Optical phase modulation module

Abstract

To provide an optical phase modulation module comprising a laser light source 13 and an optical phase modulation element 16 integrated on one substrate, which reduces operational instability of the optical phase modulation element 16 due to rise in temperature of the laser light source 13.SOLUTION: An optical phase modulation module is provided, comprising a support substrate 10 having at least two electrical insulation layers with different thermal conductivities on a surface thereof, a light input unit 15 consisting of a laser light source 13 mounted on a first electrical insulation layer 11 with a higher thermal conductivity of the at least two electrical insulation layers, an optical phase modulation element 16 made of an electro-optical material and formed on a second electrical insulation layer 12 with a lower thermal conductivity of the at least two electrical insulation layers connected to the light input unit via a waveguide, and an optical phase modulation unit 17 consisting of a conductive semiconductor waveguide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an optical phase modulation module. [Background technology]

[0002] Optical phase modulation modules used in the fields of optical wireless communication and IoT are required to be faster, more compact, and more dense as the amount of information increases and they are deployed in in-vehicle devices and other applications. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-184528 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides an optical phase modulation module in which a laser light source and an optical phase modulation element are integrated on the same substrate, which can reduce operational instability of the optical phase modulation element caused by a rise in temperature of the laser light source. [Means for solving the problem]

[0005] The optical phase modulation module disclosed herein comprises a support substrate having at least two electrical insulating layers with different thermal conductivities on its surface, an optical input section consisting of a laser light source mounted on a first electrical insulating layer having a high thermal conductivity among the electrical insulating layers, an optical phase modulation element consisting of an electro-optical material formed on a second electrical insulating layer having a low thermal conductivity among the electrical insulating layers connected to the optical input section by a waveguide, and an optical phase modulation section consisting of a conductive semiconductor waveguide. Effect of the Invention

[0006] According to the present disclosure, it is possible to reduce operational instability of an optical phase modulation element caused by a rise in temperature of a laser light source. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing a main part of a structure of an optical phase modulation module according to an embodiment of the present disclosure. [Diagram 2] 1 is a top plan view showing a structure of an optical phase modulation module according to an embodiment of the present disclosure. [Diagram 3] FIG. 1 is a diagram showing the physical properties of semiconductor materials. [Figure 4] FIG. 2 is a diagram showing a schematic diagram of temperature changes of substrates with different electrical insulating layers. [Diagram 5] FIG. 10 is a diagram illustrating a relationship between optical phase modulation efficiency and temperature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Before describing the embodiments of the present disclosure, the findings on which the present disclosure is based will be described. Patent Document 1 is an example of an optical phase modulation module using silicon photonics technology. It has an optical waveguide, an optical phase modulation element, a light emitting element, etc., formed on the surface of a silicon substrate. Light from the LD element of the light emitting element enters the optical phase modulation element via the optical waveguide, is phase-modulated in the optical phase modulation element, and then is emitted from the optical phase modulation module via the optical waveguide. However, in this structure, the phase is modulated, for example, by changing the refractive index by applying an electric field to the electro-optic material layer, but the modulation becomes unstable due to thermal effects from the light-emitting element, and in a phased array using a phase modulator, it becomes difficult to reduce the waveguide spacing, resulting in a small deflection angle.

[0009] One possible solution would be to increase the distance between the light-emitting element and the optical phase modulation element; however, this would result in an increase in the size of the optical phase modulation module and in optical loss, and therefore this structure would not be able to reduce operational instability caused by temperature changes in the optical phase modulation element 15 that accompany an increase in temperature of the light-emitting element, which is a heat source.

[0010] The present invention has arrived at an optical phase modulation module described in the following items, which can reduce the operational instability of an optical phase modulation element caused by a temperature rise of a laser light source.

[0011] The optical phase modulation module according to the first item includes a support substrate having at least two electrical insulating layers with different thermal conductivities on its surface, an optical input section consisting of a laser light source mounted on a first electrical insulating layer having a high thermal conductivity among the electrical insulating layers, an optical phase modulation element made of an electro-optical material formed on a second electrical insulating layer having a low thermal conductivity among the electrical insulating layers connected to the optical input section by a waveguide, and an optical phase modulation section consisting of a conductive semiconductor waveguide.

[0012] In this optical phase modulation module, the temperature of the laser chip, which is the light source, can be prevented from increasing by dissipating the heat to the first electrical insulating layer, which has high thermal conductivity and is located below the mounting surface.

[0013] The optical phase modulation module according to the second item includes a support substrate having at least two electrical insulating layers with different thermal conductivities on its surface, an optical input section consisting of a laser light source mounted on a first electrical insulating layer having a high thermal conductivity among the electrical insulating layers, an optical phase modulation element consisting of an electro-optical material from the optical input section mounted on a second electrical insulating layer having a low thermal conductivity among the electrical insulating layers connected to the optical input section by a waveguide, an optical phase modulation section consisting of a conductive semiconductor waveguide, and an output section in which optical phase signals output from a plurality of the optical phase modulation sections are mode-coupled as a multi-slot waveguide.

