JP4623894B2 - Optical waveguide type optical modulator with output light monitor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveguide modulator with an output light monitor. In particular, the present invention uses radiation mode light radiated from an optical waveguide as output light for monitoring in an appropriate direction, and the actual modulator itself. The present invention relates to an optical waveguide modulator with an output light monitor in which output light is monitored by simple monitoring means without changing the structural structure, feedback control of the operating point of the optical modulator is performed, and noise in the monitor signal is reduced. .
[0002]
[Prior art]
In general, in order to maintain the output light of an optical modulator using an optical waveguide element in a constant output state, the output light of the optical modulator is monitored, and optical modulation is performed in response to changes in the output light. It is necessary to change the magnitude of the modulation voltage applied to the device.
As a method of monitoring the output light of an optical modulator using an optical waveguide element, conventionally, a directional coupler (coupler) or the like is disposed in the optical waveguide element to monitor light separately from the optical waveguide for optical signal output. A method of providing an output optical waveguide is generally performed. In this method, it is necessary to newly provide an optical circuit for monitoring light splitting in the optical waveguide element, and it is necessary to connect the optical fiber for monitor output to the optical waveguide element separately from the optical fiber for optical output signal There is.
[0003]
As another monitoring method, as disclosed in Japanese Patent Laid-Open No. 11-194237, an inclined hole is formed in the clad portion on the optical waveguide, or a diffractive lens is disposed on the optical waveguide element, and the optical waveguide A system is known in which a part of the signal output light is taken out of the element substrate by this lens or the like. In this method, it is necessary to newly attach a monitor light extraction lens or the like on the optical waveguide type optical waveguide element. Since the monitor light is extracted above the optical waveguide element, The light receiving member must be attached to the optical waveguide element after it is mounted in the housing case, and this attachment requires considerable labor.
[0004]
Furthermore, Japanese Patent Laid-Open No. 5-34650 discloses a system in which the end of an optical waveguide element is formed obliquely, a part of light output from the waveguide is reflected obliquely, and this reflected light is received as monitor light. Has been. In this method, it is necessary to select the inclined shape of the element end face within a range that does not adversely affect the main output light from the element. Therefore, there is a problem in practicality of this method.
[0005]
Japanese Patent Application Laid-Open No. 5-53086 describes a device that directly installs a light receiving element on an optical waveguide element and directly receives and monitors a part of signal output light in the optical waveguide. In this device, it is necessary to mount the light receiving element mounting means on the optical waveguide element, and the mounting of the mounting means and the work for connecting the light receiving element to it and the adjustment work are performed by attaching the optical waveguide element to the optical waveguide element. This is done after mounting in the housing case. For this reason, the mounting and adjustment operations of the light receiving element are considerably difficult, and the possibility of damaging the optical waveguide element is increased.
[0006]
Based on the above, the applicant of the present application (Japanese Patent Application No. 2000-101316, dated March 31, 2000) uses, as an output light for monitoring, radiation mode light emitted from an optical waveguide in an appropriate direction. The light intensity of the output light is monitored by a monitoring means using a capillary having a simple structure and excellent workability and optical fiber operability without changing the substantial structure of the optical modulator itself. We proposed an optical waveguide modulator with an output light monitor.
[0007]
The “optical waveguide optical modulator with output monitor” disclosed in the previous application will be described below.
In an optical modulator that obtains an ON / OFF optical signal output using a Mach-Zehnder type optical waveguide or the like, an optical waveguide is formed for radiation mode light generated in an OFF mode state, that is, an optical signal is not output. Within the substrate, the optical signal output is emitted obliquely outward with respect to the output optical waveguide through which the optical signal output is guided. This radiation mode light normally propagates in the substrate while making a radiation angle of about 0.7 degrees and away from the optical waveguide output portion, and finally is emitted to the outside from the substrate end face. Further, since the light amount of the radiation mode light has a complementary relationship with the light amount of the optical signal output passing through the output optical waveguide, the optical signal output can be monitored by detecting the radiation mode light.
