|Publication number||US20060034567 A1|
|Application number||US 11/183,029|
|Publication date||16 Feb 2006|
|Filing date||15 Jul 2005|
|Priority date||16 Jul 2004|
|Also published as||US7660499, US20060044987|
|Publication number||11183029, 183029, US 2006/0034567 A1, US 2006/034567 A1, US 20060034567 A1, US 20060034567A1, US 2006034567 A1, US 2006034567A1, US-A1-20060034567, US-A1-2006034567, US2006/0034567A1, US2006/034567A1, US20060034567 A1, US20060034567A1, US2006034567 A1, US2006034567A1|
|Inventors||Betty Anderson, Victor Argueta-Diaz|
|Original Assignee||Anderson Betty L, Victor Argueta-Diaz|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (1), Referenced by (5), Classifications (11), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This utility application claims the benefit of the filing date of the U.S. Provisional Application 60/588,729, entitled “Optical Beam Combiner”, and filed Jul. 16, 2004.
The present invention relates to optical devices, in general, and more particularly, to an optical beam combiner for receiving a plurality of light beams and superimposing spot images of the plurality of light beams onto a single location with a single incident angle.
Generally, an optical cross-connection device, like a White cell optical switch, for example, comprises a plurality of optical elements disposed in a predetermined spatial three dimensional pattern for directing one or more light beams from an input through a plurality of reflections to an output. Multiple light beams may bounce through various stages of the device simultaneously. A problem arises at the final or output stage of the White cell cross-connection device where the multiple light beams are ultimately directed from different spatial locations and different incidence angles. Thus, the multiple light beams will illuminate spots in various locations within the region of the output stage. Accordingly, each light beam of the multiplicity has a distinct incidence angle depending onto which region of the output stage it is being directed. This variation in the angle of incidence complicates the coupling of the light beams into an optical fiber or a light detector.
The present invention is intended to overcome or at least mitigate this drawback to the optical coupling in the output stages of optical cross-connection devices.
In accordance with one aspect of the present invention, an optical beam combiner for combining a plurality of light beams comprises: a plurality of spherical mirrors; and a flat mirror, the plurality of spherical mirrors and the flat mirror configured to form at least one multiple pass light beam optical arrangement for receiving the plurality of light beams and for superimposing spot images of the light beams onto a single location with a single incident angle.
In accordance with another aspect of the present invention, an optical beam combiner for combining an array of light beams comprises: a plurality of spherical mirrors; and a flat mirror, the plurality of spherical mirrors and the flat mirror configured to form at least one multiple pass light beam optical arrangement for receiving simultaneously the array of light beams and for superimposing spot images of each light beam of the array onto a single location with a single incident angle.
In accordance with yet another aspect of the present invention, a waveguide-based optical White cell comprises: a waveguide having front and rear edges, the inside surfaces thereof being coated with a reflective material, wherein the front edge including an input section for the passage of at least one light beam into the waveguide; at least one waveguide lens disposed in front of the inside surface of the rear edge to form a plurality of waveguide spherical mirrors at the rear edge; a plurality of angled micro mirrors disposed at the inside surface of the front edge; and the plurality of waveguide spherical mirrors and the coated front edge configured to form at least one waveguide White cell.
An optical switch based on the principles of an optical White cell will exemplify an optical cross-connection device for the purposes of describing one or more embodiments of the present invention. The optical White cell is an example of a multi-pass light beam optical system for generating a series of spot illuminations in sequence for an input light beam as will be better understood from the following description. Other examples of multi-pass light beam systems include a Herriot cell or any of the alternative spot pattern generators disclosed in U.S. Pat. No. 6,266,176. For the present example, a White cell comprising a set of three spherical mirrors with identical radii of curvature will be used. The multi-pass system of spherical mirrors will refocus the beam continuously within the White cell. One of the White cell's spherical mirrors may be replaced with an array of micro mirrors which may be made using micro-electromechanical systems (MEMS) techniques and will hereinafter be referred to as the MEMS micro mirrors, MEMS array or MEMS device.
Each of the micro mirrors of the MEMS device may be independently tilted to different angles. Also, multiple light beams may be directed to reflect or bounce off of the optical elements within the White cell simultaneously, and each light beam may be focused to illuminate a spot on a different micro mirror on each bounce or pass. Thus, in the exemplary optical switch of the present embodiment, there is an opportunity to switch a light beam with the MEMS device toward a new destination on each bounce. In addition, the number of possible attainable outputs of the exemplary switch will depend on the number of bounces that the light beams make in the White Cell. So, the number of attainable outputs may be controlled by controlling the number of bounces.
