Optical angle modulator and optical transmitter

Abstract

To provide a technique capable of increasing a band width of an angle modulation light.SOLUTION: An optical angle modulator comprises: generation means of generating a first angle modulation light and a second angle modulation light each of which an angle of a continuous light is modulated by an electric signal; a first non-liner medium that generates one or more third angle modulation lights of a band width that is wider than that of the first and second angle modulation lights by a four wave mixing of the first angle modulation light and the second angle modulation light; and first processing means. The first processing means contains: adjustment means of individually adjusting each phase of three or more angle modulation lights contained in a light input into the first processing means; and a second non-liner medium that generates one or more four angle modulation lights of which the band width is wider than that of the three or more angle modulation lights by the four wave mixing of the three or more angle modulation light after a phase adjustment by the adjustment means. in the first processing means, a light including the first angle modulation light, the second angle modulation light, and the one or mothe third angle modulation light is input.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Optical angle modulation is used in sensing devices such as LiDAR devices, and communication devices for transmitting or distributing information. Optical angle modulation includes optical frequency modulation and optical phase modulation. In communication applications, the signal-to-noise ratio of angle-modulated light can be reduced by increasing its bandwidth. In sensing applications, the resolution can be increased by increasing the bandwidth of angle-modulated light. Non-Patent Document 1 discloses a configuration for generating broadband frequency-modulated light. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Shota Ishimura, Hidenori Takahashi, Takehiro Tsuritani, and Masatoshi Suzuki, "Optical parametric wideband frequency modulation", APL Photonics 7,066106, June 16, 2022 Summary of the Invention [Problem to be solved by the invention]

[0004] FIG. 1 is an explanatory diagram of the configuration described in Non-Patent Document 1. First, angle-modulated light 91 and angle-modulated light 92 are generated by optically angle-modulating first and second continuous light using the same electrical signal. Note that the direction of change in the angle (frequency or phase) of the first continuous light due to a change in the amplitude of the electrical signal is opposite to the direction of change in the angle (frequency or phase) of the second continuous light. For example, the electric field components of angle-modulated light 91 and angle-modulated light 92 are complex conjugate. Non-Patent Document 1 then discloses that angle-modulated light 91 and angle-modulated light 92 are input into a nonlinear medium such as a dispersion-shifted fiber (DSF), and four-wave mixing (partially including degenerate four-wave mixing) of angle-modulated light 91 and angle-modulated light 92 is recursively generated in the nonlinear medium, thereby generating angle-modulated light with a bandwidth wider than that of angle-modulated light 91 and angle-modulated light 92.

[0005] For example, angle-modulated light 93 and angle-modulated light 94, which are second-order angle-modulated light, are generated by partially degenerate four-wave mixing of angle-modulated light 91 and angle-modulated light 92. If the bandwidths of angle-modulated light 91 and angle-modulated light 92 are both B, the bandwidth of angle-modulated light 93 and angle-modulated light 94 is 3B. Angle-modulated light 95, which is third-order angle-modulated light, is generated, for example, by four-wave mixing of angle-modulated light 91, angle-modulated light 92, and angle-modulated light 93, or by partially degenerate four-wave mixing of angle-modulated light 91 and angle-modulated light 93, and its bandwidth is 5B. Similarly, angle-modulated light 96, which is third-order angle-modulated light, is generated, for example, by four-wave mixing of angle-modulated light 91, angle-modulated light 92, and angle-modulated light 94, or by partially degenerate four-wave mixing of angle-modulated light 92 and angle-modulated light 94, and its bandwidth is 5B.

[0006] 1, for example, by four-wave mixing or partially degenerate four-wave mixing involving angle-modulated light 96 (hereinafter, four-wave mixing and partially degenerate four-wave mixing will be collectively referred to as four-wave mixing), fourth-order angle-modulated light with a bandwidth larger than that of angle-modulated light 96 can also be generated. In this way, Non-Patent Document 1 discloses that angle-modulated light with a bandwidth larger than the original bandwidth can be generated by recursive four-wave mixing.

[0007] As mentioned above, the higher the order of the angle-modulated light generated by four-wave mixing, the wider its bandwidth. One way to increase the order of the angle-modulated light generated by four-wave mixing is to increase the power of each of the multiple angle-modulated light beams input into the nonlinear medium. However, there is generally a limit to the power of each frequency component that can be input into a nonlinear medium. For example, in DSF, the power of each frequency component that can be input is limited by stimulated Brillouin scattering. Therefore, the power of each angle-modulated light beam that can be input into DSF is limited, and this limit also limits the order of the angle-modulated light that can be generated by four-wave mixing in DSF.

