Vertically integrated electroabsorption modulated laser and method of manufacture

Abstract

Monolithic integrated electro-absorption modulated lasers (EMLs) and methods of fabrication are disclosed. Vertical integration of vertically stacked waveguides for distributed feedback (DFB) lasers, electro-absorption modulators (EAMs), and passive output waveguides, optically coupled using lateral taper vertical optical couplers. Vertical integration using lateral taper vertical optical couplers provides an alternative to traditional butt coupling of lasers and EAMs, with the potential to improve reliability for high power operation with extended lifetimes. Optionally, the EML includes monolithically integrated electronic circuitry, such as drive and control electronics for the DFB laser and EAM. Advantageously, the integrated EAM drive and control circuitry includes high speed electro-optic control loops for very high speed linearization and temperature compensation, for example, to enable advanced modulation schemes such as PAM-4 and DP-QPSK for analog optical data center interconnect applications. Some embodiments are compatible with fabrication using a single epitaxial growth.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 936,629, filed November 18, 2019, entitled “Vertically Integrated Electro-Absorption Modulated Lasers and Methods of Fabrication,” which is incorporated herein by reference in its entirety. This application is related to U.S. Patent Application No. 16 / 708,887, filed December 10, 2019, entitled “Electro-Absorption Modulator with Integrated Control Loop for Linearization and Temperature Compensation,” which is a continuation of U.S. Patent Application No. 16 / 263,169, filed January 31, 2019, entitled “Integrated Control Loop for Linearization and Temperature Compensation of an Electro-Absorption Modulator,” which claims priority to U.S. Provisional Patent Application No. 62 / 625,311, filed February 1, 2018, entitled the same; which applications are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0003] The present invention relates to the field of integrated photonics, photonic integrated circuits (PICs) based on III-V compound semiconductor materials, and more particularly to integrated electro-absorption modulated lasers (EMLs) for high-speed optical data center interconnects and next generation gigabit passive optical networks (GPONs) and other applications. BACKGROUND

[0004] There is a growing demand for high-speed optical transmitters and receivers capable of high performance modulation suitable for data center interconnects and next generation (GPON) applications at greater than 100 Gb / s. Currently, some of the available solutions are not optimized for >100 Gb / s interconnects and / or have performance and reliability issues.

[0005] In the field of optical fibers, electro-absorption modulators (EAMs) are commonly used as external modulators of continuous wave laser output light. For example, EAMs can be used with inexpensive slow lasers for high performance applications, i.e., transmission at data rates, not limited by the laser characteristics, but by the EAM characteristics. The combination of a laser and an EAM is referred to as an electro-absorption modulated laser (EML).

[0006] Conventional EML assemblies can be made from discrete components, i.e., DFB laser chips and EAM chips manufactured separately, which can include different semiconductor materials. The laser and EAM are butt coupled on a common substrate, requiring cooling, e.g., backside cooling using a thermoelectric cooler (TEC). The coupling can be achieved, for example, by direct fusion of the facets of the DFB laser and EAM, or by bonding the facets with a sealant or adhesive material. However, in these types of EML assemblies, the interface region between the DFB laser and EAM components, especially when made from semiconductor materials having different crystal compositions, is a high stress and strain region, e.g., due to lattice mismatch, different coefficients of thermal expansion (CTE), and other inherent different characteristics as a function of operating conditions. As a result, these EML assemblies typically have a very narrow operating temperature range, e.g., about 1 C, even when cooled. For some EML assemblies, reliable operating time is reportedly limited to about 2000 hours, with failure possible below 3000 hours.

[0007] In principle, monolithic integration of optical waveguide devices with different waveguide core regions and functions can be achieved by one of the following:

[0008] a) Direct butt coupling: multiple epitaxial growth steps of selective area etching and regrowth to provide each waveguide device with the required semiconductor layers, which are laterally coupled through a common horizontal optical plane on the PIC chip;

[0009] b) Improved butt coupling: growth of a single epitaxial layer stack with selective area post-growth modification to form regions to each waveguide device, which are laterally coupled through a common horizontal optical plane on the PIC chip; and

[0010] c) Evanescent field coupling: epitaxial layer stack defines a vertical stack waveguide device that is vertically coupled through resonant or non-resonant evanescent field coupling.

[0011] For example, a device structure for monolithically integrated EMLs using direct or improved butt coupling is described as follows:

[0012] U.S. Patent No. 7,120,183 to Krasulick et al., issued October 10, 2006, entitled "Electro-absorption modulated laser with high operating temperature tolerance";

[0013] U.S. Patent No. 7,809,038 to Makino, issued October 5, 2010, entitled "Electro-absorption modulator integrated with laser to produce long range low power 1550 nm optical devices with optimized parameters";

[0014] U.S. Patent No. 7,476,558, issued January 13, 2009, entitled "Method of manufacturing selective area growth stacked electro-absorption modulated laser structure";

[0015] U.S. Patent No. 7,476,558, issued January 13, 2009, entitled "Method of manufacturing selective area growth stacked electro-absorption modulated laser structure";

[0016] U.S. Patent Publication No. US2010 / 0290489 to Agresti, published November 18, 2010, entitled "Electro-absorption modulated laser (EML) assembly with a front facet of a distributed feedback, DFB, having a % wavelength shift and a method";

[0017] PCT International Patent Publication No. WO2018 / 091094A1 to Moehrle, published May 24, 2018, entitled "Manufacturing and electro-absorption modulated laser and method of electro-absorption modulated laser".

[0018] The fabrication of a multi-waveguide vertical integration (MGVI) structure based on non-resonant evanescent field vertical coupling is described as follows:

[0019] PCT International Patent Publication No. WO2013 / 185218A1 to Tolstikhin, published December 19, 2013, entitled "Spatially wavelength division multiplexed transmitter and receiver photonic integrated circuits".

[0020] To date, in most applications of EAMs, the modulator and the electronics driving the modulator are separate chips mounted on a common substrate and interconnected by matched impedance stripline circuits. At the speeds typically used with EAMs, matched impedance drive circuits are required unless the interconnect length is much less than a wavelength. The commonly used packaging approach does not meet this requirement, requiring matched impedance interconnects. However, the use of matched impedance striplines results in significant power loss, i.e., half of the drive voltage is lost due to the matched impedance. With a typical EAM drive voltage of about 2 volts and a 50 ohm impedance, the drive power is quite high due to the low impedance. To reduce power loss and improve performance, an alternative solution is needed that eliminates the need for matched impedance striplines.

[0021] Another issue is that EAMs are nonlinear, temperature and wavelength dependent. Therefore, they are typically used in applications where the modulation of light is simple on-off modulation. Analog modulation schemes for high performance applications such as optical data center interconnects use other types of modulators such as Mach-Zehnder (MZ) modulators. MZ modulators are typically larger, more costly, and require digital signal processors (DSPs) or other methods to compensate for their sinusoidal modulation function. In the case of modulation using EAMs, it is known that a simple manual tuning needs to be performed on each device to select the most linear region of operation. High performance modulation, for example PAM4, can not be achievable with currently available low cost transmitters, as well as discrete driving and control electronics.

[0022] In certain applications, currently available directly modulated or EML lasers cannot provide sufficient optical output power for long distance optical interconnects, which requires the use of more sensitive avalanche photodiode detectors, which are expensive and have poor long term reliability. Higher power output lasers are needed to allow the use of receivers consisting of low cost, reliable PIN diode detectors.

