Measurement circuit for optical circuit, and measurement method for optical circuit

Abstract

The present invention comprises: a circuit (5) under measurement; a light input / output unit (7A) that is connected to the circuit (5) under measurement; a light input / output unit (7B) that is not connected to the circuit (5) under measurement; connecting branch couplers (21, 22) that are connected to the light input / output unit (7A); a connecting branch coupler (23) that is connected to the light input / output unit (7B); and a multiplexing unit (3) that inputs light which was branched by the branch coupler (22) and light which was branched by the branch coupler (23). The branch couplers (21, 22, 23) form paths in which light is inputted from the light input / output unit (7A) and outputted from the light input / output unit (7B) or the multiplexing unit (3), said paths being greater in number than the sum of the light input / output unit (7A) and the light input / output unit (7B).

Description

Optical circuit measurement circuit and optical circuit measurement method

[0001] The present disclosure relates to an optical measurement circuit for inspecting an optical semiconductor circuit and a method for measuring an optical circuit.

[0002] For example, in an optical semiconductor circuit such as a silicon photonics chip, light is input / output by placing an optical fiber close to an optical input / output unit such as edge coupling using a spot size converter or a grating coupler, and a circuit under test included in the optical semiconductor circuit is tested. Such testing is disclosed in Non-Patent Document 1. The optical semiconductor circuit to be tested may be in the form of a wafer or a chip. The circuit under test may be an optical waveguide, an optical modulator, a photodiode, or an optical transmitter circuit or an optical receiver circuit that combines these.

[0003] Choon BS,at el.(2020). Test Setup Optimization and Automation for Accurate Silicon Photonics Wafer Acceptance Production Tests. INTERNATIONAL CONFERENCE ON MICROELECTRONIC TEST STRUCTURES, April 6-9.

[0004] However, the width of a spot size converter at the chip end face is on the order of several hundred nanometers, and the grating structure of a grating coupler is also on the order of several hundred nanometers. Manufacturing such small sizes can cause variations in optical coupling characteristics due to size errors caused by mask misalignment during the wafer manufacturing process and the roughness of the sidewalls of the spot size converter and grating coupler structures. This variation in the optical coupling characteristics of the optical input / output sections makes it impossible to determine the optical coupling loss. As a result, it becomes impossible to accurately measure the intensity of light input to or output from the circuit under test.

[0005] The present disclosure has been made in consideration of the above points, and aims to provide an optical circuit measurement circuit and an optical circuit measurement method that are capable of identifying optical coupling loss and accurately measuring the characteristics of a circuit under measurement, regardless of the optical coupling characteristics of the circuit under measurement and the optical input / output section.

[0006] In order to achieve the above object, one embodiment of the optical circuit measurement circuit disclosed herein comprises a circuit under test, at least one connected optical input / output unit optically connected to the circuit under test, at least one unconnected optical input / output unit not optically connected to the circuit under test, a connected branch coupler connected to one of the connected optical input / output units, a unconnected branch coupler connected to one of the unconnected optical input / output units, and a multiplexing unit that inputs light branched by the connected branch coupler and light branched by the unconnected branch coupler, wherein the connected branch coupler and the unconnected branch coupler form input / output paths through which light is input from some of the connected optical input / output units and unconnected optical input / output units and output from some of the connected optical input / output units and unconnected optical input / output units or the multiplexing unit, the number of which is greater than the total number of connected optical input / output units and unconnected optical input / output units.

[0007] A method for measuring an optical circuit according to one embodiment of the present disclosure includes a circuit under test, at least one connected optical input / output unit optically connected to the circuit under test, at least one unconnected optical input / output unit not optically connected to the circuit under test, a connected branch coupler connected to one of the connected optical input / output units, a unconnected branch coupler connected to one of the unconnected optical input / output units, and a multiplexing unit that inputs light branched by the connected branch coupler and light branched by the unconnected branch coupler, the connected branch coupler and the unconnected branch coupler forming input / output paths through which light is input from at least some of the connected optical input / output units and unconnected optical input / output units and output from at least some of the connected optical input / output units and unconnected optical input / output units or the multiplexing unit, the number of which is greater than the total number of the connected optical input / output units and unconnected optical input / output units, measuring the intensity of light input to and output from the input / output paths, and measuring the coupling loss between the circuit under test and the connected optical input / output unit.

[0008] According to the above aspects, it is possible to provide an optical circuit measuring circuit and an optical circuit measuring method that can identify the optical coupling loss and accurately measure the characteristics of the circuit under test, regardless of the optical coupling characteristics between the circuit under test and the optical input / output section.

[0009] FIG. 1 is a diagram for explaining a comparative example of an embodiment of the present disclosure. FIG. 2 is a schematic diagram for explaining a measurement circuit for an optical circuit of a first embodiment. FIG. 3 is a schematic diagram for explaining a measurement circuit for an optical circuit of a second embodiment. FIG. 4 is a schematic diagram for explaining a measurement circuit for an optical circuit of a third embodiment. FIG. 5 is a schematic diagram for explaining a measurement circuit for an optical circuit of a fourth embodiment. FIG. 6 is a schematic diagram for explaining a measurement circuit for an optical circuit of a fifth embodiment. FIG. 7 is a schematic diagram for explaining a measurement circuit for an optical circuit of a sixth embodiment. FIG. 8 is a schematic diagram for explaining a measurement circuit for an optical circuit of a seventh embodiment.

[0010] Hereinafter, first to seventh embodiments of the present disclosure (hereinafter also collectively referred to as the present embodiments) will be described. The drawings shown in the present embodiments are schematic diagrams intended to explain the configuration, arrangement, and technical concept of the present disclosure, and do not limit the specific configuration of the disclosure. Furthermore, in the drawings, the same components are assigned the same reference numerals, and their description may be partially omitted.

