OPTICAL RADAR SYSTEM

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP81-00120R000100060050-6
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 9
• Document Creation Date: December 20, 2016
• Document Release Date: November 6, 2002
• Sequence Number: 50
• Publication Date: January 2, 1968
• Content Type: CONT

Approved For Release 2007/09/21: CIA-RDP81-00120R000100060050-6
Jan. 2, 1968
-,
Tiled July 3. 1964
13, 26
A,
LASER /71w
cw
CHANNEL
ONE
30
12
R. A. FLOWER ETAL
OPTICAL RADAR SYSTEM
3,360,987
2 Sheets-Sheet 1
644 4-44. Gd-4A4e/Ullt-ce.z./
'1;-4
21
26
31
34
35
36
4
50
52
AMP
FILTER
?R
LOW
PASS
Fr_TER
DIODE
MIXER
47
54
IF
AMP
r7
OPT, PK StoFT 20k /
16 27
"lh---
277_4
111
?Fm
MorER
cHANNEL
TwO
46
tt 48
IF
PHASE
SPLITTER
45\1
IF
OSC
(10.7 MC)
SUMMING
NETWORK
AMP
FILTER
LOW
PASS
FILTER
DIODE
m!xER
IF
AMP
Fm.
DISCRiM 9
AM LIMITER
INTEG.
INDICATOR
FIG. I
61
BY
33
39
40
41
43
51
53
INVENTOR.
ROBERT A FLOwER
GUS STAvIS
171/4.'
ATTORNEY.
At
Approved For Release 2007/09/21: CIA-RDP81-00120R000100060050-6
Approved For Release 2007/09/21: CIA-RDP81-00120R000100060050-6
Jan. 2, 1968
Filed July 3., 1964
R. A. FLOWER CTAL
OPTICAL RADAR SYSTEX
3,360,987
2 Sheets-Sheet 2
CHANNEL ONE
INVENTOR.
ROBERT A. Fi..0v.ER
GUS STAVIS
BY
d1/97/ae
ATTORNEY
Approved For Release 2007/09/21: CIA-RDP81-00120R000100060050-6
IVO& _????? dfake.
Approved For Release 2007/09/21: CIA-RDP81-00120R000100060050-6 3/360,9s7
T' ?? 1
Patented Jan. 2, 1963
3.350.987
OPTICAL R:\DAR SYSTEM
Robert A. Flower, Vs hlte F1irs?ntl Gus Stasis, Briar-
clef Maror, N.Y.. av,7eftsors to General PreeiNio-n, Inc.,
a torpor:0;0o or Delavvara
tiled July 3. 1Se..4. Ser. Na,
16 Gleams. (CL 73-71.3)
The present invention relates to an optical radar sys-
tem for detecting and analyzing vibrations o' a remote
body or surface. More particularly the invention described
herein is a coherent optical radar system in which a
generating means, roch as a laser, is employed to generate
and trarsmit a continuous ave (cw) of electromagnetic
energy toward a remote target. The system provides for
receiving the reflected transmitted cw sienal and for de-
tecting and trmslathig :he information of the reflected or
echo signal in terms of the c'e.sticter of the vibrations or
motion of the remote bepity.
The tee of a cw signel et optical frequencies for detect-
ing vibrations of a rernree body has heretofore presented
problems. In microwave and radio frequency- radio. sys-
tems a stable local osciilator may he conveniently used
to pros id e a reference signal used for heterodyning with
the e-ihia signal for the Porpeoe of recovering echo phase
inforrnati.m. At optical frequencies this orrareement is
difileult to duplicate. Thos a cw coherent optical radar
system etroloying one sienal generating means is a pre-
ferred -confledzation.
Since a re:erenee sienal in the form of part of the
tranernioed sienal is ready obraiiiable, a sLstern of horn?.
dyning. rnixieg the. transmitted s:enal and the ecrin-sig-
riliF,- u ?ed in the s?ehjeet inventioa. flemodyning is a
process of mixing. Itoroody nin a is a PrC,CeSS of mixing an
echo signal and pz-.11 of the traiornitted sional so as to
provide, amongst o.her things, a signal which varies at
or about zero frequency. Such variable signal is a function
of the vibrations or movements of the remote body or
surface from which the tran,,mitied signal was reflected.
Simple homodyning cf fhis kind presents the problem
of foldover, where the ritodulation sidcbands on the echo
signal, which are the functions of the vibrations or mo-
tion of the remote body or surface, fold aboot the zero
frequency. The fcldieg cf- the sidebands abort zero fre-
quency distorts the characteristics found on the echo sig-
nal. This distortion prevents true Measurement of the
echo signal cha-acteristics. ?
Our novel approach avoids the problem of providing
a separate local oscillator at the optical frequency. Thus
only one laser is employed in the cw optical radar system
andiiianner which avoids the problem of fold-over
of the echo characteristics about the zero frequency.
Our novel cw optical radar system involves homodyne
mixing of the transmitted signal and the echo signal in
two quadrature channels fel:owed by quadrature modu-
latiOn with an intermediate frequency sianal of substen-
tially loWer frequency than the transmitted frequency but
subs:antially higher frequency than any of the character-
istics-found on the echo eignal and summing Of the modu-
lation products before final demodulation. Wit.h this new
apjnach, the echo signet i rechnstructed at an inter-
mediate frequency so that the exact quality of the char-
acteristics found on-the echo signal, is preserved.
It is an ob;ect of the r.,:z..5nt invention to provide a cw
(Ttical radr yntem fox detczi:n:; and analyzing vibra-
tions of a remote body or surface. . .
Another object-is to .provi,ie a cw radar system operat-
ing at frequencies in the oetical range for detecting and
analyzing yib,:atioc,s of a Teo:eta body or surface in which
the received echo -signal is homodyned at the carrier wave
frequencies in two quadrature channels and quadrature
2
modulated at an intermediate !revert" for reconstruct-
ing the echo signal-. at an inter.rediate freceency.
