426 can be responsible for adjusting based on the steady-state operation of the optical transceiver 400, the photocurrent measurement result at the current sensor 424 can be limited to a pre-configured rate, such as between 100 kHz and 1000 kHz.

[0045] In some instances, signal processor 426 can be configured to adjust the output of bias generator 428 when the measured photocurrent indicates that the optical power output is outside the desired operating range. Signal processor 426 can be configured to be included via a reference (e.g., with...). Figure 3A and / or Figure 3B Optical power output is determined using a lookup table (similar to the data shown) for output power data, modulation bias data, and / or photocurrent data. For example, a lookup table that can be used with... Figure 3B The optical transceiver modeled in this example is similar and can be configured to output a bias voltage of -0.75V, observing a photocurrent of approximately 15mA and corresponding to an optical power output of approximately 0.9mW. In another example, where the photocurrent measured by current sensor 424 is shown to be 13mA, signal processor 426 can determine that the actual optical power output is approximately 1.1mW, higher than expected. In this example, signal processor 426 can be configured to adjust (e.g., increase) the bias voltage until current sensor 424 measures a photocurrent of approximately 15mA. Signal processor 426 can achieve this change by transmitting one or more control commands to bias generator 428.

[0046] This adjustment can be used to correct problems caused by transient issues in the optical transceiver 400, such as heat buildup in the optical transceiver 400. In some instances, the signal processor 426 is operable to make other changes to the operation of the optical transceiver 400. For example, in instances where a detected change in photocurrent coincides with operation affected by increased heat buildup within the optical transceiver 400, the signal processor 426 can instruct the operation of cooling components within the optical transceiver 400 or external heat dissipation devices to attempt to dissipate heat from the optical transceiver 400.

[0047] In some instances, signal processor 426 is operable to adjust the laser voltage 432 of laser driver 430. This modification to laser driver 430 can be implemented when the performance of optical transceiver 400 may deteriorate (e.g., due to aging or damage to laser diode 416 caused by mechanical stress and / or electrostatic discharge). Signal processor 426 can be configured to adjust laser voltage 432 and / or laser current input to compensate for the deterioration of laser diode 416. This modification to the laser diode input can be made if a photocurrent measurement is observed to decrease over time (which may indicate deterioration of laser voltage 432). Signal processor 426 is also operable to provide a warning to a user (e.g., a data center administrator) when it can be determined that the deterioration of laser diode 416 has exceeded a predetermined threshold, where replacement of laser diode 416 and / or optical transceiver 400 may be recommended.

[0048] In some instances, signal processor 426 is operable to implement closed-loop feedback control of optical transceiver 400 based on detected photocurrent. Signal processor 426, bias generator 428, and / or laser driver 430 may include controllers, such as proportional-integral-derivative (PID) controllers, linear quadratic regulator (LQR) controllers, and / or other controllers, operable to change bias voltage 402 or laser voltage 432 in a manner that facilitates controlled transitions in steady-state operation of optical transceiver 400.

[0049] Figure 4B The illustration shows at least one embodiment of the present disclosure, including... Figure 2 The illustrated sensor circuit shows an example configuration of the optical transceiver 400. The optical transceiver 400 can be used with... Figure 4A The optical transceiver 400 is similar and may also include a fiber alignment module 436. It can be used... Figure 4B The optical transceiver 400 is configured to align the optical fiber 417 with the optical transceiver 400.

[0050] In some instances, the signal processor 426 may be positioned to communicate with the fiber optic alignment module 436, which is operable to align the fiber optic cable 417 with the laser energy exiting the modulator 414. Although the fiber optic alignment module 436 is shown within the optical transceiver 400, it should be understood that the fiber optic alignment module 436 may be located outside the optical transceiver 400, as it may be a diagnostic tool and may not be present during operation of the optical transceiver 400. In some instances, the optical transceiver 400 may include a service port (not shown) that facilitates cable attachment between the optical transceiver 400 and the fiber optic alignment module 436, wherein the cable and / or service port enables communication between the signal processor 426 and the fiber optic alignment module 436.

[0051] The fiber alignment module 436 can be configured to shift the position and / or orientation of the end of the fiber 417 based on photocurrent measurement and / or analysis results provided by the signal processor 426. In some instances, the distal end of the fiber 417 may include a reflective end, such that laser energy received by the fiber 417 can be reflected back into the modulator 414. Figure 4B The optical transceiver 400 is described in light of the use of a reflective fiber optic terminal; however, it should be understood that other reflective devices or components may be used to calibrate the proper position of the fiber optic cable 417 relative to the optical transceiver 400.

