Spectral splitter device

Abstract

A spectral beam splitter device is disclosed for converting at least one initial light beam (R0) from a light source (F) into two or more light beams, or vice versa, the spectral beam splitter device comprising a first polarization beam splitter (P1) which splits the initial light beam (R0) into two orthogonal polarized light beams (R1 and R2); two optical elements (O1 and O2) through which the two orthogonal polarized light beams (R1 and R2) pass respectively; and a second polarization beam splitter (P21) and a third polarization beam splitter (P22) which in turn split the two orthogonal polarized light beams (R1 and R2) into four respective output light beams (R11 and R12) and (R21 and R22). According to the invention, each of the two optical elements (O1 and O2) is birefringent and their birefringence depends on the wavelength.

Description

[0001] Purpose of the Invention

[0002] The present invention, as expressed in the language of this specification, relates to a spectral splitter device which provides the advantages and features described in detail below and which represent an improvement over the state of the art in the field of its application.

[0003] More specifically, the object of the invention is centered on a spectral splitter device that is based on the principle of a Lyot filter and that allows increasing the power density of a light source beam (for example a laser) by the linear superposition of two pairs of beams combined by orthogonal polarizations, by using birefringent and / or dispersive optical elements, for example a calcite crystal of the necessary thickness that modifies the wavelength in a controlled way so that the two beams have the same polarization, thus allowing their linear superposition, which in turn allows a cascade repetition of the process, again combining the linearly superposed beam with other beams subjected to the same effect, and in which the device comprises an optical assembly capable of achieving said effect by including additional elements, such as external resonators, which provide, according to each need, a larger resonance cavity and specific resonance conditions on the output beam obtained. Technical Field

[0004] The field of application of the invention lies within the industrial sector dedicated to the production of devices and components for light-emitting devices, such as laser, LED or other technologies. Background Art

[0005] It is well known that when light passes through a birefringent medium, the beam can be decomposed into two polarization components relative to the optical axis of the medium, each component experiencing a different refractive index, resulting in a relative phase shift between the two, which can cause a change in the polarization state of the light. Since all media are dispersive and have different refractive indices for different wavelengths, birefringence is usually also dispersive. Therefore, the change in polarization state depends on the wavelength. Therefore, different spectral components of light can be distinguished, filtered, separated or combined by appropriate configuration of birefringent materials and polarization beam splitters. In the simplest case, a birefringent crystal is placed between two polarizers. This filter is called a Lyot filter. Since the phase delay between the polarization states of light is periodic π times, so is the periodic transmission of the filter relative to the wavelength.

[0006] This effect is very useful for boosting the power of certain devices.

[0007] For example, laser technology is widely used in industry, which is usually used in industrial laser processes, mainly for cutting or welding. Most are made with fiber lasers or disk lasers.

[0008] Regardless, in these types of applications, it is important that the energy density can be concentrated into a very small spot. Energy density is achieved by either scaling the power or reducing the laser spot size.

[0009] However, in applications with diodes, all increases in density are based on increases in power, since the spot cannot be made smaller due to the low beam quality in the slow axis, but to date, laser technology that increases its power / capacity only allows adding multiple diode beams by polarization or per wavelength. It is therefore desirable to develop a new technology that allows increasing said power by adding more than said two single diodes, and the purpose of the present invention is to develop said new technology that allows increasing the energy density by a factor of two or four in a simple manner.

[0010] At the current state of the art, in order to combine two laser beams from two diodes, two diodes are combined, which are equal and placed vertically and focused, with different light polarizations (vertical polarization and the other polarization turned horizontally by a wave delayer inserted for this purpose), facing a polarization beam splitter so that they arrive at the polarization beam splitter and leave jointly in the same direction, since one passes through the polarization beam splitter and the other is reflected, but keeping their different polarizations. This means that the combination of the two beams cannot be recombined to increase the power of the output laser, which is desirable.

[0011] Each laser consists of a laser active region (also called gain region) in which the supplied energy is converted into coherent radiation by stimulated emission. For this purpose, a laser resonator is required to ensure that a portion of the exiting radiation returns to the gain region. It therefore contains at least one feedback element, usually a semi-transparent mirror. The resonator determines the feedback characteristics of the laser through its geometry and physical properties, in particular the spatial profile, wavelength, bandwidth and polarization.

