Achromatic spectroscopic devices with high-V and low-V waveguides.

Abstract

An optical splitter configuration is disclosed. The optical splitter may include an input waveguide, a free propagation region, and an output waveguide array. The input waveguide may be narrow enough that light in the free propagation region can diffract and provide the same light intensity at the far-field angle over a wide wavelength range. The input waveguide may have a high V value in the vertical dimension and a low V value in the horizontal dimension. Because the wavelengths of light all diffract at the same angle in the free propagation region, when the light reaches the output waveguides, it may have similar optical power in each of the output waveguides. Furthermore, the width and spacing of the output waveguides may be varied to mitigate non-uniform optical power distribution in the phase front of the light.

Description

[Technical field]

[0001] The present disclosure relates generally to optical systems for splitting light. More specifically, embodiments described herein relate to achromatic optical systems for splitting light using waveguides that have a high V value in one dimension and a low V value in another dimension.

[0002] (CROSS REFERENCE TO RELATED APPLICATIONS) This PCT (Patent Cooperation Treaty) patent application claims priority to U.S. Provisional Patent Application No. 63 / 083,691, filed September 25, 2020, and U.S. Nonprovisional Patent Application No. 17 / 479,943, filed September 20, 2021, the contents of which are incorporated by reference in their entireties. [Background technology]

[0003] In general, optical systems may use multiple light sources for use in everyday devices. These systems may have multiple output lights, and there may be more output lights than light sources because they may be demultiplexed or split. Optical systems use light splitting systems to split the light emitted by the light sources, and may include different components such as demultiplexers, diffraction gratings, optical splitters, etc. These splitting components may differ from each other in various ways, such as size, optical efficiency, energy efficiency, wavelength dependency or independence, etc. In some embodiments, cascaded light splitting systems may be used, but the optical systems tend to grow in scale with the number of cascaded light splitting stages, and may become unreasonably large in size. In other embodiments, star splitters may be used, but the free propagation region through which the light propagates may cause significant optical loss between the input and output waveguides. Even if the size of a star splitter may be appropriate, it may have too much optical power loss for use in a given optical system, and thus a compact, low optical loss optical system may be desirable. In other embodiments, the optical splitting system may not perform consistently over a wide range of wavelengths of light. Summary of the Invention

[0004] The embodiments of the systems, devices, methods and apparatus described in this disclosure relate to optical devices for splitting or combining light. Also described are systems, devices, methods and apparatus for splitting light using star splitter based optical devices. In some embodiments, the optical splitter may function as a 1×N splitter insofar as light can be input on one input waveguide and light can be output on any number of output waveguides. The optical splitter may include an input waveguide, a free propagation region and an output waveguide array. In some embodiments, a narrow input waveguide may provide light to the free propagation region, where the input waveguide is narrow enough that diffraction in the free propagation region may provide similar light intensity at the far field angle over a wide wavelength range, such as spanning about 1 micron. The input waveguide may have a mode size proportional to the wavelength, which may provide a uniform diffraction angle. If most or all of the wavelengths are diffracted at similar or the same angles, then when the light reaches the output waveguides it may have similar or the same optical power in each of the output waveguides.

[0005] In some embodiments, the present disclosure describes an optical splitter, which may include an input waveguide configured to input light of a wavelength range into a free propagation region, the input waveguide configured to achieve a proportional relationship between mode size and wavelength at an input edge of the free propagation region over the wavelength range of light, the free propagation region having an input edge and an output edge optically coupled to the input waveguide on the input edge and configured to receive light of the wavelength range from the input waveguide, and an output waveguide array optically coupled to the output edge of the free propagation region, each waveguide of the output waveguide array aligned at a predetermined angle (e.g., approximately perpendicular) with respect to a local phase front of light received by each waveguide from the free propagation region. In some embodiments, the input waveguides have a high V value in a first dimension and a low V value in a second dimension, the output waveguides of the central channels in the output waveguide array have a narrower width than the output waveguides of the outer channels of the output waveguide array, the input waveguides diffract light with the same diffraction across a range of wavelengths of light, and the output waveguides in the output waveguide array are uniformly spaced. Further, at least two waveguides in the output waveguide array have different widths, and at least some of the waveguides in the output waveguide array have non-uniform spacing between each other.

[0006] In some embodiments, the input waveguide weakly confines the light in the diffracted direction of the free propagation region. In some embodiments, a width of at least one waveguide in the output waveguide array depends at least in part on the intensity of the diffracted light in the free propagation region. In some embodiments, a first dimension of the input waveguide depends at least in part on a first V value of the input waveguide and a second dimension of the input waveguide depends at least in part on a second V value of the input waveguide, the first V value being greater than the second V value. In some embodiments, the input waveguide mode measured in the first dimension matches the waveguide mode of the free propagation region, thereby reducing optical losses. In some embodiments, the light coupled into each waveguide in the output waveguide array has the same power for each waveguide over a wavelength range of light. Additionally, the input waveguide is a first input waveguide; The optical splitter may include a second input waveguide aligned adjacent to the first input waveguide and optically coupled to the free propagation region, the first and second input waveguides being symmetrically aligned to input light into the free propagation region.

[0007] In some embodiments, the present disclosure describes an optical splitter that may include an input waveguide configured to input light of a wavelength range having a high V value in a first dimension and a low V value in a second dimension, a slab waveguide having an input edge and an output edge, the slab waveguide optically coupled to the input waveguide and configured to receive light from the input waveguide, and an output waveguide array aligned across the output edge of the slab waveguide such that some of the output waveguides are output waveguides of a center channel and other of the output waveguides are output waveguides of outer channels, each waveguide of the output waveguide array arranged to receive light having approximately the same optical power. In some embodiments, the input waveguide has a high V in the vertical dimension and a low V in the horizontal dimension, the mode size of the input waveguide is proportional to the wavelength in the wavelength range of light, in a slab waveguide the diffraction angle is the same across the wavelength range of light, the spacing of the central channel is uniform in the output waveguide of the central channel in the output waveguide array, and the spacing of the outer channels is half as large as the uniform spacing in the output waveguides of the outer channels. In some embodiments, the input waveguide may be a strip waveguide, and the output waveguide array is a strip waveguide. In some embodiments, the waveguides in the output waveguide array have non-uniform widths, and the width of at least one waveguide is related to a local phase front in that output waveguide of the output waveguide array.

