JP5161160B2 - Optical switch module - Google Patents

Description

  The present invention relates to an optical switch module for configuring an optical switching element, a wavelength selective switch, and the like for switching a light beam path in the field of optical communication.

  In the field of optical networks that serve as the foundation of Internet communication networks, optical MEMS (Micro Electro Mechanical System) technology is in the spotlight as a technology for realizing multi-channel, wavelength division multiplexing (WDM), and cost reduction. . As an example of using the optical MEMS technology, there is an optical switch disclosed in Patent Document 1, for example. The most characteristic component of the MEMS type optical switch is a micromirror array in which micromirror elements composed of a plurality of movable reflectors are arranged.

  The optical switch enables path switching without converting light into an electrical signal. By using this optical switch, it is possible to switch the path of the multiplexed light without demultiplexing it for each wavelength. Such an optical switch is used, for example, to distribute a signal to another route when a failure occurs in the route being used and to maintain a state where communication is possible.

In recent years, wavelength selective switches that individually demultiplex the multiplexed light for each wavelength and then individually select the path of each wavelength of the demultiplexed light have been researched and developed. A mirror element is used (see Patent Document 2).
In manufacturing an optical switch or the like using the micromirror element, it is necessary to evaluate the characteristics of the micromirror element. Among the basic characteristics of the micromirror element, characteristics that are particularly important for performing this characteristic evaluation include a mirror rotation angle characteristic (V-θ characteristic) with respect to the drive voltage and a response characteristic of the micromirror element. . This response characteristic is evaluated by applying a pulsed drive voltage to the micromirror element and obtaining the resonance frequency unique to the mirror.

  In order to evaluate the basic characteristics of the micromirror element, as shown in FIG. 9, light is actually reflected by the micromirror element. That is, the beam 3 is incident on the mirror 1 (MEMS mirror) from the laser light source 2 (measurement light source), and the reflected light beam 4 is received by the optical position sensor 5 (hereinafter simply referred to as PSD (Position Sensitive Detector)). The PSD 5 is a sensor that can determine the position of the light spot when one spot hits the light-receiving surface, and has high-speed response and high resolution. Therefore, the PSD 5 is a basic characteristic of the micromirror element, V−θ. It is suitable for evaluation of characteristics and response characteristics. However, the PSD 5 cannot measure the exact spot position when two spots hit the light receiving surface.

In particular, as a detection element of PSD5, a two-dimensional plane type is used, and by converting the position of the reflected light spot into an angle, as shown in FIG. 10, the rotation angle (θx, θy) of the biaxial rotating mirror is changed. It can be measured. FIG. 10 shows a state in which the light receiving surface 5a of the PSD 5 is irradiated with the reflected light beam.
In general, a commercially available PSD has a detectable light receiving wavelength of about 400 to 1100 nm. For this reason, this PSD cannot be used when the wavelength of incident light is in the 1300 nm band or 1550 nm band, which is the communication wavelength band.

  Further, in order to stably operate the micromirror element (MEMS mirror), it is effective to mount it on a housing such as a ceramic package that supports hermetic sealing. In this case, it is necessary to provide the casing with a transmission window made of a transparent material in order to input and output optical signals. For the purpose of reducing noise light due to unnecessary reflection and preventing the occurrence of signal light intensity loss, both sides of this transmission window are generally used for antireflection to transmit only light in the signal wavelength band. Coating is applied.

  The transmission window is supported by a frame-shaped lid, and is airtightly attached to the casing through the lid. The lid is fixed to the casing by joining the lid to the casing on which the micromirror element is mounted by laser welding, seam welding, or the like. By joining the lid to the housing in this manner, an optical switch module having a hermetically sealed micromirror element is formed. Since the micromirror element is hermetically sealed in the housing in this way, characteristic fluctuations caused by the influence of moisture in the atmosphere, such as fluctuations in the rotation angle, can be suppressed, and stable operation becomes possible. .

JP 2003-057575 A JP 2007-240728 A

  In evaluating the characteristics of the micromirror element, it is desirable to mount the micromirror element in a housing such as a package and seal the micromirror element (the state of the optical switch module). This is because fluctuations in the rotation angle of the mirror can be suppressed as described above. The transmission window of the casing transmits only light in the communication wavelength band. On the other hand, the optical position sensor (PSD) used for evaluating the characteristics can only transmit light in the non-communication wavelength band. It cannot be detected.

