CA1223984A - Polarization-insensitive optical multiplexing apparatus - Google Patents
Polarization-insensitive optical multiplexing apparatusInfo
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- CA1223984A CA1223984A CA000507196A CA507196A CA1223984A CA 1223984 A CA1223984 A CA 1223984A CA 000507196 A CA000507196 A CA 000507196A CA 507196 A CA507196 A CA 507196A CA 1223984 A CA1223984 A CA 1223984A
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Abstract
POLARIZATION-INSENSITIVE OPTICAL
MULTIPLEXING APPARATUS
Abstract of the Disclosure Polarization-insensitive optical multiplexing appar-atus for independently modulating perpendicularly polarized components of a collimated input beam includes a polarization beam splitter for receiving an input collimated beam which has arbitrarily polarized components, splitting the beam in-to the two components. One of the components is rotated by a 1/2 wave plate so as to yield a polarized beam which is polarized in the same direction as the other beam. The two polarized beams are then applied to a polarization sen-sitive interferometric multimode fiber optic switch and mod-ulator. The output of the interferometric multimode fiber optic switch and modulator contains two beams, both polarized in the same direction. One of the beams is rotated ninety degrees by a 1/2 wave plate, and the two mutually perpendi-cularly polarized beams are then recombined by a polariza-tion beam splitter operated in reverse to yield an output beam containing mutually perpendicular components.
MULTIPLEXING APPARATUS
Abstract of the Disclosure Polarization-insensitive optical multiplexing appar-atus for independently modulating perpendicularly polarized components of a collimated input beam includes a polarization beam splitter for receiving an input collimated beam which has arbitrarily polarized components, splitting the beam in-to the two components. One of the components is rotated by a 1/2 wave plate so as to yield a polarized beam which is polarized in the same direction as the other beam. The two polarized beams are then applied to a polarization sen-sitive interferometric multimode fiber optic switch and mod-ulator. The output of the interferometric multimode fiber optic switch and modulator contains two beams, both polarized in the same direction. One of the beams is rotated ninety degrees by a 1/2 wave plate, and the two mutually perpendi-cularly polarized beams are then recombined by a polariza-tion beam splitter operated in reverse to yield an output beam containing mutually perpendicular components.
Description
I
I
POLARIZATION-INSENSITIVE OPTICAL MULTI-FLEXING APPARATUS
This application is a division of Canadian application 416,669-8 filed November 30,. 1982.
This invention relates to polarization-insensitive optical switch apparatus, polarization-insensitive optical multiplexing apparatus, and interferometric multimedia fiber optic apparatus in which the indices of refraction of various beam paths through portions thereof can be varied with respect to that of other portions.
Accordingly, it is a general object of this invention to provide new and improved apparatus of such character.
Polariza~ion-insensitive switching of multimedia fibers has been achieved by means of mechanical switches which move an input fiber into alignment with two output fibers, at two stable positions.
Electronic carrier multiplexing of two optical sign nets has been accomplished Usually, the multiplexing stage is performed electronically; the resulting signal.
modulates the current through a light source. The drive currents of two different light sources can be modulated, and the two signal carrying fibers can be combined into a single communication fiber by means of a fiber combiner.
Disadvantageously, mechanical switching is slow, is power consuming is usually operated at high voltages, is cumbersome, and is unreliable.
Disadvantageously, the multiplexing techniques (in which a single light source is modulated by the already tnultiplexed signal) requires very high linearity of the modulated source in order to prevent crosstalk. The light sources used in communication systetns have nonuniform nonlinear responses, sufficient to make this method inapplicable in many cases.
39~19L
The modulation of the drive currents of two different light sources, utilizing an optical combiner, disadvantageously has at least a 50%, or 3 dub, loss due to the principle of combination of two light beams. Typical losses described in the literature are approximately 4 dub.
Devices in accordance with this invention are of a low-loss nature due to the collimating optics and the large aperture of an interferometric multimedia fiber optic switch and modulator, such as that described in our cop ending apply-cation Serial No. 413,612-8 filed October 18, 1982 and entitled "Interferometric Multimedia Fiber Optic Switch and Modulator". Its polarization-insensitivity facilitates the apparatus for use with unpolarized light sources, such as LED's. In a multiplexing configuration, the light source linearity problem and the combiner losses are eliminated.
Its complementary output provides a second channel (or a monk storing signal) without the interruption of the light beam.
According to one aspect of the invention, there is provided polarization-insensitive optical multiplexing appear-anus for independently modulating perpendicularly polarized components of a collimated input beam comprising a first polarization beam splitter for receiving and splitting said collimated input beam into two perpendicularly polarized beams; a first polarization rotating means for rotating a first of said two perpendicularly polarized beams by ninety degrees so that the rotated polarized beam and a second of said perpendicularly polarized beam are each polarized in the same direction; means for reflecting one of said first and said second beams so that the reflected beam and the other of said first and said second beams traverse parallel paths;
a first electro-optical crystal having a first surface adapt-Ed to receive said reflected one beam and said other beam for -transmission through said first crystal, a second surface adapted to receive such transmitted beams from said firs-t surface of said first crystal at a first pair of spots, a fist reflective surface oriented to receive light beams from said first pair of spots of said second surface of said first crystal and to reflect such light beams, a third surface I
adapted to receive such reflected light beams from said first reflective surface of said first crystal upon a second pair of spots, and a fourth surface adapted to externally pass light impinged thereupon from said second pair of spots of said first crystal; a second electro-optical crystal having a first surface, a second surface oriented to receive trays-milted light from said second surface of said first crystal at a first pair of spots, a first reflective surface oriented to receive light from said first pair of spots of said second surface of said second crystal and to reflect such received light, a third surface adapted to receive such reflected light from said first reflective surface of said second crystal upon a second pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said second pair of spots of said second crystal; a dielectric beam splitting coating, said first crystal, said second crystal, and said coating being so oriented that said first pair of spots of said second surface of said first cry-slat, and said first pair of spots of said second surface of said second crystal are substantially juxtaposed with a first portion of said coating oriented there between, and said second pair of spots of said third surface of said first crystal, and said second pair of spots of said third surface of said second crystal are substantially juxtaposed with a second portion of said coating oriented there between, whereby said one beam and said other beam traverse a first path and a second path, respectively, within said first crystal, and said one beam and said other beam traverse a third path and a fourth path, respectively, within said second crystal; first means for varying the index of refraction of said first path within said first crystal with respect to the index of refry-cation of said third path within said second crystal; second means for varying the index of refraction of said second path within said first crystal with respect to the index of refract I lion of said fourth path within said second crystal, said second index of refraction varying means being independent of said frost index of refraction varying means; means associated with said fourth surface of said first crystal for reflecting one light beam from one spot of said second pair of spots of said first crystal; a second polarization rotating means for rotating a first of said light beams from said fourth surface of said first crystal by ninety degrees so that the rotated first light beam and the unrotated second light beam are perpendicularly polarized with respect to each other; and a second polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said first crystal and to provide a first single light beam which can be coupled to a first optical output means.
