Silicon photonic symmetric distributed feedback laser

Abstract

To provide a tunable wavelength laser capable of controlling a target wavelength.SOLUTION: A symmetric distributed feedback (DFB) laser integrated in a silicon based photonic integrated circuit can output light from both sides of the symmetric DFB laser onto waveguides. The light in the waveguides can be phase adjusted and combined using an optical coupler. The symmetric DFB laser can generate light and symmetrically output the light onto different lanes of a multi-lane transmitter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001]

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

[0002]

[0002] A tunable laser is a laser whose wavelength of operation can be changed in a controlled manner using a filter to output a target wavelength. The tuning value varies with temperature and can require a complex control system to keep the tunable laser aligned during operation. Fixed lasers are easier to control. However, it is difficult to implement fixed lasers in a photonic integrated circuit (PIC) due to calibration issues, power issues, and process control issues, such as process variations found in current PIC fabrication techniques.

[0003]

[0003] The following description includes a discussion of figures having illustrations given as examples of implementations of embodiments of the present disclosure. The figures should be understood as examples and not as limitations. As used herein, reference to one or more "embodiments" should be understood as describing a particular feature, structure, or characteristic included in at least one implementation of the inventive subject matter. Thus, phrases such as "in one embodiment" or "in an alternative embodiment" appearing herein are intended to describe various embodiments and implementations of the inventive subject matter, and do not necessarily all refer to the same embodiment. However, they are not necessarily mutually exclusive. To easily identify the discussion of any particular element or operation, the most significant digit or digits in a reference number refer to the figure ("FIG.") number in which that element or operation is first introduced. Summary of the Invention

[0004] [Brief description of the drawings]

[0005] [Figure 1]

[0004] FIG. 1 illustrates a silicon-based distributed feedback (DFB) laser architecture, according to some example embodiments. [Diagram 2] FIG. 1 illustrates an exemplary multi-lane silicon low-loss DFB laser architecture, in accordance with some exemplary embodiments. [Diagram 3]

[0006] FIG. 2 illustrates an exemplary multi-lane silicon low-loss DFB architecture in which each symmetric DFB laser drives two lanes of the multi-lane architecture, according to some exemplary embodiments. [Figure 4]

[0007] FIG. 1 illustrates an example symmetric DFB laser architecture implementing a Mach-Zehnder Modulator (MZM) for power combining, in accordance with some example embodiments. [Diagram 5]

[0008] 1 illustrates an example method for implementing a symmetric DFB device in accordance with some example embodiments. [Figure 6]

[0009] 1 illustrates a flow diagram of a method for calibration of a symmetric DFB optical device, according to some exemplary embodiments. [Figure 7]

[0010] 1 illustrates an example optical transceiver in accordance with some example embodiments. [Figure 8]

[0011] 1 illustrates a side view of an opto-electrical device according to some illustrative embodiments. [Figure 9A]

[0012] 1A-1C illustrate approaches for fabricating one or more symmetric DFB lasers with vertical III-V gratings, according to some example embodiments. [Figure 9B] 1A-1C illustrate approaches for fabricating one or more symmetric DFB lasers with vertical III-V gratings, according to some example embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006]

[0013] A description of certain details and implementations follows, including illustrations of figures that may illustrate some or all of the embodiments described below, and a discussion of other potential embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the present disclosure is provided below, followed by a more detailed description with reference to the drawings.

[0007]

[0014] In the following description, for purposes of explanation, numerous specific details are set forth in order 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, well-known instruction instances, structures, and techniques are not necessarily shown in detail.

[0008]

[0015] As discussed, the PIC can implement a tunable laser, in which the laser can be tuned to output light of different wavelengths. In some exemplary embodiments, the tunable laser can implement one or more optical filters to obtain the target wavelength of the optical system. The tuning value can change with different temperatures, which can require a high-speed control loop integrated close to the PIC to ensure that the tuner is aligned during operation. A fixed wavelength silicon photonic laser with DFB can be configured in the PIC such that wavelength calibration is not required, which can reduce calibration costs and can further enable faster module boot-up times, thereby reducing power consumption and simplifying laser control. A DFB laser can be implemented as an integrated PIC laser, in which the laser cavity constitutes a periodic structure in the laser gain medium, which acts as a distributed Bragg reflector in the wavelength region of the laser action. In some exemplary embodiments, a distributed feedback laser has multiple axial cavity modes, but typically there is one mode that is preferred in terms of losses. Thus, single frequency operation can be implemented.

