Chiral fiber laser apparatus and method

• US 6,671,293 B2
• Filed: 11/19/2002
• Issued: 12/30/2003
• Est. Priority Date: 11/19/2001
• Status: Expired due to Term

• Current Assignee: Chiral Photonics, Inc.
• Original Assignee: Chiral Photonics, Inc.
• Inventors: Genack, Azriel Zelig, Kopp, Victor Ilʼich
• Primary Examiner(s): Leung, Quyen
• Assistant Examiner(s): Jackson, Cornelius H
• Application Number:
  US10/299,651
• Publication Number:
  US 20030095578A1
• Time in Patent Office: 406 Days
• Field of Search: 372/6, 372/39, 372/72
• US Class Current: 372/6
• CPC Class Codes: G02B 2006/0209 Helical, chiral gratings
• CPC Class Codes: G02B 6/02085 characterised by the grating profile, e.g. chirped, apodised, tilted, helical
• CPC Class Codes: G02B 6/021 characterised by the core or cladding or coating, e.g. materials, radial refractive index profiles, cladding shape
• CPC Class Codes: G02B 6/0239 Comprising means for varying the guiding properties, e.g. tuning means
• CPC Class Codes: H01S 3/06708 Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering optical fibres as passive waveguides G02B6/02
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06716 Fibre compositions per se C03C13/04or doping with active elements lasing materials in general H01S3/14
• CPC Class Codes: H01S 3/06741 Photonic crystal fibre, i.e. the fibre having a photonic bandgap
• CPC Class Codes: H01S 3/0675 Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/094007 Cladding pumping, i.e. pump light propagating in a clad surrounding the active core
• CPC Class Codes: H01S 3/094019 Side pumped fibre, whereby pump light is coupled laterally into the fibre via an optical component like a prism, or a grating, or via V-groove coupling

Abstract

A chiral fiber laser implemented in a fiber Bragg grating mimicking the advantageous optical properties of a cholesteric liquid crystal structure is provided. The dopant, the pitch, the core cross section and dimensions thereof, of the inventive chiral fiber laser as well as the core and cladding materials used in construction thereof, may be advantageously selected and configured to enable the inventive chiral fiber laser to produce lasing at a desirable wavelength. In another embodiment of the inventive chiral fiber laser, a tunable defect is introduced to provide tunable lasing corresponding to the wavelength at the defect mode. Multiple embodiments using coupled fiber optical pumping as well as direct optical pumping for excitation of the inventive chiral fiber laser are provided.

Claims

1. A chiral fiber laser comprising:

an elongated chiral optical fiber comprising a photonic stop band with a plurality of long-lived photonic modes occurring therein, said chiral optical fiber having a central longitudinal axis, a core disposed along said longitudinal axis, said core having a pitch, a core cross-section shape, a core length, a core height, a core width, and a core refractive index, and a cladding surrounding said core having a cladding refractive index;

active dopant disposed throughout at least one of said core and the cladding, wherein said core and cladding refractive indices, said core cross-section shape, said core length, said core height, said core width, and said pitch are configured to produce a particular long-lived photonic mode, from said plural long-lived photonic modes, corresponding to a desired lasing wavelength, and

excitation means, applied to said elongated chiral optical fiber, for causing said chiral optical fiber to emit electromagnetic radiation, wherein said active dopant is configured to produce peak gain substantially positioned at said selected particular long-lived photonic mode, such that lasing output occurs at said desired lasing wavelength with at least one of;

a maximum output power and a minimized lasing threshold.

2. The chiral fiber laser of claim 1, wherein said chiral optical fiber comprises a structure having a period that is one half of a wavelength of a signal inside said chiral optical fiber, and said pitch which is twice said period.

3. The chiral fiber laser of claim 1, further comprising:

first tuning means for dynamically tuning said desired lasing wavelength by changing said pitch of said chiral optical fiber.

4. The chiral fiber laser of claim 3, wherein said first tuning means comprise at least one of:

twisting said chiral optical fiber along said longitudinal axis, and heating, cooling, stretching or shrinking said chiral optical fiber.

5. The chiral fiber laser of claim 1, further comprising a defect disposed in said chiral optical fiber causing a long-lived defect photonic mode in said photonic stop band of said chiral optical fiber.

6. The chiral fiber laser of claim 5, wherein said core and cladding refractive indices, said core cross-section shape, said core height, said core width, and said pitch are configured such that said desired lasing wavelength corresponds to said long-lived defect photonic mode and wherein said active dopant is configured to produce peak gain substantially positioned at said long-lived defect photonic mode, such that the lasing output occurs at said desired lasing wavelength with at least one of:

a maximum output power and a minimum lasing threshold.

