Abstract:
The present invention is an optical modulator. It is fit for various wavelengths. The present invention has a logic signal of ‘0’ with a high signal level. The present invention has a high resist to noise. The present invention has advantages of a short length and a thin width to be applied to any optoelectronic related device or system.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an optical modulator; more particularly, relates to integrating an optical multi-wavelength modulator into a single chip.  
       DESCRIPTION OF THE RELATED ART  
       [0002]     Traditional data transmission, no matter it is between servers, computers, plastic circuit boards (PC B), integrated circuits (IC) or chips, is done along electric wires. Since central processing unit (CPU) is getting faster and faster, a physical limitation of an electric wire appears. Therefore, an optical connection to transfer data through fiber and optical device has become the most effective and workable solution.  
         [0003]     At the present time, an optical connection between a server and a client computer has been realized, while the optoelectronic device used is still an independent device. That is to say, in the future, the optical connection between the PCBs, the ICs, the chips or sub-systems in a chip has to use optical devices integrated in a single chip to reduce the size and to lower the cost.  
         [0004]     A general optical device is used in an optical communication, which is an independent item of a large size; and the substrate and the material used in the active and the passive devices are different. In order to integrate various optical devices into a single silicon chip, the optical route, the refinement of the optical device and the integration of the optical devices are the most essential.  
         [0005]     A general optical integrated multi-wavelength transmitting/receiving system is one of the core system. And the optical multi-wavelength modulator is the key component. Yet, the optical device still meets its size limitation owing to its independence, lack of integration. Hence, the prior art does not fulfill users&#39; requests on actual  
       SUMMARY OF THE INVENTION  
       [0006]     The main purpose of the present invention is to provide an optical multi-wavelength modulator integrated into a single chip.  
         [0007]     To achieve the above purpose, the present invention is an optical multi-wavelength modulator, comprising a 2×2 N paired wavelength division multiplexer and an optical modulator.  
         [0008]     The paired wavelength division multiplexer is an arrayed waveguide grating unit with reflective star coupler or a reflective grating unit, where the arrayed waveguide grating unit with reflective star coupler comprises an input terminal, an output terminal, a first reflective star coupler, an arrayed waveguide and a second reflective star coupler; the reflective star coupler is a refined general star coupler; and the length of the coupler is greatly reduced to shrink the size of the arrayed waveguide grating unit.  
         [0009]     The reflective grating unit comprises an input terminal, an output terminal, two mirror gratings and a concave mirror, where, through times of reflections by the mirror gratings, light of various wavelength is divided to be focused to various output waveguides by the concave mirror.  
         [0010]     The optical modulator has at least one optical modulation unit and the optical modulation unit is an optical grating modulation unit or an optical modulation unit having an annular resonator, where the optical grating modulation unit comprises a grating structure and a light-coupling structure; the grating structure reflects a certain light of wavelength through a periodical change in a waveguide structure or in a refractive index of a waveguide; the light-coupling structure is a directional coupler structure, a multi mode interference structure, a Mach -Zehnder interferometer structure or a directional coupler structure assisted with a multi mode interference.  
         [0011]     The optical grating modulation unit using a directional coupler structure couples a light by an input waveguide into two parallel waveguides to be outputted to the output waveguide. The optical grating modulation unit using a multimode interference structure couples the light by an input waveguide into an output waveguide through a mode interference after the light is transmitted to a multimode interference area. The optical grating modulation unit using a Mach-Zehnder interferometer structure couples the light by an input waveguide into two waveguides in an operational area through a first 3-decibel (dB) directional coupler structure; and, after a phase control, the light is coupled into a specific output waveguide through a second 3 dB directional coupler structure. The optical grating modulation unit using a directional coupler structure assisted with a multimode interference couples the light by an input waveguide into two parallel waveguides; and at least one multi mode interference structure is added between two parallel waveguides so that a light coupling efficiency is improved and the light is coup led to a specific output waveguide.  
         [0012]     By combining the grating structure and the light-coupling structure, a light of a specific wavelength is reflected, where the light is not reflected after the phase changes; a second output waveguides has a logic signal of ‘0’; and a waveguide outputting reflective modulated signal has a logic signal of ‘1’. In the other hand, after another phase change, the band of the reflected light is shifted so that the original light of wavelength is not reflected, but is totally transmitted with a logic signal of ‘1’ to the second output waveguide outputting transmitted modulated signals while the waveguide outputting reflective modulated signal has a logic signal of ‘0’.  
