Lasers

Details Lasers Lasers

1997-07-10

1998-12-01

Healy, Brian

Coherent light generators

Optical fiber laser

372 9, 372 23, 372 92, 372102, 385 37, H01S 330, G02B 634

Patent

active

058449264

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to lasers, and in particular to a class of laser having an optical laser cavity one end of which is formed in optical waveguide, typically optical fibre waveguide. One example of such a laser is an optically pumped erbium doped optical fibre laser provided with optical fibre Bragg grating reflectors to define the ends of its optical cavity. Another example, depicted in FIG. 1, is constituted by a semiconductor injection laser diode chip 10 provided with an anti-reflection coating 11 on one end facet 12 to which is optically coupled a length of optical fibre pigtail 13 in which there is a Bragg grating reflector 14 defining one end of a laser optical cavity whose other end is provided by the end facet 15 of the injection laser chip remote from the anti-reflection coated end facet. Interest in such diode lasers, known as external cavity diode lasers arises at least in part to the fact the Bragg grating reflector provides a means of locking the laser frequency.


SUMMARY OF THE INVENTION

The present invention is directed to a modified configuration of reflector which can be employed to provide improved laser performance by removal of out-of-band spontaneous emission from the output of laser or by enhanced inhibition of mode hopping.
According to the present invention there is provided a laser having an optical laser cavity one end of which is constituted by a partial reflector formed in optical waveguide by an unbalanced Michelson interferometer comprising an optical waveguide splitter/combiner and two optical waveguide Bragg grating reflectors.
An additional advantageous feature of this arrangement is that the reflectivity of the partial reflector can be readily trimmed for optimum power output of the laser by using the photo-refractive effect to alter the optical path length of one of the interference arms of the Michelson.


BRIEF DESCRIPTION OF THE DRAWINGS

There follows a description of lasers embodying the invention in preferred forms.
FIG. 1 (to which previous reference has already been made) schematically depicts a prior art external cavity diode laser, and FIGS. 2, 3 and 4 schematically depict external cavity diode lasers with alternative forms of imbalance Michelson interferometer type external Bragg grating type reflector.


DETAILED DESCRIPTION OF THE DRAWINGS

The lasers of FIGS. 2, 3 and 4 have the same semiconductor laser chip components as the laser of FIG. 1, and so these components have been identified in these Figures using the same index numerals as those employed in FIG. 1. In each instance the place of the fibre pigtail 13 and single Bragg grating reflector 14 has been taken by an unbalanced Michelson interferometer. In the case of the laser of FIG. 2, this unbalanced Michelson interferometer has matched Bragg grating reflectors 24a and 24b located equidistant from the coupling region 25 of a 2.times.2 waveguide splitter/combiner 23 having ports, A, B, C and D. Port A is optically coupled with the anti-reflection coated facet 12 of the diode chip 10. The two Bragg grating reflectors 24a and 24b are respectively formed in the two arms of the splitter/combiner that respectively terminate in ports C and D. Port B constitutes the optical output of the laser.
If the splitter combiner 23 were to have been a balanced 3 dB splitter/combiner, then light launched into the splitter/combiner by way of port A would have been divided by its coupling region 25 equally between the two limbs terminating in ports C and D. Light within the wavebands of Bragg grating reflectors 24a and 24b would be reflected back to the coupling region 25 where, because of the equidistance of the reflectors 24a and 24b from the coupling region, all this light would emerge from the splitter/combiner by way of port 8. This means that this (balanced) Michelson interferometer would fail to provide any feedback, and so would not function as one of the end of a laser optical cavity. Thus a laser would not be formed. It is for this reason that some form of imbalance in the Mich

REFERENCES:
patent: 4831631 (1989-05-01), Haeussler et al.
patent: 5048909 (1991-09-01), Henry et al.
patent: 5237576 (1993-08-01), DiGiovanni et al.
patent: 5475780 (1995-12-01), Mizrahi
patent: 5633965 (1997-05-01), Bricheno et al.
patent: 5638473 (1997-06-01), Byron
Tkack, "Regimes of Feedback Effects in 1.5 um Distributed Feedback Lasers", Journal of Lightwave Technology, vol. LT-4, No. 11, Nov. 1986, pp. 1655-1661.
INSPEC Abstract Accession No. A9518-4260B-003 & Proceedings of CLEO 1994. vol. 8. 1994 Technical Digest Series, pp. 349-350. Kodama et al. Novel CO/sub 2/laser with Michelson-interferometer type optical resonator.
IEEE Photonics Technology Letters, vol. 6 No. 1 Jan 1994 pp. 80-82 -- Bilodeau et al: High Return-Loss Narrowband All-Fiber Bandpass Bragg Transmission Filter.
Applied Physics Letters, vol. 64, No. 20 May 16 1994, pp. 2634-2636 -- Morton et al "Stable Single Mode Hybrid Laser with High Power and Narrow Linewidth".

Affiliated with

Also associated with

Rating

Lasers does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Lasers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lasers will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2401264