Homogenization or shaping of laser beams

Abstract

The light source 100 includes one or more deflection mirrors 118 that deflect the laser beam 104 at various angles, and a diffraction optical system 126 that diffracts the deflected laser beam. The light source 100 also includes a multimode fiber that transmits the diffracted laser beam, and a plurality of lenses 130, 132 disposed between the diffraction optical system 126 and the multimode fiber, which provide the diffracted laser beam to the multimode fiber.

Description

Technical Field

[0001] The present disclosure relates to a light source, and more particularly, to converting a coherent light source (i.e., a laser) into a uniform (e.g., uniform in both angle and space) or a specifically shaped extended light source.

Background Art

[0002] In certain optical applications (e.g., Köhler illumination microscopy), it is desirable to use an angularly and spatially uniform extended light source. Such a light source should provide both a uniform field of view and a uniform numerical aperture (NA) of illumination. However, in laser-based applications, it is difficult to design a system with an extended light source that is uniform in both angle and space. Laser beams from commercially available lasers are very often collimated with a power distribution (i.e., profile) that follows a Gaussian / Lorentz-like distribution. Also, when the coherence degree of laser irradiation is high, a noisy and unwanted speckle pattern is formed at the image plane and the object plane. As a result, the laser beam itself cannot be a good option as an extended uniform light source.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In some known techniques for forming extended light sources, a Gaussian beam is shaped by generating a uniform or otherwise designed diffraction order pattern using a single lens in conjunction with a multi-lens array (MLA) or diffractive optical element (DOE). However, the resulting illumination is sparse, and no light exists between the diffraction orders in equilibrium. In the case of Köhler illumination microscopy observations, since this illumination is projected onto the rear aperture of the objective lens, the angle on the objective plane becomes non-uniform as a result of patterning, and the continuity and uniformity of the illumination NA are lost. Furthermore, dirt, scratches, and perforations from the DOE surface are somewhat visible on the objective plane. In addition, speckle is a problem because the light source is coherent.

[0005] Another known technique for forming a uniform extended light source involves using a single lens to couple the laser beam into a square fiber waveguide (i.e., a square core). The square fiber acts as an effective mode mixer. Since each point on the Gaussian beam is associated with a propagation mode, mode mixing in the fiber results in an angularly uniform output beam. With a suitable core design, the number of modes increases, and so does the spatial uniformity at the fiber end face. However, if the core is square, the system design becomes complex because it requires the alignment of the core end face with respect to the symmetry of the imaging system or the use of a large core corresponding to the circular shape of the system's optical aperture. Furthermore, square fibers also lack flexibility in the NA range and are limited to relatively large NAs. Direct coupling also fails to solve the speckle problem. In addition, the square fiber itself has limitations in uniformity. Finally, using direct coupling with high-energy lasers can lead to high power density in the core, potentially resulting in laser-induced damage and coupling losses.

[0006] Another known technique for forming a uniform, diffused light source involves using a Powell lens along with a standard diffuser. The Gaussian beam spreads out in a fan shape, and the cross-section of the dispersed beam reaches equilibrium. However, the resulting illumination spot size is quite large (e.g., at least several millimeters, which is too large for some designs). The speckle problem also remains. [Means for solving the problem]

[0007] A system and method for generating a monochromatic and uniform (or design-shaped) extended light source are disclosed. A coherent light source (i.e., a laser) can be converted into such an extended light source, which can be uniform in both angle and space. This can, according to some embodiments, result in a uniform field of view and a uniform illumination numerical aperture (NA). Furthermore, speckle from the coherent light source can be suppressed, resulting in low optical loss (e.g., optical loss can be minimized).

[0008] In some embodiments, the light source comprises one or more deflection mirrors that deflect a laser beam at various angles, and a diffraction optical system that diffracts the deflected laser beam. The light source also comprises a multimode fiber that transmits the diffracted laser beam, and a plurality of lenses disposed between the diffraction optical system and the multimode fiber that direct the diffracted laser beam into the multimode fiber.

[0009] In some embodiments, the optical illumination method includes generating a laser beam, deflecting the laser beam at various angles, diffracting the deflected laser beam, supplying the diffracted laser beam to a multimode fiber, and transmitting the diffracted laser beam through the multimode fiber.

[0010] For a deeper understanding of the various embodiments described, please refer to the detailed descriptions below in conjunction with the following drawings. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows a single-channel light source according to several embodiments. [Figure 2] This figure shows the arrangement of components that make up a part of the light source in Figure 1, according to several embodiments. [Figure 3A] This graph shows the simulated spatial power distribution of the laser beam in Figure 2 at the output of the multimode fiber (MMF) in Figure 2 at a specific point in time. [Figure 3B] This graph shows the simulated angular power distribution of the laser beam in Figure 2 at the output of the MMF in Figure 2. [Figure 3C] This graph shows a simulated radiance cross-section corresponding to the angular power distribution in Figure 3B. [Figure 3D] Figure 3A is an enlarged view of the simulated spatial power distribution. [Figure 4] This is a schematic diagram of a multi-channel light source according to several embodiments. [Figure 5] This is a flowchart showing a light illumination method according to several embodiments. [Figure 6A] This figure shows an image of a laser beam diffracted by a multi-lens array on the plane of the end face of an MMF. [Figure 6B] This figure shows the images in the Fourier plane of three different tilts of a deflection mirror. [Figure 6C] This figure shows an image at the far end face of the MMF (Multi-Motor Frame) illustrating the spatial distribution of the laser beam for a single tilt of the deflection mirror. [Figure 6D] This figure shows an image illustrating the angular distribution of the laser beam for a single tilt of a deflection mirror. [Figure 7A] Figures 6A to 6D are graphs comparing the angular uniformity of the light sources with that of a light source using direct coupling without a diffraction optical system. [Figure 7B] Figures 6A to 6D are graphs comparing the spatial uniformity of the light sources with that of a light source using direct coupling without a diffraction optical system. [Figure 8] This figure shows a uniform extended light source in a Köhler illumination configuration for microscopic observation, according to some embodiments.

