Optical modulator, communication system, and processing method

Abstract

To provide an optical modulator that is capable of efficiently and properly modulating light in a waveguide within an optical modulator.SOLUTION: An optical modulator comprises: a circular patch antenna provided with a gap; and a waveguide provided along the gap.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] The present disclosure relates to optical modulators, communication systems, and processing methods. [Background technology]

[0002] Wireless communication is used in various fields. Patent Document 1 discloses a related technique, which relates to a communication system including an optical modulator using a rectangular patch antenna. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] “Proposal of InGaAs / InAlAs multiple quantum well Mach-Zehnder modulator integrated with array of planar antennas,”Yusuke Miyazeki and Taro Arakawa 2019 Jpn. J. Appl. Phys. 58 SJJE05. Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in a communication system related to Non-Patent Document 1, when modulating light in a waveguide in an optical modulator with a resonant electric field generated by received radio waves, the vibration direction (polarization) of the electric field differs depending on the direction of arrival of the radio waves, and therefore the magnitude of the resonant electric field may be significantly attenuated. Therefore, there is a demand for a technology that can efficiently and appropriately modulate light in a waveguide in an optical modulator regardless of polarization.

[0005] An object of each aspect of the present disclosure is to provide an optical modulator, a communication system, and a processing method that can solve the above problems. [Means for solving the problem]

[0006] In order to achieve the above object, according to one aspect of the present disclosure, an optical modulator includes a circular patch antenna having a gap therein, and a waveguide provided along the gap.

[0007] In order to achieve the above object, according to another aspect of the present disclosure, a communication system includes the above-mentioned optical modulator, a demodulator that demodulates an optical signal into an electrical signal, and an optical fiber network that connects the optical modulator and the demodulator.

[0008] In order to achieve the above object, according to another aspect of the present disclosure, a processing method includes an optical modulator having a circular patch antenna with a gap and a waveguide arranged along the gap, which modulates incident light incident on the waveguide by a resonant electric field generated by radio waves received by the circular patch antenna.

[0009] According to each aspect of the present disclosure, light in a waveguide in an optical modulator can be efficiently and appropriately modulated. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment of the present disclosure. [Diagram 2] FIG. 1 is a first diagram showing an example of the configuration of an optical modulator in which a rectangular patch antenna is integrated. [Diagram 3] FIG. 2 is a second diagram showing an example of the configuration of an optical modulator integrated with a rectangular patch antenna. [Figure 4] 2 is a diagram showing an example of the configuration of a waveguide 100b in an optical modulator 100. FIG. [Diagram 5] 13 is a diagram showing an example of the amount of change in refractive index due to an electric field of the intrinsic core FACQW of the waveguide 100b. FIG. [Figure 6] FIG. 1 is a first diagram for explaining the difference in electric field generated when a gap is provided in the center of a rectangular patch antenna and when a gap is not provided in the center of the rectangular patch antenna. [Figure 7]FIG. 2 is a second diagram for explaining the difference in electric field generated when a gap is provided in the center of the rectangular patch antenna and when a gap is not provided in the center of the rectangular patch antenna. [Figure 8] 1A and 1B are diagrams showing examples of resonant electric fields generated in a rectangular patch antenna with a gap and a circular patch antenna with a gap, respectively. [Figure 9] 1A and 1B are diagrams illustrating an example of the amount of phase change of light versus the degree of polarization in a rectangular patch antenna with a gap and a circular patch antenna with a gap. [Figure 10] 1A and 1B are diagrams for explaining the concept of phase matching between an electric field and light in a rectangular patch antenna. [Figure 11] FIG. 1 is a first diagram for explaining the concept of phase matching between the electric field and light in a circular patch antenna with no gap. [Figure 12] FIG. 2 is a second diagram for explaining the concept of phase matching between the electric field and light in a circular patch antenna with no gap. [Figure 13] 1A and 1B are diagrams for explaining the concept of phase matching between the electric field and light in a circular patch antenna with a gap. [Figure 14] 1A and 1B are diagrams for explaining an electric field generated in a circular patch antenna having a gap. [Figure 15] 1 is a diagram showing an example of the configuration of a circular patch antenna integrated optical modulator according to an embodiment of the present disclosure. [Figure 16] FIG. 1 illustrates an example of optimal dimensions for a gapped circular patch antenna according to an embodiment of the present disclosure. [Figure 17] FIG. 1 is a first diagram showing a part of the configuration of a circular patch antenna integrated optical modulator in which a circular patch antenna is combined with a microring resonator. [Figure 18] FIG. 2 is a second diagram showing a part of the configuration of a circular patch antenna integrated optical modulator in which a circular patch antenna is combined with a microring resonator. [Figure 19]FIG. 13 is a diagram showing an example of the amount of phase change caused by a circular patch antenna integrated optical modulator in the case where a circular patch antenna is combined with a micro ring resonator. [Figure 20] FIG. 1 shows an example of the resonant electric field for a gapped circular patch antenna having an elliptical profile. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments will be described in detail with reference to the drawings. In the following description, an optical modulator using a quantum well (Five-layer Asymmetric Coupled Quantum Well, hereinafter referred to as "FACQW") will be described as a specific example. However, the optical modulator according to the embodiment of the present disclosure is not limited to the optical modulator using a quantum well (FACQW). The optical modulator according to the embodiment of the present disclosure may be, for example, an optical waveguide made of other materials that produce an electro-optic effect. <Embodiment> (Communication System Configuration) A communication system 1 according to an embodiment of the present disclosure will be described with reference to the drawings. The communication system 1 is a Radio over Fiber (RoF) system including an optical modulator integrating an antenna that receives radio waves (e.g., millimeter wave signals) using a circular patch antenna with a gap, generates an electric field, and applies the generated electric field directly to a waveguide, modulating light by changing the electric field refractive index due to a quantum well (FACQW) structure. FIG. 1 is a diagram showing an example of the configuration of the communication system 1 according to an embodiment of the present disclosure. As shown in FIG. 1, the communication system 1 includes a metro network 10, an optical modulator 20, an optical fiber network 30, a demodulator 40, an antenna 50, an optical circulator 90, and a transmission / reception signal separator 91. FIG. 1 shows a communication device 60 (e.g., a mobile device).

