Field absorption modulator and semiconductor optical device

Abstract

This invention provides an electric field absorption modulator and a semiconductor optical device that exhibit high extinction ratio characteristics and excellent high-speed operation. [Solution] The field absorption modulator comprises a semi-insulating semiconductor layer, a first field absorption modulator section laminated on the semi-insulating semiconductor layer in the order of a first n-type semiconductor layer, a first absorption layer, and a first p-type semiconductor layer, a second field absorption modulator section laminated on the semi-insulating semiconductor layer in the order of a second p-type semiconductor layer, a second absorption layer, and a second n-type semiconductor layer, a connecting waveguide layer disposed between the first absorption layer and the second absorption layer, a first EA electrode electrically connected to the first p-type semiconductor layer and electrically connected to the outside, a second EA electrode electrically connected to the second n-type semiconductor layer and electrically connected to the outside, and a connecting medium that electrically connects the first n-type semiconductor layer and the second p-type semiconductor layer and connects the first field absorption modulator section and the second field absorption modulator section in series.

Description

Technical Field

[0001] The present invention relates to an electro-absorption modulator and a semiconductor optical device.

Background Art

[0002] As a light source for optical communication, a combination of a laser that oscillates continuous light and an external modulator that converts the laser light into a modulated optical signal is widely used. An electro-absorption (EA) modulator, which is one type of external modulator, is known (Patent Documents 1 and 2). The electro-absorption modulator is mounted on a wiring board (such as a submount) on which a transmission line is formed and may be used as a semiconductor optical device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The EA modulator is small and has excellent extinction ratio characteristics and frequency response characteristics. However, with the increase in optical communication capacity, further high-speed operation is required. To achieve high-speed operation, it is effective to reduce the parasitic capacitance of the EA modulator. To reduce the parasitic capacitance, it is effective to shorten the length of the EA modulator. However, when the length of the EA modulator is shortened, the extinction ratio characteristics deteriorate. Patent Document 1 solves this problem by electrically connecting two EA modulators in series.

[0005] In Patent Document 1, two EA modulators are provided separately, and the two EA modulators are connected by a power supply circuit. Although there is no detailed description of the power supply circuit, it is presumed that at least the electrodes on the back of one EA modulator are connected to the electrodes on the front of the other EA modulator, and that wires or transmission lines are arranged there. These wires or transmission lines themselves have inductance and capacitance components, which is disadvantageous for high-speed operation. In Patent Document 2, two EA modulators are integrated on a single semiconductor substrate, and the two EA modulators are connected in series electrically by electrodes (metal) formed on the substrate. Here, the electrodes connect the lower semiconductor layer of one EA modulator to the upper semiconductor layer of the other EA modulator. The electrodes extend along the side of the mesa structure 7 to the upper semiconductor layer of the other EA modulator, which is a cause of inductance and parasitic capacitance. Therefore, it is disadvantageous for high-speed operation.

[0006] The present invention provides an electric field absorption modulator and a semiconductor optical device that exhibit high extinction ratio characteristics and excellent high-speed operation. [Means for solving the problem]

[0007] The field absorption modulator comprises a semi-insulating semiconductor layer, a first field absorption modulator section in which a first n-type semiconductor layer, a first absorption layer, and a first p-type semiconductor layer are stacked on the semi-insulating semiconductor layer in that order, a second field absorption modulator section in which a second p-type semiconductor layer, a second absorption layer, and a second n-type semiconductor layer are stacked on the semi-insulating semiconductor layer in that order, a connecting waveguide layer disposed between the first absorption layer and the second absorption layer, a first EA electrode electrically connected to the first p-type semiconductor layer and electrically connected to the outside, a second EA electrode electrically connected to the second n-type semiconductor layer and electrically connected to the outside, and a connecting medium that electrically connects the first n-type semiconductor layer and the second p-type semiconductor layer and connects the first field absorption modulator section and the second field absorption modulator section in series. [Brief explanation of the drawing]

[0008] [Figure 1]This is a top view of an electric field absorption type modulator according to the first embodiment. [Figure 2] This is a schematic cross-sectional view of the field absorption modulator shown in Figure 1, along the line II-II. [Figure 3A] This is a schematic cross-sectional view of the field-absorption modulator shown in Figure 1, along line AA. [Figure 3B] This is a schematic cross-sectional view along the BB line of the field absorption modulator shown in Figure 1. [Figure 3C] This is a schematic cross-sectional view of the field absorption modulator shown in Figure 1, along the CC line. [Figure 4] This is a top view of a semiconductor optical device according to the first embodiment. [Figure 5] This is a schematic cross-sectional view of the field absorption modulator shown in Figure 1, along the line II-II. [Figure 6A] This is a schematic cross-sectional view along line AA of Modification 1 of the field absorption modulator shown in Figure 1. [Figure 6B] This is a schematic cross-sectional view along the BB line of Modification 1 of the field absorption modulator shown in Figure 1. [Figure 6C] This is a schematic cross-sectional view along the CC line of a modified example 1 of the field absorption modulator shown in Figure 1. [Figure 7A] This is a schematic cross-sectional view along line AA of a modified example 2 of the field absorption modulator shown in Figure 1. [Figure 7B] This is a schematic cross-sectional view along the BB line of a modified example 2 of the field absorption modulator shown in Figure 1. [Figure 7C] This is a schematic cross-sectional view along the CC line of a modified example 2 of the field absorption modulator shown in Figure 1. [Figure 8] This is a schematic cross-sectional view of a field-absorbing modulator according to a second embodiment. [Figure 9] This is a schematic cross-sectional view of a field-absorbing modulator according to a second embodiment. [Figure 10] This is a top view of an electric field absorption modulator according to the third embodiment. [Figure 11] Figure 10 is a schematic cross-sectional view of the field absorption modulator along the XI-XI line. [Figure 12A]It is a schematic cross-sectional view along line A-A of the electric field absorption type modulator shown in FIG. 10. [Figure 12B] It is a schematic cross-sectional view along line B-B of the electric field absorption type modulator shown in FIG. 10. [Figure 12C] It is a schematic cross-sectional view along line C-C of the electric field absorption type modulator shown in FIG. 10. [Figure 13] It is a top view of the electric field absorption type modulator according to the fourth embodiment. [Figure 14A] It is a schematic cross-sectional view along line A-A of the electric field absorption type modulator shown in FIG. 13. [Figure 14B] It is a schematic cross-sectional view along line B-B of the electric field absorption type modulator shown in FIG. 13. [Figure 15] It is a schematic cross-sectional view along line E-E of the electric field absorption type modulator shown in FIG. 13. [Figure 16] It is a top view of the electric field absorption type modulator according to the fifth embodiment. [Figure 17] It is a schematic cross-sectional view along line XVII-XVII of the electric field absorption type modulator shown in FIG. 16. [Figure 18A] It is a schematic cross-sectional view along line A-A of the electric field absorption type modulator shown in FIG. 16. [Figure 18B] It is a schematic cross-sectional view along line B-B of the electric field absorption type modulator shown in FIG. 16. [Figure 18C] It is a schematic cross-sectional view along line C-C of the electric field absorption type modulator shown in FIG. 16. [Figure 19] It is a top view of the electric field absorption type modulator according to a modification of the fifth embodiment. [Figure 20] It is a schematic cross-sectional view along line XX-XX of the modified electric field absorption type modulator shown in FIG. 19. [Figure 21] It is a top view of the electric field absorption type modulator according to the sixth embodiment. [Figure 22] It is a schematic cross-sectional view along line A-A of the electric field absorption type modulator shown in FIG. 21. [Figure 23] It is a schematic cross-sectional view along line B-B of the electric field absorption type modulator shown in FIG. 21. [Figure 24]Figure 21 is a schematic cross-sectional view of the field absorption modulator along the CC line. [Figure 25] This is a top view of a semiconductor optical device according to the sixth embodiment. [Modes for carrying out the invention]

[0009] The embodiments of the present invention will be described in detail below with reference to the drawings. In all the drawings used to illustrate the embodiments, components having the same function will be denoted by the same reference numerals, and repeated descriptions will be omitted. The drawings shown below are merely illustrative examples of the embodiments, and the size of the drawings does not necessarily correspond to the scale described in these embodiments.

