Optical angle modulator and optical transmission device

Abstract

An optical angle modulator includes a first generation unit that generates first angle-modulated light and second angle-modulated light by angle-modulating continuous light with an electrical signal, and a second generation unit that generates third angle-modulated light by partial degenerate four-wave mixing of the first angle-modulated light and the second angle-modulated light, the frequency band of the first angle-modulated light and the frequency band of the second angle-modulated light being different, the angle of the second angle-modulated light decreasing due to the electrical signal during a period in which the angle of the first angle-modulated light increases due to the electrical signal, and the angle of the second angle-modulated light increasing due to the electrical signal during a period in which the angle of the first angle-modulated light decreases due to the electrical signal.

Description

Technical Field

[0001] This invention relates to an optical angle modulation technology. Background Technology

[0002] Non-patent documents 1 and 2 disclose optical modulators (optical angle modulators) for angle modulation. Furthermore, angle modulation is a general term encompassing frequency modulation and phase modulation. The wider the bandwidth of the angle-modulated light generated by such an optical angle modulator, the more favorable its signal-to-noise ratio becomes.

[0003] Existing technical documents

[0004] Non-patent literature

[0005] Non-patent literature 1: S. Ishimura, et al., “SSBI-Free Direct-Detection System Employing Phase Modulation for Analog Optical Links”, in Journal of Lightwave Technology, vol.38, no.9, pp.2719-2725, 2020

[0006] Non-patent literature 2: D. Che, et al., “High-fidelity angle-modulated analog optical link”, Opt. Express, vol. 24, pp. 16 320-16328, 2016 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] An optical angle modulator changes the angle of continuous light, i.e., changes the phase or frequency of the continuous light, based on the amplitude of the applied electrical signal (used to transmit information). To generate broadband angle-modulated light, the amplitude of the electrical signal applied to the optical angle modulator must be increased, i.e., the voltage level of the electrical signal must be increased. However, generating an electrical signal with a high voltage level while maintaining linearity is not easy and increases power consumption.

[0009] means for solving problems

[0010] According to one aspect of the present invention, an optical angle modulator comprises: a first generating unit that generates a first angle-modulated light and a second angle-modulated light obtained by angle modulation of continuous light by an electrical signal; and

[0011] The second generation unit generates a third angle-modulated light by partially degenerate four-wave mixing of the first angle-modulated light and the second angle-modulated light. The frequency bands of the first angle-modulated light and the second angle-modulated light are different. During the period when the angle of the first angle-modulated light increases due to the electrical signal, the angle of the second angle-modulated light decreases due to the electrical signal. During the period when the angle of the first angle-modulated light decreases due to the electrical signal, the angle of the second angle-modulated light increases due to the electrical signal.

[0012] Invention Effects

[0013] According to the present invention, it is possible to generate angle-modulated light with a wide bandwidth.

[0014] Other features and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings. Furthermore, in the drawings, the same reference numerals denote the same or similar configurations. Attached Figure Description

[0015] Figure 1 This is a diagram illustrating the configuration of an optical angle modulator according to an embodiment.

[0016] Figure 2 This is a diagram illustrating the signal generated within the optical angle modulator according to an embodiment.

[0017] Figure 3 This is a diagram illustrating the configuration of the first generation unit according to an embodiment.

[0018] Figure 4 This is a diagram illustrating the configuration of the first generation unit according to an embodiment.

[0019] Figure 5 This is a diagram showing the signals generated in the first generation unit according to an embodiment.

[0020] Figure 6 This is a diagram illustrating the configuration of the second generation unit according to an embodiment. Detailed Implementation

[0021] The embodiments will now be described in detail with reference to the accompanying drawings. Furthermore, the following embodiments are not intended to limit the invention involved in the technical solutions, nor do they limit the invention to combinations of all features described in the claimed embodiments. Two or more of the multiple features described in the embodiments may be appropriately combined. In addition, the same reference numerals are assigned to the same or similar configurations, and repeated descriptions are omitted.

[0022] <First Embodiment>

[0023] Figure 1This is a diagram illustrating the configuration of the optical angle modulator according to this embodiment. The first generation unit 100 generates, based on the electrical signal transmitting information, as shown in the diagram. Figure 2 The angle-modulated light 91 with a center frequency of f1 and the angle-modulated light 92 with a center frequency of f2 are shown, and the generated angle-modulated light 91 and angle-modulated light 92 are output to the second generation unit 200. Additionally, in this embodiment, as... Figure 2 As shown, f2>f1, and the frequency difference between f2 and f1 is represented by X.

