EP1086529A2 - Dispositif d'orientation de la lumiere d'un reseau de diffraction piezoelectrique - Google Patents

Dispositif d'orientation de la lumiere d'un reseau de diffraction piezoelectrique

Info

Publication number
EP1086529A2
EP1086529A2 EP99916137A EP99916137A EP1086529A2 EP 1086529 A2 EP1086529 A2 EP 1086529A2 EP 99916137 A EP99916137 A EP 99916137A EP 99916137 A EP99916137 A EP 99916137A EP 1086529 A2 EP1086529 A2 EP 1086529A2
Authority
EP
European Patent Office
Prior art keywords
diffraction grating
piezoelectric substrate
diffraction
piezoelectric
grating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99916137A
Other languages
German (de)
English (en)
Inventor
Robert Arnold
Scott Bloom
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Trex Communications Corp
Trex Commercial Products Inc
Original Assignee
Trex Communications Corp
Trex Commercial Products Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Trex Communications Corp, Trex Commercial Products Inc filed Critical Trex Communications Corp
Publication of EP1086529A2 publication Critical patent/EP1086529A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1828—Diffraction gratings having means for producing variable diffraction

Definitions

  • This invention relates to light steering devices, and more particularly to a piezoelectric diffraction grating steering device.
  • Free-space laser communication systems transmit and receive information by means of a light beam that propagates through space or the atmosphere.
  • space-based, air-to-air or air-to-ground communications such systems pose a number of challenging problems.
  • FIG. 1 is a block diagram showing a pair of free-space atmospheric laser communication transceivers in accordance with the prior art.
  • An "A" transceiver includes a control system 100A, a laser transmitter 102A, and a receiver 104A.
  • a "B" transceiver includes a control system 100B, a laser transmitter 102B, and a receiver 104B.
  • Transceiver A sends a data stream 106A to transceiver B
  • transceiver B sends a data stream 106B to transceiver A.
  • the implementation of the respective control systems 100 A, 100B, transmitters 102 A, 102B, and receivers 104A, 104B is conventional.
  • One or both of the transceivers A, B may be mounted on a moving vehicle, such as an airplane.
  • FIG. 2 is a block diagram of an improved steering system 200, described in greater detail in co-pending patent application Serial No. , entitled "Six-Axis
  • an incoming light beam 202 from a beacon laser of a remote transceiver is received through an optical telescope (not shown) and reflected off of a tiltable steering mirror 204 mounted on piezoelectric "push- pull" actuators 206 that can control the azimuth and elevation of the mirror 204.
  • the reflected light is focused onto a sensor array (e.g., a CCD array) 208, the output of which is coupled to a centroider circuit 210 which determines the position of the focused light beam 200 on the sensor array 208.
  • a processor 212 is compared by a processor 212 to a calibrated reference signal 214, and steering correction signals are passed through an amplifier 216 to appropriate ones of the piezoelectric actuators 206.
  • the mass of the mirror element of the steering mirror 204 may be relatively high, thus limiting the adjustment rate of the steering mirror 204.
  • the fine steering system must be able to steer the communication laser beam at angular rates greater than the highest rate of disturbances that are present on the system's mounting platform; such disturbances are often referred to as
  • base motion In general, base motion has a spectrum of frequency components which cause the communication laser beam to be mispointed from an intended target, which is the source of a received beacon beam.
  • the beam steering system must be able to sense the base motion disturbances and provide error correction sufficient to keep the footprint of the communica- tion laser beam positioned on the target. If the base motion has frequency components which produce angular motion disturbances greater than can be corrected, the communication laser beam will be displaced from the location of the beacon source.
  • the base motion frequency that the beam steering device can respond to is limited by both the sensor and the beam steering device.
  • the beam steering device frequency response is generally limited by mechanical parameters of the mirror and actuators that are being moved to steer the beam.
  • the inertia of the mirror and the spring constant of the "push-pull" piezoelectric actuator form a resonant mechanical system for which operation at or near the resonance is generally the bandwidth limit of the system. Reducing the inertia of the mirror and increasing the stiffness of the piezoelectric actuator will increase its resonant frequency and extend the bandwidth of the system.
  • the system bandwidth is ultimately challenged to be greater than can be achieved with the lightest inertia mirrors and stiffest piezoelectric actuators. Accordingly, the inventors have determined that it would be useful to have a fine steering element that was less massive than a piezoelectric-actuator driven mirror and which has a higher adjustment bandwidth.
  • the present invention provides such a device.
  • the invention comprises a piezoelectric diffraction grating steering device including a piezoelectric substrate having an attached or integrally formed diffraction grating.
  • the piezoelectric actuator stretches the grating, changing the periodicity of the grating, thereby changing the angle of diffraction of the grating.
  • the preferred grating is a high efficiency reflection type grating which diffracts a maximum amount of light into the first order mode, minimizing the amount of light in the zero order and higher order modes.
  • the invention may be used in any application in which fine control over the angle of diffraction of a light beam is required, and may have an adjustment rate in excess of 100 KHz.
  • One application is as a beam steering element in a free-space laser communication system.
  • FIG. 1 is a block diagram showing a pair of free-space atmospheric laser communication transceivers in accordance with the prior art.
  • FIG. 2 is a block diagram of a tillable mirror based steering system.
