Electro-absorption modulator and integrated laser modulator element

Abstract

This invention provides an electric field absorption modulator that reduces parasitic capacitance and exhibits high high-frequency characteristics. The electric field absorption modulator includes a substrate, a first cladding layer, a light-absorbing layer, a second cladding layer, and a contact layer of a first conductivity type. The substrate is semi-insulating or insulating. The light-absorbing layer is disposed on the first cladding layer. The second cladding layer is disposed on the light-absorbing layer. The contact layer includes a portion of the first cladding layer or is disposed between the substrate and the first cladding layer. The first cladding layer, the light-absorbing layer, and the second cladding layer form a mesa structure extending in the direction of the optical waveguide. The contact layer includes: a first region including a region located between the mesa structure and the substrate; and a second region exposed from the first cladding layer for electrical connection. The contact layer is partially removed from the substrate. The first region and the second region are sandwiched between the regions where the contact layer has been removed.

Description

Technical Field

[0001] This invention relates to optical modulators and optical modulator-integrated laser elements. Background Technology

[0002] Patent document 1 discloses an electric field absorption modulator. This electric field absorption modulator has an n-electrode and a p-electrode. A positive-phase signal and an inverted signal constituting a differential signal are respectively input to the n-electrode and the p-electrode.

[0003] Existing technical documents Patent documents Patent document 1: Japanese Patent Application Publication No. 2002-277840. Summary of the Invention

[0004] The problem that the invention aims to solve In the case of differential driving of an electric field absorption modulator, electrical connection becomes easy if electrode pads connected to the n-electrode and electrode pads connected to the p-electrode are provided on the upper surface of the optical modulator. Therefore, for example, consider forming a lower cladding layer, a light-absorbing layer, and an upper cladding layer on an insulating or semi-insulating substrate, and providing a contact layer between the lower cladding layer and the substrate. In one example, the contact layer and the lower cladding layer are n-type, and the upper cladding layer is p-type. In another example, the contact layer and the lower cladding layer are p-type, and the upper cladding layer is n-type. Then, the contact layer is exposed from the lower cladding layer for electrical connection. A positive-phase signal and an inverted signal constituting the differential signal are input to the contact layer and the upper cladding layer, respectively.

[0005] However, in some structures, the optical modulator is mounted on a substrate with a reference potential (ground potential). In such structures, parasitic capacitance is generated between the contact layer and the substrate. Due to this parasitic capacitance, there is a risk of damage to the high-frequency characteristics of the optical modulator.

[0006] The purpose of this invention is to provide an electric field absorption modulator and an optical modulator integrated laser element that can reduce parasitic capacitance and improve high-frequency characteristics.

[0007] means for solving problems An embodiment of the present invention relates to an electric field absorption modulator comprising a substrate, a first cladding layer, a light-absorbing layer, a second cladding layer, and a contact layer of a first conductivity type. The substrate is semi-insulating or insulating. The light-absorbing layer is disposed on the first cladding layer. The second cladding layer is disposed on the light-absorbing layer. The contact layer includes a portion of the first cladding layer, or is disposed between the substrate and the first cladding layer. The first cladding layer, the light-absorbing layer, and the second cladding layer form a mesa structure extending in the direction of an optical waveguide. The contact layer includes: a first region including a region located between the mesa structure and the substrate; and a second region exposed from the first cladding layer for electrical connection. The contact layer is partially removed from the substrate. The first region and the second region are sandwiched between the regions where the contact layer has been removed.

[0008] Invention Effects The electric field absorption modulator and optical modulator integrated laser element according to the present invention can reduce parasitic capacitance and improve high-frequency characteristics. Attached Figure Description

[0009] Figure 1 This is a top view showing the optical modulator integrated laser element according to an embodiment of the present invention.

[0010] Figure 2 It is a schematic representation along Figure 1 A cross-sectional view of line II-II.

[0011] Figure 3 It is a schematic representation along Figure 1 A cross-sectional view of line III-III.

[0012] Figure 4 It is a schematic representation along Figure 1 A cross-sectional view of line IV-IV.

[0013] Figure 5 It is a schematic representation along Figure 1 A cross-sectional view of the VV line.

[0014] Figure 6 It is Figure 2 , Figure 3 , Figure 4 as well as Figure 5 A portion of the image is enlarged.

[0015] Figure 7 This is a further enlarged representation. Figure 6 A portion of the image.

[0016] Figure 8 It is a schematic representation along Figure 1 A cross-sectional view of line VIII-VIII.

[0017] Figure 9 This diagram illustrates the process of growing a contact layer, an etch stop layer, a first cladding layer, a light absorption layer, and a second cladding layer on a substrate.

[0018] Figure 10 This diagram illustrates the process of removing the insulating film from the countertop structure and its surrounding area.

[0019] Figure 11 It is a graph representing the frequency characteristics of the S-parameters of the optical modulator.

[0020] Figure 12 It is a graph representing the frequency characteristics of the S-parameters of the optical modulator.

[0021] Figure 13 This is a top view showing the integrated laser element of the optical modulator involved in the first variation.

[0022] Figure 14 This is a circuit diagram representing the situation where the first region reaches the light emission end face.

[0023] Figure 15 This is a top view showing how the first region does not reach the light emission end face.

[0024] Figure 16 This is a circuit diagram representing the situation where the first region has not reached the light emission end face.

[0025] Figure 17 This is a top view showing the integrated laser element of the optical modulator involved in the second variation.

[0026] Figure 18 This is a top view showing the integrated laser element of the optical modulator involved in the third variation.

[0027] Figure 19 This is a top view showing the integrated laser element of the optical modulator involved in the fourth variation.

[0028] Figure 20 This is a top view showing the optical modulator integrated laser element involved in the fifth variation.

