Compact optical splitter

Abstract

Optical splitters and systems and methods utilizing optical splitters are disclosed. An optical splitter may include an input waveguide, a free propagation region, and a plurality of output waveguides. The output waveguides are connected to the free propagation region at a plurality of corresponding output ports located along a non-circular path. The output ports may be located such that the output waveguides have the same width.

Description

Technology Field

[0001] The present disclosure generally relates to optical splitters, and systems and methods using such splitters. More specifically, the present disclosure relates to optical splitters capable of operating over a wide range of wavelengths, having output waveguides arranged along a non-circular path to provide compact optical splitters having low optical losses. Background Technology

[0002] Optical output splitters are often used in photonic integrated circuits (PICs) to split, combine, or redirect light. For example, power splitters can split light received from an input into multiple outputs. Optical splitters typically increase in size and / or complexity as the number of outputs increases, because it becomes more difficult to split light uniformly among the outputs while maintaining a small form factor and low optical losses. This becomes more complex as the target bandwidth of the splitter (i.e., the range of wavelengths the optical splitter is expected to handle) increases. Since space is precious in many devices, optical splitters can impose significant size constraints on the photonic integrated circuit depending on the number of outputs and performance requirements. Therefore, it may be desirable to provide compact optical splitters with low optical losses.

[0003] Embodiments of systems, devices, methods, and apparatuses described in the present disclosure relate to an optical device for splitting light. In some cases, the optical splitter is configured to split input light having one or more wavelengths within a predetermined wavelength range. The optical splitter comprises a free propagation region including an input port and a plurality of output ports, an input waveguide optically coupled to the free propagation region at the input port, and a plurality of output waveguides. In some of these cases, each output waveguide of the plurality of waveguides is connected to free propagation at a corresponding output port among the plurality of output ports and has substantially the same width; and is positioned such that the average dispersion factor for the plurality of output waveguides over the wavelengths of the predetermined range is less than 0.30.

[0004] In some of these variations, each output port of the plurality of output ports is located in the far-field section of the free propagation region. In some of these variations, each output waveguide of the plurality of output waveguides extends away from the corresponding output port along the Poynting vector of the input light at the corresponding output port.

[0005] In other variations, a plurality of output ports are located along a non-circular path. In some of these cases, the non-circular path has an oval shape. The oval shape may have a length axis parallel to the direction in which the input waveguide is connected to the free propagation region. Additionally or alternatively, a plurality of output waveguides includes a first set of output waveguides located on the first side of the width axis of the oval shape, and a second set of output waveguides located on the second side of the width axis of the oval shape. In some variations, the predetermined wavelength range has a bandwidth of at least 500 nanometers.

[0006] Other embodiments include an optical splitter comprising an input waveguide operable to split input light having one or more wavelengths within a predetermined wavelength range and operable to receive input light, an input port and a plurality of output ports, a slab waveguide operable to receive input light from the input waveguide at the input port, and a plurality of output waveguides connected to the slab waveguide at the plurality of output ports. The plurality of output ports are positioned along a non-circular path centered in a free propagation region, and the plurality of output waveguides are positioned such that each of the plurality of waveguides receives output light when input light is introduced into the input waveguide.

[0007] In some of these variations, multiple output waveguides have an average dispersion factor over a predetermined range of wavelengths of less than 0.30. Additionally, or alternatively, each output port of the multiple output ports is located in the far-field section of the slab waveguide. In some variations, the non-circular path has an oval shape. In some of these cases, the oval shape is elliptical.

[0008] Other embodiments include a light source unit configured to generate input light having one or more wavelengths within a predetermined range of wavelengths, and an optical system having an optical splitter optically coupled to receive the input light. The optical splitter includes a free propagation region comprising an input port and a plurality of output ports, an input waveguide optically coupled to the free propagation region at the input port, and a plurality of output waveguides. Each output waveguide of the plurality of waveguides is connected to free propagation at a corresponding output port among the plurality of output ports and has substantially the same width, and the plurality of output ports are positioned such that when input light is introduced into the input waveguide, the plurality of output waveguides have an average dispersion factor over a predetermined range of wavelengths of less than 0.30.

[0009] In some variations, each output port of a plurality of output ports is located in the far-field section of the free propagation region. In some of these variations, each output waveguide of a plurality of output waveguides extends away from a corresponding output port along the Poynting vector of the input light at the corresponding output port. In some variations, a plurality of output ports are located along a path having an oval shape. In some of these variations, the oval shape has a length axis parallel to the direction in which the input waveguide connects to the free propagation region.

[0010] Additionally or alternatively, a plurality of output waveguides include a first set of output waveguides located on the first side of the width axis of the oval shape, and a second set of output waveguides located on the second side of the width axis of the oval shape. In some cases, the predetermined wavelength range has a bandwidth of at least 500 nanometers.

