JP2011158867A - Optical module for communication, and aspherical lens used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module for communication in which efficient coupling between a light emission part and an information transmission part is achieved and the airtightness of a sealed space surrounded by a stem for securing the environment resistance of a semiconductor laser, a holding member, and a glass spherical lens is enhanced, and cost can be reduced, and to provide an aspherical lens used for the optical module. <P>SOLUTION: The optical module includes: the glass lens to which a light signal from the light emission part is incident; the stem to which the light emission part is mounted; the holding member that is attached to the stem, surrounds the light emission part, and holds the glass lens; and a plastic aspherical lens that has a concave shape having the same curvature as the outer surface of the glass lens, and is attached so as to cover a part of the outer surface of the glass lens. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion module (optical module) that converts an electrical signal into an optical signal and an aspheric lens used therefor.

In optical communication, an electrical signal, which is information, is converted into an optical signal and introduced from the light emitting unit into an optical fiber, which is an information transmission unit. Optical fibers are excellent for long-distance transmission because optical signals undergo little degradation in information transmission. The transmitted optical signal is applied to the light receiving surface of the semiconductor light receiving element at the output end of the optical fiber, converted from the optical signal to an electrical signal, and transmits information.
An optical module is an optical component in which various optical semiconductor elements are incorporated, and includes an optical connector and an optical collimator, and is used in various fields.

  Specifically, it comprises an optical semiconductor element (for example, a semiconductor light emitting element such as a laser diode or a semiconductor light receiving element such as a photodiode) and a lens, and a receptacle core that fits and holds a ferrule of an optical plug of a connection partner, The optical semiconductor element and the ferrule optical fiber are optically coupled via a lens when the optical plug is connected.

  There are various types of optical modules, and one of them includes a light emitting unit, a lens, a stem, a holding member that is held by the lens and fixed to the stem, and an information transmission unit. In this embodiment, the light emitting section is spatially provided by being sealed with a lens, a stem, and a holding member.

  The lens used in the optical module for optical communication has the first role of coupling the light of the semiconductor laser, which is the light emitting part of the optical communication unit, to the optical fiber, which is the information transmission part, and the environmental resistance of the semiconductor laser. In order to ensure, it functions as a lens cap having a second role of airtightness in a sealed space surrounded by a stem and a holding member that holds the lens.

  Until now, a lens that functions as a lens cap has been configured using a glass spherical lens or a glass aspherical lens in order to fulfill the above role. Here, the lens cap formed of a glass ball lens can be manufactured at low cost because it is easy to process the lens, but the first role, the highly efficient coupling from the light emitting part to the information transmitting part, is It was not enough.

  On the other hand, the lens cap constituted by the glass aspherical lens has a good high-efficiency coupling from the light emitting unit to the information transmitting unit, which is the first role, but it costs a lot to manufacture the lens. There has been a problem that the price of the lens cap of the glass aspheric lens becomes more expensive than the cap of the spherical lens.

  In addition, plastic aspherical lenses can be manufactured at low cost, but the adhesive used to fix plastics and aspherical lenses is hygroscopic, ensuring airtightness in the sealed space, which is the second role. There was a problem.

FIG. 7 shows a configuration diagram of an optical module using a glass ball lens cap according to a related technique.
The optical module according to FIG. 7 includes a semiconductor laser 10 as a light emitting unit, a glass ball lens 11, a metal press can 15 as a holding member, a stem 16, a low melting point sealing glass 14, an optical fiber 13 as an information transmission unit, and a heat sink 18. The lead pin 17 is provided. Among these, the glass ball lens 11 and the metal press can 15 are bonded together by a low-melting point sealing glass 14 in order to hold the glass ball lens 11 and improve the airtightness of the sealed space.

  However, in the optical module according to FIG. 7, since the optical aberration of the glass ball lens is large, high-efficiency imaging cannot be obtained and the use is limited to applications where the coupling efficiency is low.

FIG. 8 shows a configuration diagram of an optical module using a glass aspheric lens cap according to a related technique.
The optical module according to FIG. 8 includes a semiconductor laser 10, a glass aspheric lens 23, a metal press can 15, a stem 16, a low melting point seal glass 14, an optical fiber 13, a heat sink 18, and lead pins 17. The optical module according to FIG. 8 is provided with a glass aspheric lens 23 in order to increase the coupling efficiency from the light emitting unit to the information transmission unit, and to fix the glass aspheric lens 23 and the metal press can 15. The low melting point sealing glass 14 is adhered.