[0011] Comparative Example Prior to describing the present disclosure, a comparative example of the measurement of a circuit under test 100 will be described. FIG. 1 is a diagram illustrating the configuration of the comparative example, showing the circuit under test 100 and an optical input / output unit 200 connected to the circuit under test 100 via an optical waveguide 200a. In the configuration of the comparative example, the circuit under test 100, the optical input / output unit 200, and the optical waveguide 200a are integrated into a chip. The optical input / output unit 200 includes a grating coupler. For example, when the circuit under test 100 is a photodiode and the light receiving sensitivity of the photodiode is to be measured, an optical fiber is brought close to the optical input / output unit 200, and light is input from the optical input / output unit 200 to the circuit under test 100. The measurement is performed by measuring the photocurrent flowing through the anode and cathode electrodes (not shown) of the circuit under test 100.

[0012] In the above measurement, if the value of the optical coupling loss between the optical input / output unit 200 and the optical fiber is unknown, there is a problem in that it is not possible to accurately measure the light receiving sensitivity of the circuit under test 100. This problem exists not only when a grating coupler is used in the optical input / output unit 200, but also when edge coupling using a spot size converter or the like is used.

[0013] First Embodiment FIG. 2 is a schematic diagram illustrating an optical circuit measurement circuit 10 according to a first embodiment. The optical circuit measurement circuit 10 shown in FIG. 2 includes a circuit under test 5. The measurement circuit 10 includes optical input / output units 7A and 7B. Each of the optical input / output units 7A and 7B has both an optical input function and an output function. Of these, the optical input / output unit 7A is a connected optical input / output unit that is optically connected to the circuit under test 5 (inputting or outputting light), while the optical input / output unit 7B is a non-connected optical input / output unit that is not optically connected to the circuit under test 5. Therefore, in the measurement circuit 10, only the optical input / output unit 7A is used to measure the circuit under test 5. The measurement circuit 10 also includes an optical power measurement unit 1 (optical intensity detection unit). However, in the first embodiment, the optical power measurement unit 1 can also be a separate measurement device that is not included in the measurement circuit 10. The optical power measurement device 2 is a separate measurement device that is provided outside the measurement circuit 10.

[0014] The measurement circuit 10 also includes branch couplers 21 and 22, which are connection branch couplers connected to the optical input / output unit 7A, and a branch coupler 23, which is a non-connection branch coupler connected to the optical input / output unit 7B. However, the first embodiment is not limited to this configuration, and the type and number of couplers used to configure the connection branch couplers are arbitrary. Other examples of connection branch couplers include 1:N branch couplers, directional couplers, and combinations thereof.

[0015] Furthermore, the non-connection branch coupler is configured by one 1:2 branch coupler 23, but the first embodiment is not limited to this configuration.

[0016] The measurement circuit 10 also includes a multiplexer 3 that receives the light branched by the branching coupler 21 and the light branched by the branching coupler 23. The branching couplers 21, 22, and 23 form input / output paths (3) greater than the total number (2) of the optical input / output units 7A and 7B, through which light is input from the optical input / output unit 7A and part of the optical input / output unit 7B (optical input / output unit 7A in the first embodiment) and output from the optical input / output unit 7A and part of the optical input / output unit 7B (optical input / output unit 7B in the first embodiment) or the multiplexer 3.

[0017] More specifically, the branching couplers 21 and 22 branch the light input from the optical input / output unit 7A and output it to at least one of the multiplexing unit 3, the circuit under test 5, and the input of the branching coupler 23. The branching coupler 23 branches the light input from the optical input / output unit 7B and outputs it to the multiplexing unit 3 and the branching coupler 22. However, as will be described later in other embodiments, the branching coupler 23 may be connected to another branching coupler that is not connected to the circuit under test. When the optical input / output units 7A and 7B input light, the optical input / output units 7A and 7B are connected to a light source (not shown). The optical input / output units 7A and 7B may use edge coupling using a grating coupler (GC) or a spot size converter (SSC).

[0018] Furthermore, in the configuration shown in FIG. 2 , the optical power measurement unit 1 measures the intensity of light output from the multiplexer 3. The optical power measurement unit 2 measures the intensity of light output from the optical input / output unit 7B. As described above, the optical power measurement unit 1 may be incorporated into the measurement circuit 10, or may be an external measurement device to the measurement circuit 10. If the optical power measurement unit 1 is an external measurement device, a new optical input / output unit must be provided between the multiplexer 3 and the optical power measurement unit 1. The optical power measurement unit 2 must always be an external measurement device. The measurement circuit 10 is configured to output light from the multiplexer 3 and the optical input / output unit 7B and measure its intensity. When the optical power measurement unit 1 is incorporated into the measurement circuit, the optical power measurement unit 1 can be configured using a photodiode.

[0019] The measurement circuit 10 described above includes one optical input / output unit 7A and one optical input / output unit 7B. However, as will be described later, the present disclosure may include a plurality of optical input / output units 7A and 7B, and the branching coupler may be connected to any of the plurality of optical input / output units 7A and 7B. Of the branching couplers, one of the branching couplers connected to the optical input / output unit 7A outputs light to at least one of the branching couplers connected to the circuit under test 5, the multiplexing unit 3, and the optical input / output unit 7B, and one of the branching couplers connected to the optical input / output unit 7B outputs light to at least one of the branching couplers connected to the multiplexing unit 3, the branching coupler connected to the optical input / output unit 7A, and the other optical input / output unit 7B.

[0020] A method for measuring the coupling loss at the optical input / output units 7A and 7B using the measurement circuit shown in Fig. 2 will be described below. In the description, the path between the multiplexer 3 and the optical power measurement unit 1 will be referred to as path a, the two paths input to the multiplexer 3 will be referred to as paths b and c, the path between the optical input / output units 7A and 7B will be referred to as path d, the input / output path of the optical input / output unit 7A will be referred to as path e, and the input / output path of the optical input / output unit 7B will be referred to as path f.

