CN118020004A

CN118020004A - Light output device and light output method for optical system

Info

Publication number: CN118020004A
Application number: CN202280064241.5A
Authority: CN
Inventors: 涂湧铭; J·D·维特米尔; 邓辉阳; M·A·阿博尔; M·卡曼达德茨弗里; A·比斯穆托; P·马库夫
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2021-09-23
Filing date: 2022-09-22
Publication date: 2024-05-10
Also published as: US20240094466A1

Abstract

Configurations of optical systems for guiding light and reducing back reflection in an output waveguide are disclosed. The optical system may include an output waveguide defined in a slab waveguide. The output waveguide may terminate before the output side of the slab waveguide, which may reduce back reflection of light from the output side back into the output waveguide. The output side may define an optical element that may direct the output light. The optical element may collimate the output light, concentrate the output light, or diverge the output light.

Description

Light output device and light output method for optical system

Cross Reference to Related Applications

The patent cooperation treaty patent application claims priority from U.S. patent application Ser. No. 17/949,066, filed on day 20 at 9 of 2022, U.S. patent application Ser. No. 17/949,079, filed on day 20 at 9 of 2022, U.S. patent application Ser. No. 17/949,096, filed on day 20 at 9 of 2021, and U.S. provisional patent application Ser. No. 63/247,526, filed on day 23 of 2021, the contents of which are incorporated herein by reference as if fully set forth herein.

Technical Field

The present disclosure relates generally to transmitting and outputting light in photonic integrated circuits. More particularly, embodiments herein relate to an optical system having an on-chip lens for outputting light from a waveguide.

Background

Generally, photonic integrated circuits include an optical system having a light source. In some optical systems, light emitted by a light source is output from the optical system via an output facet. These output facets may be cleaved and polished to improve the efficiency of the output light from the optical system. Although most of the light will be output, a portion of the light may be reflected back from the output facet and into the optical system instead of exiting the optical system. The back reflected light may propagate back to the output waveguide and/or the light source, which typically creates a pseudo-etalon and affects the stability of the light source.

Disclosure of Invention

Embodiments of the systems, devices, methods, and apparatuses described in this disclosure relate to photonic integrated circuits including light output devices with on-chip lenses. Systems, devices, methods, and apparatus are also described that relate to optical systems having in-plane lenses that reduce back reflected light that may couple back into an output waveguide. The optical system may include an output waveguide positioned away from the output side of the slab waveguide and transmitting light such that the light may propagate through the slab waveguide before passing through the output side of the slab waveguide. The output side of the slab waveguide forms or otherwise includes a lens that can change the direction of light propagation relative to the optical axis. Since the in-plane lens is in the plane of the slab waveguide, back reflection into the output waveguide is reduced.

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 further include an output waveguide defined in the slab waveguide, the output waveguide including: a propagation region through which light propagates, and the output waveguide includes a first side and a second side opposite the first side; a first light confinement region adjacent the first side of the propagation region; and a second light confinement region adjacent 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, the light may exit the propagation region into the free propagation region, and the light may exit the free propagation region at the output side, thereby reducing back reflection into the output waveguide.

In another embodiment, the present disclosure describes a method for directing light. The method may include: propagating the light through an output waveguide; transmitting the light from the output waveguide into a free propagation region of the slab waveguide; and passing the light from the slab waveguide through an optical element located in the output side of the slab waveguide, thereby reducing back reflection of the light from the output side of the slab waveguide.

In another embodiment, the present disclosure describes an optical system. The optical system may include a slab waveguide and an output waveguide defined in the slab waveguide. The output waveguide may include: a propagation region that allows light to pass therethrough; a first light confinement region adjacent to a first side of the propagation region; and a second light confinement region adjacent a second side of the propagation region, the second side being opposite the first side of the propagation region. The optical system may further include an optical element defined in an output side of the slab waveguide, wherein the output waveguide terminates before the output side of the slab waveguide such that the 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 the light out of the optical element and into the output waveguide.

Still other embodiments relate to a photonic integrated circuit that includes a substrate, a cladding layer, and a waveguide layer. The waveguide layer includes a slab waveguide having side surfaces and an output waveguide including a first light confinement region, a second light confinement region, and a waveguide core between the first light confinement region and the second light confinement region. The side surface of the slab waveguide defines an optical element forming a cylindrical lens having a semicircular curve, the output waveguide terminating in the slab waveguide at a junction between the output waveguide and the slab waveguide, and the output waveguide being positioned such that input light introduced from the output waveguide into the slab waveguide exits the photonic integrated circuit through the side surface.

In some of these variations, the semicircular curve has a center of curvature and the output waveguide is laterally offset relative to the center of curvature. In some of these variations, the junction between the output waveguide and the slab waveguide may be aligned with the center of curvature. In other variations, the junction between the output waveguide and the slab waveguide is located behind the center of curvature such that the center of curvature is located between the junction and the optical element. In still other variations, the junction between the output waveguide and the slab waveguide is located forward of the center of curvature such that the junction is located between the junction and the optical element.

In other of these variations, the waveguide layer includes a partially etched region located at the side surfaces of the output waveguide and the slab waveguide such that the input light introduced into the slab waveguide from the output waveguide passes through the partially etched region. Additionally or alternatively, the output waveguide includes a refractive index adjustment region at the junction in which a width of one or both of the first and second light confinement regions decreases in a direction toward the junction. In other variations, the output waveguide includes a refractive index adjustment region at the junction, in which the width of the waveguide core increases in a direction toward the junction.

Still other embodiments relate to a photonic integrated circuit including a waveguide layer including: a side surface defining a plurality of optical elements; a plurality of slab waveguides; a plurality of output waveguides. Each output waveguide of the plurality of output waveguides includes a first light confining region, a second light confining region, and a waveguide core between the first light confining region and the second light confining region. Each optical element of the plurality of optical elements is associated with a corresponding slab waveguide of the plurality of slab waveguides and a corresponding output waveguide of the plurality of output waveguides such that input light introduced into the corresponding slab waveguide from the corresponding output waveguide exits the photonic integrated circuit through the optical element.

In some of these variations, each optical element forms an on-chip lens. Each of the plurality of optical elements may form a cylindrical lens having a semicircular curve 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.

Other embodiments described herein relate to an optical system including a light source unit, a photonic integrated circuit, and a controller. The photonic integrated circuit includes a side surface and a plurality of emitters optically connected to the light source unit. Each transmitter includes: an optical element formed in the side surface; a slab waveguide; and an output waveguide positioned such that input light introduced into the slab waveguide from the output waveguide exits the photonic integrated circuit through the optical element. The controller is configured to control the plurality of emitters to emit output light.

In some of these variations, the plurality of emitters have the same configuration such that each emitter generates an output beam having the same shape and direction. Additionally or alternatively, the photonic integrated circuit includes a plurality of phase shifters, wherein each phase shifter of the plurality of phase shifters is controllable to adjust a phase of light carried by an output waveguide of a corresponding emitter. In some of these variations, the controller is configured to selectively control a phase of the output light emitted by each of the plurality of emitters. Additionally or alternatively, the controller is configured to selectively control which of the plurality of 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 plurality of emitters. Additionally or alternatively, the controller is configured to selectively control one or more wavelengths of the output light emitted by each of the plurality of emitters.

Other embodiments described herein relate to a photonic integrated circuit having a substrate, a cladding layer, and a waveguide layer. The waveguide layer includes a slab waveguide and a waveguide, wherein the waveguide includes: a first light confining region, a second light confining region, and a waveguide core between the first light confining region and the second light confining region. The waveguide terminates in the slab waveguide at a junction between the waveguide and the slab waveguide, and the waveguide includes a refractive index adjustment region at the junction in which a width of one or both of the first light confinement region and the second light confinement region decreases in a direction toward the junction.

In some of these variations, the waveguide layer includes a beam splitter, wherein the beam splitter includes the slab waveguide, the waveguide, and a plurality of output waveguides. The optical splitter is configured such that input light introduced from the waveguide into the slab waveguide is split between the plurality of output waveguides. In other variations, the waveguide layer includes a side surface defining an optical element, and the waveguide is positioned such that input light introduced 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 comprises a diffraction grating.

In other variations, the width of the waveguide core is constant in the index adjustment region. In still other variations, the width of the waveguide core is adiabatically narrowed in the direction toward the junction in the refractive index adjustment region. In yet other variations, the width of the waveguide core increases non-adiabatically in the refractive index adjustment region in a direction toward the junction. Additionally or alternatively, the width of one or both of the first light confinement region and the second light confinement region decreases linearly in a direction toward the junction.

Still other embodiments relate to a photonic integrated circuit that includes a substrate, a cladding layer, and a waveguide layer, wherein the waveguide layer includes a slab waveguide and a waveguide. The waveguide includes a first light confining region, a second light confining region, and a waveguide core between the first light confining region and the second light confining region. The waveguide terminates in the slab waveguide at a junction between the waveguide and the slab waveguide, and the waveguide includes a refractive index adjustment region at the junction in which a width of the waveguide core increases in a direction toward the junction. In some of these variations, the waveguide layer includes a beam splitter, wherein the beam splitter includes the slab waveguide, the waveguide, and a plurality of output waveguides. The optical splitter is configured such that input light introduced from the waveguide into the slab waveguide is split between the plurality of output waveguides. In other variations, the waveguide layer includes a side surface defining an optical element, and the waveguide is positioned such that input light introduced 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.

Additionally or alternatively, the width of the waveguide core increases non-adiabatically in the index adjustment region. Additionally or alternatively, the widths of the first and second light confinement regions 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 is adiabatically narrowed in a direction toward the junction such that the index adjustment region is located between the additional region and the junction. Additionally or alternatively, the width of the waveguide core increases linearly in the index adjustment region.

Still 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 includes a substrate, a cladding layer, and a waveguide layer, wherein the waveguide layer includes a slab waveguide and a waveguide. The waveguide includes a first light confining region, a second light confining region, and a waveguide core between the first light confining region and the second light confining region. The waveguide terminates in the slab waveguide at a junction between the waveguide and the slab waveguide, and the waveguide includes a refractive index adjustment region positioned wherein a width of each of the first light confinement region and the second light confinement region narrows from a first width to a second width in a direction toward the junction.

In some of these variations, the portion of each of the first light confinement region and the second light confinement region having the second width has a length such that the length is one quarter of a 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 index adjustment region.

In addition to the exemplary aspects and embodiments described herein, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions.

Drawings

Fig. 1 shows a top view of a generic optical system comprising a waveguide outputting light.

Fig. 2 shows a top view of an example of an optical system including a waveguide that terminates before the output side of the optical system.

Fig. 3 shows a top view of an example of an optical system that mitigates back reflection of light.

Fig. 4 shows a top view of an example of an optical system with an optical element collimating output light.

Fig. 5 shows a top view of an example of an optical system having optical elements that direct output light to converge.

Fig. 6 shows a top view of an example of an optical system with optical elements that direct output light to diverge.

Fig. 7 shows a top view of an example of an optical system with waveguides angled with respect to the output side.

Fig. 8 shows a top view of an example of an optical system with an angled output side.

Fig. 9 shows a top view of an example of an optical system having multiple waveguides.

Fig. 10 shows a top view of an example of an optical system having an aspherical lens.

Fig. 11 shows a top view of an example of an optical system with a partially etched region between the waveguide and the output side.

Fig. 12 shows a top view of an example of an optical system with a partially etched region between the waveguide and the optical element.

Fig. 13 shows a top view of an example of an optical system with a diffraction grating located on the output side of a slab waveguide.

Fig. 14 shows a top view of an example of an optical system with metal on a slab waveguide.

Fig. 15 shows a top view of an example of an optical system with optical elements located in the angled output side.

Fig. 16A and 16B show perspective and top views, respectively, of a photonic integrated circuit having an output side surface on the outside of the photonic integrated circuit. Fig. 16C shows a top view of another variation of a photonic integrated circuit having an output side surface on the inside of the photonic integrated circuit.

Fig. 17A and 17B show top views of variants of photonic integrated circuits with optical elements configured as cylindrical lenses.

Fig. 18A to 18C show top views of variants of photonic integrated circuits having a plurality of optical elements. Fig. 18D shows a top view of a variation of an optical system including a photonic integrated circuit having a plurality of optical elements.

Fig. 19A and 19B show top views of variants of photonic integrated circuits having output waveguides that include index adjustment regions.

Fig. 20A and 20B illustrate top views of variations of photonic integrated circuits having optical splitters as described herein.

Fig. 21A-21C show top views of variations of photonic integrated circuits having output waveguides that include index adjustment regions.

Fig. 22A-22C illustrate top views of variations of photonic integrated circuits having optical splitters as described herein.

The use of cross-hatching or shading in the drawings is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the drawings. Thus, the presence or absence of a non-cross-hatching or shading does not indicate or indicate any preference or requirement for a particular material, material property, proportion of an element, dimension of an element, commonality of similar illustrated elements, or any other feature, attribute, or characteristic of any element shown in the drawings.

It should be understood that the proportions and sizes (relative or absolute) of the various features and elements (and sets and groupings thereof) and the boundaries, spacings, and positional relationships presented therebetween are provided in the drawings, merely to facilitate understanding of the various embodiments described herein, and thus may be unnecessarily presented or shown to scale and not intended to indicate any preference or requirement of the illustrated embodiments to exclude embodiments described in connection therewith.

As used throughout this specification, a reference numeral without an alpha character following the reference numeral may refer to one or more of a corresponding reference, a group of all references, or some of the references. For example, "107" may refer to any light 107 (e.g., light 107a or light 107b, etc.), or may refer to all light 107, depending on the context in which the light is used. The term light 107 may be used when discussing light emanating from a waveguide or light exiting an optical system or photonic integrated circuit.

