Optical Angle Modulator and Optical Transmitter

Abstract

To provide a technique capable of generating an optical angle modulation signal with a band width.SOLUTION: An optical angle modulator comprises: first generation means of generating a first angle modulation light and a second angle modulation light, in which an angle of a continuous light is modulated by an electric signal; and second generation means of generating a third angle modulation light by a part of degenerate fourth-wave mixtures of the first angle modulation light and the second angle modulation light. A band of the first angle modulation light and a band of the second angle modulation light are different, an angle of the second angle modulation light is reduced by the electric signal during the angle of the first angle modulation light is increased by the electric signal. The angle of the second angle modulation light is increased by the electric signal during the angle of the first angle modulation light is reduced by the electric signal.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to optical angle modulation technology.

Background Art

[0002] Non-Patent Document 1 and Non-Patent Document 2 disclose an optical modulator (optical angle modulator) that performs angle modulation. Note that angle modulation is a general term for frequency modulation and phase modulation. The signal-to-noise ratio of the angle-modulated light generated by such an optical angle modulator becomes better as its bandwidth is wider.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The optical angle modulator changes the angle of continuous light, that is, the phase and frequency, according to the amplitude of the applied electrical signal (carrying information). In order to generate wide-band angle-modulated light, the amplitude of the electrical signal applied to the optical angle modulator, that is, the voltage level of the electrical signal, must be increased. However, it is not easy to generate an electrical signal with a high voltage level while maintaining linearity, and the power consumption increases.

[0005] The present invention provides a technique for generating angle-modulated light with a wide bandwidth.

Means for Solving the Problems

[0006] According to one aspect of the present invention, an optical angle modulator includes a first generation means for generating first angle-modulated light and second angle-modulated light obtained by angle-modulating continuous light with an electrical signal wherein the band of the first angle-modulated light is different from the band of the second angle-modulated light, and while the angle of the first angle-modulated light is increasing by the electrical signal, the angle of the second angle-modulated light is decreasing by the electrical signal, and while the angle of the first angle-modulated light is decreasing by the electrical signal, the angle of the second angle-modulated light is increasing by the electrical signal, the first angle-modulated light and the second angle-modulated light and a second generation means for generating third angle-modulated light by partial degenerate four-wave mixing of the first angle-modulated light and the second angle-modulated light. being

Effects of the Invention

[0007] According to the present invention, angle-modulated light with a wide bandwidth can be generated.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential for the invention. Two or more of the features described in the embodiments may be arbitrarily combined. Also, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0010] <First Embodiment> FIG. 1 is a configuration diagram of an optical angle modulator according to the present embodiment. The first generation unit 100 generates angle-modulated light 91 having a center frequency f1 and angle-modulated light 92 having a center frequency f2 as shown in FIG. 2 based on an electrical signal that carries information, and outputs them to the second generation unit 200. In the present embodiment, as shown in FIG. 2, f2 > f1, and the frequency difference between f2 and f1 is X.

[0011] The angle-modulated light 91 and the angle-modulated light 92 are generated based on the same electrical signal, but the electric field component of the angle-modulated light 91 and the electric field component of the angle-modulated light 92 are, for example, in a complex conjugate relationship with each other. The first generation unit 100 generates the angle-modulated light 91 and the angle-modulated light 92. That is, for example, if the angle-modulated light 91 is generated by advancing the phase of the continuous light when the amplitude of the electrical signal is positive and delaying the phase of the continuous light when the amplitude of the electrical signal is negative, then the angle-modulated light 92 is generated by advancing the phase of the continuous light when the amplitude of the electrical signal is negative and delaying the phase of the continuous light when the amplitude of the electrical signal is positive. Similarly, for example, if the angle-modulated light 91 is generated by increasing the frequency of the continuous light when the amplitude of the electrical signal is positive and decreasing the frequency of the continuous light when the amplitude of the electrical signal is negative, then the angle-modulated light 92 is generated by increasing the frequency of the continuous light when the amplitude of the electrical signal is negative and decreasing the frequency of the continuous light when the amplitude of the electrical signal is positive.