         [0013]     The optical modulator of bidirectional bi-annular resonator comprises a straight waveguide and an annular coupling structure, where light is coupled by an input waveguide into two resonance cavities of an annular coupling structures the output waveguide with a logic signal of ‘0’ after a phase change, the resonance frequency is shifted and the original light of wavelength is no more coupled to the resonance cavities but is totally coupled to the output waveguide with a logic signal of ‘1’. Thus, through a coupling structure between two resonance cavities of two annular resonators, an operational band and wavelength are increased. Accordingly, a novel optical multi-wavelength modulator is obtained.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The present invention will be better understood from the following detailed descriptions of the preferred embodiments according to the present invention, taken in conjunction with the accompanying drawings, in which  
         [0015]      FIG. 1  is a structural view according to the present invention ;  
         [0016]      FIG.2A  is a structural view showing the arrayed waveguide grating unit with reflective star coupler;  
         [0017]      FIG. 2B  is a structural view showing the reflective grating unit;  
         [0018]      FIG. 3A  is a structural view showing the optical grating modulation unit using a directional coupler structure;  
         [0019]      FIG.3B  is a structural view showing the optical grating modulation unit using a multi mode interference structure;  FIG. 3C  is a structural view showing the optical grating modulation unit using a Mach-Zehnder interferometer structure;  
         [0020]      FIG. 3D  is a structural view showing the optical grating modulation unit using a directional coupler structure assisted with a multimode interference;  
         [0021]      FIG.3E  is a structural view showing the optical modulation unit using a bidirectional bi-annular resonance structure; and  
         [0022]     FIG. 4  is a simulation view showing the spectrum and the characteristic. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     The following descriptions of the preferred embodiments are provided to understand the features and the structures of the present invention.  
         [0024]     Please refer to  FIG. 1 , which is a structural view according to the present invention. As shown in the figure, the present invention is an optical multi-wavelength modulator, comprising a 2×2N paired wavelength division multiplexer  1  and an optical modulator  2 .  
         [0025]     The paired wavelength division multiplexer  1  comprises a wavelength division multiplexer unit  10 , an input terminal  11 , an output terminal  12 , a first output waveguide  13  and a first input waveguide  14 , where the wavelength division multiplexer unit  10  is a refined arrayed waveguide grating unit with reflective star coupler; a reflective grating unit; or a general arrayed waveguide grating unit. The paired wavelength division multiplexer  1  has a pair of inputs and a pair of outputs from a pair of 1×N wavelength division multiplexers (like arrayed waveguide grating) without changing the main structure of the wavelength division multiplexers.  
         [0026]     The optical modulator  2  comprises at least one optical modulation unit  21 , where the optical modulation unit  21  is an optical grating modulation unit or an optical modulation unit having an annular resonator; and the optical grating modulation unit is an optical grating modulation unit using a directional coupler structure, an optical grating modulation unit using a multimode interference structure, an optical grating modulation unit using a Mach-Zehnder interferometer structure, or an optical grating modulation unit using a directional coupler structure assisted with a multi mode interference.  
         [0027]     The paired wavelength division multiplexer  1  uses the input terminal  11  to receive a light source. The light source is divided into N parts of bandwidth by the paired wavelength division multiplexer  1 . Each bandwidth is transferred by the output waveguide  13  to the optical modulation unit  21  of the optical modulator  2 . The bandwidth is modulated by the optical modulation unit  21 . A modulated signal after reflection is obtained. By connecting an waveguide outputting reflective modulated signal  216  with the first input waveguide  14  of the paired wavelength division multiplexer  1 , light fields of various wavelengths are modulated into light signals to be reversely transferred back to the paired wavelength division multiplexer  17  to be outputted by the output terminal  12 . Thus, by using a paired wavelength division multiplexer  1  and an optical modulator  2  according to the present invention, optical signals of various wavelengths are obtained; and a whole size of the present invention is further shortened and desized to be integrated into a single chip.  
