JP5591671B2 - Optical device - Google Patents

Description

  The present invention relates to an optical device.

  In an optical communication device, for example, an optical device including a light emitting element such as an LD (Laser Diode: laser diode) and a Mach-Zehnder modulator may be used. For example, Patent Document 1 discloses a Mach-Zehnder modulator.

JP 2004-102160 A

  When the Mach-Zehnder modulator has one output end, the output light may be scattered. When the Mach-Zehnder modulator and the LD are used as one package, scattered light may cause malfunction of the LD. A Mach-Zehnder modulator having two output ends may be employed to suppress malfunction of the LD due to scattered light. However, when two output terminals are formed in the Mach-Zehnder modulator, it may be difficult to reduce the size of the Mach-Zehnder modulator. This makes it difficult to reduce the size of the optical device. In view of the above problems, an object of the present invention is to provide an optical device that can be miniaturized and can obtain good characteristics.

  The present invention provides a Mach-Zehnder modulator having an output-side MMI in which a first output optical waveguide and a second output optical waveguide are connected, first output light output from the first output optical waveguide, and second An optical isolator provided by optical coupling with both of the second output light output from the output optical waveguide, and optically coupled with the first output light via the optical isolator, and not optically coupled with the second output light. And an optical fiber. ADVANTAGE OF THE INVENTION According to this invention, the optical apparatus which can be reduced in size and can acquire a favorable characteristic can be provided.

  In the above-described configuration, the Mach-Zehnder modulator may be housed in a package, and the optical isolator and the optical fiber may be connected to an outer wall of the package. According to this configuration, good characteristics can be obtained effectively.

  In the above configuration, the package may include a light emitting element that is optically coupled to the Mach-Zehnder modulator. According to this configuration, good characteristics can be obtained more effectively, and the optical device can be miniaturized.

  In the above-described configuration, a configuration is provided that includes a first lens that is provided between the first output optical waveguide and the second output optical waveguide and the optical isolator and transmits the first output light and the second output light. It can be.

  The said structure WHEREIN: It can be set as the structure which comprises the 2nd lens which is provided between the said optical isolator and the said optical fiber, and the said 1st output light and the said 2nd output light permeate | transmit.

  In the above configuration, after the second output light passes through the optical isolator, it enters the optical isolator again, and the light intensity returning to the input side of the optical isolator is the light intensity at the output end of the second output optical waveguide. It can be set as the structure which is 1/100 or less of intensity | strength. According to this configuration, good characteristics can be obtained effectively.

  ADVANTAGE OF THE INVENTION According to this invention, the optical apparatus which can be reduced in size and can acquire a favorable characteristic can be provided.

1 is a plan view illustrating an optical device according to Comparative Example 1. FIG. FIG. 2A to FIG. 2C are explanatory diagrams of a Mach-Zehnder modulator. FIG. 3 is a plan view illustrating a Mach-Zehnder modulator included in the optical device according to Comparative Example 2. FIG. 4A is a plan view illustrating an optical device according to the first embodiment. FIG. 4B is an enlarged view of the vicinity of the Mach-Zehnder modulator in FIG. FIG. 5A and FIG. 5B are schematic views illustrating the optical isolator provided in the optical device according to the first embodiment. FIG. 6A and FIG. 6B are plan views illustrating the method for manufacturing the optical device according to the first embodiment. FIG. 7A is a plan view illustrating an optical device according to the second embodiment. FIG. 7B is an enlarged view of the vicinity of the Mach-Zehnder modulator in FIG.

  A configuration of an optical device using the Mach-Zehnder modulator will be described. 1 is a plan view illustrating an optical device according to Comparative Example 1. FIG.

  As shown in FIG. 1, the optical device 100 according to Comparative Example 1 includes an LD unit 30, a modulator unit 50, a high-frequency wiring board 56, and a package 70. The package 70 is provided with an optical fiber fixing portion 66, ceramic terminals 72a and 72b, and a window lens 74. The high frequency wiring board 56 has, for example, a plurality of strip lines. An optical fiber 64 is inserted into the optical fiber fixing portion 66 so as to face the window lens 74. A second output lens 62 is provided between the window lens 74 and the optical fiber 64. The ceramic terminal 72a and the ceramic terminal 72b are provided along the opposite sides of the package 70. The ceramic terminal 72 a includes a phase adjustment electrode 76. The ceramic terminal 72 b includes a phase adjustment electrode 76 and a modulation strip line 78. The phase adjustment electrode 76 and the modulation strip line 78 are external connection electrodes that can be connected to an electronic device outside the optical device 100.