According to another aspect of the invention there is provided polarization-insensitive optical multiplexing apparatus for independently modulating perpendicularly polar-iced components of a pair of collimated input beams comprise in a first polarization beam splitter for receiving and splitting one of said collimated input beams into two per pen-dicularly polarized beams; a first polarization rotating means to rotating a first of said two perpendicularly polar-iced beams by ninety degrees so that the rotated polarized beam and second of said perpendicularly polarized beams are each polarized in the same direction; first means for reflect tying one of said first and said second beams so that the reflected beam and the other of said first and said second beams traverse parallel paths; a first electro-optical cry-slat having a first surface adapted to receive said reflected one beam and said other beam for transmission through said first crystal, a second surface adapted to receive such trays-milted beams from said first surface of said first crystal at a first pair of spots, a first reflective surface orient-Ed to receive light beams from said first pair of spots offside second surface of said first crystal and to reflect such light beams, a third surface adapted to receive such reflected light beams from said first reflective surface of said first crystal upon a second pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said second pair of spots of said first cry-slat, whereby said one beam and said other beam traverse a first path and a second path, respectively, within said first crystal; second means associated with said fourth sun-I
face of said first crystal for reflecting one light beam from one spot of said second pair of spouts of said first crystal; a second polarization rotating means for rotating a first of said light beams from said fourth surface of said first crystal by ninety degrees so that the rotated first light beam and the unrotated second light beam are per pen-dicularly polarized with respect to each other; a second polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said first crystal and to receive a first single light beam which can be coupled to a first optical output means; a third polarization beam splitter for receiving and splitting the other of said collimated input beams into two perpendicularly polarized beams; a third polarization rotating means for rotating a first of said two perpendicularly polarized beams from said third polarization beam splitter by ninety degrees so that the rotated beam and a second of said perpendicularly polarized beams from said third polarization beam splitter are each polarized in the same direction; third means for reflecting one of said first and said second beams from said third polarization rotating means so that the reflected beam and the other of said first and said second beams from said third polarization rotating means traverse parallel paths;
a second electro-optical crystal having a first surface adapted to receive one beam reflected by said third means and said other beam from said third polarization rotating means for transmission through said second crystal, a second surface adapted to receive such transmitted beams from said first surface of said second crystal at a third pair of spots, a first reflective surface oriented to receive light beams from said third pair of spots of said second surface of said second crystal and to reflect such light beams, a third sun-face adapted to receive such reflected light beams from said first reflective surface of said second crystal upon a fourth pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said fourth pair of spots of said second crystal, whereby said one beam reflected by said third means and said other beam from said third pox larization rotating means traverse a third path and a fourth path, respectively, within said second crystal, a dielectric beam splitting coating, said first crystal, said second cry-slat, and said coating being so oriented that said first pair of spots of said second surface of said first crystal, and said third pair of spots of said second crystal are sub-staunchly juxtaposed with a first portion of said coating oriented there between, and said second pair of spots of said third surface of said first crystal, and said fourth pair of spots of said third surface of said second crystal are sub-staunchly juxtaposed with a second portion of said coating oriented there between; first means for varying the index of refraction of said first path within said first crystal with respect to the index of refraction of said third path within said second crystal; second means for varying the index of refraction of said second path within said foist crystal with respect to the index of refraction of said fourth path within said second crystal; fourth means associated with said fourth surface of said second crystal for reflecting one light beam from one spot of said fourth pair of spots of said second crystal; a fourth polarization rotating means for rotating a first of said light beams from said fourth surface of said second crystal by ninety degrees so that the rotated first light beam from said second crystal and the I unrotated second light beam from the second crystal are perpendicularly polarized with respect to each other; and a fourth polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said second crystal and to provide a second single out-I put light beam which can be coupled to a second optical output means.
According to another aspect of the invention there is provided in combination, a first electro-optical crystal, a second electro-optical crystal, a dielectric beam splitting coating affixed to portions of said crystals with coated portions of such crystals being juxtaposed, first means for varying the index of refraction of one beam path through one of said crystals with respect to the index of refraction of one beam path through the other of said crystals, and I
second means for varying the index of refraction of another beam path through said one of said crystals with respect to the index of refraction of another beam path through said other of said crystals, said second means being independent from said first means.
Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic diagram of one embodiment of this invention;
FIG. 2 is a modular version of the embodiment shown in Fig. l;
FIG. 3 is a "p" polarization version of the modulator embodiment depicted in Fig. 2;
FIG. 4 is a plan view of another embodiment of the invention utilizing an IMFOS, as described in greater detail hereinafter, the dotted lines illustrating an out-line of electrodes applied to such IMFOS;
FIG. 5 is a plan view of still another embodiment of the invention, utilizing a modified IMFOS which uses rectangular shape crystals with individual electrodes being depicted in dotted line format; and FIG. 6 is a cross sectional view of the embodiment shown in Fig. 4, taken along the line 6-6 thereof.
A polarization-insensitive optical switch and dual channel carrier multiplexer, in accordance with this in-venkion, utilizes the interferometric multimedia fiber optic switch (IMFOS) described in a cop ending patent apply-cation by the applicants hereof, entitled "Interferometric Multimedia Fiber Optic Switch and Modulator", SUN. 413,612 filed October 18, 1982. Broadly, an IMFOS, as described in the above-identified application, includes a dielectric beam splitting coating affixed to portions of two electro-optical crystals with coated portions of the crystals being juxtaposed. The index of refraction of one of the crystals is varied with respect to that of the other.
Referring to Fig. 1, an IAMB 11 is represented schematically as a rectangle. The IMFOS 11 is similar to that described in the cop ending application in which a beam path is modulated in accordance with an electrical field applied thereto. By the application of particular fields, a light beam is switched on and off ox is modulated at varying intensities. The IMFOS 11, as dejected in jig. 1 is polarization sensitive, and light of one polarity only is normally handled there through. In the embodiment depicted in Fig. 1, light, which is s plane polarized, is conveniently handled.
A collimated input beam 12 either can be unpolarized or can contain arbitrarily polarized light beams there-within. The input beam 12 is split into two perpendicu-laxly polarized beams, a p beam and an s beam, by a polarization beam splitter 13. The polarization beam splitter 13 can be constructed of birefrigent prisms, such as, or example, Russian prisms, or multi layer interference 20 polarizers.
The p polarized beam passes through a 1/2 wave plate 14 which converts it into an s polarized beam. The s polarized beam, split by the polarization beam splitter 13, is reflected by a mirror 16 so that it, and the s polarized I beam emit-ted from the 1/2 wave plate 14, traverse parallel paths and enter the IMFOS 11.
The two s polarized beams that enter the IMFOS 11 undergo an interference and intensity redistribution as described more fully in the above-identified pending Jo application.
As depicted in Fig. 1, the s polarized beam (which exited from the 1/2 wave plate 14 through the IMFOS 11) is reflected by a mirror 17 to another polarization beam splitter 18 which is operated in reverse. The s polarized I beam, which had been reflected by the mirror 16 and past through the IMFOS 11, is rotated by a 1/2 wave plate 19 ~22~
-- g into a p polarized beam. The p polarized beam from the 1/2 wave plate 19 and the s polarized beam from the mirror 17 are recombined, by the polarization beam splitter 18 (which operates in reverse) to provide an output signal or output beam 21 which contains mutually perpendicular polarized beams p and s.
A modulator version of the embodiment shown in Fig. 1, is depicted in Fig. 2. A collimated input beam 12 contains either mutually perpendicularly polarized beams p and s, or it can contain unpolarized light. The beam 12 is applied through a polarization beam splitter 13, as before, which reflects a portion of the beam to a prism 26 which reflects the s polarized portion thereof toward the IMFOS
11. That potion of the beam 12 which passes through the polarization beam splitter 13 is emitted therefrom as a p polarized beam. The p polarized beam is rotated ninety degrees by the 1/2 wave plate 14. Thus, the prism 26 send an s polarized beam to the IMFOS 11 and the 1/2 wave plate 14 sends an s polarized beam to the IMFOS 11. The s polarized beam from the 1/2 wave plate 14, which passes through the IMFOS 11, is reflected by another prism 37 to a polarization beam splitter 18 which is operated in no-verse. The s polarized beam (which had been reflected by the prism 26) passes through the IMFOS 11 and is rotated ninety degrees by the I wave plate 19 into a p polarized beam The p polarized beam passes through the polarization beam splitter 18 and the s polarized beam from the prism 37 is reflected by the polarization beam splitter 18 (which operates in reverse) so that the output 21 contains both the p and the s mutually perpendicular beams.
Fig. 3 depicts a p polarization version of that described in Fig. 2. A collimated input beam 12, as before, is either unpolarized or contains mutually per pen-dicularly polarized beams. The input beam 12 is applied to a polarization beam splitter 13, as before. A p polar-ization portion of the beam passes directly from the I
polarization beam splitter 13 to an IMFOS 11, passing there through. The s polarized beam, reflected by the polarization beam splitter 13, passes through a 1/2 wave plate 34 which converts the s polarized beam into a second p polarized beam which, in turn, is reflected by a prism 36. The p polarized beam, reflected by the prism 36, passes through the IMFOS 11 and, then passes through a polarization beam splitter 38, which operates in reverse.
The p polarized beam from the polarization beam splitter 13, which passes through the IMFOS 11, is reflected by a prism 40, and passes through a 1/2 wave plate 39 to the polarization beam splitter 33 which operates in reverse.
The p polarized beam from the prism 40 is rotated ninety degrees by the 1/2 wave plate 39 to yield an s polarized beam. The s polarized beam from the 1/2 wave plate 39 is reflected by the polarization beam splitter 38 which operates in reverse to yield an output beam 41 which con-twins both the p and the s mutually perpendicular polarized teams.
Referring to Fig. 4, there is depicted, in plane view, an IMFOS 101 which is of general shape as that depicted in our cop ending application. The IMFOS 101 includes a first electro-optical crystal 102 and a second electro-optical 103 which are separated by a dielectric beam splitting coating 104. The first crystal 102, the second crystal 103, and the coating 104 are so oriented with portions of them juxtaposed so that light paths from one crystal can puss through the dielectric beam splitting coating 104 into the other crystal.
