Optical Devices

Abstract

To provide an optical device having satisfactory optical coupling efficiency with the outside.SOLUTION: An optical device 1 includes: a first lens 10 that is joined to an end face of an optical waveguide of an optical element and radiates emission light from the optical element; and a second lens 20 that is optically coupled to the first lens 10 and converts emission light from the first lens 10 to collimate light.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to optical devices. [Background technology]

[0002] In recent years, in response to the demand for faster communication speeds, optical devices used in communication networks have been miniaturized and multiple optical elements have been densely packed to increase the capacity of the network. In order to increase the capacity of the network, efficient optical communication is required, and the optical coupling efficiency of the optical system needs to be improved. Patent Document 1 discloses a laser diode module that optically couples a laser diode to an optical fiber, and in order to introduce the light emitted from the laser diode into the optical fiber, the laser diode and the optical fiber entrance end face are fixed in a predetermined positional relationship, and a focusing lens that is optically coupled to the laser diode and the optical fiber is provided between the laser diode and the optical fiber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-281501 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the laser diode module described in Patent Document 1, in order to efficiently guide the light from the laser diode to an external optical fiber, it is required to position each component of the laser diode, the condenser lens, and the optical fiber with extremely high precision. Similarly, in an optical circuit in which a large number of optical elements are densely integrated using an optical waveguide formed on a substrate, it is necessary to efficiently input light from the optical waveguide of the optical circuit to an external element, and further to efficiently input light from the external element to the optical waveguide of the optical circuit. For this reason, an interface with good optical coupling efficiency with external elements is required.

[0005] The present disclosure has been made in consideration of these circumstances, and has an object to provide an optical device with good optical coupling efficiency with the outside. [Means for solving the problem]

[0006] The optical device according to the present disclosure includes a first lens bonded to an end face of an optical waveguide of an optical element and emitting light emitted from the optical element, and a second lens optically coupled to the first lens and converting the light emitted from the first lens into collimated light, the optical element being any one of a laser element, an optical modulation element, and an optical amplification element. The first lens is an aspheric lens having a curved surface protruding on the side opposite to the optical element, and the side of the optical element that is joined to the end face of the optical waveguide is formed in a plane perpendicular to the optical axis of the first lens, and the area of ​​the plane is smaller than the maximum area of ​​a cross section perpendicular to the optical axis of the optical waveguide. Effect of the Invention

[0008] According to the present disclosure, an optical device having good optical coupling efficiency with the outside can be obtained. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 illustrates an example of an optical device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a perspective view of the optical device shown in FIG. [Diagram 3] 2 is a diagram for explaining the spread of light from an optical waveguide in the optical device shown in FIG. [Figure 4] 2 is a diagram showing an optical path from an optical element to an optical fiber in the optical device shown in FIG. 1. [Diagram 5] 2 is a diagram showing the optical device shown in FIG. 1 in which the optical axis of the optical waveguide and the optical axis of the first lens are misaligned. [Figure 6] 2 is a characteristic diagram showing the relationship between the increase in loss and the reflection return rate with respect to the amount of axial misalignment between the optical axis of the optical waveguide and the optical axis of the first lens in the optical device shown in FIG. [Figure 7] 2 is a characteristic diagram showing the relationship between the beam diameter of an optical waveguide and loss due to vignetting when the image magnification of a first lens is changed in the optical device shown in FIG. 1. [Figure 8]2 is a characteristic diagram showing the relationship between the radius of curvature of a hemispherical portion, the image magnification, and the distance from the tip of the lens to a virtual image in the optical device shown in FIG. 1 when the lens thickness is constant. [Figure 9] 2 is a characteristic diagram showing the relationship between the radius of curvature of a lens and loss due to aberration in the optical device shown in FIG. 1. [Figure 10] 11 is a diagram for explaining the relationship between lens aberration and a virtual image when the thickness of a first lens is increased. FIG. [Figure 11] 2 is a diagram for explaining an aspheric lens used as a first lens in the optical device shown in FIG. 1. [Figure 12A] FIG. 11 is a diagram showing another example of an aspheric lens. [Figure 12B] FIG. 13 is a diagram showing yet another example of an aspheric lens. [Figure 12C] FIG. 13 is a diagram showing yet another example of an aspheric lens. [Figure 13] FIG. 1 is a diagram showing an optical path from an optical element to an optical fiber in a conventional optical device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) An optical device according to the present disclosure includes a first lens bonded to an end face of an optical waveguide of an optical element and emitting light emitted from the optical element, and a second lens optically coupled to the first lens and converting the light emitted from the first lens into collimated light, the optical element being any one of a laser element, an optical modulation element, and an optical amplification element. the first lens is an aspheric lens having a curved surface protruding on the side opposite to the optical element, the side of the optical element that is joined to the end face of the optical waveguide is formed in a plane perpendicular to the optical axis of the first lens, and the area of ​​the plane is smaller than the maximum area of ​​a cross section perpendicular to the optical axis of the optical waveguide. This makes it possible to obtain an optical device with good optical coupling efficiency with the outside world. This makes it possible to suppress light loss due to aberration in the first lens.

