JP2015222439A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical modulator that can compensate a wavelength dispersion of an optical fiber, and is applicable even to a high-speed transmission exceeding above several 10 Gbps.SOLUTION: In the optical modulator including a substrate 1 composed of a material having an electrooptical effect, an optical waveguide 2 formed on the substrate and a modulation electrode 3 for modulating a light wave propagating through the optical waveguide, emergent light L2 to be emitted from the optical waveguide is guided by the optical fiber, and by executing the substrate to polarization inversion 10 by a predetermined pattern along the optical waveguide so as to have wavelength dispersion characteristics of the optical fiber and a waveform distortion of the reverse characteristics, the wavelength dispersion characteristics of the optical fiber are compensated, and further, by disposing an adjustment member (not shown) composed of a dielectric material or a metallic material in the vicinity of the modulation electrode, the compensation of the wavelength dispersion characteristics is adjusted to a predetermined level.

Description

  The present invention relates to an optical modulator, and more particularly to an optical modulator that compensates for chromatic dispersion of an optical fiber.

  In the optical communication field and the optical measurement field, a light wave modulated by an optical modulator is transmitted through an optical fiber. In an optical fiber, the propagation speed of light and the length of the propagation path differ depending on the wavelength, so that chromatic dispersion occurs and the waveform of the optical signal is distorted. For this reason, in high-speed communication exceeding 40 Gbps, wavelength-multiplexed high-speed transmission systems, etc., a technique for compensating for the chromatic dispersion of the optical fiber is indispensable.

  As a dispersion compensation method, a dispersion compensation fiber is disposed immediately before an optical signal receiver, a method using an optical device such as a fiber Bragg grating (FBG) or an etalon as in Patent Document 1, and a patent. There are those using a digital signal processing circuit such as Document 2 and Non-Patent Document 1. The digital signal processing circuit generates an impulse response that is compensated by the digital signal processor in response to changes in the real part and imaginary part related to chromatic dispersion.

  In the dispersion compensation fiber, the compensation accuracy is limited by the minimum unit of the compensation amount, and chromatic dispersion compensation such as FBG is used for chromatic dispersion compensation such as wavelength division multiplexing (WDM) light because the WDM light is demultiplexed. A separate optical device is also required. Moreover, an optical device such as an FBG not only has a limited wavelength band to handle, but also has a large optical loss. Furthermore, the digital signal processing circuit has a problem that high-speed processing exceeding 40 Gbps is technically difficult.

JP 2004-12714 A JP 2010-226254 A

Robert I. Kelley, et al., "Electronic Dispersion Compensation by Signal Predistortion Using Digital Processing and a Dual-Drive Mach-Zehnder Modulator", IEEE Photonics Technology letters, Vol.17, No.3, pp714-716, 2005

  The problem to be solved by the present invention is to provide an optical modulator that can compensate for the chromatic dispersion of an optical fiber and can be applied to high-speed transmission exceeding several tens of Gbps.

  In order to solve the above-mentioned problem, an invention according to claim 1 is directed to a substrate made of a material having an electro-optic effect, an optical waveguide formed on the substrate, and a light wave propagating through the optical waveguide. In an optical modulator having a modulation electrode, the outgoing light emitted from the optical waveguide is guided by the optical fiber, and has a waveform distortion opposite to the wavelength dispersion characteristic of the optical fiber. The wavelength dispersion characteristic of the optical fiber is compensated by reversing the polarization of the substrate in a predetermined pattern, and an adjustment member made of a dielectric material or a metal material is disposed in the vicinity of the modulation electrode, and By adjusting the relative position between the adjustment member and the modulation electrode, the effective refractive index of the microwave propagating through the modulation electrode is changed, and the compensation of the wavelength dispersion characteristic is adjusted to a predetermined level. It is characterized by .

  The invention according to claim 2 is the optical modulator according to claim 1, wherein the modulation electrode has a coplanar electrode in which the width of the signal electrode is S and the distance between the signal electrode and the ground electrode is G. The width of the adjustment member is smaller than 3 times “S + 2G”.

  The invention according to claim 3 is the optical modulator according to claim 1 or 2, wherein the optical waveguide has a Mach-Zehnder type waveguide having two branch waveguides, and is formed in one branch waveguide. The polarization inversion pattern is a pattern corresponding to the real part response of the impulse response 1 / h (t) for compensating the impulse response h (t) of the optical fiber, and the polarization inversion formed in the other branched waveguide Is a pattern corresponding to the imaginary part responsiveness of the impulse response 1 / h (t), and is configured to multiplex the light waves that have passed through the two branch waveguides with a predetermined phase difference. It is characterized by.