A further object is to provide an oothoid radar syr-o.m
for detecting and finely-zing vihrations or motion of a
Is remote body or st.rface in which the eetieel frecorency
signal generator serves for transmitting the optiod fre-
quency signal and for providing a reference ,ieto?I thcreSy
avoiding the necossoy of prosidinet a steland local -oscil-
lator at the optical carrier frequency.
10 A furher object ts to provide an opt-cd radar system
in which the echo. signal is hotnad} ned in two quadrature
channels and the echo signel is reconstructed at an inter-
mediae frequency and is analyzed and translated by cir-
cuit elements employing conventional frequency modula-
15 tion and demodulation techniques;
'these .rind other ob.:ects will become apparent from
reddin; the follow ine description of our in,,ee!ion and
the principles related theteto with reference to the accom-
panying drawings in which:
20 JIG.- is a block diagram of the preferred form of
the invention and
HG. 2 is a circuit diagram of part of the block diagram
of FIG. I.
Referring in detail to the block diagram of FIG. I,
25 an optical frequency continuous V*3%C, (CA-) sienal gen-
crafty., reerest.inted by block 10, cw provides a
transmitted shoed in the form of a light be let or column.
The transmited beam is represent.d by lichen line 11.
For the purpose of pro-Ordine a convenient and compre-
30 Itensh.e de.scrietion of the. functions and peineiples- relat-
ing to our invention, mathematical equal:coo shell be used
to describe the various signals and fun:hs of certtin
of the compenents of our system. With this in mind let it
be aserned that the signal output of the leer 10 has :In
35 optieal carrier frequency of V,o.
The light beam 11 is directed to, and iiluminetes the
target 20, which is assumed to be vihreeiroe. An echo or
refited sifznA, represented by broken line 21, is reflected
from the target and includes thereon a phieso reodulatico
40 cemponent, which shall be referred to as oit), wls-ch is
a function of the propagation path leneth changes of
the signal arising from the vibrational reutien of the
target, with respect to the source of thc tratenmiumd sienai.
An amplitude modulation-cOmponent, which shell be re-
45 ferred to as AUL is also present on the echo signal.
Thus, at any one time the echo signal may be repre-
sented as the transmitted carrier signal, modified by the
phase modulation component, plus the amplitude modu-
lation component, at that time.
Since the frequency of the transmitted carrier signal
may be represented as "/2e, then the instantaneous value
of the transmitted signal at time t maybe represented as:
sin - (1)
55 The instantaneous ?value of the echo signal at time t
tray be reprecented as:
A(r) sin (ia-l-sti(t)) (2)
60 In our system the transmitted carrier signal serves as
a reference signal; therefore beans splitters 12 and 13
are provided, each of which extract a sarnetie of hearts
11 as indicated by broixen line -13 and hi-ex-en line 16.
It sl7ozi!d be nreed that for -ccr.venenze of iili.1,!ratioo,
rri the varicl:s beams ia:-.2 been se::.,ar: ted so as to more
and Foczsse% ?xilh:ca co
!rystem. However, reamed that,ome of the
-;:7,2';i7TIS, for exampie, lie:rot 13 and 26, 16 and 27, 2o
ad 25, :7 and 23, and 21 and 11, wi. are these beams
70 are shown parallel to each other, wollkl przferabiy ho
in coincidence and be prjeCted along substantially the
same axis. It should further be appreciated that each
50
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pair of beam splitters 12 and 24, and IS and 22 may. each
. be the same beam splitter, but each is separated and
Shown as individual beem splitters, for convenience and
clarity of description.
It should also be noted that reflectors or mirrors 14
and 17 would reflect their respective beams from Cam-
mon roints, respectively so that the beams 13 and 26,
associa:el ssith reflector 14, and beams 16 and 27 ass?.
elate,/ with relesetor 17 would each be in coincidence
respectively. Fuohen since the beam srlirers 12 and 24
may he one beant selhosr and 13 ard 22 may be another
ore beam Witter then the !sterns 26 and ZS wculd be
arplied to the seme point or area as inputs and he beams
27 and 23 would be enrl:cd ta another same point or area
as inputs. The tareee .2n ...reflects the been's. I/ . as .21 so
that 11 :IA 21 would also be in coincidence, having a
substantially common axis.
W;th the above in mind, it will be seen that beam
winter 12 deflects part of beam 11 as indicated by.13
to a mirror or reflector 14. The reflected beam from
mirror 14 is represemed as beam 26. Beam sphaer 15
deflects part of beam 11. as indicated by 16 to a mirror
or reflector 17. Bern /6 is represented as passing through
17a. Opt. Ph. Shift, representing a light beam phase
fhir:cr. The perpose of 17a i?; to shift the ph ese of beam
16 and thus beam 27, as will be mole fully deserihed
below. An ahem:1:e method of providing phase shift of
the beam 16, is by positioning the mirror or reflector
17 so as to let ;then or slierien the reth length .if the
beems 16 and 27. Beam 16 is reflected from mirror 17
whence it be: "rue beam 27.
The ce.nicr bean 11 illeminates the target 20 which
reflects the sieral as echo beam 21. Beam 21 is split by
beam splitter 22 as indicated by beam 23 and the beam
splitter 24 &fleets beam 21 as indlcated by bt!:)..n 25.
fri order to caplain the desired nhaise relationships
among the sinal and reference beams 23, 25, 26 and 27,
the points a and I are arbitrarily selec7ed. It will be
foune that as between the echo s;ereds 25 and 23 there
may he a freed ph-o.e alfference. This may be caused by
the dOTerence in path lcoeths cf the signals. This phase
difference is measurable and let it be assumed that such
phase difference between beam 25 and beam 23 at points
a and b reseectively 11,::}' be repreeented by O.
The phase shifter, ether I7a or, in the alternative, the
position of reBeeter 17 is adjusted so that the phase of
beam 26 at pcint a differs from the chase of beam 27
at point b by the annle 64-72. This is poss:ble since phase
shifter 17a affects only beam 27 (and, also, 16)- and is
not in the paths leading to beams 25, 26 and 23.
