First optical system, optical splitter and optical device

Abstract

The present application provides a first optical system, a beam splitter, and an optical device. The first optical system (10) of the present application has a first lens (111) that guides light (L0) toward a diffraction grating (3), a second lens (112) that collimates first diffracted light (L1) that is condensed by the first lens (111) at a first focal point (f1), a pair of first mirrors (12, 13) that fold back the first diffracted light (L1) toward the diffraction grating (3), a third lens (113) that condenses the first diffracted light (L1) at a second focal point (f2), and a fourth lens (114) that guides the first diffracted light (L1) condensed by the third lens (113) toward the diffraction grating (3), the first lens (111) and the fourth lens (114) have substantially the same first focal length as each other, the second lens (112) and the third lens (113) have substantially the same second focal length as each other, and a first prescribed condition is determined by a first distance along an optical path from the first focal point (f1) to the second focal point (f2).

Description

[0001] This application claims priority to Japanese Patent Application No. 2021-124790, filed on July 29, 2021, the full disclosure of which is incorporated herein by reference. Technical Field

[0002] This invention relates to a first optical system, a beam splitter, and an optical device. Background Technology

[0003] Previously, multipath beam splitters were known, which allowed the light to be measured to pass through a diffraction grating multiple times and through a slit in order to obtain high-resolution or sharpened filter characteristics in, for example, wavelength regions.

[0004] For example, Patent Document 1 discloses a two-stage beam splitter that improves wavelength resolution and substantially shortens length. For example, Patent Document 2 discloses a multipath beam splitter that suppresses the degradation of resolution and dynamic range in beam splitting characteristics when a portion of the scattered light generated in the beam splitting system before the final beam splitting system travels along the same optical path as the diffracted light in the final beam splitting system.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2000-088647

[0006] Patent Document 2: Japanese Patent Application Publication No. 2009-175038

[0007] In this prior art, in order to select a specific wavelength in the beam splitter, a diffraction grating is mounted on a drive device in a rotatable state about a rotation axis. Diffraction occurs along the arrangement direction of the grating, where scribe lines extend in one direction. On the other hand, in the extension direction of the scribe lines orthogonal to this arrangement direction, a normal reflection phenomenon occurs, similar to that of a plane mirror, where the incident and exit angles are the same.

[0008] If the scribe lines extending in one direction and the axis of rotation are ideally parallel to each other, the exit angle in the direction of the scribe line extension remains constant even if the diffraction grating rotates around the axis of rotation. However, if the scribe lines extending in one direction and the axis of rotation are not parallel to each other, the exit angle varies depending on the angle formed by these components and the rotation angle of the diffraction grating. As a result, the diffracted light cannot pass through the slit arranged in the subsequent optical path, or cannot enter the light-receiving element, due to the prescribed rotation angle of the diffraction grating.

[0009] To minimize such problems, a diffraction grating needs to be installed on the drive unit so that the gratings extending in one direction and the axis of rotation are nearly parallel to each other. This is a difficult task and requires a lot of time. Summary of the Invention

[0010] The object of the present invention is to provide a first optical system, beam splitter, and optical device that are easy to operate when mounting a diffraction grating onto a driving device.

[0011] A first optical system of a first aspect comprises: a first lens that parallelizes incident light and guides it toward a diffraction grating rotatable about a rotation axis; a second lens that parallelizes first diffracted light diffracted by the diffraction grating, the first diffracted light being focused by the first lens at a first focal point; a pair of first mirrors that reflect the first diffracted light passing through the second lens back toward the diffraction grating; a third lens that focuses the first diffracted light reflected back by the pair of first mirrors to a second focal point; and a fourth lens that parallelizes the first diffracted light focused by the third lens and guides it toward the diffraction grating, the first lens and the fourth lens having substantially the same first focal length, the second lens and the third lens having substantially the same second focal length, and a first distance along the optical path from the first focal point to the second focal point being determined by a first predetermined condition, the first predetermined condition including a condition that the deviation of the focusing position of the first diffracted light, depending on the angle formed by a scribe line extending in one direction in the diffraction grating and the rotation axis, flips between the first focal point and the second focal point.

[0012] Therefore, the operation of mounting the diffraction grating onto the drive device becomes easier. In the first optical system, even if the scribe lines extending in one direction and the rotation axis of the diffraction grating are not parallel to each other, the deviation of the focusing position in the non-dispersion direction, depending on the angle of the aforementioned components and the rotation angle of the diffraction grating, is zero when viewed as a whole optical system.

[0013] Therefore, even if the diffraction grating is not mounted on the drive device in an ideally parallel state relative to the rotation axis, the focal position of the non-dispersion direction of the second diffracted light remains constant at any rotation angle of the diffraction grating. Thus, the second diffracted light of a specific wavelength can pass through the slit arranged in the optical path after the first optical system, regardless of the rotation angle of the diffraction grating. The second diffracted light can then enter the light-receiving element arranged in the optical path after the slit, regardless of the rotation angle of the diffraction grating.

[0014] Thus, even if the scribe lines extending in one direction of the diffraction grating and the axis of rotation are not ideally parallel to each other, the beam splitter can still function normally. That is, the tolerance for deviation from the ideal parallelism of the diffraction grating relative to the axis of rotation is increased. Therefore, high precision is not required for the installation operation of the diffraction grating onto the drive device. As a result, such installation becomes easier and can be performed in a short time. As described above, due to the reduction in operating costs, the beam splitter and the optical device equipped with it can be easily made high-performance and become inexpensive as products.

