Inspection device and inspection method

Abstract

An inspection device 1 comprises: a pulse formation unit that generates a pulse train Pb in which a plurality of light pulses Pb1, Pb2 having different center wavelengths are arranged at predetermined time intervals; a light detection unit 8 that detects a time waveform of the pulse train Pb output from an optical integrated circuit 5; and an evaluation unit 9 that evaluates the optical integrated circuit 5 on the basis of the feature amount of the time waveform. For each of a plurality of waveguides having different lengths that are already known, the evaluation unit 9 refers to the feature amount of the time waveform corresponding to said waveguide to calculate the amount of change in the feature amount of the time waveform with respect to the length of the waveguide, and uses the amount of change to calculate the feature amount of a time waveform of another structure.

Description

Inspection device and inspection method

[0001] The present disclosure relates to an inspection device and an inspection method.

[0002] The dispersion measurement device described in Patent Document 1 includes a pulse forming unit that forms, from a first optical pulse output from an object to be measured, a pulse train including a plurality of second optical pulses that have a time difference from one another and different center wavelengths; a correlation optical system that receives the pulse train output from the pulse forming unit and outputs correlated light that includes the autocorrelation of the pulse train; a light detection unit that detects the time waveform of the correlated light; and a calculation unit that estimates the amount of chromatic dispersion of the object to be measured based on the feature quantities of the time waveform.

[0003] The dispersion measurement device described above is expected to be used as an inspection device for photonic integrated circuits (PICs). An optical integrated circuit is a device that integrates various optical functions and transmits information signals using light. One example of evaluating an optical integrated circuit is by evaluating the amount of chromatic dispersion. For example, when a pulse train is input into an optical integrated circuit, chromatic dispersion can occur as the pulse train propagates through the waveguide of the optical integrated circuit. Therefore, the quality of the optical integrated circuit can be determined by estimating the chromatic dispersion in the optical integrated circuit using a dispersion measurement device and inspecting whether the chromatic dispersion deviates from the design value.

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

[0005] In an optical integrated circuit, the optical transmission path that transmits a pulse train may include, in addition to a waveguide, various structures such as couplers, beam splitters, diffraction gratings, and other optical elements used for inputting and outputting pulse trains into and from the optical integrated circuit. Therefore, when inspecting an optical integrated circuit, a method is needed to easily evaluate whether various structures are formed as designed.

[0006] The present disclosure provides an inspection device and an inspection method that can easily evaluate an optical integrated circuit.

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

[0008] [1] An inspection device for inspecting an optical integrated circuit having an optical structure including a plurality of waveguides, the inspection device comprising: a pulse forming unit that generates a pulse train in which a plurality of optical pulses with different center wavelengths are arranged at a predetermined time interval; a light detecting unit that detects a time waveform of the pulse train output from the optical integrated circuit; and an evaluation unit that evaluates the optical integrated circuit based on a feature of the time waveform, wherein the evaluation unit calculates a change in the feature of the time waveform with respect to the length of the waveguide based on the feature of the time waveform corresponding to each of the plurality of waveguides having different lengths and known lengths, and calculates a feature of the time waveform of another structure based on the change.

[0009] This inspection device detects the time waveform of a pulse train by inputting a pulse train of multiple optical pulses with different center wavelengths into an optical integrated circuit to be inspected. To evaluate the optical integrated circuit, the device calculates the amount of change in the time waveform feature quantity corresponding to each of multiple waveguides with different but known lengths using the time waveform feature quantities corresponding to each of the multiple waveguides, and then calculates the time waveform feature quantities of other structures based on the amount of change. The time waveform feature quantities of other structures, which are unknown parameters, can be derived from an equation that indicates the amount of change in the time waveform feature quantities corresponding to each of multiple waveguides with known lengths. Therefore, this inspection device allows for easy evaluation of optical integrated circuits.

[0010] [2] The inspection device according to [1], wherein the pulse forming unit generates a pulse train in which the wavelength difference between the plurality of optical pulses is equal. In this case, by making the wavelength difference between the optical pulses passing through the plurality of waveguides equal, it is possible to simplify the equation for calculating the feature amount of another structure.

[0011] [3] The inspection device according to [1] or [2], wherein the feature quantity of the time waveform is a pulse shift amount on the time axis between the plurality of optical pulses included in the pulse train. In this case, the pulse shift amount on the time axis between the optical pulses has linearity with respect to the length of the waveguide. Therefore, by using the pulse shift amount on the time axis between the optical pulses as the feature quantity of the time waveform, it is possible to simplify the equation for calculating the feature quantity of other structures.

[0012] [4] The inspection device according to [3], wherein the evaluation unit derives a linear function that indicates the relationship between the pulse shift amount corresponding to each of the plurality of waveguides and the length of each of the plurality of waveguides, and evaluates the plurality of waveguides based on the slope of the linear function. The amount related to chromatic dispersion of the plurality of waveguides having different lengths appears in the slope of the linear function. Therefore, by determining the slope of the linear function, it is possible to easily evaluate whether the plurality of waveguides are manufactured as designed.

[0013] [5] The inspection device according to [3], wherein the evaluation unit derives a linear function that indicates the relationship between the pulse shift amount corresponding to each of the plurality of waveguides and the length of each of the plurality of waveguides, and evaluates the other structure based on the intercept of the linear function. The pulse shift amount of the other structure other than the plurality of waveguides appears in the intercept of the linear function. Therefore, by determining the intercept of the linear function, it is possible to easily evaluate whether the other structure is manufactured as designed.

[0014] [6] The inspection device according to [4] or [5], wherein the evaluation unit evaluates the other structure based on the difference between the pulse shift amount corresponding to the waveguide connected to the other structure and the pulse shift amount of the waveguide derived from the linear function. The pulse shift amount of the other structure connected to the waveguide appears as a difference from the pulse shift amount due to the waveguide. Therefore, by calculating this difference, the other structure can be easily evaluated.

[0015] [7] The inspection device according to any one of [1] to [6], wherein the evaluation unit evaluates the chromatic dispersion of the optical integrated circuit. In this case, the quality of the optical integrated circuit can be evaluated based on the chromatic dispersion.

[0016] [8] The inspection device according to any one of [1] to [7], wherein the other structures include at least one of a coupler connected to the input and output ends of each of the plurality of waveguides and inputting and outputting the pulse train, a splitter that splits the pulse train on the optical integrated circuit, and a ring resonator that resonates and extracts a portion of the light in the pulse train. In this case, the structures required for appropriate transmission of the pulse train can be easily evaluated.

[0017] [9] The inspection device according to any one of [1] to [8], wherein the time waveform of the pulse train is a time waveform of correlated light including cross-correlated light or autocorrelated light of the pulse train. In this case, even in the case of an optical integrated circuit having a short waveguide length, the feature quantity of the time waveform of the pulse train can be obtained with high accuracy.

[0018]

[10] An inspection device for inspecting an optical integrated circuit having an optical structure including a plurality of waveguides, the inspection device comprising: a pulse forming unit that generates a pulse train in which a plurality of optical pulses with different center wavelengths are arranged at a predetermined time interval; a light detecting unit that detects the time waveform of the pulse train output from the optical integrated circuit; and an evaluation unit that evaluates the optical integrated circuit based on feature amounts of the time waveform, wherein the evaluation unit calculates feature amounts of the time waveforms of other structures based on differences in feature amounts of the time waveforms corresponding to each of the plurality of waveguides having the same length and known lengths.

[0019] In this inspection device, since the lengths of the multiple waveguides are the same, the difference between the feature quantities of the multiple time waveforms can be the feature quantity of another structure, which allows for easy evaluation of the structure.

[0020]

[11] An inspection method for inspecting an optical integrated circuit having an optical structure including a plurality of waveguides, the inspection method comprising: a pulse forming step for generating a pulse train in which a plurality of optical pulses having different center wavelengths are arranged at a predetermined time interval; an optical detection step for detecting a time waveform of the pulse train output from the optical integrated circuit; and an evaluation step for evaluating the optical integrated circuit based on a feature of the time waveform, wherein in the evaluation step, a change in the feature of the time waveform with respect to the length of the waveguide is calculated based on the feature of the time waveform corresponding to each of the plurality of waveguides having different lengths and known lengths, and the feature of the time waveform of other structures is calculated based on the change.

[0021] In this inspection method, a pulse train consisting of multiple optical pulses with different center wavelengths is input to an optical integrated circuit to be inspected, and the time waveform of the correlated light of the pulse train is detected. In evaluating the optical integrated circuit, the feature quantities of the time waveforms corresponding to each of multiple waveguides, each having a different but known length, are used to calculate the amount of change in the feature quantities of the time waveforms with respect to the length of the waveguide, and the feature quantities of the time waveforms of other structures are calculated based on this amount of change. The feature quantities of the time waveforms of other structures, which are unknown parameters, can be derived from an equation that indicates the amount of change in the feature quantities of the time waveforms corresponding to each of multiple waveguides with known lengths. Therefore, this inspection method allows for easy evaluation of optical integrated circuits.

[0022]

[12] The inspection method according to

[11] , wherein the pulse forming step generates a pulse train in which the wavelength difference between the plurality of optical pulses is equal. In this case, by making the wavelength difference between the optical pulses passing through the plurality of waveguides equal, it is possible to simplify the equation for calculating the feature amount of another structure.

[0023]

[13] The inspection method according to

[11] or

[12] , wherein the feature quantity of the time waveform is a pulse shift amount on the time axis between the plurality of optical pulses included in the pulse train. In this case, the pulse shift amount on the time axis between the optical pulses has linearity with respect to the length of the waveguide. Therefore, by using the pulse shift amount on the time axis between the optical pulses as the feature quantity of the time waveform, the equation for calculating the feature quantity of another structure can be simplified.

[0024]

[14] The inspection method according to

[13] , wherein the evaluation step derives a linear function that indicates the relationship between the pulse shift amount corresponding to each of the plurality of waveguides and the length of each of the plurality of waveguides, and evaluates the plurality of waveguides based on the slope of the linear function. The amount related to the chromatic dispersion of the plurality of waveguides having different lengths appears in the slope of the linear function. Therefore, by determining the slope of the linear function, it is possible to easily evaluate whether the plurality of waveguides are manufactured as designed.

