JPH09311255A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfy a desired laser safety standard without complicating the optical module in terms of circuits or mechanisms, without increasing its cost and without degrading the characteristics necessary as the optical module. SOLUTION: This optical module includes a semiconductor laser 10, a lens 12, a holder 14 for both and a receptacle core 16 to be fitted with the ferrule of an optical plug to which the module is connected. The optical semiconductor laser and the optical fiber of the ferrule are optically coupled by a lens at the time of connection of the optical plug. The optical module is provided with such a step part 14c for removing the light not required to be coupled which forms a circular opening 18 on the side nearer the lens exit side than the part of the holder in contact with the lens around the optical axis. The optical module preferably satisfies 0.9<ϕ/(NA×L1 )<1.3 and L2 </2 when the diameter of the circular opening is defined as ϕ, the numerical aperture of the optical fiber as NA, the distance between the opening end on the lens side and the optical fiber as L2 and the distance between the lens end and the opening end on the lens side as L2 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module in which a semiconductor laser and an optical fiber are optically coupled with each other by a lens. More specifically, the lens emitting side of a holder holding the lens with respect to a contact portion with the lens. The present invention relates to an optical module in which a step portion having a circular opening is provided, and the unnecessary coupling light from the lens periphery is removed by the step portion. This optical module is useful as a light emitting device in, for example, an optical LAN.

[0002]

2. Description of the Related Art An optical module is a component for optically coupling a semiconductor light emitting element or a semiconductor light receiving element and an optical fiber, and is used in the field of optical communication and the like. For example, in a computer system that performs data communication, a semiconductor light emitting element module and a semiconductor light receiving element module are installed as a pair on a board. Such an optical module includes an optical semiconductor element (for example, a semiconductor light emitting element such as a semiconductor laser or a semiconductor light receiving element such as a photodiode), a lens, a holder for holding the optical semiconductor element or the lens, and an optical plug of a connection partner. And a receptacle core that holds the ferrule fitted and fixed to the holder, and has a structure in which an optical semiconductor element and an optical fiber of the ferrule are optically coupled via a lens when an optical plug is connected. .

In an optical module incorporating a semiconductor laser, when the optical fiber is pulled out from the optical module during operation, the light emitted from the semiconductor laser is emitted to the outside as it is. By the way, in the laser equipment, in order to ensure safety for the human body, laser safety standards are set according to the degree of danger with respect to the amount of light and the like. In the case of an optical module, it is desired to meet class 1. “Class 1” means that the MPE (maximum permissible exposure amount) value for the eye is not exceeded under any condition, the design is secured, and no special management is required.

In order to meet such a class 1 laser safety standard, an electronic shutter mechanism called an open fiber control has been developed. This is to electronically stop the driving of the semiconductor laser when the optical fiber is pulled out from the optical module. In addition, there is also a mechanical shutter mechanism which is devised so that the light emitted from the semiconductor laser does not leak from the optical module when the optical fiber is pulled out from the optical module (JP-A-3-132).
No. 708).

[0005]

When the laser output is higher than a certain level, it is necessary and effective to attach various shutter mechanisms that satisfy the above laser safety standards. However, in the case of a low-power laser, for example, the electronic shutter mechanism increases the number of necessary electronic components (IC, etc.), and the mechanical shutter mechanism increases the number of components, which makes assembly difficult, and in any case, the cost is low. It is also disadvantageous. Moreover, if a problem occurs with the shutter mechanism, we cannot meet the safety standards.
The simpler the device is, the less reliable it is.

The simplest and most reliable method is to keep the amount of light emitted from the laser within a range that meets the safety standard of laser device class 1. However, if the amount of light emitted from the laser is simply reduced, the characteristics of the optical module may deteriorate.

By the way, in this type of optical module, conventionally, a structure has been adopted in which a ferrule stopper is incorporated in the receptacle core to position the ferrule in the optical axis direction at the time of connection (for example, Japanese Patent Laid-Open No. 4-18190).
No. 4, etc.). The ferrule stopper is provided with a through hole smaller than the lens diameter so that the light beam can pass therethrough. Therefore, in principle, unnecessary light can be eliminated by making the hole diameter of the through hole located near the end face of the fiber sufficiently small. Is very small (about 100 μmφ), so it is necessary to accurately open the extremely small holes. In addition, it is necessary to perform alignment in order to correct the positional deviation in the direction perpendicular to the optical axis. Therefore, with such a structure, an optical module cannot be manufactured inexpensively and efficiently.

