CN103503253B - Optical communication lenses and semiconductor modules - Google Patents

Abstract

Provided are a lens for optical communication and a semiconductor module using the same, wherein the semiconductor module is provided in a compact module, and variation in coupling efficiency can be suppressed by further suppressing the effective NA to a small value. Since the diffraction structure DS is provided only on one surface OF the optical coupling lens CL, the diffraction pitch is narrowed as a whole, and at the point where the optical coupling lens section CL converges on the end surface OF the optical fiber OF, the light quantity at the peripheral portion becomes lower than the light quantity passing through the vicinity OF the optical axis OF the lens, so that the point becomes thick and the effective NA increases. This reduces the variation in coupling efficiency when a temperature change occurs.

Description

Optical communication lenses and semiconductor modules

technical field

The present invention relates to an optical communication lens and a semiconductor module for coupling laser light from a semiconductor laser to an optical fiber, which are used in optical communication or the like.

Background technique

In optical communication and the like, efficient coupling between a semiconductor laser or a light receiving element and an optical fiber is required. Therefore, an optical coupling lens is used to condense the light beam from the semiconductor laser. However, glass lenses are mainly used in conventional optical coupling lenses, but glass lenses having aspherical surfaces are generally expensive, causing a problem of high cost. Therefore, an optical coupling lens made of plastic that is easy to form a high-precision aspheric surface and can be mass-produced has been developed. However, plastic has a larger coefficient of thermal expansion than glass, and there is a problem that the refractive index of the plastic material changes with temperature. Therefore, if a plastic lens is used, when the distance between the semiconductor laser and the lens is fixed, the coupling efficiency decreases because the focal distance, that is, the imaging position in the fiber direction changes according to changes in the ambient temperature. In this regard, the use of an actuator that moves the lens in the direction of the optical axis is also considered, but there are still problems in the increase in cost due to the increase in the size of the movable part, and how to supply power.

In contrast, Patent Document 1 discloses a semiconductor module for optical communication in which a diffraction structure is provided on both surfaces of a plastic lens. According to the technique of Patent Document 1, by providing a diffraction structure on both surfaces of a plastic lens, it is possible to suppress the phenomenon that the diffraction pitch becomes too small, and to facilitate lens molding.

In addition, in Patent Document 2, by providing an embossed diffraction structure on one surface of a plastic lens, it is realized that the distribution of diffraction efficiency from the center to the periphery of the lens is suppressed, and the focus position variation due to temperature is suppressed.

Patent Document 1: Japanese Patent Application Laid-Open No. 11-274646

Patent Document 2: International Publication No. 00/17691 Pamphlet

However, one of the problems with the lens of Patent Document 1 is that, as a result of using a diffractive structure on two surfaces, the errors in the diffraction shapes of the respective surfaces have an cumulative effect, and unnecessary diffracted light and the like are generated, and manufacturing errors tend to occur on the contrary. , is not ideal. In addition, the problem of the lens in Patent Document 2 is that since it has an embossed diffraction structure, the diffraction efficiency is low, so the coupling efficiency to the optical fiber is also low, and unnecessary diffracted light often occurs, because pinholes, etc. The need to block unwanted beams is not ideal for use.

Contents of the invention

The present invention has been made in view of the above problems, and an object of the present invention is to provide a compact semiconductor module that can suppress fluctuations in coupling efficiency by suppressing sensitivity to temperature changes and the like in spite of a simple structure. A lens for optical communication and a semiconductor module using the lens.

The lens for optical communication according to claim 1 is a lens for optical communication that condenses a beam of wavelength λ emitted from a semiconductor laser, and is characterized in that the above-mentioned lens is made of plastic, and the above-mentioned lens is only on 1 of the optical surface. Each surface forms an optical path difference imparting structure that suppresses a change in the focal point position when the temperature changes. The above-mentioned optical path difference imparting structure includes a plurality of annular zones centered on the optical axis of the above-mentioned lens, and is cut by a plane passing through the optical axis of the above-mentioned lens. The cross-sectional shape of the annular zone is a blazed shape, and the pupil transmittance distribution of the light beam passing through the above-mentioned lens satisfies the conditional expression (1),

0.5≤T1/T0≤0.85 (1),

Here, T0: the transmittance near the optical axis of the above-mentioned lens, and T1: the transmittance around the periphery of the above-mentioned lens.

The term "near the optical axis" is preferably in the range of 0 to 0.05 when the optical axis is set to 0 and the outer periphery of the lens optical surface is set to 1, and the so-called "periphery" is preferably in the range of 0.95 to 1.

As a result of intensive studies, the present inventors have found that the diffraction efficiency can be improved by using a blazed optical path difference providing structure, and that the change in coupling efficiency can be suppressed by providing the optical path difference providing structure on only one of the optical surfaces. First, compared with the embossed diffractive structure provided in the lens of Patent Document 2, the blazed diffractive structure has the advantage of less unnecessary diffracted light and higher diffraction efficiency. That is, in the optical path difference providing structure of the blazed shape, the influence of shadows is particularly likely to occur, and it is easy to control the diffraction efficiency by controlling the steps between the annular zones.

Furthermore, for example, in Patent Document 1, diffractive structures are provided on both surfaces of the lens in order to increase the diffractive pitch. On the other hand, the present inventors made a bold attempt to narrow the diffraction pitch by providing an optical path difference imparting structure only on one surface of the lens. If the diffraction pitch is narrowed, as in the conditional expression (1), especially in the peripheral portion of the lens, the influence of the shadow of the light beam increases due to the combination with the refractive surface. This influence will be described.

