Electro-optical transmitter and receiver integrated circuit (core particle) for co-packaged optics and method of operation thereof

Abstract

An electro-optical integrated circuit comprising an optical transmitter and an optical receiver is disclosed in which a monolithically integrated electro-absorption modulated laser (EML) can operate bi-directionally in both transmitter and receiver modes. Vertically stacked waveguides for lasers and electro-absorption modulators (EAMs) are provided. The laser and the EAM are optically coupled through a transverse conical vertical optical coupler. The EML includes monolithically integrated electronic circuitry, such as drivers and control electronics for driving the laser as the EML and the EAM in the transmitter mode. The control circuit includes a transimpedance amplifier (TIA). The EAM has a first portion and a second portion that may be independently biased. In receiver mode, the laser current is reduced near a threshold, a first portion of the EAM is biased to absorb residual laser light, while a second portion of the EAM provides photocurrent to the TIA as a photodiode receiver.

Description

Cross Reference to Related Applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 521,411, filed June 16, 2023, entitled “Phosphide-based electro-optical transmitter and receiver integrated circuits (corelets) for co-packaged optics and methods of operation thereof,” the entire contents of which are incorporated herein by reference.

[0002] This application is related to U.S. Patent Application No. 17 / 687,803, filed March 7, 2022, entitled “Vertically integrated electro-absorption modulated laser and method of manufacturing the same,” which is a continuation-in-part of Application No. PCT / CA2020 / 051562, filed November 17, 2020, which claims priority to U.S. Provisional Patent Application No. 62 / 936,629, filed November 18, 2019, the entire contents of all of which are incorporated herein by reference.

[0003] This application is related to U.S. Patent Application No. 17 / 785,989, filed June 16, 2022, entitled “Optical receiver comprising monolithically integrated photodiode and transimpedance amplifier,” which is a national stage entry of PCT / CA2020 / 051666, filed December 4, 2020, which claims priority to U.S. Provisional Patent Application No. 62 / 950,479, filed December 19, 2019, the entire contents of all of which are incorporated herein by reference. TECHNICAL FIELD

[0004] The present invention relates to electro-optical integrated receiver and transmitter modules, and more particularly to indium phosphide (InP)-based electro-optical receiver and transmitter modules and co-packaging InP-based electro-optical modules with silicon electronics. BACKGROUND

[0005] For background information, please refer to the review article entitled “Co-packaged datacenter optics: Opportunities and Challenges,” published in IET Optoelectronics, Volume 15, 2021, pages 77-91. For example, the reference’s Figure 6 An exemplary roadmap for CPO (co-packaged optics) is shown to illustrate the increasing level of integration of optical modules and switch ASIC (application-specific integrated circuit), with the representation method focusing on the linear distance between the optical module and the ASIC. The long reach (LR), medium reach (MR), very short reach (VSR), extra short reach (XSR), and ultra short reach (USR) are shown in Table 3 of the reference.

[0006] Other important considerations include unit cost of capacity ($ / Gb / s), energy efficiency (pJ / bit), and reduction in pitch of high-density fiber arrays.

[0007] For example, improved or alternative InP-based electro-optical receiver and transmitter modules and solutions for co-packaging InP-based electro-optical modules with silicon electronics are needed. SUMMARY

[0008] The present invention is directed to providing improved or alternative electro-optical integrated circuits including receivers and transmitters and solutions for co-packaging electro-optical modules with other electronics, such as silicon integrated circuits, to overcome or alleviate one or more of the problems described above.

[0009] Aspects of the present invention provide an electro-optical integrated circuit capable of bidirectional operation of an electro-absorption modulated laser (EML) as a transmitter and a receiver, a method of operating an EML as a transmitter and a receiver, and a solution for co-packaging an electro-optical module with silicon electronics, such as core processors and other switch ASICs.

[0010] One aspect provides an electro-optical integrated circuit comprising an electro-absorption modulated laser (EML), the EML comprising a laser and an electro-absorption modulator (EAM), a control circuit comprising a laser driver, an EAM driver, and a transimpedance amplifier (TIA), wherein the EAM comprises a first portion and a second portion, and an electrical connection connecting the first portion and the second portion of the EAM, and wherein the control circuit is configured to bias the electrical connection to independently operate the first portion and the second portion of the EAM in a transmitter mode and a receiver mode: in the transmitter mode, the laser and the first and second portions of the EAM operate as the EML to provide a modulated optical output; and in the receiver mode, the second portion of the EAM operates as a photodiode receiver to receive an optical input and output a photocurrent to the TIA.

[0011] in the transmitter mode, the laser is turned on by the laser driver circuit to provide an appropriate laser drive current, and the EAM driver circuit operates the EAM to provide a modulated optical output; in the receiver mode, the EAM operates as a receiver by reducing the laser drive current to near threshold current, biasing the first portion of the EAM to absorb the remaining light from the laser, the second portion of the EAM receives an optical input as a photodiode receiver, and is detected by the TIA circuit.