[0012] The metro network 10 accommodates various services for consumers and corporations. The optical modulator 20 converts an electrical signal into an optical signal. The optical fiber network 30 transmits the optical signal. The demodulator 40 converts the optical signal into an electrical signal. Examples of the demodulator 40 include a photodetector and a photodiode. The antenna 50 transmits and receives radio waves (e.g., millimeter wave signals) to and from the communication device 60. The antenna 50 is a circular patch antenna with a gap. The optical circulator 90 separates the optical signals to be transmitted and received. The transmission and reception signal separator 91 separates the electrical signals to be transmitted and received. With this configuration, the communication system 1 provides the communication device 60 with various services accommodated by the metro network 10. The optical modulator 20 and the antenna 50 in the communication system 1 are optical modulators that integrate antennas that directly apply an electric field generated by receiving radio waves (e.g., millimeter wave signals) with the circular patch antenna to a waveguide and modulate light by changing the electric field refractive index due to a quantum well structure. Hereinafter, the optical modulator integrated with an antenna that receives radio waves (e.g., millimeter wave signals) using a circular patch antenna with a gap and applies the generated electric field directly to a waveguide, and modulates light by changing the electric field refractive index due to a quantum well structure, will be referred to as circular patch antenna integrated optical modulator 70, and the following description will mainly focus on this circular patch antenna integrated optical modulator 70.

[0013] (rectangular patch antenna) In order to facilitate understanding of an optical modulator integrated with an antenna that receives radio waves (e.g., millimeter wave signals) using a circular patch antenna according to one embodiment of the present disclosure, applies the electric field generated by the reception of the signal directly to a waveguide, and modulates light by changing the electric field refractive index due to a quantum well structure, a commonly known rectangular patch antenna will first be described.

[0014] FIG. 2 is a first diagram showing an example of the configuration of an optical modulator 100 in which a rectangular patch antenna is integrated. FIG. 3 is a second diagram showing an example of the configuration of an optical modulator 100 in which a rectangular patch antenna is integrated. The optical modulator 100 is, for example, an optical modulator described in Non-Patent Document 1. As shown in FIG. 2, the optical modulator 100 includes an antenna 100a and a waveguide 100b. The antenna 100a is a rectangular patch antenna. As shown in FIG. 3, the antenna 100a is connected to an Fe-doped semi-insulating InP substrate described later via an optical waveguide. In the optical modulator 100, an electric field generated by receiving a millimeter wave signal at the antenna 100a is directly applied to the waveguide 100b below, and light is directly modulated by radio waves due to the effect of a refractive index change (electric field refractive index change) when an electric field is applied due to the quantum well structure adopted for the waveguide 100b.

[0015] Fig. 4 is a diagram showing an example of the configuration of a waveguide 100b in the optical modulator 100. Fig. 4 shows a cross section of the waveguide 100b. As shown in Fig. 4, the waveguide 100b has a structure in which n-type InP, intrinsic InGaAlAs, an intrinsic core five-layer asymmetric coupled quantum well (FACQW), intrinsic InGaAlAs, intrinsic InP, and p-type InP are laminated in this order on an Fe-InP substrate.

[0016] Fig. 5 is a diagram showing an example of the electric field refractive index change Δn of the intrinsic core FACQW of the waveguide 100b. The waveguide 100b has a quantum well structure as shown in Fig. 4 so that a very large electric field refractive index change Δn as shown in Fig. 5 can be obtained in the intrinsic core FACQW.

