Patent Publication Number: US-2023163573-A1

Title: Integrated Laser Source

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/142,676, filed Sep. 26, 2018, which claims the benefit of U.S. Provisional Patent Application No. 62/564,554, filed Sep. 28, 2017, the entire disclosure of which is incorporated herein by reference for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates to a multi-wavelengths integrated laser source and methods for operating thereof. More specifically, this disclosure relates to multi-wavelengths integrated laser source including one or more heaters. 
     BACKGROUND OF THE DISCLOSURE 
     Optical spectroscopy is an analytical technique. Conventional systems and methods for optical spectroscopy can include emitting light. A portion of the light energy can be absorbed at one or more wavelengths. This absorption can cause a change in the properties of the return light. 
     The characteristics of semiconductor lasers can make lasers a suitable choice as light sources configured to emit light for optical spectroscopy applications. For example, lasers can have single frequency emissions with narrow linewidths and can be capable of being tuned to emit at target emission wavelengths. The precision and accuracy of the emission wavelengths can be important for achieving quantitatively accurate spectroscopic measurements for some applications. In some instances, optical spectroscopy may benefit from multi-wavelengths measurements. Multi-wavelengths integrated laser sources with stable and accurate emissions wavelengths while being insensitive to thermal transients and crosstalk between lasers can be desired. 
     SUMMARY OF THE DISCLOSURE 
     Integrated laser sources emitting multi-wavelengths of light with reduced thermal transients and crosstalk and methods for operating thereof are disclosed. The integrated laser sources can include one or more heaters, which can be capable of generating heat. With the addition of one or more heaters, a temperature control system can be configured to maintain a total thermal load of both the gain segment and heater(s) of a given laser to be within a range based on a predetermined target value. The system can include electrical circuitry configured to distribute current generated from the current source to the gain segment, the heater(s), or both. In some examples, the gain segment and heater(s) can be coupled (e.g., directly connected) to separate current sources. The one or more heaters included in the structure of the laser can be either symmetrically or asymmetrically located with respect to the gain segment, where the percentage of distribution of current by the circuitry can be based on the relative locations. In some examples, heaters from proximate lasers and/or heater(s) proximate to a gain segment within a laser can be used to heat a central laser prior to the central laser being activated. In some examples, one or more of the plurality of lasers can operate in a subthreshold operation mode when the laser is not lasing to minimize thermal perturbations to proximate (e.g., adjacent) lasers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an exemplary system in which examples of the disclosure can be implemented. 
         FIG.  2 A  illustrates an exemplary arrangement of a plurality of lasers included in a system according to examples of the disclosure. 
         FIG.  2 B  illustrates a perspective view of an exemplary laser according to examples of the disclosure. 
         FIG.  2 C  illustrates an exemplary relationship between laser injection current and laser output power according to examples of the disclosure. 
         FIG.  3 A  illustrates a top view of an exemplary laser including an integrated heater according to examples of the disclosure. 
         FIG.  3 B  illustrates a partial schematic diagram of an exemplary laser including a heater and circuitry configured to couple a source to the gain segment and heater according to examples of the disclosure. 
         FIG.  3 C  illustrates a partial schematic diagram of an exemplary laser including multiple heaters according to examples of the disclosure. 
         FIG.  3 D  illustrates a top view of an exemplary laser including a serpentine heater according to examples of the disclosure. 
         FIG.  3 E  illustrates a top view of an exemplary system including multiple lasers, each laser having heaters according to examples of the disclosure. 
         FIG.  4 A  illustrates an exemplary method for operating the heaters and gain segments in the plurality of lasers for multi-wavelengths emissions according to examples of the disclosure. 
         FIG.  4 B  illustrates an exemplary method for operating selectively activated heaters according to examples of the disclosure. 
         FIGS.  5 A- 5 B  illustrate exemplary plots of output power and emissions wavelengths of light emitted by two adjacent lasers during emission and subthreshold operation modes of a central laser according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples. 
     Various techniques and process flow steps will be described in detail with reference to examples as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects and/or features described or referenced herein. It will be apparent, however, to one skilled in the art, that one or more aspects and/or features described or referenced herein may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not obscure some of the aspects and/or features described or referenced herein. 
     Further, although process steps or method steps can be described in a sequential order, such processes and methods can be configured to work in any suitable order. In other words, any sequence or order of steps that can be described in the disclosure does not, in and of itself, indicate a requirement that the steps be performed in that order. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modification thereto, does not imply that the illustrated process or any of its steps are necessary to one or more of the examples, and does not imply that the illustrated process is preferred. 
     Disclosed herein are multi-wavelengths integrated laser sources and methods for operating thereof with reduced thermal transients and crosstalk. One or more of the integrated laser sources can include one or more heaters, which can be capable of generating heat. With the addition of one or more heaters, a temperature control system can be configured to maintain a total thermal load of both the gain segment and heater(s) of a given laser within a range based on a predetermined target value. The system can include an electrical switch configured to distribute current generated from the current source to either the gain segment and/or the heater(s). In some examples, the gain segment and heater(s) can be coupled to separate current sources. The one or more heaters included in the structure of the laser can be either symmetrically or asymmetrically located with respect to the gain segment, where the percentage of distribution of current by the switch can be based on the relative locations. In some examples, heaters from adjacent lasers and/or heater(s) adjacent to a gain segment within a laser can be used to heat a central laser prior to the central laser being activated. In some examples, one or more of the plurality of lasers can operate in a subthreshold operation mode when the laser is not lasing to minimize thermal perturbations to adjacent lasers. 
