JP2002169063A - Optical isolator-attached optical fiber pigtail and its assembling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a conventional problem of increased number of assembling processes, a problem caused by the inability of positioning the polarizing and transmitting direction of a polarizer on the incident side of an optical isolator element and by the resultant variance of the aligning time, depending on the manner in which an isolator attached-optical fiber pigtail is set in an assembling aligning device. SOLUTION: On the end face of an optical fiber holder, there is provided the optical isolator element in which at least one polarizer and at least one Faraday rotor are integrated, with a magnet arranged around the optical isolator element. Then, the magnet or the holder is formed with a marking part that indicates the polarizing and transmitting direction of the polarizer on the incident or outgoing side of the optical isolator element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical fiber pigtail with an optical isolator used for optical communication.

[0002]

2. Description of the Related Art An optical isolator is used in optical communication to prevent reflected light returning from an optical component to a laser light source and to prevent occurrence of light resonance in an optical fiber amplifier.

FIG. 10 is a cross-sectional view of a conventional polarization-dependent optical isolator for preventing reflected light returning to a laser light source, and FIG. 11 shows the behavior of polarized light in forward and reverse directions. The forward direction indicates a direction in which light incident on the optical isolator is transmitted, and the reverse direction indicates a direction in which light incident on the optical isolator is not transmitted. As shown in FIG. 10, the optical isolator includes a Faraday rotator 2 disposed between two polarizers 1a and 1b, a magnet 6 for applying a magnetic field to the Faraday rotator 2, and a holding jig 15.

In an optical isolator, an LD is used in a forward direction.
The light emitted from 16 becomes parallel light by the lens 17 and enters the polarizer 1a. As shown in FIG. 11, after passing through the polarizer 1a, the light becomes linearly polarized light, is rotated by 45 degrees by the Faraday rotator 2, and passes through the polarizer 1b. Also,
In the opposite direction, the light that has passed through the polarizer 1 b is rotated by the Faraday rotator 2 by 45 °. However, since the light becomes a polarization plane orthogonal to the transmission polarization plane of the polarizer 1a due to the non-reciprocity of the Faraday rotator 2, the light is attenuated by the polarizer 1a and the LD 16
Do not return to This has the function of passing light from one direction and blocking the passage of light in the opposite direction.

[0005] Japanese Patent Application Laid-Open No. 11-119155 discloses
Japanese Patent Application Laid-Open No. 2000-162475 discloses a technique of an optical isolator with an optical fiber which is used by joining an optical isolator to an end of an optical fiber. In this configuration, a rectangular parallelepiped isolator element is attached to the inclined end face of the inclined capillary 3. Optical isolator element 19
The polarization direction discriminating method in which the long side is arranged with respect to the inclination direction of the polarization direction is shown.

FIGS. 8 and 9 show a polarization direction 12 of an LD output light 18 for obtaining a desired optical coupling and an optical isolator element 19 in alignment of an LD module using an optical fiber pigtail with an optical isolator. The incident-side polarizer polarization transmission direction 8 and the inclination direction of the end face of the capillary 3 are shown. FIG. 8 shows a case where the end face of the capillary 3 is flat, and FIG. 9 shows a case where the end face of the capillary 3 is inclined. 8 and 9 use the magnet 6, but they are not shown.

In FIG. 8, in order to obtain the optimum coupling to the optical fiber 4, the optical fiber pigtail with an optical isolator is rotated (Zθ) of the optical axis C, and the LD outgoing light 1 is adjusted.
It is necessary to make the polarization direction 12 of 8 and the polarization transmission direction 8 of the incident side polarizer 1a of the optical isolator element 19 coincide.

