JPH0926528A - Optical circuit module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical circuit module stabilizing the optical characteristic of an optical circuit such as an optical switch and an optical circulator even in a high-humidity atmosphere. SOLUTION: A hole part 11a is formed at a specified position on the side surface of a case 11 which is formed by a kovar and whose upper part is opened, and an airtight window 15 made of sapphire is brazed and fixed to close the hole part 11a on the inside of the side surface of the case 11. The optical circuit (optical circulator) 10 is mounted in the case. The case is covered with a cover in a state where the case is filled with dry inactive gas, and all the periphery is welded to melt and integrate the cover and the case 11, whereby the case is perfectly sealed to hold a drying state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit module constructed by housing optical circuits such as optical switches and optical circulators used for optical communication in a case. The present invention relates to improvement of a case sealing structure.

[0002]

2. Description of the Related Art An example of a conventional optical circuit module is shown in FIGS. In this example, an optical circulator is used as an optical circuit to be stored.
As shown in the figure, two polarizing beam splitters (hereinafter referred to as “PBS”) 2 are arranged at a predetermined interval inside a metal case 1 having an upper opening, and a cylindrical shape is provided between the two PBSs 2. The Faraday rotator 4 and the half-wave plate 5 inserted in the permanent magnet 3 are arranged in a predetermined positional relationship. In this PBS 2, the first prism 2a and the second prism 2b each having a predetermined shape have a polarization separation film (not shown).
It is configured to be bonded by an optical adhesive with the film sandwiched therebetween.

A circular hole 1a penetrating the case 1 is provided at a predetermined position on the side surface of the case 1, and an optical fiber 6 with a ferrule is provided on the outer side of the hole 1a so that the axial center of the hole 1a is aligned with the hole. The collimator lens 7 is attached. As a result, an optical signal transmitted through a certain optical fiber 6 enters the optical circuit module through the hole 1a, irradiates the optical circuit in the case 1 and is subjected to predetermined processing. , Is emitted to the optical fiber 6 through another hole 1a.

Further, a flat plate-like lid 8 is attached to the upper opening of the case 1, and the both 1 and 8 are fixed and integrated with an adhesive to seal the inside. Also, in order to maintain the relative positional relationship between the optical fiber 6 and the case 1 in a desired state,
An adhesive is applied and fixed to the connecting surface between the ferrule connected to the tip of the optical fiber 6 and the case 1 at a predetermined angle. This completes the optical circuit module.

[0005]

By the way, the optical circuit module having the above-mentioned structure is used in a place (laboratory, etc.) where the use environment is relatively good (atmosphere with a low humidity and a small amount of dust). Although there was no problem, the following problems occur when it is mounted in the actual fiber transmission line for optical communication as described above.

That is, although the case 1 and the lid 8 are integrated and sealed with an adhesive, the hole 1a formed on the side surface of the case 1 is open, and the hole 1a has a cylindrical shape. Since the ferrule is inserted into the ferrule, the joint surfaces are spherical surfaces, and a gap is likely to be formed, and the inner space of the case 1 and the outer space are in communication with each other through the hole 1a, and sufficient airtightness cannot be ensured. The case 1 and the lid 8 are
Although the flat surfaces are surface-joined, the airtightness is partially reduced due to uneven adhesion of the adhesive 8 or defective adhesion.

Then, when used in a high-humidity environment where the environment of use is bad, the surrounding atmosphere invades the case 1,
Humidity in case 1 rises. Then, the PBS 2 that constitutes the optical component includes the first prism 2a and the second prism 2b.
Since they are formed by adhering each other with an optical adhesive, the optical adhesive absorbs moisture and deteriorates. Along with that, the optical characteristics such as the transmittance and extinction ratio of the PBS are changed, the desired characteristics cannot be obtained, and the optical components such as the optical circulator and the optical switch are deteriorated such as insertion loss and isolation. .

