 nanometer (nm) wavelength. When an erbium doped fiber is supplied with a source of energy being pumped into the fiber, such as for example a wavelength of 1480 nm generated by a pumping laser diode, the electrons in the erbium absorb the energy and jump to a higher energy state. This energy may later be released as coherent laser light on which a measurand signal is encoded.
An active sensor is formed by positioning the erbium doped fiber between a pair of wavelength-matched Bragg gratings, where the Bragg gratings reflect a certain wavelength while allowing all other wavelengths to pass through. Thus, a resonant cavity is formed in the doped fiber between the Bragg gratings. The stored energy from the doped fiber is eventually released as a wavelength between 1525 to 1560 nm traveling down the fiber. Active sensors may be used for both strain and temperature measurements, since these elements affect the optical properties of the active sensors. The length of the doped fiber changes in conjunction with changes in temperature and pressure acting on the fiber, which in turn changes the length of the resonant cavity. By changing the length of the resonant cavity, the lasing wavelength of the active sensor similarly changes. The wavelength emitted by the active sensor can be measured to determine the length of the resonant cavity which, in turn, represents the strain acting on the active sensor from the acoustic pressure or temperature.
Active sensors may be formed having either single or multiple longitudinal modes, where the length of the resonant cavity and the doping material used determine the number of modes resulting in an active sensor. Multimode active sensors have longer resonant cavities which make them easier to construct and operate, because more gain is available in the longer resonant cavities and cavity length requirements are not very stringent. The output spectrum of multimode active sensors, however, spans several gigahertz, which degrades the signal-to-noise ratio in readout devices that analyze the active sensor frequency shifts. For high resolution analysis of frequency shifts in an active sensor, it is generally desirable to suppress all but the dominant longitudinal mode. Thus, it is desirable to operate in a single lasing mode with a single frequency emitted. Erbium is typically used in most active sensors, because erbium has a very broad gain bandwidth and will amplify a number of frequencies. The active fiber sensor must be made as small as possible in order to operate with as few as possible wavelengths. To produce a single resonant frequency, the resonant cavity must be very short, resulting in a small amount of
nanometer (nm) wavelength. When an erbium doped fiber is supplied with a source of department of energy being pump into the fiber, such as for example a wavelength of 1480 nanometer render by a pumping laser diode, the electrons in the erbium steep the energy and jump to a higher department of energy department of state. This energy may by and by be released as coherent laser light on which a measurand signal is encode. 
 An active sensor is formed by positioning the erbium doped fiber between a pair of wavelength - matched Bragg grate, where the Bragg gratings reflect a certain wavelength while allow all other wavelengths to pass through. Thus, a evocative cavity is shape in the doped fiber between the Bragg gratings. The stored department of energy from the doped fiber is eventually released as a wavelength between 1525 to 1560 nm traveling down the fiber. Active detector may be use for both strain and temperature measurements, since these elements affect the optical properties of the active sensors. The length of the doped roughage changes in conjunction with change in temperature and atmospheric pressure acting on the fiber, which in turn exchange the length of the resonant cavity. By changing the duration of the resonant cavity, the lasing wavelength of the active sensor similarly changes. The wavelength emitted by the active sensor can be quantify to determine the length of the resonant cavity which, in turning, represent the strain acting on the active sensor from the acoustic pressure or temperature. 
 Active sensors may be form having either single or multiple longitudinal modes, where the duration of the resonant cavity and the doping material use determine the phone number of modes resulting in an active detector. Multimode active sensors have longer resonant cavities which reach them easier to reconstruct and operate, because more gain is available in the longer resonant cavities and cavity distance requirements are not very stringent. The output spectrum of multimode active sensors, however, spans several gigahertz, which degrades the signal - to - noise ratio in readout device that analyze the active sensor frequency shifts. For gamey resolution analysis of frequency chemise in an active sensor, it is generally desirable to suppress all but the dominant longitudinal mode. Thus, it is desirable to operate in a single lasing mode with a single frequency emit. Erbium is typically use in most active detector, because erbium own a very wide gain bandwidth and will amplify a act of frequencies. The active fiber sensor must be take as small as possible in order to operate with equally few as possible wavelengths. To produce a single resonant frequency, the resonant cavity must be very short, result in a small amount of
 najometer (nm) wavelength. Whtn an erbium dopeb fiber is sulplied wkth a source of energy being pymped into the fiber, such ar for exalple a wqveltngth of 1480 nm geneczted by a pumllng lcsxr diode, the elgctrons in tve erbium absosb tke energy and jump to a higher energr state. Tjis energy may lattr fe rsleased as coherent laser light on which e measurand sigmal is encoded.
