US-12623947-B2 - Infrared-transmitting, polarization-maintaining optical fiber and method for making

US12623947B2US 12623947 B2US12623947 B2US 12623947B2US-12623947-B2

Abstract

This application relates generally to an optical fiber for the delivery of infrared light where the polarization state of the light entering the fiber is preserved upon exiting the fiber and the related methods for making thereof. The optical fiber has a wavelength between about 0.9 μm and 15 μm, comprises at least one infrared-transmitting glass, and has a polarization-maintaining (PM) transverse cross-sectional structure. The infrared-transmitting, polarization-maintaining (IR-PM) optical fiber has a birefringence greater than 10 −5 and has applications in dual-use technologies including laser power delivery, sensing and imaging.

Inventors

Daniel J. Gibson
Daniel Rhonehouse
Shyam S. Bayya
L. Brandon Shaw
Rafael R. Gattass
Jesse A. Frantz
Jason D. Myers
Woohong Kim
Jasbinder S. Sanghera

Assignees

THE GOVERNMENT OF THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF THE NAVY

Dates

Publication Date: 20260512
Application Date: 20240116

Claims (2)

1 . A method of making an infrared-transmitting, polarization maintaining (IR-PM) optical fiber, comprising: making a preform with an approximately round cross-sectional shape comprising an approximately round core surrounded by a cladding, wherein the preform comprises an infrared-transmitting, non-silica glass; compressing the preform to form a compressed preform where both the core and cladding have an approximately elliptical shape; altering the compressed preform by grinding, polishing, machining, or any combination thereof to make an altered preform with an approximately round cladding; and drawing the altered preform into a fiber that is approximately round with an approximately elliptical core, wherein the fiber has a birefringence greater than 10 −5 .
2 . The method of claim 1 , wherein the infrared-transmitting, non-silica glass comprises a chalcogenide glass comprising at least one of sulfur, selenium, and tellurium; a glass based on an oxide of at least one of Te, Ge, Pb, and La; a fluoride glass, or any combination thereof.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a divisional application of U.S. application Ser. No. 16/842,033, filed on Apr. 7, 2020, which was a non-provisional application of U.S. Provisional Application No. 62/830,732, filed on Apr. 8, 2019, the contents of each are incorporated herein by reference in their entireties. TECHNICAL FIELD This application relates generally to an optical fiber for the delivery of infrared light where the polarization state of the light entering the fiber is preserved upon exiting the fiber and the related method for making. The optical fiber has a range of transmissible wavelengths between about 0.9 μm and 15 μm, comprises at least one infrared-transmitting glass, and has a polarization-maintaining (PM) transverse cross-sectional structure. BACKGROUND OF THE INVENTION Infrared (IR) fibers are used in many passive and active applications to transmit, generate, or modify infrared optical energy at wavelengths from as low as 0.9 μm to as high as 20 μm. Infrared fibers typically have axial symmetry which is agnostic with respect to the linear polarization state of the light transmitted therein. IR fibers, typically comprise a solid core region surrounded by a solid cladding region, usually surrounded by a protective coating. Solid-core IR fibers are made from IR-transmitting materials including chalcogenide glasses, fluoride glasses, and crystalline materials such as silver halides, thallium bromoiodide (KRS-5), sapphire, and yttrium aluminum garnet (YAG). This is in contrast to the more common silica glass optical fibers that transmit visible light and some near-infrared (NIR) light including wavelengths as low as about 400 nm to as high as about 1.8 μm. Axially asymmetric optical fibers for visible wavelengths have been designed with physical features that impart modal birefringence such that orthogonal polarizations have different propagation constants and there is low mode-coupling or crosstalk between them. Many types of PM fibers have been demonstrated for visible and near-infrared (NIR) telecommunications wavelengths (400 nm-1800 nm), largely built upon silica glass with various dopants. However, no PM fiber has been developed for infrared wavelengths (2-20 μm), and there have been very few IR-PM fibers reported in the scientific literature and none are commercially available. The typical IR application space: laser power delivery, low data rate communications, chemical sensing and others, has not traditionally required these types of fibers and little effort has gone into their development beyond technological curiosity. It is worth noting that solid-core silica fibers do not transmit IR light well beyond about 2 μm due to the infrared absorption of silica, and PM silica fibers cannot be used at the wavelengths of interest (2-20 μm) in this invention. Through analysis of thermal stress in silica PM fibers, Chu et al. derived functional forms for the resultant stress and the material birefringence due to the materials and geometry in common stress-induced birefringent silica-based PM fibers (Chu et al., “Analytical method for calculation of stresses and material birefringence in polarization-maintaining optical fiber,” J. Lightwave Technol., vol. 2, no. 5, pp. 650-662 (1984)). They approximate the birefringence as B≅2⁢E⁢C1-v⁢(α2-α3)⁢T⁡(d1d2)2[1-3⁢(1-2⁢(rb)2)⁢(d2b)4+3⁢(rd2)2⁢ cos⁢ 2⁢θ](Eq. 1) where E is Young's modulus of the glass, C is the stress-optic coefficient of the glass, ν is Poisson's ratio of the glass, α2 is the thermal expansion coefficient of the cladding glass, α3 is the thermal expansion coefficient of the stressor glass, T is the temperature difference between the fiber drawing and room temperatures, d1 is the half diameter or radius of each circular stressor member, d2 is the distance from the center of each stressor member and the center of the fiber core, b is the half diameter or radius of the fiber cladding and r and 0 are the usual radial coordinates. The magnitude of the birefringence is therefore strongly dependent on the materials available to the fiber engineer and the fiber drawing temperature, which for silica-based fibers is very large. The fibers of the present invention comprise non-silica-containing glasses including chalcogenide glasses, comprising at least one chalcogen element excluding oxygen (S, Se, Te); chalcohalide glasses, comprising at least one chalcogen element excluding oxygen (S, Se, Te) and at least one halogen element (F, Cl, Br, I); fluoride glasses, comprising fluorine and at least one other element (e.g. ZBLAN); and heavy-metal oxide glasses comprising oxygen and at least one metal element excluding silicon (e.g. GeO2—TeO2). It should be apparent to one skilled in the art of fiber optics and specifically the art of infrared fiber optics that one cannot simply replace silica with a more suitable IR-transmitting glass to make an IR-PM fiber as the material properties (Young's modulus, stress-optic coefficie