Optical modulator integrated semiconductor laser and optical module

Abstract

The optical modulator integrated semiconductor laser (500) of the present disclosure includes a semiconductor laser section (101) formed on a semi-insulating substrate (1), a first EA modulator section (113) formed on the semi-insulating substrate (1) and having at least an n-type first semiconductor layer, a first modulation layer (22), a p-type first semiconductor layer, and an n-type first electrode (26) electrically connected to the n-type first semiconductor layer, and a second EA modulator section (113) formed on the semi-insulating substrate (1) and having at least an n-type second semiconductor layer, a second modulation layer (42), a p-type second semiconductor layer, and a p-type The semiconductor device includes a second EA modulator section (115) having at least a p-type second electrode (45) electrically connected to the second semiconductor layer, a common electrode (47) electrically connected to the n-type first electrode (26) and the p-type second electrode (45), and a back electrode (61) formed on the back surface of the semi-insulating substrate (1) and having an opening (62) in an area facing either or both of the first EA modulator section (113) and the second EA modulator section (115) via the semi-insulating substrate (1).

Description

[Technical Field]

[0001] The present disclosure relates to an optical modulator integrated semiconductor laser and an optical module. [Background technology]

[0002] Along with the progress of digital transformation, which utilizes digital information, there has been remarkable development in communication networks that exchange digital information and data centers that store and process data. Optical communication is used for communication networks and communications within data centers, and in recent years there has been remarkable progress in increasing speed and capacity. Among these, the transmitting side of optical communication uses an electro-absorption (EA) modulator integrated semiconductor laser (EML: Electro-absorption Modulated Laser Diode), which has excellent high-speed performance and integrates an EA modulator and a semiconductor laser (LD: Laser Diode) on a single chip.

[0003] In EML, the laser light emitted from the LD is intensity-modulated by extinction (absorption) and transmission by the EA modulator, corresponding to the digital signal 0 and 1. Laser light modulated by the EA modulator can be modulated at higher speeds than by direct current modulation of the LD, and since the wavelength spectrum spread during optical modulation is small, it can be transmitted over long distances.

[0004] In recent years, EML has become the most important optical device for high-speed communications of 25 Gbit / sec or more. In particular, data centers use a method called PAM4 (Pulse Amplitude Modulation 4-level) to transmit optical signals at high symbol rates exceeding 50 Gbaud (1 Gbaud means 1 billion pulses per second).

[0005] As a layer that absorbs the light of an EA modulator and modulates the light intensity (light modulation layer), a multi-quantum well layer (MQW) is mainly used. When an electric field is applied to a pin junction in which an MQW layer, which is an i-type layer, is sandwiched between a p-type layer and an n-type layer by applying a reverse voltage, the light absorption edge wavelength of the MQW layer shifts to the long wavelength side. This is called the quantum confinement Stark effect, and light is modulated by utilizing the change in the light absorption coefficient due to the shift of the absorption edge wavelength.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] <Problems related to electromagnetic wave interference in EML> For example, in an EML used in a PAM4 transceiver, a DC current of about +100 mA is supplied to the LD, and a DC bias voltage of about -1 V and a signal voltage with an amplitude of 1 Vpp (peak-to-peak voltage) are applied to the EA modulator for driving. In the transceiver, a plurality of EMLs with different laser light wavelengths are arranged in close proximity to perform wavelength division multiplexing communication. In recent years, in order to meet the requirement for miniaturization of the transceiver, it is necessary to arrange the EMLs in parallel with a narrow pitch of about 1 mm or less, for example, four or more are mounted.

[0008] On the other hand, in order to support high-capacity communication, a voltage-modulated high-frequency signal with a modulation speed of 50 Gbaud or more as described above is applied to the EA modulator via a power supply line such as a signal line or a wire, and electromagnetic waves are emitted in the process. The LD is also connected to the LD current line by a wire or the like, and the wire portion is particularly susceptible to electromagnetic wave interference. Note that electromagnetic wave interference is also called high-frequency interference.

[0009] Furthermore, within the chip, the LD is subject to electromagnetic (high-frequency) interference via the parasitic capacitance and resistance between the EA modulator and the LD. When affected by electromagnetic (high-frequency) interference, the amount of laser light is modulated at high frequencies, resulting in intensity noise. Furthermore, when electromagnetic waves from an adjacent EA modulator couple to the EA modulator, potential fluctuations occur due to electromagnetic interference, causing the trace line of the electrical modulation waveform to become thicker. This results in a deterioration of the optical waveform quality and an increase in the error rate. Furthermore, electromagnetic interference also occurs with adjacent modulator drivers and with the light-receiving element.

[0010] In the future, advances in generative AI will further increase the volume of communication processing within datacenters, leading to the use of numerous transceivers. However, as bandwidth increases, the amount of electromagnetic interference also increases. This has led to limitations in the high-density packaging of EML and the broadband communication speeds, making solving the electromagnetic interference problem a major challenge. Currently, EML speeds of 100 to 200 Gbaud or more are required, and the cutoff frequency of EA modulators must be above 100 GHz, which is making the impact of electromagnetic interference even greater. Here, bandwidth refers to the frequency at which the frequency response is -3 dB.

[0011] A method for reducing the impact of electromagnetic interference on modulated light that is applied to EA modulators through signal lines, wires, and other power supply lines has been proposed: connecting two EA modulators in series. The first EA modulator is modulated with a positive-phase electrical signal, while the second EA modulator is modulated with a negative-phase electrical signal. In-phase electromagnetic noise applied to the two signal lines of the EA modulators is superimposed on the first and second EA modulators in opposing voltage directions. When voltage fluctuations caused by electromagnetic interference increase the amount of light passing through the first EA modulator, the second EA modulator acts to weaken the light passing through. As a result, the intensity fluctuations of the modulated light due to electromagnetic interference are canceled out by the two EA modulators. This makes it possible to suppress the impact of electromagnetic interference on modulated light.

[0012] As described above, in order for two EA modulators to cancel out the intensity fluctuations of modulated light, it is necessary for the difference in frequency response characteristics between the two EA modulators to be small. However, two EA modulators that modulate with electrical signals of opposite phases generally have different frequency response characteristics. This is because, in order to modulate two EA modulators with electrical signals of opposite phases, for example, when a modulation voltage is applied to the p-type semiconductor layer in the first EA modulator, it is necessary to apply a modulation voltage to the n-type semiconductor layer in the second EA modulator. However, the parasitic capacitance on the p-type semiconductor layer side and the parasitic capacitance on the n-type semiconductor layer side are structurally different in the EA modulators.

[0013] In other words, because the parasitic capacitance on the p-type semiconductor layer side of the EA modulator is different from the parasitic capacitance on the n-type semiconductor layer side, the frequency response characteristics of the two EA modulators, which are modulated by electrical signals of opposite phases, are different, which reduces the effect of suppressing fluctuations in modulated light caused by electromagnetic interference.In addition, if the parasitic capacitance is large in the first place, the required bandwidth cannot be obtained.

[0014] Even when modulating the p-type electrode of a single differential EA modulator with a positive-phase signal and the n-type electrode with a negative-phase signal, as in the modulator integrated laser element described in Patent Document 1, if in-phase voltage fluctuations caused by electromagnetic interference are applied to the differential signal line, they are canceled out between the positive-phase signal and the negative-phase signal, making it less susceptible to the effects of electromagnetic interference.

[0015] However, even in the case of a differential EA modulator such as the modulator-integrated laser element described in Patent Document 1, the parasitic capacitance on the p-type layer side of the differential EA modulator is different from the parasitic capacitance on the n-type layer side, resulting in different frequency responses when modulating the p-type electrode side and when modulating the n-type electrode side, which reduces the effectiveness of suppressing electromagnetic interference.In addition, there is the problem that the band is limited by the parasitic capacitance.

[0016] The present disclosure has been made to solve the above-mentioned problems, and aims to obtain an optical modulator-integrated semiconductor laser and optical module that can reduce the effects of electromagnetic interference and achieve a broadband by reducing the parasitic capacitance of the EA modulator and reducing the difference in frequency response characteristics between two EA modulators. [Means for solving the problem]

[0017] The optical modulator integrated semiconductor laser according to the present disclosure comprises: a semi-insulating substrate having a first surface and a second surface opposite to the first surface; a semiconductor laser portion formed on the first surface and having at least an n-type cladding layer, an active layer, and a p-type cladding layer; a first connecting waveguide portion formed on the first surface and having at least a lower first clad layer, a first waveguide layer, and an upper first clad layer; a first EA modulator section formed on the first surface, the first EA modulator section having at least an n-type first semiconductor layer, a first modulation layer, a p-type first semiconductor layer, an n-type first electrode electrically connected to the n-type first semiconductor layer, and a p-type first electrode electrically connected to the p-type first semiconductor layer; a second connecting waveguide portion formed on the first surface and having at least a lower second clad layer, a second waveguide layer, and an upper second clad layer; a second EA modulator section formed on the first surface, the second EA modulator section having at least an n-type second semiconductor layer, a second modulation layer, a p-type second semiconductor layer, an n-type second electrode electrically connected to the n-type second semiconductor layer, and a p-type second electrode electrically connected to the p-type second semiconductor layer; a common electrode electrically connected to the first n-type electrode and the second p-type electrode; an opening formed on the second surface and facing either or both of the first EA modulator section and the second EA modulator section via the semi-insulating substrate; The film thickness is between 1 μm and 10 μm. a back electrode; 、 The isolation resistance between the semiconductor laser section and the first EA modulator section is 500Ω or more. .

[0018] The optical module according to the present disclosure comprises: a submount having a ground electrode formed on its surface; The back electrode of the optical modulator integrated semiconductor laser is bonded to the ground electrode. do. [Effects of the Invention]

[0019] According to the optical modulator-integrated semiconductor laser and optical module of the present disclosure, the parasitic capacitance of the EA modulator is reduced and the difference in frequency response characteristics between the two EA modulators is reduced, thereby achieving the effect of reducing the effects of electromagnetic interference and enabling a broadband optical modulator-integrated semiconductor laser and optical module. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a top view illustrating an optical modulator-integrated semiconductor laser according to a first embodiment. [Figure 2A] 10 is a back view illustrating a configuration in which an opening is provided in a portion of the back electrode facing the second EA modulator portion in the optical modulator-integrated semiconductor laser according to the first embodiment. FIG. [Figure 2B] 10 is a back view illustrating a configuration in which an opening is provided in a portion of the back electrode facing the first EA modulator portion in the optical modulator-integrated semiconductor laser according to the first embodiment. FIG. [Figure 3] FIG. 10 is a rear view illustrating an optical modulator integrated semiconductor laser according to a comparative example. [Figure 4] 1 is a cross-sectional view taken along the light guiding direction of an optical modulator-integrated semiconductor laser according to a first embodiment. [Figure 5] 1 is a top view illustrating an optical module according to a first embodiment. [Figure 6] 6 is a cross-sectional view of a first EA modulator portion of an optical modulator-integrated semiconductor laser arranged on a submount in the optical module according to the first embodiment, that is, a cross-sectional view of a portion taken along line AA in FIG. 5. [Figure 7] 6 is a cross-sectional view of a second EA modulator portion of an optical modulator-integrated semiconductor laser disposed on a submount in the optical module according to the first embodiment, that is, a cross-sectional view of a portion along line BB in FIG. 5. [Figure 8] FIG. 10 is a cross-sectional view of a second EA modulator portion of an optical modulator-integrated semiconductor laser of an optical module as a comparative example. [Figure 9A] 1 is an equivalent circuit of a first EA modulator section. [Figure 9B] 1 is an equivalent circuit of the first EA modulator section when the inductance Lgrand of the ground wire is 0H. [Figure 10A] 10 is an equivalent circuit of the second EA modulator section. [Figure 10B] 10 is an equivalent circuit of the second EA modulator section when the inductance Lgrand of the ground wire is 0H. [Figure 11] 10 shows frequency response characteristics of a first EA modulator section and a second EA modulator section according to the first embodiment and a comparative example. [Figure 12] FIG. 4 is a top view illustrating another example of the optical modulator-integrated semiconductor laser according to the first embodiment. [Figure 13] FIG. 4 is a rear view showing another example of the optical modulator-integrated semiconductor laser according to the first embodiment. [Figure 14] 10 is a cross-sectional view of a second EA modulator portion of an optical modulator-integrated semiconductor laser in an optical module according to a second embodiment, taken along a direction perpendicular to the optical waveguide direction. FIG. [Figure 15] 10 is a diagram illustrating frequency response characteristics of a first EA modulator section and a second EA modulator section in the optical modulator-integrated semiconductor laser according to the second embodiment and the comparative example. FIG. [Figure 16] 11 is a cross-sectional view of a second EA modulator portion of an optical modulator-integrated semiconductor laser in an optical module according to a third embodiment, taken along a direction perpendicular to the optical waveguide direction. FIG. [Figure 17] FIG. 11 is a top view of an optical module according to a third embodiment. [Figure 18] 10 is a diagram illustrating frequency response characteristics of a first EA modulator section and a second EA modulator section in an optical modulator-integrated semiconductor laser according to the third embodiment and a comparative example. FIG. [Figure 19] FIG. 10 is a top view of an optical modulator-integrated semiconductor laser according to a fourth embodiment. [Figure 20] FIG. 10 is a rear view of the optical modulator-integrated semiconductor laser according to the fourth embodiment. [Figure 21] FIG. 10 is a top view of a submount in the optical module according to the fourth embodiment. [Figure 22]20 is a cross-sectional view of a first EA modulator portion of an optical modulator-integrated semiconductor laser arranged on a submount in an optical module according to a fourth embodiment, that is, a cross-sectional view of a portion along line AA in FIG. 19. [Figure 23] 20 is a cross-sectional view of a second EA modulator portion of an optical modulator-integrated semiconductor laser arranged on a submount in an optical module according to a fourth embodiment, that is, a cross-sectional view of a portion along line BB in FIG. 19. [Figure 24] 13 is a diagram illustrating frequency response characteristics of a first EA modulator section and a second EA modulator section in an optical modulator-integrated semiconductor laser according to the fourth embodiment and a comparative example. FIG. [Figure 25] 19. This is a cross-sectional view of the first EA modulator portion of the optical modulator-integrated semiconductor laser arranged on a submount in an optical module according to the first modification of the fourth embodiment, that is, a cross-sectional view of the portion corresponding to the portion along line AA in FIG. [Figure 26] 19. This is a cross-sectional view of the second EA modulator portion of the optical modulator-integrated semiconductor laser arranged on a submount in an optical module according to the first modification of the fourth embodiment, that is, a cross-sectional view of the portion corresponding to the portion along the line BB in FIG. [Figure 27] 19. This is a cross-sectional view of the first EA modulator portion of the optical modulator-integrated semiconductor laser arranged on a submount in an optical module according to the second modification of the fourth embodiment, that is, a cross-sectional view of the portion corresponding to the portion along line AA in FIG. [Figure 28] 19. This is a cross-sectional view of the second EA modulator portion of the optical modulator-integrated semiconductor laser arranged on a submount in an optical module according to the second modification of the fourth embodiment, that is, a cross-sectional view of the portion corresponding to the portion along the line BB in FIG. [Figure 29] FIG. 13 is a rear view of the optical modulator-integrated semiconductor laser according to the third modification of the fourth embodiment. [Figure 30] FIG. 13 is a top view of a submount in an optical module according to a third modification of the fourth embodiment. [Figure 31] FIG. 10 is a schematic view illustrating an optical module according to a fifth embodiment. [Figure 32]32 is a cross-sectional view of the optical module according to the fifth embodiment taken along the line AA in FIG. 31, in a direction perpendicular to the light guide direction of the first EA modulator section. [Figure 33] 32 is a cross-sectional view of the optical module according to the fifth embodiment, taken along a direction perpendicular to the light guide direction of the second EA modulator section, that is, along the line BB in FIG. 31. FIG. [Figure 34] 32 is a cross-sectional view of a pad portion of an EA modulator portion in the light guide direction of an optical module according to a fifth embodiment, that is, a cross-sectional view of a portion along line CC in FIG. 31. FIG. [Figure 35] 10 is a cross-sectional view of a pad portion of an EA modulator in the optical module according to the comparative example, in the waveguide direction of light. [Figure 36] FIG. 13 is a schematic view of an optical module according to a first modification of the fifth embodiment. [Figure 37] FIG. 13 is a schematic view of an optical module according to a second modification of the fifth embodiment. [Figure 38] FIG. 13 is a schematic view of an optical module according to a third modification of the fifth embodiment. [Figure 39] FIG. 13 is a schematic view of an optical module according to a fourth modification of the fifth embodiment. [Figure 40] FIG. 13 is a schematic view of an optical module according to a fifth modification of the fifth embodiment. [Figure 41] FIG. 13 is a schematic view of an optical module according to a sixth modification of the fifth embodiment. [Figure 42] FIG. 13 is a top view illustrating a differential optical modulator-integrated semiconductor laser, which is an example of an optical modulator-integrated semiconductor laser according to a sixth embodiment. [Figure 43] FIG. 13 is a rear view showing a differential optical modulator-integrated semiconductor laser, which is an example of an optical modulator-integrated semiconductor laser according to a sixth embodiment. [Figure 44] FIG. 13 is a cross-sectional view taken along the light guiding direction of the optical modulator-integrated semiconductor laser according to the sixth embodiment. [Figure 45] FIG. 13 is a top view illustrating an optical module according to a sixth embodiment. [Figure 46]43 is a cross-sectional view taken along line AA in FIG. 42 of a p-type third electrode pad of a differential EA modulator section of an optical modulator-integrated semiconductor laser according to a sixth embodiment. [Figure 47] 43 is a cross-sectional view taken along the line BB in FIG. 42 of an n-type third electrode pad of a differential EA modulator section of an optical modulator-integrated semiconductor laser according to a sixth embodiment. [Figure 48] 13 is a diagram illustrating frequency response characteristics of an EA modulator section in an optical modulator-integrated semiconductor laser according to the sixth embodiment, the first modification of the sixth embodiment, the seventh embodiment, and a comparative example. FIG. [Figure 49] 43 is a cross-sectional view taken along line AA in FIG. 42 of a p-type electrode pad of a differential EA modulator portion of an optical modulator-integrated semiconductor laser according to a first modification of the sixth embodiment. [Figure 50] 43 is a cross-sectional view taken along line BB in FIG. 42 of an n-type electrode pad of a differential EA modulator portion of an optical modulator-integrated semiconductor laser according to a first modification of the sixth embodiment. [Figure 51] 43 is a cross-sectional view taken along line AA in FIG. 42 of a p-type electrode pad of a differential EA modulator portion of an optical modulator-integrated semiconductor laser according to a second modification of the sixth embodiment. [Figure 52] 43 is a cross-sectional view taken along line BB in FIG. 42 of an n-type electrode pad of a differential EA modulator portion of an optical modulator-integrated semiconductor laser according to a second modification of the sixth embodiment. [Figure 53] FIG. 13 is a top view of a flip-chip differential optical modulator-integrated semiconductor laser, which is an example of an optical modulator-integrated semiconductor laser according to a seventh embodiment. [Figure 54] FIG. 13 is a back view of a flip-chip differential optical modulator-integrated semiconductor laser, which is an example of an optical modulator-integrated semiconductor laser according to a seventh embodiment. [Figure 55] FIG. 13 is a schematic view showing a flip-chip mounted differential optical modulator integrated semiconductor laser, which is an example of an optical modulator integrated semiconductor laser according to a seventh embodiment. [Figure 56] 13 is a cross-sectional view taken along line AA of the first p-type electrode of the differential EA modulator section of the optical modulator-integrated semiconductor laser according to the seventh embodiment. FIG. [Figure 57]13 is a cross-sectional view taken along line BB of the n-th electrode of the differential EA modulator section of the optical modulator-integrated semiconductor laser according to the seventh embodiment. FIG. [Figure 58] 13 is a cross-sectional view taken along line CC of a pier electrode of a differential EA modulator part of an optical modulator-integrated semiconductor laser according to a seventh embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] Embodiment 1 <Structure of Optical Modulator-Integrated Semiconductor Laser and Optical Module According to First Embodiment> Fig. 1 is a top view illustrating an optical modulator-integrated semiconductor laser 500 according to the first embodiment. Fig. 2A is a back view illustrating a configuration in which an opening is provided in a portion of the back electrode facing the second EA modulator portion in the optical modulator-integrated semiconductor laser 500 according to the first embodiment. Fig. 2B is a back view illustrating a configuration in which an opening is provided in a portion of the back electrode facing the first EA modulator portion in the optical modulator-integrated semiconductor laser 500 according to the first embodiment.