Referring to FIG. 1 , an example in which a blazed diffraction structure is formed on a lens will be described as an optical path difference providing structure. FIG. 1( a ) is an enlarged cross-sectional view of a lens provided with a diffractive structure on the semiconductor laser side, and FIG. 1( b ) is an enlarged cross-sectional view of a lens provided with a diffractive structure on the semiconductor laser side. In FIG. 1 , the annular belt-shaped diffractive structure DS has a step surface ST facing the unillustrated optical axis (lower in FIG. 1 ), and a step surface ST connecting the outer end and the inner end in the optical axis direction of the adjacent step surface ST. Inclined CP. Here, the light beam passing through the inclined plane CP exerts all the power for focusing with the sum of the refractive power of the refractive surface of the lens and the diffraction power of the diffraction structure DS, while the light beam passing through the stepped surface ST is not used for light focusing, causing decrease in transmittance. Call it the shadow effect.

However, compared to the vicinity of the optical axis of the lens, since the light beam is emitted parallel to the optical axis, the loss of light quantity due to the influence of the shadow is small, and the refractive surface as the parent aspheric surface collapses at the peripheral part of the lens, so relative to the light A light beam with an inclined axis is easy to enter, and in addition to the inclination of the step surface ST due to the influence of the draft of the mold, as shown in Fig. 1, the loss of light quantity due to the influence of the shadow increases. Here, at the condensing point, if the amount of light around the lens becomes lower relative to the amount of light passing through the vicinity of the optical axis of the lens, the point becomes thicker, that is, the effective NA (numerical aperture) decreases. If the effective NA can be reduced, it is possible to reduce fluctuations in coupling efficiency when temperature changes occur. That is, in the diffractive structure, under the shadow effect and the distribution of diffraction efficiency, by intentionally making the distribution in the lens center and peripheral part, it is possible to provide a lens for optical communication with little variation in coupling efficiency. In addition, when the efficiency of the peripheral portion cannot be reduced only by the shadow effect, the diffraction efficiency can be adjusted by finely adjusting the steps between the annular zones, so that the distribution of the central portion and the peripheral portion can be provided with an amount insufficient due to the shadow effect. However, if the value of T1/T0 exceeds the lower limit of the formula (1), the amount of decrease in NA is too large, which is not preferable. It is more desirable to satisfy 0.6≤T1/T0≤0.85.

The lens for optical communication according to claim 2 is the invention according to claim 1, wherein the NA on the incident side of the light beam from the semiconductor laser satisfies the conditional expression (2),

0.35≤NA≤0.85 (2).

By satisfying the conditional expression (2), it is possible to secure an appropriate diameter of the focused spot while ensuring the amount of light to be captured from the semiconductor laser.

The lens for optical communication according to claim 3 is the invention according to claim 1 or 2, wherein the optical path difference providing structure has a step toward the optical axis of the lens. This is because in such an optical path difference providing structure, the focus position during temperature changes can be suppressed, and the influence of shadows is particularly likely to occur.

The lens for optical communication according to Claim 4 is the invention according to any one of Claims 1 to 3, wherein the optical path difference imparting structure adjusts the optical path difference to approximately an integer multiple of the wavelength λ. Assigned to passing beams. Thereby, it is possible to suppress the shift of the focus position due to the change in the refractive index of the lens when the temperature changes while having high diffraction efficiency.

In the invention of claim 4, the optical communication lens according to claim 5 is characterized in that the optical path difference imparting structure is 1 times the wavelength λ in the entire range of the effective diameter of the lens. An optical path difference is imparted to the passing beam. By providing the optical path difference as small as possible, the height of the steps of the optical path difference providing structure is suppressed, forming errors are suppressed, and the light transmittance can be improved.

The lens for optical communication according to Claim 6 is the invention according to any one of Claims 1 to 5, wherein the optical path difference providing structure provides the above-mentioned An optical path difference of X times the wavelength λ is given to the passing light beam in the peripheral area outside the central area of the above-mentioned lens by Y times the above-mentioned wavelength λ, and the decimal place of X is rounded up to an integer The value of is less than the value that would round Y to an integer. Thereby, processing of the mold of the optical path difference providing structure in the peripheral region where the transfer pitch tends to be narrow can be easily performed.

The lens for optical communication according to claim 7 is the invention according to claim 6, wherein the value of rounding off one digit of the decimal point of the above-mentioned X to an integer is 1, and the value of one decimal point of the above-mentioned Y is Bits are rounded to an integer value of 2.

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

The lens for optical communication according to claim 9 is the invention according to claim 8, wherein the optical system magnification M of the coupling lens satisfies the following conditional expression (3),

1.0 ≤ M ≤ 4.0 (3).

Accordingly, it is possible to provide the best efficiency at about NA0.1 to NA0.12 that can be obtained in a general single-mode optical fiber. It is particularly desirable to satisfy the following formula,

2.0≤M≤4.0 (3').

The lens for optical communication according to claim 10 is the invention according to any one of claims 1 to 9, wherein the optical path difference providing structure is provided on a surface from which a light beam from the semiconductor laser emits.

