Patent Publication Number: US-2023163858-A1

Title: Dual-mode receiver integrated with dispersion compensator

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The invention relates generally to integrated photonics receivers, and more specifically to dual-mode integrated photonics receivers based on paired photodetectors and having tunable dispersion compensator devices. 
     2. Description of the Related Art 
     In the field of integrated photonics, optical receivers may be employed in various optical systems for optical-to-electrical (OE) conversion of optical light. A polarization insensitive integrated photonics receiver, as an example, may be realized using a 1x2 polarization splitter rotator optically connected to a dual-input photodetector (PD) (P-I-N-based PD, for example), where the input ports of the photodetector are located at opposite sides of the photodetector, for example. The integrated photonics receiver may also comprise an input optical port (e.g., an edge coupler) optically connected to the input of the polarization splitter rotator, for example. Optical light entering the integrated photonics receiver, as an example, may be polarized by the polarization splitter rotator, such that the separated transverse-electric (TE) and transverse-magnetic (TM) polarization modes of the optical light may enter the photodetector via the two input ports, respectively, wherein the TE and TM polarization modes may then be combined, for example. A drawback of using such an integrated photonics receiver is that the optical light may not be fully absorbed in the photodetector, allowing the unabsorbed optical light to travel through the opposite port (i.e., an opposite port of the two input ports of the photodetector) of the photodetector, respectively, and propagate back toward the input optical port of the integrated photonics receiver, which may degrade the optical return loss of the integrated photonics receiver, as an example. 
     An alternative approach to the one described above involves the use of a phase control element and an optical combiner, for example. As an example, a polarization insensitive integrated photonics receiver may comprise a 1x2 polarization splitter rotator optically connected to a phase tuner and a 2x1 combiner, respectively, and a single-input photodetector. The integrated photonics receiver may also comprise an input optical port (e.g., an edge coupler) optically connected to the input of the polarization splitter rotator, for example. Optical light entering the integrated photonics receiver, as an example, may be polarized by the polarization splitter rotator, such that the transverse-electric and transverse-magnetic polarization modes of the optical light are separated. One of the split polarization modes may propagate through the phase tuner, which, via active phase control algorithms programmed to control the phase of the polarization mode of light, may tune the phase of the one of the split polarization modes. The phase-matched TE and TM polarization modes may then combine constructively via the 2x1 combiner, for example, before being directed to the photodetector. Thus, as mentioned above, a drawback of using such an integrated photonics receiver is that active phase control algorithms may be required for effectively operating the phase tuner, which may be costly. 
     Therefore, there is a need to solve the problems described above by providing a dual-mode integrated photonics receiver based on two photodetectors connected in parallel, and having integrated dispersion compensator devices, and method of same, for effectively and efficiently absorbing optical light. 
     The aspects or the problems and the associated solutions presented in this section could be or could have been pursued; they are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches presented in this section qualify as prior art merely by virtue of their presence in this section of the application. 
     BRIEF INVENTION SUMMARY 
     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 aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter. 
     In an aspect, an integrated receiver chip is provided. The integrated receiver chip may comprise: a first end and a second end; at least one optical input port disposed at the first end; a polarization manipulation device optically connected to one of the at least one optical input port, the polarization manipulation device being adapted to split an optical signal into a first and a second optical signals; a first and a second dispersion compensators each optically connected to the polarization manipulation device, the first and the second dispersion compensators each being adapted to selectively induce a dispersion on an optical signal propagating through the dispersion compensator; and a first and a second photodetectors optically connected to the first and the second dispersion compensators, respectively. The optical paths from the optical input port to the first and the second photodetectors are arranged with significantly equal length for maximizing the combined optical to electrical signal conversion. Additionally, the optical paths are significantly identical in terms of propagation delay to achieve constructive signal combining. Thus, an advantage of using two parallelly connected photodetectors in the disclosed receiver is that the optical signal clarity may be maximized, which may improve upon the return loss of traditional receivers. Another advantage is that, because of the use of the first and the second photodetectors, conventionally used optical components, such as phase tuners and combiners, may be no longer be needed, which may reduce associated manufacturing costs. Another advantage is that, because the phase tuner may be negated, a control algorithm adapted to control the phase tuner is no longer needed either, which may simplify operation of the receiver and thus reduce associated operational costs. Thus, an advantage is that the disclosed dispersion compensator structure may enable large amounts of dispersion tuning for an integrated receiver chip, which may thus improve data transmission reach. An additional advantage is that, because the dispersion compensator design is simplified, manufacturing costs associated with integrating the dispersion compensator onto an integrated receiver chip may thus be reduced. 
     In another aspect, an optical to electrical (OE) conversion system is provided. The OE conversion system may comprise an integrated receiver chip, a transimpedance amplifier, and a digital signal processor (DSP), the transimpedance amplifier and the digital signal processor each being in electrical communication with the integrated receiver chip, the integrated receiver chip comprising at least one optical input port disposed at a first end of the integrated receiver chip, a first and a second dispersion compensators each optically connected to one of the at least one optical input port, the first and the second dispersion compensators each being adapted to selectively induce a dispersion on an optical signal propagating through the dispersion compensator, and a first and a second photodetectors optically connected to the first and the second dispersion compensators, respectively; wherein, when an optical signal is launched into the integrated receiver chip at one of the at least one optical input port, the first and the second dispersion compensators induce a selected dispersion on the optical signal, the optical signal being absorbed by each of the first and the second photodetectors, such that a photocurrent of the optical signal is electrically transmitted to the transimpedance amplifier by each of the first and the second photodetectors, the transimpedance amplifier being configured to convert the photocurrent to a voltage signal; and wherein the DSP is configured to monitor the inducing of the dispersion on the optical signal by digitally reading a bit error rate of the voltage signal being outputted from the transimpedance amplifier, the DSP being further configured to transmit a control signal to each of the first and the second dispersion compensators for selectively adjusting a value of the induced dispersion. Thus, an advantage of using two parallelly connected photodetectors in the disclosed receiver is that the optical signal clarity may be maximized, which may improve upon the return loss of traditional receivers. Another advantage is that, because of the use of the first and the second photodetectors, conventionally used optical components, such as phase tuners and combiners, may be no longer be needed, which may reduce associated manufacturing costs. Another advantage is that, because the phase tuner may be negated, a control algorithm adapted to control the phase tuner is no longer needed either, which may simplify operation of the receiver and thus reduce associated operational costs. An additional advantage is that the dispersion compensator design is simplified, which may thus reduce manufacturing costs associated with integrating the dispersion compensator onto an integrated receiver chip. 
