TW201110489A - Folded lasers system - Google Patents

Abstract

A folded laser system having an optical axis, the laser system comprising: (I) a coherent light source; (II) a reflector; (III) a lens component situated between the light source and the reflector; and (IV) a non-linear optical crystal, wherein the light source and the non-linear optical crystal are separated by a distance d > 50 μ m. The lens component is positioned to provide a collimated beam when intercepting light from the light source, such that the collimated beam is at an angle Θ ' to the optical axis, the reflector is situated to intercept the collimated beam and to reflect the collimated beam to the non-linear optical crystal through the lens; and the lens component is structured to provide an image on the non-linear optical crystal.

Description

201110489 VI. Description of the Invention: TECHNICAL FIELD OF THE INVENTION The present invention relates generally to folding lasers and, in particular, to a folded laser system having a nonlinear optical wavelength converter such as a frequency doubled green laser. [Prior Art] Green laser light can be generated by nonlinear multiplication of infrared rays. In general, the light beam 2 from the infrared diode 3 as shown in Fig. 1A is directed to a nonlinear optical crystal 4 such as a periodically poled tantalum chain (PPLN), in which it is converted into green light 5. The challenges of creating this type of laser reality face are as follows. The first—because the small optical waveguide is used to limit the light of the diode laser and the nonlinear optical crystal, the alignment tolerance of the component (lens, nonlinear crystal and diode laser) is about tens of microns. This will reduce the initial assembly and the two battles of the county during the use of the laser. Second, the output power of a nonlinear optical crystal is sensitive to temperature fluctuations and the displacement of the laser that provides infrared optical wavelengths. The temperature gradient across the nonlinear optical crystal may result in a decrease in the output power of the green laser (i.e., the exit power leaving the nonlinear optical crystal). [Summary of the Invention]

The present invention is a light (four) financial laser system comprising: (1) a light source; (9) a reflective pupil; (a) a lens assembly between the light source and the emitter; and (10) a hybrid optical crystal, The light source and the non-^^ crystal are separated by a distance d > 5G_. When the light is intercepted from the light source, the lens assembly reduces the straight beam and the optical axis to form an image of the coherent light source on the nonlinear optical crystal. Let the anti-201110489 emitter pass through the fresh-spun strands and straighten the filaments to the nonlinear optical crystal. The same 5 week light source and nonlinear optical crystal are preferably separated by an air gap. According to some embodiments, the laser system is a green laser and the light source is infrared (the 11 〇 diode laser 'receiver is a nonlinear optical crystal such as a second harmonic generator (SHG) for converting IR light Green light. The green laser of the laser system embodiment of the present invention provides the advantages of optical components having relatively loose alignment tolerances; low sensitivity to heat generated by diode lasers; and improved diodes The light coupling between the laser and the nonlinear optical crystal produces a maximum green performance. Other advantages provided by this side are: minimizing the temperature gradient of the entire nonlinear optical crystal, and minimizing the arrival of the diode laser Optical feedback effects caused by unpleasant reflections and/or backscattering of the hybrid optical crystals. Other features and advantages of the present invention are disclosed in the following description, and some of the following descriptions can be clearly understood, the following descriptions and the scope of patents and The prior art is well understood and the detailed description of the τ column is for exemplary and illustrative purposes only, and it is intended to provide a summary or architecture to understand the patent application. The principles and features of the present invention are defined by the accompanying drawings, which are set forth in the accompanying drawings. In the drawings, the same reference numerals are used throughout the drawings to refer to the same or similar elements. The exemplary embodiment of the present invention is disclosed by reference numeral 10. The laser system 10 is a material having a stack of empty beams 22. In the radiation system 10, the light is taken out by divergent light and the source 2G emits light and is driven by a lens assembly 30. It is best to operate in a telecentric situation. It is also in the wireless, Tulu. - Lens assembly 3, so that the optical system's exit pupil position: encounter. The same 5 weeks light source 2 is preferably small (heart , relatively high power (> =, and adjusted at high (about 1 () MHz or higher). In this embodiment 'the light source 2G is an infrared (10) semiconductor laser (IR diode laser 2 〇,) Wave = body laser 20' includes a diode waveguide 2〇, The ir ray radiates from the output face of the diode/A with a divergent beam. The output w of the diode waveguide is formed perpendicular to the waveguide, or can be reduced at an angle of the waveguide axis (not traversed. The divergent beam 22 is The half-shape θ emitted by Ι/e2, such as money, is 2G degrees in the direction, and 7 degrees in the other direction (vertical). The average radiation angle provided by the radiation, half 幵ν Θ疋 relative to the homogenous light source (in the light beam The collimating (10) beam 40 is angled ' toward the reflector 50, and the reflector 50 is reflected back to the lens assembly 30. According to some embodiments, preferably 5 radians $1 〇. 2 radians, more preferably 〇. 〇9 radians g_' 〇. 17 radians/for example, the reflector 5〇 can be a planar mirror. The reflected beam is focused on the nonlinear optical crystal 7〇 via the f-mirror, and the member 30 is directed toward the image plane 60. The input surface of the body waveguide A (waveguide portion). That is, the lens assembly 30 provides an image of the diode exit 2G, the A wheel face, on the input face of the crystal waveguide 70, A of the nonlinear optical crystal 70. For example, the 'non-linear optical crystal 70' may be, for example, a second harmonic generator (SHG) of a periodically-polarized decanoic acid 201110489 clock (PPLN) crystal. Other nonlinear optical crystals can also be used. In this embodiment, the nonlinear optical crystal 7 is received by the IR light supplied from the lens assembly 30 and converted into green light 5. Lens assembly 30 preferably has a shorter focal length (preferably less than 5 mm, more preferably less than 3 faces, and even less preferably less than 2), and a low astigmatism to achieve a coherent light source 2 非线性 and a nonlinear optical crystal 7 〇, The optimal optical fit between the crystal waveguides 70, A minimizes (i) defocusing due to temperature changes, and (ii) the size of the entire laser system 10. The reflector 50 can be a conventional (fixed) planar mirror, or a mirror that is activated at a tilt/deflection angle, such as a microelectromechanical system (MEMS) mirror. The coupling of the light between the diode waveguide 2A, a and the crystal waveguide 70, A can be adjusted in two main ways. First, the position of the lens assembly 30 can be moved in the x, y, or z (focal length) direction. Second, the mirror 5 can be tilted. Since the mirror is in the collimating space of the infrared beam, the angle adjustment causes the crystal input surface to reflect and the position (x, y) of the focused beam to move. The nonlinear optical crystal 7 〇 (e.g., PPLN crystal) converts a part of the red = line emitted from the crystal waveguide 7 〇, A output surface into green light (® 1B). Thus, the position of the lens assembly 3〇 or the angle of the reflection II 50 is moved to shift the focus on the input face of the nonlinear optical crystal 7Q' crystal waveguide 7〇'.

