Method and system for modifying a photonic chip having a semiconductor waveguide

Abstract

A method of modifying a photonic chip having a semiconductor waveguide is described. Generally, the method comprises directing a focus of a correction laser beam into and proximate to a portion of the photonic chip that is within the semiconductor waveguide, the correction laser beam having a central wavelength greater than the bandgap wavelength of the semiconductor waveguide, the directing modifying an effective refractive index of a portion of the semiconductor waveguide; performing a test routine on the semiconductor waveguide that includes determining a parameter indicative of performance of the semiconductor waveguide; and repeating the directing and the test routine until the parameter is determined to match the reference parameter associated with a reference photonic chip when the parameter is determined not to match the reference parameter.

Description

Technical Field

[0001] Field The present improvement generally relates to photonic chips, and more particularly to the manufacture and testing of such photonic chips.

Background Art

[0002] Background In a manner similar to an electronic chip that processes electronic signals, a photonic chip processes optical signals. Photonic chips are typically manufactured using a foundry process used in microelectronics manufacturing. The foundry process for microelectronics can reach an acceptable range of up to about 1.5 nm, which, although satisfactory for state-of-the-art microelectronics, may be insufficient for photonic chip manufacturing. Therefore, photonic chips manufactured using known foundry processes are subject to rigorous inspection and testing to confirm that they meet the design specifications. If a photonic chip is determined to be defective, the chip is discarded, resulting in significant losses in terms of materials and time. Existing photonic chip manufacturing technologies are somewhat satisfactory, but there is still room for improvement.

Summary of the Invention

[0003] Summary The described methods and systems are configured to correct photonic chips, particularly photonic chips identified as defective due to not meeting design tolerances and / or performance parameters by individual inspection and testing. The methods and systems include test routines that measure parameters indicative of the performance of semiconductor waveguides of the photonic chip and, optionally, monitor them over time. Examples of such parameters include, but are not limited to, wavelength, phase, amplitude, polarization, dispersion, gain, and / or loss. A corrective laser beam selected to exhibit a center wavelength greater than the bandgap wavelength of the semiconductor waveguide is used to locally modify the effective refractive index of the semiconductor waveguide. Such local modifications can be repeated until the monitored parameter matches the corresponding reference parameter of a reference photonic chip. It is noted that since the semiconductor waveguide is optically transparent to the corrective laser beam, its focus can be directed through the photonic chip, for example through its cladding layer or substrate. When the focus of the corrective laser beam supplies sufficient optical energy to a local portion of the semiconductor waveguide, a local modification of the volumetric refractive index can occur. In at least some examples, these localized volumetric matter modifications can adjust the performance of the defective photonic chip to a level where the photonic chip is defect-free.

[0004] According to a first aspect of the present disclosure, there is provided a method of correcting a photonic chip having a semiconductor waveguide, the semiconductor waveguide having a bandgap wavelength: The method includes directing the focus of a correction laser beam proximate to and within a portion of the photonic chip that is proximate to the semiconductor waveguide, the correction laser beam having a central wavelength greater than the bandgap wavelength of the semiconductor waveguide, and the directing modifying the effective refractive index of a portion of the semiconductor waveguide; The method includes performing a test routine on the semiconductor waveguide that includes determining a parameter indicative of the performance of the semiconductor waveguide; and The method includes repeating the directing and the test routine until the parameter is within a predetermined tolerance and matches a reference parameter associated with a reference photonic chip when it is determined that the parameter does not match the reference parameter.

[0005] According to a first aspect of the present disclosure, further, the directing may include, for example, moving the focus of the correction laser beam and at least one of the photonic chips along a path.

[0006] According to a first aspect of the present disclosure, still further, the moving may include, for example, supplying laser pulses to each of a plurality of spaced points distributed along the path.

[0007] According to a first aspect of the present disclosure, still further, the test routine may include, for example, guiding a test optical signal into and along the semiconductor waveguide, detecting an output signal resulting from the guiding, and determining the parameter based on the output signal.

[0008] According to a first aspect of the present disclosure, still further, the guiding may include, for example, injecting the test optical signal into a first end of the semiconductor waveguide.

[0009] According to a first aspect of the present disclosure, furthermore, the detection may include, for example, measuring the output signal using a photodiode optically coupled to a second end of the semiconductor waveguide.

[0010] According to a first aspect of the present disclosure, furthermore, the detection may include, for example, measuring the output signal that is scattered away from the semiconductor waveguide during this guiding using a camera.

[0011] According to a first aspect of the present disclosure, furthermore, the parameter may be, for example, at least one of output wavelength, output phase, output amplitude, output polarization, output dispersion, and output loss.

[0012] According to a first aspect of the present disclosure, furthermore, the central wavelength of the correction laser beam may be in the range of, for example, between about 1 μm and about 20 μm, preferably between about 1.2 μm and about 10 μm, and most preferably between about 1.5 μm and about 4 μm.

[0013] According to a first aspect of the present disclosure, furthermore, the correction laser beam may have a laser pulse having a time duration in the range of, for example, 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.

[0014] According to a first aspect of the present disclosure, furthermore, the semiconductor waveguide can be positioned, for example, with respect to a substrate, the photonic chip can further have, for example, a cladding layer covering an upper surface of the substrate and the semiconductor waveguide, and the directing can include, for example, directing the focus of the correction laser beam through at least one of the cladding layer and the substrate.

[0015] According to a first aspect of the present disclosure, furthermore, the photonic chip can have a plurality of semiconductor waveguides each having a bandgap wavelength, and for example, the method can include directing and performing the test routine on each one of the plurality of semiconductor waveguides until a plurality of parameters related to the plurality of semiconductor waveguides match their respective reference parameters within a predetermined tolerance range.

[0016] According to a second aspect of the present disclosure, a system for modifying a photonic chip having a semiconductor waveguide is provided, the semiconductor waveguide having a bandgap wavelength: The system includes a correction laser device configured to direct a focus of a correction laser beam into and within a portion of the photonic chip adjacent to and within the semiconductor waveguide, the correction laser beam having a central wavelength greater than the bandgap wavelength of the semiconductor waveguide, and the directing modifying an effective refractive index of the semiconductor waveguide; The system includes a photonic chip test device that performs a test routine on the semiconductor waveguide, including determining a parameter indicative of a performance of the semiconductor waveguide; and The system includes a controller communicatively coupled to the correction laser device and the photonic chip test device, the controller having a processor and, when executed by the processor: Comparing the parameter with a reference parameter associated with a reference photonic chip; and When it is determined that the parameter does not match the reference parameter, repeating the directing and the test routine until the parameter matches the reference parameter within a predetermined tolerance range. And having a memory storing instructions for performing the above.

[0017] According to a second aspect of the present disclosure, further, the corrective laser device can include, for example, a laser source that generates the corrective laser beam, and the central wavelength is between about 1.0 μm and about 20 μm, preferably between about 2.5 μm and about 10 μm, and most preferably between about 2.8 μm and about 3.4 μm.

[0018] According to a second aspect of the present disclosure, still further, the corrective laser device can include, for example, a laser source that generates laser pulses having a duration in the range of 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.

[0019] According to a second aspect of the present disclosure, still further, the corrective laser device can have, for example, a fiber laser source.