[0008] The present disclosure provides techniques that allow for wider bandwidth of angle-modulated light. [Means for solving the problem]

[0009] According to one aspect of the present disclosure, an optical angle modulator includes a generating means for generating first angle-modulated light and second angle-modulated light by angle-modulating continuous light using an electrical signal, a first nonlinear medium for generating one or more third angle-modulated light having a wider bandwidth than the first angle-modulated light and the second angle-modulated light by four-wave mixing of the first angle-modulated light and the second angle-modulated light, and a first processing means, wherein the first processing means includes an adjusting means for individually adjusting the phase of each of the three or more angle-modulated light included in the light input to the first processing means, and a second nonlinear medium for generating one or more fourth angle-modulated light having a wider bandwidth than the three or more angle-modulated light by four-wave mixing of the three or more angle-modulated light after phase adjustment by the adjusting means, and light including the first angle-modulated light, the second angle-modulated light, and the one or more third angle-modulated light is input to the first processing means. [Effects of the Invention]

[0010] According to the present disclosure, wider bandwidth of angle-modulated light can be achieved. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram of the background art. [Figure 2] FIG. 1 is a configuration diagram of an optical angle modulator according to an embodiment. [Figure 3] FIG. 2 is a diagram illustrating the configuration of a generation unit according to an embodiment. [Figure 4] FIG. 2 is a diagram illustrating the configuration of a generation unit according to an embodiment. [Figure 5] 4A and 4B are diagrams illustrating angle-modulated light generated by a generating unit according to an embodiment. [Figure 6] FIG. 1 is a configuration diagram of an optical angle modulator according to an embodiment. [Figure 7] 10 is a flowchart of an adjustment process according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more features among the multiple features described in the embodiments may be arbitrarily combined. Furthermore, the same reference numerals are used for the same or similar components, and redundant explanations will be omitted.

[0013] First Embodiment 2 is a diagram showing the configuration of an optical angle modulator according to this embodiment. A generating unit 100 generates angle-modulated light 91 and angle-modulated light 92 shown in FIG. 1 based on an electrical signal and outputs them to a nonlinear medium 200. When the optical angle modulator is used in a communication device, the electrical signal corresponds to the information to be carried. When the optical angle modulator is used in a sensing device, the electrical signal is a signal whose amplitude changes over time, and the manner of this change is determined depending on the sensing target and method.

[0014] Although angle-modulated light 91 and angle-modulated light 92 are generated based on the same electrical signal, generation unit 100 generates angle-modulated light 91 and angle-modulated light 92 so that the electric field components of angle-modulated light 91 and angle-modulated light 92 are, for example, complex conjugates of each other. That is, for example, if angle-modulated light 91 is generated by advancing 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, angle-modulated light 92 is generated by advancing 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, 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. In the following description, the bandwidths of angle-modulated light 91 and angle-modulated light 92 are both designated B.

[0015] The nonlinear medium 200 generates four-wave mixing between the angle-modulated light 91 and the angle-modulated light 92. The nonlinear medium 200 can be configured, for example, by an optical fiber such as a dispersion-shifted fiber. Four-wave mixing occurs strongly when the frequency (wavelength) of light input to the optical fiber is close to the frequency (wavelength) at which the chromatic dispersion value of the optical fiber becomes zero. The nonlinear medium 200 can also be configured by a semiconductor optical amplifier. Four-wave mixing can be generated by the nonlinearity of the semiconductor optical amplifier. Alternatively, the nonlinear medium 200 can be realized by using any optical device that generates four-wave mixing.

[0016] As described above, the limit on the optical power that can be input to nonlinear medium 200 also limits the order of angle-modulated light generated by four-wave mixing of angle-modulated light 91 and angle-modulated light 92. In the following description, it is assumed that second- and third-order angle-modulated light 93-96 are generated by four-wave mixing in nonlinear medium 200, as shown in FIG. 1. Therefore, nonlinear medium 200 outputs light including angle-modulated light 91-96 to processing unit 300. As described above, angle-modulated light 93 and 94 have a bandwidth of 3B, and angle-modulated light 95 and 96 have a bandwidth of 5B.

