Method, device, and recording medium for measuring optical characteristics of light modulator

Abstract

The present invention provides a method, device, and recording medium for measuring the optical characteristics of an optical modulator, which are capable of automatically aligning the optical modulator and an optical fiber. The method is a method for measuring the optical characteristics of a Mach-Zehnder optical modulator, wherein the optical modulator has an incident portion, a waveguide for transmitting light incident from the incident portion, and multiple exit portions for emitting the light. The method comprises the following steps: causing light from a light source to be incident on the incident portion of the optical modulator via a first optical fiber; multiple light receiving portions receiving light emitted from the multiple exit portions of the optical modulator; converting an electrical signal output by each of the multiple light receiving portions upon receiving the exit light into an electric current, and obtaining a total value by summing the magnitudes of the currents; and aligning the optical modulator between the incident portion of the optical modulator and the first optical fiber based on the total value.

Description

Technical Field

[0001] The present disclosure relates to a method, a measuring device, and a recording medium for measuring optical characteristics of a light modulation element. Background Art

[0002] Optical communication systems using the Quadrature Phase Shift Keying (QPSK) method use, for example, Mach-Zehnder optical modulators. These optical modulators have multiple waveguides, an input port, and multiple output ports. Modulation electrodes and phase adjustment electrodes are provided on the waveguides.

[0003] When measuring the optical characteristics of a light modulator, alignment is performed between the light modulator's incident port and the optical fiber. There is a method for aligning the optical modulator so as to maximize the photocurrent flowing through the light modulator's electrodes due to incident light (for example, Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-206977 Summary of the Invention

[0005] On the other hand, alignment is sometimes performed based on the power of light output from an optical modulator. However, for each optical modulator, the balance of optical power between the multiple output ports of the optical modulator changes. In other words, the power of light emitted from a single output port changes for each optical modulator. Therefore, it is difficult to automatically align the optical power of the output light while detecting the optical power of the output light. Therefore, the purpose of the present invention is to provide a method, a measuring device, and a recording medium for measuring the optical characteristics of an optical modulator that can automatically align the optical modulator and the optical fiber.

[0006] The method for measuring the optical characteristics of an optical modulator disclosed in the present invention is a method for measuring the optical characteristics of a Mach-Zehnder type optical modulator, wherein the optical modulator has an incident portion, a waveguide for transmitting light incident from the incident portion, and a plurality of output portions for emitting the light, wherein the measuring method includes the following steps: causing light to be incident from a light source to the incident portion of the optical modulator via a first optical fiber; a plurality of light receiving portions receiving output light emitted from a plurality of output portions of the optical modulator; converting an electrical signal output by each of the plurality of light receiving portions by receiving the output light into an electric current, and obtaining a total value by summing the magnitudes of the currents; and performing core adjustment between the incident portion of the optical modulator and the first optical fiber based on the total value.

[0007] The measuring device disclosed in the present invention is a measuring device for measuring the optical characteristics of a Mach-Zehnder type optical modulator, wherein the optical modulator has an incident portion, a waveguide for transmitting light incident from the incident portion, and a plurality of output portions for emitting the light, wherein the measuring device comprises: a first optical fiber for causing light emitted from a light source to be incident on the incident portion of the optical modulator; a plurality of light receiving portions for outputting electrical signals by causing outgoing light emitted from the plurality of output portions of the optical modulator to be incident on the plurality of light receiving portions; a current conversion portion for converting the electrical signal outputted by each of the plurality of light receiving portions into an electric current and obtaining a total value by summing the magnitudes of the currents; and a control portion for performing core adjustment between the incident portion of the optical modulator and the first optical fiber based on the total value.

[0008] The recording medium disclosed herein records a measurement program for the optical characteristics of a Mach-Zehnder type optical modulator, wherein the optical modulator has an incident portion, a waveguide for transmitting light incident from the incident portion, and multiple output portions for emitting the light, wherein the measurement program causes a computer to perform the following processing: causing light emitted from a light source to be incident on the incident portion of the optical modulator via a first optical fiber; converting an electrical signal output by each of multiple light receiving portions by receiving output light emitted from multiple output portions of the optical modulator into an electric current, and obtaining a total value by summing the magnitudes of the currents; and performing core adjustment between the incident portion of the optical modulator and the first optical fiber based on the total value.

[0009] Effects of the Invention

[0010] According to the present disclosure, it is possible to automatically align the optical modulation element and the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Schematic diagram illustrating a measuring device according to an embodiment.

[0012] Figure 2 This is a block diagram showing the hardware configuration of the control unit.

[0013] Figure 3A It is a top view illustrating an optical fiber array and a light modulation element.

[0014] Figure 3B This is a front view illustrating an optical fiber array.

[0015] Figure 4A This is a flowchart illustrating the steps of measuring optical properties.

[0016] Figure 4B This is a flowchart illustrating the alignment steps.