7. The chiral fiber laser of claim 6, wherein said chiral optical fiber comprises two sequential longitudinal portions, and wherein said defect comprises at least one of:

a predetermined spacing between said two longitudinal portions, a dielectric material positioned between said two longitudinal portions, and a circumferential twist at a predetermined twist angle between said two longitudinal portions.

8. The chiral fiber laser of claim 7, further comprising second tuning means for dynamically tuning said second lasing wavelength by at least one of:

changing said predetermined spacing between said longitudinal portions of the chiral optical fiber, and changing said predetermined twist angle.

9. The chiral laser of claim 1, wherein said excitation means comprises a direct optical pump source configured to provide optical pumping along said longitudinal axis of said chiral optical fiber through at least one of:

said core and said cladding.

10. The chiral laser of claim 1, wherein said excitation means comprises a coupled fiber optical pump source configured to deliver optical pumping by proximity to said chiral optical fiber.

11. The chiral laser of claim 1, wherein said excitation means comprises a plurality of coupled fiber optical pump sources configured to deliver optical pumping by proximity to said chiral optical fiber.

12. The chiral laser of claim 1, wherein increasing a difference between said core refractive index and said cladding refractive index corresponds to optimization of the chiral fiber laser for low threshold lasing, and wherein, decreasing said difference between said core refractive index and said cladding refractive index corresponds to optimization of the chiral fiber laser for high power lasing.

13. An apparatus for customizing a chiral fiber laser for lasing and at desired lasing wavelength, comprising:

means for selecting;

(1) an optical fiber core having cross-section shape with 180 degree symmetry, a core length, a core height, a core width, and a core refractive index, and,

(2) a cladding for surrounding said core, having a cladding refractive index, wherein active dopant is disposed throughout at least one of said core and the cladding,

means for determining a value of a desired pitch to be applied to said core given said desired lasing wavelength, said core cross-section shape, said core length, core height and core width, a core refractive index, and a cladding refractive index, such that when said core is twisted at said desired pitch, a resulting chiral optical fiber will be configured to comprise a photonic stop band with a plurality of long-lived photonic modes occurring therein, wherein a selected long-lived photonic mode of said plural long-lived photonic modes corresponds to said desired lasing wavelength;

means for applying said desired pitch to said core to produce said chiral optical fiber; and

excitation means, applied to said chiral optical fiber, for causing said chiral optical fiber to emit electromagnetic radiation, wherein said active dopant is configured to produce peak gain substantially positioned at said selected long-lived photonic mode, such that lasing output occurs at said desired lasing wavelength with at least one of;

a maximum output power and a minimized lasing threshold.

14. A method for lasing utilizing a chiral fiber structure comprising the steps of:

(a) providing an elongated chiral optical fiber comprising a photonic stop band with a plurality of long-lived photonic modes occurring therein, said chiral optical fiber having a central longitudinal axis, a core disposed along said longitudinal axis, said core having a pitch, a core cross-section shape with 180 degree symmetry, a core length, a core height, a core width, and a core refractive index, and a cladding surrounding said core having a cladding refractive index,

(b) prior to said step (a), choosing said core and cladding refractive indices, said core cross-section shape, said core length, said core height, and said core width;

(c) after said step (b) but prior to said step (a), determining a desired pitch that corresponds to a desired lasing wavelength, from;

i) said desired lasing wavelength,

ii) said core and cladding refractive indices, and

iii) said core cross-section shape, said core length, said core height, and said core width;

(d) prior to said step (a) configuring said elongated chiral optical fiber with said desired pitch such that said desired lasing wavelength corresponds to a particular long-lived photonic mode from said plural long-lived photonic modes,

(e) prior to said step (a), choosing and configuring an active dopant disposed within at least one of said core and said cladding, to produce peak gain approximately positioned at said selected particular long-lived photonic mode; and

(f) applying excitation to said chiral optical fiber, to cause said chiral optical fiber to emit electromagnetic radiation, such that lasing output occurs at said desired lasing wavelength with at least one of;

a maximum output power and a minimized lasing threshold.

15. The method of lasing of claim 14, further comprising the step of:

(g) prior to said step (a) introducing a defect into said chiral fiber structure such that said selected particular long lived photonic mode is a defect mode.

16. The method of lasing of claim 15, wherein said chiral fiber structure comprises two sequentially positioned longitudinal portions, and wherein said defect introduced at said step (g) comprises a circumferential twist at a predetermined twist angle between said two longitudinal portions, further comprising the step of:

(h) dynamically tuning said desired lasing wavelength by changing said predetermined twist angle.

17. The method of lasing of claim 14, further comprising the step of:

(i) dynamically tuning said desired lasing wavelength by changing said desired pitch of said chiral optical fiber.