In this example, the light source 2〇 and the receiver (nonlinear optical crystal 7〇,) are separated from each other with respect to the optical axis GA (the optical axis of the lens assembly 3g), and are placed symmetrically or nearly symmetrically with respect to the optical axis (from the axis of symmetry) Within 1 μm, preferably within ±5 μm). More specifically, in order to minimize the nonlinear optical crystal 7〇, the crystal waveguide 70, the aberration of the beam on the A input surface, the infrared diode 2〇, the second: 6 201110489 the output surface of the bulk waveguide 20' A and The nonlinear optical crystal 7〇, the crystal waveguide 7〇, the input surface of A is separated by a small air _, and the focal length of the lens assembly 3{) is smaller than the distance d (i.e., d "f). Preferentially, the focal length f of the lens 3Q is i ^ 1 mm, 1. 3 mm, 1. 5 mm, 1. 7 mm, 2 mm, or 2.5 mm. Preferentially, source 20 and nonlinear optical crystal? 〇, the separation between the 30 micron SdS 1500 micron, more preferentially 5 〇 micron micron, more preferentially 100 彳 SmS 600 micron, more preferential 15 〇 micron; 500 micron and most preferentially 300 micron $ dS500 micron. For example, the distance d is 75 microns '100 microns, 125 microns, 150 microns, 2 microns, 250 microns, 300 microns, 400 microns, or 450 microns. Thus, in this embodiment the source (diode laser 20') and the receiver 7〇 (nonlinear optical crystal) are eccentrically with respect to the optical axis along the γ axis to a distance d, = d/2, for example d, =d/2±1〇〇U meters. Preferably, the eccentric distance d' is equal to d/2 or within 50 microns of d/2 (i.e., d' = d/2 ± 50 microns). The finger-studded laser system design described here (see, for example, Figures 1B, 2, 6, 8A, and 8B), because the light control itself folds, has the ability to reduce the entire length of the laser cavity (and thus reduce the size of the laser set). advantage. Because the same lens assembly 3 is used twice, once is a collimated beam, and once is a refocusing beam on the input face of a nonlinear photon 曰 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 The effect of asymmetric optical aberrations produced by the lens assembly 3 is minimized. With stable and precise technology, the laser system 10 can be completely passive (ie, without moving components). (This design is shown in Figure 1〇). Alternatively, as described above, the laser system 10 can easily utilize an adjustable reflector such as a MEMS mirror to actively align the 201110489 focal beam on two laterally transposed surfaces of the PPU. Folding design can create many challenges. First, because the fold-type laser system design utilizes a light source (-polar laser 20) and a linear crystal 7() that are separated from the optical axis of the lens assembly 30, presenting _ optics, the difference may be controlled . Bixian holds a small amount of silk aberration to achieve the height of the 2G' 彳 nonlinear optical crystal 7()' from the diode laser. The superiority of the green laser embodiment 1G of the present invention maintains a small off-axis aberration even if the lens assembly 3() is not aligned. Second, the diode laser 2G, which is in close proximity to the nonlinear 'light to the body 70, may also cause heat from the diode laser 20 to be transmitted to the nonlinear optical crystal 7'. Thermal gradients in nonlinear optical crystals reduce the conversion efficiency from infrared light to green light. Since the diode waveguide 2〇' A of the diode laser 2〇_ and the nonlinear optical crystal 70, the crystal waveguide 7〇, ^ are separated by the air gap AG, the advantage of the green laser embodiment of the present invention is that it is the most Mb The heat transfer of a polar body laser to the crystal. Third, embodiments that move at least some of the laser system by moving the reflector ^ or lens assembly 3 do not require a jack to control the focus of the beam. Embodiments of these laser systems 10 do not lose focus (or have minimal out-of-focus) nor significantly change the lateral positioning of the optical element_temperature_number (or otherwise compromise the crystal waveguide 70' A input face and diode The age of the wire between the waveguides 20' A may deplete the optical output power). The embodiment of the 'post laser system 1' can also have ship control or minimize the _ of the optical feed. For example, in the green laser implementation example described herein, the reflection of the front side of the non-optical optical crystal crystal waveguide 7G' A does not cause an unpleasant hopping behavior from the infrared diode laser 2G. 81 2 shows the light installed in the embodiment of the green laser system 10. 201110489 Learning component ° Nonlinear optical crystal 70, (PPLN crystal) placed above the diode laser 20', separated by a small air gap AG The ends of the two waveguides 70, A, 20'. The presence and size of the air gap AG is important and there are several reasons for this. First, one or more wire bonds 23 are added to each section of the diode laser 2' to provide current and voltage control signals to the diode laser. These weld lines form a loop 23 having a minimum bend radius, extending above the diode laser 2 以, at a limited height. The minimum wire loop height can be, for example, 100 micrometers to 150 micrometers, defining an infrared diode laser 2 〇, a diode waveguide 20 A and a nonlinear optical crystal 7 〇, a crystal waveguide 7 〇, between eight The smallest possible vertical spacing. " First, the air gap AG thermally insulates the nonlinear optical crystal 7〇' and the diode laser 2, which acts as a heat source during operation. In particular, air and metal or many other solid materials can be used as a good thermal insulation to avoid the diode-converted non-linear optical crystal 7G. Since heat generates a thermal gradient in the nonlinear light: the body 7G, thus adversely affecting the non-I·n conversion of the crystal waveguide claw A, it is preferable to prevent the heat from reaching the nonlinear optical crystal 7〇. 5 months, the nonlinear optical crystal 7〇, the thermal gradient inside may be harmful