[0021] (1) Light is input from optical input / output unit 7A to path e using a light source (not shown). At this time, the input light is branched toward paths c, t, and d, and the light passing through path d is output from optical input / output unit 7B via path z. As a result, optical power measurement unit 2 measures the intensity of the light output from optical input / output unit 7B.

[0022] (2) The light branched to path c by the branching coupler 22 is input from path c to the multiplexer 3 and output via path a. The optical power measuring unit 1 measures the intensity of this output light.

[0023] (3) Furthermore, light is input from the optical input / output unit 7B to path f using a light source (not shown). At this time, the input light is branched toward path d and path b, and the light passing through path b is input to the multiplexer 3 and output from path a. The optical power measuring unit 1 measures the intensity of the light output from path a.

[0024] When the optical power measuring unit 1 is configured with a photodiode, the measurement of the optical intensity is realized by probing the current flowing between the electrodes of the photodiode.

[0025] By the above procedure, the intensity of light passing through the light input / output paths (hereinafter simply referred to as paths) e, d, and f, the intensity of light passing through paths e and c, and the intensity of light passing through paths f and b can be measured. The intensity of light passing through paths e, d, and f can be calculated using formula (1), the intensity of light passing through paths e and c using formula (2), and the intensity of light passing through paths f and b using formula (3).

[0026] P ｏｕｔ (A to B) = P ｉｎＡ +Loss Ａ +Loss Ｂ +Loss Ｃ１ Formula (1) I Ａ / R ｅｓｐ＿ＰＤ１ =P ｉｎＡ +Loss Ａ +Loss Ｃ２ ... Formula (2) I Ｂ / R ｅｓｐ＿ＰＤ１ =P ｉｎＢ +Loss Ｂ +Loss Ｃ３ ...Formula (3)

[0027] In the above formulas (1) to (3), the parameters indicated by the symbols are as follows:

[0028] P ｏｕｔ (A to B)...Intensity (measured value) of light input from the optical input / output unit 7A and output from the optical input / output unit 7B. ｉｎＡ ...Intensity of light input from the optical input / output unit 7A (known) P ｉｎＢ ...Intensity of light input from the optical input / output unit 7B (known) Loss Ａ Coupling loss of the optical input / output unit 7A (unknown) Ｂ Coupling loss of the optical input / output unit 7B (unknown) Ｃ１ Loss in the branch couplers 21, 22, and 23 (known) Ｃ２ Loss in the branching coupler 21 and the multiplexing unit 3 (known) Ｃ３...Losses in the branching coupler 23 and the multiplexing unit 3 (known) I Ａ ...Photocurrent (measured value) measured when light is input from the optical input / output unit 7A Ｂ ...Photocurrent (measured value) measured when light is input from the optical input / output unit 7B R ｅｓｐ＿ＰＤ１ ...sensitivity of the optical power measurement unit 1 (unknown) As described above, in the equations (1) to (3), Loss Ａ , Loss Ｂ , R ｅｓｐ＿ＰＤ１ The first embodiment solves the three equations (1) to (3) containing three unknowns to calculate Loss Ａ , Loss Ｂ , R ｅｓｐ＿ＰＤ１ It is possible to calculate the value of

[0029] For example, if the circuit under test 5 is a photodiode, the photocurrent flowing through the anode and cathode electrodes (not shown) of the photodiode is measured. Ａ By subtracting the loss, the accurate optical sensitivity characteristics of the circuit under test 5 itself can be determined. Ａ If is unknown, Loss Ａ The sensitivity is calculated based on the sensitivity of the branching couplers 21, 22, and 23, and the multiplexing unit 3, and the characteristics of the circuit under test 5 itself are unknown. Furthermore, the losses in the branching couplers 21, 22, and 23 and the multiplexing unit 3 can be calculated in advance by design. The loss here includes the decrease in optical intensity due to branching of light in the branching couplers 21, 22, and 23, as well as losses due to the manufacturing process of the branching couplers 21, 22, and 23. In particular, when the branching couplers 21, 22, and 23 and the multiplexing unit are configured using 1:2 couplers, a sufficiently high manufacturing precision can be achieved compared to the optical input / output units 7A and 7B. This is because the minimum size of a 1:2 branching coupler is approximately 500 nm, which is larger than the minimum size of a grating coupler or spot size converter (100 nm), and therefore is less susceptible to process variations. In the first embodiment, by using a 1:2 coupler that can reduce the error between the design value and the actual characteristics to approximately 0.1 dB or less, the coupling loss in particular can be calculated with high precision.

[0030] That is, in the first embodiment, the light input from the optical input / output unit 7A passes through the 1:2 coupler twice before reaching the optical power measurement unit 1 (a 1:2 coupler is also used in the multiplexer 3). Similarly, the light input from the optical input / output unit 7B passes through the 1:2 coupler twice before reaching the optical power measurement unit 1. Furthermore, the light passing through paths e, d, and f passes through the 1:2 coupler three times. Thus, in the measurement circuit 10, the light passes through the 1:2 coupler a maximum of seven times, which can result in an error of up to 0.7 dB. This error is significantly smaller than the error of a grating coupler or a spot size converter, which is approximately 1 dB. Therefore, the first embodiment can achieve particularly high accuracy by using 1:2 couplers for the branching couplers 21, 22, and 23.