[0015] In one aspect of the first optical system, the first specified condition may include the condition that the first distance is approximately four times the second focal length. Thus, the angle of the direction in which the first diffracted light travels from the second focal point of the third lens coincides with the angle of the direction in which the first diffracted light enters the second lens. Therefore, if a component of the same size as the first lens is used as the fourth lens, the first diffracted light reliably passes through the fourth lens. Therefore, the user can use the same component as the first lens as the fourth lens.

[0016] In one aspect of the first optical system, the first focal length is longer than the second focal length. Consequently, the distance between the focusing position of the first diffracted light and the first lens increases. Similarly, the distance between the focusing position of the second diffracted light and the fourth lens increases. Therefore, the distance between the focusing position of diffracted light based on one wavelength and the focusing positions of diffracted light based on other wavelengths increases at each focal point. Therefore, even when using a narrow slit, it is easy to extract only a specific wavelength of the second diffracted light. Thus, the wavelength selection accuracy based on the beam splitter is improved.

[0017] The beam splitter of the second aspect of the present invention has a first optical system as described in any of the above aspects, the diffraction grating, and a first slit located at the third focal point where the second diffracted light diffracted by the diffraction grating is focused by the fourth lens.

[0018] Therefore, the operation of mounting the diffraction grating onto the drive unit becomes easier. In the beam splitter, even if the scribe lines extending in one direction and the axis of rotation of the diffraction grating are not parallel to each other, the amount of deviation of the focusing position in the non-dispersion direction, depending on the angle formed by these components and the rotation angle of the diffraction grating, is zero when viewed as a whole optical system.

[0019] Therefore, even if the diffraction grating is not mounted on the drive device in an ideal parallel state with respect to the rotation axis, the focal position of the non-dispersion direction of the second diffracted light is constant at any rotation angle of the diffraction grating. Thus, the second diffracted light of a specific wavelength can pass through the first slit arranged in the optical path after the first optical system, regardless of the rotation angle of the diffraction grating. The second diffracted light can then enter the light-receiving element arranged in the optical path after the first slit, regardless of the rotation angle of the diffraction grating.

[0020] In this way, even if the scribe lines extending in one direction of the diffraction grating and the axis of rotation are not ideally parallel to each other, the beam splitter can still function normally. That is, the tolerance for deviation from the ideal parallelism of the diffraction grating relative to the axis of rotation is increased. Therefore, high precision is not required for the installation operation of the diffraction grating onto the drive device. As a result, such installation operations become easier and can be performed in a short time. By reducing operating costs as described above, the beam splitter and the optical device equipped with the beam splitter can be easily made high-performance and become inexpensive as a product.

[0021] One side of the beam splitter also has a second optical system, which includes: a fifth lens that parallelizes the second diffracted light focused at the third focal point by the fourth lens and guides it toward the diffraction grating; a sixth lens that parallelizes the third diffracted light diffracted by the diffraction grating, which is then focused at the fourth focal point by the fifth lens; a pair of second mirrors that reflect the third diffracted light, which has passed through the sixth lens, back toward the diffraction grating; and a seventh lens that focuses the third diffracted light reflected back by the pair of second mirrors toward the fifth focal point. An eighth lens, which parallelizes the third diffracted light focused by the seventh lens and guides it toward the diffraction grating, the fifth and eighth lenses having approximately the same third focal length, the sixth and seventh lenses having approximately the same fourth focal length, and a second distance along the optical path from the fourth focal point to the fifth focal point, determined by a second predetermined condition, the second predetermined condition including a condition that the deviation of the focusing position of the third diffracted light, depending on the angle formed by the grating and the rotation axis, flips between the fourth and fifth focal points.

[0022] Therefore, by increasing the diffraction order based on the diffraction grating, wavelength accuracy can be further improved and light can be extracted. That is, the measurement error of the wavelength of light by the beam splitter becomes smaller.

[0023] In one aspect of the beam splitter, the second specified condition may also include the condition that the second distance is approximately four times the fourth focal length. Thus, the angle of the direction in which the third diffracted light travels from the fifth focal point of the seventh lens coincides with the angle of the direction of the third diffracted light entering the sixth lens. Therefore, if a component of the same size as the fifth lens is used as the eighth lens, the third diffracted light reliably passes through the eighth lens. Therefore, the user can use the same component as the fifth lens as the eighth lens.

[0024] In one aspect of the beam splitter, the third focal length is longer than the fourth focal length. Consequently, the distance between the focusing position of the third diffracted light and the fifth lens increases. Similarly, the distance between the focusing position of the fourth diffracted light and the eighth lens increases. Therefore, the distance between the focusing positions of diffracted light based on one wavelength and those based on other wavelengths increases at each focal point. Thus, even with a narrow slit, it is easy to extract only the specific wavelength of the fourth diffracted light. Therefore, the wavelength selection accuracy of the beam splitter is improved.

[0025] One aspect of the beam splitter also includes a second slit located at the sixth focal point where the fourth diffracted light, diffracted by the diffraction grating, is focused by the eighth lens. This allows for the easy extraction of only the fourth diffracted light of a specific wavelength focused at the sixth focal point.

[0026] In one aspect of the beam splitter, the diffraction grating has: a first diffraction grating that, together with the first optical system, performs an optical action relative to light; and a second diffraction grating that, together with the second optical system, performs an optical action relative to light, wherein the first diffraction grating and the second diffraction grating are separately formed from each other.

