Optical systems and optical communication devices

Abstract

To provide an optical communication device that can be made smaller and lighter and an optical system that can be applied thereto.SOLUTION: A first lens group (L1) having negative refractive power and a second lens group (L2) having positive refractive power are arranged in this order from the side opposite to a light source (S). The second lens group (L2) is movable along an optical axis so as to change distance from other lens groups. The first lens group (L1) and the second lens group (L2) satisfy the relationship expressed by a specific formula.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an optical system and an optical communication device. [Background technology]

[0002] While radio wave communication technologies such as 5G (fifth-generation mobile communication system) have achieved dramatic speed increases, their communication speeds have theoretically reached their upper limit. Achieving further speed increases in communication is difficult from the standpoint of cost and feasibility. Among these technologies, optical wireless communication technology is attracting attention as a way to achieve even higher communication speeds.

[0003] Light is an electromagnetic wave, but it offers greater flexibility in its use compared to radio waves, and its high directivity means it does not propagate over wide areas like radio waves, giving it a security advantage. For this reason, it is considered suitable for communication between stationary objects, and is also considered advantageous as a complementary technology to radio waves in space communication between artificial satellites.

[0004] In optical communication, the communication distance is generally very long, and the receiving antenna is also small. Therefore, it is difficult to receive the communication light at the receiving end, and if the receiving end takes time to detect the light, communication may be delayed. For this reason, a separate optical system is used for beacon purposes to align the position of the receiving antenna, which is located at a distance. This beacon optical system is required to be able to handle various propagation modes of light, from collimated light to divergent or convergent light.

[0005] Optical systems for communication light with various propagation modes include a variable magnification optical system that comprises a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group that satisfies the relationship of a specific equation (see, for example, Patent Documents 1 and 2). Furthermore, a beam expander is known that comprises a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with negative refractive power, with one group fixed and two groups movable (see, for example, Patent Documents 3 and 4). In addition, a projection optical system is known that is composed of anamorphic lenses and has first to third lens groups with positive-negative-positive or negative-positive-negative refractive power, with the second lens group being movable (see, for example, Patent Document 5). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-003546 [Patent Document 2] Japanese Patent Publication No. 2006-003548 [Patent Document 3] Japanese Unexamined Patent Publication No. 55-151612 [Patent Document 4] Japanese Patent Application Publication No. 55-149914 [Patent Document 5] Japanese Patent Publication No. 2017-138490 [Overview of the project] [Problems that the invention aims to solve]

[0007] The optical system for beacons is sometimes installed separately from the optical system for optical communication. For example, when installed on an artificial satellite, miniaturization and weight reduction are required, but the conventional technology described above has problems in this regard.

[0008] For example, in the inventions described in Patent Documents 1 and 2, the imaging system requires the movement of two lens groups, the second and third lens groups, along the optical axis for focusing. As a result, there are two movable points in the optical system, which can complicate the structure of the optical communication device and make weight reduction difficult.

[0009] Furthermore, since the inventions described in Patent Documents 3 and 4 are beam expanders, in order to emit parallel light from incident parallel light, it is necessary to move two lens groups along the optical axis. Therefore, when applied to an optical system for optical communication, there are two movable locations for the lens groups in the optical system, which can complicate the structure of the optical communication device and make weight reduction difficult.

[0010] Furthermore, since the invention described in Patent Document 5 is for projection purposes, the overall length of the optical system can be very long. Therefore, miniaturization and weight reduction can be difficult.

[0011] One aspect of the present invention aims to realize an optical communication device and an optical system applicable thereto that can be miniaturized and made lighter. [Means for solving the problem]

[0012] To solve the above problems, an optical system according to one aspect of the present invention has a first lens group having negative refractive power and a second lens group having positive refractive power in that order, and the second lens group is movable along the optical axis so as to change the distance between it and the other lens groups, The following equation is satisfied. f1 / f2 ≤ -2.25 ···(1) L / f1≧-1.05···(2) however f1: Focal length of the first lens group f2: Focal length of the second lens group L: Total length of the optical system

[0013] Furthermore, in order to solve the above problem, an optical communication device according to one aspect of the present invention includes the above optical system, and a light source that emits communication light to the optical system disposed on a side opposite to the second lens group with respect to the first lens group, or a light receiving element such as a fiber core that receives communication light from the optical system.

Effects of the Invention

[0014] According to one aspect of the present invention, an optical communication device that can be reduced in size and weight and an optical system applicable thereto can be implemented.