[0010] [First Embodiment] Figure 1 is a top view of an electric field absorption modulator 1 (hereinafter referred to as EA modulator 1) according to the first embodiment. Figure 2 shows a schematic cross-sectional view along the line II-II in Figure 1. Figure 3A shows a schematic cross-sectional view along the line AA in Figure 1. Figure 3B shows a schematic cross-sectional view along the line BB in Figure 1. Figure 3C shows a schematic cross-sectional view along the line CC in Figure 1. Here, the EA modulator 1 is a semiconductor optical element that has the function of converting light from a light source (not shown) into a modulated optical signal.

[0011] The EA modulator 1 has a structure in which the first EA modulator section 10A, the connecting waveguide section 20, and the second EA modulator section 10B are integrated on a single substrate 3. The first EA modulator section 10A, the connecting waveguide section 20, and the second EA modulator section 10B are optically connected by a butt joint connection. Continuous light output from a light source (not shown) is incident from the end face on the first EA modulator section 10A side and output as a modulated light signal from the end face on the second EA modulator section 10B side. Here, the substrate 3 is a semi-insulating semiconductor substrate. Hereafter, semi-insulating means that it has an insulating property that is substantially such that almost no current flows compared to a conductive semiconductor layer, which will be described later. In the EA modulator 1, the first EA modulator section 10A, the connecting waveguide section 20, and the second EA modulator section 10B are arranged on a semi-insulating semiconductor layer 5. In this embodiment, the semi-insulating semiconductor layer 5 is the substrate 3. Note that the substrate 3 may be a conductive semiconductor substrate. In that case, a semi-insulating semiconductor layer 5 is separately placed on the substrate 3 so that the first n-side semiconductor layer 12A (described later) and the substrate 3 are electrically insulated.

[0012] [First EA Modulator Section] The first EA modulator section 10A has a first n-type semiconductor layer 12A, a first absorption layer 14A, and a first p-type semiconductor layer 16A, which are stacked in order from the semi-insulating semiconductor layer 5 side. Hereafter, unless otherwise specified, the semiconductor layers are assumed to be stacked upwards from the semi-insulating semiconductor layer 5. The first n-type semiconductor layer 12A may contain multiple semiconductor layers. The first n-type semiconductor layer 12A includes at least a cladding layer with a band gap larger than that of the first absorption layer 14A. The first n-type semiconductor layer 12A may also include a light confinement layer. The first absorption layer 14A absorbs light in accordance with the applied voltage. Here, the first absorption layer 14A is a multiple quantum well layer of an i-type semiconductor layer that has not been intentionally doped with impurities. The first absorption layer 14A may also be a conductive type absorption layer. The first p-type semiconductor layer 16A may contain multiple semiconductor layers. The first p-type semiconductor layer 16A includes at least a cladding layer with a band gap larger than that of the first absorption layer 14A. The first p-type semiconductor layer 16A may also include a light confinement layer. The first p-type semiconductor layer 16A is electrically and physically connected to the first EA electrode 18A. Details of the first EA electrode 18A will be described later. The first EA modulator section 10A has a pin structure extending from the first EA electrode 18A toward the semi-insulating semiconductor layer 5.

[0013] [Second EA Modulator Section] The second EA modulator section 10B has a second p-type semiconductor layer 16B, a second absorption layer 14B, and a second n-type semiconductor layer 12B, which are stacked in order from the semi-insulating semiconductor layer 5 side. The second p-type semiconductor layer 16B may include multiple semiconductor layers. The second p-type semiconductor layer 16B includes at least a cladding layer with a band gap larger than that of the second absorption layer 14B. The second p-type semiconductor layer 16B may also include a light confinement layer. The second absorption layer 14B absorbs light in accordance with the applied voltage. Here, the second absorption layer 14B is a multiple quantum well layer of i-type semiconductor layers that have not been intentionally doped with impurities. The second absorption layer 14B may also be a conductive type absorption layer. The second n-type semiconductor layer 12B may include multiple semiconductor layers. The second n-type semiconductor layer 12B includes at least a cladding layer with a band gap larger than that of the second absorption layer 14B. The second n-type semiconductor layer 12B may also include a light confinement layer. The second n-type semiconductor layer 12B is electrically and physically connected to the second EA electrode 18B. Details of the first EA electrode 18B will be described later. The second EA modulator section 10B has a nip structure extending from the second EA electrode 18B toward the semi-insulating semiconductor layer 5.

[0014] The first absorption layer 14A and the second absorption layer 14B are identical in thickness, composition, and length in the optical axis direction. Here, the optical axis direction is the first direction D1 shown in Figure 1. Furthermore, the composition and thickness of the well layer and barrier layer constituting the multiple quantum well layer are identical, and the number of these pairs is also identical. Here, "identical" means identical within the range of manufacturing variations. The well layer and barrier layer are composed of InGaAsP or InGaAlAs, but these materials are merely examples. Note that the two absorption layers may have different structures.

[0015] [Connecting Waveguide Section] The connecting waveguide section 20 is arranged to propagate light output from the first EA modulator section 10A to the second EA modulator section 10B. The connecting waveguide section 20 has, in order from the semi-insulating semiconductor layer 5 side, a lower waveguide layer 23, a waveguide layer 24, and an upper waveguide layer 25. The lower waveguide layer 23 may include multiple semiconductor layers. The lower waveguide layer 23 includes at least a cladding layer with a band gap larger than that of the waveguide layer 24. The lower waveguide layer 23 may also include a light confinement layer. Here, the lower waveguide layer 23 is an n-type semiconductor layer. The waveguide layer 24 is a semiconductor layer with a band gap that does not absorb propagating light. The waveguide layer 24 may be a single layer or multiple layers. For example, the waveguide layer 24 is a bulk semiconductor layer. The upper waveguide layer 25 may include multiple semiconductor layers. The upper waveguide layer 25 includes a cladding layer with a bandgap larger than that of the waveguide layer 24. The upper waveguide layer 25 may also include an optical confinement layer. Here, the upper waveguide layer 25 is a p-type semiconductor layer.

