Common path mode fiber tip diffraction interferometer for wavefront measurement

Patent metadata

Field	Value
Publication number	US-2021123716-A1
Application number	US-202016818050-A
Country	US
Kind code	A1
Filing date	Mar 13, 2020
Priority date	Oct 28, 2019
Publication date	Apr 29, 2021
Grant date	—

Abstract

Reference and test waves are directed in a common path mode in a fiber tip diffraction interferometer. A first fiber can be used to generate the reference wave and a second fiber can be used to generate the test wave. Each fiber can include a single mode fiber tip that defines a wedge at an end without a coating on end surface or a tapered fiber tip. The fiber tip diffraction interferometer can include an aplanatic pupil imaging lens or system disposed to receive both the test wave and the reference wave and a sensor configured to receive both the test wave and the reference wave.

First claim

What is claimed is:

1 . A fiber tip diffraction interferometer comprising:
a first fiber that generates a reference wave; a second fiber or a pinhole that generates a test wave, wherein the test wave is focused to a point where the test wave is reflected, and wherein the test wave and the reference wave are in a common path mode after the test wave is reflected; an aplanatic imaging lens or a pupil imaging system disposed to receive both the test wave and the reference wave; and a sensor configured to receive both the test wave and the reference wave, wherein the sensor is disposed on an opposite side of the aplanatic imaging lens or a pupil imaging system from the first fiber.

2 . The fiber tip diffraction interferometer of claim 1 , wherein the first fiber and/or the second fiber includes a single mode fiber tip that defines a wedge at an end, wherein a flat surface of the wedge is not perpendicular to an axis of the fiber, and wherein the flat surface of the wedge does not have a coating thereon.

3 . The fiber tip diffraction interferometer of claim 2 , wherein the flat surface is disposed at an angle from 14 degrees and 25 degrees relative to the axis of the fiber.

4 . The fiber tip diffraction interferometer of claim 2 , wherein the fiber has a diameter of 125 μm.

5 . The fiber tip diffraction interferometer of claim 2 , wherein the surface roughness of the flat surface is from 0 nm RMS to 0.8 nm RMS.

6 . The fiber tip diffraction interferometer of claim 5 , wherein a surface roughness of the flat surface is 0.4 nm RMS or less.

7 . The fiber tip diffraction interferometer of claim 2 , wherein the fiber defines an outer circumferential surface, and wherein at least part of the outer circumferential surface does not have a coating thereon.

8 . The fiber tip diffraction interferometer of claim 2 , wherein the fiber defines a first diameter at a point adjacent where the wedge is disposed and a second diameter at a non-zero point away from the first diameter, wherein the first diameter and the second diameter are the same.

9 . The fiber tip diffraction interferometer of claim 2 , wherein the fiber defines a first diameter at a point adjacent where the wedge is disposed and a second diameter at a non-zero point away from the first diameter, wherein the first diameter is larger than the second diameter.

10 . The fiber tip diffraction interferometer of claim 9 , wherein the first diameter is at least 1 mm and the second diameter is 125 μm.

11 . The fiber tip diffraction interferometer of claim 1 , wherein the first fiber and/or the second fiber is silica, and wherein a core of the first fiber and/or the second fiber is doped.

12 . The fiber tip diffraction interferometer of claim 1 , further comprising an imaging system, wherein the test wave passes from the second fiber through the imaging system.

13 . The fiber tip diffraction interferometer of claim 1 , wherein the first fiber and/or the second fiber has a tapered fiber tip with a side metal coating.

14 . The fiber tip diffraction interferometer of claim 1 , further comprising a calibrated optics in a path of the test wave configured to calibrate a sphericity of the test wave and the reference wave.

15 . The fiber tip diffraction interferometer of claim 1 , wherein the test wave is reflected off an end surface of the first fiber.

16 . The fiber tip diffraction interferometer of claim 1 , further comprising a thin film, wherein the test wave is reflected off the thin film and the reference wave is directed through the thin film, and wherein one surface of the thin film includes an antireflective coating.

17 . The fiber tip diffraction interferometer of claim 16 , wherein the first fiber tip and the second fiber tip are conjugate with each other to a reflective surface of the thin film.

18 . The fiber tip diffraction interferometer of claim 1 , further comprising a laser in optical communication with the first fiber and the second fiber.

19 . The fiber tip diffraction interferometer of claim 18 , further comprising:
a splitter in optical communication with the laser, wherein the splitter forms a first laser path to the second fiber or the pinhole and a second laser path to the first fiber; a first polarization control unit along the first laser path; a second polarization control unit along the second laser path; a power control unit along the second laser path; a time delay control unit along the second laser path; and a phase-shift control unit along the second laser path.

20 . A method comprising:
generating a reference wave with a first fiber; generating a test wave with a second fiber or a pinhole; reflecting the test wave from a point to be in a direction of the reference wave, wherein the test wave and the reference wave are in a common path mode after the reflecting; and directing the reference wave and the test wave at a 2D sensor after the reflecting.

21 . The method of claim 20 , wherein the first fiber includes a single mode fiber tip that defines a wedge at an end, wherein a flat surface of the wedge is not perpendicular to an axis of the fiber, wherein the flat surface of the wedge does not have a coating thereon, and wherein the test wave is directed at the flat surface of the first fiber and the point for reflecting the test wave is on the flat surface.

22 . The method of claim 20 , further comprising directing the test wave and the reference wave through an aplanatic imaging lens or system.

23 . The method of claim 20 , wherein the test wave is directed at a thin film and wherein the reference wave is directed through the thin film, wherein the point for reflecting the test wave is on the thin film, and wherein one surface of the thin film includes an antireflective coating.

24 . The method of claim 23 , further comprising calibrating a diffraction wavefront of the test wave.

25 . The method of claim 20 , wherein the first fiber and/or the second fiber have a tapered fiber tip with a side metal coating.

26 . The method of claim 20 , further comprising calibrating a diffraction wavefront of the test wave using a calibrated optics.

Assignees

• Kla Corp

Inventors

• Huang Haifeng
• Shi Rui-Fang
• Wack Dan
• Kestner Robert

Classifications

• G01B9/02015

  characterised by the beam path configuration · CPC title

• G01M11/0271 Primary

  by using interferometric methods · CPC title

• G01B9/02039

  by matching the wavefront with a particular object surface shape · CPC title

• G01B9/02007

  Two or more frequencies or sources used for interferometric measurement (using only beat G01B9/02003) · CPC title

• G01B11/255

  for measuring radius of curvature {(measuring diameter G01B11/08)} · CPC title