The ratio of the wavelength of the green output is a function of sin(x)/x (the uniformity of the body waveguide % A) is roughly the same as the wavelength of the inner crystal waveguide 70, A. ), while the thermal gradient will twist the function. (Note that the symbol X is the paper indicating the wavelength A and the optimum wavelength, and the model, which shows how the heat in the laser system similar to that in Fig. 2 is transmitted from the diode laser. Figure 3 shows the thermal model of the detail of the diode laser 20 separated by the air gap 201110489 gap, and the cantilever nonlinear optical crystal 7〇. Although the diode laser is 2 〇, it is used as a heat source, as shown in Figure 3. As shown, the air gap AG thermally insulates it. The diode laser is supported by a metal socket base. As shown in this figure, almost all of the heat generated by the diode is directed to the metal socket base. Say, although the exact thermal conditions are based on the material and the specific design, due to the relatively high thermal resistance of the air gap, this model shows that heat can be effectively extracted by any metal contact and does not come from the diode, the laser 20 'Through the nonlinear optical crystal 7〇. The experimental data also confirmed that the conversion efficiency of the hybrid optical crystal 7() is not deteriorated by the thermal effect due to the presence of the air gap AG. Third, the two waveguides 7〇 , A, 2〇, A should keep the distance as much as possible Small, because the larger distance requires the output face of the diode waveguide or the nonlinear optical crystal 70, the crystal waveguide 7〇, the input face of A, or both, is truly opposite to the optical axis (Z-axis) (4)). In general, the optical axis of the lens assembly 3〇 is located halfway between the two waveguides 70, A, 2〇' A. This provides optical coupling of the light between the two waveguides 70' A, 20, A, and also allows the active mirror (providing the active mirror to be used) to be centered in the starting range so that the tilt of the mirror can be used to compensate for the small size of the waveguide mobile. (For example, these movements occur due to changes in temperature and humidity). The farther away from the optical axis of either of the two waveguides, the more the optical aberration occurs in the input of the crystal plane 7(), a input plane t of the nonlinear optical crystal 7G. Such aberrations include astigmatism, ^ difference', and spherical county. Figure 4 shows an example in which the two waveguides are shown, and the contact efficiency between turns is reduced as the vertical distance from the γ axis increases. When the distance d increases, the optical aberration will distort the beam. In 201110489 A, the power between 2G'A will become smaller. Since the lens element has an image with less optical aberration, when the image and the object are moved by the same distance d', a way to minimize these aberrations is a long focal length lens assembly. However, we try to keep the size of the second laser set, which we must try to use the shortest distance =. The focal length of the woven lens assembly 3 可 can be _ in the 曰 body. = 川, that is, the lens element 3 〇 preferably has a short focal length, providing a minimum amount of aberration in the body wave _ A input surface, Wei 2 The higher _ combined performance determines the two waveguides 7(), A and spacing. (Please note that due to the dipole laser 2, the second = the peak age in Figure 4 is known, micron instead of zero (no gap)

