Polarization-diverse receiver with delay section

Abstract

A first portion of the incident light and a second portion of the incident light propagate in opposite directions within the first optical waveguide. A ring resonator incouples the first portion of the incident light and the second portion of the incident light from the first optical waveguide such that the first portion of the incident light and the second portion of the incident light travel in opposite directions within the ring resonator. A second optical waveguide is positioned to incouple the first portion of the incident light and the second portion of the incident light from the ring resonator such that the first portion of the incident light and the second portion of the incident light travel in opposite directions away from the ring resonator within the second optical waveguide. One or more optical detectors are optically connected to receive the first portion of the incident light and the second portion of the incident light from the second optical waveguide.

Description

[Technical field]

[0001]

[0002] The disclosed embodiments relate to optical data communications.

[0003] [Background technology]

[0004] Optical data communication systems operate by modulating laser light to encode a digital data pattern. The modulated laser light is transmitted from a sending node to a receiving node through an optical data network. Upon reaching the receiving node, the modulated laser light is demodulated to obtain the original digital data pattern. Thus, the implementation and operation of optical data communication systems depends on having reliable and efficient devices for the transmission of optical signals, the coupling of optical signals between optical waveguides, the modulation of optical signals, and the reception of optical signals. It is in this context that the disclosed embodiments arise. Summary of the Invention

[0005] In one example embodiment, an electro-optic receiver is disclosed. The electro-optic receiver includes a first optical waveguide optically coupled to transmit a first portion of incident light through the first optical waveguide in a first direction and to transmit a second portion of incident light through the first optical waveguide in a second direction, the second direction being opposite to the first direction. The electro-optic receiver further includes a ring resonator disposed within an evanescent optical coupling distance of the first optical waveguide such that the first portion of incident light and the second portion of incident light couple from the first optical waveguide into the ring resonator, and the first portion of incident light and the second portion of incident light travel in opposite directions within the ring resonator. The electro-optic receiver further comprises a second optical waveguide disposed within an evanescent optical coupling distance of the ring resonator such that the first portion of the incident light and the second portion of the incident light couple from the ring resonator into the second optical waveguide and the first portion of the incident light and the second portion of the incident light travel in opposite directions away from the ring resonator within the second optical waveguide. The electro-optic receiver further comprises a photodetector optically connected to both the first end of the second optical waveguide and the second end of the second optical waveguide.

[0006] In an example embodiment, an electro-optical receiver is disclosed. The electro-optical receiver comprises an optical waveguide having a first end and a second end. The electro-optical receiver further comprises a plurality of wavelength division multiplexing (WDM) demultiplexers disposed along the optical waveguide. Each WDM demultiplexer of the plurality of WDM demultiplexers is configured to incouple an optical signal of a respective wavelength of a plurality of wavelengths propagating through the optical waveguide in a first direction as a first in-coupled optical signal. Each WDM demultiplexer of the plurality of WDM demultiplexers is configured to incouple an optical signal of a respective wavelength of a plurality of wavelengths propagating through the optical waveguide in a second direction as a second in-coupled optical signal. The second direction is opposite to the first direction. Each WDM demultiplexer of the plurality of WDM demultiplexers is further configured to direct the first in-coupled optical signal to a first optical detector and the second in-coupled optical signal to a second optical detector.

[0007] Other aspects and advantages of the disclosed embodiments will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate disclosed embodiments. [Brief description of the drawings]

[0008] [Figure 1A] 1 illustrates a portion of an optical receiver train in a wavelength division multiplexing electro-optical receiver with a wavelength division multiplexing (WDM) multiplexer in accordance with some embodiments.

[0009] [Figure 1B] FIG. 1B illustrates how a first portion of incident light (e.g., TE polarized light) propagates along a path (represented by the thick dashed line) through the portion of the optical receiver train and WDM demultiplexer shown in FIG. 1A in accordance with some embodiments.

[0010] [Figure 1C] FIG. 1B illustrates how a second portion of the incident light (e.g., TE rotated from TM polarization) propagates along a path (represented by the thick dashed line) through the portion of the optical receiver train shown in FIG. 1A and the WDM demultiplexer, in accordance with some embodiments.

[0011] [Figure 1D] 3 illustrates an example of an optical signal timing delay section in accordance with some embodiments.

[0012] [Figure 1E] 1 illustrates an optical signal timing delay section incorporating a resonant device in accordance with some embodiments.

[0013] [Figure 1F] FIG. 1 illustrates an implementation of a resonant device as a single ring resonator with a through port output, in accordance with some embodiments.

[0014] [Figure 1G]FIG. 13 illustrates another implementation of a resonator device as a single ring resonator with a drop port output in accordance with some embodiments.

[0015] [Figure 1H] FIG. 1 illustrates an example implementation of a resonant device comprising multiple coupled ring resonators with a throughport output in accordance with some embodiments.

[0016] [Figure 1I] FIG. 2 illustrates an example implementation of a resonant device comprising multiple coupled ring resonators with a drop port output in accordance with some embodiments.

[0017] [Figure 1J] FIG. 2 illustrates an example implementation of a resonant device in which multiple ring resonators are cascaded to increase optical signal delay with a through port output in accordance with some embodiments.

[0018] [Figure 1K] FIG. 2 illustrates an example implementation of a resonant device in which specially designed periodic structures are formed from photonic bandgap material to create a resonant cavity, in accordance with some embodiments.

[0019] [Diagram 2] 1 illustrates a top view of an example of a photodetector according to some embodiments.

[0020] [Diagram 3] 1 illustrates an example configuration of an electro-optical receiver implemented in a photonic integrated circuit (PIC) in accordance with some embodiments.

[0021] [Figure 4A] FIG. 2 illustrates an example configuration of a polarization splitter rotator (PSR), according to some embodiments.

[0022] [Figure 4B]4B is a vertical cross-sectional view of the example PSR of FIG. 4A taken along line AA of FIG. 4A, according to some embodiments.

[0023] [Figure 5A] 1 illustrates an example configuration of a PSR, according to some embodiments.

[0024] [Figure 5B] 5B is a vertical cross-sectional view of the PSR example of FIG. 5A taken along line AA of FIG. 5A, according to some embodiments.

[0025] [Figure 5C] 5B is a vertical cross-sectional view of the PSR example of FIG. 5A taken along line BB of FIG. 5A, according to some embodiments.

[0026] [Figure 6] 1 illustrates an example of a WDM receiver chain in accordance with some embodiments.

[0027] [Figure 7] 1 illustrates an example of a WDM receiver chain in accordance with some embodiments.

[0028] [Figure 8A] 4 illustrates an example of a time plot of optical power of a first optical signal propagating from port A and a second optical signal propagating from port B in accordance with some embodiments.

[0029] [Figure 8B] FIG. 1 illustrates an example of a time plot of the optical power of a first optical signal propagating from port A and a second optical signal propagating from port B when implementing a delay DA or delays DA and DB to mitigate the differential time delay (τAB) in accordance with some embodiments.

[0030] [Figure 9A] 1 illustrates a WDM receiver chain in accordance with some embodiments.

[0031] [Figure 9B] 1 illustrates a WDM receiver chain in accordance with some embodiments.

[0032] [Figure 10A] 1 illustrates a WDM receiver string with 8 WDM demultiplexers (8 channels) in accordance with some embodiments.

[0033] [Figure 10B] 10B illustrates an expanded view of a portion of the WDM receiver string of FIG. 10A in accordance with some embodiments.

[0034] [Figure 10C] 10B illustrates an expanded view of a portion of the WDM receiver string of FIG. 10A in accordance with some embodiments.

[0035] [Figure 10D] 10B illustrates an expanded view of a portion of the WDM receiver string of FIG. 10A in accordance with some embodiments.

[0036] [Figure 11A] 4 illustrates a floorplan of a receiver circuit unit cell for use in constructing a WDM receiver string in accordance with some embodiments.

[0037] [Figure 11B] 4 illustrates a floor plan of another receiver circuit unit cell for use in constructing a WDM receiver string in accordance with some embodiments.

[0038] [Figure 11C] 11C illustrates a first half of a WDM receiver string implemented using the receiver circuit unit cells of FIGS. 11A and 11B in accordance with some embodiments.

[0039] [Figure 11D] 11D illustrates a complete WDM receiver string including the first half of FIG. 11C and a second half implemented as an inverted configuration of the first half, in accordance with some embodiments.

[0040] [Figure 12] 4 is a flow chart illustrating a method for operating a WDM receiver string in accordance with some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] In the following description, numerous specific details are set forth in order to provide an understanding of the disclosed embodiments. However, it will be apparent to one of ordinary skill in the art that the disclosed embodiments may be practiced without some or all of these specific details. Additionally, detailed descriptions of well-known process operations are omitted in order to avoid unnecessarily obscuring the disclosed embodiments.

[0042] The integration of photonic components on a semiconductor chip has many advantages. However, the integrated photonic components often have high polarization sensitivity, while standard single-mode optical fibers used to convey digital data as modulated optical signals to and / or from the integrated photonic components are often non-polarization maintaining. In optical data communication systems, it is common for modulated optical signals conveying digital data to arrive at the optical fiber of a photonic receiver device with an unknown and uncontrolled mixture of polarization components. In these circumstances, it is difficult for the photonic receiver device to efficiently process the input modulated optical signal with integrated photonic components with high polarization sensitivity. The present invention was born in this context.

[0043] Optical data communication systems operate by modulating laser light to encode a digital data pattern in the electrical domain as a modulated optical signal in the optical domain. The modulated optical signal is transmitted through an optical fiber to an electro-optical receiver where it is detected and decoded to obtain the original encoded digital data pattern in the electrical domain. In many optical data communication systems, the polarization state of the light in the optical fiber is not controlled and can be perturbed by small movements of the optical fiber and / or changes in ambient temperature during operation of the system. In these systems, the electro-optical receiver must handle incoming optical signals with arbitrary polarizations that vary with time.

[0044] Electro-optical receiver systems have been incorporated into photonic integrated circuits (PICs) to enable compact and high performance detection of modulated optical signals received as input from optical fibers. Optical coupling of light from an optical fiber to a PIC requires an optical coupling configuration that can accept input light from either polarization of the optical fiber (transverse electric (TE) or transverse magnetic (TM)) and output it to one or more optical waveguides on the PIC, often with a preferred polarization state. In some embodiments disclosed herein, an optical coupling configuration is provided in which the incident light is received through either a dual polarization vertical grating coupler or an edge coupler and conveyed to a PIC polarization splitter that splits the incident light from the two input optical fiber polarizations (TE and TM) and outputs the incident light of a first polarization and a second polarization to two separate optical waveguides on the PIC, respectively. Also, in some embodiments, either the first polarization or the second polarization is rotated to the other polarization in route to the two separate optical waveguides on the PIC, so that light having the same polarization is conveyed to each of the two separate optical waveguides on the PIC. In some embodiments, significant advantages are obtained by using optical devices that can efficiently detect such split optical signals based on polarization, and in some embodiments, additional advantages are obtained by using a single photodiode (e.g., in a photodetector) for both polarization mode components of the incident light, rather than doubling the number of photodiodes to provide separate detection of the two polarization mode components of the incident light, where such additional advantages include reduced optical circuit complexity, reduced detector capacitance per channel, and reduced dark current leading to increased photodiode / photodetector sensitivity.

[0045] Various embodiments of electro-optical receivers are disclosed herein. The electro-optical receiver allows detection of optical signals of any input polarization with a single photodetector or set of photodetectors. The electro-optical receiver comprises an input optical fiber that transmits incident light (modulated light) with any (uncontrolled) polarization carrying a signal decodable into a digital data pattern. The electro-optical receiver further comprises an optical combiner that transfers the incident light from the input fiber to the PIC. The electro-optical receiver further comprises a polarizing beam splitter that receives any input polarization state and splits it into two separate optical waveguides of the PIC, where each of the two separate optical waveguides contains one of the orthogonal components of the input polarization state of the incident light (possibly converted to another polarization state). In some embodiments of the electro-optical receiver, the functionality of the polarizing beam splitter is combined with an optical combiner in the form of a dual polarization grating coupler. In some embodiments of the electro-optic receiver, the two optical waveguides of the PIC support a single polarization mode with a propagation constant well separated from other spatial modes (e.g., other polarization states), making it operationally single-mode, single-polarized. The electro-optic receiver further comprises an optical routing system in which the two optical waveguides of the PIC are routed to the same photodetector or set of photodetectors. In some embodiments, the electro-optic receiver further comprises a timing skew management system that compensates for signal degradation resulting from time delay mismatch between the two optical waveguides of the PIC and the photodetector or set of photodetectors.

[0046] The electro-optic receiver disclosed herein is particularly useful in applications where the electro-optic receiver implemented in a PIC detects light from an input optical fiber with uncontrolled polarization. The electro-optic receiver is particularly advantageous in applications where multiple data channels on the input optical fiber are encoded at different wavelengths, for example using wavelength division multiplexing (WDM), and where the polarization diversity WDM electro-optic receiver architecture has timing skew. This timing skew can typically vary from channel to channel in a well-known manner. Some existing electro-optic receivers that can handle uncontrolled input polarization require two separate electro-optic receivers (one for each orthogonal polarization state) along with extensive digital signal processing to combine the signals. It should be appreciated that the electro-optic receiver embodiments disclosed herein provide a single compact and power efficient electro-optic receiver to combine and detect signals from two polarization states of any wavelength channel. In some embodiments disclosed herein, a bidirectional polarization diverse electro-optical receiver system is provided in which a WDM receiver array comprises a plurality of WDM demultiplexers, each configured to incouple optical signals propagating along a common optical bus in either direction and direct the incoupled optical signals to either the same photodetector or a matched pair of photodetectors.

