Patent Grant
6879433
The present invention is related to a wavelength conversion apparatus, and more specifically, to an optical fiber wavelength conversion apparatus having a high conversion efficiency.
All optical type wavelength converters are very important devices used to construct advanced wavelength division multiplexing (WDM) networks with flexibility in the future. A specific attention has been paid to wavelength conversion operations using four-wave mixing (FWM) operations within optical fibers, since the wavelength conversion techniques can own very broad wavelength conversion bands, and also can convert multi-channel WDM signals in a batch-manner. The wavelength conversions using the four-wave mixing (FWM) operations within the optical fibers own very wide wavelength conversion bands and can convert wavelength division multiplexing signals for multiple channels in the batch mode. It is, therefore, desirable to provide an improved wavelength converter.
An improved wavelength converter (wavelength conversion apparatus) is provided herein. Generally speaking, in order to increase a conversion efficiency by FWM operation, it is effective to increase pumping light power. However, an upper limit value of injection power of pumping light would be limited by the stimulated brillouin scattering (SBS) phenomenon occurred in optical fibers. As one of methods for suppressing the SBS, a spread spectrum technique based upon a frequency modulation, or a phase modulation may be available. There is described that the FWM efficiency can be actually improved by this spread spectrum technique.
However in the case that the spread spectrum technique is employed, since spectra of pumping light are widened, spectra of signals whose wavelengths are converted are furthermore widened, and are largely influenced by dispersion of optical fibers.
The present invention has been made to solve the above-described problems, and therefore, has an object to provide a wavelength conversion apparatus whose conversion efficiency is high with employment of optical fibers. In particular, the present invention owns an object capable of obtaining such an FWM light having a less broadened spectrum by also phase-modulating signal light at the same frequency, while a stimulated Brillouin scattering phenomenon is suppressed by way of either a phase modulating operation or a frequency modulating operation of pumping light.
A first solving means of the present invention is to provide a wavelength conversion apparatus comprising:
A second solving means of the present invention is to provide a wavelength conversion apparatus comprising:
A third solving means of the present invention is to provide a wavelength conversion apparatus comprising:
A fourth solving means of the present invention is to provide a wavelength conversion apparatus comprising:
A fifth solving means of the present invention is to provide a wavelength conversion apparatus comprising:
A sixth solving means of the present invention is to provide a wavelength conversion apparatus comprising:
A seventh solving means of the present invention is to provide a wavelength conversion apparatus comprising:
A more detailed explanation of the invention is provided in the following description and appended claims take in conjunction with the accompanying drawings.
A detailed description of the preferred embodiments and best modes are described therein.
(1) Four-Wave Mixing Operation
First, a description is made of four-wave mixing (FWM) operation. Polarization “P” occurred in an optical fiber may be expressed by the following formula (1), while being divided into a linear term “PL” which is directly proportional to an electric field “E”, and a non-linear term “PNL”:
P=PL+PNL(1)
Among these terms, the non-linear polarization PNL may be written by employing electric susceptibilities χ(2), χ(3) and the like:
PNL=P(2)+P(3)+. . .
=ε0χ(2)EE=ε01χ(3)EEE= (2)
In this formula, symbol “ε0” shows a vacuum permittivity, and symbol P(n) represents nth order non-linear polarization. In the non-linear polarization expressed by the formula (2), a 2nd order non-linear polarization of a first term in a right hand does not occur in the optical fiber. On the other hand, 3rd order non-linear polarization of the 2nd term appears in all of substances. In general, when three sets of light having angular frequencies ωi, ωj, ωk are entered into an optical fiber, these three sets of light produce via this 3rd order non-linear polarization fourth light which is expressed by the following formula (3). This phenomenon is referred to be “four-wave mixing” (FWM) operation:
ωijk=ωi=ωj−ωk (3)
In this case,
ωFWM=2ωp−ωs (4)
In this case, as indicated in
In general, if an optical electric field “Es” of signal light and an optical electric field “Ep” of pumping light are defined by the following formulae (5) and (6), then an electric field “Ef” of FWM light is given by the below-mentioned formula (7), while symbol “k” is used as a proportional constant:
Es=ES0 expj (ωpt+φp) (5)
Ep=Ep0 expj (ωpt+φp) (6)
Ef=kEs*Ep2=kEs0*Ep02 expj[(2ωp−ωs)t+(2φp−φs)] (7)
In this case, in order to suppress the SBS phenomenon, if the pumping light is phase-modulated based upon an angular frequency “ωm” and a modulation index “mp”, then it becomes:
φp=mp cosωmt (8)
As a result, the FWM light is phase-modulated based upon a modulation index “2 m”, so that a spectrum is largely widened.
