JP2007147774A - Optical modulator and optical modulation module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical modulator operating at low voltage and capable of modulating light at high speed and to provide an optical modulation module having the optical modulator. <P>SOLUTION: The optical modulator has an incident waveguide, an emission waveguide, a multi-mode waveguide, a modulation electrode and a ground electrode. In the multi-mode waveguide, light beams made incident from the incident waveguide interfere with each other to form a plurality of light images and at least one part of the modulation electrode is formed so as to be positioned on the optical images formed in the multi-mode waveguide. The optical modulation module has the optical modulator. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical modulator and an optical modulation module, and more specifically, an optical modulator that modulates an optical signal using interference of a plurality of guided mode light propagating in a multimode interference waveguide, and the optical modulation The present invention relates to a light modulation module having an optical device.

  Propagation systems that can manipulate the phase and intensity of an optical signal are very important. The most common devices that modulate the phase and intensity of optical signals are optical modulators, which quickly became important devices.

  To date, a Mach-Zehnder Modulator (MZM) has been most widely used as an optical modulator.

  The Mach-Zehnder type optical modulator is an optical modulator that configures a Mach-Zehnder type interferometer using a Y-branch waveguide or the like and performs intensity modulation using an electro-optic effect or the like. In this device, the optical path of the optical signal is divided into two, and the optical signals from both optical paths are recombined to form an interference pattern. When an electric field is applied to the waveguide arm of each optical path, a phase shift occurs between optical signals obtained from both optical paths, and the interference pattern changes. Thereby, the intensity | strength of an optical signal is continuously modulated according to the applied electric field.

  For the above reasons, the Mach-Zehnder type optical modulator is widely used. However, the manufacturing conditions of this device are quite severe, and as a result, the manufacturing yield is low. For example, when the input optical signal is divided into two, in order to obtain the maximum attenuation rate, the optical signal should ideally be divided exactly in half. The division of the optical signal is usually performed using a Y-branch waveguide or an optical directional coupler.

When using a Y-branch waveguide, it is necessary to precisely form the tip of the branch part, and in order to achieve a high yield, a high-performance stepper capable of performing photolithography with high resolution is required. Become. On the other hand, the optical directional coupler is generally not strong because it is easily affected by the light separation ratio and refractive index at the branching portion.

  As described above, since the general-purpose Mach-Zehnder type optical modulator uses a Y-branch waveguide or an optical directional coupler, it is extremely difficult to divide the optical power equally into each route. was there. In addition, it is difficult to manufacture a high-precision optical modulator with a high yield.

  An optical modulator comprising an optical waveguide formed by laminating a core layer and a pair of clad layers sandwiching the core layer on a substrate as an optical modulation element that solves the above problem, An input-side single-mode waveguide that propagates input light in a single mode; a multi-mode waveguide that propagates light propagated from the input-side single-mode waveguide in a plurality of waveguide modes; An output-side single mode waveguide that propagates and outputs light propagated from the multimode waveguide in a single mode; a lower electrode layer provided below the multimode waveguide; and the multimode There has been proposed an optical modulator that is provided above a waveguide and includes an upper electrode that applies an electric field or heat to the multimode waveguide together with the lower electrode layer (Patent Document 1).

  Unlike the ordinary Mach-Zehnder type optical modulator, the optical modulator is excellent in robustness because neither a Y-branch waveguide nor an optical directional coupler is required.

In the optical modulator, the multimode waveguide functions as a multimode optical interference section. Therefore, by applying an electric field to the multimode waveguide, a plurality of waveguides propagating through the multimode waveguide are provided. Each mode is phase-modulated, and the intensity of light output from the output-side single-mode waveguide can be continuously modulated by the interference of the plurality of phase-modulated waveguide modes.
JP 2005-221999 A

  As the upper electrode, a planar electrode having various planar shapes such as a quadrangle, a triangle, and a bullet shape is used. If the upper electrode is a planar shape, the optical modulator has a high speed of 10 GHz or more. When the light is modulated, there is a problem that a large parasitic capacity is generated between the upper electrode and the multimode waveguide, and the light modulation timing is greatly delayed with respect to the input electric signal.

  As a countermeasure against this, Patent Document 1 proposes that a striped traveling-wave electrode is provided as an upper electrode so as to intersect the light propagation direction in the multimode waveguide.

  In an optical modulator having a traveling wave type electrode as the upper electrode, even if optical modulation is performed at a high speed of 10 GHz or higher, the phase is not adjusted due to the parasitic capacity generated between the upper electrode and the multimode waveguide. Delays are prevented from occurring.

  However, even in such an optical modulator, there is a problem that optical modulation does not occur in the multimode waveguide due to the electric signal applied to the upper electrode unless the drive voltage is increased.