[0024] Angle-modulated light 91 and angle-modulated light 92 are generated based on the same electrical signal, but the first generation unit 100 generates angle-modulated light 91 and angle-modulated light 92 such that the electric field components of angle-modulated light 91 and angle-modulated light 92 are, for example, complex conjugates of each other. Specifically, for example, if angle-modulated light 91 is generated by leading the phase of continuous light when the amplitude of the electrical signal is positive and delaying the phase of continuous light when the amplitude of the electrical signal is negative, then angle-modulated light 92 is generated by leading the phase of continuous light when the amplitude of the electrical signal is negative and delaying the phase of continuous light when the amplitude of the electrical signal is positive. Similarly, for example, if angle-modulated light 91 is generated by increasing the frequency of continuous light when the amplitude of the electrical signal is positive and decreasing the frequency of continuous light when the amplitude of the electrical signal is negative, then angle-modulated light 92 is generated by increasing the frequency of continuous light when the amplitude of the electrical signal is negative and decreasing the frequency of continuous light when the amplitude of the electrical signal is positive.

[0025] Therefore, when the electrical signal is represented by m(t), the electric field component E1 of the angle-modulated light 91 and the electric field component E2 of the angle-modulated light 92 are represented as follows.

[0026]

[0027]

[0028] Here, ω1 = 2πf1, ω2 = 2πf2, and k represents the modulation index. km(t) corresponds to the change in phase or frequency of the continuous light caused by angle modulation (angle change). The larger the maximum value of km(t), the wider the bandwidth of the angle-modulated light becomes. In other words, the bandwidth of angle-modulated light 91 and angle-modulated light 92 corresponds to km(t), and the larger the value of km(t), the wider the bandwidth of angle-modulated light 91 and angle-modulated light 92 becomes. Furthermore, as... Figure 2 As shown, in this example, the bandwidths of the angle-modulated light 91 and the angle-modulated light 92 corresponding to km(t) are represented by B1.

[0029] The second generation unit 200's four-wave mixing (FWM) unit 20 generates angle-modulated light 91 and angle-modulated light 92 through partially degenerate four-wave mixing. Partially degenerate four-wave mixing is a type of four-wave mixing, referring to a phenomenon where light 91 and angle-modulated light 92, respectively, are mixed. x and frequency f y The two light sources have a frequency of 2f x -f y (or 2f) y -f x The new light. If it has a frequency f x Let the electric field component of the light be E. x And make it have a frequency of f y Let the electric field component of the light be E. y The frequency 2f generated by partially degenerate four-wave mixing is then... x -f y The electric field component of the light is E x E x E* y Additionally, E* y E represents y The complex conjugate of . Similarly, the frequency 2f generated by partially degenerate four-wave mixing. y -f x The electric field component of the light is E y E y E* x .

[0030] Therefore, through the partially degenerate four-wave mixing of FWM unit 20, the following can be generated: Figure 2 The angle-modulated light 93 with a center frequency of 2f1-f2 and the angle-modulated light 94 with a center frequency of 2f2-f1 are shown. Here, the electric field component E3 of the angle-modulated light 93 and the electric field component E4 of the angle-modulated light 94 are respectively represented as follows.

[0031]

[0032]

[0033] From equations (3) and (4), it can be seen that the angular change of each of angle-modulated lights 93 and 94 is 3 km(t), which is three times the angular change of each of angle-modulated lights 91 and 92. Therefore, as Figure 2 As shown, the bandwidth B2 of each of the angle-modulated light 93 and the angle-modulated light 94 is three times the bandwidth of each of the angle-modulated light 91 and the angle-modulated light 92, in other words, it is 3B1. Figure 2 This represents the frequency component of the signal light output by FWM unit 20.

[0034] Filter unit 21 enables Figure 2 The angle-modulated light 93 within the signal light output from the FWM unit 20 shown passes through, while other angle-modulated lights are attenuated and blocked. Additionally, the filter unit 21 can allow angle-modulated light 94 to pass through while attenuating and blocking other angle-modulated lights. Therefore, the optical angle modulator can generate and output angle-modulated light with a frequency bandwidth three times that of each of the angle-modulated lights 91 and 92. Thus, it is possible to generate angle-modulated light with a frequency bandwidth three times that of prior art electrical signals based on the same voltage level.