[0008] In some embodiments, the output waveguide arrays are uniformly spaced apart from one another, and the width of the output waveguide of the central channel is narrower than the width of the output waveguide of the outer channels, so that the amount of optical power received by each output waveguide of the output waveguide array is equalized. In some embodiments, the wavelength range of the light is 1 micron. In some embodiments, the optical power incident on the slab waveguide is higher in the central channel of the output waveguide array and decreases in the outer channels of the output waveguide array, and the output waveguides of the central channel in the waveguide array are narrower than the output waveguides of the outer channels, so that uniform optical power is received across the output waveguide array, and the output waveguides of the central channel are spaced apart the same distance from one another. In some embodiments, the output waveguides of the outer channels of the output waveguide array are half the width of the output waveguides of the adjacent channels, and the outer channel spacing between the output waveguides of the outer channels is half the channel spacing of the output waveguides of the adjacent channels.

[0009] In some embodiments, the present disclosure describes an optical splitter that may include a strip waveguide for inputting light over a wavelength range of light, a slab waveguide configured to receive the wavelength range of light from the strip waveguide, and an output waveguide array aligned to receive the wavelength range of light from the slab waveguide, and wherein each output waveguide in the output waveguide array receives the same amount of optical power of the light, the mode size of the strip waveguide is proportional to one of the wavelengths of the light, and the diffraction angle of the light in the slab waveguide is similar over the wavelength range of light. In some embodiments, the spacing between a first output waveguide and an adjacent second output waveguide of the output waveguide array is non-uniform and dependent on the optical power received by the first output waveguide and the adjacent second output waveguide, the phase front of the light in the slab waveguide has a cylindrical phase front, each waveguide in the output waveguide array is aligned perpendicular to the local phase front of the light in the slab waveguide, and the output waveguide array is a strip waveguide. In some embodiments, the strip waveguide has a high V value in a first dimension and a low V value in a second dimension, and the mode of the strip waveguide in the first dimension matches the waveguide mode of the slab waveguide, thereby reducing optical losses. Furthermore, the non-uniform spacing between each output waveguide in the output waveguide array is based on the optical power received by each of the output waveguides such that each output waveguide receives uniform optical power of light over a wavelength range of light spanning one micron. Additionally, the output waveguide array has varying waveguide widths, which equalizes the optical power received from the slab waveguides.

[0010] In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a block diagram showing a 1×8 cascading splitter. [Figure 2A]FIG. 2 is a block diagram illustrating an exemplary waveguide. [Figure 2B] 3 illustrates another embodiment of a waveguide. [Diagram 3] 1 shows an embodiment of a 1×8 optical splitter. [Figure 4A] 1 illustrates an embodiment of an output waveguide array. [Figure 4B] 1 illustrates an embodiment of an output waveguide array. [Diagram 5] 1 illustrates an embodiment of an optical splitter. [Figure 6] 1 shows an embodiment of a 2×3 optical splitter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The use of cross-hatching or shading in the accompanying figures is generally provided to clarify boundaries between adjacent elements and also to facilitate visibility of the figures. As such, neither the presence nor absence of cross-hatching or shading is intended to convey or indicate any preference or requirement for specific materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristics, attributes, or properties with respect to any element shown in the accompanying figures.

[0013] It should be understood that the proportions and dimensions (relative or absolute) of the various features and elements (and collections and groupings thereof), as well as the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein, and therefore may not necessarily be presented or drawn to scale, and are not intended to imply any preferences or requirements with respect to the depicted embodiments, exclusive of the embodiments described with reference to those figures.

[0014] Description will now be made in detail of representative embodiments as illustrated in the accompanying drawings. It should be understood that the following description is not intended to limit these embodiments to one preferred embodiment. On the contrary, the following description is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the described embodiments as defined by the appended claims.

[0015] Directional terms, such as "top," "bottom," "upper," "lower," "above," "below," "beneath," "front," "back," "over," "under," "left," "right," and the like, are used in connection with the orientation of some components in some of the figures described below. Because components in various embodiments may be positioned in many different orientations, the directional terms are used for illustrative purposes only and are not intended to be limiting in any manner. The directional terms are intended to be broadly interpreted and therefore should not be interpreted to exclude components that are positioned in different ways.

[0016] As used herein, the term "abutting" means that two elements share a common boundary or otherwise contact each other, while the term "adjacent" means that two elements are in close proximity to each other and may (or may not) contact each other. Thus, elements that abut are also adjacent, although the reverse is not necessarily true. Two elements that are "coupled" to each other may be physically coupled to each other, either permanently or removably, and / or operably or functionally coupled to each other. Furthermore, two elements that are "optically coupled" to each other may allow light to pass from one element to the other.

[0017] In the following description of the embodiments, reference is made to the accompanying drawings, in which is shown by way of illustration specific embodiments which may be practiced It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the various embodiments.

[0018] In general, an optical system may use multiple light sources that emit light that can be split, and thus the number of output ports may be greater than the number of light sources. To split the light emitted by the light sources, various light splitting systems may be used, which may include different components such as demultiplexers, diffraction gratings, optical splitters, etc., and may differ from each other in their size, optical efficiency, energy efficiency, wavelength dependence or independence, any combination of these, etc.

[0019] In some embodiments, the multi-wavelength light may be split using cascaded stages in an optical splitting system, and the size of the optical splitting system may increase with the number of cascaded optical splitting stages. That is, the more optical splitting stages used, the larger the optical splitting system. Because the number of cascaded optical splitters is proportional to the number of output ports, these optical splitting systems may be unreasonably large and therefore may not be easily integrated into an overall optical system. Furthermore, cascaded optical splitters may introduce undesirable optical beats into the overall optical system.

[0020] In some embodiments, the light may be split using a multimode interferometer. Generally, a multimode interferometer may be smaller than a cascading splitter and may have consistent performance over a small wavelength range, such as 10 nanometers to 50 nanometers, but may not be suitable for having consistent performance over a broadband wavelength range, which may span approximately 1 micron.

[0021] In other embodiments, a star splitter may be used to split light in combination with an input waveguide, a free propagation region, and an output waveguide. The input waveguide typically terminates in a free propagation region with little confinement in the plane of the propagation region. The size of the star splitter cannot be scaled with the number of output ports because another output waveguide can be added without significantly increasing the footprint. However, the free propagation region, which is the propagation path of the light, may cause significant optical loss between the input and output waveguides. Even if the star splitter may be of suitable size, it may have too much optical power loss for use in a given optical system, and thus a compact, low optical loss optical system may be desirable. Furthermore, star splitters may be wavelength dependent in performance and may not be suitable for having consistent performance over a broadband wavelength range that may span approximately 1 micron.

[0022] In some embodiments, starting from a narrower input waveguide than typically used in star splitters, the light provided to the free propagation region may be expanded or diverged. In some embodiments, the narrower the input waveguide, the faster the diffraction rate of the light in the free propagation region. Diffraction in the free propagation region may result in similar light intensity at the far field angle over a wide wavelength range, such as extending to about 1 micron. If most or all wavelengths diffract at similar or identical angles, the light may have similar optical power at most or all wavelengths in each of the output waveguides when it reaches the output waveguides. It may be understood that when the term "same" is used herein (e.g., same angle, same optical power, same diffraction, same diffraction angle, etc.), in addition to being same, the term "same" may also mean similar to an extent that does not significantly affect performance and / or the same within standard measurement tolerances. Additionally, when the term "about" is used herein, it can also be understood that this term can include a reasonably allowed variation of 5 to 10 percent within the stated specifications.