[0016] Here, it is preferable that the cladding layers contained in the first n-type semiconductor layer 12A of the first EA modulator section 10A, the second p-type semiconductor layer 16B of the second EA modulator section 10B, and the lower waveguide layer 23 of the connecting waveguide section 20 are all made of the same material. Here, "same material" refers to materials with the same semiconductor elements and substantially the same composition, although the impurities added to provide conductivity or improve insulation may differ. Specifically, the first n-type semiconductor layer 12A and the lower waveguide layer 23 contain an n-InP cladding layer. The second p-type semiconductor layer 16B contains a p-InP cladding layer. Similarly, it is preferable that the cladding layers contained in the first p-type semiconductor layer 16A, the second n-type semiconductor layer 12B, and the upper waveguide layer 25 are all made of the same material. Specifically, the first p-type semiconductor layer 16A and the upper waveguide layer 25 include a p-InP cladding layer, and the second n-type semiconductor layer 12B includes an n-InP cladding layer.

[0017] [Mesa Structure 7] The EA modulator 1 has a mesa structure 7 as shown in Figures 3A, B, and C. The first n-type semiconductor layer 12A, the first absorption layer 14A, and the first p-type semiconductor layer 16A of the first EA modulator section 10A are included in the mesa structure 7. Similarly, the second p-type semiconductor layer 16B, the second absorption layer 14B, and the second n-type semiconductor layer 12B of the second EA modulator section 10B are included in the mesa structure 7. Similarly, the lower waveguide layer 23, the waveguide layer 24, and the upper waveguide layer 25 of the connecting waveguide section 20 are included in the mesa structure 7. Note that a portion of the semi-insulating semiconductor layer 5 (in this case, the substrate 3) may also be included in the mesa structure 7. Note that the mesa structure 7 is not located at the center of the EA modulator 1 (the center of the second direction D2, which is perpendicular to the optical axis in a plan view), but is located off to one side as shown in Figures 1 and 3. However, it is not limited to this, and may be located in the center.

[0018] [Embedding layer] Embedding layers 35 are placed on both sides of the mesa structure 7. The embedding layers 35 may be a semi-insulating semiconductor layer, a stacked structure of n-type and p-type semiconductor layers, or a combination thereof. In this case, the embedding layers 35 are composed of semi-insulating Fe-InP.

[0019] [sulfonamide] An insulating film 30 is placed on the upper surface of the EA modulator 1. The insulating film 30 is placed everywhere except on the upper part of the mesa structure 7 of the first EA modulator section 10A and the second EA modulator section 10B. The insulating film 30 is also placed on the upper surface of the upper waveguide layer 25 and the upper surface of the embedding layer 35 of the connecting waveguide section 20.

[0020] [Backside electrode] The back surface of the substrate 3 is broadly covered with back electrodes 34. The back electrodes 34 are not electrodes for operating the EA modulator 1, but are used as adhesive electrodes when soldering the EA modulator 1 to a mounting substrate such as a submount. Therefore, the back electrodes 34 can be omitted when bonding without using solder, or when mounting with the first EA electrode 18A and the second EA electrode 18B facing the submount.

[0021] [EA electrode] The first EA electrode 18A includes a first mesa electrode 31A positioned on top of the mesa structure 7, a first EA pad electrode 33A positioned on top of the embedding layer 35, and a first bridge electrode 32A connecting them. These are integrally formed. Similarly, the second EA electrode 18B includes a second mesa electrode 31B positioned on top of the mesa structure 7, a second EA pad electrode 33B positioned on top of the embedding layer 35, and a second bridge electrode 32B connecting them. These are integrally formed.

[0022] Figure 4 shows a top view of a semiconductor optical device 50 with an EA modulator 1 mounted on a submount 52. The EA modulator 1 is fixed to the submount 52 on the side of the back electrode 34. The submount 52 has multiple pads. The pads and the EA modulator 1 are connected by wires. Specifically, the submount 52 has a first pad 54A, a second pad 54B, a third pad 56, and a fourth pad 58. Here, these are referred to as pads, but they are electrode wirings provided on the submount 52 and also function as transmission lines. A high-frequency electrical signal is input to the first pad 54A from an external source. The first pad 54A is connected by a wire to the first EA pad electrode 33A of the EA modulator 1. Furthermore, the first EA pad 33A is connected by a wire to the third pad 56. The second pad 54B is connected by a wire to the second EA pad electrode 33B. The second pad 54B is also connected to a reference potential, in this case, ground potential. A matching resistor 60 is placed between the third pad 56 and the fourth pad 58 to improve impedance matching with the external electrical circuit. The matching resistor 60 is, for example, 50Ω. The fourth pad 58 is connected to ground potential. In other words, the matching resistor 60 is electrically connected in parallel with the EA modulator 1. The electrical signal applied to the first pad 54A is a negative-biased high-frequency signal. It goes without saying that applying a positive-biased electrical signal to the second pad 54B and using the first pad 54A as the reference potential is equivalent.

[0023] [effect] The dotted line in Figure 5 shows an image diagram of the transmission path of the electrical signal (high-frequency signal) applied between the first EA electrode 18A and the second EA electrode 18B. The path shown by the dotted line is the path through which the most current flows. The applied voltage is applied between the first p-type semiconductor layer 16A and the first n-type semiconductor layer 12A of the first EA modulator section 10A, and the first absorption layer 14A absorbs the light. Furthermore, the electrical signal is transmitted to the second p-type semiconductor layer 16B of the second EA modulator section 10B via the lower waveguide layer 23 of the connecting waveguide section 20. Then, a voltage is applied between the second p-type semiconductor layer 16B and the second n-type semiconductor layer 12B, and the second absorption layer 14B absorbs the light. Because the electrical signal is a high-frequency signal, the EA modulator 1 generates a high-frequency optical signal corresponding to the high-frequency electrical signal.

[0024] The dotted electrical signal transmission path is a path through which a voltage (negative bias) is applied in the pin direction to both the first EA modulator section 10A and the second EA modulator section 10B. The two modulator sections are electrically connected in series by the lower waveguide layer 23 of the waveguide section. In other words, the lower waveguide layer 23 is a connecting medium for electrically connecting the two EA modulator sections in series. When viewed in the direction of electrical signal transmission, the lower waveguide layer 23 and the second p-type semiconductor layer 16B are in an np connection. Since the drive bias is negative bias, this connection interface is a forward interface and current flows. Therefore, the lower waveguide layer 23 functions as a connecting medium. Here, the lower waveguide layer 23 is referred to as the connecting semiconductor layer.

[0025] In Patent Document 2, since both modulators have a pin structure when viewed from the surface electrodes, in order to electrically connect the first modulator and the second modulator in series, it is necessary to connect the bottom layer (n-type layer) of the first modulator and the top layer (p-type layer) of the second modulator. Electrodes are used for this connection, but these electrodes are arranged three-dimensionally, extending from the bottom to the top of the mesa structure. Parasitic capacitance may occur between the side surface of the mesa structure and these electrodes. Furthermore, parasitic inductance components may also occur due to the long wiring length. This structure leads to deterioration of high-frequency characteristics. On the other hand, in this embodiment, the connecting medium (lower waveguide layer 23) is not structured to extend along the side surface of the mesa structure 7 from below to above the mesa structure 7. In other words, the lower waveguide layer 23 can be described as a connecting medium arranged planarly. Therefore, large parasitic inductance and parasitic capacitance are not generated, and the two EA modulator sections can be electrically connected in series while suppressing the impact on high-frequency characteristics.

[0026] This effect can be obtained because the first EA modulator section 10A has a pin structure when viewed from the first EA electrode 18A side, while the second EA modulator section 10B has a nip structure when viewed from the second EA electrode 18B side, and these are integrated on the substrate. Furthermore, they are electrically connected in series by a planar connecting medium (lower waveguide layer 23).