An object of the present invention is to meet desired laser safety standards without mechanically complicating the cost, increasing the cost, and deteriorating the characteristics required as an optical module. To provide a simple optical module.

[0009]

SUMMARY OF THE INVENTION The present invention comprises a semiconductor laser, a lens, a holder containing the lens, and a receptacle core which is fitted and held by a ferrule of an optical plug to be connected and fixed to the holder. An optical module having a structure in which the semiconductor laser and the optical fiber of the ferrule are optically coupled by a lens when the optical plug is connected.
Here, a feature of the present invention is that a step portion for removing unnecessary coupling light that forms a circular opening is provided on the lens emission side of the contact portion of the holder with the lens with the optical axis as the central axis.

The circular opening to be formed has a diameter of φ,
When the numerical aperture of the optical fiber is NA, the distance between the lens-side opening end and the optical fiber in the optical axis direction is L ₁ , and the distance between the lens end and the lens-side opening end in the optical axis direction is L ₂ , 0.9 < φ / (NA × L ₁ ) <1.3 and L ₂ <L
_It is desirable to set the size and position so as to satisfy 1/2.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Light emitted from a semiconductor laser is refracted by a lens and condensed on an end face of an optical fiber. However, at this time, some light that does not contribute to the coupling to the optical fiber, that is, coupling unnecessary light is also generated. This is due to the aberration of the lens itself and to the refraction / scattering due to the fixing material that wraps around the contact portion between the lens and the holder. When the optical fiber is pulled out from the optical module, not only the coupling light to the optical fiber but also the coupling unnecessary light is emitted from the receptacle core together. Therefore, if this coupling-unnecessary light can be removed (shielded), the total amount of emitted light will be reduced, so that the required amount of coupling light can be maintained while maintaining the required amount of coupling light in terms of the characteristics of the optical module, and it is possible to comply with the light amount restriction of the safety standard of laser device class 1. It will be possible. Then, there is no need to take special measures such as open fiber control. From this point of view, the present invention eliminates unnecessary coupling light by providing the holder with a step forming a circular opening, and achieves the intended purpose.

If a step portion that forms a circular opening is integrally formed on the lens exit side of the holder with respect to the contact with the lens, it is possible to block unnecessary coupling light that wraps around the lens at the step portion. By providing the circular opening near the lens, unnecessary ambient light can be removed in a state where the outgoing beam is expanded, and therefore, the tolerance of the opening size is increased and the holder is extremely easily manufactured. Actually, since this step portion is integrated with the holder and can be formed at the same time when the holder is formed, the number of parts does not increase and the processing cost does not increase.

[0013]

1 is a sectional view showing an embodiment of an optical module according to the present invention, and FIG. 2 is a perspective view of the optical module main body. This optical module includes a semiconductor laser 10
A ball lens 12, a holder 14 for holding the semiconductor laser 10 and the ball lens 12, and a receptacle core 16 into which a ferrule (not shown) of an optical plug to be connected is fitted.

The detailed structure of the holder 14 is shown in FIG. The holder 14 is a substantially cylindrical member made of, for example, stainless steel, and has a first step portion 14a for attaching the spherical lens 12 to the inner wall, a second step portion 14b for attaching the semiconductor laser, and a circular shape. This is a structure having a third step portion 14c that forms the opening 18. The feature of the present invention is that the third step portion 14c is provided. When the ball lens 12 is dropped inside the holder 14, the ball lens 12 is supported by the edge of the first step portion 14a. As a result, the center of the spherical lens 12 and the center axis (optical axis) of the holder 14 automatically coincide with each other. Next, a low-melting glass (for example, a melting point of about 365 ° C.) compacted into a ring shape is dropped between the ball lens 12 and the holder 14 on the first step 14 a. In this order, conversely, the low-melting-point glass molded into a ring shape may first be mounted, and then the spherical lens 12 may be dropped. Put this in the heating furnace 400
Heat treatment is performed at a temperature around ℃. The spherical lens 12 is fixed to the holder 14 by the low-melting-point glass 20 melted by this.

As shown in the figure, during the glass welding, a part of the low melting point glass which has been melted is part of the spherical lens 12 and the first step portion 14a.
It goes through the gap with the edge of and solidifies. Refraction or scattering of the incident light is caused by the wraparound glass, which causes the incident light to leak to the emission side of the spherical lens 12.

