Achromatic lens and manufacturing method

Abstract

This achromatic lens comprises a first glass lens, an intermediate layer containing glass, and a second glass lens. The second glass lens is bonded to the first glass lens via the intermediate layer. The phosphorus content of the first glass lens is smaller than the phosphorus content of the second glass lens. The phosphorus content of the intermediate layer is larger than the phosphorus content of the first glass lens and smaller than the phosphorus content of the second glass lens.

Description

Achromatic lens and manufacturing method

[0001] The present disclosure generally relates to an achromatic lens and a manufacturing method thereof, and more particularly to an achromatic lens in which a first glass lens and a second glass lens are cemented together, and a manufacturing method thereof.

[0002] The optical element described in Patent Document 1 includes a first glass lens made of a first glass material and a second glass lens made of a second glass material molded in close contact with the optical surface of the first glass lens. The refractive index of the second glass material is made larger than the refractive index of the first glass material, thereby reducing chromatic aberration of the optical element.

[0003] Japanese Patent Application Laid-Open No. 2008-241816

[0004] The optical element described in Patent Document 1 has a problem in that, due to the difference in refractive index between the first glass material and the second glass material, reflection occurs at the interface between the first glass lens and the second glass lens, deteriorating the optical characteristics (light transmittance, etc.) of the entire optical element.

[0005] An achromatic lens according to one aspect of the present disclosure includes a first glass lens, an intermediate layer containing glass, and a second glass lens. The second glass lens is bonded to the first glass lens via the intermediate layer. The phosphorus content of the first glass lens is lower than the phosphorus content of the second glass lens. The phosphorus content of the intermediate layer is higher than the phosphorus content of the first glass lens and lower than the phosphorus content of the second glass lens.

[0006] A manufacturing method according to one aspect of the present disclosure is a method for manufacturing an achromatic lens, which includes preparing a first glass lens and a second glass lens having a higher phosphorus content than the first glass lens, and bonding the first glass lens and the second glass lens together by applying pressure in an atmosphere whose temperature is between the glass transition temperatures of the first glass lens and the second glass lens.

[0007] The present disclosure has the advantage of improving the optical properties of an achromatic lens.

[0008] Fig. 1 is a cross-sectional view of an achromatic lens according to one embodiment. Fig. 2 is a flowchart showing a method for manufacturing the achromatic lens. Fig. 3 is a cross-sectional view showing a method for manufacturing the achromatic lens. Fig. 4 is a cross-sectional view showing a method for manufacturing the achromatic lens.

[0009] (Embodiments) An achromatic lens 10 and a manufacturing method according to an embodiment will be described below with reference to the drawings. However, the following embodiment is merely one of various embodiments of the present disclosure. The following embodiment can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved. Furthermore, each figure described in the following embodiments is a schematic diagram, and the ratios of the sizes and thicknesses of the components in the figures do not necessarily reflect the actual dimensional ratios.

[0010] 1 , an achromatic lens 10 of this embodiment includes a first glass lens 1, an intermediate layer 3 containing glass, and a second glass lens 2. The second glass lens 2 is cemented to the first glass lens 1 via the intermediate layer 3. In other words, the achromatic lens 10 is a cemented lens formed by cementing the first glass lens 1 and the second glass lens 2 together.

[0011] One of the first glass lens 1 and the second glass lens 2 has a higher dispersion than the other. In the achromatic lens 10, chromatic aberration is corrected by the difference in dispersion between the first glass lens 1 and the second glass lens 2. In this embodiment, an example will be described in which the first glass lens 1 has a higher dispersion than the second glass lens 2.

[0012] Here, the phosphorus (element symbol P) content of the first glass lens 1 is lower than the phosphorus content of the second glass lens 2. The phosphorus content of the intermediate layer 3 is higher than the phosphorus content of the first glass lens 1 but lower than the phosphorus content of the second glass lens 2. The intermediate layer 3 configured in this manner has the effect of buffering the difference in dispersion between the first glass lens 1 and the second glass lens 2, and suppresses reflection at the interface between the first glass lens 1 and the second glass lens 2. Therefore, the provision of the intermediate layer 3 can improve the optical characteristics (light transmittance, etc.) of the achromatic lens 10.

