BROADBAND OPTICAL BEAM STEERING SYSTEM AND METHOD

Abstract: A small, compact optical scanning system with small aperture size requirements, wide field-of-regard and minimal color dispersion characteristics. The inventive system includes a novel device for receiving an input wavefront of electromagnetic energy along a first axis and refracting the wavefront as an output wavefront along a second axis. The device is a unique form of a liquid crystal array which can be electrically manipulated to change the effective refractive index of each pixel. The index of refraction of the device varies in response to an applied voltage. The voltage is supplied by a microprocessor and/or a servo-control system. By changing the index, the incident phase front can be steered at an angle with respect to the first axis and otherwise manipulated according to the index variant pattern induced in the array. Accordingly, the output beam is steered in response to the applied voltage.

Description: BROADB AN D OPTICAL BEAM STEERING SYSTEM AND METHOD BACKGROUND OF THE INVENTION Field ot the Invention. The piesent invention iclates to in f t ared and optical systems Moie specifically the piesent inv ention relates to svstems and methods toi ef fecting steei mg ot lnliaied and optical beams Description ol the Related Art: For many applications, theie is a need to generate images optically Mihtaiy and commercial aircralt applications, for example, utilize systems which tiansmit and/oi receive mlrared. near-infrared, optical or other electromagnetic energy The input and/oi output beams must be steered in a desired pointing dπection For beam steeπng, the prior art includes steenng minors, pointing gimbals and monochromatic electro-optical, beam steeπng mechanisms. Steeπng mirrors require output windows many times the size ol the system optical entrance pupil to scan over a large field of regard Unfortunately the miπ'or form factor requirements greatly increase the size of the sensor package The gimbaled approach involves use of an imaging system mounted in a dome that is gimbaled to provide a desired pointing angle The gimbals must point the entire sensor to scan the field-of-regard. Unfortunately, for aitcraft applications, this requires a mirror below the platform line, w hich necessitates a hole in the platform In addition. the dome and optical assembly is bulky, typically requires considerable volume, and has a idai u oss-section which tends to inucases the obsei v e ability ot the vehicle The monochi omatic electi o-optical beam steeπng appi oach involv es the use ol a liquid ciystal as the manipulated medium This appi oach iehes on a ditti activ e giating pattern in a liquid ciystal anav Displacing the giating causes a phase delay that steei s the beam Untortunatel) this appioach only opeiates effectively foi monochiomatic or neai -monochromatic light so uces Foi non-monochiomatic light souices this appioach causes undesuable coloi dispeision Accoidingly a need exists in the ai t foi small, compact optical scanning svstem with small apeituie size lequuements wide f ield ot-iegaid and minimal coloi dispei sion chaiactenstics SUMMARY OF THE INVEN flON The need in the ait is addiessed by the beam steenng system and method of the piesent invention The invention pi ov ides a means foi optical beam steering ovei a bioad spectral band and ovei a wide lield-ot-iegard in a small compact optical scanning system with small aperture size iequuements wide field-of-iegaid and minimal color dispersion charactenstics The inventive system includes a novel device for receiving an input wavefiont of electiomagnettc energy along a first axis and for refracting the input wavefront as an output wavefront along a second axis The device is a unique form of a liquid ci ystal array which can be electncally manipulated to change the effective refractive index ot each pixel The index of refiaction of the device varies in iesponse to an applied voltage The voltage is supplied by a microprocessor and/or a servo-control system By changing the index, the incident phase front can be steered at an angle with respect to the first axis and otherwise manipulated accoi ding to the index variant pattern induced in the array Accordingly, the output beam is steeied in response to the applied voltage In the illustrative implementation, the device is an an ay of liquid ciystal devices Countei rotating optical wedges aie pi ovided toi icstoi ing coloi balance to the output vvavefiont In the illustiativ e embodiment a min oi is included toi compensating the vvav efiont output by said l u st and second countei-iotating optical wedges The vvavefiont lefiected by the minoi may be output by an imaging lens oi othei suitable device In accoidance w ith the pi esent teachings beam steei mg is accomplished thi ough a lefi active v ai iation not a di tfi activ e one This allows the spectial bandw idth to be much bioader than foi a ciitfi actively manipulated phase waveh ont BRIEF DESCRIPTION OF THE DR VVVINGS Fig 1 is a diagram which illustrates an illustiative application a typical conventional gimbaled optical scanning system Fig 2 is a diagram which illustrates the field-of-regard of the typical conventional gimbaled optical scanning system ot Fig 1 Fig 3 is a diagram showing an illustrative application of the optical beam steenng system of the present invention Fig 4 is an isolated view of the optical beam steering system of the piesent invention with associated control circuitiy Fig 5 is a diagram ot the liquid crystal array utilized in the