JP2021533577A - Compact high-spectral radiance light source including parabolic mirror and plano-convex fluorescent body - Google Patents

Abstract

The fluorescent light source to be pumped includes one or more mirrors that direct pumping light from one or more pump sources onto a fluorescent body having a flat top surface and a convex back surface. To improve efficiency, the top surface can be coated with an antireflection coating and the back convex surface can be coated with an antireflection coating. Further, the upper surface of the main body can be roughened so as to scatter a part of the excitation light provided from the mirror to generate a white output beam. The mirror has a reflective surface located outside the collection area of the output beam of the light source. Therefore, the collection area is not blocked by the mirror. The light source also includes a condenser lens that collects the light emitted by the body. The mirror may be a single parabolic mirror that focuses the excitation light on the body and stimulates radiation. [Selection diagram] FIG. 4

Description

The present invention relates to a light source in general, and more particularly to a high radiance fluorescent light source including a parabolic mirror that directs excitation light toward a plano-convex fluorescent body.

In biomedical applications, as well as other applications that require fluorescence stimulation or other similar lighting requirements, narrowband illumination is often used for fluorescence imaging applications due to the speckle field produced by narrowband illumination. Wideband light sources are usually required as they are unsuitable for biomedical and imaging applications. Ultra-wideband incoherent sources of the past have been relatively large optical systems and require large lenses and / or reflectors to produce low divergence output beams. The size of such an optical system limits the efficiency of coupling the output beam to a waveguide such as an optical fiber.

Current solid broadband fluorescent light sources, such as so-called "white LEDs" (light emitting diodes), are LEDs for pumping fluorescent material such as fluorescent crystal powder or individual fluorescent crystals embedded in epoxy resin. Is often used. On the one hand, using LEDs as pumps reduces cost and size. However, the spectral radiance (W / Hz / m ^{2 / sr) of these fluorescent light sources is transmitted from the radiance (W / m 2} / sr) of the pump LED in the absorption band of the fluorescent material and the excitation to the fluorescent material. Limited by the heat management of the heat that is done. When a low radiance light pump source such as an LED is used, low radiance fluorescence emission is generated. Such low spectral radiance sources are suitable for coupling in light beams with poor collimation that are not suitable for long applications, or in high resolution applications, especially light paths such as liquid light guides and submm core fiber optics. It provides one of the light beams that is not well focused.

Front surface or front end pumping schemes can be used to cool the fluorescent body in higher radiance applications. In such geometry, the output fluorescence beam is on the same side as the input pump beam. In these front side pumping schemes, the pumping light source (laser diode, LED, etc.) and the beam steering and focusing optics of these pump sources need to be placed in front of the fluorescent material. Such an arrangement has some drawbacks. First, the location of the optics in front of the fluorescent body has practical space limitations. Next, the focused optics of the output fluorescence beam and additional optical components such as bandpass filters, beam combiners, fiber coupling optics, etc. must be located in front of the fluorescence body. Second, if the pump sources are located in front of the fluorescent body, the fact that each pump source generates its own heat load, in addition to the pumped fluorescent material, complicates the thermal management of the device. The resulting device requires the use of multiple heat sinks located apart from each other. Therefore, the thermal interface between the resulting light source and the passive or active cooling system is complicated. Ultimately, the resulting light source requires assembly procedures that are more difficult to mass-produce and optically align.

Therefore, it is desired to provide a light source with high spectral radiance while maintaining a compact design and low manufacturing cost.

The above task of providing a compact light source with low manufacturing cost and high spectral radiance is provided with respect to the light source and the method of operating the light source.

The light source is a body having a plano-convex shape and a material doped to have fluorescent properties when stimulated at an excitation wavelength, a condenser lens that collects the light emitted by the body, and one or more. Includes a mirror and one or more light sources that provide excitation light at the excitation wavelength. The light source has an output directed at the corresponding one of the mirrors. As a result, the mirror directs the excitation light provided by one or more light sources towards the body, stimulating the radiation of light emitted by the body. One or more mirrors include a reflective surface located outside the collection area of the output beam so that the collection area is not obstructed by the mirror. The one or more mirrors may be a single parabolic mirror arranged with the focus axis directed towards the top surface of the body in order to focus the output of the light source on the top surface of the body.

The above and other objects, features, and advantages of the invention will be apparent from the following description, more specifically, the description of preferred embodiments of the invention, as shown in the accompanying drawings.

The novel features considered to be the features of the present invention are described in the appended claims. However, the invention itself, as well as preferred embodiments, further objectives, and advantages thereof, are best understood by reference to the following detailed description of exemplary embodiments when read in conjunction with the accompanying drawings. NS. Here, similar reference numbers indicate similar parts.

FIG. 3 is a side sectional view of an axisymmetric parabolic mirror used in various embodiments of the present disclosure. FIG. 3 is a side sectional view of an axisymmetric parabolic mirror used in various embodiments of the present disclosure. It is a side sectional view. It is a top sectional view. It is a perspective sectional view. It is an exploded view. It is a perspective view of the light source 200 by one Embodiment of this disclosure. FIG. 2 is a simplified schematic representation of the light source 200 of FIGS. 2A-2E, including an alternative thermal management subsystem. FIG. 3 is a side sectional view of a light source according to another embodiment of the present disclosure. FIG. 3 is a side sectional view of a light source according to still another embodiment of the present disclosure.

