Optical Element Mounting Method

Abstract

An optical device mounting method for mounting an optical device to a holding mechanism, including a step of designing a shape of the optical device in accordance with a stress expected to be applied to the optical device, such as not to cause the optical device to deform or to inhibit deformation to achieve desired performance.

Claims

1. An optical device mounting method for mounting an optical device to a holding mechanism, comprising a step of: designing a shape of the optical device in accordance with a stress expected to be applied to the optical device, such as not to cause the optical device to deform or to inhibit deformation to achieve desired performance.

2. The optical device mounting method according to claim 1, wherein thickness is varied between a portion having a function of the optical device and a portion not having the function to prevent distortion of the optical device.

3. An optical device mounting method for mounting an optical device to a holding mechanism, comprising a step of: designing a shape of the optical device in a way intentionally distorted such as to cancel out any deformation that is measured or estimated in accordance with a stress expected to be applied to the optical device in a mounted state, so that desired performance is achieved when mounted.

4. An optical device mounting method that uses a cooling or heating mechanism therewith, comprising a step of: making a linear expansion coefficient of a material used for the cooling or heating mechanism substantially equal to a linear expansion coefficient of a material of the optical device, to prevent deformation of the optical device.

5.-7. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0033] FIG. 1 is a diagram for explaining an example of how a reflective diffractive optical element, as one example of a conventional optical device, is mounted.

[0034] FIG. 2 shows a perspective view and a cross-sectional view illustrating a conventional cooling mechanism that uses a viscous fluid cooling.

[0035] FIG. 3 shows a perspective view and a cross-sectional view of an optical device illustrating Embodiment 1 of the present invention.

[0036] FIG. 4 shows a perspective view and a cross-sectional view of an optical device illustrating Embodiment 2 of the present invention.

DESCRIPTION OF EMBODIMENTS

[0037] Hereinafter, embodiments of the present invention will be described in detail.

Embodiment 1

[0038] Let us consider a circulatory system for the cooling mechanism of FIG. 2: The viscous fluid 401 flowing out of the outlet 205 flows through a pipe such as a hose (not shown) to be collected in a thermostatic tank that regulates the temperature of the viscous fluid, from which the viscous fluid 401 is pumped into a pipe to flow into the container 203 from the inlet 204 in FIG. 2. The drive pressure P.sub.out at the inlet 204 required for causing the viscous fluid 401 to flow out from the outlet 205 (assuming it is atmospheric) in such a circulatory system can be calculated by the following equation, by applying the Bernoulli's principle:

[00001]$\mathrm{Math}.1$$\begin{array}{cc}{P}_{\mathrm{out}}={\left(\frac{\mathrm{Flow}\mathrm{amount}}{\mathrm{Discharge}\mathrm{coefficient}\times \mathrm{Flow}\mathrm{path}\mathrm{area}}\right)}^2\times \frac{\mathrm{Density}}{2}+\begin{array}{c}\mathrm{Pressure}\mathrm{loss}\\ \left(\mathrm{per}\mathrm{unit}\mathrm{length}\right)\end{array}\times \mathrm{Flow}\mathrm{path}\mathrm{length}+\begin{array}{c}\mathrm{Atmospheric}\mathrm{Pessure}\\ \left(\mathrm{hydraulic}\mathrm{pressure}\right)\end{array}& \mathrm{Equation}\left(1\right)\end{array}$

[0039] The first term of this equation (1) is the dynamic pressure as determined by the Bernoulli's principle, the second term is the total pressure loss required for passage of the flow path, and the third term is the static pressure. The flow path area is the cross-sectional area of the outlet 205, the density is the density of the viscous fluid, and the discharge coefficient is a proportional coefficient determined by the viscous fluid.

[0040] If the amounts of inflow and outflow are both 2 L/sec, for example, the pressure of the viscous fluid 401 in FIG. 2 is substantially equal to the P.sub.out defined above, meaning the optical device 101 is subjected to P.sub.out. The present invention allows for mounting of the optical device in a way that inhibits deformation of the optical device against such a pressure.