  The LD unit 30 includes an LD 32 (light emitting element), an LD lens 33, an optical isolator 34, an LD carrier 36, an LD carrier mount 38, and a TEC (Thermoelectric Cooler) 39. The TEC 39 is mounted on the upper surface of the package 70. The LD carrier mount 38 is mounted on the upper surface of the TEC 39. The LD lens 33, the optical isolator 34, and the LD carrier 36 are mounted on the upper surface of the LD carrier mount 38. The LD 32 is mounted on the upper surface of the LD carrier 36. The LD lens 33 and the optical isolator 34 are disposed between the LD 32 and the modulator unit 50.

  The modulator unit 50 includes a Mach-Zehnder modulator 10, beam splitters 40a and 40b, PDs (Photo Diodes) 42a and 42b, an etalon 44, an input lens 46, a first output lens 48, a modulator carrier 52, and a modulator carrier. A mount 53 and a TEC 54 are provided. The TEC 54 is mounted on the upper surface of the package 70. The modulator carrier mount 53 is mounted on the upper surface of the TEC 54. Beam splitters 40 a and 40 b, PDs 42 a and 42 b, etalon 44, input lens 46, first output lens 48, and modulator carrier 52 are mounted on the upper surface of modulator carrier mount 53. The Mach-Zehnder modulator 10 is mounted on the upper surface of the modulator carrier 52. The beam splitters 40 a and 40 b and the input lens 46 are disposed between the LD unit 30 and the Mach-Zehnder modulator 10. The first output lens 48 is disposed between the Mach-Zehnder modulator 10 and the window lens 74. As described above, the first output lens 48, the window lens 74, and the second output lens 62 are arranged between the Mach-Zehnder modulator 10 and the optical fiber 64 in order from the side closer to the Mach-Zehnder modulator 10. The high-frequency wiring board 56 is mounted on the upper surface of the package 70 and the upper surface of the modulator carrier mount 53. The modulator carrier 52 is provided with a phase adjustment wiring 51 and a modulation strip line 55.

  The phase adjustment electrode 16 (described later in FIG. 2A) of the Mach-Zehnder modulator 10 is connected to the phase adjustment wiring 51 by a wire 41. The phase adjustment wiring 51 is connected to the phase adjustment electrode 76 provided on the package 70 by the wire 41. The modulation electrode 17 (described later in FIG. 2A) of the Mach-Zehnder modulator 10 is connected to the modulation strip line 55 by a wire 41. The modulation strip line 55 is connected to the strip line of the high-frequency wiring board 56 by the wire 41. The strip line of the high-frequency wiring board 56 is connected to the modulation strip line 78 provided in the package 70 by the wire 41. The package 70 is made of an insulator such as ceramic. The LD carrier 36 and the modulator carrier 52 are made of ceramic such as aluminum nitride (AlN). The LD carrier mount 38 and the modulator carrier mount 53 are made of metal such as Kovar (KOVAR), for example. The LD lens 33, the input lens 46, the first output lens 48, the second output lens 62, and the window lens 74 are made of, for example, glass or plastic. The first output lens 48 and the second output lens 62 are, for example, aspheric lenses. Each wire 41 is made of a metal such as aluminum (Al) or gold (Au). The phase adjustment electrodes 16 and 76, the modulation electrode 17, the phase adjustment wiring 51, and the modulation strip lines 55 and 78 are made of metal such as gold (Au), for example.

  The operation of the optical device 100 will be described. The configuration and operation of the Mach-Zehnder modulator 10 will be described in detail with reference to FIGS. 2 (a) to 2 (c). The LD 32 is a type of LD that adjusts the wavelength of output light, for example, by changing the temperature of the LD. The TEC 39 adjusts the temperature of the LD 32. As a result, the wavelength of the output light of the LD 32 can be adjusted. The TEC 54 can maintain the temperature of the Mach-Zehnder modulator 10 at a certain constant temperature. The LD 32 and the Mach-Zehnder modulator 10 operate at different temperatures. Therefore, it is preferable that the temperature of the LD 32 and the Mach-Zehnder modulator 10 is adjusted independently. For this reason, it is preferable to use separate parts for the TEC 39 on which the LD 32 is mounted and the TEC 54 on which the Mach-Zehnder modulator 10 is mounted. The LD carrier mount 38 on which the LD 32 is mounted and the modulator carrier mount 53 on which the Mach-Zehnder modulator 10 is mounted are preferably separate parts. In other words, the LD unit 30 and the modulator unit 50 are preferably separate parts. The TECs 39 and 54 are made of Peltier elements, for example.