[0022] As shown in FIG. 1, the optical modulator-integrated semiconductor laser 500 according to the first embodiment includes a semiconductor laser section 101, which is a DFB (Distributed Feedback) laser, a first connecting waveguide section 102, a first EA modulator section 103, a second connecting waveguide section 104, a second EA modulator section 105, and an output waveguide section 106, which are connected in sequence along the optical waveguide direction on a semi-insulating substrate 1, i.e., on a first surface side of the semi-insulating substrate 1. The semiconductor laser section 101 to the output waveguide section 106 are also collectively referred to as an optical waveguide section. The semiconductor laser section 101 functions as a DFB laser, the first EA modulator section 103 functions as a first EA modulator, and the second EA modulator section 105 functions as a second EA modulator. In the following description, the optical modulator-integrated semiconductor laser may also be simply referred to as a chip.

[0023] On the surface of the optical modulator integrated semiconductor laser 500 according to the first embodiment, a p-type third electrode 5 and an n-type third electrode 6 of the semiconductor laser section 101, a p-type first electrode 25 and an n-type first electrode 26 of the first EA modulator section 103, and a p-type second electrode 45 and an n-type second electrode 46 of the second EA modulator section 105 are formed.

[0024] The n-type third electrode 6 of the semiconductor laser section 101, the n-type first electrode 26 of the first EA modulator section 103, and the n-type second electrode 46 of the second EA modulator section 105 are electrically connected to n-type semiconductor layers such as n-type conductive layers that also serve as their respective contact layers. The p-type third electrode 5 of the semiconductor laser section 101, the p-type first electrode 25 of the first EA modulator section 103, and the p-type second electrode 45 of the second EA modulator section 105 are each connected to a p-type semiconductor layer (not shown) above the optical waveguide section.

[0025] Here, the n-type semiconductor layer is a general term for an n-type contact layer, an n-type conductive layer, an n-type cladding layer, etc. The p-type semiconductor layer is a general term for a p-type contact layer, a p-type cladding layer, etc. The n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are electrically connected on the surface of the optical modulator-integrated semiconductor laser 500.

[0026] As shown in FIG. 2A , a back electrode 61 is formed over almost the entire back surface of the optical modulator-integrated semiconductor laser 500, i.e., the second surface side of the semi-insulating substrate 1, with the exception of a portion. In the first embodiment, the back electrode 61 is removed from a portion of the second EA modulator section 105 on the upper surface side of the optical modulator-integrated semiconductor laser 500, facing the second EA modulator section 105 across the semi-insulating substrate 1, and an opening 62 of the back electrode 61, i.e., an opening 62 without a metal film, is formed in that portion. Typically, as in the optical modulator-integrated semiconductor laser 510 according to the comparative example shown in the back view of FIG. 3 , no opening of the back electrode 61 is provided directly below the second EA modulator section 105. In other words, the back electrode 61 is formed over almost the entire second surface side of the semi-insulating substrate 1. An example of the semi-insulating substrate 1 is an Fe-doped InP substrate.

[0027] 4 is a cross-sectional view taken along the optical waveguide of the optical modulator-integrated semiconductor laser 500 according to the first embodiment. The semiconductor laser portion 101 is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3 an n-type third semiconductor layer having a layer thickness of 0.1 μm or more and 5.0 μm or less; an active layer 3; and a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3 and a p-type third semiconductor layer having a thickness of 0.1 μm or more and 5.0 μm or less.

[0028] The n-type third semiconductor layer is composed of an n-type third conductive layer 2a and an n-type third cladding layer 2b, which also function as contact layers. The p-type third semiconductor layer is composed of a p-type third cladding layer 4a and a p-type third contact layer 4b. The n-type third conductive layer 2a is composed of InP, InGaAsP, InGaAs, InAlGaAs, InAlAs, or the like. The n-type third cladding layer 2b is composed of InP, InAlAs, or InGaAsP, InAlGaAs, or the like, which do not absorb the laser light wavelength, i.e., have a bandgap wavelength shorter than the laser light wavelength. The p-type third cladding layer 4a is composed of InP, InAlAs, or InGaAsP, InAlGaAs, or the like, which do not absorb the laser light wavelength, i.e., have a bandgap wavelength shorter than the laser light wavelength. The p-type third contact layer 4b is composed of InP, InGaAsP, InGaAs, InAlGaAs, InAlAs, or the like.

[0029] The semiconductor laser portion 101 further includes a p-type third electrode 5 electrically connected to the p-type third semiconductor layer of the semiconductor laser portion 101, and an n-type third electrode 6 electrically connected to the n-type third semiconductor layer.

[0030] The active layer 3 is composed of a diffraction grating layer, a multiple quantum well layer, and light confinement layers (none of which are shown) formed above and below the multiple quantum well layer. The diffraction grating layer is made of InGaAsP or InAlGaAs. The multiple quantum well layer has a structure in which InGaAsP or InAlGaAs layers with different compositions and a layer thickness of several nm to 10 nm are stacked. The light confinement layer is made of InGaAsP, InAlGaAs, InAlAs, or the like. The total layer thickness of the active layer 3 is in the range of 100 nm to 500 nm. Both sides of the active layer 3 of the semiconductor laser section 101 are buried with current blocking layers (not shown) made of a semiconductor such as p-type InP, n-type InP, or Fe-doped InP.

[0031] The first connection waveguide portion 102, in which the optical waveguide is connected to the semiconductor laser portion 101, is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×10 17 cm -3 and an i-type lower first cladding layer 11 having a layer thickness of 0.1 μm or more and 5.0 μm or less, and a carrier concentration of 5×10 17 cm -3 the i-type first waveguide layer 12 (also referred to as a core layer) having a layer thickness of 50 nm or more and 500 nm or less, and a carrier concentration of 5×10 17 cm -3 and an i-type first upper cladding layer 13 having a thickness of 0.1 μm or more and 5.0 μm or less. The refractive index of the i-type first waveguide layer 12 is higher than the refractive indexes of the i-type first lower cladding layer 11 and the i-type first upper cladding layer 13. An insulating film 60 is formed on the surface of the i-type first upper cladding layer 13 as a surface protection film.

[0032] In addition, if the i-type lower first cladding layer 11, the i-type first waveguide layer 12, and the i-type upper first cladding layer 13 have a waveguide width of 2 μm or less, the separation resistance between the semiconductor laser section 101 and the first EA modulator section 103 becomes high. Therefore, instead of the i-type, a layer having a carrier concentration of 5×10 18 cm -3The i-type first lower cladding layer 11, the i-type first waveguide layer 12, and the i-type first upper cladding layer 13 may be made of InP, InGaAsP, InGaAs, InAlGaAs, InAlAs, or the like.

[0033] Here, the isolation resistance refers to the resistance between layers of the same conductivity type, such as the resistance between the p-type third semiconductor layer of the semiconductor laser section 101 and the p-type first semiconductor layer of the first EA modulator section 103, and the resistance between the n-type third semiconductor layer of the semiconductor laser section 101 and the n-type first semiconductor layer of the first EA modulator section 103, that is, the resistance between both ends of the first connecting waveguide section 102. In other words, the isolation resistance refers to the resistance between electrodes of the same conductivity type between the semiconductor laser section 101 and the first EA modulator section 103 adjacent to each other across the first connecting waveguide section 102, or between the first EA modulator section 103 and the second EA modulator section 105 adjacent to each other across the second connecting waveguide section 104.

[0034] The isolation resistance between the semiconductor laser section 101 and the first EA modulator section 103 is preferably set to 500Ω or more, which is 10 times higher than the 50Ω impedance when the EA modulator is driven. This is because an isolation resistance of 500Ω or more can reduce leakage of high-frequency signals from the first EA modulator section 103 to the semiconductor laser section 101.

[0035] The first EA modulator section 103 connected to the first connection waveguide section 102 is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3 an n-type first semiconductor layer having a layer thickness of 0.1 μm or more and 5.0 μm or less; an i-type first modulation layer 22; and a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3 The p-type first semiconductor layer is composed of a p-type semiconductor layer having a thickness of 0.1 μm or more and 5.0 μm or less, a p-type first electrode 25 electrically connected to the p-type first semiconductor layer, and an n-type first electrode 26 electrically connected to the n-type first semiconductor layer.

[0036] The n-type first semiconductor layer is composed of an n-type first conductive layer 21a and an n-type first cladding layer 21b, which also function as contact layers. The p-type first semiconductor layer is composed of a p-type first cladding layer 23a and a p-type first contact layer 23b. The n-type first conductive layer 21a is composed of InP, InGaAsP, InGaAs, InAlGaAs, InAlAs, or InGaAsP or InAlGaAs, which do not absorb the laser light wavelength, i.e., have a bandgap wavelength shorter than the laser light wavelength. The p-type first cladding layer 23a is composed of InP, InAlAs, or InGaAsP or InAlGaAs, which do not absorb the laser light wavelength, i.e., have a bandgap wavelength shorter than the laser light wavelength. The p-type first contact layer 23b is composed of InP, InGaAsP, InGaAs, InAlGaAs, InAlAs, or InAlAs.

[0037] The i-type first modulation layer 22 has a carrier concentration of 5×10 17 cm -3 It is composed of the following i-type multiple quantum well layer and optical confinement layers (neither of which are shown) formed above and below the i-type multiple quantum well layer. The total layer thickness of the i-type first modulation layer 22 is within the range of 50 nm to 500 nm. The i-type multiple quantum well layer has a structure in which InGaAsP or InAlGaAs with different compositions are stacked to a layer thickness of several nm to 10 nm. The optical confinement layer is composed of InGaAsP, InAlGaAs, InAlAs, or the like.

[0038] The second connection waveguide section 104, in which the optical waveguide is connected to the first EA modulator section 103, is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×10 17 cm -3 and an i-type lower second cladding layer 31 having a layer thickness of 0.1 μm or more and 5.0 μm or less, and a carrier concentration of 5×10 17 cm -3and a carrier concentration of 5×10 17 cm -3 and an i-type upper second cladding layer 33 having a thickness of 0.1 μm to 5.0 μm. The refractive index of the i-type second waveguide layer 32 is higher than the refractive indexes of the i-type lower second cladding layer 31 and the i-type upper second cladding layer 33. An insulating film 60 is formed on the surface of the i-type upper second cladding layer 33 as a surface protection film.

[0039] In addition, if the waveguide width of the lower second cladding layer 31, the i-type second waveguide layer 32, and the upper second cladding layer 33 is 2 μm or less, the separation resistance between the first EA modulator section 103 and the second EA modulator section 105 becomes high, and the carrier concentration becomes 5×10 18 cm -3 The second lower cladding layer 31, the second i-type waveguide layer 32, and the second upper cladding layer 33 may be made of InP, InGaAsP, InGaAs, InAlGaAs, InAlAs, or the like.

[0040] The isolation resistance between the first EA modulator section 103 and the second EA modulator section 105 is preferably set to 500Ω or more, which is 10 times higher than the 50Ω impedance when the EA modulator is driven. This is because leakage of high-frequency signals from the second EA modulator section 105 to the first EA modulator section 103 can be reduced.

[0041] The second EA modulator section 105 connected to the second connection waveguide section 104 is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3 an n-type second semiconductor layer having a layer thickness of 0.1 μm or more and 5.0 μm or less; an i-type second modulation layer 42; and a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3the second EA modulator section 105 is composed of a p-type second semiconductor layer having a thickness of 0.1 μm or more and 5.0 μm or less, a p-type second electrode 45 electrically connected to the p-type second semiconductor layer of the second EA modulator section 105, and an n-type second electrode 46 electrically connected to the n-type second semiconductor layer.

[0042] The n-type second semiconductor layer is composed of an n-type second conductive layer 41a and an n-type second cladding layer 41b, which also function as contact layers. The p-type second semiconductor layer is composed of a p-type second cladding layer 43a and a p-type second contact layer 43b. The n-type second conductive layer 41a is composed of InP, InGaAsP, InGaAs, InAlGaAs, InAlAs, or InGaAsP or InAlGaAs, which do not absorb the laser light wavelength, i.e., have a bandgap wavelength shorter than the laser light wavelength. The p-type second cladding layer 43a is composed of InP, InAlAs, or InGaAsP or InAlGaAs, which do not absorb the laser light wavelength, i.e., have a bandgap wavelength shorter than the laser light wavelength. The p-type second contact layer 43b is composed of InP, InGaAsP, InGaAs, InAlGaAs, InAlAs, or InAlAs.

[0043] The i-type second modulation layer 42 has a carrier concentration of 5×10 17 cm -3 It is composed of the following i-type multiple quantum well layer and optical confinement layers (neither of which is shown) formed above and below the i-type multiple quantum well layer. The i-type multiple quantum well layer has a structure in which InGaAsP or InAlGaAs with different compositions are stacked to a layer thickness of several nm to 10 nm. The optical confinement layer is composed of InGaAsP, InAlGaAs, InAlAs, or the like. The total layer thickness of the i-type second modulation layer 42 is within the range of 50 nm to 500 nm.

[0044] The second EA modulator section 105 is connected to an output waveguide section 106, and emits light from the chip end face. The output waveguide section 106 is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×1017 cm -3 and an i-type lower third cladding layer 51 having a layer thickness of 0.1 μm or more and 5.0 μm or less, and a carrier concentration of 5×10 17 cm -3 an i-type third waveguide layer 52 (core layer) having a layer thickness of 50 nm or more and 500 nm or less; and a carrier concentration of 5×10 17 cm -3 and an i-type upper third cladding layer 53 having a thickness of 0.1 μm to 5.0 μm. The refractive index of the i-type third waveguide layer 52 (core layer) is higher than the refractive indexes of the i-type lower third cladding layer 51 and the i-type upper third cladding layer 53. An insulating film 60 is formed on the surface of the i-type upper third cladding layer 53 as a surface protection film.

[0045] The i-type lower third cladding layer 51, the i-type third waveguide layer 52 (core layer), and the i-type upper third cladding layer 53 are made of InP, InGaAsP, InGaAs, InAlGaAs, InAlAs, etc. If the resistance of the i-type lower third cladding layer 51, the i-type third waveguide layer 52 (core layer), and the i-type upper third cladding layer 53 increases, they will no longer affect the output waveguide portion as a parasitic capacitance. 18 cm -3 The following p-type or n-type conductivity types are also acceptable. The width of the i-type third waveguide layer 52 (core layer) is preferably within the range of 1 μm to 2 μm.

[0046] In order to provide the i-type third waveguide layer 52 (core layer) with a waveguide lens function, the width of the i-type third waveguide layer 52 (core layer) may be gradually changed between 0.3 μm and 5 μm.

[0047] An Fe-doped InP substrate, an example of a semi-insulating substrate 1, is ground or polished to a thickness of approximately 100 μm. On the back surface of the chip, i.e., the second surface side of the semi-insulating substrate 1, a back electrode 61 is formed over almost the entire back surface of the chip, excluding an opening 62, as shown in the back view of FIG. 2A. The back electrode 61 has a layered structure made up of AuGe, Ti, Ni, Pt, an Au vapor deposition layer, an Au plating layer, an AuSn solder layer, and the like. The film thickness of the back electrode 61 is in the range of 1 μm to 10 μm.

