Photo mixer

Abstract

To provide a photomixer that can achieve at least one of miniaturization and increased output of electrical signals. [Solution] The photomixer 10 according to this disclosure includes a light receiving unit 11 that receives incident light and converts it into an electrical signal having a predetermined frequency, an amplification unit 12 that amplifies the electrical signal output from the light receiving unit 11, and a coaxial connector 13 that receives and outputs the electrical signal amplified by the amplification unit 12.

Description

Technical Field

[0001] The present disclosure relates to a photomixer.

Background Art

[0002] In recent years, technologies related to Beyond 5G have been attracting attention as technologies for next-generation high-speed and large-capacity networks. In Beyond 5G, it is required to further improve and enhance the main performance in 5G wireless, for example, by more than 10 times. The main performance includes, for example, communication speed, latency, and simultaneous connection. For example, in Beyond 5G, ultra-high speed exceeding 10 Gbps / ch, ultra-low latency of about 100 μs, and ultra-large number of simultaneous connections of about 100 ch / m are required.

[0003] In order to achieve ultra-high speed in Beyond 5G, it is easy to secure a communication band by shifting the wireless carrier frequency to a high-frequency band in the terahertz band including 100 GHz to 10 THz. Thereby, it is also possible to achieve ultra-high speed of 50 Gbps / ch. In recent years, proposals of systems in which optical fiber and wireless communication are integrated have been reported, and a conventional technique for generating THz waves from the two-tone signal of optical fiber using the principle of a photomixer is also known.

[0004] Conventionally, electromagnetic waves included in the spectral band of 0.1 to 10 THz are defined as THz waves, and as a device for generating THz waves, a photomixer using a photodiode is known. For example, Patent Document 1 discloses a photomixer that enables the efficient use of the optical input power of an input optical signal to generate electromagnetic waves of millimeter waves and terahertz waves.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] However, conventional technology used waveguide connectors to output terahertz waves from photomixers, resulting in a large package size. In addition, there was no amplification circuit to amplify the electrical signal output from the photodiode, resulting in a low electrical signal output. Conventional photomixers had room for improvement in terms of miniaturization and increasing the electrical signal output.

[0007] This disclosure aims to provide a photomixer capable of achieving at least one of miniaturization and increased electrical signal output. [Means for solving the problem]

[0008] The means to achieve the above objectives are as follows:

[0009] (1) A light receiving unit that receives incident light and converts it into an electrical signal having a predetermined frequency, An amplification unit that amplifies the electrical signal output from the light receiving unit, A coaxial connector that receives and outputs the electrical signal amplified by the amplification unit, Equipped with, Photo mixer.

[0010] (2) The photomixer described in (1) above, A pair of ground lines are continuously connected from the light receiving unit to the coaxial connector, A signal line is continuously connected between the pair of ground lines from the light receiving unit to the coaxial connector, Furthermore, Photo mixer.

[0011] (3) A photomixer as described in (1) or (2) above, The light receiving unit includes a photodiode that receives the light and outputs the electrical signal, and a termination resistor that connects the photodiode and the ground. Photomixer.

[0012] (4) The photomixer according to any one of (1) to (3) above, which is further provided with a waveguide section disposed between the amplification section and the coaxial connector and transmitting the electrical signal output from the amplification section to the coaxial connector. Photomixer.

[0013] (5) The photomixer according to (4) above, which further includes a metal package in which the light receiving unit, the amplification unit, and the waveguide section are incorporated by hybrid mounting. Photomixer.

[0014] (6) The photomixer according to any one of (1) to (5) above, where the light includes two frequency components separated from each other at the predetermined frequency, and the light receiving unit outputs the electrical signal as a beat signal of the predetermined frequency. Photomixer.

[0015] (7) The photomixer according to any one of (1) to (6) above, where the predetermined frequency is included in a frequency band of 100 GHz or higher. Photomixer. [Advantages of the Invention]

[0016] According to the present disclosure, it is possible to provide a photomixer capable of realizing at least one of miniaturization and an increase in the output of an electrical signal. [Brief Description of the Drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of an optical system including a photomixer according to an embodiment of the present disclosure. [Figure 2] It is a circuit diagram showing a first example of the schematic configuration of the photomixer in FIG. 1. [Figure 3] It is an implementation diagram showing a second example of the schematic configuration of the photomixer in FIG. 1. [Figure 4] It is an enlarged view of the portion IV surrounded by the dashed-dotted line in FIG. 3. [Figure 5] It is a graph showing an example of the spectrum of light incident on the photomixer in FIG. 1. [Figure 6] It is a graph showing an example of the spectrum of the electrical signal output from the photomixer in FIG. 1.