[0029] Figure 21 This is a top view showing the integrated laser element of the optical modulator involved in the sixth variation.

[0030] Figure 22 This is a diagram showing another structural example where the first region of the contact layer has been removed.

[0031] Figure 23 This is a diagram showing another structural example where the first region of the contact layer has been removed.

[0032] Figure 24This diagram illustrates the process of depositing embedded areas in the etched region.

[0033] Figure 25 This diagram illustrates the process of depositing embedded areas in the etched region.

[0034] Figure 26 This is a diagram showing another structural example where the first region of the contact layer has been removed.

[0035] Figure 27 This is a diagram showing a cross-section of the laser section excluding the first region.

[0036] Explanation of reference numerals in the attached figures 1, 1A, 1B, 1C, 1D, 1F, 1G: Optical modulator integrated laser element; 1a: Light exits from the end face; 2: Substrate; 3. 3A: Optical modulator; 4: Laser section; 5: Semiconductor optical amplifier; 31: First optical modulator; 32: Second optical modulator; 50: concave part; 51: Contact layer (electrode connecting to semiconductor layer); 51a: First region; 51a1: Part (First Part); 51b: Second region; 51c: Third region; 51d: Fourth region; 52: First coating layer; 53: Light absorption layer; 54: Second coating layer; 55: Active layer; 57, 58: Countertop structure; 60: Etching stop layer; 61, 62: Area; 71: First electrode pad; 71A, 71B, 72A, 75, 76, 77, 78: Electrode pads; 72: Second electrode pad; 73, 73A, 73B, 74, 74A, 74B: Wiring; 81: Insulating film; 82: Burial area; 83: Etching mask; 84: Layer; 90, 91: Ohmic electrodes; D1: Optical waveguide direction; E1: Conductive path; G11, G12, G13, G21, G22, G23: Curves; L1: Distance; Rn1, Rp1: Separation resistors; Rn2, Rp2: Front-end separation resistors; W1: Width. Detailed Implementation

[0037] [Description of embodiments of the present invention] First, embodiments of the present invention will be described. (1) An electric field absorption modulator according to one embodiment of the present invention includes a substrate, a first cladding layer, a light-absorbing layer, a second cladding layer, and a contact layer of a first conductivity type. The substrate is semi-insulating or insulating. The light-absorbing layer is disposed on the first cladding layer. The second cladding layer is disposed on the light-absorbing layer. The contact layer includes a portion of the first cladding layer, or is disposed between the substrate and the first cladding layer. The first cladding layer, the light-absorbing layer, and the second cladding layer form a mesa structure extending in the direction of the optical waveguide. The contact layer includes: a first region including a region located between the mesa structure and the substrate; and a second region exposed from the first cladding layer for electrical connection. The contact layer is partially removed from the substrate. The first region and the second region are sandwiched by the region where the contact layer has been removed.

[0038] In the electric field absorption modulator described in (1) above, the contact layer is partially removed from the substrate, and the first region between the mesa structure and the substrate, as well as the second region exposed from the first cladding layer for electrical connection, are sandwiched by the region where the contact layer has been removed. In this way, by removing the contact layer around the first and second regions, the parasitic capacitance generated between the first and second regions of the contact layer and the substrate can be reduced, thereby improving the high-frequency characteristics of the optical modulator.

[0039] (2) Alternatively, the electric field absorption modulator of (1) above may also include a first electrode pad electrically connected to the contact layer and a second electrode pad electrically connected to the second cladding layer. Alternatively, the contact layer may also include a third region located between the first electrode pad and the substrate and a fourth region located between the second electrode pad and the substrate. Alternatively, the third and fourth regions may be electrically separated from the first and second regions by removing regions of the contact layer. The first and second electrode pads may be disposed on the second cladding layer, for example, with an insulating film in between, to maintain their height. In this case, the third and fourth regions of the contact layer located below the first and second electrode pads remain. Such third and fourth regions are electrically separated from the first and second regions by removing regions of the contact layer, thereby reducing the parasitic capacitance generated between the first and second regions of the contact layer and the substrate, and improving the high-frequency characteristics of the optical modulator.

[0040] (3) Alternatively, based on the electric field absorption modulator described in (2) above, there may be regions where the contact layer has not been removed, in addition to the first region, the second region, the third region, and the fourth region. In this case, the area where the contact layer is removed can be reduced, and the time required for removing the contact layer can be shortened.

[0041] (4) Alternatively, based on the electric field absorption modulator described in (1) above, the contact layer is removed in all regions except the first and second regions. In this case, the parasitic capacitance generated between the first and second regions of the contact layer and the substrate can be further reduced, thereby further improving the high-frequency characteristics of the electric field absorption modulator.

[0042] (5) Alternatively, based on any of the electric field absorption modulators described in (1) to (4) above, the region where the contact layer has been removed extends to the light emission end face. In this case, the first region is held by the region where the contact layer has been removed until the light emission end face. As a result, the parasitic capacitance generated between the first region of the contact layer and the substrate can be further reduced, and the high-frequency characteristics of the electric field absorption modulator can be further improved. Based on this, when the laser section is provided as described in (8) below, the resistance separating the electric field absorption modulator from the front-end side region (front-end side separation resistance) can be increased, thereby increasing the separation resistance between the electric field absorption modulator and the laser section.

[0043] (6) Alternatively, the electric field absorption modulator of any one of (1) to (5) above may also include semi-insulating or insulating buried regions that bury both sides of the mesa structure. Alternatively, the region where the contact layer is removed may be a region where a recessed portion of the buried region and the contact layer are formed. In this case, the contact layer can be easily partially removed from the substrate.