[0009]

[0016] While some non-silicon-based DFB sources can implement anti-reflection (AR) and high-reflection (HR) coatings on the facets to obtain higher power, this approach is not compatible with silicon-based photonic DFBs because the facets of silicon-based photonic DFBs cannot have coatings applied to them. This approach also wastes power because the coatings have the drawback of wasting a portion of the light (e.g., 20%). These approaches also exhibit poor feedback tolerance and are more sensitive to feedback and reflections. Also, applying the coatings requires access to both of the DFB output sides to apply the coatings, and coatings cannot be applied to silicon designs with integrated sources that are integrated in the center of the design, thereby making such access impossible.

[0010]

[0017] To address the above, a silicon photonic symmetric DFB can be implemented to provide light to a PIC in an approach that has similar power efficiency as a non-silicon photonic DFB by utilizing power from both outputs of the silicon photonic symmetric DFB.

[0011]

[0018] In contrast to the bends in III-V based DFBs, which cause high loss and high reflection and therefore cannot be used to implement symmetric DFBs, the bends in the routing of silicon photonic symmetric DFBs can be configured such that they are low loss and have no reflection to silicon photonic symmetric DFBs. In fiber based DFBs, large and expensive components are required to adjust and stabilize the phase of both outputs and combine them in a 2x1 coupler. The large size of fiber based DFB lasers prevents their use in typical multi-lane transceivers such as Ethernet applications (e.g., multi-lane transceivers where both laser outputs are utilized, such as combined for a single lane or each output is run on a separate lane).

[0012]

[0019] In some exemplary embodiments, the silicon photonic symmetric DFB is configured such that no wavelength tuning is required for operation, which increases output efficiency while achieving high optical mode stability. In some exemplary embodiments, the silicon photonic symmetric DFB outputs to two waveguides and combines the light using a 2x1 optical combiner, where the waveguides are fully symmetrical waveguides to reduce phase errors, and a thermal phase tuner provides matching optical phase at the input to the 2x1 optical combiner, which outputs the light beam. In some exemplary embodiments, the silicon photonic symmetric DFB outputs to two different waveguides, where the two different waveguides drive separate optical lanes having the same operating wavelength, which achieves high power efficiency due to the optical power from both output ports being used.

[0013]

[0020] FIG. 1 illustrates a silicon-based DFB laser architecture 100 according to some exemplary embodiments. In the example of FIG. 1, the silicon-based DFB laser 105 has a symmetrical grating and a symmetrical cavity design. In some exemplary embodiments, each of the gratings has a coupling constant (kappa) that is symmetrical about a center point of the DFB or can vary (e.g., periodically) over the length of the DFB. Light is output from both sides of the silicon-based DFB laser 105 into output waveguides including a first waveguide 107A and a second waveguide 107B. The light output into the waveguides is not perfectly in phase (e.g., due to manufacturing variations) and can be phase-tuned using heaters such as heater 110A and heater 110B (e.g., resistive metal on the top surface of a given waveguide). In some exemplary embodiments, the waveguides are coiled under their respective heaters via s-bends in the silicon architecture so that heater power can be reduced. The light from the first waveguide 107A and the second waveguide 107B are then combined in a coupler 115 (e.g., a multi-mode interference (MMI) coupler, a directional coupler, a Y-branch coupler). In some exemplary embodiments, a portion of the output from coupler 115 is tapped to a monitor photodiode 120 to measure the power level for calibration and operation, as discussed in more detail below.

[0014]

[0021] FIG. 2 illustrates a multi-lane silicon-based DFB laser architecture 200 according to some exemplary embodiments. The multi-lane silicon-based DFB laser architecture 200 is an example of a coarse wavelength division multiplexing (CWDM) transmitter architecture (e.g., 400G-FR4 application) that can be integrated into a multi-lane transceiver PIC (e.g., 700). As illustrated, a first symmetric DFB laser 205A (e.g., set to a first wavelength) outputs to a coupler 210A, which combines the light, which is then modulated by a modulator 215A (e.g., an electroabsorption modulator) and output via an output port 220A. In the example of FIG. 2, the heater is omitted for clarity in FIG. 2.