[0027] Therefore, the aforementioned effect of simplifying the process of mounting diffraction gratings onto the drive unit becomes even more significant. For example, in the prior art, when mounting two diffraction gratings onto the drive unit, the operation of mounting each diffraction grating onto the drive unit in such a way that the extension direction of the grating lines is parallel to the rotation axis is more complex compared to mounting a single diffraction grating. In one aspect of the beam splitter, high precision in the mounting operation is not required for each diffraction grating. Therefore, the effect of simplifying the process of mounting diffraction gratings onto the drive unit is more significant than with a single diffraction grating.

[0028] Furthermore, using two diffraction gratings is less expensive than using a single, large diffraction grating. As a result, beam splitters and optical devices that incorporate beam splitters can be easily upgraded to high performance and become cheaper products.

[0029] Several optical devices have beam splitters as described in any of the above aspects.

[0030] Therefore, the operation of mounting the diffraction grating onto the drive device becomes easier. In the optical device, even if the scribe lines extending in one direction and the axis of rotation of the diffraction grating are not parallel to each other, the amount of deviation of the focusing position in the non-dispersion direction, depending on the angle formed by these components and the rotation angle of the diffraction grating, is zero when viewed as a whole optical system.

[0031] Therefore, even if the diffraction grating is not mounted on the drive device in an ideally parallel state relative to the rotation axis, the focal position of the diffracted light in the non-dispersion direction remains constant at any rotation angle of the diffraction grating. Thus, diffracted light of a specific wavelength can pass through a slit positioned in the optical path behind the optical system, independent of the rotation angle of the diffraction grating. The diffracted light can then enter a light-receiving element positioned in the optical path behind the slit, independent of the rotation angle of the diffraction grating.

[0032] Thus, even if the scribe lines extending in one direction of the diffraction grating and the axis of rotation are not ideally parallel to each other, the optical device can still operate normally. That is, the tolerance for deviation from the ideal parallelism of the diffraction grating relative to the axis of rotation is increased. Therefore, the installation operation of the diffraction grating to the drive device does not require high precision. As a result, such installation becomes easier and can be performed in a short time. By reducing operating costs as described above, the optical device equipped with the beam splitter becomes inexpensive while easily achieving high performance.

[0033] According to the present invention, a first optical system, beam splitter, and optical device are provided that make it easy to install a diffraction grating onto a driving device. Attached Figure Description

[0034] Figure 1 This is a schematic diagram showing the general configuration of the beam splitter according to the first embodiment of the present invention.

[0035] Figure 2 It only means Figure 1 A schematic diagram of the general structure of the optical system.

[0036] Figure 3 This is a schematic diagram illustrating the situation of light entering a diffraction grating.

[0037] Figure 4 This is a schematic diagram showing the general configuration of the beam splitter according to the second embodiment of the present invention.

[0038] Figure 5 This is a schematic diagram showing the general configuration of the beam splitter according to the third embodiment of the present invention.

[0039] Figure 6 This is a schematic diagram illustrating the diffraction and reflection of light in a diffraction grating.

[0040] Explanation of reference numerals in the attached figures

[0041] 1: Spectrometer

[0042] 2: Fiber optic

[0043] 10: Optical System (First Optical System)

[0044] 111: First Lens

[0045] 112: Second lens

[0046] 113: Third Lens

[0047] 114: Fourth Lens

[0048] 12: Reflector (First Reflector)

[0049] 13: Reflector (First Reflector)

[0050] 20: Second optical system

[0051] 211: The Fifth Lens

[0052] 212: The Sixth Lens

[0053] 213: The Seventh Lens

[0054] 214: The Eighth Lens

[0055] 22: Reflector (Second Reflector)

[0056] 23: Reflector (Second Reflector)

[0057] 3: Diffraction grating

[0058] 3a: First diffraction grating

[0059] 3b: Second diffraction grating

[0060] 4: Slit (First Slit)

[0061] 4a: First slit

[0062] 4b: Second slit

[0063] 5: Light receiving element

[0064] 6: Lens

[0065] 7: Reflector

[0066] 8: Reflector

[0067] 9: Lens

[0068] C: Rotation axis

[0069] L0: Light

[0070] L1: First diffraction beam

[0071] L2: Second diffraction beam

[0072] L3: Third diffraction beam

[0073] L4: Fourth diffraction beam

[0074] d1: Direction

[0075] d2: Direction

[0076] f0: Focus

[0077] f1: First Focus

[0078] f2: Second focus

[0079] f3: Third Focus

[0080] f4: Fourth Focus

[0081] f5: Fifth Focus

[0082] f6: Sixth Focus Detailed Implementation

[0083] A more detailed explanation of the background and problems of the existing technology is provided.

[0084] In the two-stage beam splitter described in Patent Document 1, light incident from the entrance slit is converted into parallel light by a collimator and then incident on a diffraction grating. The diffraction grating is a reflective plate having multiple parallel gratings at regular intervals, which disperses and splits the incident light, emitting its diffracted light. This diffraction grating is rotatably constructed by a driving device (not shown) around a rotation axis extending parallel to the direction of the grating's extension at its center. The diffraction grating is configured to allow for arbitrary changes in its angle relative to the incident light.

[0085] The light dispersed by the diffraction grating is converted into converging light by a collimator and then reflected back by a reflector. The reflected light is again converted into parallel light by the collimator and enters the diffraction grating. The incident light is dispersed a second time and exits the diffraction grating as diffracted light. The exiting light is focused by the collimator and selected by the exit slit.

[0086] In the beam splitter described in Patent Document 2, light incident from an optical fiber that serves as an entrance slit is converted into parallel light by a collimator and then incident on a diffraction grating. The light dispersed by the diffraction grating is then focused by the collimator. Light reflected back by the reflection device is incident on the collimator, converted into parallel light, and then incident on the diffraction grating. The incident light is dispersed a second time and then emitted as diffracted light from the diffraction grating. The emitted light is focused by the collimator and then extracted through the exit slit.