This White cell technology offers a highly scaleable all-optical cross-connect switch for a large number of ports (N inputs×N outputs), that avoids the effects of beam divergence and high precision angle control of the MEMS micro mirrors. Because several beams may bounce inside the White cell, each one of them may be controlled individually in such a way to control the destination of each beam. That is, each beam can be directed to any of multiple output regions. As noted above, however, on the final stage each beam will have a distinct incidence angle depending on which output region a particular beam is directed, which complicates the coupling into a fiber optic core or light detector. The beam spot illumination may also land in various locations within the output region. An optical beam combiner may be included at the output stage of the exemplary optical switch to cause all the possible beam illumination spot locations to be superimposed, and to correct for the variation in the angles of incidence. Thus, with the inclusion of the beam combiner, each output light beam may be modified such that it can be coupled properly into an optical fiber or onto a light detector.
The principles of operation of an exemplary White cell on which the present optical photonic switch is based will be reviewed briefly in connection with the illustration of
The center of curvature of mirror M (CC(M)) lies on the optical axis 12 thereof. Because Mirrors B and C are mounted across from mirror M and separated from it by a distance equal to the radius of curvature R, either mirror B or C images the surface of mirror M onto itself, whereas mirror M images B and C onto each other. The centers of curvature of mirror B and C (CC(B) and CC(C), respectively) are located on mirror M, at a distance δ left and right of the optical axis 12, respectively. Hence the centers of curvatures CC(B) and CC(C) are separated by 2δ. The locations of the centers of curvature are key to the operation of a binary optical cross-connection device.
An exemplary path of a single light beam 16 through the White Cell 10 is shown by light rays in the top view illustrations of
A feature of the exemplary White cell 10 is shown in
This multiple-reflection White cell configuration 10 will result in an illumination spot pattern on the surface of mirror M. The spot pattern as shown in the front view illustrations of mirror M in
The spacing between the illuminating spot images for a given input beam is directly related to the distance 2δ between the centers of curvature of mirrors B and C. The total number of spot images on mirror M is therefore dependent on the spacing δ and the overall size of mirror M. Note that the spot locations on mirror M depend entirely on the alignment of the two Mirrors B and C, and not on Mirror M. This will become of interest when we replace Mirror M with the MEMS micro mirrors and the beam illuminating spot images are made to land on the tilting micro mirrors thereof.
A second beam may be introduced into the White cell 10 as shown in
As noted above, Mirror M may be replaced with a MEMS micro mirror array, and two additional spherical mirrors may be added to form an alternate White cell 50 as shown in the illustration of
Several cell configurations may be used to enhance the number of possible outputs with the least number of light beam bounces. The cell configurations may be divided in two categories: polynomial and exponential cells. In the “polynomial cells,” the number of possible outputs N is proportional to the number of bounces m raised to some power. For example, in a quadratic cell N is proportional to m4, where m is the number of bounces on the MEMS device. In the “exponential cells,” the number of possible outputs is proportional to a base number raised to the number of bounces (N is proportional to 2m for the binary case). The exponential approach has the advantage of providing far more connectivity for a given number of bounces (and thus loss), but the disadvantage of not having the built-in redundancy of the polynomial devices. In this application, all of these configurations will not be discussed. A binary system will be briefly discussed to ease the introduction of an optical beam combiner.
In the example of
The architecture of the embodiment of
The embodiment of
Let us assume that an input beam going from the plane of the MEMS array 52 is directed to mirror 64, for example, after light beam bounce 1. A light image reflected from this spot on mirror 64 is imaged to a new spot image on auxiliary mirror 56, in a column labeled “2” at the far left thereof as shown in
Accordingly, when micro mirror of the MEMS array 52 that the light beam strikes on bounce 3 is tipped to −θ, the light returns to auxiliary mirror 56 via mirror 64 and may be focused a spot in column 4, for example. On the other hand, if the micro mirror of the MEMS array 52 that the light beam strikes at bounce 3 is instead turned to +θ, then the light beam from mirror 66 will be reflected from the MEMS array 52 at an angle of +3θ along the plane of axis 76 with respect to the normal axis 72. Recall that there are two more mirrors 68 and 70 along the axis 76. So, when the reflecting micro mirror is set at +θ, a light beam from mirror 66 will be directed to mirror 68 instead of mirror 64. In the present embodiment, a light beam is always directed to an upper mirror 64 or 68 from the MEMS array 52.