[0015]

[0022] Then, the second symmetric DFB laser 205B (e.g., set to a second wavelength higher than the first wavelength) outputs to coupler 210B, which combines the light, which is then modulated by modulator 215B, and output via output port 220B. Furthermore, the third symmetric DFB laser 205C (e.g., set to a third wavelength higher than the second wavelength) outputs to coupler 210C, which combines the light, which is then modulated by modulator 215C, and output via output port 220C. Furthermore, the fourth symmetric DFB laser 205D (e.g., set to a fourth wavelength higher than the third wavelength) outputs to coupler 210D, which combines the light, which is then modulated by modulator 215D, and output via output port 220D.

[0016]

[0023] 3 shows an exemplary multi-lane silicon-based DFB architecture 300, in which each symmetric DFB drives two lanes of the multi-lane architecture, according to some exemplary embodiments. In particular, one side of the silicon photonic integrated symmetric DFB laser 305A can provide light of a given wavelength (e.g., Λ0) to a first lane, where the light is modulated by a modulator 310A and then output via an output port 315A, where the components are coupled via a co-fabricated low-loss integrated silicon waveguide. Furthermore, the other side of the silicon photonic integrated symmetric DFB laser 305A provides light of a given wavelength (e.g., Λ0) to a second lane, where the light is modulated by a modulator 310B and then output via an output port 315B, where the first lane and the second lane receive half the optical power provided by the silicon photonic integrated symmetric DFB laser 305A.

[0017]

[0024] Similarly, for the third lane and the fourth lane, one side of the silicon photonic integrated symmetric DFB laser 305B can provide light of a given wavelength (e.g., Λ1) to the third lane, where the light is modulated by the modulator 310C and then output via the output port 315C. Furthermore, the other side of the silicon photonic integrated symmetric DFB laser 305B provides light of a given wavelength (e.g., Λ1) to the fourth lane, where the light is modulated by the modulator 310D and then output via the output port 315D, where the third lane and the fourth lane receive half the optical power provided by the silicon photonic integrated symmetric DFB laser 305B. In some exemplary embodiments, the multi-lane silicon-based DFB architecture 300 does not include a heater, and the light emitted from either side of the silicon photonic integrated symmetric DFB laser 305A may be out of phase, but the light from different sides is not combined (e.g., in a 2x1 coupler as in Figures 1 and 2). In some exemplary embodiments, the multi-lane silicon-based DFB architecture 300 is a low power design where 305A and 305D are 10mW silicon DFBs each, and the DFB where the symmetric DFB outputs are combined is a higher power design where the symmetric DFBs are each 20mW silicon-based DFBs.

[0018]

[0025] FIG. 4 illustrates an exemplary symmetric DFB architecture implementing a Mach-Zehnder Modulator (MZM) for power combining according to some exemplary embodiments. A Mach-Zehnder Modulator is an interferometer structure made from materials with electro-optical effects (e.g., LiNbO3, GaAs, InP), in which an electric field is applied to the arms to change the optical path length, thereby resulting in phase modulation. In some exemplary embodiments, coupling two arms with different phase modulation (e.g., via a 2x2 coupler) converts the phase modulation to intensity modulation. In the exemplary architecture 400, the DFB 405 generates light that is split into an upper modulator arm and a lower modulator arm via a 1x2 coupler 410. A radio frequency (RF) source 435 controls one or more phase shifters, such as RF phase shifter 415A and RF phase shifter 415B, to implement the modulation. Additionally, a heater 420A and a heater 420B are implemented to compensate for phase imbalance in the arms. In some exemplary embodiments, one of the heaters is activated to phase balance the arms to keep the MZM at the correct bias point for the differential high speed signal applied to RF phase shifters 415A and 415B to modulate the signal. The modulated light is then coupled through a 2x2 coupler 425 and then output to a data output port and monitor photodiode 430 for device calibration and monitoring.

[0019]

[0026] 3, architecture 450 illustrates a low-loss approach in which 1x2 coupler 410 is omitted and instead, a symmetric DFB 455 provides light for both lanes. In some exemplary embodiments, coupler 2x2 425 is also omitted from the silicon design and instead, bias control is managed by the MZM bias control unit.