[0044] (7) Alternatively, based on the electric field absorption modulator of (6) above, the first region includes a first portion having a light-emitting end face and a second portion located on the side opposite to the light-emitting end face relative to the first portion. Alternatively, the width of the first portion in the direction orthogonal to the light-guiding wave direction is larger than the width of the second portion in the direction orthogonal to the light-guiding wave direction. In this case, the width of the portion held by the recess becomes wider at the light-emitting end face, thus increasing the mechanical strength of the portion held by the recess and making it easier to cleave the light-emitting end face.

[0045] (8) Alternatively, the electric field absorption modulator of any of (1) to (7) above may include a first optical modulator and a second optical modulator.

[0046] (9) An embodiment of the present invention includes an optical modulator integrated laser element comprising: an optical modulator that is an electric field absorption modulator as any one of (1) to (8) above; and a laser section disposed on a substrate to output laser light. The optical modulator receives laser light from the laser section. According to this optical modulator integrated laser element, by including the electric field absorption modulator as any one of (1) to (8) above, the parasitic capacitance generated between the contact layer and the substrate can be reduced, thereby improving the high-frequency characteristics.

[0047] (10) Alternatively, based on the optical modulator integrated laser element described in (9) above, the contact layer is partially removed from the substrate of the laser section. In this case, the parasitic capacitance generated between the contact layer and the substrate can be further reduced, and the high-frequency characteristics of the optical modulator can be further improved.

[0048] (11) Alternatively, the optical modulator integrated laser element of (9) above may also include a semiconductor optical amplifier disposed on the light emitting end face side of the optical modulator. Alternatively, the semiconductor optical amplifier may input the modulated laser from the optical modulator, amplify the modulated laser, and output it.

[0049] (12) Alternatively, in the optical modulator integrated laser element described in (11) above, a semiconductor optical amplifier may be disposed on the substrate. In this case, the optical modulator integrated laser element with a semiconductor optical amplifier can be miniaturized.

[0050] [Detailed Description of Embodiments of the Invention] Hereinafter, specific examples of the invention will be described with reference to the accompanying drawings. It should be noted that the invention is not limited to these examples, but is illustrated by the claims and is intended to include all modifications within the meaning and scope of the claims. In the following description, the same elements are labeled with the same reference numerals, and repeated descriptions are omitted.

[0051] Figure 1This is a top view showing the optical modulator integrated laser element 1 according to an embodiment of the present invention. Figure 2 , Figure 3 , Figure 4 as well as Figure 5 These are schematic representations of along Figure 1 A cross-sectional view of lines II-II, III-III, IV-IV, and VV. Figure 6 It is Figure 2 , Figure 3 , Figure 4 as well as Figure 5 A portion of the image is shown in magnified form. Figure 7 This is a further enlarged representation. Figure 6 A portion of the image.

[0052] The optical modulator integrated laser element 1 of this embodiment includes an optical modulator 3 and a laser section 4. The optical modulator 3 and the laser section 4 are monolithically disposed on a common substrate 2. The optical modulator 3 and the laser section 4 are adjacent to each other on the substrate 2 along the optical waveguide direction D1. The laser section 4 outputs laser light. The optical modulator 3 receives laser light from the laser section 4.

[0053] The optical modulator 3 is an electric field absorption type optical modulator, comprising a substrate 2, a contact layer 51, a first cladding layer 52, a light-absorbing layer 53, and a second cladding layer 54. The substrate 2 is semi-insulating or insulating. The substrate 2 may contain, for example, a III-V compound semiconductor, and in one example, an InP substrate.

[0054] Contact layer 51 is the electrode connection semiconductor layer in this invention. Contact layer 51 is disposed on substrate 2 and has a first conductivity type. The first conductivity type is, for example, n-type. Contact layer 51 contains a semiconductor lattice-matched to substrate 2, in one example being n-type. + A type of InP layer. In this embodiment, a contact layer 51 is disposed on and in contact with the substrate 2. The thickness of the contact layer 51 is less than the thickness of the first cladding layer 52. The thickness of the contact layer 51 is 100 nm or more and 1000 nm or less, and in one example is 400 nm. The impurity concentration of the contact layer 51 is greater than the impurity concentration of the first cladding layer 52. The impurity concentration of the contact layer 51 is 1 × 10⁻⁶. 18 cm -3 Above and 2×10 19 cm -3 In one example, it is 8×10 18 cm -3 .

[0055] A first cladding layer 52 is disposed on the contact layer 51 and has a first conductivity type. The first cladding layer 52 contains a semiconductor lattice-matched to the contact layer 51, in one example being an n-type InP layer. In this embodiment, the first cladding layer 52 is disposed on and in contact with the contact layer 51. The thickness of the first cladding layer 52 is 0.5 μm or more and 2 μm or less, in one example being 1.2 μm. The impurity concentration of the first cladding layer 52 is 1 × 10⁻⁶. 17 cm -3 Above and 2×10 18 cm -3 In one example, it is 5×10 17 cm -3 .

[0056] A light-absorbing layer 53 is disposed on the first cladding layer 52. The band gap of the light-absorbing layer 53 is smaller than that of the first cladding layer 52. The refractive index of the light-absorbing layer 53 is greater than that of the first cladding layer 52. The light-absorbing layer 53 contains a semiconductor with a lattice match to the first cladding layer 52. The light-absorbing layer 53 may also have a multiple quantum well structure. In one example, the light-absorbing layer 53 is formed by stacking InGaAsP layers or InGaAlAs layers with different compositions. In this embodiment, the light-absorbing layer 53 is disposed on and in contact with the first cladding layer 52.