The semiconductor laser 10 is coupled to the holder 14 having the spherical lens 12 built therein. The base portion 10a of the package of the semiconductor laser 10 is connected to the second step portion 14b of the holder 14.
Position it by fitting it so that it presses against
Fix with adhesive or YAG laser welding.
Here, the mounting position of the semiconductor laser 10 is determined by the processing size of the holder 14, and the alignment in the optical axis direction is not performed.

The receptacle core 16 is a cylindrical integrally molded product made of stainless steel (for example, SUS304),
CVD (chemical vapor deposition) on at least the inner surface of the bore
The high hardness film 17 made of TiC or the like is formed to have a film thickness of about 1 to 10 μm by the method. This receptacle core 16
A ferrule stopper 22 is mounted on the proximal side of the bore.

The receptacle core 16 as described above is fixed to the holder 14 by YAG laser welding (the welding portion is indicated by a symbol W) in an aligned state. This is the optical module body shown in FIG. A plastic connector housing 24 is mounted on the outer peripheral side of the optical module main body, if necessary.

When an optical plug is connected to the optical module,
The ferrule of the optical plug fits into the bore of the receptacle core 16, and the plug frame of the optical plug fits and mechanically connects with the connector housing 24. In this state, optical axis alignment and coupling are achieved at the same time so that the emitted light from the semiconductor laser 10 is condensed by the spherical lens 12 and condensed and incident on the end face of the ferrule optical fiber.

Here, the third step portion 14c provided on the lens emission side of the contact portion of the holder 14 with the spherical lens 12 is
It has a function of removing (blocking) unnecessary light due to aberration of the spherical lens itself and unnecessary light due to refraction and scattering caused by the low-melting-point glass 20 wrapping around the contact portion between the spherical lens 12 and the holder 14. This is shown in FIG. As described above, the light emitted from the semiconductor laser 10 is refracted by the spherical lens 12 and condensed on the end face of the optical fiber.
However, such optical fiber coupled light (shown by the solid line)
Besides, unnecessary light is generated. It is due to the aberration of the spherical lens itself (shown by a broken line m) and due to refraction and scattering by the low melting point glass 20 used for glass welding (shown by a chain line n). When the optical fiber is pulled out from the optical module, there is a possibility that the coupling unnecessary light (m, n) is also emitted. However, these un-coupled lights are
Passes a point away from the center of the ball lens. Therefore, as described above, the spherical lens 1 of the holder 14 has the optical axis as the central axis.
A circular opening 1 is provided in the vicinity of the lens exit side with respect to the contact portion with 2.
If the stepped portion 14c forming 8 is provided on the entire circumference, unnecessary coupling light passing through the peripheral portion is blocked by this. Therefore, even if the optical fiber is pulled out, the unnecessary light for coupling is hardly emitted to the outside, and the emitted light is almost only the optical fiber coupled light.

In the present invention, the circular opening has an opening diameter of φ,
When the numerical aperture of the optical fiber is NA, the distance between the lens-side opening end and the optical fiber in the optical axis direction is L ₁ , and the distance between the lens end and the lens-side opening end in the optical axis direction is L ₂ , 0.9 < φ / (NA × L ₁ ) <1.3 and L ₂ <L
_It is desirable to set it so that the relationship of 1/2 is satisfied. The first equation is obtained from the graph shown in FIG. Fig. 5 shows
The relationship between the coupling efficiency of the optical fiber coupling light and the coupling efficiency of all the emitted light including the coupling unnecessary light with respect to / (NA × L ₁ ) is shown. The difference between the two represents the amount of unnecessary coupling light.
When the value of φ / (NA × L ₁ ) is 0.9 or less, the optical fiber coupling light is also blocked by the step portion, and conversely φ
When / (NA × L ₁ ) becomes large and becomes 1.7 or more, ambient light cannot be blocked. In practice, it is desirable to reduce the amount of unnecessary coupling light emitted and to reduce the optical fiber coupling light as much as possible. There are also cases where it is desired to cut unnecessary light even if the optical fiber coupled light is slightly reduced. Therefore, the value of φ / (NA × L ₁ ) is 0.9 to 0.9 as described above.
It would be desirable to set it within the range of 1.3.
More preferably, the value of φ / (NA × L ₁ ) is 1.0 to
It is to be set within the range of 1.3. In FIG. 5, in the region where φ / (NA × L ₁ ) is 1.1 or less, there is a difference in value between the coupling efficiency of all emitted light including unnecessary light and the coupling efficiency of optical fiber coupling light. The difference is due to the aperture shape (that is, the actual spot shape of the emitted light is not circular,
(Because it is generally elliptical), there is no particular problem. This difference can be further reduced by making the aperture shape an elliptical shape that matches the spot shape of the emitted light. However, in that case, since the elliptical opening is formed, the processing cost is increased, and in order to match the spot shape with the elliptical opening, alignment in the rotational direction is required.