Means are provided for varying the index of rework-lion of one of the crystals 102 with respect to -that of the other crystal 103. Such means for varying the index ox retraction can include electrodes 106, 107 formed on oppo-site sides ox the crystal 103, and electrodes 108, 109 wormed on opposite sides of the crystal 102. The elect troves 106, 107, 108, 109 can each be formed by depositing ~23~8~
a layer 111 of chromium onto the respective crystals 102, 103 and, in turn, depositing individual layers of gold 112 onto the chromium layers 111. The chromium layers 111 adhere effectively to the electro-optical crystals 102, s 103 and the gold layers 112 adhere effectively to the chromium layers 111. As depicted in Fig. 3, the crystal-lo graphic axes of the two crystals 102 and 103 are oriented in opposite directions. The voltages applied to the respective crystals are such that the polarities are alike in the same direction. As depicted in Fig. 6, it is positive at the top for both crystals and negative (with respect to the top) at the bottom of the two cry-ifs In lieu thereof, though are not depicted in Fig. 6 but more fully described in the cop ending application, the two crystals can be oriented loath their crystallographic axes it the same direction but with the voltage polarities applied in opposite directions; that is, with the cry-telegraphic axes both directed upward one crystal Jan have a positive polarity at the top and negative at the bottom, while the other crystal can have a negative polar-fly at the top and. a positive polarity at the bottom.
An unpolarized beam of light 12, applied to the device depicted in Fig. 4, is applied to a polarization beam splitter 13~ A p polarized beam from the polarization beam splitter 13 continues there through and is rotated by 1/2 wave plate 14 to yield an s polarized beam 16.
The polarization beam splitter 13 also directs an s polarized beam 117 away therefrom toward a prism 118 which reflects the s polarized beam 117 in-to the first electron optical crystal 102. The s polarized beam 116, upon pass-in through the crystal 102, hits -the dielectric beam splitter 104 at a first spot 121. The s polarized beam 117 hits the polarized beam splitter 104 at a second spot 122. The beam 116, upon hitting the spot 121, is split into two parts: 50~ is reflected as a beam 216, while 50 passes through the beam splitter 104 as a beam 316 into :~223~
the crystal 103. In similar fashion, the beam 117, upon hitting the spot 122 of the beam splitter 104, splits into two parts: 50~ is reflected as a beam 217 while the remain-in 50~ passes through the beam splitter 104 as a beam 317, the beam 317 passing through the crystal 103. The beams 216, 217, which have been reflected by the beam splitter 104, remain within the crystal 102 and is reflected by one surface (a reflective surface) 123 thereof down onto a second pair ox spots 126, 127, respectively, so that the beam 216 can pass through the dielectric beam splitter 104 as a beam 416 or can be reflected as a buckwheat 516, the no-floated beam 516 being within the crystal 102, the beam 216 being within the crystal 103. In similar fashion, the beam ~17, which had been reflected by the surface 123, upon reaching the spot 127 of the beam splitter 104, passes there through as a beam 417 within the crystal 103 or is reflected by the beam splitter 104 as a beam 517 within the crystal 102.
The beam 416, which passes through the crystal 103, is reflected by a prism 131 to a polarization beam split-ton 132 that is operated in reverse. The beam 417, an s polarized beam, exits from the crystal 103 and is rotated ninety degrees by a 1/2 wave plate 133 to a p polarized beam. The emitting p polarized beam enters the polarize-lion beam splitter 132, which is operated in reverse spas to yield an output beam 134 which contains both p and g components.
In similar fashion, the beam 516, which exits from the crystal 102, is reflected by a prism 136 toward a Polaris I ration beam splitter 137 that is operated in reverse. Thea; polarized beam 517 from the crystal 102 is rotated ninety degrees by 1/2 wave plate 138 to yield a p polarized beam, which, in turn, passes through the polarization beam split-ton 137. Since the polarization beam splitter 137 also I emits the s polarized beam which had been reflected by the prism 136, the output beam 139 therefrom contains both p 23~8~
and s mutually perpendicularly polarized components of light, As described in our cop ending application, referenced hereinabove, the phase velocity for a beam ox light through one crystal can be changed with respect to that of another crystal by varying the index of refraction of one crystal with respect to the other. This is achieved by applying potentials ox appropriate polarities across the electron optical crystals so as to cause the phase velocity for one beam path through one crystal to be different from that of a beam path through the other crystal. pence, as depicted in Fig. 4, the entire crystal 102 can have its index of refraction varied independently of the entire crystal 103, and vice versa.
Referring to Fig. 5, there is depicted a device Siam far to that shown in Fig. 4 with several major changes.
The device shown in Fist 5 depicts a rectangular crystal version of an IMFO'; including a first crystal 501 and a second crystal, 502 adjacent to each other with a dielectric beam splitting coating 503 between their juxtaposed sun-faces. A first collimated input beam 504 is applied as in put A to the crystal 501. Optionally a second input beam 506 can be applied to the crystal 502. Two possible outputs can be achieved: output A can be obtained as an output beam 507, output B can be obtained as an output beam 505.
the input collimated beams 504, 506 are unpolarized or, optionally, are beams which are mutually perpendicu-laxly polarized. The input beams 504, 506 are applied to polarization beam splitters 507, 508, respectively. The beam splitter 507 permits a p polarized beam 510 to pass there through into the crystal 501. The polarization hem splitter 507 reflects a p polarized beam through a 1/2 wave plate 509 (changing it to an s polarized beam) to a prism 511 which reflects that s polariæecl beam 512 within I thy crystal 501.
In similar fashion, the optionally applied input beam 506 to the polarization beam splitter 508 passes through to the crystal 502 as an s polarized beam 513, a portion being reflected as a p polarized beam which enters a 1/2 wave plate 514 rotating it to an s polarized beam which is reflected by the prism 511 as an s polarized beam 516 which enters the crystal 502. The beams 510, 512 impinge upon the dielectric beam splitter 503 at spots 517, 518, respectively. The orientation of the components are such thaw beams 513, 516 impinge upon the spots 517, 518, respectively. The beams 510, 512, hitting the spots 517, 518, respectively, of the dielectric beam splitting coat-in 503~ pass directly through (at a 50% reduction the crystal 502 as beams 519, 521, respectively, and are no-floated by the 50~ beam splitter 503 (at a 50~ reduction) as beams 522, 523, respectively, within the first crystal 501. Similarly, the beams 513, 516, impinging upon the spots 517, 518, pass direct through (at a 50~ reduction) the dielectric beam splitting coating 503 as beams 522, 523, respectively, and are reflected (at 50% reduction) as beams 519, 521, respectively.
The beams 522, 523 are reflected at the surface 524 of the crystal 501 so that the beams 522, 523 impinge upon spots 526 ! 527 at the dielectric beam splitting coat-in 503. Likewise, the beams 519, 521, upon briny reflect-Ed at the surface 528 of the crystal 502, also impinge upon the spots 526, 527 of the dielectric beam splitter 503. The reflected portions of the beams 523, 524 from the dielectric beam splitter 503, and the transmitted portions of the beams 519, 521 within the crystal 501, appear as beams 529, 531, respectively. In similar Asian, the transmitted components of the beams 522, 523 and the reflected components of the beams 519, 521 within the crystal 502, appear as beams 532, 533, respectively.
The s polarized beam 531 passes through the dielectric beam splitter 534 (which is operated in reverse) as an s :~Z3~4 component of the output beam 505. The s polarized beam 529 is reflected by a prism 536 to a 1/2 wave plate 537 which rotates it into a p polarized beam which is reflected by the polarization beam splitter 534 so that the output beam 508 also contains a p component.
In similar fashion, the s polarized beam 533 passes through a polarization beam splitter 538 (which is operated in reverse) as an s polarized beam component of an output beam 507. The polarized beam 532 is reflected by the prism 536 and is rotated by a 1/2 wave plate 539 to a p polarized beam to the polarization beam splitter 538 Tao is operated in reverse) to reflect that p polarized berm as component of the output beam 507. The output beam 507 contains both the p and s components.
The beam 522, -us depicted in Fig. 5, avarices a path from the spot 517 (at the interface of the two cry-tats 501, 502) up to the top (as viewed in the drawing) surface 524 of the crystal 503 and down to the spot 526 at the interface of the two crystals 501, 502. Separately, Jo it is noted that within the same crystal 501, there is a team path 523 from the spot 518 at the interface of the two crystals 591, 502 to a top surface 504 and down to the spot 527 at the interface of the two crystals 501, 502..