[0017] Label Description

[0018] 10 Light Modulation Element

[0019] 10a, 70a surfaces

[0020] 11 base plate

[0021] 13a, 13b Mach-Zehnder modulator

[0022] 14 Incident Port

[0023] 12a~12d output port

[0024] 16, 20a, 20b, 24a-24d, 28a-28h, 32a-32d, 36a-36d waveguide

[0025] 18, 22a, 22b, 26a-26d, 30a-30d, 34a, 34b couplers

[0026] 40a~40h, 42a~42h, 44a~44d electrodes

[0027] 46, 48 pads

[0028] 50 Temperature Controller

[0029] 51 Current Converter

[0030] 52 Automatic centering controller

[0031] 54 Wavelength-variable laser light source

[0032] 53, 55 connectors

[0033] 56a~56d Optical power meter

[0034] 57 Monitor

[0035] 59 Camera

[0036] 60 Alignment stage

[0037] 61 Clamping parts

[0038] 62 fixture

[0039] 63 Fixing tools

[0040] 64 Temperature Control Stage

[0041] 65° Angle adjustment stage

[0042] 66 Multi-contact probe

[0043] 67 pins

[0044] 70 fiber array

[0045] 71 bottom plate

[0046] 72a~72d, 74 optical fiber

[0047] 76 polarizing plate

[0048] 80 Control Department

[0049] 81 Position control unit

[0050] 82 Total value acquisition unit

[0051] 83 Light source control unit

[0052] 84 Voltage Control Unit

[0053] 100 measuring device

[0054] 101 CPU

[0055] 102 RAM

[0056] 103 Storage Device

[0057] 104 interfaces DETAILED DESCRIPTION

[0058] [Description of Embodiments of the Present Disclosure]

[0059] First, the contents of the embodiments of the present disclosure are listed for description.

[0060] One embodiment of the present disclosure is (1) a measurement method, which is a method for measuring the optical characteristics of a Mach-Zehnder type optical modulator, wherein the optical modulator has an incident portion, a waveguide that transmits light incident from the incident portion, and a plurality of output portions that emit the light, wherein the measurement method includes the following steps: causing light from a light source to be incident on the incident portion of the optical modulator via a first optical fiber; a plurality of light receiving portions receiving output light emitted from the plurality of output portions of the optical modulator; converting an electrical signal output by each of the plurality of light receiving portions upon receiving the output light into an electric current, and obtaining a total value by summing the magnitudes of the electric currents; and performing alignment between the incident portion of the optical modulator and the first optical fiber based on the total value. For each optical modulator, the balance of the intensities of the light emitted from the plurality of output portions changes. On the other hand, the total of the intensities is constant. Therefore, alignment between the optical modulator and the optical fiber can be automatically performed based on the total value of the converted electric current.

[0061] (2) In the step of aligning the incident portion of the light modulator and the first optical fiber, the alignment is performed so that the total value becomes maximum. The alignment between the light modulator and the optical fiber can be automatically performed based on the total value.

[0062] (3) The following method may be adopted, that is, the incident portion and the plurality of emission portions are provided on one surface of the light modulator, and the measuring method includes the following steps: before the step of causing light from the light source to enter the incident portion, an optical fiber array in which the first optical fiber and the plurality of second optical fibers are arranged is made to face the one surface of the light modulator, and the step of the plurality of light receiving portions receiving the emission light is the step of the plurality of light receiving portions receiving the emission light via the plurality of second optical fibers. By making the light modulator face the optical fiber array, the incident portion is made to face the first optical fiber, and the emission portion is made to face the second optical fiber. This enables the light to enter via the first optical fiber and the light to exit via the second optical fiber.

[0063] (4) Alternatively, the step of performing alignment between the incident portion of the light modulator and the first optical fiber includes adjusting the position of at least one of the optical fiber array and the light modulator based on the total value. Alignment between the incident portion of the light modulator and the first optical fiber can be performed while alignment between the output portion of the light modulator and the second optical fiber is also performed.

[0064] (5) Alternatively, the step of performing alignment between the incident portion of the light modulator and the first optical fiber may include the steps of: performing alignment between the incident portion of the light modulator and the first optical fiber without applying a voltage to electrodes provided in the waveguide of the light modulator; and performing alignment between the incident portion of the light modulator and the first optical fiber by applying a voltage to electrodes provided in the waveguide of the light modulator. Since the two alignment steps are performed automatically, the time and effort required for alignment are reduced compared to a case where alignment is performed manually.

[0065] (6) A measuring device for measuring the optical characteristics of a Mach-Zehnder type optical modulator, the optical modulator having an incident portion, a waveguide for transmitting light incident from the incident portion, and a plurality of output portions for emitting the light, wherein the measuring device comprises: a first optical fiber for allowing light emitted from a light source to enter the incident portion of the optical modulator; a plurality of light receiving portions for outputting electrical signals when light emitted from the plurality of output portions of the optical modulator enters the plurality of light receiving portions; a current conversion portion for converting the electrical signals output by each of the plurality of light receiving portions into a current and obtaining a total value by summing the magnitudes of the currents; and a control portion for performing alignment between the incident portion of the optical modulator and the first optical fiber based on the total value. For each optical modulator, the balance of the intensities of the light emitted from the plurality of output portions changes. On the other hand, the total intensities are constant. Therefore, alignment between the optical modulator and the optical fiber can be automatically performed based on the total value of the converted currents.

[0066] (7) The following method may also be adopted, namely, the measuring device includes an optical fiber array in which the first optical fiber and a plurality of second optical fibers are arranged, the outgoing light is incident on the plurality of light receiving units via the plurality of second optical fibers, and the control unit adjusts the position of at least one of the optical fiber array and the optical modulator based on the total value, thereby performing the core adjustment. The incident portion is made to face the first optical fiber, and the exit portion is made to face the second optical fiber. It is possible to allow light to be incident via the first optical fiber and light to be emitted via the second optical fiber. In addition, it is possible to perform core adjustment between the incident portion of the optical modulator and the first optical fiber while also performing core adjustment between the exit portion and the second optical fiber.

[0067] (8) Alternatively, the diameter of the second optical fiber may be larger than that of the first optical fiber. By increasing the diameter of the light-receiving portion, optical coupling with the light emitted from the emitting portion can be increased, thereby suppressing light loss and allowing the emitted light to be transmitted to the second optical fiber.

