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JP7467398B2 - Optical modulator and optical transmitter - Google Patents

Optical modulator and optical transmitter Download PDF

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JP7467398B2
JP7467398B2 JP2021144925A JP2021144925A JP7467398B2 JP 7467398 B2 JP7467398 B2 JP 7467398B2 JP 2021144925 A JP2021144925 A JP 2021144925A JP 2021144925 A JP2021144925 A JP 2021144925A JP 7467398 B2 JP7467398 B2 JP 7467398B2
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JP2023038036A (en
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昇太 石村
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  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
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Description

本発明は、光変調技術に関する。 The present invention relates to optical modulation technology.

光変調器は、情報を搬送する電気信号に基づき連続光の振幅や、振幅及び位相の両方を変調することで変調光を生成する。ここで、光変調器の動作電力を低減させるためには光変調器に入力する電気信号の振幅レベルを小さくすれば良い。しかしながら、単に、電気信号の振幅レベルを小さくすると、変調光の振幅の変化量も小さくなり変調光の品質が劣化する。したがって、光変調器の動作電力を低減させるためには、所定の品質を満たすのに必要な変調光の振幅の変化量を維持しつつ、光変調器に入力する電気信号の振幅レベルを小さくする必要がある。 An optical modulator generates modulated light by modulating the amplitude or both the amplitude and phase of continuous light based on an electrical signal that carries information. Here, to reduce the operating power of an optical modulator, it is sufficient to reduce the amplitude level of the electrical signal input to the optical modulator. However, simply reducing the amplitude level of the electrical signal also reduces the amount of change in the amplitude of the modulated light, degrading the quality of the modulated light. Therefore, in order to reduce the operating power of an optical modulator, it is necessary to reduce the amplitude level of the electrical signal input to the optical modulator while maintaining the amount of change in the amplitude of the modulated light required to meet a specified quality.

非特許文献１及び非特許文献２は、いずれも光変調器に入力する電気信号の振幅レベルを小さくするための構成を開示している。 Both Non-Patent Document 1 and Non-Patent Document 2 disclose a configuration for reducing the amplitude level of an electrical signal input to an optical modulator.

Ｙｏｓｈｉｈｉｒｏ Ｏｇｉｓｏ，ｅｔ．ａｌ．，"８０－ＧＨｚ Ｂａｎｄｗｉｄｔｈ ａｎｄ １．５－Ｖ Ｖπ ＩｎＰ－Ｂａｓｅｄ ＩＱ Ｍｏｄｕｌａｔｏｒ"，Ｊ．Ｌｉｇｈｔｗａｖｅ Ｔｅｃｈｎｏｌ．３８，２４９－２５５ （２０２０）Yoshihiro Ogiso, et. al. , "80-GHz Bandwidth and 1.5-V Vπ InP-Based IQ Modulator", J. Lightwave Technol. 38, 249-255 (2020) Ｍ．Ｚｈａｎｇ，ｅｔ．ａｌ．，"Ｕｌｔｒａ－Ｈｉｇｈ Ｂａｎｄｗｉｄｔｈ Ｉｎｔｅｇｒａｔｅｄ Ｌｉｔｈｉｕｍ Ｎｉｏｂａｔｅ Ｍｏｄｕｌａｔｏｒｓ ｗｉｔｈ Ｒｅｃｏｒｄ－Ｌｏｗ Ｖπ"， ｉｎ Ｏｐｔｉｃａｌ Ｆｉｂｅｒ Ｃｏｍｍｕｎｉｃａｔｉｏｎ Ｃｏｎｆｅｒｅｎｃｅ Ｐｏｓｔｄｅａｄｌｉｎｅ Ｐａｐｅｒｓ，ＯＳＡ Ｔｅｃｈｎｉｃａｌ Ｄｉｇｅｓｔ （ｏｎｌｉｎｅ）（Ｏｐｔｉｃａｌ Ｓｏｃｉｅｔｙ ｏｆ Ａｍｅｒｉｃａ， ２０１８），ｐａｐｅｒ Ｔｈ４Ａ．５．M. Zhang, et al. al. , "Ultra-High Bandwidth Integrated Lithium Niobate Modulators with Record-Low Vπ", in Optical Fiber Communication Conference Postdeadline Papers, OSA Technical Digest (online) (Optical Society of America, 2018), paper Th4A. 5.

非特許文献１及び非特許文献２は、いずれも、特定の性質を有する材料を光変調器に使用し、当該特定の性質を利用して電気信号の振幅レベルを小さくするものである。しかしながら、特定の性質を有する材料に依存することなく、電気信号の振幅レベルを小さくすることが望まれている。 Both Non-Patent Document 1 and Non-Patent Document 2 use a material with specific properties in an optical modulator and utilize the specific properties to reduce the amplitude level of an electrical signal. However, it is desirable to reduce the amplitude level of an electrical signal without relying on a material with specific properties.

本発明は、光変調器に入力する必要がある電気信号の振幅レベルを小さくすることができる技術を提供するものである。 The present invention provides a technology that can reduce the amplitude level of the electrical signal that needs to be input to an optical modulator.

本発明の一態様によると、光変調器は、電気信号により連続光を位相変調した第１位相変調光、第２位相変調光、第３位相変調光及び第４位相変調光を生成する第１生成手段であって、前記電気信号の振幅による前記第１位相変調光と前記第２位相変調光の位相の変化方向は同じであり、前記電気信号の振幅による前記第３位相変調光と前記第４位相変調光の位相の変化方向は同じであり、前記電気信号の振幅による前記第１位相変調光と前記第３位相変調光の位相の変化方向は互いに逆方向である、前記第１生成手段と、前記第１位相変調光と前記第３位相変調光との一部縮退四光波混合により第５位相変調光を生成し、前記第２位相変調光と前記第４位相変調光との一部縮退四光波混合により第６位相変調光を生成し、前記第５位相変調光と前記第６位相変調光を合波する第２生成手段と、を備え、前記第５位相変調光の中心周波数及び帯域幅は、前記第６位相変調光の中心周波数及び帯域幅に等しいことを特徴とする。 According to one aspect of the present invention, the optical modulator includes a first generating means for generating first, second, third, and fourth phase modulated light obtained by phase-modulating continuous light using an electrical signal, the first generating means being configured to generate the first and second phase modulated light in the same phase change direction due to the amplitude of the electrical signal, the third and fourth phase modulated light in the same phase change direction due to the amplitude of the electrical signal, and the first and third phase modulated light in the opposite phase change directions due to the amplitude of the electrical signal, and a second generating means for generating a fifth phase modulated light by partial degenerate four-wave mixing of the first phase modulated light and the third phase modulated light, generating a sixth phase modulated light by partial degenerate four-wave mixing of the second phase modulated light and the fourth phase modulated light, and multiplexing the fifth and sixth phase modulated lights, the central frequency and bandwidth of the fifth phase modulated light being equal to the central frequency and bandwidth of the sixth phase modulated light.

本発明によると、光変調器に入力する必要がある電気信号の振幅レベルを小さくすることができる。 According to the present invention, it is possible to reduce the amplitude level of the electrical signal that needs to be input to the optical modulator.

