JP3932276B2 - Multi-channel optical modulator with output optical monitor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multi-channel optical modulator having a plurality of optical modulator units on the same substrate, and in particular, monitors output light of each optical modulator unit and feedback controls the operating point of the optical modulator unit. The present invention relates to a multi-channel optical modulator having an output optical monitor.
[0002]
[Prior art]
In response to the increasing demand for high-speed, large-capacity information communication in recent years, optical communication has attracted attention. In particular, as an optical modulator corresponding to high-speed modulation, a Mach-Zehnder (MZ) type external optical modulator (hereinafter referred to as a CW (Continuous Wave) laser and a material having an electrooptic effect such as lithium niobate (LN)) And LN optical modulators) have been proposed and put into practical use.
The LN optical modulator is used as an optical modulator suitable for high-density wavelength multiplexing (DWDM system) and high-speed communication because it has less wavelength dependency.
[0003]
However, in the LN optical modulator, the operating point of the fluctuation curve indicating the change in the optical output with respect to the applied voltage shifts due to the temperature change of the environment or the accumulation of charges on the substrate surface due to continuous driving, etc. Phenomena such as fluctuations in light output occur due to fluctuations in the light transmittance of the inner optical waveguide.
For this reason, in order to stabilize the operating point of the optical modulator and control the output light quantity to be constant, the output light from the optical modulator is monitored and the drive voltage of the optical modulator is controlled in accordance with the detected output light quantity. To be done.
As a method for monitoring the output light from the optical modulator, a method is proposed in which a part of the output light is taken out and detected by a light receiving element, as disclosed in Japanese Patent Application Laid-Open No. H5-224044. In this case, since a part of the output light from the optical modulator is used, the amount of output light decreases, which causes a decrease in transmission distance and a deterioration in extinction ratio.
On the other hand, in an optical modulator having a multiplexing unit such as a Mach-Zehnder type optical waveguide, radiation mode light is radiated from the multiplexing unit. The radiation mode light is light that is emitted separately from the output light from the modulator and indicates a light amount proportional to the output light amount. Therefore, the applicant of the present application is disclosed in Japanese Patent Application Laid-Open No. 2001-215455, Japanese Patent Laid-Open No. 2001-281507 proposes a method of actively using the radiation mode light for output light monitoring.
[0004]
On the other hand, in order to support high-speed and large-capacity information communication, a plurality of optical modulators are used side by side or in combination. In particular, the optical modulators are expensive, and each optical modulator is housed in a case. When a plurality of optical modulators are installed, there arises a problem that an occupied space becomes large. For this reason, there is a need for a multi-channel type optical modulator in which a plurality of optical modulators are arranged on the same substrate.
However, in such a multi-channel type optical modulator, when the output light monitoring using the above-described radiation mode light is performed, each optical modulator section is disposed close to the same substrate, so that each optical modulation is performed. It has been difficult to properly monitor the output light, for example, the radiation mode light radiated from the vessel part interferes with each other or a plurality of radiation mode lights enter a specific light receiving element.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems and to provide a multi-channel with an output light monitor capable of properly monitoring radiation mode light from each light modulator section even when having a plurality of light modulator sections on the same substrate. Type optical modulator.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problem, in the invention according to claim 1, the substrate is formed of a material having an electro-optic effect, a plurality of light modulator portions formed on the substrate, and formed on an end surface of the substrate. and input and output optical unit provided corresponding to each optical modulator unit with a plurality of optical fibers to be connected to the input and output light portion, and a reinforcing member for reinforcing the connection between the substrate and the optical fiber, the In the multi-channel type optical modulator with an output light monitor having a light receiving element that receives radiation mode light emitted from a part of the optical waveguide constituting the optical modulator section, the reinforcing member is provided for each end face of the substrate. A single through-hole that penetrates the plurality of optical fibers, a propagation portion that propagates radiation mode light from the plurality of optical modulator portions, and a single light that reflects the radiation mode light to the light receiving element. A light having a reflecting surface and emitting the radiation mode light In a period from a portion of the waveguide to the reflecting surface, and providing a radiation mode light removing means for bring the only radiation mode light in the specific direction on the reflecting surface.
[0007]
According to the first aspect of the invention, when monitoring the output light from the optical modulator, only the radiation mode light in a specific direction is left out of the radiation mode light radiated from each light modulator, and other unnecessary radiation modes In order to remove light, attention is paid only by arranging the light receiving element on the optical extension line in the specific direction (in the case of passing through the reflecting surface as in the present invention, on the traveling direction of the light reflected by the reflecting surface). It becomes possible to easily monitor the output light of the optical modulator section.