  The output light of the LD 32 passes through the LD lens 33 and the optical isolator 34 and is input to the beam splitter 40a. The beam splitter 40a branches the input light. One of the branched lights is input to the PD 42a, and the other light is input to the beam splitter 40b. The PD 42a detects the light intensity of the input light. The beam splitter 40b branches the input light. One of the branched lights is input to the etalon 44 and the other is input to the input lens 46. The etalon 44 transmits light having a specific wavelength among the input light. The PD 42 b detects the light intensity of the light transmitted through the etalon 44. By comparing the light intensity of the light detected by the PD 42a with the light intensity of the light detected by the PD 42b, the output wavelength (the wavelength of the output light) of the LD 32 can be detected. Based on the detection result, the output wavelength of the LD 32 can be feedback-controlled.

  The light transmitted through the beam splitter 40b is converged by the input lens 46 and input to one of the first input terminal 21a or the second input terminal 21b (described later in FIG. 2A) provided in the Mach-Zehnder modulator 10. A voltage for phase adjustment is applied to the Mach-Zehnder modulator 10 from, for example, an external electronic device via the phase adjustment electrode 76, the phase adjustment wiring 51, and the wire 41. Further, a voltage for modulation is applied to the Mach-Zehnder modulator 10 from, for example, an external electronic device via the modulation stripline 78, the stripline of the high-frequency wiring board 56, the modulation stripline 55, and the wire 41. Is done. The voltage for modulation is, for example, an RF (Radio Frequency) signal. From the Mach-Zehnder modulator 10, the light input from the LD 32 and modulated is output to the first output lens 48. The TEC 54 cools the Mach-Zehnder modulator 10. The light modulated by the Mach-Zehnder modulator 10 enters the first output lens 48. The first output lens 48 is a collimator lens, for example, and generates parallel light. The light that has passed through the first output lens 48 passes through the window lens 74 and the second output lens 62. The light is converged by the second output lens 62, input to the optical fiber 64, and output to the outside of the optical device 100 through the optical fiber 64. Thus, the optical device 100 functions as a light emitting device. Next, the Mach-Zehnder modulator 10 will be described in detail.

  FIG. 2A to FIG. 2C are explanatory diagrams of the Mach-Zehnder modulator 10. The Mach-Zehnder modulator 10 is a modulator configured by combining paths of mesa-shaped optical waveguides on a semiconductor substrate. FIG. 2A is a top view of the Mach-Zehnder modulator 10. FIG. 2B is a cross-sectional view taken along line AA in FIG. FIG. 2C is a cross-sectional view taken along line BB in FIG. In FIG. 2A, the light passage route is drawn with a dotted line.

  Referring to FIG. 2B, the optical waveguide is formed on the semiconductor substrate 11. The optical waveguide has a structure in which a lower cladding layer 12a, a core 13, and an upper cladding layer 12b are stacked in this order on a semiconductor substrate 11. A passivation film 14 and an insulating film 15 are sequentially stacked on the upper surface of the semiconductor substrate 11 and the upper surface and side surfaces of the optical waveguide.

  The semiconductor substrate 11 is made of a semiconductor such as InP. The lower cladding layer 12a and the upper cladding layer 12b are made of a semiconductor such as InP. The core 13 is made of a semiconductor having a smaller band gap energy than the lower cladding layer 12a and the upper cladding layer 12b, and is made of, for example, InGaAsP. Thereby, light passing through the core 13 is trapped by the lower cladding layer 12a and the upper cladding layer 12b. The passivation film 14 is made of a semiconductor such as InP. The insulating film 15 is made of an insulator such as SiN.

  Referring to FIG. 2A, the Mach-Zehnder modulator 10 is provided with a first input optical waveguide 22a connected to the first input end 21a, and a second input optical waveguide connected to the second input end 21b. 22b is provided. The first input optical waveguide 22a and the second input optical waveguide 22b join at a first MMI (Multi Mode Interference) 23 and branch to the first optical waveguide 24a and the second optical waveguide 24b. When the longitudinal direction of the Mach-Zehnder modulator 10 is the axis of symmetry, the first optical waveguide 24a is arranged on the same side as the first input end 21a, and the second optical waveguide 24b is arranged on the same side as the second input end 21b. ing.

  The first optical waveguide 24a and the second optical waveguide 24b merge at the second MMI 25, and the first output optical waveguide 26a connected to the first output end 27a and the second output optical waveguide 26b connected to the second output end 27b. Branch to. When the longitudinal direction of the Mach-Zehnder modulator 10 is the axis of symmetry, the first output end 27a is disposed on the same side as the second optical waveguide 24b, and the second output end 27b is disposed on the same side as the first optical waveguide 24a. ing. A difference is provided in advance between the optical path length of the first optical waveguide 24a and the optical path length of the second optical waveguide 24b. For example, the optical path length difference is set such that a phase difference of −0.5π is generated between the light propagating through the first optical waveguide 24a and the light propagating through the second optical waveguide 24b.