As shown in FIG. 9A, an optimum coupling is obtained from the inclination angle of the end face of the optical fiber 4 (capillary 3), the refractive index of the fiber core, and the refractive index of the optical isolator element 19 using Snell's law. Direction to the optical fiber 4 can be calculated. In order to obtain a desired coupling to the optical fiber 4, the direction of incidence of the LD outgoing light 18 on the optical fiber 4 and the inclination direction of the end face of the capillary 3 are matched, and the polarization direction 12 from the LD outgoing light 18 and the optical isolator It is necessary to make the polarization transmission direction 8 of the incident side polarizer 1a of the element 19 coincide.

[0009]

However, in the case of FIG. 8, the polarization direction is defined by the shape of the optical isolator element 19 in the prior art. However, since the optical isolator element 19 is included in the magnet 6, it is difficult to align the optical isolator element 19 during alignment. Incident side polarizer 1a
It is difficult to confirm the polarization transmission direction 8 of Therefore, when setting the optical fiber pigtail with an optical isolator in the assembly alignment device, the polarization transmission direction 8 of the incident side polarizer 1a of the optical isolator element 19 cannot be positioned, and the alignment time depends on the setting method. However, there has been a problem in that variations are caused in the device, and the number of assembling steps is increased.

[0010] Similarly, as shown in FIG. 9 (b), in the assembly alignment of the LD module, the polarization transmission direction 8 of the incident-side polarizer 1 a of the optical isolator element 19 and the end face 3 a of the capillary 3.
It is necessary to align the rotation axis (Zθ) of the optical axis C that matches the polarization direction 12 of the LD output light 18 with the optical fiber pigtail with an optical isolator in which the inclination direction of the optical fiber is optimally arranged (orthogonal arrangement). In order to shorten the alignment time, the end face 3 of the capillary 3 must be aligned with the polarization direction 12 of the LD emission light 18 before alignment.
It is desirable to set the inclination direction of a at a predetermined position in advance, but such a specific method is not proposed in the prior art. Therefore, when setting the optical fiber pigtail with an optical isolator in the assembly alignment device, the inclination direction of the end face 3a of the capillary 3 cannot be positioned in a predetermined direction, and the alignment time varies depending on the setting method. This causes a problem that the number of assembling steps increases.

Furthermore, in the prior art, the polarization transmission direction 8 of the incident-side polarizer 1a of the optical isolator element 19 and the inclination direction of the end face 3a of the capillary 3 are predetermined according to the polarization direction 12 and the incident direction of the LD emission light 18. No specific method for positioning at any angle is provided. Therefore, FIG.
As shown in (c), the polarization transmission direction 8 of the incident side polarizer 1a of the optical isolator element 19 and the end face 3a of the capillary 3
Cannot be accurately positioned in the inclination direction, and L
Polarization direction 12 of D outgoing light 18 and optical isolator element 19
Since the polarization transmission directions 8 of the incident-side polarizer 1a do not match, there is a problem that the coupling loss to the optical fiber 4 increases.

[0012]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an optical isolator element in which at least one polarizer and at least one Faraday rotator are integrated on an end face of a holder for holding an optical fiber. Wherein a magnet is arranged around the optical isolator element, and a marking portion for displaying the polarization transmission direction of the incident side or the output side polarizer of the optical isolator element is formed on the holder. I do.

[0013] The end face of the holder is inclined,
The inclination direction and the polarization transmission direction of the entrance side or exit side polarizer of the optical isolator element are set at a predetermined angle, and the inclination direction of the marking part formed on the holder and the end face of the holder is set at a predetermined angle. It is characterized by having done.

The end face of the holder has an obliquely polished surface including an optical fiber and an unpolished surface, and one side of the optical isolator element is substantially parallel or perpendicular to a boundary between the obliquely polished surface and the unpolished surface. It is characterized by being arranged in.

[0015] A linear portion of at least one side formed on the outer peripheral side surface of the optical isolator element is set at a predetermined angle with respect to the polarization transmission direction of the incident side or output side polarizer.

[0016] The Faraday rotator in the optical isolator element is a garnet having a square hysteresis curve.

