JP2011090332A - Optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-speed and high-performance optical modulator capable of reducing a driving voltage by securing a modulation band. <P>SOLUTION: The optical modulator includes an optical waveguide, a signal electrode, a ground electrode, and a ridge. The optical waveguide is formed on a lithium niobate substrate. The signal electrode is formed near the optical waveguide such that a range of characteristics impedance is 45 to 50 Ω, a reflection amount of a microwave is -20 dB or lower, and an operation length is 50 mm or more. The ground electrodes are formed on both sides of the signal electrode with thicknesses of 28 μm or more. The ridge has a height of 6 μm to 8 μm such that an effective refractive index when the signal electrode is formed in an upper part and the microwave travels through the signal electrode is equal to that when light travels through the optical waveguide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light modulation device, and more particularly to a light modulation device using a crystal substrate having an electro-optic effect.

  With the progress of multimedia, there is a strong demand for the construction of an optical communication network in order to transmit high-speed and large-capacity information to a long distance at a low cost. There is an optical modulator as an important device as the heart for realizing the optical communication network.

  An optical modulator is a device that converts an electrical signal into an optical signal by forming an optical waveguide on a substrate and performing external modulation that changes the phase of light on the optical waveguide by a voltage applied to the optical waveguide. .

  On the other hand, in recent years, optical communication systems for 40 Gb / s class have been developed from conventional 10 Gb / s class optical communication to 40 Gb / s class as further high speed and large capacity communication (for example, DWDM (Dense Wavelength Division Multiplex) system).

  In order to realize such an ultra-high-speed and large-capacity system, for example, in order to generate 40 Gb / s light, the optical modulator has a light modulation speed higher than that for conventional 10 Gb / s communication. Need to be 4 times faster. In addition, in order to drive the optical modulator, an ultrahigh-speed electronic circuit cannot generate a large voltage, so the driving voltage of the optical modulator must be reduced.

  However, in the optical modulator as described above, the drive voltage and the operation speed (modulation band) are in a trade-off relationship. That is, when the length of the optical waveguide is shortened (when the length of the signal electrode for applying an electric field to the optical waveguide is shortened), the electric capacity is reduced and the operation speed is increased, but the phase change at the same voltage. Will be less. For this reason, in order to obtain sufficient modulation, a contradiction arises in that the drive voltage must be increased. Thus, it has been difficult for conventional optical modulators to achieve a certain speed or voltage reduction.

  The present invention has been made in view of these points, and an object of the present invention is to provide a high-speed and high-performance optical modulation device that secures a modulation band and realizes a reduction in drive voltage.

  In order to solve the above problems, an optical modulation device is provided. This light modulation device has an optical waveguide formed on a lithium niobate substrate, a characteristic impedance range of 45 to 50Ω, a microwave reflection amount of −20 dB or less, and an action length of 50 mm or more. A signal electrode formed in the vicinity of the optical waveguide, a ground electrode having a thickness of 11 μm or more and formed on both sides of the signal electrode, the signal electrode formed on the upper portion, and the signal electrode A ridge having a height of 6 μm to 8 μm, wherein an effective refractive index when the microwave travels is the same as an effective refractive index when light travels through the optical waveguide.

  With a reduced driving voltage, it is possible to secure a sufficient modulation band and perform high-speed and high-performance optical modulation.

