JP2006162984A - Light-intensity modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-intensity modulator whose driving current is small and which can operate at high speed. <P>SOLUTION: The light-intensity modulator has, on a substrate 5, a 3dB coupler 18, a 1st optical waveguide 19 and a 2nd optical waveguide 20 coupled to the 3dB coupler 18, and a 3dB coupler 24 coupled to the 1st optical waveguide 19 and 2nd optical waveguide. The 1st optical waveguide 19 is a waveguide including a core made of a material which has secondary electrooptical effect and a higher dielectric constant than the substrate 5. The waveguide is provided with a plus electrode 21 and a minus electrode 22, which are arranged at an interval L<SB>1</SB>wider than the width W of the core in the direction where light in the 1st optical waveguide 19 travels and further arranged on the 1st optical waveguide 19 so as to apply an electric field to the core in the above direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light intensity modulator applied to an optical switch or the like that switches a path of an optical signal with an electric signal.

  With the spread of the Internet in recent years, optical communication technology has been developed, and there is a demand for the formation of an optical network capable of transmitting a large amount of information. In realizing such an optical network, there is an increasing demand for an optical intensity modulator. In particular, in order to perform routing on optical packets, a small light intensity modulator that realizes high speed and high integration is required.

As such a light intensity modulator, there is a Mach-Zehnder type light intensity modulator configured using a phase modulator, and an electro-optical element is required to configure this phase modulator. As a material constituting the electro-optic element, a dielectric material having a secondary electro-optic effect and having a high dielectric constant is used. As such a dielectric material, KTa _x Nb _1-x O ₃ (0 <x <1) (also referred to as KTN) is preferably used.

  KTN crystals have the property of changing the crystal system depending on temperature from cubic to tetragonal to rhombohedral, and it is known that cubic crystals have a large secondary electro-optic effect. In particular, in a region close to the phase transition temperature from cubic to tetragonal, a phenomenon in which the relative permittivity diverges occurs, and the secondary electro-optic effect proportional to the square of the relative permittivity is a very large value. Therefore, it is possible to keep the applied voltage required for phase modulation low.

  Now, for example, as a general light intensity modulator according to the well-known prior art, as shown in FIG. 1, a + electrode and one electrode are formed in the core portion of the waveguide, and a voltage is applied between the two electrodes. Has been proposed (see Patent Document 1). 1A and 1B are configuration diagrams of a conventional optical phase modulator, FIG. 1A is a top view of the conventional optical phase modulator, and FIG. It is AA 'line cutting | disconnection sectional drawing of 1 (a).

JP-A-5-346560

In FIG. 1, a core 2 is formed on a substrate 1, and a positive electrode 3 and a negative electrode 4 are provided on both sides of the core 2 so as to face each other. In such a configuration, an electric field E _core is generated in a region between the electrodes 3 and 4 due to the potential difference applied between the electrodes 3 and 4. Then, when the core 2 is a substance having an electro-optic effect, the refractive index of the portion to which the electric field is applied changes, and the refractive index of the core 2 changes according to the electric field generated in the core 2. When the material constituting the core 2 is a substance in which the primary electro-optic effect is dominant, the refractive index change amount Δn of the core 2 is proportional to the amount of electric field generated in the core 2.
Δn∝E _core

When the material constituting the core 2 is a substance in which the secondary electro-optic effect is dominant, the refractive index change amount Δn of the core 2 is proportional to the square of the amount of the electric field generated in the core 2.
Δn∝E _core ²

At this time, in both the primary and secondary electro-optic effects, the light propagating along the core 2 undergoes a phase change Δφ with a change in refractive index.
Δφ = 2πΔn * L / λ
Here, L is the length of the core portion where the refractive index has changed, and λ is the wavelength of the propagating light.

  Therefore, in the prior art, the phase of the light traveling through the core 2 can be modulated by Δφ by the voltage applied between the two electrodes 3 and 4.