According to the present invention, there is provided a holder for holding an optical fiber, wherein the end face is an inclined surface, and a marking portion is formed on the holder so as to be at a predetermined angle with respect to the inclination direction, and at least one polarizer is provided. A linear portion of at least one side set at a predetermined angle with respect to the polarization transmission direction of the incident-side or output-side polarizer is formed on the outer peripheral side surface of the optical isolator element in which at least one Faraday rotator is integrated; An assembling method comprising the step of arranging the optical isolator element on the holder end face such that the linear portion is at a predetermined angle with respect to the inclination direction of the holder end face.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1A is a sectional view of an optical fiber pigtail with an optical isolator according to a first embodiment of the present invention. The optical fiber 4 is held by a capillary 3 and a ferrule 5, which are holders, and includes an optical isolator element 19 in which two polarizers 1a and 1b and one Faraday rotator 2 are integrated on an end face 3a of the capillary 3. The magnet 6 is disposed around the optical isolator element 19.
Is adhered and fixed to the end face of the ferrule 5.

Then, the marking part 7 formed at a predetermined angle (90 ° in this example) with respect to the polarization transmission direction 8 of the incident side polarizer 1a of the optical isolator element 19 has the ferrule 5
It is formed on the outer peripheral surface. Therefore, the polarization direction 12 of the LD output light 18 and the polarization transmission direction 8 of the incident-side polarizer 1a of the optical isolator element 19 are determined by using the marking portion 7 on the outer peripheral surface of the ferrule 5 as a reference when aligning the LD module.
Can be arranged at a predetermined position, so that the optical axis C
In this way, it is possible to eliminate the variation in the rotation (Zθ) alignment time of the above, and to greatly reduce the alignment time.

FIG. 1B is a sectional view of an optical fiber pigtail with an optical isolator according to another embodiment of the present invention. End face 3 of capillary 3 which is a holder for optical fiber 4
a is inclined, and the direction of the inclination and the marking portion 7 formed on the outer peripheral surface of the ferrule 5 are set at a predetermined angle in advance. The polarization transmission direction 8 of the incident side polarizer 1a of the optical isolator element 19 is set to a predetermined angle with respect to the inclination direction of the end face 3a of the capillary 3.

Therefore, the polarization direction 12 of the LD output light 18 and the polarization transmission direction of the incident side polarizer 1a of the optical isolator element 19 are determined with reference to the marking portion 7 on the outer peripheral surface of the ferrule 5 when the LD module is aligned. 8 can be arranged at a predetermined position, the rotation of the optical axis C (Z
θ) It has become possible to eliminate variations in alignment time and greatly reduce alignment time.

The positional relationship between the marking portion 7 on the outer peripheral surface of the ferrule 5 and the inclination direction of the end surface 3a of the capillary 3 can be set in any direction. FIG. 1 (a), FIG.
In (b), the marking part 7 is the end face 3 a of the capillary 3.
Although it is located at a position of 0 ° with respect to the inclination direction, it is also possible to arrange at 90 °. Further, the marking part 7 can be made to have an arbitrary shape on the outer peripheral surface of the ferrule 5 by magic or the like. FIG. 1C shows a case where a flat portion 7 is provided on a part of the outer peripheral surface of the ferrule 5.

FIG. 2 (a) shows a cross-sectional view of an optical fiber pigtail with an optical isolator according to a second embodiment of the present invention and a view seen from the direction of the incident side polarizer 1a.

Capillary 3 as holder for optical fiber 4
The end face 3a has an obliquely polished surface 9 including the optical fiber 4 and an unpolished surface 10, and one side of an optical isolator element 19 is arranged substantially parallel or perpendicular to a boundary 11 therebetween. Since the boundary 11 between the obliquely polished surface 9 and the unpolished surface 10 of the end surface 3a of the capillary 3 is perpendicular to the inclination direction, the optical isolator element 19 is moved to the end surface 3 of the capillary 3.
When arranging at a predetermined angle with respect to the inclination direction of a, a method based on the boundary line 11 is preferable.