[0047] Some embodiments of the electro-optic receiver disclosed herein are particularly useful in situations where the polarization state of the incident light of different wavelength channels is approximately the same between wavelength channels and the polarization state of the incident light of different wavelength channels is unknown. Some embodiments of the electro-optic receiver disclosed herein are particularly useful in situations where the polarization state of the incident light of a given wavelength channel is unknown and the polarization state of the incident light of a given wavelength channel changes in a slow and controlled manner (e.g., monotonically) compared to the other wavelength channels of the incident light. For example, these situations may occur when all WDM signal wavelength channels originate from the same source, travel through the same optical fiber, and are received together, as in a WDM point-to-point link. Some embodiments of the electro-optic receiver disclosed herein are useful in more generalized situations where each wavelength channel of the incident light has a completely different unknown polarization and the polarization states of the different wavelength channels of the incident light are uncorrelated. For example, these situations may occur when different WDM channels originate from different locations and may not share the same optical fiber throughout their propagation paths from their respective sources of the incident light to the electro-optic receiver. The electro-optic receivers disclosed herein are configured to handle incident optical signals with unknown polarization states, either static in time or dynamically changing in time. Various embodiments of the electro-optic receivers disclosed herein provide for reception of incident optical signals with unknown polarization states, even when the polarization states change rapidly (e.g., into the gigahertz (GHz) regime, and more typically into the kilohertz (kHz) (or millisecond) or even slower regimes).

[0048] Various embodiments of electro-optical receivers are disclosed herein that include an arrangement of optical signal timing delay sections with respective predetermined optical signal timing delay magnitudes (optical waveguide lengths) that provide effective timing difference compensation for different polarization components (TE and TM) in an input optical signal (modulated optical signal) received at the electro-optical receiver. The arrangement and configuration of the various signal timing delay sections are defined to minimize the impact on the chip floor plan of the overall larger electro-optical receiver system. In some embodiments, a polarization diverse electro-optical receiver is disclosed in which the polarization components (TE and TM) of an input optical signal (modulated optical signal) received at the electro-optical receiver are each fed in opposite directions to an optical receiver string, with the optical signal timing of the two polarization components being equalized by placing one or more optical signal timing delay sections, each with a predetermined optical signal timing delay magnitude (optical waveguide length) along the optical receiver string. The various optical signal timing delay section arrangements and optical signal timing delay magnitudes (optical waveguide lengths) provide low optical signal delay impairment, low optical signal waveguide loss, and chip layout advantages.

[0049] FIG. 1A illustrates a portion of an optical receiver train in a wavelength division multiplexing electro-optical receiver including a WDM multiplexer 100, according to some embodiments. In some embodiments, the WDM demultiplexer 100 is arranged in a single polarization WDM receiver train, provided that the TM polarization of the incoming optical signal is rotated relative to the TE polarization, such as by a polarization splitter rotator (PSR). In some embodiments, the portion of the optical receiver train including the WDM demultiplexer 100 is implemented in a PIC. The portion of the optical receiver train 100 includes an optical waveguide 101. The WDM demultiplexer 100 includes a ring resonator 103 and an optical waveguide 105 configured to extend past the ring resonator 103. The optical waveguide 105 is arranged within an evanescent optical coupling distance of the ring resonator 103 such that light passing through the ring resonator 103 is evanescent optically coupled into the optical waveguide 105. The optical waveguide 105 has a first end optically connected to an input of the first optical signal timing delay section 107. The optical waveguide 105 has a second end optically connected to an input of the second optical signal timing delay section 109. In some embodiments, the first optical signal timing delay section 107 and the second optical signal timing delay section 109 are each configured as an optical waveguide of a respective predetermined length. The first optical signal timing delay section 107 has an output optically connected to a first end of the optical waveguide 111. Similarly, the second optical signal timing delay section 109 has an output optically connected to a first end of the optical waveguide 113. The optical waveguide 111 has a second end optically connected to a first input of the photodetector 115. Similarly, the optical waveguide 113 has a second end optically connected to a second input of the photodetector 115. In some embodiments, the photodetectors are implemented as a matched photodetector pair, where the optical input of a first photodetector in the matched photodetector pair is optically connected to the second end of optical waveguide 111 and the optical input of a second photodetector in the matched photodetector pair is optically connected to the second end of optical waveguide 113.

[0050] In some embodiments, optical waveguide 111 and optical waveguide 105 are integrally formed as the same optical waveguide that extends through first optical signal timing delay section 107. In these embodiments, optical waveguide 105 extends through first optical signal timing delay section 107 such that a first end of optical waveguide 105 is connected to a first input of optical detector 115. Also, in some embodiments, optical waveguide 113 and optical waveguide 105 are integrally formed as the same optical waveguide that extends through second optical signal timing delay section 109. In these embodiments, optical waveguide 105 extends through second optical signal timing delay section 109 such that a second end of optical waveguide 105 is connected to a second input of optical detector 115.

[0051] Each of the optical waveguides 101, 105, 111, 113, and the ring resonator 103 is formed of a material capable of in-coupling, out-coupling, and guiding light therethrough. Each of the optical waveguides 101, 105, 111, 113, and the ring resonator 103 has a refractive index that is sufficiently different from the surrounding material to enable guiding of light through the optical waveguides 101, 105, 111, 113, and the ring resonator 103. In some embodiments, the optical waveguides 105, 111, 113, and the optical signal timing delay sections 107 and 109 are formed as respective portions of the same continuous optical waveguide structure. In some other embodiments, one or more of optical waveguides 105, 111, 113, and optical signal timing delay sections 107 and 109 are formed as separate optical waveguide structures that are optically coupled to others of optical waveguides 105, 111, 113, and optical signal timing delay sections 107 and 109, as shown in FIG. 1A.

[0052] In some embodiments, the optical receiver train with the WDM demultiplexer 100 receives incident light from an optical fiber (such as a single mode optical fiber that is not polarization maintaining). In some embodiments, the incident light is modulated light carrying a digital bit pattern. The incident light is not polarization controlled when it reaches the electro-optical receiver through the optical fiber. Thus, the polarization of the incident light received from the optical fiber is unknown when it reaches the electro-optical receiver. In some embodiments, the electro-optical receiver comprises an optical coupler configured to receive the incident light from the optical fiber and direct the incident light to an optical waveguide 101 of the optical receiver train with the WDM demultiplexer 100. In some embodiments, the optical coupler is configured as a dual polarization grating coupler (either an edge grating coupler or a vertical grating coupler) that splits the two polarizations (TE and TM) of the incident light. In some embodiments, the dual wave grating coupler is configured to direct a first portion of the incident light having a first polarization (either TE or TM) to a first end of the optical waveguide 101. The dual polarization grating coupler is further configured to rotate the polarization of the second portion of the incident light from a second polarization opposite to the first polarization (e.g., if the first polarization is TE, then the second polarization is TM, and vice versa) to the first polarization to provide a polarization-rotated second portion of the incident light having the first polarization. The dual polarization grating coupler is configured to direct the polarization-rotated second portion of the incident light to a second end of the optical waveguide 101.

[0053] The optical waveguide 101 is configured to extend in a continuous loop configuration from a first end to a second end. In this manner, a first portion of incident light having a first polarization propagates through the optical waveguide 101 in a first optical propagation direction, as indicated by arrow 117, and a polarization-rotated second portion of the incident light (also having the first polarization) propagates through the optical waveguide 101 in a second optical propagation direction opposite the first optical propagation direction, as indicated by arrow 119. Thus, the first portion of the incident light (e.g., TE polarization) and the polarization-rotated second portion of the incident light (e.g., TM polarization rotated to TE polarization) propagate through the optical waveguide 101 in opposite optical propagation directions.

[0054] The ring resonator 103 is disposed along the optical waveguide 101 within an evanescent light coupling distance of the optical waveguide 101. The ring resonator 103 is configured to operate at a specific resonant wavelength. In some embodiments, the specific resonant frequency at which the ring resonator 103 operates is a narrow wavelength range. For ease of description, any ring resonator (e.g., 103) disclosed herein is described as operating at a specific resonant wavelength, with the understanding that the specific resonant wavelength is, in fact, a narrow wavelength range that is distinguishable from other different resonant wavelength ranges. Thus, a given ring resonator (e.g., 103) is configured to evanescently couple light at a specific resonant wavelength (within a narrow wavelength range around the specific resonant wavelength). In some embodiments, a heater 104 is implemented to thermally tune the resonant wavelength of the ring resonator 103. In some embodiments, the heater 104 is a resistive heating device that converts electrical current into thermal energy. In these embodiments, the heater 104 is controlled by a control circuit. In some embodiments, the control circuitry is connected to receive a feedback signal from the photodetector 115, where the feedback signal is indicative of the amount of light detected by the photodetector 115. The feedback signal is used by the control circuitry to control the heater 104 to optimize the resonant wavelength of the ring resonator 103 in order to maximize the amount of light transmitted to and detected by the photodetector 115.

[0055] In some embodiments, the ring resonator 103 is implemented as an annular waveguide having a circumferential configuration (e.g., circular, elliptical, racetrack, or any other circumferential shape). In some embodiments, the ring resonator 103 is configured to have a ring or disk shape with an outer diameter of less than about 50 micrometers. In some embodiments, the ring resonator 103 is configured to have a ring or disk shape with an outer diameter of less than about 10 micrometers.

[0056] FIG 1B illustrates how a first portion of incident light (e.g., TE polarization) propagates through the portion of the optical receiver train and WDM demultiplexer 100 illustrated in FIG 1A along path 121 (represented by the thick dashed line) according to some embodiments. FIG 1C illustrates how a second portion of incident light (e.g., TE rotated from TM polarization) propagates through the portion of the optical receiver train and WDM demultiplexer 100 illustrated in FIG 1A along path 123 (represented by the thick dashed line) according to some embodiments. The ring resonator 103 is configured and controlled to operate at a particular resonant wavelength such that a first portion of incident light having a wavelength substantially equal to the particular resonant wavelength optically couples into the ring resonator 103 in a first propagation direction (counterclockwise direction) and a second polarization-rotated portion of incident light having a wavelength substantially equal to the particular resonant wavelength optically couples into the ring resonator 103 in a second propagation direction opposite the first propagation direction (clockwise direction). It should be understood that both the first portion of the incident light and the polarization-rotated second portion of the incident light have the same polarization state within the optical waveguide 101, the ring resonator 103, the optical waveguides 105, 111, 113, and the optical signal timing delay sections 107 and 109. Thus, the ring resonator 103 operating at a particular resonant wavelength can optically incouple and detect both the first portion of the incident light and the polarization-rotated second portion of the incident light having the particular resonant wavelength.

[0057] Due to imbalances and different delays in the optical routing of TE and TM polarizations in the PSR and the optical components preceding the PSR (e.g., waveguides, fiber couplers, etc.), a first portion of the incident light (indicated by arrow 117) and a corresponding polarization-rotated second portion of the incident light (indicated by arrow 119) may not arrive at the ring resonator 103 at the same time. One or both of the first optical signal timing delay section 107 and the second optical signal timing delay section 109 are provided to compensate for the time difference in the arrival times of the first portion of the incident light and the corresponding polarization-rotated second portion of the incident light to the ring resonator 103 such that the first portion of the incident light and the corresponding polarization-rotated second portion of the incident light arrive at the photodetector 115 at substantially the same time to provide recovery of the optical signal carried in the incident light. In some embodiments, the difference in arrival times of the first portion of the incident light and the corresponding polarization-rotated second portion of the incident light to the ring resonator 103 may be caused by differences in the optical path lengths through the optical waveguide 101 to the ring resonator 103 and / or by delays in outputting the polarization-rotated second portion of the incident light from a polarization splitter-rotator (PSR) and / or optical coupler (e.g., from a dual polarization grating coupler) relative to the first portion of the incident light. It should be understood that "incident light" is the light in the optical fiber, not the light at the input or output of the PSR. In some embodiments, on the way to the PSR, the light propagates as TE and TM light through the coupler and some portion of the waveguide from the fiber to the chip. Because the propagation velocities of TE and TM light on the chip are different, there is a time delay between the two polarizations (TE and TM) at the input of the PSR. The systems and methods disclosed herein function at least in part to compensate for the time delay between the two polarizations (TE and TM) through the implementation of a suitably configured optical delay line.

[0058] The first optical signal timing delay section 107 and the second optical signal timing delay section 109 are defined to equalize delays in transmitting a first portion of the incident light and a corresponding polarization-rotated second portion of the incident light, respectively, to the photodetector 115. In some embodiments, the first optical signal timing delay section 107 and / or the second optical signal timing delay section 109 are configured to provide additional optical waveguide length beyond the minimum optical waveguide length required to route light from the ring resonator 103 to the photodetector 115.

[0059] 1D illustrates an example optical signal timing delay section 125 according to some embodiments. In some embodiments, one or both of the first optical signal timing delay section 107 and the second optical signal timing delay section 109 may be implemented in a manner similar to the example optical signal timing delay section 125. In some embodiments, the optical signal timing delay section 125 is configured as a length L of an optical waveguide 127. In some embodiments, the length L of the optical waveguide 127 within the optical signal timing delay section 125 is defined to provide a particular amount of time delay of optical propagation, where the time delay is defined by the time it takes light to travel from an input 129 of the optical signal timing delay section 125 to an output 131 of the optical signal timing delay section 125. The length L of the optical waveguide 127 within the optical signal timing delay section 125 and the corresponding time delay of optical propagation are determined by the group velocity of light (V g For example, the length L of the optical waveguide 127 in the optical signal timing delay section 125 is related through approximately (L / V g ) contributes a time delay to the propagation of light equal to the group velocity of light (V g) depends on several factors, such as the type of optical waveguide 127, the width of the optical waveguide 127, the wavelength of the propagating light, and the polarization of the propagating light, among other parameters. In some embodiments, the length L of the optical waveguide 127 in the optical signal timing delay section 125 is formed in one or more of a folded shape, a spiral, a helix, a loop, and a zigzag shape, among others, to give the optical signal timing delay section 125 a compact footprint within the PIC.