Preferably, the micro-flat spacing is greater than 5G microns, but less than · 诚木' is preferably less than 700 microns. When your lU A is about 1. 5mm, 15G micron to 45G micro = component 3G focal length is . (When the distance d follows the paste (4), the good mine is larger or smaller than the (4) distance f is less than (10) micrometers. The smallest _ is the inter-electrode bond line back (4), the adaptability can be placed in the nonlinear Outside the optical crystal, the crystal waveguide is 7 〇, A is not layer 2 =:: = micron thick taste, the waveguide... is shown in layer 70c, and the crystal between them may be the minimum required for the Naoma 201110489 bond wire 23 The distance is set. For example, if the wire loop 23' requires a height of 150 microns, if the nonlinear optical crystal 7〇 has a cap layer 70' B of j〇〇 micron thickness, then the minimum waveguide spacing distance d (center) To the center) 疋 350 μm (200 μm + 150 μm = 350 μm). The maximum waveguide distance d is mainly determined by the optical aberration of the lens assembly 30 because of the relationship between the two waveguides 70' A and 20 ' A The optical coupling efficiency is reduced as the distance d increases. Alternatively, the nonlinear optical crystal 70' need not be placed above the diode laser 20'. Instead, the nonlinear optical crystal 7〇 can be placed on the pole Body laser 2 〇, on both sides. This side is designed against the side Shown in Figure 6. The advantage of this design is that it allows for a larger vertical space of the laser bond wire 23. However, since the structure of the diode laser has a predetermined width (about 3 〇〇 micron), the two waveguides In general, a larger width is required. In addition, the crystal waveguide 7〇'A may not be located at the edge of the nonlinear optical crystal 7〇'. When using the design of Fig. 6, in order to avoid thermal crosstalk, in the diode laser An air gap AG should be provided as a separation between the nonlinear crystal and the side. The design of the side edge against the side is very similar to the design shown in Figure 2, except in this embodiment, the diode laser 2 〇, and The linear optical crystal 70' is rotated 9 degrees so that the separation is horizontal (X-axis) rather than vertical separation. A small air gap AG is used to ensure the diode-ray 20' and the nonlinear optical crystal 70, Thermal isolation between the two. The green laser system shown in Figure 6 also has this advantage, allowing the system to operate along the diode's laser-valued aperture or horizontal direction (ie, the beam 22 along the X-axis ratio). There is less divergence along the y-axis, making the image Slower than the vertical axis • Optical surface combination. These instructions are shown in Figure 7. More specifically, Figure 7 shows the coupling performance versus waveguide spacing for two different 2011 10489 different laser system designs. The linear optical crystal 70 is placed above the laser 20 (along the gamma axis) as shown in Figure 2 (see curve CC), while in another design (ss), the nonlinear optical crystal 70 is located near the laser 2〇, (along the X axis), as shown in the side of Figure 6 with the side design shown. The circular line corresponds to the design of the side edge against the side, and the rectangular line corresponds to the cantilever Design. Because the numerical aperture of the beam 22 of the diode laser is small (less divergent) in the horizontal direction, the side of the side of Figure 6 is designed to be larger than the cantilever of Figure 2. Higher coupling performance. Thus the side edges are designed to allow for the same fit by allowing the larger spacing d' between the two waveguides. Preferentially, the side is further moved against the side, preferably with a non-linear optical crystal 7〇 mounted from the top surface, i.e., the surface furthest from the waveguide corresponds to the top layer c of the nonlinear optical crystal 70. This is illustrated in Figure 8A (side view) and 8β (input diagram). The advantage of this top-mounted technology is that the same laser system can be used interchangeably with a variety of cap thicknesses (the distance between the crystal waveguide and the bottom surface of the nonlinear crystal) linear optical crystal 7G. The benefit of this interchange (iv) is that it allows the use of non-linear optical crystals 70' from the same source (locker), which have different cap thicknesses due to different manufacturing techniques. As long as the nonlinear optical crystal 70, the spacing d between the top and the diode lasers 2〇' does not change, the diodes 20, the -2 2' of the polar body material and the crystal waveguide A of the non-hybrid optical crystal 7 The interval between the two will also be fixed in the county. _Wei's erecting can also be used on the side shown in Figure 6 against the side mounting design, the crystal mounting surface is the farthest surface from the diode laser. Also 201110489 Figure 1B, 2, 6' 8A and 8B shows the optical path length between the laser system 20 (diode waveguide 2〇, the output surface of A) and the receiver her day: ^ There are two and two poles = the length of the light melon. The sail is also x Ni, where Di is the distance between the surfaces of the different elements 'Ni is the refractive index between these surfaces). That is to say, the laser system 1 所示 shown in FIG. 1B, 2' 6' 8A and 8B is designed to operate in the case of a light-combined cavity to make the diode 2 in the diode 2 (), the diode waveguide 2 (a) The output surface and the nonlinear optical crystal 70, the crystal waveguide 7Q, the cavity formed between the A input faces and the diode laser cavity have the same optical path length. _, for example, if the diode length of the diode is 2 〇, the length of the optical path of the A is 9. 5 mm, then the length of the optical path through the laser system 1 (from the light source to the receiver) deer 9 . 5 coffee. Therefore, if the light source 20 is a diode laser, the optical path length (0PL) from the light source lens assembly 30 to the reflector 50 via the lens assembly 30 is 1/2 of the 〇PL passing through the diode waveguide 2G' A. The advantage of this design is to minimize the instability of the laser wavelength caused by the parasitic reflection of the A input surface from the nonlinear optical crystal 7〇'. Preferably, the lens assembly 30 is used to collimate the diode laser 2, provide IR light, and refocus the light onto the nonlinear optical crystal 7A, the crystal waveguide 70 A. The lens unit 30 is at an amplification factor m, and the plane of the diode waveguide 2A is formed on the input surface of the body waveguide 70A. Preferably, 〇. gg丨Μ丨1 is better 疋0. 95 S I μ丨$1. 05. The numerical aperture NA of the lens assembly 3 最好 is preferably between about 0.35 and about 〇. 6, the focal length is from 1 mm to 3 faces, and the front end operating distance _) is 3. 3 mm to 3 mm, the back end operating distance (10)) It is 〇. 5 coffee to 3mm. The FWD is the distance from the light source 20 to the front end surface of the lens assembly 3 along the optical axis (201110489 is the lens surface facing the light source). The excitation is the distance from the lens surface S2 to the reflector 50. The reflector 5〇 is preferably placed on the rear end focus surface of the lens, and the direction of the average emission angle (beam center) of the light source 2 is parallel to the average beam scale on the receiving H 70 (corrected parallel by the nonlinear optical crystal 7G' The face-to-face matte dance towel ^) can be optimally optically coupled. 