Abstract:
According to an aspect of the embodiment, an optical device has a first optical element and a second optical element. The first optical element for inputting wavelength multiplexed light, the wavelength multiplexed light including a plurality of light channels which is arranged on predetermined frequency interval, the first optical element outputting an angular dispersion light in parallel, the angular dispersion light being arranged positions of the light channels on different interval spaces, respectively. The second optical element for receiving the angular dispersion light from the first optical element and for changing positions in accordance with the light channels on different interval spaces into on predetermined interval space.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    This art relates to an optical device. For example, the optical device includes an angular dispersion device performing for disperse wavelength multiplexed light. 
         [0003]    2. Description of the Related Art 
         [0004]    Recently, high-speed access networks with a band of about several Mbit/s to 100 Mbit/s, for example, FTTH (Fiber To The Home) and ADSL (Asymmetric Digital Subscriber Line) have spread rapidly. Due to these high-speed access networks, an environment in which one can enjoy a broadband Internet service is being improved. To keep up with increasing telecommunications demand, in backbone networks (core networks), an extra large capacity optical communication system using WDM (Wavelength Division Multiplexing) technology is being laid. 
         [0005]    On the other hand, at the junction between a metro network and a core network, there is concern that a band bottleneck may occur due to the limit of electric switching capability. Accordingly, there are energetically carried out research and development of a new photonic network architecture in which a new optical switching node is provided in the metro region where a band bottleneck occurs, and a metro network that users directly access and a core network are directly connected in an optical region without providing an electric switch therebetween. 
         [0006]    Optical switching nodes that connect a core network and a metro network include a wavelength selective switch (see, for example, Patent Document 1). In a wavelength selective switch, input multiplexed light is wavelength-demultiplexed, and each wavelength of light is output to a desired output port. 
         [0007]      FIG. 6  illustrates optical demultiplexing of a known wavelength selective switch. As shown, the wavelength selective switch includes an angular dispersive element  101  and MEMS (Micro Electro Mechanical System) mirrors  102   a  to  102   d.    
         [0008]    Wavelength-multiplexed light  111  is input into the angular dispersive element  101 . The angular dispersive element  101  has a relationship of θ∝λ (θ: the angle of output light, λ: wavelength). The angular dispersive element  101  inputs the input light  111  and outputs angular dispersion light in accordance with wavelength. 
         [0009]    The angular dispersion light beams  112   a  to  112   d  outputted from the angular dispersive element  101  are inputted to the MEMS mirrors  102   a  to  102   d  that are arranged one-dimensionally. 
         [0010]    The MEMS mirrors  102   a  to  102   d  are minute mirrors whose angles are variable. The MEMS mirrors  102   a  to  102   d  reflect the light beams  112   a  to  112   d  output from the angular dispersive element  101  in desired angular directions and guide them to a plurality of output optical ports (not shown) disposed in the angular directions. 
         [0011]    According to the regulation of ITU (International Telecommunication Union), the frequency interval spacing of WDM channels is 100 GHz or 50 GHz. In terms of wavelength, the wavelength interval spacing is not equal. 
         [0012]      FIG. 7  shows the relationship between frequencies of WDM. The horizontal axis of the graph represents frequency, and the vertical axis represents intensity of light. As described above, in WDM defined by ITU, the light channels of WDM are set on equal frequency space. 
         [0013]      FIG. 8  shows the relationship between wavelengths of WDM. The horizontal axis of the graph represents wavelength, and the vertical axis represents intensity of light. As shown in  FIG. 7 , in WDM defined by ITU, the light channels of WDM are set at equal spacings. Therefore, the wavelengths are at unequal wavelength spaces as shown in  FIG. 8 . 
         [0014]    As illustrated in  FIG. 6 , the angular dispersive element  101  has the relationship of θ∝λ. The angular dispersive element  101  disperses the inputted wavelength-multiplexed light into angular dispersion light in accordance with wavelength. Since the wavelength interval spacing of the wavelength multiplexed light are unequal as shown in  FIG. 8 . The wavelength interval spaces between wavelengths outputted from the angular dispersive element  101  are unequal as shown by arrows A 101  of  FIG. 6 . 
         [0015]    Japanese Laid-open Patent Publication No. 2006-284740 discusses that an angular dispersive element is used the optical device. 
         [0016]    Since the light channels of WDM is unequal as described above. The light beams output from the angular dispersive element are at unequal space. Therefore, the spaces between, for example, mirrors that reflect the wavelength-dispersed light beams need to be unequal. This lowers the yield. 
       SUMMARY 
       [0017]    An object of an aspect of the present invention is to provide an optical device that can change positions of light channels. 