[0013] When the first glass lens 1 and the second glass lens 2 are bonded together via an adhesive, the adhesive has a relatively low light transmittance, which may deteriorate the optical properties (light transmittance, etc.) of the achromatic lens 10. In contrast, the intermediate layer 3 containing glass has a relatively high light transmittance, so by bonding the first glass lens 1 and the second glass lens 2 together via the intermediate layer 3, the optical properties (light transmittance, etc.) of the achromatic lens 10 can be improved.

[0014] Furthermore, when the first glass lens 1 and the second glass lens 2 are bonded together via an adhesive, it is not possible to obtain the effect of suppressing reflection at the interface between the first glass lens 1 and the second glass lens 2. In contrast, when the first glass lens 1 and the second glass lens 2 are bonded together via an intermediate layer 3, it is possible to suppress reflection at the interface.

[0015] (Details) The achromatic lens 10 of this embodiment will be described in more detail below.

[0016] 1, for example, the first glass lens 1 is a biconvex lens, and for example, the second glass lens 2 is a biconcave lens.

[0017] The optical axis of the first glass lens 1 is aligned with the optical axis of the second glass lens 2. The first glass lens 1 is disposed on the optical axis of the second glass lens 2. The second glass lens 2 is disposed on the optical axis of the first glass lens 1.

[0018] The first glass lens 1 has a first surface S1 (convex surface) and a second surface S2 (convex surface). The first surface S1 is a surface on one side of the first glass lens 1 in the optical axis direction, and the second surface S2 is a surface on the other side of the first glass lens 1 in the optical axis direction.

[0019] The second glass lens 2 has a third surface S3 (concave surface) and a fourth surface S4 (concave surface). The third surface S3 is a surface on one side of the second glass lens 2 in the optical axis direction, and the fourth surface S4 is a surface on the other side of the second glass lens 2 in the optical axis direction. The third surface S3 faces the second surface S2. The third surface S3 has a shape that follows the second surface S2. More specifically, the third surface S3 is parallel to the second surface S2.

[0020] The first surface S1, the second surface S2, the third surface S3, and the fourth surface S4 are each, for example, a spherical surface, although at least one of the first surface S1, the second surface S2, the third surface S3, and the fourth surface S4 may be an aspherical surface.

[0021] The intermediate layer 3 is interposed between the first glass lens 1 and the second glass lens 2. The intermediate layer 3 has a fifth surface S5 connected to the first glass lens 1 and a sixth surface S6 connected to the second glass lens 2.

[0022] The shape of the fifth surface S5 is the same as the shape of the second surface S2 of the first glass lens 1. The first glass lens 1 and the intermediate layer 3 are in close contact with each other at the second surface S2 and the fifth surface S5.

[0023] The shape of the sixth surface S6 is the same as the shape of the third surface S3 of the second glass lens 2. The second glass lens 2 and the intermediate layer 3 are in close contact with each other at the third surface S3 and the sixth surface S6.

[0024] The second surface S2 of the first glass lens 1 has a shape that coincides with the third surface S3 of the second glass lens 2.

[0025] As an example, the thickness T1 of the first glass lens 1 is 1 mm. As an example, the thickness T2 of the second glass lens 2 is 0.7 mm. As an example, the thickness T3 of the intermediate layer 3 is 1 μm. Here, the thicknesses T1 to T3 are defined as lengths on the optical axis A1 of the achromatic lens 10.

[0026] The thicknesses T1 to T3 can be changed as appropriate. However, it is preferable that the thickness T3 of the intermediate layer 3 be 0.05 μm or more and 40 μm or less. It is also preferable that the thickness T3 of the intermediate layer 3 be 1 / 10 or less of the thickness T1 of the first glass lens 1 and 1 / 10 or less of the thickness T2 of the second glass lens 2.