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

Detailed Description

Reference will now be made in detail to the exemplary embodiments illustrated in the drawings. It should be understood that the following description is not intended to limit the disclosure to any preferred embodiment. On the contrary, it is intended to cover alternatives, modifications and equivalents as may be included within the spirit and scope of the embodiments as defined by the appended claims.

Photonic integrated circuits having optical components designed to reduce back reflection during operation of the optical components and associated optical systems and methods are described herein. In some embodiments, the photonic integrated circuit includes facets designed to emit light received from the output waveguide while reducing back reflection back into the output waveguide. Additionally or alternatively, the photonic integrated circuit includes a junction between the output waveguide and the slab waveguide, the junction configured to reduce back reflection at the junction.

The optical systems described herein may include one or more photonic integrated circuits that transmit light using one or more waveguides. In photonic integrated circuits, the waveguide is typically supported on a planar substrate and constrains the 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 a horizontal plane (e.g., through a top or bottom surface of the photonic integrated circuit) using a vertical output coupler, or may exit horizontally along a lateral side surface of the photonic integrated circuit.

Typically, where light is emitted horizontally from a lateral side surface of the photonic integrated circuit, the waveguide terminates at the lateral side surface such that light exits the photonic integrated circuit directly from a facet of the waveguide. That is, the waveguide terminates at a side surface of the photonic integrated circuit such that light from the waveguide passes directly out of the optical system from the waveguide. When light passes through the interface between the waveguide and another material (e.g., air surrounding the photonic integrated circuit, another optical component placed in contact with the photonic integrated circuit), a portion of the light may undesirably reflect back into the waveguide from one side of the photonic integrated circuit. The back-reflected light may produce an etalon and negatively impact the stability of the light source used to generate the illumination in the photonic integrated circuit. While solutions such as anti-reflective coatings may mitigate some of the back reflections of light, they may not completely eliminate these back reflections. Accordingly, in many cases, it is desirable to configure the emission surface of the photonic integrated circuit to minimize the amount of light back reflected into the waveguide.

Additionally, in some cases, it may be desirable to shape the light emitted from the photonic integrated circuit such that the light forms one or more light beams having a particular shape, divergence, or the like. While the optical system may incorporate one or more free-space lenses to aid, adding free-space lenses may increase the cost, design complexity, and overall size of the optical system. Accordingly, it may be desirable to reduce the number of free space lenses used in a given optical system.

The photonic integrated circuits described herein and optical systems incorporating these photonic integrated circuits receive and transmit light from one or more light sources (e.g., light sources of a light source unit as described in more detail herein). The light source generates light that is received by the one or more waveguides directly or indirectly via one or more intermediate components (e.g., multiplexers, demultiplexers, optical splitters, switches, optical couplers, phase shifters, combinations thereof, etc.). Waveguides are used to transmit light in photonic integrated circuits and, for some waveguides, to emit light from photonic integrated circuits.

Some embodiments described herein are directed to output facets of a photonic integrated circuit that allow light from a waveguide ("output waveguide") (such as a strip waveguide, rib waveguide, etc.) to be emitted from the photonic integrated circuit while reducing the amount of back-reflected light that is coupled back into the output waveguide. The output facets may be further configured to control or otherwise adjust the beam divergence of light emitted from the output facet light sub-assembly circuit. In these cases, the output waveguide is connected to the slab waveguide such that the slab waveguide connects the output waveguide to the output facet of the photonic integrated circuit. The output waveguide receives input light generated from one or more light sources and passes the input light to the slab waveguide. The slab waveguide has an output side forming an output facet of the photonic integrated circuit, and input light received from the output waveguide exits the slab waveguide through the output side.

In particular, the output waveguide terminates before the output facet 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. The input light diffracts as it reaches the slab waveguide, 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 intermediate optical component, such as a partially etched region as discussed in more detail herein). Since the output side of the slab waveguide forms part of the output facet of the photonic integrated circuit, light exiting the slab waveguide is emitted from the photonic integrated circuit.

In some embodiments, the output side of the slab waveguide may be further configured to adjust the divergence of the input light as it exits the slab waveguide. The output side includes an optical element, such as a lens, that directs or otherwise controls the direction of light passing through the output side to exit 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").

The output side may be shaped to define an optical element having any suitable shape and orientation relative to other output waveguides. For example, the optical element may be concave, convex, flat and/or oriented at an angle relative to another portion of one side of the slab waveguide, or any combination thereof. Depending on the structure of the optical element, the light passing therethrough is directed 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 a reduced or small impact on the shaping of the light as it exits the optical system, but positioning the output waveguide away from the output side may reduce back reflected light coupling into the output waveguide.

These and other embodiments are discussed herein with reference to fig. 1-22C. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting.

Fig. 1 shows a top view of a portion of an optical system 100 that includes an output waveguide 103 that terminates at an output side 110 (e.g., an output facet on one side of a photonic integrated circuit) of the optical system 100 to facilitate emission of light from the output side 110. The output waveguide 103 may receive input light 108 generated by one or more light sources (not shown) and may output a portion of the light (depicted as rays 107c, 107d, and 107 e) through an output side 110 of the optical system 100. As shown, the output waveguide 103 abuts and terminates at the output side 110.

As shown in fig. 1, the output waveguide 103 includes a waveguide core 120 through which the input light 108 may propagate, and includes a pair of light confinement regions 105 that define the waveguide core 120 and provide optical confinement to the waveguide core 120. Generally, photonic integrated circuits described herein include a substrate, a cladding layer, and a waveguide layer positioned over the cladding layer. The waveguide layer may be etched or patterned to define cavities in the waveguide layer that define light confinement regions (e.g., light confinement region 105 of fig. 1). These light confinement regions may in turn define the shape of the waveguide (e.g., 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 one or more additional cladding layers that fill the light confinement region. In some of these cases, one or more additional cladding layers may also cover the top side of the waveguide. In other cases, the light confinement region may remain unfilled to provide an air interface with the lateral side surfaces of the waveguide. In some of these cases, the top surface of the waveguide may also be uncovered to provide an air interface with the top surface of the waveguide.

Thus, in some cases, one or more cladding layers collectively surround the waveguide core along the length of the waveguide to provide optical confinement to the waveguide core. 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 just mentioned above (which may also provide optical confinement to the waveguide). The various layers of the photonic integrated circuits described herein may be formed of any suitable material depending on the wavelength or wavelengths of light that the waveguides defined in the photonic integrated circuits are to carry. For example, in some variations, the waveguide layer (and thus any waveguide core) is formed of silicon, silicon nitride, silicon dioxide, or the like, the cladding layer(s) is formed of dielectric material(s) such as silicon dioxide, and the substrate is formed of silicon.

Returning to fig. 1, the light confinement region 105 separates the waveguide 120 from the adjacent slab waveguide 115. Thus, the input light 108 may be confined within the waveguide core 120 until it reaches the output side 110 of the optical system 100. At this time, the input light 108 is mainly emitted from the output side 110 of the optical system 100 (as indicated by rays 107c, 107d, and 107 e). Depending on the width of the waveguide core 120, the wavelength(s) of the input light 108, and the refractive index difference between the waveguide core 120 and any material (e.g., air) contacting the output side 110 of the optical system 100, a portion of the input light 108 reaching the output side 110 will be back reflected into the output waveguide 103 as back reflected light 109. When back-reflected light 109 is coupled back into output waveguide 103, back-reflected light 109 may create an undesirable etalon and negatively impact light source stability (e.g., stability of the light source generating input light 108).

Fig. 2 is an example of an optical system 200 as described herein that includes an output waveguide 203 that terminates before an output side 210 of a slab waveguide 215 of the optical system 200 such that light travels through the slab waveguide 215 before reaching the output side 210. Thus, the optical system 200 may be designed to help mitigate back reflection compared to the output waveguide 103 described with respect to fig. 1. In some embodiments, optical system 200 includes an optical element 225. Although the optical element 225 is shown in fig. 2 as being formed as part of the output side 210, the optical element may additionally or alternatively be formed within the slab waveguide 215. Embodiments of the optical element and its variants will be described in more detail with reference to fig. 3 to 19B and fig. 21A to 21C.

The output waveguide 203 may be part of a photonic integrated circuit as described herein, and the output side 210 may be an output facet of the photonic integrated circuit such that light received by the output waveguide 203 emanates from a side surface of the photonic integrated circuit. In these cases, depending on the design of the optical system, light emitted from the output facet of the photonic integrated circuit may be emitted from the optical system or may be transmitted to another element of the optical system. In particular, the output waveguide 203 may terminate at a distance 223 from the output side 210 and emit light into the slab waveguide 215. The input light diffracts as it reaches the slab waveguide 215 and the slab waveguide acts as a free propagation region 207 that allows the input light to expand as it propagates toward the output side 210.

Where a waveguide (e.g., an output waveguide or an input waveguide) is described herein as terminating at a slab waveguide, the waveguide includes a waveguide core that is positioned between a pair of light confining regions such that a first light confining region is adjacent a first side of the waveguide core and a second light confining region is adjacent a second side of the waveguide core. The pair of light confinement regions define the shape of the waveguide core and serve to optically confine light within the waveguide core. The waveguide terminates at the slab waveguide at a junction between the waveguide and the slab waveguide. The pair of light confining regions also terminate at the junction, resulting in the waveguide core being converted into a slab waveguide. Light passing from the waveguide core to the slab waveguide may diffract and freely propagate in the slab waveguide as described herein.

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, such as described herein. The light confinement region 205 terminates at a junction between the output waveguide 203 and the slab waveguide 215 to couple the output waveguide 203 to the slab waveguide 215. Since the light confinement region 205 no longer confines light as it enters the slab waveguide 215, the light can expand in the plane of the waveguide layer as it travels through the free propagation region 207. The distance 223 that the output waveguide 203 is separated from the output side 210 (i.e., between the terminal end of the output waveguide 203 and the output side 210) controls the amount by which light expands before exiting the waveguide layer. This may thereby control the size of the light beam reaching the output side 210, which may affect the amount of back-reflected light as the input light passes through the output side 210 (e.g., through the optical element 225) into the material on the other side of the output side (e.g., into free space or into another material adjacent to the optical system 200).

While most of the emitted light exits the slab waveguide 215 through the output side 210 (e.g., through the optical element 225 in the variation shown in fig. 2), a small amount of light may be back reflected from the output side 210 (e.g., from the optical element 225 in the variation shown in fig. 2). Depending on the design of the output side 210, some or all of this back reflected light will not couple back into the output waveguide 203. Instead, the back reflected light may be directed to a different portion of the photonic integrated circuit such that it does not reach the waveguide core 220 of the output waveguide 203.

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 produce a desired shape in a side surface of the photonic integrated circuit. To form the optical element, the photonic integrated circuit is etched at least through the waveguide layer to define the optical element 225. As discussed herein, a photonic integrated circuit may include a substrate supporting a cladding layer (e.g., a lower cladding layer), a waveguide layer positioned over the cladding layer (and defining the output waveguide 203 and the slab waveguide 215), and optionally an additional cladding layer (e.g., an upper cladding layer) positioned over the waveguide layer. In some cases, the photonic integrated circuit may be etched through the upper cladding layer (where the layer is included), through the waveguide layer, and at least partially through the lower cladding layer. In some of these variations, the photonic circuit may be etched through the lower cladding layer and at least partially through the substrate.

In this way, at least a portion of the output facet of the photonic integrated circuit may be an angled and/or curved vertical surface such that light exits the photonic integrated circuit horizontally through the vertical surface. The optical element may be defined as having any suitable shape (e.g., concave symmetric curve, convex to curved curve, concave asymmetric curve, convex asymmetric curve, square, grating, any combination thereof, etc.) as desired. 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 the incorporation of the optical element adds little additional time or complexity to the fabrication of the photonic integrated circuit.

To further reduce back reflection from the output side 210, one or more portions of the output side 210 (e.g., the optical element 225) may be coated with an anti-reflective coating. In some embodiments, the antireflective coating may be one or more layers of dielectric material. The anti-reflective coating may be coated, deposited, bonded, any combination thereof, etc., such that the anti-reflective coating may be adjacent to the optical element 225. It should be appreciated that the anti-reflective coating may be applied to any of the output facets of the various embodiments of the photonic integrated circuits described herein (e.g., to the output side of the slab waveguide through which light is emitted).

In some implementations, at least a portion of the photonic integrated circuit can extend beyond the output facet through which light is emitted. For example, fig. 16A shows a perspective view of a variation of photonic integrated circuit 1600 as described herein. As shown, photonic integrated circuit 1600 includes substrate 1602, first dielectric layer 1604, waveguide layer 1606, and second dielectric layer 1608. First dielectric layer 1604 is supported (directly or indirectly) by substrate 1602, waveguide layer 1606 is positioned over first dielectric layer 1604, and second dielectric layer 1608 is positioned over waveguide layer 1606. In this way, first dielectric layer 1604 and second dielectric layer 1608 may optically confine light carried by photonic integrated circuit 1600 within the plane of waveguide layer 1606.

Photonic integrated circuit 1600 includes lateral side surfaces 1610 that form a portion of the perimeter of photonic integrated circuit 1600. For example, photonic integrated circuit 1600 may be formed as part of a larger wafer that is diced to expose lateral side surfaces 1610. A portion of photonic integrated circuit 1600 is etched to define an output facet 1612 for outputting light from photonic integrated circuit 1600, as described herein. Specifically, in the variation shown in fig. 16A, photonic integrated circuit 1600 is etched through second dielectric layer 1608, waveguide layer 1606, first dielectric layer 1604, and a portion of substrate 1602. The photonic integrated circuit 1600 may be etched to define an optical element 1614 in an output facet 1612 (which may be defined in an output surface of a slab waveguide, as previously described). The etch depth may preferably be chosen to be deep enough so that the output light is not truncated by surrounding portions of photonic integrated circuit 1600 as it propagates away from output facet 1612.