[0017] As a result, in the optical modulator 100, the refractive index of the intrinsic core FACQW changes when a resonant electric field generated by the antenna 100a is applied to the intrinsic core FACQW, and the phase of the light passing through the intrinsic core FACQW is directly modulated by the received radio wave.

[0018] FIG. 6 is a first diagram for explaining the difference in electric field generated when a gap is provided in the center of the rectangular patch antenna 100a and when it is not provided. FIG. 7 is a second diagram for explaining the difference in electric field generated when a gap is provided in the center of the rectangular patch antenna 100a and when it is not provided. Part (a) of FIG. 6 shows an example of the configuration of the rectangular patch antenna 100a when no gap is provided in the rectangular patch antenna 100a and an example of the electric field generated. Part (b) of FIG. 6 shows an example of the configuration of the rectangular patch antenna 100a when a gap is provided in the center of the rectangular patch antenna 100a and an example of the electric field generated. Part (b) of FIG. 7 shows the electric field amplification factor (the multiplication factor when the magnitude of the received electric field is 1) according to the position on the cross section from L1 to L2 shown in part (a) of FIG. 7.

[0019] In the case of the rectangular patch antenna 100a without a gap, a resonant electric field is generated only at the ends of the rectangular patch antenna 100a, as shown in part (a) of Fig. 6. On the other hand, when a gap is provided in the center of the rectangular patch antenna 100a, a resonant electric field is generated not only at the outer ends of the rectangular patch antenna 100a but also at the end where the gap is provided, as shown in part (b) of Fig. 6. As a result, the electric field amplification factor at the end where the gap is provided is high, as shown in part (b) of Fig. 7.

[0020] The waveguide 100b is provided along the gap, as shown in part (b) of Fig. 6 and part (a) of Fig. 7. Therefore, when a gap is provided in the center of the rectangular patch antenna 100a, it is possible to apply a resonant electric field generated by providing the gap to the waveguide 100b, compared to the rectangular patch antenna 100a without a gap. As a result, when a gap is provided in the center of the rectangular patch antenna 100a, it is possible to modulate light to a much greater extent by the resonant electric field, compared to the rectangular patch antenna 100a without a gap.

[0021] (Circular patch antenna) As described later, the rectangular patch antenna 100a with a gap in the center has a drawback in that its characteristics deteriorate with respect to the vibration direction (polarization) of the electric field (specifically, there are places where the resonant electric field becomes small due to differences in the vibration direction of the electric field). Therefore, the communication system 1 according to an embodiment of the present disclosure includes, as the optical modulator 20 and the antenna 50, a circular patch antenna integrated optical modulator 70 including a circular patch antenna with a gap.

[0022] FIG. 8 is a diagram showing an example of a resonant electric field generated in each of the rectangular patch antenna 100a with a gap and the circular patch antenna 50 with a gap. Part (a) of FIG. 8 shows a resonant electric field generated in the rectangular patch antenna 100a with a gap. Part (b) of FIG. 8 shows a resonant electric field generated in the circular patch antenna 50 with a gap. Part (c) of FIG. 8 shows an angle θ of the polarization plane (hereinafter, referred to as the polarization angle θ). As shown in part (a) of FIG. 8, in the rectangular patch antenna 100a with a gap, the resonance length changes depending on the polarization plane of the radio wave (i.e., the direction of the resonant electric field), so that the characteristics of the resonant electric field deteriorate when the resonance direction changes (there are places where the resonant electric field becomes small). In contrast, in the circular patch antenna 50, the resonance length does not change depending on the polarization plane of the radio wave (i.e., the direction of the resonant electric field). Therefore, as shown in part (b) of FIG. 8, the resonant electric field generated in the circular patch antenna 50 remains large and almost constant, even when the vibration direction (polarization) of the electric field changes, compared with the resonant electric field generated in the rectangular patch antenna 100a. That is, the characteristics of the resonant electric field generated in the circular patch antenna 50 do not deteriorate with respect to the vibration direction (polarization) of the electric field. In addition to the effect of increasing the resonant electric field described above, the circular patch antenna 50 having a gap has the effect of matching the phase of the electric field and light, as described later, due to the gap. As shown in part (c) of FIG. 8, the degree of polarization θ is expressed as an angle with the left direction from the center of the antenna as the reference (i.e., 0 degrees).

[0023] Fig. 9 is a diagram showing an example of the amount of phase change of light with respect to the degree of polarization θ in each of the rectangular patch antenna 100a with a gap and the circular patch antenna 50 with a gap. In the rectangular patch antenna 100a with a gap, the amount of phase change decreases as the degree of polarization θ increases, as shown in Fig. 9. On the other hand, in the circular patch antenna 50 with a gap, the amount of phase change of light in the optical modulator 20 remains large and almost constant even when the degree of polarization θ increases, as shown in Fig. 9.