[0041] FIG. 3 shows a perspective view (a) and a cross-sectional view (b) of an optical device illustrating Embodiment 1 of the present invention. In FIGS. 3(a) and (b), a surface that is functional as an optical device, e.g., a mirror if the device is a flat mirror, and a micro-structured surface if the device is a diffractive optical element, referred to as functional surface 102 (portion having a function of an optical device), is a thin circular part in the center, which is formed thinner than the surrounding non-functional surface 103 (portion not having the function of the optical device) that does not have the function of the optical device.

[0042] The optical device with the configuration used in the mounting method according to Embodiment 1 of the present invention illustrated in FIG. 3, which is mounted to the cooling mechanism 201, has a non-functional surface 103 with a thickness large enough not to warp under the P.sub.out defined above, or able to inhibit deformation. When mounted, the optical device 101 is pressed down and held by the frame component 202 of the cooling mechanism, but typically, the non-functional surface 103 of the optical device is formed such as to withstand the pressure or stress associated with the mounting and to prevent distortion, or to inhibit deformation, of the optical device. For reference, the tolerable limit of deformation is about several tens meters in terms of the radius of curvature of the optical device, for example.

[0043] Making a portion that functions as an optical device of the optical device thin while making the surrounding parts thick, or conversely, making a portion that functions as an optical device thick while making the surrounding parts thin, can increase the overall rigidity against the stress or pressure applied to the optical device, so that the optical device can be mounted in the form that has the desired function.

[0044] In other words, the point of the present invention is to design the shape of the optical device in accordance with the stress expected to be applied to the optical device, such as not to cause the optical device to deform or to inhibit deformation to achieve desired performance when mounted to a mechanism that holds the optical device. Varying the thickness of the optical device, for example, between a portion having the function as the optical device and a portion not having the function, can enhance the overall rigidity and prevent distortion of the optical device.

[0045] Set in an optical system with the configuration described above, processing was performed using a laser beam of 10 kW, which was successfully carried out with desired precision, without any thermal lens effect occurring.

Embodiment 2

[0046] FIG. 4 shows a perspective view (a) and a cross-sectional view (b) of an optical device used in a mounting method according to Embodiment 2 of the present invention. If the same level of pressure as that of Embodiment 1 is applied to the optical device 101 in the cooling mechanism of the conventional configuration in FIG. 2, and if the optical device 101 is a flat mirror, the pressure as applied in Embodiment 1 will cause the optical device, which is a few millimeter-thick metal member, to warp into a shape like a convex mirror, and can no longer function as a flat mirror.

[0047] Accordingly, in the optical device mounting method in Embodiment 2 of the present invention illustrated in FIG. 4, deformation of the optical device caused by pressure and/or stress applied to the optical device in the mounted state is measured, or deformation is calculated and estimated by calculations from physical properties of the metal material of the optical device or the like, and the optical device is designed in a shape resembling a concave mirror in anticipation of the pressure and/or stress applied when actually mounted or during use so that the optical device will function as a flat mirror.

[0048] In FIG. 4, similarly to FIG. 3, the functional surface 102 is a portion having the function of the optical device, and the non-functional surface 103 is a portion that does not have the function of the optical device. In the configuration of Embodiment 1 in FIG. 3, the thickness is varied from one portion to another so as to increase the overall rigidity of the optical device. In Embodiment 2 in FIG. 4, instead of increasing rigidity, the shape is designed in anticipation and in consideration of deformation so that when mounted, the pressure or the like applied during operation or use cancels the deformation to achieve a desired, optimal shape.

[0049] In other words, it is an optical device mounting method wherein the optical device shape is designed in a way intentionally distorted such as to cancel out any deformation that is measured or estimated in accordance with a stress expected to be applied to the optical device in a mounted state, so that desired performance is achieved when mounted.

[0050] This optical device mounting method according to Embodiment 2 is equally applicable to address the stress or deformation caused by not only a cooling mechanism but also a heat-retaining or heating mechanism that uses a heater or a heating fluid, for example.

[0051] With the configuration described above, processing was performed using a laser beam of 10 kW, which proved that the optical device of Embodiment 2 functioned as a flat mirror as desired, and the processing was carried out successfully as desired, without any thermal lens effect occurring.

Embodiment 3

[0052] Embodiment 3 of the present invention adopts a mounting method wherein a Peltier element that works on current to control temperature is attached to the back side of the optical device and used as a cooling mechanism to suppress a temperature rise of the optical device.

