Method for manufacturing optical integrated circuit

Abstract

This method for manufacturing an optical integrated circuit comprises a detection step S01 for inputting inspection light L to an optical integrated circuit S having a structure including a waveguide Se and detecting the inspection light L output from the optical integrated circuit S, a calculation step S02 for calculating a feature amount of the time waveform or a feature amount of the wavelength spectrum of the inspection light L detected in the detection step S01; and a processing step S04 for performing refractive index adjustment processing to the waveguide Se on the basis of the result of comparison between the feature amount calculated in the calculation step S02 and a design value of a preset feature amount.

Description

Optical integrated circuit manufacturing method

[0001] The present disclosure relates to a method for manufacturing an optical integrated circuit.

[0002] In recent years, research and development of optical integrated circuits, which integrate light sources, optical switches, modulators, detectors, waveguides, and other components on a substrate, has been progressing. Since structures such as waveguides provided in optical integrated circuits are designed with great precision, the circuit characteristics of optical integrated circuits depend heavily on the processing accuracy of each structure. Therefore, in the manufacture of optical integrated circuits, it is necessary to inspect whether each structure is manufactured as designed.

[0003] An example of an apparatus applicable to the inspection of optical integrated circuits is the dispersion measurement apparatus described in Patent Document 1. This dispersion measurement apparatus includes a pulse forming unit, a correlation optical system, a light detection unit, and a calculation unit. The pulse forming unit forms a pulse train including a plurality of light pulses having a time difference and different center wavelengths from the optical pulses to be measured output from a pulse laser light source. The correlation optical system receives the pulse train output from the pulse forming unit and outputs correlated light including cross-correlation or autocorrelation of the pulse train. The light detection unit detects the time waveform of the correlated light output from the correlation optical system. The calculation unit estimates the amount of chromatic dispersion of the object to be measured based on feature quantities of the time waveform of the correlated light.

[0004] Japanese Patent Application Laid-Open No. 2020-169946

[0005] Currently, studies are being conducted to provide an optical integrated circuit with a temperature control means such as a heater, and to adjust the temperature during operation of the optical integrated circuit in accordance with deviations from the design values ​​of the circuit characteristics of the manufactured optical integrated circuit. Because the refractive index of structures such as waveguides is temperature-dependent, adjusting the temperature of the optical integrated circuit makes it possible to operate the optical integrated circuit with the circuit characteristics as designed. However, if it becomes necessary to provide a temperature control means in the optical integrated circuit, the configuration of the optical integrated circuit becomes more complex, and an increase in energy consumption for operation can become a problem.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a method for manufacturing an optical integrated circuit that can obtain an optical integrated circuit that can operate with desired circuit characteristics without relying on temperature adjustment.

[0007] The gist of the present disclosure is as follows.

[0008] [1] A method for manufacturing an optical integrated circuit, comprising: a detection step of inputting inspection light into an optical integrated circuit having a structure including a waveguide and detecting the inspection light output from the optical integrated circuit; a calculation step of calculating a feature of a time waveform or a feature of a wavelength spectrum of the inspection light detected in the detection step; and a processing step of performing refractive index adjustment processing on the waveguide based on a comparison result between the feature calculated in the calculation step and a predetermined design value of the feature.

[0009] In this method for manufacturing an optical integrated circuit, a refractive index adjustment process is performed on the waveguide based on the results of comparing the feature quantities of the time waveform or wavelength spectrum of the test light output from the optical integrated circuit with the preset design values ​​of the feature quantities. This method makes it possible to accurately determine whether the actual structure of the waveguide is formed as designed based on the feature quantities of the time waveform or wavelength spectrum of the test light. By eliminating the discrepancy between the actual structure of the waveguide and the design values ​​through the refractive index adjustment process, an optical integrated circuit can be obtained that can operate with desired circuit characteristics without relying on temperature adjustment.

[0010] [2] The manufacturing method of an optical integrated circuit according to [1], wherein the processing step uses a lookup table that associates a difference value between a design value of the feature amount and the feature amount calculated in the calculation step with an adjustment amount of the refractive index for the waveguide. By using the lookup table, it is possible to uniquely determine the adjustment amount of the refractive index for the waveguide with respect to the difference value, thereby reducing processing variations in the refractive index adjustment processing.

[0011] [3] The method for manufacturing an optical integrated circuit according to [1] or [2], wherein the processing step includes applying a refractive index material to the waveguide as the refractive index adjustment processing. In this case, the refractive index of the waveguide can be gradually reduced depending on the amount of the applied refractive index material.

[0012] [4] The method for manufacturing an optical integrated circuit according to any one of [1] to [3], wherein the processing step includes reducing the cladding constituting the waveguide as the refractive index adjustment processing. In this case, the refractive index of the waveguide can be gradually reduced according to the amount of cladding reduction.

[0013] [5] The method for manufacturing an optical integrated circuit according to any one of [1] to [4], wherein the processing step includes reducing the refractive index material already applied to the waveguide as the refractive index adjustment processing. In this case, the refractive index of the waveguide can be gradually reduced depending on the amount of refractive index material applied.

[0014] [6] The method for manufacturing an optical integrated circuit according to any one of [1] to [5], wherein the processing step performs the refractive index adjustment processing so as to include at least a part of the range of evanescent waves seeping out when light is guided through the waveguide. By adjusting the refractive index so as to include at least a part of the range of evanescent waves seeping out, the refractive index of the waveguide can be adjusted with high precision.