Best Mode for Carrying Out the Invention

[0012] Throughout the drawings and the specification, the same reference numerals represent corresponding parts.

[0013] Hereinafter, various embodiments illustrated in the accompanying drawings will be referred to in detail. In the following detailed description, many specific details are set forth in order to provide a thorough understanding of the various embodiments described. However, it will be apparent to those skilled in the art that the various embodiments can be realized without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail in order to avoid unnecessarily obscuring aspects of the embodiments.

[0014] FIG. 1 shows a single-channel light source 100 according to some embodiments. In the light source 100, a laser 102 generates a laser beam 104. The laser beam 104 is not spatially or angularly uniform. Instead, the laser beam 104 has a Gaussian-like or Lorentzian-like profile. The light source 100 converts the laser beam 104 into a beam that is substantially uniform in angle and space. Thus, the light source 100 can become a substantially uniform extended light source (i.e., a homogenized light source). Alternatively, the light source 100 shapes the laser beam 104 into a desired shape (in this case, the light source 100 is not homogenized).

[0015] In the light source 100, the beam alignment assembly 106 receives the laser beam 104 from the laser 102 and aligns it with components downstream of the light source 100 (including the lens assemblies 110 and one or more deflection mirrors 118). The beam alignment assembly 106 includes a plurality of mirrors 108 that adjust the optical path (e.g., the optical axis) of the laser beam 104 to direct the laser beam 104 toward the lens assembly 110 and one or more deflection mirrors 118. In some embodiments, the beam alignment assembly 106 has six mirrors 108 that allow for separate control of each degree of freedom. The six mirrors 108 may be configured as a dual orthogonal mirror assembly and a tip / tilt mirror assembly. Alternatively, the beam alignment assembly 106 may have four mirrors or two mirrors instead of the six-mirror assembly (i.e., it may be a four-mirror assembly or a two-mirror assembly).

[0016] The lens assembly 110 (which may also be referred to as a zoom assembly) includes lenses 112, 114, and 116 that integrally adjust (e.g., expand) the size of the laser beam 104 and collimate the laser beam 104. In some embodiments, the lens assembly 110 adjusts the laser beam 104 to have a diameter that is a specified value (a fixed value independent of the original diameter of the laser beam 104 generated by the laser 102). The lens assembly 110 is disposed along the optical path of the laser beam 104, between the beam alignment assembly 106 and one or more deflection mirrors 118 and thus between the plurality of mirrors 108 and one or more deflection mirrors 118. Although the size of the laser beam 104 is changed and collimated when it exits the lens assembly 110, it is still non-uniform (e.g., still has a Gaussian-like or Lorentzian-like profile).

[0017] One or more deflection mirrors 118 receive the laser beam 104, which has been resized and parallelized by the lens assembly 110, and deflect it at various angles. By deflecting the laser beam 104, the one or more deflection mirrors 118 direct the laser beam 104 towards the diffraction optical system 126. In some embodiments, the one or more deflection mirrors 118 include a first mirror 120 and a second mirror 122, which together may be referred to as a scanning assembly. The first mirror 120 may be a first scanning mirror. For example, the first mirror 120 may be a fast-scanning mirror (FSM) (the term “fast-scanning mirror” is a known technical term, and FSMs are commercially available). The scanning motion of the first scanning mirror directs the laser beam 104 to different parts of the second mirror 122 at different angles. The second mirror 122 may be a second scanning mirror (e.g., a second FSM) or a fixed mirror (e.g., a right-angle mirror), and directs the laser beam 104 towards the diffraction optical system 126. In this way, the two mirrors work together to direct the laser beam 104 towards the diffraction optical system 126 at various angles and spatial offsets. As a result of the various angles and spatial offsets, the beam projection position of the laser beam 104 in the diffraction optical system 126 changes over time. According to some embodiments, by using scanning mirrors for both the first mirror 120 and the second mirror 122, both the incident angle and the beam projection position of the laser beam 104 in the diffraction optical system 126 can be controlled.

[0018] In some other embodiments, one or more deflection mirrors 118 may consist of only one mirror which is tiltable. For example, one or more deflection mirrors 118 may be a single tiltable right-angle mirror. This mirror projects the laser beam 104 onto the diffraction optical system 126 (at different angles and beam projection positions, for example, as a result of changing the tilt of the mirror).

[0019] The diffractive optical system 126 diffracts the laser beam 104 (i.e., the laser beam 104 deflected by one or more deflection mirrors 118). In some embodiments, the diffractive optical system 126 is a multi-lens array (MLA) that diffracts the laser beam 104. For example, the MLA may be a 4×4, 5×5, 6×6, or 7×7 array of microlenses. Other array sizes are also possible. The MLA may be a single-sided array of microlenses or a double-sided array of microlenses. Alternatively, the diffractive optical system 126 is a diffractive optical element (DOE) that diffracts the laser beam 104 (the term "diffractive optical element" is a known technical term, and DOEs are commercially available and can be custom-made to give a desired simulated beam profile).

[0020] Multiple lenses 128 (including a projection lens 130 and a coupling lens 132) are arranged between the diffractive optical system 126 and the multimode fiber (MMF) 134 along the optical path of the laser beam 104. The multiple lenses 128 (sometimes referred to as the imaging assembly) direct the laser beam 104 diffracted by the diffractive optical system 126 to the MMF 134. The projection lens 130 focuses and parallelizes the diffractive laser beam 140 (i.e., projects it to infinity). The coupling lens 132 focuses the diffractive laser beam 104 parallelized by the projection lens 130 onto the first end face of the MMF 134. The first end face of the MMF 134 is positioned at the back focal plane of the coupling lens 132 (i.e., the focal plane of the coupling lens 132 downstream of the coupling lens 132 along the optical path of the laser beam 104). Thus, the coupling lens 132 couples the laser beam 104 to the MMF 134.

