Abstract:
There is provided an optical receiving device for deriving a signal using for data identification. The optical receiving device includes a demodulator for demodulating a modulated optical signal to an demodulated optical signal, a convertor for converting the demodulated optical signal to a first and a second electric signals, a generator for generating a complement signal by summing the first electric signal of a normal in phase component and the second electric signal of a reverse in phase component, and a suppressor for suppressing, by the use of the complement signal, a variation of potential which appears in a data signal at a time of phase changing of the modulated optical signal, the data signal being a difference of the normal in phase component and the reverse in phase component.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-305656, filed on Nov. 28, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to an optical receiving device, an optical receiving circuit, and a method for receiving optical signals. 
     BACKGROUND 
     In these years, photonic networks for a large capacity communication are building for practicing the next generation network (NGN) which needs an optical transmission system capable of fast transmission. For the fast optical transmission, it will be necessary to adopt a modulation scheme which is able to convert effectively electrical signals to optical signals. The differential phase shift-keying scheme is receiving attention as a superior sensitivity modulation scheme. 
     Referring to  FIG. 7 , a conventional optical transmission system using a phase modulation scheme is explained.  FIG. 7  illustrates schematically a configuration of the conventional optical transmission system  1  with a phase modulation scheme. The conventional optical transmission system  1  includes an optical transmitter  2  and an optical receiver  3 . The optical transmitter  2  includes an optical phase modulator  21  which performs a conversion from an electric signal to an optical signal and a phase modulation of the optical signal, and transmits the phase-modulated optical signal to the optical receiver. The optical signal which is phase-modulated by the optical phase modulator  21  is hereinafter referred to as “a DPSK optical signal.” 
     The optical receiver includes a delay interferometer  31  and an optical receiving circuit  32  which are illustrated in detail in  FIG. 8 . The delay interferometer  31  compares the DPSK optical signal received from the optical phase modulator  21  with an optical signal which is derived from the DPSK optical signal delayed by one bit to demodulate the DPSK optical signal. The delay interferometer  31  outputs, to the optical receiving circuit  32 , a normal in phase and a reverse in phase components of the optical signal demodulated. The normal in phase component and the reverse in phase component are hereinafter referred to as the normal in phase optical signal and the reverse optical phase signal, respectively. 
     The optical receiving circuit includes a photo-detector  41 , which is also referred to as a photo-detector and hereinafter abbreviated as PD, and an amplifier  42 . The PD  41  comprises PDs  41   a  and  41   b . The PD  41   a  converts the normal in phase optical signal to a corresponding electric signal and the PD  41   b  converts the reverse in phase optical signal to a corresponding electric signal. The PD  41  outputs, to the amplifier  42 , a difference value of the normal and the reverse in phase signals. The difference value is amplified by the amplifier  42  and fed to a device or a circuit which is referred to as a data indentifying device and not shown in  FIG. 8 . 
     The data-identifying device determines data, which is corresponding to data sent from the optical transmitter  2 , based on the received difference value from the amplifier  42 . The data-identifying device determines, as example, the data being “1” when the received difference value is larger than the predetermined value and the data being “0” when the received difference value is smaller or equal to than the predetermined value. A conventional optical transmission system using DPSK optical signal is, for example, disclosed in Japanese Laid-open Patent Publication No. 11-4196. 
     SUMMARY 
     According to an aspect of the invention, there is provided an optical receiving device for deriving a signal using for data identification. The optical receiving device includes a demodulator for demodulating a modulated optical signal to an demodulated optical signal, a convertor for converting the demodulated optical signal to a first electric signal and a second electric signal, a generator for generating a complement signal by summing the first electric signal of a normal in phase component and the second electric signal of a reverse in phase component, and a suppressor for suppressing, by the use of the complement signal, a variation of potential in a data signal which appears at a time of phase changing of the modulated optical signal, the data signal being a difference of the first electric signal of the normal in phase component and the second electric signal of the reverse in phase component. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram for explaining an optical receiving device according to the first embodiment; 
         FIG. 2A  is a diagram illustrating an example of an electric signal outputted from the optical receiving device according to the first embodiment, and  FIG. 2B  is a diagram illustrating an example of an eye-pattern of the electric signal; 
         FIG. 3  is a diagram illustrating a configuration of the optical receiving device according to the first embodiment; 
         FIG. 4  is a diagram illustrating a flow chart of a process for receiving optical signals by the use of the optical receiving device according to the first embodiment; 