optical beam steering system of the present invention Fig 6 is a sectional side v iew of a single liquid crystal channel of the array of Fig 7 is a sectional side v iew of multiple liquid crystal channels of the arrav of Fig 8a is an end view of multiple liquid crystal channels of the array of Fig 5 Fig 8b is a sectional side v iew of multiple liquid crystal channels ot the array ot Fig 5 showing an arrangement bv which leads aie brought out ot the cells Fig 9 is a diagi am w inch lllusti ates that the beam steel ing dev ice ol the piesent invention may be used f oi multiple lasei f requency steel ing DESCRIPTION OF THE INVENTION Illustiative embodiments and exemplaiy applications ill now be desci ibed with ieteience to the accompanying diaw ings to disclose the advantageous teachings of the piesent invention While the piesent invention is desci ibed heiem with ieteience to illustiativ e embodiments toi paiticulai applications, it should be undeistood that the invention is not limited theieto Those having ordinaiy skill in the ai t and access to the teachings piov ided heiem will lecognize additional modifications, applications, and embodiments w ithin the scope thereof and additional fields in which the piesent invention would be ot significant utility Fig 1 is a diagram which illustrates a illustiative application ot a typical conventional gimbaled optical scanning system The conventional scanning system 10 ' includes a gimbaled minor 12 ' (not shown in Fig I ) mounted within a dome 13 gimbaled in an aircraft plattoim 14 ' The mirroi 12 ' scans a beam 16' thiough a window 18' Fig 2 is a diagram which illustrates the field-ot-iegard of the typical conventional gimbaled optical scanning system ot Fig 1 As lllustiated in Fig 2 the gimbaled mirror 12' receives the beam 16 ' through an entrance pupil 19 ' over a field of regard θ Cleai ly, as mentioned above, this use of steering miπoi s requires an output window 18' many times the size of the system optical entrance pupil 16' to scan over a large field of regard θ Unfortunately, for aircraft applications, this requires necessitates a large hole in the platform 14' In addition, the dome 13 ' and associated optical assembly is bulky, typically requires consideiable volume, and has a radar cross-section which tends to increases the obseive-abihty ot the vehicle Hence, a need exists m (lie ai t f oi small, compact optical scanning system w ith small apei tuie si/e lequiiements w ide l ield-of -iegaid and minimal coloi dispei sion chaiactenstics Fig is a diagi am show ing an illusti ativ e application ot the optical beam steering system of the piesent inv ention The beam steeπng sy stem ot the piesent invention 10 includes a dev ice 20 which allows toi electionic oi electio-optical lefi activ e steenng ot an input oi output beam 16 As discussed moie tullv below in the illustiative implementation the dev ice is a bioadban liquid crystal an ay The beam 16 is letiacted thiough an w indow 18 which is approximately equal in dimension, to the enti ance pupil 19 of the de ice 20 Fig 4 is an isolated v iew ot the optical beam steenng system 10 ol the pi esent invention with associated contiol cucuitiy As lllustiated in Fig 4 the leti acted beam 16 is corrected tor dispeision by a dispei sion aπangement 22 consisting ol tn st and second counter-rotating wedges 24 and 26 The diameter ot the wedges 24 and 26 is determined by the diameter ot the beam 16 The wedge angles ate determined by the color dispeision inherent in the material in the device 20 through which the beam piopagates toi the spectral components of the beam The onentation of the wedges 24 and 26 is controlled by a seivo-contiol system 28, which operates under command of a controller 30 The contiollei 30 may be implemented with a micioprocessor, application specific integiated ciicuit, programmable digital logic circuit or other suitable circuit as will be appieciated by those of ordinary skill in the art The controller may operate under command of a system contioller 32, which would receive input horn and piovide output to a user via an intei face 34 As discussed more fully below, the controller 30 applies a v oltage to the beam steering device 20, which determines the angle at which the beam is refractively steered theieby Simultaneously, the controller supplies signals to the servo-conti oiler 28 to make oi ientational adjustments to the wedges 24 and 26 required to correct for any color dispersion caused by the dev ice 20 The dispersion coπected beam is directed to a mπ roi 36 The minor 36 is a component of a compensating gi oup 37 w hich includes a lens 38 The min oi 36 compensates toi any small angulai change in the beam 16 caused bv the dispei sion gioup 22 As w ill be appi eciated by those skilled in the ait. the flatness and spectial lefiectance of the minoi aie primary design considei ations The minor should be as fiat as piactical foi the application The spectial icfiectance will be set by the ietlective coatings selected toi the application The lens sel ves to tocus the beam 16 to a detectoi , cameia oi eyepiece 40 Fig 5 is a diagram ot the liquid ciystal an ay 20 utilized in the optical beam steering system 10 of the piesent invention As shown m Fig 5, the bioadband beaming steenng device 20 consists ot a multi-channel aπ av of channels 2 1 Fig 6 is a sectional side v iew ot a single liquid ciystal channel ol the an ay 20 ot Fig 5 As depicted in Fig 6, each channel 21 of the aπay 20 is filled w ith a liquid ciystal foi mulation 25 and acts as a waveguide Application