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Virtual Journal for Biomedical Optics

Virtual Journal for Biomedical Optics

| EXPLORING THE INTERFACE OF LIGHT AND BIOMEDICINE

  • Editor: Gregory W. Faris
  • Vol. 5, Iss. 1 — Jan. 4, 2010
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Polarization maintaining fiber based ultra-high resolution spectral domain polarization sensitive optical coherence tomography

Erich Götzinger, Bernhard Baumann, Michael Pircher, and Christoph K. Hitzenberger  »View Author Affiliations


Optics Express, Vol. 17, Issue 25, pp. 22704-22717 (2009)
http://dx.doi.org/10.1364/OE.17.022704


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Abstract

We present a new ultra high resolution spectral domain polarization sensitive optical coherence tomography (PS-OCT) system based on polarization maintaining (PM) fibers. The method transfers the principles of our previous bulk optic PS-OCT systems to a fiberized setup. The phase shift between the orthogonal polarization states travelling in the two orthogonal modes of the PM fiber is compensated by software in post processing. Thereby, the main advantage of our bulk optics setups, i.e. the use of only a single input polarization state to simultaneously acquire reflectivity, retardation, optic axis orientation, and Stokes vector, is maintained. The use of a broadband light source of 110 nm bandwidth provides improved depth resolution and smaller speckle size. The latter is important for improved resolution of depolarization imaging. We demonstrate our instrument for high-resolution PS-OCT imaging of the healthy human retina.

© 2009 OSA

1. Introduction

During the last 20 years optical coherence tomography (OCT) has developed into a powerful technique for imaging of transparent and translucent structures [1,2]. Originally developed as a time domain technique, its spectral domain counterpart [3–5] has been long overlooked. However, in 2003 it has been shown that spectral domain (SD) OCT has huge advantages in terms of sensitivity and imaging speed [6–8], thus enabling high speed imaging in 2 and 3 dimensions [9,10]. Recent developments of high speed CMOS cameras and high speed swept source lasers have enabled an imaging speed of up to ~300k A-lines per second [11].

Polarization sensitive (PS) OCT is a functional extension of OCT [12–14]. PS-OCT takes advantage of the additional polarization information carried by the reflected light, and can therefore add new image contrast compared to intensity based OCT. PS-OCT can reveal important information about biological tissue, such as quantitative distribution of birefringence, which is unavailable in conventional OCT.

A very interesting application field for PS-OCT is retinal imaging. One can distinguish between polarization preserving (e.g. photoreceptor layer), birefringent (e.g. retinal nerve fiber layer (RNFL), Henle’s fiber layer) and depolarizing layers (e. g. retinal pigment epithelium (RPE)). In addition, PS-OCT can provide quantitative information on birefringent [15–20] and depolarizing tissues [21–24].

In 1992 Hee et al. proposed the first PS-OCT setup [12

12. M. R. Hee, D. Huang, E. A. Swanson, and J. G. Fujimoto, “Polarization-sensitive low-coherence reflectometer for birefringence characterization and ranging,” J. Opt. Soc. Am. B 9(6), 903–908 ( 1992). [CrossRef]

]. In 1997 the first images of retardation of scattering tissue imaged with a PS-OCT setup have been presented [13

13. J. F. de Boer, T. E. Milner, M. J. C. van Gemert, and J. S. Nelson, “Two-dimensional birefringence imaging in biological tissue by polarization-sensitive optical coherence tomography,” Opt. Lett. 22(12), 934–936 ( 1997). [CrossRef] [PubMed]

]. However, this early work was based on bulk optics, which is not as convenient in terms of easy alignment and handling compared to fiber based systems. Nevertheless, free space PS-OCT setups have the advantage of easy control of the polarization state of light in the reference and the sample arms. Due to the fact that single mode fibers change the polarization state of the transmitted light in an unknown manner, a fiber based PS-OCT setup cannot be as easily implemented as free space setups. To overcome these problems, Saxer et al. proposed a first fiber based PS-OCT setup in 2000 [25

25. C. E. Saxer, J. F. de Boer, B. H. Park, Y. Zhao, Z. Chen, and J. S. Nelson, “High-speed fiber based polarization-sensitive optical coherence tomography of in vivo human skin,” Opt. Lett. 25(18), 1355–1357 ( 2000). [CrossRef] [PubMed]

] which needed at least two A-scans with different input polarization states per measurement location to retrieve the polarization properties of the measured sample. Recently, a fiber based swept source PS-OCT system has been described where the incident polarization state is modulated during the sweep of the light source [26

26. M. Yamanari, S. Makita, and Y. Yasuno, “Polarization-sensitive swept-source optical coherence tomography with continuous source polarization modulation,” Opt. Express 16(8), 5892–5906 ( 2008). [CrossRef] [PubMed]

]. In this system only one A-scan per measurement location is necessary to calculate the retardation, but with the disadvantage that the measurement depth is reduced by a factor of 2 or more. Another approach combined swept source OCT with frequency multiplexing, thus maintaining full imaging depth, however, requiring additional frequency shifters [27

27. W. Y. Oh, S. H. Yun, B. J. Vakoc, M. Shishkov, A. E. Desjardins, B. H. Park, J. F. de Boer, G. J. Tearney, and B. E. Bouma, “High-speed polarization sensitive optical frequency domain imaging with frequency multiplexing,” Opt. Express 16(2), 1096–1103 ( 2008). [CrossRef] [PubMed]

].

