PATENT DOCUMENT

Publication Number: US-11886007-B2
Application Number: US-202217985615-A
Country: US
Kind Code: B2

Title: Asymmetric optical power splitting system and method

Abstract:
A waveguide structure and a method for splitting light is described. The method may include optically coupling a first waveguide and a second waveguide, where the optical coupling may be wavelength insensitive. The widths of the first and second waveguides may be non-adiabatically varying and the optical coupling may be asymmetric between the first and second waveguides. A gap between the first and second waveguides may also be varied non-adiabatically and the gap may depend on the widths of the first and second waveguides. The optical coupling between the first and second waveguides may also occur in the approximate wavelength range of 800 nanometers to 1700 nanometers.

Claims:
What is claimed is: 
     
       1. An optical system comprising:
 an optical splitter comprising:
 an input waveguide; 
 a first waveguide; and 
 a second waveguide, wherein: 
 
 the optical splitter includes a first section in which the input waveguide is positioned between the first waveguide and the second waveguide; 
 the first waveguide is optically coupled to the first waveguide and the second waveguide in the first section; 
 the optical splitter includes a second section in which the first waveguide is optically coupled to the second waveguide; and 
 a width of the first waveguide in the second section is different than a width of the second waveguide in the second section. 
 
     
     
       2. The optical system of  claim 1 , wherein:
 a width of the input waveguide decreases in the first section in a direction toward the second section. 
 
     
     
       3. The optical system of  claim 2 , wherein:
 the width of the input waveguide decreases adiabatically in the first section. 
 
     
     
       4. The optical system of  claim 1 , wherein:
 the width of the first waveguide increases in the first section in a direction toward the second section. 
 
     
     
       5. The optical system of  claim 1 , wherein:
 the input waveguide is separated from the first waveguide in the first section by a first gap; 
 the input waveguide is separated from the second waveguide in the first section by a second gap; and 
 the first gap and the second gap have the same width. 
 
     
     
       6. The optical system of  claim 1 , wherein:
 the input waveguide is configured to symmetrically couple light between the first waveguide and the second waveguide. 
 
     
     
       7. The optical system of  claim 1 , wherein:
 the optical splitter includes a third section in which the first waveguide and the second waveguide are optically decoupled. 
 
     
     
       8. The optical system of  claim 7 , wherein:
 the width of the first waveguide in the second section increases between the first section and the third section; and 
 the width of the second waveguide in the second section decreases between the first section and the third section. 
 
     
     
       9. The optical system of  claim 8 , wherein:
 the width of the first waveguide in the second section increases non-adiabatically; and 
 the width of the second waveguide in the second section decreases non-adiabatically. 
 
     
     
       10. The optical system of  claim 1 , wherein:
 the input waveguide terminates between the first section and second section. 
 
     
     
       11. The optical system of  claim 1 , comprising:
 one or more light sources optically connected to the input waveguide, wherein: 
 the input waveguide receives light generated by the one or more light sources; and 
 the optical splitter splits light received by the input waveguide between the first waveguide and the second waveguide. 
 
     
     
       12. An optical system comprising:
 an optical splitter comprising:
 an input waveguide; 
 a first waveguide; and 
 a second waveguide, wherein: 
 
 the optical splitter includes a first section in which the input waveguide is optically coupled to the first waveguide and the second waveguide; 
 the optical splitter includes a second section in which the first waveguide is optically coupled to the second waveguide; and 
 wherein the first waveguide and the second waveguide are configured in the second section to propagate different modes. 
 
     
     
       13. The optical system of  claim 12 , wherein:
 the input waveguide is configured to propagate a fundamental mode in the first section. 
 
     
     
       14. The optical system of  claim 13 , wherein:
 the first waveguide is configured to propagate a symmetric supermode in the second section; and 
 the second waveguide is configured to propagate an asymmetric supermode in the second section. 
 
     
     
       15. The optical system of  claim 12 , wherein:
 the first waveguide includes a first starting end positioned in the first section; 
 the second waveguide includes a second starting end positioned in the first section; and 
 the first starting end is closer to the second section than the second starting end. 
 
     
     
       16. The optical system of  claim 12 , wherein:
 a width of the input waveguide decreases adiabatically in the first section. 
 
     
     
       17. The optical system of  claim 12 , wherein:
 a width of the first waveguide increases in the first section in a direction toward the second section. 
 
     
     
       18. The optical system of  claim 12 , wherein:
 a width of the second waveguide increases in the first section in a direction toward the second section. 
 
     
     
       19. The optical system of  claim 12 , wherein:
 a width of the first waveguide in the second section increases non-adiabatically; and 
 a width of the second waveguide in the second section decreases non-adiabatically. 
 
     
     
       20. The optical system of  claim 12 , comprising:
 one or more light sources optically connected to the input waveguide, wherein: 
 the input waveguide receives light generated by the one or more light sources; and 
 the optical splitter splits light received by the input waveguide between the first waveguide and the second waveguide.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/073,393, filed Oct. 18, 2020, which is a nonprovisional of and claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/923,333, filed Oct. 18, 2019, the contents of which are incorporated herein by reference as if fully disclosed herein. 
    
