Heterogeneous integrated DFB laser with single lateral mode

Abstract

The invention relates to a heterogeneous integrated DFB laser with a single lateral mode. The DFB laser includes a semiconductor structure having a laser active region and a grating etched on a bonding surface for providing optical feedback to generate output light. The DFB laser includes a silicon structure having a silicon waveguide configured to receive output light from a first end of the laser active region. The bonding surface of the III-V semiconductor structure is bonded to the surface of the silicon structure. The silicon structure includes a DFB region having a surface defining at least two laterally separated silicon portions extending longitudinally and overlapping with two leaves of a second lateral mode of the output light in the laser active region with respect to a layering direction to suppress laser of a second order mode of the output light.

Description

Technical Field

[0001] The present disclosure relates generally to optical devices and, more particularly, to optical sources. Background Art

[0002] A tunable laser is a laser in which the wavelength of operation can be changed in a controlled manner using filters to output a target wavelength. The tuning value varies with temperature, and a complex control system may be required to keep the tunable laser aligned during operation. Fixed lasers are easier to control; however, they are difficult to implement in photonic integrated circuits (PICs) due to calibration issues, power issues, and process control issues (such as process variations exhibited in modern PIC fabrication techniques). Summary of the invention

[0003] A distributed feedback DFB laser comprises: a III-V semiconductor structure comprising: a laser active region having a first end and a second end offset from the first end in a longitudinal direction; and a grating etched on a bonding surface of the III-V semiconductor structure to provide optical feedback to the laser active region, thereby generating output light output from the active region; and a silicon structure comprising a silicon waveguide, the silicon waveguide being configured to receive the output light from the first end of the laser active region, the III-V semiconductor structure being bonded to the silicon structure so that the bonding surface is bonded to a surface of the silicon structure, the silicon structure further comprising: a DFB region comprising a surface of the silicon structure defining at least two laterally separated silicon portions, the at least two laterally separated silicon portions extending in the longitudinal direction and overlapping with two lobes of a second transverse mode of the output light in the laser active region with respect to a layering direction perpendicular to the longitudinal direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The following description includes a discussion of the accompanying drawings, which have diagrams given by examples of implementation methods of embodiments of the present disclosure. The accompanying drawings should be understood by way of example rather than by way of limitation. As used herein, at least in some cases, reference to one or more "examples" or "embodiments" should be understood as describing a specific feature, structure or characteristic included in at least one implementation method of the inventive subject matter. Therefore, phrases such as "in one example", "in some examples", "in some embodiments", "in one embodiment" or "in an alternative embodiment" appearing herein describe various embodiments and implementation methods of the inventive subject matter, and may not all refer to the same embodiment. However, they are not necessarily mutually exclusive. In order to simply identify the discussion of any particular element or action, the most important number or multiple digits in the figure mark can refer to the figure ("FIG.") mark that first introduces the element or action.

[0005] Figure 1Illustrated is a top plan view of a single waveguide design for a DFB laser architecture, according to some examples.

[0006] Figure 2 A single waveguide design for a DFB laser architecture according to some examples is illustrated by Figure 1 Front section view of line AA.

[0007] Figure 3 Illustrated is a simplified side view of an example optoelectronic device incorporating a DFB laser, according to some examples.

[0008] Figure 4 FIG. 1 illustrates a method for illustrating light propagation according to some examples. Figure 1 Side view of the single-waveguide design of the DFB laser architecture.

[0009] Figure 5 FIG. 1 illustrates a method for illustrating light propagation according to some examples. Figure 1 Side view of an asymmetric version of the single-waveguide design of the DFB laser architecture.

[0010] Figure 6 Illustrated is a top plan view of a double-rib design for a DFB laser architecture, according to some examples.

[0011] Figure 7 A dual rib design for a DFB laser architecture according to some examples is illustrated. Figure 6 Front section view of line AA.

[0012] Figure 8 Illustrated is a top plan view of a three-rib design for a DFB laser architecture, according to some examples.

[0013] Fig. 9 Illustrated is a top plan view of a narrow trench design for a DFB laser architecture, according to some examples.

[0014] Fig.10 FIG. 1 illustrates a non-absorber region of a narrow trench design for a DFB laser architecture according to some examples. Fig. 9 Front section view of line AA.

[0015] Fig.11 FIG. 1 illustrates a narrow trench absorber region for a narrow trench design for a DFB laser architecture according to some examples. Fig. 9 Front cross-sectional view of line BB.

[0016] Fig.12 A flow chart showing operations of a method of manufacturing a DFB laser is illustrated, according to some examples.

[0017] The following description of certain details and implementation methods includes a description of the accompanying drawings, which may depict some or all of the embodiments described below, and discuss other potential embodiments or implementation methods of the inventive concepts presented herein. An overview of the embodiments of the present disclosure is provided below, followed by a more detailed description with reference to the accompanying drawings. DETAILED DESCRIPTION

[0018] In the following description, for the purpose of explanation, a large number of specific details are set forth to provide an understanding of various embodiments of the inventive subject matter. However, it will be apparent to those skilled in the art that embodiments of the inventive subject matter may be practiced without these specific details. In general, it is not necessary to show known instruction examples, structures, and techniques in detail.

[0019] As described above, the PIC may implement a tunable laser, where the laser can be tuned to output light of different wavelengths. In some examples, the tunable laser may implement one or more optical filters to obtain a target wavelength for the optical system. The tuning value may vary with different temperatures, which may require a fast control loop integrated close to the PIC to ensure that the tuner is aligned during operation.

[0020] In contrast, fixed wavelength silicon photonic lasers with distributed feedback (DFB) can be configured in a PIC so that wavelength calibration is not required, which can reduce calibration costs and can further allow faster block startup times, thus reducing power consumption and simplifying laser control. DFB lasers can be implemented as integrated PIC lasers, where the laser resonator includes a periodic structure in the laser gain medium that acts as a distributed Bragg reflector in the wavelength range of laser action.

[0021] In addition to fixed wavelength lasers, DFB technology can also be combined with other laser designs including high power lasers, isolator-less lasers, and rapidly tunable lasers.

[0022] Conventional non-silicon photonic DFB lasers, which have been widely used for decades, use anti-reflection (AR) and high-reflection (HR) coatings on the laser structure facets to achieve higher power efficiency. However, these facet coatings are associated with laser reliability issues such as catastrophic optical mirror damage (COMD).

[0023] Designs for silicon photonic DFB lasers with gratings built into III-V epitaxial structures and laser output light coupled into silicon by evanescent coupling are described in U.S. patent application Ser. No. 17 / 736,490, filed May 4, 2022, and named by inventors Antonio Labaro, Erik Norberg, Hanxing Shi, and HanYun (hereinafter “Original III-V DFB Laser Applications”), which is incorporated herein by reference in its entirety. Some of the designs described herein take advantage of DFB epitaxial growth and heterogeneous integration to avoid facet coatings, potentially achieving power efficiencies similar to conventional non-silicon photonic DFB lasers.