[0021] In some embodiments, the MMF134 is a large-core MMF134, having a larger core than the MMF used for network communication. For example, the core may be circular with a diameter in the range of 400 μm to 1 mm. In another example, the MMF134 may have a square core with a width in the range of 400 μm to 1 mm. Other core shapes (e.g., hexagonal or octagonal) are also possible for the MMF134. The laser beam 104 is emitted from the MMF134 at a first end face and a second end face opposite to it. The laser beam 104 emitted from the MMF134 is the output of the light source 100. The laser beam 104 emitted from the second end face of the MMF134 can be substantially uniform in space and angle. Using a non-circular core in the MMF134 can improve the uniformity of the laser beam 104 emitted from the second end face compared to the case of a circular core. For example, a square core provides greater uniformity than a circular core (and the same applies to hexagonal and octagonal cores). Alternatively, the laser beam 104 has a specific heterogeneity that differs from the beam profile of the laser beam 104 when it is generated by the laser 102. This specific heterogeneity may be achieved, for example, by using a DOE designed to give that heterogeneity as the diffraction optical system 126. Furthermore, the change in the beam projection position of the laser beam 104 in the diffraction optical system 126 over time reduces the speckle in the laser beam 104 by averaging over time. As a result of this change in beam projection position, the image position of the laser beam 104 in the MMF 134 also changes over time, thus avoiding localized heating in the MMF 134 and extending the lifetime of the MMF 134.

[0022] In some embodiments, the light source 100 further comprises a beam sampling assembly 124 that reflects a small portion of the laser beam 104 (for example, 1% of the power) to a photodetector, thereby providing the photodetector with the reflected portion of the laser beam 104. The photodetector measures the power of the reflected portion of the laser beam 104. Since the reflected portion is a known portion, this determines the total power of the laser beam 104, and by comparing it with the expected power, it is possible to determine whether the laser 102 is on and whether the laser beam 104 has the expected power. The beam sampling assembly 124 may be a two-window beam sampling assembly in which a first portion of the laser beam 104 is reflected through a first window and a second portion of the laser beam 104 is reflected through a second window. In this way, the beam sampling assembly 124 can generate a first reflection involving the first window and a second reflection involving the second window. Since the first window is in the opposite direction to the second window, the effects of the first and second reflections on the optical path of the unreflected laser beam 104 cancel each other out, so the optical path is not disturbed. In the example in Figure 1, the beam sampling assembly 124 is positioned between one or more deflection mirrors 118 and the diffraction optical system 126. Other positions are possible; for example, the beam sampling assembly 124 may be positioned between the lens assembly 110 and one or more deflection mirrors 118, or between the laser 102 and the beam alignment assembly 106 (for example, immediately after the aperture of the laser 102).

[0023] Figure 2 shows the arrangement of components 200 that constitute part of the light source 100 according to several embodiments. Components 200 include an MLA 204, a first lens (L1) 206, a second lens (L2) 210, and an MMF 214. The MLA 204 is an example of a diffraction optical system 126 (Figure 1), the first lens 206 is an example of a projection lens 130 (Figure 1), the second lens 210 is an example of a coupling lens 132 (Figure 1), and the MMF 214 is an example of an MMF 134 (Figure 1). The first lens 206 and the second lens 210 together are an example of a plurality of lenses 128 (Figure 1). The first lens 206 is disposed between the MLA 204 and the second lens 210. The second lens 210 is disposed between the first lens 206 and the end face 216 of the MMF 214. End face 216 is the near end face of MMF214 (i.e., it is an example of the first end face of MMF134 (Figure 1)).

[0024] The first lens 206 has a focal length f1, the second lens 210 has a focal length f2, and MLA204 has a focal length f MLA The first lens 206 is separated from the second lens 210 by a distance equal to the sum of f1 + f2. This distance is along the optical axis and thus the optical path of the laser beam 202, which is an example of the laser beam 104 (Figure 1). In this configuration, the Fourier plane 208 is the back focal plane of the first lens 206 and the front focal plane of the second lens 210. The end face 216 is separated from the second lens 210 by a distance equal to f2 along the optical axis. Therefore, the end face 216 is positioned at the back focal plane 212 of the second lens 210. MLA204 is f MLA It is separated from the first lens 206 by a distance along the optical axis equal to the sum of +f1.

[0025] The laser beam 202 is supplied to the MLA 204 by one or more deflection mirrors 118 (Figure 1). In this respect, the laser beam 202 is not uniform. In the example in Figure 2, it has a Gaussian profile 203. As shown in Figure 2, each lens of the MLA 204 samples light from each position of the laser beam 202 and aligns the sampled light along various rays (for simplicity, Figure 2 shows the propagation of rays from the three microlenses of the MLA 204). Each point on the Fourier plane 208 (corresponding to each diffraction order) is generated by combining the rays from all the microlenses of the MLA 204 (by the intersection of rays in the Fourier plane 208, as shown in Figure 2). Thus, each point on the Fourier plane 208 has equivalent energy. Furthermore, the rays from different points on the Fourier plane 208 are projected onto the back focal plane 212 at different projection angles. Therefore, multiple beams, each containing a ray from a microlens, are projected at different angles onto the back focal plane 212 (and consequently, the end face 216 of the MMF214). Figure 2 shows three such beams. These beams have equivalent amplitudes because they are associated with equivalent power diffraction orders. When beams at different angles are projected onto the end face 216 of the MMF214, they generate different modes in the MMF214. Thus, the arrangement of the components 200 in Figure 2 brings the amplitudes of each mode into equilibrium, resulting in substantial angular uniformity at the far end face (i.e., output) of the MMF214. The far end face is an example of the second end face of the MMF134 (Figure 1).