[0025]

[15] The inspection method according to

[13] , wherein the evaluation step derives a linear function that indicates the relationship between the pulse shift amount corresponding to each of the plurality of waveguides and the length of each of the plurality of waveguides, and evaluates the other structure based on the intercept of the linear function. The pulse shift amount of the other structure other than the plurality of waveguides appears in the intercept of the linear function. Therefore, by determining the intercept of the linear function, it is possible to easily evaluate whether the other structure is manufactured as designed.

[0026]

[16] The inspection method according to

[14] or

[15] , wherein the evaluation step evaluates the other structure based on the difference between a pulse shift amount corresponding to a waveguide connected to the other structure and a pulse shift amount of the waveguide derived from the linear function. The pulse shift amount of the other structure connected to the waveguide appears as a difference from the pulse shift amount due to the waveguide. Therefore, by calculating the difference, the other structure can be easily evaluated.

[0027]

[17] The inspection method according to any one of

[11] to

[16] , wherein the evaluation step evaluates the chromatic dispersion of the optical integrated circuit. In this case, the quality of the optical integrated circuit can be evaluated based on the chromatic dispersion.

[0028]

[18] The inspection method according to any one of

[11] to

[17] , wherein the other structure includes at least one of a coupler connected to the input and output ends of each of the plurality of waveguides and inputting and outputting the pulse train, a splitter that splits the pulse train on the optical integrated circuit, and a ring resonator that resonates and extracts a portion of the light in the pulse train. In this case, the structure required for appropriate transmission of the pulse train can be easily evaluated.

[0029]

[19] The inspection method according to any one of

[11] to

[18] , wherein the time waveform of the pulse train is a time waveform of correlated light including cross-correlated light or auto-correlated light of the pulse train. In this case, even in the case of an optical integrated circuit having a short waveguide length, the feature quantity of the time waveform of the pulse train can be obtained with high accuracy.

[0030]

[20] An inspection method for inspecting an optical integrated circuit having an optical structure including a plurality of waveguides, the inspection method comprising: a pulse forming step for generating a pulse train in which a plurality of optical pulses having different center wavelengths are arranged at a predetermined time interval; a light detection step for detecting a time waveform of the pulse train output from the optical integrated circuit; and an evaluation step for evaluating the optical integrated circuit based on a feature of the time waveform, wherein the evaluation step calculates a feature of the time waveform of another structure based on a difference between the feature of the time waveform corresponding to each of the plurality of waveguides having the same length and known lengths.

[0031] In this inspection method, since the lengths of the multiple waveguides are the same, the difference between the feature quantities of the multiple time waveforms can be the feature quantity of another structure, which allows for easy evaluation of the structure.

[0032]

[21] The inspection device according to [1] or

[10] , wherein the pulse forming unit generates a pulse train in which the wavelength difference between the plurality of optical pulses is equal. In this case, by making the wavelength difference between the optical pulses passing through the plurality of waveguides equal, it is possible to simplify the equation for calculating the feature amount of another structure.

[0033]

[22] The inspection device according to [1], [2], or

[10] , wherein the feature quantity of the time waveform is a pulse shift amount on the time axis between the plurality of optical pulses included in the pulse train. In this case, the pulse shift amount on the time axis between the optical pulses has linearity with respect to the length of the waveguide. Therefore, by using the pulse shift amount on the time axis between the optical pulses as the feature quantity of the time waveform, it is possible to simplify the equation for calculating the feature quantity of other structures.

[0034]

[23] The inspection device according to any one of [1] to [6] and

[10] , wherein the evaluation unit evaluates the chromatic dispersion of the optical integrated circuit. In this case, the quality of the optical integrated circuit can be evaluated based on the chromatic dispersion.

[0035]

[24] The inspection device according to any one of [1] to [7] and

[10] , wherein the other structures include at least one of a coupler connected to the input and output ends of each of the plurality of waveguides and inputting and outputting the pulse train, a splitter that splits the pulse train on the optical integrated circuit, and a ring resonator that resonates and extracts a portion of the light in the pulse train. In this case, the structures required for appropriate transmission of the pulse train can be easily evaluated.

[0036]

[25] The inspection device according to any one of [1] to [8] and

[10] , wherein the time waveform of the pulse train is a time waveform of correlated light including cross-correlated light or autocorrelated light of the pulse train. In this case, even in the case of an optical integrated circuit having a short waveguide length, the feature quantity of the time waveform of the pulse train can be obtained with high accuracy.

[0037]

[26] The inspection method according to

[11] or

[20] , wherein the pulse forming step generates a pulse train in which the wavelength difference between the plurality of optical pulses is equal. In this case, by making the wavelength difference between the optical pulses passing through the plurality of waveguides equal, it is possible to simplify the equation for calculating the feature amount of another structure.

[0038]

[27] The inspection method according to

[11] ,

[12] , or

[20] , wherein the feature quantity of the time waveform is a pulse shift amount on the time axis between the plurality of optical pulses included in the pulse train. In this case, the pulse shift amount on the time axis between the optical pulses has linearity with respect to the length of the waveguide. Therefore, by using the pulse shift amount on the time axis between the optical pulses as the feature quantity of the time waveform, the equation for calculating the feature quantity of another structure can be simplified.

[0039]

[28] The inspection method according to any one of

[11] to

[16] and

[20] , wherein the evaluation step evaluates the chromatic dispersion of the optical integrated circuit. In this case, the quality of the optical integrated circuit can be evaluated based on the chromatic dispersion.

[0040]

[29] The inspection method according to any one of

[11] to

[17] and

[20] , wherein the other structures include at least one of a coupler connected to the input and output ends of each of the plurality of waveguides and inputting and outputting the pulse train, a splitter that splits the pulse train on the optical integrated circuit, and a ring resonator that resonates and extracts a portion of the light in the pulse train. In this case, the structures necessary for appropriate transmission of the pulse train can be easily evaluated.

[0041]

[30] The inspection method according to any one of

[11] to

[18] and

[20] , wherein the time waveform of the pulse train is a time waveform of correlated light including cross-correlated light or auto-correlated light of the pulse train. In this case, even in the case of an optical integrated circuit having a short waveguide length, the feature quantity of the time waveform of the pulse train can be obtained with high accuracy.

[0042] In this inspection method, since the lengths of the multiple waveguides are the same, the difference between the feature quantities of the multiple time waveforms can be the feature quantity of another structure, which allows for easy evaluation of the structure.

[0043] According to the present disclosure, optical integrated circuits can be easily evaluated.

[0044] 9(a), 9(b), 9(c), and 9(d) are diagrams showing examples of delay times of pulse trains. FIG. ...b), 9(c), and 9(d) are diagrams showing examples of delay times of pulse trains. FIG. 9(b), 9(c), and 9(d) are diagrams showing examples of delay times of pulse trains. FIG. 9(b), 9(c), and 9(d) are diagrams showing examples of delay times of pulse trains. FIG. 9(b), 9(c), and 9(d) are diagrams showing examples of delay times of pulse trains. FIG. 9(b), 9(c), and 9(d) are diagrams showing examples of delay times of pulse trains. FIG. 9(b), 9(c), and 9(d) are diagrams showing examples of delay times of pulse trains. FIG. FIG. 16( a) is a diagram schematically showing an optical integrated circuit according to a third embodiment. FIG. 16( b) is a diagram showing an example of a method for evaluating structures included in the optical integrated circuit according to the third embodiment. FIG. 17( a) is a diagram schematically showing an optical integrated circuit according to a fourth embodiment. FIG. 17( b) is a diagram showing an example of a method for evaluating structures included in the optical integrated circuit according to the fourth embodiment. FIG. 18( a) is a diagram schematically showing an optical integrated circuit according to a fifth embodiment. FIG. 18( b) is a diagram showing an example of a method for evaluating structures included in the optical integrated circuit according to the fifth embodiment. A flowchart showing an inspection method for evaluating the optical integrated circuit according to the fifth embodiment. FIG. 20( a) is a diagram schematically showing an optical integrated circuit according to a sixth embodiment. FIG. 20( b) is a diagram showing an example of a method for evaluating structures included in the optical integrated circuit according to the sixth embodiment. FIG. 21( a) is a diagram schematically showing an optical integrated circuit according to a seventh embodiment. FIG. 21( b) is a diagram showing an example of a method for evaluating structures included in the optical integrated circuit according to the seventh embodiment. A flowchart showing an inspection method for evaluating the optical integrated circuit according to the seventh embodiment.

[0045] Hereinafter, a preferred embodiment of an inspection device according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0046] [Configuration of Inspection Apparatus] Fig. 1 is a diagram schematically showing the configuration of an inspection apparatus according to one embodiment of the present invention. This inspection apparatus 1 is an apparatus for inspecting an optical integrated circuit 5. The optical integrated circuit 5 includes various optical structures (see Fig. 4) in addition to a waveguide 53 provided on a substrate 50. In this embodiment, the inspection apparatus 1 is an apparatus for measuring the chromatic dispersion of light to be measured that has propagated through the structures of the optical integrated circuit 5. The inspection apparatus 1 includes a pulsed laser light source 2, a pulse forming unit 3, a correlation optical system 7, a light detection unit 8, and an evaluation unit 9.

[0047] The optical input end 3a of the pulse forming unit 3 is optically coupled to the pulse laser light source 2 either spatially or via an optical waveguide such as an optical fiber. The optical input end 5a of the optical integrated circuit 5 to be inspected is optically coupled to the optical output end 3b of the pulse forming unit 3 either spatially or via an optical waveguide such as an optical fiber. The optical input end 7a of the correlation optical system 7 is optically coupled to the optical output end 5b of the optical integrated circuit 5 either spatially or via an optical waveguide such as an optical fiber. The optical detection unit 8 is optically coupled to the optical output end 7b of the correlation optical system 7 either spatially or via an optical waveguide such as an optical fiber. The evaluation unit 9 is electrically connected to the pulse forming unit 3, the optical integrated circuit 5, and the optical detection unit 8, respectively.

