WO2002014943A1

WO2002014943A1 - Arbitrary deflection waveform generation using cascaded scanners

Info

Publication number: WO2002014943A1
Application number: PCT/US2001/025687
Authority: WO
Inventors: Timothy K. Deis; Jr. Herbert S. Gass; Daniel D. Stancil; Tuviah E. Schlesinger; Robert M. Unetich
Original assignee: Accelight Investments, Inc.
Priority date: 2000-08-16
Filing date: 2001-08-16
Publication date: 2002-02-21
Also published as: WO2002014943A9; WO2002014943A8; AU2001288276A1

Abstract

The present invention is directed to an optical beam deflection system (10) and includes a substrate (12) having a plurality of spaced electro-optic scanning devices (14) disposed thereon. These electro-optic scanning devices (14) are capable of deflecting an optical beam (16) in response to electrical control signals. The optical beam (16) passes through all of the scanning devices (14). Electrical leads (18) are used to communicate electrical control signals individually to each scanning device (14), and a controller (20) selects and applies these electrical control signals to the scanning devices (14) through the electrical leads (18).

Description

ARBITRARY DEFLECTION WAVEFORM

GENERATION USING CASCADED SCANNERS

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates generally to optical beam deflection systems, and, in particular, to an electro-optic beam deflection system used for telecommunications fiber optic switch applications and other scanning applications to direct an optical beam to desired positions or angles.

2. Brief Description of the Prior Art

[0002] In various fields, particularly in the fiber optic telecommunication field, electro-optic scanners are used in order to bend or deflect a light beam in response to an electric signal. See U.S. Patent Nos. 5,317,446 to Mir et al. and 5,668,657 to Talbot. For example, an electro-optic scanner can be a crystal, such that, when a light beam is passed through the crystal, the path of the light beam is bent. The deflection angle of the light beam is proportional to an applied electric field. Optical beam deflection systems are presently used in order to deflect an incoming light beam in proportion to the applied voltage. In the area of fiber optics, a single optical beam deflection system could be used to switch the input light beam to a selected receiving fiber by applying the specific voltage necessary to deflect the light beam to that receiving fiber. This requires generating a highly stable voltage at numerous different levels, complicating the circuitry.

[0003] If an arbitrary scan is required, the applied voltage will have the waveform of the required scan. In a resonant (sinusoidal scan) application, the instantaneous power may be passed back and forth between the scanner capacitance and its resonant inductor, with little net overall power used. If the scan takes an arbitrary periodic wave shape, the net power needed can increase dramatically, because the convenient energy storage in the resonant inductor is not so easily accomplished in other manners. Switch-mode techniques may be used, but achieving low-ripple voltage waveforms at the frequencies of interest with reasonable complexity has not been reasonably achievable in the prior art.

[0004] Multiple scanners integrated on a common substrate to increase the scan angle are known in the art. See U.S. Patent No. 5,714,240 to Gupta et al. However, the use of cascaded scanners for arbitrary scan synthesis has not been achieved.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide an optical beam deflection system that overcomes the deficiencies of the prior art. It is another object of the present invention to provide an optical beam deflection system that may generate a highly stable voltage at numerous different levels, without the need for complicated circuitry. It is a further object of the present invention to provide an optical beam deflection system for specific application in the telecommunications fiber optic industry. It is a still further object of the present invention to provide an optical beam deflection system that can satisfy arbitrary waveform scanning requirements.

[0006] Accordingly, we have invented an optical beam deflection system which includes a plurality of cascaded electro-optic scanning devices. These electro-optic scanning devices are capable of deflecting an optical beam in response to electrical control signals applied to the devices, such that the optical beam can pass through all of the scanning devices. The optical beam deflection system also includes electrical leads for communicating electrical control signals individually to each scanning device. In order to control the optical beam deflection system, a controller is provided for selecting and applying electrical control signals to the scanning devices through the electrical leads.

[0007] In the preferred embodiment, multiple scanners are disposed on a single substrate, fabricated using patterned ferroelectric domain inversion. However, those skilled in the art will recognize that the present invention may also, in achieving arbitrary deflection, use other types of electro-optic scanners that may or may not be on the same substrate.

[0008] The present invention, both as to its construction and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of the specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Fig. 1 is a block diagram of an optical beam deflection system according to the present invention;

[0010] Fig. 2 is a block diagram of an optical beam deflection system for use in connection with digital signals according to the present invention; and

[0011] Fig. 3 is a block diagram of an optical beam deflection system for use in connection with analog signals according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention is an optical beam deflection system 10, as illustrated in Fig. 1, and includes a substrate 12 having multiple spaced electro-optic scanning devices 14 displaced thereon. In the preferred embodiment, these electro-optic scanning devices 14 are integrated on the substrate 12 and cascaded so as to produce a desired output scan angle θ(t). The electro-optic scanning devices 14 deflect an optical beam 16 as it passes through the electro-optic scanning devices 14 and in response to electrical control signals applied to the devices 14. The optical beam 16 must pass through all of the electro-optic scanning devices 14, which are positioned in series.