     Representative applications of methods and apparatuses according to the present disclosure are described in this section. These examples are provided solely to add context and aid in the understanding of the described examples. It will be apparent to one skilled in the art that the described examples may be practiced without some or all of the specific details. Other applications are possible, such that the following examples should not be taken as limiting. 
       FIG.  1    illustrates an exemplary system in which examples of the disclosure can be implemented. System  110  can include a display  112 , laser source  114 , detector  116 , and buttons  118 . Laser source  114  can be configured to emit multiple wavelengths of light. More specifically, laser source  114  can include one or more semiconductor lasers. In some instances, some or all of the individual semiconductor lasers may be tunable, which may provide for adjustments to the wavelengths emitted by an individual semiconductor laser. Although typically used in large, bulky systems, semiconductor lasers can have many uses (e.g., trace gas detection, environmental monitoring, biomedical diagnostics, telecommunications, and industrial process controls) in portable electronic devices. Buttons  118  can be provided for the user to provide input to system  110 . System  110  can output information to the user on the display  112  and can optionally transmit the information to a remote computer. In response, the remote computer can receive and store the information for tracking purposes. 
     Systems and methods for optical spectroscopy can include emitting light using a light source. The wavelength emitted by a light source (e.g., a laser source) can depend on the temperature of the light source, where any change in temperature can cause a shift in wavelength (i.e., a deviation from the target wavelength). For example, light emitted by a semiconductor laser can shift 0.1-1 nm/K, which can depend on the materials used and the design of the laser. When multiple lasers are positioned in close proximity to each other, waste heat generated by the operation of one or more lasers may alter the temperature of a nearby laser, which may then alter the emission wavelength of that laser. 
     In some examples, when the amplitude of the lasers are modulated (e.g., by changing the drive currents), resulting thermal effects can cause transient wavelength shifts. Closed-loop temperature control of a laser (e.g., of the laser cladding, the chip substrate, etc.) or its surroundings can be used to reduce the temperature swings, and such control may be limited in how much it can mitigate external perturbations, how quickly the control may correct for temperature perturbations, etc. For example, there can be a non-zero delay between any active temperature control and resultant effects. Thus, even a system with closed-loop temperature control may experience some transient wavelength effects caused by the amplitude modulation of the lasers. 
     The transient effects can be multiplied in instances where multiple layers may be placed in close proximity to each other. Although optical spectroscopy generally can require at least two wavelengths, certain applications can be better suited with a greater number of distinct wavelengths of emitted light. In some spectroscopic applications (e.g., applications where narrow spectroscopic absorption features can be measured or highly precise quantifications can be made), producing highly accurate wavelengths can be beneficial. Highly accurate wavelengths can include no more than 0.01 nm deviations from a target wavelength, for example. 
     For spectroscopy systems including a plurality of lasers configured to emit a plurality of distinct wavelengths, each laser can experience transient effects. Additionally, a plurality of the lasers can be arranged in close proximity to one another (e.g., in portable electronic devices), which can cause the lasers to be susceptible to thermal crosstalk.  FIG.  2 A  illustrates an exemplary arrangement of a plurality of lasers included in a system according to examples of the disclosure. System  200  can include a plurality (e.g., at least 3-10) of lasers, such as laser  210 , laser  212 , and laser  214 , located proximate to one another. The plurality of lasers can be formed on substrate  218  (e.g., a die, chip, or wafer). For example, the plurality of lasers can be formed using lithographic means. In some examples, the integration can be based on silicon waveguides (e.g., silicon photonics) and/or indium phosphide (InP) waveguides. For example, the reflective section(s) (e.g., grating section(s)), gain section, and heater(s) of each laser can be included on the same III-V substrate. Alternatively, the reflective section(s) (e.g., grating section(s)) of each laser can be included on the same silicon substrate, while the gain section and heater(s) of each laser can be included on the same III-V substrate. 
     In some examples, the separation distance between adjacent lasers can be 10-100 μm. For example, laser  212  can be adjacent to and located between laser  210  and laser  214 . The plurality of lasers can be integrated using, for example, wafer-bonding, evanescent coupling, grating coupling, butt-coupling (e.g., near-field facet coupling), epitaxial growth, or any other suitable means. In some instances, once formed and integrated, the outputs of some or all of the plurality of lasers can be combined. 
     The plurality of lasers can be coupled to voltage or current sources  204 , which can be coupled to controller  202 . Controller  202  can send one or more signals to each source  204 , which can be indicative of a drive current (or voltage) to one or more of the plurality of lasers. In some examples, each laser can be coupled to a unique (i.e., not shared with other lasers) source  204 . In some examples, more than one laser can be coupled to the same source  204 . 