It is a top view of a light modulation device. It is sectional drawing of the A section of a light modulation apparatus. It is a figure which shows the conventional problem with respect to an optical modulation apparatus. It is a figure which shows the relationship between the attenuation amount of the microwave per unit length of a signal electrode, and a gap. It is a figure which shows the relationship between a drive voltage x action length, and a gap. It is a figure which shows the relationship between an action length and a gap at the time of making attenuation amount of a microwave constant (a modulation band is constant). It is a figure which shows the relationship between the drive voltage and gap based on the action length shown in FIG. It is a figure which shows the relationship between the conventional gap and action length. It is a figure which shows the relationship between the gap and action length of this invention. It is a figure which shows the relationship between a microwave reflection and characteristic impedance. It is a figure which shows the relationship between the effective refractive index of a microwave, and a gap. It is a figure which shows the relationship between the effective refractive index of a microwave, and a gap. It is a figure which shows the relationship between the effective refractive index of a microwave, and a gap. It is a figure which shows the relationship between characteristic impedance and a gap. It is a figure which shows the relationship between characteristic impedance and a gap. It is a figure which shows the relationship between characteristic impedance and a gap. It is a figure which shows the relationship between a gap and the thickness of a ground electrode. It is a figure which shows the relationship between a gap and the thickness of a ground electrode. It is a figure which shows the relationship between a gap and the thickness of a ground electrode. It is a figure which shows the relationship between the gap which satisfy | fills characteristic impedance Z0 = 45-55ohm in the case of effective refractive index neff = 2.15, and ground electrode thickness. It is a figure which shows the relationship of the gap of this invention, the ground electrode thickness, and a drive voltage. It is a figure which shows the relationship of the gap of this invention, the ground electrode thickness, and action length. It is a figure which shows the conventional cross-section. It is a top view of the light modulation apparatus of a single electrode structure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of the light modulation device, and FIG. 2 is a cross-sectional view of part A of the light modulation device. The light modulation device 10 is formed of an optical waveguide 11 on a crystal substrate using lithium niobate (LiNbO ₃ : hereinafter referred to as LN) having an electro-optic effect (a phenomenon in which a refractive index changes when an electric field is applied). It is a device that controls light propagating in the optical waveguide 11 via a Mach-Zehnder interferometer. A signal electrode 12 is formed in the vicinity of the optical waveguide 11, and a ground electrode 13 is formed on both sides of the signal electrode 12.

  In the light modulation device 10, a metal film is formed on a part of the LN crystal (having advantages such as a large electro-optic effect and easy formation of an optical waveguide) and thermally diffused, or protons in benzoic acid after patterning. The optical waveguide 11 is formed by replacement.

  The optical waveguide 11 is branched into two parallel waveguides 11a and 11b, and two signal electrodes 12 are provided on the parallel waveguides 11a and 11b (dual electrode structure). The length of the parallel waveguides 11a and 11b (or the length of the signal electrode 12 in this portion) is defined as an action length L.

Further, since the light modulation device 10 uses a Z-cut LN crystal, in order to prevent light propagating through the optical waveguide 11 from being absorbed by the signal electrode 12 and the ground electrode 13, the light modulation device 10 is interposed between the substrate and the electrode. A buffer layer 14 is provided. As the buffer layer 14, for example, SiO ₂ having a thickness of 0.2 to 1 μm is used.

  In the light modulation device 10 having such a configuration, the range of the characteristic impedance Z0 of the signal electrode 12 is determined so that the reflection of the microwave is not more than a certain value, and the signal electrode 12 is matched when the phases of the light and the microwave are matched. 12 and the ground electrode 13 have a gap S of 50 μm or more, the working length L of the signal electrode 12 is 50 mm or more, a drive voltage of 1.7 V or less, and light modulation of 40 Gb / s or more is performed. For the following description, the thickness of the ground electrode 13 is denoted by Hg, and the height of the ridge 15 is denoted by Hr.

  Next, a method for designing the light modulation device 10 will be described in detail. First, problems to be solved by the present invention will be described, including an outline of the operation of the light modulation device. When the light modulation device is driven at high speed, the signal electrode 12 and the ground electrode 13 are connected by a terminating resistor to form a traveling wave electrode, and the signal sources Sa and Sb shown in FIG. The complementary signals are input respectively.

  At this time, the refractive index of the parallel waveguides 11a and 11b changes as + Δn and −Δn, respectively, due to the electric field applied to the optical waveguide 11, and the phase difference between the parallel waveguides 11a and 11b changes. Signal light whose intensity is modulated is output (if the phase difference between the parallel waveguides 11a and 11b is 0 °, the light is strengthened, and if the phase difference is π, the light is weakened).

