Photonic integrated circuit

Abstract

The present disclosure relates to a Photonic Integrated Circuit, PIC, device (200) including: a cladding structure (202); and a plurality of waveguide structures (204) disposed in the cladding structure (202), wherein each waveguide structure (204) includes an output facet (208) for outputting light from the waveguide structure (204), the output facet (208) being disposed at an output side (214) of the cladding structure (202), wherein the output side (214) of the cladding structure (202) is structured such that the respective output facet (208) of each waveguide structure (204) is at a respective distance from a reference plane (230) that is perpendicular to a main emission direction of light by the plurality of waveguide structures (204) wherein the plurality of waveguide structures (204) includes, at least: a first waveguide structure (204-1) configured to guide light having a first wavelength, wherein the output side (214) of the cladding structure (202) is structured such that a first output facet (208-1) of the first waveguide structure (204-1) is at a first distance from the reference plane (230); and a second waveguide structure (204-2) configured to guide light having a second wavelength different from the first wavelength, wherein the output side (214) of the cladding structure (202) is structured such that a second output facet (208-2) of the second waveguide structure (204-2) is at a second distance from the reference plane (230), different from the first distance.

Description

P96280 from P92961 1PHOTONIC INTEGRATED CIRCUITTechnical Field

[0001] The present disclosure relates generally to a photonic integrated circuit (PIC) having an output side adapted to define different output positions for different waveguide structures.Background

[0002] In general, a photonic integrated circuit (PIC) is a chip that includes photonic components that define a circuit, in which photons are transported and processed to implement various functionalities. A PIC may include various integrated optical components that constitute building blocks of the circuit, e.g., waveguides, optical amplifiers, optical splitters, modulators, light sources, light detectors, and the like. PICs have advantageous properties that make them an attractive alternative to electronic circuits, such as a fast operation, a relatively low energy consumption and heat generation, ease of miniaturization, and the like. PICs may be applied in various different technological fields, such as for communication systems, data processing systems, biomedical sensing, light-based sensing (e.g., Light Detection and Ranging, LIDAR), quantum computing, etc. Thus, improvements in the field of photonic integrated circuits may be of particular relevance for the further advancements of several technologies.Brief Description of the Drawings

[0003] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various aspects of the invention are described with reference to the following drawings, in which:FIG.1 A and FIG. IB show a PIC pitch converter, in a schematic representation according to various aspects;FIG.2A to FIG.2D show a PIC device, in a schematic representation according to various aspects;FIG.2E shows a schematic front view of the PIC device, according to various aspects;FIG.2F shows different configurations for the end portion of a waveguide structure at the coupler edge, in a schematic representation according to various aspects;P96280 from P92961 2FIG.3A shows a system including the PIC device and a lens optically coupled with the PIC device, in a schematic representation according to various aspects;FIG.3B shows the system of FIG.3A further including a plurality of light sources optically coupled with the PIC device, in a schematic representation according to various aspects;FIG.4A and FIG.4B show an exemplary realization of the PIC device, in a schematic representation according to various aspects;FIG.5 A and FIG.5B show an exemplary realization of the PIC device, in a schematic representation according to various aspects;FIG.6 A and FIG.6B show an exemplary realization of the PIC device, in a schematic representation according to various aspects;FIG.7 shows a schematic flow diagram of a method of forming a PIC device, according to various aspects; andFIG.8 A to FIG.8G show results of simulations of the operation of the PIC device, according to various aspects.Description

[0004] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and aspects in which the invention may be practiced. These aspects are described in sufficient detail to enable those skilled in the art to practice the invention. Other aspects may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various aspects are not necessarily mutually exclusive, as some aspects may be combined with one or more other aspects to form new aspects. Various aspects are described in connection with methods and various aspects are described in connection with devices (e.g., a PIC device). However, it is understood that aspects described in connection with methods may similarly apply to the devices, and vice versa.

[0005] In general, photonic integrated circuits exploit optical components to implement various functionalities at chip level. In this context, photons are used to transport information within the circuit, and the integrated optical components carry out various manipulations of the photons, such as amplification, detection, filtering, and the like. Photonic integrated circuits are usually fabricated using wafer-level processing techniques, e.g., including etching, material deposition, photolithography, and the like. In a PIC, optical components may be integrated withP96280 from P92961 3 a relatively high density in a single chip, thus providing an attractive approach for the implementation of multiple functionalities in a miniaturized device.

[0006] Various materials may be used for fabricating PICs, e.g., for use as a substrate on which the optical components are formed or for use as materials with which the optical components are fabricated. Exemplary materials for fabrication of PICs may include semiconductor materials, dielectric materials, crystal materials, and the like. For example, PICs may include silicon nitride (SiN), indium phosphide (InP), gallium arsenide (GaAs), lithium niobate (LiNbCh), as examples. The type of material may be selected depending on the fabrication technique to be used, and depending on the wavelength of interest of the light to be manipulated in the PIC.

[0007] A typical component in a PIC device may be waveguides, which are used to transport light within the circuit. A waveguide may receive light at an input side (e.g., from a coupled light source), and may deliver the light at an output side, e.g., for further propagation outside of the PIC. In this context, several optical aberrations may occur, in particular for PICs having waveguides that guide light of different colors. Illustratively, at the output side at which the light from the waveguides is directed towards a further optical component, such as a lens, several aberrations may be observed, e.g., due to the different colors of the light, due to the different spatial position of the output light rays, due to properties of the lens, and the like.

[0008] These aberrations may include, for example, longitudinal and / axial chromatic aberrations, due to which light of different colors is focused at different focal points along the optical axis of the lens towards which the output of the waveguides is directed. As another example, the aberrations may include astigmatism, such that light from different planes is focused at different focal points. As a further example, the aberrations may include Koma aberrations (illustratively, spheric aberration and astigmatism), such that off-axis point sources appear distorted. As a further example, the aberrations may include a curved focal plane of the lens (rather than a planar focal plane).

[0009] In this regard, FIG.1A and FIG.1B show an exemplary PIC pitch converter 100 in different configurations 100a, 100b, in a schematic representation according to various aspects. The PIC pitch converter 100 may include multiple waveguides 102, each coupled to a respective light-source 104 (e.g., a respective edge-emitting laser). In the exemplary scenario of FIG.1 A and FIG. IB, the PIC pitch converter 100 may include a first waveguide 102-1 coupled to a blue light source 104-1, a second waveguide 102-2 coupled to a green light source 104-2, and a third waveguide 102-3 coupled to a red light source 104-3. At the output side, the waveguides 102 may be optically coupled with a lens 106 that collimates the output light.P96280 from P92961 4

[0010] The configuration 100a in FIG.1A illustrates a multicolor pitch converter 100a. The light emitted by three individual light sources 104 (e.g., three individual lasers, red, green and blue) may be imaged and / or scanned by a single optical system, for example inside augmented reality (AR) glasses. As the light sources 104 may consist of different material systems, they cannot be fabricated such that they emit the light close enough to enable imaging in a common and small optical system. For this purpose, a pitch converter 100 in PIC may be used. The light is coupled from the light sources 104 into three waveguides 102 and these waveguides 102 are structured such that their out-coupling surfaces are much closer together than their in-coupling surfaces. This enables using the same optics for imaging, still creating distinct light paths for each color. The challenge is that the common optics (illustratively, the lens 106) will have a different focal length for each color, unless a complex achromatic optical system is used, thus potentially introducing optical aberrations in the system.

[0011] The configuration 100b in FIG. IB illustrates a multi -ridge pitch converter 100b, which is designed to convert multiple channels of red, green and blue light sources 104 (e.g., lasers). Illustratively, in this scenario the light sources 104 may include multiple channels for emitting light, and the waveguides 102 may correspondingly include multiple waveguide channels for guiding the light. The resulting output extends over a larger area (width), as a minimum pitch of a few micrometers (pm) is required to avoid optical crosstalk between adjacent waveguides 104. Hence, the curvature of the focal plane 108 of standard lenses results in improper focusing for some of the outputs, even if their wavelength is identical, thus potentially introducing optical aberrations in the system.

[0012] The correction of optical aberrations in the PIC pitch converter 100 or, more in general, in PIC devices in which waveguides are used to output light from the circuit, may be corrected by using complex optical systems to collect the output light. Illustratively, while a simple lens may present the aberrations described above in relation to the focusing of the light, more complex optical systems (e.g., including an achromatic doublet lens having two lenses attached to each other) may compensate for the aberrations (e.g., for chromatic aberration). However, the use of such more complex lenses increases the costs and the volume of the system, and is thus unattractive in the context of cost-effective and miniaturized devices.

[0013] Aspects of the present disclosure are related to a PIC device having an adapted configuration of the output side that pre-compensates at least some of the potential optical aberrations, without the need for complex optical systems to collect the output light. According to the configuration proposed herein, the output side of the PIC may be structured to obtain different outcoupling positions for different waveguides (e.g., waveguides guiding differentP96280 from P92961 5 colors of light). The relative misalignment of the output facets of the waveguides may be configured to reduce or ideally eliminate the optical aberrations mentioned above, in particular chromatic aberrations and the curved focal plane of the lens.

[0014] Illustratively, aspects of the present disclosure may be based on the realization that rather than having a straight edge of the PIC chip at the output side, and accordingly the output facets of the waveguides all at the same position, the out-coupling surface of the PIC chip may be structured in such a way that the output facet of each waveguide is at a respective position, e.g., shifted with respect to the output facets of the other waveguides. According to various aspects, the structuring may be configured such that the output facets of the waveguides are each at a respective distance from a plane perpendicular to the optical axis of the lens towards which the waveguides emit light. In this scenario, light from different waveguides (e.g., light of different colors) may propagate along a longer or shorter distance before reaching the lens, thus pre-compensating at least some of the optical aberrations mentioned above.

[0015] By way of illustration, the PIC device proposed herein may include a plurality of waveguide structures, and the out-coupling side of the PIC device may be structured such that at least a first output facet of a first waveguide structure is shifted with respect to a second output facet of a second waveguide structure along a direction parallel to a main emission direction of light by the waveguide structures (e.g., along a direction parallel to an optical axis of the lens towards which the waveguide structures emit light). Optionally, the first output facet and / or second output facet may be shifted with respect to a third output facet of a third waveguide structure, to a fourth output facet of a fourth waveguide structure, etc. The lateral shift may be adapted according to system parameters, such as wavelength of the light, type of lens, properties of the lens, etc., to pre-compensate the optical aberrations.

