JPWO2014073305A1 - Optical communication module and optical communication lens - Google Patents

Abstract

Provided are an optical communication lens and an optical communication module using the same, which can reduce cost and are easy to manufacture, and can realize high-precision optical communication by suppressing focus position fluctuation even when a large environmental temperature change occurs. By using a diffractive structure to correct focus position fluctuations caused by temperature changes, 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 resin lens. The fluctuation can be canceled by changing the diffraction power of the light that has passed through the diffractive structure. That is, it is possible to suppress the focus position fluctuation when the environmental temperature change occurs, and to increase the optical coupling efficiency. Since it is desirable that the wavelength of light used in optical communication applications is substantially constant regardless of environmental changes, optical elements with small wavelength fluctuations due to temperature changes in the range shown in equation (2) may be used. desirable. When the value of the formula (1) exceeds the lower limit, for example, sufficient diffraction power can be obtained in a wide environmental temperature range of −40 ° C. to + 100 ° C. so that the fluctuation of the focus position occurring in the resin lens can be canceled. On the other hand, when the value of the formula (1) is below the upper limit, the diffraction pitch of the diffractive structure does not become too small, and it becomes easy to process because it is easy to manufacture. By balancing the diffraction power within a range that satisfies the expression (1), it is possible to provide a lens that secures manufacturability while suppressing variations in focus position. 0.6 ≦ dP / P ≦ 0.8 (1) 0 <dλ / dt ≦ 0.2 (2) where dP: diffraction power due to optical path difference providing structure [1 / mm] P: power of entire lens system [ 1 / mm] dλ / dt: wavelength variation due to temperature change of optical element

Description

  The present invention relates to a lens for optical communication and an optical communication module that 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, a lens for optical coupling is used for efficient 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 characteristics of the resin lens compared to the glass lens is that the refractive index change and the surface shape change with respect to the temperature change are relatively large. The inside of the module for optical communication may be exposed to a wide temperature environment of -40 ° C to + 100 ° C, but in the case of a general resin lens, the refractive index and surface shape change according to the environmental temperature change. As a result, the focus position varies. 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 a change in the refractive index and the surface shape of the lens, the coupling efficiency varies greatly. There are problems inherent in optical systems for optical communications. 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, the glass aspherical lens is more expensive than the resin, and there is a strong need to use a resin lens in order to reduce the cost of the optical communication module.

  As a countermeasure when using a resin lens, as shown in Patent Document 1, by adopting a configuration in which the distance between the optical element and the lens changes due to a temperature change, it is possible to suppress a focus position fluctuation due to an environmental temperature change. However, the effect is not sufficient to completely cancel the influence of the refractive index change and the surface shape change. That is, the effect amount is completely different, and the correction effect is weak because the fluctuation of the focus position due to the temperature change of the lens optical surface is dominant and the effect is greater.

JP 2011-003857 A Japanese Patent Laid-Open No. 11-274646

  On the other hand, as shown in Patent Document 2, a wavelength-dependent diffraction structure is added to a resin lens, and wavelength fluctuations (dλ / dT) due to the temperature of the semiconductor laser are generated. There is a technical idea of canceling the focus position fluctuation at the time of change. That is, the focus position fluctuation due to expansion / contraction due to temperature change of the resin lens and the focus position fluctuation due to the wavelength fluctuation of the semiconductor laser are usually in the opposite directions when adding a diffractive structure to the lens, and are directions to cancel each other. However, with the technique of Patent Document 2, the ratio of the diffraction power to the total power is small, and it is not always possible to sufficiently suppress the variation of the focus position over a wide temperature change of −40 ° C. to + 100 ° C.