[0012] The estimated achievable characteristics depend on the material gain and resonator and are usually negatively correlated with each other and the achievable output power. Therefore, an improvement in one selected parameter often degrades other parameters.

[0013] Of particular practical importance are semiconductor lasers, since they are small, convert electrical energy directly into light, are very efficient, and can be manufactured using established semiconductor production technologies and are therefore inexpensive when used in large quantities. The resonators are integrated in series via reflective layers applied to the facets and / or epitaxially bonded refractive index gratings. At present, the output power or the achievable power density is still too low for many applications of interest. This is because the volume in which the light is generated is significantly smaller than 1 mm 3 , therefore, when increased further, it leads to a power density that destroys the components.

[0014] Increasing the volume is not a solution, as the modal selectivity will decrease and thus the beam quality will degrade, keeping the power density approximately constant.

[0015] As mentioned above, a long-standing practice to at least double the output power involves superimposing two orthogonal laser polarizations using a polarization beam splitter so that the resulting light contains crossed polarizations and can only be increased to this doubled power.

[0016] The object of the present invention is therefore to develop a spectral splitter device to increase the power and thus increase the efficiency of the use of light beams in various industrial applications, for example in laser devices to significantly increase said power by combining pairs of laser beams, allowing an exponential increase of the same power, depending on the number of pairs combined.

[0017] Furthermore, as a reference to the current state of the art, it should be noted that, although at least the applicant is aware of documents and literature published concerning concepts in the art, it is believed that none of them, either alone or in combination, discloses an apparatus such as described herein or has technical, structural and constitutive characteristics identical or similar to those presented by the apparatus claimed herein.

[0018] In this regard, it is worth mentioning (e.g. WO 03 / 055018) that it is known that highly compact external resonators can significantly improve the beam quality of high-power diode lasers at high average powers. However, several such lasers must be operated simultaneously to achieve greater beam powers. This usually significantly reduces the beam quality and the possibility of producing small focal spots. The achievable power density remains almost unchanged.

[0019] To overcome this problem, Daneu et al. (Opt. Lett., Vol. 25, No. 6, pp. 405-407) and Sanchez-Rubio (US 6,192,062) proposed spectral multiplexing. This is a method of using multiple laser sources, each operating at a different wavelength, so that they can overlap in space by appropriately selected elements (usually diffraction gratings). Other patent applications (e.g., WO 03 / 036766, WO 20 / 02091077) are also based on this.

[0020] All of these patents have a central dispersive element (prism or grating) that splits the resonator in two. On one side of the element, the various laser emissions are collinear, i.e., the beam cross-sections and emission directions are nearly identical. On the second side of the element, the different beams are spatially dispersed by dielectric dispersion or diffraction, making it possible to operate separate lasers of the appropriate wavelength in each direction. Typically, this includes lasers with feedback mirrors in the common path, as this ensures that each gain region operates precisely at the appropriate wavelength, which is determined by the dispersion.

[0021] What these patents have in common is that the spectral distance of the wavelengths to be multiplexed is determined by the dispersion and geometry of the resonator. The dispersion expressed in "wavelengths per angle" must be multiplied by the angle of "emitter spacing divided by the distance to the dispersive element". For dense spectral multiplexing, larger configurations can be obtained, or for a given resonator footprint and dispersion, spectral steps of typically larger than 1 nm result in adjacent emitters. Furthermore, it is well known that most highly dispersive gratings have only low diffraction efficiency and / or spectral acceptance and / or low damage threshold, which makes practical implementation rather difficult. Summary of the invention

[0022] Therefore, the spectral splitter device proposed by the present invention is configured as an optimal solution to achieve the above-mentioned objectives, the characteristic details of which are listed in the final claims attached to this description.

[0023] In particular, as mentioned above, the present invention proposes a spectral beam splitter that, based on the principle of a Lyot filter, allows increasing the power density of a light source beam (e.g. a laser) from the linear superposition of each pair of beams of orthogonal polarization combination by using birefringent and dispersive optical elements, for example, a calcite crystal of the necessary thickness that modifies the wavelength in a controlled manner, causing the two beams to have the same linear polarization again, allowing their linear superposition, which in turn allows a cascade repetition of the process, recombining the linearly superposed beam with the other beams that have undergone the same process. The spectral beam splitter device includes an optical assembly plate in order to achieve the effect by adding additional elements to the output beam obtained, such as an external resonator that provides a larger resonance cavity and specific resonance conditions.

