Multi-wavelength laser beam homogenizer-beam expander light engine

Abstract

The invention relates to laser beam shaping, intended to achieve a controlled intensity profile distribution, typically a flattop distribution, by means of a plurality of laser beam sources having a non-uniform beam intensity distribution (incident Gaussian laser beams or other higher order multi-lateral modes in the visible, infrared or ultraviolet spectrum). The laser beam homogenizer-expander splits the incident beam into sub-beams along the primary optical axis using a first beam shaping element and uses a second beam shaping element, i.e., a second optical integrator, which defines a flat-topped intensity distribution output, thereby providing a second homogenization stage. The invention also comprises a plurality of light diffusers (F1, F2), mirrors, filters (D1, D2) and output lenses (L1, L2, L3) to achieve good homogenization at the desired output angle, which will be described hereinafter in detail. The invention is directed to fully integrating / mixing laser sources of one or more wavelengths, such as red, green and blue, but may also integrate other wavelengths in the visible / invisible spectrum. If multiple wavelengths are used as the initial laser source (LSI), the output of the light engine can provide good homogenization and color mixing, little noticeable spots, near flat-topped intensity distribution, and no visible hot spots or interference patterns. The invention can be used in many applications, such as microlenses, material processing, fluorescence, lighting fixtures, holography, fiber coupling, and the like, which require the spectral characteristics (narrowband, monochromatic) of the laser, but at the same time require a uniform distribution of the intensity.

Description

Technical Field

[0001] The present invention is in the field of laser beam shaping and relates to a laser emission source suitable for spectroscopy, material processing, fluorescence, heat treatment, communications, entertainment and many other applications. Background Art

[0002] Most laser types in use today have an output beam profile of circular or elliptical cross-section with a Gaussian or near-Gaussian intensity profile distribution. This is acceptable and often advantageous in many applications where the laser beam needs to be focused to a small spot. However, in many different use cases, a uniform, equal intensity distribution ("top-hat") is desired. For example, a uniform intensity distribution ensures that the entire laser impact area is treated uniformly in material processing tasks. It is also valuable in cases where the laser is used primarily for illumination, because uniform illumination makes identical features appear to have the same brightness regardless of their position in the illuminated field, which simplifies image processing tasks and improves contrast and resolution.

[0003] There are a variety of techniques and methods to achieve a uniform distribution pattern. Price-optimized setups with lasers typically use a Gaussian beam source that can be physically truncated by an aperture to create a pseudo flat-top profile.

[0004] This technical approach is inefficient and has significant energy waste in the outer regions of the Gaussian profile, but it helps minimize the complexity and overall cost of the device.

[0005] High performance applications with higher efficiency requirements typically use different types of refractive beam shapers, similar to some portions of the present invention.

[0006] These systems typically use field-mapping phase elements such as aspheric lenses and diffractive elements to simultaneously redistribute the irradiance and phase distribution.

[0007] The amplitude and phase of the incident light beam are altered after passing through two elements in a conjugate lens telescope setup.

[0008] The output beam has high efficiency (performance above 97%) and is wavelength independent within the optical setup.

[0009] Refractive beam shapers enable uniform irradiance profiles and flat phase fronts.

[0010] A laser beam integrator or homogenizer is an optical element, typically formed from multiple sub-lenses (microlenses), that splits an incoming laser beam into an array of smaller beams or "beamlets", all of which are then superimposed at a target plane by lenses or other focusing elements.

[0011] It can be used with coherent laser sources, but can also be used with other incoherent light sources.

[0012] Typically, the final output beam profile is the sum of the diffraction pattern characteristics of the sub-lens array.

[0013] Most laser beam integrators are used to generate a uniform flat-top distribution profile from an incident Gaussian laser beam or other higher order multiple transverse modes. Summary of the invention

[0014] The present invention is based on a laser beam integrator, which belongs to the group of refractive beam shapers; however, it has a unique optical setup, mainly due to the second-stage integrator, custom-designed diffusers and the overall design for the optical setup and optical mount.

[0015] Each integrator consists of an array of microlenses, but designed metasurfaces can also be considered as an alternative, which should give good results.

[0016] According to Kohler The principle of an integrator, which collects light from a non-uniform laser source in an integration region and provides uniform irradiance in the Fourier plane of a Fourier lens.

[0017] The external illumination area is the superposition of these individual images of the lens array sub-apertures, providing a sharp cutoff known in the art as a flat top or flat top profile.

[0018] Adding a second integrator to further improve the homogenization effect is one of the features of the present invention.

[0019] To eliminate possible hot spots and obtain a more uniform distribution profile, the beam can be diffused by a holographic refractive diffuser with a custom-designed surface that provides the required output angle and over 97% light transmission.

[0020] The optical and mechanical properties of the microlenses and engineered diffusers are custom designed and carefully tuned to achieve excellent beam homogenization performance while minimizing light losses.