     In another aspect, a method of enabling dispersion compensation on an integrated receiver chip having a first and a second photodetectors is provided. The method may comprise the steps of integrating a first and a second dispersion compensators on the integrated receiver chip, the first and the second dispersion compensators being optically connected to the first and the second photodetectors, respectively, and providing a digital signal processor (DSP) in electrical communication with the first and the second dispersion compensators, the DSP being programmed to scan through predefined dispersion parameters for each of the first and the second dispersion compensators, digitally read a bit error rate (BER) from a voltage signal, the voltage signal being received from a transimpedance amplifier in electrical communication with the first and the second photodetectors, evaluate the read BER, such that to determine a sufficiency of the predefined dispersion parameters, and if the evaluation of the read BER yields insufficiency, adjust the predefined dispersion parameters to a tuned dispersion parameters, scan through the tuned dispersion parameters for each of the first and the second dispersion compensators, digitally read a bit error rate (BER) from a voltage signal, the voltage signal being received from the transimpedance amplifier in electrical communication with the first and the second photodetectors, and evaluate the read BER, such that to determine a sufficiency of the tuned dispersion parameters. Thus, an advantage is that the disclosed dispersion compensator structure may enable large amounts of dispersion tuning for an integrated receiver chip, which may thus improve data transmission reach. An additional advantage is that the dispersion compensator design is simplified, which may thus reduce manufacturing costs associated with integrating the dispersion compensator onto an integrated receiver chip. Another advantage is that, because of the DSP with FEC feedback loop, the tuning of the tunable dispersion compensator may be autonomously controlled and adjusted, as needed, in real time. 
     The above aspects or examples and advantages, as well as other aspects or examples and advantages, will become apparent from the ensuing description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For exemplification purposes, and not for limitation purposes, aspects, embodiments or examples of the invention are illustrated in the figures of the accompanying drawings, in which: 
         FIG.  1    is a diagram illustrating a top view of an optical-to-electrical conversion system comprising an integrated photonics receiver chip, a transimpedance amplifier, and a digital signal processor, according to an aspect. 
         FIG.  2    is a diagram illustrating a top view of exemplary electrical connections between the photodetectors of the integrated photonics receiver chip and the transimpedance amplifier of  FIG.  1   , according to an aspect. 
         FIGS.  3 A -  3 B  illustrate top views of exemplary tunable dispersion compensator structures, realized by cascaded ring resonators and cascaded Mach-Zehnder interferometers, respectively, according to an aspect. 
         FIG.  4    is an exemplary plot illustrating a simulation of the tunable dispersion compensator with cascaded ring topology depicted in  FIG.  3 A  according to an aspect. 
         FIG.  5    is a diagram illustrating a top view of cascaded Mach-Zehnder interferometer switches with multiple dispersion compensators, according to an aspect. 
         FIG.  6    is a flowchart illustrating an exemplary control algorithm for controlling the tunable dispersion compensator of  FIG.  1   , according to an aspect. 
         FIG.  7    is a diagram illustrating a top view of an alternative embodiment of the optical-to-electrical conversion system of  FIG.  1   , according to an aspect. 
     
    
    
     DETAILED DESCRIPTION 
     What follows is a description of various aspects, embodiments and/or examples in which the invention may be practiced. Reference will be made to the attached drawings, and the information included in the drawings is part of this detailed description. The aspects, embodiments and/or examples described herein are presented for exemplification purposes, and not for limitation purposes. It should be understood that structural and/or logical modifications could be made by someone of ordinary skills in the art without departing from the scope of the invention. Therefore, the scope of the invention is defined by the accompanying claims and their equivalents. 
     It should be understood that, for clarity of the drawings and of the specification, some or all details about some structural components or steps that are known in the art are not shown or described if they are not necessary for the invention to be understood by one of ordinary skills in the art. 
     For the following description, it can be assumed that most correspondingly labeled elements across the figures (e.g.,  105 A and  205 A, etc.) possess the same characteristics and are subject to the same structure and function. If there is a difference between correspondingly labeled elements that is not pointed out, and this difference results in a non-corresponding structure or function of an element for a particular embodiment, example or aspect, then the conflicting description given for that particular embodiment, example or aspect shall govern. 
       FIG.  1    is a diagram illustrating a top view of an optical-to-electrical conversion system  101  comprising an integrated photonics receiver chip  102 , a transimpedance amplifier  106 , and a digital signal processor  107 , according to an aspect. As described previously in the Background above, an integrated photonics receiver may be configured to receive optical light, such that the optical light may be absorbed by a photodetector contained within the receiver, as an example. The absorbed optical light may be converted to an electrical signal within the photodetector, and the electrical signal may be electrically transmitted to a transimpedance amplifier (e.g., a photocurrent to voltage converter), for example, contained within an electrical chip/die positioned at or near an output of the integrated photonics receiver. As will be described throughout this disclosure below, an improved integrated photonics receiver may be provided having two photodetectors and dispersion compensators, as an example, to enable a more effective and efficient optical-to-electrical conversion. 
