WO2014050442A1

WO2014050442A1 - Optical communication lens and optical communication module

Info

Publication number: WO2014050442A1
Application number: PCT/JP2013/073495
Authority: WO
Inventors: 雄三中塚
Original assignee: コニカミノルタ株式会社
Priority date: 2012-09-28
Filing date: 2013-09-02
Publication date: 2014-04-03
Also published as: CN104662461A; JPWO2014050442A1

Abstract

An optical communication lens (20) for condensing light flux emitted from an optical element or an optical fiber is a single lens formed from a plastic material, and has an optical-fiber-side optical surface (S2 surface) having a diffraction structure (D) for correcting focus-position fluctuations caused by temperature changes, and an opposite-optical-fiber-side optical surface (S1 surface) which is convex. The optical communication lens (20) is characterized by satisfying these formulas: φSF>φSL (1); │SgFmax-SgFmin│<0.05 (2). Additionally, φSF: effective diameter (mm) of optical-fiber-side optical surface; φSL: effective diameter (mm) of opposite-optical-fiber-side optical surface; SgFmax: maximum sag (mm) of optical-fiber-side optical surface; SgFmin: minimum sag (mm) of optical-fiber-side optical surface.

Description

Optical communication lens and optical communication module

The present invention relates to a lens for optical communication and an optical communication module which are used for optical communication or the like and couple light from an optical element such as a semiconductor laser to an optical fiber or a light receiving element.

In an optical communication module, an optical coupling lens is used in order to efficiently perform optical coupling between a semiconductor laser or a light receiving element and an optical fiber. By the way, in the conventional lens for optical coupling, the structure which mainly supports a glass lens with a stainless steel leg part is widely used. However, a glass lens having an aspheric surface is generally expensive, and there is a problem that the cost is significantly increased. Therefore, is it possible to replace the plastic lens, which enables easy high-precision aspherical molding and mass production, with a glass lens and realize optical coupling between the semiconductor laser or light receiving element and the optical fiber? There is an attempt.

Here, one of the features of plastic lenses compared to glass lenses is that the refractive index change with respect to temperature change is relatively large. The inside of an optical communication module may be exposed to a wide range of temperatures from -40 ° C to + 100 ° C. However, in the case of a general plastic lens, the refractive index changes according to changes in the environmental temperature. The position will be changed. However, since the coupling efficiency of light to the end face of the optical fiber is determined by the transverse mode (beam diameter) of the light source, if the best focus position varies due to the change in the refractive index of the lens, the coupling efficiency varies greatly. There are problems inherent to the system. For this reason, there is a fact that glass lenses having a relatively small linear expansion coefficient have been heavily used. However, as described above, an aspheric lens made of glass is more expensive than plastic, and there is a strong need to use a plastic lens in order to reduce the cost of an optical communication module.

As a countermeasure when using a plastic lens, as described in Patent Document 1, by adopting a configuration in which the optical element-lens distance is changed by a temperature change, the focus position fluctuation due to the environmental temperature change is suppressed. However, the effect is not sufficient to completely cancel the influence of the refractive index change.

JP 2011-003857 A JP 2006-235293 A

In contrast, a wavelength-dependent diffraction structure is added to a plastic lens, and wavelength fluctuation (dλ / dT) due to the temperature of the semiconductor laser is used to cancel the focus position fluctuation when the environmental temperature changes. There is a technical idea to do. However, a larger wavelength fluctuation (dλ / dT) due to temperature change of the semiconductor laser is more effective in correcting focus position fluctuation due to temperature change, but in optical communication, it is assumed that the wavelength of light is substantially constant. Therefore, a general semiconductor laser used for optical communication tends to be used preferably having a small wavelength variation (dλ / dT) due to temperature change. Therefore, when a semiconductor laser having such a small wavelength variation (dλ / dT) due to a temperature change is used, the correction effect by the diffraction structure is reduced even when the wavelength changes because the wavelength variation is small. The focus position fluctuation correction function cannot be fully exhibited. That is, in a lens for optical communication, since the correction effect by the diffraction structure is small, a stronger diffraction power is required. On the other hand, in order to further improve the correction function based on the diffraction power, it can be considered to make the diffraction structure finer.
However, if the diffractive structure becomes finer, the manufacturing difficulty such as processability and moldability of the molding die increases, and manufacturing errors tend to occur. If a manufacturing error occurs in the diffractive structure of the molded lens, the diffraction efficiency decreases, the coupling efficiency of the lens decreases, and unnecessary light increases. Such a decrease in coupling efficiency and an increase in unnecessary light are obstacles in using a plastic lens for optical communication.