Embodiments for Carrying out the Invention

[0018] Hereinafter, an embodiment of the present disclosure will be mainly described with reference to the accompanying drawings.

[0019] FIG. 1 is a schematic diagram showing an example of the configuration of an optical system 1 including a photomixer 10 according to an embodiment of the present disclosure. With reference to FIG. 1, an example of the configuration and function of the optical system 1 that generates an optical two-tone signal and makes it incident on the photomixer 10 will be mainly described. The optical system 1 includes a light source unit 20, a modulation unit 30, a signal generator 40, a filter unit 50, a branching unit 60, and a monitor unit 70 in addition to the photomixer 10 disposed on the light receiving side.

[0020] The optical system 1 generates an optical two-tone signal including two frequency components separated from each other at a predetermined frequency and makes it incident on the photomixer 10. The optical system 1 receives the generated optical two-tone signal by the photomixer 10 and outputs an RF (Radio Frequency) signal as a beat signal at a predetermined frequency from the photomixer 10.

[0021] In this disclosure, the “predetermined frequency” may be included in a frequency band of, for example, 100 GHz or higher. Although 100 GHz is given as an example of the lower limit of the frequency band, this lower limit is not limited to exactly “100 GHz” with 0% error. This lower limit may include a predetermined error. The “predetermined error” may include an error of preferably 1% or less, more preferably 0.1% or less, more preferably 0.01% or less, and even more preferably 0.001% or less.

[0022] In addition, the "predetermined frequency" may be included in a frequency band of, for example, 10 THz or less. Although 10 THz is given as an example of the upper limit of the frequency band, this upper limit is not limited to exactly 10 THz with 0% error. This upper limit may include a predetermined error. The "predetermined error" may include an error of preferably 1% or less, more preferably 0.1% or less, more preferably 0.01% or less, and even more preferably 0.001% or less.

[0023] The light source unit 20 irradiates the modulation unit 30 with light that will be the source of the optical two-tone signal in the optical system 1. The light source unit 20 has a laser light source, such as a semiconductor laser (Laser Diode: LD). The light irradiated from the light source unit 20 has any wavelength that can be used for optical communication in the optical system 1. The wavelength of the light irradiated from the light source unit 20 is, for example, included in the 1.5 μm optical communication wavelength band. However, it is not limited to this, and the wavelength of the light irradiated from the light source unit 20 may be included in other near-infrared regions, other infrared regions, visible regions, and ultraviolet regions that are different from the 1.5 μm optical communication wavelength band.

[0024] The modulation unit 30 receives light irradiated from the light source unit 20 and performs intensity modulation or phase modulation on the light. The modulation unit 30 has, for example, a Mach-Zehnder type optical modulator using a LiNbO3 crystal. The modulation unit 30 receives an RF signal output from the signal generator 40 and generates multiple sidebands centered on a carrier wave having frequency fc for the light irradiated from the light source unit 20. For example, the modulation unit 30 generates a first sideband having a frequency f1 greater than frequency fc and a second sideband having a frequency f2 less than frequency fc. The frequency difference between the first sideband and the second sideband, f1-f2, corresponds to a predetermined frequency.

[0025] The signal generator 40 is electrically connected to the optical modulator of the modulation unit 30 and outputs an RF signal to the optical modulator. The signal generator 40 includes, for example, a function generator. The signal generator 40 outputs an RF signal having a frequency of (f1-f2) / 2 to the optical modulator of the modulation unit 30 in order to generate a first sideband and a second sideband with a frequency difference f1-f2 corresponding to a predetermined frequency for the light emitted from the light source unit 20.

[0026] In this case, the frequency f1 of the first sideband is fc + (f1 - f2) / 2. The frequency f2 of the second sideband is fc - (f1 - f2) / 2. That is, fc = (f1 + f2) / 2, and the carrier frequency fc is located midway between the frequency f1 of the first sideband and the frequency f2 of the second sideband.