         FIG. 5  is a diagram illustrating a configuration of an optical receiving device according to the second embodiment; 
         FIG. 6  is a diagram illustrating a flow chart of a process for receiving optical signals by the use of the optical receiving device according to the second embodiment; 
         FIG. 7  is a diagram illustrating a configuration of a conventional optical transmission system using a phase modulation method; 
         FIG. 8  is a diagram illustrating a delay interferometer and an optical receiving circuit used in an optical receiving device of the conventional optical transmission system illustrated in  FIG. 7 ; 
         FIG. 9  is a diagram illustrating a phase modulated optical signal; 
         FIG. 10  is a diagram illustrating an optical signal demodulated by the delay interferometer illustrated in  FIG. 8 ; and 
         FIG. 11A  is a diagram of an electric signal outputted from the optical receiving circuit illustrated in  FIG. 8  and  FIG. 11B  is a diagram illustrating an example of an eye-pattern of the electric signal illustrating in  FIG. 11A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     However the conventional optical transmission system might have a possibility of erroneous determination of the data. The reason of the possibility will be described in detail below, referring to  FIGS. 9 to 11B . For the sake of a concise explanation, it is assumed that the demodulation processing in the optical transmission system as an example is performed based on comparison of the optical signal with a delayed optical which is delayed by one or smaller bit behind the optical signal. 
       FIG. 9  is a diagram illustrating an example of change of intensity of an optical signal which is phase-modulated, where the horizontal axis represents time in picoseconds and the vertical axis represent intensity of the optical signal in arbitrary unit.  FIG. 9  depicts the characteristic that the intensity of the optical signal falls, for example, to zero level at every time the phase changes. Incidentally, the intensity in a region P 91  circled by a dotted line, as example, falls at the time corresponding to the phase change π to zero. At every time of the phase change such as π to 0 or 0 to π of the modulation data in  FIG. 9 , the intensity of the optical signal falls to 0 level other than the region P 91 . 
     The delay interferometer  31  demodulates the optical signal having the characteristic described above. An example of an optical signal demodulated by the delay interferometer  31  is illustrated in  FIG. 10 , where the light solid line and the heavy solid line illustrate the normal in phase and the reverse in phase optical signals respectively. Referring to the regions P 101  and P 102  circled by dotted lines, intensity of the normal in phase and of the reverse in phase optical signals is individually changing at every change of the phase due to the characteristic of the optical signal described above and illustrated in  FIG. 9 . The intensity of the both optical signals in each circle in  FIG. 10  is preferable or ideal to be a steady value. 
     The optical receiving circuit  32  converts the optical signals having such a variation to the corresponding electric signals and feeds them to the data-identifying circuit. The exemplary output signal of the conventional optical receiving circuit  32  is illustrated in  FIG. 11A  and the eye pattern or eye diagram concerning to the exemplary output signal is illustrated in  FIG. 11B . 
     As illustrated in  FIG. 11A , the electric potential of the electric signal E 1  varies in the portions P 111  and P 112 . The variation in the electric potential, such as in the portions P 111  and P 112 , causes the difficulty in determination in which the electric potential is higher or lower than a predetermined value. Accordingly, the data corresponding to the portions P 111  or P 112  may be determined incorrectly. 
     The eye pattern illustrated in  FIG. 11B  is distorted because the cross-point C 1  circled with a dotted line shifts from the center of the peak-to-peak amplitude of the electric signal outputted from the optical receiving circuit  32 . The distortion of the eye pattern results in the difficulty in determination or an erroneous determination of the data. Accordingly, it is found that the electric signal E 1  causes the problem in determining the corresponding data. The variation of the electric potential, such as the variations in P 111  or P 112  illustrated in  FIG. 11A , occurring in every change of the phase is referred to as the “phase-potential variation” hereinafter. 
     Further, the problem described above will be serious in the case of the demodulation in which the data is determined using comparison of DPSK optical signal with an optical signal delayed by 1 bit or smaller bits. That is, a processing of the comparison is easily suffered from the phase-potential variation. 
     The embodiments below intends to solve the problem described above and provide an optical receiving device, an optical receiving circuit, and method for receiving an optical signal to improve an error rate in a determination of data corresponding the optical signal. 
     Preferred embodiments will now be described in detail with reference to the accompanying drawings. In the following embodiments is described as an example of an optical receiving device, an optical receiving circuit, or method for receiving an optical signal. The present invention is not limited to the embodiments described below. 
     The optical receiving device  100  according the first embodiment is described with reference to  FIGS. 1 to 4 . The optical receiving device  100 , which is described in detail later, generates two electric signals. One of the electric signals is an electric signal of which value is a difference between values of a normal and a reverse in phase signals derived in the same manner as the conventional optical receiving circuit, and is referred to as a “data signal.” The other of the electric signals is a signal of which value is a sum of the values of the normal and the reverse in phase signals, and is referred to as a “complement signal.” Further, the optical receiving device  100  derives a difference between the data and complement signals. The difference is used for suppressing variation in the data signal. 