Polarization maintaining (PM) fibers maintain only linear polarization states. Due to the elliptic core and different refractive index of the two propagation modes, the relative phase between these modes is lost, preventing the undistorted propagation of arbitrary elliptical polarization states. Recently, a time domain system based on PM fibers has been described, where the difference in propagation velocitiy of the two orthogonal modes within the fiber is compensated with the help of two birefringent prisms [28

28. M. K. Al-Qaisi and T. Akkin, “Polarization-sensitive optical coherence tomography based on polarization-maintaining fibers and frequency multiplexing,” Opt. Express 16(17), 13032–13041 ( 2008). [CrossRef] [PubMed]

].

The development of ultra broad band light sources has enabled the possibility for ultra high resolution (UHR) OCT with a depth resolution down to 2µm [29

29. W. Drexler, “Ultrahigh-resolution optical coherence tomography,” J. Biomed. Opt. 9(1), 47–74 ( 2004). [CrossRef] [PubMed]

]. In recent years also UHR spectral domain systems have been presented [30

30. M. Wojtkowski, V. Srinivasan, J. G. Fujimoto, T. Ko, J. S. Schuman, A. Kowalczyk, and J. S. Duker, “Three-dimensional retinal imaging with high-speed ultrahigh-resolution optical coherence tomography,” Ophthalmology 112(10), 1734–1746 ( 2005). [CrossRef] [PubMed]

33

33. R. Leitgeb, W. Drexler, A. Unterhuber, B. Hermann, T. Bajraszewski, T. Le, A. Stingl, and A. Fercher, “Ultrahigh resolution Fourier domain optical coherence tomography,” Opt. Express 12(10), 2156–2165 ( 2004). [CrossRef] [PubMed]

]. However, up to now only a few time domain ultra high resolution PS-OCT systems have been published, and none of them was used for retinal imaging [34

34. M. Pircher, E. Götzinger, R. Leitgeb, H. Sattmann, and C. K. Hitzenberger, “Ultrahigh resolution polarization sensitive optical coherence tomography,” Proc. SPIE 5690, 257–262 ( 2005). [CrossRef]

36

36. J. Moreau, V. Loriette, and A. C. Bocarra, “Full-Field Birefringence Imaging by Thermal-Light Polarization-Sensitive Optical Coherence Tomography. II. Instrument and Results,” Appl. Opt. 42(19), 3811–3818 ( 2003). [CrossRef] [PubMed]

]. In this paper we present, as we believe for the first time, an ultra high resolution SD-PS-OCT system based on PM fibers. This system transfers the principles of our previously reported bulk optics SD PS-OCT instrument to a fiberized setup, i.e. the sample is illuminated by circularly polarized light and measures an arbitrary elliptical polarization state. Contrary to the recently presented TD-OCT system [28

28. M. K. Al-Qaisi and T. Akkin, “Polarization-sensitive optical coherence tomography based on polarization-maintaining fibers and frequency multiplexing,” Opt. Express 16(17), 13032–13041 ( 2008). [CrossRef] [PubMed]

], the direct access to the signal phase after the Fourier transform of the spectral data allows the recovery of the phase information directly by a software algorithm. Thereby, the main advantages of this principle become available for fiber based systems: only a single input state is needed to retrieve reflectivity, retardation and birefringent axis orientation. No polarization or phase modulators are needed.

In addition, the use of a broadband light source with a bandwidth of 110 nm results in a smaller speckle size. This increases the density of independent sampling points, leading to improved resolution of PS measurements, which is especially important for measurements of the thinner part of the retinal nerve fiber layer. In addition, the smaller speckle size allows a smaller evaluation window for depolarization measurements, leading to improved spatial resolution of RPE segmentation.

2. Methods

Figure 1
Fig. 1 Schematic drawing of the setup. SLD, superluminescent diode; PP, polarization control paddle; PM-fiber, polarization maintaining fiber; QWP, quarter waveplate; VDF, variable density filter; DC, dispersion compensation.
shows a sketch of the optical setup. We used a light source with a bandwidth of 110 nm (Broadlighter T840, Superlum, Moscow) and a center wavelength at 840 nm. Light emitted from the source enters a fiber based isolator to prevent damage of the source due to backreflection. A polarization control paddle is implemented to match the polarization state of light with the orientation of the fiber based polarizer. The polarizer provides vertically polarized light which enters the fiber based interferometer, where it is split by a 50/50 coupler into a reference and a sample arm. In the reference arm, light exits the polarization maintaining fiber via a collimator and passes a variable neutral density filter (for optimizing reference power), a quarter wave plate (QWP) oriented at 22.5°, a pair of glass prisms for variable dispersion compensation, and is finally reflected by the reference mirror. After double passage of the QWP, the orientation of the polarization plane is at 45° to the horizontal, providing equal reference power in both channels of the polarization sensitive detection unit. In the sample arm, after exiting the fiber trough a collimator, light passes a QWP oriented at 45° which provides circularly polarized light onto the sample. With the help of an x-y galvanometer scanner and a telescope the beam is scanned over the retina. After recombination of light from the reference and the sample arm at the 2x2 fiber coupler, light is directed via a PM fiber to a fiber based polarizing beam splitter. The two orthogonally polarized beams are guided into two separate, identical spectrometers. Each spectrometer consists of a reflection grating (1200 lines/mm), a camera lens with a focal length of 200 mm, and a 2048 element line scan CCD camera (Atmel Aviiva M2 CL 2014). The spectrometer design is discussed in detail in ref [21