[0021] Technical issues

[0022] The present invention aims to achieve a controlled, generally flat-top intensity profile based on a laser beam source with non-uniform intensity, supporting an incident Gaussian laser beam or other higher order multiple transverse modes in the visible, infrared or ultraviolet spectrum.

[0023] Solution to the problem

[0024] The laser beam homogenizer-expander uses a first beam shaper element to split the incident beam into sub-beams along the main optical axis and uses a second beam shaper element, namely a second light integrator, which defines a flat-top intensity distribution output, thereby providing a second homogenization stage.

[0025] The present invention also includes a plurality of light diffusers, mirrors, filters and output lenses.

[0026] Advantages of the invention

[0027] The present invention provides very precise beam shaping performance with minimal light loss. Specifically, the present invention achieves good homogenization at a desired output angle, fully integrating / mixing laser sources of one or more wavelengths, such as red, green, blue and / or other wavelengths in the visible / invisible spectrum.

[0028] If multiple wavelengths are used as the initial laser source, the light engine output provides good homogenization and color mixing, with little noticeable speckle, a nearly flat-top intensity profile, and no visible hot spots or interference patterns. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic block diagram showing an example of all beam path setups with all optical elements and an RGB laser source.

[0030] Figure 2 is a schematic diagram of an integrator and its components.

[0031] Figure 3 is a schematic diagram of the proposed laser source and its components. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention will be described below, and the present invention will be described more clearly and completely in conjunction with the accompanying drawings.

[0033] Figure 1 An overview of the beam propagation paths within an optical arrangement based on a red-green-blue laser source LS1 is provided. As is known, the laser source LS1 may take the form of a single wavelength laser in the infrared, visible and ultraviolet spectrum.

[0034] The laser source LS1 comprises a multi-die package (MDP) consisting of packaged laser diodes LD1, LD2, LD3 with an integrated short-focus spherical collimator CL.

[0035] In the given example, the peak wavelength of laser diode LD3 is in the red spectrum, while the peak wavelength of laser diode LD2 is in the blue spectrum and the peak wavelength of laser diode LD1 is in the green spectrum, illustrating a laser source suitable for visible band applications. As mentioned above, other types of active medium lasers can be used, including infrared or ultraviolet lasers.

[0036] It can be seen that in order to improve the integration, the laser source LS1 is composed of multiple optical elements M1, D1, and D2. Its purpose is to superimpose the light beams from all laser diodes LD1, LD2, and LD3 on the main optical axis. This technology is usually called spectral incoherent combination.

[0037] Each optical element M1, D1, D2 is held in place by an optical bracket S1, S2 or S3, respectively, which is equipped with push-pull screws SW to allow fine adjustment of the corresponding optical element along three axes to superimpose all beams.

[0038] The dielectric coated mirror M1 reflects the green light emitted by the laser diode LD1 orthogonally to the first integrator IN1.

[0039] The dichroic filter D1 selectively passes the green light component while completely orthogonally reflecting the blue light emitted by the laser diode LD2.

[0040] Therefore, when the beam passes through the position marked "a", its green and blue components are incoherently combined and aligned in the near and far fields.

[0041] Output dichroic filter D2 selectively passes green and blue components emitted by laser diode LD1 or LD2, respectively, while reflecting red light emitted by laser diode LD3 completely orthogonally.

[0042] All dichroic layers are designed to obtain maximum transmission and reflectance at a 45° angle of incidence.

[0043] At position "b", all three components are spectrally combined and aligned along the principal optical axis in both the near and far fields, thereby improving the homogenization performance of the downstream integrators IN1 and IN2.

[0044] Figure 2 The first integrator IN1 is shown in further detail, showing two microlens arrays ml, m2. The two arrays may be identical, having the same pitch and focal length, typically corresponding to their mutual distance s1.

[0045] To avoid overfilling of the lens aperture and the consequent loss of brightness, the diameter of the individual sub-beams at the downstream microlens array m2 is smaller than its lens pitch. Otherwise, such overfilling of the lens array could result in unwanted multiple images in the Fourier plane.

[0046] As mentioned before, a designed surface may be used instead of the microlens arrays m1, m2 without affecting the objectives of the present invention.

[0047] Now back to Figure 1 , a plano-convex spherical lens L1, which acts as a Fourier lens, focuses on a second spherical plano-convex lens L2, which acts as a field lens. Depending on the setup, the focal lengths of lenses L1 and L2 may be different, but it is generally considered that near-infinite focus (resulting in a beam with a minimum divergence angle when it reaches the second integration stage) is more desirable.

[0048] The first holographic diffuser F1 features a custom surface design that reduces any hot spots or speckles while improving the mixing of all wavelengths.

[0049] Therefore, in such a diffused state, the mixed laser beam enters a second integration stage based on a second integrator IN2, which may have the same specifications as the first integrator IN1.

