JP7293605B2 - Optical waveguide element and optical modulator - Google Patents

Description

The present invention relates to an optical waveguide element and an optical modulator provided with the optical waveguide element.

Optical modulators used in optical fiber communication systems are installed in devices such as transponders. There is a need for substantial longitudinal shortening or miniaturization of the vessel. Therefore, in response to this, there is known an optical modulator in which the input portion of the optical fiber of the optical modulator is arranged on the long side of a rectangular substrate to reduce the size (see, for example, Patent Document 1, etc.). .

Furthermore, in addition to reducing the mounting area, in order to suppress performance deterioration due to connection between the signal processing LSI and the high-frequency wiring of the optical modulator, a high-frequency signal input section is provided on one short side of the modulator, and the other short side is An optical modulator has been proposed in which an optical input/output is provided in the optical modulator (for example, see Patent Document 2, etc.). In such an optical modulator, one end of the optical waveguide formed on the substrate of the optical waveguide element is bent in an L shape and led to the side surface of the substrate, thereby connecting the optical fiber on the input side and the optical fiber on the output side. It is possible to connect in parallel with the housing.

JP-A-2004-125854 JP 2014-164243 A

In the optical waveguide element described in Patent Document 1, since light propagates through the substrate, it is necessary to arrange the optical fiber in a position that shortens the propagation distance in order to achieve a low-loss structure. There is a problem that it can only be applied to cases where the fiber is directly connected to the substrate. Moreover, there is also the problem that it is difficult to deal with a structure in which an optical fiber is arranged on the short side of the output side.

In the optical waveguide element described in Patent Document 2, a semiconductor (InP) is used for the substrate, and an L-shaped optical waveguide is led to the side surface of the substrate. Here, compared to an optical waveguide element using a semiconductor substrate, the size of an optical waveguide element using a substrate having an electro-optical effect such as lithium niobate (LiNbO ₃ ) is generally 0.5 to several mm in width. It has a very long and narrow shape with a side length of several tens of millimeters. For this reason, polishing the entire side surface of the substrate to form an optical surface is difficult in terms of the method of fixing the substrate and finishing the side surface to a predetermined surface roughness with high precision, which leads to a rise in manufacturing costs. I had a problem.

In general, in optical waveguide devices, reinforcing blocks are attached to the upper surface of the substrate in order to prevent chipping of the end portion when the substrate is polished and to obtain sufficient adhesive strength for optical parts such as optical fibers to be connected. There is At this time, in order to make the side surface a polished surface, it is necessary to secure a margin on the substrate for attaching the reinforcing block to the entire side surface extending in the longitudinal direction, which increases the width of the substrate. As a result, the size of the optical waveguide device is increased, and when the devices are obtained by dividing them from one wafer, the number of devices obtained is reduced, resulting in a rise in manufacturing cost. Furthermore, since the control electrode cannot be wired to the portion where the reinforcing block is attached, there is a problem that the installation place of the electric parts such as the high frequency relay board and the connector pin is limited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. It is an object of the present invention to provide an optical waveguide element and an optical modulator that can improve the degree of freedom in designing the installation location of electrical components.

An optical waveguide device according to the present invention includes: (1) a substrate having an optical waveguide having an electro-optic effect and formed so that a light wave propagates; wherein the optical waveguide extends between an input end and an output end and the input end and the output end of the optical modulator the substrate has a side surface substantially parallel to the extending direction of the optical waveguide constituting the optical modulation section and an end surface intersecting the side surface; and the input side end of the optical waveguide. has a bent end that is bent toward the side surface, the bent end has a port at the tip of which a light wave is incident, and is part of the upper surface of the substrate on the side of the end surface of the substrate. A reinforcing block is affixed to, a portion of the side surface of the reinforcing block is configured by an optical surface, the bent end extends to the optical surface, and the port of the bent end extends to the optical surface. located on the optical surface, the optical surface is composed of an inclined surface formed from the side surface side to the end surface side of the substrate, the substrate is made of lithium niobate with a refractive index n _LN =2.22, The medium on the incident side of the light wave incident on the optical surface is air with a refractive index n _air = 1, and at the bent end, for the first straight optical waveguide extending substantially parallel to the side surface of the substrate, The bending angle θ _WG of the second straight optical waveguide extending toward the side surface of the substrate is θ _WG =80° to 90°, and the inclination angle φ of the inclined surface with respect to the side surface of the substrate is φ= It is characterized by being 1° to 10°.

With this configuration, the optical waveguide device according to the present invention does not need to form the entire side surface of the substrate having an electro-optical effect with an optical surface, so that the area of the optical surface can be reduced. As a result, it is possible to easily and inexpensively form the optical surface by reducing the time and effort of polishing the side surface to form the optical surface, and to form the entire surface of the optical surface with a predetermined surface roughness with high precision. can be done.

Further, the optical waveguide element according to the present invention has a configuration in which the optical waveguide is bent within the substrate by forming a bent end portion in which the input side end portion of the optical waveguide element is bent toward the side surface. . Therefore, it is possible to reduce the size of the optical modulator using the optical waveguide device.

Further, with this configuration, the optical waveguide element according to the present invention can easily and inexpensively form an optical surface by forming an inclined surface by polishing the side surface of the substrate. Since there is no need to secure a margin for installing the reinforcing block in the substrate, it is possible to suppress an increase in the width of the substrate.