[0023] Therefore, there is a need to improve EAMs and monolithically integrated EMLs to address at least one of the above performance, output power, reliability, linearization, and temperature compensation issues. For example, there is a need to improve integrated EMLs to meet the needs of applications such as data center interconnects at greater than 100 Gb / s and next generation GPONs. SUMMARY

[0024] The present invention aims to eliminate or alleviate one or more of the above-mentioned disadvantages of known devices and systems comprising EAMs and EMLs, or at least to provide an alternative.

[0025] Various aspects of the present invention provide monolithically integrated EMLs based on vertical integration of active elements with MGVI structures compatible with a single epitaxial growth process, and methods for manufacturing monolithically integrated EMLs, including integrated driving and control circuitry and non-integrated driving and control circuitry.

[0026] One aspect provides a monolithically integrated electro-absorption modulated laser (EML) comprising:

[0027] a substrate;

[0028] an epitaxial layer structure comprising a plurality of semiconductor layers grown on the substrate;

[0029] the epitaxial layer structure defines a plurality of vertically stacked optical waveguides, wherein:

[0030] the first order waveguide comprises layers structured as an output (passive) waveguide;

[0031] the second order waveguide comprises layers structured as an EAM waveguide;

[0032] The third stage waveguide includes layers structured as a DFB laser waveguide;

[0033] The patterned layers of the third stage waveguide are used to define a laser mesa including a DFB laser cavity having a surface etched grating (SEG) and a first lateral taper vertical optical coupler extending from an optical output of the laser cavity;

[0034] The patterned layers of the second stage waveguide are used to define a mesa of the EAM, and a second lateral taper vertical optical coupler extending from an optical output of the EAM;

[0035] The patterned layers of the first stage waveguide are used to provide an output waveguide;

[0036] The DFB laser cavity is laterally spaced apart from the EAM along an optical propagation direction, the first lateral taper vertical optical coupler is configured to couple an emitted optical mode from the DFB laser to an input of the EAM; and

[0037] The second lateral taper vertical optical coupler is configured to vertically couple a modulated output from the EAM to the output waveguide; and

[0038] Electrical interconnections to the DFB laser and the EAM for operating the DFB laser in a CW mode and driving the EAM.

[0039] The integrated EML can further include a passive waveguide vertically disposed under the first stage waveguide and patterned to form a spot size converter (SSC); the first stage waveguide includes a third lateral taper vertical optical coupler configured to couple an optical output from the output waveguide to the SSC for coupling to a single mode optical fiber.

[0040] In some embodiments, the epitaxial layer structure includes a plurality of semiconductor layers for electronic circuitry disposed vertically below the plurality of vertically stacked optical waveguides, the plurality of semiconductor layers for electronic circuitry being vertically separated from the plurality of vertically stacked optical waveguides by spacers; the optical assembly includes a DFB laser, an EAM waveguide, an output waveguide, and lateral taper vertical optical couplers formed on a first region (island) of the substrate;

[0041] The electronic circuitry is formed on a second region (island) of the substrate adjacent to the first region, wherein the semiconductor layers of the epitaxial layer stack including the spacers and all overlying layers have been removed; and

[0042] The interconnect metallization provides electrical interconnections between the electronic circuitry and electrical connections of the DFB laser and the EAM for operating the DFB laser and driving the EAM.

[0043] The electronic circuit can include an EAM drive and control circuit for linearization and temperature compensation, including one of:

[0044] a photoelectric current sensor for monitoring the EAM optical output and an electrical temperature sensor for monitoring the EAM operating temperature; and

[0045] an optical tap and a photodetector for monitoring the EAM optical output and an electrical temperature sensor for monitoring the EAM operating temperature.

[0046] For example, the electronic circuit includes an EAM drive and control circuit, the EAM having first and second electrical terminals for applying a bias voltage to operate the EAM, and an electrical control terminal for receiving an input analog modulation signal, which is fed to a drive transistor of the EAM driver circuit through the control circuit; and

[0047] wherein the control circuit includes first sensing means for detecting the temperature of the EAM and generating a first feedback signal in dependence on the temperature of the EAM, and first control loop elements for combining the first feedback signal and the input analog modulation signal to provide a temperature-compensated modulation signal; second sensing means for detecting the output level of the EAM and generating a second feedback signal dependent on the output level of the EAM, and second control loop elements for combining the second feedback signal and the temperature-compensated modulation signal to provide a linearized modulation signal.

[0048] In one embodiment, the first sensing means for detecting the temperature of the electro-absorption modulator includes an electrical temperature sensor placed in the vicinity of the EAM, and the first control loop elements for combining includes a coupler for adding the first feedback signal to the input analog modulation signal to provide the temperature-compensated modulation signal. For example, the first feedback signal includes a temperature-dependent offset bias.

[0049] For example, the second sensing means includes electrical components for detecting the photocurrent of the electro-absorption modulator and generating the second feedback signal; or, the second sensing means includes an electro-optical assembly including an optical tap for sampling the optical output of the electro-absorption modulator, a photodetector for generating the second feedback signal, and a transimpedance amplifier.

[0050] In one embodiment, the second control loop elements for combining the second feedback signal and the temperature-compensated modulation signal includes a differential amplifier, and the temperature-compensated modulation signal is input to the non-inverting input of the differential amplifier, the second feedback signal is input to the inverting input of the differential amplifier, an error voltage is generated from the difference between the two signals and fed to the driver.

[0051] Advantageously, the length of the conductive interconnect tracks between the EAM drive and control circuitry and the EAM is in the range of microns to tens of microns, thereby reducing timing and phase delays, for example, in order to enable advanced modulation schemes.

[0052] In example embodiments, the DFB laser is a VC SEG DFB laser.

[0053] In the EML of some embodiments, the epitaxial layer structure is compatible with a single epitaxial growth process for fabrication using III-V semiconductor materials. In some embodiments, the integrated EML is fabricated using an InP-based material system including selected binary, ternary and quaternary compositions of In, Ga, As, P and Al.

[0054] Another aspect provides a method of fabricating a monolithically integrated electro-absorption modulated laser (EML) in which a DFB laser is vertically integrated with an EAM through a lateral taper vertical optical coupler, comprising:

[0055] providing a substrate;

[0056] growing an epitaxial layer structure on the substrate,

[0057] the epitaxial layer structure includes a plurality of vertically stacked optical waveguides, wherein:

[0058] a first order waveguide includes layers structured as an output (passive) waveguide;

[0059] a second order waveguide includes layers structured as an EAM waveguide;

[0060] a third order waveguide includes layers structured as a DFB laser waveguide;

[0061] patterned layers of the third order waveguide are used to define a laser mesa including a DFB laser cavity having a surface etched grating (SEG) and a first lateral taper vertical optical coupler extending from an optical output of the laser cavity;

[0062] patterned layers of the second order waveguide are used to define a mesa of the EAM, and a second lateral taper vertical optical coupler extending from an optical output of the EAM;

[0063] patterned layers of the first order waveguide are used to define an output waveguide;

[0064] the DFB laser cavity is laterally spaced apart from the EAM along an optical propagation direction, the first lateral taper vertical optical coupler is configured to couple an emitted optical mode from the DFB laser to an input of the EAM; and

[0065] the second lateral taper vertical optical coupler is configured to vertically couple a modulated output from the EAM to the output waveguide;

[0066] and

[0067] providing electrical connections for the DFB laser and the EAM to operate the DFB laser in CW mode and to drive the EAM.