[0024] Here, the reason why the amount of phase change of light differs between the rectangular patch antenna 100a with a gap and the circular patch antenna 50 with a gap will be described. The amount of phase change of light shown in FIG. 9 is the amount of phase change during modulation. It is known that the magnitude of the resonant electric field and the amount of phase change in the optical waveguide are approximately proportional to the amount of change in the refractive index. Therefore, the vertical axis in FIG. 9 can be considered to represent the magnitude of the resonant electric field applied to the optical waveguide. When the vibration direction of the electric field is the best direction (θ=0) for the rectangular patch antenna 100a, the amount of phase change of light in the rectangular patch antenna 100a is approximately equal to the amount of phase change of light in the circular patch antenna 50. Moreover, the more the polarization is tilted from the best direction (θ=0), the smaller the magnitude of the resonant electric field in the rectangular patch antenna 100a becomes. Therefore, the amount of phase change of the rectangular patch antenna 100a becomes smaller. On the other hand, in the circular patch antenna 50, regardless of the polarized wave received, a resonant electric field of the same degree as the resonant electric field in the best direction (θ=0) for the rectangular patch antenna 100a can be generated and applied to the optical waveguide. Therefore, since the circular patch antenna 50 can efficiently receive radio waves of any polarization, when radio waves of various polarizations arrive, the circular patch antenna 50 can obtain a more efficient phase change overall than the rectangular patch antenna 100a. In this way, the circular patch antenna 50 can maintain the phase change characteristics of light almost constant regardless of the electric field oscillation direction (polarization) of the radio waves.

[0025] (Phase matching of electric field and light) The concept of phase matching of the electric field and light will be described. In the embodiment of the present disclosure, "phase matching of the electric field and light" means "matching (matching) the oscillation period of the radio wave and the time when the light passes through the gap part in the antenna". FIG. 10 is a diagram for explaining the concept of phase matching of the electric field and light in the rectangular patch antenna 100a. The TRF shown in FIG. 10 represents the oscillation period of the radio wave. That is, TRF / 4 represents a quarter of the period of the radio wave. Part (a) of FIG. 10 shows the resonant electric field and the travel of light when the phase matching of the electric field and light is not taken into consideration (i.e., this is an example of a case where the length of the waveguide 100b provided along the gap of the rectangular patch antenna 100a is not taken into consideration, and is longer than the desired length). Part (b) of FIG. 10 shows the resonant electric field and the travel of light when the phase matching of the electric field and light is taken into consideration (i.e., the length of the waveguide 100b provided along the gap of the rectangular patch antenna 100a is taken into consideration and is the desired length). The desired length is the length of the waveguide 100b at which the light stops passing through the waveguide 100b at the time t=TRF / 2.

[0026] From time t=0 to time t=TRF / 2, a positive resonant electric field is generated in the upper part of the rectangular patch antenna 100a in Fig. 10, and a negative resonant electric field is generated in the lower part of the rectangular patch antenna 100a in Fig. 10. The light that entered the gap part of the rectangular patch antenna 100a at time t=0 starts to undergo a positive phase change after time t=0. If the waveguide 100b is longer than the desired length, that is, if light passes through the inside of the waveguide 100b after time t=TRF / 2 as shown in part (a) of Fig. 10, a negative resonant electric field is generated in the upper part of the rectangular patch antenna 100a, and a positive resonant electric field is generated in the lower part of the rectangular patch antenna 100a as shown in part (a) of Fig. 10. In this way, when the waveguide 100b is longer than the desired length, light passes through the inside of the waveguide 100b even after time t=TRF / 2, and a resonant electric field having a polarity opposite to that of the resonant electric field generated between time t=0 and time t=TRF / 2 is generated in the rectangular patch antenna 100a. That is, after time t=TRF / 2, the light begins to undergo a negative phase change due to the resonant electric field having the opposite polarity. As a result, the phase change of the light caused by the resonant electric field generated between time t=0 and time t=TRF / 2 is cancelled by the phase change of the light caused by the resonant electric field having the opposite polarity generated after time t=TRF / 2.

[0027] On the other hand, when the waveguide 100b has a desired length, that is, when light just exits the waveguide 100b at time t=TRF / 2 as shown in part (b) of FIG. 10, no phase change of light occurs due to the resonant electric field having the opposite polarity generated in the rectangular patch antenna 100a after time t=TRF / 2. As a result, the phase change of light due to the resonant electric field generated between time t=0 and time t=TRF / 2 is not canceled after time t=TRF / 2, as in the case where the waveguide 100b is longer than the desired length. In other words, it is preferable that the length of the waveguide 100b provided along the gap in the rectangular patch antenna 100a is set to a length that allows light to just finish passing through the waveguide 100b at time t=TRF / 2.