[0015] [7] The method for manufacturing an optical integrated circuit according to any one of [1] to [6], wherein the processing step performs the refractive index adjustment processing on a part of the waveguide. By limiting the range in which the refractive index adjustment processing is performed to a part of the waveguide, the refractive index adjustment processing can be easily performed.

[0016] [8] A method for manufacturing an optical integrated circuit according to any one of [1] to [7], wherein in the calculation step, a chromatic dispersion value of the waveguide is calculated based on a feature amount of the time waveform of the inspection light detected in the detection step, and in the processing step, a refractive index adjustment process is performed on the waveguide based on a comparison result between the chromatic dispersion value calculated in the calculation step and a preset design value of the chromatic dispersion value. According to this method, it is possible to more accurately determine whether the actual structure of the waveguide is formed as designed using the chromatic dispersion value.

[0017] [9] The method for manufacturing an optical integrated circuit according to any one of [1] to [7], wherein the calculation step calculates at least one of a centroid wavelength, a variance, a standard deviation, a skewness, and a kurtosis as a feature quantity of the wavelength spectrum of the inspection light detected in the detection step. This method makes it possible to more accurately determine whether the actual structure of the waveguide is formed as designed.

[0018]

[10] A method for manufacturing an optical integrated circuit according to any one of [1] to [9], wherein the detection step, the calculation step, and the processing step are repeatedly performed until a difference between the feature calculated in the calculation step and a design value of a preset feature becomes equal to or less than a predetermined threshold. By performing refractive index adjustment processing while monitoring the difference between the feature and the design value, an optical integrated circuit having desired circuit characteristics can be obtained with a high yield.

[0019] According to the present disclosure, an optical integrated circuit that can operate with desired circuit characteristics without relying on temperature adjustment can be obtained.

[0020] 1A and 1B are schematic diagrams showing an example of an inspection device applied to a manufacturing method of an optical integrated circuit according to the present disclosure. (a) and (b) are schematic diagrams showing an example of an optical integrated circuit. (a) is a widthwise cross-sectional view showing an example of a waveguide, and (b) is a lengthwise cross-sectional view of the waveguide shown in (a). (a) is a schematic diagram showing a time waveform of correlated light in a pulse train without chromatic dispersion in the waveguide, and (b) is a schematic diagram showing a time waveform of correlated light in a pulse train with chromatic dispersion in the waveguide. (b) is a diagram showing an example of a look-up table stored in a computer. (a) is a widthwise cross-sectional view showing an example of refractive index adjustment processing on a waveguide, and (b) is a lengthwise cross-sectional view of the waveguide shown in (a). (a) is a cross-sectional view showing another example of refractive index adjustment processing on a waveguide, and (b) is a cross-sectional view showing yet another example of refractive index adjustment processing on a waveguide. (b) is a flowchart showing an example of a manufacturing method of an optical integrated circuit according to the present disclosure. (c) is a schematic diagram showing another example of an inspection device applied to a manufacturing method of an optical integrated circuit according to the present disclosure. 14(a) and 14(b) are cross-sectional views showing another example of a waveguide; FIG. 14(a) is a cross-sectional view showing an example of a refractive index adjustment process for the waveguide shown in FIG. 14(a), and FIG. 14(b) is a cross-sectional view showing an example of a refractive index adjustment process for the waveguide shown in FIG. 14(a);

[0021] Hereinafter, a preferred embodiment of a method for manufacturing an optical integrated circuit according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0022] [Inspection Apparatus for Optical Integrated Circuits] FIG. 1 is a schematic diagram showing an example of an inspection apparatus applied to a manufacturing method for an optical integrated circuit according to the present disclosure.

[0023] 1, the inspection device 1A is configured as a device for inspecting whether an optical integrated circuit S, during or after manufacture, is manufactured as designed. The inspection device 1A includes a stage 2 on which the optical integrated circuit S is placed, an input optical system 3 that guides inspection light L to the optical integrated circuit S, an output optical system 4 that guides the inspection light L output from the optical integrated circuit S to a detection system, a photodetector 5 that detects the inspection light L guided by the output optical system 4, a computer 6 that evaluates the structures that make up the optical integrated circuit S based on the detection results of the photodetector 5, and a processing device 7 that performs refractive index adjustment processing on the optical integrated circuit S based on control from the computer 6.

[0024] An optical integrated circuit S is a circuit in which a light source, an optical switch, a modulator, a detector, a waveguide, etc. are integrated on a substrate. Figures 2(a) and 2(b) are schematic diagrams showing an example of an optical integrated circuit S. In the optical integrated circuit S shown in Figure 2(a), an input terminal Sa, an output terminal Sb, a ring resonator Sc, a grating Sd, and a waveguide Se optically connected thereto are mounted on a substrate Sg. In the optical integrated circuit S shown in Figure 2(b), an input terminal Sa, an output terminal Sb, an optical modulator Sf, and a waveguide Se optically connected thereto are mounted on a substrate Sg.

[0025] The input terminal Sa is a portion used for inputting light into the optical integrated circuit S. The output terminal Sb is a portion used for outputting light from the optical integrated circuit S. The input terminal Sa and the output terminal Sb may be composed of, for example, optical fibers. The ring resonator Sc is a structure that sets the resonant wavelength of light. The grating Sd is a structure that disperses light of a certain band by wavelength. Other structures that may be implemented in the optical integrated circuit S include an optical modulator, an optical multiplexer, an optical demultiplexer, an optical antenna, an optical coupler, an optical converter, etc.

