Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-04-16
2001-04-03
Negash, Kinfe-Michael (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S326000
Reexamination Certificate
active
06211983
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an optical communication network unit and, more particularly, to an optical signal converting apparatus and an optical signal receiving apparatus for use in the optical communication network unit.
As is well known in the art, it is possible for optical communication to make a transmission capacity for a single optical transmission path larger by carrying out a wavelength multiplexing on a plurality of optical signals. However, it is impossible to multiplex a plurality of optical signals each of which has the same wavelength into a multiplexed optical signal. This is because it is impossible to demultiplex or separate the multiplexed optical signal having a single wavelength into a plurality of multiplexed or separated optical signals. For this purpose, it is necessary to carry out wavelength conversion in a case of multiplexing a plurality of optical signals each of which has the same wavelength.
A wavelength conversion device converts an input optical signal having an input wavelength into an output optical signal having an output wavelength. Among wavelength conversion devices, wavelength conversion devices for digital modulated optical signals are classified into a noninverting wavelength conversion device and an inversion wavelength conversion device. The noninverting wavelength conversion device is a conversion device where the output optical signal has bit logic which is equal to that of the input optical signal. On the other hand, the inverting wavelength conversion device is a conversion device where the output optical signal has bit logic which is obtained by inverting bit logic of the input optical signal. If desired, reference should be made to any relevant publication that is most readily available. An example of such publications is an article contributed by J. Zhou et al. to IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 6, NO. 8, AUGUST 1994, pages 984-987, under the title of “Four-Wave Mixing Wavelength Conversion Efficiency in Semiconductor Traveling-Wave Amplifiers Measured to 65 nm of Wavelength Shift.”
As an example of noninverting wavelength conversion, a wavelength conversion using four-wave mixing in a semiconductor laser is cited. As an instance of inverting wavelength conversion, a wavelength conversion device using mutual gain modulation in a semiconductor optical amplifier is cited. An instance of the inverting wavelength conversion device is disclosed in an article which is contributed by C. Joergensen et al. to ELECTRONICS LETTERS, Vol. 32, No.4 (Feb. 15, 1996), pages 367-368, and which has a title of “40 Gbit/s All-Optical Wavelength Conversion by Semiconductor Optical Amplifiers.”
As described above, inasmuch as there are the inverting wavelength conversion device and the noninverting wavelength conversion device, there are two types of optical signals which are transmitted in an optical communication network system. That is, a first type of optical signal is an optical signal whose bit logic is inverted while a second type of optical signal is an optical signal whose bit logic is not inverted. The former is called an inverted optical signal and the latter is referred to as a noninverted optical signal. Accordingly, an optical receiving unit in the communication network system may be supplied with, as an input optical signal, either the inverted optical signal or the noninverted optical signal.
In the manner which will later be described in conjunction with
FIGS. 1 and 2
, each of a conventional optical signal receiving apparatus and a conventional optical signal converting apparatus comprises an optical branching unit and an optical switch. As a result, each of the conventional optical signal receiving apparatus and the conventional optical signal converting apparatus is disadvantageous in that it results in having a larger mounted space and in increasing cost of product.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an optical signal converting apparatus, which is capable of reducing a mounted space.
It is another object of this invention to provide an optical signal converting apparatus of the type described, which is capable of reducing cost of product.
It is still another object of this invention to provide an optical signal receiving apparatus, which is capable of reducing a mounted space.
It is yet another object of this invention to provide an optical signal receiving apparatus of the type described, which is capable of reducing cost of product.
It is a further object of this invention to provide an optical communication network node which is provided with the optical signal converting apparatus and/or the optical signal receiving apparatus.
Other objects of this invention will become clear as the description proceeds.
According to a first aspect of this invention, an optical signal converting apparatus converts an input optical signal having an input wavelength into an output optical signal having an output wavelength. The optical signal converting apparatus comprises an optical oscillator for oscillating an oscillation optical signal having an oscillation wavelength. Supplied with the input optical signal and connected to the optical oscillator, an optical coupler optically coupling the input optical signal and the oscillation optical signal to produce a coupled optical signal. Connected to the optical coupler, an optical amplifier optically amplifies the coupled optical signal into an amplified optical signal. The optical amplifier optically amplifies an optical signal having the input wavelength in the coupled optical signal as is. The optical amplifier optically amplifies another optical signal having the oscillation wavelength in the coupled optical signal with bit logic in the optical signal having the input wavelength inverted. Set with a transmission wavelength and connected to the optical amplifier, an optical filter optically filters the amplified optical signal so as to transmit, as a transmitted optical signal, an optical signal having the transmission wavelength in the amplified optical signal. Connected to the optical oscillator, a mode setting arrangement sets a mode for the optical oscillator in one of an active mode for making the optical oscillator supply the oscillation optical signal to an output and an inactive mode for stopping the optical oscillator from supplying the oscillation optical signal as an output. The transmitted optical signal is produced as the output optical signal.
According to a second aspect of this invention, an optical signal receiving apparatus receives an input optical signal having an input wavelength to produce reception data. The optical signal receiving apparatus comprises an optical oscillator for oscillating an oscillation optical signal having an oscillation wavelength. Supplied with the input optical signal and connected to the optical oscillator, an optical coupler optically couples the input optical signal and the oscillation optical signal to produce a coupled optical signal. Connected to the optical coupler, an optical amplifier optically amplifies the coupled optical signal into an amplified optical signal. The optical amplifier optically amplifies an optical signal having the input wavelength in the coupled optical signal as is. The optical amplifier optically amplifies another optical signal having the oscillation wavelength in the coupled optical signal with bit logic in the optical signal having the input wavelength inverted. Set with a transmission wavelength and connected to the optical amplifier, an optical filter optically filters the amplified optical signal so as to transmit, as a transmitted optical signal, an optical signal having the transmission wavelength in the amplified optical signal. Connected to the optical filter, an optical receiving unit receives the transmitted optical signal to produce the reception data. Connected to the optical oscillator, a mode setting arrangement sets a mode for the optical oscillator in one of an active mode for making the optical oscillator supply the
NEC Corporation
Negash Kinfe-Michael
Ostrolenk Faber Gerb & Soffen, LLP
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