[0027] If the thickness T3 of the intermediate layer 3 is too large, spherical aberration will worsen, which is undesirable. If the thickness T3 of the intermediate layer 3 is too small, the effect of the intermediate layer 3 in buffering the difference in dispersion between the first glass lens 1 and the second glass lens 2 will be weakened, which will make reflection more likely to occur at the interface between the first glass lens 1 and the second glass lens 2, which is also undesirable. If the thickness T3 of the intermediate layer 3 is too small, the strength of the bond between the first glass lens 1 and the second glass lens 2 may be insufficient, which is also undesirable.

[0028] By setting the thickness T3 of the intermediate layer 3 to 0.05 μm or more, spherical aberration can be effectively corrected. Furthermore, by setting the thickness T3 of the intermediate layer 3 to 40 μm or less and / or 1 / 10 or less of the thicknesses T1 and T2, reflection at the interface between the first glass lens 1 and the second glass lens 2 can be easily suppressed, and the bonding strength between the first glass lens 1 and the second glass lens 2 can be increased.

[0029] Next, the compositions of the first glass lens 1, the second glass lens 2, and the intermediate layer 3 will be described.

[0030] The first glass lens 1 does not contain phosphorus. The first glass lens 1 contains glass (first glass) that does not contain phosphorus. The first glass that constitutes the first glass lens 1 contains elements such as Si (silicon), O (oxygen), and Na (sodium).

[0031] The second glass lens 2 contains glass (second glass) containing phosphorus. The second glass constituting the second glass lens 2 contains, in addition to phosphorus, elements such as Si (silicon), O (oxygen), Na (sodium), Al (aluminum), and Ca (calcium).

[0032] The intermediate layer 3 contains a phosphorus-containing glass (third glass). The third glass constituting the intermediate layer 3 contains, in addition to phosphorus, elements such as Si (silicon), O (oxygen), Na (sodium), Al (aluminum), and Ca (calcium). The intermediate layer 3 does not contain a resin.

[0033] As described above, the phosphorus content of the first glass lens 1 is smaller than the phosphorus content of the second glass lens 2. More specifically, the phosphorus content of the first glass lens 1 is zero. The phosphorus content of the intermediate layer 3 is larger than the phosphorus content of the first glass lens 1 and smaller than the phosphorus content of the second glass lens 2. In the present disclosure, the "content" is expressed as an elemental composition ratio.

[0034] In order to obtain the effect of suppressing reflection at the interface between the first glass lens 1 and the second glass lens 2, the phosphorus content of the intermediate layer 3 is preferably 35% or more, and more preferably 40% or more, of the phosphorus content of the second glass lens 2. Furthermore, the phosphorus content of the intermediate layer 3 is preferably 85% or less, and more preferably 80% or less, of the phosphorus content of the second glass lens 2.

[0035] Furthermore, the silicon content of the intermediate layer 3 is a value between the silicon content of the first glass lens 1 and the silicon content of the second glass lens 2. For example, the silicon content of the first glass lens 1 is greater than the silicon content of the second glass lens 2, and the silicon content of the intermediate layer 3 is less than the silicon content of the first glass lens 1 and greater than the silicon content of the second glass lens 2. Alternatively, the silicon content of the first glass lens 1 is less than the silicon content of the second glass lens 2, and the silicon content of the intermediate layer 3 is greater than the silicon content of the first glass lens 1 and less than the silicon content of the second glass lens 2.

[0036] The sodium content of the intermediate layer 3 is a value between the sodium content of the first glass lens 1 and the sodium content of the second glass lens 2. For example, the sodium content of the first glass lens 1 is greater than the sodium content of the second glass lens 2, and the sodium content of the intermediate layer 3 is less than the sodium content of the first glass lens 1 and greater than the sodium content of the second glass lens 2. Alternatively, the sodium content of the first glass lens 1 is less than the sodium content of the second glass lens 2, and the sodium content of the intermediate layer 3 is greater than the sodium content of the first glass lens 1 and less than the sodium content of the second glass lens 2.