    
     FIELD 
     Some of the described embodiments relate generally to optical systems with light emitting components and more specifically to asymmetrically splitting optical power between multiple waveguides. 
     BACKGROUND 
     Optical splitters may split such light to facilitate operation of the optical system. Optical splitters may be used to provide multiple outputs from an optical system and/or to split light in order to enable various operations within an optical system. An optical splitter might split light to facilitate control of one or more components within the optical system, such as controlling a power output from the system, to provide simultaneous transmission of data to multiple destinations, as in a point-to-multipoint network, for feedback or feedforward control of an optical system or components therein, and so on. 
     Optical splitters may reduce the amount of light provided to components of the optical system. Additionally, the splitting components are highly sensitive to wavelength changes and function over a very limited and narrow wavelength range. 
     SUMMARY 
     Embodiments of the systems, devices, methods, and apparatus described in the present disclosure are directed to a waveguide structure for asymmetrically splitting optical power over a broad wavelength range while remaining wavelength insensitive. Also described are systems, devices, methods, directed to splitting optical power by non-adiabatically coupling waveguides to one another and varying the widths of waveguides to achieve the desired optical power split. 
     In some examples, the present disclosure describes a light guiding device which may include: a first waveguide optically coupled to and located between a first portion of a second waveguide and a first portion of a third waveguide, wherein the optical coupling is wavelength insensitive; a second portion of the second waveguide, optically coupled to and separated by a first gap from a second portion of the third waveguide, wherein the second portion of the second waveguide and the second portion of the third waveguide are unequal in width; and a third portion of the second waveguide optically decoupled from a third portion of the third waveguide, wherein the third portion of the second waveguide and the third portion of the third waveguide are separated by a second gap. In some examples, the width of the second portion of the second waveguide may increase in width and the second portion of the third waveguide may decrease in width. In some examples, the optical coupling may occur over a wavelength range of 800 nanometers to 1700 nanometers. In some examples, the width of the second portion of the second waveguide and the width of the second portion of the third waveguide may vary non-adiabatically. In still further examples, the walls of the second waveguide may be nonlinear and the walls of the third waveguide may be nonlinear. In some examples, the present disclosure describes an optical system that comprises an optical splitter. The optical splitter comprises an input waveguide, a first waveguide, and a second waveguide, wherein: i) the optical splitter includes a first section in which the input waveguide is optically coupled to the first waveguide and the second waveguide; ii) the optical splitter includes a second section in which the first waveguide is optically coupled to the second waveguide; and iii) the first waveguide and the second waveguide are configured in the second section to propagate different modes. 
     In some examples, the present disclosure describes a method for asymmetrically splitting optical power, which may include: optically coupling a first waveguide to a second waveguide and a third waveguide, in a section of a waveguide structure, where the optical coupling may be wavelength insensitive; non-adiabatically varying a width of the second waveguide and non-adiabatically varying a width of the third waveguide; where a first portion of optical power couples from the first waveguide to the second waveguide and a second portion of optical power couples from the first waveguide to the third waveguide and the first portion and the second portion of optical power are different. In some examples, the method may include varying a width of a gap between the second waveguide and the third waveguide in the section of the waveguide structure, based at least in part on the width of the second waveguide and the width of the third waveguide. In some examples, the optical coupling may occur over a wavelength range of 800 nanometers to 1700 nanometers. In some examples, the width of the second waveguide may be increased and the width of the third waveguide may be decreased in the section of the waveguide structure. 
     In some examples, the method may further include one or more of the following: optically decoupling the second waveguide and the third waveguide in a second section of the waveguide structure, varying a width of a gap between the second waveguide and the third waveguide, in a second section of the waveguide structure, to optically decouple the second waveguide from the third waveguide, and/or controlling an amount of power coupled from the first waveguide to the second waveguide and the third waveguide by varying the widths of the second waveguide and the third waveguide. In some examples, the first portion of optical power may be approximately 90 percent of the optical power of the first waveguide and the second portion of optical power is approximately 10 percent of the optical power of the first waveguide. 
     In some examples, the present disclosure describes a method of splitting optical power, which may include optically coupling a first waveguide to a second waveguide and a third waveguide, in a first section of a waveguide structure; varying a first width of the second waveguide and varying a first width of the third waveguide, in a second section of the waveguide structure, to optically couple the second waveguide with the third waveguide; and varying a gap between the second waveguide and the third waveguide, in a third section of the waveguide structure, to optically decouple the second waveguide from the third waveguide. In some examples, the method may further include non-adiabatically varying the widths of the optically coupled second waveguide and third waveguide. In some examples, non-adiabatically varying the widths of the optically coupled second waveguide and third waveguide may include optically coupling optical power from the second waveguide to the third waveguide. 
     In still further examples, the method may include adiabatically tapering the first waveguide to couple the first waveguide to the second waveguide and the third waveguide. In some examples, optically coupling the first waveguide to the second waveguide and the third waveguide in the first section of the waveguide structure may include splitting the optical power from the first waveguide symmetrically between the second waveguide and the third waveguide. In some examples, the method may include varying a width of the gap between the second waveguide and the third waveguide, based at least in part on the first width of the second waveguide and the first width of the third waveguide. 
     In some examples, the present disclosure describes an optical power splitting device, which may include a tapered input waveguide optically coupled to a waveguide pair in a first section of the optical power splitting device, where the optical coupling is wavelength insensitive; a first waveguide of the waveguide pair non-adiabatically tapered and optically coupled to the tapered input waveguide; and a second waveguide of the waveguide pair non-adiabatically tapered and optically coupled to the tapered input waveguide; where a first quantity of optical power from the tapered input waveguide is coupled to the first waveguide of the waveguide pair and a second quantity of optical power from the tapered input waveguide is coupled to the second waveguide of the waveguide pair and the first quantity of optical power is different from the second quantity of optical power and a difference between the first and second quantity of optical power is based at least in part on a width of the first waveguide of the waveguide pair and a width of the second waveguide of the waveguide pair. In some examples, the first quantity of optical power is 80 percent of the optical power from the tapered input waveguide and the second quantity of optical power is 20 percent of the optical power from the tapered input waveguide. In still further examples, the optical coupling may occur over a wavelength range of 800 nanometers to 1700 nanometers. 
     In addition to the example aspects and embodiments described herein, further aspects and embodiments will become apparent by reference to the drawings and by study of the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG.  1    illustrates a block diagram of an example optical system, which can include a waveguide structure that asymmetrically splits optical power; 
         FIG.  2    illustrates an example layout of a waveguide system. 
         FIG.  3    illustrates another example layout of a waveguide system. 
         FIG.  4    illustrates another example layout of a waveguide system. 
         FIG.  5 A  illustrates another example layout of a waveguide system. 
         FIG.  5 B  illustrates another example layout of a waveguide system. 
         FIG.  6 A  illustrates another example layout of a waveguide system. 
         FIG.  6 B  illustrates another example layout of a waveguide system. 
         FIG.  7    illustrates an example of a process flow. 
         FIG.  8    illustrates an example of a process flow. 
         FIG.  9    illustrates an example of a process flow. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented between them, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following description is not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     Many optical systems may include a light source with one or more light emitters. The light emitters may emit light with various properties such as intensity, wavelength, frequency, and so forth. Optical splitters may split such light to facilitate operation of the optical system. Optical splitters may be used to provide multiple outputs from an optical system and/or to split light in order to enable various operations within an optical system. An optical splitter might split light to facilitate control of one or more components within the optical system, such as controlling a power output from the system, to provide simultaneous transmission of data to multiple destinations, as in a point-to-multipoint network, for feedback or feedforward control of an optical system or components therein, and so on. 