  In addition, when a diffractive structure is added to the lens, the amount of focus position variation that contributes to focus position correction is proportional to the wavelength variation due to temperature change (dλ / dT), so the wavelength variation due to semiconductor laser temperature variation (dλ / dT) ) Is more effective in correcting focus position fluctuations due to temperature changes, and since cited reference 2 uses a laser having a large wavelength fluctuation (dλ / dT), focus position fluctuations due to semiconductor laser wavelength fluctuations. It is an invention that is easy to hold down. However, in optical communication, the wavelength of light is required to be substantially constant in consideration of applications such as wavelength multiplexing communication. In recent years, the performance of semiconductor lasers has improved, and there is a tendency for lasers with smaller wavelength fluctuations (dλ / dT) due to temperature changes to be demanded. For this reason, the invention of the cited document 2 has a problem that it becomes difficult to suppress the fluctuation of the focus position when a laser having a small wavelength fluctuation (dλ / dT) due to a temperature change is used. As described above, when a semiconductor laser capable of suppressing the wavelength variation (dλ / dT) to be small even when a large temperature change of −40 ° C. to + 100 ° C. occurs, the correction effect by the diffraction structure is reduced, and the temperature change The focus position fluctuation correction function cannot be fully used. On the other hand, it is conceivable to increase the diffraction power. However, if the diffraction power is increased, the diffraction structure becomes finer. Manufacturing difficulty such as processability and formability increases, and manufacturing errors are likely to occur. If manufacturing errors (such as sagging of the fine structure) occur in the diffractive structure of the molded lens, the diffraction efficiency decreases. When the diffraction pitch reaches the wavelength order, the diffraction efficiency decreases because it approaches the region of vector diffraction. As a result, 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 when a resin lens is used for optical communication.

  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 optical communication module according to claim 1 is an optical communication module having an optical element, an optical fiber, and a lens for optical communication that collects the optical element or a light beam emitted from the optical fiber,
It is a single lens formed of a resin material, and has an optical surface (S2 surface) on the optical fiber side and an optical surface (S1 surface) opposite to the optical fiber, and an optical surface (S2) on the optical fiber side. The optical path difference providing structure for correcting the focus position fluctuation caused by the temperature change is formed on the surface), and the following equation is satisfied.
0.6 ≦ dP / P ≦ 0.8 (1)
0 <dλ / dt ≦ 0.2 (2)
However,
dP: diffraction power [1 / mm] by the optical path difference providing structure
P: Power of the entire lens system [1 / mm]
dλ / dt: wavelength variation due to temperature change of the optical element (nm / ° C.)

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 and the surface shape change of the resin lens. It can be canceled by changing the diffraction power, that is, the focus position fluctuation when the environmental temperature change occurs can be suppressed, and the optical coupling efficiency can be increased. Here, since it is desirable that the wavelength of light used for optical communication applications is substantially constant regardless of environmental changes, an optical element having a small wavelength variation in a range such as the equation (2) may be used. Although it is desirable, since the amount of wavelength fluctuation is very small, it is difficult to correct the focus position fluctuation accompanying the temperature change when the optical path difference providing structure is formed on the optical surface of the lens. However, if the value of the expression (1) exceeds the lower limit, for example, sufficient diffraction power can be obtained in a wide environmental temperature range of −40 ° C. to + 100 ° C. so as to cancel the variation of the focus position generated in the resin lens. . On the other hand, when the value of the formula (1) is below the upper limit, the diffraction pitch of the diffractive structure does not become too small, and it becomes easy to process because it is easy to manufacture. Therefore, by balancing the diffraction power within a range satisfying the expression (1), it is possible to provide an optical communication module having a lens that secures manufacturability while suppressing variations in focus position. It is more preferable that the following expression is satisfied.
0.62 ≦ dP / P ≦ 0.77 (1 ′)

  As the “optical element”, for example, a semiconductor laser can be used. The “optical path difference providing structure” is, for example, a diffractive structure.

  In a general transmission optical system, the numerical aperture (NA) is relatively smaller on the optical fiber side than on the light source side, so that the light incident angle on the lens optical surface is small. Since the diffraction efficiency of light increases as the incident angle to the optical surface decreases, the diffraction efficiency can be increased by forming the optical path difference providing structure on the optical surface (S2 surface) on the optical fiber side.

In addition, the optical path difference providing structure in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure of the present invention is preferably a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. In addition, when the lens provided with the optical path difference providing structure is a single aspherical lens, the incident angle of the light flux to the coupling lens differs depending on the height from the optical axis. Each will be slightly different.
For example, when the lens is a single lens aspherical convex lens, even if it is an optical path difference providing structure that provides the same optical path difference, generally the distance from the optical axis tends to increase.