[0026] The position of the laser beam 202 on the MLA204 and the angle at which the MLA204 receives the laser beam 202 change according to the operation of one or more deflection mirrors 118 (e.g., scanning operation). As a result, the diffraction pattern generated by the MLA204 is shifted at the back focal plane 212 and consequently at the end face 216 of the MMF214, which further contributes to achieving substantial uniformity of the laser beam 202 when output by the MMF214, for example, by reducing speckle. In addition, the shift in the diffraction pattern suppresses localized heating in the MMF214, thus extending the lifespan of the MMF214.

[0027] In the example in Figure 2, MLA204 is shown as a single-sided MLA. MLA204 may be a double-sided MLA instead, or it may be replaceable by a DOE. The DOE may be located in front of the focal plane of the first lens 206 (i.e., separated from the first lens 206 by a distance f1 along the optical axis).

[0028] Figure 3A is a graph 300 showing the simulated spatial power distribution of the laser beam 202 at the output of the MMF214 (Figure 2) at a specific point in time. As shown in Figure 3A, there is no single hotspot of power intensity in the MMF214. Speckles 310 are formed on the output end face, and their positions are evenly distributed in both the x and y directions on this end face. As shown in Figure 3D, an enlarged view of the speckles 310 in Figure 3A, the spatial distribution of power in the speckles 310 is substantially uniform. The positions of these speckles 310 change over time as the beam position and angle at which the MLA204 (or DOE) receives the laser beam 202 changes due to the operation (e.g., scanning) of one or more deflection mirrors 118 (Figure 1). As a result, the speckles 310 are averaged over time, resulting in substantial spatial uniformity.

[0029] Figure 3B is a graph 320 showing the simulated angular power distribution of laser beam 202 at the output of MMF214 (Figure 2). Figure 3C is a graph 340 showing the corresponding simulated radiance cross-section of laser beam 202. The cross-section in Figure 3C is a cross-section that passes through the angular power distribution in Figure 3B (for example, at a specific point in the x-angle space or y-angle space of Figure 3B). Figures 3B and 3C demonstrate that substantial angular uniformity of the power distribution is achieved in MMF214.

[0030] The light source 100 (Figure 1) is a single-channel light source that outputs a single laser beam. As an alternative to the single-channel light source 100, a multi-channel light source may output multiple laser beams (for example, multiple uniform laser beams and / or multiple laser beams of a specific shape).

[0031] Figure 4 is a schematic diagram of a multi-channel light source 400 according to several embodiments. The light source 400 comprises a laser 102 (Figure 1) that generates a laser beam 402, an alignment assembly 106 including a plurality of mirrors 108 (for example, six mirrors 108 or four or two mirrors 108), a lens assembly 110 including lenses 112, 114, and 116, and one or more deflection mirrors 118 (for example, including a first mirror 120 and a second mirror 122). These components have the same configuration as the light source 100 (Figure 1).

[0032] The light source 400 further comprises a first half-wave plate 404, a first beam splitter 406, a second half-wave plate 408, and a second beam splitter 410. The first half-wave plate 404 is located in front of one or more deflection mirrors 118 (i.e., somewhere between the laser 102 and one or more deflection mirrors 118). For example, the first half-wave plate 404 is located between the lens assembly 110 and one or more deflection mirrors 118. The second half-wave plate 408 follows the first beam splitter 406 and is located between the first beam splitter 406 and the second beam splitter 410, as the second beam splitter 410 follows it.

[0033] The first and second half-wave plates 404 and 408 each have a first polarization, a second polarization, or a mixed polarization of the first and second polarizations, by adjusting the polarization of the laser beam 402. In some embodiments, the half-wave plates 404 and 408 can be moved in and out of the optical path of the laser beam 402 by motor drive. For example, the half-wave plates 404 and 408 may each be mounted on a motor-driven rotatable disk that can rotate to move the half-wave plates 404 and 408 in and out of the optical path. Each rotatable disk may mount multiple half-wave plates, and the desired polarization of the laser beam 402 may be obtained by selecting and positioning the desired half-wave plate in the optical path.

[0034] The first beam splitter 406 and the second beam splitter 410 each transmit light of the first polarization in a first direction and light of the second polarization in a second direction. Thus, the first beam splitter 406 and the second beam splitter 410 each direct the laser beam 402 according to its polarization. The first beam splitter 406 directs the laser beam 402 to at least one of the first optical path 414-1 and the second optical path 414-2 according to the polarization of the laser beam 402 adjusted by the first half-wave plate 404. For example, the first beam splitter 406 provides the first laser beam 402-1 by transmitting the light of the first polarization in the laser beam 402 along the first optical path 414-1, and transmits the light of the second polarization in the laser beam 402 toward the second half-wave plate 408 and the second beam splitter 410. When the laser beam 402 (or a portion thereof) reaches the second beam splitter 410, the second beam splitter 410 directs the laser beam 402 (or a portion thereof) according to the polarization of the laser beam 402, which has been adjusted by the first half-wave plate 404 and readjusted by the second half-wave plate 408. For example, the second beam splitter 410 transmits the first polarization of light in the laser beam 402 along the second optical path 414-2 and the second polarization of light in the laser beam 402 along the third optical path 414-3 (or vice versa). In this way, the second beam splitter 410 provides the second laser beam 402-2 along the second optical path 414-2 and the third laser beam 402-3 along the third optical path 414-3. The first laser beam 402-1, the second laser beam 402-2, and the third laser beam 402-3 are sometimes referred to as deflected laser beams because they originate from a laser beam 402 deflected by one or more deflection mirrors 118.