         [0028]     Please refer to  FIG. 2A , which is a structural view showing the arrayed waveguide grating unit with reflective star coupler. As shown in the figures, the paired wavelength division multiplexer of the present invention is an arrayed waveguide grating unit with reflective star coupler  1   a,  comprising an input terminal  11   a,  an output terminal  12   a,  a first reflective star coupler  15   a,  at least one arrayed waveguide  151 , a second reflective star coupler  15   b,  at least one first output waveguide  13   a  and at least one first input waveguide  14   a,  where the first and the second reflective star couplers  15   a,    15   b  are two refined general star couplers connected through an arrayed waveguide and have two mirrors  152   a,    152   b,    152   c,    152   d  separately; another end of the first reflective star coupler  15   a  to the arrayed waveguide is connected to the input terminal  11   a  and the output terminal  12   a;  another end of the second reflective star coupler  15   b  to the arrayed waveguide is connected to the first output waveguide  13   a  and the first in put waveguide  14   a  the in put terminal  11   a  comprises at least one input waveguide; and the output terminal  12   a  comprises at least one output waveguide.  
         [0029]     When light source enters from the input terminal  11   a,  a light field is propagated in the first reflective star coupler  15   a.  When the light field arrives at the two mirrors  152   a,    152   b  of the first reflective star coupler  15   a,  the light field reflects and a fild size obtained is increased constantly to be coupled to the arrayed wave guide  151  in the end. After the light field passes through the arrayed waveguide  151  to obtain a phase difference, light field is focused again at the second reflective star coupler  15   b  and is reflected to the first output waveguide  13   a  through the mirrors  152   c,    152   d  for dividing light having various wavelength. Therein, the mirrors  152   a,    152   b,    152   c,    152   d  of the first and the second reflective star couplers  15   a,    15   b  have an etched surface, an etched surface with a high-reflection coating, an etched surface with a metal coating, a photon crystal, or a grating. The reflective star coupler structure made of the above first and second reflective star couplers  15   a,    15   b  is greatly decreased in length and so the size of the arrayed waveguide grating unit is shortened.  
         [0030]     Please refer to  FIG. 2B , which is a structural view showing the reflective grating unit. As shown in the figure, the paired wavelength division multiplexer of the present invention is a reflective grating unit  1   b,  comprising an input terminal  11   b,  an output terminal  12   b,  two mirror grating  16   a,    16   b,  a concave mirror  17 , at least one first output waveguide  13   b,  and at least one first input waveguide, where the input terminal  11   b  comprises at least one input waveguide and the output terminal  12   b  comprises at least one output waveguide.  
         [0031]     When a light source enters from the input terminal  11   b,  a light field is propagated in the reflective grating unit  1   b.  When the light field arrives at the two mirrors  16   a,    16   b,  the light field is reflected for times where the light field comprises various wavelengths having various reflecting angles. After the reflections, the light field is divided into at least one light route having various wavelength. Then the light route having various wavelength is scattered by the concave mirror  17  to be focused at various first output waveguide  13   b  for separate various light of wavelength. Hence, the reflective grating unit  1   b  has an extremely small size to be integrated easily.  
         [0032]     Please refer to  FIG.3A , which is a structural view showing the optical grating modulation unit using a directional coupler structure. The optical modulation unit according to the present invention reflects a certain light of wavelength through a periodical change in a wavelength structure or in a refractive index of a waveguide. As shown in the figure, the optical modulation unit according to the present invention is an optical grating modulation unit using a directional coupler structure  21   a,  which comprises a second input waveguide  211   a,  a second output waveguide  212   a,  at least one grating structure  213   a,   214   a,  a light-coupling structure using a directional coupler structure  215   a,  and an waveguide outputting reflective modulated signal  216   a.  When using the optical grating modulation unit using a directional coupler structure  21   a,  the second input waveguide  211   a  receives a non-modulated continuous wave light source outputted from a paired wavelength division multiplexer. After the light source enters into the directional coupler structure  215   a,  a light is gradually coupled from a first parallel waveguide  2151   a  of the directional coupler structure  215   a  into a second parallel waveguide  2152   a  of the directional coupler structure  215   a  to be outputted from the second output waveguide  212   a.  Two of the grating structures  213   a,   214   a  are separately set in the first parallel waveguide  2151   a  and the second parallel waveguide  2152   a  and thus the light field is changed when being coupled in the directional coupler structure  215   a.  That is, when the wavelength of the light field does not lie within the reflective wavelength band of the grating structures  213   a,   214   a,  the grating structures  213   a,   214   a  do not function; and so the light field is outputted from the second output waveguide  212   a,  where the outputted energy of the light field is 100% as a logic signal of ‘1’.  