[0020]

[0027] FIG. 5 illustrates a flow diagram of an exemplary method 500 for implementing an optical device having one or more silicon low-loss symmetric DFB lasers fabricated with other components of the optical device (e.g., waveguides, couplers) in a PIC according to some exemplary embodiments. In operation 505, the symmetric DFB laser generates light, e.g., the silicon-based DFB laser 105 generates light at a target wavelength. In operation 510, the generated light is output symmetrically from the symmetric DFB. For example, half of the generated light is output from one side of the DFB and the other half of the light is output from the other side of the symmetric DFB onto a silicon waveguide. In operation 515, the light in the waveguide is phase balanced. For example, the light exiting opposite sides of the symmetric DFB is slightly out of phase due to manufacturing variations (e.g., process variations), and one of the heaters (e.g., heater 110A, heater 110B) is activated to phase balance the light in one of the waveguides. In some exemplary embodiments, the symmetrically output light is output to different lanes of the transmitter, the heater is omitted, and operation 515 is skipped.

[0021]

[0028] In operation 520, the light is combined. For example, referring to Figure 2, the phase corrected light is combined using coupler 210A. In some exemplary embodiments, the light is not combined and the output from each side of the symmetric DFB is output to a different lane, and operation 520 is omitted.

[0022]

[0029] In operation 525, the light is modulated. For example, the modulator 215A modulates the first lane of light, which is the light from both sides of the first symmetric DFB laser 205A that is combined via the coupler 210A. As an additional example, the modulator 310A in FIG. 3 modulates the light output from one of the two sides of the silicon photonic integrated symmetric DFB laser 305A.

[0023]

[0030] At operation 530, the light is output from the device, for example, each lane of light is output from a respective output port (eg, output ports 220A-220D in FIG. 2, output ports 315A-315D in FIG. 3).

[0024]

[0031] 6 shows a flow diagram of a method 600 for calibration of a symmetric DFB optical device according to some exemplary embodiments. The advantage of a heater-based architecture (e.g., silicon-based DFB laser architecture 100) is that the phase imbalance from the silicon-based DFB laser 105 between the two arms can be compensated for after fabrication, and the phase adjustment only requires monitoring the optical tap power at the monitor photodiode 120.

[0025]

[0032] In some exemplary embodiments, heaters are added on both sides (e.g., heater 110A, heater 110B), but only one is used at a given time to compensate for small positive or negative imbalances due to process variations in the fabrication of a PIC with a symmetric DFB. In operation 605, the current to the symmetric DFB laser (e.g., silicon-based DFB laser 105) is set to a nominal value (e.g., 100 milliamps). In operation 610, the maximum power to one of the heaters is recorded. For example, the power of heater 110A is swept while the value of the monitor photodiode 120 is monitored, and the power value to heater 110A is recorded when the monitor photodiode (MPD) measurement is maximized.

[0026]

[0033] The maximum power to another of the heaters is recorded in operation 615. For example, the power to heater 110B is swept while the value of the monitor photodiode 120 is monitored, and the power value for heater 110B is recorded when the MPD measurement is maximized.

[0027]

[0034] In operation 620, it is determined whether heater 110A or heater 110B is more efficient when the MPD measurement is maximized (e.g., which has less power consumption at the maximum MPD measurement), and heater power is applied to the most efficient of the heaters to phase balance the arms.

[0028]

[0035] In operation 625, the currents of the symmetric DFBs are adjusted until a target optical power is reached on the MPD. In operation 630, the heater values ​​and current settings are saved in a system memory (e.g., flash memory) to be implemented when the optical system (e.g., optical transceiver 700) is initialized for operation. In some exemplary embodiments, method 600 is performed multiple times for additional DFBs (e.g., DFBs 205A-205D) in the device, and the respective values ​​for each lane are stored in operation 630.

[0029]

[0036] In operation 635, an optical system having one or more symmetric DFBs is initialized for operation (e.g., in the field, in product) and the stored values ​​are applied to the one or more symmetric DFBs and one or more heaters for efficient operation of the optical device.