[0020] According to a second aspect of the present disclosure, still further, the system can further include, for example, a multi-axis movement stage having a support area on which the photonic chip is received, and the multi-axis movement stage can move the photonic chip, for example, during the directing.

[0021] According to a second aspect of the present disclosure, still further, the photonic chip test device can include, for example, a test light source that guides a test optical signal into and along the semiconductor waveguide, and a detector that detects an output signal resulting from the guiding, and the controller can determine the parameter, for example, based on the output signal.

[0022] According to a second aspect of the present disclosure, still further, the detector can be, for example, a photodiode optically coupled to a first end of the semiconductor waveguide for detecting the output signal.

[0023] According to a second aspect of the present disclosure, still further, the detector can be, for example, an infrared camera that measures the output signal scattered away from the semiconductor waveguide during the guiding.

[0024] According to a third aspect of the present disclosure, a method of testing a photonic chip is provided, the photonic chip having a semiconductor waveguide and a plurality of semiconductor components optically coupled to the semiconductor waveguide, the semiconductor components having a bandgap wavelength: During performing a test routine on the semiconductor waveguide, guiding a test optical signal into and along the semiconductor waveguide, detecting an output signal resulting from the guiding, and monitoring the output signal based on the output signal; and directing a focus of a probing laser beam into a portion of the photonic chip proximate to and within one of the plurality of semiconductor components, the corrective laser beam having a central wavelength greater than the bandgap wavelength of the semiconductor component, the directing modifying an effective refractive index of a portion of the semiconductor component; the method including identifying an optical feature in the output spectrum modified in response to the directing; and the method including associating the optical feature with one of the semiconductor components.

[0025] According to a third aspect of the present disclosure, further, the modifying can include modifying the effective refractive index of a portion of the semiconductor waveguide in an amount in the range, for example, between about 0.1 and about 0.00000001, preferably between about 0.05 and about 0.0005, and most preferably between about 0.01 and about 0.001.

[0026] In accordance with a fourth aspect of the present disclosure, a system for testing a photonic chip is provided, the photonic chip having a semiconductor waveguide and a plurality of semiconductor components optically coupled to the semiconductor waveguide, the semiconductor components having a bandgap wavelength: The system includes a photonic chip testing apparatus that performs a test routine including guiding a test optical signal into and along the semiconductor waveguide, detecting an output signal resulting from the guiding, and monitoring an output spectrum based on the output signal; The system includes a correction laser device configured to direct a focus of a correction laser beam into a portion of the photonic chip proximate to and within one of the semiconductor components, the correction laser beam having a central wavelength greater than the bandgap wavelength of the semiconductor waveguide, the directing modifying an effective refractive index of a portion of one of the semiconductor components; and The system includes a controller communicatively coupled to the photonic chip testing apparatus and the correction laser device, the controller having a processor and, when executed by the processor: Identifying optical features in the output spectrum that are modified in response to the directing; Associating the optical features with one of the semiconductor components; and A memory storing instructions to perform.

[0027] All technical implementation details and advantages described for a particular aspect of the present disclosure are, of course, applicable to all other aspects of the present disclosure with necessary modifications.

[0028] The expression "proximate to the semiconductor waveguide" is meant to encompass any location on the photonic chip outside the semiconductor waveguide, which is noted to be capable of affecting the effective refractive index of the semiconductor waveguide when modified using the focus of a corrective laser beam. For example, in some embodiments, such locations may include the material matrix surrounding the semiconductor waveguide, the substrate on which the semiconductor waveguide is mounted, or the substrate from which the semiconductor waveguide is suspended.

[0029] Many further features and combinations thereof regarding this improvement will be apparent to those skilled in the art upon reading this disclosure.

[0030] Description of the Drawings In the figures, BRIEF DESCRIPTION OF THE DRAWINGS

[0031]

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[0032] DETAILED DESCRIPTION FIG. 1 shows an example of a system 100 for modifying a photonic chip 10 having a semiconductor waveguide 12. System 100 can be used at any test stage of the fabrication of photonic chip 10. For example, system 100 can be used during a design stage where prototypes of photonic chip 10 are fabricated and iteratively corrected as desired, a foundry stage where photonic chip 10 is mass-produced, and / or a packaging stage where photonic chip 10 is integrated into a package, for example.

[0033] The semiconductor waveguide 12 may include any type of semiconductor material, including, but not limited to, all types of doped semiconductors including silicon, silicon nitride (SiN), silicon on insulator (SOI), silicon nitride (Si3N4), germanium (Ge), indium phosphide (InP), silicon carbide (SiC), gallium nitride (GaN), indium gallium arsenide (InGaAs), gallium arsenide (GaAs), lithium niobate (LiNbO3), indium antimonide (InSb), mercury cadmium telluride (MCT), indium arsenide (InAs), lead selenide (PbSe), lead sulfide (PbS), chalcogenide-based materials such as sulfide-based materials, selenide-based materials, telluride-based materials, etc., n-type doping, p-type doping, germanium doping, silicon doping, boron doping, arsenic doping, carbon doping, helium doping, antimony doping, and / or active laser material doping such as erbium, ytterbium, quantum dot, rare earth ion doping such as gas, etc.

[0034] The semiconductor waveguide 12 can be any type of semiconductor waveguide used in a photonic chip. For example, the semiconductor waveguide 12 can have a strip waveguide, rib waveguide, slot waveguide, photonic crystal waveguide, subwavelength waveguide diffraction grating (SWG) waveguide, SWG slot waveguide, SPP slot waveguide, and the like. Typically, the photonic chip 10 includes a substrate 14 on which the semiconductor waveguide 12 is relatively disposed. The semiconductor waveguide 12 can be directly received, for example, on the substrate 14, or can be indirectly received on the substrate 14, for example, via an embedded oxide layer. The substrate 14 can be a silicon substrate, polymer substrate, glass substrate, or any other suitable type of substrate. In some embodiments, the semiconductor waveguide 12 is disposed on the substrate 14. In these embodiments, the semiconductor waveguide 12 can travel along a path that is substantially parallel to the surface of the substrate 14. The path can be linear, arched, or circular, depending on the embodiment. In some other embodiments, the semiconductor waveguide 12 can be suspended above or embedded within the substrate 14. The photonic chip 10 can include one or more cladding or metal layers 16 that partially or entirely cover the upper surface of the semiconductor waveguide 12 and / or the substrate 14. The cladding or metal layer 16 can be made of an oxide in some embodiments. Further, in some embodiments, an oxide layer embedded between the substrate 14 and the semiconductor waveguide 12 can be present. In some embodiments, the cladding or metal layer 16 can be made of any material having a lower refractive index than the waveguide material that can enable confinement and propagation of optical signals.

[0035] As shown, system 100 includes a corrective laser device 110 and a photonic chip test device 120. In some embodiments, system 100 can also incorporate a computer vision device 130 that includes a camera 132 for imaging the photonic chip 10 in real time. A multi-axis movement stage 140 can be optionally used to move the photonic chip 10 within the 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 device 110 can be integrated with an existing photonic test device.