21. E. Götzinger, M. Pircher, and C. K. Hitzenberger, “High speed spectral domain polarization sensitive optical coherence tomography of the human retina,” Opt. Express 13(25), 10217–10229 ( 2005). [CrossRef] [PubMed]

]. With a power of 750 µW illuminating the sample and an integration time of 50 µs we achieved a sensitivity of 98 dB. The transverse resolution is ~12 µm. The depth range of the system is ~3 mm in air. Our system was operated at an A-scan rate of 20 k A-lines /sec, covering a scan field of 15°x15°.

3. Signal processing

Compared to normal single mode fibers, PM fibers have the advantage to maintain linear polarization states oriented parallel to the axes of their elliptic cores. However, due to the different propagation velocity of the two orthogonal modes, the phase between the vertical and the horizontal polarization state is changed, destroying the original arbitrary elliptical polarization state, back reflected from the sample. An exact determination of the elliptical polarization state, however, is required to calculate the sample birefringence parameters [37

37. C. K. Hitzenberger, E. Goetzinger, M. Sticker, M. Pircher, and A. F. Fercher, “Measurement and imaging of birefringence and optic axis orientation by phase resolved polarization sensitive optical coherence tomography,” Opt. Express 9(13), 780–790 ( 2001). [CrossRef] [PubMed]

].

In case of perfect length matched PM fibers in the reference arm and the sample arm, the phase shifts cancel each other and the elliptical polarization state can again be measured in the detection arm. In other words, the shift of the coherence functions of the two states caused by the different light speeds is canceled, and the coherence functions overlap perfectly again, the only remaining phase difference being caused by the sample birefringence, which is exactly what we want to measure. However, if the two fibers are not exactly length matched, the resulting coherence functions of the two orthogonal detection channels are not at the same depth position. This mismatch has to be compensated. Contrary to [28

28. M. K. Al-Qaisi and T. Akkin, “Polarization-sensitive optical coherence tomography based on polarization-maintaining fibers and frequency multiplexing,” Opt. Express 16(17), 13032–13041 ( 2008). [CrossRef] [PubMed]

], where this mismatch was compensated with a pair of birefringent wedges, we take advantage of the fact that, after the Fourier transform of the spectral data, we have direct access to the phase of the A-scan signals. Therefore, we can compensate the length mismatch of the PM fibers by data post processing.

For explanation of the method, we consider the structure term (A-scan signal) obtained by inverse Fourier transform of the acquired spectral data I(k) (DC, autocorrelation, and mirror terms are neglected in this analysis):
FT1{IH,V(k)}Γ(zΔzH,V)=AH,V(zΔzH,V)exp[iΦH,V(zΔzH,V)],
where z is the depth coordinate, Δz is the optical path length difference between reference arm and sample arm, A and Φ are the amplitude and the phase of the interference signal, respectively, and H and V denote the horizontal and the vertical polarization channel, respectively. Prior to compensation, ΔzH is unequal ΔzV .

To compensate the fiber length mismatch of sample and reference arm, we add a complex number C to the horizontal or vertical component of the complex valued structure term Γ (z-Δz). The value of the complex number C is found empirically from a calibration measurement. It is iteratively adapted until the coherence functions of the vertical and horizontal components are exactly depth matched. To achieve sub pixel depth matching, one can apply zero padding before Fourier transform, or apply sub pixel interpolation. This procedure has to be done only once for a specific PM fiber based PS-OCT setup.

4. Results

Figure 3
Fig. 3 Spectrum of the Superlum Broadlighter T840 measured via the reference arm with the spectrometer of the SD-PS-OCT setup. The FWHM of the light source is 110 nm.
shows the spectrum of light within the reference arm measured with the spectrometer of our SD-PS-OCT system. The FWHM of the light source is 110 nm. The non Gaussian shape leads to side lobes of the coherence function (cf. Fig. 4
Fig. 4 Coherence functions obtained with a mirror as sample. Channel 1 (horizontal polarization) and 2 (vertical polarization) are represented in black and red color. (a) coherence function of channel 1 with a depth resolution of 2.9 µm (assuming a refractive index of 1.38 for retinal tissue); (b) coherence function of channel 1 and 2 before compensation of PM fibers; (c) coherence function of channel 1 and 2 after compensation of PM fibers. Intensity in linear scale.
).

