Photonic chip having a guiding structure and a surrounding cladding matrix, and method of modifying same

Abstract

There is described a method for modifying a photonic chip having a guiding structure and a cladding matrix surrounding the guiding structure, where the guiding structure and the cladding matrix are configured for guiding an optical mode within the photonic chip. The method generally has directing a focal point of a corrective laser beam within a portion of the cladding matrix, the portion of the cladding matrix being spaced away from and proximate to the guiding structure, the corrective laser beam having a central wavelength greater than a bandgap wavelength of the cladding matrix, wherein, upon said directing, the portion of the cladding matrix absorbs at most 10 photons of said corrective laser beam thereby creating a local permanent matrix change spaced apart from the guiding structure, the permanent matrix change modifying an effective refractive index of the guiding structure.

Description

PHOTONIC CHIP HAVING A GUIDING STRUCTURE AND A SURROUNDING CLADDING MATRIX, AND METHOD OF MODIFYING SAMEFIELD

[0001] The improvements generally relate to photonic chips and more particularly to the manufacturing and testing of such photonic chips.BACKGROUND

[0002] In a manner analogous to electronic chips processing electronic signals, photonic chips process optical signals. Photonic chips are typically manufactured using foundry processes used for microelectronics manufacturing. Microelectronics foundry processes can reach tolerances of about 1 .5 nm at the most which while satisfactory for state-of-the-art microelectronics may be insufficient for photonic chip manufacturing. As such, each photonic chip manufactured using known foundry processes is rigorously inspected and tested to make sure it is conform to design specifications. Once a photonic chip has been identified as defective, it may be discarded which can lead to significant losses in terms of materials and time. Although existing techniques for manufacturing photonic chips are satisfactory to a certain degree, there always remains room for improvement.SUMMARY

[0003] There is described methods and systems for modifying photonic chips having guiding structure(s) surrounded by a cladding matrix, and especially photonic chips that have been identified as defective for failing to meet design tolerance(s) and / or performances parameter(s) according to individual inspection and testing. The methods and systems involve a testing routine in which parameter(s) indicative of a performance of the photonic chip’s guiding structure(s), such as semiconductor waveguide(s), is measured and in some cases even monitored over time. Examples of such parameters can include, but are not limited to, wavelength, phase, amplitude, polarization, dispersion, gain and / or loss, to name a few examples. When a defective photonic chip is identified, a corrective laser beam is used, e.g., before, during or after the monitoringof the parameter(s), to perform one or more permanent matrix changes into portion(s) of the cladding matrix that are located proximate to one or more guiding structures which actually propagate optical modes during use of the photonic chip. The portion(s) of the cladding matrix where the permanent matrix changes are laser induced are spaced apart from, but relatively proximate to, the corresponding guiding structures. These permanent matrix changes can in turn cause changes in effective refractive indexes of the proximate guiding structures. In some embodiments, the laser-induced permanent matrix changes are provided in the form of mechanical stress or more region of increased density. Such permanent matrix changes and testing routine can be performed iteratively until the monitored parameters match corresponding reference parameters of a reference photonic chip. In at least some instances, the laser-induced permanent matrix changes can result in the tuning of the performance of a defective photonic chip up to a level where the photonic chip can become effectively defectless.

[0004] It is known to laser-induce an effective refractive index modification within a photonic chip by directing a mid infrared laser beam within a semiconductor waveguide. In this existing technique, the mid infrared laser beam is generally chosen to have a central wavelength which is greater than a bandgap wavelength of the semiconductor waveguide structure. It was found that, in this existing technique, multiphoton absorption is allowed to occur with only a limited number of simultaneous incident photons as the bandgap wavelength of the semiconductor waveguide is only a little greater than the central wavelength of the mid infrared laser beam. For example, Fig. 1 shows an example of a photonic chip having a silicon waveguide surrounding in a fused silica cladding matrix. As schematically illustrated in Fig. 1A, to create multiphoton absorption within the silicon waveguide, as few as 3 simultaneous 3-pm photons are required.

[0005] Although modifying the guiding structure with a satisfactory precision was possible, it was found that laser-inducing effective refractive index modifications proximate to the semiconductor waveguide and outside thereof, e.g., in a cladding matrix surrounding the semiconductor waveguide, could not be made with as much precision or repeatability. Indeed, creating an effective refractive index modification within the cladding matrix requires multiphoton absorption, which is the main mechanism by whichintense laser beams can modify matter in a deterministic, repeatable, and controllable fashion. This drawback stems from the generally significant difference between a bandgap wavelength of the cladding matrix and the central wavelength of the mid infrared laser beam which can require at least 20-30 simultaneous mid infrared photons to create multiphoton absorption. As depicted in Fig. 1 B, in the case of the fused silica cladding matrix, multiphoton absorption would require at least 22 incident 3.0-pm photons to simultaneously or hit the fused silica cladding matrix. For a precise permanent matrix change to be made in those conditions, the 22 3-pm photons would have to be received at exactly the same time and exactly the same position, which is understandably a statistically unlikely and unrepeatable event. Of course, the probability and repeatability of such an event increase with an intensity of the corrective laser beam. However, using a corrective laser beam having an intensity greater than an intensity threshold (i.e., triggering nonlinear phenomenon other than multiphoton absorption) could undesirably and irreversibly damage neighbouring components of the photonic chip. As such, with a corrective laser beam of reasonable intensity, multiphoton absorption with 22 simultaneous photons remains mostly unlikely or unrepeatable. Practically, a corrective laser beam of reasonable intensity, it has been observed that the 22 3-pm photons would arrive chaotically within a certain delay from one another, and within a certain spatial region from one another, thereby creating rough permanent matrix changes of different, uncontrollable morphologies and depth dimensions (across the depth of the photonic chip). Accordingly, any permanent cladding change made by such a 3-pm mid infrared laser would have dimensions that would vary greatly from one experiment to another. Such poor dimensioning and tolerancing of the permanent cladding change greatly limits the attractiveness of this technique, especially for different foundry processes which each have their specific photonic chip designs and tolerances. Improvements were thus required to repeatably create local permanent matrix changes with a satisfactory precision and tolerancing.

[0006] The methods and systems described herein involve a step of directing a focal point of a corrective laser beam within a portion of the cladding matrix. An example of which is shown in Fig. 2. As shown, the portion of the cladding matrix where the corrective laser beam is focalised is spaced away from, but proximate to, the guidingstructure. Hence, any resulting permanent matrix change can modify an effective refractive index of the guiding structure. However, in this disclosure, the corrective laser beam is selected to have a central wavelength greater than the bandgap wavelength of the cladding matrix by only a limited amount. As shown in Fig. 2A, multiphoton absorption can be reached with at most 10 photons, more preferably at most 8 photons, and most preferably at most 5 photons, of the corrective laser beam. Multiphoton absorption in these latter conditions is thus statistically more likely to occur where the focal point of the correction laser beam is directed. As a result, a local permanent matrix change can be precisely and repeatably created proximate to the guiding structure. For instance, the dimensions Dx and Dy, as well as the positioning P(x,y,z) of such local permanent matrix change, can be precise and repetitive. As the required number of simultaneous photons is relatively limited, precision and repeatability with which the permanent matrix change is laser induced can be significantly enhanced. In an experiment, quasi-lossless phase shift of the order of the free-spectral range of an example integrated interferometer was obtained using the methods and systems described herein.