[0060] It should be appreciated that in various embodiments, in addition to or instead of the length of the optical waveguide (e.g., length L of optical waveguide 127 in optical signal timing delay section 125), one or both of first optical signal timing delay section 107 and second optical signal timing delay section 109 may be implemented to include various other photonic devices, such as resonant devices (e.g., all-pass ring resonator filters), slow-light structures, and / or other photonic devices that provide a time delay of the optical signal propagation. For example, FIG. 1E illustrates an optical signal timing delay section 125A incorporating a resonant device 135 according to some embodiments. Optical signal timing delay section 125A is a variation of optical signal timing delay section 125 of FIG. 1D. Optical signal timing delay section 125A includes an input optical waveguide section 137 having a first length L1 that extends from input 129 of optical signal timing delay section 125A to input 135I of resonant device 135. Timing delay section 125A further comprises an output optical waveguide section 139 having a second length L2 that extends from the output 135O of ​​resonant device 135 to the output 131 of the optical signal timing delay section 125A. The optical delay provided by timing delay section 125A is the sum of the optical delays of the input optical waveguide section 137, the output optical waveguide section 139, and the resonant device 135.

[0061] In various embodiments, the resonant device 135 may be implemented in different ways. For example, FIG. 1F illustrates an implementation of the resonant device 135 as a single ring resonator 141 with a through port output 143, according to some embodiments. FIG. 1G illustrates another implementation of the resonant device 135 as a single ring resonator 145 with a drop port output 147, according to some embodiments. FIG. 1H illustrates an implementation of the resonant device 135 with multiple coupled ring resonators 149-1 to 149-N (where N is greater than 1) with a through port output 151, according to some embodiments. FIG. 1I illustrates an implementation of the resonant device 135 with multiple coupled ring resonators 153-1 to 153-N (where N is greater than 1) with a drop port output 155, according to some embodiments. In some embodiments, the individual resonators are cascaded to increase the optical signal delay. For example, Figure 1J shows an example implementation of resonant device 135 in which multiple ring resonators 157-1 to 157-N (where N is greater than 1) are cascaded to increase the optical signal delay, with a through port output 159, according to some embodiments. Also, in some embodiments, resonant device 135 is implemented using a photonic crystal cavity. For example, Figure 1K shows an example implementation of resonant device 135 in which specially designed periodic structures 161-1 to 161-N (where N is greater than 1) are formed from photonic band gap material to construct a resonant cavity, according to some embodiments.

[0062] FIG. 2 is a top view of an example photodetector 200, according to some embodiments. In some embodiments, the photodetector 200 is used for the photodetector 115 of FIG. 1A. The photodetector 200 is shown as a PIN type photodetector with a P-doped region 201, an intrinsic region 203, and an N-doped region 205. The intrinsic region 203 is disposed between the P-doped region 201 and the N-doped region 205. In some embodiments, the P-doped region 201 and the N-doped region 205 are swapped. In some embodiments, the intrinsic region 203 is an optical waveguide for directing light to be detected. In some embodiments, at least a portion of the P-doped region 201 and at least a portion of the N-doped region 205 are formed in the optical waveguide. In operation, the photodetector 200 is reverse biased such that charge carriers generated by light absorption in the intrinsic region 203 are swept to an electrical contact 207 connected along the length of the photodetector 200.

[0063] The photodetector 200 allows for independent detection of incident light from each polarization. More specifically, a first portion of incident light having a first polarization is input through a first end of the photodetector 200, and a polarization-rotated second portion of the incident light having the first polarization (but corresponding to the incident light having the second polarization) is input through a second end of the photodetector 200. Due to optical absorption along the length of the photodetector 200, the intensity of the first portion of the incident light having the first polarization input through the first end of the photodetector 200 decays exponentially according to an optical absorption coefficient as the light propagates in a first direction along the length of the photodetector 200, as shown by arrow 209. Similarly, the intensity of the second polarization-rotated portion of the incident light having the first polarization input through the second end of the photodetector 200 decays exponentially according to an optical absorption coefficient as the light propagates in a second direction along the length of the photodetector 200, as shown by arrow 211. Thus, most of the first portion of the incident light having the first polarization is absorbed in the first half 213 of the photodetector 200, and most of the polarization-rotated second portion of the incident light having the first polarization is absorbed in the second half 215 of the photodetector 200. In some embodiments, the electrical contacts 207 along the first half 213 of the photodetector 200 are segmented and connected to a first reverse bias circuit and a first receiver circuit, and the electrical contacts 207 along the second half 215 of the photodetector 200 are segmented and connected to a second reverse bias circuit and a second receiver circuit. In these embodiments, considering that the polarization-rotated second portion of the input signal actually corresponds to the second polarization in the incident optical signal, the photocurrent measured by the first receiver circuit and the photocurrent measured by the second receiver circuit can be compared to determine the relative optical power divided between the different polarizations in the incident optical signal.

[0064] In some embodiments, the electro-optic receiver implements the WDM demultiplexer 100 as described with respect to Figures 1A-1E. In these embodiments, the electro-optic receiver comprises a first optical waveguide (e.g., 101) optically coupled to transmit a first portion of incident light (e.g., 117) in a first direction through the first optical waveguide. The first optical waveguide is also optically coupled to transmit a second portion of incident light (e.g., 119) in a second direction through the first optical waveguide, where the second direction is opposite to the first direction. The electro-optic receiver further comprises a ring resonator (e.g., 103) disposed within an evanescent optical coupling distance of the first optical waveguide such that the first portion of incident light and the second portion of incident light couple from the first optical waveguide into the ring resonator, and the first portion of incident light and the second portion of incident light travel in opposite directions within the ring resonator. The electro-optic receiver further comprises a second optical waveguide (e.g., 105) disposed within an evanescent optical coupling distance of the ring resonator such that the first portion of the incident light and the second portion of the incident light couple from the ring resonator into the second optical waveguide, and the first portion of the incident light and the second portion of the incident light travel in opposite directions away from the ring resonator in the second optical waveguide. The electro-optic receiver further comprises a photodetector (e.g., 115) optically connected to both the first end of the second optical waveguide and the second end of the second optical waveguide. In some embodiments, the photodetector is a double-ended photodetector configured to separately detect light entering the first end of the photodetector from the first end of the second optical waveguide and light entering the second end of the photodetector from the second end of the second optical waveguide, as described with respect to FIG. 2.

[0065] In some embodiments, the electro-optic receiver comprises a heater (e.g., 104) disposed within the ring resonator. The heater is controllable to control the resonant wavelength of the ring resonator such that only light within a narrow band around the resonant wavelength can be coupled into and out of the ring resonator. The term narrowband means a band of wavelengths defined with respect to a given channel wavelength of light such that the band of wavelengths is considered to correspond to the given channel wavelength of light. The narrowband wavelength range is defined to ensure that adjacent channel wavelengths of light are distinguishable from one another for resonant coupling of light of the target wavelength into and out of the ring resonator 103.

[0066] In some embodiments, the electro-optical receiver includes an optical signal timing delay section (e.g., 107 and / or 109) disposed along the second optical waveguide at a location between the ring resonator and the optical detector. The optical signal timing delay section is configured to impart a controlled amount of time delay to an optical signal passing through the optical signal timing delay section. In some embodiments, the optical signal timing delay section is formed as an optical waveguide section having one or more of a folded shape, a spiral shape, a helical shape, a loop shape, and a zigzag shape, among other shapes. In some embodiments, the optical waveguide section includes an input optical waveguide and an output optical waveguide extending side-by-side toward a central location, where the input optical waveguide and the output optical waveguide are optically connected. For example, optical signal timing delay section 125 has an input optical waveguide extending from input 129 toward a central location of the spiral shape, and an output optical waveguide extending from output 131 toward the central location of the spiral shape, where the input optical waveguide and the output optical waveguide are optically connected. In some embodiments, the input optical waveguide and the output optical waveguide are integrally formed as a single optical waveguide structure.

[0067] In some embodiments, the optical signal timing delay section comprises an input optical waveguide, an output optical waveguide, and a resonant device (e.g., 135) having an input optically connected to the input optical waveguide and an output optically connected to the output optical waveguide. For example, FIG. 1E shows an optical signal timing delay section 125A having an input optical waveguide extending from an input 129 toward the resonant device 135 and an output optical waveguide extending from an output 131 toward the resonant device 135. In some embodiments, the input optical waveguide and the output optical waveguide extend side by side for a distance and are optically connected to the resonant device. In some embodiments, the input optical waveguide and the output optical waveguide extend side by side in one or more of a folded shape, a spiral, a helix, a loop, and a zigzag shape (such as the helix shown in the example of FIG. 1E) toward the location where the resonant device is located.

[0068] In some embodiments, the electro-optical receiver includes both a first optical signal timing delay section (e.g., 107) disposed at a location between the ring resonator (e.g., 103) and a first end of the second optical waveguide at the photodetector 115, and a second optical signal timing delay section (e.g., 109) disposed at a location between the ring resonator (e.g., 103) and a second end of the second optical waveguide at the photodetector 115. Similar to the first optical signal timing delay section (e.g., 107), the second optical signal timing delay section (e.g., 109) is configured to impart a controlled amount of time delay to the optical signal passing through the second optical signal timing delay section (e.g., 109). In some embodiments, the controlled amount of time delay imparted by the first optical signal timing delay section (e.g., 107) is different from the controlled amount of time delay imparted by the second optical signal timing delay section (e.g., 109).

[0069] In some embodiments, the electro-optical receiver comprises a polarizing beam splitter rotator (e.g., 401 / 501) having an input optically connected to receive incident light. The polarizing beam splitter rotator is configured to direct a first portion of the incident light having a first polarization to a first output of the polarizing beam splitter rotator to provide the first portion of the incident light to a first end of a first optical waveguide (e.g., 101). The polarizing beam splitter rotator is also configured to direct a second portion of the incident light having a second polarization to a second output of the polarizing beam splitter rotator. The polarizing beam splitter rotator is also configured to rotate the polarization of the second portion of the incident light from the second polarization to the first polarization in route to the second output of the polarizing beam splitter rotator to provide the second portion of the incident light to a second end of the first optical waveguide (e.g., 101). Thus, a first end of the first optical waveguide (e.g., 101) is optically connected to a first output of the polarizing beam splitter rotator and a second end of the first optical waveguide (e.g., 101) is optically connected to a second output of the polarizing beam splitter rotator. In some embodiments, the opto-electrical receiver comprises an optical coupling device (e.g., 153) configured to transfer incident light from an optical fiber to an input of the polarizing beam splitter rotator.

[0070] In some embodiments, the electro-optic receiver includes an optical signal timing delay (e.g., DA) disposed along the first optical waveguide (e.g., 101) at a location between the first output of the polarizing beam splitter / rotator (e.g., 401 / 501) and the ring resonator (e.g., 103). In some embodiments, the optical signal timing delay (e.g., DA) is configured to impart a time delay to the arrival time of a first portion (e.g., 117) of the incident light to the ring resonator (e.g., 103), where the time delay is set such that the arrival time of a second portion (e.g., 119) of the incident light to the ring resonator (e.g., 103) is substantially equal to the arrival time of the first portion (e.g., 117) of the incident light to the ring resonator. In some embodiments, the optical signal timing delay unit (e.g., DA) is configured to compensate for the time delay between a first portion (e.g., 117) of the incident light exiting a first output of the polarizing beam splitter rotator (e.g., 401 / 501) and a second portion (e.g., 119) of the incident light exiting a second output of the polarizing beam splitter rotator (e.g., 401 / 501).

[0071] 3 illustrates an example configuration of electro-optical receiver 300 implemented within PIC 302 in accordance with some embodiments. In some embodiments, electro-optical receiver 300 is a WDM receiver comprising a series of N demultiplexers 311-1 through 311-N, where each of the N demultiplexers 311-1 through 311-N transmits its wavelength band (λ1 through λ2, respectively) from optical data bus 157 to photodetectors 305-1 through 305-N, respectively. N) of light. In some embodiments, a series of N demultiplexers 311-1 to 311-N are arranged along a demultiplexer row 313. In a bidirectional polarization diverse system, an optical input signal is received from an optical fiber / waveguide 152 through an optical coupler 153 and split into two optical input signals by a polarization split rotation (PSR) device 156. The two split optical input signals are then transmitted in opposite directions to an optical data bus 157 of the demultiplexer row 313, as indicated by arrows 158 and 159. In some embodiments, optical signal timing delay compensation is provided at each of the photodetectors 305-1 to 305-N of the N demultiplexers 311-1 to 311-N. Also, in some embodiments, an optical signal timing delay 315 is provided on the optical data bus 157 at either end of the demultiplexer row 313. The optical signal timing delay is configured to ensure that corresponding portions of the two split optical input signals (corresponding to the two different polarizations of the original optical input signal) arrive at a given photodetector 305-1-305-N of each of the N demultiplexers 311-1-311-N at substantially the same time. Additionally, in some embodiments, a variable optical attenuator 163 is provided on the optical data bus 157 to manage light returning to the optical coupler 153 of the electro-optic receiver 300 (returning to the optical fiber / waveguide 152 through which the original optical input signal was received), which can appear as optical return loss in the larger system and present system operation challenges, such as destabilizing laser operation.

[0072] The electro-optical receiver 300 receives an incoming optical signal from the optical fiber / waveguide 152 through the optical coupler 153, as indicated by arrow 154. The incoming optical signal is conveyed from the optical coupler 153 through the optical waveguide 155 to the optical input 156A of the PSR 156. The PSR 156 is configured to direct a first portion of the incoming light having a first polarization through a first optical output 156B of the PSR 156. The PSR 156 is also configured to rotate the polarization of the second portion of the incoming light from the second polarization to the first polarization, such that the second portion of the incoming light becomes a polarization-rotated second portion of the incoming light. The PSR 156 is configured to direct the polarization-rotated second portion of the incoming light through a second optical output 156C of the PSR 156. In some embodiments, the optical data bus 157 is implemented as an optical waveguide within the PIC 302. A first end 157A of the optical data bus 157 is optically connected to a first optical output 156B of the PSR 156. A second end 157B of the optical data bus 157 is optically connected to a second optical output 156C of the PSR 156. The optical data bus 157 is formed of a material through which light can be in-coupled, out-coupled, and guided. The optical data bus 157 is formed in a surrounding material that has an optical index of refraction that is sufficiently different from that of the optical data bus 157 to allow light to be guided within the optical data bus 157. The optical data bus 157 has a continuous loop-like structure. Thus, a first portion of the incident light propagates in a first direction from the first optical output 156A of the PSR 156 through the optical data bus 157, as indicated by arrow 158. A second polarization-rotated portion of the incident light travels from second optical output 156C of PSR 156 through optical data bus 157 in a second direction opposite to the first direction, as indicated by arrow 159.

