Optical: systems and elements – Optical frequency converter
Reexamination Certificate
1999-08-17
2001-06-26
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical frequency converter
C359S199200, C359S199200, C359S199200, C359S199200, C359S246000, C385S002000, C385S011000, C385S016000, C385S024000, C372S096000, C372S106000, C372S108000
Reexamination Certificate
active
06252698
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and device for wavelength conversion, and a system including the device.
2. Description of the Related Art
As a technique for increasing a transmission capacity by a single optical fiber, wavelength division multiplexing (WDM) is known. In a system adopting WDM, a plurality of optical carriers having different wavelengths are used. The plural optical carriers are individually modulated to thereby obtain a plurality of optical signals, which are wavelength division multiplexed by an optical multiplexer to obtain WDM signal light, which is output to an optical fiber transmission line. On the receiving side, the WDM signal light received is separated into individual optical signals by an optical demultiplexer, and transmitted data is reproduced according to each optical signal. Accordingly, by applying WDM, the transmission capacity in a single optical fiber can be increased according to the number of WDM channels.
It is now being considered to construct a wide-area photonic network in the future by connecting WDM systems, and the development of a node configuration or an optical cross-connect (OXC) device required for such a photonic network is being pursued. The node is provided by an optical add/drop multiplexer (OADM) for extracting (dropping) an optical signal from a network and inserting (adding) an optical signal into the network. The optical cross-connect device is used to switch the paths of optical signals.
It is considered that direct connection of largely demanded IP packet information to a photonic network without through a current SONET/SDH device or ATM device will become a mainstream (IP over WDM). Accordingly, a wavelength converter for converting the wavelength of an optical signal is one of the key technologies for realization of such a photonic network.
Conventionally, research has been made on a method for wavelength conversion by generation of four-wave mixing with a semiconductor optical amplifier or a DFB laser.
However, the conventional method for wavelength conversion has a problem such that the efficiency of generation of converted light after wavelength conversion is very low. Further, a conventional device for wavelength conversion requires control light for generating four-wave mixing, causing a complicated configuration.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for wavelength conversion which can achieve a high efficiency of generation of converted light.
It is another object of the present invention to provide a device for wavelength conversion which can achieve a high efficiency of generation of converted light with a simple configuration.
It is a further object of the present invention to provide a novel system including such a device.
In accordance with an aspect of the present invention, there is provided a method for wavelength conversion, comprising the steps of (a) separating an optical signal received into a first polarization component having a first polarization plane and a second polarization component having a second polarization plane perpendicular to the first polarization plane; (b) supplying the first polarization component to a first optical waveguide structure over which a first surface acoustic wave propagates, in a direction identical with the propagation direction of the first surface acoustic wave; (c) supplying the second polarization component to a second optical waveguide structure over which a second surface acoustic wave propagates, in a direction opposite to the propagation direction of the second surface acoustic wave; and (d) combining first converted light output from the first optical waveguide structure and second converted light output from the second optical waveguide structure.
The first and second optical waveguide structures are provided as a part of an acoustic optical tunable filter (AOTF), for example. In this case, the first polarization component having the first polarization plane and the second polarization component having the second polarization plane are polarization-converted to respectively have the second polarization plane and the first polarization plane, so that the first and second converted lights have the second and first polarization planes, respectively. Further, the first and second converted lights are frequency-shifted from the optical signal received by a quantity determined by the frequency of each surface acoustic wave, thereby effecting wavelength conversion of the optical signal. Since the wavelength of the optical signal to be wavelength-converted can be changed according to the frequency of each surface acoustic wave, an optical signal of an arbitrary wavelength channel in WDM signal light can be selectively wavelength-converted. The reason why the propagation direction of each surface acoustic wave is limited as described above is to make the direction of frequency shift from the first polarization component to the first converted light identical with the direction of frequency shift from the second polarization component to the second converted light. This will be hereinafter described in detail.
In accordance with another aspect of the present invention, there is provided a device for wavelength conversion, comprising a first polarization beam splitter having a first input port and first and second output ports, the first input port and the first output port of the first polarization beam splitter coupled by a first polarization plane, the first input port and the second output port of the first polarization beam splitter being coupled by a second polarization plane perpendicular to the first polarization plane; a first polarization converter having an input port and an output port, the input port of the first polarization converter being connected to the first output port of the first polarization beam splitter, the first polarization converter converting the first polarization plane into the second polarization plane concerning light having a predetermined wavelength; a second polarization converter having an input port and an output port, the input port of the second polarization converter being connected to the second output port of the first polarization beam splitter, the second polarization converter converting the second polarization plane into the first polarization plane concerning light having the predetermined wavelength; and a second polarization beam splitter having first and second input ports and a first output port, the first input port of the second polarization beam splitter being connected to the output port of the first polarization converter, the second input port of the second polarization beam splitter being connected to the output port of the second polarization converter, the first input port and the first output port of the second polarization beam splitter being coupled by the second polarization plane, the second input port and the first output port of the second polarization beam splitter being coupled by the first polarization plane; each of the first and second polarization converters having an optical waveguide structure over which a surface acoustic wave propagates; the propagation directions of the light and the surface acoustic wave in one of the first and second polarization converters being opposite to each other; the propagation directions of the light and the surface acoustic wave in the other of the first and second polarization converters being identical with each other.
In accordance with a further aspect of the present invention, there is provided a system comprising first to fourth optical fiber transmission lines each adapted to wavelength division multiplexing; and an optical add/drop multiplexer connected to the first to fourth optical fiber transmission lines; the optical add/drop multiplexer comprising a first polarization beam splitter having first and second input ports and first and second output ports, the first and second input ports of the first polarization beam splitter b
Ben Loha
Fujitsu Limited
Staas & Halsey , LLP
LandOfFree
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