The present disclosure discloses a light source that provides high spectral radiance in a compact package with improved manufacturability due to a reduced number of components. Light produced by a light source by collecting pumping light on the surface of a parabolic mirror located outside the output fluorescent beam, including multiple pump light sources for stimulating the fluorescent body to emit a fluorescent beam. Increase the amount of. At the same time, the pump light source is located behind the output of the light source to provide better thermal management. The fluorescent body has a plano-convex shape. The lower surface of the convex shape can be coated with a reflective coating. The flat top surface of the body can be coated with an antireflection coating that facilitates the emission of emitted fluorescence without interfering with the introduction of excitation light received from the parabolic mirror. Since the fluorescent body generally emits "yellow" light, for example a mixture of wavelengths in the red and green wavelength regions, some of the excitation light, which is generally blue wavelength, is used to "whiten" the resulting output beam. The top surface can be polished to roughen the top surface for scattering. The parabolic mirror may have a circular contour or an annular contour to provide an aperture for extracting the emitted output beam. The pump light source can be coupled to the same heat sink as the fluorescent body. The light source also provides a systematic and simplified alignment procedure. By removing obstacles that should be located in front of the fluorescence body, the large solid angle of collection is supported by the collector forming the light source output beam. Further, in the configuration of the light source shown in the present specification, since the direction of the pump beam is outside the solid angle of the output beam acquisition optical system, safer operation is provided in the event of a failure. Also, the optical alignment process for the illustrated light sources is suitable for mass production because of its reduced complexity to suit automated optical alignment and assembly systems. The resulting configuration is efficient focusing of the output fluorescent beam over a large stereo angle, compact packaging of the pump light source, fluorescent material, and output light acquisition optics, and the back of the light source facing the output fluorescent beam. It provides compact and simplified thermal management with a single flat high temperature surface located in. The number of optical elements can also be reduced. The geometry of the device is a compact hermetic package similar to the butterfly hermetic package used in the telecommunications industry, especially the high heat load (HHL) hermetic package used primarily for high power laser diodes and quantum cascade lasers. Compatible with.

To illustrate the operation of various embodiments of the light source disclosed herein, the basic properties of a parabolic mirror will be described with reference to FIGS. 1A and 1B. Figure 1A ^is represented by ^{(x 2} + ^y 2) ≦ any is ^(d 2/4) with respect to (x, y), wherein ^{z (x, y) = (} x 2 + y 2) / (4f) A cross section of an axisymmetric parabolic mirror having a reflecting surface 100 is shown. In the equation, z is the position of the reflecting surface of the mirror, x and y are the lateral positions expressed in Cartesian coordinates, d is the outer diameter of the parabolic mirror, and the parameter f is the focal length. Such a mirror is a collimated light beam parallel to the z-axis, or equivalently to the z-axis, at the focal point F102 of the mirror located at coordinates (x, y, z) = (0,0, f). It reflects a bundle of incident rays 101 that reach in parallel. Parabolic mirrors have two well-known advantages. First, there is no spherical aberration that leads to blurring of the focal point even for a high numerical aperture (NA), that is, when the ratio d / f of the mirror diameter d to the focal length f is large. Second, like other purely reflective optics, there is no chromatic aberration. This means that the characteristics of the mirror, more specifically the focal length f, do not depend on wavelengths within the reflectance bandwidth of the reflective surface 100. As a result, the position of the focal point F102 does not depend on the wavelength. This leads to a tight focus, even for wideband light beams such as fluorescent beams. The absence of chromatic aberration also means that a single parabolic mirror can be used for both focusing the pump light beam and collimating the wideband fluorescent beam. The main drawback associated with parabolic mirrors is that they are difficult to manufacture due to the need for surface accuracy and quality (ie, low surface roughness). This is because submicron accuracy is required to provide a suitable parabolic reflector for the visible spectrum, eg, wavelengths in the range of 400-700 nm. However, optical surface shaping techniques are now becoming more accessible and affordable. Among them, computer numerical control (CNC) grinding and polishing, diamonds, as those that can be used to manufacture parabolic mirrors as used in the embodiments of the light source disclosed below. Examples include turning, glass or plastic molding, and magneto-rheological surface finishing (MRF).