Further, dust or the like floating around may enter through the hole 1a. Then, the dust or the like adheres to the optical component, and the optical signal transmitted by the optical fiber is scattered,
It will be absorbed. Therefore, the optical characteristics of each optical component deteriorate (the loss of optical signals increases).

Further, the fiber transmission line is used not only in the atmosphere but also in a submarine cable, and if an optical component is to be mounted in the middle of the submarine cable, the operating environment is high humidity, low temperature and high temperature. The above problem becomes more prominent because it becomes a pressure and further decreases. Moreover, application of high pressure may cause cracks or the like in a part of the adhesive, which may further reduce airtightness. Therefore, it becomes a bottleneck for installation on the seabed, which is unreliable for a long period of time and maintenance cannot be performed frequently.

Further, seawater may infiltrate from the adhesive to the inside, and in such a case, moisture and salt damage may occur inside the case, which makes it impractical.

As an optical circuit to be mounted in the case,
In addition to the above-mentioned optical circulator, for example, there is an optical switch, and there is a self-holding type magneto-optical type instead of the mechanical type optical path switching conventionally used. That is, an electromagnet having a yoke of a semi-hard magnetic material is used as the magnetic field applying means for the Faraday rotator. Then, by energizing the electromagnet with a pulse current, a magnetic field in a predetermined direction is generated to reverse the Faraday rotation angle. After the reversal, the energization is released, but the self-holding force of the yoke continues to supply the magnetic field in the predetermined direction. As a result, since there is no movable part, it can be used stably for a long period of time, and it can be considered to be applied to a place where maintenance of the above-mentioned submarine cable is difficult to perform. Moreover, since it consumes power only when switching, it is economical, and various fields of use can be envisioned regardless of the submarine cable.

However, since the coercive force of the yoke is about several tens Oe, there is an advantage that the switching speed becomes fast, but on the other hand, there is a possibility that the yoke is erroneously switched under the influence of an external magnetic field of several tens Oe or more.

Further, the problem is not limited to the optical switch having the above-mentioned structure, and even when the magnetic field is applied to the Faraday rotator 4 from the permanent magnet 3 as shown in FIG. If a magnetic field in the direction of canceling 3 is applied from the outside, there is a risk of malfunction.

The present invention has been made in view of the above background, and an object of the present invention is to solve the above-mentioned problems and to be used for an optical component constituting an optical circuit such as an optical switch or an optical circulator. While preventing moisture from being absorbed by the optical adhesive, it prevents dust and other particles floating in the outside air from entering the case and adhering to the optical components.
Deterioration of the optical characteristics of the optical components, and eventually of the optical circuit, can stabilize the optical characteristics of the optical circuit even under high humidity conditions such as the seabed, and is less susceptible to external magnetic fields. An object is to provide an optical circuit module.

[0015]

In order to achieve the above object, in an optical circuit module according to the present invention, a plurality of holes are formed in a side surface of a case having an upper opening, and the plurality of holes are formed on an inner side surface of the case. An airtight window for closing the hole was provided, an optical circuit was installed inside the case, a lid was attached to the upper opening of the case, and the entire circumference was welded to be integrated.
Then, a dry inert gas is filled or evacuated inside the case (claim 1).

Preferably, the material of the case is Kovar, and the airtight window is made of sapphire (claim 2). Further, when mounting an optical fiber for transmitting and receiving an optical signal in the hole, the side surface outside of the case 11 is inserted through a cylindrical holder directly or indirectly mounted on a ferrule mounted at the tip of the optical fiber. It may be fixed at a predetermined position (claim 3).

An optical signal transmitted by an optical fiber or the like passes through the hole and the airtight window having transparency, and is transmitted to an optical circuit installed inside the case, where the optical circuit performs a predetermined process. After that, the light is emitted from a predetermined hole. By the way, according to the present invention, the case and the lid are fixed to each other by welding around the entire periphery thereof, and the airtight window is also installed in the hole formed on the side surface of the case. Does not penetrate inside. Furthermore, since the case is filled with dry inert gas in advance or is in a vacuum, the case is always kept in a dry state.
The optical adhesive used for the polarization beam splitter or the like does not absorb moisture and its refractive index does not change, so that the optical characteristics of the polarization beam splitter do not deteriorate. Therefore, the optical signal is stably transmitted, reflected, polarized wave separated, polarized wave combined and the like by the optical parts, and is sent to a predetermined optical fiber or the like. That is, the functions of the optical circuits such as the optical circulator and the optical switch are stably performed.