(2) First Embodiment
The laser diode (LD) 103 is a light emitting unit for outputting pumping light (Pump). The polarization controllers (PCs) 101, 104, and 111 control polarization planes of input light. The oscillator 110 outputs a modulation signal. The phase modulators (PMs) 102 and 105 phase-modulate signal light (Signal) and pumping light (Pump) based upon the modulation signal outputted from the oscillator 110, respectively. The coupler 106 multiplexes input light. The Erbium-doped fiber amplifier (EDFA) 107 amplifies input light and then outputs the amplified input light. The dispersion-shifted fiber (DSF) 108 executes a wavelength conversion operation of input light, namely an FWM (four-wave mixing) operation. The band-pass filter (BPF) 109 outputs only a necessary band of input light. The signal light and the pumping light outputted from the laser diode (LD) 103 pass through polarization controllers (PCs) 101 and 104 respectively, and are phase-modulated by the phase modulators (PMs) 102 and 105 based upon the modulation signal outputted from the oscillator 110, respectively. The light outputted from the phase modulator (PM) 102 is multiplexed with the light outputted from the phase modulator (PM) 105 by the coupler 106. In this embodiment mode, the polarization controller (PC) 111 is properly interposed between the phase modulators 102, 105 and the coupler 106. However, if the PCs 101 and 104 are continuously controlled under optimum conditions, and also the output power of the two PMs 102 and 105 is continuously maintained at maximum power, then a relative polarization state of the light outputted from the two PMs 102 and 105 is continuously constant. As a consequence, if fibers located at such a portion defined just after the PMs 102 and 105 and just before the EDFA 107 are constituted by employing a polarization maintaining fiber (PMF), then the fiber located just after one of these PMs 102 and 105 may be fitted to a polarization state of the other fiber by twisting the own fiber. Thus, the polarization controller (PC) 111 located before the coupler 106 may be omitted. Subsequently, both the signal light and the pumping light, which have been multiplexed, are amplified by the Eribium-doped fiber amplifier (EDFA) 107, and thereafter, the amplified signal light and the amplified pumping light are processed by the dispersion-shifted fiber (DSF) 108 and the band-pass filter (BPF) 109, so that FWM light is outputted.
As represented in the drawing, in accordance with the present invention, the pumping light is phase-modulated based upon a modulation index of “mp” and a frequency of “ωm”, namely (mp cos (ωmt+φ)). Furthermore, not only the pumping light, but also the signal light are phase-modulated based upon a modulation index of “ms,” and the frequency of “ωm”, namely (ms cos ωmt). In this case, assuming now that symbol “τ” shows a time delay between both the phase-modulated signals, it becomes:
φs=ms cos ωm(t−τ) (9)
As a result, if the below-mentioned relationship can be satisfied, then the phase modulation component (2φp−φs) of the electric field Ef of the FWM light defined in the formula (7) can be canceled, so that broadening of the spectrum of the FWM light can be suppressed:
2mp=ms (10)
ωmτ=2nπ(n:integer) (11)
(3) Second Embodiment
Pumping light derived from the laser diode (LD) 103 penetrates the polarization controller (PC) 104, and then, is phase-modulated based upon the modulation signal outputted from the oscillator 110 (mp cos(ωmt=φ)). In the coupler 106, signal light passing through the polarization controller (PC) 101 is multiplexed with the above-described pumping light. The polarization controller (PC) 111 may be properly interposed between the phase modulator 105 and the coupler 106. However, if the PCs 101 and 104 are continuously controlled under optimum conditions, and also the output power of the (PM) 105 and the output power of the signal light are continuously maintained at maximum power, then a relative polarization state of the light outputted from the signal light and the (PM) 105 is continuously constant. As a consequence, if fibers located at such a portion defined just after the (PM) 105 and just before the EDFA 107 are constituted by employing a polarization maintaining