Laser diode illuminator device and method for optically conditioning the light beam emitted by the same

• US 7,873,091 B2
• Filed: 03/10/2009
• Issued: 01/18/2011
• Est. Priority Date: 08/13/2008
• Status: Active Grant

• Current Assignee: Institut national d'optique
• Original Assignee: Institut national d'optique
• Inventors: Taillon, Yves, Parent, André, Labranche, Bruno, Grenier, Paul
• Primary Examiner(s): Van Roy; Tod T
• Assistant Examiner(s): Zhang; Yuanda
• Application Number:
  US12/401,402
• Publication Number:
  US 20100040098A1
• Time in Patent Office: 679 Days
• Field of Search: 372/36, 372/50.12, 372/50.23, 372/98, 372/101, 372/107, 372/108, 359/641, 359/871
• US Class Current: 372/50.12
• CPC Class Codes: G02B 19/0009 having refractive surfaces only
• CPC Class Codes: G02B 19/0014 at least one surface having optical power
• CPC Class Codes: G02B 19/0057 in the form of a laser diode array, e.g. laser diode bar semiconductor laser arrays with beam combining arrangement H01S5/4012
• CPC Class Codes: G02B 27/0966 Cylindrical lenses cylindrical lenses per se G02B3/06
• CPC Class Codes: H01S 5/4031 Edge-emitting structures
• CPC Class Codes: H01S 5/405 Two-dimensional arrays
• CPC Class Codes: H01S 5/4081 Near-or far field control

Abstract

A laser diode illuminator device and a method for optically conditioning the output beam radiated from such a device, so that highly-demanding illumination application requirements that call for high output powers within a specified field of illumination can be addressed. At the heart of the device is a two-dimensional stack of laser diode bars wherein the linear array of beamlets radiated by each laser diode bar is optically conditioned through its passage in a refractive-type micro-optics device followed by a cylindrical microlens. The micro-optics device performs collimation of the linear array of beamlets along the fast axis of the bars, and it also acts as a beam symmetrization device by interchanging the divergences of the laser beamlets along the fast and slow axes. The cylindrical microlens is for collimation of the beamlets along the slow axis. The optical conditioning is performed individually for each linear array of beamlets so that the radiance or brightness of the laser diode illuminator can be optimized while any specified field of illumination can be filled with an excellent uniformity of the radiant intensity.

Claims

1. A laser diode apparatus for illumination, said apparatus comprising:

(a) a plurality of laser diode bars packaged in the form of at least one stacked laser diode array, said at least one array radiating a two-dimensional array of laser beamlets,

(b) a plurality of micro-optics devices for perfoming collimation of the beamlets along the fast axis of said laser diode bars and for interchanging divergence angles of said beamlets along the orthogonal fast and slow axes, the number of said micro-optics devices being equal to the number of said laser diode bars,

(c) a plurality of cylindrical microlenses elongated along a direction parallel to said diode laser bars for performing collimation along the slow axis of the beamlets exiting from said micro-optics devices, the number of said cylindrical microlenses being equal to the number of said laser diode bars and their spacing being equal to the spacing between said diode laser bars, and their maximum diameter being determined by the spacing between said laser diode bars,

(d) a support structure having a front face on which said plurality of cylindrical microlenses are bonded, said support structure being attached to said array of laser diode bars and said support structure securing said plurality of cylindrical microlenses, said support structure providing spacing between said plurality of cylindrical microlenses and said array of laser diode bars so that the plane of emission of said array of laser diode bars is substantially in the back focal plane of said cylindrical microlenses,

(e) means for supplying electrical power to said at least one stacked laser diode array and for controlling its operation,

(f) means for controlling the operating temperature of said at least one stacked laser diode array,

wherein the interchange of the divergence angles of said array of laser beamlets performed by said plurality of micro-optics devices provides for the use of cylindrical microlenses having their focal length long enough to provide collimation with a predetermined residual divergence angle along the slow axis of said array of laser beamlets.

2. The apparatus of claim 1, wherein each of said micro-optics device is formed of a cylindrical microlens having high numerical aperture followed by a refractive micro-optics element for interchanging the divergence angles of said incoming laser beamlets along the fast and slow axes, said cylindrical microlens with high numerical aperture being used for collimation along the fast axis of a linear array of laser beamlets.

3. The apparatus of claim 2, wherein said high-numerical-aperture cylindrical microlens and said micro-optics element are integrated in the same subassembly.

4. The apparatus of claim 2, wherein said high-numerical-aperture cylindrical microlens and said micro-optics element are mounted as separate components.

7. The apparatus of claim 1, wherein said support structure comprises a material selected from the group consisting of aluminum, copper and glass ceramic.

5. A method for generating a laser beam for use in light illumination applications, comprising the steps of :

(a) providing a stacked laser diode array comprising a plurality of laser diode bars, the number of said laser diode bars being selected so that a predetermined output power can be radiated,

(b) optically registering a first micro-optics device to the linear array of laser beamlets radiated by a first laser diode bar of said stacked laser diode array, said micro-optics device performing collimation along the fast axis and interchange of fast-axis and slow-axis divergence angles of said linear array of laser beamlets,

(c) repeating step (b) for the linear array of laser beamlets radiated by each individual laser diode bar mounted in said stacked laser diode array,

(d) securing a support structure to said stacked laser diode array, said support structure having a front face,

(e) optically registering a first cylindrical microlens to a first linear array of laser beamlets exiting from said first micro-optics device, said first cylindrical microlens performing collimation along the slow axis of said first linear array of laser beamlets, said first cylindrical microlens being elongated along a direction parallel to said laser diode bars and said first cylindrical microlens being bonded to said front face of said support structure,

(f) repeating step (e) for the linear array of laser beamlets exiting from each of said micro-optics devices,

(g) driving said stacked laser diode array at a drive current selected to get the desired optical output power,

wherein the combined actions of said micro-optics devices and said cylindrical microlenses enable optical conditioning of the plurality of laser beamlets emitted from said stacked laser diode array to radiate an output laser beam having its radiant intensity profile that fills a predetermined field of illumination with a predetermined uniformity.

6. A method for generating a laser beam for use in light illumination applications, comprising the steps of :

(a) mounting a first laser diode bar in a submount compatible with a rack-and-stack array packaging architecture,

(b) optically registering a first micro-optics device to the linear array of laser beamlets radiated by said first laser diode bar mounted in said submount, said micro-optics device performing collimation along the a fast axis and interchange of the fast-axis and slow-axis divergence angles of said linear array of laser beamlets,

(c) repeating steps (a) and (b) for a plurality of laser diode bars, the number of laser diode bars being selected so that a predetermined output power can be radiated,

(d) packaging the plurality of laser diode bars according to a rack-and-stack array packaging architecture to provide a stacked laser diode array,

(e) securing a support structure to said stacked laser diode array, said support structure having a front face,

(f) optically registering a first cylindrical microlens to a first linear array of laser beamlets exiting from said first micro-optics device, said first cylindrical microlens performing collimation along the slow axis of said first linear array of laser beamlets, said first cylindrical microlens being elongated along a direction parallel to said laser diode bars and said first cylindrical microlens being bonded to said front face of said support structure,

(g) repeating step (f) for the linear array of laser beamlets exiting from each of said micro-optics devices,

(h) driving said stacked laser diode array at a drive current selected to get the desired a predetermined optical output power,

whereby wherein the combined actions of said micro-optics devices and said cylindrical microlenses enable optical conditioning of the plurality of laser beamlets emitted from said stacked laser diode array to radiate an output laser beam having its radiant intensity profile that fills a predetermined field of illumination with a predetermined uniformity.