According to the second aspect of the present invention, since Kovar and sapphire, which are materials having the same thermal expansion coefficient, are used for the material of the case and the hermetic window, distortion and cracks will not occur in both of them even if the temperature changes. Does not happen. In particular, as described in the examples, when brazing or the like is performed in order to more firmly fix the airtight window, once heated to a very high temperature,
Although it is cooled, the airtight window is not distorted or cracked even with such a large temperature change.

Further, by making the material of the case kovar, the optical parts are surrounded by the ferromagnetic material, and the optical parts (Faraday rotator etc.) susceptible to the magnetic field are shielded from the external magnetic field.

When the optical fiber is attached to the case via the holder separately provided as described in claim 3, the joint strength between the case and the holder can be increased and the joint portion is not damaged. In addition, when welding is performed at the time of joining, and when welding is performed over the entire circumference, the airtightness is maintained inside the holder as well as the inside of the case, and the characteristics are further improved by pre-filling with a dry inert gas. To do.

[0021]

Preferred embodiments of an optical circuit module according to the present invention will be described below in detail with reference to the accompanying drawings.
1 to 4 show a first embodiment of an optical circuit module according to the present invention. As shown in FIG. 1, a predetermined optical circuit 1
0 is mounted inside a flat rectangular case 11 having an upper opening. In the present embodiment, an example in which a circulator is used as the optical circuit 10 is shown, and since it has the same configuration as that of the prior art shown in FIG. 7, the configuration of the optical circuit 10 is given the same reference numeral. The description is omitted.

A hole 11a is formed at a predetermined position on the side surface of the case 11, and the hole 11a has a circular cross section and both ends open inside and outside the case 11. As a result, an optical signal is incident from the outside through the hole 11a, is irradiated to the optical circuit 10, and is subjected to a predetermined process to be emitted to the outside through the other hole 11a. In this example, since it is a 4-port circulator, two holes 11a are provided on each side of the case 11 (a total of four holes).
) Are provided. Further, as shown in FIG. 2, each hole 11a is formed at a position higher by a predetermined distance so that the periphery thereof does not contact the inner bottom surface of the case 11.

Then, a collimator lens 12 and an optical fiber 13 with a ferrule are attached to each hole 11a (see FIG. 3), and a lid 14 is attached so as to cover the upper side of the case 11 to close it (FIG. 3). 4). The basic configuration is the same as that of the conventional optical circuit module.

In the present invention, the case 11 is made of Fe--N.
Kovar, which is an i-Co alloy (coefficient of thermal expansion: 4.5 to
It is formed by using 6.2 × 10 ⁻⁶ / ° C.). further,
An airtight window 15 is attached to the inside of the side surface of the case 11 so as to close each hole 11a. The airtight window 15 is made of sapphire (coefficient of thermal expansion: 4.6 to 5.3 × 10 ⁻⁶ / ° C.), which has a thermal expansion coefficient substantially equal to that of Kovar, which is a constituent material of the case 11, and has relatively high strength. Are configured. More specifically, as shown in FIG. 3, the hole 1a is formed in a rectangular flat plate shape having a side larger than the inner diameter.
It is placed so as to completely cover 1a. At this time, since a predetermined distance is provided between the hole 11a and the inner bottom surface of the case 11 as described above, the portion between them serves as a margin when the airtight window 15 is attached, and it is possible to surely make surface contact. . The airtight window 15 and the case 11 are fixed by brazing.