Brief Description of Drawings

[0015] [Figure 1] It is a diagram schematically illustrating an optical configuration of the optical system of Example 1. [Figure 2] It is a spherical aberration diagram at a wavelength of 1550 nm obtained by reverse ray tracing of collimated light in the optical system of Example 1. [Figure 3] It is a diagram illustrating beam profile characteristics of collimated light in a far field in Example 1. [Figure 4] It is a diagram illustrating beam profile characteristics of divergent light in a far field in Example 1. [Figure 5] It is a diagram illustrating beam profile characteristics of convergent light in a far field in Example 1. [Figure 6] It is a diagram schematically illustrating an optical configuration of the optical system of Example 2. [Figure 7] It is a spherical aberration diagram at a wavelength of 1550 nm obtained by reverse ray tracing of collimated light in the optical system of Example 2. [Figure 8] It is a diagram schematically illustrating an optical configuration of the optical system of Example 3. [Figure 9] It is a spherical aberration diagram at a wavelength of 1550 nm obtained by reverse ray tracing of collimated light in the optical system of Example 3. [Figure 10] It is a diagram schematically illustrating an optical configuration of the optical system of Example 4. [Figure 11]This is a spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of collimated light in the optical system of Example 4. [Figure 12] This diagram schematically shows the optical configuration of the optical system in Example 5. [Figure 13] This is a spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of collimated light in the optical system of Example 5. [Figure 14] This diagram schematically shows the optical configuration of the optical system of Example 6. [Figure 15] This is a spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of collimated light in the optical system of Example 6. [Figure 16] This diagram schematically shows the optical configuration of the optical system in Example 7. [Figure 17] This is a spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of collimated light in the optical system of Example 7. [Figure 18] This diagram schematically shows the optical configuration of the optical system in Example 8. [Figure 19] This is a spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of collimated light in the optical system of Example 8. [Figure 20] This diagram schematically shows the optical configuration of the optical system of Example 9. [Figure 21] This is a spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of collimated light in the optical system of Example 9. [Figure 22] This diagram schematically shows the optical configuration of the optical system of Example 10. [Figure 23] This is a spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of collimated light in the optical system of Example 10. [Figure 24] This diagram schematically shows the optical configuration of the optical system in a specific lens arrangement of Comparative Example 1. [Figure 25] This figure shows the beam profile characteristics of light in the far field for the lens arrangement in Figure 24 (1). [Figure 26]This figure shows the beam profile characteristics of light in the far field for the lens arrangement in Figure 24 (2). [Figure 27] This figure shows the beam profile characteristics of light in the far field for the lens arrangement in (3) of Figure 24. [Figure 28] This diagram schematically shows the optical configuration of the optical system in a specific lens arrangement of Comparative Example 2. [Figure 29] This figure shows the beam profile characteristics of light in the far field for the lens arrangement in Figure 28 (1). [Figure 30] This figure shows the beam profile characteristics of light in the far field for the lens arrangement in Figure 28 (2). [Figure 31] This figure shows the beam profile characteristics of light in the far field for the lens arrangement in (3) of Figure 28. [Figure 32] This diagram schematically shows the configuration of an optical communication device according to one embodiment of the present invention. [Modes for carrying out the invention]

[0016] One embodiment of the present invention will be described in detail below.

[0017] 1.Optical system 1-1.Optical configuration An optical system according to an embodiment of the present invention has a first lens group and a second lens group in this order, starting from the side opposite the light source or photodetector. In this specification, a "lens group" includes one or more lenses, and the spacing between the lenses included in the lens group does not change.

[0018] Furthermore, within this specification, a lens group may include a cemented lens. When a lens group includes a cemented lens, the number of lenses is counted by counting the lenses that are bonded together. An example of a cemented lens is a cemented lens in which multiple lenses are integrated without an air gap in between. In this case, only the multiple lenses that make up the cemented lens are counted. Another example of a cemented lens is a cemented lens in which multiple lenses are integrated by a very thin layer of adhesive that is of a thickness that does not substantially affect the optical properties. In this case, the adhesive layer is not counted as a lens.

[0019] Furthermore, the lens group may include a composite lens in which one lens and resin are integrated. For example, a composite lens in which one lens and resin are integrated is counted as one lens.

[0020] (1) First lens group The first lens group is positioned furthest towards the far field in the optical system. The far field side is the outward side if the optical system is an illumination optical system that emits light from a light source outward, and is opposite to the light source. If the optical system is a light-receiving optical system that receives light from the outside with a light-receiving element, the far field side is the outward side, and is opposite to the light-receiving element. The first lens group has negative refractive power.

[0021] (2) Second lens group The second lens group is positioned on the far-field side, next to the first lens group. The second lens group has positive refractive power. Furthermore, the second lens group is arranged to be movable along the optical axis so as to vary the spacing between it and the other lens groups. From the viewpoint of miniaturization and weight reduction, it is preferable that the other lens groups are not configured to be movable along the optical axis for the purpose of controlling the form of light (collimation, divergence, and convergence).