[0036] System 100 can have, for example, a controller 150 communicatively coupled to the corrective laser device 110, the photonic chip test device 120, the computer vision device 130, and / or the multi-axis movement stage 140. The controller 150 has a processor and a memory storing instructions that, when executed by the processor, perform pre-programmed instructions and / or method steps. To do so, the controller 150 generally incorporates a hardware component provided in the form of a computing device and a software component provided in the form of a program, algorithm, etc. for performing the method steps. An example of a computing device is described below.

[0037] As depicted, the correction laser device 110, the photonic chip test device 120, the computer vision device 130, and the multi-axis moving stage 140 can be fixedly or removably attached to the frame 102. In this specific embodiment, the frame 102 is provided in the form of an optical bench or a table. However, in some other embodiments, it is understood that the correction laser device 110, the photonic chip test device 120, the computer vision device 130, and the multi-axis moving stage 140 can be attached independently of each other at different locations on, for example, a photonic chip manufacturing line. In some embodiments, the electronic probe and / or the fiber probe of the photonic chip test device 120 can be in the path of the correction laser beam of the correction laser device 110. In these embodiments, the correction laser device 110, its laser source, or its output can be moved above or below the photonic chip 10 as desired. Such movement can be generated using a two-axis or three-axis galvanometer scanner, a coarse gantry mechanism for movement within one square centimeter, a fine gantry mechanism for movement within a relatively small area (e.g., 100 μm × 100 μm, 10 × 10 μm), a piezo micropositioner (e.g., hexapod, spatial light modulator (SLM)), an optical fiber cable with a microlens chip, a six-degree-of-freedom robotic arm, other motion devices with or without movable parts capable of moving and / or deflecting the correction laser beam, and / or combinations thereof.

[0038] It is noted that all semiconductor materials have their own bandgap energy and corresponding bandgap wavelength linked by Planck's relation. The bandgap energy and bandgap wavelength define the wavelength or photon energy at which the semiconductor material exhibits at least some transparency. The corrective laser beam is intended to be selected to have a central wavelength greater than the bandgap wavelength of the corresponding semiconductor waveguide. Similarly, the corrective laser beam can have a photon energy below the bandgap energy of the semiconductor waveguide.For example, to give some examples, lead selenide (PbSe) has a direct band gap of 0.27 eV or 4.57 μm; lead telluride (PbTe) has a direct band gap of 0.32 eV or 3.86 μm; indium arsenide (InAs) has a direct band gap of 0.36 eV or 3.43 μm; lead sulfide (PbS) has a direct band gap of 0.37 eV or 3.34 μm; germanium (Ge) has an indirect band gap of 0.67 eV or 1.84 μm; gallium antimonide (GaSb) has a direct band gap of 0.726 eV or 1.70 μm; silicon (Si) has an indirect band gap of 1.12 eV or 1.1 μm; indium phosphide (InP) has a direct band gap of 1.35 eV or 915 nm; gallium arsenide (GaAs) has a direct band gap of 1.441 eV or 857 nm; cadmium telluride (CdTe) has a direct band gap of 1.5 eV or 823 nm; cadmium selenide (CdSe) has a direct band gap of 1.74 eV or 710 nm; aluminum arsenide (AlAs) has an indirect band gap of 2.12 eV or 583 nm; gallium phosphide (GaP) has an indirect band gap of 2.24 eV or 551 nm; cadmium sulfide (CdS) has a direct band gap of 2.42 eV or 510 nm; gallium nitride (GaN) has a direct band gap of 3.4 eV or 363 nm; cubic zinc sulfide (ZnS) has a direct band gap of 3.54 eV or 349 nm; hexagonal zinc sulfide (ZnS) has a direct band gap of 3.91 eV or 316 nm; and aluminum nitride (AlN) has a direct band gap of 6.015 eV or 205 nm.

[0039] Referring now to FIG. 2, it is noted that the semiconductor waveguide of the photonic chip has a bandgap energy defining an optical transmission window 20 and a corresponding bandgap wavelength. The optical transmission window 20 can range between about 1 μm to about 25 μm, preferably between about 2.0 μm to about 20 μm, and most preferably between about 2.5 μm to about 10 μm. For example, in an embodiment where the semiconductor waveguide includes silicon having a bandgap wavelength of about 1.1 μm, the optical transmission window can range between about 1.1 μm to about 15 μm. In such an embodiment, the central wavelength of the corrective laser beam can be selected to be greater than 1.1 μm. For example, it has been found that a mid-infrared laser beam is satisfactory. The optical transmission window typically exhibits a transmittance in the range of, for example, between about 1% / cm to about 10% / cm.

[0040] In view of the above, it is intended that the corrective laser beam have a central wavelength 112 that at least partially or entirely spans within the optical transmission window 20 of the semiconductor waveguide. For example, the central wavelength 112 of the corrective laser beam can range between about 1.0 μm to about 20 μm, preferably between about 2.5 μm to about 10 μm, and most preferably between about 2.8 μm to about 3.4 μm. Thus, optical energy can be delivered into the photonic chip, including, for example, within and / or in the vicinity of the semiconductor waveguide. In embodiments where the semiconductor includes silicon, it has been found convenient to use a mid-infrared laser beam having a narrow spectral bandwidth (or equivalently a central wavelength) centered at, for example, about 3.2 μm. It is pointed out that the mid-infrared laser beam can be generated using a fiber laser source having a low phonon energy glass fiber segment and at least one laser active doped region extending along the fiber segment. An example of such a fiber laser source is described in U.S. Patent No. 10,084,287B2, the content of which is incorporated herein by reference.

[0041] Figure 3A shows the photonic chip 10 of FIG. 1 in which a test routine is performed by the photonic chip test apparatus 120. As shown, the photonic chip test apparatus 120 determines a parameter P indicative of the performance of the semiconductor waveguide 12. When the measured parameter P and the reference parameter P REF of the reference photonic chip are not in agreement with each other within a predetermined tolerance TOL, i.e.,

[0042]

Number

[0043] if so, the photonic chip 10 can be identified as having a defect. Instead of discarding the defective photonic chip 10, the system 100 is used to correct the photonic chip 10. The reference photonic chip can correspond to, for example, a photonic chip that is defect-free or is considered to be within the design tolerance. The reference parameter P REF can be stored in a memory system accessible to the controller 150. In some embodiments, each photonic chip being tested has an identifier that identifies the type of photonic chip and one or more reference parameters P REF associated with the type of photonic chip. When such a photonic chip is tested, the controller can retrieve the type of photonic and / or the associated reference parameter P REF .

[0044] In some embodiments, the photonic chip test apparatus 120 includes a test light source 122 that directs a test optical signal 124 into and along a first end 12a of the semiconductor waveguide 12, and a detector 126 that detects an output signal 128 resulting from guiding the test optical signal 124. The test optical signal 124 can be injected using grating coupler(s), side coupler(s), free-space injection setup(s), etc. The output optical signal 128 can be detected using, for example, an integrated photodiode, a fiber probe, a free-space detector, a spectrophotometer, a standard infrared or hyperspectral camera that images the scattering outgoing from the photonic chip 10. In these embodiments, the controller can determine the parameter P based on the output signal 128. As shown in a particular embodiment of FIG. 3A, the detector can be a photodiode optically coupled to the second end 12b of the semiconductor waveguide 12 to detect the output signal 128. In some embodiments, the detector is an infrared camera that measures an output signal that scatters away from the semiconductor waveguide during the guiding of the test optical signal 124. The camera can be part of a computer vision device 130. It is intended that the test routine need not be based solely on optical techniques. For example, in some other embodiments, the test routine includes optical modulation based on radio-frequency signals and / or electronic measurements.