For example, when the rotation angle of a mirror is measured using the optical position sensor while the micromirror element is sealed in a casing, unnecessary reflection occurs at the antireflection coating formed on the surface of the transmission window. Therefore, accurate measurement cannot be performed.
For this reason, the characteristic evaluation of the micromirror element has to be performed before airtight sealing (in the state where there is no antireflection coating), and there is a problem that it cannot be performed in a stable state.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide an optical switch module capable of performing accurate characteristic evaluation after hermetically sealing a micromirror element.

In order to achieve this object, an optical switch module according to the present invention is an optical switch module that controls a reflection direction of incident light by a micromirror element having a movable reflector, and the micromirror element is hermetically sealed inside. The package includes a transmission window that transmits incident light and reflected light, and the transmission window includes at least two communication wavelength bands and a visible light wavelength band that can be detected by an optical position sensor . An antireflection treatment for transmitting light in the wavelength band is performed , the wavelength of light in the communication wavelength band is 1400 nm to 1630 nm, and the wavelength of light in the visible light wavelength band is 630 nm to 700 nm .

In the present invention, since light in a non-communication wavelength band can be transmitted through the transmission window in addition to light in a communication wavelength band, the optical position sensor (PSD) is in a state where the micromirror element is sealed in a package. ) Can be used to evaluate the characteristics of the micromirror element.
Therefore, according to the present invention, an optical switch module capable of stably and accurately evaluating the characteristics of the micromirror element can be provided.

1 is a perspective view of an optical switch module according to the present invention. It is a disassembled perspective view which shows the state before joining the transmission window part of the optical switch module which concerns on this invention to a package main body. It is sectional drawing of the optical switch module which concerns on this invention. It is sectional drawing which shows the other Example of the optical switch module which concerns on this invention. It is sectional drawing which shows the other Example of the optical switch module which concerns on this invention. It is a graph which shows the relationship between the wavelength of an antireflection coating, and the transmittance | permeability. It is a graph which shows the relationship between the wavelength and transmittance | permeability of another antireflection coating. It is a side view which shows the other Example of an optical switch module. It is a block diagram of the measurement system for evaluating the basic characteristic of a micromirror element. It is a figure which shows typically the state by which the reflected light beam is irradiated to the light-receiving surface of an optical position sensor.

(First embodiment)
Hereinafter, an embodiment of an optical switch module according to the present invention will be described in detail with reference to FIGS.
The optical switch module 11 shown in this embodiment is formed by hermetically sealing a MEMS mirror array chip 13 in a package 12 , as shown in FIGS.

The package 12 includes a PGA (Pin Grid Array) type package main body 14 formed in a substantially box shape with ceramics, and a lid 15 that closes an opening portion of the package main body 14. As a material for forming the package body 14, various materials such as alumina ceramic and glass ceramic can be used.

  A large number of connection pins 16 (see FIG. 3) are erected on the outer bottom surface of the package main body 14, and a seal ring 17 is attached to an opening edge of the package main body 14 in order to join a lid 15 described later. Is provided. The seal ring 17 extends without interruption along the opening edge of the package body 14 and is formed in a square shape so as to surround the opening. The thickness of the seal ring 17 according to this embodiment is substantially constant over the entire area.

The MEMS mirror array chip 13 is formed by arranging a plurality of micromirror elements (not shown) on the same plane and supporting them on one support member. That is, the micromirror elements are arranged in a plurality of arrays. The MEMS mirror array chip 13 is mounted on the inner bottom portion of the package body 14 as shown in FIG. The electrodes (not shown) of the MEMS mirror array chip 13 are connected to the electrodes (not shown) of the package body 14 using bonding wires denoted by reference numeral 18 in FIG.
For the electrical connection between the mirror array chip 13 and the package body 14, in addition to the bonding wire method described above, an electrode pad (not shown) is formed on the bottom of the mirror array chip 13 as shown in FIG. It is also possible to adopt a configuration in which direct connection is made by solder balls 25 or the like.

