TW202037931A - Condensing lens and optical module - Google Patents

Abstract

The present invention provides a condensing lens that implements a light condensing function and an optical path conversion function by a simple configuration, and an optical module using the same. This condensing lens has a bottom surface, an inclined surface extending obliquely at an obtuse angle with respect to the bottom surface, a curved surface formed on the inclined surface, and a reflective film formed on the curved surface. The curved surface changes the traveling direction of incident light, and condenses the incident light at a predetermined position within a plane parallel to the bottom surface.

Description

Collecting lens, and light module

The present invention relates to a light collecting lens and a light module.

Due to the popularization of mobile devices such as smartphones and the introduction of IoT (Internet of Things), the data communication volume of optical networks is increasing year by year, and there is a demand for higher communication speed and quality. On the other hand, various optoelectronic components mounted in optical communication equipment require miniaturization and high density.

In an optical module for optical communication, the light receiving surface of a light receiving element such as a photodiode (PD) is located in a plane parallel to the substrate. Since the optical fiber that transmits the optical signal is generally connected in a direction parallel to the substrate surface of the optical module, the positional relationship between the transmission axis of the optical fiber and the light receiving surface becomes parallel. In order to collect the input optical signal to the light receiving surface, as shown in Figure 1, a collecting lens and a reflecting mirror are used. The reflecting mirror bends the light collected by the collecting lens by approximately 90 degrees in the direction in which it is incident on the light-receiving surface.

In the configuration of FIG. 1, separate optical elements are used for light collection and optical path conversion, which hinders the miniaturization of the optical module. In addition, a process of precise alignment and assembly with the collecting lens and mirror is required. From the viewpoint of miniaturization of the optical module, it is desirable to use an optical element that integrates a light collection function and an optical path conversion function.

It is proposed to process a semiconductor substrate to produce a curved mirror surface on a base substrate, and to convert the direction of the output light from the light-emitting element while collimating it into parallel light (for example, refer to Patent Document 1).

In addition, an optical element has been proposed in which a concave surface is provided on the bottom surface and the inclined surface forming an acute angle, and the expansion angle of the light emitted from a point light source supported on the mount frame is deflected from the propagation direction (for example, refer to Patent Document 2). [Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP 2008-83255 A [Patent Document 2] JP 2006-145781 A

[The problem to be solved by the invention]

When the light-collecting lens and the reflecting mirror of FIG. 1 are integrated in this way, precise processing of the plural surfaces and film formation on the plural surfaces are required. Specifically, it is necessary to form an anti-reflection film on the light-collecting surface where light enters, to form a reflection film on the mirror surface that changes the optical path, and to form an anti-reflection film on the light exit surface. Because of the complexity of processing and the multiple film-forming processes, it is difficult to reduce costs.

The object of the present invention is to provide a light collecting lens having a light collecting function and an optical path conversion function with a simplified configuration. [Means to solve the problem]

In order to solve the above-mentioned problems, in the first aspect of the present invention, the collecting lens has: Underside An inclined surface extending at an obtuse angle with respect to the aforementioned bottom surface; The curved surface formed on the aforementioned inclined surface; The reflective film formed on the aforementioned curved surface; among them, The curved surface changes the direction of the incident light while condensing the incident light to a predetermined position in a plane parallel to the bottom surface.

In the second aspect of the present invention, the optical module has: Light receiving element Make incident light incident on the condenser lens of the aforementioned light receiving element; The aforementioned light collecting lens has: Located on the bottom surface of the mounting surface of the aforementioned light receiving element; An inclined surface extending at an obtuse angle with respect to the aforementioned bottom surface; The curved surface formed on the aforementioned inclined surface; The reflective film formed on the aforementioned curved surface; among them, The curved surface changes the direction of the incident light to collect the incident light to the light receiving surface of the light receiving element. [Effects of the invention]

According to the above configuration, the light collection function and the optical path conversion function can be realized with a simplified configuration. Because the configuration of the collecting lens is simplified, the assembly cost of the optical module using the collecting lens can be reduced.