[0052] As described, modulator 414 can be configured to generate a photocurrent regardless of the direction in which photons propagate through modulator 414. Therefore, light reflected back into modulator 414 may affect the photocurrent sensed by current sensor 424, and the reflected light can be used to provide feedback to fiber alignment module 436 regarding the accuracy of alignment of fiber 417 with the laser energy exiting modulator 414. Fiber alignment module 436 can change the position of fiber 417 relative to modulator 414, and by referencing the measured changes in photocurrent, fiber alignment module 436 can identify the position of fiber 417 relative to modulator 414. The methods described herein can be used to help confirm and / or locate the position of optical ports on optical transceiver 400. For example, using the photocurrent generated by modulator 414 for feedback during alignment processing eliminates the need for fiber alignment module 436 to have a dedicated sensor to monitor the energy output through modulator 414.

[0053] Figure 5An example configuration of a distributed amplifier system 500 (or system 500) according to at least one embodiment of the present disclosure is shown. System 500 may include amplifiers 502, 504, 506, and 508, a modulator 514, a pre-driver 516, a first transmission line 518, a second transmission line 522, a measuring device 524, an inductor 526, an analog-to-digital converter 528, a switching element 530, and an optical fiber 540. In some instances, system 500 is operable to improve the performance of modulators associated with high-speed communication systems (such as a second diode 108, as described herein). Amplifiers 502, 504, 506, and 508 used in system 500 may be transistors, but may also take the form of diodes and / or traveling-wave amplifiers. Figure 5 The illustrated system 500 includes a four-amplifier configuration; however, it should be understood that many other amplifier configurations can be implemented, such as incorporating two, or up to ten or twenty, amplifiers in parallel in example systems similar to system 500. Some examples of transistor-type amplifiers include heterojunction bipolar transistors (HBTs), high electron mobility transistors (HEMTs), indium gallium phosphide (InGaP) HBTs, and / or silicon germanium (SiGe) HBTs. Compared to communication systems that do not include the aforementioned distributed amplifiers, using system 500 for communication can provide wider bandwidth, lower gain ripple, higher power handling capability, improved linearity, and / or enhanced efficiency.

[0054] System 500 may include two inputs: an input signal voltage 510 and a bias voltage 512. The input signal voltage 510 may be modulated to encode data, and the bias voltage 512 may be set at a level designed to allow the synthesized signal to drive the operation of modulator 514. In some instances, the input signal voltage 510 may be input to a pre-driver 516 before entering a first transmission line 518. The pre-driver 516 may have a resistor, for example, such as a resistor of approximately 40 ohms. The first transmission line 518 may be a waveguide or a coaxial cable. The length of the first transmission line 518 may be set to a multiple of the wavelength associated with the input signal voltage 510 exiting the pre-driver 516 to minimize signal reflection. In some instances, the distance 520 between the branches of the first transmission line 518 leading to the respective amplifiers in amplifiers 502, 504, 506, and / or 508 may correspond to the wavelength associated with the input signal voltage 510. The distance 520 between the branches that extend from amplifiers 502, 504, 506 and 508 and intersect with the second transmission line 522 can be approximately the same length, and / or can correspond to the wavelength associated with the input signal voltage 510.

[0055] With, for example, and Figure 4ACompared to a conventional amplifier configuration similar to the driver 420, the distributed amplifiers in system 500 can facilitate improved signal linearity. Since the gain stages can be distributed along the first transmission line 518, improved linearity can be achieved with the distributed amplifiers in system 500. Thus, any nonlinearity caused by individual amplifiers can be averaged out. Amplifier averaging can help determine the modulator's output using photocurrent measurements performed at measurement device 524, which can be configured to measure the photocurrent generated by modulator 514. Although in Figure 5 Not depicted in the system 500 shown, but for EML settings, the configuration may also include a laser diode configured to output laser light traveling through modulator 514 and optical cable 540, and / or may also include a signal processor, as previously described herein, for adjusting the performance of modulator 514 based on measurements taken by measuring device 524.

[0056] In some instances, the measuring device 524 may be configured to measure device reflections and / or channel reflections moving upstream from the modulator 514 via the second transmission line 522, in order to measure and / or optimize the performance of the modulator 514. In some instances, the photocurrent and / or reflections measured at the measuring device 524 may be used together to further improve the performance of the modulator 514. In some instances, the inductor 526 may be operable to further reduce signal reflections and / or perform frequency filtering.