The output facet 1612 is recessed relative to the lateral side surface 1610 such that light exiting the photonic integrated circuit 1600 from the output facet 1612 may travel past the lateral side surface 1610 (if not redirected by another optical component of the optical system that includes the photonic integrated circuit 1600). For example, fig. 16B shows a top view of a portion of photonic integrated circuit 1600. As shown, output waveguide 1616 may be defined in waveguide layer 1606 via a pair of light confinement regions 1618 to define waveguide core 1620. These light confinement regions 1618 may be filled by the second cladding layer 1608 or by additional cladding layers (e.g., formed from a different material and/or deposited in a separate step from the second cladding layer 1608). The output waveguide 1616 terminates in a slab waveguide 1622 also defined in the waveguide layer 1606. The output waveguide 1616 may transfer the light 1624 into a slab waveguide 1622 where the light 1624 diverges as it approaches the output facet 1612. Light 1624 passes through output facet 1612 (which forms the output surface of slab waveguide 1622) to exit photonic integrated circuit 1600. As shown in fig. 16B, light 1624 travels through lateral side surface 1610 after exiting photonic integrated circuit 1600 through output facet 1612.

While the output facet 1612 forms an outer surface of the photonic integrated circuit 1600 (i.e., forms a portion of an outer perimeter of the photonic integrated circuit 1600), in other variations, the photonic integrated circuit may be configured to emit light from an inner surface of a cavity defined in the photonic integrated circuit. For example, fig. 16C shows a top view of another embodiment of photonic integrated circuit 1630. Photonic integrated circuit 1630 may include, for example, a substrate 1632, a lower cladding layer (not shown) supported by substrate 1632, and a waveguide layer 1634 positioned on the lower cladding layer. In some cases, photonic integrated circuit 1630 also includes an upper cladding layer (not shown) positioned over waveguide layer 1634. Photonic integrated circuit 1630 defines a cavity 1650 that extends at least partially through photonic integrated circuit 1630 to expose a portion of waveguide layer 1634. For example, in the variation shown in fig. 1C, the cavity extends through the upper cladding layer (in a variation that includes this layer), the waveguide layer 1634, and the lower cladding layer, and extends partially through the substrate 1632.

In these variations, photonic integrated circuit 1630 is configured such that the surface of cavity 1650 acts as an output facet 1644 through which light is emitted from photonic integrated circuit 1630. As shown, photonic integrated circuit 1630 includes an output waveguide 1636 that includes a waveguide core 1640 defined by a pair of light confinement regions 1638. The output waveguide 1636 terminates at a slab waveguide defined in the waveguide layer 1634. The output facet 1644 defines an output surface of the slab waveguide such that light introduced into the slab waveguide from the output waveguide 1636 is emitted from the slab waveguide through the output facet 1644. The light will exit the waveguide layer 1634 into the cavity 1650.

Since the interior of cavity 1650 is defined by the surface of photonic integrated circuit 1630, at least a portion of the light exiting waveguide layer 1634 through output facet 1644 will be directed toward the opposite surface of cavity 1650. Accordingly, photonic integrated circuit 1630 may be configured to redirect the light out of cavity 1650. For example, in some variations, the surface of the cavity 1650 opposite the output facet 1644 may be angled non-vertically (and optionally coated with a reflective material such as metal) to redirect light away from the plane of the waveguide layer 1634 and out of the cavity 1650. In other variations, the additional component 1646 may be at least partially inserted into the cavity. The additional component 1646 may include one or more angled surfaces and/or other features configured to redirect 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 component 1646 may be filled with another type of material that may be used to limit the divergence of the light before it reaches the additional component 1646.

To generate light carried 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 of a single wavelength, or may be capable of generating a plurality of different wavelengths spanning 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 is selectively operable to emit a set of light of a corresponding wavelength.

Each light source may be any component capable of generating light of one or more specific wavelengths, such as a light emitting diode or a laser. Lasers may include semiconductor lasers such as laser diodes (e.g., distributed bragg reflector lasers, distributed feedback lasers, external cavity lasers), quantum cascade lasers, and the like. A given light source may be single frequency (fixed wavelength) or may be tunable to selectively generate one of a plurality of wavelengths (i.e., the light source may be controlled to output different wavelengths at different times). The set of light sources may comprise any suitable combination of light sources and may work together to generate light of any of a plurality of different wavelengths.

To the extent that the light source unit is capable of generating a plurality of different wavelengths, the light source unit may be configured to simultaneously and/or sequentially generate light of different wavelengths. 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 circuit and couple light into the photonic integrated circuit. As mentioned previously, the optical system may comprise additional components (not shown) between the light source of the light source unit and the output waveguide, so that the light may be changed before reaching the output waveguide as input light.

While the waveguides described herein are discussed as carrying and/or operating over a range of wavelengths (e.g., a "target wavelength range"), it should be understood that in some cases the light source units need not be capable of generating the entire spectrum within that range (i.e., each wavelength between the longest wavelength and the shortest wavelength of that range). Instead, the light source units may generate a discrete number or set of wavelengths within the range. Similarly, the output waveguides may not necessarily carry each of these wavelengths at the same time, but may instead receive these wavelengths at different times depending on the operation of the optical system. In addition, the target wavelength range may span any particular bandwidth, depending on the needs of the optical system. For example, in some cases, the target wavelength range may span at least 100nm. In some of these variations, the target wavelength range may span at least 500nm. In some of these variations, the target wavelength range may span at least 1000nm.

Fig. 3 is an example of another optical system 300 that mitigates back reflection of light. In particular, the optical system 300 is configured to emit light from an output side 310 (which may be an output facet of a photonic integrated circuit as discussed herein) that does not include optical elements defined by the output side 310. 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 may include a waveguide core 320 defined by a pair of light confinement regions 305 such that light propagating through the waveguide core 320 is confined by the light confinement regions 305. The output waveguide 303 terminates at a junction with a slab waveguide 315 that serves as a free propagation region for light exiting the output waveguide 303.

Early termination of the output waveguide 303 (i.e., before the output side 310) may reduce the amount of back-reflected light 307a, 307b coupled back into the waveguide core 320 of the slab waveguide 315 (back-reflected light may be further mitigated where the output side 310 is coated with an anti-reflective coating). Specifically, the input light exiting the output waveguide 303 (the external rays of which are represented by rays 307a, 307 b) will diverge as it travels through the slab waveguide 315, which may reduce the amount of back reflected light that is directed into the output waveguide 303. As light exits the slab waveguide 315 through the output side 310, a change in refractive index between the slab waveguide 315 and surrounding material (e.g., air) may cause an increase in the divergence of the output light (the external rays of which are represented by rays 307d, 307 e) relative to the divergence of the input light. Although the light beams are shown as external light rays in fig. 3 to 15, it is understood that the light fills the space between the external light rays, and the external light rays represent external restrictions of the emitted light.

Depending on the refractive index change that occurs at the output side 310, the magnitude of this divergence change may be greater than what is otherwise desired for a given optical system. Thus, in some variations, the output facet of the photonic integrated circuit may be configured to define an optical element that may help shape the beam exiting the output side. For example, fig. 4 shows an example of an optical system 400 having a side surface 410 defining an optical element 425, where the optical element 425 forms an on-chip lens. In this variation, the optical element 425 is configured to collimate light as it is emitted from the side surface 410.

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

As the input light passes through the optical element 425 to generate an output beam, the optical element 425 will act as a positive lens (i.e., a lens with positive refractive power) collimating the output light (represented by outermost rays 407d and 407 e). This collimation occurs in the plane of the waveguide layers defining slab waveguide 415 (i.e., in the slow axis), and it should be appreciated that the light may still diverge in a direction perpendicular to the plane of slab waveguide 415 (i.e., the fast axis) after exiting through side surface 410. While additional free-space optical elements (e.g., lens elements such as fast axis collimators) may be added to optical system 400 to adjust the beam profile in the fast axis, optical element 425 may reduce the number and/or complexity of free-space optical elements necessary to achieve a desired beam profile of the output light in the slow axis.

In the variation shown in fig. 4, the optical element 425 has a convex shape, such as a curve with a positive radius of curvature (i.e., curved toward the output waveguide 403). Although the beam width of the input light is sized in fig. 4 such that the beam passes through only a portion of the optical element 425, this is for illustrative purposes only. The optical element 425 may be sized as desired such 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 may be sized and positioned such that as the input light passes through the optical element 425, the input light expands to approximately the width of the optical element 425 (e.g., within 5% of the width of the optical element 425).

In other cases, the optical element may be configured to focus light emitted from the side surface such that the light is concentrated. Fig. 5 is an example of an optical system 500 having a side surface 510 defining an optical element 525, wherein the optical element 525 forms an on-chip lens configured to direct light emitted from the side surface 510 to converge.

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, slab waveguide 515 and output waveguide 503 may be defined in a waveguide layer of a photonic integrated circuit, such as previously described, where side surface 510 is an output facet of the photonic integrated circuit. The output waveguide 503 has a waveguide core 520 (such as previously discussed, defined by a pair of light confinement regions 505) connected to a slab waveguide 515. In this way, the output waveguide 503 terminates before reaching the side surface 510. Thus, the input light received by the output waveguide 503 is transferred to the slab waveguide 515 (which acts as a free propagation region) where the input light, the boundary of which is represented by rays 507a, 507b, will diverge as it approaches the optical element 525.

The optical element 525 of the optical system 500 is positioned and/or curved such that as divergent input light passes through the optical element 525, the optical element 525 generates a converging output light beam (the boundaries of which are represented by outermost rays 507d and 507 e). As with optical element 425 of fig. 4, optical element 525 will act as a positive lens (i.e., a lens with positive refractive power) except that the curvature of optical element 525 and/or the distance between the output waveguide and optical element 525 (as compared to optical element 425) is adjusted to direct the output light to converge. The optical element 525 has a convex shape, such as a curve with a positive radius of curvature, and may be manufactured in any suitable manner as previously described. As discussed herein, this focusing occurs in the plane of slab waveguide 515 and may reduce the number, size, and/or complexity of free space optics that would otherwise be used to focus light on the slow axis.

In other variations, it may not be desirable to significantly alter the beam profile of the input light as it exits the side surfaces of the photonic integrated circuit. Thus, 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 curve such that the cylindrical lens has a constant radius of curvature. Fig. 17A illustrates one such variation of a photonic integrated circuit 1700 (which may be part of the optical system described herein). Although fig. 17A only shows waveguide layer 1702 of photonic integrated circuit 1700, as previously discussed, photonic integrated circuit 1700 may also include a substrate, a lower cladding layer, and optionally an upper cladding layer.

Photonic integrated circuit 1700 includes a side surface 1704 that serves as an output facet through which light may be emitted from photonic integrated circuit 1700. The side surfaces 1704 define an optical element 1706 that forms a cylindrical on-chip lens having a semi-circular curve. The photonic integrated circuit also includes an output waveguide 1708 and a slab waveguide 1714 defined in the waveguide layer 1702. In particular, the output waveguide 1708 includes a waveguide core 1710 that is bounded and defined by a pair of light confinement regions 1712. The output waveguide 1708 terminates in a slab waveguide 1714 at the junction between the output waveguide 1708 and the slab waveguide 1714.

As previously described, when input light is introduced into the slab waveguide 1714 from the output waveguide 1708, the input light (the boundaries of which are represented by arrows 1718a and 1718 b) will diverge within the slab waveguide 1714. If the junction between the output waveguide 1708 and the slab waveguide 1714 is located at the center of curvature of the optical element 1706, as shown in FIG. 17A, the light will not change its divergence as the input light emitted from the output waveguide 1708 exits the photonic integrated circuit 1700 through the optical element 1706. Specifically, when input light is introduced into the slab waveguide 1714 from the output waveguide 1708, each ray within the input light will strike the optical element 1706 at a normal incidence angle (assuming the optical element 1706 is sized such that the input light reaches its far field before striking the optical element 1706). As each ray strikes the optical element 1706 at a normal angle of incidence, each ray continues to travel in the same direction due to the refractive index change 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 and 1720 b) having the same beam divergence as the input light.

When a ray strikes an optical element 1706 at normal incidence, back reflections caused as the light exits the slab waveguide 1714 will be retroreflected back to the output waveguide 1708. In practice, back reflected light (the boundaries of which are also represented by arrows 1718a and 1718 b) is focused by the optical element 1706 at the entrance of the output waveguide 1708. To alleviate this, the output waveguide may be positioned such that it is laterally offset with respect to the center of curvature of the semicircular curve. As used herein, an output waveguide is considered to be "laterally offset" with respect to the center of curvature of an optical element when the beam of light exiting the output waveguide (i.e., the input light in a slab waveguide) is centered along a line that does not intersect the center of curvature of the optical element. In the variation shown in fig. 17A, the input light exiting the output waveguide 1708 is centered on a line 1716 intersecting the center of curvature of the optical element 1706 and, thus, the output waveguide 1708 is not laterally offset relative to the optical element 1706.

Fig. 17B shows another variation of photonic integrated circuit 1730 that includes waveguide 1738 laterally offset relative to optical element 1736. As with photonic integrated circuit 1700 of fig. 17B, photonic integrated circuit 1730 can be part of the optical system described herein and can include a substrate, a lower cladding layer, waveguide layer 1732, and optionally an upper cladding layer (although fig. 17B depicts only waveguide layer 1732).