[0087] Figure 6 This is a schematic diagram illustrating the diffraction and reflection of light within a diffraction grating. The wavelength extracted from the exit slit can be rotated by controlling the angle of the diffraction grating. This wavelength is represented by Equation 1 below.

[0088] m·λ1=d·cosθ·(sinα+sinβ)···(Formula 1)

[0089] Where m is the diffraction number, λ1 is the wavelength of light, and d is the grating spacing of the diffraction grating. α is as follows Figure 6 As shown, β is the angle of incidence of the measured light relative to the reflecting surface of the diffraction grating. Figure 6 As shown, θ is the exit angle of the diffracted light relative to the reflecting surface of the diffraction grating. Figure 6 The figure shows the incident angle and reflection angle of light along the extension direction of the grating lines.

[0090] Regarding the dispersion direction of the reflected light from a diffraction grating, the desired wavelength can be selected by controlling the rotation angle of the diffraction grating. In this specification, "dispersion direction" includes the arrangement direction of gratings extending in one direction within the diffraction grating, for example, including... Figure 6 The direction d1. On the other hand, regarding the non-dispersive direction, regardless of the rotation angle, light is reflected in the same manner as a plane mirror, with the incident angle θ and the reflection angle θ being consistent. In this specification, "non-dispersive direction" includes the direction of extension of a scribe line extending in one direction in a diffraction grating, for example, containing Figure 6 The direction d2. The exit angle of light in the non-dispersive direction is constant and does not depend on the rotation angle of the diffraction grating.

[0091] Suppose that the scribe lines extending in one direction of the diffraction grating are not parallel to the rotation axis, and the diffraction grating is mounted on the driving device at an angle γ, then the exit angle of light in the non-dispersive direction changes by angle γ. In this case, when the diffraction grating rotates by an angle α1, the exit angle component of angle γ changes according to the relationship γ / cosα1.

[0092] The diffracted light, with its varying exit angle, is focused using a collimator. The deviation of the focusing position in the non-dispersion direction is proportional to sin(γ / cosα1). The focusing position varies depending on the rotation angle, i.e., angle α1. As a result, due to the prescribed rotation angle of the diffraction grating, the diffracted light cannot pass through the slit configured in the subsequent optical path, or cannot enter the light-receiving element. Therefore, the selection and extraction of light as a beam splitter cannot be performed properly, and the device cannot function. By increasing the slit width, such obstruction of light passage can be suppressed, but in this case, components other than the necessary light can easily pass through the slit, resulting in a decrease in the optical properties of the beam splitter.

[0093] To avoid the aforementioned problems, the emission angle in the direction of the grating extension needs to be constant, independent of the rotation of the diffraction grating. In other words, the diffraction grating needs to be mounted on the drive unit so that the grating extending in one direction and the axis of rotation are nearly perfectly parallel. Typically, because the drive unit and the diffraction grating are constructed as separate components, considerable time is spent on the installation process to achieve near-ideal parallelism.

[0094] To address the aforementioned problems, the present invention aims to provide a first optical system, beam splitter, and optical device that facilitates the mounting of a diffraction grating onto a driving device. Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0095] (First Implementation)

[0096] Figure 1 This is a schematic diagram showing the general configuration of the beam splitter 1 according to the first embodiment of the present invention. Figure 2 It only means Figure 1 A schematic diagram of the general configuration of the optical system 10. (Refer to...) Figure 1 and Figure 2 This section mainly describes the structure and function of the beam splitter 1 in the first embodiment.

[0097] Beam splitter 1 utilizes the diffraction phenomenon to extract only diffracted light of a specific wavelength from the light incident from optical fiber 2. As a major component, beam splitter 1 includes an optical system 10, a diffraction grating 3, a slit 4, and a light-receiving element 5.

[0098] The optical system 10 has a first lens 111, a second lens 112, a reflector 12, a reflector 13, a third lens 113, and a fourth lens 114 arranged sequentially along the optical path from the optical fiber 2.

[0099] The first lens 111 parallelizes the light L0 incident from the optical fiber 2, which also has an entrance slit, and guides it toward the diffraction grating 3, which is rotatable around the rotation axis C. The first lens 111 acts on the first diffracted light L1 diffracted by the diffraction grating 3 and focuses the first diffracted light L1 to the first focal point f1. The second lens 112 focuses the light to the first focal point f1 through the first lens 111 and parallelizes the first diffracted light L1 that has diffused again.

[0100] A pair of mirrors 12 and 13 reflect the first diffracted light L1, which has passed through the second lens 112, back to the diffraction grating 3. Mirror 12 causes the first diffracted light L1, which has become parallel light by the second lens 112, to reflect back to mirror 13 at an angle of 90° or close to 90°. Mirror 13 further causes the first diffracted light L1 reflected by mirror 12 to reflect back to the third lens 113 at an angle of 90° or close to 90°.

[0101] The third lens 113 focuses the first diffracted light L1, reflected back by a pair of mirrors 12 and 13, onto the second focal point f2. The fourth lens 114 parallelizes the first diffracted light L1, which has been focused onto the second focal point f2 by the third lens 113 and diffused again, and guides it towards the diffraction grating 3. The fourth lens 114 acts on the second diffracted light L2 diffracted by the diffraction grating 3, focusing the second diffracted light L2 onto the third focal point f3.