     The reason why the variation in the data signal is suppressed with the difference between the data and the complement signals will be explained below. Referring to  FIG. 10 , a sum of the values of the normal and the reverse in phase optical signals is constant except in the portions P 101  and P 102 . That is, the sum of the values is constant because the two signals except in the portions P 101  and P 102  are not suffered from the characteristic that the intensity of the optical signal falls at every time the phase changes. 
     The sum of the values of the normal and the reverse in phase optical signals in the portions P 101  and P 102  is not constant. That is, the sum of the values is not constant because of the characteristic. 
     Accordingly, the complement signal generated has a characteristic that the value is fluctuating only in a duration in which both values of the normal in phase and the reverse in phase signals are fluctuating, while the value is constant in a duration in which the both values of the normal in phase and the reverse in phase signals are constant. With use of the difference value between the data signal and the complement signal, the optical receiving device  100  may be able to derive, from the data signal, an electric signal in which the phase potential variation is suppressed. 
     Referring to  FIG. 1 , the first embodiment will be described in detail.  FIG. 1  illustrates an example of a pair of a data signal and a complement signal generated by the optical receiving device  100  according to the first embodiment. First, the method for the optical signal according the first embodiment is explained with use of the data and the complement signals. The data signal E 1  is similar to the electric signal E 1  illustrates in  FIG. 11A . Accordingly, a normal in phase and a reverse in phase optical signals in the first embodiment are used and are similar to individual the normal in phase and the reverse in phase optical signals illustrated in  FIG. 10 . The complement signal is derived from a sum of electric signals which are converted individually from the normal in phase optical signal and the reverse in phase optical signal. The optical receiving device  100  generates a signal to be difference of the data signal E 1  and the complement signal E 2  and outputs the signal. 
       FIG. 2A  illustrates an electric signal, as an example, outputted from the optical receiving device  100 . The electric signal E 3  depicted in  FIG. 2A  is the electric signal as the difference of the data signal E 1  and the complement signal E 2 . The electric potential in the portion P 21  of the electric signal E 3  has smaller variation than that of the portion P 111  of the electric signal E 1  illustrated in  FIG. 11A . Similarly, the electric potential in the portion P 22  of the electric signal E 3  has smaller variation than that of the portion P 112  of the electric signal E 1 . Accordingly, the electric signal E 3 , a data-identifying device to be connected to the optical receiving device  100  will perform the data determining process more accurately than with the use of the electric signal E 1 . 
     The eye pattern of the electric signal E 3  is illustrated in  FIG. 2B . The eye pattern illustrates also that the data-identifying device determines associated with the received DPSK optical signal more accurately with the use of outputs derived by the optical receiving device. The eye pattern of the electric signal E 3  has a cross point C 2  more close to the center of the peak-to-peak amplitude than that of the eye pattern in illustrated  FIG. 11B  and the waveform of the eye pattern E 3  appears like a wide-open eye. Since the electric signal has the eye pattern having characteristics described above, the data-identifying device will perform the data-identifying process with a high degree of accuracy. 
     As described above, the optical receiving device  100  generates the data signal and the complement signal, where the data signal and the complement signal are respectively corresponding to a difference and a sum of the normal in phase and the reverse in phase components of the electric signal. Then, the optical receiving device  100  outputs an electric signal as the difference of the data signal and the complement signal, that is, the optical receiving device  100  outputs the electronic signal with suppressed variation of a phase electric potential. As a result, the data-identifying device will performs the data determining process with a high degree of accuracy by using the output signal from the optical receiving device  100 . 
     The configuration of the optical receiving device  100  is explained with reference to  FIG. 3 , where the configuration of the optical receiving device  100  is illustrated. The optical receiving device  100  includes a delay interferometer  31  and an optical receiving circuit  110 . The delay interferometer  31  is similar to the delay interferometer  31  illustrated in  FIG. 8 . 
     The optical receiving circuit  110  includes photo-detector units  111  and  112 , and amplifiers  113  to  115 . The photo-detector unit  111  includes photo-detectors (PDs)  111   a  and  111   b . The PD  111   a  converts the normal in phase optical signal, which is inputted from the delay interferometer  31 , to the electric signal. In addition, the PD  111   b  converts the reverse in phase optical signal, which is inputted from the delay interferometer  31 , to the electric signal. Further, the photo-detector  111  outputs to the amplifier  113  an electric signal as the difference of the normal in phase electric signal from the PD  111   a  and the reverse in phase electric signal from the PD  111   b.    