The invention according to claim 4 is the optical modulator according to claim 3, wherein the impulse response h (t) of the optical fiber is given by the following equation.
However, H (ω) is a transfer function of the optical fiber, and H (ω) = exp (jβ (ω) L). β (ω) is a phase constant of the light wave propagating through the optical fiber, and L is the length of the optical fiber.

  According to a fifth aspect of the present invention, in the optical modulator according to any one of the first to fourth aspects, the adjustment member is made of a dielectric material, and the temperature of the adjustment member is adjusted, whereby the wavelength dispersion characteristic is obtained. The compensation is adjusted to a predetermined level.

  The invention according to claim 6 is the optical modulator according to claim 5, further comprising a mechanism for adjusting the temperature of at least the dielectric material.

  The invention according to claim 7 is the optical modulator according to any one of claims 1 to 4, wherein the adjustment member is made of a dielectric material, and the relative dielectric constant of the dielectric material is 100 or more. Features.

  According to the first aspect of the present invention, an optical modulation comprising a substrate made of a material having an electro-optic effect, an optical waveguide formed on the substrate, and a modulation electrode for modulating an optical wave propagating through the optical waveguide In this device, the light emitted from the optical waveguide is guided by an optical fiber, and the substrate is formed in a predetermined pattern along the optical waveguide so as to have a waveform distortion opposite to the wavelength dispersion characteristic of the optical fiber. The wavelength dispersion characteristic of the optical fiber is compensated for by reversing the polarization at, and the wavelength dispersion characteristic is compensated by arranging an adjustment member made of a dielectric material or a metal material in the vicinity of the modulation electrode. Since it is adjusted to a predetermined level, when converting an electrical signal into an optical signal by an optical modulator, the wavelength dispersion due to the optical fiber is reduced in advance by giving the inverse characteristics of the waveform distortion due to the wavelength dispersion of the optical fiber. Departure It becomes possible to compensate for the characteristic degradation by. In addition, it is possible to compensate for waveform deterioration without depending on the wavelength, and since no digital signal processing technique is used, an optical modulator applicable to high-speed transmission exceeding several tens of Gbps can be provided.

  In addition, an adjustment member made of a dielectric material or a metal material is disposed in the vicinity of the modulation electrode, and the relative position between the adjustment member and the modulation electrode is adjusted, so that the microwave propagating through the modulation electrode can be adjusted. It is possible to change the effective refractive index. As a result, the compensation for the chromatic dispersion characteristic of the optical fiber can be adjusted to a predetermined level.

It is a figure which shows an example of the optical modulator (modulator chip | tip) of this invention. It is a graph which shows an example of the real part response (Reh ^* (t)) and imaginary part response (Imh ^* (t)) which compensate the impulse response of an optical fiber. It is a figure which shows the state which has arrange | positioned the adjustment member to the optical modulator of this invention. FIG. 4 is a graph for explaining a change in effective refractive index and compensationable optical fiber length with respect to a distance between a modulation electrode and an adjustment member when a dielectric material is used for the adjustment member in FIG. 3. FIG. 4 is a graph for explaining a change in effective refractive index and compensationable optical fiber length with respect to a distance between a modulation electrode and an adjustment member when a metal material is used for the adjustment member in FIG. 3. It is an example of the optical modulator of the present invention, and is a diagram showing an example in which signal electrodes are arranged corresponding to each branching waveguide. It is an example of the optical modulator of the present invention, and is a diagram showing an example in which a common signal electrode is arranged for two branch waveguides. It is an example of the optical modulator of the present invention, and is a diagram showing an example using an X plate as a substrate.

Hereinafter, the present invention will be described in detail using preferred examples.
As shown in FIG. 1, the present invention includes a substrate 1 made of a material having an electro-optic effect, an optical waveguide 2 formed on the substrate, and a modulation electrode for modulating a light wave propagating through the optical waveguide. 3 so that the outgoing light L2 emitted from the optical waveguide is guided by an optical fiber (not shown) and has a waveform distortion having a characteristic opposite to the wavelength dispersion characteristic of the optical fiber. The chromatic dispersion characteristics of the optical fiber are compensated by polarization inversion 10 in a predetermined pattern along the optical waveguide, and an adjustment member made of a dielectric material or a metal material is provided in the vicinity of the modulation electrode. By arranging, compensation of the chromatic dispersion characteristic is adjusted to a predetermined level.