[0045] As shown in FIG. 3B, the correction laser device 110 is used to direct the focus 114 of the correction laser beam 116 into or proximate to a portion of the photonic chip 10 that is either within or proximate to the semiconductor waveguide 12. Due to the optical transparency of the semiconductor waveguide 12 to the correction laser beam 116, the effective refractive index of a portion of the semiconductor waveguide 12 can be modified to some extent, which includes a positive or negative refractive index change. The modification of the effective refractive index can in turn modify the performance of the semiconductor waveguide 12 and the overall photonic chip 10 accordingly.

[0046] As depicted in FIG. 3C, the modified photonic chip 10 determines whether the measured parameter P is within the predetermined tolerance TOL of the reference parameter P REF and thus,

[0047]

Number

[0048] To determine whether it is so, it can be retested using a test routine. These steps can be repeatedly iterated until a match is found, i.e., until the photonic chip 10 functions to a level where it can be considered defect - free. When the corrected photonic chip 10 passes the test routine, it can be returned to the photonic chip manufacturing line, thereby reducing the amount of photonic chips that are discarded after the test routine fails. In some aspects, considering that 50% - 80% of all photonic chips manufactured using existing microelectronics foundry technology may be defective, by using the methods and systems described herein, it is hypothesized that the system 100 can reduce the discard rate of such photonic chips by at least 25%, preferably below at least 50%, and most preferably at least 75% compared to conventional manufacturing processes. It is also pointed out that the methods and systems described herein can correct defective photonic chips relatively quickly.

[0049] FIG. 4 shows an example of a method 400 for correcting a photonic chip having a semiconductor waveguide. Method 400 is described with reference to the system 100 and the photonic chip 10 of FIG. 1, but it is understood that method 400 can be applied to any photonic chip using any photonic chip correction system.

[0050] In step 402, the focus 114 of the corrective laser beam 116 is directed proximate to and into a portion of the photonic chip 10 within the semiconductor waveguide 12. As described above, the corrective laser beam 116 has a central wavelength 112 that is greater than the bandgap wavelength of the semiconductor waveguide 12. Thus, step 402 modifies the effective refractive index of a portion of the semiconductor waveguide 12. The effective refractive index of the portion of the semiconductor waveguide 12 can be modified by an amount in the range of from about 0.1 to about 0.00000001, preferably from about 0.05 to about 0.0005, and most preferably from about 0.01 to about 0.001. It is noted that the effective refractive index can be modified to increase or decrease the current effective refractive index of the semiconductor waveguide 12, depending on the aspect.

[0051] In step 404, a test routine is performed on the semiconductor waveguide 12. The test routine generally includes steps of determining a parameter P indicative of the performance of the semiconductor waveguide 12. Depending on the aspect, the parameter can be an output wavelength, output phase, output amplitude, output bias, output dispersion, output loss, and / or combinations thereof. The parameter P can be determined based on an output signal 128 detected by a detector 126 of the photonic chip test apparatus 120.

[0052] In step 406, if it is determined that the parameter P does not match the reference parameter P REF associated with the reference photonic chip, steps 402 of directing and 404 of performing the test routine are repeatedly iterated until the parameter P matches the reference parameter P REF within a predetermined tolerance TOL. If the test routine results in a pass, a pass signal is generated and the photonic chip without defects can be labeled accordingly, for example, in a database of a photonic chip manufacturing line.

[0053] In some embodiments, it is noted that the photonic chip 10 may have a number of semiconductor waveguides 12, each having a bandgap wavelength. In these embodiments, the method 400 may include performing steps 402 and 404 for each one of the semiconductor waveguides 12 until the parameters associated with the semiconductor waveguides 12 match their respective reference parameters within a predetermined tolerance range. In some embodiments, the reference parameters may be the same for each of the semiconductor waveguides 12. In some other embodiments, each semiconductor waveguide 12 has a dedicated reference parameter.

[0054] In step 408, the directing step 402 may include moving the focus 114 of the corrective laser beam 116 and at least one of the photonic chips 10 along a path. For example, step 408 may include moving the focus 114 of the corrective laser beam 116 relative to the semiconductor waveguide 12 of the photonic chip 10. Additionally or alternatively, step 402 may include moving the photonic chip 10 relative to the focus 114 of the corrective laser beam 116. In these embodiments, the relative movement between the focus 114 of the corrective laser beam 116 and the semiconductor waveguide 12 may define a path. The path may, in some embodiments, be parallel to the surface of the photonic chip 10. For example, the path may be linear, arched, circular, or any according to the embodiment. The path need not be limited to a plane as it may also have a three-dimensional topography. It is noted that step 408 may be optional in some embodiments as it may be omitted.

[0055] In some embodiments, the corrective laser beam 116 is pulsed, and the step of moving the focus 114 of the corrective laser beam 116 along the path includes delivering one or more laser pulses at each of a number of discrete points that are distributed uniformly or non-uniformly along the path. The laser pulses may have a duration in the range of about 10 fs to about 1000 ns, preferably in the range of about 100 fs to about 500 ns, and most preferably in the range of about 250 fs to about 250 ns. The laser pulses may have an energy density of about 0.01 J / cm2 ~about 100 J / cm 2can carry an optical fluence within a range between. The laser pulse can carry an optical energy in the range between about 1 nJ to about 1 mJ, preferably between about 10 nJ to about 0.1 mJ, and most preferably between about 100 nJ to about 10 μJ. The focus 114 of the corrective laser beam 116 is intended to be of sufficient intensity to cause non-linear absorption in the photonic chip 10. Examples of such non-linear absorption mechanisms include, but are not limited to, multi-photon absorption, tunnel ionization, free carrier absorption, impact ionization, etc. Such non-linear absorption mechanisms are generally achieved using fast (sub-μs) melting and re-solidification photo-material processes. More specifically, such non-linear absorption mechanisms can excite electrons from the valence band to the conduction band and generate free carriers. The modification of the material and the resulting refractive index change can depend on the carrier density, excitation energy level (electron temperature), and / or the temporal dynamics of the energy transfer between photons, electrons, and phonons. Generally, the carrier density and electron temperature can be maximized to maximize the possible bandwidth of the refractive index change. Generally, fast (sub-μs) melting and re-solidification can occur in the fast time regime reaching the modification threshold. In some applications, laser wavelengths below the semiconductor bandgap wavelength are employed. In these applications, strong surface 1-photon photo-ionization can drive the absorption process, resulting in a tuning bandwidth limited by weak and shallow material modification. Furthermore, semiconductor modification driven by photo-ionization can lead to limited excited electron temperature and increased plasma shielding. On the other hand, by using laser pulses with wavelengths exceeding the semiconductor bandgap wavelength, direct photo-ionization can be eliminated and deeper in-volume nonlinear absorption processes can be utilized. Similarly, it is known that the effects of increasing the electron temperature by tunnel ionization, free carrier absorption, and impact ionization are all proportional to the square of the laser wavelength, so higher electron temperatures can be reached by increasing the laser wavelength.To induce a refractive index change through a crystalline semiconductor phase, compressive stress is generated using pulses from femtoseconds to nanoseconds to induce a positive or negative refractive index change (e.g., 0.0002) at 1550 nm. To induce a refractive index change through an amorphous semiconductor phase, femtosecond to picosecond pulses are used to cause a rapid quench to induce a larger refractive index change (e.g., 0.06) at 1550 nm.