When a light beam is directed from MEMS array 52 to mirror 68, the light beam is refocused to auxiliary mirror 58 and forms a spot image in a column 4 of that mirror, for example. From there the light beam is directed to the lower mirror 70, and then back to the MEMS plane 52. Accordingly, mirrors 68 and 70 together with the MEMS array 52, lens 54, auxiliary mirror 58 and lens 62 comprise another White Cell of the embodiment. If the micro mirror in the MEMS array 52 struck by the light beam on bounce 5 is tilted to −θ, the light beam from mirror 70 is again directed to the other White cell (specifically to mirror 64). Conversely, if the same micro mirror at bounce 5 is set tilted to +θ, the light beam from mirror 70 is instead reflected at +4θ, a direction that is not being used in this design, and the beam is lost.
Thus, according to the connectivity diagram shown in
Note also that an input light beam may be sent to mirror 64 from the MEMS array 52 every even-numbered bounce, and to mirror 68 every fourth bounce (i.e. 4, 8, 12 . . . ). The odd-numbered bounces always appear on the MEMS array 52, and the even-number spots can appear either on auxiliary mirror 56 or auxiliary mirror 58. The light beam may be directed to auxiliary mirror 58 by the MEMS array 52 on any particular even-numbered bounce, but when the light beam is directed there, four consecutive light beam bounces are required before the light beam may be resent to auxiliary mirror 58 again.
Now, suppose that in the embodiment of
Shifting the spot images can control at which row any given input light beam reaches the output turning mirror and in the present example, each row may be associated with a different output. The number of possible outputs is determined by the total number of possible shifts for a given number of bounces. In the design of
where m is the number of bounces.
In the mirror face diagrams of
The example of
In operation, the “white” beam should be directed to the SDD 58 on the fourth and twelfth bounces, which correspond to row displacements of 4Δ and Δ, respectively. Accordingly, the “white” beam may initially bounce in the 64, 66 White Cell (i.e. the corresponding micro mirrors on the MEMS array 52 are tilted to −θ position) for three bounces. Then, the “white” beam is directed to the SDD 58 on the fourth bounce (i.e. the corresponding micro mirror on the MEMS array 52 is tilted to +θ), and more particularly to the column in the SDD 58 that has a shift value of 4Δ. After being shifted four rows in the SDD 58, the “white” beam is directed back to the MEMS array 52 on the fifth bounce and images on the row four (4) instead of row zero (0). The “white” beam is then kept bouncing in the 64,66 White cell, until the 12th bounce, when it is again directed to the SDD 58, and more specifically directed to land in the column with the shift value of Δ. After being shifted an additional row in the SDD 58, the “white” beam is directed back to the MEMS array 52 on the next bounce and images on the row five (5) of the output column 90.
In a similar manner, the “shaded” beam may be shifted to the row two (2) of the output column 90 in twelve bounces (12). The “black” beam may be left unshifted throughout the 12 bounces to be output at row zero (0) of the output column 90.
In the foregoing described embodiment, it is noted that any input directed to a particular output will land in a different place within that output region. For example, in
The first angle is the more severe than the second.
One way to solve this condition of difference in which mirror the beam comes from is to add one additional bounce to the system as shown in the illustration of
Furthermore, the light input to the multi-pass, cross-connection device may be a two-dimensional spot array, having both columns and rows. Therefore, all the rows and columns of the spot array should be combined to a single spot, and this should be done taking into account the varying angles of incidence. The output should be a single spot, of substantially the same size and shape as any individual input spot, and the output should emerge at a specific angle, independent of the arrival angle of any particular beam. A method for superimposing all the potential spot images onto a single location and with a single angle using passive White cell technology will now be discussed.
An exemplary optical beam combiner 110 suitable for solving the aforementioned conditions is shown in the illustration of
The plane of mirror 118 comprises a passive flat mirror that has fixed tilted micro mirrors in some locations. These micro mirrors may be essentially small prisms whose hypotenuses are coated with a high reflectivity coating to direct a light beam incident at a particular pixel in a specific direction. This is in contrast to the MEMS device 52 itself, which has micro mirrors at every location that may be tilted to a variety of directions. In the beam combiner 110, the angles of the “pixels” of mirror 118 may be fixed.