[0068] In another aspect, there is provided a method of fabricating a monolithically integrated electro-absorption modulated laser (EML) in which a DFB laser is vertically integrated with an EAM and an integrated electronic circuit, comprising:

[0069] providing a substrate;

[0070] growing a cladding epitaxial layer structure on first and second regions of the substrate,

[0071] the first region is designated for optical components of the EML and the second region is designated for the electronic circuit;

[0072] the cladding epitaxial layer structure comprises:

[0073] a first plurality of semiconductor layers for fabricating the electronic circuit;

[0074] at least one spacer comprising a selectively etch stop; and

[0075] a plurality of vertically stacked optical waveguides, wherein:

[0076] a first order waveguide comprises layers structured as an output (passive) waveguide;

[0077] a second order waveguide comprises layers structured as an EAM waveguide;

[0078] a third order waveguide comprises layers structured as a DFB laser waveguide;

[0079] protecting the first region and selectively removing the plurality of vertically stacked optical waveguides and the at least one spacer from the second region;

[0080] processing the first plurality of semiconductor layers to define the electronic circuit;

[0081] protecting the second region comprising the electronic circuit;

[0082] processing the plurality of vertically stacked optical waveguides, comprising:

[0083] patterning layers of the third order waveguide to define a laser mesa comprising a DFB laser cavity having a surface etched grating (SEG) and a first lateral taper vertical optical coupler extending from an optical output of the laser cavity;

[0084] patterning layers of the second order waveguide to define a mesa of the EAM, and a second lateral taper vertical optical coupler extending from an optical output of the EAM;

[0085] the patterned layer of the first stage waveguide is used to define an output waveguide;

[0086] the DFB laser cavity is laterally spaced apart from the EAM along the light propagation direction, the first lateral taper vertical optical coupler is configured to couple an emission light mode from the DFB laser to an input of the EAM; and

[0087] a second lateral taper vertical optical coupler is configured to vertically couple a modulated output from the EAM to the output waveguide; and

[0088] electrical connections are provided between the electronic circuit, the DFB laser and the EAM in order to operate the DFB laser in a CW mode and to drive the EAM.

[0089] When the EML further comprises a vertically integrated spot size converter (SSC) for coupling the optical output of the EML to a single mode optical fiber, the method further comprises, after growing the first plurality of semiconductor layers for fabricating the electronic circuit and the at least one spacer comprising a selectively etch stopper,

[0090] etching a deep trench through the first plurality of semiconductor layers and the at least one spacer comprising a selectively etch stopper and into the underlying substrate;

[0091] growing within the deep trench epitaxial layer of the SSC;

[0092] wherein the patterning of the first stage waveguide to define an output waveguide further comprises defining a third lateral coupling vertical coupler to couple an optical output from the output waveguide to the SSC.

[0093] The foregoing and other objects, features, aspects and advantages of the present application will become more apparent from the following detailed description of an embodiment thereof, when taken in conjunction with the accompanying drawings, which describe, by way of example only, the principles of the application. BRIEF DESCRIPTION OF DRAWINGS

[0094] Figure 1 (prior art) shows a schematic block diagram of a butt-coupled EML assembly example;

[0095] Figure 2 (prior art) shows a typical transfer function of the EML of Figure 1 ;

[0096] Figure 3 (prior art) shows a longitudinal cross-sectional schematic of an integrated EML comprising a DFB laser and an EAM, fabricated on the same substrate using different epitaxial layer structures for the DFB laser and the EAM;

[0097] Figure 4 (prior art) shows a longitudinal cross-sectional schematic of an integrated EML of a stack structure fabricated by selective area growth;

[0098] Figure 5 (prior art) shows a longitudinal cross-sectional schematic of an integrated EML comprising a DFB laser and an EAM, fabricated on the same substrate, with a shared epitaxial layer structure of the DFB laser and the EAM;

[0099] Figure 6 A longitudinal cross-sectional schematic of a first example of a monolithic integrated EML fabricated using MGVI is shown;

[0100] Figure 7 A schematic plan view of the first example of a monolithic integrated EML is shown;

[0101] Figure 8 (prior art) shows an isometric view of a DFB laser example in the form of a vertically coupled SEG DFB laser, compatible with the fabrication of a monolithic integrated EML using MGVI;

[0102] Figure 9 A longitudinal cross-sectional schematic of a second example of an integrated EML fabricated using MGVI, comprising integrated electronic circuitry, is shown;

[0103] Figure 10 A schematic plan view of the second example of an integrated EML is shown;

[0104] Figure 11A And 11B A schematic cross-sectional view showing some steps in the fabrication of a device structure representing Figure 9 And 10 A schematic cross-sectional view showing some steps in the fabrication of a device structure representing

[0105] Figure 12A A schematic plan view of a third example of an integrated EML, comprising integrated drive and control circuitry, is shown;

[0106] Figure 12B A schematic plan view of a fourth example of an integrated EML, comprising integrated drive and control circuitry, is shown;

[0107] Figure 13 A longitudinal cross-sectional schematic of a fifth example of an integrated EML fabricated using MGVI, comprising a spot size converter (SSC) and integrated drive electronics, is shown;

[0108] Figure 14 A schematic cross-sectional view showing some steps in the fabrication of a device structure representing Figure 13 A schematic cross-sectional view showing some steps in the fabrication of a device structure representing

[0109] Figure 15 A circuit schematic of a first example of an electro-absorption modulator with monolithically integrated control circuitry for linearization and temperature compensation is shown; and

[0110] Figure 16 shows a circuit schematic of a second example of an electroabsorption modulator with monolithically integrated control circuitry for linearization and temperature compensation;

[0111] Figure 17 shows a schematic plan view of an integrated EML of a sixth embodiment, including monolithically integrated driver and control electronics; and

[0112] Figure 18 shows a schematic plan view of an integrated EML of a seventh embodiment, including monolithically integrated driver and control electronics. DETAILED DESCRIPTION

[0113] Figure 1 (prior art) shows a schematic block diagram of a butt-coupled EML assembly example. The EML assembly comprises a continuous wave laser diode connected to an EAM, mounted on a common substrate, which is backside cooled using a thermoelectric cooler (TEC). Figure 2 (prior art) shows a typical normalized transfer function of the EML as shown in Figure 1, i.e. the normalized transmission of the EAM as a function of the applied voltage. In this example, the EAM has a 100% transmission at the specified wavelength at zero bias voltage and a 0% transmission at a reverse bias of -2V.

[0114] Figures 3 to 5 (prior art) show schematic longitudinal cross-sectional views (i.e. through the optical propagation axis) of three monolithically integrated EML examples. The EML schematically shown in Figure 3 comprises a DFB laser and an EAM, which are fabricated on the same substrate using two different epitaxial layer structures, the waveguide structures for the DFB laser and the EAM are optically coupled by a separation region (see, for example, WO2018 / 091094A1). The EML schematically shown in Figure 4 has a stacked structure fabricated by selective area growth of a plurality of epitaxial layers 1 to 12 on a stepped substrate (see, for example, US7,476,558), wherein epitaxial layers 5 to 8 forming the waveguide of a laser diode (LD) section 17 are selectively removed from the section forming an EAM section 15, which includes epitaxial layer 4 on a step formed by the thicker sections of layers 2 and 3, such that the optical axes of the EAM and the LD are horizontally coplanar, and the EAM and the LD are laterally butt-coupled through the upper portion of the separation region 16. The EML schematically shown in Figure 5 (prior art) comprises a DFB laser and an EAM, which are fabricated on the same substrate with a shared epitaxial layer structure (see, for example, US2010 / 0290489A1).