[0048] 2A, an opening 62 is provided in the rear electrode 61 directly below the second EA modulator section 105, i.e., a portion where the rear electrode 61 is not formed. That is, the rear electrode 61 has the opening 62 in a region facing the second EA modulator section 105 across the semi-insulating substrate 1. The semi-insulating substrate 1 is exposed through the opening 62. The opening 62 in the rear electrode 61 is formed by metal lift-off, dry etching, or wet etching.

[0049] The length of the semiconductor laser section 101 along the light waveguide direction is within a range of 100 μm or more and 600 μm or less. The lengths of the first connection waveguide section 102, the second connection waveguide section 104, and the output waveguide section 106 along the light waveguide direction are each within a range of 25 μm or more and 500 μm or less. The lengths of the first EA modulator section 103 and the second EA modulator section 105 along the light waveguide direction are each within a range of 25 μm or more and 200 μm or less. The total length of the optical modulator-integrated semiconductor laser 500 according to the first embodiment along the light waveguide direction is within a range of 225 μm or more and 2500 μm or less.

[0050] 5 is a top view of the optical modulator-integrated semiconductor laser 500 according to the first embodiment mounted on the upper surface of a submount 200 and connected to a wiring board 201 via a wire. A current is supplied to the semiconductor laser portion 101 from a current source via a semiconductor laser portion current line LN3 and a wire W3 to a p-type third electrode 5 of the semiconductor laser portion 101. An n-type third electrode 6 of the semiconductor laser portion 101 is electrically connected to a ground electrode 48 on the submount 200 via a ground wire Wg1.

[0051] Here, a submount is a general term for a component on which an optical modulator-integrated semiconductor laser is mounted on its upper surface. Submounts are made of dielectric or high-resistance materials such as aluminum nitride (AlN), silicon, silicon carbide (SiC), alumina, or epoxy, or conductive materials such as copper, iron, gold, silver, or aluminum. When a dielectric or high-resistance material is used as the submount's base material, an electrode made of gold or other material (hereinafter referred to as the submount ground electrode or submount backside ground electrode) is formed on the top or backside of the submount on which the optical modulator-integrated semiconductor laser is mounted. The top surface of the submount is called the first surface of the submount, and the backside of the submount is called the second surface of the submount.

[0052] Also, when a dielectric or high-resistance material is used as the base material for the submount, the ground electrode on the top surface of the submount and the submount backside ground electrode on the backside may be electrically connected by a grounding through electrode, side metallization, etc. Furthermore, when a conductive material such as copper, iron, gold, silver, or aluminum is used as the base material for the submount, the top surface of the submount is covered with an insulator (film) on which electrode wiring, etc. is formed.

[0053] In the following description, the configuration in which the optical modulator-integrated semiconductor laser 500 according to the first embodiment is mounted on the submount 200 will be referred to as the optical module 1000 according to the first embodiment. The configuration of the optical module 1000 shown in Fig. 5 will be described in detail below. Note that in the first and subsequent embodiments, the configuration in which the optical modulator-integrated semiconductor laser is mounted on the submount will also be referred to as the optical module.

[0054] The wiring board 201 has formed on alumina or epoxy resin a first modulation signal line La1 and a second modulation signal line La2, which are strip lines or coplanar lines for transmitting high-frequency signals, and a semiconductor laser section current line La3 for feeding power to the DFB laser constituting the semiconductor laser section 101. A first modulation signal S1 and a second modulation signal S2 are transmitted to the first modulation signal line La1 and the second modulation signal line La2, respectively, from an external EA modulator driver.

[0055] At least two termination resistor electrode pads 57, 58 are provided on the submount 200. A first termination resistor R1 and a second termination resistor R2 are arranged to electrically connect each termination resistor electrode pad 57, 58 to the ground electrode 48.

[0056] As shown in FIG. 5, the semiconductor laser section current line La3 on the wiring substrate 201, the semiconductor laser section current line LN3 on the submount 200, and the p-type third electrode 5 of the semiconductor laser section 101 are electrically connected in sequence via wires.

[0057] The first modulation signal line La1 on the wiring substrate 201, the first modulation signal line LN1 on the submount 200, the p-type first electrode pad 54, and the termination resistor electrode pad 57 electrically connected to the first termination resistor R1 are electrically connected in sequence via wires.

[0058] Similarly, the second modulation signal line La2 on the wiring substrate 201, the second modulation signal line LN2 on the submount 200, the n-type second electrode pad 55 of the second EA modulator section 105, and the termination resistor electrode pad 58 electrically connected to the second termination resistor R2 are electrically connected in sequence via wires.

[0059] The common electrode 47, to which the n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are electrically connected, is electrically connected to a ground electrode 48 on the submount 200 via ground wires Wg2 and Wg3. The n-type third electrode 6 of the semiconductor laser section 101 is electrically connected to the ground electrode 48 on the submount 200 via a ground wire Wg1.

[0060] An inverted-phase electrical signal is input from the modulator driver to a second n-type electrode pad 55 of the second EA modulator section 105 via a second modulation signal line LN2 and a wire W2. The second n-type electrode pad 55 of the second EA modulator section 105 is connected to a termination resistor electrode pad 58 by a wire, and the termination resistor electrode pad 58 is connected to the ground electrode 48 on the submount 200 via a second termination resistor R2.

[0061] A common electrode 47 to which the n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are electrically connected is connected to a ground electrode 48 on the submount 200, and the ground electrode 48 on the submount 200 is grounded via a grounding through electrode 56.

[0062] <Function of the Optical Modulator Integrated Semiconductor Laser According to the First Embodiment> The operation of the optical modulator-integrated semiconductor laser 500 according to the first embodiment will be described below with reference to Fig. 5. When a DC current is injected into the semiconductor laser section 101 from the semiconductor laser section current line LN3, the DFB laser constituting the semiconductor laser section 101 emits light. The light emitted from the semiconductor laser section 101 passes through the first connecting waveguide section 102 and reaches the first EA modulator section 103.

[0063] A first modulation signal S1, i.e., a modulated positive-phase voltage signal, is input from a first modulation signal line LN1 to the p-type first semiconductor layer of the first EA modulator section 103, and the light intensity is modulated with an extinction ratio Ex1 (dB). The light modulated by the first EA modulator section 103 passes through the second connecting waveguide section 104 and enters the second EA modulator section 105.

[0064] A second modulation signal S2, i.e., a modulated voltage signal of opposite phase, is input from the second modulation signal line LN2 to the n-type second semiconductor layer of the second EA modulator section 105, which modulates the light intensity with an extinction ratio Ex2 (dB) and emits the modulated light to the outside from the end face.

[0065] Since the voltage signal modulating the p-type first semiconductor layer of the first EA modulator section 103 and the voltage signal modulating the n-type second semiconductor layer of the second EA modulator section 105 are in opposite phase to each other, the total extinction ratio Ex12 is expressed by the following equation (1). Ex12=Ex1+Ex2 (dB) (1)

[0066] When high-frequency interference causes potential fluctuations in the first modulation signal line LN1 and the second modulation signal line LN2 in phase, if the fluctuations in the extinction ratio due to the potential fluctuations are ΔEx1 and ΔEx2, respectively, the total extinction ratio Ex12 is expressed by the following equation (2). Ex12=Ex1+ΔEx1+Ex2-ΔEx2 (dB) (2)

[0067] In equation (2), the sign of ΔEx2 is negative because the in-phase potential fluctuation is applied to the p-type first electrode 25 in the first EA modulator section 103, whereas it is applied to the n-type second electrode 46 in the second EA modulator section 105. Note that the first modulation signal line LN1 and the second modulation signal line LN2 are arranged close to each other to form differential lines, and therefore potential fluctuations due to external electromagnetic field (high frequency) interference are in-phase and are applied to the first modulation signal line LN1 and the second modulation signal line LN2.

[0068] If the first EA modulator section 103 and the second EA modulator section 105 have the same response to high frequencies, the following equation (3) holds. ΔEx1-ΔEx2=0 (3) It can be seen from equation (3) that no fluctuations in the extinction ratio occur. In other words, if the difference in frequency response characteristics between the first EA modulator unit 103 and the second EA modulator unit 105 is small, high-frequency interference is suppressed.

[0069] The frequency response characteristics of an EA modulator depend on the parasitic capacitance of the electrode pads, conductive layers, etc., assuming the same pn junction capacitance and resistance. Here, parasitic capacitance refers to the electrical capacitance between the back electrode and the n-type conductive layer, which also functions as a contact layer in each EA modulator section, the n-type electrode pad, and the p-type electrode pad. However, the electrical capacitance of the pn junction of each modulation layer is not included in the parasitic capacitance.

[0070] Fig. 6 is a cross-sectional view of the first EA modulator section 103 of the optical modulator-integrated semiconductor laser 500 arranged on the submount 200 in the optical module 1000 according to the first embodiment, i.e., a cross-sectional view of a portion along the line AA in Fig. 5. Fig. 7 is a cross-sectional view of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 500 arranged on the submount 200 in the optical module 1000 according to the first embodiment, i.e., a cross-sectional view of a portion along the line BB in Fig. 5.

[0071] As shown in FIG. 6, in the first EA modulator section 103, a parasitic capacitance C is generated between the common electrode 47 and the rear electrode 61 to which the n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are electrically connected. common However, a parasitic capacitance C Nlayer However, a parasitic capacitance C Ppad occurs respectively.

[0072] As shown in Figure 7, since the opening 62 of the back electrode 61 is located directly below the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 500, an air layer is generated between the back side of the optical modulator-integrated semiconductor laser 500 and the submount 200.

[0073] In the second EA modulator section 105, a parasitic capacitance C is formed between the common electrode 47 and the rear electrode 61 to which the n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are electrically connected. common However, a parasitic capacitance C Nlayer However, a parasitic capacitance C Npad occurs respectively.

[0074] 8 is a cross-sectional view of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 510 of the optical module 1010, which is a comparative example. Similarly, as a parasitic capacitance, a parasitic capacitance C between the common electrode 47 and the back electrode 61 to which the n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are electrically connected, common , a parasitic capacitance C between the n-type second conductive layer 41a, which also functions as a contact layer, and the back electrode 61 Nlayer , the parasitic capacitance C between the n-type first electrode pad 54 of the second EA modulator section 105 and the rear electrode 61 Npad occurs.

[0075] 9A is an equivalent circuit of the first EA modulator section 103. FIG. 9B is an equivalent circuit of the first EA modulator section 103. grand 10A is an equivalent circuit of the first EA modulator section 103 when the inductance L is sufficiently small. FIG. 10B is an equivalent circuit of the second EA modulator section 105. grand is an equivalent circuit of the second EA modulator section 105 when is sufficiently small.

[0076] In the equivalent circuit, the inductance of the ground wires Wg2 and Wg3 ​​connecting the common electrode 47 to which the n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are electrically connected, and the ground electrode 48 on the submount 200 is defined as L. grand It was decided.

[0077] The ground wires Wg2 and Wg3 ​​are short enough, andgrand Consider the case where is small enough to be considered a short circuit. grand 9A and 10A become equivalent circuits shown in FIGS. 9B and 10B, respectively. If the areas of the p-type first electrode pad 54 of the first EA modulator section 103 and the n-type second electrode pad 55 of the second EA modulator section 105 are the same, the parasitic capacitance C Npad is the parasitic capacitance C of the first EA modulator section 103. Ppad Therefore, the parasitic capacitance of the second EA modulator section 105 is approximately equal to the parasitic capacitance C Nlayer Therefore, the frequency response band of the second EA modulator section 105 is narrower than that of the first EA modulator section 103.

[0078] On the other hand, in the case of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 500 according to the first embodiment, an opening 62 is provided in the back electrode 61. Therefore, when the optical modulator-integrated semiconductor laser 500 is mounted on the submount 200, an air layer is formed between the optical modulator-integrated semiconductor laser 500 and the surface of the submount 200 at the opening 62. This reduces the parasitic capacitance C Ppad and parasitic capacitance C Nlayer Therefore, the following relationships in equations (4) and (5) hold: C Npad (Embodiment 1) <C Npad (Comparative Example) (4) C Nlayer (Embodiment 1) <C Nlayer (Comparative Example) (5) That is, the parasitic capacitance of the second EA modulator section 105 of the optical modulator integrated semiconductor laser 500 according to the first embodiment is smaller than the parasitic capacitance of the second EA modulator section 105 of the comparative example.

[0079] The improvement effect of the optical modulator-integrated semiconductor laser 500 according to the first embodiment is specifically estimated as follows.

[0080] The dielectric constant and thickness of the semi-insulating substrate 1 made of Fe-doped InP are ε InP and t InP , the relative permittivity and thickness of the air layer are ε Air and t Air , the dielectric constant of vacuum is ε0, the total area of ​​the n-type first electrode pad 54 of the second EA modulator section 105 and the area of ​​the n-type first conductive layer 21a is S, and ε Air If is set to 1, the relationships of the following equations (6) and (7) hold. C Npad (Comparative example) +C Nlayer (Comparative Example) =ε InP ·ε0·S / t InP (6) C Npad (Embodiment 1) +C Nlayer (Embodiment 1) =ε InP ·ε0·S / (t InP +ε InP ·t Air ) (7)

[0081] In equations (6) and (7), ε InP is 12.1, t InP is about 100 μm, the reduction rate of the parasitic capacitance is given by the following formula (8). Parasitic capacitance reduction rate (times) = Equation (7) / Equation (6) =100 / (100+12.1·t Air ) (8)

[0082] In addition, t in equation (8) Air The unit is μm. Here, the reduction rate of parasitic capacitance indicates how many times the parasitic capacitance of the first embodiment is compared to the parasitic capacitance of the comparative example (FIG. 9B). For example, a reduction rate of parasitic capacitance of 0.5 times means that the parasitic capacitance of the first embodiment is half the parasitic capacitance of the comparative example.

[0083] Here, if the film thickness of the rear electrode 61 is 5 μm, t Air= 5 μm, and therefore, from equation (8), the reduction rate of the parasitic capacitance is approximately 0.62. That is, in the first embodiment, the sum of the parasitic capacitance of the n-type second electrode pad 55 of the second EA modulator section 105 and the parasitic capacitance of the n-type second conductive layer 41 a (= C Npad +C Nlayer ) is reduced to 0.62 times the parasitic capacitance of the comparative example.

[0084] Fig. 11 shows frequency response characteristics of the first EA modulator section and the second EA modulator section in the first embodiment and the comparative example when mounted on the submount 200 shown in Fig. 5. In Fig. 11, the dotted line represents the first EA modulator section 103 in the first embodiment and the comparative example, the dashed-dotted line represents the second EA modulator section 105 in the first embodiment, and the solid line represents the second EA modulator section 105 in the comparative example.

[0085] 7, the thickness of the air layer in the opening 62 of the rear electrode 61 is set to 5 μm, the pn junction capacitance of each EA modulator unit is set to 69 fF, the pn junction resistance and wiring inductance are set to zero, and the termination resistance and driver impedance are set to 50 Ω. As shown in FIG. 11, the second EA modulator unit 105 of the first embodiment has a reduced parasitic capacitance compared to the second EA modulator unit 105 of the comparative example, and therefore the second EA modulator unit 105 of the first embodiment has a wider frequency response band than the comparative example.

[0086] As a result, the frequency response characteristics of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 500 according to the first embodiment become closer to the response characteristics of the first EA modulator section 103. Therefore, ΔEx1−ΔEx2 in equation (3) approaches zero, which has the effect of reducing fluctuations in the extinction ratio due to high-frequency interference.

[0087] If the thickness of the air layer in the opening 62 of the back electrode 61, i.e., the film thickness of the back electrode 61, is thin, a sufficient effect of reducing parasitic capacitance cannot be obtained. On the other hand, if the film thickness of the back electrode 61 is thick, a problem occurs in that the wafer warps during the manufacturing process due to the stress of the back electrode 61. In other words, there is a suitable range for the film thickness of the back electrode 61.

[0088] According to formula (8), the film thickness of the back electrode 61 that can reduce the parasitic capacitance of the second EA modulator section 105 by 0.9 times, that is, by 10%, is 1 μm. If the film thickness of the back electrode 61 is 10% or more of the substrate thickness of the InP substrate, wafer warpage increases due to electrode stress. If the wafer warpage is large, defects such as abnormal cracks and poor conductivity occur during the wafer cleavage process and chip test process. Therefore, the film thickness of the back electrode 61 is preferably in the range of 1 μm to 10 μm. A more preferable film thickness of the back electrode 61 is in the range of 3 μm to 6 μm, at which the parasitic capacitance is reduced to 0.75 times or less and wafer warpage hardly occurs.

[0089] The opening 62 in the back electrode 61 is provided in a region including the n-type second conductive layer 41a, which also functions as a contact layer for the second EA modulator section 105, and the area directly below the n-type second electrode pad 55. However, because the thickness of the semi-insulating substrate 1 made of Fe-doped InP is approximately 100 μm, the electromagnetic field spreads horizontally between the second EA modulator section 105 on the top surface of the chip and the back surface of the chip, that is, in a direction parallel to the surface of the semi-insulating substrate 1. In order to reduce parasitic capacitance, it is preferable to make the opening 62 in the back electrode 61 wider than the distance the electromagnetic field spreads in the horizontal direction.

[0090] Specifically, if the length of the second EA modulator section 105 along the light guide direction is L2 (shown in FIG. 1), the length of the opening 62 in the rear electrode 61 along the light guide direction must be at least L2 or more. Furthermore, the electric field from the EA modulator section toward the rear electrode 61 also spreads in the horizontal direction. The width of the electric field spreads to both sides by approximately half the thickness of the semi-insulating substrate 1. Therefore, the opening width of the opening 62 in the rear electrode 61 is set to be equal to the thickness t of the semi-insulating substrate 1. InP In other words, the opening width of the opening 62 in the rear electrode 61 along the light guide direction is preferably set to a value that is equal to the length L2 and the substrate thickness t InP A width equal to or greater than the sum of the above is preferable.