That is, first, a metal is attached to the bonding surface of the airtight window 15 by sputtering or the like except the optical path portion (a portion facing the hole 11a) (hatched portion in FIG. 3B), and the metal and the case 11 are attached. Insert the silver solder between the and, and align and fix the position. While maintaining this state, the silver solder is melted by heating to about 600 to 800 ° C., and the capillary phenomenon is utilized to uniformly interpose between the joint surface of the airtight window 15 and the case 11 without a gap. Then, by cooling the whole, the silver solder is hardened and the airtight window 15 and the case 11 are firmly fixed. The silver solder is present in the hatched portion of FIG. 3B and is arranged so as to surround the periphery of the hole 11a, so that the hole 11a is completely sealed.

At this time, if the thermal expansion coefficients of the case 11 and the airtight window 15 are different, either the case 11 or the airtight window 15 undergoes a large volume change, and when cooled, the two are contracted and bonded. However, due to the difference in shrinkage, the weaker one (usually the airtight window) is distorted or cracked. However, in this embodiment, since the material of the case 11 is Kovar and the material of the airtight window 15 is sapphire, the thermal expansion coefficients of the both are almost the same, so that they shrink to the same extent during cooling, and the airtight window 15 or the case is closed. No distortion, cracking or the like is generated in 11, and no gap is formed by peeling off a part of the joint surface between the hermetic window 15 and the case 11.

In the present invention, the case 11 and the lid 14 are
It is integrated by welding. That is, the lid 14 is formed of the same material (Kovar) as the case 11, and as shown in FIG. 4, the lid 14 has a shape outside the concave portion 11b formed by cutting the inner peripheral side of the upper surface of the case 11 into a concave shape. It is formed in the same shape as the frame. Then, the lid 14 is attached to the recess 11b.
In the state of being matched with the inside, the periphery of the lid 14 and the joint surface of the case 11 are heated and welded while applying pressure (seam welding).
Then, the lid 14 is integrated with the case 11. As shown in FIG. 4, the welded portion 16 is formed in an endless shape on the entire circumference of the lid 14, and the case 11 and the lid 14 are fused and integrated by welding, so that airtightness is maintained.

As a result, the opening 11a of the case 11 is attached to the case 1 by the airtight window 14 and the upper portion of the case 11 is attached by welding the lid 14 thereto.
1 Since the inside is shut off from the outside, even if it is used in a high humidity atmosphere, the high humidity atmosphere does not enter the inside.
Furthermore, dust and the like will not enter. Therefore, since the inside of the case 11 is maintained in the atmosphere at the time of manufacturing, in order to stabilize the characteristics, this embodiment is
A dry inert gas (such as nitrogen) is enclosed in the case 11. In addition, in order to fill the dry inert gas, at least the work of welding the lid 14 is performed in the dry inert gas atmosphere so that the dry inert gas can be easily filled. In addition, the inside may be evacuated instead of the inert gas.

In this embodiment, the optical circuit (optical component) 1
Since the case 11 and the lid 14 for accommodating 0 are formed of Kovar, the Kovar is a ferromagnetic material, so that the optical circuit module exerts a magnetic shield effect, and the magnetic field from the outside is shielded by the case and lid. Therefore, even if the built-in optical circuit includes parts that are affected by the magnetic field such as the Faraday rotator, it is not affected by the external magnetic field.
Can work correctly.

In this embodiment, the case and the lid are made of Kovar to block the magnetic field from the outside. In order to obtain such an effect, for example, another ferromagnetic material such as SUS430 is used. You may use the material of.

Next, the connection structure between the optical fiber 13 and the case 11 will be described. In FIG. 1 and FIG. 2, the optical fiber 13 and the collimator lens 12 are connected to the hole 11 a of the case 11.
Although it is schematically shown that they are mounted so as to face each other, the actual mounting structure can take a configuration as shown in FIG. 5 or 6.