  Each of the first optical waveguide 24a and the second optical waveguide 24b is provided with a phase adjustment electrode 16 and a modulation electrode 17. The phase adjustment electrode 16 and the modulation electrode 17 are separated from each other. The positional relationship between the phase adjustment electrode 16 and the modulation electrode 17 is not particularly limited, but in the present embodiment, the phase adjustment electrode 16 is disposed closer to the light input end than the modulation electrode 17. . A light intensity detection electrode 18 is provided in each of the first output optical waveguide 26a and the second output optical waveguide 26b.

  Referring to FIG. 2C, the modulation electrode 17 is disposed on the upper cladding layer 12b via the contact layer 19. The contact layer 19 is made of a semiconductor such as InGaAs. Note that the passivation film 14 and the insulating film 15 are not provided between the upper cladding layer 12 b and the contact layer 19. The phase adjustment electrode 16, the modulation electrode 17 and the light intensity detection electrode 18 are made of a metal such as Au.

  When a voltage is applied to each modulation electrode 17, the refractive index of the core 13 changes in the first optical waveguide 24a and the second optical waveguide 24b, and the light passing through the first optical waveguide 24a and the second optical waveguide 24b changes. The phase changes. In this embodiment, each modulation electrode 17 receives a modulation signal in which a high signal and a low signal are alternately superimposed on a predetermined DC bias voltage. The modulation signals input to the respective modulation electrodes 17 have a phase relationship with each other. That is, when a high signal is input to the modulation electrode 17 of the first optical waveguide 24a, a low signal is input to the modulation electrode 17 of the second optical waveguide 24b, and the modulation electrode 17 of the first optical waveguide 24a is input. When a low signal is input to the high-frequency signal, a high signal is input to the modulation electrode 17 of the second optical waveguide 24b. In this case, a difference occurs in the refractive index of each optical waveguide. Therefore, a phase difference occurs between the light that has passed through the first optical waveguide 24a and the light that has passed through the second optical waveguide 24b.

  Depending on the phase difference between the light that has passed through the first optical waveguide 24a and the light that has passed through the second optical waveguide 24b, the output end from which light is output is between the first output end 27a and the second output end 27b. Switch. Specifically, when the difference between the phase of the light passing through the first optical waveguide 24a and the phase of the light passing through the second optical waveguide 24b becomes “−π”, light is output from the first output end 27a. When the phase difference becomes “0”, light is output from the second output end 27b. In the present embodiment, the output signal of the first output end 27a is used as modulated light.

  A DC voltage for adjusting the phase difference between the light that has passed through the first optical waveguide 24a and the light that has passed through the second optical waveguide 24b is applied to each phase adjustment electrode 16. For example, when a high signal is input to the modulation electrode 17 of the first optical waveguide 24a and a low signal is input to the modulation electrode 17 of the second optical waveguide 24b, the phase difference is adjusted to “−π”. When the low signal is input to the modulation electrode 17 of the first optical waveguide 24a and the high signal is input to the modulation electrode 17 of the second optical waveguide 24b, the phase difference is adjusted to “0”. A DC voltage is applied to each phase adjustment electrode 16.

  The light intensity of the output signal at each output end can be detected based on the electrical signal detected by each light intensity detection electrode 18. Here, when the phase difference between the light that has passed through the first optical waveguide 24a and the light that has passed through the second optical waveguide 24b changes in accordance with “0” or “π”, the first output end 27a The light intensity of the output light and the light intensity of the light output from the second output end 27b substantially coincide with each other with a predetermined time width. Accordingly, the voltage applied to each phase adjustment electrode 16 is feedback-controlled so that the light intensities detected by each light intensity detection electrode 18 coincide with each other, so that the light passing through the first optical waveguide 24a and the second light guide The phase difference with the light that has passed through the waveguide 24b can be matched with “0” and “π”.

  As shown in FIG. 2A, the Mach-Zehnder modulator 10 has a first output end 27a and a second output end 27b. Of the two output ends, one output end is optically coupled to the optical fiber 64 shown in FIG. Here, for example, the first output end 27a is optically coupled. In other words, the first output light output from the first output end 27 a is input to the optical fiber 64. The second output light output from the second output end 27b that is not optically coupled to the optical fiber 64 is reflected by, for example, the inner wall of the package 70 and becomes reflected light. The reflected light becomes stray light in the package 70. When the reflected light reaches, for example, the first output end 27a, the LD 32, and the PDs 42a and 42b, the characteristics of the optical device 100 may deteriorate. Optical devices are required to suppress deterioration of characteristics due to reflected light.