[0023] Disclosed herein is an optical splitter including an input waveguide, a free propagation region, and an output waveguide array. The input waveguide may achieve a proportional relationship between the mode size and the wavelength of the light in the wavelength range, and is optically coupled to the free propagation region. The free propagation region may have input and output edges, and may receive the light in the wavelength range from the input waveguide, and the input waveguide may be optically coupled to the input edge of the free propagation region. The input waveguide may be narrow enough that the diffraction angle is the same over a wide range of wavelengths of the light. The waveguides may each be optically coupled to and aligned across the output edge of the free propagation region, and each of the multiple output waveguides is positioned at a predetermined angle (e.g., approximately perpendicular or any other suitable angle) with respect to the local phase front of the light in the wavelength range. The phase front is the phase of the propagating wave front. In some embodiments, the proportional relationship between the mode size and the wavelength need not be strictly proportional. The relationship between mode size and wavelength may be plus or minus 10 percent of the proportional relationship. As used herein, the term "proportional" not only encompasses relationships in which one object, element, or attribute (collectively, "objects") varies directly with another mathematical function or varies according to a particular mathematical function, but also includes instances in which the change in an object depends primarily on another object. In other words, an object is proportional to another object if its variance is within 10% of the direct or mathematical variance of the other object.

[0024] In some embodiments, the input waveguides may have a high V value in the vertical dimension and a low V value in the horizontal dimension to match the waveguide mode of the free propagation region of the optical splitter. In general, a high V value (e.g., vertical dimension) may result in low optical loss, while a low V value (e.g., horizontal dimension) may result in wavelength independence. A high V value in the vertical dimension and a low V value in the horizontal dimension to match the waveguide mode of the free propagation region of the optical splitter may reduce optical loss. In some embodiments, the width and spacing may vary (e.g., may be non-uniform) between the output waveguides in the array to provide uniform optical power coupling and reduce the total optical loss of the system. Furthermore, the width of the output waveguide of the center channel may be narrower than the output waveguide of the outer channels. Furthermore, the spacing between the output waveguides may be uniform or may vary based on the optical power of the light coupled into the output waveguides.

[0025] These and other embodiments are discussed below with reference to Figures 1-6. However, those skilled in the art will readily appreciate that the detailed description provided herein with respect to these figures is for illustrative purposes only and should not be construed as limiting.

[0026] FIG. 1 is a block diagram illustrating a 1×8 cascading splitter. The 1×8 cascading splitter 100 may include an input light 102, a 1×4 splitter 104, intermediate optical paths 106a-106d, 1×2 splitters 108a-108d, and output lights 112a-112d. In FIG. 1, the 1×8 splitter 100 receives a single optical input via input 102 and has eight different output ports, i.e., outputs 112a-112d. This type of splitting system may become large in size as the number of output ports increases, and thus may not be suitable for applications where space is tightly controlled or at a premium, such as in many modern electronic devices.

[0027] The input 102 may be an input waveguide that provides input light to the 1×4 splitter 104. The input light may be provided by a light source, which may be connected to or otherwise integrated into the photonics device. In some embodiments, the photonics device may include two or more light sources, such as lasers, light emitting diodes, semiconductor lasers, coherent light sources, semi-coherent light sources, any combination thereof, and the like. In some embodiments, the photonics device is a device having photonic and / or optical functions and components. The photonics device may include an optical splitter.

[0028] In a first splitting stage, the 1×4 splitter 104 may split and output the light equally among the four intermediate optical paths 106a-106d. In some embodiments, there may be optical losses associated with each splitting stage. In some embodiments, the intermediate optical paths 106a-106d may be waveguides optically coupled to the 1×4 splitter 104 and receive light therefrom. The intermediate optical paths 106a-106d may also be optically coupled to the 1×2 splitters 108a-108d and may provide light to the 1×2 splitters 108a-108d. The 1×2 splitters 108a-108d may each provide output light 112a-112d. The 1×2 splitter 108a may provide two optical outputs 112a, the 1×2 splitter 108b may provide two optical outputs 112b, and so on. 1, 1×2 splitter 108a may split light from intermediate optical path 106a and provide the split light along optical output 112a, 1×2 splitter 108b may split light from intermediate optical path 106b and provide the split light along output optical path 112b, and so on. Similar to 1×4 splitter 104, 1×2 splitters 108a-108d may each split their input light equally and provide such split light on output optical path 112. A second splitting stage (e.g., 1×2 splitters 108a-108d) may also introduce optical loss into system 100.

[0029] Also, the 1×8 splitter 100 may increase in size with each additional splitting stage. For example, instead of using a 1×4 splitter 104, the input 102 may be provided to a 1×2 splitter, and then for each of these two outputs, another set of 1×2 splitters may be used to achieve four intermediate outputs. In the described embodiment, because additional splitting stages are added, this exemplary system may be larger than the system shown in FIG. 1. As form factor devices into which optical systems are incorporated become smaller and smaller, cascading splitters may be too large in size to be reasonably incorporated into smaller form factor devices, such as mobile devices.

[0030] FIG. 2A is a block diagram illustrating an exemplary waveguide. The input waveguide 200 may generate a far-field angle that may be independent of the wavelength of light in the free-propagation region in that most or all wavelengths of light may diffract at similar or identical angles in the propagation region. As previously discussed, unlike a star splitter, when a narrow input waveguide is used to input light into the free-propagation region of the optical splitter, diffraction in the free-propagation region may result in similar light intensity at the far-field angle over a wide wavelength range, such as spanning up to about 1 micron. Although a wavelength range of 1 micron is described herein, it may be understood that the optical splitter may function similarly for all light wavelengths below 1 micron, such as 100 nanometers or less. The input light may propagate in the propagation region in a diffracted direction from the input waveguide to the output waveguide while diverging in the propagation region. If most or all wavelengths diffract similarly or at the same angle, when the light reaches the output waveguides, the output light in each of the output waveguides may have the same or similar optical power. One way to achieve this is to use an input waveguide 200 that produces a mode size that is wavelength dependent to the extent that a proportional relationship between mode size and wavelength can be achieved. The diffraction angle of the light may be similar when the mode size is proportional to the wavelength at the wavelength of the light. Furthermore, the diffraction angle of the light may be determined by the ratio of the mode size to the wavelength, which may result in a wavelength independent diffraction angle. In one embodiment, the width of a waveguide supporting one mode of light at an optical wavelength of about 3 microns may be twice as wide as the same waveguide supporting one mode of light at an optical wavelength of about 1.5 microns.

