WO2012015596A1

WO2012015596A1 - Optical package and method for aligning optical packages

Info

Publication number: WO2012015596A1
Application number: PCT/US2011/043818
Authority: WO
Inventors: Douglas Llewellyn Butler; Jr. Lawrence Charles Hughes; Garrett A Piech
Original assignee: Corning Incorporated
Priority date: 2010-07-30
Filing date: 2011-07-13
Publication date: 2012-02-02

Abstract

An optical package includes a semiconductor laser, a wavelength conversion device and a MEMS-actuated mirror oriented on a base module to form a folded optical pathway between an output of the semiconductor laser and an input of the wavelength conversion device. An optical assembly is located in a mechanical positioning device and the mechanical positioning device is disposed on the base module along the optical pathway such that the beam of the semiconductor laser passes through the optical assembly, is reflected by the MEMS-actuated mirror back through the optical assembly and into the waveguide portion of the wavelength conversion device. The MEMS-actuated mirror is operable to scan the beam of the semiconductor laser over the input of the wavelength conversion device. The optical assembly may be adjusted along the optical pathway with the mechanical positioning device to focus the beam into the waveguide portion of the wavelength conversion device.

Description

OPTICAL PACKAGE AND METHOD FOR ALIGNING OPTICAL PACKAGES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.

Provisional Application Serial No. 61/369446 filed on July 30, 2010, the content of which is relied upon and incorporated herein by reference in its entirety

BACKGROUND

[0002] The present invention generally relates to semiconductor lasers, laser controllers, optical packages, and other optical systems incorporating semiconductor lasers and wavelength conversion devices. More specifically, the present invention relates to optical packages and methods for aligning optical packages that include, inter alia, a semiconductor laser and a second harmonic generation (SHG) crystal or another type of wavelength conversion device.

BRIEF SUMMARY

[0003] According to one embodiment shown and described herein an optical package comprising a semiconductor laser, a wavelength conversion device, a MEMS-actuated mirror, an optical assembly, a mechanical positioning device and a base module, wherein: the wavelength conversion device comprises a waveguide portion; the semiconductor laser, the wavelength conversion device and the MEMS-actuated mirror are oriented on the base module to form a folded optical pathway between an output of the semiconductor laser and an input of the wavelength conversion device such that an output beam of the semiconductor laser may be reflected by the MEMS-actuated mirror into the waveguide portion of the wavelength conversion device; the MEMs-actuated mirror is operable to scan the output beam of the semiconductor laser over the input of the wavelength conversion device; and the optical assembly is located in the mechanical positioning device, wherein the mechanical positioning device is made of a glass filled liquid crystal polymer material, had CTE of not greater than 25 xlO ⁶ cm/cm/°C, and heat deflection temperature > 200°C, and said mechanical positioning device is disposed on the base module along the folded optical pathway such that the output beam of the semiconductor laser passes through the optical assembly and is reflected back through the optical assembly and into the waveguide portion of the wavelength conversion device, wherein a position of the optical assembly along the folded optical pathway may be adjusted with the mechanical positioning device such that the output beam of the semiconductor laser is focused into the waveguide portion of the wavelength conversion device.

[0004] According to another embodiment shown and described herein, a method

of assembling and aligning an optical package, the optical package comprising a

semiconductor laser, a wavelength conversion device comprising a waveguide portion, a MEMS-actuated mirror, an optical assembly, a mechanical positioning device and a base module, the method comprising:

(i) assembling the semiconductor laser and the wavelength conversion device, such that an optical pathway defined by the semiconductor laser, the MEMS-actuated mirror and the wavelength conversion device is a folded optical pathway;

(ii) inserting the optical assembly into the folded optical pathway with the mechanical positioning device such that the optical assembly is nominally aligned with the semiconductor laser and the wavelength conversion device, and an output beam of the semiconductor laser passes through the optical assembly and is reflected back through the optical assembly and into the waveguide portion of the wavelength conversion device; and wherein the reflective surface of the MEMS-actuated mirror is situated within a protective recess in the mechanical positioning device; aligning the output beam of the semiconductor laser with an input face of the waveguide portion of the wavelength conversion device by

(a) varying the position of the MEMS-actuated mirror, or

(b) adjusting a position of the optical assembly with the mechanical positioning device, to focus the output beam of the semiconductor laser into the waveguide portion of the wavelength conversion device such that the output beam of the semiconductor laser is aligned with the waveguide portion of the wavelength conversion device and an output intensity of the wavelength conversion device is optimized.

[0005] Additional features and advantages of the invention will be set forth in the detailed description which follows and, in part, will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings. It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The following detailed description of specific embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0007] Fig. 1 is a schematic illustration of a MEMS mirror-enabled optical alignment package according to one or more embodiments shown and described herein;

[0008] Fig. 2 is a cross sectional view of an optical package according to one or more embodiments shown and described herein;

[0009] Fig. 3 is an exploded view of an optical assembly holder and optical assembly according to one or more embodiments shown and described herein;

[0010] Fig. 4A is an exploded view of an another optical assembly holder and optical assembly according to one or more embodiments shown and described herein;

[0011] Fig. 4B is a view of the assembled an optical package, according to one or more embodiments shown and described herein, including the optical assembly holder and the optical assembly of Fig 4 A;

[0012] FIG. 5 illustrates a rear side view of the optical assembly holder shown in an Fig 4A; and

[0013] FIG. 6 illustrates a front side view (optical assembly's side) of the optical assembly holder shown in Fig 4 A.