[0024] To this end, more specifically, the device proposed by the present invention is a spectral beam splitter, which is used to split an initial light beam into two or more light beams, mainly comprising:

[0025] - a first polarizing beam splitter, which splits the light into two orthogonally polarized beams;

[0026] - two optical elements, through which the two polarized light beams pass respectively; and

[0027] - a second polarization beam splitter and a third polarization beam splitter, which in turn split the two polarization beams into four corresponding output beams,

[0028] Every optical element is birefringent, and the birefringence of both elements is wavelength dependent.

[0029] Furthermore, in a preferred embodiment, the lights of the obtained output light beams have at least one orthogonal polarization state or different wavelengths with respect to each other.

[0030] Likewise, in a preferred embodiment of the apparatus of the invention, the initial light beam passes through a preceding birefringent dispersive optical element before entering the first polarizing beam splitter, and optionally also through a preceding polarizing beam splitter before entering the first polarizing beam splitter.

[0031] Furthermore, in a preferred embodiment, the initial light beam passes through a partially reflecting mirror before entering said preceding polarization beam splitter or said preceding birefringent optical element, respectively.

[0032] Optionally, at least one of the four output light beams passes through a third birefringent and / or dispersive optical element.

[0033] On the other hand, it should be noted that the spectral beam splitter device, when used with a reverse beam path as described above, may optionally act as a beam combiner.

[0034] In such a case, the device comprises more than one individual light sources, preferably lasers or laser gain devices, which can obtain feedback from a partially reflecting mirror as the light beams to be combined.

[0035] In any case, the spectral splitter device of the invention is configured as a plate comprising separate mutual control means for the optical delay and / or dispersion of the first and second optical elements and, if applicable, of the preceding optical element.

[0036] In a preferred embodiment, each individual optical element comprises a birefringent dispersive crystal of integer multiple and base thickness, and an additional phase delay comprising any one or combination of the following:

[0037] - Single retarder plate or combination of multiple retarder plates

[0038] -Supports individual tilt of optics for latency adjustment

[0039] -Babinet-Soleil optical wedge

[0040] - Liquid crystal elements with retardation which is controlled by their manufacturing process or by electric fields.

[0041] More specifically, in a preferred embodiment, each individual optical element comprises at least two portions having a slight optical wedge, so that the effective thickness can be adjusted by moving the two portions relative to each other.

[0042] Furthermore, preferably, the relative optical delay is achieved using fewer physical elements than conceptually necessary and wherein at least one element is passed more than once.

[0043] Finally, it should be noted that in a preferred embodiment the light source can be a laser, a semiconductor laser with or without low reflectivity, an LED, a laser bar, a bar stack.

[0044] In any case, the light source is the matrix and some polarizers are the displacers. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] To supplement the description made, and to help better understand the characteristics of the invention, the present description is accompanied, as an integral part thereof, by the accompanying drawings, in which the following are represented for illustrative and non-limiting purposes:

[0046] FIG. 1 shows a schematic diagram of an embodiment of a spectral splitter device, illustrating the main components and elements it comprises and their arrangement.

[0047] Figure 2 shows a schematic diagram of a spectral beam splitter device, in this case a beam combiner, showing the arrangement of its components.

[0048] FIG. 3 shows a top view of an example of an embodiment of a device as a beam combiner on an optical plate, showing the main components and elements it comprises, as well as their arrangement, with the different beams being indicated by dashed lines.

[0049] 4 and 5 show two perspective views of an embodiment of a laser diode assembly, respectively with passive cooling and with active cooling, as an example of a light source comprising a spectrum splitter device object of the present invention, showing its general configuration.

[0050] 6 and 7 show perspective views of a laser diode with passive cooling and active cooling, as shown in FIGS. 1 and 2 , in this case represented by a base with water as the cooling medium.

[0051] Figures 8 and 9 show perspective views of laser diodes with passive cooling and active cooling, respectively, using water as the cooling medium mounted on their mounts as shown above, and in this case including their respective circular lens adjustments.

