JP7189977B2 - optical isolator - Google Patents

Description

The present invention relates to an optical isolator, which is an optical component used in optical communication and optical measurement, for preventing light reflected from a fiber end or a lens end from returning to a laser serving as a light source.

In optical communication and optical measurement, laser oscillation becomes unstable when light emitted from a semiconductor laser is reflected by the surface of a member provided in the transmission line and returned to the semiconductor laser. In order to block this reflected return light, an optical isolator using a Faraday rotator that non-reciprocally rotates the plane of polarization is used (see, for example, Patent Document 1, etc.).

For example, the optical isolator may be joined and fixed to the end surface of the stub and integrated with the receptacle. An optical isolator having such a configuration is used by being incorporated in a semiconductor laser module or the like.

Japanese Unexamined Patent Application Publication No. 2011-150208

There are demands for cost reduction, space saving, weight saving, etc. for semiconductor laser modules, and likewise there are demands for cost reduction, space saving, weight saving, etc. for each part constituting the module.

In addition, when manufacturing a semiconductor laser module, temperature rise and impact due to YAG welding, temperature rise due to AuSn soldering, and the like affect the joint interface between the optical isolator and a member such as a stub.

The present invention has been made in view of the above problems. An object of the present invention is to provide an optical isolator with high efficiency.

In order to achieve the above object, the present invention provides an optical isolator chip in which a first polarizer, a Faraday rotator made of a ferromagnetic material, and a second polarizer are joined and fixed in this order, and a device for applying a magnetic field to the optical isolator chip. an optical isolator comprising a magnet of
an incident end surface or an output end surface of the optical isolator chip is bonded and fixed to a member;
The center of the magnetic flux formed by the magnet on the optical axis of the optical isolator is located closer to the end surface joined and fixed to the member than the central position of the Faraday rotator on the optical axis. An optical isolator is provided comprising:

In this way, by locating the center of the magnetic flux generated by the magnet on the side of the end surface bonded and fixed to the member of the optical isolator chip rather than the central position on the optical axis of the Faraday rotator, the optical isolator chip is applied to the member, an optical isolator with high bonding reliability to the member can be obtained. In addition, since the magnet is miniaturized, the cost of the optical isolator can be reduced accordingly, the space can be saved, and the weight can be reduced.

At this time, the end of the magnet on the same side as the end face side of the optical isolator chip bonded and fixed to the member may be bonded and fixed to the member.

By thus joining and fixing the ends of the optical isolator chip and the magnet on the same side to the member, the member for attaching the optical isolator can have a simple structure, and the reliability of the joint of the optical isolator can be improved.

At this time, it is preferable that the member to which the optical isolator chip is bonded and fixed and the member to which the magnet is bonded and fixed are members integrally forming the same part.

In this way, by joining and fixing the optical isolator chip and the magnet to the member that constitutes the same component, the component composed of them can be easily manufactured, and the component can be applied to a wide range of applications. can do.

At this time, the member to which the optical isolator chip is bonded and fixed can be a stub of the receptacle.

By joining and fixing the optical isolator chip and the stub of the receptacle in this way, the receptacle can be made to have a simple structure, and the optical isolator can have a higher joining reliability.

At this time, the member to which the magnet is joined and fixed can be the housing of the receptacle.

By joining and fixing the housing of the optical isolator chip and the receptacle in this way, the structure of the receptacle can be simplified, and the joint reliability of the optical isolator can be improved.

According to the present invention, it is possible to provide an optical isolator that has higher junction reliability, reduced cost, space saving, and lighter weight than conventional ones.