With such arrangement the operation of the receiver
is not greatly depenaent upon the relative positions of the
laser, the photemixers, and the target. After initial align-
ment to establish the proper or desired phase relationship
within the network, the path lengths external to the
network become noncritical..
With the desired phase alignment accomplished the
beam 26, at point a may be represented as:
sin wt (3)
and the beam 27 atpoint b may be represented as:
cos: (ra-Fa) (4)
In other words it may be said that the reference beams are
in quadrature- displacement. Further, since points a and 6
b were arbitrarily selected, they could also be chosen
so as to make the phase difference equal to zero. Theta
9 becomes zero.
T's the echo signals 25 and 23 at points a and b,
reeptectively, each may be referred to as:
4
filter, a diode mixer and an /F amplifier, each channel
providing an output respectively to a aurnming network.
A common intermediate frequency (IF) encilletor (osc)
provides an output !signal to an IF rh.a:e srlOter which
Provides IF sinalas in phase quadrature, saith resneet
to each other, to the respective diode rn,:xers. Thus the
signal inputs to the diode mixers may operate to add to
the phaa: shift between the reference sO-eals so as to
provide a phase shift of ISO or may seh.reet from the
nhasc shift between the reference sieends oa as to sub-
:earl:jelly eliminate the phase difference develored
by 17a or, in the alternative, 17. The intermediate fre-
quency 5ignat in its unthifted form, is ereiied to the
summing network to serve as a carrier signal.
j 3 Referrin.g to the input signals to Chanael One, the
signals 26 and 25 or.
sinaar-1-4(1) sin (wr-i-10(1)) (6)
are applied to the rhotomixer 30,
ceerrine to the input signals to Channel Two, the
signals 27 and 23or?
cos oit-f-A(1) sin (or-Fo(r)) (7)
are applied to the photomixer 32.
25 The pnotorniser, which may he a phot onultiptier or
other tvpe of photedelector may he in the eonventienal
form of photoserniiiae dealer. sk Kell pros ides coroorionof ?
Fglit to photocurrene and current moltHication.
For a comprehensise description of :he functions and
rrocesaes of a photodetector reference may be made to
an article, "resole:1On, Light Demodaletion" by D. F..
Caelais. and B. J. McMurtry, on een;es 54 to 60 of the
publication "Electronics." April 6, 1964
issue. The peers of the article partici:ler-1y aeciieable, are
r:-,,7.e.s 55 and 56.
Referring again to the optical inputs to Chine! One,
the foilowing equations may be set forth:
Fi=karfo sir u.S (8)
arid
4o
fOeeka/P.(r) sin (wt-f-ge(r).) t9It
v. here F1 equals the electromagnetic tielel strength of the
optle-al -reference beam 26: F2 equals the electrom;onetic
field strength of the optical echo beam 25; Fo is the effe.c-
45 tive reference beam- power fellieg on the face of the
P5(t) is the effective incident echo optical
power faflirg on the face of the phototube and k is a
conoant re:atcd to the impedance of free space.
Thus,
50
1=--p(Fri-F2)2 (10)
Where 1 is the current emitted from the photocathode;
p is the responsivity of the photocathode in amperes per
watt.
55 Therefore,
esi=iRy.---rpRL(Fil-Far (11)
Where en is the output of the phototube and Rz, is the
terminating [cad of the phototube.
Thus,
60
A(t) sin (art-fati(t))
(5)
The block diagram shows two channels, Channel One
and Channel Two, in broken line blocks. Eaeh shannel
includes a plaotomiXer, sn amplifler-filter, a low-pass
e31=p/4,[kagg5
Let:
5 and
then
sin (tot-Fsgr))-Ft?iicsin 4ar (12)
PR5AVP1(1)=4(1)
PRik'V'Pa=1
fsin ost-VA(t) sift [carfo(t)j}2 (13)
Relative to the optical inputs to Channel Two, a cone-
70 spondhea eceation may be draart eaceet :hat F1 the aiela
streneth Of beam ZT would be represented as:
= ka/P0 cos art (14)
while the term for Fa coreespcnding to sigaal beam 23
75 would be the same as the term for -.gnat beam 25.
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10.7 mc. is a convenient rretqaene.y to use because of the
ready availability of demodulation eqiipment.
It aboolal be poin*.cd out that the 10.7 mc. siaaal series
as an intermediate freeaeancy sienel and intermediate fre-
e carency signals of other frequencies. may be used, as de-
sined..o lOng as the principles presented herein arc main-
tained- It is dettiraNe, thialeh net necessary, that the fre-
quency of the intermedia-e frectoesecy sienal to be at leaA
double. or in caeca., of dobe, the fiequency of the high-
in est normally expected sidebend frequency in the echo
The frequency of the sianal output 44 of the IF oscil-
lator 45 may be referred to as:
Thus the output 31 of photomixer 30 may he a voltage
havies a value as en above (Equation 13) ad the out-
put 33 of photomixer 32 may be a voltage having a
*aloe en:
en=foos irr+A(t) 5 in flar+(r))}2 (15)
Referring to the signal output 31 of photomixer 30 the
equation may be expanded to:
eat ts?la eir-1-4(1) sin la.;4-0(t)1)3
se-.(sin )2 +24 it ) sin at sin [apt-i-a(t)I
+(A(') sin (*4-1-09(01)2 (16)
The term (sin att)2 contains a D.C. term and the sec-
ond harmonic of the optical or transmitted carried fre-
quency and is not aorepted 'ey the amplifier filter, 34. The
term fal(r) sin beta-ofill /2 may he ignored because
IVO, the echo sigal ro%cr, is substantially smaller than
Pee the refeience beam power, as a result of progagation
losses. Hence. A(s) which equals Fikkv-i1-iI5 is much
smaller than unity, ani A(t)12 beeomes negligibly
small. The cross-product term 2,1(:) sin ad sin
Iot+o(r) is the term of interest since this term includes
the charaeterioics alit,: vibrations of the target in a value
sufficiently high as to be processed. The term of interest
may be expressed as:
LS(t) sin &at sin rao-1-#(1)1
e--A(t)(?cos t2er+a(t))1-cos 10(0)) (17)
Signal 31 is naped to empli5er-filter, Hoek 34, which
amplifies the seeal and filter; out the high frequency
competeents, Low-pess filter 35 further filters the sig-
nal. Thus the sigaal at 35 may be expressed as:
e,n)=A(t) cos [16(t)] (18)
Titus the charasteristics on the echo sianal, ahich are
a function of the vibrational .motions of the tareet, as
expressed in mahematical equatiors have been isolated
in Channel Ore at 36.