[0011] In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by referring to the drawings and studying the following description. Brief explanation of the drawing

[0012] Figure 1 illustrates an exemplary star coupler used to split light. FIG. 2a illustrates an example of an optical splitter as described in the present specification. FIGS. 2B and FIGS. 2C show enlarged views of a portion of the optical splitter of FIG. 2A. FIG. 3 illustrates an exemplary optical system that splits light received from a light source unit using the optical splitters of FIG. 2a to 2c. It should be understood that the various features and elements (and sets and groups thereof) and the ratios and dimensions (relative or absolute) of the boundaries, separations, and positional relationships presented between them are provided in the accompanying drawings merely to facilitate understanding of the various embodiments described herein and are therefore not necessarily presented or illustrated to scale, and are not intended to indicate any preference or requirement for the exclusion of the embodiments described by reference with respect to the illustrated embodiments. Specific details for implementing the invention

[0013] Now, reference to representative embodiments illustrated in the accompanying drawings will be made in detail. It should be understood that the following description is not intended to limit the embodiments to a single preferred embodiment. On the contrary, it is intended to include alternatives, modifications, and equivalents that may be included within the spirit and scope of the described embodiments as defined by the appended claims.

[0014] The present specification discloses optical splitters as well as systems and methods utilizing such optical splitters. In some cases, the optical splitter comprises an input waveguide, a free propagation region connected to the input waveguide at an input port, and a plurality of output waveguides connected to the free propagation region at a plurality of corresponding output ports. The optical splitter is configured to receive input light at one or more wavelengths within a predetermined wavelength range and to split the input light among a plurality of output waveguides. In some cases, each of the plurality of output waveguides has substantially the same width at its corresponding output port and is positioned so that each output waveguide receives a similar portion of the input light. The output waveguides are arranged along a non-circular path. The non-circular path may have a shape having a length dimension longer than its maximum width, as described in more detail below. The length dimension may be parallel to the direction in which the input waveguide is connected to the free propagation region. In some cases, the non-circular path may have an oval shape.

[0015] These and other embodiments are discussed below with reference to FIGS. 2a through 3. However, those skilled in the art will readily recognize that the detailed description provided herein in relation to these figures is for illustrative purposes only and should not be interpreted as restrictive.

[0016] Representative applications of the methods and apparatus according to the present disclosure are described in this section. These examples are provided merely to add context and to aid in understanding the described examples. Accordingly, it will be apparent to those skilled in the art that the described examples may be practiced without some or all of the specific details. Other applications are possible, and therefore the following examples should not be taken as limiting.

[0017] Overall, the optical splitters described herein may include a range of different numbers of output waveguides (e.g., more than 15 output waveguides, more than 30 output waveguides) while still maintaining a small profile and low optical loss compared to other optical splitters having the same number of outputs. For example, known optical splitters may use directional couplers, each of which may be used to split light from one input into two output waveguides. To increase the number of output waveguides, multiple directional couplers need to be chained together in multiple stages. In these cascaded optical splitters, the number of directional couplers scales with the number of output waveguides, and the overall size of the optical splitter increases significantly with each new stage added. As a result, cascaded optical splitters can quickly become too large to fit within the size constraints of a given photonic integrated circuit ("PIC"). Insertion losses associated with individual directional couplers will result in larger total losses as the number of directional couplers increases. Furthermore, manufacturing variations across the larger area covered by the directional couplers can further impair performance.

[0018] In other known optical splitters, a star coupler is used to split light. FIG. 1 illustrates one such example of a star coupler (100). As illustrated therein, the star coupler (100) comprises an input waveguide (110), a propagation region (120), and a plurality of output waveguides (130a to 130r). Although lines are illustrated in FIG. 1 as splitting the input waveguide (110) from the propagation region (120) and splitting the propagation region (120) from the plurality of output waveguides (130a to 130r), it should be understood that all of these components can be formed together from a single material. Light introduced through the input waveguide (110) is diffracted when it reaches the propagation region (120). A plurality of output waveguides (130a to 130r) are connected to a free propagation region (120) along an arc (e.g., a Rowland circle), and diffracted light reaches each of the plurality of output waveguides (130a to 130r) to split the light between the plurality of output waveguides (130a to 130r).

[0019] The intensity of diffracting light within the free propagation region (120) is not uniform, and light at the periphery of the free propagation region (120) is less intensive than light traveling through the center of the free propagation region (120) (i.e., along the path of the input waveguide (110). In order to enable the star coupler (100) to uniformly split the input light among a plurality of output waveguides (130a to 130r), the width of the output waveguides (130a to 130r) is varied such that the width of the waveguides increases toward the periphery of the free propagation region (120). For example, as illustrated in FIG. 1, each of the output waveguides within the periphery (e.g., waveguides (130a to 130e, 130n to 130r)) is wider than the central waveguides (e.g., waveguides (130f to 130m)).

[0020] Increasing the width of the output waveguide typically increases the insertion losses associated with the light entering the waveguide. Thus, a star coupler as illustrated in FIG. 1 can provide a relatively uniform splitting of the input light at the cost of increased optical losses. Additionally, in cases where it is desirable for the optical splitter to have the same output waveguide widths, at least some of the output waveguides will be tapered as they move away from the free propagation region (120) to achieve the same width as the other output waveguides. The space required for the output waveguides to be tapered (particularly when adiabatic tapering is used to avoid changing the mode of light within the output waveguide) can significantly increase the size of the star coupler (100), particularly as the number of output waveguides increases.