  The present invention has been made to solve the above problems, and provides an optical modulator capable of performing optical modulation at high speed even with a driving voltage lower than that of the prior art, and an optical modulation module having the optical modulator. Objective.

  According to the first aspect of the present invention, there is provided an incident waveguide and an output waveguide that propagate light in a single mode, the incident waveguide is connected to one end, and the output waveguide is connected to the other end. A multimode waveguide in which incident light is propagated in multiple modes toward the output waveguide; a modulation electrode to which a modulation signal for modulating light propagated in the multimode waveguide is applied; A ground electrode located on the opposite side of the modulation electrode across the mode waveguide. In the multimode waveguide, when light enters from the incident waveguide, the light interferes with each other and The modulation electrode is formed so that at least a part thereof is positioned above the optical image formed in the multimode waveguide.

  In the optical modulator, light that has propagated through the incident waveguide in a single mode is dispersed at the connection between the incident waveguide and the multimode waveguide, and is incident on the multimode waveguide in multiple modes. The The light propagated in the multimode through the multimode waveguide is converged to a single mode light at the connection portion between the multimode waveguide and the output waveguide, and propagates through the output waveguide in a single mode. Is done.

  Therefore, an optical image is generated both in the connection portion between the incident waveguide and the multimode waveguide and in the connection portion between the multimode waveguide and the output waveguide, and also in the inside of the multimode waveguide. The light propagating in the mode interferes with each other to form an optical image.

  Here, the modulation electrode is formed so that at least a part thereof is positioned above the optical image formed in the multimode waveguide.

  Therefore, when an electric field is applied to the modulation electrode, the electrical properties change in the portion where the light in the multimode waveguide interferes with each other, and the phase of the light passing through the portion is shifted. Light propagating through the waveguide can be effectively modulated by electrolysis with a lower voltage than in the past.

  According to a second aspect of the present invention, the modulation electrode is provided along a side edge parallel to a light propagation direction in the multimode waveguide, and a pair of parallel electrodes to which an electric field for modulating light is input. 2. The optical modulator according to claim 1, further comprising: a first portion and a pair of parallel portions coupled to each other and a skew portion provided obliquely with respect to the light propagation direction.

According to a third aspect of the present invention, an angle α formed by the parallel portion and the skew portion is expressed by the following equation:
arctan (W ₂ / L) <α <π / 2
The optical modulator according to claim 2, wherein W ₂ is a width of the multimode waveguide, and L is a length of the multimode waveguide.

  In the optical modulator, when an electric field is applied to the parallel part, the skewed part functions as a traveling wave type electrode. Therefore, even when the frequency of the input electric field exceeds 10 GHz and reaches 100 GHz, a large phase lag occurs. The light modulation can be performed without causing the above. Therefore, it is particularly preferably used for high-speed modulation of light.

In the invention according to claim 4, if the width of the incident waveguide and the outgoing waveguide is W ₁ , the ratio W ₂ / W ₁ of the width of the multimode waveguide to the incident waveguide and the outgoing waveguide is
1 <W ₂ / W ₁ <100
It is related with the optical modulator of any one of Claims 1-3.

If the ratio W ₂ / W ₁ of the width of the multimode waveguide to the incident waveguide and the output waveguide is within the above range, light propagated in a single mode through the incident waveguide Propagated stably in the mode and propagated again in the single mode from the output waveguide.

  The invention according to claim 5 is a substrate, a lower clad layer formed on the substrate, an upper clad layer located above the lower clad layer, the lower clad layer, and the upper clad layer And a core layer that forms the multimode waveguide layer, the incident waveguide, and the output waveguide, and the core layer is larger than any of the upper cladding layer and the lower cladding layer 5. The structure according to claim 1, wherein the modulation electrode has a refractive index, the modulation electrode is formed on or above the surface of the upper cladding layer, and the ground electrode is formed between the substrate and the lower electrode. The present invention relates to the described optical modulator.

  In the optical modulator, the light propagating through the core layer propagates while being totally reflected at the boundary surface between the core layer and the clad layer, so that the light does not leak to the outside. The electric field applied to the modulation electrode reaches the multimode waveguide in the core layer via the upper cladding layer, and modulates light passing through the multimode waveguide.

  The invention according to claim 6 relates to the optical modulator according to claim 5, wherein the multimode waveguide is a waveguide having a rib structure in which the core layer protrudes in a rib shape toward the upper cladding layer.

  In the optical modulator, since a large electric field is generated in the core layer by the electric field applied to the modulation electrode, light propagating through the multimode waveguide can be efficiently modulated even when a low voltage electric field is applied.

  The invention according to claim 7 is the optical modulator according to claim 5, wherein the multimode waveguide is a waveguide having an inverted rib structure in which the core layer protrudes in a rib shape toward the lower cladding layer. About.