     As one example, one or more properties of light emitters in an optical system may drift over time due to varying conditions, such as temperature, driving current, general aging of the light emitters, and so forth. Light properties may be monitored using one or more monitoring components that receive a portion of the light split off from the emitted light. By monitoring the property (or properties) of the light, the optical system may correct for light emitter drift. Light may be split by an optical splitter in the optical system in order to provide the split light to a monitoring component. 
     The light may be split by ratio tapping components, which split optical power. The light may be split by using components, such as ratio tapping components, that split optical power (e.g., by using optical coupling) from an input waveguide into two separate output waveguides. In some prior solutions, the split ratio may be 50:50 between each of the output waveguides and in some cases may be 0:100, but other split ratios such as 80:20 may not be achieved. 
     In some prior solutions, the ratio tapping components (or other monitoring components) may be capable of achieving an arbitrary splitting ratio, but may be very sensitive to wavelength change. Some monitoring components may be capable of optically splitting power over a wide range of wavelengths, but their splitting ratio is fixed at 50:50. In further prior solutions, some monitoring components may be capable of arbitrarily splitting optical power, but the wavelength range over which they may perform the optical splitting is very narrow and may only be 100 nanometers or less. In still further prior solutions, multiple monitoring components may be used together, but may not be compatible with optical platforms with a relatively large feature size, for example one to two microns. 
     By contrast and as discussed herein, certain waveguide structures may have an asymmetric optical power splitting ratio which may operate over a large wavelength range such as 800 nanometers to 1700 nanometers and may be relatively wavelength insensitive when compared to, for example, directional couplers. Further, the waveguide structure discussed herein may be fabricated for silicon photonics optical platforms which employ a large minimum feature size such as one to three microns or so. In some examples, the waveguide structure may employ silicon waveguides or silicon-on-insulator waveguides for use in silicon photonics systems. Additionally, certain embodiments discussed herein may achieve practically any split ration from 0:100 to 100:0. 
     In some examples, in a first section of the waveguide structure, an input waveguide may be adiabatically tapered and coupled to a first waveguide and a second waveguide, where the fundamental mode in a first section may propagate and convert into a symmetric supermode. Further, the input waveguide may be adiabatically tapered so that the local first-order mode of the input waveguide may propagate through the taper while undergoing relatively few mode conversions to higher-order modes. 
     In a second section of the waveguide structure, the input waveguide may couple to the first and the second waveguides so that each of the first and second waveguides may receive approximately 50 percent of the light from the input waveguide in a 50:50 optical power split. In a third section, the first waveguide may be coupled to the second waveguide so that a designed fraction of optical power may couple between the two waveguides. In the third section, the widths of the first and second waveguides and the gap between the two waveguides may be varied non-adiabatically which may allow asymmetric optical power coupling between the two waveguides. The widths of the first and second waveguides and the gap between the two waveguides may vary so that the designed fraction of power may couple from the symmetric supermode to the antisymmetric supermode. The optical coupling may be wavelength insensitive and the waveguide may operate over a broad wavelength range such as in the approximate wavelength range of 750 nanometers to 1750 nanometers. In a fourth region, the gap between the first and second waveguides may increase so that the first and second waveguides become decoupled from one another and the symmetric and antisymmetric supermodes adiabatically change into the fundamental modes of the decoupled first and second waveguides. 
     Described herein are various configurations for using optical elements, such as waveguides, to monitor one or more properties of light emitting components in optical systems. In some embodiments, the waveguides may split off part of the light from the light emitting components to monitor for drift, while maintaining wavelength insensitivity in the coupling between the waveguides over a broad wavelength range. 
     As used herein, the term “abutting” means that two elements share a common boundary or otherwise contact one another, while the term “adjacent” means that two elements are near one another and may (or may not) contact one another. Thus, elements that are abutting are also adjacent, although the reverse is not necessarily true. Two elements that are “coupled to” one another may be permanently or removably physically coupled to one another and/or operationally or functionally coupled to one another. Additionally, two elements that are “optically coupled” to one another may allow light to pass from one element to the other element. 
     These and other embodiments are discussed below with reference to  FIGS.  1 - 9   . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG.  1    illustrates a block diagram of an example optical system, which can include a waveguide structure that asymmetrically splits optical power. In some examples, the optical system  100  may include a light source  110 , a multiplexer  115 , a waveguide structure  105 , a detector  120 , and a controller  125 . In some examples of  FIG.  1   , monitoring the optical properties of emitted light may employ the use of the optical system  100 . The optical system may be used to verify whether the light sources are emitting a target wavelength and/or have a certain amount of wavelength stability and, in some examples, make adjustments accordingly. The optical system  100  may be configured with one or more functions: multiplexing, combining, selecting, filtering, or any combination thereof, and so forth. In some examples, the number of components in the optical system  100  may include fewer or more components. 
     In  FIG.  1   , the optical system  100  may include one or more light sources  110  and a multiplexer  115 . The light sources  110  can be configured to emit light along one or more light paths  130 . In some examples, the light sources  110  can be configured to emit light having different ranges of wavelengths. In some examples, the light sources  110  may emit in the approximate wavelength range of 800 nanometers to 1600 nanometers. 
     The light paths  130  can be input into the multiplexer  115  which may receive the emitted light along the light path(s)  130  and can combine the emitted light to output light path  135 . The light path  135  can be input to the waveguide structure  105 . The waveguide structure  105  may select and output the light on light path  140 , which can be one of the outputs of the optical system  100 . The waveguide structure  105  may also generate outputs along the light paths  145  to the detector(s)  120 . Although two light paths  145  are depicted in  FIG.  1   , the waveguide structure  105  may output more than two light paths  145 . Similarly, even though one detector is depicted in  FIG.  1   , multiple detectors  120  may receive light on multiple light paths  145  from the waveguide structure  105 . 
     In  FIG.  1   , the detector  120  may receive the light paths  140  and output a signal or signals to a controller  125 . Even though the detector  120  illustrates a combined, single output to the controller  125 , in some examples, an individual output from one or more of the detectors  120  may be output to the controller  125  such that the controller receives an output from a first detector  120  and an output from a second detector (not shown in  FIG.  1   ). 
     The waveguide structure may be a component that receives light on an input light path via an input waveguide, splits light from the input waveguide between two waveguides, and outputs the split light. In some examples, the waveguide structure may output multiple light paths, which may include at least a first light path with a first portion of the input optical power and a second light path with a second portion of input optical power. The splitting of the optical power by the waveguide structure will be discussed in further detail in at least  FIGS.  2 - 4   . Further, the waveguide structure discussed herein may be fabricated for silicon photonics optical platforms which employ a large minimum feature size such as one to three microns or so. In some examples, the waveguide structure may include silicon waveguides or silicon-on-insulator waveguides for use in silicon photonics systems. 