[0012] An electro-optic integrated circuit includes an electroabsorption modulated laser (EML) capable of bidirectional operation in transmitter and receiver modes, with monolithically integrated control electronics, and can be fabricated using an InPr-based semiconductor material system. Advantageously, a compact, small-scale structure is achieved by using a lateral tapered vertical optical coupler to vertically couple the laser waveguide and the EAM waveguide. In an alternative embodiment, the laser and EAM can be laterally optically coupled.

[0013] For example, an electro-optic integrated circuit is provided, comprising: a semi-insulating (SI) substrate; an epitaxial layer structure including a plurality of semiconductor layers grown on the SI substrate; the epitaxial layer structure defining: a first set of semiconductor layers including control circuitry; and a second set of semiconductor layers providing a plurality of vertically stacked optical waveguides, wherein: the first waveguide includes a layer configured as an electro-absorption modulator (EAM) waveguide; the second waveguide includes a layer configured as a laser waveguide; the layer of the second waveguide is patterned to define a laser mesa providing a laser cavity and a laterally tapered vertical optical coupler extending from the optical output end of the laser cavity; the layer of the first waveguide is patterned to define the EAM mesa; wherein the laser cavity is laterally spaced from the EAM along the optical propagation direction, and the laterally tapered vertical optical coupler is configured to... The laser emits a light mode coupled to the input of the EAM; the control circuitry includes a laser driver circuit, an EAM driver circuit, and a transimpedance amplifier (TIA); a first electrical connection between the laser driver circuitry and the laser is used to operate the laser in CW mode; a second electrical connection between the EAM driver circuitry and the EAM is used to drive the EAM, wherein the EAM includes a first portion (e.g., one half) and a second portion (e.g., the other half) that can be independently biased; the control circuitry enables bidirectional operation, wherein: in transmitter mode, the laser and EAM operate as an EML to provide modulated light output; in receiver mode, the second portion of the EAM acts as a photodiode receiver to receive light input and output photocurrent to the TIA.

[0014] In transmitter mode, the laser is turned on by the laser driver circuit to provide the appropriate laser drive current, and the EAM driver circuit operates the EAM to provide modulated light output; in receiver mode, the EAM operates as a receiver by reducing the laser drive current to near the threshold current, causing the first part of the EAM to be biased to absorb the remaining light from the laser, and the second part of the EAM to operate as a photodiode receiver to receive the light input, which is detected by the TIA circuit.

[0015] For example, the SI substrate is Fe-doped InP, and the EML is fabricated from an InP-based material system that includes selected binary, ternary, and quaternary components of In, Ga, As, P, Al, and Sb, as well as other components.

[0016] The control circuitry may include a switch for switching between transmitter mode and receiver mode, the switch having an input for receiving a transmit enable or receive enable signal from the data bus logic circuitry.

[0017] In some embodiments, the electro-optic integrated circuit includes multiple EAMs, and the laser is optically coupled to the multiple EAMs via a 1:N beam splitter. For example, an example embodiment of the electro-optic integrated circuit includes four EAMs, and the laser output is optically coupled to the four EAMs via a 1:4 beam splitter.

[0018] The passive waveguide can be vertically positioned below the EAM waveguide and patterned to form a spot size converter (SSC); and the EAM waveguide can include a second transversely tapered vertical optical coupler configured to couple optical output / input from / to the SSC to a single-mode fiber.

[0019] In an exemplary embodiment, a plurality of semiconductor layers for control circuitry are vertically separated from a plurality of vertically stacked optical waveguides by at least one spacer layer; optical components including a laser and an EAM are formed on a first region of the SI substrate; and control circuitry is formed on a second region of the SI substrate adjacent to the first region.

[0020] Electro-optic integrated circuits can be fabricated using III-V group semiconductor materials, such as InP-based material systems including selected binary, ternary, and quaternary components of In, Ga, As, P, Al, and Sb, as well as other components. In some embodiments, the epitaxial layer structure is compatible with a single epitaxial growth process.

[0021] Another aspect of the present invention provides a surface-mount electro-optic module comprising: a substrate; a plurality of electro-optic integrated circuits as disclosed herein, the plurality of electro-optic integrated circuits being disposed in a peripheral region of the substrate to provide optical I / O along each edge of the substrate; and a plurality of electronic integrated circuits being mounted in an internal region of the substrate.

[0022] For example, in some embodiments, the multiple electronic integrated circuits are silicon integrated circuits, such as core processors or other ASICs.

[0023] Surface-mount electro-optic modules can be configured to edge-couple optical fibers to the optical ports of each electro-optic integrated circuit. For example, the port-to-port spacing is in the range of 200µm to 300µm, and 128 ports are distributed on the periphery of the substrate.