     As shown in  FIG.  1   , the integrated photonics receiver chip (“integrated photonics receiver chip,” “integrated photonics receiver,” “receiver,” “receiver chip”)  102  may be provided with a polarization splitter rotator  103 , a first and a second dispersion compensators  104 A and  104 B, and a first and a second photodetectors  105 A and  105 B, as an example. As shown as an example, the polarization splitter rotator  103  may be provided with an input optical port  112  disposed at a first end (“first end,” “input end,” “input”)  102 A of the receiver chip  102 , and a first and a second output optical ports  113 A and  113 B. As will be described in more detail later, the input port  112  may be adapted to receive an optical signal  115 , as an example. As shown, the first and the second dispersion compensators  104 A and  104 B may each be provided with an input port  114 , each optically connected (via optical waveguides/channels (not shown)) to the polarization splitter rotator output ports  113 A and  113 B, respectively. Additionally, the first and the second dispersion compensators  104 A and  104 B may each further comprise an output port  116 , as shown. The first and the second photodetectors  105 A and  105 B may each be provided with an input port  117 , as shown, each optically connected (via optical waveguides/channels (not shown)) to the output port of each of the first and the second dispersion compensators  104 A and  104 B, respectively, as an example. Finally, as shown, an output of each of the first and the second photodetectors  105 A and  105 B may be electrically connected (via electrical connections  111 ) to the transimpedance amplifier  106 , which will be described in more detail later. 
     As shown in  FIG.  1   , the first and the second photodetectors  105 A and  105 B may be electrically connected in parallel (e.g., at  111 ), such that photocurrents from the first and the second photodetectors, corresponding to the TE polarizations of two optical signals (e.g.,  115 A and  115 B), for example, may be constructively combined, as will be discussed in more detail later. As mentioned above, the first and the second photodetectors  105 A and  105 B may electrically connect to the transimpedance amplifier  106 . As an example, the transimpedance amplifier  106  may be contained within an electrical chip positioned at or near a second end (“second end,” “output end,” “output”)  102 B of the receiver chip  102 , as will be discussed in more detail when referring to  FIG.  2   . It should be noted that the first end  102 A and second end  102 B are shown opposite each other in  FIG.  1   , the first end  102 A and second end  102 B may also be disposed in alternate ways, such as at a right angle with respect to each other. 
     As shown in  FIG.  1   , the transimpedance amplifier  106  may be electrically connected (via electrical connection  119 , for example) to a digital signal processor (DSP)  107 . The digital signal processor  107  may be an application-specific integrated circuit (not shown) integrated on the electrical chip with the transimpedance amplifier  106 , as an example. As will be described in more detail later in this disclosure below, the digital signal processor  107  may be provided with forward error correction capabilities, such that the DSP  107  can provide digital feedback via electrical signals (“electrical signals,” “digital signal,” “control signals”)  121 A and  121 B, for example, to each of the first and the second dispersion compensators  104 A and  104 B, respectively, for automating the control of the dispersion compensators, for example. 
     As shown as an example in  FIG.  1   , an optical signal  115  having TE and TM polarization modes may be launched into the receiver  102  at the input optical port  112  of the polarization splitter rotator  103 . As indicated, within the polarization splitter rotator  103 , the optical signal  115  is split into two signals, such the split optical signals  115 A and  115 B exiting the output optical ports  113 A and  113 B, respectively. The TM polarization mode of the optical signal  115  may be split and rotated to TE polarization and exit the output optical port  113 B and the TE polarization mode of the optical signal  115  may be split and keep TE polarization and exit the output optical port  113 A, as an example. As an example, the polarization splitting and rotation (within  103 , for example) may be achieved either by an edge coupler (not shown) with a suitable integrated polarization splitter rotator device or by a dual-polarization grating coupler (not shown). As shown, the split optical signals  115 A and  115 B may propagate toward and enter the first and the second dispersion compensators  104 A and  104 B, respectively, via the input ports  114 , as an example. As will be described in greater detail later in this disclosure, the first and the second dispersion compensators  104 A and  104 B may, using the DSP feedback loop (realized via digital signals  121 A and  121 B), may enable the receiver chip  102  to reduce/compensate for dispersion (e.g., chromatic dispersion, intermodal dispersion, polarization mode dispersion) incurred by the optical signals  115 A and  115 B being received by the parallel photodetectors  105 A and  105 B, respectively, as an example. It should be understood that the optical paths from the optical input port  112  to the first and the second photodetector input ports  117  are arranged with significantly equal length, i.e., significantly identical in terms of propagation delay, to achieve constructive signal combining, as disclosed in greater detail hereinafter. 
       FIG.  2    is a diagram illustrating a top view of exemplary electrical connections  211  between the photodetectors  105 A and  105 B of the integrated photonics receiver chip  102  and the transimpedance amplifier  106  of  FIG.  1   , according to an aspect. As mentioned previously above when referring to  FIG.  1   , the first and the second photodetectors  205 A and  205 B may be electrically connected to the transimpedance amplifier  206 , which may be integrated on an electrical chip  220 , as shown in  FIG.  2   , as an example. As will be described in detail below, the first and the second photodetectors  205 A and  205 B may be electrically connected to the transimpedance amplifier  206  in parallel, such that the photocurrents being electrically transmitted from each of the first and the second photodetectors  205 A and  205 B may be combined. 
     As an example, let the function blocks module  222  represent each of the additional exemplary optical components of the receiver chip  202  shown previously in  FIG.  1   , such as the dispersion compensators ( 104 A and  104 B) and the polarization splitter rotator ( 103 ), for example. Similarly, let the function blocks module  223  represent each of the additional exemplary electrical components of the electrical chip  220  shown previously in  FIG.  1   , such as the DSP ( 107 ) and feedback loop ( 121 A and  121 B), for example. As shown as an example, the receiver chip  202  may further comprise a signal pad  202 S (labeled S) and a pair of ground pads  202 G (labeled G) disposed along the second end  202 B, such that a GSG pad configuration is formed at the output end  202 B of the receiver chip  202 . It should be noted that the receiver chip  202  can also be configured with a single ground pad instead of pairs. The GSG pad configuration of the receiver  202  may thus model the GSG pad configuration of a traditional transimpedance amplifier, as an example. As such, as shown in  FIG.  2   , the electrical chip  220  may be provided with a signal pad  220 S and a pair of ground pads  220 G disposed at a first end  220 A of the electrical chip  220 , such that the GSG configurations of both receiver and electrical chips  202  and  220 , respectively, are parallelly aligned. As an example, the first and the second photodetectors  205 A and  205 B may be electrically connected to each of the electrical pads via signal traces (e.g., copper traces) etched into the receiver chip  202 . As such, for example, the first and the second photodetectors  205 A and  205 B may each electrically connect to one of the pair of ground pads  202 G via signal trace  218 G and to the signal pad  202 S via signal trace  218 S, respectively, as shown. Finally, as shown, each corresponding pair of electrical pads between the receiver  202  and the electrical chip  220  may be electrically connected via the electrical connections  211  (e.g., wires), such that ground pads  202 G electrically connect to ground pads  220 G, and signal pad  202 S electrically connects to signal pad  220 S, as an example. 