[0016] According to various aspects, a PIC device includes: a cladding structure; and a plurality of waveguide structures disposed in the cladding structure, wherein each waveguide structure includes: an input facet for coupling light into the waveguide structure; and an output facet for outputting light from the waveguide structure, the output facet being disposed at an output side of the cladding structure, wherein the output side of the cladding structure is structured such that the respective output facet of each waveguide structure is at a respective distance from a reference plane that is normal to the light output direction of the plurality of waveguide structures. In some aspects, the respective output facet of each waveguide structure is at a respective distance from a reference plane that is normal to the optical axis of a lens that is optically coupled with the output facets of the waveguide structures.P96280 from P92961 6

[0017] According to various aspects, a method of forming a PIC device includes: forming a cladding structure; forming a plurality of waveguide structures in the cladding structure, wherein each waveguide structure includes: an input facet for coupling light into the waveguide structure; and an output facet for outputting light from the waveguide structure, the output facet being disposed at an output side of the cladding structure; and structuring the output side of the cladding structure such that the respective output facet of each waveguide structure is at a respective distance from a reference plane that is normal to the light output direction of the plurality of waveguide structures. In some aspects, the respective output facet of each waveguide structure is at a respective distance from a reference plane that is normal to the optical axis of a lens that is optically coupled with the output facets of the waveguide structures.

[0018] The term “photonic integrated circuit” may be used herein as commonly understood in the art, to describe a device (e.g., a chip or microchip) in which photonic components are integrated in a single platform. In the present disclosure particular reference is made to a PIC device that includes a plurality of waveguide structures, to illustrate the principles behind the adapted configuration proposed herein. It is however understood that the PIC device may include further photonic components in addition to the waveguide structures, e.g., further photonic components that operate independently from the waveguide structures and / or further photonic components that operate together with the waveguide structures. Thus, in some aspects the photonic components of the PIC device may consist of the waveguide structures, without any additional photonic component present. In other aspects, the PIC device may include one or more additional photonic components, such as a ring resonator, an optical coupler, an optical modulator, a photo diode, a photonic crystal, and the like.

[0019] In some aspects, the “PIC device” described herein may be a self-standing circuit configured to implement an optical functionality (e.g., a waveguiding functionality). In this scenario, the PIC device may be an independent component within a system, in which the PIC device contributes to the operation of the system via its optical functionality, e.g., to guide light from a plurality of light sources towards a lens. In other aspects, the “PIC device” described herein may be part of a more complex PIC. Illustratively, in this other scenario the PIC device may be understood as a component for use in a PIC, in which the PIC device implements a certain optical functionality (e.g., a waveguiding functionality) in the context of a more complex optical operation further carried out by other components of the PIC. The term “PIC device” may be used to refer to the device adapted as described herein in both cases.

[0020] FIG.2A to FIG.2D show various configurations 200a-200d of an adapted PIC device 200, in a schematic representation, according to various aspects. The PIC device 200 in FIG.2AP96280 from P92961 7 to FIG.2D is illustrated in a schematic manner to introduce the relevant aspects of the approach proposed in the present disclosure. Various exemplary realizations of the PIC device 200 will be discussed in further detail in relation to FIG.4A to FIG.6B.

[0021] In general, the PIC device 200 may include a cladding structure 202, and a plurality of waveguide structures 204 disposed in the cladding structure 202. The waveguide structures 204 may be embedded in the cladding structure 202, e.g., between an upper cladding portion and a lower cladding portion (see also FIG.2E), e.g., such that each waveguide structure 204 is completely surrounded by the material of the cladding structure 202 (e.g., except for an output facet of the waveguide structure 204). The cladding structure 202 may thus be understood as a surrounding medium in which the waveguide structures 204 are formed. A waveguide structure 204 may illustratively a light path that is integrated or embedded in the cladding material.

[0022] A waveguide structure 204 may be configured to (wave)guide light, as commonly known in the art. Illustratively, a waveguide structure 204 may have a refractive index greater than the refractive index of the cladding structure 202 (at the same wavelength), such that total internal reflection occurs at the interface between the waveguide structure 204 and the cladding structure 202 causing confinement of light within the waveguide structure 204. A waveguide structure 204 may be configured to guide light having a certain wavelength (e.g., a certain color in case of visible light), or a wavelength in a certain range. In this regard, the material of the waveguide structure 204 may be selected according to the wavelength of the light to be guided via the waveguide structure 204. Each waveguide structure 204 may have a refractive index greater than the refractive index of the cladding structure 202 at least at the wavelength of interest for that waveguide structure 204, or at least in the wavelength range of interest for that waveguide structure 204.

[0023] In FIG.2A to FIG.2D, the PIC device 200 is shown with three waveguide structures 204, e.g., a first waveguide structure 204-1, a second waveguide structure 204-2, and a third waveguide structure 204-3. A configuration with three waveguide structures 204 may represent a relevant use case for the PIC device 200, considering that the three waveguide structures 204 may be configured to guide light of different colors, e.g., red, blue, and green, which may be used to produce a wide range of colors at the output. Thus, in some aspects the PIC device 200 may include exactly three waveguide structures 204 (e.g., one configured to guide blue light, one configured to guide red light, and one configured to guide green light). It is however understood that, in principle, the PIC device 200 may include any suitable number of waveguide structures 204, e.g., two, three, four, five, ten, or more than ten, depending on the desired application, and the number is not limited to three.P96280 from P92961 8

[0024] In general, each waveguide structure 204 may include an input facet 206 for coupling light into the waveguide structure 204, and an output facet 208 for outputting light from the waveguide structure 204. In the configuration in FIG.2A to FIG.2D, the first waveguide structure 204-1 may include a first input facet 206-1 and a first output facet 208-1, the second waveguide structure 204-2 may include a second input facet 206-2 and a second output facet 208-2, and the third waveguide structure 204-3 may include a third input facet 206-3 and a third output facet 208-3. An input facet 206 may also be referred to herein as in-coupling facet or coupling facet, and an output facet 208 may also be referred to herein as out-coupling facet or emission facet.

[0025] The input facet 206 may be understood as the portion at which a waveguide structure 204 receives input light. The disposition of the input facet 206 may vary depending on the coupling mechanism, and depending on whether the PIC device 200 includes light sources integrated therein. For example, the input facet 206 of a waveguide structure 204 may be disposed at a first side 212 of the cladding structure 202 (e.g., an input side of the cladding structure 202). In this scenario, the input facet 206 of a waveguide structure 204 may be aligned with a first edge, or first lateral surface of the cladding structure 202, and may thus allow edgecoupling of light into the waveguide structure 204.

[0026] In other aspects, the input facet 206 of a waveguide structure 204 may be at a certain distance from the first side 212 of the cladding structure 202, e.g., laterally shifted towards the inside of the cladding structure 202. This configuration may be provided, for example, in case the PIC device 200 includes a light source integrated within the cladding structure 202 and / or in case of a different coupling mechanism, such as evanescent coupling. As another example, this configuration may be provided case the PIC device 200 includes a coupler (e.g., a grating coupler) disposed between the first side 212 of the cladding structure 202 and the input facet 206 of a waveguide structure 204. In this case, light from a light source may be coupled into the waveguide structure 204 through the coupler that is optically coupled with the input facet 206.

[0027] An input facet 206 of a waveguide structure 204 may thus be at an arbitrary position laterally on the PIC 200, including several possible mechanisms for coupling light from external light sources, e.g., edge coupling from edge emitting lasers, evanescent coupling, coupling via a grating coupler, etc. For example, if a laser is integrated in the cladding structure 202, then the laser or the coupling interface of the laser would play the role of the “input facet”. In this case, the input facet 206 of a waveguide structure 204 will not be at the edge of the cladding structure 202, but in the central part thereof. For ease of representation, in the figures the inputP96280 from P92961 9 facet 206 of the waveguide structures 204 is shown aligned with the first side of the cladding structure 202, but it is understood that the input facets 206 may be at any suitable position, as discussed above.

[0028] The output facet 208 may be understood as the portion from which a waveguide structure 204 outputs light. Illustratively, the output facet 208 may be the portion from which a waveguide structure 204 delivers light towards the outside of the PIC device 200. The output facets 208 of the waveguide structures 204 may be disposed at a second side 214 of the cladding structure 202, illustratively an output side from which light is emitted. The output facets 208 of the waveguide structures 204 may thus be aligned with a second edge, or second lateral surface of the cladding structure 202. The second side 214 of the cladding structure 202 may be opposite to the first side 212 (e.g., along a main emission direction 220 of light, discussed in further detail below).

[0029] In FIG.2A to FIG.2D, the waveguide structures 204 are shown as extending along a straight line, e.g., from the first side 212 to the second side 214 of the cladding structure 202. It is however understood that a waveguide structure 204 may have any suitable shape depending on the desired application. For example, a waveguide structure 204 may extend along a substantially straight trajectory, as shown in FIG.2A to FIG.2D. As another example, a waveguide structure 204 may include one or more curved portions. As a further example, additionally or alternatively, a waveguide structure 204 may include one or more loops, e.g., one or more ring-like portions, and the like.

[0030] According to aspects of the present disclosure, the output side 214 of the cladding structure 202 may be structured in such a way that the respective output facet 208 of each waveguide structure 204 is at a respective position, e.g., a respective distance from a reference plane 230 that is normal to the light output direction 220 of the plurality of waveguide structures 204. Illustratively, the cladding structure 202 may be configured (e.g., structured) such that the output facets 208 of the waveguide structures 204 are each at a respective spatial coordinate along a direction parallel to the main output direction 220 of light from the plurality of waveguide structures 204.

[0031] By way of illustration, the output side 214 of the cladding structure 202 may be structured such that the outermost facets of different waveguide structures 204 may be laterally shifted with respect to one another along the main emission direction 220 of light from the PIC device 200. In this regard, the main emission direction 220 may be understood as the direction towards which the waveguide structures 204 emit light. In general, the waveguide structures 204 may be configured to output light along the main emission direction 220 and / or along aP96280 from P92961 10 direction that converges towards the main emission direction 220. Illustratively, each waveguide structure 204 may be configured such that the light output by the waveguide structure 204 either propagates parallel to the main emission direction 220, or propagates along a tilted direction at a relatively small angle with the main emission direction 220 and pointing towards the main emission direction 220.