[0008]
Also, an optical fiber for receiving an optical signal output from the optical waveguide and guiding it to the outside of the modulator is attached to the end face of the optical modulator substrate, but the outer diameter of this optical fiber is as very small as 125 μm. If the substrate is simply bonded to the end face of the substrate (output light output portion), the adhesive strength is insufficient. For this reason, an optical fiber is covered using an “optical fiber reinforcing member”, and one end face of this reinforcing member is bonded to the end face of the substrate to reinforce and protect the connection portion between the optical fiber and the optical waveguide, and its adhesive strength Has improved.
Generally, a silicon material or a ceramic material is usually used for the optical fiber reinforcing member. The present applicant selects a material that transmits signal light / radiation mode light as a material of the optical fiber reinforcement member, and further receives the radiation mode light emitted from the end face of the substrate, based on the thickness of the optical fiber reinforcement member. By setting the size to be possible, the radiation mode light can be guided into the optical fiber reinforcing member.
[0009]
Then, the opposite end surface of the optical fiber reinforcing member (the surface opposite to the bonding end surface bonded to the output end surface of the optical waveguide element in the optical fiber reinforcing member) is bonded and protected. When formed so as to be inclined with respect to the extending direction of the optical fiber, radiation mode light propagating through the reinforcing member is reflected at the inclined end face, and is different from the direction outside the reinforcing member (the output optical fiber is taken out). (In one desired direction, such as up, right, down, left). This radiated light is detected by a photodetector, for example, a photodiode (PD), arranged separately from the optical waveguide element in the optical waveguide element case, and the amount of radiation mode light is measured, and the value is measured. Thus, the amount of light output from the optical waveguide can be monitored.
[0010]
Further, by appropriately setting the inclination angle and direction of the inclined end face of the reinforcing member, the reflection radiation direction of the radiation mode light is changed, and the arrangement position of the photodetector that receives the radiation mode light is changed to the position of the optical waveguide element. It is possible to select optimally so as not to affect the function and the arrangement position of each member.
[0011]
FIG. 1 shows the above-described conventional example.
FIG. 1 is a plan view (partial cross section) illustrating a part of an apparatus for monitoring radiation mode light. In FIG. 1, the output side end face of the substrate 1 of the light modulation element is made of a material having the same optical characteristics as the substrate 1, and a reinforcing member 12 that reinforces the end face forms a waveguide of the substrate 12. It is bonded to the surface. The substrate 1 and the reinforcing member 12 have the same optical axis.
[0012]
One end face 16 of the capillary 13 is bonded and fixed to the output-side end face 10 of the substrate 1. In FIG. 1, the output side end face 10 and the capillary end face 16 of the substrate are drawn apart from each other, but both are firmly bonded and fixed by an adhesive. A hollow portion 14 is formed along the longitudinal center axis of the capillary 13, and the optical fiber 15 is accommodated in the hollow portion 14 and fixed by an adhesive. The output end of the optical waveguide output portion 7 is exposed in the hollow portion 14 of the capillary 13, and the distal end surface of the optical fiber 15 is bonded and fixed to the output end. The diameter of the hollow portion 14 is set to be approximately the same as the diameter of the optical fiber 15 and slightly larger so that the optical fiber 15 can be accommodated and the optical fiber can be prevented from being lost.
[0013]
The other end face (tip face) 17 of the capillary 13 is formed to be inclined with respect to the longitudinal axis of the hollow portion 14 of the capillary 13. The radiation mode lights 8 and 9 propagated through the inside 18 of the capillary 13 are reflected by the tip surface 17, and the reflected radiation mode lights 23 and 24 are received by the light receiving surface of the photoelectric conversion element 20 constituting the photodetector. Is done. The photoelectric conversion element outputs a monitor signal based on the received radiation mode light.
[0014]
However, in the conventional example according to FIG. 1, since both the radiation mode lights 23 and 24 are detected, the following problems occur.