[0024] Some exemplary embodiments of InP-based electro-optic integrated circuits (chips) are disclosed, which are capable of bidirectional operation in both transmit and receive modes and are suitable for co-packaging with other integrated circuits (e.g., silicon chips), for example, for providing electro-optic transceiver modules.

[0025] Another aspect of the present invention provides a method of operating an electro-optic integrated circuit, the electro-optic integrated circuit comprising: an electroabsorption modulated laser (EML) serving as a transmitter and a receiver, the EML including a laser and an electroabsorption modulator (EAM); and control circuitry including a laser driver, an EAM driver, and a transimpedance amplifier (TIA), wherein the EAM includes a first portion (e.g., one half) and a second portion (e.g., the other half) that can be independently biased, the method comprising: operating the laser and the EAM as an EML in transmitter mode to provide modulated light output; and operating the second portion of the EAM as a photodiode receiver in receiver mode to receive light input and output photocurrent to the TIA.

[0026] For example, in transmitter mode, the laser is turned on by the laser driver circuit to provide an appropriate laser drive current to provide cw laser output, and the EAM driver circuit operates the first and second parts of the EAM to provide modulated light output; in receiver mode, the EAM operates as a receiver by reducing the laser drive current to near the threshold current, causing the first part of the EAM to be biased to absorb the remaining light from the laser, and the second part of the EAM to act as a photodiode receiver to receive the light input and generate a photocurrent, which is detected by the TIA circuit.

[0027] Therefore, an electro-optic integrated circuit including a receiver and a transmitter, as well as a solution for co-packaging the electro-optic module with other electronic devices (such as silicon integrated circuits), are disclosed. Attached Figure Description

[0028] Figure 1 A schematic cross-sectional view of an electro-optical integrated circuit is shown, including an exemplary embodiment of an EML, which includes a DFB laser and an EAM with integrated electronic circuitry.

[0029] Figure 2 It shows including Figure 1 A schematic top view of the electro-optical integrated circuit of the EML shown.

[0030] Figure 3 A schematic block diagram of an electro-optic module is shown, including an exemplary embodiment of an EML configured to operate bidirectionally in transmitter and receiver modes.

[0031] Figure 4 A schematic diagram is shown, illustrating... Figure 3 The electro-optical module shown is shown to operate bidirectionally in transmitter and receiver modes.

[0032] Figure 5A schematic top view of an electro-optic module including an EML of the first embodiment is shown, the EML being configured to operate bidirectionally as both a transmitter and a receiver.

[0033] Figure 6 A schematic top view of first and second electro-optical modules including an EML of the first embodiment is shown, the EML being configured to operate bidirectionally as a transmitter and a receiver.

[0034] Figure 7 A schematic top view of a four-port electro-optic module according to a second exemplary embodiment is shown. The four-port electro-optic module includes four integrated EMLs configured to operate bidirectionally as a transmitter and a receiver.

[0035] Figure 8 A schematic top view of the substrate of a co-packaged optical module is shown to illustrate an exemplary use case, the co-packaged optical module comprising 128 optical ports provided by an InP optoelectronic chip of an exemplary embodiment and multiple switch ASICs.

[0036] Figure 9 A simplified circuit diagram is shown to illustrate the drive logic for bidirectional operation of the integrated EML in transmitter and receiver modes in the first embodiment.

[0037] Figure 10 A simplified circuit diagram is shown to illustrate further details of the drive logic for bidirectional operation of the integrated EML in transmitter and receiver modes in the first embodiment.

[0038] Figure 11 A simplified circuit diagram is shown to illustrate the driving logic for bidirectional operation of the integrated EML in transmitter and receiver modes in the second embodiment, where each laser has four channels.

[0039] Figure 12 A schematic diagram of a surface-mount optical module configured for vertically coupling optical fibers is shown.

[0040] Figure 13 A schematic diagram of a surface-mount optical module configured for laterally coupling optical fibers is shown.

[0041] Figure 14 It shows Figure 13 A schematic cross-sectional view of a portion of the optical module shown illustrates the lateral coupling of the optical fiber to the surface-mount optical module.

[0042] Figure 15 A and Figure 15 B shows a schematic plan view and a schematic cross-sectional view of an exemplary monolithic integrated pin-TIA.

[0043] The above and other features, aspects and advantages will become more apparent from the following detailed description of exemplary embodiments taken in conjunction with the accompanying drawings, which are merely exemplary. Detailed Implementation

[0044] The aforementioned U.S. Patent Application No. 17 / 687,803, filed on March 7, 2022, entitled "Vertically Integrated Electro-Absorption Modulated Laser and Method of Manufacturing Thereof," discloses some exemplary embodiments of a monolithically integrated EML, which includes a vertically integrated DFB laser and an EAM, manufactured using MGVI (Multi-Waveguide Vertical Integration), wherein the DFB laser and the EAM are vertically coupled via a transverse tapered vertical optical coupler.