[0068] (9) A recording medium recording a program for measuring the optical characteristics of a Mach-Zehnder type optical modulator, the optical modulator having an incident portion, a waveguide for transmitting light incident from the incident portion, and a plurality of output portions for emitting the light, wherein the program causes a computer to execute the following processing: causing light emitted from a light source to be incident on the incident portion of the optical modulator via a first optical fiber; converting an electrical signal output by each of a plurality of light receiving portions upon receiving light emitted from a plurality of output portions of the optical modulator into an electric current, and obtaining a total value by summing the magnitudes of the electric currents; and performing alignment between the incident portion of the optical modulator and the first optical fiber based on the total value. For each optical modulator, the balance of the intensities of the light emitted from the plurality of output portions changes. On the other hand, the total of the intensities is constant. Therefore, alignment between the optical modulator and the optical fiber can be automatically performed based on the total value of the converted electric currents.

[0069] [Details of the embodiments of the present disclosure]

[0070] Specific examples of methods, devices, and recording media for measuring the optical characteristics of light modulators according to embodiments of the present disclosure will be described below with reference to the accompanying drawings. The present disclosure is not limited to these examples but is defined by the claims, which are intended to encompass all modifications within the meaning and scope of equivalents to the claims.

[0071] (Measurement device)

[0072] Figure 1 Schematic diagram of a measuring device 100 according to an exemplary embodiment. Figure 1As shown, the measuring device 100 has an optical fiber array 70, a core adjustment stage 60, a temperature adjustment stage 64, an angle adjustment stage 65, a monitor 57, a camera 59, a temperature controller 50, an automatic core adjustment controller 52, a wavelength-variable laser light source 54, a current converter 51 (current conversion unit), four optical power meters 56a to 56d, a current and voltage source 58, a multi-contact probe 66 and a control unit 80.

[0073] The measuring device 100 is a device that measures the optical characteristics of the light modulator 10 by injecting laser light into the light modulator 10 and receiving light emitted from the light modulator 10 , and is used, for example, in a procedure for inspecting the light modulator 10 .

[0074] Figure 1 The X-axis, Y-axis, and Z-axis directions shown are mutually orthogonal. The X-axis and Y-axis directions are the directions of the sides of the optical fiber array 70, the alignment stage 60, the temperature control stage 64, the angle adjustment stage 65, and the optical modulator 10. The Z-axis direction is orthogonal to the top surfaces of the optical modulator 10 and the optical fiber array 70.

[0075] The alignment stage 60 is electrically connected to the automatic alignment controller 52. A clamp 61 is provided on the alignment stage 60, and an optical fiber array 70 is mounted on the clamp 61. The optical fiber array 70 includes optical fibers 72a to 72d and an optical fiber 74 extending in the X-axis direction. Figure 1 The illustrated fixing tool 63 presses down on the optical fibers 72a to 72d and 74 from above, thereby securing the plurality of optical fibers on the optical fiber array 70. One end face of the optical fiber array 70 in the Y-axis direction abuts against the fixture 62, thereby positioning the optical fiber array 70 on the alignment stage 60. The fixture 62 and fixing tool 63 are made of, for example, Teflon (registered trademark).

[0076] An angle adjustment stage 65 is disposed at a position opposite to the alignment stage 60 in the X-axis direction. A temperature control stage 64 is mounted on the angle adjustment stage 65, and the light modulation element 10 is mounted on the temperature control stage 64. The temperature control stage 64 includes, for example, a Peltier element and is electrically connected to the temperature controller 50.

[0077] The multi-contact probe 66 is disposed on the temperature-controlled stage 64 , extends in the X-axis and Y-axis directions, is electrically connected to the current and voltage source 58 , and has a plurality of pins 67 . The optical modulation element 10 is electrically connected to the multi-contact probe 66 via the pins 67 .

[0078] The current-voltage source 58 is a multi-channel DC power source, and applies voltage to the plurality of electrodes of the optical modulation element 10 via the multi-contact probe 66 , and can measure the current flowing through the plurality of electrodes.

[0079] Optical power meters 56a-56d (light receiving units) have light receiving elements such as photodiodes, and output a voltage in response to incident light. The magnitude of this voltage is proportional to the intensity of the light. Current converter 51 converts the voltages input from optical power meters 56a-56d into currents and sums the magnitudes (current values) of these currents to calculate a total value. Current converter 51 inputs this total current to the automatic alignment controller 52. The higher the light intensity, the greater the voltage output from optical power meters 56a-56d and the current obtained by current converter 51.

[0080] The camera 59 is arranged so that the surface of the light modulator 10 facing the optical fiber array 70 is within its field of view. The monitor 57 is connected to the camera 59 and displays the image captured by the camera 59. The monitor 57 displays a reference line that serves as a reference for the alignment of the light modulator 10.

[0081] The control unit 80 is a computer such as a personal computer (PC), and is electrically connected to the temperature controller 50 , the automatic alignment controller 52 , the wavelength-variable laser light source 54 , the current converter 51 , the four optical power meters 56 , and the current-voltage source 58 .