Photonic integrated circuit 1730 includes a side surface 1734 that serves as an output facet through which light may be emitted from photonic integrated circuit 1730. The side surfaces 1734 define optical elements 1736 that form cylindrical on-chip lenses with semi-circular curves. The photonic integrated circuit also includes an output waveguide 1738 and a slab waveguide 1744 defined in the waveguide layer 1732. In particular, the output waveguide 1738 includes a waveguide core 1740 bounded and defined by a pair of light confinement regions 1742. The output waveguide 1738 terminates in the slab waveguide 1744 at a junction between the output waveguide 1738 and the slab waveguide 1744.

Unlike the output waveguide 1708 of fig. 17A, the output waveguide 1738 of the photonic integrated circuit 1730 is positioned such that the junction between the output waveguide 1708 and the slab waveguide 1714 is not located 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 relative to the center of curvature 1760 of the optical element 1736. In particular, the output waveguide 1738 is positioned such that the output waveguide 1738 directs an input light beam (the outer boundaries of which are represented by rays 1748a, 1748 b) into the slab waveguide 1744 such that the light beam is centered along a line 1746 that does not intersect the center of curvature 1760 of the optical element 1736.

When the output waveguide 1738 is laterally offset relative to the center of curvature 1760, individual rays of the input light will strike the optical element 1736 at non-perpendicular angles. Thus, back reflections caused by these rays as they leave slab waveguide 1744 are not retroreflected back to output waveguide 1738. Instead, back reflections (the outer boundaries of which are represented by rays 1752a, 1752B in FIG. 17B) are effectively focused onto different points in slab waveguide 1744. If the output waveguide 1738 is sufficiently laterally offset relative to the center of curvature 1760 of the optical element 1736, no back reflection from the side surface 1734 is directly coupled into the output waveguide 1738.

When the input light reaches optical element 1736, side surface 1734 generates an output light beam (the boundaries of which are represented by rays 1750a and 1750 b). While laterally displacing the output waveguide 1738 may adjust the divergence direction and/or divergence level of the output beam (as compared to the beam generated by the side surface 1704 in fig. 17A), the output beam may still be within the system specifications of a given optical system while achieving reduced back reflection as just described above. Indeed, in some cases, the output waveguide 1738 may be positioned to intentionally increase or decrease the divergence of the output beam, such as will be described herein with respect to fig. 18A-18C.

Although the optical element previously described with respect to fig. 4, 5, 17A, and 17B is configured as an on-chip lens having a convex shape, in other variations, the optical element may be configured as an on-chip lens 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, where the optical element 625 forms an on-chip lens. In this variation, the optical element 625 is configured to increase the divergence of the light as it is emitted from the side surface 610.

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

As the input light passes through the optical element 625 to generate an output beam, the optical element 625 will act as a negative lens (i.e., a lens with negative refractive power) to increase the divergence of the output light (whose boundaries are represented by rays 607d and 607 e). This steering occurs in the plane of the waveguide layers defining the slab waveguide 615 (i.e., in the slow axis), and the output light may also diverge in the fast axis, as previously discussed. In the variation shown in fig. 6, the optical element 625 has a concave shape, such as a curve with a negative radius of curvature (i.e., curved away from the output waveguide 603). As discussed herein, the optical element 625 reduces the number, size, and/or complexity of free-space optics that would otherwise be used for focusing on the slow axis.

While the optical systems and photonic integrated circuits described herein with respect to fig. 4-6, 17A, and 17B are each shown as having a side surface that includes a single optical element formed as an on-chip lens, it should be understood that the photonic integrated circuits (and associated optical systems) described herein may include multiple optical elements formed in the side surfaces thereof. For example, fig. 18A shows one such variation of photonic integrated circuit 1800. Although fig. 18A only shows waveguide layer 1802 of photonic integrated circuit 1800, photonic integrated circuit 1800 may also include a substrate, a lower cladding layer, and optionally an upper cladding layer, as previously discussed.

The photonic integrated circuit 1800 includes a side surface 1804 that acts as an output facet through which light may be emitted from the photonic integrated circuit 1800. The side surface 1804 defines a plurality of optical elements 1806a-1806c, each of which forms an on-chip lens. Although the plurality of optical elements 1806a-1806c are 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 1806 c), the plurality of optical elements 1806a-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 is configured as any one of the on-chip lenses as described herein, and thus the plurality of optical elements 1806a-1806c may include any combination of on-chip lenses as desired. The plurality of optical elements 1806a-1806c may each have the same shape, or alternatively, some or all of the plurality of optical elements 1806a-1806c may have different shapes.

The photonic integrated circuit 1800 also includes a plurality of output waveguides 1808a-1808c and a plurality of slab waveguides 1810a-1810c defined in the waveguide layer 1802. Each of the plurality of output waveguides 1808a-1808c and each of the plurality of slab waveguides 1810a-1810c is associated with a corresponding one of the plurality of optical elements 1806a-1806c such that each optical element receives light from one of the plurality of output waveguides 1808a-1808c (via a corresponding slab waveguide of the plurality of slab waveguides 1810a-1810 c) and generates a corresponding output light beam. Each optical element, its corresponding output waveguide, and its corresponding slab waveguide collectively form an emitter capable of generating an output light beam. Thus, photonic integrated circuit 1800 includes a plurality of emitters, each of which is capable of emitting a corresponding light beam through side surface 1804 of photonic integrated circuit 1800. The side surfaces 1804 may emit a plurality of individual output beams that may collectively form a larger output beam.

In the variation shown in fig. 18A, the plurality of output waveguides 1808A-1808c includes a first output waveguide 1808A, a second output waveguide 1808b, and a third output waveguide 1808c. Similarly, the plurality of slab waveguides 1810a-1810c includes a first slab waveguide 1810a, a second slab waveguide 1810b, and a third slab waveguide 1810c. It should be appreciated that the plurality of slab waveguides 1810a-1810c may be different portions of a common slab waveguide such that the slab waveguides 1810a-1810c are optically connected to each other (such as shown in fig. 18A) or may be optically separated (e.g., via intermediate light confinement regions) such that light cannot travel between the plurality of slab waveguides 1810a-1810 c.

The first output waveguide 1808a terminates in the first slab waveguide 1810a at a junction between the first output waveguide 1808a and the first slab waveguide 1810 a. As previously described, when an input light beam 1814a is introduced into the first slab waveguide 1810a from the first output waveguide 1808a, the input light 1814a will diverge within the first slab waveguide 1810 a. The input light 1814a passes through the first optical element 1806a to generate a first output light beam 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 output beam 1816b from the input beam 1814b introduced into the second slab waveguide 1810b from the second output waveguide 1808 b. Third output waveguide 1808c, third slab waveguide 1810c, and third optical element 1806c generate third output beam 1816c from corresponding input beam 1814c in the same manner.

In the variation shown in fig. 18A, the plurality of optical elements 1806a-1806c are each configured as a cylindrical lens having a semicircular curve. In some of these variations, each of the plurality of output waveguides 1808a-1808c is laterally offset from the center of curvature of its corresponding optical element. This may reduce or prevent back reflection from reaching the plurality of output waveguides 1808a-1808c as light passes through the corresponding optical elements 1806a-1806c, such as described herein with respect to photonic integrated circuit 1730 of fig. 17B.

In some variations, each of the plurality of transmitters has the same configuration. In these variations, the corresponding optical element, output waveguide, and slab waveguide of each emitter are of the same relative size, positioning, and orientation. In particular, each of the plurality of output waveguides 1808a-1808c has the same position and orientation relative to a corresponding one of the plurality of optical elements 1806a-1806 c. In addition, each of the plurality of optical elements 1806a-1806c has the same shape, and thus the output beams 1816a-1816c generated by the plurality of emitters will have the same shape and direction. In other variations, different transmitters may have different configurations. For example, at least some of the plurality of optical elements 1806a-1806c may have a different shape (e.g., to change the shape or direction of a corresponding output beam). Additionally or alternatively, some of the plurality of output waveguides 1808a-1808c will have different positions and/or orientations relative to their corresponding optical elements, and will therefore generate output beams having different shapes and/or directions. Thus, these positions and orientations can be adjusted within each of the plurality of output waveguides 1808a-1808c to customize the shape of the overall beam collectively generated by the plurality of optical elements 1806a-1806 c.

In the variation shown in fig. 18A, the junctions between the plurality of output waveguides 1808A-1808c and their corresponding slab waveguides 1810a-1810c are aligned with the centers of curvature (not shown) of the plurality of optical elements 1806a-1806 c. This is represented by line 1812, which intersects the center of curvature of each of the plurality of optical elements 1806a-1806c in FIG. 18A. When the bond is positioned along 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 of first optical element 1806a, back reflected light 1818b of second optical element 1806b, and back reflected light 1818c of third optical element 1806 c) will focus on a point that also falls along line 1812, but on the opposite side of the center of curvature. Thus, these junctions may be positioned such that back reflected light does not enter the plurality of output waveguides 1808a-1808c, as previously discussed.

In other cases, the junction between the output waveguide and the corresponding slab waveguide is not aligned with the center of curvature of the semicircular curve of the corresponding optical element, which may be used to increase or decrease the divergence of the output light as it exits the side surface of the photonic integrated circuit. For example, fig. 18B shows another variation of photonic integrated circuit 1820. Specifically, fig. 18B illustrates a waveguide layer 1822 of photonic integrated circuit 1820, including: 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 1826 c); a plurality of output waveguides (including a first output waveguide 1828a, a second output waveguide 1828b, and a third output waveguide 1828 c); and a plurality of slab waveguides (including a first slab waveguide 1830a, a second slab waveguide 1830b, and a third slab waveguide 1830 c). These components together form a plurality of emitters, as previously described. The side surface 1824 serves as an output facet through which light may be emitted from the photonic integrated circuit 1820.

The photonic integrated circuit 1820 may be configured identical to the photonic integrated circuit 1800 of fig. 18A, except that each of the plurality of output waveguides 1828A-1828c terminates behind a center of curvature of its corresponding optical element (as represented by line 1832 in fig. 18B intersecting the center of curvature of each of the plurality of optical elements 1826a-1826 c). In other words, the junction between the output waveguide and its corresponding slab waveguide is positioned such that the center of curvature of the corresponding optical element is located between the junction and the optical element. This may result in the output beam being slightly collimated (i.e., having less divergence) than its corresponding input beam. For example, when the first output waveguide 1828a introduces the input light beam 1834a into the first slab waveguide 1830a (i.e., at the junction behind the line 1832), the input light beam 1834a will be partially collimated as it passes through the first optical element 1826 a. Thus, the first optical element 1826a will generate a first output light beam 1836a having a smaller divergence than the input light beam 1834 a. Similarly, the second optical element 1826b may generate a second output light beam 1836b having a smaller divergence than the corresponding input light beam 1834b, and the third optical element 1826c may generate a third output light beam 1836c having a smaller divergence than the corresponding input light beam 1834 c. It should be appreciated that each of the plurality of output waveguides 1828a-1828c may be laterally offset from a center of curvature of the corresponding optical element. This may result in the back-reflected light (not shown) being focused at a point on the opposite side of the line 1832, but the plurality of output waveguides 1828a-1828c may still be positioned such that the back-reflected light is not coupled into the plurality of output waveguides 1828a-1828 c.

Fig. 18C shows yet another variation of photonic integrated circuit 1840. Specifically, fig. 18C shows a waveguide layer 1842 of a photonic integrated circuit 1840, the waveguide layer comprising: 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 1846 c); a plurality of output waveguides (including a first output waveguide 1848a, a second output waveguide 1848b, and a third output waveguide 1848 c); and a plurality of slab waveguides (including a first slab waveguide 1850a, a second slab waveguide 1850b, and a third slab waveguide 1850 c). These components together form a plurality of emitters, as previously described. The side surface 1844 acts as an output facet through which light may be emitted from the photonic integrated circuit 1840.

The photonic integrated circuit 1840 may be configured identical to the photonic integrated circuit 1800 of fig. 18A, except that the plurality of output waveguides 1848A-1428C each extend beyond and terminate in front of the center of curvature of their corresponding optical elements (as represented by line 1852 in fig. 18C intersecting the center of curvature of each of the plurality of optical elements 1846 a-1846C). In other words, the junction between each output waveguide and its corresponding slab waveguide is positioned such that the junction is between the corresponding optical element and its center of curvature. This may result in the output beam having an increased divergence compared to its corresponding input beam. For example, when the first output waveguide 1848a introduces the input light beam 1854a into the first slab waveguide 1850b (i.e., at the junction ahead of the line 1852), the input light beam 1854a will diverge as it passes through the first optical element 1846 a. Thus, the first optical element 1846a will generate a first output beam 1856a having a larger divergence than the input beam 1854 b. Similarly, the second optical element 1846b may generate a second output beam 1856b having a larger divergence than the corresponding input beam 1854b, and the third optical element 1846c may generate a third output beam 1856c having a larger divergence than the corresponding input beam 1854 c. It should be appreciated that each of the plurality of output waveguides 1848a-1848c may be laterally offset from the center of curvature of the corresponding optical element. This may result in the back reflected light (not shown) being focused at a point on the opposite side of line 1852, but the plurality of output waveguides 1848a-1848c may still be positioned such that the back reflected light is not coupled into the plurality of output waveguides 1848a-1848 c.

In the case of multiple output beams generated using multiple emitters, it may be desirable to allow for individual control of some or all of the output beams. This may allow for adjusting the overall illumination emitted from the photonic integrated circuit of the optical system. For example, a photonic integrated circuit may be able to selectively control the intensity, wavelength(s), and/or phase of different output beams. Fig. 18D shows an example of an optical system 1860 having a photonic integrated circuit 1862 configured to emit a plurality of output light beams via a plurality of emitters. Specifically, photonic integrated circuit 1862 has a side surface 1864 that defines a plurality of optical elements 1866a-1866 d. Side surface 1864 serves as an output facet of photonic integrated circuit 1862. The plurality of optical elements 1866a-1866d includes four optical elements (e.g., first optical element 1866a, second optical element 1866b, third optical element 1866c, and fourth optical element 1866 d), but may include any suitable number of optical elements as previously described.

