Abstract:
An optical cell may include a first port coupled to a second port by an optical path. The optical cell may also include a compensator disposed in the optical path. The compensator may be rotatable about an axis. Rotating the compensator about the axis may vary a distance that the optical path passes through the compensator thereby changing the optical path length of the optical path.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is a continuation of U.S. patent application Ser. No. 13/935,276, filed Jul. 3, 2013, which claims priority to Chinese Patent Application No. 201210229043.8, filed Jul. 4, 2012, which applications are incorporated herein by reference. 
     
    
     BACKGROUND 
     Field of the Invention 
       [0002]    The present invention generally relates to optical communication systems. More particularly, some example embodiments relate to an optical cell that may be used in some optical communication systems. 
         [0003]    Related Technology 
         [0004]    Some optical communication system may rely on splitting a light beam into multiple components. For example, optical communication systems that employ the use of delay line interferometers (DLIs) and interleavers may split light beams into multiple components. In some circumstances, wavelength uniformity between the multiple components of the light beam, and in particular, uniformity of the central wavelengths of the multiple components, may allow for better polarization mode dispersion performance and chromatic dispersion performance in these optical communication systems. 
         [0005]    One method to achieve central wavelength uniformity in multiple components of a light beam may be to select materials with certain qualities to split the light beam and manipulate the multiple components of the light beam. Obtaining material with the desired qualities may be difficult in some circumstances and the screening process to identify the material with the desired qualities may be time consuming. 
         [0006]    The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced. 
       SUMMARY 
       [0007]    Some example embodiments generally relate to an optical cell. 
         [0008]    In an embodiment, an optical cell may include a first port coupled to a second port by an optical path. The optical cell may also include a compensator disposed in the optical path. The compensator may be rotatable about an axis. Rotating the compensator about the axis may vary a distance that the optical path passes through the compensator thereby changing the optical path length of the optical path. 
         [0009]    In an embodiment, an optical cell may include a first block that may be configured to split a light beam into first and second components and direct the first component into a first optical path having a first optical path length and the second component into a second optical path having a second optical path length. The optical cell may also include a second block that may be positioned within the first and second optical paths and configured to join the first and second components into an output beam. The optical cell may also include a compensator that may be disposed in the first optical path between the first and second blocks. The compensator may be rotatable about an axis. Rotating the compensator about the axis may vary a distance that the first optical path passes through the compensator thereby changing the optical path length of the first optical path. 
         [0010]    In an embodiment, an optical cell may include a splitter that may be configured to split a light beam into first and second components. The optical cell may also include a coupler that may be configured to join the first and second components into an output beam. The optical cell may also include a compensator that may be disposed between the splitter and the coupler and positioned to receive the first component from the splitter. The compensator may be rotatable about an axis. Rotating the compensator about the axis may vary a distance that the first component passes through the compensator thereby changing an optical path length through which the first component travels. 
         [0011]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential characteristics of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0012]    Additional features and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    A more particular description of the invention will be rendered by reference to embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only some embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0014]      FIG. 1  illustrates a perspective view of an optical cell; 
           [0015]      FIG. 2A  illustrates a top view of the optical cell of  FIG. 1 ; 
           [0016]      FIG. 2B  illustrates another top view of the optical cell of  FIG. 1 ; 
           [0017]      FIG. 2C  illustrates a side view of the optical cell of  FIG. 1 ; 
           [0018]      FIG. 3  illustrates a top view of another optical cell; 
           [0019]      FIG. 4  illustrates a top view of yet another optical cell, all arranged in accordance with at least some embodiments described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  illustrates a perspective view of an optical cell  100 , arranged in accordance with at least some embodiments described herein. In some embodiments, the optical cell  100  and/or other optical cells disclosed herein may be implemented in, for instance, a DLI, an interleaver, a deinterleaver, or other environments in which it may be desirable to improve polarization mode dispersion (PMD), chromatic dispersion (CD) and/or polarization dependent frequency shift by, e.g., providing central wavelength uniformity between two separate light beams propagating within the optical cell  100 . 
