Optical waveguides – Optical transmission cable – Tightly confined
Reexamination Certificate
2002-01-23
2004-04-20
Stafira, Michael P. (Department: 2877)
Optical waveguides
Optical transmission cable
Tightly confined
C385S088000, C385S139000
Reexamination Certificate
active
06724962
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to a wavelength to optical power converter and a method thereof, and more particularly to a fiber-optic winding wavelength to optical power converter and a method for converting the wavelength into the optical power in a fiber-optic communication system.
BACKGROUND OF THE INVENTION
The present Dense Wavelength Division Multiplexing (DWDM) system is adopted by using a 100/200 GHz channel spacing and is capable of operating in a long-term and acquiring a crosstalk specification. A distributed feedback (DFB) is capable of being normally operated in a short-term but a wavelength drift will be generated over a long period of time. Therefore, it is important and necessary to monitor an actual operating wavelength of the DWDM system. Consequently, it would be an urgent issue how to stably operate in a fiber-optic broadband network which is of a gradually raised demand in the market, besides adding the fiber-optic bandwidth.
Presently, an interferometer and a Fiber Bragg Grating (FBG) sensor such as a Fabry-Perot interferometer and a linear FBG are adopted for being regarded as a wavelength discriminator to convert a variable signal of the distributed feedback (DFB) laser wavelength variation into a variable optical intensity. Therefore, the practical operation of the wavelength discriminator in a Wavelength Division Multiplexing (WDM) fiber-optic network is a future tendency and the present invention is a practical application in relation to this field.
Many wavelength detecting techniques are applied in the Wavelength Division Multiplexing/Dense Wavelength Division Multiplexing (WDM/DWDM) broadband fiber-optic network, but active components or passive components developed by these wavelength detecting techniques are more complicated to be not easily obtainable or identifiable by the users. Consequently, these techniques don't include better practicability and technical maturity. Certain other techniques include a higher price level and the cost thereof is difficult to be reduced.
A real time and full wave-band wavelength monitoring system including a 0.076 nm/dB resolution, 0.02 nm precision, 16 channels and 200 GHz channel spacing and composed of a Phased Array Wavelength Grating (PAWG), an array of 32 detectors and an A/D (alternating current/direct current) converter of 64 channels is disclosed by Shan Zhong, Chau-Han Lee, Xiao-Hui Yang, Yung-Jui Chen and Dennis Stone, in “Integrated real time multi-channel wavelength monitoring circuit using phased-array waveguide grating”, Digest of Optical Fiber Communication, Volume 3, 1997, pages 30-32. The PAWG accomplished by a double WDM channel resolution and an &agr;/2 angle difference is capable of covering full wave-band frequency spectrum to generate two differential curves by using a drift of a central wavelength at the halfway of the channel spacing to confirm the convergence of the blind spot. The system is used for a real time and full wave-band wavelength monitoring in the DWDM system. This wavelength detecting method by using an Array Wavelength Grating (AWG) is a more complicated, undeveloped technique and easily affected by the environment temperature so that it has a lower reliability and includes a more expensive cost.
A simple method of stabilizing wavelength used for monitoring and controlling the wavelength of the DWDM system in order to solve an output or a display of a long-wavelength drift over the limit of a free-running DFB laser transmitter is disclosed by B. Villeneuve, H. B. Kim, M. Cry and D. Gariepy, in “A Compact Wavelength Stabilization Scheme for Telecommunication Transmitters”, Digest of the IEEE/LEOS Summer Topical Meeting, 1997, pages 19-20. The method includes the steps of providing two very close optical diodes, capturing two spectral responses by using a periodic transmissive frequency response of a Fabry-Perot (FP) filter, and calculating a measurable wavelength value via the difference between the two spectral responses. A unit is independently existent under the above-mentioned conception and can be merged into an existent laser module without an extra electric power because of its tiny volume. But the unit includes a high level of manufacturing technique, a highly difficult components assembly, a high rejection rate and a higher cost and is difficult for sourcing components to maintain. Consequently, because the unit does not arrive at the stage of being put in mass production and practical application yet, it is not proper to be applied in a local area network (LAN), i.e. Fiber to the Home (FTTH) WDM/DWDM network system, and particularly to be the consumer end without any professional backgrounds.
A wavelength monitoring technique by using a relation between a carrier from a semiconductor optical amplifier and an incident optical wavelength, and detecting a transmission point of the semiconductor optical amplifier to measure and track the wavelength in the DWDM system is disclosed by San-Liang Lee, Ching-Tang Pien and Yu-Yi Hsu, in “Wavelength monitoring with low cost laser diodes for DWDM applications”, Electronics Letters, Volume 36, Issue 6, 2000. Consequently, the above-mentioned purpose is achieved by biasing a laser diode under the threshold limit value (TLV) or using the semiconductor optical amplifier on an anti-reflective coating layer. Moreover, it also is very suitable to detect the discontinuous or separate components by using the external wavelength or stabilizing the wavelength of the laser diode.
This kind of wavelength monitoring technique is capable of being used to discriminate the operating interface thereof by using the fixed bias or scan the mode type. This technique is used for stabilizing the wavelength with regard to the wavelength drift because of a lower cost of the laser diode, but the semiconductor optical amplifier used therein is very expensive. Therefore, it is not suitable to be applied to the wavelength detection in the general local area network (LAN).
A wavelength meter having multiple wavelength laser inputs is disclosed by Hackel et al., in “Wavelength meter having single mode fiber optics multiplexed inputs”, U.S. Pat. No. 5,189,485, filed on Feb. 21, 1991. This wavelength meter has a multiplexer to remote-control multiple lasers via a single mode fiber-optic for inputting one of the plurality of laser beam signal inputs into a wavelength measuring device, and thus is capable of improving the calibration capability of the wavelength measuring device in a real-time and online manner by referring to a predetermined laser beam wavelength. Thus, the wavelength measuring technique includes a practicability and is available by the present invention having a lower cost.
A method and apparatus for determining the wavelength of optical radiation, i.e. the visible radiation light are disclosed by Varnham, in “Determining the wavelength of optical radiation”, U.S. Pat. No. 5,022,754, filed on Aug. 7, 1989. The optical radiation is subjected to two or more wavelength dependent phase modulations having a net effect which is wavelength dependent and is zero at a predetermined wavelength. The net modulation is then determined so as to obtain the difference between the predetermined wavelength and the actual wavelength of the optical radiation. However, it is difficult for one skilled in the modulation technique so that it does not include a practicability.
A microprocessor having an interferometer with linearizing interference fringe pattern for determining the wavelength of laser light is disclosed by Kachanov, in “Interferometer with processor for linearizing fringers for determining the wavelength of laser light”, U.S. Pat. No. 5,420,687, filed on Oct. 4, 1993. The interference fringe pattern is detected by a charge-coupled device (CCD) array and is sent to a computer to be processed. The computer compares the result to determine the wavelength of laser light.
The above-mentioned papers and patents are the presently main techniques for monitoring and measuring the wavelength in Wavelength Division Multiplexing
Cheng Wen-Ming
Tsao Shyh-Lin
Stafira Michael P.
Valentin Juan D
Yuan Ze University
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