一実施形態による光変調器の構成図。FIG. 1 is a configuration diagram of an optical modulator according to an embodiment. 一実施形態による光変調器の内部で生成される信号を示す図。FIG. 2 illustrates a signal generated within an optical modulator according to an embodiment. 一実施形態による光変調器の内部で生成される信号を示す図。FIG. 2 illustrates a signal generated within an optical modulator according to an embodiment. 一実施形態による光変調器の内部で生成される信号を示す図。FIG. 2 illustrates a signal generated within an optical modulator according to an embodiment. 振幅変調光が生成されることの説明図。FIG. 2 is a diagram illustrating generation of amplitude-modulated light. 一実施形態による光変調器の構成図。FIG. 1 is a configuration diagram of an optical modulator according to an embodiment. 一実施形態による光変調器の内部で生成される信号を示す図。FIG. 2 illustrates a signal generated within an optical modulator according to an embodiment. 一実施形態による光変調器の内部で生成される信号を示す図。2 illustrates a signal generated within an optical modulator according to one embodiment. 一実施形態による光変調器の内部で生成される信号を示す図。2 illustrates a signal generated within an optical modulator according to one embodiment. 一実施形態による光変調器の内部で生成される信号を示す図。FIG. 2 illustrates a signal generated within an optical modulator according to an embodiment.

以下、添付図面を参照して実施形態を詳しく説明する。なお、以下の実施形態は特許請求の範囲に係る発明を限定するものではなく、また実施形態で説明されている特徴の組み合わせの全てが発明に必須のものとは限らない。実施形態で説明されている複数の特徴のうちの二つ以上の特徴が任意に組み合わされてもよい。また、同一若しくは同様の構成には同一の参照番号を付し、重複した説明は省略する。 The following embodiments are described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. In addition, the same reference numbers are used for the same or similar configurations, and duplicate descriptions are omitted.

＜第一実施形態＞
図１は、本実施形態による光変調器の構成図である。光変調器は、第１生成部１００と、第２生成部２００と、を有する。まず、第１生成部１００について説明する。光源１１は、周波数ｆ１の連続光を生成し、生成した連続光を２×２カップラ２０に出力する。光源１２は、周波数ｆ２の連続光を生成し、生成した連続光を２×２カップラ２０に出力する。なお、本実施形態では、周波数ｆ２が周波数ｆ１より高く、周波数ｆ２と周波数ｆ１との周波数差をＸとする。２×２カップラ２０は、周波数ｆ１の連続光を位相変調部３１及び３２に出力し、かつ、周波数ｆ２の連続光を位相変調部３１及び３２に出力する。つまり、位相変調部３１及び３２それぞれには、周波数ｆ１の連続光及び周波数ｆ２の連続光が入力される。 First Embodiment
FIG. 1 is a configuration diagram of an optical modulator according to this embodiment. The optical modulator includes a first generating section 100 and a second generating section 200. First, the first generating section 100 will be described. The light source 11 generates continuous light of frequency f 1 and outputs the generated continuous light to the 2×2 coupler 20. The light source 12 generates continuous light of frequency f 2 and outputs the generated continuous light to the 2×2 coupler 20. In this embodiment, the frequency f 2 is higher than the frequency f 1 , and the frequency difference between the frequency f 2 and the frequency f 1 is X. The 2×2 coupler 20 outputs the continuous light of frequency f 1 to the phase modulation sections 31 and 32, and outputs the continuous light of frequency f 2 to the phase modulation sections 31 and 32. That is, the continuous light of frequency f 1 and the continuous light of frequency f 2 are input to the phase modulation sections 31 and 32, respectively.

位相変調部３１は、情報を搬送する電気信号により周波数ｆ１の連続光及び周波数ｆ２の連続光の位相変調を行う。図２（Ａ）は、位相変調部３１が出力する信号光の周波数成分を示している。位相変調光９１は、周波数ｆ１の連続光を電気信号により位相変調したものであり、位相変調光９２は、周波数ｆ２の連続光を電気信号により位相変調したものである。なお、位相変調光９１の電界成分Ｅ１及び位相変調光９２の電界成分Ｅ２は、それぞれ、 The phase modulation unit 31 performs phase modulation on continuous light of frequency f1 and continuous light of frequency f2 using an electrical signal carrying information. FIG. 2A shows the frequency components of the signal light output by the phase modulation unit 31. Phase-modulated light 91 is continuous light of frequency f1 phase-modulated using an electrical signal, and phase-modulated light 92 is continuous light of frequency f2 phase-modulated using an electrical signal. Note that the electric field component E1 of the phase-modulated light 91 and the electric field component E2 of the phase-modulated light 92 are respectively

で表される。ここで、ω１＝２πｆ１であり、ω２＝２πｆ２であり、Ｓ（ｔ）は位相変化量である。位相変調光９１及び位相変調光９２の帯域幅は、位相変化量Ｓ（ｔ）の最大値に依存し、ここでは、位相変調光９１及び位相変調光９２の帯域幅をＢ１としている。 Here, ω1 = 2πf1 , ω2 = 2πf2 , and S(t) is the amount of phase change. The bandwidth of phase-modulated light 91 and phase-modulated light 92 depends on the maximum value of the amount of phase change S(t), and here, the bandwidth of phase-modulated light 91 and phase-modulated light 92 is represented as B1 .

位相変調部３２は、位相変調部３１に入力される電気信号の振幅を反転させた反転電気信号により周波数ｆ１の連続光及び周波数ｆ２の連続光の位相変調を行う。図２（Ｂ）は、位相変調部３２が出力する信号光の周波数成分を示している。位相変調光９３は、周波数ｆ１の連続光を反転電気信号により位相変調したものであり、位相変調光９４は、周波数ｆ２の連続光を反転電気信号により位相変調したものである。位相変調部３２は、反転電気信号で位相変調を行うため、位相変調光９３及び位相変調光９４の位相変化の方向と、位相変調光９１及び位相変調光９２の位相変化の方向とは、互いに逆方向となる。したがって、位相変調光９３の電界成分Ｅ３及び位相変調光９４の電界成分Ｅ４は、それぞれ、 The phase modulation unit 32 performs phase modulation of the continuous light of frequency f1 and the continuous light of frequency f2 by an inversion electrical signal obtained by inverting the amplitude of the electrical signal input to the phase modulation unit 31. FIG. 2B shows the frequency components of the signal light output by the phase modulation unit 32. The phase-modulated light 93 is obtained by phase-modulating the continuous light of frequency f1 by the inversion electrical signal, and the phase-modulated light 94 is obtained by phase-modulating the continuous light of frequency f2 by the inversion electrical signal. Since the phase modulation unit 32 performs phase modulation by the inversion electrical signal, the phase change directions of the phase-modulated light 93 and the phase-modulated light 94 are opposite to each other, and the phase change directions of the phase-modulated light 91 and the phase-modulated light 92 are opposite to each other. Therefore, the electric field component E3 of the phase-modulated light 93 and the electric field component E4 of the phase-modulated light 94 are respectively:

となる。なお、位相変調光９３及び位相変調光９４の帯域幅は、位相変調光９１及び位相変調光９２の帯域幅と同じＢ１である。 The bandwidth of the phase-modulated light 93 and the phase-modulated light 94 is the same as the bandwidth of the phase-modulated light 91 and the phase-modulated light 92, that is, B1 .