[0031] The input waveguide 200 may generate a mode size that achieves a proportional relationship with wavelength by weakly confining the input waveguide 200 in the plane or horizontal dimension of the substrate. As shown in FIG. 2A, the input waveguide 200 may have a first cladding layer 202, a propagation region 205, and a second cladding layer 204. The first cladding layer 202 and the second cladding layer 204 may be silicon dioxide, an oxide material, or any other suitable dielectric, while the propagation region 205 may be silicon. In FIG. 2A, light may propagate into or out of the depicted diagram shown in FIG. 2A. In some embodiments, the cladding layers 202 and 204 may extend beyond the boundaries shown in FIG. 2A and FIG. 2B. 2A-2B, the input waveguide 200 may be confined in each direction around the propagation region 205, except in the direction of light propagation within the propagation region 205, by cladding layers. In general, the material used for confinement may be any material with a lower index of refraction than silicon can work (e.g., silicon dioxide). Other materials, such as silicon nitride or any number of polymers, may also work to confine light propagation to the propagation region 205.

[0032] The physical size of the input waveguide 200 may be set based on the first and second target V values ​​and the wavelength of light transmitted by the input waveguide. The V values ​​and the wavelength of light are used to generate mode sizes as discussed herein. In some embodiments, the input waveguide 200 may have a propagation region with a first dimension (e.g., vertical dimension) of about 2-5 microns and a second dimension (e.g., horizontal dimension) of less than 1 micron. In some embodiments, the input waveguide may have a vertical dimension of 3 microns and a horizontal dimension of 0.6 microns. These sizes may be used, for example, for a rectangular cross-section input waveguide transmitting light having a wavelength between 1.4 microns and 2.4 microns.

[0033] The V value is a normalized frequency that determines the number of modes that the fiber can transmit. As used herein, "high V" and "low V" are relative terms. Specifically, a high V value supports multiple modes of light, while a low V value supports a single mode of light. It should be recognized that the devices described herein are configured to operate over a range of wavelengths, and therefore the high and low V values ​​in these contexts are intended to apply to single or multimode light over this wavelength range. Thus, the actual values ​​for a given waveguide will depend on the targeted wavelength range. Furthermore, given these optical wavelengths and the aforementioned sizes of the input waveguides, the first (or "high") V value is 3 or greater, and the second (or "low") V value is less than 3. Many embodiments may use this same cutoff, e.g., a high V value that is 3 or greater and a low V value that is less than 3, even if their sizes differ. In other embodiments, the low V value may be 3 rather than the high V value. Generally, in many embodiments, the cutoff between high and low V occurs when the light transitions from single-mode light to multimode light and may vary with the wavelength of the light propagating through the waveguide, as well as the size of the waveguide. Thus, an input waveguide may have a low V along a first axis and a high V along a second axis, for example, if the size of the waveguide is smaller along the first axis and larger along the second axis.

[0034] Because the waveguide may be smaller than the wavelength of light along the short axis of the wafer plane (e.g., the horizontal dimension as shown in FIG. 2A), light propagating through the input waveguide 200 may be weakly confined in this one dimension, thus generating appropriate mode sizes. Furthermore, this may result in a waveguide that generates optical modes whose sizes are approximately proportional to the wavelength.

[0035] The geometry of the input waveguide 200 has a high V value in a first dimension (in this case, the vertical dimension) and a low V value in a second dimension (in this case, the horizontal dimension) as shown. Because the input waveguide 200 has a high V value in the vertical dimension and a low V value in the horizontal dimension, the optical mode of the input waveguide can match the waveguide mode of the free propagation region of the optical division device, which can reduce optical losses. The low V value achieves a proportional relationship between mode size and wavelength, and thus, for input waveguides that follow a high exponential approximation, the high V value dimension (e.g., the vertical dimension) defines a common mode size in a single axis for all wavelengths with high V values.

[0036] FIG. 2B illustrates another embodiment of a waveguide. Input waveguide 201 may function similarly to input waveguide 200 of FIG. 2A. Input waveguide 201 may include a first cladding layer 202, a propagation region 205, a second cladding layer 204, and a base 206. First cladding layer 202 and second cladding layer 204 may be silicon dioxide, an oxide material, or any other suitable dielectric, while propagation region 205 may be silicon. In the depiction of FIG. 2A, light may propagate along the waveguide and thus into and out of the page (e.g., FIG. 2A is a cross-sectional view of waveguide 205 looking toward one end of the waveguide). Base 206 may be included as a foundation for the waveguide to facilitate manufacturing. The thickness of base 206 should be sufficient to relax manufacturing constraints without substantially changing the functionality of input waveguide 201 compared to input waveguide 200 of FIG. 2A.

[0037] FIG. 3 illustrates an example of an optical splitter. The optical splitter 300 may receive light from an input waveguide and output light onto eight output waveguides. Although eight output waveguides are described with reference to FIG. 3, this is for illustrative purposes only and any number of output waveguides may be used. The number of input and output waveguides used in FIG. 3 is for illustrative purposes only and any number of output waveguides may be used for a 1×N optical splitter. Furthermore, the input waveguides are used for illustrative purposes only and thus, two, three or more input waveguides may be used for the optical splitter, such as in an M×N splitter (where M is the number of input waveguides and N is the number of output waveguides for the optical splitter). Furthermore, any number of input waveguides may be used with any number of output waveguides and any number of input ports may be used with any number of output ports, as described herein with respect to any embodiment. Furthermore, in some embodiments, the number of input waveguides may be two or more, and the total area defined by all the input waveguides (e.g., the maximum distance from the centerline along the input face of the free propagation region) may be much smaller than the length of the free propagation region or the length of the output port or waveguide array (the maximum distance from the centerline along the output face).

[0038] The specific examples used herein are provided for illustrative purposes only. Optical splitter 300 can produce approximately uniform power across all output waveguides and over a wavelength range of light spanning approximately 1 micron, all while maintaining a relatively small form factor. Additionally, in Figures 3-6, the input waveguides, free propagation regions, and output waveguides all have the same pattern, but may be separate elements through which light propagates and which are optically coupled to one another.