ot a voltage acioss each channel 2 1 induces a change in lefiactive index ot the liquid crystal mateπal This introduces a phase delay in the beam 16 as it piopagates through each channel Fig 7 is a sectional side view ot multiple liquid ciystal channels ot the airay 20 ol Fig 5 By vaiying the iclativ e voltage channel-to-channel across the aπay, a variation between the channel indices is cieated As depicted in Fig 7. the vai iation between channel indices applies a phase delay acioss an incident optical vvavefi ont 16 to create an electro-optical wedge The optical wedge can be manipulated electio- optically to scan the field-of-regard The optical wedge of the liquid crystal component is manipulated by varying the applied voltage The rotating wedges correct the lesidual dispei sive color that is inherent in any optical medium This dispersive color collection is a small angular component compared to the large angular scan generated by the liquid crystal component Fig 8a is a cross-sectional end view ot multiple liquid ciystal channels 21 of the array 20 of Fig 5 As shown in Fig 6 and 8a. each channel 21 is created by etching a cavity in a substiate 33 to create a cell 3 1 The cell size should be kept small to ensure single mode operation In the illustiative embodiment the cell thickness (channel length) is several centimeters and the operating tempei atuie T = 23°C The substiate 33 mav be any suitable etchable matenal In the illustiative implementation the cells aie 3 3 micions and aie sepaiated w ith 1 micion ol substiate A conductive matenal is flashed into the flooi of the cell 31 to piov ide a giound 27 Next in the illustiativ e implementation the cell 3 1 is tilled with a liquid crystal matenal to piov ide a medium 25 Those skilled in the ai t will appieciate that any matenal can be used as a medium so long as it leti acts a beam ot electi o-magnetic eneigv in lesponse to an applied v oltage In the illustiative embodiment a solution ot \ c r PTTP- 1 dissolved in methylene chlonde was chosen as the liquid ci ystal matenal foi the medium 25 A voltage stnp 29 of conductive matenal is applied as a cov ei foi each cell The voltage stnp may be common in some embodiments Ho evci in most conseivativ e embodiment each cell has its own unique ciicuit and theietoie does not act as a common giound When a voltage is applied between the voltage stnp 29 and the gi ound 27 a capacitive field is created theiebetween The field lines up the molecules of the medium and induces a rotation in the polarization of electromagnetic energy (e g light or infrared eneigy) propagating therethrough Transmittance is maximized in the individual channel by creating eithei 1 ) total internal reflection by index cavity index selection oi 2) by coating the intei ior with a lellective film A filter 23 is piov ided at the input apeituie of each channel An aπ ay (not shown) ot conductoi s would be piovided to allow for selective application of an applied voltage to an individual cell Fig 8b is a sectional side view of multiple liquid crystal channels of the arrav of Fig 5 showing an arrangement by which leads are bi ought out ot the cells Each row has a layered insulated wiring iouting as shown The dimensions aie exaggerated to illustrate the path Each of the row outputs are staggered in space to avoid physical interference when organized along the column Fig 9 is a diagram which illustrates that the beam steering device of the piesent invention may be used for multiple laser frequency steenng Thus, the present invention has been described heiein with refeience to a paiticulai embodiment for a particulai application Those having ordinary skill in the ait and access to the pi esent teachings will iccogni/e additional modifications applications and embodiments within the scope theieol It is theiefoic intended by the appended claims to cov ei any and all such applications, modifications and embodiments within the scope ol the piesent invention Accoidingly, WHAT IS CLAIMED IS

Claims: EUROSTYLE CLAIMS 1. A system (10) for steeπng a beam (16) of electromagnetic energy characteπzed by: a beam steeπng device (20) for receiving an input wavefront of electromagnetic energy along a first axis and refracting said input wavefront as an output wavefront along a second axis at an angle with respect to said first axis in response to an applied voltage; contacts (27 and 29) for providing said voltage response to a control signal; and a controller (30) for providing said control signal. 2. The invention of Claim 1 wherein the index of refraction of said beam steeπng device (20) vanes in response to said applied voltage. 3. The invention of Claim 2 wherein said beam steeπng device (20) is a liquid crystal device. 4. The invention of Claim 3 wherein said beam steeπng device (20) includes an array of liquid crystal devices (21). 5. The invention of Claim 1 further including an arrangement (22) for restoπng color balance to said output wavefront. 6. The invention of Claim 5 wherein said arrangement (22) for restoπng color balance to said output wavefront includes first and second counter-rotating optical wedges (24, 26). 7. The invention of Claim 6 further including a minor (36) for compensating a wavefront output by said first and second counter-rotating optical wedges. 8. The invention of Claim 7 further including an imaging lens (38).

Inventors: ANDERSON J STEVE, PINES MICHAEL S, ANDERSON, J., STEVE, PINES, MICHAEL, S.
Applicants: RAYTHEON CO, RAYTHEON COMPANY
Application year: 2001
Main classification: G02F1
IPC codes: G02F1