However, when a high dielectric constant material is used for the core 2 in particular, the following drawbacks become apparent in the prior art. That is, when a high dielectric constant material is used for the core 2, the electric capacity C between the electrodes 3 and 4 increases. At this time, the amount of current required to apply a constant voltage between the electrodes 3 and 4 increases as the electric capacity C increases. A voltage applied between the electrodes 3 and 4 necessary for applying an electric field necessary and sufficient for phase modulation to the core 2 is V ₀ . The amount of charge Q that needs to be charged to apply this voltage V ₀ is Q = CV ₀ . In order to change the phase of light propagating through the core 2 with time, it is necessary to change the electric field applied to the core 2 with time. For example, to charge the charge Q during a certain time τ,
I = Q / τ = CV ₀ / τ (1)
It is necessary to flow the drive current. For example, C = driven by a switch having a capacity of 1nF voltage _V 0 = 3V, when an attempt to operate at an operating frequency 1 GHz, the time τ becomes approximately 300 ps. For this reason, a current of up to 10 A is required at the time of charging, and a driving circuit that requires a high speed, a large driving current, and a large power consumption is required.

As described above, when a high dielectric constant material is used for the core portion, it is necessary to design the drive voltage V ₀ as small as possible and the capacitance C as small as possible in order to prevent the drive current from increasing. become. However, this requires that the voltage applied to the electrode first be effectively applied to the core.

In order to generate an electric field only in the core as much as possible, it is necessary to reduce the distance between the electrodes as much as possible to the width of the core (waveguide). However, the capacitance C between about electrodes to narrow the electrode spacing in order to reduce the driving voltage V ₀ (spacing between disposed opposite to both sides of the core electrodes) will be increased, determined by the formula (1) It is difficult to greatly reduce the current required for charging. On the contrary, in order to reduce the electric capacity C, the distance between the electrodes may be increased. However, since the applied voltage is less likely to be effectively applied to the core portion, the voltage V for generating the necessary electric field in the core is reduced. There was a problem that ₀ increased and the drive current could not be reduced.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a light intensity modulator that has a small driving current and can operate at high speed.

  In order to achieve the above object, the present invention is characterized in that the invention according to claim 1 includes a branching unit formed on a substrate for branching incident light into first and second optical paths, and the first optical path. Are coupled to the first and second optical waveguides, and are incident on the first and second optical waveguides. A light intensity modulator comprising a light combining means for combining light, wherein at least one of the first and second optical waveguides has a secondary electro-optic effect and has a higher dielectric constant than the substrate. A waveguide including a core made of a material having a plus electrode and a minus electrode provided on the waveguide, and the plus electrode and the minus electrode travel light in the waveguide at an interval wider than the width of the core. Arranged along the direction of Characterized in that it is arranged on the waveguide so as to apply an electric field to the direction Te.

  According to a second aspect of the present invention, in the first aspect of the invention, there are a plurality of the positive electrodes and the negative electrodes, and the wave guides are arranged so that the positive electrodes and the negative electrodes alternate along the direction. It is arranged on the road.

The invention described in claim 3 is the invention described in claim 1 or 2, characterized in that the material is KTa _x Nb _1-x O ₃ (0 <x <1).

The invention according to claim 4 is the invention according to claim 1 or 2, wherein the material is K _1-y Li _y Ta _x Nb _1-x O ₃ (0 <x <1, 0 <y <1). It is characterized by being.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects of the present invention, an electric field is applied to the waveguide other than the core in the plus electrode and the minus electrode. It is characterized in that at least a part of the region is removed.

  A sixth aspect of the invention is characterized in that, in the invention of any one of the first to fifth aspects, the waveguide is a ridge waveguide.

  As described above, according to the present invention, the interval between the plus electrode and the minus electrode can be widened, and the electric capacity between the electrodes can be greatly reduced. At this time, although the magnitude of the voltage to be applied is increased, the effect of reducing the electric capacity is greater than that, so that it is possible to provide a light intensity modulator that can operate at a high speed with a small driving current.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
2A and 2B are configuration diagrams of the optical phase modulator according to the first embodiment of the present invention, and FIG. 2A is a top view of the optical phase modulator according to the present embodiment. FIG. 2B is a cross-sectional view taken along the line BB ′ of FIG.