[0039] The optical splitter 300 may include an input waveguide 305, a free propagation region 310, and a number of output waveguides 315a-315h. The free propagation region 310 may be formed of a material similar to the input waveguide 305 and the number of output waveguides 315a-315h. In some embodiments, the free propagation region 310 and the input waveguide 305 and the output waveguides 315a-315h may be surrounded by a cladding region 320, which may be an oxide material such as silicon dioxide or any other dielectric that provides the same light confinement function. The cladding region 320 may extend beyond the boundaries depicted in FIG. 3. In other embodiments, the cladding region 320 may closely surround the perimeter of the optical splitter 300. In this specification, the terms "multiple output waveguides" and "array of waveguides" may be used interchangeably. The optical splitter 300 may differ from a typical star splitter in that the input waveguide 305 may confine light to a specific mode size due to its high V / low V settings. Furthermore, the output waveguides are configured and spaced apart from each other to account for local phase front and optical power variations. Furthermore, the input waveguide 305 has a different pattern than the input waveguide 205 of FIG. 2, but both function similarly to each other and have similar or equal physical characteristics (such as V and physical size). Similarly, the input waveguides 405 and 505 may have similar functions and characteristics compared to the input waveguides 205 and 305. Furthermore, the output waveguides 315, 415, 515, and 615 may be depicted as having different lengths in the corresponding figures, but this is for illustrative purposes only. In some embodiments, these output waveguides may be the same length or similar lengths. Similarly, although the output waveguides 315, 415, 515, 615 are shown as having curved output edges, in some embodiments the output edges of the output waveguides 315, 415, 515, 615 may be straight, angular, or other shapes, or may be shaped to efficiently couple to adjacent or abutting optical elements. Although the input waveguides 305, 405, 505, and 605 are depicted as having a given length, the input waveguides may be any length.Similarly, although input waveguides 305, 405, 505 and 605 are shown as having curved input edges, in some embodiments the input edges of input waveguides 305, 405, 505 and 605 may be straight, angular or other shapes, or may be shaped to efficiently couple to adjacent or abutting optical elements.

[0040] In some embodiments, the input waveguide 305 may be optically coupled to, provide light to, and terminate in the free propagation region 310. The light propagating through the input waveguide may be of a broad wavelength range that may span approximately 1 micron. The free propagation region 310 may be configured to receive light of a wavelength range from the input waveguide 305, which may freely propagate and diffract within the free propagation region 310. In general, the narrower the input waveguide 305, the faster the light may diffract or spread out in the free propagation region 310. As previously discussed with reference to Figures 2A and 2B, the input waveguide 305 may be narrow, thus confining the light to a mode size that is on the order of a wavelength.

[0041] In some embodiments, the input waveguide 305 may be a strip waveguide and the output waveguides 315a-315h may also be strip waveguides. In some embodiments, the output waveguides 315a-315h may instead be rib waveguides or some combination of strip and rib waveguides. Furthermore, the free propagation region 310 may be a slab waveguide. It may be understood that all of the waveguides may be surrounded by a low index cladding region to confine the light to the waveguide. In general, the waveguides described herein may include a core or propagation region with cladding layers on either side of the propagation region. Furthermore, the propagation region of a waveguide is distinct from the free propagation region of an optical splitter because the free propagation region is the region where light may diffract and spread out.

[0042] When light travels from the input waveguide 305 to the free propagation region 310, it may diffract at approximately the same angle, forming an approximately Gaussian diffracted wavefront that may be reproduced similarly at all wavelengths. The diffracted light in the free propagation region 310 may propagate to form approximately the same (or identical) far-field angles over a wide wavelength range. If light of different wavelengths in the wavelength range diffracts at approximately the same angle, when the light reaches the output waveguides, the waveguides may each output light with approximately the same, or identical, optical power. By providing mode sizes that may be proportional to wavelength, the far-field angle may be independent of wavelength. In some embodiments, the input waveguide mode in the vertical dimension may be approximately matched to the waveguide mode of the free propagation region 310, thereby reducing optical losses.

[0043] In some embodiments, by creating a waveguide mode size that is wavelength dependent and proportional to the wavelength, light may be diffracted at the same angle for all component wavelengths, thus providing a far-field angle that may be independent of the wavelength of the light. It may be understood that the mode size of a waveguide is the mode size that results from light passing through the waveguide. In some embodiments, by using an input waveguide 305 with a high V value in the vertical dimension and a low V value in the horizontal dimension (or vice versa depending on the orientation of the waveguide), as described with reference to FIG. 2A, the far-field angle may be independent of wavelength.

[0044] In some embodiments, the free propagation region 310 may include an input edge 380 and an output edge 381, and the input waveguide may be optically coupled to the input edge 380. The output waveguides 315a-315h of the optical splitter 300 may be coupled to the output edge 381 of the free propagation region 310. Additionally, each of the multiple output waveguides 315a-315h may be aligned at a predetermined individual angle (e.g., approximately perpendicular or any other suitable angle) to the local phase front of the light. In the free propagation region variation 310 shown in FIG. 3, the light may have a phase front, which may be a substantially cylindrical phase front, as it propagates and diffracts through the free propagation region.

[0045] The position, width, and angle of a given output waveguide collectively affect the amount of light coupled into the output waveguide, and thus each may be selected to achieve a given light coupling into a particular output waveguide. For example, each waveguide may preferably be aligned perpendicular to the local phase front to increase the amount of light and optical power coupled into the output waveguide, although it should be recognized that other angles are possible for otherwise identical waveguides, although this may result in increased loss. In some embodiments, the array of waveguides 315a-h may be aligned along a preferably circular curve (e.g., centered where the input waveguide meets the free propagation region), such that each waveguide is aligned along the same phase front. It should be recognized that the array of waveguides 315a-h may be aligned along other curves, provided that the losses associated with these other curves are acceptable and within the overall system specifications. As shown in FIG. 3, output waveguide 315a may be at a different angle to the free propagation region 310 than output waveguide 315f, since each output waveguide is oriented (approximately) perpendicular to the local phase front of the light reaching that particular output waveguide.

[0046] As shown in FIG. 3, at least some of the output waveguides may have different widths, and these widths may vary depending on the position of the output waveguide relative to the center of the output waveguide array. That is, the widths of the output waveguides may be non-uniform. As shown in FIG. 3, output waveguides 315d and 315e may be narrower because they are aligned closer to the center of the array, while output waveguides 315a and 315h may be wider because they are aligned further out to the outside of the output waveguide array. In some embodiments, the widths of output waveguides 315a-315h may depend, at least in part, on the intensity of diffracted light within free propagation region 310. Thus, the widths of the waveguides may increase as the distance of the waveguide from the centerline of the free propagation region increases. As shown, the center-to-center spacing of the output waveguides relative to one another may also increase as the output waveguides widen toward the outside of the array, although the spacing of the output waveguides may be uniform (e.g., the distance between the sidewalls or edges of adjacent waveguides may be the same regardless of which waveguide pair is considered) or may be spaced the same distance from one another. The output waveguides may be wider toward the edges of the array because optical power and / or light intensity may decrease as the light diverges toward the edges of the free propagation region 310.

[0047] In some embodiments, the overall system efficiency may be approximately the same across all wavelengths of light, such that the output waveguide has the same or approximately the same power across all wavelengths of light.