Before describing the configuration of the embodiment in detail, there will be more detailed descriptions of the problems that occur in the configuration in which the collecting lens and the reflecting mirror of FIG. 1 are simply integrated.

Fig. 2 shows a configuration in which the collecting lens and the reflecting mirror of Fig. 1 are integrated in this way. The optical element has a convex surface provided on the incident side of light, an inclined surface that bends the transmission direction of light by 90 degrees, and an exit surface facing the light receiving element (PD). The convex surface has a light collection function, and the inclined surface has a reflection function.

A reflective film is formed on the inclined surface to reflect incident light in the direction of the light receiving element (PD). On the other hand, an anti-reflection film is formed on the convex surface and the exit surface on the incident side to suppress light loss and maintain high light receiving efficiency.

In this configuration, at least the convex surface on the incident side and the inclined surface for reflection must ensure molding accuracy. In addition, a total of three film-forming processes of film formation on two surfaces of the antireflection film and film formation on one surface of the reflective film are required. Furthermore, a supporting member for supporting the integrated optical element above the light receiving element is additionally required. It is desired that the number of surfaces requiring forming accuracy and the number of surfaces requiring film formation are less.

In the embodiments described below, the number of precise processing surfaces and the number of film forming processes is reduced, and the condensing lens that can be easily mounted on the substrate with a simplified configuration, and the optical module using the same.

FIG. 3 is a schematic diagram of the collecting lens 10 of the embodiment. The collecting lens 10 is used, for example, together with the light receiving element 40 to constitute a light receiving sub-assembly (ROSA: Receiver Optical Sub-Assembly) 30. ROSA 30 is an example of an optical module to which the collecting lens 10 is applied.

The condensing lens 10 has a bottom surface 11 located on the surface 50S of the substrate 50 on which the light receiving element 40 is arranged, and a curved surface 13 covering the light receiving surface 41 of the light receiving element 40. The light-receiving surface 41 may be located at the same height as the surface 50S of the substrate 50 on which the condensing lens 10 is arranged, or may be offset to some extent in the vertical direction (Z direction) with respect to the surface 50S.

The curved surface 13 is a concave surface formed on an inclined surface inclined at an obtuse angle with respect to the bottom surface 11 as described later. A reflective film 15 is formed to cover the concave surface. The curved surface 13 and the reflective film 15 form a mirror. The curved surface 13 forming the reflective film 15 has both a direction conversion function for converting the transmission direction of the incident light Lin and a light collection function for collecting the incident light Lin to the light receiving element 40. The incident light Lin is reflected by the reflective film 15 formed on the curved surface 13. The reflected light is directly incident on the light receiving surface 41 by the lens function of the curved surface 13.

In this configuration, only the curved surface 13 is the only surface with molding accuracy. The reflective film 15 is formed on the curved surface 13, and there is no need to form a film on the other surfaces. In addition, the condensing lens 10 is directly located on the substrate 50, and because the curved surface 13 protrudes so as to cover the light-receiving surface 41, no supporting member for supporting the condensing lens 10 is required.

The condensing lens 10 may be fixed to the surface 50S of the substrate 50 with an optical adhesive or the like. The fixed position of the light-collecting lens 10 is set at a position where the amount of light received by the light-receiving element 40 becomes the maximum by an active alignment method, for example.

The arrangement of the reflecting mirror (or the curved surface 13) set so as to cover the light receiving surface 41 of the light receiving element 40 can make the upper surface of the reflecting mirror a flat surface. Since the upper surface is set as a flat surface, it can be easier to hold by attaching the light collecting lens 10 which is an optical element.

The light-collecting lens 10 is formed of, for example, optical glass, quartz glass, synthetic quartz glass, or the like, but a lens made of polymer or plastic material may be used. The same is true when a quartz-based material is used. Only the curved surface 13 requires precision in the molding of the condensing lens 10, which is easier to mold than the configuration of FIG. 2.