Figure 4 shows the coherence functions (linear scale) obtained from a mirror in the sample arm. To obtain equal intensity from the sample mirror in both polarization channels, the QWP in the sample arm was oriented at 22.5° for these measurements. Fig. 4(a) shows the coherence function of channel 1. The FWHM width of the coherence function is 2.9 µm, which is in agreement with results published previously, where a very similar light source was used [39,40]. Due to the non Gaussian profile of the spectrum side lobes can be seen. Figure 4(b) shows the coherence functions of channels 1 and 2 before numerical compensation of the PM fiber length. Due to fiber length mismatch of the reference and the object arm, the coherence functions appear at different depth positions. Figure 4(c) shows the two coherence functions after the compensation procedure. As can be seen, the coherence functions appear at exactly the same depth position. However, small differences in shape and height of the side lobes can be seen, which might originate from a slight spectral dependence of the fiber splitters. As described in detail in [21], an SD-PS-OCT system based on two separate spectrometers requires two identical spectrometers to record the horizontally and vertically polarized spectral interferograms. This requires careful alignment of the two spectrometers with respect to each other. Figure 4(c) shows that even when using a light source with a bandwidth of 110 nm, this can still be achieved.

5. In vivo imaging

Figure 5
Fig. 5 PS-OCT B-scan (1000 A-scans) image of healthy human fovea in vivo. (a) Intensity (log scale); (b) retardation (color bar: 0°-90°); (c) optic axis orientation (color bar: 0°-180°). To avoid erroneous polarization data, areas below a certain intensity threshold are displayed in gray. Image size: 15° (horizontal) x 0.75 mm (vertical, optical distance).
shows images of intensity, retardation, and optic axis orientation of the fovea of a healthy volunteer. In the intensity image (Fig. 5(a)), all the layers and features known from non polarization sensitive ultra high resolution OCT systems can be observed [38

38. M. Wojtkowski, V. Srinivasan, T. Ko, J. Fujimoto, A. Kowalczyk, and J. Duker, “Ultrahigh-resolution, high-speed, Fourier domain optical coherence tomography and methods for dispersion compensation,” Opt. Express 12(11), 2404–2422 ( 2004). [CrossRef] [PubMed]

]. The polarization sensitive images (Fig. 5(b), (c)) show, that most of the retinal layers in this area do not alter the polarization state. However, the RPE (arrow) changes the polarization state of backscattered light in a random way (random variation from speckle to speckle). This polarization scrambling indicates depolarization [22

22. M. Pircher, E. Götzinger, O. Findl, S. Michels, W. Geitzenauer, C. Leydolt, U. Schmidt-Erfurth, and C. K. Hitzenberger, “Human macula investigated in vivo with polarization-sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. 47(12), 5487–5494 ( 2006). [CrossRef] [PubMed]

].

From the PS-OCT data the DOPU image can be calculated [23

23. E. Götzinger, M. Pircher, W. Geitzenauer, C. Ahlers, B. Baumann, S. Michels, U. Schmidt-Erfurth, and C. K. Hitzenberger, “Retinal pigment epithelium segmentation by polarization sensitive optical coherence tomography,” Opt. Express 16(21), 16410–16422 ( 2008). [CrossRef] [PubMed]

]. The DOPU image (Fig. 6(a)
Fig. 6 PS-OCT B-scan (1000 A-scans) image of healthy human fovea in vivo. (a) degree of polarization uniformity DOPU (color bar: 0-1) image measured with UHR fiber based PS-OCT system, evaluation window size for DOPU calculation: 35(x) µm x 9(y); (b) DOPU imaged with old system (c.f. our paper [23]): evaluation window size: 70(x) µm x 18(y). Image size: 15° (horizontal) x 0.75 mm (vertical, optical distance).
) quantitatively shows the extent of the depolarization caused by the RPE, while simultaneously showing the high DOPU values retained by the other layers. For calculation of DOPU, due to the smaller speckle size, we choose a smaller evaluation window as compared to our previously published results (Fig. 6(b)). In our old system we used a window size of ~70(x) µm x 18(y) µm whereas with our new UHR system we used a window size of ~35(x) µm x 9(y) µm. By increasing the numerical aperture (increased sample beam diameter at the cornea) we also improved the transversal resolution by a factor of two, as compared to [23

23. E. Götzinger, M. Pircher, W. Geitzenauer, C. Ahlers, B. Baumann, S. Michels, U. Schmidt-Erfurth, and C. K. Hitzenberger, “Retinal pigment epithelium segmentation by polarization sensitive optical coherence tomography,” Opt. Express 16(21), 16410–16422 ( 2008). [CrossRef] [PubMed]

]. With this improved resolution we could also reduce the window size in transversal direction. The better spatial resolution of DOPU images, due to the smaller evaluation window size of the UHR PS SD-OCT system is clearly visible.