  In addition, in order to obtain a broadband optical response characteristic by making the modulation band of light as wide as possible, it is necessary to match the effective refractive indexes of light and microwave and match the phases of light and microwave. In the case of LN, the effective refractive index of light is 2.15, whereas the effective refractive index of microwaves is nearly twice that. Therefore, as shown in FIG. 2, the effective refractive index of the microwave is set to 2.15 of the refractive index of the light by etching the vicinity of the optical waveguide 11 to form a ridge or increasing the thickness of the ground electrode 13. It will be devised to lower.

  On the other hand, in driving with a high-speed signal exceeding 40 Gb / s, the output of the driver amplifier for driving the optical modulation device is small, so the driving voltage must be reduced. In this case, conventionally, the signal electrode 12 and the ground electrode 13 are brought as close as possible to narrow the gap S in order to give a strong electric field to the optical waveguide 11 at a low voltage (conventional gap S≈30 μm). .

  However, if the microwave is input with the gap S narrowed, the loss of the high frequency component of the microwave increases due to the conductor loss (the high frequency cannot be transmitted), and the optical broadband is prevented. Therefore, if an attempt is made to secure the modulation band with the gap S narrowed, it is necessary to shorten the action length L this time in order to reduce high-frequency component loss. Since the phase change is small, a contradiction arises in that the drive voltage must be increased.

FIG. 3 is a diagram showing a conventional problem with the light modulation device.
[S1] Conventionally, an attempt is first made to reduce the drive voltage.
[S2] In order to apply a strong electric field to the optical waveguide 11 by reducing the drive voltage, the gap S is narrowed.
[S3] If the gap S is narrow, the influence of the conductor loss increases, so the high-frequency loss quality increases.
[S4] The action length L is shortened in order to reduce the influence of the conductor loss.
[S5] Since the action length L is short, the phase change of light becomes small.
[S6] In order to increase the phase change of light, the drive voltage must be increased, which contradicts step S1.

  As described above, it has been difficult to develop an optimum apparatus with the design policy of conventional optical devices (particularly, high-speed optical devices of 40 Gb / s or more). In the present invention, the optimum range of these parameters for the light modulation device is found, and the gap S and the action length L are increased compared to the conventional case, thereby reducing the high-frequency component loss of the drive voltage and the microwave. An optical modulation device 10 realizing high performance is provided.

  Next, assuming that the output of the driver amplifier is 2 V at the maximum, the light modulation device 10 performs a light modulation operation of 40 Gb / s or more (40 to 43.5 Gb / s) when the drive voltage in the dual drive is 2 V or less. A specific design method will be described with reference to FIGS.

FIG. 4 is a diagram showing the relationship between the microwave attenuation per unit length of the signal electrode 12 and the gap S. FIG. The vertical axis represents the microwave attenuation [dB / (GHz) ^1/2 / cm], and the horizontal axis represents the gap S [μm]. FIG. 5 is a diagram showing the relationship between drive voltage × action length L and gap S. FIG. The vertical axis represents drive voltage × action length (= Vπ · L) [V · cm], and the horizontal axis represents gap S [μm]. Vπ is called a half-wave voltage and indicates a voltage required to change the phase of light propagating in the optical waveguide 11 by π.

  From FIG. 4, it can be seen that the greater the gap S, the smaller the attenuation of the microwave, and FIG. 5 indicates that the drive voltage increases as the gap S increases. That is, there is an inconvenient relationship in which, if the attenuation of microwaves is reduced and the gap S is increased, the driving voltage increases.

  On the other hand, when the attenuation amount of the microwave is constant (for example, when the −6 dB band can be taken at 40 GHz), the relationship between the action length L and the gap S is as shown in FIG. FIG. 6 is a diagram showing the relationship between the action length L and the gap S when the microwave attenuation is constant (modulation band is constant). The vertical axis represents the action length L [mm], and the horizontal axis represents the gap S [μm].