[0021] Conversely, the optical splitters described herein include a plurality of output waveguides positioned along a non-circular path, which allows the optical splitter to have a smaller size and less insertion loss compared to cascade optical splitters or star couplers having the same number of outputs. FIG. 2a illustrates a variation of the optical splitter (200) as described herein, and FIG. 2b and FIG. 2c illustrate enlarged views of the optical splitter (200). The optical splitter (200) includes an input waveguide (210), a free propagation region (220), and a plurality of output waveguides (230a to 230r). The optical splitter (200) is configured to receive input light at any wavelength within a predetermined wavelength range through the input waveguide (210), and to split the input light among the plurality of output waveguides (230a to 230r), as described in more detail below. The input light can have a single wavelength at a time, or it can split the input light into different wavelengths at different time points. Additionally, or alternatively, the input light can have multiple wavelengths simultaneously.

[0022] The input waveguide (210), the free propagation region (220), and the output waveguides (230a to 230r) are formed from one or more waveguide materials (e.g., silicon, silicon nitride, silica, etc.) surrounded by one or more cladding materials (e.g., dielectrics such as silicon dioxide, air, etc.). For example, the input waveguide (210), the free propagation region (220), and the output waveguides (230a to 230r) may be formed from one or more waveguide materials on a first cladding layer (not shown), for example, using optical photolithography and etching techniques. A second cladding layer (215) (parts thereof shown in FIG. 2a to 2c) or air may surround the remaining sides of the components of the optical splitter (200) to provide optical confinement therefor. Although the input waveguide (210), free propagation region (220), output waveguides (230a to 230r), and some or all of their subsections are shown as being formed from a single waveguide material in FIGS. 2a to 2c, some or all of them may be formed from different waveguide materials.

[0023] The input waveguide (210) is connected to the free propagation region (220) at the input port (222). The width of the free propagation increases from the input port (222) toward the output waveguides, which causes diffraction of the input light as it enters the free propagation region. The angle of diffraction for a given input light depends on the ratio between the wavelength and the mode size of the input light when it reaches the free propagation region (200), which can result in different diffraction angles (and consequently, different power distributions between the output waveguides (230a to 230r)). These performance effects may be negligible when the optical splitter (200) is designed to be used with a small range of predetermined wavelengths (e.g., a single wavelength), but may become more significant when the optical splitter (200) is used with a wider range of predetermined wavelengths.

[0024] Accordingly, in some variations of the optical splitters described herein, the input waveguide (210) is tapered such that its width decreases as the input waveguide (210) approaches the free propagation region (220) and the input port (222). When the input waveguide (210) is sufficiently narrow at the input port (222), the magnitude of the mode of the input light becomes proportional to the wavelength of the input light over a predetermined range of wavelengths. This can ultimately reduce the wavelength dependence of the diffraction and provide a uniform diffraction angle over a predetermined range of wavelengths, resulting in similar splitting of performance over this range. The tapered input waveguide (210) can be used to provide wavelength independence over a relatively wide range of wavelengths. For example, in some cases, the predetermined range of wavelengths spans at least 500 nanometers (i.e., the difference between the longest and shortest wavelengths of the predetermined range is at least 500 nanometers). In some of these cases, the predetermined range of wavelengths spans at least 1,000 nanometers.

[0025] The free propagation region (220) is configured as a slab waveguide that allows light received from the input waveguide (210) to propagate toward a plurality of output waveguides (230a to 230r). In some variations, the free propagation region (220) is configured such that the input light diffracted into the free propagation region (220) reaches its farfield before entering any of the output waveguides (230a to 230r). Because the boundary between the nearfield and farfield for the input light is wavelength-dependent, the "farfield section" of the free propagation region (220) for a given optical splitter is determined based on the longest wavelength within a predetermined range of wavelengths in which the optical splitter is configured to split the light. In this way, regardless of which wavelength or wavelengths within the predetermined range of wavelengths are included in the input light, the input light will exhibit farfield behavior when in the farfield section of the free propagation region (220).

[0026] An exemplary far-field boundary (260) is illustrated in FIG. 2c, which represents a crossover between the near-field section of the free propagation region (220)—wherein at least one wavelength within a predetermined range of wavelengths will exhibit near-field behavior—and the far-field section of the free propagation region (220). It should be understood that the shape of the far-field boundary depends on the size, shape, and number of input ports. When the input light reaches the far-field section of the free propagation region (220), the mode shape of the input light does not change as the light travels along its Poynting vector (in contrast to variations occurring within the near-field section). In this way, the mode shape of the input light remains constant as a function of the propagation angle, which can help reduce insertion losses when the light enters the output waveguides (230a to 230r).

[0027] Specifically, the free propagation region (220) includes a plurality of output ports, and each of the plurality of output waveguides (230a to 230r) is connected to the free propagation region (220) at a corresponding output port among the plurality of output ports. To help illustrate this, FIG. 2c shows a first output waveguide (230a) and a second output waveguide (230b) connected to the free propagation region (220) at a first output port (224a) and a second output port (224b), respectively.

[0028] The boundaries of the free propagation region (220) are defined by a plurality of edge segments, one or more input ports, and a plurality of output ports. Each input waveguide and output waveguide has two sides (i.e., a first side and a second side) that terminate in the free propagation region (220). Specifically, for a given waveguide (e.g., an input waveguide or an output waveguide), the first side terminates in the free propagation region (220) at the first end point, and the second side terminates in the free propagation region (220) at the second end point. The distance between the first end point and the second end point defines the corresponding port (e.g., an input port or an output port) for the waveguide.