[0057] Alternatively or additionally, system 500 may be operable to remove or substantially remove reflections that may occur from system 500, such that detected reflections may represent reflections that may occur in a channel (such as in optical cable 540). Using channel reflections can improve the understanding of the channel, which may include whether alignment exists within the channel. Thus, since channel reflections can be used to determine alignment, a receiver device (e.g., a receiver device that may be located remotely from system 500) may not be required to determine the alignment of the optical components. Alternatively or additionally, a remote laser may be directed to system 500 via optical cable 540, and system 500 may operate as a photodiode; and using the characteristics of system 500 described herein, the alignment of the optical components can be determined by maximizing the power from the remote laser to align with optical cable 540.

[0058] Figure 5 The diagram also illustrates how the bias voltage 512 is represented via the analog-to-digital converter 528 and the switching element 530. In some instances, the switching element 530 may be a high-speed switching element. The analog-to-digital converter 528 and the switching element 530 may facilitate matching and / or synchronizing the bias voltage 512 and the input signal voltage 510, for example, when synthesizing them at the second transmission line 522.

[0059] Figure 6 A flowchart of an example method 600 for photocurrent sensing for feedback control according to at least one embodiment of the present disclosure is shown. Method 600 may be performed by processing logic, which may include hardware (circuit, dedicated logic, etc.), software (e.g., software running on a general-purpose computer system or a dedicated machine), or a combination of both, wherein the processing logic may be included in any computer system or device.

[0060] For simplicity, the method 600 described herein is depicted and described as a series of actions. However, the actions according to this disclosure may occur in various orders and / or simultaneously, and may occur together with other actions not presented and described herein. Furthermore, not all actions shown can be used to implement the method according to the disclosed subject matter. Additionally, those skilled in the art will understand and appreciate that the method may be represented alternatively as a series of interrelated states via a state diagram or events. Furthermore, the methods disclosed in this specification can be stored on an article of writing, such as a non-transitory computer-readable medium, to facilitate delivery and transmission of the method to a computing device. As used herein, the term "article of writing" is intended to encompass any computer program accessible from any computer-readable device or storage medium. Although shown as discrete boxes, various boxes may be divided into additional boxes, combined into fewer boxes, or eliminated depending on the desired implementation.

[0061] At box 602, a first voltage can be obtained at the first diode. In some instances, the first voltage may be a laser bias voltage.

[0062] At block 604, a first output can be generated in response to a first voltage. The first output can be generated by a first diode.

[0063] At block 606, a second voltage can be obtained at the second diode. In some instances, the second voltage can be a modulated voltage.

[0064] At block 608, a photocurrent can be generated by a second diode. The photocurrent can be generated in response to a first output and a second voltage. In some instances, the laser bias voltage can be kept constant, and the modulation voltage can be varied, such that the photocurrent may include coded data transmission. Alternatively or additionally, the photocurrent can be used to adjust the bias point associated with the second voltage to improve the optical modulation amplitude and / or extinction ratio.

[0065] Modifications, additions, or omissions may be made to method 600 without departing from the scope of this disclosure. For example, in some instances, an optical signal may be output from an electroabsorption modulated laser that can be associated with a first diode and a second diode. The optical signal may be based at least on photocurrent. In another example, reflection of the optical signal may be obtained, and the optical signal and / or the reflected optical signal may be used for optical alignment of the electroabsorption modulated laser.

[0066] In another example, the naming of the different components in the manner described is intended to help illustrate the concepts described herein, not to limit them. Furthermore, method 600 may include any number of other elements, or may be implemented in a system or context other than those described.

[0067] The terminology used in this disclosure, particularly in the appended claims (e.g., the body of the appended claims), is generally intended to be “open-ended terms” (e.g., the term “comprising” should be interpreted as “including but not limited to”).

[0068] Furthermore, if the intention is to specify a particular number of claim statements introduced, this intention will be explicitly stated in the claims, and without such a statement, this intention does not exist. For example, to aid understanding, the appended claims may contain the introductory phrases “at least one” and “one or more” to introduce claim statements. However, the use of such phrases should not be construed as implying that a claim statement introduced by the indefinite article “a” or “an” will limit any particular claim containing such an introductory claim statement to containing only one implementation of such a statement, even if the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and / or “an” should be interpreted as meaning “at least one” or “one or more”); the same applies to the use of definite articles used to introduce claim statements.