なお、本実施形態では、位相変調部３１が入力信号の振幅に応じて連続光の位相を変化（増減）させる方向と、位相変調部３２が入力信号の振幅に応じて連続光の位相を変化（増減）させる方向とが同じであるものとし、よって、位相変調部３２には電気信号の振幅レベルを反転させた反転電気信号を入力していた。しかしながら、位相変調部３１が出力する位相変調光の位相の変化方向と、位相変調部３２が出力する位相変調光の位相の変化方向が異なれば良く、位相変調部３２に電気信号を入力する構成とすることもできる。例えば、位相変調部３２に電気信号の振幅（正負）を反転させる回路を設ける構成とすることもできる。 In this embodiment, the direction in which the phase modulation unit 31 changes (increases or decreases) the phase of the continuous light according to the amplitude of the input signal is the same as the direction in which the phase modulation unit 32 changes (increases or decreases) the phase of the continuous light according to the amplitude of the input signal, and therefore an inverted electrical signal with the amplitude level of the electrical signal inverted is input to the phase modulation unit 32. However, as long as the direction of change in the phase of the phase-modulated light output by the phase modulation unit 31 and the direction of change in the phase of the phase-modulated light output by the phase modulation unit 32 are different, an electrical signal can also be input to the phase modulation unit 32. For example, the phase modulation unit 32 can be configured to have a circuit that inverts the amplitude (positive or negative) of the electrical signal.

分離部４１は、位相変調部３１からの信号光の波長分離を行い、位相変調光９１を合波部５１に出力し、位相変調光９２を合波部５２に出力する。分離部４２は、位相変調部３２からの信号光の波長分離を行い、位相変調光９３を合波部５２に出力し、位相変調光９４を合波部５１に出力する。合波部５１は、位相変調光９１及び位相変調光９４を含む信号光を、第２生成部２００の四光波混合（ＦＷＭ）部６１に出力し、合波部５２は、位相変調光９３及び位相変調光９２を含む信号光を、第２生成部２００のＦＷＭ部６２に出力する。図３（Ａ）は、ＦＷＭ部６１に入力される信号光を示し、図３（Ｂ）は、ＦＷＭ部６２に入力される信号光を示している。 The separation unit 41 separates the wavelengths of the signal light from the phase modulation unit 31, outputs the phase-modulated light 91 to the multiplexing unit 51, and outputs the phase-modulated light 92 to the multiplexing unit 52. The separation unit 42 separates the wavelengths of the signal light from the phase modulation unit 32, outputs the phase-modulated light 93 to the multiplexing unit 52, and outputs the phase-modulated light 94 to the multiplexing unit 51. The multiplexing unit 51 outputs the signal light including the phase-modulated light 91 and the phase-modulated light 94 to the four-wave mixing (FWM) unit 61 of the second generation unit 200, and the multiplexing unit 52 outputs the signal light including the phase-modulated light 93 and the phase-modulated light 92 to the FWM unit 62 of the second generation unit 200. FIG. 3(A) shows the signal light input to the FWM unit 61, and FIG. 3(B) shows the signal light input to the FWM unit 62.

ＦＷＭ部６１は、位相変調光９１と、位相変調光９４との一部縮退四光波混合を生じさせる。一部縮退四光波混合とは、四光波混合の一態様であり、周波数ｆｘ及び周波数ｆｙの２つの光から、周波数２ｆｘ－ｆｙ（又は、２ｆｙ－ｆｘ）の新たな光が発生する現象を意味する。周波数ｆｘの光の電界成分をＥｘとし、周波数ｆｙの光の電界成分をＥｙとすると、一部縮退四光波混合により生じる周波数２ｆｘ－ｆｙの光の電界成分は、ＥｘＥｘＥ* ｙとなる。なお、Ｅ* ｙは、Ｅｙの複素共役である。同様に、一部縮退四光波混合により生じる周波数２ｆｙ－ｆｘの光の電界成分は、ＥｙＥｙＥ* ｘとなる。 The FWM unit 61 generates partially degenerate four-wave mixing of the phase-modulated light 91 and the phase-modulated light 94. Partially degenerate four - wave mixing is one aspect of four-wave mixing, and refers to a phenomenon in which new light of frequency 2f x -f y (or 2f y -f x ) is generated from two lights of frequency f x and frequency f y. If the electric field component of the light of frequency f x is E x and the electric field component of the light of frequency f y is E y , the electric field component of the light of frequency 2f x -f y generated by partially degenerate four-wave mixing is E x E x E * y . Note that E * y is the complex conjugate of E y . Similarly, the electric field component of the light of frequency 2f y -f x generated by partially degenerate four-wave mixing is E y E y E * x .

したがって、ＦＷＭ部６１における一部縮退四光波混合により、図４（Ａ）に示す、中心周波数が２ｆ１－ｆ２の位相変調光９５と、中心周波数が２ｆ２－ｆ１の位相変調光９６が生成される。ここで、位相変調光９５の電界成分Ｅ５及び位相変調光９６の電界成分Ｅ６は、それぞれ、 4A, phase-modulated light 95 having a center frequency of 2f 1 -f 2 and phase-modulated light 96 having a center frequency of 2f 2 -f 1 are generated by partially degenerate four-wave mixing in the FWM unit 61. Here, the electric field component E5 of the phase-modulated light 95 and the electric field component E6 of the phase-modulated light 96 are respectively expressed as follows:

となる。式（５）及び式（６）より、位相変調光９５の電界成分Ｅ５及び位相変調光９６の電界成分Ｅ６は、それぞれ、位相変調光９１と位相変調光９４の帯域幅の３倍、つまり、３Ｂ１になる。 From equations (5) and (6), the electric field component E5 of phase-modulated light 95 and the electric field component E6 of phase-modulated light 96 are three times the bandwidths of phase-modulated light 91 and phase-modulated light 94, respectively, that is, 3B1 .

同様に、ＦＷＭ部６２における一部縮退四光波混合により、図４（Ｂ）に示す、中心周波数が２ｆ１－ｆ２の位相変調光９７と、中心周波数が２ｆ２－ｆ１の位相変調光９８が生成される。ここで、位相変調光９７の電界成分Ｅ７及び位相変調光９８の電界成分Ｅ８は、それぞれ、 Similarly, partially degenerate four-wave mixing in the FWM unit 62 generates phase-modulated light 97 having a center frequency of 2f 1 -f 2 and phase-modulated light 98 having a center frequency of 2f 2 -f 1 , as shown in FIG. 4B. Here, the electric field component E 7 of the phase-modulated light 97 and the electric field component E 8 of the phase-modulated light 98 are respectively expressed as follows:

となる。式（７）及び式（８）より、位相変調光９７の電界成分Ｅ７及び位相変調光９８の電界成分Ｅ８は、それぞれ、位相変調光９３と位相変調光９２の帯域幅の３倍、つまり、３Ｂ１になる。 From equations (7) and (8), the electric field component E7 of phase-modulated light 97 and the electric field component E8 of phase-modulated light 98 are three times the bandwidths of phase-modulated light 93 and phase-modulated light 92, respectively, that is, 3B1 .