[0073] Each of the N demultiplexers 311-1 to 311-N includes a corresponding ring resonator 301-1 to 301-N, respectively, disposed along the optical data bus 157 within an evanescent optical coupling distance of the optical data bus 157. It should be understood that in various embodiments, the electro-optical receiver 300 may include any number (N) of demultiplexers 311-1 to 311-N and corresponding ring resonators 301-1 to 301-N disposed along the optical data bus 157, so long as the ring resonators 301-1 to 301-N and associated signal processing circuitry can be spatially and electrically contained on a chip with the PIC 302. In some embodiments, the ring resonators 301-1 to 301-N are implemented as annular waveguides having a circumferential configuration (e.g., circular, elliptical, racetrack, or any other circumferential shape). In some embodiments, the ring resonators 301-1 to 301-N are implemented as disks. The ring resonators 301-1 to 301-N are formed of a material through which light can be in-coupled, out-coupled, and guided. Each of the ring resonators 301-1 to 301-N is formed in a surrounding material that has a sufficiently different optical index than the ring resonators 301-1 to 301-N to allow light to be guided within the ring resonators 301-1 to 301-N and around the circular path defined by each of the ring resonators 301-1 to 301-N. In some embodiments, each of the ring resonators 301-1 to 301-N is configured to have a ring or disk shape with an outer diameter of less than about 50 micrometers. In some embodiments, each of the ring resonators 301-1 to 301-N is configured to have a ring or disk shape with an outer diameter of less than about 10 micrometers.

[0074] Each of the multiple ring resonators 301-1 to 301-N has a respective resonant wavelength λ1 to λ NIn this manner, a first portion of incident light having a wavelength substantially equal to a resonant wavelength corresponding to a given one of the plurality of ring resonators 301-1 to 301-N is optically coupled in a first propagation direction (e.g., counterclockwise) to the given one of the plurality of ring resonators 301-1 to 301-N, and a polarization-rotated second portion of incident light having a wavelength substantially equal to a resonant wavelength corresponding to a given one of the plurality of ring resonators 301-1 to 301-N is optically coupled in a second propagation direction opposite to the first propagation direction (e.g., clockwise) to the given one of the plurality of ring resonators 301-1 to 301-N. For example, a specific wavelength λ x A first portion of the incident light having a particular wavelength λ x The light propagates in a counterclockwise direction within the ring resonator 301-x. x A second polarization-rotated portion of the incident light having a particular wavelength λ x The light propagates in the clockwise direction within the ring resonator 301-x.

[0075] Each of the N demultiplexers 311-1 to 311-N includes an output optical waveguide 303-1 to 303-N that is disposed within the evanescent light coupling distance of the corresponding ring resonator 301-1 to 301-N. Each of the output optical waveguides 303-1 to 303-N includes a coupling section 303A-1 to 303A-N. Each of the output optical waveguides 303-1 to 303-N includes a short section 303B-1 to 303B-N. Each of the output optical waveguides 303-1 to 303-N includes a long section 303C-1 to 303C-N. Each of the coupling sections 303A-1 to 303A-N is disposed to evanescently incouple light from a corresponding one of the ring resonators 301-1 to 301-N. In this manner, each of the ring resonators 301-1 to 301-N corresponds to a specific wavelength λ1 to λN The ring resonators 301-1 to 301-N are operative to transfer a first portion of the incident light and a polarization-rotated second portion of the incident light from the optical data bus 157 to a corresponding one of the output optical waveguides 303-1 to 303-N. The first portion of the incident light propagating in a counterclockwise direction in the ring resonators 301-1 to 301-N is optically coupled through a corresponding coupling section 303A-1 to 303A-N, respectively, to a corresponding longer section 303C-1 to 303C-N, respectively, as indicated by arrows 307-1 to 307-N. The second portion of the incident light propagating in a clockwise direction in the ring resonators 301-1 to 301-N is optically coupled through a corresponding coupling section 303A-1 to 303A-N, respectively, to a corresponding shorter section 303B-1 to 303B-N, respectively, as indicated by arrows 309-1 to 309-N.

[0076] The output optical waveguides 303-1 to 303-N are formed of a material that allows light to be in-coupled, out-coupled, and guided. Each of the output optical waveguides 303-1 to 303-N is formed in a surrounding material that has a sufficiently different optical index than the output optical waveguides 303-1 to 303-N, respectively, to allow light to be guided within the output optical waveguides 303-1 to 303-N. In some embodiments, the output optical waveguides 303-1 to 303-N are implemented to have a racetrack-type shape. However, it should be understood that in other embodiments, the output optical waveguides 303-1 to 303-N may be implemented to have any shape so long as they include corresponding coupling sections 303A-1 to 303A-N, corresponding short sections 303B-1 to 303B-N, and corresponding long sections 303C-1 to 303C-N, respectively.

[0077] Each of the N demultiplexers 311-1 to 311-N includes a corresponding photodetector 305-1 to 305-N associated with a corresponding ring resonator 301-1 to 301-N. The short sections 303B-1 to 303B-N of the output optical waveguides 303-1 to 303-N extend from a first end of the corresponding coupling section 303A-1 to 303A-N to the corresponding photodetector 305-1 to 305-N. The long sections 303C-1 to 303C-N of the output optical waveguides 303-1 to 303-N extend from a second end of the corresponding coupling section 303A-1 to 303A-N to the corresponding photodetector 305-1 to 305-N. In some embodiments, each of the photodetectors 305-1 to 305-N is a photodetector such as the photodetector 200 described with respect to FIG. 2. In these embodiments, short sections 303B-1 to 303B-N of corresponding ones of output optical waveguides 303-1 to 303-N are optically connected to a first end of the photodetector, and long sections 303C-1 to 303C-N of corresponding ones of output optical waveguides 303-1 to 303-N are optically connected to a second end of the photodetector.

[0078] The length of each corresponding longer section 303C-1-303C-N and each corresponding shorter section 303B-1-303B-N in a given one of the output optical waveguides 303-1-303-N is specified to reduce the difference in arrival time of a first portion of incident light and a polarization-rotated second portion of the incident light at a corresponding photodetector 305-1-305-N. The length of the longer sections 303C-1-303C-N is different for each of the output optical waveguides 303-1-303-N due to the different distances along the optical data bus 157 from the second end 157B of the optical data bus 157 to each of the ring resonators 301-1-301-N. In some embodiments, the lengths of elongated sections 303C-1 to 303C-N decrease as the distance between the corresponding ring resonators 301-1 to 301-N and a midpoint of optical data bus 157 decreases, where the midpoint of optical data bus 157 is approximately halfway between first end 157A and second end 157B of optical data bus 157.

[0079] In some embodiments, the electro-optical receiver 300 further comprises a timing skew management system 165 configured to electronically compensate for a time difference in the generation of a photocurrent by a given one of the photodetectors 305-1-305-N caused by a difference in the arrival time of a first portion of the incident light and a polarization-rotated second portion of the incident light at any given one of the photodetectors 305-1-305-N. After the timing skew management system 165 operates to electronically compensate for a time difference in the generation of a photocurrent by each of the photodetectors 305-1-305-N, the photocurrent generated by each of the photodetectors 305-1-305-N is transmitted to a photocurrent processing circuit 167 for decoding the photocurrent into a digital data pattern carried by the incident optical signal. In some embodiments where light from different polarizations is made to have the same polarization and directed to the same photodetectors 305-1-305-N, there may be a time delay difference (timing skew) between the optical signals from each polarization state. After converting the combined optical signals to electrical signals by photodetectors 305-1 to 305-N, the timing skew appears as a notch filter around the electrical high frequency components of the baseband signal. The center frequency of the notch filter depends on the magnitude of the timing skew, and the depth of the notch filter is determined by the relative division of the optical power between the two polarization states. In digital communication applications, this notch filter leads to an increase in inter-symbol interference (ISI). Timing skew management system 165 is configured to detect the presence of timing skew, determine the magnitude of the timing skew, and compensate for the timing skew in the photocurrent-based signal transmitted to photocurrent processing circuit 167.

[0080] FIG. 4A illustrates an example configuration of a PSR 401, according to some embodiments. It should be understood that the example PSR 401 can be utilized with PSR 156 and / or any of the PSRs mentioned herein. It should also be understood that PSR 401 is provided as an example and in no way limits how PSR 156 and / or any of the PSRs mentioned herein can be configured in various embodiments. PSR 401 includes a first optical waveguide 403 and a second optical waveguide 405. FIG. 4B illustrates a vertical cross-sectional view of the example PSR 401 along line AA of FIG. 4A, according to some embodiments. In some embodiments, the first optical waveguide 403 is a silicon nitride optical waveguide and the second optical waveguide 405 is a silicon optical waveguide. In some embodiments, PSR 401 is formed on a buried oxide (BOX) layer 407 that is disposed on a substrate 409. In some embodiments, the first optical waveguide 403 and the second optical waveguide 405 are formed within an optical cladding 411. In some embodiments, the optical cladding 411 is silicon dioxide. The first optical waveguide 403 is vertically separated from the second optical waveguide 405 by a layer of optical cladding 411, as indicated by arrow 413.

[0081] The first optical waveguide 403 comprises an input section 403A coupled to receive incident light including both TE and TM polarizations. In some embodiments, the input section 403A is configured as an inverse taper to convert the spot size of the incident light to an optical mode of the first optical waveguide 403. After the input section 403A (with respect to the optical propagation direction), the first optical waveguide 403 comprises a rotating / splitting section 403B. In some embodiments, the rotating / splitting section 403B has a substantially linear shape. After the rotating / splitting section 403B, the first optical waveguide 403 comprises an output section 403C optically coupled to a first optical output 403D of the PSR 401. The first optical waveguide 403 is configured such that a portion of the incident light having a first polarization (TE or TM) propagates through the first optical waveguide 403 to the first optical output 403D of the PSR 401 substantially unchanged. The example PSR 401 shows that the TE polarization of the incident light propagates through the first optical waveguide 403 to the first optical output 403D of the PSR 401 substantially unchanged.

[0082] The second optical waveguide 405 comprises a rotating / splitting section 405A configured to evanescently incouple the TM polarization of the incident light from the rotating / splitting section 403B of the first optical waveguide 403 and simultaneously rotate the incoupled TM polarization to TE polarization. To achieve this, the rotating / splitting section 405A of the second optical waveguide 405 has an inverse taper configuration that is positioned off-center (has a lateral offset in a direction perpendicular to the light propagation direction) with respect to the rotating / splitting section 403B of the first optical waveguide 403. The lateral offset of the rotate / split section 405A of the second optical waveguide 405 relative to the rotate / split section 403B of the first optical waveguide 403 acts to break the horizontal and vertical symmetry in order to rotate the TM0 mode in the rotate / split section 403B of the first optical waveguide 403 into a rotated TE0 mode and couple the rotated TE0 mode into the rotate / split section 405A of the second optical waveguide 405. The rotated TE0 mode is transmitted through the output section 405B of the second optical waveguide 405 to the second optical output 405C of the PSR 401. While PSR example 401 shows the TE polarization of the incident light propagating through the first optical waveguide 403 to the first optical output 403D of PSR401 substantially unchanged, and the TM polarization of the incident light being rotated to TE polarization on the way to the second optical output 405C of PSR401, other embodiments of PSR401 are configured to propagate the TM polarization of the incident light through the first optical waveguide 403 to the first optical output 403D of PSR401 substantially unchanged, while rotating the TE polarization of the incident light to TM polarization on the way to the second optical output 405C of PSR401.

[0083] FIG. 5A illustrates an example configuration of a PSR 501, according to some embodiments. It should be understood that the example PSR 501 can be utilized for PSR 156 and / or any of the PSRs mentioned herein. It should also be understood that the PSR 501 is provided as an example and in no way limits how PSR 156 and / or any of the PSRs mentioned herein can be configured in various embodiments. The PSR 501 is a broadband PSR that implements a rib-type optical waveguide. The PSR 501 comprises a first branch 503 and a second branch 505. The PSR 501 is configured as an optical waveguide system with a first branch slab waveguide 507, a first branch rib waveguide 509, a second branch slab waveguide 511, and a second branch rib waveguide 513. FIG. 5B illustrates a vertical cross-sectional view of the example PSR 501 along line AA of FIG. 5A, according to some embodiments. FIG. 5C is a vertical cross-sectional view of an example PSR 501 taken along line BB of FIG. 5A, according to some embodiments. In some embodiments, the first branch slab waveguide 507, the second branch slab waveguide 511, the first branch rib waveguide 509, and the second branch rib waveguide 513 are integrally formed as a monolithic optical waveguide structure, where the first branch slab waveguide 507, the second branch slab waveguide 511, the first branch rib waveguide 509, and the second branch rib waveguide 513 form different portions of the monolithic optical waveguide structure. In some embodiments, the monolithic optical waveguide structure is formed as a silicon optical waveguide. In some embodiments, the monolithic optical waveguide structure is formed as a silicon nitride optical waveguide. In some embodiments, the PSR 501 is formed on a BOX layer 515 that is disposed on a substrate 517. In some embodiments, a monolithic optical waveguide structure comprising first branch slab waveguide 507, second branch slab waveguide 511, first branch rib waveguide 509, and second branch rib waveguide 513 is formed within optical cladding 519. In some embodiments, optical cladding 519 is silicon dioxide.

[0084] The first branch rib waveguide 509 comprises an input section 509A having a substantially straight shape, followed (with respect to the light propagation direction in the PSR 501) by a tapered section 509B, followed by an output section 509C. The first branch slab waveguide 507 comprises a tapered input section 507A, followed by a tapered section 507B (corresponding to the rib tapered section 509B), followed by an output section 507C (corresponding to the rib output section 509C). The second branch rib waveguide 513 comprises a tapered section 513A, followed (with respect to the light propagation direction in the PSR 501) by an output section 513B. The second branch slab waveguide 511 comprises a tapered section 511A (corresponding to the rib tapered section 513A), followed by an output section 511B (corresponding to the rib output section 513B). In some embodiments, a portion of the output section 511B of the second branch slab waveguide 511, which is disposed between the first branch rib waveguide 509 and the second branch rib waveguide 513, has a width that increases along the optical propagation direction to provide easy optical routing of the outputs of the first branch 503 and the second branch 505 for the purpose of separating the output optical waveguides.