[0032] In general, at least one waveguide structure 204 (e.g., more than one waveguide structure 204, e.g., each waveguide structure 204) may emit light along the main emission direction 220. In some aspects, at least one another waveguide structure 204 may emit light along a tilted direction at an angle less than a predefined angle value with the main emission direction 220. For example, the predefined angle value may be 20°, or 10°, or 5°, as numerical examples for the absolute value of the angle. In some aspects, the main emission direction 220 may be understood as a mean (or average) emission direction, defined by the mean or average of the individual emission directions of the waveguide structures 204. By way of illustration, the main emission direction 220 may be a center emission direction around which the individual emission directions may slightly vary. The main emission direction may also be referred to herein as main output direction, central emission direction, or central output direction.

[0033] According to various aspects, the main emission direction 220 may coincide with a center axis of the PIC device 200. Illustratively, the main emission direction 220 may be parallel to the center axis of the PIC device 200. For example, the main emission direction 220 may be parallel to the direction along which at least one of the waveguide structures 204 extends. For example, the main emission direction 220 may be parallel to a lateral side of the PIC device 200 (other than the input side 212 and output side 214). In some aspects, the main emission direction 220 may coincide with the optical axis of a lens towards which the waveguide structures 204 emit light (see also FIG.3 A).

[0034] The reference plane 230 may be any plane perpendicular to the main emission direction 220 and disposed downstream of the PIC device 200 along the direction towards which the light is output by the waveguide structures 204. In some aspects, the reference plane 230 may be disposed at the position of the lens towards which the waveguide structures 204 emit light (see also FIG.3A). In some aspects, the structuring of the output side 214 of the cladding structure 202 may thus cause each output facet 208 to be at a respective distance from the lens.

[0035] As shown in FIG.2A to FIG.2D, the output side 214 of the cladding structure 202 may be structured (in other words, shaped) to define, for each output facet 208, a respective position along the main emission direction 220. For example, the first output facet 208-1 may be at a first distance di from the reference plane (and at a first coordinate along the main emissionP96280 from P92961 11 direction 220), the second output facet 208-2 may be at a second distance d2 from the reference plane (and at a second coordinate along the main emission direction 220), the third output facet 208-3 may be at a third distance ds from the reference plane (and at a third coordinate along the main emission direction 220), etc.

[0036] The specific positions and distances of the output facets 208 may illustratively define specific positions and distances of “light sources” from which light is emitted. The adaptation of the position / distance may be tailored to pre-correct optical aberrations. In a conventional PIC, the output side of the cladding in which waveguides are embedded has generally a straight edge, such that all the output facets are at the same position, and accordingly at a same distance from the reference plane (and lens).

[0037] In this regard, various options exist for structuring the profile of the output side 214 to obtain different output positions for different waveguide structures 204, and will be described in further detail in relation to FIG.4A to FIG.6B. In general, the output side 214 may be structured to define a straight profile (as in FIG.2A to FIG.2D) or non-straight profile that is shaped such that different portions of the profile are at different positions with respect to the reference plane 230.

[0038] The approach proposed herein, may be applied for waveguide structures 204 that guide light in any suitable wavelength range. In a preferred configuration, the waveguide structures 204 may be configured to provide waveguiding of light with wavelength in the visible range (e.g., from about 380 nm to about 700 nm). In other aspects, at least one waveguide structure 204 (e.g., each waveguide structure 204) may be configured to provide waveguiding of light with wavelength outside the visible spectrum, e.g., in the infrared and / or near-infrared range (e.g., in the range from about 700 nm to about 5000 nm), or ultraviolet range (e.g., from about 100 nm to about 400 nm).

[0039] In general, each waveguide structure 204 may be configured to provide waveguiding in a respective wavelength range or at a respective wavelength (illustratively, a center wavelength of the range). With reference to FIG.2A, the first waveguide structure 204-1 may be configured to guide light having a first wavelength (or having wavelength in a first range), the second waveguide structure 204-2 may be configured to guide light having a second wavelength (or having wavelength in a second range), the third waveguide structure 204-3 may be configured to guide light having a third wavelength (or having wavelength in a third range), etc.

[0040] The strategy proposed herein may be of particular relevance in case of light having different wavelength, as the adaptation of the distance allows addressing chromatic aberrations. In this regard, for example, the first wavelength (range) may be different from the secondP96280 from P92961 12 wavelength (range), and the first distance di may be different from the second distance d2. In a corresponding manner, the first wavelength (range) may be different from the third wavelength (range), and the first distance di may be different from the third distance ds, and / or the second wavelength (range) may be different from the third wavelength (range), and the second distance d2 may be different from the third distance ds.

[0041] In particular, there may be a direct relationship between the wavelength and the distance of the corresponding waveguide structure 204. Illustratively, the output facet 208 of a waveguide structure 204 may be at a shorter distance from the reference plane 230 for decreasing wavelength of the light guided by the waveguide structure 204. For example, the first wavelength (e.g., blue) may be less than the second wavelength (e.g., green), and the first distance di may be less than the second distance d2. Furthermore, the second wavelength may be less than the third wavelength (e.g., red), and the second distance d2 may be less than the third distance ds, etc.

[0042] It is however understood that the proposed configuration may be applied also to scenarios in which waveguide structures 204 configured for the same wavelength or wavelength range are used. Thus, in some aspects, the first wavelength (range) may be equal to the second wavelength (range), and / or equal to the third wavelength (range), etc. In this scenario, the first distance di may be equal to the second distance d2, and / or equal to the third distance ds, etc. In case two waveguide structures 204 are configured for the same wavelength (range) and have the respective output facet 208 at the same distance from the reference plane 230, there may be at least one further waveguide structure 204 having the respective output facet 208 at a different distance from the reference plane 230 (e.g., a further waveguide structure 204 configured for a different wavelength or wavelength range).

[0043] In some aspects, the output side 214 of the cladding structure 202 may be configured such that the output facets 208 of at least two waveguide structures 204 are at a different distance from the reference plane 230 (e.g., two waveguide structures 204 emitting light at different wavelength). For example, the output side 214 of the cladding structure 202 may be configured such that each output facet 208 is at a respective unique distance from the reference plane 230, different from the other output facets 208.

[0044] For example, the output side 214 of the cladding structure 202 may be configured such that the output facets 208-1, 208-2 of the first and second waveguide structures 204-1, 204-2 are at a different distance from the reference plane 230, and such that the output facet 208-3 of the third waveguide structure 204-3 is at the same distance from the reference plane 230 as one of the first output facet 208-1 or second output facet 208-2. This configuration may be providedP96280 from P92961 13 for waveguides associated with different colors, or for waveguides configured to guide light having the same wavelength (e.g., same color, see also FIG.5 A).

[0045] In principle, the waveguide structures 204 may have any suitable configuration. As shown for example in FIG.2A and FIG.2B, in some aspects the waveguide structures 204 may consist of a single light path for guiding light. In this scenario, each waveguide structure 204 may define an individual channel through the cladding structure 202 for guiding light. In other aspects, as shown in FIG.2C and FIG.2D, at least one waveguide structure 204 (e.g., each waveguide structure 204) may include a plurality of waveguide channels. Illustratively, in this configuration a waveguide structure 204 may be comprised of multiple paths (parallel to one another) that define multiple propagation channels for the light through the cladding structure 202.

[0046] Considering the exemplary configuration in FIG.2C and FIG.2D, the first waveguide structure 204-1 may include a first plurality of waveguide channels 216-1, the second waveguide structure 204-2 may include a second plurality of waveguide channels 216-2, the third waveguide structure 204-3 may include a third plurality of waveguide channels 216-3, etc. A waveguide structure 204 may include any suitable number of waveguide channels, e.g., two, three, four, five, or more than five. A “waveguide channel” may also be referred to herein as ridge.

[0047] In general, the waveguide structures 204 may include the same number of waveguide channels, e.g., a single channel or a plurality of channels having the same cardinality. It is however understood that also “mixed” configurations may be provided depending on the desired application, e.g., a configuration in which one waveguide structure 204 includes a single channel and another waveguide structure 204 includes a plurality of channels, or a configuration in which different waveguide structures 204 include pluralities of channels having different cardinality, etc.

[0048] The configuration with a plurality of waveguide channels may be provided, for example, to adapt the geometry of the structure at the output side 214 compared to the input side. For example, a waveguide structure 204 (e.g., each waveguide structure 204-1, 204-2, 204-3) may include a plurality of waveguide channels that have an initial pitch (illustratively, a center-to- center distance among neighboring channels) at the input facet(s) and have a final, different pitch at the output facet(s). For example, in this configuration the PIC device 200 may be configured as a pitch converter. In particular, the final pitch at the output facet(s) may be smaller than the initial pitch.P96280 from P92961 14

[0049] In the scenario with a plurality of waveguide channels 216-1, 216-2, 216-3, the distance to the reference plane 230 may be defined as the distance between the reference plane 230 and the output facet of a central channel among the plurality of waveguide channels 216-1, 216-2, 216-3. In general, the structuring of the output side 214 may be such that the output facets of channels belonging to a waveguide structure 204 are all at the same distance from the reference plane 230 with respect to one another, while being at a different distance from the reference plane 230 compared to the output facets of channels belonging to another waveguide structure 204.

[0050] According to various aspects, the orientation of the waveguide structures 204 with respect to the main emission direction 220 may be freely adapted. For example, as shown in FIG.2A and FIG.2C, the waveguide structures 204, or at least an output portion of the waveguide structures 204 may be oriented parallel to the main emission direction 220. Illustratively, in this scenario the end portion of the waveguide structures 204 may extend along a straight line, parallel to the main emission direction 220.

[0051] In other aspects, as shown in FIG.2B and FIG.2D, a waveguide structure 204 (e.g., each waveguide structure 204) may be oriented at an angle with respect to the main emission direction 220, or at least an end portion of the waveguide structure 204 may be oriented at an angle with respect to the main emission direction 220. Illustratively, the end portion of a waveguide structure 204 may be tilted by a certain angle with respect to the main emission direction 220, e.g., an angle greater than 0° and less than 90°. In particular, the end portion of a waveguide structure 204 may be tilted such that the end portion points towards the main emission direction 220. Illustratively, the tilting angle may be positive or negative depending on the position of the waveguide structure 204 with respect to a center axis of the PIC device 200. The “tilting” of a waveguide structure 204 will be discussed in further detail in relation to FIG.2F.