[0027] The filter section 50 acts on the light generated by the modulation section 30, which has multiple sidebands, to extract only the components of the first sideband and the second sideband. The filter section 50 attenuates the carrier wave with frequency fc to a very low level, allowing the first sideband and the second sideband, which have frequencies f1 and f2 respectively, to pass through almost unchanged.

[0028] The filter section 50 includes, for example, a bandstop filter and a bandpass filter. The bandstop filter, for example, attenuates light to a very low level in a predetermined frequency band centered around frequency fc, while allowing light to pass through almost unchanged in other frequency bands. The bandpass filter, for example, allows light to pass through almost unchanged in a predetermined frequency band centered around frequencies f1 and f2, while attenuating light to a very low level in other frequency bands.

[0029] The branching section 60 directs a portion of the power of the optical two-tone signal having a first sideband and a second sideband extracted by the filter section 50 to the photomixer 10, and the other portion to the monitor section 70. The branching section 60 includes, for example, a 10dB optical coupler and a 3dB optical coupler. The branching section 60, for example, uses a 10dB optical coupler to direct most of the power of the optical two-tone signal to the photomixer 10, and the other portion to the monitor section 70 for power monitoring.

[0030] The monitoring unit 70 monitors the power of a portion of the optical two-tone signal branched at the branching unit 60. The monitoring unit 70 includes, for example, an optical power meter.

[0031] Figure 2 is a circuit diagram showing a schematic first example of the configuration of the photomixer 10 shown in Figure 1. In Figure 2, the waveguide section 14, ground line 15, signal line 16, and metal package 17 of the photomixer 10, which will be described later, are omitted from the illustration for the purpose of simplifying the drawing. Referring to Figure 2, a schematic first example of the configuration of the photomixer 10 according to one embodiment of this disclosure will be mainly described.

[0032] In one embodiment, the photomixer 10 receives an optical two-tone signal generated in the optical system 1 and outputs an RF signal as a beat signal of a predetermined frequency. The photomixer 10 includes a light receiving unit 11, an amplification unit 12, and a coaxial connector 13.

[0033] The light-receiving unit 11 receives incident light and converts it into an electrical signal having a predetermined frequency. The light contains two frequency components that are separated from each other at the predetermined frequency. The light-receiving unit 11 receives a portion of the optical two-tone signal that has been branched at the branching section 60 of the optical system 1 in Figure 1. The light-receiving unit 11 outputs an electrical signal as a beat signal of a predetermined frequency. The light-receiving unit 11 includes a photodiode 111 that receives light and outputs an electrical signal, and a termination resistor 112 that connects the photodiode 111 to ground.

[0034] The photodiode 111 includes an ultra-wideband photoelectric conversion element such as a UTC-PD (Uni-Traveling Carrier Photodiode). A DC (Direct Current) bias voltage Vpd is applied to one end of the photodiode 111. A termination resistor 112 and an amplification unit 12 are connected in parallel to the other end of the photodiode 111. The termination resistor 112 connected to the other end of the photodiode 111 includes, for example, a 50Ω resistor. The termination resistor 112 is connected to the photodiode 111 at one end and to ground at the other end. The light receiving unit 11 is composed of, for example, a UTC-PD with a 50Ω termination resistor capable of achieving a frequency bandwidth of 100 GHz or higher.

[0035] The amplification unit 12 amplifies the electrical signal output from the light receiving unit 11. The amplification unit 12 receives the electrical signal output by photoelectric conversion from the light received by the photodiode 111 of the light receiving unit 11 and amplifies it so that the signal-to-noise ratio (S / N) is large. The amplification unit 12 includes an amplification circuit 121 that amplifies the electrical signal, a first capacitor 122 located on the input side of the amplification circuit 121, and a second capacitor 123 located on the output side of the amplification circuit 121.

[0036] The amplification circuit 121 includes, for example, an integrated circuit of a low-noise element such as a HEMT (High Electron Mobility Transistor) or HBT (Heterojunction Bipolar Transistor) using an InP (Indium Phosphide) or GaAs (Gallium Arsenide) compound semiconductor process. The amplification circuit 121 is connected to the other end of the photodiode 111 of the light receiving unit 11 via a first capacitor 122 for AC (Alternating Current) coupling. The amplification circuit 121 receives an electrical signal as an RF signal from the photodiode 111 via the first capacitor 122. The amplification circuit 121 is similarly connected to the coaxial connector 13 via a second capacitor 123. The amplification circuit 121 amplifies the electrical signal as an RF signal and outputs it to the coaxial connector 13 via the second capacitor 123.