[0115] Each of the EML structures shown in Figures 1 to 5 is an example of a direct or indirect butt-coupled laser and EAM. Butt-coupled EMLs tend to suffer from early failure and reliability issues, for example due to stress / strain in the interface region between the laser and the EAM, especially at high power operation.

[0116] Monolithic integrated EMLs of some example embodiments of the application will now be described by way of example. Each integrated EML comprises a DFB laser and an EAM which are vertically integrated using MGVI fabrication in which the DFB laser and EAM are vertically coupled by a lateral taper vertical coupler.

[0117] Figure 6 A schematic longitudinal cross-section view of a monolithic integrated EML 100 of a first embodiment is shown, the EML 100 comprising a DFB laser and an EAM, fabricated using MGVI. This fabrication method provides vertical integration of active and passive elements formed in multiple vertically stacked waveguides and is compatible with single epitaxial growth, for example using an InP-based material system. In the example, the structure comprises a semi-insulating (SI) substrate, for example Fe-doped InP, on which an epitaxial layer stack (which can be referred to as an epitaxial layer stack or epitaxial layers) is grown to define the following layers: a first order waveguide, labelled the output waveguide; a second order waveguide, labelled the EAM waveguide; and a third order waveguide, labelled the DFB laser waveguide, on which a surface-etched grating SEG is defined. As shown in the schematic plan view of the monolithic integrated EML 100 of the first embodiment, the waveguides are vertically optically coupled by vertical couplers formed by lateral taper portions of the respective waveguides. The third order waveguide is processed to define a laser mesa and a first lateral taper vertical coupler 1. The SEG is etched on the top surface of the DFB laser portion of the mesa to form the DFB laser, the taper vertical coupler extending from the optical output of the laser over the length of the second order waveguide for vertical optical coupling of the emission mode from the laser to the second order waveguide. Electrical contact regions for driving the DFB laser are provided, for example, the mesa top along the mesa edge and each side of the mesa, as shown in the schematic plan view of the monolithic integrated EML 100 of the first embodiment. Figure 7 Figure 7

[0118] ​​As an example, FIG. 8 (prior art) shows an isometric view of a vertical coupling (VC) SEG DFB laser 200 embodiment compatible with monolithic integration of EMLs using MGVI fabrication. The structure and fabrication of the VC SEG DFB laser shown in FIG. 8 is described in US2012 / 0106583A1 and related applications. That is, the epitaxial layer structure forming the waveguide of the DFB laser includes, for example: a substrate layer 210, upper and lower emitter layers 231 and 232, upper and lower separate confinement heterostructures 233A and 233B, and a multi-quantum well active gain region 234, with at least one of the laser mesas, for example aperture layer 235, configured to provide lateral optical confinement of the fundamental optical mode and lateral confinement of current injection. SEG 270 includes a trench 265 etched on the top surface of the laser mesa. Electrical contacts 275A and 275B are provided to the lower and upper emitter layers. The output facet of the DFB laser, i.e. in the plane 250, is the etched facet.

[0119] Referring back to Figure 6 , the epitaxial layers of the second stage waveguide are configured to form an EAM waveguide, i.e. including upper and lower cladding layers and a multi-quantum well semiconductor structure with components of electrically controllable absorption to provide an appropriate transfer function, e.g. high transmission (essentially transparent) of light at the laser wavelength at zero bias voltage, and minimum transmission at a few volts reverse bias. The electrical contact regions of the EAM are provided along the length of the EAM portion of the waveguide, i.e. on top of the EAM mesa and on each side of the EAM mesa, as shown in the schematic view in Figure 7 . The second stage waveguide extends from the EAM in the direction of optical propagation and is patterned to form a lateral taper of the second vertical optical coupler 2 for optical coupling of the modulated light transmitted by the EAM to the underlying first stage waveguide as the optical output waveguide. The lateral taper of the vertical optical couplers 1 and 2 of the second and third stage waveguides is shown in Figure 7 . The cw output optical path of the laser is coupled vertically through the first vertical coupler, the modulated output is generated by the EAM, and the modulated output is coupled vertically through the second vertical coupler to the first stage (output) waveguide, as shown by the large arrows in the longitudinal cross-sectional schematic view in Figure 6 . If desired, the third stage waveguide can also be structured to provide a detector (not shown) for back facet power monitoring.

[0120] The epitaxial layer structure can be selected to be compatible with a single epitaxial growth process. Multiple epitaxial growth steps can also be used.

[0121] The general principle of material selection and construction of waveguide layers for vertical optical coupling using lateral taper vertical optical couplers is to select the bandgap wavelength and refractive indices appropriately, as in US 7,444,055 B2 to Tolstikhin, entitled "Integrated optical device for wavelength (de)multiplexing in multi-guide vertical stack", and references cited therein.

[0122] A longitudinal cross-section schematic of an integrated EML 300 of a second embodiment manufactured using MGVI is shown in Figure 9 In this embodiment, the EML is integrated with EAM drive circuitry and laser drive circuitry. The latter includes bias control for the laser to operate as a CW light source, and optionally includes other elements such as for temperature sensing, power monitoring, control loops for temperature stabilization and power regulation. The layers constituting the three vertically stacked waveguides of the DFB laser and EAM modulator, the output waveguide and the lateral taper vertical coupler are similar to those shown in Figure 6 Figure 9 The structure shown schematically in Figure 6 differs from that shown in by the provision of an additional layer between the SI substrate and the waveguide layers. That is, the additional layer includes layers for forming high speed electronic circuitry for the laser driver and EAM driver circuitry. The additional layer includes InP-based semiconductor layers for manufacturing heterojunction bipolar transistors (HBTs), which are labelled HBT epitaxial layers for the electronic circuitry, and a spacer, which includes one or more layers and includes one or more etch stops that allow for separate processing of the optical elements and the electronic circuitry.

[0123] Figure 10 The figure is a schematic plan view of the EML 300 of the second embodiment, as shown in

[0124] Figure 11A and 11B schematically illustrates an example of some processing steps 300-1 to 300-6 for manufacturing an EML device structure with integrated drive circuitry, as shown in Figure 9 10 ​​The first epitaxial layer stack, including semiconductor layers for the fabrication of InP heterojunction bipolar transistors, is referred to as the "HBT epi stack." The HBT epi stack for the high speed electronic devices is grown on the silicon substrate (step 300-1). If the high speed electronic devices are grown on top of the optical elements, the conductivity of the layers forming the laser and EAM waveguides would reduce the speed of operation of the transistors. Therefore, the second epi layer stack for the optical waveguides ("optical epi stack") is grown on top of the layers for the electronic devices and includes a spacer or stitching layer (step 300-2) that includes etch stops that separate the epi stack and the overlying epi stack for the optical waveguides (step 300-3). Note that the epitaxial layers can be chosen to be compatible with a single epitaxial growth process for forming all of the HBT epitaxial layer stack, the stitching layer, and the optical epitaxial layer stack, if desired. Alternatively, multiple epitaxial growth steps can be used.

[0125] For example, to fabricate the integrated EML structure schematically shown in Figure 9 and 10 The optical epi layer stack is configured to form first, second, and third order waveguides (steps 300-1 and 300-3 in Figure 11A The HBT and optical epitaxial layer stacks, as well as the stitching layer, are all deposited overlying the entire substrate. Then, the device regions (islands) of the optical components are protected, for example by a mask layer, and the exposed portions of the optical epi stack are etched back to the HBT epi stack (step 300-4). The dimensions of the islands of the optical components and the electronic components are chosen so that, during subsequent processing, each island has sufficient planar area to allow proper alignment and step photolithography, including placement of alignment marks on the exposed surface layers. The material of the stitching layer between the HBT epi stack and the optical epi stack is chosen so that there is at least one high selectivity etch stop between the optical epi stack and the HBT epi stack for subsequent processing steps, for example for independent processing of the circuit components and the optical components.

