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(12) United States Patent (10) Patent N0.: US 7,058,110 B2 Zhao Et A] US007058110B2 (12) United States Patent (10) Patent N0.: US 7,058,110 B2 Zhao et a]. (45) Date of Patent: Jun. 6, 2006 (54) EXCITED STATE ATOMIC LINE FILTERS 6,009,111 A * 12/1999 CorWin et a1. .............. .. 372/32 (75) Inventors: Zhong-Quan Zhao, San Diego, CA * Cited by examiner (US); Michael Joseph Lefebvre, Del Mar; _CA (Us); Damel H‘ Leshe’ Primary ExamineriMinsun Oh Harvey Enclmtas’ CA (Us) Assistant ExamineriDung (Michael) T. Nguyen ( 73 ) A sslgnee' : CIZXGJSH)T E t erpnses' C Orp . ’ S an D'lego’ (74) Attorney, Agent, or Firmilohn R. Ross ( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 (57) ABSTRACT U.S.C. 154(b) by 364 days. ( 21 ) APP 1, N0.: 10/682 , 567 An excited state atomic line ?lter. The P resent invention solves the problem of lack of ground state resonant lines in 22 Filed: Oct. 9, 2003 at Waveleng ths substantiall y lon g er than those of visible light. Atomic line ?lters of the Faraday or Voigt crossed (65) PI‘iOI‘ PllbliCatiOIl Data polarizer type are provided in Which alkali metal atomic Us 2005/0078729 A1 Apr 14 2005 vapor in a vapor cell is excited With a pump beam to an ' ’ intermediate excited state Where a resonant absorption line, (51) Int_ CL at a desired Wavelength, is available. A magnetic ?eld is Hols 3/22 (200601) applied to the cell producing a polarization rotation for (52) U 5 Cl 372/56, 372/32 polarized light at Wavelengths near the resonant absorption (58) Fi'el'd 0 """ " ’ 372/56 lines. Thus all light is blocked by the cross polarizers except See application ?le for comple light near one of the spaced apart resonant lines. However, ' the polarization of light at certain Wavelengths near the (56) References Cited resonant is rotated in the cell and therefore passes through the output polarizer. U.S. PATENT DOCUMENTS 5,731,585 A * 3/1998 Menders et a1. .......... .. 250/382 11 Claims, 14 Drawing Sheets 19/00‘:T‘EMF. M Co/vrRL. PUMP L/FSER U/Y/ 7" “grim cad-r122. PROCESSOR 554cm!) 4,4554 uxv/r §6 42/? 3>6 vw 0/0012’ 40H\ 40B PROCESSO f? Pam /7 L. AsE/Z ¢\=780.027 K50 / c 70 76 r 60 38 5 02/8510‘ / 6'2 4 I 5mm 1- ca/vrfeo L RA F . .. CELL L 44 \ L/P-Sfl? 7 7¢ 72 ‘23+ 72 6% com map: c {Mn 06/2 HEAT EX¢/r£a rem/9 I‘EM P 84- 86 T3 SPA-TE ca/vrm c my 7784 48 l A141: / I.____ . 9'6 U.S. Patent Jun. 6, 2006 Sheet 3 0f 14 US 7,058,110 B2 Pump Laser Wavelength I Power: 852.112 nm (6 i!S1,.‘, - 6 2PM) I ~10 W/cm2 Cs Cell Temperature 1 Length: 120 C“! 1 cm Magnetic Held: 80 Gauss M <—— ~100%transmissio1| (1767/3 ‘ I ‘ ' ‘0.0054 mm c8 b 1 .2 E 2 m - 1 ,: <€——‘- 075 Q 1 l A . , Z‘r‘?Yl-Yml?'w/v F/ 6. 2 “l L /, Sac/3 0.0/ nm /¢69. 49320271 U.S. Patent Jun. 6, 2006 Sheet 4 0f 14 US 7,058,110 B2 OM ‘Emma/WOWl8QMGMUQNQ U.S. Patent Jun. 6, 2006 Sheet 5 0f 14 US 7,058,110 B2 F/G. 3F? F/6.- 35 /D0 027.0 mwm\(QM W. WMWNMI m /\ (Wm) A \I/ F/6. 3 c l F/é. 3,0 U.S. Patent Jun. 6, 2006 Sheet 6 6f 14 US 7,058,110 B2 15/6, 35' U.S. Patent Jun. 6, 2006 Sheet 7 0f 14 US 7,058,110 B2 Rb Atomic Line Filter at 1529.3 nm VPiezo-Pump = 47.0 Volt ~ ALFTransmittance llJllllIJ‘IAJ_IAJlllllLllllllllLlgLlliljj Frequency Scan (GHz/Divsion) Rb vapor temperature: 120 "C Rb cell length: 1 cm Magnetic field Strength: 140 Gauss Pump laser Wavelength: 780.24 nm (vaccum) Pump power: 10.8 mW Pump laser effective area: 0.778 mm2 /C/ 4 U.S. Patent Jun. 6, 2006 Sheet 8 0f 14 US 7,058,110 B2 30 OH Absorption Peak Flrst Second 2. Window Window 1‘39 m 2 8%:55E52 1 Rayleigh Scattering 0.5 0 1000 1 400 1600 wavelength (nm) FIG, 5' U.S. Patent Jun. 6, 2006 Sheet 9 0f 14 US 7,058,110 B2 7-76.61!) U.S. Patent Jun. 6, 2006 Sheet 10 0f 14 US 7,058,110 B2 90 v ‘- f. _ SIGNAL l A’ SIGNAL FREOU ENCY FREOUE NCY Hg. 78 Fig. 7A Fig. 7C RECEIVER FAHADAY : E FILTER TRANSMISSION ; L = I cm (FOR FILTERING I : B = so a Fig 8A BEACON BEAM AT . : T=121 C - RECEIVING : : TRANSCEIVER) i 5 i I VOIGT EFFECT E i E 1 ‘ cm STABILIZATION FILTER I ; g = _ TRANSMISSION : I : B = em Go FIg. as (FoR LOCKING TRANSMIT : _- . T = 102.5 c BEAM) i I i l - t J l I 3 l l I i I TRANSMISSIONREFERENCE CELL 92-16“?' ‘ (Cs ABSORPTION 0.22 nm Fig. 8C PEAKS No MAGNETIC + FIELD} OPTICAL FREQUENCY L (INCREASING TO