     In some examples, the waveguide structure  105  may receive light on the light path  135  as an input and can output light along light paths  140  and  145 . The waveguide structure  105  may include an input waveguide (not illustrated in  FIG.  1   ) and at least a first waveguide and a second waveguide (the first and second waveguides not illustrated in  FIG.  1   ). The light received via the input waveguide may be asymmetrically split between the first and second waveguides over a very wide wavelength range and while remaining relatively wavelength insensitive. In some examples, the light may be split and/or optically coupled from one waveguide to another regardless of the wavelength. That is, approximately the same amount of power may be split or coupled in the wavelength range of approximately 700 nanometers to 1700 nanometers and the amount of light that is split or coupled may not noticeably vary even though the light may be one or more wavelengths. Thus, wavelength insensitivity may provide stable power splitting or optical coupling even though the light wavelength may vary within a range. Furthermore, the amount of power split between the waveguides may not vary when the wavelength is within or around the approximate range of 700 nanometers to 1700 nanometers, however, outside of this 700 to 1700 nanometer wavelength range, the power split or optical coupling may vary, but the waveguide structure may still be wavelength insensitive. By splitting the optical power using the waveguide structure  105  asymmetrically, the optical system may output more optical power via output light path  140  and may provide significantly less optical power via output light path  145  to the detector  120 . The asymmetrical split of light may allow a significant reduction in the amount of optical power lost to the optical system  100  for monitoring the properties of light source  110 . In some examples, 90 percent of the input optical power may be output via output light path  140  and ten percent of the input optical power may be output to the detector, thus losing ten percent of the input optical power in the optical system  100 . In some examples, the split of optical power may be 80 percent via the output light path  140  and 20 percent may be output to the detector  120 . The configuration of the input waveguide and the first and second waveguides will be discussed in further detail in at least  FIGS.  2 - 4   . 
     In  FIG.  1   , the detector  120  can include any type of diode that can respond to or measure photons impinging on its active area. The detector  120  may generate one or more signals indicative of the light along the light paths  145 . In some examples of  FIG.  1   , these one or more signals may be an output signal or output signals to the controller  125 . 
     Although  FIG.  1    illustrates the multiplexer  115  as included in the optical system  100 , other examples may include the multiplexer  115  as being a component separate from the optical system  100  (not shown in  FIG.  1   ). Examples of the optical system  100  can further include one or more additional components, such as filters, amplifiers, analog-to-digital converters (ADCs), etc. (not shown) located between the detector(s)  120  and the controller  125 . These additional components can perform one or more operations on or with the signals from the detector(s)  120  such as processing the signals, amplifying the signals, performing one or more calculations or comparisons, and so forth. 
     In some examples, the signal(s) from the optical system  100  may be used as feedback in a control loop. As illustrated in  FIG.  1   , the optical system  100  may also include a controller  125  that may receive and analyze the signal(s) from the detector(s)  120  along path  150 . The controller  125  may generate one or more signals that may be inputs to the light source  110  along path  155 . In some examples, the analysis by the controller  125  may include monitoring the wavelength of the emitted light as discussed herein and determining the difference between the monitored wavelength and a target wavelength. The controller  125  may be configured to provide a signal to the light source  110  via path  155 , and the signal may be employed to lock the monitored wavelength to a target wavelength. 
     The signal(s) from the controller  125  may be used to control the light source  110  (e.g., control signal(s) transmitted to the light source  110  via path  155 ) and the properties of light emitted by the light source  110  along the light paths  130 . In some examples, the signal(s) from the controller  125  can be indicative of changes in one or more properties (e.g., temperature, current, etc.) of the light source  110 . The changes may be associated with locking the monitored wavelength to the target wavelength. In some examples, the controller  125  can use other information (e.g., measured temperature of the light source  110 ) in generating the signal(s). 
     The controller  125  may lock the monitored wavelength to the target wavelength, and if the monitored wavelength is not within a certain threshold wavelength from the target wavelength, the controller  125  can adjust or send a new signal to the light source  110 . In some examples, the controller  125  may transmit the new signal to another controller (not illustrated in  FIG.  1   ) that controls the light source  110 . 
     In some instances, the light source  110  may emit light from at least two of the light sources at different times. For example, the individual lights of the light source  110  may be activated sequentially or one at a time. The optical system  100  may monitor the wavelength of the emitted light, and the controller  125  may adjust the individual signals to one or more light sources. Alternatively, the controller  125  may receive signals from the detectors sequentially, and the controller  125  may adjust the signals to the light sources in response to the sequentially received, multiple signals from the detectors  120 . 
       FIG.  2    illustrates an example layout of a waveguide system. In some examples, the waveguide system  200  may include an input waveguide  205 , a first waveguide  210 , a second waveguide  215 , a first gap  220 , a second gap  225 , a third gap  230 , and a fourth gap  255 . The input waveguide, the first waveguide, the second waveguide, and the corresponding gaps between the waveguides may be included in the waveguide structure  105  described in  FIG.  1   . Additionally in  FIG.  2   , the waveguide system  200  may include a first section  235  extending between S 0  and S 1 , a second section  240  extending between S 1  and S 2 , a third section  245  extending between S 2  and S 3 , and a fourth section  250  between S 3  and S 4 . There may be fewer or more sections in the waveguide system as will be discussed in further detail herein with respect to at least  FIGS.  3  and  4   . In  FIG.  2   , the elements are not drawn to scale and may be thicker or thinner than depicted or spaced apart by varying gap widths as described herein at least with respect to  FIGS.  2 - 4   . The S 0  and the S 4  lines as used herein, indicate start and termination points of the first section and the last section, respectively, and are not indicative of termination of the input waveguide, the first waveguide or the second waveguide. Additionally, the cladding is illustrated as a rectangle and in cross-section but is not cross-hatched for clarity. Further, the waveguides may be positioned above a substrate, but the exposed portion of the waveguides may be less than depicted in the cross-sectional views of the figures. 
     As illustrated in  FIG.  2   , in the first section  235 , the input waveguide  205  may depict input light entering the waveguide system  200  and in some examples, the input waveguide  205  may be a single input waveguide. In some examples, the light in the input waveguide  205  may be received via the light path  135  and from the multiplexer  115  of  FIG.  1    or from the light source  110  of  FIG.  1   . In the first section  235 , the input waveguide  205  may be configured to reduce optical power loss, thus in some examples and as shown in  FIG.  1   , the input waveguide  205  may not be tapered. Generally, one of the approaches to arbitrary ratio tapping via waveguides is available using CMOS processing technology. In CMOS technology, 600 nanometers is a large minimum feature size. A second approach to arbitrary ratio tapping via waveguides is using larger minimum feature sizes of approximately one micron and this approach will be discussed in further detail herein with respect to  FIGS.  2 - 7   . 
     In the first section  235 , the input end of the input waveguide  205  and at S 0  may be in the approximate size range of two-three microns and, in some examples, may be approximately 2.6 microns. The received light may include light with multiple wavelengths with a broad range such as in the approximate wavelength range of 800 nanometers to 1600 nanometers or in some cases in the approximate wavelength range of 700 nanometers to 1800 nanometers. Although the input waveguide  205  may be depicted as having linear walls or edges, the input waveguide  205  may have any type of nonlinear walls such as, but not limited to, curved, sinusoidal, and so forth. The taper of the input waveguide  205  in first section  235  of the waveguide system  200  may be configured so that little to no optical loss may occur in the first section. In some examples, the portion of the input waveguide  205  in the first section  235  may be referred to herein as a first portion or a first section of the input waveguide  205 . 
     The second section  240  of the waveguide system  200  may include the input waveguide  205 , the first waveguide  210 , and the second waveguide  215 . As depicted in  FIG.  2   , a second portion of the input waveguide  205  may be spaced apart from the first waveguide  210  by a first gap  220  and the input waveguide  205  may be optically coupled to the first waveguide  210 . Similarly, the second portion of the input waveguide  205  may be spaced apart from the second waveguide  215  by a second gap  225  and the input waveguide  205  may be optically coupled to the second waveguide  215  as well. 
     The input waveguide  205  may be tapered in the second section  240  of the waveguide system  200 . Further, the input waveguide  205  may be adiabatically tapered so that the local first-order mode of the input waveguide  205  may propagate through the taper while undergoing relatively few mode conversions to higher-order modes. The input waveguide  205  may taper from a consistent width at S 1  in the first section  235  of the waveguide system  200  to a minimum feature size at S 2  in the second section  240 . In some examples, the minimum features size may be less than approximately one micron. Additionally, the input waveguide  205  may be optically coupled to the first waveguide  210  and the second waveguide  215 . 