[0126] The HBT and other components of the electronic circuit are processed while the optical epi stack is protected until the interconnect metallization is needed. First order interconnect metallization can be provided for the electronic circuit. Second order interconnect metallization for electrical connections of the electronic circuit and the optoelectronic elements is provided later in the processing sequence after the optical elements are processed.

[0127] Referring to Figure 11BThe device structure of the HBT epi stack is then protected, for example, by a mask (see step 300-5), and the mask is removed from the optical epi stack (see step 300-4). The optical components, consisting of the DFB laser, EAM, and the lateral taper of the vertical optical coupler, are then processed from top to bottom to define the structure of each waveguide. These process steps may include, for example, a) patterning and etching the laser waveguide to define the laser mesa and the sidewalls of the lateral taper first vertical optical coupler 1, and etching the SEG of the laser; b) patterning and etching the EAM waveguide to define the EAM and the sidewalls of the lateral taper second vertical optical coupler 2; and c) patterning and etching the output waveguide.

[0128] After completing these optical waveguide structures, the mask is removed from the electronic device structure of the HBT epi stack, and the circuits and electrical connections of the optical devices are back-end metallized and interconnected, including planarization and post-processing.

[0129] As described above, in some embodiments, if desired, the epitaxial layer can be selected to be compatible with a single epitaxial growth process used to form the HBT epitaxial layer stack, the stitching layer, and the optical epitaxial layer stack. Alternatively, in other embodiments, multiple epitaxial growth steps can be used.

[0130] It should be understood that the above-mentioned Figures 6 to 10 The schematic diagrams shown in 11A and 11B are highly simplified representations of the device structure layers; layer thicknesses and lateral dimensions are not drawn to scale. While only one element of an EML device structure is shown in each drawing, fabrication is actually performed at the wafer scale, with numerous EML devices on each wafer. As will be understood, each waveguide includes numerous epitaxial layers, such as a core comprising the MQW active region of the waveguide, a SCH layer, and a cladding layer; the substrate and HBT epitaxial layer stacks, as well as the optical epitaxial layer stacks, may include additional layers, such as buffer layers, intermediate layers, spacers, as appropriate. Semiconductor materials include III-V semiconductor materials suitable for fabricating HBT epitaxial layer stacks for high-speed electronic circuits and optical epitaxial layer stacks for waveguides used in active and passive optical components. For example, semiconductor materials may include III-V semiconductors based on InP material systems, such as selected binary, ternary, and quaternary compositions comprising In, Ga, As, P, and Al.

[0131] refer to Figure 10 The schematic plan view shown, in the EML 300 of the second embodiment, schematically shows the DFB laser control circuit and the EAM drive and control circuit located on the side of the EML. Figure 11BIn the cross-sectional view shown in step 300-6, the driving electronics are schematically shown as being located in a region longitudinally spaced from the EML waveguide structure, for example, behind the back of the DFB laser. As described above, a back-side power monitor for the laser, i.e., a pin diode detector (not shown), may be included. In practice, integrated electronic circuitry may be placed, as appropriate, on the substrate surrounding the EML, for example, to optimize interconnects, distribute heat generated by the electronics, and optimize the use of the device area. Advantageously, integrated EAM driver circuitry is located near the EAM to minimize interconnect lengths, for example, to achieve higher performance modulation. Figure 12A A schematic plan view of the device area of ​​the integrated EML400-1 according to the third embodiment is shown, including monolithically integrated drive and control circuitry. In this embodiment's layout, the EAM driver and control electronics are located near the EAM to optimize interconnection, for example, to provide shorter interconnect lengths for high-performance modulation, and the laser drive electronics are located behind the back of the DFB laser. It should be understood that, for example, in Figure 12B In the integrated EML 400-2 of the alternative embodiment schematically illustrated, the EML is integrally integrated with the EAM driver and control electronics, while other electronics, such as laser drivers, monitoring and control circuitry, are provided on separate chips. In other embodiments, based on Figure 6 and 7 The monolithic integrated EML structure shown provides the laser and EAM drive and control electronics as separate chips, without integrated electronics.

[0132] A longitudinal cross-sectional schematic diagram of the integrated EML 500 of the fifth embodiment manufactured using MGVI is shown below. Figure 13 As shown. EML 500 is different. Figure 9 and 10 The EML 300, schematically shown, also includes a Spot Size Converter (SSC) for directly coupling the optical output to the single-mode fiber. Specifically, the first-stage waveguide is a coupling waveguide that is vertically coupled to the waveguide layer of the SSC by a laterally tapered third vertical optical coupler. The SSC forms a diluted coupling waveguide at the bottom of the vertical stack for low-loss, high-alignment-tolerance single-mode fiber coupling. The SSC is formed in deep trenches etched into the spacers, HBT epi stack, and substrate.

[0133] In manufacturing Figure 13 In the EML 500 of the illustrated embodiment, due to the terrain required by the SSC, such as Figure 14As shown, the process flow has been adjusted. For example, the SSC has a height and width, such as approximately 7 μm, for alignment and optical coupling to a standard single-mode fiber, while the thickness of the HBT epi stack and spacers may be, for example, approximately 2 μm. To successfully integrate the SSC, as... Figure 14 As illustrated in process steps 500-1 to 500-3, the HBT epitaxial layer is grown on the SI substrate along with layers for spacers. Backside alignment marks are etched into the substrate wafer to allow alignment for subsequent processing. Next, deep trenches are etched through the HBT epitaxial layer into the substrate wafer and into the substrate (500-1). These trenches define the SSC location for each island. An SSC epitaxial layer stack is then grown in the trenches, for example using a lift-off process. The top layer of the SSC epitaxial layer stack is selected to have a material with selective etching of the surrounding layers of the HBT epitaxial layer stack. The SSC epi stack is grown slightly centered on the trenches, and then the SSC material is planarized onto the HBT epi stack surface using selective dry etch chemistry. Rapid wet etching may be necessary at this point to remove any surface roughness. Next, an optical epi stack for coupling waveguides, EAM, and DFB lasers is grown on wafer (500-2). The SSC waveguide in its trench is aligned using back-side alignment marks, the optical epi stack is protected, and the process continues to fabricate electronic circuits and optical components (500-3), for example, as referenced above. Figure 11A and 11B As described. Figure 14 As shown in Figure 500-3, the EML electronic circuit of this embodiment occupies the area next to the EML waveguide stack.

[0134] Figure 15 A circuit diagram of a first example of an electroabsorption modulator with monolithically integrated control circuitry for linearization and temperature compensation is shown. Figure 16 A circuit diagram of a second example of an electroabsorption modulator with monolithically integrated control circuitry for linearization and temperature compensation is shown, as disclosed in related U.S. applications US 16 / 263,169 and US16 / 708,887.