[0045] For example, Figure 1 A schematic longitudinal cross-sectional view 100 of an electro-optic module including a monolithically integrated EML is shown. The EML includes a DFB laser and an EAM, fabricated using MGVI. This fabrication method enables the vertical integration of active and passive components formed in multiple vertically stacked waveguides and is compatible with single epitaxial growth of III-V semiconductors, for example, using InP-based material systems. In this example, the structure includes a semi-insulating (SI) substrate, such as Fe-doped InP, on which an epitaxial stack (which may be referred to as an epitaxial stack, epitaxial pile, or epitaxial layer) is grown to define the following layers: a first waveguide, labeled as the output waveguide; a second waveguide, labeled as the EAM waveguide; and a third waveguide, labeled as the DFB laser waveguide, on which a surface etched grating (SEG) is defined. Figure 1 A schematic top view 200 of a monolithic integrated EML is shown (in Figure 2As schematically shown in the diagram, these waveguides are vertically optically coupled via vertical optical couplers formed by the lateral tapered portions of their respective waveguides. A third waveguide is processed to define the laser mesa and the first lateral tapered vertical optical coupler 1. An SEG is etched into the top surface of the DFB laser portion of the laser mesa to form the DFB laser, and the lateral tapered vertical optical coupler extends from the laser's output end, vertically optically coupling the emission modes from the laser to the second waveguide along its length. In this embodiment, the EML is monolithically integrated with the EAM driver circuitry and the laser driver circuitry. The latter includes bias control for operating the laser as a CW source and optionally includes other components, such as components for temperature sensing, power monitoring, and control loops for temperature stabilization and power regulation. Additional semiconductor layers for the laser driver circuitry and the EAM driver circuitry are disposed between the SI substrate and the waveguide layers, as schematically shown. These layers include layers for forming high-speed electronic circuitry for the laser driver and EAM driver circuitry. For example, the additional layers include: InP-based semiconductor layers configured to fabricate heterojunction bipolar transistors (HBTs), these layers being labeled as HBT epitaxial layers for electronic circuitry; and one or more spacer layers, including one or more etch stop layers, which allow for separate processing of optical components and electronic circuitry. The laser driver circuitry includes bias control for operating the laser as a CW light source and optionally includes other components, such as components for temperature sensing, components for power monitoring, and control loops for temperature stabilization and power regulation.

[0046] like Figure 2 As shown, it includes Figure 1 The schematic top view 200 of the EML electro-optical module shown in this embodiment shows a multilayer optical waveguide structure for the DFB laser, EAM and output waveguide formed on a first region of the SI substrate, and electronic circuitry formed on an adjacent second region of the SI substrate, for example laterally spaced from the optical components.

[0047] For some embodiments of the EML, the epitaxial layer structure is compatible with a single epitaxial growth process using III-V semiconductor materials. For example, in some embodiments, the integrated EML is fabricated using an InP-based material system comprising selected binary, ternary, and quaternary components of In, Ga, As, P, Al, and Sb, as well as other components. For example, the SI substrate may be iron-doped InP. Alternatively, it may be fabricated using a multi-epitaxy growth process.

[0048] The general principles of selecting materials and structural waveguide layers for vertical optical coupling using a transversely tapered vertical optical coupler are described in, for example, Tolstikhin’s U.S. Patent 7,444,055B2 entitled “Integrated Optical Device Apparatus for Wavelength (De)Multiplication in a Multi-Waveguide Vertical Stack” and the references cited therein, namely, the appropriate selection of bandgap wavelength and refractive index.

[0049] Using an InP-based material system and vertical integration, electro-optical circuit modules, including EML and monolithically integrated EAM driver circuits and laser driver circuits, are fabricated, achieving small and compact structures, such as EML modules with a length of approximately 1 mm and a width of less than 1 mm.

[0050] Advantageously, the integrated EAM driver and control circuitry includes a high-speed electro-optical control loop for ultra-high-speed linearization and temperature compensation, to enable, for example, advanced modulation schemes such as PAM-4 and DP-QPSK for analog optical data center interconnect applications.

[0051] Figure 3 A schematic block diagram of an electro-optic module is shown, including an exemplary embodiment of an EML configured for bidirectional operation in transmitter and receiver modes. The electro-optic module includes a laser, an electro-absorption (EAM) modulator, and integrated electronic control circuitry including a laser driver, an EAM driver, and a transimpedance amplifier (TIA). The laser and EAM forming the EML are optically coupled, for example, using a lateral tapered vertical optical coupler, a lateral waveguide optical coupler, or a docking coupling. The EAM includes a first portion M1, a second portion M2, and electrical connections from the EAM driver to the first and second portions of the EAM, such that the first and second portions of the EAM can be independently biased. The control circuitry is configured to bias the electrical connections to independently operate the first and second portions of the EAM in transmitter and receiver modes. In transmitter mode, the laser and the first and second portions of the EAM operate as an EML to provide modulated light output; in receiver mode, the second portion of the EAM operates as a photodiode receiver to receive light input and output photocurrent to the TIA. This configuration saves die area and power consumption associated with separate photodetectors, including pin-TIA. The control circuitry has a connector for a bidirectional data bus and includes a mode selection input for receiving a transmit / receive enable signal to switch between transmitter and receiver modes.

