JP4912274B2 - Light modulator - Google Patents

Description

  The present invention relates to an optical modulator, and more particularly to an optical modulator using an electro-optic crystal having a secondary electro-optic effect.

  Currently, demands for large capacity, high speed and high functionality of optical communication systems are increasing rapidly. One of the promising optical signal processing devices used in such an optical communication system is an optical modulator, and an optical modulator using an electro-optic crystal is being developed.

An optical phase modulator using an electro-optic crystal changes the phase of light by changing the speed of light passing through the crystal by changing the refractive index of the crystal. When the electro-optic crystal is installed in one of the optical waveguides of the Mach-Zehnder interferometer and the Michelson interferometer, the light intensity of the output of the interferometer changes according to the voltage applied to the crystal. These interferometers can be used as optical switches and optical modulators. In Patent Document 1, KTN (KTa _1-x Nb _x O ₃ (0 <x <1)) and KLTN (K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1) are used as electro-optic crystals. , 0 <y <1)) is disclosed.

  FIG. 1 shows a configuration of an optical phase modulator using an electro-optic crystal disclosed in Patent Document 1. In the optical phase modulator, a positive electrode 2 and a negative electrode 3 are formed on opposite surfaces of a rectangular electro-optic crystal 1. In such a configuration, when a voltage V is applied between the positive electrode 2 and the negative electrode 3, the phase of light propagating through the electro-optic crystal 1 changes according to the voltage V.

International Publication No. 2006/137408 Pamphlet

  Since KTN or KLTN is a dielectric crystal having a cubic crystal structure and a large secondary electro-optic effect, low-voltage driving can be realized without depending on polarization, and a large secondary electro-optic effect can be obtained depending on the composition. Therefore, it is preferable to use it for an optical modulator.

  In particular, since the relative permittivity changes greatly in the vicinity of the ferroelectric transition, it is preferable to operate by setting the vicinity of the phase transition as the operating temperature.

  However, in this temperature range, the dielectric constant of KTN or KLTN is high as described above, so that a large refractive index change can be caused efficiently, which is very effective from the viewpoint of operating the optical modulator efficiently. At the same time, the electric capacity between the positive electrode and the negative electrode is increased. For example, when switching is performed, charging / discharging corresponding to the electric capacity is performed, but power consumption corresponding to the switching speed is generated. Therefore, when KTN or KLTN is used, the electric capacity becomes high at an operating temperature at which modulation can be performed efficiently, so that the burden on the drive power supply becomes very large, making practical application difficult.

  In addition to KTN and KLTN, there is a demand for reducing the burden on the driving power source due to the high electric capacity without impairing the modulation effect for all electro-optic crystals having secondary electro-optic effect. .

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical modulator capable of reducing the burden on the drive power supply.

In order to achieve the above object, an invention according to claim 1, an optical modulator, an electro-optical crystal having a secondary electro-optic effect, the first surface of the electro-optical crystal, the N first electrodes (N is an integer of 3 or more) arranged along a direction P in which light of the electro-optic crystal is guided, and a second surface facing the first surface of the electro-optic crystal in, and a pre-Symbol direction P arranged along the N second electrodes, said and each of the N first electrodes, 1 wherein as corresponding in pairs 1 N second by placing the electrode, to form N pairs of electrodes, wherein among the N electrode pairs, one electrode of the first electrode pair along the leading Symbol direction P external electrically connected is, the other electrode is electrically and next electrode pair one of the electrodes of connected along the leading Symbol direction P, among the N electrode pairs, before Symbol direction P One electrode of the N-th electrode pair along is electrically connected to the outside, the other electrode is one electrode electrically connected to the electrode pairs before along the leading Symbol Direction P, the among the N electrode pairs, K-th (K is 2 or more and N-1 an integer) one electrode of the electrode pair is pre SL side of the next along the direction P electrode pairs of either electrode and is electrically connected, and the other electrode of the K-th electrode pair, characterized in that it is pre-Symbol side electrically connected to one of the electrodes of the front electrode pair along the direction P .

The invention according to claim 2 is an optical modulator, which is an electro-optic crystal having a secondary electro-optic effect, and a direction in which light of the electro-optic crystal is guided to the first surface of the electro-optic crystal. a plurality of first electrodes arranged along P, the electricity second surface opposite the first surface of the optical crystal, before Symbol sides plurality of second electrodes arranged along the direction P with bets, of the first electrode which is the arrangement, the first electrode along the leading Symbol direction P are electrically connected to the external, the disposed, the first electrode or the second electrode of, pre SL side end of the electrode along the direction P is externally electrically connected, in the first and second electrodes, the outside electrode electrically connected to the other electrode, respectively , As seen from a part of each of the adjacent electrodes arranged on the surface facing itself, and the first surface and the second surface Characterized in that it is arranged so that.