         [0018]    According to an aspect of the embodiment, an optical device has a first optical element and a second optical element. 
         [0019]    The first optical element for inputting wavelength multiplexed light, the wavelength multiplexed light including a plurality of light channels which is arranged on predetermined frequency interval, the first optical element outputting an angular dispersion light in parallel, the angular dispersion light being arranged positions of the light channels on different interval spaces, respectively. 
         [0020]    The second optical element for receiving the angular dispersion light from the first optical element and for changing positions in accordance with the light channels on different interval spaces into on predetermined interval space. 
         [0021]    Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended-claims. 
         [0022]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows the outline of an optical wavelength demultiplexer. 
           [0024]      FIG. 2  is a perspective view of a wavelength selective switch. 
           [0025]      FIG. 3  shows the wavelength selective switch of  FIG. 2  viewed from the X direction. 
           [0026]      FIG. 4  shows the wavelength selective switch of  FIG. 2  viewed from the Y direction. 
           [0027]      FIG. 5  is a perspective view of a performance monitor. 
           [0028]      FIG. 6  illustrates optical demultiplexing of a known wavelength selective switch. 
           [0029]      FIG. 7  shows the relationship between frequencies of WDM. 
           [0030]      FIG. 8  shows the relationship between wavelengths of WDM. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0031]    The embodiments will now be described with reference to the drawings in detail. 
         [0032]      FIG. 1  shows the outline of an optical wavelength demultiplexer. As shown, the optical wavelength demultiplexer includes a first dispersion element  1  and a second dispersion element  2 . 
         [0033]    A wavelength multiplexed light includes a plurality of light channels which are arranged on predetermined frequency interval in accordance with ITU-T standard. 
         [0034]    The first dispersion element  1  inputs a wavelength multiplexed light. The each light channels in wavelength multiplexed light is set on equally frequency interval on the frequency axis and on unequally wavelength interval on the wavelength axis. 
         [0035]    The first dispersion element  1  outputs a beam which is an angular dispersion light to each of the light channels in the wavelength multiplexed light. The first dispersion element  1  has a relationship of θ∝λ. The first dispersion element  1  outputs angular dispersion light in accordance with the wavelength of the light channels. The light channels of the outputted angular dispersion light from the first dispersion element  1  are arranged on unequal interval space as shown by arrows A 1   a  to A 1   c  in the  FIG. 1  because the wavelengths of the light channels in wavelength multiplexed light are unequal spaced on the wavelengths axis. The first dispersion element  1  includes, for example, a diffraction grating. 
         [0036]    Light beam outputted from the first dispersion element  1  is inputted into the second dispersion element  2 . The second dispersion element  2  is an element whose refractive index varies depending on the wavelength, for example, a lens made of fluorite. The second dispersion element  2  changes unequal interval spaces between the light channels from the first dispersion element  1  into equal interval spaces between the light channels as shown by arrows A 2   a  to A 2   c  in the  FIG. 1 , and outputs them. Specifically, the thickness (d 1  in the  FIG. 1 ) of the second dispersion element  2  and the angle (θ 1  in the  FIG. 1 ) of incident with the surface of the second dispersion element  2 , are adjusted so as to output the light channels with equal interval spaces. 
         [0037]    As described above, in the optical wavelength demultiplexer has the first dispersion element  1  and the second dispersive element  2 . The first dispersion element  1  disperses wavelength multiplexed light into angular dispersion light in accordance with each wavelength of light channels. 
         [0038]    The second dispersive element  2  changes positions of the light channels of the angular dispersion light outputted from the first dispersion element  1  into equally interval spaced positions. 
         [0039]    Therefore, if the light channels of WDM light outputted from the first dispersion element  1  have unequal spaces, the light channels of WDM light can be equally spaced by the second dispersion element  2 . 
         [0040]    Next, a first embodiment of the present invention will be described with reference to the drawings in detail. In the first embodiment, an example in which an optical wavelength demultiplexer is applied to a wavelength selective switch will be described. 
         [0041]      FIG. 2  is a perspective view of a wavelength selective switch. As shown, the wavelength selective switch includes an input fiber  11 , a lens array  12 , an angular dispersive element  13 , a convex lens  14 , an anomalous dispersion element  15 , an MEMS substrate  16 , and output fibers  17 . 
         [0042]    The input fiber  11  and the output fibers  17  are arranged in the Y direction. Wavelength-multiplexed light is input into the input fiber  11 . The light is output to the lens of the lens array  12  assigned to the input fiber  11 . 
         [0043]    The lenses of the lens array  12  are arranged to the input fiber  11  and the output fibers  17 . The lenses of the lens array  12  collimate diffused, light and output the collimated light. 