[0050] Downstream of the second integrator IN2, a field lens in the form of another condenser lens L3 is used to shape the output beam into an inverted cone of the desired angle θ, which typically depends on the envisaged application or integration with any downstream optical devices. Apart from achieving said angle θ, the focal length of the integrator IN2 does not appear to be critical to a large extent.

[0051] The second holographic diffuser F2 also uses a custom surface design to reduce any hot spots, color spots or interference that may remain when the light beam passes through the second integrator IN2, further improving the mixing of all wavelengths and the distribution profile of the final output beam.

[0052] Industrial Applications

[0053] The invention is applicable to the entire entertainment industry. The advantages of the invention are further applicable to a wide range of other applications that can be broadly classified as "lighting", including machine vision, inspection, medical uses, etc. Specifically, the invention can be used in applications such as microlenses, material processing, fluorescence, lighting fixtures, holography, fiber coupling, etc., which require the spectral characteristics of lasers (narrow band, monochromaticity), but at the same time require a uniform distribution of intensity.

[0054] List of Reference Numerals

[0055] LS1 Laser source LD1, LD2, LD3 Laser Diode CL Collimator M1 Mirror D1, D2 Dichroic Filters S1, S2, S3 Bracket SW Screws IN1, IN2 Integrator m1, m2 Microlens array s1 distance L1, L2, L3 lens F1, F2 Diffuser θ angle a, b Reference location

Claims

1. An optical device having a laser source (LS1) for providing a laser beam, characterized in that a first integrator (IN1) for splitting the incident light beam into sub-beams, and A second integrator (IN2) is arranged coaxially with the first integrator (IN1), and the second integrator (IN2) is used to shape the sub-beams into an output beam with a defined, preferably flat-top spatial irradiance profile.

2. The device according to claim 1, characterized in that Each integrator (IN1, IN2) comprises two microlens arrays (m1, m2) with the same focal length, the arrays (m1, m2) being coaxially juxtaposed at a distance (s1), the distance (s1) preferably being equal to the focal length.

3. The device according to claim 2, characterized in that Two preferably afocal spherical plano-convex lenses (L1, L2) are arranged between the integrators (IN1, IN2), and the plano-convex lenses (L1, L2) are coaxially juxtaposed with opposite planar sides.

4. The device according to claim 3, characterized in that A first diffuser (F1), preferably a holographic diffuser, is arranged between the plano-convex lenses (L1, L2) and the second integrator (IN2).

5. The device according to claim 4, characterized in that A condenser lens (L3) is arranged downstream of the second integrator (IN2) for shaping the output light beam into a cone with a defined angle (θ).

6. The device according to claim 5, characterized in that Downstream of the condenser lens (L3) a second diffuser (F2) is arranged, which is preferably a holographic diffuser.

7. A device according to any one of the preceding claims, characterised in that The light source (LS1) comprises a first laser diode (LD1) for emitting a first light beam at a first wavelength in the light beam, the first wavelength being perceived as a blue color, for example.

8. The device according to claim 7, characterized in that The light source (LS1) comprises a mirror (M1), preferably a dielectric coated mirror, for reflecting the first light beam, preferably orthogonally, to the first integrator (IN1).

9. The device according to claim 8, characterized in that The light source (LS1) comprises a second laser diode (LD2) for emitting a second light beam in the light beam at a second wavelength different from the first wavelength, the second wavelength being perceived as a green color, for example.

10. The device according to claim 9, characterized in that The light source (LS1) comprises a first dichroic filter (D1) for passing a first light beam while reflecting, preferably orthogonally, a second light beam to a first integrator (IN1), such that the first light beam and the second light beam are co-aligned at a first position (a) between the first dichroic filter (D1) and the integrator (IN1).

11. The device according to claim 10, characterized in that The light source (LS1) comprises a third laser diode (LD3) for emitting a third light beam in the light beam at a third wavelength different from the first wavelength and the second wavelength, the third wavelength being perceived as a red color, for example.

12. The device according to claim 11, characterized in that The light source (LS1) comprises a second dichroic filter (D2) for passing the first light beam and the second light beam while reflecting the third light beam to, preferably orthogonally to, the first integrator (IN1) so that all light beams are co-aligned at a second position between the second dichroic filter (D2) and the integrator (IN1).

13. The device according to claim 12, characterized in that The light source (LS1) comprises optical supports (S1, S2, S3), preferably each optical support having a push-pull screw (SW) for spatial alignment, for fixing a mirror (M1) and a dichroic filter (D1, D2).

14. The device according to any one of claims 7 to 13, characterized in that Each laser diode (LD1, LD2, LD3) is integrated with a short-focus collimator (CL).

15. The device according to claim 14, characterized in that The diodes (LD1, LD2, LD3) and the collimator (CL) form a multi-die package.

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