[0052] For example, Figure 4 A schematic diagram is shown to illustrate. Figure 3The electro-optic module shown operates bidirectionally in transmitter and receiver modes. In transmitter mode, the laser is turned on to provide the cw output optically coupled to the modulator, and the EAM driver drives both sections (M1 and M2) of the modulator to provide modulated light output. That is, the device operates as an EML. In receiver mode, the laser is almost off: the laser driver reduces the laser drive current to near the threshold current to reduce light output; the EAM driver drives the first section M1 of the modulator to absorb residual laser light, and the second section M2 of the modulator operates as a photodiode receiver to receive light input and provide photocurrent input to the TIA.

[0053] For example, to achieve a compact design, electro-optic modules with monolithically integrated electronics can be manufactured using InP-based semiconductor material systems and vertical integration, and optical coupling between the laser waveguide and the EAM waveguide can be achieved using a transversely tapered vertical optical coupler. Figure 5 A schematic top view 300 of an electro-optic module including an integrated EML of the first embodiment is shown, the integrated EML being configured to operate bidirectionally as both a transmitter and a receiver. The integrated bidirectional EML includes a laser 302 and an EAM modulator 310, which are vertically integrated via a lateral tapered vertical coupler 304. In this embodiment, an integrated driver circuit 306 enables driving the EML in both transmit and receive modes. The driver circuit 306 includes on-chip laser driver circuitry and driver circuitry for the EAM modulator, and includes a transimpedance amplifier (TIA) 308.

[0054] Figure 6 A schematic top view 400 of the first EML300A and the second EML300B is shown, as follows. Figure 5As shown, these EMLs are configured to operate bidirectionally as both transmitters and receivers, with one EML configured as a transmitter and the other as a receiver. When one of the EMLs is configured in transmit mode, it functions normally as an EML, the laser is turned on via laser driver circuitry to provide the appropriate laser drive current, and the EAM driver circuitry operates the modulator. When one of the EMLs is configured in receive mode, the EAM operates as a receiver by “turning off” the laser (e.g., by reducing the laser drive current to the threshold current Ith plus a small value (e.g., +20mA)), and one half of the EAM is biased to absorb the remaining light, while the other half operates to see only the light from the other end, which is detected by the TIA circuitry. Thus, in receive mode, the modulator and TIA become the receiver. This configuration saves die area and power consumption associated with separate detectors including pin-TIAs. During receive mode operation, if the laser drive current drops below the threshold current and the laser is completely turned off, this will introduce undesirable delay when the laser is turned on in transmit mode. Therefore, it is best to maintain a low drive current that is slightly higher than the threshold current (Ith), such as high enough to maintain fast switching, and to use part of the EAM waveguide to absorb the remaining laser during operation in receive mode.

[0055] In one exemplary embodiment, the EML is fabricated to be 1.2 mm long and 0.6 mm wide per channel. This is significantly shorter than the length of a TFLN modulator (e.g., approximately 15 to 20 times longer) and also much shorter than any microring resonator schemes that have been demonstrated. For example, in some EML embodiments, the laser, EAM, and driver circuitry can be integrated to provide 250 millivolts at a 50-ohm input, while the pin-TIA output can provide 50 millivolts to 50 ohms at 100 GB (e.g., 10 Gb / s NRZ or 212 b / s PAM4).

[0056] Monolithically integrated lasers and EAMs can be tuned without generating heat. For DFB lasers, for example, with a wavelength temperature sensitivity of 0.09 nm / C and a QCSE EAM of 0.46 nm / C, a bandgap-based temperature sensor can be used to adjust the bias voltage Vb on the EAM to control Vb for temperature compensation, as disclosed in, for example, U.S. Patent US10,673,532, entitled “Electroabsorption modulator with integrated control loop for linearization and temperature control,” published June 2, 2020.