     In some examples, the plurality of lasers can be coupled to a single temperature control system  220  or multiple temperature control systems. Temperature control system  220  can, in some instances, include a closed-loop temperature control system configured to measure the temperature of the plurality of lasers, compare the measured temperature(s) to target temperature(s), and/or control the temperature(s) when a difference between the measured and target temperatures exists. Temperature control system  220  can include a plurality of temperature sensors. Each laser can be coupled to a separate temperature sensor(s). In some examples, controller  202  can be in communication with temperature control system  220 . In some examples, controller  202  can include temperature control system  220 . 
     The plurality of distinct wavelengths of emitted light can be generated by a plurality of light sources (e.g., laser sources), where each (or some) of the plurality of light sources can be configured to emit one or more wavelengths distinct from some or all of the wavelengths emitted by other light sources. Thereby, a system capable of multi-wavelengths spectroscopic measurements can be created. The lasers can be switched on (and off) simultaneously, in a sequence, or driven with a predetermined amplitude modulation pattern (e.g., simple sequencing of wavelengths in a predetermined order, sine-wave modulation for FFT analysis, Hadamard schemes, etc.). 
       FIG.  2 B  illustrates a perspective view of an exemplary laser according to examples of the disclosure. Shown is one exemplary laser; in some examples, each of the plurality of lasers included in system  200  can have the same design and/or operation. Laser  212  can be configured as a Distributed Bragg Reflector (DBR) laser, which can include DBR section  212 A, phase section  212 C, gain region or gain segment  212 D, and DBR section  212 B. DBR section  212 A and DBR section  212 B can include one or more diffraction gratings located on or above the active region (not shown). The diffraction gratings can be configured to provide optical feedback to at least partially reflect light back into the cavity of the laser to form a resonator. In some examples, the diffraction gratings can be configured to reflect only narrow bands of wavelength(s) to produce a single longitudinal mode wavelength. The period of the gratings can be adjusted to achieve specific emission wavelengths. DBR section  212 A can be configured to have partial transmission and can be configured as an outcoupler, while DBR section  212 B can be configured to have complete reflection. 
     Although  FIG.  2 B  illustrates a laser including DBR sections, examples of the disclosure can include reflective sections (e.g., a metal mirror at the rear facet of the laser). Additionally, examples of the disclosure are not limited to DBR lasers and the disclosure herewith can be applicable to any type of laser. 
     In some examples, laser  212  can be a sampled-grating DBR (SGDBR), which can include DBR section  212 A and DBR section  212 B configured with distinct combs of reflection peaks. The SGDBR can be a highly tunable laser with independent shifting of the reflection peaks using temperature or current injection. 
     Phase section  212 C can be configured for tuning by aligning the cavity mode (i.e., lasing wavelength) to the peaks of the DBR reflectivity spectra. In some examples, phase section  212 C can be omitted from laser  212 . Gain segment  212 D can be configured to amplify light energy. In some examples, gain segment  212 D can be a III-V gain segment. 
     Heat from any of the sections (e.g., DBR section  212 A, phase section  212 C, gain segment  212 D, and DBR section  212 B) of laser  212  can spread to any of the other sections. In some examples, one or more of the DBR and phase sections can be coupled to a temperature sensor included in a temperature control system (e.g., temperature control system  220  illustrated in  FIG.  2 A ). While the DBR and phase sections may be temperature controlled (e.g., nominally held at a nearly target temperature), gain segment  212 D can be affected by changes in generated heat (e.g., from the laser being driven by a current source). For example, source  204  can reduce the drive current of gain segment  212 D of laser  212 . The lower drive current can lead to a reduced heat load in gain segment  212 D, which can lead to a drop in the temperature of gain segment  212 D. The temperature drop in gain segment  212 D can cause an increase in heat flow between gain segment  212 D and one or more of DBR section  212 A, DBR section  212 B, and phase section  212 C. Alternatively, the temperature drop in gain segment  212 D can lead to a decrease in heat flow in the opposite direction. 
     Temperature control system  220  can detect the change in temperature within a given laser (e.g., laser  212 ) and can try to correct for the change in heat flow (e.g., increasing the amount of applied heat to gain segment  212 D). In some examples, temperature control system  220  can maintain a small change in steady-mode temperature and can likely require a finite time period to correct for the change in heat flow. Although temperature control system  220  can maintain a small change in steady-mode temperature, finite gain and/or non-zero thermal impedance between the DBR sections (e.g., DBR section  212 A and DBR section  212 B) or phase section  212 C and corresponding temperature sensors can lead to imperfect temperature control by temperature control system  220 . 
     A laser can experience the heating effects even when the laser is not emitting light (i.e., the laser output power is equal to zero). For example, a laser can experience heat from a nearby laser.  FIG.  2 C  illustrates an exemplary relationship between laser injection current and laser output power according to examples of the disclosure. The operation mode of the laser can be categorized as off, subthreshold, or emission. When the laser is operating in the off mode, no injection current is provided to the laser. The injection current refers to the current input to the laser from a source and used to drive the laser to a non-off operation mode. The laser can be operating in the subthreshold operation mode when some injection current may be provided to the active region of a laser and the injection current is below the laser threshold current. Within the subthreshold operation mode, the laser output power can be zero. The laser can be operating in the emission operation mode when the injection current is above the laser threshold current and can generate light. The laser output power can be greater than zero and can be linearly dependent on the injection current, for a given submount temperature. The slope efficiency of the laser can be determined based on this linear dependency. At high injection currents, this linear dependence can break down due to an increase in the temperature of the active region. The increase in temperature of the active region can cause a decrease in internal quantum efficiency, which in turn can cause the output power to saturate (i.e., thermal rollover). 