'If the light source 20 provides the largest half-shape θ of the divergent beam reflector 5 〇 is best placed on the ( 4 front 职 4 job surface, the direction of the storage 2 () average emission angle is parallel to the average spectacles on the emission ϋ . Preferably, when the centrifugal light source is in the focal plane of the lens assembly, the lens assembly 3 is constructed from the axis 75 () micrometers or more (Ux lifts the straight beam, so that the angle of the collimated beam is one, (relative to the surface of the reflector) Line) is: 〇. 05 radians $θ, ^0. 2 radians. The example lens assembly 30 is constructed to provide an image of the light source on the receiver. The characteristics of the image are (1) when the optical axis of the permeable member is the axis of Jingneng. (the center line between the two waveguide faces), or the average emission angle of the opposite light source (~ in the beam) / when there is misalignment, the astigmatism phenomenon is more than 〇. 〇5 wave legs, and less than 〇. 1 wave RMS And (ii) when the lens assembly is tilted by 2 degrees with respect to the average emission angle of the light source, the astigmatism of the inclination angle of 2 degrees is less than 〇. 05. Therefore, it is useful to use the lens assembly 3 even if it is laser. The system i〇 is not aligned during assembly (such as slightly tilting or centrifugation), and the receiver's upper wavefront error (view) is S0.1, where ^ is the central wavelength provided by the source 2〇. Note that the astigmatism The phenomenon can be generated by (1) the wedge body in the lens assembly '(11) the surface of a certain lens component The centrifugation, or (iii) the inclination of a certain surface to each other. 201110489 Preferably, the embodiment of the lens assembly 30 described herein is optimized to allow the diode laser 20' and the crystal waveguide with minimal coupling cost. A relatively wide air gap AG between 70, A. That is, even if the output face of the diode waveguide 20'A and the input face of the crystal waveguide 70' A are separated by a considerable distance d, the lens assembly 30 remains high. Since the optical path is folded and only one lens assembly 30 is used, the object (diode waveguide 20' A output face) and the image (position on the crystal waveguide 70' A input face) are the light leaving the lens assembly. Axis. As discussed above, lens assembly 30 is preferably designed to have low astigmatism (e.g., between 0.01 λ and 〇. 1 λ, where λ is the wavelength provided by the polar laser 2 〇 ') To provide the most small distortion of the beam spot on the off-axis image plane of the waveguides 20, Α, 70, 。. Figure 9 shows the achievable wear efficiency (CE) of the various commercially available lens assemblies to the LD-SHG vertical Comparison of distances. First 'example lens assembly (lens# 1) The lower dispersion of the waveguide is caused by the lower astigmatism than the second example lens assembly (Lens #2). Two different lens-to-mirror distances (BWD) can be deleted by 2mm and 2.3. The light-weight curve of the first lens assembly is calculated. In addition, lens assembly 30 is preferably a shorter focal length to minimize the length of the laser system (mirror 50 and two waveguides 70' A and 20, The distance between A is approximately two focal lengths. Further, the short focal length lens assembly 30 is less out of focus than the long focal length through mirror assembly 30' as a function of temperature. In the first approximation, the temperature causes the lens The approximate value of the focal length of the lens caused by the change in the refractive index of the component 30 is df / dT = - (d - T ) [f / (n - l)], where f is the focal length, n is the nominal refractive index of the lens material, and dn / dT is the change in temperature of the refracting surface. Therefore, the shorter focal length lens assembly provides a movement in the focus position (less than df/dT) than 201110489. Therefore, the focal length f is preferably less than 5 mm, more preferably 'and even more preferably 1 mm. Finally, it is best to choose a lens material with a lower dn/dT value. Although the large distance between the lens assembly 30 and the mirror 5〇 (ie, the back end, the distance BWW is about a focal length, the exact choice will be affected by several other exams. The first consideration is from two Polar laser beam emission angle (the average emission angle of the beam 22, or the angle of the beam center). If the one-pole waveguide 2〇'a has an uneven split surface, the emitted light is easy. The emission is a few degrees above or below the z-axis. This means that the best BWD is said to be slightly different from a focal length, so that the reflected beam enters at an optimal angle (perpendicular to the input face of the crystal waveguide 7G'A). The skin guide 2G, the input face of A. For example, as shown in Fig. 10A. However, the asymmetry of the optical system causes the tight end of the alignment tolerance of the two waveguides 7〇, A, 20' A, and The lens το member 30 places the tightness of the tolerance. If the emission angle of the lightning beam 22 is not parallel to the optical axis, then the laser system can remain symmetrical, and is telecentric (10) 1 〇 B), causing the positioning of the two waveguides 7 〇, A, 20, A is looser tolerance. Therefore, it is preferable to set the emitted IR beam 22 parallel to the lens optical axis of the lens assembly 30. This can be achieved by erecting a diode laser 2G' at an angle 如图 as shown in FIG. In this embodiment, the erection angle θ = 3. 3 degrees and the cap layer is 2 〇〇 micron thick. By ensuring the proper angle of incidence of the input face of the crystal waveguide 7〇'a, this design increases the amount of coupled light at the same time and broadens the alignment tolerance of the optical system by making it telecentric. • The second consideration for choosing β WD is to set the path length of the cavity between the diode laser output face and the crystal • waveguide 70'A input face to be equal to the length of the diode 201110489 body waveguide itself. The frequency mode interval of the cavity is formed by reflection from the back of the crystal itself. The performance of the hybrid conversion process is a function of the IR laser wavelength (frequency Δ λ approximately m). This makes the green output power of the laser system sensitive to small wavelength variations of the IR light provided by the diode laser 2G'. Since the diode laser is very sensitive to a small amount of feedback, the input face of the crystal waveguide 70'A is an anti-reflective coating, and the splitting angle is minimized to reflect, and thus to the diode laser 20, feedback of. Even so, there is still enough reflection and backscatter to affect the die-off choice of the diode laser 20. If the change in the thermal or other environmental changes in the cavity formed by any optical component of the laser 1G is a function of time, then the diode laser 2G may experience a surface jump and the output of the laser system Power (green light output power) also fluctuates. The way to minimize these shocks is to make the oblique cavity (the (four) body waveguide 70, the A input face and the polar body waveguide 20' A output face) is about the same free frequency span as the diode laser itself. The formula of the column of the face or optical cavity is determined: h Δ Afsr = A2 / (2nL) : the acoustic two * as the IR wavelength of the diode laser) is as long as the length (the length of the Yang diode waveguide), "It is the cavity (10) refracting the diode laser formed by the -pole laser 20' (4)). : = Long InGaAs infrared diode Lei Yi