Further, L ₂ <L _1/2 is set so that the position of the step portion for removing the unnecessary coupling light is set at the position near the end of the lens, not the position near the end face of the optical fiber. . This allows the diameter of the circular opening to be significantly increased,
The opening forming accuracy in the direction perpendicular to the optical axis does not need to be so strict, so that the opening can be formed easily at low cost. Further, this can reduce the tolerance for the eccentricity of the laser chip. The eccentricity of the laser chip in the semiconductor laser (deviation in the direction perpendicular to the optical axis when it is attached to the package) is allowed up to about ± 80 μm from the center position of the package in an actual product. When the laser emission optical axis deviates from the center of the lens, the light transmitted through the lens causes an angle deviation, and part of the light is blocked by the step for removing unnecessary coupling light, but the position where the circular opening is formed is near the lens edge. By setting to, it is possible to prevent a decrease in the amount of light coupled to the optical fiber as much as possible.
That is, even if the actual product in which the eccentricity of the laser chip is present to some extent is used as it is, the light emitted from the semiconductor laser can be coupled to the optical fiber.

In the above embodiment, the receptacle core is made of stainless steel as an integrally molded product, and at least the inner peripheral surface of the bore is formed with a high hardness film. However, a ceramic sleeve is provided in the receptacle core. It may be a structure in which is fitted. The lens may be not only a spherical lens but also a rod lens or the like. In the case of a rod lens, the exit end face of the lens is the contact area with the holder. In addition, various optical filter films, moisture-resistant protective films, and the like may be formed on the surface of the lens, especially on the incident side surface, if necessary.

[0024]

As described above, according to the present invention, the lens holding side of the lens holding side of the holder for holding the lens is closer to the lens emitting side than
Since the stepped portion is formed so as to form the circular opening, most of unnecessary light that does not contribute to the coupling to the optical fiber can be removed (shielded). As a result, it is possible to make an optical design that satisfies the laser safety standard (laser device class 1 or the like) while making maximum use of the amount of light incident on the optical fiber. Further, it is also possible to remove scattered light and the like generated due to deterioration with time of the fixing material for fixing the lens (such as devitrification). Therefore, according to the present invention, a complicated shutter mechanism such as open fiber control is not required, and the structure is simple, so that it is possible to design reliably and at low cost to satisfy a desired laser safety standard.

[Brief description of drawings]

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

FIG. 2 is a perspective view of the optical module body.

FIG. 3 is a detailed cross-sectional view showing an example of a holder used in the present invention.

FIG. 4 is a conceptual diagram showing the design of a circular opening according to the present invention.

FIG. 5 is a graph showing the relation of coupling efficiency with φ / (NA × L ₁ ).

[Explanation of symbols]

 10 semiconductor laser 12 spherical lens 14 holder 14c step for removing unnecessary light for coupling 16 receptacle core 18 circular opening 20 low melting point glass

Claims (2)

[Claims] 1. A semiconductor laser, a lens, a holder containing the lens, and a receptacle core fixed to the holder by fitting and holding a ferrule of an optical plug of a connection partner. In an optical module in which a semiconductor laser and an optical fiber of a ferrule are optically coupled by the lens, coupling such that a circular opening is formed on the lens emission side with respect to the contact point of the holder with the lens about the optical axis. An optical module having a step for removing unnecessary light. 2. The diameter of the circular opening is φ, the numerical aperture of the optical fiber is NA, the distance between the circular opening end on the lens side and the optical fiber in the optical axis direction is L ₁ , and the light at the lens end and the circular opening end on the lens side is When the axial distance is L ₂ , 0.9 <φ / (NA × L ₁ ) <1.3 and L ₂ <L
The optical module of claim 1 wherein a circular opening that satisfies _1/2.