The paths 522, 523 are separate and distinct from each other and cross at one point as depicted in the drawing but do not interfere thereat. Toe index of refraction of the electro-optical crystal 501 can be varied in known Ann ho varying the application ox an electrical potent trial across the crystal . To change the index of refract lion of each individual path, independent electrodes are placed across the different paths, as indicated in dotted outline The electrodes are both at the top and the both Tom of the crystal. The electrodes for the paths 522 include one set of electrodes AYE, 541B. The electrode AYE, 541B are coupled to each electrically, but need not I
be performed at a surface of the crystal. In similar fashion, electrodes encompassing the path 523 can include electrodes AYE, 542B deposited at the top and bottom of the crystals encompassing the path 523. The electrodes AYE and E are coupled together.
Electrodes AYE, 543B encompass hem paths 519 from the spot 517 to the surface S28 and to the spot 526, no-spectively. Similarly, electrodes AYE, 544B encompass the beam path 521 from the spot 518 to the surface 528 and to the spot 527, respectively.
Thus, when the polarization-insensitive optical switch and dual channel carrier multiplexer, in accordance with this invention, is utilized as a switch, the phase retardation of both hems (that is, the entering p polarized beam and the entering s polarized beam) is identical and a single set of electrodes is used, as depicted generally in Fig. JO When the invention is utilized as a multiplexer, each beam propagates between its own set of electrodes, as indicated in Fig. 5, and therefore can be modulated with different modulation sign nets. At each output port, as discussed hereinabove, there are two beams emitted, though not necessarily at the same time, and these two beams are combined utilizing a polarization beam splitter operated in reverse after one beam has past through a 1/2 wave plate. The output of the polarization beam splitter is a single light beam which can be coupled into a single fiber at each output port.
Various modifications can be performed without de-parting from the spirit and scope of this invention. For example, the two polarized beams, when modulated separately, need not be recombined into a single fiber. Two output focusing optics can direct each into separate output fibers.
I
POLARIZATION-INSENSITIVE OPTICAL MULTI-FLEXING APPARATUS
This application is a division of Canadian application 416,669-8 filed November 30,. 1982.
This invention relates to polarization-insensitive optical switch apparatus, polarization-insensitive optical multiplexing apparatus, and interferometric multimedia fiber optic apparatus in which the indices of refraction of various beam paths through portions thereof can be varied with respect to that of other portions.
Accordingly, it is a general object of this invention to provide new and improved apparatus of such character.
Polariza~ion-insensitive switching of multimedia fibers has been achieved by means of mechanical switches which move an input fiber into alignment with two output fibers, at two stable positions.
Electronic carrier multiplexing of two optical sign nets has been accomplished Usually, the multiplexing stage is performed electronically; the resulting signal.
modulates the current through a light source. The drive currents of two different light sources can be modulated, and the two signal carrying fibers can be combined into a single communication fiber by means of a fiber combiner.
Disadvantageously, mechanical switching is slow, is power consuming is usually operated at high voltages, is cumbersome, and is unreliable.
Disadvantageously, the multiplexing techniques (in which a single light source is modulated by the already tnultiplexed signal) requires very high linearity of the modulated source in order to prevent crosstalk. The light sources used in communication systetns have nonuniform nonlinear responses, sufficient to make this method inapplicable in many cases.
39~19L
The modulation of the drive currents of two different light sources, utilizing an optical combiner, disadvantageously has at least a 50%, or 3 dub, loss due to the principle of combination of two light beams. Typical losses described in the literature are approximately 4 dub.
Devices in accordance with this invention are of a low-loss nature due to the collimating optics and the large aperture of an interferometric multimedia fiber optic switch and modulator, such as that described in our cop ending apply-cation Serial No. 413,612-8 filed October 18, 1982 and entitled "Interferometric Multimedia Fiber Optic Switch and Modulator". Its polarization-insensitivity facilitates the apparatus for use with unpolarized light sources, such as LED's. In a multiplexing configuration, the light source linearity problem and the combiner losses are eliminated.
Its complementary output provides a second channel (or a monk storing signal) without the interruption of the light beam.
According to one aspect of the invention, there is provided polarization-insensitive optical multiplexing appear-anus for independently modulating perpendicularly polarized components of a collimated input beam comprising a first polarization beam splitter for receiving and splitting said collimated input beam into two perpendicularly polarized beams; a first polarization rotating means for rotating a first of said two perpendicularly polarized beams by ninety degrees so that the rotated polarized beam and a second of said perpendicularly polarized beam are each polarized in the same direction; means for reflecting one of said first and said second beams so that the reflected beam and the other of said first and said second beams traverse parallel paths;
a first electro-optical crystal having a first surface adapt-Ed to receive said reflected one beam and said other beam for -transmission through said first crystal, a second surface adapted to receive such transmitted beams from said firs-t surface of said first crystal at a first pair of spots, a fist reflective surface oriented to receive light beams from said first pair of spots of said second surface of said first crystal and to reflect such light beams, a third surface I
adapted to receive such reflected light beams from said first reflective surface of said first crystal upon a second pair of spots, and a fourth surface adapted to externally pass light impinged thereupon from said second pair of spots of said first crystal; a second electro-optical crystal having a first surface, a second surface oriented to receive trays-milted light from said second surface of said first crystal at a first pair of spots, a first reflective surface oriented to receive light from said first pair of spots of said second surface of said second crystal and to reflect such received light, a third surface adapted to receive such reflected light from said first reflective surface of said second crystal upon a second pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said second pair of spots of said second crystal; a dielectric beam splitting coating, said first crystal, said second crystal, and said coating being so oriented that said first pair of spots of said second surface of said first cry-slat, and said first pair of spots of said second surface of said second crystal are substantially juxtaposed with a first portion of said coating oriented there between, and said second pair of spots of said third surface of said first crystal, and said second pair of spots of said third surface of said second crystal are substantially juxtaposed with a second portion of said coating oriented there between, whereby said one beam and said other beam traverse a first path and a second path, respectively, within said first crystal, and said one beam and said other beam traverse a third path and a fourth path, respectively, within said second crystal; first means for varying the index of refraction of said first path within said first crystal with respect to the index of refry-cation of said third path within said second crystal; second means for varying the index of refraction of said second path within said first crystal with respect to the index of refract I lion of said fourth path within said second crystal, said second index of refraction varying means being independent of said frost index of refraction varying means; means associated with said fourth surface of said first crystal for reflecting one light beam from one spot of said second pair of spots of said first crystal; a second polarization rotating means for rotating a first of said light beams from said fourth surface of said first crystal by ninety degrees so that the rotated first light beam and the unrotated second light beam are perpendicularly polarized with respect to each other; and a second polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said first crystal and to provide a first single light beam which can be coupled to a first optical output means.