[0007] In accordance with a first aspect of the present disclosure, there is provided a method for modifying a photonic chip having a guiding structure and a cladding matrix surrounding the guiding structure, the cladding matrix having a bandgap wavelength, the guiding structure and the cladding matrix configured for guiding an optical mode within the photonic chip, the method comprising: directing a focal point of a corrective laser beam within a portion of the cladding matrix, the portion of the cladding matrix being spaced away from and proximate to the guiding structure, the corrective laser beam having a central wavelength greaterthan the bandgap wavelength of the cladding matrix, wherein, upon said directing, the portion of the cladding matrix absorbs at most 10 photons of said corrective laser beam thereby creating a local permanent matrix change spaced apart from the guiding structure, the permanent matrix change modifying an effective refractive index of the guiding structure; performing a testing routine on the photonic chip including determining a parameter indicative of a performance of the guiding structure; and upon determining that the parameter mismatches a reference parameter associated with a reference photonic chip, repeating said directing and saidtesting routine until the parameter matches the reference parameter within a given tolerance.

[0008] Further in accordance with the first aspect of the present disclosure, the central wavelength of the corrective laser beam can for example be one of equal to and below a bandgap wavelength of the guiding structure.

[0009] Still further in accordance with the first aspect of the present disclosure, the local permanent matrix change can for example be caused by a simultaneous absorption of at most 8 photons, and most preferably at most 5 photons.

[0010] Still further in accordance with the first aspect of the present disclosure, said directing can for example include positioning the focal point at focal point coordinates relative to guiding structure coordinates, the local permanent matrix change positioned at the focal point coordinates within a tolerance below 0.5 pm, most preferably below 0.4 pm, and most preferably of about 0.25 pm.

[0011] Still further in accordance with the first aspect of the present disclosure, the guiding structure can for example have a first depth coordinate, the focal point of the corrective laser beam being directed to a second depth coordinate different from the first depth coordinate of the guiding structure.

[0012] Still further in accordance with the first aspect of the present disclosure, the local permanent matrix change can for example have a proximal portion proximal to the guiding structure, the proximal portion spaced away from the guiding structure by a spacing distance below 20 pm, preferably below 5 pm and most preferably below 2 pm.

[0013] Still further in accordance with the first aspect of the present disclosure, the local permanent matrix change can for example have a dimension ranging between about 0.1 pm and 50 pm, preferably between about 1 pm and 20 pm, and most preferably about 2 pm and 10 pm.

[0014] Still further in accordance with the first aspect of the present disclosure, the local permanent matrix change can for example be a first local permanent matrix change,the method can for example further comprise repeating said directing at another portion within the cladding matrix thereby forming a subsequent local permanent matrix change, the subsequent local permanent matrix change having a morphological property similar to a morphological property of the local permanent matrix change.

[0015] Still further in accordance with the first aspect of the present disclosure, the morphological property can for example include at least one of: a first dimension extending parallel to the photonic chip, a second dimension extending perpendicular to the photonic chip, a refractive index change, and a density change.

[0016] Still further in accordance with the first aspect of the present disclosure, the central wavelength of the corrective laser beam can for example range between about 300 nm and 1100 nm, more preferably between about 800 nm and 1050 nm, and is most preferably of about 500 nm.

[0017] Still further in accordance with the first aspect of the present disclosure, the corrective laser beam can for example include a series of pulses having a pulse duration below a microsecond range, preferably below a nanosecond range, and most preferably below a picosecond range.

[0018] In accordance with a second aspect of the present disclosure, there is provided a system for modifying a photonic chip having a guiding structure and a cladding matrix surrounding the guiding structure, the cladding matrix having a bandgap wavelength, the guiding structure and the cladding matrix configured for guiding an optical mode within the photonic chip, the system comprising: a corrective laser apparatus configured for directing a focal point of a corrective laser beam within a portion of the cladding matrix, the portion of the cladding matrix being spaced away from and proximate to the guiding structure, the corrective laser beam having a central wavelength greater than the bandgap wavelength of the cladding matrix, wherein, upon said directing, the portion of the cladding matrix absorbs at most 10 photons of said corrective laser beam thereby creating a local permanent matrix change spaced apart from the guiding structure, the permanent matrix change modifying an effective refractive index of the guiding structure; a photonic chip testing apparatus performing a testing routine on the guiding structureincluding determining a parameter indicative of a performance of the guiding structure; and a controller communicatively coupled to the corrective laser apparatus and to the photonic chip testing apparatus, the controller having a processor and a memory having stored thereon instructions that when executed by the processor perform the steps of: comparing the parameter to a reference parameter associated with a reference photonic chip; and upon determining that the parameter mismatches the reference parameter, repeating said directing and said testing routine until the parameter matches the reference parameter within a given tolerance.

[0019] Further in accordance with the second aspect of the present disclosure, the central wavelength of the corrective laser beam can for example be one of equal to and below a bandgap wavelength of the guiding structure.

[0020] Still further in accordance with the second aspect of the present disclosure, the local permanent matrix change can for example be caused by a simultaneous absorption of at most 8 photons, and most preferably at most 5 photons.

[0021] Still further in accordance with the second aspect of the present disclosure, the system can for example further comprise receiving guiding structure coordinates indicative of coordinates of the guiding structure within the cladding matrix; determining focal point coordinates indicative of where the focal point of the corrective laser beam is to be directed, said focal point coordinates spaced apart from said guiding structure coordinates by at most 20 pm, said directing including directing the focal point of the corrective laser beam within the cladding matrix based on the focal point coordinates.

[0022] Still further in accordance with the second aspect of the present disclosure, the corrective laser apparatus can for example include a 1030 nm-wavelength laser source.

[0023] Still further in accordance with the second aspect of the present disclosure, the corrective laser apparatus can for example include a 800 nm-wavelength laser source.

[0024] Still further in accordance with the second aspect of the present disclosure, the corrective laser apparatus can for example include a 500 nm-wavelength laser source.

[0025] In accordance with a third aspect of the present disclosure, there is provided a photonic chip comprising: a guiding structure; a cladding matrix surrounding the guiding structure, the guiding structure and the cladding matrix configured for guiding an optical mode within the photonic chip; and a laser-induced permanent matrix change localized within said cladding matrix and spaced apart from the guiding structure, the laser- induced permanent matrix change having a dimension of 4 pm or less, the permanent matrix change permanently modifying an effective refractive index of the guiding structure.

[0026] Further in accordance with the third aspect of the present disclosure, the dimension can for example be 1 pm or less.

[0027] In accordance with a fourth aspect of the present disclosure, there is provided a method for modifying a photonic chip having a guiding structure, a cladding matrix surrounding the guiding structure, and a substrate receiving the cladding matrix, the guiding structure and the cladding matrix configured for guiding an optical mode within the photonic chip, the cladding matrix having a bandgap wavelength, the method comprising: directing a focal point of a corrective laser beam within a surface portion of the substrate through the cladding matrix, the surface portion of the substrate being spaced away from and proximate to the guiding structure, the corrective laser beam having a central wavelength below the bandgap wavelength of the cladding matrix, said directing creating a local permanent substrate change spaced apart from the guiding structure and extending through the cladding matrix towards the guiding structure, the permanent substrate change modifying an effective refractive index of the guiding structure; performing a testing routine on the photonic chip including determining a parameter indicative of a performance of the guiding structure; and upon determining that the parameter mismatches a reference parameter associated with a reference photonic chip, repeating said directing and said testing routine until the parameter matches the reference parameter within a given tolerance.