[0011] (2) The optical device according to the present disclosure may further include a third lens that focuses the collimated light emitted from the second lens, and an optical fiber that is optically coupled to the third lens and into which the focused light emitted from the third lens is incident, thereby making it possible to efficiently guide the light from the optical device to the optical fiber.

[0017] ( 3 ) In the optical device according to the present disclosure, the first lens has a refractive index n, a predetermined position on the surface on the optical element side is point O, an arbitrary position on the surface excluding the surface on the optical element side is point S, and the position of a virtual image formed by the first lens is point P, where the value obtained by multiplying the distance between point O and point S by the refractive index n minus the distance between point S and point P is a constant value. This makes it possible to suppress light loss due to aberration of the first lens.

[0018] ( 4 ) In the optical device according to the present disclosure, the optical axis of the optical waveguide may be perpendicular to the surface of the first lens facing the optical element at the position of point O, and point P of the virtual image of the first lens may be on the optical axis of the optical waveguide. This allows the first lens to be formed symmetrically with respect to the optical axis, making it easier to manufacture.

[0019] ( 5 ) In the optical device according to the present disclosure, the optical axis of the optical waveguide may be perpendicular to the surface of the first lens facing the optical element at the position of point O, and point P of the virtual image of the first lens may be located at a position away from the optical axis of the optical waveguide. This makes it possible to reduce the effect of light reflected back at the surface of the first lens while suppressing light loss due to aberration of the first lens.

[0020] ( 6 ) In the optical device according to the present disclosure, the optical axis of the optical waveguide may be perpendicular to the surface on the optical element side at a position other than point O. This makes it possible to reduce the effect of light reflected back at the surface of the first lens while suppressing light loss due to aberration of the first lens.

[0021] ( 7 In the optical device according to the present disclosure, the first lens has at least a hemispherical portion on the side optically coupled to the second lens. This makes it possible to suppress the spread of light emitted from the optical waveguide and to reduce the power of the second lens. In addition, it is possible to increase the tolerance of the alignment accuracy when mounting each component.

[0022] ( 8 In the optical device according to the present disclosure, the thickness of the first lens in the optical axis direction is greater than the radius of curvature of the hemispherical portion, which increases the image magnification of the first lens and suppresses the spread of light even when the beam diameter of the optical waveguide is small.

[0023] (9) In the optical device according to the present disclosure, the optical axis of the first lens may be offset from the optical axis of the optical waveguide of the optical element by half or more of the beam diameter in the optical waveguide of the optical element, thereby making it possible to reduce the influence of light reflected back at the surface of the first lens.

[0024] ( 10 In the optical device according to the present disclosure, the first lens is made of either glass or resin. This increases the options for lens materials. In addition, when resin is used, it can be formed using 3D printing technology.

[0025] [Details of the embodiment of the present invention] Specific examples of optical devices according to the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to the following examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In addition, as long as a combination of multiple embodiments is possible, the present invention includes any combination of embodiments. Note that in the following description, components and the like with the same reference numerals in different drawings may be considered to be similar, and their description may be omitted.