First, the embodiment shown in FIG. 5 will be described. As shown in FIG. 5, a lens barrel 21 whose inner surface is a mirror surface.
A collimator lens 12 is installed inside the. Then, the optical axis of the collimator lens 12 and the center axis of the lens barrel 21 are integrated by welding so that one end of the lens barrel 21 with the collimator lens 12 is located at a predetermined position on the side surface of the case 11 (position where the hole 11a is formed). To be joined by welding. That is, the inner diameter of the lens barrel 21 is made larger than the inner diameter of the hole 11a provided in the case 11, and the lens barrel 21 is mounted so as to surround the hole 11a. It is performed by welding (welding points 23) at three or more points.

On the other hand, a ferrule 25 as a tip protecting component is fixed to the tip of the optical fiber 13 with an adhesive. In this example, a cylindrical ferrule holder 26 is attached to the outer circumference of the tip of the ferrule 25. Then, the ferrule holder 26 has an inner diameter that matches the outer shape of the ferrule 25, is closely adhered at the joining surface of both, and is welded in that state to be integrated. Then, this welded portion 23a is also formed at three or more places at least on the circumference in the same manner as described above.

Further, the front end of the ferrule holder 26 is fixed to the case 11 by welding (welding point 23b). At this time, the optical axis of the optical fiber 13 (ferrule 25) is aligned with the optical axis of the collimator lens 12, and the lens barrel 21 is housed in the ferrule holder 26.

As described above, the case 1 is not connected directly to the ferrule 25 but via the ferrule holder 26.
Since it is welded to 1 and integrated, it is firmly fixed and will not be damaged at the connection part. And the ferrule holder 26
If the welding points 23a and 23b are welded over the entire circumference, the airtightness is maintained up to the area where the collimator lens 12 and the ferrule 25 existing outside the airtight window 15 are maintained, and the collimator lens 12 and the ferrule 25 side are also dry and inactive. Being placed in a gas atmosphere, a high humidity atmosphere will not enter.

Further, since the inside of the case 11 is closed at two places of the airtight window 15 and the ferrule holder 26, the airtightness holding force is further increased and the characteristics are further stabilized. That is, the inside of the hole is completely sealed, and even if an optical isolator, an optical switch or the like having the optical circuit module according to the present invention is installed on the seabed or the like, water does not enter into the hole and is attached to the hole. No water pressure is applied to the airtight window.

Next, the embodiment shown in FIG. 6 will be described. In this embodiment, a sleeve 27 is attached to the tip of a cylindrical ferrule 25 ′ attached to the tip of the optical fiber 13, and a lens barrel 21 equipped with a collimator lens 12 is attached to the tip of the sleeve 27 with its axis aligned. , A fiber collimator 28 in which these respective members are integrated is formed (FIG. 8).
(A)). Then, the sleeve 27 and the ferrule 25 and the lens barrel 21 are also joined by welding (welding point 23
c).

Then, as shown in FIG. 6B, the fiber collimator 28 is used to position the tip (lens barrel 21) side of the case 11 in the hole 11a of the case 11 and maintain the state. In addition, a cylindrical collimator holder 29 with both ends opened around the fiber collimator 28
Are integrated by welding (welding point 23d). Then, the tip end side of the collimator holder 29 is fixed to the case 11 by welding (welding point 23e). This allows
The optical fiber 13 (ferrule 25) is indirectly attached to the holder 2
It is firmly fixed to the case 11 by using 9. The welding points 23d and 23e may be provided at three or more points on the circumference, as in the example shown in FIG. 5, or may be performed over the entire circumference.

Further, in the above-mentioned embodiment, an example in which an optical circulator is used as an optical circuit has been shown, but the optical circuit incorporated in the present invention is not limited to this, for example, as shown in FIG.
Various optical circuits can be mounted in addition to applying an optical switch as the optical circuit 10 'as shown in FIG. The optical circuit 10 'shown in FIG. 7 includes a Faraday rotator 4 and a 1 / Faraday rotator 4 between a pair of PBSs 2 arranged at a predetermined interval.
A two-wave plate 5 is arranged in a predetermined positional relationship, and a magnetic yoke (electromagnet) 3'having a winding is used as a magnetic field applying means for the Faraday rotator 4. And
By reversing the direction of the magnetic field generated by the electromagnet 3 ', the light incident from a certain optical fiber 13 changes its emission port. When the case 11 and the lid 14 are made of Kovar, the magnetic shielding effect is exerted, so that the internal Faraday rotator 4 is not affected by the external magnetic field and operates accurately.