[0037] The amplifier circuit 121 is configured such that the first terminal of the transistor included in the amplifier circuit 121 is connected to ground. The amplifier circuit 121 is configured such that a gate voltage Vg is applied to the second terminal of the transistor included in the amplifier circuit 121. The amplifier circuit 121 is configured such that a DC bias voltage Vd is applied to the third terminal of the transistor included in the amplifier circuit 121.

[0038] The coaxial connector 13 receives and outputs the electrical signal amplified by the amplification unit 12. The coaxial connector 13 is a connector designed to reduce the package size of the photomixer 10, and unlike conventional waveguide connectors, it is a coaxial connector with a bandwidth characteristic of DC-100GHz or higher. The coaxial connector 13 receives the electrical signal as an RF signal that has been amplified by the amplification circuit 121 of the amplification unit 12 and output via the second capacitor 123, and outputs it to the outside of the photomixer 10. The electrical signal output from the coaxial connector 13 to the outside of the photomixer 10 is guided through a flexible coaxial cable to other electro-optical components other than the photomixer 10.

[0039] Figure 3 is an implementation diagram showing a second example of the schematic configuration of the photomixer 10 shown in Figure 1. Figure 4 is an enlarged view of the area IV enclosed by the dashed line in Figure 3. In Figures 3 and 4, the circuit elements and coaxial connector 13 of each component shown in detail in Figure 2 have been omitted from the illustration for the purpose of simplifying the drawing. A second example of the schematic configuration of the photomixer 10 according to one embodiment of this disclosure will be mainly described with reference to Figures 3 and 4.

[0040] In one embodiment, the photomixer 10 further includes a waveguide section 14, a ground line 15, a signal line 16, and a metal package 17, in addition to the light receiving section 11, the amplification section 12, and the coaxial connector 13.

[0041] As shown in Figure 4, the waveguide section 14 is positioned between the amplifier section 12 and the coaxial connector 13, and transmits the electrical signal output from the amplifier section 12 to the coaxial connector 13. In the photomixer 10, the waveguide section 14 is positioned on the output side opposite to the light receiving section 11, which is located on the input side relative to the amplifier section 12.

[0042] The waveguide section 14 includes, for example, a grounded coplanar waveguide (G-CPWG) formed on the ceramic 143. The grounded coplanar waveguide of the waveguide section 14 includes, for example, a signal line 142 formed on the ceramic 143 and a ground line 141 formed on the ceramic 143 so as to sandwich the signal line 142 from both sides.

[0043] A pair of ground lines 15 are continuously connected from the light-receiving unit 11 to the coaxial connector 13. For example, each of the pair of ground lines 15 is located outside the signal line 16 and is continuously connected across several different components located up to the coaxial connector 13, including the light-receiving unit 11, the amplification unit 12, and the waveguide unit 14.

[0044] Each of the pair of ground lines 15 is configured such that the ground terminal pad 113 of the light receiving unit 11 and the ground terminal pad 124 of the amplification unit 12 are electrically connected to each other by wire bonding or soldering. Each of the pair of ground lines 15 is configured such that the ground terminal pad 124 of the amplification unit 12 and the ground line 141 of the waveguide unit 14 are electrically connected to each other by wire bonding or soldering.

[0045] The signal line 16 is continuously wired between a pair of ground lines 15 from the light receiving unit 11 to the coaxial connector 13. For example, the signal line 16 is continuously wired across several different components located up to the coaxial connector 13, including the light receiving unit 11, the amplification unit 12, and the waveguide unit 14, while being sandwiched between the pair of ground lines 15.

[0046] The signal line 16 is configured by electrically connecting the signal terminal pad 114 of the light receiving unit 11 and the signal terminal pad 125 of the amplification unit 12 to each other by wire bonding or soldering. The signal line 16 is configured by electrically connecting the signal terminal pad 125 of the amplification unit 12 and the signal line 142 of the waveguide unit 14 to each other by wire bonding or soldering.

[0047] As shown in Figure 3, the metal package 17 incorporates the light receiving unit 11, the amplification unit 12, and the waveguide unit 14 through hybrid mounting. Although only one part of the metal package 17 is schematically shown in Figure 3, in reality, it is composed of at least two parts combined to form a housing that accommodates each component of the photomixer 10.