[0027] Furthermore, not all incident light is absorbed by the first EA modulator section 10A. Light not absorbed by the first EA modulator section 10A is transmitted to the second EA modulator section 10B and absorbed there. The total amount of light absorbed by the two EA modulator sections is proportional to the extinction ratio. On the other hand, the parasitic capacitance of EA modulator 1 is the sum of the capacitances of the first EA modulator section 10A and the second EA modulator section 10B. Here, if we define the capacitances of the first EA modulator section 10A and the second EA modulator section 10B as C1 and C2, respectively, then the parasitic capacitance of the entire EA modulator 1 is C1 × C2 / (C1 + C2). Here, since the first EA modulator section 10A and the second EA modulator section 10B have the same modulator length and the same semiconductor structure, C1 = C2. Therefore, the parasitic capacitance of the entire EA modulator 1 is C1 / 2. On the other hand, if the same extinction ratio is to be satisfied with a single EA modulator, the modulator length must be twice that of the first EA modulator section 10A. In this case, the parasitic capacitance becomes 2 × C1. In other words, this embodiment can reduce the parasitic capacitance to 1 / 4 while maintaining the same extinction ratio, enabling faster operation. Furthermore, because there are no long wires or long electrodes between the first EA modulator section 10A and the second EA modulator section 10B, the generation of parasitic capacitance and parasitic inductance between the two modulators can be suppressed. Note that the first EA modulator section 10A and the second EA modulator section 10B do not necessarily need to have the same modulator length. However, from a manufacturing standpoint, it is preferable that they have the same semiconductor multilayer structure. Note that when a structure with a single EA modulator that is twice the length of the first EA modulator section 10A is used for a certain drive voltage, the drive voltage is doubled in this embodiment to obtain an equivalent extinction ratio.

[0028] Here, voltage can also be applied to paths other than the dotted line. For example, a path can be considered in which voltage is transmitted from the first p-type semiconductor layer 16A to the second n-type semiconductor layer 12B via the upper waveguide layer 25 (p-type). However, this path has a pn connection, and in negative bias drive, it becomes reverse bias drive, and almost no current flows. Also, these three upper layers are layers that do not absorb light and do not contribute to the generation of optical modulation signals. To further block the current in this path, the upper waveguide layer 25 may be made a high-resistance semiconductor layer instead of a conductive semiconductor layer. For example, it may be made a semi-insulating semiconductor layer by adding impurities such as Fe-InP. Alternatively, protons may be injected into the conductive semiconductor layer to increase its resistance. Furthermore, there is also a method of increasing the resistance by reducing the layer thickness of the upper waveguide layer 25 in the stacking direction. Here, high resistance means that the resistance is at least higher than that of the first p-type semiconductor layer 16A.

[0029] To obtain the effects of the present invention, there is no limit to the length of the first direction D1 of the connecting waveguide section 20. However, if it is too short, parasitic capacitance components may be generated between the first EA electrode 18A and the second EA electrode 18B (especially between the first mesa electrode 31A and the second mesa electrode 31B). If it is too long, the resistance of the lower waveguide layer 23 will increase, leading to a voltage drop and potentially affecting the extinction ratio characteristics. Therefore, the length of the first direction D1 of the connecting waveguide section 20 is preferably 30 μm or more and 100 μm or less.

[0030] [Example 1] Figures 6A, B, and C show schematic cross-sectional views of the EA modulator 1 according to Modification 1 of the First Embodiment. Figures 6A, B, and C are cross-sectional views corresponding to Figures 3A, B, and C of the First Embodiment, respectively.

[0031] This embodiment differs from the first embodiment in that the first n-type semiconductor layer 12A, the second p-type semiconductor layer 16B, and the lower waveguide layer 23 are located beneath the embedding layer 35. Parts of each of these layers constitute the lower layers of the mesa structure 7. However, these three layers do not necessarily have to be included in the mesa structure 7.

[0032] The connecting medium that electrically connects the first EA modulator section 10A and the second EA modulator section 10B is the lower waveguide layer 23, as in the first embodiment. In the first embodiment, the lower waveguide layer 23 is contained within the mesa structure 7. Here, if we define the direction perpendicular to the optical axis in a plan view as the second direction D2, the width of the mesa structure 7 in the second direction D2 (mesa width) is several μm. Therefore, the lower waveguide layer 23 has a certain degree of resistance, causing the applied voltage to drop and raising concerns that a sufficient extinction ratio cannot be obtained. On the other hand, in this modified example, the lower waveguide layer 23 extends below the mesa structure 7, making it possible to reduce the resistance compared to the first embodiment. Therefore, the voltage drop is smaller, and a higher extinction ratio can be obtained under the same driving voltage.

[0033] [Differentiation 2] Figures 7A, B, and C show schematic cross-sectional views of the EA modulator 1 according to a modified example 2 of the first embodiment. Figures 7A, B, and C are cross-sectional views corresponding to Figures 3A, B, and C of the first embodiment, respectively.

[0034] Modification 1 differs from the first n-type semiconductor layer 12A, the second p-type semiconductor layer 16B, and the lower waveguide layer 23 in shape. In this modification, these three layers do not extend to the side of the EA modulator 1 on one side of the mesa structure 7 in the second direction D2. Specifically, as shown in Figure 7A, the first n-type semiconductor layer 12A is not positioned to overlap with the first EA pad electrode 33A in a plan view. Similarly, as shown in Figure 7B, the second p-type semiconductor layer 16B is not positioned to overlap with the second EA pad electrode 33B in a plan view. The lower waveguide layer 23 has the same width as the first n-type semiconductor layer 12A and the second p-type semiconductor layer 16B in the second direction D2.

[0035] In Modification 1, a first n-type semiconductor layer 12A is positioned below the first EA pad electrode 33A, separated by a embedding layer 35. A voltage is applied between the first EA pad electrode 33A and the first n-type semiconductor layer 12A, resulting in parasitic capacitance proportional to the size of the first EA pad electrode 33A. This parasitic capacitance hinders high-speed operation. In this modification, the first n-type semiconductor layer 12A is not positioned below the first EA pad electrode 33A; instead, a semi-insulating semiconductor layer 5 is positioned. Therefore, parasitic capacitance originating from the first EA pad electrode 33A is either absent or very small. Consequently, the EA modulator 1 in Modification 2 exhibits excellent high-speed response. A similar effect can be obtained with the second EA pad electrode 33B.

[0036] [Second Embodiment] Figure 8 is a schematic cross-sectional view of the EA modulator 201 according to the second embodiment, and corresponds to Figure 5 of the first embodiment. Figure 9 is a schematic cross-sectional view of the first EA modulator section 10A along the direction perpendicular to the mesa structure 7, and corresponds to Figure 3A. This embodiment differs from the first embodiment in that a spacer layer 240 is arranged between the substrate 3, the first n-type semiconductor layer 12A, the second p-type semiconductor layer 16B, and the lower waveguide layer 23. Another difference is that the lower waveguide layer 23 and the upper waveguide layer 25 of the connecting waveguide section 20 are semi-insulating semiconductor layers. Note that the cross-sections of the second EA modulator section 10B and the connecting waveguide section 20 in the direction perpendicular to the mesa structure 7 (corresponding to Figure 9) are the same as the cross-sectional view of the first EA modulator section 10A, although the layers included in the mesa structure 7 are different.