         [0021]    The optical cell  100  includes one or more optical elements that may include opposing first and second blocks  110 ,  150  displaced from one another by an optical block  140  and first and second compensators  120 ,  130 . The first block  110  contains a splitter  112  and a first reflector  114 . The second block  150  contains a coupler  152  and a second reflector  154 . Each of the first and second compensators  120 ,  130  has a first respective axis of rotation  122 ,  132  and second a respective axis of rotation  126 ,  136 . The first compensator  120  may be configured to rotate around the first axis  122  in the direction of arrow  124  and may be configured to rotate around the second axis  126  in the direction of arrow  128 . The second compensator  130  may be configured to rotate around the first axis  132  in the direction of arrow  134  and may be configured to rotate around the second axis  136  in the direction of arrow  138 . 
         [0022]    As illustrated, the optical cell  100  is configured to split an incoming light beam  160  into two components or channels using the splitter  112  and to later realign the components using the coupler  152  onto a common propagation axis as an output beam  170 . The two components of the light beam  160  follow two distinct optical paths  162 ,  163 . In some embodiments, a first component of the light beam  160  follows a first optical path  162 . The first optical path  162  passes through the first block  110 , the first compensator  120 , the optical block  140 , and the second block  150 . A second component of the light beam  160  follows a second optical path  163  that includes first, second, and third legs  164 ,  166 ,  168 . The second optical path  163  passes through the first block  110 , the second compensator  130 , and the second block  150 . 
         [0023]    In some embodiments, the first and second optical paths  162 ,  163  have different optical path lengths. Furthermore, in some embodiments, the optical path lengths of the first and second optical paths  162 ,  163  may be changed by rotating the first and second compensators  120 ,  130  respectively on their respective first axes  122 ,  132  and/or their respective second axes  126 ,  136 . In some embodiments, adjusting the optical path lengths of the first and second optical paths  162 ,  163  may allow for adjusting a center wavelength of the components of the light beam  160 . Furthermore, with different optical path lengths, a delay may be introduced between the two components of the light beam  160 . 
         [0024]    With the introduction of a delay between different components of the light beam  160 , the optical cell  100  may be used in an interleaver to space apart the components of the light beam  160  within the output beam  170 . In some embodiments, the optical cell  100  may be used in a DLI for converting an optical differential phase-shift keying (DPSK) signal to an intensity-keyed signal. In some embodiments, the optical cell  100  may be used for other purposes within an optical system or device. Further explanation of how the optical cell  100  affects the light beam  160  is explained with respect to  FIGS. 2A and 2B . 
         [0025]      FIG. 2A  illustrates a top view of the optical cell  100  in accordance with at least some embodiments described herein. In some embodiments, the light beam  160  enters the optical cell  100  at a first port  272  located in the first block  110 . The first block  110  may be configured to split the light beam  160  into first and second components. The first block  110  may also be configured to direct the first and second components of the light beam  160  on to first and second optical paths  162 ,  163  respectively. To split the light beam  160 , the first port  272  may be aligned so that the light beam  160  strikes the splitter  112  in the first block  110 . The splitter  112  may be configured to split the light beam  160  into the first and second separate components or channels. In some embodiments, the splitter  112  may split the light beam  160  into first and second components with different polarization vectors. For example, the splitter  112  may split the light beam  160  into first and second components with orthogonal polarizations. In these and other embodiments, the splitter  112  may be a multilayer dielectric polarizing beam splitter that passes one polarization component of the light beam  160  and reflects another polarization of the light beam  160 . In some embodiments, the splitter  112  may split the light beam  160  into first and second components with equal or unequal intensities. In these and other embodiments, the splitter  112  may be a multi-layer dielectric beam splitter. In some embodiments, the splitter  112  may split the light beam  160  into first and second components in another manner. 
         [0026]    After the light beam  160  is split into first and second components, the splitter  112  may be configured to direct the first component into the first optical path  162 . The first component is transmitted through the splitter  112  and out of the first block  110 . The first component passes through the first compensator  120  and the optical block  140  and enters the second block  150 . 
         [0027]    The splitter  112  may also be configured to direct the second component of the light beam  160  into the first leg  164  of the second optical path  163  by reflecting the second component toward the first reflector  114 . The second component strikes the first reflector  114  and is reflected into the second leg  166  of the second optical path  163  and out of the first block  110 . The second component passes through the second compensator  130  and into the second block  150 . The second component strikes the second reflector  154  and is reflected toward the coupler  152  and into the third leg  168  of the second optical path  163 . 