fiber (PMF), then the fiber located after the (PM) 105 may be fitted to a polarization state of the other fiber by twisting the own fiber. Thus, the polarization controller (PC) 111 located before the coupler 106 may be omitted. Subsequently, both the signal light and the pumping light, which have been multiplexed, are amplified by the Eribium-doped fiber amplifier (EDFA) 107. Then the amplified signal light and the amplified pumping light are entered via the dispersion-shifted fiber (DSF) 108 and the band-pass filter (BPF) 109 into the phase modulator (PM) 301. In this phase shifter (PM) 301, the FWM light is phase-modulated based upon the modulation signal outputted from the oscillator 110, and thereafter, the phase-modulated FWM light is outputted. In this embodiment mode, as shown in this drawing, the FWM light is phase-modulated based upon a modulation index of “−ms” and a frequency of “ωm”, namely (−ms cos ωm(t−τ)), instead of such a phase modulation as to the signal light. In this case, assuming now that an initial value of an optical electric field of the signal light expressed in the formula (5) is equal to φs=0, an optical electric field Ef of FWM light outputted from the BPF 109 after the DSF 108 may be expressed as:
Ef=kEs0*Ep02 expj[(2ωp−ωs)t+2mp cos(ωmt+φ)] (12)
At this time, a phase of an optical electric field of output light from the phase modulator 301 becomes 2mp cos(ωmt+φ)−m3 cosωm(t−τ). As a result, if both the formula (10) and the below-mentioned formula (13) can be satisfied, then the phase modulation component (2φp=φs) defined in the formula (7) can be canceled in a similar manner to that of
ωmτ=2nπ=φ (13)
In this case, since the phase modulators employed in the case of
(4) Third Embodiment
Next,
The signal light is entered via the polarization controller (PC) 101 to the phase modulator (PM) 102. In this phase modulator 102, the signal light is phase-modulated based upon the modulation signal outputted from the oscillator 110, and thereafter, the phase-modulated signal light is outputted (ms cos ωmt). On the other hand, the pumping light is directly frequency-modulated based upon the modulation signal outputted from the oscillator 110 by the laser diode (LD) 401 (mp cos(ωmt+φ)), and then, the frequency-modulated pumping light passes through the polarization controller (PC) 104. Thereafter, the above-described signal light is multiplexed with the pumping light by the coupler 106. Subsequently, after the multiplexed pumping light has been amplified by the Eribium-doped fiber amplifier (EDFA) 107, the amplified pumping light are processed by the dispersion-shifted fiber (DSF) 108 and the band-pass filter (BPF) 109, so that FWM light is outputted.
When an injection current to the semiconductor laser diode (LD) 401 is changed, an oscillating frequency may be changed. A change amount of an oscillating frequency is directly proportional to a magnitude of a change amount of an injection current. When the optical electric field “Ep” of pumping light is defined by the following formula (14), a change in oscillating frequencies may be expressed by “dφp/dt”:
Ep=Ep0 expj (ωpt+φp (14)
On the other hand, assuming now that an injection current “Ip” is defined by that a sine wave is superimposed on a DC component as expressed by:
Ip=Ip0=Im cos ωmt (15)
maximum frequency deviation “B” is directly proportional to a magnitude of a current “Im”. The maximum frequency deviation “B” is equal to an oscillating frequency difference between (Ip0+Imm), namely when the injection current value becomes maximum, and (Ip0−Im), namely when the injection current value becomes minimum. As a consequence, a change in the oscillating frequencies may be expressed by the following formula (16) at this time;
dφp/dt=πB cos ωmt (16)
As a consequence, since it becomes:
φp=(πB/ωm)sin ωmt+const (17),
if the signal light is phase-modulated which can satisfy the below-mentioned formulae (18) and (19), then the phase modulation component in the formula (7) can be canceled, so that broadening of the spectrum of the FWM light can be suppressed:
2πB/ωm=ms (18)
ωmτ=(2n+1/2)π(n:integer) (19)
(5) Fourth Embodiment
Alternatively, both signal light and pumping light may be phase-modulated by using a single set of phase modulator.