[0029] Each of the multiple waveguides (230a to 230r) has a first end connected to a free propagation region (220) and a second end providing light to another part of the optical system utilizing the optical splitter (200). In other words, when the optical splitter (200) receives input light within a predetermined wavelength range from the input waveguide (210), all output waveguides of the optical splitter (200) will receive a portion of the input light at their first end and output the corresponding light as "output light" at their second end. Additionally, each output waveguide may be separated from adjacent output waveguides via an edge segment. Specifically, the plurality of output waveguides (230a to 230r) have a first end output waveguide (230a), a second end output waveguide (230r), and a set of intermediate output waveguides (230b to 230q) located between the end output waveguides (i.e., the first end output waveguide (230a) and the second end output waveguide (230r)) along a non-circular path (226). The first end output waveguide (230a) represents the output waveguide closest to the input waveguide (210) on one side of the free propagation region (220), and the second end output waveguide (230r) represents the output waveguide closest to the input waveguide (210) on the opposite side of the free propagation region (220).

[0030] Each set of intermediate output waveguides (230b to 230q) is positioned between two other immediately adjacent output waveguides and has a trailing side connected to the free propagation region at the trailing edge segment, and a leading side opposite the trailing side connected to the free propagation region at the leading edge segment. Thus, the gap between the trailing edge segment and the leading edge segment for a given output waveguide also defines the output port for that waveguide. The trailing edge segment for the output waveguide is positioned closer to the input port (222) than the leading edge segment (except for cases where the edge segments associated with a given output waveguide are equidistant from the input port (222) at the point where either side of the waveguide can be considered the "leading side").

[0031] Similarly, each end output waveguide may have a leading side and a trailing side as discussed above. The leading side of the end waveguide is connected to the free propagation region at the leading edge segment of the free propagation region (220). In some cases, the free propagation region (220) may include an edge segment connecting the trailing sides of each of the first and second edge output waveguides (230a, 230r) to their respective sides of the input port (222) (or ports). For example, as illustrated in FIG. 2c, the first end output waveguide (230a) is separated from the input port (222) by an edge segment (240). In these cases, the edge segments connecting the end output waveguides to the input waveguides cause the free propagation region (220) to provide an amount of optical confinement for the light reaching at least some of the output waveguides (230a to 230r). However, in other cases, the free propagation region (220) between the input waveguide and the end output waveguides is sized so that this part of the free propagation region does not provide any optical confinement for the light reaching the output waveguides (230a to 230r). In these cases, the free propagation region (220) is considered not to have edge segments between the input waveguide and the end output waveguides, because the actual boundary (if any) between this part of the free propagation region (220) and the cladding layer (215) will not affect the operation of the optical splitter (200).

[0032] FIG. 2c illustrates a first edge segment (240), a second edge segment (242), and a third edge segment (244) in a free propagation region. The edge segments (240, 242) act as trailing and leading edge segments, respectively, for the first end output waveguide (230a) to define the first output port (224a), while the edge segments (242, 244) act as trailing and leading edge segments, respectively, for the second output waveguide (230b) to define the second output port (224b). The size of the edge segments between two immediately adjacent output ports determines the spacing between their corresponding output waveguides. Since insertion losses increase as this spacing between output ports increases, it may be desirable to minimize the size of the edge segment between two immediately adjacent output ports. In some cases, a given edge segment may approach a certain point depending on manufacturing tolerances.

[0033] As mentioned above, in some variations, the free propagation region (220) is configured such that each of the plurality of output ports is located in the far field. In some of these variations, each output waveguide of the plurality of output waveguides (230a to 230r) extends away from its corresponding output port along the Poynting vector of the input light at that location. This can reduce insertion losses when the input light passes between the free propagation region (220) and the plurality of output waveguides (230a to 230r), which collectively reduces the total optical losses associated with the optical splitter (200). In these variations, it should be understood that once light is coupled to a given output waveguide, the output waveguide can be bent or otherwise redirect the light as desired.

[0034] To help reduce the size of the output coupler (200) and facilitate splitting light between multiple waveguides (230a to 230r), it may be desirable to position at least some of the output ports very close to the far-field boundary (260). For example, in some cases, each of the first and second end output waveguides (230a, 230r) is positioned such that its output port is within a critical distance of the input port (222). In some cases, this critical distance is less than eight times the longest wavelength of a predetermined wavelength range. In some of these variations, this critical distance is less than five times the longest wavelength of a predetermined wavelength range.

[0035] As mentioned above, a plurality of output waveguides (230a to 230r) are positioned along a non-circular path (226). In some cases, each of the plurality of output waveguides (230a to 230r) has substantially the same width at its corresponding output port. For the purposes of this application, the width of the output waveguide at its corresponding output port is measured as the distance from the leading edge segment of the waveguide to the trailing side in a direction perpendicular to the trailing side. For example, as shown in FIG. 2c, a line (250) extends from the edge segment (242) to the trailing side of the first waveguide (230a) in a direction perpendicular to the trailing side of the first waveguide (230a), and thus represents the width of the first waveguide (230a) at the first output port (224a). Similarly, line (252) represents the width of the second waveguide (230b) at the second output port (224b).