  In addition, the diffractive structure referred to in this specification is a general term for structures that have a step and have an action of converging or diverging a light beam by diffraction. For example, a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront. The diffractive structure preferably has a plurality of steps, and the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. In addition, when the lens provided with the diffractive structure is a single aspherical lens, the incident angle of the light flux to the lens differs depending on the height from the optical axis, and therefore the step amount of the diffractive structure is slightly different for each annular zone. Become. For example, when the lens is a single aspherical convex lens, even if it is a diffractive structure that generates diffracted light of the same diffraction order, generally, the distance from the optical axis tends to increase.

  By the way, it is preferable that the optical path difference providing structure has a plurality of concentric annular zones centered on the optical axis. The optical path difference providing structure can generally have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shapes including the optical axis are roughly classified into a blazed structure and a step structure.

  The optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated. As used herein, “unit shape is periodically repeated” naturally includes shapes in which the same shape is repeated in the same cycle. In addition, the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”. Suppose that

  The light beam emitted from the light source and passed through the optical path difference providing structure of the lens makes the X-order diffracted light amount larger than any other order diffracted light amount. The diffraction structure preferably uses first-order diffracted light with X = 1 in order to suppress a decrease in efficiency when the wavelength changes, but this is not restrictive.

  The optical path difference providing structure for correcting the focus position fluctuation caused by the temperature change is an optical path difference providing structure having a function of correcting the focus position of the lens for optical communication when the ambient temperature of the communication module changes. is there.

  An optical communication module according to a second aspect of the present invention is the optical communication module according to the first aspect, wherein the optical path difference providing structure is a lens for optical communication including a rotationally symmetric diffraction surface.

  By providing a rotationally symmetric diffractive surface, the refractive power can be dispersed on both surfaces of the lens, and the diffractive power generated by the diffractive structure can be used to correct focus position fluctuations due to environmental changes, and sine conditions can be corrected appropriately. It becomes. The “rotationally symmetric diffractive surface” means that the surface of the base to which the diffractive structure is provided is a spherical surface or an aspherical surface. In particular, it is possible to ensure on-axis performance / off-axis performance by making the surface forming the diffractive structure a rotationally symmetric aspherical surface. However, the optical surface on the optical fiber side may be a flat surface.

  The optical communication module according to claim 3 is the invention according to claim 1 or 2, wherein the absolute value of the radius of curvature of the optical surface on the optical fiber side is the absolute value of the radius of curvature of the optical surface on the side opposite to the optical fiber. It is a lens for optical communication larger than the value.

  By adding the optical path difference providing structure to the optical surface on the side of the optical fiber having the larger absolute value of the radius of curvature, the diffraction pitch of the optical path difference providing structure can be easily increased, and the manufacturability can be improved. . In addition, the light incident angle on the optical surface provided with the optical path difference providing structure is reduced, and a reduction in diffraction efficiency can be prevented.

An optical communication module according to a fourth aspect of the present invention is the optical communication module according to any one of the first to third aspects, wherein the optical communication module satisfies the following expression.
dP> 0.5 (3)

When the diffraction power of the optical path difference providing structure satisfies the expression (3), it is possible to maintain good optical coupling efficiency in a wide environmental temperature range of, for example, −40 ° C. to + 100 ° C. It is more preferable to satisfy the following formula.
0.5 <dP <0.7 (3 ′)

An optical communication module according to a fifth aspect is the optical communication module according to any one of the first to fourth aspects, wherein the optical communication module satisfies the following expression.
dP / M · P ≧ 0.2 (4)
However,
M: Optical system magnification of the lens

By satisfying the formula (4), the optical coupling efficiency can be kept good in a wide environmental temperature range of, for example, −40 ° C. to + 100 ° C. without causing an extreme decrease in the diffraction efficiency of the optical path difference providing structure. Become. It is more preferable to satisfy the following formula.
0.2 ≦ dP / M · P ≦ 0.25 (4 ′)

  The optical communication module according to claim 6 is the optical communication module according to any one of claims 1 to 5, wherein the lens is an optical communication lens formed integrally with a holder. To do.