[0135] refer to Figure 15The elements of the electro-optical integrated circuit 100-1 are fabricated monolithically on the device region 102 of the substrate and include an electro-absorption modulator 120 and integrated drive and control circuit elements. The electro-absorption modulator 120 has an optical input 122 for receiving a continuous wave (CW) optical input and an optical output 124 for outputting a modulated optical output. The CW optical input can be provided by a discrete or integrated laser diode (not shown) coupled to the electro-absorption modulator via an optical waveguide and / or a spot size converter (SSC), for example. The optical output 124 can also include a SSC for coupling to other optical components. Electrical terminals 126 and 128 of the electro-optical modulator are used to apply a reverse DC bias to operate the electro-absorption modulator 120. An input modulation signal, i.e., an analog electrical signal, is provided at a control input 132 and fed through elements of the control circuit to a control terminal of a drive transistor 138 of the drive circuit of the electro-absorption modulator 120 for modulating the optical output signal. The integrated drive and control circuit forms a fast feedback control loop including a first sensing means with first control loop elements for temperature compensation and a second sensing means with second control loop elements for linearization of the electro-absorption modulator.

[0136] The first sensing means is for detecting a temperature of the electro-absorption modulator and generating a first feedback signal in dependence on the temperature of the electro-absorption modulator, and the first control loop elements are for combining the first feedback signal and the input analog modulation signal to provide a temperature compensated modulation signal. The first sensing means includes an electrical sensor 140 for detecting the temperature of the electro-absorption modulator and generating a temperature dependent bias voltage. The temperature dependent bias voltage is fed to a control circuit element 136 where it is combined with the input modulation signal to generate the temperature compensated modulation signal. The temperature sensor generates a DC bias in dependence on the temperature of the modulator for adjusting the analog input signal to compensate for temperature variations.

[0137] Preferably, the electrical temperature sensor placed in the vicinity of the electro-absorption modulator and the first control loop elements for combining includes a coupler 136 for adding the first feedback signal, e.g., the temperature dependent bias voltage, to the input analog modulation signal to provide the temperature compensated modulation signal.

[0138] The second detection means comprises an electrical circuit 150 for detecting the output level of the electro-absorption modulator, for example a photogalvanic detection element for detecting the photogalvanic current of the electro-absorption modulator absorption and generating a second feedback signal, depending on the output level of the electro-absorption modulator. The second control loop element comprises a differential amplifier 134 for combining the second feedback signal and the temperature-compensated modulation signal to provide a linearized modulation signal. That is, the temperature-compensated modulation signal is input to the non-inverting input of the differential amplifier and the second feedback signal is input to the inverting input of the differential amplifier to produce an error voltage from the difference between the two signals. The fast feedback control circuit thus measures the output optical signal and compares it to the electrical input signal to the drive block. The error voltage is produced from the difference between the two signals and fed to the driver.

[0139] With reference to Figure 16 , many of the elements of the circuit 100-2 are similar to those of the first example circuit 100-2 and are labelled with the same reference numbers. The temperature sensor 140 provides temperature compensation as described for the circuit 100 shown in Figure 15 . The fast feedback circuit shown in Figure 16 differs from that shown in Figure 15 in that it comprises an electro-optical circuit for measuring the output optical signal level. That is, the fast feedback circuit comprises an optical tap 152, an output sense photodiode 154 and an output sense transimpedance amplifier (TIA) 156 to measure the output optical signal and provide a second feedback signal to the differential amplifier 134. That is, as in the electro-absorption modulator 100-1, the temperature-compensated modulation signal is input to the non-inverting input of the differential amplifier and the second feedback signal is input to the inverting input of the differential amplifier to produce an error voltage from the difference between the two signals fed to the driver.

[0140] The two embodiments of the integrated EAM driver described above differ in the way the output optical feedback is measured, that is, they comprise different forms of output monitor (second sensing means) for detecting the EAM output level. Figure 15 The first embodiment is shown to use the absorbed photocurrent to measure the output level. Figure 16 The second embodiment is shown to tap a small amount of the output optical signal and detect it using a high-speed photodetector and TIA. In each case, the feedback circuit measures the output optical signal and compares it to the electrical input signal to the drive block. The error voltage is produced from the difference between the two signals and fed to the driver. In both implementations, the first sensing means comprises a temperature sensor located in the vicinity of the modulator. In this way a DC bias is produced which is set in dependence on the temperature of the modulator.

[0141] For small, low cost, and relatively short distance applications, such as 400G data center interconnect, the stripline driver circuit and associated power dissipation to match impedance can be eliminated when the drive electronics and EAM are integrated into a device area that is small enough. Monolithic integration of the optical modulator and associated drive and control electronics brings the components closer together and significantly reduces the length of the conductive interconnect tracks, for example, from millimeters to microns. The distance over which electrical signals must be transmitted is reduced by about 1000:1, greatly reducing the phase and time delay between blocks, enabling fast feedback circuits, either electronic or electro-optical in form, even at very high speeds. The feedback approach can linearize the overall transfer function of the modulator, closely monitor the temperature of the modulator, and apply appropriate temperature dependent bias voltages to keep the operating range of the modulator properly centered.

[0142] Monolithic integration shrinks the interconnect scale to microns, combined with very high speed transistors, enables a drive circuit that linearizes the electro-optical transfer function of the modulator over a limited range of input electrical and optical signals using feedback. When operated within the range, the input continuous wave (CW) optical signal can be linearly modulated, allowing advanced modulation schemes such as QPSK (quadrature phase shift keying), PAM-4 (4-level pulse amplitude modulation), or even QAM (quadrature amplitude modulation) to be applied to the optical signal. For limited range applications, such as data center interconnect, the path loss and impairments due to dispersion are limited, enabling the complex analog modulation of the optical signal to be effectively implemented over a limited dynamic range, while providing good bit error rate performance over the entire link. By using the EA modulator and its associated integrated analog electronics as simpler building blocks to replace the more complex Mach-Zehnder modulator assembly, stripline packaging, and DSP, the transmitter is implemented, resulting in a significant reduction in the complexity, cost, and power of the link.

[0143] Figure 17 A schematic plan view of the integrated EML 600 of the sixth embodiment is shown, which includes integrated drive circuitry, for example, including integrated EAM drive and control circuitry, as shown in Figure 15 . Figure 17 Many of the elements of the integrated EAM drive and control circuitry of the sixth embodiment are similar to those shown schematically in Figure 10 . Figure 17 The schematic plan view in Figure 15 illustrates how the optical current sensing and temperature sensing of the integrated EAM drive and control circuitry of the sixth embodiment are incorporated into the device layout.

[0144] Figure 18 A plan schematic view of the integrated EML 700 of the seventh embodiment is shown, which has integrated drive circuitry, for example, integrated EAM drive and control circuitry, as shown in Figure 16are shown. In the described embodiment, the waveguide layer of the epitaxial layer stack proximate to the optical output waveguide is patterned to provide an optical tap: that is, the second stage waveguide layer is patterned, as shown, to define an optical detector, i.e. using the active layer of the EAM waveguide stack, and is patterned below the first stage waveguide to form a lateral optical coupler configured to tap a small percentage, e.g. 1%, of the modulated light output, which is coupled by another lateral taper vertical optical coupler to the optical detector. Figure 18

[0145] Monolithic integration of EMLs is described by way of example for a number of example embodiments. In each example embodiment, the vertical integration of a DFB laser and EAM fabricated based on MGVI provides integration of these components in a device structure that can provide higher reliability compared to conventional butt coupling of DFB lasers and EAMs. As described in the background section, direct or indirect butt coupling interfaces between DFB lasers and EAMs result in high stress and strain interfaces that can lead to reliability issues or premature failure, especially at high power operation. The structure of the lateral taper vertical optical coupler of the EMLs of the example embodiments provides efficient vertical optical coupling between the output of the DFB laser and the input of the EAM. The epitaxial layer structure of the vertically integrated waveguides of the DFB laser and EAM can be designed to reduce stress / strain between the optical components, and the vertically integrated EML avoids the high stress / strain interface region between the conventionally butt coupled DFB laser and EAM.