[0028] All technical implementation details and advantages described with respect to a particular aspect of the present invention are self-evidently mutatis mutandis applicable for all other aspects of the present invention.

[0029] Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.DESCRIPTION OF THE FIGURES

[0030] In the figures,

[0031] Fig. 1 is a cross-sectional view of an example of a photonic chip having a silicon waveguide and a surrounding fused silica cladding matrix, shown with a rough local permanent matrix change laser-induced using mid infrared photons directed proximate to the guiding structure, in accordance with one or more embodiments;

[0032] Fig. 1A is a graph showing a band diagram of the silicon waveguide of Fig. 1 , showing that, with a correction laser beam having a central wavelength at about 3.0 pm, about 3 photons are required to bridge a bandgap of the silicon waveguide for multiphoton absorption, in accordance with one or more embodiments;

[0033] Fig. 1 B is a graph showing a band diagram of the fused silica cladding matrix of Fig. 1 , showing that, with a correction laser beam having a central wavelength at about 3.0 pm, about 22 photons are required to bridge a bandgap of the fused silica cladding matrix for multiphoton absorption, which can cause a local permanent matrix change with rough dimensions and poor tolerances, in accordance with one or more embodiments;

[0034] Fig. 2 is a cross-sectional view of an example of a photonic chip having a silicon waveguide and a surrounding fused silica cladding matrix, shown with a precisely positioned local permanent matrix change proximate to the guiding structure, in accordance with one or more embodiments;

[0035] Fig. 2A is a graph showing a band diagram of the fused silica cladding matrix of Fig. 2, showing that, with a correction laser beam having a central wavelength at about 800 nm, about 6 photons are required to bridge a bandgap of the fused silica cladding matrix for multiphoton absorption, which can cause a local permanent matrix changewith a finely tuned dimensions and tighter tolerances, in accordance with one or more embodiments;

[0036] Fig. 3 is a schematic view of an example of a system for modifying a photonic chip having a guiding structure and a cladding matrix surrounding the guiding structure, showing an exemplary permanent matrix change within the cladding matrix, in accordance with one or more embodiments;

[0037] Fig. 4A is an oblique view of the photonic chip of Fig. 3 onto which a testing routine is being performed and showing a measured parameter mismatch, in accordance with one or more embodiments;

[0038] Fig. 4B is an oblique view of the photonic chip of Fig. 3 receiving a corrective laser beam within the cladding matrix, in accordance with one or more embodiments;

[0039] Fig. 4C is an oblique view of the photonic chip of Fig. 3 onto which a subsequent testing routine is being performed and showing a measured parameter match, in accordance with one or more embodiments;

[0040] Fig. 5 is a graph showing the spatial mode propagating into the photonic chip of Fig. 4A, in accordance with one or more embodiments;

[0041] Fig. 6 is a graph showing the spatial mode propagating into the guiding structure of the photonic chip of Fig. 4C, in accordance with one or more embodiments;

[0042] Fig. 6A is microscope image showing a top plan view of some local permanent matrix changes of the photonic chip of Fig. 4C, taken along section 6A-6A of Fig. 6, in accordance with one or more embodiments;

[0043] Fig. 6B is a microscope image showing an enlarged view of the local permanent matrix changes of Fig. 6A, in accordance with one or more embodiments;

[0044] Fig. 7 is a flow chart of an example method of modifying a photonic chip having a guiding structure and a cladding matrix surrounding the guiding structure, in accordance with one or more embodiments;

[0045] Fig. 8 is a top plan view of an example of a guiding structure and local permanent matrix changes made on either lateral side thereof, in accordance with one or more embodiments;

[0046] Fig. 8A is a cross-sectional view of the guiding structure of Fig. 8, taken along section 8A-8A of Fig. 8, in accordance with one or more embodiments;

[0047] Fig. 9 is a cross-sectional view of another example of a photonic chip having a guiding structure, and a cladding matrix surrounding the guiding structure, shown with four local permanent matrix change about the guiding structure, in accordance with one or more embodiments;

[0048] Fig. 10 is a cross-sectional view of an example of a photonic chip having a guiding structure, a cladding matrix surrounding the guiding structure, and a substrate receiving the cladding matrix, shown with two local permanent substrate changes at an interface of the substrate and the guiding structure, in accordance with one or more embodiments;

[0049] Fig. 10A is a microscope image showing a top plan view of the photonic chip of Fig. 10, showing the guiding structure and two local permanent substrate changes, in accordance with one or more embodiments; and

[0050] Fig. 11 is a schematic view of an example of a computing device of a controller of the system of Fig. 3, in accordance with one or more embodiments.DETAILED DESCRIPTION

[0051] Fig. 3 shows an example of a system 100 for modifying a photonic chip 10. The system 100 can be used at any testing stages of the manufacture or the life of the photonic chip 10. For instance, the system 100 can be used at a design stage where the photonic chip 10 is prototyped and corrected iteratively as desired, at a foundry stage where the photonic chip 10 is mass produced and / or at a packaging stage where the photonic chip 10 is integrated into a package, for instance. In any case, the photonic chip 10 can be modified at any time after its performance is monitored to be insufficient.

[0052] As shown, the photonic chip 10 generally has a guiding structure 12, and a cladding matrix 14 wholly or partially surrounding the guiding structure 12. The guiding structure 12 can have any size, shape or form. For instance, the guiding structure 12 can be a rib waveguide, a ridge waveguide, a cylindrical waveguide, and the like. In some embodiments, the cladding matrix 14 can be made of any material having a refractive index lower than a refractive index of the material of the guiding structure 12 to allow proper confinement and propagation of an optical mode along the guiding structure 12. In this example, the guiding structure 12 and the cladding matrix 14 are received directly on a substrate 11 . However, in some other embodiments, the guiding structure 12 can be suspended over the substrate 11. The substrate 11 can be omitted in some other embodiments.

[0053] Still referring to Fig. 3, the system 100 is configured for directing a corrective laser beam 1 12, or a focal point 114 thereof, within a portion the cladding matrix 14. It is intended that the corrective laser beam 112 is selected to its central wavelength is well- suited for causing the permanent matrix changes 20 to the material of the cladding matrix 14 via multiphoton absorption. Not any type of multiphoton absorption is targeted in this disclosure as it was found that few-photon absorption within the cladding matrix 14 can lead to more satisfactory results. More specifically, the central wavelength of the corrective laser beam 112 is selected so that at most 10 simultaneous photons are quired to create multiphoton absorption within the cladding matrix 14. For example, when the cladding matrix is made of fused silica glass, the bandgap wavelength of the cladding matrix is of about 139 nm. As such, at least in these embodiments, the central wavelength of the corrective laser beam can range between about 300 nm and about 1 100 nm, preferably between about 800 nm and about 1050 nm and most preferably about between of about 1030 nm. For instance, the corrective laser apparatus can include a 1030 nm-wavelength laser source, a 800 nm-wavelength laser source, a 500 nm-wavelength laser source, or a combination thereof. It is intended that optical energy can be delivered within the photonic chip 10, i.e., and more specifically within the cladding matrix, in a way that can cause precise and repeatable permanent matrix changes. For instance, the local permanent matrix change can have a dimension ranging between about 0.1 pm and 50 pm, preferably between about 1 pm and 20 pm, and mostpreferably about 2 pm and 10 pm. The dimension of the local permanent matrix change can have tolerances ranging between about 0.5 pm and 2 pm, and most preferably of about 0.25 pm for smaller dimensions, or of about 5% for greater dimensions. Alternatively or additionally, the positioning of the local permanent matrix change 20 within the cladding matrix 14 can have tolerances ranging between about 0.5 pm and 0.2 pm, and most preferably of about 0.25 pm.