[0037] Next, the characteristics of the first glass lens 1, the second glass lens 2, and the intermediate layer 3 will be described.

[0038] The refractive index of the first glass lens 1 is greater than the refractive index of the second glass lens 2. The refractive index of the first glass lens 1 is, for example, 1.58. The refractive index of the second glass lens 2 is, for example, 1.50. The refractive index of the intermediate layer 3 is smaller than the refractive index of the first glass lens 1 and greater than the refractive index of the second glass lens 2.

[0039] The Abbe number for the d-line (wavelength 587.562 nm) of the first glass lens 1 is smaller than the Abbe number for the d-line of the second glass lens 2. In other words, the dispersion of the first glass lens 1 is larger than the dispersion of the second glass lens 2. The Abbe number for the d-line can be calculated from the refractive index for the d-line, the refractive index for the F-line (wavelength 486.133 nm), and the refractive index for the C-line (wavelength 656.273 nm).

[0040] The Abbe number of the intermediate layer 3 for the d-line is larger than the Abbe number of the first glass lens 1 for the d-line, and smaller than the Abbe number of the second glass lens 2 for the d-line. In other words, the dispersion of the intermediate layer 3 is smaller than the dispersion of the first glass lens 1, and larger than the dispersion of the second glass lens 2.

[0041] The difference in composition between the first glass lens 1, the second glass lens 2 and the intermediate layer 3 causes the refractive index, the Abbe number for the d-line and the dispersion to vary.

[0042] The glass transition temperature of the first glass lens 1 is higher than that of the second glass lens 2. The glass transition temperature of the first glass lens 1 is, for example, 550°C. The glass transition temperature of the second glass lens 2 is, for example, 458°C. The glass transition temperature of the intermediate layer 3 is lower than that of the first glass lens 1 and higher than that of the second glass lens 2.

[0043] The glass transition temperature varies depending on the composition of the first glass lens 1, the second glass lens 2, and the intermediate layer 3. The glass tends to have a lower glass transition temperature as it contains more phosphorus.

[0044] (Manufacturing Method) Next, an example of a manufacturing method for the achromatic lens 10 will be described.

[0045] The manufacturing method of the achromatic lens 10 includes a molding step (steps ST1 and ST2 in FIG. 2 ) and a bonding step (step ST3 in FIG. 2 ). In the molding step, the first glass lens 1 and the second glass lens 2, which has a higher phosphorus content than the first glass lens 1, are molded into predetermined shapes (see FIG. 3 ), respectively, to prepare the first glass lens 1 and the second glass lens 2, each having a predetermined shape. In the bonding step, the first glass lens 1 and the second glass lens 2 are bonded together by applying pressure in an atmosphere whose temperature is between the glass transition temperatures of the first glass lens 1 and the second glass lens 2 (see FIG. 4 ). In the bonding step, an intermediate layer 3, which is a mixture of the molten components of the first glass lens 1 and the second glass lens 2, is formed at the interface between the first glass lens 1 and the second glass lens 2. Thus, the achromatic lens 10 is manufactured through the above steps.

[0046] An example of a method for manufacturing the achromatic lens 10 will now be described in more detail.

[0047] In the molding step, the first glass lens 1 is molded into a biconvex lens shape as shown in FIG. 3 by, for example, press molding.

[0048] In the molding step, the second glass lens 2 is molded into a biconcave lens shape as shown in FIG. 3 by, for example, press molding.

[0049] In the bonding step, the first glass lens 1 and the second glass lens 2 are brought into close contact with each other and fixed to a first mold 4 in an atmosphere whose temperature is lower than the glass transition temperature of the first glass lens 1 and higher than the glass transition temperature of the second glass lens 2, as shown in Fig. 3. At this time, the second surface S2 of the first glass lens 1 and the third surface S3 of the second glass lens 2 are in close contact with each other.