[0048] The pulsed laser light source 2 outputs a coherent optical pulse Pa to be measured. The pulsed laser light source 2 is, for example, a femtosecond laser, and in one embodiment, is a solid-state laser light source such as an LD directly pumped Yb:YAG pulsed laser. The time waveform of the optical pulse Pa to be measured is, for example, a Gaussian function. The optical pulse Pa to be measured is an optical pulse having a certain bandwidth and includes multiple continuous wavelength components. The pulsed laser light source 2 may be a light source that outputs an attosecond laser, a femtosecond laser, or a picosecond laser, or may be a titanium sapphire laser light source, a semiconductor laser light source, or an F2 laser light source.

[0049] The pulse shaping unit 3 forms a pulse train Pb including a plurality of optical pulses from the measured optical pulse Pa. The pulse train Pb is a group of single pulses generated using each of the wavelength bands that are obtained by dividing the spectrum constituting the measured optical pulse Pa into a plurality of wavelength bands. Note that there may be overlapping portions at the boundaries between the plurality of wavelength bands. In the following example, the pulse train Pb includes two single-pulse optical pulses Pb1 and Pb2. The central wavelength and wavelength band of the optical pulse Pb1 are different from the central wavelength and wavelength band of the optical pulse Pb2.

[0050] The pulse train Pb comprises a plurality of optical pulses Pb1 and Pb2 with different center wavelengths arranged at a predetermined time interval. The peaks of the two optical pulses Pb1 and Pb2 are separated in time, and the propagation timings of the two optical pulses Pb1 and Pb2 are shifted from each other. In other words, one optical pulse Pb2 is delayed in time with respect to the other optical pulse Pb1. However, the tail portions of adjacent optical pulses Pb1 and Pb2 may overlap each other.

[0051] FIG. 2 is a diagram showing an example configuration of the pulse shaping unit 3. The pulse shaping unit 3 includes a diffraction grating 31, a lens 32, a spatial light modulator (SLM) 33, a lens 34, and a diffraction grating 35. The diffraction grating 31 is an example of a spectroscopic element. The diffraction grating 31 is optically coupled to the pulse laser light source 2. The spatial light modulator 33 is optically coupled to the diffraction grating 31 via a lens 32. The diffraction grating 31 spatially separates multiple wavelength components contained in the measured optical pulse Pa into individual wavelengths. Note that other optical components such as a prism may be used as the spectroscopic element instead of the diffraction grating 31. The measured optical pulse Pa is incident obliquely on the diffraction grating 31 and is split into multiple wavelength components. The light P1 containing the multiple wavelength components is focused by the lens 32 into each wavelength component and formed into an image on the modulation surface of the spatial light modulator 33. The lens 32 may be a convex lens made of a light-transmitting member or a concave mirror having a concave light-reflecting surface.

[0052] The spatial light modulator 33 converts the light P1 into modulated light P2. The spatial light modulator 33 may be a reflective spatial light modulator or a transmissive spatial light modulator. Furthermore, the spatial light modulator 33 may be a liquid crystal spatial light modulator or a digital mirror device. The modulated light P2 includes light pulses Pb1 and Pb2. The spatial light modulator 33 selects any two wavelength components from the light P1, which includes multiple wavelength components, as the light pulses Pb1 and Pb2. For example, the spatial light modulator 33 may intensity-modulate the wavelength components of the light pulses Pb1 and Pb2 to a level that does not affect the other wavelength components. The wavelength difference, which is the difference between the wavelength of the light pulse Pb1 and the wavelength of the light pulse Pb2, changes depending on the value of the selected wavelength component. This allows the spatial light modulator 33 to set the wavelength difference between the two light pulses Pb1 and Pb2 to any desired value. The wavelength difference that can be set is, for example, 1 nm to 50 nm.

[0053] The spatial light modulator 33 shifts the phases of the two light pulses Pb1 and Pb2 from each other. To do this, the spatial light modulator 33 performs phase modulation on the light P1. As a result, the light pulse Pb2 has a time delay with respect to the light pulse Pb1. In other words, the spatial light modulator 33 sets the time difference between the two light pulses Pb1 and Pb2 to an arbitrary magnitude. The spatial light modulator 33 performs intensity modulation and phase modulation on the light P1 to generate modulated light P2.

[0054] The modulation of light P1 by the spatial light modulator 33 will be described in more detail. Fig. 3 is a diagram showing the modulation surface 33a of the spatial light modulator 33. As shown in Fig. 3, on the modulation surface 33a, a plurality of modulation regions 33b are arranged along a certain direction A, and each modulation region 33b extends in a direction B intersecting with direction A. Direction A is the direction of light dispersion by the diffraction grating 31. This modulation surface 33a functions as a Fourier transform plane, and each corresponding wavelength component after dispersion is incident on each of the plurality of modulation regions 33b.

[0055] The spatial light modulator 33 modulates the intensity and phase of each incident wavelength component in each modulation region 33b independently of other wavelength components. Each modulation region 33b includes, for example, an intensity modulation pattern and a phase modulation pattern. The intensity modulation pattern and phase modulation pattern are, for example, different for each modulation region 33b. The intensity modulation pattern and phase modulation pattern in each modulation region 33b vary, for example, along direction A and are constant in direction B. The modulation amount of the intensity pattern of the modulation region 33b onto which the wavelength components of the light pulses Pb1 and Pb2 are incident may be greater than the modulation amount of the intensity pattern of the modulation region 33b onto which the other wavelength components are incident. The modulation amount of the phase pattern of the modulation region 33b onto which the wavelength component of the light pulse Pb1 is incident may be greater than the modulation amount of the phase pattern of the modulation region 33b onto which the wavelength component of the light pulse Pb2 is incident.

[0056] The optical pulses Pb1 and Pb2 contained in the modulated light P2 modulated by the spatial light modulator 33 are focused by the lens 34 to a single point on the diffraction grating 35. In this case, the lens 34 functions as a focusing optical system that focuses the modulated light P2. The lens 34 may be a convex lens made of a light-transmitting member, or a concave mirror having a concave light-reflecting surface. The diffraction grating 35 also functions as a combining optical system that combines the optical pulses Pb1 and Pb2. That is, the optical pulses Pb1 and Pb2 of the modulated light P2 are focused and combined by the lens 34 and the diffraction grating 35 to form a bandwidth-controlled multi-pulse (pulse train Pb).

[0057] FIG. 4 is a schematic diagram illustrating an optical integrated circuit 5. The optical integrated circuit 5 is a device that integrates various optical functions and transmits information signals using light. The optical integrated circuit 5 includes a substrate 50. As shown in FIG. 4, the optical integrated circuit 5 is configured to include various elements, which are mounted on the substrate 50. In the example shown in FIG. 4, the optical integrated circuit 5 includes an optical input section 51, an optical output section 52, a waveguide 53, photodiodes 54 and 57, an optical ring resonator circuit 55, a photonic crystal 56, a microheater 58, and the like. In the example shown in FIG. 4, only one waveguide 53 is provided, but multiple waveguides may be provided. In this case, other structures may be connected to each of the multiple waveguides. An example using multiple waveguides will be described later.

[0058] The substrate 50 has a first surface 50a and a second surface 50b opposite to the first surface 50a. In the example of Fig. 4, the optical input section 51, the optical output section 52, the waveguide 53, the photodiodes 54 and 57, the optical ring resonator circuit 55, and the photonic crystal 56 are mounted on the second surface 50b. The microheater 58 is mounted on the first surface 50a.

[0059] The optical input section 51 is a section where light is input from the pulse forming section 3 into the optical integrated circuit 5. The optical input section 51 is formed at an optical input end 5a which is one side surface of the optical integrated circuit 5. Although only one optical input section 51 is shown in Fig. 4, a plurality of optical input sections 51 are formed at the optical input end 5a. For example, in a practical state after testing, an optical cable is connected to the optical input section 51.

[0060] The optical output unit 52 is a part that outputs the pulse train Pb from the optical integrated circuit 5 toward the correlation optical system 7. The optical output unit 52 is formed at the optical output end 5b, which is the other end face of the optical integrated circuit 5. Although a single optical output unit 52 is shown in FIG. 4, a plurality of optical output units 52 may be formed at the optical output end 5b. For example, in a practical state after inspection, an optical cable may be connected to each of the plurality of optical output units 52. The optical output unit 52 may output light guided by the waveguide 53 to the outside of the optical integrated circuit 5.

[0061] The photodiodes 54 and 57 are photodetectors provided inside the optical integrated circuit 5. The optical ring resonator circuit 55 is a circuit that sets the resonant wavelength. The photonic crystal 56 has a structure in which the refractive index changes periodically, and is a structure that confines light in a small region and manipulates the light. Note that the optical integrated circuit 5 may include various elements in addition to the above-mentioned components (elements).

[0062] The microheater 58 may be formed on each element, such as the waveguide 53, the optical ring resonator circuit 55, or the optical modulator. In the example of Fig. 4, the microheater 58 is formed so as to straddle a portion of the waveguide 53 and overlap the optical ring resonator circuit 55. The microheater 58 may, for example, receive an instruction for a set temperature from the evaluation unit 9, increase the temperature of the microheater 58 until the temperature reaches the set temperature, and heat a portion of the waveguide 53 at the set temperature. The microheater 58 can change the refractive index of a portion of the waveguide 53 by the thermo-optic effect, thereby adjusting the amount of chromatic dispersion of the waveguide.

[0063] 4, the waveguide 53 is provided linearly from the optical input portion 51 to the optical output portion 52, but the waveguide 53 may be formed, for example, in a curved or spiral shape. When the waveguide 53 is curved or spiral, the direction of curvature of the waveguide 53 coincides with the in-plane direction of the substrate 50. The direction of curvature of the waveguide 53 refers, for example, to the direction in which the waveguide 53 is curved, that is, the direction in which the curve of the waveguide 53 is described.

[0064] Chromatic dispersion occurs in the pulse train Pb input to the optical integrated circuit 5 as it propagates through the waveguide 53. Since the optical pulses Pb1 and Pb2 have different wavelengths, they propagate at different speeds through the waveguide 53. This causes a difference in the propagation time between the optical pulse Pb1 and the optical pulse Pb2, and the time interval between the optical pulse Pb1 and the optical pulse Pb2 varies.