         [0044]    A lens of the lens array  12  in combination with input fiber  11  collimates diffused light from the input fiber  11  and outputs the collimated light. The outputted light from the lens in combination with input fiber  11  is imputed into the angular dispersive element  13 . 
         [0045]    Lenses of the lens array  12  in combination with output fibers.  17  input light beams reflected by the MEMS substrate  16 , respectively. The lenses in combination with the output fibers  17  collimates diffused light beams from the MEMS substrate  16  and output the collimated light toward the output fibers  17 . 
         [0046]    In  FIG. 2 , the first dispersion element  1  as shown in  FIG. 1  may includes angular dispersion element  13  and lens  14 . 
         [0047]    The angular dispersion element  13  is, for example, a diffraction grating. The angular dispersion element  13  input the wavelength-multiplexed light outputted from the input fiber  11 . The angular dispersion element  13  has a relationship of θ∝λ, disperses the wavelength multiplexed light and outputs the inputted the wavelength multiplexed light. The spread direction of angular dispersion light is a mirrors arrangement direction on the MEMS substrate  16 . The dispersed light beams from the angular dispersion element  13  are inputted into the convex lens  14 . 
         [0048]    The convex lens  14  focuses beams of the angular dispersion light in accordance with wavelength of light channel onto the MEMS substrate  16 . 
         [0049]    The light beams outputted from the angular dispersion element  13  are inputted into the anomalous dispersion element  15  through the convex lens  14 . The anomalous dispersion element  15  is made, for example, of fluorite. The anomalous dispersion element  15  corrects the unequal interval space positions of the light channels become equal interval space positions. The anomalous dispersion element  15  outputs the corrected light to the MEMS substrate  16 . 
         [0050]    The MEMS substrate  16  includes a plurality MEMS mirrors  16   a.  The plurality MEMS mirrors  16   a  is arranged one dimensional and equally-spaced interval on the MEMS substrate  16 . The MEMS substrate  16  includes a mechanism that varies the angles of the MEMS mirrors  16   a  in accordance, for example, with control signals. The MEMS substrate  16  can reflect inputted light beams to desired ones of the output fibers  17 . 
         [0051]      FIG. 3  shows the wavelength selective switch of  FIG. 2  viewed from the X direction.  FIG. 4  shows the wavelength selective switch of  FIG. 2  viewed from the Y direction. In  FIGS. 3 and 4 , the same reference numerals will be used to designate the same components as those in  FIG. 2 , so that the description thereof will be omitted. 
         [0052]    The wavelength multiplexed light is outputted from the input fiber  11 . The wavelength multiplexed light is inputted into the lens of the lens array  12  corresponding to the input fiber  11 . The lens of the lens array  12  restrains the divergence of light output from the input fiber  11 , collimates the light outputted from the input fiber  11 , and outputs the collimated light to the angular dispersive element  13 . 
         [0053]    As shown in  FIG. 4 , the angular dispersive element  13  provides the angular dispersion in accordance with wavelength of the inputted the wavelength multiplexed light. 
         [0054]    The convex lens  14  focuses the angular dispersion light beams from the angular dispersive element  13  onto the MEMS substrate  16 . 
         [0055]    As illustrated in  FIGS. 7 and 8 , since frequencies of the light channels are set at equal frequency interval space on frequency axis, therefore the light channels are on unequal wavelength interval space on wavelength axis. Since the angular dispersive element  13  has the relationship of θ∝λ as described above, when the wavelengths (λ) are unequally wavelength spaced, the angles (θ) of light beams output from the angular dispersive element  13  are also unequally angles between each light channels. Therefore, the light beams output from the angular dispersive element  13  and focused by the convex lens  14  are unequally spaced as shown by arrows A 11  and A 12  of  FIG. 4 . 
         [0056]    The anomalous dispersion element  15  corrects the unequally-spaced light beams output from the angular dispersive element  13  through the convex lens  14  so that they become equally spaced. Specifically, the anomalous dispersion element  15  is substantially a rectangular parallelepiped in shape. The anomalous dispersion element  15  is adjusted its thickness (d 11  in  FIG. 4 ) and the angle (θ 11  in  FIG. 4 ) to the normal to the surface on which light beams fall. The anomalous dispersion element  15  performs to correct input light so that beam positions of light channels are arranged on desired equal interval spaces (the spaces between the MEMS mirrors  16   a  of the MEMS substrate  16 ). In this way, light beam in accordance with the light channels passing through the anomalous dispersion element  15  are corrected so as to be equally spaced as shown by arrows A 21  and A 22  of  FIG. 4 . 