Suppose that in the present embodiment the output regions of the optical switch each contains a linear array of spot image positions such as exemplified in
In the embodiment of
A region 130 of the mirror 118 illuminated by the new spot array includes a series of fixed micro mirrors, all tipped to some angle θ. The positions of the micro mirrors of region 130 correspond directly by column and row to all of the spot image locations of the imaged spot array. The tipped micro mirrors of region 130 direct the beams to mirror 114 which, in turn, directs the beams back to mirror 118 to a region 132 in the lower left hand corner thereof. Region 132 includes another series of micro mirrors, all tipped to some angle. The positions of the micro mirrors of region 132 correspond directly by column and row to all of the spot image locations of the imaged spot array from mirror 114.
At this point the entire spot array image set has been stepped sideways by some distance greater than or equal to the original spot array size. The tipped mirrors of region 132 direct the entire beam array back to mirror 116, which, in turn, directs the beam array back to mirror 118 to illuminate another set of spot images in region 134 at the top left corner thereof. At region 134, there is another corresponding set of micro mirrors which are tipped to direct the entire spot array back to mirror 116, where another set of spot images are formed.
From here on in, each of the array imaged regions of mirror 118 may include corresponding fixed micro mirror arrays that may be angled such that the light circulates only between mirror 112 and mirror 114. If it may be arranged that a flat angle, e.g. the plane of mirror 118, may be all that is needed to circulate the light beam array between mirror 112 and mirror 114, then no additional micro mirrors need to be added to mirror 118 at the array imaged regions thereof.
To achieve this result, the distance S′ between the centers of curvature of mirrors 112 and 114 are set to be smaller than the centers of curvature between mirrors 114 and 116. Also, the sideways step described herein above in connection with each bounce of the beam array will be smaller to the spacing between two spot positions in the linear array. In this design configuration, some of the spot images may land on array positions or pixels that have been previously visited by another spot image of the array, but the direction of tilt of the micro-mirror is the same so there is no adverse consequence. As the beams continue to bounce, each resulting spot illumination of a bounce will move one spot position of the linear array over on each bounce.
Since by design this mirror's center of curvature CC(C′) is located 12 units from the input spot position 140 or approximately 16 on the index scale, when the beam returns to mirror 118 from mirror 116, it is re-imaged at an approximate index location 4+2(12)=28 depicted by line 142. At position 142, there is an angled or tipped mirror 146 which directs the light beam to mirror 114 or B′. Since by design the center of curvature of mirror 114 or B′ is 10 units to the left of position 142, the spot image from mirror 114 appears at an approximate location 28−2(10)=8 depicted by a line 148. The angled or tipped mirror 150 at this location 148 directs the light beam back to mirror 116 or C′, creating a return spot image on mirror 118 at an approximate index location 23 depicted by line 152.
In region 152, the face of mirror 118 is flat. Thus, by design, the light beam is directed from position 152 to mirror 114 or B′. Since the center of curvature of mirror B′ is set by design halfway between index locations 18 and 19, the spot image of the return beam from mirror 114 will appear approximately at an index location 14 depicted by line 154. Therein after, the light beam may circulate by design only between mirrors 114 or B′ and 112 or A′. Accordingly, at the next bounce, the light beam will illuminate a spot image at approximately an index location 22 depicted by line 156, which may have already been visited on the previous bounce by the fifth positioned beam in the linear input array, but it is of no consequence. Since the centers of curvature of the mirrors 112 and 114 are spaced one-half index unit apart, the spot images of the light beam with each subsequent bounce will form one unit apart on each such bounce.
By bouncing exclusively between mirrors 112 and 114, any spot image of a particular array will scan all the array positions ahead of it, eventually landing on each one. Suppose an exit port, like a hole or “trap door”, for example, is disposed at position 158 as shown in
Note that in the foregoing described embodiment, the spot images of the linear beam array all arrive at the same exit port or hole location, with the same angle of propagation, albeit at different times. If variations in latency are a consideration, the light beams of the array may be pre-delayed in advance (in another White cell-based or other optical delay line, for example) such that when they pass through the beam combiner 110, they exit at the same time as well. The tradeoff is added complexity.
