Compact hybrid laser rod and laser system

Patent metadata

Field	Value
Publication number	US-9831629-B2
Application number	US-201615382852-A
Country	US
Kind code	B2
Filing date	Dec 19, 2016
Priority date	Dec 28, 2015
Publication date	Nov 28, 2017
Grant date	Nov 28, 2017

Abstract

A hybrid fiber rod includes a fiber core and inner and outer cladding layers. The core is doped with an active element. The inner cladding layer surrounds the core, and has a refractive index substantially equal to that of the core. The outer cladding layer surrounds the inner cladding layer, and has a refractive index less than that of the core and inner cladding layer. The core length is about 30 to 2000 times the core diameter. A hybrid fiber rod laser system includes an oscillator laser, modulating device, the rod, and pump laser diode(s) energizing the rod from opposite ends. The rod acts as a waveguide for pump radiation but allows for free-space propagation of laser radiation. The rod may be used in a laser resonator. The core length is less than about twice the Rayleigh range. Degradation from single-mode to multi-mode beam propagation is thus avoided.

First claim

What is claimed is:

1. A hybrid fiber rod comprising:
a silicate fiber core doped with an active element and having a first refractive index;
an inner cladding layer coaxial with and surrounding the fiber core, wherein the inner cladding layer has a second refractive index substantially equal to the first refractive index; and
an outer cladding layer coaxial with and surrounding the inner cladding layer, and having a refractive index that is less than the first and second refractive indexes;
wherein a ratio of a length of the fiber core to a diameter of the fiber core is in a range of about 30 to 2000, and the length of the fiber core is less than about twice the Rayleigh range of a Gaussian beam propagating in free space, such that degradation from single-mode to multi-mode propagation of a laser beam in the fiber core and the inner cladding layer is avoided.

2. The hybrid fiber rod of claim 1 , wherein the fiber core has a length of less than or equal to about 0.5 meters (m) and a diameter in a range of about 100 micrometers (μm) to 1000 μm.

3. The hybrid fiber rod of claim 2 , wherein the length of the fiber core is greater than about 0.03 m and less than 0.5 m.

4. The hybrid fiber rod of claim 3 , wherein the length of the fiber core is less than about 0.1 m.

5. The hybrid fiber rod of claim 1 , wherein an outer diameter of the inner cladding layer is about 150 percent of the diameter of the fiber core.

6. The hybrid fiber rod of claim 1 , wherein the active element has a doping concentration of about 0.5 to 10 percent by weight of the fiber core.

7. The hybrid fiber rod of claim 6 , wherein the active element having the doping concentration includes Neodymium, Erbium, Holmium, and wherein the fiber core is configured to output a single-mode laser beam having a wavelength in the range of 1 μm to 2 when irradiated by laser light from a pump laser.

8. A hybrid fiber rod laser system comprising:
a master oscillator laser configured to generate an input laser beam along an optical axis;
one or more modulating devices positioned along the optical axis and configured to receive and modulate a frequency, a wavelength, or an amplitude of the input laser beam, and to thereby output a modulated laser beam; and
a hybrid fiber rod having:
a silicate fiber core doped with an active element and having a first refractive index;
an inner cladding layer coaxial with and surrounding the fiber core, wherein the inner cladding layer has a second refractive index that is substantially equal to the first refractive index; and
an outer cladding layer coaxial with and surrounding the inner cladding layer, and having a refractive index that is less than the first and second refractive indexes, wherein a ratio of a length of the fiber core to a diameter of the fiber core is in a range of about 30 to 2000, and the length of the fiber core is less than about twice the Rayleigh range of a Gaussian beam propagating in free space, such that degradation from single-mode to multi-mode propagation of a laser beam in the fiber core and the inner cladding, layer is avoided; and

at least one pump laser diode configured to energize the hybrid fiber rod from a respective distal end of the hybrid fiber rod with a calibrated wavelength of laser.

9. The laser system of claim 8 , wherein the hybrid fiber rod is configured to receive and amplify the modulated laser beam.

10. The laser system of claim 8 , wherein the laser system includes a plurality of the hybrid fiber rods coaxially arranged along the optical axis.

11. The laser system of claim 8 , further comprising a laser resonator formed via first and second mirrors disposed at opposite distal ends of the hybrid laser rod, the first mirror having a reflectivity of about 100 percent and the second mirror having a reflectivity of less than about 90 percent.

12. The laser system of claim 8 , wherein the fiber core has a length of less than about 0.1 meters (m) and a diameter that is greater than about 100 micrometers (μm) and less than about 1000 μm.

13. The laser system of claim 12 , wherein the length of the fiber core is greater than about 0.03 m.

14. The laser system of claim 8 , wherein an outer diameter of the inner cladding layer is about 150 percent of the diameter of the fiber core.

15. The laser system of claim 8 , wherein the pair of pump laser diodes are configured to provide in-band pumping at a wavelength that is substantially equal to a laser wavelength of the hybrid fiber rod.

16. The laser system of claim 8 , wherein the active element includes Neodymium, Erbium, or Holmium with a doping concentration of about 0.5 to 10 percent by weight of the fiber core.

17. The laser system of claim 8 , wherein the active element includes thulium or ytterbium with a doping concentration of about 0.5 to 10 percent by weight of the fiber core.

18. A hybrid fiber rod comprising:
a silicate fiber core doped with an active element in the form of Neodymium, Erbium, or Holmium with a doping concentration of about 0.5 to 10 percent by weight of the fiber core, the fiber core having a first refractive index, and further having a length between about 0.03 meter (m) and 0.5 m and a diameter of between about 100 micrometers (μm) and 1000 μm;
an undoped inner cladding layer arranged coaxially with and surrounding the silicate fiber core, wherein the inner cladding layer has an outer diameter of about 130 to 200 percent of the diameter of the silicate fiber core, and a second refractive index that is substantially equal to the first refractive index; and
an outer cladding layer arranged coaxially with and surrounding the inner cladding layer, and having a refractive index that is less than about 95 percent of the first and second refractive indexes;
wherein the length of the fiber core is between 30 and 2000 times the diameter of the silicate fiber core, the hybrid fiber rod is configured to emit a single-mode laser beam, and the length of the fiber core is less than about twice the Rayleigh range of a Gaussian beam propagating in free space such that degradation from single-mode to multi-mode propagation of a laser beam in the fiber core arid the inner cladding layer is avoided.

19. The hybrid fiber rod of claim 18 , wherein the active element is Erbium, and wherein the single-mode laser beam has a wavelength of 1.5 μm.

20. The hybrid fiber rod of claim 18 , wherein the length of the fiber core is less than about 0.1 m.

Assignees

• Nasa
• The Us Administrator Of The Nasa

Inventors

• Busch George E
• Amzajerdian Farzin
• Pierrottet Diego F

Classifications

• H01S3/1603

  rare earth · CPC title

• H01S3/161

  holmium · CPC title

• H01S3/06708 Primary

  Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering (optical fibres as passive waveguides G02B6/02) · CPC title

• H01S3/1608

  erbium · CPC title

• H01S3/06733 Primary

  Fibre having more than one cladding · CPC title