[0012] Therefore, when the electrical signal is denoted as 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 respectively

[0013]

number

[0014] The four-wave mixing (FWM) section 20 of the second generation section 200 generates partially degenerate four-wave mixing of the angle-modulated light 91 and the angle-modulated light 92. The partially degenerate four-wave mixing is one form of four-wave mixing, and is generated at a frequency f x and frequency f y From the two lights of frequency 2f x -f y (or 2f y -f x This refers to the phenomenon in which new light with a frequency of f is generated. x The electric field component of the light is E x and the frequency f y The electric field component of the light is E y Then, the frequency 2f generated by partially degenerate four-wave mixing x -f y The electric field component of the light is E x E x E * y In addition, E * y E y Similarly, the frequency 2f y -f x The electric field component of the light is E y E y E * x It becomes.

[0015] Therefore, by partial degenerate four-wave mixing in the FWM unit 20, 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, as shown in FIG. 2, are generated. 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

[0016] [Number] become. From equations (3) and (4), it can be seen that the amount of angle change of the angle-modulated light 93 and the angle-modulated light 94 is 3km(t), that is, three times that of the angle-modulated light 91 and the angle-modulated light 92. Therefore, as shown in FIG. 2, the bandwidth B2 of the angle-modulated light 93 and the angle-modulated light 94 is three times the bandwidth of the angle-modulated light 91 and the angle-modulated light 92, that is, 3B1. FIG. 2 shows the frequency components of the signal light output from the FWM unit 20.

[0017] The filter unit 21 allows the angle-modulated light 93 among the signal light output from the FWM unit 20 shown in FIG. 2 to pass through, and attenuates and blocks the other angle-modulated light. Note that the filter unit 21 may allow the angle-modulated light 94 to pass through and attenuate and block the other angle-modulated light. Thereby, the optical angle modulator can generate and output angle-modulated light having a bandwidth three times that of the angle-modulated light 91 and 92. Therefore, angle-modulated light with a bandwidth three times that of the conventional one can be generated based on an electrical signal with the same voltage level.

[0018] The FWM unit 20 can be constituted by an optical fiber such as a dispersion-shifted fiber, for example. Four-wave mixing strongly occurs when the frequency (wavelength) of the light input to the optical fiber is close to the frequency (wavelength) at which the wavelength dispersion value of the optical fiber becomes zero. For example, in the case of partial degenerate four-wave mixing, when the wavelength dispersion value of the optical fiber at the frequency of the angle-modulated light 91 is near zero, the angle-modulated light 93 with the frequency 2f1 - f2 is strongly generated. Therefore, when the filter unit 21 allows the angle-modulated light 93 to pass through, by determining the frequencies f1 and f2 such that the frequency (wavelength) at which the dispersion of the optical fiber becomes 0 is located within the band of the angle-modulated light 91, the angle-modulated light 93 can be efficiently generated. As an example, by setting the frequency f1 to the frequency at which the dispersion of the optical fiber becomes 0, the angle-modulated light 93 can be efficiently generated.

[0019] Similarly, when the wavelength dispersion value of the optical fiber at the frequency of the angle-modulated light 92 is near zero, the angle-modulated light 94 with the frequency 2f2 - f1 is strongly generated. Therefore, when the filter unit 21 allows the angle-modulated light 94 to pass through, by determining the frequencies f1 and f2 such that the frequency (wavelength) at which the dispersion of the optical fiber becomes 0 is located within the band of the angle-modulated light 92, the angle-modulated light 94 can be efficiently generated. As an example, by setting the frequency f2 to the frequency at which the dispersion of the optical fiber becomes 0, the angle-modulated light 94 can be efficiently generated.