[0040]

As described above, in the optical circuit module according to the present invention, the case in which the optical parts are installed is sealed with the lid and the airtight window, and further the dry inert gas is sealed or evacuated inside the case. Thus, the atmosphere around the outside of the case containing moisture does not enter, and the inside of the case is kept in a dry atmosphere state for a long period of time. Therefore, the optical adhesive used for forming the optical components forming the built-in optical circuit does not absorb moisture and can maintain desired characteristics. Furthermore, dust or the like floating in the outside air does not enter, and the dust or the like does not adhere to the optical component. Therefore, the optical characteristics of the optical component can be maintained in a stable state without deterioration.

When the case is made of Kovar and the airtight window is made of sapphire (Claim 2), the coefficients of thermal expansion of the two are almost the same, so brazing or the like is required when forming such an optical circuit module. Thus, even if the case and the airtight window are adhered to each other, no distortion, cracking or the like occurs, and the hermeticity inside the case can be maintained. Further, the airtight window is not distorted by a change in the outside temperature, a gap is not formed between the airtight window and the case, and the airtightness inside the case can be maintained for a long time.

Further, since Kovar, which is the material of the case, is a ferromagnetic material, the magnetic shield effect is exerted, and the Faraday rotator, the magnetic yoke, etc., which are easily affected by the magnetic field, are present in the optical parts installed inside the case. Even if used, it is not affected by external magnetic fields. Therefore, malfunction of the optical switch or the like can be prevented.

The hole is sealed by the holder by directly or indirectly mounting the optical fiber for sending the light inside the case through the holder while aligning it with the hole of the case. Therefore, water pressure is not applied to the airtight window even under conditions such as the sea bottom, and the airtight window is not distorted and no gap is formed between the airtight window and the case.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of an optical circuit module according to the present invention.

FIG. 2 is a sectional view taken along line AA showing the first embodiment of the optical circuit module according to the present invention.

FIG. 3A is a perspective view showing a mounting structure for an airtight window. (B) is a figure which shows the attachment position of an airtight window.
(C) is a plan view of (A).

FIG. 4A is a plan view showing a state in which a lid is attached to the case. (B) is a side view thereof.

FIG. 5 is a diagram showing an example of a structure for attaching an optical fiber to a case.

FIG. 6 is a diagram showing another example of a structure for attaching an optical fiber to a case.

FIG. 7 is a diagram showing a modification of the present invention.

FIG. 8 is a diagram showing a conventional optical circuit module.

FIG. 9 is a diagram showing a conventional optical circuit module.

[Explanation of symbols]

 11 Case 11a Hole 13 Optical Fiber 14 Lid 15 Airtight Window 26, 29 Holder

Claims (3)

[Claims] 1. A plurality of holes (11a) are formed on a side surface of a case (11) having an upper opening, and an airtight window (15) for closing the plurality of holes is provided on an inner side surface of the case. An optical circuit is installed inside the case, a lid (14) is attached to the upper opening of the case, the entire circumference is welded to be integrated, and a dry inert gas is sealed or evacuated inside the case. Optical circuit module characterized by. 2. The material of the case is Kovar, and the airtight window is sapphire.
The optical circuit module described in. 3. A cylindrical holder that is directly or indirectly attached to a ferrule (25) attached to the tip of the optical fiber when the optical fiber (13) for transmitting and receiving an optical signal is attached to the hole. The optical circuit module according to claim 1 or 2, wherein the case 11 is fixed at a predetermined position outside the side surface of the case 11 via (26, 29).