     Even though the laser output power can be effectively zero below the laser threshold current, driving the laser (i.e., increasing the laser injection current) can still lead to significant heat generation. Furthermore, power consumption and heat generation can come from sections in the laser structure other than the laser gain medium. 
     In addition to thermal impacts from sections within a given laser, a laser, when configured in the arrangement shown in  FIG.  2 A , can experience thermal crosstalk, where the modulation of at least one laser can thermally affect a nearby (e.g., adjacent) laser. For example, laser  212  (illustrated in  FIG.  2 A ) can experience thermal crosstalk from laser  210  and/or laser  214 . Accordingly, a system capable of reducing the driving transients of a thermal load to reduce the magnitude of thermally-induced wavelength transients within a given laser and a system capable of reducing the magnitude of thermally-induced wavelength crosstalk transients between nearby lasers may be desired. In some examples, a system capable of reducing the magnitude of thermally-induced amplitude transients within a given laser and thermally-induced amplitude crosstalk transients between nearby lasers may be desired. 
     In some examples, the laser can include a heater to reduce thermal transients and crosstalk. The heater can be located proximate to the gain segment and can include materials common to the gain segment.  FIG.  3 A  illustrates an exemplary laser including an integrated heater according to examples of the disclosure. Laser  312  can include DBR section  312 A, DBR section  312 B, phase section  312 C, and gain segment  312 D. One or more of DBR section  312 A, DBR section  312 B, phase section  312 C, and gain segment  312 D can have a design and/or operation similar to DBR section  212 A, DBR section  212 B, phase section  212 C, and gain segment  212 D, respectively, as discussed above and illustrated in  FIG.  2 B . 
     Laser  312  can further include heater  312 E. In some examples, heater  312 E can be any type of element capable of generating heat, including but not limited to a resistor (e.g., patterned metal or lightly-doped, ohmic semiconductor material). In some examples, heater  312 E can have one or more material properties (e.g., same epitaxial structure) that can be the same as gain segment  312 D. The heater  312 E may be thermally coupled to the gain segment  312 D. The term “thermal coupling” and “thermally coupled” refer to a connection (e.g., a thermal path) between two or more components for transferring heat between the components. 
     In some examples, heater  312 E may not be optically coupled to the laser cavity. The terms “optical coupling” and “optically coupled” refer to a connection (e.g., an optical path) between two or more components for transferring an optical signal between the components, and “optical decoupling” refers to the lack of such connection. For example, the heater  312 E may be optically decoupled from the gain segment  312 D, thereby preventing an optical signal from the gain segment  312 D from transferring to the heater  312 E. The heater  312 E can be fabricated and operated differently from the gain segment  312 D. 
     A temperature control system (e.g., temperature control system  220  illustrated in  FIG.  2 A ) can be coupled to gain segment  312 D and heater  312 E. In some examples, separate temperature sensors can be coupled to gain segment  312 D and heater  312 E, and the temperature control system can individually control the temperatures of gain segment  312 D and heater  312 E. In some examples, a single temperature sensor can be coupled to both gain segment  312 D and heater  312 E, and the temperature control system can control the total thermal load of both gain segment  312 D and heater  312 E. The term “thermal load” refers to the amount of heat generated by a given component. In some examples, a single temperature sensor can be coupled to gain segment  312 D, and the temperature values can be used as input information to the one or more heaters. In some instances, the temperature control system may not monitor the temperature of the gain segment  312 D, but may instead apply a certain current or voltage to the gain segment  312 D, where the applied current/voltage may be based on a targeted temperature value. 
     The temperature control system can be configured to maintain a total thermal load of both gain segment  312 D and heater  312 E to be within a range of a predetermined target value. That is, if the thermal load of gain segment  312 D is represented by TL GS  and the thermal load of heater  312 E is represented by TL HG , the temperature control system can be configured to maintain (TL GS +TL HG ) within the range (e.g., within 10% from the target value). 
     As the drive current to gain segment  312 D decreases, for example, the temperature of gain segment  312 D can decrease, and the current to heater  312 E can increase. With the current to heater  312 E increasing, the temperature of heater  312 E can increase. The temperature control system can ensure that while the temperature of gain segment  312 D decreases, the change in total thermal load can be zero. If heater  312 E is a gain segment (like gain segment  312 D), since heater  312 E may be optically decoupled from the laser cavity, heater  312 E may not lase when electrically energized. 