     As mentioned above, the GSG pad configuration electrically connected to the first and the second photodetectors  205 A and  205 B may match the conventional GSG pad configuration of the transimpedance amplifier  206 , for example. As shown in  FIG.  2   , the transimpedance amplifier  206  may be electrically connected to the ground pads  220 G via signal traces  222 G, for example, and to the signal pad  220 S via signal trace  222 S. Thus, a secure electrical link is formed from each of the first and the second photodetectors  205 A and  205 B to the transimpedance amplifier  206 , as shown. As is known, an optical photodetector is adapted to absorb optical light and convert the absorbed optical light into an electrical signal (i.e., a photocurrent, for example). As discussed previously in the Background above, traditional optical receivers comprise a single photodetector having two inputs. As described throughout this disclosure herein above, the optical receiver  202  may comprise two parallelly aligned, single-input photodetectors ( 205 A and  205 B, for example). The use of the first and the second photodetectors  205 A and  205 B, as compared to the traditional single photodetector, helps mitigate channel impediments (e.g., waveguide impurities, reflection, loss) by ensuring fuller optical absorption, such that to maximize the optical signal clarity at the output (at the transimpedance amplifier  206 , for example). Thus, an advantage of using two parallelly connected photodetectors in the disclosed receiver is that the optical signal clarity may be maximized, which may improve upon the return loss of traditional receivers. 
     As mentioned above, an electrical link (i.e., an electrical circuit) may be formed between each of the first and the second photodetectors  205 A and  205 B and the transimpedance amplifier  206  via the electrically connected and paired GSG pads, respectively. As an example, as similarly shown previously in  FIG.  1   , let an optical signal (e.g.,  115  in  FIG.  1   ) be launched into the optical receiver  202 . As mentioned previously above, the optical signal may be split into two optical signals and each having the same polarization (TE polarization, for example). Within the first and the second photodetectors  205 A and  205 B, each of the split optical signals, respectively, may be absorbed, and a photocurrent (not shown) corresponding to each of the optical signals may be outputted from the first and the second photodetectors  205 A and  205 B. As an example, the two photocurrents (not shown) may be electrically transmitted, via the signal traces  218 S, for example, to the signal pad  202 S, where the two photocurrents may be combined constructively into a single photocurrent. The single photocurrent (not shown) may travel electrically between the signal pads  202 S and  220 S, via the electrical connection  211 , for example, and the single photocurrent may electrically flow from the signal pad  220 S into the transimpedance amplifier  206  via the signal trace  222 S. The transimpedance amplifier  206  may then convert the single photocurrent into a voltage signal (not shown), as an example. 
     Thus, as outlined above, the use of the first and the second photodetectors  205 A and  205 B and the electrically connected GSG pads ( 202 G and  202 S), respectively, may not only improve the optical reflection issues traditionally experienced by conventional receivers, but may also negate the need for using phase tuners and combiners to control the optical signal’s phase, as outlined previously in the Background above. Thus, an advantage is that, because of the use of the first and the second photodetectors, conventionally used optical components, such as phase tuners and combiners, may be no longer be needed, which may reduce associated manufacturing costs. Another advantage is that, because the phase tuner may be negated, a control algorithm adapted to control the phase tuner is no longer needed either, which may simplify operation of the receiver and thus reduce associated operational costs. 
       FIGS.  3 A -  3 B  illustrate top views of exemplary tunable dispersion compensator structures  304 , realized by cascaded ring resonators  326  and cascaded Mach-Zehnder interferometers  327 , respectively, according to an aspect. As described previously throughout this disclosure above, the integrated receiver chip (e.g.,  102  in  FIG.  1   ) may be provided with a first and a second dispersion compensators (e.g.,  104 A and  104 B in  FIG.  1   ) parallelly connected to the first and the second photodetectors (e.g.,  105 A and  105 B), respectively. As an example, each of the first and the second dispersion compensators may be or may comprise a tunable dispersion compensator (e.g.,  532  in  FIG.  5   ). The tunable dispersion compensators  304  may be an integrated optical tunable filter, which is capable of compensating phase distortion of light signals  115  caused by optical fiber dispersion. As will be described in detail below, the tunable dispersion compensator may be implemented using either cascaded ring resonators  326  or cascaded Mach-Zehnder interferometers (MZIs)  327 , as an example. 
     As shown in  FIG.  3 A , the tunable dispersion compensator  304  may be realized by cascaded ring resonators  326 , as an example. Such ring resonators  326  may be constructed using silicon photonics technology, for example, and be optically connected to a silicon waveguide  325 , resulting in the cascaded arrangement shown, as an example. The cascaded ring resonators  326  may be integrated onto an optical channel of the receiver chip (e.g.,  102  in  FIG.  1   ), such that optical light being launched into the receiver chip may be propagated and coupled into each ring resonator  326 , and thus resulting in a tuning of the dispersion of the optical light. Tuning the dispersion of the optical light may be performed by tuning the resonance frequency of the ring resonator  326  with phase turners  326 A. As an example, the phase tuners  326 A may each be a thermo-optic phase shifter, which can change the resonance frequency of the ring resonator  326 . Alternatively, as shown in  FIG.  3 B , the tunable dispersion compensator  304  may be realized by cascaded MZIs  327 , as an example. As shown in  FIG.  3 B , the tunable dispersion compensator is composed of cascaded alternating symmetrical and asymmetrical MZIs as shown by  328 B and  328 A, respectively, for example. Furthermore, each MZI  327  may be optically connected such that the output ports of a first MZI optically connect to the input ports of an adjacent second MZI, as shown at  329 , for example, and such that to form the cascaded arrangement shown. As an example, the cascaded MZIs  327  may be integrated onto an optical channel of the receiver chip (e.g.,  102  in  FIG.  1   ), such that optical light being launched into the receiver chip may be propagated through each MZI (e.g.,  328 A,  328 B). The symmetric MZIs (inter couplers)  328 B function as tunable couplers for guiding the path on which the optical signal will take, while the asymmetric MZIs (outer couplers)  328 A function as the dispersive element. The two outer couplers  328 A may be set to 50% coupling ratio. Controlling the coupling ratio of the inter couplers  328 B will result in a tuning of the dispersion applying to the optical light. As an example, the coupling ratios of the inter couplers  328 B may be controlled by phase tuners  360 , which may each be a thermo-optic phase shifter. It should be understood that either structure  304  may be configured to receive a control signal for causing a tuning of the dispersion, for example. 