[0065] 1 again, the correlation optical system 7 generates correlation light including cross-correlated light or auto-correlated light of the pulse train Pb output from the optical integrated circuit 5 through the waveguide 53. In this embodiment, the correlation optical system 7 includes a lens 71, an optical element 72, and a lens 73. The lens 71 is provided on the optical path between the pulse forming unit 3 and the optical element 72, and focuses the pulse train Pb output from the second adjustment unit 6 onto the optical element 72.

[0066] The optical element 72 is a light emitter including at least one of a nonlinear optical crystal that generates second harmonic waves (SHG) and a phosphor. Examples of nonlinear optical crystals include KTP (KTiOPO4) crystal, LBO (LiB3O5) crystal, and BBO (β-BaB2O4) crystal. Examples of phosphors include coumarin, stilbene, and rhodamine. The optical element 72 receives a pulse train Pb and generates correlated light Pc containing cross-correlation or auto-correlation of the pulse train Pb. The optical element 72 has polarization dependence in a predetermined direction. For example, the optical element 72 is an element that has polarization dependence in the polarization direction of the optical pulses Pb1 and Pb2 of the pulse train Pb. The lens 71 collimates or focuses the correlated light Pc output from the optical element 72.

[0067] An example of the configuration of the correlation optical system 7 will now be described in detail. FIG. 5 is a diagram schematically illustrating an example of the configuration of the correlation optical system 7. The beam splitter 74 is optically coupled to the optical integrated circuit 5 shown in FIG. 1 and transmits a portion of the pulse train Pb input from the optical integrated circuit 5 and reflects the remainder. One of the pulse trains Pba split by the beam splitter 74, called the pulse train Pba, passes through an optical path 7c including multiple mirrors 75 and reaches a lens 71. The other of the pulse trains Pbb split by the beam splitter 74 passes through an optical path 7d including multiple mirrors 76 and reaches the lens 71. The optical lengths of the optical paths 7c and 7d are different from each other. Therefore, the multiple mirrors 75 and 76 form a delay optical system that imparts a time difference between the one of the pulse trains Pba and Pbb split by the beam splitter 74. Furthermore, by varying the optical length of the optical path 7d using a moving stage 77, the time difference between the pulse trains Pba and Pbb can be varied.

[0068] Lens 71 focuses each of pulse trains Pba and Pbb toward optical element 72, and causes the optical axes of pulse trains Pba and Pbb to intersect at a predetermined angle in optical element 72, which includes a nonlinear optical crystal. As a result, a second harmonic is generated in optical element 72, originating from the intersection of pulse trains Pba and Pbb. This second harmonic is correlated light Pc, which includes the autocorrelation of pulse train Pb. This correlated light Pc is collimated or focused by lens 73, and then input to photodetector 8.

[0069] FIG. 6 is a diagram schematically illustrating another exemplary configuration of the correlation optical system 7B. In this correlation optical system 7B, the pulse train Pb passes through an optical path 7e to reach a lens 71, and the reference light pulse Pr, which is a single pulse, passes through an optical path 7f to reach the lens 71. The optical path 7f includes multiple mirrors 78 and is bent in a U-shape. Furthermore, the optical length of the optical path 7f is variable by a moving stage 79. In this example, the optical element 72, which is a nonlinear optical crystal, generates a second harmonic wave originating from the intersection of the pulse train Pb and the reference light pulse Pr. This second harmonic wave is correlation light Pc, which includes the cross-correlation of the pulse train Pb. This correlation light Pc is collimated or focused by a lens 73 and then input to the photodetector 8.

[0070] 7A and 7B are diagrams for conceptually explaining the characteristic quantities of the correlated light Pc. FIG. 7A shows an example of the time waveform of the correlated light Pc when no chromatic dispersion occurs in the pulse train Pb in the waveguide 53 of the optical integrated circuit 5 (the chromatic dispersion is zero). FIG. 7B shows an example of the time waveform of the correlated light Pc when chromatic dispersion occurs in the pulse train Pb in the waveguide 53 of the optical integrated circuit 5 (the chromatic dispersion is not zero). In the example of FIG. 7 , the correlated light Pc includes two optical pulses Pc1 and Pc2 corresponding to the optical pulses Pb1 and Pb2, respectively. Here, the peak intensity of the optical pulse Pc1 is denoted as PE1, and the peak intensity of the optical pulse Pc2 is denoted as PE2. The full width at half maximum (FWHM) of the optical pulse Pc1 is denoted as W1, and the full width at half maximum (FWHM) of the optical pulse Pc2 is denoted as W2. The peak time interval (pulse interval) between the peaks of the optical pulses Pc1 and Pc2 is denoted as G.

[0071] 7(a) and 7(b), when chromatic dispersion occurs in the pulse train Pb, the peak intensities PE1 and PE2 of the optical pulses Pc1 and Pc2 are lower, and the full widths at half maximum W1 and W2 of the optical pulses Pc1 and Pc2 are larger, compared to when chromatic dispersion does not occur. Furthermore, the peak time interval G is longer.

[0072] In this way, when chromatic dispersion occurs in the pulse train Pb, the feature quantities (peak intensities PE1, PE2, full widths at half maximum W1, W2, and peak time interval G) of the time waveform of the correlated light Pc change significantly compared to when chromatic dispersion does not occur. The amount of change depends on the amount of chromatic dispersion of the pulse train Pb in the waveguide 53. Therefore, by observing the change in the feature quantities of the time waveform of the correlated light Pc, the amount of chromatic dispersion of the pulse train Pb in the waveguide 53 can be determined accurately and easily.

[0073] Referring again to FIG. 1 , the photodetector 8 receives the correlated light Pc output from the correlation optical system 7 and detects the time waveform of the correlated light Pc. The photodetector 8 includes a photodetector such as a photodiode. The photodetector 8 detects the time waveform of the correlated light Pc by converting the intensity of the correlated light Pc into an electrical signal. The electrical signal that is the detection result is provided to the evaluation unit 9.

[0074] The evaluation unit 9 calculates the amount of chromatic dispersion based on the feature quantities of the time waveform of the correlated light Pc provided by the light detection unit 8, and evaluates the structure of the optical integrated circuit 5. As described above, when the correlated light Pc including the cross-correlation or autocorrelation of the pulse train Pb is generated, various feature quantities (e.g., pulse interval, peak intensity, pulse width, etc.) in the time waveform of the correlated light Pc have a significant correlation with the amount of chromatic dispersion of the measurement target. Therefore, the evaluation unit 9 can accurately calculate the amount of chromatic dispersion of the pulse train Pb in the optical integrated circuit 5 that is the measurement target, based on the feature quantities of the time waveform of the correlated light Pc.

[0075] The time waveform of the correlated light Pc will be described in more detail. Fig. 8 is a graph showing an example of the time waveform of the correlated light Pc. The horizontal axis of the graph of the time waveform of the correlated light Pc represents the delay time, and the vertical axis of the graph of the time waveform of the correlated light Pc represents the intensity of the correlated light Pc.

[0076] In the correlation optical system 7A shown in FIG. 5, the pulse train Pb is separated into pulse trains Pba and Pbb by a beam splitter 74. The pulse trains Pba and Pbb are then input to an optical element 72. The optical element 72 generates correlated light Pc, which is a second harmonic, and the correlated light Pc is input to a photodetector 8. The photodetector 8 detects the intensity of the correlated light Pc. The intensity of the correlated light Pc varies depending on the time difference between the pulse trains Pba and Pbb—in other words, the delay time of the pulse train Pba relative to the pulse train Pbb, or the delay time of the pulse train Pbb relative to the pulse train Pba. The delay time is adjusted by a moving stage 77. As shown in FIGS. 9( a) to 9(d), delay times T1, T2, and T3 are the times from the midpoint of two pulses included in the pulse train Pba to the midpoint of two pulses included in the pulse train Pbb.

[0077] The light detection unit 8 may include, for example, a control unit in addition to the photodetector, and the delay time may be changed by gradually changing the position of the moving stage 77 using the control unit. The control unit may also include, for example, a counter, and measure the delay time each time the pulse train Pb is input. The control unit may then generate a time waveform of the correlated light Pc by plotting the intensity of the electrical signal of the correlated light Pc detected by the photodetector for each measured delay time.

[0078] The example of Figure 8 illustrates the intensity of the correlated light Pc when the delay times are T1, T2, 0, and T3. As shown in Figure 9(a), delay time T1 is the delay time of pulse train Pba relative to pulse train Pbb. At delay time T1, pulse train Pba lags pulse train Pbb, and pulse train Pbb and pulse train Pba do not overlap at all. As shown in Figure 9(b), delay time T2 is the delay time of pulse train Pba relative to pulse train Pbb. At delay time T2, pulse train Pba lags pulse train Pbb, and part of pulse train Pbb and part of pulse train Pba overlap. When delay time is 0, as shown in Figure 9(c), there is no time difference between pulse train Pba and pulse train Pbb, and in this case, pulse train Pbb and pulse train Pba completely overlap. As shown in FIG. 9(d), delay time T3 is the delay time of pulse train Pbb relative to pulse train Pba. During delay time T3, pulse train Pbb lags behind pulse train Pba, and part of pulse train Pbb overlaps part of pulse train Pba.

[0079] 8 and 9, the smaller the time difference between the pulse trains Pba and Pbb and the larger the overlapping area between the pulse trains Pbb and Pba, the stronger the optical intensity of the correlated light Pc. The time waveform of the correlated light Pc includes a first peak PK1, a second peak PK2, and a third peak PK3. The first peak PK1 occurs when the delay time is zero. The second peak PK2 occurs when the pulse train Pba lags behind the pulse train Pbb, and one of the two pulses in the pulse train Pbb completely overlaps with one of the two pulses in the pulse train Pba. The third peak PK3 occurs when the pulse train Pbb lags behind the pulse train Pba, and the other of the two pulses in the pulse train Pbb completely overlaps with the other of the two pulses in the pulse train Pba.

[0080] The light detection unit 8 detects, for example, the interval between the first peak PK1 and the second peak PK2 or the interval between the first peak PK1 and the third peak PK3 as a peak time interval G, which is a type of feature quantity of the time waveform. The light detection unit 8 may provide the detected peak time interval G to the evaluation unit 9.