     The photo-detector unit  112  includes photo-detectors (PDs)  112   a  and  112   b . As well as the performance of the PD  111   a , PD  112   b  converts the normal in phase optical signal and the reverse in phase optical signal, which are inputted from the delay interferometer  31 , to the electric signals respectively. The PD unit  112  outputs the sum of the normal in phase electric signal and the reverse in phase electric signal, which are individually outputted from the PD  112   a  and from the PD  112   b , to the amplifier  114 . 
     The amplifier  113  receives the electric signal from the PD unit  111  amplifies and output the electric signal to the amplifier  115 , where the electric signal amplified by the amplifier  113  is corresponding to the data signal. The gain or the amplification factor of the amplifier  113  is “−A” as depicted in  FIG. 3 . 
     Also the amplifier  114  receives the electric signal from the PD unit  112 , amplifies and output the electric signal to the amplifier  115 . The electric signal amplifier  114  is corresponding to the complement signal. The gain or the amplification factor of the amplifier  113  is A′ as depicted in  FIG. 3 . 
     The gain such as −A or A′ is preferably determined or set according to the amount of variation of the phase electric potential by such as a designer or the like. The individual gain of the amplifier  113  and the amplifier  114  is preferably determined so as to suppress the amount of variation of the phase electric potential in the data signal to within the allowable range. 
     The amplifier  115  outputs, to the data-identifying device (not illustrated), a signal of the difference between the data signal and the complement signal which are received from the amplifiers  113  and  114  respectively. That is, the amplifier  115  outputs the signal of the difference which is less affected by the variation of the phase potential as the electric signal E 3  illustrated the in  FIG. 2A . 
     Referring to  FIG. 4 , explained is the flowchart of an optical signal receiving process in the optical receiving device  100  according the first embodiment. The PD unit  111  of the optical receiving device  100  converts the normal in phase and the reverse in phase signals, which are received from the delay interferometer  31 , to each of the electric signals as the normal in phase and the reverse in phase components respectively, and then determines a electric signal as the difference between the electric signals (Step S 101 ). The electric signal as the difference is fed to the amplifier  113 . 
     On receiving the electric signal as the difference, the amplifier  113  amplifies the electric signal as the difference (Step S 102 ). The amplified electric signal as the difference is corresponding to the data signal. 
     The PD unit  112  converts the normal in phase and the reverse in phase optical signals, which are received from the delay interferometer  31 , to each of the electric signals as the normal in phase and the reverse in phase components respectively, and then determines a electric signal as the sum between the electric signals (Step S 103 ). The electric signal as the sum is fed to the amplifier  114 . 
     On receiving the electric signal as the sum, the amplifier  114  amplifies the electric signal as the sum (Step S 104 ). The amplified electric signal as the sum is corresponding to the complement signal. The amplifier  115  derives the difference between the data signal and the complement signal, which are received from the amplifiers  113  and  114  respectively, and feeds the resultant electric signal as the difference. (Step S 105 ). 
     As described above, the optical receiving device  100  according to the first embodiment generates the data signal and the complement signal as the difference and the sum, respectively, of the normal in phase component and the reverse in phase component of the electric signals. Further, the optical receiving device  100  determines the electric signal as the difference of the data signal and the complement signal, and outputs the electric signal as the difference to such as the data-identifying device (not illustrated in  FIG. 3 ). Since the optical receiving device  100  may suppress the variation of phase potential in the signal using for data identifying, the optical receiving device  100  may provide the high accurate data-identifying process performed by such a data-identifying device (not illustrated in  FIGS. 1 to 3 ). 
     Next, the second embodiment will be described below. In brief, the first embodiment generates the data signal and the complement signal to derive, by using the difference of the both signals, the electric signal in which the phase potential variation is suppressed. However, it is also preferable to suppress the phase potential variation in the data signal without generating the data signal and the complement signal. Therefore, the optical receiving device  200  according to the second embodiment may suppress the phase potential variation in the data signal without generating the data signal and the complement signal. 
     First, the method for receiving an optical signal by the optical receiving device  200  is explained. The optical receiving device  200  amplifies the normal in phase and the reverse in phase optical signals by predetermined gains respectively to suppress the phase potential variation appearing in the electric signal using for data identifying. Referring to  FIG. 3 , the “predetermined gains” will be explained in detail by discussing on the electric signal outputted from the optical receiving device  100 . 
     The signal outputted from the PD unit  111  in the optical receiving device  200  may be represented as follows.
 