合波部７０は、図４（Ａ）に示すＦＷＭ部６１からの信号光と、図４（Ｂ）に示すＦＷＭ部６２からの信号光と、を合波して出力する。位相変調光９５と位相変調光９７の周波数帯域は等しいため、位相変調光９５と位相変調光９７が合波されるが、式（５）及び式（７）から明らかな様に、位相変調光９５と位相変調光９７の位相変化量の絶対値は等しく、その方向（正負）のみが異なる。したがって、位相変調光９５と位相変調光９７を合波することで得られる信号光は、振幅のみが変化する振幅変調光となる。この様子を図５に示す。図５から明らかな様に、位相変調光９５と位相変調光９７を合波することで得られる信号光は、位相変化量Ｓ（ｔ）の値に拘わらず、その位相は、基準位相（図５のベクトル９９の位相）で一定であり、位相変化量Ｓ（ｔ）の値に応じて振幅のみが異なる振幅変調光９９となる。位相変調光９６と位相変調光９８とを合波して得られる信号光も同様に振幅変調光となる。 The multiplexing unit 70 multiplexes the signal light from the FWM unit 61 shown in FIG. 4A and the signal light from the FWM unit 62 shown in FIG. 4B, and outputs the multiplexed signal. Since the frequency bands of the phase-modulated light 95 and the phase-modulated light 97 are equal, the phase-modulated light 95 and the phase-modulated light 97 are multiplexed. As is clear from equations (5) and (7), the absolute values of the phase changes of the phase-modulated light 95 and the phase-modulated light 97 are equal, and only the directions (positive and negative) are different. Therefore, the signal light obtained by multiplexing the phase-modulated light 95 and the phase-modulated light 97 becomes amplitude-modulated light in which only the amplitude changes. This is shown in FIG. 5. As is clear from FIG. 5, the signal light obtained by multiplexing the phase-modulated light 95 and the phase-modulated light 97 becomes amplitude-modulated light 99 in which the phase is constant at the reference phase (the phase of the vector 99 in FIG. 5) regardless of the value of the phase change amount S(t), and only the amplitude changes depending on the value of the phase change amount S(t). The signal light obtained by combining the phase-modulated light 96 and the phase-modulated light 98 is also amplitude-modulated light.

フィルタ部８０は、位相変調光９５と位相変調光９７の合波により得られる振幅変調光又は位相変調光９６と位相変調光９８の合波により得られる振幅変調光を通過させ、残りの変調光を抑圧することで振幅変調光を出力する。 The filter unit 80 passes the amplitude modulated light obtained by combining the phase modulated light 95 and the phase modulated light 97, or the amplitude modulated light obtained by combining the phase modulated light 96 and the phase modulated light 98, and outputs the amplitude modulated light by suppressing the remaining modulated light.

例えば、通常の振幅変調においては、図２に示す位相変調光９１と位相変調光９３を合波することで振幅変調光を生成する。一方、本実施形態では、一部縮退四光波混合により位相変調光の位相変化量（帯域幅）を３倍にした後に合波する。２つの位相変調光を合波して得られる振幅変調光の振幅の変化量は、位相変調光の位相変化量が大きい程、大きくなる。したがって、電気信号の振幅レベルが同じであっても、位相変調光９１と位相変調光９３を合波することで振幅変調光を生成する場合と比較して、生成される振幅変調光の振幅の変化量は大きくなる。 For example, in normal amplitude modulation, the amplitude-modulated light is generated by multiplexing the phase-modulated light 91 and phase-modulated light 93 shown in FIG. 2. On the other hand, in this embodiment, the phase change amount (bandwidth) of the phase-modulated light is tripled by partially degenerate four-wave mixing before being multiplexed. The amount of change in the amplitude of the amplitude-modulated light obtained by multiplexing two phase-modulated lights increases as the amount of phase change in the phase-modulated light increases. Therefore, even if the amplitude level of the electrical signal is the same, the amount of change in the amplitude of the generated amplitude-modulated light is larger than when the amplitude-modulated light is generated by multiplexing the phase-modulated light 91 and phase-modulated light 93.

ＦＷＭ部６１及び６２は、例えば、分散シフトファイバ等の光ファイバにより構成することができる。四光波混合は、光ファイバに入力される光の周波数（波長）が、当該光ファイバの波長分散値が零となる周波数（波長）に近い場合に強く発生する。例えば、ＦＷＭ部６１の場合、位相変調光９１の周波数における光ファイバの波長分散値が零近傍である場合、周波数２ｆ１－ｆ２の位相変調光９５が強く生じる。 The FWM units 61 and 62 can be composed of optical fibers such as dispersion shifted fibers. 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 is zero. For example, in the case of the FWM unit 61, when the chromatic dispersion value of the optical fiber at the frequency of the phase-modulated light 91 is close to zero, phase-modulated light 95 with a frequency of 2f 1 -f 2 is strongly generated.

したがって、光ファイバの分散が０となる周波数（波長）が位相変調光９１の帯域内、位相変調光９４の帯域内、或いは、位相変調光９１と位相変調光９４との間の帯域内に位置する様に周波数ｆ１及び周波数ｆ２を決定することで、位相変調光９５～９８を効率的に生成することができる。例えば、位相変調光９５と位相変調光９７の合波により得られる振幅変調光を出力する場合、ＦＷＭ部６１及びＦＷＭ部６２の光ファイバの分散が０となる周波数（波長）が位相変調光９１及び９３の帯域内となる様に周波数ｆ１及び周波数ｆ２を決定することで、位相変調光９５と位相変調光９７を効率的に生成することができる。また、例えば、位相変調光９６と位相変調光９８の合波により得られる振幅変調光を出力する場合、ＦＷＭ部６１及びＦＷＭ部６２の光ファイバの分散が０となる周波数（波長）が位相変調光９４及び９８の帯域内となる様に周波数ｆ１及び周波数ｆ２を決定することで、位相変調光９６と位相変調光９８を効率的に生成することができる。 Therefore, by determining the frequency f1 and the frequency f2 so that the frequency (wavelength) at which the dispersion of the optical fiber becomes zero is located within the band of the phase-modulated light 91, within the band of the phase-modulated light 94 , or within the band between the phase-modulated light 91 and the phase-modulated light 94 , it is possible to efficiently generate the phase-modulated light 95 to 98. For example, when outputting the amplitude-modulated light obtained by multiplexing the phase-modulated light 95 and the phase-modulated light 97, by determining the frequency f1 and the frequency f2 so that the frequency (wavelength) at which the dispersion of the optical fiber of the FWM unit 61 and the FWM unit 62 becomes zero is located within the bands of the phase-modulated light 91 and 93, it is possible to efficiently generate the phase-modulated light 95 and the phase-modulated light 97. Furthermore, for example, when outputting amplitude-modulated light obtained by multiplexing phase-modulated light 96 and phase-modulated light 98, by determining frequencies f1 and f2 so that the frequencies (wavelengths) at which the dispersion of the optical fibers of FWM unit 61 and FWM unit 62 becomes zero are within the bands of phase-modulated light 94 and 98, phase-modulated light 96 and phase-modulated light 98 can be generated efficiently.

なお、光ファイバの分散が０となる周波数が位相変調光９１の帯域より低くても、位相変調光９４の帯域より高くても一部縮退四光波混合は生じるため、光ファイバの分散が０となる周波数は上述したものに限定されない。 Note that even if the frequency at which the dispersion of the optical fiber becomes zero is lower than the band of the phase-modulated light 91 or higher than the band of the phase-modulated light 94, some degenerate four-wave mixing will occur, so the frequency at which the dispersion of the optical fiber becomes zero is not limited to the above.

また、ＦＷＭ部６１及び６２は、半導体光増幅器で構成することができる。半導体光増幅器の非線形性により、四光波混合を生じさせることができる。 FWM units 61 and 62 can be configured with semiconductor optical amplifiers. The nonlinearity of semiconductor optical amplifiers can cause four-wave mixing.

なお、位相変調光９５及び位相変調光９６が位相変調光９１及び９４と干渉しない様にするには、図４から明らかな様に、Ｘ＞２Ｂ１とする。 In order to prevent the phase-modulated light 95 and the phase-modulated light 96 from interfering with the phase -modulated light 91 and 94, as is clear from FIG.

以上の構成により、振幅変調光の振幅の変化量を維持しながら、入力する電気信号の振幅レベルを小さくすることができる。なお、図１の構成では、フィルタ部８０を合波部７０の下流側に設けていたが、フィルタ部８０を合波部７０の上流側に設ける構成とすることもできる。 The above configuration makes it possible to reduce the amplitude level of the input electrical signal while maintaining the amount of change in the amplitude of the amplitude-modulated light. In the configuration of FIG. 1, the filter unit 80 is provided downstream of the multiplexing unit 70, but the filter unit 80 can also be provided upstream of the multiplexing unit 70.