[0035] For example, FWM unit 20 can be constructed from optical fibers such as dispersion-shifted fibers. Strong four-wave mixing occurs when the frequency (wavelength) of light input into the fiber is close to the frequency (wavelength) at which the fiber's wavelength dispersion is zero. For example, in partially degenerate four-wave mixing, when the wavelength dispersion of the fiber at the frequency of the angle-modulated light 91 is close to zero, angle-modulated light 93 with frequencies 2f1-f2 is strongly generated. Therefore, when filter unit 21 allows angle-modulated light 93 to pass, frequencies f1 and f2 can be determined such that the frequency (wavelength) at which the fiber dispersion is zero lies within the frequency band of angle-modulated light 91, thereby enabling efficient generation of angle-modulated light 93. As an example, angle-modulated light 93 can be efficiently generated by setting frequency f1 to the frequency at which the fiber dispersion is zero.

[0036] Similarly, when the wavelength dispersion of the optical fiber at the frequency of the angle-modulated light 92 is close to zero, angle-modulated light 94 with frequencies of 2f2-f1 is strongly generated. Therefore, when the filter unit 21 allows the angle-modulated light 94 to pass through, the frequencies f1 and f2 can be determined such that the frequency (wavelength) at which the fiber dispersion is zero lies within the frequency band of the angle-modulated light 92, thereby enabling the efficient generation of the angle-modulated light 94. As an example, by setting the frequency f2 to the frequency at which the fiber dispersion is zero, the angle-modulated light 94 can be generated efficiently.

[0037] Furthermore, the present invention is not limited to this configuration, wherein the frequency with zero fiber dispersion is set in the frequency band of angle-modulated light 91 or angle-modulated light 92. A configuration can be adopted in which, for example, the frequency with zero fiber dispersion is set in the frequency band between the frequency bands of angle-modulated light 91 and angle-modulated light 92, thereby generating angle-modulated light 93 or angle-modulated light 94. Moreover, regardless of whether the frequency with zero fiber dispersion is lower than or higher than the frequency band of angle-modulated light 91 or angle-modulated light 92, partial degenerate four-wave mixing will occur; therefore, as long as angle-modulated light 93 and angle-modulated light 94 are generated, the frequency with zero fiber dispersion can be lower than or higher than the frequency band of angle-modulated light 91 or angle-modulated light 92.

[0038] Furthermore, the FWM unit 24 can be constructed from a semiconductor optical amplifier. The four-wave mixing can be generated by the nonlinearity of the semiconductor optical amplifier.

[0039] Furthermore, in the above description, as indicated by equations (1) and (2), the modulation index of angle-modulated light 91 and the modulation index of angle-modulated light 92 are the same value, i.e., "k". However, the modulation index of angle-modulated light 91 and the modulation index of angle-modulated light 92 do not need to be the same. If the modulation index of angle-modulated light 91 is k and the modulation index of angle-modulated light 92 is 0.5k, for example, as clearly indicated by equations (1) to (4), the bandwidth of angle-modulated light 93 is 2.5B1 and the bandwidth of angle-modulated light 94 is 2B1, which is smaller than the bandwidth of 3B1 when both modulation indices are k. However, in any case, the bandwidth of each of angle-modulated light 93 and angle-modulated light 94 remains wider than the bandwidth of each of angle-modulated light 91 and angle-modulated light 92. In short, as clearly indicated by equations (1) to (4), if the bandwidths of the two angle-modulated lights are the same (the modulation indices are the same), then the bandwidth of the angle-modulated light generated by the partially degenerate four-wave mixing is three times that of the original angle-modulated light. On the other hand, if the bandwidths of the two angle-modulated lights are different (the modulation indices are different), then the bandwidth of one of the angle-modulated lights generated by the partially degenerate four-wave mixing is less than three times the bandwidth of the angle-modulated light with a wider bandwidth in the original two angle-modulated lights, but more than twice the bandwidth of the angle-modulated light with a wider bandwidth in the original two angle-modulated lights.