[0035] The first optical path 414-1 comprises a first diffraction optical system 126-1 that diffracts the first laser beam 402-1, a first MMF 134-1 that transmits the first laser beam 402-1 diffracted by the first diffraction optical system 126-1, and a first set of lenses 128-1 disposed between the first diffraction optical system 126-1 and the first MMF 134-1, which provide the first laser beam 402-1 diffracted by the first diffraction optical system 126-1 to the first MMF 134-1. The first beam splitter 406 is disposed between one or more deflection mirrors 118 and the first diffraction optical system 126-1. The first diffraction optical system 126-1 may be a first MLA (for example, an example of an MLA 204 (Figure 2)) or a first DOE. The first set of lenses 128-1 includes examples of projection lenses 130 and coupling lenses 132 (Figure 1). In some embodiments, these examples of projection lenses 130 and coupling lenses 132 are arranged as shown in Figure 2, and the first set of lenses 128-1 includes a first lens 206 as the projection lens 130 and a second lens 210 as the coupling lens 132. The first optical path 414-1 may also comprise a beam sampling assembly 124-1 (for example, a two-window beam sampling assembly).

[0036] The second optical path 414-2 comprises a second diffraction optical system 126-2 that diffracts the second laser beam 402-2, a second MMF 134-2 that transmits the second laser beam 402-2 diffracted by the second diffraction optical system 126-2, and a second set of lenses 128-2 disposed between the second diffraction optical system 126-2 and the second MMF 134-2, which provide the second laser beam 402-2 diffracted by the second diffraction optical system 126-2 to the second MMF 134-2. The second diffraction optical system 126-2 may be a second MLA (for example, an example of MLA 204 (Figure 2)) or a second DOE. The second set of lenses 128-2 include examples of a projection lens 130 and a coupling lens 132 (Figure 1). In some embodiments, examples of these projection lenses 130 and coupling lenses 132 are arranged as shown in Figure 2, with a second set of lenses 128-2 including the first lens 206 as the projection lens 130 and the second lens 210 as the coupling lens 132. The second optical path 414-2 may also comprise a beam sampling assembly 124-2 (for example, a two-window beam sampling assembly).

[0037] The first beam splitter 406 is positioned between one or more deflection mirrors 118 and the first diffraction optical system 126-1, and also between one or more deflection mirrors 118 and the second diffraction optical system 126-2. The second half-wave plate 408 is positioned between the first beam splitter 406 and the second diffraction optical system 126-2. Furthermore, since the second half-wave plate 408 is positioned between the first beam splitter 406 and the second beam splitter 410, the second beam splitter 410 is positioned between the first beam splitter 406 and the second diffraction optical system 126-2.

[0038] The third optical path 414-3 comprises a third diffraction optical system 126-3 that diffracts the third laser beam 402-3, a third MMF 134-3 that transmits the third laser beam 402-3 diffracted by the third diffraction optical system 126-3, and a third set of lenses 128-3 disposed between the third diffraction optical system 126-3 and the third MMF 134-3, which deliver the third laser beam 402-3 diffracted by the third diffraction optical system 126-3 to the third MMF 134-3. The third diffraction optical system 126-3 may be a third MLA (for example, an example of MLA 204 (Figure 2)) or a third DOE. The third set of lenses 128-3 include examples of a projection lens 130 and a coupling lens 132 (Figure 1). In some embodiments, examples of these projection lenses 130 and coupling lenses 132 are arranged as shown in Figure 2, with a third set of lenses 128-3 including the first lens 206 as the projection lens 130 and the second lens 210 as the coupling lens 132. In some embodiments, the third optical path 414-3 is disposed along the third optical path 414-3 between the second beam splitter 410 and the third diffraction optical system 126-3 and further comprises a fixed mirror 412 (e.g., a right-angle mirror) that directs the laser beam 402-3 from the second beam splitter 410 towards the third diffraction optical system 126-3. The third optical path 414-3 may also comprise a beam sampling assembly 124-3 (e.g., a two-window beam sampling assembly).

[0039] The first beam splitter 406 is positioned between one or more deflection mirrors 118 and the first diffraction optical system 126-1, between one or more deflection mirrors 118 and the second diffraction optical system 126-2, and between one or more deflection mirrors 118 and the third diffraction optical system 126-3. The second half-wave plate 408 is positioned between the first beam splitter 406 and the second diffraction optical system 126-2, and also between the first beam splitter 406 and the third diffraction optical system 126-3. Furthermore, since the second half-wave plate 408 is positioned between the first beam splitter 406 and the second beam splitter 410, the second beam splitter 410 is positioned between the first beam splitter 406 and the second diffraction optical system 126-2, as well as between the first beam splitter 406 and the third diffraction optical system 126-3.

[0040] The first beam splitter 406 directs the laser beam 402, which has been deflected by one or more deflection mirrors 118 according to the polarization of the laser beam adjusted by the first half-wave plate 404, toward at least one (for example, one or both) of the first optical path 414-1 and the second half-wave plate 408. By directing the laser beam 402 toward the second half-wave plate 408, the first beam splitter 406 also directs the laser beam 402 toward the second beam splitter 410. The second beam splitter 410, after deflecting the laser beam 402, which has been adjusted by the first half-wave plate 404 and the second half-wave plate 408, with one or more deflection mirrors 118, directs the laser beam 402 toward the second beam splitter 410 towards at least one (for example, one or both) of the second optical path 414-2 and the third optical path 414-3 by the first beam splitter 406.