[0017] The angle-modulated light 91-96 input to the processing unit 300 is input to the nonlinear medium 31 via the phase adjustment unit 30. The nonlinear medium 31 is similar to the nonlinear medium 200. The phase adjustment unit 30 is a device that can individually control the phase of each of the angle-modulated light 91-96. For example, the phase adjustment unit 30 can be realized using a liquid crystal-based device called LCoS (Liquid Crystal on Silicon). More specifically, the light input to the phase adjustment unit 30 is separated into frequency components. The light of each frequency component passes through a liquid crystal individually and then is combined. The phase of the light of each frequency component can be adjusted when passing through the liquid crystal. Note that the phase adjustment unit 30 is not limited to being a liquid crystal-based device, and any device that can individually control the amount of phase shift for each frequency component can be used.

[0018] The monitor and control unit 32 sets the phase shift amount to be applied to each of the angle-modulated light beams 91-96 by the phase adjustment unit 30 so that, due to four-wave mixing of the angle-modulated light beams 91-96 in the nonlinear medium 31, fourth-order or higher-order angle-modulated light beams are output from the nonlinear medium 31 in addition to the angle-modulated light beams 91-96. Note that, to suppress distortion of the angle-modulated light beams, the phase shift amount of each frequency component within the band of one angle-modulated light beam is set to be the same. In other words, the phase shift amount is set in units of angle-modulated light beams. Below, we will explain why adjusting the phase of each of the angle-modulated light beams 91-96 generates higher-order angle-modulated light beams in the nonlinear medium 31 without increasing the power of each of the angle-modulated light beams 91-96 input to the nonlinear medium 31.

[0019] It is known that in a signal containing various frequency components, the overlap of large amplitude portions of the signal of each frequency component results in a very large amplitude. Therefore, by adjusting the phase of each of the angle-modulated light beams 91-96, it is possible to increase the amplitude peak in the time domain of the light containing the angle-modulated light beams 91-96. In a nonlinear medium, this amplitude peak induces a nonlinear effect, so by adjusting the phase of each of the angle-modulated light beams 91-96, it is possible to generate higher-order angle-modulated light in the nonlinear medium 31.

[0020] Nonlinear medium 31 outputs fourth- or higher-order angle-modulated light generated in nonlinear medium 31 to filter 400, in addition to angle-modulated light 91-96. The bandwidth of fourth- or higher-order angle-modulated light is greater than 5B. For example, the bandwidth of fourth-order angle-modulated light is 7B, and the bandwidth of fifth-order angle-modulated light is 9B. More specifically, the bandwidth of n-th-order (n is an integer greater than or equal to 2) angle-modulated light is (2n-1)B. Filter 400 passes one angle-modulated light of the one or more angle-modulated light generated by nonlinear medium 31, i.e., one fourth- or higher-order angle-modulated light, and attenuates and blocks the remaining angle-modulated light. As a result, the optical angle modulator outputs angle-modulated light with a bandwidth greater than 5B, which is the maximum bandwidth of angle-modulated light output by nonlinear medium 200.

[0021] The monitor and control unit 32 performs an "adjustment process" to adjust and set the phase shift amounts of the angle-modulated light beams 91 to 96 so that fourth-order or higher-order angle-modulated light beams are output from the nonlinear medium 31. Note that during the adjustment process, the output of the nonlinear medium 31 is connected to the monitor and control unit 32, not the filter 400. In this embodiment, the monitor and control unit 32 first determines that six angle-modulated light beams 91 to 96 are being output from the nonlinear medium 200, based on the frequency components of the input light beams input from the nonlinear medium 31. Then, while varying the phase shift amounts of the six angle-modulated light beams 91 to 96 to various values, the monitor and control unit 32 determines the phase shift amounts of the angle-modulated light beams 91 to 96 such that the number of angle-modulated light beams included in the input light beam is greater than six or the number of angle-modulated light beams included in the input light beam is maximized. The monitor and control unit 32 then sets the determined phase shift amounts in the phase adjustment unit 30.

[0022] The monitoring and control unit 32 can also be configured to adjust the amount of phase shift for each of the angle-modulated light beams 91-96 so as to maximize the peak level (amplitude) of the light output from the phase adjustment unit 30. In this case, the monitoring and control unit 32 determines the amount of phase shift for each of the angle-modulated light beams 91-96 so as to maximize the peak level of the light output from the phase adjustment unit 30, that is, so as to maximize the peak power of the light, and sets the amount of phase shift for the phase adjustment unit 30. In this case, the output of the phase adjustment unit 300 is input to the monitoring and control unit 32 during the adjustment process.