An optical modulator according to the present invention includes: (2) the optical waveguide element according to the present invention; a housing for housing the optical waveguide element; An input-side optical transmission means for inputting a light wave into an optical waveguide and an output-side optical transmission means for outputting a light wave from the optical waveguide, wherein the input-side optical transmission means and the output-side optical transmission means are: an input-side optical fiber and an output-side optical fiber connected in parallel to the housing, respectively, wherein the input-side optical fiber and the output-side optical fiber cross the extending direction of the optical waveguide; They are arranged so as to pass through the same end face of the body perpendicularly.

With this configuration, in the optical modulator according to the present invention, the optical surface can be easily and inexpensively formed on the side surface of the substrate having the electro-optic effect, and the entire surface of the optical surface can have a predetermined surface roughness with high accuracy. An optical modulator with an optical waveguide element that can be formed can be provided. Furthermore, since it is sufficient to attach the reinforcing block only to the part forming the optical surface, it is possible to secure a space for wiring the control electrode while suppressing an increase in the width of the substrate. This improves the degree of freedom in designing the installation locations of electrical parts such as pins.

In addition, since the optical modulator according to the present invention includes the optical transmission means for inputting or outputting the light wave to or from the bent end of the optical waveguide, a configuration in which the optical transmission means are connected in series is avoided. It is possible to reduce the size of the modulator.

According to the present invention, by forming an optical surface on the side surface of a substrate having an electro-optical effect, it is possible to effectively reduce the size of the optical modulator at a low cost, and to design the installation location of the electrical components to be installed side by side. It is possible to provide an optical waveguide element and an optical modulator with improved flexibility.

1 is a plan view of an optical modulator according to a first embodiment of the invention; FIG. 1 is a plan view of an optical waveguide device according to a first embodiment of the present invention; FIG. FIG. 2 is a partial plan view of the optical waveguide device according to the first embodiment of the present invention, showing in detail an optical surface forming part of the side surface of the substrate; FIG. 4 is a plan view showing an optical waveguide element comparative to the present invention, which has an optical surface configuration different from that of the present invention. FIG. 2 is a plan view showing a case where an optical waveguide element is provided with a reinforcing block, in which (a) is an optical waveguide element having a configuration different from that of the present invention, and (b) and (c) are according to the first embodiment of the present invention. It is a figure which shows an optical waveguide element. FIG. 4 is a plan view of an optical modulator according to a second embodiment of the invention; FIG. 4 is a plan view of an optical waveguide device according to a second embodiment of the present invention; FIG. 8 is a plan view of an optical modulator according to a third embodiment of the invention; It is a figure which shows the input structure of the light wave from the optical-path change part which concerns on the 3rd Embodiment of this invention. FIG. 10 is a plan view of an optical waveguide device according to a fourth embodiment of the present invention; FIG. 10 is a plan view of an optical waveguide device according to a fifth embodiment of the present invention;

An optical waveguide element and an optical modulator provided with the optical waveguide element according to embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
First, the configuration will be explained.

As shown in FIG. 1, the optical modulator 1 according to the first embodiment includes an optical waveguide element 10 and a housing 20 that houses the optical waveguide element 10 . As will be described later, the optical modulator 1 according to the first embodiment includes an input side optical fiber 31 for inputting a light wave to the optical waveguide 12 of the optical waveguide element 10 and an output side for outputting the light wave from the optical waveguide 12. and an optical fiber 32 on the side. Each optical fiber 31, 32 constitutes the optical transmission means of the present invention.

The housing 20 according to the first embodiment is composed of a rectangular parallelepiped metal case made of metal such as stainless steel. The optical waveguide device 10 is housed in a housing 20, and a cover (not shown) is attached to the housing 20 so that the housing 20 is hermetically sealed.

The optical waveguide element 10 according to the first embodiment has an electro-optic effect and includes a substrate 11 having an optical waveguide 12 formed to propagate light waves, a signal electrode 18 formed on the surface of the substrate 11, and a ground. and electrodes 19a and 19b. The signal electrode 18 and the ground electrodes 19a, 19b constitute control electrodes of the present invention.

As the substrate 11 according to the first embodiment, for example, a substrate made of lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), PLZT (lead lanthanum zirconate titanate), EO polymer, or the like is used. In particular, a so-called LN substrate (X plate, Z plate) using crystals of lithium niobate is preferably used because it exhibits a high electro-optical effect. The substrate 11 is made of other materials such as quartz-based material except for the later-described optical modulation section 123 where the control electrodes (the signal electrode 18 and the ground electrodes 19a and 19b) are arranged. good too.

The substrate 11 is a thin plate and has a substantially rectangular shape when viewed from above. Here, in FIG. 1, L and W indicate the longitudinal direction and width direction of the optical modulator 1 and the optical waveguide element 10, respectively. The longitudinal direction and width direction in the following description refer to the directions indicated by L and W, respectively.

As shown in FIG. 1, the substrate 11 has a pair of long side surfaces 11a and 11b extending in the longitudinal direction, and a pair of short side end surfaces 11c and 11d intersecting with the side surfaces 11a and 11b. have. Further, the housing 20 has side plate portions 20a and 20b facing the side surfaces 11a and 11b of the optical waveguide element 10, respectively, and end plate portions 20c and 20d facing the end surfaces 11c and 11d of the optical waveguide element 10, respectively. .