[0082] The control unit 80 includes a position control unit 81, a total value acquisition unit 82, a light source control unit 83, a voltage control unit 84, and a temperature control unit 85. The temperature control unit 85 adjusts the temperature of the optical modulator 10 on the temperature control stage 64 by controlling the power supplied from the temperature controller 50 to the temperature control stage 64. The voltage control unit 84 controls the current source 58 to apply a reverse bias voltage to the optical modulator 10 and acquires the value of the current flowing through the optical modulator 10 from the current source 58. The light source control unit 83 controls the on / off operation of the wavelength-variable laser light source 54 and also controls the wavelength and intensity of the light emitted from the wavelength-variable laser light source 54. The total value acquisition unit 82 acquires the total value of the current values ​​calculated by the current converter 51. Based on the total value, the position control unit 81 controls the automatic alignment controller 52 and adjusts the position of the optical fiber array 70 on the alignment stage 60.

[0083] Figure 2 80 is a block diagram showing the hardware structure of the control unit 80. Figure 2As shown, the control unit 80 includes a CPU (Central Processing Unit) 101, a RAM (Random Access Memory) 102, a storage device 103, and an interface 104. The CPU 101, RAM 102, the storage device 103, and the interface 104 are connected to each other via a bus or the like. The RAM 102 is a volatile memory that temporarily stores programs and data. The storage device 103 is, for example, a ROM (Read Only Memory), a solid-state drive (SSD) such as a flash memory, or a hard disk drive (HHD). The storage device 103 stores programs for performing alignment, which will be described later, and programs for confirming the operation of the optical modulator 10.

[0084] The CPU 101 executes the program stored in the RAM 102, whereby the control unit 80 implements the position control unit 81, the total value acquisition unit 82, the light source control unit 83, the voltage control unit 84, and the temperature control unit 85. Each unit of the control unit 80 may be hardware such as a circuit.

[0085] Figure 3A FIG is a top view illustrating the optical fiber array 70 and the light modulation element 10. Figure 3A In the figure, the centering stage 60, the clamp 62, the fixing tool 63, the temperature control stage 64, the angle adjustment stage 65 and the multi-contact probe 66 are omitted. Figure 3A As shown, the optical fiber array 70 and the light modulation element 10 are opposed to each other in the X-axis direction.

[0086] (Fiber Array)

[0087] The optical fiber array 70 includes a base plate 71, optical fibers 72a to 72d, and an optical fiber 74. The base plate 71 has an X-axis length of, for example, 3 mm to 30 mm, and a Y-axis width of, for example, 3 mm to 8 mm.

[0088] Optical fiber 74 is located near the center of base plate 71 along the Y axis. Optical fibers 72a and 72b are arranged on one side of optical fiber 74 in the Y axis direction, and optical fibers 72c and 72d are arranged on the other side. In other words, optical fibers 72a, 72b, 74, 72c, and 72d are arranged in order along the Y axis direction.

[0089] Figure 3B FIG is a front view illustrating an example of an optical fiber array 70. Figure 3B As shown, four V-shaped grooves 73 and one groove 75 are provided on the upper surface of the bottom plate 71. The grooves 73 and 75 extend in the X-axis direction. One of the optical fibers 72a to 72d is disposed in one groove 73. The optical fiber 74 is disposed in the groove 75.

[0090] Optical fiber 74 is a single-mode fiber (SMF) with polarization-maintaining properties and is a lensed fiber with a convex tip. Optical fiber 74 is coated with glass. The outer diameter of optical fiber 74, including the coating, is, for example, 250 μm, and the core diameter (core diameter) is, for example, 8 μm. Laser light of a single wavelength and a single mode, for example, in the range of 1.53 μm to 1.57 μm, is transmitted through optical fiber 74.

[0091] Optical fibers 72a to 72d are multimode fibers (MMF). The core diameter of each optical fiber 72a to 72d is larger than that of optical fiber 74, for example, 400 μm. The length of each optical fiber 72a to 72d is, for example, 730 μm, and the bending radius is, for example, 47 mm.

[0092] Surface 70a of the optical fiber array 70 in the X-axis direction faces the light modulator 10. One end of each of optical fibers 72a to 72d is located on surface 70a. Two polarizing plates 76 are provided on surface 70a. One of the polarizing plates 76 covers one end of each of optical fibers 72a and 72b, while the other covers one end of each of optical fibers 72c and 72d. One end of an optical fiber 74 protrudes outward from surface 70a in the X-axis direction. The amount of protrusion of optical fiber 74 from surface 70a is, for example, 0.1 mm.

[0093] like Figure 1 As shown, the other end of optical fiber 72a is optically connected to optical power meter 56a using connector 55. The other end of optical fiber 72b is optically connected to optical power meter 56b. The other end of optical fiber 72c is optically connected to optical power meter 56c. The other end of optical fiber 72d is optically connected to optical power meter 56d. The other end of optical fiber 74 is optically connected to wavelength-variable laser light source 54 using connector 53.

[0094] (Light modulation element)

[0095] Figure 3A The optical modulator 10 shown is formed, for example, from a gallium arsenide (GaAs)-based semiconductor or an indium phosphide (InP)-based semiconductor, and is a one-input, four-output device that includes multiple Mach-Zehnder modulators. The optical modulator 10 includes a substrate 11, multiple waveguides, phase adjustment electrodes, and input and output pads.

[0096] The substrate 11 is a semiconductor substrate formed of a compound semiconductor such as a GaAs-based or InP-based semiconductor. Electrodes 40a to 40h, electrodes 42a to 42h, electrodes 44a to 44d, a plurality of pads 46, and a plurality of pads 48 are provided on the upper surface of the substrate 11. Figure 3A In the figure, the electrodes are marked with oblique lines. A wiring pattern (not shown) for electrically connecting the electrodes and the pads is also provided on the substrate 11.