DETAILED DESCRIPTION

[0014] Short wavelength light sources can be formed by combining a single-wavelength semiconductor laser, such as an infrared or near-infrared distributed feedback (DFB) laser, distributed Bragg reflector (DBR) laser, or Fabry-Perot laser, with a light wavelength conversion device, such as a second harmonic generation (SHG) crystal. Typically, the SHG crystal is used to generate higher harmonic waves of the fundamental laser signal. To do so, the lasing wavelength is preferably tuned to the spectral center of the wavelength converting SHG crystal and the output of the laser is preferably aligned with the waveguide portion at the input facet of the wavelength converting crystal.

[0015] Waveguide optical mode field diameters of typical SHG crystals, such as MgO-doped periodically poled lithium niobate (PPLN) crystals, can be in the range of a few microns. As a result, the present inventors have recognized that it can be very challenging to properly align and focus the beam from the laser diode with the waveguide of the SHG crystal, particularly during assembly of the optical package. Accordingly, one of the advantages of at least some of the exemplary embodiments of the present invention is an optical packages and methods for aligning components in optical packages that utilize a laser diode in conjunction with an SHG crystal or other type of wavelength conversion device to generate shorter wavelength radiation (e.g., green laser light) from a longer wavelength source (e.g., a near- infrared laser diode).

[0016] Referring initially to Fig. 1, although the general structure of the various types of optical packages in which the concepts of particular embodiments of the present invention can be incorporated is taught in readily available technical literature relating to the design and fabrication of frequency or wavelength-converted semiconductor laser sources, the concepts of particular embodiments of the present invention may be conveniently illustrated with general reference to an optical package 10 including, for example, a semiconductor laser 104 (labeled "λ" in Fig. 1) and a wavelength conversion device 102 (labeled "2v" in Fig. 1). In the configuration depicted in Fig. 1, the near infrared light emitted by the semiconductor laser 104 (for example, a laser diode) is coupled into a waveguide portion of the wavelength conversion device 102 by one or more adjustable optical components, such as a MEMS- actuated mirror 114, and a suitable optical assembly 112, which optical assembly 112 may comprise one or more optical elements (e.g., lenses) of unitary or multi-component configuration. The optical package 10 illustrated in Fig. 1 is particularly useful in generating a variety of shorter wavelength laser beams from a variety of longer wavelength

semiconductor lasers and can be used, for example, as a visible laser source in a laser projection system.

[0017] The adjustable optical component is particularly helpful because it is often difficult to align and focus the output beam emitted by the semiconductor laser 104 into the waveguide portion of the wavelength conversion device 102 (e.g., SHG crystals). For example, waveguide optical mode field diameters of typical SHG crystals, such as MgO-doped periodically poled lithium niobate (PPLN) crystals, can be in the range of a few microns. Referring to Fig. 1, the optical assembly 112 cooperates with the MEMS-actuated mirror 114 to direct a beam of the semiconductor laser 104 into waveguide portion of the wavelength conversion device 102. The MEMS-actuated mirror 114 is operable to introduce beam angular deviation by adjusting a position or state of the mirror 116 (also referred herein as reflective surface 116) and, as such, can be used to actively align the beam of the

semiconductor laser 104 with the waveguide portion of the wavelength conversion device 102 in the x-y plane by altering the position of the beam on the wavelength conversion device 102 until it is aligned with the waveguide portion of the wavelength conversion device 102.

[0018] In one embodiment, beam alignment may be monitored by providing, for example, a beam splitter 40 and an optical detector 50 in the optical path of the wavelength conversion device 102. The optical detector 50 may be operably connected to a microcontroller or controller 60 (labeled "μΰ" in Fig. 1) such that an output signal from the optical detector 50 is received by the controller 60. The controller 60 may be configured to control the position or state of the MEMS-actuated mirror 114 by adjusting the MEMS actuator(s) and, as such, position the output beam of the semiconductor laser 104 on the wavelength conversion device 102. In one embodiment the controller 60 may be used to control the position or state of the MEMS-actuated mirror 114 as a function of the output signal received from the optical detector 50. In another embodiment, the controller 60 may be used to perform an alignment routine such that the output beam of the semiconductor laser 104 is aligned with the waveguide portion 24 of the wavelength conversion device 102.

[0019] As described herein, the adjustable optical component may comprise a MEMS- actuated mirror 114, such as when the adjustment mechanism operative ly associated with the mirror 116 comprises one or more micro-opto-electromechanical systems (MOEMS) or micro-electro-mechanical systems (MEMS) operatively coupled to a mirror 116. The MEMS or MOEMS devices may be configured and arranged to vary the position of the output beam of the semiconductor laser 104 on the wavelength conversion device 102 in the x-y plane. Because the mirror 116 is located in the collimated or nearly-collimated beam space of the optical assembly 112, adjustment of the mirror angle will result in a change in the x/y position of the refocused beam on the wavelength conversion device. Use of a MOEMS or MEMS-actuated mirror enables adjustment of the refocused beam position to be done extremely rapidly over large ranges. For example, a MEMS-actuated mirror with +/- 1 degree of mechanical deflection, when used in conjunction with an optical assembly having a 3 mm focal length, may allow the beam to be angularly displaced +/- 100 μιη on the wavelength conversion device. The adjustment and/or repositioning of the beam may be done at frequencies on the order of 100 Hz to 10 kHz due to the fast response time of the MOEMS or MEMS-actuated mirror. It is noted that the optical assembly 112 may have a shorter focal length, for example 1.2 mm, 1.5 mm, 1.7 mm or 2 mm. The optical assembly 112 with the shorter focal length could be used advantageously with a smaller optical package and/or smaller optical assembly holder, allowing the total assembly to be more compact.