  However, the optical module according to FIG. 8 has a problem that it cannot be manufactured at low cost because the manufacturing cost of the glass aspheric lens 23 is high.

FIG. 9 shows a configuration diagram of an optical module using a glass aspheric lens cap according to a related technique.
The optical module according to FIG. 9 includes a semiconductor laser 10, a glass aspheric lens 23, a metal cutting holder 24, a stem 16, an optical fiber 13, a heat sink 18, and a lead pin 17. Since the optical module according to FIG. 9 has high coupling efficiency from the light emitting unit to the information transmission unit, a glass aspheric lens 23 is disposed, and the glass aspheric lens 23 and the metal cutting holder 24 are directly joined. It has become.

  The optical module according to FIG. 9, like the optical module according to FIG. 8, has a problem that it cannot be manufactured at low cost because the manufacturing cost of the glass aspheric lens 23 is high.

  For example, Patent Document 1 describes an invention related to an optical subassembly including a photoelectric exchange module used for optical communication. The optical subassembly includes an optical receptacle member that receives a ferrule of an optical connector, and a ball lens. A photoelectric conversion module that transmits signal light to and receives signal light from the optical fiber, and is tilted with respect to the optical axis of the signal light on the optical path between the ball lens and the optical fiber. And a flat plate-shaped optical member, and an aberration correction member for correcting wavefront aberration caused by the ball lens and the optical member. According to the optical subassembly according to Patent Document 1, since spherical aberration and astigmatism can be suppressed by the phase difference correction unit formed integrally with the receptacle member, good optical characteristics can be obtained. is there.

  However, it is necessary to increase the number of parts because an aberration correction member and a member holding part are required, and to increase the precision of the part or to add a centering process to ensure the positional accuracy of the aberration correction member, which is costly. There was such a problem.

JP 2009-258320 A

  As described above, it is difficult for the lens cap used in the optical module according to the background art to efficiently couple the light of the light emitting unit of the optical communication unit to the optical fiber that is the information transmitting unit while reducing the manufacturing cost. In addition, there is a problem that it is difficult to improve the airtightness of the sealed space surrounded by the stem and the lens cap, which is required to ensure the environmental resistance of the light emitting portion.

  The present invention has been made to solve such a problem, and achieves high-efficiency coupling from the light emitting unit to the information transmission unit while reducing the cost, and also improves airtightness in a sealed space. An object of the present invention is to provide a communication optical module that can be used and an aspherical lens used therefor.

  An optical module for communication according to the present invention includes a glass lens on which an optical signal from a light emitting unit is incident, a stem on which the light emitting unit is mounted, and is attached to the stem, surrounds the light emitting unit, and includes the glass lens. A holding member to be held and a plastic aspherical lens having a concave shape having the same curvature as the outer surface of the glass lens and attached so as to cover a part of the outer surface of the glass lens.

  The plastic aspherical lens according to the present invention has a concave shape having the same curvature as the outer surface of the glass lens at the end of the holding member that surrounds the light emitting portion that transmits the signal light and holds the glass lens. It joins so that a part of outer surface may be covered.

  According to the present invention, low cost can be realized, high efficiency coupling from the light emitting part to the information transmission part is realized, and the environment of the semiconductor laser is ensured and surrounded by the stem, the holding member and the glass ball lens. In addition, it is possible to provide an optical module for communication and an aspherical lens used therefor that can improve the airtightness of the sealed space.

It is sectional drawing of the optical module which concerns on this invention. It is a figure which shows operation | movement of the optical module for communication based on this invention. It is the figure which cut the optical fiber at the predetermined angle. FIG. 6 is a layout diagram that constitutes an optical fiber condensing principal ray angle α. It is the figure which inclined the angle of the semiconductor laser by (alpha). It is a shape figure of the plastic aspherical lens 12 actually used. It is a block diagram of the optical module using the glass-made spherical lens cap concerning related technology. It is a block diagram of the optical module using the glass-made aspherical lens cap concerning related technology. It is a block diagram of the optical module using the glass-made aspherical lens cap concerning related technology.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Note that the description and drawings relating to the following embodiments are omitted and simplified as appropriate for the sake of clarity. In the drawings, components having the same configuration or function and corresponding parts are denoted by the same reference numerals, and description thereof will be omitted.