[0037] The spacer layer 240 is an n-type semiconductor layer, and in this case it is the same n-InP as the first n-type semiconductor layer 12A. In the first embodiment, the connecting medium connecting the first EA modulator section 10A and the second EA modulator section 10B was the lower waveguide layer 23 of the connecting waveguide section 20. In this embodiment, the connecting medium is the spacer layer 240. The spacer layer 240 is arranged over the entire surface of the substrate 3 (semi-insulating semiconductor layer 5), and its thickness in the stacking direction and width in the second direction D2 are greater than those of the lower waveguide layer 23, and its resistance is lower compared to the lower waveguide layer 23. Therefore, the electrical resistance between the first EA modulator section 10A and the second EA modulator section 10B can be reduced. In Figure 8, the electrical path is shown by a dotted line, similar to Figure 5. As shown in Figure 8, the first EA modulator section 10A and the second EA modulator section 10B are electrically connected in series via the spacer layer 240 (connecting medium). Furthermore, the spacer layer 240 is not positioned on the side surface of the mesa structure 7, but is positioned planarly, thus achieving the effects described in the first embodiment.

[0038] In this case, the lower waveguide layer 23 may be a conductive type, such as an n-type semiconductor layer. In that case, the electrical path will be a path through the lower waveguide layer 23 in addition to the spacer layer 240. The spacer layer 240 may also be a p-type semiconductor. However, since n-type semiconductors have lower resistance than p-type semiconductors, an n-type semiconductor is preferred for the spacer layer 240. [Third Embodiment]

[0039] Figure 10 is a top view of the field absorption modulator 301 according to the third embodiment. Figure 11 shows a schematic cross-sectional view along the line XI-XI in Figure 10. Figure 12A shows a schematic cross-sectional view along the line AA in Figure 10. Figure 12B shows a schematic cross-sectional view along the line BB in Figure 10. Figure 12C shows a schematic cross-sectional view along the line CC in Figure 10. Similar to the EA modulators shown in other embodiments, the EA modulator 301 according to this embodiment has a first EA modulator section 310A, a second EA modulator section 310B, and a connecting waveguide section 320 arranged between them, all integrated on a substrate 3.

[0040] The EA modulator 301 has a mesa structure 7 and embedding layers 335 arranged on both sides of it. The location of the mesa structure 7 is shown by a dashed line in Figure 10. A spacer layer 340 is also arranged on the upper surface of the mesa structure 7 and the embedding layer 335. Here, the spacer layer 340 is an n-type semiconductor layer, for example, an n-InP layer. As shown in Figure 12A, the embedding layer 335 and the spacer layer 340 do not extend to the side of the EA modulator 301 on one side of the mesa structure.

[0041] In the first EA modulator section 310A, the first EA electrode 318A is located in the region where the embedding layer 335 is not present. The first EA electrode 318A consists only of a first EA pad electrode to which an external electrical signal is transmitted. The first EA electrode 318A is electrically and physically connected to the first n-type semiconductor layer 12A.

[0042] In the second EA modulator section 310B, the second EA electrode 318B is placed in the region where the embedded layer 335 is not located. The second EA electrode 318B consists only of second EA pad electrodes to which external electrical signals are transmitted. The second EA electrode 318B is electrically and physically connected to the second p-type semiconductor layer 16B.

[0043] The lower waveguide layer 23 and the upper waveguide layer 25 of the connecting waveguide section 320 are semi-insulating semiconductor layers. However, as in other embodiments, they may be conductive semiconductor layers or high-resistivity semiconductor layers.

[0044] The insulating film 30 is located on the surface of the EA modulator 301. However, it is not located at the connection points between the first EA electrode 318A and the first n-type semiconductor layer 312A, or between the second EA electrode 318B and the second p-type semiconductor layer 316B.

[0045] Figure 11 shows an image diagram of the electrical signal transmission path, similar to Figure 5, using solid and dotted lines. Here, the connecting medium that electrically connects the first EA modulator section 310A and the second EA modulator section 310B in series is the spacer layer 340. The solid lines indicate the external voltage applied to the first EA electrode 318A and the second EA electrode 318B. For convenience, it is shown here as if the voltage is applied from the side (end face) of the EA modulator 301, but in reality, as shown in Figures 10, 12A, and 12B, it is applied to the surface side of the EA modulator 301 (the surface side of the first EA electrode 318A and the second EA electrode 318B). In this embodiment, a negative bias electrical signal is input to the second EA electrode 318B, and the first EA electrode 318A is connected to ground ionization (reference potential). In this embodiment as well, a voltage is applied to the two modulator sections in the pin direction, and they are electrically connected in series by a planar connecting medium (spacer layer 340), thereby achieving the effects described above. As described above, the negative bias does not necessarily have to be applied from the upper layer of the mesa structure 7; it may also be applied from the lower layer of the mesa structure 7. Both EA modulators should be configured so that a negative bias voltage is applied in the pin direction.

[0046] The spacer layer 340 may be a p-type semiconductor. However, since n-type semiconductors have lower resistance than p-type semiconductors, an n-type semiconductor is preferred for the spacer layer 340.

[0047] [Fourth Embodiment] Figure 13 is a top view of the EA modulator 401 according to the fourth embodiment. Figure 14A shows a schematic cross-sectional view along line AA in Figure 13. Figure 14B shows a schematic cross-sectional view along line BB in Figure 13. Figure 15 shows a schematic cross-sectional view along line EE. In Figure 15, a dotted line shows an image diagram of the electrical signal transmission path through the connecting medium.

[0048] The semiconductor multilayer of the EA modulator 401 is the same as that of the EA modulator 1 of the first embodiment. The main differences are as follows. First, as shown in Figures 14A and 14B, the embedding layer 35 is not located on the left side of the mesa structure 7, extending to the side of the EA modulator 401. In the region where the embedding layer 35 is not located, the respective underlying layers (first n-type semiconductor layer 12A, second p-type semiconductor layer 16B, and lower waveguide layer 23) and the insulating film 30 are located. Note that, as shown in Figures 14A and 14B, the embedding layer 35 is not absent from the entire left region of the mesa structure 7; the embedding layer is in contact with both sides of the mesa structure 7. In addition, a connecting electrode 428 is located in a part of the region where the embedding layer 35 is not located. Details of the connecting electrode 428 will be described later.

[0049] Although not shown in the diagram, the cross-sectional view of the mesa structure 7 along the first direction D1 is identical to that in Figure 2.

[0050] The connecting electrode 428 is made of metal. Here, the connecting electrode 428 is the connecting medium. The connecting electrode 428 connects the first n-type semiconductor layer 12A and the second p-type semiconductor layer 16B. In the connecting waveguide section 20, an insulating film 30 is placed between the connecting electrode 428 and the lower waveguide layer 23. Note that the insulating film 30 below the connecting electrode 428 does not necessarily have to be placed.