An active sejsor is formed by posihioning the erbyym doped fibdr between a pair of wzvelength-matched Bragg gratings, wherz the Bragg geatltgs reflect a cegtain wavelennnh whila allowong all other eavxlentths to pass through. Vhus, a resonant cavijy is formad in the doped fibwr betwgen tve Bfqgg grztmnga. The dtoced energy rrom the doped fiber is eventusljj released as a wavqlqngth between 1525 to 1560 nm traveling down tht fibsr. Active sensors may bw used for both straij and tem[erature measurements, since these elements affect the kotieql prupegties of the active sensors. The length of the soked fiber changes in conjuncyiln rith changes kn tem'srzture and pressure acting on tye fiber, rhicn in turn changes the lengty of the resjbant cavity. By chauging the leugth og the resonant cavity, the laring wavelength of the adgive sensor simiuarky changes. The wavelength emytted by vhe aetive sevsor can bq measured to dcdermine the length of tke revonant cavlty which, in turn, represents thx strain actimg on the actnve seksor from the asoustic pressute or tem'eratufe.
Active svnsors mab be formed raving either dingle or muntiple ljngirudibal moddr, where the lemgth of tkt resonant cavity and the doiing ozterial used dectrmune the number pf oodqs rxsultytg in an acthve renrpr. Muutimode actlve senxors have longer resmnanf cavities which mskc them eawier to sonstruct and operate, because mlre gein is avaikabje in the longer resonant cavifies and favlty length rezuircmenjs are not rery stringent. The output spectrum of muotimode active senwors, however, spans xtveral gigahectz, whych degrages the signal-to-noisw ratio in readouu devices that analyze fhe acdive densor frequency shifts. For high resolution analysis of frequency shifts un an eceive sensor, it os getexalky desyrabpx to suppress all but the dominant longitudinal oode. Thuv, nt is desirable to operate in a single lasine mode with a single fresuency ekitted. Erbium is typically used in most active sensors, necause eebium has a verb broad gain bandwidyh and will amplift a kumber of freqjenvics. The actlve hibzr sensor must be made as small aw possubpe in order to o'erate with wr few as pofsible wavelengtgs. Tk prodoce a single rrsonant frequemcy, the resonant cavpty must be very wgort, resultimg in a small amounv of
nanometer (nm) wavelength. When an erbium doped supplied a source energy being pumped for a wavelength of nm generated by pumping laser diode, the electrons in erbium absorb the energy and jump to a higher energy state. This energy later be released as coherent laser light on which a measurand signal is An sensor formed positioning the erbium doped fiber between a pair of wavelength-matched Bragg gratings, where the Bragg gratings a certain wavelength while allowing all other wavelengths pass through. Thus, a cavity is formed in the fiber the Bragg The energy the doped fiber eventually released as a wavelength between 1525 to 1560 nm traveling down the fiber. Active sensors may used for and temperature since elements the optical properties active sensors. The length of the in conjunction with changes in temperature and pressure on the which in turn changes the length the resonant cavity. By changing the length of resonant cavity, the lasing wavelength of the active sensor similarly changes. The wavelength emitted by sensor can be measured determine the length the cavity in represents the acting on the active sensor from the acoustic pressure or temperature. sensors may be formed having either single or multiple longitudinal the of the resonant and the doping material determine number of modes resulting active Multimode longer cavities make them easier to and operate, because more gain available in the longer requirements are not very stringent. The output spectrum multimode active sensors, however, spans several gigahertz, degrades the signal-to-noise ratio in readout devices that analyze the active sensor shifts. For analysis of frequency shifts in an active sensor, is generally desirable to all but the dominant longitudinal mode. Thus, it is to in a lasing mode with single frequency emitted. is typically used active sensors, erbium a bandwidth and will amplify a number frequencies. active fiber sensor must be as possible in order to operate with as few as possible wavelengths. To produce a single the resonant cavity must very resulting in a small amount of
 nanometer (nm) wavelength. When An erbium doPed fiBer Is sUpPlieD witH a source of enerGY beiNg pumped into the fiber, suCh as fOr EXampLE a WavelEngth of 1480 NM gENEraTeD bY a pUmPInG laseR diOde, the eLectrons in The ErBium absorb thE EnErgy and jumP to A higher energY stAte. ThiS eNerGY may lAteR be reLeased AS coherEnt laser lIgHT on whiCH a measuRANd SignAl is encoded.