[0056] Figures 5A - D show examples of different photonic chips 10 having a semiconductor waveguide 12. It is understood that the semiconductor waveguide 12 is not limited to a single straight semiconductor waveguide, but rather may include one or more semiconductor waveguides of any shape. In some cases, the semiconductor waveguide 12 forms a particular optical function. For example, FIG. 5A shows an example of a photonic chip 10 having a first semiconductor waveguide 12' and a second semiconductor waveguide 12'' optically coupled to the first semiconductor waveguide. More specifically, the second semiconductor waveguide 12'' has a closed - loop shape that forms a semiconductor resonator 18. In this specific example, the focus 114 of the corrective laser beam can be directed to two or more circumferentially spaced positions around the semiconductor resonator 18. In some aspects, each position is tapped with a single laser pulse of a predetermined energy (hereinafter referred to as "laser tap"). Thus, in this specific aspect, the photonic chip 10 is corrected using only three laser taps of the corrective laser beam. In some other aspects, fewer than three or more than three laser taps may be used to correct the photonic chip 10. The laser taps can also be spaced apart from each other and directed towards a common area of the photonic chip.

[0057] In FIG. 5B, the photonic chip 10 includes first and second semiconductor waveguides 12' and 12'' having a coupling region 13 therebetween. In this configuration, the first and second semiconductor waveguides 12' and 12'' can form an optical coupler such as a directional coupler. In this specific example, the focus 114 of the corrective laser beam can be directed, for example, to two or more axially spaced positions along the coupling region 13. It is pointed out that the number and / or position of the laser taps can vary in several other ways and are merely exemplary.

[0058] In FIG. 5C, the photonic chip 10 has a semiconductor waveguide 12 that branches into two arms 12' and 12'' that recombine with each other at a downstream position. In this specific embodiment, the semiconductor waveguide 12 can form a Mach-Zehnder interferometer. For example, the focus 114 of the corrective laser beam can be directed to a splitter region across each of the two arms 12' and 12'', and can also be directed to a combiner region of the semiconductor waveguide 12.

[0059] In FIG. 5D, the semiconductor waveguide 12 is reversely tapered and expands to an output portion from which two auxiliary semiconductor waveguides 12' and 12'' protrude. In this configuration, the semiconductor waveguide 12 can form a multimode interferometer. The portion of the semiconductor waveguide 12 at which the focus 114 of the corrective laser beam is directed can vary from embodiment to embodiment. For example, it can be directed to any region along the multimode interferometer. It is understood that the exemplary optical functions presented herein are provided by way of example only, since other optical functions can also be modified using the methods and systems described herein.

[0060] The number and / or position of the laser taps may depend on the optical function of the semiconductor waveguide. For example, in the case of a Mach-Zehnder interferometer (MZI), by directing the laser taps towards the coupling region or individual arms, the contrast of the MZI, for example, from 45% - 55% to 50% - 50%, and / or its phase can be modified. In the case of a directional coupler, since it is known that the coupling ratio depends on the refractive index change between the two semiconductor waveguides in the coupling region, by directing the laser taps towards the coupling region, the overall coupling can be modified. In the case of a splitter (1xN), by directing the laser taps towards the coupling (multimodal) transition region, its coupling ratio and / or extinction ratio can be changed. In the case of a combiner (Mx1), by directing the laser taps towards the coupling (multimodal) transition region, its combining ratio and / or the phase of each arm can be modified. In the case of a microring resonator (MRR), the transmission of the thru or drop port directly depends on the round-trip phase in the ring, which is known to depend on the refractive index of the semiconductor waveguide in the ring. By directing the laser taps towards the coupling region or ring section, its resonant wavelength, Q factor, and / or extinction ratio can be modified. In the case of an arrayed waveguide grating (AWG), by directing the laser taps towards the coupling (multimode) transition region, the coupling of one channel can be varied with respect to the coupling of other channels. In the case of a taper, by directing the laser taps towards the taper region, its loss can be modified and the non-linear and dispersion characteristics can be changed. In the case of grating couplers, by directing the laser taps onto the grating, its injection efficiency can be modified. In the case of Bragg gratings, by irradiating the laser along the Bragg grating, its wavelength, Q factor, and / or extinction ratio can be modified. In the case of a photodetector, by performing the laser taps along the detector, its detection efficiency or annealing can be modified.In the case of distributed feedback lasers (DFB), the wavelength can be changed by directing the laser tap towards the active region. It is intended that the above aspects are for illustration only.

[0061] Figures 6A - 6G show an example of a photonic chip 10 having a semiconductor waveguide 12 and a semiconductor resonator 18 optically coupled to the semiconductor waveguide 12. The semiconductor resonator 18 has a closed-loop shape, but it is understood that the semiconductor resonator 18 is also regarded as part of the semiconductor waveguide 12. Thus, the step of directing the focus 114 of the corrective laser beam into or in the vicinity of the semiconductor waveguide 12 means that it encompasses the situation where the focus 114 of the corrective laser beam is directed into or in the vicinity of the semiconductor resonator 18. In other words, the semiconductor waveguide 12 may include the semiconductor resonator 18.

[0062] In FIG. 6A, the corrective laser beam 114 is first directed towards a first portion of the semiconductor resonator 18 and then towards a second portion of the semiconductor resonator 18 or vice versa. As shown, the first portion is disposed at a first circumferential position of the semiconductor resonator 18, while the second portion is disposed at a second circumferential position that is diametrically opposite to the first circumferential position. However, in some other aspects, the two portions may be separated by 10 degrees, 25 degrees, 90 degrees, etc. circumferentially. In this specific example, the focus 114 of the corrective laser beam is moved along the z-axis, thereby increasing the area of the second portion relative to the first portion. Thus, the second portion may have an area (e.g., 10 μm) larger than the area of the first portion (e.g., 1 μm). It is noted that the first and second portions may each receive one or more laser pulses or be exposed to a continuous wave (CW) laser for a predetermined period. In some other aspects, two different laser corrective laser beams may be used.

[0063] In FIG. 6B, the focus 114 of the correction laser beam is moved radially inward along a straight path 115 across a part of the semiconductor resonator 18. However, in some other embodiments, the focus 114 of the correction laser beam can be moved radially outward across a part of the semiconductor resonator 18. In such embodiments, the overlap between consecutive laser taps can result in enhanced optical energy delivery in these overlapping portions.

[0064] In FIG. 6C, the focus 114 of the correction laser beam is moved tangentially along an arcuate path 117 along a part of the semiconductor resonator 18. The arcuate path 117 is shown as being in the clockwise direction of rotation, but the arcuate path 117 can be in the counterclockwise direction of rotation depending on the embodiment. The arcuate path 117 can span 15 degrees, 20 degrees, 45 degrees, or other circumferential arcs or offsets.