  In the optical modulator, after forming the ground electrode and the lower clad layer on the substrate, the surface of the lower clad layer is etched by an appropriate method, and the mode waveguide layer to be formed in the core layer and the incident waveguide are formed. By forming the recesses corresponding to the waveguide and the output waveguide, and then forming the core layer, the mode waveguide layer, the incident waveguide, and the output waveguide can be formed. Therefore, it is suitable when the surface of the core layer cannot be etched for some reason.

  The invention according to claim 8 is provided with a dielectric layer formed on a surface of the upper cladding layer and having a dielectric constant larger than that of the upper cladding layer, and the modulation electrode is formed on the surface of the dielectric layer. The optical modulator according to any one of claims 5 to 7.

  In the optical modulator, since the dielectric layer is disposed between the upper cladding layer and the modulation electrode, there is no dielectric layer even when an electric field having the same strength is applied to the modulation electrode. As compared with the above, a large electric field is generated in the upper cladding layer and the core layer.

  Therefore, light modulation can be effectively performed even at a lower voltage.

  According to a ninth aspect of the present invention, a ground electrode, a lower clad layer, a core layer, and an upper clad layer are formed on the substrate, and then a seed electrode is formed above the upper clad layer, The optical modulator according to claim 5, wherein an electric field in a thickness direction is applied between the ground electrode and the core layer to perform polarization alignment treatment.

  The light modulator can be manufactured by a conventional process.

  The invention according to claim 10 is any one of claims 5 to 8, wherein the core layer is previously subjected to polarization orientation treatment, and an upper clad layer and a lower clad layer are formed on both sides of the core layer subjected to the polarization orientation treatment. The optical modulator according to Item 1.

  Since the optical modulator uses a core layer that has been subjected to polarization orientation treatment in advance, even when a material having low polarization orientation efficiency is used as the core layer, the core layer has high photoelectric characteristics, in other words, For example, even when a weak electric field is applied, the refractive index of the core layer can be greatly changed.

  Therefore, the optical modulator can efficiently modulate light with a low voltage.

  According to an eleventh aspect of the present invention, there is provided the optical modulator according to any one of the first to tenth aspects, an electric signal input unit that inputs an electric signal to a modulation electrode of the optical modulator, and the optical modulator. The present invention relates to a light modulation module comprising: a continuous light source that inputs continuous light into the incident waveguide.

  A twelfth aspect of the present invention relates to the light modulation module according to the eleventh aspect, wherein the electrical signal input section is a digital signal input section for inputting a digital signal.

  A thirteenth aspect of the present invention relates to the light modulation module according to the eleventh aspect, wherein the electric signal input unit is an analog signal input unit that inputs an analog signal.

  Since the optical modulator included in the optical modulation module can perform high-speed optical modulation with a low voltage, it is not necessary to generate a high voltage in the electric signal input unit. Also, since microwaves can be used for optical modulation, large-capacity data transmission is possible.

  As described above, according to the present invention, an optical modulator capable of performing optical modulation at high speed even with a driving voltage lower than that of the prior art and an optical modulation module having the optical modulator are provided.

1. Embodiment 1
1-1 Optical Modulator (1) Configuration As shown in FIGS. 1 to 7, the optical modulator 100 according to the first embodiment includes an incident waveguide 1, an output waveguide 6, and an incident waveguide 1 at one end. A multimode waveguide 2 having an output waveguide 6 connected to the other end, and a modulation electrode 3 to which a modulation signal such as a radio wave for modulating light propagating in the multimode waveguide 2 is applied. Have.

  As shown in FIGS. 5 to 7, the incident waveguide 1, the output waveguide 6, and the multimode waveguide 2 are integrally formed by a core layer 10 sandwiched between a lower cladding layer 9 and an upper cladding layer 11. Has been. The core layer 10 has a higher refractive index than both the lower cladding layer 9 and the upper cladding layer 11. The lower cladding layer 9 and the upper cladding layer 11 may have the same or different refractive indexes.

  The lower clad layer 9 is formed on the surface of the substrate 7, and a ground electrode 8 is formed between the lower clad layer 9 and the substrate 7 to be grounded so that the potential becomes zero.

  Between the upper cladding layer 11 and the modulation electrode 3, a dielectric layer 12 having a dielectric constant larger than that of the upper cladding layer 11 is formed.

  As shown in FIG. 6, the incident waveguide 1, the outgoing waveguide 6, and the multimode waveguide 2 are shown in FIG. 7 even if they are waveguides having a rib structure protruding in a rib shape toward the upper cladding layer 11. As described above, a waveguide having an inverted rib structure protruding in a rib shape toward the lower clad layer 9 may be used. However, in the case of a waveguide having a rib structure, the core layer 10 is modulated by a modulation signal applied to the modulation electrode 3. Specifically, since a large electric field is generated in the multimode waveguide 2, light can be more efficiently modulated in the multimode waveguide 2 even if the modulation signal has a low voltage. If the core layer 10 cannot be etched for some reason to form the incident waveguide 1, the output waveguide 6, and the multimode waveguide 2, the core layer 10 is etched after the lower cladding layer 9 is etched into a predetermined shape. By casting, heating, and curing a forming solution for forming, the incident waveguide 1, the output waveguide 6, and the multimode waveguide 2 can be formed as a waveguide having an inverted rib structure.