Here, with reference to FIG. 1B, the working principle of the parabolic mirror used in the embodiments disclosed herein is further shown. The optical path of the light ray 101A is generated from the pump source located at the point P and is reflected by the reflecting surface 100 at the point A. The ray 101A is initially parallel to the z-axis and is located at coordinate x = r in the plane defined by coordinate y = 0. The line located at the coordinate z = −f is a parabolic quasi-line 103. The parabola is known to be the locus of all points equidistant from the focal point F102 and the quasi-line 103. Therefore, the length of the segment AB extending between the points A and B is equal to the length of the segment AF extending between the points A and the focal point F102. Therefore, the triangle ABF is an isosceles triangle in which the angle φ and the angle β are equal. The segment AP extending between points A and P is parallel to the z-axis. Therefore, the segment PB extending between the points P and B must also be parallel to the axis z, and the angles γ and β must be equal as alternating internal angles. Therefore, as alternating internal angles, the angle δ = ∠SFA = γ + φ. Therefore, γ = φ = β and δ = 2β. _{The incident angle θ i of the} light ray 101A, for example, the pump light ray on the front surface 104 of the main body having the fluorescence characteristic arranged in the plane z = f is the angle ∠SFA. The point S is the apex of the parabola located at the origin (x, y, z) = (0,0,0). A is a reflection point of the light ray 101A by the reflection surface 100. By direct identification, the angle θ _i = ∠SFA = γ + φ = 2β. Therefore, r = 2f × tan (β) and r = 2f × tan (θ _i / 2). The formula r = 2f × tan (θ _i / 2) connecting r, f, and θ _i is a basic design formula for a parabolic mirror used in the embodiments disclosed herein. Since the illustrated parabolic mirror is axisymmetric, the illustrated example can be applied to any pump source located at a distance r from the z-axis. The examples herein use an axially symmetric parabolic mirror to direct light from a pump source to a fluorescent body, i.e., a material body with fluorescent properties, but an axially symmetric parabolic mirror is not required. Other parabolic mirrors, such as parabolic cylindrical mirrors with a parabolic focus along a single axis, may be used in alternative embodiments. In another embodiment, a plurality of finite conjugated lenses and plane mirrors can be used to reimage the pump source output onto the fluorescence body.

In embodiments described below, a plurality of high power laser pump beams are focused on the front surface of the body containing the fluorescent material. In such devices, the pump power density can reach very high values and the body containing the fluorescent material can be significantly locally heated. Such local heating can create an environment where it is difficult to apply an anti-reflective coating on the front surface of the body. In order to minimize the reflection loss of the excitation light and maintain a compact assembly _{, an incident angle θ i equal to the Brewster angle θ B} = tan ^-1 (n) and (n is the refractive index of the fluorescent substance) is provided. Therefore, the reflection of the excitation light can be advantageously reduced. When θ _j = θ _B , Fresnel reflections at the front air-body interface are eliminated for p-polarized beams (ie, rays with an electric field parallel to the plane of incidence). The laser diode output beam is generally TE polarized with a polarization ratio on the order of 100: 1. Therefore, the Fresnel reflection of all pump beams is applied to the junction surface of each pump laser diode along the radial axis, for example, as shown in FIG. 1B, with respect to the pump laser diode located at the point P. By orienting parallel to the axis, it can be essentially eliminated without the use of an AR coating. As an example, the Ce: YAG single crystal has a refractive index n = 1.85 at a pump wavelength of 450 nm. Therefore, θ _B = tan ^-1 (n) = 61.6 °. The relationship between the radial position r of the pump source and the focal length f of the parabolic mirror is r _B = 2f × tan (θ _B / 2) = 1.19 × f. To achieve a compact design, the value of r _B, can be set to, for example, 10 mm. The focal length of the parabolic mirror is _{given by f = r B /} 1.19 = 8.39 mm. Such a design is also compatible with fluorescence collection over very large NAs through an opening provided through the center of the parabolic mirror. As a first approximation, the parabolic mirror central aperture diameter _{can be approximated to 2r B} , providing a numerical aperture close to NA = sin (θ _{B) = 0.871.} The embodiments described above are compatible with the Brewster's angle front pumping scheme, while allowing the collection of fluorescent beams emitted over very large NAs without interfering with the pump laser beam. Is shown. However, this example does not limit the possibilities of other devices, including the principles manifested by the present disclosure, as described in the claims and their equivalents. Moreover, embodiments of the present disclosure are not limited to Brewster's angle pumping. Therefore, the pumping beam may be provided at a non-Brewster's angle. In order to maximize fluorescence emission, the embodiments disclosed herein can use an antireflection coating to increase radiation from the fluorescence body. Applying such an antireflection coating at the emission wavelength affects the Brewster's angle conditions described above for the excitation light. However, thin film designs, which are generally stacks of materials with different indices of refraction, reduce internal rereflection at emission wavelengths over a particular angular range, while external to the body at excitation wavelengths over another specific angular range. It can be specially adjusted to reduce reflections at the boundaries.