[0091] For a high-speed EA modulator, the length L2 is 50 μm and the substrate thickness t InPis assumed to be about 100 μm, so it must be at least 50 μm, that is, the length L2 or more, and the width of the opening in the optical waveguide direction must be 150 μm, that is, the length L2 and the substrate thickness t InP A width equal to or greater than the sum of the above is preferable.

[0092] The opening width of the opening 62 in the back electrode 61 in the direction perpendicular to the light guiding direction, i.e., the direction along the line BB in Fig. 2A, needs to be equal to or greater than the distance W from the center of the optical waveguide to the outer edge of the n-type second electrode pad 55. The distance W is shown in Fig. 1.

[0093] Furthermore, the opening 62 is formed to have a thickness equal to or larger than the substrate thickness t InP In other words, the opening width of the opening 62 is determined by the distance W and the substrate thickness t InP A width equal to or greater than the sum of the above is preferable.

[0094] For a high-speed EA modulator, the distance W is 50 μm and the substrate thickness t InP Since the distance is assumed to be about 100 μm, it is preferable that the distance be at least 50 μm, that is, the distance W or more. Furthermore, the opening width of the opening 62 along the light guide direction is 150 μm, that is, the distance W and the substrate thickness t InP In order to prevent solder from flowing into the opening 62 of the rear electrode 61, an insulating film such as SiN or SiO2, or an organic material such as polyimide or benzocyclobutene may be formed.

[0095] 12 and 13 are a top view and a back view of an optical modulator-integrated semiconductor laser 520, which is another example of the optical modulator-integrated semiconductor laser according to embodiment 1. The optical modulator-integrated semiconductor laser 520 has a configuration in which the order of the first EA modulator section 103 and the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 500 is reversed.

[0096] As shown in the top view of FIG. 12, the optical modulator-integrated semiconductor laser 520 is configured with a semiconductor laser section 101, a first connecting waveguide section 102, a second EA modulator section 105, a second connecting waveguide section 104, a first EA modulator section 103, and an output waveguide section 106, which are connected in sequence on a semi-insulating substrate 1, i.e., on the first surface side of the semi-insulating substrate 1, along the optical waveguide direction.

[0097] 13, the optical modulator-integrated semiconductor laser 520 has an opening 62 in the back electrode 61 provided directly below the second EA modulator section 105. The cross-sectional structures of the first EA modulator section 103 and the second EA modulator section 105 are similar to those of the optical modulator-integrated semiconductor laser 500 according to the first embodiment.

[0098] The optical modulator-integrated semiconductor laser 520, which is another example of the optical modulator-integrated semiconductor laser according to the first embodiment, also achieves the same effects as the optical modulator-integrated semiconductor laser 500 according to the first embodiment.

[0099] The parasitic capacitance C between the common electrode 47 and the rear electrode 61 to which the n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are electrically connected, common As shown in Figures 9B and 10B, the ground wires Wg2 and Wg3 ​​are sufficiently short and L grand Therefore, an opening may be provided in the corresponding portion of the rear electrode 61 directly below the common electrode 47, or it may not be provided.

[0100] For simplicity, we have used L grand However, as shown in Figures 9A and 10A, grand Even if the parasitic capacitance C Npad , C NlayerAs a result, the frequency response characteristics of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 500 according to the first embodiment become closer to the response characteristics of the first EA modulator section 103. Therefore, ΔEx1-ΔEx2 in equation (3) approaches zero, which has the effect of reducing fluctuations in the extinction ratio due to high-frequency interference.

[0101] Photocurrent flows in the EA modulator due to the absorption of light. The photocurrents flowing in the first EA modulator section 103 and the second EA modulator section 105 are represented by I ph1 and I ph2 Since the light emitted from the semiconductor laser section 101 is attenuated by the first EA modulator section 103 and then incident on the second EA modulator section 105, the photocurrent generated by the light absorption in the first EA modulator section 103 is larger. ph1 >I ph2 It becomes. I ph1 When the resistance R ea1 Voltage drop due to (=I ph1 ×R ea1 ), the DC bias voltage applied to the i-type first modulation layer 22 decreases. As a result, the thickness of the depletion layer of the i-type first modulation layer 22 decreases, and the capacitance increases.

[0102] Therefore, I ph1 2B, the parasitic capacitance of the first EA modulator section 103 can be reduced by providing an opening 62 in the portion of the back electrode facing the first EA modulator section 103, thereby making the frequency response characteristic closer to that of the second EA modulator section 105.

[0103] In addition, as the photocurrent increases, the DC bias voltage decreases and the extinction ratio decreases. ph1 I ph22B , the parasitic capacitance of the first EA modulator section 103 can be reduced by providing an opening 62 in the back electrode 61 at a portion facing the first EA modulator section 103, thereby enabling the frequency response characteristics of the first EA modulator section 103 to approach those of the second EA modulator section 105.

[0104] As shown in Fig. 2A, whether to provide an opening 62 in the back electrode 61 facing the second EA modulator section 105 or, as shown in Fig. 2B, whether to provide an opening 62 in the back electrode 61 facing the first EA modulator section 103 can be selected so that the difference in frequency response characteristics between the two EA modulators becomes small depending on the magnitude of the photocurrent and the magnitude of the parasitic capacitance, and ΔEx1 - ΔEx2 in equation (3) becomes small. As a result, there is an effect of reducing fluctuations in the extinction ratio due to high-frequency interference.

[0105] 2A, 2B and 7, the corresponding portions of the back surface electrode 61 directly below the common electrode 47 to which the n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are electrically connected are partially opened. In the following second to fifth embodiments as well, the back surface electrode directly below the common electrode does not necessarily have to be opened, and may be opened entirely or partially.

[0106] The optical modulator-integrated semiconductor laser 500 according to the first embodiment includes two EA modulators, and the semiconductor laser section 101, the first EA modulator section 103, and the second EA modulator section 105 are connected by a connection waveguide section of the same optical mode. The first n-type semiconductor layer of the first EA modulator section 103 is grounded, and a positive-phase signal is applied to the first p-type semiconductor layer. The second p-type semiconductor layer of the second EA modulator section 105 is grounded, and a negative-phase signal is applied to the second n-type semiconductor layer.

[0107] By providing an opening 62 by removing the back surface electrode 61 directly below the n-type second semiconductor layer and the n-type second electrode pad 55 of the second EA modulator section 105, the parasitic capacitance of the second EA modulator section 105 is reduced. As a result, the difference between the frequency response characteristics of the first EA modulator section 103 and the second EA modulator section 105 is reduced. Therefore, even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section 105 cancels out the fluctuation, and the influence of electromagnetic interference on the light emitted from the optical modulator-integrated semiconductor laser 500 is reduced.

[0108] Furthermore, the configuration of the optical modulator-integrated semiconductor laser 500 and optical module 1000 according to the first embodiment enables wideband operation of the second EA modulator section 105. Using the optical modulator-integrated semiconductor laser 500 as a light source enables the optical transceiver to have a wider bandwidth and be highly densely mounted. The optical modulator-integrated semiconductor laser 500 and optical module 1000 do not suffer from deterioration in error rate due to electromagnetic interference, making it possible to simplify the error rate correction circuit. Thus, by applying the optical modulator-integrated semiconductor laser 500 and optical module 1000 according to the first embodiment, it becomes possible to increase the transmission rate of an optical communication transceiver and reduce the power consumption per bit of a transmitted signal.

[0109] <Advantages of First Embodiment> As described above, the optical modulator-integrated semiconductor laser and optical module according to the first embodiment have at least a semiconductor laser section, a first EA modulator section, and a second EA modulator section provided on the first surface of the semi-insulating substrate along the waveguide direction of light, and have a back surface electrode formed on the second surface of the semi-insulating substrate and having an opening in an area facing the second EA modulator section across the semi-insulating substrate. This reduces parasitic capacitance, thereby achieving the effect of providing an optical modulator-integrated semiconductor laser and optical module with a wide frequency response band and reduced fluctuations in the extinction ratio due to high-frequency interference.

[0110] Embodiment 2 <Structure of Optical Modulator Integrated Semiconductor Laser and Optical Module According to Second Embodiment> The device structures of the optical modulator-integrated semiconductor laser 550 and the optical module 1050 according to the second embodiment will be described below. Fig. 14 is a cross-sectional view taken along a direction perpendicular to the optical waveguide direction of the second EA modulator section 105 in the optical modulator-integrated semiconductor laser 550 of the optical module 1050 according to the second embodiment. The optical modulator-integrated semiconductor laser 550 according to the second embodiment differs from the optical modulator-integrated semiconductor laser 500 according to the first embodiment in that a recess 65 is provided in the semi-insulating substrate 1 exposed in the opening 62a of the back electrode 61 immediately below the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 550.

[0111] 14, a recess 65 is provided in the semi-insulating substrate 1 directly below the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 550 according to the second embodiment. The depth of the bottom surface of the recess 65 is within a range of 1 μm to 30 μm from the rear surface of the semi-insulating substrate 1, i.e., the surface of the second surface.

[0112] To enhance the capacitance reduction effect, the depth of the bottom of the recess 65 is preferably at least 3 μm, which is the film thickness of the back electrode 61. On the other hand, if the depth of the bottom of the recess 65 is too large, defects such as wafer cracking may occur during the manufacturing process, so the depth of the bottom of the recess 65 is preferably 10 μm or less.

[0113] 14, the recess 65 may be formed inside the opening 62 of the back electrode 61. Alternatively, the opening 62 of the back electrode 61 may be formed so as to be inside the recess 65. Furthermore, the boundary of the opening 62 of the back electrode 61 may be formed so as to coincide with the boundary of the recess 65.

[0114] <Method for fabricating device structure of optical modulator integrated semiconductor laser according to second embodiment> The recess 65 is formed by thinning the semi-insulating substrate 1 made of Fe-doped InP to a thickness of about 100 μm by grinding or polishing, and then wet-etching or dry-etching the semi-insulating substrate 1. An example of an etching solution for wet etching is a mixture of hydrochloric acid, phosphoric acid, HBr, Br, and Br.

[0115] In addition, in the case of dry etching, the recesses 65 may be formed by reactive ion etching using vacuum discharge plasma such as inductively coupled plasma or capacitively coupled plasma. The recesses 65 may be formed after or before the back surface electrode 61 is formed.

[0116] <Operation of the Optical Modulator Integrated Semiconductor Laser Device According to the Second Embodiment> 14, an air layer having a thickness equal to the thickness of the rear surface electrode 61 and a depth equal to the depth of the recess 65 is formed directly below the n-type second conductive layer 41a, which also functions as a contact layer for the second EA modulator section 105, and the n-type second electrode pad 55. If the thickness of the rear surface electrode 61 is 5 μm and the depth of the recess 65 is 10 μm, an air layer having a thickness of 15 μm is formed. The formation of such an air layer reduces parasitic capacitance.

[0117] From the above equation (8), when the thickness of the air layer is 15 μm, the reduction rate of the parasitic capacitance is 0.36 times, which is a significant reduction effect. Fig. 15 is a diagram showing the frequency response characteristics when mounted on the submount 200 when the thickness of the air layer is 15 μm. In Fig. 15, the solid line shows the frequency response characteristics of the second EA modulator section 105 of the second embodiment, the dotted line shows the frequency response characteristics of the second EA modulator section 105 of the comparative example, and the dashed-dotted line shows the frequency response characteristics of the first EA modulator section 103 of the second embodiment and the comparative example.

[0118] The frequency response characteristics of the second EA modulator section 105 of the second embodiment coincide with the frequency response characteristics of the first EA modulator section 103. As a result, ΔEx1−ΔEx2 in equation (3) approaches zero, and fluctuations in the extinction ratio due to high-frequency interference are suppressed.

[0119] In the optical modulator-integrated semiconductor laser 550 according to the second embodiment, the n-type second semiconductor layer of the second EA modulator section 105 and the back electrode 61 directly below the n-type second electrode pad 55 are removed to form an opening 62, and a recess 65 is formed in the semi-insulating substrate 1 exposed in the opening 62, thereby making it possible to thicken the air layer and reducing the parasitic capacitance of the second EA modulator section 105. As a result, the frequency response characteristics of the first EA modulator section 103 and the second EA modulator section 105 are approximately the same. Therefore, even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section 105 cancels the fluctuation, and the light emitted from the optical modulator-integrated semiconductor laser 550 is not affected by the electromagnetic interference.

[0120] Furthermore, the configuration of the optical modulator-integrated semiconductor laser 550 according to the second embodiment enables wideband operation of the second EA modulator section 105. Using the optical modulator-integrated semiconductor laser 550 as a light source enables the optical transceiver to have a wider bandwidth and be mounted at a higher density. The optical modulator-integrated semiconductor laser 550 and the optical module 1050 do not suffer from deterioration in error rate due to electromagnetic interference, making it possible to simplify the error rate correction circuit. Thus, by applying the optical modulator-integrated semiconductor laser 550 and the optical module 1050 according to the second embodiment, it becomes possible to increase the transmission rate of the optical communication transceiver and reduce the power consumption per bit of the transmitted signal.

[0121] <Advantages of the Second Embodiment> As described above, the optical modulator-integrated semiconductor laser and optical module according to the second embodiment have at least a semiconductor laser section, a first EA modulator section, and a second EA modulator section provided on the first surface of the semi-insulating substrate along the waveguide direction of light, a back electrode formed on the second surface of the semi-insulating substrate and having an opening in a region facing the second EA modulator section across the semi-insulating substrate, and a recess provided in the semi-insulating substrate 1 exposed to the opening, which further reduces parasitic capacitance, thereby achieving the effect of obtaining an optical modulator-integrated semiconductor laser and optical module with a wider frequency response band and further reduced fluctuations in the extinction ratio due to high-frequency interference.

[0122] Embodiment 3 <Structure of Optical Modulator-Integrated Semiconductor Laser and Optical Module According to Third Embodiment> The following describes the structures of the optical modulator-integrated semiconductor laser 600 and the optical module 1100 according to the third embodiment. The optical modulator-integrated semiconductor laser 600 has the same device structure as the optical modulator-integrated semiconductor laser 500 according to the first embodiment.

[0123] Fig. 16 is a cross-sectional view of the second EA modulator section 105 and the submount 200 after the optical modulator-integrated semiconductor laser 600 according to the third embodiment has been mounted on the submount 200, that is, after being assembled into an optical module. That is, Fig. 16 is a cross-sectional view of the optical module 1100 according to the third embodiment, taken along a direction perpendicular to the optical waveguide direction of the second EA modulator section 105 in the optical modulator-integrated semiconductor laser 600. Fig. 17 is a top view of the optical module 1100 according to the third embodiment.

[0124] 17, an opening 49 is formed in the ground electrode 48 on the submount 200. The aluminum nitride base material of the submount 200 is exposed through the opening 49 in the ground electrode 48. The solder on the submount 200 also has an opening in the same location as the ground electrode 48 on the submount 200. The size of the opening 49 in the ground electrode 48 on the submount 200 is approximately the same as the opening 62b in the back electrode 61.

[0125] Similar to the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 500 according to the first embodiment, the optical modulator-integrated semiconductor laser 600 according to the third embodiment also has an opening 62b formed in the back electrode 61 directly below the second EA modulator section 105, and is mounted so that the opening 62b in the back electrode 61 and the opening 49 in the ground electrode 48 on the submount 200 overlap in part or in whole.

[0126] The base material of the submount 200 may be other dielectric or high-resistance materials such as SiC or alumina. The thickness of the submount 200 is preferably in the range of 100 μm to 1000 μm. A submount backside grounding electrode 205 is formed on the backside of the submount 200 and is electrically connected to the grounding electrode 48 on the top side of the submount 200 via a grounding through electrode 56.

[0127] 16, the areas of the openings increase in the order of opening 62b in back electrode 61, opening 49 in bump or solder layer 72, and opening 49 in ground electrode 48 on submount 200, but the areas of the openings do not necessarily increase in this order. The same applies to the following Embodiment 4, Modification 3 of Embodiment 4, and Modification 2 of Embodiment 6.

[0128] <Functions of the Optical Modulator Integrated Semiconductor Laser and Module According to the Third Embodiment> As shown in Figure 16, the back electrode 61 is mounted so that the opening 62b and the opening 49 of the ground electrode 48 on the submount 200 overlap, so that the n-type second conductive layer 41a, which also functions as a contact layer for the second EA modulator section 105, and the ground electrode 48 directly below the n-type second electrode pad 55 are electrically connected to the submount back ground electrode 205 on the back side of the submount 200 via parasitic capacitance.

[0129] The reduction rate of the parasitic capacitance compared to the comparative example (FIG. 8) in which the thickness of the semi-insulating substrate 1 made of Fe-doped InP is 100 μm is calculated by adding the thickness t Sub Adding the term (μm), it is expressed by the following equation (9). Parasitic capacitance reduction rate (times) =100 / (100+12.1·t Air +1.42·t Sub ) (9)

[0130] In formula (9), the dielectric constant of aluminum nitride is set to 8.5. Also, 1.42 in formula (9) is the value obtained by dividing 12.1, which is the dielectric constant of InP, by 8.5, which is the dielectric constant of aluminum nitride.

[0131] Between the n-type second conductive layer 41a, which also functions as a contact layer, and the submount back surface ground electrode 205 on the back surface side of the submount 200, there is a semi-insulating substrate 1 made of Fe-doped InP with a substrate thickness of 100 μm, an air layer thickness corresponding to the thickness of the back surface electrode 61, bump or solder layer 72, and ground electrode 48 on the submount 200 of 20 μm, and a thickness of the submount 200 of 1000 μm. From equation (9), the reduction rate of the parasitic capacitance compared to the comparative example (FIG. 8) is 0.0568 times, or 1 / 18, which enables a significant reduction in parasitic capacitance.