[0024] The examples described herein include techniques for achieving a single transverse mode in a heterogeneously integrated DFB laser. Single-mode operation can be beneficial for telecommunications, data communications, and many other applications such as light detection and ranging (LiDAR). In the case where single-mode operation cannot be achieved, the DFB laser can generate higher-order modes in the transverse direction in the laser chamber, which generally cannot be coupled into a silicon waveguide and thus reduce the efficiency of the laser.

[0025] Accordingly, the examples described herein may attempt to address one or more technical problems related to achieving a single transverse mode in a heterogeneous integrated laser, such as a DFB laser, a discrete mode (DM) laser, a distributed Bragg reflector (DBR) laser, an optical amplifier, an optical modulator, or a tunable laser requiring single mode control along a transverse direction.

[0026] Figure 1 A top view of a single waveguide design 100 for a DFB laser architecture is shown. The single waveguide design 100 is an example of a DFB laser design according to the disclosure of the original III-V DFB laser application cited above. Figures 1 to 5 The principles and techniques of DFB lasers fabricated in III-V structures for silicon photonic devices as originally disclosed in the III-V DFB laser application are illustrated. Figures 6 to 12 Then the technique for realizing a single transverse mode in a heterogeneous integrated DFB laser is illustrated. It should be understood that Figures 6 to 12 An example can be based on Figures 1 to 5 Similar principles to the single waveguide design 100 (such as Figure 4 and Figure 5 The general propagation of light shown in , and reference Figure 1 and Figure 2 The preparation technique described herein) was performed.

[0027] Figure 1The view is along the Z dimension, defining the layering direction for epitaxial growth of the stacked and / or DFB laser architecture. The longitudinal direction 120 (along the X dimension) and the transverse direction 122 (along the Y dimension) are perpendicular to each other and perpendicular to the layering direction, which define the visible dimensions of the illustrated device. The dimensions of the devices described herein may be marked in micrometers (um) and / or nanometers (nm).

[0028] The single waveguide structure 100 includes a III-V structure 104 (e.g., a III-V semiconductor structure, a III-V epitaxial die, a III-V wafer) bonded to the top side (as defined by the Z dimension) of a silicon structure 102 including a silicon waveguide. Figure 2 As further described, the silicon structure 102 may be a silicon wafer (such as a silicon on insulator (SOI) device). The silicon waveguide defines a silicon rib 110 extending downward from the center of the device along a longitudinal direction 120, and the silicon rib 110 extends upward (in the layered direction, in the Figure 1 The trench 106 may be formed in a dielectric material such as SiO2, SiN, or Al2O3.

[0029] Silicon ribs 110 efficiently receive light output coupled from III-V structure 104. III-V structure 104 generates light using gain material in a laser active region (e.g., a light radiating multiple quantum well (MQW) region) of III-V structure 104. In some examples, the output light is generated by the laser active region (which may be coupled to a laser beam) Figure 1 The grating 116 and the DFB region 114 shown in the figure partially or completely overlap and propagate from the laser active region, and propagate from the left and right ends of the laser active region to the two semiconductor optical amplifier (SOA) regions (SOA regions 112) of the III-V structure 104. The SOA regions 112 of the III-V structure 104 couple the light from the III-V structure 104 to the silicon waveguide of the silicon structure 102 via the taper, which is formed in the taper region of the silicon rib 110 below each SOA region 112. Reference will be made to Figure 4 and Figure 5 This propagation and decoupling of the output light generated by the laser active region is described in further detail.

[0030] In the single waveguide design 100, the tapered region 118 tapers the silicon rib 110 to a narrow width segment extending along the DFB region 114 (e.g., from 2um to ~0.5um or less, such as 0.3um) to minimize coupling from the III-V structure 104 to the silicon structure 102 along this segment (e.g., within the laser active region of the III-V structure 104). Minimizing the decoupling of light within the DFB region 114 keeps the output light reflection within the III-V material so that the mode is fully distributed inside the laser active region of the III-V structure 104, thereby maximizing modal gain and power efficiency. It should be understood that a modified version of this behavior of the single waveguide design 100 can be exhibited by the single transverse mode designs described herein, such as Figure 6 and Figure 7 The double rib design shown in 600 and Figures 9 to 11 The narrow trench design 900 shown in FIG. The designs described below can similarly minimize decoupling within the central DFB while using different distributions of ribs and trenches defined by the silicon structure to further minimize the generation of second and higher order lateral modes of the output light by the laser active region.

[0031] Figure 1 The top view of the grating 116 shows the teeth or lines of the grating 116 as grating lines 108. As described below, the grating 116 can be formed in the surface of the III-V structure 104 before the III-V structure 104 is bonded to the silicon structure 102. The grating 116 is formed along the longitudinal direction 120 of the DFB region 114 (e.g., below the laser active region of the III-V structure 104), and it terminates at each SOA region 112, so that the mode selection of the output light from the laser active region is completed via the grating 116 within the DFB region 114 (e.g., the grating 116 provides optical feedback so that the multi-mode light originally generated by the gain material is instead generated as dual-mode or single-mode light). In some examples, the grating 116 extends outside the DFB region 114 (e.g., partially extends into the SOA region 112 of the III-V structure 104), thereby increasing the reflectivity of the cavity or otherwise modifying the coupling of light.

[0032] In some examples, a quarter wave shift (QWS) feature 128 is formed in the middle portion of the grating 116 (e.g., by changing the grating comb tooth spacing to add a peak) to generate a symmetrical cavity to improve mode selection (e.g., from dual-mode light to single-mode light, light at a fixed wavelength), thereby symmetrically providing light from each end of the DFB region 114, thereby providing a symmetrical DFB laser. Figure 5), an asymmetric DFB laser can be formed by placing the QWS feature toward one end of the cavity of the DFB region 114. In some examples, the grating is configured as an adiabatic chirped grating or a non-uniform grating, which can be configured according to a given design to further adjust the mode and power fraction toward one longitudinal end of the DFB region 114. In some example embodiments, the DFB laser with the grating in the III-V structure 104 is a distributed phase-delayed DFB laser. In some examples of implementing a symmetric DFB laser (e.g., with an intermediate QWS feature 128), a reflector can be integrated in the silicon waveguide to reflect half of the light from one longitudinal end port of the silicon waveguide to the other longitudinal end port, thereby maximizing the output from the other longitudinal end port.

[0033] Down Fig.12 An example method for fabricating a DFB laser is shown, which is potentially applicable to manufacturing a single waveguide design 100, a dual rib design 600, a narrow trench design 900, and other possible designs of DFB laser architectures.

