| US 7,583,896 B2 | ||
| Optical-wireless hybrid transmission system and optical-wireless hybrid transmission method | ||
| Tomohiro Taniguchi, Chiba (Japan); and Naoya Sakurai, Tokyo (Japan) | ||
| Assigned to Nippon Telegraph and Telephone Corporation, Tokyo (Japan) | ||
| Appl. No. 10/577,636 PCT Filed Jun. 24, 2005, PCT No. PCT/JP2005/011594 § 371(c)(1), (2), (4) Date Apr. 28, 2006, PCT Pub. No. WO2006/001362, PCT Pub. Date Jan. 05, 2006. |
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| Claims priority of application No. 2004-185956 (JP), filed on Jun. 24, 2004; and application No. 2005-075305 (JP), filed on Mar. 16, 2005. | ||
| Prior Publication US 2009/0016723 A1, Jan. 15, 2009 | ||
| Int. Cl. H04J 14/00 (2006.01) | ||
| U.S. Cl. 398—72 [398/152; 398/115; 398/185; 398/74; 398/66] | 19 Claims |
| 1. An optical-wireless hybrid transmission system in which a central office has an optical transmitter and an optical receiver,
said optical transmitter transmits an optical carrier signal to a base station via an optical transmission line, said base
station receives an RF signal (frequency: fRF) that is modulated according to transmit-data, optically modulates said optical carrier signal according to the received
RF signal, and transmits a resulting modulated optical signal to said central office via an optical transmission line, and
said optical receiver receives and demodulates the modulated optical signal and reproduces said transmit-data, the system
characterized in:
that said optical transmitter comprises:
a first single-mode optical source which outputs a first single-mode optical signal (center frequency: fC1);
a second single-mode optical source which outputs a second single-mode optical signal (center frequency: fC2);
a third single-mode optical source which outputs a third single-mode optical signal (center frequency: fC3); and
a polarization-coupling part which orthogonal-polarization-couples said second single-mode optical signal with said third
single-mode optical signal while adjusting polarization directions and optical powers of two waves so as to make the polarization
directions orthogonal and the optical powers identical, and outputs a resulting polarization-coupled optical signal, in which
the center frequencies fC1, fC2, and fC3 of said first, second, and third single-mode optical signals are controlled so as to satisfy
|fC1−fC2|=fRF±fIF1
|fC1−fC3|=fRF±fIF2 where fRF is a frequency of said RF signal and fIF1 and fIF2 are prescribed intermediate frequencies; and
said first single-mode optical signal is transmitted to said base station as said optical carrier signal and said polarization-coupled
optical signal is output to said optical receiver; and
that said optical receiver comprises:
an optical coupler which couples the modulated optical signal transmitted from said base station with said polarization-coupled
optical signal output from said optical transmitter;
a photodetector which photodetects a coupled optical signal output from said optical coupler, and thereby outputs an electrical
signal having the intermediate frequencies fIF1 and fIF2;
an electrical demodulator which demodulates the electrical signal having the intermediate frequencies fIF1 and fIF2 and output from said photodetector; and
a low-pass filter which filters an output signal of said electrical demodulator and thereby outputs said transmit-data.
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