       FIG.  4    is an exemplary plot  430  illustrating a simulation of the tunable dispersion compensator comprising cascaded ring resonators illustrated in  FIG.  3 A  according to an aspect. As described previously above when referring to  FIGS.  3 A -  3 B , the integration of a dispersion compensator structure (e.g., cascaded ring resonators or cascaded MZIs) may enable the dispersion of a propagating optical signal on the integrated receiver chip (e.g.,  102  in  FIG.  1   ) to be tuned, as an example. As shown in  FIG.  4   , the plot  430  illustrates a dispersion curve (“dispersion curve,” “simulation curve”)  431 , measured in picoseconds/nanometer (ps/nm), as indicated on the y-axis, against increasing values of wavelength, measured in nm, as indicated on the x-axis, for example. As mentioned above, the exemplary dispersion curve  431  shown in  FIG.  4    was obtained via a simulation of a dispersion compensator using cascaded ring topology illustrated in  FIG.  3 A . 
     As shown by the dispersion curve  431  in  FIG.  4   , for a single dispersion compensator device (e.g.,  104 A in  FIG.  1   ), the amount of dispersion compensation provided can be up to -100 ps/nm, which may occur at 1551.5 nm (along the x-axis), for example, and remain for about 0.5 nm, such that the optical bandwidth  431 A is about 0.5 nm, as an example. Within the bandwidth region  431 A, for example, the phase ripples may be smaller than 0.1 radians, which may be preferred for optimal compensator functionality. Ideally, the optical bandwidth  431 A should preferably be as wide as feasibly possible, for example. Thus, as shown by the simulation curve  431  of  FIG.  4   , the amount of dispersion of a propagating optical signal can be tuned by an effectively configured dispersion compensator, such that the dispersion compensation can be adjusted to compensate for changes in temperature in the optical transmission system or for a fiber length variation, for example. However, it should be noted that a trade-off between the dispersion compensation capability and the optical bandwidth needs to be considered when implementing such dispersion compensator devices, for example. 
       FIG.  5    is a diagram illustrating a top view of cascaded Mach-Zehnder interferometer switches  534  with multiple dispersion compensators  532 ,  533 , according to an aspect. As described previously above when referring to  FIGS.  3 A-  3 B , cascaded ring resonators (e.g.,  326 ) or cascaded MZIs (e.g.,  327 ) can be used to implement a dispersion compensator structure, as an example. Additionally, as described previously above when referring to  FIG.  4   , such a dispersion compensator structure may be capable of providing up to -100 ps/nm of dispersion compensation. As will be described in detail below, for applications requiring larger amounts of dispersion tuning (e.g., long transmission, or high-speed applications) where a single dispersion compensator structure may not suffice, cascaded MZI switches paired with multiple types of dispersion compensator devices may alternatively be provided to form another dispersion compensator structure  504  (e.g., in place of  104 A,  104 B in  FIG.  1   ), as an example. 
     As shown in  FIG.  5   , multiple-stage MZI switches  534  may be integrated with three fixed dispersion compensators  533 , as an example, to form the dispersion compensator structure  504 . As shown as an example, let the structure  504  be optically connected to an optical waveguide  525  integrated on an optical receiver chip (e.g.,  102  in  FIG.  1   ). As shown, a tunable dispersion compensator  532  (based on either structure  304  shown previously in  FIGS.  3 A -  3 B , for example) may be provided on the optical waveguide  525 , as an example. For example, the tunable dispersion compensator  532  may be adapted to provide dispersion in a range from 0 to D, where D is an amount of dispersion (e.g., 100 ps/nm). As shown, following the tunable dispersion compensator  532 , a first MZI switch  534 A may be optically connected to an output of the tunable dispersion compensator  532 , as shown. As an example, the first MZI switch  534 A may be implemented as a 1x2 MZI structure, such that the first MZI switch  534 A has one input and two outputs, as shown, branching into an upper and a lower arms  535 A- a  and  535 A- b , respectively, for example. As shown, the upper arm  535 A- a  may be provided with a first fixed dispersion compensator  533 A. As an example, the first fixed dispersion compensator  533 A may be adapted to provide a fixed dispersion of D, again, where D is an amount of dispersion (set by the tunable dispersion compensator  532 ). As shown, the upper and lower arms  535 A- a  and  535 A- b  may optically connect to the inputs, respectively, of a second MZI switch  534 B, as an example. 
     As an example, the second MZI switch  534 B may be implemented as a 2x2 MZI structure, as shown, such that the second MZI switch  534 B has two inputs and two outputs, for example, branching into an upper and a lower arms  535 B- a  and  535 B- b , respectively. As shown, the upper arm  535 B- a  may be provided with a second fixed dispersion compensator  533 B. As an example, the second fixed dispersion compensator  533 B may be adapted to provide a fixed dispersion of 2 ∗ D. As shown, the upper and lower arms  535 B- a  and  535 B- b  may optically connect to the inputs, respectively, of a third MZI switch  534 C, as an example. As an example, the third MZI switch  534 C may be implemented as a 2x2 MZI structure, as shown, such that the third MZI switch  534 C has two inputs and two outputs, for example, branching into an upper and a lower arms  535 C- a  and  535 C- b , respectively. As shown, the upper arm  535 C- a  may be provided with a third fixed dispersion compensator  533 C. As an example, the third fixed dispersion compensator  533 C may be adapted to provide a fixed dispersion of 4 ∗ D. Finally, as shown, the upper and lower arms  535 C- a  and  535 C- b  may optically connect to the inputs, respectively, of a fourth MZI switch  534 D, as an example. As an example, the fourth MZI switch  534 D may be implemented as a 2x1 MZI structure, as shown, such that the fourth MZI switch  534 D has two inputs and a single output, for example. 