     In some examples, the temperature control system can be further configured to maintain DBR section  312 A, DBR section  312 B, and/or phase section  312 C at target temperatures. The temperature control system can be configured to maintain target temperature in one or more sections (e.g., DBR section  312 A, DBR section  312 B, phase section  312 C, and gain segment  312 D and heater  312 E) when the laser is in the off operation mode (i.e., no injection current is applied to the laser, as illustrated in  FIG.  2 C ), subthreshold operation mode (i.e., a non-zero injection current below the laser threshold current is applied to the laser, as illustrated in  FIG.  2 C ), and/or emission operation mode (i.e., an injection current greater than or equal to the laser threshold current is applied, such that the laser can be emitting light, as illustrated in  FIG.  2 C ). 
     With laser  312  including heater  312 E, the required swing in phase-section heating current can be reduced. Less required swing in phase-section heating current can lead to a reduced load on the temperature control system (e.g., temperature control system  220  illustrated in  FIG.  2 A ). In some instances, the temperature control system can achieve steady-mode faster and can consume less power due to the reduced load. Moreover, the perturbations in the total cavity optical phase can be reduced, which can reduce the likelihood of mode-hops. 
       FIG.  3 B  illustrates a partial schematic diagram of an exemplary configuration of the system including lasers having heaters according to examples of the disclosure. System  300  can include controller  302 , one or more sources (e.g., source  304 ), one or more circuitry  306  (e.g., a switch, a splitter, etc.), and one or more lasers (e.g., laser  312 ). Source  304  can be a fixed current source configured to generate a predetermined and constant current. The current from source  304  can flow into circuitry  306 . Circuitry  306  can be any electrical (e.g., analog or digital) switch including, but not limited to a CMOS nFET switch. In some examples, circuitry  306  can direct the current into either gain segment  312 D or heater  312 E. In some examples, gain segment  312 D and heater  312 E can be configured with the same electrical properties (e.g., resistivity), which can prevent or reduce the effect of switching operations, performed by circuitry  306 , on source  304 . Alternatively, circuitry  306  can be configured to share the current from source  304  between gain segment  312 D and heater  312 E. Although  FIG.  3 B  illustrates a single source (e.g., source  304 ) being shared between gain segment  312 D and heater  312 E, examples of the disclosure can include the gain segment and heater(s) being electrically coupled to separate sources (not shown). 
     In some examples, a laser can include multiple heaters.  FIG.  3 C  illustrates an exemplary laser including multiple heaters according to examples of the disclosure. Laser  312  can further include heater  312 F. In some examples, heater  312 F can be located on the other side of gain segment  312 D than heater  312 E is located. In some examples, heater  312 F can have the same properties and/or performance (e.g., electrical properties and/or thermal performance) as heater  312 E. In some examples, circuitry  306  can be electrically coupled to gain segment  312 D, heater  312 E, and heater  312 F. Circuitry  306  can be dynamically configured (or dynamically reconfigured) to direct the current from source  304  to segment  312 D, heater  312 E, or heater  312 F. The term “dynamic” refers to performing an action in real-time. A dynamic action may not include actions that are pre-determined, for example. In some examples, a junction (e.g., y-junction) can be used to divide (e.g., 33% each) the current from source  304  to the three different sections of laser  312 . In some examples, the junction can split (e.g., 50%) the current from source  304  between heater  312 E and heater  312 F. 
     The separation distance between heater  312 E and gain segment  312 D, as measured from edge-to-edge, can be x 1 . The separation distance between heater  312 F and gain segment  312 D, as measured edge-to-edge, can be x 2 . Both heater  312 E and heater  312 F can be configured to heat up gain segment  312 D. In some examples, heating of gain segment  312 D by the heaters can be limited to when laser  312  is off. The amount of heat experienced by gain segment  312 D can depend on the current from source  304  and the separation distance from a given heater. In some examples, the separation distances x 1  and x 2  can be the same, and in some instances, the heaters can be symmetrically placed relative to gain segment  312 D. Circuitry  306  can be configured to route a portion (e.g., half) of the current from source  304  to heater  312 E and the other portion of the current to heater  312 F. 
     In some examples, the separation distances x 1  and x 2  can be different, and in some instances, the heaters can be asymmetrically placed relative to gain segment  312 D. Circuitry  306  can be configured to distribute unequal amounts of current from source  304 . For example, separation distance x 2  can be equal to 1.5 times the separation distance x 1 , and circuitry  306  can route 60% of the current from source  304  to heater  312 F and 40% of the current to heater  312 E. 
     Examples of the disclosure can include the heater having any type of shape and/or size.  FIG.  3 D  illustrates a top view of an exemplary laser including a serpentine heater according to examples of the disclosure. Heater  312 E can include, for example, a metal (e.g., aluminum) routed around one or more sides of gain segment  312 D. In some examples, the serpentine heater can have a length longer than the length(s) of the edge(s) of the laser that serpentine heater runs along. Heater  312 E can be coupled to a current source, where current running through the metal can lead to heat dissipation, which can thermally couple to gain segment  312 D. Although the figure illustrates the serpentine heater routed along two edges of laser  312 , examples of the disclosure can include the heater routed along one or more than two edges of laser  312 . Additionally, although the figure illustrates the serpentine heater weaving back and forth along two edges of laser  312 , examples of the disclosure can include patterns or techniques to lengthen the metal or increase its resistance. 