[0040] Furthermore, if the modulation index of angle-modulated light 91 and angle-modulated light 92 are different, then the electric field components E1 and E2 of angle-modulated light 91 and angle-modulated light 92 do not have a complex conjugate relationship. Specifically, if the electric field components E1 and E2 of angle-modulated light 91 and angle-modulated light 92 have a complex conjugate relationship, then the bandwidth of the angle-modulated light generated by partially degenerate four-wave mixing can be maximized. However, the complex conjugate relationship between electric field components E1 and E2 is not a condition required to extend the bandwidth of the angle-modulated light generated by partially degenerate four-wave mixing to a bandwidth wider than that of each of angle-modulated light 91 and angle-modulated light 92. That is, for angle-modulated light 91 and angle-modulated light 92 generated by the same electrical signal, angle-modulated light 91 and angle-modulated light 92 can be generated in such a way that the angle (phase or frequency) of angle-modulated light 91 increases while the angle of angle-modulated light 92 decreases and the angle of angle-modulated light 92 increases while the angle of angle-modulated light 91 decreases. This method is within the scope of the present invention.

[0041] Furthermore, in the above description, the amplitudes of angle-modulated light 91 and angle-modulated light 92 are the same. If the amplitudes of angle-modulated light 91 and angle-modulated light 92 are different from each other, then the amplitudes of angle-modulated light 93 and angle-modulated light 94 will also be different accordingly, but since it is angle modulation, this is not a problem. Therefore, the amplitudes of angle-modulated light 91 and angle-modulated light 92 can be different.

[0042] Furthermore, when the bandwidth of each of angle-modulated lights 93 and 94 is three times the bandwidth of each of angle-modulated lights 91 and 92, in order to prevent angle-modulated lights 93 and 94 from interfering with angle-modulated lights 91 and 92, as follows: Figure 2 As shown, it needs to be set to X > 2B1. Furthermore, as mentioned above, when the modulation indices of the two angle-modulated lights are different, the bandwidth of each of angle-modulated lights 93 and 94 is not three times the bandwidth of each of angle-modulated lights 91 and 92. Therefore, more generally, if the bandwidth of the angle-modulated light with the wider bandwidth in angle-modulated lights 93 and 94 is B... x This makes the bandwidth of the angle-modulated light with a narrow frequency band B. y Let X > (3B) x +B y ) / 2 is sufficient.

[0043] Next, an example of the configuration of the first generation unit 100 will be described. Figure 3 An example of the configuration of the first generation unit 100 is shown. An electrical signal is input to the optical modulation unit 12 and then to the inversion unit 15. The inversion unit 15 outputs an inverted electrical signal, obtained by inverting the amplitude of the electrical signal, to the optical modulation unit 13. The light source 10 generates continuous light with a frequency f1, and the light source 11 generates continuous light with a frequency f2.

[0044] Optical modulation unit 12 uses an electrical signal to modulate the optical angle of continuous light with frequency f1 generated by light source 10, and outputs angle-modulated light 91. On the other hand, optical modulation unit 13 uses an inverted electrical signal to modulate the optical angle of continuous light with frequency f2 generated by light source 11, and outputs angle-modulated light 92. Furthermore, regarding optical modulation units 12 and 13, the direction (increase or decrease) of the angle change of the continuous light is the same depending on whether the amplitude of the electrical signal is positive or negative. Figure 3In the example, an electrical signal m(t) is input to the optical modulation unit 12, and an inverted electrical signal -m(t) is input to the optical modulation unit 13. Therefore, the phase or frequency of the electric field component of the angle-modulated light 92 and the electric field component of the angle-modulated light 93 increase / decrease in opposite directions. Alternatively, a configuration can be adopted in which the inversion unit 15 is omitted, and instead, the direction in which the angle of the continuous light changes (increases or decreases) depending on whether the amplitude of the electrical signal is positive or negative is different for the optical modulation units 12 and 13. Another configuration can be adopted in which a functional block containing, for example, the inversion unit 15 and the optical modulation unit 13 is used as the optical modulation unit; in other words, the inversion unit 15 is used as a component of the optical modulation unit 13.

[0045] Coupler 14 combines the angle-modulated light 91 from optical modulation unit 12 and the angle-modulated light 92 from optical modulation unit 13, and outputs a signal light containing the angle-modulated light 91 and the angle-modulated light 92.