In FIG. 2, a waveguide core 7 and clad 6 made of high dielectric constant KTa _x Nb _1-x O ₃ (0 <x <1) (KTN) are made of KTaO ₃ having a lower dielectric constant than KTN. 5 is formed to form a waveguide. That is, it is a buried waveguide formed so that the waveguide core 7 is surrounded by the clad 6 formed on the substrate 5. At this time, it goes without saying that the refractive index of the cladding 6 is effectively lower than the refractive index of the waveguide core 7.

  On the clad 6, in order to apply an electric field to the waveguide core 7, two metal electrodes, that is, a positive electrode 8 and a negative electrode 10 are both comb-shaped so that both sides of the waveguide core 7 face each other. Are arranged. The + electrode 8 includes a plurality of electrode pieces 9a and an electrode portion 9b that connects one end of each of the electrode pieces 9a. The − electrode 10 includes a plurality of electrode pieces 11a and each of the electrode pieces 11a. It consists of the electrode part 11b which connects one end. At this time, each electrode piece 9a and each electrode piece 11a are substantially parallel to each other, and the longitudinal direction of these electrode pieces is substantially orthogonal to the traveling direction P of the light propagating through the waveguide core 7. Are arranged as follows. Each electrode piece 9a and each electrode piece 11a are arranged so as to substantially cover a corresponding region of the waveguide core 7 so that an electric field can be applied to the waveguide core 7 and the minimum required cladding 6. Yes.

  Further, between the electrode pieces 9a of the clad 6 and between the electrode pieces 11a, a removal region 12 having a substantially rectangular shape and a depth penetrating the clad 6 is formed. That is, the removal region 12 is a region where the high dielectric constant portion is removed from the cladding 6, and an electric field can be prevented from being applied as much as possible to a portion other than the waveguide core 7 and the minimum necessary cladding 6. Of these, at least part of the region to which the electric field is applied. Thus, by removing the high dielectric constant portion other than the waveguide core 7 between the electrode pieces in the waveguide, an electric field is generated as much as possible in the portions other than the waveguide core 7 and the minimum required cladding 6. It does not take.

  Note that the shape of the removal region 12 is not limited to a substantially rectangular shape. That is, in order to prevent an electric field from being applied as much as possible to portions other than the waveguide core 7 and the minimum required cladding 6, a high dielectric constant is applied from the cladding 6 to each electrode piece 9a and between the electrode pieces 11a. It is important to remove the portion, and the shape of the removal region 12 can be any shape as long as an electric field is not applied to the portion other than the waveguide core 7 and the minimum required cladding 6 as much as possible. Also good.

Further, the spacing L ₁ between the electrode piece 9a and the electrode pieces 11a adjacent the on waveguide core 7, they become wider than the width W of the waveguide core (L _{1> W),} electric between electrodes The capacity is getting smaller. The number of each electrode piece on the waveguide may be a number such that both + and-are formed by an electric field formed by adjacent electrodes having different signs, and n pieces (n ≧ 2) of the electrode pieces 9a and 11a. do it. Moreover, either one of the electrode piece 9a or the electrode piece 11a may be n pieces, and the other may be n-1. Furthermore, the width W ₂ of the electrode piece on the waveguide core 7 is set to be very small compared to the interval L ₁ (L ₁ >> W ₂ ).

The relation between the distance L ₁ and the width W of the above will be described below.