Patent Document 2 discloses a lens for optical communication in which a diffractive structure is formed on one optical surface. However, the diffractive structure of the lens of Patent Document 2 is used for transmitting light and receiving light. Utilizing the fact that the wavelengths of light are different from each other, the optical path is distributed by the diffractive structure, and the focus position fluctuation caused by the temperature change is not corrected.

The present invention has been made in view of such problems, and is capable of reducing costs and is easy to manufacture, and realizes highly accurate optical communication by suppressing focus position fluctuations even when a large environmental temperature change occurs. An object of the present invention is to provide a lens for optical communication and an optical communication module using the same.

The lens for optical communication according to claim 1 is a lens for optical communication that collects a light beam emitted from an optical element or an optical fiber,
The optical communication lens is a single lens formed of a plastic material, and an optical surface (S2 surface) on the optical fiber side having a diffractive structure for correcting a focus position variation caused by a temperature change; And an optical surface (S1 surface) on the side opposite to the optical fiber that is a convex surface, and satisfies the following expression.
φSF> φSL (1)
│SgFmax-SgFmin│ <0.05 (2)
However,
φSF: Effective diameter of the optical surface on the optical fiber side (mm)
φSL: Effective diameter of the optical surface on the side opposite to the optical fiber (mm)
SgFmax: Maximum sag amount (mm) of the optical surface on the optical fiber side
SgFmin: Minimum sag amount (mm) of the optical surface on the optical fiber side

According to the present invention, the diffractive structure for correcting the focus position fluctuation caused by the temperature change is used. Thus, the fact that the wavelength of the light incident on the lens changes according to temperature changes the focus position due to the refractive index change of the plastic lens, and changes the diffraction power of the light that has passed through the diffraction structure. Therefore, it is possible to cancel, that is, the focus position fluctuation when the environmental temperature change occurs can be suppressed, and the optical coupling efficiency can be increased. Further, the effective diameter of the optical surface on the optical fiber side is increased so that the optical surface on the anti-fiber side has a larger effective diameter so that the NA of the fiber-side light beam can be reduced. When it is smaller than NA, the power balance of each optical surface can be secured, and a design capable of securing sufficient on-axis performance can be performed. Further, by providing a diffractive structure on the optical surface on the side of the optical fiber having a large effective diameter, the diffraction pitch can be increased as compared with the case where diffraction is provided on the S1 surface, and the ease of manufacture can be improved. In addition, by satisfying the expression (2), the difference between the most protruding amount (SgFmax) and the most retracted amount (SgFmin) of the optical surface on the optical fiber side is reduced, and the optical surface providing the diffraction structure is flat. Close to. For example, when a diffractive structure is formed on a deep curved surface, when processing a mold having a transfer surface for forming the diffractive structure, the expected angle (inclination angle with respect to the axis) of the surrounding transfer surface is increased, resulting in tool interference. It becomes easier. On the other hand, by making the optical surface close to a plane as in the present invention, it becomes easy to form a diffractive structure, and the ease of manufacture can be improved. The “optical surface” is a surface in a range where a diffractive structure is formed through which a light beam emitted from the optical element or the optical fiber can pass. As the “optical element”, for example, a semiconductor laser can be used. Also, the effective diameter means a light beam that contributes to optical coupling from the optical element to the optical fiber, or a condensing light from the optical fiber into the optical element, among the light beams emitted from the optical element or the optical fiber. This is the diameter of the luminous flux passing through each optical surface. The sag amount represents the amount of displacement in the optical axis direction when a plane that passes through the intersection of the optical surface and the optical axis and is perpendicular to the optical axis is used as the reference plane. Is the maximum sag amount, and the difference between the intersection and the position closest to the light source is the minimum sag amount, and the range is the entire optical surface.