(Embodiment 1)
An optical module for communication according to Embodiment 1 of the present invention will be described with reference to FIG.
FIG. 1 is a sectional view of an optical module according to the present invention. As shown in FIG. 1, a semiconductor laser 10 that is an electro-optical conversion element (light emitting unit) is installed in a sealed space with a stem 16, a holding member 15, a glass ball lens 11, and a low melting point sealing glass 14. Has been. Here, in addition to the semiconductor laser 10, the light emitting unit may be a photodiode, a super luminescent diode, a light emitting diode, or the like.

  The stem 16 and the holding member 15 are joined using resistance welding, and the holding member 15 and the glass ball lens 11 are joined via a low melting point sealing glass 14. On the other hand, a plastic aspheric lens 12 is bonded to one side of the glass ball lens 11. One surface of the plastic aspherical lens 12 has a concave shape having the same curvature as that of the glass spherical lens 11. With such a shape, the glass ball lens 11 and the plastic ball lens 12 can be joined, and the holding member for the plastic aspheric lens 12 can be reduced.

  The glass ball lens 11 and the plastic aspherical lens 12 can be joined by directly molding the plastic aspherical lens 12 on the glass spherical lens 11, or by separately forming and manufacturing the plastic aspherical lens 12. It is possible to use a method of joining the two using an adhesive.

  Examples of the molding method include injection molding, press molding, and UV curable molding.

  In general, the refractive index nd of the optical plastic material used for the aspherical lens is 1.6 or less. On the other hand, some optical glass materials have a refractive index nd exceeding 2.1. When the refractive index of the lens is high, the light can be bent more, and the coupling in the semiconductor laser 10 having a larger FFP (Far Field Pattern) can be enhanced. Therefore, in the present invention, the glass material used for the glass ball lens 11 preferably has a refractive index nd of 1.7 or more.

  Optical plastic materials (resin materials) used for aspherical lenses are polymethyl methacrylate (PMMA), norbornene resin (COP), liquid crystal polymer (LCP), polyetheretherketone (PEE), polyetherimide (PEI), Examples include polyphenyl sulfide (PPS), polybutylene terephthalate (PBT), polyphenylene ether (PPE), polycarbonate (PC), polyamide, cyclic olefin copolymer (COC), polyolefin, polyester, and the like. From the viewpoint of hygroscopicity, norbornene resin (COP) is preferable.

  Further, since the wavelength of light for long-distance optical communication is 1.31 μm or 1.55 μm, the amount of light is attenuated if the plastic material is absorbed. Therefore, it is preferable to select a material having excellent hygroscopicity, that is, a material having low hygroscopic property. Specifically, a norbornene resin (COP) can be used. Furthermore, it is preferable to make the thickness of the plastic aspheric lens as thin as possible. The thickness of the plastic aspheric lens can be appropriately selected according to the type of plastic material.

An optical fiber 13 as an information transmission unit is disposed at the tip of the plastic aspheric lens 12.
The following description will be given for the case where an optical fiber is applied as the information transmission unit.

  The optical fiber 13 is fixed to the holding member 15 via the ferrule 22 and the sleeve 21. A method of fixing the holding member 15 and the sleeve 21 by an adhesive or a laser is preferable.

  The optical fiber 13 and the ferrule 22 can be cut obliquely. This is a device for preventing the reflected light from the end face of the optical fiber 13 from returning to the semiconductor laser 10. This point will be described later.

  By adopting such a configuration, it is possible to reduce the number of optical isolators that are optical elements. In the present invention, the plastic aspherical lens 12 is decentered to correspond to the obliquely cut optical fiber 13.

  The holding member 15 is preferably a metal press can or a metal cutting holder in order to ensure the airtightness of the sealed space covered with the stem 16, the holding member 15, the glass ball lens 11, and the low melting point sealing glass 14. . In addition, the type of metal is not particularly limited, and examples thereof include stainless steel, iron, and Ni alloy. Further, the metal surface may be subjected to Ni plating or gold plating.

Next, the operation method of the optical module for communication according to the present invention will be described with reference to the drawings.
FIG. 2 is a diagram showing the operation of the optical module for communication according to the present invention.