[0026] As shown in FIGS. 3A and 3B, the waveguide Se is composed of a core K1 and a clad K2. The waveguide Se allows light to propagate while suppressing radiation loss due to the difference in refractive index between the core K1 and the clad K2. In the example shown in FIGS. 3A and 3B, the core K1 and the clad K2 both have rectangular cross sections, and the core K1 is embedded in the clad K2 so that one surface of the clad K2 in the thickness direction is flush with one surface of the core K1 in the thickness direction. A portion of the light propagating through the core K1 seeps out around the core K1 as evanescent waves E. Therefore, by adjusting the thickness of the waveguide Se in at least a portion of the range in which the evanescent waves E seep out, the discrepancy between the actual structure of the waveguide Se and the design value can be eliminated. Details will be described later.

[0027] As shown in FIG. 1 , the input optical system 3 includes a light source 11, a pulse forming unit 12, and an optical scanner 13. The light source 11 is a device that outputs coherent pulsed light P as the inspection light L. Examples of the light source 11 include an LD directly pumped Yb:YAG laser light source, a titanium sapphire laser light source, a semiconductor laser light source, and an F2 laser light source. The time waveform of the pulsed light P output from the light source 11 has, for example, a Gaussian shape. The pulsed light P output from the light source 11 may be any of an attosecond pulse, a femtosecond pulse, and a picosecond pulse, and includes multiple continuous wavelength components.

[0028] The pulse forming unit 12 is a part that forms a pulse train Pc consisting of a plurality of optical pulses from the pulsed light P output from the light source 11. The pulse train Pc is a group of single pulses formed by separating the spectrum that constitutes the pulsed light P into a plurality of wavelength bands. Here, the pulse train Pc is composed of two optical pulses Pc1 and Pc2 that have different center wavelengths. The optical pulse Pc2 is delayed in time with respect to the optical pulse Pc1. The tail portions of the optical pulse Pc1 and the optical pulse Pc2 may overlap in time.

[0029] The pulse forming unit 12 includes, for example, a diffraction grating and a spatial light modulator. In this case, the pulse forming unit 12 spatially separates the multiple wavelength components contained in the pulsed light P by wavelength using the diffraction grating, and uses a lens or the like to image the light containing the multiple wavelength components on the modulation surface of the spatial light modulator. The spatial light modulator then selects optical pulses Pc1 and Pc2 from the light containing the multiple wavelength components, and shifts their phases relative to each other to temporally delay the optical pulse Pc2 with respect to the optical pulse Pc1. The pulse train Pc formed by the pulse forming unit 12 is input to the optical scanner 13.

[0030] The optical scanner 13 is a device that scans the input position of the pulse train Pc to the optical integrated circuit S. The optical scanner 13 incorporates an optical system composed of a plurality of mirrors and prisms. The pulse train Pc output from the optical scanner 13 passes through a mirror 14 and an objective lens 15, and is then input to an input end Sa of the optical integrated circuit S via a mirror 16 on the stage 2.

[0031] The output optical system 4 is configured to include an optical scanner 21 and a correlation optical system 22. The optical scanner 21 has a configuration equivalent to that of the optical scanner 13 of the input optical system 3. After propagating through the waveguide Se of the optical integrated circuit S, the pulse train Pc output from the output end Sb passes through a mirror 23 and an objective lens 24 on the stage 2, and is then input to the optical scanner 21 via a mirror 25. The pulse train Pc output from the optical scanner 13 is input to the correlation optical system 22.

[0032] The correlation optical system 22 is a part that generates correlation light Ps that includes cross-correlation light or auto-correlation light of the pulse train Pc. As an example, the correlation optical system 22 is configured to include a beam splitter, a pair of delay optical systems composed of multiple mirrors, a pair of lenses, and an optical element disposed between the lenses. The optical element is, for example, a nonlinear optical crystal that generates second harmonic (SHG), and a light emitter that includes at least one of a phosphor. As the nonlinear optical crystal, for example, KTP (KTiOPO ４ ) crystal, LBO (LiB ３ O ５ ) crystal, BBO (β-BaB ２ O ４) crystals, etc. Examples of fluorescent substances include coumarin, stilbene, and rhodamine.

[0033] The correlation optical system 22 splits the pulse train Pc using a beam splitter and inputs each of the split pulse trains Pc to a pair of delay optical systems. The pulse train Pc guided to one delay optical system is given a predetermined delay and input to the optical element. The pulse train Pc guided to the other delay optical system is given a delay different from that of the pulse train Pc guided to the first delay optical system and input to the optical element so that they intersect at a predetermined angle. The optical element generates optical pulses Ps1 and Ps2, which are second harmonics, starting from the intersection of these pulse trains. The second harmonic is correlated light Ps including autocorrelation due to the optical pulses Ps1 and Ps2. The correlated light Ps is collimated or focused by a lens and then input to the photodetector 5.

