Integrated two-dimensional planar optical phased array

An optical phased array includes, in part, a multitude of optical signal emitters and a multitude of optical signal phase/delay elements each associated with and disposed between a different pair of the optical signal emitters. Each optical signal phase/delay element is adapted to cause a phase/delay shift between the optical signals emitted from its associated pair of optical signal emitters. Each optical signal phase/delay element is optically a ring resonator that includes a p-i-n junction. By varying the bias applied to the p-i-n junction, the phase/delay generated by the ring resonator is varied. Furthermore, each optical signal emitter is optionally an optical grating having a multitude of grooves. The groove lengths of the optical gratings are optionally selected so as to increase along the direction of travel of the input optical signal through the optical phase array.

FIELD OF THE INVENTION

The present invention is related to phased arrays, and more particularly to an integrated optical phase array.

BACKGROUND OF THE INVENTION

RF and mm-wave phased arrays are being increasingly used in a variety of applications, such as communication, imaging, beam steering, and radar. However, efforts in developing optical phased arrays have had limited success.

Conventional optical phased arrays are formed using such techniques as injection locking of lasers in the array, single laser with array of phase modulators, and phase locking of multiple semiconductor lasers. However, conventional optical phased arrays have a number of disadvantages. For example, they are formed using bulky optical components, require complex control systems to minimize the effect of environment fluctuations, consume a significant area, and are otherwise difficult to scale

A need continues to exist for an optical phased array that is highly integrated, has a reduced sensitivity to environment fluctuations, and consumes a significantly smaller area than conventional optical phased arrays.

BRIEF SUMMARY OF THE INVENTION

An optical phased array, in accordance with one embodiment of the present invention includes, in part, a first array of N optical signal emitters and a first array of M optical signal delay elements, wherein N is an integer greater than or equal to 2 and M is an integer greater than or equal to one. Each optical signal delay element is associated with and disposed between a different pair of optical signal emitters and is adapted to cause a phase/delay shift between optical signals emitted from its associated pair of optical signal emitters in response to a first input optical signal received by the optical phased array.

In one embodiment, the phase/delay shift caused by each of the optical signal delay elements is variable. In one embodiment, the delays caused by at least a subset of the optical signal phase/delay elements are varied so as to change the angle of an optical signal generated due to interference between one or more of the optical signals. In one embodiment, each of the optical signal phase/delay elements is a ring resonator. In one embodiment, each of the optical ring resonators is a p-i-n junction adapted to cause a phase/delay shift in response to an applied bias.

In one embodiment, each of the optical signal emitters is an optical grating that includes a plurality of grooves. In one embodiment, the groove lengths of the optical gratings are selected so as to increase along a direction of travel of the first input optical signal through the optical phase array. In one embodiment, the groove lengths of the optical gratings are selected so as to achieve a substantially similar intensity for the emitted optical signals.

In one embodiment, the phased array includes, in part, a second array of N optical signal emitters formed parallel to the first array of the N optical signal emitters, and a second array of M optical signal delay elements. Each optical signal delay element of the second array is associated with and disposed between a different pair of optical signal emitters of the second array and is adapted to cause a phase/delay shift between optical signals emitted from its associated pair of optical signal emitters in response to a second input optical signal received by the optical phased array.

In one embodiment, the N optical signals emitted from the first array of N optical signal emitters and the N optical signals emitted from the second array N of optical signal emitters have substantially similar wavelengths. In one embodiment, the first array of optical signal emitters and the first array of optical signal delay elements are formed in the same semiconductor substrate. In one embodiment, the first and second arrays of optical signal emitters, and the first and second arrays of optical signal delay elements are formed in the same semiconductor substrate. In one embodiment, the first and second input optical signals are derived from the same source of optical signal.

In one embodiment, the phased array further includes, in part, a second array of optical signal emitters and a second array of optical signal delay elements. Each optical signal delay element of the second array is associated with and disposed between a different pair of optical signal emitters of the second array and is adapted to cause a phase/delay shift between optical signals emitted from its associated pair of optical signal emitters in response to a second input optical signal received by the optical phased array. The second array of N optical signal emitters may be formed either above or below the first array of the N optical signal emitters.