[0052] As shown in FIG.2B and FIG.2D, one or more waveguide structures 204-1, 204-3 (e.g., their end portions) may be tilted with respect to the main emission direction 220, and one or more waveguide structures 204-2 (e.g., their end portions) may be parallel to the main emission direction 220. In another exemplary configuration, all waveguide structures may be tilted with respect to the main emission direction 220. In a further exemplary configuration, all waveguide structures may be parallel to the main emission direction 220.

[0053] FIG.2E shows a schematic front view of the PIC device 200, according to various aspects. The representation in FIG.2E shows in further detail the embedding of the waveguideP96280 from P92961 15 structures 204 in the cladding structure 202. It is understood that the aspects discussed in relation to FIG.2E apply to any of the configurations discussed in relation to FIG.2A to FIG.2D.

[0054] In general, as shown in FIG.2E, the waveguide structures 204 may be disposed between an upper cladding portion 203 (illustratively, an upper cladding layer), and a lower cladding portion 205 (illustratively, a lower cladding layer). Illustratively, the waveguide structures 204 may define a core that is embedded (sandwiched) between an upper-cladding 203 and a lower- cladding 205.

[0055] The materials and the overall geometry of the PIC device 200 may be freely adapted depending on the desired application. For example, the cladding material of the cladding structure 202 may include a polymer, a silica-based material, a dielectric material, and the like, and in general any suitable material having a refractive index lower than the core may be selected. In a corresponding manner, the waveguide structures 204 may include or consist of any suitable material that defines a higher refractive index compared to the cladding. Exemplary materials may include silica-based materials, polymer materials, dielectric materials, and the like. Exemplary materials for the waveguide structures 204 for applications in the visible range may include Silicon Nitride, Aluminum (Gallium) Nitride, Aluminum oxide, Lithium Niobate. For applications outside the visible range (e.g., in the infrared range), exemplary materials for the waveguide structures 204 may include Silicon, Indium Gallium Arsenide Phosphide / Indium Phosphide, Aluminum Gallium Arsenide / Gallium Arsenide, and the like.

[0056] Turning to the geometry, the PIC device 200 may generally have a relatively small footprint, which may be adapted depending on the application and desired complexity of the design. As a numerical example, the PIC device 200 may occupy an area in the range from 1 mm2(square millimeters) to 10 cm2(square centimeters), e.g., an area in the range from 10 mm2to 1 cm2. In a corresponding manner, the waveguide structures 204 may have any suitable dimension. For example, the core of a waveguide structure 204 (e.g., of a waveguide channel) may have a width and / or height in the range from 0.1 pm to 5 pm, e.g., in the range from 0.2 pm to 1 pm. The cross-section of a waveguide structure 204 may have any suitable shape, e.g., depending on fabrication constraints. For example, the cross-section of a waveguide structure 204 may have a rectangular shape as shown in FIG.2E. Other exemplary shapes may include an elliptical shape, a square shape, a circular shape, and the like.

[0057] According to various aspects, as shown in FIG.2E, the PIC device 200 may further include a substrate 240 on which the cladding structure 202 is disposed (e.g., formed). The substrate 240 may include or consist of any suitable material, e.g., silicon, glass, and the like. For example, the substrate 240 may be a wafer or a portion of a wafer on which the claddingP96280 from P92961 16 structure 202 and waveguide structures 204 are formed, and which is then singulated (e.g., diced) to obtain the individual PIC device 200.

[0058] Turning back to the “tilting” of the waveguide structures 204, FIG.2F shows various options for the configuration and orientation of a waveguide structure 204 at the output edge of the PIC device 200. The aspects discussed in relation to FIG.2F may apply to one waveguide structure 204, or more than one waveguide structure 204, or each waveguide structure 204 of the PIC device 200, depending on the desired optical functionality to be provided.

[0059] In general, a waveguide structure 204 may end at the edge coupler under a 90° angle, or at an angle different from 90°. In this regard, FIG.2F shows two exemplary scenarios, e.g., a configuration 250a in which the output facets 208 of the waveguide structures 204 are defined in a portion of the output side 214 that is parallel to the reference plane 230 (and perpendicular to the main emission direction 220), and a configuration 250b in which the output facets 208 of the waveguide structures 204 are defined in a portion of the output side 214 that is tilted with respect to the reference plane 230.

[0060] If the angle at the output differs from 90° (as shown for the first and second waveguide structures 204-1, 204-2 in the configuration 250a, and for the waveguide structure 204 in the configuration 250b), the emission angle will be tilted with respect to the waveguide direction due to refraction. In this case, further adaptations may be provided to ensure that the emission angle of the beam center is in the desired direction, e.g., towards the center of the lens (see FIG.3A).

[0061] The simplest case includes the use of a normal intersection of the waveguide with the coupling edge, as shown for the third waveguide structure 204-3 in the configuration 250a. In this scenario, the output facet 208 of a waveguide structure 204 may be normal to the waveguide axis. Illustratively, considering the central longitudinal line along which the waveguide structure 204 extends and light propagates, the output facet 208 may be normal to such longitudinal line.

[0062] However, in case the edge is not coated with an antireflection coating, Fresenel reflection will occur at the waveguide edge. For a normal coupler, the reflected light will be coupled back into the waveguide, which could lead to unwanted reflected back-propagating light in the PIC. Thus, in some aspects the output side 214 of the PIC device 200 may include an anti-reflection coating. Another possibility to reduce or avoid the back-reflections is to provide the waveguides at a small tilt from normal (e.g., at an angle of 5°-15°, as a numerical example), which causes the back-reflected light to end up outside the guided waveguide mode,P96280 from P92961 17 so that inside the waveguide almost no reflected light will propagate. The light will instead be just lost into non-guided modes. Possibly, the emitted beam might become slightly asymmetric.

[0063] The structuring proposed herein may be applicable for any of the presented configurations, thus allowing to choose any coupler angle, as the functionality of reflectance suppression is independent from the distance-related features, provided that refraction is properly considered in the design.

[0064] As mentioned, the PIC device 200 may be used in combination with a lens that is configured to receive (e.g., collect) the light output by the waveguide structures 204 and to manipulate the received light according to a predefined lens functionality implemented by the lens. In this regard, FIG.3A shows a system 300 (in a first configuration 300a) including the PIC device 200 and a lens 302 that is optically coupled with the waveguide structures 204. In the configuration in FIG.3A (and FIG.3B) the PIC device 200 is shown with the exemplary configuration 200a, but it is understood that the PIC device 200 in the system may have any of the configurations discussed in relation to FIG.2A to FIG.2D, and that the aspects discussed in relation to FIG.3 A (and FIG.3B) apply to any of such configurations.

[0065] In general, the lens 302 may be disposed with respect to the PIC device 200 such that the waveguide structures 204 emit light towards the lens 302, and the lens collects the light that is output by the waveguide structures 204. The lens 302 may be configured to manipulate light passing through the lens 302 according to a corresponding lens function for which the lens 302 is designed. A lens 302 may illustratively be an optical surface configured (e.g., shaped) to define a predefined manipulation of the light. For example, the lens function may include focusing light, diffracting light, collimating light, diverging light, projecting a light pattern, etc. A “lens function” may be understood as an optical manipulation of light according to the lens type of the respective lens (e.g., concave lens, convex lens, etc.). In a preferred configuration, the lens 302 may be configured to focus the received light and deliver, at an output side of the lens 302, focused light.

[0066] In this scenario, as also shown in FIG.3A, the main emission direction mentioned in relation to FIG.2A-2D may correspond to the optical axis 320 of the lens 302. Illustratively, the aspects discussed in relation to the main emission direction 220 may apply in a corresponding manner to the optical axis 320 of the lens 302. For example, the output side 214 of the cladding structures 202 may be structured such that each output facet 208 is at a respective coordinate along the optical axis 320, e.g., such that output facet 208 is at a respective distance from a reference plane 330 perpendicular to the optical axis 320 of the lens 302. As another example, for “tilted” waveguide structures, the tilting of the end portion may be with respect to the opticalP96280 from P92961 18 axis 320 of the lens 302, such that the end portion of a tilted waveguide structure forms an angle greater than 0° (and less than 90°) with the optical axis 320.

[0067] In this regard, the reference plane 330 may be any plane perpendicular to the optical axis 320 of the lens 302 and located downstream of the output facets 208 along the emission direction of light. In particular, the reference plane 330 may be the lens plane, i.e., the reference plane 330 may be disposed at the lens 302 and perpendicular to the optical axis 320.

[0068] The pre-correction of the optical aberrations provided by the adapted configuration of the PIC device 200 allows using a simple lens 302 rather than a complex lens system, thus providing a simple and cost-effective implementation. Thus, in a preferred configuration the system 300 may include a single lens 302 to collect and manipulate the light output by the waveguide structures 204. For example, the lens 302 may consist of a single material. Illustratively, the lens 302 may include a first surface facing towards the PIC device 200, a second surface facing away from the PIC device 200, and the space between the first surface and second surface may be full of the material of the lens (e.g., the single material). In the preferred configuration the lens 302 may thus be a single lens that implements a single lens function (e.g., collimation, focusing, or the like).

[0069] It is however understood that, in principle, the adapted PIC device 200 may be used in combination with more complex lens systems. In some aspects, the lens 302 may thus be understood as a lens system including a plurality of lenses that are optically coupled together. For example, the lens system may include a lenses of different lens types that in combination provide a further correction of the aberrations. For example, the lens system may include lenses of different materials. As another example, the lens 302 may include a microscope objective.

[0070] The structuring of the output side 214 of the cladding structure 200 may allow correcting the aberration for which the lens 302 has different focal lengths for light of different colors. In this regard, the different distances of the output facets 208 to the reference plane 330 defined by the structuring of the output side 214 may be configured (e.g., selected) such that the lens 302 focuses light from different waveguide structures 204 to the same focal plane. Illustratively, the focal points for the different waveguide structures 204 may be in the same plane. As mentioned in relation to FIG.2A to FIG.2D, there may be a direct relationship between wavelength and distance, such that structuring the output side 214 to define shorter distances for shorter wavelengths allows obtaining a single focal plane for light of different colors emitted by the different waveguide structures 204.

[0071] In some aspects, the first wavelength of light guided by first waveguide structure 204-1 (e.g., blue) may be less than the second wavelength guided by second waveguide structureP96280 from P92961 19204-2 (e.g., green), and the first distance di to the reference (lens) plane 330 may be less than the second distance d2 to the reference (lens) plane 330, such that the lens 302 focuses the (blue) light from the first waveguide structure 204-1 and the (green) light from the second waveguide structure 204-2 to the same focal plane. The same applies to the third wavelength (e.g., red) guided by third waveguide structure 204-3 and this distance ds, such that the lens 302 further focuses the (red) light from the third waveguide structure 204-3 to the same focal plane, etc.