[0048] The coaxial connector 13 is attached to the waveguide section 14 by electrically connecting the signal line 142 of the waveguide section 14 to the signal line 142 of the waveguide section 14 and the ground line of the coaxial connector 13 to the ground line 141 of the waveguide section 14. The coaxial connector 13 is fixed to the metal package 17, which serves as the housing, so that it protrudes outward from the side of the metal package 17 when attached to the waveguide section 14.

[0049] As described above, the photomixer 10 achieves miniaturization by, for example, integrating a transmission line with electrode wiring design into a metal package 17 using hybrid mounting technology. The photomixer 10 uses wire bonding or solder for signal electrical connection and outputs electrical signals from the coaxial connector 13.

[0050] Figure 5 is a graph showing an example of the spectrum of light incident on the photomixer 10 in Figure 1. Figure 5 shows an example of the spectrum of an optical two-tone signal generated by the optical system 1 in Figure 1. In Figure 5, the horizontal axis represents wavelength, and the vertical axis represents spectral intensity. As an example, the optical two-tone signal may have a spectral intensity as shown in Figure 5 in the 1.5 μm optical communication wavelength band.

[0051] The optical two-tone signal has, for example, a first sideband and a second sideband with a frequency difference f1-f2 corresponding to a predetermined frequency of 100 GHz. When the predetermined frequency of 100 GHz is converted to wavelength, the first sideband and the second sideband have a wavelength difference of 0.8 nm from each other, corresponding to the interval indicated by the arrows in Figure 5.

[0052] Figure 6 is a graph showing an example of the spectrum of an electrical signal output from the photomixer 10 in Figure 1. Figure 6 shows an example of the spectrum of an electrical signal as an RF signal amplified by the amplifier 12 in Figure 2 and output from the coaxial connector 13. In Figure 6, the horizontal axis represents frequency, and the vertical axis represents spectral intensity.

[0053] As an example, the electrical signal was obtained as an RF signal exhibiting a very high signal-to-noise ratio spectrum with a center frequency of 99.9999717 GHz. The noise of the electrical signal at this time was -63.74 dBm / Hz. Thus, the photomixer 10 is able to output an electrical signal having a predetermined frequency of approximately 100 GHz from an optical two-tone signal.

[0054] According to the photomixer 10 of the above embodiment, it is possible to achieve at least one of miniaturization and increased electrical signal output. For example, the photomixer 10 can achieve both miniaturization and increased electrical signal output simultaneously.

[0055] For example, the photomixer 10 has a coaxial connector 13 that receives and outputs the electrical signal amplified by the amplification unit 12. This allows the photomixer 10 to have a smaller connector size and a smaller package size compared to conventional photomixers that use waveguide connectors. Therefore, the photomixer 10 can be miniaturized. In addition, since the photomixer 10 allows wiring using a flexible coaxial cable via the coaxial connector 13, the degree of freedom in placement when it is incorporated into devices and systems is improved. In other words, the mounting efficiency of the photomixer 10 is improved. As a result, the convenience of the photomixer 10 is improved.

[0056] For example, the photomixer 10 has an amplification unit 12 that amplifies the electrical signal output from the light-receiving unit 11. This allows the photomixer 10 to incorporate an amplification circuit 121 that amplifies the electrical signal output from the light-receiving unit 11, thereby improving the output of the electrical signal. Compared to conventional photomixers without an amplification circuit, the photomixer 10 can improve the signal-to-noise ratio of the electrical signal. Therefore, the photomixer 10 can increase the output of the electrical signal.

[0057] The photomixer 10 includes a pair of ground lines 15 that are continuously connected from the light receiving unit 11 to the coaxial connector 13, and a signal line 16 that is continuously connected between the pair of ground lines 15 from the light receiving unit 11 to the coaxial connector 13.

[0058] As a result, the photomixer 10 can obtain stable output characteristics for electrical signals simply by connecting the light receiving unit 11 and the amplification unit 12, and the amplification unit 12 and the coaxial connector 13 in a ground-signal-ground manner. The photomixer 10 can stabilize the output characteristics of electrical signals by simplifying the implementation of each component. For example, in conventional photomixers that use waveguide connectors, the output characteristics tend to change sensitively depending on the implementation state of the wire bonding between the photodiode and the waveguide connector. The photomixer 10 according to one embodiment can obtain stable output characteristics compared to such conventional technology, and can improve convenience.