According to another aspect of the invention there is provided polarization-insensitive optical multiplexing apparatus for independently modulating perpendicularly polar-iced components of a pair of collimated input beams comprise in a first polarization beam splitter for receiving and splitting one of said collimated input beams into two per pen-dicularly polarized beams; a first polarization rotating means to rotating a first of said two perpendicularly polar-iced beams by ninety degrees so that the rotated polarized beam and second of said perpendicularly polarized beams are each polarized in the same direction; first means for reflect tying one of said first and said second beams so that the reflected beam and the other of said first and said second beams traverse parallel paths; a first electro-optical cry-slat having a first surface adapted to receive said reflected one beam and said other beam for transmission through said first crystal, a second surface adapted to receive such trays-milted beams from said first surface of said first crystal at a first pair of spots, a first reflective surface orient-Ed to receive light beams from said first pair of spots offside second surface of said first crystal and to reflect such light beams, a third surface adapted to receive such reflected light beams from said first reflective surface of said first crystal upon a second pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said second pair of spots of said first cry-slat, whereby said one beam and said other beam traverse a first path and a second path, respectively, within said first crystal; second means associated with said fourth sun-I
face of said first crystal for reflecting one light beam from one spot of said second pair of spouts of said first crystal; a second polarization rotating means for rotating a first of said light beams from said fourth surface of said first crystal by ninety degrees so that the rotated first light beam and the unrotated second light beam are per pen-dicularly polarized with respect to each other; a second polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said first crystal and to receive a first single light beam which can be coupled to a first optical output means; a third polarization beam splitter for receiving and splitting the other of said collimated input beams into two perpendicularly polarized beams; a third polarization rotating means for rotating a first of said two perpendicularly polarized beams from said third polarization beam splitter by ninety degrees so that the rotated beam and a second of said perpendicularly polarized beams from said third polarization beam splitter are each polarized in the same direction; third means for reflecting one of said first and said second beams from said third polarization rotating means so that the reflected beam and the other of said first and said second beams from said third polarization rotating means traverse parallel paths;
a second electro-optical crystal having a first surface adapted to receive one beam reflected by said third means and said other beam from said third polarization rotating means for transmission through said second crystal, a second surface adapted to receive such transmitted beams from said first surface of said second crystal at a third pair of spots, a first reflective surface oriented to receive light beams from said third pair of spots of said second surface of said second crystal and to reflect such light beams, a third sun-face adapted to receive such reflected light beams from said first reflective surface of said second crystal upon a fourth pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said fourth pair of spots of said second crystal, whereby said one beam reflected by said third means and said other beam from said third pox larization rotating means traverse a third path and a fourth path, respectively, within said second crystal, a dielectric beam splitting coating, said first crystal, said second cry-slat, and said coating being so oriented that said first pair of spots of said second surface of said first crystal, and said third pair of spots of said second crystal are sub-staunchly juxtaposed with a first portion of said coating oriented there between, and said second pair of spots of said third surface of said first crystal, and said fourth pair of spots of said third surface of said second crystal are sub-staunchly juxtaposed with a second portion of said coating oriented there between; first means for varying the index of refraction of said first path within said first crystal with respect to the index of refraction of said third path within said second crystal; second means for varying the index of refraction of said second path within said foist crystal with respect to the index of refraction of said fourth path within said second crystal; fourth means associated with said fourth surface of said second crystal for reflecting one light beam from one spot of said fourth pair of spots of said second crystal; a fourth polarization rotating means for rotating a first of said light beams from said fourth surface of said second crystal by ninety degrees so that the rotated first light beam from said second crystal and the I unrotated second light beam from the second crystal are perpendicularly polarized with respect to each other; and a fourth polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said second crystal and to provide a second single out-I put light beam which can be coupled to a second optical output means.
According to another aspect of the invention there is provided in combination, a first electro-optical crystal, a second electro-optical crystal, a dielectric beam splitting coating affixed to portions of said crystals with coated portions of such crystals being juxtaposed, first means for varying the index of refraction of one beam path through one of said crystals with respect to the index of refraction of one beam path through the other of said crystals, and I
second means for varying the index of refraction of another beam path through said one of said crystals with respect to the index of refraction of another beam path through said other of said crystals, said second means being independent from said first means.
Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic diagram of one embodiment of this invention;
FIG. 2 is a modular version of the embodiment shown in Fig. l;
FIG. 3 is a "p" polarization version of the modulator embodiment depicted in Fig. 2;
FIG. 4 is a plan view of another embodiment of the invention utilizing an IMFOS, as described in greater detail hereinafter, the dotted lines illustrating an out-line of electrodes applied to such IMFOS;
FIG. 5 is a plan view of still another embodiment of the invention, utilizing a modified IMFOS which uses rectangular shape crystals with individual electrodes being depicted in dotted line format; and FIG. 6 is a cross sectional view of the embodiment shown in Fig. 4, taken along the line 6-6 thereof.
A polarization-insensitive optical switch and dual channel carrier multiplexer, in accordance with this in-venkion, utilizes the interferometric multimedia fiber optic switch (IMFOS) described in a cop ending patent apply-cation by the applicants hereof, entitled "Interferometric Multimedia Fiber Optic Switch and Modulator", SUN. 413,612 filed October 18, 1982. Broadly, an IMFOS, as described in the above-identified application, includes a dielectric beam splitting coating affixed to portions of two electro-optical crystals with coated portions of the crystals being juxtaposed. The index of refraction of one of the crystals is varied with respect to that of the other.
Referring to Fig. 1, an IAMB 11 is represented schematically as a rectangle. The IMFOS 11 is similar to that described in the cop ending application in which a beam path is modulated in accordance with an electrical field applied thereto. By the application of particular fields, a light beam is switched on and off ox is modulated at varying intensities. The IMFOS 11, as dejected in jig. 1 is polarization sensitive, and light of one polarity only is normally handled there through. In the embodiment depicted in Fig. 1, light, which is s plane polarized, is conveniently handled.
A collimated input beam 12 either can be unpolarized or can contain arbitrarily polarized light beams there-within. The input beam 12 is split into two perpendicu-laxly polarized beams, a p beam and an s beam, by a polarization beam splitter 13. The polarization beam splitter 13 can be constructed of birefrigent prisms, such as, or example, Russian prisms, or multi layer interference 20 polarizers.
The p polarized beam passes through a 1/2 wave plate 14 which converts it into an s polarized beam. The s polarized beam, split by the polarization beam splitter 13, is reflected by a mirror 16 so that it, and the s polarized I beam emit-ted from the 1/2 wave plate 14, traverse parallel paths and enter the IMFOS 11.
The two s polarized beams that enter the IMFOS 11 undergo an interference and intensity redistribution as described more fully in the above-identified pending Jo application.
As depicted in Fig. 1, the s polarized beam (which exited from the 1/2 wave plate 14 through the IMFOS 11) is reflected by a mirror 17 to another polarization beam splitter 18 which is operated in reverse. The s polarized I beam, which had been reflected by the mirror 16 and past through the IMFOS 11, is rotated by a 1/2 wave plate 19 ~22~
-- g into a p polarized beam. The p polarized beam from the 1/2 wave plate 19 and the s polarized beam from the mirror 17 are recombined, by the polarization beam splitter 18 (which operates in reverse) to provide an output signal or output beam 21 which contains mutually perpendicular polarized beams p and s.
A modulator version of the embodiment shown in Fig. 1, is depicted in Fig. 2. A collimated input beam 12 contains either mutually perpendicularly polarized beams p and s, or it can contain unpolarized light. The beam 12 is applied through a polarization beam splitter 13, as before, which reflects a portion of the beam to a prism 26 which reflects the s polarized portion thereof toward the IMFOS
11. That potion of the beam 12 which passes through the polarization beam splitter 13 is emitted therefrom as a p polarized beam. The p polarized beam is rotated ninety degrees by the 1/2 wave plate 14. Thus, the prism 26 send an s polarized beam to the IMFOS 11 and the 1/2 wave plate 14 sends an s polarized beam to the IMFOS 11. The s polarized beam from the 1/2 wave plate 14, which passes through the IMFOS 11, is reflected by another prism 37 to a polarization beam splitter 18 which is operated in no-verse. The s polarized beam (which had been reflected by the prism 26) passes through the IMFOS 11 and is rotated ninety degrees by the I wave plate 19 into a p polarized beam The p polarized beam passes through the polarization beam splitter 18 and the s polarized beam from the prism 37 is reflected by the polarization beam splitter 18 (which operates in reverse) so that the output 21 contains both the p and the s mutually perpendicular beams.
Fig. 3 depicts a p polarization version of that described in Fig. 2. A collimated input beam 12, as before, is either unpolarized or contains mutually per pen-dicularly polarized beams. The input beam 12 is applied to a polarization beam splitter 13, as before. A p polar-ization portion of the beam passes directly from the I
polarization beam splitter 13 to an IMFOS 11, passing there through. The s polarized beam, reflected by the polarization beam splitter 13, passes through a 1/2 wave plate 34 which converts the s polarized beam into a second p polarized beam which, in turn, is reflected by a prism 36. The p polarized beam, reflected by the prism 36, passes through the IMFOS 11 and, then passes through a polarization beam splitter 38, which operates in reverse.
The p polarized beam from the polarization beam splitter 13, which passes through the IMFOS 11, is reflected by a prism 40, and passes through a 1/2 wave plate 39 to the polarization beam splitter 33 which operates in reverse.
The p polarized beam from the prism 40 is rotated ninety degrees by the 1/2 wave plate 39 to yield an s polarized beam. The s polarized beam from the 1/2 wave plate 39 is reflected by the polarization beam splitter 38 which operates in reverse to yield an output beam 41 which con-twins both the p and the s mutually perpendicular polarized teams.
Referring to Fig. 4, there is depicted, in plane view, an IMFOS 101 which is of general shape as that depicted in our cop ending application. The IMFOS 101 includes a first electro-optical crystal 102 and a second electro-optical 103 which are separated by a dielectric beam splitting coating 104. The first crystal 102, the second crystal 103, and the coating 104 are so oriented with portions of them juxtaposed so that light paths from one crystal can puss through the dielectric beam splitting coating 104 into the other crystal.