[0041] The light source 400 may be operated to output one, two, or three substantially uniform (or shaped) laser beams by adjusting the polarization of the laser beam 402 with the first half-wave plate 404 and / or the second half-wave plate 408. For example, the first half-wave plate 404 and / or the second half-wave plate 408 may adjust the polarization of the laser beam 402 so that the first beam splitter 406 and / or the second beam splitter 410 direct the laser beam 402 as laser beam 402-1 to the first optical path 414-1, or as laser beam 402-2 to the second optical path 414-2, or as laser beam 402-3 to the third optical path 414-3. This results in a single beam being output from the first MMF134-1, the second MMF134-2, or the third MMF134-3. In another example, the first half-wave plate 404 adjusts the polarization of the laser beam 402 to have a mixed polarization of first and second polarizations. The first beam splitter 406 directs the first-polarized light as the laser beam 402-1 to the first optical path 414-1, which is ultimately output by the first MMF 134-1 as a uniform (or shaped) beam. The first beam splitter 406 also directs the second-polarized light to the second beam splitter 410. Depending on the polarization adjustment by the second half-wave plate 408 (or, if that is not possible, the second half-wave plate 408 may be removed from the optical path), the second beam splitter 410 directs all of the received beam as laser beam 402-2 to the second optical path 414-2 (for example, if the beam has only first or second polarization), or directs all of the received beam as laser beam 402-3 to the third optical path 414-3 (for example, if the beam has only second or first polarization), or directs the portion of the received light having one polarization (for example, first polarization) as laser beam 402-2 to the second optical path 414-2, while directing the portion of the received light having the other polarization (for example, second polarization) as laser beam 402-3 to the third optical path 414-3.

[0042] The light source 400 has three outputs. By omitting the components of the second half-wave plate 408, the second beam splitter 410, and the second optical path 414-2, a light source with two outputs can be realized. Similarly, by omitting the second half-wave plate 408, omitting the components of the third optical path 414-3, and replacing the second beam splitter 410 with a fixed mirror (e.g., a right-angle mirror) 412, a two-output light source can be realized. By adding additional half-wave plates, beam splitters, and optical paths, light sources with four or more outputs can be realized.

[0043] Figure 5 is a flowchart showing a light illumination method 500 according to several embodiments. Method 500 is performed using, for example, a single-channel light source (e.g., light source 100 (Figure 1)) or a multi-channel light source (e.g., a multi-channel light source 400 (Figure 4)). The steps of Method 500 are shown in a specific order, but may be performed simultaneously. The order of the steps of Method 500 is spatial, not temporal.

[0044] In method 500, a laser beam is generated (502). For example, a laser 102 (Figure 1 or Figure 4) generates a laser beam 104 (Figure 1) or 402 (Figure 4). The laser beam may be an example of a laser beam 202 (Figure 2).

[0045] The laser beam may be aligned with a first scanning mirror (for example, a first mirror 120 (Figure 1 or Figure 4)) (504). This alignment may be performed, for example, by a beam alignment assembly 106 (Figure 1 or Figure 4). Alternatively, this alignment may also involve aligning the laser beam with a lens assembly 110 (Figure 1 or Figure 4).

[0046] The diameter of the laser beam may be adjusted to a specified value and the laser beam may be parallelized (for example, by the lens assembly 110 (Figure 1 or Figure 4)) (506).

[0047] The laser beam is deflected at various angles (for example, by one or more deflection mirrors 118 (Figure 1 or Figure 4)) (508). In some embodiments, the laser beam is polarized at various angles and various spatial offsets by a first scanning mirror (for example, a first mirror 120 (Figure 1 or Figure 4)) and a second mirror (for example, a second mirror 122 (Figure 1 or Figure 4)) (510). For example, the second mirror is a second scanning mirror or a fixed mirror (512).

[0048] In some embodiments, the deflected laser beam is split between multiple optical paths (514). For example, the deflected laser beam is split between a first optical path and a second optical path (for example, between two of the three optical paths 414-1, 414-2, and 414-3 of the light source 400 (Figure 4)) (for example, between the two optical paths of a two-output light source) (516). In another example, the deflected laser beam is split between a first optical path, a second optical path, and a third optical path (for example, between the three optical paths 414-1, 414-2, and 414-3 of the light source 400 (Figure 4)) (518). Alternatively, the deflected laser beam continues to propagate along a single optical path (for example, along the single optical path of light source 100 (Figure 1)) (for example, along one of the three optical paths 414-1, 414-2, and 414-3 of light source 400 (Figure 4)) (for example, along one of the two optical paths of a two-output light source).

[0049] The deflected laser beam is diffracted by (for example, a diffraction optical system 126 (Figure 1)) (for example, diffraction optical systems 126-1, 126-2, and / or 126-3 (Figure 4)) (520). For example, the laser beam is diffracted by an MLA (for example, an MLA 204 (Figure 2)) or a DOE. If the deflected laser beam is split between multiple optical paths (514), the portion of the laser beam along each optical path is diffracted by its respective diffraction optical system (for example, its respective MLA and / or DOE).

[0050] The deflected laser beam is directed to an MMF (e.g., MMF134 (Figure 1)) (e.g., MMF214 (Figure 2)) (e.g., one of three MMFs 134-1, 134-2, and 134-3 (Figure 4)) (522). If the deflected laser beam is split across multiple optical paths (514), it is directed to multiple MMFs for each optical path (i.e., each split portion of the diffracted laser beam is directed to multiple MMFs for each optical path). In some embodiments, the diffracted light is parallelized by a projection lens (e.g., projection lens 130 (Figure 1 or Figure 4)) (e.g., a first lens 206 (Figure 2)) (524). The parallelized diffracted light is focused onto the end face of the MMF by a coupling lens (e.g., coupling lens 132 (Figure 1 or Figure 4)) (e.g., a second lens 210 (Figure 2)) (526). The end face is located at the back focal plane of the coupling lens.

[0051] A diffracting laser beam is transmitted through a multi-mechanism-forming (MMF) (528). The output from the MMF can be a substantially uniform laser beam in space and angle, or a laser beam of a specific shape. If a diffracting laser beam is supplied to multiple MMFs, the output from each MMF can be a substantially uniform laser beam in space and angle, or a laser beam of a specific shape.