[0036] For the purposes of this application, two or more waveguides are considered to have "substantially identical" widths if the values ​​of the widths of these waveguides are within 10% of each other. It should be understood that in some cases, an optical splitter can be designed with less variation between the output waveguides at the corresponding output ports of the output waveguides. For example, in some variations, a plurality of output waveguides (230a to 230r) have corresponding widths at their respective output ports that are within 5% of each other. When a plurality of output waveguides have substantially identical widths at a plurality of output ports, tapering the output waveguides to achieve a common waveguide size is not essential (although some level of tapering may still occur if desired), which can result in size reduction for designs involving tapering of the output waveguides.

[0037] When the output ports of multiple output waveguides (230a to 230r) are positioned along a non-circular path as described above, light can be diffused more uniformly compared to star couplers having the same number of output ports. For the purposes of this application, the distribution of light among a certain set of output waveguides is characterized by an “average dispersion factor,” which is the standard deviation obtained by dividing the average optical outputs of the set of output waveguides by the average of the average optical outputs of the set of output waveguides. The “average optical output” of a given output waveguide is the average of the percentages of input light accommodated by the corresponding output waveguide over a predetermined range of wavelengths. The exact distribution of light among output waveguides may vary as a function of wavelength, and thus the average optical outputs of the output waveguides (and the resulting average dispersion factor) represent the overall performance of the optical splitter over a predetermined range of wavelengths.

[0038] In some variations, a plurality of output waveguides (230a to 230r) may be positioned such that the average dispersion factor for the plurality of output waveguides (230a to 230r) over a predetermined range of wavelengths is less than 0.30. In some of these variations, the average dispersion factor for the plurality of waveguides (230a to 230r) over a predetermined range of wavelengths is less than 0.20. In some of these variations, the average dispersion factor for the plurality of waveguides (230a to 230r) over a predetermined range of wavelengths is less than 0.10. These average dispersion factors may be achieved in embodiments where the plurality of waveguides have substantially the same width. Furthermore, such performance can also be achieved over a wide bandwidth, for example, when a predetermined range of wavelengths spans at least 500 nanometers or when a predetermined range of wavelengths spans at least 1000 nanometers. Thus, the optical splitters described herein can have significantly improved splitting performance compared to conventional star couplers having the same number of output waveguides, while still realizing space savings resulting from the output waveguides (230a to 230r) having substantially the same width at their corresponding output ports.

[0039] The shape of the non-circular path (226) may depend on the number and size of the output waveguides (230a to 230r), as well as the desired light distribution between the output waveguides (230a to 230r). The non-circular path (226) has a shape in which a length axis passes through the center of the shape and represents its longest dimension. The shape also has a width axis representing the longest dimension of the shape in a direction perpendicular to its length axis.

[0040] In some variations, the length axis of the shape of the non-circular path (226) is parallel to the direction in which the input waveguide (210) is connected to the free propagation region (220). Accordingly, the width axis of the shape is perpendicular to this direction. In other variations, the length axis of the shape is positioned at a non-zero angle with respect to this direction. For example, in some variations, the length axis is positioned at an angle of less than 10 degrees with respect to the direction in which the input waveguide (210) is connected to the free propagation region (220).

[0041] In some cases, such as the variations illustrated in FIGS. 2a through 2c, the non-circular path (226) has an oval shape. The non-circular path (226) is centered around the free propagation area (220) and also defines a portion of the free propagation area (220) (specifically, a portion of the free propagation area (220) including a plurality of output ports and any intervening edge segments). As such, this portion of the free propagation area (220) also has an oval shape.

[0042] As illustrated in FIG. 2b, the oval shape has a length axis (270) passing through the center of the oval and representing its longest dimension, and also has a width axis (272) representing the longest dimension of the oval in a direction perpendicular to its length. In some cases, the oval is an ellipse, in which case the length axis (270) corresponds to the major axis of the ellipse and the width axis (272) corresponds to the minor axis of the ellipse. For the purposes of this application, the terms “oval” and “ellipse” are used to refer to a non-circular oval and a non-circular ellipse, respectively. In the variations illustrated in FIG. 2a through 2c, the length axis (270) of the oval shape of the non-circular path (226) is parallel to the direction in which the input waveguide (210) is connected to the free propagation region (220), and thus, the width axis (272) of the oval shape is perpendicular to this direction. This direction is represented by line (262) in FIG. 2c. In other variations, the length axis (270) of the oval shape is positioned at a non-zero angle with respect to this direction. For example, in some variations, the length axis is positioned at an angle of less than 10 degrees with respect to the direction in which the input waveguide (210) is connected to the free propagation region (220).