LEFT) U.S. Patent Jun. 6, 2006 Sheet 11 0f 14 US 7,058,110 B2 9 10a — F/G. 5 1o7 — 1o6 - 5 It o 1 10 Wavelength (pm) U.S. Patent Jun. 6, 2006 Sheet 12 0f 14 US 7,058,110 B2 U.S. Patent Jun. 6, 2006 Sheet 13 0f 14 US 7,058,110 B2 F/ 6, m A U.S. Patent Jun. 6, 2006 Sheet 14 0f 14 US 7,058,110 B2 US 7,058,110 B2 1 2 EXCITED STATE ATOMIC LINE FILTERS ?lters described in the above referenced patents utiliZe alkali metals such as cesium and rubidium to produce these metal The present invention related to optical ?lters and espe vapors. These metals are preferred because their vapors may cially to atomic line ?lters (ALF). be produced at relatively loW temperatures. HoWever, good absorption lines from these alkali metal vapors are generally BACKGROUND OF THE INVENTION in the visible and the near visible spectral region such as 780 nm and 852 nm. Atomic line ?lters are a class of optical ?lters Which have Many optical symptoms operate at Wavelengths substan acceptance bandwidths on the order of 0.001 nm. In one tially longer than the visible and near visible. A good prior art type of ALF, broadband light containing narroW example is light With Wavelengths in the range of 1.5 band signal light is passed through a ?rst color glass ?lter micron. For example, ?ber optic communication is typically Which cuts off light at Wavelengths beloW a threshold value. at Wavelengths in the range of about 1.2 micron to about The signal and remaining noise light enter an atomic vapor 1.65 microns (see FIG. 5). Typical long haul ?lter optics that only absorbs the signal light Within the atom’s 0.001 nm operate Within a C or L band. (C band is 1520 nm to 1570 acceptance bandWidth thereby exciting those absorbing nm, and L band is 1570 nm to 1620 nm). Shorter range ?ber atoms to an intermediate energy level. A pump beam further optics requiring higher quality ?ber optics may operate excites those atoms to a second, higher energy level that then Within an s band (13141.48 microns). Also, there is a need decays through various processes including ?uorescence, to for ?lters at even longer Wavelength such as about 1.5 to 5 the ground state of the atom. The emitted ?uorescence microns for laser tracking and for free space laser commu occurs at Wavelengths beloW the threshold value of the ?rst 20 nications. Applicants have searched for good resonance lines color glass ?lter. A second color glass ?lter then cuts off any in the alkali metals at these Wavelengths Without success. Wavelengths above the threshold which effectively permits passage of only the emitted narroWband ?uorescence. In SUMMARY OF THE INVENTION effect, the incoming signal has been internally shifted in Wavelength by the atomic vapor, Which then alloWs the use 25 The present invention solves the problem of lack of of tWo overlapping color glass ?lters to block any back ground state resonant lines in at Wavelengths substantially ground radiation. longer than those of visible light. Atomic line ?lters of the Another type of prior art atomic line ?lter takes advantage Faraday or Voigt crossed polariZer type are provided in of either the Faraday effect or the Voigt effect where an Which alkali metal atomic vapor in a vapor cell is excited atomic vapor in a magnetic ?eld produces polarization 30 With a pump beam to an intermediate excited state Where a rotation in order to pass a narroW spectral band of light resonant absorption line, at a desired Wavelength, is avail through tWo crossed polariZers. These ?lters are known able. A magnetic ?eld is applied to the cell producing a respectively as Faraday ?lters or Voigt ?lters. An important polariZation rotation for polariZed light at Wavelengths near use for these ?lters is to block background light so that a the resonant absorption lines. Thus all light is blocked by the beacon laser beam can be detected by a Wide ?eld-of-vieW 35 cross polariZers except light near one of the spaced apart detector. resonant lines. HoWever, the polarization of light at certain Operational principles of Faraday ?lters can be under Wavelengths near the resonant is rotated in the cell and stood by reference to FIGS. 7AiC. Crossed polariZers 90 therefore passes through the output polariZer.
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