In one embodiment, the optical signals emitted by the first array of optical signal emitters are substantially parallel to the surface of the substrate in which the first array of optical signal emitters and the first array of optical signal delay elements are formed. In another embodiment, the optical signals emitted by the first array of optical signal emitters are substantially perpendicular to the surface of a substrate in which the first array of optical signal emitters and the first array of optical signal delay elements are formed.

A method of generating N optical signals, in accordance with one embodiment of the present invention, includes, in part, forming a first array of N optical signal emitters, and forming a first array of M optical signal delay elements. Each optical signal delay element is associated with and disposed between a different pair of optical signal emitters and is adapted to cause a phase/delay shift between optical signals emitted from its associated pair of optical signal emitters in response to a first input optical signal received by the optical phased array. N is an integer greater than or equal to 2 and M is an integer greater than or equal to one.

In one embodiment, the method further includes, in part, varying the delay across one or more of the optical signal phase/delay elements. In one embodiment, the method further includes, in part, varying the delay across at least a first subset of the optical signal delay elements so as to change the angle of an optical signal generated due to interference between one or more of the optical signals emitted by the optical signal emitters.

In one embodiment, at least one of the optical signal phase/delay elements is a ring resonator. In one embodiment, at least one of the optical ring resonators is a p-i-n junction adapted to cause a phase/delay shift in response to an applied bias. In one embodiment, at least one of the optical signal emitters is an optical grating that includes a multitude of grooves.

In one embodiment, the method further includes, in part, selecting groove lengths of the optical gratings in an increasing order along a direction of travel of the first input optical signal through the optical phase array. In one embodiment, the method further includes, in part, selecting the groove lengths of the optical gratings such that intensities of the emitted optical signals are substantially similar.

In one embodiment, the method further includes, in part, forming a second array of N optical signal emitters parallel to the first array of the N optical signal emitters, and forming a second array of M optical signal delay elements. Each optical signal delay element of the second array is associated with and disposed between a different pair of optical signal emitters of the second array and is adapted to cause a phase/delay shift between optical signals emitted from its associated pair of optical signal emitters in response to a second input optical signal received by the optical phased array.

In one embodiment, the optical signals emitted from the first array of optical signal emitters and the optical signals emitted from the second array of optical signal emitters have the same wavelength. In one embodiment, the first array of optical signal emitters and the first array of optical signal delay elements are formed in the same semiconductor substrate. In one embodiment, the first and second arrays of optical signal emitters, and the first and second arrays of the optical signal delay elements are formed in the same semiconductor substrate. In one embodiment, the first and second optical signals are generated from the same source of optical signal.

In one embodiment, the method further includes, in part, forming the first array of optical signal emitters and the first array of optical signal delay elements in the same semiconductor substrate. The method further includes, in part, forming the second array of optical signal emitters and optical signal phase/delay elements either above or below the first array of optical signal emitters. Each optical signal delay element of the second array is associated with and disposed between a different pair of optical signal emitters of the second array and is adapted to cause a phase/delay shift between the optical signals emitted from its associated pair of optical signal emitters in response to a second input optical signal received by the optical phased array.

In one embodiment, the optical signals emitted by the first array of optical signal emitters are substantially parallel to the surface of the substrate in which the first array of optical signal emitters and the first array of optical signal delay elements are formed. In another embodiment, the optical signals emitted by the first array of optical signal emitters are substantially perpendicular to the surface of a substrate in which the first array of optical signal emitters and the first array of optical signal delay elements are formed.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a one-dimensional optical phased array50having 2N+1 collimated optical signals3001,3002. . .300(2N+1)travelling along the z axis. Each optical signal (alternatively referred to herein as beam) is shown as having a diameter d, and spaced away from an adjacent beam by distance D along the x-axis. Assume that each beam has a Gaussian profile, and has the same wavelength λ0with the same optical power P0. Accordingly, the electric field at the point of emission for each beam may be obtained using the following expression:
En(x,y,0)=E0ejnØe−4/d2[(x−nD)2+y2](1)
where E0, n, and Ø are respectively the electric field constant, element index, and the constant phase difference between adjacent elements.