[0057] The second cladding layer 54 is disposed on the light-absorbing layer 53 and has a second conductivity type. The second conductivity type is, for example, p-type. The second cladding layer 54 contains a semiconductor lattice-matched with the light-absorbing layer 53, in one example being a p-type InP layer. In this embodiment, the second cladding layer 54 is disposed on and connected to the light-absorbing layer 53.

[0058] like Figure 6 As shown, the optical modulator 3 also includes an etch stop layer 60. The etch stop layer 60 is disposed between the contact layer 51 and the first cladding layer 52. In one example, the etch stop layer 60 is in contact with both the contact layer 51 and the first cladding layer 52. The etch stop layer 60 is used to stop etching when forming the ohmic electrode 90 in contact with the contact layer 51, based on the difference in etching rate with respect to the first cladding layer 52. The etch stop layer 60 has a first conductivity type. The etch stop layer 60 is, for example, an n-type InGaAsP layer.

[0059] The first cladding layer 52, the light-absorbing layer 53, and the second cladding layer 54 form a mesa structure 58 extending along the optical waveguide direction D1. The width of the mesa structure 58 in the lateral direction is, for example, 1.4 μm. The base of the mesa structure 58 is located in the first cladding layer 52. Therefore, when viewed from above, the contact layer 51, the etch stop layer 60, and the lower part of the first cladding layer 52 also extend to the outside of the mesa structure 58.

[0060] The contact layer 51 includes a first region 51a and a second region 51b. The first region 51a includes the region located between the mesa structure 58 and the substrate 2 and its surrounding region. When viewed from above, the distances L1 and L2 between the end of the first region 51a and the mesa structure 58 in a direction orthogonal to the optical waveguide direction D1 and along the upper surface of the substrate 2 (hereinafter referred to as the lateral direction) are (refer to...). Figure 3 For example, it is 3μm or larger and 20μm or smaller, and in one example, it is 10μm. The second region 51b is the region exposed from the first cladding layer 52 and the etch stop layer 60 for electrical connection with the wiring 73 described later. The second region 51b is adjacent to the first region 51a.

[0061] The optical modulator 3 also includes an insulating film 81 and buried regions 82. The buried regions 82 are disposed on both sides of the mesa structure 58, burying both sides of the mesa structure 58. The buried regions 82 are insulating or semi-insulating. For example, the buried regions 82 are semi-insulating InP regions. The material of the buried regions 82 can be the same as or different from the material of the substrate 2. The insulating film 81 is disposed on the buried regions 82, covering the buried regions 82. The insulating film 81 is, for example, a silicon compound film such as SiO2 or SiN.

[0062] The optical modulator 3 includes a first electrode pad 71, a second electrode pad 72, a wiring 73, and a wiring 74. The first electrode pad 71, the second electrode pad 72, the wiring 73, and the wiring 74 are metal films, in one example, gold (Au) films. Figure 4 as well as Figure 5 As shown, the first electrode pad 71 and the second electrode pad 72 are disposed above the buried region 82 and on the insulating film 81. Figure 1 As shown, the first electrode pad 71 and the second electrode pad 72 are arranged laterally relative to the mesa structure 58. Furthermore, the first electrode pad 71 and the second electrode pad 72 are arranged along the optical waveguide direction D1. The planar shape of the first electrode pad 71 and the second electrode pad 72 is, for example, circular.

[0063] Wiring 73 electrically connects the first electrode pad 71 to the contact layer 51. Wiring 73 includes an ohmic electrode 90 and a portion connected to the first electrode pad 71. The ohmic electrode 90 is disposed on and in ohmic contact with the second region 51b of the contact layer 51. The portion of wiring 73 other than the portion in contact with the second region 51b is disposed on the insulating film 81. Wiring 74 electrically connects the second electrode pad 72 to the second cover layer 54. Wiring 74 includes an ohmic electrode 91 and a portion connected to the second electrode pad 72. The ohmic electrode 91 is disposed on and in ohmic contact with the second cover layer 54. The portion of wiring 74 other than the portion in contact with the second cover layer 54 is disposed on the insulating film 81.

[0064] The contact layer 51 also includes a third region 51c and a fourth region 51d. The third region 51c is located between the first electrode pad 71 and the substrate 2. The planar shape of the third region 51c is the same as that of the first electrode pad 71 (e.g., circular). The fourth region 51d is located between the second electrode pad 72 and the substrate 2. The planar shape of the fourth region 51d is the same as that of the second electrode pad 72 (e.g., circular).

[0065] A recess 50 is formed in the buried region 82. The recess 50 extends through the buried region 82, the first cover layer 52, the etch stop layer 60, and the contact layer 51. The recess 50 is formed to partially remove the contact layer 51 on the substrate 2. Figure 1 In the image, the region 61 where the contact layer 51 has been removed is shown using halftone dots. That is, region 61 is the region where the recess 50 is formed. For example... Figure 1 As shown, the integral region formed by the first region 51a and the second region 51b is sandwiched by region 61 in the lateral direction. In this embodiment, region 61 extends to the light emitting end face 1a. Thus, the first region 51a is sandwiched by region 61 up to the light emitting end face 1a. An insulating film 81 is provided on the surface of the recess 50. The third region 51c and the fourth region 51d are electrically separated from the first region 51a and the second region 51b by the region 61, i.e., the recess 50, where the contact layer 51 is removed.

[0066] In the optical modulator 3, the first region 51a includes a portion 51a1 having a light emitting end face 1a (the first portion, see reference 1). Figure 1 The remaining portion (second part) is located on the side opposite to the light emission end face 1a relative to the portion 51a1. Moreover, the width W1 of the portion 51a1 in the lateral direction is greater than the width of the remaining portion in the lateral direction.

