Optical output devices and optical output methods for optical systems

Abstract

Configurations for an optical system used to guide light and reduce back-reflection back into an output waveguide are disclosed. The optical system may include an output waveguide defined in a slab waveguide. The output waveguide may be terminated before the output side of the slab waveguide, which can reduce back-reflection of light back into the output waveguide from the output side. The output side may define an optical element capable of steering the output light. The optical element may collimate the output light to cause the output light to converge or diverge.

Description

Technology Field

[0001] Cross-reference of related applications

[0002] This Patent Cooperation Treaty application claims priority to U.S. Patent Application No. 17 / 949,066 filed September 20, 2022, U.S. Patent Application No. 17 / 949,079 filed September 20, 2022, U.S. Patent Application No. 17 / 949,096 filed September 20, 2022, and U.S. Provisional Patent Application No. 63 / 247,526 filed September 23, 2021, the contents of which are incorporated herein by reference as described herein in their entirety.

[0003] Technology field

[0004] The present disclosure generally relates to routing and outputting light in photonic integrated circuits. More specifically, the embodiments of this specification relate to an optical system having an on-chip lens for outputting light from a waveguide. Background Technology

[0005] Generally, photonic integrated circuits include optical systems equipped with light sources. In some optical systems, light emitted by the light sources is output from the optical system through output ends. These output ends can be cut and polished to increase the efficiency of the light output from the optical system. While much light will be output, some light may be reflected backward from the output ends and re-enter the optical system instead of exiting the optical system. This backward-reflected light may propagate back to the output waveguide and / or light source, which typically generates false etalons and affects the stability of the light source.

[0006] Embodiments of the systems, devices, methods, and apparatus described in this disclosure relate to photonic integrated circuits having on-chip lenses. Also described are systems, devices, methods, and apparatus relating to an optical system having an in-plane lens that reduces backreflected light that can be recoupled into an output waveguide. The optical system may include an output waveguide positioned away from the output side of a slab waveguide and transmitting light so that the light can propagate through the slab waveguide before passing through the output side of the slab waveguide. The output side of the slab waveguide forms a lens that can change the direction in which the light propagates with respect to the optical axis, or otherwise includes such a lens. Because the in-plane lens is in the plane of the slab waveguide, backreflections into the output waveguide are reduced.

[0007] In some embodiments, the present disclosure describes an optical system. The optical system may include a slab waveguide having a free propagation region and an output side. The optical system may also include an output waveguide defined in the slab waveguide, the output waveguide having a propagation region in which light propagates and which includes a first side and a second side opposite the first side, a first light confinement region adjacent to the first side of the propagation region, and a second light confinement region adjacent to the second side of the propagation region. The output waveguide may terminate before the output side of the slab waveguide and before the free propagation region, and light may exit the propagation region and enter the free propagation region, and light may exit the free propagation region at the output side, thereby reducing back reflections into the output waveguide.

[0008] In another embodiment, the present disclosure describes a method for guiding light. The method may include the steps of propagating light through an output waveguide, emitting light from the output waveguide into a free propagation region of a slab waveguide, and passing light from the slab waveguide through an optical element at the output side of the slab waveguide, thereby reducing back reflections of light from the output side of the slab waveguide.

[0009] In another embodiment, the present disclosure describes an optical system. The optical system may include a slab waveguide and an output waveguide defined within the slab waveguide. The output waveguide may include a propagation region that allows light to pass through, a first light confinement region adjacent to a first side of the propagation region, and a second light confinement region adjacent to a second side of the propagation region, the second side being opposite to the first side of the propagation region. The optical system may also include an optical element defined on the output side of the slab waveguide, and the output waveguide terminates before the output side of the slab waveguide so that light emitted from the propagation region of the output waveguide propagates through the slab waveguide before passing through the optical element, thereby reducing back reflection of light from the optical element into the output waveguide.

[0010] Other embodiments relate to a photonic integrated circuit comprising a substrate, a cladding layer, and a waveguide layer. The waveguide layer comprises a slab waveguide having a side surface, and an output waveguide comprising a first optical confinement region, a second optical confinement region, and a waveguide core positioned between the first optical confinement region and the second optical confinement region. The side surface of the slab waveguide defines an optical element forming a cylindrical lens having a semicircular curved surface, and the output waveguide enters the slab waveguide and terminates at a junction between the output waveguide and the slab waveguide, and the output waveguide is positioned so that input light incident from the output waveguide into the slab waveguide exits the photonic integrated circuit through the side surface.

[0011] In some of these variations, the semicircular surface has a center of curvature, and the output waveguide is laterally offset with respect to the center of curvature. In some of these variations, the junction between the output waveguide and the slab waveguide can be aligned with the center of curvature. In other variations, the junction between the output waveguide and the slab waveguide is positioned behind the center of curvature so that the center of curvature is located between the junction and the optical element. In yet another variation, the junction between the output waveguide and the slab waveguide is positioned in front of the center of curvature so that the junction is located between the junction and the optical element.

[0012] In other of these variations, the waveguide layer includes a partially etched region between the side surfaces of the output waveguide and the slab waveguide so that input light incident from the output waveguide into the slab waveguide passes through the partially etched region. Additionally or alternatively, the output waveguide includes a refractive index adjustment region located at a junction where the widths of one or both of the first optical confinement region and the second optical confinement region decrease in the direction toward the junction. In other variations, the output waveguide includes a refractive index adjustment region located at a junction where the width of the waveguide core increases in the direction toward the junction.

[0013] Other embodiments relate to a photonic integrated circuit comprising a waveguide layer including a side surface defining a plurality of optical elements, a plurality of slab waveguides, and a plurality of output waveguides. Each of the plurality of output waveguides includes a first optical confinement region, a second optical confinement region, and a waveguide core positioned between the first optical confinement region and the second optical confinement region. Each optical element of the plurality of optical elements is associated with a corresponding slab waveguide among the plurality of slab waveguides and a corresponding output waveguide among the plurality of output waveguides so that input light incident from a corresponding output waveguide into a corresponding slab waveguide exits the photonic integrated circuit through the optical element.

[0014] In some of these variations, each optical element forms an on-chip lens. Each optical element of the plurality of optical elements may form a cylindrical lens having a semicircular surface with a center of curvature. In some of these embodiments, each output waveguide of the plurality of waveguides is laterally offset from the center of curvature of the optical element associated with the output waveguide. In other variations, all of the plurality of slab waveguides are optically connected.

[0015] Other embodiments described herein relate to an optical system comprising a light source unit, a photonic integrated circuit, and a controller. The photonic integrated circuit comprises a plurality of emitters optically connected to a side surface and a light source unit. Each emitter comprises an optical element formed on a side surface, a slab waveguide, and an output waveguide, positioned so that input light incident from an output waveguide into a slab waveguide exits the photonic integrated circuit through an optical element. The controller is configured to control the plurality of emitters to emit output light.

[0016] In some of these variations, multiple emitters have the same configuration so that each emitter generates an output beam of light having the same shape and direction. Additionally or alternatively, the photonic integrated circuit includes multiple phase shifters, each of which is controllable to adjust the phase of the light transmitted by the output waveguide of the corresponding emitter. In some of these variations, the controller is configured to selectively control the phase of the output light emitted by each of the multiple emitters. Additionally or alternatively, the controller is configured to selectively control which of the multiple emitters emits the output light. Additionally or alternatively, the controller is configured to selectively control the intensity of the output light emitted by each of the multiple emitters. Additionally or alternatively, the controller is configured to selectively control the wavelength or wavelengths of the output light emitted by each of the multiple emitters.

[0017] Other embodiments described herein relate to a photonic integrated circuit having a substrate, a cladding layer, and a waveguide layer. The waveguide layer comprises a slab waveguide and a waveguide, wherein the waveguide comprises a first optical confinement region, a second optical confinement region, and a waveguide core positioned between the first optical confinement region and the second optical confinement region. The waveguide enters the slab waveguide and terminates at a junction between the waveguide and the slab waveguide, and the waveguide comprises a refractive index adjustment region positioned at the junction, wherein the widths of one or both of the first optical confinement region and the second optical confinement region are reduced in a direction toward the junction.

[0018] In some of these variations, the waveguide layer includes an optical splitter, and the optical splitter includes a slab waveguide, a waveguide, and a plurality of output waveguides. The optical splitter is configured so that input light incident from the waveguide into the slab waveguide is split among the plurality of output waveguides. In other variations, the waveguide layer includes a side surface defining an optical element, and the waveguide is positioned so that input light incident from the waveguide into the slab waveguide exits the photonic integrated circuit through the side surface. In some of these variations, the optical element forms an on-chip lens. In other variations, the optical element includes a diffraction grating.

[0019] In other variations, the width of the waveguide core is constant in the refractive index adjustment region. In yet another variation, the width of the waveguide core gradually narrows in the refractive index adjustment region in the direction toward the junction. In yet another variation, the width of the waveguide core increases non-gradually in the refractive index adjustment region in the direction toward the junction. Additionally, or alternatively, the widths of one or both of the first optical confinement region and the second optical confinement region decrease linearly in the direction toward the junction.

[0020] Other embodiments relate to a photonic integrated circuit comprising a substrate, a cladding layer, and a waveguide layer, wherein the waveguide layer comprises a slab waveguide and a waveguide. The waveguide comprises a first optical confinement region, a second optical confinement region, and a waveguide core positioned between the first optical confinement region and the second optical confinement region. The waveguide enters the slab waveguide and terminates at a junction between the waveguide and the slab waveguide, and the waveguide comprises a refractive index adjustment region positioned at the junction where the width of the waveguide core increases in the direction toward the junction. In some of these variations, the waveguide layer comprises an optical splitter, and the optical splitter comprises a slab waveguide, a waveguide, and a plurality of output waveguides. The optical splitter is configured such that input light incident from the waveguide into the slab waveguide is split among the plurality of output waveguides. In other variations, the waveguide layer includes a side surface defining an optical element, and the waveguide is positioned so that input light incident from the waveguide into the slab waveguide exits the photonic integrated circuit through the side surface. In some of these variations, the optical element forms an on-chip lens.

[0021] Additionally or alternatively, the width of the waveguide core increases non-gradually in the refractive index adjustment region. Additionally or alternatively, the widths of the first optical confinement region and the second optical confinement region are constant in the refractive index adjustment region. In some variations, the waveguide includes an additional region in which the width of the waveguide core gradually narrows toward the junction so that the refractive index adjustment region is positioned between the additional region and the junction. Additionally or alternatively, the width of the waveguide core increases linearly in the refractive index adjustment region.

[0022] Other embodiments relate to an optical system comprising a light source unit configured to generate a set of wavelengths within a target wavelength range and a photonic integrated circuit. The photonic integrated circuit comprises a substrate, a cladding layer, and a waveguide layer, wherein the waveguide layer comprises a slab waveguide and a waveguide. The waveguide comprises a first optical confinement region, a second optical confinement region, and a waveguide core positioned between the first optical confinement region and the second optical confinement region. The waveguide enters the slab waveguide and terminates at a junction between the waveguide and the slab waveguide, and the waveguide comprises a positioned refractive index adjustment region in which the respective widths of the first optical confinement region and the second optical confinement region narrow from a first width to a second width in a direction toward the junction.

[0023] In some of these variations, a portion of each of the first optical confinement region and the second optical confinement region having a second width has a length such that the length is 1 / 4 of the wavelength within the target wavelength range. Additionally or alternatively, the width of the waveguide core increases from a third width to a fourth width in the refractive index adjustment region.

[0024] In addition to the exemplary aspects and embodiments described in this specification, additional aspects and embodiments will become apparent by referring to the drawings and studying the following description. Brief explanation of the drawing

[0025] Figure 1 shows a plan view of a general optical system including a waveguide that outputs light. FIG. 2 shows a plan view of an example of an optical system including a waveguide that terminates before the output side of the optical system. Figure 3 shows a plan view of an example of an optical system that mitigates back reflection of light. FIG. 4 shows a plan view of an example of an optical system equipped with an optical element that collimates output light. FIG. 5 illustrates a plan view of an example of an optical system having an optical element that steers the output light to converge. FIG. 6 illustrates a plan view of an example of an optical system having an optical element that steers to emit output light. FIG. 7 shows a plan view of an example of an optical system having a waveguide tilted toward the output side. FIG. 8 shows a plan view of an example of an optical system having a tilted output side. FIG. 9 illustrates a plan view of an example of an optical system having a plurality of waveguides. FIG. 10 shows a plan view of an example of an optical system equipped with an aspherical lens. FIG. 11 shows a plan view of an example of an optical system having a partially etched region between a waveguide and an output side. FIG. 12 shows a plan view of an example of an optical system having a partially etched region between a waveguide and an optical element. FIG. 13 shows a plan view of an example of an optical system having a diffraction grating on the output side of a slab waveguide. FIG. 14 shows a plan view of an example of an optical system having a metal on a slab waveguide. FIG. 15 shows a plan view of an example of an optical system having an optical element on a tilted output side. FIGS. 16a and FIGS. 16b respectively show a perspective view and a plan view of a photonic integrated circuit having an output side surface positioned on the outer side of the photonic integrated circuit. FIG. 16c shows a plan view of another variation of a photonic integrated circuit having an output side surface on the inner side of the photonic integrated circuit. FIGS. 17a and FIGS. 17b illustrate plan views of variations of photonic integrated circuits having optical elements configured as cylindrical lenses. FIGS. 18a through 18c illustrate plan views of variations of photonic integrated circuits having a plurality of optical elements. FIG. 18d illustrates a plan view of one variation of an optical system comprising a photonic integrated circuit having a plurality of optical elements. FIGS. 19a and FIGS. 19b illustrate plan views of variations of photonic integrated circuits having output waveguides with refractive index adjustment regions. FIGS. 20a and FIGS. 20b illustrate plan views of variations of photonic integrated circuits equipped with optical splitters as described in this specification. FIGS. 21a to 21c illustrate plan views of variations of photonic integrated circuits having output waveguides with refractive index adjustment regions. FIGS. 22a to 22c illustrate plan views of variations of photonic integrated circuits equipped with optical splitters as described in this specification. The use of cross-hatching or shading in the attached drawings is generally provided to clarify the boundaries between adjacent elements and to facilitate the readability of the drawings. Accordingly, the presence or absence of cross-hatching or shading does not convey or indicate any preference or requirement regarding specific materials, material properties, element ratios, element dimensions, commonalities of similarly depicted elements, or any other characteristics, attributes, or properties of any element depicted in the attached drawings. 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. As used throughout this specification, a reference number without an alphabetic character following it may refer to one or more of the corresponding references, a group of all references, or parts of the references. For example, "107" may refer to any of the light (107) (e.g., light (107a) or light (107b), etc.) or, depending on the context in which it is used, may refer to all light (107). The term light (107) may be used when discussing light emitted out of a waveguide or light exiting an optical system or photonic integrated circuit. In the following description of the examples, the attached drawings are referenced, and specific examples that may be implemented are illustrated within the drawings. It should be understood that other examples may be used and structural modifications may be made without departing from the scope of the various examples. Specific details for implementing the invention

[0026] Now, reference will be made in detail to representative embodiments illustrated in the accompanying drawings. It will be understood that the following description is not intended to limit the present disclosure to any 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.

[0027] Photonic integrated circuits having optical components designed to reduce backreflections during the operation of such optical components, as well as associated optical systems and methods, are described herein. In some embodiments, the photonic integrated circuit includes a cross section designed to emit light received from an output waveguide while reducing backreflections returning to the output waveguide. Additionally or alternatively, the photonic integrated circuit includes a junction between an output waveguide and a slab waveguide configured to reduce backreflections at the junction.

