Coherent light generators – Particular beam control device – Mode locking
Patent
1987-09-30
1989-08-01
Sikes, William L.
Coherent light generators
Particular beam control device
Mode locking
372 21, 372 97, 372105, 307426, H01S 3098
Patent
active
048539333
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to radiation generators in which substantially all the radiation modes are locked with respect to one another.
BACKGROUND AND SUMMARY OF THE INVENTION
The invention is particularly concerned with improving the mode locking performance of imperfectly mode locked lasers producing non-transform limited pulses. Short, transform limited pulses are achieved by ensuring that the lasing modes have a specific phase relationship to each other. If all the modes within the laser gain curve could be locked then the laser pulse width would only depend on the gain bandwidth. In most lasers the extent to which this can be achieved is limited by the physical properties of the mode locking element. In a Nd:YAG laser the limitation is the modulation depth and in F centre laser the limitation is the thermal destruction of the lasing medium.
In a paper entitled "The Soliton Laser" published in Optics Letters Vol 9, page 13, 1984, a method of improving the mode locking performance of lasers is described. This method consists in selecting a particular length of optical fibre to form a feedback loop. The idea behind this proposal was to reinject the light from the fibre into the laser cavity so as to force the laser to produce solitons in the optical fibre. The authors suggest that the reason why this improves a mode locked laser is due to the periodic nature of the solitons in their propagation along the fibre. This results in a stable operating point as the input and output pulses of the fibre are identical thus leaving the circulating pulses in the laser cavity undisturbed.
In a later paper by LF Mollenauer entitled "Solitons in Optical Fibres and the Soliton Laser" in Phil. Trans. R. Soc. Lond. A 315,437-450 (1985) it is indicated that soliton effects are possible only in the region of negative group velocity dispersion. This has a limiting effect on the wavelengths which can be produced using a soliton laser. The wavelength used typically is 1.55.mu.m. A further problem is in the difficulty of selecting an appropriate medium for the external cavity. The papers mentioned above both indicate that the non-linear and dispersive affects of the medium are equally important and it is necessary to select a medium in which these two effects exactly balance one another or at least nearly balance so that the frequency modifications imposed on the pulse by the two effects are of opposite sign and cancel each other out. This again leads to limitations in the type of media which can be chosen for the external cavity. Furthermore, very high peak powers are required in the fibre cavity.
In accordance with a first aspect of the present invention, a radiation generator in which substantially all the radiation modes are locked with respect to one another comprises a radiation generating cavity for generating a continuous train of non-transform limited pulses of coherent radiation; an external cavity positioned in association with the radiation generating cavity whereby radiation may pass in use in both directions between the two cavities, the external cavity being defined by a medium having a non-linear loss characteristic which predominates over any non-linear refractive index property of the medium, as hereinafter defined, for radiation from the generating cavity, and having a radiation path length such that pulses fed into the external cavity are fed back to the radiation generating cavity in synchronism with a later pulse from the generating cavity.
In accordance with a second aspect of the present invention, a radiation generator in which substantially all the radiation modes are locked with respect to one another comprises a radiation generating cavity for generating a continuous train of non-transform limited pulses of coherent radiation; an external cavity positioned in association with the radiation generating cavity whereby radiation may pass in use in both directions between the two cavities, the external cavity being defined by a medium which has a non-linear transmission characteris
REFERENCES:
patent: 3975693 (1976-08-01), Barry et al.
patent: 4019156 (1977-04-01), Fountain et al.
patent: 4025875 (1977-05-01), Fletcher et al.
patent: 4180751 (1979-12-01), Ammann
patent: 4268801 (1981-05-01), Stappaerts
patent: 4435808 (1984-04-01), Javan
patent: 4635263 (1987-01-01), Mollenauer
Optics Communications, vol. 56, No. 4, Dec. 1985 (Amsterdam, NL), L. K. Johnson et al: "Self Frequency-Locking of Dye Laser Emission to the Center of an Intracavity Absorption Frequency", pp. 275-278.
Optics Letters, vol. 9, No. 1, Jan. 1984 (New York, US), L. F. Mollenauer et al.; "The Soliton Laser", pp. 13-15.
Blow Keith J.
Wood David C.
British Telecommunications
Holloway B. R. R.
Sikes William L.
LandOfFree
Non-transform limited pulse locked radiation mode radiation gene does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Non-transform limited pulse locked radiation mode radiation gene, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Non-transform limited pulse locked radiation mode radiation gene will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-137393