In FIG. 1( a ), since the diffraction structure DS is provided on the side of the semiconductor laser, the ratio of the light beam incident on the stepped surface ST increases, and the influence of shadows increases. On the other hand, in Fig. 1(b), since the diffraction structure DS is provided on the side opposite to the semiconductor laser, the light beam tends to advance in the direction along the stepped surface ST of the annular zone, that is, the light beam incident on the stepped surface ST The proportion of relatively becomes lower, and the influence of the shadow becomes smaller. That is, by having a diffractive structure on the surface from which the light beam from the semiconductor laser exits, even if the step surface ST of the annular zone is inclined due to a manufacturing error, the coupling efficiency is hardly lowered, and a lens that is highly resistant to manufacturing errors can be realized. , In addition, compared with the laser side, the area of the optical surface on the fiber side is relatively wider, so the area where the diffraction structure is provided becomes wider, so the pitch of the annular zone can be enlarged accordingly, and the decrease in transmittance can be easily suppressed.

The semiconductor module according to Claim 11 is characterized in that the optical communication lens and the semiconductor laser according to any one of Claims 1 to 10 are integrally assembled.

In the semiconductor module according to claim 12, in the invention according to claim 11, the lens is mounted on a housing that seals the semiconductor laser.

The semiconductor module according to claim 13, in the invention according to claim 11, is characterized in that the lens and the housing sealing the semiconductor laser are integral.

The so-called "semiconductor laser" is a laser that emits light by re-coupling of a semiconductor. Generally, the oscillation wavelength becomes longer when the ambient temperature rises, and the oscillation wavelength becomes shorter when the ambient temperature falls.

The so-called lens includes: a lens that condenses the light beam emitted from the semiconductor laser, a lens that condenses the light beam emitted from the end face of the optical fiber, an optical coupling lens that condenses the light beam emitted from the semiconductor laser to the end face of the optical fiber, Optical coupling lens that condenses the light beam emitted from the end face of the optical fiber to the light receiving surface of the light receiving element. The lens is made of plastic.

The so-called optical path difference imparting structure referred to in this specification is a generic term for structures that add an optical path difference to incident light beams. A phase difference providing structure that provides a phase difference is also included in the optical path difference providing structure. In addition, the phase difference imparting structure includes a diffractive structure. The optical path difference imparting structure of the present invention is preferably a diffractive structure. The optical path difference providing structure has a step, and preferably has a plurality of steps. This step adds an optical path difference and/or a phase difference to the incident light beam. The optical path difference added by the optical path difference imparting 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 at periodic intervals in the direction perpendicular to the optical axis, or may be arranged at non-periodic intervals in the direction perpendicular to the optical axis. In addition, when the lens provided with the optical path difference providing structure is a single aspheric lens, the incident angle of the light beam to the lens is different due to the height from the optical axis, so the step difference of the optical path difference providing structure is different for each annular zone. Each of them is different. For example, when the lens is a single aspheric convex lens, even with an optical path difference imparting structure that imparts the same optical path difference, the step difference generally tends to increase as the distance from the optical axis increases.

In addition, the so-called diffractive structure referred to in this specification is a general term for a structure having steps and having a function of converging or diverging light beams by diffraction. For example, it includes a structure in which a plurality of unit shapes are arranged around the optical axis, and the wavefront of transmitted light is lost in each adjacent annular zone for each unit shape incident on the light beam. As a result, the light is either converged or diverged by forming new wavefronts. The diffractive structure has a plurality of steps, and the steps may be arranged at periodic intervals in the direction perpendicular to the optical axis, or may be arranged at non-periodic intervals in the direction perpendicular to the optical axis. In addition, when the lens provided with the diffractive structure is a single aspherical lens, since the height from the optical axis is different, the incident angle of the light beam to the lens is different, so the step difference of the diffractive structure is slightly different for each annular zone. different. For example, when the lens is a single aspherical convex lens, even if it is a diffraction structure that produces diffracted light of the same order of diffraction, the step difference tends to increase as the distance from the optical axis increases.

However, the optical path difference providing structure preferably has a plurality of concentric ring-shaped zones centering on the optical axis. In addition, the optical path difference imparting structure can generally take various cross-sectional shapes (cross-sectional shapes in a plane including the optical axis), and the cross-sectional shapes including the optical axis are roughly classified into a flare structure and a stepped structure.

The blazed structure means that, as shown in FIGS. 2( a ) and ( b ), an optical element having an optical path difference providing structure has a zigzag cross-sectional shape including the optical axis. In addition, in the example of FIG. 2, the upper side is the light source side, the lower side is the optical disc side, and the optical path difference providing structure is formed in the plane which is a mother aspheric surface. In the blazed structure, the length in the direction perpendicular to the optical axis of one blazed unit is referred to as a pitch P (see FIG. 2( a ), ( b )). In addition, the length of the step in the direction parallel to the optical axis of the blaze is referred to as a step B (see FIG. 2( a )). Moreover, in the blazed shape, as shown in Fig. 1, for example, in order to easily cut the mold with a turning tool, the stepped surface may not be set parallel to the optical axis, but may be set at a slight inclination. In this case, a blazed shape is preferred. The position of the apex is within the range of 0 to 25% of the pitch in the direction perpendicular to the optical axis.