[0020] Note that the present invention is not limited to setting the frequency at which the dispersion of the optical fiber becomes 0 within the bands of the angle-modulated light 91 or the angle-modulated light 92. For example, by setting the frequency at which the dispersion of the optical fiber becomes 0 within the band between the band of the angle-modulated light 91 and the band of the angle-modulated light 92, a configuration can be adopted to generate the angle-modulated light 93 or the angle-modulated light 94. Furthermore, since partial degenerate four-wave mixing occurs even if the frequency at which the dispersion of the optical fiber becomes 0 is lower than the band of the angle-modulated light 91 or higher than the band of the angle-modulated light 92, as long as the angle-modulated light 93 or the angle-modulated light 94 is generated, the frequency at which the dispersion of the optical fiber becomes 0 may be lower than the band of the angle-modulated light 91 or higher than the band of the angle-modulated light 92.

[0021] In addition, the FWM unit 24 can be composed of a semiconductor optical amplifier. Due to the non-linearity of the semiconductor optical amplifier, four-wave mixing can be generated.

[0022] In the above description, as shown in Equations (1) and (2), the modulation indices of the angle-modulated light 91 and the angle-modulated light 92 are set to the same value "k". However, it is not necessary for the modulation indices of the angle-modulated light 91 and the angle-modulated light 92 to be the same. For example, if the modulation index of the angle-modulated light 91 is k and the modulation index of the angle-modulated light 92 is 0.5k, as is clear from Equations (1) to (4), the bandwidth of the angle-modulated light 93 is 2.5B1, the bandwidth of the angle-modulated light 94 is 2B1, which is smaller than 3B1, the bandwidth in the case where both modulation indices are k. However, it is certain that the bandwidths of the angle-modulated light 93 and the angle-modulated light 94 are wider than the bandwidths of the angle-modulated light 91 and the angle-modulated light 92. In summary, as is clear from Equations (1) to (4), when the bandwidths of the two angle-modulated lights are the same (the modulation indices are the same), the bandwidth of the angle-modulated light generated by partial degenerate four-wave mixing is three times that of the original angle-modulated light. On the other hand, when the bandwidths of the two angle-modulated lights are different (the modulation indices are different), the bandwidth of one of the two angle-modulated lights generated by partial degenerate four-wave mixing is smaller than three times the bandwidth of the wider-band one of the original two angle-modulated lights, but larger than twice the bandwidth of the wider-band one of the original two angle-modulated lights.

[0023] In addition, when the modulation indices of the angle-modulated light 91 and the angle-modulated light 92 are different, the electric field component E1 of the angle-modulated light 91 and the electric field component E2 of the angle-modulated light 92 do not have a complex conjugate relationship. That is, by making the electric field component E1 of the angle-modulated light 91 and the electric field component E2 of the angle-modulated light 92 have a complex conjugate relationship, the bandwidth of the angle-modulated light generated by partial degenerate four-wave mixing can be maximized. However, making the electric field component E1 and the electric field component E2 have a complex conjugate relationship is not a necessary condition for making the bandwidth of the angle-modulated light generated by partial degenerate four-wave mixing wider than the bandwidths of the angle-modulated light 91 and the angle-modulated light 92. That is, for the angle-modulated light 91 and the angle-modulated light 92 generated from the same electrical signal, while the angle (phase or frequency) of the angle-modulated light 91 is increasing, the angle of the angle-modulated light 92 is decreasing, and while the angle of the angle-modulated light 91 is decreasing, the angle of the angle-modulated light 92 is increasing. As long as the angle-modulated light 91 and the angle-modulated light 92 are generated in such a manner, such a form is within the scope of the present invention.

[0024] Also, in the above description, the amplitudes of the angle-modulated light 91 and the angle-modulated light 92 were made the same. When the amplitudes of the angle-modulated light 91 and the angle-modulated light 92 are different, the amplitudes of the angle-modulated light 93 and the angle-modulated light 94 will also be different accordingly, but since it is angle modulation, it does not pose a problem. Therefore, the amplitudes of the angle-modulated light 91 and the angle-modulated light 92 may be different.