[0034] Figure 2 A single waveguide design 100 for a DFB laser architecture is shown. Figure 1 It should be understood that Figure 2 The lateral dimensions of the various layers of the stack shown in FIG. Figure 1 Dimensional alignment of overlapping layers shown in the plan view (this can also be applied to Figure 6 , Figure 8 and Fig. 9 The relationship between the plan view and its corresponding front section view). Figure 2 The layers are shown stacked in a layering direction 124 .

[0035] The layer stack forms the silicon structure 102 from bottom to top with respect to the layering direction 124: silicon substrate 216, silicon oxide 214, silicon device layer 212, and dielectric bonding layer 210. The layer stack forms the III-V structure 104 again from bottom to top with respect to the layering direction 124: n-type material 208 (with grating 116 formed on or in its bottom surface), laser active region 202, and p-type material 206.

[0036] therefore Figure 1 and Figure 2The single waveguide design 100 shown in is formed of both silicon material and non-silicon material. In this example, the non-silicon material (alternatively referred to as "heterogeneous material") is a III-V material, but it should be understood that the techniques and DFB architecture designs described herein are also applicable to devices in which the non-silicon heterogeneous material is a magneto-optical (MO) material or a crystalline substrate material. III-V semiconductors have elements found in Group III and Group V of the periodic table (e.g., indium gallium arsenic phosphide (InGaAsP), indium gallium arsenide nitride (GaInAsN), aluminum indium gallium arsenide (AlInGaAs)). The carrier dispersion effect of III-V based materials can be significantly higher than that in silicon based materials because the electron speed in III-V semiconductors is much faster than that in silicon. In addition, III-V materials have a direct band gap, which allows efficient generation of light from an electrical pump. Therefore, III-V semiconductor materials can perform photonic operations with higher efficiency than silicon for generating light and modulating the refractive index of light. As a result, III-V semiconductor materials are able to perform photonic operations with greater efficiency, generating light from electrical energy and converting light back into electrical energy.

[0037] Thus, in some examples of hetero-optical devices described herein, the low optical losses and high quality oxidation of silicon are combined with the electro-optical efficiency of III-V semiconductors; in some examples, the hetero-optical devices utilize low-loss hetero-optical waveguides to transition between heterogeneous and pure silicon waveguides in the device.

[0038] Magneto-optical (MO) materials allow heterogeneous PICs to operate based on the MO effect. Such devices can exploit the Faraday effect, where a magnetic field associated with an electrical signal modulates a light beam, providing an electric field that modulates and rotates the optical mode with high bandwidth, realizing an optical isolator. The MO material may include, for example, materials such as iron, cobalt, or yttrium iron garnet (YIG). Furthermore, in some example embodiments, a crystalline substrate material provides a heterogeneous PIC with high electromechanical coupling, linear electro-optic coefficient, low transmission loss, and stable physicochemical properties. The crystalline substrate material may include, for example, lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

[0039] The following references Fig.12 The method describes the formation of a silicon structure 102 and a III-V structure 104, and combining them together to prepare Figure 2 The stacked single waveguide design 100 is shown in FIG.

[0040] Figure 3A simplified side view of an example optoelectronic device 300 incorporating a DFB laser according to various examples described herein is illustrated. In some examples, a DFB laser described herein (e.g., a single waveguide design 100, a dual rib design 600, or a narrow groove design 900 DFB laser) can be fabricated as a PIC 310 or a portion thereof. The PIC 310 can thus be incorporated into an optoelectronic device 300, which can include other components such as a printed circuit board (PCB) substrate (shown as PCB 302), an organic substrate 304 mounted to a top surface of the PCB 302, and an application specific integrated circuit (ASIC 308) mounted to a top surface of the organic substrate 304. The PIC 310 incorporating a DFB laser can also be mounted to a top surface of the organic substrate 304 (where “top” can be defined with respect to the layering direction 124).

[0041] In some examples, PIC 310 (e.g., a DFB laser device according to single waveguide design 100 or other designs described herein) can exchange light with an external light source 312 via an optical fiber 314, in which the top side of PIC 310 is connected to organic substrate 304 in a flip-chip configuration, and the light propagates outward (or inward) from the bottom side of PIC 310 away from organic substrate 304 (e.g., toward a coupler). According to some examples, optical fiber 314 can be coupled to PIC 310 using a prism, grating, or lens. Control circuitry included in ASIC 308 at least partially controls optical components (e.g., optical modulators, optical switches) of PIC 310. Both ASIC 308 and PIC 310 are shown as being placed on copper pillars 316, which are used to communicatively couple ASIC 308 and PIC 310 via organic substrate 304. PCB 302 is coupled to organic substrate 304 via ball grid array (BGA) interconnects (BGA interconnects 306) and may be used to interconnect organic substrate 304 (and thus ASIC 308 and PIC 310) to other components of optoelectronic device 300 (eg, interconnect blocks, power supplies, etc.) not shown.

[0042] Figure 4 The diagram shows the Figure 1 A side view of a single waveguide design 100 of a symmetric version of a DFB laser architecture showing symmetric light propagation during operation.

[0043] like Figure 4As shown in , according to some examples, a grating 116 is formed in a III-V structure 104, which is then flipped and bonded to a silicon structure 102 (e.g., in a flip-chip configuration). In addition, a DFB electrode 408 applies a current (e.g., a feed-forward bias) to generate output light (e.g., single-mode light from a QWS feature 128 in the grating 116, shown as DFB region light 402), and an SOA electrode 410 is configured to further amplify the light, which is then evanescently coupled (shown as output coupled light 404) to a tapered portion of a silicon rib 110 of a silicon waveguide. The light can then propagate through the silicon waveguide and into other components of the device (e.g., a PIC 310 or a device in optical communication therewith), shown as waveguide light 406. In some examples, the SOA electrode 410 is a local electrode or can be omitted from the single waveguide design 100.

[0044] Simulations of the decoupling of light from the III-V structure 104 to the silicon structure 102 of the single waveguide design 100 indicate that some versions of the single waveguide design 100 may cause the generation of second or higher order light. Versions of the single waveguide design 100 were simulated using a light wavelength of 1310 nm. The simulated single waveguide design 100 had a III-V structure 104 with a ridge of p-type material 206 of 2.7 um wide, a grating 116 etched to a depth of 17.5 nm, and a 0.3 um silicon rib 110 in a narrow portion below the DFB region 114. (It should be understood that while the wavelength was 1310 nm in this simulation example, the single waveguide design 100 and other designs described herein can be applied to any other light wavelength.)