[0102] Slit 4 is located at the third focal point f3, which, through the fourth lens 114, focuses the second diffracted light L2 diffracted by the diffraction grating 3. Slit 4 extracts only the second diffracted light L2 of a specific wavelength. The light-receiving element 5 receives only the second diffracted light L2 of a specific wavelength that has passed through slit 4. The beam splitter 1 measures the light intensity of the second diffracted light L2 received by the light-receiving element 5.

[0103] The first lens 111 and the fourth lens 114 have approximately the same first focal length. That is, the first lens 111 and the fourth lens 114 have the same or approximately the same first focal length. The second lens 112 and the third lens 113 have approximately the same second focal length. In other words, the second lens 112 and the third lens 113 have the same or approximately the same second focal length. The first focal length is longer than the second focal length.

[0104] like Figure 2 As shown, the distance along the optical path from the first focal point f1 to the second focal point f2 is determined by predetermined conditions. These conditions include the condition that the deviation of the focusing position of the first diffracted light L1 is such that it flips between the first focal point f1 and the second focal point f2, the focusing position of the first diffracted light L1 depending on the angle formed by the scribe line extending in one direction and the rotation axis C in the diffraction grating 3. More specifically, the predetermined conditions include the condition that the distance is approximately four times the second focal length f. That is, the predetermined conditions include the condition that the distance is a multiple of the second focal length f multiplied by four or approximately four times the value of the second focal length f.

[0105] The specified conditions are not limited to the condition that the distance along the light path from the first focal point f1 to the second focal point f2 is approximately four times the second focal length f. Any condition may be included if the first diffracted light L1 diffused through the second focal point f2 is within the size of the fourth lens 114.

[0106] According to the first embodiment described above, the operation of mounting the diffraction grating 3 onto the drive device becomes easier. In the optical system 10 and the beam splitter 1, even if the scribe lines extending in one direction and the rotation axis C in the diffraction grating 3 are not parallel to each other, as a whole, the deviation of the focusing position in the non-dispersion direction, depending on the angle formed by these components and the rotation angle of the diffraction grating 3, is zero when considering the optical system 10 as a whole.

[0107] More specifically, the deviation of the focusing position of the first diffracted light L1 in the non-dispersion direction at the second focal point f2 is reversed relative to the deviation of the focusing position of the first diffracted light L1 in the non-dispersion direction at the first focal point f1. Since the first diffracted light L1 is further diffracted by the diffraction grating 3, at the third focal point f3, the second diffracted light L2 produces the same deviation as at the first focal point f1. Therefore, at the third focal point f3, the deviation cancels out the deviation at the second focal point f2, and the deviation is zero.

[0108] Therefore, even if the diffraction grating 3 is not mounted on the drive device in an ideal parallel state relative to the rotation axis C, the focal position of the second diffracted light L2 in the non-dispersion direction remains constant at any rotation angle of the diffraction grating 3. Thus, the second diffracted light L2 of a specific wavelength can pass through the slit 4 arranged in the optical path after the optical system 10 regardless of the rotation angle of the diffraction grating 3. The second diffracted light L2 can also enter the light-receiving element 5 arranged in the optical path after the slit 4, regardless of the rotation angle of the diffraction grating 3.

[0109] Thus, even if the scribe lines extending in one direction in the diffraction grating 3 and the rotation axis C are not ideally parallel to each other, the beam splitter 1 still operates normally as a device. That is, the tolerance for deviation from the ideal parallelism of the diffraction grating 3 relative to the rotation axis C is increased. Therefore, high precision is not required for the installation operation of mounting the diffraction grating 3 to the drive device. As a result, such installation operations become easier and can be performed in a short time. As described above, due to the reduction in operating costs, the beam splitter 1 and the optical device equipped with the beam splitter 1 can easily achieve high performance and become inexpensive as a product.

[0110] Figure 3 This is a schematic diagram illustrating the situation where light enters the diffraction grating 3. (Refer to...) Figure 3 We also use mathematical formulas to more rigorously explain the above effects.

[0111] When the extension direction of the scribe lines in the diffraction grating 3 is offset by an angle γ relative to the rotation axis C, the focusing position of the first diffracted light L1, focused by the first lens 111, in the non-dispersion direction at the first focal point f1, compared to the position when the angle γ is 0, is represented by f(sinθ-sin(γ / cosα)). Here, f is the second focal length. θ is the incident angle of light along the extension direction of the scribe lines of the diffraction grating 3. α is the angle formed by the perpendicular line to the reflecting surface of the diffraction grating 3 and the dispersion component of the incident light. The focusing position of the first diffracted light L1 at the first focal point f1 is, compared to the position when the angle γ is 0, in a direction orthogonal to the optical axis, for example... Figure 2 The amount of displacement in the left and right directions on the paper is proportional to -sin(γ / cosα).

[0112] Because the first diffracted light L1 passes through the second lens 112, a pair of mirrors 12 and 13, and the third lens 113, the shift in the focusing position at the first focal point f1 of the first lens 111 is reversed by an amount proportional to +sin(γ / cosα). More specifically, the focusing position of the first diffracted light L1 in the non-dispersive direction at the second focal point f2 is represented by f(sinθ+sin(γ / cosα)).

[0113] At the second focal point f2, the first diffracted light L1, entering the fourth lens 114 from the focusing position represented by f(sinθ+sin(γ / cosα)), is converted into parallel light and re-enters the diffraction grating 3. At this time, the focusing position of the second diffracted light L2 at the third focal point f3 is shifted by an amount proportional to -sin(γ / cosα), similar to the first incident light L0 relative to the diffraction grating 3. Therefore, the error produced at the second focal point f2, proportional to the sign-flipped +sin(γ / cosα), cancels out the error proportional to -sin(γ / cosα) produced by reflection at the second diffraction grating 3.