[0028] The optical systems described herein may include one or more photonic integrated circuits that route light using one or more waveguides. In a photonic integrated circuit, waveguides are typically supported on a planar substrate and constrain light to travel along the horizontal plane of the photonic integrated circuit. To emit light from the photonic integrated circuit, the light may be redirected from the horizontal plane using a vertical output coupler (e.g., through the upper or lower surface of the photonic integrated circuit) or exit horizontally along the lateral surface of the photonic integrated circuit.

[0029] Typically, when light is emitted horizontally from a lateral side surface of a photonic integrated circuit, the waveguide terminates at this lateral side surface so that the light exits the photonic integrated circuit directly from the cross-section of the waveguide. In other words, the waveguide terminates at the side surface of the photonic integrated circuit so that the light from the waveguide passes directly out of the optical system. When light passes through the interface between the waveguide and other materials (e.g., air surrounding the photonic integrated circuit, other optical components placed in contact with the photonic integrated circuit), some of the light may be unintentionally reflected back into the waveguide from one side of the photonic integrated circuit. This backreflected light generates etalons and can negatively affect the stability of light sources used to generate illumination in the photonic integrated circuit. Solutions such as anti-reflective coatings can mitigate some of the backreflection of light, but they may not completely eliminate such backreflections. Therefore, in many cases, it is desirable to configure the emission surfaces of the photonic integrated circuit to minimize the amount of light back-reflected into the waveguide.

[0030] Additionally, in some cases, it may be desirable to shape the light emitted from a photonic integrated circuit so that the light forms one or more beams having a specific shape, divergence, etc. While optical systems can be aided by including one or more free-space lenses, the addition of free-space lenses can increase the cost, design complexity, and overall size of the optical system. Therefore, it may be desirable to reduce the number of free-space lenses used in a given optical system.

[0031] The photonic integrated circuits described herein, as well as optical systems comprising such photonic integrated circuits, receive and route light from one or more light sources (e.g., a light source unit as described in more detail herein). The light source(s) generate light that is received directly or indirectly by one or more intermediate components (e.g., a multiplexer, a demultiplexer, an optical output splitter, a switch, an optical coupler, a phase shifter, a combination thereof, etc.) by one or more waveguides. The waveguides route light within the photonic integrated circuit and, in some cases, are used to emit light from the photonic integrated circuit.

[0032] Some embodiments described herein relate to output sections of a photonic integrated circuit that reduce the amount of back-reflected light coupled back into the output waveguide while allowing light from a waveguide ("output waveguide"), e.g., a strip waveguide, a rib waveguide, etc., to be emitted from the photonic integrated circuit. These output sections may be further configured to control or otherwise adjust the beam divergence of light emitted from the output section photonic integrated circuit. In these cases, the output waveguide is connected to a slab waveguide so that the slab waveguide connects the output waveguide to the output section of the photonic integrated circuit. The output waveguide receives input light generated from one or more light sources and transmits the input light to the slab waveguide. The slab waveguide has an output side that forms the output section of the photonic integrated circuit, and the input light received from the output waveguide exits the slab waveguide through the output side.

[0033] Specifically, the output waveguide terminates before the output cross-section of the photonic integrated circuit, and thus light exiting the output waveguide will propagate through the slab waveguide before reaching the output side of the slab waveguide. When the input light reaches the slab waveguide, it is diffracted, and the slab waveguide acts as a free propagation region. The input light diverges within the slab waveguide until it reaches the output side of the slab waveguide (or an interposed optical component, e.g., a partially-etched region as described in more detail herein). Since the output side of the slab waveguide forms part of the output cross-section of the photonic integrated circuit, light exiting the slab waveguide is emitted from the photonic integrated circuit.

[0034] In some embodiments, the output side of the slab waveguide may also be configured to adjust the divergence of the input light as the input light exits the slab waveguide. The output side includes an optical element, such as a lens, that steers or otherwise controls the direction of the light passing through the output side and exiting the photonic integrated circuit. For example, a portion of the output side of the slab waveguide may be shaped to form a lens (which is also referred to herein as an "on-chip lens").

[0035] The output side may be shaped to define an optical element having any suitable shape and orientation for other output waveguides. For example, the optical element may be concave, convex, flat, and / or oriented at a certain angle to another part of one side of the slab waveguide, or any combination thereof. Depending on the structure of the optical element, light passing through it is steered in a desired direction to produce converging, diverging, or collimated light. In some embodiments, the output side of the optical system may be flat and have little to no effect on the shaping of light as it leaves the optical system, but positioning the output waveguide away from the output side may reduce backreflected light coupled into the output waveguide.

[0036] These and other embodiments are discussed herein with reference to FIGS. 1 through 22c. However, those skilled in the art will readily recognize that the specific details regarding the practice of the invention provided herein with respect to these figures are for illustrative purposes only and should not be interpreted as restrictive.

[0037] FIG. 1 illustrates a plan view of a portion of an optical system (100) comprising an output waveguide (103) that terminates at the output side (110) of the optical system (100) (e.g., an output cross-section on the side of a photonic integrated circuit) to facilitate the emission of light from the output side (110). The output waveguide (103) can receive input light (108) generated by one or more light sources (not shown) and can output a portion of this light (illustrated as rays (107c, 107d, 107e)) through the output side (110) of the optical system (100). As illustrated, the output waveguide (103) is adjacent to and terminates at the output side (110).

[0038] As illustrated in FIG. 1, the output waveguide (103) includes a waveguide core (120) through which input light (108) can propagate, and includes a pair of optical confinement regions (105) that define the waveguide core (120) and provide optical confinement to the waveguide core (120). Typically, the photonic integrated circuits described herein include a substrate, a cladding layer, and a waveguide layer positioned on the cladding layer. The waveguide layer may be etched or patterned to define cavities within the waveguide layer that define the optical confinement regions (e.g., the optical confinement regions (105) of FIG. 1). These optical confinement regions may subsequently define waveguides (e.g., the waveguide (103) of FIG. 1) and other optical components within the waveguide layer of the photonic integrated circuit. In some variations, the photonic integrated circuit includes additional cladding layers or layers that fill the optical confinement regions. In some of these cases, the additional cladding layers or layers may also cover the upper side of the waveguide. In other cases, the optical confinement regions may be left unfilled to provide an air interface to the lateral side surfaces of the waveguide. In some of these cases, the upper surface of the waveguide may also not be covered to provide an air interface with the upper surface of the waveguide.

[0039] Accordingly, in some cases, one or more cladding layers collectively surround the waveguide core along the length of the waveguide to provide optical confinement. In other cases, one or more surfaces of the waveguide core may be exposed along the length of the waveguide to provide an air interface as mentioned immediately above (which may also provide optical confinement to the waveguide). The various layers of the photonic integrated circuits described herein may be formed from any suitable materials depending on the wavelength or wavelengths of light to be transmitted by the waveguides defined in the photonic integrated circuit. For example, in some variations, the waveguide layer (and thus any waveguide core) is formed of silicon, silicon nitride, silica, etc., the cladding layer (or layers) is formed of a dielectric material (or materials) such as silicon dioxide, and the substrate is formed of silicon.

[0040] Returning to FIG. 1, the optical confinement regions (105) separate the waveguide (120) from the adjacent slab waveguide (115). Thus, the input light (108) can be confined within the waveguide core (120) until it reaches the output side (110) of the optical system (100). At this point, most of the input light (108) is emitted from the output side (110) of the optical system (100) (as indicated by the rays (107c, 107d, 107e)). Depending on the width of the waveguide core (120), the wavelength (or wavelengths) of the input light (108), and the difference in refractive index between the waveguide core (120) and any material (e.g., air) in contact with the output side (110) of the optical system (100), a portion of the input light (108) reaching the output side (110) will be reflected back into the output waveguide (103) as back-reflected light (109). When the back-reflected light (109) is coupled back into the output waveguide (103), the back-reflected light (109) generates unwanted etalons and can have a negative effect on the stability of the light source (e.g., the light source generating the input light (108).

[0041] FIG. 2 is an example of an optical system (200) as described herein, comprising an output waveguide (203) that terminates before the output side (210) of the slab waveguide (215) of the optical system (200) so that light passes through the slab waveguide (215) before reaching the output side (210). Consequently, the optical system (200) may be designed to help mitigate back-reflected light compared to the output waveguide (103) described for FIG. 1. In some embodiments, the optical system (200) includes an optical element (225). Although the optical element (225) is shown as being formed as part of the output side (210) in FIG. 2, the optical element may additionally or alternatively be formed within the slab waveguide (215). Examples of optical elements and variations thereof will be described in more detail with reference to FIGS. 3 to 19b and FIGS. 21a to 21c.

[0042] The output waveguide (203) may be part of a photonic integrated circuit as described herein, and the output side (210) may be an output cross-section of the photonic integrated circuit such that light received by the output waveguide (203) is emitted from the side surface of the photonic integrated circuit. In these cases, the light emitted from the output cross-section of the photonic integrated circuit may be emitted from the optical system or transmitted to other elements of the optical system, depending on the design of the optical system. Specifically, the output waveguide (203) may terminate at a certain distance (223) from the output side (210) and emit light into a slab waveguide (215). When the input light reaches the slab waveguide (215), it diffracts, and the slab waveguide acts as a free propagation region (207) that allows the input light to spread as it propagates toward the output side (210).

[0043] Although a waveguide (e.g., an output waveguide or an input waveguide) is described herein as terminating in a slab waveguide, the waveguide comprises a waveguide core positioned between a pair of optical confinement regions such that a first optical confinement region is adjacent to a first side of the waveguide core and a second optical confinement region is adjacent to a second side of the waveguide core. The pair of optical confinement regions defines the shape of the waveguide core and acts to optically confine light within the waveguide core. The waveguide terminates in a slab waveguide at a junction between the waveguide and the slab waveguide. The pair of optical confinement regions also terminates at this junction, thereby causing the waveguide core to transition into a slab waveguide. Light passing from the waveguide core to the slab waveguide may be diffracted in the slab waveguide and propagate freely as described herein.

[0044] For example, the output waveguide (203) includes a waveguide core (220) positioned between a pair of optical confinement regions (205) within a planar waveguide layer as described herein. The optical confinement regions (205) terminate at a junction between the output waveguide (203) and the slab waveguide (215) to couple the output waveguide (203) to the slab waveguide (215). As light enters the slab waveguide (215), the optical confinement regions (205) no longer confine the light, so the light can diffuse in the plane of the waveguide layer as it travels through a free propagation region (207). The distance (223) between the output waveguide (203) and the output side (210) (i.e., between the end of the output waveguide (203) and the output side (210)) controls how much light is spread out before passing through the waveguide layer. This allows for controlling the size of the beam of light reaching the output side (210), which can affect the amount of back-reflected light as the input light passes through the output side (210) (e.g., through the optical element (225)) to the material on the other side of the output side (e.g., into free space or to another material adjacent to the optical system (200)).

[0045] Most of the emitted light leaves the slab waveguide (215) through the output side (210) (e.g., through the optical element (225) in the variant shown in FIG. 2), but a small amount of light may be back-reflected from the output side (210) (e.g., from the optical element (225) in the variant shown in FIG. 2). Depending on the design of the output side (210), some or all of this back-reflected light will not be coupled back into the output waveguide (203). Instead, the back-reflected light may be directed to a different part of the photonic integrated circuit so as not to reach the waveguide core (220) of the output waveguide (203).

[0046] In cases where the output side (210) includes an optical element (225), the optical element may be formed in any suitable manner. For example, the optical element (225) may be defined by etching (e.g., wet or dry etching) a portion of the photonic integrated circuit to create a desired shape on the side surface of the photonic integrated circuit. To form the optical element, the photonic integrated circuit is etched through at least a waveguide layer to define the optical element (225). As discussed herein, the photonic integrated circuit may include a substrate supporting a cladding layer (e.g., a lower cladding layer), a waveguide layer positioned on the cladding layer (and defining the output waveguide (203) and the slab waveguide (215)), and optionally an additional cladding layer on the waveguide layer (e.g., an upper cladding layer). In some cases, the photonic integrated circuit can be etched through an upper cladding layer (where this layer is included), a waveguide layer, and at least partially through a lower cladding layer. In some of these variations, the photonic circuit can be etched through a lower cladding layer and at least partially through a substrate.

[0047] In this way, at least a portion of the output cross-section of the photonic integrated circuit may be a vertical surface that is tilted / tilted or bent so that light exits the photonic integrated circuit horizontally through this vertical surface. The optical element may be defined to have any suitable shape as desired (e.g., a concave symmetric surface, a convex symmetric surface, a concave asymmetric surface, a convex asymmetric surface, a square, a lattice, any combination thereof, etc.). The etching used to define the output side (210) and the optical element (225) may be part of the process steps used to define other components of the photonic integrated circuit, and thus including the optical element may require little or no additional time or complexity in the manufacture of the photonic integrated circuit.

[0048] To further reduce back reflections from the output side (210), one or more portions of the output side (210) (e.g., optical element (225)) may be coated with an anti-reflective coating. In some embodiments, the anti-reflective coating may be one or more layers of dielectric materials. The anti-reflective coating may be a coating, deposition, bonding, or any combination thereof so that the anti-reflective coating may be adjacent to the optical element (225). It will be understood that the anti-reflective coating may be applied to any output surface of various embodiments of the photonic integrated circuits described herein (e.g., output sides of slab waveguides from which light is emitted).

[0049] In some embodiments, at least a portion of the photonic integrated circuit may extend beyond the output cross-section where light is emitted. For example, FIG. 16a illustrates a perspective view of one variant of the photonic integrated circuit (1600) as described herein. As illustrated, the photonic integrated circuit (1600) comprises a substrate (1602), a first dielectric layer (1604), a waveguide layer (1606), and a second dielectric layer (1608). The first dielectric layer (1604) is supported (directly or indirectly) by the substrate (1602), the waveguide layer (1606) is positioned on the first dielectric layer (1604), and the second dielectric layer (1608) is positioned on the waveguide layer (1606). In this way, the first and second dielectric layers (1604, 1608) can optically confine light transmitted by the photonic integrated circuit (1600) within the plane of the waveguide layer (1606).

[0050] The photonic integrated circuit (1600) includes a lateral side surface (1610) that forms part of the periphery of the photonic integrated circuit (1600). For example, the photonic integrated circuit (1600) may be formed as part of a larger wafer that is diced to expose the lateral side surface (1610). A part of the photonic integrated circuit (1600) is etched to define an output cross-section (1612) used to output light from the photonic integrated circuit (1600) as described herein. Specifically, in the variation shown in FIG. 16a, the photonic integrated circuit (1600) is etched through a second dielectric layer (1608), a waveguide layer (1606), a first dielectric layer (1604), and a part of the substrate (1602). The photonic integrated circuit (1600) can be etched to define an optical element (1614) on the output cross-section (1612) (which can be defined on the output surface of a slab waveguide as previously described). It may be desirable to select an etching depth that is sufficiently deep so that the output light is not clipped by the surrounding parts of the photonic integrated circuit (1600) as it propagates away from the output cross-section (1612).

[0051] The output section (1612) is recessed with respect to the lateral side surface (1610) so that light exiting the photonic integrated circuit (1600) from the output section (1612) can pass through the lateral side surface (1610) (unless diverted by other optical components of the optical system including the photonic integrated circuit (1600)). For example, FIG. 16b illustrates a plan view of a portion of the photonic integrated circuit (1600). As illustrated, the output waveguide (1616) can be defined in the waveguide layer (1606) through a pair of optical confinement regions (1618) to define the waveguide core (1620). These light confinement regions (1618) may be filled by the second cladding layer (1608) or by an additional cladding layer (e.g., formed of a different material and / or deposited at a separate stage from the second cladding layer (1608)). The output waveguide (1616) also enters and terminates into the slab waveguide (1622) defined in the waveguide layer (1606). The output waveguide (1616) can transmit light (1624) into the slab waveguide (1622), where the light (1624) diverges as it approaches the output cross-section (1612). The light (1624) passes through the output cross-section (1612) (which forms the output surface of the slab waveguide (1622)) and exits the photonic integrated circuit (1600). As illustrated in FIG. 16b, light (1624) travels through the lateral side surface (1610) after exiting the photonic integrated circuit (1600) through the output cross-section (1612).