[0052] Figures 6A to 6D show empirical data for one embodiment of a single-channel light source 100 (Figure 1). In this embodiment, the laser 102 is a deep ultraviolet (DUV) laser that generates a laser beam 104 with a wavelength of 266 nm. The beam alignment assembly 106 is a two-mirror assembly followed by a lochon prism that acts as a polarizer to attenuate the laser beam 104. The lochon prism deflects a portion of the laser beam 104 from the optical axis to the aperture diaphragm. The lens assembly 110 expands the diameter of the laser beam 104 from approximately 0.6 μm to approximately 2.0 μm while maintaining the parallelism of the laser beam 104. One or more deflection mirrors 118 are implemented as a single right-angle mirror with a variable tilt. The diffraction optical system 126 is implemented as a single-sided MLA. The MLA and multiple lenses 128 are implemented as shown in Figure 2.

[0053] In this embodiment, Figure 6A shows an image 600 of the laser beam 104 diffracted by the MLA in the plane of the end face 216 where coupling to the MMF214 occurs (i.e., the back focal plane 212 (Figure 2)). The pattern shown in Figure 6A moves across the core of the MMF214 as the tilt of the right-angle mirror changes, but the lifetime of the MMF214 is extended because it avoids hot spots in the core. Figure 6B is an image 610 in the Fourier plane 208 (Figure 2) showing three different tilts of right-angle mirrors used in one or more deflection mirrors 118. Figure 6B shows that the mode amplitudes (i.e., diffraction order amplitudes) are similar, and because different modes are injected into the MMF by changing the tilt of the right-angle mirror, substantial angular uniformity occurs over time. Figure 6C is an image 620 showing the spatial distribution of the laser beam 104 at the far end face of the MMF214 for a single tilt of the right-angle mirror. Figure 6D is an image 630 showing the angular distribution of the laser beam 104 for a single tilt of a right-angle mirror.

[0054] Figures 7A and 7B show a comparison of this embodiment with a light source that directly couples the laser beam to an MMF without a diffraction optical system such as an MLA. Figure 7A is a graph 700 comparing the angular uniformity of these two cases. As shown in Figure 7A, the laser beam output intensity 702 in this embodiment has much better angular uniformity than the laser beam output intensity 704 in the case of direct coupling without a diffraction optical system such as an MLA, because an MLA is used as the diffraction optical system. Figure 7B is a graph 720 comparing the spatial uniformity of these two cases. As shown in Figure 7B, the laser beam output intensity 722 in this embodiment has better spatial uniformity than the laser beam output intensity 724 in the case of direct coupling without a diffraction optical system such as an MLA, because an MLA is used as the diffraction optical system. The spatial and angular uniformity of this embodiment can be further improved, for example, by using a square MMF instead of a circular MMF, using an improved beam alignment assembly 106 (e.g., a 4-mirror or 6-mirror assembly), customizing the MLA, and / or replacing a single-sided MLA with a double-sided MLA or a multi-spot DOE.

[0055] Light sources as described herein can be used for microscopic observation. Figure 8 shows a uniform extended light source 800 in a Köhler illumination configuration for microscopic observation according to several embodiments. Light source 800 is an example of light source 100 (Figure 1) with the arrangement of components 200 (Figure 2). From the uniform light source 800, the MMF 214 provides a laser beam to the microscopic observation illumination system 810. The laser beam fills the aperture plane (conjugate with AS) and the field plane (conjugate with FS) of the illumination system 810. The aperture plane is conjugate with AS and the fiber core, while the field plane is conjugate with FS and the Fourier plane 208. As a result, high-quality imaging is achieved, the NA is properly filled, and the amplitude of the field of view is in equilibrium.

[0056] Another application of the light source described herein is in ultraviolet (UV) cleaning systems for photomask (i.e., reticle) inspection tools. The uniform field of view provided by this light source can be projected onto different optical systems within the tool during the process of removing contamination (e.g., cleaning the contaminating carbon layer). Otherwise, contamination would reduce the effectiveness of the tool. Furthermore, other applications are also possible.

[0057] The above description has been made with reference to specific embodiments for illustrative purposes. However, the above illustrative discussion is not intended to be exhaustive, nor is it intended to limit the claims to the strict form of the disclosure. Many variations and modifications are possible in light of the above teachings. The above embodiments have been selected so as to best illustrate the principles underlying the claims and their respective practical applications, and so as to enable others in the art to best utilize various variations to suit specific conceivable uses.

Claims

1. One or more deflection mirrors that deflect the laser beam at various angles, A diffraction optical system that diffracts a deflected laser beam, A multimode fiber that transmits a diffracting laser beam, A plurality of lenses are disposed between the diffraction optical system and the multimode fiber, and the diffracted laser beam is directed to the multimode fiber. A light source characterized by having the following features.

2. A light source according to claim 1, characterized in that the diffraction optical system comprises a multi-lens array (MLA) that diffracts the deflected laser beam.

3. A light source according to claim 1, characterized in that the diffraction optical system comprises a diffractive optical element (DOE) that diffracts the deflected laser beam.

4. A light source according to claim 1, characterized in that the multimode fiber has a square core.

5. A light source according to claim 1, The multimode fiber has an end face, The aforementioned multiple lenses A projection lens that focuses and parallelizes the aforementioned diffracting laser beam, A coupling lens that focuses the parallelized diffracted laser beam onto the end face, wherein the end face is positioned at the back focal plane of the coupling lens, A light source characterized by having the following features.

6. A light source according to claim 5, The projection lens has a first focal length, The aforementioned combined lens has a second focal length, The projection lens is separated from the coupling lens by a distance along the optical axis of the laser beam equal to the sum of the first focal length and the second focal length. A light source characterized in that the end face of the multimode fiber is separated from the coupling lens by a distance along the optical axis of the laser beam equal to the second focal length.

7. A light source according to claim 1, characterized in that the one or more deflection mirrors include a first scanning mirror.