FIG. 2 (b) shows an optical fiber pigtail with an optical isolator according to a second other embodiment of the present invention, in which three polarizers 1 and two Faraday rotators 2 are provided.
So-called 1.5-stage optical isolator element 1 having
9 is mounted. The case where the polarization transmission directions 8 of the polarizers 1 on the incident side and the output side of the optical isolator element 19 are orthogonal to each other can be achieved by making the directions of applying the magnetic field to the two Faraday rotators 2 the same.
In the case where the polarization transmission direction 8 of the input side 9 and the output side polarizer 1 is the same, it can be achieved by dividing the magnet 6 and reversing the direction in which the magnetic field is applied to the two Faraday rotators 2.

FIG. 2C shows four polarizers 1 and two Faraday rotators 2 in an optical fiber pigtail with an optical isolator according to a second other embodiment of the present invention.
A case is shown in which a so-called two-stage optical isolator element 19 having the following is mounted. The control of the polarization transmission direction of the optical isolator element 19 with respect to the incident side and the exit side polarizer 1 is the same as that of the 1.5-stage type.

FIG. 3 shows a cross-sectional view of an optical fiber pigtail with an optical isolator according to a third embodiment of the present invention and a view from the direction of the incident side polarizer 1a. At least one side linear portion 20 formed on the outer peripheral side surface of the optical isolator element 19 is set at a predetermined angle with respect to the polarization transmission direction 8 of the incident side polarizer 1a.

FIG. 3 (a) shows a case where the optical isolator element 19 is cut into a polygon having at least one side when viewed from the direction of the incident side polarizer 1a, and a polygon having more than a triangle or an arc. Show. In FIG. 3B, the linear portion 20 on the outer peripheral side surface of the quadrangular optical isolator element 19 is parallel or orthogonal to the polarization transmission direction 8 of the incident side polarizer 1a.
The case where the angle is 5 degrees is shown. By arranging the straight line portion 20 in parallel with the boundary line 11, the capillary 3
Can be accurately matched with the polarization transmission direction 8 of the incident side polarizer 1a of the optical isolator element 19, so that the mounting accuracy can be improved and the variation in coupling loss can be improved.

The capillary 3 used for the pigtail in the present invention can be made of glass or resin in addition to zirconia or alumina ceramics. Although not shown, the connector used for the pigtail is an FC connector,
An SC connector, MU connector, LC connector, or the like is used, and signal light emitted from a laser diode (LD) (not shown) can be transmitted via the connector. The polarizer 1 used in the present invention includes, in addition to a polarizer that absorbs a polarization direction perpendicular to the transmission polarization direction, such as a type in which dielectric particles are included in a glass substrate or a dielectric laminate type, a polarized light such as a birefringent crystal. LD that separates and returns the reflected light
It can also be implemented with a polarizer that is shifted from the optical path.

The Faraday rotator 2 has Tb, Gd,
Bi-substituted garnet or YIG garnet to which Ho is added can be used.

FIG. 4 is a sectional view of an optical fiber pigtail with an optical isolator according to a fourth embodiment of the present invention.
The Faraday rotator 2 has a square hysteresis curve, and can be implemented by a garnet having a self-magnetic field.
In the case of a garnet having a rectangular hysteresis curve and having a self-magnetic field, the magnet 6 is not required, so that the number of parts and the number of steps can be reduced.

FIG. 4A shows a case where a so-called one-stage type optical isolator element 19 having two polarizers 1 and one Faraday rotator 1 is mounted. FIG. 4B shows a case where a so-called 1.5-stage optical isolator element 19 having three polarizers 1 and two Faraday rotators 2 is mounted. The incident side of the optical isolator element 19,
When the polarization transmission direction 8 of the exit side polarizer 1 is orthogonal, 2
The rotation directions of the two Faraday rotators 2 can be achieved by making the rotation directions of the two Faraday rotators 2 the same. Can be achieved by reversing the rotation direction.