As will be described later, there is a trade-off between applied voltage and electric capacity. In order to compare the driving current determined by the trade-off between the capacitance C and the voltage V ₀ with the prior art, as an example, in the present embodiment, the waveguide core is assumed to be a rectangular parallelepiped, and the size of the cross-sectional area is defined as the area. Let S (= W × W). At this time, for example, it is assumed that the electrode pieces 9a and the electrode pieces 11a are periodically arranged alternately every time the length of the waveguide core advances by 10W. The electric capacity between the electrodes (between the adjacent electrode piece 9a and the electrode piece 11a) can be approximated by an electric capacity including a field in which electrodes are attached to both ends in the longitudinal direction of a cuboid of W * W * 10W. it can. The electric capacity is C ₁ = εWW / (10 W) = 0.1εW (2)
It becomes. Where ε is the dielectric constant of the waveguide core.

Further, as in the prior art, when the + and one electrodes are arranged in a direction orthogonal to the longitudinal direction of the waveguide core, the capacity of the same rectangular parallelepiped as the above-mentioned rectangular parallelepiped is W * W * 10W rectangular parallelepiped. It can be approximated by the capacity when electrodes are attached to long faces facing each other along the longitudinal direction. The capacity at this time is
C ₂ = εW (10W) / W = 10εW (3)
It becomes.

As can be seen from the equations (2) and (3), C ₁ according to the present embodiment has a capacity that is 1/100 of that of C ₂ of the prior art. This is an improvement over the prior art 100. Further, the distance between the + electrode and the − electrode is 10 W of the long side in the present embodiment, whereas the length of the short side is W in the prior art. Therefore, 10 times the voltage is required to apply the same electric field to the waveguide core as compared with the prior art (in this case, a constant phase (refractive index) change in the direction along the waveguide core is generated). The applied electric field required to do this is the same regardless of whether a voltage is applied in the longitudinal direction of the waveguide core or in a direction perpendicular thereto.

However, as a result, as can be seen from equation (1) described above, the total current required to charge, C, the combined effect of V ₀ It can be seen that 1/10 compared to the prior art. That is, similarly, even in a situation where an electric field is applied only to the waveguide core, the phase modulator according to the present embodiment can reduce the amount of current required for driving than the conventional one. Thus, by greater than the width W of the waveguide core spacing L _1, + and - electrical capacitance between the electrodes can be reduced, even in consideration of voltage applied between the electrodes, the phase modulation operation The drive current required for this can be suppressed.

When the electrode piece is actually formed on the waveguide core, during a certain required length (the length of the portion of the waveguide core where the refractive index changes due to electric field application) L, for example, N = 2n in total Or 2n-1 electrode pieces are formed. Among them, n pieces are + electrode pieces as described above, and the remaining N−n pieces are − electrode pieces, and these + and − electrode pieces are alternately formed at equal intervals. Become. At this time, the voltage V ₀ to be applied between the + and − electrode pieces increases as the total number N of electrode pieces decreases and the distance between the + and − electrode pieces increases. Instead, the distance between adjacent electrode pieces with different signs is increased, and the number of electrodes is reduced. For this reason, the electrical capacitance C between adjacent electrode pieces of different signs is reduced. That is, there is a trade-off between the applied voltage and the electric capacity by changing the total number N of electrode pieces.

  As can be seen from the prior art related to the trade-off described above, the effect of this embodiment becomes more prominent as the distance between the electrodes is increased. When the electric field is completely applied only to the waveguide core, it is ideal to arrange + and − electrodes (electrode pieces) only at both ends of the entire waveguide, and at this time, the drive current is minimized. . However, in reality, as the distance between the + and − electrodes increases, an electric field is more likely to be applied to unnecessary portions other than the waveguide core, and the capacitance is likely to increase unnecessarily. In addition, if the distance between the + and − electrodes is too large, the driving voltage becomes too large. Accordingly, the number of the + and − electrode pieces is determined in consideration of the voltage applied to the unnecessary portion and the drivable voltage. Thus, by providing an appropriate number of electrode pieces, it is possible to further limit the portion to which the electric field is applied to the waveguide core.