[0046] In addition, Figure 3 In the configuration example, the modulation index of the angle-modulated light 91 and the angle-modulated light 92 can be made the same by using the same modulator as optical modulation unit 12 and optical modulation unit 13. Therefore, the bandwidth of each of the angle-modulated lights 93 and 94 can be three times the bandwidth of each of the angle-modulated lights 91 and 92. However, as mentioned above, the modulation index of the optical angle modulation of optical modulation unit 12 and the modulation index of the optical angle modulation of optical modulation unit 13 do not need to be the same.

[0047] Figure 4 Another configuration example of the first generating unit 100 is shown. The angle modulator 16 includes an oscillator that generates a frequency f. C A sinusoidal signal with frequency f3 = (f1 + f2) / 2 is generated. An electrical signal m(t) is used to modulate the angle of this sinusoidal signal, and an angle-modulated signal is output. Light source 17 generates continuous light with a frequency f3 = (f1 + f2) / 2. Optical modulation unit 18 uses the angle modulation signal from angle modulator 16 to modulate the intensity (amplitude) of the continuous light with frequency f3, and outputs intensity-modulated light.

[0048] Figure 5 The intensity-modulated light output by the optical modulation unit 18 is shown. Figure 5In the attached figure, reference numeral 95 denotes the optical carrier component (carrier) at frequency f3. Upper and lower frequency bands corresponding to the angle-modulated signal are generated through optical intensity modulation. The frequency difference between the center frequencies of the upper and lower frequency bands and the optical carrier component 95 is X / 2 of the frequency of the sine wave signal. Therefore, the center frequency of the lower frequency band is f1, and the center frequency of the upper frequency band is f2. Furthermore, the upper and lower frequency bands have a complex conjugate relationship. Therefore, the lower frequency band corresponds to angle-modulated light 91, and the upper frequency band corresponds to angle-modulated light 92.

[0049] return Figure 4 The band-stop filter (BSF) 19 attenuates and blocks the optical carrier component 95 of the intensity-modulated light output from the optical modulation unit 18. Therefore, the signal light output by the BSF 19 is similar to... Figure 3 The signal light output by coupler 14 in the middle.

[0050] In addition, Figure 4 In the configuration, the modulation index of angle modulation light 91 is the same as that of angle modulation light 92. Therefore, the bandwidth of each of angle modulation lights 93 and 94 is three times the bandwidth of each of angle modulation lights 91 and 92. Therefore, X > 2B1 is required. Furthermore, bandwidth B1 is also the bandwidth of the angle modulation signal output by angle modulation unit 16. Therefore, the frequency of the sine wave signal generated by angle modulator 16 needs to be f. C =X / 2>B1.

[0051] In addition, Figure 4 In this configuration, the optical carrier component 95 is suppressed by the BSF19. However, one configuration can be used in which the optical modulation unit 18 performs carrier suppression intensity (amplitude) modulation and omits the BSF19. Alternatively, another configuration can be used in which the remaining optical carrier component 95 is further suppressed by the BSF19 while performing carrier suppression intensity (amplitude) modulation.

[0052] <Second Embodiment>

[0053] Next, the second embodiment will be described focusing on its differences from the first embodiment. In the first embodiment, only one partially degenerate four-wave mixing is performed to generate angle-modulated light 93 and angle-modulated light 94, which are considered to be the output of the optical angle modulator. In this embodiment, two or more partially degenerate four-wave mixing operations are performed, thus generating angle-modulated light with a wider bandwidth than in the first embodiment. Furthermore, as described in the first embodiment, regarding the electric field component E1 of angle-modulated light 91 and the electric field component E2 of angle-modulated light 92, it is sufficient that the directions of increase and decrease in the angle of the electrical signal are opposite to each other; a complex conjugate relationship is not required. However, in the following description, for ease of description, the electric field component E1 of angle-modulated light 91 and the electric field component E2 of angle-modulated light 92 are assumed to have a complex conjugate relationship.

[0054] Figure 6 This is a configuration diagram of the second generation unit 200 according to this embodiment. Additionally, Figure 6 A configuration is shown in which a partially degenerate four-wave mixer is generated twice. Furthermore, the configuration of the first generation unit 100 is similar to that in the first embodiment. The FWM unit 20 is similar to the unit in the first embodiment, thus generating… Figure 2 The signal light shown is suppressed by filter unit 22. Figure 2 The signal light shown includes angle-modulated light 91 and angle-modulated light 92, and outputs signal light including angle-modulated light 93 and angle-modulated light 94 to FWM unit 23.