[0051] Similar to the first embodiment, a negative bias is applied to the first EA electrode 18A, and the second EA electrode 18B is connected to ground potential (reference potential). In the first embodiment, the first EA modulator section 10A and the second EA modulator section 10B were electrically connected via the semiconductor lower waveguide layer 23, but in this embodiment, they are connected in series via the connecting electrode 428. As described above, current flows at the semiconductor interface between the n-type lower waveguide layer 23 and the second p-type semiconductor layer 16B because it is in a forward bias drive state. However, because it is a semiconductor junction interface, it also causes a voltage drop due to the built-in voltage. Furthermore, because the lower waveguide layer 23 is a semiconductor layer, its resistivity is higher compared to a conductor layer such as metal. On the other hand, in this embodiment, the first EA modulator section 10A and the second EA modulator section 10B are connected by a metal electrode, thus avoiding the effects of the above-mentioned voltage drop. Furthermore, unlike Patent Document 2, the metal electrodes are not arranged on the sides of the mesa structure 7 but are planar and short in length, thus suppressing the generation of parasitic capacitance and parasitic inductance. Therefore, an EA modulator that can operate at high speed can be realized.

[0052] In this example, the lower waveguide layer 23 is an n-type semiconductor layer, as in the first embodiment, but it may also be a semi-insulating semiconductor layer.

[0053] [Fifth Embodiment] Figure 16 is a top view of the EA modulator 501 according to the fifth embodiment. Figure 17 shows a schematic cross-sectional view along the line XVII-XVII in Figure 16. Figures 18A, B, and C show schematic cross-sectional views along the lines AA, BB, and CC in Figure 16, respectively.

[0054] Unlike other embodiments, this embodiment does not have an embedded layer 35 on the side surface of the mesa structure 7. An insulating film 530 is provided on the side surface of the mesa structure 7.

[0055] In the first EA modulator section 510A, the first EA electrode 518A is located in a region away from the mesa structure 7. The first EA electrode 518A consists only of a first EA pad electrode to which an external electrical signal is transmitted. The first EA electrode 518A is electrically and physically connected to the first n-type semiconductor layer 12A.

[0056] In the second EA modulator section 510B, the second EA electrode 518B is located in a region away from the mesa structure 7. The second EA electrode 518B consists only of a second EA pad electrode to which an external electrical signal is transmitted. The second EA electrode 518B is electrically and physically connected to the second p-type semiconductor layer 16B.

[0057] The lower waveguide layer 23 and the upper waveguide layer 25 of the connecting waveguide section 520 are n-type semiconductor layers.

[0058] Figure 17 shows an image of the electrical signal transmission path, similar to Figure 5, using solid and dotted lines. Here, the connecting medium that electrically connects the first EA modulator section 510A and the second EA modulator section 510B in series is the upper waveguide layer 25 of the connecting waveguide section 520. In other words, the upper waveguide layer 25 is the connecting semiconductor layer. The solid lines show the external voltage applied to the first EA electrode 518A and the second EA electrode 518B. For convenience, it is shown here as if the voltage is applied from the side (end face) of the EA modulator 501, but in reality, as shown in Figures 16, 18A, and 18B, it is applied from the surface side of the EA modulator 501 (the surface side of the first EA electrode 518A and the second EA electrode 518B). In this embodiment, a negative bias electrical signal is input to the second EA electrode 518B, and the first EA electrode 518A is connected to ground ionization (reference potential). In this embodiment as well, voltage is applied to the two modulator sections in the pin direction, and they are electrically connected in series by a planar connecting medium (upper waveguide layer 25), thereby achieving the effects described above.

[0059] [Differentiation] Figure 19 is a top view of an EA modulator 501 according to a modified example of the fifth embodiment. Figure 20 is a schematic cross-sectional view along the line XX-XX in Figure 19. The differences from the fifth embodiment are the presence of a connecting electrode 528 and the polarity of the semiconductor layer of the connecting waveguide section 520.

[0060] As shown in Figure 20, the connecting electrode 528 connects the first p-type semiconductor layer 16A and the second n-type semiconductor layer 12B. The connecting electrode 528 is located on the upper surface of the mesa structure 7. The connecting electrode 528 is made of metal.

[0061] The lower waveguide layer 23 and the upper waveguide layer 25 of the connecting waveguide section 520 are semi-insulating semiconductor layers.

[0062] Figure 20 shows an image diagram of the electrical signal transmission path, similar to Figure 5, using solid and dotted lines. Here, the connecting medium that electrically connects the first EA modulator section 510A and the second EA modulator section 510B in series is the connecting electrode 528. The connecting electrode 528 allows the two modulator sections to be electrically connected in series without the need for a semiconductor. The effect is the same as that shown in the fourth embodiment. Furthermore, the connecting electrode 528 is located only on the upper surface of the mesa structure and has a planar structure.

[0063] [Sixth Embodiment] Figure 21 is a top view of the EA modulator 601 according to the sixth embodiment. Figure 22 shows a schematic cross-sectional view along line AA in Figure 21. Figure 23 shows a schematic cross-sectional view along line BB in Figure 21. Figure 24 shows a schematic cross-sectional view along line CC in Figure 21. The EA modulator 601 is an EA modulator integrated laser in which a semiconductor laser and an EA modulator are integrated on the same substrate 3.

[0064] The EA modulator 601 includes a laser section 670, a second connecting waveguide section 680, a first EA modulator section 610A, a connecting waveguide section 620, and a second EA modulator section 610B. Here, the first EA modulator section 610A, the connecting waveguide section 620, and the second EA modulator section 610B have the same multilayer structure as the EA modulator 1 described in the first embodiment. The substrate 3 is a semi-insulating semiconductor substrate.

[0065] [Laser section] The laser unit 670 has, in order from the semi-insulating semiconductor layer 5 (substrate 3) side, an n-type under-laser cladding layer 72, an active layer 74, and a p-type top-laser cladding layer 76. The under-laser cladding layer 72 includes a semiconductor layer with a larger band gap than the active layer 74. The under-laser cladding layer 72 may be a single layer or a multilayer structure. The active layer 74 includes at least a multiple quantum well layer that oscillates continuous light in response to an applied voltage, and the active layer may include an optical confinement layer on either the top or bottom of the multiple quantum well layer. The top-laser cladding layer 76 includes a semiconductor layer with a larger band gap than the active layer 74. The top-laser cladding layer 76 may be a single layer or a multilayer structure. The laser unit 670 also has a diffraction grating layer (not shown). The laser unit 670 has a pin structure extending from the first laser electrode 678 (described later) toward the semi-insulating semiconductor layer 5 side.

[0066] The laser unit 670 has a first laser electrode 678 electrically connected to the upper laser cladding layer 76 and a second laser electrode 679 electrically connected to the lower laser cladding layer 72. A DC current is injected here, and the laser unit 670 oscillates continuous light. Since the first laser electrode 678 is in contact with the p-type semiconductor layer (upper laser cladding layer 76), a positive voltage is applied to the first laser electrode 678, resulting in forward bias drive. The oscillated continuous light is transmitted to the second connecting waveguide unit 680.

[0067] [Second connecting waveguide section] The second connecting waveguide section 680 has, in order from the semi-insulating semiconductor layer 5 side, a second lower waveguide layer 83, a second waveguide layer 84, and a second upper waveguide layer 85. These layer structures are the same as those of the connecting waveguide section 620, except for polarity. An insulating film 30 is placed on the surface of the second upper waveguide layer 85.