[0028] Next, we will explain the concept of phase matching between the electric field and light in the circular patch antenna 50 with a gap. The concept that the length of the waveguide 100b provided along the gap in the rectangular patch antenna 100a is desirably set to a length that allows light to just finish passing through the waveguide 100b at time t=TRF / 2 can also be applied to the circular patch antenna 50 with a gap.

[0029] In order to facilitate understanding of the concept of phase matching of the electric field and light in the circular patch antenna 50 with a gap, the concept of phase matching of the electric field and light in the circular patch antenna 200a without a gap will also be described here. FIG. 11 is a first diagram for explaining the concept of phase matching of the electric field and light in the circular patch antenna 200a without a gap. FIG. 12 is a second diagram for explaining the concept of phase matching of the electric field and light in the circular patch antenna 200a without a gap. FIG. 13 is a diagram for explaining the concept of phase matching of the electric field and light in the circular patch antenna 50 with a gap. First, the concept of phase matching of the electric field and light in the circular patch antenna 200a without a gap will be described with reference to FIG. 11 and FIG. 12. The waveguide 200b shown in FIG. 11 is configured so that light passes from the left side to the right side on the upper side of FIG. 11 of the outer periphery of the circular patch antenna 200a without a gap. On the other hand, the waveguide 200b shown in FIG. 12 is configured such that light passes from the left side to the right side on the upper side of the circumference of the circular patch antenna 200a without a gap in FIG. 12, and returns to the left side through the lower side of the circumference of the circular patch antenna 200a without a gap in FIG. 12. The outer end of the circular patch antenna 200a (i.e., the outer shape of the circular patch antenna 200a) is determined to resonate at the frequency of the radio wave transmitted and received by the circular patch antenna 200a. The circular patch antenna 200a without a gap is an example of a circular patch antenna having a waveguide 200b longer than a desired length. The resonant electric field generated in the description of FIG. 11 to FIG. 13 is an example, and shows the resonant electric field when the polarization angle θ=90 degrees.

[0030] First, the concept of phase matching of the electric field and light in the circular patch antenna 200a without a gap shown in Fig. 11 will be described. When light enters the circular patch antenna 200a without a gap at time t=0, the circular patch antenna 200a without a gap starts to undergo a positive phase change after time t=0, and a positive resonant electric field is generated in the upper part of the circular patch antenna 200a without a gap in Fig. 11 from time t=0 to time t=TRF / 4, and a negative resonant electric field is generated in the lower part of the circular patch antenna 200a without a gap in Fig. 11. The light that enters the circular patch antenna 200a without a gap at time t=0 starts to undergo a positive phase change after time t=0. In the circular patch antenna 200a without a gap, the waveguide 200b is longer than the desired length, so that the light passes through the inside of the waveguide 200b after time t=TRF / 2 as shown in Fig. 11. In this case, as shown in Fig. 11, a negative resonant electric field is generated in the upper part of the circular patch antenna 200a without a gap in Fig. 11, and a positive resonant electric field is generated in the lower part of the circular patch antenna 200a without a gap in Fig. 11. In this way, when the waveguide 200b is longer than the desired length, light passes through the inside of the waveguide 200b even after time t = TRF / 2, and a resonant electric field having a polarity opposite to that of the resonant electric field generated between time t = 0 and time t = TRF / 2 is generated in the circular patch antenna 200a without a gap. As a result, the phase change of light caused by the positive resonant electric field generated between time t = 0 and time t = TRF / 2 is canceled by the phase change of light caused by the negative resonant electric field having the opposite polarity generated after time t = TRF / 2.

[0031] Next, the concept of phase matching of the electric field and light in the circular patch antenna 200a without a gap shown in Fig. 12 will be described. From time t=0 to time t=TRF / 4, a positive resonant electric field is generated in the upper part of the circular patch antenna 200a without a gap shown in Fig. 12, and a negative resonant electric field is generated in the lower part of the circular patch antenna 200a without a gap shown in Fig. 12. The light that enters the circular patch antenna 200a without a gap at time t=0 starts to undergo a positive phase change after time t=0. In the circular patch antenna 200a without a gap, the waveguide 200b is longer than the desired length, so that the light still passes through the upper inside of the waveguide 200b at time t=TRF / 2 as shown in Fig. 12. After time t=TRF / 2, the resonant electric field has the opposite polarity, and a negative resonant electric field is generated in the upper part of the circular patch antenna 200a without a gap in Fig. 12, and a positive resonant electric field is generated in the lower part of the circular patch antenna 200a without a gap in Fig. 12. Therefore, in this case, the phase change of light caused by the positive resonant electric field generated between time t=0 and time t=TRF / 2 is cancelled out by the phase change of light caused by the negative resonant electric field after time t=TRF / 2.

