Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-03-04
2001-12-04
Pascal, Leslie (Department: 2774)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06327060
ABSTRACT:
FIELD OF THE INVENTION
This invent ion r elates to an optical transmission system, an optically branching apparatus and an optical signal processing apparatus.
BACKGROUND OF THE INVENTION
In an optical fiber transmission system, especially such a long distance transmission system as an undersea optical fiber transmission system, a fault detection technique remotely monitoring a condition of an optical transmission line using a reflection or scattering light (referred as a supervisory light hereinafter) of a signal light or as special signal for supervision based on C-OTDR(Coherent optical Time Domain Reflectometry) is widely known.
Further, an optical fiber transmission system has a pair of optical transmission lines consisting of an up flow use and a down flow use as a basis and in a long distance optically amplifying repeater transmission system, a structure wherein an optically amplifying repeater has a loop back circuit for transmitting a reflection light or a scattering light from the up system to the down system and also from the down system to the up system is well known. Such a loop back circuit is designed for sending back an output light from an optical amplifier and a return light resulted from scattering or reflection in the up system to the down system and also sending back an output light of an optical amplifier and a scattering or reflection light in the down system to the up system.
With a loop back circuit of a conventional system, transmission characteristics of each part of a fiber transmission line can be monitored at a terminal of a transmission end. There is no problem using the conventional system in the connection of two points. However, in case of providing one or more branch stations, measurement or monitoring in accordance with C-OTDR cannot be performed between an optically branching unit connecting a branch station to a primary optical fiber transmission (specifically, an add/dropping circuit for add/dropping a specific wavelength assigned to the branch station) and an adjacent optically amplifying repeater (precisely, a loop back circuit in it). The reason is that a scattering light in the section is sometimes cut off by an add/dropping apparatus.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical transmission system, an optically branching apparatus and an optical signal processing apparatus with the above mentioned problems all solved.
A further object of the present invention is to provide an optical signal processing apparatus of a simplified structure which sends back a scattering light to an up flow side for preventing the scattering light to enter an optically processing means.
In an optical transmission system according to the present invention, wherein one or more optically branching units for add/dropping a specific wavelength to an optical transmission line that has up and down systems and loops back a supervisory light between said up and down systems, a bypass line for bypassing a supervisory light is provided to each of one or more optically branching units.
By this structure, the supervisory light substantially passes through the optically branching units. In other words, the supervisory light continuously returns in the transmission line except the bypass line and, therefore, monitoring of the transmission condition at substantially all points by the supervisory light can be achieved.
By providing the bypass line to each of the up and down systems, it becomes possible for both trunk stations to monitor the condition in accordance with C-OTDR.
The optically branching unit further comprises an optically add/drop means for add/dropping the specific wavelength, first optically coupling means for passing through an optical signal added an optical signal of the specific wavelength at the optically add/drop means and for transmitting a supervisory light entered from a down flow side of the optical transmission line to the bypass line, and second optically coupling means for providing an input light, including optical signals to be dropped, inputted from an up flow side of the optical transmission line to the add/dropping means and for transmitting the supervisory light from the bypass line to the up flow side of the optical transmission line. Adopting this arrangement, it becomes possible for the supervisory light to bypass the optically add/dropping means and transmit in the opposite direction with a signal light. This system is useful in cases like the supervisory light should not be entering the optically add/dropping means and the optically add/dropping means cannot pass the supervisory light.
In each of the up and down systems, the optically branching units may be arranged to further comprise reflecting means for reflecting the specific wavelength selectively and first and second optical circulators having four input/output ports of A, B, C and D for outputting an input light of the port A from the port B, an input light of the port B from the port C and an input light of the port D from the port A. The first optical circulator has the port A connected to the up flow side of the optical transmission line, the port B connected to one end of the reflecting means, the port C connected to dropped light output means and the port D connected to one end of the bypass line. The second optical circulator has the port A connected to the other end of the reflecting means, the port B connected to the down flow side of the optical transmission, the port C connected to the other end of the bypass line and the port D connected to adding light input means. In this arrangement, the first and second optical circulators serve both roles of add/dropping the signal light and making the supervisory light to bypass and, therefore, both functions can be materialized with very few elements. With this arrangement, excellent transmission characteristics without any increase of unnecessary loss can be expected.
Each of the adding light input means and the dropped light output means comprises an optically amplifying means. Loop back means are provided both between an output stage of the optically amplifying means of the dropped light output means of the up system and an output stage of the optically amplifying means of the adding light input means of the down system and between an output stage of the optically amplifying means of the dropped light output means of the down system and an output stage of the optically amplifying means of the adding light input means of up system. By this structure, a quality of the transmission condition in the optically branching units can be monitored with the loop back light.
An optically branching apparatus according to the invention for dropping a specific wavelength light from an input light of the first optical transmission line, adding the specific wavelength light and outputting the result to the second optical transmission line comprises a reflecting means for reflecting the specific wavelength selectively, a bypass line for bypassing the reflecting means and first and second optical circulators having four ports of A, B, C and D and outputting an input light of the port A from the port B, an input light of the port B from the port C, an input light of the port D from the port A wherein the first optical circulator has the port A connected to the first optical transmission line, the port B connected to the one end of the reflecting means, the port C connected to a dropped light output terminal and the port D connected to one end of the bypass line and the second optical circulator has the port A connected to the other end of the reflecting means, the port B connected to the second optical transmission, the port C connected to the other end of the bypass line and the port D connected to an adding light input terminal.
By using a such arrangement, the first and the second optical circulators play both roles of add/dropping the signal light and making the supervisory light bypassed. Therefore, both functions can be materialized with very few elements. With this system, an excellent transmis
Goto Koji
Kawazawa Toshio
Otani Tomohiro
Christie Parker & Hale LLP
Kokusai Denshin Denwa Kabushiki Kaisha
Pascal Leslie
Sedighian M. R.
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