The reflective film 15 is formed of a material that absorbs very little light of the used wavelength. When ROSA 30 is applied to the collecting lens 10, it is desirable to use a material that does not cause light absorption in the 1.3 μm band or the 1.5 μm band. As an example, in the case of metal coating, a combination of two or more of Al, Au, Cr, and these is used. Instead of metal, a multilayer reflective film in which dielectric films with different refractive indexes are laminated may be used.

FIG. 4 is a diagram illustrating the light collection characteristics of the curved surface 13. The light reflected on the curved surface 13 enters the light receiving element 40 obliquely from 1 to several degrees with respect to the normal line n of the light receiving surface 41. By shifting the light collection axis Ox from the normal line n of the light receiving surface 41, the light reflected on the light receiving surface 41 is prevented from returning to the original optical path. In the case of optical communication, since the returning light becomes signal noise, by slightly tilting the collection axis Ox from the normal line n of the light receiving surface 41, the noise can be reduced.

FIG. 5 is an oblique view of the collecting lens 10. The condensing lens 10 has a bottom surface 11 that is a mounting surface to the substrate 50, an inclined surface 14 inclined at an obtuse angle with respect to the bottom surface 11, and a concave curved surface 13 formed on the inclined surface 14. The curved surface 13 forms the reflective film 15 as described above (refer to FIGS. 3 and 4).

In the example of FIG. 5, the inclined surface 14 is connected to the bottom surface 11 on a surface 17 rising from the bottom surface 11. Although the installation surface 17 forms a base portion that stably holds the entire condensing lens 10, the shape is not limited. The inclined surface 14 may extend obliquely from the edge of the bottom surface 11 at an obtuse angle. The upper surface 12 and the inclined surface 14 facing the bottom surface 11 are also connected to the surface 18, but the shape is not limited, and it may be inclined from the edge of the upper surface 12.

By protruding the inclined surface 14 obliquely upward with respect to the bottom surface 11 at an obtuse angle, the light reflected on the curved surface 13 can be directly guided to the light receiving surface, which is the light collection point, without passing through other optical surfaces.

The curved surface 13 may be an elliptical concave surface or a parabolic surface. This is because the paraboloid of the concave lens into which light enters is cut by the inclined surface 14 as described later. The radius of curvature, eccentricity, conic constant, etc. of the curved surface 13 are appropriately designed in accordance with the position of the exit end of the optical fiber, the position of the light receiving surface 41 of the light receiving element 40, and the like. In a preferred example, the direction of the incident light is changed by about 90 degrees, and the curved surface 13 is designed to collect light on the light receiving surface 41. At this time, the light reflected on the curved surface 13 enters the light receiving surface 41 at the smallest point close to a true circle. As an example, the radius of curvature R of the curved surface 13 is 0.75 mm, and the conic constant K is -1.

FIG. 6 is a front view and a side view of the light collecting lens 10. The front view shown in FIG. 6(a) is a view when the collecting lens 10 is viewed from the incident direction (Y direction). The side view shown in FIG. 6(b) is a view in the YZ plane including the optical axis of incident light.

The contour of the curved surface 13 formed on the inclined surface 14 is an elliptical shape as shown in FIG. 5, but when viewed from the direction (Y direction) of the incident light to the condenser lens 10, it can be as shown in FIG. 6(a). Seen almost circular.

In FIG. 6(b), the collecting lens 10 has a bottom surface 11, an upper surface 12, a back surface 16, and front surfaces 17 and 18 on the light incident side. The forming of this surface does not require too high precision. The inclined surface 14 is inclined at a front-back angle of 135 degrees with respect to the bottom surface 11. Since the actual optical path conversion and light collection are performed on the curved surface 13, the self-forming on the inclined surface 14 does not require high precision. On the other hand, the curved surface 13 is precisely shaped so that the light collection efficiency to the light receiving surface 41 is maximized, and the light spot on the light receiving surface 41 becomes a true circle.

FIG. 7 is a diagram showing the characteristics of the curved surface 13 of the collecting lens 10, and FIG. 8 is a diagram explaining the decentering of the lens. 7(a) is a schematic diagram showing reflection and light collection by a concave lens formed on the curved surface 13, and FIG. 7(b) shows the relationship between the eccentricity (mm) of the concave lens and the reflection angle (degree). In FIGS. 7(a) and 7(b), the curvature radius R of the concave lens formed on the curved surface 13 is 0.75 mm, and the conic constant K is -1 (paraboloid).