[0081] In the above example, the control unit included in the photodetector 8 generates the time waveform of the correlated light Pc. However, the evaluation unit 9 may generate the time waveform of the correlated light Pc. That is, the evaluation unit 9 may function as the photodetector. In this case, the photodetector 8 may include a photodetector and output an electrical signal of the detected correlated light Pc to the evaluation unit 9. Alternatively, the evaluation unit 9 may include a photodetector instead of the photodetector 8. In this case, the correlated light Pc may be input to the evaluation unit 9 from the correlation optical system 7A, and the photodetector of the evaluation unit 9 may detect the time waveform of the correlated light Pc and convert the intensity of the correlated light Pc into an electrical signal. The evaluation unit 9 may generate the time waveform of the correlated light Pc by plotting the intensity of the electrical signal of the correlated light Pc output from the photodetector 8 or the electrical signal converted by the photodetector of the evaluation unit 9 for each measured delay time. The evaluation unit 9 may change the delay time by gradually changing the position of the moving stage 77.

[0082] In the above example, the correlation optical system 7A has been described as an example, but the above example may also be applied to the correlation optical system 7B. In this case, the light detection unit 8 or the evaluation unit 9 may change the delay time of the pulse train Pb with respect to the reference light pulse Pr, or the delay time of the reference light pulse Pr with respect to the pulse train Pb, by gradually changing the position of the moving stage 79. The light detection unit 8 or the evaluation unit 9 may then generate the time waveform of the correlation light Pc by plotting the intensity of the electrical signal of the correlation light Pc for each measured delay time. When applied to the correlation optical system 7B, the evaluation unit 9 may also function as a light detection unit, as in the case of application to the correlation optical system 7A.

[0083] Fig. 10 is a diagram schematically illustrating an example of the hardware configuration of the evaluation unit 9. As shown in Fig. 10, the evaluation unit 9 can be physically configured as a typical computer including a processor (CPU) 91, main storage devices such as a ROM 92 and a RAM 93, input devices 94 such as a keyboard, mouse, and touch screen, output devices 95 such as a display (including a touch screen), a communication module 96 such as a network card for transmitting and receiving data to and from other devices, an auxiliary storage device 97 such as a hard disk, etc.

[0084] The processor 91 of the computer can realize the functions of the evaluation unit 9 by means of a chromatic dispersion amount calculation program. In other words, the chromatic dispersion amount calculation program causes the processor 91 of the computer to operate as the evaluation unit 9. The chromatic dispersion amount calculation program is stored in a storage device (storage medium) inside or outside the computer, such as the auxiliary storage device 97. The storage device may be a non-transitory recording medium. Examples of the recording medium include recording media such as a flexible disk, CD, DVD, recording media such as ROM, semiconductor memory, cloud server, etc.

[0085] [First Embodiment of Inspection Method] FIG. 11 is a flowchart showing an inspection method MT1 using the inspection device 1 having the above configuration. In this method, first, in step ST1 (pulse forming step), a pulse train Pb is generated in which multiple optical pulses Pb1, Pb2 having different center wavelengths are arranged at a predetermined time interval. For example, multiple wavelength components contained in the measured optical pulse Pa are spatially separated by wavelength, and the multiple wavelength components are intensity-modulated and phase-modulated using a spatial light modulator 33, and then the multiple wavelength components are focused. The pulse forming unit 3 generates the pulse train Pb so that the wavelength differences between the multiple optical pulses are equal. Note that the pulse forming unit 3 may also generate the pulse train Pb so that the wavelength differences between the multiple optical pulses are different. In this case, the pulse forming unit 3 may generate multiple pulse trains Pb having different wavelength differences from each other.

[0086] Subsequently, in step ST2 (propagation step), the pulse train Pb is propagated through the waveguide 53 of the optical integrated circuit 5. The optical pulses Pb1 and Pb2 are input through the optical input unit 51, guided through the waveguide 53, and then output from the optical output unit 52. In step ST2, chromatic dispersion occurs in the pulse train Pb as it propagates through the waveguide 53. For example, a difference occurs between the propagation time of the optical pulse Pb1 and the propagation time of the optical pulse Pb2, and the time interval between the optical pulse Pb1 and the optical pulse Pb2 varies.

[0087] Next, in step ST3 (correlated light generating step), correlated light Pc including cross-correlation or auto-correlation of the pulse train Pb is generated using an optical element 72 including at least one of a nonlinear optical crystal and a phosphor. For example, as shown in Fig. 5, the pulse train Pb is branched into two, and one of the branched pulse trains Pbb is time-delayed relative to the other pulse train Pba. Then, based on the time-delayed one pulse train Pbb and the other pulse train Pba, correlated light Pc including auto-correlation of the pulse train Pb is generated.

[0088] Next, in step ST4 (light detection step), the time waveform of the correlated light Pc is detected. In steps ST5 to ST11 (evaluation steps), the optical integrated circuit 5 is evaluated based on the feature quantities of the time waveform. The evaluation unit 9 evaluates, for example, the chromatic dispersion of the optical integrated circuit 5. For example, the evaluation unit 9 calculates the amount of chromatic dispersion in each of the various structures including the waveguide 53, and evaluates whether the various structures are formed as designed.

[0089] In the following description, the pulse shift amount will be taken as an example of a feature amount of a time waveform for evaluating the optical integrated circuit 5. The pulse shift amount is a parameter corresponding to the peak time interval G, and is the pulse shift amount on the time axis between multiple optical pulses included in the pulse train Pb.

[0090] In this embodiment, an optical integrated circuit 5A including a plurality of waveguides shown in Fig. 12 will be described as an example of the optical integrated circuit 5. The optical integrated circuit 5A has an optical structure including a plurality of waveguides. The optical integrated circuit 5A has three waveguides, each of which is an example of a waveguide 53, and which are composed of a waveguide L1, a waveguide L2, and a waveguide L3.

[0091] A coupler C is connected to the input and output ends of each of the three waveguides L1 to L3. The coupler C on the input end side is an example of an optical input unit 51, and inputs the pulse train Pb from the pulse forming unit 3 into the optical integrated circuit 5. The coupler C on the output end side is an example of an optical output unit 52, and outputs the pulse train Pb from the optical integrated circuit 5 toward the correlation optical system 7.

[0092] In the optical integrated circuit 5A, the waveguide L1 and the coupler C constitute the optical transmission line LT1. The waveguide L2 and the coupler C constitute the optical transmission line LT2. The waveguide L3 is partially divided, and another structure U1 is provided at the divided portion. That is, the structure U1, in addition to the waveguide L3 and the coupler C, constitute the optical transmission line LT3.

[0093] The three waveguides L1 to L3 have the same material, structure, and optical properties, but are different in length. The lengths of the three waveguides L1 to L3 are known. The lengths of the coupler C and the structure U1 are also known. In the example of Figure 12, the lengths of the waveguides are shorter in the order of L2, L1, and L3. The length of the waveguide L3 is the length of the optical transmission line LT3 minus the length of the structure U1.

[0094] 11 , in step ST5, it is determined whether or not time waveforms have been detected for all of the optical transmission lines LT1 to LT3. In evaluating the optical integrated circuit 5A, a pulse train Pb is propagated through each of the optical transmission lines LT1 to LT3 to generate correlated light Pc corresponding to each optical transmission line, and a time waveform is detected for each optical transmission line. The pulse train Pb may be propagated through the optical transmission lines LT1 to LT3 in any order, or may be propagated simultaneously. If detection of time waveforms for all of the optical transmission lines LT1 to LT3 has not been completed (step ST5: NO), steps ST1 to ST4 are repeatedly executed until detection of time waveforms for all of the transmission lines is completed.

[0095] When the detection of the time waveforms has been completed for all of the optical transmission lines LT1 to LT3 (step ST5: YES), in step ST6, the change amount of the pulse shift of the time waveforms with respect to the lengths of the waveguides L1 and L2 is calculated based on the pulse shift amount of the time waveforms corresponding to the waveguides L1 and L2 among the plurality of waveguides L1 to L3. The pulse shift amount of the time waveforms corresponding to the waveguides L1 and L2 corresponds to the pulse shift amount of the time waveforms detected in the optical transmission lines LT1 and LT2, respectively.

[0096] 13 is a diagram showing an example of a method for evaluating the structures included in the optical integrated circuit 5A. In step ST6, the evaluation unit 9 calculates, for example, the pulse shift amounts P Ｌ１ , P Ｌ２ and the lengths of the waveguides L1 and L2. The evaluation unit 9 derives the linear function F1 based on the linear relationship between the lengths of the waveguides and the pulse shift amounts.

[0097] The evaluation unit 9 may derive the linear function F1 as follows, for example. In Fig. 13, the linear function F1 is illustrated in a coordinate system in which the X-axis direction represents the length of the waveguide and the Y-axis direction represents the pulse shift amount. For example, the evaluation unit 9 may derive the linear function F1 as follows, where the lengths of the waveguides L1 and L2 are the X-coordinate values ​​and the pulse shift amount P corresponding to the waveguide L1 is the Y-coordinate value. Ｌ１ , and the pulse shift amount P corresponding to the waveguide L2 Ｌ２ The evaluation unit 9 calculates the pulse shift amount P Ｌ１ , P Ｌ２ are plotted, and the straight line connecting the two points is defined as the linear function F1. In this case, the evaluation unit 9 may substitute these X coordinate values ​​and Y coordinate values ​​into the equation of the linear function F1, y = ax + b, and solve the simultaneous equations to find the slope a and the intercept b.

