Optical: systems and elements – Optical frequency converter – Dielectric optical waveguide type
Patent
1999-02-03
2000-12-19
Lee, John D.
Optical: systems and elements
Optical frequency converter
Dielectric optical waveguide type
359327, 359334, 359341, 372 3, 385 15, 385 27, 385122, G02F 1365, H01S 330
Patent
active
061633968
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an optical wavelength converter suitable for providing from a laser a high power converted wavelength suitable for use as a pump for a remote optically pumped amplifier (ROPA). The converter of the invention may also be adapted to provide signal amplification by stimulated Raman Scattering and may be employed in an optical signal transmission system.
BACKGROUND OF THE INVENTION
A timetable fiber Raman ring laser is disclosed in Electronic letters, Vol 26. No. 9. Apr. 26, 1990 page 579-580 which is centered at 1.41 .mu.m and which is pumped at 1.319 .mu.m. Such a construction has a limited output power of 40 mW.
U.S. Pat. No. 5,323,404 describes an Optical Fibre laser or amplifier including high reflectivity gratings. This is a linear design where light is reflected backwards and forwards to stimulate generation of a different wavelength with low efficiency.
A high gain, monolithic, cascade fiber Raman amplifier operating at 1.3 .mu.m is described in Electronic letters, Vol. 31. No. 6. Mar. 16, 1995 pages 472-473. This employs a plurality of loops each loon comprising two optical couplers to complete a closed loop and in order to transfer a Stokes shifted wavelength from the loop. The use of two couplers in each loop is costly and introduces significant losses.
A synchronously pumped ring fiber Raman laser is described in European Patent specification EP-A-0253590 in which a single multiplexing coupler is employed in a reentrant loop to permit stimulated emission at a Stokes shifted wavelength.
This invention has resulted from a consideration of the difficulty of obtaining a high power pump for a ROPA e.g. 1 Watt at 1480 nm. Such a power and wavelength is not currently obtainable by means of semiconductor devices such as previously mentioned. Accordingly, the invention seeks to enable such a drive power to be achieved and has led to the provision of a wavelength converter.
SUMMARY OF THE INVENTION
According to the invention there is provided a wavelength converter comprising a loop of optical fiber an entry end of which loop forms an input for a pump wavelength and an exit end of which loop forms an outlet for a converted signal, which loop is arranged to produce Stokes shifted wavelength components from a pump wavelength by Raman effect which loop has a single, wavelength selective coupler between the entry and exit ends of the loop, which coupler permits exit of a predetermined wanted Stokes shifted wavelength component but causes coupling of lower order Stokes wavelength(s) to the entry for recirculation in the loop to enhance generation of the predetermined wavelength component characterized in.
In a refinement of the invention it is arranged that from the entry and exit ends of the loop the fiber extends to form a second loop, one end of the second loop forms an entry end which forms a loop input for pump wavelength and the other end of the second loop forms a loop output for a converted signal and wherein a single second wavelength selective coupler is provided in the second loop between the entry and exit ends of the second loop, which second coupler permits exit of a predetermined second Stokes shifted component of wavelength longer than said predetermined wavelength but causes coupling of the other wavelengths to the entry of the second loop for recirculation through the loops to enhance generation of the second predetermined wavelength. The second coupler may permit exit to line of the second predetermined wavelength.
In a further refinement it is arranged that from the entry and exit ends of the second loop the fiber extends to form one or more additional loops each having an entry end which forms a loop input for the pump wavelength and an exit end of the loop for a converted signal, each loop having a wavelength selective coupler between its entry and exit ends which permits exit of a predetermined Stokes Shifted wavelength component of wavelength longer than that at the exit of the preceding loop but causes coupling back of other waveleng
REFERENCES:
patent: 4720684 (1988-01-01), Byron
patent: 4738503 (1988-04-01), Desurvire et al.
patent: 4794598 (1988-12-01), Desurvire et al.
patent: 5323404 (1994-06-01), Grubb
Greer et al, "Tunable CW Fibre Raman Ring Laser Centred at 1.41 .mu.m", Electronics Letters, vol. 26, No. 9, Apr. 26, 1990, pp. 579-580.
Chernikov et al, "High-gain, monolithic, cascaded fibre Raman amplifier operating at 1.3.mu.m", Electronics Letters, vol. 31, No. 6, Mar. 16, 1995, pp. 472-473.
Alcatel
Lee John D.
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