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Bi-directional optical communications subscriber transmission system using a single wavelength
| Details |
Inventors: Ichikawa, Akihiko;
Assignee: Fujitsu LImited (Kawasaki, JP)
Primary Examiner: Boudreau; Leo H.
Assistant Examiner: Mehta; Bhavesh
Attorney, Agent or Firm: Staas & Halsey, LLP
With regard to an optical communications system, in a system using a single optical fiber cable between subscribers and an exchange and in which bi-directional transmission is performed using the same 1.3-.mu.m wavelength, the exchange-to-subscriber signal is a high-speed, wideband signal which is bandwidth limited by means of a lowpass filter, and the subscriber-to-exchange signal is a carrier having a frequency higher than the upper limit of the exchange-to-subscriber signal and which is modulated with a low-speed, narrowband signal. |
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DETAILED DESCRIPTION In consideration of the above-described problems, an object of the present invention is to achieve bi-directional communications using a single wavelength, thereby achieving a system that is simple and low cost.
Another object of the present invention is, by means of appropriating assignment bandwidths respectively to the path from the exchange to the subscriber, and to the path from the subscriber to the exchange, to actually take advantage of the above-noted asymmetry of the transmission directions, to achieve efficient bi-directional signal transmission.
Yet another object of the present invention is to achieve a further reduction of cost and complexity of the system, by, for example, making use of signals used in current systems respectively for the subscriber-to-exchange signal (used synonymously herein and in the claims with the expression "upward signal"); and the exchange-to-subscriber signal (used synonymously hereinafter and in the claims with the expression "downward signal"), thereby enabling sharing of hardware with current systems.
According to the present invention, an optical communications system performing single-wavelength bi-directional communications is provided, in which the exchange and a subscriber are linked by a single optical fiber cable, and a high-speed, wideband signal, the bandwidth of which is limited by a lowpass filter, is used as the exchange-to-subscriber signal.
For the subscriber-to-exchange signal, a carrier of a frequency higher than the upper limit of the above-noted exchange-to-subscriber signal is modulated by the low-speed, narrowband signal.
As the above-noted exchange-to-subscriber signal, an ITU standard STM-1 (155.
52 MB/s) or STM-4 (622.
08 Mb/s) signal is used and, as the carrier of the subscriber-to-exchange signal, the 800-MHz mobile telephone band, the 1.
5-GHz band or the Personal Handy Phone 1.
9-GHz band is used.
In addition, as the exchange-to-subscriber signal, an FDM signal of a number of carriers modulated with a video signal and a number of carriers modulated by low-speed signals assigned to individual subscribers are used and, as the subscriber-to-exchange signal, the 800-MHz mobile telephone band, the 1
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Optical Systems 