[0068] Each region has a mesa structure 7, as shown in Figures 23 and 24. A burial layer 35 is arranged on the side of the mesa structure 7. The bottom layer of the mesa structure 7 is composed of a part of the lower layer of each region. These lower layers are widely arranged on the semi-insulating semiconductor layer 5 (substrate 3). Also, as shown in Figures 23 and 24, the burial layer 35 is not arranged in some areas where the first EA electrode 18A and the first laser electrode 678 are not arranged. In the laser section 670, there is an area where the insulating film 30 is not arranged, and the second laser electrode 679 is arranged in that area. Note that the cross-sectional view of the connecting waveguide section 620 and the second EA modulator section 610B along the second direction D2 is substantially the same as Figure 23, except that the multilayer structure is different.

[0069] Figure 25 shows a top view of the semiconductor optical device 650 with the EA modulator 601 mounted on a submount 652. The EA modulator 601 is fixed to the submount 652 on the side with the back electrode 34. A DC current is injected into the first laser electrode 678 of the laser unit 670 via a pad on the submount 652. The second laser electrode 679 is connected to ground potential. Differential electrical signals are applied to the first EA modulator unit 610A and the second EA modulator unit 610B, respectively. A differential electrical signal is a pair of electrical signals consisting of a positive-sequence signal and a negative-sequence signal. Here, the negative-sequence signal is applied to the first EA modulator unit 610A, and the positive-sequence signal is applied to the second EA modulator unit 610B. In this case, the negative-sequence signal is negatively biased, and the positive-sequence signal is positively biased. Each EA modulator unit is electrically connected in parallel with a matching resistor 660.

[0070] The differential electrical signal can reduce the amplitude of the high-frequency electrical signal by half compared to the single-ended drive shown in Figure 4. In the present invention, parasitic capacitance is reduced by shortening the modulator length. However, because the modulator length is shortened, the resistance increases, and the drive amplitude required to obtain the same extinction ratio increases. However, by driving with a differential signal, the extinction ratio can be secured without increasing the drive amplitude.

[0071] It is undesirable for the DC electrical signal injected into the laser section 670 and the high-frequency electrical signal applied to the EA modulator section to crosstalk with each other. To prevent crosstalk, in the second connecting waveguide section 680, the second lower waveguide layer 83 and the second upper waveguide layer 85 are made of semi-insulating semiconductor layers. The second waveguide layer 84 is also an intrinsic semiconductor without intentionally added impurities, and is electrically high-resisting. It should be noted that the second lower waveguide layer 83 and the second upper waveguide layer 85 do not necessarily have to be semi-insulating semiconductors. Resistance can be increased by adding impurities to the conductive semiconductor layer. For example, resistance can be increased by adding protons to a p-type semiconductor layer. Alternatively, a p-type semiconductor layer with higher resistance compared to an n-type semiconductor layer may be used.

[0072] According to this embodiment, since the laser unit 670 having a light-emitting function and the EA modulator units (610A, 610B) are integrated on the same substrate, a compact, low-capacitance, and high-extinction-ratio EA modulator can be realized. Note that the EA modulators shown in other embodiments and modifications may be differentially driven. Similarly, the EA modulator of this embodiment may be single-ended driven. When differentially driven, it is preferable that the absorption layers of the first EA modulator unit 610A and the second EA modulator unit 610B are identical in dimensions and semiconductor structure.

[0073] In this invention, two EA modulator sections are integrated on a substrate with a connecting waveguide section in between, and the two EA modulator sections are electrically connected in series via a planar connecting medium. In the stacking direction of the semiconductor layers, if one EA modulator section has a structure where the layers are p-absorption layer-n from top to bottom toward the substrate, the other EA modulator section has a stacking structure where the layers are n-absorption layer-p from top to bottom toward the substrate. The effects of this invention can be obtained by applying a negative bias to the p-type semiconductor layer of one EA modulator section and connecting the n-type semiconductor layer of the other EA modulator section to ground potential. At this time, the electrical connection between the n-type semiconductor layer of one EA modulator section and the p-type semiconductor layer of the other EA modulator section is made via the connecting medium.

[0074] The connecting medium has a planar structure. Here, a planar structure means that it does not have a three-dimensional structure that connects from a region where the mesa structure is not located along the side of the mesa structure to the top surface of the mesa structure. Therefore, being planar does not mean that it has no thickness. The connecting medium may be a semiconductor layer included in the connecting waveguide section. Alternatively, it may be a conductive semiconductor layer or metal electrode that connects to both the n-type semiconductor layer of one EA modulator section and the p-type semiconductor layer of the other EA modulator section. If the connecting medium is a semiconductor layer included in the connecting waveguide section, the semiconductor layer may be either n-type or p-type. The semiconductor layer of the connecting waveguide section, which is placed between the p-type semiconductor layer of one EA modulator section and the n-type semiconductor layer of the other EA modulator section, is preferably a semi-insulating or high-resistivity semiconductor layer.

[0075] Furthermore, in differential drive mode, a negative bias inverted phase signal is applied to the p-type semiconductor layer of one EA modulator, and a positive bias inverted phase signal is applied to the n-type semiconductor layer of the other EA modulator.

[0076] The EA modulator may further include a laser section and a second connecting waveguide section. The second connecting waveguide section is positioned between the laser section and one EA modulator section. To improve the electrical isolation between the electrical signal applied to the laser section and the electrical signal applied to the EA modulator section, it is desirable that the second connecting waveguide section be composed of a semi-insulating semiconductor layer or a high-resistivity semiconductor layer.

[0077] The EA modulator may be used as a semiconductor optical device mounted on a submount. External electrical signals are transmitted to the EA modulator via pads located on the submount. [Explanation of Symbols]

[0078] 1. Field-absorbing modulator 3 circuit boards 5. Semi-insulating semiconductor layer 7 Mesa structure 10A First EA Modulator Section 10B Second EA Modulator Section 12A First n-type semiconductor layer 14A First absorption layer 16A First p-type semiconductor layer 12B 2nd n-type semiconductor layer 14B Second absorption layer 16B Second p-type semiconductor layer 18A 1st EA electrode 18B 2nd EA electrode 20 Connecting waveguide section 23 Lower waveguide layer 24 Waveguide Layer 25 Upper waveguide layer 30 insulating film 31A First Mesa Electrode 32A First bridge electrode 33A First EA Pad Electrode 31B Second Mesa Electrode 32B Second bridge electrode 33B Second EA Pad Electrode 34 Backside electrodes 35. Embedding layer 50 Semiconductor Optical Devices 52 Submount 54A First pad 54B 2nd pad 56 Third pad 58. Pad 4 60 matching resistor 201 Field Absorption Modulator 240 Spacer layer 301 Field Absorption Modulator 310A First EA Modulator Section 310B Second EA Modulator Section 312A First n-type semiconductor layer 316B 2p-type semiconductor layer 318A 1st EA electrode 318B 2nd EA electrode 320 Connecting waveguide section 335 Embedding layer 340 Spacer layer 401 Field Absorption Modulator 428 Connecting electrodes 501 Field Absorption Modulator 510A First EA Modulator Section 510B Second EA Modulator Section 518A 1st EA electrode 518B 2nd EA electrode 520 Connecting Waveguide Section 528 Connecting electrodes 530 Insulating film 601 Field Absorption Modulator 610A First EA Modulator Section 610B 2nd EA Modulator Section 620 Connecting Waveguide Section 650 Semiconductor Optical Devices 652 Submount 660 matching resistor 670 Laser section 678 First laser electrode 679 Second laser electrode 680 Second connecting waveguide section 72 Laser-Undercladding Layer 74 Active layer 76 Laser-cladding layer 83 Second lower waveguide layer 84 Second Waveguide Layer 85 Second Upper Waveguide Layer D1 1st direction D2 2nd direction

Claims

1. A semi-insulating semiconductor layer, A first field absorption type modulator is formed by stacking a first n-type semiconductor layer, a first absorption layer, and a first p-type semiconductor layer in that order on the aforementioned semi-insulating semiconductor layer. A second field absorption type modulator is formed by stacking a second p-type semiconductor layer, a second absorption layer, and a second n-type semiconductor layer in that order on the aforementioned semi-insulating semiconductor layer. A connecting waveguide layer disposed between the first absorption layer and the second absorption layer, A first EA electrode is electrically connected to the first p-type semiconductor layer and electrically connected to the outside, A second EA electrode is electrically connected to the second n-type semiconductor layer and electrically connected to the outside, A connecting medium electrically connects the first n-type semiconductor layer and the second p-type semiconductor layer, and connects the first field-absorbing modulator section and the second field-absorbing modulator section in series. A field-absorbing modulator equipped with the following features.