  As the substrate using the material having the electro-optic effect of the present invention, for example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), and a substrate combining these materials can be used. In particular, a material that has a high electro-optic effect and can easily form an arbitrary domain-inverted structure is preferable. Specifically, lithium niobate, lithium tantalate, and electro-optic polymer.

  The optical waveguide 2 can be formed on the substrate by diffusing Ti or the like on the substrate surface by a thermal diffusion method or a proton exchange method. It is also possible to use a ridge-shaped waveguide having a convex portion corresponding to the optical waveguide, such as etching a substrate other than the optical waveguide or forming grooves on both sides of the optical waveguide.

On the substrate 1, modulation electrodes such as the signal electrode 3 and the ground electrode are formed. Such an electrode can be formed by forming a Ti / Au electrode pattern, a gold plating method, or the like. Further, if necessary, a buffer layer such as a dielectric SiO ₂ may be provided on the substrate surface after the optical waveguide is formed, and a modulation electrode may be formed on the buffer layer. The code S in FIG. 1 is a modulation signal.

  An optical fiber is optically coupled to the optical modulator of the present invention. A method of directly bonding an optical fiber to a substrate having an electro-optic effect using a capillary or the like, or a quartz substrate having an optical waveguide formed on a substrate having an electro-optic effect, and the optical fiber being attached to the quartz substrate or the like. It is also possible to join. Furthermore, it is also possible to configure so that outgoing light is introduced into an optical fiber via a spatial optical system on a substrate having an electro-optic effect, a quartz substrate, or the like.

  In the optical modulator of the present invention, a substrate made of a material having an electro-optic effect as shown in FIG. 1 is used, and a part of the substrate is subjected to polarization inversion 10. Arrows P1 and P2 indicate the polarization direction of the substrate. When such a domain-inverted structure is applied to a traveling wave electrode type optical modulator, useful characteristics such as pseudo speed matching, complete zero chirp intensity modulation, and optical SSB modulation can be obtained. The present inventor has completed the present invention by paying attention to the fact that the modulation frequency characteristic of a traveling wave electrode type optical modulator having a polarization inversion structure is given by Fourier transform of an impulse response that directly corresponds to the polarization inversion pattern. Has been reached.

  That is, as in the present invention, an optical modulator having a pre-equalizing function can be realized by using this characteristic. Moreover, unlike the ordinary baseband modulator, the optical modulator of the present invention does not need to match the group velocity of the modulated light and the phase velocity of the modulation signal, so that the traveling wave type electrode with an extremely low loss having a large cross-sectional area is used. By using, an ultra-high speed response exceeding several tens of GHz is possible. In addition, like a conventional digital signal processing circuit, an operation exceeding the limit of electrical equalizing technology using high-speed A / D conversion technology is possible. The optical modulator of the present invention does not require a high-speed digital signal processing circuit, and can be driven with low power consumption. Furthermore, various applications such as phase rotation compensation of transmission signals by chromatic dispersion of fibers can be expected.

  In the following, the description will focus on the optical modulator that performs dispersion compensation of the optical fiber. The optical modulator of the present invention has an inverse characteristic of waveform distortion due to wavelength dispersion of an optical fiber in advance when an electric signal is converted into an optical signal by using an electro-optic modulation technique using polarization inversion. This compensates for characteristic deterioration.

The optical modulator of the present invention is also applicable to high-speed transmission of several tens of Gbps or more, and more than 100 Gbps. In addition, waveform deterioration can be compensated regardless of the wavelength. Therefore, the present invention is also an epoch-making technique that surpasses the conventional dispersion compensation technique. The features of the dispersion compensation technology used by the present invention can be listed as follows.
(1) Capable of handling high-speed electrons exceeding 40 Gbps, which is difficult to cope with digital signal processing technology (2) No limitation on wavelength band as in the FBG method (3) Integration with data modulators

  The feature combining the above (1) and (2) is not present in the conventional dispersion compensation technique, and the technique of the present invention is particularly excellent as a dispersion compensation technique in a wavelength multiplexing high-speed transmission system. .

A dispersion compensation technique in the optical modulator of the present invention will be described in detail.
When the phase constant of the light wave propagating in the optical fiber is β (ω), the transfer function H (ω) of the optical fiber having the length L is expressed by the following equation.
H (ω) = exp (jβ (ω) L)

Further, in dispersion compensation, a second-order term when β (ω) is Taylor-expanded around the carrier angular frequency ω = ω ₀ may be considered, and can be modified as follows.
H (ω) = exp (jβ ₂ ω ² L / 2)
Here, β2 means a quadratic term of Taylor expansion and represents group velocity dispersion.