[0054] The corrective laser beam 112 forms a laser-induced permanent matrix change 20 within the cladding matrix 14. The energy carried by the focal point 114 can cause internal mechanical stress within the photonic chip 10, and more specifically within the portion of the cladding matrix 14 surrounding. In some embodiments, the permanent matrix change 20 is provided in the form of one or more region of different density 20’ running through the cladding matrix 14 proximate to the guiding structure 12. Additionally or alternatively, the permanent matrix change 20 can be provided in the form of a compressive stress, a tensile stress, a shear stress, a torsion stress, or a combination thereof. As shown, the laser-induced permanent matrix changes 20 and 20’ spatially extend into the cladding matrix 14 proximate enough to the guiding structure 12 to cause a modification of an effective refractive index of the guiding structure 12. It is thus intended that, during use of the photonic chip 10, the guiding structure 12 and the cladding matrix 14 are configured for guiding the optical mode across the photonic chip 10 along the guiding structure 12 while the laser-induced permanent matrix change 20 slightly modify the guiding properties of the guiding structure 12. Modifying the photonic chip 10 in this manner can thus be seen as a fix-and-go process.

[0055] As shown, the system 100 has a corrective laser apparatus 110 and a photonic chip testing apparatus 120. In some embodiments, the system 100 can also incorporate a computer vision apparatus 130 incorporating a camera 132 imaging the photonic chip 10 in real time. A multi-axis movement stage 140 can optionally be used for moving the photonic chip 10 within a working zone as desired. The multi-axis movement stage 140 can be a translation stage and / or a rotation stage. In some embodiments, the corrective laser apparatus 110 can be made integral to existing photonic testing apparatuses.

[0056] The system 100 can have a controller 150 which is communicatively coupled to the corrective laser apparatus 110, the photonic chip testing apparatus 120, the computer vision apparatus 130 and / or the multi-axis moving stage 140, for instance. The controller 150 has a processor and a memory having stored thereon instructions that when executed by the processor perform preprogrammed instructions and / or method steps. To do so, the controller 150 generally incorporates hardware components provided in the form of a computing device and software components provided in the form of programs, algorithms and the like for performing the method steps. An example of the computing device is described below.

[0057] As depicted, the corrective laser apparatus 110, the photonic chip testing apparatus 120, the computer vision apparatus 130 and the multi-axis moving stage 140 can be fixedly or removably mounted to a frame 106. In this specific embodiment, the frame 106 is provided in the form of an optical bench or table. However, it is understood that in some other embodiments the corrective laser apparatus 110, the photonic chip testing apparatus 120, the computer vision apparatus 130 and the multi-axis moving stage 140 can be mounted independently from one another at different locations of a photonic chip production line, for instance. In some embodiments, electronic probes and / or fiber probes of the photonic chip testing apparatus 120 can be in the path of the corrective laser beam 112 of the corrective laser apparatus 110. In these embodiments, the corrective laser apparatus 110, a laser source thereof or an output thereof can be moved as desired above or below the photonic chip 10. Such movement can be generated using a two-axes or three-axes galvanometer scanner, a coarse gantry mechanism for movement within a centimeter squared, a fine gantry mechanism for movement within a relatively small area (e.g., 100 pm x 100 pm, 10 x 10 pm), a piezo micropositioner (e.g., an hexapod, a spatial light modulator (SLM)), an optical fiber cable with a microlens tip, a 6 degrees of freedom robotic arm, any other motion apparatus with or without moving part(s) that can translate and / or deflect the corrective laser beam 112, and / or any combination thereof

[0058] The guiding structure 12 can include any type of semiconductor waveguide used in photonic chips. For instance, the guiding structure 12 can have a stripwaveguide, a rib waveguide, a slot waveguide, a photonic crystal waveguide, a subwavelength waveguide grating (SWG) waveguide, fiber waveguide, a SWG slot waveguide, a SPP slot waveguide, a suspended waveguide, and the like. The guiding structure 12 can be part of a photonic component including, but not limited to, coupler(s), directional coupler(s), star coupler(s), Y combiner(s), star coupler(s), array waveguide grating(s), interferometer(s), Mach-Zehnder interferometer(s), multimode interferometer(s)), ring resonator(s), spot size converter(s), waveguide Bragg grating(s), and the like.

[0059] It is understood that to enhance the laser-induced permanent matrix change 20, the material of the cladding matrix 14, which is targeted by the corrective laser beam 112, is different from the material of the guiding structure 12. For instance, in some embodiments where the guiding structure 12 is made of silicon, the cladding matrix 14 may be made of glass, silicon dioxide or any other suitable material different from silicon (e.g., doped silicon). The cladding matrix 14 can be made of any semiconductor or glass material (especially those easily implementable in a complementary metal-oxide semiconductor (CMOS) process like germanium, silicon nitride, etc.), other glass structures (doped glass) or even polymer structures, depending on the embodiment. The guiding structure 12 and the cladding matrix 14 can include one or more materials such as semiconductor materials, glass materials and the like. Examples of glass materials can include, but are not limited to, doped or undoped silica-based glasses, doped or undoped chalcogenide glasses, doped or undoped fluoride-based glass, buried oxide (BOX), and the like.

[0060] It is intended that the permanent matrix change 20 can be provided in any suitable size, shape or form. Typically, the permanent matrix change 20 is sufficiently spaced apart from the guiding structure 12 to prevent the corrective laser beam 112 to laser-induce modifications within the guiding structure 12, but sufficiently close to the guiding structure 12 so that the laser-induced permanent matrix change 20 extending within the cladding matrix 14 can affect the guiding properties of the nearby guiding structure 12. For instance, in some embodiments, the guiding structure 12 and the permanent matrix change 20 are spaced-apart by 10 pm, preferably 5 pm, and mostpreferably below 1 pm. In some embodiments, the photonic chip 1 1 extends in a x-y plane, with a thickness extending along a z-axis. In these embodiments, the permanent matrix change 20 may be spaced apart from the guiding structure 12 along one or more of the x-, y- and z-axes, depending on the embodiment. In certain embodiments, the permanent matrix change 20 runs alongside the guiding structure 12. In these embodiments, the spacing between the guiding structure 12 and the permanent matrix change 20 can be even. In some other embodiments, this spacing can be converging, diverging, uneven, and the like. As discussed in further detail below by way of examples, the guiding structure 12 and the permanent matrix change 20 may be similar in shape or size, albeit spaced-apart from one another. However, in some other embodiments, the guiding structure 12 and the permanent matrix change 20 bear dissimilar shape or size.