[0023] When the adjustment process is completed, the monitor and control unit 32 controls the phase adjustment unit 30 so that the phase shift amount of each of the angle-modulated light 91 to 96 becomes the phase shift amount determined in the adjustment process. Furthermore, the output of the nonlinear medium 31 or the output of the phase adjustment unit 30 is connected to the filter 400 or the nonlinear medium 31. Note that, instead of switching the output destination of the output of the nonlinear medium 31 and / or the phase adjustment unit 30 during the adjustment process, a configuration may be adopted in which the output of the nonlinear medium 31 and / or the phase adjustment unit 30 is branched and a part of the output of the nonlinear medium 31 and / or the phase adjustment unit 30 is output to the monitor and control unit 32.

[0024] In this embodiment, it is assumed that angle-modulated light of up to third order is generated in the nonlinear medium 200. Therefore, the monitor and control unit 32 controls the phase adjustment unit 30 so that angle-modulated light of fourth order or higher is generated. However, this embodiment is not limited to the generation of angle-modulated light of up to third order in the nonlinear medium 200. Generally speaking, this embodiment can be applied when angle-modulated light of pth order (p is an integer equal to or greater than 2) is generated in the nonlinear medium 200. In this case, the monitor and control unit 32 controls the phase adjustment unit 30 so that angle-modulated light of (p+1)th order or higher is generated.

[0025] Furthermore, although this embodiment assumes that two angle-modulated light beams are generated for each of the second and higher orders, there is no problem even if only one angle-modulated light beam is generated for each of the second and higher orders. That is, this embodiment can be applied, for example, to a case where, in the nonlinear medium 200, second-order angle-modulated light 94 is generated but second-order angle-modulated light 93 is not generated, or where second-order angle-modulated light 94 and third-order angle-modulated light 96 are generated but second-order angle-modulated light 93 and third-order angle-modulated light 95 are not generated. In other words, it is sufficient that at least three angle-modulated light beams, namely, angle-modulated light 91, angle-modulated light 92, and at least one angle-modulated light generated by four-wave mixing of the angle-modulated light 91 and angle-modulated light 92, are input to the processing unit 300.

[0026] Next, a configuration example of the generation unit 100 will be described. Fig. 3 shows a configuration example of the generation unit 100. An electrical signal is input to the optical modulation unit 12 and also to the inversion unit 15. The inversion unit 15 inverts the amplitude of the electrical signal and outputs an inverted electrical signal to the optical modulation unit 13. The light source 10 generates continuous light of frequency f1, and the light source 11 generates continuous light of frequency f2.

[0027] The optical modulation unit 12 optically angle-modulates the continuous light having frequency f1 generated by the light source 10 using an electrical signal, and outputs angle-modulated light 91. Meanwhile, the optical modulation unit 13 optically angle-modulates the continuous light having frequency f2 generated by the light source 11 using an inverted electrical signal, and outputs angle-modulated light 92. Note that the optical modulation units 12 and 13 change the angle of the continuous light in the same direction (increase or decrease) depending on whether the amplitude of the electrical signal is positive or negative. In the example of FIG. 3, an electrical signal is input to the optical modulation unit 12, and an inverted electrical signal with the amplitude of the electrical signal inverted is input to the optical modulation unit 13. Therefore, the phase or frequency of the electric field component of the angle-modulated light 91 and the electric field component of the angle-modulated light 92 increase or decrease in opposite directions. Note that the inversion unit 15 may be omitted, and instead the direction (increase or decrease) of the angle of the continuous light depending on whether the amplitude of the electrical signal is positive or negative may be different between the optical modulation units 12 and 13.

[0028] Coupler 14 combines angle-modulated light 91 from optical modulation unit 12 and angle-modulated light 92 from optical modulation unit 13, and outputs signal light including angle-modulated light 91 with a center frequency of f1 and angle-modulated light 92 with a center frequency of f2.