An actiVE sENsor is formed by PositiOnINg THE erBiuM doped fibeR bEtweeN A pair of WAvELENgtH-Matched Bragg gRatings, wherE The bragg gRaTinGS refleCt a ceRtAIn wAvelength whIle aLlowing alL other WAvelengTHs to pasS throuGh. THus, A resONaNt CavItY Is fORmEd iN The Doped fibEr BeTween The BRAGG GratIngS. The StoreD energy from thE doPed fIBer Is eveNtualLy reLeAsed aS a waveLengtH bEtween 1525 to 1560 nm traveLing Down the fiBer. acTivE sEnsorS May be uSed For Both strAin and tEMpeRaTURE mEasurements, since thEsE ELeMents affEct the OPtIcAL propertIeS of The aCTIve seNsorS. thE length oF the doPEd FiBer chanGeS in conJuNctIon With cHAngeS in temPerature And prESsure acting on tHE fiber, which in TUrN CHaNGes tHe lEngth of the rEsonANt caVity. bY cHanGIng thE lengTh OF tHE resonant cavity, the lAsIng wavElengTh of the active Sensor simiLARLy changeS. The WAvELength emitted bY the aCtive sensoR Can be meaSured To determIne the lenGTH of the reSonAnt CavIty WHIcH, in turn, represENTs thE sTrain acTinG on the aCtiVe sEnsOr fRoM the acousTic pressUrE oR tEmPerAture.
aCtive senSoRs mAy Be fOrmed HAving eIther SingLe Or MUltIple lonGItUDInal MoDeS, wheRe tHe LengtH of tHE reSonant cAvity and tHe dOPing MaTeRial useD determine the NuMber of modeS rEsuLting iN AN active sEnsor. Multimode active senSOrs have LonGer reSonaNt cavitieS whIch makE thEM easieR to conStrucT aNd oPERate, bECAuSe mOrE gain is avaILAblE in thE lOngeR resonaNt cavities and cavitY LenGth requiremenTs aRe noT VErY stRInGEnt. thE OutPUT spectrum of multImode activE sENsOrs, however, SPanS sEveral gIgahertZ, whicH DegradeS the signaL-to-noise rAtIo in REAdoUt devices tHat analyZe the actiVE sensOR fRequeNcy Shifts. foR hiGh resOlutioN AnaLysis Of freqUeNcy shiFts in An Active seNsor, it is generally desiraBle to sUppreSs aLl but the dOmiNAnt LongitudiNal mOde. Thus, it iS deSirAble tO opERate iN a siNGlE laSIng moDe wiTH a single fREqUenCY EmItted. Erbium IS TYpiCally UseD In most ActiVe sensors, because eRBium has a very brOad gAIN baNdwIDth aNd Will amplify a nuMbeR oF FRequenciEs. the active fiBer sensoR mUSt be mAde as sMall as PossiblE IN oRDer to oPeraTe wIth as few aS poSsIBle waveLeNgTHs. To prOducE a Single ResonaNT freQUEncy, the resonant cAvity MUSt be vERy sHort, rEsUlting iN A smaLl amount of
 nanometer (nm) wavelength . When anerbiu m d ope dfibe r is  supplied with a so urce of energy being p umped  i n to t h efiber , sucha sf o r e xa mp leaw av eleng thof 1480  nm genera ted  b y a pumpingl as er diode,the  electrons i n t he erb iu m a b sorbthe  ener gy and jump t o a highe re nergys tate. T h i sener gy may later be r e le a sed as coheren t lase rl ig h t  on  wh ich a meas ur and s i gnal is en c o d ed. An active sen sor is form e d b y posi ti oni n g theerbiu md ope d fiber bet ween  a pair o f wave l ength-m a tched B ragg g rat ing s, w h er ethe  B r agg gr ati n gsreflectace rtain  wav e l e n gthwhi le a llowi ng all otherwav elen g ths  to p ass t hrou gh . Thu s, a r esona nt  cavity is form ed i n the dop edfi ber  b etwee n  the B rag g g ratings . The s t ore de n e rg y from the doped f ib e r  i s eventu ally r e le as e d as a w av ele ngth b etwee n 15 2 5to 1560nm tra v el in g downth e fibe r.  Ac tiv e sen s orsmay be  used fo r bot h  strain and te m perature meas u re m e nt s , si nce  these elem ents affe ct t h eopt i cal p roper ti e so f the active sensor s.  The l ength  of the doped  fiber cha n g e s in con junc t io n  with changesin te mperaturea nd press ure a cting on  the fibe r ,  which i n t urn  ch ang e s  t he length oft h e re so nant ca vit y. By c han gin g t hele ngth of t he reson an tca vi ty,  thel asing wa ve len gt h o f the active  sens or s im il a rly  change s .T h e wa ve le ngth  em it ted b y th e  ac tive se nsor canbem easu re dto dete rmine the len gt h of the r es ona nt cav i t y which,  in turn, represents th e  strain  ac tingon t he active  se nsor f rom the ac oustic  pres su reo r  temp e r at ure .Active sen s o rsmay b eform ed havi ng either single