[0132] Fig. 18 shows the frequency response characteristics of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 600 according to the third embodiment when mounted on the submount 200 shown in Fig. 17. In Fig. 18, the solid line represents the frequency response characteristics of the second EA modulator section 105 of the third embodiment, the dotted line represents the frequency response characteristics of the second EA modulator section 105 of the comparative example, and the dashed-dotted line represents the frequency response characteristics of the first EA modulator section 103 of the third embodiment and the comparative example.

[0133] 18, the reduction in parasitic capacitance broadens the bandwidth of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 600 according to the third embodiment, resulting in frequency response characteristics that are substantially the same as those of the first EA modulator section 103. Compared to the first embodiment, the third embodiment reduces fluctuations in the extinction ratio due to high-frequency interference because ΔEx1-ΔEx2 in equation (3) approaches zero. Furthermore, since no recess is provided on the back side of the semi-insulating substrate that constitutes the optical modulator-integrated semiconductor laser as in the second embodiment, the third embodiment also has the advantage of making it less likely for wafer cracking to occur during the manufacturing process.

[0134] In the optical modulator-integrated semiconductor laser 600 according to the third embodiment, the n-type second semiconductor layer of the second EA modulator section 105 and the back electrode 61 directly below the n-type second electrode pad 55 are removed to form an opening 62b, and an opening 49 is provided in the ground electrode 48 on the upper surface of the submount 200, and the two are mounted in an overlapping manner, thereby reducing the parasitic capacitance of the second EA modulator section 105. As a result, in a configuration in which the optical modulator-integrated semiconductor laser 600 is mounted on the upper surface of the submount 200, the frequency response characteristics of the first EA modulator section 103 and the second EA modulator section 105 are approximately the same.

[0135] Therefore, even if the intensity of the light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section 105 cancels out this fluctuation, and the light emitted from the optical modulator-integrated semiconductor laser 600 is not affected by electromagnetic interference.

[0136] Furthermore, the configuration of the optical modulator-integrated semiconductor laser 600 and the optical module 1100 according to the third embodiment enables wideband operation of the second EA modulator section 105. Using the optical modulator-integrated semiconductor laser 600 as a light source enables the optical transceiver to have a wider bandwidth and be highly densely mounted. The optical modulator-integrated semiconductor laser 600 and the optical module 1100 do not suffer from deterioration in error rate due to electromagnetic interference, making it possible to simplify the error rate correction circuit. Thus, by applying the optical modulator-integrated semiconductor laser 600 and the optical module 1100 according to the third embodiment, it becomes possible to increase the transmission rate of an optical communication transceiver and reduce the power consumption per bit of a transmitted signal.

[0137] <Advantages of the Third Embodiment> As described above, the optical modulator-integrated semiconductor laser and optical module according to the third embodiment have at least a semiconductor laser section, a first EA modulator section, and a second EA modulator section provided on the first surface of the semi-insulating substrate along the waveguide direction of light, and a back electrode formed on the second surface of the semi-insulating substrate and having an opening in a region facing the second EA modulator section across the semi-insulating substrate.In addition, an opening is provided in the ground electrode on the upper surface side of the submount, and the two are mounted by overlapping each other.This further reduces parasitic capacitance, thereby achieving the effect of obtaining an optical modulator-integrated semiconductor laser and optical module with a wider frequency response band and further reduced fluctuations in the extinction ratio due to high-frequency interference.

[0138] Embodiment 4 <Structure and Function of Optical Modulator-Integrated Semiconductor Laser and Optical Module According to Fourth Embodiment> The device structures of the optical modulator integrated semiconductor laser 650 and the optical module 1150 according to the fourth embodiment will be described below.

[0139] Fig. 19 is a top view of an optical modulator-integrated semiconductor laser 650 according to the fourth embodiment. Fig. 20 is a rear view of the optical modulator-integrated semiconductor laser 650 according to the fourth embodiment.

[0140] The top surface side of the optical modulator-integrated semiconductor laser 650 according to the fourth embodiment has the same device structure as the optical modulator-integrated semiconductor laser 500 according to the first embodiment. On the other hand, on the back surface side, while the opening 62 in the back surface electrode 61 is formed only directly below the second EA modulator section 105 in the first embodiment, the optical modulator-integrated semiconductor laser 650 according to the fourth embodiment differs in that the opening 62c in the back surface electrode 61 extends not only to the region directly below the second EA modulator section 105 but also to the region directly below the first EA modulator section 103, as shown in Fig. 20. That is, the device structure of the optical modulator-integrated semiconductor laser 650, other than the arrangement and size of the opening 62c in the back surface electrode 61, is the same as that of the optical modulator-integrated semiconductor laser 500 according to the first embodiment.

[0141] 19, when the lengths of the first EA modulator section 103 and the second EA modulator section 105 along the light waveguide direction are L1 and L2, respectively, and the length of the second connection waveguide section 104 between the first EA modulator section 103 and the second EA modulator section 105 along the light waveguide direction is L3, the size of the opening 62c in the back electrode 61 along the light waveguide direction is preferably L1+L2+L3 or more. However, even if the length of the opening 62c along the light waveguide direction is smaller than L1+L2+L3, the effect of reducing parasitic capacitance is still achieved.

[0142] Furthermore, since the electric field from each EA modulator portion to the back electrode 61 also spreads in the horizontal direction, the opening 62c of the back electrode 61 is formed to be larger than the substrate thickness t of the semi-insulating substrate 1 made of Fe-doped InP. InP Therefore, it is preferable to widen the length corresponding to L1+L2+L3+t InP The above is preferable.

[0143] In the case of a high-speed EA modulator, for example, L1 and L2 are 50 μm, L3 is 30 μm, and t InP Therefore, the length of the opening 62c of the rear electrode 61 along the light guide direction is preferably at least 130 μm (= L1 + L2 + L3) or more, and more preferably 230 μm (= L1 + L2 + L3 + t InP) or more is more preferable.

[0144] The width of the opening 62c of the rear electrode 61 in the direction perpendicular to the light guiding direction, i.e., the direction of line AA in Fig. 20, must be at least equal to or greater than the distance W from the center of the optical waveguide to the outer edge of the n-type first electrode pad 54 or the p-type second electrode pad 55. Furthermore, taking into consideration the horizontal spread of the electric field in the semi-insulating substrate 1 made of Fe-doped InP, the substrate thickness t InP Therefore, it is preferable to widen the width of the opening 62c of the rear electrode 61 in the direction perpendicular to the light guide direction, which corresponds to W+t InP , i.e., the distance W and the substrate thickness t InP It is preferable that the sum of these is equal to or greater than the above.

[0145] For a high-speed EA modulator, the distance W is 50 μm and the substrate thickness t InP Therefore, the width of the opening 62c of the rear electrode 61 in the direction perpendicular to the light guide direction is preferably at least 50 μm, that is, the distance W or more, and more preferably 150 μm (=W+t InP ) or more is more preferable.

[0146] 21 is a top view of the submount 200 in the optical module 1150 according to the fourth embodiment. As shown in Fig. 21, an opening 49 is formed in the ground electrode 48 on the submount 200. The aluminum nitride base material of the submount 200 is exposed through the opening 49 in the ground electrode 48. The solder on the submount 200 also has an opening at the same location as the opening 49 in the ground electrode 48 on the submount 200.

[0147] The size of the opening 49 in the ground electrode 48 on the submount 200 is approximately the same as the opening 62c in the back surface electrode 61. The base material of the submount 200 is a dielectric or high-resistance material such as aluminum nitride, SiC, or alumina. The thickness of the submount 200 is preferably in the range of 100 μm to 1000 μm. A submount back surface ground electrode 205 is formed on the back surface of the submount 200 and is electrically connected to the ground electrode 48 on the top surface of the submount 200 via a grounding through electrode 56.

[0148] Fig. 22 is a cross-sectional view of the first EA modulator section 103 of the optical modulator-integrated semiconductor laser 650 arranged on the submount 200 in the optical module 1150 according to the fourth embodiment, i.e., a cross-sectional view of a portion along the line AA in Fig. 19. Fig. 23 is a cross-sectional view of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 650 arranged on the submount 200 in the optical module 1150 according to the fourth embodiment, i.e., a cross-sectional view of a portion along the line BB in Fig. 19.

[0149] As shown in FIG. 22, the optical modulator integrated semiconductor laser 650 is mounted so that the opening 62c of the back electrode 61 is aligned with part or all of the opening 49 of the ground electrode 48 on the submount 200.

[0150] <Function of Fourth Embodiment> In the fourth embodiment, similarly to the third embodiment, the second EA modulator section 105 is mounted so that the opening 62c of the back electrode 61 and the opening 49 of the ground electrode 48 on the submount 200 overlap. As a result, the n-type second conductive layer 41a, which also functions as a contact layer for the second EA modulator section 105, and the ground electrode directly below the n-type second electrode pad 55 become the submount back ground electrode 205 of the submount 200. Therefore, the distance from the second EA modulator section 105 to the submount back ground electrode 205 is long, and thus the parasitic capacitance is reduced.

[0151] Furthermore, the ground electrode directly below the p-type first electrode pad 54 of the first EA modulator section 103 also serves as the submount back surface ground electrode 205 of the submount 200. Therefore, since the distance to the ground electrode is long, the parasitic capacitance of the first EA modulator section 103 is also small.

[0152] Fig. 24 shows the frequency response characteristics of the first EA modulator section 103 and the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 650 according to the fourth embodiment when mounted on the submount 200 shown in Fig. 21. In Fig. 24, the solid line shows the frequency response characteristics of the first EA modulator section 103 and the second EA modulator section 105 according to the fourth embodiment, the dotted line shows the frequency response characteristics of the second EA modulator section 105 of the comparative example, and the dash-dot line shows the frequency response characteristics of the first EA modulator section 103 of the comparative example.

[0153] Due to the reduction in parasitic capacitance, both the first EA modulator section 103 and the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 600 according to the fourth embodiment have wider bandwidths than those of the comparative example, and the first EA modulator section 103 and the second EA modulator section 105 have substantially the same frequency response characteristics. Compared with the third embodiment, the fourth embodiment has ΔEx1-ΔEx2 in equation (3) closer to zero, so that fluctuations in the extinction ratio due to high-frequency interference are more suppressed.

[0154] In the optical modulator-integrated semiconductor laser 650 according to the fourth embodiment, the n-type second semiconductor layer 46 of the second EA modulator section 105 and the back electrode 61 directly below the n-type second electrode pad 55 are removed to form an opening 62c, and an opening 49 is provided in the ground electrode 48 on the upper surface of the submount 200, and the two are mounted in an overlapping manner, thereby reducing the parasitic capacitance of the second EA modulator section 105. As a result, the frequency response characteristics of the first EA modulator section 103 and the second EA modulator section 105 are approximately the same.

[0155] Therefore, even if the intensity of the light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section 105 cancels out this fluctuation, and the light emitted from the optical modulator integrated semiconductor laser 650 is not affected by electromagnetic interference.

[0156] Furthermore, the configuration of the optical modulator-integrated semiconductor laser 650 according to the fourth embodiment enables wideband operation of the second EA modulator section 105. Using the optical modulator-integrated semiconductor laser 650 as a light source enables the optical transceiver to have a wider bandwidth and be highly densely mounted. The optical modulator-integrated semiconductor laser 650 and the optical module 1150 do not suffer from deterioration in error rate due to electromagnetic interference, making it possible to simplify the error rate correction circuit. Thus, by applying the optical modulator-integrated semiconductor laser 650 and the optical module 1150 according to the fourth embodiment, it becomes possible to increase the transmission rate of an optical communication transceiver and reduce the power consumption per bit of a transmitted signal.

[0157] <Advantages of the Fourth Embodiment> As described above, the optical modulator-integrated semiconductor laser and optical module according to the fourth embodiment have at least a semiconductor laser section, a first EA modulator section, and a second EA modulator section provided on the first surface of the semi-insulating substrate along the waveguide direction of light, and a back electrode formed on the second surface of the semi-insulating substrate and having an opening in a region facing the second EA modulator section across the semi-insulating substrate.In addition, an opening is provided in the ground electrode on the upper surface of the submount, and the two are mounted by overlapping each other.This further reduces parasitic capacitance, thereby achieving the effect of obtaining an optical modulator-integrated semiconductor laser and optical module with a wider frequency response band and further reduced fluctuations in the extinction ratio due to high-frequency interference.

[0158] Variation 1 of embodiment 4 Fig. 25 is a cross-sectional view of the first EA modulator section 103 of the optical modulator-integrated semiconductor laser 660 arranged on the submount 200 in the optical module 1160 according to the first modification of the fourth embodiment, i.e., a cross-sectional view of the portion corresponding to the portion along the line AA in Fig. 19. Fig. 26 is a cross-sectional view of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 660 arranged on the submount 200 in the optical module 1160 according to the first modification of the fourth embodiment, i.e., a cross-sectional view of the portion corresponding to the portion along the line BB in Fig. 19.

[0159] The optical modulator integrated semiconductor laser 660 in the optical module 1160 relating to the first variant of the fourth embodiment has an opening 62 in the back electrode 61 provided directly below the first EA modulator section 103 and the second EA modulator section 105, similar to the fourth embodiment, but differs from the fourth embodiment in that no opening is provided in the ground electrode 48 on the submount 200.

[0160] The effect of the optical module 1160 and optical modulator-integrated semiconductor laser 660 relating to variant example 1 of embodiment 4 is that, compared to embodiment 4, the reduction in parasitic capacitance of the first EA modulator section 103 and the second EA modulator section 105 is small, but since there is no need to mount the opening 62 of the back electrode 61 so that it overlaps the opening of the ground electrode 48 on the submount 200, the precision of chip mounting alignment is relaxed, and there is an effect that no reduction in yield occurs even when a large number of optical modules 1160 are densely mounted in an optical transceiver.

[0161] <Modification 2 of Embodiment 4> Fig. 27 is a cross-sectional view of the first EA modulator section 103 of the optical modulator-integrated semiconductor laser 670 arranged on the submount 200 in the optical module 1170 according to the second modification of the fourth embodiment, i.e., a cross-sectional view of the portion corresponding to the portion along the line AA in Fig. 19. Fig. 28 is a cross-sectional view of the second EA modulator section 105 of the optical modulator-integrated semiconductor laser 670 arranged on the submount 200 in the optical module 1170 according to the second modification of the fourth embodiment, i.e., a cross-sectional view of the portion corresponding to the portion along the line BB in Fig. 19.

[0162] The optical modulator integrated semiconductor laser 670 in the optical module 1170 relating to the second variant of the fourth embodiment has an opening 62 in the back electrode 61 directly below the first EA modulator section 103 and the second EA modulator section 105, as in the first variant of the fourth embodiment, but does not have an opening in the ground electrode 48 on the submount 200.

[0163] The difference between the second modification of the fourth embodiment and the first modification of the fourth embodiment is that in the optical modulator-integrated semiconductor laser 670 in the optical module 1170 according to the second modification of the fourth embodiment, a recess 65 is formed in the semi-insulating substrate 1 exposed in the opening 62 of the back electrode 61 immediately below the first EA modulator section 103 and the second EA modulator section 105. The method for forming the recess 65 is the same as the method for forming the recess in the second embodiment.

[0164] The optical module 1170 and optical modulator-integrated semiconductor laser 670 according to the second modification of the fourth embodiment have the advantage that, compared to the first modification of the fourth embodiment, the reduction in parasitic capacitance of the first EA modulator section 103 and the second EA modulator section 105 is greater, thereby enabling a further broadening of the bandwidth. Also, as with the first modification of the fourth embodiment, it is not necessary to mount the optical module 1170 so that the opening of the back electrode is aligned with the opening of the ground electrode on the submount, and therefore the alignment precision required when mounting the chip is relaxed, resulting in the effect that even if a large number of optical modules 1170 are densely mounted in an optical transceiver, a decrease in yield does not occur and a broadening of the bandwidth is possible.

[0165] Variation 3 of embodiment 4 Fig. 29 is a back view of an optical modulator-integrated semiconductor laser 680 according to a third modification of the fourth embodiment. Fig. 30 is a top view of a submount 200 in an optical module 1180 according to the third modification of the fourth embodiment. The base material of the submount 200 is a dielectric or high-resistance material such as aluminum nitride, SiC, or alumina.

[0166] In the optical module 1180 relating to the third variant of the fourth embodiment, the optical modulator integrated semiconductor laser 680 has openings 62f and 62g in the back electrode 61 provided directly below the first EA modulator section 103 and the second EA modulator section 105, respectively, as in the fourth embodiment, while the opening 62f directly below the first EA modulator section 103 and the opening 62g directly below the second EA modulator section 105 are not connected.

[0167] Also, an opening is provided in the ground electrode 48 on the submount 200, but it is separated into two parts. That is, when the optical modulator-integrated semiconductor laser 680 is mounted, the ground electrode 48 on the submount 200 has a portion that overlaps with the opening 62f of the back surface electrode 61 directly below the first EA modulator section 103 and a portion that overlaps with the opening 62g of the back surface electrode 61 directly below the second EA modulator section 105, which are not connected.

[0168] In the optical modulator-integrated semiconductor laser 650 according to the fourth embodiment, the opening 62 of the back electrode 61 directly below the first EA modulator section 103 and the second EA modulator section 105 is connected and forms one whole. Therefore, since the area of ​​the opening 62 is wide and the bonding area of ​​the chip is narrow, the bonding strength of the optical modulator-integrated semiconductor laser may be insufficient.