[0029] The bandwidths of angle-modulated light 91 and angle-modulated light 92 depend on the modulation index of the optical angle modulation in optical modulation unit 12 and optical modulation unit 13. In this embodiment, the modulation indexes of optical modulation unit 12 and optical modulation unit 13 are the same, and therefore the bandwidths of angle-modulated light 91 and angle-modulated light 92 are the same. However, the bandwidths of angle-modulated light 91 and angle-modulated light 92 do not have to be the same. For example, if the bandwidth of angle-modulated light 91 is B1 and the bandwidth of angle-modulated light 92 is B2, the bandwidth of angle-modulated light 93 is 2B1+B2 and the bandwidth of angle-modulated light 94 is 2B2+B1; however, the bandwidth of the angle-modulated light generated by four-wave mixing remains larger than the bandwidth of the original angle-modulated light.

[0030] 4 shows another example of the configuration of the generator 100. The angle modulator 16 generates a frequency f CThe optical modulator 16 has an oscillator that generates a sine wave signal of frequency f3, and angle-modulates the sine wave signal with an electrical signal to output an angle-modulated signal. The light source 17 generates continuous light of frequency f3. The optical modulator 18 intensity-modulates (amplitude-modulates) the continuous light of frequency f3 with the angle-modulated signal from the angle modulator 16, and outputs intensity-modulated light.

[0031] 5 shows the intensity-modulated light output by the optical modulation unit 18. In FIG. 5, reference numeral 80 denotes an optical carrier component (carrier wave) of frequency f3. The optical intensity modulation generates an upper sideband and a lower sideband corresponding to the angle-modulated signal. The frequency difference between the center frequency of each of the upper sideband and the lower sideband and the optical carrier component 80 is f3, which is equal to the frequency of the sine wave signal. C Therefore, the center frequency f1 of the lower sideband is f3-f c The center frequency of the upper sideband, f2, is f3+f c In addition, the upper sideband and the lower sideband have a complex conjugate relationship. Therefore, the lower sideband corresponds to angle-modulated light 91, and the upper sideband corresponds to angle-modulated light 92.

[0032] Returning to Fig. 4, the band-stop filter (BSF) 19 attenuates and blocks the optical carrier component 80 of the intensity-modulated light output by the optical modulation unit 18. Therefore, the signal light output by the BSF 19 is similar to the signal light output by the coupler 14 in Fig. 3. Note that Figs. 3 and 4 show exemplary configurations of the generation unit 100, and the configuration of the generation unit 100 is not limited to those shown in Figs. 3 and 4.

[0033] Second Embodiment Next, the second embodiment will be described, focusing on the differences from the first embodiment. Fig. 6 is a configuration diagram of an optical angle modulator according to this embodiment. In this embodiment, N (N is an integer of 2 or more) processing units 300 are connected in series. Hereinafter, the N processing units 300 will be referred to as the first processing unit 300 to the Nth processing unit 300 in the order in which they are connected.

[0034] Three or more angle-modulated lights are input to the phase adjustment unit 30 of the k-th processing unit 300 (k is an integer from 1 to N). The phase adjustment unit 30 of the k-th processing unit 300 individually adjusts the phase of each of the three or more angle-modulated lights. In the nonlinear medium 31 of the k-th processing unit 300, one or more angle-modulated lights having a bandwidth larger than that of the three or more angle-modulated lights are generated by four-wave mixing of the three or more angle-modulated lights after phase adjustment by the phase adjustment unit 30 of the k-th processing unit 300.

[0035] As explained in the first embodiment, light including at least three angle-modulated light beams is input from the nonlinear medium 200 to the first processing unit 300. Light from the nonlinear medium 31 of the (n-1)th processing unit 300 is input to the nth processing unit 300 (n is an integer from 2 to N). The output of the nonlinear medium 31 of the Nth processing unit 300 is input to the filter 400. The filter 400 has a passband including the band of one of the angle-modulated light beams generated by four-wave mixing in the nonlinear medium 31 of the Nth processing unit 300, and passes that angle-modulated light beam while attenuating and blocking the remaining angle-modulated light beams.

[0036] As described above, angle-modulated light with a wider bandwidth can be generated by connecting a plurality of processing units 300 in series. In this embodiment, the adjustment process is performed individually in the order of the first processing unit 300 to the Nth processing unit 300.