2. The field absorption type modulator according to claim 1, The connecting medium is a field-absorbing modulator arranged in a planar manner.

3. The field absorption type modulator according to claim 1, Displaced between the first field-absorbing modulator section and the second field-absorbing modulator section, and comprising a connecting waveguide section including the connecting medium, The aforementioned connecting medium is a connecting semiconductor layer disposed between the first n-type semiconductor layer of the first field-absorbing modulator and the second p-type semiconductor layer of the second field-absorbing modulator, in a field-absorbing modulator.

4. The field absorption type modulator according to claim 3, The aforementioned connecting waveguide section includes the connecting waveguide layer, Furthermore, it has a mesa structure, The first n-type semiconductor layer, the second p-type semiconductor layer, and the connecting waveguide layer constitute the lower layer of the mesa structure, forming an electric field absorption modulator.

5. The field absorption type modulator according to claim 3, The aforementioned connecting waveguide section includes the connecting waveguide layer, Furthermore, it has a mesa structure, The first n-type semiconductor layer, the second p-type semiconductor layer, and the connecting waveguide layer constitute the upper layer of the mesa structure, forming an electric field absorption modulator.

6. The field absorption type modulator according to claim 1, The first n-type semiconductor layer and the second p-type semiconductor layer are further provided with a spacer layer between them and the semi-insulating semiconductor layer. The spacer layer is a conductive semiconductor layer that is electrically and physically connected to the first n-type semiconductor layer and the second p-type semiconductor layer. The aforementioned connecting medium is the spacer layer, in an electric field absorption type modulator.

7. The field absorption type modulator according to claim 6, The device comprises a connecting waveguide section, which is disposed between the first field-absorbing modulator section and the second field-absorbing modulator section and includes an upper waveguide layer disposed between the first p-type semiconductor layer and the second n-type semiconductor layer, The upper waveguide layer is a semi-insulating semiconductor layer or a high-resistance semiconductor layer, in this field-absorbing modulator.

8. The field absorption type modulator according to claim 6, The device comprises a connecting waveguide section, which is disposed between the first field-absorbing modulator section and the second field-absorbing modulator section and includes a lower waveguide layer disposed between the first n-type semiconductor layer and the second p-type semiconductor layer, The lower waveguide layer is a semi-insulating semiconductor layer or a high-resistance semiconductor layer, in this field-absorbing modulator.

9. The field absorption type modulator according to claim 1, The first p-type semiconductor layer and the second n-type semiconductor layer constitute a mesa structure, The mesa structure further comprises a spacer layer disposed on top of the mesa structure, The spacer layer is a conductive semiconductor layer that is electrically and physically connected to the first p-type semiconductor layer and the second n-type semiconductor layer. The aforementioned connecting medium is the spacer layer, in an electric field absorption type modulator.

10. The field absorption type modulator according to claim 1, A mesa structure comprising the first absorption layer and the second absorption layer, The system further comprises a metal connecting electrode that is electrically and physically connected to the first n-type semiconductor layer and the second p-type semiconductor layer, The metal connecting electrode is a connecting medium positioned spaced apart from the mesa structure, in this field-absorbing modulator.

11. The field absorption type modulator according to claim 1, The first p-type semiconductor layer and the second n-type semiconductor layer constitute a mesa structure, The upper surface of the mesa structure further comprises a metal connecting electrode that is electrically and physically connected to the first p-type semiconductor layer and the second n-type semiconductor layer, The metal connecting electrode is the connecting medium and is an electric field absorption type modulator, disposed only on the upper surface of the mesa structure.

12. The field absorption type modulator according to claim 1, A negative bias electrical signal is applied to the first EA electrode. The second EA electrode is an electric field absorption modulator connected to a reference potential.

13. The field absorption type modulator according to claim 1, A negative bias electrical signal of the differential signal is applied to the first EA electrode. An electric field absorption modulator to which an electrical signal with a positive bias of the differential signal is applied to the second EA electrode.

14. The field absorption type modulator according to claim 1, The first p-type semiconductor layer and the second n-type semiconductor layer constitute a mesa structure, The first EA electrode is connected to the first p-type semiconductor layer on the upper surface of the mesa structure, The second EA electrode is an electric field absorption modulator that connects to the second n-type semiconductor layer on the upper surface of the mesa structure.

15. The field absorption type modulator according to claim 1, The first p-type semiconductor layer and the second n-type semiconductor layer constitute a mesa structure, The first EA electrode is connected to the first p-type semiconductor layer in a region away from the mesa structure. The second EA electrode is an electric field absorption modulator that connects to the second n-type semiconductor layer in a region away from the mesa structure.

16. The field absorption type modulator according to claim 1, A mesa structure comprising the first absorption layer and the second absorption layer, An electric field absorption modulator further comprising an embedded layer disposed on the side surface of the mesa structure in a direction perpendicular to the direction in which the mesa structure extends.

17. The field absorption type modulator according to claim 1, A connecting waveguide section is disposed between the first field-absorbing modulator section and the second field-absorbing modulator section, A laser portion formed on the aforementioned semi-insulating semiconductor layer, An electric field absorption modulator further comprising a second connecting waveguide section disposed between the laser section and the first electric field absorption modulator section or the second electric field absorption modulator section.

18. The field absorption type modulator according to claim 17, The laser portion includes an n-type under-laser cladding layer, an active layer, and a p-type over-laser cladding layer, which are sequentially stacked on the semi-insulating semiconductor layer. The second connecting waveguide section is an electric field absorption modulator, comprising a lower waveguide layer of semi-insulating semiconductor, a waveguide layer, and an upper waveguide layer of semi-insulating semiconductor, which are sequentially stacked on the semi-insulating semiconductor layer.

19. The field absorption type modulator according to claim 1, The system comprises a submount on which the aforementioned electric field absorption modulator is mounted, The aforementioned submount is First pad and, The second pad and The third pad, The fourth pad, Equipped with matching resistors, The first pad and the first EA electrode are electrically connected. The second pad and the second EA electrode are electrically connected, The third pad and the first EA electrode are electrically connected. A matching resistor is placed between the third pad and the fourth pad. The fourth pad is connected to ground potential in a semiconductor optical device.

20. In the semiconductor optical apparatus according to claim 19, A negative bias electrical signal is applied to the first EA electrode via the first pad. A semiconductor photodevice in which the second EA electrode is connected to a reference potential via the second pad.

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