The photonic integrated circuit 1862 also includes a plurality of output waveguides 1868A-1868d, each of which is associated with a corresponding optical element of the plurality of optical elements 1866a-1866d, such as described herein with respect to the photonic integrated circuits of fig. 18A-18C. In particular, first output waveguide 1868a may direct input beam 1872a to first optical element 1866a to generate first output beam 1874a, and second output waveguide 1868b may direct input beam 1872b to second optical element 1866b to generate second output beam 1874b. Similarly, third output waveguide 1868c may direct input light beam 1872c to third optical element 1866c to generate third output light beam 1874c, and fourth output waveguide 1868d may direct input light beam 1872d to fourth optical element 1866d to generate fourth output light beam 1874d. This may together form the plurality of transmitters mentioned previously. Depending on the relative placement of optical elements 1866a-1866d and the divergence of output beams 1874a-1874d, some or all of the output light speeds of output beams 1874a-1874d may at least partially overlap.

In some cases, optical system 1860 may selectively control which of the emitters are emitting light (i.e., which optical elements 1866a-1866d are actively generating output beams) such that different combinations of output beams 1874a-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 intensities of these output light beams 1874a-1874d such 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. The light source unit 1869 is optically connected to each of the plurality of emitters. Specifically, light source unit 1869 is optically coupled to each of the plurality of output waveguides 1868a-1868d such that each of input light beams 1872a-1872d (and thus output light beams 1874a-1874 d) is initially generated by one or more light sources of light source unit 1869. Although light source unit 1869 is shown in fig. 18D as being incorporated into photonic integrated circuit 1862, in other cases some or all of the light sources of light source 1869 are separate from photonic integrated circuit 1862 and are arranged to couple light into photonic integrated circuit 1862.

In some variations, the light source unit 1869 may control which of the output waveguides 1868a-1868d receive output light by selectively activating different light sources of the light source unit 1869. Additionally or alternatively, photonic integrated circuit 1862 may include one or more additional optical components (e.g., optical switches, variable optical attenuators, combinations thereof, etc.) located between light source unit 1869 and one or more of output waveguides 1868a-1868 d. These components may be controlled to determine whether light generated by the light source unit 1869 reaches a particular output waveguide of the plurality of output waveguides 1868a-1868 d. The intensity of a given output light beam may be similarly adjusted, such as by varying the intensity of the light generated by light source unit 1869 and/or controlling how much light reaches the corresponding output waveguide.

Accordingly, the optical system 1860 may select (via the light source unit 1869 and/or any intermediate components) which of the output waveguides 1868a-1868d will receive the input light, and thus which of the optical elements 1866a-1866d will emit the output light beam. For example, the optical system 1860 may direct input light to all of the output waveguides 1868a-1868d such that all of the emitters (and their respective optical elements) emit corresponding output light beams. At other times, the optical system 1860 may select a subset of the output waveguides 1868a-1868d and may direct only the input light to the selected output waveguides. In this way, only a corresponding subset of the emitters (and their respective optical elements) emit output light beams. Depending on the design of the optical system 1860, the optical system may select different subsets of the output waveguides 1868a-1868d at different times to change the selection of the emitters that are emitting light.

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

Additionally or alternatively, the optical system 1860 may selectively control the wavelength(s) of the output light beam emitted by each optical element such that the wavelength may vary between different emitters. In particular, different subsets of the output waveguides 1868a-1868d may receive input light having different sets of wavelengths such that different subsets of the emitters (and their corresponding optical elements) generate output light beams having different sets of wavelengths. For example, the optical system 1860 may be controlled such that a first subset of the optical elements 1866a-1866d may generate a corresponding set of output beams, each of the corresponding set of output beams having a first set of wavelengths. The optical system 1860 may be further controlled such that a second subset of the optical elements 1866a-1866d simultaneously generate a second set of output beams, each of the second set of output beams having a second set of wavelengths different from the first set of wavelengths. In these cases, the first set of wavelengths and the second set of wavelengths are considered to be different as long as one set includes light of at least one wavelength not included in the other set.

In still other variations, the optical system 1860 may control the light emitted by each emitter such that the phase may be different between different output beams. For example, the optical system 1860 shown in fig. 18D includes a plurality of phase shifters 1870a-1870D, each of which is controllable to selectively adjust the phase of a corresponding output waveguide (i.e., an emitter or group of emitters may be individually controlled to emit light having a different phase). For example, the first phase shifter 1870a may be controlled to adjust the phase of the input light carried by the first output waveguide 1868a, the second phase shifter 1870b may be controlled to adjust the phase of the input light carried by the second output waveguide 1868b, the third phase shifter 1870c may be controlled to adjust the phase of the input light carried by the third output waveguide 1868c, and the fourth phase shifter 1870d may be controlled to adjust the phase of the input light carried by the fourth output waveguide 1868 d. This may allow each of the optical elements 1866a-1866d (or a subset thereof) to generate an output beam having a unique phase relative to other output beams generated by the optical elements 1866a-1866 d. The plurality of phase shifters may include any suitable phase shifter, such as a thermo-optic phase shifter that changes the refractive index of the waveguide by changing the temperature of the waveguide, a carrier-based phase shifter that changes the refractive index of the waveguide by changing the amount of charge carriers present in the waveguide, an opto-mechanical phase shifter that moves a movable structure relative to the waveguide to change the effective refractive index experienced by light traveling through the waveguide, combinations thereof, and the like.

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

As shown in fig. 18D, the optical system 1860 may include a controller 1876 configured to control a plurality of emitters. Specifically, controller 1876 controls the operation of photonic integrated circuit 1862 to emit light from side surface 1864, as previously described. Specifically, the controller 1876 may control the light source unit 1869 such that the light source unit 1869 generates the light necessary to generate the output light beams 1874a-1874d (or a subset thereof as selected by the optical system 1860). In addition, the controller 1876 may control any intermediate components as needed to transfer light from the light source unit 1869 to the selected output waveguide. In variations in which optical system 1860 includes one or more phase shifters (such as multiple phase shifters 1870a-1870 d), controller 1876 may control these phase shifters to adjust the relative phases of output beams 1874a-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), which are required to perform these functions, including any method steps described herein.

In various embodiments of the photonic integrated circuits described herein, it may be desirable to angle the output waveguides such that the output waveguides are not perpendicular to the side surfaces 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, where the output waveguide 703 is angled with respect to an output side 710 of the slab waveguide 715. In these cases, angling the output waveguide 703 may mitigate back reflection of the light 707 from the output side 710. The particular positioning depicted in fig. 7 is for illustrative purposes only, and the output waveguide 703 may be positioned at any suitable angle that mitigates back reflection of light.

In particular, the output waveguide 703 (which may include a waveguide core 720 defined at least in part by a pair of light confinement regions 705, as previously discussed) may terminate at the slab waveguide 715 such that input light carried by the output waveguide 703 is transferred to the slab waveguide 715. The output waveguide 703 is angled such that the input light beam (the boundaries of which are represented by rays 707a, 707 b) is similarly angled with respect to the output side 710 of the slab waveguide 715. In these cases, the center of the input beam (represented by ray 708) strikes the output side 710 at a non-normal angle of incidence.

As the input light beam passes through output side 710 to generate an output light beam (the boundaries of which are represented by rays 707d and 707e, and also including ray 707 c), back reflected light (not shown) may return to 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 the case of some back-reflected light returning to the output waveguide 703, the back-reflected light may have less intensity than a similar design in which the center of the input beam impinges the output side 710 at normal incidence. In some implementations, the output side 710 may have optical elements etched into the profile of the output side 710, and the optical elements may be any lens as described herein.

The relative angle between the output waveguide 703 and the output side 710 may 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 the side surface of the photonic integrated circuit that is exposed by dicing the wafer, in which case the output waveguide may be defined at an angle relative to the side surface. Where a portion of the photonic integrated circuit is etched to form a side surface (as discussed herein with respect to fig. 16A-16C), the etching may produce a relative angle between the side surface and the output waveguide. Fig. 8 is one such example of an optical system 800 having an output waveguide 803 and a slab waveguide 815 that includes an angled output side 810. In these cases, the output side 810 may be etched from the side surface of the photonic integrated circuit to create a relative angle between the output waveguide 803 and the output side 810.

As shown in fig. 8, plane 811 represents a plane parallel to the side surface of the photonic integrated circuit. The output waveguide 803 (which may include a waveguide core 820 defined by the light defining region 805 as previously discussed) is positioned perpendicular to the plane 811. Thus, the input light beam (whose boundaries are represented by rays 807a, 807 b) propagating from the output waveguide 803 to the slab waveguide 815 is perpendicular to the plane 811 (i.e., the center of the input light beam will intersect the plane 811 at a normal angle of incidence). However, the output side 810 of the slab waveguide 815 may be etched such that it is angled 845 with respect to the lateral side surfaces. This creates a relative angle between the output waveguide 803 and the output side 810 that is similar to the relative angle described with respect to fig. 7. Thus, as the input light passes through the output side 810 to generate an output light beam (the boundaries of which are represented by rays 807d, 807 e), some or all of the back reflected light may be directed away from the output waveguide 803. As with any of the embodiments described herein, an anti-reflective coating may be applied to the output side 810.

In some variations, it may be desirable for an optical element, such as an on-chip lens, to receive light from multiple output waveguides. For example, fig. 9 shows an optical system 900 having an output side 910 defining an optical element 925. The optical system further includes a plurality of output waveguides 903a, 903b, 903c, each of which is configured to direct light through the optical element 925 via the slab waveguide 915.

The slab waveguide 915 and the plurality of output waveguides 903a-903c may be defined in a waveguide layer of a photonic integrated circuit, such as previously described, where the side surface 910 is a lateral side surface of the photonic integrated circuit. Each of the output waveguides 903a-903c may be configured as previously described (e.g., the first output waveguide 903a includes a first waveguide core 920a defined by a pair of corresponding light confinement regions 905a, the second output waveguide 903b includes a second waveguide core 920b defined by a pair of corresponding light confinement regions 905b, and the third output waveguide 903c includes a third waveguide core 920c defined by a pair of corresponding light confinement regions 905 c). The output waveguides 903a-903c deliver input light beams (shown as individual rays 907a-907 c) into the slab waveguide 915. Slab waveguide 915 acts as a free propagation region allowing these beams to expand to form an output beam (represented by rays 907d, 907 e) before exiting the photonic integrated circuit through optical element 925. The input light may be introduced into the output waveguides 903a-903c at the same time or may be introduced into different output waveguides at different times. The shape and/or direction of the output light may vary depending on which output waveguides 903a-903c are transmitting the input light into the slab waveguide 915.

Optical element 925 may be configured in any suitable manner as described herein. For example, optical element 925 may be configured as an on-chip lens. Further, the plurality of output waveguides 903a-903c may be positioned at any suitable location and angle relative to each other and relative to the optical element 925, as desired. For example, the output waveguides 903a-903c may be positioned the same distance from the output side 910, or may be positioned different distances from the output side 910.

Fig. 10 is an example of an optical system 1000 including an output waveguide 1003 and a slab waveguide 1015 having an output side 1010, where the output side 1010 (which may be a side surface of a photonic integrated circuit) defines an optical element 1025. In this variation, optical element 1025 is shaped to form an aspheric on-chip lens. Unlike optical elements 1706 and 1736 of fig. 17A and 17B, optical element 1025 lens does not have a semicircular curve. In contrast, the radius of curvature of the vertical plane of optical element 1025 varies from the center of optical element 1025 to either end. The output waveguide 1003 (which may include a waveguide core 1020 defined by a pair of confinement regions 1005) may transfer input light into the slab waveguide 1015. The input light (whose boundaries are represented by rays 1007a, 1007 b) passes through an optical element 1025 to generate an output light beam (whose boundaries are represented by rays 1007d, 1007 e). In the variant shown in fig. 10, the optical element is shaped such that it directs the output beam to converge. In these cases, the concentrated light may be concentrated to a smaller spot than when using a spherical lens. Thus, when an aspherical lens is used instead of a spherical lens, fewer wavefront errors can be generated.

Fig. 11 and 12 are examples of optical systems that include a partially etched region between the output waveguide and the output side of the slab waveguide (which may form the output facet of the photonic integrated circuit). The partially etched region may act as a lens between the output waveguide and the output side that allows the input light to be redirected before it reaches the output side. Specifically, fig. 11 shows an optical system 1100 having a partially etched region 1150 between the output waveguide 1103 and the output side 1110 defining the optical element 1125. Fig. 12 shows an optical system 1200 having a partially etched region 1250 between an output waveguide 1203 and an output side 1210 that does not include optical elements.

Similar to the previous embodiments, in fig. 11, the output waveguide 1103 includes a waveguide core 1120 that is bounded and defined by a pair of light confining regions 1105 and terminates at a junction with the slab waveguide 1115. Input light (whose boundaries are represented by rays 1107a and 1107 b) introduced into slab waveguide 1115 from output waveguide 1103 will pass through partially etched region 1150 before reaching the output side 1110 of slab waveguide 1115 (which may form the output facet of a photonic integrated circuit). In particular, the input light may pass through the optical element 1125 to generate an output light beam (the boundaries of which are represented by rays 1107d, 1107 e), as previously described. Depending on the shape of the partially-etched region 1150, the partially-etched region 1150 may change its divergence and/or redirect the input beam as it passes through the partially-etched region. For example, in a variation shown in fig. 11, the partially etched region 1150 may partially focus the input light before it reaches the optical element 1125. In this way, the partially etched region 1150 and the optical element 1125 may collectively form a dual lens system to achieve a desired shape and direction of the output light emitted from the optical element 1125.