[0034] 4(a) is a schematic diagram showing the time waveform of correlated light in a pulse train without chromatic dispersion in the waveguide. Also, FIG. 4(b) is a schematic diagram showing the time waveform of correlated light in a pulse train with chromatic dispersion in the waveguide. Here, the peak intensity of optical pulse Ps1 is referred to as PE1, and the peak intensity of optical pulse Ps2 is referred to as PE2. The full width at half maximum (FWHM) of optical pulse Ps1 is referred to as W1, and the full width at half maximum of optical pulse Ps2 is referred to as W2. The peak time interval (pulse interval) between the peak of optical pulse Ps1 and the peak of optical pulse Ps2 is referred to as G.

[0035] 4(a) and 4(b), when chromatic dispersion occurs in the waveguide Se, the peak intensities PE1 and PE2 of the optical pulses Ps1 and Ps2 decrease, the full widths at half maximum W1 and W2 increase, and the peak time interval G becomes longer, compared to when chromatic dispersion does not occur in the waveguide Se. When chromatic dispersion occurs in the waveguide Se, the amount of change in each of the peak intensities PE1 and PE2, the full widths at half maximum W1 and W2, and the peak time interval G depends on the amount of chromatic dispersion in the waveguide Se. Therefore, by using the peak intensities PE1 and PE2, the full widths at half maximum W1 and W2, and the peak time interval G as feature quantities of the time waveform of the correlation light Ps and detecting the amount of change in these feature quantities, the amount of chromatic dispersion of the pulse train Pc in the waveguide Se can be determined.

[0036] The photodetector 5 is a part that detects the correlated light Ps output from the correlation optical system 22. The photodetector 5 is configured with, for example, a photodiode. The photodetector 5 outputs an electrical signal that indicates the time waveform of the correlated light Ps based on the intensity of the detected correlated light Ps. The electrical signal output from the photodetector 5 is input to the computer 6.

[0037] The computer 6 is a part that evaluates the waveguide Se in the optical integrated circuit S based on the electrical signal from the photodetector 5. The computer 6 is physically configured to include a processor (CPU), main storage devices such as ROM and RAM, input devices such as a keyboard, mouse and touch screen, output devices such as a display (including a touch screen), a communication module such as a network card for transmitting and receiving data to and from other devices, and auxiliary storage devices such as a hard disk.

[0038] The computer 6 stores in advance feature quantities of the time waveform of the correlated light Ps that are theoretically calculated, for example, assuming no chromatic dispersion. The computer 6 calculates the amount of chromatic dispersion of the pulse train Pc in the waveguide Se by comparing the stored feature quantities with the feature quantities of the time waveform of the correlated light Ps detected by the photodetector 5.

[0039] The computer 6 also functions as a control unit for the processing device 7. For this function, the computer 6 stores a reference table T, as shown in FIG. 5 , that associates the difference between the design value of the feature amount of the correlated light Ps (here, the amount of chromatic dispersion of the pulse train Pc) and the feature amount of the time waveform of the correlated light Ps detected by the photodetector 5 with the refractive index adjustment amount for the waveguide Se. In the example of FIG. 5 , the reference table T associates the difference values ​​A1, A2, A3, ..., An with adjustment amounts X1, X2, X3, ..., Xn. The adjustment amount is a parameter including at least one of, for example, the amount of refractive index material Q applied (or reduced), height, length, and width. The computer 6 determines the adjustment amount corresponding to the difference value using the reference table T and controls the operation of the processing device 7 based on the determined adjustment amount.

[0040] The processing device 7 is a device that performs refractive index adjustment processing on the waveguide Se. The processing device 7 is, for example, a dispenser that dispenses a refractive index material Q (see FIG. 6 ). In the processing device 7, a head portion that dispenses the refractive index material Q may be displaceable in the in-plane direction and the thickness direction of the optical integrated circuit S on the stage 2. The amount of refractive index material Q dispensed by the processing device 7 is controlled based on the adjustment amount determined by the computer 6. The coating thickness of the refractive index material Q on the waveguide Se increases in accordance with the amount of refractive index material Q dispensed, thereby making it possible to increase the refractive index of the waveguide Se compared to its pre-processing state.

[0041] Examples of refractive index materials include polyimide, resist material, spin-on glass, and epoxy resin adhesives. Polyimide may be used in a state dissolved in a solvent, for example. The resist may be transparent to the wavelength used in the optical integrated circuit S. The spin-on glass may be, for example, a SiON-based low-k material used as an interlayer insulating film in LSI (Large-Scale Integration). When an epoxy resin adhesive is used, ultraviolet light irradiation is performed as necessary.

[0042] In this embodiment, as shown in FIGS. 6A and 6B, the processing device 7 performs refractive index adjustment processing so as to include at least a portion of the range into which the evanescent wave E seeps when light is guided in the waveguide Se. Furthermore, in this embodiment, the processing device 7 performs refractive index adjustment processing on a portion of the waveguide Se. The portion of the waveguide Se can be any range at any position of the waveguide Se in the optical integrated circuit S. In the optical integrated circuit S shown in FIG. 2A, for example, a portion of the waveguide Se constituting the ring resonator Sc is set as the processing range. In the optical integrated circuit S shown in FIG. 2B, for example, a portion of the waveguide Se constituting the optical modulator Sf is set as the processing range.

[0043] Generally, the radius of the seepage of the evanescent wave E is in a range of about half the wavelength of the light guided in the waveguide Se. For example, when the wavelength of the light is 1500 nm, the radius of the seepage range of the evanescent wave E is about 750 nm. Therefore, when the refractive index adjustment processing at one location on the waveguide Se is insufficient to adjust the amount of the refractive index material Q, the refractive index adjustment processing may be performed at multiple locations on the waveguide Se.