=, force 疋〇 6nm. This means that in this embodiment, the required 〇pL between the output faces of the crystal waveguide body waveguide 20' A can be achieved by using the lens assembly 3G of the cut-off distance f of 1.5.

Figure 12 shows two different example lens assemblies, the length of the dipole waveguide 20, A and the crystal waveguide 70 A as a function of _ (lens to mirror spacing or distance). The required optical path is 9.36 mm, matching the cavity spacing of the diode 20 . Figure 13 shows the coupling effect of the same two example lens assemblies as a function of BWD. As shown in Figure 13, only a small adjustment (hundreds of micrometers or less) of BWD and an optimum coupling distance are required to produce the optimum path length. For example, Figure 13 shows an interval providing 〇 pl = 9.36 mm. EXAMPLES The present invention is further illustrated by the following examples. Example 1: Figure 14 illustrates the lens assembly 30 shown in Figure 11. In this embodiment, the lens assembly 3 of Figures 2 and 3 is optimized to provide a soil 2 〇〇 micron field with a root mean square '(RMS) less than 〇. u wavefront error at _nm wavelength, 〇. The numerical aperture μ, the focal length and the thickness are added such that the optical path length between the light source and the receiver is 9.36 mm 〇 selectable radius of curvature (1·), n), thickness Th (point to point), and aspherical surface of the lens assembly 30. Coefficients to: 2 彗 彗 aberration and astigmatism (two (four) 'the worst performance aberrations of the system'); = larger field of view: low field aberrations and larger apertures (such as (4). 4), shot The system has a good separation performance between the waveguide portion of the diode laser 20 and the waveguide portion of the nonlinear optical d (4)% 1 wood has good coupling performance; and the appropriate combination of distance and thickness allows the laser system Ι〇 operates in a cavity to form a cavity between the 20' turn of the diode laser and the input surface of the nonlinear optical 201110489 crystal 70' (such as the SHG body), and two The cavity of the polar body has the same path length. As described above, the lens assembly 30 has a front end surface S1 and a rear end surface S2. The crucible surface si is preferably convex and aspherical, and the radius of curvature is the gate. The rear end surface S2 is also preferably a convex surface and an aspherical curvature radius L2, so that the lens assembly 30 of the I η I > | r2 I 0 ' diagram has the following characteristics: (1) the case where the laser is a county cavity Operation (the 〇PL between the two optical crystals is equal to the 仏1 of the length of the diode laser): 〇PL=(0. 9mm+l. 744mraxl. 5+l. i8mm)x2=9> 3 · shot and 05 Between the equalizer diode length · u 744mmxL 5iL 18ram) x2 = 9 · 39m ^ · ^ the rate of 1. 5 two 76mm; (1V) at _nm lower the effective diameter of the S2 is 2 cut ground It is 2. 5 coffee to 3mm. Outside the lens assembly, the surface illusion and the surface sagging of S2 are represented by the following formula: z = one cxr2

+ al: ^a2xr4 + α3χ〆

Where C + 〇r4xr8 + . is the conic coefficient ^ rate radius, r is the radial distance from the center of the member and k is the surface parameter of the lens assembly 3 图 shown in the following table i. 20 201110489 Table 1 Parameter S1 S2 Radius 1.716884 -1.193855 k -7.316630 -0.795432 αΐ 0 0 α2 0 0 α3 0 4.107084.10-3 α4 0 1.121478.10-3 a The effect of the lens assembly 30 of the 牡 由 10 For restaurants and the use of greens, the two examples of the spheres are aspheric = lunar, (1 and 2) performance. As described above, the infrared ray = the exit surface and the nonlinear optical crystal 70, the front side of the waveguide = . Figure 15 shows a lens assembly 3G__test that has a higher efficiency than an aspherical lens that can be transmitted by two g. Example ^, the polar body 20' waveguide wheel exit surface and the nonlinear optical crystal? ^^ 疋 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 450 : When the d value of the meter is maintained, it is maintained at about 9.嶋二冋样地,#External line: pole (four), the output of the waveguide is ^7〇, the front of the waveguide is at the distance of the micrometer, when it is opened, ^ and = maintains the best performance of about _ or above, while the other two The lens is only = d _ in the micro-forest 27 ,, the maximum light-weight 30 in the maintenance position, and the other is suitable for the example lens assembly 3 雷 in the laser system. The lens assembly 3G of Fig. 16 has the following characteristics: (1) Let Ray (four), the system is the laser between her working body and the laser of the 201110489 nonlinear laser system; η. 4 in the pole Body laser length +/-0.05. Refractive index A, (111) focal length: f = 1. 4 mm; (1 V) refractive index of 1.674 at 1 G6Gnm; (v)na=〇.4〇 . The surface parameters of the lens assembly 3A of the main diagram 16 are shown in Table 2 below. Table 2

