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spectral information reveals the reflectivity vs. depth information. Thedrawbackofthismethodisthesmallsizeoftheachievabledepth range, which is limited by the spectral resolution of the spectrometer.

Figures1,2,and3alsoshowthekeyopticalcomponentsusedtoconstructanOCTsystem. Twoprimary issues foranOCTsystemarepolarization control andoptical delaybalance. Inorder to produce a good interferometric signal, the state of polarization(SOP)ofthetwointerferingarmsshouldbealigned;therefore, polarization controllersmust be used. For someapplications, dynamic polarization control is required for tracking real timepolarizationchanges.ForapolarizationsensitiveOCT(PS-OCT)system,moresophisticatedpolarizationcontrol andanalysis devices are required, such as a polarization switch or polarization state generator. General Photonics is proud to offer a complete array of polarization control and analysis solutions, ranging from manual polarization controllers to high speed dynamic polarization controllers and high speed polarimeters.

Fig.3SpectrometerbasedFrequencyDomainOpticalCoherenceTomography(FD-OCT)

Another factor necessary to achieve good interferometric signals inbothTD-OCTandFD-OCTsystems is theopticalpath lengthbalance of the two interfering arms. General Photonics’ manual variabledelay lines(VDL)areperfect for thisapplication. Witha delay variation range up to 40 cm, these delay lines can quickly compensate for large delay imbalances between the two interfering arms.

Adepth“zooming” function isdesirable forsomeapplications,such as opthalmological imaging of the front and back of an eye. GeneralPhotonics’motorizeddelay line (MDL-002) is ideal forsuchanapplication.Withsub-micronresolutionandatotaldelayofupto40cm,theMDL-002enablestheOCTsystemto“zoom”to any desired position.

Themost importantcomponent forTD-OCT isa fastscanningdelay line with a range of 3 to 5 mm and a speed of up to a few kHz. GeneralPhotonics provides fiber stretchers (FST)withvarying speeds and delay ranges for this application

General Photonics also provides other components forOCTapplications, such as wideband couplers, polarization maintaining couplers,circulators,andFaradaymirrors. Ourbench-topSLEDsource isconvenientforOCTrelatedresearch.Wearetheone-stopshopforalmostallopticalcomponentsforOCTapplications.Please contact us if you do not see the products you need in the catalog. Wewillbehappy to listen toyour requirementsandmodify or customize our products to meet your needs

OpticalCoherenceTomography(OCT)productsfromGeneralPhotonics

Optical coherence tomography (OCT) is an optical imagingtechnique which can provide high resolution, cross-sectional tomographic (or 3-dimensional) imaging of the internalmicrostructure of materials and biological systems by measuring backscatteredorbackreflectedlight.TheresolutionoftheOCTimage is1 to15µm,about100 timesbetter thanconventionalultrasound, and therefore has profound implications for the diagnosis of internal problems in biological tissues (such ashumanbodies) aswell as inorganic samples. It hasbecomeincreasingly popular for medical applications such as noninvasive opthalmological imaging and endoscopic gastrointestinal tract imaging.Italsohasapplicationsinotherfieldsthatrequirerapid,nondestructive imaging.

Two typesofOCT technologiesareavailable today: frequencydomainOCT (FD-OCT) and timedomainOCT (TD-OCT).TD-OCT isbasedon lowcoherence interferometry,with thedepthresolution of the system determined by the coherence length of the light source. Thebasic setup resemblesaMichelsoninterferometer, as shown in Fig. 1. Light fromabroadbandoptical source is divided to illuminate both the sample and referencearmsof the interferometer.The reflected light fromboth arms is recombined and sent to a detector. An interference pattern is created only when the path lengths in the two arms are matched to within the coherence length of the light source. Scanning the length of the reference armover the range ofinterest using a fast delay line thus yields a one-dimensional reflectivity vs. depth profile of the sample. Adding x-y scanning optics in the sample arm enables the combination of depth scans frommultiplepointstocreate2or3-dimensionalimages.

Fig.1TimeDomainOpticalCoherenceTomography(TD-OCT)

FD-OCTcanbefurtherdividedintoscanninglaser-basedFD-OCTandspectrometer-basedFD-OCT,asshowninFig.2andFig.3,respectively.LikeTD-OCT,theyareconstructedwithaMichelsoninterferometer, but they do not require a fast scanning delay line. ForascanninglaserbasedFD-OCT,afastscanninglaserisusedto replace thebroadbandsource. TheFourier transformof thedetected interferometric signal gives the reflectivity vs. depth information of the sample to be imaged. One problem associated withscanninglaserFD-OCTisthehighcostofthetunablelaser.General Photonics has developed a new wide range, low ripple, high power wavelength swept laser for just this application.

Fig.2ScanningLaserBasedFrequencyDomainOCT(FD-OCT)

SpectrometerbasedFD-OCTusesabroadbandsourceas theinput and a high speed spectrometer to receive and analyze the returned interferometric signal. TheFourier transformof the

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8.Balancedphotodetector(BPD,p.70-71)

Function:

Lownoisebalanceddetectorforaccuratedetection of small signals.

9.SLEDsource(SLD-101S,p.33)

Function:

A wideband light source with Gaussian spectral distribution.

10.Fiberpigtailedfree-spaceinterferometer(MZI-001,p.76)

Function:

Acts as a frequency clock in frequency domainOCT(FD-OCT).

11.PolarizationDiversityDetector(PDD,p.74)

Function:

Simultaneouslydetectthepowersofthetwoorthogonalpolarizationstates.UsefulforPS-OCT.

12.Faradaymirror(FRM-001,p.88)

Functions:

a)Reflectlightbacktothecoupler

b)Passivelycompensateforpolarizationfluctuations in the reference arm of the interferometer

13.Fibercouplers(NTC,PMC,pp.85-86)

Function:

Divide and combineoptical beams forthe interferometer.

14.Opticalcirculator(CIR,p.92)

Function:

Isolateback-reflected lightanddirect itto the detector.

1.Wavelengthsweptlasersource(WSL-001,p.68)

Function:

Scanning laser for resolutionofdepthinformation in frequencydomainOCT(FD-OCT).

2.Manualvariabledelaylines(VDL-001/002,seepp.61-63)

Function:

Manuallyadjusttheopticalpathlengthsof the interferometer arms.

3.Motorizedvariabledelaylines(MDL-002/003pp.58-60)

Functions:

a)Automaticallyadjusttheopticalpathlengths of the interferometer arms.

b)Provide“zoom”functiontolookfordetails around a certain depth.

4.Manualpolarizationcontroller(PLC-003&PLC-006,pp.56)

Function:

Manuallyadjust thepolarizationstatesof the interferometer arms.

5.Dynamicpolarizationcontroller(PCD-M02,p.50)

Function:

Dynamicallytunethepolarizationstatesof the interferometer arms.

6.Polarizationscrambler(PCD-005,PSMpp.41-46)

Function:

Randomize the polarization state toeliminate polarization effects.

7.Polarizationswitch(PSW-002,p.54)

Functions:

a) Switch polarization state by 90degrees to decrease the polarization sensitivityoftheOCTsystem.

b)EnablespolarizationsensitiveOCT(PS-OCT)

KeyOCTcomponentsfromGeneralPhotonics