[0098] Subsequently, in step ST7, the evaluation unit 9 evaluates the plurality of waveguides L1 and L2 based on the slope a of the linear function F1. The pulse shift amounts of the plurality of waveguides L1 and L2 having different lengths appear in the slope a of the linear function F1. The evaluation unit 9 may evaluate the plurality of waveguides L1 and L2 based on the slope a of the linear function F1. The evaluation unit 9 may, for example, calculate the amount of chromatic dispersion of the waveguide and evaluate the waveguides based on the amount of chromatic dispersion. As described above, the three waveguides L1 to L3 have the same material, structure, and optical characteristics, so a single common value is calculated as the amount of chromatic dispersion of the waveguides. In this case, the unit of chromatic dispersion D is expressed in, for example, [ps / nm / km]. Chromatic dispersion D is the wavelength of two light λ s with a wavelength difference of 1 nm. １ , λ ２ The time difference that occurs when light propagates 1 km through the waveguide is expressed in picoseconds. Ｌ is calculated by the following formula 1. In formula 1, WS is the wavelength difference between the multiple optical pulses of the pulse train Pb. Ｌ =a / WS...(1)

[0099] Next, in step ST8, the evaluation unit 9 calculates the amount of pulse shift of the time waveform of the other structure based on the amount of change in the amount of pulse shift of the time waveform with respect to the lengths of the waveguides L1 and L2. In this case, the other structure refers to the coupler C. The amount of pulse shift of the coupler C appears in the intercept b of the linear function F1. In the example of FIG. 13, the intercept b of the linear function F1 corresponds to the amount of pulse shift of the two couplers C.

[0100] Subsequently, in step ST9, the evaluation unit 9 evaluates the coupler C based on the intercept b of the linear function F1. The evaluation unit 9, for example, calculates the amount of chromatic dispersion of the coupler C and evaluates the coupler C based on the amount of chromatic dispersion. The amount of chromatic dispersion D of the coupler C Ｃ is calculated by the following formula 2. In formula 2, Lc represents the length of one coupler. Ｃ =b / (WS×2×Lc)...(2)

[0101] Subsequently, in step ST10, the evaluation unit 9 calculates the feature amount of the structure U1. Fig. 14 is a diagram showing an example of a method for evaluating the structure U1. For example, the evaluation unit 9 calculates the pulse shift amount P Ｌ３ and the pulse shift amount of the waveguide L3 derived from the linear function F1 is defined as the pulse shift amount P Ｕ１ Let's say.

[0102] Next, in step ST11, the evaluation unit 9 calculates the pulse shift amount P Ｕ１ The structure U1 is evaluated based on the wavelength dispersion amount D of the structure U1. Ｕ１ is calculated by the following formula 3. In formula 3, L Ｕ１ denotes the length of the unknown structure U1. Ｕ１ =P Ｕ１ / (WS x L Ｕ１ ) ... (3)

[0103] [Operations and Effects] As described above, in the present disclosure, a pulse train Pb consisting of multiple optical pulses Pb1 and Pb2 with different center wavelengths is input to an optical integrated circuit 5A to be inspected, and the time waveform of the pulse train Pb is detected. In evaluating the optical integrated circuit 5A, the time waveform feature quantities corresponding to each of multiple waveguides L1 and L2, which have different but known lengths, are used to calculate the amount of change in the time waveform feature quantities with respect to the length of the waveguide, and the time waveform feature quantities of another structure, the coupler C, are calculated based on this amount of change. The time waveform feature quantities of the coupler C, which are unknown parameters, can be derived from an equation indicating the amount of change in the time waveform feature quantities corresponding to each of multiple waveguides L1 and L2, whose lengths are known. Therefore, the present disclosure allows for easy evaluation of the optical integrated circuit 5A.

[0104] In the present disclosure, a pulse train Pb may be generated in which the wavelength difference between the plurality of optical pulses Pb1 and Pb2 is equal. In this case, by making the wavelength differences between the optical pulses passing through the plurality of waveguides L1 to L3 equal, the equation for calculating the characteristic quantity of the coupler C can be simplified.

[0105] The feature quantity of the time waveform may be the amount of pulse shift on the time axis between the multiple optical pulses Pb1 and Pb2 included in the pulse train Pb. In this case, the amount of pulse shift on the time axis between the optical pulses has linearity with respect to the length of the waveguide. Therefore, by using the amount of pulse shift on the time axis between the optical pulses as the feature quantity of the time waveform, the equation for calculating the feature quantity of the coupler C can be simplified.

[0106] In the present disclosure, the pulse shift amount P Ｌ１ , P Ｌ２ A linear function F1 that indicates the relationship between the wavelength dispersion of each of the waveguides L1 and L2 and the lengths of the waveguides L1 and L2 may be derived, and the waveguides L1 and L2 may be evaluated based on the slope a of the linear function F1. In this case, the amount related to the wavelength dispersion of the waveguides L1 and L2 having different lengths appears in the slope a of the linear function F1. Therefore, by determining the slope a of the linear function F1, it is possible to easily evaluate whether the waveguides L1 and L2 are manufactured as designed.

[0107] In the present disclosure, the pulse shift amount P Ｌ１ , P Ｌ２ and the lengths of the multiple waveguides L1 and L2, and the coupler C may be evaluated based on the intercept b of the linear function F1. The amount of pulse shift of a structure (coupler C) other than the multiple waveguides appears in the intercept b of the linear function F1. Therefore, by finding the intercept b of the linear function F1, it is possible to easily evaluate whether the coupler C has been manufactured as designed.

[0108] In the present disclosure, the pulse shift amount P corresponding to the waveguide L3 connected to the other structure U1 is Ｌ３ The other structure U1 may be evaluated based on the difference between the pulse shift amount P of the other structure U1 connected to the waveguide L3 and the pulse shift amount P of the other structure U1 derived from the linear function F1. Ｕ１ appears as a difference from the amount of pulse shift due to the waveguide L3. Therefore, by determining this difference, another structure U1 can be easily evaluated.

[0109] In the present disclosure, the chromatic dispersion of the optical integrated circuit 5A may be evaluated. In this case, the quality of the optical integrated circuit 5A can be evaluated based on the chromatic dispersion.

[0110] In the present disclosure, the time waveform of the pulse train Pb may be the time waveform of the correlated light Pc including cross-correlated light or auto-correlated light of the pulse train Pb. In this case, even in the case of a short waveguide such as the optical integrated circuit 5A, the feature quantity of the time waveform of the pulse train Pb can be obtained with high accuracy.

[0111] [Second Embodiment of Inspection Method] Fig. 15(a) is a diagram schematically illustrating an optical integrated circuit 5B according to a second embodiment. Fig. 15(b) is a diagram illustrating an example of a method for evaluating structures included in the optical integrated circuit 5B. The optical integrated circuit 5B differs from the optical integrated circuit 5A in that the optical transmission line LT3 includes multiple structures U1, U2, and U3. Therefore, in the inspection method for the optical integrated circuit 5B, in step ST10, the pulse shift amounts of the multiple structures U1, U2, and U3 are calculated, and in step ST11, the pulse shift amounts of the multiple structures U1, U2, and U3 are evaluated. As shown in Fig. 15(b), the evaluation unit 9 calculates, for example, the pulse shift amount P corresponding to the waveguide L3 connected to the multiple structures U1, U2, and U3. Ｌ３ and the pulse shift amount of the waveguide L3 derived from the linear function F1 are defined as the pulse shift amounts P Ｕ１ , P Ｕ２ , P Ｕ３ The evaluation unit 9 then calculates the pulse shift amount P Ｕ１ +P Ｕ２ +P Ｕ３ The plurality of structures U1, U2, and U3 are evaluated based on the wavelength dispersion amount D Ｕ１＋Ｕ２＋Ｕ３ is calculated by Equation 4. In Equation 4, L Ｕ１ , L Ｕ２ , L Ｕ３ indicates the length of each of the other structures U1, U2, and U3. Ｕ１＋Ｕ２＋Ｕ３ = (P Ｕ１ +P Ｕ２ +P Ｕ３ ) / {WS × (L Ｕ１ +L Ｕ２ +L Ｕ３ ) ... (4)

[0112] [Third Embodiment of Inspection Method] FIG. 16( a) is a schematic diagram illustrating an optical integrated circuit 5C according to a third embodiment. FIG. 16( b) is a diagram illustrating an example of a method for evaluating structures included in the optical integrated circuit 5C. The optical integrated circuit 5C differs from the optical integrated circuit 5A in that the optical transmission line LT3 includes a ring resonator U4 instead of the structure U1. In the following description, for convenience of explanation, the coupler C may be referred to as the input-side coupler C1 and the output-side coupler C2. In the optical integrated circuit 5C, the coupler C1 of the optical transmission line LT1 and the coupler C1 of the optical transmission line LT3 are common. Furthermore, portions of the waveguides L1 and L3 are common, and the waveguides L1 and L3 are separated by the ring resonator U4. For example, the ring resonator U4 may resonate and extract a portion of the light in the pulse train Pb, and the optical transmission line LT3 may output the light extracted from the output-side coupler C2.

[0113] As shown in FIG. 16B, the evaluation unit 9 calculates, for example, the pulse shift amount P Ｌ３ and the pulse shift amount of the waveguide L3 derived from the linear function F1 is defined as the pulse shift amount P Ｕ４ Then, the evaluation unit 9 calculates the pulse shift amount P Ｕ４ The amount of chromatic dispersion of the ring resonator U4 may be calculated based on the length of the ring resonator U4 and the wavelength of the ring resonator U4, and the ring resonator U4 may be evaluated.

[0114] [Fourth Embodiment of Inspection Method] FIG. 17( a) is a diagram schematically illustrating an optical integrated circuit 5D according to a fourth embodiment. FIG. 17( b) is a diagram illustrating an example of a method for evaluating structures included in the optical integrated circuit 5D. The optical integrated circuit 5D differs from the optical integrated circuit 5A in that the optical transmission line LT3 includes a reflecting element U5 instead of the structure U1. The reflecting element U5 is, for example, a reflective diffraction grating. A pulse train Pb input to the optical transmission line LT3 may propagate through the waveguide L3, be reflected by the reflecting element U5, and then propagate again through the waveguide L3 and be output from the coupler C1. The length of the waveguide L3 illustrated in FIG. 17( b) indicates the length of the round trip of the pulse train Pb.

[0115] As shown in FIG. 17B, the evaluation unit 9 calculates, for example, the pulse shift amount P Ｌ３ and the pulse shift amount of the waveguide L3 derived from the linear function F1 is defined as the pulse shift amount P Ｕ５ Then, the evaluation unit 9 calculates the pulse shift amount P Ｕ５ The amount of wavelength dispersion of the reflecting element U5 may be calculated based on the wavelength and the length of the reflecting element U5, and the reflecting element U5 may be evaluated.