[0114] As a result, the focusing position of the second diffracted light L2, focused by the fourth lens 114, is represented by f(sinθ) and does not depend on the angle γ. That is, the rotation axis C is parallel to the extension direction of the scribe lines in the diffraction grating 3, and corresponds to the focusing position when the angle γ is zero. The focusing position of the second diffracted light L2 is constant and does not depend on the rotation angle of the diffraction grating 3.

[0115] Since the specified conditions include the condition that the distance along the optical path from the first focal point f1 to the second focal point f2 is approximately four times the second focal length f, the angle in the direction in which the first diffracted light L1 travels from the second focal point f2 of the third lens 113 coincides with the angle in the direction in which the first diffracted light L1 enters the second lens 112. Therefore, if a component of the same size as the first lens 111 is used as the fourth lens 114, the first diffracted light L1 reliably passes through the fourth lens 114. Thus, the user can use the same component as the first lens 111 as the fourth lens 114.

[0116] Because the first focal length is greater than the second focal length f, the distance between the focusing position of the first diffracted light L1 and the first lens 111 increases. Similarly, the distance between the focusing position of the second diffracted light L2 and the fourth lens 114 increases. Therefore, the distance between the focusing position of diffracted light based on one wavelength and the focusing position of diffracted light based on other wavelengths increases at each focal point. Therefore, even when using a narrow slit 4, it is easy to extract only a specific wavelength with respect to the second diffracted light L2. Thus, the wavelength selection accuracy based on the beam splitter 1 is improved.

[0117] (Second Implementation)

[0118] Figure 4 This is a schematic diagram showing the general configuration of the beam splitter 1 according to the second embodiment of the present invention. (Refer to...) Figure 4 This section mainly describes the structure and function of the beam splitter 1 in the second embodiment.

[0119] In the second embodiment, the difference from the first embodiment is that, in addition to the optical system 10 which is the first optical system, the beam splitter 1 also has a second optical system 20, and the light undergoes four diffractions instead of two diffractions when passing through the diffraction grating 3. Other configurations, functions, effects, and modifications are the same as in the first embodiment, and the corresponding descriptions also apply to the beam splitter 1 of the second embodiment. Hereinafter, the same reference numerals are used for components identical to those in the first embodiment, and their descriptions are omitted. The main focus is on the configuration and functions that differ from those in the first embodiment.

[0120] The beam splitter 1 of the second embodiment has a further optical system having a second optical system 20 between the slit 4 and the light-receiving element 5 of the beam splitter 1 of the first embodiment. The beam splitter 1 has an optical system 10 as the first optical system, a diffraction grating 3, a first slit 4a, a lens 6, a mirror 7, a mirror 8, a lens 9, a second optical system 20, a second slit 4b, and a light-receiving element 5.

[0121] Lens 6 parallelizes the second diffracted light L2 of a specific wavelength that diffuses again through the first slit 4a. A pair of mirrors 7 and 8 reflect the second diffracted light L2, which has passed through lens 6, back to the diffraction grating 3. Mirror 7 reflects the second diffracted light L2, now paralleled by lens 6, back to mirror 8 at an angle of 90° or approximately 90°. Mirror 8 further reflects the second diffracted light L2 reflected by mirror 7 back to lens 9 at an angle of 90° or approximately 90°. Lens 9 focuses the second diffracted light L2 reflected back by mirrors 7 and 8 to a focal point f0.

[0122] The second optical system 20 has a fifth lens 211, a sixth lens 212, a mirror 22, a mirror 23, a seventh lens 213, and an eighth lens 214 arranged sequentially along the optical path of the second diffracted light L2 focused at the focal point f0.

[0123] The fifth lens 211 parallelizes the second diffracted light L2, which is focused to the third focal point f3 by the fourth lens 114 of the optical system 10, and guides it towards the diffraction grating 3. More specifically, the fifth lens 211 parallelizes the second diffracted light L2, which is focused to the focal point f0 by the lens 9 and diffused again, and guides it towards the diffraction grating 3. The fifth lens 211 acts on the third diffracted light L3 diffracted by the diffraction grating 3 and focuses the third diffracted light L3 to the fourth focal point f4. The sixth lens 212 parallelizes the third diffracted light L3, which is focused to the fourth focal point f4 by the fifth lens 211 and diffused again.

[0124] A pair of mirrors 22 and 23 reflect the third diffracted light L3, which has passed through the sixth lens 212, back to the diffraction grating 3. Mirror 22 reflects the third diffracted light L3, which has become parallel light after passing through the sixth lens 212, back to mirror 23 at an angle of 90° or approximately 90°. Mirror 23 further reflects the third diffracted light L3 reflected by mirror 22 back to the seventh lens 213 at an angle of 90° or approximately 90°.

[0125] The seventh lens 213 focuses the third diffracted light L3, reflected back by a pair of mirrors 22 and 23, to the fifth focal point f5. The eighth lens 214 parallelizes the third diffracted light L3, which has been focused to the fifth focal point f5 by the seventh lens 213 and diffused again, and guides it towards the diffraction grating 3. The eighth lens 214 acts on the fourth diffracted light L4 diffracted by the diffraction grating 3 and focuses the fourth diffracted light L4 to the sixth focal point f6.