[0052] While the output cross-section (1612) forms the outer surface of the photonic integrated circuit (1600) (i.e., forms part of the outer periphery of the photonic integrated circuit (1600)), in other variations, the photonic integrated circuit may be configured to emit light from the inner surface of a cavity defined in the photonic integrated circuit. For example, FIG. 16c illustrates a top view of another embodiment of the photonic integrated circuit (1630). The photonic integrated circuit (1630) may include, for example, a substrate (1632), a lower cladding layer (not shown) supported by the substrate (1632), and a waveguide layer (1634) positioned on the lower cladding layer. In some cases, the photonic integrated circuit (1630) further includes an upper cladding layer (not shown) positioned on the waveguide layer (1634). The photonic integrated circuit (1630) defines a cavity (1650) that extends at least partially through the photonic integrated circuit (1630) to expose a portion of the waveguide layer (1634). For example, in the variant shown in FIG. 1c, the cavity extends through the upper cladding layer (in variants including this layer), the waveguide layer (1634), and the lower cladding layer, and partially through the substrate (1632).

[0053] In these variations, the photonic integrated circuit (1630) is configured such that the surface of the cavity (1650) serves as an output section (1644) through which light is emitted from the photonic integrated circuit (1630). As illustrated, the photonic integrated circuit (1630) includes an output waveguide (1636) comprising a waveguide core (1640) defined by a pair of light confinement regions (1638). The output waveguide (1636) terminates in a slab waveguide defined in the waveguide layer (1634). The output section (1644) defines the output surface of the slab waveguide so that light introduced from the output waveguide (1636) into the slab waveguide is emitted from the slab waveguide through the output section (1644). This light will exit the waveguide layer (1634) and enter the cavity (1650).

[0054] Because the interior of the cavity (1650) is bounded by the surfaces of the photonic integrated circuit (1630), at least some of the light exiting the waveguide layer (1634) through the output section (1644) will be directed toward the opposite surface of the cavity (1650). Thus, the photonic integrated circuit (1630) can be configured to redirect this light out of the cavity (1650). For example, in some variations, the surface of the cavity (1650) opposite the output section (1644) may be tilted non-perpendicularly (and optionally coated with a reflective material such as metal) to redirect the light away from the plane of the waveguide layer (1634) and out of the cavity (1650). In other variations, an additional component (1646) may be inserted at least partially into the cavity. These additional components (1646) may include one or more inclined surfaces and / or other features configured to divert light away from the plane of the waveguide layer (1634) and out of the cavity (1650). In some variations, any space between the side surface (1644) and the additional components (1646) may be filled with a different type of material, which may act to limit the divergence of light before the light reaches the additional components (1646).

[0055] To generate light transmitted and emitted by the output waveguides described herein, the optical systems described herein may include a light source unit configured to generate light. The light source unit may be configured to generate light at a single wavelength, or may be capable of generating a plurality of different wavelengths over a predetermined wavelength range. The light source units described herein include a set of light sources (which may be a single light source or a plurality of different light sources), each of which may be optionally operable to emit light at a corresponding set of wavelengths.

[0056] Each light source may be any component capable of generating light at one or more specific wavelengths, such as a light-emitting diode or a laser. Lasers may include semiconductor lasers, e.g., laser diodes (e.g., dispersed Bragg reflector lasers, dispersed feedback lasers, external resonator lasers), quantum cascade lasers, etc. A given light source may be single-frequency (fixed wavelength) or 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). A 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.

[0057] To the extent that the light source unit can generate a number of different wavelengths, the light source unit may be configured to generate light of different wavelengths simultaneously and / or sequentially. Some or all of the light sources of the light source unit may be integrated into the photonic integrated circuits described herein. Additionally or alternatively, some or all of the light sources of the light source unit may be located separately from the photonic integrated circuits to couple light to the photonic integrated circuits. As previously mentioned, the optical system may include additional components (not shown) between the light sources of the light source unit and the output waveguides so that the light can be modified before reaching the output waveguide as input light.

[0058] When the waveguides described herein are discussed as having a range of wavelengths (e.g., "target range of wavelengths") and / or operating over it, it will be understood that in some cases, the light source unit does not need to be able to generate the entire spectrum within that range (i.e., all wavelengths between the longest and shortest wavelengths of the range). Instead, the light source unit may generate a discontinuous number or set of wavelengths within the range. Similarly, output waveguides may not necessarily transmit all of these wavelengths simultaneously, but instead may receive these wavelengths at different times depending on the operation of the optical system. Additionally, the target wavelength range may span any specific bandwidth as required by the optical system. For example, in some cases, the target wavelength range may span at least 100 nm. In some of these variations, the target wavelength range may span at least 500 nm. In some of these variations, the target wavelength range may span at least 1000 nm.

[0059] FIG. 3 is an example of another optical system (300) that mitigates back reflection of light. Specifically, the optical system (300) is configured to emit light from an output side (310) that does not include an optical element defined by the output side (310) (which may be an output cross-section of a photonic integrated circuit as discussed herein). The optical system (300) includes an output waveguide (303) and a slab waveguide (315), each of which may be defined in a waveguide layer as previously discussed. The output waveguide (303) includes a waveguide core (320) defined by a pair of optical confinement regions (305), so that light propagating through the waveguide core (320) may be confined by the optical confinement regions (305). The output waveguide (303) terminates at the junction with the slab waveguide (315), which serves as a free propagation region for light exiting the output waveguide (303).

[0060] Early termination of the output waveguide (303) (i.e., before the output side (310)) can reduce the amount of back-reflected light (307a, 307b) from being coupled back into the waveguide core (320) of the slab waveguide (315) (this can be further mitigated in cases where the output side (310) is coated with an anti-reflective coating). Specifically, input light exiting the output waveguide (303) (outer light rays of such input light are represented as rays (307a, 307b)) will diverge as it passes through the slab waveguide (315), which can reduce the amount of back-reflected light directed into the output waveguide (303). As light exits the slab waveguide (315) through the output side (310), the change in refractive index between the slab waveguide (315) and the surrounding material (e.g., air) can cause the divergence of the output light (outer light rays of this light are represented as rays (307d, 307e)) to be increased compared to the divergence of the input light. Although the light beams are depicted as outer light rays in FIGS. 3 through 15, it can be understood that the light fills the space between the outer light rays and the outer light rays represent the outer limit of the light from which the light is emitted.

[0061] Depending on the change in refractive index occurring at the output side (310), the magnitude of this divergence change may be greater than otherwise required for a given optical system. Accordingly, in some variations, the output cross-section of the photonic integrated circuit may be configured to define an optical element that can help shape the beam of light exiting the output side. For example, FIG. 4 illustrates an example of an optical system (400) having a side surface (410) that defines an optical element (425), wherein the optical element (425) forms an on-chip lens. In this variation, the optical element (425) is configured to collimate the light as the light is emitted from the side surface (410).

[0062] The optical system (400) includes a slab waveguide (415) and an output waveguide (403). For example, the slab waveguide (415) and the output waveguide (403) may be defined in the waveguide layer of the photonic integrated circuit as described above, and the side surface (410) is the output cross-section of the photonic integrated circuit. The output waveguide (403) has a waveguide core (420) connected to the slab waveguide (415) (defined by a pair of optical confinement regions (405) configured as described above). In this way, the output waveguide (403) terminates before reaching the side surface (410). Accordingly, the input light received by the output waveguide (403) is transmitted to the slab waveguide (415) (which acts as a free propagation region), where the input light, with boundaries represented by the rays (407a, 407b), will diverge as it approaches the optical element (425).

[0063] As input light passes through the optical element (425) to generate an output light beam, the optical element (425) will act as a defining lens (i.e., a lens having a defining refractive power) that collimates the output light (represented by the outermost rays (407d, 407e)). It will be understood that this collimation occurs within the plane of the waveguide layer defining the slab waveguide (415) (i.e., the slow axis) and that after the light exits through the side surface (410), it can still diverge in a direction perpendicular to the plane of the slab waveguide (415) (i.e., the fast axis). Additional free-space optical elements (e.g., lens elements such as a fast axis collimator) can be added to the optical system (400) to adjust the beam profile on the fast axis, and the optical element (425) can reduce the number and / or complexity of free-space optical elements required to achieve the desired beam profile for the output light on the slow axis.

[0064] In the variant shown in FIG. 4, the optical element (425) has a convex shape, for example, a curved surface having a defined radius of curvature (i.e., a curved surface toward the output waveguide (403)). The beam width of the input light is sized in FIG. 4 so that the beam passes through only a portion of the optical element (425), but this is for exemplary purposes only. The optical element (425) can be sized as desired so that the input light passes through a larger or smaller portion of the optical element (425). For example, in some cases, the optical element (425) can be sized and positioned so that as the input light passes through the optical element (425), the input light spreads out to the approximate width of the optical element (425) (e.g., within 5% of the width of the optical element (425)).

[0065] In other cases, the optical element may be configured to concentrate light emitted from a side surface so that the light converges. FIG. 5 is an example of an optical system (500) having a side surface (510) defining an optical element (525), and the optical element (525) forms an on-chip lens configured to steer light emitted from the side surface (510) to converge.

[0066] As with the optical system (400) of FIG. 4, the optical system (500) includes a slab waveguide (515) and an output waveguide (503). For example, the slab waveguide (515) and the output waveguide (503) may be defined in the waveguide layer of the photonic integrated circuit as previously described, and the side surface (510) is the output cross-section of the photonic integrated circuit. The output waveguide (503) has a waveguide core (520) connected to the slab waveguide (515) (defined by a pair of optical confinement regions (505) as previously discussed). In this way, the output waveguide (503) terminates before reaching the side surface (510). Accordingly, the input light received by the output waveguide (503) is transmitted to the slab waveguide (515) (which acts as a free propagation region), where the input light, with boundaries represented by the rays (507a, 507b), will diverge as it approaches the optical element (525).

[0067] The optical element (525) of the optical system (500) is positioned and / or curved so that as diverging input light passes through the optical element (525), the optical element (525) produces a convergent output light beam (the boundaries of which are represented by outermost rays (507d, 507e)). Except for the curvature of the optical element (525) and / or the distance between the output waveguide and the optical element (525) being adjusted to steer the output light to converge (compared to the optical element (425)), the optical element (525) will act as a defined lens (i.e., a lens having a defined refractive power). The optical element (525) may have a convex shape, such as a curved surface having a defined radius of curvature, and may be manufactured in any suitable manner as previously described. As discussed in this specification, such concentration occurs in the plane of the slab waveguide (515) and can reduce the number, size, and / or complexity of free-space optical bodies that would otherwise be used to concentrate light on the slow axis.

[0068] In other variations, it may not be desirable to significantly alter the beam profile of the input light as the input light exits the side surface of the photonic integrated circuit. Accordingly, in some variations, the output side surface of the photonic integrated circuit may include an optical element configured as a cylindrical lens having a semicircular surface such that the cylindrical lens has a constant radius of curvature. FIG. 17a illustrates one such variation of the photonic integrated circuit (1700) (which may be part of the optical systems described herein). Although only the waveguide layer (1702) of the photonic integrated circuit (1700) is shown in FIG. 17a, the photonic integrated circuit (1700) may also include a substrate, a lower cladding layer, and optionally an upper cladding layer as previously discussed.

[0069] The photonic integrated circuit (1700) includes a side surface (1704) that serves as an output cross-section from which light can be emitted from the photonic integrated circuit (1700). The side surface (1704) defines an optical element (1706) that forms a cylindrical on-chip lens having a semicircular curved surface. The photonic integrated circuit further includes an output waveguide (1708) and a slab waveguide (1714) defined in a waveguide layer (1702). Specifically, the output waveguide (1708) includes a waveguide core (1710) that is bounded and defined by a pair of optical confinement regions (1712). The output waveguide (1708) enters the slab waveguide (1714) and terminates at a junction between the output waveguide (1708) and the slab waveguide (1714).

[0070] As previously described, when input light is introduced from the output waveguide (1708) into the slab waveguide (1714), this input light (its boundaries are indicated by arrows (1718a, 1718b)) will diverge within the slab waveguide (1714). If the junction between the output waveguide (1708) and the slab waveguide (1714) is positioned at the center of the curvature of the optical element (1706), as illustrated in FIG. 17a, the input light emitted from the output waveguide (1708) will not change its divergence as the light exits the photonic integrated circuit (1700) through the optical element (1706). Specifically, when input light is introduced from the output waveguide (1708) into the slab waveguide (1714), each ray within the input light will strike the optical element (1706) with perpendicular incidence (assuming the optical element (1706) is sized so that the input light reaches its far field before striking the optical element (1706)). As each ray strikes the optical element (1706) with perpendicular incidence, each ray continues to travel along the same direction while undergoing a change in refractive index between the slab waveguide (1714) and the material (e.g., air) in contact with the side surface (1704). Thus, the optical element (1706) will generate output light (represented by outermost rays (1720a, 1720b)) having the same beam divergence as the input light.

[0071] When a beam of light strikes the optical element (1706) with perpendicular incidence, the back reflections caused as the light exits the slab waveguide (1714) will be retroreflected back into the output waveguide (1708). In effect, the backreflected light (its boundaries are also indicated by arrows (1718a, 1718b)) is focused by the optical element (1706) at the entrance of the output waveguide (1708). To mitigate this, the output waveguide may be positioned so that it is laterally offset with respect to the center of the curvature of the semicircular surface. As used herein, the output waveguide is considered to be "latitudinally offset" with respect to the center of the curvature of the optical element when the light beam exiting the output waveguide (i.e., the input light within the slab waveguide) is centered along a line that does not intersect the center of the curvature of the optical element. In the modified example illustrated in FIG. 17a, the input light exiting the output waveguide (1708) is centered on a line (1716) that intersects the center of the curvature of the optical element (1706), and thus the output waveguide (1708) is not laterally offset with respect to the optical element (1706).

[0072] FIG. 17b illustrates another variation of a photonic integrated circuit (1730) comprising a waveguide (1738) laterally offset with respect to an optical element (1736). Like the photonic integrated circuit (1700) of FIG. 17b, the photonic integrated circuit (1730) may be part of the optical systems described herein and may comprise a substrate, a lower cladding layer, a waveguide layer (1732), and optionally an upper cladding layer (but only the waveguide layer (1732) is shown in FIG. 17b).

[0073] The photonic integrated circuit (1730) includes a side surface (1734) that serves as an output cross-section from which light can be emitted from the photonic integrated circuit (1730). The side surface (1734) defines an optical element (1736) that forms a cylindrical on-chip lens having a semicircular curved surface. The photonic integrated circuit further includes an output waveguide (1738) and a slab waveguide (1744) defined in a waveguide layer (1732). Specifically, the output waveguide (1738) includes a waveguide core (1740) that is bounded and defined by a pair of optical confinement regions (1742). The output waveguide (1738) enters the slab waveguide (1744) and terminates at a junction between the output waveguide (1738) and the slab waveguide (1744).

[0074] Unlike the output waveguide (1708) of FIG. 17a, the output waveguide (1738) of the photonic integrated circuit (1730) is positioned so that the junction between the output waveguide (1708) and the slab waveguide (1714) is not positioned at the center of curvature (1760) of the optical element (1706). In the variation shown in FIG. 17b, the output waveguide (1738) is laterally offset with respect to the center of curvature (1760) of the optical element (1736). Specifically, the output waveguide (1738) is positioned so that the output waveguide (1738) introduces a beam of input light (its outer boundaries are represented by rays (1748a, 1748b)) into the slab waveguide (1744) so ​​that the beam is centered along a line (1746) that does not intersect the center (1760) of the curvature of the optical element (1736).