[0045] In the single waveguide design 100, the fundamental mode of the output light generated by the laser active region is also called the first transverse mode or the first-order transverse mode, which is mainly confined in the DFB region 114 of the III-V structure 104 to obtain sufficient material gain to emit laser light. A small part of the fundamental mode light reaches the grating 116 to achieve sufficient coupling and resonate along the longitudinal cavity of the DFB laser. The grating pitch and the effective index of the mode define the resonant wavelength of this light.

[0046] This mode of light is then coupled from the III-V structure 104 via tapered ribs in the SOA region 112 adjacent the end of the DFB chamber into a silicon waveguide, which is designed (in this example) to have a narrow operating window of approximately 1310 nm.

[0047] In this simulation example, a second-order transverse mode with two symmetrical lobes may exist and resonate at 1300.5 nm, which may be within the gain spectrum of the epitaxially grown III-V material of the laser. Therefore, this second-order mode light may emit laser light at 1300.5 nm within the III-V DFB region 114 confined by the grating 116. A small portion of this second-order mode may still be coupled into the silicon waveguide via the tapered output of the silicon ribs 110 in the SOA region 112, which are designed to couple the fundamental mode at 1310 nm wavelength light. The second-order light at the output of the laser results in a poor side mode suppression ratio (SMSR), which is a serious performance impairment for single-mode optical data communication applications, where the laser is only single wavelength. The second-order light also potentially causes reduced efficiency and / or reliability risks for the laser. Accordingly, it may be beneficial to provide an alternative design of the silicon structure 102 to avoid laser emission of second-order and / or higher-order transverse modes of the output light.

[0048] One potential implementation method to achieve single-mode operation is to further narrow the width of the ridge of the p-type material 206 along the lateral direction 122. According to simulation data, if the ridge of the p-type material 206 is narrowed from 2.7um to 2.0um, the second transverse mode has a resonant wavelength at 1291.84nm, which is shorter than the fundamental mode by >15nm, so the chance of second-order light laser emission decreases. If the width of the p-type material 206 is further reduced to 1.7um, the second transverse mode is blue-shifted by more than 5nm, making it impossible for light in this mode to laser at high transmission. However, low transmission operation of the laser may still pose a risk of generating second transverse mode light. In addition, narrowing the ridge of the p-type material 206 may cause challenges to reliability and / or manufacturing in the SOIDFB laser range.

[0049] The following references Figure 6 The double rib design shown in 600 and Fig. 9 The narrow trench design 900 shown in illustrative embodiments depicts two other examples of designs for single transverse mode operation. In some examples, these other designs may provide greater benefits than reducing the width of the p-type material 206 ridges.

[0050] Figure 5 A side view of an asymmetric version of the single waveguide design 100 (asymmetric design 500) is illustrated, showing asymmetric light propagation during operation. In the illustrated example, the asymmetric design 500 includes only a single SOA region 112, and the grating 116 is configured with an asymmetric QWS feature 502 that is offset from the center of the DFB region 114, as described above.

[0051] Figure 6A top view of a double rib design 600 for a DFB laser architecture is shown. In some examples, the double rib design 600 can enable single transverse mode operation for a DFB laser by suppressing a second order transverse mode to avoid lasing.

[0052] Figure 1 The lateral direction 122 is shown here as a first lateral direction 608 , and the opposite direction thereof is identified as a second lateral direction 610 .

[0053] While the first lateral mode of the output light is concentrated within the III-V structure 104 along the lateral centerline 614 of the DFB region 114, the second lateral mode of the output light is concentrated within the III-V structure 104 in two lateral lobes to the sides of the DFB region 114, shown as second mode lobes 804. The exact locations of these second mode lobes 804 are generally used as the dimensions of the III-V structure 104 and the wavelength of light generated by the laser active region 202.

[0054] Therefore, in order to minimize the generation of the second-order transverse mode in the III-V structure 104, the silicon structure 102 may include two laterally separated silicon portions that are located below the location of the second mode lobe 804 (e.g., at least partially overlapped along the layering direction 124) and extend longitudinally (e.g., in the longitudinal direction 120 or opposite to the longitudinal direction 120). These laterally separated silicon portions may effectively increase the mode confinement of the second transverse mode of the output light within the silicon structure 102. Thus, the number of the second transverse modes of the output light trapped within the III-V structure 104 is reduced.

[0055] In the illustrated double rib design 600, two laterally separated silicon portions of the silicon structure 102 are formed as two parallel ribs 602 with a high refractive index, which are located directly below the second mode lobe 804 (with respect to the layering direction 124). These parallel ribs 602 serve to couple the second transverse mode of the output light from the III-V structure 104 into the silicon structure 102, potentially reducing the optical modal gain (lower MQW mode confinement) and the grating efficiency. As a result, the second transverse mode of the output light will be suppressed within the DFB region 114 of the III-V structure 104, which experiences a lower modal gain due to the coupling away from the laser active region 202 (e.g., opposite to the layering direction 124). In addition, the second transverse mode of the output light will be less disturbed by the grating 116 and therefore experience a weaker reflection along the grating 116, which avoids the III-V structure 104 from acting as a resonant cavity for the second transverse mode of the output light. As described above, these factors make it unlikely that the second-order mode will compete with the first-order mode of light and lase, and thus the second-order mode can be effectively suppressed, making it less likely to cause reduced laser efficiency, reduced side mode suppression ratio, and / or reliability risks.

[0056] In some examples, the lateral positions of the two parallel ribs 602 within the DFB region 114 are selected based on the wavelength of the output light and the dimensions of the device at or near the center of the second mode leaf 804. As described above, the parallel ribs 602 are laterally separated by a central trench 604 that can be filled with a gas or dielectric material. Two lateral trenches 606 extend from the outer lateral sides of the parallel ribs 602 to at least the edge of the ridge of p-type material 206; these lateral trenches 606 can also be filled with a gas or dielectric material.

[0057] The SOA region 112 of the double rib design 600 includes a tapered waveguide portion 612 that is similar to the silicon rib 110 of the single waveguide design 100 within the tapered region 118. However, in some examples of the double rib design 600, the tapered waveguide portion 612 may taper continuously from the distal longitudinal edge of the SOA region 112 until it ends at the proximal longitudinal edge. Figure 6 As shown in , in some examples, the tapered waveguide portion 612 extends longitudinally outward from the SOA region 112 into a portion of the DFB region 114 such that a portion of the tapered waveguide portion 612 overlaps the grating 116 .