[0022] (3) Third lens group The optical system of the embodiment of the present invention may further include a third lens group. The third lens group is arranged following the first and second lens groups. That is, the third lens group is arranged on the opposite side from the far-field side (closest to the light source or photodetector) relative to the second lens group. For example, if the optical system is an output system, the third lens group is arranged between the light source and the second lens group, and if the optical system is a photodetector system, the third lens group is arranged between the photodetector and the second lens group. The third lens group may have a positive refractive power or a negative refractive power.

[0023] (4) Other configurations At least one of the lens groups may include an aspherical lens. In a light-receiving optical system, it is required to focus the received light into a small spot diameter, such as the core of an optical fiber. It is preferable that at least one of the lens groups in the optical system of the embodiment of the present invention includes an aspherical lens from the viewpoint of good aberration correction and from the viewpoint of reducing the spot diameter when focusing. From the viewpoint of being advantageous for reducing the spot size when focusing, it is preferable that the first lens group has an aspherical lens.

[0024] Furthermore, the glass material of any lens in any lens group may be radiation-resistant glass. As will be described later, the optical system of the embodiment of the present invention has a simple optical configuration and can pass light of various characteristics while substantially maintaining the beam profile shape. Therefore, it is advantageous for mounting on artificial satellites and is advantageous for optical communication in outer space. In this application, radiation in outer space may discolor the glass material of the lenses, reducing the transmittance of the lenses and affecting optical communication through the optical system. From the viewpoint of suppressing such effects of radiation on the optical properties of lenses, it is preferable to use radiation-resistant glass for the glass material of the lenses.

[0025] The optical system of the embodiment of the present invention may further include other optical elements other than the lenses constituting the lens group, to the extent that the effects of the embodiment of the present invention are obtained. The other optical elements may be appropriately arranged in the optical system to the extent that they exert their effects.

[0026] 1-2. Operation of the optical system In the optical system according to an embodiment of the present invention, the second lens group moves along the optical axis so as to change the distance between it and the other lens groups. By operating in this manner, the form of light emitted from the optical system can be freely changed from collimated light to divergent or focused light with a simple configuration. Therefore, when this optical system is used in optical communication, it is suitable for achieving miniaturization of the optical system of an optical communication device.

[0027] 1-3. Equations representing the conditions of the optical system The optical system according to an embodiment of the present invention preferably has the configuration described above and satisfies one or more of the following formulas. f1 / f2 ≤ -2.25 ···(1) L / f1≧-1.05···(2) however f1: Focal length of the first lens group f2: Focal length of the second lens group L: Total length of the optical system

[0028] In optical communication, even if a light source generates light with a Gaussian distribution and emits collimated, divergent, or focused light as communication light through an optical system, it is preferable that the characteristics of the light after passing through the optical system remain the same Gaussian distribution as when emitted from the light source. When the optical system satisfies both equations (1) and (2) above, it is possible to emit light with various characteristics such as collimated, divergent, and focused light from the optical system. When the optical system does not simultaneously satisfy both equations (1) and (2) above, it may be difficult to emit focused light from the optical system. In this case, the beam profile shape of the light emitted from the optical system may be greatly distorted from the shape of a Gaussian distribution, which may adversely affect optical communication. From the above viewpoint, if equation (1) is true, it is more preferable that f1 / f2 is -3.22 or less, and more preferably -3.30 or less. Also, if equation (2) is true, from the above viewpoint, it is more preferable that L / f1 is -0.70 or more, and more preferably -0.66 or more.

[0029] Furthermore, it is preferable that the optical system according to the embodiment of the present invention has the above-described configuration and satisfies the following formula (3). md² / f²≧0.06···(3) however md2: Distance traveled by the second group f2: Focal length of the second lens group

[0030] It is preferable for the optical system to satisfy equation (3) from the viewpoint of achieving appropriate control of the beam angle by moving the second lens group. If the optical system does not satisfy equation (3), the movement sensitivity of the second lens group may become excessively high in controlling the characteristics of the signal light (collimation, divergence, or convergence, etc.) by moving the second lens group, which may reduce the stopping accuracy of the second lens group and increase the error in the beam angle of the signal light. From the viewpoint of achieving appropriate movement sensitivity and appropriate stopping accuracy of the second lens group, it is preferable that md2 / f2 is 0.21 or higher.