According to a third aspect of the invention of claim 1 Symbol placement, in the area of the electro-optic crystal between the pair of electrodes has a low dielectric constant low dielectric constant insulating material is inserted than the electro-optical crystal It is characterized by.

According to a fourth aspect of the present invention, in the second aspect of the invention, the electro-optic crystal region between the first electrodes and the electro-optic crystal region between the second electrodes are arranged in the electro-optic region. A low dielectric constant insulating material having a dielectric constant lower than that of the crystal is inserted.

The invention according to claim 5 is the invention according to claim 3 or 4 , wherein the low dielectric constant insulating material is a multicomponent oxide glass or polymer material, KTaO3, or a multilayer structure thereof. .

The invention according to claim 6 is the invention according to any one of claims 1 to 4 , wherein the material of the first electrode and the second electrode is Pt, Co, Ge, Au, Pd, Ni, Ir, Pt, Se, Cs, Rb, K, Sr, Ba, Na, Ca, Li, Y, Sc, La, Mg, As, Ti, Hf, Zr, Mn, In, Ga, Cd, Bi, Ta, Pb, Ag, Al, V, Nb, Ti, Zn, Sn, B, Hg, Cr, Si, Sb, W, Mo, Cu, Fe, Ru, Os, Te, Re, Be, Rh Features.

  According to the present invention, a plurality of electrodes for applying an electric field to a secondary electro-optic crystal are arranged, and the electrodes are connected in series, so that an optical modulator capable of reducing the burden on the drive power supply is provided. It becomes possible to do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.

In one embodiment of the present invention, KTN (KTa _1-x Nb _x O ₃ (0 <x <1)) and KLTN (K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 <y <1)), etc., which is an optical modulator using an electro-optic crystal having a secondary electro-optic effect, wherein electrodes are arranged on opposite surfaces of the electro-optic crystal, and an electric field is applied to the electro-optic crystal. When applying and performing predetermined modulation (phase modulation, intensity modulation, etc.), each of the electrodes arranged opposite to each other is divided into N pieces (an integer of 2 or more) and connected in series, and the electric capacity is It is to reduce.

The above KTN and KLTN exhibit a large secondary electro-optic effect when an electric field is applied in the crystal axis direction. The value is (1200 to 8000 pm / V), which is significantly larger than the nonlinear constant 30 pm / V of LiNO ₃ (LN), which is a material having a primary electro-optic effect. Furthermore, KTN and KLTN can change the phase transition temperature from paraelectricity to ferroelectricity from almost absolute zero to 400 ° C. by changing the composition ratio of Ta and Nb. Therefore, the operating temperature can be set as desired, such as room temperature, without using a temperature controller. Thus, KTN and KLTN are preferable materials for the optical modulator.

In one embodiment of the present invention, the material used as the modulation region of the optical modulator is not limited to KTN or KLTN. An object of one embodiment of the present invention is not to perform a modulation operation at a low voltage, but to reduce the capacitance of the electrode when a material having a secondary electro-optic effect is applied to the modulation region. Therefore, the material used for the modulation material is not limited to KTN and KLTN, but LiTaO ₃ , LiIO ₃ , KNbO ₃ , KTiOPO ₄ , BaTiO ₃ , SrTiO ₃ , Ba _1-x Sr _x TiO ₃ (0 <x <1). _{, Ba 1-x Sr x Nb} 2 O 6 (0 <x <1), Sr 0.75 Ba 0.25 Nb 2 O 6, Pb 1-y La y Ti 1-x Zr x O 3 (0 <x <1,0 <Y <1), Pb (Mg _1/3 Nb _2/3 ) O ₃ —PbTiO ₃ , KH ₂ PO ₄ , KD ₂ PO ₄ , (NH ₄ ) H ₂ PO ₄ , BaB ₂ O ₄ , LiB ₃ O ₅ , CsLiB ₆ O ₁₀ , GaAs, CdTe, GaP, ZnS, ZnSe, ZnTe, CdS, CdSe, and ZnO, and any dielectric material having a secondary electro-optic effect may be used.