[0061] Fig. 4A shows the photonic chip 10 of Fig. 3 onto which a testing routine is being performed by the photonic chip testing apparatus 120. As shown, the photonic chip testing apparatus 120 determines a parameter P indicative of a performance of the guiding structure 12. When the measured parameter P and a reference parameter PREF of a reference photonic chip mismatch to one another within a given tolerance TOL, i.e., when P £ [PREF ~ TOL PREF+ TOL], the photonic chip 10 may be identified as defective. Instead of discarding the defective photonic chip 10, the photonic chip 10 is modified using the system 100. The reference photonic chip may correspond to a reference photonic chip that is deemed to be defectless or conform to design tolerance(s), for instance. The reference parameter(s) P EF can be stored on a memory system accessible to the controller 150. In some embodiments, each photonic chip being tested has an identifier identifying the type of photonic chip and one or more reference parameters PREF associated to the type of photonic chip. When such a photonic chip is being tested, the controller 150 can fetch the photonic type and / or the associated reference parameters PREF

[0062] In some embodiments, the photonic chip testing apparatus 120 has a test optical source 122 guiding a test optical signal 124 into and along a first end 12a of the guiding structure 12 and a detector 126 detecting an output signal 128 resulting from the guiding of the test optical signal 124. The test optical signal 124 can be injected usinggrating coupler(s), side coupler(s), tree-space injection setup(s) and the like. In some embodiments, the test optical signal can also be generated using an integrated laser on the chip. The output optical signal 128 can be detected using an integrated photodiode, a fiber probe, a free space detector, a spectrophotometer, a standard, infrared or hyperspectral camera imaging scattering outgoing from the photonic chip 10, to name a few examples. In these embodiments, the controller 150 can determine the parameter P based on the output signal 128. As shown in the specific embodiment of Fig. 4A, the detector can be a photodiode optically coupled to a second end 12b of the guiding structure 12 for detecting the output signal 128. In some embodiments, the detector is an infrared camera measuring the output signal scattering away from the guiding structure during the guiding of the test optical signal 124. The camera(s) can be part of the computer vision apparatus 130. It is intended that the testing routine needs not to be based solely on optical technologies. For instance, in some other embodiments, the testing routine involves optical modulation based on radio-frequency signals and / or electronic measurements.

[0063] As shown in Fig. 4B, the corrective laser apparatus 110 is used to direct a corrective laser beam 112, and more specifically a focal point 114 thereof, within a portion of the cladding matrix 14. The corrective laser beam 112 can be moved along a path 21 of the cladding matrix 14. In some embodiments, the path can be linear or can otherwise follow a shape of the guiding structure 12, albeit next to it. Due to the permanent matrix changes made proximate to the guiding structure 12, an effective refractive index of the portion of the guiding structure 12 can be modified by a certain extent, including positive or negative refractive index changes. The effective refractive index modification can cause the performance of the guiding structure 12 and overall photonic chip 10 to be modified accordingly.

[0064] As depicted in Fig. 4C, the modified photonic chip 10 can be tested again using the testing routine to determine whether the measured parameter P now matches the reference parameter PREF within the given tolerance TOL, i.e., if f e [PREF ~ T°L>' PREF + TOL], These steps can be repeated iteratively until a match is found, i.e., until the photonic chip 10 performs to a level where it can be deemed to be defectless. Once themodified photonic chip 10 has a pass on the testing routine, it can be put back into and along the photonic chip production line, thereby reducing the amount of photonic chips that are discarded after a failed testing routine. Considering that in some embodiments 50 % to 80 % of all photonic chips being produced using existing microelectronics foundry techniques may be defective, it is hypothesised that the system 100 can reduce such a photonic chip discard rate by at least 25 %, preferably below at least 50 % and most preferably at least 75 % using the methods and systems described herein compared to conventional manufacturing processes. It is also noted that the methods and systems described herein can correct defective photonic chips at relatively high speed.

[0065] Fig. 5 shows a visual representation of the optical mode propagating unaltered along the guiding structure 12 of the photonic chip of Fig. 4A, prior to the formation of the permanent matrix change within the portion of the cladding matrix 14 proximate to the guiding structure 12. In contrast, Fig. 6 shows a visual representation of the optical mode propagating in an altered fashion along the guiding structure 12 of the photonic chip of Fig. 4A, after the laser-inducing of the permanent matrix change 20 within the cladding matrix 14 proximate to the guiding structure 12. As shown, the optical mode illustrated in Fig. 6 slightly differs from the optical mode shown in Fig. 5, as the permanent matrix change 20 affects the coupling conditions of the guiding structure 12. An enlarged view of some exemplary permanent matrix changes 20 is shown in Figs. 6A and 6B. These images have been acquired using a camera positioned “in-line” with the corrective laser beam. The thin dark line in Fig. 6A corresponds to the guiding structure 12 while the white circles correspond to the permanent matrix changes 20. The phase change induced in the guiding structure 12 can be incrementally controlled by the number of dots which are permanently inscribed into the cladding matrix 14. As best shown in Fig. 6B, the permanent matrix changes 20 have permanently stressed portions forming spaced apart dot shapes extending within the cladding matrix 14 proximate to the guiding structure 12. In this example, the permanent matrix changes 20 have a dimension d of 4 pm or lower.

[0066] Fig. 7 shows a flow chart of an example method 700 of modifying a photonic chip having a guiding structure and a cladding matrix surrounding the guiding structure. As discussed above, the guiding structure and the cladding matrix are configured for guiding an optical mode within the photonic chip. It is understood that the method 700 can be performed using the system of Fig. 3 or any other suitable system for lasermodifying a photonic chip.

[0067] At step 702, a focal point of a corrective laser beam is directed within a portion of the cladding matrix. The portion of the cladding matrix is spaced away from and proximate to the guiding structure. It is noted that the corrective laser beam has a central wavelength greater than the bandgap wavelength of the cladding matrix, wherein, upon said directing, the portion of the cladding matrix simultaneously or quasi simultaneously absorbs at most 10 photons of the corrective laser beam thereby creating a local permanent matrix change spaced apart from the guiding structure. In some embodiments, the central wavelength is selected so that multiphoton absorption can occur with at most 12 simultaneous photons, preferably at most 8 simultaneous photons, and most preferably at most 6 simultaneous photons. The proximity of the permanent matrix change relative to the guiding structure modifies an effective refractive index of the guiding structure, and can affect the optical mode propagating therein. In some embodiments, the central wavelength of the corrective laser beam is, while being greater than a bandgap wavelength of the cladding matrix, one of equal to and below a bandgap wavelength of the guiding structure.

[0068] At step 704, a testing routine is performed on the photonic chip. The step 704 includes a step of determining a parameter P indicative of a performance of the guiding structure.

[0069] At step 706, upon determining that the parameter mismatches a reference parameter associated with a reference photonic chip, the steps 702 and 704 are repeated until the parameter matches the reference parameter PREF within a given tolerance TOL. If the parameter P is deemed to match the reference parameter P EF, within a given tolerance TOL, the steps 704 and 704 are not necessarily repeated.

[0070] In some embodiments, the testing routine of step 704 can be performed before, during, and / or afterthe step 702 of directing the corrective laser beam within the cladding matrix. In embodiments where the testing routine is performed before the step 702 of directing, a baseline of the performance of the photonic chip can be established before corrective actions can be performed. In some situations, the performance of a given photonic chip is satisfactory, and the rest of the steps are omitted. In some other situations, the performance of the given photonic chip is unsatisfactory, and the rest of the steps are performed (and in some cases repeated) until the parameter indicative of the performance reaches the reference parameter PREF.

[0071] It is noted that in some embodiments the photonic chip can have a number of different guiding structures. In these embodiments, the method 700 can include a step of performing the step 702 and the step of 704 with respect to a number of portions of cladding matrix each being associated with one or more of the guiding structures until the parameters Pi pertaining to the guiding structures match a respective reference parameter PREF within a given tolerance TOL i. In some embodiments, the reference parameters can be the same for each of the guiding structures (i.e., PREF.I = PREF, 2= PREF ). However, in some other embodiments, each guiding structure has a dedicated, different reference parameter.