On the other hand, when the electrode interval L ₁ of the present embodiment is the same as the width W of the waveguide core 7, the capacitance between the electrodes is the same as the conventional one, and an electric field of the same level as the conventional one is applied to the waveguide core 7. The voltage required for this is also the same as before. Therefore, in order to exhibit the effects described above in the present embodiment should not no wider than the electrode spacing L ₁ is the waveguide core width W.

  The electro-optic effect received by the light propagating through the waveguide core 2 will be described below.

  With the above-described electrode arrangement, the waveguide core 7 has an electric field in the first direction parallel to the direction P from the electrode piece 9a to the electrode piece 11a, and from the electrode piece 11a to the electrode piece 9a in the direction opposite to the direction P. Electric fields in the second direction are applied alternately. In this configuration, when a material using a primary electro-optic effect is used as the waveguide core 7, if the number of the electrode pieces 9 a and the electrode pieces 11 a is two or more, the electric field is in the first direction and the second direction. Since the voltage is applied, the modulation effect is canceled. However, when a material using the secondary electro-optic effect is used as the waveguide core 7, even if there are two or more electrode pieces 9a and electrode pieces 11a, the change amount Δn of the refractive index is as described above. Regardless of the direction of the electric field, it is proportional to the square of its absolute value. Therefore, regardless of whether the direction of application of the electric field is the first direction or the second direction, the phase change is not canceled in the same direction and is accumulated. For this reason, even if the number of + and − electrode pieces is increased, phase modulation having a size proportional to the length of the phase modulation region as a whole becomes possible.

Also, the + and - spacing L ₁ of the electrode pieces for wider than the width W of the waveguide core 7, becomes parallel to the traveling direction of the principal applied electric field waveguide core (longitudinal direction). At this time, the phase change due to the electric field received by the light propagating through the waveguide core 7 does not depend on the polarization of the light, and a polarization-independent phase modulator can be realized. Since the optical switch requires a polarization-independent operation, if the interferometer is configured using the optical phase modulator according to the present embodiment, it can be used as it is as an optical switch.

  Hereinafter, the operation of the optical phase modulator according to the present embodiment will be described.

That is, the voltage _{V bias} is constantly applied between the electrode piece 9a and the electrode pieces 11b adjacent intervals _{L 1.} Here, V ₀ is further added, and a voltage of V _bias + V ₀ (= V _all ) is applied. Then, an electric field mainly parallel to the direction P is applied to the waveguide core 7 portion.
E = V _all / L ₁ = (V _bias + V ₀ ) / L ₁
Is applied. Then, the refractive index of the waveguide core 7 in the direction P changes by Δn due to the secondary electro-optic effect of KTN. The refractive index change Δn from when V ₀ = 0 has the following voltage dependence.
^{_{Δnα (V bias + V 0)}} 2 / L 1 2 -V bias 2 / L 1 2
= 2V _bias V ₀ / L ₁ ² + V ₀ ² / L ₁ ² (4)

V For the _bias >> _{V 0,} into play only the first term of the right side of the equation (4) ^{_{is, 2V bias V 0 / L 1}} 2 refractive index change is proportional to occur. As a result, compared with the case where the phase of the light traveling in the direction P through the waveguide core 7 is V ₀ = 0,
Δφ ₁ = 2πΔn * L ₁ / λ∝4πV _bias V ₀ / (λ · L ₁ )
Will only change.

In FIG. 2, there are three regions where the electric field application direction is the first direction and two regions where the electric field application direction is the second direction, so there are a total of five regions to which the electric field is applied. since ₁ is >> W _2, the overall length of the portion of which the refractive index is changed by electric field application of the waveguide core 7 (the length of the phase modulation region) becomes 5 * L _1. Here, the “phase modulation region” refers to a region of the waveguide core to which an electric field is applied in the longitudinal direction of the waveguide core and that modulates the phase of light traveling through the region. .