[0085] The input section 509A and tapered section 509B of the first branch rib waveguide 509 and the tapered input section 507A and tapered section 507B of the first branch slab waveguide 507 collectively function as a polarization rotator. The output section 509C of the first branch rib waveguide 509 and the output section 507C of the first branch slab waveguide 507 and the tapered section 513A of the second branch rib waveguide 513 and the tapered section 511A of the second branch slab waveguide 511 collectively function as a polarization splitter. In this manner, the TE0 polarization of the incident light is transmitted substantially unchanged through the first branch 503 to the first optical output 521 of the PSR 501. The TM0 polarization of the incident light is rotated to TE1 polarization while this portion of the incident light is transmitted through the first branch 503, and then rotated to TE0 polarization and optically coupled into the second branch 505 en route to the second optical output 523 of the PSR 501. Alternatively, in some other embodiments, the PSR 501 is configured to pass the TM polarization of the incident light substantially unchanged and rotate / split the TE polarization of the incident light into the output TM polarization.

[0086] It should be understood that PSR401 and PSR501 are provided as examples of how the PSRs described herein may be implemented in some example embodiments. It should also be understood that in some embodiments, any of the PSRs described herein may be implemented as a dual polarization grating coupler. It should be understood that example PSR401 and example PSR501 in no way limit how the various PSRs described herein may be implemented in various embodiments. Any of the PSRs described herein may be implemented in different ways, so long as one of the two input polarizations (TE or TM) of the incident light received by the PSR is rotated to the other polarization and directed to one of the two outputs of the PSR, and the non-rotated polarization of the incident light is directed to the other of the two outputs of the PSR.

[0087] FIG. 6 illustrates an example WDM receiver string 600 in accordance with some embodiments. WDM receiver string 600 includes N WDM demultiplexers 601-1 through 601-N positioned within an evanescent optical coupling distance of optical waveguide 602. Optical waveguide 602 functions as an optical data bus within WDM receiver string 600. In some embodiments, number N is an integer value equal to or greater than 1. In some embodiments, WDM receiver string 600 includes a plurality of WDM demultiplexers 601-1 through 601-N, where number N is an integer value equal to or greater than 2. In some embodiments, WDM receiver string 600 includes a plurality of WDM demultiplexers 601-1 through 601-N, where number N is an even integer value equal to or greater than 2. In some embodiments, WDM receiver string 600 includes a plurality of WDM demultiplexers 601-1 through 601-N, where number N is an odd integer value equal to or greater than 1. In some embodiments, each of the WDM demultiplexers 601-1 to 601-N is configured in the same manner as the WDM demultiplexer 100 described with respect to Figures 1A to 1E. In particular, each of the WDM demultiplexers 601-1 to 601-N includes a respective ring resonator 103-1 to 103-N that is disposed within an evanescent optical coupling distance of the optical waveguide 602. In some embodiments, each of the WDM demultiplexers 601-1 to 601-N includes a respective heater 104-1 to 104-N that is disposed within the respective ring resonator 103-1 to 103-N. The heaters 104-1 to 104-N are configured to adjust the resonant wavelength λ1 to λ2 of the respective ring resonator 103-1 to 103-N. N and the corresponding operating wavelength ranges of WDM demultiplexers 601-1 through 601-N, respectively.

[0088] Each of the WDM demultiplexers 601-1 to 601-N includes a corresponding first optical signal timing delay section 107-1 to 107-N and a corresponding second optical signal timing delay section 109-1 to 109-N optically connected to the opposite end of the corresponding optical waveguide 105-1 to 105-N. The optical waveguides 105-1 to 105-N extend through the evanescent light coupling distance range of the corresponding ring resonators 103-1 to 103-N such that light propagating through the ring resonators 103-1 to 103-N is coupled to the corresponding optical waveguide 105-1 to 105-N. The first optical signal timing delay sections 107-1 to 107-N apply corresponding optical signal delays D to the first optical signals traveling from the first port A through the optical waveguide 602 to the corresponding WDM demultiplexers 601-1 to 601-N, respectively. 1A ~D NA As described with respect to FIG. 1B, the wavelength λ x The first optical signal having a resonant wavelength λ x The first optical signal is coupled to ring resonator 103-x operating at 100 Hz, travels counterclockwise within ring resonator 103-x, optically couples to optical waveguide 105-x, and travels to first optical signal timing delay section 107-x (where x is any of 1 to N). From first optical signal timing delay section 107-1 to 107-N, the first optical signal travels through optical waveguides 111-1 to 111-N, respectively, to corresponding first inputs 115A-1 to 115A-N of corresponding photodetectors 115-1 to 115-N, respectively.

[0089] The second optical signal timing delay sections 109-1 to 109-N apply corresponding optical signal delays D to the second optical signals traveling from the second port B through the optical waveguide 602 to the corresponding WDM demultiplexers 601-1 to 601-N, respectively. 1B ~D NB As described with respect to FIG. 1C, the wavelength λ x A second optical signal having a resonant wavelength λ xThe second optical signal travels from the second optical signal timing delay section 109-1 through 109-N through the optical waveguides 113-1 through 113-N, respectively, to the corresponding second inputs 115B-1 through 115B-N of the corresponding photodetectors 115-1 through 115-N, respectively. In some embodiments, the first optical signal traveling from the first port A and the second optical signal traveling from the second port B are oppositely polarized portions of the same original input signal received by the electro-optical receiver with WDM receiver array 600, where one of the two polarizations (TE or TM) of the same original input signal has been rotated to the other polarization. For example, in some embodiments, the first port A is a first output port of a PSR (such as PSR 401 in FIGS. 4A and 4B or PSR 501 in FIGS. 5A-5C) and the second port B is a second output port of the PSR. xA and optical signal timing delay section D xB Implementing both of these is equivalent to implementing a single differential optical signal timing delay for the optical signal traveling through optical waveguide 105-x to optical detector 115-x. Thus, in some embodiments, an optical signal timing delay D xA and optical signal timing delay section D xB The optical signal timing delay unit D xA or optical signal timing delay section D xB may be implemented within a given WDM demultiplexer 601-x.

[0090] Additionally, in some embodiments, one or more optical signal timing delays are implemented along the optical waveguide 602. For example, in some embodiments, an optical signal timing delay D is implemented to receive and delay the first optical signal traveling from the first port A before reaching the first WDM demultiplexer 601-1. A is mounted on the first end of the optical waveguide 602. A is configured to introduce a controlled amount of time delay into the propagation of the first optical signal from the first port A to the first WDM demultiplexer 601-1. In some embodiments, an optical signal timing delay D is configured to receive and delay a second optical signal traveling from the second port B before reaching the Nth WDM demultiplexer 601-N. B is implemented at the second end of the optical waveguide 602. B is configured to introduce a controlled amount of time delay into the propagation of the second optical signal from the second port B to the Nth WDM demultiplexer 601-N. In some embodiments, the optical signal timing delay unit D A and optical signal timing delay section D B is mounted at the opposite end of the optical waveguide 602. A and optical signal timing delay section D B Implementing both of these is equivalent to implementing a single differential optical signal timing delay for the optical signal traveling through optical waveguide 602. Thus, in some embodiments, optical signal timing delay D A or optical signal timing delay section D B is implemented at one end of the optical waveguide 602. In some embodiments, the optical signal timing delay unit D A and optical signal timing delay section D B Each of the optical signal timing delay units D A and optical signal timing delay section D B provide different amounts of optical signal timing delay.

[0091] The WDM demultiplexers 601-1 to 601-N are arranged such that adjacent ones of the WDM demultiplexers 601-1 to 601-N have the lengths L1 to L2 of the optical waveguides 602, respectively. N-1 The optical waveguides 602 are arranged along the optical waveguide 602 so that they are separated from each other by a length L m extend between the optical coupling positions of the ring resonators 103-m and 103-(m+1) of the corresponding WDM demultiplexers 601-m and 601-(m+1), respectively, where m is an integer ranging from 1 to (N-1). For example, the optical coupling positions of the ring resonators 103-1 and 103-2 of the corresponding WDM demultiplexers 601-1 and 602-2, respectively, are separated by the length L1 of the optical waveguide 602. Similarly, the optical coupling positions of the ring resonators 103-(N-1) and 103-N of the corresponding WDM demultiplexers 601-(N-1) and 601-N, respectively, are separated by the length L N-1 In some embodiments, the optical coupling location of a given ring resonator 103-1 to 103-N is the location along the optical waveguide 602 where there is a minimum distance between the given ring resonator 103-1 to 103-N and the optical waveguide 602. The lengths L1 to L2 of the various portions of the optical waveguide 602 between adjacently located ones of the WDM demultiplexers 601-1 to 601-N are N-1 determines the inherent optical signal delay between the various WDM demultiplexers 601-1 through 601-N along the WDM receiver chain 600.

[0092] As mentioned above, in some embodiments of the WDM receiver chain 600, the (N+1) differential optical signal timing delay control parameters (D A / D B and D. 1A / D 1B ~D NA / D NB ), there are N optical signals traveling through WDM receiver array 600 that require differential optical signal timing delays to be equalized. Thus, according to WDM receiver array 600, all WDM wavelength channels λ1 to λ NIn some embodiments, the optical signal timing delay D A and / or optical signal timing delay section D B , other optical signal timing delay units D in various WDM demultiplexers 601-1 to 601-N. 1A / D 1B ~D NA / D NB In some embodiments, the differential time delay τ between the first port A and the second port B (e.g., between the first and second output ports of the PSR) is AB In general, the optical signal delay at the first port A and the optical signal delay at the second port B include the polarization dependent optical signal delay of the optical coupler (e.g., edge coupler) of the electro-optical receiver, the optical signal delay of the PSR, and the optical signal delay of all other optical elements leading to the first port A and the second port B, respectively. A and / or D. B Together with knowing the differential time delay τ AB is known, the differential optical signal timing delay D 1A / D 1B ~D NA / D NB are the WDM wavelength channels λ1 to λ N The timing delays are determined so as to equalize the differential spectroscopic signal timing delays at photodetectors 115-1 to 115-N relative to the received light.

[0093] 7 illustrates an example WDM receiver string 700 in accordance with some embodiments. WDM receiver string 700 is a variation of WDM receiver string 600 of FIG. 6. WDM receiver string 700 includes WDM demultiplexers 601-1 through 601-N. However, each of the first halves 601-1 through 601-(N / 2) of the WDM demultiplexers includes an optical signal delay unit D1 disposed between a corresponding ring resonator 103-1 through 103-(N / 2) and a second input 115B-1 through 115B-(N / 2) of a corresponding optical detector 115-1 through 115-(N / 2), respectively.1B ~D (N / 2)B Instead, in each of the WDM demultiplexers 601-1 to 601-(N / 2), the optical waveguides 105-1 to 105-(N / 2) extend from positions adjacent to the corresponding ring resonators 103-1 to 103-(N / 2) to the second inputs 115B-1 to 115B-(N / 2) of the corresponding photodetectors 115-1 to 115-(N / 2). Similarly, each of the second half WDM demultiplexers 601-[(N / 2)+1] to 601-N does not include an optical signal delay unit D disposed between the corresponding ring resonators 103-[(N / 2)+1] to 103-N and the first inputs 115A-[(N / 2)+1] to 115A-N of the corresponding photodetectors 115-[(N / 2)+1] to 115-N. [(N / 2)+1]B ~D NB Instead, in each of the WDM demultiplexers 601-[(N / 2)+1] to 601-N, the optical waveguides 105-[(N / 2)+1] to 105-N extend from positions close to the corresponding ring resonators 103-[(N / 2)+1] to 103-N to the first inputs 115A-[(N / 2)+1] to 115A-N of the respective photodetectors 115-[(N / 2)+1] to 115-N. In addition, an optical signal timing delay unit D between the first port A and the first WDM demultiplexer 601-1 is not provided. A is implemented, but between the second port B and the N-th WDM demultiplexer 601-N, there is an optical signal timing delay D B is not implemented.

[0094] Due to the time required for light to travel through the optical waveguide 602, the first half 601-1 to 601-(N / 2) of the WDM demultiplexer closest to the first port A receives the first optical signal propagating from the first port A before receiving the second optical signal propagating from the second port B. In other words, the WDM demultiplexer 601-1 to 601-(N / 2) closest to the first port A has a shorter delay in the first optical signal propagating from the first port A compared to the second optical signal propagating from the second port B at the position of the respective ring resonator 103-1 to 103-(N / 2) along the optical waveguide 602. Thus, each optical signal delay section D 1B ~D (N / 2)B Without implementing each optical signal delay unit D 1A ~D (N / 2)A By implementing only the above, the arrival timing of the first optical signal (propagating from the first port A) and the second optical signal (propagating from the second port B) at the photodetectors 115-1 to 115-(N / 2) can be substantially equalized. 1B ~D (N / 2)B It should be appreciated that not implementing , reduces the footprint of WDM receiver array 700 on a chip, reducing the overall complexity and cost of WDM receiver array 700.

[0095] Similarly, due to the time required for light to travel through the optical waveguide 602, the second half WDM demultiplexer 601-[(N / 2)+1] to 601-N closest to the second port B receives the second optical signal propagating from the second port B before receiving the first optical signal propagating from the first port A. In other words, the WDM demultiplexer 601-[(N / 2)+1] to 601-N closest to the second port B has a shorter delay in the second optical signal propagating from the second port B compared to the first optical signal propagating from the first port A at the position of the respective ring resonator 103-[(N / 2)+1] to 103-N along the optical waveguide 602. Thus, each optical signal delay section D [(N / 2)+1]A ~D NAWithout implementing each optical signal delay unit D [(N / 2)+1]B ~D NB By implementing only the first optical signal delay unit D in each of the WDM demultiplexers 601-[(N / 2)+1] to 601-N closest to the second port B, the arrival timing of the first optical signal (propagating from the first port A) and the second optical signal (propagating from the second port B) can be substantially equalized at the photodetectors 115-[(N / 2)+1] to 115-N. [(N / 2)+1]A ~D NA It should be appreciated that not implementing , reduces the footprint of WDM receiver array 700 on a chip, reducing the overall complexity and cost of WDM receiver array 700.