[0072] At step 708, the step 702 of directing can include a step of moving at least one of the corrective laser beam and the photonic chip along a path overlapping with the cladding matrix. In some embodiments, the path can be circumscribed by a x-y plane in which the photonic chip extends. In some other embodiments, the path can be three- dimensional and rather extend within the x, y and z space. For instance, the step 708 includes moving the focal point of the corrective laser beam relative to the guiding structure of the photonic chip. Additionally or alternatively, the step 702 includes moving the photonic chip relative to the focal point of the corrective laser beam. In these embodiments, the relative movement between the focal point of the corrective laser beam and the guiding structure can define a path. The path can be parallel to a plane of the photonic chip in some embodiments. For instance, the path can be linear, arcuate, continuous or discontinuous, circular and arbitrary depending on the embodiment. Thepath can be within a plane of the photonic chip (i.e., in the x-y plane). However, in some other embodiments, the path can extend three-dimensionally within the whole volume of the cladding matrix. For instance, the path can oscillate at different depths within the cladding matrix. The path needs not to be confined to a plane as it can have a three- dimensional topography as well. It is noted that step 708 is optional as it can be omitted in some embodiments.

[0073] In some embodiments, the step 702 of directing includes a step of positioning the focal point at focal point coordinates relative to guiding structure coordinates. The focal point coordinates can be predetermined based on known photon chip design parameters and / or foundry processes. In these embodiments, the local permanent matrix change can be found to be positioned (e.g., centered) at the focal point coordinates within a tolerance below 0.5 pm, most preferably below 0.4 pm, and most preferably of about 0.25 pm, from the expected focal point coordinates. In some embodiments, the focal point coordinates are based on a manufacturing line with which the photonic chip has been initially manufactured.

[0074] In some embodiments, the corrective laser beam is pulsed and the step of moving the focal point of the corrective laser beam along the path includes the delivery of one or more laser pulses at each of a number of spaced apart points distributed evenly or unevenly along the cladding matrix overlapping with the path. In certain embodiments, the corrective laser beam includes a series of pulses having a pulse durations below a microsecond range, preferably below a nanosecond range, and most preferably below a picosecond range. For instance, the laser pulses can have a pulse duration ranging between about 10 fs and about 1000 ns, preferably between about 100 fs and about 500 ns and most preferably between about 250 fs and about 250 ns. The laser pulses can carry an optical fluence ranging between about 0.01 J / cm2and about 100 J / cm2. The laser pulses can carry an optical energy ranging between about 1 nJ and about 1 mJ, preferably between about 10 nJ and about 0.1 mJ and most preferably between about 100 nJ and about 10 pJ. It is intended that the focal point of the corrective laser beam can be sufficiently intense to cause multiphoton absorption into the photonic chip. Depending on the embodiment, the absorption of the corrective laser beam by thecladding matrix can include other nonlinear absorption processes as well, or a combination of both nonlinear and linear absorption. Examples of such nonlinear absorption mechanisms can include, but are not limited to, multi-photon absorption, tunnel ionisation, free-carrier absorption, impact ionisation, and the like. Such nonlinear absorption mechanisms are generally achieved using fast (sub ps) melting and resolidification light-matter processes. More specifically, such non-linear absorption mechanisms can excite the electrons from the valence band to the conduction band, thus generating free-carriers. The material modification, causing the refractive index change, can depend on the density of carriers, their excited energy level (electron temperature) and / or the temporal dynamics of the energy transfers between the photon, electron and phonons. The material modification can include, but is not limited to, crack or defect formation, ablation, melting and solidification, refractive index change, to name a few examples. Generally, to maximize the possible bandwidth of the refractive index change, carrier density and electron temperature can be maximized. In some embodiments, the corrective laser beam causes an explosion (or implosion) of a portion (or a totality) of the portion of the cladding matrix, which then causes the permanent matrix change causing the effective refractive index change of the guiding structure nearby. Generally, in the fast (sub ps) temporal regime when the modification threshold is reached, fast melting and resolidification can occur.

[0075] Fig. 8 shows a top plan view of an exemplary photonic chip 10’ having a guiding structure 12’ and a cladding matrix 14’ surrounding the guiding structure 12’. As depicted, the corrective laser beam is directed alongside the guiding structure 12’ in multiple passes of the corrective laser beam. Each one of these passes are labeled L1 , L2, ... , L6. Although six passes of the corrective laser beam are shown in this embodiment, it is intended that fewer than six passes, or more than six passes, can be performed in some other embodiments. In this embodiment, each pass has a length of about 50 pm and is laterally spaced apart from the guiding structure 12’ by a lateral spacing distance Sx of about 2 pm. As best shown in Fig. 8A, which shows a cross-sectional view of the photonic chip 10’, and its substrate 11 ’ and cladding matrix 14’, the local permanent matrix change 20’ has a proximal portion 20a proximal to the guiding structure 12’, the proximal portion spaced away from the guiding structure by a spacing distance below 5 pm, preferablybelow 3 pm and most preferably below 2 pm. Still referring to Fig. 8A, the permanent matrix changes 20’ are spaced apart from a top surface of the photonic chip 10’ by a depth spacing distance Sz of about 10 pm. The tolerances of the spacing distances Sx and Sz can range between about 0.2 pm and 0.5 pm, and most preferably of about 0.25 pm. It is understood that, in some other embodiments, the lateral spacing distance can be below 20 pm, preferably below 5 pm, and most preferably below 2 pm. However, these values, the number of passes of corrective laser beam, and the resulting number of local permanent matrix changes, can change from one embodiment to another. As discussed above, thanks to the relatively small gap between the bandgap wavelength of the cladding matrix 14’ and the central wavelength of the corrective laser beam, each of the permanent matrix changes that is performed with each pass of the corrective laser beam can have precise and repeatable coordinates. As such, the guiding properties of the guiding structure 12’ can be fine tuned as desired.

[0076] Fig. 9 shows a top plan view of an exemplary photonic chip 10” having a guiding structure 12” and a cladding matrix 14” surrounding the guiding structure 12”. As illustrated, the cladding matrix 14” is modified with an array of four different local permanent matrix changes 20”. Although an array of four local permanent matrix changes 20” is shown in this figure, it is encompassed that, in some other embodiments, fewer than four local permanent matrix changes, or more than four local permanent matrix changes, can be created within the cladding matrix 14” in some other embodiments. As shown in this specific embodiment, each of the local permanent matrix changes 20” has been created at a respective depth spacing distances Sz1 , Sz2, Sz3 and Sz4, with two of the local permanent matrix changes 20” made on a first lateral side of the guiding structure 12” and the othertwo of the local permanent matrix changes 20” made on a second lateral side of the guiding structure 12”. As shown, all the local permanent matrix changes 20” share a similar height Hz in this specific embodiment. However, in some other embodiments, the depth dimension (or height) of the local permanent matrix changes 20” can change from one another. The local permanent matrix changes 20” are similar to one another in the sense that they share similar morphological properties. For instance, examples of such morphological properties can include, but are not limited to, a first dimension extending parallel to the photonic chip, asecond dimension extending perpendicular to the photonic chip, a refractive index change, a density change, and the like. As a result, the local permanent matrix changes 20” may modify the guiding properties of the guiding structure 12” in a similar and repeatable fashion.