 S pd1 =S normal− S reverse,
 
where
 
     Spd 1  is the signal outputted from the PD unit  111 , 
     Snormal is the normal in phase component of the electric signal, and 
     Sreserve is the reverse in phase component of the electric signal. 
     Accordingly, the signal outputted from the amplifier  113  is represented as follows.
 
 S out1=− A×{S normal− S reverse}.
 
     Further, the PD unit  112  outputs the signal represented as follows.
 
 S pd2 =S normal+ S reverse,
 
where Spd 2  is the signal outputted from the PD unit  112 . Accordingly, the signal outputted from the amplifier  114  is represented as follows.
 
 S out2= A′×{S normal+ S reverse}.
 
     Further, since the amplifier  115  outputs the electric signal as the difference of the electric signals outputted from the amplifier  113  and from the amplifier  114 , the electric signal outputted from the optical receiving device  100  is represented as following expression 1.
 
 S=−A×{S normal− S reverse}− A′×{S normal+ S reverse}  (1),
 
where S is the electric signal outputted from the optical receiving device  100 .
 
     The expression 1 may be transformed as following expression 2.
 
 S =(− A−A ′)× S normal−(− A+A ′)× S reverse  (2).
 
     The expression 2 indicates that the electric signal outputted from the optical receiving device  100  is derived from the difference of the normal in phase component of the electric signal amplified by the gain (−A−A′) and the reverse in phase component of the electric signal amplified by the gain (−A+A′). 
     Therefore, the optical normal in phase signal and the optical reverse in phase signal from the delay interferometer  31  are converted into each of the corresponding electric signals and are amplified by each of the gains (−A−A′) and (−A+A′), where the gains are those of the amplifiers included in the device  200 . Setting individually the amplifier gains to (−A−A′) and (−A+A′), the optical receiving device  200  may outputs the electric signal substantially equivalent to that of the optical receiving device  100 . 
     Referring to  FIG. 5 , the configuration of the optical receiving device  200  according to the second embodiment will be described in detail below. The optical receiving device  200  includes a delay interferometer  31 , which is similar to the delay interferometer  31  illustrated in  FIG. 8 , and an optical receiving circuit  210 . 
     The optical receiving circuit  210  includes photo-detectors (PD)  211   a  and PD  211   b , amplifiers  212   a  and  212   b , and an amplifier  213 . The PD  211   a  converts the normal in phase optical signal, which is received from the delay interferometer  31 , to an electric signal and feeds the electric signal to an amplifier  212   a . The PD  211   b  converts the reverse in phase optical signal, which is received from the delay interferometer  31 , to an electric signal and feeds the electric signal to an amplifier  212   b.    
     The amplifier  212   a  amplifies the electric signal received from the PD  211   a  by the gain (−A−A′) and feeds the electric signal amplified to the amplifier  213 . The amplifier  212   b  amplifies the electric signal received from the PD  211   b  by the gain (−A+A′) and feeds the electric signal amplified to the amplifier  213 . Here, it is assumed that the gains A and A′ depicted in  FIG. 5  are equivalent to those depicted in  FIG. 3  and that the optical receiving device  100  outputs the electric signal of which the phase potential variation is suppressed to a sufficiently small degree. 
     An amplifier  213  determines or calculates the difference between the electric signals received from the amplifier  212   a  and from the amplifier  212   b , and outputs the electric signal as the difference. That is, the amplifier  213  outputs the electronic signal represented with the expression 2. As the gains are set as described above, the optical receiving device  200  may output the electric signal equivalent to or similar to the electric signal outputted from the optical receiving device  100 . 