[0146] As shown in the example embodiments, the vertically integrated EMLs can or can not be fabricated with integrated driver and control electronics. Advantageously, at least the EAM driver and control electronics are also vertically integrated into the device structure, e.g. to optimize interconnects from the driver to the EAM, e.g. to reduce interconnect length / inductance / resistance, etc., to enable reliable, higher performance modulation of the EAM, e.g. PAM4. The DFB laser operates in CW mode, so proximity of the laser driver and control electronics can be less important, but the integrated electronics circuit optionally includes the laser driver. Other electrical and optical components, e.g. temperature sensors, optical probes for power monitoring, etc., can be integrated separately as appropriate.

[0147] The device topology, i.e. the physical layout on the device area, of the optoelectronic components and the electronics circuit can be selected to optimize interconnects, improve heat dissipation, efficient use of the device area, etc. Thus, where feasible, the various elements of the EMLs of the example embodiments can be combined to provide additional or alternative embodiments. For example, the vertically integrated EML of the first embodiment does not have integrated driver and control circuitry, and reference is made to Figure 6 and 7 ​For purposes of description, the vertically integrated EML can be mounted on a substrate with discrete drive and control circuitry. For example, the vertically integrated EML of another embodiment can include integrated EAM drive and control circuitry, for example, as described with reference to Figure 9 and 10 The EML of the described embodiments can be integrated with other optical elements and / or electronic circuitry.

[0148] The vertically integrated EML of the exemplary embodiments and variants and modifications thereof can be implemented using III-IV based semiconductor material systems. In particular, InP based semiconductor material systems can be used, for example, selected binary, ternary and quaternary compositions containing In, Ga, As, P and Al. InP based material systems can be used to fabricate passive optical elements, for example, passive waveguides, optoelectronic device structures, for example, waveguides for DFB lasers and EAMs, and also high speed electronic circuitry containing InP transistors, for example, InP HBTs.

[0149] In summary, the present disclosure is directed to monolithically integrated EMLs and fabrication methods that include vertically stacked waveguides for DFB lasers, EAMs and passive output waveguides. The DFB lasers, EAMs and output waveguides are optically coupled using lateral taper vertical optical couplers. The passive output waveguides can also be used to provide optical taps, for example, for output power monitoring. If desired, the third stage waveguide of the DFB laser can also be configured to provide a diode detector for back facet power monitoring.

[0150] The vertical integration using lateral taper vertical optical couplers provides an alternative to the conventional butt coupling of lasers and EAMs, with the potential to improve the reliability of high power operation with extended lifetimes. The availability of higher power lasers enables the receiver to be replaced by a lower cost, more reliable PIN diode detector instead of a higher sensitivity avalanche photodiode.

[0151] Optionally, the vertically integrated EML includes monolithically integrated electronic circuitry, for example, drive and control electronics for the DFB laser and EAM. Advantageously, the integrated EAM drive and control circuitry includes a high speed electro-optic control loop for very high speed linearization and temperature compensation, for example, to enable advanced modulation schemes such as PAM-4 and DP-QPSK for analog optical data center interconnect applications.

[0152] The EML of some embodiments is compatible with fabrication using a single epitaxial growth.

[0153] While embodiments of the present disclosure have been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation. The scope of the present disclosure is to be limited only by the appended claims.

Claims

1. A monolithic integrated electro-absorption modulated laser (EML), comprising: Semi-insulating (SI) substrate; The epitaxial layer structure includes multiple semiconductor layers grown on the semi-insulating substrate; The epitaxial layer structure defines multiple vertically stacked optical waveguides, wherein: The first-stage waveguide consists of layers with an output waveguide structure; The second-stage waveguide includes a layer with an electro-absorption modulator (EAM) waveguide structure; The third-level waveguide includes a layer with a distributed feedback (DFB) laser waveguide structure; The third-level waveguide layer is patterned to define a laser mesa, including a distributed feedback (DFB) laser cavity with a surface etched grating (SEG) and a first transverse tapered vertical optical coupler extending from the optical output of the distributed feedback (DFB) laser cavity. The second-stage waveguide layer is patterned to define the mesa of the electro-absorption modulator (EAM) and a second transverse tapered vertical optical coupler extending from the optical output of the electro-absorption modulator (EAM). The layers of the first-stage waveguide are patterned to provide the output waveguide; The distributed feedback (DFB) laser cavity is laterally separated from the electroabsorption modulator (EAM) along the light propagation direction, and the first lateral tapered vertical optical coupler is configured to couple the emitted light mode from the distributed feedback (DFB) laser to the input of the electroabsorption modulator (EAM); The second transverse tapered vertical optical coupler is configured to vertically couple the modulated output from the electroabsorption modulator (EAM) to the output waveguide; and The first electrical connection is to the distributed feedback (DFB) laser for operating the DFB laser in continuous wave mode; the second electrical connection is to the electroabsorption modulator (EAM) and is used to drive the EAM. The epitaxial layer structure has an additional layer between the semi-insulating substrate and the plurality of vertically stacked optical waveguides, the additional layer including a layer for forming electronic circuitry for at least the electro-absorption modulator (EAM).

2. The monolithic integrated electroabsorption modulated laser (EML) of claim 1, wherein the additional layer includes a layer for forming the electronic circuitry of the distributed feedback (DFB) laser.

3. The monolithically integrated electro-absorption modulated laser (EML) according to any one of claims 1 and 2, wherein, The additional layer includes a plurality of semiconductor layers for electronic circuits, located below the plurality of vertically stacked optical waveguides, and the semiconductor layers for electronic circuits are vertically separated from the plurality of vertically stacked optical waveguides by at least one spacer layer. The optical components include the distributed feedback (DFB) laser waveguide, the electro-absorption modulator (EAM) waveguide, the output waveguide, and the transverse tapered vertical optical coupler formed on a first region of the semi-insulating substrate; Electronic circuitry is formed on a second region of the semi-insulating substrate, adjacent to the first region, including at least one spacer layer and all epitaxial layers of the semiconductor layer stacked with capping layers that have been removed; and Interconnect metallization provides electrical interconnection between the electronic circuitry and a first electrical connection to the distributed feedback (DFB) laser and a second electrical connection to the electroabsorption modulator (EAM) for operating the distributed feedback (DFB) laser and driving the electroabsorption modulator (EAM).

4. The monolithic integrated electro-absorption modulated laser (EML) according to any one of claims 1 to 2, further comprising a passive waveguide vertically disposed below the first-stage waveguide and patterned to form a spot size converter (SSC); the first-stage waveguide comprising a third transverse tapered vertical optical coupler configured to couple light output from the output waveguide to the spot size converter (SSC) for coupling to a single-mode fiber.

5. The monolithically integrated electroabsorption modulated laser (EML) of claim 4, wherein the electronic circuitry includes an electroabsorption modulator (EAM) drive and control circuitry for linearization and temperature compensation, comprising one of the following: A photoelectric current sensor for monitoring the optical output of the electro-absorption modulator (EAM) and an electrical temperature sensor for monitoring the operating temperature of the EAM; and An optical tap and photodetector for monitoring the optical output of the electroabsorption modulator (EAM) and an electrical temperature sensor for monitoring the operating temperature of the electroabsorption modulator (EAM).