[0169] On the other hand, in the optical modulator-integrated semiconductor laser 680 according to the third modification of the fourth embodiment, the openings 62g and 62f are minimized, thereby improving the mounting strength between the chip and the submount and increasing the heat dissipation of the chip. As a result, even when a large number of optical modulator-integrated semiconductor lasers 680 are densely mounted in an optical transceiver, the chip has high heat dissipation, and furthermore, since a decrease in yield due to insufficient strength does not occur, the temperature cycle test durability is improved. In addition, the effects of widening the bandwidth and suppressing fluctuations in the extinction ratio due to high-frequency interference are the same as those of the fourth embodiment. Therefore, the optical modulator-integrated semiconductor laser 680 and the optical module 1180 according to the third modification of the fourth embodiment have the effect of enabling the realization of an optical transceiver that is wideband, resistant to high-frequency interference, and highly reliable.

[0170] Embodiment 5 <Structure of Optical Module According to Fifth Embodiment> 31 is a schematic diagram showing an optical module 1200 according to the fifth embodiment. The optical module 1200 according to the fifth embodiment is configured by flip-chip mounting the optical modulator-integrated semiconductor laser 650 according to the fourth embodiment. Note that flip-chip mounting is also called junction-down mounting.

[0171] The optical modulator-integrated semiconductor laser 650 is mounted with the back electrode 61 facing up. Therefore, the surface of the epitaxial crystal growth layer on which the EA modulator section is formed faces down. The semiconductor laser section current line LN3 on the submount 200 is electrically connected to the p-type third electrode 5 (not shown) of the semiconductor laser section 101 by a bump or a solder layer 72.

[0172] Fig. 32 is a cross-sectional view of the first EA modulator section 103 in a direction perpendicular to the light guiding direction, i.e., a cross-sectional view taken along line AA in Fig. 31. Fig. 33 is a cross-sectional view of the second EA modulator section 105 in a direction perpendicular to the light guiding direction, i.e., a cross-sectional view taken along line BB in Fig. 31.

[0173] 32, the p-type first electrode 25 of the first EA modulator section 103 is electrically connected to the first modulation signal line LN1 via a bump or a solder layer 72. As shown in Fig. 33, the n-type second electrode 46 of the second EA modulator section 105 is electrically connected to the second modulation signal line LN2 via a bump or a solder layer 72.

[0174] A common electrode 47, to which the n-type first electrode 26 of the first EA modulator section 103 and the p-type second electrode 45 of the second EA modulator section 105 are connected, is electrically connected to a ground electrode 48 on the submount 200 by a bump or a solder layer 72. The base material of the submount 200 is a dielectric or high-resistance material such as aluminum nitride, SiC, or alumina.

[0175] <Operation of the Fifth Embodiment> 34 is a cross-sectional view of the pad portion of the EA modulator section in the light guide direction of the optical module 1200 according to the fifth embodiment, that is, a cross-sectional view of the portion along the CC line in FIG. 31. FIG. 35 is a cross-sectional view of the pad portion of the EA modulator section in the light guide direction of the optical module 1210 in the comparative example. In the comparative example in FIG. 35, the parasitic capacitance between the p-type first electrode 25 and the back electrode 61 of the first EA modulator section 103 is defined as C EA1 , the parasitic capacitance between the n-type second electrode 46 and the back electrode 61 of the second EA modulator section 105 is C EA2The parasitic capacitance between the p-type third electrode 5 and the back electrode 61 of the semiconductor laser portion 101 is C DFB Let's say.

[0176] In the comparative example shown in FIG. 35, when a high-frequency signal is input from the first modulation signal line LN1 to the p-type first electrode 25 of the first EA modulator section 103, the parasitic capacitance C EA1 The high frequency signal is transmitted to the rear electrode 61 via the parasitic capacitance C DFB to the p-type third electrode 5 of the semiconductor laser portion 101. As a result, fluctuations occur in the optical output of the DFB laser.

[0177] The first p-type electrode 25 of the first EA modulator section 103 has a parasitic capacitance C EA1 , back electrode 61, parasitic capacitance C EA2 Since the n-th second electrode 46 of the second EA modulator section 105 is connected at high frequency via the n-th second electrode 46, the parasitic capacitance increases and the frequency response characteristics are impaired.

[0178] On the other hand, in the optical module 1200 according to the fifth embodiment shown in FIG. 34, the back electrode 61 is not provided on the surface facing the first EA modulator section 103 and the second EA modulator section 105, that is, the opening 62 is provided, so that the parasitic capacitance C EA1 and parasitic capacitance C EA2 becomes sufficiently small. As a result, no high-frequency signal is propagated to the semiconductor laser section 101 via the back electrode 61. Therefore, there is no increase in parasitic capacitance between the p-type first electrode 25 of the first EA modulator section 103 and the n-type second electrode 46 of the second EA modulator section 105.

[0179] Furthermore, in the optical module 1200 according to the fifth embodiment, the surface facing each EA modulator section does not have the back electrode 61, i.e., the opening 62 is provided, so that the parasitic capacitances of the first EA modulator section 103 and the second EA modulator section 105 are equal. In other words, the frequency response characteristics of the first EA modulator section 103 and the second EA modulator section 105 are equal, so that high-frequency interference can be canceled out.

[0180] <Effects of the Fifth Embodiment> By providing an opening in the back electrode of the surface of the optical modulator-integrated semiconductor laser 650 facing the first EA modulator section 103 and the second EA modulator section 105 and flip-chip mounting the optical modulator-integrated semiconductor laser 650, the parasitic capacitance of the first EA modulator section 103 and the second EA modulator section 105 is sufficiently reduced. As a result, the frequency response characteristics of the first EA modulator section 103 and the second EA modulator section 105 are approximately the same. Even if the intensity of light passing through the first EA modulator section 103 fluctuates due to electromagnetic interference, the second EA modulator section 105 cancels this fluctuation, so the light emitted from the optical modulator-integrated semiconductor laser 650 is not affected by electromagnetic interference. Furthermore, there is no increase in parasitic capacitance between the first EA modulator section 103 and the second EA modulator section 105, enabling wideband operation.

[0181] Furthermore, since no high-frequency signal is transmitted from the first EA modulator section 103 to the semiconductor laser section 101, no fluctuations in the light intensity of the DFB laser occur. As a result, the optical transceiver can be made wider bandwidth and more densely packed. Also, since there is no deterioration in the error rate due to electromagnetic interference or fluctuations in the light intensity of the DFB laser, the error rate correction circuit can be simplified. In this way, it is possible to increase the transmission rate of the optical communication transceiver, and it is possible to reduce the power consumption per bit of the transmitted signal.

[0182] Variation 1 of embodiment 5 FIG. 36 is a schematic diagram of an optical module 1250 according to Modification 1 of Embodiment 5. The optical module 1250 according to Modification 1 of Embodiment 5 is configured by flip-chip mounting the optical modulator-integrated semiconductor laser 680 according to Modification 3 of Embodiment 4 on a submount 200. The opening 62 in the back electrode 61 is limited to only the portion opposite the first EA modulator section 103 and the second EA modulator section 105, so the area of ​​the opening 62 in the back electrode 61 is small. The smaller opening 62 in the back electrode 61 increases the wafer strength during the manufacturing process, thereby preventing a decrease in yield due to cracks in the wafer and chips. The effects of Modification 1 of Embodiment 5 are similar to those of Embodiment 5.

[0183] Variation 2 of embodiment 5 37 is a schematic view of an optical module 1300 according to a second modification of the fifth embodiment. In the optical module 1300 according to the second modification of the fifth embodiment, the optical modulator-integrated semiconductor laser 690 is flip-chip mounted on the submount 200, as in the fifth embodiment. In the optical modulator-integrated semiconductor laser 690 according to the second modification of the fifth embodiment, the back electrode 61 is divided into two: a back electrode 61s (first back electrode) of each EA modulator section, and a back electrode 61t (second back electrode) of the semiconductor laser section 101.

[0184] The back electrode 61s of each EA modulator receives a high-frequency signal through the parasitic capacitance C EA1 However, because a separation opening is provided between the semiconductor laser portion 101 and the back surface electrode 61t (first back surface electrode) of the semiconductor laser portion 101, the high frequency signal is not transmitted to the semiconductor laser portion 101. As a result, fluctuations in the light amount of the DFB laser are suppressed.

[0185] In the optical modulator integrated semiconductor laser 690 according to the second modification of the fifth embodiment, the opening of the entire back electrode 61 is small, which increases the strength of the wafer during the manufacturing process. In addition, as in the fifth embodiment, the error rate does not deteriorate due to fluctuations in the light intensity of the DFB laser caused by electromagnetic interference from each EA modulator section, which makes it possible to simplify the error rate correction circuit.

[0186] Variation 3 of embodiment 5 38 is a schematic diagram of an optical module 1350 according to a third modification of the fifth embodiment. In the optical module 1350 according to the third modification of the fifth embodiment, the optical modulator-integrated semiconductor laser 700 is flip-chip mounted as in the fifth embodiment. Compared to the second modification of the fifth embodiment, the optical modulator-integrated semiconductor laser 700 according to the third modification of the fifth embodiment has the back surface electrode 61 divided into three parts: a back surface electrode 61t (first back surface electrode) of the semiconductor laser section 101, a back surface electrode 61u (second back surface electrode) of the first EA modulator section 103, and a back surface electrode 61v (second back surface electrode) of the second EA modulator section 105.

[0187] A high frequency signal is input to the back electrode 61u of the first EA modulator section 103 through the parasitic capacitance CEA1 However, since a separation opening is provided between the semiconductor laser portion 101 and the back surface electrode 61t (first back surface electrode) of the semiconductor laser portion 101 and the separation opening is provided, the light is not transmitted to the semiconductor laser portion 101.

[0188] Furthermore, since a separation opening is provided between the first EA modulator section 103 and the second EA modulator section 105, no parasitic capacitance occurs between the first EA modulator section 103 and the second EA modulator section 105. As a result, fluctuations in the light intensity of the DFB laser are suppressed, and each EA modulator section operates over a wide band.

[0189] In the optical modulator-integrated semiconductor laser 700 according to the third modification of the fifth embodiment, the opening of the back electrode 61 is small, which increases the wafer strength during the wafer process. In addition, as in the fifth embodiment, the error rate does not deteriorate due to fluctuations in the light intensity of the DFB laser caused by electromagnetic interference from the EA modulator. This makes it possible to simplify the error rate correction circuit and realize a wider bandwidth for the optical transceiver.

[0190] Variation 4 of embodiment 5 39 is a schematic diagram of an optical module 1400 according to the fourth modification of the fifth embodiment. In the optical module 1400 according to the fourth modification of the fifth embodiment, the optical modulator-integrated semiconductor laser 710 is flip-chip mounted as in the fifth embodiment. In the optical modulator-integrated semiconductor laser 710 according to the fourth modification of the fifth embodiment, the back electrode portion of the first EA modulator section 103 and the back electrode portion of the second EA modulator section 105 in the optical modulator-integrated semiconductor laser 700 according to the third modification of the fifth embodiment are formed as openings.

[0191] Furthermore, in the portions that were open in the third modification of the fifth embodiment, a back electrode 61w between the first EA modulator section 103 and the second EA modulator section 105 and a back electrode 61x on the front end face of the second EA modulator section are formed.

[0192] The effect of the fourth modification of the fifth embodiment is that, like the third modification of the fifth embodiment, fluctuations in the light intensity of the DFB laser are suppressed, and each EA modulator unit operates in a wide band. Furthermore, since there is no deterioration in the error rate due to fluctuations in the light intensity of the DFB laser caused by electromagnetic interference from each EA modulator unit, it is possible to simplify the error rate correction circuit and realize a wideband optical transceiver.

[0193] Modifications 5 and 6 of Embodiment 5 Fig. 40 is a schematic view of an optical module 1450 according to a fifth modification of the fifth embodiment. Fig. 41 is a schematic view of an optical module 1500 according to a sixth modification of the fifth embodiment. In the fifth and sixth modifications of the fifth embodiment, the optical modulator-integrated semiconductor lasers 720 and 730 are flip-chip mounted on silicon submounts, as in the fifth embodiment.

[0194] In the fifth modification of the fifth embodiment, the back electrode of the EA modulator section is eliminated, and in the sixth modification of the fifth embodiment, the back electrode is eliminated, including the semiconductor laser section 101. Therefore, no parasitic capacitance occurs between the back electrode and each EA modulator section, and therefore, as an effect of the fifth and sixth modifications of the fifth embodiment, similar to the fifth embodiment, fluctuations in the light amount of the DFB laser are suppressed, and each EA modulator section operates in a wide band.

[0195] In the optical modules 1450 and 1500 according to the fifth and sixth variations of the fifth embodiment, the error rate does not deteriorate due to fluctuations in the light intensity of the DFB laser caused by electromagnetic interference from each EA modulator, which makes it possible to simplify the error rate correction circuit and realize a broadband optical transceiver. Furthermore, in the sixth variation of the fifth embodiment, the process of forming a back electrode on the chip is not required.

[0196] Embodiment 6 <Structure of Optical Modulator Integrated Semiconductor Laser and Optical Module According to Sixth Embodiment> FIG. 42 is a top view showing a differential optical modulator-integrated semiconductor laser 800, which is an example of an optical modulator-integrated semiconductor laser according to the sixth embodiment, and FIG. 43 is a rear view of the differential optical modulator-integrated semiconductor laser 800.

[0197] As shown in FIG. 42, in a differential optical modulator integrated semiconductor laser 800 according to the sixth embodiment, a semiconductor laser section 111, a connecting waveguide section 112, a differential EA modulator section 113, and an output waveguide section 114 are connected in this order by an optical waveguide.

[0198] A p-type third electrode 5j and an n-type third electrode 6j of the semiconductor laser section 111, and a p-type first electrode 25j and an n-type first electrode 26j of the differential EA modulator section 113 are formed on the upper surface of the differential optical modulator integrated semiconductor laser 800. The n-type third electrode 6j of the semiconductor laser section 111 and the n-type first electrode 26j of the differential EA modulator section 113 are connected to n-type semiconductor layers such as n-type first conductive layers that also function as their respective contact layers. The p-type third electrode 5j of the semiconductor laser section 111 and the p-type first electrode 25j of the differential EA modulator section 113 are connected to a p-type semiconductor layer (not shown) above the optical waveguide.

[0199] In this disclosure, a differential EA modulator refers to an EA modulator formed on a semi-insulating substrate 1 such as an Fe-doped InP substrate. When the EA modulator is formed on the semi-insulating substrate 1, the resistance between the p-type first electrode 25j and the n-type first electrode 26j and the backside electrode 61j on the backside of the chip is high. This allows different modulation signals to be applied to the p-type first electrode 25j and the n-type first electrode 26j, respectively. For example, applying a positive-phase signal to the p-type first electrode 25j and a negative-phase signal to the n-type first electrode 26j allows the EA modulator to be differentially driven. In other words, neither the p-type first electrode 25j nor the n-type first electrode 26j is grounded.

[0200] Furthermore, in the differential EA modulator of the present application, it is also possible to ground the n-type first electrode 26j with a wire or the like and drive the p-type first electrode 25j as a single layer. Therefore, the differential EA modulator of the present application does not necessarily need to be driven by a differential signal. In the first embodiment, the first EA modulator section 103 and the second EA modulator section 105 are formed on the semi-insulating substrate 1 made of Fe-doped InP, so it can also be said to be a double differential EA modulator.

[0201] In the first embodiment, the p-type electrode or the n-type electrode is grounded by a wire or the like, and a modulation signal is applied to the paired n-type electrode or the p-type electrode, respectively, so that each EA modulator section can be said to be driven in a single phase. Generally, a single-phase EA modulator is an EA modulator formed on a conductive substrate such as an n-type substrate or a p-type substrate.

[0202] 43, a back electrode 61 is formed on a semi-insulating substrate 1 made of Fe-doped InP on the back side of the chip. In the sixth embodiment, the back electrode is removed from the portion facing the differential EA modulator section 113 on the top surface of the chip, and an opening 62j (without metal) is formed in the back electrode 61j. On the other hand, in the comparative example, there is no opening in the back electrode on the back side of the chip.

[0203] As shown in Figures 42 and 43, it is preferable that the size of the opening 62j in the back electrode 61j be larger than the size of the differential EA modulator section 113, i.e., the length Lea along the light waveguide direction and the length Wea in the direction perpendicular to the light waveguide direction.

[0204] The thickness of the semi-insulating substrate 1 is t InP Then, the electric field spreads to both sides in the horizontal direction, approximately half the thickness of the substrate, so the Lea+t InP , Wea+t in the direction perpendicular to the light guiding direction InP It is more desirable to use this region as an opening 62j of the rear electrode 61j.

[0205] 44 is a cross-sectional view taken along the light guide direction of a differential optical modulator integrated semiconductor laser 800 according to the sixth embodiment. The semiconductor laser portion 111 is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3 an n-type third semiconductor layer having a layer thickness of 0.1 μm or more and 5.0 μm or less; an active layer 3j; and a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3and a p-type third semiconductor layer having a thickness of 0.1 μm or more and 5.0 μm or less.

[0206] The n-type third semiconductor layer is composed of an n-type third conductive layer 2j and an n-type third cladding layer 2k, which also function as a contact layer, and the p-type third semiconductor layer is composed of a p-type third cladding layer 4j and a p-type third contact layer 4k.

[0207] The semiconductor laser portion 111 further includes a p-type third electrode 5j electrically connected to the p-type third semiconductor layer of the semiconductor laser portion 111, and an n-type third electrode 6j electrically connected to the n-type third semiconductor layer.

[0208] The active layer 3j is composed of a diffraction grating layer, a multiple quantum well layer, and light confinement layers (none of which are shown) formed above and below the multiple quantum well layer. The width of the active layer 3j in a direction perpendicular to the light guiding direction is in the range of 1 μm to 2 μm. The total thickness of the active layer 3j is in the range of 100 nm to 500 nm. Both sides of the active layer 3 of the semiconductor laser section 101 are embedded with current blocking layers (not shown) made of semiconductor.