The optical waveguide 12 according to this embodiment has a Mach-Zehnder wiring structure. The optical waveguide 12 is formed by providing a portion having a higher refractive index than the surroundings in the vicinity of the surface within the substrate 11 . When the substrate 11 is an LN substrate, the optical waveguide 12 can be formed by a thermal diffusion method such as Ti or a proton exchange method.

As shown in FIG. 2, the optical waveguide 12 according to the present embodiment includes a bent input-side end 121 and a linear output-side end 122, and an input-side end 121 and an output-side end 122. and an optical modulation section 123 extending between and.

The optical waveguide 12 includes an input-side optical waveguide, an input-side branch optical waveguide connected to the input-side optical waveguide, a parallel optical waveguide connected to the input-side branch optical waveguide and constituting parallel optical waveguides, and the It has an output-side branch optical waveguide connected to a parallel optical waveguide, and an output-side optical waveguide connected to the output-side branch optical waveguide.

In this embodiment, the input-side end 121 of the optical waveguide 12 constitutes the above-described input-side optical waveguide. The output-side end 122 constitutes the above-described output-side branch optical waveguide. The optical modulation section 123 constitutes the above-described input-side branch optical waveguide, parallel optical waveguide, and output-side branch optical waveguide.

The optical modulation section 123 includes a first optical waveguide 124a and a second optical waveguide 124b forming parallel waveguides parallel to each other, and a first optical waveguide 124a and a second optical waveguide 124b branched from the input-side end 121. A third optical waveguide 125 and a fourth optical waveguide 126 connected to the optical waveguide 124b, respectively, and a third optical waveguide 125 branched from the end 122 on the output side and connected to the first optical waveguide 124a and the second optical waveguide 124b, respectively. 5 optical waveguides 127 and a sixth optical waveguide 128 . The first optical waveguide 124a and the second optical waveguide 124b each extend along the longitudinal direction.

The bent input-side end 121 includes a first straight optical waveguide 121b extending longitudinally from a branch point 129a to the third optical waveguide 125 and the fourth optical waveguide 126 toward the end face 11d, and a side surface. and a second straight optical waveguide 121c extending in the width direction toward 11a. This input-side end portion 121 constitutes the bent end portion of the present invention.

The second straight optical waveguide 121c at the input-side end 121 extends to an optical surface 13, which constitutes a part of the side surface 11a of the substrate 11 and will be described later. The port 121a of the side end 121 is located.

The end 122 on the output side is composed of a straight optical waveguide 122d extending from a junction 129b of the fifth optical waveguide 127 and the sixth optical waveguide 128 along the longitudinal direction to the end face 11c. A port 122a of an end portion 122 on the output side from which light waves are emitted is positioned on the end face 11c of the substrate 11. As shown in FIG.

The side surfaces 11 a and 11 b of the substrate 11 are parallel or substantially parallel to the first optical waveguide 124 a and the second optical waveguide 124 b that constitute the optical modulation section 123 .

In this embodiment, the first straight optical waveguide 121b and the second straight optical waveguide 121c forming the input-side end 121 correspond to the above-described input-side optical waveguide. Also, the third optical waveguide 125 and the fourth optical waveguide 126 that constitute the optical modulation section 123 correspond to the input-side branch optical waveguides described above. Also, the first optical waveguide 124a and the second optical waveguide 124b that constitute the optical modulation section 123 correspond to the parallel optical waveguides described above. Also, the fifth optical waveguide 127 and the sixth optical waveguide 128 that constitute the optical modulation section 123 correspond to the output-side branch optical waveguides described above. Further, the straight optical waveguide 122d forming the end portion 122 on the output side corresponds to the output-side optical waveguide described above.

As shown in FIG. 1, the substrate 11 has a signal electrode 18 and a pair of ground electrodes 19a and 19b sandwiching the signal electrode 18 on its surface. The signal electrode 18 and the ground electrodes 19a and 19b are formed on the surface of the substrate 11 by plating the surface of the substrate 11 with a conductive material such as Au.

As shown in FIG. 2, one side surface 11a of the substrate 11 has an optical surface 13 at one end. The optical surface 13 is composed of an inclined surface 13a formed from the side surface 11a of the substrate 11 to the end surface 11d. An input-side port 121 a of the optical waveguide 12 is located on the optical surface 13 .

The side surface 11a of the substrate 11 has the optical surface 13 formed by the inclined surface 13a and the portion along the longitudinal direction other than the optical surface 13. As shown in FIG. Therefore, in the following description, the portion along the longitudinal direction of the side surface 11a other than the optical surface 13 is referred to as a main side surface 11f. That is, side surface 11 a has main side surface 11 f and optical surface 13 .

As shown in FIG. 3, the optical surface 13 can be formed by removing the corner 11e of the substrate 11 by polishing.

As a polishing method for forming the optical surface 13, for example, there is a method of polishing by pressing the corner portion 11e of the substrate 11 against a polisher. In this embodiment, the removed portion of the corner 11e has a triangular shape that is long on the side 11a side and short on the end face 11d side. Thereby, the optical surface 13 is formed so as to be gently inclined from the main side surface 11f toward the end surface 11d.

