1. Field of the Invention
The present invention relates to an apparatus which performs, by OCDMA (Optical Code Division Multiplex Access), at least one of encoding and decoding of wavelength-division-multiplexed light. More particularly, the present invention relates to an apparatus which employs fiber gratings to perform encoding/decoding by OCDMA.
2. Description of the Related Art
In OCDMA, a technique similar to the CDMA technology which has been practically used in the field of mobile communications is employed to perform encoding of an optical signal at a transmitting end, and decoding of an optical signal at a receiving end. The encoding/decoding of an optical signal is performed by using optical devices such as diffraction gratings, optical waveguides, or fiber gratings.
In OCDMA, even if a number of encoded optical signals exist in the same wavelength band, interferences therebetween are prevented because of code-by-code independence. Therefore, by assigning different codes to different users, it becomes possible for a large number of users to simultaneously share one optical signal propagating medium, even though optical signals in the same wavelength band are used.
Currently proposed encoding methods can be classified into, for example: Frequency-encoding techniques; Frequency-Hopping techniques; Fast-Frequency-Hopping techniques; and direct-sequence techniques. A Frequency-encoding technique is a method of encoding which varies the intensities of optical signals for different wavelengths. A Frequency-Hopping technique and a Fast-Frequency-Hopping technique are methods of encoding which vary wavelength and delay. A direct-sequence technique is a method of encoding which varies delay and phase for a single wavelength.
In “Passive Optical Fast Frequency-Hop CDMA Communications System”, Habib Fathallah, Journal of Lightwave Technology, Vol. 17, No. 3, March 1999, there is proposed a Fast-Frequency-Hopping technique (hereinafter abbreviated as “FFH technique”) which is performed by using fiber gratings which are assigned with different delays corresponding to different wavelengths. The present invention relates to this optical encoding method. This optical encoding method may sometimes be referred to as “time-spread/wavelength-hop optical CDMA”.
First, with reference to
Since the grating period of each optical fiber varies in accordance with the tension applied thereto, the wavelength band in which Bragg reflection occurs is shifted from optical fiber to optical fiber. Therefore, each wavelength component contained in an incoming optical signal (a broadband light pulse) is reflected by a fiber grating in a different position, depending on the wavelength. Different reflection positions result in different amounts of time being required for the optical signal to make back and forth trips. As a result, the respective wavelength components of the optical signal are output from the optical fibers at different points in time. In other words, if a single broadband pulse is input to the encoder of
Now, assume that N optical fiber gratings F1 to FN are employed, with tensions being applied to the optical fiber gratings F1 to FN so that they reflect light at central wavelengths λ1 to λN, respectively. In this case, the reflection central wavelengths λ1 to λN may be of the following order of magnitude (ascending from left to right), for example:
In this exemplary case, the wavelength λ1 of light to be reflected by the optical fiber grating F1 is the shortest, while the wavelength λN of light to be reflected by the optical fiber grating FN is the longest. Such an order of reflection wavelengths can be easily changed by changing the combination of tensions to be applied to the N optical fibers F1 to FN. The number of possible permutations is N!=N×(N−1)×(N×2)× . . . 3×2×1. However, among these possible permutations, there may be some which are difficult to be distinguished from one another. Therefore, in actuality, the number of codes (described later) will be smaller than N!.
In the encoder of
Thus, in the encoder of
On the other hand, the apparatus of
Next, with reference to
In
When the apparatus shown in
However, when OCDMA is to be used in conjunction with WDM, as many OCDMA encoder/decoders will be required as there are wavelength channels. As the number of WDM wavelength channels increases beyond ten, and even twenty in the future, a substantial increase in the encoder/decoder size would be inevitable.
In order to overcome the problems described above, preferred embodiments of the present invention provide an apparatus which can realize OCDMA encoding and/or decoding of wavelength-division-multiplexed light with a simple structure.
According to the present invention, there is provided an apparatus for performing, by optical code division multiplex access (OCDMA), at least one of encoding and decoding of wavelength-division-multiplexed (WDM) light, comprising: an optical input/output section for handling input/output of the wavelength-division-multiplexed light; and N fiber gratings (where N is an integer equal to or greater than two) which are in a series connection to the optical input/output section, wherein, each of the N fiber gratings has a sampled grating structure defining a plurality of reflection wavelength bands; and an interval ΔT between central values of the reflection wavelength bands of the sampled grating structure is equal to an interval S between central wavelengths of wavelength bands contained in the wavelength-division-multiplexed light, and the central values of the respective reflection wavelength bands differ from one fiber grating to another at least during operation.