It has the same width W ₁ and the input waveguide 1 and the output waveguide 6. The width W ₂ of the multimode waveguide ₂ is expressed by the following relational expression:
1 <W ₂ / W ₁ <100
It is preferable that the multimode waveguide 2 stably satisfies the multimode transmission.

The length L of the multimode waveguide 2, the lower cladding layer 9 and the difference Δn between the refractive index n ₁ of the refractive index n ₂ and the core layer 10 of the upper cladding layer 11, the emitting waveguide with input waveguide 1 6 As a function of the width W ₁ of the multimode waveguide 2 and the width W ₂ of the multimode waveguide 2.

  The modulation electrode 3 is located above the multimode waveguide 2 on the surface of the dielectric layer 12 as shown in FIGS. The parallel part 4c and parallel part 4d parallel to the light propagation direction in the multimode waveguide 2 and the parallel part 4c and parallel part 4d are coupled to each other and provided obliquely with respect to the light propagation direction. It has a skew part 4a and a skew part 4b.

The skew portion 4a and the skew portion 4b, and the parallel portion 4b and the parallel portion 4c are parallel to each other. The skew portion 4a and the skew portion 4b are integrally connected to the parallel portion 4c and the parallel portion 4d at their respective end portions. Therefore, the modulation electrode 3 is formed in a parallelogram shape as a whole by the parallel portion 4c and the parallel portion 4d and the skew portion 4a and the skew portion 4b. Therefore, the angle α formed by the skew portion 4a and the parallel portion 4d, and the skew portion 4b and the parallel portion 4c is expressed by the following equation:
arctan (W ₂ / L) <α <π / 2
(W ₂ is the width of the multimode waveguide 2 and L is the length of the multimode waveguide 2). In the example of the first embodiment, α = arctan (3W ₂ / L), but the angle α is not limited to the angle.

  In a state where no electric field is applied to the modulation electrode 3, the light incident from the incident waveguide 1 is connected between the incident waveguide 1 and the multimode waveguide 2, and between the multimode waveguide 2 and the output waveguide 6. An optical image is formed at the connecting portion. Since the light propagates in the multimode waveguide 2 in a multimode, the light interferes with each other to generate an optical image also in the multimode waveguide 2. In the optical modulator 100, the modulation electrode 3 is formed so that the parallel part 4c and the parallel part 4d are located above the optical image as shown in FIG. The row portion 4b may be formed so as to pass above the optical image.

The dimension of the modulation electrode 3 along the width direction of the multimode waveguide 2, that is, the width W of the modulation electrode 3 may be equal to or less than the width W ₂ of the multimode waveguide 2. If it is larger than W _2, it is preferable because a strong electric field can be generated by the multimode waveguide 2 even when an electric field having the same strength is applied.

  The skew portion 4a, the skew portion 4b, the parallel portion 4c, and the parallel portion 4d may have different widths, but are preferably the same.

  The parallel part 4c and the parallel part 4d are formed so that the end edges thereof coincide with the end edges of the multimode waveguide 2 or slightly outside. The parallel portions 4c and 4d are integrally provided with an electric field application piece 5a and an electric field application piece 5b to which an alternating electric field such as a radio wave is applied as a conversion signal. The electric field applying piece 5a is connected to the parallel portion 4d and connected to a high frequency power source that generates a high frequency such as a radio wave. On the other hand, the electric field load piece 5b is connected to the parallel portion 4c and grounded via the resistor R. The electric field application piece 5a and the electric field application piece 5b may be rectangular, but as shown in FIGS. 3 and 4, a tapered microwave strip extending toward the end is formed at the end. It is preferable because a radio wave can be applied with less loss. Moreover, it is preferable that the width | variety of the side connected to the parallel parts 4c and 4d of the electric field application piece 5a and the electric field application piece 5b is equal to the width of the parallel parts 4c and 4d.

  Materials for the core layer 10, the upper clad layer 11, and the lower clad layer 9 are acrylic resin, epoxy resin, polyethylene terephthalate resin, polycarbonate resin, polyurethane resin, polyimide resin, fluorinated polyimide resin, polyetherimide resin, polysulfone. Electricity that changes its refractive index when an electric field is applied, such as resin, polyethersulfone resin, polyarylate resin, polysiloxane resin, translucent polymer materials, silicon oxide, various glasses, strontium titanate, gallium arsenide, indium phosphorus, etc. Any material that has an optical effect and is transparent to the light to be modulated can be used. When using the light-transmitting polymer, in order to develop a nonlinear optical effect, a pigment having an electro-optical effect is dispersed, or a group having a nonlinear optical effect is bonded to the main chain or side chain. It is preferable to make it.