[0097] A surface 10a of the optical modulator 10 in the X-axis direction faces the surface 70a of the optical fiber array 70. Surface 10a is provided with an input port 14 (input portion) and four output ports 12a, 12b, 12c, and 12d (output portions). The input port 14 is located near the center of the substrate 11 along the Y-axis. Output ports 12a and 12b are provided on one side of the input port 14 in the Y-axis direction, and output ports 12c and 12d are provided on the other side. That is, the output ports 12a and 12b, the input port 14, and the output ports 12c and 12d are arranged in order along the Y-axis direction. For example, among the four output ports, output ports 12b and 12c emit signal light, while output ports 12a and 12d emit light for monitoring.

[0098] The output port 12a is opposite to the front end of the optical fiber 72a of the optical fiber array 70 in the X-axis direction. The output port 12b is opposite to the front end of the optical fiber 72b in the X-axis direction. The output port 12c is opposite to the front end of the optical fiber 72c in the X-axis direction. The output port 12d is opposite to the front end of the optical fiber 72d in the X-axis direction. The input port 14 is opposite to the front end of the optical fiber 74 in the X-axis direction.

[0099] The area from the input port 14 to the output ports 12a and 12b functions as a single Mach-Zehnder modulator (primary Mach-Zehnder modulator) 13a, and the area from the input port 14 to the output ports 12c and 12d functions as a single Mach-Zehnder modulator (primary Mach-Zehnder modulator) 13b. Each of the Mach-Zehnder modulators 13a and 13b further includes two Mach-Zehnder modulators (secondary Mach-Zehnder modulators).

[0100] One end of waveguide 16 is coupled to input port 14, and the other end is coupled to coupler 18. Waveguide 16 branches into two waveguides 20a and 20b at coupler 18. Waveguide 20a branches into two waveguides 24a and 24b at coupler 22a. Waveguide 24a branches into two waveguides 28a and 28b at coupler 26a. Waveguides 28a and 28b merge at coupler 30a to form waveguide 32a. Waveguide 24b branches into two waveguides 28c and 28d at coupler 26b. Waveguides 28c and 28b merge at coupler 30b to form waveguide 32b. Waveguides 28a to 28d bend and return twice. Waveguides 32a and 32b bend and return once.

[0101] Waveguides 32a and 32b merge at coupler 34a and branch into waveguides 36a and 36b at a later stage after coupler 34a. Waveguide 36a has one end coupled to coupler 34a and the other end coupled to output port 12a. Waveguide 36b has one end coupled to coupler 34a and the other end coupled to output port 12b. The entire circuit from coupler 26a to coupler 30a functions as a single secondary Mach-Zehnder modulator. The entire circuit from coupler 26b to coupler 30b functions as a single secondary Mach-Zehnder modulator.

[0102] Electrodes 40a and 42a are sequentially provided on waveguide 28a from the coupler 26a side toward the coupler 30a side. Electrodes 40b and 42b are sequentially provided on waveguide 28b from the coupler 26a side toward the coupler 30a side. Electrodes 40c and 42c are sequentially provided on waveguide 28c from the coupler 26b side toward the coupler 30b side. Electrodes 40d and 42d are sequentially provided on waveguide 28d from the coupler 26b side toward the coupler 30b side. Electrode 44a is provided on waveguide 32a, and electrode 44b is provided on waveguide 32b.

[0103] The waveguides 20b, 24c, 24d, 28e-28h, 32c, 32d, 36c, 36d, couplers 22b, 26c, 26d, 30c, 30d, 34b, and output ports 12c and 12d of Mach-Zehnder modulator 13b are arranged in the same manner as the corresponding structures of Mach-Zehnder modulator 13a. The circuit from coupler 26c to coupler 30c functions as a single sub-Mach-Zehnder modulator. The circuit from coupler 26d to coupler 30d functions as a single sub-Mach-Zehnder modulator.

[0104] Electrodes 40e and 42e are sequentially provided on waveguide 28e, extending from the coupler 26c side toward the coupler 30c side. Electrodes 40f and 42f are sequentially provided on waveguide 28f, extending from the coupler 26c side toward the coupler 30c side. Electrodes 40g and 42g are sequentially provided on waveguide 28g, extending from the coupler 26d side toward the coupler 30d side. Electrodes 40h and 42h are sequentially provided on waveguide 28h, extending from the coupler 26d side toward the coupler 30d side. Electrode 44c is provided on waveguide 32c, and electrode 44d is provided on waveguide 32d.

[0105] A plurality of pads 46 and a plurality of pads 48 are provided on the upper surface of the substrate 11 of the optical modulator 10. The pads 46 are, for example, phase adjustment electrodes for adjusting the phase of light and are electrically connected to the electrodes 42a to 42h and the electrodes 44a to 44d. The pads 48 are, for example, modulation electrodes for modulating light and are electrically connected to the electrodes 40a to 40h and to the electrodes 44d. Figure 1Pins 67 of the multi-contact probe 66 are shown electrically connected.

[0106] Light is incident on the optical modulator 10 from the incident port 14, and light is emitted from the output ports 12a to 12d. Light modulation is performed by inputting a high-frequency (RF: Radio Frequency) signal to the electrodes 40a to 40h. The phase is adjusted by applying a voltage to the electrodes 42a to 42h and the electrodes 44a to 44d. For example, the phase difference between the light emitted from the output port 12b and the light emitted from the output port 12c can be adjusted to π / 2, etc. The phase adjustment can be performed so that the intensity of the light (signal light) emitted from the output ports 12b and 12c is maximized and the intensity of the light (monitor light) emitted from the output ports 12a and 12d is minimized.