  Comparative Example 2 is an example in which the configuration of the Mach-Zehnder modulator is changed. The optical device according to Comparative Example 2 has the same configuration as that shown in FIG. 1 except for the Mach-Zehnder modulator. FIG. 3 is a plan view illustrating a Mach-Zehnder modulator included in the optical device according to Comparative Example 2. FIG. 3 is a schematic diagram, and the phase adjustment electrode 16, the modulation electrode 17, and the light intensity detection electrode 18 are omitted. The description of the same configuration as that already described in FIGS. 2A to 2C is omitted.

  As shown in FIG. 3, the first output end 27a is provided on the surface 10A of the Mach-Zehnder modulator 10a facing the optical fiber 64 (see FIG. 1). The second output end 27b is provided on a surface 10B different from the surface 10A. Compared to the case of FIG. 2A, the distance from the second MMI 25 to the first output end 27a is large. The second output optical waveguide 26b connected to the second output end 27b is bent toward the surface 10B. With such a configuration, most of the second output light of the Mach-Zehnder modulator 10 is absorbed. Accordingly, generation of reflected light and deterioration of characteristics due to the reflected light are suppressed. However, in the configuration of FIG. 3, since the Mach-Zehnder modulator 10 is increased in size, it is difficult to reduce the size of the optical device. In addition, some of the second output light of the Mach-Zehnder modulator 10 may not be absorbed by the second output optical waveguide 26b and may leak from the second output end 27b. For this reason, generation | occurence | production of reflected light and the characteristic deterioration by reflected light will occur. Next, Example 1 will be described.

  In the first embodiment, an optical isolator is provided. FIG. 4A is a plan view illustrating an optical device according to the first embodiment. FIG. 4B is an enlarged view of the vicinity of the Mach-Zehnder modulator in FIG. 4A, and the window lens 74, the package 70, and the like are omitted. The description of the configuration already described in FIGS. 1 to 2C is omitted.

  As shown in FIG. 4A and FIG. 4B, the optical device 100a according to the first embodiment is in the optical fiber fixing portion 66 and between the window lens 74 and the second output lens 62. An optical isolator 60 is provided. In other words, the optical isolator 60 is provided between the Mach-Zehnder modulator 10 b and the optical fiber 64. As shown in FIG. 4B, the first output end 27a and the second output end 27b are provided on the surface 10A of the Mach-Zehnder modulator 10b so as to be separated from each other. The optical isolator 60 faces the first output end 27a and the second output end 27b. The distance L1 between the output ends is, for example, 0.04 mm. A distance L2 between the Mach-Zehnder modulator 10b and the first output lens 48 is, for example, 0.2 mm. A distance L3 between the first output lens 48 and the optical isolator 60 is, for example, 3.5 mm. A distance L4 between the first output lens 48 and the second output lens 62 is, for example, 5 mm. The diameter of the core of the optical fiber 64 is, for example, 0.125 mm. Since the first output end 27a and the second output end 27b are provided on the same surface 10A, both the first output light and the second output light are output in the right direction in the figure. As shown by a solid arrow in FIG. 4A, the first output light output from the first output end 27 a is input to the optical fiber 64. As indicated by the broken arrow, the second output light output from the second output end 27 b is not input to the optical fiber 64 but is reflected by, for example, the inner wall of the optical fiber fixing portion 66. This will be described in detail with reference to FIG.

  As shown in FIG. 4B, the first output light indicated by a solid line in the drawing passes through the first output lens 48 and then goes straight in the direction of the optical fiber 64 (right direction in the drawing). It passes through the isolator 60. The optical axis of the first output light coincides with the center of the core of the optical fiber 64. For this reason, the first output light is converged by the second output lens 62 and input to the optical fiber 64. On the other hand, the second output light indicated by a broken line in the figure passes through the first output lens 48, the optical isolator 60, and the second output lens 62, and reaches, for example, the inner wall of the optical fiber fixing portion 66. The distance L5 between the location where the second output light reaches and the optical fiber 64 is, for example, 0.215 mm. The second output light is reflected by the inner wall of the optical fiber fixing portion 66 and becomes reflected light indicated by a left arrow in the drawing. The reflected light passes through the second output lens 62 and enters the optical isolator 60. In the optical isolator 60, the reflected light is blocked or greatly attenuated. The mechanism for attenuating the reflected light will be described in more detail.

  FIGS. 5A and 5B are schematic views showing the principle of the optical isolator. As indicated by solid arrows, the polarization direction of light is 0 ° in the vertical direction, 90 ° in the horizontal direction, and 45 ° in the diagonal direction. The thickness direction is the left-right direction in the figure.