The sienal otareat 33 of rhotornixer 32, the result of
mixing sienek 27 and 23, hits been espressed above in
Equatioa 15. The cross-product term, the term of interest,.
may be obtained in the same manner as shown for obtain-
ing the crosoprod act term of signal ese The equivalent
cross-production term for signal 33 (eu) may be rep-
resented as:
al(t),`sin I2r-1-0(1)1-Fsin (19)
The term of interest developed in the Channel Two
photomixer 32 is applied to amplifier-filter 39 and low-
pass filter 40 by which the high frequency components
are attenuated. The components 39 and 40 of Channel
Two serve the same functions in Channel Two as com-
ponents 34 and 35 serve in Channel One, so that the sig-
nal 41 may be expressed as:
eqn=A(t) sin Isti(t)] (20)
Thus the characteristics on the echo signal, which are
a function of the vibrational motion of the target, as ex-
pressed in metherratical equations have been isolated in
Channel Two at 41.
The signal 36 is applied o diode mixer 42 and the
signal 41 is applied to diode mixer 43.
Also applied to diode mixer 42 is the IF reference
signal 47, with IF reference signal 48 being applied to
diode mixer 43.
As previously described, en intermedia:e frequency sig-
nal is &veto:led in IF oscillator, block 45. We employ a
stable oscilla:or providing an output signal of 10.7 mega-
cycles (10.7 me.) since such oscillalor is readily available
and the frequency of the signal is sufilciently high so as
to be scbst.amin:y above the highest frequeecy of the
charac:eristics which may normally be found on the echo
signal as a result of the vibration of the tarr:et 20, and
sufficiently low so as to he ,ubstanzially loAer than the
frequency of the carrier signal. Further, the frequency of
13
mita.
This sianal it applied to the IF phase splitter. block 46.
Lich erovides quadrature output signals 47 and 44,
whieh may be represented as:
(4 4T) = sin n"
20 and
23
30
35
40
(21)
e(4$)= cos Pit . (22)
The signals 47 and 36 areapplied to the diode miaer 42
which provides an output 50 Which may be represented as:
ea,)=[..4(t) cos [a(t)]-1-sin int)*
=[4(0)2 cos2 [55(1)1-1-2A(r) cos
sin rind-sin2 int (23)
The signets 48 and 41 are apalital to the diode mixer 43
uhich provides an output 51 which may be represented as:
rale-se-M(t) sin fo(t)l?ease ot112
=MOW sin 2 [o(t)]4-2A ft) sin [a(t))
cos art+c052 nu (24)
Fach of the signal, 50 and el are applied ost IF am-
peiers 52 and 53 renezziv..ly. As seen previou../y,
is an iefinitesimai and therefore tl.e 9r t tern ci
Eci...nzions 23 and 24 may be Ako, sir2 Int and
cos = In: lead to D.C. and double frequency outputs. Dur-
ing aincl;fication each of the re,pzc:i%e sienals are 4.!:ec-
ti.-ely filieled thus eliminating ac..:.nd double
components so that the signal 54 may be expressed as:
e54=2.4(t) sin no cos [s(r)]
and the signal 55 may be expreaed as:
e(50=2/1(t) cos in! sin fo(r)] (26)
Expansion of the latter two signal equations may be ex-
pressed as:
(25)
50 e(54)=--/1 (/) [sin [trit-1-4(0] ?sin rint-0(()]) (27)
and
el55)=i1(i)(sin Eint-kb(1)1-Fsin 0:11-4,(W) (28)
As previously described :he D.C. term representing
55 the cross-product of the reference signal and .the echo
signal was attenuated by the filter new arks in each chan-
nel so that the signals 36 and 41 are the isolated echo
information signals With carrier information suppressed.
-By Mixing the echo information signals 36 and 41 with
Go the phase shifted intermediate freceency -signals 47 arid'
48 respectively two signals 50-and 51 are obtained each of -
? which include the echo information on the intermediate
frequency signal, each intermediate frequency signal
shifted in phase with respect to each other.
G5 The signals -54 and 55 are the ampli.fied signals 50 and
51 resractively.
It N; 1 be appreciated that the sinnals 54 and 55 rnay be
added or summed, as by the s.l.mrninz network, bt:.>ck S.
Th'...s will provide a signal v h is the echo information
70 reccnstrunted iii ampl;tud- t frequency -modulation
form at the intermediate tey level. In -order to
reconstruct
. has prec4cly bee.
the circuit elements alreacie
75 For the purpose of provi,
signal, the carrier,
-ed by the action of
.d, must be reinserted.
required carrier fre-
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oiow,u0
quencv signal the output 44, which is substantially the
sum.; output as 44 of block 45, is also applied to the
summing network 58 so that the signals 54, 55 and 44-
a r - summed. Since the signal 44 is substantially un-
shifted and is of the intermediate frequency value. the
signal 44' serves as the carrier signal, thereby providing
signal 56, the summed signal, which is the reconstructed
cello signal at the intermediate frequency kvel.