[0020] While specific reference has been made herein to the adjustable optical component being a MEMS-actuated mirror 114, it should be understood that the adjustable optical component may take a variety of conventional or yet to be developed forms. For example, the adjustable optical component may comprise one or more liquid lens components configured for beam steering and/or beam focusing. Still further, it is contemplated that the adjustable optical component may comprise one or more mirrors and/or lenses mounted to micro -actuators. In one contemplated embodiment, the adjustable optical component takes the form of a movable or adjustable lens in the optical assembly 112 and the otherwise adjustable optical component takes the form of a fixed mirror.

[0021] In the optical configuration illustrated in Fig. 1, the adjustable optical component is a MEMS-actuated mirror incorporated in a relatively compact, folded-path optical

configuration. As shown in FIG. 1, the MEMS-actuated mirror 114 may be configured to fold the optical path such that the optical path of the output beam of the semiconductor laser 104 initially passes through the optical assembly 112 to reach the MEMS-actuated mirror 114 as a collimated or nearly collimated beam and subsequently returns through the same optical assembly 112 to be focused on the wavelength conversion device 102. In this configuration, the optical path is "folded" as the output beam of the semiconductor laser is initially directed through the optical assembly 112 and then reflected back through the same optical assembly 112. This type of optical configuration is particularly applicable to wavelength converted laser sources where the cross-sectional size of the laser beam generated by the semiconductor laser is close to the size of the waveguide on the input face of the wavelength conversion device 102, in which case a magnification close to one would yield optimum coupling in focusing the output beam on the wavelength conversion device 102. For the purposes of defining and describing the present invention, it is noted that reference herein to a

"collimated or nearly collimated" beam is intended to cover any beam configuration where the degree of beam divergence or convergence is reduced, directing the beam towards a more collimated state.

[0022] The optical assembly 112 can be described as a dual function, collimating and focusing optical component or lens because it serves to collimate the divergent light output of the semiconductor laser 104 and then refocus the laser light propagating along the optical path of the optical package 10 into the waveguide portion of the wavelength conversion device. This dual function optical component is well suited for applications requiring magnification factors close to one because a single optical assembly 112 is used for both collimation and focusing. More specifically, as is illustrated in Fig. 1, the output beam of the semiconductor laser 104 is, in sequence, refracted at the first face 131 of the optical assembly 112, refracted at the second face 132 of the optical assembly 112, and reflected by the MEMS-actuated mirror 114 in the direction of the optical assembly 112. Once the laser light is reflected back in the direction of the optical assembly 112, it is first refracted at the second face 132 of the optical assembly 112 and subsequently refracted at the first face 131 of the optical assembly 112 and directed into the waveguide portion of the wavelength conversion device 102.

[0023] In particular embodiments of the present invention, the MEMS-actuated mirror 114 may be placed close enough to the image focal point of the optical assembly 112 to ensure that the principle ray incident on the input face of the wavelength conversion device 102 is approximately parallel to the principle ray at the output of the optical package 10. It may also be shown that the configuration illustrated in Fig. 1 also presents some advantages in terms of aberration. Indeed, when the output face of the semiconductor laser 104 and the input face of the wavelength conversion device 102 are positioned in approximate alignment with the object focal plane of the optical assembly 112 and the output waveguide of the semiconductor laser 104 and the input waveguide of the wavelength conversion device 102 are symmetric with respect to the optical axis of the optical assembly 112, it is contemplated that anti symmetric field aberrations, such as coma, can be automatically corrected.

[0024] While reference has been made herein to FIG. 1 to describe the general orientation of the components of the optical package 10, specific reference will now be made to FIGS. 2-6 to further describe the orientation, assembly, and alignment of the optical package and, more specifically, structures and methods for aligning and focusing the beam of the semiconductor laser into the waveguide portion of the wavelength conversion device.

[0025] FIGS. 2, 3, 4A and 4B show two embodiment of an optical package 100. In these embodiments, the semiconductor laser 104 and the wavelength conversion device 102 are in a stacked configuration and mounted atop a base module 106. In these embodiments, the MEMS-actuated mirror 114 is positioned in the optical assembly holder 110 which, in turn, is positioned on and attached to the base module 106. The MEMS-actuated mirror 114 is positioned and oriented such that the mirror portion is opposed to the output of the semiconductor laser 104 and the input of the wavelength conversion device 102. More specifically, the MEMS-actuated mirror is oriented on the base module such that a normal to the surface of the mirror 116 is parallel to the optical axis of both the semiconductor laser 104 and the wavelength conversion device 102 when the mirror of the MEMS-actuated mirror is in a neutral position (e.g., without any tip or tilt applied to the mirror by the MEMS actuator). Specifically referring to the coordinate system shown in FIG. 2, when the MEMS-actuated mirror 114 is positioned in this orientation, the surface of the mirror 116 is substantially co- planar with the x-y plane. However, it will be understood that, when the MEMS-actuated mirror is adjusted, the mirror may tip and tilt in and out of the x-y plane about axes of rotation parallel to the x-axis and the y-axis.

[0026] It should now be understood that, while FIG. 2 shows the semiconductor laser 104 and the wavelength conversion device 102 in a vertically stacked configuration, the semiconductor laser 104 and the wavelength conversion device 102 may also be oriented in a side-by-side configuration which may also yield a folded optical pathway as described herein.

[0027] The base module 106 may generally comprise electrical interconnects (not shown) such that, when the MEMS-actuated mirror 114 is positioned on the base module 106 via the optical assembly holder 110, the corresponding electrical interconnects 114A of the MEMS- actuated mirror 114 may be electrically coupled to the electrical interconnects 106A of the base module 106 by directly connecting to the base module's electrical interconnect pads 106A using conductive adhesive or solder without requiring additional processing or components (e.g., wires, leads etc.). However, in another embodiment, the electrical interconnects between the MEMS-actuated mirror 114 and the base module 106 are created using additional components (flexible interconnects) or by wire bonding (e.g., using wire(s) 106B), welding or soldering leads to the base module interconnection pads and/or

combinations thereof.