[0013] The optical beam deflection system 10 also includes electrical leads 18 for communicating electrical control signals individually to each of the electro-optic scanning devices 14. The electrical leads 18 may be any device for communicating and transporting electrical control signals as known in the art. Finally, the optical beam deflection system 10 includes a control device 20 for selecting and applying the electrical control signals to the electro-optic scanning devices 14 through the electrical leads 18.

[0014] It is envisioned that any number or geometry of electro-optic scanning devices 14 may be utilized in order to achieve the desired scan angle θ(t). The present invention is equally applicable in both analog and digital applications or in applications where digital signals are applied to some electrodes, while analog signals are applied to other electrodes.

[0015] Fig. 2 illustrates one embodiment of a digital application, which includes a binary scanner using incremental electro-optic scanning devices 14, which are switched "on" or "off to achieve the required total scan, thereby eliminating the need for a continuously adjustable single drive voltage. Preferably, each electro-optic scanning device 14 varies individually, with one device 14 producing the least scan and each other section having increased scan, allowing each device 14 to add a different scan increment. Each of the electro- optic scanning devices 14 are driven by a driver 22, which produces and communicates a binary- coded , parallel logic signal that is easily generated with switching circuits, eliminating the need for precise voltage control of arbitrary analog levels. However, precise control is still required for digital levels. Each of the drivers 22 is controlled by the controller 20.

[0016] The substrate 12 uses multiple electro-optic scanning devices 14 connected to corresponding external voltages produced by the drivers 22. The electro-optic scanning devices 14 are aligned such that the excited optical beam 16 can be directed to fiber optic cables 24. In order to direct the optical beam 16 into the fiber optic cables 24, an appropriate lens 26 is included, where the lens 26 focuses the optical beam 16 into the fiber core 28. As seen in Fig. 2, a three-segment array of electro-optic scanning devices 14 directs light to eight fiber optic cables 24. [0017] In the specific embodiment illustrated in Fig. 2, by applying voltages from each of the first, second and third drivers 22 to the corresponding electro-optic scanner device 14, the output optical beam 16 is deflected to fiber optic cable 24, one through eight, corresponding to the binary combinations of the logical state of the three drivers 22 where a logic 1 represents an "on" condition of a drive voltage, and a logic 0 represents an "off condition of a drive voltage period. This digital-type optical beam deflection system 10 may be utilized for any number of electro-optic scanning devices 14, allowing the construction of a 1 x 4, 1 x 8, 1 x 16, etc., binary control fiber optic switch. In using the cascaded electro-optic scanning devices 14, the need to vary the potential on any individual scanning device in a continuous incremental fashion is eliminated. In this manner, the electronic circuitry is simplified and has greater power efficiency. The different degrees of deflection of the electro-optic scanning devices 14 should be in 2ⁿ, with n = # scanning devices 14 cascaded to effect binary control. While a 3-bit binary scanner embodiment is illustrated, such cascading electro-optic scanning devices 14 may be equal or greater than a 2-bit binary scanner. Further, the electro-optic scanning devices 14 may also be arranged and controlled to achieve multiple logical levels per scanning device 14.

[0018] The optical beam deflection system 10 is equally applicable to an analog application, as shown in one embodiment, in Fig. 3. In such an application, the present invention produces an arbitrary periodic wave shape that has only slightly mpre complexity and nearly the same power requirements as a sinusoidal (resonant) scan. As opposed to using a single electro-optic scanning device 14 and driving it with the complex arbitrary periodic wave shape, the present invention uses the cascaded series of electro-optic scanning devices 14 operating on the optical beam 16 and each driven by a respective driver 22. As opposed to the previous embodiment, the drivers 22 of this embodiment are resonant drivers and drive the optical beam 16 with one of the sinusoidal Fourier components of the arbitrary periodic wave shape. Even though in theory an arbitrary periodic wave shape is made up of an infinite Fourier series, the amplitude and significance of each component decreases as the order of the harmonics increases. The last electro-optic scanning device 14 in the optical path can be driven by the largest amplitude harmonic, and the other electro-optic scanning devices 14 in line would each receive the next lower amplitude Fourier component. The last of the finite number of scanners 14 (typically the first in the optical path) would be driven (if necessary to achieve the scanning specifications) by an analog linear error driver 30 with the error wave form between the partial Fourier series and the actual desired arbitrary periodic wave shape. The electro-optic scanning devices 14, which are resonantly driven with the amplitude and phase of the scan via the respective driver 22, can be easily controlled by the controller 20 and will consume a small amount of net power. Using this array of electro-optic scanning devices 14, an arbitrary period wave shape scan is achievable.