[0050] 4 , the first glass lens 1 and the second glass lens 2 are sandwiched between a first mold 4 and a second mold 5, thereby applying pressure to the first glass lens 1 and the second glass lens 2. In other words, the first glass lens 1 and the second glass lens 2 are pressed together. The first glass lens 1 and the second glass lens 2 are bonded together by maintaining this pressure on each other for a predetermined period of time. Thereafter, the ambient temperature is lowered to a temperature lower than the glass transition temperature of the second glass lens 2.

[0051] That is, in the bonding step, the first glass lens 1 and the second glass lens 2 are bonded together by thermocompression.

[0052] In the bonding step, an intermediate layer 3, in which the molten component of the first glass lens 1 and the molten component of the second glass lens 2 are mixed, is formed at the interface between the first glass lens 1 and the second glass lens 2. Therefore, the phosphorus content of the intermediate layer 3 is a value between the phosphorus content of the first glass lens 1 and the phosphorus content of the second glass lens 2. More specifically, the phosphorus content of the intermediate layer 3 is greater than the phosphorus content of the first glass lens 1 and less than the phosphorus content of the second glass lens 2.

[0053] The silicon content of the intermediate layer 3 is a value between the silicon content of the first glass lens 1 and the silicon content of the second glass lens 2 .

[0054] The sodium content of the intermediate layer 3 is a value between the sodium content of the first glass lens 1 and the sodium content of the second glass lens 2 .

[0055] In the bonding step, the thickness of the intermediate layer 3 can be controlled by controlling the length of time that the first glass lens 1 and the second glass lens 2 are held together under pressure.

[0056] Since the first glass lens 1 does not contain phosphorus, it is possible to increase the difference between the glass transition temperature of the first glass lens 1 and the glass transition temperature of the second glass lens 2. This makes it easier to adjust the temperature in the bonding step.

[0057] (Modifications of the embodiment) Modifications of the embodiment are listed below. The following modifications may be implemented in appropriate combination. Hereinafter, the configuration of the above-described embodiment will be referred to as a basic example.

[0058] The shapes of the first glass lens 1 and the second glass lens 2 are not limited to those shown in the basic example. In the basic example, the first glass lens 1 is a biconvex lens, and the second glass lens 2 is a biconcave lens. Alternatively, for example, the first glass lens 1 may be a biconcave lens, and the second glass lens 2 may be a biconvex lens. Furthermore, for example, one of the first glass lens 1 and the second glass lens 2 may be a meniscus lens, and the other may be a biconvex lens, a biconcave lens, or a meniscus lens.

[0059] In a basic example, the refractive index of the first glass lens 1 is greater than the refractive index of the second glass lens 2. Conversely, the refractive index of the first glass lens 1 may be smaller than the refractive index of the second glass lens 2. In this case, the refractive index of the intermediate layer 3 may be greater than the refractive index of the first glass lens 1 and smaller than the refractive index of the second glass lens 2.

[0060] In the basic example, the Abbe number for the d-line of the first glass lens 1 is smaller than the Abbe number for the d-line of the second glass lens 2. Conversely, the Abbe number for the d-line of the first glass lens 1 may be larger than the Abbe number for the d-line of the second glass lens 2. In this case, the Abbe number for the d-line of the intermediate layer 3 may be smaller than the Abbe number for the d-line of the first glass lens 1 and larger than the Abbe number for the d-line of the second glass lens 2.

[0061] The thickness of the intermediate layer 3 may vary. In other words, the distance between the second surface S2 of the first glass lens 1 and the third surface S3 of the second glass lens 2 does not have to be a constant distance. For example, the distance between the second surface S2 and the third surface S3 on the optical axis A1 may be different from the distance between the second surface S2 and the third surface S3 at a location different from that on the optical axis A1.