  The material of the electrode for applying an electric field to the electro-optic crystal is Pt, Co, Ge, Au, Pd, Ni, Ir, Pt, Se, Cs, Rb, K, Sr, Ba, Na, Ca, Li Y, Sc, La, Mg, As, Ti, Hf, Zr, Mn, In, Ga, Cd, Bi, Ta, Pb, Ag, Al, V, Nb, Ti, Zn, Sn, B, Hg, Cr , Si, Sb, W, Mo, Cu, Fe, Ru, Os, Te, Re, Be, and Rh can be used. Further, an alloy using a plurality of the above materials may be used.

(First embodiment)
FIG. 2 is a diagram illustrating a configuration of the optical modulator according to the present embodiment.
In FIG. 2, the optical phase modulator 20 includes an electro-optic crystal 21 having a secondary electro-optic effect. On the first surface of the electro-optic crystal 21, electrodes 22a, 23a, 24a, 25a, and 26a are arranged at predetermined intervals. On the other hand, the electrodes 22b, 23b, 24b, 25b, and 26b are arranged at the predetermined interval on the second surface of the electro-optic crystal 21 that faces the first surface. In addition, each electrode 22a-26b shall have the same area S.
Hereinafter, a case where the electro-optic crystal 21 is KTN will be described.

  In the present embodiment, the electrode 22a and the electrode 22b form a first electrode pair, and when a voltage is applied to the electrodes 22a and 22b, an electric field is formed therebetween. Similarly, the electrode 23a and the electrode 23b form a second electrode pair, the electrode 24a and the electrode 24b form a third electrode pair, and the electrode 25a and the electrode 25b form a fourth electrode pair. The electrode 26a and the electrode 26b form a fifth electrode pair.

  Thus, in this embodiment, electrode pairs are formed as many as the number of electrodes arranged on one surface of the electro-optic crystal 21. Therefore, when N electrodes (N is an integer of 2 or more) are arranged on one surface of the electro-optic crystal 21, N electrodes are also arranged on the second surface facing the one surface. Each of the electrodes formed on the first surface forms a one-to-one electrode pair with respect to each of the electrodes formed on the second surface. Therefore, N electrode pairs are formed.

  As will be described later, in this embodiment, it is important to connect each electrode pair in series along the direction P in which the light of the electro-optic crystal 21 is guided. Therefore, how to electrically connect each electrode pair becomes important.

  In FIG. 2, the electrodes 22 a constituting the first electrode pair are connected to the electrical wiring 27. The electrical wiring 27 is connected to a positive electrode of a power source (not shown) for applying a modulation voltage. The electrode 22b constituting the first electrode pair is electrically connected to the electrode 23a constituting the second electrode pair and the electric wiring 28a. With such a configuration, the first electrode pair and the second electrode pair are connected in series along the direction P.

  Similarly, the electrode 23b constituting the second electrode pair and the electrode 24a constituting the third electrode pair are electrically connected by the electric wiring 28b, and the electrode 24b constituting the third electrode pair and the fourth electrode The electrode 25a constituting the second electrode pair is electrically connected by the electric wiring 28c, and the electrode 25b constituting the fourth electrode pair and the electrode 26a constituting the fifth electrode pair are electrically connected by the electric wiring 28d. It is connected. The electrode 26b constituting the fifth electrode pair is connected to the negative electrode of the power source via an electric wiring 29. With such a configuration, the first to fifth electrode pairs are connected in series.

  In such a configuration, when a voltage is applied from the power source during the modulation operation, the electric field extends from the electrode 22a toward the electrode 22b, that is, in a direction perpendicular to the direction in which the incident light incident on the electro-optic crystal 21 propagates. E occurs. Similarly, an electric field E is generated from the electrode 23a to the electrode 23b, from the electrode 24a to the electrode 24b, from the electrode 25a to the electrode 25b, and from the electrode 26a to the electrode 26b. At this time, when light passes through the electro-optic crystal 21 in the direction P, the light that has passed through undergoes phase modulation.

Below, the effect | action and effect of this embodiment are demonstrated.
FIG. 3 is a diagram showing a configuration of a conventional optical phase modulator as a comparative example.
In FIG. 3, the optical phase modulator 30 includes an electro-optic crystal (KTN) 31 having a secondary electro-optic effect, and a positive electrode 32 having an area of 5S is formed on the first surface of the electro-optic crystal 31. Is disposed, and the negative electrode 33 having an area of 5S is disposed on the second surface opposite to the first surface. The electric capacity of the optical phase modulator 30 is C ₁ .

In general, when a conductor plate of a capacitor having an electric capacity C ₀ is equally divided into N pieces and N capacitors formed by the division are connected in series, the electric capacity C _N of each divided capacitor is:

Satisfy the relationship. That is, the electric capacity of each capacitor after division becomes smaller than the electric capacity of the capacitor before division in proportion to the square of the number of divisions.