When the eccentricity of the lens is 0 mm, as shown in Fig. 8(a), the beam is incident from the normal direction at the center of the mirror, and the light is reflected in the incident direction. The reflection angle at this time is 0 degrees. The position of the eccentricity 0, in other words, the incident beam may coincide with the rotational symmetry axis of the parabola.

As the incident beam moves away from the parabola's rotational symmetry axis in the radial direction, the reflection angle becomes larger. Here, the angle of the central axis of the reflected beam with respect to the central axis of the incident beam is called the "reflection angle". In addition, the amount of eccentricity in the direction approaching the light receiving surface from the rotationally symmetrical axis of the parabola is positive, and the amount of eccentricity in the direction away from the light receiving surface is negative.

In order to make the light incident on the collecting lens 10 bend about 90 degrees on the curved surface 13 and collect the light to the light receiving surface, as shown in FIG. 8(b), it is designed so that the light enters from the center of the concave mirror formed on the parabolic surface. (That is, the rotational symmetry axis of the parabola) is eccentric at -0.75mm.

Fig. 9 is a diagram showing the relationship between the positional deviation of the light receiving element and the dot size. As in FIG. 7, the curvature radius R of the concave lens formed on the curved surface 13 is 0.75 mm, and the conic constant K is -1.

As shown in FIG. 9(a), the light reflected on the curved surface 13 is collected toward the light receiving surface. FIG. 9(b) is a diagram showing the relationship between the positional deviation (mm) of the light receiving element (PD) 40 in the Z direction and the dot size (μm) on the light receiving element 40. As described above, the curved surface 13 is designed so that the point on the light receiving surface of the light receiving element 40 becomes a true circle and the smallest. The deviation in the height direction of the light receiving element 40 is relatively the position deviation in the height direction of the curved surface.

The position of the curved surface 13 of the collecting lens 10 is set at a position where the spot size of the light receiving surface becomes the smallest.

Fig. 10 shows an example of application to a multi-channel condenser lens. The condensing lens 20 has a plurality of curved surfaces 23-1 to 23-4 (hereinafter, collectively referred to as "curved surface 23" as appropriate) on an inclined surface 24 protruding at an obtuse angle from the bottom surface 21. The collecting lens 20 can be applied to a 4-channel light receiver. At this time, an array of four light receiving elements 40 is used on the substrate side.

As described with reference to FIGS. 7 to 9, the curved surfaces 23-1 to 23-4 are designed so that the direction of the incident light is curved by approximately 90 degrees and the light is collected to the light receiving surface to design the amount of eccentricity and the height position. The light reflected on each curved surface 23 does not pass through other optical surfaces, but is directly collected by the corresponding light receiving element 40 with the smallest spot size. Thereby, high light receiving efficiency can be maintained.

FIG. 11 is a front view and a side view of the light collecting lens 20. The front view shown in FIG. 11(a) is a view when the collecting lens 20 is viewed from the incident direction (Y direction). The side view shown in FIG. 11(b) is a view in the YZ plane including the optical axis of incident light.

The contours of the bottom surfaces of the curved surfaces 23-1 to 23-4 of the inclined surface 24 are elliptical, but with respect to the incident light to the condenser lens 20 (beam transmitted in the Y direction), as shown in FIG. 11(a) Almost circular.

In the side view of FIG. 11(b), the bottom surface 21, the top surface 22, the back surface 26, the light incident side surface 27, and the surface 28 of the condensing lens 20 do not require such high precision in shaping. The inclined surface 24 is inclined at a front-rear angle of 135 degrees with respect to the bottom surface 21. Since the actual optical path conversion and light collection are performed on each of the curved surfaces 23-1 to 23-4, the self-forming on the inclined surface 24 does not require high precision.