Figure 7
Fig. 7 Images of the RPE region of a healthy fovea measured with two different light sources (source 1: 110 nm bandwidth, source 2: 50 nm bandwidth). (a, b) retardation; (c, d) optic axis orientation); (e, f) DOPU; Image size: 1.8° (horizontal) x 150 µm (vertical, optical distance). Color bar see Figs. 5 and 6.
shows a detailed high density image (1.8° x 150 µm, 500 A-scans) of the RPE region of a healthy fovea measured with two different light sources. One light source had a bandwidth of 50 nm, the second light source had a bandwidth of 110 nm. Figures 7(a),(c),(e) were acquired with 110 nm bandwidth, Figs. 7(b),(d),(f) with 50 nm bandwidth. 7 a,b show retardation, 7 c,d show axis orientation, and 7e,f show the DOPU value. The smaller speckle size obtained at 110 nm bandwidth is clearly visible. The thickness of the layers (e.g. the RPE) appearing in the DOPU images is a convolution of the real tissue extension with the point spread function of the system and with the size of the evaluation window. Due to the smaller evaluation window size in Fig. 7(e), the depolarizing RPE appears thinner than in Fig. 7(f), where the 50 nm light source was used, and therefore a larger evaluation window size had to be used. For these measurements we did not compensate the corneal birefringence [41

41. M. Pircher, E. Götzinger, B. Baumann, and C. K. Hitzenberger, “Corneal birefringence compensation for polarization sensitive optical coherence tomography of the human retina,” J. Biomed. Opt. 12(4), 10 ( 2007). [CrossRef]

]. Therefore the slightly different colors of retardation and optic axis orientation of the UHR and the normal resolution PS-OCT images might be caused by a different influence of corneal birefringence, generated by a slight transversal offset of the beam entrance into the pupil between the two measurements.

A possible application of PS-OCT is glaucoma diagnosis. In glaucoma, the RNFL is damaged, leading to reduced RNFL thickness and birefringence. This effect can best be observed in the areas of thick RNFL bundles around the optic nerve head. Therefore, circular scans around the optic nerve head are standard protocols of glaucoma diagnostics by OCT.

Figure 8
Fig. 8 Circumpapillary PS-OCT scan (4000 A-scans) from healthy human retina in vivo. Scan diameter: ~10 deg (corresponds to a circumference of ~9.4 mm, equal to horizontal image width; optical image depth: 1.8 mm). (a) Intensity (log scale); (b) retardation (color bar: 0°-90°); (c) optic axis orientation (color bar: 0°-180°). Orientation of scan from left to right: (S)uperior, (T)emporal, (I)nferior, (N)asal, (S)uperior.
shows a circular scan around the optic nerve head (healthy subject) with a diameter of ~10 deg (~3 mm diameter). Figure 8(a) shows the intensity image. Because of disturbing ghost images in the area in front of the retina, this region is set to black (see discussion). These ghost images have been eliminated by detecting the front surface of the retina, and setting all intensity pixels in front of the retina to zero, which corresponds to black color in the intensity image and to grey color in the retardation and axis orientation images. The image shows increased thickness of the RNFL, the topmost bright reflecting layer, in the superior and inferior region, and a thin RNFL in the nasal and temporal region. Figures 8(b) and (c) show the retardation and optic axis orientation. To reveal the true birefringent properties of the RNFL we had to compensate for the corneal birefringence. We used the retardation and axis orientation measured locally at the retinal surface around the nerve head to correct for anterior segment birefringence by a software algorithm [41

41. M. Pircher, E. Götzinger, B. Baumann, and C. K. Hitzenberger, “Corneal birefringence compensation for polarization sensitive optical coherence tomography of the human retina,” J. Biomed. Opt. 12(4), 10 ( 2007). [CrossRef]

]. One has to be aware that this compensation algorithm works best when compensating low birefringence. In rare cases, if the corneal retardation exceeds 90°, the method would fail. However, in most cases the central corneal retardation is considearbly lower (below ~43° in 80% of eyes [42

42. R. W. Knighton and X. R. Huang, “Linear birefringence of the central human cornea,” Invest. Ophthalmol. Vis. Sci. 43(1), 82–86 ( 2002). [PubMed]

]). Problems might arise in keratoconus corneas where even in the center of the cornea large birefringence can occur [43

43. E. Götzinger, M. Pircher, I. Dejaco-Ruhswurm, S. Kaminski, C. Skorpik, and C. K. Hitzenberger, “Imaging of birefringent properties of keratoconus corneas by polarization-sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. 48(8), 3551–3558 ( 2007). [CrossRef] [PubMed]

].

The increase of retardation with depth at the thickest RNFL bundles can be observed in the retardation image 8b. The optic axis orientation image (Fig. 8(c)) shows two full color oscillations from left to right, in good agreement with the radial orientation of the nerve fiber bundles around the optic nerve head (corresponding to 2 x 180° orientation change).

6. Discussion

We have presented a new fiber optic SD PS-OCT scheme based on PM fibers and demonstrated its use for UHR imaging of the human retina in vivo. The method transfers the principles of our previously reported bulk optics PS-OCT systems to fiber optics, thereby combining the main advantages of the bulk optics system with the flexibility and simple alignment of fiber optics based systems, an important step towards the development of commercial PS-OCT systems (the presently available commercial OCT systems are based on fiber optics).