[0025] In addition, when the bandwidths of the angle-modulated light 93 and the angle-modulated light 94 are three times the bandwidths of the angle-modulated light 91 and 92, in order to prevent the angle-modulated light 93 and the angle-modulated light 94 from interfering with the angle-modulated light 91 and 92, as is clear from FIG. 2, it is necessary to make X > 2B1. As described above, when the modulation indices of the two angle-modulated lights are different, the bandwidths of the angle-modulated light 93 and the angle-modulated light 94 will not be three times the bandwidths of the angle-modulated light 91 and 92. Therefore, more generally, 91 for the angle-modulated light 92 and the angle-modulated light x if the wider bandwidth of the two is designated as B y and the narrower bandwidth is designated as B x , then X > (3B y + B x ) / 2 is sufficient.

[0026] Next, a configuration example of the first generation unit 100 will be described. FIG. 3 shows a configuration example of the first generation unit 100. The electrical signal is input to the optical modulation unit 12 and also input to the inversion unit 15. The inversion unit 15 outputs an inverted electrical signal with the amplitude of the electrical signal inverted 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.

[0027] The optical modulation unit 12 optically angle-modulates the continuous light with the frequency f1 generated by the light source 10 by the electrical signal and outputs angle-modulated light 91. On the other hand, the optical modulation unit 13 optically angle-modulates the continuous light with the frequency f2 generated by the light source 11 by the inverted electrical signal and outputs angle-modulated light 92. Note that the optical modulation unit 12 and the optical modulation unit 13 shall have the same direction (increase or decrease) of changing the angle of the continuous light according to the positive and negative of the amplitude of the electrical signal. In the example of FIG. 3, since the electrical signal m(t) is input to the optical modulation unit 12 and the inverted electrical signal -m(t) is input to the optical modulation unit 13, the phase or the increasing and decreasing direction of the frequency of the electric field component of the angle-modulated light 92 and the electric field component of the angle-modulated light 93 are opposite to each other. Note that the inversion unit 15 may be omitted, and instead, a configuration may be adopted in which the direction (increase or decrease) of changing the angle of the continuous light according to the positive and negative of the amplitude of the electrical signal is different between the optical modulation unit 12 and the optical modulation unit 13. For example, a functional block including the inversion unit 15 and the optical modulation unit 13 may be made into one optical modulation unit, that is, a configuration in which the inversion unit 15 is an element within the optical modulation unit 13 may be adopted.

[0028] The coupler 14 multiplexes the angle-modulated light 91 from the optical modulation unit 12 and the angle-modulated light 92 from the optical modulation unit 13 and outputs signal light including the angle-modulated light 91 and the angle-modulated light 92.

[0029] In the configuration example of FIG. 3, by using the same modulator as the optical modulation unit 12 and the optical modulation unit 13, the modulation indices of the angle-modulated light 91 and the angle-modulated light 92 can be made the same. Therefore, the bandwidths of the angle-modulated light 93 and the angle-modulated light 94 can be made three times that of the angle-modulated light 91 and the angle-modulated light 92. However, as described above, the modulation indices of the optical angle modulation in the optical modulation unit 12 and the optical modulation unit 13 do not have to be the same.

[0030] FIG. 4 shows another configuration example of the first generation unit 100. The angle modulator 16 has an oscillator that generates a sine wave signal with a frequency f C = X / 2, and angle-modulates the sine wave signal with an electrical signal m(t) to output an angle-modulated signal. The light source 17 generates continuous light with a frequency f3 = (f1 + f2) / 2. The optical modulation unit 18 intensity-modulates (amplitude-modulates) the continuous light with a frequency f3 with the angle-modulated signal from the angle modulator 16 and outputs intensity-modulated light.