Example 3 Figure 17 shows an example lens assembly 30 suitable for use in a laser system 10. The lens assembly 3G of Figures 2 and 3 has the following characteristics: (I) The laser system is operated in the case of a coupling cavity (the sail between the diode laser and the nonlinear laser system is equal to the diode laser) The length of the 仏〇. 〇5 mm); (Π) has the following parameters: (i) FWD = l. 〇 lmm; (ii) thickness Th (vertex to page) is 1. 578mm; (iii) focal length: f = i. 789 mm; (iv) refractive index of glass at i 〇 6 〇 nm is 15; (v) na = 〇. 4 〇. 22 201110489 Figure 3 The surface parameters of the lens assembly 30 are shown in Table 3 below. Aspherical parameters Droop = C h. (丨+((丨 _(1+K)xCA2xhA2))A〇 5) +A4hA h; radius 1

·· +A16hA16

Optimization of the lens assembly: The traditional way to optimize the lens system is to place all of the optical components in their nominal position, and the optical design can best optimize the area minimum or in order to maximize the tolerance of the positioning optical components. Probably large, the usual way to optimize is to minimize the aberrations in the intermediate space (ie between the optical components). In the general optimization period, the lens designer tries to confirm that in each After providing the optical work surface wire, (4) is as close as possible to the beautiful (spherical or planar) wave front. Some of the limitations on the Seidel coefficient (aberration) can be achieved by optimizing the space between the functional pins (space between different surfaces and optical components).

By applying this method to the folding design, we get the best results in the case where the diode is irradiated to ppLN 23 201110489 and the distance d of the crystal is G. 5 ug or more. Unfortunately, the design of the __ surface is very rigid in manufacturing and assembly positioning tolerances. The most severe possibility is that the tilt of the lens assembly is limited to about 1 degree. The slight tilting of the impact on the lens assembly 30 or the mirror 50 is mostly due to the fact that both the dance aberration and the astigmatism county will result in a reduction in the efficiency of the θ (lower between the diode laser and the nonlinear optical crystal) Performance _ combined). Figure 18 shows the evolution of lens aberration and lens tilt, more specifically the entire wavefront error (10), as a function of the tilt of the example lens assembly 3G. In this calculation, the distance d between the fine σ _ crystals of the diode is kept constant .35 faces), and the value of each oscillating slope is adjusted. When the tilt increases, the amplitude of the coma (C) and the astigmatism (4) (the aberration of the master) increases. As a result, when there is no tilt, the wavefront error increases rapidly as it increases. F hanging - pretty In order to relax this tolerance, we try another optimization method. Secondly, the lens assembly is optimized, and its shape and asphericity are very similar to those of the first lens assembly. However, the tolerance analysis indicates that the lens is tilted and the mirror angle is relaxed by one-fifth. To understand how to relax the tolerance, we calculate the image as a function of the tilt of the lens. Fig. 19 also illustrates the lens aberration and the astigmatism phenomenon when the tilt is zero: this (A) is not at the minimum value, and the 岐 lens _ obliquely increases when it is increased. ^本上; This means that when the money of the money is not tilted in its standard (four) ❸ ❸ ❸ 提出 - some residual astigmatism phenomenon, when the tilt of the lens increases, compensate for the astigmatism phenomenon. 24 201110489 , the result is that the total aberration is relatively flat at a wide range of lens angles. In other words, the nominal design accommodates a wider range of positioning tolerances. Figure 2 shows the coupling performance calculated by the two designs (Lens Design #1 and #2). The tilt of the lens and the tilt of the mirror. As we have seen, when the component is in its nominal position, the tolerance is improved and does not have a significant effect. σ This analysis shows that the tolerance of positioning can be dramatically improved by using some residual astigmatism in the design. This astigmatism compensates for the astigmatism that occurs when the elements are aligned, allowing the system to accommodate more positioning tolerances. It is apparent to those skilled in the art that the present invention is capable of various changes and modifications without departing from the spirit of the invention. The present invention encompasses various changes and modifications of the present invention and is made in the following application and in the equivalents. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A shows a prior art laser system. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a pictorial representation of a folding laser system in accordance with one embodiment of the present invention. 2 is a folded airborne laser system in accordance with one embodiment of the present invention. Solid 3 is ..., simulation, which shows the heat conduction between the nonlinear crystal of FIG. 2 and the diode laser. ▲ Figure 4 shows the change in optical fit efficiency between the diode waveguide and the crystal waveguide as a function of the waveguide-to-waveguide spacing d; Figure 5A shows a cross-sectional side view of an exemplary nonlinear crystal; 25 201110489 Figure 5B shows 5A is a cross-sectional end view of an exemplary nonlinear crystal of FIG. 5A; FIG. 6 is a cross-sectional view of a folded cavity green laser system in accordance with another embodiment. Figure 7 shows the coupling efficiency of two different laser system configurations versus the waveguide spacing cl. The diagram shows that in another embodiment the nonlinear optical crystal is mounted on a diode laser. Figure 9 is a graph showing coupling efficiency (CE) that can be utilized with commercially available lens assembly 4 in some embodiments of the invention. Figures iOA and 10B show a folded cavity green laser system of two exemplary embodiments. Figure 11 is a cross-sectional view of a lens assembly, a crystal waveguide, and a tilted diode laser waveguide in accordance with one embodiment of the present invention. Figure 12 is a graph of optical path length versus back end operating distance for two exemplary lens assemblies. 〃 Figure 13 is a graph of the efficiency and back-end operating distance. Figure 14 is a cross-sectional view of a lens assembly in accordance with an embodiment of the present invention. With the miscellaneous (four) - item real paste, the business is profitable: and the face-to-face performance and the waveguide component pitch relationship. Figure. Θ 16 If the domain of the invention is another item, the section of the ship 实施 is implemented. The cross-section of the lens assembly according to another embodiment of the present invention, such as aberration (wavefront error), evolves as a function of the tilt of the exemplary lens assembly 26 201110489. Figure 19 shows the evolution of aberrations (wavefront error) as a function of the tilt of the exemplary lens assembly. Figure 20 is a plot of the efficiency curve for the tilting of two exemplary lens assemblies. [Description of main component symbols] Beam 2; Infrared diode 3; Nonlinear optical crystal 4; Green light 5; Laser system 10; Light source 20; Diode laser 20, Diode waveguide 2A ; beam 22; bond wire 23; wire loop 23; lens assembly outer collimated beam 40; reflection H 50; image plane 6 〇; receiver 7 〇; linear 曰 body 70; crystal waveguide 70'A; cap layer 70, B; top layer 70, C. 27