FIG. 4C shows a case where a so-called two-stage optical isolator element 19 having four polarizers 1 and two Faraday rotators 2 is mounted. The control of the polarization transmission direction 8 between the incident side and the output side polarizer 1 of the optical isolator element 19 is the same as that of the 1.5-stage type.

FIG. 5 is a cross-sectional view for explaining the method of assembling the optical fiber pigtail with an optical isolator of the present invention and a diagram viewed from the direction of the incident side polarizer 1a. For optical coupling,
The polarization direction 12 of the LD outgoing light 18, the polarization transmission direction 8 of the incident side polarizer 1 a of the optical isolator element 19, the end surface inclination direction of the capillary 3, and the position of the marking unit 7 before and after the alignment of the LD module are shown.

First, an obliquely polished surface 9 and an unpolished surface 10 are formed on the end surface 3a of the capillary 3 holding the optical fiber 4,
The marking part 7 is formed on the outer peripheral surface of the ferrule 5 so as to be at a predetermined angle with respect to the inclination direction.

On the other hand, an optical isolator element 19 in which two polarizers 1a and 1b and one Faraday rotator 2 are integrated
A linear part 20 of at least one side set parallel to the polarization transmission direction 8 of the incident side polarizer 1a is formed on the outer peripheral side surface of the 9 and the unpolished surface 10 are arranged in parallel with the boundary 11.

Thus, the polarization direction 12 of the LD outgoing light 18 and the polarization transmission direction 8 of the incident side polarizer 1a of the optical isolator element 19 are changed with respect to the marking portion 7 on the outer peripheral portion of the ferrule 5 at the time of assembling the LD module. Since it is possible to dispose the optical axis C at a predetermined position, it is possible to eliminate the variation in the rotation (Zθ) alignment time of the optical axis C and to greatly reduce the alignment time. Furthermore, since the direction of inclination of the end face of the capillary 3 and the direction of polarization transmission 8 of the incident side polarizer 1a of the optical isolator element 19 can be accurately matched, the mounting accuracy is improved, and the variation in coupling loss can be improved. Was.

Here, a method of polishing the end face 3a of the capillary 3 will be described.

As shown in FIG. 6A, the inclination direction of the end face of the capillary 3 can be set to a predetermined direction in advance.
A flat part was provided as a marking part 7 on a part of the outer peripheral part of the ferrule 5. As shown in FIG. 6B, the end face of the capillary 3 is polished on the basis of the outer peripheral flat portion 7 of the ferrule 5, so that the polishing direction of the end surface of the capillary 3 and the outer peripheral flat portion 7 of the ferrule 5 have a fixed positional relationship.

In the arrangement shown in FIG. 6C, the inclination direction of the end face of the capillary 3 and the outer peripheral flat portion 7 of the ferrule 5 can always be set in the same direction. 11 between the surface and the unpolished surface 10
Is always orthogonal to the direction of inclination of the end face of the capillary 3 and is parallel to the outer peripheral flat portion 7 of the ferrule 5.

FIG. 7 shows another example of the fifth embodiment according to the present invention. FIG. 7A shows a case where a so-called 1.5-stage optical isolator element 19 having three polarizers 1 and two Faraday rotators 2 is mounted. The case where the polarization transmission directions of the polarizer 1 on the incident side and the exit side of the optical isolator element 19 are orthogonal to each other can be achieved by making the directions of applying the magnetic field to the two Faraday rotators 2 the same. When the polarization transmission directions of the side and emission side polarizers 1 are the same, it can be achieved by dividing the magnet 6 and reversing the direction in which the magnetic field is applied to the two Faraday rotators 2.

FIG. 7B shows a case where a so-called two-stage optical isolator element 19 having four polarizers 1 and two Faraday rotators 2 is mounted. The control of the polarization transmission direction of the optical isolator element 19 with respect to the incident side and the exit side polarizer 1 is the same as that of the 1.5-stage type.