[0058] In a first example, as described above with reference to the first simulation example single waveguide design 100, the double rib design 600 uses a ridge of p-type material 206 in the III-V structure 104, which has a width of 2.7um. Each parallel rib 602 in the DFB region 114 has a lateral width of 0.54um, and the lateral distance from each parallel rib 602 to the lateral edge of the ridge of p-type material 206 occupied by the lateral groove 606 is 0.06um. The central rib in each SOA region 112 has a lateral width of 2.0um at its widest point (at the far end of the SOA region 112 from the DFB region 114), which tapers to a width of 0um at 20um longitudinally within the DFB region 114. In simulations, the design has been demonstrated to suppress second-order mode output light having a wavelength of 1310nm, such that the confinement of the second lateral mode of the output light within the MQW forming the laser active region 202 is reduced to about 6%. At the same time, the first-order mode of light maintains about 10% confinement in the MQW and keeps lasing.

[0059] Figure 7 The double rib design 600 through Figure 61. A front cross-sectional view of line AA of the III-V structure 104. Two symmetrical second mode lobes 804 are shown within the III-V structure, and two parallel ribs 602 are located below the centerline of these lobes. In operation, the parallel ribs 602 effectively couple a high proportion of the second transverse mode of the output light downward (e.g., opposite to the layering direction 124) into the parallel ribs 602 of the silicon structure 102, thereby preventing this light from lasing from within the DFB region 114 of the III-V structure 104. Therefore, it should be understood that in at least some examples, the dual-rib design 600 effectively shifts the position of the second mode lobe 804 downward, at least partially into the parallel ribs 602; Figure 7 The second mode lobe 804 shown in represents the position of the second mode lobe 804 in the absence of this output coupling effect.

[0060] The following references Figures 8 to 11 Additional designs for outcoupling a second lateral mode of the output light are described.

[0061] Figure 8 A top plan view of a triple rib design 800 for a DFB laser architecture is illustrated. The triple rib design 800 differs from the double rib design 600 in that a central third rib 802 is added down the lateral centerline 614 of the DFB region 114. The third rib 802 is thus continuous with the tapered waveguide portion 612. In this respect, the triple rib design 800 is similar to some aspects of the single waveguide design 100, which adds two parallel ribs 602 that are laterally separated from and also parallel to the third rib 802. A pair of intermediate grooves 806 laterally separate the third rib 802 from the parallel ribs 602, which, like the other grooves described herein, can be filled with a gas or a dielectric material.

[0062] In a first example, the triple rib design 800 has the same dimensions as the example double rib design 600 described above, where the lateral width of the third rib 802 is 0.3 um.

[0063] Fig. 9 A top view of a narrow trench design 900 for a DFB laser architecture is shown. Similar to the double rib design 600 and the triple rib design 800, the narrow trench design 900 can also achieve single transverse mode operation for a DFB laser by suppressing the second order transverse mode from lasing in some examples.

[0064] In the narrow trench design 900, two laterally separated silicon portions within the DFB region 114 are formed as plates 912 that extend at least to the lateral sides of the ridge of the p-type material 206. Similar to the parallel ribs 602 of the double-rib design 600 and the third rib 802 of the triple-rib design 800, these plates 912 are elevated and separated from each other by the trenches. The plates 912 can effectively convert well-confined second-order or higher-order modes into lossy or leaky plate modes, avoiding lasing of these modes. The second lateral mode of the second output light does not appear as a well-confined mode within the III-V structure 104, but can appear as a leaky mode within the plate 912, whose resonant tail penetrates the silicon structure 102 without termination.

[0065] In the narrow trench design 900, the trench is a relatively narrow DFB trench 904 centered about the transverse centerline 614, such that the plate 912 is located below the second mode lobe 804. In some examples of the narrow trench design 900, the DFB region 114 can be considered to be the longitudinal length of the extended grating 116, and the SOA region 112 can be considered to be the remaining longitudinal portion of the III-V structure 104. In some examples, the DFB trench 904 does not extend the entire length of the grating 116; instead, the longitudinal span of the DFB trench 904 can be referred to as a narrow trench absorber region 906, which is bounded on both sides along the longitudinal direction 120 by two non-absorber regions 908 that largely overlap the SOA region 112.

[0066] Each non-absorber region 908 includes other portions of a plate 912 that taper for at least a portion of its length toward the outer lateral edges of the III-V structure 104. These portions of the plate 912 define the outer lateral edges of the two SOA trenches 902. Similar to the silicon ribs 110 of the single waveguide design 100, between the two SOA trenches 902 is a tapered waveguide portion 910 that extends longitudinally along the lateral centerline 614 and tapers within the tapered region 118 to narrow near the DFB region 114 and widen near the outer longitudinal ends of the SOA region 112.

[0067] Due to the tapered waveguide portion 612 with the double rib design 600 and the triple rib design 800, the tapered waveguide portion 910 can extend into the DFB region 114 such that it overlaps a portion of the grating 116. The longitudinal span of the tapered waveguide portion 910 can be considered to define the non-absorber region 908; the longitudinal location where the tapered waveguide portion 910 ends (e.g., tapers to zero width) and the DFB trench 904 can be referred to as the end of the non-absorber region 908 and the beginning of the narrow trench absorber region 906.

[0068] In some examples, two SOA trenches 902 are continuous with the DFB trench 904. The inward widening of portions of the plate 912 and the inward tapering of the tapered waveguide portion 910 can cause each SOA trench 902 to taper to a narrower portion that overlaps the grating 116. These narrower portions of the SOA trenches 902 are connected to the DFB trenches 904.

[0069] The illustrated example narrow groove design 900 has a central DFB groove 904. However, similar to the silicon rib 110 of the single waveguide design 100 or the third rib 802 of the triple rib design 800, in some examples, the waveguide of the narrow groove design 900 may include another narrow rib (not shown) extending downward from the transverse centerline 614 in the middle of the DFB groove 904 and continuous with the tapered waveguide portion 910.

[0070] In the first example, the narrow groove design 900 has a DFB groove 904 with a lateral width of 1.7um. The tapered waveguide portion 910 in each SOA region 112 has a lateral width of 2.0um at its widest point (at the far end of the SOA region 112 from the DFB region 114), ends at a length of 20um longitudinally below the grating 116, and tapers to a width of 0um. The two SOA grooves 902 are each 1.75um wide at the far end of the SOA region 112 from the DFB region 114.

[0071] In simulations, this design has been demonstrated to increase the modal loss of second order mode output light having a wavelength of 1310 nm, where simulated widths of the DFB trench 904 ranging from approximately 1.5 um to 2 um result in a first order mode to second order mode modal loss ratio ranging from approximately 2 to 3.

[0072] In some examples, narrow trench design 900 may exhibit various trade-offs with respect to dual-rib design 600 and / or triple-rib design 800. In some cases, the modal loss ratio of narrow trench design 900 may not be as favorable as the modal loss ratio of dual-rib design 600 or triple-rib design 800; however, narrow trench design 900 may use more silicon in silicon structure 102 (because the size of plate 912 is relatively large), thereby improving thermal performance.