[0209] The connection waveguide section 112, in which the optical waveguide is connected to the semiconductor laser section 111, is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×10 17 cm -3 and an i-type lower first cladding layer 11j having a layer thickness of 0.1 μm or more and 5.0 μm or less, and a carrier concentration of 5×10 17 cm -3 the i-type first waveguide layer 12j (also referred to as a core layer) having a layer thickness of 50 nm or more and 500 nm or less, and a carrier concentration of 5×10 17 cm -3 and an i-type first upper cladding layer 13j having a thickness of 0.1 μm or more and 5.0 μm or less. The refractive index of the i-type first waveguide layer 12j is higher than the refractive indexes of the i-type first lower cladding layer 11j and the i-type first upper cladding layer 13j.

[0210] In addition, if the i-type lower first cladding layer 11j, the i-type first waveguide layer 12j, and the i-type upper first cladding layer 13j have a waveguide width of 2 μm or less, the isolation resistance between the semiconductor laser section 111 and the differential EA modulator section 113 becomes high. Therefore, instead of the i-type, 18 cm -3 The following p-type or n-type conductivity types may also be used.

[0211] The isolation resistance between the semiconductor laser section 111 and the differential EA modulator section 113 is preferably set to 500Ω or more, which is 10 times higher than the 50Ω impedance of the differential EA modulator when it is driven. This is because an isolation resistance of 500Ω or more can reduce high-frequency leakage from the differential EA modulator section 113 to the semiconductor laser section 111.

[0212] The differential EA modulator section 113 connected to the connection waveguide section 112 is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3 an n-type first semiconductor layer having a layer thickness of 0.1 μm or more and 5.0 μm or less; an i-type first modulation layer 22j; and a carrier concentration of 5×10 17 cm -3 Over 8 x 10 18 cm -3 The p-type first semiconductor layer has a thickness of 0.1 μm or more and 5.0 μm or less, a p-type first electrode 25j electrically connected to the p-type first semiconductor layer, and an n-type first electrode 26j electrically connected to the n-type first semiconductor layer.

[0213] The n-type first semiconductor layer is composed of an n-type first conductive layer 21j and an n-type first cladding layer 21k, which also function as a contact layer, and the p-type first semiconductor layer is composed of a p-type first cladding layer 23j and a p-type first contact layer 23k.

[0214] The i-type first modulation layer 22j has a carrier concentration of 5×10 17 cm -3It is composed of the following i-type multiple quantum well layer and light confinement layers (neither of which is shown) formed above and below the i-type multiple quantum well layer. The width of the i-type first modulation layer 22j in the direction perpendicular to the light guiding direction is in the range of 1 μm to 2 μm. The total layer thickness of the i-type first modulation layer 22j is in the range of 50 nm to 500 nm.

[0215] The differential EA modulator section 113 is connected to an output waveguide section 114, and emits light from the chip end face. The output waveguide section 114 is formed on the semi-insulating substrate 1, that is, on the first surface side of the semi-insulating substrate 1, and has a carrier concentration of 5×10 17 cm -3 and an i-type lower third cladding layer 51j having a thickness of 0.1 μm or more and 5.0 μm or less, and a carrier concentration of 5×10 17 cm -3 an i-type third waveguide layer 52j (core layer) having a layer thickness of 50 nm or more and 500 nm or less; and a carrier concentration of 5×10 17 cm -3 and an i-type upper third cladding layer 53j having a thickness of 0.1 μm or more and 5.0 μm or less. The refractive index of the i-type third waveguide layer 52j (core layer) is higher than the refractive indexes of the i-type lower third cladding layer 51j and the i-type upper third cladding layer 53j.

[0216] In addition, when the width of the i-type lower third cladding layer 51j, the i-type third waveguide layer 52j (core layer), and the i-type upper third cladding layer 53j becomes narrower and the resistance becomes higher, they no longer affect the output waveguide portion as a parasitic capacitance. Therefore, instead of the i-type, a layer having a carrier concentration of 5×10 18 cm -3 The following p-type or n-type may also be used. The width of the i-type third waveguide layer 52j (core layer) is preferably within the range of 1 μm to 2 μm.

[0217] In order to provide the i-type third waveguide layer 52j (core layer) with a waveguide lens function, the width of the i-type third waveguide layer 52j (core layer) may be gradually changed between 0.3 μm and 5 μm.

[0218] An Fe-doped InP substrate, which is an example of the semi-insulating substrate 1, is ground or polished to a thickness of approximately 100 μm. A backside electrode 61j is formed on the backside of the chip, i.e., the second surface side of the semi-insulating substrate 1. The backside electrode 61j has a layered structure made up of AuGe, Ti, Ni, Pt, an Au vapor deposition layer, an Au plating layer, an AuSn solder layer, and the like. The film thickness of the backside electrode 61j is in the range of 1 μm to 10 μm.

[0219] An opening 62j, i.e., a portion where no back electrode is formed, is provided in the back electrode 61j directly below the differential EA modulator section 113. That is, the opening 62j is provided in the back electrode 61j in a region facing the differential EA modulator section 113 across the semi-insulating substrate 1. The semi-insulating substrate 1 is exposed through the opening 62j. The opening 62j in the back electrode 61j is formed by metal lift-off, dry etching, or wet etching.

[0220] The length of the semiconductor laser section 111 along the light waveguide direction is within a range of 100 μm or more and 600 μm or less. The lengths of the connection waveguide section 112 and the emission waveguide section 114 along the light waveguide direction are each within a range of 25 μm or more and 500 μm or less. The length of the differential EA modulator section 113 along the light waveguide direction is within a range of 25 μm or more and 200 μm or less. The total length of the differential optical modulator integrated semiconductor laser 800 according to the sixth embodiment along the light waveguide direction is within a range of 300 μm or more and 1500 μm or less.

[0221] 45 is a top view of an optical module 1600 in which a differential optical modulator-integrated semiconductor laser 800 according to the sixth embodiment is mounted on a submount 200j and connected to a wiring board 201j via a wire. A current is supplied from a current source to a p-type third electrode 5j of the semiconductor laser portion 111 via a semiconductor laser portion current line LN3 and a wire W3. An n-type third electrode 6j of the semiconductor laser portion 111 is electrically connected to a ground electrode 48j on the submount 200j via a ground wire Wg1. The base material of the submount 200j is a dielectric or high-resistance material such as aluminum nitride, SiC, or alumina.

[0222] A positive-phase voltage signal is input from the modulator driver to the first p-type electrode pad 54j of the differential EA modulator section 113 via the first modulation signal line LN1 and wire W1. The first p-type electrode pad 54j of the differential EA modulator section 113 is electrically connected to the termination resistor electrode pad 57j via a wire. The termination resistor electrode pad 57j is electrically connected to the ground electrode 48j on the submount 200j via a first termination resistor R1 on the p-type first electrode pad 54j side of the differential EA modulator section 113.

[0223] An inverted-phase voltage signal is input from the modulator driver to the n-type second electrode pad 55j of the differential EA modulator unit 113 via the second modulation signal line LN2 and wire W2. The n-type second electrode pad 55j of the differential EA modulator unit 113 is electrically connected to the termination resistor electrode pad 58j via a wire. The termination resistor electrode pad 58j is electrically connected to the ground electrode 48j on the submount 200j via the second termination resistor R2 on the n-type second electrode pad 55j side of the differential EA modulator unit 113.

[0224] <Functions of the Optical Modulator-Integrated Semiconductor Laser and Optical Module According to the Sixth Embodiment> The frequency response characteristics of the differential EA modulator section 113 depend not only on the pn junction capacitance and resistance but also on the parasitic capacitance of the electrode pads, conductive layers, etc. Here, the parasitic capacitance refers to the electrical capacitance between the back electrode 61j and the n-type first conductive layer 21j, which also functions as a contact layer in the differential EA modulator section 113, the n-type second electrode pad 55j, and the p-type first electrode pad 54j, and does not include the electrical capacitance of the pn junction of the i-type third waveguide layer 52j.

[0225] 46 is a cross-sectional view of the p-type first electrode pad 54j of the differential EA modulator section 113 of the differential optical modulator integrated semiconductor laser 800 according to the sixth embodiment, taken along the line AA in FIG. 42. As a parasitic capacitance, a parasitic capacitance C Ppad , the parasitic capacitance C between the n-type conductive layer / contact layer and the solder Nlayer exists.

[0226] 47 is a cross-sectional view of the n-type second electrode pad 55j of the differential EA modulator section 113 of the differential optical modulator integrated semiconductor laser 800 according to the sixth embodiment, taken along the line BB in FIG. 42. As a parasitic capacitance, a parasitic capacitance C Npad , a parasitic capacitance C between the n-type first conductive layer 21j, which also functions as a contact layer, and the bump or solder layer 72 Nlayer There is a parasitic capacitance C in Figure 46. Nlayer and the parasitic capacitance C in Figure 47 Nlayer are connected and are the same thing.

[0227] In the opening 62j of the rear electrode 61j, an air layer having a thickness of about 5 μm and a dielectric constant smaller than that of the semi-insulating substrate 1 made of Fe-doped InP is generated, as in the first embodiment. As a result, the parasitic capacitance C Ppad , C Npad , C Nlayer Since the difference becomes small, the differential EA modulator of the sixth embodiment has a wide bandwidth.

[0228] FIG. 48 shows the frequency response characteristics of the sixth embodiment when mounted on the submount 200j shown in FIG. 45 with an air gap thickness of 5 μm. The sixth embodiment has a wider bandwidth than the comparative example. Here, the comparative example in FIG. 48 refers to an element structure in which the chip does not have an opening or recess in the back electrode.

[0229] In addition, a parasitic capacitance C that does not exist on the side of the p-type first electrode pad 54j of the differential EA modulator section 113 is present on the side of the n-type second electrode pad 55j. NlayerBecause of the presence of the parasitic capacitances, the equivalent circuits on the p-type electrode side and the n-type electrode side are asymmetric. As a result, even if symmetrical differential signals are applied to the p-type electrode side and the n-type electrode side, the electric field applied to the modulation layer is asymmetric between the positive-phase signal and the negative-phase signal. A differential signal line in which two signal lines are arranged close to each other in parallel, such as the first modulation signal line LN1 and the second modulation signal line LN2 in Figure 45, is essentially effective in canceling out common-phase high-frequency interference applied to the differential signal line. However, if the parasitic capacitances on the p-type electrode side and the n-type electrode side are asymmetric, a problem occurs in which the positive-phase signal and the negative-phase signal cannot cancel each other out.

[0230] In the sixth embodiment, the parasitic capacitance C Nlayer Since the difference in parasitic capacitance between the p-type electrode side and the n-type electrode side becomes smaller, the effect of being able to cancel out high frequency interference applied to the differential line is achieved.

[0231] In the differential EA modulator section 113, which applies a modulation voltage to both the p-type first electrode 25j and the n-type first electrode 26j, if the p-side isolation resistance value between the p-type first electrode 25j of the differential EA modulator section 113 and the p-type third electrode 5j of the semiconductor laser section 111 is different from the n-side isolation resistance value between the differential EA modulator section 113 and the n-type third electrode 6j of the semiconductor laser section 111, it is not possible to cancel out the in-phase high-frequency interference applied to the differential signal line.

[0232] For example, if the n-side isolation resistance is small, the modulation signal leaks to the n-type third electrode 6j of the semiconductor laser section 111 and then flows to the ground electrode 48, reducing the amplitude of the voltage applied to the n-type first electrode 26j of the differential EA modulator section 113. As a result, the positive and negative phase signals become asymmetric during differential driving. Therefore, particularly in the case of a differential EA modulator, reducing the difference in parasitic capacitance between the p-type electrode side and the n-type electrode side and simultaneously reducing the difference between the p-side isolation resistance and the n-side isolation resistance improves the cancellation effect of high-frequency interference.

[0233] Furthermore, even if there is a difference in isolation resistance between the p-side and n-side, high-frequency interference can be canceled out if the resistances of both sides are sufficiently high. In the case of InP, the resistance of the n-type InP layer is one order of magnitude smaller than the resistance of the p-type InP layer at the same carrier concentration, so it is necessary to increase the isolation resistance value on the n-side. Therefore, to fully achieve the high-frequency interference reduction effect of the present disclosure, the n-side isolation resistance value must be higher than the high-frequency resistance leaking to the ground electrode 48j via the parasitic capacitance on the n-side of the differential EA modulator section 113.

[0234] A case where a high-frequency signal flows to the ground electrode 48j via the parasitic capacitance on the n-side of the differential EA modulator section 113 will be described below.

[0235] The parasitic capacitance Cn on the n-side (=C Npad +C Nlayer ) the high frequency resistance Rn at high frequencies (frequency f) is Rn = 1 / (2πCn·f). Cn of a typical Fe-doped InP substrate with a substrate thickness (100 μm) is about 10 fF. If frequency f is 100 GHz, Rn becomes 160 Ω. In other words, to fully obtain the effects of the present disclosure, the n-side isolation resistance value must be at least 160 Ω or more. When the air layer thickness is 5 μm, the parasitic capacitance is reduced to about 60%, so it is preferable that the n-side isolation resistance value between the differential EA modulator section 113 and the semiconductor laser section 111 be 260 Ω or more.

[0236] Variation 1 of Embodiment 6 <Optical Modulator-Integrated Semiconductor Laser and Optical Module According to Modification 1 of the Sixth Embodiment> The following describes a differential optical modulator integrated semiconductor laser 810 and an optical module 1610 according to a first modification of the sixth embodiment. Similar to the concept of the second embodiment, the opening 62j of the back electrode 61j may be formed by forming a recess 65j in the semi-insulating substrate 1 exposed in the opening 62j.

[0237] Fig. 49 is a cross-sectional view of the p-type first electrode pad 54j of the differential EA modulator unit 113 of the differential optical modulator integrated semiconductor laser 810 according to the first modification of the sixth embodiment, taken along the line AA in Fig. 42. Fig. 50 is a cross-sectional view of the n-type second electrode pad 55j of the differential EA modulator unit 113 of the differential optical modulator integrated semiconductor laser 810 according to the first modification of the sixth embodiment, taken along the line BB in Fig. 42.

[0238] If the depth of the recess 65j is 10 μm, the thickness of the air layer is 15 μm, adding the thickness of the back electrode 61j, which is 5 μm. Ppad , C Ppad , C Nlayer becomes even smaller, the differential EA modulator of the first modification of the sixth embodiment has a wider bandwidth than that of the sixth embodiment.

[0239] 48 shows the frequency response characteristics when the thickness of the air layer is set to 15 μm in the first modification of the sixth embodiment. As can be seen from Fig. 48, the differential optical modulator-integrated semiconductor laser 810 according to the first modification of the sixth embodiment has a wider bandwidth than the sixth embodiment.

[0240] In the differential optical modulator integrated semiconductor laser 810 and the optical module 1610 according to the first modification of the sixth embodiment, the parasitic capacitance C Nlayer is smaller than that in the sixth embodiment, the difference in parasitic capacitance between the p-type electrode side and the n-type electrode side is reduced, and the effect of canceling out high frequency interference applied to the differential line is enhanced.

[0241] Variation 2 of Embodiment 6 <Optical Modulator-Integrated Semiconductor Laser and Optical Module According to Modification 2 of Sixth Embodiment> The following describes a differential optical modulator integrated semiconductor laser 820 and an optical module 1620 according to a second modification of the sixth embodiment. In the second modification of the sixth embodiment, similar to the concept of the third embodiment, openings may be provided in the ground electrode and solder on the submount, and the mounting may be performed so that they overlap with the openings in the back electrode.

[0242] Fig. 51 is a cross-sectional view of the p-type first electrode pad 54j of the differential EA modulator unit 113 of the differential optical modulator integrated semiconductor laser 820 and the optical module 1620 according to the first modification of the sixth embodiment, taken along line AA in Fig. 42. Fig. 52 is a cross-sectional view of the n-type second electrode pad 55j of the differential EA modulator unit 113 of the differential optical modulator integrated semiconductor laser 820 and the optical module 1620 according to the second modification of the sixth embodiment, taken along line BB in Fig. 42.

[0243] Parasitic capacitance C Ppad , C Npad , C Nlayer is generated between the upper surface of the differential optical modulator integrated semiconductor laser 820 and the submount rear surface ground electrode 205j on the rear surface side of the submount 200j, and therefore the distance to the ground electrode 48j is large, resulting in a low capacitance. Ppad , C Npad , C Nlayer is smaller than that of the first modification of the sixth embodiment, the differential EA modulator section 113 of the second modification of the sixth embodiment has an even wider bandwidth.

[0244] In the second modification of the sixth embodiment, the parasitic capacitance C Nlayer is smaller than that of the first modification of the sixth embodiment, the difference in parasitic capacitance between the p-type electrode side and the n-type electrode side is reduced, and the effect of canceling out high frequency interference applied to the differential line is enhanced.

[0245] <Effects of Sixth Embodiment and Modifications 1 and 2 of Sixth Embodiment> In the sixth embodiment and the first and second variations of the sixth embodiment, a differential EA modulator section 113 is provided on a semi-insulating substrate, and the semiconductor laser section 111 is connected by a connecting waveguide section 112 of the same optical mode, and a positive-phase modulation signal is applied to the p-type first electrode 25j of the differential EA modulator section 113, and a negative-phase signal is applied to the n-type first electrode 26j, thereby performing differential driving.

[0246] An opening 62j of the back electrode 61j is provided directly below the differential EA modulator section 113, a recess 65j is provided in the semi-insulating substrate 1 exposed in the opening 62j, and an opening is provided in the ground electrode 48j on the submount 200j facing the opening 62j, thereby reducing the parasitic capacitance CPpad , C Nlayer , C Npad As a result, wideband operation of the differential EA modulator section 113 can be achieved. In addition, since the parasitic capacitances on the p-type electrode side and the n-type electrode side of the differential EA modulator section 113 do not become asymmetric, high-frequency interference in the differential lines can be canceled out.