[0065] In FIG. 6D, the path 119 created by the focus 114 of the correction laser beam is arbitrary with respect to the semiconductor waveguide 12. It is understood that the scan speed at which the focus 114 of the correction laser beam is moved along the path can be constant or vary over time depending on the embodiment.

[0066] In FIG. 6E, the correction laser beam is adjusted between consecutive laser taps to modify its intensity. More specifically, a first part of the semiconductor resonator 18 is irradiated with a first intensity or a first pulse energy of the correction laser beam, while a second part of the semiconductor resonator 18 is irradiated with a second intensity or a second pulse energy that is greater than the first intensity or pulse energy, or vice versa. For example, the first pulse energy can be 100 nJ, while the second pulse energy can be 1000 nJ. In some embodiments, there can be multiple correction laser beams.

[0067] For example, as shown in FIG. 6F, the first focus 114a of the first correction laser beam is directed towards the first portion of the semiconductor resonator 18, while the second focus 114b of the second correction laser beam is directed towards the second portion of the semiconductor resonator. In this specific embodiment, the first and second correction laser beams have different central wavelengths. However, the central wavelengths of both the first and second correction laser beams are greater than the bandgap wavelength of the semiconductor resonator so as to propagate through the photonic chip 10. For example, in this embodiment, the spectral bandwidth of the first correction laser beam can be centered around about 1550 nm, while the spectral bandwidth of the second correction laser beam can be centered around about 2800 nm.

[0068] In FIG. 6G, a single portion of the semiconductor resonator 18 is irradiated with different spatial modes of the correction laser beam. For example, the portion can be modified using a first spatial mode of light (e.g., LP01), while it can be modified using a second spatial mode of light (e.g., LP02, LP11, LP21) that is different from the first spatial mode of light. In other embodiments, different portions of the semiconductor resonator are modified using different spatial modes of light.

[0069] Referring now to FIGS. 7A and 7B, the photonic chip 10 has a substrate 14, a semiconductor waveguide 12 on top of the substrate 14, and a cladding layer 16 covering the upper surfaces of the semiconductor waveguide 12 and the substrate 14. In these embodiments, it is pointed out that the focus 114 of the corrective laser beam can be directed into or proximate to the semiconductor waveguide 12 from above through the cladding layer 16 as shown in FIG. 7A, or from below through the substrate 14 as shown in FIG. 7B. In some embodiments, the corrective laser beam 116 can be directed through one or more waveguides, cladding layers, or other layers of material to reach the desired semiconductor waveguide 12. As shown, the focus 114 of the corrective laser beam can be directed into or proximate to the semiconductor waveguide 12. It is also understood that in these embodiments the substrate 14 and the cladding layer 16 have bandgap wavelengths and / or optical transmission windows that allow transmission of the corrective laser beam 116. In embodiments where refractive index modification is performed within the semiconductor waveguide 12, the effective refractive index of the semiconductor waveguide 12 can change. It is understood that in embodiments where external refractive index modification is performed slightly outside the semiconductor waveguide 12, e.g., within an adjacent cladding layer, the effective refractive index of the semiconductor waveguide 12 can also change. In fact, since an optical beam propagating along the semiconductor waveguide 12 typically has an evanescent tail that extends outside the semiconductor waveguide, when the evanescent tail reaches the external refractive index modification, it affects the optical signal and thus the effective refractive index of the semiconductor waveguide 12.

[0070] It is contemplated that the size of the focus spot relative to the size of the semiconductor waveguide can vary for each aspect. Referring now to FIG. 8, the focus spot 114 can have a Rayleigh range (depth of focus, zr) extending along the corrective laser beam and a spot size (d) extending laterally across the corrective laser beam. The semiconductor waveguide 12 has a waveguide width w across the plane of the photonic chip 10 and a thickness t across the plane of the photonic chip 10. As shown in this particular aspect, the spot size is larger than the waveguide width w and the Rayleigh range zr is larger than the waveguide thickness t. However, in some other aspects, the spot size d can be smaller than the waveguide width w. Additionally, or alternatively, the Rayleigh range zr of the focus spot of the corrective laser beam can be smaller than the waveguide thickness t. Any combination of these dimensions can be used depending on the aspect.

[0071] In another aspect, FIG. 9 shows a flowchart of an example of a method 900 for testing a photonic chip. In this aspect, the photonic chip has a semiconductor waveguide and a number of semiconductor components optically coupled to the semiconductor waveguide. Each of the semiconductor components has a bandgap wavelength. In some aspects, the semiconductor components are semiconductor resonators such as ring resonators or photonic crystal resonators, semiconductors, etc.

[0072] In step 902, a test routine for the semiconductor waveguide is performed. More specifically, the test routine includes steps of guiding a test optical signal into and along the semiconductor waveguide, detecting an output signal resulting from the guiding, and monitoring an output spectrum based on the output signal. In some embodiments, the output spectrum can be an optical output spectrum, a radio-frequency output spectrum, etc. While the test routine is being performed, step 902 includes another step of directing the focus of a probing laser beam proximate to and within a portion of the photonic chip that is within one of the semiconductor components. It is noted that the probing laser beam has a central wavelength greater than the bandgap wavelength of the semiconductor component. Additionally or alternatively, it is intended that the central wavelength partially or wholly overlaps with the optical transmission window of the semiconductor component. Thus, the semiconductor component is optically transparent to the probing laser beam. Step 902 results in a step of modifying the effective refractive index of one portion of the semiconductor component. In some embodiments, multiple semiconductor components can be laser-tapped in one or more iterations.

[0073] In step 904, optical features in the output spectrum that are modified in response to the directing step 902 are identified. Examples of optical features can include, but are not limited to, spectral features, resonance features, etc.

[0074] In step 906, the optical features are associated with one of the semiconductor components.

[0075] In this way, when the photonic chip has a significant number of components, method 900 may be used to map the optical characteristics of the output spectrum to the corresponding semiconductor components. It is noted that method 900 is generally performed for identification and / or mapping purposes and is not intended to cause significant effective refractive index variations. Accordingly, the directing step may be limited to lower power in order to modify the effective refractive index by a small amount. For example, the effective refractive index of a portion of a semiconductor waveguide may be modified by an amount in the range between about 0.01 and about 0.00001, preferably between about 0.001 and about 0.00005, and most preferably between about 0.005 and about 0.0001. In some embodiments, the refractive index modification may be temporary or permanent.

[0076] As shown in the embodiment of FIG. 10, the photonic chip 10 has a main semiconductor waveguide 12 and three auxiliary semiconductor components 18', 18'', and 18''' optically coupled to the main semiconductor waveguide 12. Each semiconductor component has its own optical characteristics, such as spectral resonances, and the optical characteristics are different from each other. In this embodiment, a test routine is continuously performed to monitor the respective optical characteristics R of the auxiliary semiconductor components 18', 18'', and 18'''. By directing the focus 114 of the probing laser beam 116 to a given one of the auxiliary semiconductor components 18', 18'', and 18''', the test routine indicates that the optical characteristic R1 experiences a slight spectral shift. Thus, a given auxiliary semiconductor component 18' can be associated with the optical characteristic R1. Accordingly, if it is later determined that the optical characteristic R1 is a parameter that does not match the corresponding reference parameter, the focus 114 of the probing laser beam 116 may be used to transmit a large amount of optical energy to a given auxiliary semiconductor component 18' to modify its effective refractive index until the measured parameter matches the reference parameter within a given tolerance range.