[0067] In addition, on substrate 2, in addition to region 61, there is also region 62. Region 62 is the area where the contact layer 51 has not been removed, except for the first region 51a, the second region 51b, the third region 51c, and the fourth region 51d. No recess 50 is formed in region 62. Therefore, the contact layer 51, the etch stop layer 60, the first cover layer 52, and the buried region 82 remain. In this embodiment, region 62 is electrically isolated in the shape of an island.

[0068] Figure 8 It is a schematic representation along Figure 1 A cross-sectional view of line VIII-VIII. The laser unit 4 has the same configuration as the optical modulator 3, except for the following aspects: The laser unit 4 has an active layer 55 replacing the light absorption layer 53 of the optical modulator 3. The first cladding layer 52, the active layer 55, and the second cladding layer 54 form a mesa structure 57 extending along the optical waveguide direction D1. The laser unit 4 has electrode pads 75 replacing the first electrode pads 71 ​​and wiring 73 of the optical modulator 3. The laser unit 4 has electrode pads 76 replacing the second electrode pads 72 and wiring 74 of the optical modulator 3. The electrode pads 75 are disposed above the buried region 82 and on the insulating film 81, extending to one side of the mesa structure 57. The electrode pads 75 include ohmic electrodes 90 that are in ohmic contact with the exposed portion of the contact layer 51. The electrode pads 76 are disposed above the buried region 82 and on the insulating film 81, extending to the other side of the mesa structure 57. The electrode pad 76 includes an ohmic electrode 91 that makes ohmic contact with the exposed portion of the second overlay layer 54. It should be noted that, as... Figure 1 As shown, in this embodiment, region 61 is not formed in the laser section 4.

[0069] Next, the method for forming region 61 of the optical modulator 3 will be explained. First, as... Figure 9 As shown, a contact layer 51, an etch stop layer 60, a first cladding layer 52, a light-absorbing layer 53, and a second cladding layer 54 are grown on substrate 2. A mesa structure 58 is formed by etching (e.g., dry etching). Buried regions 82 are deposited in areas of substrate 2 other than the mesa structure 58 to bury the mesa structure 58. Then, as... Figure 10 As shown, an etching mask 83 is formed on the mesa structure 58 and the buried region 82 around it. The portion of the buried region 82 exposed from the etching mask 83, the underlying first overlay layer 52, the etch stop layer 60, and the contact layer 51 are removed by etching (e.g., dry etching), exposing the substrate 2. Through this process, region 61 (recess 50) is formed. Then, an insulating film 81 (see reference) is formed on the buried region 82. Figures 2 to 6 ,as well as Figure 8 ).

[0070] The effects obtained by the optical modulator integrated laser element 1 and optical modulator 3 according to the above-described embodiment will be explained. In the optical modulator 3 according to this embodiment, the contact layer 51 is partially removed from the substrate 2, and the first region 51a between the mesa structure 58 and the substrate 2 and the second region 51b exposed from the first cladding layer 52 for electrical connection are clamped by the region 61 where the contact layer 51 has been removed. In this way, by removing the contact layer 51 around the periphery of the first region 51a and the second region 51b, the parasitic capacitance generated between the first region 51a and the second region 51b of the contact layer 51 and the conductive substrate on which the optical modulator integrated laser element 1 is mounted can be reduced, thereby improving the high-frequency characteristics of the optical modulator 3.

[0071] As in this embodiment, the optical modulator 3 may also include a first electrode pad 71 electrically connected to the contact layer 51 and a second electrode pad 72 electrically connected to the second cladding layer 54. The contact layer 51 may also include a third region 51c located between the first electrode pad 71 and the substrate 2 and a fourth region 51d located between the second electrode pad 72 and the substrate 2. The third region 51c and the fourth region 51d may also be electrically separated from the first region 51a and the second region 51b by removing region 61 of the contact layer 51. The first electrode pad 71 and the second electrode pad 72 are provided above the buried region 82, for example, to maintain height. In this case, the third region 51c and the fourth region 51d of the contact layer 51 located below the first electrode pad 71 and the second electrode pad 72 remain. By utilizing the region 61 where the contact layer 51 has been removed to electrically separate the third region 51c and the fourth region 51d from the first region 51a and the second region 51b, the parasitic capacitance generated between the first region 51a and the second region 51b of the contact layer 51 and the substrate can be reduced, thereby improving the high-frequency characteristics of the optical modulator 3.

[0072] Figure 11 as well as Figure 12 This is a graph representing the frequency characteristics of the S-parameters of optical modulator 3. The horizontal axis represents frequency (GHz), and the vertical axis represents the magnitude of the S-parameters (dB). Curves G11 and G21 represent the frequency characteristics of transmission on the positive phase side (S21 parameter), curves G12 and G22 represent the frequency characteristics of transmission on the negative phase side (S23 parameter), and curves G13 and G23 represent the frequency characteristics of differential transmission (Ssd21 parameter). Figure 11 Unlike this embodiment, this embodiment shows the case where the third region 51c of the contact layer 51 is electrically connected to the second region 51b. Figure 12 This indicates that, as in this embodiment, the third region 51c of the contact layer 51 is electrically separated from the second region 51b. (Refer to...) Figure 11 as well as Figure 12 Compared to the case where the third region 51c is electrically connected to the second region 51b, the S21, S23, and Ssd21 parameters are all improved in the high-frequency band when the third region 51c is electrically separated from the second region 51b. Therefore, it can be seen that by electrically separating the third region 51c from the second region 51b, parasitic capacitance can be reduced and the high-frequency characteristics of the optical modulator 3 can be improved.

[0073] As in this embodiment, in the optical modulator 3, in addition to the first region 51a, the second region 51b, the third region 51c, and the fourth region 51d, there may also be a region 62 where the contact layer 51 has not been removed. In this case, the area of ​​the region 61 where the contact layer 51 has been removed can be reduced, and the time required to remove the contact layer 51 can be shortened.