The signal light is entered via the circulator 501 to the phase modulator (PM) 102. In this phase modulator 102, the signal light is phase-modulated based upon the modulation signal outputted from the oscillator 110, and thereafter, the phase-modulated signal light is reached via the coupler 106 to the mirror 502. Then the signal light is reflected on the mirror 502, and the reflected light is again entered via the coupler 106 into the phase modulator (PM) 102. In this phase modulator (PM) 102, this entered signal light is again phase-modulated based upon the modulation signal outputted from the oscillator 110. On the other hand, the pumping light outputted from the laser diode (LD) 103 is entered via the coupler 106 into the phase modulator (PM) 102. In this phase modulator (PM) 102, this entered pumping light is phase-modulated based upon the modulation signal outputted from the oscillator 110. In this phase modulator (PM) 102, both the signal light and the pumping light, which are outputted from the phase modulator (PM) 102, are amplified via the circulator 501 by the Eribium-doped fiber amplifier (EDFA) 107, and thereafter, the amplified signal light and the amplified pumping light are processed by the dispersion-shifted fiber (DSF) 108 and the band-pass filter (BPF) 109, so that FWM light is outputted. In this arrangement, the signal light is phase-modulated two times by the phase modulator based upon the frequency of “ωm” and the modulation index of “m”, whereas the pumping light is phase-modulated only one time. Assuming now that symbol “τ” indicates a time delay between the phase modulator and the mirror, since it becomes:
φp=m cos ωmt (20),
φs=m cos ωmt=m cos ωm(t−2τ) (21),
the phase modulation can be canceled by the following formula (22) based upon the formula (7):
ωmτ=nπ(n:integer) (22).
As a result, broadening of the spectrum of the FWM light can be suppressed. It should be understood that generally speaking, since a phase modulator is a traveling wave type phase modulator, this phase modulator owns a directional characteristic. However, such a fact is known that the phase modulator may own substantially same modulation characteristics along a forward direction and a reverse direction up to approximately 500 MHz (see “Information distributing system and Polarization independent external modulator by optical circuit” written by HASEGAWA and ISHIDA, No. B707, 1995, Communication Society Conference of Japanese Electronic Information Communication Institute).
(6) Fifth Embodiment
In general, an FWM operation in an optical fiber owns a polarization dependent characteristic. However, the FWM operation in the optical fiber may have a polarization independent characteristic by way of orthogonal polarization two-wavelength pumping, and a polarization diversity arrangement (see S. Yamashita, S. Y. Set, and R. I. Laming, “Polarization independent, all-fiber phase conjugation incorporating inline fiber DFB lasers”, IEEE Photonics Technology Letters, vol. 10, no. 10, pp. 1407-1409, October 1998., S. Watanabe, S. Takeda, and T. Chikama, “Interband wavelength conversion of 320 Gb/s (32×10 Gb/s) WDM signal using a polarization-insensitive fiber four-wave mixer”, ECOC'98, Postdeadline paper.) Even when any of these methods is employed, it is possible to realize a high-efficiency optical fiber wavelength converter without a broadened spectrum to which the methods of
Signal light which is entered via the circulator 601 into the polarization beam splitter (PBS) 602 is split into polarized waves which are orthogonal to each other. The polarized waves are propagated through a ring along opposite directions, while this ring is constructed of the PBS 602 and the (PM) 603. In this case, if distances from respective ports of the PBS 602 up to the (PM) 603 are made equal to each other, then two polarization waves may be modulated by the same modulations in the (PM) 603. Furthermore, the 90-degree twisting unit 606 is inserted into any one of two paths routed from the PBS 602 to the (PM) 603. In this case, the 90-degree twisting unit 606 twists the input light by 90 degrees, and then outputs the 90-degree twisted input light. It should also be noted that two sets of returned polarization waves are multiplexed with each other by the PB 602, and then, the multiplexed polarization wave is outputted from the original input port. Thereafter, this multiplexed polarization wave is processed based upon the polarization independent wavelength conversion by the polarization independent fiber FWM 604, so that FWM light is outputted.
It should also be noted that in the above-described embodiment mode, since the phase modulator basically does not own the wavelength dependent characteristic, even when the signal light is the WDM signal, the arrangements of
(7) Measuring Experiment
To confirm an effective characteristic of the present invention, as one example, the measuring experiment was carried out as to the wavelength conversion apparatus of the first embodiment mode with employment of the below-mentioned arrangement.