  Here, it can be seen from FIGS. 4 and 6 that when the attenuation amount of the microwave is reduced, the gap S is widened and the action length L corresponding to the widened gap S is taken (longened). For example, in FIG. 4, when the attenuation amount of the microwave is to be reduced to a half of 0.2 → 0.1, the value of the gap S at that time is 40 → 60. As seen, the action length L becomes 33 → 82 (if the microwave attenuation is halved, the gap S should be increased by about 1.5 times and the action length L should be increased by about twice).

  FIG. 7 is a diagram showing the relationship between the drive voltage and the gap S based on the action length L shown in FIG. The vertical axis represents drive voltage [V] and the horizontal axis represents S [μm]. From FIG. 7, it can be seen that in the signal electrode 12 in which the action length L is increased, the drive voltage decreases as the gap S increases.

Here, the difference between the prior art and the present invention viewed from the relationship between the gap S and the action length L will be described with reference to FIGS. FIG. 8 is a diagram showing the relationship between the conventional gap S and the action length L. In FIG.
[S11] The gap S is narrowed.
[S12] If the gap S is narrow, the high frequency loss increases, but the drive voltage can be reduced.
[S13] The action length L is shortened in order to reduce high frequency loss.
[S14] Since the action length L is shortened, the high-frequency loss can be reduced. However, since the phase change of light is reduced, there arises a problem that the drive voltage must be increased.

FIG. 9 is a diagram showing the relationship between the gap S and the action length L of the present invention.
[S21] The gap S is widened based on the graph shown in FIG. 6 in which the relationship between the action length L and the gap S when the attenuation amount of the microwave is made constant is obtained. At this time, the action length L is extended according to the gap S.
[S22] When only the gap S is widened, the high-frequency loss is reduced, but the drive voltage must be increased. Further, when only the action length L is increased, the high-frequency loss increases, but the drive voltage can be reduced.
[S23] As in step S21, the gap S is widened and the action length L is extended to reduce high-frequency loss (FIGS. 4 and 6) and drive voltage (FIG. 7).

  As described above, in the present invention, in order to reduce the driving voltage, instead of starting from the narrowing of the gap S as in the prior art, the driving voltage and the driving voltage L are increased by widening the gap S and extending the action length L. This is to reduce the high-frequency component loss of the microwave.

  Next, preconditions (range of characteristic impedance Z0 in reflection, phase matching between light and microwave) when the optical modulation device 10 is configured with the gap S widened and the action length L widened will be described. First, the range of the characteristic impedance Z0 of the signal electrode 12 in microwave reflection will be described.

  When the microwave propagates on the signal electrode 12, a standing wave (a wave that does not appear to move due to interference between the traveling wave and the reflected wave on the transmission path) is generated on the signal electrode 12. Then, a part of the transmitted power is reflected back, which may adversely affect the input circuit that inputs a signal to the light modulator 10. In order to prevent this, the reflection of the microwave is required to be −20 dB or less.

  FIG. 10 is a diagram showing the relationship between the microwave reflection and the characteristic impedance Z0. The vertical axis represents the microwave reflection [dB], and the horizontal axis represents the characteristic impedance Z0 [Ω] of the signal electrode 12. As can be seen from the figure, the characteristic impedance Z0 should be in the range of about 45 to 55Ω in order for the microwave reflection to be −20 dB or less.

  Next, phase matching between light and microwave will be described. In order to expand the modulation band, it is necessary to match the phases of light and microwave. In the case of LN, since the effective refractive index neff of light is 2.15, phase matching is performed by matching the effective refractive index of the microwave with this value.

  Therefore, the relationship between the ridge height Hr, the ground electrode thickness Hg, and the gap S is determined so that the effective refractive index of the microwave is 2.15 in the range of the characteristic impedance Z0 = 45 to 55Ω.