Next, with reference to FIG. 2A, a side sectional view of the light source 200 according to the first embodiment is shown. The illustrated example is a plano-convex shape of a fluorescent material thermally and mechanically bound to a heat spreader 202 that is centrally located in the mounting base 203 and has a profile that fits the convex back surface (bottom surface) of the fluorescent body 201. The fluorescent main body 201 is provided with optical pumping. The heat spreader 202 and mounting base 203 are preferably made of a highly thermally conductive material such as copper, aluminum, or a tungsten-copper (W-Cu) alloy. Alternatively, the heat spreader 202 can be formed as a stack of multiple materials to improve thermal management, in which the thermal paste and adhesive used to mount the fluorescent body 201 within the light source 200. Contains the agent. Optical pumping is achieved via an annular parabolic mirror 204 that combines and focuses a plurality of pump beams provided by a plurality of pump laser diodes 206. In this example, the divergent pump beam 205A emitted from the pump laser diode 206 provided in the TO can package is a lens 207 (eg, high NA aspheric molded glass lens), fast axis and slow axis stiffness with appropriate shape and focal length. Initially collimated or nearly collimated using a combination of mating lenses, or any single or multi-element beam shaper suitable for providing a substantially collimated beam. The resulting collimated or nearly collimated pump beam 205B is then redirected after reflection from the high reflectance coating 204A of the annular parabolic mirror 204 to the front surface of the fluorescent body 201 ( Focused on the top surface). The annular parabolic mirror 204 is fixed above the pump laser diode 206 and the lens 207 by a mirror mount 208 so that the focal point of the annular parabolic mirror 204 is centered on the front surface of the fluorescent body 201. .. The annular parabolic mirror 204 defines an aperture 211 for emitting an output beam 209A through a collimating lens 210 fixed within the aperture 211. The collimating lens 210 collimates the output beam 209A to form a collimated output beam 209B. Each of the excitation beams provided by the pump laser diode 206 and the lens 207 is steered and focused such that the pump beam 205C is coupled onto the center of the top surface of the fluorescence body 201. The front surface of the fluorescence body 201 can be roughened to cause reflection of a portion of the light provided by the pump beam 205C. As a result, the light output of the light source 200 is such that the nearly blue wavelength provided by the pump laser diode 206 produces a spectrum that is whiter (broadband over the optical spectrum) rather than yellow (mainly red-green). Combines with the approximately red-green wavelength emitted by the fluorescent body 201. Further, the front surface of the fluorescent main body 201 may be coated with an antireflection coating that is active at the emission wavelength in order to increase the output efficiency of the fluorescent main body 201 without interfering with the pump beam 205C directed to the Brewster angle.

FIG. 2A also shows a particular embodiment of a thermal management subsystem mounted behind the fluorescent body 201. The air director 220 fits into the conical recess on the back of the heat spreader 202 that includes the inlet path 222A and the outlet path 222B. Through these, air is supplied by the outlet port 212A of the electric fan 212 mounted in the recess behind the housing 216 under the heat spreader 202. The air supplied by the fan 212 is guided by the inlet path 222A through the cavity 221 close to the back side of the fluorescence body 201. Air is ventilated from the outlet path 222B through one or more ducts on the back of the housing 216 at a location provided with a vent at any base to which the light source 200 is attached. The entire illustrated thermal management subsystem, including the air director 220 and the fan 212, is outside the hermetically sealed portion of the light source 200. As a result, the operation of the internal optics of the light source 200 is not compromised by the thermal management subsystem. As an alternative to the airflow-based cooling shown, liquid cooling can also be guided through inlet passage 222A and outlet passage 222B, if desired, using appropriate external accessories.

Further referring to FIG. 2B, a simplified top view of the light source 200 of FIG. 2A is shown. Here, we can see the positions of the five pump laser diodes 206 arranged in a circle around the fluorescent body 201. The illustrated light source 200 includes a plurality of pump laser diodes 206 in the housing 216. These are distributed around the axis of symmetry of the system. However, an asymmetrical arrangement as well as an arrangement in which everything is arranged on one side of the fluorescent body 201 is also possible. In that case, some embodiments involve a change to an annular parabolic mirror 204 that does not require an opening through the annular parabolic mirror 204. All of the pump beam 205C, of which only three are shown in FIG. 2A as an example, is at least partially absorbed by the fluorescent body 201. The fluorescence body 201 responds to the excitation provided by the pump beams 205A-205C by deexciting the doping element after an average fluorescence lifetime, eg, about 70 ns when the Ce: YAG crystal is used as the fluorescence body 201. Occasionally emits fluorescent output. Fluorescence is generally emitted isotropically, i.e., over the solid angle of 4π steradians. Therefore, a broadband high reflectance coating is applied to the back convex surface of the fluorescent main body 201, or a high reflective upper surface is provided on the heat spreader 202 optically bonded to the fluorescent main body 201, or fluorescent light emission that does not contribute to the output beam 209A. It is advantageous to reflect. The output beam 209A diverges as it passes through the opening 211 extending through the annular parabolic mirror 204. The output beam 209A is generally subject to further spatial or spectral beam shaping by additional optics or devices. In this embodiment, the aperture 211 is filled with a collimating lens 210 having a large numerical aperture (NA), and the rear focal point of the collimating lens 210 is placed at the pumped position of the fluorescent body 201 to emit fluorescence. Designed to collect. A collimated output beam 209B is generated by the collimating lens 210 to provide the output of the light source. The large NA collimating lens 210 is preferably aspherical and achromatic, minimizing the effects of spherical and chromatic aberrations on the residual divergence of the collimated output beam 209B. Alternatively, in each of the embodiments presented herein, the collimating device, eg, the collimating lens 210, is an on-axis or off-axis parabolic mirror, a Fresnel lens, or any other refraction. It may be provided by a reflective or diffractive optical device. The collimating lens 210 is located within the opening 211. On the other hand, such collocation is not a requirement to reduce the size of the package. The collimating device is located above or below the annular parabolic mirror 204 and is provided through the annular parabolic mirror 204 as long as the focus of the collimating device coincides with the pumped position of the fluorescent body 201. Light emitted through a large opening can be collected and collimated.