  The lens is formed integrally with the holder. For example, the lens is preferably a cap type in which legs integrally formed from the same plastic material are connected. In particular, when the leg portion is fixed on the substrate, the distance between the optical element and the lens optical surface changes due to expansion / contraction of the resin leg portion due to temperature change, which is advantageous for defocus correction.

  An optical communication module according to a seventh aspect is characterized in that the optical communication lens according to any one of the first to sixth aspects is assembled to a substrate that supports the optical element.

  An optical communication lens according to an eighth aspect is mounted on the optical communication module according to any one of the first to seventh aspects.

  The lens is preferably a cap type in which legs integrally molded from the same plastic material are connected. For example, if the leg portion is fixed on the substrate, the distance between the optical element and the lens optical surface changes due to expansion / contraction of the resin leg portion due to temperature change, which is advantageous for defocus correction.

  Further, since the ratio of the diffraction power in the power of the entire lens system is large, it can be used for an optical element (for example, a semiconductor laser) having a small wavelength variation due to a change in operating temperature. The wavelength variation (dλ / dT) of the optical element is preferably 0.2 (nm / ° C.) or less. However, in order to obtain an appropriate correction effect, (dλ / dT) is preferably 0.01 (nm / ° C.) or more, and more preferably 0.1 or less.

  The lens is preferably used in the range of −40 ° C. to + 100 ° C. If there is an inflection point on the optical surface on the optical fiber side (the vicinity of the optical axis is convex and the periphery is concave, or vice versa), spherical aberration can be easily corrected even when high NA light is incident. ,desirable. Further, it is desirable that the focus fluctuation amount is suppressed to several tens of μm, for example, about 30 to 35 μm within a temperature range of −40 ° C. to + 100 ° C.

  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. 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. It is optical axis direction sectional drawing of the optical communication module 10 concerning another embodiment.

  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 about 0.1 (nm / ° C.).

  A lens 20 is disposed 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 a focus position variation caused by a temperature change. A rotationally symmetric 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 having an effective diameter φSF preferably has an inflection point. In the lens unit 22, the optical surface (S1 surface) opposite to the optical fiber having an effective diameter φSL (<φSF) is a convex spherical surface or aspherical surface that is rotationally symmetric. Furthermore, the lens unit 22 satisfies the following expression.
0.6 ≦ dP / P ≦ 0.8 (1)
0 <dλ / dt ≦ 0.2 (2)
However,
dP: diffraction power by diffraction structure [1 / mm]
P: Power of the entire lens system [1 / mm]
dλ / dt: wavelength variation due to temperature change of the laser chip 15 (nm / ° C.)

  A cylindrical holder 30 made of stainless steel 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.

  An 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 and the surface shape 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, even if the environmental temperature changes in the range of −40 ° C. to + 100 ° C., the optical coupling efficiency can be maintained. In the present embodiment, since the leg portion 21 is integrally formed of resin, there is also an effect that the focus position change is supplementarily canceled by the thermal expansion of the leg portion 21. Further, when the lens axial thickness is thicker, the longer the leg portion 21 is, the more the focus position variation due to the environmental variation can be canceled and further suppressed.

  FIG. 10 is a cross-sectional view in the optical axis direction of an optical communication module 10 according to another embodiment. In the present embodiment, the light receiving element 16 is arranged on the stem 12 via the mounting portion 13 instead of the laser chip. Other configurations are the same as those of the above-described embodiment.

  Explaining the operation of the present embodiment, the light beam emitted from the end face of the optical fiber FB is incident on the lens unit 22, but is diffracted by the diffractive surface of the optical surface S2 (when the optical surface S2 is a refracting surface, the refractive power). In addition, since the light is further refracted by the optical surface S1, the light is appropriately condensed on the light receiving surface of the light receiving element 16. Even if the focus position changes due to the refractive index change and the surface shape change caused by the temperature change of the lens unit 22, the wavelength change occurs in the light beam emitted from the optical fiber FB due to the same temperature change. Such a change in focus position can be canceled by the generated diffraction power change.