[0037] Third Embodiment Next, the third embodiment will be described, focusing on differences from the first and second embodiments. In the first embodiment, the monitor and control unit 32 controls the phase adjustment unit 30 to vary the phase shift amounts of the six angle-modulated light beams 91 to 96 to determine the phase shift amounts of the six angle-modulated light beams 91 to 96. However, such a method requires a long time for the adjustment process. In this embodiment, a more efficient adjustment process will be described. Note that in this embodiment, the angle-modulated light beams 91 to 96 are also output from the nonlinear medium 200. In the following description, the monitor and control unit 32 determines the phase shift amounts of the angle-modulated light beams 91 to 96 while monitoring the light from the phase adjustment unit 30. However, the monitor and control unit 32 may be configured to determine the phase shift amounts of the angle-modulated light beams 91 to 96 while monitoring the light from the nonlinear medium 31.

[0038] In this embodiment, the phase adjustment unit 30 has a variable filter function. As described in the first embodiment, when a liquid crystal-based device called LCoS is used as the phase adjustment unit 30, light input to the phase adjustment unit 30 is separated into frequency components, and the light of each frequency component passes through the liquid crystal individually before being combined. Typically, such devices are configured to block light of specific frequency components using the liquid crystal. In other words, such devices also have a filter function that blocks any angle-modulated light. Note that the phase adjustment unit 30 is not limited to using a liquid crystal-based device, and can also be a combination of any filter that can change the passband and any device that can individually control the phase shift amount for each frequency component.

[0039] In the adjustment process of this embodiment, the monitor and control unit 32 first selects three of the six angle-modulated light beams 91 to 96 and controls the phase adjustment unit 30 so that only the selected three angle-modulated light beams pass through the phase adjustment unit 30. Hereinafter, it is assumed that angle-modulated light beams 95, 93, and 91 are selected. The monitor and control unit 32 determines the phase shift amounts of the angle-modulated light beams 95, 93, and 91 that maximize the level of the light output from the phase adjustment unit 30, and sets the phase shift amounts in the phase adjustment unit 30. Because the level of the light output from the phase adjustment unit 30 is based on the relative phase difference between the angle-modulated light beams 95, 93, and 91, the monitor and control unit 32 sets the phase shift amount of one of the three angle-modulated light beams 95, 93, and 91 to a predetermined value, for example, 0. Then, the monitor and control unit 32 varies the phase shift amounts of the remaining two angle-modulated light beams to various values, thereby determining the phase shift amounts of the angle-modulated light beams 95, 93, and 91 that maximize the level of the light output from the phase adjustment unit 30.

[0040] Next, the monitoring and control unit 32 selects three angle-modulated lights: two of the three angle-modulated lights 95, 93, and 91 selected previously, and one of the angle-modulated lights 92, 94, and 96 that was not previously selected, and controls the phase adjustment unit 30 so that only the three selected angle-modulated lights pass through the phase adjustment unit 30. Here, these three angle-modulated lights are referred to as angle-modulated lights 93, 91, and 92. Because the phase shift amounts of the angle-modulated lights 93 and 91 have already been determined, the monitoring and control unit 32 varies the phase shift amount of the added angle-modulated light 92 to various values, thereby determining the phase shift amount of the angle-modulated light 92 that maximizes the level of the light output by the phase adjustment unit 30.

[0041] Thereafter, the monitoring and control unit 32 controls the phase adjustment unit 30 so that only three angle-modulated light beams, two for which the phase shift amount has been determined and one for which the phase shift amount has not been determined, pass through the phase adjustment unit 30. This process is repeated until all angle-modulated light beams for which the phase shift amount has not been determined are eliminated. In the above example, in the repetitions after determining the phase shift amount of angle-modulated light 92, the monitoring and control unit 32 first determines the phase shift amount of angle-modulated light 94, and in the next repetition, determines the phase shift amount of angle-modulated light 96. This determines the phase shift amount for each of the angle-modulated light beams 91 to 96. The reason for repeating the process in units of three angle-modulated light beams is that at least three angle-modulated light beams are required to obtain an amplitude peak through phase control.

[0042] FIG. 7 is a flowchart of the adjustment process described above. In S10, monitor and control unit 32 selects three angle-modulated light beams as control-target angle-modulated light beams from the unprocessed angle-modulated light beams, which are angle-modulated light beams for which the phase shift amount has not yet been determined. The selection method is arbitrary. In S11, monitor and control unit 32 first controls phase adjustment unit 30 so that only the three control-target angle-modulated light beams are output from phase adjustment unit 30. In this state, monitor and control unit 32 determines the phase shift amount of the three control-target angle-modulated light beams based on the output of phase adjustment unit 30. As described above, monitor and control unit 32 determines the phase shift amount of one of the three control-target angle-modulated light beams to a predetermined value and sets it in phase adjustment unit 30. In this state, monitor and control unit 32 determines the phase shift amount of the remaining two control-target angle-modulated light beams by monitoring the output of phase adjustment unit 30 while varying the phase shift amount of the remaining two control-target angle-modulated light beams.