＜第二実施形態＞
続いて、第二実施形態について第一実施形態との相違点を中心に説明する。第一実施形態の構成において光変調器は、２つのＦＷＭ部を必要としていた。本実施形態では、光変調器に必要なＦＷＭ部の数を１つにする。 Second Embodiment
Next, the second embodiment will be described, focusing on the differences from the first embodiment. In the configuration of the first embodiment, the optical modulator requires two FWM units. In this embodiment, the number of FWM units required for the optical modulator is reduced to one.

図６は、本実施形態による光変調器の構成図である。第１生成部１００のコム光源１０は、図７（Ａ）に示す５つの連続光８１～８５を含む複数の連続光を生成する。複数の連続光の周波数の間隔はＸである。なお、連続光８１～８５の周波数をそれぞれ周波数ｆ１～ｆ５とする。分離部４０は、連続光８１及び８４を位相変調部３１に出力し、連続光８２及び８５を位相変調部３２に出力する。図７（Ｂ）及び図７（Ｃ）は、それぞれ、位相変調部３１及び位相変調部３２に入力される連続光を示している。 FIG. 6 is a configuration diagram of an optical modulator according to this embodiment. The comb light source 10 of the first generating unit 100 generates a plurality of continuous light beams including five continuous light beams 81 to 85 shown in FIG. 7A. The frequency interval between the plurality of continuous light beams is X. The frequencies of the continuous light beams 81 to 85 are f 1 to f 5 , respectively. The separating unit 40 outputs the continuous light beams 81 and 84 to the phase modulating unit 31, and outputs the continuous light beams 82 and 85 to the phase modulating unit 32. FIG. 7B and FIG. 7C show the continuous light beams input to the phase modulating unit 31 and the phase modulating unit 32, respectively.

第一実施形態と同様に、位相変調部３１は電気信号で連続光８１及び８４を位相変調し、位相変調部３２は反転電気信号で連続光８２及び８５を位相変調する。図８（Ａ）は、位相変調部３１が出力する信号光の周波数成分を示している。位相変調光７１は、周波数ｆ１の連続光を電気信号により位相変調したものであり、位相変調光７２は、周波数ｆ４の連続光を電気信号により位相変調したものである。なお、位相変調光７１の電界成分Ｅ１及び位相変調光７２の電界成分Ｅ２は、それぞれ、 As in the first embodiment, the phase modulation unit 31 phase-modulates the continuous light beams 81 and 84 with an electrical signal, and the phase modulation unit 32 phase-modulates the continuous light beams 82 and 85 with an inverted electrical signal. Fig. 8(A) shows the frequency components of the signal light output by the phase modulation unit 31. The phase-modulated light 71 is obtained by phase-modulating continuous light of frequency f1 with an electrical signal, and the phase-modulated light 72 is obtained by phase-modulating continuous light of frequency f4 with an electrical signal. Note that the electric field component E1 of the phase-modulated light 71 and the electric field component E2 of the phase-modulated light 72 are, respectively,

で表される。ここで、ω１＝２πｆ１であり、ω４＝２πｆ４であり、Ｓ（ｔ）は位相変化量である。 Here, ω 1 =2πf 1 , ω 4 =2πf 4 , and S(t) is the amount of phase change.

図８（Ｂ）は、位相変調部３２が出力する信号光の周波数成分を示している。位相変調光７３は、周波数ｆ２の連続光を反転電気信号により位相変調したものであり、位相変調光７４は、周波数ｆ５の連続光を反転電気信号により位相変調したものである。なお、位相変調光７３の電界成分Ｅ３及び位相変調光７４の電界成分Ｅ４は、それぞれ、 8B shows the frequency components of the signal light output by the phase modulation unit 32. Phase-modulated light 73 is obtained by phase-modulating continuous light of frequency f2 with an inverted electrical signal, and phase-modulated light 74 is obtained by phase-modulating continuous light of frequency f5 with an inverted electrical signal. Note that the electric field component E3 of the phase-modulated light 73 and the electric field component E4 of the phase-modulated light 74 are respectively

で表される。ここで、ω２＝２πｆ２であり、ω５＝２πｆ５である。 Here, ω 2 =2πf 2 and ω 5 =2πf 5 .

合波部７０は、位相変調部３１からの信号光と位相変調部３２からの信号光を合波して得られた信号光を第２生成部２００のＦＷＭ部６０に出力する。図９は、ＦＷＭ部６０に入力される信号光を示している。ＦＷＭ部６０は、入力される信号光の一部縮退四光波混合を生じさせる。図１０（Ａ）は、位相変調光７１と位相変調光７３との一部縮退四光波混合により生じる周波数ｆ３＝２ｆ２－ｆ１の位相変調光７５を示している。また、図１０（Ｂ）は、位相変調光７２と位相変調光７４との一部縮退四光波混合により生じる周波数ｆ３＝２ｆ４－ｆ５の位相変調光７６を示している。ここで、位相変調光７５の電界成分Ｅ５及び位相変調光７６の電界成分Ｅ６は、それぞれ、 The multiplexing unit 70 outputs the signal light obtained by multiplexing the signal light from the phase modulation unit 31 and the signal light from the phase modulation unit 32 to the FWM unit 60 of the second generation unit 200. FIG. 9 shows the signal light input to the FWM unit 60. The FWM unit 60 generates partial degenerate four-wave mixing of the input signal light. FIG. 10A shows phase-modulated light 75 with a frequency f 3 =2f 2 -f 1 generated by partial degenerate four-wave mixing of the phase-modulated light 71 and the phase-modulated light 73. FIG. 10B shows phase-modulated light 76 with a frequency f 3 =2f 4 -f 5 generated by partial degenerate four-wave mixing of the phase-modulated light 72 and the phase-modulated light 74. Here, the electric field component E 5 of the phase-modulated light 75 and the electric field component E 6 of the phase-modulated light 76 are respectively:

となる。位相変調光７５及び位相変調光７６の中心周波数及び周波数帯域は同じであるため、ＦＷＭ部６０での一部縮退四光波混合により位相変調光７５及び位相変調光７６を合波した信号光が生じる。式（１３）及び式（１４）から明らかな様に、この信号光は、振幅変調光となる。 Since the phase-modulated light 75 and the phase-modulated light 76 have the same center frequency and frequency band, a signal light is generated by multiplexing the phase-modulated light 75 and the phase-modulated light 76 by partially degenerate four-wave mixing in the FWM unit 60. As is clear from equations (13) and (14), this signal light becomes amplitude-modulated light.

本実施形態においてもＸ＞２Ｂ１とする。なお、ＦＷＭ部６０に分散シフトファイバを使用する場合、例えば、光ファイバの分散が０となる周波数（波長）を周波数ｆ３とすることができる。 In this embodiment as well, X> 2B1 . When a dispersion shifted fiber is used in the FWM unit 60, for example, the frequency (wavelength) at which the dispersion of the optical fiber becomes 0 can be set to frequency f3 .