[0126] The second slit 4b is located at the sixth focal point f6, where the fourth diffracted light L4, diffracted by the diffraction grating 3, is focused by the eighth lens 214. The second slit 4b extracts only the fourth diffracted light L4 of a specific wavelength. The light-receiving element 5 receives only the fourth diffracted light L4 of a specific wavelength that has passed through the second slit 4b. The beam splitter 1 measures the intensity of the fourth diffracted light L4 received by the light-receiving element 5.

[0127] The fifth lens 211 and the eighth lens 214 have approximately the same third focal length. That is, the fifth lens 211 and the eighth lens 214 have the same or approximately the same third focal length. The sixth lens 212 and the seventh lens 213 have approximately the same fourth focal length. That is, the sixth lens 212 and the seventh lens 213 have the same or approximately the same fourth focal length. The third focal length is longer than the fourth focal length. The third focal length can be the same as the first focal length. The fourth focal length can be the same as the second focal length.

[0128] and Figure 2 Similarly, the distance along the optical path from the fourth focal point f4 to the fifth focal point f5 is determined by specified conditions. These specified conditions include the condition that the deviation of the focal position of the third diffracted beam L3 flips between the fourth focal point f4 and the fifth focal point f5, the third diffracted beam L3 depending on the angle formed by the scribe line extending in one direction and the rotation axis C in the diffraction grating 3. More specifically, the specified conditions include the condition that the distance is approximately four times the fourth focal length f. That is, the specified conditions include the condition that the distance is a multiple of the fourth focal length f multiplied by four or approximately four times the value of the fourth focal length f.

[0129] The specified conditions are not limited to the condition that the distance along the optical path from the fourth focal point f4 to the fifth focal point f5 is approximately four times the fourth focal length f. Any condition can be included as long as the third diffracted light L3 passing through the fifth focal point f5 and diffusing is within the size of the eighth lens 214.

[0130] According to the second embodiment of the beam splitter 1 described above, by increasing the diffraction order of the diffraction grating 3, the wavelength accuracy and light extraction can be further improved. That is, the measurement error of the wavelength of light performed by the beam splitter 1 is reduced.

[0131] Since the specified conditions include the requirement that the distance along the optical path from the fourth focal point f4 to the fifth focal point f5 is approximately four times the fourth focal length f, the angle in which the third diffracted light L3 travels from the fifth focal point f5 of the seventh lens 213 coincides with the angle in which the third diffracted light L3 enters the sixth lens 212. Therefore, if a component of the same size as the fifth lens 211 is used as the eighth lens 214, the third diffracted light L3 reliably passes through the eighth lens 214. Thus, the user can use the same component as the fifth lens 211 as the eighth lens 214.

[0132] Because the third focal length is greater than the fourth focal length f, the distance between the focusing position of the third diffracted light L3 and the fifth lens 211 increases. Similarly, the distance between the focusing position of the fourth diffracted light L4 and the eighth lens 214 increases. Therefore, the distance between the focusing position of diffracted light based on one wavelength and the focusing position of diffracted light based on other wavelengths increases at each focal point. Therefore, even when using the narrow second slit 4b, it is easy to extract only a specific wavelength with respect to the fourth diffracted light L4. Thus, the wavelength selection accuracy based on beam splitter 1 is improved.

[0133] The beam splitter 1 has a second slit 4b located at the sixth focal point f6 where the fourth diffracted light L4 diffracted by the diffraction grating 3 is focused by the eighth lens 214, thereby enabling the easy extraction of only the specific wavelength of the fourth diffracted light L4 focused at the sixth focal point f6.

[0134] (Third Implementation)

[0135] Figure 5 This is a schematic diagram showing the general configuration of the beam splitter 1 according to the third embodiment of the present invention. (Refer to...) Figure 5 This section mainly describes the structure and function of the beam splitter 1 in the third embodiment.

[0136] In the third embodiment, the difference from the second embodiment is that light is diffracted through a pair of first diffraction gratings 3a and second diffraction gratings 3b instead of a single diffraction grating 3. Other configurations, functions, effects, and variations are the same as in the second embodiment, and the corresponding descriptions also apply to the beam splitter 1 of the third embodiment. Hereinafter, the same reference numerals are used for components identical to those in the second embodiment, and their descriptions are omitted. The main focus is on the configuration and functions that differ from those in the second embodiment.

[0137] The diffraction grating 3 has a first diffraction grating 3a and a second diffraction grating 3b. The first diffraction grating 3a acts optically on light together with the optical system 10, which is a first optical system, and the second diffraction grating 3b acts optically on light together with the second optical system 20. More specifically, the first diffraction grating 3a acts on light L0 to produce a first diffracted light L1. The first diffraction grating 3a acts on the first diffracted light L1 to produce a second diffracted light L2. The second diffraction grating 3b acts on the second diffracted light L2 to produce a third diffracted light L3. The second diffraction grating 3b acts on the third diffracted light L3 to produce a fourth diffracted light L4. The first diffraction grating 3a and the second diffraction grating 3b are separately constructed from each other.

[0138] According to the beam splitter 1 of the third embodiment described above, the effects of the first embodiment are more significant. For example, in the prior art, when two diffraction gratings 3 are mounted on the driving device, the operation of mounting each diffraction grating 3 on the driving device such that the extension direction of the scribe lines in the diffraction grating 3 is parallel to the rotation axis C is more complex compared to the operation with only one diffraction grating 3. According to the beam splitter 1 of the third embodiment, high precision is not required for the mounting operation of each diffraction grating 3. Therefore, the ease of operation when mounting the diffraction grating 3 on the driving device is more significant than that with only one diffraction grating 3.