In the conventional apparatus shown in FIG. 1, the radiation mode light 23 reflected from the upper half 17 a close to the photoelectric conversion element 20 on the reflection surface 17 of the capillary 13 and the lower half 17 b far from the photoelectric conversion element 20 are used. The reflected radiation mode light 24 is incident on the incident rectangular surface areas 25 and 26 of the light receiving surface of the photoelectric conversion element 20 as shown in FIG. Since the rectangular surface areas 25 and 26 overlap with each other in the surface area 27, the radiation mode lights 23 and 24 incident on the surface area 27 interfere with each other, and the monitor light output of the photoelectric conversion element 20 has an ambient temperature. The problem of fluctuating (fluctuating) due to other disturbances arises.
[0015]
In the earlier application of the present applicant (Japanese Patent Application No. 2000-101316), in order to solve this problem and stabilize the monitor light output from the photoelectric conversion element, the radiation mode light 8 propagating through the inside 18 of the capillary 13, Only one of 9 is made to enter the photoelectric conversion element.
As a specific example, as shown in FIG. 3, a reflection surface is formed on the upper half portion 17a (about half portion close to the photoelectric conversion element 20) of the tip end surface of the capillary 13, and is reflected by the upper half reflection surface 17a. Only the radiation mode light 23 is received by the photoelectric conversion element 20. As shown in FIG. 3, the lower half of the capillary tip is cut from the tip surface to a depth W, and the portion 28 having a depth F is removed from the peripheral surface of the capillary. On the end face 29 formed in the lower half portion of the capillary 13 by the removal of the removal portion 28, the radiation mode light is reflected in the direction of the arrow 29a and is not received by the photoelectric conversion element 20. For this reason, in the optical modulator of FIG. 3, a part 9 of the radiation mode light is reflected from the lower half portion of the tip end surface of the capillary and is not received by the photoelectric conversion element. As a result, as shown in FIG. Thus, an interference region such as the surface area 27 is not generated, and the monitor signal output from the photoelectric conversion element is stabilized.
[0016]
Further, as shown in FIG. 3, by removing the lower half portion 28 of the tip surface portion of the capillary 13, the following effects can be obtained.
(1) The hollow portion 14 of the capillary 13 desirably has a diameter as large as possible so that the optical fiber 15 can pass through. However, since the radiation angle of the radiation mode light is as small as about 0.7 degrees, the radiation mode light is converted into the fleshy portion of the capillary. In order to propagate 18, the smaller the hole diameter of the hollow portion, the better. Therefore, the hole diameter is about 1 mm larger than the outer diameter of the optical fiber. In this case, as shown in FIG. 1, it is very difficult to introduce the optical fiber into the hollow portion when the entire end face of the capillary is inclined. is there. Usually, the optical fiber introduction part is provided with a tapered portion to facilitate the introduction of the optical fiber, but such a tapered introduction part cannot be employed for the reason related to the radiation angle. However, with the structure as shown in FIG. 3, the hollow portion facing the removal portion 28 functions as an optical fiber introduction groove, and can guide the optical fiber and facilitate the introduction of the hollow portion of the optical fiber. .
(2) Further, the optical fiber is usually bonded and fixed to the capillary for reinforcement after alignment, and this adhesive wraps around the reflecting surface 17a to cause a problem of fluctuation in reflection performance. In contrast, the trap function can be prevented, and the wraparound to the reflecting surface 17a can be prevented.
[0017]
In FIG. 3, the output end of the substrate 1 and the end face of the output end of the reinforcing member 12 bonded thereto are inclined with respect to a plane perpendicular to the longitudinal central axis of the optical waveguide output 7, for example, It is formed with an inclination angle of 5 degrees. This is to eliminate the influence of the reflection of the radiation mode light on the substrate 1 at the reinforcing member 12 attached to the substrate 1 and the end surface 10 of the substrate 1.
Correspondingly, the direction of the longitudinal central axis 14a of the capillary 13 also extends in a direction inclined with respect to the longitudinal direction of the optical waveguide output unit 7, and accordingly, the output end face 10 of the optical waveguide output unit 7; The connection end faces (not shown) of the optical fibers are connected to each other with an inclination. For example, the end surface of the reinforcing member 12 and the plane perpendicular to the longitudinal center axis 14a of the hollow portion 14 of the capillary 13 form an inclination angle of 7 degrees.