[0028] In the embodiment shown in FIGS. 2, 3 and 4A-4B, the optical element 112 may be positioned in a mechanical positioning device. In the embodiment shown in FIGS., 3A and 3B, the mechanical positioning device comprises an optical assembly holder 110 in which the optical assembly 112 may be positioned. The optical assembly holder 110 and optical assembly 112 are then positioned on the base module 106 such that the optical element is disposed in the optical pathway between the semiconductor laser 104 and wavelength conversion device 102 and the MEMS-actuated mirror 114. In one embodiment, the optical assembly 112 is integrally formed with the optical assembly holder 110. In another embodiment, the optical assembly 112 and the optical assembly holder 110 are discrete components, as shown in FIGS. 3 and 4A, 4B, and the optical assembly 112 is inserted in the optical assembly holder 110 and fixed in position.

[0029] The optical assembly holder 110 may comprise a material with a suitable coefficient of thermal expansion so as to minimize the effects of thermal expansion on the optical alignment of the optical package during operation of the optical package. In another embodiment, the optical assembly holder 110 may comprise a material with a suitable coefficient of thermal expansion so as to fully or partially compensate for the effects of thermal expansion during operation of the optical package.

[0030] In one embodiment, the optical assembly holder 110 may comprise one or more positioning features (not shown) for engaging base module 106, and the base module 106 may comprise a plurality of locating features (not shown) generally corresponding to the positioning features of the optical assembly holder. For example, the positioning features of the optical assembly holder may include, without limitation, pins, posts, slots, channels, dovetails, holes, grooves and/or combinations thereof. Similarly, the locating features of the base module 106 for engaging the optical assembly holder 110 may comprise the

corresponding part to the positioning features of the optical assembly holder 110 such as grooves, holes, channels, dovetail slots, posts, pins and/or combinations thereof. [0031] The optical assembly holder 110 may be adjustably positioned on the base module 106 to form the optical pathway between the MEMS-actuated mirror, optical assembly 112, and the semiconductor laser 104/wave length conversion device 102, such that the optical assembly 112 is positioned in the optical pathway between the MEMS-actuated mirror and the semiconductor laser 104/wave length conversion device 102. The optical assembly holder 110 may be positioned by connecting the positioning features of the optical assembly holder 110 with the corresponding locating features of the base module 106. In this manner the position of the optical assembly holder 110 may be precisely controlled in the z-direction with respect to the base module 106 and the folded optical pathway defined by the MEMS- actuated mirror 114, the semiconductor laser 104 and the wavelength conversion device 102. The adjustability of the optical assembly holder 110 and, thus the adjustability of the optical assembly 112 supported by the optical assembly holder 110 in the z-direction facilitates focusing the output beam of the semiconductor laser 104 into the waveguide portion of the wavelength conversion device 102.

[0032] More specifically, the optical assembly holder 110 may be configured such that MEMS-actuated mirror 114 is attached to the optical assembly holder 110, thereby aligning the MEMS-actuated mirror with the optical assembly 112 as is shown in FIGS. 2, 3 A and 3B. When the optical assembly holder 110 and optical assembly 112 are attached to the MEMS-actuated mirror 114, the combination is referred to as a MEMS-lens unit or

MEMSLU 108.

[0033] The optical assembly holder 110 of the MEMS-lens unit (MEMSLU) 108 holds the MEMS-actuated mirror 114 close enough to the focal point of the optical assembly 112 at a spacing such that the distance L between the mirror 116 and the principal plane of the optical assembly 112 is about equal to the effective focal length (EFL) of the optical assembly 112. In some embodiments, 0.8EFL<L<1.2EFL, preferably 0.9EFL<L<1.1EFL, more preferably 0.95EFL<D<1.05EFL.

[0034] The optical assembly holder 110 of the MEMS-lens unit (MEMSLU) 108 includes a bore 110B for insertion of the optical assembly 112 therein. The diameter D of the bore is preferably at least equal to twice the numerical aperture NA of the semiconductor laser 104 times focal length of the optical assembly 112 (i.e., D>2NA x EFL).

[0035] Preferably, the optical assembly holder 110 of the MEMS-lens unit (MEMSLU) 108 aligns the center of the mirror 116 optical axis of the optical assembly 112 to within +/- 100 um, so the bore HOB for the optical assembly 112 is centered on mirror's center. Injection molding of the optical assembly holder 110 makes it inexpensive to manufacture the optical assembly holder 110 within the tight tolerances required. (Tolerances of tens of microns, so as accurate mechanical positioning of the optical assembly 112 relative to the mirror 116 to tolerances of better than +/-100um in the x/y/z axes).

[0036] The optical assembly holder 110 may be made of metal, ceramic, plastic, or any suitable material. However, it is preferentially made of a material that is thermally stable and does not swell significantly (e.g., <0.1 %, preferably 0.05 %) in the presence of water. This is because, once the MEMS-lens unit 108 is attached to the laser package, adjustments can no longer be made of the relative position of components in the optical axis or focus direction (Z axis direction). Even small changes in focus, for example about 1 μιη, can cause significant optical coupling penalties in the optical package 10 or 100. Given the approximate distance between the optical assembly 112 and the mirror 116, for example of about 1.5 mm, and the approximate operational temperature range of the semiconductor laser 104 (10° to 60 °C, or +/-25 °C range), this means that the material for the optical assembly holder 110 of the MEMS-lens unit 108 preferably has a coefficient of thermal expansion of less than 25 xlO^"6 cm/cm/°C within this temperature range. When made with the proper materials such as a liquid-crystal co-polymer (LCP), the optical assembly holder 110 provides stable mechanical positioning of the optical assembly 112 relative to the mirror 116, such that changes in temperature or humidity do not cause the relative position of the optical components to shift. For example, along the optical axis, the position of the optical assembly 112 in the package can be maintained to <1 micron, helping to maintain optical coupling and hence output power.