         [0057]    The light beams outputted from the anomalous dispersion element  15  are reflected by the MEMS mirrors  16   a  of the MEMS substrate  16 . The MEMS mirrors  16   a  can vary their angles and can output light beams input from the input fiber  11  to target ones of the output fibers  17 . For example, as shown in  FIG. 3 , the MEMS mirrors  16   a  can reflect input light beams as shown by a solid arrow or a dashed arrow in the figure by varying their angles and can output them to target ones of the output fibers  17 . 
         [0058]    The light beams reflected by the MEMS mirrors  16   a  are refracted by the convex lens  14  so as to be parallel to the Z axis, pass through the angular dispersive element  13 , and are inputted into the lens array  12 . The lens array  12  collimates divided light beams and output them to the output fibers  17 . 
         [0059]    In this way, in the wavelength selective switch has angular dispersive element  13 , the anomalous dispersion element  15 , MEMS mirrors  16   a  and the output fibers  17 . 
         [0060]    The angular dispersive element  13  disperses a wavelength multiplexed light into an angular dispersion light in accordance with the wavelength of the light channels. The anomalous dispersion element  15  outputs the angular dispersion light beam on equally interval spaces. The pluralities of MEMS mirrors  16   a  reflect the angular dispersion light beam to ones of the output fibers  17 . 
         [0061]    Therefore, the angular dispersive element  13  outputs light on unequal spaces in accordance with the wavelength of the light channels but the anomalous dispersion element  15  corrects light beam positions in equally interval spaces in accordance with the wavelength of the light channels, and the anomalous dispersion element  15  outputs the light beams to the plurality of MEMS mirrors  16   a.    
         [0062]    Therefore, the plurality of MEMS mirrors  16   a  can be formed at equal space, and the yield of the MEMS substrate  16  can be improved. 
         [0063]    Next, a second embodiment will be described with reference to the drawings in detail. In the first embodiment, an example in which an optical wavelength demultiplexer is applied to a wavelength selective switch is described, whereas in the second embodiment, an example in which an optical wavelength demultiplexer is applied to a performance monitor will be described. 
         [0064]      FIG. 5  is a perspective view of a performance monitor. A performance monitor is a device that can measure the light intensity of each wavelength of wavelength-multiplexed light. In  FIG. 5 , the same reference numerals will be used to designate the same components as those in  FIG. 2 , so that the description thereof will be omitted. 
         [0065]    Compared to the wavelength selective switch of  FIG. 2 , the performance monitor of  FIG. 5  does not include the output fibers  17  and includes a lens  21  instead of the lens array  12 . In addition, it includes, instead of the MEMS substrate  16 , a light monitor substrate  22  that detects the intensity of light. The light monitor substrate  22  includes a plurality of one-dimensionally equally-spaced PDs (Photo Diodes)  22   a.    
         [0066]    Light output from the input fiber  11  is input into the angular dispersive element  13  through the lens  21 . The light input into the angular dispersive element  13  is angularly wavelength-dispersed and output to the convex lens  14 . The convex lens  14  focuses wavelengths of light output from the angular dispersive element  13  onto the light monitor substrate  22 . 
         [0067]    The anomalous dispersion element  15  corrects the unequally-spaced light beams output from the angular dispersive element  13  through the convex lens  14  so that they become equally spaced, and outputs them to the light monitor substrate  22 . Specifically, the anomalous dispersion element  15  is substantially a rectangular parallelepiped in shape. Specifically, the anomalous dispersion element  15  is substantially a rectangular parallelepiped in shape. The anomalous dispersion element  15  is adjusted its thickness and the angle to the normal to the surface on which light beams fall. The anomalous dispersion element  15  performs to correct input light so that beam positions of light channels are arranged on desired equal interval spaces (the spacings between the PDs  22   a  of the light monitor substrate  22 ). 
         [0068]    The PDs  22   a  of the light monitor substrate  22  convert equally-spaced light beams, output from the anomalous dispersion element  15  into electric currents. By measuring the electric currents output from the PDs  22   a,  the light intensity of each wavelength of wavelength-multiplexed light can be measured. 
         [0069]    In this way, in the performance monitor, the wavelength-multiplexed light is angularly wavelength-dispersed by the angular dispersive element  13 , and the angularly-dispersed wavelengths of light are equally spaced and output by the anomalous dispersion element  15 . The intensities of equally-spaced wavelengths of light output from the anomalous dispersion element  15  are measured by the plurality of PDs  22   a.    
         [0070]    Therefore, if wavelengths of light are output from the angular dispersive element  13  at unequal spacings, they are equally spaced by the anomalous dispersion element  15  and are input into the plurality of PDs  22 . Therefore, the plurality of PDs  22   a  can be formed at equal spacings, and the yield of the light monitor substrate  22  can be improved.