[0073] Fig.10 The non-absorber region 908 of the narrow groove design 900 is shown by Fig. 9 The figure shows two SOA trenches 902, a tapered waveguide portion 910 and other portions of the plate 912 within the non-absorber region 908.

[0074] Fig.11 The narrow groove absorber region 906 of the narrow groove design 900 is shown by Fig. 9BB. The figure shows the DFB trench 904 located between two plates 912. The centralmost portion of each plate 912 is located below the center of the corresponding second mode lobe 804 in the III-V structure 104; each plate extends laterally from the centralmost position below the center of the corresponding second mode lobe 804 to a lateral position at the far lateral edge of the structure ( Fig.11 left or right edge of the Figure 7 , the position of the second mode lobe 804 shown in the figure represents the position of the second mode lobe 804 in the absence of the output coupling effect of the plate 912: in at least some examples, the second mode is not present at all, but is replaced by a lossy or leakage plate mode that is at least partially located within the plate 912.

[0075] Fig.12 Operations of a method 1200 for manufacturing a DFB laser having a single transverse mode, such as a single transverse mode DFB laser according to the double rib design 600 or the narrow groove design 900, are shown. Although the example method 1200 depicts a particular order of operations, the order may be changed without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different order that does not significantly affect the functionality of the method 1200. In other examples, different components of an example device or system implementing the method 1200 may perform functions substantially simultaneously or in a particular order.

[0076] According to some examples, method 1200 includes forming a III-V semiconductor structure (e.g., III-V structure 104) by growth at operation 1202. For example, a III-V wafer including one or more layers of InP, GaAs, AlAs, or InAs is partially grown (e.g., using a III-V epitaxial growth fabrication process) to form p-type material 206, laser active region 202, and n-type material 208.

[0077] According to some examples, method 1200 includes etching grating 116 in III-V structure 104 at operation 1204. For example, DFB region 114 grating 116 is then patterned on the III-V structure (e.g., using nanoimprint or e-beam lithography, including wet and / or dry etching, on a top surface of n-type material 208).

[0078] According to some examples, method 1200 further includes: forming III-V structure 104 by regrowth at step 1206. In some examples, after patterning DFB grating 116 on III-V structure 104 (e.g., wet and / or dry etching), additional layers of III-V material are grown onto the etch. In other examples, grating 116 is a top surface grating and further regrowth above grating 116 does not occur; instead, as will be discussed in further detail below, a bonding surface of the top surface grating is bonded to a silicon wafer (e.g., silicon structure 102).

[0079] According to some examples, method 1200 includes filling the teeth of grating 116 (e.g., grating lines 108) at operation 1208. In some example embodiments, a dielectric bonding layer 210 (e.g., SiO2, SiN, or Al2O3) is added to the surface of the etched III-V structure 104 prior to bonding to improve bonding.

[0080] According to some examples, method 1200 includes: bonding the III-V structure 104 to the silicon structure 102 at operation 1210. In some example embodiments, the etched III-V structure 104 is bonded to the silicon structure 102 using plasma enhanced wafer bonding. For example, (1) a III-V epitaxial wafer is patterned with one or more DFB gratings 116 and alignment marks to align the III-V structure 104 on the silicon wafer; (2) the III-V epitaxial wafer is mounted face down on UV release tape and a singulation process is performed on the back side of the III-V epitaxial wafer to protect the front side surface (e.g., top surface grating, bonding side) from damage and contamination; and (3) each III-V epitaxial die is precisely bonded to a target SOI using the alignment marks so that the grating and laser active region 202 are placed above the narrow width of the silicon waveguide (e.g., overlapped in the layering direction) and the taper of the silicon waveguide is placed below the corresponding SOA region of the III-V die.

[0081] In some examples, micro transfer printing (uTP) is used to bond the etched III-V structure 104 to the silicon structure 102. For example, (1) a III-V epitaxial wafer is patterned with a DFB grating and alignment marks to align the III-V epitaxial structure on silicon; (2) the III-V epitaxial wafer is singulated into III-V epitaxial dies using a uTP process of etching and drilling; and (3) each III-V epitaxial die is precisely bonded to a target SOI using a uTP marking process.

[0082] In some examples, the etched III-V structure 104 is then cut into small rectangles (e.g., epitaxial dies) using alignment marks on the etched III-V structure 104 to align the cutting positions with the gratings. The etched III-V structure 104 (e.g., epitaxial dies) is then bonded to the SOI structure to form a bonded structure (e.g., multiple III-V structures 104 bonded to multiple silicon structures 102). In some examples, the bonded structure is then further processed to form additional circuit components, and vias and metal pads are integrated into the bonded structure to provide current and drive the DFB laser.

[0083] As mentioned above, although DFB lasers can have gratings fabricated in silicon waveguides, the fabrication process uses specialized lithography equipment to generate grating patterns with sufficiently small dimensions. Unfortunately, silicon foundries may not have lithography capabilities for grating fabrication and it generally requires a large capital investment in further equipment (e.g., deep UV lithography equipment). Further, the development time for Si grating processes can be long, and poor process repeatability remains a problem. In addition, moving production wafers out of the Si foundry to perform the grating step elsewhere increases cycle time and presents a risk of contamination.

[0084] Thus, in some examples described herein, the grating 116 is formed in the III-V structure 104 using III-V epitaxial growth (and optionally regrowth). In some example embodiments, the III-V epitaxial structure is first half-grown (at operation 1202), then the grating 116 is patterned and etched (at operation 1204), and the laser structure is completed by regrowth (at operation 1206) to embed the grating inside the material. In some example embodiments, the III-V layers are grown to specification and the top surface grating 116 is etched, and regrowth does not occur (e.g., the III-V epitaxial die is flip-chip bonded to SOI using the top surface so that the mode is adiabatically coupled to the silicon waveguide in the SOI), so operation 1206 is omitted. One advantage of forming the DFB grating 116 in the III-V structure 104 is that it enables parallelization of manufacturing processes between foundries: for example, between a III-V manufacturing facility that produces the III-V grating structure and a silicon wafer manufacturing facility to complete silicon wafer front-end processing. In addition, a DFB laser with a grating in a III-V structure avoids additional process steps at a silicon foundry outside of existing silicon photonics (SiPh) process flows (e.g., for designing silicon wafers). In this way, many Si foundries can be more prepared to manufacture DFB lasers using wafer bonding processes. For example, a given SiPh foundry may be configured for a silicon thickness of 500nm in an SOI wafer, while other SiPh foundries may be configured for a silicon thickness of 220nm; however, when the silicon is as thin as 220nm, it may be difficult or impossible to form a grating in a silicon wafer. Thus, forming the grating 116 in the III-V structure 104 may make the design and fabrication process insensitive to SOI thickness, which allows the examples described herein to be implemented on various SOI structures including 220 nm Si.