The use of the irtermealiate frequency signal 44' as a
carrier signal for the rceonstrecteal echo signal is con-
venient since the signal output is readily available. Ho-s-
ever, in practicing our insention another intermediate
frequency stellate may be used for a earlier signal, if
desired, so long os the carrier signal is substantially in
phase and frequency to the intermediate frequency signal
used for mixing with the isolated eato signals in tooth
channels.
Relative to the summing of the signals 54 and 55, it
will he found that the sum of the sierals may be repre-
sented as the sum of Equations 27 and 28 or,
e(50.2A(r) sin [ei1-1-0(1))
The amplitude modulation component ? on the recon-
structed signal may be eliminated by a conventional Fon-
iter and the frequency modulation components may bc?
recovered by conventional frequency demodulation tasnata-
niques.
This may involve the use of a frequency modulation
discriminator, such as represented by black 59, which
represents both the amplitude modulation limiter (AM
limiter) and the frettuency modulation discriminator (FM
discrim).
An integrator, such as represented by block 60 (Integ.)
may be emplosed so as ta provide an output rept esentiag
the instantaneous prei.ion of the target and this latter
output may be applied to an indicator, such as 61 which
may be a meter or recorder. A nansducer, such as a
speaker or set of earphones, may he used so as to provide
an auditle indication Li the vibrations of the target, if
desired.
Referring to FIG. 2, a circuit diaanarn illustrating part
of the circuitry which is represenad in block form in
FIG. 1 is presented. The circuit diagram of FIG. 2 is
marked nff with broken lines so as to indicate Channel
One and Chnnnel Two. Between the.rnarked off channels,
a circuit which may be employed for a phase splitter,
a summing network, a limiter and FM discriminator is
shown.
It will be noticed that the circuit labeled Channel One
is a substantial duplication of the circuit labeled Channel
Two. Therefore the circuit functions of Channel One will
be described and such description should be considered
a description of the circuit functions of corresponding
parts of Channel Two.
Similar reference characters are used as between FIG.
I and FIG. 2 to indicate circuitry corresponding to the
block form representations of FIG. I.
It will be noted that FIG. 2 indicates that two direct
current (DC) voltage sources (-1-150 v. and ?150 v.)
arc employed to drive the circuit with a common ground
or return represented by the conventional ground symboL
It will be appre, ted that the various signal values may
be measure? or detected by conventional means, between
the electrical points indicated by the refe:ence character
and common ground.
Referring particularly to the circuit blocked off and
labeled 46, the signal 44 from the IF oscillator (not
shown) is appliei to the input labeled 44. The resiv.or-
capacitor network 71, 72 serves as a phase shift netwerk
to shift the phase of the signal 44 by 45" in one direction.
The shifted signal is applled via lead 75 to the grid of
tube 76. The capacitor-resistor netasork 73, 74 serves as
a phase shift network to shift the signal 44 by 45* in the
other direction. This shifted signal is applied via lead 77 7
10
8 -
to the grid of tube 78. This network provides two output
signals, at the frequency of signal 44, shifted in phase 90'
with respect to each oth.
Signal 47 is pickee off the cathode circuit of tube 7i
and applied to the diode miser 42 of Channel One via
the lead 47. Siena! 43 is risked off the cathode circuit of
tube 78 and is applied to the Ciode mixer 43 of Channel
Two via lead Each signal :s individually capacitor
coupled, as shown.
"Ilhe photo7nixer 30 is represented in part, schematically,
as the anode 80 of tube of the p'notomixer 30 coupled to
a preamplifier, block 81. The sinal output of the phoo
mixer at 31 is applied to the control grid of a pentode 02
in the amplifier-filter 34. The amplified signal is asupkd
from the anode circuit of tube 82 to the low-pass filter.
network 35, including capacitor 84 and coil 85. The sig-
nal output of the low-pass filter is applied via lead 36 to
-the input of the diode mixer 42 along with the IF signal
on 47.
It will be appreciated that the signal at 31 may include
Isw frequency ramble or noise that is not necessarily
,characteristic of the vibrations or motions not of interest
of the target.
Such noise or disturbances may arise, for example, from
a-, changes in the refractive index of tIe air med:rea through
which the optical, signal propagates. It may Cat desirable
to ettenuate such low frequency noise. This may be ac-
complished by selecting the values of cripacit;,e-resistise
neteork 63 and 64 so as to substantially attermate such
lew frequencies. This may have the'r 'feet of iasreasing the
frequency level of the low freeuency-of the 'and of fre-
quencies passed by the fiber network. The values of the
resioive-capacitive network of resistor 65 and capacitor
84 may also be selected so as to effectively control the
range of frequency values o the band of frequencies
passed, if desired.
It will be noticed that the circuit of the several eampo-
nents of each channel are in conventicaial form,
It will be appreciated that the optical frequencies in-
-Or eluded in the signal at 31 are filtered out so that the signal
at 36 includes the characteristics of the vibrations of the
- target found on the echo signaL
The combined signals at 36 and 47 are passed through
the mixer diodes 86 and 87 to the primary coil of trans-
45 former 83. The mixed signal is induce( into the secondary
of transformer 88- and applied at 50 to the control grid of
pentode 89 of IF amplifier 52. The amplified signal is
picked off the plate circuit of tube 89 and applied via lead
54 to the summing network 58.
50 . The signal on lead 55 is developed Sy Channel Two in
the same manner as that described for Channel One. Sig-
nal 55 is also applied to the summing network. .
The signal 44'' which is substantially the same signal
as 44, is also applied to the slimming network to be added
55 to the signals 54 and 55, the signal 44' to serve as the
carrier signal. The summing network, including capaci-
tors 91 and 92, junction 93 and resistor 94, provides an
output at junction 55 which output is applied to the con-
trol grid of pentode 95 an FM limiter-discriminator driver.
GO The anode circuit of tube 95 includes the primary of the
tuned discriminator transformer 96 which together with
rectifier tube 97 and its associated filter network performs
the desired phase detection.