When an electro-optic crystal having a secondary electro-optic effect such as KTN is inserted between the conductor plates constituting the capacitor, an optical phase modulator as shown in FIG. 3 is obtained. When the driving voltage of such an optical phase modulator is V ₀ and the driving voltage V ₀ is applied to each of the divided capacitors, the total driving voltage V _N of the divided optical phase modulator is divided as described above. Since the capacitors are connected in series,

Satisfy the relationship. That is, the sum of the drive voltages after the division increases in proportion to the number of divisions with respect to the drive voltage before the division.

In the optical phase modulator 30, a capacitor having an electric capacity C ₁ is formed by disposing the two electrodes 32 and 33 so as to face each other, but there are M electrodes (M) (M Is an integer equal to or greater than 2), and M capacitors formed by the divided electrodes are connected in series, the electric capacity C ₂ of the M capacitors is based on the equation (1). ,

It becomes.

On the other hand, regarding the drive voltage, assuming that the drive voltage of the optical phase modulator 30 before the division is V ₁ and the drive voltage after the division is V ₂ , V ₂ = MV based on the equation (2) because it is connected in series. ₁

Thus, when the electrodes of the optical phase modulator 30 are divided into M pieces and connected in series, the drive voltage is M times before division, but the electric capacity is 1 / M ² , The electric capacitance C ₂ in the capacitor can be greatly reduced. Therefore, although the drive voltage is increased, the electric capacity can be greatly reduced, so that the load on the drive power supply can be reduced.

  The optical phase modulator 20 according to this embodiment shown in FIG. 2 is exactly equivalent to the above-described form in which the electrode of FIG. 3 is divided into M pieces.

  The area of the positive electrode 32 which is an electrode arranged on the first surface of the optical phase modulator 30 is 5S, and the electrodes 22a, 23a, 24a, 25a, 26a arranged on the first surface of the optical phase modulator 20 are. The total area is 5S. Similarly, the area of the negative electrode 33 which is an electrode disposed on the second surface of the optical phase modulator 30 is 5S, and the electrodes 22b, 23b, 24b, which are disposed on the second surface of the optical phase modulator 20, The total area of 25b and 26b is 5S. Therefore, each electrode of the optical phase modulator 20 is equivalent to one obtained by dividing the positive electrodes 32 and 33 of the optical phase modulator 30 into five.

Therefore, when the capacitance of each electrode pair of the optical phase modulator 20 is C ₃ , from the relationship of Expression (1),

Thus, the electric capacity can be greatly reduced.

  In the optical phase modulator 20 according to the present embodiment, each electrode is arranged at a predetermined interval, so that the phase modulation region is larger than that of the optical phase modulator 30. However, by setting the predetermined interval to an interval that does not reduce the modulation effect, the optical phase modulator 20 can perform phase modulation equivalent to that of the optical phase modulator 30. That is, the optical phase modulator 20 according to the present embodiment can reduce the electric capacity while realizing a phase modulation effect equivalent to that of the optical phase modulator 30 shown in FIG.

  The predetermined interval for arranging the electrodes should be at least 1/5 of the interval between the first surface and the second surface in order to keep the electric field strength that can be generated between the electrodes formed on the same surface sufficiently small. Is preferred. For example, when the interval between the first surface and the second surface is 1 mm, the predetermined interval for arranging the electrodes is preferably 0.2 mm or more.

  As described above, in the present embodiment, when desired modulation is performed in the optical modulator, the electrode for performing the desired modulation is divided in order to reduce the capacitance of the electrode for performing the modulation. It is essential to form N electrode pairs and connect the N electrode pairs in series. In other words, in the present embodiment, a plurality of electrodes smaller than the electrodes conventionally required for performing desired modulation are formed, and modulation equivalent to the desired modulation is performed. Therefore, in this embodiment, although the area of the electrodes 22a to 26b is constant, it is not essential to keep the areas constant. That is, it is essential that the electric capacities of the first to fifth electrode pairs are made smaller than the electric capacities of the electrode pair composed of the positive electrode 32 and the negative electrode 33. In consideration of the essence, the electrode 22a Each of .about.26b may have a constant area or a different area.

  Further, in the present embodiment, an electrode formed on the second surface of a certain electrode pair is electrically connected to an electrode formed on the first surface of the next electrode pair along the direction P by electric wiring or the like. Although the series connection is realized by connecting, it is not limited to this. For example, in FIG. 2, the electrode 23b and the electrode 24a are connected by the electric wiring 28b. However, by connecting the electrode 23b and the electrode 24b by the electric wiring 28b, the second electrode pair and the third electrode The electrode pair may be connected in series. At this time, considering that the electrode pairs are connected in series, the third electrode pair and the fourth electrode pair are connected in series by connecting the electrode 24a and the electrode 25a with the electric wiring 28c.