On the other hand, the direction of the incident light of each of the curved surfaces 23-1 to 23-4 is changed by approximately 90 degrees, and the light collection efficiency on the light receiving surface 41 of the corresponding light receiving element 40 is precisely processed. The curved surfaces 23-1 to 23-4 form the reflective film 25. Since the curved surfaces 23-1 to 23-4 form the same inclined surface 24, it is possible to form the reflective film 25 on the plural curved surfaces 23 in one film formation. In this way, a compact multi-channel light collecting lens 20 with high light-collecting performance is realized.

FIG. 12 is a schematic diagram of the optical transceiver 100 using the collecting lens 10 or 20 of the embodiment. The optical transceiver 100 is an example of an optical module to which the condenser lens of the embodiment is applied.

The optical transceiver 100 includes a ROSA 30, an optical transmission sub-assembly (TOSA: Transmitter Optical Sub-Assembly) 60, and a digital signal processor (DSP: Digital Signal Processor) 70. The collecting lens 10 or 20 (hereinafter, simply referred to as "collecting lens 10") is used for the ROSA 30 on the receiving side.

The optical transceiver 100 is connected to the optical fibers 81 and 82 through the optical connector 80. In this example, ROSA30 and TOSA60 are connected by one optical fiber, but when the 4-channel collecting lens 20 shown in FIG. 9 is used, 4-core fiber optic cables may be used on the receiving side and transmitting side.

The ROSA 30 has a light receiving element 40, a collecting lens 10 that guides the received light to the light receiving element 40, and a transimpedance amplifier (TIA) that amplifies and converts the photocurrent detected by the light receiving element 40 into a voltage signal. The optical signal emitted from the end surface of the optical fiber 81 is converted by approximately 90 degrees in the transmission direction of the collecting lens 10 and the light is collected to the light receiving surface of the light receiving element 40. The condensing lens 10 is arranged on the packaging substrate of ROSA 30 or the like with a simple configuration, and the ROSA 30 can be miniaturized. In addition, since the reflective film 15 is provided only on the curved surface 13, the manufacturing cost is reduced. The curved surface 13 has parameters designed so that the light spot on the light receiving surface becomes the smallest and circular shape, so that high light receiving efficiency can be maintained.

The analog electrical signal output from ROSA30 is digitally sampled and processed in DSP70.

The configuration of the transmission side is not directly related to the present invention, so the description will be omitted, but an electrical signal representing a logical value corresponding to the input data is input from the DSP 70 to the TOSA 60. In TOSA60, the light emitted from a light source such as a laser is modulated at high speed with an analog drive signal representing the input data, and the optical signal is output to the optical fiber 82.

The optical module of the embodiment is useful for optical communication.

In the above-mentioned embodiments and the scope of the patent application, when the direction of incident light is referred to as "90-degree conversion", it does not strictly mean that the central axis of the incident light is bent only by 90 degrees, but it means reflection at 90 degrees or its front and back angles. Also, when the light spot on the light-receiving surface is called a "true circle", it does not mean a point that forms a complete true circle, but instead means that the light is collected into a shape close to a true circle, which includes deformation within the allowable range.

The present invention is not limited to the above-mentioned embodiment, and includes various modifications. The back surface 16 of the condensing lens 10 does not necessarily need to stand vertically from the bottom surface 11, and may stand at an acute or obtuse angle with respect to the bottom surface 11. Similarly, the back surface 26 of the condensing lens 20 does not necessarily need to stand vertically from the bottom surface 21, and may stand at an acute or obtuse angle with respect to the bottom surface 21. The number of channels realized by the multi-channel collecting lens 20 is not limited to four, and can be set to 8 channels, 16 channels, etc., according to the number of cores and the arrangement of the optical fiber array. The arrangement of the curved surface 23 on the inclined surface 24 is not limited to one row, and for example, 4 channels×2 rows or 8 channels×2 rows can be formed.