Most of the previously reported fiber based PS-OCT systems used standard (non-PM) single mode fibers. These fibers do not maintain the polarization state of transmitted light: they introduce a phase retardation that varies with fiber bending. To overcome this problem, PS-OCT systems based on these fibers typically probe the sample with at least two polarization states, and the additional information gained in that way is used to compensate for the unknown retardation introduced by the fiber. Some of these systems record two polarization states in parallel while others record them successively. The latter approach has the advantage of a simpler setup requiring just one sensor, however, on the downside, a very stable phase relationship between successive A-scans is required.

Our method is based on PM single mode fibers. It records both polarization channels in parallel and requires only a single input polarization state per measurement location to derive reflectivity, retardation, axis orientation, and Stokes vector. This has some advantages compared to methods that require two or more input states or that record the two polarization channels subsequently: (i) the overall imaging speed can be increased; (ii) lateral oversampling is not required (although it still improves overall image quality by an averaging effect); (iii) the method is insensitive to phase shifts between adjacent A-scans that can occur by vibrations, bulk sample motions, or blood flow. Compared to PS-OCT schemes that modulate the polarization state within an A-scan, our method has the advantage that the full depth resolution is maintained (the sampling density is not split between the two polarization channels), and that neither expensive polarization modulators nor complicated triggering schemes are needed. While our system presently uses two separate spectrometer cameras, it can easily be adapted to single camera systems [44

44. B. Baumann, E. Götzinger, M. Pircher, and C. K. Hitzenberger, “Single camera based spectral domain polarization sensitive optical coherence tomography,” Opt. Express 15(3), 1054–1063 ( 2007). [CrossRef] [PubMed]

,45

45. B. Cense, M. Mujat, T. C. Chen, B. H. Park, and J. F. de Boer, “Polarization-sensitive spectral-domain optical coherence tomography using a single line scan camera,” Opt. Express 15(5), 2421–2431 ( 2007). [CrossRef] [PubMed]

] thereby further reducing costs.

One drawback of our present setup are ghost images that occur at a distance of ~1 mm from the main image. These are probably caused by imperfect optical elements that cause cross coupling of polarization states into the wrong mode of the PM fibers. This problem has also been addressed in ref [28

28. M. K. Al-Qaisi and T. Akkin, “Polarization-sensitive optical coherence tomography based on polarization-maintaining fibers and frequency multiplexing,” Opt. Express 16(17), 13032–13041 ( 2008). [CrossRef] [PubMed]

]. In Fig. 8 the ghost images were eliminated by simply cutting them out. For comparison, Fig. 9
Fig. 9 Circumpapillary B-scan from human retina in vivo. Same data set as in Fig. 8, ghost images not removed.
shows the intensity data set before this operation. The ghost image is clearly visible. While this simple elimination method usually works well with a normal, healthy retina (they are usually thinner than the separation of the ghost image), problems can arise in various cases of diseases where retinal thickness is increased and the ghost and real images overlap. Solutions could either be to use better optical elements that avoid cross coupling, or to use longer PM fibers that further separate the position of the ghost [28

28. M. K. Al-Qaisi and T. Akkin, “Polarization-sensitive optical coherence tomography based on polarization-maintaining fibers and frequency multiplexing,” Opt. Express 16(17), 13032–13041 ( 2008). [CrossRef] [PubMed]

].

While we have shown that our PM fiber based approach works well with a stationary setup, applications that require movements of fibers (e.g. endoscopy) might suffer from fiber bending and twisting. To investigate this influence, we made an experiment where we introduced a 360° loop into the fiber of the sample arm in between two measurements. The influence on the measured sample retardation was negligible (< 1°), however, the measured axis orientation changed by ~10 – 15°. This indicates that endoscopy based applications that measure only retardation should work well with our scheme. Applications requiring quantitative axis orientation would need an additional reflector (e.g. a weakly reflecting glass plate) at the distal fiber end that can be used for calibration.

7. Conclusion

Acknowledgments

Financial support from the Austrian Science Fund (FWF grant P19624-B02) and from the European Union project FUN OCT (FP7 HEALTH, contract no. 201880) is gratefully acknowledged.

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R. Leitgeb, C. K. Hitzenberger, and A. F. Fercher, “Performance of fourier domain vs. time domain optical coherence tomography,” Opt. Express 11(8), 889–894 ( 2003). [CrossRef] [PubMed]

7.

J. F. de Boer, B. Cense, B. H. Park, M. C. Pierce, G. J. Tearney, and B. E. Bouma, “Improved signal-to-noise ratio in spectral-domain compared with time-domain optical coherence tomography,” Opt. Lett. 28(21), 2067–2069 ( 2003). [CrossRef] [PubMed]

8.

M. A. Choma, M. V. Sarunic, C. H. Yang, and J. A. Izatt, “Sensitivity advantage of swept source and Fourier domain optical coherence tomography,” Opt. Express 11(18), 2183–2189 ( 2003). [CrossRef] [PubMed]

9.

T. C. Chen, B. Cense, M. C. Pierce, N. Nassif, B. H. Park, S. H. Yun, B. R. White, B. E. Bouma, G. J. Tearney, and J. F. de Boer, “Spectral domain optical coherence tomography: ultra-high speed, ultra-high resolution ophthalmic imaging,” Arch. Ophthalmol. 123(12), 1715–1720 ( 2005). [CrossRef] [PubMed]

10.