  As illustrated in FIG. 5A, the optical isolator 60 includes polarizing plates 80 and 84 and a Faraday rotator 82. In the figure, solid line blocks indicate polarizing plates 80 and 84, broken line blocks indicate a Faraday rotator 82, and block arrows indicate light. Each of the polarizing plates 80 and 84 is made of glass, for example. The Faraday rotator 82 is made of, for example, garnet. Each of the polarizing plates 80 and 84 transmits light polarized in a specific direction and blocks light polarized in a direction other than the direction. A solid line arrow in each of the polarizing plates 80 and 84 indicates a polarization direction of light transmitted by the polarizing plate. The polarizing plate 80 transmits light polarized at 0 °. The polarizing plate 84 transmits light polarized at 45 °. The Faraday rotator 82 rotates the polarization direction of light. The solid line arrow in the Faraday rotator 82 indicates the angle of the polarization direction of the light rotated by the Faraday rotator 82. The Faraday rotator 82 rotates the polarization direction of the light incident on the Faraday rotator 82 by, for example, 45 °. The solid arrow in the block arrow indicates the polarization direction of light.

  The incident light I in FIG. 5A corresponds to the first output light or the second output light shown in FIGS. 4A and 4B, and is, for example, 0 ° before entering the optical isolator 60. It is polarized. The polarization direction of the incident light I coincides with the polarization direction of the light that the polarizing plate 80 passes. Accordingly, the incident light I passes through the polarizing plate 80. The polarization direction of the incident light I is rotated by the Faraday rotator 82 to be 45 °. The polarization direction of the incident light I transmitted through the Faraday rotator 82 and the polarization direction of the light transmitted through the polarizing plate 84 coincide with each other. Accordingly, the incident light I passes through the polarizing plate 84. As described above, the first output light and the second output light shown in FIGS. 4A and 4B pass through the optical isolator 60. Next, the reflected light R will be described.

  As shown in FIG. 5B, the polarization direction of the reflected light R is 45 °. This is because the incident light I that is transmitted through the optical isolator 60 and polarized at 45 ° is reflected to become reflected light R. The polarization direction of the reflected light R and the polarization direction of the light transmitted by the polarizing plate 80 are the same. Accordingly, the reflected light R passes through the polarizing plate 84. The polarization direction of the reflected light R is rotated by the Faraday rotator 82 and becomes 90 °. The polarization direction of the reflected light R transmitted through the Faraday rotator 82 does not match the polarization direction of the light transmitted through the polarizing plate 80. Therefore, all or most of the reflected light R is blocked by the polarizing plate 80 and is absorbed by the polarizing plate 80 as heat, for example. Thus, the reflected light R is blocked or greatly attenuated in the optical isolator 60. The light intensity of the reflected light R transmitted through the optical isolator 60 is, for example, 1/100 or less of the light intensity of the incident light I. This means that the light intensity of the reflected light of the second output light in FIGS. 4A and 4B is attenuated to about 1/100 of the light intensity of the second output light.

  Next, a method for manufacturing the optical device 100a according to the first embodiment will be described. FIG. 6A and FIG. 6B are plan views illustrating the method for manufacturing the optical device according to the first embodiment.

  As shown in FIG. 6A, the TEC 39 and the TEC 54 are mounted on the package 70. The LD 32 is mounted on the LD carrier 36. After mounting the LD 32, the LD lens 33, the optical isolator 34, and the LD carrier 36 are mounted on the LD carrier mount 38 so that the output light of the LD 32 is input. The LD carrier mount 38 is mounted on the TEC39. Next, the Mach-Zehnder modulator 10 b is mounted on the modulator carrier 52. A modulator carrier 52 on which the Mach-Zehnder modulator 10b is mounted and PDs 42a and 42b are mounted on the modulator carrier mount 53. A modulator carrier mount 53 is mounted on the TEC 54. Further, the beam splitter 40a is mounted on the modulator carrier mount 53 so that the light transmitted through the optical isolator 34 is input and the branched light is input to the PD 42a. The beam splitter 40b is mounted on the modulator carrier mount 53 so that the light output from the beam splitter 40a is input. The input lens 46 is mounted on the modulator carrier mount 53 so that the light output from the beam splitter 40b is input. After mounting the input lens 46, the first output lens 48 is mounted on the modulator carrier mount 53 so that the light output from the Mach-Zehnder modulator 10b is input. A wavelength meter (not shown) is provided outside the package 70, and the etalon 44 is mounted on the modulator carrier mount 53 while detecting the wavelength output from the first output lens 48 with the wavelength meter. The TEC 39 and the TEC 54 are fixed to the package 70 by a brazing material such as SuAgCu (bell silver copper). As a result, the Mach-Zehnder modulator 10 b is mounted on the package 70.