As shown in FIGS. 2 and 3, the lid 15 includes a lid frame 21 formed in a frame shape that covers the opening edge of the package body 14, and a transmission window 22 that closes the opening of the lid frame 21. It is constituted by. The transmission window 22 is for transmitting incident light and reflected light. As will be described in detail later, the transmission window 22 is formed in a plate shape with a transparent material and is adhered to the lid frame 21 so as to be airtight.
The position where the transmission window 22 is attached to the lid frame 21 may be inside the module as shown in FIG. 3 or outside the module as shown in FIG.

The lid frame 21 is joined so as to be airtight by seam welding in a state of being superimposed on the seal ring 17. As shown in FIG. 1, the seam welding is performed so that the entire area around the lid frame 21 becomes a seam welded portion 23. In FIG. 1, the seam welded portion 23 is indicated by hatching.
The lid frame 21 is welded in a state where the inside of the package 12 is replaced with an inert gas such as dry nitrogen or argon. That is, the MEMS mirror array chip 13 is hermetically sealed in the package 12 filled with the inert gas.
Here, an example in which seam welding is used for joining the lid frame 21 and the seal ring 17 has been described. However, the joining method is not limited to seam welding. For example, a method such as laser welding may be used. Good. When laser welding is used, the shape of the seal ring 17 is not limited to a rectangle, but may be a circle or an ellipse.
In addition, as a method for joining the lid frame 21 and the seal ring 17, it is also possible to use an adhesive such as a thermosetting type or an ultraviolet curable type.

The transmission window 22 is formed to be transparent by a plate-like sapphire having a thickness of about 0.5 mm. The plate-like sapphire is formed so that the main surface (front surface and back surface) of the transmission window 22 is a C surface.
An antireflection coating 24 (see FIG. 3) is applied to the front and back surfaces of the transmission window 22 as an antireflection treatment in the present invention. The antireflection coating 24 is configured to transmit light in at least two wavelength band regions including a communication wavelength band and a visible light wavelength band. Such an antireflection coating 24 can be formed by laminating a predetermined number of layers of dielectric films on the front and back surfaces of the transmission window 22.

In this embodiment, an antireflection coating is formed on the transmission window 22 by forming a multilayer film using ion assisted vapor deposition using tantalum pentoxide (Ta ₂ 0 ₅ ) and silicon dioxide (SiO ₂ ) as materials. 24 is given. In addition, when performing the antireflection process to the transmissive window 22, it is not limited to the coating by the vapor deposition method mentioned above, and can also be formed by using a sputtering method or the like.

The characteristics of the antireflection coating 24 according to this embodiment are shown in FIG. FIG. 6 is a graph showing an example of transmittance characteristics (transmission spectrum) with respect to the wavelength of the antireflection coating 24 according to this embodiment. As can be seen from FIG. 6, by applying the antireflection coating 24 according to this embodiment to the transmission window 22, the wavelength band (630-700 nm) of the visible light laser light source used in the measurement system and the communication wavelength band (1400-1630 nm). The light in the two wavelength bands is transmitted through the transmission window 22. The reflectance in the communication wavelength band is 0.1% or less, and the reflectance in the measurement wavelength band is 1% or less. Even when the transmission window 22 is tilted by 15 degrees, substantially the same characteristics as in the case of normal incidence are obtained.
In addition, as shown in FIG. 7, the antireflection coating 21 has a high transmittance in the entire region including the two wavelength regions, instead of a property in which the transmissive regions are separated in the two wavelength regions. May be.

In the optical switch module 11 configured as described above, light in the non-communication wavelength band can be transmitted through the transmission window 22 in addition to the light in the communication wavelength band. Therefore, the characteristics of the MEMS mirror array chip 13 can be evaluated using the optical position sensor (PSD) in a state where the MEMS mirror array chip 13 is sealed in the package 12.
Therefore, according to this embodiment, it is possible to provide an optical switch module that can stably and accurately evaluate the characteristics of the MEMS mirror array chip 13 (micromirror element).

(Second embodiment)
The transmission window can be tilted with respect to the MEMS mirror array chip as shown in FIG. FIG. 8 is a side view showing another embodiment, in which FIG. 8A shows an example in which the welding surface of the seal ring is inclined, and FIG. 8B shows that the mounting seat for the transmission window of the lid frame is inclined. An example is shown. 8, the same or equivalent members as those described with reference to FIGS. 1 to 5 are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

The seal ring 17 shown in FIG. 8A has a welding surface 17a for welding the lid frame 21 inclined at a predetermined angle with respect to the MEMS mirror array chip 13 (the mirror of the micromirror element in a stationary state). Is formed.
The lid frame 21 shown in FIG. 8B has a mounting seat 21a for mounting the transmission window 22 so as to be inclined at a predetermined angle with respect to the MEMS mirror array chip 13 (the mirror of the micromirror element in a stationary state). Is formed.