[0031] FIG. 5 shows the intensity-modulated light output by the optical modulation unit 18. In FIG. 5, the reference numeral 95 is an optical carrier component (carrier wave) with a frequency f3. Due to the optical intensity modulation, an upper sideband and a lower sideband corresponding to the angle-modulated signal are generated. The frequency difference between the center frequencies of each of the upper sideband and the lower sideband and the optical carrier component 95 is equal to X / 2, which is the frequency of the sine wave signal. Therefore, the center frequency of the lower sideband is f1, and the center frequency of the upper sideband is f2. Also, the upper sideband and the lower sideband have a complex conjugate relationship. Therefore, the lower sideband corresponds to the angle-modulated light 91, and the upper sideband corresponds to the angle-modulated light 92.

[0032] Returning to FIG. 4, the band-stop filter (BSF) 19 attenuates and blocks the optical carrier component 95 of the intensity-modulated light output by the optical modulation unit 18. Therefore, the signal light output by the BSF 19 is the same as the signal light output by the coupler 14 in FIG. 3.

[0033] In the configuration of FIG. 4, since the modulation indices of the angle-modulated light 91 and the angle-modulated light 92 are the same, the bandwidths of the angle-modulated light 93 and the angle-modulated light 94 are three times the bandwidths of the angle-modulated light 91 and the angle-modulated light 92. Therefore, it is necessary to set X>2B1. Note that the bandwidth B1 is also the bandwidth of the angle-modulation signal output by the angle-modulation unit 16. Therefore, the frequency f of the sine-wave signal generated by the angle-modulator 16 C =X / 2>B1 must be satisfied.

[0034] In FIG. 4, the optical carrier component 95 is suppressed by the BSF19. However, in the optical modulation unit 18, a configuration can be adopted in which carrier suppression intensity (amplitude) modulation is performed to omit the BSF19. Also, a configuration can be adopted in which while performing carrier suppression intensity (amplitude) modulation, the optical carrier component 95 remaining in the BSF19 is further suppressed.

[0035] <Second Embodiment> Subsequently, the second embodiment will be described focusing on the differences from the first embodiment. In the first embodiment, the partially degenerate four-wave mixing is caused only once, thereby generating the angle-modulated light 93 and the angle-modulated light 94, and using the angle-modulated light 93 or the angle-modulated light 94 as the output of the optical angle modulator. In this embodiment, the partially degenerate four-wave mixing is caused two or more times, thereby generating angle-modulated light with a wider bandwidth than in the first embodiment. As described in the first embodiment, the electric field component E1 of the angle-modulated light 91 and the electric field component E2 of the angle-modulated light 92 only need to have opposite directions of increase and decrease in angle due to the electric signal, and it is not essential that they are in a complex conjugate relationship. However, for simplicity of explanation below, it is assumed that the electric field component E1 of the angle-modulated light 91 and the electric field component E2 of the angle-modulated light 92 are in a complex conjugate relationship.

[0036] FIG. 6 is a configuration diagram of the second generation unit 200 according to the present embodiment. Note that FIG. 6 shows a configuration in the case where partial degenerate four-wave mixing occurs twice. The configuration of the first generation unit 100 is the same as that of the first embodiment. The FWM unit 20 is the same as that of the first embodiment, and thus generates the signal light shown in FIG. 2. The filter unit 22 suppresses the angle-modulated lights 91 and 92 among the signal lights shown in FIG. 2, and outputs the signal light including the angle-modulated lights 93 and 94 to the FWM unit 23.