[0055] FWM unit 23 generates a partially degenerate four-wave mixer of angle-modulated light 93 and angle-modulated light 94. As shown in equations (3) and (4), angle-modulated light 93 and angle-modulated light 94 have a complex conjugate relationship. Therefore, by generating a partially degenerate four-wave mixer of angle-modulated light 93 and angle-modulated light 94, it is possible to generate a signal light that includes angle-modulated light with a wider bandwidth than angle-modulated light 93 and angle-modulated light 94 as its component. In addition, the center frequencies of the angle-modulated light generated by generating a partially degenerate four-wave mixer of angle-modulated light 93 and angle-modulated light 94 are 5f1-4f2 and 5f2-4f1, respectively. Furthermore, the bandwidth of the angle-modulated light generated by generating a partially degenerate four-wave mixer of angle-modulated light 93 and angle-modulated light 94 is 9 times the bandwidth of each of angle-modulated light 91 and angle-modulated light 92. The filter unit 24 receives two angle-modulated lights generated by partially degenerate four-wave mixing of angle-modulated light 93 and angle-modulated light 94, allowing only one of the two angle-modulated lights to pass through and blocking the other angle-modulated light.

[0056] in addition, Figure 6The second generation unit 200 performs two partially degenerate four-wave mixing operations, but it can also be configured to perform three or more partially degenerate four-wave mixing operations. Generally, the second generation unit 200 has a configuration in which multiple sets of FWM units and filter units for input to the outputs of the FWM units are connected in series. Furthermore, the number of sets connected in series is equal to the number of partially degenerate four-wave mixing operations.

[0057] First, angle-modulated light 91 and angle-modulated light 92 are input as input angle-modulated light to the FWM unit in the first group of the cascaded group. Then, the two input angle-modulated lights are input from the filter unit of the immediately preceding group to the FWM units in the other groups of the cascaded group. Each group's FWM unit generates two new angle-modulated lights (new angle-modulated lights) by partially degenerate four-wave mixing of the two input angle-modulated lights, and outputs a signal light containing the two input angle-modulated lights and the two new angle-modulated lights to the filter unit in the same group.

[0058] In the cascaded groups, the filter units in all groups except the last one block the two input angle modulated beams contained in the signal light input from the FWM unit in the same group, and output two new angle modulated beams to the FWM unit of the subsequent group. In the subsequent group, the two new angle modulated beams are treated as two input angle modulated beams.

[0059] Furthermore, the filter unit in the last group of the series-connected group receives four angle-modulated lights contained in the signal light input from the FWM unit in the same group, and only allows one of the four received angle-modulated lights to pass through, which is regarded as the output of the optical angle modulator.

[0060] As described above, by generating two angle-modulated lights based on the same electrical signal but different in the direction of angle increase and decrease through partial degenerate four-wave mixing, angle-modulated light with a wider bandwidth than these two angle-modulated lights is generated. Therefore, it is possible to generate wideband angle-modulated light without increasing the voltage level of the electrical signal. Furthermore, the optical angle modulator according to the above embodiment can be applied to optical transmitting devices in optical communication systems that use optical angle modulation. Therefore, optical transmitting devices including the optical angle modulator according to this embodiment are also included within the scope of this invention.

[0061] The above configuration enables the generation of angle-modulated light with a wide bandwidth. Therefore, it can contribute to achieving Goal 9 of the UN-led Sustainable Development Goals (SDGs): “Building resilient infrastructure, promoting sustainable industrialization and fostering innovation.”

[0062] This invention is not limited to the embodiments described above, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, to inform the public of the scope of the invention, the following claims are made.

[0063] This application claims priority to Japanese Patent Application No. 2021-092498, filed on June 1, 2021, which is incorporated herein by reference.