In a preferred embodiment, between fiber gratings, the central value of each respective reflection wavelength band has a difference which is greater than a bandwidth of each reflection wavelength band and smaller than ΔT/N.
In a preferred embodiment, the apparatus comprises, for each fiber grating, a code program device for controlling the sampled grating structure, wherein the code program device is capable of shifting the central values of the reflection wavelength bands defined by each sampled grating structure.
In a preferred embodiment, the code program device is capable of causing a period of refractive index modulation of the sampled grating structure of each fiber grating to be changed via heat or stress.
In a preferred embodiment, an amount of change in the period of refractive index modulation of each sampled grating structure introduced by the code program device is prescribed to be a value which is greater than the bandwidth of each reflection wavelength band.
In a preferred embodiment, the refractive index modulation of each sampled grating structure is modulated according to a sinc function.
In a preferred embodiment, each sampled grating structure has a first region which provides a refractive index modulation with a relatively large amplitude and a second region which provides a refractive index modulation with a relatively small amplitude, the period of modulation of the first region being equal to the period of modulation of the second region.
In a preferred embodiment, the apparatus operates as an encoder.
In a preferred embodiment, the apparatus operates as a decoder.
In a preferred embodiment, the apparatus decodes a signal which is encoded by the aforementioned apparatus.
An encoding/decoding system according to the present invention comprises the aforementioned apparatus functioning as an encoder and the aforementioned apparatus functioning as a decoder.
By employing fiber gratings each having a sampled grating structure, it becomes possible to replicate light reflection wavelength bands at predetermined wavelength intervals. By employing a series connection of a plurality of sampled fiber gratings having respectively different light reflection wavelength bands, it becomes possible to perform CDMA encoding/decoding for an optical signal which is wavelength-division-multiplexed. As a result, it becomes unnecessary to provide a separate encoding/decoding apparatus for each wavelength channel.
Other features, elements, processes, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.
Hereinafter, preferred embodiments of the apparatus of the present invention will be described with reference to the accompanying drawings.
First, with reference to
The encoder shown in
In the present embodiment, each of the fiber gratings 101, 102, and 103 has a sampled grating structure. Each sampled grating structure includes an alternating array of: first regions (11 to 14; 21 to 24; or 31 to 34) which provide a refractive index modulation with a relatively large amplitude; and second regions (201) which provide a refractive index modulation with a relatively small amplitude, the two types of regions being disposed with a constant period P. Hereinafter, the period P will be referred to as a “sampling period”. In the present embodiment, it is assumed that the second region 201 has a substantially constant refractive index, and provides a refractive index modulation with a zero amplitude. However, it is not a requirement that the amplitude of refractive index modulation by the second region 201 be zero.
Assuming that the central wavelengths of the respective channels of wavelength-division-multiplexed light are at an interval “S” (i.e., interval between the bands of the respective channels of WDM), the aforementioned sampled grating structure is able to form a plurality of reflection wavelength bands that are “replicated” with a period equal to the interval S between the central wavelengths of the respective channels of wavelength-division-multiplexed light, as will be described in detail later. In other words, ΔT=S is true according to the present invention, where ΔT is the interval between the central wavelengths of the reflection wavelength bands which are replicated by the sampled grating structure. Note that the formation of the reflection wavelength bands (based on Bragg reflection) with the period ΔT is ascribable to the nature of the sampled grating. AT is in proportion with an inverse of the sampling period P, as is expressed by the following equation.
ΔT=λB2/2nP
In the above equation, λB is a Bragg wavelength given a grating period d, and n is an effective refractive index.
Therefore, the size of ΔT can be controlled by adjusting the sampling period P. In the present embodiment, a sampling period P which realizes a ΔT value that matches the band interval of the wavelength-division-multiplexed light is determined, and then each fiber grating is assigned with a refractive index modulation with the sampling period P.