[0247] This allows for broadband and high-density mounting of optical transceivers, and simplifies error rate correction circuits because there is no deterioration in error rate due to electromagnetic interference. This makes it possible to increase the transmission rate of optical communication transceivers, and reduces the power consumption per bit of the transmitted signal.

[0248] Embodiment 7 <Structure of Optical Modulator Integrated Semiconductor Laser and Module According to Seventh Embodiment> Fig. 53 is a top view of a flip-chip differential optical modulator-integrated semiconductor laser 900, which is an example of an optical modulator-integrated semiconductor laser according to the seventh embodiment. Fig. 54 is a back view of the flip-chip differential optical modulator-integrated semiconductor laser 900, which is an example of an optical modulator-integrated semiconductor laser according to the seventh embodiment.

[0249] The differential optical modulator integrated semiconductor laser 900 according to the seventh embodiment differs from the differential optical modulator integrated semiconductor laser 800 according to the sixth embodiment in that a pier electrode 75 for flip-chip mounting is formed near the differential EA modulator section 113 on the top surface of the chip.

[0250] The pier electrode 75 is made of Ti, Au, Pt, plating, etc., and may be formed simultaneously with the p-type or n-type electrode pad of the differential EA modulator section 113 and the p-type or n-type electrode pad of the semiconductor laser section 111. The pier electrode 75 is electrically isolated from the differential EA modulator section 113. It is preferable for the pier electrode 75 to be formed on an insulating film, as this increases adhesion. The pier electrode 75 may be higher than the p-type and n-type electrode pads, but it is preferable for them to be the same height. The film thickness of the pier electrode 75 is in the range of 1 μm to 6 μm. The size of the pier electrode 75 is preferably 30 μm x 30 μm or more.

[0251] 55 is a schematic diagram showing a differential optical modulator-integrated semiconductor laser 900 and an optical module 1700 flip-chip mounted on a submount 200j, which is an example of an optical modulator-integrated semiconductor laser according to the seventh embodiment. The differential optical modulator-integrated semiconductor laser 900 is mounted on the submount 200j with the back electrode 61j facing up. The base material of the submount 200j is a dielectric or high-resistance material such as aluminum nitride, SiC, or alumina. The semiconductor laser section current line LN3 on the submount 200j is electrically connected to the p-type third electrode 5j (not shown) of the semiconductor laser section 111 by a bump or a solder layer 72j.

[0252] Figure 56 is a cross-sectional view along line AA of the p-type first electrode 25j of the differential EA modulator section 113 of the differential optical modulator integrated semiconductor laser 900 and optical module 1700 of embodiment 7, Figure 57 is a cross-sectional view along line BB of the n-type first electrode 26j of the differential EA modulator section 113, and Figure 58 is a cross-sectional view along line CC of the pier electrode 75.

[0253] The p-type first electrode 25j of the differential EA modulator section 113 is electrically connected to the first modulation signal line LN1 on the submount 200j, and the n-type first electrode 26j of the differential EA modulator section 113 is electrically connected to the second modulation signal line LN2 by a bump or a solder layer 72j. The pier electrode 75 is electrically connected to the pier base electrode 78 on the submount 200j by a bump or a solder layer 72j. Current blocking layers 81 for current confinement are provided on both side surfaces of the i-type third waveguide layer 52j (core layer).

[0254] <Operation of the Seventh Embodiment> In the differential optical modulator integrated semiconductor laser 900 and the optical module 1700 according to the seventh embodiment, there is no back electrode on the surface facing the differential EA modulator section 113, that is, an opening 62j is provided. Therefore, the parasitic capacitance C Ppad Similarly, the parasitic capacitance C between the n-th first electrode 26j and the rear electrode 61j of the differential EA modulator section 113 is zero. Npad and a parasitic capacitance C between the n-type first conductive layer 21j, which also functions as a contact layer, and the back electrode 61j. Nlayer As a result, in the differential optical modulator integrated semiconductor laser 900 and the optical module 1700 according to the seventh embodiment, similarly to the fifth embodiment, no high-frequency signal is propagated to the semiconductor laser portion 111 via the back electrode 61j, and therefore no increase in parasitic capacitance occurs between the p-type first electrode 25j and the n-type first electrode 26j of the differential EA modulator portion 113.

[0255] 48 shows the high-frequency response characteristics of the seventh embodiment. The differential optical modulator integrated semiconductor laser 900 according to the seventh embodiment has an even wider bandwidth than that of the sixth embodiment. Furthermore, since the parasitic capacitances on the p-type first electrode 25j side and the n-type first electrode 26j side of the differential EA modulator section 113 are not asymmetric, it is possible to cancel out high-frequency interference in the differential lines.

[0256] If an opening 62j is provided in the back electrode 61j facing the differential EA modulator section 113 of the differential optical modulator-integrated semiconductor laser 900, the strength of the chip will decrease after flip-chip mounting, which could lead to cracking. In the seventh embodiment, the pier electrode 75 of the differential optical modulator-integrated semiconductor laser 900 is electrically connected to the pier base electrode 78 on the submount 200j by a bump or solder layer 72j. When stress loads are applied during assembly using a collet or due to temperature fluctuations, stress is dispersed across the pier electrode 75 rather than concentrating locally on the chip, as compared to when only the p-type electrode and n-type electrode are connected. This has the effect of reducing the likelihood of chip cracking.

[0257] <Effects of the Seventh Embodiment> By providing an opening 62j in the back electrode 61j on the surface of the differential optical modulator-integrated semiconductor laser facing the differential EA modulator section 113 and flip-chip mounting the differential optical modulator-integrated semiconductor laser on a submount, parasitic capacitance is eliminated on the p-type electrode side and n-type electrode side of the differential EA modulator section 113. As a result, the frequency response characteristics of the p-type electrode side (positive phase signal side) and n-type electrode side (negative phase signal side) of the differential EA modulator section 113 are approximately the same.

[0258] External electromagnetic interference applied to the first modulation signal line LN1 and the second modulation signal line LN2, which are differential, is canceled out by the differential operation, so that the light emitted from the differential optical modulator integrated semiconductor laser 900 is not affected by electromagnetic interference. Furthermore, there is no increase in parasitic capacitance on the p-type electrode side and the n-type electrode side of the differential EA modulator section 113, so wideband operation can be achieved.

[0259] Furthermore, since no high-frequency signal is transmitted from the differential EA modulator section 113 to the semiconductor laser section 111, no fluctuations in the light intensity of the DFB laser occur. As a result, it is possible to widen the bandwidth and achieve high-density packaging of the optical transceiver. Since there is no deterioration in the error rate due to electromagnetic interference or fluctuations in the light intensity of the DFB laser, it is possible to simplify the error rate correction circuit.

[0260] As described above, it is possible to increase the transmission rate of optical transceivers and reduce the power consumption per bit of the transmitted signal. In addition, since chip cracking is less likely to occur, highly reliable transceivers can be realized.

[0261] Also, as shown in FIGS. 12 and 13 of the first embodiment, in the second to fifth embodiments as well, the EA modulator section on the semiconductor laser section side may be a second EA modulator section.

[0262] In the first to fourth embodiments, the first to third variations of the fourth embodiment, the sixth embodiment, and the first and second variations of the sixth embodiment, the back electrode of the optical modulator-integrated semiconductor laser and the ground electrode on the submount do not necessarily have to be low-resistance and DC-conductive (meaning that they are electrically connected and allow a direct current to flow). Therefore, instead of connection using a bump or solder layer, they may be fixed using a non-conductive adhesive such as resin or paste, or a conductive adhesive. Alternatively, they may be fixed by thermocompression bonding between the electrodes. In this disclosure, fixation using bumps, solder, thermocompression bonding between electrodes, conductive adhesive, non-conductive adhesive, etc. is referred to as "bonding."

[0263] On the other hand, in the flip-chip mounting exemplified in the fifth embodiment, the first to sixth variations of the fifth embodiment, and the seventh embodiment, the electrodes of the semiconductor laser section and the electrodes of the EA modulator section of the optical modulator-integrated semiconductor laser must be DC-conductive to the wiring on the submount, the ground electrode, etc. In other words, they must be "electrically connected" by bumps or solder, thermocompression bonding between the electrodes, or a conductive adhesive.

[0264] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.

[0265] Therefore, countless variations not illustrated are conceivable within the scope of the technology of the present disclosure, including, for example, cases where at least one component is modified, added, or omitted, and cases where at least one component is extracted and combined with a component of another embodiment. [Explanation of symbols]

[0266] 1 semi-insulating substrate, 2a, 2j n-type third conductive layer, 2b, 2k n-type third cladding layer, 3, 3j active layer, 4a, 4j p-type third cladding layer, 4b, 4k p-type third contact layer, 5, 5j p-type third electrode, 6, 6j n-type third electrode, 11, 11j i-type lower first cladding layer, 12, 12j i-type first waveguide layer, 13, 13j i-type upper first cladding layer, 21a, 21j n-type first conductive layer, 21b, 21k n-type first cladding layer, 22, 22j i-type first modulation layer, 23a, 23j p-type first cladding layer, 23b, 23k p-type first contact layer, 25, 25j p-type first electrode, 26, 26j n-type first electrode, 31 i-type lower second cladding layer, 32 i-type second waveguide layer, 33 i-type upper second cladding layer, 41a n-type second conductive layer, 41b n-type second cladding layer, 42 i-type second modulation layer, 43a p-type second cladding layer, 43b p-type second contact layer, 45 p-type second electrode, 46 n-type second electrode, 47 common electrode, 48, 48j ground electrode, 49 opening, 51, 51j i-type lower third cladding layer, 52, 52j i-type third waveguide layer, 53, 53j i-type upper third cladding layer, 54, 54j p-type first electrode pad, 55, 55j n-type second electrode pad, 56 grounding through electrode, 57, 57j, 58, 58j termination resistor electrode pad, 60 insulating film, 61, 61j, 61s, 61t, 61u, 61v, 61w, 61x Back electrode, 62, 62b, 62c, 62j, 62f, 62g Opening, 65, 65j Recess, 72, 72j Bump or solder layer, 75 Pier electrode, 78 Pier base electrode, 81 Current blocking layer, 101, 111 Semiconductor laser section, 102 First connecting waveguide section, 103 First EA modulator section, 104 Second connecting waveguide section, 105 Second EA modulator section, 106 Output waveguide section, 112 Connection waveguide section, 113 Differential EA modulator section, 114 Output waveguide section, 200, 200j Submount, 201, 201j Wiring board, 205, 205j Submount backside ground electrode, 500, 510, 520, 550, 600, 650, 660, 670, 680, 690, 700, 710, 720, 730 Optical modulator integrated semiconductor laser, 800, 810, 820, 900Differential optical modulator integrated semiconductor laser, 1000, 1010, 1050, 1100, 1150, 1160, 1170, 1180, 1200, 1210, 1250, 1300, 1350, 1400, 1450, 1500, 1600, 1610, 1620, 1700 Optical module, LN1, La1 First modulation signal line, LN2, La2 Second modulation signal line, LN3, La3 Semiconductor laser current line, R1 First termination resistor, R2 Second termination resistor, W1, W2, W3 Wire, Wg1, Wg2, Wg3 Ground wire

Claims

1. a semi-insulating substrate having a first surface and a second surface opposite to the first surface; a semiconductor laser portion formed on the first surface and having at least an n-type cladding layer, an active layer, and a p-type cladding layer; a first connecting waveguide portion formed on the first surface and having at least a lower first cladding layer, a first waveguide layer, and an upper first cladding layer; a first EA modulator section formed on the first surface, the first EA modulator section having at least an n-type first semiconductor layer, a first modulation layer, a p-type first semiconductor layer, an n-type first electrode electrically connected to the n-type first semiconductor layer, and a p-type first electrode electrically connected to the p-type first semiconductor layer; a second connecting waveguide portion formed on the first surface and having at least a lower second cladding layer, a second waveguide layer, and an upper second cladding layer; a second EA modulator section formed on the first surface, the second EA modulator section having at least an n-type second semiconductor layer, a second modulation layer, a p-type second semiconductor layer, an n-type second electrode electrically connected to the n-type second semiconductor layer, and a p-type second electrode electrically connected to the p-type second semiconductor layer; a common electrode electrically connected to the n-type first electrode and the p-type second electrode; a back surface electrode formed on the second surface, having an opening in a region facing either or both of the first EA modulator section and the second EA modulator section via the semi-insulating substrate, and having a film thickness of 1 μm or more and 10 μm or less; 1. An optical modulator integrated semiconductor laser, wherein an isolation resistance between said semiconductor laser section and said first EA modulator section is 500 Ω or more.

2. 2. The optical modulator integrated semiconductor laser according to claim 1, wherein a recess is provided in the semi-insulating substrate exposed at the opening of the back electrode.

3. a submount having a ground electrode formed on its surface; 3. An optical module, wherein the back electrode of the optical modulator-integrated semiconductor laser according to claim 1 is bonded to the ground electrode.

4. 4. The optical module according to claim 3, wherein the opening of the ground electrode and the opening of the back electrode are bonded together so as to overlap part or all of the opening.

5. a submount having a first surface and a second surface opposite to the first surface, the submount having at least a first modulation signal line, a second modulation signal line, and a ground electrode provided on the first surface; 3. An optical module characterized in that the first surface side of the semi-insulating substrate of the optical modulator-integrated semiconductor laser according to claim 1 and the first surface of the submount are bonded face to face, and the first modulation signal line and the p-type first electrode, the second modulation signal line and the n-type second electrode, and the common electrode and the ground electrode are electrically connected, respectively.

6. a semi-insulating substrate having a first surface and a second surface opposite to the first surface; a semiconductor laser portion formed on the first surface and having at least an n-type cladding layer, an active layer, and a p-type cladding layer; a first connecting waveguide portion formed on the first surface and having at least a lower first cladding layer, a first waveguide layer, and an upper first cladding layer; a first EA modulator section formed on the first surface, the first EA modulator section having at least an n-type first semiconductor layer, a first modulation layer, a p-type first semiconductor layer, an n-type first electrode electrically connected to the n-type first semiconductor layer, and a p-type first electrode electrically connected to the p-type first semiconductor layer; a second connecting waveguide portion formed on the first surface and having at least a lower second cladding layer, a second waveguide layer, and an upper second cladding layer; a second EA modulator section formed on the first surface, the second EA modulator section having at least an n-type second semiconductor layer, a second modulation layer, a p-type second semiconductor layer, an n-type second electrode electrically connected to the n-type second semiconductor layer, and a p-type second electrode electrically connected to the p-type second semiconductor layer; a common electrode electrically connecting the first n-type electrode and the second p-type electrode; a backside first electrode formed on the second surface, facing the semiconductor laser portion via the semi-insulating substrate, and having a film thickness of 1 μm or more and 10 μm or less; a back surface second electrode formed on the second surface, facing either or both of the first EA modulator section and the second EA modulator section via the semi-insulating substrate, electrically isolated from the back surface first electrode, and having a film thickness of 1 μm or more and 10 μm or less; 1. An optical modulator integrated semiconductor laser, wherein an isolation resistance between said semiconductor laser section and said first EA modulator section is 500 Ω or more.

7. a submount having a first modulation signal line, a second modulation signal line, and a ground electrode provided on a first surface thereof; 7. An optical module characterized in that the first surface side of the semi-insulating substrate of the optical modulator-integrated semiconductor laser according to claim 6 and the first surface of the submount are bonded face to face, and the first modulation signal line and the p-type first electrode, the second modulation signal line and the n-type second electrode, and the common electrode and the ground electrode are electrically connected, respectively.

8. a semi-insulating substrate having a first surface and a second surface opposite to the first surface; a semiconductor laser portion formed on the first surface, the semiconductor laser portion having at least an n-type cladding layer, an active layer, a p-type cladding layer, an n-type third electrode electrically connected to the n-type cladding layer, and a p-type third electrode electrically connected to the p-type cladding layer; a connecting waveguide portion formed on the first surface and having at least a lower first cladding layer, a first waveguide layer, and an upper first cladding layer; a single EA modulator section formed on the first surface, the single EA modulator section having at least an n-type first semiconductor layer, a first modulation layer, a p-type first semiconductor layer, an n-type first electrode electrically connected to the n-type first semiconductor layer, and a p-type first electrode electrically connected to the p-type first semiconductor layer; a back surface electrode formed on the second surface, having an opening in a region facing the EA modulator section with the semi-insulating substrate interposed therebetween, and having a film thickness of 1 μm or more and 10 μm or less; 1. An optical modulator integrated semiconductor laser, wherein the isolation resistance between the semiconductor laser section and the EA modulator section is 500 Ω or more.

9. 9. The optical modulator integrated semiconductor laser according to claim 8, wherein an isolation resistance between the n-type third electrode and the n-type first electrode is greater than 160 ohms.

10. 10. The optical modulator integrated semiconductor laser according to claim 8, wherein a recess is provided in the semi-insulating substrate exposed at the opening of the back electrode.

11. An optical modulator integrated semiconductor laser as described in claim 8 or 9, characterized in that a pier electrode is provided spaced apart from the EA modulator section and electrically independent of the n-type first electrode and the p-type first electrode.

12. a submount having a ground electrode formed on a first surface thereof; 10. An optical module, wherein the back electrode of the optical modulator-integrated semiconductor laser according to claim 8 is bonded to the ground electrode.

13. 13. The optical module according to claim 12, wherein the opening of the ground electrode and the opening of the back electrode are bonded so as to overlap part or all of each other.

14. A device comprising: a first modulation signal line; a second modulation signal line; and a submount having a ground electrode provided on a first surface thereof; 10. An optical module characterized in that the first surface side of the semi-insulating substrate of the optical modulator-integrated semiconductor laser according to claim 8 or 9 and the first surface of the submount are bonded face to face, and the first modulation signal line and the p-type first electrode, and the second modulation signal line and the n-type first electrode are electrically connected, respectively.

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