Means are provided for varying the index of rework-lion of one of the crystals 102 with respect to -that of the other crystal 103. Such means for varying the index ox retraction can include electrodes 106, 107 formed on oppo-site sides ox the crystal 103, and electrodes 108, 109 wormed on opposite sides of the crystal 102. The elect troves 106, 107, 108, 109 can each be formed by depositing ~23~8~
a layer 111 of chromium onto the respective crystals 102, 103 and, in turn, depositing individual layers of gold 112 onto the chromium layers 111. The chromium layers 111 adhere effectively to the electro-optical crystals 102, s 103 and the gold layers 112 adhere effectively to the chromium layers 111. As depicted in Fig. 3, the crystal-lo graphic axes of the two crystals 102 and 103 are oriented in opposite directions. The voltages applied to the respective crystals are such that the polarities are alike in the same direction. As depicted in Fig. 6, it is positive at the top for both crystals and negative (with respect to the top) at the bottom of the two cry-ifs In lieu thereof, though are not depicted in Fig. 6 but more fully described in the cop ending application, the two crystals can be oriented loath their crystallographic axes it the same direction but with the voltage polarities applied in opposite directions; that is, with the cry-telegraphic axes both directed upward one crystal Jan have a positive polarity at the top and negative at the bottom, while the other crystal can have a negative polar-fly at the top and. a positive polarity at the bottom.
An unpolarized beam of light 12, applied to the device depicted in Fig. 4, is applied to a polarization beam splitter 13~ A p polarized beam from the polarization beam splitter 13 continues there through and is rotated by 1/2 wave plate 14 to yield an s polarized beam 16.
The polarization beam splitter 13 also directs an s polarized beam 117 away therefrom toward a prism 118 which reflects the s polarized beam 117 in-to the first electron optical crystal 102. The s polarized beam 116, upon pass-in through the crystal 102, hits -the dielectric beam splitter 104 at a first spot 121. The s polarized beam 117 hits the polarized beam splitter 104 at a second spot 122. The beam 116, upon hitting the spot 121, is split into two parts: 50~ is reflected as a beam 216, while 50 passes through the beam splitter 104 as a beam 316 into :~223~
the crystal 103. In similar fashion, the beam 117, upon hitting the spot 122 of the beam splitter 104, splits into two parts: 50~ is reflected as a beam 217 while the remain-in 50~ passes through the beam splitter 104 as a beam 317, the beam 317 passing through the crystal 103. The beams 216, 217, which have been reflected by the beam splitter 104, remain within the crystal 102 and is reflected by one surface (a reflective surface) 123 thereof down onto a second pair ox spots 126, 127, respectively, so that the beam 216 can pass through the dielectric beam splitter 104 as a beam 416 or can be reflected as a buckwheat 516, the no-floated beam 516 being within the crystal 102, the beam 216 being within the crystal 103. In similar fashion, the beam ~17, which had been reflected by the surface 123, upon reaching the spot 127 of the beam splitter 104, passes there through as a beam 417 within the crystal 103 or is reflected by the beam splitter 104 as a beam 517 within the crystal 102.
The beam 416, which passes through the crystal 103, is reflected by a prism 131 to a polarization beam split-ton 132 that is operated in reverse. The beam 417, an s polarized beam, exits from the crystal 103 and is rotated ninety degrees by a 1/2 wave plate 133 to a p polarized beam. The emitting p polarized beam enters the polarize-lion beam splitter 132, which is operated in reverse spas to yield an output beam 134 which contains both p and g components.
In similar fashion, the beam 516, which exits from the crystal 102, is reflected by a prism 136 toward a Polaris I ration beam splitter 137 that is operated in reverse. Thea; polarized beam 517 from the crystal 102 is rotated ninety degrees by 1/2 wave plate 138 to yield a p polarized beam, which, in turn, passes through the polarization beam split-ton 137. Since the polarization beam splitter 137 also I emits the s polarized beam which had been reflected by the prism 136, the output beam 139 therefrom contains both p 23~8~
and s mutually perpendicularly polarized components of light, As described in our cop ending application, referenced hereinabove, the phase velocity for a beam ox light through one crystal can be changed with respect to that of another crystal by varying the index of refraction of one crystal with respect to the other. This is achieved by applying potentials ox appropriate polarities across the electron optical crystals so as to cause the phase velocity for one beam path through one crystal to be different from that of a beam path through the other crystal. pence, as depicted in Fig. 4, the entire crystal 102 can have its index of refraction varied independently of the entire crystal 103, and vice versa.
Referring to Fig. 5, there is depicted a device Siam far to that shown in Fig. 4 with several major changes.
The device shown in Fist 5 depicts a rectangular crystal version of an IMFO'; including a first crystal 501 and a second crystal, 502 adjacent to each other with a dielectric beam splitting coating 503 between their juxtaposed sun-faces. A first collimated input beam 504 is applied as in put A to the crystal 501. Optionally a second input beam 506 can be applied to the crystal 502. Two possible outputs can be achieved: output A can be obtained as an output beam 507, output B can be obtained as an output beam 505.
the input collimated beams 504, 506 are unpolarized or, optionally, are beams which are mutually perpendicu-laxly polarized. The input beams 504, 506 are applied to polarization beam splitters 507, 508, respectively. The beam splitter 507 permits a p polarized beam 510 to pass there through into the crystal 501. The polarization hem splitter 507 reflects a p polarized beam through a 1/2 wave plate 509 (changing it to an s polarized beam) to a prism 511 which reflects that s polariæecl beam 512 within I thy crystal 501.
In similar fashion, the optionally applied input beam 506 to the polarization beam splitter 508 passes through to the crystal 502 as an s polarized beam 513, a portion being reflected as a p polarized beam which enters a 1/2 wave plate 514 rotating it to an s polarized beam which is reflected by the prism 511 as an s polarized beam 516 which enters the crystal 502. The beams 510, 512 impinge upon the dielectric beam splitter 503 at spots 517, 518, respectively. The orientation of the components are such thaw beams 513, 516 impinge upon the spots 517, 518, respectively. The beams 510, 512, hitting the spots 517, 518, respectively, of the dielectric beam splitting coat-in 503~ pass directly through (at a 50% reduction the crystal 502 as beams 519, 521, respectively, and are no-floated by the 50~ beam splitter 503 (at a 50~ reduction) as beams 522, 523, respectively, within the first crystal 501. Similarly, the beams 513, 516, impinging upon the spots 517, 518, pass direct through (at a 50~ reduction) the dielectric beam splitting coating 503 as beams 522, 523, respectively, and are reflected (at 50% reduction) as beams 519, 521, respectively.
The beams 522, 523 are reflected at the surface 524 of the crystal 501 so that the beams 522, 523 impinge upon spots 526 ! 527 at the dielectric beam splitting coat-in 503. Likewise, the beams 519, 521, upon briny reflect-Ed at the surface 528 of the crystal 502, also impinge upon the spots 526, 527 of the dielectric beam splitter 503. The reflected portions of the beams 523, 524 from the dielectric beam splitter 503, and the transmitted portions of the beams 519, 521 within the crystal 501, appear as beams 529, 531, respectively. In similar Asian, the transmitted components of the beams 522, 523 and the reflected components of the beams 519, 521 within the crystal 502, appear as beams 532, 533, respectively.
The s polarized beam 531 passes through the dielectric beam splitter 534 (which is operated in reverse) as an s :~Z3~4 component of the output beam 505. The s polarized beam 529 is reflected by a prism 536 to a 1/2 wave plate 537 which rotates it into a p polarized beam which is reflected by the polarization beam splitter 534 so that the output beam 508 also contains a p component.
In similar fashion, the s polarized beam 533 passes through a polarization beam splitter 538 (which is operated in reverse) as an s polarized beam component of an output beam 507. The polarized beam 532 is reflected by the prism 536 and is rotated by a 1/2 wave plate 539 to a p polarized beam to the polarization beam splitter 538 Tao is operated in reverse) to reflect that p polarized berm as component of the output beam 507. The output beam 507 contains both the p and s components.
The beam 522, -us depicted in Fig. 5, avarices a path from the spot 517 (at the interface of the two cry-tats 501, 502) up to the top (as viewed in the drawing) surface 524 of the crystal 503 and down to the spot 526 at the interface of the two crystals 501, 502. Separately, Jo it is noted that within the same crystal 501, there is a team path 523 from the spot 518 at the interface of the two crystals 591, 502 to a top surface 504 and down to the spot 527 at the interface of the two crystals 501, 502..