Further, as shown in FIG. 2, the end surface 11c of the substrate 11 is formed into an optical surface by polishing the entire surface thereof as described above.

Hereinafter, the optical surface formed by the inclined surface 13a on the side surface 11a side will be referred to as the input-side optical surface 13, and the end surface 11c will be referred to as the output-side optical surface 11c.

As shown in FIGS. 1 and 3, the input-side optical fiber 31 penetrates the side plate portion 20a of the housing 20 substantially orthogonally, and its tip is optically connected to the input-side port 121a of the optical waveguide 12. It is provided in the housing 20 so as to do so. As shown in FIG. 1, the side plate portion 20a of the housing 20 is provided with a holding sleeve 33a through which the optical fiber 31 on the input side passes. The optical fiber 31 on the input side is kept fixed to the housing 20 by a holding sleeve 33a.

As shown in FIGS. 1 and 3, the optical fiber 32 on the output side passes through the end plate portion 20c of the housing 20 substantially orthogonally, and the tip of the optical fiber 32 optically connects to the port 122a on the output side of the optical waveguide 12. It is provided in the housing 20 so as to be connected. As shown in FIG. 1, one end of a holding sleeve 33b through which the output-side optical fiber 32 passes is fixed to the end plate portion 20c of the housing 20. As shown in FIG. The optical fiber 32 on the output side is kept fixed to the housing 20 by a holding sleeve 33b.

In the optical waveguide element 10 of this embodiment, a light wave is emitted from the input-side optical fiber 31 toward the input-side port 121 a of the optical waveguide 12 located on the input-side optical surface 13 , and the light wave is input to the optical waveguide 12 . It is designed to be An electric field is applied to the light wave propagating through the optical modulation section 123 of the optical waveguide 12 by the signal electrode 18 and the ground electrodes 19a and 19b to modulate the light wave, and the modulated light wave is output from the optical fiber 32 on the output side as a modulated signal. It is designed to be

As shown in FIG. 3, the input-side optical surface 13 is inclined at an angle φ with respect to the main side surface 11f of the substrate 11 . The inclination angle φ of the optical surface 13 on the input side with respect to the main side surface 11f is set to such an angle that the return light reflected by the optical surface 13 does not enter the optical fiber 31 on the input side. That is, the optical waveguide device 10 according to this embodiment is configured so that the return light reflected by the optical surface 13 does not enter the optical fiber 31 on the input side.

Next, the action will be described.

In the optical modulator 1 according to this embodiment, a light wave is emitted from the input-side optical fiber 31 toward the input-side port 121a of the optical waveguide element 10, and the light wave is transmitted from the port 121a to the input-side end of the optical waveguide 12. It is input to the part 121 . A light wave input to the input-side end 121 passes through third and fourth optical waveguides 125 and 126 and is demultiplexed into first and second optical waveguides 124a and 124b, respectively. After passing through the wave paths 127 and 128, the waves are collected at the end portion 122 on the output side. The light wave enters the output side optical fiber 32 from the output side port 122a and is output from the output side optical fiber 32. FIG.

Here, an electric field is applied as a modulation signal to the light wave propagating through the optical modulation section 123 by the signal electrode 18 and the ground electrodes 19a and 19b. As a result, the light wave propagating through the light modulating section 123 is modulated, and the modulated light wave is output from the optical fiber 32 on the output side. Modulation of the light wave is, for example, phase modulation, intensity modulation, or the like.

In the optical waveguide element 10 of the present embodiment, on the input side of the optical waveguide 12, the input-side end portion 121 extends in the longitudinal direction and then bends in the width direction, and the input-side port 121a is It is located on the optical surface 13 on the input side. On the other hand, on the output side of the optical waveguide 12, the output-side end 122 extends linearly to the output-side optical surface 11c, and the output-side port 122a is positioned on the optical surface 11c. With such a configuration, the optical waveguide 12 of this embodiment is bent at approximately 90° inside the substrate 11 .

Therefore, in the optical modulator 1 according to the present embodiment having such an optical waveguide element 10, the optical fiber 31 on the input side does not extend from the housing 20 in the longitudinal direction, so that the length can be reduced.

Further, in the optical waveguide element 10 according to the present embodiment, the optical surface 13 on the input side, which had to be formed on the side surface 11a of the substrate 11 by bending the optical waveguide 12, is formed on a part of the side surface 11a. It is

Here, FIG. 4 shows an optical waveguide element 10B in which the entire surface of the side surface 11a of the substrate 11 is composed of an optical surface on the input side as a contrast to this embodiment. Also in this optical waveguide device 10B, the port 121a of the input-side end portion 121 of the optical waveguide 12 is located on the input-side optical surface, that is, the side surface 11a. The side surface 11a is polished so that the entire surface thereof has a predetermined surface roughness, and is configured as an optical surface.

On the other hand, in the optical waveguide device 10 according to this embodiment, the optical surface 13 on the input side is formed on part of the side surface 11 a of the substrate 11 . Therefore, the optical waveguide element 10 according to the present embodiment does not need to use the entire side surface 11a of the substrate 11 as an optical surface as in the comparison shown in FIG. be able to. As a result, the labor for polishing the side surface 11a to form the optical surface 13 is reduced, and the optical surface 13 can be formed easily and inexpensively. Moreover, the entire surface of the optical surface 13 can be formed to have a predetermined surface roughness with high precision.