[0037] If the assembly holder 110 is manufactured from a plastic such as a liquid-crystal copolymer (LCP), it can be made via injection molding process. When made with an injection molded material such as LCP, the lens holder may be made very accurately (tolerances of tens of microns) yet inexpensively, so as to allow accurate mechanical positioning of the optical assembly 112 relative to the mirror 116 to tolerances of better than +/-100um in the x/y/z axes.

[0038] preferably, the LCP material is a glass reinforced or glass filled liquid-crystal copolymer, preferably glass-fiber reinforced liquid-crystal co-polymer, for example Dupont Zenite 6130 available from Dupont , or Ticona Vectra el30i available from Ticona.

Alternatively the LCP material is mineral filled. Preferably the amount of glass or mineral filler in this material is between 20 % and 50%, for example 25%-30%. This range provides the required CTE for the application while retaining the desirable mechanical properties of the fabricated optical assembly holder (e.g., bending strength and surface roughness)

Preferably, the assembly holder 110 is made from liquid-crystal co-polymer that has relatively small CTE such that thermal expansion of the material along the optical beam axis is no more than 30 xlO^"6 cm/cm/°C , and preferably <25ppm/°C ( less than 25 xlO^"6 cm/cm/°C). Preferably the glass-fiber reinforced liquid-crystal co-polymer has low water absorption (preferably <0.1%, more preferably less than 0.05%,) and/or a high heat deflection temperature, preferably > 200°C (for example, 210 °C, 215 °C, 225 °C, 230 °C, 250 °C, 260 °C, 270 °C or 300 °C). For example, Dupont's Zenite 6130 material has heat deflection temperature of about 260 °C, while Ticona Vectra el30i has heat deflection temperature of about 216°C. Preferably the LCP material can be modified when exposed to oxygen or argon (or a combination thereof) plasma. After optical assembly holder 110 is exposed to plasma, if the adhesive material is utilized for mounting the optical assembly 112, and or MEMS- actuated mirror 114 on the assembly holder 110, the plasma modification of those surfaces can provide a better grip for adhesive, so that the adhesive material can have improved adhesion by gripping to glass fibers and modified polymer exposed by the plasma treatment. For example, after the assembly holder 110 is molded, its surfaces can be modified to expose glass fibers and roughen the surface, by treating it in plasma chamber (argon or oxygen plasma, about 300W run through plasma for 5-15 min), to prepare the surfaces for receiving adhesive so that the optical assembly 112 and MEMS-actuated mirror 114 can be fixedly attached to the optical assembly holder 110. Thus, the assembly holder 110 itself provides an attachment surface where the optical assembly 112 and MEMS-actuated mirror 114 may be adhesively attached to the assembly holder 110, and where the assembly holder 110 itself may be adhesively attached to base module 106. Preferably the adhesive bond to the

MEMSLU 108 should exhibit shear strength > 2kg (f) when attached to the base module 106. In addition, because the adhesive is applied to the surface of the bore situated within the assembly holder 110, the adhesive does not directly contact the MEMS-actuated mirror 114 or the optical assembly 112, helping to prevent adhesive from wicking to the optical surfaces. Preferably the adhesive bond between the MEMS-actuated mirror 114 and the optical assembly holder 110 exhibits shear strength > 1kg (f) when attached to the base module 106. Preferably the adhesive bond between the MEMS-actuated mirror 114 and the optical assembly 112 exhibits shear strength > 1kg (f) when attached to the base module 106.

Preferably optical assembly holder 110 material will not significantly outgas (e.g., total condensable matter or total weight loss from the optical assembly holder 110 of less than 0.2%) into the base module 106 or the MEMS -actuated mirror 114 or the optical assembly 112, when exposed to elevated temperature. Preferably the adhesive is UV curable and provides fast processing times (set time <5 seconds). For example, such materials may be acrylates, cationic polymers, or other rapid cure systems.

[0039] In order to assemble the optical package 100 shown in FIG. 2, the semiconductor laser 104 and wavelength conversion device 102 are first mounted on the base module 106 using standard mounting techniques for assembling electronic and/or electro-optic devices. For example, in one embodiment, a microscope and camera may be used to identify the output of the semiconductor laser 104 and the waveguide portion of the wavelength conversion device 102 and align them with one another such that the output of the semiconductor laser 104 and the waveguide portion of the wavelength conversion device 102 lie in the same vertical plane along the z-axis (e.g., the output of the semiconductor laser 104 and the waveguide portion of the wavelength conversion device lie in a y-z plane). Because the wavelength conversion 102 device may generally comprise a transparent optical material such as, for example, lithium niobate and the wavelength conversion device 102 is positioned on top of the semiconductor laser 104, a camera or microscope may be used to view the wavelength conversion device 102 and semiconductor laser 104 from above the wavelength conversion device and thereby assist in positioning and alignment. The semiconductor laser 104 and the wavelength conversion device 102 may be attached to the base module 106 with epoxy, glue, solder or other conventional attachment methods.

[0040] In one embodiment, when the optical assembly 112 is not integral with the optical assembly holder 110, the optical assembly 112 may be inserted into the optical assembly holder 110 and fixed into place with adhesive, solder, frit or mechanical attachments such as screws, clips or the like. The optical assembly holder 110 provides a clear aperture for the optical beam, and also the mounting surface HOD for optical assembly 112, as well as the surface HOD' that is capable of receiving the adhesive material for attaching the optical assembly 112 to the optical assembly holder 110.