[0107] As described later, during inspection of the light modulator 10, after alignment is performed between the incident port 14 of the light modulator 10 and the optical fibers 74 of the optical fiber array 70, the optical characteristics of the light modulator 10 are evaluated. During alignment, light is injected from the wavelength-variable laser light source 54 into the incident port 14 of the light modulator 10, and the intensity of light emitted from the output ports 12a to 12d is measured using optical power meters 56a to 56d.

[0108] Table 1 shows the intensity (optical power) of light emitted from multiple optical modulators. In the example in Table 1, the optical modulator 10 is in its initial phase state, and the phase of the light emitted by the optical modulator 10 is not adjusted. Alignment is performed between the input port 14 and the optical fiber 74, and the intensity of the light incident on the input port 14 is maximized. If the positions of the input port 14 and the optical fiber 74 deviate from the optimal position, the intensity of the light incident on the input port 14 decreases, and the intensity of the emitted light also decreases from the example in Table 1.

[0109]

Table 1

[0110]

[0111] In Table 1, multiple light modulators 10 are numbered 1 through 3. Due to manufacturing variations, the balance of light intensity between the output ports of each light modulator 10 may vary. In light modulator 10 No. 1, the intensity of light emitted from output ports 12a and 12c is P / 6, while the intensity of light emitted from output ports 12b and 12d is P / 3. The total of the intensities of these four output lights is P.

[0112] In light modulator element 10 No. 2, the intensity of the light emitted from exit ports 12a and 12c is P / 3, and the intensity of the light emitted from exit ports 12b and 12d is P / 6. ​​In light modulator element 10 No. 3, the intensity of the light emitted from exit ports 12a and 12d is 4P / 10, and the intensity of the light emitted from exit ports 12b and 12c is P / 10. The intensity balance also changes for each of the other multiple light modulator elements 10 omitted in Table 1. On the other hand, in any light modulator element 10, the total value of the intensities of the four exit lights is P.

[0113] For example, assume that alignment is performed using the light emitted from output port 12b, while not using the light emitted from the other three output ports. Light is injected from the wavelength-variable laser light source 54 into the input port 14 via the optical fiber 74, and the light emitted from the output port 12b is received by the optical power meter 56b. Using the alignment stage 60, the position of the optical fiber array 70 is adjusted so that the electrical signal (voltage) output by the optical power meter 56 is maximized.

[0114] However, as shown in Table 1, the balance of the intensity of the outgoing light varies for each of the multiple optical modulators 10. The intensity of the light outgoing from the output port 12b is P / 3 for No. 1, half that, P / 6 for No. 2, and even smaller, P / 10 for No. 3. Thus, the intensity of the light outgoing from the output port 12b varies significantly for each of the multiple optical modulators 10. Specifically, the intensity of the outgoing light varies depending on the positional relationship between the input port 14 and the optical fiber 74, and also varies due to manufacturing variations in the optical modulator 10. Therefore, it is difficult to perform core alignment using only the intensity of the light outgoing from the output port 12b.

[0115] Alternatively, the output port may be switched for each light modulator 10 , such as using the output light from output port 12 b for alignment No. 1 and using output port 12 a for alignment No. 2. However, the alignment procedure becomes complicated and difficult to automate.

[0116] As shown in Table 1, the sum of the outgoing light intensities in each optical modulator 10 is P. That is, after alignment, the balance of the outgoing light intensities varies for each optical modulator 10, but the sum of the outgoing light intensities remains the same. Therefore, the summed value increases or decreases across all optical modulators 10 depending on the positional relationship between the input port 14 and the optical fiber 74. The closer the positional relationship is to the optimal one (after alignment), the closer it is to the maximum value P. Deviating from the optimal positional relationship, the smaller the summed value. Therefore, in this embodiment, alignment is automatically performed based on the summed value.

[0117] Figure 4AThis is a flowchart illustrating the steps of measuring optical properties. Figure 4B This is a flowchart illustrating the steps of core alignment. The steps of measuring optical characteristics include Figure 4B The alignment step shown is performed, for example, during the manufacturing process of the light modulation element 10 as a part of the inspection of the light modulation element 10. The optical fiber array 70 is placed on the stage 60 for alignment.

[0118] The operator places the light modulator 10 on the temperature-controlled stage 64 and moves the angle adjustment stage 65 while observing the image captured by the camera 59 on the monitor 57. The angle between the surface 10a of the light modulator 10 and the surface 70a of the optical fiber array 70 is adjusted using the reference line marked on the monitor 57 so that the surface 10a and the surface 70a are parallel ( Figure 4A Step S10).

[0119] The pins 67 of the multi-contact probe 66 are brought into contact with the pads 46 and 48 of the optical modulator 10. A voltage of, for example, 1V is applied from the current-voltage source 58 to the electrodes of the optical modulator 10 via the multi-contact probe 66. The current output from the optical modulator 10 is detected by the current-voltage source 58, and the operator confirms whether the current is 10 μA or greater. This checks the electrical continuity between the current-voltage source 58, the multi-contact probe 66, and the optical modulator 10 (step S12). After the continuity check, the voltage application to the optical modulator 10 is stopped.

[0120] Laser light with a wavelength of, for example, 1.55 μm is injected from the wavelength-variable laser light source 54 via the optical fiber 74 of the optical fiber array 70 into the input port 14 of the optical modulator 10 (step S14). Light is emitted from the output ports 12a to 12d of the optical modulator 10. The emitted light propagates through the optical fibers 72a to 72d and is input to the optical power meters 56a to 56d. The optical power meters 56a to 56d output a voltage corresponding to the intensity of the emitted light to the current converter 51. The current converter 51 converts the voltage input from the optical power meters 56a to 56d into a current and calculates the total value of the current. No voltage is applied to the optical modulator 10.