1(a) is a schematic diagram showing an example of the optical isolator of the present invention, and FIG. 1(b) is a schematic diagram showing the relationship between the center of the Faraday rotator and the center of the magnetic flux (magnet center) Example 1). FIG. 2(a) is a schematic diagram showing another example of the optical isolator of the present invention, and FIG. 2(b) is a schematic diagram showing the relationship between the center of the Faraday rotator and the center of magnetic flux (magnet center). (Example 2). In a schematic diagram (Fig. 3(a)) showing still another example of the optical isolator of the present invention and a schematic diagram (Fig. 3(b)) showing the relationship between the center of the Faraday rotator and the center of the magnetic flux (magnet center), Yes (Example 3). A schematic diagram showing still another example of the optical isolator of the present invention (Fig. 4(a)) and a schematic diagram showing the relationship between the center of the Faraday rotator and the center of the magnetic flux (magnet center) (Fig. 4(b)). Yes (Example 4). FIG. 5A is a schematic diagram showing an example of a conventional optical isolator, and FIG. 5B is a schematic diagram showing the relationship between the center of a Faraday rotator and the center of magnetic flux (magnet center).

Hereinafter, the present invention will be described in detail as an example of embodiments with reference to the drawings, but the present invention is not limited thereto.

FIG. 5(a) is a schematic diagram showing a conventional optical isolator. This optical isolator 200 includes an optical isolator chip 7 in which a first polarizer 3, a Faraday rotator 4 made of a ferromagnetic material, and a second polarizer 5 are joined and fixed in this order, and a magnet for applying a magnetic field to the optical isolator chip 7. 62. This magnet 62 has a cylindrical shape surrounding the optical isolator chip 7 . The left end (incident end surface or exit end surface) of the optical isolator chip 7 of the optical isolator 200 and the left end of the magnet 62 are each fixedly joined to the metal holder 11 .

The optical axis of optical isolator 200 coincides with the central axis of cylindrical magnet 62 . A magnetic flux is formed between the left and right ends of the magnet 62, and the center of the magnetic flux on the optical axis is defined as the magnet center. FIG. 5B shows the magnetic flux center (magnet center) and the center position of the Faraday rotator 4 on the optical axis (hereinafter referred to as FR center) relationship is shown. In the conventional optical isolator 200 , the magnetic flux center (magnet center) is located on the right side of the optical axis center position of the Faraday rotator 4 , that is, on the side opposite to the joint end face side with the metal holder 11 . 5(b), the attachment point of the magnet 62 to the metal holder 11 (represented as a magnet attachment point in the figure) and the attachment point of the optical isolator chip 7 to the metal holder 11 (represented as a chip attachment point in the figure). ) are also shown.

A magnetic force acts from the magnet 62 on the Faraday rotator 4 placed in the magnetic field formed by the magnet 62 . At the center position of the Faraday rotator 4 on the optical axis, a force acts toward the center of the magnetic flux (magnet center). That is, in the structure shown in FIG. 5(a), a force acts to separate the metal holder 11 and the optical isolator chip 7 (see the bold arrow in FIG. 5(b)). For this reason, separation and breakage are likely to occur between the metal holder 11 and the optical isolator chip 7 . Also, when the optical isolator 200 is placed in a high-temperature environment, the adhesive bonding the optical isolator chip 7 to the metal holder 11 softens and the fixation becomes unstable. In particular, peeling and breakage are likely to occur due to stress generated at

Next, a schematic diagram showing an example of the optical isolator of the present invention (Fig. 1(a)) and a schematic diagram showing the relationship between the center of the Faraday rotator and the center of the magnetic flux (magnet center) (Fig. 1(b)) are shown. The configuration of the optical isolator of the present invention will be described below with reference to FIG.

The optical isolator 110 of the present invention shown in FIG. 1(a) comprises an optical isolator chip 7 in which a first polarizer 3, a Faraday rotator 4 made of a ferromagnetic material, and a second polarizer 5 are joined and fixed in this order, and this optical isolator. and a magnet 12 for applying a magnetic field to the chip 7 . An incident end face or an exit end face of the optical isolator chip 7 is bonded and fixed to a metal holder 11 . Then, as shown in FIG. 1B, the center of the magnetic flux formed by the magnet 12 (magnet center) on the optical axis of the optical isolator 110 is the center position (FR center) of the Faraday rotator 4 on the optical axis. It is located on the side of the end surface joined and fixed to the metal holder 11. As shown in FIG.