[0044] The cross-sectional shape of the refractive index material Q applied to the waveguide Se may be rectangular, or may have a cross-sectional shape that flares toward the waveguide Se, as shown in FIGS. 6( a) and 6(b). In the examples of FIGS. 6(a) and 6(b), the cross-sectional shape of the refractive index material Q is trapezoidal when viewed in the width direction and length direction of the waveguide Se. The corners of the cross-sectional shape of the refractive index material Q may be rounded. By making the corners obtuse or rounded in this way, the change in the refractive index of the waveguide Se due to the refractive index material Q becomes gradual, and the influence on light propagating through the waveguide Se (e.g., reflection at the edge of the refractive index material) can be reduced.

[0045] The refractive index adjustment process is not limited to the application of the refractive index material Q to the waveguide Se as described above, and may be performed in other ways. For example, as shown in FIG. 7( a), the refractive index adjustment process may involve the reduction of the cladding K2 constituting the waveguide Se. Alternatively, as shown in FIG. 7( b), the refractive index adjustment process may involve the reduction of the refractive index material Q already applied to the waveguide Se. The reduction of the cladding K2 and the reduction of the applied refractive index material Q can be performed by, for example, laser processing or physical processing using a cantilever. Such a method can reduce the refractive index of the waveguide Se compared to its pre-processing state. The application of the refractive index material Q, the reduction of the cladding K2, and the reduction of the applied refractive index material Q may be performed independently, or at least two of these may be performed in combination.

[0046] [Method for Manufacturing an Optical Integrated Circuit] Next, a method for manufacturing an optical integrated circuit will be described. Fig. 8 is a flowchart showing an example of a method for manufacturing an optical integrated circuit according to the present disclosure. The method for manufacturing an optical integrated circuit according to this embodiment is carried out using the inspection device 1A described above. As shown in Fig. 8, this method for manufacturing an optical integrated circuit includes a detection step S01, a calculation step S02, and a processing step S04.

[0047] The detection step S01 is a step of inputting inspection light L into an optical integrated circuit S having a structure including a waveguide Se and detecting the inspection light L output from the optical integrated circuit S. In the detection step S01, the optical integrated circuit S to be inspected is placed on the stage 2, and pulsed light P is output from the light source 11. The pulsed light P is converted into a pulse train Pc by optical pulses Pc1 and Pc2 in the pulse forming unit 12, and is input to the input end Sa of the optical integrated circuit S via the optical scanner 13 of the input optical system 3, etc.

[0048] The pulse train Pc input to the optical integrated circuit S propagates through a structure including the waveguide Se, and is then output from the output end Sb of the optical integrated circuit S. The pulse train Pc output from the output end Sb of the optical integrated circuit S is input to the correlation optical system 22 via the optical scanner 21 of the output optical system 4, etc. The correlation optical system 22 generates correlation light Ps containing the autocorrelation of the input pulse train Pc, and the correlation light Ps is detected by the photodetector 5.

[0049] The calculation step S02 is a step of calculating feature quantities of the time waveform of the inspection light L detected in the detection step S01. Here, the peak intensities PE1 and PE2, full widths at half maximum W1 and W2, and peak time interval G of the optical pulses Ps1 and Ps2 contained in the correlated light Ps are used as feature quantities of the time waveform of the correlated light Ps. The computer 6 calculates the amount of chromatic dispersion of the pulse train Pc in the waveguide Se based on a comparison between the feature quantities stored in advance and the feature quantities of the time waveform of the correlated light Ps detected by the photodetector 5.

[0050] After the calculation step S02, it is determined whether the difference between the calculated feature amount and the design value is equal to or less than a threshold value (step S03). If it is determined in step S03 that the difference between the calculated feature amount (here, the amount of chromatic dispersion of the pulse train Pc) and the design value is equal to or less than the threshold value, it is assumed that an optical integrated circuit S having circuit characteristics according to the design values ​​has been obtained, and the process ends. If it is determined in step S03 that the difference between the calculated feature amount and the design value exceeds the threshold value, a processing step S04 is executed.

[0051] The processing step S04 is a step of performing a refractive index adjustment process on the waveguide Se based on the comparison result between the feature calculated in the calculation step S02 and a preset design value of the feature. In the processing step S04, the computer 6 refers to a lookup table T (see FIG. 5 ) and determines an adjustment amount for the refractive index adjustment process based on a difference value between the design value of the feature of the correlated light Ps (here, the amount of chromatic dispersion of the pulse train Pc) and the feature of the time waveform of the correlated light Ps detected by the photodetector 5. The computer 6 controls the processing device 7 based on the determined adjustment amount, and performs a refractive index adjustment process on a portion of the waveguide Se, such as adding a refractive index material Q, reducing the cladding K2, and reducing the applied refractive index material Q, so as to include the range of evanescent wave E seepage. In this case, the refractive index adjustment process may be performed so as to include at least a portion of the range of evanescent wave E seepage. The refractive index adjustment process may also be performed so as to include the entire range of evanescent wave E seepage.

[0052] After the processing step S04 is performed, the process returns to the detection step S01 and performs each process again. That is, in this embodiment, the detection step S01, the calculation step S02, and the processing step S04 are repeatedly performed until the difference between the feature amount calculated in the calculation step S02 and the preset design value of the feature amount becomes equal to or less than a predetermined threshold.