  A metallized pattern made of a metal such as gold is formed on the ceramic terminals 72a and 72b of the package 70, for example. Thereby, the phase adjusting electrode 76 and the modulation strip line 78 are formed. Further, the phase adjustment electrode 16 provided in the Mach-Zehnder modulator 10 and the phase adjustment wiring 51 are wire-bonded. The phase adjustment wiring 51 and the phase adjustment electrode 76 provided in the package 70 are wire-bonded. As a result of the wire bonding, the phase adjustment electrode 16 and the phase adjustment electrode 76 are connected via the wire 41 and the phase adjustment wiring 51. Further, the modulation electrode 17 included in the Mach-Zehnder modulator 10 and the modulation strip line 55 of the modulator carrier 52 are wire-bonded. The modulation strip line 55 and the strip line of the high-frequency wiring board 56 are wire-bonded. The strip line of the high-frequency wiring board 56 and the modulation strip line 78 formed on the ceramic terminals 72a and 72b of the package 70 are wire-bonded. As a result of the wire bonding, the modulation electrode 17 and the modulation strip line 78 are connected via the wire 41, the modulation strip line 55, and the strip line of the high-frequency wiring board 56.

  As shown in FIG. 6B, a window lens 74 and an optical fiber fixing portion 66 are provided in the package 70 of FIG. An optical isolator 60 and a second output lens 62 are mounted on the optical fiber fixing portion 66, and an optical fiber 64 is connected thereto. That is, the optical fiber fixing part 66 on which the optical isolator 60 and the optical fiber 64 are mounted is provided in the package 70. In other words, the optical isolator 60 and the optical fiber 64 are connected to the outer wall of the package 70. At this time, a voltage is applied to the phase adjustment electrode 76 and the modulation strip line 78 so that output light is output from a desired output terminal (the first output terminal 27a in the first embodiment). For example, alignment can be performed by providing the optical fiber fixing portion 66 while detecting the output light of the Mach-Zehnder modulator 10 via the optical fiber 64. The optical isolator 60 is provided so that the first output light is incident thereon. Through the above steps, the optical device 100a according to the first embodiment is completed.

  According to the first embodiment, the optical device 100a includes both the Mach-Zehnder modulator 10b, the first output light output from the first output optical waveguide 26a, and the second output light output from the second output optical waveguide 26b. And an optical isolator 60 that is optically coupled to the first output light via the optical isolator 60 and an optical fiber 64 that is not optically coupled to the second output light. While the first output end 27a of the Mach-Zehnder modulator 10b and the optical fiber 64 are optically coupled, the second output end 27b is not optically coupled to the optical fiber 64. The second output light becomes reflected light reflected by the inner wall of the optical fiber fixing portion 66, and the reflected light is absorbed by the optical isolator 60. As a result, the reflected light is suppressed from reaching the LD 32, PDs 42a and 42b, the first output end 27a, and the like. Therefore, the optical device 100a capable of obtaining good characteristics is realized. The first output end 27a and the second output end 27b are provided on the same surface 10A, and the second output light may be emitted without being absorbed by the Mach-Zehnder modulator 10b. Therefore, it is not necessary to increase the size of the Mach-Zehnder modulator 10b as in the second comparative example. As a result, the optical device 100a can be reduced in size and good characteristics can be obtained.

  In particular, the Mach-Zehnder modulator 10 and the LD 32 are mounted on the same package 70. In this case, the reflected light that has become stray light in the package 70 may reach the LD 32. According to the first embodiment, since the optical isolator 60 absorbs reflected light, the reflected light is suppressed from becoming stray light. Therefore, it is possible to obtain good characteristics more effectively. Further, by mounting the Mach-Zehnder modulator 10 and the LD 32 in the same package 70, the optical device 100a can be reduced in size.

  By adjusting the materials and configurations of the polarizing plates 80 and 84, the magnitude of light blocked by the polarizing plates 80 and 84 can be changed. Further, the angle of rotation by the Faraday rotator 82 may vary depending on the wavelength of light, the temperature of the environment in which the optical isolator 60 is placed, and the like. When the angle changes, the polarization direction of the reflected light R changes, and the magnitude of the light blocked by the polarizing plate 80 also changes. If the reflected light that passes through the polarizing plate 80 becomes large, the possibility that the characteristics of the optical device 100 deteriorate will increase. In order to effectively improve the characteristics of the optical device 100, for example, the light intensity of the reflected light R transmitted through the polarizing plate 80 is preferably 1/100 or less of the light intensity of the incident light I. Furthermore, it is preferable to make the light intensity of the reflected light R smaller, for example, 1/1000 of the light intensity of the incident light I. In other words, after the second output light is transmitted through the optical isolator 60, the light intensity that reenters the optical isolator 60 and returns to the input side of the optical isolator 60 is the light intensity at the second output end 27b of the second output optical waveguide 26b. The strength is preferably 1/100 or less, and more preferably 1/1000 or less. Further, although the optical isolator 60 includes the two polarizing plates 80 and 84 and the one Faraday rotator 82, the configuration is not limited thereto. For example, the optical isolator 60 may further include two polarizing plates and one Faraday rotator in addition to the polarizing plates 80 and 84 and the Faraday rotator 82. Thereby, the reflected light R can be attenuated more greatly.