Hereinafter, examples suitable for the present embodiment will be described in comparison with comparative examples. In the following (including 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 each formed as an aspherical surface that is symmetric about the optical axis and is defined by mathematical formulas in which the coefficients shown in Table 1 are substituted into Formula 1.

  Here, X is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A2i 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} blazed wavelength (the wavelength at which the diffraction efficiency is highest), 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. Note that λB in the examples and comparative examples in this specification are all 1310 nm. The diffraction orders of the examples and comparative examples in this specification are all the first order.

(Comparative example)
FIG. 2 is a cross-sectional view of a lens LS according to a comparative example. Table 1 shows lens data of the comparative example. In addition, LD is a light emission part, FB is an end surface of an optical fiber, and S is a stop. 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. In addition, LD is a light emission part, FB is an end surface of an optical fiber, and S is a stop. 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 radius of curvature of the S2 surface is larger than that of the S1 surface), and the vicinity of the optical axis is convex and the periphery is concave. Have.

(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. In addition, LD is a light emission part, FB is an end surface of an optical fiber, and S is a stop. 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 (the radius of curvature of the S2 surface is larger than that of the S1 surface), and the vicinity of the optical axis is convex and the periphery is concave. Have.

(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. In addition, LD is a light emission part, FB is an end surface of an optical fiber, and S is a stop. 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 almost flat (the radius of curvature of the S2 surface is larger than that of the S1 surface), and the vicinity of the optical axis is convex and the periphery is concave. Have.

  In Table 5, each value of a comparative example and Examples 1-3 is shown collectively.

  For the lenses of the comparative example and Examples 1 to 3, the change in the optical coupling rate with respect to the temperature change was measured. Prior to this measurement, the position of the optical fiber was finely adjusted so that the fiber coupling efficiency was maximized. FIG. 6 is a diagram illustrating a change in the optical coupling rate with respect to a temperature change according to the comparative example, and FIGS. 7 to 9 are diagrams illustrating a change in the optical coupling rate with respect to the temperature change according to the first to third examples. In the case of the comparative example shown in FIG. 6, 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 to FIGS. 7-9, all of Examples 1-3 can suppress the fall of optical coupling efficiency 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 part 21b Tip 22 Lens part 30 Holder 31 Sleeve 32 Ferrule FB Optical fiber

Claims (8)

An optical communication module having an optical element, an optical fiber, and an optical communication lens that collects the optical element or a light beam emitted from the optical fiber,
The lens is a single lens made of a resin material, and has an optical surface (S2 surface) on the optical fiber side and an optical surface (S1 surface) on the side opposite to the optical fiber. An optical communication module characterized in that an optical path difference providing structure for correcting a focus position variation caused by a temperature change is formed on the surface (S2 surface) and satisfies the following expression.
0.6 ≦ dP / P ≦ 0.8 (1)
0 <dλ / dt ≦ 0.2 (2)
However,
dP: diffraction power [1 / mm] by the optical path difference providing structure
P: Power of the entire lens system [1 / mm]
dλ / dt: wavelength variation due to temperature change of the optical element (nm / ° C.)   The optical communication module according to claim 1, wherein the optical path difference providing structure is a lens including a rotationally symmetric diffraction surface on an optical axis.   3. The optical communication module according to claim 1, wherein an absolute value of a curvature radius of the optical surface on the optical fiber side is a lens larger than an absolute value of a curvature radius of the optical surface on the anti-optical fiber side. . The optical communication module according to claim 1, wherein the optical communication module is a lens satisfying the following formula.
dP> 0.5 (3) The optical communication module according to claim 1, wherein the optical communication module is a lens satisfying the following formula.
dP / M · P ≧ 0.2 (4)
However,
M: Optical system magnification of the lens   The optical communication module according to claim 1, wherein the lens is formed integrally with a holder.   The optical communication module according to claim 1, wherein the lens is assembled to a substrate that supports the optical element.   A lens for optical communication, which is mounted on the optical communication module according to claim 1.

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