[0048] FIG. 4A illustrates an embodiment of another optical splitter. FIG. 4A illustrates an embodiment of an optical splitter as described herein and incorporated into a larger optical system including an outcoupler. As shown, the optical splitter 400 may include an input waveguide 405, a free propagation region 410, an array of output waveguides 415a-g, and a cladding region 420. The optical splitter 400 may be configured in any suitable manner as described herein and with reference to the optical splitter 300 of FIG. 3. Additionally, the array of output waveguides 415a-g may be a representation of a portion of the output waveguides shown in FIG. 3. As previously described with reference to FIG. 3, the output waveguides may couple light along a phase front in the free propagation region 315. The output waveguides may each be aligned perpendicular to the local phase front of the light, and thus each output waveguide may have a different phase of light. In FIG. 4A, the output waveguide array includes waveguides 415a-g. The output waveguides 415a-g may be uniformly spaced and of different non-uniform widths such that the waveguide channels may receive approximately the same optical power. It may be understood that the output waveguides of the central channels may be narrower than the output waveguides of the outer channels because the optical power may be greater toward the center of the free propagation region 410 and may drop off toward the edges. The central channel spacing between the central channel output waveguides, such as 415c and 415d, may be limited primarily by the manufacturing technique and may be uniform.

[0049] In some instances, the output waveguides 415a-g may be configured such that the light received by the outcouplers 430a-g may have different phases. That is, the output waveguides 415a-g may provide light having different phases 425a-g to the outcouplers 430a-g. In other words, the output waveguides 415a-g may provide light having different group delays. The outcouplers 430a-g are used for illustrative purposes only, since the light from the output waveguides 430a-g may be provided to any type of optical element, such as a prism, a mirror, a lens, a collimator, any combination thereof, and the like. In some embodiments, the output waveguides 430a-g may provide light for a sample measurement or to a reference detector for light monitoring. In some embodiments, the waveguides may be divided into groups such that light from multiple output waveguides may be received by one outcoupler. In this embodiment, the grouped output waveguides may be aligned closer to each other within the group than to the corresponding outcouplers. By grouping the output waveguides, this may create the effect of a "single output" per waveguide group. In yet other embodiments, the output waveguides within a group may provide the same phase light to the corresponding outcouplers, although some output waveguides may provide different phases from each other.

[0050] In the previous discussion of output waveguides being aligned perpendicular to the local phase front, it should be recognized that the waveguides are aligned perpendicular to the local phase front at a point in space (since a waveguide cannot be perpendicular to multiple points on a curve at the same time). This point may be selected to help minimize losses (e.g., by aligning the waveguide perpendicular to the average slope of the local phase front surrounded by the waveguide), but may not be able to address all losses caused by bending of the local phase front. This is magnified as the output waveguides become larger, and thus may disproportionately affect the outer waveguides. For example, in the output waveguides shown in FIG. 4A, since the center-aligned output waveguides (e.g., 415d) are smaller, they will experience less bending of the phase front (and thus the phase front will more closely approximate a plane wave), whereas the outer output waveguides (e.g., 415a and 415g) are larger and therefore experience a greater amount of bending. For these reasons, it may be desirable to split a given output waveguide into two smaller waveguides (each at a different angle to the free propagation region) to provide smaller phase front curvature where the individual waveguides meet.

[0051] FIG. 4B illustrates an embodiment of another optical splitter with an output waveguide array. Optical splitter 450 may include an output waveguide array, shown as an alternative arrangement of the output waveguides shown in FIG. 4A. As previously described with reference to FIG. 3, the output waveguides may couple light along a phase front within the free propagation region 310. The output waveguides may each be aligned perpendicular to their local optical phase front, and thus each output waveguide may accept or receive light of a different phase. In FIG. 4B, optical splitter 450 includes waveguides 455a1-455g1. The output waveguides 455a1-455g1 may be non-uniformly spaced and have similar or different widths such that the waveguide channels may receive approximately the same optical power. The output waveguides 455a1-455g1 may provide light having different phases 465a1-465g1 to the out-couplers 470a1-470g1.

[0052] The optical splitter 450 may alleviate the problems described with reference to FIG. 4A by replacing the outer channel output waveguide with multiple smaller output waveguides. Specifically, the outer channel output waveguide 415a in FIG. 4A may be replaced with the smaller outer channel output waveguides 455a1 and 455a2 in FIG. 4B. For example, the width 517 of the inner channel output waveguide 455d is wider than the width 518 of the outer channel waveguides 455a1, 455a2, 455g1, 455g2. Furthermore, the outer channel output waveguide 415b in FIG. 4A may be replaced with the smaller outer channel output waveguides 455b1 and 455b2 as shown in FIG. 4B. By using multiple smaller outer channel output waveguides, each output waveguide may be illuminated with an increased uniform local intensity and the output waveguides may be shifted to match the local phase front.

[0053] The outer channel output waveguide 455a1 may output light along optical path 465a1 to outcoupler 470a1, and the outer channel output waveguide 455a2 may output light along optical path 456a2 to outcoupler 470a2. The outcouplers 470a1, 470a2 may be aligned closer to each other than the outcouplers 470c, 470d that receive light from the inner channel output waveguides. The outer channel outcouplers 470a1, 470a2 may be aligned close enough that two portions of launched light act as a single portion of light from a single outcoupler of the inner channel, such as outcoupler 470d. Due to the size and spacing of the outer channel output waveguides 455a1, 455a2, the light from these waveguides may be launched by the two outcouplers 470a1 and 470a2 as if they were single. These smaller output waveguides 455a1, 455a2 of the outer channel may launch light with close to the same (or nearly the same) phase as one another through the outer channel's outcoupler. Thus, the optical power of the launched light may combine and thus be the same or similar to the optical power of the light launched by the single output waveguide 415a of the outer channel in FIG. 4A. In some embodiments, the optical paths 465a1-465g1 may propagate through air, one or more waveguides, and / or other optical elements that may direct the light to the corresponding outcoupler.

[0054] Although the optical splitter 400 of FIG. 4A may compensate for local intensity variations by using wider outer channel waveguides, when the size of the outer channel waveguides is about twice that of the central channel waveguides, optical losses may be better mitigated using the optical splitter 450 of FIG. 4B with an increased number of smaller output waveguides in the outer channels. The increased number of smaller output waveguides in the outer channels may reduce the non-uniform intensity of the Gaussian diffracted wavefront of light by changing the density and / or spacing of the output waveguides. FIG. 4B shows two smaller output waveguides in the outer channels that may replace a single output waveguide in the outer channels for illustrative purposes only, and the waveguides that may replace the output waveguides in the outer channels may be two or any other number. The splitting function using multiple smaller output waveguides in the outer channels may provide low total optical losses and wavelength independence.