[0062] (Summary) The above-described embodiments and the like disclose the following aspects.

[0063] The achromatic lens (10) according to the first aspect includes a first glass lens (1), an intermediate layer (3) containing glass, and a second glass lens (2). The second glass lens (2) is bonded to the first glass lens (1) via the intermediate layer (3). The phosphorus content of the first glass lens (1) is lower than that of the second glass lens (2). The phosphorus content of the intermediate layer (3) is higher than that of the first glass lens (1) and lower than that of the second glass lens (2).

[0064] According to the above configuration, the provision of the intermediate layer (3) suppresses reflection at the interface between the first glass lens (1) and the second glass lens (2), thereby improving the optical characteristics (light transmittance, etc.) of the achromatic lens (10).

[0065] In the achromatic lens (10) according to the second aspect, the first glass lens (1) does not contain phosphorus in the first aspect.

[0066] According to the above configuration, the difference between the dispersion of the first glass lens (1) and the dispersion of the second glass lens (2) can be made large, thereby enhancing the effect of the achromatic lens (10) in correcting chromatic aberration.

[0067] In the achromatic lens (10) according to the third aspect, the refractive index of the first glass lens (1) is greater than the refractive index of the second glass lens (2) in the first or second aspect.

[0068] When the phosphorus content of the first glass lens (1) is lower than that of the second glass lens (2), the refractive index of the first glass lens (1) is likely to be higher than that of the second glass lens (2), and therefore, according to the third aspect, it is easy to manufacture an achromatic lens (10).

[0069] In addition, in the achromatic lens (10) according to the fourth aspect, in the third aspect, the refractive index of the intermediate layer (3) is smaller than the refractive index of the first glass lens (1) and larger than the refractive index of the second glass lens (2).

[0070] According to the above configuration, the effect of suppressing reflection at the interface between the first glass lens (1) and the second glass lens (2) is enhanced.

[0071] In addition, in the achromatic lens (10) according to the fifth aspect, in any one of the first to fourth aspects, the Abbe number of the first glass lens (1) for the d-line is smaller than the Abbe number of the second glass lens (2) for the d-line.

[0072] When the phosphorus content of the first glass lens (1) is smaller than that of the second glass lens (2), the Abbe number of the first glass lens (1) for the d line is likely to be smaller than the Abbe number of the second glass lens (2) for the d line, and therefore, according to the fifth aspect, it is easy to manufacture the achromatic lens (10).

[0073] In the achromatic lens (10) according to the sixth aspect, in the fifth aspect, the Abbe number of the intermediate layer (3) for the d-line is larger than the Abbe number of the first glass lens (1) for the d-line and smaller than the Abbe number of the second glass lens (2) for the d-line.

[0074] According to the above configuration, the effect of suppressing reflection at the interface between the first glass lens (1) and the second glass lens (2) is enhanced.

[0075] In addition, in the achromatic lens (10) according to the seventh aspect, in any one of the first to sixth aspects, the glass transition temperature of the first glass lens (1) is higher than the glass transition temperature of the second glass lens (2).

[0076] According to the above configuration, the achromatic lens (10) is easy to manufacture.

[0077] In addition, in the achromatic lens (10) according to the eighth aspect, in the seventh aspect, the glass transition temperature of the intermediate layer (3) is lower than the glass transition temperature of the first glass lens (1) and higher than the glass transition temperature of the second glass lens (2).

[0078] According to the above configuration, the achromatic lens (10) is easy to manufacture.

[0079] In addition, in the achromatic lens (10) according to the ninth aspect, in any one of the first to eighth aspects, the thickness (T3) of the intermediate layer (3) is 0.05 μm or more and 40 μm or less.