As described above, in general, in the optical waveguide element, in order to obtain chipping of the end portion when polishing the substrate, and to obtain the adhesive strength of the portion where optical parts such as optical fibers are connected, A reinforcing block may be attached. Therefore, when the entire side surface 11a of the substrate 11 is configured as an optical surface as shown in FIG. must be pasted. However, in this case, the width of the substrate 11 is increased in order to secure a blank area on the substrate 11 for attaching the reinforcing block 41 . In the substrate 11 shown in FIG. 5A, a reinforcing block 42 is attached to the upper surface of the substrate 11 corresponding to the optical surface 11c on the short side to which the optical fiber 32 on the output side is connected.

On the other hand, in this embodiment, since the optical surface 13 on the input side is formed on a portion of the side surface 11a, a reinforcing block may be provided on the portion corresponding to the optical surface 13. FIG. For example, as shown in FIG. 5(b), a reinforcing block 43 may be attached to the upper surface of the substrate 11 corresponding to the entire area of the end face 11d on the short side, or as shown in FIG. The reinforcing block 44 may be attached only to the portion corresponding to the surface 13 . Both reinforcement blocks 43 , 44 are provided to cover the area of the optical surface 13 . 5(b) and 5(c), on the upper surface of the substrate 11 corresponding to the optical surface 11c on the short side to which the optical fiber 32 on the output side is connected, The reinforcing blocks 42 are respectively attached in the same manner as in a).

In the form of FIG. 5(b), since the reinforcing block 43 can be provided using a conventional technique, there is an advantage that it is possible to suppress an increase in the manufacturing cost. Further, in the embodiment of FIG. 5(c), when the control electrode necessary for arranging the high-frequency component near the end surface 11d of the substrate 11 is arranged in the direction of the input-side end 121 of the optical waveguide 12, the control electrode can be avoided to provide the reinforcing block 44 . Therefore, it is advantageous in that the risk of disconnection of the control electrode and the deterioration of high frequency characteristics are suppressed.

(Second embodiment)
Next, a second embodiment will be described.

In the optical waveguide element 10 of the second embodiment described below, the output-side end 122 of the optical waveguide 12 in the first embodiment is bent in the direction of the side surface 11a in the same manner as the input-side end 121. It has a configuration. In addition, an output-side optical surface 14 is formed on the side surface 11 a of the substrate 11 so as to correspond to the output-side end portion 122 . The second embodiment differs from the first embodiment in these respects. Therefore, in the following description, the same components as in the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted. 1 will be described.

FIG. 6 shows an optical modulator 1 according to a second embodiment. The optical waveguide element 10 provided in the optical modulator 1 has an input-side optical surface 13 and an output-side optical surface 14 at both ends of the side surface 11a of the substrate 11, respectively. In the optical waveguide device 10 according to the second embodiment, both the input-side end portion 121 and the output-side end portion 122 constitute the bent ends of the present invention.

As shown in FIG. 7, the optical surface 14 on the output side is composed of an inclined surface 14a formed from the side surface 11a of the substrate 11 to the end surface 11c.

As shown in FIG. 7, the output-side end 122 of the optical waveguide 12 according to the second embodiment extends in the longitudinal direction from the junction 129b of the fifth and sixth optical waveguides 127, 128 toward the end surface 11c. It has an extending first linear optical waveguide 122b and a second linear optical waveguide 122c extending in the width direction toward the side surface 11a. The second straight optical waveguide 122c extends to the optical surface 14 forming part of the side surface 11a of the substrate 11, and the port 122a of the output end 122 is located on the optical surface 14. As shown in FIG.

As shown in FIGS. 6 and 7, the optical fiber 32 on the output side according to the second embodiment passes through the side plate portion 20a of the housing 20 at right angles, and the tip of the optical fiber 32 passes through the end of the optical waveguide 12 on the output side. It is provided on the housing 20 so as to be optically connected to the port 122 a of the section 122 .

The optical surface 14 on the output side according to the second embodiment, like the optical surface 13 on the input side, has a surface with respect to the main side surface 11f such that return light reflected by the optical surface 14 does not enter the end portion 122 on the output side. slanted at an angle. In other words, the optical waveguide device 10 according to the second embodiment is configured so that the return light reflected by the optical surface 14 does not enter the end portion 122 on the output side.

The optical waveguide device 10 according to the second embodiment has a configuration in which the optical waveguide 12 returns to the side surface 11a after passing through the light modulation section 123 from the side surface 11a of the substrate 11 . Therefore, the optical fiber 31 on the input side and the optical fiber 32 on the output side connected to the optical waveguide element 10 are installed in parallel on the same side surface 11a. Therefore, in the optical modulator 1 according to the second embodiment having such an optical waveguide element 10, the optical fiber 31 on the input side and the optical fiber 32 on the output side do not extend from the housing 20 in the longitudinal direction. Further shortening can be achieved.