     In some examples, the separation distances and distribution of current among the heaters can be based on the properties and/or activation modes of heaters in adjacent lasers.  FIG.  3 E  illustrates a top view of an exemplary system including lasers having heaters according to examples of the disclosure. System  300  can include laser  310 , laser  312 , and laser  314 . Each laser can be coupled to a circuitry  306  and a source  304 . In some examples, all sources  304  can be coupled to controller  302 . One or more sections of each laser can be coupled to a temperature control system (e.g., temperature control system  220  illustrated in  FIG.  2 A ). 
     Laser  310  can have one adjacent laser (e.g., laser  312 ) located on the side closest to heater  310 E. In some instances, heater  312 F of laser  312  can be activated (i.e., a current can be applied to the heater). The separation distance between laser  310  and laser  312  can be such that the heat generated by heater  312 F can be thermally coupled to laser  310 . To compensate for this thermal cross-talk, circuitry  306  of laser  310  can route a higher percentage of current from source  304  to heater  310 F to prevent or reduce uneven distribution of heat (e.g., in the area between heater  310 E and heater  312 F) and/or thermal crosstalk between laser  310  and laser  312 . 
     In some examples, the system can be configured such that the separation distances between adjacent lasers (e.g., laser  310  and laser  312 ) can prevent or reduce thermal crosstalk. In some examples, the separation distance between a gain segment (e.g., gain segment  310 D) and heater (e.g., heater  310 E) with a given laser (e.g., laser  310 ) can be less (e.g., 5 times less, 10 times less, etc.) than the separation distance between heaters (e.g., heater  310 E and heater  312 F) in adjacent lasers. For example, the separation distance between gain segment  310   d  and heater  310 E can be 10 μm, while the separation distance between heater  310 E and heater  312 F can be 100 μm. 
       FIG.  4 A  illustrates an exemplary method for operating the heaters and gain segments in the plurality of lasers included in a system configured for multi-wavelengths emissions according to examples of the disclosure. The process can begin with each laser source turned off. The lasers can be heated by routing a certain amount (including, but not limited to, 100%) of the current from each current source (e.g., current source  304  illustrated in  FIG.  3 D ) using an associated switch (e.g., circuitry  306  illustrated in  FIG.  3 D ) to one or more heaters (e.g., heater  312 F illustrated in  FIG.  3 D ) (step  452  of process  450 ). Alternatively, each laser can be coupled to a separate current source, and the controller can configure each current source. For each laser (e.g., laser  310 , laser  312 , and laser  314  illustrated in  FIG.  3 D ), a total thermal load of the gain segment (e.g., gain segment  312 D illustrated in  FIG.  3 B ) and one or more heaters can be maintained (e.g., by controller  320  illustrated in  FIG.  3 D ) (step  454  of process  450 ). When the laser is to be activated (step  456  of process  450 ), the percentage of current (e.g., from the current source that is routed using the associated switch) to the gain segment can increase, and the percentage of current that is routed to the one or more heaters can decrease (step  458  of process  450 ). In this manner, the current injected into the laser can increase to turn on the laser and/or increase the intensity of emitted light. At the same time, the amount and/or percentage of current to the heater(s) can decrease to compensate for the increase in temperature in the gain segment (e.g., due to the increased injection currents). The increase in current to the gain segment and the decrease in current to the heaters can be such that the total thermal load of both the gain segment and heaters can be within a pre-determined range from a target value. The increase in current to the gain segment can continue until some or all of the current from the current source can be routed to the gain segment (step  460  or process  450 ). In some examples, the temperature changes (and/or applied current) to the gain segment can be incrementally increased (e.g., by increasing the injection current), and the temperature changes (and/or applied current) to the one or more heaters can be incrementally decreased. 
     While the laser is operating in the emission operation mode, the temperature control system can be configured to maintain the total thermal load (step  468  of process  450 ). When the laser is to be turned off (step  462  of process  450 ), the amount and/or percentage of current (e.g., from the current source that can be routed using the associated switch) to the gain segment can be decreased, and the amount and/or percentage of current that can be routed to the one or more heaters can increase (step  464  of process  450 ). In this manner, the current injection into the laser can decrease to turn off the laser or decrease the intensity of emitted light. The decrease in current to the gain segment and the increase in current to the heaters can be such that the total thermal load of both the gain segment and heaters can be within a range from a pre-determined target value. The decrease in current to the gain segment can continue until some or all of the current from the current source can be routed to the heater(s) (step  466  or process  450 ). In some examples, the temperature changes (and/or applied current) to the gain segment can be incrementally decreased (e.g., by decreasing the injection current), and the temperature changes (and/or applied current) to the one or more heaters can be incrementally increased. 
     Examples of the disclosure can include applying the steps of process  450  to only those lasers to be activated. Heaters can be heated in a given time period prior to when the associated laser can be activated (e.g., in the next time period). For example, steps  452 - 456  can be executed during the given time period (when the soon-to-be activated laser can be off), and steps  458 - 466  can be executed during the next time period (when the laser is operating in the subthreshold or emission operation mode). All other lasers can remain off (e.g., to conserve power) during the given time period and next time period. 