[0041] The optical assembly holder 110 is preferably made such that adhesive mounting and handling features are integral to the part. For example, if the optical assembly 112 is to be fixed into place with adhesive, the adhesive can be deposited into the optical assembly holder 110 through the opening 110A on the surface HOD', after the assembly 112 is inserted into the optical assembly holder 110, through the bore aperture HOB. This protects the lens face 132 facing the mirror 116 from being contaminated by the adhesive. That is, because the adhesive is applied to the lens holding portion HOD of the optical assembly holder 110, it does not directly contact the mirror 116 or the lens face 132, 131, helping to prevent adhesive from wicking to the optical surfaces. The optical assembly holder 110 is then attached to the MEMS-actuated mirror using adhesive, solder, frit or mechanical attachments such as screws, clips or the like to form the MEMSLU 108.

[0042] The optical assembly holder 110 is made with reference or datum features 111A, 111B that allow precise positioning of the mirror 116 with respect to the optical assembly holder 110. These datum features may be pins, tabs, or other features compatible with injection molding process tolerances. These datum features are shown, for example, as the tab features 111A, and optional pin features 11 IB in Figs. 4A, 5 and 6. They constrain the MEMS-actuated mirror 114, centering it relative to the lens optical axis. They also help to position the MEMS-actuated mirror 114 a precise distance away from the optical assembly 112.

[0043] The assembled MEMSLU 108 is positioned on the base module 106 such that the mirror 116 of the MEMS-actuated mirror 114 is facing the output of the semiconductor laser 104. The MEMSLU 108 is generally aligned with the semiconductor laser such that the optical assembly 112 is positioned in the optical pathway of the output beam of the semiconductor laser. The MEMSLU 108 may be mechanically held in place on the base module 106. In one embodiment, this may be accomplished using the positioning features on optical assembly holder 110 of the MEMSLU 108 in conjunction with the corresponding locating features on the base module 106. The optical package is then powered on and the MEMS-actuated mirror 114 is aligned under the control of the controller (e.g., the

microcontroller 60 shown in FIG. 1) in order to position the MEMSLU 108 and align the beam of the semiconductor laser 104 with the waveguide portion of the wavelength conversion device 102 in the x-y plane. The alignment routine generally comprises scanning the output beam of the semiconductor laser 104 over the input face of the wavelength conversion device 102 in the x-y plane by adjusting the position of the MEMS-actuated mirror 114. As the output beam is scanned over the wavelength conversion device 102, the output intensity of the wavelength conversion device may be monitored using an optical detector coupled to the controller as shown in FIG. 1. The optimum alignment of the output beam with the waveguide may be determined by the controller using feedback from the optical detector. For example, when the output intensity of the wavelength conversion device reaches a maximum, the output beam of the semiconductor laser is generally aligned with the waveguide portion of the wavelength conversion device in the x-y plane. Accordingly, the position of the mirror of the MEMS-actuated mirror corresponding to the maximum output intensity should generally produce alignment between the semiconductor laser and the wavelength conversion device.

[0044] In one particular embodiment, the method used to align the output beam of the semiconductor laser with the waveguide portion of the wavelength conversion device in the x-y plane may be the method disclosed in U.S. Patent Application No. 12/072,386 filed February 26, 2008 and entitled "METHODS AND SYSTEMS FOR ALIGNING OPTICAL PACKAGES," although other methods may be used as will be apparent to one skilled in the art, including, without limitation, raster scanning and the like. Such methodologies will generally yield alignment of the output beam of the semiconductor laser with the waveguide portion of the wavelength conversion device in the x-y plane.

[0045] With the output beam of the semiconductor laser 104 aligned with the waveguide portion of the wavelength conversion device 102 in the x-y plane, the position of the

MEMSLU 108 is adjusted in the z-direction such that the output beam of the semiconductor laser 104 is focused into the waveguide portion of the wavelength conversion device 102. As the position of the MEMSLU 108 is adjusted in the z-direction, the controller of the optical package continuously runs an adaptive waveguide alignment algorithm (e.g., the controller varies the position of the mirror 116 of the MEMS-actuated mirror 114) so as to optimize the position of the output beam of the semiconductor laser 104 in the x-y plane on the waveguide portion of the wavelength conversion device and thereby achieve and/or maintain peak coupling of the output beam with the waveguide portion of the wavelength conversion device as the output beam is focused.

[0046] Once peak coupling between the semiconductor laser 104 and the wavelength conversion device is obtained (e.g., the output of the wavelength conversion device is optimized and/or the desired output intensity of the wavelength conversion device is achieved, including, without limitation, the maximum output intensity), the controller determines the optimum position or deflection of the mirror 116 of the MEMS-actuated mirror 114 based on the electronic signals used to drive the mirror during alignment. Using this information, the MEMS-actuated mirror 114 is adjusted to utilize electronic drive signals requiring minimum power consumption to achieve and maintain the optimum coupling position of the mirror 116. Thereafter the MEMSLU 108 is fixed into place using adhesive, solder and/or welding and permanent electrical interconnects are attached to the MEMS- actuated mirror 114 using wires, solder, adhesive or the like.

[0047] Alternatively the MEMSLU 108 may be aligned to the input of the wavelength conversion device using the controller and external apparatus (stages and motors) to position the MEMSLU at the desired location as determined by monitoring the output of the conversion device as previously mentioned. The MEMS-actuated mirror 114 is not activated during this operation. This enables a simpler process for attachment of the MEMSLU 108 to the base package without requiring electrical contact to the MEMSLU 108. Thereafter the MEMSLU 108 is fixed into place on the package module 106 using adhesive, solder and/or welding and permanent electrical interconnects are attached to the MEMS-actuated mirror 114 using wires, solder, adhesive or the like.