  Examples of the material of the modulation electrode 3, the electric field application piece 5a, and the electric field application piece 5b include various metal materials and metal oxides known as electrode materials such as aluminum, titanium, gold, copper, and ITO.

(2) Manufacturing Procedure The optical modulator 100 can be manufactured by the procedure shown in FIGS.

  First, a substrate 7 is prepared as shown in FIG. As the substrate 7, a substrate made of an arbitrary material such as a glass substrate, a quartz substrate, a silicon substrate, or a polyimide substrate can be used. If a silane coupling agent or the like is applied to the substrate 7, the adhesion with the ground electrode 8 can be improved.

  Next, a ground electrode 8 is formed on the surface of the substrate 7 as shown in FIG. The ground electrode 8 may be formed by vapor-depositing or plating a metal such as aluminum, titanium, gold, or copper on the surface of the substrate 7, or the metal foil may be bonded together.

  When the ground electrode 8 is formed, a lower clad layer 9 is formed on the surface of the ground electrode 8 as shown in FIG. First, a transparent polymer solution for forming the lower clad layer 9 is applied to the surface of the ground electrode 8. Examples of the method for applying the solution to the ground electrode 8 include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, and printing coating. Is mentioned. After the solution of the above material solution is applied to the first substrate, the solvent is removed by heating, and the lower clad layer 9 is formed by reacting and curing as necessary.

  Next, as shown in FIG. 3D, the core layer 10 is formed on the surface of the lower clad layer 9. The core layer 10 can be formed, for example, by applying a light-transmitting polymer solution forming the core layer 10 to the surface of the lower clad layer 9 and heating and curing. As the solution application method, the same method as described in the lower clad layer 9 is used.

  When the core layer 10 is formed, as shown in FIG. 9A, waveguides such as the input waveguide 1, the output waveguide 6, and the multimode waveguide 2 are formed in the core layer 10. Examples of means for forming the waveguide include etching. Further, a concave portion having a shape corresponding to the waveguide is formed in the lower clad layer 9, and the waveguide is formed by applying a light-transmitting polymer solution on the lower clad layer 9 and heating and curing the solution. Also good.

  Next, as shown in FIG. 2B, an upper cladding layer 11 is formed on the core layer 10, and as shown in FIG. 2C, a dielectric layer 12 is further formed thereon. . The formation of the upper cladding layer 11 and the dielectric layer 12 can be performed in the same procedure as the formation of the lower cladding layer 9 and the core layer 10. As the dielectric layer 12, acrylic resin, epoxy resin, silica, or the like is used.

  When the dielectric layer 12 is formed, a seed electrode 13 made of a metal film is formed on the surface of the dielectric layer 12 as shown in FIG. The seed electrode 13 can be formed in the same manner as the ground electrode 8. Then, a predetermined positive voltage is applied to the seed electrode 13 to apply an electric field to the core layer 10, and the portion of the core layer 10 where the incident waveguide 1, the outgoing waveguide 6, and the multimode waveguide 2 are formed is polarized. Alignment treatment.

  When the polarization alignment process is completed, the seed electrode 13 is etched into the planar shape of the modulation electrode 3 as shown in FIG. Then, as shown in FIG. 10C, the modulation electrode 3 is formed by increasing the thickness of the seed electrode 13 by means such as electroplating.

(3) Operation As described above, when light is incident on the multimode waveguide 2 from the incident waveguide 1 without applying an electric field to the modulation electrode 3 of the optical modulator 100, the incident waveguide 1 is made in a single mode. The propagated light is separated into multimode light by the multimode waveguide 2. As a result, an optical image is generated at the connection portion between the incident waveguide 1 and the multimode waveguide 2. In the multimode waveguide 2, light propagates in multiple modes, and thus forms an optical image by interfering with each other inside the multimode waveguide 2. The light propagated in the multimode in the multimode waveguide 2 is converged to the single mode light while interfering with each other at the connection portion between the multimode waveguide 2 and the output waveguide 6. An optical image is generated, and light having substantially the same intensity as that incident from the incident waveguide 1 is emitted to the outside through the emission waveguide 6.

  Here, since the multi-mode waveguide 2 is formed of a material having an electro-optic effect, when an electric field is applied to the modulation electrode 3, the refractive index of the multi-mode waveguide 2 changes, particularly in a place where an optical image is generated. The refractive index changes greatly. Therefore, the light image is not generated at the place where the light image has been generated so far, so that the light incident from the incident waveguide 1 does not reach the output waveguide 6.