  The inclination angle of the welding surface 17a shown in FIG. 8A and the inclination angle of the mounting seat 21a shown in FIG. 8B are twice the rotation angle range of the micromirror element provided in the MEMS mirror array chip 13. It is set above. For example, when the rotation angle of the micromirror element is ± 2 deg, the tilt angle is set to 5 deg. For this reason, in this embodiment, by welding the lid frame 21 having the transmission window 22 to the seal ring 17, the transmission window 22 is inclined at an angle larger than the maximum inclination angle of the micromirror element. It is no longer parallel to the mirror of the micromirror element.

As the transmission window 22 is inclined with respect to the micromirror element in this way, the effect of the antireflection coating 24 can be further enhanced, and the reflected light does not return to the incident direction, so that the reflected return light is −40 dB or less. It was possible to reduce it. For this reason, the optical switch module 11 according to this embodiment can reduce the reflected return light and suppress the generation of noise and the influence on the light source, so that the characteristic evaluation can be performed more accurately.
In particular, when the rotation direction of the micromirror element is uniaxial, the transmission window 22 is inclined in a direction orthogonal to the rotation direction, and when the rotation direction of the micromirror element is two axes, the rotation angle is further increased. By tilting the transmission window 22 in a direction perpendicular to the rotation direction with a large angle, the effect of the present invention can be further enhanced. Further, in the case of two axes in which the rotation directions of the micromirror element are orthogonal to each other and the rotation angles of the respective axes are equal, the transmission window 22 may be inclined in any direction.

In each of the above-described embodiments, an example in which the PGA type package 2 is used has been described. However, the form of taking out wiring from the package is not limited to PGA, and BGA (Ball Grid Array), LGA (Land) Various forms such as Grid Array) and QFP (Quad Flat Package) can be adopted.
In the present invention, the wavelength band of light to be transmitted can be arbitrarily designed by the material and configuration of the film. Furthermore, the present invention should be used without depending on the shape, size, wiring method, etc. of the micromirror element to be mounted, and without depending on the package material, shape, size, type, window material, shape, etc. Can do.

DESCRIPTION OF SYMBOLS 5 ... Optical position sensor, 11 ... Optical switch module, 12 ... Package, 13 ... MEMS mirror array chip, 22 ... Transmission window, 23 ... Antireflection coating

Claims (8)

An optical switch module that controls the reflection direction of incident light by a micromirror element having a movable reflector,
A package that houses the micromirror element and hermetically seals;
The package includes a transmission window that transmits incident light and reflected light.
The transmission window is subjected to an antireflection treatment for transmitting light in at least two wavelength bands including a communication wavelength band and a visible light wavelength band detectable by an optical position sensor ,
The wavelength of light in the communication wavelength band is 1400 nm to 1630 nm,
The optical switch module according to claim 1, wherein a wavelength of light in the visible light wavelength band is 630 nm to 700 nm . 2. The optical switch module according to claim 1, wherein the antireflection treatment is a treatment of forming a film made of tantalum pentoxide and silicon dioxide on the transmission window . 3. The optical switch module according to claim 1 , wherein the micromirror elements are arranged in a plurality of arrays. 3. The optical switch module according to claim 1 , wherein the transmission window is inclined at an angle larger than a maximum inclination angle of the micromirror element. 5. The optical switch module according to claim 4 , wherein an inclination angle of the transmission window is at least twice as large as a maximum inclination angle of the micromirror element. 6. The optical switch module according to claim 5 , wherein the micromirror elements are arranged in a plurality of arrays. The optical switch module according to claim 5 or 6 , wherein the rotation direction of the micromirror element is a uniaxial direction.
An optical switch module characterized in that the transmission window is inclined in a direction perpendicular to the rotation direction. The optical switch module according to claim 5 or 6 , wherein the rotation directions of the micromirror element are two directions orthogonal to each other,
An optical switch module characterized in that the transmission window is inclined in a direction orthogonal to a rotation direction having a larger rotation angle among the rotation directions.

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