[0018]
As a configuration for causing only one of the radiation mode lights 8 and 9 to enter the photoelectric conversion element, there is the following method in addition to the method of excising a part of the capillary described above.
(1) As shown in FIG. 4, a part of the reflecting surface 50 of the capillary 13 is made non-reflecting.
(2) As shown in FIG. 5, before the radiation mode light reflected from the capillary 13 reaches the photoelectric conversion element, a light shielding means 51 for shielding a part thereof is provided.
(3) As shown in FIG. 6, a light-blocking recess or light-blocking plate 52 is provided inside the capillary 13 to block part of the radiation mode light before reaching the reflecting surface.
[0019]
[Problems to be solved by the invention]
In addition to the radiation mode light described above, various light leaks from the substrate of the optical waveguide type optical modulator, and when the substrate and the capillary are joined, the inside of the capillary is not limited to the radiation mode light. Will also be incident.
For this reason, the light directed to the photodetector from the reflecting surface formed on the capillary also contains a lot of unnecessary light other than the radiation mode light (see FIG. 7), and the monitor signal output from the photodetector is also backed up. The waveform contains a lot of ground noise (see FIG. 8).
Further, as shown in FIGS. 3 and 6, when part of the capillary is excised, the radiation mode light to be cut is irregularly reflected on the excision surface when the smoothness of the excision surface is low, and a part of the light detector There will be a problem of going to.
[0020]
The present invention solves the above-described problems and provides an optical waveguide type optical modulator with an output light monitor for more accurately detecting radiation mode light emitted from an optical waveguide as output light for monitoring. It is.
[0021]
[Means for Solving the Problems]
As a means for solving the above-mentioned problem, the invention according to claim 1 is directed to a dielectric substrate, two or more branch optical waveguide portions formed on the substrate, and extending from a joint point of the branch optical waveguide portions. An optical waveguide element having an optical waveguide having an optical waveguide output section, an optical fiber connected to an output end of the optical waveguide output section, an output end of the optical waveguide output section, and an end face of the optical fiber; A part of the radiation mode light radiated from a joint point of the optical fiber reinforcing member that reinforces the connection part of the optical fiber and the branched optical waveguide part and propagated through both sides of the optical waveguide output part. And an optical waveguide type optical modulator with an output light monitor having a photodetector for receiving light through the optical fiber reinforcing member, wherein the optical fiber reinforcing member has a hollow portion that accommodates a connection end portion of the optical fiber. And having the radiation mode light A capillary for sowing, the end face of the dielectric substrate side of the capillary, wherein the light shielding means for passing only a portion of the radiation mode light is provided.
[0022]
According to a second aspect of the present invention, in the optical waveguide type optical modulator with an output light monitor according to the first aspect, the light shielding means is passed through the end surface of the capillary opposite to the dielectric substrate side. Reflecting means for reflecting a part of the radiation mode light toward the photodetector is provided.
[0023]
Furthermore, the invention according to claim 3 is the optical waveguide type optical modulator with an output light monitor according to claim 2, wherein the reflecting means includes the radiation within the end surface opposite to the dielectric substrate side of the capillary. It is characterized in that it is provided only in a portion where a part of mode light is incident.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
An example of an optical waveguide type optical modulator with an output light monitor of the present invention is shown in FIG.
In FIG. 9, a substrate 1 made of a ferroelectric material such as LiNbO ₃ is fixed in a case (housing) 30, and an optical waveguide 1a is formed on the surface portion thereof. This optical waveguide 1a is an optical waveguide input section. 32, branch optical waveguide sections 2 and 3 branched therefrom, output sections 4 and 5 of the branch sections, joint point 6 and optical waveguide output section 7, and electrodes 33 and 34 on the branch sections 2 and 3, respectively. Has been placed. An input end reinforcing member 12a is arranged at the input end of the substrate 1, and an input side capillary 31 is joined to the input end face (both are separated from each other in FIG. 9). The input-side optical fiber 15 a is introduced through a section (not shown), and the tip end face thereof is connected to the input end face of the optical waveguide input section 32.