[0043] In variations where output waveguides are positioned along a non-circular path (226) having an oval shape, the output waveguides are spaced at different distances from the length axis of the oval shape. These distances will vary based on how close each waveguide is to the width axis. For example, in the variations illustrated in FIGS. 2a through 2c, a plurality of output waveguides comprises a first set of output waveguides (230a through 230d) having output ports located on a first side of the length axis (270) and a first side of the width axis (272), so that they are positioned between the width axis (272) and the input waveguide (210). Although the output port of the output waveguide (230d) intersects the width axis (272), for the sake of discussion, it is considered to be part of the first set of output waveguides. The output ports of the first set of output waveguides (230a to 230e) are further from the length axis in a direction away from the input waveguide (210) (e.g., along line (262)). Specifically, the first end waveguide (230a) has an output port located closer to the length axis (270) than the output port of the output waveguide (230b). The output port of the output waveguide (230b) is closer to the length axis (270) than the output port of the output waveguide (230c), and the output port of the output waveguide (230c) is closer to the length axis (270) than the output port of the output waveguide (230d).

[0044] A plurality of output waveguides (230a to 230r) comprises a second set of output waveguides (230e to 230i) having output ports located on a first side of the length axis (270) and a second side of the width axis (272), such that the width axis (272) is located between the input waveguide (210) and the output ports of the second set of output waveguides (230e to 230i). The output ports of the second set of output waveguides (230e to 230i) are closer to the length axis in a direction away from the input waveguide (210) (e.g., along line (262)). In this way, the first set of output waveguides (230a to 230d) may have at least one output port closer to the length axis (270) than at least one output port of the second set of output waveguides (230e to 230i), and at least one output port further from the length axis (270) than at least one output port of the second set of output waveguides (230e to 230i).

[0045] Similarly, a plurality of output waveguides (230a to 230r) include a third set of output waveguides (230j to 230n) having output ports located on the second side of the length axis (270) and the second side of the width axis (272), as well as a fourth set of output waveguides (230o to 230r) having output ports on the second side of the length axis (270) and the first side of the width axis (272). Like the first set of output waveguides (230a to 230d), the output ports of the fourth set of output waveguides (230o to 230r) are located further along the length axis (270) in a direction away from the output port (210). As with the second set of output waveguides (230e to 230i), the output ports of the third set of output waveguides (230j to 230n) are positioned closer to the length axis (270) in a direction away from the output port (210).

[0046] Although variations of the optical splitter (200) illustrated in FIGS. 2a through 2c are depicted as having 18 output waveguides (230a through 230r), it should be understood that the optical splitters described herein may have any suitable number of output waveguides depending on the requirements of the optical systems comprising these splitters. For example, in some variations, the optical splitter as described herein includes at least 8 outputs. In some of these cases, the optical splitter includes at least 15 outputs. In some of these cases, the optical splitter includes at least 30 outputs. Similarly, although the optical splitter (200) is depicted in FIGS. 2a through 2c as having a single output waveguide, the optical splitter (200) may instead include two or more input waveguides, each connected to a free propagation region at a corresponding input port, and may split the input light received through any of the input waveguides. The same principles described above apply in these variations, regardless of which input waveguide introduces light into the free propagation region (220), except that the far-field boundary (260) represents the boundary where the input light has reached the far-field. For example, a location within the free propagation region (220) is not considered part of the far-field when the input light received from the first input waveguide reaches the far-field at that location, but rather part of the far-field when the input light received from the second input waveguide does not reach the far-field at that location.

[0047] The optical splitters described herein may be used in an optical system to split light generated by one or more light sources. For example, FIG. 3 illustrates an exemplary optical system (300) comprising the optical splitter (200) of FIGS. 2a through 2c. The optical system (300) comprises a light source unit (305) and an optical splitter (200). The light source unit (305) is optically coupled to an input waveguide (210) so that light generated by the light source unit (305) is received by the input waveguide (210) and split by the optical splitter (200). This input light is split as output light between a plurality of output waveguides (230a through 230r) as discussed in relation to FIGS. 2a through 2c. The output light for each of the output waveguides (230a to 230c, 230p to 230r) is respectively illustrated in FIG. 3 by arrows (360a to 360c, 360p to 360r), but it should be understood that all of the output waveguides (230a to 230r) receive the output light. The optical system (300) can route the output light from the plurality of output waveguides (230a to 230r) to other parts of the optical system as desired.

[0048] The light source unit (305) is configured to generate light having one or more wavelengths within a predetermined wavelength range associated with the optical splitter (200), so that the optical splitter (200) can achieve a desired amount of splitting between the output waveguides (230a to 230r) for any wavelength generated by the light source unit (305). For example, in some cases, the light source unit (305) can generate a set of wavelengths having a bandwidth of at least 500 nanometers, and in this case, the optical splitter (200) is similarly configured to split the light at all wavelengths within the set of wavelengths. In some of these cases, the light source unit (305) can generate a certain set of wavelengths having a bandwidth of at least 1000 nanometers, and the optical splitter (200) is configured to split them. The light source unit (305) can generate wavelengths outside of a predetermined wavelength range, but in these cases, the optical splitter (200) may not perform as intended.

[0049] To generate light in a predetermined range of wavelengths, the light source unit (305) comprises a set of light sources (not shown), each of which is operable to selectively emit light in a corresponding set of wavelengths. Each light source may be any component capable of generating light in one or more specific wavelengths, such as a light-emitting diode or a laser. The laser may include a semiconductor laser, for example, a laser diode (e.g., a dispersive Bragg reflector laser, a dispersive feedback laser, an external resonator laser), a quantum cascade laser, etc. A given light source may be single-frequency (fixed wavelength) or may be tunable to selectively generate one of a plurality of wavelengths (i.e., the light source may be controlled to output different wavelengths at different times). The set of light sources may include any combination of suitable light sources and may be operated collectively to generate light at any of a plurality of different wavelengths.