＜まとめ＞
上記各実施形態で説明した様に、第１生成部１００は、情報を搬送する電気信号に基づき連続光を位相変調することで、第１位相変調光、第２位相変調光、第３位相変調光及び第４位相変調光の４つの位相変調光を生成する。ここで、電気信号の振幅による第１位相変調光と第２位相変調光の位相の変化方向は同じであり、電気信号の振幅による第３位相変調光と第４位相変調光の位相の変化方向は同じであるが、電気信号の振幅による第１位相変調光と第３位相変調光の位相の変化方向は互いに逆方向である。 <Summary>
As described in each of the above embodiments, the first generating unit 100 generates four phase-modulated lights, namely, the first phase-modulated light, the second phase-modulated light, the third phase-modulated light, and the fourth phase-modulated light, by phase-modulating the continuous light based on the electrical signal carrying information. Here, the first phase-modulated light and the second phase-modulated light change in the same direction due to the amplitude of the electrical signal, and the third phase-modulated light and the fourth phase-modulated light change in the same direction due to the amplitude of the electrical signal, but the first phase-modulated light and the third phase-modulated light change in opposite directions due to the amplitude of the electrical signal.

例えば、第一実施形態においては、位相変調光９１が第１位相変調光に対応し、位相変調光９２が第２位相変調光に対応し、位相変調光９４が第３位相変調光に対応し、位相変調光９３が第４位相変調光に対応する。また、例えば、第二実施形態においては、位相変調光７１が第１位相変調光に対応し、位相変調光７２が第２位相変調光に対応し、位相変調光７３が第３位相変調光に対応し、位相変調光７４が第４位相変調光に対応する。 For example, in the first embodiment, phase modulated light 91 corresponds to the first phase modulated light, phase modulated light 92 corresponds to the second phase modulated light, phase modulated light 94 corresponds to the third phase modulated light, and phase modulated light 93 corresponds to the fourth phase modulated light. Also, for example, in the second embodiment, phase modulated light 71 corresponds to the first phase modulated light, phase modulated light 72 corresponds to the second phase modulated light, phase modulated light 73 corresponds to the third phase modulated light, and phase modulated light 74 corresponds to the fourth phase modulated light.

第２生成部２００は、第１位相変調光と第３位相変調光との一部縮退四光波混合により、第５位相変調光を生成し、第２位相変調光と第４位相変調光との一部縮退四光波混合により、第６位相変調光を生成し、第５位相変調光と第６位相変調光を合波する。なお、第５位相変調光の中心周波数及び帯域幅は、第６位相変調光の中心周波数及び帯域幅に等しい。また、図５を用いて説明した様に、第５位相変調光と第６位相変調光の振幅及び位相の絶対値は等しく、かつ、第５位相変調光と第６位相変調光の位相の正負は互いに異なる。 The second generation unit 200 generates a fifth phase modulated light by partially degenerate four-wave mixing of the first phase modulated light and the third phase modulated light, generates a sixth phase modulated light by partially degenerate four-wave mixing of the second phase modulated light and the fourth phase modulated light, and combines the fifth phase modulated light and the sixth phase modulated light. The center frequency and bandwidth of the fifth phase modulated light are equal to the center frequency and bandwidth of the sixth phase modulated light. As described with reference to FIG. 5, the absolute values of the amplitude and phase of the fifth phase modulated light and the sixth phase modulated light are equal, and the positive and negative phases of the fifth phase modulated light and the sixth phase modulated light are different from each other.

一部縮退四光波混合により生じる位相変調光の帯域幅は、元の２つの位相変調光の帯域幅より大きくなるため、第５位相変調光と第６位相変調光を合波して得られる振幅変調光の振幅の変化量は、第１生成部１００の位相変調器が生成した位相変調光を合波して得られる振幅変調光の振幅の変化量より大きくなる。 The bandwidth of the phase-modulated light generated by partially degenerate four-wave mixing is larger than the bandwidth of the original two phase-modulated lights, so the amount of change in the amplitude of the amplitude-modulated light obtained by combining the fifth phase-modulated light and the sixth phase-modulated light is larger than the amount of change in the amplitude of the amplitude-modulated light obtained by combining the phase-modulated light generated by the phase modulator of the first generation unit 100.

なお、上記各実施形態において、第１位相変調光から第４位相変調光の帯域幅は同じであったが、第１位相変調光から第４位相変調光の帯域幅を同じとすることに本発明は限定されない。例えば、第一実施形態において、位相変調光９１の帯域幅をＢ１とし、位相変調光９４の帯域幅を０．５Ｂ１とする。この場合、式（５）及び式（６）から明らかな様に、位相変調光９５の帯域幅は２．５Ｂ１となり、位相変調光９６の帯域幅は２Ｂ１となる。同様に、位相変調光９３の帯域幅をＢ１とし、位相変調光９２の帯域幅を０．５Ｂ１とする。この場合、式（７）及び式（８）から明らかな様に、位相変調光９７の帯域幅は２．５Ｂ１となり、位相変調光９８の帯域幅は２Ｂ１となる。したがって、位相変調光９５と位相変調光９７を合波しても、位相変調光９６と位相変調光９８を合波しても振幅変調光が得られる。したがって、第１位相変調光と第４位相変調光の帯域幅が等しく、かつ、第２位相変調光と第３位相変調光の帯域幅が等しければ良い。 In the above embodiments, the bandwidths of the first to fourth phase modulated lights are the same, but the present invention is not limited to the bandwidths of the first to fourth phase modulated lights being the same. For example, in the first embodiment, the bandwidth of the phase modulated light 91 is B1 , and the bandwidth of the phase modulated light 94 is 0.5B1 . In this case, as is clear from the formulas (5) and (6), the bandwidth of the phase modulated light 95 is 2.5B1 , and the bandwidth of the phase modulated light 96 is 2B1 . Similarly, the bandwidth of the phase modulated light 93 is B1 , and the bandwidth of the phase modulated light 92 is 0.5B1 . In this case, as is clear from the formulas (7) and (8), the bandwidth of the phase modulated light 97 is 2.5B1 , and the bandwidth of the phase modulated light 98 is 2B1 . Therefore, whether the phase modulated light 95 and the phase modulated light 97 are multiplexed or the phase modulated light 96 and the phase modulated light 98 are multiplexed, the amplitude modulated light can be obtained. Therefore, it is only necessary that the bandwidths of the first phase-modulated light and the fourth phase-modulated light are equal, and that the bandwidths of the second phase-modulated light and the third phase-modulated light are equal.

なお、第一実施形態においては、第１位相変調光の中心周波数と第４位相変調光の中心周波数は等しく、第２位相変調光の中心周波数と第３位相変調光の中心周波数は等しい。また、第二実施形態において、第１位相変調光から第４位相変調光は、周波数軸上において重複しない。また、第二実施形態において、第１位相変調光の中心周波数ｆ１と第３位相変調光の中心周波数ｆ３との周波数差Ｘは、第２位相変調光の中心周波数ｆ２と第４位相変調光の中心周波数ｆ４との周波数差Ｘに等しい。さらに、第二実施形態においては、第１位相変調光の中心周波数ｆ１と第４位相変調光の中心周波数ｆ４の中心周波数は周波数ｆ３であり、第２位相変調光の中心周波数ｆ２と第３位相変調光の中心周波数ｆ３の中心周波数は周波数ｆ３であり、等しい。 In the first embodiment, the center frequency of the first phase modulated light is equal to the center frequency of the fourth phase modulated light, and the center frequency of the second phase modulated light is equal to the center frequency of the third phase modulated light. In the second embodiment, the first phase modulated light to the fourth phase modulated light do not overlap on the frequency axis. In the second embodiment, the frequency difference X between the center frequency f1 of the first phase modulated light and the center frequency f3 of the third phase modulated light is equal to the frequency difference X between the center frequency f2 of the second phase modulated light and the center frequency f4 of the fourth phase modulated light. In the second embodiment, the center frequency of the center frequency f1 of the first phase modulated light and the center frequency f4 of the fourth phase modulated light is frequency f3 , and the center frequency of the center frequency f2 of the second phase modulated light and the center frequency f3 of the third phase modulated light are frequency f3 , which are equal.