That is, the electrode piece 9a which is a + electrode is disposed at the start point of the phase modulation region in the direction P, and n regions where the electric field application direction is the first direction and n-1 regions where the second direction is the second direction. If these are combined, there are 2n−1 regions, and the length of the phase modulation region is (2n−1) * L ₁ considering L ₁ >> W ₂ . Since the waveguide core 7 is made of a material having a secondary electro-optic effect, the direction in which the received phase changes is the same regardless of whether the applied electric field direction is the first direction or the second direction. The phase change amount Δφ _tot as a whole is added,
Δφ _tot ∝ (2n−1) * 4πV _bias V ₀ / (λ · L ₁ ) (5)
It becomes.

  In this way, the phase of the optical signal input to the optical phase modulator can be modulated while suppressing the amount of drive current. Further, the phase modulation amount can be controlled in accordance with the number of electrode pieces 9a and electrode pieces 11a.

In this embodiment, KTN is used for the waveguide core and the clad. However, the present invention is not limited to this, and any material can be used as long as it has a higher dielectric constant than the substrate and has a secondary electro-optic effect. May be. For example, K _1-y Li _y Ta _x Nb _1-x O ₃ (0 <x <1, 0 <y <1) (KLTN) may be used.

  In this embodiment, the same material is used for the waveguide core and the clad, but different materials may be used. In this case, it goes without saying that the waveguide core is a material having a dielectric constant higher than that of the substrate and having a secondary electro-optic effect. On the other hand, the clad need not be a material having the above-mentioned properties, and any material can be used as long as it is transparent to the wavelength of light propagating through the waveguide core and has an effective refractive index lower than the waveguide core. Good.

  Further, the arrangement order of the + electrode 8 and the − electrode 10 is not limited to the arrangement of the electrode piece 9 a and the electrode piece 11 a with respect to the direction P, and the electrode piece 11 a and the electrode piece 9 a with respect to the direction P are not limited. You may make it arrange | position in order.

(Second Embodiment)
3A and 3B are configuration diagrams of an optical phase modulator according to the second embodiment of the present invention, and FIG. 3A is a top view of the optical phase modulator according to the present embodiment. FIG. 3B is a cross-sectional view taken along the line CC ′ of FIG. In addition, in this embodiment, what has the same function as FIG. 2 attaches | subjects the same code | symbol, and the repeated description is abbreviate | omitted.

In this embodiment, as in the first embodiment, the waveguide core 7 and the clad 6 made of KTa _x Nb _1-x O ₃ (0 <x <1) (KTN) having a high dielectric constant are compared with KTN. forming a waveguide by being formed on a substrate 5 made of low KTaO ₃ dielectric constant Te. However, in the present embodiment, after the high dielectric constant portion (cladding 6) is reduced as much as possible to form a ridge-type waveguide, the + electrode 13 and the-electrode 15 are combed in the same manner as the electrode structure of the first embodiment. It is formed into a mold. That is, the ridge structure is formed by projecting the clad 6 embedded with the waveguide core 7 on the substrate 5.

  The + electrode 13 includes a plurality of electrode pieces 14a and an electrode portion 14b that connects one end of each of the electrode pieces 14a. The − electrode 15 includes a plurality of electrode pieces 16a and each of the electrode pieces 16a. It consists of the electrode part 16b which connects one end. At this time, each electrode piece 14a and each electrode piece 16a are disposed so that they are substantially parallel to each other and the longitudinal direction of the electrode pieces is substantially perpendicular to the direction P. Each electrode piece 14a and each electrode piece 16a are disposed so as to surround the clad 6 having a ridge structure.

  Because of such an electrode structure, there are fewer unnecessary high dielectric constant portions than in the first embodiment, and the electric capacity between the adjacent electrode pieces with different signs can be reduced. A phase modulator can be realized.

Distance L ₁ of the electrodes is again first embodiment and they become wider than the width W of the waveguide core 7 as well, so as to reduce the electrical capacitance between the opposite sign of the electrode pieces adjacent Yes. Since the situation of operation is the same as that of the first embodiment, the description thereof is omitted.