[0026] (Embodiment 1) In this embodiment, a laser element is described as an example of an optical element used in the optical device, but the optical element is not limited to a laser element and may be an optical modulation element or an optical amplification element as long as it emits light from an optical waveguide to the outside. FIG. 1 is a diagram showing an example of an optical device according to an embodiment of the present disclosure, and FIG. 2 is a perspective view of the optical device shown in FIG. 1. FIG. 3 is a diagram for explaining the spread of light from an optical waveguide in the optical device shown in FIG. 1, and FIG. 4 is a diagram showing an optical path from an optical element to an optical fiber in the optical device shown in FIG. 1. Note that the optical element and the optical fiber are omitted in FIG. 4.

[0027] The optical device 1 of this embodiment includes, as components of the optical system, a laser diode chip (hereinafter referred to as "LD chip") 40 which is a laser element, a first lens 10, a second lens 20, a third lens 30, and an optical fiber 60 which is a single mode fiber (SMF). The LD chip 40 is mounted on a subcarrier 52 made of, for example, aluminum nitride, which has a high thermal conductivity. The second lens 20 is a collimating lens which converts the light incident from the first lens into a collimated light which is a parallel beam, as described later, and is fixed on a carrier 51 together with the subcarrier 52 on which the LD chip 40 is mounted. The carrier 51 is disposed in a package 50 which uses, for example, an Fe-Ni-Co alloy (for example, Kovar, which is a product name). A drive signal for the LD chip 40 is supplied from the outside of the package 50 via a feedthrough 53.

[0028] The first lens 10 of this embodiment is formed from resin and is bonded to the end face of the optical waveguide 41 of the LD chip 40. When the first lens 10 is formed from resin, it can be manufactured using 3D printing technology. The first lens 10 and the second lens 20 are optically coupled, and the second lens is fixed on the carrier 51 with high precision using an adhesive such as an epoxy adhesive in an aligned state. The optical fiber 60 is positioned and held in the receptacle 62 in a state where it is housed in the ferrule 61. The third lens 30 is a condenser lens, and the collimated light from the second lens 20 is condensed by the third lens 30 and coupled to the optical fiber 60. The third lens 30 is housed in a holder 63 arranged outside the package 50, and the third lens 30 and the optical fiber 60 are aligned so as to obtain optical coupling, and the holder 63 and the package 50 are fixed by, for example, YAG welding.

[0029] The LD chip 40 of the present disclosure is an optical element having an optical waveguide 41. Not limited to semiconductor lasers with optical waveguides, for example, semiconductor lasers having double heterojunctions form optical waveguides because the active layer has a larger refractive index than the surrounding cladding layers, and can be said to be optical elements having optical waveguides. As shown in FIG. 3, in this embodiment, the first lens 10 is formed as a hemispherical lens and is bonded to the end face of the optical waveguide 41 of the LD chip 40. The optical axis (center axis) of the first lens 10 is provided without offset so as to coincide with the optical axis of the optical waveguide 41 of the LD chip 40.

[0030] In the optical device 1, the first lens 10 is provided on the end face of the optical waveguide 41 of the LD chip 40, so that the light emitted from the optical waveguide 41 of the LD chip 40 (not shown) is efficiently guided to the second lens 20 by the first lens 10 as shown in Fig. 4. Then, after being converted into collimated light A by the second lens 20, the light is collected by the third lens and guided to the optical fiber 60 (not shown). Therefore, the optical device 1 realizes an optical device 1 with better optical coupling efficiency with the external optical fiber 60 than the conventional optical device 1.

[0031] Here, the difference between the optical device of the present disclosure and the conventional optical device will be described. FIG. 13 is a diagram showing an optical path from an optical element to an optical fiber in a conventional optical device as a model for comparison, and similarly to FIG. 4, the optical element and the optical fiber are omitted. The conventional optical device 1' also includes a first lens 10', a second lens 20' which is a collimating lens, and a third lens 30 which is a condensing lens, and the light emitted from the optical waveguide 41 of the LD chip 40 (not shown) is guided to the second lens 20' by the first lens 10', and further converted into collimated light A by the second lens 20', and then condensed by the third lens 30 and guided to the optical fiber 60 (not shown).