[0031] Furthermore, it is preferable that the optical system according to the embodiment of the present invention has the above-described configuration and satisfies the following formula (4). D3 / fa≧0.16···(4) however D3: Distance along the optical axis from the lens surface closest to the light source in the third lens group to the point of emission of the light source. fa: Focal length of the optical system

[0032] When the optical system has a third lens group as the lens group closest to the light source, satisfying equation (4) is preferable from the viewpoint of achieving appropriate control of the beam angle by moving the second lens group. If the optical system does not satisfy equation (4), the distance from the light source to the optical system (third lens group) becomes excessively short, which may make it difficult to properly control the beam angle. From the viewpoint of setting the distance from the light source to the optical system to an appropriate distance for achieving appropriate control of the beam angle, it is preferable that D3 / fa is 0.32 or greater.

[0033] 2. Optical communication equipment Next, an optical communication device according to one embodiment of the present invention will be described. This optical communication device has an optical system according to the above embodiment and a light source or light-receiving element arranged on the opposite side of the optical system from the far field. Hereinafter, an embodiment of the present invention will be described using an optical communication device equipped with this optical system as an illumination optical system as an example.

[0034] Figure 32 is a schematic diagram showing the configuration of an optical communication device according to one embodiment of the present invention. As shown in Figure 32, the optical communication device 1 has a casing 2, a base 3, and a support part 4. The casing 2 houses a light source 21 for communication light and an optical system 22. The base 3 is a base fixed to the installation location of the optical communication device 1. The support part 4 supports the casing 2 so that it can rotate relative to the base 3 in a direction perpendicular to the optical axis of the optical system.

[0035] The light source 21 is an element that generates communication light, for example, used in optical communication. The light source 21 can be an element that converts electricity into light. Examples of the light source 21 include light-emitting diodes and semiconductor lasers.

[0036] The optical system 22 is composed of a first lens group L1, a second lens group L2, and a third lens group L3, arranged in this order from the far-field side. The first lens group L1 has a negative refractive power, and the second lens group L2 has a positive refractive power. The first lens group L1 and the third lens group L3 are fixed within the casing 2 with respect to the direction along the optical axis of the light source 21. The second lens group L2 is arranged to be movable along the optical axis. Furthermore, the optical system 22 is configured to satisfy the aforementioned equations (1) and (2). Each lens group consists of a single lens.

[0037] Optical communication device 1 can change the characteristics of the communication light in various ways, from collimated light to divergent or focused light, using three lenses. Therefore, it is advantageous for use in beacon applications. Furthermore, the adjustment of the characteristics of the communication light is achieved solely by moving the second lens group L2 along the optical axis. Therefore, it is advantageous in terms of miniaturization and weight reduction of the optical communication device.

[0038] The optical communication device on the light-receiving side can be configured by replacing the light source 21 with a light-receiving element. The light-receiving element can be any optical element capable of receiving communication light that has passed through the optical system. Examples of light-receiving elements include optical fibers for transmitting the received light, as well as solid-state image sensors such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors.

[0039] The optical system according to an embodiment of the present invention is capable of emitting and receiving light with various characteristics, from collimated light to divergent or focused light, while substantially maintaining the beam profile shape, through a simple optical configuration. Optical communication devices equipped with such an optical system are applicable not only to optical communication but also to beacons. Therefore, it is suitable not only for optical communication between fixed base stations but also for optical communication between relatively moving base stations. Furthermore, because the optical system has a simple configuration, it is advantageous for miniaturization and weight reduction of optical communication devices. Therefore, it is also advantageous for optical communication in outer space, such as optical communication between artificial satellites.

[0040] [Variation] In embodiments of the present invention, the number of lenses in each lens group of the optical system is preferably one from the viewpoint of simplifying the optical configuration, but it may be two or more.

[0041] Furthermore, in embodiments of the present invention, the optical system may further include a configuration that indicates information relating to a light source or photodetector. Examples of such information include the type of light source or photodetector to be applied, a suitable distance from the lens surface closest to the light source or photodetector to the light source or photodetector when arranging the optical system, and an arrow indicating the direction of signal light passage. Examples of configurations that indicate such information include printed and engraved materials of the information. The information may also be formed directly on the optical system.

[0042] 〔summary〕 As is clear from the above description, the optical system according to the first aspect of the present invention has a first lens group (L1) having a negative refractive power and a second lens group (L2) having a positive refractive power in that order, and the second lens group is movable along the optical axis so as to change the distance between it and the other lens groups, and satisfies the following equation. However, in the following equation, f1 represents the focal length of the first lens group, f2 represents the focal length of the second lens group, and L represents the total length of the optical system. f1 / f2 ≤ -2.25 ···(1) L / f1≧-1.05···(2)

[0043] Therefore, the optical system according to the first aspect of the present invention is applicable to optical communication devices that can be miniaturized and lightened.