[0019] The optical beam 16 is passed through the series of electro-optic scanning devices 14, with the largest deflection scanner (usually the fundamental frequency) last in the optical path before a target. The resonant drivers 22 drive the electro-optic scanning devices 14 with sinusoidal waveforms, which are the most significant harmonics of the complex pattern being scanned.

[0020] Since a harmonic is significant if the amplitude of the Fourier component is greater that the allowed scan pattern error, harmonic frequencies that are not significant are ignored. The resonant drivers 22 must keep the proper phase relationship with each, such that each is synchronized with an output from a synchronization signal generator 32, which also controls a complex wave form generator 34. The controller 20, in this case a harmonic amplitude controller, controls the amplitude of each harmonic to best approximate the complex waveform generated by the complex waveform generator 34. A signal pickup monitor 36 receives information from each of the drivers 22, as well as the electro-optic scanning devices 14, and transmits this information to a Fourier component combiner 38. An error amplifier 40 then compares the output from the Fourier component combiner 38 with the originally desired complex wave form in order to get an overall error signal. If it is necessary to achieve the scan specification, the analog linear error driver 30 is used together with the error amplifier 40, which is typically positioned first in the optical path, in order to eliminate the differences between the finite significant harmonic sum and the full complex wave form.

[0021] One practical application of this technique is to provide a number of distinct scan positions from one optical beam 16. The complex waveform, in this case, is a stairstep or a stepped triangle. The amount of scanned light going into each of the positions can be calculated by integrating the intensity of the Gaussian spot that falls within a given aperture. If this implementation would meet the desired specification, no linear error driver 30 or error amplifier 40 is required. In another practical application, a linear ramp or triangle scan generator may be used. This application would typically make use of the analog linear error driver 30 and the error amplifier 40, due to the need for highly precise linear scans.

[0022] Overall, the present invention provides an optical beam deflection system that is equally applicable in both digital, analog or mixed signal applications. Further, the optical beam deflection system 10 minimizes the need for precise voltage control and associated complicated circuitry. The present invention is also ideal for applications requiring arbitrary scanning requirements, and has multiple applications, with particular application in the fiber optic industry.

[0023] This invention has been described with reference to the preferred embodiments. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.

Claims

We Claim:

1. An optical beam deflection system for generating arbitrary beam deflection, comprising: a plurality of electro-optic scanning devices capable of deflecting an optical beam in response to electrical control signals applied thereto, such that an optical beam passes through all of the scanning devices; electrical leads for communicating electrical control signals individually to each scanning device; and a controller for selecting and applying electrical control signals to said scanning devices through the electrical leads.

2. The optical beam deflection system of claim 1, further comprising a substrate, wherein the plurality of electro-optic scanning devices are disposed on the substrate.

3. The optical beam deflection system of claim 1, further comprising a plurality of substrates, wherein at least one of the plurality of electro-optic scanning devices is disposed upon at least one of the plurality of substrates.

4. The optical beam deflection system of claim 1 , wherein the control signals are continuously variable analog signals.

5. The optical beam deflection system of claim 1 , wherein the control signals are digital signals selected from a plurality of step values.

6. The optical beam deflection system of claim 1 , wherein the control signals comprise digital and analog signals.

7. The optical beam deflection system of claim 1 , wherein the control signals include at least one sinusoidally varying signal.

8. The optical beam deflection system of claim 1 , wherein the substrate has at least two scanning devices disposed thereon and wherein digital signals are applied to each scanning device, and each scanning device, when addressed by a control signal, causes a different degree of deflection of the optical signal beam.

9. The optical beam deflection system of claim 8, wherein different degrees of deflection are 2ⁿ, where n equals the number of electro-optic scanners.

10. The optical beam deflection system of claim 7, wherein at least three sinusoidally varying signals are applied to each scanning device respectively, the frequencies thereof being in whole number ratios to each other.

11. The optical beam deflection system of claim 10, wherein the maximum deflections due to the sinusoidally varying control signals are selected by a harmonic amplitude controller using the Fourier theorem to define the output deflection pattern of the optical signal beam.

12. The optical beam deflection system of claim 11 , wherein, in addition to the at least three scanning devices to which sinusoidally varying confrol signals are applied, at least one additional scanning device is controlled by a linear signal to correct error.

13. The optical beam deflection system according to claim 12, wherein the sinusoidally varying control signal or signals corresponding thereto are summed and compared to a desired wave form in an error amplifier, the output of which is applied to control at least one additional scanning device.

14. The optical beam deflection system according to claim 7, wherein the control signals are generated by a complex wave form generator.

15. The optical beam deflection system according to claim 14, wherein the complex wave form generator further comprises a synchronized signal generator that produces an output which synchronizes the proper phase relationship between optical signal beams.

16. ^' The system of claim 1, wherein the controller is in communication with at least one driver, the at least one driver applying an electrical potential to a scanning device.