The partially etched region 1150 is shown as elliptical in fig. 11, but may be any shape such as, but not limited to, circular, square, rectangular, trapezoidal, asymmetric, etc. The partially etched region 1150 may be etched during a different process step than the etching step used to form the optical element 1125, as these features may be etched to two different depths. That is, the partially etched region 1150 may be a shallower etch than the etch used to define the optical element 1125. The partially etched region 1150 may be filled with additional material and may have a different refractive index than the surrounding slab waveguide 1115. For example, the partially etched region 1150 may be configured such that the additional material is positioned on the lower cladding layer (i.e., the cladding layer on which the waveguide layer defining slab waveguide 1115 is formed). Where the photonic integrated circuit includes an upper cladding layer, the 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.

The optical system 1200 of fig. 12 may function similarly to the optical system 1100, except that the output side 1210 does not include optical elements. Specifically, the output waveguide 1203 includes a waveguide core 1220 that is bounded and defined by a pair of light confinement regions 1205 and terminates at a junction with the slab waveguide 1215. Input light introduced into slab waveguide 1215 from output waveguide 1203, the boundaries of which are represented by rays 1207a and 1207b, will pass through partially etched region 1250 before reaching output side 1210 (which may be a side surface of a photonic integrated circuit) of slab waveguide 1215. In particular, the input light may pass through the output side 1210 to generate an output light beam (the boundaries of which are represented by rays 1207d, 1207 e), as previously described. Depending on the shape of the partially-etched region 1250, the partially-etched region 1250 may change its divergence and/or redirect the input beam as it 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.

Fig. 13 is an example of an optical system 1300 having a diffraction grating 1355 located on an output side 1310 of a slab waveguide 1315. Light may propagate through the output waveguide 1303, where the output waveguide 1303 includes a waveguide core 1320 bounded and defined by a pair of light confinement regions 1305. It will be appreciated that as light propagates through the output waveguide 1303, light propagates through the waveguide core 1320. The diffraction grating 1355 may receive light propagating through the slab waveguide 1315. The output light propagating through the diffraction grating 1355 may produce light of different orders (e.g., zero order, first order, second order, etc.). In some embodiments, first order light may appear on either side of the zero order, and may appear when the path light of light from other gratings is approximately equal to one wavelength of light. In some implementations, if the diffraction grating 1355 receives more than one wavelength of light, the output light may be decomposed into different wavelengths.

Fig. 14 is an example of an optical system 1400 having a metal 1460 located on a slab waveguide 1415. Metal 1460 may be deposited on slab waveguide 1415 and may act 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. Thus, the output side 1410 of the slab waveguide 1415 may emit an output beam having a different relative polarization than the input light carried by the output waveguide 1403.

In some embodiments, the light may include polarization, such as TE polarization and/or TM polarization. The metal 1460 may attenuate the TM polarization of light and pass the TE polarization of light, or may attenuate the TE polarization of light and pass the TM polarization of light. As used herein, when TE polarization of light passes, it is understood that relatively more TE polarization is allowed to propagate through the polarizer than TM polarization. Similarly, when the TM polarization of light passes, it is understood that relatively more TM polarization is allowed to propagate through the polarizer than TE polarization. In some examples, an absorber layer may be deposited under metal 1460 on slab waveguide 1415. The absorbing layer may reduce loss of selected light polarization therethrough. The terms "pass" and "attenuate" may be relative terms. In some examples, the term "pass" may indicate that the throughput of a first polarization may be greater than the throughput of a second polarization when the first polarization passes, and vice versa. In some examples, the term "attenuate" may indicate that when attenuating the second polarization, the second polarization is attenuated by a greater amount than the first polarization.

Although metal 1460 is shown as rectangular, the metal may be deposited in any suitable shape. In some embodiments, metal 1460 may be deposited on slab waveguide 1415 and extend to the shape of optical element 1425. In fig. 14, the optical element 1425 is a positive lens depicted as a semicircle, and in some examples, the metal may cover the area shown and also extend to cover the semicircle shape.

Fig. 15 is an example of an optical system 1500 having an optical element 1525 located in an angled output side 1510. Fig. 15 is an example of combining the different embodiments described herein with reference to fig. 5 and 8. The output side 1510 may be angled with respect to a plane 1511 perpendicular to an end surface of the output waveguide 1503 (which includes a waveguide core 1520 bounded and defined by a pair of light confinement regions 1505), wherein the output waveguide 1503 terminates in a slab waveguide 1515. The output side 1510 may be angled 1540 between the output side 1510 and a plane 1511 (shown as a dashed line). In other words, all light (the boundaries of which are represented by rays 1507a, 1507 b) may pass through the optical element 1525 of the output side 1510 at an angle even though the output waveguide 1503 is not positioned at an angle as in fig. 7. The output light (whose boundaries are represented by rays 1507d, 1507 e) may exit the optical element 1525. As previously described, the optical element 1525 may be any element described herein or any suitable optical element that achieves the desired type of output light.

In some cases, it may be desirable for the photonic integrated circuits and optical systems described herein to be capable of operating over a wide range of wavelengths. Depending on the intended use of a given optical system (e.g., performing spectral measurements), a light source unit as described herein may be configured to generate multiple wavelengths spanning tens or hundreds of nanometers, and various optical components of the optical system may need to accommodate wavelengths spanning part or all of that range. In these cases, it is desirable that a given optical component have similar performance levels, regardless of the wavelength of light it receives.

As mentioned previously, in the case where the output waveguide terminates in a slab waveguide, light will diffract as it enters the slab waveguide (which acts as a free propagation region). The diffraction angle of a given incident light depends on the ratio between its wavelength and mode size when it reaches the slab waveguide, which may result in different diffraction angles for incident light of different wavelengths. This in turn may result in a wavelength dependent change in the beam size in the free propagation region, which may result in a wavelength dependent change in the optical system performance.

To help reduce this wavelength dependence, the waveguide core of the output waveguide may be sized to be sufficiently narrow (e.g., via tapering) as it approaches the slab waveguide (e.g., the junction between the output waveguide and the slab waveguide) such that the mode size of the input light is proportional to the wavelength of the input light across a predetermined target wavelength range. Thus, when the output waveguide is configured to carry a target range of wavelengths, the width of the waveguide may be selected based on the target range of wavelengths.

Narrowing the output waveguide in this manner may provide improved diffraction angle uniformity across the target wavelength range, but this may also increase back reflection at the interface between the output waveguide and the slab waveguide. In particular, narrowing the output waveguide may result in modes for at least some of the wavelengths being poorly constrained and thereby experiencing a change in effective refractive index between the light confinement region defining the output waveguide and the slab waveguide. This change in effective refractive index produces back reflection at the junction between the output waveguide and the slab waveguide.

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 a varying effective refractive index before the output waveguide terminates. This may include varying the width of the waveguide core and/or the light confinement region near the junction. For example, fig. 19A shows an example of a photonic integrated circuit 1900 as described herein. Although fig. 19A only shows waveguide layer 1902 of photonic integrated circuit 1900, as previously discussed, photonic integrated circuit 1900 may also include a substrate, a lower cladding, and optionally an upper cladding.

Photonic integrated circuit 1900 includes a side surface 1904 that serves as an output facet through which light may be emitted from photonic integrated circuit 1900. In the variation shown in fig. 19A, side surface 1904 defines an optical element 1906 (which may be configured as any of the optical elements previously described). The photonic integrated circuit 1900 also includes an output waveguide 1908 and a slab waveguide 1915 defined in the waveguide layer 1902. In particular, the output waveguide 1908 includes a waveguide core 1912 that is bounded and defined by a pair of light confinement regions 1910a, 1910 b. The pair of light confinement regions includes a first light confinement region 1910a and a second light confinement region 1910b, each of which may be filled with cladding material or air, as previously discussed, to provide optical confinement to the waveguide core 1912. The output waveguide 1908 terminates in the slab waveguide 1915 at a junction between the output waveguide 1908 and the slab waveguide 1915. Thus, input light (not shown) may pass from the waveguide core 1912 to the slab waveguide 1915 and may exit the photonic integrated circuit 1900 via the side surfaces 1904 as previously described.

The output waveguide 1908 includes a refractive index adjustment region 1914 that is positioned at the junction between the output waveguide 1908 and the slab waveguide 1915 such that the distal end of the refractive index adjustment region 1914 coincides with the junction between the output waveguide 1908 and the slab waveguide 1915. The index adjustment region 1914 is configured to change the effective index of refraction experienced by light traveling through the output waveguide 1908 as it approaches the junction with the slab waveguide 1915. In the modification shown in fig. 19A, the width of one or both of the light confinement regions 1910a, 1910b narrows (i.e., decreases in a direction toward the junction) in the refractive index adjustment region 1914 as the light confinement region approaches the junction with the slab waveguide 1915. While the width of one or both of the light confinement regions 1910a, 1910b is shown in fig. 19A as narrowing in the refractive index adjustment region 1914, in other cases, the width of only one of the light confinement regions (i.e., the first light confinement region 1910a or the second light confinement region 1910 b) narrows in the refractive index adjustment region 1914.

In the variation shown in fig. 19A, the width of the waveguide core may remain constant within the index adjustment region 1914. Alternatively, the width of the waveguide core 1912 may adiabatically narrow within the refractive index adjustment region 1914 as the waveguide core 1912 approaches the junction with the slab waveguide 1915 (i.e., in a direction toward the junction). In these cases, the change in width of the light confinement regions 1910a, 1910b will spread the change in effective refractive index across the length of the refractive index adjustment region 1914, which will reduce the instantaneous refractive index change experienced by the back reflection of light associated with the change in effective refractive index at the termination of the output waveguide. In addition, the reduced width of the light confinement regions 1910a, 1910b at the junction provides a narrower surface to receive the back reflection generated at the side surface 1904. Thus, the back-reflected light is less likely to reflect from the light confinement regions 1910a, 1910b in a manner that ultimately results in the back-reflected light being coupled into the output waveguide 1908.

In the variation shown in fig. 19A, the decreasing width of the light-confining regions 1910a, 1910b taper linearly in a direction toward the junction. While the width is shown as tapering linearly to a zero width, in other cases the width may taper to a non-zero minimum width (which may depend in part on the manufacturing capabilities used to define the light-confining regions 1910a, 1910 b). In some of these variations, the width of one or both of the light confinement regions 1910a, 1910b is tapered non-adiabatically such that the mode shape of the input light carried by the waveguide core 1912 cannot change significantly within the refractive index adjustment region 1914. For example, while an adiabatic taper may require hundreds of microns to achieve a particular change in width of the light-confining regions 1910a, 1910b, a non-adiabatic taper as described herein may achieve the same change in width over a length of a few microns or less.

In other variations, the width of the light-confining regions 1910a, 1910b may be narrowed in a non-linear fashion. Fig. 19B illustrates one such variation of an example of photonic integrated circuit 1920 as described herein. Although fig. 19B only shows waveguide layer 1922 of photonic integrated circuit 1920, photonic integrated circuit 1920 may also include a substrate, a lower cladding, and optionally an upper cladding, as previously discussed. Photonic integrated circuit 1920 includes an output waveguide 1928 including a waveguide core 1932 defined and bounded by a first light-confining region 1930a and a second light-confining region 1930b, and a slab waveguide 1935 having side surfaces 1924 defining optical elements 1926. These components may be configured in the same manner as discussed herein with respect to fig. 19A, except that output waveguide 1928 has a different index adjustment region 1934.

The index adjustment region 1934 is positioned at the junction between the output waveguide 1928 and the slab waveguide 1935 such that the distal end of the 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 light confinement regions 1930a, 1930b are stepped. Specifically, the width of each of the light confinement regions 1930a, 1930b changes from a first width to a narrower second width within the index adjustment region 1934 (i.e., before the output waveguide 1928 terminates at the junction with the slab waveguide 1935). Where the output waveguide is configured to carry multiple wavelengths across a target wavelength range, the length of the portion of the light confinement regions 1930a, 1930b having the narrower second width may be selected to be one quarter of one of the wavelengths in the target wavelength range (e.g., a center wavelength within the target wavelength range). The width of the waveguide core 1932 may remain constant within the index adjustment region 1934. Alternatively, the width of the waveguide core 1932 may adiabatically narrow within the index adjustment region 1934 as the waveguide core 1932 approaches the junction with the slab waveguide 1935.

The index adjustment regions 1914 and 1934 described with respect to fig. 19A and 19B may be used in any optical component including a junction between an output waveguide and a slab waveguide. For example, fig. 20A shows an example of a photonic integrated circuit 2000 as described herein. Although fig. 20A only shows waveguide layer 2002 of photonic integrated circuit 2000, photonic integrated circuit 2000 may also include a substrate, a lower cladding layer, and optionally an upper cladding layer, as previously discussed. In this variation, photonic integrated circuit 2000 includes beam splitter 2004.

As shown, the waveguide layer includes an input waveguide 2006 that includes a waveguide core 2009 defined by light bounded and defined by a pair of light confining regions 2008a, 2008 b. The input waveguide 2006 may be configured identically to the output waveguide 1908 of fig. 19A, including a refractive index adjustment region 2010 configured identically to the refractive index adjustment region 1914 to reduce the width of each of the light confining regions 2008a, 2008b as it approaches the junction with the slab waveguide 2012 in the refractive index adjustment region 2010.