The optical surface 14 on the output side is formed on a part of the side surface 11a similarly to the optical surface 13 on the input side, and has a smaller area than the entire surface of the side surface 11a. Therefore, the optical surface 14 can be formed easily and inexpensively, and the entire surface of the optical surface 14 can be formed to have a predetermined surface roughness with high precision.

(Third Embodiment)
Next, a third embodiment will be described.

The optical modulator 1 according to the third embodiment described below is different from the first embodiment in that the optical wave is input to the optical waveguide element 10 of the first embodiment described above via the optical path changing section 50. different from the form. Therefore, in the following description, the same components as those of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted, and differences from the first embodiment are mainly described.

As shown in FIG. 8, the optical modulator 1 according to the third embodiment includes an input-side optical fiber 31 and an output-side optical fiber 32 that are connected in parallel to a housing 20 . A high-frequency driver amplifier 60 is accommodated on the side of the side plate portion 20b in the housing 20, and an RF interface 410 is provided on the outer surface of the side plate portion 20b correspondingly. The RF interface 410 consists of a coaxial connector, PIN, FPC, feedthrough, or the like. Further, the housing 20 accommodates an optical path changer 50 that refracts the optical path of the light wave emitted from the optical fiber 31 on the input side and guides it to the optical waveguide element 10 .

In the third embodiment, the optical fiber 31 on the input side is arranged in parallel with the optical fiber 32 on the output side and connected to the end plate portion 20 c of the housing 20 . The optical fiber 31 on the input side passes through the end plate portion 20c of the housing 20 and extends in the longitudinal direction between the optical waveguide element 10 in the housing 20 and the side plate portion 20a. The optical fiber 31 on the input side is provided so that its tip is close to the optical path changing section 50 . In the third embodiment, the optical fiber 31 and the optical path changer 50 constitute the optical transmission means on the input side of the present invention.

The high-frequency driver amplifier 60 is arranged inside the housing 20 between the optical waveguide element 10 and the side plate portion 20b. The high frequency driver amplifier 60 drives the optical waveguide element 10 by supplying a high frequency signal to the signal electrode 18 . The high-frequency driver amplifier 60 may be mounted as a single semiconductor element, or may be mounted on a relay board made of ceramic or the like.

The optical path changing section 50 has lenses 51 and 52 and a prism 53 . Lenses 51 and 52 and prism 53 are arranged on the side of substrate 11 within housing 20 .

In the optical modulator 1 of the third embodiment, the optical fiber 31, housing 20 and optical waveguide element 10 are substantially parallel. As shown in FIG. 9, the light wave emitted from the optical fiber 31 is collimated by the lens 51 and enters the prism 53 inclined so as to suppress the return light reflected by the boundary surface. Then, it is reflected at the critical angle θ _C within the prism 53 and emitted from the boundary surface on the optical waveguide element 10 side. The light wave emitted from the boundary surface on the side of the optical waveguide element 10 is condensed by the lens 52, and the input side port located on the optical surface 13 of the optical waveguide element 10 having an inclined surface at an arbitrary angle φ with the housing 20. 121a.

Although the optical path conversion unit 50 of the present embodiment shows an example of a collimating optical system using two lenses 51 and 52, the light wave emitted from the optical fiber 31 is converted into the optical waveguide 10 by one lens. The configuration may be such that the light is condensed on the port 121a on the input side.

Here, as shown in FIG. 9, when the second straight optical waveguide 121c is inclined at an angle θ _WG with respect to the first straight optical waveguide 121b at the input side end 121 of the optical waveguide 12, the The bending angle θ _WG is determined based on the tilt angle φ of the optical surface 13 , the refraction angle of the light wave passing through the prism 53 and the refractive index of the substrate 11 .

For example, as shown in FIG. 9, when a crystal of lithium niobate (LiNbO ₃ ) is used for the substrate 11, the bending angle θ _WG of the second straight waveguide 121c is 80° to 90°, The inclination angle φ of the optical surface 13 is preferably 1° to 10°. Other parameters are as shown below.

・Refractive index of the material of the prism 53 In the case of optical glass: n _prism =1.5
・Refractive index on output side (refractive index of air): n _air =1
・Refractive index of substrate 11 (LiNbO ₃ ) on incident side: n _LN =2.22
- Casing 20 || Optical fiber 31 || Optical waveguide element 10
・Bending angle of the second straight waveguide 121c: θ _WG =80° to 90°
・Incline angle φ of the optical waveguide element 10: 1° to 10°

In the optical modulator 1 according to the third embodiment, since the optical path conversion unit 50 for inputting the light wave to the optical waveguide 12 of the optical waveguide element 10 is arranged on the side of the substrate 11 in the housing 20, the optical path It is possible to reduce the size of the optical modulator 1 including the conversion section 50 .

In addition, in the optical modulator 1 according to the third embodiment, the optical paths 50 and the high-frequency driver amplifier 60 are accommodated in the housing 20 by installing the respective optical fibers 31 and 32 in parallel in the housing 20. Even with such a configuration, it is possible to reduce the size.

In addition, the optical modulator 1 according to the third embodiment has the optical fibers 31 and 32 connected in parallel to the housing 20, which allows the optical modulator 1 to be mounted on equipment in combination with the above-described miniaturization. As a result, the selection range of mounting locations is widened, and the degree of freedom in designing the device is improved.

(Fourth embodiment)
Next, a fourth embodiment will be described.