         [0033]     On the contrary, when the wavelength of the light field lies within the reflective wavelength band of the grating structures  213   a,   214   a,  the grating structures  213   a,   214   a  is functioned to reflect the light field to be coupled to the waveguide outputting reflective modulated signal  216   a,  whose logic signal is ‘1’. Therein, the light energy of the light field outputted from the second output waveguide  212   a  is 0% as a logic signal of ‘0’. At this moment, if a light field is required to be outputted from the second output waveguide  212   a,  a wavelength of the light field is fixed and a reflective wavelength band of the grating structures  213   a,   214   a  is changed through the modulation area  2153   a  of the optical modulation unit  21   a  to pass and output the light field from the second output waveguide  212   a,  whose logic signal is ‘1’. Therein, the logic signal of the waveguide outputting reflective modulated signal  216   a  is ‘0’. Yet the light field is still possible to be reflected by the grating structures again to be outputted by the waveguide outputting reflective modulated signal  216   a  so that the logic signal of the second output waveguide  212   a  is ‘0’ and the logic signal of the waveguide outputting reflective modulated signal  216  a is Please refer to  FIG. 3B , which is a structural view showing the optical grating modulation unit using a multimode interference structure. As shown in the figure, the optical modulation unit according to the present invention is an optical grating modulation unit using a multimode interference structure  21   b,  which comprises a second input waveguide  21   b,  a second output waveguide  212   b,  at least one grating structure  213   b,  a light-coupling structure using a multi mode interference structure  215   b,  and an waveguide outputting reflective modulated signal  216   b.  When using the optical grating modulation unit using a multimode interference structure  21   b,  the second input waveguide  211   b  receives a non-modulated continuous wave light source outputted from a paired wavelength division multiplexer. After the light source enters into the multimode interference structure  215   b,  the light field changed from a single mode to a multimode and the modes are constructive interfered. Finally, a self-imaging is obtained to be outputted from the second output waveguide  212   b.  The grating structure  213   b  is set in a multimode interference area of the multimode interference structure  215   b  and thus the light field is changed when being coupled in the multimode interference structure  215   b.  That is, when the wavelength of the light field does not lie within the reflective wavelength band of the grating structures  213   b,  the grating structures  213   b  do not function; and so the light field is outputted from the second output waveguide  212   b,  where the outputted energy of the light field is 100% as a logic signal of ‘1’.  
         [0034]     On the contrary, when the wavelength of the light field lies with in the reflective wavelength band of the grating structures  213   b,  the grating structures  213   b  is functioned to reflect the light field to be coupled to the waveguide outputting reflective modulated signal  216   b,  whose logic signal is ‘1’. There in, the light energy of the light field outputted from the second output waveguide  212   b  is 0% as a logic signal of ‘0’. At this moment, if a light field is required to be outputted from the second output waveguide  212   b,  a wavelength of the light field is fixed and a reflective wavelength band of the grating structures  213   b  is changed through the modulation area  2153   b  of the optical modulation unit  21   b  to pass and output the light field from the second output waveguide  212   b,  whose logic signal is ‘1’. The rein, the logic signal of the waveguide outputting reflective modulated signal  216   b  is ‘0’. Yet the light field is still possible to be reflected by the grating structures again to be outputted by the waveguide outputting reflective modulated signal  216   b  so that the logic signal of the second output waveguide is ‘0’ and the logic signal of the waveguide outputting reflective modulated signal is ‘1’.  