     In some examples, heaters in one or more lasers adjacent to a central laser can be selectively activated to assist in heating the central laser.  FIG.  4 B  illustrates an exemplary method for operating selectively activated heaters according to examples of the disclosure. The process can begin with each laser source turned off. In a given time period, one or more lasers can be selected as central lasers, which can be lasers that are to be activated in the next time period (step  472  of process  470 ). For example, laser  312  (illustrated in  FIG.  3 D ) can be designated as a central laser, while laser  310  and laser  314  can be designated as adjacent lasers (i.e., lasers adjacent to the central laser). All other lasers can remain off for the given time period and next time period. 
     For each adjacent laser, current can be applied from each current source to one or more heaters (step  474  of process  470 ). In some examples, the current applied to the one or more heaters can be based on the target total thermal load to be maintained for a given central laser. For example, the target total thermal load can be equal to the thermal load of the central laser when operating with its predetermined final injection current and optionally can account for any heat loss due to heating via thermal cross-talk. For each central laser, the target total thermal load of both its gain segment and its heater(s) can be maintained (step  476  of process  470 ). Optionally, the heater(s) of the central laser can be used in addition to the heater(s) of adjacent lasers to achieve total thermal load of the central laser that is within a range of a predetermined target value. 
     When the central laser is activated (step  478  of process  470 ), the current to the gain segment of the central laser can be increased (step  480  of process  470 ). The increase in current to the gain segment can lead to an increase in temperature of the gain segment. To compensate for this increase in temperature, the current to the heaters of the adjacent lasers can be decreased (step  480  of process  470 ). Optionally, the heater(s) of the central laser can be decreased. For each central laser, the total thermal load of both its gain segment and its heater(s) can be maintained (step  482  of process  470 ) until the laser is to be turned off (step  484  of process  470 ). The current in the gain segment of the central laser can be decreased (step  486  of process  470 ). In some examples, the current(s) to the heater(s) can drop to zero after the central laser is no longer operating in the emission operation mode. Optionally, the current to the heater(s) of the adjacent laser(s) and/or central laser can be increased. 
     In some examples, one or more of the plurality of lasers can be operated in a subthreshold operation mode to reduce thermal transients and crosstalk.  FIGS.  5 A- 5 B  illustrate exemplary plots of output power and emissions wavelength of light emitted by two adjacent lasers during the emission operation modes and subthreshold operation modes of the central laser according to examples of the disclosure. Adjacent lasers can include laser  510  and laser  512 , which can be arranged such that the adjacent laser can experience thermal crosstalk from the central laser. The figure illustrates two light emission plots for laser  512 : one plot for laser  512  operating in outside of a subthreshold operation mode (e.g., operating in the off operation mode), indicated as laser  512 - 1 ; and another plot for laser  512  operating in a subthreshold operation mode, indicated as laser  512 - 2 . 
     During time t 1 , the adjacent lasers can be activated (i.e., the current injected in each laser can be greater than or equal to the laser&#39;s threshold current such that the laser can be emitting light, as illustrated in  FIG.  2 C ). During time t 2 , the controller can be configured to prevent or reduce laser  512  from emitting light. To prevent or reduce laser  512  from emitting light, the current injected into laser  512 - 2  can be reduced to below the laser threshold current. In some examples, laser  512 - 2  can be configured to operate in a subthreshold operation mode, where the current injected into laser  512 - 2  can be below the laser threshold current and between the normal operating current (e.g., when the laser can be emitting light) and zero current. In some examples, the subthreshold operation mode can include an injection current that can be between 10-50% of normal operating current. 
     Due to the change in injection current to laser  512 - 2 , the output power of laser  510  can change, as illustrated in  FIG.  5 A . The output power of laser  510  can increase (after a small time, equal to the thermal time-constant of the relevant portion of the semiconductor material, to reach steady-mode) due to the reduced heating of laser  512 - 2  when laser  512 - 2  is operating in the subthreshold operation mode. Additionally, as illustrated in  FIG.  5 B , laser  510  can experience a shift in wavelength when laser  512 - 2  switches to operating in the subthreshold operation mode. The shift in wavelength can be a shift towards either shorter or longer wavelengths depending on the design of the laser cavity. Although there can be some increase in output power and shift in wavelength of laser  510 , the increase and shift can be reduced compared to laser  512 - 1 , which can experience a more significant drop in temperature due to the injection current dropping to zero. By operating laser  512 - 2  in subthreshold operation mode, the thermal perturbation to laser  510  can be reduced (e.g., cut in half if the subthreshold operation mode for laser  512  includes 50% of normal operating current). In some examples, the temperature control system and/or controller can anticipate laser  512  switching to subthreshold operation mode and can, in advance, adjust the temperature of the adjacent laser  510  to compensate (e.g., slightly decrease the temperature through the heater(s) to reduce the impact). 