  11 to 13 are diagrams showing the relationship between the effective refractive index neff of the microwave and the gap S (calculated by the finite element method). The vertical axis represents the effective refractive index neff, and the horizontal axis represents the gap S [μm]. 11 to 13 show cases where the ground electrode thickness Hg = 4, 16, and 28 μm, respectively. Further, Hr1 to Hr3 are 6, 8, and 10 μm, respectively, with respect to the ridge height Hr.

  14 to 16 are diagrams showing the relationship between the characteristic impedance Z0 and the gap S (calculated by the finite element method). The vertical axis represents the characteristic impedance Z0 [Ω], and the horizontal axis represents the gap S [μm]. 14 to 16 show cases where the ground electrode thickness Hg is 4, 16, and 28 μm, respectively. Further, Hr1 to Hr3 are 6, 8, and 10 μm, respectively, with respect to the ridge height Hr.

  FIG. 17 is a diagram showing the relationship between the gap S and the ground electrode thickness Hg. The vertical axis represents the gap S [μm], and the horizontal axis represents the ground electrode thickness Hg [μm]. Further, Hr1 to Hr3 are 6, 8, and 10 μm, respectively, with respect to the ridge height Hr.

  FIG. 17 is a diagram obtained by converting the data of FIGS. 11 to 13 when the effective refractive index neff = 2.15 (first relationship diagram). In contrast to this figure, for example, when Hr = 8 μm (= Hr2) and Hg = 33 μm, S = 50 μm and neff = 2.15, and phase matching can be achieved.

  FIG. 18 is a diagram showing the relationship between the gap S and the ground electrode thickness Hg. The vertical axis represents the gap S [μm], and the horizontal axis represents the ground electrode thickness Hg [μm]. Further, Hr1 to Hr3 are 6, 8, and 10 μm, respectively, with respect to the ridge height Hr. FIG. 18 is a diagram obtained by converting the data of FIGS. 14 to 16 when the characteristic impedance Z0 = 45Ω (second relationship diagram).

  FIG. 19 is a diagram showing the relationship between the gap S and the ground electrode thickness Hg. The vertical axis represents the gap S [μm], and the horizontal axis represents the ground electrode thickness Hg [μm]. Further, Hr2 and Hr3 are 8 and 10 μm, respectively, with respect to the ridge height Hr. FIG. 19 is a diagram obtained by converting the data of FIGS. 14 to 16 when the characteristic impedance Z0 = 55Ω (second relationship diagram).

  18 and 19, for example, when Hr = 10 μm (= Hr3) and Hg = 25 μm, S = 42 to 65 μm, Z0 = 45 to 55Ω, and reflection can be made −20 dB or less.

  Next, FIGS. 17 and 18 are graphs regarding the case where the effective refractive index neff = 2.15 and the characteristic impedance Z0 = 45Ω, and FIGS. 17 and 19 are the graphs regarding the case where the effective refractive index neff = 2.15 and the characteristic impedance Z0 = 55Ω. create.

  FIG. 20 is a diagram showing the relationship between the gap S satisfying the characteristic impedance Z0 = 45 to 55Ω and the ground electrode thickness Hg when the effective refractive index neff = 2.15. The vertical axis represents the gap S [μm], and the horizontal axis represents the ground electrode thickness Hg [μm].

  In the condition range 20 in the figure, the effective refractive index neff = 2.15 and the characteristic impedance Z0 = 45 to 55Ω is satisfied. Therefore, the optimum values of the gap S, the action length L, the drive voltage, and the ground electrode thickness Hg are obtained within the condition range 20.

  FIG. 21 is a diagram showing the relationship among the gap S, the ground electrode thickness Hg, and the drive voltage according to the present invention. The vertical axis represents the gap S [μm] and the drive voltage [V], and the horizontal axis represents the ground electrode thickness Hg [μm]. FIG. 22 is a diagram showing the relationship among the gap S, the ground electrode thickness Hg, and the action length L of the present invention. The vertical axis represents the gap S [μm], and the horizontal axis represents the ground electrode thickness Hg [μm].