[0077] Experiments were conducted using the methods and systems described herein, demonstrating that fine and coarse tuning of the effective refractive index of a semiconductor waveguide can be effectively achieved. One of these experiments involves a photonic chip having a Mach-Zehnder interferometer (MZI) formed using one or more semiconductor waveguides. More specifically, the MZI has a main semiconductor waveguide that is split into two MZI arms of equal length at a first coupling point. The two MZI arms recombine at a second coupling point downstream from the first coupling point. As can be understood, when an optical signal propagates along the main semiconductor, it is split into two optical signal portions that interfere destructively or constructively when they recombine at the second coupling point. Typically, when the lengths or effective refractive indices of the MZI arms are similar, the optical signal portions experience similar propagation conditions in each of the MZI arms, and the interference occurring at the second coupling point is constructive. However, if there is a difference in length or effective refractive index between the two MZI arms, the MZI becomes unbalanced, resulting in spectral shaping of the optical signal after recombination, which can be observed in the output optical signal.

[0078] In this experiment, subsequent sets of refractive index modification were made proximate to only one of the MZI arms of an MZI with equal arm lengths as described above. After each set of refractive index modification, the spectral response of the resulting MZI was measured. As schematically shown in FIG. 11A, the set corresponds to the linear paths L1, L2, ... L6 of the focus of a correction laser beam proximate to and parallel to the MZI arm. The linear passes L1, L2 and L3 were made on one lateral side of the MZI arm and the other passes L4, L5 and L6 were made on the other lateral side of the MZI arm. In this specific embodiment, each linear path has a length of about 50 μm and is laterally spaced from the MZI arm by about 7 μm. As best shown in FIG. 11B showing the spectral response measured following each one of the series of linear paths described above, the spectral response of the MZI changes slightly for each additional linear path. The results shown in FIG. 11B confirm that by carefully placing refractive index modification proximate to the MZI arm, a slight or subtle adjustment of the effective refractive index of the semiconductor waveguide can be achieved, if desired.

[0079] In another experiment, subsequent sets of refractive index modification were made within only one of the MZI arms of an MZI with equal arm lengths as described above. After each set of refractive index modification, the spectral response of the resulting MZI was measured. As shown in FIG. 12A, the set corresponds to the linear paths P1, P2, ... P6 of the focus of a correction laser beam within and across the MZI arm. Each of these linear paths has a length of about 15 μm and is arranged at intervals of about 10 μm from each other. As shown in FIG. 12B, it was demonstrated that a coarser adjustment of the effective refractive index of the semiconductor waveguide can be effectively achieved by such invasive refractive index modification.

[0080] In yet another experiment, six different photonic chips, each having a corresponding MZI, were fabricated using known techniques. As shown, the spectral responses of these MZIs vary widely from each other, as is typical in the industry. However, using the methods and systems described herein, the six different photonic chips were modified using refractive index modifications applied proximate to and / or within the semiconductor waveguides, and both coarse and fine tuning of each spectral response was performed until the reference parameters were reached.

[0081] It is noted that the controller described above with reference to FIG. 1 may 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. 14. Further, the software components of the controller can be implemented in the form of a software application that performs some or all of the steps of a method for modifying a photonic chip or a method for testing a photonic chip.

[0082] Referring further to FIG. 14, the computing device 1100 may include a processor 1102, a memory 1104, and an I / O interface 106. Instructions 1108 for performing the methods 400 or 900 described above may be stored in the memory 1104 and accessible by the processor 1102.

[0083] 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.

[0084] Memory 1104 may include a suitable combination of any type of computer-readable memory, either internal or external, 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), electrically erasable programmable read-only memory (EEPROM), ferroelectric RAM (FRAM), etc.

[0085] Each I / O interface 1106 enables the computing device 1100 to interconnect with one or more input devices such as a photonic chip test apparatus, a detector, a computer vision system, or with one or more output devices such as a multi-axis moving stage, an external network, or an accessible memory system.

[0086] Each I / O interface 1106 enables the controller to communicate with, exchange data with, access and connect to network resources, connect to server applications, and perform other computing applications by connecting to a network (or networks) that can transmit data, including the Internet, Ethernet, plain old telephone service (POTS) lines, public switched telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fiber optic, satellite, mobile, wireless (e.g., Wi-Fi, WiMAX), SS7 signaling network, landline, local area network, wide area network, and other combinations thereof.

[0087] The controller may execute one or more software applications configured to operate the system described herein using instruction 108. In some aspects, the software applications are stored in memory 1104 and are accessible by processor 1102 of computing device 1100. The computing device 1100 and software applications described above are intended to be exemplary. Other suitable aspects of controller 1132 may also be provided, as will be apparent to those skilled in the art.

[0088] As can be understood, the examples described and illustrated above are only intended to be exemplary. For example, the methods and systems described herein can be performed using multiple corrective laser beams. It is noted that the photonic chip can have a number of photonic functions and / or photonic components, each having a dedicated channel. The methods and the systems can be applied to each photonic function, each photonic component, and each photonic channel of the photonic chip 10. Depending on the aspect, the characteristics of the corrective laser beam can be varied. Examples of such characteristics include, but are not limited to, pulse duration, repetition rate, presence or absence of burst mode, pulse energy, laser wavelength, laser intensity, beam shape (e.g., Gaussian distribution, top hat, Bessel, elliptical), fixed or moving beam, scan speed, hatching, and laser path. The number and / or position of the laser taps can depend on the shape and material of the semiconductor waveguide. Further, the methods and systems described herein can be adapted to limit the losses occurring in the photonic chip, ensure accurate positioning of the corrective laser beam with respect to the photonic chip, maximize the compensation range, and impart positive or negative refractive index changes. When the semiconductor waveguide is surrounded by a number of material layers (e.g., glass insulator, other semiconductor layers), a change in the effective refractive index can be selectively imparted to a specific layer. The refractive index can be varied by various processes including, but not limited to, amorphization, stress induction, void generation, densification, etc. Laser-induced refractive index modification can be combined with other heat sources, such as a heater, an ionization source (e.g., input voltage of the semiconductor waveguide), or another laser beam absorbed by the semiconductor waveguide, to optimize the methods and systems described herein. The corrective laser beam can be perpendicular to the surface of the photonic chip or can have an acute or obtuse angle with respect to the surface of the photonic chip. Structures such as fiber-Bragg gratings or polarizers can be fabricated in some aspects with a change in the effective refractive index inside the semiconductor waveguide.It is understood that the effective refractive index correction may include correction of the real part of the refractive index, correction 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 process parameters and optimize the correction according to the type of semiconductor material. In some embodiments, the refractive index correction can be imparted in such a way as to affect the polarization of the optical signal propagating along the semiconductor waveguide. For example, the refractive index correction can extend to opposite sides of the semiconductor waveguide to maintain or vary the polarization. In a specific embodiment, by way of example only, the refractive index correction as shown in FIG. 11A can be used to mimic the structure of a polarization-maintaining optical fiber. In embodiments where the photonic chip is based on an InP semiconductor platform, such refractive index correction can form matrix defects that can attract electrons, thereby reducing the optical loss that occurs along the semiconductor waveguide. Although the semiconductor waveguide shown in the above example is quite simple and one-dimensional, in some other embodiments, a complex structure can also be used for the semiconductor waveguide. For example, the semiconductor waveguide can include one or more semiconductor waveguides running side by side with each other and a matrix (e.g., a glass matrix) therebetween. The scope is indicated by the appended claims.