In addition, the so-called stepped structure means that as shown in Fig. 2(c) and (d), the cross-sectional shape of the optical element having the optical path difference imparting structure including the optical axis is a structure with a plurality of small steps (referred to as the shape of the step unit). Moreover, in this specification, the so-called "V class" means that the surface of the annular zone corresponding to (orienting to) the direction perpendicular to the optical axis (hereinafter sometimes referred to as a mesa) in one step unit of the stepped structure is divided by steps. Each of the V endless belt surfaces is divided, and in particular, a stepped structure having three or more stages has small steps and large steps.

For example, the optical path difference providing structure shown in FIG. 2(c) is called a 5-stage stepped structure, and the optical path difference providing structure shown in FIG. 2(d) is called a 2-stage stepped structure (also called a double structure). The two-stage stepped structure will be described below. The cross-sectional shape of the plurality of annular zones including the optical axis of the objective lens is composed of a plurality of concentric annular zones centered on the optical axis, and the adjacent stepped surfaces are connected by a plurality of stepped surfaces Pa and Pb extending parallel to the optical axis. The light source side mesa Pc between the light source side ends of Pa and Pb is formed by connecting the disc side mesa Pd between the disc side ends of the adjacent stepped surfaces Pa and Pb, and the light source side mesa Pc and the disc side mesa are formed. The Pds are alternately arranged in a direction intersecting the optical axis.

Furthermore, the optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated. The term "periodically repeating a unit shape" as used herein naturally includes shapes in which the same shape repeats at the same period. Furthermore, the unit shape which becomes one unit of a period has regularity, and the shape which a period gradually becomes longer or becomes shorter is also included in "the unit shape which repeats periodically".

When the optical path difference providing structure has a blazed structure, it becomes the shape which repeats the zigzag shape which is a unit shape. Either the same saw-tooth shape can be repeated as shown in Figure 2(a), or the pitch of the saw-tooth shape (also known as the diffraction pitch) can be increased as it advances in the direction away from the optical axis as shown in Figure 2(b). A shape that gradually becomes longer, or a shape that gradually becomes shorter in pitch. In addition, in a certain area, the steps of the blazed structure may be provided in a shape opposite to the optical axis (center) side, and in other areas, the steps of the blazed structure may be provided in a shape facing the optical axis (center) side. The shape is provided in a shape in which a transition area required for switching the direction of the steps of the sparkle structure is provided therebetween. Furthermore, in the case where the step direction of the blazed structure is switched midway, the annular zone pitch can be enlarged, and the decrease in transmittance due to the manufacturing error of the optical path difference providing structure can be suppressed.

In the case where the optical path difference providing structure has a stepped structure, a shape such as a repeating five-stage step unit can be obtained as shown in FIG. 2( c ). Furthermore, it may be a shape in which the pitch of the step unit gradually becomes longer as it advances in a direction away from the optical axis, or a shape in which the pitch of the step unit gradually becomes shorter. Furthermore, when the blazed shape is approximated by the stepped shape, although the diffraction efficiency is lowered, the same effect as the present invention can be obtained.

The optical path difference providing structure preferably has a step toward the optical axis of the lens. "The step faces the optical axis" refers to a state as shown in FIG. 3( a ).

The optical path difference providing structure preferably provides an optical path difference substantially an integer multiple of the wavelength λ to the passing light beam. The term “approximately integer multiple” means that when N is an integer other than 0, it is greater than or equal to (N−0.4)λ and less than or equal to (N+0.4)λ. The optical path difference imparting structure is preferably such that an optical path difference of 1 time the wavelength λ is provided in the entire range of the effective diameter of the lens, or an optical path difference 1 time the wavelength λ is provided in the central region near the optical axis of the lens, and the optical path difference of λ is provided in the lens. The peripheral region outside the central region imparts an optical path difference twice the wavelength λ. The boundary between the central area and the peripheral area is preferably, for example, at a height from the optical axis of 2/3 of the effective diameter.

It is preferable that the pupil transmittance distribution of the luminous flux passing through the lens satisfies conditional expression (1). The so-called pupil transmittance distribution is the transmittance distribution of the exit pupil surface, which corresponds to the luminance distribution of the exit pupil surface of an incident light beam of relatively uniform intensity. Moreover, the vicinity of the optical axis of the so-called lens is, for example, within the height of the optical axis of 1/3 of the effective diameter, more preferably within 0.2, and the so-called periphery of the lens is, for example, within the height of the optical axis of 2/3 of the effective diameter. The outer side of the height, more ideally the outer side of 0.8.

0.4≤T1/T0≤0.8 (1)

T0: Transmittance near the optical axis of the above lens

T1: Transmittance around the above lens

The NA from the beam incident side of the semiconductor laser preferably satisfies the conditional formula (2)

0.30≤NA≤0.85 (2)

Furthermore, it is desirable to preferably satisfy conditional expression (4).

0.35≤NA≤0.65 (4)

According to the present invention, there are provided a lens for optical communication in which a semiconductor module is provided in a compact module, and furthermore, by suppressing the effective NA of the light-converging point on the fiber side to be small, fluctuations in coupling efficiency can be suppressed, and a lens using the same can be provided. semiconductor module.

Description of drawings

1( a ) is an enlarged cross-sectional view of a lens provided with a diffractive structure on the semiconductor laser side, and FIG. 1( b ) is an enlarged cross-sectional view of a lens provided with a diffractive structure on the semiconductor laser side.