     The optical signal receiving process by the optical receiving device  200  will be described bellow, referring to  FIG. 6  in which the procedure of receiving the optical signal is illustrated. 
     As illustrating in  FIG. 6 , the amplifier  212   a  amplifies the electric signal (normal in phase electric signal) from the PD  211   a  by the gain of −A−A′ (in S 201 ), where the electric signal is derived by converting the normal in phase optical signal outputted from the delay interferometer  31 . In addition, the amplifier  212   b  amplifies the electric signal (reverse in phase electric signal) from the PD  211   b  by the gain −A+A′ (in S 202 ), where the electric signal is derived by converting the reverse in phase optical signal outputted from the delay interferometer  31 . 
     Subsequently, the amplifier  213  determines or calculates the difference of the electric signals outputted from the amplifiers  212   a  and  212   b , and outputs the electric signal which may be expressed with the expression 2 (S 203 ). 
     As described above, the optical receiving device  200  according to the second embodiment includes the amplifier  212   a  for amplifying the normal in phase optical signal and the amplifier  212   b  for amplifying the reverse in phase optical signal, where both of the normal in phase and the reverse in phase optical signals are outputted from the delay interferometer  31 . The gain of the amplifier  212   a  is set to a value which is equal to the coefficient of the normal in phase component when the electric signal outputted from the optical receiving device  100  is expressed with the terms of the normal in phase and the reverse in phase components. That is the gain of the amplifier  212   a  is set to (−A−A′) in the expression 2. Similarly, the gain of the amplifier  212   b  is set to a value of the coefficient (−A+A′) of the reverse in phase component in the expression 2. 
     As the gain of each of the amplifier  212   a  and  212   b  is set to the values of (−A−A′) and (−A+A′) respectively, the optical receiving device  200  may be able to output the electric signal in which the phase potential variation is suppressed as the optical receiving device  100 . Accordingly, the accurate processing for identifying or determining the data may be able to be carried on in the data-identifying device, for example, to be connected to the optical receiving device  200 . Further, the optical receiving device  200  will be built at a lower cost than that of the optical receiving device  100 , because the device  200  needs a smaller number of photo-diodes than that of the optical receiving device  100 . 
     Since the parts or components illustrated in each drawings are explained schematically or from a functional viewpoint, the first and the second embodiments are not necessarily to be built as same as illustrated in the drawings. Further, it is preferable to deploy a plurality of the optical receiving devices  100  or  200  in the form of the distributed or the integrated. Still further, it is preferable to configure an optical receiving device with adequate number of the optical receiving devices  100  or  200  to meet an amount of traffic to be processed or of various types of loads and to meet the usage status of the optical receiving device. In addition, all or a part of the functions for processing in the optical receiving devices  100  and  200  may be performed by the use of a central processing unit (CPU), a computer program executed by the CPU, or a hardware with wired logic. 
     It is preferable to execute, automatically or manually, all or a part of the processes in the first and the second embodiments. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.