The optical communication lens according to claim 2 is characterized in that, in the invention according to claim 1, the diffraction structure includes a rotationally symmetric diffraction surface.

By providing a rotationally symmetric diffractive surface, the diffractive power by the diffractive structure can be used to correct focus position variation due to environmental changes.

According to a third aspect of the present invention, in the optical communication lens of the first or second aspect, the optical surface on the optical fiber side is formed by forming the diffractive structure on a spherical surface or an aspheric surface. To do.

Especially, it is possible to correct the sine condition by making the surface forming the diffractive structure a rotationally symmetric simple spherical surface. On the other hand, by making the surface forming the diffractive structure a rotationally symmetric aspherical surface, the on-axis performance can be secured and the sine condition can be corrected better, and the off-axis performance can be sufficiently secured. However, the optical surface on the optical fiber side may be a flat surface.

According to a fourth aspect of the present invention, in the optical communication lens according to the third aspect, the optical surface on the optical fiber side has an inflection point.

This makes it possible to ensure higher on-axis performance / off-axis performance. The “inflection point” is the direction of the tangent line drawn on the optical surface when taking a cross section in the optical axis direction of the lens, depending on the position, from the positive direction to the negative direction, or vice versa, across the optical axis orthogonal direction. When changing, it means a position facing in the direction perpendicular to the optical axis.

The optical communication lens according to claim 5 is characterized in that, in the invention according to

claim

3 or 4, Δsag on the optical surface on the optical fiber side has an inflection point.

This makes it possible to ensure higher on-axis performance / off-axis performance. Δsag refers to the rate of change of the sag amount on the optical surface.

The lens for optical communication according to claim 6 is the invention according to any one of claims 1 to 5, wherein the lens is used in a range of −40 ° C. to + 100 ° C.

The lens of the present invention can sufficiently suppress focus position fluctuations even when used in such a wide temperature environment.

The optical communication lens according to claim 7 is the optical communication lens according to any one of claims 1 to 6, wherein the wavelength variation (dλ / dT) of the optical element is 0 <(dλ / dT) <0. 2 (nm / ° C.).

The wavelength variation (dλ / dT) of the optical element for optical communication is often 0 <(dλ / dT) <0.2 (nm / ° C.). Under this condition, the focus position variation caused by the temperature change is not observed. The effect of correction by the diffractive structure is small. Therefore, since the diffractive structure tends to become finer in order to enhance the correction function, the lens of the present invention is particularly suitable.

The optical communication lens according to claim 8 is the invention according to any one of claims 1 to 7, wherein the lens condenses the light beam emitted from the optical element on the end face of the optical fiber. And

Because the area of the end face of the optical fiber is small, fluctuations in the focus position will immediately affect the decrease in optical coupling efficiency. Therefore, it is preferable that the lens of the present invention having a small focus position fluctuation is used for condensing the light beam emitted from the optical element on the end face of the optical fiber. However, the light beam emitted from the optical fiber may be used for condensing the light receiving element.

An optical communication module according to claim 9 is characterized in that the optical communication lens according to any one of claims 1 to 8 is assembled to a substrate that supports an optical element.

According to the present invention, a lens for optical communication capable of reducing costs and realizing high-accuracy optical communication by suppressing focus position fluctuations even when a large environmental temperature change occurs, and cost can be reduced, and light using the same. A communication module can be provided.