[0096] The optical signal timing delay equalization condition at a given photodetector 115-k among photodetectors 115-1 through 115-N in WDM receiver chain 600, 700 is given by Equation 1.

[0097]

number

[0098] Differential time delay τ AB is the time difference between the arrival of the first optical signal at port A and the arrival of the second optical signal at port B. Hence, the differential time delay τ AB is the differential time delay that exists between a first optical signal leaving port A and a second optical signal leaving port B. The term D A is the time required for the first optical signal to propagate from port A to the WDM receiver chain 600, 700. B is the time required for the second optical signal to propagate from port B to the WDM receiver chain 600, 700. The term L x is the length along the WDM receiver string 600, 700 between WDM demultiplexer 601-x and WDM demultiplexer 601-(x+1). Thus, the term L xis the length of the optical waveguide 602 between the reference optical coupling position of the ring resonator 103-x of the WDM demultiplexer 601-x and the reference optical coupling position of the ring resonator 103-(x+1) of the WDM demultiplexer 601-(x+1), where the reference optical coupling position of a given ring resonator 601-1 to 601-N is the position along the optical waveguide 602 at which the given ring resonator 601-1 to 601-N is closest to the optical waveguide 602. kA is the time it takes for a first optical signal propagating from port A to propagate from the point where the first optical signal couples into the ring resonator 103-k of the k-th WDM demultiplexer 601-k to the photodetector 115+k of the k-th WDM demultiplexer 601-k. kB is the time it takes for the second optical signal propagating from port B to propagate from the point where the second optical signal couples to the ring resonator 103-k of the k-th WDM demultiplexer 601-k to the photodetector 115+k of the k-th WDM demultiplexer 601-k.

[0099] Equation 1 represents the condition for a first optical signal propagating through port A and a second optical signal propagating through port B to arrive at photodetector 115-k of k-th WDM demultiplexer 601-k at substantially the same time. Because the first optical signal propagating through port A and the second optical signal propagating through port B correspond to respective portions of the same original incident optical signal, Equation 1 represents the condition for each portion of the same original incident optical signal to arrive at photodetector 115-k of k-th WDM demultiplexer 601-k at substantially the same time. Because Equation 1 defines the optical signal timing delay equalization condition for k-th WDM demultiplexer 601-k, considering Equation 1 for each of WDM demultiplexers 601-1 through 601-N defines a linear system of N equations that describe the delay equalization condition of WDM receiver chain 600, 700.

[0100] Equation 2 is obtained by subtracting Equation 1 for the k-th WDM demultiplexer 601-k from Equation 1 for the (k+1)-th WDM demultiplexer 601-(k+1). Equation 2 can be rewritten as shown in Equation 3. Equation 3 can be rewritten as shown in Equation 4.

[0101] Formula 2:L k / V g +D (k+1)A -D kA =-L k / V g +D (k+1)B -D kB

[0102] Formula 3:(D (k+1)B -D (k+1)A )-(D kB -D kA )=2L k / V g

[0103] Equation 4:ΔD (k+1) -ΔD k =2L k / V g

[0104] term ΔD (k+1) is the difference in propagation times of the second optical signal and the first optical signal through the (k+1)-th WDM demultiplexer 601-(k+1) (from the reference optical coupling position of the ring resonator 103-(k+1) to the photodetector 115-(k+1)), where the second optical signal propagates from port B and the first optical signal propagates from port A. The term ΔD k is the difference in propagation times of the second optical signal and the first optical signal through the k-th WDM demultiplexer 601-k (from the reference optical coupling position of the ring resonator 103-k to the photodetector 115-k), where the second optical signal is propagating from port B and the first optical signal is propagating from port A.

[0105] Equation 4 shows that to achieve optical signal timing delay equalization at the photodetector 115-(k+1) of the (k+1)-th WDM demultiplexer 601-(k+1), the optical signal timing delay difference (i.e., ΔD (k+1) ) is the optical signal timing delay difference (i.e., ΔD k) by an amount of twice the time required for an optical signal to propagate through the portion of optical waveguide 602 separating the reference optical coupling location of ring resonator 103-(k+1) and the reference optical coupling location of ring resonator 103-k. In other words, in order for a first optical signal propagating from port A and a second optical signal propagating from port B to arrive at photodetector 115-(k+1) of the (k+1)th WDM demultiplexer 601-(k+1) at substantially the same time, the optical signal timing delay difference implemented in the (k+1)th WDM demultiplexer 601-(k+1) (i.e., ΔD(k+1)) should be longer than the optical signal timing delay difference implemented in the kth WDM demultiplexer 601-k (i.e., ΔDk) by an amount twice the time required for light to propagate through the portion of optical waveguide 602 separating the (k+1)th WDM demultiplexer 601-(k+1) from the kth WDM demultiplexer 601-k. For example, in WDM receiver array 600, in order for a first optical signal propagating from port A and a second optical signal propagating from port B to arrive at photodetector 115-2 of WDM demultiplexer 601-2 at substantially the same time, a differential optical signal timing delay (i.e., D 2B -D 2A ) is the optical signal timing delay difference (i.e., D 1B -D 1A ) should be longer than the time required for light to propagate through the L1 portion of optical waveguide 602 that separates the reference optical coupling location of ring resonator 103-2 of WDM demultiplexer 601-2 from the reference optical coupling location of ring resonator 103-1 of WDM demultiplexer 601-1. Also, by way of example, in WDM receiver string 700, in order for a first optical signal propagating from port A and a second optical signal propagating from port B to arrive at photodetector 115-2 of WDM demultiplexer 601-2 simultaneously, the optical signal timing delay difference (i.e., D 2A ) is the optical signal timing delay difference (i.e., D 1A) by twice the amount of time required for light to propagate through the L1 portion of optical waveguide 602 that separates the reference optical coupling location of ring resonator 103-2 of WDM demultiplexer 601-2 from the reference optical coupling location of ring resonator 103-1 of WDM demultiplexer 601-1.

[0106] In some embodiments, the WDM receiver array 600, 700 is substantially symmetrically configured. For example, in some embodiments, the number N of WDM demultiplexers 601-1 through 601-N is an even value, WDM demultiplexers 601-1 through 601-(N / 2) are disposed along a first half of the WDM receiver array 600, 700, and WDM demultiplexers 601-[(N / 2)+1] through 601-N are disposed along a second half of the WDM receiver array 600, 700, where the spacing between adjacent WDM demultiplexers 601-1 through 601-N is substantially symmetric between the first and second halves of the WDM receiver array 600, 700. Also, by way of example, in some embodiments, the number N of WDM demultiplexers 601-1 through 601-N is an odd value greater than 1, WDM demultiplexers 601-1 through 601-[(N-1) / 2] are positioned along a first half of WDM receiver array 600, 700, WDM demultiplexer 601-[(N+1) / 2] is positioned at the center of WDM receiver array 600, 700, and WDM demultiplexers 601-[(N+3) / 2] through 601-N are positioned along a second half of WDM receiver array 600, 700, where the spacing between adjacently positioned WDM demultiplexers 601-1 through 601-N is substantially symmetric between the first and second halves of WDM receiver array 600, 700.

[0107] In such an embodiment in which the WDM receiver array 600, 700 is formed substantially symmetrically, the distance L1 along the optical waveguide 602 is equal to the distance L N-1 and the distance L2 along the optical waveguide 602 is substantially equal to the distance L N-2and so on. In these embodiments, to achieve optical signal timing delay equalization at each of photodetectors 115-1-115-N of WDM demultiplexers 601-1-601-N, the optical signal timing delay differences implemented within WDM demultiplexers 601-1-601-N are made substantially symmetrical between the first and second halves of WDM receiver chain 600, 700. For example, with respect to WDM receiver chain 600, the optical signal timing delay difference implemented within WDM demultiplexer 601-1 (i.e., ΔD1=D 1B -D 1A ) is the optical signal timing delay difference (i.e., ΔD N =D NB -D NA ) and the optical signal timing delay difference implemented in WDM demultiplexer 601-2 (i.e., ΔD2=D 2B -D 2A ) is the optical signal timing delay difference (i.e., ΔD (N-1) =D (N-1)B -D (N-1)A ) and so on. Also, by way of example, with respect to WDM receiver chain 700, the optical signal timing delay difference implemented within WDM demultiplexer 601-1 (i.e., (D 1A ) is the optical signal timing delay difference (i.e., D NB ) and is substantially equal to the optical signal timing delay difference implemented in WDM demultiplexer 601-2 (i.e., D 2A ) is the optical signal timing delay difference (i.e., D (N-1)B ), etc.

[0108] FIG. 8A illustrates an example of a time plot of optical power of a first optical signal propagating from port A and a second optical signal propagating from port B, according to some embodiments. Curve 801 represents the optical power as a function of time for the first optical signal propagating from port A. Curve 803 represents the optical power as a function of time for the second optical signal propagating from port B. The first optical signal 801 propagating from port A and the second optical signal 803 propagating from port B are respective portions of the same original optical signal received at an electro-optical receiver device. In some embodiments, the first optical signal 801 and the second optical signal 803 correspond to different polarizations of light contained within the original optical signal. In some embodiments, a first polarization of light in the original optical signal is split (separated) from the original optical signal and transmitted through the first port A as the first optical signal 801 that maintains the first polarization. Also, in these embodiments, a second polarization of light in the original optical input signal is split (isolated) from the original light and polarization rotated from the second polarization to the first polarization to generate a second optical signal 803 that is transmitted through the second port B. Thus, in these embodiments, the first optical signal 801 propagating from port A and the second optical signal 803 propagating from port B have the same polarization (the first polarization). This allows the WDM demultiplexers 601-1 through 601-N in the WDM receiver string 600, 700 to be configured and optimized to operate on light having the first polarization, thereby providing processing of both the first optical signal 801 and the second optical signal 803 that collectively represent the entire original optical signal, without the need to process light having the second polarization. However, the optical splitting and polarization rotation performed to separate and generate the first optical signal 801 and the second optical signal 803 from the original optical signal does not eliminate the differential time delay (τ ) that exists between the first optical signal exiting port A and the second optical signal exiting port B. AB ) will be introduced.

[0109] FIG. 8B illustrates a differential time delay (τ AB ) to mitigate the delay D A or delay D A And D B1 illustrates an example of a time plot of the optical power of a first optical signal propagating from port A and a second optical signal propagating from port B when implementing the delay D A is the time required for the first optical signal 801 to propagate from port A of the PSR to the WDM receiver chain 600, 700, and the delay D B is the time required for the second optical signal 803 to propagate from port B of the PSR to the WDM receiver chain 600, 700. A The magnitude of delay D is controlled by adding an optical delay on the optical propagation path between the first port A of the PSR and the WDM receiver array 600, 700. Similarly, the delay D B The magnitude of delay D is controlled by adding an optical delay on the optical propagation path between the second port B of the PSR and the WDM receiver array 600, 700. A and delay D B The difference between the differential time delay (τ AB ), a first optical signal propagating from port A and a second optical signal propagating from port B arrive at the WDM receiver string 600, 700 at substantially the same time. This condition is expressed by Equation 5.

[0110] Formula 5:D A -D B = τ AB

[0111] Delay D A and D. B The magnitude of is the differential time delay (τ AB ) between the first and second optical signals at corresponding ports A and B of the PSR. AB ) to offset the delay D A and D. BEstablishing and utilizing the differential optical signal timing delay ΔD that needs to be implemented in the k-th WDM demultiplexer 601-k to cause the first optical signal 801 and the second optical signal 803 to arrive at the photodetector 115-k of the k-th WDM multiplexer 601-k at substantially the same time, particularly when the WDM receiver chains 600, 700 are configured substantially symmetrically. k (Here, ΔD k =D kB -D kA When the condition of Equation 5 holds, Equation 1 simplifies to the optical signal timing delay equalization condition shown by Equation 6. Equation 6 can be rewritten as shown in Equation 7, which provides the required optical signal timing delay difference ΔD k However, the first optical signal from port A is delayed D along the optical waveguide 602. A the time required for the second optical signal from port B to propagate along the optical waveguide 602, and the delay D B In general, the optical signal timing delay difference ΔD required within the k-th WDM demultiplexer 601-k is substantially equal to the difference between the time required for the optical signal to propagate from k is equal to the cumulative delay when the second optical signal reaches the k-th WDM demultiplexer 601-k from the second port B of the PSR minus the cumulative delay when the first optical signal reaches the k-th WDM demultiplexer 601-k from the first port A of the PSR.

[0112]

number

[0113]

number

[0114] The optical signal timing delay difference ΔD required in a given one (k-th WDM demultiplexer) of the WDM demultiplexers 601-1 to 601-N arranged near the center of the WDM receiver array 600, 700 is k is the optical signal timing delay difference ΔD required within a given one (k'th WDM demultiplexer) of the WDM demultiplexers 601-1 to 601-N located near the end of the WDM receiver array 600, 700. k’ This is smaller than the delay D A Lengths L1 to L2 along the optical waveguide 602 from the k-th WDM demultiplexer 601-k to the k-th WDM demultiplexer 601-k (k-1) and the delay D B The length L along the optical waveguide 602 from k From L (N-1) This is because the difference between the sum of the optical signal timing delay difference ΔD and the k-th WDM demultiplexer 601-k is small when the k-th WDM demultiplexer 601-k is located near the center of the WDM receiver string 600, 700. Also, in some embodiments, the number N of WDM demultiplexers 601-1 through 601-N is an odd value (an odd integer value). In some embodiments, when the number N of WDM demultiplexers 601-1 through 601-N is an odd integer greater than 1 and the WDM receiver string 600, 700 is configured substantially symmetrically, the centrally located WDM demultiplexer 601-[(N+1) / 2] has an optical signal timing delay difference ΔD that is essentially zero. [(N+1) / 2] (i.e., D [(N+1) / 2]B =D [(N+1) / 2]A =0).