[0075] If the output waveguide (1738) is laterally offset with respect to the center of curvature (1760), various rays of input light will strike the optical element (1736) at non-vertical angles. Consequently, back reflections caused by these rays exiting the slab waveguide (1744) are not retroreflected back into the output waveguide (1738). Instead, back reflections (the outer boundaries of which are represented as rays (1752a, 1752b) in FIG. 17b) are effectively concentrated at different points within the slab waveguide (1744). If the output waveguide (1738) is sufficiently laterally offset with respect to the center of curvature (1760) of the optical element (1736), back reflections from the side surface (1734) will not be directly coupled into the output waveguide (1738).

[0076] As the input light reaches the optical element (1736), the side surface (1734) generates a beam of output light (its boundaries are represented by rays (1750a, 1750b)). Laterally moving the output waveguide (1738) can adjust the direction and / or level of divergence of the output light beam (compared to the beam generated by the side surface (1704) of FIG. 17a), but the output light beam can realize reduced back reflections as described above while remaining within the system specifications for a given optical system. In practice, in some cases, the output waveguide (1738) can be positioned to intentionally increase or decrease the divergence of the output beam, as described herein for FIG. 18a through 18c.

[0077] The optical elements described above for FIGS. 4, FIG. 5, FIG. 17a, and FIG. 17b consist of on-chip lenses having a convex shape, but in other variations, the optical elements may consist of on-chip lenses having a concave shape. For example, FIG. 6 is an example of an optical system (600) having a side surface (610) defining an optical element (625), wherein the optical element (625) forms an on-chip lens. In this variation, the optical element (625) is configured to increase the divergence of light as light is emitted from the side surface (610).

[0078] The optical system (600) includes a slab waveguide (615) and an output waveguide (603). For example, the slab waveguide (615) and the output waveguide (603) may be defined in the waveguide layer of the photonic integrated circuit as previously described, so that the side surface (610) forms the output cross-section of the photonic integrated circuit. The output waveguide (603) has a waveguide core (620) connected to the slab waveguide (615) (defined by a pair of optical confinement regions (605) as previously discussed). In this way, the output waveguide (603) terminates before reaching the side surface (610). Accordingly, the input light received by the output waveguide (603) is transmitted to the slab waveguide (615) (which acts as a free propagation region), where the input light, with boundaries represented by the rays (607a, 607b), will diverge as it approaches the optical element (625).

[0079] As input light passes through the optical element (625) to generate an output light beam, the optical element (625) acts as a negative lens (i.e., a lens having negative refractive power) to increase the divergence of the output light (its boundaries are represented by rays (607d, 607e)). This steering occurs within the plane of the waveguide layer defining the slab waveguide (615) (i.e., the slow axis), and the output light can also diverge along the fast axis as previously discussed. In the variation illustrated in FIG. 6, the optical element (625) has a concave shape, for example, a surface with a negative radius of curvature (i.e., a surface moving away from the output waveguide (603)). As discussed herein, the optical element (625) reduces the number, size, and / or complexity of the free-space optical system that would otherwise be used to focus along the slow axis.

[0080] Although the optical systems and photonic integrated circuits described herein with respect to FIGS. 4 through 6, FIG. 17a, and FIG. 17b are each illustrated having a side surface having a single optical element formed as an on-chip lens, it will be understood that the photonic integrated circuits (and associated optical systems) described herein may include a plurality of optical elements formed on their side surfaces. For example, FIG. 18a illustrates such a variation of a photonic integrated circuit (1800). Although only the waveguide layer (1802) of the photonic integrated circuit (1800) is illustrated in FIG. 18a, the photonic integrated circuit (1800) may also include a substrate, a lower cladding layer, and optionally an upper cladding layer as previously discussed.

[0081] The photonic integrated circuit (1800) includes a side surface (1804), which serves as an output cross-section from which light can be emitted from the photonic integrated circuit (1800). The side surface (1804) defines a plurality of optical elements (1806a to 1806c), each of which forms an on-chip lens. Although the plurality of optical elements (1806a to 1806c) is illustrated in FIG. 18a as having three optical elements (i.e., a first optical element (1806a), a second optical element (1806b), and a third optical element (1806c)), the plurality of optical elements (1806a to 1806c) may include any suitable number of optical elements (e.g., two, three, four, five, ten, twenty, or thirty or more optical elements). Each of these optical elements may be configured as any of the on-chip lenses as described in this specification, and thus the plurality of optical elements (1806a to 1806c) may include any combination of on-chip lenses as desired. The plurality of optical elements (1806a to 1806c) may each have the same shape, or alternatively, some or all of the plurality of optical elements (1806a to 1806c) may have different shapes.

[0082] The photonic integrated circuit (1800) further comprises a plurality of output waveguides (1808a to 1808c) and a plurality of slab waveguides (1810a to 1810c) defined in a waveguide layer (1802). Each output waveguide of the plurality of output waveguides (1808a to 1808c) and each slab waveguide of the plurality of slab waveguides (1810a to 1810c) are associated with a corresponding optical element among a plurality of optical elements (1806a to 1806c) so that each optical element receives light from one of the plurality of output waveguides (1808a to 1808c) (through the corresponding slab waveguide among the plurality of slab waveguides (1810a to 1810c)) and generates a corresponding beam of output light. Each optical element, its corresponding output waveguide, and its corresponding slab waveguide collectively form an emitter capable of generating a beam of output light. Accordingly, the photonic integrated circuit (1800) includes a plurality of emitters, each of which can emit a corresponding light beam through a side surface (1804) of the photonic integrated circuit (1800). The side surface (1804) can emit a plurality of individual beams of output light, which collectively form a larger beam of output light.

[0083] In the variant shown in FIG. 18a, a plurality of output waveguides (1808a to 1808c) include a first output waveguide (1808a), a second output waveguide (1808b), and a third output waveguide (1808c). Similarly, a plurality of slab waveguides (1810a to 1810c) include a first slab waveguide (1810a), a second slab waveguide (1810b), and a third slab waveguide (1810c). It will be understood that a plurality of slab waveguides (1810a to 1810c) may be different parts of a common slab waveguide so that the slab waveguides (1810a to 1810c) are optically connected to each other (as shown in FIG. 18a), or may be optically separated so that light cannot travel between the plurality of slab waveguides (1810a to 1810c) (e.g., through interposed optical confinement regions).

[0084] The first output waveguide (1808a) enters the first slab waveguide (1810a) and terminates at the junction between the first output waveguide (1808a) and the first slab waveguide (1810a). As previously described, when a beam of input light (1814a) is introduced from the first output waveguide (1808a) into the first slab waveguide (1810a), this input light (1814a) will diverge within the first slab waveguide (1810a). The input light (1814a) passes through the first optical element (1806a) to generate a first beam of output light (1816a). The second output waveguide (1808b), the second slab waveguide (1810b), and the second optical element (1806b) may be similarly configured to generate a second beam of output light (1816b) from a beam of input light (1814b) introduced from the second output waveguide (1808b) into the second slab waveguide (1810b). The third output waveguide (1808c), the third slab waveguide (1810c), and the third optical element (1806c) generate a third beam of output light (1816c) from a corresponding beam of input light (1814c) in the same manner.

[0085] In the variant shown in FIG. 18a, a plurality of optical elements (1806a to 1806c) are each configured as cylindrical lenses having a semicircular curved surface. In some of these variants, each of the plurality of output waveguides (1808a to 1808c) is laterally offset from the center of curvature of its corresponding optical element. As light passes through the corresponding optical elements (1806a to 1806c) as described herein for the photonic integrated circuit (1730) of FIG. 17b, back reflections reaching the plurality of output waveguides (1808a to 1808c) can be reduced or prevented.

[0086] In some variations, each of the plurality of emitters has the same configuration. In these variations, each emitter has its corresponding optical element, output waveguide, and slab waveguide of the same relative size, positioning, and orientation. Specifically, each of the plurality of output waveguides (1808a to 1808c) has the same position and orientation with respect to the corresponding optical element among the plurality of optical elements (1806a to 1806c). Additionally, each of the plurality of optical elements (1806a to 1806c) has the same shape, and thus the beams of output light (1816a to 1816c) generated by the plurality of emitters will have the same shape and direction. In other variations, different emitters may have different configurations. For example, at least some of the plurality of optical elements (1806a to 1806c) may have different shapes (e.g., to change the shape or direction of the corresponding beams of output light). Additionally or alternatively, some of the plurality of output waveguides (1808a to 1808c) will have different positions and / or orientations with respect to their corresponding optical elements and thus will produce beams of output light having different shapes and / or directions. Accordingly, these positions and orientations can be adjusted within each of the plurality of output waveguides (1808a to 1808c) to match the shape of the entire beam of light collectively produced by the plurality of optical elements (1806a to 1806c).

[0087] In the modified example illustrated in FIG. 18a, the junctions between the plurality of output waveguides (1808a to 1808c) and their corresponding slab waveguides (1810a to 1810c) are aligned with the centers (not shown) of the curvatures of the plurality of optical elements (1806a to 1806c). This is represented by a line (1812) which intersects the centers of the respective curvatures of the plurality of optical elements (1806a to 1806c) in FIG. 18a. If the junction is positioned along the line (1812) and laterally offset from the center of curvature of the corresponding optical element, the back-reflected light from the corresponding optical element (e.g., back-reflected light (1818a) for the first optical element (1806a), back-reflected light (1818b) for the second optical element (1806b), and back-reflected light (1818c) for the third optical element (1806c)) will also follow the line (1812) but will be concentrated at a point on the opposite side of the center of curvature. Thus, these junctions can be positioned so that the back-reflected light does not enter the plurality of output waveguides (1808a to 1808c) as previously discussed.

[0088] In other cases, the junctions between the output waveguide and the corresponding slab waveguide are not aligned with the center of the curvature of the semicircular surface of the corresponding optical element, which can be used to increase or decrease its divergence as the output light exits the side surface of the photonic integrated circuit. For example, FIG. 18b illustrates another variation of the photonic integrated circuit (1820). Specifically, FIG. 18b illustrates a waveguide layer (1822) of a photonic integrated circuit (1820), which includes a side surface (1824) defining a plurality of optical elements (including a first optical element (1826a), a second optical element (1826b), and a third optical element (1826c)), a plurality of output waveguides (including a first output waveguide (1828a), a second output waveguide (1828b), and a third output waveguide (1828c)), and a plurality of slab waveguides (including a first slab waveguide (1830a), a second slab waveguide (1830b), and a third slab waveguide (1830c)). These components collectively form a plurality of emitters as previously described. The side surface (1824) serves as an output cross-section through which light can be emitted from the photonic integrated circuit (1820).

[0089] The photonic integrated circuit (1820) can be configured identically to the photonic integrated circuit (1800) of FIG. 18a, except that each of the plurality of output waveguides (1828a to 1828c) terminates behind the center of curvature of its corresponding optical element (as represented by line (1832), which intersects the centers of curvature of each of the plurality of optical elements (1826a to 1826c) of FIG. 18b). In other words, the junction between the output waveguide and its corresponding slab waveguide is positioned so that the center of curvature of the corresponding optical element is set between the junction and the optical element. This can produce beams of output light that are slightly collimated (i.e., have less divergence) than their corresponding beams of input light. For example, when the first output waveguide (1828a) introduces a beam of input light (1834a) into the first slab waveguide (1830a) (i.e., at the junction behind line (1832)), the beam of input light (1834a) will be partially collimated as it passes through the first optical element (1826a). Consequently, the first optical element (1826a) will produce a first beam of output light (1836a) having less divergence than the beam of input light (1834a). Similarly, the second optical element (1826b) can generate a second beam of output light (1836b) having less divergence than the corresponding beam of input light (1834b), and the third optical element (1826c) can generate a third beam of output light (1836c) having less divergence than the corresponding beam of input light (1834c). It will be understood that each of the plurality of output waveguides (1828a to 1828c) can be laterally offset from the center of curvature of the corresponding optical element. This can generate back-reflected light (not shown) concentrated at a point on the opposite side of the line (1832), but the plurality of output waveguides (1828a to 1828c) can still be positioned so that the back-reflected light is not coupled into the plurality of output waveguides (1828a to 1828c).

[0090] FIG. 18c illustrates another variation of the photonic integrated circuit (1840). Specifically, FIG. 18c illustrates a waveguide layer (1842) of the photonic integrated circuit (1840), which includes a side surface (1844) defining a plurality of optical elements (including a first optical element (1846a), a second optical element (1846b), and a third optical element (1846c)), a plurality of output waveguides (including a first output waveguide (1848a), a second output waveguide (1848b), and a third output waveguide (1848c)), and a plurality of slab waveguides (including a first slab waveguide (1850a), a second slab waveguide (1850b), and a third slab waveguide (1850c)). These components collectively form a plurality of emitters as previously described. The side surface (1844) serves as an output cross-section through which light can be emitted from the photonic integrated circuit (1840).

[0091] The photonic integrated circuit (1840) may be configured identically to the photonic integrated circuit (1800) of FIG. 18a, except that each of the plurality of output waveguides (1848a to 1428c) extends beyond the centers of curvature of its corresponding optical element (as represented by line (1852), which intersects the centers of curvature of each of the plurality of optical elements (1846a to 1846c) of FIG. 18c) and terminates in front of them. In other words, the junction between each output waveguide and its corresponding slab waveguide is positioned such that the junction is located between the corresponding optical element and the center of curvature of its slab waveguide. This can generate beams of output light having increased divergence than their corresponding beams of input light. For example, when the first output waveguide (1848a) introduces a beam of input light (1854a) into the first slab waveguide (1850b) (i.e., at the junction in front of line (1852)), the beam of input light (1854a) will diverge as it passes through the first optical element (1846a). Consequently, the first optical element (1846a) will generate a first beam of output light (1856a) having more divergence than the beam of input light (1854b). Similarly, the second optical element (1846b) can generate a second beam of output light (1856b) having more divergence than the corresponding beam of input light (1854b), and the third optical element (1846c) can generate a third beam of output light (1856c) having more divergence than the corresponding beam of input light (1854c). It will be understood that each of the plurality of output waveguides (1848a to 1848c) may be laterally offset from the center of curvature of the corresponding optical element. This may produce back-reflected light (not shown) concentrated at a point on the opposite side of the line (1852), but the plurality of output waveguides (1848a to 1848c) may still be positioned so that the back-reflected light is not coupled into the plurality of output waveguides (1848a to 1848c).

[0092] In cases where multiple output beams are generated using multiple emitters, it may be desirable to allow individual control of some or all of the output beams. This may allow adjustment of the total illumination emitted from the photonic integrated circuit of the optical system. For example, the photonic integrated circuit may be able to selectively control the intensity, wavelength (or wavelengths), and / or phase of different output beams. FIG. 18d illustrates an example of an optical system (1860) having a photonic integrated circuit (1862) configured to emit multiple beams of output light through multiple emitters. Specifically, the photonic integrated circuit (1862) has a side surface (1864) defining a plurality of optical elements (1866a to 1866d). The side surface (1864) serves as an output cross-section of the photonic integrated circuit (1862). The plurality of optical elements (1866a to 1866d) includes four optical elements (e.g., a first optical element (1866a), a second optical element (1866b), a third optical element (1866c), and a fourth optical element (1866d)), but it may include any suitable number of optical elements as described above.