[0008]
According to a second aspect of the present invention, in the multi-channel optical modulator with an output light monitor according to the first aspect, the specific direction is the same direction in adjacent optical modulator units or from each optical modulator unit. It is set so that it may become the direction which radiation mode light diverges.
[0009]
According to the second aspect of the present invention, radiation mode light in the same direction is made incident on the light receiving element in the adjacent optical modulator sections, so that interference of the radiation mode light can be prevented between the adjacent optical modulator sections. In addition, when the number of optical modulator units is small, or when the traveling direction of the light waves of adjacent optical modulator units is reversed as described later, the optical modulator units travel in directions away from each other. By using the radiation mode light, not only can the interference of the radiation mode light be prevented, but also a sufficient space between the light receiving elements can be secured, and the target radiation mode light can be monitored appropriately. It becomes possible.
[0010]
According to a third aspect of the present invention, in the multi-channel optical modulator with an output light monitor according to the first or second aspect, the radiation mode light removing means is a groove formed in the substrate. In the invention according to claim 4, the radiation mode light removing means is a light blocking means provided between the substrate and the reinforcing member.
Further, the invention according to claim 5 is characterized in that the radiation mode light removing means is a groove formed in the reinforcing member.
[0011]
According to the invention according to any one of claims 3 to 5, it is possible to provide radiation mode light removing means suitable for each part between a part of the optical waveguide that emits radiation mode light and the reflection surface. Therefore, unnecessary radiation mode light can be removed more effectively.
For example, in a substrate or a reinforcing member, unnecessary grooves can be easily removed by simply forming grooves in the path of the radiation mode light. These grooves can be used for chemical etching or mechanical cutting of the substrate and the like. It is possible to form it easily. Further, unnecessary radiation mode light can be effectively removed between the substrate and the reinforcing member simply by applying a light blocking means such as carbon black.
[0012]
According to a sixth aspect of the present invention, in the multi-channel optical modulator with an output light monitor according to any one of the first to fifth aspects, the plurality of optical modulator units are light waves of adjacent optical modulator units. It is characterized by arrange | positioning so that the advancing direction of these may become a mutually reverse direction.
[0013]
According to the invention of claim 6, since the traveling directions of the light waves of the adjacent optical modulator portions are opposite to each other, the number of radiation mode lights to be detected on the same end face side of the substrate is reduced by half, and the adjacent optical modulation is performed. Since only one radiation mode light of the vessel is detected, it is possible to prevent interference between the respective radiation mode lights and incidence on a plurality of radiation mode lights to the light receiving element. In addition, the light receiving elements can be arranged with a space.
Furthermore, according to the present invention, it is possible to prevent crosstalk of modulation signals between adjacent optical modulator sections, and to realize a multi-channel optical modulator that can be stably driven.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail using preferred examples.
FIG. 1 is a diagram for explaining the outline of a multichannel optical modulator according to the present invention. As a substrate constituting the optical modulator, a material having an electro-optic effect, such as lithium niobate (LiNbO ₃ ; hereinafter referred to as LN), lithium tantalate (LiTaO ₃ ), PLZT (lead lanthanum zirconate titanate), In particular, LiNbO ₃ crystal, LiTaO ₃ crystal, or solid solution crystal composed of LiNbO ₃ and LiTaO ₃ is used because it is easy to configure as an optical waveguide device and has high anisotropy. Is preferred. In this example, an example using lithium niobate (LN) will be mainly described.
[0015]
As a method of manufacturing an optical modulator, an optical waveguide is formed by thermally diffusing Ti on an LN substrate, and then an electrode is directly formed on the LN substrate without providing a buffer layer over a part or the whole of the substrate. In order to reduce the propagation loss of light in the optical waveguide, a buffer layer such as a dielectric SiO ₂ is provided on the LN substrate, and further a Ti / Au electrode pattern is formed thereon and a gold plating method is used. There is a method in which a signal electrode and a ground electrode having a height of several tens of μm are formed and the electrodes are indirectly formed.
A multilayer structure in which a film body such as SiN or Si is provided on the buffer layer is also possible.
In general, a multi-channel optical modulator is manufactured by forming a plurality of optical modulators on one LN wafer and finally separating a predetermined number of optical modulators or a predetermined optical modulator combination as one chip. Is done.
