Broadband, freeform focusing micro optics for side-viewing imaging catheters

Abstract

The disclosed embodiments relate to a system that implements a side-viewing imaging catheter. This system includes a catheter sheath enclosing an imaging core, wherein the imaging core presents an internal optical channel coupled to an optical element located at the distal end of the imaging core. The optical element includes an internal reflective surface that reflects and focuses light transmitted via the optical channel in a direction orthogonal to a rotational axis of the catheter toward a target location, and returns reflected light from the target location back through the optical channel. This internal reflective surface of the optical element is shaped to focus the light so that a resulting beam shape at the target location has a small cross section area and substantially equal axial and transaxial dimensions.

1 . A side-viewing imaging catheter, comprising:
 a catheter sheath enclosing an imaging core;   wherein the imaging core presents an internal optical channel coupled to an optical element located at the distal end of the imaging core;   wherein the optical element includes an internal reflective surface that reflects and focuses light transmitted via the optical channel in a direction orthogonal to a rotational axis of the catheter toward a target location, and returns reflected light from the target location back through the optical channel; and   wherein the internal reflective surface of the optical element is shaped to focus the light so that a resulting beam shape at the target location has a small cross section area and substantially equal axial and transaxial dimensions.   
     
     
         2 . The side-viewing imaging catheter of  claim 1 , wherein a shape of the internal reflective surface is numerically computed by optimizing a polynomial surface to minimize a radius of the beam shape at the target location. 
     
     
         3 . The side-viewing imaging catheter of  claim 2 , wherein the internal reflective surface comprises an aspheric surface with additional polynomial aspheric terms. 
     
     
         4 . The side-viewing imaging catheter of  claim 1 , wherein the internal reflective surface is fabricated through direct-write laser machining in combination with a secondary surface reflow operation. 
     
     
         5 . The side-viewing imaging catheter of  claim 1 , wherein the internal reflective surface is fabricated using a grayscale lithography technique. 
     
     
         6 . The side-viewing imaging catheter of  claim 1 , wherein the internal reflective surface is shaped to reflect the light with a beam tilt in a forward axial direction. 
     
     
         7 . The side-viewing imaging catheter of  claim 1 , wherein the optical element includes a reflective coating to provide broadband reflectivity. 
     
     
         8 . The side-viewing imaging catheter of  claim 1 , wherein the side-viewing imaging catheter is configured to perform ultraviolet (UV) imaging. 
     
     
         9 . The side-viewing imaging catheter of  claim 1 , wherein the optical element is comprised of fused silica. 
     
     
         10 . The side-viewing imaging catheter of  claim 1 , wherein the side-viewing imaging catheter is a multimodal catheter, which supports both optical and ultrasonic imaging;
 wherein the catheter tube additionally encloses an electrical channel; and wherein the probe additionally includes an ultrasonic transducer coupled to the electrical channel; and   wherein the ultrasonic transducer is oriented orthogonally to a rotational axis of the catheter and is configured to generate an ultrasonic acoustic signal and to return resulting echo information.   
     
     
         11 . The side-viewing imaging catheter of  claim 10 , wherein the multimodal catheter supports both intravascular ultrasound (IVUS) imaging and multispectral fluorescence-lifetime imaging microscopy (FLIm). 
     
     
         12 . A micro optic for a side-viewing imaging catheter, comprising:
 an optical element including an internal reflective surface that reflects and focuses light transmitted via an optical channel in the catheter in a direction orthogonal to a rotational axis of the catheter toward a target location, and returns reflected light from the target location back through the optical channel;   wherein the internal reflective surface of the optical element is shaped to focus the light so that a resulting beam shape at the target location has substantially equal axial and transaxial dimensions.   
     
     
         13 . The micro optic of  claim 12 , wherein a shape of the internal reflective surface is numerically computed by optimizing a polynomial surface to minimize a radius of the beam shape at the target location. 
     
     
         14 . The micro optic of  claim 13 , wherein the internal reflective surface comprises an aspheric surface with additional polynomial aspheric terms. 
     
     
         15 . The micro optic of  claim 12 , wherein the internal reflective surface is fabricated through direct-write laser machining in combination with a secondary surface reflow operation. 
     
     
         16 . The micro optic of  claim 12 , wherein the internal reflective surface is fabricated using a grayscale lithography technique. 
     
     
         17 . The micro optic of  claim 12 , wherein the internal reflective surface is shaped to reflect the light with a beam tilt in a forward axial direction. 
     
     
         18 . The micro optic of  claim 12 , wherein the optical element includes a reflective coating to provide broadband reflectivity. 
     
     
         19 . The micro optic of  claim 12 , wherein the optical element is configured to perform ultraviolet (UV) imaging. 
     
     
         20 . The micro optic of  claim 12 , wherein the optical element is comprised of fused silica. 
     
     
         21 . A method for manufacturing a side-viewing micro optic for a catheter, comprising:
 creating one or more curved surfaces in a silica wafer, wherein the one or more curved surfaces have a geometry suitable to shape an internal optical beam by reflection;   depositing a reflective coating on the silica wafer to provide reflectivity, thereby converting the one or more curved surfaces into one or more internal freeform reflective surfaces; and   cutting the silica wafer to obtain one or more micro-optic elements, which are configured to receive an incoming optical beam along a rotational axis of the catheter, wherein each micro-optic element includes a freeform reflective internal surface to reflect the incoming optical beam in a substantially orthogonal direction from the optical axis toward a target location, and wherein the internal reflective surface is shaped to focus the light so that a resulting beam shape at the target location has substantially equal axial and transaxial dimensions.   
     
     
         22 . The method of  claim 21 , wherein the one or more curved surfaces are created using direct laser machining. 
     
     
         23 . The method of  claim 21 , wherein the one or more curved surfaces are created using a grayscale lithography technique. 
     
     
         24 . The method of  claim 21 , wherein the reflective coating is not deposited in cases where a total internal reflection with a surrounding medium is sufficient to reflect the optical beam. 
     
     
         25 . The method of  claim 21 , wherein creating the one or more curved surfaces involves creating a microlens array comprising a large number of curved surfaces organized in a rectangular pattern on the silica wafer. 
     
     
         26 . The method of  claim 25 , wherein the cutting of the silica wafer is performed using a dicing saw by:
 mounting the coated silica wafer on a silicon wafer using mounting media; cutting the microlens array along a vertical direction of the microlens array to create individual strips of microlenses;   removing each microlens strip from the silicon wafer by heating the mounting media;   positioning and securing each microlens strip so that a side of the microlens strip is attached to a second silicon wafer using mounting media;   using a dicing saw to cut each microlens strip into individual microlenses; and   performing a trimming operation on each microlens.   
     
     
         27 . The method of  claim 26 , wherein performing the trimming operation on each microlens comprises:
 removing the microlens from an underlying wafer;   mounting the microlens on a support such that the only part to be removed protrudes from the support; and   polishing the microlens to a specified length.   
     
     
         28 . The method of  claim 21 , wherein the cutting of the silica wafer is performed using a laser. 
     
     
         29 . The method of  claim 21 , wherein the cutting of the silica wafer is performed in a single operation by tilting a cutting plane. 
     
     
         30 . The method of  claim 21 , further comprising polishing an upper surface of each microlens to limit scattering caused by roughness created by the dicing process. 
     
     
         31 . The method of  claim 22 , wherein while using the direct laser machining process to create the microlens array, the method ensures that a spacing between microlenses corresponds to a kerf width of a blade of the dicing saw.