  As described above, in this embodiment, in order to connect each electrode pair in series, focusing on a certain electrode pair, each of the two electrodes constituting the electrode pair is connected to only one of the front and rear electrode pairs. It establishes an electrical connection.

  That is, when N electrodes (N is an integer of 3 or more) are arranged on the first and second surfaces of the electro-optic crystal, respectively, the Kth electrode (K; an integer of 2 or more and N-1 or less) One electrode of the pair is electrically connected to one electrode of the next electrode pair along the direction P, and the other electrode of the Kth electrode pair is the previous electrode pair along the direction P. It is made to be electrically connected to any one of the electrodes. One electrode of the first electrode pair is connected to the positive electrode of the power supply (that is, electrically connected to the outside of the optical phase modulator), and the other electrode is the next electrode pair along the direction P. One electrode of the Nth electrode pair is connected to the negative electrode of the power source, and the other electrode is connected to one electrode of the previous electrode pair along the direction P. To be.

  In addition, when two electrodes are arranged on the first and second surfaces of the electro-optic crystal, one of the two electrode pairs in the first electrode pair along the direction P is: Connected to the positive electrode of the power supply, the other electrode is electrically connected to one electrode of the second electrode pair along the direction P. On the other hand, the electrode that is not electrically connected to the first electrode pair of the second electrode pair is connected to the negative electrode of the power source.

  Thus, in the present embodiment, the electrodes can be connected regardless of the direction of the electric field generated between the electrodes. The reason for this effect is that a dielectric crystal having a secondary electro-optic effect is used as the electro-optic crystal.

  If a dielectric crystal having a first-order electro-optic effect is used as the electro-optic crystal to be used, the modulation operation cannot be performed satisfactorily without considering the connection of the electrode pair when the series connection is made. That is, in the dielectric crystal having the primary electro-optic effect, the refractive index changes in proportion to the applied electric field. Therefore, when a plurality of electrode pairs are arranged along the direction P as in the present invention, If the direction of the electric field generated between the electrode pairs is not aligned, the modulation effect will be canceled.

  On the other hand, in the present embodiment, since a dielectric crystal having a secondary electro-optic effect whose refractive index change is proportional to the square of the electric field is used, a plurality of electrode pairs are arranged along the direction P. Even if the direction of the electric field generated between the electrode pairs is not uniform, the modulation effect is not affected. Therefore, the electrodes can be freely connected without considering the direction of the electric field generated between the electrodes.

  As described above, in the present invention, it is important to arrange a plurality of electrode pairs along a predetermined direction from one side of the electro-optic crystal to the other, and to connect the electrode pairs in series. In order to reduce the limitation of electrical connection when performing the above, a dielectric crystal having a secondary electro-optic effect is used as the electro-optic crystal.

(Second Embodiment)
In the present embodiment, a form of series connection different from the first embodiment will be described.
FIG. 4 is a cross-sectional view showing the configuration of the optical modulator according to this embodiment.
In FIG. 4, the optical phase modulator 40 includes an electro-optic crystal 41 having a secondary electro-optic effect. On the first surface of the electro-optic crystal 41, electrodes 42, 43, and 44 are arranged at a predetermined interval. On the other hand, the electrodes 45, 46 and 47 are arranged at the predetermined interval on the second surface of the electro-optic crystal 41 facing the first surface.
Further, a low dielectric constant insulating material 48 a such as SiO ₂ is inserted (arranged) in the region of the electro-optic crystal 41 between the electrode 42 and the electrode 43. Similarly, a low dielectric constant insulating material 48 b is inserted (arranged) in the region of the electro-optic crystal 41 between the electrode 45 and the electrode 46, and the region of the electro-optic crystal 41 between the electrode 43 and the electrode 44 is inserted. A low dielectric constant insulating material 48 c is inserted (arranged), and a low dielectric constant insulating material 48 d is inserted (arranged) in the region of the electro-optic crystal 41 between the electrode 46 and the electrode 47.

  Hereinafter, a case where the electro-optic crystal 41 is KTN will be described.