[0074] As in this embodiment, the region 61 where the contact layer 51 is removed can also be a region where the recess 50 through the buried region 82 and the contact layer 51 is formed. In this case, the contact layer 51 can be easily partially removed from the substrate 2.

[0075] As in this embodiment, the region 61 where the contact layer 51 has been removed can also reach the light emission end face 1a. In this case, the first region 51a is held by the region 61 where the contact layer 51 has been removed until it reaches the light emission end face 1a. As a result, the parasitic capacitance generated between the first region 51a of the contact layer 51 and the substrate can be further reduced, and the high-frequency characteristics of the optical modulator 3 can be further improved.

[0076] As in this embodiment, the first region 51a may also include a portion 51a1 having a light-emitting end face 1a and a remaining portion located on the side opposite to the light-emitting end face 1a relative to the portion 51a1. Furthermore, the lateral width W1 of the portion 51a1 may be greater than the lateral width of the remaining portion. In this case, the width of the portion held by the recess 50 widens at the light-emitting end face 1a, thus increasing the mechanical strength of the portion held by the recess 50 and facilitating the cleaving of the light-emitting end face 1a.

[0077] The optical modulator integrated laser element 1 of this embodiment includes an optical modulator 3 and a laser section 4 disposed on a substrate 2 and outputting laser light. The optical modulator 3 receives laser light from the laser section 4. According to this optical modulator integrated laser element 1, by including the optical modulator 3, the parasitic capacitance generated between the contact layer 51 and the substrate can be reduced, thereby improving high-frequency characteristics.

[0078] (First variation) Figure 13This is a top view showing the optical modulator integrated laser element 1A involved in the first modification. The optical modulator integrated laser element 1A of this modification differs from the above embodiment in the shape of regions 61 and 62, but is otherwise consistent with the above embodiment.

[0079] In this modified example, region 62 of the optical modulator 3 is disposed along the periphery of the substrate 2 and is connected to region 62 of the laser section 4. Additionally, region 61 is formed in a wider region adjacent to the mesa structure 58. Furthermore, recesses 50 are formed below the first electrode pad 71 and below the second electrode pad 72. That is, the first electrode pad 71 and the second electrode pad 72 are formed in region 61. Specifically, the first electrode pad 71 and the second electrode pad 72 are disposed on the substrate 2 exposed from the contact layer 51, separated by an insulating film 81. Therefore, in this modified example, the contact layer 51 does not have a third region 51c and a fourth region 51d.

[0080] Even in the manner described in this modified example, the same effect as the above-described embodiment can be obtained. Furthermore, by providing a region 62 along the periphery of the substrate 2 as in this modified example, cutting can be easily performed when integrating the optical modulator into a single laser element.

[0081] Furthermore, in this modified example, similarly to the above embodiment, the region 61 where the contact layer 51 reaches the light emitting end face 1a is removed. Here, Figure 14 This is a circuit diagram showing the situation where region 61 reaches the light emission end face 1a, as in this modified example. Figure 15 This is a top view showing that region 61, which differs from this modified example, does not reach the light-emitting end face 1a. Figure 16 This is a circuit diagram illustrating this situation. In Figure 14 as well as Figure 16 In this diagram, the optical modulator 3 and the laser unit 4 are simply represented by diodes. The cathode of the optical modulator 3 and the cathode of the laser unit 4 are connected via a separation resistor Rn1, and the anode of the optical modulator 3 and the anode of the laser unit 4 are connected via a separation resistor Rp1. Furthermore, a front-end separation resistor Rn2 extends from the cathode of the optical modulator 3 toward the light emission end face 1a, and a front-end separation resistor Rp2 extends from the anode of the optical modulator 3 toward the light emission end face 1a. It should be noted that the separation resistors Rn1 and Rp1, as well as the front-end separation resistors Rn2 and Rp2, are... Figure 13 as well as Figure 15 The image is also shown schematically.

[0082] like Figure 15 As shown, when region 61 does not reach the light emission end face 1a, as Figure 16As shown, the cathode of the optical modulator 3 and the cathode of the laser unit 4 are connected via a conductive path E1 formed at the periphery. This reduces the separation resistance between the optical modulator 3 and the laser unit 4. In contrast, as... Figure 13 As shown, when region 61 reaches the light emission end face 1a, as Figure 14 As shown, the cathode of the optical modulator 3 and the cathode of the laser unit 4 are not connected via a conductive path formed at the periphery. This increases the separation resistance between the optical modulator 3 and the laser unit 4. Consequently, interference between the drive signal input to the optical modulator 3 and the bias voltage input to the laser unit 4 is reduced.

[0083] (Second variation) Figure 17 This is a top view showing the optical modulator integrated laser element 1B according to the second modification. The optical modulator integrated laser element 1B of this modification differs from the above embodiment in that the laser section 4 also has a region 61 where the contact layer 51 has been removed, but it is the same as the above embodiment in other respects.

[0084] In this modified example, a recess 50 is formed in a region of the substrate 2 other than the peripheral portion, and this region is designated as region 61 where the contact layer 51 has been removed. Region 61 is formed in a relatively wide area adjacent to the mesa structure 57. Furthermore, recesses 50 are also formed below the electrode pads 75 and 76. That is, electrode pads 75 and 76 are formed in region 61. Specifically, electrode pads 75 and 76 are disposed on the substrate 2 exposed from the contact layer 51 through an insulating film 81.