[0025]
The output end capillary 13 and the output side optical fiber 15 are connected to the output end of the optical waveguide 1a in the same manner as in FIG.
Light enters the optical waveguide input section 32 from the input side optical fiber 15a reinforced by the reinforcing member 12a and is distributed to the branch sections 2 and 3. When the applied electric signal 35 is applied to the electrodes 33 and 34 via, for example, the connector 36 disposed on the side surface of the case 30, the optical phase of the light wave propagating through the branched optical waveguide portions 2 and 3 is changed to the applied electric signal 35. These light waves are combined at the unifying point 6 and interfere with each other to generate signal light. The signal light after the interference is output to the outside of the case 30 through the optical fiber 15 reinforced by the capillary 13.
[0026]
Of the two radiation mode lights 8 and 9 radiated into the substrate 1 at the union point 6, the radiation mode light 8 passes through the inside 18 of the capillary 13 and is reflected on the upper half of the tip surface of the capillary 13. While being reflected on the surface 17a and being collected on the cylindrical peripheral surface of the capillary 13, the light is emitted in a direction substantially perpendicular to the output portion 7 of the optical waveguide 1a (a direction substantially perpendicular to the side surface of the case 30). The radiation mode light 23 is arranged substantially perpendicular to the direction, and is arranged so that the reflected light from the light receiving surface can be received at an angle that does not return to the reflecting surface 17a (fixed to the side surface of the case 30). The light is received by the light receiving surface of the photoelectric conversion element (PD) 20. The received signal of the radiation mode light is converted into an electric signal in the photoelectric conversion element 20, and this electric signal 38 is output to the outside of the case 30 through the connector 37 as an optical output monitor signal.
[0027]
The radiation mode light 9 emitted from the union point 6 is blocked from entering the inside of the capillary 13 by the light shielding means 60 provided on the end face of the capillary 13 on the substrate 1 side.
As shown in FIG. 10, the light shielding means 60 has a shape that allows only a part of the radiation mode light required in the radiation mode light to pass and shields other light as much as possible. Is provided on the end face of the capillary 13. As a method for forming the light shielding member, for example, a part of the end face of the capillary 13 (a place where the radiation mode light is allowed to pass) is covered with a mask member, a material having a light shielding characteristic such as Ti is deposited, and the mask member is removed later. Can be formed.
[0028]
As described above, since unnecessary light incident on the capillary 13 is limited, the monitor signal output of the photodetector is generated as background noise (caused by unnecessary light as shown in FIG. 11). (Bottom level) decreases.
In addition, one of the configurations shown in FIGS. 3 to 6, which is a configuration for extracting only a part of the radiation mode light as in the previous application (Japanese Patent Application No. 2000-101316), is used together. Accordingly, it is possible to significantly reduce unnecessary light (including unnecessary radiation mode light) incident on the photodetector.
[0029]
In FIG. 9, in order to reduce the reflection of the radiation mode light on the end surface of the substrate, the substrate end surface is changed from the plane perpendicular to the direction of the optical waveguide output portion 7 on the substrate surface within the substrate surface (horizontal The case where the substrate is inclined by about 5 degrees has been described. However, when the end surface of the substrate is inclined with respect to the substrate surface, the capillary is formed as shown in FIG. 12 (side view of the light modulator). Is effective in facilitating the processing.
[0030]
【The invention's effect】
As described above, according to the first aspect of the present invention, the optical fiber reinforcing member used for connecting the optical fiber is a capillary that propagates the radiation mode light, so that the shape and structure of the conventional optical modulator are obtained. In addition, radiation mode light can be detected without changing the mounting method of the optical waveguide element, and unnecessary light incident on the capillary is shielded, thus detecting stable light output with little signal noise. Is possible.
[0031]
Further, according to the invention of claim 2, radiation mode light passing through the capillary can be emitted in a necessary direction as appropriate depending on the direction of the reflecting surface, so that the arrangement of the photodetectors and the like is optimized. It becomes possible to do.
[0032]
According to the invention of claim 3, since the light reflecting means directed to the photodetector is formed at a limited position, unnecessary light incident on the photodetector is further eliminated and the signal noise is less. Stable light output can be detected.