[0030]

[0037] FIG. 7 illustrates a multi-lane wavelength division multiplexing optical transceiver 700 according to some exemplary embodiments. In the illustrated embodiment, the optical transceiver 700 comprises an integrated photonic transmitter structure 705 and an integrated photonic receiver structure 710. In some exemplary embodiments, the integrated photonic transmitter structure 705 and the integrated photonic receiver structure 710 are exemplary optical components fabricated as PIC devices, such as the PIC 820 of FIG. 8, discussed below. The integrated photonic transmitter structure 705 is an example of a dense wavelength division multiplexing (DWDM) transmitter having multiple lanes (transmitter lanes 1-N), with each lane handling a different wavelength of light. The integrated photonic receiver structure 710 is an example of a DWDM receiver that receives DWDM light (e.g., from an optical network or from the integrated photonic transmitter structure 705 in a loopback mode). The integrated photonic receiver structure 710 can receive and process light by filtering, amplifying, and converting the light into an electrical signal using components such as a multiplexer, a semiconductor optical amplifier (SOA), and a detector, such as one or more photodetectors (e.g., photodiodes).

[0031]

[0038] 8 illustrates a side view of an opto-electrical device 800 including one or more optical devices, according to some illustrative embodiments. In the illustrated embodiment, the opto-electrical device 800 is shown to include a printed circuit board (PCB) substrate 805, an organic substrate 860, an application specific integrated circuit 815 (ASIC), and a PIC 820.

[0032]

[0039] In some exemplary embodiments, the PIC820 may include silicon-on-insulator (SOI) or silicon-based (e.g., silicon nitride (SiN)) devices, or devices formed from both silicon and non-silicon materials. The non-silicon materials (alternatively referred to as "heterogeneous materials") may include one of III-V materials, magneto-optical (MO) materials, or crystalline substrate materials. III-V semiconductors have elements found in groups III and V of the periodic table (e.g., indium gallium arsenide phosphide (InGaAsP), gallium indium arsenide nitride (GaInAsN)). Because the electron velocity in III-V semiconductors is much faster than that in silicon, carrier dispersion effects in III-V based materials may be significantly higher than in silicon based materials. III-V materials also have a direct band gap, which allows for efficient creation of light from electrical pumping. Thus, III-V semiconductor materials enable photonic operations with greater efficiency than silicon for both generating light and modulating the refractive index of light. Thus, III-V semiconductor materials enable photonic operation with high efficiency in generating light from electricity and converting light back to electricity.

[0033]

[0040] Thus, the low optical loss and high quality oxides of silicon are combined with the electro-optical efficiency of III-V semiconductors in the heterogeneous optical devices described below. In embodiments of the present disclosure, the heterogeneous devices utilize a low-loss heterogeneous optical waveguide transition between the device's heterogeneous waveguide and a silicon-only waveguide.

[0034]

[0041] The MO material allows the heterogeneous PIC to operate based on the MO effect. Such devices may utilize the Faraday effect, in which a magnetic field associated with an electrical signal modulates an optical beam to achieve high bandwidth modulation and rotate the electric field of the optical mode to enable an optical isolator. The MO material may include materials such as iron, cobalt, or yttrium iron garnet (YIG). Furthermore, in some exemplary embodiments, the crystalline substrate material provides the heterogeneous PIC with high electromechanical coupling, linear electro-optic coefficient, low transmission loss, and stable physical and chemical properties. The crystalline substrate material may include, for example, lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

[0035]

[0042] In the illustrated example, the PIC 820 exchanges light with an external light source 825 via an optical fiber 821 in a flip-chip configuration where the top side of the PIC 820 is connected to the organic substrate 860 and light propagates out (or in) from the bottom side of the PIC 820 facing away (e.g., toward the coupler), according to some exemplary embodiments. The optical fiber 821 may be coupled to the PIC 820 using a prism, a diffraction grating, or a lens, according to some exemplary embodiments. The optical components of the PIC 820 (e.g., optical modulator, optical switch) are at least partially controlled by control circuitry included in the ASIC 815. Both the ASIC 815 and the PIC 820 are shown disposed on a copper pillar 814, which is used to communicatively couple the PICs through the organic substrate 860. The PCB substrate 805 is coupled to the organic substrate 860 via ball grid array (BGA) interconnects 816, which may be used to interconnect the organic substrate 860 (and thus the ASIC 815 and PIC 820) to other components of the optical-electrical device 800 (e.g., interconnect modules, power supplies, etc.) that are not shown.