[0069] Furthermore, even if a specific number of claims is explicitly stated, those skilled in the art will recognize that such a statement should be interpreted as meaning at least the number stated (e.g., in the absence of other modifiers, a simple statement of "two statements" means at least two statements, or two or more statements). Moreover, in instances where conventions similar to "at least one of A, B, and C" or "one or more of A, B, and C" are used, this construction is generally intended to include a single A, a single B, a single C, A and B together, A and C together, B and C together, or A, B, and C together, etc.

[0070] Furthermore, any transition words or phrases preceding two or more alternative terms, whether in the specification, claims, or drawings, should be understood to include the possibility of including one of the terms, either one of the terms, or both of the terms. For example, the phrase "A or B" should be understood to include the possibility of including "A" or "B" or "A and B".

[0071] All examples and conditional language set forth in this disclosure are intended for pedagogical purposes to aid the reader in understanding the concepts of this disclosure and those contributed by the inventors to advance the art, and should be interpreted as not being limited by the examples and conditions stated therein. Although implementations of this disclosure have been described in detail, various changes, substitutions, and alterations may be made thereto without departing from the spirit and scope of this disclosure.

Claims

1. An electroabsorption modulated laser, comprising: A first diode, which is operable to receive a first voltage to generate a first output; as well as A second diode, coupled to the first diode and operable to receive a second voltage, wherein the second diode uses the first output and the second voltage to generate a photocurrent.

2. The electroabsorption modulated laser of claim 1, wherein, The first voltage is the laser bias voltage, and the second voltage is the modulation voltage.

3. The electroabsorption modulated laser of claim 2, wherein, The laser bias voltage remains constant, and the modulation voltage varies such that the photocurrent includes encoded data transmission.

4. The electroabsorption modulated laser according to claim 1, wherein, The photocurrent is proportional to the light wave output from the electroabsorption modulated laser.

5. The electroabsorption modulated laser according to claim 4, wherein, The photocurrent provides feedback to the electroabsorption modulated laser, and the feedback is used to improve the quality of the eye diagram associated with the optical waveform.

6. The electroabsorption modulated laser according to claim 1, wherein, The photocurrent is used to adjust the bias point associated with the second voltage to improve the light modulation amplitude and extinction ratio.

7. The electroabsorption modulated laser according to claim 1, wherein, The photocurrent is used for optical alignment associated with the electroabsorption modulated laser.

8. An apparatus comprising: Electroabsorption modulated lasers, including: A first diode, operable to receive a first voltage to generate a first output, and A second diode, coupled to the first diode and operable to receive a second voltage, wherein the second diode uses the first output and the second voltage to generate a photocurrent; and Sensing circuit, In response to the sensing circuit determining that the photocurrent exceeds a threshold, the sensing circuit causes an adjustment to the second voltage, thereby adjusting the output from the electroabsorption modulated laser.

9. The apparatus according to claim 8, wherein, The first voltage is the laser bias voltage, and the second voltage is the modulation voltage.

10. The apparatus according to claim 8, wherein, The laser bias voltage remains constant, and the modulation voltage varies such that the photocurrent includes encoded data transmission.

11. The apparatus according to claim 8, wherein, The photocurrent is proportional to the light wave output from the electroabsorption modulated laser.

12. The apparatus according to claim 11, wherein, The photocurrent provides feedback to the electroabsorption modulated laser, and the feedback is used to improve the quality of the eye diagram associated with the optical waveform.

13. The apparatus according to claim 8, wherein, The photocurrent is used to adjust the bias point associated with the second voltage to improve the light modulation amplitude and extinction ratio.

14. The apparatus according to claim 8, wherein, The photocurrent is used for optical alignment associated with the electroabsorption modulated laser.

15. A method comprising: A first voltage is obtained at the first diode; The first output is generated by utilizing the first diode in response to the first voltage; A second voltage is obtained at the second diode; The photocurrent is generated using the second diode, wherein the photocurrent is generated in response to the first output and the second voltage.

16. The method of claim 15, further comprising outputting an optical signal from an electroabsorption modulated laser associated with the first diode and the second diode based at least on the photocurrent.

17. The method of claim 16, further comprising: The reflection of the optical signal is obtained; The optical signal and the reflected optical signal are used to perform optical alignment of the electroabsorption modulated laser.

18. The method according to claim 15, wherein, The first voltage is the laser bias voltage, and the second voltage is the modulation voltage.

19. The method according to claim 18, wherein, The laser bias voltage remains constant, and the modulation voltage varies such that the photocurrent includes encoded data transmission.

20. The method of claim 15, wherein, The photocurrent is used to adjust the bias point associated with the second voltage to improve the light modulation amplitude and extinction ratio.

Images