[0037] The FWM unit 23 causes partial degenerate four-wave mixing between the angle-modulated light 93 and the angle-modulated light 94. From equations (3) and (4), the angle-modulated light 93 and the angle-modulated light 94 are in a complex conjugate relationship. Therefore, by partial degenerate four-wave mixing between the angle-modulated light 93 and the angle-modulated light 94, a signal light including, as its components, angle-modulated lights having a wider bandwidth than the angle-modulated lights 93 and 94 can be generated. Note that the center frequencies of the angle-modulated lights generated by partial degenerate four-wave mixing between the angle-modulated light 93 and the angle-modulated light 94 are 5f1 - 4f2 and 5f2 - 4f1, respectively. Also, the bandwidth of the angle-modulated light generated by partial degenerate four-wave mixing between the angle-modulated light 93 and the angle-modulated light 94 is nine times the bandwidths of the angle-modulated lights 91 and 92. The filter unit 24 allows only one of the two angle-modulated lights generated by partial degenerate four-wave mixing between the angle-modulated light 93 and the angle-modulated light 94 to pass through, and blocks the other angle-modulated light.

[0038] Note that the second generation unit 200 in FIG. 6 causes partial degenerate four-wave mixing to occur twice, but the configuration of the second generation unit 200 may be such that partial degenerate four-wave mixing occurs three or more times. Generally speaking, the second generation unit 200 has a configuration in which a plurality of sets each including an FWM unit and a filter unit to which the output of the FWM unit is input are connected in series. Note that the number of sets connected in series is equal to the number of times partial degenerate four-wave mixing occurs.

[0039] First, angularly modulated light 91 and angularly modulated light 92 are input as input angularly modulated light to the first set of FWM units connected in series. Further, two input angularly modulated lights are input from the filter unit of the previous set to the FWM unit of a set different from the first set connected in series. Each set of FWM units generates two new angularly modulated lights (new angularly modulated lights) by partial degenerate four-wave mixing of the two input angularly modulated lights, and outputs the signal light including the two input angularly modulated lights and the two new angularly modulated lights to the filter unit of the same set.

[0040] The filter unit of a set different from the last set connected in series blocks the two input angularly modulated lights included in the signal light input from the FWM unit of the same set, and outputs the two new angularly modulated lights to the FWM unit of the subsequent set. These two new angularly modulated lights are treated as two input angularly modulated lights in the subsequent set.

[0041] Further, the filter unit of the last set connected in series allows only one new angularly modulated light out of the four angularly modulated lights included in the signal light input from the FWM unit of the same set to pass through, and outputs it as the output of the optical angular modulator.

[0042] As described above, by partial degenerate four-wave mixing of two angularly modulated lights generated based on the same electrical signal and having different angular increase and decrease directions, an angularly modulated light having a wider bandwidth than these two angularly modulated lights is generated. Therefore, a wideband angularly modulated light can be generated without increasing the voltage level of the electrical signal. Note that the optical angular modulator according to each of the above embodiments can be applied to an optical transmission device of an optical communication system using optical angular modulation. Therefore, an optical transmission device including the optical angular modulator according to the present embodiment is also included in the scope of the present invention.

[0043] The invention is not limited to the above embodiments, and various modifications and changes are possible within the scope of the gist of the invention.

[0044] With the above configuration, it is possible to generate angle-modulated light with a wide bandwidth. Therefore, it becomes possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "build resilient infrastructure, promote sustainable industrialization, and foster innovation."

Explanation of symbols

[0045] 100: First generation unit, 200: Second generation unit

Claims

1. A first angle-modulated light and a second angle-modulated light obtained by angularly modulating continuous light with an electrical signal, wherein the band of the first angle-modulated light is different from the band of the second angle-modulated light, and while the angle of the first angle-modulated light is increasing by the electrical signal, the angle of the second angle-modulated light is decreasing by the electrical signal, and while the angle of the first angle-modulated light is decreasing by the electrical signal, the angle of the second angle-modulated light is increasing by the electrical signal, a first generating means for generating the first angle-modulated light and the second angle-modulated light; A second generating means for generating a third angle-modulated light by partially degenerate four-wave mixing of the first angle-modulated light and the second angle-modulated light; An optical angle modulator comprising the same.