[0053] As described above, in this method for manufacturing an optical integrated circuit, a refractive index adjustment process is performed on the waveguide Se based on the comparison result between the feature quantities of the time waveform of the inspection light L output from the optical integrated circuit S and the preset design values ​​of the feature quantities. This method makes it possible to accurately determine whether the actual structure of the waveguide Se is formed as designed, based on the feature quantities of the time waveform of the inspection light L. By eliminating the discrepancy between the actual structure of the waveguide Se and the design values ​​through the refractive index adjustment process, it is possible to obtain an optical integrated circuit S that can operate with desired circuit characteristics without relying on temperature adjustment.

[0054] In this embodiment, in the processing step S04, a reference table T is used which associates a difference value between the design value of the feature amount and the feature amount calculated in the calculation step S02 with an adjustment amount of the refractive index for the waveguide Se. By using the reference table T, it becomes possible to uniquely determine the adjustment amount of the refractive index for the waveguide Se for the difference value, thereby reducing processing variations in the refractive index adjustment processing.

[0055] In this embodiment, in the processing step S04, the refractive index adjustment processing includes applying a refractive index material Q to the waveguide Se, reducing the cladding K2 that constitutes the waveguide Se, and reducing the refractive index material Q that has already been applied to the waveguide Se. By using such a method, the refractive index of the waveguide Se can be adjusted to be gradually smaller or to be gradually decreased.

[0056] In this embodiment, in processing step S04, the refractive index adjustment process is performed so as to include at least a portion of the range into which evanescent waves E seep when light is guided through the waveguide Se. By adjusting the refractive index so as to include at least a portion of the range into which evanescent waves E seep, the refractive index of the waveguide Se can be adjusted with high precision. Also, in this embodiment, the refractive index adjustment process is performed on a portion of the waveguide Se in processing step S04. By limiting the range into which the refractive index adjustment process is performed to a portion of the waveguide Se, it is possible to avoid the need for complex adjustments to the position of the processing device 7 relative to the optical integrated circuit S, and the refractive index adjustment process can be performed easily.

[0057] In this embodiment, in the calculation step S02, the chromatic dispersion value of the waveguide Se is calculated based on the feature amount of the time waveform of the inspection light L detected in the detection step S01, and in the processing step S04, the refractive index adjustment processing for the waveguide is performed based on the comparison result between the chromatic dispersion value calculated in the calculation step S02 and a preset design value of the chromatic dispersion value. According to this method, it is possible to more accurately determine whether the actual structure of the waveguide Se is formed as designed using the chromatic dispersion value.

[0058] In this embodiment, the detection step S01, the calculation step S02, and the processing step S04 are repeatedly performed until the difference between the feature amount calculated in the calculation step S02 and the preset design value of the feature amount becomes equal to or less than a predetermined threshold. In this way, by performing the refractive index adjustment processing while monitoring the difference between the feature amount and the design value, an optical integrated circuit S having desired circuit characteristics can be obtained with a high yield.

[0059] [Another Example of Inspection Apparatus] Fig. 9 is a schematic diagram showing another example of an inspection apparatus applied to the manufacturing method of an optical integrated circuit according to the present disclosure. The inspection apparatus 1B shown in Fig. 9 differs from the above-described inspection apparatus 1A in that it calculates at least one of the centroid wavelength, variance, standard deviation, skewness, and kurtosis as a feature quantity of the wavelength spectrum of the inspection light L detected in the detection step S01. Here, a case where the centroid wavelength is used as the feature quantity of the wavelength spectrum of the inspection light L is illustrated.

[0060] The input optical system 33 of the inspection device 1B differs from the input optical system 3 of the inspection device 1A in that it does not have a pulse forming unit 12, but is otherwise similar in configuration to the input optical system 3 of the inspection device 1A. That is, in the inspection device 1B, the pulsed light P output from the light source 11 is input directly to the optical integrated circuit S as inspection light L. The output optical system 4 of the inspection device 1B is configured to include, instead of the correlation optical system 22 and the photodetector 5, an optical element 31 having transmission characteristics in which the transmittance changes linearly in a predetermined wavelength range, and a pair of cameras 32A and 32B, located downstream of the objective lens 24.

[0061] The optical element 31 has a transmission characteristic in which the transmittance changes linearly in a predetermined wavelength range. Here, the optical element 31 is configured as a light dividing element (beam splitter) called a linear reflectance gradient (LRG) dichroic mirror. The dichroic mirror is configured, for example, of a dielectric multilayer film, and transmits and reflects the inspection light L output from the optical integrated circuit S according to the wavelength, thereby dividing the inspection light L into transmitted light Lt and reflected light Lr.

[0062] Fig. 10 is a diagram showing an example of the relationship between the inspection light and the transmission characteristics of the optical element. As shown in Fig. 10, the wavelength range in which the transmittance of the optical element 31 changes linearly is set based on the wavelength range of the inspection light L. In the example of Fig. 10, the transmittance of the optical element 31 is near 0% in the wavelength range shorter than the central wavelength λ1, and increases at a constant slope in the wavelength range including the central wavelengths λ1 to λ5. The transmittance of the optical element 31 is near 100% in the wavelength range longer than the central wavelength λ5. The transmittance and reflectance of the optical element 31 are negatively correlated, and an increase in one causes a decrease in the other.