The output of the discriminator s picked off the cath-
Ga ode circuit of tube 97, the output at 98 being a voltage,
the instantaneous value of which is representative of the
instantaneous frequency. of the echo signal, which is a
. measure of the instananeous velocity of the vibrating tar-
get. The output 93 may be in.cgrated beeRC network 60 .
70 to give a vc.,:tage vLich varies as the -instantaneous posi-
tion of the vibrating target. The integrator output 99 may.
be connected to an indicatcr and/or meter, 61, which may
provide an indication and/or record, as for example, by
Use of a recorder, of the vibrations of the target 20
(shown in FIG. 1).
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9
Thus we have described an optical radar systm for
detecting and translating vibrations of a remote target
which avoids the LIFe of a second beat oscillator ter pro-
viding a reference signal and which includes a dual chan-
nel quadrature arra n mment, which has reconstrumed the 5
optical echo fregeunay at an intermediate frequency aie-
nal. This system has the dvantage of overeomine the
fold-over emblem and avoids the use of complex dersedu-
lation of signals at optical freqtrenciese Obviously, al-
though certain ahernate parts of the arrangement pre- 10
sented herein hese been sueeested, other alternate ar- ?
tenements including rearraegement and suboitution of
parts may be made, as will be familiar to thoce skilled in
the art, without departing from the spirit of the invention
as defined be the appended
What is claimed is:
1. An optical system for determining the frequency
of sibration of a remote body including:
means for generating and transmitting a eenerally co-
herent light energy beam tweak' the remote body,
means fOr receiving reflected light energies from such
remote body, said reflected. lieht energies shifted in
frequency from-the-Carrier frequency thereof in ac-
cordance with the frequency of vibrations of such
body, and for piov :ding a signal which is a function
of said frequency shift,
means for isolating said signal,
means for generating a substantially constant inter-
mediate frequency signal, the fiequency of which
exceeds the frgerency of the la .gest frequenca shift eo
of the reflected light energies,
means for mixing said _isolated signal and the constant
intermediate frequency sigeal for providing a com-
plex signal has:ag intermediate frequency character-
istics modulated in frequency in accordance wita said aa
frequency shift of the notated
a frequency modulation &?-ariminata. far deteeeing the
frequency modulation of tlie intermediate frequency
-characteristics and for providing an output variable
in accordance with such frequency modulation, 40
means responsive to said output for providing an. :in-
dication in accordance a:th the value of said output
so that the indiaaTion V, l 1, ary proaorttona:ly to the
vibration of the remote body.
2. An optical system for detecting and measuring the aa
frequency of vibration of a remote body including;
means for generating a continuous coherent electro-
magnetic wave energy signal and for transmitting
said signal to a remote body,
means for receiving signals so transmitted and reflected 50
from the body, the reflected signal including a char-
acteristics, the value of which is proportional to the
frequency of vibration of the remote body,
means for homodyning a . portion of the transmitted
signal and the reflected signal for providing A corn- 55
plex
means for isolating the said characteristic from said
complex signal,
means for generating an intermediate frequency signal
taaquency of which is .areater than the frequency Go
value of said characteristic included on said reeled
-
mears for mixing said isolated characteristic and said
intermediate frequency signal so that the intermedi-
ate frequency signal is modulated in accordance with 65
the characteristic on said reflected signal,
means, for separating the modulation of the modulated
intermediate frequency signals,
means for detecting the modo:atian.of said modulated
intermediate signal and for providing an output rep- 70
resenting such modulation.
3. An optieal system as in claim 2- and in which said
output is proportional-to the modulation characteristic of
said modulated intermediate frequency signal and further
including, 75
20
25
10
means responsive to said output for providing an in-
dicant:on of the value of said output.
4. An optical system for determining the frequency
of vibration of 4 rem ate, vibrating body including.
means for genera:one, and transmitting generally co-
herert light bean enemy t3 a-remote vibrating body,
means for receiving refit-a:leo lieht energies from such
remote, vihratine body and said reficened light en-
ergies including thereon erergy chereetcristia3 rep-
resenting the frequency of such vibrations,
means for mixing a portion of the transmitted light
energies with the reflected light energies in each
em.h two channels,
means for attenua.irg, the lieht energies a the mired
energies and for iaisaing and amalifying the %mar-
acteriatics tep-reaceting said vibrations, in each of
two channels,
meate for generming a substantially constant inter-
mediate fretreney signal, the frequency of which
exceeds the frequency value of the characteristia
rep7esenting said sib-ations,
means for providirg two intermediate frequency signal
c utputs in phase quadrature,
means for mixing said characteristics of one channel
iih one outran of said two intermediate frequency
s ma! outputs, .
means for m-is ine- said characteristics of. the other chan-
nel v.ith the other output of said two intermediate
I .equeney sigral output';,
means far surniping the outputs of the last two men-
tioncd means- for mixime, and for adding said con-
stant .iatermediete fregeency signal as a carrier sig-
nal,
means for dem-adulating the output of said summing
raems for paaviina an output, variahle in aacord-
aaae aith tie frequency modulation of the output
of the summing means,
means resNrrive to the output of the demodulating
means for prcniding an inCication in accordance with
t%a value of the vari?ible output .so that the indi-
cation will vary proaarthanally with the frequency
of ?ibraition of the remote, vibrating body.