しかしながら、第１位相変調光と第３位相変調光との一部縮退四光波混合により第５位相変調光を生成し、第２位相変調光と第４位相変調光との一部縮退四光波混合により第６位相変調光を生成し、第５位相変調光と第６位相変調光を合波することで振幅変調光を生成すれば良く、本発明は上述した実施形態の具体的な構成に限定されない。 However, it is sufficient to generate the fifth phase modulated light by partially degenerate four-wave mixing of the first phase modulated light and the third phase modulated light, generate the sixth phase modulated light by partially degenerate four-wave mixing of the second phase modulated light and the fourth phase modulated light, and generate the amplitude modulated light by combining the fifth phase modulated light and the sixth phase modulated light, and the present invention is not limited to the specific configurations of the above-mentioned embodiments.

また、本発明による光変調器は、振幅のみを変化させる光振幅変調器や、振幅及び位相の両方を変化させる光直交振幅変調器を含み得る。 In addition, the optical modulator according to the present invention may include an optical amplitude modulator that changes only the amplitude, or an optical quadrature amplitude modulator that changes both the amplitude and the phase.

さらに、本発明によると、上記光変調器を含む光送信装置が提供される。 Furthermore, the present invention provides an optical transmission device including the above optical modulator.

発明は上記の実施形態に制限されるものではなく、発明の要旨の範囲内で、種々の変形・変更が可能である。 The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the invention.

以上の構成により、光変調器に入力する必要がある電気信号の振幅レベルを小さくすることができる。したがって、国連が主導する持続可能な開発目標（ＳＤＧｓ）の目標９「レジリエントなインフラを整備し、持続可能な産業化を推進するとともに、イノベーションの拡大を図る」に貢献することが可能となる。 The above configuration makes it possible to reduce the amplitude level of the electrical signal that needs to be input to the optical modulator. This makes it possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

１００：第１生成部、２００：第２生成部 100: First generation unit, 200: Second generation unit

Claims (14)