[0031] In the first embodiment described above, the optical power measurement unit 1 is integrated into a chip together with the circuit under test 5 and the like, and the sensitivity thereof is unknown. When the optical power measurement unit 1 is an optical intensity measurement device external to the measurement circuit 10, the sensitivity of the external device is naturally known. However, as described above, when the optical power measurement unit 1 is an external device, it is necessary to provide a new optical input / output unit between the multiplexer 3 and the optical power measurement unit 1. For this reason, the coupling loss of the optical input / output unit (grating coupler) for connecting the optical power measurement unit 1 to the measurement circuit 10 Ｄ In such a case, the above equations (2) and (3) are changed to the following equations (2)' and (3)'.

[0032] P ｏｕｔＤ１ (Optical power measured by optical power measurement unit 1) = P ｉｎＡ +Loss Ａ +Loss Ｃ２ +Loss Ｄ ...Formula (2)' P ｏｕｔＤ２ (Optical power measured by optical power measurement unit 1, part 2) = P ｉｎＢ +Loss Ｂ +Loss Ｃ３ +Loss Ｄ ...Formula (3)'

[0033] Second Embodiment Fig. 3 is a schematic diagram for explaining a measurement circuit 20 according to a second embodiment of the present disclosure. The measurement circuit 20 of the second embodiment differs from the first embodiment in that, instead of the optical power measurement unit 1 and the multiplexing unit 3 shown in Fig. 2, the measurement circuit 20 includes an optical power measurement unit 13 that integrates the optical power measurement unit 1 and the multiplexing unit 3 and has the functions of both the optical power measurement unit 1 and the multiplexing unit 3. The optical power measurement unit 13 may be, for example, a multi-input photodiode in which an input port is provided in the optical power measurement unit 1, which is a photodiode.

[0034] The measurement circuit 20 of the second embodiment can calculate the coupling loss of the optical input / output units 7A and 7B using a procedure similar to that used in the measurement circuit 10. However, the coupling loss in the multiplexer 3 of the measurement circuit 10 can be reduced. Compared to the measurement circuit 10, this measurement circuit 20 can increase the amount of optical power input to the circuit under test 5 when measuring the circuit under test 5. Therefore, high measurement accuracy can be achieved even when the optical power loss within the circuit under test 5 is large. This is because, when the optical power loss in the circuit under test 5 is large and the optical power input into the circuit under test 5 is small, the measurement may be impossible because it exceeds the lower limit of measurement, or the measurement accuracy may be reduced due to noise.

[0035] The reason why the optical loss in the measurement circuit 20 is smaller than that in the measurement circuit 10 is as follows. That is, the measurement circuit 10 of the first embodiment has a path (paths e, c, and a) through which light input from the optical input / output unit 7A passes through the multiplexer 3 and heads toward the optical power measurement unit 1, and a path (paths f, b, and a) through which light input from the optical input / output unit 7B passes through the multiplexer 3 and heads toward the optical power measurement unit 1. Therefore, the multiplexer 3 can be configured using a 1:2 coupler. In principle, a 1:2 coupler generates an optical loss of 3 dB. If the multiplexer 3 is eliminated and light is input directly to the optical power measurement unit, as in the measurement circuit 20 shown in FIG. 3 , it becomes possible to measure the optical intensity without generating an optical loss of 3 dB.

[0036] Third Embodiment Next, a third embodiment will be described. The third embodiment aims to provide a separate optical input / output unit that inputs light to other optical input / output units, reduce the number of branches between the circuit under test 5 and the optical input / output unit 7A, and increase the intensity of light input to the circuit under test 5. FIG. 4 is a schematic diagram for explaining a measurement circuit 30 of the third embodiment. As shown in FIG. 4, the measurement circuit 30 differs from the measurement circuit 10 in that it includes two optical input / output units 7Ba and 7Bb that are not optically connected to the circuit under test 5. In the measurement circuit 30, the path between the optical input / output unit 7Ba and the optical input / output unit 7Bb is denoted as path d, the input / output path of the optical input / output unit 7Ba is denoted as path g, and the input / output path of the optical input / output unit 7Bb is denoted as path f. The path between the optical input / output unit 7Ba and the multiplexer 3 is denoted as path h, the branch coupler connected to path g is denoted as branch coupler 41, and the branch coupler connected to path f is denoted as branch coupler 43.

[0037] The third embodiment, which has three optical input / output units 7A, 7Ba, and 7Bb, calculates four unknown quantities: three coupling losses and the sensitivity of the optical power measurement unit 1. The procedure for calculating the unknown quantities in the third embodiment will be described below.

[0038] (1) Light is input from optical input / output unit 7Ba to path g using a light source (not shown). At this time, the input light is branched toward paths h and d, and the light that passes through path d passes through path z and is output from optical input / output unit 7Bb. Optical power measurement unit 2 measures the intensity of the light output from optical input / output unit 7Bb.

[0039] (2) The light branched to path h by the branching coupler 41 is input to the multiplexer 3 and output via path a. The optical power measuring unit 1 measures the intensity of the output light.

[0040] (3) Furthermore, light is input from the optical input / output unit 7A to path e using a light source (not shown). The light is branched into paths t and h, and the light passing through path h is input to the multiplexer 3 and output from path a. The optical power measurement unit 1 measures the output light.

[0041] (4) Furthermore, light is input from the optical input / output unit 7Bb to path f using a light source (not shown). At this time, the input light is branched toward paths b and d, and the light passing through path b is input to the multiplexer 3 and output from path a. The optical power measuring unit 1 measures the intensity of the light output from path a.

[0042] By the above procedure, the intensities of light passing through paths g, d, and f, the intensities of light passing through paths e and c, the intensities of light passing through paths f and b, and the intensities of light passing through paths g and h can be measured. The intensities of light passing through paths g, d, and f can be calculated using equation (4), the intensities of light passing through paths e and c using equation (5), the intensities of light passing through paths f and b using equation (6), and the intensities of light passing through paths g and h using equation (7).