[0085] As in this modified example, a region 61 in which the contact layer 51 has been removed can also be provided in the laser section 4. Furthermore, the contact layer 51 can also be partially removed from the substrate 2 of the laser section 4. In this case, the parasitic capacitance generated between the contact layer 51 and the substrate can also be reduced in the laser section 4. Therefore, the parasitic capacitance generated between the contact layer 51 and the substrate can be further reduced, further improving the high-frequency characteristics of the optical modulator 3.

[0086] (Third variation) Figure 18 This is a top view showing the optical modulator integrated laser element 1C according to the third modification. The optical modulator integrated laser element 1C of this modification differs from the above embodiment in the shape of regions 61 and 62, but is otherwise consistent with the above embodiment.

[0087] In this modified example, the contact layer 51 is removed from all regions except for the first region 51a and the second region 51b in the optical modulator 3. That is, recesses 50 are formed in all regions except for the first region 51a and the second region 51b, forming region 61. According to this modified example, the parasitic capacitance generated between the first region 51a and the second region 51b of the contact layer 51 and the substrate can be further reduced, further improving the high-frequency characteristics of the optical modulator 3. It should be noted that, as... Figure 18 As shown, in the laser section 4, the contact layer 51 can also be removed in all areas except the area between the mesa structure 57 and the substrate 2 and its surrounding area.

[0088] (Fourth variation) Figure 19 This is a top view showing the optical modulator integrated laser element 1D according to the fourth modification example. In the optical modulator integrated laser element 1D of this modification example, the width W1 of the portion 51a1 (first portion) including the light emitting end face 1a is equal to or less than the width of the remaining portion in the lateral direction. Even in this manner, the same effect as the above-described embodiment can be obtained.

[0089] (Fifth variation) Figure 20 This is a top view showing the optical modulator integrated laser element 1F according to the fifth modification. The optical modulator integrated laser element 1F of this modification differs from the above embodiments in that it includes an optical modulator 3A instead of an optical modulator 3, but is otherwise identical to the above embodiments. The optical modulator 3A includes a first optical modulator 31 and a second optical modulator 32 coupled in series. Therefore, the optical modulator 3A replaces the first electrode pad 71, the second electrode pad 72, the wiring 73, and the wiring 74 of the above embodiments, and has electrode pads 71A, 71B, and 72A, as well as wirings 73A, 73B, 74A, and 74B.

[0090] Electrode pad 72A belongs to the first optical modulator 31. Electrode pad 71B belongs to the second optical modulator 32. Electrode pad 71A belongs to both the first optical modulator 31 and the second optical modulator 32. In the first optical modulator 31, electrode pad 71A is equivalent to the first electrode pad, and electrode pad 72A is equivalent to the second electrode pad. In the second optical modulator 32, electrode pad 71B is equivalent to the first electrode pad, and electrode pad 71A is equivalent to the second electrode pad.

[0091] Electrode pads 71A, 71B, and 72A, as well as wirings 73A, 73B, 74A, and 74B, are metal films, in one example gold (Au) films. Electrode pads 71A, 71B, and 72A are positioned above the embedded region 82 and on the insulating film 81. Figure 20 As shown, electrode pad 71A is disposed on one side relative to mesa structure 58. Electrode pads 71B and 72A are disposed on the other side relative to mesa structure 58. The planar shape of electrode pads 71A, 71B, and 72A is, for example, circular.

[0092] Wiring 73A and wiring 74A belong to the first optical modulator 31. Wiring 73A electrically connects electrode pad 71A to the contact layer 51 of the first optical modulator 31. Wiring 73A includes a portion disposed on and in ohmic contact with the second region 51b of the contact layer 51, and a portion connected to the electrode pad 71A. Wiring 74A electrically connects electrode pad 72A to the second cladding layer 54 of the first optical modulator 31.

[0093] Wiring 73B and wiring 74B belong to the second optical modulator 32. Wiring 73B electrically connects electrode pad 71B to the contact layer 51 of the second optical modulator 32. Wiring 73B includes a portion disposed on and in ohmic contact with the second region 51b of the contact layer 51, and a portion connected to the electrode pad 71B. Wiring 74B electrically connects electrode pad 71A to the second cladding layer 54 of the second optical modulator 32.

[0094] Even when the optical modulator 3A has a first optical modulator 31 and a second optical modulator 32 as in this modified example, the same effect as the above embodiment can be obtained by partially removing the contact layer 51 on the substrate 2.

[0095] (Sixth variation) Figure 21This is a top view showing the optical modulator-integrated laser element 1G according to the sixth modification. The optical modulator-integrated laser element 1G has the same configuration as the optical modulator-integrated laser element 1 of the above embodiment, and further includes a semiconductor optical amplifier (SOA) 5. The semiconductor optical amplifier 5 is monolithically disposed on a substrate 2 shared with the optical modulator 3 and the laser section 4. The semiconductor optical amplifier 5 is disposed on the side opposite to the laser section 4 relative to the optical modulator 3, adjacent to the optical modulator 3 in the optical waveguide direction D1. The semiconductor optical amplifier 5 receives modulated laser light from the optical modulator 3, amplifies the modulated laser light, and outputs it. The semiconductor optical amplifier 5 includes electrode pads 77 forming ohmic contacts with the contact layer 51 and electrode pads 78 forming ohmic contacts with the second cladding layer 54. In this modification, by partially removing the contact layer 51 of the optical modulator 3 from the substrate 2, the same effect as in the above embodiment can also be obtained. Furthermore, by placing the semiconductor optical amplifier 5 on the substrate 2 shared with the optical modulator 3 and the laser unit 4, the integrated laser element 1G of the optical modulator equipped with the semiconductor optical amplifier 5 can be miniaturized. It should be noted that the semiconductor optical amplifier 5 can also be provided in the first to fifth modifications described above.