[0085] Although examples have been described as providing a DFB laser formed in a III-V semiconductor layer of a PIC, it should be understood that the techniques and designs described herein can be applicable to achieving a single lateral mode in various types of heterogeneous integrated lasers, such as DFB lasers, discrete mode (DM) lasers, distributed Bragg reflector (DBR) lasers, optical amplifiers, optical modulators, or tunable lasers that require single mode control in a lateral direction. The described designs can be applied to waveguides and silicon structures of optical devices that are used to output couple second-order mode light from various laser structures or other light sources. Thus, in some examples, a device can be provided that includes a silicon structure having a silicon waveguide configured to receive light from a first end of an active region of a light source. The active region of the light source is in contact with a surface of the silicon structure in a layered direction. The silicon structure includes a DFB region that overlaps at least partially with the active region with respect to the layered direction. The DFB region includes a surface of the silicon structure, the surface defining at least two laterally separated silicon portions, the at least two laterally separated silicon portions extending in a longitudinal direction perpendicular to the stratification direction and overlapping with two lobes of a second lateral mode of light in the active region with respect to the stratification direction. In some examples, the silicon structure also includes an SOA region offset from the DFB region in the longitudinal direction. The SOA region includes a surface of the silicon waveguide defining a tapered waveguide portion, the tapered waveguide portion increasing in lateral width in the longitudinal direction.

[0086] Other examples of such optical devices may include features and combinations or sub-combinations of features of the various examples described herein.

[0087] In view of the above disclosure, various examples are explained below. It should be noted that one or more features of the examples, whether alone or in combination, should be considered within the disclosure of this application.

[0088] The following are example embodiments:

[0089] Example 1 is a distributed feedback (DFB) laser, comprising: a III-V semiconductor structure, comprising: a laser active region having a first end and a second end offset from the first end in a longitudinal direction; and a grating etched on a bonding surface of the III-V semiconductor structure to provide optical feedback to the laser active region, thereby generating output light output from the laser active region; and a silicon structure, comprising a silicon waveguide, which is configured to receive the output light from the first end of the laser active region, the III-V semiconductor structure being bonded to the silicon structure so that the bonding surface is bonded to a surface of the silicon structure, the silicon structure further comprising: a DFB region, comprising a surface of the silicon structure defining at least two laterally separated silicon portions, the at least two laterally separated silicon portions extending in the longitudinal direction and overlapping with two lobes of a second transverse mode of the output light in the laser active region with respect to a layering direction perpendicular to the longitudinal direction.

[0090] In Example 2, the subject matter of Example 1 includes: wherein the silicon structure further includes: a semiconductor optical amplifier (SOA) region, which is offset from the DFB region in a longitudinal direction, the SOA region includes a surface defining a tapered waveguide portion of the silicon waveguide, and the tapered waveguide portion has an increased lateral width in the longitudinal direction.

[0091] In Example 3, the subject matter of Example 2 includes: wherein: the DFB laser is a symmetric DFB laser; the laser active region is configured to output output light from a first end and a second end; and a silicon waveguide configured to receive the output light from the first end and the second end of the laser active region.

[0092] In Example 4, the subject matter of Example 3 includes: wherein: the silicon structure also includes a second SOA region, which is offset from the DFB region in a direction opposite to the longitudinal direction, the second SOA region includes a surface of the silicon waveguide defining a second tapered waveguide portion, and the lateral width of the second tapered waveguide portion in the longitudinal direction decreases.

[0093] In Example 5, the subject matter of Examples 1-4 includes wherein: at least two laterally separated silicon portions are laterally separated by at least one trench filled with a gas.

[0094] In Example 6, the subject matter of Examples 1-5 includes, wherein: the at least two laterally separated silicon portions are laterally separated by at least one trench filled with a dielectric material.

[0095] In Example 7, the subject matter of Examples 2-6 includes: wherein: the tapered waveguide portion extends longitudinally into a portion of the DFB region.

[0096] In Example 8, the subject matter of Example 7 includes: wherein: the at least two laterally separated silicon portions include two parallel ribs.

[0097] In Example 9, the subject matter of Example 8 includes: wherein: the silicon structure further includes a third rib parallel to and between the two parallel ribs in the DFB region, the third rib being continuous with the tapered waveguide portion.

[0098] In Example 10, the subject matter of Examples 2-9 includes: wherein: the at least two laterally separated silicon portions include two silicon plates separated by a narrow trench, the narrow trench having a narrower lateral width than either of the silicon plates.

[0099] In Example 11, the subject matter of Example 10 includes: wherein: the grating overlaps at least partially with the tapered waveguide portion with respect to the layering direction.

[0100] In Example 12, the subject matter of Examples 10-11 includes: wherein: the SOA region also includes a surface of two other parts of the silicon structure defining a silicon plate, the two other parts of the silicon plate being laterally separated from the tapered waveguide portion by two tapered grooves having increasing lateral widths in a longitudinal direction, the two tapered grooves being continuous with the narrow grooves of the DFB region.

[0101] The device of Example 13 includes: a silicon structure, which includes a silicon waveguide, which is configured to receive light from a first end of an active region of a light source, wherein the active region of the light source contacts a surface of the silicon structure in a layered direction; the silicon structure also includes: a distributed feedback (DFB) region, which includes a surface of the silicon structure that defines at least two laterally separated silicon portions, the at least two laterally separated silicon portions extending in a longitudinal direction perpendicular to the layered direction and overlapping with two lobes of a second transverse mode of light in a second active region with respect to the layered direction.

[0102] In Example 14, the subject matter of Example 13 includes: wherein the silicon structure further includes: a semiconductor optical amplifier (SOA) region, which is offset from the DFB region in the longitudinal direction, the SOA region includes a surface defining a tapered waveguide portion of the silicon waveguide, and the tapered waveguide portion has an increased lateral width in the longitudinal direction.

[0103] In Example 15, the subject matter of Example 14 includes: wherein: the tapered waveguide portion extends longitudinally into a portion of the DFB region.

[0104] In Example 16, the subject matter of Example 15 includes: wherein: the at least two laterally separated silicon portions include two parallel ribs.

[0105] In Example 17, the subject matter of Example 16 includes: wherein: the silicon structure further includes a third rib parallel to and between the two parallel ribs in the DFB region, the third rib being continuous with the tapered waveguide portion.

[0106] In Example 18, the subject matter of Examples 14-17 includes: wherein: the at least two laterally separated silicon portions include two silicon plates separated by a narrow trench, the narrow trench having a narrower lateral width than either of the silicon plates.

[0107] In Example 19, the subject matter of Example 18 includes: wherein: the tapered waveguide portion overlaps at least a portion of the active region with respect to the layering direction.