[0032] Next, the concept of phase matching between the electric field and light in the circular patch antenna 50 with a gap will be described with reference to FIG. 13. As shown in FIG. 13, in the circular patch antenna 50 with a gap, the waveguide 100b is provided along the gap. Therefore, in the circular patch antenna 50 with a gap, the length of the gap can be adjusted to a desired length. In this case, the desired length is the length of the waveguide 100b in which, when light enters the circular patch antenna 50 with a gap at time t=0, the light passes through the waveguide 100b on the upper side of FIG. 13 of the circular patch antenna 50 at time t=TRF / 2 and then passes through the waveguide 100b on the lower side of FIG. 13 of the circular patch antenna 50 and passes through the waveguide 100b at time t=TRF. From time t=0 to time t=TRF / 4, a positive resonant electric field is generated at the outer part of the upper gap of the circular patch antenna 50 in FIG. 13, a negative resonant electric field is generated at the inner part of the upper gap, and a negative resonant electric field is generated at the outer part of the lower gap of the circular patch antenna 50 in FIG. 13, a positive resonant electric field is generated at the inner part of the lower gap. In the case of the circular patch antenna 50 with a gap in which the waveguide 100b is adjusted to a desired length, as shown in FIG. 13, the light that enters the outer waveguide of the circular patch antenna 50 with a gap at time t=0 starts to undergo a positive phase change after time t=0. Then, until time t=TRF / 2, the light passes through the upper part of the waveguide 100b of the circular patch antenna 50 with a gap in FIG. 13. Also, after time t=TRF / 2, the light passes through the lower part of the waveguide 100b of the circular patch antenna 50 with a gap in FIG. 13. After time t=TRF / 2, the polarity of the resonant electric field is reversed, and a negative resonant electric field is generated at the outer part of the upper gap of the gap-provided circular patch antenna 50 in Fig. 13, a positive resonant electric field is generated at the inner part of the upper gap of the gap-provided circular patch antenna 50 in Fig. 13, and a positive resonant electric field is generated at the outer part of the lower gap of the gap-provided circular patch antenna 50 in Fig. 13, and a negative resonant electric field is generated at the inner part of the lower gap of the gap-provided circular patch antenna 50 in Fig. 13. In other words, even after time t=TRF / 2, the light continues to undergo a positive phase change.As a result, in the case of the circular patch antenna 50 with a gap, the effect of modulation is not cancelled out by the phase change of light due to the resonant electric field having the opposite polarity. Furthermore, in the circular patch antenna 50 with a gap, the time during which light undergoes a positive phase change can be doubled compared to the rectangular patch antenna 100a with a gap and the circular patch antenna 200a without a gap shown in Fig. 11. Therefore, in the circular patch antenna 50 with a gap, the effect of modulation is doubled (the amount of modulation is doubled) compared to the rectangular patch antenna 100a with a gap and the circular patch antenna 200a without a gap shown in Fig. 11.

[0033] Fig. 14 is a diagram for explaining the electric field generated in the circular patch antenna 50 with a gap. Part (b) of Fig. 14 shows the electric field amplification factor according to the position on the cross section from L1 to L2 shown in part (a) of Fig. 14.

[0034] When a gap is provided in the center of the circular patch antenna 50, as shown in part (b) of FIG. 14, a resonant electric field is generated not only at the outer end of the circular patch antenna 50 but also at the end of the circular patch antenna 50 with the gap. As a result, as shown in part (b) of FIG. 14, the electric field amplification factor at the end of the circular patch antenna 50 with the gap is high. As a result, the circular patch antenna 50 with a gap in the center can modulate light to a much greater extent by the resonant electric field compared to the circular patch antenna 200a without a gap. In the case of the circular patch antenna 200a without a gap, a resonant electric field is generated at the end of the antenna and no resonant electric field is generated anywhere else.

[0035] (Circular patch antenna integrated optical modulator) FIG. 15 is a diagram showing an example of the configuration of a circular patch antenna integrated optical modulator 70 according to an embodiment of the present disclosure. As shown in FIG. 15, the circular patch antenna integrated optical modulator 70 includes an antenna 50 and a waveguide 100b. The antenna 50 is a circular patch antenna with a gap in the center. The antenna 50 is connected to an Fe-doped semi-insulating InP substrate via an optical waveguide. In the circular patch antenna integrated optical modulator 70, an electric field generated by receiving an electric wave (e.g., a millimeter wave signal) at the antenna 50 is directly applied to the waveguide 100b below, and light is directly modulated by the electric wave due to the effect of the electric field refractive index change due to the quantum well structure adopted for the waveguide 100b. In the configuration of the circular patch antenna integrated optical modulator 70, in order to utilize the above-mentioned advantages of the circular patch antenna 50 with a gap in the center, the rectangular patch antenna 100a shown in FIG. 2 is replaced with a circular patch antenna 50 with a gap in the center. This is a Mach-Zehnder interference system, and efficient optical intensity modulation can be achieved by differential operation (push-pull operation).