The paths 522, 523 are separate and distinct from each other and cross at one point as depicted in the drawing but do not interfere thereat. Toe index of refraction of the electro-optical crystal 501 can be varied in known Ann ho varying the application ox an electrical potent trial across the crystal . To change the index of refract lion of each individual path, independent electrodes are placed across the different paths, as indicated in dotted outline The electrodes are both at the top and the both Tom of the crystal. The electrodes for the paths 522 include one set of electrodes AYE, 541B. The electrode AYE, 541B are coupled to each electrically, but need not I
be performed at a surface of the crystal. In similar fashion, electrodes encompassing the path 523 can include electrodes AYE, 542B deposited at the top and bottom of the crystals encompassing the path 523. The electrodes AYE and E are coupled together.
Electrodes AYE, 543B encompass hem paths 519 from the spot 517 to the surface S28 and to the spot 526, no-spectively. Similarly, electrodes AYE, 544B encompass the beam path 521 from the spot 518 to the surface 528 and to the spot 527, respectively.
Thus, when the polarization-insensitive optical switch and dual channel carrier multiplexer, in accordance with this invention, is utilized as a switch, the phase retardation of both hems (that is, the entering p polarized beam and the entering s polarized beam) is identical and a single set of electrodes is used, as depicted generally in Fig. JO When the invention is utilized as a multiplexer, each beam propagates between its own set of electrodes, as indicated in Fig. 5, and therefore can be modulated with different modulation sign nets. At each output port, as discussed hereinabove, there are two beams emitted, though not necessarily at the same time, and these two beams are combined utilizing a polarization beam splitter operated in reverse after one beam has past through a 1/2 wave plate. The output of the polarization beam splitter is a single light beam which can be coupled into a single fiber at each output port.
Various modifications can be performed without de-parting from the spirit and scope of this invention. For example, the two polarized beams, when modulated separately, need not be recombined into a single fiber. Two output focusing optics can direct each into separate output fibers.
Claims (6)
1. Polarization-insensitive optical multiplexing ap-paratus for independently modulating perpendicularly polarized components of a collimated input beam comprising a first polarization beam splitter for receiving and splitting said collimated input beam into two perpendicularly polarized beams;
a first polarization rotating means for rotating a first of said two perpendicularly polarized beams by ninety degrees so that the rotated polarized beam and a second of said perpendicularly polarized beam are each polarized in the same direction;
means for reflecting one of said first and said second beams so that the reflected beam and the other of said first and said second beams traverse parallel paths;
a first electro-optical crystal having a first surface adapted to receive said reflected one beam and said other beam for transmission through said first crystal, a second surface adapted to receive such transmitted beams from said first surface of said first crystal at a first pair of spots, a first reflective surface oriented to receive light beams from said first pair of spots of said second surface of said first crystal and to reflect such light beams, a third surface adapted to receive such reflected light beams from said first reflective surface of said first crystal upon a second pair of spots, and a fourth surface adapted to externally pass light im-pinged thereupon from said second pair of spots of said first crystal;
a second electro-optical crystal having a first surface, a second surface oriented to receive transmitted light from said second surface of said first crystal at a first pair of spots, a first reflective surface oriented to receive light from said first pair of spots of said second surface of said second crystal and to reflect such received light, a third surface adapted to receive such reflected light from said first reflective surface of said second crystal upon a second pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said second pair of spots of said second crystal;
a dielectric beam splitting coating, said first crystal, said second crystal, and said coating being so oriented that said first pair of spots of said second surface of said first crystal, and said first pair of spots of said second surface of said second crystal are substantially juxtaposed with a first portion of said coating oriented there-between, and said second pair of spots of said third surface of said first crystal, and said second pair of spots of said third surface of said second crystal are substantially juxta-posed with a second portion of said coating oriented there-between, whereby said one beam and said other beam traverse a first path and a second path, respectively, within said first crystal, and said one beam and said other beam traverse a third path and a fourth path, respectively, within said second crystal;
first means for varying the index of refraction of said first path within said first crystal with respect to the index of refraction of said third path within said second crystal;
second means for varying the index of refraction of said second path within said first crystal with respect to the index of refraction of said fourth path within said second crystal, said second index of refraction varying means being independent of said first index of refraction varying means;
means associated with said fourth surface of said first crystal for reflecting one light beam from one spot of said second pair of spots of said first crystal;
a second polarization rotating means for rotating a first of said light beams from said fourth surface of said first crystal by ninety degrees so that the rotated first light beam and the unrotated second light beam are perpendi-cularly polarized with respect to each other; and a second polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said first crystal and to provide a first single light beam which can be coupled to a first optical output means.
a first polarization rotating means for rotating a first of said two perpendicularly polarized beams by ninety degrees so that the rotated polarized beam and a second of said perpendicularly polarized beam are each polarized in the same direction;
means for reflecting one of said first and said second beams so that the reflected beam and the other of said first and said second beams traverse parallel paths;
a first electro-optical crystal having a first surface adapted to receive said reflected one beam and said other beam for transmission through said first crystal, a second surface adapted to receive such transmitted beams from said first surface of said first crystal at a first pair of spots, a first reflective surface oriented to receive light beams from said first pair of spots of said second surface of said first crystal and to reflect such light beams, a third surface adapted to receive such reflected light beams from said first reflective surface of said first crystal upon a second pair of spots, and a fourth surface adapted to externally pass light im-pinged thereupon from said second pair of spots of said first crystal;
a second electro-optical crystal having a first surface, a second surface oriented to receive transmitted light from said second surface of said first crystal at a first pair of spots, a first reflective surface oriented to receive light from said first pair of spots of said second surface of said second crystal and to reflect such received light, a third surface adapted to receive such reflected light from said first reflective surface of said second crystal upon a second pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said second pair of spots of said second crystal;
a dielectric beam splitting coating, said first crystal, said second crystal, and said coating being so oriented that said first pair of spots of said second surface of said first crystal, and said first pair of spots of said second surface of said second crystal are substantially juxtaposed with a first portion of said coating oriented there-between, and said second pair of spots of said third surface of said first crystal, and said second pair of spots of said third surface of said second crystal are substantially juxta-posed with a second portion of said coating oriented there-between, whereby said one beam and said other beam traverse a first path and a second path, respectively, within said first crystal, and said one beam and said other beam traverse a third path and a fourth path, respectively, within said second crystal;
first means for varying the index of refraction of said first path within said first crystal with respect to the index of refraction of said third path within said second crystal;
second means for varying the index of refraction of said second path within said first crystal with respect to the index of refraction of said fourth path within said second crystal, said second index of refraction varying means being independent of said first index of refraction varying means;
means associated with said fourth surface of said first crystal for reflecting one light beam from one spot of said second pair of spots of said first crystal;
a second polarization rotating means for rotating a first of said light beams from said fourth surface of said first crystal by ninety degrees so that the rotated first light beam and the unrotated second light beam are perpendi-cularly polarized with respect to each other; and a second polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said first crystal and to provide a first single light beam which can be coupled to a first optical output means.
2. Apparatus as recited in claim 1 further compris-ing means associated with said fourth surface of said second crystal for reflecting one light beam from one spot of said second pair of spots of said second crystal;
a third polarization rotating means for rotating a first of said light beams from said fourth surface of said second crystal by ninety degrees so that the rotated first light beam and the unrotated second beam, from said second crystal, are perpendicularly polarized with respect to each other; and a third polarization beam splitter, operated in re-verse, coupled to receive the perpendicularly polarized output beams from said second crystal, and to provide a second single light beam which can be coupled to a second optical output means.
a third polarization rotating means for rotating a first of said light beams from said fourth surface of said second crystal by ninety degrees so that the rotated first light beam and the unrotated second beam, from said second crystal, are perpendicularly polarized with respect to each other; and a third polarization beam splitter, operated in re-verse, coupled to receive the perpendicularly polarized output beams from said second crystal, and to provide a second single light beam which can be coupled to a second optical output means.