Applying the Fraunhofer far field approximation, the far field intensity of the electric field at distance z=L may be determined using the following:

As is seen from expression (3), the electric field intensity of at any point L may be varied by varying Ø, which is the difference between phases of adjacent beams. The Fourier transform of the profile of the individual beams defines the envelope (proportional to λ0L/d) within which the beam may be steered.

Due to finite size of the optical phased array50and periodic nature of G(Ω), side lobes appear in the far field pattern. The position of the main lobe and the position of its adjacent side lobes may be calculated from Expression 3. The ratio between the main lobe and the adjacent side lobe, commonly referred to as the side lobe suppression ratio (SLSR), may be calculated using the following expression:

Using Expressions 3 and 4, the maximum steering angle for a given SLSR may be substantially defined as:

FIG. 2is a simplified perspective view of an array100of optical signal radiators and delay element (also referred to hereinbelow as optical phased array or phased array), in accordance with one embodiment of the present invention. Phased array100is shown as including first and second optical signals radiators101,102—forming an array of optical signal radiators (signal emitters)—and an optical phase/delay element15disposed between the optical signal radiators. Although phased array100is shown as including two optical signal radiators and an optical delay element, it is understood that a phased array in accordance with the present invention may include any number of optical signal radiators and optical phase/delay elements. For example,FIG. 3Ashows a one-dimensional optical phased array175having four optical signal radiators101,102,103,104—forming an array of optical signal emitters—and three variable optical phase/delay elements151,152,153—forming an array of optical signal phase/delay elements—disposed between the optical radiators.

Referring toFIG. 2, in response to an incident optical signal110received by phased array100, optical signal radiators101and102respectively generate first and second optical signals501,502that are combined (due to interference) to generate an output optical signal200at a far field of the phased array. The difference between the phases of optical signals501,502is defined by the amount of delay generated by variable optical phase/delay element15. By controlling and varying this phase difference, the degree of interference between optical signals501,502and thereby the direction of the output optical signal200may be varied. For example, the delay across delay element15may be selected such that optical signals501,502have substantially the same phase thereby to achieve constructive interference between these signals, thus moving optical signal200in one direction. Similarly, the delay across delay element15may be selected such that the phase difference between output signals501,502satisfies one or more other conditions thus moving optical signal200in another direction.

Referring toFIG. 3A, optical phase/delay elements151is adapted to control the phase difference between optical signals501,502radiated respectively by optical signal radiators101,102; optical phase/delay elements152is adapted to control the phase difference between optical signals502,503radiated respectively by optical signal radiators102,103; and optical phase/delay elements153is adapted to control the phase difference between optical signals503,504radiated respectively by optical signal radiators103,104. By controlling such phase differences, the direction of optical output signal250—generated as a result of interference between optical signals501,502,503and504—may be varied.

In one embodiment, each of optical radiators10i(i is an integer equal to or greater than 2) may be an optical grating, and each delay element15j(j is an integer equal to or greater than 1) may be a ring resonator for the embodiment shown inFIG. 2. The following description, in accordance with the present invention, is provided with reference to an optical phased array formed using optical gratings that radiate optical signals (i.e., optical signal radiators), and ring resonators that generates optical signal phase/delay (i.e., optical delay element). It is understood, however, that an optical phased array, in accordance with the present invention, may include any other optical radiator such as edge couplers, and any other delay element such as disk resonators and cavity resonators.