  The Faraday rotator 82 shown in FIGS. 5A and 5B rotates the polarization direction of light by 45 °, but the rotation angle is not limited to 45 °. For example, the angle that the Faraday rotator 82 rotates may be 30 °, 40 °, or the like. However, since the angle at which the Faraday rotator 82 is rotated is 45 °, the difference between the polarization direction of the reflected light R transmitted through the Faraday rotator 82 and the polarization direction transmitted through the polarizing plate 80 is 90 °. Thus, the greater the difference in polarization direction, the more effectively the polarizing plate 80 blocks light. Therefore, the Faraday rotator 82 preferably rotates the polarization direction of light by 45 °.

  The distance shown in FIG. 4B can be changed. For example, if L4 is 3 mm, L5 is 0.212 mm. As described above, even when the distance is changed, the first output light may not be input to the optical fiber 64 and the second output light may not be input to the optical fiber 64. As described with reference to FIG. 4B, the optical axis of the first output light and the center of the core of the optical fiber 64 coincide with each other, but may be shifted by, for example, about 0.01 mm.

  Example 2 is an example in which the number of lenses is changed. FIG. 7A is a plan view illustrating an optical device according to the second embodiment. FIG. 7B is an enlarged view of the vicinity of the Mach-Zehnder modulator of FIG. 7A, and the configuration described above with reference to FIGS. 1 to 2C, FIG. 4A, and FIG. Description is omitted.

  As shown in FIG. 7A, the optical device 200 according to the second embodiment has the same configuration as the optical device 100a according to the first embodiment, except that the second output lens 62 is not provided. As shown in FIG. 7B, the first output light indicated by the solid line in the drawing is converged by the first output lens 48, passes through the window lens 74 and the optical isolator 60, and is input to the optical fiber 64. . On the other hand, the second output light indicated by the broken line in the drawing passes through the first output lens 48 and then proceeds in the lower right direction in the drawing. The second output light passes through the window lens 74 and the optical isolator 60 and is reflected by, for example, the inner wall of the optical fiber fixing portion 66. The reflected light enters the optical isolator 60 and is greatly attenuated in the optical isolator 60. Since the manufacturing method of the optical device 200 according to the second embodiment is the same as that shown in FIGS. 6A and 6B except that the second output lens 62 is not mounted, the description thereof is omitted. . According to the second embodiment, as in the first embodiment, it is possible to provide the optical device 200 that can be downsized and can obtain good characteristics.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Mach-Zehnder modulator 10, 10a, 10b
Surface 10A, 10B
Semiconductor substrate 11
Phase adjustment electrode 16, 76
Modulation electrode 17
First input terminal 21a
Second input terminal 21b
1st MMI 23
Second MMI 25
First output optical waveguide 26a
Second output optical waveguide 26b
First output end 27a
Second output terminal 27b
LD 32
LD lens 33
Wire 41
Input lens 46
First output lens 48
High frequency wiring board 56
Optical isolator 60
Second output lens 62
Optical fiber 64
Package 70
Polarizing plate 80, 84
Faraday rotator 82
Optical device 100, 100a, 200

Claims (6)

A Mach-Zehnder modulator having an output-side MMI connected to the first output optical waveguide and the second output optical waveguide;
An optical isolator provided in optical coupling with both the first output light output from the first output optical waveguide and the second output light output from the second output optical waveguide;
An optical device comprising: an optical fiber that is optically coupled to the first output light via the optical isolator and is not optically coupled to the second output light. The Mach-Zehnder modulator is housed in a package;
The optical apparatus according to claim 1, wherein the optical isolator and the optical fiber are connected to an outer wall of the package. 3. The optical device according to claim 2 , wherein a light emitting element optically coupled to the Mach-Zehnder modulator is mounted on the package.   A first lens is provided between the first output optical waveguide, the second output optical waveguide, and the optical isolator, and transmits the first output light and the second output light. The optical device according to any one of claims 1 to 3.   The optical apparatus according to claim 4, further comprising a second lens that is provided between the optical isolator and the optical fiber and transmits the first output light and the second output light. After the second output light passes through the optical isolator, it enters the optical isolator again, and the light intensity returning to the input side of the optical isolator is 100 minutes of the light intensity at the output end of the second output optical waveguide. The optical device according to claim 1, wherein the optical device is 1 or less.

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