  2 includes a semiconductor laser 10, a glass ball lens 11, a plastic aspheric lens 12, a metal press can 15, a low melting point seal glass 14, a stem 16, a heat sink 18, an optical fiber 13, a lead pin 17, And a synthetic lens 26 composed of the glass ball lens 11 and the plastic aspheric lens 12.

  First, an electrical signal which is a communication signal is input to the lead pin 17 and is subjected to electro-optical conversion by the semiconductor laser 10. The converted signal light is divergent light, but when it passes through the glass ball lens 11 and the plastic aspheric lens 12, light is refracted and converted into condensed light. Light is introduced into the optical fiber 13 by arranging the end face of the optical fiber 13 at this condensing point.

  The optical signal introduced into the optical fiber 13 is transmitted through the core of the optical fiber 13. In particular, if the optical fiber 13 is a quartz single-mode fiber, the transmission distance that is a characteristic of the optical fiber 13 can be further increased.

  However, since there is a loss in the optical fiber 13, there is a limit to long-distance transmission. In order to transmit a longer distance, it is necessary to increase the energy introduced into the optical fiber 13 as much as possible. In order to increase the energy, there are methods of increasing the power of the semiconductor laser 10 and increasing the coupling efficiency described later.

  Here, the coupling efficiency refers to the ratio of the light emission energy of the semiconductor laser 10 and the light energy introduced into the optical fiber 13. In order to increase the coupling efficiency, the divergence angle of the semiconductor laser 10 at the time of design is an arbitrary condensing angle depending on the magnification of the synthetic lens 26 (the synthetic lens of the glass spherical lens 11 and the plastic aspherical lens 12) in the optical module. And the like.

  The magnification of the synthetic lens 26 is determined by the focal length of the synthetic lens 26 and the distance between the semiconductor laser 10 and the glass ball lens 11. By selecting the magnification at the time of design, the optical fiber 13 is a means for matching the optimum angle at which light can be introduced and the light collection angle. For example, if the numerical aperture of the semiconductor laser 10 is 0.4 and the numerical aperture of the optimum angle of the optical fiber 13 is 0.1, the magnification may be selected to be 4.

  As a means for increasing the coupling efficiency, there is a method in which the lens surface reduces the light passing through the lens by surface reflection, and a deposition film for preventing reflection at the emission wavelength of the semiconductor laser 10 to be used is attached to the lens surface. Further, by increasing the condensing ability of the synthetic lens 26, that is, the spherical lens 11 has a large spherical aberration and the condensing ability is not good, but the aspherical lens 12 has a shape that improves this condensing ability. As a result, the coupling efficiency can be increased.

  In the present invention, the light collecting ability is improved by using a plastic aspherical lens 12 shaped so as to cancel the aberration generated in the spherical lens 11. In addition, a method using wavefront aberration can be used as an optical aberration notation expressing the characteristics of the light collecting ability of the synthetic lens 26.

  The semiconductor laser 10 oscillates when its own emitted light returns to the light emitting section. Since this oscillation changes signal information of communication, it is necessary to eliminate return light as much as possible. In order to eliminate this return light, a method of inserting an optical isolator and a method of obliquely cutting the optical fiber 13 can be used.

FIG. 3 is a diagram in which the optical fiber is cut at a predetermined angle.
In FIG. 3, the end face oblique cut optical fiber 13b, the condensed light beam 27, the optical fiber condensing principal ray angle α, and the end face oblique cut angle β are shown.
When the oblique cut angle of the end face of the cut fiber 13b is β, the combined luminous flux has the best coupling efficiency at the optical fiber condensing principal ray angle α. This can be obtained from the following equation (1).

sin (α−β) = nsinβ (1)
(In the formula (1), α (degree) represents an optical fiber condensing principal ray angle, β (degree) represents an oblique cut angle, and n (λ) represents a refractive index.)

  For example, when the wavelength of the semiconductor laser 10 is 1.31 μm and the optical fiber 13 is a quartz optical single mode fiber, the necessary angle α can be obtained by calculation. The results are shown in Table 1.

FIG. 4 is a layout diagram for configuring the optical fiber condensing principal ray angle α.
In FIG. 4A, a semiconductor laser 10, a glass ball lens 11, a plastic aspheric lens 12, and an end-face flat optical fiber 13a are shown. 4B shows an end face oblique cut optical fiber 13b.