[0016]
In the multi-channel optical waveguide of FIG. 1, four MZ optical waveguides 2 are arranged in parallel.
Reference numeral 1 denotes an LN substrate, and a waveguide is formed on the surface of the substrate by Ti internal diffusion or the like as described above. Reference numeral 2 denotes a Mach-Zehnder (MZ) type optical waveguide, which guides light from a CW laser light source (not shown) and is connected to the left end face of the substrate 1 and a fiber having a polarization maintaining function.
The light propagating through the MZ type optical waveguide 2 is equally divided at the Y branch, and enters each of the two branch waveguides. The light propagating through the branch waveguide is subjected to phase modulation by an electric field formed by a signal electrode and a ground electrode arranged in the vicinity (not shown) and interferes with each other at the multiplexing unit 3.
As a result of the interference, the light whose intensity is modulated is output to the outside of the substrate 1 as output light (OUT).
[0017]
Usually, radiation mode light a to h is radiated at the multiplexing portion 3 of the MZ type optical waveguide 2.
In the present invention, when detecting the characteristics (such as fluctuations in the amount of output light) of the optical modulator unit including any one of the MZ type optical waveguides 2, the light is emitted from the multiplexing unit 3 of the corresponding MZ type optical waveguide. Use radiation mode light. For example, in order to measure the characteristic of the optical modulator unit including the uppermost MZ type optical waveguide of FIG. 1, the characteristic of the optical modulator unit is evaluated by measuring either the radiation mode light a or b. It becomes possible to do.
[0018]
However, in the case of a multi-channel type optical modulator as shown in FIG. 1, the radiation mode light b and c, d and e, and f and g interfere with each other when measuring the characteristics of each optical modulator section separately. Alternatively, there is a problem that an appropriate amount of radiation mode light cannot be detected by inputting to the same light receiving element.
For this reason, in the present invention, as shown in FIG. 2, by providing the radiation mode light removing means 6, 7, and 8, unnecessary radiation mode light b ′, d ′, e ′, and g ′ are removed, and light reception is performed. Only the radiation mode lights a, c, f, and h required for the element are incident.
[0019]
Reference numeral 4 in FIG. 2 denotes a capillary as a reinforcing member, which has a reinforcing function when the optical fiber 5 is penetrated inside and the end face of the substrate 1 and the optical fiber 5 are joined. The substrate 1 and the capillary 4 as well as the optical fiber are joined by a light-transmitting adhesive such as an ultraviolet curable adhesive.
FIG. 3 shows an enlarged cross-sectional view of the vicinity of the junction between the substrate 1 and the capillary 4.
It is also possible to provide a substrate side reinforcing member 11 for assisting the bonding of the substrate 1 and the capillary 4 as needed.
[0020]
As a feature of the capillary 4, as shown in FIG. 3, a reflection surface A is formed in order to allow the radiation mode light a to be incident on a light receiving element arranged in a lower direction of the capillary 4.
The radiation mode light removing means shown in FIG. 2 is appropriately arranged so as to remove unnecessary radiation mode light between the multiplexing section 3 that emits radiation mode light and the reflecting surface A. For example, in FIG. 2, a groove is formed on the substrate 1 by chemical etching or mechanical cutting, and the radiation mode light b ′ is effectively removed by the groove. 2 of FIG. 2 removes unnecessary radiation mode light d ′ and e ′ by applying a light shielding material such as carbon black between the substrate 1 and the capillary 4. Further, reference numeral 8 in FIG. 2 forms a groove in the capillary 4 by cutting or the like, and the groove is formed from either the upper surface side or the lower surface side of the capillary 4. On which side the groove is formed is appropriately selected depending on the passage position of the radiation mode light propagating through the capillary.
Note that the groove may be configured to be filled with a light shielding material such as carbon black in order to enhance the radiation mode light removal effect.
[0021]
The reflective surface A shown in FIG. 3 can be provided with a reflective film made of a metal or a dielectric, if necessary, to increase the reflection efficiency of the radiation mode light a. This reflective film can be formed by, for example, sputtering metal aluminum.
Further, the capillary 4 can be divided into upper and lower parts with an optical fiber through hole interposed therebetween as required, and the optical fiber 5 can be sandwiched and bonded with divided capillaries. In addition, it goes without saying that a technique known in the technical field can be applied as necessary.