[0052] FIG. 10 shows a perspective view of an example of mounting an optical element on a tilt bracket. DETAILED DESCRIPTION

[0053] In view of the above-mentioned figures, and according to the adopted numbers, it can be understood that therein are non-limiting examples of embodiments of the spectral splitter device of the present invention, more specifically as examples of laser optical devices, which include what is indicated and described in detail below.

[0054] Therefore, as shown in FIG. 1 , the spectral splitter device ( 1 ) of the present invention is used to convert an initial light beam ( R0 ) from a light source (F) into two or more light beams, and basically comprises:

[0055] - a first polarization beam splitter (P1) which splits said initial light beam (R0) into two orthogonally polarized light beams (R1 and R2);

[0056] - two optical elements (O1 and O2) through which the two orthogonally polarized light beams (R1 and R2) pass respectively; and

[0057] - a second polarizing beam splitter and a third polarizing beam splitter (P21 and P22) which in turn split the two orthogonally polarized light beams (R1 and R2) into four respective output light beams (R11 and R12) and (R21 and R22),

[0058] Each of these optical elements (O1 and O2) is birefringent, and the birefringence of both elements is wavelength dependent.

[0059] Preferably, the lights obtained from the four output light beams (R11 and R12) and (R21 and R22) have at least one orthogonal polarization state or different wavelengths with respect to each other.

[0060] Preferably, the initial light beam (R0) passes through a preceding birefringent dispersive optical element (O0) before entering the first polarization beam splitter (P1).

[0061] Alternatively, the initial light beam (R0) passes through a pre-polarization beam splitter (P0) before entering the first polarization beam splitter (P1).

[0062] And, optionally, the initial light beam (R0) passes through a partial reflective mirror (M) before entering the aforementioned pre-polarization beam splitter (P0) or the preceding birefringent optical element (O0).

[0063] In any case, preferably, at least one of the four output light beams (R11 and R12) and (R21 and R22) passes through a third optical element (O3) having birefringence and / or dispersion.

[0064] It should be noted that, optionally, in one embodiment, the spectral splitter device is capable of being applied as a beam combiner when used with a reverse beam path as described above, i.e. obtaining the sum of two pairs of light beams (R11 and R12) and (R21 and R22) generated by multiple separate light sources (F) and combining them into a single light beam (R0).

[0065] In such case, to obtain the light beams (R), the device comprises more than one individual light source (F), preferably lasers or laser gain devices, which generate the light beams to be combined. The single light source can obtain feedback from a partially reflecting mirror (M).

[0066] In a preferred embodiment, the spectral splitter device (1) of the present invention is implemented with at least one phase delay plate, which is used to individually control the optical delay and / or dispersion of the first and second optical elements (O1, O2) with each other, and if applicable, to individually control the optical delay and / or dispersion of the preceding optical element (O0) with each other.

[0067] Preferably, the phase plate is a special type of phase plate called a quarter wave plate.

[0068] In a preferred embodiment, each individual optical element (O1, O2, O0) comprises a birefringent dispersive crystal of integer multiple and base thickness, and an additional phase delay comprising any one or combination of the following:

[0069] - Single retarder plate or combination of multiple retarder plates

[0070] -Supports individual tilt of optics for latency adjustment

[0071] - Babinet-Soleil Wedge

[0072] - Liquid crystal elements with retardation, controlled by their manufacturing process or by electric fields.

[0073] More specifically, in a preferred embodiment, each individual optical element comprises at least two portions having a slight optical wedge, so that the effective thickness can be adjusted by moving the two portions relative to each other.

[0074] Furthermore, preferably, the relative optical delay is performed using fewer physical elements than is conceptually necessary and wherein at least one element is passed more than once.

[0075] It should be noted that the light source (F) can be a laser, a semiconductor laser with or without low reflectivity, an LED, a laser bar, or a bar stack.

[0076] Furthermore, the light source (F) can be either a point light source or a matrix light source, and some polarizers are displacers.

[0077] With reference to FIG. 3 , one can see an example of realizing the device of the invention on a plate ( 3 ), in particular, an example of combining four light beams in an output lens (L), wherein one can see that a heat sink (D) is also included.