M. Wojtkowski, V. Srinivasan, J. G. Fujimoto, T. Ko, J. S. Schuman, A. Kowalczyk, and J. S. Duker, “Three-dimensional retinal imaging with high-speed ultrahigh-resolution optical coherence tomography,” Ophthalmology 112(10), 1734–1746 ( 2005). [CrossRef] [PubMed]

11.

B. Potsaid, I. Gorczynska, V. J. Srinivasan, Y. Chen, J. Jiang, A. Cable, and J. G. Fujimoto, “Ultrahigh speed Spectral / Fourier domain OCT ophthalmic imaging at 70,000 to 312,500 axial scans per second,” Opt. Express 16(19), 15149–15169 ( 2008). [CrossRef] [PubMed]

12.

M. R. Hee, D. Huang, E. A. Swanson, and J. G. Fujimoto, “Polarization-sensitive low-coherence reflectometer for birefringence characterization and ranging,” J. Opt. Soc. Am. B 9(6), 903–908 ( 1992). [CrossRef]

13.

J. F. de Boer, T. E. Milner, M. J. C. van Gemert, and J. S. Nelson, “Two-dimensional birefringence imaging in biological tissue by polarization-sensitive optical coherence tomography,” Opt. Lett. 22(12), 934–936 ( 1997). [CrossRef] [PubMed]

14.

J. F. de Boer, T. E. Milner, and J. S. Nelson, “Determination of the depth-resolved Stokes parameters of light backscattered from turbid media by use of polarization-sensitive optical coherence tomography,” Opt. Lett. 24(5), 300–302 ( 1999). [CrossRef] [PubMed]

15.

B. Cense, T. C. Chen, B. H. Park, M. C. Pierce, and J. F. de Boer, “Invivo depth-resolved birefringence measurements of the human retinal nerve fiber layer by polarization-sensitive optical coherence tomography,” Opt. Lett. 27(18), 1610–1612 ( 2002). [CrossRef] [PubMed]

16.

B. Cense, T. C. Chen, B. H. Park, M. C. Pierce, and J. F. de Boer, “Thickness and birefringence of healthy retinal nerve fiber layer tissue measured with polarization-sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. 45(8), 2606–2612 ( 2004). [CrossRef] [PubMed]

17.

M. Mujat, B. H. Park, B. Cense, T. C. Chen, and J. F. de Boer, “Autocalibration of spectral-domain optical coherence tomography spectrometers for in vivo quantitative retinal nerve fiber layer birefringence determination,” J. Biomed. Opt. 12(4), 04125 ( 2007). [CrossRef]

18.

M. Yamanari, M. Miura, S. Makita, T. Yatagai, and Y. Yasuno, “Phase retardation measurement of retinal nerve fiber layer by polarization-sensitive spectral-domain optical coherence tomography and scanning laser polarimetry,” J. Biomed. Opt. 13(1), 014013 ( 2008). [CrossRef] [PubMed]

19.

E. Götzinger, M. Pircher, B. Baumann, C. Hirn, C. Vass, and C. K. Hitzenberger, “Retinal nerve fiber layer birefringence evaluated with polarization sensitive spectral domain OCT and scanning laser polarimetry: A comparison,” J.f Biophoton. 1(2), 129–139 ( 2008). [CrossRef]

20.

M. Pircher, E. Götzinger, R. Leitgeb, H. Sattmann, O. Findl, and C. K. Hitzenberger, “Imaging of polarization properties of human retina in vivo with phase resolved transversal PS-OCT,” Opt. Express 12(24), 5940–5951 ( 2004). [CrossRef] [PubMed]

21.

E. Götzinger, M. Pircher, and C. K. Hitzenberger, “High speed spectral domain polarization sensitive optical coherence tomography of the human retina,” Opt. Express 13(25), 10217–10229 ( 2005). [CrossRef] [PubMed]

22.

M. Pircher, E. Götzinger, O. Findl, S. Michels, W. Geitzenauer, C. Leydolt, U. Schmidt-Erfurth, and C. K. Hitzenberger, “Human macula investigated in vivo with polarization-sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. 47(12), 5487–5494 ( 2006). [CrossRef] [PubMed]

23.

E. Götzinger, M. Pircher, W. Geitzenauer, C. Ahlers, B. Baumann, S. Michels, U. Schmidt-Erfurth, and C. K. Hitzenberger, “Retinal pigment epithelium segmentation by polarization sensitive optical coherence tomography,” Opt. Express 16(21), 16410–16422 ( 2008). [CrossRef] [PubMed]

24.

M. Miura, M. Yamanari, T. Iwasaki, A. E. Elsner, S. Makita, T. Yatagai, and Y. Yasuno, “Imaging polarimetry in age-related macular degeneration,” Invest. Ophthalmol. Vis. Sci. 49(6), 2661–2667 ( 2008). [CrossRef] [PubMed]

25.

C. E. Saxer, J. F. de Boer, B. H. Park, Y. Zhao, Z. Chen, and J. S. Nelson, “High-speed fiber based polarization-sensitive optical coherence tomography of in vivo human skin,” Opt. Lett. 25(18), 1355–1357 ( 2000). [CrossRef] [PubMed]

26.