     As illustrated in  FIG.  2   , the first waveguide  210  and the second waveguide  215  may also be tapered similarly to one another. In some examples, the first waveguide  210  and the second waveguide  215  may not be tapered similarly to one another as will be discussed in further detail herein with respect to at least  FIGS.  2 - 4   . The first waveguide  210  and the second waveguide  215  may both have the minimum feature size width, at S 1  and in the second section  240 , which may be the same approximate minimum feature size at the end of the input waveguide  205  at S 2 . The first waveguide  210  and the second waveguide  215  may be separated from the input waveguide  205  by gaps  220 , and  225 , respectively. In the second section  240  of the waveguide system  200 , the gaps  220  and  225  may approximately the same width. In some examples, the widths of these gaps may vary as will be discussed in further detail herein with respect to at least  FIGS.  2 - 4   . 
     In the second section  240 , the input waveguide  205  may couple to the first waveguide  210  and the second waveguide  215  so that each of the first and second waveguides may receive approximately 50 percent of the light from the input waveguide  205 . In  FIG.  2   , an ideal optical system with no optical losses is assumed for discussion purposes. In some examples, where a physical optical system is built with physical optical components, optical losses may occur throughout the system due to propagation losses, general optical leaking, and so forth, thus less than 50 percent of the optical power may be coupled from the input waveguide  205  to the first waveguide  210  and the second waveguide  215 , but the coupled optical power may be approximately symmetrically coupled between the first and second waveguides. Although the first and second waveguides and the corresponding gaps are depicted as symmetric in the second section  240  of the waveguide system  200 , the first and second waveguides may be asymmetrically tapered with different size gaps so long as approximately 50 percent of the light from the input waveguide  205  is split between the first waveguide and the second waveguide at S 2 . 
     As illustrated in the third section  245  and from S 2  to S 3 , the first waveguide  210  may have a different taper than the second waveguide  215 . At S 3 , the width of the first waveguide  210  may be greater than the width of the second waveguide  215 . In the third section  245 , the first waveguide  210  may be optically coupled to the second waveguide  215  so that a designed fraction of optical power may couple between the two waveguides. In the third section  245 , the widths of the first and second waveguides and the gap  230  between the two waveguides may be varied non-adiabatically which may allow asymmetric optical power coupling between the two waveguides. 
     Although the walls or sides of the first and second waveguides are depicted as linear, the walls or sides of the two waveguides may be nonlinear, curved, sinusoidal, or any profile so long as the widths of the two waveguides allow for asymmetric optical power coupling. Similarly, the gap  230  is depicted as a consistent gap between S 2  and S 3  in the third section  245 , but the gap may vary in width within the third section  245 , so long as the gap  230  allows for the first waveguide  210  and the second waveguide  215  to asymmetrically couple optical power between the two waveguides. Additionally, the widths of the first and second waveguides and the width of gap  230  may be selected to produce a flat response versus wavelength, or to produce wavelength insensitive coupling between the first waveguide  210  and the second waveguide  215 . 
     Further, in the third section  245 , the distance S 2  to S 3  may be selected based at least partially on that coupling being a periodic event. For example, once the light is appropriately coupled from the second waveguide  215  to the first waveguide  210  (e.g., approximately 80 percent of the light is in the first waveguide  210  and 20 percent of the light is in the second waveguide  215 ), the distance between S 2  and S 3  may be selected so that the light from the second waveguide  215  may not couple back to the first waveguide  210 . 
     In the third section  245  of  FIG.  2   , the first waveguide  210  and the second waveguide  215  may be coupled to one another and the widths of the first waveguide  210  and the second waveguide  215  and the gap  230  therebetween may be varied non-adiabatically so that a designed fraction may couple from the symmetric supermode to the antisymmetric supermode while maintaining wavelength insensitivity. At S 3  of the third section  245 , the first waveguide  210  may be at a symmetric supermode and the second waveguide  215  may be at an antisymmetric supermode. In some examples, the symmetric supermode of the first waveguide  210  and the antisymmetric supermode of the second waveguide  215  may be achieved without coupling fifty percent of the optical power into each of the first and second waveguides as described in this example of  FIG.  2   . The asymmetric coupling into the first waveguide  210  and the second waveguide  215  may be achieved by coupling directly from the input waveguide  205  to the first waveguide  210  and the second waveguide  215  as opposed to coupling the first waveguide  210  and the second waveguide  215  with one another as will be discussed in further detail herein and with respect to at least  FIGS.  2 - 4   . 
     In the fourth section  250  in  FIG.  2   , the first waveguide  210  and the second waveguide  215  may become optically decoupled from one another. As depicted in the fourth section  250 , the gap  255  may gradually increase from S 3  to S 4  to optically decouple the first waveguide  210  from the second waveguide  215 . In the example of  FIG.  2   , the symmetric supermode and the antisymmetric supermode at S 3  may adiabatically evolve into the fundamental modes of the decoupled first waveguide  210  and the second waveguide  215  at S 4 . 
       FIG.  3    illustrates an example layout of a waveguide system. In some examples, the waveguide system  300  may include an input waveguide  305 , a first waveguide  310 , a second waveguide  315 , a first gap  320  a second gap  325 , and a third gap  355 . The input waveguide, the first waveguide, the second waveguide, and the corresponding gaps between the waveguides may be included in the waveguide structure  105  described in  FIG.  1   . Additionally in  FIG.  3   , the waveguide system  300  may include a first section  335  extending between S 0  and S 1 , a second section  345  extending between S 1  and S 2 , and a third section  350  extending between S 2  and S 3 . There may be fewer or more sections in the waveguide system as will be discussed in further detail herein with respect to at least  FIGS.  2 - 4   . In  FIG.  3   , some of the waveguide elements and gaps of the waveguide system  300  are similarly numbered such as the input waveguide  305  of  FIG.  3    and the input waveguide  205  of  FIG.  2    and in some examples may share similar properties. In  FIG.  3   , the elements are not drawn to scale and may be thicker or thinner than depicted or spaced apart by varying gap widths as described herein at least with respect to  FIGS.  2 - 4   . Further, the end of the input waveguide  305  at S 2  is depicted as smaller than the end of the first waveguide and the end of the second waveguide at S 1 , but may be the same size or larger than the end of the first waveguide and the end of the second waveguide at S 1 . The S 0  and the S 3  lines as used herein, indicate start and termination points of the first section and the last section, respectively, and are not indicative of termination of the input waveguide, the first waveguide or the second waveguide. 
     Similar to  FIG.  2    and as illustrated in  FIG.  3   , in the first section  335  of the waveguide system  300 , the input waveguide  305  may receive input light entering the waveguide system  300  and, in some examples, the input waveguide  305  may be a single input waveguide. In the first section  335 , the input waveguide  305  may be configured to reduce optical power loss, thus in some examples and as shown in  FIG.  3   , the input waveguide  305  may not be substantially tapered. Similar to the input waveguide  205  of  FIG.  2   , the approximate size range of the input end of the input waveguide  305  may be in the approximate range of two-three microns and, in some examples, may be approximately 2.6 microns. The received light may include light with multiple wavelengths with a broad range such as in the approximate wavelength range of 800 nanometers to 1600 nanometers. Although the input waveguide  305  may be depicted as having linear walls or edges, the input waveguide  305  may have any type of nonlinear walls such as, but not limited to, curved, sinusoidal, and so forth. The taper of the input waveguide  305  in the first section  335  of the waveguide system  300  may be configured so that little to no optical loss may occur in the first section. 
     As illustrated in  FIG.  3    and different from  FIG.  2   , there may not be a section of the waveguide system  300  where the input waveguide  305  couples approximately 50 percent of the light to each of the first waveguide  310  and the second waveguide  315 . Additionally and alternatively in  FIG.  3   , in the second section  345  and from S 1  to S 2 , the first waveguide  310  may have a different taper than the second waveguide  315 . At S 2 , the width of the first waveguide  310  may be greater than the width of the second waveguide  315 . In the second section  345  the input waveguide  305  may be optically coupled to each of the first waveguide  310  and the second waveguide  315  so that a designed fraction of optical power may couple from the input waveguide  305  to the first waveguide  310  and the second waveguide  315 . In the second section  345 , the widths of the first and second waveguides and the widths of gaps  320  and  325  between the input waveguide  305  and the two waveguides may be varied non-adiabatically which may allow asymmetric optical power coupling from the input waveguide  305  to the first waveguide  310  and the second waveguide  315 . 