All structures of the present invention except for the fourth embodiment of the present invention have a configuration in which the capillary 3 protrudes from the end of the ferrule 5, and the magnet 6 includes the protruding portion of the capillary 3 and is provided on the end of the ferrule 5. Fixed. At this time, the projection of the capillary 3 serves as a guide for the inner diameter of the magnet 6,
The magnet 6 serves as a mechanism for preventing the magnet 6 from protruding from the outer diameter of the ferrule 5.

[0045]

EXAMPLE Here, a sample prototype in the present invention was produced.

A polarizer 1 and a Faraday rotator 2 wafer, each of which includes a dielectric material such as a metal, are fixed to a glass substrate with an adhesive, and the assembly and another polarizer 1 are optically adjusted, and then fixed with an adhesive. Thus, a wafer for an optical isolator was manufactured. At this time, the polarizer 1a on the side where the LD emission light is incident
Are coated with an anti-air AR coating, and both sides of the light passing surface of the Faraday rotator 2 are coated with an adhesive AR coating.

The optical fiber pigtail is a metal ferrule 5
The capillary 3 is press-fitted and fixed, and the optical fiber 4 is inserted into the capillary 3 and fixed with an adhesive. The metal ferrule 5 is provided with a flat marking portion 7 on a part of the outer periphery.
The end face of the capillary 3 is obliquely polished at a surface including the optical fiber 4 at 8 degrees, and a boundary line 11 with the unpolished surface 10 is orthogonal to the inclination direction. The manufactured wafer was cut by dicing or the like so that the light passing surface side became a rectangle of 0.5 × 0.6 mm. The polarization transmission direction 8 of the incident side polarizer 1a of the manufactured optical isolator element 19 was set to be parallel to the short side.

The short side of the optical isolator element 19 was arranged parallel to the boundary 11 of the capillary 3 and fixed with an adhesive.
After fixing the optical isolator element 19 to the end face of the capillary 3, the capillary 3 was arranged so as to fit into the inner diameter of the cylindrical magnet 6, and the end face of the magnet 6 and the end face of the ferrule 5 were fixed with an adhesive. Evaluation of the characteristics of the sample according to the present invention showed that the insertion loss was 0.14 dB on average and the isolation was 4
The result was 5.7 dB, which sufficiently satisfied the desired standard.

Further, an optical fiber pigtail with an optical isolator of the present invention having a flat portion 7 as a marking on the outer periphery of the ferrule 5 and a product without the marking are assembled and aligned using an LD chip and a lens. And the alignment tact was compared. In the conventional example, the alignment time is about 5 minutes on average, whereas in the present invention, the tact time can be reduced to about 2 minutes or less, which is less than half.

[0050]

As described above, according to the present invention, an optical isolator element in which at least one polarizer and at least one Faraday rotator are integrated on an end face of a holder for holding an optical fiber, A magnet is arranged around the optical isolator element, and a marking portion for displaying the polarization transmission direction of the incident side or the output side polarizer of the optical isolator element is formed on the holder,
This eliminates variations in the optical axis rotation alignment time, making it possible to significantly reduce the alignment time.

Furthermore, since the direction of inclination of the end face of the holder and the direction of polarization transmission of the incident-side polarizer of the optical isolator element can be made to coincide with each other with high accuracy, the mounting accuracy can be improved and the variation in coupling loss can be improved. Was. Further, the use of a Faraday rotator having a rectangular hysteresis curve in the optical isolator element eliminates the need for a magnet, and has the effect of reducing the number of components.

[Brief description of the drawings]

FIGS. 1A to 1C are cross-sectional views of an optical fiber pigtail with an optical isolator according to a first embodiment of the present invention.

FIGS. 2A to 2C are cross-sectional views showing another embodiment of the present invention.