[0077] It is intended that the methods and systems described herein can provide access to modification inside the cladding matrix, including to the silicon surface or below. Depth and height of the local permanent matrix changes can be adjusted as desired. In fact, it was found that controlling the depth and height of the local permanent matrix changes may be mandatory to address differing foundry process parameters (e.g., height of the guiding structure, type of substrate, etc) to induce larger stress or to precisely control the stress on the guiding structure for larger tuning and better tuning accuracy while limiting waveguide loss. Multiple modifications at different depths and heights can be induced for a better control of the energy deposition in glass cladding to induce higher stress without increasing waveguide loss. Easier way to control the beam shape (via optics or spatial light modulator) for a better control of the stress induced while limiting waveguide loss.

[0078] Fig. 10 is a cross-sectional view of an example of a photonic chip 10”’ having a guiding structure 12”’, a cladding matrix 14’” surrounding the guiding structure 12’”, and a substrate 11 ’” receiving the cladding matrix 14’”. As depicted, two local permanent substrate changes 21 ’” have been laser-induced at an interface of the substrate 11 ’” and the cladding matrix 14’”. In this aspect, the focal point of the corrective laser beam is directed towards a surface portion of the substrate 11 ’” through the cladding matrix 14’”, besides the guiding structure 12. As depicted, the surface portion of the substrate 11 ’” is spaced away from and proximate to the guiding structure 12’”. In this case, since the absorption of the corrective laser beam is made by way of linear absorption by the substrate 1 1 ’”, intensity of the corrective laser beam is kept at linear (i.e., low) levels to avoid causing multiphoton absorption or other nonlinear effects within the cladding matrix 14’”. As such, the corrective laser beam has a central wavelength below the bandgap wavelength of the cladding matrix. The central wavelength can be any wavelength between 300 nm and 1100 nm, depending on the embodiment. As shown, the correctivelaser beam can create local permanent substrate changes 21 ”’ spaced apart from the guiding structure 12”’ and extending through the cladding matrix 14’” towards the guiding structure 12’”. It was found that the guiding properties of the guiding structure 12’” can be modified by causing such modifications at the interface between the substrate 11 ’” and the cladding matrix 14’”. Fig. 10A shows a top plan view of the photonic chip 10’”. In this embodiment, the overlap and energy of the laser pulses delivered by the corrective laser beam have been changed (compared to the dots shown at Fig. 6A). Indeed, in this embodiment, the dots are overlapping in a way which leaves two local permanent substrate changes extending linearly alongside the guiding structure 12’”. In this embodiment, the top surface of the substrate underneath the cladding matrix 14’” is deformed by the corrective laser beam and accordingly the local permanent substrate changes can also push on the cladding matrix 14’” and create slight changes therein.

[0079] It is noted that the controller discussed above with reference to Fig. 3 can be provided as a combination of hardware and software components. The hardware components can be implemented in the form of a computing device 1100, an example of which is described with reference to Fig. 11 . Moreover, the software components of the controller can be implemented in the form of a software application performing some or more steps of a method of modifying a photonic chip or a method of testing a photonic chip.

[0080] Still referring to Fig. 11 , the computing device 1100 can have a processor 1102, a memory 1104, and I / O interface 11 16. Instructions 1108 for performing the method 700 described above can be stored on the memory 1104 and accessible by the processor 1 102.

[0081] The processor 1102 can be, for example, a general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, a programmable read-only memory (PROM), or any combination thereof.

[0082] The memory 1104 can include a suitable combination of any type of computer- readable memory that is located either internally or externally such as, for example,random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like.

[0083] Each I / O interface 1106 enables the computing device 1 100 to interconnect with one or more input devices, such as a photonic chip testing apparatus, detector(s), a computer vision system, or with one or more output devices such as a multi-axis movement stage, an external network or an accessible memory system.

[0084] Each I / O interface 1106 enables the controller to communicate with other components, to exchange data with other components, to access and connect to network resources, to server applications, and perform other computing applications by connecting to a network (or multiple networks) capable of carrying data including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fiber optics, satellite, mobile, wireless (e.g. Wi-Fi, WiMAX), SS7 signaling network, fixed line, local area network, wide area network, and others, including any combination of these.

[0085] The controller can run one or more software applications configured to operate the system described herein using instructions 1 108. In some embodiments, the software applications are stored on the memory 1 104 and accessible by the processor 1 102 of the computing device 1100. The computing device 1100 and the software applications described above are meant to be examples only. Other suitable embodiments of the controller can also be provided, as it will be apparent to the skilled reader.As can be understood, the examples described above and illustrated are intended to be exemplary only. For instance, the methods and systems described herein can be performed using more than one corrective laser beam. For instance, a first corrective laser beam of a first central wavelength can be used for modifying a structure of the guiding structure whereas a second corrective laser beam of a second centralwavelength (which is different from the first central wavelength) can be used for modifying a structure of the cladding matrix. It is noted that a photonic chip can have a multitude of photonic functions and / or photonic components each having dedicated channels. The methods and systems described here can be applied to each of the photonic functions, each of the photonic components and each of the photonic channels of the photonic chip. Depending on the embodiment, the characteristics of the corrective laser beam can be varied. Examples of such characteristics can include, but are not limited to, pulse duration, repetition rate, burst mode or not, pulse energy, laser wavelength, laser intensity, beam shape (e.g., Gaussian, top-edge, Bessel, elliptical), fixed or moving beam, scan speed, hatch and laser path, to name a few examples. The number and / or locations of the laser taps can depend based on a geometry and material of the portion of the cladding matrix where local permanent matrix changes are to be created. Moreover, the methods and systems described herein can be adapted to limit losses incurred to the photonic chip, to ensure precise positioning of the corrective laser beam relative to the photonic chip, to maximize a compensation range and to impart positive or negative refractive index changes. When the guiding structure is surrounded by many layers of material (e.g., glass insulator, other semiconductor layers), the effective refractive index change can be selective to the particular layer. Refractive index can be changed by different processes including, but not limited to, amorphization, stress induced, void creation, densification and the like. The laser-induced refractive index modification can be paired with other sources of heating, e.g., thermal heater(s), sources(s) of ionization (e.g., input voltage in the cladding matrix) or another laser beam absorbed by the cladding matrix, to optimize the methods and systems described herein. The corrective laser beam can be perpendicular to a plane of the photonic chip or have an acute or obtuse angle with respect to a plane of the photonic chip. Structures such as fiber-Bragg gratings or polarisers can be created with the effective refractive index change inside the cladding matrix in some embodiments. It is understood that modifying the effective refractive index can include a modification of the real part of the refractive index, a modification of the imaginary part of the refractive index, or a combination thereof. In some embodiments, the central wavelength of the corrective laser beam can be adapted to control the process parameters and optimize correction depending on the type of semiconductor material. In some embodiments, the refractive index modificationscan be imparted in such a way that can influence the polarization of the optical signal propagating along one or more semiconductors of the guiding structure. For instance, the refractive index modifications can extend on opposite sides of the guiding structure to maintain or change polarization. In one specific embodiment, refractive index modifications such as those shown described herein can be used to mimic the structure of polarization-maintaining optical fibers, to name only one example. In embodiments where the photonic chip is based on the indium phosphide (InP) semiconductor platform, such refractive index modifications can form matrix defects which can attract electrons and thereby reduce optical losses occurring along the guiding structure. Although the guiding structure shown in the examples aboves are rather simple and unidimensional, complex structures for the guiding structure can be used in some other embodiments. For instance, the guiding structure can include one or more guiding structures running alongside each other, and the cladding matrix (e.g., glass matrix) extending between them. In addition to not incurring losses to the neighbouring guiding structure, the laser- induced permanent matrix change disclosed herein have been shown to resist thermal annealing procedures lasting at least 24h at 200°C, which is not necessarily the case for guiding structure modifications involving conventional amorphization. The method described herein can be used to create local permanent matrix changes into different layers of a stack of layers of a photonic chip. The local permanent matrix changes can be made within the cladding matrix and proximate to metal components therewithin. The scope is indicated by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method for modifying a photonic chip having a guiding structure and a cladding matrix surrounding the guiding structure, the cladding matrix having a bandgap wavelength, the guiding structure and the cladding matrix configured for guiding an optical mode within the photonic chip, the method comprising: directing a focal point of a corrective laser beam within a portion of the cladding matrix, the portion of the cladding matrix being spaced away from and proximate to the guiding structure, the corrective laser beam having a central wavelength greater than the bandgap wavelength of the cladding matrix, wherein, upon said directing, the portion of the cladding matrix absorbs at most 10 photons of said corrective laser beam thereby creating a local permanent matrix change spaced apart from the guiding structure, the permanent matrix change modifying an effective refractive index of the guiding structure; performing a testing routine on the photonic chip including determining a parameter indicative of a performance of the guiding structure; and upon determining that the parameter mismatches a reference parameter associated with a reference photonic chip, repeating said directing and said testing routine until the parameter matches the reference parameter within a given tolerance.