[0043] P ｏｕｔ (Ba to Bb)=P ｉｎＢａ +Loss Ｂａ +Loss Ｂｂ +Loss Ｃ４ ... Formula (4) I Ａ / R ｅｓｐ＿ＰＤ１ =P ｉｎＡ +Loss Ａ +Loss Ｃ５ ... Formula (5) I Ｂａ / R ｅｓｐ＿ＰＤ１ =P ｉｎＢａ +Loss Ｂａ +Loss Ｃ６ ... Formula (6) I Ｂｂ / R ｅｓｐ＿ＰＤ１ =P ｉｎＢｂ +Loss Ｂｂ +Loss Ｃ７ ...Formula (7)

[0044] In the above formulas (4) to (7), the parameters indicated by the symbols that are different from those in the first embodiment are as follows:

[0045] P ｏｕｔ (Ba to Bb)...intensity (measured value) of light input from the optical input / output unit 7Ba and output from the optical input / output unit 7Bb ｉｎBａ ...Intensity of light input from the optical input / output unit 7Ba (known) P ｉｎBｂ ...Intensity of light input from the optical input / output unit 7Bb (known) Loss ＢａCoupling loss of the optical input / output unit 7Ba (unknown) Ｂｂ Coupling loss of the optical input / output unit 7Bb (unknown) Ｃ４ Loss in the branch couplers 41 and 43 (known) Ｃ５ Loss in the branching coupler 22 and the multiplexing unit 3 (known) Ｃ６ Loss in the branching coupler 41 and the multiplexing unit 3 (known) Ｃ７ ...Losses in the branching coupler 43 and the multiplexing unit 3 (known) I Ｂａ ...Photocurrent (measured value) measured when light is input from the optical input / output unit 7Ba Ｂｂ ...Photocurrent (measured value) measured when light is input from the optical input / output unit 7Bb

[0046] According to the third embodiment, four equations, Equation (4) through Equation (7), can be obtained, thereby enabling the calculation of the four unknowns, namely, the coupling loss of the optical input / output units 7A, Ba, and Bb and the sensitivity of the optical power measurement unit 1. Obtaining accurate values ​​for the optical input / output units and the sensitivity through calculations allows the accurate intensity of the input light input to the circuit under test 5 to be determined, thereby providing a measurement circuit that can accurately measure the characteristics of the circuit under test 5. For example, if the circuit under test 5 is a photodiode, the accurate input light intensity to the photodiode can be determined, allowing the photocurrent flowing between the anode and cathode (not shown) of the photodiode to be measured and the accurate optical sensitivity characteristics of the photodiode to be measured to be obtained. Although the third embodiment requires more measurement steps than the first embodiment, it reduces the number of branches from the optical input / output unit 7A to the circuit under test 5, thereby increasing the intensity of the light input to the circuit under test 5. This allows the provision of a measurement circuit 30 that is less susceptible to noise caused by low optical power and enables accurate measurements.

[0047] In the third embodiment, as in the first and second embodiments, the optical power measurement unit 1 is included in the measurement circuit 30. However, in the third embodiment, the optical power measurement unit 1 can also be an external measurement device. When the optical power measurement unit 1 is an external measurement device, its sensitivity is known, but the coupling loss of the optical input / output unit for connecting the optical power measurement unit 1 to the measurement circuit 30 is unknown. In order to obtain the unknown coupling loss, in the third embodiment, the above equations (5), (6), and (7) are replaced with equations showing the relationship between the intensity of light input to each of the three paths for inputting light to the optical power measurement unit 1, the coupling loss, and the intensity of light to be measured.

[0048] (Fourth Embodiment) Next, a fourth embodiment will be described. The fourth embodiment differs from the first to third embodiments in that the circuit under test 51 has not only an input port but also an output port. For example, an optical transmitter circuit or an optical receiver circuit that combines an optical waveguide, an optical modulator, a photodiode, etc., can be used as the circuit under test 51.

[0049] FIG. 5 is a schematic diagram illustrating a measurement circuit 40 according to a fourth embodiment. The measurement circuit 40 of the fourth embodiment includes a circuit under test 51 instead of the circuit under test in the measurement circuit 30. In addition to the components of the measurement circuit 30, the measurement circuit 40 also includes an optical input / output unit 7Ab optically connected to the circuit under test 51. A branching coupler 53 is connected to the optical input / output unit 7Ab, and a path l is defined between the optical input / output unit 7Ab and the branching coupler 53. The branching coupler 53 connects path l to path k and to path i, which is connected to the multiplexer 3. Path k is the path through which light output from the circuit under test 51 passes when measuring the circuit under test 51. Path k branches into path l and path i, and path i is connected to the multiplexer 3. The measurement circuit 40 calculates the coupling losses of the optical input / output units Aa, Ab, Ba, and Bb, which are unknowns, and the sensitivity of the optical power measurement unit 1, using the following procedure.

[0050] (1) Light is input from optical input / output unit 7Ba to path g using a light source (not shown). At this time, the input light is branched toward paths h and d, and the light that passes through path d is output from optical input / output unit 7Bb via path z. Optical power measurement unit 2 measures the intensity of the light output from optical input / output unit 7Bb.

[0051] (2) The light branched to path h by the branching coupler 41 is input to the multiplexer 3 and output via path a. The optical power measuring unit 1 measures the intensity of the output light.

[0052] (3) Furthermore, light is input from the optical input / output unit 7Aa to path e using a light source (not shown). The light is branched into path t and path c, and the light passing through path c is input to the multiplexer 3 and output from path a. The optical power measurement unit 1 measures the output light.

[0053] (4) Furthermore, light is input from optical input / output unit 7Bb to path f using a light source (not shown). At this time, the input light is branched toward paths b and d, and the light passing through path b is input to multiplexer 3 and output from path a. Optical power measurement unit 1 measures the intensity of the light output from path a.