[0096] (Seventh variation) Figures 22 to 25 This is a diagram used to illustrate another structural example of region 61 where contact layer 51 has been removed. In this example, firstly, as... Figure 22 as well as Figure 23 As shown, etching (e.g., dry etching, indicated by arrow E in the figure) is performed around the first region 51a and the second region 51b of the contact layer 51 to remove the contact layer 51 around the first region 51a and the second region 51b. Then, as... Figure 24 as well as Figure 25 As shown, a buried region 82 is deposited in the etched area, and an insulating film 81 is formed on the buried region 82. It should be noted that... Figure 22 as well as Figure 24 This refers to the optical modulator 3 and the laser unit 4. Figure 23 as well as Figure 25 This refers to the portion between the optical modulator 3 and the laser unit 4. Even in this modified structure, it is possible to obtain a region 61 where the contact layer 51 has been removed. Furthermore, according to this modified example, the surface roughness of the integrated laser element in the optical modulator can be reduced, making it easier to perform processes such as surface wiring formation.

[0097] (Eighth variation) Figure 26 as well as Figure 27 This is a diagram used to illustrate another structural example of region 61 where the contact layer 51 has been removed. Figure 26This is a schematic diagram showing a cross-section of region 61 where the contact layer 51 has been removed. Figure 27 This is a schematic cross-sectional view of the laser section 4 excluding region 61, shown for comparison purposes. (See diagram below.) Figure 26 As shown, in region 61, an insulating or semi-insulating layer 84 can also be provided instead of the contact layer 51. Even in this way, the same effect as the above-described embodiment can be obtained.

[0098] The optical modulator and optical modulator integrated laser element involved in this invention are not limited to the embodiments and modifications described above, and various other modifications are possible. For example, in the embodiments and modifications described above, an optical modulator integrated laser element having both an optical modulator and a laser section monolithically is shown, but the configuration of this invention can also be applied to elements that only have an optical modulator and no laser section. Furthermore, the structure in which the contact layer region is removed is not limited to the embodiments and modifications described above. Additionally, in the embodiments and modifications described above, the case where the electrode connection semiconductor layer is a contact layer is shown, but the electrode connection semiconductor layer may also include a portion of the first cladding layer 52, or may consist only of a portion of the first cladding layer 52. In this case, in the embodiments and modifications described above, the contact layer is replaced by the electrode connection semiconductor layer. Furthermore, in the embodiments and modifications described above, the case where the first conductivity type is n-type and the second conductivity type is p-type is shown, but the first conductivity type may also be p-type and the second conductivity type n-type.

Claims

1. An electric field absorption modulator, wherein, The electric field absorption modulator includes: Semi-insulating or insulating substrates; A first coating layer of a first conductivity type is disposed on the substrate; A light-absorbing layer is disposed on top of the first coating layer; A second coating layer of the second conductivity type is disposed on the light absorption layer; as well as A contact layer of the first conductivity type includes a portion of the first covering layer, or is disposed between the substrate and the first covering layer. The first coating layer, the light absorption layer, and the second coating layer form a mesa structure extending in the direction of the optical waveguide. The contact layer comprises: The first region includes the region located between the mesa structure and the substrate; as well as The second region is exposed from the first covering layer for electrical connection. The contact layer is partially removed on the substrate. The first region and the second region are clamped by the region where the contact layer has been removed.

2. The electric field absorption modulator according to claim 1, wherein, The electric field absorption modulator also features: The first electrode pad is electrically connected to the contact layer; and The second electrode pad is electrically connected to the second cladding layer. The contact layer further includes a third region located between the first electrode pad and the substrate, and a fourth region located between the second electrode pad and the substrate. The third and fourth regions are electrically separated from the first and second regions by removing the areas of the contact layer.

3. The electric field absorption modulator according to claim 2, wherein, In addition to the first region, the second region, the third region, and the fourth region, there are regions where the contact layer has not been removed.

4. The electric field absorption modulator according to claim 1, wherein, The contact layer was removed in all regions except the first and second regions.

5. The electric field absorption modulator according to any one of claims 1 to 4, wherein, The area where the contact layer has been removed reaches the light emission end face.

6. The electric field absorption modulator according to any one of claims 1 to 5, wherein, The electric field absorption modulator also includes semi-insulating or insulating embedded areas that embed both sides of the mesa structure. The area where the contact layer has been removed is the area where a recess is formed that extends through the embedded area and the contact layer.

7. The electric field absorption modulator according to claim 6, wherein, The first region includes a first portion having a light-emitting end face and a second portion located on the side opposite to the light-emitting end face relative to the first portion. The width of the first portion in the direction orthogonal to the direction of the optical waveguide is greater than the width of the second portion in the direction orthogonal to the direction of the optical waveguide.

8. The electric field absorption modulator according to any one of claims 1 to 7, wherein, The electric field absorption modulator includes a first optical modulator and a second optical modulator.

9. An optical modulator integrated laser element, wherein, The optical modulator integrates a laser element comprising: An optical modulator as an electric field absorption modulator according to any one of claims 1 to 8; and A laser unit, disposed on the substrate, outputs laser light. The optical modulator receives the laser from the laser unit.

10. The optical modulator integrated laser element according to claim 9, wherein, The contact layer is partially removed from the substrate of the laser unit.

11. The optical modulator integrated laser element according to claim 9, wherein, The integrated laser element of the optical modulator also includes a semiconductor optical amplifier disposed on the light emitting end face of the optical modulator. The semiconductor optical amplifier receives the modulated laser light from the optical modulator, amplifies the modulated laser light, and outputs it.

12. The optical modulator integrated laser element according to claim 11, wherein, The semiconductor optical amplifier is disposed on the substrate.

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