  • FIG. 3 A is a block diagram of a fine steering system in accordance with the invention, shown in a first steering state.
  • FIG. 3B is a block diagram of a fine steering system in accordance with the invention, shown in a second steering state.
  • FIG. 4 is a diagram of a diffraction grating surface, showing the blaze angle. Like reference numbers and designations in the various drawings indicate like elements.
  • the invention includes a piezoelectric substrate having an attached or integrally formed diffraction grating.
  • the diffraction grating is most preferably of the reflection type, but may be of the refractive type.
  • the invention may be used in any application in which fine control over the angle of diffraction of a light beam is required, and may have an adjustment rate in excess of 100 KHz.
  • One application is as a beam steering element in a free-space laser communication system.
  • FIG. 3 A is a block diagram of a fine steering system in accordance with the invention, shown in a first steering state. Shown is an actuator 300 having a length D which includes a material 301 (e.g., a quartz crystal) that exhibits a piezoelectric effect. That is, when a suitable voltage is applied to the actuator 300, the length of the actuator 300 changes.
  • the actuator 300 may include a frame or other supporting structure 302 as desired.
  • the actuator 300 is configured to be coupled to a voltage source 304.
  • a reflective diffraction grating 303 is integrally formed on, or is attached to, one surface of the actuator 300, or is mechanically affixed to the actuator 300 such that the diffraction grating 303 will stretch when the length of the actuator 300 increases.
  • finely-ruled grooves in excess of 3,000 grooves/cm may be cut in one surface of a piezoelectric substrate using, for example, a diamond tool.
  • a separately formed diffraction grating comprising molded plastic film or a sheet material may be glued or otherwise affixed to one surface of the actuator 300.
  • a diffraction grating may be made using a replicating process, and then mechanically attached to a supporting structure 302 of the actuator 300, as shown in FIGS. 3A and 3B.
  • the diffraction grating 303 is preferably situated so that the diffraction grooves are perpendicular to the axis of greatest elongation and contraction so that the spacing between the centers of such grooves will change as the actuator 300 expands or contracts.
  • the spacing of the grooves of the diffraction grating 303 equals d.
  • An incident light beam 306 is reflected and diffracted by the diffraction grating 303 as a steered light beam 308 at an initial angle ⁇ .
  • FIG. 3B is a block diagram of a fine steering system in accordance with the invention, shown in a second steering state in which an electric field ⁇ V has been applied to the actuator 300 so as to cause an overall expansion by an amount ⁇ D, resulting in an increase in the spacing between grooves of the diffraction grating 303. Because the distance between diffraction grating grooves has changed (increased in this instance), the amount of diffraction of the incident light beam 306 will also change, thus changing the angle ⁇ of the steered light beam 308' by an amount ⁇ . A similar effect will occur if the actuator 300 contracts (i.e., AD is negative).
  • n ⁇ ds ' ⁇
  • n an integer
  • ⁇ the wavelength of light.
  • Ad/dis typically about 10' 3 . With an angle of 45 ° for the first order Littrow diffraction angle, this value would provide approximately ⁇ 1 milliradian deflection angle for the deflected beam.
  • the diffraction grating design must be carefully specified.
  • the fraction of light that is diffracted from the incident beam into the desired deflection angle must be high for the device to replace a highly reflective conven- tional steering mirror (for which typically ⁇ 98% of the incident light is reflected).
  • the reflection efficiency ratio of light in the desired diffraction angle to the incident light
  • Diffraction gratings are available in a range of blaze angles: very low (1 °- 5°), low (5°-10°), medium (10°-18°), high (22°-38°) and very high (38°-76°).
  • the selection of blaze angle will set the first order Littrow diffraction angle for which high efficiency diffraction will occur. The efficiency will also be seen to vary dramatically for the type of polarization of the incident light. Selection of the blaze angle is important if a high efficiency grating is desired for both s and polarizations.
  • a blaze angle of 26°, 45' will produce an efficiency of greater than 90% for both the s andp polarizations with the first order Littrow diffraction angle at approximately 20°.
  • Stretching of the grating can readily be achieved with the same piezoelectric actuators used for deflecting the mirror, but now the system inertia is much less since the motion of the diffraction grating is linear and not rotational, and the mass of the diffraction grating is much less than the mirror. Thus, the resonant frequency of the system can be much higher, thereby giving a larger steering angle bandwidth.
  • a number of piezoelectric materials have a resonant frequency of more than 100 KHz, making for a very fast steering device.
  • a piezoelectric diffraction grating steering device of the type shown in FIGS. 3A and 3B may be substituted for the steering mirror 204 in FIG. 2.
  • the overall system would be calibrated so that incoming light beam 202 from a beacon laser is diffracted at appropriate diffraction angles ⁇ to the sensor array 208 based on closed-loop feedback through the centroider 210, reference 214, processor 212, and any necessary amplifiers 216 to the actuator 300.
  • the diffraction angle of the piezoelectric diffraction grating steering device will then be set to diffract the output from one or more transmission lasers 218 with assurance that the resulting light beams 220 will be aimed at the remote transceiver.
  • piezoelectric diffraction grating steering device may be made from a refractive diffraction grating, since the actuator 300 may be of a transparent material.
  • absorption losses of the incoming light may make such a device suitable only for certain applications. Accordingly, other embodiments are within the scope of the following claims.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)
  • Mechanical Light Control Or Optical Switches (AREA)