[0072] According to various aspects, as shown for the configuration 300b in FIG.3B, the system 300 may further include a plurality of light sources 352 that are optically coupled with the waveguide structures 204 (illustratively, with the input facets 206 of the waveguide structures 204). A light source 352 may be configured to emit light into a respective waveguide structure 204. For example, as shown in FIG.3B, the system 300 may include a first light source 352-1 coupled with the first waveguide structure 204-1, a second light source 352-2 coupled with the second waveguide structure 204-2, and a third light source 352-3 coupled with the third waveguide structure 204-3. It is however understood that the system 300 may include any suitable number of light sources 352, e.g., one for each waveguide structure 204.

[0073] The type of light source 352 and the type of coupling with the waveguide structures 204 may be adapted in any suitable manner known in the art. For example, the light sources 352 may be coupled with the waveguide structures 204 via edge coupling, as shown in FIG.3B. In this scenario, a light source 352 may be for example an edge emitting laser. As another example, the light sources 352 may be coupled with the waveguide structures 204 via top coupling or bottom coupling. As a further example, the light sources 352 may be coupled with the waveguide structures 204 via evanescent coupling.

[0074] The light sources 352 may be coupled with the waveguide structures 204 directly or indirectly. For direct coupling, a light source 352 may emit light directly into the corresponding waveguide structure 204. For indirect coupling there may be one or more intervening elements between the light source 352 and the corresponding waveguide structure 204, e.g., an optical fiber that delivers the light to the waveguide structure 204, an optical coupler (e.g., a grating coupler), and the like.

[0075] In some aspects, as shown in FIG.3B, the light sources 352 may be disposed externally to the PIC device 200, e.g., externally to the cladding structure 202. In other aspects, at least one light source 352 (e.g., each light source 352) may be at least partially embedded in the cladding structure 202. In this scenario, the input facet 206 of the corresponding waveguide structure 204 may be shifted inside the cladding structure 202 depending on the position of the light source 352 within the cladding structure 202.P96280 from P92961 20

[0076] A light source 352 may be configured to emit light having a wavelength that matches the configuration of the corresponding waveguide structure 204. Illustratively, each light source 352 may be configured to emit light at a wavelength guided by the corresponding waveguide structure 204. In this regard, the first light source 352-1 may be configured to emit light having a first wavelength (e.g., blue), the second light source 352-2 may be configured to emit light having a second wavelength (e.g., green), the third light source 352-3 may be configured to emit light having a third wavelength (e.g., red), etc. The wavelengths of the emitted light may be different from one another or equal to one another depending on the configuration of the waveguide structures 204.

[0077] As mentioned in relation to FIG.2A to FIG.2F, a waveguide structure 204 may be configured to guide a specific wavelength. Illustratively, a waveguide structure 204 (e.g., each waveguide structure) may be configured as a single-mode waveguide, thus enhancing the guiding efficiency for the light emitted by a corresponding light source. The mode selection may be implemented for example by adapting the waveguide cross-section, in particular the waveguide width. In this regard, waveguide structures 204 adapted for single-mode waveguiding for a smaller (shorter) wavelength exhibit a smaller width than waveguide structures 204 designed for single-mode waveguiding for a longer wavelength.

[0078] The light sources 352 may have any suitable configuration. In general, a light source 352 may include a solid-state light emitting element, e.g., a semiconductor-based light emitting element. In a preferred configuration, at least one light source 352 (e.g., each light source 352) may be or include a laser source configured to emit laser light. For example, at least one light source 352 (e.g., each light source 352) may include a VCSEL, an edge-emitting laser, a Vertical-External-Cavity-Surface-Emitting Laser (VECSEL), a light emitting diode (LED), a Micro-LED, a superluminescent LED, and the like. In general, the light sources 352 may be of the same type, but in principle also as combination of light sources of different types may be used.

[0079] As mentioned in relation to FIG.2A to FIG.2D there may be various options for the structuring of the output side of the cladding structure 202, which will be described in further detail in relation to FIG.4A to FIG.6B. It is understood that the aspects discussed in relation to the PIC devices 400, 500, 600, of FIG.4A to FIG.6B may apply to the PIC device 200 of FIG.2A to FIG.2D, and vice versa. Illustratively, the PIC devices 400, 500, 600, of FIG.4A to FIG.6B may illustrate possible realizations of the PIC device 200.

[0080] FIG.4A and FIG.4B show various configurations 400a, 400b of a PIC device 400. The PIC device 400 may generally be configured as the PIC device 200, and may include a claddingP96280 from P92961 21 structure 402 with an input side 412 and output side 414, and waveguide structures 404 (e.g., first to third waveguide structures 404-1, 404-2, 404-3) having input facets 406 (e.g., first to third input facets 406-1, 406-2, 406-3) and output facets 408 (e.g., first to third output facets 408-1, 408-2, 408-3). As for the PIC device 200, the number of waveguide structures 404 is exemplary, and the PIC device 400 may include any suitable number of waveguide structures 404.

[0081] In general, the output side 414 of the cladding structure 402 may be structured such that the output facets 408 of the waveguide structures 404 are at a respective distance from the reference plane 430 perpendicular to the main emission direction 420 (e.g., a respective distance from the reference plane perpendicular to the optical axis of a lens that receives light from the waveguide structures).

[0082] In the configuration in FIG.4A and FIG.4B, the output side 414 of the cladding structure 402 may be structured to define a step-like profile. In this configuration, the output side 414 of the cladding structure 402 may include a plurality of straight portions, each at a respective distance from the reference plane 430. Illustratively, the structuring of the output side 414 may include defining a plurality of discrete steps, each at a respective position along a direction parallel to the main emission direction 420 (e.g., a direction parallel to the optical axis of a lens coupled with the waveguide structures 404). A step-like profile may provide a simple, yet accurate realization of the approach proposed herein. In this regard, a “straight portion” may include a portion of the output side 414 that is parallel to the reference plane 430, e.g., a portion of the output side 414 that defines a plane parallel to the reference plane 430 (and perpendicular to the main emission direction 420).

[0083] In this scenario, the output facet 408 of each waveguide structure 404 may be disposed in a respective straight portion of the plurality of straight portions. Considering the scenario with multiple waveguide channels 416-1, 416-2, 416-3, the output facets 408-1, 408-2, 408-3 of the channels 416-1, 416-2, 416-3 that belong to a certain waveguide structure 404-1, 404-2, 404-3 may be disposed in the same straight portion.

[0084] As shown in FIG.4A and FIG.4B, the structured output side 414 may have different straight portions disposed at different distances from the reference plane. For example, a first straight portion 422-1 may be at a first distance, a second straight portion 422-2 may be at a second distance, a third straight portion may be at a third distance 422-3, etc. In this regard, the considerations made in relation to FIG.2A to FIG.2D apply, such that the distance between a straight portion and the reference plane 430 may be adapted depending on the wavelength of the light emitted by the waveguide structure 404 associated with that straight portion. In general,P96280 from P92961 22 straight portions associated with waveguide structures 404 guiding light of different wavelength may be at different distances form the reference plane 430.

[0085] For example, the first waveguide structure 404-1 guiding a first wavelength may have the output facet 408-1 at the first straight portion 422-1. The second waveguide structure 404-2 guiding a second wavelength may have the output facet 408-2 at the second straight portion 422-2. The third waveguide structure 404-3 guiding a third wavelength may have the output facet 408-3 at the third straight portion 422-3, etc. The first wavelength may be less than the second wavelength, and the first distance between the first straight portion 422-1 and the reference plane 430 may be less than the second distance between the second straight portion 422-2 and the reference plane 430. Correspondingly, the second wavelength may be less than the third wavelength, and the second distance between the second straight portion 422-2 and the reference plane 430 may be less than the third distance between the third straight portion 422-3 and the reference plane 430, etc.

[0086] In the exemplary representation in FIG.4A and FIG.4B the waveguide structures 404 are shown oriented along a straight line, parallel to the main emission direction 420. It is however understood that the step-like structuring may also be provided for waveguide structures 404 that are tilted with respect to the main emission direction 420, e.g., for waveguide structures 404 that have an end portion that forms an angle greater than 0° (and less than 90°) with the main emission direction 420 (as shown in FIG.2F).

[0087] The configuration with a step-like profile may be particularly suitable for compensating chromatic aberrations, as it allows to position waveguide structures 404 associated with different colors at different distances from the reference plane 430 (and from a corresponding lens, which may then focus the light to the same focal point, as discussed above). To compensate other types of aberrations, in particular non-axial aberrations and curved focal plane of the lens, another configuration may be provided, as shown in FIG.5 A and FIG.5B.

[0088] FIG.5A and FIG.5B show various configurations 500a, 500b of a PIC device 500. The PIC device 500 may generally be configured as the PIC device 200, and may include a cladding structure 502 with an input side 512 and output side 514, and waveguide structures 504 (e.g., first to third waveguide structures 504-1, 504-2, 504-3) having input facets 506 (e.g., first to third input facets 506-1, 506-2, 506-3) and output facets 508 (e.g., first to third output facets 508-1, 508-2, 508-3). As for the PIC device 200, the number of waveguide structures 504 is exemplary, and the PIC device 500 may include any suitable number of waveguide structures 504.P96280 from P92961 23

[0089] In general, the output side 514 of the cladding structure 502 may be structured such that the output facets 508 of the waveguide structures 504 are at a respective distance from the reference plane 530 perpendicular to the main emission direction 520 (e.g., a respective distance from the reference plane perpendicular to the optical axis of a lens that receives light from the waveguide structures).

[0090] In the configuration in FIG.5 A and FIG.5B, the output side 514 of the cladding structure 502 may be structured to define a curved profile. In this scenario, the respective output facets 508 of the waveguide structures 504 may be disposed at a respective position along the curved profile of the output side 514. This applies both to the scenario in which the waveguide structures 504 include a single channel, as well as to the scenario in which the waveguide structures 504 include a plurality of channels 516-1, 516-2, 516-3. The curvature of the output side 514 may provide that different positions along the curved profile are at a different distance from the reference plane 530, such that disposing the output facet 508 of a waveguide structure 504 at a respective location of the curve may define a respective distance from the reference plane 530 (e.g., from a lens plane perpendicular to the optical axis of the lens).