Laser light LD701 for signal light and laser light LD103 for pumping light are entered via the polarization controller (PCs) 101 and 104 into the phase modulators (PMs) 102 and 105, respectively. In these phase modulators (PMs) 102 and 105, the laser light LD701 and the laser light LD 103 are phase-modulated based upon a sine wave having a frequency of 500 MHz outputted from the oscillator 110. In this case, a modulation factor of signal light must be made two times higher than a modulation factor of pumping light in accordance with the formula (10) of the above description. At this time, the modulation factors are directly proportional to peak-to-peak values of voltages applied to the phase modulators 102 and 105, respectively. It should be understood that in the phase modulators 102 and 105 employed in
FIG. 8(c) indicates a spectrum of output light obtained by executing such a method that both the pumping light and the signal light, provided by the present invention, are phase-modulated, and spectra of the phase-modulated light are broadened. Similar to FIG. 8(b), since the power (for example, 18 dBm) of the pumping light can be increased, a converting efficiency of FIG. 8(c) may be improved, as compared with FIG. 8(a). Also, in comparison with FIG. 8(b), a spectrum of phase conjugate light is not broadened, and corresponds to such an inverted spectrum of the original signal, so that the spectrum is restored. Since the method provided by the present invention is carried out, such a confirmation could be made that the ideal wavelength conversion operation could be carried out in view of the spectrum, while achieving the higher conversion efficiency.
Also,
Furthermore, a spectrum change of FWM light was investigated in high resolution by way of such a heterodyne detection that another wavelength tunable light source was employed as a local oscillator.
(8) Sixth Embodiment
A wavelength conversion operation, which does not depend upon a polarized wave of signal light, may be realized in such a manner that polarized waves of pumping light having different wavelengths are entered into an optical fiber in such a manner that these polarized waves are orthogonal to each other by a polarization beam splitter (PBS) by employing two sets of pumping light (orthogonal polarization two-wavelength pumping system) (see S. Yamashita, S. Y. Set, and R. I. Laming, “Polarization independent, all-fiber phase conjugation incorporating inline fiber DFB lasers, “IEEE Photonics Technology Letters”, vol. 10, no. 10, pp. 1407-1409, October 1998).
The laser diode (LD) 141 corresponds to a light emitting unit for outputting pumping light (Pump). The polarization controller (PC) 142 controls a polarization plane of input light. The phase modulator (PM) 143 phase-modulates the pumping light (Pump) based upon a modulation signal outputted from the oscillator 110, and then, outputs the phase-modulated pumping light. The polarization beam splitter (PBS) 144 splits input light to polarized waves which are orthogonal to each other, and multiplexes these polarized waves with each other. Other structural elements of this wavelength conversion apparatus are similar to those of FIG. 2. Both signal light and pumping light outputted from the laser diodes (LD) 103 and (LD) 141 penetrate the polarization controllers (PCs) 104 and 142, respectively, and then, are phase-modulated by the phase modulators (PMs) 105 and 143 based upon the modulation signal outputted from the oscillator 110. The light outputted from the phase modulator (PM) 105 and the light outputted from the phase modulator (PM) 143 are multiplexed with each other by the polarization beam splitter (PBS) 144 in such a manner that the polarized planes thereof are orthogonal with each other. Furthermore, the signal light traveled through the polarization controller (PC) 101 is multiplexed with the light outputted from the polarization beam splitter (PBS) 144. Subsequently, both the signal light and the pumping light, which have been multiplexed with each other, are amplified by the Erbium-doped fiber amplifier (EDFA) 107, and thereafter, the amplified signal and pumping light are processed by the dispersion-shifted fiber (DSF) 108 and the band-pass filter (BPF) 109, so that FWM light is outputted.
As indicated in the drawing, in accordance with the present invention, it is so assumed that the respective pumping light is phase-modulated based upon the frequency of “ωm,” and the modulation index of “mp” so as to suppress the SBS. In this case, assuming now that symbol “τ” indicates a time delay between both the phase-modulated signals, the following formulae (23) and (24) are given:
φp1=mp cos ωmt (23)
φp2=mp cos ωm(t=τ) (24)
In this case, symbols “φp1” and “φp2” represent a phase difference between a modulation signal of a first modulator and a modulation signal of a second modulator. In this case, assuming now that an initial value of an optical electric field of the signal light expressed in the formula (5) is equal to φs=0, an optical electric field “Ef” of FWM light outputted from the BPF 109 after the DSF 108 may be expressed as:
Ef=kEs*Ep1Ep2
=kEs0*Ep01Ep02 expj[(ωp1+ωp2=ωs)t+(φp1+φp2)] (25)
while symbol “K” is defined as a proportional constant. In this case, symbols “Ep1” and “Ep2” indicate optical electric fields of first and second pumping light, respectively. As a consequence, if the below-mentioned relationship can be satisfied, then the phase modulation component (φp1+φp2) of the electric field Ef of the FWM light defined in the formula (25) can be canceled, so that broadening of the spectrum of the FWM light can be suppressed:
ωmτ=(2n+1)π(n:integer) (26)
In this embodiment mode, the angular frequency “ωFWM” of the fourth light may be obtained as “ωijk”, assuming now that in the formula (3), for instance, symbol “ωj” is the angular frequency “ωp1” of the first pumping light; symbol “ωj” is the angular frequency “ωp2” of the second pumping light; and symbol “ωk” is the angular frequency “ωs” of the signal light. It should also be understood that plural sets of corresponding relationships other than this relationship may be conceived.