3. Polarization-insensitive optical multiplexing apparatus for independently modulating perpendicularly pol-arized components of a pair of collimated input beams compri-sing a first polarization beam splitter for receiving and splitting one of said collimated input beams into two per-pendicularly polarized beams;
a first polarization rotating means to rotating a first of said two perpendicularly polarized beams by ninety degrees so that the rotated polarized beam and second of said perpendicularly polarized beams are each polarized in the same direction;
first means for reflecting one of said first and said second beams so that the reflected beam and the other of said first and said second beams traverse parallel paths;
a first electro-optical crystal having a first surface adapted to receive said reflected one beam and said other beam for transmission through said first crystal, a second surface adapted to receive such transmitted beams from said first surface of said first crystal at a first pair of spots, a first reflective surface oriented to receive light beams from said first pair of spots of said second surface of said first crystal and to reflect such light beams, a third surface adapted to receive such reflected light beams from said first reflective surface of said first crystal upon a second pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said second pair of spots of said first crystal, whereby said one beam and said other beam traverse a first path and a second path, respectively, within said first crystal;
second means associated with said fourth surface of said first crystal for reflecting one light beam from one spot of said second pair of spots of said first crystal;
a second polarization rotating means for rotating a first of said light beams from said fourth surface of said first crystal by ninety degrees so that the rotated first light beam and the unrotated second light beam are perpendi-cularly polarized with respect to each other;
a second polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said first crystal and to receive a first single light beam which can be coupled to a first optical output means;
a third polarization beam splitter for receiving and splitting the other of said collimated input beams into two perpendicularly polarized beams;
a third polarization rotating means for rotating a first of said two perpendicularly polarized beams from said third polarization beam splitter by ninety degrees so that the rotated beam and a second of said perpendicularly polarized beams from said third polarization beam splitter are each polarized in the same direction;
third means for reflecting one of said first and said second beams from said third polarization rotating means so that the reflected beam and the other of said first and said second beams from said third polarization rotating means traverse parallel paths;
a second electro-optical crystal having a first surface adapted to receive one beam reflec-ted by said third means and said other beam from said third polarization rotating means for transmission through said second crystal, a second surface adapted to receive such trans-mitted beams from said first surface of said second crystal at a third pair of spots, a first reflective surface oriented to receive light beams from said third pair of spots of said second surface of said second crystal and to reflect such light beams, a third surface adapted to receive such reflected light beams from said first reflective surface of said second crystal upon a fourth pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said fourth pair of spots of said second crystal, whereby said one beam reflected by said third means and said other beam from said third polariza-tion rotating means traverse a third path and a fourth path, respectively, within said second crys-tal;
a dielectric beam splitting coating, said first crystal, said second crystal, and said coating being so oriented that said first pair of spots of said second surface of said first crystal, and said third pair of spots of said second crystal are substantially juxtaposed with a first portion of said coating oriented there-between, and said second pair of spots of said third surface of said first crystal, and said fourth pair of spots of said third surface of said second crystal are sub-stantially juxtaposed with a second portion of said coating oriented therebetween;
first means for varying the index of refraction of said first path within said first crystal with respect to the index of refraction of said third path within said second crystal;
second means for varying the index of refraction of said second path within said first crystal with respect to the index of refraction of said fourth path within said second crystal;
fourth means associated with said fourth surface of said second crystal for reflecting one light beam from one spot of said fourth pair of spots of said second crystal;
a fourth polarization rotating means for rotating a first of said light beams from said fourth surface of said second crystal by ninety degrees so that the rotated first light beam from said second crystal and the unrotated second light beam from the second crystal are perpendicular-ly polarized with respect to each other; and a fourth polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said second crystal and to provide a second single output light beam which can be coupled to a second optical output means.
a first polarization rotating means to rotating a first of said two perpendicularly polarized beams by ninety degrees so that the rotated polarized beam and second of said perpendicularly polarized beams are each polarized in the same direction;
first means for reflecting one of said first and said second beams so that the reflected beam and the other of said first and said second beams traverse parallel paths;
a first electro-optical crystal having a first surface adapted to receive said reflected one beam and said other beam for transmission through said first crystal, a second surface adapted to receive such transmitted beams from said first surface of said first crystal at a first pair of spots, a first reflective surface oriented to receive light beams from said first pair of spots of said second surface of said first crystal and to reflect such light beams, a third surface adapted to receive such reflected light beams from said first reflective surface of said first crystal upon a second pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said second pair of spots of said first crystal, whereby said one beam and said other beam traverse a first path and a second path, respectively, within said first crystal;
second means associated with said fourth surface of said first crystal for reflecting one light beam from one spot of said second pair of spots of said first crystal;
a second polarization rotating means for rotating a first of said light beams from said fourth surface of said first crystal by ninety degrees so that the rotated first light beam and the unrotated second light beam are perpendi-cularly polarized with respect to each other;
a second polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said first crystal and to receive a first single light beam which can be coupled to a first optical output means;
a third polarization beam splitter for receiving and splitting the other of said collimated input beams into two perpendicularly polarized beams;
a third polarization rotating means for rotating a first of said two perpendicularly polarized beams from said third polarization beam splitter by ninety degrees so that the rotated beam and a second of said perpendicularly polarized beams from said third polarization beam splitter are each polarized in the same direction;
third means for reflecting one of said first and said second beams from said third polarization rotating means so that the reflected beam and the other of said first and said second beams from said third polarization rotating means traverse parallel paths;
a second electro-optical crystal having a first surface adapted to receive one beam reflec-ted by said third means and said other beam from said third polarization rotating means for transmission through said second crystal, a second surface adapted to receive such trans-mitted beams from said first surface of said second crystal at a third pair of spots, a first reflective surface oriented to receive light beams from said third pair of spots of said second surface of said second crystal and to reflect such light beams, a third surface adapted to receive such reflected light beams from said first reflective surface of said second crystal upon a fourth pair of spots, and a fourth surface adapted to externally pass light beams impinged thereupon from said fourth pair of spots of said second crystal, whereby said one beam reflected by said third means and said other beam from said third polariza-tion rotating means traverse a third path and a fourth path, respectively, within said second crys-tal;
a dielectric beam splitting coating, said first crystal, said second crystal, and said coating being so oriented that said first pair of spots of said second surface of said first crystal, and said third pair of spots of said second crystal are substantially juxtaposed with a first portion of said coating oriented there-between, and said second pair of spots of said third surface of said first crystal, and said fourth pair of spots of said third surface of said second crystal are sub-stantially juxtaposed with a second portion of said coating oriented therebetween;
first means for varying the index of refraction of said first path within said first crystal with respect to the index of refraction of said third path within said second crystal;
second means for varying the index of refraction of said second path within said first crystal with respect to the index of refraction of said fourth path within said second crystal;
fourth means associated with said fourth surface of said second crystal for reflecting one light beam from one spot of said fourth pair of spots of said second crystal;
a fourth polarization rotating means for rotating a first of said light beams from said fourth surface of said second crystal by ninety degrees so that the rotated first light beam from said second crystal and the unrotated second light beam from the second crystal are perpendicular-ly polarized with respect to each other; and a fourth polarization beam splitter, operated in reverse, coupled to receive the perpendicularly polarized output beams from said second crystal and to provide a second single output light beam which can be coupled to a second optical output means.
4. In combination, a first electro-optical crystal, a second electro-optical crystal, a dielectric beam splitting coating affixed to portions of said crystals with coated portions of such cry-stals being juxtaposed, first means for varying the index of refraction of one beam path through one of said crystals with respect to the index of refraction of one beam path through the other of said crystals, and second means for varying the index of refraction of another beam path through said one of said crystals with respect to the index of refraction of another beam path through said other of said crystals, said second means being independent from said first means.
5. The combination as recited in claim 4 wherein said first means comprises a first set of electrodes deposit-ed upon opposite portions of said crystals so as to encompass said one beam paths, and said second means comprises a second set of electrodes deposited upon opposite portions of said crystals so as to encompass said another beam paths.
6. The combination as recited in claim 5 wherein said first set of electrodes and said second set of elec-trodes are independent of each other.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000507196A CA1223984A (en) | 1981-12-07 | 1986-04-21 | Polarization-insensitive optical multiplexing apparatus |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US327,873 | 1981-12-07 | ||
| US06/327,873 US4474434A (en) | 1981-12-07 | 1981-12-07 | Polarization-insensitive optical switch apparatus |
| CA000416669A CA1208379A (en) | 1981-12-07 | 1982-11-30 | Polarization-insensitive optical switch and multiplexing apparatus |
| CA000507196A CA1223984A (en) | 1981-12-07 | 1986-04-21 | Polarization-insensitive optical multiplexing apparatus |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000416669A Division CA1208379A (en) | 1981-12-07 | 1982-11-30 | Polarization-insensitive optical switch and multiplexing apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1223984A true CA1223984A (en) | 1987-07-07 |
Family
ID=25669874
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000507196A Expired CA1223984A (en) | 1981-12-07 | 1986-04-21 | Polarization-insensitive optical multiplexing apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1223984A (en) |
-
1986
- 1986-04-21 CA CA000507196A patent/CA1223984A/en not_active Expired
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