     Although the walls or sides of the first and second waveguide are depicted as linear, the walls or sides of the two waveguides may be nonlinear, curved, sinusoidal, or any profile so long as the widths of the two waveguides allow for asymmetric optical power coupling. Similarly, the gap  320  and the gap  325  are depicted as a consistent gap between S 1  and S 2  in the second section  345 , but the gaps may vary in width within the second section  345 , so long as the gap  320  and the gap  325  allow for the input waveguide  305  to asymmetrically couple optical power to the first waveguide  310  and to the second waveguide  315 . Similar to  FIG.  2   , in  FIG.  3   , the widths of the first and second waveguides and the width of the gaps  320  and  325  may be selected to produce a flat response versus wavelength, or to produce wavelength insensitive coupling from the input waveguide  305  to the first waveguide  310  and the second waveguide  315 . 
     In the second section  345  of  FIG.  3   , the width of the first waveguide  310  and the width of the second waveguide  315  may vary non-adiabatically so that a designed fraction may couple from the symmetric supermode to the antisymmetric supermode while maintaining wavelength insensitivity. At S 2  of the second section  345 , the first waveguide  310  may be at a symmetric supermode and the second waveguide  315  may be at an antisymmetric supermode. The asymmetric coupling into the first waveguide  310  and the second waveguide  315  may be achieved by coupling directly from the input waveguide  305  to the first waveguide  310  and the second waveguide  315  as opposed to coupling the first waveguide  210  and the second waveguide  215  with one another as discussed in  FIG.  2   . 
     In the third section  350  in  FIG.  3   , the first waveguide  310  and the second waveguide  315  may become optically decoupled from one another. As depicted in the third section  350 , the gap  355  may gradually increase from S 2  to S 3  to optically decouple the first waveguide  310  from the second waveguide  315 . In the example of  FIG.  3   , the symmetric supermode and the antisymmetric supermode at S 2  may adiabatically evolve into the fundamental modes of the decoupled first waveguide  310  and the second waveguide  315  at S 3 . 
       FIG.  4    illustrates an example layout of a waveguide system. In some examples, the waveguide system  400  may include an input waveguide  405 , a first waveguide  410 , a second waveguide  415 , a first gap  420 , a second gap  425 , a third gap  430 , and a fourth gap  455 . The input waveguide, the first waveguide, the second waveguide, and the corresponding gaps between the waveguides may be included in the waveguide structure  105  described in  FIG.  1   . Additionally in  FIG.  4   , the waveguide system  400  may include a first section  435  extending between S 0  and S 1 , a second section  440  extending between S 1  and S 2 , a third section  445  extending between S 2  and S 3 , and a fourth section  450  extending between S 3  and S 4 . There may be fewer or more sections in the waveguide system as will be discussed in further detail herein with respect to at least  FIG.  3   . In  FIG.  4   , the elements are not drawn to scale and may be thicker or thinner than depicted or spaced apart by varying gap widths as described herein at least with respect to  FIGS.  2 - 4   . The S 0  and the S 4  lines as used herein, indicate start and termination points of the first section and the last section, respectively, and are not indicative of termination of the input waveguide, the first waveguide or the second waveguide. 
     Similar to  FIG.  2   , the waveguide structure of  FIG.  4    includes four sections. As illustrated in  FIG.  4   , the walls or sides of the input waveguide  405 , the first waveguide  410 , and the second waveguide  415  may be curved. Although the walls or sides of the waveguides in  FIGS.  2  and  3    were depicted as linear, the walls or sides of the waveguides may be nonlinear, curved (as depicted in  FIG.  4   ), or approximately sinusoidal in profile. The widths of the first waveguide  410  and the second waveguide  415  and the gap or gaps therebetween may be selected based at least partially to accommodate asymmetric coupling to the first and second waveguides and while remaining insensitive to wavelength changes over a broad wavelength range. The profile of the first waveguide  410  and the second waveguide  415  and the profile of the gap may vary non-adiabatically so that a designed fraction of power may couple from the symmetric supermode to the antisymmetric supermode while maintaining wavelength change insensitivity over a broad wavelength range. 
     Similar to  FIG.  2   , in the first section  435 , the input waveguide  405  may depict input light entering the waveguide system  400  and the input waveguide  405  may be configured to reduce optical power loss, thus, as illustrated in  FIG.  4   , the input waveguide  405  may not be tapered. In the first section  435 , the input end of the input waveguide  405  and at S 0  may be in the approximate size range of two-three microns and, in some examples, may be approximately 2.6 microns. The received light may include light with multiple wavelengths with a broad range such as in the approximate wavelength range of 800 nanometers to 1600 nanometers. The input waveguide  405  in the first section  435  may be configured so that little to no optical loss may occur in the first section. 
     The second section  440  of  FIG.  4    is similarly configured to  FIG.  2    and the waveguide system  400  may include the input waveguide  405 , the first waveguide  410 , and the second waveguide  415 . As depicted in  FIG.  4   , a second portion of the input waveguide  405  may be spaced apart from the first waveguide  410  by a first gap  420  and the input waveguide  405  may be optically coupled to the first waveguide  410 . Similarly, the second portion of the input waveguide  405  may be spaced apart from the second waveguide  415  by a second gap  425  and the input waveguide  405  may be optically coupled to the second waveguide  415  as well. 
     The input waveguide  405  may be adiabatically tapered so that the local first-order mode of the input waveguide  405  may propagate through the taper while undergoing relatively few mode conversions to higher-order modes. The input waveguide  405  may taper from a consistent width at S 1  in the first section  435  to a minimum feature size at S 2  in the second section  440 . In some examples, the minimum feature size may be less than approximately one micron. Additionally, the input waveguide  405  may be optically coupled to the first waveguide  410  and the second waveguide  415  such that approximately fifty percent of the light from the input waveguide  405  may couple to the first waveguide  410  and approximately fifty percent of the light from the input waveguide  405  may couple to the second waveguide  415 . Similar to  FIG.  2   , in  FIG.  4   , an ideal optical system with no optical losses is assumed for discussion purposes. In some examples, in a physical optical system built with physical optical components, optical losses may occur throughout the system due to propagation losses, general optical leaking, and so forth, thus less than 50 percent of the optical power may be coupled from the input waveguide  405  to the first and second waveguides, but the coupled optical power may be approximately symmetrically coupled between the first and second waveguides. 
     As illustrated in the third section  445  and from S 2  to S 3 , the first waveguide  410  may have a different taper than the second waveguide  415 . At S 3 , the width of the first waveguide  410  may be greater than the width of the second waveguide  415 . In the third section  445 , the first waveguide  410  may be optically coupled to the second waveguide  415  so that a designed fraction of optical power may couple between the two waveguides. In the third section  445 , the widths of the first and second waveguides and the gap  430  between the two waveguides may be varied non-adiabatically which may allow asymmetric optical power coupling between the two waveguides. Additionally, the widths of the first and second waveguides and the width of gap  430  may be selected to produce a flat response versus wavelength, or to produce wavelength insensitive coupling between the first waveguide  410  and the second waveguide  415 . 
     In the third section  445  of  FIG.  4   , the first waveguide  410  and the second waveguide  415  may be coupled to one another and the widths of the first waveguide  410  and the second waveguide  415  and the gap  430  therebetween may be varied non-adiabatically so that a designed fraction may couple from the symmetric supermode to the antisymmetric supermode while maintaining wavelength insensitivity. At S 3  of the third section  445 , the first waveguide  410  may be at a symmetric supermode and the second waveguide  415  may be at an antisymmetric supermode. 
     In the fourth section  450  in  FIG.  4   , the first waveguide  410  and the second waveguide  415  may become optically decoupled from one another. As depicted in the fourth section  450 , the gap  455  may gradually increase from S 3  to S 4  to optically decouple the first waveguide  410  from the second waveguide  415 . In the example of  FIG.  4   , the symmetric supermode and the antisymmetric supermode at S 3  may adiabatically evolve into the fundamental modes of the decoupled first waveguide  410  and the second waveguide  415  at S 4 . 
       FIG.  5 A  illustrates another example layout of a waveguide system. The waveguide system  500  is similar to the other waveguide systems described herein, such as with respect to  FIGS.  3  and  4   . Similarly numbered elements may perform similar functions and thus have the same or similar functionality and/or structure, and so are not discussed at length. The waveguide system  500  includes an input waveguide  505   a , a first waveguide  510   a , a second waveguide  515   a , a first gap  520   a , a second gap  525   a , and a third gap  530   a . Additionally, the waveguide system  500  may include a first section  535   a  extending between S 0  and S 1 , a second section extending  540   a  between S 1  and S 2 , and a third section extending  550   a  between S 2  and S 3 . The S 0  and the S 3  lines as used herein, indicate start and termination points of the first section and the last section, respectively, and are not indicative of the termination of the input waveguide, the first waveguide or the second waveguide. 