[0053] However, an optical system could not be configured as desired due to warpage of the optical device caused by thermal stress, resulting from a difference in coefficient of linear thermal expansion between the optical device and the ceramics used for the Peltier element.

[0054] Accordingly, in the mounting method of Embodiment 3, the material of the optical device was changed to one that has more or less the same linear expansion coefficient as that of the ceramics of the Peltier element. As a result, no warpage occurred in the optical device, and an optical system could be configured as desired. The linear expansion coefficient of the material used for the cooling or heating mechanism is substantially matched with the linear expansion coefficient of the material of the optical device, to prevent distortion of the optical device. The range of linear expansion coefficient values assumed to be substantially the same depends on the thickness and the like of the two materials and cannot be uniquely defined. Generally, the thicker, the easier to suppress warpage or distortion, and therefore wider the range of values assumed to be equal.

[0055] The optical device mounting method according to this embodiment is equally applicable to address the stress or deformation caused by not only a cooling mechanism but also a heat-retaining or heating mechanism that uses a heater or a heating fluid, for example.

Embodiment 4

[0056] In the configuration of Embodiment 1 in which a diffractive optical element is mounted in a cooling mechanism, the element is warped into a state like a convex mirror because of the pressure during use, resulting in the focal distance of 30 cm being increased by 10 cm. This necessitated a mechanism for moving the optical device to adjust the focus and resulted in bulkiness of the apparatus.

[0057] Accordingly, in the mounting method in Embodiment 4 of the present invention, this warpage (radius of curvature) is calculated in advance, and the diffractive optical element is fabricated such that the focal distance will be 30 cm when the radius of curvature is the determined value, and mounted and used. The result was that processing was possible with the focal distance of 30 cm even under pressure during use, which made the moving mechanism for the optical device unnecessary.

[0058] The optical device mounting method according to this embodiment is equally applicable to address the stress or deformation caused by not only a cooling mechanism but also a heat-retaining or heating mechanism that uses a heater or a heating fluid, for example.

Embodiment 5

[0059] In the mounting method according to Embodiment 5 of the present invention, the drive pressure P.sub.out of the cooling mechanism in the configuration of Embodiment 1 applied to the optical device was reduced by increasing the flow path area in Equation (1), or by shortening the flow path length, or by doing both, while keeping the same flow rate and the same cooling capability, the result being that no warpage occurred in the optical device and processing was successfully performed as desired.

[0060] Namely, it is an optical device mounting method in which the pressure is set to a value that does not cause deformation of the optical device by a configuration with an adjustment made to at least one or all of the cross-sectional area of the inlet or outlet of the viscous fluid, and the flow path length.

[0061] The optical device mounting method according to this embodiment is equally applicable to address the stress or deformation caused by not only a cooling mechanism but also a heat-retaining or heating mechanism that uses a heater or a heating fluid, for example.

Embodiment 6

[0062] Even when no cooling function is required, if the optical device is as large as 20 cm or more in diameter, for example, a force of several tens N or more is required for retaining the optical device in a manner not affected by temperature fluctuations or vibration. It has been known that such a holding force causes distortion in the optical device.

[0063] According to the mounting method of Embodiment 6 of the present invention, an optical system not susceptible to temperature fluctuations, vibration, or holding force was configured, with an outer peripheral portion of the optical device including the points at which the optical device is retained being increased in thickness so that the optical device will not be distorted by the holding force.

INDUSTRIAL APPLICABILITY

[0064] As described above, the optical device mounting method according to the present invention allows for mounting of an optical device whereby changes in characteristics of the optical device resulting from deformation of the optical device caused by drive pressure of a cooling or heating mechanism, thermal stress, holding force and the like can be prevented.

REFERENCE SIGNS LIST

[0065] 101 Optical device [0066] 102 Functional surface (portion having a function of an optical device) [0067] 103 Non-functional surface (portion not having a function of an optical device) [0068] 201 Cooling or heating mechanism [0069] 202 Frame component [0070] 203 Viscous fluid holding part (container) [0071] 204 Inlet [0072] 205 Outlet [0073] 301 Incident light [0074] 302 Reflected light [0075] 303 Diffracted light (light intensity distribution) [0076] 401 Viscous fluid