Wideband multichannel fiber lasers with output power equalization

• US 6,567,432 B1
• Filed: 01/14/2000
• Issued: 05/20/2003
• Est. Priority Date: 12/09/1999
• Status: Expired due to Term

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Lee, Dong Ho, Kim, Seung Kwan, Kim, Jae Geun
• Primary Examiner(s): Leung; Quyen
• Assistant Examiner(s): Rodriguez; Armando
• Application Number:
  US09/482,351
• Time in Patent Office: 1,222 Days
• Field of Search: 372/6,20,70
• US Class Current: 372/6
• CPC Class Codes: G02B 6/2766 Manipulating the plane of polarisation from one input polarisation to another output polarisation, e.g. polarisation rotators, linear to circular polarisation converters
• CPC Class Codes: G02B 6/29319 With a cascade of diffractive elements or of diffraction operations forming interferometer by splitting and recombining G02B6/29347 - G02B6/29358
• CPC Class Codes: G02B 6/2935 Mach-Zehnder configuration, i.e. comprising separate splitting and combining means
• CPC Class Codes: G02B 6/29358 Multiple beam interferometer external to a light guide, e.g. Fabry-Pérot, etalon, VIPA plate, OTDL plate, continuous interferometer, parallel plate resonator G02B6/29347, G02B6/29349, G02B6/2935, G02B6/29361 take precedence; resonator evanescently coupled to light guide G02B6/29335
• CPC Class Codes: G02B 6/29391 Power equalisation of different channels, e.g. power flattening
• CPC Class Codes: H01S 2301/04 Gain spectral shaping, flattening
• CPC Class Codes: H01S 3/067 Fibre lasers
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• 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 3/06791 Fibre ring lasers fibre laser gyrometers G01C19/72
• CPC Class Codes: H01S 3/10023 by functional association of additional optical elements, e.g. filters, gratings, reflectors
• CPC Class Codes: H01S 3/1068 using an acousto-optical device
• CPC Class Codes: H01S 3/108 using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering mode locking using a non-linear element H01S3/1112

Abstract

A multichannel fiber laser whose wavelength range is expansible to increase the number of lasing channel, and whose channel output powers are equalized, in order to provide a useful multichannel laser source having a wide bandwidth is described. The laser comprises a gain offering means; a gain equalizing means; and a resonating means. In addition, a method for designing the spectral profile of a gain equalizing filter for the purpose of this invention is described.

Claims

1. A multichannel fiber laser in which all the laser channels share one or more gain offering means comprising:

a gain offering means for providing optical gain;

a gain equalizing means for enlarging laser oscillation wavelength range, increasing the number of laser channels, and equalizing the optical gain from the gain offering means and output powers of all laser channels; and

a resonating means including the gain equalizing means for selecting light channels, adjusting loss, controlling state of polarization, and outputting light to outside of the fiber laser.

2. A laser in accordance with claim 1, the gain offering means comprises:

a pumping light source;

a wavelength division multiplexing coupler for coupling output of the pumping light source into the resonating means; and

a gain medium connected at rear of the wavelength division multiplexing coupler for amplifying oscillating light in the resonating means and offering a gain.

3. A laser in accordance with claim 2, the gain medium is an erbium-doped fiber.

4. A laser in accordance with claim 1, the gain offering means has a gain medium of such a length that small signal gain offered by the gain offering means may be the same as or larger than loss of the resonating means at all wavelengths within a range of interest at a given pump power as well as the small signal gain profile per unit length may be flattened by the gain equalizing means.

5. A laser in accordance with claim 1, the gain equalizing means comprises a gain equalizing filter.

6. A laser in accordance with claim 1, the gain equalizing means uses population inversion of the gain offering means in order to obtain a flat gain spectrum within the range of interest at the threshold pump power.

7. A laser in accordance with claim 5, the gain equalizing filter comprises either long period fiber Bragg gratings or short period fiber Bragg gratings.

8. A laser in accordance with claim 5, the gain equalizing filter comprises acousto-optic tunable filters.

9. A laser in accordance with claim 7, the gain equalizing filter comprising the short period fiber Bragg gratings further comprises optical isolators at the input/output of the gratings to eliminate back-reflection induced effect.

10. A laser in accordance with claim 5, the gain equalizing filter comprises unbalanced Mach-Zehnder interferometers.

11. A laser in accordance with claim 1, the resonating means comprises:

a first and second optical isolators respectively located at the front and rear of the gain offering means for suppressing back-reflection induced effect as well as enabling unidirectional operation;

an output coupler located between the rear of the first optical isolator and the gain equalizing means for outputting laser light to outside of the resonating means;

a frequency shifter located at the rear of the gain equalizing means for suppressing single wavelength oscillation;

a multichannel filter located at the rear of the frequency shifter for selectively filtering the wavelengths of light;

a variable attenuator located at the rear of the multichannel filter for adjusting the loss of the resonating means; and

a polarization controller located at the rear of the variable attenuator for controlling the state of polarization.

12. A laser in accordance with claim 11, the multichannel filter is a Fabry-Perot etalon.

13. A laser in accordance with claim 11, the multichannel filter is a Fabry-Perot tunable filter.

14. A laser in accordance with claim 11, the multichannel filter is a birefringence filter.

15. A laser in accordance with claim 11, the frequency shifter is either a bulk optic acousto-optic frequency shifter or a fiber-optic acousto-optic frequency shifter.

16. A laser in accordance with claim 1, the pumping light source is a laser diode having a wavelength of 980 nm or 1480 nm.