         [0028]    The second block  150  may be configured to join the first and second components into the output beam  170 . To do so, the first and second components of the light beam  160  may both strike the coupler  152 . The coupler  152  may be configured to transmit the first component along the axis of the output beam  170 . The coupler  152  may also be configured to reflect the second component along the axis of the output beam  170 . In this manner, the first and second components may be joined in the output beam  170  and pass out of the second block  150  through a second port  274 . In some embodiments, a light beam may propagate through the optical cell  100  in a direction opposite from light beam  160 . In these and other embodiments, the coupler  152  may act as a splitter and the splitter  112  may act as a coupler. 
         [0029]    Both of the optical paths  162 ,  163  have physical path lengths and optical path lengths. The optical path lengths of the optical paths  162 ,  163  are the sum of the product of the physical length and the index of refraction of all of the optical elements and optical material on each of the distinct optical paths  162 ,  163 . Thus, the optical path length of the first optical path  162  is the sum of the physical lengths of the first optical path  162  through the first block  110 , splitter  112 , first compensator  120 , optical block  140 , second block  150 , and coupler  152 , and the optical material, i.e. air, plasma, liquid, solid, if any, between the above optical elements, where the physical length of each optical element and optical material is multiplied by the index of refraction of that optical element or material. The optical path length of the second optical path  163  is the sum of the physical lengths of the second optical path  163  through the first block  110 , second compensator  130 , second block  150 , and the optical material, i.e. air, plasma, liquid, solid, if any, between the above optical elements, where the physical length of each optical element and optical material is multiplied by the index of refraction of that optical element or material. In some embodiments, the optical path lengths of the optical paths  162 ,  163  may be different. In some embodiments, the physical path lengths of the optical paths  162 ,  163  may be different. 
         [0030]    The optical path lengths of the optical paths  162 ,  163  may be adjusted by adjusting the length of the physical path that each optical path  162 ,  163  makes through their respective compensator  120 ,  130 . The physical lengths that each optical path  162 ,  163  may make through their respective compensator  120 ,  130  may be adjusted by rotating the respective compensator  120 ,  130  as illustrated in  FIG. 2B  and/or  FIG. 2C . In particular, as illustrated in  FIG. 2B , the second compensator  130  has been rotated about its first axis  132 , thereby adjusting the physical path length through the second compensator  130  and thus the optical path length of the optical path  163 . In  FIG. 2C , the second compensator  130  has been rotated about its second axis  136 , thereby adjusting the physical path length through the second compensator  130  and thus the optical path length of the optical path  163 . Adjusting the optical path lengths of the optical paths  162 ,  163  may adjust the center wavelength of the components of the light beam  160  traversing the respective optical paths  162 ,  163 . In the illustrated embodiment, adjusting the optical path lengths of the optical paths  162 ,  163  does not alter the total physical lengths of the optical paths  162 ,  163 . The total physical lengths of the optical paths  162 ,  163  remain constant when the first and second compensators  120 ,  130  are rotated. 
         [0031]    In some embodiments, the ability to adjust the central wavelengths of the components of light may be beneficial. For example, in some embodiments, the central wavelengths of the components of light in the optical cell  100  may be adjusted to improve central wavelength uniformity, which may reduce or substantially eliminate polarization mode dispersion. In some embodiments, improving central wavelength uniformity between components may reduce or substantially eliminate chromatic dispersion. In some embodiments, improving central wavelength uniformity between components may improve polarization dependent frequency shifts. Furthermore, the ability to adjust the central wavelengths of light may lead to reduced manufacturing costs. This may be so because the screening yield for optical elements that produce the correct optical path lengths may be low and time consuming in the absence of the first and second compensators  120  and  130  or other compensating means. The ability to adjust the optical path length allows for lowered screening criteria for optical elements and subsequently an increase in yield. 