FIG. 3Bis a perspective view of a two-dimensional optical phased array270having four arrays2751,2752,2753,2754each shown as including four optical signal emitters and three optical signal phase/delay elements. The optical signal phase/delay in each array is associated with and disposed between a different pair of optical signal emitters of that array. Phased array270thus has sixteen optical signal emitters10ijand fifteen optical phase/delay elements15ij, where i is an index identifying the array number and j is an index identifying a relative position of the optical signal emitter or the optical signal phase/delay element disposed in that array. For example, array2751is shown as including optical signal emitters1011,1012,1013,1014and optical phase/delay elements1511,1512,1513. Likewise, array2754is shown as including optical signal emitters1041,1042,1043,1044and optical phase/delay elements1541,1542,1543. In each array, each optical signal phase/delay element is associated with and disposed between a different pair of optical signal emitters disposed in that array. For example, optical signal phase/delay element1511is associated with and disposed between optical signal emitter1011,1012; optical signal phase/delay1512is associated with and disposed between optical signal emitter1012,1013; and optical signal phase/delay1532is associated with and disposed between optical signal emitter1032,1033.

As seen inFIG. 3B, each array275iis shown as receiving an input optical signal278i. Input optical signals2781,2782,2783, and2784may have the same wavelength. As described herein, the phase/delay of the optical signal travelling through each array is independently controlled—using the optical signal phase/delay elements of that array—so as to vary the degree of interference between the four optical signals emitted from that array in order to vary the angle of the optical signal that is formed as a result of this interference. For example, by varying the phase/delay of the optical phase/delay elements1511,1512,1513, the degree of interference between the optical signals (not shown) emitted by emitters1011,1012,1013,1014may be varied so as to change the angle of optical signal2801generated as a result of the interference between these four signals. Likewise, by varying the phase/delay of the optical phase/delay elements1541,1542,1543, the degree of interference between the optical signals (not shown) emitted by emitters1041,1042,1043,1044may be varied so as to change the angle of optical signal2804generated as a result of the interference between these four signals. In one embodiment, optical phased array270is formed on one or more semiconductor substrates.

FIG. 3Cshows a three-dimensional optical phased array290formed using a stack of four two-dimensional arrays2921,2922,2923,2924each having four arrays2751,2752,2753,2754, as described above with reference toFIG. 3B. Each of the arrays292k, where k is an integer varying from 1 to 4 in this exemplary embodiment, may be formed in a different substrate or layer. Arrays292kare then positioned above or below each other to form the stack.

FIG. 4Ais a perspective view of an exemplary embodiment of an optical grating10as used in an optical phased array, such as those shown in FIGS.2and3A-3C, in accordance with the present invention. Optical grating10is shown as including four similarly sized grooves301,302,303and304. Although exemplary optical grating10is shown as including four grooves, it is understood that optical grating10may have more or fewer than four groves. Incoming optical signal110incident on surface20of optical grating (hereinafter alternatively referred to as grating)10is scattered due to Bragg effect, thus resulting in a fraction of the incident optical signal to radiate (emit) outward, identified using reference number25. Grating10emits light if the wavelength of the optical signal (alternatively referred to herein as “light beam” or “beam”)110travelling through the grating is smaller than the grating period.

FIG. 4Bis a cross-sectional view of grating10having a groove width d, a grating period T, and a groove span of D. The groove width to grating period d/T defines the angle of propagation of the outgoing optical beam25, the coupling efficiency, and the beam divergence.FIGS. 5A-5Dshow the effect of the grating period on the beam divergence. The groove width to grating period d/T associated with each ofFIGS. 5A-5Dis 0.75, and the grating periods T associated withFIGS. 5A,5B,5C, and5D are respectively 1.0, 0.93, 0.85, and 0.78. As seen by comparingFIGS. 5A-5D, for the same groove width to grating period d/T, the smaller the grating period, the larger is the degree of divergence of the output beam.

FIGS. 6A-6Dshow the effect of the grating period on the beam emission angle. The groove span D to the grating period associated T withFIGS. 6A,6B,6C, and6D are respectively selected to have values of 10, 8, 6, and 4. As seen by comparingFIGS. 6A-6D, the higher the grating period, the larger is the emission angle relative to the normal emission plane35(seeFIG. 4B).