FIGS. 3A and 3B are diagrams showing various embodiments of the optical fiber pigtail with an optical isolator according to the present invention as viewed from the end face of the capillary.

FIGS. 4A and 4B are cross-sectional views showing another embodiment of the present invention.

FIG. 5 is a view for explaining a method of assembling the optical fiber pigtail with an optical isolator according to the present invention.

6 (a) to 6 (c) are views for explaining a method of assembling an optical fiber pigtail with an optical isolator according to the present invention.

FIGS. 7A and 7B are cross-sectional views showing another embodiment of the present invention.

FIG. 8 is a cross-sectional view of a conventional optical fiber pigtail with an optical isolator.

FIGS. 9A to 9C are a cross-sectional view of a conventional optical fiber pigtail with an optical isolator and a diagram showing a polarization direction of each element.

FIG. 10 is a cross-sectional view of a conventional polarization-dependent optical isolator.

FIG. 11 is a diagram showing the behavior of forward and backward polarized light in a polarization-dependent optical isolator.

[Explanation of symbols]

 1: Polarizer 1a: Incident side polarizer 1b: Exit side polarizer 2: Faraday rotator 3: Capillary 4: Optical fiber 5: Ferrule 6: Magnet 7: Marking section 8: Polarized light transmission direction 9: Capillary end face polishing section 10 : Capillary end face unpolished portion 11: Boundary line 12: Polarization direction of LD emission light 13: Polishing device 14: Isolator mounting jig 15: Holding fixture 16: LD 17: Lens 18: LD emission light 19: Optical isolator element 20: Linear part C: Optical axis

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H036 QA12 QA14 QA29 QA59 2H037 AA01 BA02 DA18 2H099 AA01 BA02 CA11 DA05

Claims (6)

[Claims] 1. An optical isolator element comprising at least one polarizer and at least one Faraday rotator integrated on an end face of a holder for holding an optical fiber, and a magnet is arranged around the optical isolator element. An optical fiber pigtail with an optical isolator, wherein a marking portion for indicating the polarization transmission direction of the incident-side or exit-side polarizer of the optical isolator element is formed on the holder. 2. An end face of the holder is inclined, and the direction of the inclination and the polarization transmission direction of the incident side or the exit side polarizer of the optical isolator element are set to a predetermined angle, and the holder is formed on the holder. 2. The optical fiber pigtail with an optical isolator according to claim 1, wherein the inclined direction between the marking part and the end face of the holder is set at a predetermined angle. 3. An optical isolator element having at least one polarizer and at least one Faraday rotator integrated on an end face of a holder for holding an optical fiber, and a magnet is arranged around the optical isolator element. The end face of the holder has an obliquely polished surface including an optical fiber and an unpolished surface, and one side of the optical isolator element is substantially parallel to a boundary between the obliquely polished surface and the unpolished surface, or An optical fiber pigtail with an optical isolator, which is vertically arranged. 4. The optical isolator element according to claim 1, wherein at least one side linear portion formed on the outer peripheral side surface is set at a predetermined angle with respect to the polarization transmission direction of the incident-side or exit-side polarizer. 3. An optical fiber pigtail with an optical isolator according to 3. 5. The optical fiber pigtail with an optical isolator according to claim 1, wherein the Faraday rotator in the optical isolator element is a garnet having a square hysteresis curve. 6. An end face of a holder for holding an optical fiber is formed as an inclined surface, and a marking portion is formed on the holder so as to be at a predetermined angle with respect to the inclination direction, and at least one polarizer and at least one polarizer are formed. A linear portion of at least one side set at a predetermined angle with respect to the polarization transmission direction of the incident-side or output-side polarizer is formed on the outer peripheral side surface of the optical isolator element in which the Faraday rotators are integrated. A method for assembling an optical fiber pigtail with an optical isolator, comprising the step of arranging the optical isolator element on the end face of the holder such that the angle is a predetermined angle with respect to the inclination direction of the end face of the holder.