Claims (1)

201110489 VII. Patent application scope 1. A folding laser system with an optical axis, the laser system comprising: (I) a homology light source; (Π) a reflector; (111) a lens between the light source and the reflector And a (IV) nonlinear optical crystal in which the light source and the nonlinear optical crystal are separated by a distance d &gt; 50 microns and an air gap; wherein: (a) when intercepting the light from the light source, positioning the lens assembly to provide collimation a beam such that the collimated beam and the optical axis are at an angle, (b) the reflector is placed to intercept the collimated beam through the lens, and the collimated beam is reflected to the nonlinear optical crystal; and (c) the lens assembly is constructed to provide An image on a nonlinear optical crystal. ', 2. A folding laser system with an optical axis, the laser system comprising: (I) a coherent light source; (Π) a reflector; (III) a lens assembly between the light source and the reflector; IV) a nonlinear optical crystal in which the light source and the nonlinear optical crystal are located symmetrically to the optical axis, and the separation distance d &gt; 5 μm and the air gap are separated; 'where. (a) when the k light source intercepts the light, positioning a lens assembly to provide a collimated beam such that the collimated beam and the optical axis are at an angle, (b) the reflector is placed to intercept the collimated beam via the lens, and the collimated beam is reflected to the nonlinear optical body; and (c The lens assembly is constructed to provide an image on a nonlinear optical crystal. ' 28 201110489 3. A laser system according to the scope of claim 2, wherein the coherent light source is a diode laser, and the nonlinear optical crystal and the diode laser are tilted relative to each other. 4. A laser system according to claim 1 wherein the nonlinear optical crystal is a cantilevered diode. 5. According to the laser system of claim 2, the homophone source is a diode laser and the crystal surface of the nonlinear optical crystal diode laser is fixed. d < 1500 microns. d$500 microns. 150 micron 6. According to the laser system of claim 2, 7. The laser system according to the scope of claim 6 of the patent application, 8. The laser system according to the scope of claim 7 of the patent, which is 500 micrometers. 9 production according to the application of the detailed description of the two items of the laser moth f county characteristics is that the astigmatism phenomenon is more than 〇. 〇 5 wave warfare and less than Q chop brain. m. The laser system of claim 2, wherein the reflector is located in the focal plane of the =, so that the average direction of the light source (four degrees) is parallel to the average beam angle on the receiver. The patented 丨 之 则 则 统 透镜 透镜 透镜 透镜 透镜 透镜 透镜 透镜 透镜 透镜 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 The laser system according to claim 2, wherein the lens assembly is a double-aspheric single lens having a numerical aperture ΝΑ of 0.35 to 0.60; and a focal length of f, wherein ImmSf is $3 mm. 15. According to the laser system of claim 2, the front working distance FWD is 〇·3mm to 3mm. 16. Deleted according to the scope of the patent application scope 2, the post-working distance BWD is 1. 5 delete to 3 delete. 17. The laser system of claim 2, wherein the light emitted by the light source passes through the lens assembly twice before reaching the receiver. 18. A laser system according to claim 2, wherein (a) positioning the lens assembly to provide a collimated beam when the intercepting source emits light; and (b) placing the reflector to block the collimated beam and reflecting a straight beam passing through the lens to the non-missing optical crystal; and causing the collimating filament to be at an angle Θ ' ' 0· 05 solitude $ θ, 〇 · 2 radians when the light source is in the focal plane of the lens, and deviating from the lens assembly The axial distance d, according to the paper of the 18th item of the patent application scope = medium angle one, is: 0. 09 degree of S Θ $〇. 17 radians. 20. According to the second aspect of the patent scope of the cap, the lens assembly has: ' Γ2 is η, so that | η | &gt; 21. According to the laser system of claim 2, wherein the reflector is located at 201110489 In the image focal plane of the lens assembly, the direction of the average emission angle of the light source is parallel to the average beam angle on the receiver. 22. The laser system according to claim 1, wherein the diode laser compensates for the splitting angle of the diode according to the skirting angle, so that the laser diode emits light, and the beam center parallel lens assembly optical axis Happening. 31