[0033]
[Brief description of the drawings]
FIG. 1 is an explanatory plan view showing a main part of a conventional optical waveguide type optical modulator with an output light monitor.
2 is an explanatory diagram showing an incident surface area on a light receiving surface of a photoelectric conversion element of reflected radiation mode light in the optical modulator of FIG. 1; FIG.
FIG. 3 is an explanatory plan view showing a configuration of a main part of the optical modulator described in the previous application.
FIG. 4 is a diagram showing another configuration for cutting a part of radiation mode light (part 1);
FIG. 5 is a diagram showing another configuration for cutting off part of radiation mode light (part 2);
FIG. 6 is a diagram showing another configuration for cutting off part of the radiation mode light (part 3);
FIG. 7 is a schematic view showing a light path in a conventional capillary.
FIG. 8 is a diagram showing an example of monitor signal output in a photodetector when a conventional capillary is used.
FIG. 9 is an explanatory plan view showing an example of the configuration of an optical modulator to which the present invention is applied.
FIG. 10 is a schematic view showing the path of light in the capillary of the present invention.
FIG. 11 is a diagram showing an example of monitor signal output in a photodetector when using the capillary of the present invention.
FIG. 12 is an explanatory side view showing a main part of another optical modulator to which the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Dielectric board | substrate 1a Optical waveguide 2, 3 Branch optical waveguide part 4, 5 Output part 6 of a branch part Joint point 7 Optical waveguide output part 8, 9 Radiation mode light 10 Output side end surface 12 Reinforcement member 12a Input side reinforcement member 13 Capillary 14 hollow part 14a hollow part central axis 15 output optical fiber 15a input optical fiber 16 connection end face 17 of the capillary 17 reflecting face 17a reflecting face upper half part 17b reflecting face lower half part 18 inside capillary 20 photoelectric conversion elements 23 and 24 reflected radiation Mode light 25 Incident surface area 26 of radiation mode light from the upper half of the reflective surface Incident surface area 27 of radiation mode light from the lower half of the reflective surface Overlapping portion 28 of the incident surface areas 25 and 26 Removal portion 29 Below the capillary Half-end face 29a Direction of radiation mode light reflected on end face 29 Case 31 Input side capillary 32 Input parts 33, 34 Electrode 3 5 Applied electrical signals 36 and 37 Connector 38 Electrical signal 39 Substrate support 50 Non-reflective surface 51 Light shielding means 52 Light shielding recess or light shielding plate 60 Light shielding member F Depth from capillary peripheral surface W Depth from capillary tip surface

Claims (3)

An optical waveguide element comprising a dielectric substrate, and an optical waveguide formed on the substrate and having two or more branch optical waveguide portions and an optical waveguide output portion extending from a united point of the branch optical waveguide portions;
An optical fiber connected to the output end of the optical waveguide output section;
An optical fiber reinforcing member that reinforces a connection portion between the output end of the optical waveguide output portion and the end face of the optical fiber;
Light that receives a part of the radiation mode light that is radiated from the union point of the branched optical waveguide part and propagates through both sides of the optical waveguide output part via the dielectric substrate and the optical fiber reinforcing member A detector;
In an optical waveguide type optical modulator with an output light monitor,
The optical fiber reinforcing member has a hollow portion that accommodates a connection end portion of the optical fiber, and is a capillary that propagates the radiation mode light;
An optical waveguide type optical modulator with an output light monitor, characterized in that a light shielding means for allowing only a part of the radiation mode light to pass is provided on an end face of the capillary on the dielectric substrate side. In the optical waveguide type optical modulator with an output light monitor according to claim 1,
Reflecting means for reflecting a part of the radiation mode light that has passed through the light shielding means toward the photodetector is provided on the end surface of the capillary opposite to the dielectric substrate side. An optical waveguide type optical modulator with an output light monitor. The optical waveguide type optical modulator with an output light monitor according to claim 2,
The reflection means is provided only on a portion of the end face opposite to the dielectric substrate side of the capillary where the part of the radiation mode light is incident. Modulator.

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