Devices and applications based on tunable wave-guiding bragg gratings with nonlinear group delays

• US 6,915,040 B2
• Filed: 06/13/2002
• Issued: 07/05/2005
• Est. Priority Date: 12/15/1997
• Status: Expired due to Fees

• Current Assignee: University of Southern California
• Original Assignee: University of Southern California
• Inventors: Nezam, S.M. Reza Motaghian, Song, Yong-Won, Willner, Alan E.
• Primary Examiner(s): Palmer, Phan T. H.
• Application Number:
  US10/172,832
• Publication Number:
  US 20030086647A1
• Time in Patent Office: 1,118 Days
• Field of Search: 385 1- 12, 385/24, 385/122, 385 37- 43, 372/6, 372/27, 372/64, 372/96, 372/102, 398/113, 398/FOR.179, 359/290
• US Class Current: 385/37
• CPC Class Codes: G02B 6/02085 characterised by the grating profile, e.g. chirped, apodised, tilted, helical
• CPC Class Codes: G02B 6/02109 having polarization sensitive features, e.g. reduced photo-induced birefringence
• CPC Class Codes: G02B 6/02138 based on illuminating a phase mask
• CPC Class Codes: G02B 6/02195 characterised by means for tuning the grating
• CPC Class Codes: G02B 6/022 using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper G02B6/02204 takes precedence; optical modulation using photo-elastic effect G02F1/0131
• CPC Class Codes: G02B 6/2932 comprising a directional router, e.g. directional coupler, circulator
• CPC Class Codes: G02B 6/29322 Diffractive elements of the tunable type G02B6/02195 takes precedence; optical modulation devices based on a change of the optical properties of the medium G02F1/00
• CPC Class Codes: G02B 6/29394 Compensating wavelength dispersion G02B6/29376 takes precedence; dispersion compensated optical transmission systems H04B10/2507
• CPC Class Codes: G02B 6/29398 Temperature insensitivity
• CPC Class Codes: G02B 6/4215 the intermediate optical elements being wavelength selective optical elements, e.g. variable wavelength optical modules or wavelength lockers G02B6/4246 takes precedence
• CPC Class Codes: G02F 1/011 in optical waveguides, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0115 in optical fibres
• CPC Class Codes: G02F 1/0126 Opto-optical modulation, i.e. control of one light beam by another light beam, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0134 in optical waveguides
• CPC Class Codes: G02F 2201/307 Reflective grating, i.e. Bragg grating
• CPC Class Codes: H01S 3/0057 Temporal shaping, e.g. pulse compression, frequency chirping soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108
• CPC Class Codes: H04B 10/25133 including a lumped electrical or optical dispersion compensator H04B10/2519, H04B10/2525 takes precedence
• CPC Class Codes: H04B 10/2519 using Bragg gratings
• CPC Class Codes: H04B 2210/258 treating each wavelength or wavelength band separately

Abstract

Techniques, devices, and systems for generating tunable dispersions to control or compensate for dispersions in optical signals by using wave-guiding grating elements with nonlinear group delays.

Claims

1. A device for processing two or more optical WDM channels, comprising:

an optical fiber having an optic axis along said fiber to guide two or more WDM channels;

a fiber grating formed in said fiber to have a spatial grating pattern that has a Bragg reflection band that spectrally covers at least two adjacent WDM channels and reflects received optical spectral components within said Bragg reflection band to produce time delays in different reflected optical spectral components in said two adjacent WDM channels as a nonlinear function of wavelength; and

a grating control unit coupled to interact with said fiber grating to tune at least dispersion of said different reflected optical spectral components.

2. The device as in claim 1, wherein said fiber grating is a nonlinearly-chirped fiber grating in which a product of an effective refractive index and a grating period of said fiber grating varies nonlinearly along said optic axis.

3. The device as in claim 2, wherein said grating period changes nonlinearly along said optic axis.

4. The device as in claim 2, wherein said fiber has a refractive index that changes nonlinearly along said optic axis.

5. The device as in claim 2, wherein said nonlinear function includes a cubic dependence on wavelength to produce a tunable dispersion slope.

6. The device as in claim 1, wherein said grating control unit includes a fiber stretcher that controls and adjusts at least a length of said fiber grating to tune said dispersion.

7. The device as in claim 6, wherein said fiber stretcher includes a piezoelectric element.

8. The device as in claim 6 wherein said fiber stretcher includes a magnetostrictive element that operates in response to a control magnetic field.

9. The device as in claim 1, wherein said grating control unit controls and adjusts a refractive index of said fiber grating for tuning.

10. The device as in claim 9, wherein said refractive index changes in response to an electrical field, and wherein said grating control unit is configured to generate and adjust a varying control electrical field along said optic axis for tuning.

11. The device as in as in claim 9, wherein said refractive index changes in response to an electromagnetic radiation field, and wherein said grating control unit is configured to generate a varying control electromagnetic radiation field along said optic axis for tuning.

12. The device as in claim 1, wherein said spatial grating pattern is configured to produce a spatial-varying grating strength to produce said nonlinear function.

13. The device as in claim 1, wherein said spatial grating pattern includes a quadratic dependence on wavelength in said nonlinear function-.

14. The device as in claim 1, wherein said grating control unit includes an acoustic wave generator configured and coupled to produce a frequency-tunable acoustic wave along said optic axis so that said acoustic wave alters a frequency response of said fiber grating for tuning.

15. The device as in claim 1, wherein said grating control unit is configured to control both a length and a refractive index of said fiber along said optic axis.

16. The device as in claim 1, wherein said fiber is formed of an optical birefringent material to have two orthogonal principal polarization axes that are substantially perpendicular to said optic axis.

17. A device for processing two or more optical WDM channels, comprising:

an optical fiber having an optic axis along said fiber to guide two or more WDM channels;

a fiber grating formed in said fiber and configured to have a spatial grating pattern that has a Bragg reflection band spectrally covering at least two adjacent WDM channels and is configured to produce a time delay in a reflected signal which depends nonlinearly on wavelength and includes at least a cubic function of the wavelength; and

a grating control unit coupled to interact with said fiber grating to tune both dispersion and dispersion slope produced by said fiber grating in each reflected optical spectral component.

18. The device as in claim 17, wherein said fiber grating is a nonlinearly-chirped fiber grating in which said spatial grating pattern changes nonlinearly along said optic axis.

19. The device as in claim 18, wherein said spatial grating pattern includes a spatial-varying amplitude pattern along said optic axis.

20. The device as in claim 17, wherein said time delay further includes a quadratic dependence on the wavelength.

21. The device as in claim 17, wherein said grating control unit controls and adjusts a length of said fiber grating for tuning.

22. The device as in claim 17, wherein said grating control unit controls and adjusts a refractive index of said fiber grating for tuning.

23. The device as in claim 17, wherein said grating control unit controls and adjusts both a length and a refractive index of said fiber grating for tuning.