(Third embodiment)
In the present embodiment, a light intensity modulator is configured using the phase modulator described in the first and second embodiments.

FIG. 4 is a configuration diagram of the light intensity modulator according to the present embodiment.
In FIG. 4, a 3 dB coupler 18 is connected to the input port 17. A first optical waveguide 19 and a second optical waveguide 20 are connected to the first output port and the second output port of the 3 dB coupler 18, respectively. In this embodiment, a 3 dB coupler is used to split incident light. However, the present invention is not limited to this, and any means can be used as long as it can branch incident light at a desired ratio. Also good. The first optical waveguide 19 and the second optical waveguide 20 include the clad 6 and the waveguide core 7 described in the first embodiment.

On the first optical waveguide 19, in order to apply an electric field to the waveguide core included in the first optical waveguide 19, a + electrode 21 and a-electrode 22 are formed in a comb shape as in the first embodiment. Has been. Each of the + electrode 21 and the − electrode 22 is electrically connected to the power source 23. In the present embodiment, positive electrode 21 and the - placement of the electrodes 22, and the relationship between the width W of the distance L ₁ and the waveguide core is similar to the first embodiment, description thereof will be omitted. That is, the optical phase modulator according to this embodiment including the first optical waveguide 19, the + electrode 21, and the − electrode 22 is the same as the optical phase modulator according to the first embodiment.

  Thus, the phase of the light traveling in the first optical waveguide 19 is modulated by applying an electric field only to the first optical waveguide 19 without applying an electric field to the second optical waveguide 20.

  A first optical waveguide 19 is connected to the first input port of the 3 dB coupler 24, and a second optical waveguide 20 is connected to the second input port of the 3 dB coupler 24. In this embodiment, the 3 dB coupler 24 is used to multiplex the light traveling through the first optical waveguide 19 and the light traveling through the second optical waveguide 20, but the present invention is not limited to this. Any means may be used as long as the two input lights can be multiplexed.

  The above components are formed on the substrate 5.

  In the present embodiment, the removal region 12 may be provided so that an electric field is not applied to portions other than the waveguide core 7 and the minimum required cladding 6 constituting the first optical waveguide 19 as much as possible.

  In the present embodiment, the first optical waveguide 19 in which the + electrode 21 and the − electrode 22 are formed may be the ridge-type waveguide described in the second embodiment.

  Hereinafter, the operation of the light intensity modulator according to the present embodiment will be described.

Incident light intensity P ₀ is incident to the input port 17 is branched at 3dB coupler 18, the light intensity P _0/2, respectively, is emitted in the first optical waveguide 19 and second optical waveguides 20 The Therefore, the intensity of the light traveling through the first optical waveguide 19 and the second optical waveguide 20 is both P _0/2 .

  As described above, since the first optical waveguide 19 is provided with the same optical phase modulator as that of the first embodiment (electrodes are provided on the optical waveguide), the first optical waveguide is provided. The light emitted from 19 is modulated by the voltage applied between the + electrode 21 and the − electrode 22, and a phase difference Δφ is generated as compared with the incident light to the first optical waveguide 19. At this time, the phase of the light emitted from the second optical waveguide 20, which is a waveguide in which the other electrode is not provided, does not change.

  The light modulated by the first optical waveguide 19 and the non-modulated light traveling through the second optical waveguide 20 are combined and interfered by the 3 dB coupler 24, and as final output light, The light is emitted from the 3 dB coupler 24.

Here, the transmission loss in each optical waveguide and coupler is ignored, and when no voltage is applied, the light incident from the input port 17 is branched by the 3 dB coupler 18 which is the 3 dB coupler in the previous stage, and then each light is input. Assuming that there is no phase difference through the optical waveguides 19 and 20 until being combined by the 3 dB coupler 24, which is a subsequent 3 dB coupler, the intensity of the light output after being combined by the subsequent 3 dB coupler 24 P varies depending on the interference effect as follows.
P = P ₀ cos (Δφ) (6)

  That is, as can be seen from the equation (6), when the phase difference Δφ = 0, the light is emitted as the strongest light, but as the phase difference Δφ changes, the intensity P of the final emitted light from the 3 dB coupler 24 Changes periodically.