(9) Seventh Embodiment
The laser diode (LD) 151 corresponds to a light emitting unit for frequency-modulating pumping light based upon a modulation signal outputted from the oscillator 110 to output the frequency-modulated pumping light. The polarization controller (PC) 152 splits and multiplexes a polarization plane of input lint. Other structural elements of this wavelength conversion apparatus are similar to those of FIG. 4.
The pumping light is directly frequency-modulated by the laser diodes (LDs) 401 and 151 based upon the modulation signal outputted from the oscillator 110, and then, the frequency-modulated pumping light passes through the polarization controllers (PCs) 104 and 152. The light outputted from the phase modulator (PM) 105 and the light outputted from the phase modulator (PM) 143 are multiplexed with each other by the polarization beam splitter (PBS) 144 in such a manner that the polarized planes thereof are orthogonal with each other. Furthermore, the signal light traveled through the polarization controller (PC) 101 is multiplexed with the light outputted from the polarization beam splitter (PBS) 144. Subsequently, both the signal light and the pumping light, which have been multiplexed with each other, are amplified by the Erbium-doped fiber amplifier (EDFA) 107, and thereafter, the amplified signal and pumping light is processed by the dispersion-shifted fiber (DSF) 108 and the band-pass filter (BPF) 109, so that FWM light is outputted.
Assuming now that the initial value of the electric field of the signal light in the formula (5) is defined as φs=0, an electric field of the FWM light becomes similar to the formula (25). Assuming that maximum frequency deviation is set to “B”, frequency changes in the pumping light at this time may be expressed as:
dφp1/dt=πB cos ωmt (27)
dφp2/dt=πB cos ωm(t−τ) (28).
As a consequence, since these frequency changes are given by the following formulae (29) and (30), similar to the sixth embodiment mode, if the below-mentioned relationship can be satisfied, then the phase modulation component defined in the formula (25) can be canceled, so that broadening of the spectrum of the FWM light can be suppressed:
φp1=(πB/ωm)sin ωmt+const (29)
φp2=(πB/ωm)sin ωm(t−τ)+const (30).
In this embodiment mode, the angular frequency “ωFWM” of the fourth light may be obtained as “ωijk”, assuming now that in the formula (3), for instance, symbol “ωi” is the angular frequency “ωp2” of the first pumping light; symbol “ωj” is the angular frequency “ωp2” of the second pumping light; and symbol “ωk” is the angular frequency “ωs” of the signal light. It should also be understood that plural sets of corresponding relationships other than this relationship may be conceived.
As previously described, according to the present invention, the wavelength conversion apparatus having the high conversion efficiency with employment of the optical fiber can be provided. More specifically, in accordance with the present invention, while the SBS phenomenon is suppressed by phase-modulating, or frequency-modulating the pumping light, the signal light is also phase-modulated based upon the same frequency, so that the FWM light having less broadening of the spectrum.
Although embodiments of the invention have been shown and described, it is to be understood that various modifications and substitutions, as well as rearrangements of method steps and equipment, can be made by those skilled in the art without departing from the novel spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2000-202859 | Jul 2000 | JP | national |
This application is based upon priority International Application PCT/JP00/06867 filed Oct. 3, 2000, International Publication No. WO 02/03132 A1 published Jan. 10, 2002, which is based upon Japanese Application 2000-202859 filed Jul. 4, 2000.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCTJP00/06867 | 10/3/2000 | WO | 00 | 6/10/2003 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO0203132 | 1/10/2002 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5386314 | Jopson | Jan 1995 | A |
| 6307984 | Watanabe | Oct 2001 | B1 |
| Number | Date | Country |
|---|---|---|
| 0 862 078 | Sep 1998 | EP |
| 1306718 | May 2003 | EP |