電気信号により連続光を位相変調した第１位相変調光、第２位相変調光、第３位相変調光及び第４位相変調光を生成する第１生成手段であって、前記電気信号の振幅による前記第１位相変調光と前記第２位相変調光の位相の変化方向は同じであり、前記電気信号の振幅による前記第３位相変調光と前記第４位相変調光の位相の変化方向は同じであり、前記電気信号の振幅による前記第１位相変調光と前記第３位相変調光の位相の変化方向は互いに逆方向である、前記第１生成手段と、
前記第１位相変調光と前記第３位相変調光との一部縮退四光波混合により第５位相変調光を生成し、前記第２位相変調光と前記第４位相変調光との一部縮退四光波混合により第６位相変調光を生成し、前記第５位相変調光と前記第６位相変調光を合波する第２生成手段と、
を備え、
前記第５位相変調光の中心周波数及び帯域幅は、前記第６位相変調光の中心周波数及び帯域幅に等しいことを特徴とする光変調器。 a first generating means for generating first phase-modulated light, second phase-modulated light, third phase-modulated light, and fourth phase-modulated light obtained by phase-modulating continuous light with an electrical signal, wherein a phase change direction of the first phase-modulated light and the second phase-modulated light due to an amplitude of the electrical signal is the same, a phase change direction of the third phase-modulated light and the fourth phase-modulated light due to an amplitude of the electrical signal is the same, and a phase change direction of the first phase-modulated light and the third phase-modulated light due to the amplitude of the electrical signal are opposite to each other;
a second generating means for generating a fifth phase-modulated light by partially degenerate four-wave mixing of the first phase-modulated light and the third phase-modulated light, generating a sixth phase-modulated light by partially degenerate four-wave mixing of the second phase-modulated light and the fourth phase-modulated light, and multiplexing the fifth phase-modulated light and the sixth phase-modulated light;
Equipped with
An optical modulator, wherein a center frequency and a bandwidth of the fifth phase-modulated light are equal to a center frequency and a bandwidth of the sixth phase-modulated light. 前記第１位相変調光の帯域幅と前記第４位相変調光の帯域幅は等しく、前記第２位相変調光の帯域幅と前記第３位相変調光の帯域幅は等しいことを特徴とする請求項１に記載の光変調器。 The optical modulator according to claim 1, characterized in that the bandwidth of the first phase-modulated light is equal to the bandwidth of the fourth phase-modulated light, and the bandwidth of the second phase-modulated light is equal to the bandwidth of the third phase-modulated light. 前記第１位相変調光の中心周波数と前記第４位相変調光の中心周波数は等しく、前記第２位相変調光の中心周波数と前記第３位相変調光の中心周波数は等しいことを特徴とする請求項１又は２に記載の光変調器。 The optical modulator according to claim 1 or 2, characterized in that the center frequency of the first phase-modulated light is equal to the center frequency of the fourth phase-modulated light, and the center frequency of the second phase-modulated light is equal to the center frequency of the third phase-modulated light. 前記第１生成手段は、
第１周波数の連続光と第２周波数の連続光を前記電気信号により位相変調することで前記第１周波数の前記第１位相変調光及び前記第２周波数の前記第２位相変調光を含む第１信号光を出力する第１位相変調手段と、
前記第１周波数の連続光と前記第２周波数の連続光を前記電気信号により位相変調することで前記第１周波数の前記第４位相変調光及び前記第２周波数の前記第３位相変調光を含む第２信号光を出力する第２位相変調手段と、
前記第１信号光に含まれる前記第１位相変調光及び前記第２信号光に含まれる前記第３位相変調光を含む第３信号光を出力し、前記第１信号光に含まれる前記第２位相変調光及び前記第２信号光に含まれる前記第４位相変調光を含む第４信号光を出力する出力手段と、
を備え、
前記第２生成手段は、
前記第３信号光に含まれる前記第１位相変調光と前記第３位相変調光との一部縮退四光波混合により前記第５位相変調光を生成する第１混合手段と、
前記第４信号光に含まれる前記第２位相変調光と前記第４位相変調光との一部縮退四光波混合により前記第６位相変調光を生成する第２混合手段と、
を備えていることを特徴とする請求項１から３のいずれか１項に記載の光変調器。 The first generating means is
a first phase modulation means for outputting a first signal light including the first phase-modulated light of the first frequency and the second phase-modulated light of the second frequency by phase-modulating the continuous light of a first frequency and the continuous light of a second frequency using the electrical signal;
a second phase modulation means for outputting a second signal light including the fourth phase-modulated light of the first frequency and the third phase-modulated light of the second frequency by phase-modulating the continuous light of the first frequency and the continuous light of the second frequency using the electrical signal;
an output means for outputting a third signal light including the first phase-modulated light included in the first signal light and the third phase-modulated light included in the second signal light, and for outputting a fourth signal light including the second phase-modulated light included in the first signal light and the fourth phase-modulated light included in the second signal light;
Equipped with
The second generating means is
a first mixer that generates the fifth phase-modulated light by partially degenerate four-wave mixing of the first phase-modulated light and the third phase-modulated light included in the third signal light;
a second mixing means for generating the sixth phase-modulated light by partially degenerate four-wave mixing of the second phase-modulated light and the fourth phase-modulated light included in the fourth signal light;
4. The optical modulator according to claim 1, further comprising: 前記第１混合手段及び前記第２混合手段は、それぞれ、光ファイバ及び半導体光増幅器のいずれかを有することを特徴とする請求項４に記載の光変調器。 The optical modulator according to claim 4, characterized in that the first mixing means and the second mixing means each have either an optical fiber or a semiconductor optical amplifier. 前記第１混合手段及び前記第２混合手段は、それぞれ、光ファイバを有し、
前記第１混合手段に含まれる光ファイバの分散値が０となる周波数は、前記第１位相変調光の帯域内、前記第３位相変調光の帯域内、或いは、前記第１位相変調光の帯域と前記第３位相変調光の帯域との間の帯域内に有り、
前記第２混合手段に含まれる光ファイバの分散値が０となる周波数は、前記第２位相変調光の帯域内、前記第４位相変調光の帯域内、或いは、前記第２位相変調光の帯域と前記第４位相変調光の帯域との間の帯域内に有ることを特徴とする請求項５に記載の光変調器。 each of the first mixing means and the second mixing means includes an optical fiber;
a frequency at which the dispersion value of the optical fiber included in the first mixing means becomes zero is within a band of the first phase-modulated light, within a band of the third phase-modulated light, or within a band between the band of the first phase-modulated light and the band of the third phase-modulated light,
6. The optical modulator according to claim 5, wherein a frequency at which the dispersion value of the optical fiber included in the second mixing means becomes zero is within the band of the second phase-modulated light, within the band of the fourth phase-modulated light, or within a band between the band of the second phase-modulated light and the band of the fourth phase-modulated light. 前記第１位相変調光の帯域幅と、前記第２位相変調光の帯域幅と、前記第３位相変調光の帯域幅と、前記第４位相変調光の帯域幅は等しく、
前記第１周波数と前記第２周波数との周波数差は、前記第１位相変調光の帯域幅の２倍より大きいことを特徴とする請求項４から６のいずれか１項に記載の光変調器。 a bandwidth of the first phase-modulated light, a bandwidth of the second phase-modulated light, a bandwidth of the third phase-modulated light, and a bandwidth of the fourth phase-modulated light are equal to each other,
7. The optical modulator according to claim 4, wherein a frequency difference between the first frequency and the second frequency is greater than twice the bandwidth of the first phase-modulated light. 前記第１位相変調光、前記第２位相変調光、前記第３位相変調光及び前記第４位相変調光は、周波数軸上において重複しないことを特徴とする請求項１又は２に記載の光変調器。 The optical modulator according to claim 1 or 2, characterized in that the first phase-modulated light, the second phase-modulated light, the third phase-modulated light, and the fourth phase-modulated light do not overlap on the frequency axis. 前記第１位相変調光の中心周波数と前記第３位相変調光の中心周波数との周波数差は、前記第２位相変調光の中心周波数と前記第４位相変調光の中心周波数との周波数差に等しいことを特徴とする請求項８に記載の光変調器。 The optical modulator according to claim 8, characterized in that the frequency difference between the center frequency of the first phase-modulated light and the center frequency of the third phase-modulated light is equal to the frequency difference between the center frequency of the second phase-modulated light and the center frequency of the fourth phase-modulated light. 前記第１位相変調光の中心周波数と前記第４位相変調光の中心周波数との中心周波数は、前記第２位相変調光の中心周波数と前記第３位相変調光の中心周波数との中心周波数に等しいことを特徴とする請求項８又は９に記載の光変調器。 The optical modulator according to claim 8 or 9, characterized in that the center frequency of the first phase-modulated light and the center frequency of the fourth phase-modulated light are equal to the center frequency of the second phase-modulated light and the center frequency of the third phase-modulated light. 前記第１生成手段は、
第１周波数の連続光と第２周波数の連続光を前記電気信号により位相変調することで前記第１周波数の前記第１位相変調光及び前記第２周波数の前記第２位相変調光を含む第１信号光を出力する第１位相変調手段と、
第３周波数の連続光と第４周波数の連続光を前記電気信号により位相変調することで前記第３周波数の前記第３位相変調光及び前記第４周波数の前記第４位相変調光を含む第２信号光を出力する第２位相変調手段と、
前記第１信号光及び前記第２信号光を合波して、前記第１位相変調光、前記第２位相変調光、前記第３位相変調光及び前記第４位相変調光を含む第３信号光を出力する出力手段と、
を備え、
前記第１周波数と前記第４周波数との中心周波数は、前記第２周波数と前記第３周波数との中心周波数に等しいことを特徴とする請求項８から１０のいずれか１項に記載の光変調器。 The first generating means is
a first phase modulation means for outputting a first signal light including the first phase-modulated light of the first frequency and the second phase-modulated light of the second frequency by phase-modulating the continuous light of a first frequency and the continuous light of a second frequency using the electrical signal;
a second phase modulation means for outputting a second signal light including the third phase-modulated light of the third frequency and the fourth phase-modulated light of the fourth frequency by phase-modulating the continuous light of a third frequency and the continuous light of a fourth frequency using the electrical signal;
an output unit that multiplexes the first signal light and the second signal light and outputs a third signal light including the first phase-modulated light, the second phase-modulated light, the third phase-modulated light, and the fourth phase-modulated light;
Equipped with
11. The optical modulator according to claim 8, wherein a center frequency between the first frequency and the fourth frequency is equal to a center frequency between the second frequency and the third frequency. 前記第２生成手段は、光ファイバ及び半導体増幅器のいずれかを有することを特徴とする請求項１１に記載の光変調器。 The optical modulator according to claim 11, characterized in that the second generating means includes either an optical fiber or a semiconductor amplifier. 前記第２生成手段は、光ファイバを有し、
前記光ファイバの分散値が０となる周波数は、前記第１周波数と前記第４周波数の中心周波数に等しいことを特徴とする請求項１２に記載の光変調器。 the second generating means having an optical fiber;
13. The optical modulator according to claim 12, wherein the frequency at which the dispersion value of the optical fiber becomes zero is equal to the center frequency between the first frequency and the fourth frequency. 請求項１から１３のいずれか１項に記載の光変調器を備えることを特徴とする光送信装置。 An optical transmitter comprising an optical modulator according to any one of claims 1 to 13.
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WO2008117460A1 (en) 2007-03-27 2008-10-02 Fujitsu Limited Multilevel light intensity modulator
JP2021129208A (en) 2020-02-13 2021-09-02 Kddi株式会社 Modulation device, modulation system, and optical transmission device
WO2022254855A1 (en) 2021-06-01 2022-12-08 Kddi株式会社 Optical angle modulator and optical transmission device

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JP2002023210A (en) 2000-07-04 2002-01-23 Japan Science & Technology Corp Wavelength converter
WO2008026326A1 (en) 2006-08-30 2008-03-06 Hitachi Communication Technologies, Ltd. Optical modulator
WO2008117460A1 (en) 2007-03-27 2008-10-02 Fujitsu Limited Multilevel light intensity modulator
JP2021129208A (en) 2020-02-13 2021-09-02 Kddi株式会社 Modulation device, modulation system, and optical transmission device
WO2022254855A1 (en) 2021-06-01 2022-12-08 Kddi株式会社 Optical angle modulator and optical transmission device

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Title
S. Ishimura, et al.，"Enabling Technology for 9.5-dB SNR Enhancement Utilizing Four-Wave Mixing Between a Conjugate Pair of Angle Modulation for Analog Radio-over-Fiber Links"，2021 Optical Fiber Communications Conference and Exhibition (OFC)，2021年06月，F3C.3，pp. 1-3
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