[0078] With reference to FIGS. 3 to 9 , one can see an example of a light source (F), in particular a semiconductor laser diode, which is either passively cooled without water inside the assembly on a base (2) with a cooling system ( FIG. 4 ), or actively cooled using two water channels that cool the diode ( FIG. 5 ).

[0079] Figures 6 and 7 show two options for a diode as light source (F), passively and actively cooled, respectively, mounted on a base (2) using water as cooling medium.

[0080] The base (2) is used to assemble the diode or light source (F) to the end plate (3) and is fitted with water connections (4) to mount the tubes and cool the system. The active cooling installation shown in Figure 7 has a more robust connection to allow higher currents, although both options are the same height.

[0081] Figures 8 and 9 show two alternative assemblies of the light source (F), respectively with passive and active cooling systems, whose adjustment does not vary once the circular lens (5) is coupled, since it is identical.

[0082] Finally, in FIG. 10 it can be seen how the optical element (O), preferably a birefringent and / or dispersive crystal, such as calcite, is mounted on a support ( 6 ) inclined at 45°.

[0083] Having fully described the nature and implementation of the present invention, it is deemed unnecessary to extend the explanation thereof so that those skilled in the art may understand the scope thereof and the advantages derived therefrom.

Claims

1. A spectral splitter device for converting at least an initial light beam (R0) from a light source (F) into two or more light beams or vice versa, characterized in that It includes: - Partial reflector (M), birefringent dispersive optical element (O0), pre-polarization beam splitter (P0); - a first polarization beam splitter (P1), wherein the initial light beam (R0) passes through the partial reflector (M), the birefringent dispersive optical element (O0) and the pre-polarization beam splitter (P0) in sequence before entering the first polarization beam splitter (P1), and the first polarization beam splitter (P1) splits the initial light beam (R0) into two orthogonal polarization light beams (R1, R2); - a first optical element and a second optical element (O1, O2), through which the two orthogonally polarized light beams (R1, R2) pass, respectively; and - a second polarization beam splitter and a third polarization beam splitter (P21, P22) which in turn split the two orthogonally polarized light beams (R1, R2) into four respective output light beams (R11, R12, R21, R22), Each of the first optical element and the second optical element (O1, O2) is birefringent, and the birefringence of the first optical element and the second optical element (O1, O2) is wavelength-dependent.

2. The spectral splitter device according to claim 1, characterized in that: The lights of the four output light beams ( R11 , R12 , R21 , R22 ) obtained have at least one orthogonal polarization state or different wavelengths.

3. The spectral splitter device according to claim 1, characterized in that: At least one of the four output beams (R11, R12, R21, R22) passes through a third optical element (O3), which is birefringent and / or dispersive.

4. The spectral splitter device according to claim 1, characterized in that: It comprises one or more separate light sources (F) generating light beams (R11, R12, R21, R22) which are combined into a single light beam when a reverse path is applied to the light beams.

5. The spectral splitter device according to claim 4, characterized in that: The one or more individual light sources (F) obtain feedback from the partially reflecting mirror (M).

6. The spectral splitter device according to claim 1, characterized in that: It comprises means for individual mutual control of the optical delay and / or dispersion of the first and second optical elements (O1, O2), and also comprises means for individual mutual control of the optical delay and / or dispersion of the birefringent dispersive optical element (O0).

7. The spectral splitter device according to claim 6, characterized in that: Each individual optical element comprises a birefringent dispersion crystal of an integer multiple of the basic thickness and an additional phase delay, wherein the additional phase delay comprises any one or a combination of the following: - a single retarder plate or a combination of multiple retarder plates, -Supports individual tilting of optics to adjust latency, - Babinet-Sorley light wedge, - Liquid crystal elements with retardation which is controlled by their manufacturing process or by electric fields.

8. The spectral splitter device according to claim 6, characterized in that: Each individual optical element comprises at least two parts with micro-wedges, so that the effective thickness can be adjusted by moving the two parts relative to each other.

9. The spectral splitter device according to claim 1, characterized in that: The light source (F) is a laser diode, a semiconductor laser with or without low reflectivity, an LED, a laser bar or a bar stack.

10. The spectral splitter device according to claim 1, characterized in that: The light source (F) is a matrix, and the first polarization beam splitter, the second polarization beam splitter, and the third polarization beam splitter are displacers.

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