     In the second section  540   a , a starting end of the first waveguide  510   a  is at approximately the start of the second section  540   a  (e.g., at line S 1 ), while the starting end of the second waveguide  515   a  is closer to the end of the second section  540   a  (e.g., closer to line S 2 ). Positioning an end of the second waveguide  515   a  later than an end of the first waveguide  505   a , relative to the input waveguide  505   a  may affect the optical power coupling to the second waveguide  515   a . In some examples, less optical power may couple to the second waveguide  515   a  from the input waveguide  505   a.    
     A width of the first gap  520   a  (that is, a distance between nearest sides of the input waveguide  505   a  and the first waveguide  510   a ) may be approximately the same or the same as the second gap  525   a  (that is, a distance between nearest sides of the input waveguide  505   a  and the second waveguide  515   b ). The widths of the gaps affect the power coupling between waveguides; the larger the width, the less power that couples from the input waveguide to the waveguide in question. In some examples, it may be desirable to not introduce larger gaps, which lead to a larger footprint for the waveguide system  500 . In some embodiments and as shown in  FIG.  5 A , the first waveguide  510   a  may have a narrower width than the second waveguide  515   a , which affects what modes of light are supported by the second waveguide  515   a . In some embodiments, some of the modes couple to the first waveguide  510   a  and although the same modes may couple to the second waveguide  515   a , they will be converted to a different mode because the second waveguide  515   a  does not support the specific mode. By controlling the location of the starting end of the second waveguide  515   a  relative to the first waveguide  510   a , the ratio of optical power splitting may be affected and different ratios of optical power splitting may be achieved. For example, the closer the starting ends of the first waveguide  510   a  and the second waveguide  515   a  are to one another, the closer the amount of optical power may be coupled into each waveguide. In other examples, the farther apart the starting ends of the first waveguide  510   a  and the second waveguide  515   a  are from each other, the greater the disparity of optical power may be coupled into each of the these waveguides relative to one another. 
       FIG.  5 B  illustrates another example layout of a waveguide system. The waveguide system  501  is similar to the other waveguide systems described such as waveguide systems  300 ,  400 , and  500 . Similarly numbered elements may perform similar functions and thus have the same or similar functionality and/or structure, and so are not discussed at length. The waveguide system  501  includes an input waveguide  505   b , a first waveguide  510   b , a second waveguide  515   b , a first gap  520   b , a second gap  525   b , and a third gap  530   b . The waveguide system  501  may include a first section  535   b  extending between S 0  and S 1 , a second section  540   b  extending between S 1  and S 2 , and a third section  550   b  extending between S 2  and S 3 . The S 0  and the S 3  lines as used herein, indicate start and termination points of the first section and the last section, respectively, and are not indicative of termination of the input waveguide, the first waveguide or the second waveguide. 
     Similar to  FIG.  5 A , in the waveguide system  501 , the starting end of the first waveguide  510   b  is at the start of the second section  545   b  (e.g., at line S 1 ). However in  FIG.  5 B , the starting end of the second waveguide  515   b  is closer to the start of the second section  545   b  than in  FIG.  5 A . The second waveguide  515   b  therefore may receive more optical power coupled in from the input waveguide  505   b , than does the second waveguide  515   a  of  FIG.  5 A . 
       FIG.  6 A  illustrates another example layout of a waveguide system. Like prior embodiments, the waveguide system  600  includes the input waveguide  605   a , a first waveguide  610   a , a second waveguide  615   a , a first gap  620   a  defined between the input waveguide and the first waveguide, a second gap  625   a  defined between the input waveguide and the second waveguide, a third gap  630   a  defined between the first and second waveguides. Unlike prior-discussed waveguide systems, the waveguide system  600  also includes a first set of coupling elements  673   a  and a second set of coupling elements  674   a . The S 0  and the S 3  lines as used herein, indicate start and termination points of the first section and the last section, respectively, and are not indicative of termination of the input waveguide, the first waveguide or the second waveguide. 
     The first set of coupling elements  673   a  physically connect the input waveguide  605   a  to the first waveguide  610   a , and are typically formed from a material with a refractive index between the refractive indices of silicon and silicon dioxide. In some embodiments, the first set of coupling elements  673   a  may be formed of silicon. Another way to describe the position of the first set of coupling elements  673   a  is that they are positioned in the first gap  620   a . The first set of coupling elements  673   a  increase the rate of optical power coupling from the input waveguide  605   a  to the first waveguide  610   a . The first set of coupling elements  673   a  may be optical sub-micron structures, in other examples they may be larger. In some embodiments, the first set of coupling elements  673   a  may also increase the amount of optical coupling from the input waveguide to the first waveguide  610   a.    
     Similarly, the second set of coupling elements  674   a  are positioned in the second gap  625   a  and may also increase the rate of optical power coupling from the input waveguide  605   a  to the second waveguide  615   a . As with the first set of coupling elements  673   a , the second set of coupling elements may physically connect the input waveguide  605   a  and the second waveguide  615   a  even though the second set of coupling elements may be made of a different material than the input waveguide  605   a  and the second waveguide  615   a.    
     The first and second sets of coupling elements  673   a ,  674   a  are shown in  FIG.  6 A  as mirror opposites of one another, but may be in an offset position from one another in other examples. Additionally, the first and second sets of coupling elements  673   a  and  674   a  are shown as being the same size, but may be any size depending on the desired rate of optical power coupling. Further, any number of coupling elements may be included in the first and second sets of coupling elements  673   a  and  674   a  as appropriate for the desired rate of optical power coupling. In some embodiments, the first and second set of coupling elements  673   a  and  674   a  may be used to increase the rate of optical coupling when the first gap  620   a  and the second gap  625   a  may not be changed or is as narrow as allowed by fabrication constraints and/or application specifications. In some examples, the refractive index of the first and second coupling elements  673   a  and  674   a  may between the refractive index of silicon and silicon dioxide, and may depend at least partially, on the desired rate of optical coupling. 
     By increasing the number of coupling elements in the first and second sets of coupling elements  673   a ,  674   a , the rate of optical power that couples from the input waveguide  605   a  to the first waveguide  610   a  and the second waveguide  615   a  increases. Likewise, if the size of the coupling elements increases, but the number of coupling elements decreases in the first and second sets of coupling elements  673   a ,  674   a , the rate of optical power that couples from the input waveguide  605   a  to the first waveguide  610   a  and the second waveguide  615   a  increases. Generally, the volume of the coupling elements between the input waveguide  605   a  and the first and second waveguides  610   a ,  610   b , relative to the cladding between the input waveguide  605   a  and the first and second waveguides  610   a ,  610   b  controls the rate of optical power coupling between the input waveguide  605   a  and the first and second waveguides  610   a ,  610   b.    
     In some embodiments, the refractive index of the first and second sets of coupling elements  673   a  and  674   a  may be between the refractive index of silicon and silicon dioxide, and may depend, at least partially, on the desired rate of optical coupling. The closer the refractive indices of the first and second sets of coupling elements  673   a  and  674   a  are to silicon, the more the coupling elements facilitate optical power coupling. Further, the closer the refractive indices of the first and second sets of coupling elements  673   a  and  674   a  are to silicon dioxide, the less the coupling elements facilitate optical power coupling. 
     In some embodiments, the first and second sets of coupling elements  673   a  and  674   a  may not abut one or more of the input waveguide  605   a , the first waveguide  610   a , and/or the second waveguide  615   a . For example, the first and second sets of coupling elements  673   a  and  674   a  may abut the side of the input waveguide  605   a  toward the first set of coupling elements  673   a  and the first waveguide  610   a , but not the second waveguide  615   a . In this example, there may be faster optical coupling and/or a higher amount of optical coupling between the input waveguide  605   a  and the first waveguide  610   a  than between the input waveguide  605  and the second waveguide  615   a.    