5. An optical system for determining the frequeucy of
vibration of a ramote, vibratirg body including;
means for geaerating and transmitting generally Co-
-herein optical frequency electromagnetic waves to a
remote, vibrating body,
means for receiving reflected electromagnetic waves
from such remote- vibrating body, said reflected elec.
tromagretic wave including thereon information of
the vibrating characteristics of such remote body in
terms of amplitude change and phase shift of said
optical frequency electromagnetic waves,
means for homodyning said transmitted optical fre-
quency waves and said reflected waves in a first
channel,
means for homodyning said transmitted optical fre-
quency waves and said reflected waves in a-second-
channel,
means in each sail first and said second channel for
extracting and amplifying the amplitude change and
extracting the phase shift of said "elected waves,
resaectively to provide signals indicative thereof,
means for generating an intermediete frequency sianal
and for providing at least twa intermediate frequency
signal outputs shifted in phase with respect to each
other;
means for mixing the signal from said first channel
wil'a one intermediate frequency signal output,
means for mixing the signal from said seecnd channel
with the other intermediate frequency sianal ka.tput,
means far summing the outputs of the two mixing
means and for adding said intermaditae frequency
signal thereto as a carrier signal for providing an
intermediate frequency signal, frequency modulated
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- 11
in accordance with the phase shift oi said reflected
electrorneenetic waves and aniplittede modulated in
accord:Ince with the amplitude modulatien of said
rsilcctcj WaVCS, so that the vibrational character-
istics are reconstructed in terms of frequency modu-
laticn and amplitude modulation at the intermediate
frequency siene! fiqtiency,
means for limiting the amplitude modulation of the
output of the summing means,
mens for ieemoduloile the frequency rraelubted?
limited intermediate frequency sienei emelt: for preN.
. viding art output verieble in accordence with the
frequency mtolulation of the modulated interme-
diate frequency signal,
means responsive to the variable ?Input of the demodu-
lating meat's for prosiding an iralieation in accord-
ance with the value of said varialle output so that
the indication nee; vary in proportion to the vibra-
tion of the remote vit.,' atinp body.
t An opiteel system as in cleim 5 and in which each
said means far hornods nine includes:
a phouitaultiplier has ing an input and an output,
means for deflecting pert of the transmitted netical
frequency electrorrtenclie %vases tO '.aid ineue and
means for delleceng part of the reflected electromag-
netic waves to said input.
7. An optical cs stem as in claim 5 and in which each
said means for honitelyning includes;
a photomultiplier haying an inptit and an output,
means tor &fleeting part of the transmitted optical
frequency electromagnetic waves to said input,
means for deflecting part of the reflected electromag-
netie waves to said input, and
means for shiftine the !these of one of the deflected
transmitted optical -fiequency efeetrontaenetic waves
so that the outeuts of the respeelise photomu:tipliers
arc siihstantially 90' out of eftese with respec-t to
each other.
B. An oreizat sestein as in claim 5 and in which the
frequency of the intermediate frequency signal is sub-
mentality higher than the hi estfrequency of the phase
shift on the refleetee electrernaerietie waves and sub-
tentially loteer than the freqeency of the optical Ire-
quence transmitted sienal, and
said two intermediate frequency signal outputs are
shifted in phase 90* with respect to each other.
9. An optical receiver for an opiical radar system for
reconsttucting. information on reflected optical frequency
signals at a substantially lower, intermediate frequency
signal level including:
means for transmitting generally coherent optical fre-
quency sienals toward a reflecting surface,
a first channel for receiving and homodyning a portion
of the transmitted optical frequency sip nal and a
portion of the reflected optical frequency signal, and
. including,
means for filtering the homodyncd signal of said first
channel for providing a first output representing the
information on zhe reflected cgueal Ircao,:nry
a second channel for receiving and hornods ning an-
other peoloa of the transmitted optical frequency
signal and another eortion of the reflected optical
frequency signal, and including,
means for filterine the homods nett rienel of said second
channel for providing a second output representing
the information on the reflected - optical freqeency
signal,
means for generating andProviding an intermediate fie-
quency Signal and for further providing VA') signal
outputs equal in frequency to isaid intenrceliete fre-
quency sianal and displaced 900 in phase with re-
spect to each other,
means in said first channel for receiving and mixing
said first output and one signal output of said two
signal otitputs,?
12
means in said second channel for receiving and mixing
said second output and the other signal output of
said two signal outputs,
means for summing the mixed r'gnal outputs of each
5 said first channel and said second channel and for
adding thereto said intermediate frequency signal as
a carrier signal so that the said reflected optical fre-
quency signal is reconstructed at the intermediate fre-
quency signal level and the said information on the
19 reflected optical frequency signal is the frequency
modulation of the intermediate frequency signal.
10. A radar reeeiver for an optical radar ssoem as
in claim 9 and in whieh said receiver farther includes;
means for demodulating the intermediate frequency
13 sinal so frequency modulated for providing an out-
put %oriel-de in accordance with the frequency modu-
lation eheracteristic.
11. An optical reeeiser for an optical radar system for
reconstructing informe don on reflected optical frequency
20 sienels at a siihstantrany lower intermediate frequency
signal :evet including:
means for generating and transmitting generally co-
herent optical frequency signals toward a reflecting
surface.
a first channel for receiving and homodyning it portion
of the transmitted optical frequency signals and a
portion of the reflected optical Lecoancy s,igrrils, and
means for filtering the homodyned signal of said first
channel for providing a first (-moult representing the
110 informatien on the reflected optical frequency sig-
nal,
a second channel for receiving and homodyning an-
other portion of the transmitted optical frequency
signals and another portion of the reflected optical
35 frequency signals,
rneg71s for filtering the flomodyned signal of said second
channel far providing a second 0:tr.7.ot
the information on the reflected optical frequency
signal, and
411 means for sliiftiee the phase of said other eortien of the
transmitted critical frequency signal so that the phase
of said second output is shifted othstantially 90?
with respect to the phase of said first output
means for generating and providing an i-Iterinediate fre-
qeency si:;11:11 and for further pro',idirg two signal
outputs equal in frequency to said inte 'mediate fre-
quency signal and displaced 90" in phase with re-
speet to each other,
weans in which said first channel for receiving and
mixing said first output and one signal output of said
two signal outeuts,
means in said second channel for receiving and mixing
said second output and the other si;ial output of
said two signal outputs,
said mixed signal of said first channel and said mixed
signal of said second channel having a phase -dif-
ference ot substantially 180',
means for summing the mixed signal outputs or said
first channel and said second channel and for adding
thereto said intermediate frequency sienal as a
. carrier signal so that the said reflected optical sienal
is reconstructed at the intermediate frequency signal
level and the information on the said reflected optical
frequency signal is the frequency mo-lulation of such
intermediate frequency signal.