The slab waveguide 2012 acts as a free propagation region to optically couple the input waveguide 2006 to a plurality of output waveguides. Light introduced into slab waveguide 2012 from input waveguide 2006 will traverse the free propagation region to split the light between the plurality of output waveguides. Although the boundaries of slab waveguide 2012 are depicted as dashed lines in fig. 20A, it should be understood that the actual boundaries of slab waveguide 2012 may be located at any portion of waveguide layer 2002 that will not affect the operation of the optical splitter.

To define a plurality of output waveguides, the optical splitter 2004 includes a plurality of optical confinement regions 2016a-2016f and a plurality of waveguide cores 2014a-2014e. Each output waveguide is defined as one of the plurality of waveguide cores 2014a-2014e and a corresponding one of the plurality of light-confining regions 2016a-2016 f. For example, a first waveguide core 2014a may be bounded and defined by a first light confining region 2016a and a second light confining region 2016b to form a first output waveguide, while a second waveguide core 2014b may be bounded and defined by a second light confining region 2016b and a third light confining region 2016c to form a second output waveguide. While the beam splitter 2004 is shown in fig. 20A as having five output waveguides (i.e., one output waveguide per waveguide core of the plurality of waveguide cores 2014a-2014 e), it should be understood that the beam splitter 2004 may include any number of output waveguides as desired. Similarly, while these waveguide cores 2014a-2014e are shown in fig. 20A as having the same thickness, it should be understood that different output waveguides may include waveguide cores having different widths. The optical splitters described herein may be configured to split light received from an input waveguide uniformly or non-uniformly among a plurality of output waveguides, as desired.

The index adjustment region 2010 may allow the input waveguide 2006 to be sufficiently narrow to improve diffraction angle uniformity (as a function of wavelength) of light as it enters the slab waveguide 2012, but still reduce back reflection at the junction between the input waveguide 2006 and the slab waveguide 2012. In general, the optical splitter 2004 may have improved optical splitting performance across a wavelength range.

Fig. 20B illustrates one such variation of an example of a photonic integrated circuit 2020 as described herein. Although fig. 20B only shows the waveguide layer 2022 of the photonic integrated circuit 2020, as previously discussed, the photonic integrated circuit 2020 may also include a substrate, a lower cladding, and optionally an upper cladding. The photonic integrated circuit 2020 includes a beam splitter 2024 designed to split light introduced into the slab waveguide 2032 by the input waveguide 2026 between a plurality of output waveguides. As shown, the input waveguide 2026 includes a waveguide core 2009 defined and delimited by a first light confinement region 2028a and a second light confinement region 2028 b. The waveguide layer 2022 includes a plurality of waveguide cores 2034a-2034e and a plurality of light confinement regions 2036a-2036f that define a plurality of output waveguides. These components may be configured in the same manner as discussed herein with respect to the beam splitter 2004 of fig. 20A, except that the output waveguide 2026 has a different index adjustment region 2030. The refractive index adjustment region 2030 may be configured in the same manner as the refractive index adjustment region 1934 described herein with respect to fig. 19B. Specifically, the width of the light confinement regions 2028a, 2028b is stepwise. Specifically, the width of each of the light 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).

In other variations, the waveguide may be configured such that the width of the waveguide core increases as the waveguide approaches the junction with the slab waveguide. For example, fig. 21A shows an example of a photonic integrated circuit 2100 as described herein. Although fig. 21A only shows waveguide layer 2102 of photonic integrated circuit 2100, as previously discussed, photonic integrated circuit 2100 may also include a substrate, a lower cladding layer, and optionally an upper cladding layer.

Photonic integrated circuit 2100 includes a side surface 2104 that acts as an output facet through which light may be emitted from photonic integrated circuit 2100. In the variation shown in fig. 21A, the side surface 2104 defines an optical element 2106 (which can be configured as any of the optical elements previously described). The photonic integrated circuit 2100 also 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 light confinement regions 2110a, 2110 b. The pair of light confinement regions includes a first light confinement region 2110a and a second light confinement region 2110b, each of which may be filled with cladding material or air, as previously discussed, to provide optical confinement to the waveguide core 2112. The output waveguide 2108 terminates in a slab waveguide 2114 at the junction between the output waveguide 2108 and the slab waveguide 2114. Thus, input light (not shown) may pass from the waveguide core 2112 to the slab waveguide 2114 and may exit the photonic integrated circuit 2100 via the side surface 2104, as previously described.

The output waveguide 2108 includes a refractive index adjustment region 2116 configured to change the effective refractive index experienced by light traveling through the output waveguide 2108 as it approaches the junction with the slab waveguide 2114. The index adjustment region 2116 is positioned at the junction between the output waveguide 2108 and the slab waveguide 2114 such that the distal end of the index adjustment region 2116 coincides with the junction between the output waveguide 2108 and the slab waveguide 2114. In the modification shown in fig. 21A, the width of each of the light confinement regions 2110a, 2110b becomes narrower in the refractive index adjustment region 2116 as the light confinement region approaches the junction with the slab waveguide 2114. The width of the waveguide core 2112 increases within the index adjustment region 2116 as the width of the light confinement regions 2110a, 2110b decreases. The light confinement regions 1910a and 1910b shown in fig. 19A taper toward the waveguide core 1912 in the output waveguide 1908, while the light confinement regions 2110a and 2110b shown in fig. 21A taper away from the waveguide core 2112.

The increased width of the waveguide core 2112 in the index adjustment region 2116 provides a more gradual effective index transition of light as it travels from the output waveguide 2108 to the slab waveguide 2114, thereby reducing back reflection of light at the junction between the output waveguide 2108 and the slab waveguide 2114. In addition, the width of the waveguide core 2112 increases non-adiabatically in the refractive index adjustment region 2116. Thus, the increase in width does not significantly change the mode shape of the light traveling through the index adjustment region 2116 of the waveguide core 2112. This allows the waveguide core 2112 to be sized to provide improved uniformity of the diffraction angle across the target wavelength range, as previously described, while the non-adiabatic increase in the width of the waveguide core 2112 reduces back reflection without significantly affecting the uniformity.

Specifically, the output waveguide 2108 includes an additional region 2118 connected to the index adjustment region 2116 such that the index adjustment region 2116 is located between the additional region 2118 and the slab waveguide 2114. In some variations, the additional region 2118 has a constant width such that the width of the waveguide core 2112 is constant as it approaches the 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 is adiabatically narrowed. In this way, the third region may adiabatically taper the waveguide core 2112 from an initial width to a narrowed first width. The width of the waveguide core 2112 in the additional region 2118 will have a first width and will increase non-adiabatically from the first width to a second, wider width in the index adjustment region 2116.

In other variations, the width of the waveguide core 2112 is adiabatically narrowed in the additional region 2118 such 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 adiabatically tapered from an initial width to a first, narrower width in the additional region 2118, and may be non-adiabatically increased from the first width to a second, wider width in the index adjustment region 2116. It should be appreciated that the first width, the second width, and the selection of the length along which the waveguide core 2112 transitions between the first width and the second width may be selected as desired to achieve a particular balance of diffraction angle, diffraction angle uniformity as a function of wavelength, and amount of back-reflected light at the junction between the output waveguide 2108 and the slab waveguide 2114.

In other variations, the waveguide core of the output waveguide may be increased without a corresponding decrease in the width of the light confinement region 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 fig. 21B only shows the waveguide layer 2122 of the photonic integrated circuit 2120, 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 a first light-confining region 2130a and a second light-confining region 2130b and a slab waveguide 2134 having side surfaces 2124 that define optical elements 2126. The output waveguide 2128 includes a refractive index adjustment region 2136 connected to an additional region 2138.

Except for the refractive index adjustment region 2136, photonic integrated circuit 2120 is otherwise configured as described herein with respect to photonic integrated circuit 2100 of fig. 21A. The index adjustment region 2136 is positioned at the junction between the output waveguide 2128 and the slab waveguide 2134 such that the distal end of the index adjustment region 2136 coincides with the junction between the output waveguide 2128 and the slab waveguide 2134. As shown, while the width of the waveguide core 2132 increases from a first width to a wider second width within the index adjustment region 2136, the light confining regions 2130a, 2130b remain constant in width within the index adjustment region 2136. Accordingly, the first light confinement region 2130a and the second light confinement region 2130b are angled away from each other within the refractive index adjustment region 2136.

While the widths of the waveguide cores 2112 and 2132 linearly increase in the refractive index adjustment regions 2116 and 2136 in fig. 21A and 21B, the widths of the waveguide cores may increase in a nonlinear manner in other cases. Fig. 21C illustrates one such variation of an example of a photonic integrated circuit 2140 as described herein. Although fig. 21C only shows the waveguide layer 2142 of the photonic integrated circuit 2140, as previously discussed, the photonic integrated circuit 2140 may also include a substrate, a lower cladding layer, and optionally an upper cladding layer. Photonic integrated circuit 2140 includes an output waveguide 2148 including a waveguide core 2152 defined and bounded by a first light confining region 2150a and a second light confining region 2150b, and a slab waveguide 2154 having side surfaces 2144 defining optical elements 2146. The output waveguide 2148 includes a refractive index adjustment region 2156 connected to an additional region 2158.

Except for the index adjustment region 2156, the photonic integrated circuit 2140 is otherwise configured as described herein with respect to fig. 21A. The index adjustment region 2156 is positioned at the junction between the output waveguide 2148 and the slab waveguide 2154 such that the distal end of the index adjustment region 2156 coincides with the junction between the output waveguide 2148 and the slab waveguide 2154. Within the index tuning region 2156, the width of the waveguide core 2152 is stepped. Specifically, the width of waveguide core 2152 increases from a first width to a wider second width within index adjustment region 2156 (i.e., before output waveguide 2148 terminates at the junction with slab waveguide 2154). In some of these variations, the width of the light confining regions 2150a, 2150b may decrease as the width of the waveguide core 2152 increases.

Where the output waveguide is configured to carry multiple wavelengths across a target wavelength range, the length of the portion of waveguide core 2152 having the wider second width may be selected to be one quarter of the wavelength of one of the wavelengths in the target wavelength range (e.g., the center wavelength within the target wavelength range).

The output waveguides 2108, 2128 and 2148 of fig. 21A-21C may alternatively be used as input waveguides for a beam splitter as previously described. For example, fig. 22A shows a variation of photonic integrated circuit 2200 with waveguide layer 2202 defining optical splitter 2204. The optical splitter 2204 includes a slab waveguide 2214, a plurality of waveguide cores 2216a-2216e forming a plurality of output waveguides, and light confining regions 2218a-2218f. Except for the input waveguide 2206, the photonic integrated circuit 2200 is otherwise configured as described herein with respect to the photonic integrated circuit 2000 of fig. 20A. In this variation, the input waveguide 2206 is configured the same as the output waveguide 2108 of fig. 21A.

Specifically, the input waveguide 2206 includes a waveguide core 2212 bounded and defined by a pair of light confining regions 2208a, 2208 b. 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 described. The width of each of the light confining regions 2108a, 2108b narrows in the refractive index adjustment region 2210 as the light confining region approaches the junction with the slab waveguide 2214. Similarly, the width of the waveguide core 2212 increases with decreasing widths of the light confining regions 2210a, 2210b within the refractive index adjusting region 2210. The additional region 2211 may be configured identical to the additional region 2118 of fig. 21A.

Fig. 22B shows another variation of 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-2236e and optical confinement regions 2238a-2238f that form a plurality of output waveguides. 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, 2228 b. The input waveguide 2226 includes an additional region 2231 connected to the refractive index transition region 2230, as previously described. Except for the refractive index transition region 2230, the photonic integrated circuit 2220 is configured as described herein with respect to the photonic integrated circuit 2200 of fig. 22A. In this variation, the refractive index transition region 2230 is configured the same as the output waveguide 2128 of fig. 21B. As shown, although the width of the waveguide core 2232 increases from a first width to a wider second width within the index adjustment region 2230, the light confining regions 2228a, 2228b remain constant in width within the index adjustment region 2230. Accordingly, the first light confining regions 2228a and the second light confining regions 2228b are angled away from each other within the refractive index adjustment region 2230.

Fig. 22C shows another variation of photonic integrated circuit 2240 having a waveguide layer 2242 defining a splitter 2244. The optical splitter 2244 includes a slab waveguide 2254, a plurality of waveguide cores 2256a-2256e and optical confinement regions 2258a-2258f that form a plurality of output waveguides. Splitter 2244 includes an input waveguide 2246 having a waveguide core 2252 defined and bounded by a pair of optically confined regions 2248a, 2248 b. The input waveguide 2246 includes an additional region 2251 connected to the refractive index transition region 2250, as previously described. Except for refractive index transition region 2250, photonic integrated circuit 2240 is configured as described herein with respect to photonic integrated circuit 2200 of fig. 22A. In this variation, the refractive index transition region 2250 is configured the same as the output waveguide 2148 of fig. 21C. In particular, the width of waveguide core 2252 increases in a stepwise manner from a first width to a second, wider width within index adjustment region 2250, as previously discussed.

It should be appreciated that for each of the embodiments described herein with respect to fig. 19A-22C, various dimensions of the refractive index transition region may be selected to achieve a desired balance of diffraction angle, diffraction angle uniformity as a function of wavelength, and amount of back-reflected light, as previously described. In addition, it should be understood that the refractive index transition regions described herein with respect to fig. 19A-22C may be applied to any of the embodiments described herein with respect to fig. 2-18D, as well as any other optical component including transitions from waveguides (e.g., bar waveguides, rib waveguides, etc.) and slab waveguides, such as optical multiplexers, optical demultiplexers, etc.

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 itself indicate a need to perform the steps in that order. Furthermore, although depicted or implied as non-concurrent (e.g., because one step is described after the other steps), some steps may be performed concurrently. Furthermore, the illustration of a process by its description 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 steps thereof must be one or more of the examples, and does not imply that the illustrated process is preferred.