[0044] An optical system according to a second aspect of the present invention may satisfy the following equation in the first aspect. This configuration is even more effective in terms of achieving appropriate control of the beam angle by moving the second lens group. md² / f²≧0.06···(3) however md2: Distance traveled by the second lens group

[0045] An optical system according to a third aspect of the present invention may further include a third lens group arranged following the first and second lens groups in the first or second aspect, and when the third lens group is arranged between a light source that emits signal light to the optical system and the second lens group, the following equation may be satisfied. This configuration is even more effective in realizing appropriate control of the beam angle by moving the second lens group. D3 / fa≧0.16···(4) however D3: Distance along the optical axis from the lens surface closest to the light source in the third lens group to the point of emission of the light source. fa: Focal length of the optical system

[0046] The optical system of the fourth aspect of the present invention further comprises a third lens group (L3) following the first and second lens groups in any one of the first to third aspects, and may include aspherical lenses in at least one of the lens groups. This configuration is even more effective from the viewpoint of simplifying and reducing the weight of the optical system's optical configuration.

[0047] In the optical system according to the fifth aspect of the present invention, in the first to fourth aspects, the glass material of any lens in any lens group may be radiation-resistant glass. This configuration is even more effective in suppressing the influence of radiation from the surrounding environment on the optical properties of the lenses.

[0048] Furthermore, the optical communication device according to the sixth aspect of the present invention comprises an optical system of any one of the first to fifth aspects described above, and a light source that emits communication light to the optical system, or a light-receiving element that receives communication light from the optical system, which is arranged on the opposite side of the second lens group from the first lens group. Therefore, the optical communication device according to the sixth aspect of the present invention can be miniaturized and made lighter.

[0049] The optical system and optical communication device according to the embodiment of the present invention are expected to be applicable to higher-speed optical communication. This is expected to lead to the widespread adoption, development, and innovation of various communication technologies. Thus, the optical communication device according to the embodiment of the present invention is expected to contribute to achieving the Sustainable Development Goals (SDGs) related to infrastructure for industry and technological innovation.

[0050] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Examples]

[0051] An embodiment of the present invention is described below. In the following tables, the unit of length is "mm" and the unit of angle of view is "°". Also, "Ea" is "×10 -a This shows the following. Furthermore, while the representations in the figures and tables in Example 1 are explained, the representations in the figures and tables in Example 1 are the same as those in the figures and tables in the other examples.

[0052] The optical systems of Examples 1 to 4 shown below consist of, in order from the far-field side opposite the light source S, a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, and a third lens group L3 with positive refractive power. Furthermore, in controlling the optical path from convergent to divergent light, the first lens group L1 and the third lens group L3 remain fixed and do not move, while the second lens group L2 moves along the optical axis. Note that each lens group in the examples consists of a single lens. The numerical aperture (NA) of the light source S in each example is 0.1.

[0053] [Example 1] Figure 1 schematically shows the optical configuration of the optical system of Example 1. Figure 1 schematically shows the optical configuration of collimated light, divergent light, and convergent light in Example 1. Figure 2 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 1. In Example 1, the lens of the first lens group L1 is an aspherical lens, and the other lenses are spherical lenses.

[0054] The optical characteristics of the optical system in Example 1 are shown in Tables 1 to 3, respectively. Table 1 shows the numerical data of the optical system.

[0055] In the table, "Surface Number" indicates the order of the lens surfaces when counting the lens surfaces of the optical system from the far-field side, "ASP" indicates that the lens surface is aspherical, and "SPH" indicates that the lens surface is spherical. "R" represents the radius of curvature of the lens surface, "D" represents the spacing of the lens surfaces along the optical axis, and "N" represents the refractive index of the lens for a wavelength of 1550 nm. The value of "D" in surface number 6 represents the distance from the 6th lens surface to the light source's emission point. This corresponds to D3 in equation (4) mentioned above. In the table below, "D2" and "D4" represent the inter-lens distance from the lens surface of surface number 2 and the inter-lens distance from the lens surface of surface number 4, respectively.

[0056] [Table 1] Face number RDN 1 ASP 6045.000 1.5 1.5002 2 ASP 89.710 D2 3 SPH 24.730 2.8 1.5002 4 SPH -16.160 D4 5 SPH 17.300 1.5 1.5002 6 SPH -82.200 6.5

[0057] Table 2 shows numerical data of aspheric coefficients. An aspheric surface (ASP) even-order aspheric surface is defined by the following formula. In the following formula, c is curvature (1 / r), h is the height from the optical axis, k is the conic constant, and A4, A6, A8, A10··· represent the aspheric coefficients of respective orders. z=ch 2 / [1+{1-(1+k)c 2 h 2} 1 / 2 +A4h 4 +A6h 6 +A8h 8 +A10h 10 ···

[0058] [Table 2] Surface No. k A4 A6 A8 1 0 -5.258E-05 -1.855E-09 3.838E-07 2 0 1.004E-04 1.195E-06 3.964E-07

[0059] Table 3 shows numerical data of the changed distance in each beam state.