[0108] Example 20 is a method for manufacturing a distributed feedback (DFB) laser, comprising: etching a grating on a III-V semiconductor structure, the III-V semiconductor structure including a laser active region configured to generate light, etching the grating on a bonding surface of the III-V semiconductor structure to provide optical feedback to the laser active region, thereby generating output light, which is output from a first end of the active region and also output from a second end of the active region, the second end being offset from the first end in a longitudinal direction; and bonding the III-V semiconductor structure to a silicon structure, the silicon structure including a silicon waveguide, the silicon waveguide being configured to receive the output light from the first end of the laser active region, the III-V semiconductor structure being bonded to the silicon structure so that the bonding surface is bonded to a surface of the silicon structure, the silicon structure also including: a DFB region, comprising a surface of the silicon structure defining at least two laterally separated silicon portions, the at least two laterally separated silicon portions extending in the longitudinal direction, and overlapping with two lobes of a second transverse mode of the output light in the laser active region with respect to a layering direction perpendicular to the longitudinal direction.

[0109] Example 21 is at least one machine-readable medium comprising instructions that, when executed by processing circuitry, cause the processing circuitry to perform operations to implement any of Examples 1-20.

[0110] Example 22 is an apparatus comprising the method of implementing any of Examples 1-20.

[0111] Example 23 is a system implementing any of Examples 1-20.

[0112] Example 24 is a method of implementing any of Examples 1-20.

Claims

1. A distributed feedback DFB laser, comprising: III-V semiconductor structures, including: a laser active region having a first end and a second end offset from the first end in a longitudinal direction; and a grating etched on a bonding surface of the III-V semiconductor structure to provide optical feedback to the laser active region to generate output light output from the laser active region; and a silicon structure comprising a silicon waveguide configured to receive the output light from the first end of the laser active region, the III-V semiconductor structure being bonded to the silicon structure such that the bonding surface is bonded to a surface of the silicon structure, The silicon structure further comprises: A DFB region includes a surface of the silicon structure defining at least two laterally separated silicon portions, the at least two laterally separated silicon portions extending in the longitudinal direction and overlapping with two lobes of a second lateral mode of the output light in the laser active region with respect to a layering direction perpendicular to the longitudinal direction.

2. The DFB laser of claim 1, wherein the silicon structure further comprises: A semiconductor optical amplifier SOA region is offset from the DFB region in the longitudinal direction, the SOA region including a surface of the silicon waveguide defining a tapered waveguide portion, the tapered waveguide portion increasing in lateral width in the longitudinal direction.

3. The DFB laser according to claim 2, wherein: The DFB laser is a symmetric DFB laser; The laser active region is configured to output the output light from the first end and the second end; and The silicon waveguide is configured to receive the output light from the first end and the second end of the laser active region.

4. The DFB laser according to claim 3, wherein: The silicon structure further comprises a second SOA region offset from the DFB region in a direction opposite to the longitudinal direction, the second SOA region comprising a surface of the silicon waveguide defining a second tapered waveguide portion having a decreasing lateral width in the longitudinal direction.

5. The DFB laser according to claim 1, wherein: The at least two laterally separated silicon portions are laterally separated by at least one trench filled with a gas.

6. The DFB laser of claim 1, wherein: The at least two laterally separated silicon portions are laterally separated by at least one trench filled with a dielectric material.

7. The DFB laser of claim 2, wherein: The tapered waveguide portion extends longitudinally into a portion of the DFB region.

8. The DFB laser of claim 7, wherein: The at least two laterally separated silicon portions include two parallel ribs.

9. The DFB laser of claim 8, wherein: The silicon structure further includes a third rib parallel to and between the two parallel ribs in the DFB region, the third rib being continuous with the tapered waveguide portion.

10. The DFB laser of claim 2, wherein: The at least two laterally separated silicon portions include two silicon plates separated by a narrow trench having a narrower lateral width than either of the silicon plates.

11. The DFB laser of claim 10, wherein: The grating overlaps at least part of the tapered waveguide portion with respect to the layering direction.

12. The DFB laser of claim 10, wherein: the SOA region further comprising a surface of the silicon structure defining two other portions of the silicon plate, the two other portions being laterally separated from the tapered waveguide portion by two tapered trenches, the two tapered trenches increasing in lateral width in the longitudinal direction, The two tapered trenches are continuous with the narrow trenches of the DFB region.

13. A device comprising: a silicon structure including a silicon waveguide configured to receive light from a first end of an active region of a light source, the active region of the light source being in contact with a surface of the silicon structure in a layered direction; The silicon structure further comprises: a distributed feedback (DFB) region comprising a surface of the silicon structure defining at least two laterally separated silicon portions extending in a longitudinal direction perpendicular to the layering direction and overlapping with two lobes of a second transverse mode of light in the active region with respect to the layering direction.

14. The device of claim 13, wherein the silicon structure further comprises: A semiconductor optical amplifier SOA region is offset from the DFB region in the longitudinal direction, the SOA region including a surface of the silicon defining a tapered waveguide portion, the tapered waveguide portion increasing in lateral width in the longitudinal direction.

15. The apparatus of claim 14, wherein: The tapered waveguide portion extends longitudinally into a portion of the DFB region.

16. The apparatus of claim 15, wherein: The at least two laterally separated silicon portions include two parallel ribs.

17. The apparatus of claim 16, wherein: The silicon structure further includes a third rib parallel to and between the two parallel ribs in the DFB region, the third rib being continuous with the tapered waveguide portion.

18. The apparatus of claim 14, wherein: The at least two laterally separated silicon portions include two silicon plates separated by a narrow trench having a narrower lateral width than either of the silicon plates.

19. The apparatus of claim 18, wherein: The tapered waveguide portion overlaps at least part of the active region with respect to the layering direction.

20. A method for manufacturing a distributed feedback (DFB) laser, comprising: etching a grating on a III-V semiconductor structure, the III-V semiconductor structure including a laser active region configured to generate light, the grating being etched on a bonding surface of the III-V semiconductor structure to provide optical feedback to the laser active region to generate output light, the output light being output from a first end of the active region and also being output from a second end of the active region, the second end being offset from the first end in a longitudinal direction; as well as bonding the III-V semiconductor structure to a silicon structure, the silicon structure comprising a silicon waveguide configured to receive the output light from the first end of the laser active region, the III-V semiconductor structure being bonded to the silicon structure such that the bonding surface is bonded to a surface of the silicon structure, The silicon structure further comprises: A DFB region includes a surface of the silicon structure defining at least two laterally separated silicon portions, the at least two laterally separated silicon portions extending in the longitudinal direction and overlapping with two lobes of a second lateral mode of the output light in the laser active region with respect to a layering direction perpendicular to the longitudinal direction.

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