[0050] To the extent that the light source unit (305) can generate a number of different wavelengths, the light source unit (305) may be configured to generate light of different wavelengths simultaneously and / or sequentially. The light source unit (305) may be integrated into a PIC including an optical coupler (200), or may be separate from the PIC and may couple light to the PIC. Additionally, the optical system may include additional components (not shown) between the light sources of the light source unit (305) and the optical splitter (200) so that the light initially generated by the light source unit (305) may be altered before reaching the optical splitter (200) as input light.

[0051] The foregoing description has used specific nomenclature to provide a complete understanding of the described embodiments for the purposes of explanation. However, it will be apparent to those skilled in the art that specific details are not required to carry out the described embodiments. Accordingly, the foregoing descriptions of specific embodiments described herein are presented for the purposes of illustration and explanation. They are not intended to be comprehensive or to limit the embodiments to the exact forms disclosed. It will be apparent to those skilled in the art that many modifications and variations are possible in light of the teachings above.

[0052] Although the disclosed examples have been sufficiently described with reference to the accompanying drawings, it should be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications should be understood as falling within the scope of the disclosed examples as defined by the appended claims.

[0053] Additional statements

[0054] 1. An optical splitter configured to split input light having one or more wavelengths within a predetermined wavelength range,

[0055] A free propagation area including an input port and a plurality of output ports;

[0056] An input waveguide optically coupled to the free propagation region at the input port; and

[0057] It includes a plurality of output waveguides, and

[0058] Each output waveguide of the plurality of waveguides is connected to the free propagation region at a corresponding output port among the plurality of output ports;

[0059] Each of the above plurality of output waveguides has substantially the same width;

[0060] An optical splitter in which the plurality of output ports are positioned such that the average dispersion coefficient for the plurality of output waveguides over the predetermined wavelength range is less than 0.30.

[0061] 2. An optical splitter according to Statement 1, wherein each of the plurality of output ports is located in the far-field section of the free propagation area.

[0062] 3. An optical splitter according to Statement 1 or Statement 2, wherein each of the plurality of output waveguides extends away from the corresponding output port along the pointing vector of the input light at the corresponding output port.

[0063] 4. An optical splitter in any one of statements 1 to 3, wherein the plurality of output ports are positioned along a non-circular path.

[0064] 5. In Statement 4, the non-circular path is an optical splitter having an oval shape.

[0065] 6. An optical splitter according to statement 5, wherein the oval shape has a length axis parallel to the direction in which the input waveguide is connected to the free propagation region.

[0066] 7. In Statement 5 or Statement 6, the plurality of output waveguides are,

[0067] A first set of output waveguides located on a first side of the width axis of the above-mentioned oval shape; and

[0068] An optical splitter comprising a second set of output waveguides located on a second side of the width axis of the above-mentioned oval shape.

[0069] 8. An optical splitter, wherein in any one of statements 1 to 7, the predetermined wavelength range has a bandwidth of at least 500 nanometers.

[0070] 9. An optical splitter operable to split input light having one or more wavelengths within a predetermined wavelength range,

[0071] An input waveguide operable to receive the above input light;

[0072] A slab waveguide having an input port and a plurality of output ports, and operable to receive the input light from the input waveguide at the input port; and

[0073] It includes a plurality of output waveguides connected to the slab waveguide at the plurality of output ports, and

[0074] The above plurality of output ports are located along a non-circular path centered in the free propagation region;

[0075] An optical splitter in which the plurality of output waveguides are positioned such that each of the plurality of waveguides receives output light when the input light is introduced into the input waveguide.

[0076] 10. An optical splitter according to statement 9, wherein the average dispersion coefficient for the plurality of output waveguides over the predetermined wavelength range is less than 0.30.

[0077] 11. An optical splitter in Statement 9 or Statement 10, wherein each of the plurality of output ports is located in the far-field section of the slab waveguide.

[0078] 12. An optical splitter, wherein in any one of statements 9 to 11, the non-circular path has an oval shape.

[0079] 13. An optical splitter in Statement 12, wherein the oval shape is elliptical.

[0080] 14. As an optical system,

[0081] A light source unit configured to generate input light having one or more wavelengths within a predetermined range of wavelengths; and

[0082] It includes an optical splitter optically coupled to receive the input light, and the optical splitter,

[0083] A free propagation area including an input port and a plurality of output ports;

[0084] An input waveguide optically coupled to the free propagation region at the input port; and

[0085] It includes a plurality of output waveguides, and

[0086] Each output waveguide of the plurality of waveguides is connected to the free propagation region at a corresponding output port among the plurality of output ports;

[0087] Each of the above plurality of output waveguides has substantially the same width;

[0088] An optical system in which the plurality of output ports are positioned such that the average dispersion coefficient for the plurality of output waveguides over the predetermined wavelength range is less than 0.30.

[0089] 15. An optical system according to Statement 14, wherein each of the plurality of output ports is located in the far-field section of the free propagation area.