In certain embodiments that use Brewster's angle laser diode pumping, each junction of the pump laser diode 206 is radially located. That is, the junctions are aligned perpendicular to the illustrated circular arrangement to obtain the required p-polarized beam on the surface of the fluorescent body 201. As described above, it is advantageous to apply a high-reflectivity (HR) broadband coating on the back surface of the fluorescent body 201, or to optically bond the fluorescent body 201 to the heat spreader 202. The heat spreader 202 can be highly polished to reflect the emitted fluorescence towards the light output, i.e. towards the focusing and collimating lens 210. It is also preferable to extend the bandwidth of the HR coating to the pump wavelength in order to double the optical path length (OPL) of each pump beam inside the fluorescent material. By doubling the optical path length of the pump beam, _{a fluorescent substance having a low absorption coefficient μ α} can be used, or a _{thinner fluorescent substance can be used in the case of a predetermined value μ α} , so that the fluorescent body 201 can be used. By reducing the maximum thickness of the fluorescent body 201, the heat load removal from the fluorescent body 201 is improved. For example, a Ce: YAG crystal material having an absorption coefficient μ _α = 60.0 cm ^{-1 can be used.} In addition, the reflection of the pump beam in the HR coating prevents the pump beam from degrading the material (eg, solder or adhesive) used to bond the fluorescent body 201 to the heat spreader 202. Therefore, the reliability of the light source 200 is increased.

FIG. 2C shows a perspective sectional view of the light source 200. Here you can see the position of the fan 212 under the heat spreader 202. The positions of the pump laser diode 206 and the pump beam 205A can be seen in more detail. FIG. 2D shows an exploded view of the light source 200. Here, individual components including a pump laser diode 206, a fan 212, an air director 220, a heat spreader 202, a housing 216 with an integrated mounting base 203, and a plurality of hermetic electric feedthroughs 215 provided via the housing 216. Is shown. In the annular parabolic mirror 204, the position of the high reflectance coating 204A is visible, and the collimating lens 210 is also shown.

As mentioned above, the heat spreader 202 can be manufactured from a single material or a stack of materials with well-selected thermal properties. The most important properties of each material are thermal conductivity κ (represented by W / m / K) and linear coefficient of thermal expansion α (often represented by ppm / K). If the active cooling system shown in FIGS. 2A-2E is used, the air director 220 can also be selected. The choice of material was the warpage (thermally induced) of the fluorescent body 201 and the heat spreader 202 due to the large discrepancies in the mechanical stresses, in particular their coefficients of thermal expansion (CTEs). The purpose is to help cool the fluorescent material by using a high thermal conductivity material while avoiding (curving). Therefore, the heat spreader in some embodiments is mounted using a stack of different materials, such as a stack containing a very high thermal conductivity plate such as a CVD (chemical vapor deposition) diamond plate (κ> 1800 W / m / K). Will be done. The fluorescent body 201 and the heat spreader 202 are thermal interface materials such as adhesives (optical, thermal, thermal conductivity, etc.), soldering techniques, surface contact techniques, bonding techniques (diffusion bonding), or thermally conductive pastes. It can be joined using mechanical clamping or the like with or without (TIM: thermal interface materials). The heat spreader 202 and the mounting base 203 can be manufactured from adjacent heat conductive materials as shown. Alternatively, the heat spreader 202 and the mounting base 203 may be thermally insulated. The heat spreader 202 and / or the mounting base 203 can be passively or actively cooled. An alternative thermal management scheme is passive by a thermal path between the heat spreader 202 and the mounting base 203, which can be thermally coupled using TIMs such as thermal pastes, thermal adhesives, thermal pads, etc. Cooling can be achieved. Active cooling of the light source 200 can be provided via an air jet, a liquid jet directed to the back of the mounting base 203, or a liquid loop cooler thermally bonded to the back of the mounting base 203. One or more cavities for the flow of air or liquid can be formed in the mounting base 203. The cavity extends to or near the back of the fluorescent body 201 to optimize heat transfer away from the fluorescent body 201. The light source 200 is protected from ambient dust and moisture by packaging including the mounting base 203, the housing 216, and the outer (convex) surface of the collimating lens 210. These may be hermetically sealed. Electrical connections can be made via the hermetic electrical feedthrough 215 on one of the sidewalls of the housing 216. In order to passively remove heat from the light source 200, a mechanical connection with high thermal conductivity can be provided on the flat surface of the bottom of the mounting base 203. This is typically achieved by providing an external heat sink to which the mounting base 203 is mounted. Preferably, a TIM layer is used to reduce the thermal resistance of the interface. Alternatively, the air or liquid cooling configuration described above can be used for air or liquid cooling directly to the mounting base 203 or through a channel extending near the back of the fluorescent body 201. In addition, the "passive" cooler may be actively cooled using forced convection or conduction (eg, fan, air jet or circulating liquid cooling system). FIG. 2E is a perspective view of the completed packaged light source 200.