[0055] In some embodiments, the spacing between output waveguides 455a1-455g1 in FIG. 4B may be uniform or semi-uniform. In some embodiments, the central channel spacing between the output waveguides of the central channel and the output waveguides of the outer channels may differ from one another to reduce non-uniform optical power distribution of the phase front of the light. The output waveguides of the central channel may have uniform central channel spacing since the phase front may be close to that of a plane wave, while the outer channel spacing between output waveguides 455a1 and 455a2 and between 455b1 and 455b2 of the outer channels may be half the uniform spacing of the output waveguides of the central channel. The spacing of the output waveguides of the outer channels may be half the uniform spacing since the size of the output waveguides 455a1 and 455a2 of the outer channels may be half the size of the output waveguide 455d of the central channel. Furthermore, because output waveguides 455a1 and 455a2 can be treated as a single channel output, the spacing can be smaller and half the uniform spacing because the output waveguides are half the size and two output waveguides are used with the same spacing as a single channel.

[0056] In some embodiments, the width of the output waveguides 455a1 and 455a2 of the outer channels may be half the width of the adjacent output waveguides 455b1 and 455b2 of the outer channels. Similarly, the width of the waveguides 455g1 and 455g2 of the outer channels may be half the width of the adjacent waveguides 455f1 and 455f2 of the outer channels. Furthermore, the total power received by the output waveguides 455a1 and 455a2 of the outer channels may receive an amount of optical power similar to the power received by other single waveguides (such as adjacent output waveguides 455b1 and 455b2 of the outer channels) due to width variations between the output waveguides 455a1 and 455a2 of the outer channels and the adjacent output waveguides 455b1 and 455b2 of the outer channels.

[0057] In some embodiments, the grouped output waveguides 455a1 and 455a2 of the outer channels may collect the same amount of light as one of the adjacent output waveguides 455b1, 455b2 of the outer channels. Additionally, the grouped output waveguides 455a1 and 455a2 of the outer channels may collect the same amount of light (e.g., optical power) as the other grouped output waveguides of the outer channels. The light provided by each of the grouped output waveguides 455a1, 455a2 of the outer channels may or may not be distributed evenly between the output waveguides 455a1, 455a2 of the outer channels. Similarly, in any group of output waveguides, the light (e.g., optical power) provided by each output waveguide in that output waveguide group may or may not be distributed evenly between each output waveguide in the group. Additionally, each output waveguide in the grouped output waveguides 455a1, 455a2 of the outer channels may be aligned to collect light of the same phase. In general, each output waveguide in an output waveguide group may be aligned with respect to the free propagation region such that the collected light may be of the same phase as the other output waveguides in the group.

[0058] FIG. 5 illustrates one embodiment of an optical splitter. Optical splitter 500 illustrates that the spacing of output waveguides can be varied based on the optical power of light coupled into the output waveguides while maintaining similar optical power. Optical splitter 500 includes an input waveguide 505, a free propagation region 510, a cladding region 520, and an array of output waveguides 515a-i. In FIG. 5, the total optical loss may be reduced by adjusting the spacing of the output waveguides. In some embodiments, the spacing between the first and second output waveguides may depend on the optical power coupled from the free propagation region into each of the first and second output waveguides.

[0059] In FIG. 5, the spacing of the output waveguides may be determined based on the optical power coupled into the output waveguides of the central channel and the output waveguides of the outer channels. The output waveguides 515e and 515f of the central channel may be placed approximately at the center of the input waveguides so that the output waveguides of the central channel couple with light having uniform and high optical power. Furthermore, the output waveguides 515e and 515f of the central channel may receive a first optical power from the free propagation region 510 that is coupled into the output waveguides. The next adjacent output waveguide 515d may receive 80% of the first optical power, and thus the spacing between the output waveguides 515e and 515d may be 80% of the spacing between the output waveguides 515e and 515f. Further, the next adjacent output waveguide 515c may receive 60% of the first optical power, and thus the spacing between output waveguides 515c and 515d may be 60% of the spacing between output waveguides 515e and 515f, and so on for the remaining output waveguides in FIG. 5. For example, width 517 between output waveguides 515e and 515d of the inner channel and between output waveguides 515e and 515f of the inner channel may be greater than width 518 between output waveguides 515c and 515b of the outer channel and between output waveguides 515g and 515h of the outer channel. Similarly, width 519 may be less than all of widths 517 and 518. In FIG. 5, output waveguides 515a-515i may maintain uniformity of optical power received across output waveguides 515a-515i.

[0060] FIG. 6 illustrates an embodiment of a 2×3 optical splitter. The 2×3 optical splitter 600 may include a first input waveguide 605a, a second input waveguide 605b, a cladding region 620, a free propagation region 610, and three output waveguides 615a-c. In FIG. 6, two input ports and three output ports are used for illustrative purposes only, and thus any number of output ports may be used for the 2×N optical splitter. Furthermore, two input ports are used for illustrative purposes only, and thus three or more input ports may be used for the optical splitter, such as in the case of an M×N splitter (where M is the number of input ports and N is the number of output ports of the optical splitter). In some embodiments, the first and second input waveguides 605a and 605b may receive light from an upstream light source that would otherwise need to be combined before splitting it into the output waveguides 615a-c. Furthermore, in some embodiments, the number of input ports or waveguides may be two or more, and the total area defined by all the input ports or waveguides (e.g., the maximum distance from the centerline along the input face of the free propagation region) may be much smaller than the length of the free propagation region or the length of the output port or waveguide array (the maximum distance from the centerline along the output face).

[0061] In Fig. 6, the first and second input waveguides 605a and 605b may experience low optical loss similar to the single input waveguide described with reference to Figs. 3 and 5. Although there may be a small amount of optical loss that may exist as the number of input ports increases, the addition of the second input waveguide 605b may still result in acceptably low optical loss. Furthermore, the two input waveguide optical splitter 600 may have lower loss than a system including a cascading 2x1 coupler with a 1xN star splitter, and the two input waveguide optical splitter 600 may have a smaller form factor.

[0062] In some embodiments, the first and second input waveguides 605a and 605b may have similar waveguide parameters to one another and may not differ from the single input waveguide described with reference to Figures 3 and 5. For example, the first and second input waveguides 605a and 605b may have a high V value in the vertical dimension and a low V value in the horizontal dimension.

[0063] The first input waveguide 605a may be aligned proximate to the second input waveguide 605b because the manufacturing process allows for a reduction in any optical losses associated with the addition of the second input waveguide. In general, the first and second input waveguides 605a and 605b may be aligned adjacent to one another and symmetrically about a position where a single input waveguide may be aligned in a single input waveguide optical splitter. In other embodiments, the first and second input waveguides 605a, 605b may not be aligned symmetrically relative to where a single input waveguide would typically be aligned.