A sampled grating is structured so that its grating period is not uniform along the direction of light propagation, such that the phase and/or amplitude of refractive index modulation is not uniform along the direction of light propagation. In
In
In the examples shown in (a) and (b) of
In the example shown in (c) of
In the present embodiment, in order to cause the central values of the respective reflection wavelength bands of the fiber gratings 101, 102, and 103 to be shifted from one another, a different grating period is prescribed for each fiber grating.
Next, with reference to (a) to (d) of
First, (a) of
ΔT is set to a value which matches the period S of the wavelength channels of wavelength division multiplexing and which is equal to or greater than Δλ×N (where N is the number of fiber gratings).
Graph (b) of
As is clear from the comparison between (a) and (b) of
Graph (c) of
As is clear from the comparison between (a) and (c) of
Graph (d) of
In order to realize the reflectance pattern shown in (d) of
The graphs shown on the righthand sides of (a) to (c) of
Thus, by using a single encoder which is produced by using three fiber gratings, it is possible to form delay patterns corresponding to four wavelength channels (wavelengths λ1, λ2, λ3, and λ4). As a result, it is possible to perform encoding of wavelength-division-multiplexed light without increasing the size of the encoder. Moreover, this encoding can be performed simultaneously across the four wavelength channels (multiple operation).
The width Δλ of each reflection band replicated by the sampled grating structure corresponds to the “1 chip band” of FFH-CDMA. It is desirable to prescribe the length of Δλ to be 0.1 nm or more.
In a preferable embodiment of the present invention, each chip constituting a code pattern of optical encoding FFH-CDMA is “replicated” on the wavelength axis by implementing the corresponding fiber grating by using a sampled grating structure. Moreover, through similar replications on a number of chips, simultaneous encoding over a plurality of wavelength channels is enabled as a whole.
In the apparatus of the present embodiment, a plurality of sampled fiber gratings designed so that ΔT and Δλ satisfy the aforementioned conditions are used. However, the sampled fiber gratings are not limited to those having the structure as shown in (a) of
In the example shown in
The number of fiber gratings to be employed in a series connection in a single apparatus is equal to the number N of chips of the encoding pattern. Therefore, in the case where three sampled fiber gratings are used as shown in
Hereinafter, the operation of the apparatus of FIG. 5 will be described.
First, a single-mode optical signal which is radiated from a light source (not shown) enters an optical fiber 1. The light source may be, for example, a broadband light source such as a pulse light source, a super continuum light source or an LED, or a comb-type light source of Fabry-Perot type or fiber ring laser type.
Via a circulator 5, the optical signal entering the optical fiber 1 is input to the optical input/output section 203, which is connected to the fiber grating 101. A portion of the optical signal entering into the fiber grating 101 is reflected by the fiber grating 101, while the remainder enters the fiber grating 102. The light which has been reflected by the fiber grating 101 enters an optical fiber 6, via the optical input/output section 203 and the circulator 5. Out of the optical signal entering the optical fiber 1, the light to be reflected by the fiber grating 101 is light in the reflection wavelength band which is defined by the grating period d1. In the aforementioned reflection wavelength band, narrow reflection bands are replicated with the period of ΔT, as shown in (a) of
A portion of the optical signal entering the fiber grating 102 is reflected by the fiber grating 102, while the remainder enters the fiber grating 103. The light which has been reflected by the fiber grating 102 enters the optical fiber 6 via the fiber grating 101, the optical input/output section 203, and the circulator 5. The light to be reflected by the fiber grating 102 is light in the reflection wavelength band which is defined by the grating period d2. In the aforementioned reflection wavelength band, narrow reflection bands are replicated with the period of ΔT, as shown in (b) of
A portion of the optical signal entering the fiber grating 103 is reflected by the fiber grating 103. The light which has been reflected by the fiber grating 103 enters the optical fiber 6, via the fiber grating 102, the fiber grating 101, the optical input/output section 203, and the circulator 5. The light to be reflected by the fiber grating 103 is light in the reflection wavelength band which is defined by the grating period d3. In the aforementioned reflection wavelength band, narrow reflection bands are replicated with the period of ΔT, as shown in (c) of
In a preferred embodiment, the amount of shift Δλ1 between the reflection band of the second fiber grating 102 and the reflection band of the first fiber grating 101 is equal to the width Δλ of each replicated rectangular reflection band. Therefore, when the reflection bands provided by these two fiber gratings are taken together, sets of peaks resembling two adjoining combteeth emerge ((b) of
The reflected light from the second fiber grating 102 enters the optical fiber 6 after propagating over an optical path which is 2×(L+I) longer than that traveled by the reflected light from the first fiber grating 101. On the other hand, the reflected light from the third fiber grating 102 enters the optical fiber 6 after propagating over an optical path which is 4×(L+I) longer than that traveled by the reflected light from the first fiber grating 101.