FIGS. 7 and 8respectively show the emission profile and the intensity of the output beams501,502,503, and504, of optical phased array175ofFIG. 3Aformed in a semiconductor substrate. Gratings101,102,103, and104(collectively and alternatively referred to herein as gratings10) are selected to have the same period T of 650 nm, width d (seeFIGS. 4A and 4B) of 1300 nm and placed 30 μm apart from one another. Referring toFIG. 7, the mission profiles of output signals501,502,503, and504are respectively identified as601,602,603and604. Referring toFIG. 8, the intensity of output signals501,502,503, and504are respectively identified as701,702,703and704. As is seen fromFIG. 8, since each grating emits a portion of the light it receives, the intensity of the output beams decreases as the light travels through the array of gratings.

FIG. 9is a perspective view of another exemplary embodiment of an optical grating10as used in an optical phased array, in accordance with the present invention. Optical grating10ofFIG. 9is shown as including four grooves301,302,303and304that are tapered such that the length L of the grooves increases in succession along the direction of the beam travel. Accordingly, groove302is selected to be longer than groove301; groove303is selected to be longer than groove302; and groove304is selected to be longer than groove303. Although exemplary grating10ofFIG. 9is shown as including four grooves, it is understood that grating10may have more or fewer than four groves. By selecting the grooves to have increasingly greater lengths along the direction of travel of the received optical signal110, the intensity of the output beam25radiated out from grating10may be varied.

FIG. 10is a simplified top view of an optical phased array400, in accordance with another exemplary embodiment of the present invention. Phased array400is shown as including four gratings420,440,460,480, and three optical phase/delay elements151,152and153respectively disposed between gratings440/420,460/440and480/460. The grooves in each grating have substantially the same lengths and widths. Accordingly, grooves4251,4252,4253,4254(collectively referred to as grooves425) of grating420have substantially the same length L1and width W1. Likewise, grooves4451,4452,4453,4454(collectively referred to as grooves445) of grating440have substantially the same length L2and width W2; grooves4651,4652,4653,4654(collectively referred to as grooves465) of grating460have substantially the same length L3and width W3; and grooves4851,4852,4853,4854(collectively referred to as grooves485) of grating480have substantially the same length L4and width W4. Furthermore, the length of the grooves of each grating is greater than the length of the grooves of the adjacent grating from which that grating receives the incoming optical signal. In other words, the groove lengths of neighboring gratings increase along the direction of incoming beam travel. Accordingly L2is selected to be greater than L1, L3is selected to be greater than L2, and L4is selected to be greater than L2. Although optical phased array400is shown as including four gratings each having four grooves, it is understood that an optical phased array, in accordance with the present invention, may have any number of gratings each having any number of groves.

FIG. 11is a simplified top view of an optical phased array500, in accordance with another exemplary embodiment of the present invention. Phased array500is shown as including four gratings520,540,560,580each having six grooves. Phased array400is also shown as including three optical phase/delay elements151,152and153respectively disposed between gratings540/520,560/540and580/560.

The grooves in each grating of phased array500have substantially the same size. Accordingly, for example, grooves5251,5252,5253,5254,5255,5256(collectively referred to as grooves525) of grating520have substantially the same length L1and width W1. Likewise, grooves5451,5452,5453,5454,5455,5456(collectively referred to as grooves545) of grating540have substantially the same length L2and width W2; grooves5651,5652,5653,5654,5655,5656(collectively referred to as grooves565) of grating560have substantially the same length L3and width W3; and grooves5851,5852,5853,5854,5855,5856(collectively referred to as grooves585) of grating580have substantially the same length L4and width W4. Furthermore, the length and width of the grooves in each grating are greater than the length and width of the grooves of the adjacent grating from which that grating receives the incoming optical signal. In other words, the groove lengths and widths of neighboring gratings increase along the direction of the beam travel. Accordingly L2is selected to be greater than L1, L3is selected to be greater than L2, and L4is selected to be greater than L3. Likewise, W2is selected to be greater than W1, W3is selected to be greater than W2, and W4is selected to be greater than W3. Consequently, the intensity of the output beam radiating from gratings520,540,560, and580are controlled so as to be, for example, substantially similar. Gratings520,540,560, and580are respectively shown as radiating output beams522,545,562, and582. Although optical phased array500is shown as including four gratings each having six grooves, it is understood that an optical phased array, in accordance with the present invention, may have any number of gratings each having any number of groves.