1 is a cross-sectional view in the optical axis direction of an optical communication module 10 according to the present embodiment. It is sectional drawing of the lens concerning a comparative example. 1 is a cross-sectional view of a lens according to Example 1. FIG. 6 is a cross-sectional view of a lens according to Example 2. FIG. 6 is a cross-sectional view of a lens according to Example 3. FIG. In the comparative example and Examples 1 to 3, the horizontal axis represents the height from the optical axis, and the vertical axis represents Δsag. It is a figure which shows the optical coupling rate change by the temperature change in a comparative example. It is a figure which shows the optical coupling rate change by the temperature change in Example 1. FIG. It is a figure which shows the optical coupling factor change by the temperature change in Example 2. FIG. It is a figure which shows the optical coupling rate change by the temperature change in Example 3. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view in the optical axis direction of an optical communication module 10 according to the present embodiment. In the optical communication module 10, a temperature change can occur in the range of −40 ° C. to + 100 ° C. A chip mounting portion 13 is attached to the center of a disk-shaped stem 12 having rod-shaped terminals 11 for feeding power, and a laser chip 15 as a light emitting element is attached to a side surface of the chip mounting portion 13 via a heat sink 14. Yes. The laser chip 15 is connected to the terminal 11 via a wiring (not shown), and the wavelength variation (dλ / dT) is 0 <(dλ / dT) <0.2 (nm / ° C.).

The lens 20 is arranged so as to cover the outside of the laser chip 15. The lens 20 is made of plastic, and is integrally formed from a substantially cylindrical leg portion 21 and a lens portion 22 provided at an end portion of the leg portion 21. The lens 20 is attached to the stem (substrate that supports the optical element) 12 by bonding the tip 21b of the leg 21 to the stem 12. The tip 21b of the leg 21 is an attachment reference plane. Further, the lens 20 may be fixed to the stem 12 with a separate holder without providing a leg portion.

The lens unit 22 has an optical surface (S2 surface) on the optical fiber side that is a rotationally symmetrical convex or concave spherical surface or aspherical surface (however, it may be a flat surface), and is used to correct focus position fluctuations caused by temperature changes. A diffraction structure D is formed. The diffractive structure D shown exaggerated in FIG. 1 has a plurality of ring-shaped shapes around the optical axis, includes a diffractive surface, and has a diffraction pitch of 3 μm or more. The optical surface (S2 surface) on the optical fiber side preferably has an inflection point. In the lens unit 22, the optical surface (S1 surface) on the side opposite to the optical fiber is a convex spherical surface or aspherical surface that is rotationally symmetric. Furthermore, the lens unit 22 satisfies the following expression.
φSF> φSL (1)
│SgFmax-SgFmin│ <0.05 (2)
However,
φSF: Effective diameter (mm) of the optical surface S2 on the optical fiber side
φSL: Effective diameter (mm) of the optical surface S1 on the side opposite to the optical fiber
SgFmax: Maximum sag amount (mm) of the optical surface S2 on the optical fiber side
SgFmin: Minimum sag amount (mm) of the optical surface S1 on the optical fiber side

A cylindrical stainless steel holder 30 is attached to the outside of the lens 20 in the direction orthogonal to the optical axis so as to be welded to the stem 12 with a gap. A cylindrical sleeve 31 having a smaller diameter is fixed to the tip of the holder 30, and a ferrule 32 into which the optical fiber FB is inserted is inserted therein. The end of the optical fiber FB faces the lens unit 22. ing.

The operation of the optical communication module 10 of the present embodiment will be described. When power is supplied through the terminal 11, the laser chip 15 emits light, and the emitted light beam enters the lens unit 22, but is refracted by the optical surface S1, and further diffracted by the diffraction surface of the optical surface S2. When the optical surface S2 is a refracting surface, refraction power is added, and this action causes light to be condensed on the end surface of the optical fiber FB and then propagated through the optical fiber FB. Here, when a temperature change occurs in the optical communication module 10, a wavelength change occurs in the light emitted from the laser chip 15. On the other hand, the focus position fluctuation is caused by the refractive index change caused by the temperature change of the lens unit 22, but the focus position fluctuation can be canceled by the diffraction power change caused by the wavelength change of the incident light. Therefore, the optical coupling efficiency can be maintained even when the environmental temperature changes in the range of −40 ° C. to + 100 ° C. In the present embodiment, since the leg portion 21 is integrally formed of plastic, there is also an effect that the focus position change is canceled by the thermal expansion of the leg portion 21 in an auxiliary manner.