[0116] [Fifth Embodiment of Inspection Method] An optical integrated circuit may have four or more waveguides as the multiple waveguides. FIG. 18( a) is a diagram schematically illustrating an optical integrated circuit 5E according to a fifth embodiment. FIG. 18( b) is a diagram illustrating an example of a method for evaluating structures included in the optical integrated circuit 5E. As shown in FIG. 18( a), the optical integrated circuit 5E has four optical transmission lines LT1 to LT4. The optical transmission line LT1 is composed of a waveguide L1, two couplers C (a coupler C1 on the input end side and a coupler C2 on the output end side), and one splitter S that branches the waveguide. The optical transmission line LT2 is composed of a waveguide L2, two couplers C, and one splitter S. The optical transmission line LT3 is composed of a waveguide L3, two couplers C, and two splitters S. The optical transmission line LT4 is composed of a waveguide L4, two couplers C, two splitters S, and a structure U6. The optical transmission lines LT1 to LT4 share the coupler C1 on the input end side. A portion of the waveguides L1 to L4 is shared, and the common portion of the waveguides L1 to L4 is branched into three waveguides by a splitter S located on the input end side. A portion of the waveguides L3 and L4 is shared, and the common portion of the waveguides L3 and L4 is branched into two waveguides by a splitter S located on the output end side. The lengths of the waveguides L1 to L4, the couplers C, the splitter S, and the structure U6 are known.

[0117] 19 is a flowchart showing an inspection method MT2 for evaluating the optical integrated circuit 5E. In the inspection method MT2, steps ST1 to ST5 and step ST7 are the same as the inspection method MT1. In step ST6, the evaluation unit 9 calculates the pulse shift amounts P Ｌ１ , P Ｌ２ and the lengths of the waveguides L1 and L2, a linear function F2 is derived. The intercept b1 of the linear function F2 is the sum of the pulse shift amounts of the two couplers C and one splitter S.

[0118] In step ST8, the evaluation unit 9 calculates the pulse shift amount of the splitter S based on, for example, a linear function F2. For example, the evaluation unit 9 calculates the pulse shift amount P Ｌ３ and the pulse shift amount of the waveguide L3 derived from the linear function F2 is set as the pulse shift amount K1 of one splitter S.

[0119] Subsequently, in step ST9, the evaluation unit 9 evaluates the splitter S based on the pulse shift amount K1. Ｓ is calculated by Equation 5. In Equation 5, L Ｓ denotes the length of the splitter S. Ｓ = K1 / (WS × L Ｓ ) ... (5)

[0120] Subsequently, in step ST10, the evaluation unit 9 calculates the amount of pulse shift of the coupler C based on, for example, a linear function F2. The evaluation unit 9 calculates the difference (b1-K1) between the intercept b1, which is the sum of the amounts of pulse shift of the two couplers C and the amount of pulse shift of one splitter S, and the amount of pulse shift K1 of one splitter S, as the amount of pulse shift of the coupler C. Subsequently, in step ST11, the evaluation unit 9 evaluates the coupler C based on, for example, the linear function F2. The amount of chromatic dispersion D of the coupler C is calculated as follows: Ｃ is calculated by Equation 6. Ｃ =(b1-K1) / (WS×2×L Ｃ ) ... (6)

[0121] Subsequently, in step ST12, the evaluation unit 9 calculates the pulse shift amount of the structure U6 based on, for example, a linear function F2. The evaluation unit 9 calculates, for example, the pulse shift amount P Ｌ４ and the pulse shift amount of the waveguide L4 derived from the linear function F2 is set as the total value K2 of the pulse shift amounts of one splitter S and the structure U6. The evaluation unit 9 calculates the difference (K2-K1) between the total value K2 of the pulse shift amounts of one splitter S and the structure U6 and the pulse shift amount K1 of one splitter S as the pulse shift amount of the structure U6. Subsequently, in step ST13, the evaluation unit 9 evaluates the structure U6 based on, for example, the linear function F2. The chromatic dispersion amount D of the structure U6 Ｕ６ is calculated by Equation 7. In Equation 7, L Ｕ６ indicates the length of the structure U6. Ｕ６ =(K2-K1) / (WS×L Ｕ６ ) ... (7)

[0122] [Sixth Embodiment of Inspection Method] FIG. 20( a) is a diagram schematically illustrating an optical integrated circuit 5F according to a sixth embodiment. FIG. 20( b) is a diagram illustrating an example of a method for evaluating structures included in the optical integrated circuit 5F. As shown in FIG. 20( a), the optical integrated circuit 5F has four optical transmission lines LT1 to LT4. The optical transmission line LT1 is composed of a waveguide L1, two couplers C (a coupler C1 on the input end side and a coupler C2 on the output end side), and two splitters S (a splitter S1 that branches the waveguide and a splitter S2 that couples the waveguides). The optical transmission line LT2 is composed of a waveguide L2, two couplers C, and two splitters S. The optical transmission line LT3 is composed of a waveguide L3, two couplers C, and three splitters S (splitters S1 and S3 that branch the waveguide, and a splitter S2 that couples the waveguides). The optical transmission line LT4 is composed of a waveguide L3, two couplers C, three splitters S, and a structure U7. The coupler C1, splitter S1, splitter S2 on the input end side, and the coupler C2 on the output end side included in the optical transmission lines LT1 to LT4 are common. A portion of the waveguides L1 to L4 is common, and the common portion of the waveguides L1 to L4 is branched into three waveguides by the splitter S1. A portion of the waveguides L3 and L4 is common, and the common portion of the waveguides L3 and L4 is branched into two waveguides by the splitter S3. The lengths of the waveguides L1 to L4, the couplers C, the splitter S, and the structure U7 are known.

[0123] The inspection method for evaluating the optical integrated circuit 5F is the same as the inspection method MT2. In step ST6, the evaluation unit 9 calculates the pulse shift amounts P Ｌ１ , P Ｌ２ and the lengths of the waveguides L1 and L2, a linear function F3 is derived. The intercept b2 of the linear function F3 represents the sum of the pulse shift amounts of the two couplers C and the two splitters S (splitter S1 and splitter S2).

[0124] In step ST8, the evaluation unit 9 calculates the pulse shift amount of the splitter S based on, for example, a linear function F2. For example, the evaluation unit 9 calculates the pulse shift amount P Ｌ３ The difference between the pulse shift amount of the waveguide L3 derived from the linear function F3 and the pulse shift amount of the waveguide L3 derived from the linear function F3 is defined as the pulse shift amount P Ｓ Let's say.

[0125] Next, in step ST9, the evaluation unit 9 calculates the pulse shift amount P Ｓ The splitter S is evaluated based on the chromatic dispersion amount D of the splitter S. Ｓ is calculated by Equation 8. Ｓ =P Ｓ / (WS x L Ｓ ) ... (8)

[0126] Subsequently, in step ST10, the evaluation unit 9 calculates the pulse shift amount of the coupler C based on, for example, a linear function F3. The evaluation unit 9 calculates the pulse shift amount of the coupler C based on the intercept b2, which is the sum of the pulse shift amounts of the two couplers C and the two splitters S, and the pulse shift amount P Ｓ The difference between the multiples of (b2-2P Ｓ ) is calculated as the pulse shift amount of the coupler C. Subsequently, in step ST11, the evaluation unit 9 evaluates the coupler C based on, for example, the linear function F2. The chromatic dispersion amount D of the coupler C is calculated as Ｃ is calculated by Equation 9. Ｃ = (b2 - 2 x P Ｓ ) / (WS x 2 x L Ｃ ) ... (9)

[0127] Subsequently, in step ST12, the evaluation unit 9 calculates the pulse shift amount of the structure U7 based on, for example, a linear function F3. The evaluation unit 9 calculates, for example, the pulse shift amount P Ｌ４ and the pulse shift amount of the waveguide L4 derived from the linear function F3 is set as the total value K2 of the pulse shift amounts of one splitter S and the structure U6. The evaluation unit 9 calculates the sum K2 and the pulse shift amount P ＳThe difference between the wavelength dispersion amount D and the wavelength dispersion amount D of the structure U7 is calculated as the pulse shift amount of the structure U7. Subsequently, in step ST13, the evaluation unit 9 evaluates the structure U7 based on, for example, a linear function F3. Ｕ７ is calculated by Equation 10. In Equation 10, L Ｕ７ indicates the length of the structure U7. Ｕ７ = (K2-P Ｓ ) / (WS x L Ｕ７ ) ... (10)

[0128] In the present disclosure described above, the other structures may include at least one of a coupler C connected to the input and output ends of each of the multiple waveguides and inputting and outputting the pulse train Pb, a splitter S that splits the pulse train Pb on the optical integrated circuits 5E and 5F, and a ring resonator U4 that resonates and extracts a portion of the light in the pulse train Pb. The other structures may include at least one of a converter, a phase modulator, a structure that changes the width of the waveguide (e.g., a phase modulator), a temperature-dependent structure, a current-dependent structure, a voltage-dependent structure, and a stress-dependent structure. In these cases, the structures necessary for properly transmitting the pulse train Pb can be easily evaluated.

[0129] [Seventh Embodiment of Inspection Method] The multiple waveguides may have the same length. FIG. 21( a) is a diagram schematically illustrating an optical integrated circuit 5G according to the seventh embodiment. FIG. 21( b) is a diagram illustrating an example of a method for evaluating structures included in the optical integrated circuit 5G. As shown in FIG. 21( a), the optical integrated circuit 5G has two optical transmission lines LT1 and LT2. The optical transmission line LT1 is composed of a waveguide L1 and two couplers C. The optical transmission line LT2 is composed of a waveguide L2, two couplers C, and a structure U8. The length of the waveguide L2 is the length of the optical transmission line LT2 minus the length of the structure U8. In the example of FIG. 21, the lengths of the waveguides L1 and L2 are the same.