6. The monolithically integrated electroabsorption modulated laser (EML) according to claim 5, wherein the electronic circuitry includes an electroabsorption modulator (EAM) driving and control circuitry, and The electroabsorption modulator (EAM) has first and second electrical terminals for applying a bias voltage to operate the EAM, and an electrical control terminal for receiving an input analog modulation signal, which is fed through the control circuit to a drive transistor driving the EAM; wherein, The control circuit includes: a first sensing device for detecting the temperature of the electroabsorption modulator (EAM) and generating a first feedback signal based on the temperature of the EAM; a first control loop element for combining the first feedback signal and an input analog modulation signal to provide a temperature-compensated modulation signal; a second sensing device for detecting the output level of the EAM and generating a second feedback signal dependent on the output level of the EAM; and a second control loop element for combining the second feedback signal and the temperature-compensated modulation signal to provide a linearized modulation signal.

7. The monolithically integrated electro-absorption modulated laser (EML) of claim 6, wherein the first sensing device for detecting the temperature of the electro-absorption modulator (EAM) comprises an electrical temperature sensor placed near the EAM, and the first control loop element comprises a coupler for adding a first feedback signal to the input analog modulation signal to provide a temperature-compensated modulation signal.

8. The monolithic integrated electroabsorption modulated laser (EML) according to claim 6 or 7, wherein the first feedback signal includes a temperature-dependent offset bias.

9. The monolithically integrated electro-absorption modulated laser (EML) according to any one of claims 6 to 7, wherein the second sensing device comprises electrical components for detecting the photocurrent of the electro-absorption modulator (EAM) and generating the second feedback signal; or in, The second sensing device includes an electro-optic component, which includes an optical tap for sampling the light output of an electroabsorption modulator (EAM), a photodetector for generating the second feedback signal, and a transimpedance amplifier.

10. The monolithic integrated electroabsorption modulated laser (EML) according to any one of claims 6 to 7, wherein the second control loop element for combining the second feedback signal and the temperature-compensated modulation signal comprises a differential amplifier, the temperature-compensated modulation signal being input to the non-inverting input of the differential amplifier, and the second feedback signal being input to the inverting input of the differential amplifier to generate an error voltage from the difference between the two signals, the error voltage being fed to the electroabsorption modulator (EAM) driver.

11. The monolithic integrated electroabsorption modulated laser (EML) according to any one of claims 6 to 7, wherein the length of the conductive interconnect track between the electroabsorption modulator (EAM) drive and control circuit and the electroabsorption modulator (EAM) is in the range of micrometers to tens of micrometers to reduce timing delay and phase delay.

12. The monolithic integrated electro-absorption modulated laser (EML) according to any one of claims 1 to 2 and 5 to 7, wherein the distributed feedback (DFB) laser is a vertically coupled surface etched grating distributed feedback (VC SEG DFB) laser.

13. The monolithic integrated electroabsorption modulated laser (EML) according to any one of claims 1 to 2 and 5 to 7, wherein the epitaxial layer structure is compatible with a single epitaxial growth process.

14. The monolithic integrated electroabsorption modulated laser (EML) according to any one of claims 1 to 2 and 5 to 7, wherein it is made of III-V semiconductor material.

15. The monolithic integrated electroabsorption modulated laser (EML) according to any one of claims 1 to 2 and 5 to 7, which is manufactured using an InP-based material system comprising selected binary, ternary, and quaternary compositions of In, Ga, As, P, and Al.

16. The monolithically integrated electro-absorption modulated laser (EML) according to claim 15, wherein, The semi-insulating substrate is Fe-doped InP.

17. A method for manufacturing a monolithically integrated electroabsorption modulated laser (EML) according to any one of claims 1 to 16, wherein the distributed feedback (DFB) laser is vertically integrated with the electroabsorption modulator (EAM) via a transversely tapered vertical optical coupler, comprising: Provides a semi-insulating (SI) substrate; An epitaxial layer structure is grown on the semi-insulating substrate. The epitaxial layer structure includes multiple vertically stacked optical waveguides, wherein: The first-stage waveguide consists of layers with a passive output waveguide structure; The second-stage waveguide includes a layer with an electro-absorption modulator (EAM) waveguide structure; The third-level waveguide includes a layer with a distributed feedback (DFB) laser waveguide structure; The patterned layer of the third-level waveguide is used to define a laser mesa, which includes a distributed feedback (DFB) laser cavity with a surface etched grating (SEG) and a first transverse tapered vertical optical coupler extending from the optical output of the laser cavity. The patterned layer of the second-stage waveguide is used to define the mesa of the electro-absorption modulator (EAM) and a second transverse tapered vertical optical coupler extending from the optical output of the electro-absorption modulator (EAM). The patterning layer of the first-stage waveguide is used to define the passive output waveguide; The distributed feedback (DFB) laser cavity is laterally separated from the electroabsorption modulator (EAM) along the light propagation direction, and the first lateral tapered vertical optical coupler is configured to couple the emitted light mode from the distributed feedback (DFB) laser cavity to the input of the electroabsorption modulator (EAM). The second transverse tapered vertical optical coupler is configured to vertically couple the modulated output from the electroabsorption modulator (EAM) to the passive output waveguide; A first electrical connection is provided to a distributed feedback (DFB) laser to operate the DFB laser in continuous wave mode, and a second electrical connection is provided to an electroabsorption modulator (EAM) to drive the EAM. and An additional layer is disposed between the semi-insulating substrate and the plurality of vertically stacked optical waveguides, the additional layer including a layer for forming electronic circuitry for at least the electro-absorption modulator (EAM).

18. The method according to claim 17, wherein, The additional layer provided for forming electronic circuitry includes forming electronic circuitry for the distributed feedback (DFB) laser.

19. The method according to any one of claims 17 to 18, further comprising configuring the additional layer as a plurality of semiconductor layers for electronic circuitry located below the plurality of vertically stacked optical waveguides, the semiconductor layers for electronic circuitry being vertically separated from the plurality of vertically stacked optical waveguides by at least one spacer layer; An optical assembly including the distributed feedback (DFB) laser waveguide, the electro-absorption modulator (EAM) waveguide, the output waveguide, and the transverse tapered vertical optical coupler is formed on a first region of the semi-insulating substrate. The electronic circuit is formed on a second region adjacent to the first region on the semi-insulating substrate, including the removal of the at least one spacer layer and the semiconductor layer of the epitaxial stack of all capping layers; and Interconnect metallization is provided for electrical interconnection between the electronic circuit and a first electrical connection of the distributed feedback (DFB) laser and a second electrical connection of the electroabsorption modulator (EAM) to operate the distributed feedback (DFB) laser and drive the electroabsorption modulator (EAM).

20. The method of claim 19, wherein the monolithically integrated electro-absorption modulated laser (EML) further comprises a vertically integrated spot size converter (SSC) for coupling the optical output of the monolithically integrated electro-absorption modulated laser (EML) to a single-mode fiber, comprising: After growing the first plurality of semiconductor layers for manufacturing electronic circuits and at least one spacer layer including selectively etched stops, and before growing the capping layer structure of the capping layer epitaxial layer, Deep trenches are etched through the first plurality of semiconductor layers and at least one spacer layer including a selective etching stop, and etched into the underlying substrate. Grown within a deep trench epitaxial layer of a spot size converter (SSC); The patterning of the first-stage waveguide used to define the output waveguide also includes defining a third transverse tapered vertical optical coupler to couple the optical output from the passive output waveguide to a spot size converter (SSC).

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