Hereinafter, examples suitable for the present embodiment will be described in comparison with comparative examples. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) may be expressed using E (for example, 2.5 × E−3). Further, the optical surfaces (S1 surface, S2 surface) of the lens are formed as aspherical surfaces that are axisymmetric about the optical axis and are defined by mathematical formulas obtained by substituting the coefficients shown in Table 1 into Formula 1.

Here, X is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A 2i is an aspherical coefficient, h is a height from the optical axis, and r is a paraxial radius of curvature.

Further, in the case of the embodiment using the diffractive structure, the optical path difference given to the light flux of the light source wavelength by the diffractive structure is defined by an equation obtained by substituting the coefficient C ₁ shown in the formula 2 for the optical path difference function. The

Where λ _{B is the} wavelength used, h is the distance from the optical axis in the direction perpendicular to the optical axis, and C _{1 is the} optical path difference function coefficient.

(Comparative example)
FIG. 2 is a cross-sectional view of a lens LS according to a comparative example. Table 1 shows the lens data of the comparative example. Note that the optical path difference function coefficient C _{1 of} the comparative example is −0.175. LD is a light emitting part, and FB is an end face of the optical fiber. The lens LS has a convex aspheric surface on the S1 and S2 surfaces, and a diffractive structure is provided on the S2 surface. The effective diameter φSL of the S1 surface is 1.205 mm, and the effective diameter φSF of the S2 surface is 0.821 mm. As shown in FIG. 2, in the comparative example, the radius of curvature of the S2 surface is smaller than that of the S1 surface.

(Example 1)
FIG. 3 is a cross-sectional view of the lens LS according to the first embodiment. Table 2 shows lens data of Example 1. Note that the optical path difference function coefficient C _{1 of} Example 1 is −0.285. LD is a light emitting part, and FB is an end face of the optical fiber. The lens LS has a convex aspheric surface on the S1 and S2 surfaces, and a diffractive structure is provided on the S2 surface. In Example 1, the effective diameter φSL of the S1 surface is 1.345 mm, and the effective diameter φSF of the S2 surface is 0.999 mm. As shown in FIG. 3, in Example 1, the S2 surface is nearly flat, the vicinity of the optical axis is convex and the periphery is concave, that is, has an inflection point.

(Example 2)
FIG. 4 is a cross-sectional view of the lens LS according to the second embodiment. Table 3 shows lens data of Example 2. Note that the optical path difference function coefficient C _{1 in} Example 2 is −0.306. LD is a light emitting part, and FB is an end face of the optical fiber. The lens LS has a convex aspheric surface on the S1 and S2 surfaces, and a diffractive structure is provided on the S2 surface. In Example 2, the effective diameter φSL of the S1 surface is 1.331 mm, and the effective diameter φSF of the S2 surface is 1.003 mm. As shown in FIG. 4, in Example 2, the S2 surface is nearly flat, and the vicinity of the optical axis is convex and the periphery is concave, that is, has an inflection point.

(Example 3)
FIG. 5 is a cross-sectional view of the lens LS according to the third embodiment. Table 4 shows lens data of Example 3. Note that the optical path difference function coefficient C _{1 of} Example 3 is −0.337. LD is a light emitting part, and FB is an end face of the optical fiber. The lens LS has a convex aspheric surface on the S1 and S2 surfaces, and a diffractive structure is provided on the S2 surface. In Example 3, the effective diameter φSL of the S1 surface is 1.314 mm, and the effective diameter φSF of the S2 surface is 1.008 mm. As shown in FIG. 5, in Example 3, the S2 surface is nearly flat, and the vicinity of the optical axis is convex and the periphery is concave, that is, has an inflection point.