Next, with reference to FIG. 3, a simplified schematic diagram of the light source 300 according to another embodiment of the present disclosure is shown. The disclosed light source 300 may be implemented to provide a wider bandwidth or multi-wavelength light output than the aforementioned embodiments shown in FIGS. 2A-2E. In an alternative thermal management configuration, the light source 200 is attached to the heat sink 301 using the TIM layer 302. The output collimated fluorescent beam 303A is filtered by an optical filter 304 such as a bandpass or tinted glass filter. The resulting collimated beam 303B is coupled with a collimated beam 305 of a secondary light source 306 such as a laser, LED, or any other light source such as another fluorescent light source similar to the light source 200. .. A beam combiner 307, such as a dichroic beam combiner cube, combines light from a light source 200 and a secondary light source 306. Additional secondary sources and beam combiners (not shown) can be added along the path of the collimated beam 303B. The finally coupled and collimated beam 303C can be used directly or focused on the spot 308 using the focusing lens 309. For applications that require fiber coupling, the input tip of an optical fiber (not shown) can be accurately positioned on the focal spot 308 in order to maximize the fiber coupled output power. Alternatively, in each of the exemplary embodiments disclosed herein, the condensing device, eg, condensing lens 309, is a parabolic mirror, a Fresnel lens, or any other refracting, reflecting, or diffractive optics. It may be provided by an element. The focusing device produces an image of the pumped position of the fluorescent body 201 at the focal point. The input tip of the optical guide, such as the fiber optic surface, may be aligned with the image position, i.e. the pumped position of the fluorescence body 201, in order to couple the output beam of the light source 200 to another device / position. can.

Next, with reference to FIG. 4, a light source 400 according to another embodiment of the present disclosure is shown. The light source 400 is similar to the light source 200. However, the light source 400 includes a second (lower) parabolic mirror 406 that provides the apparent position of the source, i.e., shifting the fluorescence body 404 to a position near the output window 409 of the package. This makes it possible to place a collimating lens 420 that collects and collimates the output fluorescence on the outside of the package to produce the collimated light beam 405E. The light source 400 also allows for direct fiber optic coupling in the top cover of the package, similar to that described below with reference to the embodiments shown in FIG. The upper parabolic mirror 401 and the lower parabolic mirror 406 are arranged so as to face each other. The upper parabolic mirror 401 serves two purposes. Like the light source 200 of FIGS. 2A-2E, the upper parabolic mirror 401 focuses the pump beam 402 of each pump laser diode 403 on a fluorescent body 404 formed of a fluorescent material. Compared to the light source 200 of FIGS. 2A-2E, the upper parabolic mirror 401 has a very small central aperture 401B and the full bandwidth (or selection) of the light emitted by the fluorescence body 404 in addition to the pump beam wavelength. It comprises an optical coating 401C that reflects the subband). The second purpose of the upper parabolic mirror 401 is to collimate the divergent fluorescence beam 405A. The reflected fluorescence beam 405B is collimated and directed at the lower parabolic mirror 406. The lower parabolic mirror 406 comprises a small opening 406A provided by a central hole in which the fluorescence body 404 is located. In particular, the fluorescence body 404 is located at the location where the apex of the lower parabolic mirror 406 should be located if the small opening 406A does not exist. The small central opening 401B generally has a diameter of less than 20% of the diameter of the guide circle. The guide circle is not specifically shown in FIG. However, the guide circle is at the midpoint of the circle of the pump beam 402 incident on the upper parabolic mirror 401, as illustrated by the guide circle 204B of FIG. 2B. The diameter of the small opening 406A provided in the lower parabolic mirror 406 is generally equal to the diameter of the small central opening 401B. For example, the diameter of the small central opening 401B and the small opening 406A may be 10% of the diameter of the guide circle. The lower parabolic mirror 406 includes an additional hole 406B through which each of the pump beams 402 is guided. For clarity, only one pump laser diode 403, the corresponding collimating lens 407, and a small aperture 406A are shown. In practice, a plurality of pump laser diodes 403 are distributed around the central axis of the system in an arrangement similar to that shown in FIG. 2B.

The fluorescent beam 405B is reflected by the lower parabolic mirror 406, resulting in a beam 405C focused towards the focal point 408. The pumped volume of the fluorescence body 404 is imaged by the lower parabolic mirror 406 at the focal point 408 of the lower parabolic mirror 406. The image provides a source of output divergent fluorescent beam 405D through the AR coated and hermetically sealed output window 409 at the center of the top cover 410 of the hermetic package. As mentioned above, the broadband HR coating behind the fluorophore 404 redirects the back fluorescence back through the fluorescence body 404 and binds to the output divergent fluorescence beam 405A. The fluorescence body 404 is mechanically and thermally coupled to the heat spreader 411 that supports the fluorescence body 404 at the center of the pump laser diode holder 412. The thermal management of the fluorescent material 404 is similar to the operation of the heat spreader 202 of FIGS. 2A-2E and can be cooled in the same way. The hermetic package is completed by a side wall 416 and a thermally conductive base 417. The thermally conductive base 417 is coupled to the heat sink and otherwise cooled directly, as in the light source shown in FIG. In the light source 400 of FIG. 4, the upper parabolic mirror 401 and the lower parabolic mirror 406 are fixed together at the interface 418 using an optical UV curable adhesive. The resulting dual mirror assembly is mounted on top of the pump laser diode holder 412 with a ring metal spacer 419 and suitable adhesive.