The optical modulator 1 of the fourth embodiment shown in FIG. 10 has Mach-Zehnder optical waveguides 210 and 220 having a nested waveguide structure in the optical waveguide element 10 of the third embodiment described above, and an optical waveguide element It has a polarization combiner 300 that combines the polarization of the output light from 10 . Also, the optical modulator 1 of the fourth embodiment has an RF interface 410 and a high frequency relay board 420 . The optical modulator 1 of the fourth embodiment differs from the above-described third embodiment in these respects. Therefore, in the following description, the same components as those of the third embodiment are denoted by the same reference numerals, and descriptions thereof are omitted, and differences from the third embodiment are mainly described.

As shown in FIG. 10, the optical waveguide 12 of the optical waveguide element 10 according to the fourth embodiment includes a bent input-side end portion 121, first optical waveguides 124a and 124a forming parallel waveguides parallel to each other. and a second optical waveguide 124b. The optical waveguide 12 also includes a third optical waveguide 125 and a fourth optical waveguide 126 branched from the input end 121 and connected to the first optical waveguide 124a and the second optical waveguide 124b, respectively. have. A first Mach-Zehnder optical waveguide 210 and a second Mach-Zehnder optical waveguide 220 having a nested waveguide structure are connected to the downstream side of the first optical waveguide 124a and the second optical waveguide 124b, respectively. .

A first Mach-Zehnder optical waveguide 210 has a configuration in which two sub-Mach-Zehnder optical waveguides 211 and 212 are incorporated in two branch waveguides 213a and 213b that constitute a main Mach-Zehnder optical waveguide 213, respectively. The second Mach-Zehnder optical waveguide 220 has a configuration in which two sub-Mach-Zehnder optical waveguides 221 and 222 are incorporated in two branch waveguides 223a and 223b that constitute the main Mach-Zehnder optical waveguide 223, respectively.

An output side optical waveguide 214 extending to the end surface 11c of the substrate 11 is connected to the output side of the first Mach-Zehnder optical waveguide 210, and light waves are emitted from the output side optical waveguide 214 to the end surface 11c. An output port 214a is located. An output-side optical waveguide 224 extending to the end surface 11c of the substrate 11 is connected to the output side of the second Mach-Zehnder optical waveguide 220, and light waves are emitted from the output-side optical waveguide 224 to the end surface 11c. The port 224a on the output side where the

In the fourth embodiment, the forming regions of the first and second Mach-Zehnder optical waveguides 210 and 220 constitute the optical modulation section 225, respectively. That is, the optical waveguide element 10 has two optical modulation portions 225, and control electrodes (signal electrode and ground electrode) (not shown) for applying modulation signals to these optical waveguides 210 and 220 are provided in the regions.

In the fourth embodiment, a polarization combiner 300 is arranged between the end face 11c of the substrate 11 and the optical fiber 32 on the output side. The fourth embodiment has a polarization multiplexing configuration including the polarization combining section 300 .

The polarization synthesizing unit 300 includes a polarization synthesizing element 310, a lens 320 that collimates the light emitted from the port 214a on the output side and guides it to the polarization synthesizing element 310, and the light emitted from the port 224a on the output side. It has a lens 330 that converts the light into light and guides it to the polarization combining element 310 and a half-wave plate 340 that rotates the polarization of the light emitted from the lens 330 .

The polarization synthesizing element 310 orthogonally polarizes two lights (modulated lights) incident on the polarization synthesizing element 310 from the ports 214a and 224a on the output side, and converges them on the same optical path. It has a function of emitting along the optical axis of the optical fiber 32 of . According to the polarization synthesizing unit 300, for example, modulated light of 50 Gb/s is polarized and synthesized to obtain modulated light of 100 Gb/s.

Further, in the fourth embodiment, an RF interface 410 connected to a high-frequency driver amplifier (not shown) that amplifies and supplies high-frequency signals to the signal electrodes is provided on the outer surface of the end plate portion 20d of the housing 20. ing. RF interface 410 consists of a coaxial connector, PIN, FPC, feedthrough, or the like. Further, in the fourth embodiment, a high-frequency relay board 420 for relaying the connection between the optical waveguide element 10 and the RF interface 410 is arranged between the end plate portion 20d in the housing 20 and the optical waveguide element 10. is set.

In the optical modulator 1 according to the fourth embodiment, as in the third embodiment, the optical path conversion unit 50 for inputting light waves to the optical waveguide 12 of the optical waveguide element 10 is located on the substrate 11 side inside the housing 20 . Since it is arranged on the side, it is possible to reduce the size of the optical modulator 1 including the optical path changing section 50 .

Further, in the optical modulator 1 according to the fourth embodiment, by installing the optical fibers 31 and 32 in parallel in the housing 20, the optical path conversion section 50, the polarization combining section 300 and the high frequency relay board 420 are arranged in the housing. Even with the structure housed in the body 20, the size can be reduced.

In addition, the optical modulator 1 according to the fourth embodiment has the optical fibers 31 and 32 arranged in parallel in the housing 20, which allows the optical modulator 1 to be mounted on the device in combination with the above-described miniaturization. In doing so, the selection range of mounting locations is widened, and the degree of freedom in designing the device is improved.