[0036] As described above, the circular patch antenna 50 with the gap can be resonated at the frequency of the radio waves transmitted and received by the circular patch antenna 50 by adjusting the radial length of the outer part of the circular patch antenna 50, and the phase of the electric field and the light can be matched by considering the position where the gap is provided (i.e., considering the length of the optical phase modulation section). For example, the frequency of the radio waves is f, and the length of the optical phase modulation section in the antenna for matching the phase of the electric field and the light is L. In this case, the time it takes for the light to pass through the waveguide 100b, which corresponds to the length L of the optical phase modulation section in the antenna, is equal to one period of the radio waves. Therefore, the length L of the modulation section in the antenna can be expressed as in Equation (1).

[0037]

number

[0038] where TRF is the period of the radio wave, c is the speed of light in a vacuum, and n is the group refractive index of the core layer of the waveguide 100b (for example, the group refractive index of the intrinsic core FACQW in FIG. 3). If the frequency f of the radio wave is 60 GHz (TRF=1 / (60×10E-9) seconds) and the equivalent refractive index n=3.233 of the waveguide 100b is used as the group refractive index n of the core layer of the waveguide 100b, the length L of the modulation section in the antenna is calculated from formula (1) as L=(3×10E+8) / 3.233×1.667×10E-12≒1546.8 micrometers.

[0039] Fig. 16 is a diagram showing an example of optimal dimensions of the circular patch antenna 50 with a gap according to an embodiment of the present disclosure. The gap radius shown in Fig. 16 is 246 micrometers at which the phases of the radio wave and the light are matched and the amount of phase change is constant regardless of the polarization angle of the radio wave. The radial length of the outer part of the circular patch antenna 50 in Fig. 16, 330 micrometers, is the dimension when the frequency f of the radio wave is 60 GHz and the group refractive index n of the core layer of the waveguide 100b is 3.233.

[0040] The communication system 1 according to an embodiment of the present disclosure has been described above. The circular patch antenna integrated optical modulator 70 (an example of an optical modulator) of the communication system 1 includes a circular patch antenna 50 having a gap therein, and a waveguide 100b provided along the gap.

[0041] In this circular patch antenna integrated optical modulator 70 (one example of an optical modulator), a waveguide 100b is provided along the gap of the circular patch antenna 50, so that the resonant electric field generated by the radio waves received by the circular patch antenna 50 with the gap is strong and has a substantially constant magnitude regardless of the vibration direction of the radio waves. In addition, the strong and substantially constant resonant electric field can directly modulate the light in the waveguide 100b. As a result, the light in the waveguide in the optical modulator can be efficiently and appropriately modulated.

[0042] Note that the circular patch antenna integrated optical modulator 70 of the communication system 1 according to another embodiment of the present disclosure may be a combination of the circular patch antenna 50 and the micro-ring resonator 80. Fig. 17 is a first diagram showing a part of the configuration of the circular patch antenna integrated optical modulator 70 when the circular patch antenna 50 is combined with the micro-ring resonator 80. Fig. 18 is a second diagram showing a part of the configuration of the circular patch antenna integrated optical modulator 70 when the circular patch antenna 50 is combined with the micro-ring resonator 80.

[0043] As shown in FIG. 17, the micro-ring resonator 80 is provided adjacent to the waveguide 100b. The micro-ring resonator 80 is a micro-ring resonator. As shown in FIG. 18, the circular patch antenna 50 is provided on the top of the micro-ring resonator 80. The circular patch antenna 50 changes the electric field refractive index in the ring part of the micro-ring resonator 80, and phase modulation is performed. When the circular patch antenna 50 is combined with the micro-ring resonator 80, the circular patch antenna integrated optical modulator 70 has a structure in which light is confined from the waveguide 100b in the ring part of the micro-ring resonator 80, and resonates by repeatedly passing through the ring part many times. By repeatedly passing through the ring part many times, the amount of phase change obtained when the light passes through the ring part during resonance increases. Therefore, even if the amount of phase change caused by light passing through the ring portion once is insufficient, the light passes through the ring portion repeatedly, so that the circular patch antenna integrated optical modulator 70 in which the circular patch antenna 50 is combined with the micro-ring resonator 80 can extract light with a large amount of phase change. The micro-ring resonator 80 is circular. Therefore, by using the circular patch antenna 50, an electric field can be applied to the entire micro-ring resonator 80. In addition, by adjusting the gap position (i.e., the length of the modulation portion in the antenna) in the circular patch antenna 50, the electric field and the phase of the light can be matched. As a result, the circular patch antenna integrated optical modulator 70 in which the circular patch antenna 50 is combined with the micro-ring resonator 80 can increase the amount of phase change compared to when the micro-ring resonator 80 is not used. Note that if phase matching is not performed, the light is hardly modulated. Therefore, when using a micro-ring resonator, it is extremely important to achieve phase matching.