  Accordingly, when a radio wave such as a microwave is applied to the modulation electrode 3 while continuous light is incident from the incident waveguide 1, intermittent light that flickers at a period corresponding to the frequency of the radio wave is emitted from the output waveguide 6. Emitted.

(4) Features In the optical modulator 100, the modulation electrode 3 has stripe-like oblique portions 4 a and oblique portions 4 b disposed obliquely with respect to the light propagation direction in the multimode waveguide 2. Even when a microwave is applied to the electric field application piece 5a, phase matching between the applied microwave and the modulated light can be achieved. Therefore, light modulation at a high speed of about 100 GHz can be easily performed.

  Further, the parallel portions 4 c and 4 d of the modulation electrode 3 are arranged so as to pass above the optical image formed in the multimode waveguide 2, and between the modulation electrode 3 and the upper cladding layer 11. Since the dielectric layer 12 is disposed, optical modulation can be performed with a low voltage of about 3V.

  Further, unlike the conventional Mach-Zehnder type optical modulator, the shape of the waveguide is simple, so that it is easy to manufacture and excellent in robustness.

1-2 Light Modulation Module As a light modulation module using the light modulator according to the first embodiment, a digital light modulation module 200 that performs light modulation with a digital signal, and an analog light modulation module 202 that receives and modulates a radio wave. and so on.

  As shown in FIG. 15, the digital light modulation module 200 generates a modulated light and enters the output-side optical fiber, and a continuous laser light enters the incident waveguide 1 of the light modulator 100. The laser light source 102, the modulation signal generator 104 that generates a modulation signal corresponding to the input digital data and applies it to the modulation electrode 3 of the optical modulator 100, and the digital data input from the outside are integrated to generate a modulation signal An integration-side data bus 106 to be transmitted to the generator 104, a pulsed light incident from an input-side optical fiber is received and converted into a pulsed electrical signal, and a light-receiving preamplifier 108 that amplifies the electrical signal, and a light-receiving preamplifier 108 A data conversion circuit 110 that receives the electrical signal converted and amplified in step S1 and converts the electrical signal into corresponding digital data; The digital data converted by the circuit 110 and a data bus 112 to be transmitted, such as the CPU.

  When digital data is input to the digital light modulation module 200, the modulation signal generator 104 generates a pulse-shaped modulation signal A in synchronization with the input timing of the digital data. The generated modulation signal A is applied to the modulation electrode 3 of the optical modulator 100. The continuous laser light incident on the multimode waveguide 2 of the optical modulator 100 through the incident waveguide 1 from the continuous laser light source 102 is intermittently corresponding to the modulation signal A when the modulation signal A is applied to the modulation electrode 3. The light is converted into light and passes through the output waveguide 6 and enters the output side optical fiber.

  On the other hand, the pulsed light incident on the digital light modulation module 200 through the input side optical fiber is converted into a pulsed digital electric signal by the light receiving preamplifier 108. The digital electric signal is amplified by the data conversion circuit 110 and transmitted to the CPU or the like via the data bus 112.

  Thus, according to the digital light modulation module 200, digital data can be exchanged through the optical fiber.

  On the other hand, as shown in FIG. 16, the analog light modulation module 202 generates modulated light and enters the optical fiber, and the continuous laser light enters the incident waveguide 1 of the optical modulator 100. A laser light source 102, an antenna 114 that receives a radio wave, and a high-frequency amplifier circuit 116 that amplifies the radio wave received by the antenna 114 and inputs the radio wave to the optical modulator 100 are provided.

  In the analog light modulation module 202, when a radio wave including an analog signal such as an audio signal or an image signal is received by the antenna 14, the radio wave is amplified by the high frequency amplifier circuit 116 and applied to the modulation electrode 3 of the light modulator 100. Applied. As a result, the continuous laser light from the continuous laser light source 102 is modulated to produce a continuous modulated light.

  According to the analog light modulation module 202, an analog signal can be transmitted far with much less attenuation than by radio waves.

  Gold was vapor-deposited on the substrate 7 by the VCD method to form the ground electrode 8, and an acrylic resin was spin-coated on the substrate 7 and UV-cured to form a lower cladding layer 9 having a thickness of 3.5 μm.

  Then, FTC (2-dicyanomethylene-3-cyano-4- {2- [trans- (4-N, N-diacetoxyethyl-amino) phenylene-3,4-dibutylene-5] is formed on the lower clad layer 9. Vinyl} -5,5-dimethyl-2,5-dihydrofuran) in which Disperse-Red 1 was dispersed was spin-coated and heated and cured to form a core layer 10 having a thickness of 3.2 μm.

Next, the core layer was etched to form the incident waveguide 1, the multimode waveguide 2, and the output waveguide 6. The width W ₁ of the incident waveguide 1 and the output waveguide 6 was 5 μm, and the width W ₂ of the multimode waveguide ₂ was 50 μm. Therefore, W ₂ / W ₁ = 10. The length L of the multimode waveguide 2 was 6150 μm. The core layer 10 was etched to have a thickness of 2.6 μm around the incident waveguide 1, the multimode waveguide 2, and the output waveguide 6.