[0032] The optical device 1' shown in FIG. 13 shows a case where a Gaussian beam with a beam radius ω of the optical waveguide of 0.8 μm and a wavelength λ of 1.55 μm is incident on a first lens 10' with a numerical aperture NA of 0.65. Here, the numerical aperture NA of the optical waveguide 41 is calculated from NA=λ / (π×ω) and is 0.62. As can be seen from the partially enlarged view of FIG. 13, the first lens 10' causes a phenomenon in which peripheral light is vignetted as shown by the dashed line B due to the diffusion of light from the optical waveguide. In the case of the optical device 1' shown in FIG. 13, the optical loss is 1.0 dB. In general, when the NA of the beam is 0.6 or more (beam radius ω is 0.8 μm or less), the light from the optical waveguide spreads so much that it becomes difficult for the lens to receive all the light. This causes optical loss.

[0033] Next, the optical device 1 of this embodiment will be described. Fig. 3 is a diagram for explaining the spread of light from the optical waveguide 41 in the optical device of this embodiment. The optical device 1 shown in Fig. 3 shows a case where the numerical aperture NA of the optical waveguide 41 is 0.62, similar to the conventional optical device 1' (see Fig. 13), and a Gaussian beam having a beam radius ω of 0.8 µm and a wavelength λ of 1.55 µm is emitted from the optical waveguide 41. The first lens 10 is a hemispherical lens with a refractive index n of 1.5 and a radius of curvature R of 50 µm, and the second lens 20 is a collimating lens with a numerical aperture NA of 0.65.

[0034] As shown in FIG. 3, in the optical device 1 of this embodiment, the first lens 10 is formed by bonding to the end face of the optical waveguide 41 of the LD chip 40. In the optical device 1, since there is no air between the LD chip 40 and the first lens 10, the light from the optical waveguide 41 is incident on the first lens 10 without leakage. If the refractive index of the first lens 10 is n, the spread of the light from the LD chip 40 becomes 1 / n times that in air due to refraction when it enters the first lens 10. On the other hand, the light incident from the center of the first lens 10, which is a hemispherical lens, enters perpendicularly to the lens surface and is not refracted when it is emitted, so the spread is maintained. Therefore, the spread of the light from the LD chip 40 is suppressed to 1 / n times that in air throughout the first lens 10.

[0035] In the optical device 1 of this embodiment, when the refractive index n of the first lens 10 is 1.5, the light from the optical waveguide 41 can be guided to the second lens 20 with almost no loss of 0.06 dB. This allows the power of the second lens 20 to be reduced, and the tolerance for misalignment during mounting can be increased.

[0036] (Embodiment 2) In the first embodiment, the optical axis of the optical waveguide 41 and the optical axis (center axis) of the first lens 10 are aligned, so that light is incident perpendicularly on the surface of the first lens 10, and the light reflected on the surface travels in the opposite direction. This increases the effect of the reflected light returning to the optical waveguide 41. In the second embodiment, in order to deal with the problem of the reflected light returning on the surface of the first lens 10, the optical axis of the first lens 10 is shifted from the optical axis of the optical waveguide 41. Note that, even when the light travels from the second lens 20 to the first lens 10 as described later in the fifth embodiment, reflected light is generated on the surface of the first lens 10, which affects the optical waveguide such as an optical fiber, so it is desirable to shift the optical axis of the first lens 10 from the optical axis of the optical waveguide 41.

[0037] 5 is a diagram showing the optical device shown in FIG. 1 in which the optical axis of the optical waveguide and the optical axis of the first lens are shifted. For simplification, the LD chip 40 is omitted in FIG. 5. In addition, in FIG. 5, the optical axis of the first lens 10 is shifted in parallel upward from the optical axis of the optical waveguide 41 of the LD chip 40 (not shown) by an axial shift amount d to provide an offset. For this reason, among the light emitted from the first lens, the light incident on the upper part of the paper is not converted into collimated light and is vignetted by the second lens 20.