[0036]

[0043] 9A and 9B show an approach for fabricating one or more symmetric DFB lasers with vertical III-V gratings according to some exemplary embodiments. In FIG. 9A, a III-V structure 900 is partially grown. For example, a III-V wafer with one or more layers of InP, GaAs, AlAs, or InAs is partially grown. In some exemplary embodiments, a DFB grating is then patterned (e.g., using nanoimprint or e-beam lithography) on the III-V structure. After the DFB grating is patterned, the III-V structure 900 is then wet and / or dry etched, and an additional layer of III-V is grown to form an etched III-V structure 925 (e.g., a III-V epitaxial wafer) illustrated in FIG. 9B. The etched III-V structure 925 is then bonded to a silicon structure (e.g., a silicon wafer) to form a bonded structure 950 including one or more symmetric DFBs with gratings. In some exemplary embodiments, prior to bonding, a dielectric layer (e.g., SiO2, SiN, or Al2O3) is added to the surface of the etched III-V structure 925 to improve bonding. In some exemplary embodiments, the etched III-V structure 925 is then cleaved into small rectangles (e.g., epitaxial dies) using alignment marks on the etched III-V structure 925 to align the cleavage positions to the diffraction grating. The etched III-V structure 925 (e.g., epitaxial dies) are then bonded to the SOI structure 950 to form the bonded structure 950. In some exemplary embodiments, the bonded structure 950 is then further processed to form additional circuit components, and vias and metal pads are integrated into the bonded structure 950 to provide current and drive the symmetric DFB laser.

[0037]

[0044] In light of the above disclosure, various examples are set forth 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 the present application.

[0038]

[0045] The following are exemplary embodiments. Example 1. A silicon photonic integrated circuit comprising a silicon distributed feedback laser with a first output side and a second output side opposite the first output side, a plurality of silicon waveguides with a first waveguide for receiving a first light beam from the first output side and a second waveguide for receiving a second light beam from the second output side, a silicon combiner for combining the first light beam from the first output side and the second light beam from the second output side into a combined light beam, and a silicon output waveguide for outputting the combined light beam. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the method.

[0039]

[0046] Example 2. The silicon photonic integrated circuit of example 1, further comprising a heater for applying heat to one of the plurality of silicon waveguides.

[0040]

[0047] Example 3. The silicon photonic integrated circuit of any of Examples 1 or 2, wherein the heater applies heat to phase match the first light beam and the second light beam, the first light beam and the second light beam being out of phase from a silicon distributed feedback laser.

[0041]

[0048] Example 4. The silicon photonic integrated circuit of any of Examples 1-3, wherein the heater is a first heater proximate to the first waveguide.

[0042]

[0049] Example 5. The silicon photonic integrated circuit of any of Examples 1-4, further comprising a second heater proximate the second waveguide.

[0043]

[0050] Example 6. The silicon photonic integrated circuit of any of Examples 1-5, wherein the second heater is configured to remain dormant while the first heater applies heat to phase match the first and second light beams.

[0044]

[0051] Example 7. The silicon photonic integrated circuit of any of Examples 1-6, further comprising a control circuit configured to activate the first heater to apply heat while the second heater is dormant.

[0045]

[0052] Example 8. The silicon photonic integrated circuit of any of Examples 1-7, wherein the control circuit is configured to activate the first heater while the second heater is dormant based on a calibration performed on the first heater and the second heater.

[0046]

[0053] Example 9. The silicon photonic integrated circuit of any of Examples 1-8, wherein the control circuitry is further configured to apply a drive current to the silicon distributed feedback laser.

[0047]

[0054] Example 10. The silicon photonic integrated circuit of any of Examples 1-9, further comprising an optical modulator for modulating the combined optical beam.

[0048]

[0055] Example 11. The silicon photonic integrated circuit of any of Examples 1-10, wherein the silicon photonic integrated circuit is monolithically fabricated, and the silicon distributed feedback laser, the plurality of silicon waveguides, and the silicon combiner are formed from the same silicon wafer.

[0049]

[0056] Example 12. The silicon photonic integrated circuit of any of Examples 1-11, wherein the plurality of waveguides comprises low optical loss bends for coupling light from the silicon distributed feedback lasers to the silicon combiner.

[0050]

[0057] Example 13. The silicon photonic integrated circuit of any of Examples 1-12, wherein one or more of the plurality of waveguides comprises a bend proximate to a heater in the silicon photonic integrated circuit for reducing heater power for phase matching.