     A semiconductor laser is disclosed. The semiconductor laser can comprise: one or more reflective sections, where at least one reflective section is configured to at least partially reflect light back into a cavity of the laser; an optical gain region configured to amplify light energy; and one or more heaters configured to generate heat in response to a non-zero current, wherein each heater is optically decoupled and thermally coupled to the optical gain region. Additionally or alternatively, in some examples, the one or more heaters have the same electrical properties as the optical gain region. Additionally or alternatively, in some examples, the one or more heaters include at least two heaters, and a separation distance from each heater to the optical gain region is the same. Additionally or alternatively, in some examples, the one or more heaters include a first heater and a second heater, and a separation distance from the first heater to the optical gain region is different from a separation distance from the second heater to the optical gain region. Additionally or alternatively, in some examples, the one or more heaters include a serpentine metal. 
     A method of controlling a semiconductor laser is disclosed. The method can comprise: operating the semiconductor laser in one of a plurality of operation modes, the plurality of operation modes including an off operation mode, a subthreshold operation mode, and an emission operation mode, wherein the laser is configured to emit light in the emission operation mode; coupling an optical gain region included in the semiconductor laser to a first temperature sensor, the first temperature sensor measuring a first temperature of the optical gain region; optically decoupling and thermally coupling one or more heaters included in the semiconductor laser to the optical gain region; coupling the one or more heaters to one or more second temperature sensors, the one or more second temperature sensors measuring one or more second temperatures of the one or more heaters; and maintaining a total thermal load for all of the plurality of operation modes, wherein the total thermal load is equal to a first thermal load, associated with the first temperature, and the one or more second thermal loads, associated with the one or more second temperatures. Additionally or alternatively, in some examples, the method further comprises: dynamically configuring a switching operation of a switch, the switching operation including one or more of: coupling a source to the optical gain region, and coupling the source to the one or more heaters. Additionally or alternatively, in some examples, the method further comprises: configuring a junction to divide a current, from a source, between at least the one or more heaters. Additionally or alternatively, in some examples, the operation of the semiconductor laser includes increasing an injection current to transition the semiconductor laser from the off operation mode to the emission operation mode, the method further comprising: decreasing a current applied to the one or more heaters concurrent with increasing of the injection current. Additionally or alternatively, in some examples, the injection current is incrementally increased, and the current is incrementally decreased. Additionally or alternatively, in some examples, the operation of the semiconductor laser includes decreasing an injection current to transition the semiconductor laser from the emission operation mode to the subthreshold operation mode or the off operation mode, the method further comprising: increasing a current applied to the one or more heaters concurrent with the decreasing of the injection current. Additionally or alternatively, in some examples, the injection current is incrementally decreased, and the current is incrementally increased. Additionally or alternatively, in some examples, the method further comprises: when the laser is not lasing, operating the laser in the subthreshold operation mode. Additionally or alternatively, in some examples, operating the laser in the subthreshold operation mode includes driving the laser with a first current and operating the laser in the emission operation mode includes driving the laser with a second current, the first current being 10-50% of the second current. Additionally or alternatively, in some examples, the method further comprises: dividing a coupling between each of the one or more heaters and a source, the coupling based on a relative separation distance of the one or more heaters from the optical gain region. 
     A system is disclosed. The system can comprise: a plurality of integrated semiconductor lasers, at least some of the plurality of integrated semiconductor lasers configured to emit one or more different wavelengths of light; and a first laser included in the plurality of integrated semiconductor lasers, the first laser including: one or more reflective sections, wherein at least one reflective section is configured to at least partially reflect light back into a cavity of the laser, an optical gain region configured to amplify light energy, and one or more heaters configured to generate heat in response to a non-zero current, wherein each heater is optically decoupled and thermally coupled to the optical gain region. Additionally or alternatively, in some examples, the system further comprises: a second laser included in the plurality of integrated semiconductor lasers, wherein the second laser is adjacent to and thermally decoupled from the first laser. Additionally or alternatively, in some examples, a first separation distance between the first laser and the second laser is greater than a second separation distance between one of the one or more heaters and the optical gain region of the first laser, the first separation distance is at least 100 μm, and the second separation distance is at least 10 μm. Additionally or alternatively, in some examples, the plurality of integrated semiconductor lasers includes outer lasers and inner lasers, located between the outer lasers, each of the outer lasers includes two heaters, and at least one of the outer lasers includes one heater. Additionally or alternatively, in some examples, the system further comprises: one or more sources coupled to the plurality of integrated semiconductor lasers, each source configured to supply a current; a plurality of switches, each switch coupled to one of the plurality of integrated semiconductor lasers and at least one of the one or more current sources, and configured to dynamically couple the at least one of the one or more sources to one or more of an optical gain region and one or more heaters in the at least one of the plurality of integrated semiconductor lasers. Additionally or alternatively, in some examples, the system further comprises: a substrate including: the one or more reflective sections of each integrated semiconductor laser, the optical gain region of each integrated semiconductor laser, and the one or more heaters of each integrated semiconductor laser. Additionally or alternatively, in some examples, the system further comprises: a first substrate including: the one or more reflective sections of each integrated semiconductor laser; and a second substrate including: the optical gain region of each integrated semiconductor laser, and the one or more heaters of each integrated semiconductor laser. Additionally or alternatively, in some examples, the first substrate is a silicon substrate, and the second substrate is a III-V substrate. 
     Although examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the various examples as defined by the appended claims.