[0063] The pair of cameras 32A and 32B are devices that capture the transmitted light Lt and the reflected light Lr generated by the optical element 31. The pair of cameras 32A and 32B are configured to include, for example, an area sensor. The camera 32A captures the transmitted light Lt that has passed through the optical element 31, and calculates the transmitted light luminance I based on the image capture result. Ｔ The camera 32B captures an image of the reflected light Lr reflected by the optical element 31, and outputs data indicating the reflected light luminance I Ｒ The data indicating the above is output to the computer 6.

[0064] The computer 6 calculates the transmitted light luminance I input from the pair of cameras 32A and 32B as a characteristic quantity of the wavelength spectrum of the inspection light L. Ｔ and the reflected light luminance I Ｒ Based on the data indicating the above, the centroid wavelength λ of the inspection light L propagated through the waveguide Se is calculated. Ｇ Calculate the centroid wavelength λ Ｇλ is the wavelength at which the transmittance of the optical element 31 becomes 0%. Ｒ , the wavelength at which the transmittance of the optical element 31 becomes 50% is λ Ｍ , and the wavelength at which the transmittance of the optical element 31 becomes 100% is λ Ｔ In this case, λ Ｇ = λ Ｍ + (λ Ｔ -λ Ｒ ) (TR) / (2×(T+R)).

[0065] The computer 6 compares the design value of the centroid wavelength with the centroid wavelength λ of the wavelength spectrum of the inspection light L in the same manner as the reference table shown in FIG. Ｇ The computer 6 stores a reference table (not shown) that associates the difference between the difference and the refractive index adjustment amount for the waveguide Se. The computer 6 determines the adjustment amount corresponding to the difference using the reference table T, and controls the operation of the processing device 7 based on the determined adjustment amount.

[0066] Even when such an inspection device 1B is used, by performing each process of the flowchart shown in Fig. 8, it is possible to accurately determine whether the actual structure of the waveguide Se is formed as designed based on the feature quantities of the wavelength spectrum of the inspection light L. By eliminating the difference between the actual structure of the waveguide Se and the design value by refractive index adjustment processing, it is possible to obtain an optical integrated circuit S that can operate with the desired circuit characteristics without relying on temperature adjustment. In addition, the centroid wavelength λ Ｇ By using the center of gravity wavelength λ, it is possible to determine with higher accuracy whether the actual structure of the waveguide Se is formed as designed. Ｇ Since the fluctuation of is also related to the fluctuation of the resonant wavelength in the ring resonator Sc, the centroid wavelength λ Ｇ By adjusting the refractive index of the waveguide Se while monitoring the refractive index, it is also possible to adjust the resonant wavelength of the ring resonator Sc at the same time.

[0067] Fig. 11 is a schematic diagram showing yet another example of an inspection apparatus applied to the manufacturing method of an optical integrated circuit according to the present disclosure. The inspection apparatus 1C shown in Fig. 11 is a modified example of the inspection apparatus 1B shown in Fig. 9, and uses dispersion as a feature quantity of the wavelength spectrum of the inspection light L. In the inspection apparatus 1C, a pair of optical elements 31A and 31B are arranged in the output optical system 4, and corresponding cameras 32A, 32B and 32C are arranged. The transmission characteristics of the optical elements 31A and 31B are the same.

[0068] The camera 32A captures an image of the transmitted light Lt that has passed through the optical elements 31A and 31B, and calculates the transmitted light luminance I based on the image capture result. Ｔ１ The camera 32B captures an image of the first reflected light Lr1 reflected by the optical element 31A, and outputs data indicating the first reflected light luminance I Ｒ１ The camera 32B captures an image of the second reflected light Lr2 that has passed through the optical element 31A and been reflected by the optical element 31B, and outputs data indicating the second reflected light luminance I Ｒ２ The data indicating the above is output to the computer 6.

[0069] The computer 6 calculates the centroid wavelength λ 2 calculated from the separation ratio of the optical element 31A based on the data input from each of the cameras 32A, 32B, and 32C. Ｇと、 The centroid wavelength λ obtained from the separation ratio of the optical element 31B Ｇ As shown in FIG. 12, the separation ratio of the optical element 31A is calculated as Ｔ１ and the second reflected light intensity I Ｒ２ and the first reflected light luminance I Ｒ１ The separation ratio of the optical element 31B is the ratio of the transmitted light luminance I Ｔ１ and the second reflected light intensity I Ｒ２ It is a ratio of.

[0070] As shown in FIG. 13, the centroid wavelength λ Ｇ ' of the wavelength spectrum L of the inspection light L Ｐ２ is the centroid wavelength λ Ｇ The wavelength spectrum L of the inspection light L having Ｐ１In comparison, the wavelength is shifted to the longer wavelength side by the action of each of the pair of optical elements 31A and 31B. Ｇ ' is also the centroid wavelength λ Ｇ The center wavelength λ is shifted to the long wavelength side. Ｇ ' and centroid wavelength λ Ｇ The difference between (= λ Ｇ '-λ Ｇ ) is a feature quantity corresponding to the dispersion Δλ of the wavelength spectrum of the inspection light L.

[0071] 5, the computer 6 stores a lookup table (not shown) that associates the difference between the design value of dispersion and the dispersion of the wavelength spectrum of the inspection light L with the adjustment amount of the refractive index for the waveguide Se. The computer 6 determines the adjustment amount corresponding to the difference value using the lookup table T, and controls the operation of the processing device 7 based on the determined adjustment amount.