     As outlined above, the cascading of multiple MZI switches  534  each paired with a fixed dispersion compensator  533 , for example, may form a dispersion compensator structure  504  for accommodating applications requiring large amounts of dispersion tuning. As an example, each of the MZI switches  534  may be controlled (autonomously by an external signal, for example), such that optical light can selectively propagate through a portion of or all of the fixed dispersion compensators  533 . For example, as mentioned above, the tunable dispersion compensator  532  may be tuned to a certain dispersion from 0 to D (by the external signal, for example), which may then, subsequently, determine each of the dispersion values for the first, second, and third fixed dispersion compensators  533 A -  533 C, respectively. Then, as an optical signal (not shown) is propagated through the structure  504 , each of the MZI switches  534  may be individually controlled. Referring to the first MZI switch  534 A, optical light may be directed onto either the upper arm  535 A- a , such that to then pass through the first fixed dispersion compensator  533 A, or the lower arm  535 A- b , such that to avoid the first fixed dispersion compensator  533 A. Each of the second and the third MZI switches  534 B and  534 C may be controlled in the same way, for example, such that the optical light may be directed onto either of each of the upper arms  535 B- a ,  535 C- a  or lower arms  535 B- b ,  535 C- b , respectively, as the optical light propagates through the structure  504 . As mentioned previously above, in this way, the optical light may be selectively subject to increasing amounts of dispersion, induced by the dispersion compensators  533 , by the controlling of the MZI switches  534 . 
     As outlined above, from front end to back end in the dispersion compensator structure  504 , optical light may selectively achieve continuous tuning of dispersion in a large range from 0 to 8*D. As noted above, only a single dispersion compensator has to be configured as a tunable dispersion compensator (e.g.,  532 ) tunable in the range from 0 to D, for example. As such, by the use of the above-described structure  504 , there is no need to configure a dispersion compensator to be tunable in a range from 0 to 8 ∗ D, which would be challenging and costly. Thus, the design of the tunable dispersion compensator may be simplified. As an example, for 100 G PAM4 Dense Wave Division Multiplexing (DWDM) applications, data transmission reach may only extend to about 2 kilometers (km), without dispersion compensation. Utilizing the cascaded dispersion compensators in the exemplary formation described above, the data transmission reach may be improved significantly, extending to about 40 km, for example. Thus, an advantage is that the disclosed dispersion compensator structure may enable large amounts of dispersion tuning for an integrated receiver chip, which may thus improve data transmission reach. An additional advantage is that the dispersion compensator design is simplified, which may thus reduce manufacturing costs associated with integrating the dispersion compensator onto an integrated receiver chip. 
     As an example, in certain applications where even greater amounts of dispersion compensation are required (e.g., greater than 8 ∗ D), an external dispersion compensation module can be optically paired with the on-chip integrated dispersion compensator (e.g.,  104 A,  104 B in  FIG.  1   ). As such, the combination of the external dispersion compensation module with the on-chip integrated dispersion compensator may relax the dispersion compensation requirements of each component, respectively. Moreover, additional fixed dispersion compensators may be added, for example, to enable a more flexible dispersion compensation mechanism. It should be understood that the number of optical components, such as the tunable dispersion compensators  532  and the MZI switches  534 , for example, shown in  FIG.  5   , is exemplary, and thus the number of such optical components may be increased or decreased, for example. It should also be understood that the dispersion compensation structure  504  shown in  FIG.  5    may be provided as the first and the second dispersion compensators  104 A and  104 B of  FIG.  1   , as an example. 
       FIG.  6    is a flowchart illustrating an exemplary control algorithm  640  for controlling the tunable dispersion compensator  104 A,  104 B of  FIG.  1   , according to an aspect. As mentioned previously above when referring to  FIG.  1   , the integrated receiver chip (e.g.,  102 ) may electrically communicate with the transimpedance amplifier (e.g.,  106 ), which may further electrically communicate with a DSP module (e.g.,  107 ). As described previously, the DSP module may be adapted to receive the voltage signal (i.e., converted photocurrent) from the transimpedance amplifier, and be provided with forward error correction (FEC) capabilities to facilitate the tuning of the first and the second dispersion compensators (e.g.,  104 A and  104 B) for optimum link performance, as an example. As will be described in detail below, the DSP module may be programmed with the exemplary control algorithm  640  for effectively and autonomously control the tuning of the dispersion compensators. 
     As shown in  FIG.  6   , upon startup of the DSP module (i.e., operating the electrical chip (e.g.,  220  in  FIG.  2   )), indicated at  641  in  FIG.  6   , the DSP module may set the initial dispersion compensator parameters, indicated at  642 . Then, the DSP module may first enter the scan operation mode, indicated at  643   a , as disclosed in greater detail hereinbelow. Then, after the scan operation mode program has ended, indicated at  646 , the DSP module may use the tracking operation mode, indicated at  643   b , in combination with the scan operation mode (step  643   a ) to tune (step  647 ) and find (step  648 ) the optimum bit error rate (BER), as disclosed in greater detail hereinafter. 