[0139] Furthermore, using two diffraction gratings 3 results in lower costs compared to using a single, large diffraction grating 3. Therefore, the beam splitter 1 and the optical devices equipped with it are readily available for high performance while remaining inexpensive as products.

[0140] It will be apparent to those skilled in the art that the present invention can be implemented in other prescribed ways besides the embodiments described above without departing from its spirit or essential characteristics. Therefore, the foregoing description is exemplary and not limiting. The scope of the disclosure is defined by the appended claims, not by the foregoing description. In all modifications, some changes within their equivalent scope are included therein.

[0141] For example, the shape, arrangement, orientation, and number of the above-mentioned components are not limited to those shown in the description and accompanying drawings. The shape, arrangement, orientation, and number of each component can be arbitrarily configured as long as it can fulfill its function.

[0142] In the above embodiments, it is stated that the first focal length is longer than the second focal length f, but this is not a limitation. The first focal length can be less than or equal to the second focal length f.

[0143] In the above embodiments, it is stated that the third focal length is longer than the fourth focal length f, but it is not limited thereto. The third focal length can be less than or equal to the fourth focal length f.

[0144] In the second and third embodiments described above, it is explained that the beam splitter 1 has a first slit 4a and a second slit 4b, but it is not limited thereto. The beam splitter 1 may not have the first slit 4a and may only have the second slit 4b.

[0145] In the above embodiments, it is explained that the first lens 111 and the fourth lens 114 have two functions: one is to convert light into parallel light and direct it into the diffraction grating 3, and the other is to focus the diffracted light. However, they are not limited to these functions. These functions can be achieved by two different lenses with approximately the same focal length.

[0146] In the second and third embodiments described above, it was explained that the fifth lens 211 and the eighth lens 214 each have two functions: one as a lens that converts light into parallel light and directs it into the diffraction grating 3, and the other as a lens that focuses the diffracted light. However, they are not limited to this. These functions can be achieved by two different lenses with approximately the same focal length.

[0147] In the embodiments described above, a plane mirror, positioned approximately perpendicular to the propagation direction, may be placed at the reflection destination of the diffracted light from the diffraction grating 3. This facilitates the re-entry of the diffracted light into the diffraction grating 3, and increases the number of diffractions. Consequently, wavelength selectivity is further improved.

[0148] In the above embodiments, the spectrometer 1 can also be mounted on any optical device such as a spectrometer or analyzer.

Claims

1. A first optical system, wherein, have: The first lens parallelizes the incident light and guides it toward a diffraction grating that can rotate around the rotation axis. The second lens parallelizes the first diffracted light diffracted by the diffraction grating, and the first diffracted light is focused by the first lens at a first focal point. A pair of first reflecting mirrors that reflect the first diffracted light that has passed through the second lens back to the diffraction grating; The third lens focuses the first diffracted light reflected back by the pair of first reflecting mirrors to the second focal point; A fourth lens, which parallelizes the first diffracted light focused by the third lens and guides it toward the diffraction grating; The first lens and the fourth lens have the same first focal length. The second lens and the third lens have the same second focal length. The first distance along the optical path from the first focal point to the second focal point is determined by a first predetermined condition. The first specified condition includes the condition that the deviation of the focusing position of the first diffracted light in the diffraction grating, depending on the angle formed by the grating extending in one direction and the rotation axis, flips between the first focal point and the second focal point.

2. The first optical system as claimed in claim 1, wherein, The first specified condition includes the condition that the first distance is four times the second focal length.

3. The first optical system as claimed in claim 1 or 2, wherein, The first focal length is longer than the second focal length.

4. A beam splitter, wherein, have: The first optical system according to any one of claims 1 to 3; The diffraction grating; The second diffracted light, located at the third focal point of the fourth lens, is focused by the fourth lens.

5. The beam splitter as described in claim 4, wherein, It also has a second optical system. The second optical system has: The fifth lens parallelizes the second diffracted light, which is focused at the third focal point by the fourth lens, and guides it toward the diffraction grating; The sixth lens parallelizes the third diffracted light diffracted by the diffraction grating, which is then focused at the fourth focal point by the fifth lens; A pair of second mirrors reflect the third diffracted light that has passed through the sixth lens back to the diffraction grating; The seventh lens focuses the third diffracted light reflected back by the pair of second mirrors to the fifth focal point; The eighth lens parallelizes the third diffracted light focused by the seventh lens and guides it toward the diffraction grating; The fifth lens and the eighth lens have the same third focal length. The sixth lens and the seventh lens have the same fourth focal length. The second distance along the optical path from the fourth focal point to the fifth focal point is determined by the second predetermined condition. The second specified condition includes the condition that the deviation of the focusing position of the third diffracted light, which depends on the angle formed by the scribe line and the rotation axis, flips between the fourth and fifth focal points.

6. The beam splitter as claimed in claim 5, wherein, The second specified condition includes the condition that the second distance is four times the fourth focal length.

7. The beam splitter as claimed in claim 5 or 6, wherein, The third focal length is longer than the fourth focal length.

8. The beam splitter as claimed in claim 5 or 6, wherein, It also has a second slit located at the sixth focal point where the fourth diffracted light, diffracted by the diffraction grating, is focused by the eighth lens.

9. The beam splitter as claimed in claim 5 or 6, wherein, The diffraction grating has the following characteristics: The first diffraction grating, together with the first optical system, performs optical functions relative to light; The second diffraction grating, together with the second optical system, performs optical functions relative to light; The first diffraction grating and the second diffraction grating are constructed separately from each other.

10. An optical device, wherein, A beam splitter having any one of claims 5 to 9.

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