         [0032]      FIG. 2B  illustrates a top view of the optical cell  100 , in accordance with at least some embodiments described herein.  FIG. 2B  illustrates the second compensator  130  being rotated about the first axis  132 . The physical length of the second optical path  163  through the second compensator  130  in a non-rotated state is illustrated by line  280 . The non-rotated state of the second compensator  130 , as illustrated in  FIG. 2A , is presented by the dashed box and presents a rotation state of the second compensator  130  with the shortest physical path through the second compensator  130 . The physical length of the second optical path  163  through the second compensator  130  in a rotated state, as illustrated in  FIG. 2B , is illustrated by line  282 . Line  282  is longer than line  280  because the physical length of the second optical path  163  through the second compensator  130  increases when the second compensator  130  is rotated to the position depicted in  FIG. 2B . In the illustrated embodiment, rotating the second compensator  130  does not increase the total physical length of the second optical path  163 . The total physical length of the second optical path  163  remains constant when the second compensator  130  is rotated. 
         [0033]      FIG. 2C  illustrates a side view of the optical cell  100 , in accordance with at least some embodiments described herein.  FIG. 2C  illustrates the second compensator  130  being rotated about the second axis  136 . For clarity, the first compensator  120 , the optical block  140 , various components within the first and second blocks  110 ,  150 , and the second optical path  162  are not illustrated. The physical length of the second optical path  163  through the second compensator  130  in a non-rotated state is illustrated by line  290 . The non-rotated state of the second compensator  130 , as illustrated in  FIG. 2A , is represented by the dashed box and presents a rotation state of the second compensator  130  with the shortest physical path through the second compensator  130 . The physical length of the second optical path  163  through the second compensator  130  in a rotated state, as illustrated in  FIG. 2C , is illustrated by line  292 . Line  292  is longer than line  290  because the physical length of the second optical path  163  through the second compensator  130  increases when the second compensator  130  is rotated to the position depicted in  FIG. 2C . In the illustrated embodiment, rotating the second compensator  130  does not increase the total physical length of the second optical path  163 . The total physical length of the second optical path  163  remains constant when the second compensator  130  is rotated. 
         [0034]    The optical path length of the second optical path  163  may increase when the physical length of the second optical path  163  through the second compensator  130  increases because the optical path length of the second optical path  163  is equal to a sum of the physical lengths of the optical elements multiplied by the index of refraction of each optical element. The second compensator  130  may have a higher index of refraction than the optical material through which the second optical path  163  traverses between the first and second blocks  110 ,  150 . Thus, increasing the physical length of the second optical path  163  in an optical element with a higher index of refraction produces a longer optical path length of the second optical path  163  even though the physical length of the second optical path  163  does not change. 
         [0035]    The ability to rotate the first and second compensators  120 ,  130  may allow the optical path lengths of the first and second optical paths  162 ,  163  to be adjusted. Accordingly, the central wavelengths of the components of the light beam  160  traversing the first and second optical paths  162 ,  163  respectively, may be adjusted. In some embodiments, the first and second compensators  120 ,  130  may be adjusted independently. In some embodiments, the first and second compensators  120 ,  130  may be connected and may only be adjusted together. 
         [0036]    To increase the optical path length for the first optical path  162 , the first compensator  120  may be rotated so that a larger portion of the physical path length of the first optical path  162  passes through the first compensator  120 . To decrease the optical path length of the first optical path  162 , the first compensator  120  may be rotated so that a smaller portion of the physical path length of the first optical path  162  passes through the first compensator  120 . 
         [0037]    Similarly, to increase the optical path length for the second optical path  163 , the second compensators  130  may be rotated so that a larger portion of the physical path length of the second optical path  163  passes through the second compensators  130 . To decrease the optical path length of the second optical path  163 , the second compensator  130  may be rotated so that a smaller portion of the physical path length of the second optical path  163  passes through the second compensator  130 . 
         [0038]    The dimensions and shapes of the first and second compensators  120 ,  130  determine how much the optical path lengths of the first and second optical paths  162 ,  163  may be adjusted. In some embodiments, the first and second compensators  120 ,  130  may have the same physical path lengths when both the first and second compensators  120 ,  130  are in a non-rotated position, or in other words, the first and second compensators  120 ,  130  may have the same widths. In some embodiments, the first and second compensators  120 ,  130  may have different widths. In some embodiments, the first and second compensators  120 ,  130  may have cuboid shapes as illustrated in  FIGS. 1 ,  2 A, and  2 B. In some embodiments, the first and second compensators  120 ,  130  may have other shapes, such as a cube, square-based pyramid, triangular based pyramid, cylinder, triangular prism, cone, or some other shape. In some embodiments, the first and second compensators  120 ,  130  may have the same shape with the same dimensions or the same shapes with different dimensions. In some embodiments, the first and second compensators  120 ,  130  may have different shapes with some identical dimensions or different shapes with no identical dimensions. 