[0121] Next, alignment is performed between the incident port 14 of the light modulator 10 and the optical fiber 74 of the optical fiber array 70. First, rough alignment is performed manually (manual alignment, step S16), and then precise alignment is performed automatically (automatic alignment, step S18).

[0122] Manual alignment is performed, for example, as follows: the operator checks the image captured by the camera 59 on the monitor 57 and manually moves the alignment stage 60 so that the total value of the current input from the current converter 51 to the automatic alignment controller 52 becomes greater than 1 μA, thereby adjusting the position of the optical fiber array 70 (step S16).

[0123] Automatic centering Figure 4B The steps shown are performed. The position control unit 81 controls the automatic centering controller 52 to move the position of the optical fiber array 70 on the centering stage 60 (step S30). The total value acquisition unit 82 acquires the total value of the current calculated by the current converter 51 (step S32). The position control unit 81 determines whether the total value of the current is maximum (step S34). The maximum value of the total current corresponds to the total value P of the four outgoing light intensities shown in Table 1. In the case of no in step S34, the control unit 80 executes steps S30 and S32 again. In the case of yes in step S34, the control of the automatic centering ends. That is, centering is performed by moving the optical fiber array 70 by the position control unit 81 in such a way that the total value becomes the maximum. After the automatic centering, Figure 4A Step S20.

[0124] like Figure 4A As shown, the phase of the light emitted from the optical modulator 10 is adjusted (step S20). The voltage control unit 84 controls the current-voltage source 58 to apply a phase adjustment voltage from the current-voltage source 58 to the electrodes 42a to 42h of the optical modulator 10, sweeping the phase adjustment voltage from, for example, 1V to -10V. The voltage control unit 84 determines a phase adjustment voltage such that the intensity of light emitted from the four output ports 12b and 12c is maximized. The voltage control unit 84 then applies a phase adjustment voltage from the current-voltage source 58 to the electrodes 44a to 44d, sweeping the phase adjustment voltage from, for example, 1V to -10V, to determine a phase adjustment voltage such that the intensity of light is maximized.

[0125] After the phase adjustment, the automatic alignment is performed again (step S22). The automatic alignment of step S22 is the same as step S18. Figure 4B That is, the position of the optical fiber array 70 is adjusted so that the total value of the current corresponding to the intensity of the output light after phase adjustment becomes the maximum.

[0126] The control unit 80 checks the operation of the optical modulator 10 (step S24) using a program stored in the storage device 103. For example, the voltage applied to the optical modulator 10 by the current-voltage source 58 is swept, and the intensity of the light emitted from each of the four output ports is measured using an optical power meter corresponding to the output port.

[0127] After confirming the operation, the light source control unit 83 stops the light from the wavelength-variable laser light source 54 (step S26). Use the centering stage 60 to move the optical fiber array 70 away from the optical modulator 10. Separate the pins 67 of the multi-contact probe 66 from the pads 46 and 48 of the optical modulator 10. Remove the optical modulator 10 from the temperature control stage 64 (step S28). At this point, the measurement of the optical characteristics of one optical modulator 10 is completed. Repeat Figure 4A and Figure 4B The optical characteristics of multiple light modulation elements 10 are measured by processing.

[0128] According to this embodiment, the optical power meters 56a to 56d receive the light emitted from the multiple output ports 12a to 12d of the optical modulator 10 and output a voltage corresponding to the intensity of the emitted light. The current converter 51 converts the voltage into a current and obtains the total value of the current. The control unit 80 performs alignment between the input port 14 of the optical modulator 10 and the optical fiber 74 based on the total value. In each of the multiple optical modulators 10, the total value decreases when the optical modulator 10 is deviated from alignment and increases to a constant value after alignment. Therefore, by using the total value, automatic alignment can be performed. By automatically performing alignment, the time and labor required for alignment are reduced compared to manual alignment.

[0129] Specifically, alignment is performed so that the total value is maximized. Automatic alignment can be performed by using the current value (maximum value) corresponding to the total value P of the intensities as a common reference for multiple light modulators 10. A threshold value can also be used instead of the maximum value, for example, and the state in which the total value is greater than the threshold value is used as the state after alignment. Automatic alignment can be performed by storing a reference value such as the maximum value or the threshold value in the storage device 103 of the control unit 80.

[0130] An input port 14 and output ports 12a to 12d are provided on the surface 10a of the optical modulator 10. The optical fiber array 70 includes optical fibers 72a to 72d and 74. By aligning the surface 10a of the optical modulator 10 with the surface 70a of the optical fiber array 70, the output ports 12a to 12d face the optical fibers 72a to 72d, and the input port 14 faces the optical fiber 74. Light can be input to the input port 14 using the optical fiber 74. Light emitted from the output ports 12a to 12d via the optical fibers 72a to 72d can be received by the optical power meters 56a to 56d.

[0131] The optical fibers 72a to 72d are large-diameter optical fibers and have a larger diameter than the optical fiber 74. Therefore, the loss of light emitted from the output ports 12a to 12d can be suppressed, and light can be received by the optical fibers 72a to 72d.

[0132] By using the alignment stage 60 to adjust the position of the optical fiber array 70, alignment between the optical fiber 74 and the input port 14 can be performed. In the optical fiber array 70, the relative positions of the optical fibers 72a to 72d with respect to the optical fiber 74 are specified. In the optical modulator 10, the relative positions of the output ports 12a to 12d with respect to the input port 14 are specified. When alignment between the optical fiber 74 and the input port 14 is performed, alignment between the output ports 12a to 12d and the optical fibers 72a to 72d is also performed simultaneously. As a result, the steps are simplified. In the alignment step, it is sufficient to adjust the position of at least one of the optical fiber array 70 and the optical modulator 10. For example, the position of the optical modulator 10 can be adjusted by moving the angle adjustment stage 65.