Thereby, the impulse response h (t) of the optical fiber can be expressed by the following equation (2).

In order to compensate for the dispersion of the optical fiber, the transfer function for compensating the dispersion of the optical fiber is 1 / H (ω) = H ^* (ω). Therefore, in the optical modulator, h is an impulse response of the dispersion compensation. ^{* The} modulation corresponding to (t) (= 1 / h (t)) may be performed. Specifically, with the Mach-Zehnder type waveguide shown in FIG. 1, when using the MZ interferometer type optical modulator, a real part responsiveness Re {h * ^(t of h ^{* (t)} in one branch waveguides 21 )}, Modulation of the imaginary part responsiveness Im {h ^* (t)} is performed by the other branch waveguide, and the two are synthesized with a predetermined phase difference. Most preferably, the phase difference is set to 90 °.

FIG. 2 is a graph showing real part responsiveness Re {h ^* (t)}) and imaginary part responsiveness Im {h ^* (t)} of impulse response h ^* (t) for dispersion compensation.

  In general, it is difficult to freely set the impulse response, but if a material having a primary electro-optic effect such as a ferroelectric material has a polarization inversion structure, this impulse response can be easily realized. Is possible.

Specifically, as shown in FIG. 1, the optical waveguide 2 has a Mach-Zehnder type waveguide having two branch waveguides (21, 22), and the pattern of the polarization inversion 10 formed in one branch waveguide. Is a pattern corresponding to the real part response of the impulse response h ^* (t) (= 1 / h (t)) that compensates the impulse response h (t) of the optical fiber described above, and is formed in the other branching waveguide. The polarization inversion pattern may be a pattern corresponding to the imaginary part responsiveness of the impulse response h ^* (t) of dispersion compensation.

  The light waves that have passed through the two branch waveguides are combined with a predetermined phase difference. As a method of generating this phase difference, a method of adjusting the length of each branch waveguide, or a signal electrode or a DC bias electrode arranged along the branch waveguide is used to adjust the refractive index of the branch waveguide. Methods etc. are available.

  The optical modulator as shown in FIG. 1 operates as a dispersion compensation modulator having a pre-equalizing function. Further, when a double MZ modulator is used, dispersion compensation with higher accuracy can be achieved. Moreover, combined use with QPSK modulation and duobinary modulation is also possible.

  In FIG. 1, only the signal electrode 3 is shown as the modulation electrode, and the illustration of the ground electrode is omitted. However, the optical modulator of the present invention is not limited to that shown in FIG. It is possible to adopt various arrangements / configurations shown in FIG.

  In the optical modulator shown in FIG. 6, two signal electrodes 31 and 32 corresponding to the two branch waveguides 21 and 22 of the Mach-Zehnder type waveguide are formed on the substrate 1. The input ends of the signal electrodes are connected to the AC power supply 5 and the modulation signals S and S ′ are input to the respective signal electrodes. In FIG. 6, the ground electrode is omitted as in FIG.

  In the optical modulator shown in FIG. 7, a single signal electrode 3 is formed so as to cover all the two waveguides of the Mach-Zehnder type waveguide. A ground electrode 4 is formed on the back surface of the substrate 1.

Furthermore, in the optical modulator of FIG. 7, when a thin plate is used for the substrate 1, a buffer layer such as a dielectric SiO ₂ may be provided between the back surface of the substrate 1 and the ground electrode 4 as necessary. it can.

  In FIGS. 1 and 6 to 7, a Z plate is used as the substrate 1 of the optical modulator, and therefore the direction of the polarization treatment is perpendicular to the substrate surface. However, like the optical modulator shown in FIG. By using an X plate (Y plate) as the substrate, the direction of the polarization treatment can be parallel to the substrate surface. Reference numeral 3 in FIG. 8 denotes a signal electrode, and reference numeral 4 denotes a ground electrode.

  Next, a configuration for adjusting the level for compensating the wavelength dispersion characteristic of the optical fiber, which is a feature of the optical modulator of the present invention, will be described.

  FIG. 3 is a view showing a state in which an adjusting member made of a dielectric material or a metal material is arranged in the vicinity of the modulation electrode shown in the optical modulator of FIG. As described above, by loading the adjustment member on the modulator chip constituting the optical modulator, it is possible to greatly change the effective refractive index of the microwave that is the modulation signal propagating through the modulation electrode. Thereby, the dispersion compensation amount can be significantly adjusted.