[0091] In general, the curved profile may have any suitable shape. For example, the curved profile may have a symmetric shape around a center axis of the curve, but also curves that are non-symmetric may be provided. For example, the center axis of the curved profile may be aligned with the main emission direction 520, e.g., the center axis may overlap with the main emission direction 520 (e.g., the center axis may be aligned with the optical axis of the lens). In a preferred configuration, as shown in FIG.5A and FIG.5B, the output side 514 of the cladding structure 502 may be structured to have a concave profile. In this scenario, the distance between a position along the concave profile and the reference plane 530 may decrease for increasing distance of the position from a center axis of the concave profile. It is however understood that in principle also other types of curved profile may be provided, e.g., a convex profile as another example.

[0092] In some aspects, the curvature of the output side 514 may be adapted depending on the properties of the lens with which the PIC device 500 is optically coupled. Illustratively, the output side 514 may be structured to have a curved profile that is based on the curved focal plane of the lens. For example, the output side 514 may be structured to have a curved profile that is inversed with respect to the curved focal plane of the lens (illustratively, flipped along the optical axis of the lens). In some aspects, the curved profile of the output side 514 may be configured according to a Petzval surface of the lensP96280 from P92961 24

[0093] With reference to FIG.5A and FIG.5B, the first waveguide structure 504-1 may have the output facet 508-1 at a first position 522-1 along the curved profile, the second waveguide structure 504-2 may have the output facet 508-2 at a second position 522-2 along the curved profile, the third waveguide structure 504-3 may have the output facet 508-3 at a third position 522-3 along the curved profile, etc.

[0094] The configuration with the curved profile may allow correcting non-axial aberrations both for waveguides that guide light of the same color as well as for waveguides that guide lights of different colors.

[0095] For example, in some aspects, the waveguide structures 504 may all be configured to provide waveguiding for light at the same wavelength. The positions 522-1, 522-2, 522-3 may define same or different distances from the reference plane 530. For example, the first waveguide structure 504-1 may guide light at a first wavelength and the first position 522-1 may define a first distance between the first output facet 508-1 and the reference plane. The second waveguide structure 504-2 may guide light at a second wavelength equal to the first wavelength, and the second position 522-2 may define a second distance between the second output facet 508-2 and the reference plane 530 that is different from the first distance (e.g., less). The third waveguide structure 504-3 may guide light at a third wavelength equal to the first wavelength, and the third position 522-3 may define a third distance between the third output facet 508-3 and the reference plane 530 that is equal to the first distance, etc.

[0096] In other aspects, the first waveguide structure 504-1 may guide light at a first wavelength (e.g., blue) and the first position 522-1 may define a first distance between the first output facet 508-1 and the reference plane. The second waveguide structure 504-2 may guide light at a second wavelength different from the first wavelength (e.g., greater, e.g., green), and the second position 522-2 may define a second distance between the second output facet 508-2 and the reference plane 530 that is different from the first distance. The third waveguide structure 504-3 may guide light at a third wavelength different from the first wavelength (and / or from the second wavelength), e.g., red, and the third position 522-3 may define a third distance between the third output facet 508-3 and the reference plane 530 that is equal to the first distance, etc.

[0097] Also “mixed” configurations may be provided in which a subset of the waveguide structures emit / guide light at the same wavelength and are at the same or different distances from the reference plane, while another waveguide structure (or another subset) emit / guide light at a different wavelength and are at the same or different distances from the reference plane.P96280 from P92961 25

[0098] As an exemplary disposition, the first position 522-1 may be at a first side of the center axis of the curved profile, and the third position 522-3 may be at a second side of the center axis of the curved profile, opposite to the first side. The second position 522-2 may be aligned with the center axis. This configuration is particularly suitable for correcting the above- mentioned aberrations. It is however understood that any suitable disposition may be provided.

[0099] The configuration with the curved profile may be provided both for waveguide structures 504 oriented along a straight line, parallel to the main emission direction 520 (as in FIG.5A), as well as for waveguide structures 504 that are tilted with respect to the main emission direction 520, e.g., for waveguide structures 504 that have an end portion that forms an angle greater than 0° (and less than 90°) with the main emission direction 520 (as in FIG.5B).

[0100] For example, as shown in FIG.5B, the first waveguide structure 504-1 (e.g., with a single channel or multiple channels) may have an end portion defining a first angle with the main emission direction 520. The second waveguide structure 504-2 (e.g., with a single channel or multiple channels) may have an end portion defining a second angle with the main emission direction 520. The third waveguide structure 504-3 (e.g., with a single channel or multiple channels) may have an end portion defining a third angle with the main emission direction 520. For example, the first angle and the third angle may be greater than 0° (and less than 90°), e.g., the first angle and third angle may be equal to one another. For example, the second angle may be 0°, such that the end portion of the second waveguide structure 504-2 is aligned with the main emission direction 520.

[0101] In some aspects, there may be a relationship between the tilting angle and the distance defined by the corresponding position along the curved profile. For example, for increasing values of the angle between the end portion of a waveguide structure 504 and the main emission direction 520, the waveguide structure 504 may be at a point along the curve that has a shorter distance from the reference plane 530. Considering for example FIG.5B, the first angle and third angle may be greater than the second angle (e.g., considering an absolute value), and the first / third distance may be less than the second distance.

[0102] In some aspects, the features of the step-like structuring and the features of the curved structuring may be combined to provide a pre-correction of different types of optical aberrations, as shown in FIG.6.

[0103] FIG.6A and FIG.6B show various configurations 600a, 600b of a PIC device 600. The PIC device 600 may generally be configured as the PIC device 200, and may include a cladding structure 602 with an input side 612 and output side 614, and waveguide structures 604 (e.g., first to third waveguide structures 604-1, 604-2, 604-3) having input facets 606 (e.g.,P96280 from P92961 26 first to third input facets 606-1, 606-2, 606-3) and output facets 608 (e.g., first to third output facets 608-1, 608-2, 608-3). As for the PIC device 200, the number of waveguide structures 604 is exemplary, and the PIC device 600 may include any suitable number of waveguide structures 604.

[0104] In FIG.6A and 6B the waveguide structures 604 include multiple waveguide channels 616-1, 616-2, 616-3, but it is understood that the aspects discussed for the PIC device 600 may apply also to a configuration in which the waveguide structures have a single channel. Furthermore, in the exemplary representation in FIG.6 A the waveguide structures 604 are shown oriented along a straight line, parallel to the main emission direction 620. It is however understood that the structuring may also be provided for waveguide structures 604 that are tilted with respect to the main emission direction 620 (see FIG.6B), e.g., for waveguide structures 604 that have an end portion that forms an angle greater than 0° (and less than 90°) with the main emission direction 620.

[0105] In general, the output side 614 of the cladding structure 602 may be structured such that the output facets 608 of the waveguide structures 604 are at a respective distance from the reference plane 630 perpendicular to the main emission direction 620 (e.g., a respective distance from the reference plane perpendicular to the optical axis of a lens that receives light from the waveguide structures).

[0106] As shown in FIG.6 A, the output side 614 of the cladding structure 602 may be structured to define a plurality of curved portions. In the exemplary configuration in FIG.6 A, the output side 614 may include a first curved portion 622-1 and a second curved portion 622- 2, but any suitable number of curved portions may be provided. In a corresponding manner as the straight portions of the PIC device 400, the curved portions 622-1, 622-2 may each be at a respective distance from the reference plane 630. In this configuration, each waveguide structure 604 may have the output facet 608 disposed in a respective curved portion (e.g., alone, or together with the output facet 608 of another waveguide structure 604). Each curved portion 622-1, 622-2 may have a curved profile (e.g., a concave profile), and within a curved portion the output facet 608 of a waveguide structure 604 may be disposed at a corresponding position along the curved profile of the curved portion 622-1, 622-2.

[0107] For example, the first waveguide structure 604-1 may have the output facet 608-1 in the first curved portion 622-1 (at a first position along the curved profile of the first curved portion 622-1). The second waveguide structure 604-2 may have the output facet 608-2 in the first curved portion 622-1 (at a second position along the curved profile of the first curved portion 622-1). The third waveguide structure 604-3 may have the output facet 608-3 in theP96280 from P92961 27 second curved portion 622-2 (at a third position along the curved profile of the second curved portion 622-2), etc.

[0108] In this scenario, both chromatic and non-axial compensation may be provided. For example, the first curved portion 622-1 may define a first shorter distance to the reference plane 630 compared to the second portion 622-2. The first waveguide structure 604-1 may guide light having a shorter wavelength compared to the third waveguide structure 604-3. Similarly, the second waveguide structure 604-2 may guide light having a shorter wavelength compared to the third waveguide structure 604-3.

[0109] Furthermore, also the positioning along the curved profile may contribute to the correction. For example, the first waveguide structure 604-1 may guide light having a shorter wavelength compared to the second waveguide structure 604-2, and may have the output facet 608-1 disposed at a first position along the curved profile of the curved portion 622-1 that defines a shorter distance to the reference plane 630 compared to the second position at which the second output facet 608-2 of the second waveguide structure 604-2 is disposed.

[0110] In the configuration of FIG.6B, each curved portion may be associated with a single waveguide structure 604. Illustratively, the first waveguide structure 604-1 may have the output facet 608-1 at a first curved portion 622-1, the second waveguide structure 604-2 may have the output facet 608-2 at a second curved portion 622-2, the third waveguide structure 604-3 may have the output facet 608-3 at a third curved portion 622-3, etc. In some aspects, a spacing may be provided between the curved portions 622-1, 622-2, 622-3, such that each curved portion is shifted along the main emission direction 620. The additional lateral spacing may avoid optical shadowing by adjacent, but forward displaced PIC waveguides and etched facets.

[0111] As a numerical example, the first waveguide structure 604-1 may be at a displacement 626 of 60 pm from the main emission direction, and a first focus correction 624-1 of 6 pm may be provided, considering the first waveguide structure 604-1 configured for blue light (e.g., 450 nm). A second focus correction 624-2 of 22 pm may be provided for the second waveguide structure 604-2, considering the second waveguide structure 604-2 configured for green light (e.g., 530 nm). A third focus correction 624-3 of 40 pm may be provided for the third waveguide structure 604-3, considering the third waveguide structure 604-3 configured for red light (e.g., 630 nm).