As shown in Equation (5), the phase change amount Δφ _tot by the optical phase modulator provided on the first optical waveguide 19 is
Δφ _tot = a (2n−1) * 4πV _bias V ₀ / (λ · L ₁ ) (7)
It is. Here, a is a proportionality coefficient with respect to the square of the voltage change of the refractive index change in Formula (4).

From equations (6) and (7)
P = P ₀ * cos (4πa · (2n−1) · V _bias V ₀ / (λ · L ₁ ) (8)
It becomes.

As can be seen from Equation (8), the final output light intensity can be modulated by the voltage applied to the electrodes (+ electrode 21 and −electrode 22). In this case, the distance L ₁ of the electrodes, since wider than the width W of the first and second embodiments as well as the waveguide core 7, the electrical capacitance between the opposite sign of the electrode pieces adjacent Can be small. Therefore, the drive current required for modulation can be reduced.

  In this embodiment, an electric field is applied only to the first optical waveguide 19, but the present invention is not limited to this. That is, the + electrode 21 and the −electrode 22 may be provided also in the second optical waveguide 20. In this embodiment, since it is important to modulate the light intensity, when electrodes are provided on both the first and second optical waveguides, the light traveling through each optical waveguide combined by the 3 dB coupler 24 is transmitted. What is necessary is just to modulate the light which goes through each optical waveguide so that it may not become the same phase.

(A) And (b) is a block diagram of the conventional optical phase modulator, (a) is a top view of the conventional optical phase modulator, (b) is AA of (a). FIG. (A) And (b) is a block diagram of the optical phase modulator which concerns on one Embodiment of this invention, (a) is a top view of the optical phase modulator which concerns on one Embodiment of this invention, (B) is the BB 'sectional view taken on the line of (a). (A) And (b) is a block diagram of the optical phase modulator which concerns on one Embodiment of this invention, (a) is a top view of the optical phase modulator which concerns on one Embodiment of this invention, (B) is the CC 'line | wire sectional view taken on the line of (a). It is a block diagram of the light intensity modulator which concerns on one Embodiment of this invention.

Explanation of symbols

17 Input port 18, 24 3 dB coupler 19 First optical waveguide 20 Second optical waveguide 21 + electrode 22 −electrode 23 power supply

Claims (6)

A branching means for branching incident light into first and second optical paths, a first optical waveguide constituting the first optical path, and a second optical path constituting the second optical path, which are formed on the substrate. In an optical intensity modulator comprising: an optical waveguide; and a coupling means coupled to the first and second optical waveguides and configured to multiplex light incident from the first and second optical waveguides.
At least one of the first and second optical waveguides is a waveguide including a core made of a material having a secondary electro-optic effect and having a dielectric constant higher than that of the substrate. An electrode and a negative electrode are provided, and the positive electrode and the negative electrode are arranged along a direction in which light in the waveguide travels at an interval wider than the width of the core, and an electric field in the direction with respect to the core The light intensity modulator is disposed on the waveguide so as to apply the light.   2. The device according to claim 1, wherein there are a plurality of the positive electrodes and the negative electrodes, and the positive electrodes and the negative electrodes are alternately arranged along the direction. Light intensity modulator. The light intensity modulator according to claim 1, wherein the material is KTa _x Nb _1-x O ₃ (0 <x <1). The light intensity modulator according to claim 1, wherein the material is K _1-y Li _y Ta _x Nb _1-x O ₃ (0 <x <1, 0 <y <1).   5. The device according to claim 1, wherein at least a part of a region of the waveguide other than the core to which an electric field is applied by the plus electrode and the minus electrode is removed. Light intensity modulator.   The light intensity modulator according to claim 1, wherein the waveguide is a ridge waveguide.

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