Without the adjusting member of FIG. 1 or FIG. 3, the effective refractive index is 4.256 and the optical fiber length that can be compensated is about 10 km in the following parameters.
-Substrate material: lithium tantalate-Substrate thickness (b): 0.4 mm
-Substrate width (c): 2 mm
Buffer material: silicon oxide Buffer layer thickness (a): 0.3 μm
-Modulation electrode material: Aluminum-Modulation electrode (signal electrode, ground electrode) height (h ₀ ): 2 μm
・ Signal electrode width (S): 33 μm
-Distance between signal electrode and ground electrode (W): 46.5 μm
-Refractive index of light (carrier wave) ( _ng ): 2.409

As shown in FIG. 3, changes in the effective refractive index and the length of the optical fiber that can be compensated were examined when a high dielectric material of lithium tantalate was loaded as an adjustment member and when a metal of aluminum was loaded. The simulation results are shown in FIGS. FIG. 4 shows a case where a dielectric material is used for the adjustment member, and the effective refractive index (n _m ) and the optical fiber length (L) that can be compensated for the distance (h ₁ ) between the modulation electrode and the adjustment member. The state of change is shown. FIG. 5 shows the same result when a metal material is used for the adjustment member. The thickness of the adjusting member was 0.5 mm, and the width was 2 mm, similar to the substrate.

Since the dielectric anisotropy of lithium tantalate and lithium niobate is large, it is necessary to consider the anisotropy for accurate characteristic simulation. The relative permittivity ε _r of the dielectric lithium tantalate is calculated as 42. The higher the dielectric constant, the higher the effect of increasing the amount of change in refractive index, that is, the amount of adjustment of the dispersion compensation amount. In order to ensure the high frequency characteristics of the device, a material having a low dielectric loss (tan δ) at a high frequency is desirable. On the other hand, when a metal is loaded, even if the metal material is aluminum, gold, silver, or copper, if the conductor is a good conductor, the change in effective refractive index, that is, the range that can be compensated exhibits substantially the same characteristics. Here, the aluminum value is shown for the convenience of simulation, but the loaded metal also acts as part of the electrode. Therefore, in order to ensure the high frequency characteristics of the device, high frequency such as gold, silver or copper is used. It is preferable to use a metal having high conductivity.

  In addition, although the simulation is performed with the thickness of the material to be loaded being 0.5 mm, the effect of the thickness differs depending on whether the material to be loaded is a dielectric or a metal. In the case of a dielectric, since the electric field of a signal enters the dielectric, the thicker the thickness, the higher the effect of increasing the amount of change in the refractive index, that is, the amount of adjustment of the dispersion compensation amount. The thickness is set according to the relative dielectric constant of the dielectric material to be loaded and the target dispersion compensation amount. On the other hand, in the case of metal, since the electric field inside the metal becomes almost zero, even if the thickness is increased, there is no effect of increasing the amount of change in refractive index, that is, the amount of dispersion compensation. In the frequency band of the signal to be used, the thickness can be reduced within a range in which signal attenuation and deterioration due to skin loss can be tolerated.

  Referring to FIG. 4, when the dielectric is loaded, if the distance from the loaded dielectric is reduced, the refractive index for the electric signal is greatly increased, and the dispersion compensation amount can be adjusted in the range of about 0% to + 40%. Become. In addition, as shown in FIG. 5, when the metal is loaded, if the distance from the loaded metal is reduced, the refractive index with respect to the electric signal is greatly reduced, and the division compensation amount is adjusted in the range of about −50% to 0%. It can be easily understood that this is possible. For this reason, in the optical modulator of the present invention, the level for compensating the wavelength dispersion characteristic of the optical fiber can be significantly changed by using the adjusting member. Whether the dielectric is loaded or the metal is loaded, the impedance changes as the refractive index changes. However, the design is handled and addressed by designing the electrode configuration, selecting the drive circuit, and using the impedance matching circuit.

  The adjustment member can be configured not only to be fixedly arranged at a predetermined position so as to have a preset dispersion compensation amount but also to be able to adjust the position so that the dispersion compensation amount can be changed.