[0093] The photonic integrated circuit (1862) further comprises a plurality of output waveguides (1868a to 1868d), each of which is associated with a corresponding optical element among a plurality of optical elements (1866a to 1866d) as described herein for the photonic integrated circuits of FIGS. 18a to 18c. Specifically, the first output waveguide (1868a) can direct a beam of input light (1872a) toward the first optical element (1866a) to generate a first beam of output light (1874a), and the second output waveguide (1868b) can direct a beam of input light (1872b) toward the second optical element (1866b) to generate a second beam of output light (1874b). Similarly, the third output waveguide (1868c) can direct a beam of input light (1872c) toward the third optical element (1866c) to generate a third beam of output light (1874c), and the fourth output waveguide (1868d) can direct a beam of input light (1872d) toward the fourth optical element (1866d) to generate a fourth beam of output light (1874d). This can collectively form the aforementioned plurality of emitters. Depending on the relative arrangement of the optical elements (1866a to 1866d) and the divergence of the beams of output light (1874a to 1874d), some or all of the beams of output light (1874a to 1874d) may overlap at least partially.

[0094] In some cases, the optical system (1860) may selectively control which of the emitters emits light (i.e., which optical elements (1866a to 1866d) actively generate beams of output light) so that different combinations of beams of output light (1874a to 1874d) may be generated at different times. In these cases, individual emitters or groups of emitters may be individually controlled (e.g., by a controller as discussed herein) to generate light. Additionally, or alternatively, the optical system (1860) may selectively control the intensity of these beams of output light (1874a to 1874d) so that the intensity of the light varies between different emitters. For example, the optical system (1860) may include a light source unit (1869), which may be configured in any manner as previously described. A light source unit (1869) is optically connected to each of a plurality of emitters. Specifically, the light source unit (1869) is optically connected to each of a plurality of output waveguides (1868a to 1868d) such that each of the beams of input light (1872a to 1872d) (and thus the beams of output light (1874a to 1874d)) is generated by one or more light sources of the original light source unit (1869). In FIG. 18d, the light source unit (1869) is shown as being integrated into a photonic integrated circuit (1862), but in other cases, some or all of the light sources of the light source (1869) are separated from the photonic integrated circuit (1862) and arranged to couple light to the photonic integrated circuit (1862).

[0095] In some variations, the light source unit (1869) can control which of the output waveguides (1868a to 1868d) receives the output light by selectively activating different light sources of the light source unit (1869). Additionally or alternatively, the photonic integrated circuit (1862) may include one or more additional optical components (e.g., optical switches, variable optical attenuators, combinations thereof, etc.) positioned between the light source unit (1869) and one or more output waveguides (1868a to 1868d). These components may be controlled to determine whether the light generated by the light source unit (1869) reaches a specific output waveguide among the plurality of output waveguides (1868a to 1868d). The intensity of a given output light beam can be similarly adjusted, for example, by changing the intensity of the light generated by the light source unit (1869) and / or controlling how much of that light reaches the corresponding output waveguide.

[0096] Consequently, the optical system (1860) can select which of the output waveguides (1868a to 1868d) will receive the input light (via the light source unit (1869) and / or any intervening components), and thus select which optical elements (1866a to 1866d) will emit beams of the output light. For example, the optical system (1860) can direct the input light to all output waveguides (1868a to 1868d) so that all emitters (and their respective optical elements) emit the corresponding beams of the output light. At other times, the optical system (1860) can select a subset of the output waveguides (1868a to 1868d) and direct the input light only to the selected output waveguides. In this way, the corresponding subset of emitters (and their respective optical elements) emit beams of the output light. Depending on the design of the optical system (1860), the optical system may change the selection of emitters that emit light by selecting different subsets of output waveguides (1868a to 1868d) at different times.

[0097] Similarly, for any group of output waveguides and their corresponding optical elements (e.g., all such elements or a subset thereof), the optical system (1860) may selectively control the intensity of the input light provided to the different output waveguides. In these cases, different subsets of output waveguides (1868a to 1868d) may receive input light having different intensities so that different subsets of optical elements (1866a to 1866d) produce beams of output light having different intensities. For example, a first subset of emitters (and their respective optical elements) may produce beams of output light having a first intensity, and a second subset of emitters (and their respective optical elements) may simultaneously produce beams of output light having a second intensity greater than the first intensity. Thus, different emitters may simultaneously emit light of different intensities, and in some cases, may do so while other emitters are not actively emitting light.

[0098] Additionally or alternatively, the optical system (1860) may selectively control the wavelength (or wavelengths) of the beams of output light emitted by each optical element so that the wavelengths may vary between different emitters. Specifically, different subsets of output waveguides (1868a to 1868d) may receive input light having different sets of wavelengths so that different subsets of emitters (and their respective optical elements) generate beams of output light having different sets of wavelengths. For example, the optical system (1860) may be controlled so that a first subset of optical elements (1866a to 1866d) can generate a corresponding set of beams of output light, each of which has a first set of wavelengths. The optical system (1860) may be further controlled such that a second subset of optical elements (1866a to 1866d) simultaneously generates a second set of beams of output light, each of which has a second set of wavelengths different from a first set of wavelengths. In these cases, the first and second sets of wavelengths are considered different insofar as one set contains at least one wavelength of light that is not included in the other set.

[0099] In other variations, the optical system (1860) can control the light emitted by each emitter so that this phase can vary between different beams of output light. For example, the optical system (1860) illustrated in FIG. 18d includes a plurality of phase shifters (1870a to 1870d), each of which is controllable to selectively adjust the phase of the corresponding output waveguide (i.e., emitters or groups of emitters can be individually controlled to emit light having different phases). For example, the first phase shifter (1870a) is controllable to adjust the phase of the input light transmitted by the first output waveguide (1868a), the second phase shifter (1870b) is controllable to adjust the phase of the input light transmitted by the second output waveguide (1868b), the third phase shifter (1870c) is controllable to adjust the phase of the input light transmitted by the third output waveguide (1868c), and the fourth phase shifter (1870d) is controllable to adjust the phase of the input light transmitted by the fourth output waveguide (1868d). This can cause each of the optical elements (1866a to 1866d) (or a subset thereof) to produce an output light beam having a unique phase with respect to other output light beams generated by the optical elements (1866a to 1866d). Multiple phase shifters may include any suitable phase shifters, such as thermal-optical phase shifters (which change the refractive index of a waveguide by changing the temperature of the waveguide), carrier-based phase shifters (which change the refractive index of a waveguide by changing the amount of charge carriers present in the waveguide), optomechanical phase shifters (which change the effective refractive index experienced by light passing through the waveguide by moving a movable structure relative to the waveguide), combinations thereof, etc.

[0100] Accordingly, different subsets of emitters can be controlled to emit output light having different phases. For example, a first subset of emitters (and their respective optical elements) can generate beams of output light having a first phase, and simultaneously, a second subset of emitters (and their respective optical elements) can generate beams of output light having a second phase different from the first phase. Thus, different emitters can simultaneously emit light of different phases.

[0101] As illustrated in FIG. 18d, the optical system (1860) may include a controller (1876) configured to control a plurality of emitters. Specifically, the controller (1876) controls the operation of the photonic integrated circuit (1862) to emit light from the side surface (1864) as previously described. Specifically, the controller (1876) may control the light source unit (1869) to cause the light source unit (1869) to generate light necessary to produce beams of output light (1874a to 1874d) (or a subset thereof as selected by the optical system (1860)). Additionally, the controller (1876) may control any interposed components as needed to route light to selected output waveguides from the light source unit (1869). In variations in which the optical system (1860) comprises one or more phase shifters (e.g., a plurality of phase shifters (1870a to 1870d)), the controller (1876) may control these phase shifters to adjust the relative phases of the beams of the output light (1874a to 1874d) as previously discussed. The controller (1876) may include any combination of software, hardware, and firmware, including, for example, one or more processors and / or application-specific integrated circuits (ASICs), as needed to perform these functions (including any of the method steps described herein).

[0102] In various embodiments of the photonic integrated circuits described herein, it may be desirable to tilt the output waveguide so that it is not perpendicular to the side surface through which light exits the photonic integrated circuit. FIG. 7 is an example of an optical system (700) having an output waveguide (703) and a slab waveguide (715), wherein the output waveguide (703) is tilted relative to the output side (710) of the slab waveguide (715). In such cases, the back reflection (707) of light from the output side (710) can be mitigated by tilting the output waveguide (703). The specific positioning shown in FIG. 7 is for illustrative purposes only, and the output waveguide (703) may be positioned at any suitable angle to mitigate the back reflection of light.

[0103] Specifically, the output waveguide (703) (which may include a waveguide core (720) defined at least partially by a pair of optical confinement regions (705) as previously discussed) may be terminated at the slab waveguide (715) so that the input light transmitted by the output waveguide (703) is transmitted to the slab waveguide (715). The output waveguide (703) is tilted so that the beam of the input light (its boundaries are represented by rays (707a, 707b)) is similarly tilted with respect to the output side (710) of the slab waveguide (715). In these cases, the center of the beam of the input light (represented by ray (708)) strikes the output side (710) with non-perpendicular incidence.

[0104] As the beam of input light passes through the output side (710) to produce the beam of output light (its boundaries are represented by rays (707d, 707e) and additionally include ray (707c)), back-reflected light (not shown) can be returned to the slab waveguide (715). Depending on the positioning and angle of the output waveguide (703), some or all of the back-reflected light may be directed away from the output waveguide (703). In cases where some back-reflected light returns to the output waveguide (703), it may have a weaker intensity compared to similar designs where the center of the beam of input light strikes the output side (710) with perpendicular incidence. In some embodiments, the output side (710) may have an optical element etched into the profile of the output side (710), and the optical element may be any lens as described herein.

[0105] The relative angle between the output waveguide (703) and the output side (710) can be achieved in any suitable manner. For example, in the variation shown in FIG. 7, the output side (710) of the slab waveguide (715) may be a lateral surface of the photonic integrated circuit exposed by the dicing of the wafer, in which case the output waveguide may be defined at a predetermined angle with respect to this lateral surface. In cases where a portion of the photonic integrated circuit is etched to form a lateral surface (as discussed herein with respect to FIG. 16a through 16c), such etching may create a relative angle between the lateral surface and the output waveguide. FIG. 8 is such an example of an optical system (800) having a slab waveguide (815) having an output waveguide (803) and an inclined output side (810). In these cases, the output side (810) can be etched from the lateral surface of the photonic integrated circuit to create a relative angle between the output waveguide (803) and the output side (810).

[0106] As illustrated in FIG. 8, plane (811) represents a plane parallel to the lateral surface of the photonic integrated circuit. An output waveguide (803) (which may include a waveguide core (820) defined by light defining regions (805) as previously discussed) is positioned perpendicular to plane (811). Consequently, a beam of input light passing from the output waveguide (803) to the slab waveguide (815) (its boundaries are represented by rays (807a, 807b)) is perpendicular to plane (811) (i.e., the center of the input light beam will intersect plane (811) with perpendicular incidence). However, the output side (810) of the slab waveguide (815) may be etched to be inclined at a certain angle (845) with respect to the lateral surface. This creates a relative angle between the output waveguide (803) and the output side (810), similar to the relative angle described in relation to FIG. 7. Thus, as the input light passes through the output side (810) to produce a beam of output light (its boundaries are represented by rays (807d, 807e)), some or all of the back-reflected light can be directed away from the output waveguide (803). As in any of the embodiments described herein, an anti-reflective coating may be applied to the output side (810).

[0107] In some variations, it may be desirable for an optical element, e.g., an on-chip lens, to receive light from a plurality of output waveguides. For example, FIG. 9 illustrates an optical system (900) having an output side (910) defining an optical element (925). The optical system further comprises a plurality of output waveguides (903a, 903b, 903c) and is configured to direct light through the optical element (925) via their slab waveguide (915).

[0108] The slab waveguide (915) and a plurality of output waveguides (903a to 903c) may be defined in the waveguide layer of the photonic integrated circuit as previously described, and the side surface (910) is a lateral side surface of the photonic integrated circuit. Each of the output waveguides (903a to 903c) may be configured as previously described (e.g., the first output waveguide (903a) comprises a first waveguide core (920a) defined by a corresponding pair of optical confinement regions (905a), the second output waveguide (903b) comprises a second waveguide core (920b) defined by a corresponding pair of optical confinement regions (905b), and the third output waveguide (903c) comprises a third waveguide core (920c) defined by a corresponding pair of optical confinement regions (905c). Output waveguides (903a to 903c) transmit beams of input light (represented as single rays (907a to 907c)) into a slab waveguide (915). The slab waveguide (915) acts as a free propagation region, allowing these beams to spread out before exiting the photonic integrated circuit through the optical element (925) to form beams of output light (represented as rays (907d, 907e)). Input light may be introduced into the output waveguides (903a to 903c) simultaneously, or into different output waveguides at different times. The shape and / or direction of the output light may vary depending on which output waveguides (903a to 903c) transmit the input light into the slab waveguide (915).

[0109] The optical element (925) may be configured in any suitable manner as described in the specification. For example, the optical element (925) may be configured as an on-chip lens. Additionally, a plurality of output waveguides (903a to 903c) may be positioned at any suitable positions and angles relative to each other and relative to the optical element (925) as desired. For example, the output waveguides (903a to 903c) may be positioned at the same distance from the output side (910) or at different distances from the output side (910).

[0110] FIG. 10 is an example of an optical system (1000) comprising a slab waveguide (1015) having an output waveguide (1003) and an output side (1010), wherein the output side (1010) (which may be a side surface of a photonic integrated circuit) defines an optical element (1025). In this variation, the optical element (1025) is shaped to form an aspherical on-chip lens. Unlike the optical elements (1706, 1736) of FIG. 17a and FIG. 17b, the optical element (1025) lens does not have a semicircular curved surface. Instead, the radius of curvature of the vertical plane of the optical element (1025) varies from the center of the optical element (1025) to both ends. An output waveguide (1003) (which may include a waveguide core (1020) defined by a pair of confining regions (1005)) can transmit input light into a slab waveguide (1015). This input light (its boundaries are represented by rays (1007a, 1007b)) passes through an optical element (1025) to generate a beam of output light (its boundaries are represented by rays (1007d, 1007e)). In the variation illustrated in FIG. 10, the optical element is shaped to steer the beam of output light to converge. In these cases, the converging light can converge into a smaller spot than when a spherical lens is used. Thus, less wavefront error can occur when using an aspherical lens in contrast to a spherical lens.

[0111] FIGS. 11 and 12 are examples of optical systems comprising a partially etched region positioned between an output waveguide and an output side of a slab waveguide (which may form an output cross-section of a photonic integrated circuit). The partially etched region may act as a lens between the output waveguide and the output side, thereby diverting input light before it reaches the output side. Specifically, FIG. 11 illustrates an optical system (1100) having a partially etched region (1150) between an output waveguide (1103) and an output side (1110) defining an optical element (1125). FIG. 12 illustrates an optical system (1200) having a partially etched region (1250) between an output waveguide (1203) and an output side (1210) not containing an optical element.

[0112] Similar to previous embodiments, in FIG. 11, the output waveguide (1103) comprises a waveguide core (1120) bounded and defined by a pair of optical confinement regions (1105) and terminates at a junction with a slab waveguide (1115). Input light introduced from the output waveguide (1103) into the slab waveguide (1115) (its boundaries are represented by rays (1107a, 1107b)) will pass through a partially etched region (1150) before reaching the output side (1110) of the slab waveguide (1115) (which may form the output cross-section of a photonic integrated circuit). Specifically, the input light may pass through an optical element (1125), as previously described, to generate an output beam (its boundaries are represented by rays (1107d, 1107e)). Depending on the shape of the partially etched region (1150), the partially etched region (1150) can change the divergence and / or redirect the beam of input light as the beam of input light passes through the partially etched region. For example, in the variation shown in FIG. 11, the partially etched region (1150) can partially concentrate the input light before the input light reaches the optical element (1125). In this way, the partially etched region (1150) and the optical element (1125) collectively form two lens systems to achieve the desired shape and direction of the output light emitted from the optical element (1125).