[0060] [Table 3] D Collimated Divergent Convergent D2 10.168 13.168 7.168 D4 11.527 8.527 14.527

[0061] Furthermore, Figure 3 shows the beam profile characteristics of collimated light in the far field in Example 1, Figure 4 shows the beam profile characteristics of divergent light in the far field in Example 1, and Figure 5 shows the beam profile characteristics of convergent light in the far field in Example 1.

[0062] [Example 2] Figure 6 schematically shows the optical configurations for collimated, divergent, and focused light in Example 2. Figure 7 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 2. Table 4 shows the numerical data for the optical system of Example 2, Table 5 shows the numerical data for the aspherical coefficients of Example 2, and Table 6 shows the numerical data for the changed distance in each beam state of Example 2.

[0063] [Table 4] Face number RDN 1 ASP -10.422 1.5 1.5002 2 ASP -20.422 D2 3 SPH 7.718 2.500 1.5002 4 SPH -43.116 D4 5 SPH 17.983 1.300 1.5002 6 SPH 7.983 4.625

[0064] [Table 5] Surface number k A4 A6 A8 1 0 -5.076E-04 -2.757E-05 -6.733E-06 2 0 2.156E-04 1.284E-05 0.000E+00

[0065] [Table 6] D Collimate Diverge Converge D2 12.912 15.912 9.912 D4 10.567 7.567 13.567

[0066] [Example 3] Figure 8 schematically shows the optical configuration for collimated, divergent, and focused light in Example 3. Figure 9 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 3. Table 7 shows the numerical data for the optical system of Example 3, Table 8 shows the numerical data for the aspherical coefficients of Example 3, and Table 9 shows the numerical data for the changed distance in each beam state of Example 3.

[0067] [Table 7] Face number RDN 1 ASP 55.517 1.5 1.5002 2 ASP 45.517 D2 3 SPH 8.638 2.500 1.5002 4 SPH 13.424 D4 5 SPH 21.288 1.500 1.5002 6 SPH INF 17.501

[0068] [Table 8] Surface number k A4 A6 A8 1 0 1.632E-06 -1.840E-06 4.082E-07 2 0 1.047E-04 -9.022E-07 4.804E-07

[0069] [Table 9] D Collimate Diverge Converge D2 8,000 11,000 5,000 D4 8,000 5,000 11,000

[0070] [Example 4] Figure 10 schematically shows the optical configuration for collimated, divergent, and convergent light in Example 4. Figure 11 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 4. Table 10 shows the numerical data for the optical system of Example 4, Table 11 shows the numerical data for the aspherical coefficients of Example 4, and Table 12 shows the numerical data for the changed distance in each beam state of Example 4.

[0071] [Table 10] Face number RDN 1 ASP -11.097 1.5 1.5002 2 ASP -22.419 D2 3 SPH 7.614 2.500 1.5002 4 SPH -47.240 D4 5 SPH 26.834 1.300 1.5002 6 SPH 9.469 4.833

[0072] [Table 11] Surface number k A4 A6 A8 1 0 -4.107E-04 -6.573E-06 -2.704E-06 2 0 1.584E-04 1.576E-05 0.000E+00

[0073] [Table 12] D Collimate Diverge Converge D2 9.458 12.458 6.458 D4 10.670 7.670 13.670

[0074] [Example 5] Figure 12 schematically shows the optical configurations for collimated, divergent, and focused light in Example 5. Figure 13 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 5. Table 13 shows the numerical data for the optical system of Example 5, Table 14 shows the numerical data for the aspherical coefficients of Example 5, and Table 15 shows the numerical data for the changed distance in each beam state of Example 5.

[0075] [Table 13] Face number RDN 1 ASP 57.579 1.5 1.51633 2 ASP 47.576 D2 3 SPH 16.326 2.800 1.51633 4 SPH -22.889 D4 5 SPH 7.988 1.500 1.51633 6 SPH -614.186 2.500

[0076] [Table 14] Surface number k A4 A6 A8 1 0 -2.375E-05 3.599E-07 3.656E-07 2 0 7.141E-05 9.091E-07 3.963E-07

[0077] [Table 15] D Collimate Diverge Converge D2 7.626 10.626 4.626 D4 14.586 11.586 17.586

[0078] [Example 6] Figure 14 schematically shows the optical configurations for collimated, divergent, and focused light in Example 6. Figure 15 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 6. Table 16 shows the numerical data for the optical system of Example 6, Table 17 shows the numerical data for the aspherical coefficients of Example 6, and Table 18 shows the numerical data for the changed distance in each beam state of Example 6.