2. The second generating means generates a fourth angle-modulated light and a fifth angle-modulated light by partially degenerate four-wave mixing of the first angle-modulated light and the second angle-modulated light, and outputs a signal light including the first angle-modulated light, the second angle-modulated light, the fourth angle-modulated light, and the fifth angle-modulated light; a mixing means; a filter that outputs the fourth angle-modulated light as the third angle-modulated light by filtering the signal light; The optical angle modulator according to claim 1, comprising the same.

3. The mixing means is an optical fiber. The optical angle modulator according to claim 2.

4. The frequency at which the dispersion value of the optical fiber becomes zero is within the band of the first angle-modulated light, within the band of the second angle-modulated light, or within a band between the band of the first angle-modulated light and the band of the second angle-modulated light. The optical angle modulator according to claim 3.

5. The mixing means is an optical semiconductor amplifier. The optical angle modulator according to claim 2.

6. The second generating means has a configuration in which a plurality of sets are connected in series. Each of the plurality of sets has a mixing means and a filter to which the output of the mixing means is input. The mixing means of each of the plurality of sets generates two new angle-modulated lights by partial degenerate four-wave mixing of two input angle-modulated lights input thereto, and outputs signal light including the two input angle-modulated lights and the two new angle-modulated lights. The filter of a set different from the last set in the series connection among the plurality of sets blocks the two input angle-modulated lights included in the signal light from the mixing means of the same set, and outputs the two new angle-modulated lights. The filter of the last set in the series connection among the plurality of sets outputs one of the two new angle-modulated lights included in the signal light from the mixing means of the same set as the third angle-modulated light. The optical angle modulator according to claim 1, wherein the first angle-modulated light and the second angle-modulated light are input to the mixing means of the first set in the series connection among the plurality of sets. **Claim 7** The first generation means includes: a first light source that generates a first continuous light; a second light source that generates a second continuous light; a first modulation means that generates the first angle-modulated light by angle-modulating the first continuous light with the electrical signal; a second modulation means that generates the second angle-modulated light by angle-modulating the second continuous light with the electrical signal. The optical angle modulator according to any one of claims 1 to 6. **Claim 8** While the first modulation means advances the phase of the first continuous light based on the amplitude of the electrical signal, the second modulation means delays the phase of the second continuous light, or while the first modulation means increases the frequency of the first continuous light based on the amplitude of the electrical signal, the second modulation means decreases the frequency of the second continuous light. The optical angle modulator according to claim 7. **Claim 9** The frequency difference between the frequency of the first continuous light and the frequency of the second continuous light is greater than half of the sum of three times the first bandwidth of the angle-modulated light with the wider bandwidth among the first angle-modulated light and the second angle-modulated light and the second bandwidth of the angle-modulated light with the narrower bandwidth among the first angle-modulated light and the second angle-modulated light. The optical angle modulator according to claim 7 or 8.

10. The electric field components of the first angle-modulated light and the second angle-modulated light are in a complex conjugate relationship. The optical angle modulator according to any one of claims 1 to 9.

11. The first generating means Angle modulation means for angle-modulating a sine wave based on the electrical signal and outputting an angle-modulated signal A light source for generating continuous light Modulation means for outputting intensity-modulated light including the first angle-modulated light and the second angle-modulated light by intensity-modulating the continuous light generated by the light source with the angle-modulated signal The optical angle modulator according to any one of claims 1 to 6, comprising

12. The first generating means further includes a band-stop filter for suppressing the carrier component of the intensity-modulated light output by the modulation means. The optical angle modulator according to claim 11.

13. The modulation means intensity-modulates the continuous light generated by the light source with carrier suppression using the angle-modulated signal. The optical angle modulator according to claim 11.

14. The frequency of the sine wave is greater than the bandwidth of the angle-modulated signal. The optical angle modulator according to any one of claims 11 to 13.

15. An optical transmission device comprising the optical angle modulator according to any one of claims 1 to 14.

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