In the embodiment, the light source 400, the upper parabolic mirror 401 and the lower parabolic mirror 406 have equal focal lengths to image the fluorescent body 404 at a magnification of M = 1. Further, the focal points of the parabolic mirrors 401 and 406 coincide with the vertices of the opposing parabolic mirrors. The optical coating of the upper parabolic mirror 401 has two purposes. That is, it efficiently reflects the high power density pump laser beam (at least in each region), and the fluorescence emitted by the fluorescence body 404 efficiently over a large solid angle and suitable optical bandwidth. To reflect. The lower parabolic mirror 406 is generally used only to focus the fluorescence emission from the fluorescence body 404. Therefore, the optical coating on the lower parabolic mirror 406 may be optimized to reflect light only in the fluorescence emission bandwidth. The embodiment of the light source 400 is not limited to the illustrated structure of the mirror assembly. For example, another embodiment consistent with the operation of the light source 400 includes a single biconvex lens with appropriate coatings on both sides to provide an upper parabolic mirror 401 and a lower parabolic mirror 406. But it may be.

Next, with reference to FIG. 5, a light source 500 according to another embodiment of the present disclosure is shown. The illustrated embodiment is similar to the light source 400 of FIG. 4 (excluding the window 409 and the collimating lens 420) and is particularly suitable for compact fiber optic coupling of the output fluorescent beam. The tip of the input connector 501 of the optical fiber 502 is precisely aligned with the focal point 408 of the lower parabolic mirror 406 shown in FIG. Fluorescence is guided through the fiber optic 502 through the fiber optic 502 until fluorescence exits the output connector 503 of the fiber optic 502 and diverges freely as the output fluorescence beam 504.

The present invention has been shown and described in particular with reference to preferred embodiments thereof. However, one of ordinary skill in the art will appreciate that the forms and details of the aforementioned and other matters may be modified without departing from the spirit and scope of the invention.

Claims (22)