[0113] The partially etched region (1150) is shown as elliptical in FIG. 11, but may be any shape not limited to circular, square, rectangular, trapezoidal, asymmetrical, etc. The partially etched region (1150) may be etched during a process step different from the etching step used to form the optical element (1125), because these components may be etched to two different depths. That is, the partially etched region (1150) may be etched lower than the etching used to define the optical element (1125). The partially etched region (1150) may be filled with additional material and may have a refractive index different from that of the surrounding slab waveguide (1115). For example, the partially etched region (1150) may be configured so that this additional material is positioned on the lower cladding layer (i.e., the cladding layer on which the waveguide layer defining the slab waveguide (1115) is formed). In cases where the photonic integrated circuit includes an upper cladding layer, this additional material may be positioned below the upper cladding layer. The upper and / or lower cladding layers may help to keep light passing through the partially etched region confined within the plane of the waveguide layer.

[0114] The optical system (1200) of FIG. 12 may function similarly to the optical system (1100), except that the output side (1210) does not contain an optical element. Specifically, in FIG. 11, the output waveguide (1203) includes a waveguide core (1220) bounded and defined by a pair of optical confinement regions (1205) and terminates at a junction with the slab waveguide (1215). Input light introduced from the output waveguide (1203) into the slab waveguide (1215) (its boundaries are represented by rays (1207a, 1207b)) will pass through a partially etched region (1250) before reaching the output side (1210) of the slab waveguide (1215) (which may be a side surface of a photonic integrated circuit). Specifically, the input light can pass through the output side (1210), as previously described, to generate an output beam (its boundaries are represented by rays (1207d, 1207e)). Depending on the shape of the partially etched region (1250), the partially etched region (1250) may change the divergence and / or redirect the beam of the input light as the beam of the input light passes through the partially etched region. The partially etched region (1250) may be configured in any manner as described herein with respect to FIG. 11.

[0115] FIG. 13 is an example of an optical system (1300) having a diffraction grating (1355) on the output side (1310) of a slab waveguide (1315). Light can be propagated through an output waveguide (1303), and the output waveguide (1303) includes a waveguide core (1320) bounded and defined by a pair of light confinement regions (1305). When light is propagated through the output waveguide (1303), it can be understood that the light is propagating through the waveguide core (1320). The diffraction grating (1355) can receive light propagating through the slab waveguide (1315). The output light propagating through the diffraction grating (1355) can generate light of different orders (e.g., zeroth, first, second, etc.). In some embodiments, the light of the first order may occur on both sides of the zero order and may appear when the path light of the light from the other gratings is approximately equal to the light of one wavelength. In some embodiments, when light of more than one wavelength is received by the diffraction grating (1355), the output light may be decomposed into different wavelengths.

[0116] FIG. 14 is an example of an optical system (1400) having a metal (1460) on a slab waveguide (1415). The metal (1460) may be deposited on the slab waveguide (1415) and may function as a polarizer. In some embodiments, the metal may be a planar metal layer. Light propagating through the waveguide core (1420) of the output waveguide (1403) (which is defined and bounded by a pair of light confinement regions (1405)) may be randomly polarized, and the metal may absorb more of the first polarization than the second polarization. Consequently, the output side (1410) of the slab waveguide (1415) may emit a beam of output light having a different relative polarization compared to the input light transmitted by the output waveguide (1403).

[0117] In some embodiments, the light may include polarizations such as TE polarization and / or TM polarization. The metal (1460) may attenuate the TM polarized light and pass the TE polarized light, or attenuate the TE polarized light and pass the TM polarized light. As used herein, it may be understood that when TE polarized light passes, relatively more TE polarization may propagate through the polarizer than TM polarization. Similarly, when TM polarized light passes, relatively more TM polarization may propagate through the polarizer than TE polarization. In some examples, an absorption layer may be deposited on the slab waveguide (1415) and under the metal (1460). The absorption layer may reduce the loss of light of the selected polarization passing through. The terms "pass" and "attenuate" may be relative terms. In some examples, the term "passage" may indicate that when the first polarization passes, more of the first polarization can pass than the second polarization, or vice versa. In some examples, the term "attenuation" may indicate that when the second polarization is attenuated, more of the second polarization is attenuated than the first polarization.

[0118] Although the metal (1460) is depicted as a rectangle, the metal may be deposited in any suitable shape. In some embodiments, the metal (1460) may not only be deposited on the slab waveguide (1415) but may also extend across the shape of the optical element (1425). In FIG. 14, the optical element (1425) is a defined lens depicted as a semicircle, and in some examples, the metal may cover the depicted area and may extend to cover the semicircle shape.

[0119] FIG. 15 is an example of an optical system (1500) having an optical element (1525) at a tilted output side (1510). FIG. 15 is an example of combining different embodiments described herein with reference to FIG. 5 and FIG. 8. The output side (1510) may be tilted with respect to a plane (1511) perpendicular to the end surface of an output waveguide (1503) (which includes a waveguide core (1520) bounded and defined by a pair of optical confinement regions (1505)), wherein the output waveguide (1503) enters and terminates into a slab waveguide (1515). The output side (1510) may be at an angle (1540) between the output side (1510) and the plane (1511) (shown as a dashed line). Alternatively, even if the output waveguide (1503) is not positioned at an angle as in FIG. 7, all light (its boundaries are represented by rays (1507a, 1507b)) can pass through the optical element (1525) of the output side (1510) at a predetermined angle. The output light (its boundaries are represented by rays (1507d, 1507e)) can exit the optical element (1525). As previously described, the optical element (1525) may be any element described herein or any suitable optical element for obtaining the desired type of output light.

[0120] In some cases, it may be desirable for the photonic integrated circuits and optical systems described herein to be able to operate over a wide range of wavelengths. Depending on the intended use of a given optical system (e.g., performing spectroscopic measurements), a light source unit as described herein may be configured to generate multiple wavelengths over tens or hundreds of nanometers, and various optical components of the optical system may need to accommodate wavelengths over some or all of this range. In such cases, it may be desirable for a given optical component to have a similar level of performance regardless of the wavelength of the light it receives.

[0121] As previously mentioned, when the output waveguide enters and terminates within the slab waveguide, the light will be diffracted as it enters the slab waveguide (which acts as the free propagation region). The angle of diffraction for a given input light depends on the ratio between its wavelength and mode size as the input light reaches the slab waveguide, which can result in different diffraction angles for different wavelengths of the input light. This can ultimately cause the beam size within the free propagation region to vary as a function of wavelength, which can lead to wavelength-dependent variations in the performance of the optical system.

[0122] To help reduce this wavelength dependence, the waveguide core of the output waveguide can be sized to be sufficiently narrow (e.g., through tapering) as it approaches the slab waveguide (e.g., the junction between the output waveguide and the slab waveguide) so that the magnitude of the mode of input light is proportional to the wavelength of the input light over a predetermined target range of wavelengths. Thus, when the output waveguide is configured to carry the wavelengths of the target range, the width of the waveguide can be selected based on the wavelengths of this target range.

[0123] Narrowing the output waveguide in this manner can provide improved uniformity of diffraction angles across the target range of wavelengths, but it can also increase back reflections at the interface between the output waveguide and the slab waveguide. Specifically, narrowing the output waveguide can cause at least some modes of wavelengths to be poorly confined, thereby resulting in a change in the effective refractive index between the optical confinement regions defining the output waveguide and the slab waveguide. This change in the effective refractive index generates back reflections at the junction between the output waveguide and the slab waveguide.

[0124] To help reduce these back reflections, in some embodiments of the photonic integrated circuits and optical systems described herein, the junction between the output waveguide and the slab waveguide may be configured to provide an effective refractive index that changes before the output waveguide terminates. This may include changing the width of the waveguide core and / or optical confinement regions near the junction. For example, FIG. 19a illustrates an example of a photonic integrated circuit (1900) as described herein. Although only the waveguide layer (1902) of the photonic integrated circuit (1900) is shown in FIG. 19a, the photonic integrated circuit (1900) may also include a substrate, a lower cladding layer, and optionally an upper cladding layer as previously discussed.

[0125] The photonic integrated circuit (1900) includes a side surface (1904), which serves as an output cross-section from which light can be emitted from the photonic integrated circuit (1900). In the variant shown in FIG. 19a, the side surface (1904) defines an optical element (1906) (which may be composed of any of the optical elements described previously). The photonic integrated circuit (1900) further includes an output waveguide (1908) and a slab waveguide (1915) defined in the waveguide layer (1902). Specifically, the output waveguide (1908) includes a waveguide core (1912) that is bounded and defined by a pair of optical confinement regions (1910a, 1910b). A pair of optical confinement regions comprises a first optical confinement region (1910a) and a second optical confinement region (1910b), each of which is filled with cladding material or air and can provide optical confinement to the waveguide core (1912) as previously discussed. The output waveguide (1908) enters the slab waveguide (1915) and terminates at the junction between the output waveguide (1908) and the slab waveguide (1915). Thus, input light (not shown) can be transmitted from the waveguide core (1912) to the slab waveguide (1915) and can exit the photonic integrated circuit (1900) through the side surface (1904) as previously described.

[0126] The output waveguide (1908) includes a refractive index adjustment region (1914) positioned at the junction between the output waveguide (1908) and the slab waveguide (1915) such that at the distal end, the refractive index adjustment region (1914) coincides with the junction between the output waveguide (1908) and the slab waveguide (1915). The refractive index adjustment region (1914) is configured to change the effective refractive index experienced by light passing through the output waveguide (1908) as light approaches the junction with the slab waveguide (1915). In the variation illustrated in FIG. 19a, the width of one or both of the light confinement regions (1910a, 1910b) narrows in the refractive index adjustment region (1914) as it approaches the junction with the slab waveguide (1915) (i.e., decreases in the direction toward the junction). Although the widths of one or both of the optical confinement regions (1910a, 1910b) are shown as narrowing in the refractive index adjustment region (1914) in FIG. 19a, in other cases, only the width of one of the optical confinement regions (i.e., the first optical confinement region (1910a) or the second optical confinement region (1910b)) is narrowed in the refractive index adjustment region (1914).

[0127] In the variant illustrated in FIG. 19a, the width of the waveguide core may be kept constant within the refractive index adjustment region (1914). Alternatively, the width of the waveguide core (1912) may gradually narrow within the refractive index adjustment region (1914) as the waveguide core (1912) approaches the junction with the slab waveguide (1915) (i.e., in the direction toward the junction). In these cases, the change in the width of the optical confinement regions (1910a, 1910b) will spread the change in effective refractive index over the length of the refractive index adjustment region (1914), which will reduce the instantaneous change in refractive index experienced by optical backreflections associated with the change in effective refractive index as the output waveguide terminates. Additionally, the reduced width of the optical confinement regions (1910a, 1910b) at the junction provides a narrower surface to receive backreflections generated on the side surface (1904). Consequently, this back-reflected light is less likely to be reflected from the light confinement regions (1910a, 1910b) in a manner that results in this back-reflected light being coupled into the output waveguide (1908).

[0128] In the variant illustrated in FIG. 19a, the reduced width of the optical confinement regions (1910a, 1910b) is linearly tapered toward the junction. Although the widths are illustrated as being linearly tapered to a width of zero, in other cases, the widths may be tapered to a minimum width that is not zero (this may, in part, depend on the manufacturing capabilities used to define the optical confinement regions (1910a, 1910b)). In some of these variants, the widths of one or both of the optical confinement regions (1910a, 1910b) are tapered non-gradually so that the mode shape of the input light transmitted by the waveguide core (1912) cannot change significantly within the refractive index adjustment region (1914). For example, progressive tapering may take hundreds of micrometers to achieve a specific change in the width of the optical confinement regions (1910a, 1910b), but non-progressive tapering may achieve the same change in width over a length of several micrometers or less as described in this specification.

[0129] In other variations, the widths of the optical confinement regions (1910a, 1910b) may be narrowed in a non-linear manner. FIG. 19b illustrates one such variation of an example of a photonic integrated circuit (1920) as described herein. Although only the waveguide layer (1922) of the photonic integrated circuit (1920) is shown in FIG. 19b, the photonic integrated circuit (1920) may also include a substrate, a lower cladding layer, and optionally an upper cladding layer as previously discussed. The photonic integrated circuit (1920) includes an output waveguide (1928) comprising a waveguide core (1932) defined and bounded by first and second optical confinement regions (1930a, 1930b), and a slab waveguide (1935) having a side surface (1924) defining an optical element (1926). These components can be configured in the same manner as described herein for FIG. 19a, except that the output waveguide (1928) has different refractive index adjustment regions (1934).

[0130] The refractive index adjustment region (1934) is positioned at the junction between the output waveguide (1928) and the slab waveguide (1935) such that at the distal end, the refractive index adjustment region (1934) coincides with the junction between the output waveguide (1928) and the slab waveguide (1935). Within the refractive index adjustment region (1934), the widths of the optical confinement regions (1930a, 1930b) are stepped. In particular, the width of each of the optical confinement regions (1930a, 1930b) changes from a first width within the refractive index adjustment region (1934) to a second, narrower width (i.e., before the output waveguide (1928) ends at the junction with the slab waveguide (1935). In cases where the output waveguide is configured to transmit multiple wavelengths over a target range of wavelengths, the length of a portion of the optical confinement regions (1930a, 1930b) having a narrower second width may be selected to be 1 / 4 of one of the wavelengths within the target range of wavelengths (e.g., the center wavelength within the target range of wavelengths). The width of the waveguide core (1932) may be kept constant within the refractive index adjustment region (1934). Alternatively, the width of the waveguide core (1932) may gradually narrow within the refractive index adjustment region (1934) as the waveguide core (1932) approaches the junction with the slab waveguide (1935).

[0131] The refractive index adjustment regions (1914, 1934) described in FIGS. 19a and 19b may be utilized in any optical component comprising a junction between an output waveguide and a slab waveguide. For example, FIG. 20a illustrates an example of a photonic integrated circuit (2000) as described herein. Although only the waveguide layer (2002) of the photonic integrated circuit (2000) is illustrated in FIG. 20a, the photonic integrated circuit (2000) may also include a substrate, a lower cladding layer, and optionally an upper cladding layer as previously discussed. In such a variation, the photonic integrated circuit (2000) includes an optical splitter (2004).

[0132] As illustrated, the waveguide layer comprises an input waveguide (2006) comprising a waveguide core (2009) defined by light determined and defined by a pair of optical confinement regions (2008a, 2008b). The input waveguide (2006) may be configured identically to the output waveguide (1908) of FIG. 19a, for example, the refractive index adjustment region (2010) is configured identically to the refractive index adjustment region (1914) to reduce the width of each of the optical confinement regions (2008a, 2008b) within the refractive index adjustment region (2010) as it approaches the junction with the slab waveguide (2012).

[0133] The slab waveguide (2012) serves as a free propagation region to optically couple the input waveguide (2006) to a plurality of output waveguides. Light introduced from the input waveguide (2006) into the slab waveguide (2012) will traverse the free propagation region and split the light among the plurality of output waveguides. Although the boundary of the slab waveguide (2012) is shown as a dashed line in FIG. 20a, it will be understood that the actual boundary of the slab waveguide (2012) can be located at any part of the waveguide layer (2002) that does not affect the operation of the optical splitter.