[0059] The light-receiving unit 11 includes a photodiode 111 that receives light and outputs an electrical signal, and a termination resistor 112 that connects the photodiode 111 to ground. As a result, even if the frequency band of the amplification circuit 121 of the amplification unit 12 does not include DC, the photomixer 10 can arrange a path for DC current and allow DC current to flow to the photodiode 111 of the light-receiving unit 11. Therefore, the photomixer 10 can operate the photodiode 111 of the light-receiving unit 11 normally and easily obtain an electrical signal from the optical two-tone signal incident on the photodiode 111.

[0060] The photomixer 10 is positioned between the amplification unit 12 and the coaxial connector 13 and has a waveguide section 14 that transmits the electrical signal output from the amplification unit 12 to the coaxial connector 13. This allows the photomixer 10 to stably guide the electrical signal amplified by the amplification unit 12 to the coaxial connector 13. Even when it is difficult to directly connect the amplification circuit 121 of the amplification unit 12 to the coaxial connector 13, the photomixer 10 can easily achieve an electrical connection between the amplification unit 12 and the coaxial connector 13 via the waveguide section 14.

[0061] The photomixer 10 has a metal package 17 in which the light receiving unit 11, the amplification unit 12, and the waveguide unit 14 are housed using hybrid mounting. This allows the photomixer 10 to be miniaturized by housing each component inside the metal package 17 through hybrid mounting. The photomixer 10 can be easily miniaturized by continuously mounting each component along three lines: ground-signal-ground. By miniaturizing the photomixer 10, the degree of freedom in placement when it is incorporated into devices and systems is improved. In other words, the mounting efficiency of the photomixer 10 is improved. As a result, the convenience of the photomixer 10 is improved.

[0062] Light contains two frequency components that are separated from each other at predetermined frequencies. The light receiving unit 11 outputs an electrical signal as a beat signal of a predetermined frequency. This allows the photomixer 10 to easily obtain an electrical signal of a predetermined frequency from the optical two-tone signal.

[0063] The specified frequency falls within the frequency band of 100 GHz or higher. This allows the photomixer 10 to operate in the terahertz band, including 100 GHz to 10 THz. The photomixer 10 can also efficiently utilize the optical input power of the input optical signal to contribute to the generation of terahertz electromagnetic waves.

[0064] It will be apparent to those skilled in the art that this disclosure can be implemented in other predetermined forms besides the embodiments described above without deviating from its spirit or essential features. Therefore, the prior description is illustrative and not limiting. The scope of the disclosure is defined not by the prior description but by the added claims. Any modifications within their equivalent scope are included therein.

[0065] For example, the shape, pattern, size, arrangement, orientation, type, and number of each component described above are not limited to those shown in the above description and drawings. The shape, pattern, size, arrangement, orientation, type, and number of each component may be configured arbitrarily as long as they can realize their function. Each component of the illustrated optical system 1 and photomixer 10 is a functional concept. The specific form of each component is not limited to those shown.

[0066] In the above embodiment, the photomixer 10 was described as having an amplification unit 12 that amplifies the electrical signal output from the light receiving unit 11, but it is not limited to this. The photomixer 10 does not have to have an amplification unit 12. Even in such a case, the photomixer 10 can be miniaturized as long as it has a coaxial connector 13. Therefore, the photomixer 10 can achieve miniaturization and increase in electrical signal output.

[0067] In the above embodiment, the photomixer 10 is described as having a coaxial connector 13 that receives and outputs the electrical signal amplified by the amplification unit 12, but it is not limited to this. The photomixer 10 may have a waveguide connector instead of, or in addition to, the coaxial connector 13. Even in such a case, the photomixer 10 can improve the output of the electrical signal as long as it has an amplification unit 12. Therefore, the photomixer 10 can achieve miniaturization and increased output of the electrical signal, specifically by increasing the output of the electrical signal.

[0068] In the above embodiment, the photomixer 10 was described as having a pair of ground lines 15 continuously connected from the light receiving unit 11 to the coaxial connector 13, but is not limited thereto. The ground lines 15 of the photomixer 10 do not have to be continuously connected from the light receiving unit 11 to the coaxial connector 13. The photomixer 10 may have a number of ground lines 15 other than a pair. Similarly, the photomixer 10 was described as having signal lines 16 continuously connected from the light receiving unit 11 to the coaxial connector 13 between a pair of ground lines 15, but is not limited thereto. The signal lines 16 may be arranged in any manner with respect to any number of ground lines 15.