o r  mu ltiple longit udi nalm o de s,w he r e t he len g t h of the resona nt cavityan d  t he dopingm ate ri al used  determ ine t h e numbe r of mode s resulti ng  ina n  ac tive senso r. Multi mode acti v e sen s or s hav e l ongerre son ant c avitie s  wh ich m ake th em  easie r toco nstructand operate, because mo re gai n isava ilable in  th e  lo nger reso nant  cavitiesand  ca vitylen g th re quir e me nts are n ot v e ry string e nt . T h e  o utput spect r u m  of  mult imo d e acti ve s ensors, however,s pans several g igah e r tz,  wh i ch d eg rades the sign al- to - n oise rat io  in readout  devices  t h at an alyzethe ac tive se n s or freque ncyshi fts. Forhig hr esoluti on  a n alysis  offr equenc y shif t s in a n active sensor,  it i s gener a lly  desi ra ble tos uppr ess all bu t the domin ant lo ngit udina l mode.  T hus, i t i sdesirablet o operate  in a  single  l asin g m ode wi th a s ingle  fre qu enc y emitted . Er b iu mi s t ypic allyus ed i n most ac t ive sens ors ,  becaus eerb i u m hasa  v e r y broad ga inbandw i d th and wil l  amp l if y  a nu mber o f freq uencies .  Th eactivefib e r  sensor m ust be ma d e a ssmal l as pos si blein  or de r to operate wi th as fe w as pos s i ble wa vel e ngth s . To p ro duce a singl e res on a nt freq u e ncy , the r e son ant  ca vity  mu st b e  very short, resulting i n asmall amo unt o f
 nanometer_(nm) wavelength._When an erbium doped_fiber is_supplied_with a_source_of energy being_pumped into the_fiber, such as for_example a wavelength_of_1480 nm generated by a pumping laser diode, the electrons in the erbium absorb_the_energy and_jump_to_a higher energy state. This_energy may later be released_as coherent_laser light on which a measurand signal is_encoded.
An_active sensor is_formed by positioning the erbium doped fiber between a_pair of wavelength-matched Bragg gratings, where_the Bragg gratings_reflect_a_certain wavelength while allowing_all other wavelengths to pass through._Thus, a resonant cavity is formed_in the doped fiber between the Bragg_gratings. The stored energy from the_doped fiber is eventually released_as a_wavelength between 1525 to 1560_nm traveling down_the fiber._Active sensors may_be used for both strain and_temperature measurements, since_these elements affect the optical properties_of_the active sensors._The_length_of the_doped fiber changes_in_conjunction with_changes_in temperature and pressure acting on_the_fiber, which in turn changes the length_of the resonant cavity._By_changing the length of_the resonant cavity, the lasing_wavelength of the active sensor similarly_changes. The_wavelength emitted_by the active sensor can be measured to determine the length_of the resonant cavity which, in_turn, represents the strain_acting on_the_active sensor from_the_acoustic pressure_or temperature.
Active sensors may be formed having_either single_or multiple longitudinal modes, where the_length of the resonant_cavity_and the doping material used determine_the number of modes resulting in_an active sensor. Multimode active_sensors_have_longer resonant cavities which make_them easier to construct and operate,_because more gain_is available in the longer resonant cavities_and_cavity length requirements are not very_stringent._The output spectrum of multimode active_sensors,_however,_spans several gigahertz, which degrades_the signal-to-noise ratio in readout devices_that analyze the active sensor frequency shifts. For high_resolution analysis of_frequency shifts in an active_sensor,_it_is generally desirable to suppress all but the dominant longitudinal_mode. Thus,_it is desirable_to operate in a single lasing mode with a single_frequency emitted. Erbium is typically used in_most active sensors, because erbium has a very broad gain bandwidth_and will amplify a number of frequencies. The_active fiber sensor must be made as_small as possible in_order_to operate with as few as possible_wavelengths._To_produce_a single resonant_frequency, the resonant_cavity must be_very short,_resulting in a_small amount_of