[0048] The optical assembly holder 110 of the MEMSLU 108 has rails 111C along the outer edges which serve as adhesive bonding interfaces when it is installed in the laser package. The rails 111C are shown in Figs 4A, 4B, 5 and 6. These rails are preferably made accurately (<50μιη) relative to the MEMS-actuated mirror 114 and the optical assembly 112, so that the MEMSLU 108 can be properly positioned in the base module 106 with minimal adjustment. The rails provide the required mounting surface for attaching the MEMS- actuated mirror 114 to the optical assembly holder using adhesive, solder or other bonding agents on the internal surface of the rails lllC. The rails are also used to provide the required attachment surface to mount the MEMSLU 108 to the base module 106. The rails in conjunction with other features of the optical assembly holder 110 provide the ability to assemble the MEMSLU 108 without exposing the mirror 116 to the adhesive material.

[0049] In addition, the MEMSLU 108 itself is particularly useful in that once assembled, the delicate mirror 116 is protected against damage during handling. Without the optical assembly holder 110 installed, it is easy to destroy the reflective surface of the mirror 116. But once the optical assembly holder 110 is installed, such damage is minimized. The MEMSLU 108 can easily be picked up by hand or by automated production equipment without significant risk that the mirror is contacted. This makes part shipping easier, the package assembly process easier, and leads to higher yield.

[0050] As discussed above, in one embodiment, the MEMS-actuated mirror 114 is preferably positioned on the optical assembly holder 110 to form MEMSLU 108. The optical assembly holder comprise a receptacle (see Figs. 4A, 4B, 5, 6) for receiving the MEMS- actuated mirror 114 such that, when the MEMS-actuated mirror 114 is positioned in the receptacle, the MEMS-actuated mirror 114 is recessed in the optical assembly holder 110 and is in contact with one or more datum or positioning features 111A, 11 IB. The receptacle is formed, for example, by the optional rails 111C and/or the datums or positioning features 111A, 11 IB. Location of the MEMS-actuated mirror 114 using these datum features is achieved during assembly without adhesive on the mating surfaces or the positioning features 111A, 11 IB. This is achieved by using the rails to attach the MEMS-actuated mirror 114 to the optical assembly holder 110. In the exemplary embodiments shown in Figs 4-6, the posts 111A are used for providing a y axis datum reference and are used to support the MEMS- actuated mirror 114 in its precise position along the y axis. The mating surface 11 IB is used to provide accurate z axis position of the mirror 116 with respect the second face 132 of the optical assembly 112. Similarly, the mating surface 11 IB^' is used to provide accurate z axis position of the optical assembly 112 with respect to MEMS-actuated mirror 114. The positioning feature(s) 11 ID is used to provide accurate x axis positioning of the MEMS- actuated mirror 114. The features 111A, 111B, 111C and HID are preferably made integrally with the optical assembly holder 110 for example, during injection molding. It is preferable that the reflective surface 116 of the MEMS-actuated mirror 114 is situated within a protective recess HOC in optical assembly holder 110. Preferably the distance d between mirror 116 and back surface of optical assembly holder 110 is greater than 25 μιη, more preferably 50-100 μιη, and may be, for example up to 1mm, such that the reflective surface 116 does not come in contact with another surface and is well protected from the

contamination.

[0051] The MEMSLU 108 is preferentially installed in the optical package after the laser diode and crystal are installed. The laser is then powered on, and the position of the

MEMSLU 108 is adjusted along three axes (x,y,z) until light is efficiently coupled from the diode laser into the SHG crystal. This is described in more detail in references. The MEMS- actuated mirror 114 may be powered up and actuated during the installation process, but the MEMSLU 108 may also be installed completely unpowered. The latter is preferred, since this means the MLU is nominally aligned at zero power. Subsequent powering of the MEMS- actuated mirror 114 will only be needed to accommodate small positional changes from adhesive curing or small motions of components over the life of the laser. The optical assembly holder 110 positions the lens a precise distance away from MEMS-actuated mirror 114. This distance is, for example, about 1.5 mm, with the precise value being determined by the optical properties of the optical assembly 112 itself, and those of the diode laser and SHG crystal. This distance typically needs to be set to +/-100 μιη. The optical assembly holder 110 also advantageously positions the center the optical aperture of the optical assembly 112 on the center of the MEMS mirror. In the embodiments described herein, this position is set to +/-100 μιη. The optical assembly holder 110 of the MEMSLU 108 also advantageously provides safe handling surfaces for manipulation during assembly into the optical package.

[0052] For the various methods of assembly and alignment described herein, it should be understood that minor (e.g., 1-5 μιη) deviations in component placement may occur due to the fixation methods employed. These deviations may result in small angular changes of various components with respect to the semiconductor laser and the wavelength conversion device. Such deviations may be easily accommodated for by using the adaptive alignment capabilities of the MEMS-actuated mirror and controller. These adaptive alignment techniques and algorithms permit the rapid acquisition of the optical alignment and also the rapid adjustment of the position of the optical assembly.

[0053] It should now be understood that the output beam of the semiconductor laser of the optical packages described herein may be quickly and efficiently aligned and focused into the waveguide portion of the wavelength conversion device using the mechanical positioning device to adjust the position of the optical assembly. Further the methods of assembling and aligning optical packages described herein are suitable for efficiently constructing and aligning a beam spot of a semiconductor laser with a waveguide portion of a wavelength conversion device. The alignment methods described herein are particularly suited for performing the initial alignment of the beam with the wavelength conversion device during assembly of the optical package. However, it should be understood that the alignment method may also be used to maintain alignment or perform realignment of the beam spot with the wavelength conversion device during operation of the optical package or at any time during the life-cycle of the package.