[0038] FIG. 6 is a characteristic diagram showing the relationship between the loss increase and the reflection return rate with respect to the amount of axial shift between the optical axis of the optical waveguide and the optical axis of the first lens in the optical device shown in FIG. 1. In FIG. 6, the solid line shows the loss increase (dB) with respect to the amount of axial shift (μm) on the horizontal axis, and the dashed line shows the reflection return rate (dB) with respect to the amount of axial shift. The specifications of the optical waveguide 41, the first lens 10, the second lens 20, etc. in the characteristic diagram of FIG. 6 are the same as those described in the first embodiment. As can be seen from FIG. 6, if the amount of axial shift d is increased, the loss increase increases, but the reflection return rate decreases significantly. For example, if the amount of axial shift d is set to 1 μm or more, the reflection return light can be suppressed to -40 dB or less with almost no loss increase. In addition, in terms of the relationship with the beam diameter of the optical waveguide 41 of the LD chip 40, the reflected back light can be sufficiently suppressed by offsetting half the beam diameter of the optical waveguide 41, i.e., the beam radius ω (0.8 μm in this embodiment) or more.

[0039] (Embodiment 3) In the first and second embodiments, the case where the beam radius ω of the optical waveguide 41 is 0.8 μm has been described, but the spread angle of the light beam increases in inverse proportion to the beam radius ω. Therefore, even in the configuration of the second embodiment, as the beam radius ω decreases, light is vignetted by the second lens 20, resulting in a loss.

[0040] Fig. 7 is a characteristic diagram showing the relationship between the loss due to vignetting and the beam radius of the optical waveguide when the image magnification of the first lens is changed in the optical device shown in Fig. 1. Referring to Fig. 7, in a hemispherical lens with an image magnification of 1.5x, the loss becomes significantly large when the beam radius is 0.7μm or less. For example, when the beam radius is 0.5μm, the loss exceeds 1.2dB. On the other hand, when the image magnification is increased to 1.8x or 2.3x, the spread of the light becomes smaller in inverse proportion, so the loss decreases and it can be seen that it is possible to handle a smaller beam radius.

[0041] The image magnification of a hemispherical lens is determined by the ratio of the refractive index n of the hemispherical lens to the refractive index of air, so the image magnification of a hemispherical lens with a refractive index n is n times. Therefore, the first means for increasing the image magnification is to use a hemispherical lens with a large refractive index n for the first lens 10, which makes it possible to increase the image magnification in proportion to the refractive index n. The second means is to change the shape of the first lens 10 and make the radius of curvature R of the spherical surface smaller than the thickness of the lens (the length of the lens in the optical axis direction).

[0042] Fig. 8 is a characteristic diagram showing the relationship between the radius of curvature of the hemispherical portion and the image magnification and the distance from the tip of the lens to the virtual image when the lens thickness is constant in the optical device shown in Fig. 1, and Fig. 9 is a characteristic diagram showing the relationship between the radius of curvature and the loss due to aberration in the optical device shown in Fig. 1. In Fig. 8, the solid line shows the image magnification versus the radius of curvature of the lens (μm), and the dashed line shows the distance (μm) from the tip of the lens to the virtual image versus the radius of curvature of the lens (μm). Fig. 10 is a diagram for explaining the relationship between the lens aberration and the virtual image when the thickness of the first lens is increased.

[0043] FIG. 8 shows a case where the thickness (length in the optical axis direction) D of the first lens 10 is constant at 50 μm, and the radius of curvature R of the hemispherical portion 11 is small to increase the image magnification. When the radius of curvature R is 50 μm, which is equal to the lens thickness D, the first lens 10 becomes a hemispherical lens. FIG. 9 shows a case where the beam radius ω of the optical waveguide 41 is constant at 0.5 μm. In the third embodiment, the thickness D of the first lens 10 is larger than the radius of curvature R of the hemispherical portion 11, so that the large lens has a bullet shape as shown in FIG. 10. Also, point O, which indicates the incident position of the light from the optical waveguide 41, is shifted from the center of the hemispherical portion 11 toward the optical waveguide 41. In FIG. 10, the position of the virtual image is indicated by point P.