[0057] Figure 7A schematic top view 500 of a four-port electro-optic integrated circuit (EML) of a third example embodiment is shown, comprising four integrated EMLs configured to operate bidirectionally as both a transmitter and a receiver. Some dimensions are shown as examples only. For instance, the four-port integrated EMLs can be integrated on a substrate with a length of 1.2 mm and a width of 1.2 mm to provide an optical port pitch of 300 µm. Based on current technology, the port pitch can be reasonably reduced to 250 µm or 200 µm to provide a compact form factor. For example, a transmission bandwidth greater than 120 GHz allows 1 Tb PAM-4 to be implemented on four channels with an efficiency of 1.1 pJ / bit. Using a single laser for all four channels improves the efficiency to 0.5 pJ / bit. Figure 8 A schematic top view 600 of the substrate of a co-packaged optical module according to a fourth exemplary embodiment is shown to illustrate an exemplary use case. This co-packaged optical module comprises 128 optical ports provided by an InP optoelectronic chip and multiple switching core ASICs. In this example, the 128 optical ports are arranged on the periphery of a 10mm × 10mm substrate, with a port density of 32 ports per side; for example, the port spacing at 9.6mm on each side is 300µm, and the port spacing at 8mm on each side is 250µm. In this example, the total I / O area is 38mm². 2 This design leaves a large central area for the ASIC switching core to be co-packaged on the substrate. The proposed compact size matches the 125µm diameter optical fiber. The integrated bidirectional EML electro-optic module can be co-packaged as a chip with silicon chips (e.g., the switching core ASIC).

[0058] Figure 9 A simplified circuit diagram 700 is shown to conceptually illustrate an example of the drive logic for bidirectional operation of the integrated EML in transmitter and receiver modes of the first embodiment. When operating the EML in transmitter mode, it functions normally as an EML, with the laser turned on via laser driver circuitry to provide appropriate laser drive current, and the EAM driver circuitry operating the modulator. When operating the EML in receiver mode, the EAM functions as a receiver by “turning off” the laser (e.g., by reducing the laser drive current to near a threshold current Ith (e.g., Ith + ~20mA), causing one half of the EAM to be biased to absorb residual light, while the other half of the EAM is active to see only light from the other end, which is detected by the TIA circuitry. Control circuitry is connected to a bidirectional data bus and includes a mode selection input for receiving a transmit / receive enable signal to switch between transmitter and receiver modes.

[0059] Dividing the EAM into a first part as a control EAM and a second part as a modulation EAM allows the EAM to operate bidirectionally in both transmit and receive modes. This configuration saves die area and power consumption associated with separate chips with detectors including pin-TIAs (e.g., as described in the aforementioned patent publication US20230019783A1 entitled "Optical Receiver Including Monolithic Integrated Photodiode and Transimpedance Amplifier"), for example... Figure 15 A and Figure 15 As illustrated in section B. Figure 15 A shows a schematic plan view 1300 of a monolithic integrated pin-TIA chip 1310, which includes a PIN PD 1320, TIA circuitry, and contact area 1326. The PIN PD 1320 and TIA circuitry have direct on-chip connections. Figure 15 B shows a schematic cross-sectional view of a PIN PD, which includes a substrate 1302, an HBT epitaxial layer 1304 for TIA circuitry, and a PIN epitaxial layer 1306 for the PIN PD.

[0060] Figure 10 A simplified circuit diagram 800 is shown to illustrate more details of the drive logic for bidirectional operation of the integrated EML in transmitter and receiver modes in the first embodiment, thereby illustrating the components of the InP transceiver chip and CMOS bus logic that switch between the transmitter and receiver modes of the integrated EML. The control circuitry includes an Rx switch connected to a mode selection input for receiving a transmit / receive enable signal to switch between transmitter and receiver modes.

[0061] Figure 11 A simplified circuit diagram 900 is shown to illustrate further details of the drive logic for bidirectional operation of the integrated EML in transmitter and receiver modes in the third embodiment, where each laser has four channels, for example as... Figure 7 As illustrated schematically, the output of a single laser is split into four channels by a 4:1 beam splitter to provide optical input to four EMLs. Each channel is coupled to a single EML to further optimize performance, for example, reducing power consumption to <0.5 pJ / bit.

[0062] refer to Figure 12 , Figure 13 and Figure 14And U.S. Patent US11,092,762 B2, issued August 17, 2021, entitled "Surface Mount Package for Single-Mode Electro-Optical Modules" (which is incorporated herein by reference), discloses examples of surface mount packages for electro-optical modules in which connector technology is miniaturized to enable vertically coupled or edge-coupled optical fibers. As an example of surface-coupled optical fibers, Figure 12 A substrate 1002 is shown, on which a surface-mount optical module 1004 with four optical ports 1006 and an optical connector 1010 carrying four fiber optic pigtails 1012 are mounted. The optical connector is detachably secured to the surface-mount optical module 1004 by a latching device (e.g., clip 1008). As an example of edge-coupled fiber, Figure 13 A substrate 1102 and a surface-mount optical module 1104 having multiple lateral optical ports 1106 are shown; an optical connector carrying multiple fiber optic pigtails is inserted into the optical ports 1106 and is detachably secured by a latch. Figure 14 A schematic cross-sectional view of optical fiber 1200 is shown, carried by an optical connector 1110 inserted into the optical I / O port of a surface-mount optical module (containing an electro-optic chip 1202) to laterally couple the fiber to the optical I / O port. This I / O concept can be extended to multiple optical I / O ports along one or more sides of the module and allows the electro-optic chip and electronic die to be co-packaged on a ceramic substrate designed for fully automated assembly, including optical alignment. Sufficiently robust materials are selected to withstand soldering processes without damage.