[0072] Even when such an inspection device 1C is used, by performing each process of the flowchart shown in Figure 8, it is possible to accurately determine whether the actual structure of the waveguide Se is formed as designed based on the feature quantities of the wavelength spectrum of the inspection light L. By eliminating the discrepancy between the actual structure of the waveguide Se and the design value through refractive index adjustment processing, it is possible to obtain an optical integrated circuit S that can operate with desired circuit characteristics without relying on temperature adjustment. Furthermore, by using dispersion as the feature quantity of the wavelength spectrum of the inspection light L, it is possible to more accurately determine whether the actual structure of the waveguide Se is formed as designed.

[0073] The above-described inspection devices 1A, 1B, and 1C may be configured to input the inspection light L to the input terminal Sa of the optical integrated circuit S and output the inspection light L from the output terminal Sb of the optical integrated circuit S by fiber coupling. In this case, it is preferable to use a polarization-maintaining fiber that maintains the polarization direction of the inspection light L as the optical fiber used for fiber coupling. Alternatively, a lensed fiber may be used as the optical fiber, and a fiber prober with a three-dimensional stage may be applied to this. In this case, optical coupling between the input terminal Sa and output terminal Sb of the optical integrated circuit S and the optical fiber can be easily performed.

[0074] [Another Example of Waveguide] The configuration of the waveguide Se may take various forms. For example, as in the waveguide Se shown in FIG. 14( a), the core K1 may be exposed from the clad K2. In the waveguide Se, the core K1 is located on the upper surface of the clad K2, and the side and top surfaces of the core K1 are exposed to the outside. Also, as in the waveguide Se shown in FIG. 14( b), the core K1 may be entirely surrounded by the clad K2. In the waveguide Se, the bottom, side, and top surfaces of the core K1 are all buried in the clad K2.

[0075] 14(a) and 14(b), the height of the seepage range of the evanescent wave E exposed from the upper surface of the clad K2 is different, but as shown in FIGS. 15(a) and 15(b), the refractive index of the waveguide Se can be precisely adjusted by performing a refractive index adjustment process, such as adding a refractive index material Q, in the seepage range of the evanescent wave E. Note that, when adding a refractive index material Q to a waveguide Se having a core K1 on the upper surface of the clad K2 as in FIG. 15(a), it is preferable to use a refractive index material Q having a refractive index smaller than that of the clad K2. In each of the embodiments of FIGS. 14(a) and 14(b), adding the refractive index material Q, reducing the clad K2, and reducing the applied refractive index material Q may be performed independently, or at least two of these may be performed in combination.

[0076] 1A to 1C... inspection device, L... inspection light, S... optical integrated circuit, Se... waveguide, T... reference table, E... evanescent wave, Q... refractive index material.

Claims

1. A method for manufacturing an optical integrated circuit, comprising: a detection step of inputting inspection light into an optical integrated circuit having a structure including a waveguide and detecting the inspection light output from the optical integrated circuit; a calculation step of calculating a feature quantity of the time waveform or a feature quantity of the wavelength spectrum of the inspection light detected in the detection step; and a processing step of performing refractive index adjustment processing on the waveguide based on a comparison result between the feature quantity calculated in the calculation step and a preset design value of the feature quantity.

2. A method for manufacturing an optical integrated circuit according to claim 1, wherein the processing step uses a lookup table that associates the difference between the design value of the feature and the feature calculated in the calculation step with the adjustment amount of the refractive index for the waveguide.

3. A method for manufacturing an optical integrated circuit according to claim 1 or 2, wherein in said processing step, a refractive index adjusting process is performed by providing a refractive index material to said waveguide.

4. The method for manufacturing an optical integrated circuit according to any one of claims 1 to 3, wherein in the processing step, the refractive index adjustment processing comprises reducing the cladding that constitutes the waveguide.

5. The method for manufacturing an optical integrated circuit according to any one of claims 1 to 4, wherein in the processing step, the refractive index adjustment processing comprises reducing a refractive index material already applied to the waveguide.

6. A method for manufacturing an optical integrated circuit according to any one of claims 1 to 5, wherein in the processing step, the refractive index adjustment processing is performed so as to include at least a part of the range of evanescent waves that seep out when light is guided through the waveguide.

7. A method for manufacturing an optical integrated circuit according to any one of claims 1 to 6, wherein in said processing step, said refractive index adjustment processing is carried out on a part of said waveguide.

8. A method for manufacturing an optical integrated circuit according to any one of claims 1 to 7, wherein in the calculation step, a chromatic dispersion value of the waveguide is calculated based on a feature amount of the time waveform of the inspection light detected in the detection step, and in the processing step, a refractive index adjustment process is performed on the waveguide based on a comparison result between the chromatic dispersion value calculated in the calculation step and a preset design value of the chromatic dispersion value.

9. A method for manufacturing an optical integrated circuit according to any one of claims 1 to 7, wherein the calculation step calculates at least one of the centroid wavelength, variance, standard deviation, skewness, and kurtosis as a feature of the wavelength spectrum of the inspection light detected in the detection step.

10. A method for manufacturing an optical integrated circuit according to any one of claims 1 to 9, wherein the detection step, the calculation step, and the processing step are repeatedly performed until the difference between the feature calculated in the calculation step and a design value of a preset feature becomes equal to or less than a predetermined threshold value.

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