[0069] In the above embodiment, the light-receiving unit 11 was described as having a photodiode 111 that receives light and outputs an electrical signal, and a termination resistor 112 that connects the photodiode 111 to ground, but it is not limited to this. For example, if the frequency band of the amplification circuit 121 of the amplification unit 12 includes DC, and a DC current can be passed through the photodiode 111 of the light-receiving unit 11, the light-receiving unit 11 does not need to have a termination resistor 112.

[0070] In the above embodiment, the photodiode 111 was described as including a UTC-PD, but is not limited thereto. The photodiode 111 may include any other photoelectric conversion element. The photodiode 111 may include any other photoelectric conversion element with a waveguide-type InGaAs (Indium Gallium Arsenide) absorption layer. The termination resistor 112 connected to the other end of the photodiode 111 was described as including a 50Ω resistor, but is not limited thereto. The termination resistor 112 may include any other resistor with any resistance value as long as it can perform its function.

[0071] In the above embodiment, the photomixer 10 is described as having a waveguide section 14 positioned between the amplifier section 12 and the coaxial connector 13, which transmits the electrical signal output from the amplifier section 12 to the coaxial connector 13. However, it is not limited to this. The photomixer 10 does not have to have a waveguide section 14. In the photomixer 10, the amplifier section 12 and the coaxial connector 13 may be directly connected to each other without the waveguide section 14.

[0072] In the above embodiment, the photomixer 10 was described as having a metal package 17 in which the light receiving unit 11, the amplification unit 12, and the waveguide unit 14 are integrated by hybrid mounting, but it is not limited to this. The photomixer 10 may have a housing made of a material other than the metal package 17.

[0073] In the above embodiment, the light is described as containing two frequency components spaced apart at predetermined frequencies, and the light receiving unit 11 outputs an electrical signal as a beat signal of the predetermined frequency, but this is not limited to this. The photomixer 10 may generate an electrical signal of the predetermined frequency from the optical signal in any other way.

[0074] In the above embodiment, the predetermined frequency was described as being included in a frequency band of 100 GHz or higher, but it is not limited to this. The predetermined frequency may be included in a frequency band of less than 100 GHz. [Explanation of Symbols]

[0075] 1 Optical System 10 Photo Mixer 11 Light receiving section 111 Photodiode 112 Termination resistor 113 Ground terminal pad 114 Signal terminal pad 12 Amplification section 121 Amplifier Circuit 122 First Capacitor 123 Second Capacitor 124 Ground terminal pad 125 signal terminal pads 13 Coaxial connector 14 Waveguide Section 141 Grand Railway 142 Signal Line 143 Ceramics 15 Grand Line 16 signal lines 17 Metal Package 20 Light source section 30 Modulation section 40 Signal Generator 50 Filter section 60 Branching point 70 Monitor section

Claims

1. A light receiving unit that receives incident light and converts it into an electrical signal having a predetermined frequency, An amplification unit that amplifies the electrical signal output from the light receiving unit, A coaxial connector that receives and outputs the electrical signal amplified by the amplification unit, Equipped with, Photo mixer.

2. A photomixer according to claim 1, A pair of ground lines are continuously connected from the light receiving unit to the coaxial connector, A signal line is continuously connected between the pair of ground lines from the light receiving unit to the coaxial connector, Furthermore, Photo mixer.

3. A photomixer according to claim 1 or 2, The light-receiving unit includes a photodiode that receives the light and outputs the electrical signal, and a termination resistor that connects the photodiode to ground. Photo mixer.

4. A photomixer according to claim 1 or 2, The system further comprises a waveguide section disposed between the amplification unit and the coaxial connector, which transmits the electrical signal output from the amplification unit to the coaxial connector. Photo mixer.

5. A photomixer according to claim 4, The device further comprises a metal package in which the light receiving unit, the amplification unit, and the waveguide unit are integrated by hybrid mounting. Photo mixer.

6. A photomixer according to claim 1 or 2, The light includes two frequency components that are spaced apart from each other at the predetermined frequencies. The light receiving unit outputs the electrical signal as a beat signal of the predetermined frequency. Photo mixer.

7. A photomixer according to claim 1 or 2, The predetermined frequency is included in the frequency band of 100 GHz or higher. Photo mixer.

Images