In the present embodiment, an electric field is generated in the electro-optic crystal by a part of the electrode formed on one surface and a part of the electrode formed on the surface opposite to the one surface. . In FIG. 4, the electrode 45 is arranged so that an electric field E ₁ is generated between a part of the electrode 42 formed on the first surface and a part of the electrode 45 formed on the second surface. Yes. That is, the electrode 45 is arranged on the second surface so that a part of the electrode 45 overlaps a part of the electrode 42 when viewed from the first surface and the second surface, which are the surfaces on which the electrode is disposed. . The electrode 42 is connected to a positive electrode of a power source (not shown) for applying a modulation voltage via an electric wiring 49.

In addition, the electrode 43 is arranged so that the electrode 43 is separated from the electrode 42 at a predetermined interval, and a part of the electrode 43 overlaps a part of the electrode 45 when viewed from the first surface and the second surface. Yes. With this arrangement, an electric field E ₂ is generated between a part of the electrode 45 and a part of the electrode 43.

Similarly, the electrode 46 is disposed so that the electrode 46 is separated from the electrode 45 at a predetermined interval, and a part of the electrode 46 overlaps a part of the electrode 43 when viewed from the first surface and the second surface. ing. With this arrangement, an electric field E ₃ is generated between a part of the electrode 43 and a part of the electrode 46.

Similarly, the electrode 44 is disposed so that the electrode 44 is spaced apart from the electrode 43 at a predetermined interval and part of the electrode 44 overlaps part of the electrode 46 when viewed from the first surface and the second surface. ing. With this arrangement, an electric field E ₄ is generated between a part of the electrode 46 and a part of the electrode 44.

Further, the electrode 47 is arranged so that the electrode 47 is spaced apart from the electrode 46 at a predetermined interval and part of the electrode 47 overlaps part of the electrode 44 when viewed from the first surface and the second surface. Yes. With this arrangement, an electric field E ₅ is generated between a part of the electrode 44 and a part of the electrode 47. The electrode 47 is connected to the negative electrode of the power source via an electric wiring 50.

In this embodiment, when a positive voltage is applied to the electrode 42 from the power source by such an electrode arrangement, the electro-optic crystal 41 is interposed between a part of the electrode 42 and a part of the electrode 45 overlapping therewith. An electric field E ₁ is generated in a direction perpendicular to the direction in which incident incident light propagates. In the present embodiment, the region where the electric field E ₁ is generated is referred to as a first electrode pair. At this time, a positive charge is accumulated in the electrode 42, and a negative charge is accumulated in a region constituting the first electrode pair in the electrode 45 (a region overlapping with a part of the electrode 42) by electrostatic induction. Due to the charge neutral condition, positive charges are accumulated in a region of the electrode 45 overlapping with a part of the electrode 43. At the same time, a negative charge is accumulated in a portion of the electrode 43 that overlaps a part of the electrode 45. Therefore, an electric field E ₂ is generated between a part of the electrode 45 and a part of the electrode 43 overlapping therewith. In the present embodiment, the region where the electric field E ₂ is generated is referred to as a second electrode pair.

Electrostatic induction similarly occurs in the electrodes 43 to 47, and an electric field E ₃ is generated between a part of the electrode 43 and a part of the electrode 46 that overlaps the part (referred to as a third electrode pair in this embodiment). , An electric field E ₄ is generated between a part of the electrode 46 and a part of the electrode 44 that overlaps the part (referred to as a fourth electrode pair in the present embodiment), and one part of the electrode 47 that overlaps a part of the electrode 44. An electric field E ₅ is generated between the electrode portion (the fifth electrode pair in the present embodiment).
That is, in the present embodiment, as for the electrode for generating an electric field inside the electro-optic crystal, an electrode (for example, the electrode 46) other than the electrodes (electrodes 42 and 47 in FIG. 4) connected to the power source is used. And a part of each of the adjacent electrodes (for example, electrodes 43 and 44) disposed on the surface opposite to each other, as viewed from the first surface and the second surface. In FIG. 4, each of the electrodes (electrodes 42 and 47) connected to the power source, that is, an electrode for electrical connection from the optical phase modulator 40 to the outside is different from the electro-optic crystal. Although arranged on the surface, they may be arranged on the same surface.

  In addition, since the series connection is performed as described above, the electrodes for electrical connection to the outside are the electrodes at both ends along the direction P among the plurality of electrodes arranged in the electro-optic crystal 41. Become. That is, among the electrodes disposed on either the first surface or the second surface, the first electrode along the direction P is electrically connected to the outside, and the first surface or the second surface Of the electrodes arranged on one of the surfaces, the last electrode along the direction P is also electrically connected to the outside.

  Thus, in this embodiment, series connection can be realized without using electrical wiring. Therefore, as in the first embodiment, the electric capacity can be greatly reduced.