Therefore, the delay imparted to the reflected light from the second fiber grating 102 is greater than the delay imparted to the reflected light from the first fiber grating 101. Similarly, the delay imparted to the reflected light from the third fiber grating 103 is greater than either of the delays imparted to the reflected light from the first and second fiber gratings 101 and 102.
The wavelength dependence of delay (delay pattern) provided by the entire apparatus is, as shown in (d) of FIG. 7, periodically replicated so as to correspond to the wavelength channels of λ1 to λ4.
In the present embodiment, the reflection bands of the second fiber grating 102 and the third fiber grating 103 are shifted by Δλ1 and 2×Δλ1, respectively, from the reflection band of the first fiber grating 101. This encoder realizes an encoding in accordance with Code 1 shown in
Generally speaking, in a series connection of N fiber gratings, the reflection wavelength of an ith fiber grating as counted from the optical input/output section side has a shift which is expressed as mi×Δλ (where mi is an integer; 1≦i≦N).
Each code is defined by a particular combination of mi. In selecting codes, however, care is to be taken so that there will be little correlation between codes. In CDMA, codes are selected by a technique called “FH-sequence” or “one-coincidence”. As a result, the independence of the codes is improved, thus leading to a reduced decoding error rate.
In the example shown in
In the example of
A decoder for decoding an optical signal which has been encoded by the encoder shown in
Next, the effects obtained in the case where a chirped sampled fiber grating as shown in (b) of
Graphs (a) to (d) of
In order to secure a necessary band for encoding, ΔT must be prescribed to be equal to or greater than the bandwidth of a single channel of wavelength division multiplexing. As described earlier, P and ΔT are in inverse proportion with each other such that ΔT decreases as P increases. Therefore, preferably, the sampling period P in the first to third fiber gratings is prescribed to 2 mm or less.
Hereinafter, a second embodiment of the apparatus of the present invention will be described.
In the present embodiment, programming of code patterns is made possible by using a plurality of fiber gratings having an identical structure.
First,
The apparatus of the present embodiment differs from the apparatus of
The grating period of a fiber grating is changeable based on the temperature the fiber grating or a tension applied to the fiber grating, and the reflection wavelength band of the fiber grating can be changed (shifted) based on its grating period. In accordance with the apparatus of the present embodiment, programming (i.e., arbitrary changing after fabrication of the apparatus) of encoding patterns and decoding patterns is possible.
In the apparatus shown in
In the present embodiment, the grating periods of the fiber gratings 9, 10, and 11 are all equal to d1 at room temperature, so that no encoding pattern can be created.
By applying respectively different temperatures to the fiber gratings 9, 10, and 11, the reflection bands provided by the fiber gratings are shifted from one another, thus making it possible to create an encoding pattern.
Hereinafter, the operation of the apparatus of
First, a single-mode optical signal which is radiated from a light source (not shown) enters an optical fiber 7. Via a circulator 8, the optical signal entering the optical fiber 7 is coupled to the fiber grating 9. A portion of the optical signal entering into the fiber grating 9 is reflected by the fiber grating 9, while the remainder enters the fiber grating 10. The light which has been reflected by the fiber grating 9 enters an optical fiber 16, via the circulator 8. Out of the optical signal entering the optical fiber 7, the light to be reflected by the fiber grating 9 is light in a reflection wavelength band that is defined by a grating period which is altered from d1 by the temperature adjustment device 112.
Unless temperature adjustment is performed, light in the reflection band defined by the grating period d1 will be reflected by the fiber grating 9, so that no reflection will occur in the other fiber gratings 10 and 11.
In the present embodiment, the temperatures of the fiber gratings 10 and 11 are adjusted to respectively different levels, thus allowing a portion of the light which has been transmitted through the fiber grating 9 to be reflected by the fiber grating 10 or the fiber grating 11.