[0043] After the process of S11 is completed, in S12, the monitoring control unit 32 determines whether the number of unprocessed angle-modulated light beams is 0. If the number of unprocessed angle-modulated light beams is not 0, the monitoring control unit 32 repeats the processes of S13 and S14 until the number of unprocessed angle-modulated light beams becomes 0. On the other hand, if the number of unprocessed angle-modulated light beams is 0, the monitoring control unit 32 ends the adjustment process.

[0044] In S13, monitor and control unit 32 selects one angle-modulated light from the unprocessed angle-modulated light as angle-modulated light to be controlled. The selection method is arbitrary. In S14, monitor and control unit 32 first controls phase adjustment unit 30 so that only three angle-modulated light beams are output from phase adjustment unit 30: one angle-modulated light beam to be controlled and two angle-modulated light beams selected from processed angle-modulated light beams, which are angle-modulated light beams for which the phase shift amount has already been determined. Note that the selection method for the two angle-modulated light beams from the processed angle-modulated light beams is arbitrary. In this state, monitor and control unit 32 determines the phase shift amount of the one angle-modulated light beam to be controlled based on the output of phase adjustment unit 30.

[0045] As described above, in this embodiment, the number of angle-modulated light beams whose phases are controlled in the first repetition is two, and the number of angle-modulated light beams whose phases are controlled in the second and subsequent repetitions is one. Narrowing down the number of angle-modulated light beams whose phases are changed to find the phase shift amount that maximizes the light level can shorten the time required to find the optimal phase shift amount in each repetition, thereby shortening the time required for the adjustment process. In this embodiment, the number of angle-modulated light beams output from the nonlinear medium 200 is six, so the number of repetitions is four. Generally speaking, the number of repetitions is two less than the number of angle-modulated light beams input to the phase adjustment unit 30. In the configuration of the second embodiment, the adjustment process is performed individually in the order of the first processing unit 300 to the Nth processing unit 300.

[0046] The present disclosure also provides an optical transmitter having the optical angle modulator described in each of the above embodiments. The optical transmitter transmits angle-modulated light and can be used in the fields of, for example, communications and sensing.

[0047] The above configuration makes it possible to widen the bandwidth of angle-modulated light, thereby contributing to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0048] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention. [Explanation of symbols]

[0049] 100: Generator, 200, 31: Nonlinear medium, 30: Phase adjuster, 300: Processing unit

Claims

1. a generating means for generating first and second angle-modulated lights by angle-modulating continuous light using an electrical signal; a first nonlinear medium that generates one or more third angle-modulated lights having a bandwidth wider than that of the first angle-modulated light and the second angle-modulated light by four-wave mixing of the first angle-modulated light and the second angle-modulated light; a first processing means; Equipped with the first processing means includes an adjusting means for individually adjusting the phase of each of the three or more angle-modulated light beams included in the light input to the first processing means, and a second nonlinear medium for generating one or more fourth angle-modulated light beams having a bandwidth wider than that of the three or more angle-modulated light beams by four-wave mixing of the three or more angle-modulated light beams after the phase adjustment by the adjusting means; an optical angle modulator, wherein the first processing means receives light including the first angle-modulated light, the second angle-modulated light, and the one or more third angle-modulated light beams;

2. further comprising filter means connected to the output of said first processing means; 2. The optical angle modulator according to claim 1, wherein the passband of the filter means includes a band of one of the one or more fourth angle-modulated lights.

3. Further provided are second processing means to Nth processing means (N is an integer of 2 or more), Equipped with an nth processing means (n ​​is an integer from 2 to N) including an adjusting means for individually adjusting the phase of each of three or more angle-modulated lights included in the light input to the nth processing means; and a second nonlinear medium for generating one or more fourth angle-modulated lights having a bandwidth wider than that of the three or more angle-modulated lights included in the light input to the nth processing means by four-wave mixing of the three or more angle-modulated lights after phase adjustment by the adjusting means of the nth processing means; 2. The optical angle modulator according to claim 1, wherein the nth processing means receives light from the second nonlinear medium of the (n-1)th processing means.