[0130] 22 is a flowchart showing an inspection method MT3 for evaluating the optical integrated circuit 5G. The inspection method MT3 is the same as the inspection method MT1 from step ST1 to step ST5. In step ST6, the evaluation unit 9 calculates the pulse shift amount P Ｌ１ and the pulse shift amount P corresponding to the waveguide L2 Ｌ２ In the optical integrated circuit 5G, since the lengths of the plurality of waveguides L1 and L2 are the same, the pulse shift amount P Ｌ１ and the pulse shift amount P Ｌ２ The difference between the pulse shift amount P of the structure U8 and the Ｕ８ It could be.

[0131] Subsequently, in step ST7, the evaluation unit 9 evaluates the structure U8. Ｕ８ is calculated by Equation 11. In Equation 11, L Ｕ８ indicates the length of the structure U8. Ｕ８ = (P Ｕ８ ) / (WS x L Ｕ８ ) ... (11)

[0132] In the seventh embodiment, since the lengths of the plurality of waveguides L1 and L2 are the same, the difference between the feature quantities of the plurality of time waveforms can be the feature quantity of another structure U8, which allows for simple evaluation of the structure U8.

[0133] In the inspection device according to one aspect of the present disclosure described above, in step ST1, the pulse forming unit 3 generates a pulse train Pb to be input to the multiple optical transmission paths, generating a pulse train in which the wavelength difference between the multiple optical pulses is equal. However, the wavelength difference between the multiple optical pulses may differ for each optical transmission path. For example, the wavelength difference of the pulse train Pb input to the optical transmission path LT2 may be twice that of the pulse train Pb input to the optical transmission path LT1. In this case, the pulse shift amount is also doubled, so the ratio of the pulse shift amount to the wavelength difference does not change between the pulse train Pb input to the optical transmission path LT1 and the pulse train Pb input to the optical transmission path LT2. In other words, the amount of chromatic dispersion described in Equations 1 to 11 does not change. However, if the wavelength difference between the multiple optical pulses differs for each optical transmission path, the center wavelength of the pulse train Pb must be the same. By using a common center wavelength for the pulse train Pb, correction of the pulse shift amount for each optical transmission path is not required, thereby avoiding the complexity of the calculations required for evaluating the structure.

[0134] The inspection device and inspection method disclosed herein are not limited to the above-described embodiment and configuration example, and various modifications are possible. For example, in the above-described embodiment, the feature quantities of the time waveform of the pulse train Pb are obtained using the correlation optical system 7, but instead of the correlation optical system 7, the feature quantities of the time waveform of the pulse train Pb may be obtained using a pulse shift method, a phase modulation method, or spectral interference.

[0135] The pulse shift method is a method for directly measuring the group delay time of two optical pulses Pb1 and Pb2 for each wavelength in the time domain. In the pulse shift method, optical pulses Pb1 and Pb2 having a pulse width on the order of nanoseconds are propagated through an optical fiber, and the group delay time of each optical pulse is measured. This makes the measurement easy. However, to obtain a measurable delay time, the optical pulses Pb1 and Pb2 must be propagated through an optical fiber with a sufficiently long fiber length (e.g., several kilometers).

[0136] Spectral interferometry is a method of using two optical pulses Pb1 and Pb2 as sample pulse light, observing the interference between the sample pulse light and a reference pulse light in the spectral domain, and estimating the characteristics of the time waveform from changes in the spectral shape. For example, a Mach-Zehnder optical system is used as the optical system. Spectral interferometry can accurately measure relatively small changes in dispersion, making it applicable to dispersion measurements using relatively short optical fibers. However, compared to pulse shifting, this method requires more precise manipulation to synchronize the timing (delay) of the interfering pulses, and therefore requires advanced adjustments each time the sample being observed changes.

[0137] 1...Inspection device, 3...Pulse forming section, 5, 5A, 5B, 5C, 5D, 5E, 5F, 5G...Optical integrated circuit, 8...Photodetector section, 9...Evaluation section, 53, L1, L2, L3, L4...Waveguide, a...Slope, b, b1, b2...Intercept, C, C1, C2...Coupler, D...Wavelength dispersion, F1, F2, F3...Linear function, K1, P Ｌ１ , P Ｌ２ , P Ｌ３ , P Ｌ４ , P Ｓ , P Ｕ１ , P Ｕ２ , P Ｕ３ , P Ｕ４ , P Ｕ５ , P Ｕ８ ...pulse shift amount, Pc...correlated light, MT1, MT2, MT3...inspection method, Pb, Pba, Pbb...pulse train, Pb1, Pb2...optical pulse, S, S1, S2, S3...splitter, U1, U2, U3, U6, U7, U8...structure, U4...ring resonator.

Claims

1. An inspection device for inspecting an optical integrated circuit having an optical structure including a plurality of waveguides, comprising: a pulse forming unit that generates a pulse train in which a plurality of optical pulses having different center wavelengths are arranged at a predetermined time interval; a light detecting unit that detects the time waveform of the pulse train output from the optical integrated circuit; and an evaluation unit that evaluates the optical integrated circuit based on feature quantities of the time waveform, wherein the evaluation unit calculates the amount of change in the feature quantities of the time waveform with respect to the length of the waveguide based on the feature quantities of the time waveform corresponding to each of the plurality of waveguides, which have different lengths and known, and calculates the feature quantities of the time waveforms of other structures based on the amount of change.

2. The inspection device according to claim 1, wherein said pulse forming section generates a pulse train in which the wavelength differences between said plurality of optical pulses are equal.

3. An inspection device according to claim 1 or 2, wherein the feature of the time waveform is the amount of pulse shift on the time axis between the plurality of optical pulses included in the pulse train.

4. An inspection device as described in claim 3, wherein the evaluation unit derives a linear function that indicates the relationship between the pulse shift amount corresponding to each of the plurality of waveguides and the length of each of the plurality of waveguides, and evaluates the plurality of waveguides based on the slope of the linear function.

5. An inspection device as described in claim 3, wherein the evaluation unit derives a linear function that indicates the relationship between the pulse shift amount corresponding to each of the plurality of waveguides and the length of each of the plurality of waveguides, and evaluates the other structure based on the intercept of the linear function.

6. An inspection device as described in claim 4 or 5, wherein the evaluation unit evaluates the other structure based on the difference between the pulse shift amount corresponding to the waveguide connected to the other structure and the pulse shift amount of the waveguide derived from the linear function.

7. The inspection device according to any one of claims 1 to 6, wherein the evaluation section evaluates chromatic dispersion of the optical integrated circuit.

8. An inspection device according to any one of claims 1 to 7, wherein the other structure includes at least one of a coupler connected to the input and output ends of each of the plurality of waveguides and inputting and outputting the pulse train, a splitter that separates the pulse train on the optical integrated circuit, and a ring resonator that resonates and extracts a portion of the light from the pulse train.

9. An inspection device according to any one of claims 1 to 8, wherein the time waveform of the pulse train is a time waveform of correlated light including cross-correlated light or auto-correlated light of the pulse train.

10. An inspection device for inspecting an optical integrated circuit having an optical structure including a plurality of waveguides, comprising: a pulse forming unit that generates a pulse train in which a plurality of optical pulses having different center wavelengths are arranged at predetermined time intervals; a light detecting unit that detects the time waveform of the pulse train output from the optical integrated circuit; and an evaluation unit that evaluates the optical integrated circuit based on feature amounts of the time waveform, wherein the evaluation unit calculates feature amounts of the time waveforms of other structures based on differences in feature amounts of the time waveforms corresponding to each of the plurality of waveguides having the same length and known lengths.

11. An inspection method for inspecting an optical integrated circuit having an optical structure including a plurality of waveguides, the inspection method comprising: a pulse forming step of generating a pulse train in which a plurality of optical pulses having different center wavelengths are arranged at a predetermined time interval; an optical detection step of detecting the time waveform of the pulse train output from the optical integrated circuit; and an evaluation step of evaluating the optical integrated circuit based on feature quantities of the time waveform, wherein in the evaluation step, a change in the feature quantities of the time waveform relative to the length of the waveguide is calculated based on the feature quantities of the time waveform corresponding to each of the plurality of waveguides having different lengths and known lengths, and the feature quantities of the time waveforms of other structures are calculated based on the change.

12. The inspection method according to claim 11, wherein said pulse forming step generates a pulse train in which the wavelength differences between said plurality of optical pulses are equal.

13. An inspection method according to claim 11 or 12, wherein the feature of the time waveform is the amount of pulse shift on the time axis between the plurality of optical pulses included in the pulse train.

14. An inspection method according to claim 13, wherein the evaluation step derives a linear function that indicates the relationship between the pulse shift amount corresponding to each of the plurality of waveguides and the length of each of the plurality of waveguides, and evaluates the plurality of waveguides based on the slope of the linear function.

15. An inspection method according to claim 13, wherein the evaluation step derives a linear function that indicates the relationship between the pulse shift amount corresponding to each of the plurality of waveguides and the length of each of the plurality of waveguides, and evaluates the other structure based on the intercept of the linear function.

16. An inspection method according to claim 14 or 15, wherein the evaluation step evaluates the other structure based on the difference between the pulse shift amount corresponding to the waveguide connected to the other structure and the pulse shift amount of the waveguide derived from the linear function.

17. The inspection method according to any one of claims 11 to 16, wherein the evaluation step evaluates chromatic dispersion of the optical integrated circuit.

18. An inspection method according to any one of claims 11 to 17, wherein the other structure includes at least one of a coupler connected to the input and output ends of each of the plurality of waveguides and inputting and outputting the pulse train, a splitter that splits the pulse train on the optical integrated circuit, and a ring resonator that resonates and extracts a portion of the light from the pulse train.

19. An inspection method according to any one of claims 11 to 18, wherein the time waveform of the pulse train is a time waveform of correlated light including cross-correlated light or auto-correlated light of the pulse train.

20. An inspection method for inspecting an optical integrated circuit having an optical structure including a plurality of waveguides, the inspection method comprising: a pulse forming step of generating a pulse train in which a plurality of optical pulses having different center wavelengths are arranged at a predetermined time interval; an optical detection step of detecting the time waveform of the pulse train output from the optical integrated circuit; and an evaluation step of evaluating the optical integrated circuit based on feature amounts of the time waveform, wherein the evaluation step calculates feature amounts of the time waveforms of other structures based on differences in feature amounts of the time waveforms corresponding to each of the plurality of waveguides having the same length and known lengths.

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