[0051]

[0058] Example 14. The silicon photonic integrated circuit of any of Examples 1-13, wherein the silicon distributed feedback laser is a symmetric silicon distributed feedback laser configured to generate laser light, output a first half of the laser light from a first output, and output a second half of the laser light from a second output.

[0052]

[0059] Example 15. The silicon photonic integrated circuit of any of Examples 1-14, wherein the silicon distributed feedback laser does not include a reflective coating on the first output side and the second output side.

[0053]

[0060] Example 16. The silicon photonic integrated circuit of any of Examples 1-15, wherein the silicon combiner is a multi-mode interference coupler.

[0054]

[0061] Example 17. The silicon photonic integrated circuit of any of Examples 1-16, wherein the silicon distributed feedback laser is a fixed source configured to generate light at a fixed wavelength.

[0055]

[0062] Example 18. The silicon photonic integrated circuit of any of Examples 1-17, wherein the silicon photonic integrated circuit is a wavelength division multiplexing based device comprising a plurality of symmetric silicon distributed feedback lasers, each symmetric silicon distributed feedback laser configured to output light from both sides of the symmetric silicon distributed feedback laser.

[0056]

[0063] Example 19. The silicon photonic integrated circuit of any of Examples 1-18, wherein each of the plurality of symmetric silicon distributed feedback lasers is a fixed source. Implementations of the described techniques may include hardware, methods or processes, or computer software on a computer-accessible medium.

[0057]

[0064] Example 20. A method for generating light in a silicon photonic integrated circuit comprising: generating a first light beam and a second light beam by a silicon distributed feedback laser in the silicon photonic integrated circuit; outputting the first light beam from a first output side of the silicon distributed feedback laser and outputting the second light beam from a second output side of the silicon distributed feedback laser; receiving the first light beam using a first waveguide in the silicon photonic integrated circuit, the first output side and the second output side being on either side of the silicon distributed feedback laser; receiving the second light beam using a second waveguide in the silicon photonic integrated circuit; combining the first light beam and the second light beam using a silicon combiner of the silicon photonic integrated circuit; and outputting the combined light beam using a silicon output waveguide of the silicon photonic integrated circuit. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the method.

[0058]

[0065] Example 21. A symmetric distributed feedback (DFB) laser fabricated from a silicon wafer by bonding compound semiconductor materials, where the optical power from both ports of the symmetric DFB laser is combined using a phase-matched silicon waveguide and an optical power combiner. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the method.

[0059]

[0066] Example 22. The symmetric DFB laser of example 21, wherein the symmetric DFB laser is a quarter-wave shifted DFB laser.

[0060]

[0067] Example 23. The symmetric DFB laser of any of examples 21 or 22, wherein the symmetric DFB laser comprises a DFB grating.

[0061]

[0068] Example 24. A symmetric DFB laser according to any of Examples 21-23, wherein the DFB grating has kappa symmetric about a center point.

[0062]

[0069] Example 25. A symmetric DFB laser according to any of Examples 21-24, wherein the DFB grating has a kappa that varies across the length of the symmetric DFB laser.

[0063]

[0070] Example 26. A symmetric DFB laser according to any of Examples 21-25, wherein the DFB grating is formed with a lateral variation in silicon waveguide width.

[0064]

[0071] Example 27. The symmetric DFB laser of any of Examples 21-26, wherein the DFB grating is formed with vertical etching in a silicon waveguide.

[0065]

[0072] Example 28. A symmetric DFB laser according to any of Examples 21-27, wherein the DFB grating is formed by etching one or more of the III-V layers.

[0066]

[0073] Example 29. A symmetric distributed feedback (DFB) laser formed from a silicon wafer by bonding compound semiconductor materials, where optical power from both ports of the symmetric DFB laser is used to drive two separate optical lanes having different data modulation. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the method.

[0067]

[0074] Example 30. The symmetric DFB laser of Example 29, further comprising a plurality of semiconductor optical amplifiers for increasing the optical power of the light from the symmetric DFB laser. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

[0068]

[0075] In the foregoing detailed description, the method and apparatus of the inventive subject matter have been described with reference to specific exemplary embodiments thereof. It will be apparent, however, that various modifications and changes may be made thereto without departing from the broader spirit and scope of the inventive subject matter. The specification and figures are therefore to be regarded as illustrative rather than restrictive.