[0044] 19 is a diagram showing an example of a phase change amount φ by the circular patch antenna integrated optical modulator 70 when the circular patch antenna 50 is combined with the micro-ring resonator 80. α is the loss of the waveguide 100b. K is the coupling efficiency between the waveguide 100b and the micro-ring resonator 80. In the circular patch antenna integrated optical modulator 70 when the circular patch antenna 50 with a gap is combined with the micro-ring resonator 80, as shown in FIG. 19, a larger phase change amount φ can be obtained compared to the circular patch antenna integrated optical modulator 70 with the circular patch antenna 50 with a gap and no micro-ring resonator 80, and the optical-electrical modulator 100 with the rectangular patch antenna 100a with a gap and no micro-ring resonator 80.

[0045] Furthermore, the circular patch antenna integrated optical modulator 70 of the communication system 1 according to another embodiment of the present disclosure may include a circular patch antenna 50 having an elliptical outer shape with a gap. FIG. 20 is a diagram showing an example of a resonant electric field in the circular patch antenna 50 having an elliptical outer shape with a gap. In the circular patch antenna 50 having an elliptical outer shape with a gap, the antenna length changes depending on the polarization plane, and therefore the resonant frequency changes. Therefore, the circular patch antenna integrated optical modulator 70 including the circular patch antenna 50 having an elliptical outer shape with a gap can have selectivity of the resonant frequency depending on the polarization.

[0046] Although some embodiments of the present disclosure have been described, these embodiments are merely examples and do not limit the scope of the disclosure. Various additions, omissions, substitutions, and modifications may be made to these embodiments without departing from the spirit of the disclosure.

[0047] Note that some or all of the above-described embodiments can be described as, but are not limited to, the following supplementary notes.

[0048] (Appendix 1) a gapped circular patch antenna; a waveguide disposed along the gap; An optical modulator comprising:

[0049] (Appendix 2) The circular patch antenna has an outer shape: It is a perfect circle. 2. An optical modulator as defined in claim 1.

[0050] (Appendix 3) The circular patch antenna has an outer shape: It is an ellipse. 2. An optical modulator as defined in claim 1.

[0051] (Appendix 4) The radial length of the outer portion of the circular patch antenna is The length at which the circular patch antenna resonates at the frequency of the radio wave it receives. 4. An optical modulator according to any one of claims 1 to 3.

[0052] (Appendix 5) The length of the waveguide is The length is such that the phase of the electric field generated when the circular patch antenna receives an electric wave matches the phase of the light received by the waveguide. 5. An optical modulator according to any one of claims 1 to 4.

[0053] (Appendix 6) a micro-ring resonator provided adjacent to the waveguide and having the circular patch antenna provided on an upper portion thereof; 6. The optical modulator according to claim 1, comprising:

[0054] (Appendix 7) An optical modulator according to any one of claims 1 to 6; an optical-electrical modulator that modulates light into electricity; an optical fiber network connecting the optical modulator and the optoelectronic modulator; A communication system comprising:

[0055] (Appendix 8) An optical modulator comprising a circular patch antenna having a gap and a waveguide provided along the gap, The circular patch antenna modulates incident light that is incident on the waveguide by a resonant electric field generated by the radio waves received by the circular patch antenna. Processing methods. [Explanation of symbols]

[0056] 1. Communication systems 5. Computers 6, 205··CPU 7. Main memory 8. Storage 9. Interface 10. Metro Network 20, 100... Optical modulator 30. Fiber optic network 40 Demodulator 50··· antenna (gapped circular patch antenna) 60. Communications equipment 70···Circular patch antenna integrated optical modulator 100a··· antenna (rectangular patch antenna with gap) 100b...Optical waveguide 200a··· antenna (circular patch antenna without gap)

Claims

1. a gapped circular patch antenna; a waveguide disposed along the gap; An optical modulator comprising:

2. The circular patch antenna has an outer shape: It is a perfect circle.

2. The optical modulator according to claim 1.

3. The circular patch antenna has an outer shape: It is an ellipse.

2. The optical modulator according to claim 1.

4. The radial length of the outer portion of the circular patch antenna is The length at which the circular patch antenna resonates at the frequency of the radio wave it receives.

2. The optical modulator according to claim 1.

5. The length of the waveguide is The length is such that the phase of the electric field generated when the circular patch antenna receives an electric wave matches the phase of the light received by the waveguide.

2. The optical modulator according to claim 1.

6. a micro-ring resonator provided adjacent to the waveguide and having the circular patch antenna provided on an upper portion thereof; The optical modulator of claim 1 .

7. An optical modulator according to any one of claims 1 to 6; an optical-electrical modulator that modulates light into electricity; an optical fiber network connecting the optical modulator and the optoelectronic modulator; A communication system comprising:

8. An optical modulator comprising a circular patch antenna having a gap and a waveguide provided along the gap, The circular patch antenna modulates incident light that is incident on the waveguide by a resonant electric field generated by the radio waves received by the circular patch antenna. Processing methods.

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