Since the plural curved surfaces 23 are covered by the reflective film 25 in one film forming process, the manufacturing process is simplified. By placing the multi-channel light collecting lens 20 on the mounting substrate, the curved surface 23 formed on the inclined surface 24 protruding at an obtuse angle from the bottom surface 21 is opposed to the array of light-receiving elements, so that the optical path of the incident light can be converted to Light-receiving surface. Thereby, the optical module can be miniaturized and high light receiving efficiency can be maintained.

10, 20: Collecting lens 11, 21: bottom surface 13,23-1~23-4: Curved surface 14,24: Inclined surface 15,25: reflective film 30: ROSA (optical module) 40: Light receiving element 41: Light-receiving surface 50: substrate 50S: The surface of the substrate 80: Optical connector 100: Optical transceiver (optical module)

[Fig. 1] A schematic diagram of a conventional optical system in which a light signal is incident on a light receiving element. [Fig. 2] A diagram explaining the problems that occur when the collecting lens and the reflecting mirror are integrated in this way. [Fig. 3] A schematic diagram of the collecting lens of the embodiment. [Fig. 4] A diagram illustrating the light collection characteristics of the curved surface of the light collection lens. [Figure 5] An oblique view of the collecting lens. [Figure 6] Front view and side view of the collecting lens. [Fig. 7] A graph showing the characteristics of the curved surface of the collecting lens. [Fig. 8] A diagram explaining the decentering of the lens. [Fig. 9] A diagram showing the relationship between the positional deviation of the light receiving element and the dot size. [Fig. 10] A diagram showing an example of application to a multi-channel condenser lens. [Fig. 11] A front view and a side view of the collecting lens of Fig. 9. [Fig. 12] A schematic diagram of an optical transceiver using the collecting lens of the embodiment.

10: Collecting lens

11: bottom surface

12: above

13: curved surface

15: reflective film

16: back

30: ROSA (optical module)

40: Light receiving element

41: Light-receiving surface

50: substrate

50S: The surface of the substrate

Claims (11)

A light collecting lens having: a bottom surface; An inclined surface extending at an obtuse angle with respect to the aforementioned bottom surface; The curved surface formed on the aforementioned inclined surface; The reflective film formed on the aforementioned curved surface; among them, The curved surface changes the direction of the incident light while condensing the incident light to a predetermined position in a plane parallel to the bottom surface. The light collecting lens according to claim 1, wherein the curved surface is a concave surface decentered by a predetermined amount from the rotational symmetry axis of the parabola. The collecting lens according to claim 1 or 2, wherein the curved surface is designed so that the spot size at the predetermined position becomes the smallest. The light collecting lens according to any one of claims 1 to 3, wherein the curved surface bends the direction of the incident light by 90 degrees. The light collecting lens according to any one of claims 1 to 4, wherein a plurality of curved surfaces are formed on the inclined surface. An optical module having: a light receiving element; Make incident light incident on the condenser lens of the aforementioned light receiving element; The aforementioned light collecting lens has: Located on the bottom surface of the mounting surface of the aforementioned light receiving element; An inclined surface extending at an obtuse angle with respect to the aforementioned bottom surface; The curved surface formed on the aforementioned inclined surface; The reflective film formed on the aforementioned curved surface; among them, The curved surface changes the direction of the incident light to collect the incident light to the light receiving surface of the light receiving element. The optical module according to claim 6, wherein the inclined surface of the condensing lens protrudes from the bottom surface obliquely upward of the light receiving element. The optical module according to claim 6 or 7, wherein the curved surface is a concave surface eccentric by a predetermined amount from the rotational symmetry axis of the parabola. The optical module according to any one of claims 6 to 8, wherein the curved surface is designed such that the spot size on the light receiving surface becomes the smallest. For example, the optical module described in any one of Claims 6 to 9, further has: an optical fiber connected to the aforementioned optical module; among them, The aforementioned optical fiber is connected in a direction parallel to the aforementioned mounting surface; The curved surface transforms the direction of the incident light from the end surface of the optical fiber by 90 degrees, and collects the incident light to the light receiving surface. For example, the optical module described in any one of claims 6 to 9 further has: a multi-core optical fiber connected to the aforementioned optical module; among them, The inclined surface has a plurality of curved surfaces.

Images