         [0039]    In some embodiments, the first and second compensators  120 ,  130  may have axis of rotation different than the first and second axes  122 ,  126 ,  132 ,  136 . For example, the first and second compensators  120 ,  130  may each have an axis of rotation that extends diagonally through the first and second compensators  120 ,  130 . Alternately or additionally, the first and second compensators  120 ,  130  may have more or less than two axes of rotation. For example, the first and second compensators  120 ,  130  may have one, three, four, or any number of axes of rotation. Alternately or additionally, the first and second compensator  120 ,  130  may have different axes of rotation. In some embodiments, the first and second compensators  120 ,  130  may be configured to rotate about a single axis of rotation at one time. In other embodiments, the first and second compensators  120 ,  130  may be configured to rotate about more than one axis of rotation at a given time. 
         [0040]    In some embodiments, the first and second compensators  120 ,  130  may be formed from the same material, such as some form of glass. In some embodiments, the first and second compensators  120 ,  130  may be formed of different materials with different indexes of refraction. In some embodiments, the first compensator  120  may be rotated; the second compensator  130  may be rotated; both the first and second compensators  120 ,  130  may be rotated; or neither the first nor the second compensator  120 ,  130  may be rotated. In some embodiments, the optical cell  100  may contain only the first compensator  120  or the second compensator  130 . In some embodiments, the optical cell  100  may not contain the optical block  140 . In some embodiments, the optical cell  100  may not contain first and second blocks  110 ,  150 , and only have the splitter  112 , the coupler  152 , and first and second reflectors  114 ,  154 . 
         [0041]      FIG. 3  illustrates a top view of another optical cell  300 , in accordance with at least some embodiments described herein. The optical cell  300  includes all of the optical elements in the optical cell  100  illustrated in  FIGS. 1 ,  2 A, and  2 B. The optical cell  300  further includes third and fourth compensators  324 ,  334 . The third compensator  324  is located in the first optical path  162 , adjacent to the first compensator  120 , and between the first block  110  and the optical block  140 . The fourth compensator  334  is located in the second optical path  163 , adjacent to the second compensator  130 , and between the first and second blocks  110 ,  150 . 
         [0042]    The third and fourth compensators  324 ,  334  may be rotated about their respective axes  326 ,  336 . In some embodiments, rotating the third and fourth compensators  324 ,  334  may adjust the optical path lengths of the optical paths  162 ,  163 . Having the third and fourth compensators  324 ,  334  together with the first and second compensators  120 ,  130  allows for larger optical path length adjustments of the optical paths  162 ,  163  because larger physical lengths of the optical paths  162 ,  163  may be within the first and second compensators  120 ,  130 ,  324 ,  334 . In some embodiments, the third and fourth compensators  324 ,  334  may have similar characteristics to the first and second compensators  120 ,  130  discussed above. In some embodiments, the first, second, third, and fourth compensators  120 ,  130 ,  324 ,  334  may be configured to rotate independent of each other. 
         [0043]      FIG. 4  illustrates a top view of yet another optical cell  400 , in accordance with at least some embodiments described herein. The optical cell  400  includes the optical elements in the optical cell  100  illustrated in  FIGS. 1 ,  2 A, and  2 B except for the first compensator  120 . The optical cell  400  instead includes adjusted first compensator  420 . The adjusted first compensator  420  is located in the first optical path  162  between the optical block  140  and the second block  150 . The adjusted first compensator  420  may be configured to rotate about an axis of rotation  422 . As illustrated in  FIG. 4 , the adjusted first compensator  420  and the second compensator  130  are not aligned like the first and second compensators  120  and  130  in  FIGS. 1 ,  2 A, and  2 B. Nevertheless, the adjusted first compensator  420  may operate to adjust the optical path length of the first optical path  162  by rotating just as the first compensator  120  illustrated in  FIGS. 1 ,  2 A, and  2 B. 
         [0044]    The present invention may be embodied in other specific forms. The described example embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.