[0014] In this optical phase modulation module, the temperature of the laser light source, which is the heat source, can be prevented from increasing by promoting heat dissipation to the first electrical insulation layer, which has high thermal conductivity and is located below the mounting surface.

[0015] An optical phase modulation module according to a third item is the optical phase modulation module according to the first and second items, in which the first electrical insulating layer having high thermal conductivity is made of SiC or AlN.

[0016] In this optical phase modulation module, when SiO2, which has a low refractive index, is used for the second electrical insulation layer, which has a low thermal conductivity, it is possible to increase the efficiency of dissipating the heat energy in the laser light source to the bottom of the mounting surface, and to suppress the temperature rise in the optical phase modulation element section.

[0017] In the optical phase modulation module according to the fourth aspect, the waveguide is a slot waveguide, and a plurality of slot waveguides are provided. In this optical phase modulation module, the electric field is strongly concentrated along the slots by having a plurality of slot waveguides, so that the electric field intensity can be increased and the transmission loss can be reduced.

[0018] In the optical phase modulation module according to the fifth aspect, the waveguide is a slot waveguide, and a plurality of slot waveguides are provided. In this optical phase modulation module, the polarization characteristics and phase shift amount of the plurality of slot waveguides are individually controlled, and mode coupling makes it possible to widen the deflection angle compared to a single waveguide.

[0019] Hereinafter, more specific embodiments of the present disclosure will be described with reference to the drawings. EXAMPLES

[0020] Fig. 1 is a cross-sectional view of a main part showing the structure of an optical phase modulation module according to a first embodiment, Fig. 2 is a top plan view showing the structure of the optical phase modulation module according to the first embodiment.

[0021] The optical phase modulation module 100 includes a support substrate 10, a first electrical insulating layer 11, a second electrical insulating layer 12, an optical input section 15 consisting of a laser light source 13 and a plurality of optical waveguides A14, an optical phase modulation section 17 consisting of a plurality of optical phase modulation elements 16, and a multi-slot waveguide 20 consisting of a plurality of optical waveguides B18 and a mode coupling section 19.

[0022] The first electrical insulating layer 11 and the second electrical insulating layer 12 are located on the main surface of the support substrate 10. The first electrical insulating layer 11 is formed of a material having a higher thermal conductivity than the second electrical insulating layer 12. The support substrate 10 may be formed of, for example, silicon. The first electrical insulating layer 11 may be formed of, for example, at least one selected from SiC and AlN. The second electrical insulating layer 12 may be formed of, for example, SiO2. The first electrical insulating layer 11 and the second electrical insulating layer 12 are in contact with each other at the boundary in the horizontal direction. In this embodiment, the first electrical insulating layer 11 and the second electrical insulating layer 12 are in contact with each other at the boundary in the horizontal direction, but it is not necessary that the boundary is not in contact. In addition, it is not necessary that the boundary between the first electrical insulating layer 11 and the second electrical insulating layer 12 in the horizontal direction is a mixture of the first electrical insulating layer 11 and the second electrical insulating layer 12. The laser light source 13 is located on the first electrical insulating layer 11. The laser light source 13 is mainly composed of an LD. The optical phase modulation element 16 is located on the second electrical insulating layer 12. The optical waveguide A14 optically connects the laser light source 13 and the optical phase modulation element 16, and is located on both the first electrical insulating layer 11 and the second electrical insulating layer 12. The optical input section 15 is composed of the laser light source 13 and the optical waveguide A14. The optical waveguide A14 is composed of a plurality of waveguides branched into the same number as the number of the optical phase modulation elements 16. The optical phase modulation element 16 has a structure in which a plurality of optical waveguides made of an electro-optic material, for example, an electro-optic polymer, are arranged in an array, and an electrode is arranged for each optical waveguide. It has a function of controlling the phase of light by applying an electric field to the electro-optic polymer, which is an electro-optic material, and changing the refractive index of the optical waveguide. The optical phase modulation section 17 is composed of the plurality of optical phase modulation elements 16. The optical waveguide B 18 is optically connected to the optical phase modulation element 16 and is composed of a plurality of waveguides, the number of which is the same as the number of the optical phase modulation elements 16 , and constitutes a multi-slot waveguide 20 including the mode coupling portion 19 .

[0023] Next, a description will be given of a temperature rise during operation of the laser light source 13 and its effect on optical phase modulation with reference to FIGS.

[0024] Figure 3 shows the thermal conductivity of single crystal semiconductor materials. The thermal conductivity of typical semiconductor materials for support substrates is 148 W / m K for Si and SiO2, 340 W / m K for AlN, and 450 W / m K for SiC (4H-SiC), with the thermal conductivity relationship being SiC (44H-SiC)>AlN>Si, SiO2.

[0025] In this embodiment, the first electrical insulating layer 11 is made of SiC (4H-SiC) or AlN, and the second electrical insulating layer 12 is made of SiO2.