[0112] In summary, the configuration proposed herein includes an arrangement of multiple PIC outputs differing from a single straight line, such that different position of outputs along the direction of the optical axis are defined, in particular for different wavelengths (FIG.4A and FIG.4B). In some aspects, the arrangement of outputs (also for identical wavelength) may beP96280 from P92961 28 along curved line (FIG.5 A and FIG.5B). Furthermore, an arrangement may be provided according to both options together with angled or perpendicular waveguide direction with respect to output facet line (FIG.6A and FIG.6B).

[0113] The output facets of waveguides on PIC are arranged deviating significantly from a straight line (as given by the chip edge). This is combined with simple (imaging) optics consisting of lenses without a correction of curved focus planes and chromatic aberrations, i.e., the optics are much simpler than a conventionally used camera objective. The output facets are arranged in a manner that corrects the lens aberrations by using optimum output positions for each color and position.

[0114] As discussed, the deviations from a straight line may include: varying distance from the PIC chip edge, with longer wavelength emitting waveguide facets retreated further backwards from the chip edge. Varying distance from the chip edge, with facets emitting identical wavelength positioned closer to the chip edge for further lateral distance from the optical axis. Varying angle with respect to the chip edge, resulting in the central beam pointing closer towards the center of the first lens than for parallel emission. Output facets of waveguides on PIC are (optionally, in addition) structured altogether in a variable distance from the PIC chip edge, in order to allow for a compensation of the eyeglass lens in AR systems with eyesight correcting glasses. Depending on the desired correction, a different PIC variant with different waveguide facet positions may be selected. This enables simple lens mounting using the PIC chip edge aside the output facets as mechanical reference without individual lens focus alignment.

[0115] The arrangement proposed herein may thus provide pre-compensation of lens aberrations, mainly chromatic aberration and curved focal plane via structuring the PIC output arrangement. The PIC device provides a cost-efficient solution compared to better lens implementations with less aberrations, and allows reducing the system size due to smaller possible optics. An adaption to eyesight correction is made possible.

[0116] As discussed above, various approaches have been proposed, which may be implemented individually or in combination with one another. The approaches may include: only varying lateral coupler position (step-wise, depending on wavelength) for compensation of chromatic aberration (FIG.4A and 4B); only varying lateral coupler position along a curved line for compensation of the curvature of the focus plane of the lens (FIG.5 A); varying outcoupling angle to target the center of the lens for efficiency improvement and Koma reduction (FIG.5B); partial combination, where the correction of chromatic aberration is onlyP96280 from P92961 29 applied for a part of the colors (FIG.6A); and full combination of all described properties (FIG.6B) including dimensions for a simulated optical system.

[0117] FIG.7 shows a schematic flow diagram of a method 700 of forming a PIC device, according to various aspects. It is understood that the aspects discussed in relation to the PIC device 200, 400, 500, 600, may apply in a corresponding manner to the method 700, and vice versa.

[0118] The method 700 may include, in 710, forming a cladding structure. The cladding structure may be formed using any suitable technique, such as growth, deposition, and the like. For example, the method 700 may include forming (e.g., growing, depositing) a cladding material on a substrate to form the cladding structure, e.g., to form a lower cladding portion.

[0119] The method 700 may further include, in 720, forming a plurality of waveguide structures in the cladding structure. For example, the method 700 may include forming a plurality of waveguide cores on the lower cladding portion, and then forming an upper cladding portion on the cores, thus embedding the waveguide structures within the cladding structure.

[0120] The method 700 may further include, in 730, structuring the output side of the cladding structure to provide a respective output facet of each waveguide structure for outputting light from the waveguide structure. The structuring of the output side may be provided such that each output facet is at a respective distance from a reference plane that is normal to the light output direction of the plurality of waveguide structures. The structuring may be carried out using any suitable technique, such as micromachining, laser-assisted machining, etching, dicing, and the like. In this regard, the method 700 may further include providing, for each waveguide structure, an input facet for coupling light into the waveguide structure

[0121] FIG.8A to FIG.8G shows simulation results 800a-800g, 810c-810g, 820d, 820f, 850g, 860g to illustrate the functioning of the proposed PIC device compared to a “non-corrected” configuration. According to the performed simulations, typical variations of the coupler plane for chromatic correction are in the range of 0.1 ... 0.5 pm per nm of the wavelength difference to be corrected. For focal plane curvature correction, the coupler plane correction is typically 2% . . . 20% of the lateral distance from the optical axis.

[0122] In this regard, FIG.8 A shows that for an optimized aspheric lens (material BK7) for collimation of 450 nm point source, NA=0.3, with f = 2 mm, a change of wavelength to 630 nm leads to imperfect collimation, and thus to a slightly divergent beam. The collimation can be corrected by moving the source 45 pm away from the lens. The first panel 801 shows the parallel beam as optimized for 450 nm. The second panel 802 shows that the beam becomes slightly divergent as the wavelength of the source is changed to 630 nm without changing anyP96280 from P92961 30 geometry. The third panel 803 shows the again parallel beam for 630 nm, which is achieved by increasing the distance to the lens by 45 pm. From FIG.8 A it may thus be appreciated that varying the wavelength causes a corresponding change in the focal length (e.g., 45 pm in this situation), which may be compensated adopting the approach proposed in the present disclosure.

[0123] FIG.8B shows simulations with a first lens for collimation to parallel beam, and a second lens for focusing on a receiver (f=l .7 mm) to visualize the focusing effect. The first source is simulated to be on the optical axis, providing an imaging quality optimized by aspherical lenses. The second source is simulated to be 60 pm off axis. The source divergence is simulated to be 17°, and the radius is simulated to be defined according to Gaussian beam properties (241 nm for blue, 289 nm for green, 340 nm for red).

[0124] FIG.8C shows a simulation of focusing optics, with a first lens having a 1 mm focal length, and a second focusing lens with 1.7 mm focal length. The focus may be optimized for the central blue source, having a single-mode gaussian, 17° divergence, and 241 nm beam width. For a second identical blue source at 60 pm distance, no adaption is provided, resulting in lower focus quality as shown in the simulation 810c (upper focus is first optimized source, lower focus is second source). FIG.8D shows an improvement by rotation and displacement of second source, considering as new coordinates a 6 pm movement towards the lens, and a rotation by 0.92° towards the lens.

[0125] FIG.8E shows a simulated scenario with a central blue emitter (450 nm) and a second red emitter (630 nm) with a shift of 60 pm to the side. The central blue emitter provides the “blue” focus point 802e, and the red emitter provides the “red” focus point 804e. Still no correction is implemented, resulting in a shift of the focal points.

[0126] In FIG.8F a shift is implemented as proposed herein and as shown in the simulation 81 Of, resulting in focal points at the same location, as shown in the simulation 820f. In FIG.8F, the central blue emitter provides the “blue” focus point 802f, and the red emitter provides the “red” focus point 804f. The emitter position correction is simulated to include a shift of 35 pm away from lens (41 pm relative to ideal position for blue), and a tilt of 1°.

[0127] FIG.8G shows a simulated scenario with a with a central blue emitter (450 nm) and a second green emitter (530 nm) with a shift of 60 pm to the side. The central blue emitter provides the “blue” focus point 802g, 852g and the green emitter provides the “green” focus point 806g, 856g. The simulations 800g, 810g show the non-corrected scenario, with a shift in the focal points. The simulations 850g, 860g show the corrected scenario with a 16 pm shift away from lens, and a 1° tilt, bringing the focal points in the same plane.P96280 from P92961 31

[0128] The following examples pertain to aspects of the present disclosure.

[0129] Example 1 is a Photonic Integrated Circuit, PIC, device including: a cladding structure; and a plurality of waveguide structures disposed in the cladding structure, wherein each waveguide structure includes an output facet for outputting light from the waveguide structure, the output facet being disposed at an output side of the cladding structure, wherein the output side of the cladding structure is structured such that the respective output facet of each waveguide structure is at a respective distance from a reference plane that is perpendicular to a main emission direction of light by the plurality of waveguide structures.

[0130] In Example 2, the PIC device according to example 1 may optionally further include that the plurality of waveguide structures includes, at least: a first waveguide structure configured to guide light having a first wavelength, wherein the output side of the cladding structure is structured such that a first output facet of the first waveguide structure is at a first distance from the reference plane; and a second waveguide structure configured to guide light having a second wavelength different from the first wavelength, wherein the output side of the cladding structure is structured such that a second output facet of the second waveguide structure is at a second distance from the reference plane, different from the first distance.

[0131] In Example 3, the PIC device according to example 2 may optionally further include that the first wavelength is shorter than the second wavelength; and that the first distance is less than the second distance.

[0132] In Example 4, the PIC device according to any one of examples 1 to 3 may optionally further include that the output side of the cladding structure is structured to define a step like profile including a plurality of straight portions, that each straight portion is at a respective distance from the reference plane, and that each waveguide structure has the respective output facet in a respective straight portion of the plurality of straight portions.

[0133] In Example 5, the PIC device according to example 4 may optionally further include that the plurality of waveguide structures includes, at least: a first waveguide structure having a first output facet in a first straight portion at a first distance from the reference plane; and a second waveguide structure having a second output facet in a second straight portion at a second distance from the reference plane, wherein the first distance is different from the second distance.

[0134] In Example 6, the PIC device according to any one of examples 1 to 3 may optionally further include that the output side of the cladding structure is structured to define a curved profile, such that the respective output facet of each waveguide structure is at a respective position along the curved profile of the output side.P96280 from P92961 32

[0135] In Example 7, the PIC device according to example 6 may optionally further include that the curved profile is a concave profile.

[0136] In Example 8, the PIC device according to example 6 or 7 may optionally further include that the plurality of waveguide structures includes, at least: a first waveguide structure having a first output facet at a first position along the curved profile defining a first distance from the reference plane; and a second waveguide structure having a second output facet at a second position along the curved profile defining a second distance from the reference plane, wherein the first distance is different from the second distance.

[0137] In Example 9, the PIC device according to example 8 may optionally further include that the plurality of waveguide structures further includes a third waveguide structure aving a third output facet at a third position along the curved profile defining a third distance from the reference plane; wherein the third distance is equal to the first distance.

[0138] In Example 10, the PIC device according to example 9 may optionally further include that the first position along the curved profile is at a first side of a center axis of the curved profile, that the second position along the curved profile is aligned with the center axis of the curved profile, and that the third position along the curved profile is at a second side of a center axis of the curved profile, opposite to the first side.