2 is an enlarged cross-sectional view showing an example of an optical path difference providing structure, (a) and (b) are diagrams showing examples of a blazed structure, and (c) and (d) are diagrams showing examples of a stepped structure.

FIG. 3( a ) is a diagram showing a state where the steps face the direction of the optical axis, and FIG. 3( b ) is a view showing a state where the steps face the direction opposite to the optical axis.

4( a ) is a sectional view in the optical axis direction of the semiconductor module LM according to the first embodiment, and FIG. 4( b ) is an enlarged view showing a lens surface indicated by an arrow IVB.

5( a ) is a sectional view in the optical axis direction of the semiconductor module LM according to the second embodiment, and FIG. 5( b ) is an enlarged view showing a lens surface indicated by an arrow VB.

6( a ) is a sectional view in the optical axis direction of the optical coupling lens CL according to the third embodiment, and ( b ) is an enlarged view showing a lens surface indicated by an arrow VIB.

FIG. 7 is a graph of coupling efficiency in Examples 1 to 4 and a comparative example.

FIG. 8 is a graph of coupling efficiency in Examples 5 to 8 and a comparative example.

FIG. 9 is a graph of coupling efficiency in Example 9. FIG.

FIG. 10 is a graph showing the relationship between the phase difference given by the steps of the diffraction structure and the diffraction efficiency.

Symbol Description

AP: opening

BS: base

CG: cover glass

CL: Optical coupling lens or optical coupling lens unit

CV: cover

DS: diffractive structure

FL: Flange

LD: semiconductor laser

LG: pin part

LM: semiconductor module

OF: optical fiber

PD: Photodiode

PDa: light-receiving surface

S1: Semiconductor laser side optical surface

S2: Anti-semiconductor laser side optical surface

Detailed ways

Embodiments of the present invention will be described below with reference to the drawings. 4 is a sectional view in the optical axis direction of the semiconductor module LM according to the first embodiment. A substrate of a semiconductor laser LD is mounted on a base BS having three pins LG for power supply, and the semiconductor laser LD emitting a beam of wavelength λ is covered with a cover (casing) CV having an opening AP. The opening AP is covered with a transparent cover glass CG from the inside to seal the semiconductor laser LD from the outside atmosphere.

The flange portion FL of the optical coupling lens portion CL is bonded to the cover CV so as to cover the outside of the opening AP. The optical coupling lens CL made of plastic has an optical surface S1 as a refraction surface on the semiconductor laser side, and an optical surface S2 on the opposite side thereof, and a diffraction structure DS is formed on the refraction surface on the optical surface S2. The radius of curvature of optical surface S1 is larger than the radius of curvature of optical surface S2. The blazed diffractive structure DS imparts an optical path difference that is an integer multiple of the wavelength λ when a beam of wavelength λ is incident.

The base BS of the semiconductor module LM is connected to the optical fiber OF at a predetermined distance via a housing not shown. Furthermore, the optical fiber OF is covered with a sheath SL.

The operation of the semiconductor module LM of this embodiment will be described. When power is supplied through the pin portion LG, the semiconductor laser LD emits light, and the emitted light beam enters the optical coupling lens CL through the cover glass CG and the opening AP. The light beam incident on the optical coupling lens CL is refracted on the refraction plane, exits through the diffraction structure DS, is focused on the end face of the optical fiber OF, and then propagates in the optical fiber OF.

If the ambient temperature rises (or falls), because the oscillation wavelength of the semiconductor laser LD increases (or decreases), the diffraction angle of the diffracted light from the diffraction structure DS changes accordingly, thereby making it possible to correct for changes in the ambient temperature. The shift of the focus position caused by the change in the refractive index of the optical coupling lens CL. In addition, according to this embodiment, since the diffraction structure DS is provided only on one side of the optical coupling lens CL, the diffraction pitch becomes narrow as a whole. The amount of light in the portion becomes lower than the amount of light passing through the vicinity of the optical axis of the lens, so the dots become thicker and the effective NA decreases. As a result, fluctuations in coupling efficiency when temperature changes occur are reduced.

5 is a sectional view in the optical axis direction of the semiconductor module LM according to the second embodiment. A substrate of a semiconductor laser LD is mounted on a base BS having three pins LG for power supply. In the present embodiment, the cover (casing) CV sealingly covering the semiconductor laser LD that emits the light beam of wavelength λ is in the shape of a plastic hat, and the optical coupling lens portion CL is integrally formed on the shielding end side.

The optical coupling lens portion CL has an optical surface S1 as a refraction surface on the semiconductor laser side and an optical surface S2 as a refraction surface on the opposite side, and a diffraction structure DS is formed on the refraction surface on the optical surface S2. The radius of curvature of optical surface S1 is larger than the radius of curvature of optical surface S2. The blazed diffractive structure DS imparts an optical path difference that is an integer multiple of the wavelength λ when a beam of wavelength λ is incident.

The base BS of the semiconductor module LM is connected to the optical fiber OF at a predetermined distance via a housing not shown. Furthermore, the optical fiber OF is covered with a sheath SL.

The operation of the semiconductor module LM of this embodiment will be described. When power is supplied through the pin LG, the semiconductor laser LD emits light, and the emitted light beam directly enters the optical coupling lens portion CL. The light beam incident on the optical coupling lens unit CL is refracted on the refraction surface, exits through the diffraction structure DS, is condensed on the end surface of the optical fiber OF, and then propagates in the optical fiber OF.