12. An optical receiver as in claim 11 and further
means for demodulating said intermediate frequency
signet for providing an output representing such tee-
quencY modulation.
13. An optical receiver as in c:aim -12 and in -which
said. output of said demodulation means is eariebie and
proportional to the frequency modulation of said inter-
mediate frequency signal, and further including,
23
45
50
55
60
65
70
75
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13 , . 14
means responsive to said output or said demodulation and for directing said first reference signal to said
.. means for providing an indication of the value of such input of said first photomixer,
output means for deflecting another part of the optical fre-
Pt An optical receiver for an optical radar system in quency transmitted signals for providing a rocond
which generally coherent signals at optical frequencies 5 reference sienet and for directing said second refer-
are generated and transmitted to a body in motion and ence aienal to said input of said securd ehotornixer.
said transmitted signals are re:lected front said body to means or denecting one part of the optical re:gurney
said receiver, said reflected signals including thereon reflected sienals to said input of said first rbDlornixer.
characteristics ,related and eroeortional to the motien of means for deflecting another ran of the optical Ire-
said body, said optical receiver including: 10 quency reflected signals to said input cf said second
means for hotnodyne rrisdrig a portion of the trans- photomixer,
mined optical frequency signals and a partisan cf said one part of the reflected signataand said other part
the reflected sienaie in each of two quadrature of the reflened sienals having a eltroe difference of
channels, at two seen:led at-hitt:try points in the network,
each channel further including, la means for shifting the phase of said second reference
means for isolating the characteristics related and pro- signed by Ws so that the phase shift differential be-
portional to the motion of said body from the barna- In :en the chase dirreseece between the teid first ref-
dyned signals provided by each homodyning means erence signal and said one part of the tenoned signal
respectively, as outputs, ' and the ehose difference between said second refer-
means for mixing the itolated characteristics outputs 20 ence sienel :tad std oiher part of the reflected sieitals
with an intermediate frequency signal, is suboentielly ria at the said arbitrary points in the
means, common to both channels, for generating said network,
intermediate frequency signal, means for attenuating the _optical frequency corn-
mearis, common to both channels, for providing two ponenta f;..-_,m the output signed of the first photo-
signals at the frequency of the said intermediate Ire- 25 MiNer,.so as to provide a first filtered signal farce-
guency signal, with each sir:nal displaced in phase so sentina the cherecteristics on said reflected sienal,
as to be 90* ot t of phase with respect to each other, means for atten eating the optical frequency compements
means for applying one sig-al of said two signals to from the output sientil of the second ehotorri ter, so
the mixing means of one channel of said two quad- - as to proa isle a second filtered signal representing the
rature i channels and for applying the other signal 30 characterittics on said reflected signal,
of said two signals to the mixing means of the other means for providing .a first intermediate frequency
channel of eaid two quadrature channels, signal,
means, common to both cherncls, for electrically add- -means for prothiing two signals, substarnially equal in
jog the outputs of both said mixing means, and for frequency to said first intermediate frequency signal
adding thereto said intermediate frequency signal so 35 and shifted in phase sets with respect to e:%-.h other,
as to provide a signal the carrier frequency of whichmeans for mitiatt said first filtered stieeal and one sanni
is equal to the frequency of the intermediate free of said two ,s,e-nals. for presidia:: a first ontrot sit nal
quency signal and -frequency modulated in accord- at the internediate ft equency and freaueney reedu-
en te with the characteristics related and proportional fated in ace:a-dance with the mocleletion of said that
to the motion of said body, 40 filtered signal.
means for demodulating the !Irma] output of the adding means for mieing said second filtered signal and the
means for providing a eiena1 variable in accordance other signal of said two signals, for psoeiding a
with the frequency modulation or said signal output second outran signal at the internedate frequency
of the adding means, and frequency modulated in accords-lee with the
means responsive to said variable signal for providing 45 modulation of said second filtered sienal,
an indication in accordance with the value of said said frequency modulation of said fir ,L oinput sienal
. variable signal so that the indication will vary pro- being subset mien)/ 180' out of phase vi oh the free
portionally to the motion of the said body. quency modulation of said second output signal,
15. An optical receiver as in claim 12 and in which means for summing said first output sienal and said
one said means for homodyre mixing of one channel of 50 second output signal and for adding thereto said first
said two quadrature channels includes, intermediate frequency signal for providing a final
means for shifting the phase of the said portion of the frequency modulated intermediate frequency signal,
transmitted optical frequency signal so that the homoe meanhfor demodulating said final frequency modulated
dyned signal of one channel is shifted substantially signal and for providing a final output which varies
50* with respect to the hornodyned signal of the other 55 in value in accordance with and proportional to the
channel. motion of said body.
16. An optical receiver for 23 optical radar system in
which generally coherent signals of radiant electromagnetic References Cited
energies at optical frequencies. are generated and trans- An article entitled, 'Proposed Massless Remote Vibra-
mined to a body in motion and in which the transmitted 00 tion Pickup" by Stewart from "The Journal of the Aeons-
signals are reflected from said body to said optical re- tical Society of America," vol. 30, No. 7, July 1953, pages
ceiver, said reflected signals including thereon charac- 644-645.
teristleS related to and proportienal to the motion of said ' An article entitled, "Doppler Laser" by Solomon from
body, said optical receiver including; "Electronics," Ray 20,1962, page 26. .
a first photomixer for mixing optical frequency signals 63 An article entitled, "Requirements of a Coherent Laser
and having art input and an output, Pulse-Doppler Redar," by Biernsoo et ate from "Proceed-
a second photomixer fee mixing optical frequency sig- ings of the IEEE," .January 1963, pastes 202-213.
nals and having an input and art output,
means for deflecting part of the optical frequency trans-. JAMES J. GILL, Primary Examiner.
mitted signals for providieg a first reference signal 70
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