[0044] Referring to FIG. 8, it can be seen that the radius of curvature R should be 30 μm in order to make the image magnification of the first lens 10 2.3 times. In this case, the position P of the virtual image is 75 μm from the tip of the lens. On the other hand, referring to FIG. 9, the smaller the radius of curvature R, the greater the loss due to aberration. At an image magnification of 2.3 times (radius of curvature 30 μm), the loss is 0.29 dB, which is greater than the loss due to vignetting. The enlarged partial view shown in FIG. 10 is an enlarged view of the vicinity of the virtual image position, and shows that the virtual image is not focused on one point due to aberration. Thus, in this embodiment, the first lens 10 is used, the thickness of which is greater than the radius of curvature R of the hemispherical portion 11, so that the image magnification can be increased and a small beam radius ω can be accommodated. However, in this embodiment, the position of the incident light on the first lens 10 (light source) is different from the center position of the lens sphere, so that a loss due to aberration occurs, and the smaller the radius of curvature R, the greater the loss due to aberration.

[0045] (Embodiment 4) In order to suppress loss due to aberration, an aspheric design of the first lens 10 is necessary. Fig. 11 is a diagram for explaining an aspheric lens used in the first lens in the optical device shown in Fig. 1. In this embodiment, in order to focus light from a light source on one point of a virtual image, the property of the first lens 10A is utilized that when light emitted from one point is focused on one point, the optical path length is equal regardless of the path taken.

[0046] 11, the refractive index of first lens 10A is n, a predetermined position on the surface on the LD chip 40 side is point O, an arbitrary position on the surface of first lens 10A excluding the end face side of optical waveguide 41 is point S, and the position of a virtual image formed by first lens 10A is point P, the value obtained by multiplying the distance between points O and S by the refractive index n and subtracting the distance between points S and P is a constant value. This relationship can be expressed by the following equation. n × distance between points OS – distance between points SP = constant value (Equation 1)

[0047] The first lens 10A shown in FIG. 11 shows a case where the optical axis of the optical waveguide 41 is perpendicular to the surface of the first lens 10A on the LD chip 40 side at the position of point O, and is designed so that the position point P of the virtual image is located on the optical axis of the optical waveguide 41. In this case, the optical axis of the first lens 10A coincides with the optical axis of the optical waveguide 41, and the lens shape can be formed symmetrically with respect to the optical axis. The first lens 10A is formed on a plane perpendicular to the optical axis of the first lens 10A on the side that is joined to the end face of the optical waveguide 41, and the area of ​​this plane is smaller than the maximum area of ​​the cross section perpendicular to the optical axis of the first lens 10A, and shows an aplanatic lens with an image magnification of 2.3 times that satisfies the relationship of formula 1. In the first lens 10A, the loss when the beam radius ω of the optical waveguide 41 (not shown) is 0.5 μm is 0.09 dB, but this loss is due to vignetting and not due to aberration. Furthermore, since the light from the optical waveguide 41 is not perpendicularly incident on the lens surface except for the optical axis, the reflection return rate is good at -45 dB even without shifting the optical axis of the first lens 10 from the optical axis of the optical waveguide 41. In this way, the numerical aperture NA of the beam can be reduced by the first lens 10A, which makes it easier to design the second and subsequent lenses.

[0048] FIG. 12A is a diagram showing another example of an aspherical lens, and the first lens 10B shows a case where the magnitude of the fixed value in Equation 1 is smaller (larger on the negative side) than that of the first lens 10A shown in FIG. 11. FIG. 12B is a diagram showing yet another example of an aspherical lens, and the first lens 10C shows a case where the magnitude of the fixed value in Equation 1 is minus infinity. In this way, in this embodiment, it is possible to select various shapes of the first lens. In addition, the first lens 10A of this embodiment is less affected by reflected return light, but as described in the second embodiment, the influence of reflected return light from the lens surface can be further suppressed by shifting the optical axis of the first lens 10A from the optical axis of the optical waveguide 41.