If the ambient temperature rises (or falls), because the oscillation wavelength of the semiconductor laser LD increases (or decreases), the diffraction angle of the diffracted light from the diffraction structure DS changes accordingly, thereby making it possible to correct for changes in the ambient temperature. The focus position shifts due to the change in the refractive index of the optical coupling lens portion CL. In addition, the lens expands (or shrinks) due to temperature rise (or fall), thereby enabling correction of focus position shift. According to this embodiment, because the diffraction structure DS is provided only on the outer surface of the optical coupling lens portion CL, the diffraction pitch becomes narrow as a whole. The amount of light that passes through the lens near the optical axis becomes lower, so the dots become thicker and the effective NA decreases. Thus, fluctuations in coupling efficiency when temperature changes occur are reduced.

6 is a sectional view in the optical axis direction of the optical coupling lens CL according to the third embodiment. In this embodiment, a semiconductor laser (not shown) propagates through the optical fiber OF, and the light beam emitted from the end surface thereof is condensed to the light receiving surface PDa of the photodiode PD through the optical coupling lens CL. On the refractive surface of one optical surface (optical surface on the optical fiber OF side) S1 of the optical coupling lens CL, a blazed diffraction structure DS for correcting focal position shift due to temperature changes is provided. The other optical surface S2 consists only of refractive surfaces. The radius of curvature of optical surface S1 is smaller than the radius of curvature of optical surface S2. Also, CG is the cover glass of the photodiode.

According to this embodiment, since the blazed diffraction structure DS is provided only on one side S1 of the optical coupling lens CL, the diffraction pitch is narrowed as a whole, and at the point where the optical coupling lens CL condenses light onto the light receiving surface PDa of the photodiode PD On the other hand, since the amount of light in the peripheral portion is lower than the amount of light passing through the vicinity of the optical axis of the lens, the occurrence point becomes thicker and the effective NA increases. Thus, fluctuations in coupling efficiency when temperature changes occur are reduced. Other effects are the same as the above-mentioned embodiment.

(example)

Examples that can be used in the above-mentioned embodiments will be described below. Examples 1 to 4 are all resin lenses, and are optical coupling lenses suitable for the semiconductor module shown in FIG. 4 . In addition, a glass lens and a resin lens without a diffractive structure are referred to as comparative examples. Table 1 shows the specifications of the semiconductor modules of Examples 1 to 4, Table 2 shows the specifications of the semiconductor modules of Examples 5 to 8, Table 3 shows the specifications of the semiconductor module of Example 9, and Table 4 shows the specifications of the semiconductor module of Example 1. The refractive index of each material of -4 shows the refractive index of each material of Examples 5-8 in Table 5, and shows the refractive index of each material of Example 9 in Table 6.

[Table 1]

Specifications of semiconductor modules

LD half value full width 32 Spend NA 0.4 Coupling ratio 4 times Wavelength change with temperature change 0.2 nm/degC

[Table 2]

Specifications of semiconductor modules

LD half value full width 32 Spend NA 0.4 Coupling ratio 2.5 times Wavelength change with temperature change 0.2 nm/degC Linear expansion coefficient 0.00006 cm/cm℃

[table 3]

Specifications of semiconductor modules

LD half value full width 32 Spend NA 0.4 Coupling ratio 4 times Wavelength change with temperature change 0.2 nm/degC

[Table 4]

Refractive index in examples

temperature (°C) wavelength (nm) Refractive Index (Glass) Refractive Index (Resin) 0 1305 1.52313 1.52504 25 1310 1.52311 1.52311 40 1313 1.52309 1.52179 60 1317 1.52307 1.51946

80 1321 1.52305 1.51671

[table 5]

Refractive index in examples

temperature (°C) wavelength (nm) Refractive Index (Glass) Refractive Index (Resin) 0 1305 1.52313 1.52504 25 1310 1.52311 1.52311 40 1313 1.52309 1.52179 60 1317 1.52307 1.51946 80 1321 1.52305 1.51671

[Table 6]

Refractive index in examples

temperature (°C) wavelength (nm) Refractive Index (Glass) Refractive Index (Resin) 0 1305 1.52313 1.52504 25 1310 1.52311 1.52311 40 1313 1.52309 1.52179 60 1317 1.52307 1.51946 80 1321 1.52305 1.51671

Furthermore, the optical surface of the optical coupling lens is formed as an aspheric surface that is axisymmetric around the optical axis and defined by the equations in which the coefficients shown in Table 1 are respectively substituted into the equations.

[number 1]

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&kappa;</span>}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 10</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; i</span>}}$

Here, X(h) is the axis in the direction of the optical axis (taking the forward direction of light as positive), k is the conic coefficient, Ai is the aspheric coefficient, h is the height from the optical axis, and r is the paraxial radius of curvature.

In addition, in the case of an embodiment using a diffractive structure, the optical path difference given to the light beams of each wavelength by the diffractive structure is defined by a formula in which the coefficients shown in the table are substituted into the optical path difference function in Equation 2.

(number 2)

Φ(h)=B ₂ h ² ×λ×m/λB

Here, λ: wavelength used, m: diffraction order, λB: blazed wavelength, h: distance from the optical axis in the direction perpendicular to the optical axis.