     After, the DSP module enters the scan operation mode  643   a , the DSP module may scan through the preset dispersion compensation parameters, indicated by  644 . As described previously above when referring to  FIG.  5   , the tunable dispersion compensator structure (e.g.,  504 ) may be thus configured such that the dispersion is tuned in a range from 0 to D using  532  of  FIG.  5    (or 0 to 8 ∗ D, including the fixed dispersion compensators (e.g.,  533 )), for example. As an optical signal (e.g.,  115 ) propagates along the optical receiver (e.g.,  102 ) and through the tunable dispersion compensators (as well as any fixed dispersion compensators (e.g.,  533 )), the optical signal may be subject to dispersion, as defined by the value of D, for example. Once the optical signal passes through the photodetectors (e.g.,  105 A and  105 B), the optical signal may be electrically transmitted (as a photocurrent, for example) to the transimpedance amplifier  106 / 206 , as described previously above when referring to  FIG.  2   . The transimpedance amplifier may convert the photocurrent of the originally received optical signal, for example, into a voltage signal that may be electrically processed by the DSP  107 , for example. As mentioned above, the DSP may be provided with FEC functionality for monitoring the OE link between the receiver and transimpedance amplifier via the bit error rate (BER). As shown in  FIG.  6   , the DSP may process the voltage signal, obtain the OE link bit error rate (BER), then set the dispersion compensator parameters  104  A-B for the best BER, a step indicated at  645 . It should be noted that the OE link BER may be hindered by impairments of the optical link, such as, for example, reflection, fiber dispersion, etc. Then, the program may end, as indicated by step  646 , or enter tracking operation mode. 
     Upon entering tracking operation mode, indicated by  643   b , the DPS module may set the dispersion compensator parameters which are found in step  645  with the best BER or the initial dispersion compensator parameters from the step  642  if the parameters with the best BER from the scan operation mode are not available.. As shown in  FIG.  1   , the DSP ( 107 ) may obtain BER and generate control signals ( 121 A and  121 B), which may be electrically transmitted to the first and the second dispersion compensators ( 104 A and  104 B), respectively, for example. The control signals may then cause a tuning of the tunable dispersion compensators, such that the dispersion may be set to a new value in the range between 0 and D (or 0 and 8 ∗ D), indicated at step  647 . As the optical signal is propagated through the OE conversion system ( 101 ) of  FIG.  1   , a new photocurrent will be generated, and thus a new voltage signal, which will be electrically sent to the DSP, as an example. As before, the DSP will obtain the BER of the new voltage signal. Subsequently, the DSP will evaluate the BER value, such that to determine whether the obtained BER is optimum, indicated by step  648 . More specifically, the DSP may determine whether the obtained BER yields sufficiency, by, for example, comparing the BER value to a predefined value/threshold. In an example, the BER value should be as low as possible. If the read BER value is insufficient (i.e., worse than the predefined value, for example), then the dispersion compensator parameters will be tuned, indicated at  647 , as an example. However, if the read BER value is sufficient (i.e., equal to or better than the predefined value, for example), then no further dispersion compensator tuning may be required. The DSP module may continue to monitor the OE link signal performance. If the BER is worse than the predefined value due to any changes on the optical link, such as, temperature-induced link dispersion changes, it may autonomously start the tuning to find the best operation point for the OE link, indicated by steps  647  and  648 . 
     Again, it should be understood that the tracking operation mode may be used in combination with the scan operation mode to tune and obtain the optimum bit error rate (BER). It should also be understood that the tuning (tracking operation mode) may allow the DSP to continually keep the dispersion compensator parameters set at optimum link BER performance. 
       FIG.  7    is a diagram illustrating a top view of an alternative embodiment  701  of the optical-to-electrical conversion system  101  of  FIG.  1   , according to an aspect. As described previously above when referring to  FIG.  1   , the integrated receiver chip ( 102 ) may be provided with a polarization splitter rotator ( 103 ) adapted to split an optical signal into two optical signals, and rotate the polarization mode of the optical signal, such that the two optical signals possess the same polarization (e.g., TE polarization). As will be discussed in detail below, the polarization splitter rotator may be replaced by a polarization splitter, such that to allow both TM and TE polarizations (“dual-mode”) to be propagated along the integrated receiver chip, as an example. 
     As shown in  FIG.  7   , the OE conversion system  701  may comprise an integrated receiver chip  702 , a transimpedance amplifier  706 , and a DSP module  707 . As described previously above when referring to  FIG.  2   , for example, the transimpedance amplifier  706  and the DSP  707  may each be integrated on an electrical chip (e.g.,  220 ) disposed at or near the output of the receiver chip  702 , as an example. As shown, the polarization splitter rotator of  FIG.  1    may be replaced with the polarization splitter  748 , for example, having input port  749  and output ports  750 A and  750 B, as an example. As similarly described above when referring to  FIG.  1   , the integrated receiver  702  may comprise a first and a second dispersion compensators  704 A and  704 B having input and output ports  714  and  716 , and a first and a second photodetectors  705 A and  705 B having input ports  717 , respectively, for example. As an example, the output ports  750 A and  750 B may be optically connected to the input ports  714  of the first and the second dispersion compensators  704 A and  704 B, respectively, and the output ports  716  of the first and the second dispersion compensators  704 A and  704 B may be optically connected to the input ports  717  of the first and the second photodetectors  705 A and  705 B, respectively, as shown. For example, the above-described on-chip optical connections may be made using integrated channels/waveguides (not shown). 