  After forming the incident waveguide 1, the multimode waveguide 2, and the output waveguide 6 on the core layer 10, spin coating is performed with the same acrylic resin used to form the lower cladding layer 9 thereon. Cured with UV light. The refractive index of the lower cladding layer 9 and the upper cladding layer 11 was 1.471, and the refractive index of the core layer 10 was 1.582.

  When the upper clad layer 11 was formed, a two-component room temperature curable epoxy resin adhesive was applied thereon and cured to form a dielectric layer 12 having a thickness of 0.8 μm. And the seed electrode 13 was formed by vapor-depositing gold | metal | money on it.

  When the seed electrode 13 is formed, a voltage of 400 to 2000 V is applied between the ground electrode 8 and the seed electrode 13 at a high temperature of 90 to 250 ° C., and the core layer is allowed to cool to room temperature with the voltage applied. 10 was subjected to polarization orientation treatment.

  When the polarization alignment treatment was completed, the seed electrode 13 was etched so as to have the shape of the modulation electrode 3 shown in FIG. 1, and was plated to a thickness of 4.5 μm to form the modulation electrode 3.

Width W of the modulation electrode 3 was set to 50μm equal to the width W ₂ of the multimode waveguide 2, was 6150μm it is also equal to the length L of the multimode waveguide 2 length. The angle α was set to 24.4 milliradians. The widths of the skewed portion 4a, the skewed portion 4b, the parallel portion 4c, and the parallel portion 4d were all 10 μm, and the widths of the electric field applying piece 5a and the electric field applying piece 5b were all 38 μm. The intrinsic inductance of the modulation electrode 3 was 40Ω.

  In the optical modulator 100, the width w of the skew portion 4a, the skew portion 4b, the parallel portion 4c, and the parallel portion 4d, the microwave applied to the electric field application piece 5a, and the modulated light modulated by the multimode waveguide 2 12 and the overlap EO overlap of the microwave and the modulated light, as shown in FIG. 12, as the width w increases, the phase mismatch and the EO overlap It can be seen that there is an increasing relationship. Here, in this embodiment, the width w of the skew portion 4a, the skew portion 4b, the parallel portion 4c, and the parallel portion 4d is 10 μm, and therefore, the phase mismatch and the EO overlap are 0. It can be seen that they are 04 and 0.92.

Here, in order to achieve the 100 GHz band with the electrode attenuation constant of 0.6 dB / (GHz) ^1/2 × cm, the phase mismatch needs to be 0.06 or less as shown in FIG. However, as described above, in the optical modulator 100 according to the present embodiment, the phase mismatch is smaller than 0.04 and 0.06, and thus it can be seen that the 100 GHz band can be sufficiently achieved. In addition, since EO overlap is 0.92, it can be seen that low voltage driving is sufficiently possible.

  In the optical modulator 100 according to this example, the output of the outgoing light emitted from the outgoing waveguide 6 was measured by changing the voltage of the electric field applied to the modulation electrode 3 from 0 V to 4 V, as shown in FIG. Shows the lowest output of -37 dB at 3 V. This also shows that the optical modulator 100 can be driven at a low voltage of about 3V.

Further, as shown in FIG. 14, when the optical loss is −3 dB, that is, the electrode attenuation constant is 0.6 dB / (GHz) ^1/2 × cm, it can be seen that the frequency is 80 GHz or more.

FIG. 1 is a plan view illustrating a configuration of an optical modulator according to the first embodiment. FIG. 2 is a plan view showing a positional relationship between an optical image formed in a multimode waveguide and a modulation electrode in the optical modulator according to the first embodiment. FIG. 3 is a perspective view illustrating a configuration of another example of the optical modulator according to the first embodiment. 4 is a plan view of the optical modulator shown in FIG. FIG. 5 is a cross-sectional view showing a cross section of the optical modulator according to the first embodiment cut in the thickness direction. FIG. 6 is a cross-sectional view showing a cross section of the optical modulator according to the first embodiment in which the waveguide is a rib type. FIG. 7 is a cross-sectional view showing a cross section of the optical modulator according to the first embodiment in which the waveguide is an inverted rib type. FIG. 8 is a process diagram showing a part of a procedure for manufacturing the optical modulator according to the first embodiment. FIG. 9 is a process diagram illustrating a part of a procedure for manufacturing the optical modulator according to the first embodiment. FIG. 10 is a process diagram illustrating the remainder of the procedure for manufacturing the optical modulator according to the first embodiment. FIG. 11 is a graph showing the relationship between the band and the electrode attenuation constant. FIG. 12 is a graph showing changes in phase mismatch and EO-overlap when the widths of the skew portion and the parallel portion constituting the modulation electrode are changed in the optical modulator of the first embodiment. FIG. 13 is a graph showing the relationship between the voltage applied to the modulation electrode and the output of outgoing light from the outgoing waveguide. FIG. 14 is a graph showing the relationship between the frequency band and the optical loss in the optical modulator of the first embodiment. FIG. 15 is a block diagram illustrating a configuration of a digital light modulation module using the light modulator according to the first embodiment. FIG. 16 is a block diagram illustrating a configuration of an analog light modulation module using the light modulator according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Incident waveguide 2 Multimode waveguide 3 Modulation electrode 4a Oblique part 4b Oblique part 4c Parallel part 4d Parallel part 5a Electric field application piece 5b Electric field application piece 6 Output waveguide 7 Substrate 8 Ground electrode 9 Lower clad layer 10 Core Layer 11 upper cladding layer 12 dielectric layer 13 seed electrode 14 antenna 100 optical modulator 102 continuous laser light source 104 modulation signal generator 106 integration side data bus 108 light receiving preamplifier 110 data conversion circuit 112 data bus 114 antenna 116 high frequency amplifier circuit 200 digital Light modulation module 202 Analog light modulation module