[0079] [Table 16] Face number RDN 1 ASP 107.207 1.500 1.51633 2 ASP 97.207 D2 3 SPH 24.967 2.500 1.51633 4 SPH 13287.157 D4 5 SPH 15.264 1.500 1.51633 6 SPH -70.386 11.910

[0080] [Table 17] Surface number k A4 A6 A8 1 0 2.981E-05 -3.966E-06 1.708E-07 2 0 4.104E-05 -4.062E-06 1.775E-07

[0081] [Table 18] D Collimate Diverge Converge D2 8,000 11,000 5,000 D4 23.590 20.590 26.590

[0082] [Example 7] Figure 16 schematically shows the optical configuration for collimated, divergent, and focused light in Example 7. Figure 17 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 7. Table 19 shows the numerical data for the optical system of Example 7, Table 20 shows the numerical data for the aspherical coefficients of Example 7, and Table 21 shows the numerical data for the changed distance in each beam state of Example 7.

[0083] [Table 19] Face number RDN 1 ASP -18.324 1.5 1.51633 2 ASP -95.222 D2 3 SPH 7.725 2.500 1.51633 4 SPH -58.068 D4 5 SPH 4606.439 1.300 1.62230 6 SPH 11.620 6.605

[0084] [Table 20] Surface number k A4 A6 A8 1 0 -3.253E-04 -4.527E-05 8.773E-06 2 0 1.562E-04 -2.342E-05 7.916E-06

[0085] [Table 21] D Collimate Diverge Converge D2 8,000 11,000 5,000 D4 11.193 8.193 14.193

[0086] [Example 8] Figure 18 schematically shows the optical configurations for collimated, divergent, and focused light in Example 8. Figure 19 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 8. Table 22 shows the numerical data for the optical system of Example 8, Table 23 shows the numerical data for the aspherical coefficients of Example 8, and Table 24 shows the numerical data for the changed distance in each beam state of Example 8.

[0087] [Table 22] Face number RDN 1 ASP 36.667 1.5 1.51633 2 ASP 26.667 D2 3 SPH 14.616 2.500 1.51633 4 SPH -33.028 D4 5 SPH INF 1.500 1.62230 6 SPH -71.371 7.132

[0088] [Table 23] Surface number k A4 A6 A8 1 0 -1.138E-05 -2.173E-06 8.589E-07 2 0 5.884E-05 -2.063E-06 9.764E-07

[0089] [Table 24] D Collimate Diverge Converge D2 11.000 14.000 8.000 D4 10.159 7.159 13.159

[0090] [Example 9] Figure 20 schematically shows the optical configurations for collimated, divergent, and focused light in Example 9. Figure 21 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 9. Table 25 shows the numerical data for the optical system of Example 9, Table 26 shows the numerical data for the aspherical coefficients of Example 9, and Table 27 shows the numerical data for the changed distance in each beam state of Example 9.

[0091] [Table 25] Face number RDN 1 ASP -26.220 1.5 1.51633 2 ASP -765.088 D2 3 SPH 7.413 2.500 1.51633 4 SPH -126.246 D4 5 SPH 890.627 1.300 1.51633 6 SPH 56.212 5.085

[0092] [Table 26] Surface number k A4 A6 A8 1 0 -3.546E-04 1.310E-05 -1.397E-06 2 0 1.412E-04 2.841E-05 0.000E+00

[0093] [Table 27] D Collimate Diverge Converge D2 10,000 13,000 7,000 D4 10.615 7.615 13.615

[0094] [Example 10] Figure 22 schematically shows the optical configuration for collimated, divergent, and focused light in Example 10. Figure 23 shows the spherical aberration diagram at a wavelength of 1550 nm obtained by back-ray tracing of the collimated light in the optical system of Example 10. Table 28 shows the numerical data for the optical system of Example 10, Table 29 shows the numerical data for the aspherical coefficients of Example 10, and Table 30 shows the numerical data for the changed distance in each beam state of Example 10.