In this way, by locating the center of the magnetic flux (magnet center) closer to the end surface of the optical isolator chip 7 than the central position of the Faraday rotator 4 on the optical axis, the optical isolator chip Since there is a force that always presses 7 against the metal holder 11 (see the bold arrow in FIG. 1B), the reliability of bonding of the optical isolator 110 to the member (metal holder 11) can be made extremely high. In addition, since the magnet dimensions can be shortened, cost reduction, space saving, and weight reduction can be achieved.

The force acting on the center of the Faraday rotator 4 is determined by the balance of forces acting on the Faraday rotator 4 in the horizontal direction in FIG. 1(a). When the center of the magnetic flux (the center of the magnet) coincides with the center position of the Faraday rotator 4 on the optical axis, the forces acting in the left and right directions are almost equal, and there is almost no force in any of the left and right directions. doesn't work In other words, when the center of the magnetic flux (magnet center) and the center position of the Faraday rotator 4 on the optical axis do not match, the center position of the Faraday rotator 4 on the optical axis should be the center of the magnetic flux (magnet center). ) will act. The force for pressing the optical isolator chip 7 against the metal holder 11 described above is such a force.

Also, the magnet 12 can be fixed to the metal holder 11 at the end on the same side as the end face side of the optical isolator chip 7 fixed to the metal holder 11 . In this way, by joining and fixing the ends of the optical isolator chip 7 and the magnet 12 on the same side to the metal holder 11, the structure of the member for mounting the optical isolator 110 can be simplified, and the joint reliability (joint stability) of the optical isolator can be improved. ) can be further enhanced.

In the optical isolator 110 of the present invention described with reference to FIG. 1, the optical isolator chip 7 and the magnet 12 are jointed and fixed to the same member, but the present invention is not limited to this, as shown in FIG. 3(a). It is also possible to join and fix to a member that constitutes the same part integrally. For example, the member to which the optical isolator chip is bonded and fixed can be the stub of the receptacle, and the member to which the magnet is bonded and fixed can be the housing of the receptacle.

Specifically, as shown in FIG. 3(a), a schematic diagram of another example of the optical isolator of the present invention is shown, and FIG. 3(b) shows the Faraday rotator center and the magnetic flux center. It is a schematic diagram which shows the relationship of (magnet center). In the embodiment shown in FIG. 3(a), the member to which the optical isolator chip 7 is bonded and fixed can be the stub 31 of the receptacle. Also, the member to which the magnet 32 is joined and fixed can be the housing 33 of the receptacle. By adopting such a structure, the receptacle can have a simple structure, and the bonding reliability of the optical isolator 130 can be further improved.

Also in FIG. 3A, the magnetic flux center (magnet center) is positioned closer to the bonded and fixed end surface of the optical isolator chip 7 than the center position of the Faraday rotator 4 on the optical axis. Therefore, as shown in FIG. 3(b), a force acts to press the optical isolator chip 7 (Faraday rotator 4) against the stub 31 of the receptacle, thereby improving the reliability of the joint of the optical isolator.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these.

(Example 1)
An optical isolator shown in FIG. 1(a) was fabricated as follows. First, (TbEu) ₂ Bi ₁ Fe _4.8 Ga _0.2 O ₁₂ was used as the Faraday rotator 4 and polished so that the Faraday rotation angle was 45 degrees at 25° C. for light with a wavelength of 1550 nm. (0.60 mm in length), and both end faces were coated with anti-epoxy AR coating film.

Next, prepare polarizing glasses (second polarizer 5, first polarizer 3) with anti-air AR coating films on the entrance surface side and the exit surface side, and fix them to the Faraday rotator 4 with an epoxy adhesive. did. This was cut into 0.8 mm square (having a square section of 0.8 mm on each side) to obtain an optical isolator chip 7 .