[0064] Furthermore, although process steps or method steps may be described in sequential order, such processes and methods may be configured to work in any suitable order. In other words, any sequence or order of steps that may be described in this disclosure does not in itself indicate a requirement that the steps be performed in that order. Furthermore, some steps may be performed simultaneously despite being described or suggested as not being performed simultaneously (e.g., by one step being described after another step). Furthermore, the illustration of a process by its description in a drawing does not imply that the illustrated process is exclusive of other variations and modifications thereto, nor does it imply that the illustrated process, or any of its steps, is required for one or more embodiments, nor does it imply that the illustrated process is preferred.

[0065] Representative application examples of the method and apparatus according to the present disclosure are described in this section. These examples are provided only to add context and aid in understanding the described examples. Therefore, it will be apparent to one of ordinary skill in the art that the described examples can be practiced without some or all of the specific details. Other applications are possible, and therefore the following examples should not be construed as limiting.

[0066] Although the embodiments of the present disclosure have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art, and such changes and modifications are to be understood as being included within the scope of the embodiments of the present disclosure, as defined by the appended claims.

Claims

1. an input waveguide configured to input light of a wavelength range into a free propagation region, the input waveguide configured to achieve a proportional relationship between mode size and wavelength at an input edge of the free propagation region over the wavelength range of light; an input waveguide, the free propagation region having an input edge and an output edge optically coupled to the input waveguide on the input edge and configured to receive light in the wavelength range from the input waveguide, thereby generating a phase front of light; an output waveguide array optically coupled to the output edge of the free propagation region, each waveguide of the output waveguide array is aligned at a predetermined angle with respect to a local phase front of light received by each waveguide from the free propagation region; an optical splitter, the output waveguide array comprising a central channel waveguide having a first width and a first pair of adjacent outer channel waveguides, each of the outer channel waveguides having a width narrower than the first width, the first pair of adjacent outer channel waveguides being arranged to receive a total optical power that is approximately the same as the optical power received by the central channel waveguide.

2. the input waveguide has a high V in a first dimension and a low V in a second dimension, whereby light is diffracted at the same diffraction angle across the wavelength range of light; the predetermined angle is approximately perpendicular to the local phase front of light received by each waveguide from the free propagation region.

2. The optical splitter of claim 1.

3. at least some of the waveguides in the output waveguide array have non-uniform spacing between each other; 2. The optical splitter of claim 1.

4. the output waveguide array comprising a second pair of adjacent outer channel waveguides having widths narrower than the first pair of adjacent outer channel waveguides; 2. The optical splitter of claim 1, wherein the second pair of adjacent outer channel waveguides are arranged to receive a total optical power that is approximately the same as the total optical power received by the first pair of adjacent outer channel waveguides.

5. 10. The optical splitter of claim 1, wherein a width of at least one waveguide in the output waveguide array depends, at least in part, on an intensity of diffracted light in the free propagation region.

6. a first dimension of the input waveguide that depends at least in part on a first V value of the input waveguide; a second dimension of the input waveguide that depends at least in part on a second V value of the input waveguide; and The first V value is greater than the second V value.

2. The optical splitter of claim 1.

7. The optical splitter of claim 1 , wherein an input waveguide mode measured in a first dimension matches a waveguide mode of the free propagation region, thereby reducing optical losses.

8. the input waveguide is a first input waveguide; the optical splitter further comprising a second input waveguide aligned adjacent to the first input waveguide and optically coupled to the free propagation region; and the first and second input waveguides are symmetrically aligned to input light into the free propagation region; 2. The optical splitter of claim 1.

9. an input waveguide having a high V value in a first dimension and a low V value in a second dimension and configured to input light of a wavelength range; a slab waveguide having an input edge and an output edge, the slab waveguide optically coupled to and configured to receive light from the input waveguide; an output waveguide array aligned across the output edge of the slab waveguide, some output waveguides of the output waveguide array being center channel output waveguides and other output waveguides of the output waveguide array being outer channel output waveguides, an optical splitter, the output waveguide array comprising a central channel waveguide having a first width and a first pair of adjacent outer channel waveguides, each of the outer channel waveguides having a width narrower than the first width, the first pair of adjacent outer channel waveguides being arranged to receive a total optical power that is approximately the same as the optical power received by the central channel waveguide.

10. the input waveguide has the high V value in a vertical dimension and the low V value in a horizontal dimension; a mode size of the input waveguide in the horizontal dimension proportional to the wavelength of light in the wavelength range; In the slab waveguide, the diffraction angle is the same in the horizontal dimension over the wavelength range of light; and a central channel spacing is uniform in the output waveguides of the central channels in the output waveguide array, and an outer channel spacing is less than the uniform spacing in the output waveguides of the central channels.

10. The optical splitter of claim 9.

11. 10. The optical splitter of claim 9, wherein at least one of the input waveguide or the output waveguide array is a strip waveguide.

12. 10. The optical splitter of claim 9, wherein the wavelength range of light is 1 micron.

13. the output waveguide array comprising a second pair of adjacent outer channel waveguides having widths narrower than the first pair of adjacent outer channel waveguides; the second pair of adjacent outer channel waveguides being arranged to receive a total optical power that is approximately the same as the total optical power received by the first pair of adjacent outer channel waveguides.

10. The optical splitter of claim 9.

14. a strip waveguide for inputting light over a range of wavelengths of light; a slab waveguide configured to receive light in the wavelength range from the strip waveguide; an output waveguide array aligned to receive light in the wavelength range from the slab waveguide, the mode size of the strip waveguide is proportional to a wavelength in said wavelength range of light; the diffraction angle of light in the slab waveguide is similar across the wavelength range of light; an optical splitter, the output waveguide array comprising a central channel waveguide having a first width and a first pair of adjacent outer channel waveguides, each of the outer channel waveguides having a width narrower than the first width, the first pair of adjacent outer channel waveguides being arranged to receive a total optical power that is approximately the same as the optical power received by the central channel waveguide.

15. a spacing between a first output waveguide and an adjacent second output waveguide of the output waveguide array is non-uniform and depends on the optical power received by the first output waveguide and the adjacent second output waveguide; the phase front of the light in the slab waveguide has a cylindrical phase front; each waveguide in the output waveguide array is aligned perpendicular to the local phase front of the light in the slab waveguide; and the output waveguide array is a strip waveguide; 15. The optical splitter of claim 14.

16. the output waveguide array comprising a second pair of adjacent outer channel waveguides having widths narrower than the first pair of adjacent outer channel waveguides; 15. The optical splitter of claim 14, wherein the second pair of adjacent outer channel waveguides are arranged to receive a total optical power that is approximately the same as the total optical power received by the first pair of adjacent outer channel waveguides.

17. the strip waveguide has a high V in a first dimension and a low V in a second dimension; and a mode of the strip waveguide in the first dimension matches a waveguide mode of the slab waveguide, thereby reducing optical losses; 15. The optical splitter of claim 14.

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