In the fourth embodiment, it is sufficient to attach the reinforcing block 43 only to the portion where the optical surface 13 is formed. Therefore, it is possible to secure a space for wiring the control electrodes while suppressing an increase in the width of the substrate 11. . For this reason, the degree of freedom in designing the installation location of the electrical component is improved. Accordingly, a signal processing LSI may be arranged on the end side where the RF interface 410 is arranged. Alternatively, a high frequency driver amplifier may be mounted on the high frequency relay board 420 in the housing 20 and directly connected to the optical waveguide element 10 .

(Fifth embodiment)
Next, a fifth embodiment will be described.

The optical waveguide element 10 of the fifth embodiment described below differs from the first embodiment in that it has an optical surface 15 instead of the optical surface 13 of the optical waveguide element 10 of the first embodiment. ing. Therefore, in the following description, the same components as those of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted, and differences from the first embodiment are mainly described.

As shown in FIG. 11, an optical waveguide element 10 according to the fifth embodiment has an optical surface 15 on a part of the side surface 11a. The optical surface 15 is composed of a stepped surface 15a formed from the side surface 11a of the substrate 11 to the end surface 11d. In the optical waveguide 12 , the second straight optical waveguide 121 c at the input-side end 121 extends to the optical surface 15 , and the input-side port 121 a is located on the optical surface 15 .

The optical surface 15 can be formed by removing the corner portion (portion corresponding to 11e in FIG. 3) of the substrate 11 formed by the side surface 11a and the end surface 11d by cutting and polishing. can.

In the optical waveguide device 10 according to the fifth embodiment, the optical surface 15 is formed at an angle such that the return light reflected by the optical surface 15 does not enter the optical fiber 31 on the input side.

In the optical waveguide element 10 according to the fifth embodiment, the optical surface 15 can be easily and inexpensively formed by cutting the side surface 11a of the substrate 11 with a dicer or the like and then polishing the same. Further, when a reinforcing block is installed corresponding to the optical surface 15, it is sufficient to install the reinforcing block only on the processed portion of the formed optical surface 15, thereby suppressing an increase in the width of the substrate 11. can be done. Further, in the optical waveguide device 10 according to the fifth embodiment, it is possible to suppress return light that is reflected without being transmitted by the optical surface 15 .

In each of the above-described embodiments, a part of the side surface 11a of the substrate 11 constitutes an optical surface, but a part of the side surface 11b of the substrate 11 may constitute an optical surface. Alternatively, optical surfaces may be formed on both side surfaces 11a and 11b, and the ends of the optical waveguide 12 may be guided to these optical surfaces.

According to the present invention, an optical surface can be formed on the side surface of a substrate having an electro-optical effect at a low cost. It is useful as an optical waveguide device and an optical modulator that can improve the

1 optical modulator 10 optical waveguide element 11 substrates 11a, 11b side surfaces 11c, 11d end surface 12 optical waveguides 13, 14, 15 optical surface 13a inclined surface 15a stepped surface 18 signal electrode (control electrode)
19a, 19b ground electrodes (control electrodes)
20 housing 31 optical fiber (optical transmission means on the input side)
32 optical fiber (optical transmission means on the output side)
121 input side end (bent end)
121a Input side port 122 Output side end (bent end)
122a, 214a, 224a Output side port 123 225 Optical modulator

Claims (2)

a substrate having an optical waveguide having an electro-optical effect and formed to propagate light waves;
a control electrode formed on the substrate and applying a modulation signal to the light wave propagating in the optical waveguide;
The optical waveguide has an input-side end, an output-side end, and an optical modulation section extending between the input-side end and the output-side end,
the substrate has a side surface substantially parallel to the extending direction of the optical waveguide constituting the optical modulation section and an end surface intersecting the side surface;
the input-side end of the optical waveguide has a bent end bent toward the side surface;
the bent end has a port at its tip through which a light wave is incident,
a reinforcing block is attached to a portion of the upper surface of the substrate on the end surface side of the substrate, and a portion of the side surface side of the reinforcing block is configured by an optical surface;
said bent end extending to said optical surface, said port of said bent end being located at said optical surface;
the optical surface is composed of an inclined surface formed from the side surface side to the end surface side of the substrate;
the substrate is made of lithium niobate with a refractive index n _LN =2.22;
a medium on the incident side of the optical surface where the light wave is incident is air with a refractive index n _air =1;
At the bent end, the bending angle θWG of the second linear optical waveguide extending toward the side surface of the substrate with respect to the first linear optical waveguide extending substantially parallel to the side surface of the substrate is _{θ WG} = 80° to 90°, and an inclination angle φ of the inclined surface with respect to the side surface of the substrate is φ = 1° to 10°. The optical waveguide device according to claim 1;
a housing for housing the optical waveguide element;
an optical transmission means on the input side that is optically connected to the optical waveguide element and inputs an optical wave to the optical waveguide of the optical waveguide element and an optical transmission means on the output side that outputs an optical wave from the optical waveguide;
the input-side optical transmission means and the output-side optical transmission means each include an input-side optical fiber and an output-side optical fiber connected in parallel to the casing;
The optical fiber on the input side and the optical fiber on the output side are arranged to perpendicularly penetrate the same end surface of the housing that intersects the extending direction of the optical waveguide. vessel.

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