         [0035]     Please refer to  FIG. 3C , which is a structural view showing the optical grating modulation unit using a Mach-Zehnder interferometer structure. As shown in the figure, the optical modulation unit according to the present invention is an optical grating modulation unit using a Mach-Zehnder interferometer structure  21   c,  which comprises a second input waveguide  211   c,  a second output waveguide  212   c,  at least one grating structure  213   c,   214   c,  a light-coupling structure of Mach-Zehnder interferometer structure  215   c,  and an waveguide outputting reflective modulated signal  216   c.  When using the optical grating modulation unit using a Mach-Zehnder interferometer structure  21   c,  the second input waveguide  211   c  receives a non-modulated continuous wave light source outputted from a paired wavelength division multiplexer. After the light source enters into the Mach-Zehnder interferometer structure  215   c,  a light field outputted from a first 3 dB directional coupler structure  2154   c  is evenly spread to a first parallel waveguide  2151   c  of the Mach-Zehnder interferometer structure  215   c  and a second parallel waveguide  2152   c  of the Mach-Zehnder interferometer structure  215   c.  By a phase controlling, the light field is finally coupled and outputted to the second output waveguide  212   c  through a second 3 dB directional coupler structure  2155   c.  Two of the grating structures  213   c,   214   c  are separately set in the first parallel waveguide  2151   c  and the second parallel waveguide  2152   c  and thus the light field is changed when being coupled in the Mach-Zehnder interferometer structure  215   c.  That is, when the wavelength of the light field does not lie with in the reflective wavelength band of the grating structure s  213   c,   214   c,  the grating structures  213   c,   214   c  do not function; and so the light field is outputted from the second output waveguide  212   c,  where the outputted energy of the light field is 100% as a logic signal of On the contrary, when the wavelength of the light field lies within the reflective wavelength band of the grating structures  213   c,   214   c,  the grating structures  213   c,   214   c  is functioned to reflect the light field to be coupled to the waveguide outputting reflective modulated signal  216   c,  whose logic signal is ‘1’. The rein, the light energy of the light field outputted from the second output waveguide  212   c  is 0% as a logic signal of ‘0’. At this moment, if a light field is required to be outputted from the second output waveguide  212   c,  a wavelength of the light field is fixed and a reflective wavelength band of the grating structures  213   c,   214   c  is changed through the modulation area  2153   c  of the optical modulation unit  21   c  to pass and output the light field from the second output waveguide  212   c,  whose logic signal is ‘1’. Therein, the logic signal of the waveguide outputting reflective modulated signal  216   c  is ‘0’. Yet the light field is still possible to be reflected by the grating structures again to be outputted by the waveguide outputting reflective modulated signal  216   c  so that the logic signal of the second output waveguide  212   c  is ‘0’ and the logic signal of the waveguide outputting reflective modulated signal is ‘1’.  
         [0036]     Please refer to  FIG. 3D , which is a structural view showing the optical grating modulation unit using a directional coupler structure assisted with a multimode interference. As shown in the figure, the optical modulation unit according to the present invention is an optical grating modulation unit using a directional coupler structure assisted with a multimode interference  21   d,  constructed with an optical grating modulation unit using a directional coupler structure  21   a  (as shown in  FIG.3A ) and a directional coupler structure assisted with a multimode interference  22 , where the directional coupler structure  215   a  (as shown in  FIG. 3A ) as a part of the optical grating modulation unit using a directional coupler structure  21   a  is replaced with the directional coupler structure assisted with a multimode interference  22  to further shorten the length.  
         [0037]     The optical grating modulation unit using a directional coupler structure assisted with a multimode interference  21   d  comprises a second input waveguide  211   d,  a second output waveguide  212   d,  two grating structures  213   d,   214   d,  an waveguide outputting reflective modulated signal  216   d,  and a directional coupler structure assisted with a multimode interference  22 , where the directional coupler structure assisted with a multimode interference  22  comprises a first parallel waveguide  221 , a second parallel waveguide  222 , and at least one multi mode interference are a  223 ; the multimode interference area  223  is located between the first parallel waveguide  221  and the second parallel waveguide  222 ; and every multimode interference area  223  has a various length.  
         [0038]     Through the second input waveguide  211   d,  the optical grating modulation unit using a directional coupler structure assisted with a multi mode interference  21   d  receives a non-modulated continuous wave light source outputted from a paired wavelength division multiplexer. After the light source enters into the directional coupler structure assisted with a multimode interference  22 , a light is gradually coupled from a first parallel waveguide  221  of the directional coupler structure assisted with a multi mode interference  22  into a second parallel waveguide  222  of the directional coupler structure assisted with a multi mode interference  22  to be outputted from the second output waveguide  212   d.  Two of the grating structures  213   d,   214   d  are separately set in the first parallel waveguide  221  and the second parallel waveguide  222  and thus the light field is changed when being coupled in the directional coupler with a multimode interference structure  22 .  