  By the way, in the present embodiment, a plurality of electrodes are disposed on the first surface and the second surface of the electro-optic crystal 41, respectively, so as to partially overlap the electrodes disposed on the opposing surfaces. A certain electrode may be affected by lines of electric force generated from an electrode arranged on the same plane as the electrode. That is, in this embodiment, in order to reduce the electric capacity, a plurality of electrodes are arranged on the first surface and the second surface of the electro-optic crystal from the viewpoint that the electrodes are divided and arranged. The electrodes arranged on the surface may be affected by the lines of electric force, weakening the electric field generated in the electro-optic crystal. For example, in FIG. 4, positive charge is accumulated in the electrode 42, and negative charge is accumulated in a region on the electrode 42 side of the electrode 43 (region on the left side of the electrode 43 in the drawing). From there, electric lines of force may occur in the left side of the electrode 43 in the drawing.

Thus, in the present embodiment, low dielectric materials 48a to 48d such as SiO ₂ are disposed between the electrode pairs. These low dielectric constant insulating materials 48a to 48d can reduce the influence of adjacent electrodes, such as reducing the influence of electric lines of force.

In this embodiment, the low dielectric constant insulating material is arranged in the region of the electro-optic crystal between the electrodes arranged on the same surface, thereby reducing the influence of unwanted electric lines of force between the electrodes. Since the function is achieved, a material having a dielectric constant lower than that of the electro-optic crystal to be used is used as the low dielectric constant insulating material. For example, it is preferable to use a multicomponent oxide glass or polymer such as SiO ₂ , KT (KTaO ₃ ), or a multilayer structure thereof.

  As described above, since the dielectric constant of the low dielectric constant insulating material according to the present embodiment is lower than that of the electro-optic crystal used, the refractive index of the low dielectric constant insulating material is lower than the refractive index of the electro-optic crystal used. Become. Therefore, the low dielectric constant insulating material according to the present embodiment has an AR (Anti-Reflection) function.

In the present embodiment, the low dielectric constant insulating material preferably has a multilayer structure in order to sufficiently function as an AR coat. Low dielectric constant insulating material, for example, with a refractive index
(N ₁ / n ₂ ) ² = n _KTN
(N ₁ , n ₂ , and n _KTN represent the refractive index of the first low dielectric constant insulating material, the refractive index of the second low dielectric constant insulating material, and the refractive index of KTN, respectively)
Using a first low dielectric constant insulating material and a second low dielectric constant insulating material satisfying
n ₁ × d ₁ = λ / 4, n ₂ × d ₂ = λ / 4
(D ₁ and d ₂ represent the thickness of the first low dielectric constant insulating material and the thickness of the second low dielectric constant insulating material, respectively, and λ represents the wavelength of light in vacuum)
A sufficient AR function is realized by forming the first low dielectric constant insulating material / the second low dielectric constant insulating material / the first low dielectric constant insulating material to satisfy the above three-layer structure.

For example, since the refractive index of KTN in visible light is 2.4, KT (KTaO ₃ ) (refractive index: 2.24) is used as the first low dielectric constant insulating material, and SiO is used as the second low dielectric constant insulating material. ₂ By using (refractive index: 1.45), the above-mentioned conditions regarding the refractive index are almost satisfied. For example, when the wavelength of incident light is 500 nm in vacuum, the above d ₁ and d ₂ are 56 nm and 86 nm, respectively, so KT (56 nm thickness) / SiO ₂ (86 nm thickness) / KT (56 nm thickness) A sufficient AR function is realized by the three-layer structure.

  In the present embodiment, it is preferable to dispose a low dielectric constant insulating material because the influence of electric lines of force from adjacent electrodes can be reduced as described above, but it is not necessary to dispose the material. .

  It goes without saying that a low dielectric constant insulating material may be disposed in a region between each electrode pair in the electro-optic crystal in the first embodiment.

Next, a manufacturing method of the optical phase modulator 40 according to the present embodiment will be described.
FIG. 5 is a diagram for explaining a method of manufacturing the optical phase modulator according to the present embodiment.
A conventional method is used to form KTN51 as an electro-optic crystal (FIG. 5A). Next, SiO ₂ 52 as a low dielectric constant insulating material is formed on the KTN 51 (FIG. 5B). The SiO ₂ may be formed by any method such as vapor deposition, sputtering, or sol-gel method. Next, KTN 51 is formed again on SiO ₂ 52 (FIG. 5C). By repeating the steps shown in FIG. 5B and FIG. 5C three times, the laminate 53 is formed (FIG. 5D).