When provided with an appropriate temperature distribution, each of the fiber gratings 9, 10, and 11 acquires a plurality of narrow replicated reflection bands as shown in (a) to (c) of
Based on the temperature settings of the fiber gratings 9, 10, and 11, an encoding pattern according to Code 1, Code 2, or Code 3 as shown in
The apparatus of the present embodiment can also operate not only as an encoder but also as a decoder, similarly to the earlier-described embodiment. Moreover, chirped sampled gratings may be used as the fiber gratings. Note that it is not a requirement that the initial grating structures of the fiber gratings be identical. Rather, the grating periods may initially be different as in the case of the apparatus shown in
Hereinafter, results of simulations and experiments which have been performed with respect to embodiments of the present invention will be described.
Firstly, the relationship between parameters which are necessary in the simulations will be described. A relationship expressed by eq. 1 below must be satisfied by: the bandwidth Δλ of each of the reflection bands replicated by sampling effects on the fiber grating; a period ΔT of the replicated reflection bands; and the number N of chips composing a code.
[Eq. 1]
Ideally, no ripple or the like exists outside the reflectance pattern defining each reflection band, and each reflectance pattern is completely rectangular. In practice, however, each reflectance pattern is not completely rectangular. Therefore, N must be prescribed to be smaller than ΔT/Δλ.
As N increases, the code length increases, and therefore the number of codes increases. The more codes there are, the more users can utilize the same wavelength channel, which is preferable (number of users=number of codes).
In the case where the optical signal is in pulse form, ΔT corresponds to the bandwidth of each pulse, and is usually 0.6 nm or more. In order to increase ΔT, the sampling period P should be decreased. In order to reduce Δλ by realizing a thin, near-rectangular reflection band, it is preferable to increase the overall length L of each fiber grating.
Therefore, in order to increase N, it is preferable to reduce the sampling period P and increase the overall length L of each fiber grating.
On the other hand, among the reflection bands replicated by the sampled grating structure, the total number of those which are available for use depends on the longitudinal direction length W of each refractive index-modulated region provided by the sampled grating structure (see
As described earlier, it is preferable that each replicated reflection band is completely rectangular. If unwanted ripple exists on either side of the reflection band, when overlaying as shown in (d) of
[Simulations]
Next, results of simulations performed with respect to the apparatus of
With reference to
In the delay pattern shown in (b) of
The simulations were performed under the conditions as shown in Table 1 below.
In order to obtain the delay pattern shown in (b) of
In each case, calculations were performed by prescribing the coefficient of thermal expansion of each fiber grating to be 5.5×10−7, and the thermooptic constant of each fiber grating to be 8.3×10−6.
At an upper left corner of (b) of
In the simulations, the temperatures of the six fiber gratings were set at six different levels in a range from 10° C. to 85° C. In order to set more (than six) levels of temperature for increasing the number N of chips, it is preferable to increase the maximum temperature level. If the temperature differences between fiber gratings were reduced, the amounts of shift between the reflection wavelength bands of the fiber gratings might be insufficient. Therefore, the temperature of the fiber grating that is supposed to have the greatest wavelength shift amount is preferably set to a level higher than 85° C.
However, in the case of using Peltier devices, the highest temperature that can be set is about 85° C. Moreover, there are limits to the amount of changes in the grating period that can be obtained through adjustments of temperature or tension alone. Therefore, devices such as temperature adjustment devices may be used in combination with a plurality of fiber gratings having different initial grating period values.
Hereinafter, experimental results will be described with reference to
The central wavelengths of reflection bands provided by the six fiber gratings are shifted with respect to one another by an integer multiple of Δλ(=0.12 nm). In the results shown in
In the matrix chart of
When the encoder performs an encoding in accordance with the matrix chart of
According to a simulation performed by the inventors, as shown in
Thus, it was confirmed that, by using sampled fiber gratings, optical signals contained on a plurality of WDM channels can be simultaneously encoded or decoded, by using a single encoder or decoder.
In order to obtain the delay pattern shown in
Next, by using the same apparatus, the temperatures of the fiber gratings were changed to the levels shown in Table 6 below.
Thus, by merely changing the fiber temperatures, the central wavelengths of the reflection bands provided by the fiber gratings were shifted by integer multiples of Δλ(=0.12 nm), whereby different code patterns were realized.