FIG. 12Ais a simplified top view of an optical phased array300, in accordance with another exemplary embodiment of the present invention. Phased array300is shown as including, in part, four gratings320,340,360,380, and three optical phase/delay elements151,152,153disposed between the gratings, as shown. Each grating is shown as including six grooves. The grooves in all the gratings have substantially the same width. The grooves in grating320have the length of 850 nm; the grooves in grating340have the length of 1.15 μm; the grooves in grating360have the length of 1.30 μm; and the grooves in grating380have the length of 2.0 μm. Accordingly, the lengths of the grooves increase along the direction of the incoming input optical signal110.

FIGS. 12B,12C and12D respectively show the simulation results of the emission profiles, the projections of the beams 2000 nm above the phased array, and the intensity of the beams radiating from gratings320,340,360,380of phased array300ofFIG. 12A(seeFIG. 4). As is seen fromFIG. 12D, intensity plots442,444,464,484associated respectively with output beams422,442,462,482(emitted respectively by gratins420,440,460and480) have substantially similar peaks and characteristics. In other words, by selecting the grating lengths, in accordance with the present invention and as described above, substantially equal beam intensities are radiated from the gratings of the phased array.

FIG. 13is a top view of an exemplary embodiment of a ring resonator15as used in an optical phased array (such as those shown inFIGS. 2 and 3), in accordance with the present invention. An incoming optical signal is received by ring resonator15via its input port610, and supplied as an output optical signal via its output port (also commonly known as through port)612. Ring resonator15is a p-i-n junction formed in a semiconductor substrate and includes a highly doped P++ region602, a highly doped N++ region604, and an intrinsic region606. Ring resonator15is adapted to perform optical phase shifting around its resonance frequency by changing its index of refraction through biasing of the p-i-n junction. Distances AD, DC, and CB, characterized by a line radially extending from the center of the ring and away from the input/output ports, respectively define the widths of the P++, intrinsic, and N++ regions. Ring resonator15is also shown as including a drop port620and an isolation port622. As is seen fromFIG. 13, near the coupling regions624and626, intrinsic region606has a reduced width of k to maximize the coupling. Away from the coupling regions624,626, the intrinsic region has a greater width defined by the distance DC to minimize signal loss in the ring.

In one example, the width of the p-i-n junction along a radial line extending from the center of the ring (e.g., from point A to point B) is 2.5 μm; the radius of the circle from the center of the ring to center of the intrinsic region in areas away from the ports is 3.2 μm. Near the coupling regions624,626, the intrinsic region has a width K of 300 nm. Away from the coupling regions, the width of the intrinsic region (e.g., the distance between points D and C) is 1.2 μm. With these dimensions, simulations show that the ring may cause more than 50° phase shift for an amplitude change of less than 10%.

FIGS. 14A and 14Bare computer simulation results for amplitude and phase response of a ring resonator, having the dimensions described above, normalized with respect to an optical signal having a wavelength of 1556 nm received via the resonator's input port and supplied via the resonator's drop port. Referring toFIG. 14A, plot640shows the phase response of the resonator when the resonator receives no bias and thus its index of refraction is unchanged. Plots642and644show the phase response of the resonator when the index of the refraction of the resonator is changed respectively by 2×10−3and −2×10−3in response to the voltages applied to the resonator. Referring toFIG. 14B, plot650shows the amplitude response of the resonator when the resonator receives no bias and thus its index of refraction is unchanged. Plots652and654show the phase response of the resonator when the index of the refraction of the resonator is changed respectively by 2×10−3and −2×10−3in response to the voltages applied to the resonator.

FIG. 15is a simplified schematic diagram of an array700of optical signal radiators and delay elements, in accordance with another embodiment of the present invention. Phased array700is shown as including four gratings7101,7102,7103, and7104and three ring resonators151,152, and153each associated with and disposed between a different pair of the gratings. Each ring resonator15k(k is an integer varying from 1 to 3 in this exemplary embodiment) is shown as having an input port15k1, a through port15k2, and a drop port15k3. Associated with each resonator15kis a photo-diode formed along the resonator's through port. Accordingly, photo-diode1514is formed in through port1512of resonator151; photo-diode1524is formed in through port1522of resonator152; and photo-diode1534is formed in through port1532of resonator153. Photo-diodes15k4are used to achieve ring resonance frequency alignment. The gratings in phased array700have similarly sized grooves.