[0054] (5) Furthermore, light is input from the optical input / output unit 7Ab to path l using a light source (not shown). The light is branched into path k and path i, and the light passing through path i is input to the multiplexer 3 and output from path a. The optical power measurement unit 1 measures the output light.

[0055] By the above procedure, the intensities of light passing through paths g, d, and f, the intensities of light passing through paths e and c, the intensities of light passing through paths f and b, and the intensities of light passing through paths g, h, and paths l and i can be measured. The intensities of light passing through paths g, d, and f can be calculated using equation (8), the intensities of light passing through paths e and c using equation (9), the intensities of light passing through paths f and b using equation (10), the intensities of light passing through paths g and h using equation (11), and the intensities of light passing through path il using equation (12).

[0056] P ｏｕｔ (Ba to Bb)=P ｉｎＢａ +Loss Ｂａ +Loss Ｂｂ +Loss Ｃ４ ... Formula (8) I Ａａ / R ｅｓｐ＿ＰＤ１ =P ｉｎＡａ +Loss Ａａ +Loss Ｃ８ ... Formula (9) I Ｂａ / R ｅｓｐ＿ＰＤ１ =P ｉｎＢａ+Loss Ｂａ +Loss Ｃ５ ... Formula (10) I Ｂｂ / R ｅｓｐ＿ＰＤ１ =P ｉｎＢｂ +Loss Ｂｂ +Loss Ｃ６ ... Formula (11) I Ａｂ / R ｅｓｐ＿ＰＤ１ =P ｉｎＡｂ +Loss Ａｂ +Loss Ｃ９ ...Formula (12)

[0057] In the above equations (8) to (12), the parameters indicated by the symbols that are different from those in the third embodiment are as follows:

[0058] P ｉｎＡａ ...Intensity of light input from the optical input / output unit 7Aa (known) P ｉｎＡｂ ...Intensity of light input from the optical input / output unit 7Ab (known) Loss Ａａ Coupling loss of the optical input / output unit 7Aa (unknown) Ａｂ ...coupling loss of the optical input / output unit 7Ab (unknown) ｃ８ Loss in the branching coupler 52 and the multiplexing unit 3 (known) ｃ９ ...Losses in the branching coupler 53 and the multiplexing unit 3 (known) I Ａａ ...Photocurrent (measured value) measured when light is input from the optical input / output unit 7A Ａｂ ...Photocurrent (measured value) measured when light is input from the optical input / output unit 7A

[0059] According to the fourth embodiment, five equations, from equation (8) to equation (12), can be obtained, making it possible to calculate the five unknowns, namely, the coupling loss of the optical input / output units 7Aa, 7Ab, 7Ba, and 7Bb and the sensitivity of the optical power measurement unit 1. If accurate values ​​of the optical input / output units and the sensitivity can be obtained through calculation, the accurate intensity of the input light input to the circuit under test 51 and the accurate intensity of the output light output from the circuit under test 51 can be determined, making it possible to provide a measurement circuit that can accurately measure the characteristics of the circuit under test 51. According to the fourth embodiment, accurate insertion loss and characteristics can also be obtained for a circuit under test that has an input / output such as an optical modulator, an optical waveguide, or an optical transmitter configured by combining them.

[0060] In the fourth embodiment, as in the first to third embodiments, the optical power measurement unit 1 is included in the measurement circuit 40. However, in the fourth embodiment, the optical power measurement unit 1 can also be an external measurement device. When the optical power measurement unit 1 is an external measurement device, its sensitivity is known, but the coupling loss of the optical input / output unit for connecting the optical power measurement unit 1 to the measurement circuit 40 is unknown. In order to obtain the unknown coupling loss, the fourth embodiment replaces the above equations (9) to (12) with equations that show the relationship between the intensity of light input to each of the four paths through which light is input to the optical power measurement unit 1, the coupling loss, and the intensity of light to be measured.

[0061] Fifth Embodiment Next, a fifth embodiment will be described. The optical input / output unit 7Ab of the fourth embodiment described above inputs light when measuring the coupling loss, and measures the light output from the circuit under test 51 when measuring the circuit under test 51. For this reason, in the fourth embodiment, it is necessary to connect both an external light source and an external optical power meter to the optical input / output unit 7Ab, and therefore it is necessary to provide a selector switch external to the measurement circuit 40. The fifth embodiment aims to avoid the need to provide an external selector switch by not inputting light from the optical input / output unit 7Ab, thereby avoiding an increase in complexity and cost of the measurement circuit configuration.

[0062] 6 is a schematic diagram illustrating a measurement circuit 50 according to a fifth embodiment. The measurement circuit 50 includes a branch coupler 61 on path i of the measurement circuit 40, a branch coupler 62 on path d, and a path n between the branch coupler 61 and the branch coupler 62. In this fifth embodiment, the output port of the circuit under test 51 is connected to an optical input / output unit 7ab, which is a connected optical input / output unit, and an optical input / output unit 7Bb, which is an unconnected optical input / output unit, and light input from the optical input / output unit 7Bb is output from the optical input / output unit 7Ab. The fifth embodiment calculates the coupling losses of the optical input / output units Aa, Ab, Ba, and Bb, which are unknowns, and the sensitivity of the optical power measurement unit 1, using the following procedure.

[0063] (1) Light is input from optical input / output unit 7Ba to path g using a light source (not shown). At this time, the input light is branched toward paths h and d, and the light that passes through path d is output from optical input / output unit 7Bb via path z. Optical power measurement unit 2 measures the intensity of the light output from optical input / output unit 7Bb.

[0064] (2) The light branched to path h by the branching coupler 41 is input to the multiplexer 3 and output via path a. The optical power measuring unit 1 measures the intensity of the output light.