Claims

1. An optical angle modulator, wherein, The optical angle modulator includes: The first generating unit generates a first angle-modulated light and a second angle-modulated light obtained by angle modulation of continuous light using an electrical signal; and The second generation unit generates the third angle-modulated light by partially degenerate four-wave mixing of the first angle-modulated light and the second angle-modulated light. The frequency band of the first angle-modulated light is different from that of the second angle-modulated light. During the period when the angle of the first angle-modulated light increases due to the electrical signal, the angle of the second angle-modulated light decreases due to the electrical signal; and during the period when the angle of the first angle-modulated light decreases due to the electrical signal, the angle of the second angle-modulated light increases due to the electrical signal.

2. The optical angle modulator according to claim 1, wherein, The second generation unit has: A mixing unit generates a fourth angle modulated light and a fifth angle modulated light through partially degenerate four-wave mixing of the first angle modulated light and the second angle modulated light, and outputs signal light comprising the first angle modulated light, the second angle modulated light, the fourth angle modulated light, and the fifth angle modulated light; and A filter is used to filter the signal light, thereby outputting the fourth angle modulated light as the third angle modulated light.

3. The light angle modulator of claim 2, wherein, The mixing unit is an optical fiber.

4. The light angle modulator of claim 3, wherein, The frequency of the optical fiber with zero dispersion is located within the frequency band of the first angle-modulated light, within the frequency band of the second angle-modulated light, or within the frequency band between the first angle-modulated light and the second angle-modulated light.

5. The light angle modulator of claim 2, wherein, The mixing unit is an optical semiconductor amplifier.

6. The optical angle modulator according to claim 1, wherein, The second generating unit has a configuration obtained by connecting multiple groups in series. Each of the plurality of groups has a mixing unit and a filter for inputting the output of the mixing unit. Each of the plurality of groups of mixing units generates two new angle-modulated lights by partially degenerate four-wave mixing of the two input angle-modulated lights, and outputs a signal light containing the two input angle-modulated lights and the two new angle-modulated lights. The filters in the multiple groups that are different from the last group in the series connection block the two input angle modulated lights contained in the signal light from the mixer unit of the same group, and output the two new angle modulated lights. The filter of the last group in the series connection of the plurality of groups outputs one of the two new angle modulated lights contained in the signal light from the mixing unit of the same group as the third angle modulated light. The first angle-modulated light and the second angle-modulated light are input to the mixing unit of the first group in the series connection of the plurality of groups.

7. The optical angle modulator according to claim 1, wherein, The first generation unit has: The first light source generates the first continuous light; A second light source, which generates a second continuous light; A first modulation unit uses the electrical signal to angle-modulate the first continuous light, thereby generating the first angle-modulated light; and a second modulation unit that angularly modulates the second continuous light using the electric signal, thereby generating the second angularly modulated light.

8. The light angle modulator of claim 7, wherein, The second modulation unit delays a phase of the second continuous light during a period in which the first modulation unit advances the phase of the first continuous light based on the amplitude of the electric signal, or decreases a frequency of the second continuous light during a period in which the first modulation unit increases the frequency of the first continuous light based on the amplitude of the electric signal.

9. The optical angle modulator of claim 7, wherein, A frequency difference between the frequency of the first continuous light and the frequency of the second continuous light is greater than three times a bandwidth of the angularly modulated light of a side of the first angularly modulated light and the second angularly modulated light in which a frequency band is wider, and half a sum of the bandwidths of the angularly modulated light of a side of the first angularly modulated light and the second angularly modulated light in which the frequency band is narrower.

10. The light angle modulator of claim 1, wherein, An electric field component of the first angularly modulated light and an electric field component of the second angularly modulated light have a complex conjugate relationship.

11. The optical angle modulator according to claim 1, wherein the first generation unit includes: an angle modulation unit that angularly modulates a sinusoidal wave signal based on the electric signal, and outputs an angularly modulated signal; a light source that generates continuous light; and a modulation unit that intensity-modulates the continuous light generated by the light source using the angularly modulated signal.

12. The light angle modulator of claim 11, wherein, The first generation unit further includes a band elimination filter that suppresses a carrier component of the intensity-modulated light output by the modulation unit.

13. The light angle modulator of claim 11, wherein, The modulation unit carrier-suppressively intensity-modulates the continuous light generated by the light source using the angularly modulated signal.

14. The light angle modulator of claim 11, wherein, A frequency of the sinusoidal wave signal is greater than a bandwidth of the angularly modulated signal.

15. An optical transmitting apparatus, comprising: The optical transmission device includes the optical angle modulator according to any one of claims 1 to 14.

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