[0115] 9A illustrates a WDM receiver array 900 in accordance with some embodiments. The WDM receiver array 900 is implemented in a manner similar to the WDM receiver array 700 of FIG. 7 such that the optical waveguide 602 has a U-shape such that both the first optical signal propagating from port A of the PSR and the second optical signal propagating from port B of the PSR enter the WDM receiver array 900 from the same side 901. Specifically, the optical waveguide 602 includes a U-shaped section 905 on a side 903 of the WDM receiver array 900 opposite the side 901 of the WDM receiver array 900 on which both the first optical signal propagating from port A and the second optical signal propagating from port B enter. In this manner, the second optical signal propagating from port B of the PSR travels a distance L through the optical waveguide 602, including through the U-shaped section 905. across 9 and reaches the Nth WDM demultiplexer 601-N of the WDM receiver array 900. In the WDM receiver array 900, the WDM demultiplexers 601-1 to 601-N are aligned on one side of the U-shaped optical waveguide 602. In some embodiments, the optical signal delay D A The magnitude of the differential time delay (τ AB ), where the differential time delay (τ AB ) is the time it takes for the second optical signal propagating from port B to travel a distance L across More specifically, the optical signal delay D A is the differential time delay (τ AB ), where the differential time delay (τ AB ) is (L across In these embodiments, the optical signal delay D A is approximately the same as the time it takes light to propagate through optical waveguide 602 across WDM receiver array 900. Thus, in these embodiments, the optical signal delay D A is implemented as an optical waveguide delay line, the optical signal delay D AIn this case, the portion of the optical waveguide 602 that carries the second optical signal from port B of the PSR across the WDM receiver array 900 to the U-shaped section 905 is called the return waveguide, and the optical signal delay line D A The portion of optical waveguide 602 that passes through each of ring resonators 103-1 through 103-N of WDM demultiplexers 601-1 through 601-N, respectively, is referred to as the main optical signal bus, and the return waveguide and the main optical signal bus are optically connected by a U-shaped section 905 of optical waveguide 602. In some embodiments, the return waveguide is a substantially straight portion of optical waveguide 602 that runs parallel to the main optical signal bus.

[0116] 9B illustrates a WDM receiver array 950, according to some embodiments. In the WDM receiver array 950, the optical waveguide 602 is U-shaped and includes a first linear section 602A, a U-shaped section 602B, and a second linear section 602C. The first linear section 602A is optically connected to the second linear section through the U-shaped section 602B. The WDM receiver array 950 is folded such that half of the WDM demultiplexers 601-1 through 601-(N / 2) are disposed along the first linear section 602A of the optical waveguide 602, and half of the WDM demultiplexers 601-[(N / 2)+1] through 601-N are disposed along the second linear section 602A of the optical waveguide 602. In some embodiments, the number N of WDM demultiplexers is an odd integer, with the central WDM demultiplexer 601-[(N+1) / 2] disposed along the U-shaped section 602B, the WDM demultiplexers 601-1 through 601-[(N-1) / 2] disposed along the first linear section 602A of the optical waveguide 602, and the WDM demultiplexer 601-{[(N+1) / 2]+1} disposed along the second linear section 602C of the optical waveguide 602. In the WDM receiver string 950, both the first optical signal propagating from port A of the PSR and the second optical signal propagating from port B of the PSR enter the same side of the WDM receiver string 950. In some embodiments, both the first optical signal propagating from port A of the PSR and the second optical signal propagating from port B of the PSR enter the side of the WDM receiver string 950 closest to the PSR. In the WDM receiver array 950, the optical signal delay D A is the differential time delay (τ) between a first optical signal exiting port A of the PSR and a second optical signal exiting port B of the PSR. AB ) is set substantially equal to the optical signal delay D A is the optical signal delay D of the WDM receiver chain 900 of FIG. A In particular, the present invention does not contribute much to optical power loss in the optical waveguide, nonlinear optical power loss, and wiring congestion because it has an optical signal delay line that is shorter than that included in the optical waveguide.

[0117] FIG. 10A illustrates a WDM receiver string 1001 with eight WDM demultiplexers 601-1 through 601-8 (8 channels), according to some embodiments. FIG. 10B illustrates a close-up view of section 1007 of WDM receiver string 1001, according to some embodiments. FIG. 10C illustrates a close-up view of section 1009 of WDM receiver string 1001, according to some embodiments. FIG. 10D illustrates a close-up view of section 1011 of WDM receiver string 1001, according to some embodiments. WDM receiver string 1001 is implemented in a similar manner to WDM receiver string 700 of FIG. 7, such that optical waveguide 602 has a U-shape such that a first optical signal propagating from port A of the PSR and a second optical signal propagating from port B of the PSR both enter the WDM receiver string 1001 from the same side. Optical waveguide 602 includes a U-shaped section 1002 on a side of WDM receiver array 1001 opposite the side of WDM receiver array 1001 on which both the first optical signal propagating from port A and the second optical signal propagating from port B enter. In this manner, the second optical signal propagating from port B of the PSR travels a distance L through optical waveguide 602, including through U-shaped section 1002. across , and reaches the eighth WDM demultiplexer 601-8 in WDM receiver row 1001. In WDM receiver row 1001, WDM demultiplexers 601-1 to 601-8 are arranged in a straight line on one side of U-shaped optical waveguide 602.

[0118] The WDM receiver 1001 applies an optical signal delay D to the first optical signal from port A of the PSR before it reaches the first WDM demultiplexer 601-1. A An optical signal delay D is arranged to propagate through A In some embodiments, the optical signal delay D A The magnitude of the differential time delay (τ AB ), where the differential time delay (τ AB ) is the time it takes for the second optical signal propagating from port B to travel a distance L across More specifically, the optical signal delay D A is the differential time delay (τAB ), where the differential time delay (τ AB ) is (L across In the example WDM receiver string 1001, the optical signal delay D A is configured as the length of optical waveguide 1005 that forms part of or is optically connected to optical waveguide 602. Also, in the example WDM receiver string 1001, the optical signal delay D A is the optical signal delay D A In order to reduce / minimize the chip area occupied by the conductive layer, the conductive layer is configured to have one or more of a folded shape, a spiral shape, a helical shape, a loop shape, and a zigzag shape, among other shapes.

[0119] The first half 601-1 to 601-4 of the WDM demultiplexer include a corresponding first optical signal timing delay section 107-1 to 107-4, respectively, but not a corresponding second optical signal timing delay section 109-1 to 109-4, respectively. The second half 601-5 to 601-8 of the WDM demultiplexer include a corresponding second optical signal timing delay section 109-5 to 109-8, respectively, but not a corresponding first optical signal timing delay section 107-5 to 107-8, respectively. The first half 601-1 to 601-4 of the WDM demultiplexer and the second half 601-5 to 601-8 of the WDM demultiplexer are configured such that the WDM receiver string 1001 receives (optical signal delays D ASpecifically, the first optical signal timing delay section 107-1 and the second optical signal timing delay section 109-8 have substantially the same configuration and provide substantially the same amount of optical signal timing delay; the second optical signal timing delay section 107-2 and the second optical signal timing delay section 109-7 have substantially the same configuration and provide substantially the same amount of optical signal timing delay; the third optical signal timing delay section 107-3 and the second optical signal timing delay section 109-6 have substantially the same configuration and provide substantially the same amount of optical signal timing delay; and the fourth optical signal timing delay section 107-4 and the second optical signal timing delay section 109-5 have substantially the same configuration and provide substantially the same amount of optical signal timing delay.

[0120] Additionally, each of the first optical signal timing delay sections 107-1-107-4 and each of the second optical signal timing delay sections 109-5-109-8 are configured to have one or more of folded, spiral, helical, loop, and zigzag shapes, among others, to reduce / minimize the chip area they occupy. The amount of optical signal timing delay provided by the first optical signal timing delay sections 107-1-107-4 decreases monotonically in a direction extending from the outside of the WDM receiver string 1001 to the midpoint of the WDM receiver string 1001. The midpoint of the WDM receiver string 1001 is a location along the optical waveguide 602 midway between the ring resonator 103-4 of the WDM demultiplexer 601-4 and the ring resonator 103-5 of the WDM demultiplexer 601-5. Similarly, the amount of optical signal timing delay provided by second optical signal timing delay sections 107-5 through 107-8 decreases monotonically in a direction extending from the outside of WDM receiver string 1001 to the midpoint of WDM receiver string 1001. In WDM receiver string 1001, the amount of optical signal timing delay provided by k-th delay section 107-k of the first optical signal timing delay section is given by the optical signal timing delay difference ΔDk In addition, in the WDM receiver chain 1001, the amount of optical signal timing delay provided by the k-th delay section 109-k of the second optical signal timing delay sections is substantially equal to the magnitude (absolute value) of the optical signal timing delay difference ΔD given by Equation 7 for N=8: k is essentially equal to the magnitude (absolute value) of

[0121] In some embodiments, the photodiodes are connected to on-chip receiver circuits (such as transimpedance amplifiers (TIAs)). When densely integrating photonics and circuits, a challenge is that photonic waveguides and photonic devices should be kept away from circuit wiring (conductive structures) to avoid metal-induced optical losses (such as optical absorption or scattering). Also, in some situations, the use of long optical delay lines potentially blocks a large chip area that could be used for circuit wiring. The WDM receiver array 1001 addresses the above-mentioned challenges by locating each of the first optical signal timing delay sections 107-1 to 107-4 outboard from their corresponding optical detectors 115-1 to 115-4, and each of the second optical signal timing delay sections 109-5 to 109-8 outboard from their corresponding optical detectors 115-5 to 115-8. Specifically, each of photodetectors 115-1-115-4 is connected to a corresponding first optical signal timing delay section 107-1-107-4 located on the left side (outside relative to the midpoint of WDM receiver string 1001). And each of photodetectors 115-5-115-8 is connected to a corresponding second optical signal timing delay section 109-5-109-8 located on the right side (outside relative to the midpoint of WDM receiver string 1001). In some embodiments, within WDM receiver string 1001, outermost first optical signal timing delay section 107-1 and outermost second optical signal timing delay section 109-8 are located outside the main circuit area, which minimizes the impact of the optical signal delay lines on the circuit layout.

[0122] 11A illustrates a floor plan of a receiver circuit unit cell 1101 for use in constructing a WDM receiver string, according to some embodiments. The floor plan of the receiver circuit unit cell 1101 includes an area 1101 (shaded area) available for implementation of an integrated circuit. In some embodiments, the TIA circuit 105 is implemented within the area 1101. The floor plan of the receiver circuit unit cell 1101 further includes an area 1107 (unshaded area) available for implementation of a photonic component. Placement of electronic circuitry within the area 1107 is constrained to ensure acceptable optical interactions between the photonic and electronic components.

[0123] 11B illustrates a floor plan of a receiver circuit unit cell 1109 for use in constructing a WDM receiver string, according to some embodiments. The floor plan of the receiver circuit unit cell 1109 is a flipped version of the floor plan of the receiver circuit unit cell 1101. The floor plan of the receiver circuit unit cell 1109 includes an area 1111 (shaded area) available for implementation of an integrated circuit. In some embodiments, the TIA circuit 105 is implemented within the area 1111. The floor plan of the receiver circuit unit cell 1109 further includes an area 1113 (unshaded area) available for implementation of a photonic component. Placement of electronic circuitry within the area 1113 is constrained to ensure acceptable optical interaction between the photonic and electronic components.

[0124] FIG 11C shows a first half 1115A of a WDM receiver string 1115 implemented using the receiver circuit unit cells 1101 and 1109 of FIGS. 11A and 11B, respectively, in accordance with some embodiments. FIG 11D shows a complete WDM receiver string 1115 including a first half 1115A and a second half 1115B in accordance with some embodiments. The second half 1115B of the WDM receiver string 1115 is a flipped version of the first half 1115A of the WDM receiver string 1115 with respect to the midpoint of the WDM receiver string 1115. In some embodiments, it is advantageous for some of the receiver circuit unit cells 1101 / 1109 in the WDM receiver string 1115 to be flipped with respect to one another. Also, in some embodiments, the optical delay lines (optical waveguides) of first optical signal timing delay sections 107-1 through 107-N and second optical signal timing delay sections 109-1 through 109-N are positioned toward the outside of the WDM receiver string 1115. Also, in some embodiments, the optical delay lines (optical waveguides) of the outermost first optical signal timing delay section 107-1 and the outermost second optical signal timing delay section 109-N are positioned outside the entire WDM receiver string 1115. In some embodiments, the TIA circuits are positioned toward the outer edges of the receiver circuit unit cells 1101 / 1109.

[0125] In some embodiments of the WDM receiver string 1115, each ring resonator 103-1-103-N of each WDM demultiplexer 601-1-601-N is positioned closer to the outside of the WDM receiver string 1115 than the corresponding optical detector 115-1-115-N to which it is connected. Also, in some embodiments of the WDM receiver string 1115, each first optical signal timing delay section 107-1-107-N of each WDM demultiplexer 601-1-601-N (if present) is positioned closer to the outside of the WDM receiver string 1115 than the corresponding optical detector 115-1-115-N to which it is connected. Also, in some embodiments of the WDM receiver string 1115, one or more of the first optical signal timing delay sections 107-1-107-N are positioned outside the receiver circuit unit cell 1101 / 1109 to which it is connected. Also, in some embodiments of the WDM receiver string 1115, each second optical signal timing delay section 109-1-109-N of each WDM demultiplexer 601-1-601-N, if present, is positioned closer to the outside of the WDM receiver string 1115 than the respective corresponding photodetector 115-1-115-N to which it is connected. Also, in some embodiments of the WDM receiver string 1115, one or more of the second optical signal timing delay sections 109-1-109-N are positioned outside the receiver circuit unit cell 1101 / 1109 to which it is connected. In various embodiments, the symmetry of the photonic components in the WDM receiver string 1115 differs from the symmetry of the receiver circuit unit cells 1101 / 1109 in the WDM receiver string 1115. However, in various embodiments of the WDM receiver string 1115, the photonic components are arranged as a string of cells having similar elements and functions.