[0063] In an alternative embodiment, a monolithic electro-optic integrated module (chip) can be fabricated using lateral optical coupling rather than vertical optical coupling between a laser and an EAM waveguide. This monolithic electro-optic integrated module includes an EML and integrated control electronics for bidirectional operation in both transmitter and receiver modes. Structures incorporating either vertical or lateral optical coupling can be fabricated using InP-based semiconductor materials or other semiconductor materials capable of monolithically integrating the optical components of the EML and the control electronics.

[0064] The monolithic electro-optic integrated module (chip) disclosed in some exemplary embodiments herein is fabricated using InP-based semiconductor materials and achieves vertical optical integration via a lateral tapered vertical optical coupler. Its compact design and small form factor offer higher speed, lower power consumption (e.g., <0.5 pJ / bit), higher reliability, and lower cost compared to some existing solutions. The electro-optic chip can be co-packaged with other electronic devices (e.g., silicon chips including switching cores). Its small form factor can match the 125 µm diameter of optical fiber. For example, an electro-optic module (with 128 optical ports) on a 10 mm × 10 mm substrate can provide high optical performance (e.g., 30 Tb / s), while reserving an 8 mm × 8 mm area in the central region for the processor core.

[0065] While exemplary embodiments have been described and illustrated in detail, it should be clearly understood that these exemplary embodiments are merely illustrative and exemplary, and not restrictive, and the scope of the invention is defined only by the appended claims.

Claims

1. An electro-optic integrated circuit including an electroabsorption modulated laser (EML), The EML includes a laser and an electroabsorption modulator (EAM), and the control circuitry includes a laser driver, an EAM driver, and a transimpedance amplifier (TIA). The EAM includes a first part and a second part, and an electrical connector connecting the first part and the second part of the EAM, and the control circuit is operable to bias the electrical connector to operate the first part and the second part of the EAM independently in transmitter mode and receiver mode. In the transmitter mode, the laser and the first and second portions of the EAM operate as an EML to provide modulated light output; and In the receiver mode, the second part of the EAM operates as a photodiode receiver to receive light input and output photocurrent to the TIA.

2. The electro-optical integrated circuit of claim 1, wherein in the transmitter mode, the laser is turned on by the laser driver circuit to provide an appropriate laser drive current, and the EAM driver circuit operates the EAM to provide the modulated light output; in the receiver mode, the laser drive current is reduced to near the threshold current, causing a first portion of the EAM to be biased to absorb residual light from the laser, and a second portion of the EAM acts as a photodiode receiver to receive light input.

3. The electro-optic integrated circuit according to claim 1 or 2, having a vertical integration structure, wherein the waveguide of the laser and the waveguide of the EAM are vertically coupled by a transverse tapered vertical coupler.

4. The electro-optic integrated circuit according to any one of claims 1 to 3 is manufactured using an InP-based semiconductor material system.

5. An electro-optic integrated circuit, comprising: Semi-insulating (SI) substrate; The epitaxial layer structure includes multiple semiconductor layers grown on the SI substrate; The epitaxial layer structure defines: The semiconductor layers include a first set of semiconductor layers for control circuitry; and a second set of semiconductor layers providing multiple vertically stacked optical waveguides, wherein: The first waveguide includes a layer constructed as an electro-absorption modulator (EAM) waveguide; The second waveguide includes a layer constructed as a laser waveguide; The layer of the second waveguide is patterned to define a laser mesa providing a laser cavity and a transversely tapered vertical optical coupler extending from the optical output end of the laser cavity; The layer of the first waveguide is patterned to define the mesa of the EAM; The laser cavity is laterally spaced from the EAM along the light propagation direction, and the laterally tapered vertical optical coupler is configured to couple the light mode emitted by the laser to the input of the EAM; and The control circuit includes a laser driver circuit, an EAM driver circuit, and a transimpedance amplifier (TIA). The first electrical connection between the laser driver circuit and the laser is used to operate the laser in continuous wave (CW) mode; The second electrical connection between the EAM driver circuit and the EAM is used to drive the EAM. The EAM includes a first part and a second part that can be independently biased; The control circuit provides bidirectional operation, wherein: In transmitter mode, the laser and the first and second portions of the EAM operate as an EML to provide modulated light output; and In receiver mode, the second part of the EAM operates as a photodiode receiver to receive light input and output photocurrent to the TIA.

6. The electro-optic integrated circuit according to claim 5, wherein: In the transmitter mode, the laser is turned on by the laser drive circuit to provide cw laser output, and the EAM driver circuit operates the EAM to provide the modulated light output; and In the receiver mode, the EAM operates as a receiver by reducing the laser drive current to near a threshold current, with a first portion of the EAM biased to absorb residual light from the laser, while a second portion of the EAM operates as a photodiode receiver to receive light input.