Claims (13)

An input waveguide and an output waveguide that propagate light in a single mode;
A multimode waveguide in which the incident waveguide is connected to one end, the output waveguide is connected to the other end, and light incident from the incident waveguide is propagated in a multimode toward the output waveguide;
A modulation electrode to which a modulation signal for modulating light propagating in the multimode waveguide is applied;
A ground electrode located on the opposite side of the modulation electrode across the multimode waveguide;
In the multimode waveguide, when light is incident from the incident waveguide, the light interferes with each other to form a plurality of optical images, and at least a part of the modulation electrode is the multimode waveguide. An optical modulator formed so as to be positioned on an optical image formed in the above. The modulation electrode is
A pair of parallel portions provided along side edges parallel to the light propagation direction in the multimode waveguide, to which an electric field for modulating light is input;
The optical modulator according to claim 1, wherein the pair of parallel portions are coupled to each other, and has an oblique portion provided obliquely with respect to the light propagation direction. The angle α formed between the parallel portion and the skew portion is expressed by the following equation:
arctan (W ₂ / L) <α <π / 2
(However, W ₂ is the width of the multimode waveguide, L is the length of the multimode waveguide.)
The optical modulator according to claim 2, wherein: When the width of the input waveguide and the output waveguide and W _1, the ratio W _{2 /} W ₁ of the relative said input waveguide and the output waveguide of the multimode waveguide width is
1 <W ₂ / W ₁ <100
The optical modulator according to any one of claims 1 to 3. A substrate,
A lower cladding layer formed on the substrate;
An upper cladding layer located above the lower cladding layer;
A core layer sandwiched between the lower clad layer and the upper clad layer to form the multimode waveguide layer, the incident waveguide and the output waveguide;
The core layer has a refractive index larger than any of the upper cladding layer and the lower cladding layer,
5. The optical modulator according to claim 1, wherein the modulation electrode is formed on or above the surface of the upper cladding layer, and the ground electrode is formed between the substrate and the lower electrode.   The optical modulator according to claim 5, wherein the multimode waveguide is a waveguide having a rib structure in which the core layer protrudes in a rib shape toward the upper cladding layer.   The optical modulator according to claim 5, wherein the multimode waveguide is a waveguide having an inverted rib structure in which the core layer protrudes in a rib shape toward the lower clad layer.   The dielectric layer according to claim 5, further comprising a dielectric layer formed on a surface of the upper cladding layer and having a dielectric constant larger than that of the upper cladding layer, wherein the modulation electrode is formed on the surface of the dielectric layer. The optical modulator according to item 1.   After forming a ground electrode, a lower clad layer, a core layer, and an upper clad layer on the substrate, a seed electrode is formed above the upper clad layer, and a thickness direction is formed between the seed electrode and the ground electrode. The optical modulator according to claim 5, wherein the core layer is subjected to polarization orientation processing by applying an electric field of 10 to 10.   The optical modulator according to any one of claims 5 to 8, wherein the core layer is subjected to polarization orientation processing in advance, and an upper cladding layer and a lower cladding layer are formed on both surfaces of the core layer subjected to polarization orientation processing. The optical modulator according to any one of claims 1 to 10,
An electric signal input unit for inputting an electric signal to the modulation electrode of the optical modulator;
An optical modulation module comprising: a continuous light source that inputs continuous light into an incident waveguide of the optical modulator.   The light modulation module according to claim 11, wherein the electrical signal input unit is a digital signal input unit that inputs a digital signal.   The optical modulation module according to claim 11, wherein the electrical signal input unit is an analog signal input unit that inputs an analog signal.

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