[0049] In addition, the aspherical lens shown in this embodiment can also set the position point P of the virtual image to a position away from the optical axis of the optical waveguide 41. FIG. 12C is a diagram showing yet another example of an aspherical lens. The first lens 10D shown in FIG. 12C is designed using (Formula 1) so that the optical axis of the optical waveguide is perpendicular to the surface of the first lens 10D on the LD chip 40 side at the position O, and the position point P of the virtual image of the first lens 10D is a position away from the optical axis of the optical waveguide 41. For this reason, the straight line (optical axis) connecting the position point O (position of the light source) where the first lens 10D is in contact with the optical waveguide 41 and the position point P of the virtual image intersects with the optical axis of the optical waveguide 41 and is shifted. Thus, in this embodiment, an aspherical design is possible even when the optical axis of the first lens 10D is shifted from the optical axis of the optical waveguide, and this not only suppresses the influence of the reflected light, but also eliminates aberration due to the shift of the optical axis, and suppresses an increase in loss.

[0050] In this embodiment, similarly to the second embodiment, the optical axis of the first lens 10A and the optical axis of the optical waveguide 41 may be shifted from each other. In this case, the optical axis of the optical waveguide 41 may be made perpendicular to the surface of the first lens 10A on the LD chip 40 side at a position other than point O. In addition, in the case of the first lens 10D in which the position P of the virtual image shown in Fig. 12C is located away from the optical axis of the optical waveguide 41, the optical axis of the optical waveguide 41 may be made perpendicular to the surface of the first lens 10D on the LD chip 40 side at a position other than point O. [Explanation of symbols]

[0053] 1, 1'...optical device, 10, 10', 10A, 10B, 10C...first lens, 11...hemispherical portion, 20, 20'...second lens, 30...third lens, 40...LD chip, 41...optical waveguide, 50...package, 51...carrier, 52...subcarrier, 53...feedthrough, 60...optical fiber, 61...ferrule, 62...receptacle, 63...holder.

Claims

1. a first lens bonded to an end surface of an optical waveguide of an optical element and configured to emit light emitted from the optical element; a second lens that is optically coupled to the first lens and converts the light emitted from the first lens into collimated light, the optical element is any one of a laser element, an optical modulation element, and an optical amplification element; an optical device, wherein the first lens is an aspheric lens having a curved surface protruding on the side opposite to the optical element, and a side of the optical element that is joined to the end face of the optical waveguide is formed in a plane perpendicular to the optical axis of the first lens, and an area of ​​the plane is smaller than a maximum area of ​​a cross section perpendicular to the optical axis of the optical waveguide.

2. a third lens that collects the collimated light emitted from the second lens; The optical device according to claim 1 , further comprising: an optical fiber optically coupled to the third lens, into which the focused light emitted from the third lens is incident.

3. 3. The optical device of claim 1, wherein the first lens has a refractive index n, a predetermined position on the surface facing the optical element is point O, an arbitrary position on the surface of the first lens excluding the surface facing the optical element is point S, and a position of a virtual image formed by the first lens is point P, and a value obtained by multiplying the distance between point O and point S by the refractive index n minus the distance between point S and point P is a constant value.

4. 4. The optical device according to claim 3, wherein the optical axis of the optical waveguide is perpendicular to the surface of the first lens facing the optical element at the position of the point O, and the position point P of the virtual image of the first lens is on the optical axis of the optical waveguide.

5. 4. The optical device according to claim 3, wherein the optical axis of the optical waveguide is perpendicular to the surface of the first lens facing the optical element at the point O, and the position point P of the virtual image of the first lens is located away from the optical axis of the optical waveguide.

6. The optical device according to claim 3 , wherein an optical axis of the optical waveguide is perpendicular to a surface on the optical element side at a position other than the point O.

7. The optical device according to claim 1 , wherein the first lens has at least a hemispherical portion on a side optically coupled to the second lens.

8. The optical device according to claim 7 , wherein the first lens has a lens thickness in an optical axis direction that is greater than a radius of curvature of the hemispherical portion.

9. 9. The optical device according to claim 7, wherein the optical axis of the first lens is offset from the optical axis of the optical waveguide of the optical element by half or more of a beam diameter in the optical waveguide of the optical element.

10. The optical device according to claim 1 , wherein the first lens is made of glass or resin.

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