FIG. 16is a simplified schematic diagram of an array800of optical signal emitter and delay elements, in accordance with another embodiment of the present invention. Phased array800is similar to phased array700except that in phased array800the length of the grooves in each grating is larger than the length of the grooves of the adjacent grating from which that grating receives the incoming optical signal. In other words, the groove lengths of neighboring gratings increase along the direction of beam travel. Accordingly L2is selected to be greater than L1, L3is selected to be greater than L2, and L4is selected to be greater than L3, thus causing the intensity of the output beams radiating from gratings8101,8102,8103, and8104to vary in accordance with the grove lengths of the gratings. In one embodiment, L1, L2, L3and L4are selected such that the intensity of the optical signals emitted from gratings8101,8102,8103,8104are substantially similar.

FIG. 17shows a two-dimensional optical phased array900having four arrays9751,9752,9753,9754each of which is similar to one-dimensional array800shown inFIG. 16. Optical phased array900is thus a 4×4 array of optical emitters and phase/delay elements. In one embodiment an 8×8 array (not shown) of optical emitters and phase/delay elements formed by doubling the array sizes of phased array900may occupy an area of 100 μm2. Furthermore, since each ring resonator may be tuned and used as a switch to disconnect an associated signal emitter, the number of the phased array elements in both dimensions may be adjusted electronically. It is understood that any of the one-dimensional phased arrays described herein may be used to form a two-dimensional phased array, such as that shown inFIG. 17. Furthermore, any of the two-dimensional optical phased arrays may be stacked to form a three-dimensional phased array, as shown for example by stacking a multitude of two dimensional arrays ofFIG. 3Bto form the three-dimensional array ofFIG. 3C. For example, although not shown, it is understood that a three-dimensional phased-array may be formed by stacking a multitude of two-dimensional phased-arrays ofFIG. 17.

FIG. 18Ashows the near-field simulated beam pattern of a two-dimensional 4×4 planar optical phased array. Each of the arrays is similar to array800shown inFIG. 16.FIG. 18Bshows the far field simulated pattern of a two-dimensional 4×4 planar optical phased array when the optical signals emitted are selected to be in phase.FIGS. 18C and 18Drespectively show the far-field simulated pattern with phase progression in horizontal and vertical directions respectively.

FIG. 19is a perspective view of another exemplary embodiment of an optical grating10as used in an optical phased array, in accordance with the present invention. Optical grating10ofFIG. 20is shown as including five grooves301,302,303,304,305that are tapered and curved such that the length L of the grooves increases in succession along the direction of the beam travel. Accordingly, groove302is selected to be longer than groove301; groove303is selected to be longer than groove302; groove304is selected to be longer than groove303; and groove305is selected to be longer than groove304. Although exemplary grating10ofFIG. 20is shown as including five grooves, it is understood that grating10may have more or fewer than four groves. By selecting the grooves to have increasingly greater lengths along the direction of travel of the received optical signal110, the intensity of the output beam25radiated out from grating10may be varied.

The above embodiments of the present invention are illustrative and not limitative. Embodiments of the present invention are not limited by the type of optical signal radiator or optical signal phase/delay elements disposed in a phased array. Embodiments of the present invention are not limited by the number of grooves in an optical grating, or the number of optical gratings disposed in a phased array when optical gratings are used as optical signal radiators. Embodiments of the present invention are not limited by the wavelength of the incoming optical signal, nor are they limited by the type of substrate, semiconductor or otherwise, in which the optical phased array may be formed. Embodiments of the present invention are not limited by the number of arrays used to form a two-dimensional array or the number of two-dimensional arrays used to a form a stack of three-dimensional array. Other additions, subtractions or modifications are obvious in view of the present disclosure and are intended to fall within the scope of the appended claims.