  In the example shown in FIG. 3, a high dielectric material that is sufficiently wide with respect to the width of the coplanar electrode on the modulator substrate (= S + 2W) is loaded. In this case, the gap h of the high dielectric material loaded with the modulator is an effective parameter for position adjustment. When the width of the high dielectric material is smaller than about three times the width of the coplanar electrode (= S + 2W), the position of the high dielectric material is adjusted in the horizontal direction in FIG. can get. In this case, the smaller the width of the high dielectric constant material to be loaded and the higher the dielectric constant, the larger the adjustment amount can be obtained. For this configuration, a material such as PLZT, PZT, or KTN having a large relative dielectric constant of 100 or more is preferably selected as the high dielectric constant material. Further, when a material having a very high temperature dependence of dielectric constant such as KTN is used, a large amount of dispersion compensation can be adjusted depending on the temperature. When loading metal, the effect on the amount of adjustment of the width and position of the loaded metal is the same as in the case of a high dielectric constant material. However, in the case of metal, the adjustment amount of the dispersion compensation amount due to temperature is very small. Whether the material to be loaded is a high dielectric constant material or a metal, the position may be adjusted in the height direction and the horizontal direction, both may be adjusted, or the temperature of the dielectric constant may be adjusted. In the case of using a high dielectric constant material having a large dependency, adjustment with temperature may be used in combination.

  In the above description, the example of the coplanar electrode has been described. However, the same effect can be obtained in the configuration using the microstrip type electrode or the slot type electrode in which the signal electrode is arranged on the surface of the substrate, similarly to the coplanar electrode. . The effect is reduced when the electrode is buried in the dielectric, but there is a practical effect when the buried depth is sufficiently thin with respect to the electrode interval (about half or less of the electrode interval).

  As described above, according to the optical modulator of the present invention, it is possible to provide an optical modulator that can compensate for chromatic dispersion of an optical fiber and can be applied to high-speed transmission exceeding several tens of Gbps.

DESCRIPTION OF SYMBOLS 1 Substrate using material having electro-optic effect 2 Optical waveguide 21, 22 Branched waveguide 3, 31, 32 Signal electrode 4 Ground electrode 10 Polarization inversion pattern L 1 Incident light L 2 Output light S Modulation signal

Claims (7)

In an optical modulator having a substrate made of a material having an electro-optic effect, an optical waveguide formed on the substrate, and a modulation electrode for modulating a light wave propagating through the optical waveguide,
The output light emitted from the optical waveguide is guided by an optical fiber, and the substrate is inverted in a predetermined pattern along the optical waveguide so as to have a waveform distortion opposite to the wavelength dispersion characteristic of the optical fiber. To compensate for the chromatic dispersion characteristics of the optical fiber,
In addition, an adjustment member made of a dielectric material or a metal material is disposed in the vicinity of the modulation electrode, and a relative position between the adjustment member and the modulation electrode is adjusted, so that a micro wave propagating through the modulation electrode can be obtained. An optical modulator characterized by changing the effective refractive index of the wave and adjusting the compensation of the wavelength dispersion characteristic to a predetermined level.   2. The optical modulator according to claim 1, wherein the modulation electrode has a coplanar electrode in which the width of the signal electrode is S and the distance between the signal electrode and the ground electrode is G, and the width of the adjustment member is An optical modulator characterized by being smaller than three times “S + 2G”. The optical modulator according to claim 1 or 2, wherein the optical waveguide includes a Mach-Zehnder type waveguide having two branch waveguides,
The polarization inversion pattern formed in one branching waveguide is a pattern corresponding to the real part response of the impulse response 1 / h (t) for compensating the impulse response h (t) of the optical fiber,
The pattern of polarization inversion formed in the other branch waveguide is a pattern corresponding to the imaginary part responsiveness of the impulse response 1 / h (t),
An optical modulator configured to multiplex light waves having passed through the two branch waveguides with a predetermined phase difference. 4. The optical modulator according to claim 3, wherein the impulse response h (t) of the optical fiber is given by the following equation.
However, H (ω) is a transfer function of the optical fiber, and H (ω) = exp (jβ (ω) L). β (ω) is a phase constant of the light wave propagating through the optical fiber, and L is the length of the optical fiber.

  5. The optical modulator according to claim 1, wherein the adjustment member is made of a dielectric material, and the compensation of the wavelength dispersion characteristic is adjusted to a predetermined level by adjusting a temperature of the adjustment member. An optical modulator characterized by that.   6. The optical modulator according to claim 5, further comprising a mechanism for adjusting at least a temperature of the dielectric material.   5. The optical modulator according to claim 1, wherein the adjustment member is made of a dielectric material, and the relative dielectric constant of the dielectric material is 100 or more.

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