[0065] (3) Furthermore, light is input from the optical input / output unit 7Aa to path e using a light source (not shown). The light is branched into path t and path c, and the light passing through path c is input to the multiplexer 3 and output from path a. The optical power measurement unit 1 measures the output light.

[0066] (4) Furthermore, light is input from optical input / output unit 7Bb to path f using a light source (not shown). At this time, the input light is branched toward paths b, d, and n, and the light passing through path b is input to multiplexer 3 and output from path a. Optical power measurement unit 1 measures the intensity of the light output from path a.

[0067] (5) Light input from the optical input / output unit 7Bb and branched to the path n is output from the optical input / output unit 7Ab via paths m and 1. The light output from the optical input / output unit 7Ab is measured by a measuring instrument used to measure the characteristics of the circuit under test 51.

[0068] By the above procedure, it is possible to measure the intensities of light passing through paths g, d, and f, the intensities of light passing through paths e and c, the intensities of light passing through paths f and b, and the intensities of light passing through paths g, h, and paths i, m, and l. The intensities of light passing through paths g, d, and f can be calculated using equation (13), the intensities of light passing through paths e and c using equation (14), the intensities of light passing through paths f and b using equation (15), the intensities of light passing through paths g and h using equation (16), and the intensities of light passing through paths i, m, and l using equation (17).

[0069] P ｏｕｔ (Ba to Bb)=P ｉｎＢａ +Loss Ｂａ +Loss Ｂｂ +Loss Ｃ４ ... Formula (13) I Ａａ / R ｅｓｐ＿ＰＤ１ =P ｉｎＡａ +Loss Ａａ +Loss Ｃ８ ... Formula (14) I Ｂａ / R ｅｓｐ＿ＰＤ１ =P ｉｎＢａ +Loss Ｂａ +Loss Ｃ５ ... Formula (15) I Ｂｂ / R ｅｓｐ＿ＰＤ１ =P ｉｎＢｂ +Loss Ｂｂ +Loss Ｃ６ ...Formula (16) P ｏｕｔ (Bb to Ab)=P ｉｎＢｂ +Loss Ｂｂ +Loss Ａｂ +Loss Ｃ１０ ...Formula (17)

[0070] In the above equations (13) to (17), the parameters indicated by the symbols that are different from those in the fourth embodiment are as follows:

[0071] P ｏｕｔ (Ba to Bb)...intensity (measured value) of light input from the optical input / output unit 7Bb and output from the optical input / output unit 7Ab. Ｃ１０ ...Losses in branch couplers 43, 62, 61, 53 (known)

[0072] In the fifth embodiment, too, five equations, equations (13) to (17), can be obtained, making it possible to calculate the five unknown quantities, namely the coupling loss of the optical input / output units 7Aa, 7Ab, 7Ba, and 7Bb and the sensitivity of the optical power measurement unit 1. Furthermore, the external changeover switch required in the fourth embodiment is eliminated, avoiding the complication of the measurement circuit configuration and the increase in cost.

[0073] In the fifth embodiment, as in the first to fourth embodiments, the optical power measurement unit 1 is included in the measurement circuit 50. However, in the fifth embodiment, the optical power measurement unit 1 can also be an external measurement device. When the optical power measurement unit 1 is an external measurement device, its sensitivity is known, but the coupling loss of the optical input / output unit for connecting the optical power measurement unit 1 to the measurement circuit 50 is unknown. In order to obtain the unknown coupling loss, in the fifth embodiment, the above equations (14) to (16) are replaced with equations showing the relationship between the intensity of light input to three of the four paths through which light is input to the optical power measurement unit 1, the coupling loss, and the intensity of the light to be measured.

[0074] Sixth Embodiment Next, a sixth embodiment will be described. FIG. 7 is a schematic diagram illustrating a measurement circuit 60 according to the sixth embodiment. The measurement circuit 60 according to the sixth embodiment includes a plurality of circuits under measurement. Therefore, the measurement circuit 60 further includes an optical input / output unit 7Ac, which is a connection optical input / output unit connected to the circuits under measurement. As in the first to fifth embodiments, the measurement circuit 60 can acquire the coupling loss of the optical input / output units 7Aa, 7Ab, 7Ac, Ba, and Bb and the sensitivity of the optical power measurement unit 1. In addition to the measurement circuit 40 according to the fourth embodiment, the measurement circuit 60 includes an optical input / output unit 7Ac and a circuit under measurement 5 having only an input port. A branching coupler 71 is connected to the optical input / output unit Ac, and a path q is defined between the optical input / output unit Ac and the branching coupler 71. The coupler 71 branches path q into paths o and p. Path p is connected to the multiplexer 3, and light input from the optical input / output unit Ac is measured by the optical power measurement unit 1 via the multiplexer 3. According to the sixth embodiment, it is possible to realize a measuring circuit 60 that measures a plurality of circuits under test.

[0075] Seventh Embodiment Next, a seventh embodiment will be described. Optical communication modules and devices are being applied not only to long-distance communications but also to links between data centers, between mobile phone base stations, and between edge routers, and there is a growing demand for them. To reduce the cost of optical circuit chips containing optical circuits used in optical communication modules, it is necessary to accurately inspect the circuits under test at the wafer level, confirm that they are good chips, and then fabricate them into chips and incorporate them into optical communication modules. As an optical input / output unit for an optical circuit in a wafer state, a grating coupler that emits light toward the wafer's upper surface is used. Meanwhile, as an optical input / output unit for an optical circuit fabricated into a chip, a spot size converter can also be used in addition to a grating coupler. Some optical communication modules require an optical input / output unit using a spot size converter rather than a grating coupler with a narrow wavelength band, which may require wafer inspection using a grating coupler and optical connection at the time of module assembly using a spot size converter. The seventh embodiment provides a measurement circuit that takes these points into consideration.