Then, an optical isolator 110 is manufactured by bonding and fixing the output end face of the optical isolator chip 7 and the SmCo magnet 12 (outer diameter 2 mm, inner diameter 1.3 mm, length 0.4 mm) to the metal holder (first member) 11 . did. At this time, as shown in FIG. 1(b), the center of the magnetic flux on the optical axis formed by the magnet 12 (magnet center) is located farther from the center position (FR center) on the optical axis of the Faraday rotator 4. It is located on the end face side (left side). The forward insertion loss of the fabricated optical isolator 110 was 0.14 dB, and the isolation was 43 dB.

In the optical isolator 110 of Example 1, compared with the optical isolator of Comparative Example 1 (to be described later), the weight, volume, and cost of the magnet could be reduced to about 4/15, respectively.

In the process of incorporating the optical isolator 110 into the laser module, even after one hour at a temperature of 260.degree.

(Example 2)
An optical isolator shown in FIG. 2(a) was fabricated as follows. First, an optical isolator chip 7 was manufactured in the same manner as in the first embodiment. Then, the output end face of the optical isolator chip 7 and the SmCo magnet 22 (outer diameter 2 mm, inner diameter 1.3 mm, length 0.6 mm) are adhered and fixed to a disk-shaped metal holder (second member) 21, and the An optical isolator 120 was fabricated in the same manner as in Example 1. Example 2 differs from Example 1 in the shape of the metal holder and the size of the SmCo magnet.

At this time, as shown in FIG. 2B, the center of the magnetic flux on the optical axis formed by the magnet 22 is located on the output end face side (left side) of the center position (FR center) on the optical axis of the Faraday rotator 4. ). The forward insertion loss of the fabricated optical isolator 120 was 0.16 dB, and the isolation was 42 dB.

In the optical isolator 120 of Example 2, the weight, volume, and cost of the magnet could each be reduced to about 6/15 of those of the optical isolator of Comparative Example 1, which will be described later.

In the process of incorporating the optical isolator 120 into the laser module, even after one hour at a temperature of 260.degree.

(Example 3)
An optical isolator shown in FIG. 3(a) was fabricated as follows. First, an optical isolator chip 7 was manufactured in the same manner as in the first embodiment. Then, the output end face of the optical isolator chip 7 is adhesively fixed to the stub (third member) 31 of the receptacle, and the SmCo magnet 32 (outer diameter 2 mm, inner diameter 1.3 mm) is attached to the receptacle housing (fourth member) 33. , length 0.8 mm) were adhered and fixed to produce the optical isolator 130 . In the third embodiment, the member to which the optical isolator chip 7 is bonded and fixed and the member to which the magnet 32 is bonded and fixed are integrated to constitute the same component, and the member to which the optical isolator chip 7 is bonded and fixed ( It differs from Examples 1 and 2 in that the end surface of the stub 31) is inclined with respect to the optical axis.

At this time, as shown in FIG. 3B, the center of the magnetic flux on the optical axis formed by the magnet 32 is located on the output end face side (left side) of the center position (FR center) on the optical axis of the Faraday rotator 4. ). The forward insertion loss of the fabricated optical isolator 130 was 0.15 dB, and the isolation was 43 dB.

Compared with the optical isolator of Comparative Example 1, the optical isolator 130 of Example 3 was able to reduce the magnet weight, volume, and cost to about 8/15.

Further, in the process of incorporating the optical isolator 130 into the laser module, even after 10 hours at a temperature of 150.degree.

(Example 4)
As shown in FIG. 4(a), in this embodiment, the incident end surface of the optical isolator chip 7 is located outside the positions of the end surfaces of the magnets and members, unlike the optical isolator 130 of the third embodiment shown in FIG. 3(a). One end of the receptacle housing 43 is extended so that it does not protrude out. SmCo magnet 42 is similar to SmCo magnet 32 and receptacle stub 41 is similar to receptacle stub 31 .