[0126] 12 is a flow chart illustrating a method for operating a WDM receiver chain in accordance with some embodiments. The method comprises step 1201, in which a first optical signal is communicated from a first output of a PSR to the WDM receiver chain and a second optical signal is communicated from a second output of the PSR to the WDM receiver chain, where a differential time delay (τ AB ) exists between the first and second optical signals at the first and second outputs of the PSR. The method further comprises: determining a differential time delay (τ AB ) and a time substantially equal to (D A ) in a route to the string of WDM receivers. The method further comprises: delaying 1203 the first optical signal in a route to the string of WDM receivers by an optical signal delay (ΔD k 12. The method includes a step 1205 of implementing a method for detecting a plurality of WDM demultiplexers 601-1 through 601-N in a WDM receiver string. Step 1205 is performed for each of a plurality (N) of WDM demultiplexers 601-1 through 601-N in the WDM receiver string. It should be understood that any of the principles and concepts described herein with respect to the WDM receiver strings 313, 600, 700, 900, 950, 1001, 115 are suitable for use in conjunction with the method of FIG. 12. It should also be understood that any of the principles and concepts described herein with respect to the WDM demultiplexer 100 of FIGS. 1A-1E and 2 are suitable for use in conjunction with the method of FIG.

[0127] In some embodiments, an electro-optical receiver is disclosed that includes an optical waveguide (e.g., 602) and a plurality of WDM demultiplexers (e.g., 601-1 through 601-N) disposed along the optical waveguide. Each WDM demultiplexer of the plurality of WDM demultiplexers is configured to incouple an optical signal of a respective wavelength among a plurality of wavelengths propagating through the optical waveguide in a first direction as a first incoupled optical signal. Each WDM demultiplexer of the plurality of WDM demultiplexers is further configured to incouple an optical signal of a respective wavelength among a plurality of wavelengths propagating through the optical waveguide in a second direction as a second incoupled optical signal, where the second direction is opposite to the first direction. Each WDM demultiplexer of the plurality of WDM demultiplexers is further configured to direct the first in-coupled optical signal to a first optical detector (e.g., 115-1 through 115-N) and direct the second in-coupled optical signal to a second optical detector (e.g., 115-1 through 115-N). In some embodiments, the first optical detector is a first portion of an optical detector and the second optical detector is a second portion of the same optical detector. In some embodiments, the first optical detector and the second optical detector are implemented separately from one another.

[0128] In some embodiments, each WDM demultiplexer of the plurality of WDM demultiplexers is configured to implement an optical signal timing delay section (e.g., 107-x / 109-x, where x is 1 to N) configured to ensure that both a first in-coupled optical signal corresponding to a given incident optical signal and a second in-coupled optical signal corresponding to the given incident optical signal arrive at the first and second optical detectors, respectively, at substantially the same time. The amount of time delay provided by the optical signal timing delay section of a given WDM demultiplexer of the plurality of WDM demultiplexers depends on the position of the given WDM demultiplexer along the optical waveguide.

[0129] In some embodiments, the plurality of WDM demultiplexers includes a first half of the plurality of WDM demultiplexers (e.g., 601-1 to 601-(N / 2)) that are sequentially arranged with respect to the first end of the optical waveguide, and a second half of the plurality of WDM demultiplexers (e.g., 601-[(N / 2)+1] to 601-N) that are sequentially arranged with respect to the first end of the optical waveguide. The first half of the plurality of WDM demultiplexers that are sequentially arranged implements an optical signal timing delay section (e.g., 107-1 to 107-(N / 2)) to delay the first in-coupled optical signal before reaching the first optical detector. The second half of the plurality of WDM demultiplexers that are sequentially arranged implements an optical signal timing delay section (e.g., 109-[(N / 2)+1] to 109-N) to delay the second in-coupled optical signal before reaching the second optical detector. In some embodiments, the amount of time delay provided by the optical signal timing delay section in the first half of the sequentially arranged WDM demultiplexers and the amount of time delay provided by the optical signal timing delay section in the second half of the sequentially arranged WDM demultiplexers are symmetrical about a midpoint location between the first half of the sequentially arranged WDM demultiplexers and the second half of the sequentially arranged WDM demultiplexers. In some embodiments, the amount of time delay provided by the optical signal timing delay section (e.g., 107-1 through 107-(N / 2)) in the multiple WDM demultiplexers of the first half of the sequentially arranged WDM demultiplexers increases with increasing distance of the corresponding WDM demultiplexer from a midpoint location between the first half of the sequentially arranged WDM demultiplexers and the second half of the sequentially arranged WDM demultiplexers.Also, in some embodiments, the amount of time delay provided by the optical signal timing delay section (e.g., 109-[(N / 2)+1] to 109-N) in the second half of the sequentially arranged WDM demultiplexers increases with increasing distance of the corresponding WDM demultiplexer from a location of the midpoint between the first half of the sequentially arranged WDM demultiplexers and the second half of the sequentially arranged WDM demultiplexers.

[0130] The above description of the embodiments is for illustrative and descriptive purposes and is not intended to be exhaustive or limiting. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment and, where applicable, can be substituted and utilized in selected embodiments unless otherwise shown or described. Thus, one or more features from one or more embodiments disclosed herein can be combined with one or more features from one or more other embodiments disclosed herein to form another embodiment that is not explicitly disclosed herein but is implicitly disclosed herein. This other embodiment may also be modified in many ways. Such variations of the embodiments are not considered departures from the present disclosure, and all such variations and modifications of the embodiments are intended to be included within the scope of the disclosure provided herein.

[0131] Although some method steps may be described in a particular order herein, it should be understood that other housekeeping steps may be performed between method steps, and / or method steps may be coordinated to be performed at slightly different times or simultaneously, or distributed into a system that permits process steps to be performed at various intervals related to the process, so long as the processing of the method steps is performed in a manner such that the method is successfully performed.

[0132] Although the present embodiments have been described in some detail for ease of understanding, it will be apparent that certain changes and modifications may be made within the scope of the appended claims. Accordingly, the embodiments disclosed herein are considered to be illustrative and not restrictive, and therefore should not be limited to only the details set forth herein, but may be modified within the scope and equivalents of the appended claims.

Claims

1. 1. An electro-optical receiver comprising: a first optical waveguide, the first optical waveguide being optically connected to transmit a first portion of incident light in a first direction through the first optical waveguide, the first optical waveguide also being optically connected to transmit a second portion of incident light in a second direction through the first optical waveguide, the second direction being opposite to the first direction; a ring resonator, the ring resonator being positioned within an evanescent optical coupling distance of the first optical waveguide such that the first portion of the incident light and the second portion of the incident light couple from the first optical waveguide into the ring resonator, the first portion of the incident light and the second portion of the incident light traveling in opposite directions within the ring resonator; a second optical waveguide, the second optical waveguide being positioned within an evanescent optical coupling distance of the ring resonator such that the first portion of the incident light and the second portion of the incident light couple from the ring resonator into the second optical waveguide, and the first portion of the incident light and the second portion of the incident light travel in opposite directions away from the ring resonator within the second optical waveguide; a photodetector optically connected to both the first end of the second optical waveguide and the second end of the second optical waveguide; An electro-optical receiver comprising:

2. 2. The electro-optic receiver of claim 1, further comprising:

1. An electro-optic receiver comprising: a heater disposed within the ring resonator, the heater being controllable to control the resonant wavelength of the ring resonator such that only light within a narrow band around a resonant wavelength is allowed to couple into and out of the ring resonator.

3. 2. The electro-optic receiver of claim 1, further comprising: an optical signal timing delay section disposed along the second optical waveguide at a location between the ring resonator and the optical detector, the optical signal timing delay section configured to impart a controlled amount of time delay to an optical signal passing through the optical signal timing delay section.

4. 4. The electro-optic receiver of claim 3, wherein the optical signal timing delay section is formed as an optical waveguide section.

5. 5. The electro-optic receiver of claim 4, wherein the optical waveguide section includes input and output optical waveguides extending side-by-side in one or more of the following shapes toward a central location: a folded shape, a spiral shape, a helical shape, a loop shape, and a zigzag shape, and the input and output optical waveguides are optically connected at the central location.

6. 6. The electro-optic receiver of claim 5, wherein the input optical waveguide and the output optical waveguide are integrally formed as a single optical waveguide structure.

7. 4. The electro-optic receiver of claim 3, wherein the optical signal timing delay section comprises an input optical waveguide, an output optical waveguide, and a resonant device having an input optically connected to the input optical waveguide and an output optically connected to the output optical waveguide.

8. 8. An electro-optic receiver as claimed in claim 7, wherein the input optical waveguide and the output optical waveguide extend side-by-side over a distance and are optically coupled to the resonant device.

9. 4. The electro-optic receiver of claim 3, wherein the optical signal timing delay section is a first optical signal timing delay section disposed at a position between the ring resonator and the first end of the second optical waveguide, the electro-optic receiver further comprising a second optical signal timing delay section disposed at a position between the ring resonator and the second end of the second optical waveguide, the second optical signal timing delay section configured to impart a controlled amount of time delay to an optical signal passing through the second optical signal timing delay section.

10. 10. The electro-optic receiver of claim 9, wherein the controlled amount of time delay imparted by the first optical signal timing delay section is different from the controlled amount of time delay imparted by the second optical signal timing delay section.

11. 10. The electro-optical receiver of claim 9, wherein the photodetector is a photodetector configured to separately detect light entering a first end of the photodetector from the first end of the second optical waveguide and light entering a second end of the photodetector from the second end of the second optical waveguide.

12. 2. The electro-optic receiver of claim 1, further comprising:

1. An electro-optic receiver comprising: a polarizing beam splitter rotator having an input optically connected to receive incident light, the polarizing beam splitter rotator configured to direct a first portion of the incident light having a first polarization to a first output of the polarizing beam splitter rotator to provide a first portion of the incident light, the polarizing beam splitter rotator configured to direct a second portion of the incident light having a second polarization to a second output of the polarizing beam splitter rotator, the polarizing beam splitter rotator further configured to rotate the polarization of the second portion of the incident light from a second polarization to the first polarization in route to the second output of the polarizing beam splitter rotator to provide the second portion of the incident light, a first end of the first optical waveguide optically connected to the first output of the polarizing beam splitter rotator, and a second end of the first optical waveguide optically connected to the second output of the polarizing beam splitter rotator.

13. 13. The electro-optic receiver of claim 12, further comprising: An electro-optical receiver comprising an optical coupling device configured to transmit the incident light from an optical fiber to the input of the polarizing beam splitter rotator.

14. 13. The electro-optic receiver of claim 12, further comprising: an optical signal timing delay disposed along the first optical waveguide at a location between the first output of the polarizing beamsplitter rotator and the ring resonator;

15. 15. The electro-optic receiver of claim 14, wherein the optical signal timing delay is configured to impart a time delay to an arrival time of a first portion of the incident light at the ring resonator, the time delay being set such that an arrival time of a second portion of the incident light at the ring resonator is substantially equal to the arrival time of the first portion of the incident light at the ring resonator.

16. 1. An electro-optical receiver comprising: an optical waveguide having a first end and a second end; and a plurality of wavelength division multiplexing (WDM) demultiplexers disposed along the optical waveguide, each WDM demultiplexer of the plurality of WDM demultiplexers configured to incouple an optical signal of a respective wavelength among a plurality of wavelengths propagating through the optical waveguide in a first direction as a first incoupled optical signal, each WDM demultiplexer of the plurality of WDM demultiplexers further configured to incouple an optical signal of the respective wavelength among the plurality of wavelengths propagating through the optical waveguide in a second direction as a second incoupled optical signal, the second direction being opposite to the first direction, and each WDM demultiplexer of the plurality of WDM demultiplexers further configured to direct the first incoupled optical signal to a first optical detector and the second incoupled optical signal to a second optical detector.

17. 17. The electro-optical receiver of claim 16, wherein each WDM demultiplexer of the plurality of WDM demultiplexers is configured to implement an optical signal timing delay section configured to ensure that both the first in-coupled optical signal corresponding to a given incident optical signal and the second in-coupled optical signal corresponding to the given incident optical signal arrive at the first and second optical detectors, respectively, at substantially the same time.

18. 20. The electro-optic receiver of claim 17, wherein an amount of time delay provided by the optical signal timing delay section of a given WDM demultiplexer of the plurality of WDM demultiplexers depends on a position of the given WDM demultiplexer along the optical waveguide.

19. 20. The electro-optical receiver of claim 17, wherein the plurality of WDM demultiplexers includes a first half of the plurality of WDM demultiplexers arranged in sequence with respect to the first end of the optical waveguide and a second half of the plurality of WDM demultiplexers arranged in sequence with respect to the first end of the optical waveguide, the first half of the ordered plurality of WDM demultiplexers implementing the optical signal timing delay section to delay a first in-coupled optical signal before reaching the first optical detector, and the second half of the ordered plurality of WDM demultiplexers implementing the optical signal timing delay section to delay the second in-coupled optical signal before reaching the second optical detector.

20. 20. The electro-optical receiver of claim 19, wherein an amount of time delay provided by the optical signal timing delay sections in a first half of the plurality of sequentially arranged WDM demultiplexers and an amount of time delay provided by the optical signal timing delay sections in a second half of the plurality of sequentially arranged WDM demultiplexers are symmetrical about a midpoint between the first half of the plurality of sequentially arranged WDM demultiplexers and the second half of the plurality of sequentially arranged WDM demultiplexers.

21. 20. The electro-optic receiver of claim 19, wherein an amount of time delay provided by the optical signal timing delay sections in a first half of the sequentially arranged plurality of WDM demultiplexers increases with increasing distance of the corresponding WDM demultiplexer from the midpoint location, and an amount of time delay provided by the optical signal timing delay sections in a second half of the sequentially arranged plurality of WDM demultiplexers increases with increasing distance of the corresponding WDM demultiplexer from the midpoint location.

22. 17. The electro-optic receiver of claim 16, wherein the first photodetector is a first portion of a photodetector and the second photodetector is a second portion of the photodetector.

23. 17. The electro-optic receiver of claim 16, wherein the first photodetector and the second photodetector are implemented separately from one another.

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