Table 7 shows lens data of Examples 1 to 4 and Comparative Example, Table 8 shows lens data of Examples 5 to 8, and Table 9 shows lens data of Example 9. The pitch and step of each diffractive structure in the examples were optimized using the optical path difference function, diffraction order, and blaze wavelength shown in Tables 7, 8, and 9.

[Table 7]

[Table 8]

[Table 9]

As explained with reference to Table 1, the coupling efficiency of the lens having a diffractive structure is lowered due to the influence of shadows that increase in accordance with the step manufacturing error of the diffractive annular zone. The decrease in coupling efficiency tends to increase as the pitch between the annular zones becomes narrower. In this example, when the transmittance at the central portion is assumed to be 100%, Tables 10 to 12 show the decrease in the vicinity of the effective diameter of the lens. degree (T1/T0).

In glass lenses and resin lenses without a diffractive structure, theoretically, no decrease in transmittance occurs near the effective diameter of the lens, but it was found that at least 15% or greater decrease in transmittance occurred in Examples 1 to 9.

[Table 10]

glass lens resin lens Example 1 Example 2 Example 3 Example 4 T1/T0 (%) 100 100 59 64 79 84

[Table 11]

Example 5 Example 6 Example 7 Example 8 T1/T0 (%) 85 75 68 60

[Table 12]

Example 9 T1/T0 (%) 80

Graphs of coupling efficiency in Examples and Comparative Examples are shown below in FIGS. 7 to 9 . In FIGS. 7 to 9 , the vertical axis is the coupling efficiency, and the horizontal axis is the ambient temperature. Referring to FIGS. 7 to 9, it can be seen that since the glass lens has no change in refractive index due to temperature, there is little change in efficiency. However, there is a problem of increasing the cost of the semiconductor module because of the high price. Secondly, it is known that a resin lens without a diffractive structure has a large efficiency fluctuation due to the influence of the refractive index fluctuation caused by the ambient temperature, for example, the coupling efficiency is lower than 10% at an ambient temperature of 80°C.

In contrast, Examples 1 to 9 having a diffractive structure are all resin lenses having a diffractive structure, and it is known that fluctuations in efficiency can be suppressed to be small compared to resin lenses without a diffractive structure. In particular, in Example 2, if only efficiency variation is considered, it is suppressed to be equivalent to a glass lens. Furthermore, in Example 4, the coupling efficiency was 20% or less at an ambient temperature of 0° C., but even so, the variation in coupling efficiency was smaller than that of a resin lens without a diffractive structure. Furthermore, in Example 4, at about 60° C. on the high temperature side, the coupling efficiency is higher than that of other Examples. That is, the temperature of the semiconductor module rises due to the light emission of the semiconductor laser LD, and the fourth embodiment is effective in an environment where the temperature of the semiconductor module is always used at about 60°C. Furthermore, Example 9 is a lens capable of achieving a coupling efficiency of 10% when used at about 60° C. while suppressing a change in coupling efficiency due to a change in ambient temperature. Furthermore, by manufacturing the lens in consideration of not only the influence of the shadow but also the depth of the flare, the relationship between the phase difference and the diffraction efficiency is shown in Fig. , the phase difference adjustment is performed in such a way that the phase difference of the efficiency of about 50% near the effective diameter becomes 0.6λ or 1.4λ steps, and T1/T0=80%×50%=40%. At this time, the vicinity of the optical axis is set to 1λ, and the phase difference is adjusted stepwise to gradually become 0.6λ or 1.4λ for the step up to the effective diameter.

On the other hand, Examples 7 and 8 are suitable for the implementation shown in FIG. 4, except that when the ambient temperature rises (or falls), the oscillation wavelength of the semiconductor laser LD increases (or decreases) and changes from In addition to the effect of the diffraction angle of the diffracted light generated by the diffraction structure DS, by adjusting the distance between the light source and the optical coupling lens CL caused by the thermal expansion of the cover CV, it is possible to correct the change in the refractive index of the optical coupling lens CL caused by the change in ambient temperature. focus position shift. Here, the linear expansion coefficient of the cover CV is 0.00006 cm/cm°C.

As can be seen from FIG. 8 , in Examples 7 and 8, if only efficiency fluctuations are considered, they are suppressed to be equivalent to glass lenses.

The present invention is not limited to the embodiments described in the specification, and those including other embodiments and modified examples will be clear to those skilled in the art from the examples and concepts described in the specification.

Claims (32)