     As shown as an example in  FIG.  7   , an optical signal  715  having TE and TM polarization modes may be launched into the receiver  702  at the input optical port  749  of the polarization splitter  748 . As indicated, within the polarization splitter  748 , the optical signal  715  is split into two signals each having different polarization modes, such the split optical signals  715 A and  715 B exiting the output optical ports  750 A and  750 B, respectively, contain TE polarization and TM polarization, respectively, as shown. In comparison with the polarization splitter rotator  103  described previously when referring to  FIG.  1   , the polarization splitter  749  does not rotate the TM polarization mode of the optical signal  715 , as an example, allowing both TE and TM polarizations to be propagated along the optical receiver  702 . However, using the polarization splitter  748  in place of the polarization splitter rotator ( 103 ) requires that the first and the second dispersion compensators  704 A and  704 B and the photodetector launch waveguides (e.g.,  717 ) to be polarization insensitive. This requirement may be met by using an optical waveguide having a square frontal cross-section (e.g., square prism shaped waveguide, from a top view) for each of the dispersion compensators and the photodetector launch waveguides, for example. As shown, the split optical signals  715 A and  715 B may propagate toward and enter the first and the second dispersion compensators  704 A and  704 B, respectively, via the input ports  714 , as an example. As described previously throughout this disclosure above, the first and the second dispersion compensators  704 A and  704 B may, using the DSP  107  feedback loop (realized via control signals  721 A and  721 B), may enable the receiver chip  702  to reduce dispersion (e.g., polarization mode dispersion) incurred by the optical signals  715 A and  715 B being received by the parallel photodetectors  705 A and  705 B, respectively, as an example. Because each of the optical signals  715 A and  715 B possesses a different polarization (e.g., TE and TM polarizations, respectively), the TE polarization mode and the TM polarization mode of the input optical signal  715  are compensated by the first and the second dispersion compensators  704 A and  704 B, respectively, as an example. In this way, because both TE and TM polarization modes are being propagated, the first and the second dispersion compensators  704 A and  704 B may compensate the polarization mode dispersion (PMD) between the two polarization modes. For example, due to random imperfections and/or asymmetries of the optical waveguides (not shown) of the receiver chip  702  or fiber link, the TE and TM polarizations may propagate along the optical link at different speeds, which may cause optical pulse distortions, and thus reduce data transmission or optical signal clarity, for example. The DSP  707  may be adapted to monitor such instances of PMD (via FEC and BER, for example), such that to control the tuning of the first and the second dispersion compensators  704 A and  704 B and compensate for the PMD (by speeding up or slowing down one or both polarizations, for example) between the TE and TM polarizations, respectively, as an example. Thus, an advantage of utilizing a polarization splitter is that the polarization mode dispersion may be compensated for the polarizations of an optical signal propagating along the disclosed integrated receiver chip. 
     It should be understood that the control algorithm shown in  FIG.  6    and described previously above may be included in the OE conversion system  701  and programmed on the DSP  707 , such that to control the tuning of the first and the second dispersion compensators  704 A and  704 B, as an example. It should also be understood that the first and the second photodetectors  705 A and  705 B may be electrically connected to the transimpedance amplifier  706  in the same manner as that shown previously in  FIG.  2    (e.g., parallelly paired GSG pad configurations). As an example, the dispersion compensator structures disclosed herein above can be integrated not only on the receiver side, as shown herein, but also on the transmitter side (not shown). Having dispersion compensators integrated on both the transmitter and receiver ends, for example, allows the required total amount of dispersion compensation for either end to be less, and thus also loosens the requirement for the number of cascaded MZI switches (e.g.,  534  in  FIG.  5   ). 
     Furthermore, the disclosed receiver embodiments (e.g.,  102  and  702 ) may be provided as wavelength division multiplexing (WDM) receivers as well. As such, the polarization manipulating component (e.g.,  103 ,  748 ) may be broadband, and the dispersion compensators can be configured with a wavelength periodic feature to match the channel spacing of multiple wavelengths, as is needed for WDM receivers, for example. The multiplexing feature can be disposed on the receiver chip after the polarization manipulation and dispersion compensator components, for example (i.e., positioned on the chip between components  704 A,  704 B and  705 A,  705 B, for example). In this way, only one set of polarization manipulation and dispersion compensator components is needed to accommodate multiple wavelengths on a WDM receiver. 
     It should be understood that the above-described integrated receiver may be based on various integrated photonics platforms, such as, for example, silicon, silicon nitride, silica, lithium niobate, polymer, III-V materials, hybrid platforms, etc. It should also be understood that the integrated receiver disclosed herein may be adapted for use with multiple wavelength ranges, including, but not limited to, visible light, O, E, S, C, and L-band. It should also be understood that the potential applications of the disclosed invention are not limited to optical communications, but may also include optical sensing, optical computing, automotive applications, quantum applications, etc. For example, the disclosed receiver may be implemented in single-wavelength 100Gbit/s PAM4 DWDM transceivers in pluggable form factor. 
     It may be advantageous to set forth definitions of certain words and phrases used in this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. 
     Further, as used in this application, “plurality” means two or more. A “set” of items may include one or more of such items. Whether in the written description or the claims, the terms “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of,” respectively, are closed or semi-closed transitional phrases with respect to claims. 
     If present, use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence or order of one claim element over another or the temporal order in which acts of a method are performed. These terms are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. As used in this application, “and/or” means that the listed items are alternatives, but the alternatives also include any combination of the listed items. 
     As used throughout this disclosure, the terms/phrases “optical signal,” “optical test signal,” “optical light,” “laser light,” “laser signal,” and the like are used interchangeably. It should be understood that the aforementioned terms each individually and collectively refer to light, and more specifically, electromagnetic radiation. 
     Throughout this description, the aspects, embodiments or examples shown should be considered as exemplars, rather than limitations on the apparatus or procedures disclosed or claimed. Although some of the examples may involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objectives. 
     Acts, elements and features discussed only in connection with one aspect, embodiment or example are not intended to be excluded from a similar role(s) in other aspects, embodiments or examples. 
     Aspects, embodiments or examples of the invention may be described as processes, which are usually depicted using a flowchart, a flow diagram, a structure diagram, or a block diagram. Although a flowchart may depict the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. With regard to flowcharts, it should be understood that additional and fewer steps may be taken, and the steps as shown may be combined or further refined to achieve the described methods. 
     If means-plus-function limitations are recited in the claims, the means are not intended to be limited to the means disclosed in this application for performing the recited function, but are intended to cover in scope any equivalent means, known now or later developed, for performing the recited function. 
     Claim limitations should be construed as means-plus-function limitations only if the claim recites the term “means” in association with a recited function. 
     If any presented, the claims directed to a method and/or process should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention. 
     Although aspects, embodiments and/or examples have been illustrated and described herein, someone of ordinary skills in the art will easily detect alternate of the same and/or equivalent variations, which may be capable of achieving the same results, and which may be substituted for the aspects, embodiments and/or examples illustrated and described herein, without departing from the scope of the invention. Therefore, the scope of this application is intended to cover such alternate aspects, embodiments and/or examples. Hence, the scope of the invention is defined by the accompanying claims and their equivalents. Further, each and every claim is incorporated as further disclosure into the specification.