[0095] [Table 28] Face number RDN 1 ASP -53.949 1.5 1.51633 2 ASP -63.949 D2 3 SPH 16.672 2.500 1.51633 4 SPH -23.752 D4 5 SPH 132.878 1.300 1.51633 6 SPH 52.878 5.412

[0096] [Table 29] Surface number k A4 A6 A8 1 0 -1.747E-05 -2.580E-06 8.981E-07 2 0 6.672E-05 -1.934E-06 8.383E-07

[0097] [Table 30] D Collimate Diverge Converge D2 9.849 12.849 6.849 D4 13.394 10.394 16.394

[0098] [Comparative Examples 1 and 2] Figure 24 schematically shows the optical configuration of Comparative Example 1 in a specific lens arrangement. The optical system of Comparative Example 1 does not satisfy either of the relationships shown in equations (1) and (2) above. Figure 25 shows the beam profile characteristics of light in the far field for lens arrangement (1) in Figure 24, Figure 26 shows the beam profile characteristics of light in the far field for lens arrangement (2) in Figure 24, and Figure 27 shows the beam profile characteristics of light in the far field for lens arrangement (3) in Figure 24. The light in lens arrangement (1) of Comparative Example 1 is collimated light. The light in lens arrangements (2) and (3) of Comparative Example 1 is divergent light.

[0099] Figure 28 schematically shows the optical configuration of Comparative Example 2 in a specific lens arrangement. The optical system of Comparative Example 2 does not satisfy either of the relationships shown in equations (1) and (2) above. Figure 29 shows the beam profile characteristics of light in the far field for lens arrangement (1) in Figure 28, Figure 30 shows the beam profile characteristics of light in the far field for lens arrangement (2) in Figure 28, and Figure 31 shows the beam profile characteristics of light in the far field for lens arrangement (3) in Figure 28. The light in lens arrangement (1) of Comparative Example 2 is collimated light. The light in lens arrangement (2) of Comparative Example 2 is divergent light. The light in lens arrangement (3) of Comparative Example 2 is focused light.

[0100] Table 31 shows the values ​​calculated using the aforementioned formulas in Examples 1 to 10 and Comparative Examples 1 and 2.

[0101] [Table 31] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 (1) f1 / f2 -9.10 -3.37 -12.88 -2.26 -29.53 -43.86 (2) L / f1 -0.19 -0.77 -0.08 -1.04 -0.05 -0.02 (3) md / f2 0.16 0.23 0.07 0.23 0.15 0.06 (4) D3 / fa 0.42 0.32 0.69 0.31 0.16 0.47 Example 7 Example 8 Example 9 Example 10 Comparative Example 1 Comparative Example 2 (1) f1 / f2 -3.31 -9.98 -8.52 -36.30 -1.40 -1.76 (2) L / f1 -0.07 -0.17 -0.27 -0.05 -1.89 -1.50 (3) md / f2 0.22 0.15 0.21 0.15 0.19 0.20 (4) D3 / fa 0.32 0.34 0.33 0.26 0.15 0.16 [Explanation of symbols]

[0102] 1. Optical communication device 2 Casing 3 bases 4 Support part L1 First lens group L2 Second lens group L3 Third lens group 21, S light source 22 Optical system

Claims

1. From the far field side toward the light source or light receiving element side, The first lens group consists of a single lens and has negative refractive power, A second lens group consisting of a single lens having positive refractive power, The third lens group consists of a single lens, An optical system comprising, in which, when changing the characteristics of the communication light from collimated light to divergent light or convergent light, the first lens group and the third lens group are fixed, and the second lens group is movable along the optical axis so as to change the distance between it and the other lens groups, An optical system that satisfies the following equation. f1 / f2≦-2.25...(1) L / f1≧-1.05...(2) however f1: Focal length of the first lens group f2: Focal length of the second lens group L: Distance along the optical axis from the far-field side surface of the first lens group to the position of the light source or the photodetector.

2. The optical system according to claim 1, satisfying the following formula. md2 / f2≧0.06...(3) however md2: Distance traveled by the second lens group

3. The optical system according to claim 1, further comprising a third lens group arranged following the first lens group and the second lens group, wherein the following equation is satisfied when the third lens group is arranged between a light source that emits signal light to the optical system and the second lens group. D3 / fa≧0.16...(4) however D3: Distance along the optical axis from the lens surface closest to the light source in the third lens group to the light source's emission point. fa: Focal length of the optical system

4. The optical system according to claim 1, further comprising a third lens group arranged following the first lens group and the second lens group, wherein at least one of the lens groups includes an aspherical lens.

5. The optical system according to claim 1, wherein the glass material of any lens in any of the lens groups is radiation-resistant glass.

6. An optical system according to any one of claims 1 to 5, A light source that emits communication light to the optical system, or a light-receiving element that receives communication light from the optical system, is positioned on the opposite side of the first lens group from the second lens group, An optical communication device equipped with the following features.

Images