1. A lens for optical communication is a lens for optical communication that condenses the beam of wavelength λ emitted from a semiconductor laser, characterized in that: The above lens is made of plastic, Only one of the optical surfaces of the above-mentioned lens is formed with an optical path difference imparting structure that suppresses changes in the focus position when the temperature changes, The above-mentioned optical path difference imparting structure includes a plurality of annular zones centered on the optical axis of the above-mentioned lens, and the cross-sectional shape of the above-mentioned annular zone cut by a plane passing through the optical axis of the above-mentioned lens is a blazed shape, The pupil transmittance distribution of the beam passing through the above lens satisfies the conditional expression (1), 0.5≤T1/T0≤0.85 (1), in, T0: Transmittance near the optical axis of the above lens, T1: Transmittance at the periphery of the above-mentioned lens. 2. The lens for optical communication according to claim 1, characterized in that: The NA of the incident side of the beam from the above-mentioned semiconductor laser, that is, the numerical aperture satisfies the conditional formula (2), 0.35≤NA≤0.85 (2). 3. The lens for optical communication according to claim 1, characterized in that: The optical path difference providing structure has a step toward the optical axis of the lens. 4. The lens for optical communication according to claim 2, characterized in that: The optical path difference providing structure has a step toward the optical axis of the lens. 5. The lens for optical communication according to claim 1, characterized in that: The optical path difference providing structure provides an optical path difference substantially an integer multiple of the wavelength λ to the passing light beam. 6. The lens for optical communication according to claim 2, characterized in that: The optical path difference providing structure provides an optical path difference substantially an integer multiple of the wavelength λ to the passing light beam. 7. The lens for optical communication according to claim 3, characterized in that: The optical path difference providing structure provides an optical path difference substantially an integer multiple of the wavelength λ to the passing light beam. 8. The lens for optical communication according to claim 4, characterized in that: The optical path difference providing structure provides an optical path difference substantially an integer multiple of the wavelength λ to the passing light beam. 9. The lens for optical communication according to claim 5, characterized in that: The optical path difference imparting structure imparts an optical path difference of one time the wavelength λ to the passing light beam over the entire range of the effective diameter of the lens. 10. The lens for optical communication according to claim 6, characterized in that: The optical path difference imparting structure imparts an optical path difference of one time the wavelength λ to the passing light beam over the entire range of the effective diameter of the lens. 11. The lens for optical communication according to claim 7, characterized in that: The optical path difference imparting structure imparts an optical path difference of one time the wavelength λ to the passing light beam over the entire range of the effective diameter of the lens. 12. The lens for optical communication according to claim 8, characterized in that: The optical path difference imparting structure imparts an optical path difference of one time the wavelength λ to the passing light beam over the entire range of the effective diameter of the lens. 13. The lens for optical communication according to any one of claims 1 to 12, characterized in that: The above-mentioned optical path difference imparting structure is in the central area near the optical axis of the above-mentioned lens, and the optical path difference of X times the above-mentioned wavelength λ is given to the light beam passing through, and in the peripheral area outside the central area of the above-mentioned lens, the optical path difference of the above-mentioned wavelength λ An optical path difference of Y times is given to the passing light beam, and the value obtained by rounding off one decimal place of X to an integer is smaller than the value obtained by rounding off one decimal place of Y to an integer. 14. The lens for optical communication according to claim 13, characterized in that: The value obtained by rounding off one decimal place of said X to an integer is 1, and the value obtained by rounding off one decimal place of said Y to an integer is 2. 15. The optical communication lens according to any one of claims 1 to 12, characterized in that: The lens is an optical coupling lens that condenses the light beam emitted from the semiconductor laser on the end face of the optical fiber. 16. The lens for optical communication according to claim 13, characterized in that: The lens is an optical coupling lens that condenses the light beam emitted from the semiconductor laser on the end face of the optical fiber. 17. The lens for optical communication according to claim 14, characterized in that: The lens is an optical coupling lens that condenses the light beam emitted from the semiconductor laser on the end face of the optical fiber. 18. The lens for optical communication according to claim 15, characterized in that: The optical system magnification M of the above-mentioned coupling lens satisfies the following conditional formula (3), 1.0 ≤ M ≤ 4.0 (3). 19. The lens for optical communication according to claim 16, characterized in that: The optical system magnification M of the above-mentioned coupling lens satisfies the following conditional formula (3), 1.0 ≤ M ≤ 4.0 (3). 20. The lens for optical communication according to claim 17, characterized in that: The optical system magnification M of the above-mentioned coupling lens satisfies the following conditional formula (3), 1.0 ≤ M ≤ 4.0 (3). 21. The lens for optical communication according to any one of claims 1 to 12, characterized in that: The said optical path difference providing structure is provided in the surface from which the light beam from the said semiconductor laser emits. 22. The lens for optical communication according to claim 13, characterized in that: The said optical path difference providing structure is provided in the surface from which the light beam from the said semiconductor laser emits. 23. The lens for optical communication according to claim 14, characterized in that: The said optical path difference providing structure is provided in the surface from which the light beam from the said semiconductor laser emits. 24. The lens for optical communication according to claim 15, characterized in that: The said optical path difference providing structure is provided in the surface from which the light beam from the said semiconductor laser emits. 25. The lens for optical communication according to claim 16, characterized in that: The said optical path difference providing structure is provided in the surface from which the light beam from the said semiconductor laser emits. 26. The lens for optical communication according to claim 17, characterized in that: The said optical path difference providing structure is provided in the surface from which the light beam from the said semiconductor laser emits. 27. The lens for optical communication according to claim 18, characterized in that: The said optical path difference providing structure is provided in the surface from which the light beam from the said semiconductor laser emits. 28. The lens for optical communication according to claim 19, characterized in that: The said optical path difference providing structure is provided in the surface from which the light beam from the said semiconductor laser emits. 29. The lens for optical communication according to claim 20, characterized in that: The said optical path difference providing structure is provided in the surface from which the light beam from the said semiconductor laser emits. 30. A semiconductor module characterized by: A lens for optical communication according to any one of claims 1 to 29 is integrally assembled with a semiconductor laser. 31. The semiconductor module according to claim 30, characterized in that: The lens is attached to a housing that seals the semiconductor laser. 32. The semiconductor module according to claim 30, characterized in that: The above-mentioned lens is integrated with a casing that seals the above-mentioned semiconductor laser.