Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-07-06
2003-03-11
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06532099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical communications apparatuses and, more specifically, to an optical communications apparatus for transmitting an optical signal by switching optical communications paths based on the wavelength and modulating frequency of the optical signal as address information.
2. Description of the Background Art
FIG. 10
is a block diagram showing the structure of a conventional optical communications apparatus. One example of such apparatus is disclosed in detail in “Hyperspace Addressed Optical Access Architecture using Active Arrayed Waveguide Gratings”, F. Farjaday, M. C. Parker, and S. D. Walker, OECC98, 15A2-2, 1998.
In
FIG. 10
, the optical communications apparatus includes an optical transmitting circuit
10001
, a main optical transmission path
1004
, an optical router
1005
, first and second distribution optical transmission paths
10061
and
10062
, and first and second optical receiving circuits
10091
and
10092
. The optical transmitting circuit
10001
includes an address extractor
1010
and a variable wavelength optical modulator
1003
.
In the above structured optical communications apparatus, the address extractor
1010
extracts, from a signal received by the optical transmitting circuit
10001
, address information indicating the destination to which the signal should go. Alternatively, the address extractor
1010
may be provided with the address information itself separately.
The variable wavelength optical modulator
1003
is composed of a variable wavelength light source capable of changing the wavelength of output light. This wavelength is uniquely determined based on the address information extracted by the address information extractor
1010
or separately provided. The variable wavelength optical modulator
1003
optically modulates the signal including the above described data information, and then sends out light having the determined wavelength to the main optical transmission path
1004
.
The optical router
1005
, exemplarily composed of an AWG (Arrayed WaveGuide), has a plurality of output terminals (in this example, first and second output terminals
10051
and
10052
) for selectively outputting the optical signal based on the wavelength of the input light. When supplied with the optical signal through the main optical transmission path
1004
, the optical router
1005
outputs it from the first terminal
10051
when the optical wavelength thereof is &lgr;1, while outputting from the second terminal
10052
when &lgr;2.
The first and second optical receiving circuits
10091
and
10092
are each connected to the optical router
1005
at the first output terminal
10051
and at the second output terminal
10052
, respectively. The first and second optical receiving circuits
10091
and
10092
each convert the optical signal from each corresponding output terminal into an electrical signal for output.
As described above, in the conventional optical communications apparatus, a variable wavelength light source is used as the light source in the optical transmitting circuit to control the wavelength of the output light based on the address information indicating the destination to which the data information should go. Also, the optical router is provided on the optical transmission path, enabling routing of the input light for output from each different terminal based on the wavelength thereof. Thus, the conventional optical communications apparatus can carry out autonomous switching among the transmission paths in optical domain, and therefore a high-speed optical communications network can be achieved.
One disadvantage here is, when the wavelength of the optical signal is used as an address, the number of wavelengths or wavelength bands available on the optical transmission path is limited. This disadvantage is described below with reference to FIG.
11
.
FIG. 11
is a schematic diagram demonstrating the limitation of the number of wavelengths in the conventional optical communications apparatus. Specifically, as shown in
FIG. 11
, Erbium-doped fiber optical amplifiers (EDFA) widely used in optical transmission systems can generally carry out amplification only within approximately 30 to 40 nm in a wavelength band of 1.55 &mgr;m. On the other hand, AWGs and optical filters generally have a wavelength resolving power (dividable optical wavelength period) of approximately 0.8 nm. In
FIG. 11
, the band pass characteristics of the optical filter is represented as a dotted line. Consequently, the number of wavelengths available in address space is very limited, approximately 40 to 50. Thus, in the conventional optical communications apparatus, the number of optical receiving terminals that can be connected thereto or covered thereby (the number of subscribers) is disadvantageously limited, and a large optical communications network cannot be constructed.
In order to construct a large optical communications network using the conventional optical communications apparatus, one structure can be suggested, where further routing is made using electrical signals outputted from the first and second optical receiving circuits
10091
and
10092
for transmitting information to end receiving terminals (subscribers). In such structure, however, unauthorized information extraction and tampering are highly possible due to the use of the electrical signals for information transmission to the end receiving terminals (subscribers), compared to the case where optical signals are used. Also, conventional communications networks using electrical signals are inferior, in transmission speed and amount of transmittable information, to optical communications networks using optical signals for transmitting information up to end users.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an optical communications apparatus achieving a large optical communications network with high speed and security by using the wavelength of an optical signal as an address for switching among transmission paths in optical domain.
The present invention has the following features to achieve the object above.
A first aspect of the present invention is directed to an optical communications apparatus for optically transmitting a transmission signal including data information a destination, and the apparatus includes:
a variable frequency RF modulator for modulating the transmission signal into an RF modulated signal, with a predetermined carrier frequency that corresponds to a lower address of address information uniquely set to the destination, the lower address representing the destination in a predetermined group to which the destination belongs;
a variable wavelength optical modulator for modulating the RF modulated signal outputted from the variable frequency RF modulator into an optical signal, with a predetermined optical wavelength that corresponds to an upper address of the address information, the upper address representing the predetermined group to which the destination belongs;
an optical router provided with a plurality of output terminals, for selectively outputting the optical signal outputted from the variable wavelength optical modulator from one of the output terminals that corresponds to the wavelength of the optical signal;
a plurality of RF optical routers each provided with a plurality of output terminals, for selectively outputting the optical signal coming from the output terminal of the optical router from one of the output terminals that corresponds to the carrier frequency of the RF modulated signal on the optical signal; and
a plurality of optical receiving circuits each for converting the optical signal outputted from the corresponding output terminal of the RF optical router into an electrical signal that corresponds to the transmission signal.
In the first aspect, by using the structure capable of selecting a signal transmission route in optical domain for switching (routing), the optical wavelength is related to the upper address of the addre
Dang Hung Xuan
Matsushita Electric - Industrial Co., Ltd.
Tra Tuyen
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Optical communications apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical communications apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical communications apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3043454