Abstract

L'invention concerne un dispositif d'orientation d'un réseau de diffraction piézoélectrique comprenant un substrat piézoélectrique comportant un réseau de diffraction rattaché ou solidaire. Lorsqu'un champ électrique est appliqué au substrat piézoélectrique, l'actionneur piézoélectrique étend le réseau, changeant la périodicité du réseau, changeant ainsi l'angle de diffraction du réseau. Le réseau de diffraction est un réseau de type à réflexion à haut rendement diffractant une quantité maximum de lumière dans le mode de premier ordre, réduisant au minimum la quantité de lumière dans l'ordre zéro et des modes d'ordre supérieur. L'invention peut être utilisée dans n'importe quelle application dans laquelle on recherche un réglage fin de l'angle de diffraction d'un faisceau de lumière, et une fréquence de réglage supérieure à 100 KHz. Une application est un élément d'orientation de faisceau dans un système de communication à laser à espace libre.
EP99916137A 1998-03-16 1999-03-16 Dispositif d'orientation de la lumiere d'un reseau de diffraction piezoelectrique Withdrawn EP1086529A2 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US4259998A 1998-03-16 1998-03-16
US42599 1998-03-16
PCT/US1999/005694 WO1999048197A2 (fr) 1998-03-16 1999-03-16 Dispositif d'orientation de la lumiere d'un reseau de diffraction piezoelectrique

Publications (1)

Publication Number Publication Date
EP1086529A2 true EP1086529A2 (fr) 2001-03-28

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP99916137A Withdrawn EP1086529A2 (fr) 1998-03-16 1999-03-16 Dispositif d'orientation de la lumiere d'un reseau de diffraction piezoelectrique

Country Status (3)

Country Link
EP (1) EP1086529A2 (fr)
AU (1) AU3451499A (fr)
WO (1) WO1999048197A2 (fr)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6577786B1 (en) * 2000-06-02 2003-06-10 Digital Lightwave, Inc. Device and method for optical performance monitoring in an optical communications network
JP2009524229A (ja) * 2006-01-21 2009-06-25 セーエスエーエム サントル スイス ドュレクトロニック エ ドゥ ミクロテクニック エスアー ルシェルシュ エ デヴロプマン 波長可変レーザ
EP1816493A1 (fr) * 2006-02-07 2007-08-08 ETH Zürich Réseau de diffraction accordable
US8659835B2 (en) 2009-03-13 2014-02-25 Optotune Ag Lens systems and method
CN112859223A (zh) * 2021-01-25 2021-05-28 上海交通大学 表面褶皱机械复合光栅系统及调谐方法
US11550163B2 (en) 2021-04-05 2023-01-10 Apple Inc. Tunable blazed grating

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3573463A (en) * 1967-11-01 1971-04-06 Hughes Aircraft Co Laser heterodyne transceiver communication system with afc
US4716444A (en) * 1985-08-01 1987-12-29 The United States Of America As Represented By The Secretary Of The Army Optical radar transceiver control apparatus
US4736132A (en) * 1987-09-14 1988-04-05 Rockwell International Corporation Piezoelectric deformable mirrors and gratings
US5379310A (en) * 1993-05-06 1995-01-03 Board Of Trustees Of The University Of Illinois External cavity, multiple wavelength laser transmitter

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9948197A3 *

Also Published As

Publication number Publication date
WO1999048197A2 (fr) 1999-09-23
WO1999048197A3 (fr) 1999-12-16
AU3451499A (en) 1999-10-11

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