As a result, it is possible to avoid the possibility that the end face of the optical isolator chip 7 hits the lens housing or the like and causes chipping or the like when it is built into the laser module.

(Comparative example 1)
An optical isolator shown in FIG. 5(a) was fabricated as follows. First, (TbEu) ₂ Bi ₁ Fe _4.8 Ga _0.2 O ₁₂ was used as the Faraday rotator 4 and polished so that the Faraday rotation angle was 45 degrees at 25° C. for light with a wavelength of 1550 nm. (0.60 mm in length), and both end faces were coated with anti-epoxy AR coating film.

Next, prepare polarizing glasses (second polarizer 5, first polarizer 3) with anti-air AR coating films on the entrance surface side and the exit surface side, and fix them to the Faraday rotator 4 with an epoxy adhesive. did. An optical isolator chip 7 was obtained by cutting this into a square of 0.8 mm.

Then, an optical isolator 200 was manufactured by adhesively fixing the output end face of the optical isolator chip 7 and the SmCo magnet 62 (outer diameter 2 mm, inner diameter 1.3 mm, length 1.5 mm) to the metal holder 11 . At this time, the incident end surface of the optical isolator chip 7 generally has a structure in which it does not protrude from the end of the magnet 62 that is not joined and fixed to the metal holder 11 . The center of the magnetic flux on the optical axis (magnet center) formed by the magnet 62 is located on the incident end surface side (right side) of the center position (FR center) on the optical axis of the Faraday rotator 4 . The forward insertion loss of the fabricated optical isolator 200 was 0.15 dB, and the isolation was 42 dB.

In the process of assembling this optical isolator 200 into a laser module, the bonding portion between the optical isolator chip 7 and the metal holder 11 was broken and separated after 10 hours at a temperature of 150°C.

This is probably because when the temperature of the optical isolator 200 rises and the epoxy adhesive softens, force acts on the magnetic Faraday rotator 4 in the direction of the magnetic flux center (magnet center) ( See FIG. 5(b)).

In addition, in Comparative Example 1, the weight and volume of the magnets are larger than those in Examples 1 to 4, which makes it difficult to reduce the size (space saving and weight reduction) and cost reduction of the optical isolator.

It should be noted that the present invention is not limited to the above embodiments. The above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present invention and produces similar effects is the present invention. It is included in the technical scope of the invention.

3... First polarizer, 4... Faraday rotator, 5... Second polarizer,
7... Optical isolator chip, 11... Metal holder,
12, 22, 32, 42, 62... magnets,
21... A disk-shaped metal holder,
31, 41... receptacle stubs, 33, 43... receptacle housings,
110, 120, 130... the optical isolator of the present invention,
200... Conventional optical isolator.

Claims (3)

An optical isolator comprising an optical isolator chip in which a first polarizer, a Faraday rotator made of a ferromagnetic material, and a second polarizer are joined and fixed in this order, and a magnet for applying a magnetic field to the optical isolator chip,
an incident end surface or an output end surface of the optical isolator chip is bonded and fixed in a concave portion of the receptacle;
The center of the magnetic flux formed by the magnet on the optical axis of the optical isolator is located closer to the end surface joined and fixed to the receptacle than the central position of the Faraday rotator on the optical axis. can be,
the end of the magnet on the same side as the end face side of the optical isolator chip bonded and fixed to the receptacle is bonded and fixed to the receptacle;
The position of the bonding point between the end of the magnet and the receptacle on the optical axis of the optical isolator is the position of the bonding point between the optical isolator chip and the receptacle on the optical axis of the optical isolator. and the center position of the magnetic flux formed by the magnet on the optical axis of the optical isolator. 2. The optical isolator according to claim 1, wherein said optical isolator chip is bonded and fixed to a stub of said receptacle. 3. The optical isolator according to claim 1, wherein said magnet is joined and fixed to a housing of said receptacle.

Images