  Here, each parameter of the light modulation device 10 that performs light modulation of 40 Gb / s or more using a range 21 (range surrounded by a thick solid line) in which the gap S is 50 μm or more and the drive voltage is 1.7 V or less is used. Determine the value.

  In the present invention, a 40 Gb / s optical modulation device 10 is designed with a drive voltage in a dual drive of 1.6 V or less, a gap S of 56 μm or more, and a ground electrode 13 thickness Hg of 11 μm or more with respect to the range 21. To do. Alternatively, a 40 Gb / s optical modulation device 10 is designed with respect to the range 21 in which the drive voltage in the dual drive is 1.5 V or less, the gap S is 62 μm or more, and the thickness Hg of the ground electrode 13 is 28 μm or more.

  However, the thickness Hg of the ground electrode 13 is set to an upper limit value of 50 μm as a limitation in the manufacturing process, and the position P where each parameter of the conventional light modulation device exists is shown in FIGS. 21 and 22. . It can be seen that in the present invention, the drive voltage is low, the gap S is wide, the action length L is long, and the ground electrode thickness Hg is thick in the present invention.

  Next, the difference in cross-sectional structure between the conventional and the light modulation device of the present invention will be described. FIG. 23 is a diagram showing a conventional cross-sectional structure. In addition, since description of each structure part was mentioned above, only the point from which a cross-sectional structure differs is demonstrated.

  In the conventional cross-sectional structure 100, the gap S 'is narrow and the thickness Hg' of the ground electrode 13a is thin. On the other hand, in the cross-sectional structure of the present invention described above with reference to FIG. 2, the gap S is wide and the thickness Hg of the ground electrode 13 is thick. That is, S ′ <S and Hg ′ <Hg.

  Next, the case of a single electrode structure for the light modulation device of the present invention will be described. Although the dual electrode structure has been described in the above description, the present invention can also be applied to a single electrode structure.

  FIG. 24 is a plan view of a light modulation device having a single electrode structure. A sectional view is omitted. In the optical modulation device 10 a, an optical waveguide 11 is formed on an LN crystal substrate, one signal electrode 12 is formed in the vicinity of the optical waveguide 11, and ground electrodes 13 are formed on both sides of the signal electrode 12. Since the others are the same, the description is omitted.

  As described above, according to the present invention, it is possible to reduce the high-frequency component loss of the drive voltage and microwave by widening the gap S and extending the action length L, and high-speed and high-quality optical modulation. An apparatus can be realized.

(Supplementary note 1) An optical waveguide formed on a crystal substrate having an electro-optic effect, a signal electrode formed in the vicinity of the optical waveguide, and a ground electrode formed on both sides of the signal electrode A light modulator,
When the range of the characteristic impedance of the signal electrode is determined so that the reflection of the microwave is a certain value or less, and the phase of the light and the microwave is matched,
A light modulation device characterized in that a light modulation device performs light modulation of 40 Gb / s or more when a gap between the signal electrode and the ground electrode is 50 μm or more and a working length of the signal electrode is 50 mm or more.

(Supplementary note 2) The light modulation device according to supplementary note 1, wherein the drive voltage is 1.6 V or less, the gap is 56 μm or more, and the thickness of the ground electrode is 11 μm or more.
(Supplementary note 3) The light modulation device according to supplementary note 1, wherein the drive voltage is 1.5 V or less, the gap is 62 μm or more, and the thickness of the ground electrode is 28 μm or more.

(Additional remark 4) The thickness of the said ground electrode is 50 micrometers or less, The light modulation apparatus of Additional remark 1 characterized by the above-mentioned.
(Additional remark 5) The said signal electrode is a shape of a dual electrode or a single electrode, The optical modulation apparatus of Additional remark 1 characterized by the above-mentioned.