         [0039]     Please refer to  FIG. 3E , which is a structural view showing the optical modulation unit using a bidirectional bi-annular resonance structure. As shown in the figure, the optical modulation unit using a bidirectional bi-annular resonance structure according to the present invention comprises a straight waveguide  231 , a first annular waveguide  233 , a second annular waveguide  234  and an waveguide outputting reflective modulated signal  236 , where the straight waveguide  231  has a third input waveguide  2311  and a third output waveguide  2312 ; and the first annular waveguide  233  is made by circling a single-mode waveguide. A coupling is happened between the first annular waveguide  233  and the straight waveguide  231  so that a first annular resonance coupling structure  235   a  is obtained. In the other hand, a second annular waveguide  232  is further set in the first annular waveguide  231 ; and a second annular coupling structure  235   b  is obtained with the first annular waveguide  233  and the second annular waveguide When using the optical modulation unit using a bi-annular resonator  23 , the third input waveguide  2311  receives a non-modulated continuous wave light source outputted from a paired wavelength division multiplexer. After the light source enters into the directional coupler structure  235   a  when the wavelength of the light field lies with in an bi-annular resonance band, the light field is coupled into a resonance cavity. At this moment, no light field is outputted from the third output waveguide  2312 , whose logic signal is ‘0’. Light field in the bi-annular resonator is formed to obtain a reflective modulated signal by a coupling in the waveguide outputting reflective modulated signal  236  through a bi-directional transmission. Thus, a modulated signal and a reflective modulated signal are provided at the same time.  
         [0040]     In addition, for obtaining a light field from the third output waveguide, a voltage or a current is further added to a modulation area to change the effective refractive index of the waveguide so that the resonance band is shifted and the light field is not coupled to the resonance cavity. Consequently, the light field is transmitted to the third output waveguide  2312  as a logic signal of ‘1’; and, in this way, an electrical signal can be transformed to an optical signal. It is clear that the optical modulation unit using a bidirectional bi-annular resonance structure  23  has a wide operational band for a multi-wavelength operation.  
         [0041]     Please refer to  FIG. 4 , which is a simulation view showing the spectrum and the characteristic. The present invention is an optical multi-wavelength modulator, comprising a paired wavelength division multiplexer and an optical modulator, where the paired wavelength division multiplexer is an arrayed waveguide grating unit with reflective star coupler or a reflective grating unit; the optical modulator has at least one optical modulation unit; the optical modulation unit is an optical grating modulation unit using a directional coupler structure, an optical grating modulation unit using a multimode interference structure, an optical grating modulation unit using a Mach-Zehnder interferometer structure, an optical grating modulation unit using a directional coupler structure assisted with a multi mode interference, or an optical modulation unit using a bidirectional bi-annular resonance structure. By changing a refractive index of the grating structure in a coupling area through a voltage or a current, a reflective band of the grating is shifted to decide whether passing a light field or not so that an optical logic signal of ‘1’ or ‘0’ is obtained at an output waveguide of every optical modulation unit.  
         [0042]     As shown in the figure, the simulation curve  4  shows the transmission wavelength band of the optical multi-wavelength modulator when reflective wavelength band of grating is unchanged; and the simulation curve  5  shows the shifted transmission wavelength band when reflective wavelength band of grating is changed by modulating. When operation wavelength is fixed, the logical signals can be modulated by changing the reflective wavelength band of grating. Hence, the optical multi-wavelength modulator according to the present invention is operated under a transmission energy of 12 decibel with a band wider than 1.5 nanometer (nm), where the present invention is fit for multi-wavelength; the logic signal of ‘0’ has a high isolation level; and the present invention has a high resist to noise with advantages of a device length shorter than 2 mm and a width thinner than 4 micron.  
         [0043]     To sum up, the present invention is an optical multi-wavelength modulator, where the present invention is fit for mu It i-wavelength operation with a high resist to noise, a high level ratio between logic signal ‘1’ and ‘0’, and advantages of a device length of the optical grating modulation unit shorter than 2 mm and a width of the optical grating modulation unit thinner than 4 micron.  
         [0044]     The preferred embodiments herein disclosed are not intended to unnecessarily limit the scope of the invention. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present invention.