       FIG.  6 B  illustrates another example layout of a waveguide system  601  that includes a set of coupling elements  673   b , which function similarly to those described above with respect to  FIG.  6 A . The waveguide system  601  also includes an input waveguide  605   b , first waveguide  610   b  separated by a gap  620   b  from the input waveguide, and a second waveguide  615   b  separated by a gap  625   b  from the input waveguide. These components function as described above with equivalent components shown in  FIGS.  2 ,  3   , and the like, and so are not described in more detail herein. 
     The first set of coupling elements  673   b  are positioned in the first gap  620   b  to facilitate optical coupling from the input waveguide  605   b  to the first waveguide  610   b , but not to the second waveguide  615   b . The first set of coupling elements  673   b  enhance the optical coupling rate between the input waveguide  605   b  and the first waveguide  610   b , which increases the rate of optical coupling when compared with the optical coupling rate to the second waveguide  615   b . In some embodiments, the first set of coupling elements  673   b  may be used when the first gap  620   b  and the second gap  625   b  are as narrow as allowed by fabrication constraints or the form factor of the device into which the waveguide system  601  may be incorporated. 
       FIG.  7    illustrates an example process flow  700 . In some examples, the process flow  700  depicted in  FIG.  7    may include additional processes not depicted in  FIG.  7   , or may exclude some of the processes included in  FIG.  7   . Further, the processes of  FIG.  7    are ordered for purposes of discussion, but may, in some examples, be performed in a different order. In the example of  FIG.  7   , the process flow  700  may include a light guiding device which may include a waveguide structure capable of asymmetric optical power splitting of light. 
     In  FIG.  7    and at  705 , a first waveguide may be optically coupled to and located between a first portion of a second waveguide and a first portion of a third waveguide. In some examples, the optical coupling between the first waveguide and the second and third waveguides may be wavelength insensitive. In some examples, the first waveguide may be an input waveguide and the first waveguide may be adiabatically tapered and coupled to the waveguide pair, such that the fundamental mode changes into the symmetric supermode as described herein with respect to at least  FIGS.  1 - 6 B . 
     At  710 , a second portion of the second waveguide may be optically coupled to and separated by a first gap, from a second portion of the third waveguide. In some examples, the second portion of the second waveguide and the second portion of the third waveguide may be unequal in width. Further, the widths of the second portions of the second and third waveguides may be varied non-adiabatically to allow for asymmetric optical power splitting between the second and third waveguides as described herein with respect to at least  FIGS.  1 - 6 B . 
     At  715 , a third portion of the second waveguide may be optically decoupled from a third portion of the third waveguide. In some examples, the third portion of the second waveguide and the third portion of the third waveguide may be separated by a second gap. Additionally, the symmetric supermode of the second waveguide and the antisymmetric supermode of the third waveguide may change into the fundamental modes of the decoupled second and third waveguides as described herein with respect to at least  FIGS.  1 - 6 B . 
       FIG.  8    illustrates an example process flow  800 . In some examples, the process flow  800  depicted in  FIG.  8    may include additional processes not depicted in  FIG.  8   , or may exclude some of the processes included in  FIG.  8   . Further, the processes of  FIG.  8    are ordered for purposes of discussion, but may, in some examples, be performed in a different order. In the example of  FIG.  8   , the process flow  800  may include a light guiding device which may include a method for asymmetrically splitting optical power. 
     In  FIG.  8    and at  805 , a first waveguide may be optically coupled to both a second waveguide and a third waveguide in a waveguide structure. In some examples, the optical coupling may be wavelength insensitive in that changes in the wavelength of light may not affect the coupling between the first waveguide and the second waveguide and may not affect the coupling between the first waveguide and the third waveguide as described herein with respect to at least  FIGS.  1 - 6 B . Further, in some examples, the optical coupling may occur over an approximate wavelength range of 800 nanometers to 1700 nanometers. 
     At  810 , the width of the second waveguide and the width of the third waveguide may be non-adiabatically varied, where a first portion of optical power couples from the first waveguide to the second waveguide and a second portion of optical power couples from the first waveguide to the third waveguide and the first portion and the second portion of optical power may be different as described herein with respect to at least  FIGS.  1 - 6 B . 
       FIG.  9    illustrates an example process flow  900 . In some examples, the process flow  900  depicted in  FIG.  9    may include additional processes not depicted in  FIG.  9   , or may exclude some of the processes included in  FIG.  9   . Further, the processes of  FIG.  9    are ordered for purposes of discussion, but may, in some examples, be performed in a different order. In the example of  FIG.  9   , the process flow  900  may include a light guiding device which may include an optical power splitting device. 
     At  905  and in  FIG.  9   , a first waveguide may be optically coupled to a second waveguide and a third waveguide, in a first section of a waveguide structure. In some examples, the first waveguide may be an input waveguide and the second waveguide and third waveguide may be output waveguides as described herein with respect to at least  FIGS.  1 - 6 B . Further, in some examples, in the first section of the waveguide structure the input waveguide may couple the optical power in a 50:50 split to the second waveguide and the third waveguide. 
     At  910 , a first width of the second waveguide may be varied and a first width of the third waveguide may be varied in a second section of the waveguide structure to optically couple the second waveguide with the third waveguide. In the second section of the waveguide structure, the widths of the coupled waveguides may asymmetrically split the optical power and couple the power such that the symmetric supermode changes to the antisymmetric supermode while maintaining wavelength insensitivity as described herein with respect to at least  FIGS.  1 - 6 B . 
     At  915 , a gap may be varied between the second waveguide and the third waveguide, in a third section of the waveguide structure, to optically decouple the second waveguide from the third waveguide. In the third section, the symmetric and antisymmetric supermodes may adiabatically evolve into the fundamental modes of the decoupled second waveguide and third waveguide as described herein with respect to at least  FIGS.  1 - 6 B . 
     In some examples, a tapered input waveguide may be optically coupled to a waveguide pair in a first section of the optical power splitting device, where the optical coupling may be wavelength insensitive. Similarly to  FIG.  8    and as described herein, the optical coupling may be wavelength insensitive in that changes in wavelength of the coupled waveguide pair may not affect the coupling between the first waveguide and the second waveguide and may not affect the coupling between the first waveguide and the third waveguide as described herein with respect to at least  FIGS.  1 - 6 B . 
     Additionally, in some examples, a first waveguide of the waveguide pair may be non-adiabatically tapered and optically coupled to the tapered input waveguide and a second waveguide of the waveguide pair may be non-adiabatically tapered and optically coupled to the tapered input waveguide. In some examples, a first quantity of optical power from the tapered input waveguide may be coupled to the first waveguide of the waveguide pair and a second quantity of optical power from the tapered input waveguide may be coupled to the second waveguide of the waveguide pair. Additionally, the first quantity of optical power may be different from the second quantity of optical power and the difference between the first and second quantities of optical power may be based at least in part on a width of the first waveguide of the waveguide pair and a width of the second waveguide of the waveguide pair as described herein with respect to at least  FIGS.  1 - 6 B . 
     The described layouts and configurations of the arbitrary ratio tapping waveguide system in  FIGS.  1 - 9    have been for explanatory purposes. In alternative embodiments, the described embodiments may include a different combination or configuration of components, or may perform additional or alternative functions. The layouts and configurations described herein may be used as part of any optical system and/or electronic device that employs light sources, such as, in a watch, a biometric sensor, a laptop computer, a tablet, or in any other appropriate device. 
     The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art, after reading this description, that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art, after reading this description, that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20221111
Publication Date: 20240130
Grant Date: 20240130
Priority Date: 20191018
Inventors: WU, YI-KUEI
TU, YONGMING
BISMUTO, ALFREDO
TRITA, Andrea
LIU, Yangyang
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/1228", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/12004", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/12004", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/1228", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/1228", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/122", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/12016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/1006", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/12004", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/10", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 84000762