(Additional remark 6) In the design method of the optical modulation apparatus which performs an optical modulation and converts an electric signal into an optical signal,
Find the acceptable range of the characteristic impedance where the reflection of the microwave is below a certain value,
Matching the effective refractive index of the microwave to the effective refractive index of the light to perform phase matching,
Determining the first relationship between the gap between the signal electrode and the ground electrode and the thickness of the ground electrode when the phase matching is performed;
Determining a second relationship between the gap and the thickness of the ground electrode within the allowable range;
From the first relationship and the second relationship, a condition range that defines the relationship between the gap and the thickness of the ground electrode is obtained within the allowable range and in the phase matching,
Within the condition range, plot the operating length of the drive voltage and the signal electrode,
In order to reduce the high-frequency component loss of the drive voltage and the microwave, the gap, the action length, the drive voltage, and the drive voltage when the gap is widened and the action length is extended, A method for designing an optical modulation device, characterized in that an optimum value for the thickness of a ground electrode is obtained.

  (Supplementary note 7) The design of the light modulation device according to supplementary note 6, wherein the light modulation device that performs light modulation of 40 Gb / s or more is designed with the action length of 50 mm or more and the gap of 50 μm or more. Method.

  (Supplementary note 8) The light modulation device according to Supplementary note 7, wherein the working length is 50 mm or more, the drive voltage is 1.6 V or less, the gap is 56 μm or more, and the thickness of the ground electrode is 11 μm or more. Design method.

  (Supplementary note 9) The light modulation device according to supplementary note 7, wherein the working length is 50 mm or more, the driving voltage is 1.5 V or less, the gap is 62 μm or more, and the thickness of the ground electrode is 28 μm or more. Design method.

(Additional remark 10) The design method of the optical modulation apparatus of Additional remark 7 characterized by designing with the thickness of the said ground electrode being 50 micrometers or less.
(Additional remark 11) The said signal electrode is designed in the shape of a dual electrode or a single electrode, The design method of the optical modulation apparatus of Additional remark 7 characterized by the above-mentioned.

(Supplementary note 12) An optical waveguide formed on a lithium niobate substrate;
A signal electrode formed in the vicinity of the optical waveguide having a characteristic impedance range of 45 to 50Ω, a microwave reflection amount of −20 dB or less, and an action length of 50 mm or more;
A ground electrode having a thickness of 11 μm or more and formed on both sides of the signal electrode;
A height of 6 μm to 8 μm, in which the signal electrode is formed on the upper portion, and an effective refractive index when the microwave travels through the signal electrode is the same as an effective refractive index when light travels through the optical waveguide A ridge having
Comprising
An optical modulation device characterized by that.

(Additional remark 13) The said signal electrode is a shape of a dual electrode or a single electrode, The optical modulation apparatus of Additional remark 12 characterized by the above-mentioned.
(Supplementary note 14) The light modulation device according to supplementary note 12, wherein a buffer layer is provided between the lithium niobate substrate and the signal electrode and between the lithium niobate substrate and the ground electrode.

DESCRIPTION OF SYMBOLS 10 Optical modulation apparatus 11, 11a, 11b Optical waveguide 12 Signal electrode 13 Ground electrode L Action length Sa, Sb Signal source

Claims (3)

An optical waveguide formed on a lithium niobate substrate;
A signal electrode formed in the vicinity of the optical waveguide having a characteristic impedance range of 45 to 50Ω, a microwave reflection amount of −20 dB or less, and an action length of 50 mm or more;
A ground electrode having a thickness of 11 μm or more and formed on both sides of the signal electrode;
A height of 6 μm to 8 μm, in which the signal electrode is formed on the upper portion, and an effective refractive index when the microwave travels through the signal electrode is the same as an effective refractive index when light travels through the optical waveguide A ridge having
Comprising
An optical modulation device characterized by that.   The light modulation device according to claim 1, wherein the signal electrode has a shape of a dual electrode or a single electrode.   The light modulation device according to claim 1, wherein a buffer layer is provided between the lithium niobate substrate and the signal electrode and between the lithium niobate substrate and the ground electrode.

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