  The aspherical lens 12 made of plastic has a shape that provides optimum light condensing at α = 0 ° in FIG. When the oblique cut angle β of the optical fiber 13 to be used is determined, the optical axis is inclined with the center of the glass ball lens 11 as the rotation axis while maintaining the positional relationship between the plastic aspheric lens 12 and the semiconductor laser 10. At this time, the semiconductor laser 10 is also rotated together, but the optical fiber 13 is not rotated but shifted to the condensing point. FIG. 4B shows the structure configured in this way, and the best coupling efficiency can be obtained.

FIG. 5 is a diagram in which the angle of the semiconductor laser is inclined by α.
In FIG. 5, the semiconductor laser 10, the heat sink 18, the stem 16, the post 25, and the optical fiber condensing main light beam angle α are shown.
In order to incline the angle of the semiconductor laser by α, the post 25 on the stem 16 may be inclined by an angle of α.

FIG. 6 is a shape diagram of the plastic aspherical lens 12 actually used.
In FIG. 6, a plastic aspherical lens 12, a cemented spherical part 28, an aspherical part 29, an optical fiber focusing principal ray angle α, an inner diameter φ1, and an outer diameter φ2 are shown.

  The aspherical surface 29 is tilted at an angle α with the spherical surface of the cemented spherical surface 28 to be bonded to the glass ball lens as the rotation axis. It does not become an obstacle when covering. The aspherical surface 29 may be a rotationally symmetric shape, a non-rotation target shape, or a diffractive optical surface.

  In the communication optical module according to the present embodiment, the glass ball lens is used as the glass lens to be bonded to the aspheric lens, but a glass flat plate may be used.

The aspheric lens according to the present invention may be a diffractive optical element. This diffractive optical element (DOE) is an optical element that utilizes the diffraction phenomenon of light, and is an element in which a diffraction grating or a hologram is processed on the surface, and has the effect of improving condensing using the refraction effect by diffraction. can get.
The aspheric lens according to the present invention may be used as a light receiving module.

  In addition, this invention is not limited to embodiment shown above. Within the scope of the present invention, it is possible to change, add, or convert each element of the above-described embodiment to a content that can be easily considered by those skilled in the art.

10 Semiconductor Laser 11 Glass Ball Lens
12 Aspherical lenses made of plastic
13 Optical fiber
13a End face flat optical fiber
13b End face oblique cut optical fiber
14 Low melting point sealing glass
15 Holding member
16 stem
17 Lead pin
18 Heat sink
19 Monitor light receiving element
21 sleeve
22 Ferrule
23 Glass aspheric lens
24 Metal cutting holder
25 posts
26 Synthetic lens
27 Condensed light flux
28 Joint spherical surface
29 Aspheric surface
α Optical fiber focusing chief ray angle
β Diagonal cut angle on end face
n Optical fiber core refractive index

Claims (9)

A glass lens on which an optical signal from the light emitting unit is incident;
A stem on which the light emitting unit is mounted;
A holding member attached to the stem and surrounding the light emitting unit and holding the glass lens;
An optical module for communication comprising a plastic aspherical lens having a concave shape having the same curvature as the outer surface of the glass lens and attached to cover a part of the outer surface of the glass lens.   The optical module for communication according to claim 1, wherein the optical axes of the inner surface and the outer surface of the aspheric lens are decentered.   The optical module for communication according to claim 1 or 2, wherein the glass lens is a spherical lens.   The optical module for communication according to any one of claims 1 to 3, wherein the refractive index of the glass lens is 1.7 or more.   The optical module for communication according to any one of claims 1 to 4, wherein the aspheric lens is a diffractive optical element.   The optical module for communication according to any one of claims 1 to 5, wherein the aspheric lens is integrally molded and joined to the glass lens.   6. The communication optical module according to claim 1, wherein the aspherical lens is bonded and bonded to the glass lens.   8. The communication optical module according to claim 1, wherein the light emitting unit is a semiconductor laser.   A plastic that encloses a light emitting portion that transmits signal light and is bonded to an end portion of a holding member that holds a glass lens in a concave shape having the same curvature as the outer surface of the glass lens so as to cover a part of the outer surface of the glass lens. Made aspheric lens.

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