[0133] The alignment is automatically performed without applying voltage to the electrodes of the light modulator 10 and without adjusting the phase. Figure 4A After the phase of the optical modulator 10 is adjusted by applying voltage to its electrodes (step S18), alignment is also automatically performed (step S22). Since both alignment steps are performed automatically, the time and effort required for alignment are reduced compared to manual alignment.

[0134] The light modulator 10 has multiple output ports, which may be four or more, or four or less. Output ports 12a to 12d are provided on surface 10a, while input port 14 is provided on a surface different from surface 10a. Four optical fibers 72a to 72d are arranged in the optical fiber array 70. Optical fiber 74 is not provided in the optical fiber array 70, but is arranged at a position opposite to input port 14.

[0135] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the specific embodiments involved, and various modifications and changes are possible within the scope of the gist of the present disclosure described in the claims.

Claims

1. A method for measuring optical characteristics of a Mach-Zehnder type optical modulator, wherein the optical modulator comprises an incident portion, a waveguide for transmitting light incident from the incident portion, and a plurality of output portions for emitting the light, wherein: The determination method comprises the following steps: allowing light from a light source to enter an incident portion of the light modulation element via a first optical fiber; A plurality of light receiving units receiving outgoing light emitted from a plurality of outgoing units of the light modulation element; converting the electrical signal output by each of the plurality of light receiving units upon receiving the emitted light into a current, and obtaining a total value by summing the magnitudes of the currents; and performing alignment between the incident portion of the light modulator and the first optical fiber based on the total value, The step of performing core alignment between the incident portion of the light modulator and the first optical fiber comprises the following steps: performing alignment between the incident portion of the light modulator and the first optical fiber without applying a voltage to an electrode provided in a waveguide of the light modulator; and A voltage is applied to an electrode provided in the waveguide of the light modulator to perform alignment between the incident portion of the light modulator and the first optical fiber.

2. The assay method according to claim 1, wherein In the step of performing alignment between the incident portion of the light modulator and the first optical fiber, the alignment is performed so as to maximize the total value.

3. The measuring method according to claim 1 or 2, wherein The incident portion and the plurality of emission portions are provided on one surface of the light modulation element. The measuring method includes the following steps: before the step of causing light from the light source to enter the incident portion, placing an optical fiber array in which the first optical fiber and a plurality of second optical fibers are arranged opposite to the one surface of the light modulating element; The step of the plurality of light receiving units receiving the outgoing light is a step of the plurality of light receiving units receiving the outgoing light via the plurality of second optical fibers.

4. The measuring method according to claim 3, wherein The step of performing alignment between the incident portion of the light modulator and the first optical fiber includes the step of adjusting the position of at least one of the optical fiber array and the light modulator based on the total value.

5. A measuring device for measuring optical characteristics of a Mach-Zehnder type optical modulator, the optical modulator comprising an incident portion, a waveguide for transmitting light incident from the incident portion, and a plurality of output portions for emitting the light, wherein: The measuring device comprises: a first optical fiber for allowing light emitted from a light source to enter an incident portion of the light modulation element; a plurality of light receiving sections configured to output electrical signals when the outgoing light emitted from the plurality of outgoing sections of the light modulating element is incident on the plurality of light receiving sections; a current conversion unit that converts the electrical signal outputted by each of the plurality of light receiving units into a current and obtains a total value by summing the magnitudes of the currents; and a control unit that performs alignment between the incident portion of the light modulator and the first optical fiber based on the total value, The control unit performs centering between the incident part of the optical modulator and the first optical fiber by not applying a voltage to the electrodes arranged in the waveguide of the optical modulator and performing centering between the incident part of the optical modulator and the first optical fiber, and performs centering between the incident part of the optical modulator and the first optical fiber by applying a voltage to the electrodes arranged in the waveguide of the optical modulator.

6. The measuring device according to claim 5, wherein The measuring device includes an optical fiber array in which the first optical fiber and a plurality of second optical fibers are arranged. The outgoing light is incident on the plurality of light receiving parts via the plurality of second optical fibers, The control unit adjusts the position of at least one of the optical fiber array and the light modulation element based on the total value to perform the alignment.

7. The measuring device according to claim 6, wherein The diameter of the second optical fiber is larger than the diameter of the first optical fiber.

8. A recording medium recording a program for measuring optical characteristics of a Mach-Zehnder type optical modulator, the optical modulator comprising an incident portion, a waveguide for transmitting light incident from the incident portion, and a plurality of output portions for emitting the light, wherein: The measurement program causes the computer to execute the following processing: causing light emitted from the light source to enter the incident portion of the light modulator via the first optical fiber; converting an electrical signal outputted by each of the plurality of light receiving units upon receiving light emitted from the plurality of emission units of the light modulating element into a current, and obtaining a total value by summing the magnitudes of the currents; and performing alignment between the incident portion of the light modulator and the first optical fiber based on the total value, The process of performing core alignment between the incident portion of the light modulator and the first optical fiber includes the following processes: performing alignment between the incident portion of the light modulator and the first optical fiber without applying a voltage to an electrode provided in a waveguide of the light modulator; and A voltage is applied to an electrode provided in the waveguide of the light modulator to perform alignment between the incident portion of the light modulator and the first optical fiber.

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