For a large cross-connection device or optical switch with many inputs and outputs, the spot images of the input beams may be in a two-dimensional array. In this case, a second White cell group may be added behind the first group 112, 114 and 116 to combine the rows of each region to a single spot. The optical losses of the beam combiner 110 are expected to be very small, since all the optical elements are passive, fixed, and may be treated with very high-reflectivity coatings.
In the operational example described in connection with the illustration of
There exist different implementations of a lens for planar waveguide technology. For example, a geodesic lens, a chirped grating lens, or a Luneberg lens have all been documented in literature for several years as a suitable implementation of a waveguide lens. Any of these (or other) lens configurations may be used for the lenses 174, 176 and 178 in a planar waveguide embodiment.
Still referring to
From mirror 178/180, the light beam is re-imaged at the input edge 186 of the waveguide beam combiner 170. At the first image location 188, there may be a series of angled or tipped micro mirrors 190, which could be etched into the waveguide input edge 186 or be micro prisms that are glued to the input face 186, for example. In any case, the micro mirrors 190 are also coated for high reflectivity. The tip angle of the micro mirrors 190 may be such that they send the beams to mirror 176/180 or B″.
The input edge or face 186 of the waveguide beam combiner 170 is illustrated in
In summary, an apparatus and method are described for combining light beams coupled from an optical cross-connection device at different spatial locations and different angles. Also, such light beams are combined to a single spot with a single arrival angle. While light beams output from a White-cell based optical cross-connection device were utilized herein above to describe various embodiments of the beam combiner by way of example, it will be appreciated that the beam combiner could be applied to other situations in which beams need to be superposed. The superposition is achieved in the exemplary embodiments by introducing all the beams into a White cell, and using the White cell to shift each beam over by one position or slot on each bounce or pass, until the light beam falls or passes through an exit port leading out to another optical device. At the exit port, the spot images may be all superimposed in space (but not in time), and have the same angle of propagation as the corresponding light beams are all coming from the same direction.
A binary White cell optical cross-connection device was used by way of example in the above descriptions for the purposes of discussion, but the beam combiner solutions apply equally well to any optical device which combines multiple beams into a single beam, a multi-pass optical cross-connection device being one example. Further, the beam combiner may be applied anywhere were beams arriving from different places and from different angles should be superimposed. A three-dimensional White cell beam combiner arrangement with spherical mirrors and lenses may be used to combine an array of rows of light beams to a single column of spot images, albeit at different times. In addition, the light beams of the array may be pre-delayed in advance (in another White cell-based or other optical delay line, for example) such that when they pass through the beam combiner 110, they may exit at the same time as well. Alternatively, the beam combiner may be embodied in a waveguide approach in which one waveguide for each row of light beams may be used to combine all of the beams.
While the present embodiment has been described herein above in connection with a plurality of embodiments, it is understood that such presentations were made merely by way of example with no intent of limiting the invention to any single embodiment or a combination of embodiments. Rather, the present invention should be construed in breadth and broad scope in accordance with the recitation of the claims appended hereto.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US6266176 *||16 Oct 2000||24 Jul 2001||The Ohio State University||Device for optical interconnection|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US7430347||18 Jul 2005||30 Sep 2008||The Ohio State University||Methods, systems, and apparatuses for optically generating time delays in signals|
|US7630598||8 May 2007||8 Dec 2009||The Ohio State University||Apparatus and method for providing an optical cross-connect|
|US7633670||18 Jul 2005||15 Dec 2009||The Ohio State University||Methods, systems, and devices for steering optical beams|
|US7660499||15 Jul 2005||9 Feb 2010||The Ohio State University||Optical spot displacement apparatus|
|US7911671||8 May 2007||22 Mar 2011||The Ohio State University||Apparatus and method for providing true time delay in optical signals using a Fourier cell|
|Cooperative Classification||G02B19/0023, G02B19/0033, G02B6/0018, G02B6/0068, G02B26/0833|
|European Classification||G02B17/06N, G02B6/00L6I4R, G02B26/08M4, G02B6/00L6S2|
|3 Nov 2005||AS||Assignment|
Owner name: THE OHIO STATE UNIVERSITY, OHIO
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:ANDERSON, BETTY LISE;ARGUETA-DIAZ, VICTOR;REEL/FRAME:016727/0287;SIGNING DATES FROM 20051013 TO 20051018
|4 Nov 2005||AS||Assignment|