7. The electro-optic integrated circuit according to claim 5 or 6, wherein the SI substrate is Fe-doped InP, and the EML is fabricated by an InP-based material system comprising selected binary, ternary, and quaternary components of In, Ga, As, P, Al, and Sb, as well as other components.

8. The electro-optical integrated circuit according to any one of claims 5 to 7, wherein the control circuit includes a switch for switching between the transmitter mode and the receiver mode, the switch having an input for receiving a transmit enable or receive enable signal from a data bus logic circuit.

9. The electro-optical integrated circuit according to any one of claims 5 to 8, wherein the control circuit includes a connector for a bidirectional data bus and includes a mode selection input for receiving a transmit / receive enable signal to switch between the transmitter mode and the receiver mode.

10. The electro-optic integrated circuit according to any one of claims 5 to 9, comprising a plurality of EAMs, wherein the laser is coupled to the plurality of EAMs via a 1:N beam splitter.

11. The electro-optic integrated circuit according to any one of claims 5 to 10, comprising four EAMs, wherein the laser is coupled to the four EAMs via a 1:4 beam splitter.

12. The electro-optic integrated circuit according to any one of claims 5 to 11, further comprising a passive waveguide disposed vertically below the EAM waveguide and patterned to form a spot size converter (SSC); the EAM waveguide comprising a second transversely tapered vertical optical coupler configured to couple the optical output / input from / to the SSC to a single-mode optical fiber.

13. The electro-optic integrated circuit according to any one of claims 5 to 12, wherein the plurality of semiconductor layers for the control circuit are vertically separated from the plurality of vertically stacked optical waveguides by at least one spacer layer.

14. The electro-optical integrated circuit according to any one of claims 5 to 13, wherein the optical components of the laser and the EAM are formed on a first region of the SI substrate; and the control circuit is formed on a second region of the SI substrate adjacent to the first region.

15. The electro-optic integrated circuit according to any one of claims 5 to 14, wherein the epitaxial layer structure is compatible with a single epitaxial growth process.

16. The electro-optic integrated circuit according to any one of claims 5 to 15, manufactured using III-V group semiconductor materials.

17. The electro-optic integrated circuit according to any one of claims 5 to 15, manufactured using an InP-based material system, said InP-based material system comprising selected binary, ternary, and quaternary components of In, Ga, As, P, Al, and Sb, as well as other components.

18. A surface-mount electro-optic module, comprising: Substrate; A plurality of electro-optic integrated circuits as defined in any one of claims 1 to 17, the plurality of electro-optic integrated circuits being disposed on a peripheral region of the substrate to provide optical I / O ports along at least one edge of the substrate; and a plurality of electronic integrated circuits being mounted on another region of the substrate, and having electrical connections between the plurality of electro-optic integrated circuits and the plurality of electronic integrated circuits.

19. The surface mount electro-optic module of claim 18, wherein the plurality of electro-optic integrated circuits are disposed in the peripheral region of the substrate to provide optical I / O ports along each edge of the substrate; and the plurality of electronic integrated circuits are mounted in the internal region of the substrate.

20. The surface mount electro-optic module according to claim 18 or 19, wherein the plurality of electronic integrated circuits are silicon integrated circuits.

21. The surface mount electro-optic module according to any one of claims 18 to 20, configured to edge-couple optical fibers to the optical I / O ports of each electro-optic integrated circuit.

22. The surface mount electro-optic module according to any one of claims 18 to 21, wherein the port-to-port spacing is in the range of 200µm to 300µm.

23. The surface mount electro-optic module according to claim 19, comprising 128 optical I / O ports distributed around the substrate.

24. A method of operating an electro-optic integrated circuit, the electro-optic integrated circuit comprising: An electroabsorption modulated laser (EML) serves as both a transmitter and a receiver, the EML comprising a laser and an electroabsorption modulator (EAM). The method includes control circuitry, including a laser driver, an EAM driver, and a transimpedance amplifier (TIA), wherein the EAM comprises a first portion and a second portion that can be independently biased. In transmitter mode, the laser and the first and second portions of the EAM operate as an EML to provide modulated light output; and In receiver mode, the second part of the EAM operates as a photodiode receiver to receive light input and output photocurrent to the TIA.

25. The method of claim 24, wherein: In the transmitter mode, the laser is turned on by the laser driver to provide an appropriate laser drive current to provide cw light output, and the EAM driver operates the first and second parts of the EAM to provide the modulated light output; and In the receiver mode, the EAM operates as a receiver by reducing the laser drive current to near a threshold current, with a first portion of the EAM biased to absorb residual light from the laser, while a second portion of the EAM acts as a photodiode receiver to receive light input.

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