[0090] 16. An optical system according to statement 14 or statement 15, wherein each of the plurality of output waveguides extends away from the corresponding output port along the pointing vector of the input light at the corresponding output port.

[0091] 17. An optical system in which, in any one of statements 14 to 16, the plurality of output ports are positioned along a path having an oval shape.

[0092] 18. An optical system according to statement 17, wherein the oval shape has a length axis parallel to the direction in which the input waveguide is connected to the free propagation region.

[0093] 19. In Statement 17 or Statement 18, the plurality of output waveguides are,

[0094] A first set of output waveguides located on a first side of the width axis of the above-mentioned oval shape; and

[0095] An optical system comprising a second set of output waveguides located on a second side of the width axis of the above-mentioned oval shape.

[0096] 20. An optical system in which, in any one of statements 14 to 19, the predetermined wavelength range has a bandwidth of at least 500 nanometers.

Claims

Claim 1 An optical splitter configured to split input light having one or more wavelengths within a predetermined wavelength range, comprising: a free propagation region including an input port and a plurality of output ports; an input waveguide optically coupled to the free propagation region at the input port; and a plurality of output waveguides including at least 15 output waveguides, wherein each of the output waveguides is connected to the free propagation region at a corresponding output port among the plurality of output ports; each of the plurality of output ports is positioned along a non-circular path; each of the plurality of output waveguides has substantially the same width; and the plurality of output ports are positioned such that the average dispersion coefficient for the plurality of output waveguides over the predetermined wavelength range is less than 0.

30. Claim 2 An optical splitter according to claim 1, wherein each of the plurality of output ports is located in the far-field section of the free propagation area. Claim 3 An optical splitter according to claim 1 or 2, wherein each of the plurality of output waveguides extends away from the corresponding output port along the Poynting vector of the input light at the corresponding output port. Claim 4 delete Claim 5 In claim 1, the non-circular path is an optical splitter having an oval shape. Claim 6 In claim 5, the optical splitter, wherein the oval shape has a length axis parallel to the direction in which the input waveguide is connected to the free propagation region. Claim 7 An optical splitter according to claim 5, wherein the plurality of output waveguides comprises: a first set of output waveguides located on a first side of the width axis of the oval shape; and a second set of output waveguides located on a second side of the width axis of the oval shape. Claim 8 An optical splitter according to claim 1 or 2, wherein the predetermined wavelength range has a bandwidth of at least 500 nanometers. Claim 9 An optical splitter operable to split input light having one or more wavelengths within a predetermined wavelength range, comprising: an input waveguide operable to receive said input light; a slab waveguide operable to receive said input light from said input waveguide at said input port, defining a free propagation region having an input port and a plurality of output ports; and a plurality of output waveguides connected to said slab waveguide at said output ports, wherein said output ports are positioned along a non-circular path centered in the free propagation region and have a length axis and a width axis; said output waveguides are positioned such that each of said output waveguides receives said output light when said input light is introduced into said input waveguide, and said output waveguides include: a first set of output waveguides located on a first side of said length axis of said non-circular path; and a second set of output waveguides located on a second side of said length axis of said non-circular path. Claim 10 An optical splitter according to claim 9, wherein the average dispersion coefficient for the plurality of output waveguides over the predetermined wavelength range is less than 0.

30. Claim 11 An optical splitter according to claim 9 or 10, wherein each of the plurality of output ports is located in the far-field section of the slab waveguide. Claim 12 In claim 9 or 10, the non-circular path is an optical splitter having an oval shape. Claim 13 In Clause 12, the above-mentioned oval shape is an elliptical optical splitter. Claim 14 An optical system comprising: a light source unit configured to generate input light having one or more wavelengths within a predetermined range of wavelengths; and an optical splitter optically coupled to receive said input light, wherein the optical splitter comprises: a free propagation region including an input port and a plurality of output ports; an input waveguide optically coupled to the free propagation region at the input port; and a plurality of output waveguides, wherein each output waveguide of the plurality of waveguides is connected to the free propagation region at a corresponding output port among the plurality of output ports; wherein each of the plurality of output ports is positioned along a non-circular path having an oval shape; wherein the oval shape has a width axis and a length axis longer than the width axis; wherein the length axis is parallel to the direction in which the input waveguide is connected to the free propagation region; wherein each of the plurality of output waveguides has substantially the same width; and wherein the plurality of output ports are positioned such that the average dispersion coefficient for the plurality of output waveguides over the predetermined range of wavelengths is less than 0.

30. Claim 15 An optical system in which, in paragraph 14, each of the plurality of output ports is located in the far-field section of the free propagation area. Claim 16 An optical system according to claim 14 or 15, wherein each of the plurality of output waveguides extends away from the corresponding output port along the pointing vector of the input light at the corresponding output port. Claim 17 delete Claim 18 delete Claim 19 An optical system according to claim 14, wherein the plurality of output waveguides comprises: a first set of output waveguides located on a first side of the width axis of the oval shape; and a second set of output waveguides located on a second side of the width axis of the oval shape. Claim 20 An optical system according to claim 14 or 15, wherein the predetermined wavelength range has a bandwidth of at least 500 nanometers.

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