[0076] 8 is a schematic diagram for explaining a measuring circuit 70 according to the seventh embodiment, showing the measuring circuit 50 shown in FIG. 6 in a chip form. The measuring circuit 70 is formed by cutting the dicing line L Ｄ and dicing line L ＤThe measuring circuit 70 includes a pair of spot size converters (SSCs) facing each other on the wafer surface, corresponding to each path. The spot size converter SSC generally uses an inverted tapered waveguide, in which the waveguide width narrows toward the optical connection end face (chip end face). Therefore, by forming the narrower side of the inverted tapered shape facing each other, the measuring circuit 70 functions as a continuous waveguide before being formed into a chip. Therefore, inspection of the measuring circuit 70 in the wafer state before being formed into a chip is performed using a grating coupler that can be coupled from the top surface of the wafer as an optical input / output unit. After inspection on the wafer, the measuring circuit 70 is diced along the dicing lines Ld to be mounted in the chip state and modularized. Then, the grating couplers are removed from the chips containing the diced measuring circuits 70, revealing the spot size converters (SSCs). This makes it possible to create modules capable of optical connection using spot size converters, which have less wavelength dependency than grating couplers.

[0077] The measurement circuit of the present embodiment described above integrates the circuit under test and the optical input / output unit into a chip. This fixes the coupling state between the circuit under test and the optical input / output unit, allowing both calculation of the coupling loss of the optical input / output unit and measurement of the characteristics of the circuit under test. This allows accurate measurement of the characteristics of the circuit under test, regardless of the optical coupling characteristics between the optical input / output unit and the optical fiber, which are required when inputting and outputting light to and from the circuit under test. That is, light can be input and output to and from a chip or wafer by placing an optical fiber close to an optical input / output unit formed by a grating coupler or the like. However, variations in the quality of the grating couplers can result in some grating couplers having low coupling loss with the fiber, while other grating couplers have high coupling loss with the fiber. The present disclosure addresses this issue and provides a measurement circuit that is not affected by manufacturing variations in grating couplers or the like. In order to realize such a configuration, in this embodiment, couplers connected to optical input / output units (connected optical input / output units) connected to the circuit under test and couplers connected to optical input / output units (non-connected optical input / output units) that are not connected to the circuit under test are connected so that light is input from at least some of the connected optical input / output units and non-connected optical input / output units, and the number of input / output paths output from at least some of the connected optical input / output units and non-connected optical input / output units, or from the multiplexing unit, is greater than the total number of connected optical input / output units and non-connected optical input / output units.

[0078] 1, 2, 13 Optical power measurement unit 3 Multiplexing unit 5, 51, 100 Circuit to be measured 7A, 7Aa, 7Ab, 7Ac, 7B, 7Ba, 7Bb Optical input / output unit 10, 20, 30, 40, 50, 60, 70 Measurement circuit 21, 22, 23, 41, 43, 52, 53, 61, 62, 71, 200 Branching coupler Optical waveguide 200a SSC Spot size converter

Claims

1. at least one optical input / output unit optically connected to the circuit under test; at least one non-connected optical input / output unit that is not optically connected to the circuit under test; a connection branching coupler connected to any one of the connection optical input / output units; a non-connected branch coupler connected to any one of the non-connected optical input / output units; a multiplexing unit that inputs the light branched by the connection branching coupler and the light branched by the non-connection branching coupler, The connection branch coupler and the non-connection branch coupler form input / output paths in which light is input from the connection optical input / output units and some of the non-connection optical input / output units, and output from the connection optical input / output units and some of the non-connection optical input / output units, or the multiplexer, the number of which is greater than the total number of the connection optical input / output units and the non-connection optical input / output units. Optical circuit measurement circuit.

2. 2. The optical circuit measurement circuit according to claim 1, further comprising a light intensity measurement unit that measures the intensity of the light output from said multiplexing unit, said light intensity measurement unit being a photodiode.

3. 3. The optical circuit measuring circuit according to claim 2, wherein the light intensity measuring section and the multiplexing section are integrated into a photodiode having another input function.

4. 2. The optical circuit measuring circuit according to claim 1, wherein the circuit under test is an optical circuit having only an optical input port.

5. 2. The optical circuit measuring circuit according to claim 1, wherein the circuit under test is an optical circuit having an optical input port and an optical output port.

6. 6. The optical circuit measuring circuit according to claim 5, wherein the connected optical input / output unit, an output port of the circuit under test, and the unconnected optical input / output unit are connected to each other.

7. 2. The optical circuit measurement circuit according to claim 1, wherein the connection optical input / output section and the non-connection optical input / output section are grating couplers, and a spot size converter is included between the connection optical input / output section and the connection branch coupler, and between the non-connection optical input / output section and the non-connection branch coupler.

8. an optical circuit measurement circuit including a circuit under test, at least one connection optical input / output unit optically connected to the circuit under test, at least one non-connection optical input / output unit not optically connected to the circuit under test, a connection branch coupler connected to one of the connection optical input / output units, a non-connection branch coupler connected to one of the non-connection optical input / output units, and a multiplexing unit that inputs light branched by the connection branch coupler and light branched by the non-connection branch coupler, the connection branch coupler and the non-connection branch coupler form input / output paths in which light is input from the connection optical input / output units and some of the non-connection optical input / output units, and output from the connection optical input / output units and some of the non-connection optical input / output units, or the multiplexer, the number of which is greater than the total number of the connection optical input / output units and the non-connection optical input / output units; measuring the intensity of light input to and output from the input / output path, and measuring the coupling loss between the circuit under test and the connecting optical input / output unit; Optical circuit measurement methods.

9. The optical circuit measurement circuit according to claim 1 , further comprising the circuit under test.