[0054] It is contemplated that the methods of the present invention may be applicable to color image-forming laser projection systems, laser-based displays such as heads-up displays in automobiles, or any laser application where optical alignment and/or wavelength tuning are issues. It is further contemplated that the alignment methods discussed herein will have utility in conjunction with a variety of semiconductor lasers, including but not limited to DBR and DFB lasers, Fabry-Perot lasers, and many types of external cavity lasers. [0055] It is to be understood that the preceding detailed description of the invention is intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided such modifications and variations come within the scope of the appended claims and their equivalents.

[0056] It is noted that terms like "preferably," "commonly," and "typically," if utilized herein, should not be read to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention.

[0057] For purposes of describing and defining the present invention it is noted that the terms "substantially" and "approximately" may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The terms "substantially" and "approximately" may also be utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0058] It is noted that recitations herein of a component being "programmed" in a particular way, "configured" or "programmed" to embody a particular property or function, are structural recitations as opposed to recitations of intended use. More specifically, the references herein to the manner in which a component is "programmed" or "configured" denotes an existing physical conditions of the component and, as such, is to be taken as a definite recitation of the structural characteristics of the component. For example, references herein to a optical assembly and an adjustable optical component being "configured" to direct a laser beam in a particular manner denotes an existing physical condition of the optical assembly and the adjustable optical component and, as such, is to be taken as a definite recitation of the structural characteristics of the optical assembly and the adjustable optical component.

[0059] Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.

Claims

What is claimed:

1. An optical package comprising a semiconductor laser, a wavelength conversion device, a MEMS-actuated mirror, an optical assembly, a mechanical positioning device and a base module, wherein:

the wavelength conversion device comprises a waveguide portion;

the semiconductor laser, the wavelength conversion device and the MEMS-actuated mirror are oriented on the base module to form a folded optical pathway between an output of the semiconductor laser and an input of the wavelength conversion device such that an output beam of the semiconductor laser may be reflected by the MEMS-actuated mirror into the waveguide portion of the wavelength conversion device;

the MEMs-actuated mirror is operable to scan the output beam of the semiconductor laser over the input of the wavelength conversion device; and

the optical assembly is located in the mechanical positioning device, wherein the mechanical positioning device is made of a glass filled liquid crystal polymer material, had CTE of not greater than 25 xlO ⁶ cm/cm/°C, and heat deflection temperature > 200°C, and said mechanical positioning device is disposed on the base module along the folded optical pathway such that the output beam of the semiconductor laser passes through the optical assembly and is reflected back through the optical assembly and into the waveguide portion of the wavelength conversion device, wherein a position of the optical assembly along the folded optical pathway may be adjusted with the mechanical positioning device such that the output beam of the semiconductor laser is focused into the waveguide portion of the wavelength conversion device.

2. The optical package of claim 1 wherein MEMS-actuated mirror is integrated into the mechanical positioning device; the distance L between mirror and principal plane of the optical assembly is 0.8EFL<L< 1.2 EFL, where FL is the effective focal length of the optical assembly; the bore having a clear aperture diameter D of at least D=2NA x F, where NA is the numerical aperture of the semiconductor laser times and F is the focal length of the optical assembly.

3. The optical package of claims 1 or 2, wherein the MEMS-actuated mirror is oriented on the base module such that a normal to a surface of the MEMS-actuated mirror is parallel to an optical axis of the semiconductor laser and an optical axis of the wavelength conversion device.

4. The optical package of claim 3 wherein the mechanical positioning device comprises an optical assembly holder in which the optical assembly is positioned, wherein the optical assembly holder is attached to the MEMS-actuated mirror. And said glass or mineral filled material includes 20%-30% glass and/or mineral fill.

5. The optical package of claim 4 wherein the optical assembly holder comprises at least one positioning feature for positioning the MEMS-actuated mirror at a predetermined location along the z axis.

6. The optical package of claim 1 -3, wherein the optical assembly holder comprises at least one positioning feature; and the base module comprises a plurality of locating features corresponding to the at least one positioning feature of the optical assembly holder such that the optical assembly holder may be adjustably positioned along the base module.

7. A mechanical positioning device comprising:

an optical assembly holder with mounting features for a mirror and for an optical assembly, wherein the optical assembly holder is made of a glass filled liquid crystal polymer material, with CTE of not greater than 25 xlO ⁶ cm/cm/°C, and heat deflection temperature > 200°C.

8. A mechanical positioning device of claim 7, further comprising:

a mirror and an optical assembly, wherein said mirror is situated within a protective recess in the mechanical positioning device.

9. A method of assembling and aligning an optical package, the optical package comprising a semiconductor laser, a wavelength conversion device comprising a waveguide portion, a MEMS-actuated mirror, an optical assembly, a mechanical positioning device and a base module, the method comprising:

(ii) inserting the optical assembly into the folded optical pathway with the

mechanical positioning device such that the optical assembly is nominally aligned with the semiconductor laser and the wavelength conversion device, and an output beam of the semiconductor laser passes through the optical assembly and is reflected back through the optical assembly and into the waveguide portion of the wavelength conversion device; and wherein the reflective surface of the MEMS -actuated mirror is situated within a protective recess in the mechanical positioning device;

aligning the output beam of the semiconductor laser with an input face of the waveguide portion of the wavelength conversion device by

(a) varying the position of the MEMS-actuated mirror, or

(b) adjusting a position of the optical assembly with the mechanical positioning device,

to focus the output beam of the semiconductor laser into the waveguide portion of the wavelength conversion device such that the output beam of the semiconductor laser is aligned with the waveguide portion of the wavelength conversion device and an output intensity of the wavelength conversion device is optimized.

10. A method of assembling and aligning an optical package according to claim 9, wherein said MEMS-actuated mirror and said lens assembly are positioned into a mechanical positioning device that has been plasma treated.