Table 5 summarizes the values of | SgFmax−SgFmin | in the comparative example and Examples 1 to 3. In the comparative example, the position of SgFmax is on the axis, and the position of SgFmin is the outer edge of the optical surface. On the other hand, in Examples 1 to 3, the position of SgFmax is the outer edge of the optical surface, and the position of SgFmin is the position of the inflection point.

FIG. 6 is a diagram showing the height from the optical axis on the horizontal axis and Δsag on the vertical axis in the comparative example and Examples 1 to 3. As is clear from FIG. 6, Δsag of the comparative example monotonically becomes negative as it goes away from the optical axis and does not have an inflection point. However, Δsag of Examples 1 to 3 goes negative as it goes away from the optical axis. Then it goes positive, so it has an inflection point.

FIG. 7 is a diagram showing a change in the optical coupling rate with respect to a temperature change according to the comparative example, and FIGS. 8 to 10 are diagrams showing a change in the optical coupling rate with respect to the temperature change according to the comparative example. In the case of the comparative example shown in FIG. 7, it can be seen that when the environmental temperature increases from room temperature (20 ° C.) to + 100 ° C., the optical coupling efficiency decreases by nearly 30%. On the other hand, as shown in FIGS. 8 to 10, any of Examples 1 to 3 can suppress the decrease in optical coupling efficiency to within 10%. In particular, Example 3 has almost no decrease in optical coupling efficiency and has optical performance comparable to a glass lens.

The present invention is not limited to the embodiments and examples described in the specification, and includes other examples and modifications based on the embodiments, examples, and technical ideas described in the present specification. It will be apparent to those skilled in the art. For example, the lens of the present invention may be used to collect light emitted from an optical fiber on a light receiving element.

DESCRIPTION OF SYMBOLS 10 Optical communication module 11 Terminal 12 Stem 13 Chip mounting part 14 Heat sink 15 Laser chip 20 Lens 21 Leg 21b Tip 22 Lens part 30 Holder 31 Sleeve 32 Ferrule FB Optical fiber

Claims

A lens for optical communication that collects a light beam emitted from an optical element or an optical fiber,
The optical communication lens is a single lens formed of a plastic material, and an optical surface (S2 surface) on the optical fiber side having a diffractive structure for correcting a focus position variation caused by a temperature change; An optical communication lens having a convex anti-optical fiber side optical surface (S1 surface) and satisfying the following expression:
φSF> φSL (1)
│SgFmax-SgFmin│ <0.05 (2)
However,
φSF: Effective diameter of the optical surface on the optical fiber side (mm)
φSL: Effective diameter of the optical surface on the side opposite to the optical fiber (mm)
SgFmax: Maximum sag amount (mm) of the optical surface on the optical fiber side
SgFmin: Minimum sag amount (mm) of the optical surface on the optical fiber side
2. The lens for optical communication according to claim 1, wherein the diffractive structure includes a rotationally symmetric diffractive surface.
3. The optical communication lens according to claim 1, wherein the optical surface on the optical fiber side is formed by forming the diffractive structure on a spherical surface or an aspherical surface.
4. The lens for optical communication according to claim 3, wherein the optical surface on the optical fiber side has an inflection point.
The optical communication lens according to claim 3 or 4, wherein Δsag on the optical surface on the optical fiber side has an inflection point.
6. The lens for optical communication according to claim 1, wherein the lens is used in a range of −40 ° C. to + 100 ° C.
The optical communication according to any one of claims 1 to 6, wherein a wavelength variation (dλ / dT) of the optical element is 0 <(dλ / dT) <0.2 (nm / ° C.). Lens.
The optical communication lens according to any one of claims 1 to 7, wherein the lens condenses a light beam emitted from the optical element on an end face of the optical fiber.
9. An optical communication module comprising: the optical communication lens according to claim 1 assembled on a substrate that supports an optical element.