[0026] 4 is a diagram showing temperature changes in the mounting portion of the laser light source 13. The supporting substrate 10 is a Si substrate, the first electrical insulating layer 11 is SiC, and the second electrical insulating layer 12 is SiO2. The diagram shows a schematic diagram of temperature changes in the mounting portion of the laser light source 13 located on the first electrical insulating layer 11. The vertical axis represents the temperature of the mounting portion of the laser light source 13, and the horizontal axis represents the operating time of the laser light source 13. The mounting portion refers to the connection portion between the first electrical insulating layer 11 and the laser light source 13.

[0027] When a laser light source 13 is mounted and operated on the surface of a supporting substrate 10 made of Si and a first electrical insulating layer 11 made of SiO2, the temperature of the mounting part rises from 25°C before operation to 80°C within 5 seconds after the start of operation.

[0028] When a laser light source 13 is mounted and operated on the surface of a supporting substrate 10 made of Si and a first electrical insulating layer 11 made of SiC, the temperature of the mounting part rises from 25°C before operation to 45°C within 10 seconds after the start of operation.

[0029] A substrate in which SiC is formed on the first electrical insulating layer 11 has a suppressed temperature rise compared to a substrate in which the first electrical insulating layer is SiO2. This shows that because SiC has a higher thermal conductivity than SiO2, the temperature rise is suppressed by heat transfer and heat dissipation to the electrical insulating layer made of SiC. Even when the first electrical insulating layer 11 is made of AlN and the second electrical insulating layer 12 is made of SiO2, the effect of suppressing the temperature rise can be obtained by heat transfer and heat dissipation to the electrical insulating layer made of AlN because AlN has a higher thermal conductivity than SiO2.

[0030] Figure 5 is a diagram showing a schematic diagram of the relationship between the temperature of the optical phase modulation element 16 and the optical modulation efficiency. The vertical axis indicates the optical modulation efficiency, and the horizontal axis indicates the temperature of the optical phase modulation element. The optical modulation efficiency on the vertical axis uses VπL (V·cm), which is the product of the voltage required to change the phase by π (180 degrees) and the length of the phase modulator, as an index. The smaller the index VπL, the lower the required voltage and the less power consumption. In addition, the bandwidth of the optical modulator becomes wider, enabling higher speeds.

[0031] In this embodiment, an optical phase modulation element having a structure in which multiple optical waveguides made of electro-optic polymer, an electro-optic material, are arranged in an array is used, and the relationship between the temperature of the optical phase modulation element and the optical modulation efficiency VπL is shown in Figure 5. The specific optical modulation efficiency VπL is 0.16 V cm at 25°C to 45°C, and 1.10 V cm at 85°C.

[0032] If the temperature of the optical phase modulation element rises by 40°C from 45°C to 85°C, the optical modulation efficiency VπL will decrease by about 1 / 7, the required voltage will increase, the power consumption will become larger, the bandwidth of the optical modulator will become narrower, and the conversion will become slower.

[0033] In an optical phase modulation element, a rise in temperature causes a decrease in modulation efficiency or destabilization of the optical phase modulation operation.

[0034] As described above, the embodiment of the present disclosure can reduce operational instability of an optical phase modulation element caused by a rise in temperature of a laser light source. [Industrial Applicability]

[0035] The optical phase modulation module according to the embodiment of the present disclosure can be used in the fields of optical wireless communication and IoT, for example. [Explanation of symbols]

[0036] 10 Support substrate 11 First Electrical Insulation Layer 12 Second Electrical Insulation Layer 13 Laser light source 14 Optical waveguide A 15 Optical input section 16 Optical phase modulation element 17 Optical phase modulation section 18 Optical waveguide B 19 Mode coupling section 20 Multi-slot waveguide 100 Optical Phase Modulation Module

Claims

1. An optical phase modulation module comprising: a substrate having at least two types of electrical insulating layers with different thermal conductivities on its surface; an optical input section consisting of a laser light source mounted on a first electrical insulating layer of the electrical insulating layers having a high thermal conductivity; an optical phase modulation element made of an electro-optical material formed on a second electrical insulating layer of the electrical insulating layers having a low thermal conductivity and connected to the optical input section by a waveguide; and an optical phase modulation section consisting of a conductive semiconductor waveguide.

2. a support substrate having at least two electrical insulating layers with different thermal conductivities on a surface thereof; an optical input section made of a laser light source mounted on a first electrical insulating layer having a high thermal conductivity among the electrical insulating layers; and an optical phase modulation element made of an electro-optical material from the optical input section mounted on a second electrical insulating layer having a low thermal conductivity among the electrical insulating layers connected to the optical input section by a waveguide; An optical phase modulation module comprising an optical phase modulation section made of a conductive semiconductor waveguide and an output section to which optical phase signals output from a plurality of waveguides are mode-coupled.

3. 3. The optical phase modulation module according to claim 1, wherein the electrical insulating layer of the optical input section is made of SiC or AlN.

4. 3. The optical phase modulation module according to claim 2, wherein the plurality of waveguides are made up of a plurality of slot waveguides.

5. 3. The optical phase modulation module according to claim 2, wherein optical phase signals obtained by individually phase-controlling the plurality of waveguides in the output section are mode-coupled.

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