Representative applications of methods and apparatus in accordance with the present disclosure are described in this section. These examples are provided solely to add context and aid in the understanding of the examples. It will be apparent, therefore, to one skilled in the art, that the examples may be practiced without some or all of the specific details. Other applications are possible, such that the following examples should not be taken as limiting.

While the disclosed examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. It is to be understood that such changes and modifications are to be considered as included within the scope of the disclosed examples as defined by the appended claims.

Additional detailed description of the embodiments

Embodiment 1: a photonic integrated circuit, the photonic integrated circuit comprising:

A substrate;

A cladding layer; and

A waveguide layer, the waveguide layer comprising:

A slab waveguide having a side surface; and

An output waveguide, the output waveguide comprising:

A first light confinement region;

a second light confinement region; and

A waveguide core located between the first light confinement region and the second light confinement region; wherein:

the side surface of the slab waveguide defines an optical element forming a cylindrical lens having a semicircular curve;

The output waveguide terminating in the slab waveguide at a junction between the output waveguide and the slab waveguide; and

The output waveguide is positioned such that input light introduced from the output waveguide into the slab waveguide exits the photonic integrated circuit through the side surface.

Embodiment 2: the photonic integrated circuit of embodiment 1, wherein:

The semicircular curve has a center of curvature; and

The output waveguide is laterally offset with respect to the center of curvature.

Embodiment 3: the photonic integrated circuit of embodiment 2, wherein:

the junction between the output waveguide and the slab waveguide is aligned with the center of curvature.

Embodiment 4: the photonic integrated circuit of embodiment 2, wherein:

The junction between the output waveguide and the slab waveguide is positioned behind the center of curvature such that the center of curvature is positioned between the junction and the optical element.

Embodiment 5: the photonic integrated circuit of embodiment 2, wherein:

the junction between the output waveguide and the slab waveguide is positioned in front of the center of curvature such that the junction is positioned between the junction and the optical element.

Embodiment 6: the photonic integrated circuit of any of embodiments 1-5, wherein:

The waveguide layer includes a partially etched region between the output waveguide and the side surface of the slab waveguide such that the input light introduced into the slab waveguide from the output waveguide passes through the partially etched region.

Embodiment 7. The photonic integrated circuit of any of embodiments 1-6, wherein the output waveguide includes a refractive index adjustment region at the junction in which a width of one or both of the first light confinement region and the second light confinement region decreases in a direction toward the junction.

Embodiment 8. The photonic integrated circuit of any of embodiments 1-7, wherein the output waveguide includes a refractive index adjustment region at the junction in which the width of the waveguide core increases in a direction toward the junction.

Embodiment 9: a photonic integrated circuit, the photonic integrated circuit comprising:

A waveguide layer, the waveguide layer comprising:

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 comprising:

A first light confinement region;

a second light confinement region; and

Each optical element of the plurality of optical elements is associated with a corresponding slab waveguide of the plurality of slab waveguides and a corresponding output waveguide of the plurality of output waveguides such that input light introduced into the corresponding slab waveguide from the corresponding output waveguide exits the photonic integrated circuit through the optical element.

Embodiment 10: the photonic integrated circuit of embodiment 9, wherein:

Each optical element forms an on-chip lens.

Embodiment 11: the photonic integrated circuit of embodiment 10, wherein:

each of the plurality of optical elements forms a cylindrical lens having a semicircular curve with a center of curvature.

Embodiment 12: the photonic integrated circuit of embodiment 11, wherein:

Each output waveguide of the plurality of output waveguides is laterally offset from the center of curvature of the optical element associated with the output waveguide.

Embodiment 13: the photonic integrated circuit of any of embodiments 10 to 12,

Wherein:

All of the plurality of slab waveguides are optically connected.

Embodiment 14: an optical system, the optical system comprising:

A light source unit;

a photonic integrated circuit, the photonic integrated circuit comprising:

A side surface; and

A plurality of emitters optically connected to the light source unit, each of the emitters

The device comprises:

An optical element formed in the side surface;

A slab waveguide; and

An output waveguide positioned such that input light introduced into the slab waveguide from the output waveguide exits the photonic integrated circuit through the optical element;

And

A controller configured to control the plurality of emitters to emit output light.

Embodiment 15: the optical system of embodiment 14, wherein:

Each of the plurality of emitters has a common configuration such that each emitter generates an output beam having the same shape and direction.

Embodiment 16: the optical system according to any one of embodiments 14 to 15, wherein the photonic integrated circuit comprises:

a plurality of phase shifters, each of the plurality of phase shifters controllable to adjust a phase of light carried by an output waveguide of a corresponding transmitter.

Embodiment 17: the optical system of embodiment 16, wherein the controller is configured to selectively control the phase of the output light emitted by each of the plurality of emitters.

Embodiment 18: the optical system according to any one of embodiments 14-17, wherein the controller is configured to selectively control which of the plurality of emitters emits the output light.

Embodiment 19: the optical system according to any one of embodiments 14-18, wherein the controller is configured to selectively control the intensity of the output light emitted by each of the plurality of emitters.

Embodiment 20: the optical system according to any one of embodiments 14-19, wherein the controller is configured to selectively control one or more wavelengths of the output light emitted by each of the plurality of emitters.

Embodiment 21: a photonic integrated circuit, the photonic integrated circuit comprising:

A substrate;

A cladding layer; and

A waveguide layer, the waveguide layer comprising:

A slab waveguide; and

A waveguide, the waveguide comprising:

A first light confinement region;

a second light confinement region; and

the waveguide terminating in the slab waveguide at a junction between the waveguide and the slab waveguide; and

The waveguide includes a refractive index adjustment region at the junction, in which a width of one or both of the first light confinement region and the second light confinement region decreases in a direction toward the junction.

Embodiment 22: the photonic integrated circuit of embodiment 21, wherein the waveguide layer comprises:

A beam splitter, the beam splitter comprising:

The slab waveguide;

the waveguide; and

A plurality of output waveguides, wherein:

The optical splitter is configured such that input light introduced from the waveguide into the slab waveguide is split between the plurality of output waveguides.

Embodiment 23: the photonic integrated circuit of embodiment 21, wherein:

the waveguide layer includes side surfaces defining an optical element; and

The waveguide is positioned such that the input light introduced from the waveguide into the slab waveguide exits the photonic integrated circuit through the side surface.

Embodiment 24: the photonic integrated circuit of embodiment 23, wherein:

The optical element forms an on-chip lens.

Embodiment 25: the photonic integrated circuit of any of embodiments 23-24, wherein:

the optical element includes a diffraction grating.

Embodiment 26: the photonic integrated circuit of any of embodiments 21-25, wherein:

the width of the waveguide core is constant in the index adjustment region.

Embodiment 27: the photonic integrated circuit of any of embodiments 21-25, wherein:

The width of the waveguide core is adiabatically narrowed in a direction toward the junction in the refractive index adjustment region.

Embodiment 28: the photonic integrated circuit of any of embodiments 21-25, wherein:

the width of the waveguide core increases non-adiabatically in the direction toward the junction in the refractive index adjustment region.

Embodiment 29: the photonic integrated circuit of any of embodiments 21-28, wherein:

the width of one or both of the first light confinement region and the second light confinement region decreases linearly in a direction toward the junction.

Embodiment 30: a photonic integrated circuit, the photonic integrated circuit comprising:

A substrate;

A cladding layer; and

A waveguide layer, the waveguide layer comprising:

A slab waveguide; and

A waveguide, the waveguide comprising:

A first light confinement region;

a second light confinement region; and

The waveguide includes a refractive index adjustment region at the junction, in which a width of the waveguide core increases in a direction toward the junction.

Embodiment 31: the photonic integrated circuit of embodiment 30, wherein the waveguide layer comprises:

A beam splitter, the beam splitter comprising:

The slab waveguide;

the waveguide; and

A plurality of output waveguides, wherein:

Embodiment 32: the photonic integrated circuit of embodiment 30, wherein:

the waveguide layer includes side surfaces defining an optical element; and

The waveguide is positioned such that input light introduced from the waveguide into the slab waveguide exits the photonic integrated circuit through the side surface.

Embodiment 33: the photonic integrated circuit of embodiment 32, wherein:

The optical element forms an on-chip lens.

Embodiment 34: the photonic integrated circuit of any of embodiments 30-33, wherein:

the width of the waveguide core increases non-adiabatically in the index adjustment region.

Embodiment 35: the photonic integrated circuit of any of embodiments 30-34, wherein:

The widths of the first light confinement region and the second light confinement region are constant in the refractive index adjustment region.

Embodiment 36: the photonic integrated circuit of any of embodiments 30-35, wherein:

The waveguide includes an additional region in which a width of the waveguide core is adiabatically narrowed in a direction toward the junction; and

The refractive index adjustment region is located between the additional region and the bonding portion.

Embodiment 37: the photonic integrated circuit of any of embodiments 30-36, wherein the width of the waveguide core increases linearly in the index adjustment region.

Embodiment 38: an optical system, the 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 comprising:

A substrate;

A cladding layer; and

A waveguide layer, the waveguide layer comprising:

A slab waveguide; and

A waveguide, the waveguide comprising:

A first light confinement region;

a second light confinement region; and

The waveguide includes a refractive index adjustment region positioned wherein a width of each of the first and second light confinement regions narrows from a first width to a second width in a direction toward the junction.

Embodiment 39: the optical system of embodiment 38, wherein:

the portion of each of the first light confinement region and the second light confinement region having the second width has a length; and

The length is one quarter of a wavelength within the target wavelength range.

Embodiment 40: the optical system according to any one of embodiments 38 to 39, wherein:

The width of the waveguide core increases from a third width to a fourth width in the index adjustment region.

Claims

1. An optical system, the optical system comprising:

a slab waveguide, the slab waveguide comprising:

A free propagation region; and

An output side; and

An output waveguide defined in the slab waveguide, the output waveguide comprising:

a waveguide core through which light propagates, and comprising a first side and a second side opposite the first side;

A first light confining region adjacent to the first side of the waveguide core; and

A second light confining region adjacent to the second side of the waveguide core, wherein:

The output waveguide terminates before the output side of the slab waveguide and before the free propagation region;

the light exits the waveguide core into the free propagation region; and

The light exits the free propagation region at the output side, reducing back reflection into the output waveguide.

2. The optical system of claim 1, wherein:

The output side of the slab waveguide includes an optical element through which the light passes;

The optical element is defined in the output side of the slab waveguide; and

The optical element serves as a positive or negative lens.

3. The optical system of claim 1, wherein the output side of the slab waveguide comprises an optical element that collimates the light.

4. The optical system of claim 1, wherein:

The output side of the slab waveguide includes an optical element; and

The optical system further includes an anti-reflective coating on the optical element.

5. The optical system of any one of claims 1-4, wherein the output side of the slab waveguide comprises an aspheric optical element.

6. The optical system of any one of claims 1-5, wherein the output side of the slab waveguide comprises a diffraction grating.

7. The optical system of any one of claims 1-6, further comprising a metal that polarizes the light propagating through the slab waveguide and is positioned on the slab waveguide between the output waveguide and the output side of the slab waveguide.

8. The optical system according to any one of claims 1 to 7, wherein:

the output waveguide is one of a plurality of output waveguides for emitting light into the slab waveguide; and

The optical system further includes an optical element defined in a profile of the output side of the slab waveguide and configured to combine light from the plurality of output waveguides.

9. A method for guiding light, the method comprising:

Propagating the light through an output waveguide;

Transmitting the light from the output waveguide into a free propagation region of a slab waveguide; and

The light is passed from the slab waveguide through an optical element located in an output side of the slab waveguide, thereby reducing back reflection of the light from the output side of the slab waveguide.

10. The method of claim 9, wherein emitting the light from the output waveguide comprises: the light is propagated from the output waveguide through the free propagation region of the slab waveguide.

11. The method of any one of claims 9 to 10, the method further comprising: a partially etched region is formed between the output waveguide and the output side of the slab waveguide such that the light emitted from the output waveguide passes through the partially etched region.

12. The method of claim 11, wherein the partially etched region acts as a positive lens.

13. The method of any of claims 11-12, wherein the output side of the slab waveguide includes the optical element.

14. An optical system, the optical system comprising:

A slab waveguide;

an output waveguide defined in the slab waveguide and comprising:

a waveguide core that allows light to pass therethrough;

a first light confining 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, the second side opposite the first side of the waveguide core; and

An optical element defined in an output side of the slab waveguide, wherein the output waveguide terminates before the output side of the slab waveguide such 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 back reflection of the light out of the optical element and into the output waveguide.

15. The optical system of claim 14, wherein:

the optical element is part of the slab waveguide and includes a positive or negative radius of curvature for guiding a direction of outgoing light with respect to an optical axis; and

The optical system further includes an anti-reflective coating applied over the optical element to reduce back reflection of light passing through the optical element.

16. The optical system according to any one of claims 14 to 15, wherein:

the output waveguide is angled with respect to the output side of the slab waveguide.

17. The optical system of any one of claims 14 to 16, wherein the optical element diverges the light passing therethrough.

18. The optical system according to any one of claims 14 to 17, further comprising:

a planar metal layer adjacent to the slab waveguide, wherein:

the planar metal layer extends over the optical element; and

The planar metal layer is located in a region between the output waveguide and the output side of the slab waveguide.

19. The optical system of any one of claims 14 to 15 or 17 to 18, wherein the output waveguide is positioned perpendicular to the output side of the slab waveguide.

20. The optical system of any one of claims 14 to 19, wherein the output waveguide includes a refractive index adjustment region in which a width of the waveguide core increases non-adiabatically in a direction toward the slab waveguide.