[0134] To define a plurality of output waveguides, the optical splitter (2004) includes a plurality of optical confinement regions (2016a to 2016f) and a plurality of waveguide cores (2014a to 2014e). Each output waveguide is defined as one of the plurality of waveguide cores (2014a to 2014e) and a corresponding pair of optical confinement regions among the plurality of optical confinement regions (2016a to 2016f). For example, a first waveguide core (2014a) may be bounded and defined by a first optical confinement region (2016a) and a second optical confinement region (2016b) to form a first output waveguide, while a second waveguide core (2014b) may be bounded and defined by a second optical confinement region (2016b) and a third optical confinement region (2016c) to form a second output waveguide. Although the optical splitter (2004) is illustrated in FIG. 20a as having five output waveguides (i.e., one for each of the plurality of waveguide cores (2014a to 2014e)), it will be understood that the optical splitter (2004) may include any number of output waveguides as desired. Similarly, although these waveguide cores (2014a to 2014e) are illustrated in FIG. 20a as having the same thickness, it will be understood that different output waveguides may have waveguide cores having different widths. The optical splitters described herein may be configured to split light received from an input waveguide between a plurality of output waveguides evenly or unevenly as desired.

[0135] The refractive index adjustment region (2010) may be narrow enough to improve the uniformity of the diffraction angle (as a function of wavelength) as light enters the slab waveguide (2012), but may still allow for the reduction of back reflection at the junction between the input waveguide (2006) and the slab waveguide (2012). Overall, the optical splitter (2004) may have improved splitting performance over a range of wavelengths.

[0136] FIG. 20b illustrates one such variation of an example of a photonic integrated circuit (2020) as described herein. Although only the waveguide layer (2022) of the photonic integrated circuit (2020) is illustrated in FIG. 20b, the photonic integrated circuit (2020) may also include a substrate, a lower cladding layer, and optionally an upper cladding layer as previously discussed. The photonic integrated circuit (2020) includes an optical splitter (2024) designed to split light introduced into a slab waveguide (2032) by an input waveguide (2026) among a plurality of output waveguides. As illustrated, the input waveguide (2026) includes a waveguide core (2009) defined and bounded by first and second light confinement regions (2028a, 2028b). The waveguide layer (2022) includes a plurality of waveguide cores (2034a to 2034e) defining a plurality of output waveguides and a plurality of optical confinement regions (2036a to 2036f). These components may be configured in the same manner as described herein for the optical splitter (2004) of FIG. 20a, except that the output waveguide (2026) has different refractive index adjustment regions (2030). These refractive index adjustment regions (2030) may be configured in the same manner as the refractive index adjustment region (1934) described herein for FIG. 19b. Specifically, the widths of the optical confinement regions (2028a, 2028b) are stepped. In particular, the width of each of the optical confinement regions (2028a, 2028b) changes from a first width to a narrower second width within the refractive index adjustment region (2030) (i.e., before the input waveguide (2026) ends at the junction with the slab waveguide (2032).

[0137] In other variations, the waveguide may be configured such that the width of the waveguide core increases as the waveguide core approaches the junction with the slab waveguide. For example, FIG. 21a illustrates an example of a photonic integrated circuit (2100) as described herein. Although only the waveguide layer (2102) of the photonic integrated circuit (2100) is shown in FIG. 21a, the photonic integrated circuit (2100) may also include a substrate, a lower cladding layer, and optionally an upper cladding layer as previously discussed.

[0138] The photonic integrated circuit (2100) includes a side surface (2104), which serves as an output cross-section from which light can be emitted from the photonic integrated circuit (2100). In the variant shown in FIG. 21a, the side surface (2104) defines an optical element (2106) (which may be composed of any of the optical elements described previously). The photonic integrated circuit (2100) further includes an output waveguide (2108) and a slab waveguide (2114) defined in the waveguide layer (2102). Specifically, the output waveguide (2108) includes a waveguide core (2112) bounded and defined by a pair of optical confinement regions (2110a, 2110b). A pair of optical confinement regions includes a first optical confinement region (2110a) and a second optical confinement region (2110b), each of which is filled with cladding material or air and can provide optical confinement to the waveguide core (2112) as previously discussed. The output waveguide (2108) enters the slab waveguide (2114) and terminates at the junction between the output waveguide (2108) and the slab waveguide (2114). Thus, input light (not shown) can be transmitted from the waveguide core (2112) to the slab waveguide (2114) and can exit the photonic integrated circuit (2100) through the side surface (2104) as previously described.

[0139] The output waveguide (2108) includes a refractive index adjustment region (2116) configured to change the effective refractive index experienced by light passing through the output waveguide (2108) as light approaches the junction with the slab waveguide (2114). The refractive index adjustment region (2116) is positioned at the junction between the output waveguide (2108) and the slab waveguide (2114) such that at the distal end, the refractive index adjustment region (2116) coincides with the junction between the output waveguide (2108) and the slab waveguide (2114). In the variation shown in FIG. 21a, the width of each of the light confinement regions (2110a, 2110b) narrows in the refractive index adjustment region (2116) as each of the light confinement regions (2110a, 2110b) approaches the junction with the slab waveguide (2114). The width of the waveguide core (2112) increases within the refractive index adjustment region (2116) as the width of the optical confinement regions (2110a, 2110b) decreases. While the optical confinement regions (1910a, 1910b) shown in FIG. 19a are tapered toward the waveguide core (1912) from the output waveguide (1908), the optical confinement regions (2110a, 2110b) shown in FIG. 21a are tapered away from the waveguide core (2112).

[0140] In the refractive index adjustment region (2116), the increasing width of the waveguide core (2112) provides a more gradual effective refractive index transition as light travels from the output waveguide (2108) to the slab waveguide (2114), thereby reducing back reflections of light at the junction between the output waveguide (2108) and the slab waveguide (2114). Additionally, the width of the waveguide core (2112) increases non-gradually within the refractive index adjustment region (2116). Consequently, the increase in width does not significantly alter the shape of the light mode passing through the refractive index adjustment region (2116) of the waveguide core (2112). Thus, the waveguide core (2112) can be sized to provide improved uniformity of diffraction angles over a target range of wavelengths, while reducing back reflections without the non-gradual increase in the width of the waveguide core (2112) as previously described having a significant effect on this uniformity.

[0141] Specifically, the output waveguide (2108) includes an additional region (2118) connected to the refractive index adjustment region (2116) so that the refractive index adjustment region (2116) is positioned between the additional region (2118) and the slab waveguide (2114). In some variations, the additional region (2118) has a constant width so that the width of the waveguide core (2112) becomes constant as it approaches the refractive index adjustment region (2116). In some of these variations, the output waveguide (2108) further includes a third region (not shown) in which the width of the waveguide core (2112) gradually narrows. In this way, the third region can gradually tape the waveguide core (2112) from an initial width to a first width that has narrowed. The width of the waveguide core (2112) within the additional region (2118) will have a first width and will increase non-gradually from the first width to a wider second width within the refractive index adjustment region (2116).

[0142] In other variations, the width of the waveguide core (2112) is gradually narrowed in an additional region (2118) so that the width of the waveguide core (2112) narrows as it reaches the refractive index adjustment region (2116). In these cases, the width of the waveguide core (2112) may be gradually tapered from an initial width to a narrower first width in the additional region (2118), and may increase non-gradually from the first width to a wider second width in the refractive index adjustment region (2116). It will be understood that the choice of the first width, the second width, as well as the length at which the waveguide core (2112) transitions between the first and second widths, can be chosen as desired to obtain a specific balance of diffraction angles, uniformity of diffraction angles as a function of wavelength, and the amount of back-reflected light at the junction between the output waveguide (2108) and the slab waveguide (2114).

[0143] In other variations, the waveguide core of the output waveguide may be increased without a corresponding reduction in the width of the optical-confined regions defining the output waveguide. For example, FIG. 21b illustrates one such variation of an example of a photonic integrated circuit (2120) as described herein. Although only the waveguide layer (2122) of the photonic integrated circuit (2120) is shown in FIG. 21b, the photonic integrated circuit (2120) may also include a substrate, a lower cladding layer, and optionally an upper cladding layer as previously discussed. The photonic integrated circuit (2120) includes an output waveguide (2128) comprising a waveguide core (2132) defined and bounded by first and second optical confinement regions (2130a, 2130b) and a slab waveguide (2134) having a side surface (2124) defining an optical element (2126). The output waveguide (2128) includes a refractive index adjustment region (2136) connected to an additional region (2138).

[0144] The photonic integrated circuit (2120) is configured differently from the photonic integrated circuit (2100) of FIG. 21a as described herein, except for the refractive index adjustment region (2136). The refractive index adjustment region (2136) is positioned at the junction between the output waveguide (2128) and the slab waveguide (2134) such that at the distal end, the refractive index adjustment region (2136) coincides with the junction between the output waveguide (2128) and the slab waveguide (2134). As illustrated, while the width of the waveguide core (2132) increases from a first width to a wider second width within the refractive index adjustment region (2136), the optical confinement regions (2130a, 2130b) maintain a constant width within the refractive index adjustment region (2136). Accordingly, the first and second light confinement regions (2130a, 2130b) are tilted away from each other within the refractive index adjustment region (2136).

[0145] The widths of the waveguide cores (2112, 2132) increase linearly within the refractive index adjustment regions (2116, 2136) of FIG. 21a and FIG. 21b, but in other cases, the width of the waveguide core may increase in a non-linear manner. FIG. 21c illustrates one such variation of an example of a photonic integrated circuit (2140) as described herein. Although only the waveguide layer (2142) of the photonic integrated circuit (2140) is shown in FIG. 21c, the photonic integrated circuit (2140) may also include a substrate, a lower cladding layer, and optionally an upper cladding layer as previously discussed. The photonic integrated circuit (2140) includes a slab waveguide (2154) having a side surface (2144) defining an optical element (2146) and an output waveguide (2148) comprising a waveguide core (2152) defined and bounded by first and second optical confinement regions (2150a, 2150b). The output waveguide (2148) includes a refractive index adjustment region (2156) connected to an additional region (2158).

[0146] The photonic integrated circuit (2140) is configured in a different manner as described herein with respect to FIG. 21a, except for the refractive index adjustment region (2156). The refractive index adjustment region (2156) is positioned at the junction between the output waveguide (2148) and the slab waveguide (2154) such that at the distal end, the refractive index adjustment region (2156) coincides with the junction between the output waveguide (2148) and the slab waveguide (2154). Within the refractive index adjustment region (2156), the width of the waveguide core (2152) is stepped. Specifically, the width of the waveguide core (2152) increases from a first width to a wider second width within the refractive index adjustment region (2156) (i.e., before the output waveguide (2148) ends at the junction with the slab waveguide (2154). In some of these variations, the width of the optical confinement regions (2150a, 2150b) may be reduced as the width of the waveguide core (2152) increases.

[0147] In cases where the output waveguide is configured to transmit multiple wavelengths over a target range of wavelengths, the length of the portion of the waveguide core (2152) having a wider second width may be selected to be 1 / 4 of one of the wavelengths within the target range of wavelengths (e.g., a center wavelength within the target range of wavelengths).

[0148] The output waveguides (2108, 2128, 2148) of FIGS. 21a through 21c may instead be used as input waveguides for an optical splitter as previously described. For example, FIG. 22a illustrates a variation of a photonic integrated circuit (2200) having a waveguide layer (2202) defining an optical splitter (2204). The optical splitter (2204) comprises a slab waveguide (2214), a plurality of waveguide cores (2216a through 2216e) forming a plurality of output waveguides, and optical confinement regions (2218a through 2218f). The photonic integrated circuit (2200) is configured in a different manner as described herein for the photonic integrated circuit (2000) of FIG. 20a, except for the input waveguide (2206). In this modified example, the input waveguide (2206) is configured in the same way as the output waveguide (2108) of FIG. 21a.

[0149] Specifically, the input waveguide (2206) includes a waveguide core (2212) bounded and defined by a pair of optical confinement regions (2208a, 2208b). The input waveguide (2206) includes a refractive index adjustment region (2210) and an additional region (2211) connected to the refractive index adjustment region (2210), as previously discussed. The width of each of the optical confinement regions (2108a, 2108b) narrows in the refractive index adjustment region (2210) as each of the optical confinement regions (2110a, 2110b) approaches the junction with the slab waveguide (2214). Similarly, the width of the waveguide core (2212) increases within the refractive index adjustment region (2210) as the width of the optical confinement regions (2210a, 2210b) decreases. The additional region (2211) can be configured in the same way as the additional region (2118) of FIG. 21a.

[0150] FIG. 22b illustrates another variation of a photonic integrated circuit (2220) having a waveguide layer (2222) defining an optical splitter (2224). The optical splitter (2224) includes a slab waveguide (2234), a plurality of waveguide cores (2236a to 2236e) forming a plurality of output waveguides, and optical confinement regions (2238a to 2238f). The optical splitter (2224) includes an input waveguide (2226) having a waveguide core (2232) defined and bounded by a pair of optical confinement regions (2228a, 2228b). The input waveguide (2226) includes an additional region (2231) connected to a refractive index switching region (2230) as previously described. The photonic integrated circuit (2220) is configured as described herein for the photonic integrated circuit (2200) of FIG. 22a, except for the refractive index switching region (2230). In this variation, the refractive index switching region (2230) is configured identically to the output waveguide (2128) of FIG. 21b. As illustrated, while the width of the waveguide core (2232) increases from a first width to a wider second width within the refractive index adjusting region (2230), the optical confinement regions (2228a, 2228b) maintain a constant width within the refractive index adjusting region (2230). Thus, the first and second optical confinement regions (2228a, 2228b) are tilted away from each other within the refractive index adjusting region (2230).

[0151] FIG. 22c illustrates another variation of a photonic integrated circuit (2240) having a waveguide layer (2242) defining an optical splitter (2244). The optical splitter (2244) includes a slab waveguide (2254), a plurality of waveguide cores (2256a to 2256e) forming a plurality of output waveguides, and optical confinement regions (2258a to 2258f). The optical splitter (2244) includes an input waveguide (2246) having a waveguide core (2252) defined and bounded by a pair of optical confinement regions (2248a, 2248b). The input waveguide (2246) includes an additional region (2251) connected to a refractive index switching region (2250) as previously described. The photonic integrated circuit (2240) is configured as described herein for the photonic integrated circuit (2200) of FIG. 22a, except for the refractive index switching region (2250). In this variation, the refractive index switching region (2250) is configured identically to the output waveguide (2148) of FIG. 21c. Specifically, the width of the waveguide core (2252) increases in a stepwise manner from a first width to a wider second width within the refractive index adjustment region (2250) as previously discussed.

[0152] For each of the embodiments described herein with respect to FIGS. 19a through 22c, it will be understood that various dimensions of the refractive index switching regions may be selected to achieve a desired balance of diffraction angles, uniformity of diffraction angles as a function of wavelength, and the amount of back-reflected light as described above. Additionally, it will be understood that the refractive index switching regions described herein with respect to FIGS. 19a through 22c may be applied to any of the embodiments described herein with respect to FIGS. 2 through 18d, as well as to any other optical components including switching between waveguides (e.g., strip waveguides, rib waveguides, etc.) and slab waveguides, e.g., optical multiplexers, optical demultiplexers, etc.

[0153] Although process steps or method steps may be described in a sequential order, such processes and methods may be configured to operate in any suitable order. In other words, any sequence or order of steps that may be described in this disclosure does not, in itself, imply a requirement that the steps be performed in that order. Furthermore, although some steps are described or implied to occur asynchronously (e.g., because one step is described after another), they may be performed concurrently. Also, illustrating a process by describing it in the drawings does not imply that the illustrated process excludes other variations and modifications thereof, does not imply that any of the illustrated process or its steps are required for one or more of the examples, and does not imply that the illustrated process is preferred.

[0154] 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.

[0155] 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.