[0080] According to the above configuration, the deterioration of spherical aberration can be suppressed compared to when the thickness (T3) of the intermediate layer (3) is greater than 40 μm. Also, compared to when the thickness (T3) of the intermediate layer (3) is smaller than 0.05 μm, the effect of the intermediate layer (3) in absorbing the difference in dispersion between the first glass lens (1) and the second glass lens (2) is enhanced, and the first glass lens (1) and the second glass lens (2) can be firmly bonded together.

[0081] In addition, in the achromatic lens (10) according to the tenth aspect, in any one of the first to ninth aspects, the thickness (T3) of the intermediate layer (3) is 1 / 10 or less of the thickness (T1) of the first glass lens (1) and 1 / 10 or less of the thickness (T2) of the second glass lens (2).

[0082] According to the above configuration, it is possible to suppress the deterioration of spherical aberration.

[0083] The configurations other than the first aspect are not essential for the achromatic lens (10) and can be omitted as appropriate.

[0084] A manufacturing method according to an eleventh aspect is a method for manufacturing an achromatic lens (10), which includes preparing a first glass lens (1) and a second glass lens (2) having a higher phosphorus content than the first glass lens (1). The first glass lens (1) and the second glass lens (2) are bonded together by applying pressure in an atmosphere whose temperature is between the glass transition temperatures of the first glass lens (1) and the second glass lens (2).

[0085] According to the above configuration, an intermediate layer (3) can be formed between the first glass lens (1) and the second glass lens (2), and the phosphorus content of the intermediate layer (3) can be made greater than the phosphorus content of the first glass lens (1) and less than the phosphorus content of the second glass lens (2). Furthermore, the provision of the intermediate layer (3) suppresses reflection at the interface between the first glass lens (1) and the second glass lens (2), thereby improving the optical properties (light transmittance, etc.) of the achromatic lens (10).

[0086] 1 First glass lens 2 Second glass lens 3 Intermediate layer 10 Achromatic lens T1, T2, T3 Thickness

Claims

1. An achromatic lens comprising: a first glass lens; an intermediate layer containing glass; and a second glass lens bonded to the first glass lens via the intermediate layer, wherein the phosphorus content of the first glass lens is lower than the phosphorus content of the second glass lens; and the phosphorus content of the intermediate layer is higher than the phosphorus content of the first glass lens and lower than the phosphorus content of the second glass lens.

2. The achromatic lens according to claim 1, wherein the first glass lens does not contain phosphorus.

3. The achromatic lens according to claim 1, wherein the refractive index of the first glass lens is greater than the refractive index of the second glass lens.

4. The achromatic lens according to claim 3, wherein the refractive index of the intermediate layer is smaller than the refractive index of the first glass lens and larger than the refractive index of the second glass lens.

5. The achromatic lens according to claim 1, wherein the Abbe number of the first glass lens for the d-line is smaller than the Abbe number of the second glass lens for the d-line.

6. The achromatic lens according to claim 5, wherein the Abbe number of said intermediate layer for the d-line is greater than the Abbe number of said first glass lens for the d-line and less than the Abbe number of said second glass lens for the d-line.

7. The achromatic lens according to claim 1, wherein the glass transition temperature of the first glass lens is higher than the glass transition temperature of the second glass lens.

8. The achromatic lens according to claim 7, wherein the glass transition temperature of the intermediate layer is lower than the glass transition temperature of the first glass lens and higher than the glass transition temperature of the second glass lens.

9. The achromatic lens according to claim 1, wherein the thickness of the intermediate layer is 0.05 μm or more and 40 μm or less.

10. The achromatic lens according to claim 1, wherein the thickness of the intermediate layer is 1 / 10 or less of the thickness of the first glass lens and 1 / 10 or less of the thickness of the second glass lens.

11. A method for manufacturing an achromatic lens, comprising the steps of: preparing a first glass lens and a second glass lens having a higher phosphorus content than the first glass lens; and bonding the first glass lens and the second glass lens together by applying pressure in an atmosphere at a temperature between the glass transition temperatures of the first glass lens and the second glass lens.

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