As has been confirmed with the experimental results above, by varying the temperatures of the fiber gratings for realizing different code patterns, the plurality of delay patterns replicated on the wavelength axis are also changed simultaneously. In other words, the present invention makes possible a simultaneous optical encoding program for multiple wavelengths.
In the above experimentation, three code patterns of FFH-CDMA are used in conjunction with three wavelength channels of WDM, thereby realizing encoding/decoding on a total of nine channels. By increasing the number of fiber gratings in the encoder or decoder for increasing the number N of chips of each code, it will be possible to further increase the total number of channels.
As described earlier, in order to increase the number N of chips, it will be effective to bring the shape of the reflection band provided by each fiber grating as close to a rectangular shape as possible. In order to realize a near-rectangular reflection band shape, “apodization” would be effective, as mentioned above. An apodization function A(z) can be expressed by the following equation, for example.
By ensuring that each fiber grating has changes in refractive index which are obtained by multiplying by such an apodization function A(z) the changes in refractive index δn(z) as shown in (a) of
Next, an advantage of using sampled gratings (sinc function-type sampled gratings) which are refractive index-modulated with a sinc function as shown in (c) of
By using such sinc function-type sampled gratings, it becomes possible to realize uniform replication of reflection bands for a greater number of WDM channels, thus enabling simultaneous encoding/decoding.
In a sinc function-type sampled grating, a reflectance distribution is uniformly replicated over a plurality of reflection bands, due to sampling. The changes in refractive index as shown in (c) of
Hereinafter, a simulation result of an apparatus according to the present invention which was produced by using sinc function-type sampled gratings will be described. In the simulations, fiber gratings which were produced under the conditions shown in Table 7 below were used.
As shown in
From the above simulation, it was confirmed that the use of sampled gratings makes it possible for a single apparatus to perform optical signal encoding/decoding (in which ten chips are used) simultaneously on eight channels of wavelength division multiplexing.
As described earlier, instead of using gratings of different structures having individual central reflection bands which are initially shifted by Δλ×integer, gratings having the same structure may be used, with their temperatures or tensions being adjusted so that the central wavelengths of their reflection bands are shifted. For example, ten sampled fiber gratings may be used, with their temperatures being respectively set to e.g. 168° C., 96° C., 216° C., 192° C., 144° C., 48° C., 120° C., 0° C., 24° C., and 72° C. In order to prescribe a temperature over 80° C., another type of heaters may be used instead of Peltier devices. By changing the distribution of temperatures to be applied to the ten sampled fiber gratings, a different code pattern can be programmed.
In each of the above embodiments, the reflection bands are shifted by adjusting the temperatures of the fiber gratings. Alternatively, the reflection bands of the fiber gratings may be changed by using other types of devices. For example, piezoelectric devices may be used to change the tensions to be applied to the fiber gratings and shift their reflection wavelengths. What is important is the ability to independently change the grating period of each fiber grating for enabling arbitrary changes (programming) in the encoding pattern or decoding pattern.
Note that sampled grating structures are classified into those with modulated amplitudes and those with modulated phases. Both types of sampled grating structure are applicable to the present invention.
In each of the above present embodiments, sampled grating structures with modulated phases are adopted. When producing sampled grating structures with modulated phases, their refractive indexes may be modulated as shown in
The apparatus of the present invention can realize an OCDMA encoding and/or decoding of wavelength-division-multiplexed light by using a simple structure. Therefore, it is possible to support an increased number of channels with a simple apparatus structure.
The apparatus of the present invention is suitably used for not only mobile devices such as mobile phone terminals, but also in combination with any other known constituent elements for composing a communications system.
The present invention is applicable to an encoding/decoding system which comprises an apparatus functioning as an encoder and an apparatus functioning as a decoder.
While the present invention has been described with respect to preferred embodiments thereof, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than those specifically described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention that fall within the true spirit and scope of the invention.
Number | Date | Country | Kind |
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2004-208137 | Jul 2004 | JP | national |
This is a continuation of International Application PCT/JP2005/004633, with an international filing date of Mar. 16, 2005.
Number | Date | Country | |
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Parent | PCT/JP05/04633 | Mar 2005 | US |
Child | 11262954 | Nov 2005 | US |