It ’s a light source,
A body that is formed from a material doped to have fluorescent properties when stimulated at an excitation wavelength, has a flat top surface and a convex back surface, and emits light in the emission band.
A collimating device that collects at least a portion of the light emitted by the body over the collection area and produces a collimated output beam.
One or more mirrors arranged with the focus axis directed towards the body and outside the collection area so that the collection area is not obscured by the one or more mirrors. With one or more mirrors with reflective surfaces,
One or more light sources that provide excitation light at said excitation wavelength and have corresponding one or more outputs directed at said one or more mirrors along one or more corresponding light paths. As a result, the one or more mirrors direct substantially all of the excitation light provided by the one or more light sources towards the body and stimulate the radiation of light emitted by the body. A light source, including one or more light sources. The light source according to claim 1, wherein the one or more mirrors comprises a parabolic mirror arranged so that the focus axis is directed toward the main body, and the one or more light sources of the one or more light sources. One or more outputs have outputs directed at the parabolic mirror along one or more corresponding light paths having a direction parallel to the focal axis of the parabolic mirror, and as a result, said. 1 The light source described. The light source according to claim 2, wherein the parabolic mirror includes a central opening through which the portion of light emitted by the main body passes through, and the collimating device is the parabolic mirror. A light source located in the central opening of the light source, characterized in that it collects at least a portion of the light emitted by the body. The light source according to claim 3, wherein the parabolic mirror is a first parabolic mirror having a small central opening, and the light source further includes a second parabolic mirror, and the second parabolic surface. The mirror is arranged outside the opening to reflect the light emitted by the body that is incident on the first parabolic mirror and directed at the second parabolic mirror and is emitted by the fluorescent body. A light source that exits the small central opening of the first parabolic mirror and increases the portion of light collected by the collimating device. The light source according to claim 4, wherein the second parabolic mirror focuses an image of the main body on an image surface, the light source further includes an optical waveguide, and the optical waveguide is the second parabolic surface. A light source having an input surface arranged on the image plane to receive the image of the body generated by the mirror. The light source according to claim 1, wherein the flat upper surface of the main body is roughened so as to scatter a part of the excitation light, and as a result, the portion of the excitation light is formed by the main body. A light source that is combined with the emitted light. The light source according to claim 1, wherein the flat upper surface of the main body is antireflection in the emission band with respect to an incident angle smaller than the Brewster angle, and the incident angle at the Brewster angle and the above. A light source coated with an antireflection coating that is antireflection in the excitation band at an incident angle near Brewster's angle. The light source according to claim 1, wherein the one or more light sources are a plurality of light sources arranged in a circular arrangement around the main body outside the protrusion of the central opening toward the main body. ,light source. The light source according to claim 1, wherein the one or more light sources and the corresponding one or more mirrors have the excitation light incident on the fluorescent body at an angle substantially equal to the Brewster's angle. The one or more light sources emit the excitation light with lateral polarization, and the one or more light sources are p-polarized when the excitation light is incident on the fluorescent body. A light source with a smooth rotation alignment. The light source according to claim 1, further comprising a heat spreader thermally and mechanically coupled to the convex back surface of the fluorescent body in order to remove heat from the body. The light source according to claim 10, wherein the one or more light sources are one or more laser diodes, and each substrate of the one or more laser diodes is mechanically and heat-heated to the heat spreader. Combined light source. It ’s a light source,
A body that is formed from a material doped to have fluorescent properties when stimulated at an excitation wavelength, has a flat top surface and a convex back surface, and emits light in the emission band. The flat top surface comprises a body coated with an antireflection coating that is antireflection in the emission band.
A collimating device that collects and collimates at least a portion of the light emitted by the body over the collection area.
A parabolic mirror with the focus axis oriented towards the body, provided by a central opening through the parabolic mirror so that the collection area is not obstructed by the parabolic mirror. A parabolic mirror with a reflective surface located outside the collection area,
A plurality of laser diodes that provide excitation light at the excitation wavelength and are arranged in a circular arrangement around the body outside the protrusion of the central opening toward the body, each of which is a plurality of laser diodes. The parabolic mirror has an output directed to the parabolic mirror so that substantially all of the excitation light provided by the plurality of laser diodes is focused on the body. Stimulating the emission of light emitted by the body, the plurality of laser diodes and the paradoxical mirror are arranged such that the excitation light is incident on the parabolic mirror at an angle substantially equal to the Brewster angle. The one or more laser diodes have a junction surface oriented parallel to the reflection surface of the excitation light in the parabolic mirror, and the flat top surface of the body is of the excitation light. The surface is roughened to scatter a portion, and as a result, the portion of the excitation light is coupled with a plurality of laser diodes coupled to the light emitted by the body.
A heat spreader thermally and mechanically coupled to the body to remove heat from the body, wherein each substrate of the one or more laser diodes is mechanically and thermally coupled to the heat sink. A light source with a heat spreader. It ’s a way to generate light,
A step of providing a body that is formed from a material doped to have fluorescent properties when stimulated at an excitation wavelength and has a flat top surface and a convex back surface.
A step of stimulating the body with one or more light sources producing a corresponding one or more excitation beams having a wavelength substantially equal to the excitation wavelength, with one or more corresponding mirrors. A step of directing the one or more excitation beams toward the main body and causing the main body to emit light in the emission band.
A method of generating light, comprising collecting and collimating at least a portion of the light emitted by the body by a collimating device to generate a collimated output beam. 13. The method of claim 13, wherein the one or more mirrors are parabolic mirrors, the parabolic mirror having a focus axis directed at the body and the one or more light sources. The output has an output directed at the parabolic mirror along one or more corresponding optical paths having a direction parallel to the focus axis of the parabolic mirror, and as a result, the parabolic mirror. A method in which substantially all of the excitation light provided by the one or more light sources is focused on the body. The method according to claim 14, wherein the parabolic mirror includes a central opening through which the portion of light emitted by the body enters, and at least a portion of the light emitted by the body is said to be. A method of performing collection by a collimating device arranged for collection at the central opening of a parabolic mirror. The method according to claim 15, wherein the parabolic mirror is a first parabolic mirror, and the method is a second parabolic mirror incident on the first parabolic mirror outside the opening. Further comprising the step of reflecting the light emitted by the body directed at the surface mirror, the portion of the light emitted by the body and collected by the condenser lens using the second parabolic mirror is increased. Method. The method according to claim 16.
The second parabolic mirror focuses the image of the main body on the image surface.
A method further comprising receiving an image of the body generated by the second parabolic mirror in an optical waveguide having an input surface disposed on the image surface. The method according to claim 13, wherein the flat upper surface of the main body is roughened so as to scatter a part of the excitation light, and as a result, the portion of the excitation light is radiated by the main body. A method of combining with the light that is made. The method according to claim 13, wherein the flat upper surface of the main body is antireflection in the emission band with respect to an incident angle smaller than the Brewster angle, and the incident angle at the Brewster angle and the above. A method of coating with an antireflection coating that is antireflection in the excitation band at an incident angle near Brewster's angle. 13. The method of claim 13, wherein the one or more light sources are a plurality of light sources arranged in a circular arrangement around the body outside the protrusion of the central opening toward the body. ,Method. The method according to claim 13.
The step of arranging the one or more light sources and the corresponding one or more mirrors so that the excitation light is incident on the fluorescent body at an angle substantially equal to the Brewster's angle. One or more light sources emit the excitation light with laterally polarized light,
A method further comprising the step of rotationally aligning the one or more light sources so that the excitation light is p-polarized upon incident on the one or more mirrors. 13. The method of claim 13, further comprising providing a heat spreader thermally and mechanically coupled to the convex back surface of the body to remove heat from the body.

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