Claims

1. A method of modifying a photonic chip having a semiconductor waveguide, the semiconductor waveguide having a bandgap wavelength: the method includes directing the focus of a corrective laser beam within and proximate to a portion of the photonic chip that is within the semiconductor waveguide, the corrective laser beam having a central wavelength greater than the bandgap wavelength of the semiconductor waveguide, the directing modifying the effective refractive index of a portion of the semiconductor waveguide; the method includes performing a test routine on the semiconductor waveguide that includes determining a parameter indicative of the performance of the semiconductor waveguide; and the method includes repeating the directing and the test routine until the parameter is in agreement with a reference parameter associated with a reference photonic chip when it is determined that the parameter does not match the reference parameter.

2. The method of claim 1, wherein the directing includes moving the focus of the corrective laser beam and at least one of the photonic chips along a path.

3. The method of claim 2, wherein the moving includes delivering laser pulses to each of a plurality of spaced points distributed along the path.

4. The method of claim 1, wherein the test routine includes directing a test optical signal into and along the semiconductor waveguide, detecting an output signal resulting from the directing, and determining a parameter based on the output signal.

5. The method of claim 4, wherein the directing includes injecting the test optical signal into a first end of the semiconductor waveguide.

6. The method of claim 5, wherein the detecting includes measuring the output signal using a photodiode optically coupled to a second end of the semiconductor waveguide.

7. The method of claim 4, wherein the detecting includes measuring the output signal scattered away from the semiconductor waveguide during the directing using a camera.

8. The method of claim 1, wherein the parameter is at least one of an output wavelength, an output phase, an output amplitude, an output bias, an output dispersion, and an output loss.

9. The method of claim 1, wherein the central wavelength of the corrective laser beam is between about 1 μm and about 20 μm, preferably between about 1.2 μm and about 10 μm, and most preferably between about 1.5 μm and about 4 μm.

10. The method of claim 1, wherein the corrective laser beam has a laser pulse having a duration in the range of from about 10 fs to about 1000 ns, preferably from about 100 fs to about 500 ns, and most preferably from about 250 fs to about 250 ns.

11. The method of claim 1, wherein the semiconductor waveguide is positioned with respect to a substrate, the photonic chip further has a cladding layer covering the upper surfaces of the substrate and the semiconductor waveguide, and the directing includes directing the focus of the corrective laser beam through at least one of the cladding layer and the substrate.

12. The method of claim 1, wherein the photonic chip has a plurality of semiconductor waveguides each having a bandgap wavelength, and the method further includes performing the directing and the test routine for each one of the plurality of semiconductor waveguides until a plurality of parameters associated with the plurality of semiconductor waveguides match respective reference parameters within a predetermined tolerance range.

13. A system for modifying a photonic chip having a semiconductor waveguide, the semiconductor waveguide having a bandgap wavelength: The system includes a corrective laser device configured to direct a focus of a corrective laser beam within and in proximity to the semiconductor waveguide and within a portion of the photonic chip, the corrective laser beam having a central wavelength greater than the bandgap wavelength of the semiconductor waveguide, the directing modifying an effective refractive index of the semiconductor waveguide; The system includes a photonic chip test device for performing a test routine on the semiconductor waveguide, the test routine including determining a parameter indicative of performance of the semiconductor waveguide; and The system includes a controller communicatively coupled to the corrective laser device and the photonic chip test device, the controller having a processor and, when executed by the processor: comparing the parameter to a reference parameter associated with a reference photonic chip; and when it is determined that the parameter does not match the reference parameter, repeating the directing and the test routine until the parameter matches the reference parameter within a predetermined tolerance range. A system having a memory storing instructions for performing the steps.

14. The system of claim 13, wherein the corrective laser device includes a laser source that generates the corrective laser beam, and the central wavelength is between about 1.0 μm and about 20 μm, preferably between about 2.5 μm and about 10 μm, and most preferably between about 2.8 μm and about 3.4 μm.

15. The system of claim 13, wherein the corrective laser device includes a laser source that generates a laser pulse having a duration 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.

16. The system of claim 13, wherein the corrective laser device has a fiber laser source.

17. The system of claim 13, further comprising a multi-axis moving stage having a support area on which the photonic chip is received, and the multi-axis moving stage moves the photonic chip during the directing.

18. The system of claim 13, wherein the photonic chip testing device includes a test light source that guides a test optical signal into and along the semiconductor waveguide, and a detector that detects an output signal resulting from the guiding, and the controller determines the parameter based on the output signal.

19. The system of claim 13, wherein the detector is a photodiode optically coupled to a first end of the semiconductor waveguide for detecting the output signal.

20. The system of claim 13, wherein the detector is an infrared camera that measures the output signal scattered away from the semiconductor waveguide during the guiding.

21. A method of testing a photonic chip, wherein the photonic chip has a semiconductor waveguide and a plurality of semiconductor components optically coupled to the semiconductor waveguide, and the semiconductor components have a bandgap wavelength: During performing a test routine on the semiconductor waveguide, guiding a test optical signal into and along the semiconductor waveguide, detecting an output signal resulting from the guiding, and monitoring the output signal based on the output signal; and directing a focus of a probing laser beam into a portion of the photonic chip proximate to and within one of the plurality of semiconductor components, the correction laser beam having a central wavelength greater than a bandgap wavelength of the semiconductor component, the directing correcting an effective refractive index of a portion of the semiconductor component; the method including identifying an optical feature in the output spectrum corrected in response to the directing; and the method including associating the optical feature with one of the semiconductor components.

22. The method of claim 21, wherein the correcting corrects the effective refractive index of a portion of the semiconductor waveguide in an amount in a range between about 0.1 and about 0.00000001, preferably between about 0.05 and about 0.0005, and most preferably between about 0.01 and about 0.

001.

23. A system for testing a photonic chip, the photonic chip having a semiconductor waveguide and a plurality of semiconductor components optically coupled to the semiconductor waveguide, the semiconductor components having a bandgap wavelength: the system including a photonic chip test apparatus for performing a test routine including guiding a test optical signal into and along the semiconductor waveguide, detecting an output signal resulting from the guiding, and monitoring an output spectrum based on the output signal; the system including a correction laser apparatus configured to direct a focus of a correction laser beam into a portion of the photonic chip proximate to and within one of the semiconductor components, the correction laser beam having a central wavelength greater than a bandgap wavelength of the semiconductor waveguide, the directing correcting an effective refractive index of a portion of the semiconductor component; and the system including a controller communicatively coupled to the photonic chip test apparatus and the correction laser apparatus, the controller including a processor and, when executed by the processor: A step of identifying an optical feature in the output spectrum that is corrected in response to the directing; A step of associating the optical feature with one of the semiconductor components; A system having a memory storing instructions for performing the above.

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