[0156] Further description of the embodiments:

[0157] Example 1: As a photonic integrated circuit,

[0158] Substrate;

[0159] Cladding layer; and

[0160] It includes a waveguide layer, and the waveguide layer is:

[0161] Slab waveguide having side surfaces; and

[0162] It includes an output waveguide, and the output waveguide is:

[0163] First light restraint region;

[0164] 2nd optical confinement region; and

[0165] It includes a waveguide core positioned between a first optical confinement region and a second optical confinement region; wherein,

[0166] The side surface of the slab waveguide defines an optical element forming a cylindrical lens having a semicircular curved surface;

[0167] The output waveguide enters the slab waveguide at the junction between the output waveguide and the slab waveguide and terminates;

[0168] A photon integrated circuit in which an output waveguide is positioned so that input light incident from the output waveguide into the slab waveguide exits the photon integrated circuit through a side surface.

[0169] Example 2: In Example 1,

[0170] A semicircular surface has a center of curvature;

[0171] An output waveguide is a photonic integrated circuit that is laterally offset with respect to the center of curvature.

[0172] Example 3: In Example 2,

[0173] A photonic integrated circuit in which the junction between the output waveguide and the slab waveguide is aligned with the center of curvature.

[0174] Example 4: In Example 2,

[0175] A photonic integrated circuit in which the junction between the output waveguide and the slab waveguide is positioned behind the center of curvature so that the center of curvature is positioned between the junction and the optical element.

[0176] Example 5: In Example 2,

[0177] A photonic integrated circuit in which the junction between the output waveguide and the slab waveguide is positioned in front of the center of the curvature so that the junction is positioned between the junction and the optical element.

[0178] Example 6: In any one of Examples 1 to 5,

[0179] A photonic integrated circuit comprising a waveguide layer that includes a partially etched region between the side surfaces of the output waveguide and the slab waveguide so that input light incident from the output waveguide into the slab waveguide passes through the partially etched region.

[0180] Example 7. In any one of Examples 1 to 6, the output waveguide comprises a photonic integrated circuit including a refractive index adjustment region positioned at a junction where the widths of one or both of a first optical confinement region and a second optical confinement region decrease in a direction toward the junction.

[0181] Example 8. In any one of Examples 1 to 7, the output waveguide comprises a photonic integrated circuit including a refractive index adjustment region positioned at a junction where the width of the waveguide core increases in the direction toward the junction.

[0182] Example 9: As a photonic integrated circuit,

[0183] It includes a waveguide layer, and the waveguide layer is:

[0184] Side surface defining multiple optical elements;

[0185] Multiple slab waveguides, and

[0186] It includes a plurality of output waveguides, and each of the plurality of output waveguides is:

[0187] First light restraint region;

[0188] 2nd optical confinement region; and

[0189] It includes a waveguide core positioned between a first optical confinement region and a second optical confinement region; wherein,

[0190] A photonic integrated circuit, wherein each optical element of a plurality of optical elements is associated with a corresponding slab waveguide among a plurality of slab waveguides and a corresponding output waveguide among a plurality of output waveguides, so that input light incident from a corresponding output waveguide into a corresponding slab waveguide exits the photonic integrated circuit through the optical element.

[0191] Example 10: In Example 9,

[0192] Each optical element is a photonic integrated circuit forming an on-chip lens.

[0193] Example 11: In Example 10,

[0194] A photon integrated circuit in which each optical element of a plurality of optical elements forms a cylindrical lens having a semicircular curved surface having a center of curvature.

[0195] Example 12: In Example 11,

[0196] A photonic integrated circuit in which each of the multiple output waveguides is laterally offset from the center of the curvature of the optical element associated with the output waveguide.

[0197] Example 13: In any one of Examples 10 to 12,

[0198] A photonic integrated circuit in which all multiple slab waveguides are optically connected.

[0199] Example 14: As an optical system:

[0200] Light source unit;

[0201] Photonic Integrated Circuit - Photonic Integrated Circuit is:

[0202] Side surface; and

[0203] Multiple emitters optically connected to the light source unit - each emitter is:

[0204] Optical element formed on the side surface;

[0205] Slab waveguide; and

[0206] Includes an output waveguide positioned so that input light incident from the output waveguide into the slab waveguide exits the photonic integrated circuit through an optical element - including -; and

[0207] An optical system comprising a controller configured to control a plurality of emitters to emit output light.

[0208] Example 15: In Example 14,

[0209] An optical system in which each of the multiple emitters has a common configuration in which each emitter generates an output beam of light having the same shape and direction.

[0210] Example 16: In Example 14 or Example 15, the photonic integrated circuit is:

[0211] An optical system comprising a plurality of phase shifters, each of which is controllable to adjust the phase of light transmitted by the output waveguide of a corresponding emitter.

[0212] Example 17: An optical system in Example 16, wherein the controller is configured to selectively control the phase of the output light emitted by each of the plurality of emitters.

[0213] Example 18: An optical system in any one of Examples 14 to 17, wherein the controller is configured to selectively control which of the plurality of emitters emits output light.

[0214] Example 19: An optical system in any one of Examples 14 to 18, wherein the controller is configured to selectively control the intensity of output light emitted by each of a plurality of emitters.

[0215] Example 20: An optical system in any one of Examples 14 to 19, wherein the controller is configured to selectively control the wavelength or wavelengths of output light emitted by each of a plurality of emitters.

[0216] Example 21: As a photonic integrated circuit,

[0217] Substrate;

[0218] Cladding layer; and

[0219] It includes a waveguide layer, and the waveguide layer is:

[0220] Slab waveguide; and

[0221] It includes a waveguide, and the waveguide is:

[0222] First light restraint region;

[0223] 2nd optical confinement region; and

[0224] It includes a waveguide core positioned between a first optical confinement region and a second optical confinement region; wherein,

[0225] The waveguide enters the slab waveguide at the junction between the waveguide and the slab waveguide and terminates;

[0226] A photon integrated circuit comprising a waveguide including a refractive index adjustment region located at a junction where the widths of one or both of a first optical confinement region and a second optical confinement region decrease in a direction toward the junction.

[0227] Example 22: In Example 21, the waveguide layer is:

[0228] It includes an optical splitter, and the optical splitter is:

[0229] Slab waveguide;

[0230] Waveguide; and

[0231] It includes a plurality of output waveguides, and

[0232] An optical splitter is a photonic integrated circuit configured such that input light incident from a waveguide into a slab waveguide is split among a plurality of output waveguides.

[0233] Example 23: In Example 21,

[0234] The waveguide layer includes a side surface defining an optical element;

[0235] A photon integrated circuit in which an input light incident from a waveguide into a slab waveguide is positioned to exit the photon integrated circuit through a side surface.

[0236] Example 24: In Example 23,

[0237] An optical element is a photonic integrated circuit that forms an on-chip lens.

[0238] Example 25: In Example 23 or Example 24,

[0239] An optical element is a photon integrated circuit containing a diffraction grating.

[0240] Example 26: In any one of Examples 21 to 25,

[0241] A photon integrated circuit in which the width of the waveguide core is constant in the refractive index adjustment region.

[0242] Example 27: In any one of Examples 21 to 25,

[0243] A photon integrated circuit in which the width of the waveguide core gradually narrows in the direction toward the junction in the refractive index adjustment region.

[0244] Example 28: In any one of Examples 21 to 25,

[0245] A photon integrated circuit in which the width of the waveguide core increases non-gradually in the refractive index adjustment region in the direction toward the junction.

[0246] Example 29: In any one of Examples 21 to 28,

[0247] A photonic integrated circuit in which the widths of one or both of the first optical confinement region and the second optical confinement region decrease linearly in the direction toward the junction.

[0248] Example 30: As a photonic integrated circuit,

[0249] Substrate;

[0250] Cladding layer; and

[0251] It includes a waveguide layer, and the waveguide layer is:

[0252] Slab waveguide; and

[0253] It includes a waveguide, and the waveguide is:

[0254] First light restraint region;

[0255] 2nd optical confinement region; and

[0256] It includes a waveguide core positioned between a first optical confinement region and a second optical confinement region; wherein,

[0257] The waveguide enters the slab waveguide at the junction between the waveguide and the slab waveguide and terminates;

[0258] A photon integrated circuit comprising a waveguide including a refractive index adjustment region located at a junction where the width of the waveguide core increases in the direction toward the junction.

[0259] Example 31: In Example 30, the waveguide layer is:

[0260] It includes an optical splitter, and the optical splitter is:

[0261] Slab waveguide;

[0262] Waveguide; and

[0263] It includes a plurality of output waveguides, and

[0264] An optical splitter is a photonic integrated circuit configured such that input light incident from a waveguide into a slab waveguide is split among a plurality of output waveguides.

[0265] Example 32: In Example 30,

[0266] The waveguide layer includes a side surface defining an optical element;

[0267] A photon integrated circuit in which an input light incident from a waveguide into a slab waveguide is positioned to exit the photon integrated circuit through a side surface.

[0268] Example 33: In Example 32,

[0269] An optical element is a photonic integrated circuit that forms an on-chip lens.

[0270] Example 34: In any one of Examples 30 to 33,

[0271] A photon integrated circuit in which the width of the waveguide core increases non-gradually in the refractive index adjustment region.

[0272] Example 35: In any one of Examples 30 to 34,

[0273] A photon integrated circuit in which the widths of the first optical confinement region and the second optical confinement region are constant in the refractive index adjustment region.

[0274] Example 36: In any one of Examples 30 to 35,

[0275] The waveguide includes an additional region in which the width of the waveguide core gradually narrows toward the junction;

[0276] A photon integrated circuit in which a refractive index adjustment region is positioned between an additional region and a junction.

[0277] Example 37: In any one of Examples 30 to 36, a photonic integrated circuit in which the width of the waveguide core increases linearly in the refractive index adjustment region.

[0278] Example 38: As an optical system,

[0279] A light source unit configured to generate a set of wavelengths within a target wavelength range; and

[0280] It includes a photonic integrated circuit, and the photonic integrated circuit is:

[0281] Substrate;

[0282] Cladding layer; and

[0283] It includes a waveguide layer, and the waveguide layer is:

[0284] Slab waveguide; and

[0285] It includes a waveguide, and the waveguide is:

[0286] First light restraint region;

[0287] 2nd optical confinement region; and

[0288] It includes a waveguide core positioned between a first optical confinement region and a second optical confinement region; wherein,

[0289] The waveguide enters the slab waveguide at the junction between the waveguide and the slab waveguide and terminates;

[0290] An optical system comprising a waveguide having a positioned refractive index adjustment region in which the respective widths of a first optical confinement region and a second optical confinement region narrow from a first width to a second width in a direction toward a junction.

[0291] Example 39: In Example 38,

[0292] Each part of the first optical confinement region and the second optical confinement region having a second width has a predetermined length;

[0293] An optical system whose length is 1 / 4 of the wavelength within the target range.

[0294] Example 40: In Example 38 or Example 39,

[0295] An optical system in which the width of the waveguide core increases from the third width to the fourth width in the refractive index adjustment region.

Claims

Claim 1 As an optical system, a slab waveguide—the slab waveguide comprises: a free propagation region; and an output side—; and an output waveguide defined in the slab waveguide, wherein the output waveguide comprises: a waveguide core having a first side and a second side opposite the first side through which light propagates; and a first light confinement region adjacent to the first side of the waveguide core. An optical system comprising a second optical confinement region adjacent to the second side of the waveguide core, wherein the output waveguide terminates before the output side of the slab waveguide and at a junction between the output waveguide and the free propagation region; the light exits the waveguide core and enters the free propagation region; the light exits the free propagation region at the output side, thereby reducing back reflections into the output waveguide; and the output waveguide comprises a positioned refractive index adjustment region in which the widths of the first optical confinement region and the second optical confinement region, respectively, narrow from a first width to a second width in a direction toward the junction. Claim 2 An optical system according to claim 1, wherein the output side of the slab waveguide comprises an optical element through which light passes; said optical element is defined on the output side of the slab waveguide; and said optical element functions as a positive or negative lens. Claim 3 An optical system according to claim 1, wherein the output side of the slab waveguide includes an optical element for collimating the light. Claim 4 An optical system according to claim 1, wherein the output side of the slab waveguide comprises an optical element; and the optical system further comprises an anti-reflective coating on the optical element. Claim 5 An optical system according to any one of claims 1 to 4, wherein the output side of the slab waveguide comprises an aspherical optical element. Claim 6 An optical system according to any one of claims 1 to 4, wherein the output side of the slab waveguide comprises a diffraction grating. Claim 7 An optical system according to any one of claims 1 to 4, further comprising a metal positioned on the slab waveguide between the output waveguide and the output side of the slab waveguide, which polarizes the light propagating through the slab waveguide. Claim 8 An optical system according to any one of claims 1 to 4, wherein the output waveguide is one of a plurality of output waveguides for emitting light into the slab waveguide; and the optical system further comprises an optical element defined in the profile of the output side of the slab waveguide and configured to combine the light from the plurality of output waveguides. Claim 9 A method for guiding light comprises the steps of: propagating the light through an output waveguide; emitting the light from the output waveguide into a free propagation region of a slab waveguide; and passing the light from the slab waveguide through an optical element located at the output side of the slab waveguide, thereby reducing back reflection of the light from the output side of the slab waveguide, wherein the output waveguide is defined in the slab waveguide, and the output waveguide comprises: a waveguide core having a first side and a second side opposite the first side through which the light propagates; and a first light confinement region adjacent to the first side of the waveguide core. A method comprising a second optical confinement region adjacent to the second side of the waveguide core, wherein the output waveguide terminates at a junction between the output waveguide and the free propagation region; and wherein the output waveguide comprises a positioned refractive index adjustment region in which the respective widths of the first optical confinement region and the second optical confinement region narrow from a first width to a second width in a direction toward the junction. Claim 10 In claim 9, the step of emitting light from the output waveguide comprises the step of propagating the light from the output waveguide through the free propagation region of the slab waveguide. Claim 11 A method according to claim 9 or 10, further comprising the step of forming a partially etched region between the output waveguide and the output side of the slab waveguide so that the light emitted from the output waveguide passes through the partially etched region. Claim 12 In claim 11, the method wherein the partially etched area functions as a defining lens. Claim 13 In claim 11, the output side of the slab waveguide comprises the optical element. Claim 14 As an optical system, a slab waveguide; an output waveguide defined in the slab waveguide, wherein the output waveguide comprises: a waveguide core that allows light to pass through; a first light confinement region adjacent to a first side of the waveguide core; and a second light confinement region adjacent to a second side of the waveguide core, wherein the second side is opposite to the first side of the waveguide core. An optical system comprising an optical element defined on the output side of the slab waveguide, wherein the output waveguide terminates before the output side of the slab waveguide and at a junction between the output waveguide and the slab waveguide so that the light emitted from the waveguide core of the output waveguide propagates through the slab waveguide before passing through the optical element, thereby reducing the back reflection of the light from the optical element into the output waveguide, and wherein the output waveguide comprises a positioned refractive index adjustment region in which the widths of the first optical confinement region and the second optical confinement region respectively narrow from the first width to the second width in a direction toward the junction. Claim 15 In claim 14, the optical element is part of the slab waveguide and includes a positive or negative radius of curvature for steering the direction of light exiting with respect to the optical axis; the optical system further includes an anti-reflective coating coated on the optical element to reduce the back reflection of the light passing through the optical element. Claim 16 An optical system according to claim 14 or 15, wherein the output waveguide is at a predetermined angle with respect to the output side of the slab waveguide. Claim 17 An optical system according to claim 14 or 15, wherein the optical element causes the light passing through it to emit. Claim 18 An optical system according to claim 14 or 15, further comprising a planar metal layer adjacent to the slab waveguide, wherein the planar metal layer extends across the optical element; and wherein the planar metal layer is located in the region between the output waveguide and the output side of the slab waveguide. Claim 19 An optical system according to claim 14 or 15, wherein the output waveguide is positioned vertically on the output side of the slab waveguide. Claim 20 An optical system according to claim 14 or 15, wherein the width of the waveguide core increases non-adiabatically in the direction toward the slab waveguide in the refractive index adjustment region.

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