US3742375A

US3742375A - Continuously variable delay line

Info

Publication number: US3742375A
Application number: US00256750A
Authority: US
Inventors: O Farah
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1972-05-25
Filing date: 1972-05-25
Publication date: 1973-06-26
Anticipated expiration: 1990-06-26

Abstract

Microwave information is applied to a LiNbO3 crystal by way of a thin film transducer, and is then convolved with an ultrasonic delta -function. The delta -function is generated by a laser beam and is applied to the crystal at a particular point. The point at which the delta -function is applied to the crystals affects the convolved signal such that the original microwave information may be delayed by a particular amount of time. The delay time is a function of the laser position and as a result may be made to vary. Also, since the principles of convolution are employed, the delayed microwave information will also be amplified.

Description

United States Patent 1 [111 3,742,375

Farah 5] June 26, 1973 CONTINUOUSLY VARIABLE DELAY LINE Primary ExaminerRoy Lake 75 I t z 0 F h v Assistant Examiner-'Darwin R. Hostetter 1 men or Scar am lenna a Attorney-R. S. Sciascia, Arthur L. Branning et al.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC. ABSTRACT 22 Filed; M 25 1 72 Microwave information is applied to a LiNbO crystal by way of a thin film transducer, and is then convolved [2]] Appl. No.: 256,750 with an ultrasonic S-function. The 8-function is generated by a laser beam and is applied to the crystal at a 521 U.S. Cl. 330/55, 333/ R Particular point The Point at which the 8-funetieh is 51 Int. Cl. H03h 7/30, 333 30 R applied to the crystals affects the convolved signal Such [58] Field of Search 307/883; 330/55 that the Original microwave information y be layed by a particular amount of time.

[56] References Cited The delay time is a function of the laser position and as UNITED STATES PATENTS a result may be made to vary. Also, since the principles 3 602 725 8 1971 De Maria 307/883 are employed the delayed micmwave OTHER PUBLICATIONS Piltch et al., Applied Physics Letters, 15 July 1970,

information will also be amplified.

2 Claims, 1 Drawing Figure EOUT /22 I2 k 8 &\l .8 EIN I32 P LASER SPLITTER l6 l t. ..V d 22 TRl6GERlNG- v SYSTEM 1 CONTINUOUSLY VARIABLE DELAY LINE BACKGROUND OF THE INVENTION Time delay systems for microwave frequencies have many drawbacks. The most serious disadvantage is the fact that most of the present devices are incapable of being adjusted from one delay time to another. In the past the only versatility available in the selection of particular delay lines was the substitution of one entire delay system for a different delay system.

It has been found advantageous to provide a microwave delay system which can be continuously varied to provide easily selectable and precise delay times.

OBJECTS OF THE INVENTION It is therefore an object of the present invention to provide a continuously variable delay system.

Another object of the invention is to provide a variable delay system capable of being used at microwave frequencies.

Another object of the invention is to provide amplification of the delayed microwave signal.

Other objects, advantages and novel features of the invention will become readily apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing wherein:

THE DRAWING The FIGURE depicts the system capable of producing a variable time delay at microwave frequencies.

SUMMARY OF THE INVENTION A microwave signal is applied to an ultrasonic transducer which is attached to a LiNbO crystal. The microwave energy is therefore transformed into an acoustic waveform and is propagated through the crystal. A trigger is provided to pulse a high powered picosecond laser into the opposite end of the crystal to provide an ultrasonic S-function. The laser beam is controllably positioned a distance d from the ultrasonic transducer by a movable lens such that a convolution between the ti-function and the microwave signal takes place. The resultant convolved signal is a signal proportional to the original microwave input but is time delayed an amount proportional to the distance d.

DETAILED DESCRIPTION Referring to the FIGURE, microwave energy E, enters the system 10 and is applied to signal splitter 12. The signal splitter 12 divides the energy into two parts 13 and 15. The microwave energy denoted as 13 is made to impinge upon ultrasonic transducer 14 and the energy denoted as 15 is directed to a laser triggering system 16 which controls the operation of laser 18.

The ultrasonic transducer is affixed to ferroelectric crystal 20. The combination is disposed in microwave cavity 22 which is attached to output waveguide 28.

The purpose of the system shown in the FIGURE is to provide a signal E in waveguide 28 which is delayed in time from energy E The delay is accomplished by acoustical convolution and the amount of delay is a direct function of the distance d. That is to is focussed at point P by lens 24, or a distance d from the transducer/crystal interface.

When microwave energy E, is applied to transducer 14, an acoustic wave is propagated through the crystal 20 from left to right as shown in the FIGURE. This acoustical energy passes energy burst E, from the opposite direction to give a third signal E (a result of a nonlinear interaction) such that:

)our f m 2 which is the convolution of E (t) with E (1). The laser 18 produces the 6 function for the convolution process, and the amount of delay is expressed as:

Delay AT 'r where AT is the time delay 17 between trigger l6 and laser 18 and A d/ V where V is the velocity of sound. The only restriction is that the delay 17 in the laser triggering circuit be equal to or smaller than the time required for the sonic signal from E to reach point P.

Examining the individual components of the system, signal splitter 12 can be a directional coupler.

Typically the transducer 14 is a thin film deposit of zinc oxide sputtered on a thin gold electrode laid on the LiNbO crystal 20.

The LiNbO is a YZ-cut LiNbO delay rod as described by M. Luukkala and G. S. Kino in Applied Physics Letters, Volume l8, Number 9, May l, 1971 entitled Convolution and Time Inversion Using Parametric Interactions of Acoustic Surface Waves.

The microwave cavity 22 and its associated wave guide 28 are well known in the art as is double convex lens 24.

The laser 18 is a pulsed high powered picosecond laser such as a Q-switched ruby laser.

Finally, the electronic delay 17 may be constructed of flip-flops or the like.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by letters patent of the United States is:

1. A continuously variable microwave delay line comprising:

means for splitting a microwave signal into a first and a second part;

means for triggering a high powered ruby laser by the use of said first part;

transducer means for transforming said second part into acoustical energy being physically attached to crystal means for propagating said acoustical enmova ble optical focusing means for focusing the energy from said ruby laser into said crystal means at a distance d from said transducer means to propagate a second burst or acoustical energy such that an acoustical convolution results in said crystal to produce a signal which is delayed from said second part. 2. The device is claimed in claim 1 wherein said crystal means is'a LiNbO crystal.

Claims

1. A continuously variable microwave delay line comprising: means for splitting a microwave signal into a first and a second part; means for triggering a high powered ruby laser by the use of said first part; transducer means for transforming said second part into acoustical energy being physically attached to crystal means for propagating said acoustical energy; movable optical focusing means for focusing the energy from said ruby laser into said crystal means at a distance d from said transducer means to propagate a second burst or acoustical energy such that an acoustical convolution results in said crystal to produce a signal which is delayed from said second part.

2. The device is claimed in claim 1 wherein said crystal means is a LiNbO3 crystal.