[0139] In Example 11, the PIC device according to any one of examples 1 to 3 may optionally further include that the output side of the cladding structure is structured to define a plurality of curved portions, that each curved portion is at a respective distance from the reference plane, and that each waveguide structure has the respective output facet in a respective curved portion of the plurality of curved portions.

[0140] In Example 12, the PIC device according to example 11 may optionally further include that the plurality of waveguide structures includes, at least: a first waveguide structure having a first output facet in a first position of a first curved portion; and a second waveguide structure having a second output facet in a second position of the first curved portion.

[0141] In Example 13, the PIC device according to example 11 may optionally further include that the plurality of waveguide structures includes, at least: a first waveguide structure having a first output facet in a first curved portion at a first distance from the reference plane; and a second waveguide structure having a second output facet in a second curved portion at a second distance from the reference plane, wherein the first distance is different from the second distance.

[0142] Example 14 is a system including: the PIC device according to any one of examples 1 to 13; and a lens optically coupled with the PIC device and configured to receive the light outputP96280 from P92961 33 from the plurality of waveguide structures, wherein the main emission direction corresponds to the optical axis of the lens.

[0143] In Example 15 the system according to example 14 may optionally further include that the lens consists of a single material.

[0144] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

[0145] The phrase “at least one” and “one or more” may be understood to include a numerical quantity greater than or equal to one (e.g., one, two, three, four, [...], etc.). The phrase “at least one of’ with regard to a group of elements may be used herein to mean at least one element from the group consisting of the elements. For example, the phrase “at least one of’ with regard to a group of elements may be used herein to mean a selection of: one of the listed elements, a plurality of one of the listed elements, a plurality of individual listed elements, or a plurality of a multiple of individual listed elements.

[0146] All acronyms defined in the above description additionally hold in all claims included herein.

[0147] While the invention has been particularly shown and described with reference to specific aspects, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes, which come within the meaning and range of equivalency of the claims, are therefore intended to be embraced.P96280 from P92961 34List of reference signs 208-3 Third output facet 212 Input side100 PIC pitch converter 214 Output side100a Configuration 216-1 First waveguide channels100b Configuration 216-2 Second waveguide channels102 Waveguides 216-3 Third waveguide channels102- 1 First waveguide 220 Main emission direction102-2 Second waveguide 230 Reference plane102-3 Third waveguide 240 Substrate104 Light Sources 250a First configuration104-1 Blue light source 250b Second configuration104-2 Green light source 300 System104-3 Red light source 300a First configuration106 Lens 300b Second configuration108 Curved focal plane 302 Lens200 PIC device 320 Optical axis200a First configuration 330 Lens plane200b Second configuration 352 Light Sources200c Third configuration 352-1 First light source200d Fourth configuration 352-2 Second light source202 Cladding structure 352-3 Third light source203 Upper cladding portion 400 PIC device204 Waveguide structures 400a First configuration205 Lower cladding portion 400b Second configuration 204-1 First waveguide structure 402 Cladding structure 204-2 Second waveguide structure 404 Waveguide structures 204-3 Third waveguide structure 404-1 First waveguide structure206 Input facet 404-2 Second waveguide structure206-1 First input facet 404-3 Third waveguide structure206-2 Second input facet 406 Input facet206-3 Third input facet 406-1 First input facet208 Output facet 406-2 Second input facet208-1 First output facet 406-3 Third input facet208-2 Second output facet 408 Output facetP96280 from P92961 35408-1 First output facet 522-3 Third position 408-2 Second output facet 530 Reference plane 408-3 Third output facet 600 PIC device 412 Input side 602 Cladding structure 414 Output side 604 Waveguide structures416-1 First waveguide channels 604-1 First waveguide structure 416-2 Second waveguide channels 604-2 Second waveguide structure 416-3 Third waveguide channels 604-3 Third waveguide structure 420 Main emission direction 606 Input facet 430 Reference plane 606-1 First input facet 500 PIC device 606-2 Second input facet500a First configuration 606-3 Third input facet 500b Second configuration 608 Output facet 502 Cladding structure 608-1 First output facet 504 Waveguide structures 608-2 Second output facet 504-1 First waveguide structure 608-3 Third output facet 504-2 Second waveguide structure 612 Input side 504-3 Third waveguide structure 614 Output side 506 Input facet 616-1 First waveguide channels 506-1 First input facet 616-2 Second waveguide channels 506-2 Second input facet 616-3 Third waveguide channels 506-3 Third input facet 620 Main emission direction 508 Output facet 622-1 First curved portion 508-1 First output facet 622-2 Second curved portion 508-2 Second output facet 622-3 Third curved portion 508-3 Third output facet 624-1 First focus correction 512 Input side 624-2 Second focus correction 514 Output side 624-3 Third focus correction516-1 First waveguide channels 626 Displacement 516-2 Second waveguide channels 630 Reference plane 516-3 Third waveguide channels 700 Method 520 Main emission direction 710 Method step 522-1 First position 720 Method step 522-2 Second position 730 Method stepP96280 from P92961 36800a-800g Simulation results801 First panel802 Second panel 802e Blue focus point 802f Blue focus point 802g Blue focus point803 Third panel 804e Red focus point 804f Red focus point806g Green focus point810c-810g Simulation results820d, 820f Simulation results850g, 860g Simulation results856g Green focus point

Claims

P96280 from P92961 37Claims1. A Photonic Integrated Circuit, PIC, device (200) comprising: a cladding structure (202); and a plurality of waveguide structures (204) disposed in the cladding structure (202), wherein each waveguide structure (204) comprises an output facet (208) for outputting light from the waveguide structure (204), the output facet (208) being disposed at an output side (214) of the cladding structure (202), wherein the output side (214) of the cladding structure (202) is structured such that the respective output facet (208) of each waveguide structure (204) is at a respective distance from a reference plane (230) that is perpendicular to a main emission direction of light by the plurality of waveguide structures (204), wherein the plurality of waveguide structures (204) comprises, at least: a first waveguide structure (204-1) configured to guide light having a first wavelength, wherein the output side (214) of the cladding structure (202) is structured such that a first output facet (208-1) of the first waveguide structure (204-1) is at a first distance from the reference plane (230); and a second waveguide structure (204-2) configured to guide light having a second wavelength different from the first wavelength, wherein the output side (214) of the cladding structure (202) is structured such that a second output facet (208-2) of the second waveguide structure (204-2) is at a second distance from the reference plane (230), different from the first distance.

2. The PIC device (200) according to claim 1, wherein the plurality of waveguide structures (204) further comprises a third waveguide structure (204-3) configured to guide light having a third wavelength different from the first wavelength and different from the second wavelength,P96280 from P92961 38 wherein the output side (214) of the cladding structure (202) is structured such that a third output facet (208-3) of the third waveguide structure (204-3) is at a third distance from the reference plane (230), different from the first distance and different from the second distance.

3. The PIC device (200) according to claim 1 or 2, wherein the first wavelength is shorter than the second wavelength; and wherein the first distance is less than the second distance.

4. The PIC device (200, 400) according to any one of claims 1 to 3, wherein the output side (414) of the cladding structure (402) is structured to define a step-like profile comprising a plurality of straight portions (422-1, 422-2, 422-3), wherein each straight portion (422-1, 422-2, 422-3) is at a respective distance from the reference plane (430), and wherein each waveguide structure (404) has the respective output facet (408) in a respective straight portion of the plurality of straight portions (422-1, 422-2, 422-3).

5. The PIC device (200, 400) according to claim 4, wherein the first waveguide structure (404-1) has the first output facet (408-1) in a first straight portion (422-1) at the first distance from the reference plane (430); and wherein the second waveguide structure (404-2) has the second output facet (408- 2) in a second straight portion (422-2) at the second distance from the reference plane (430).

6. The PIC device (200, 500) according to any one of claims 1 to 3, wherein the output side (514) of the cladding structure (502) is structured to define a curved profile, such that the respective output facet (508) of each waveguideP96280 from P92961 39 structure (504) is at a respective position along the curved profile of the output side (514).

7. The PIC device (200, 500) according to claim 6, wherein the curved profile is a concave profile.

8. The PIC device (200, 500) according to claim 6 or 7, wherein the first waveguide structure (504-1) has the first output facet (508-1) at a first position along the curved profile defining the first distance from the reference plane (530); and wherein the second waveguide structure (504-2) has the second output facet (508-2) at a second position along the curved profile defining the second distance from the reference plane (530).

9. The PIC device (200, 500) according to claim 8, wherein the plurality of waveguide structures (504) further comprises a third waveguide structure (504-3) having a third output facet (508-3) at a third position along the curved profile defining a third distance from the reference plane (530); wherein the third distance is equal to the first distance.

10. The PIC device (200, 500) according to claim 9, wherein the first position along the curved profile is at a first side of a center axis of the curved profile, wherein the second position along the curved profile is aligned with the center axis of the curved profile, and wherein the third position along the curved profile is at a second side of a center axis of the curved profile, opposite to the first side.P96280 from P92961 4011. The PIC device (200, 600) according to any one of claims 1 to 3, wherein the output side (614) of the cladding structure (602) is structured to define a plurality of curved portions (622-1, 622-2, 622-3), wherein each curved portion (622-1, 622-2, 622-3) is at a respective distance from the reference plane (630), and wherein each waveguide structure (604) has the respective output facet (608) in a respective curved portion of the plurality of curved portions (622-1, 622-2, 622-3).

12. The PIC device (200, 600) according to claim 11, wherein the first waveguide structure (604-1) has the first output facet (608-1) in a first position of a first curved portion (622-1); and wherein the second waveguide structure (604-2) has the second output facet (608- 2) in a second position of the first curved portion (622-1).

13. The PIC device (200, 600) according to claim 11, wherein the first waveguide structure (604-1) has the first output facet (608-1) in a first curved portion (622-1) at the first distance from the reference plane (630); and wherein the second waveguide structure (604-2) has the second output facet (608- 2) in a second curved portion (622-2) at the second distance from the reference plane (630).

14. A system (300) comprising: the PIC device (200) according to any one of claims 1 to 13; and a lens (302) optically coupled with the PIC device (200) and configured to receive the light output from the plurality of waveguide structures (204),P96280 from P92961 41 wherein the main emission direction (220) corresponds to the optical axis (320) of the lens (302).

15. The system (300) according to claim 14, wherein the lens (302) consists of a single material.

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