4. further comprising filter means connected to the output of said N processing means; 4. The optical angle modulator according to claim 3, wherein the passband of the filter means includes a band of one fourth angle-modulated light of the one or more fourth angle-modulated lights generated by the second nonlinear medium of the Nth processing means.

5. a control unit for controlling the phase shift amount of each of the three or more angle-modulated beams in the adjustment unit, 2. The optical angle modulator according to claim 1, wherein the control means determines the amount of phase shift of each of the three or more angle-modulated lights in the adjustment means based on the output of the adjustment means or the second nonlinear medium.

6. 6. The optical angle modulator according to claim 5, wherein the control means monitors the number of angle-modulated lights contained in the output of the second nonlinear medium and determines the phase shift amount of each of the three or more angle-modulated lights so that the number of angle-modulated lights contained in the output of the second nonlinear medium is greater than the number of the three or more angle-modulated lights.

7. the adjusting means includes filter means for individually blocking each of the three or more angle-modulated lights from being output from the adjusting means; The control means performing a first process of selecting three angle-modulated light beams to be controlled from the three or more angle-modulated light beams, and determining phase shift amounts of the three angle-modulated light beams to be controlled based on the number of angle-modulated light beams included in the output of the second nonlinear medium in a state in which the filter means is controlled so that only the three angle-modulated light beams to be controlled are output from the adjustment means; 7. The optical angle modulator of claim 6, wherein, after the first processing, the filter means is controlled so that only two processed angle-modulated light beams selected from the processed angle-modulated light beams for which the phase shift amounts have been determined among the three or more angle-modulated light beams and one angle-modulated light beam to be controlled selected from the unprocessed angle-modulated light beams for which the phase shift amount has not yet been determined among the three or more angle-modulated light beams are output from the adjustment means, and a second processing step is performed to determine the phase shift amount of the one angle-modulated light beam to be controlled based on the number of angle-modulated light beams included in the output of the second nonlinear medium, and the second processing step is repeated until there is no more unprocessed angle-modulated light beam.

8. 8. The optical angle modulator according to claim 7, wherein in the first process, the control means determines the phase shift amount of one of the three angle-modulated light beams to be controlled to a predetermined value, and determines the phase shift amounts of the remaining two of the three angle-modulated light beams to be controlled based on the number of angle-modulated light beams included in the output of the second nonlinear medium.

9. 6. The optical angle modulator according to claim 5, wherein the control means monitors the level of the light output from the adjustment means and determines the amount of phase shift for each of the three or more angle-modulated lights so as to maximize the peak of the level.

10. the adjusting means includes filter means capable of individually blocking each of the three or more angle-modulated lights from being output from the adjusting means; The control means performing a first process of selecting three control-target angle-modulated light beams from the three or more angle-modulated light beams, controlling the filter means so that only the three control-target angle-modulated light beams are output from the adjustment means, and determining phase shift amounts of the three control-target angle-modulated light beams based on the levels of light output from the adjustment means; 10. The optical angle modulator of claim 9, wherein, after the first processing, the filter means is controlled so that only two processed angle-modulated light beams selected from processed angle-modulated light beams for which the phase shift amounts have been determined among the three or more angle-modulated light beams and one angle-modulated light beam to be controlled selected from unprocessed angle-modulated light beams for which the phase shift amount has not yet been determined among the three or more angle-modulated light beams are output from the adjustment means, and a second processing step is performed to determine the phase shift amount of the one angle-modulated light beam to be controlled based on the level of the light output from the adjustment means, and the second processing step is repeated until all of the unprocessed angle-modulated light beams are exhausted, thereby determining the phase shift amount of each of the three or more angle-modulated light beams.

11. 11. The optical angle modulator according to claim 10, wherein in the first process, the control means determines a phase shift amount of one of the three angle-modulated light beams to be controlled to a predetermined value, and determines phase shift amounts of the remaining two of the three angle-modulated light beams to be controlled based on the level of light output from the adjustment means.

12. The optical angle modulator according to claim 1 , wherein the first angle-modulated light and the second angle-modulated light have different directions of change in angle due to a change in the amplitude of the electrical signal.

13. An optical transmitter comprising the optical angle modulator according to any one of claims 1 to 12.

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