[0022]
A light receiving element 10 is arranged in the lower direction of the capillary 4 as shown in FIG. In the light receiving element, optical sensors are discretely arranged corresponding to the incident positions of the radiation mode light to be received.
The shape of the light receiving element is not limited to that shown in FIG. 4, but a line-type photosensor may be used to simultaneously receive a plurality of radiation mode lights and output a light detection signal corresponding to the light receiving position. good.
In addition, 12 of FIG. 4 has shown a part of case which accommodates a multichannel type | mold optical modulator.
[0023]
As another embodiment of the present invention, a plurality of optical modulator portions formed on the substrate 1 shown in FIG. 1 are configured such that the traveling directions of light waves in adjacent optical modulator portions are opposite to each other. Is also possible. In this case, the input (IN) and the output (OUT) of the light wave are alternately arranged as shown in FIG.
With this configuration, the number of radiation mode lights to be detected on the same end face side of the substrate is halved (it is two in FIG. 5), and only one radiation mode light of the adjacent optical modulator section is detected. Therefore, it is possible to prevent interference between the respective radiation mode lights and incidence on a plurality of radiation mode lights to the light receiving element. In addition, the light receiving elements can be arranged with a space.
Furthermore, when high frequency signals are individually applied to adjacent optical modulator sections in the same direction, crosstalk between channels is likely to occur. However, as in the configuration of the present invention, the input of light waves and electrical signals is likely to occur. By alternately reversing the output direction between channels, the crosstalk can be mitigated.
[0024]
【The invention's effect】
As described above, according to the present invention, even when a plurality of optical modulator units are provided on the same substrate, a multi-channel type with an output light monitor that can appropriately monitor radiation mode light from each optical modulator unit. An optical modulator can be provided.
[Brief description of the drawings]
FIG. 1 is a plan view of a multi-channel optical modulator.
FIG. 2 is a plan view of a multi-channel optical modulator having a radiation mode light removing unit.
FIG. 3 is a cross-sectional view of the vicinity of the junction between the substrate and the capillary.
FIG. 4 is a diagram showing an arrangement of light receiving elements in a multi-channel optical modulator.
FIG. 5 is a diagram showing a state in which the input / output directions of light waves in a multi-channel optical modulator are alternately reversed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 Mach-Zehnder type optical waveguide 3 Multiplexing part 4 Capillary 5 Optical fiber 6-8 Radiation mode light removal means 10 Light receiving element ah Radiation mode light A Reflecting surface

Claims (6)

A substrate made of a material having an electro-optical effect, a plurality of optical modulator section which is formed on the substrate, input and output light provided corresponding to the optical modulator unit is formed into an end face of the substrate and parts, are emitted from a portion of the optical waveguide constituting a plurality of optical fibers to be connected to the input and output light portion, and a reinforcing member for reinforcing the connection between the substrate and the optical fiber, the optical modulator unit In a multichannel optical modulator with an output light monitor having a light receiving element for receiving radiation mode light,
The reinforcing member is provided for each end surface of the substrate , and includes a through hole that penetrates the plurality of optical fibers, a propagation portion that propagates radiation mode light from the plurality of light modulator portions, and the radiation mode. A single reflecting surface for reflecting light to the light receiving element;
An output light comprising a radiation mode light removing means for causing only the radiation mode light in a specific direction to reach the reflection surface between a part of the optical waveguide that emits the radiation mode light and the reflection surface. Multi-channel optical modulator with monitor.   2. The multi-channel optical modulator with an output light monitor according to claim 1, wherein the specific direction is the same direction in adjacent optical modulator units or a direction in which radiation mode light from each optical modulator unit deviates. A multi-channel optical modulator with an output optical monitor, characterized in that   3. A multichannel optical modulator with an output light monitor according to claim 1, wherein the radiation mode light removing means is a groove formed in the substrate. Modulator.   3. The multi-channel optical modulator with an output light monitor according to claim 1, wherein the radiation mode light removing means is a light blocking means provided between the substrate and the reinforcing member. Multi-channel optical modulator with output optical monitor.   3. A multi-channel type optical modulator with an output light monitor according to claim 1, wherein said radiation mode light removing means is a groove formed in said reinforcing member. Light modulator.   6. The multi-channel type optical modulator with an output light monitor according to claim 1, wherein the plurality of optical modulator units have light waves traveling in adjacent optical modulator units in opposite directions. A multi-channel optical modulator with an output optical monitor, characterized in that it is arranged.

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