8. A light source according to claim 7, characterized in that the one or more deflection mirrors further include a fixed mirror that receives the laser beam from the first scanning mirror and directs the laser beam toward the diffraction optical system.

9. A light source according to claim 7, characterized in that the one or more deflection mirrors further include a second scanning mirror that receives the laser beam from the first scanning mirror and directs the laser beam toward the diffraction optical system.

10. A light source according to claim 1, wherein the diffraction optical system is a first diffraction optical system, the multimode fiber is a first multimode fiber, the plurality of lenses is a first plurality of lenses, and the light source is A second diffraction optical system for diffracting the deflected laser beam, A second multimode fiber that transmits the laser beam diffracted by the second diffraction optical system, A second set of lenses is disposed between the second diffraction optical system and the second multimode fiber, and provides the laser beam diffracted by the second diffraction optical system to the second multimode fiber. A first beam splitter is disposed between the one or more deflection mirrors and the first diffraction optical system, and between the one or more deflection mirrors and the second diffraction optical system, Furthermore, The first diffraction optical system, the first multimode fiber, and the first plurality of lenses are arranged along the first optical path. A light source characterized in that the second diffraction optical system, the second multimode fiber, and the second plurality of lenses are arranged along a second optical path.

11. A light source according to claim 10, further comprising a first half-wave plate for adjusting the polarization of the laser beam, in front of one or more deflection mirrors, A light source characterized in that the first beam splitter directs the deflected laser beam toward at least one of the first optical path or the second optical path according to the polarization of the laser beam adjusted by the first half-wave plate.

12. A light source according to claim 10, The first diffractive optical system is selected from the group consisting of a first multi-lens array (MLA) and a first diffractive optical element (DOE). A light source characterized in that the second diffraction optical system is selected from the group consisting of a second MLA and a second DOE.

13. A light source according to claim 10, A third diffraction optical system for diffracting the deflected laser beam, A third multimode fiber that transmits the laser beam diffracted by the third diffraction optical system, A plurality of third lenses are disposed between the third diffraction optical system and the third multimode fiber, and provide the laser beam diffracted by the third diffraction optical system to the third multimode fiber, A second beam splitter is disposed between the first beam splitter and the second diffraction optical system, and between the first beam splitter and the third diffraction optical system, Furthermore, A light source characterized in that the third diffraction optical system, the third multimode fiber, and the third plurality of lenses are arranged along a third optical path.

14. A light source according to claim 13, A first half-wave plate for adjusting the polarization of the laser beam is placed in front of one or more deflection mirrors, A second half-wave plate is disposed between the first beam splitter and the second beam splitter to adjust the polarization of the laser beam, Furthermore, The first beam splitter directs the deflected laser beam toward at least one of the first optical path or the second optical path according to the polarization of the laser beam adjusted by the first half-wave plate. A light source characterized in that the second beam splitter directs the deflected laser beam toward at least one of the second optical path or the third optical path according to the polarization of the laser beam adjusted by the first half-wave plate and the second half-wave plate.

15. A light source according to claim 13, The first diffractive optical system is selected from the group consisting of a first multi-lens array (MLA) and a first diffractive optical element (DOE). The second diffraction optical system is selected from the group consisting of a second MLA and a second DOE. A light source characterized in that the third diffraction optical system is selected from the group consisting of a third MLA and a third DOE.

16. A light source according to claim 13, further comprising a fixed mirror disposed between the second beam splitter and the third diffraction optical system along the third optical path, which directs the deflected laser beam from the second beam splitter toward the third diffraction optical system.

17. A light source according to claim 1, A laser that generates the aforementioned laser beam, A plurality of alignment mirrors are disposed between the laser and one or more deflection mirrors to adjust the optical path of the laser beam and direct the laser beam toward one or more deflection mirrors, A lens assembly is disposed between the plurality of alignment mirrors and one or more deflection mirrors, which adjusts the diameter of the laser beam to a specified value and parallelizes the laser beam. A light source characterized by further comprising the features described above.

18. Generating a laser beam, The laser beam is deflected at various angles, Diffraction of a deflected laser beam, Applying a diffracting laser beam to a multimode fiber, The diffracting laser beam is transmitted through the multimode fiber, A method of light illumination characterized by including the following.

19. A method according to claim 18, characterized in that deflecting the laser beam includes using a first scanning mirror and a second mirror to deflect the laser beam at various angles and various spatial offsets.

20. The method according to claim 18, further comprising splitting the deflection laser beam between a first optical path and a second optical path, The multimode fiber is either a first multimode fiber or a second multimode fiber. The first optical path comprises a first diffraction optical system for diffracting the deflected laser beam, a first multimode fiber, and a first set of lenses for supplying the laser beam diffracted by the first diffraction optical system to the first multimode fiber. The method is characterized in that the second optical path comprises a second diffraction optical system for diffracting the deflected laser beam, a second multimode fiber, and a second plurality of lenses for supplying the laser beam diffracted by the second diffraction optical system to the second multimode fiber.

21. The method according to claim 18, further comprising splitting the deflection laser beam between a first optical path, a second optical path, and a third optical path, The multimode fiber is a first multimode fiber, a second multimode fiber, or a third multimode fiber. The first optical path comprises a first diffraction optical system for diffracting the deflected laser beam, a first multimode fiber, and a first set of lenses for supplying the laser beam diffracted by the first diffraction optical system to the first multimode fiber. The second optical path comprises a second beam splitter, a second diffraction optical system for diffracting the deflected laser beam, a second multimode fiber, and a second set of lenses for supplying the laser beam diffracted by the second diffraction optical system to the second multimode fiber. The method is characterized in that the third optical path comprises a third diffraction optical system for diffracting the deflected laser beam, a third multimode fiber, and a third plurality of lenses for supplying the laser beam diffracted by the third diffraction optical system to the third multimode fiber.

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