Claims

1. a silicon distributed feedback laser having a first output and a second output opposite the first output; a plurality of silicon waveguides, the plurality of silicon waveguides comprising a first waveguide for receiving a first light beam from the first output and a second waveguide for receiving a second light beam from the second output; a silicon combiner for combining the first light beam from the first output and the second light beam from the second output into a combined light beam; and a silicon output waveguide for outputting the combined light beam.

2. The silicon photonic integrated circuit of claim 1 , further comprising a heater for applying heat to one of said plurality of silicon waveguides.

3. 3. The silicon photonic integrated circuit of claim 2, wherein the heater applies heat to phase match the first and second light beams, the first and second light beams being out of phase from the silicon distributed feedback laser.

4. The silicon photonic integrated circuit of claim 2 , wherein the heater is a first heater proximate to the first waveguide.

5. The silicon photonic integrated circuit of claim 4 further comprising a second heater proximate to said second waveguide.

6. 6. The silicon photonic integrated circuit of claim 5, wherein the second heater is configured to remain dormant while the first heater applies heat to phase match the first and second light beams.

7. The silicon photonic integrated circuit of claim 5 further comprising a control circuit configured to activate the first heater to apply heat while the second heater is dormant.

8. 8. The silicon photonic integrated circuit of claim 7, wherein the control circuit is configured to activate the first heater while the second heater is dormant based on a calibration performed on the first heater and the second heater.

9. The silicon photonic integrated circuit of claim 7 , wherein the control circuitry is further configured to apply a drive current to the silicon distributed feedback laser.

10. The silicon photonic integrated circuit of claim 1 further comprising an optical modulator for modulating the combined optical beam.

11. The silicon photonic integrated circuit of claim 1 , wherein the silicon photonic integrated circuit is fabricated and the silicon distributed feedback laser, the plurality of silicon waveguides, and the silicon combiner are formed using a same silicon wafer.

12. The silicon photonic integrated circuit of claim 11 , wherein the plurality of waveguides comprise low optical loss bends for coupling light from the silicon distributed feedback lasers to the silicon combiner.

13. The silicon photonic integrated circuit of claim 11 , wherein one or more of the plurality of waveguides comprises a bend proximate to a heater in the silicon photonic integrated circuit for reducing heater power for phase matching.

14. 2. The silicon photonic integrated circuit of claim 1, wherein the silicon distributed feedback laser is a symmetric silicon distributed feedback laser configured to generate laser light, output a first half of the laser light at the first output, and output a second half of the laser light at the second output.

15. The silicon photonic integrated circuit of claim 1 , wherein said silicon distributed feedback laser does not include a reflective coating on said first output side and said second output side.

16. The silicon photonic integrated circuit of claim 1 , wherein the silicon combiner is a multi-mode interference coupler.

17. The silicon photonic integrated circuit of claim 1 , wherein the silicon photonic integrated circuit is formed using silicon and III-V layers.

18. 18. The silicon photonic integrated circuit of claim 17, wherein the silicon distributed feedback laser comprises one or more diffraction gratings, the one or more diffraction gratings being formed in the III-V layer, and the III-V layer having the one or more diffraction gratings is bonded to the silicon layer of the silicon photonic integrated circuit.

19. 2. The silicon photonic integrated circuit of claim 1, wherein the silicon photonic integrated circuit is a wavelength division multiplexing based device comprising a plurality of symmetric silicon distributed feedback lasers, each symmetric silicon distributed feedback laser configured to output light from both sides of the symmetric silicon distributed feedback laser.

20. 1. A method for generating light in a silicon photonic integrated circuit, comprising: generating a first light beam and a second light beam with a silicon distributed feedback laser in the silicon photonic integrated circuit; outputting the first light beam from a first output side of the silicon distributed feedback laser and outputting the second light beam from a second output side of the silicon distributed feedback laser, the first output side and the second output side being on opposite sides of the silicon distributed feedback laser; receiving the first light beam using a first waveguide in the silicon photonic integrated circuit; receiving the second optical beam using a second waveguide in the silicon photonic integrated circuit; combining the first light beam and the second light beam using a silicon combiner of the silicon photonic integrated circuit; and outputting the combined light beam using a silicon output waveguide of the silicon photonic integrated circuit.

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