  Next, an electrode 56 is formed at a predetermined position on the first surface 54 of the stacked body 53 using photolithography and dry etching. Next, an electrode 57 is formed at a predetermined position on the second surface 55 of the stacked body 53 using photolithography and dry etching. In this way, the optical phase modulator shown in FIG. 4 is manufactured (FIG. 5E).

When a low dielectric constant insulating material having a three-layer structure of KT / SiO ₂ / KT is used to realize the AR function, KT may be formed on the KTN 51 by, for example, MOCVD before forming the SiO ₂ 52. .

It is sectional drawing which shows the structure of the optical phase modulator using the conventional electro-optic crystal. 1 is a perspective view showing a configuration of an optical modulator according to an embodiment of the present invention. It is a figure for demonstrating the effect | action of one Embodiment of this invention, Comprising: It is a perspective view which shows the structure of the conventional optical phase modulator. It is sectional drawing which shows the structure of the optical modulator which concerns on one Embodiment of this invention. (A)-(e) is a figure for demonstrating the manufacturing method of the optical phase modulator which concerns on one Embodiment of this invention.

Explanation of symbols

20, 40 Optical phase modulator 21, 41 Electro-optic crystal 22a-26b, 42-47 Electrode 27-29, 49, 50 Electrical wiring

Claims (6)

An electro-optic crystal having a secondary electro-optic effect;
N first electrodes (N is an integer of 3 or more) arranged on a first surface of the electro-optic crystal along a direction P in which light of the electro-optic crystal is guided ;
Wherein the second surface facing the first surface of the electro-optic crystal, and a second electrode of the N, which is arranged along the front Symbol Direction P,
By arranging the N second electrodes so as to correspond to each of the N first electrodes on a one-to-one basis, N electrode pairs are formed,
Wherein among the N electrode pairs, one electrode of the first electrode pair along the leading Symbol Direction P is externally electrically connected, next electrode and the other electrode along the leading Symbol Direction P Electrically connected to one electrode of the pair,
Wherein among the N electrode pairs, one electrode of the N-th electrode pairs along the front Symbol Direction P is externally electrically connected to the electrode before the other electrode along the leading Symbol Direction P Electrically connected to one electrode of the pair,
Among the N electrode pairs, K-th (K is 2 or more and N-1 an integer) one electrode of the electrode pair is either one of the following electrode pairs along the front Symbol Direction P connected electrodes and electrically, and the other electrode of the K-th electrode pair, and being connected before Symbol direction P either of the previous electrode pairs along the electrode and electrically Light modulator. An electro-optic crystal having a secondary electro-optic effect;
A plurality of first electrodes disposed on a first surface of the electro-optic crystal along a direction P in which light of the electro-optic crystal is guided ;
Wherein the second surface opposite the first surface of the electrooptic crystal, before SL direction and a plurality of second electrodes arranged along the direction P,
Of the first electrode which is the arrangement, the first electrode along the leading Symbol Direction P is electrically connected to an external,
Wherein arranged, of the first electrode or the second electrode, the final electrode along the leading Symbol Direction P is electrically connected to the outside,
In the first electrode and the second electrode, each of the electrodes other than the electrode electrically connected to the outside is a part of each of the adjacent electrodes disposed on a surface facing the first electrode and the second electrode, and the first electrode An optical modulator, wherein the optical modulator is disposed so as to overlap each other when viewed from the second surface and the second surface. The electricity area of the optical crystal, 1 Symbol placement of the optical modulator according to claim, characterized in that the low dielectric constant insulating material having a lower dielectric constant than the electro-optical crystal is inserted between the electrode pair. A low dielectric constant insulating material having a dielectric constant lower than that of the electro-optic crystal is inserted in the electro-optic crystal region between the first electrodes and the electro-optic crystal region between the second electrodes. The optical modulator according to claim 2, wherein: The low dielectric constant insulating materials, multicomponent oxide glass or polymeric material or KTaO3 or optical modulator according to claim 3 or 4, wherein the is these multilayer structures,,. The materials of the first electrode and the second electrode are Pt, Co, Ge, Au, Pd, Ni, Ir, Pt, Se, Cs, Rb, K, Sr, Ba, Na, Ca, Li, Y, Sc, La, Mg, As, Ti, Hf, Zr, Mn, In, Ga, Cd, Bi, Ta, Pb, Ag, Al, V, Nb, Ti, Zn, Sn, B, Hg, Cr, Si, sb, W, Mo, Cu, Fe, Ru, Os, Te, Re, be, optical modulator according to any one of claims 1 to 5, characterized in that either Rh.

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