2. The method of claim 1 wherein the central wavelength of the corrective laser beam is one of equal to and below a bandgap wavelength of the guiding structure.

3. The method of claim 1 or 2 wherein the local permanent matrix change is caused by a simultaneous absorption of at most 8 photons, and most preferably at most 5 photons.

4. The method of any one of claims 1 to 3 wherein said directing includes positioning the focal point at focal point coordinates relative to guiding structure coordinates, the local permanent matrix change positioned at the focal point coordinates within a tolerance below 0.5 pm, most preferably below 0.4 pm, and most preferably of about 0.25 pm.

5. The method of any one of claims 1 to 4wherein the guiding structure has a first depth coordinate, the focal point of the corrective laser beam being directed to a second depth coordinate different from the first depth coordinate of the guiding structure.

6. The method of any one of claims 1 to 5 wherein the local permanent matrix change has a proximal portion proximal to the guiding structure, the proximal portion spaced away from the guiding structure by a spacing distance below 20 pm, preferably below 5 pm and most preferably below 2 pm.

7. The method of any one of claims 1 to 6 wherein the local permanent matrix change has a dimension ranging between about 0.1 pm and 50 pm, preferably between about 1 pm and 20 pm, and most preferably about 2 pm and 10 pm.

8. The method of any one of claims 1 to 7 wherein the local permanent matrix change is a first local permanent matrix change, the method further comprising repeating said directing at another portion within the cladding matrix thereby forming a subsequent local permanent matrix change, the subsequent local permanent matrix change having a morphological property similarto a morphological property of the local permanent matrix change.

9. The method of any one of claims 1 to 8 wherein the morphological property includes at least one of: a first dimension extending parallel to the photonic chip, a second dimension extending perpendicular to the photonic chip, a refractive index change, and a density change.

10. The method of any one of claims 1 to 9 wherein the central wavelength of the corrective laser beam ranges between about 300 nm and 1100 nm, more preferably between about 800 nm and 1050 nm, and is most preferably of about 500 nm.1 1 . The method of any one of claims 1 to 10 wherein the corrective laser beam includes a series of pulses having a pulse duration below a microsecond range, preferably below a nanosecond range, and most preferably below a picosecond range.

12. A system for modifying a photonic chip having a guiding structure and a cladding matrix surrounding the guiding structure, the cladding matrix having a bandgap wavelength, the guiding structure and the cladding matrix configured for guiding an optical mode within the photonic chip, the system comprising: a corrective laser apparatus configured for directing a focal point of a corrective laser beam within a portion of the cladding matrix, the portion of the cladding matrix being spaced away from and proximate to the guiding structure, the corrective laser beam having a central wavelength greater than the bandgap wavelength of the cladding matrix, wherein, upon said directing, the portion of the cladding matrix absorbs at most 10 photons of said corrective laser beam thereby creating a local permanent matrix change spaced apart from the guiding structure, the permanent matrix change modifying an effective refractive index of the guiding structure; a photonic chip testing apparatus performing a testing routine on the guiding structure including determining a parameter indicative of a performance of the guiding structure; and a controller communicatively coupled to the corrective laser apparatus and to the photonic chip testing apparatus, the controller having a processor and a memory having stored thereon instructions that when executed by the processor perform the steps of: comparing the parameter to a reference parameter associated with a reference photonic chip; and upon determining that the parameter mismatches the reference parameter, repeating said directing and said testing routine until the parameter matches the reference parameter within a given tolerance.

13. The system of claim 12 wherein the central wavelength of the corrective laser beam is one of equal to and below a bandgap wavelength of the guiding structure.

14. The system of claim 12 or 13 wherein the local permanent matrix change is caused by a simultaneous absorption of at most 8 photons, and most preferably at most 5 photons.

15. The system of any one of claims 12 to 14 further comprising receiving guiding structure coordinates indicative of coordinates of the guiding structure within the cladding matrix; determining focal point coordinates indicative of where the focal point of the corrective laser beam is to be directed, said focal point coordinates spaced apart from said guiding structure coordinates by at most 20 pm, said directing including directing the focal point of the corrective laser beam within the cladding matrix based on the focal point coordinates.

16. The system of any one of claims 12 to 15 wherein the corrective laser apparatus includes a 1030 nm-wavelength laser source.

17. The system of any one of claims 12 to 16 wherein the corrective laser apparatus includes a 800 nm-wavelength laser source.

18. The system of any one of claims 12 to 17 wherein the corrective laser apparatus includes a 500 nm-wavelength laser source.

19. A photonic chip comprising: a guiding structure; a cladding matrix surrounding the guiding structure, the guiding structure and the cladding matrix configured for guiding an optical mode within the photonic chip; and a laser-induced permanent matrix change localized within cladding matrix and spaced apart from the guiding structure, the laser-induced permanent matrix change having a dimension of 4 pm or less, the permanent matrix change permanently modifying an effective refractive index of the guiding structure.

20. The photonic chip of claim 19 wherein the dimension is 1 pm or less.21 . A method for modifying a photonic chip having a guiding structure, a cladding matrix surrounding the guiding structure, and a substrate receiving the cladding matrix, the guiding structure and the cladding matrix configured for guiding an optical mode within the photonic chip, the cladding matrix having a bandgap wavelength, the method comprising: directing a focal point of a corrective laser beam within a surface portion of the substrate through the cladding matrix, the surface portion of the substrate being spaced away from and proximate to the guiding structure, the corrective laser beam having a central wavelength below the bandgap wavelength of the cladding matrix, said directing creating a local permanent substrate change spaced apart from the guiding structure and extending through the cladding matrix towards the guiding structure, the permanent substrate change modifying an effective refractive index of the guiding structure; performing a testing routine on the photonic chip including determining a parameter indicative of a performance of the guiding structure; and upon determining that the parameter mismatches a reference parameter associated with a reference photonic chip, repeating said directing and said testing routine until the parameter matches the reference parameter within a given tolerance.

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