M. Yamanari, S. Makita, and Y. Yasuno, “Polarization-sensitive swept-source optical coherence tomography with continuous source polarization modulation,” Opt. Express 16(8), 5892–5906 ( 2008). [CrossRef] [PubMed]

27.

W. Y. Oh, S. H. Yun, B. J. Vakoc, M. Shishkov, A. E. Desjardins, B. H. Park, J. F. de Boer, G. J. Tearney, and B. E. Bouma, “High-speed polarization sensitive optical frequency domain imaging with frequency multiplexing,” Opt. Express 16(2), 1096–1103 ( 2008). [CrossRef] [PubMed]

28.

M. K. Al-Qaisi and T. Akkin, “Polarization-sensitive optical coherence tomography based on polarization-maintaining fibers and frequency multiplexing,” Opt. Express 16(17), 13032–13041 ( 2008). [CrossRef] [PubMed]

29.

W. Drexler, “Ultrahigh-resolution optical coherence tomography,” J. Biomed. Opt. 9(1), 47–74 ( 2004). [CrossRef] [PubMed]

30.

M. Wojtkowski, V. Srinivasan, J. G. Fujimoto, T. Ko, J. S. Schuman, A. Kowalczyk, and J. S. Duker, “Three-dimensional retinal imaging with high-speed ultrahigh-resolution optical coherence tomography,” Ophthalmology 112(10), 1734–1746 ( 2005). [CrossRef] [PubMed]

31.

U. Schmidt-Erfurth, R. A. Leitgeb, S. Michels, B. Povazay, S. Sacu, B. Hermann, C. Ahlers, H. Sattmann, C. Scholda, A. F. Fercher, and W. Drexler, “Three-dimensional ultrahigh-resolution optical coherence tomography of macular diseases,” Invest. Ophthalmol. Vis. Sci. 46(9), 3393–3402 ( 2005). [CrossRef] [PubMed]

32.

T. C. Chen, B. Cense, M. C. Pierce, N. Nassif, B. H. Park, S. H. Yun, B. R. White, B. E. Bouma, G. J. Tearney, and J. F. de Boer, “Spectral domain optical coherence tomography: ultra-high speed, ultra-high resolution ophthalmic imaging,” Arch. Ophthalmol. 123(12), 1715–1720 ( 2005). [CrossRef] [PubMed]

33.

R. Leitgeb, W. Drexler, A. Unterhuber, B. Hermann, T. Bajraszewski, T. Le, A. Stingl, and A. Fercher, “Ultrahigh resolution Fourier domain optical coherence tomography,” Opt. Express 12(10), 2156–2165 ( 2004). [CrossRef] [PubMed]

34.

M. Pircher, E. Götzinger, R. Leitgeb, H. Sattmann, and C. K. Hitzenberger, “Ultrahigh resolution polarization sensitive optical coherence tomography,” Proc. SPIE 5690, 257–262 ( 2005). [CrossRef]

35.

K. Wiesauer, M. Pircher, E. Goetzinger, C. K. Hitzenberger, R. Engelke, G. Ahrens, G. Gruetzner, and D. Stifter, “Transversal ultrahigh-resolution polarizationsensitive optical coherence tomography for strain mapping in materials,” Opt. Express 14(13), 5945–5953 ( 2006). [CrossRef] [PubMed]

36.

J. Moreau, V. Loriette, and A. C. Bocarra, “Full-Field Birefringence Imaging by Thermal-Light Polarization-Sensitive Optical Coherence Tomography. II. Instrument and Results,” Appl. Opt. 42(19), 3811–3818 ( 2003). [CrossRef] [PubMed]

37.

C. K. Hitzenberger, E. Goetzinger, M. Sticker, M. Pircher, and A. F. Fercher, “Measurement and imaging of birefringence and optic axis orientation by phase resolved polarization sensitive optical coherence tomography,” Opt. Express 9(13), 780–790 ( 2001). [CrossRef] [PubMed]

38.

M. Wojtkowski, V. Srinivasan, T. Ko, J. Fujimoto, A. Kowalczyk, and J. Duker, “Ultrahigh-resolution, high-speed, Fourier domain optical coherence tomography and methods for dispersion compensation,” Opt. Express 12(11), 2404–2422 ( 2004). [CrossRef] [PubMed]

39.

B. Cense, E. Koperda, J. M. Brown, O. P. Kocaoglu, W. Gao, R. S. Jonnal, and D. T. Miller, “Volumetric retinal imaging with ultrahigh-resolution spectral-domain optical coherence tomography and adaptive optics using two broadband light sources,” Opt. Express 17(5), 4095–4111 ( 2009). [CrossRef] [PubMed]

40.

R. J. Zawadzki, B. Cense, Y. Zhang, S. S. Choi, D. T. Miller, and J. S. Werner, “Ultrahigh-resolution optical coherence tomography with monochromatic and chromatic aberration correction,” Opt. Express 16(11), 8126–8143 ( 2008). [CrossRef] [PubMed]

41.

M. Pircher, E. Götzinger, B. Baumann, and C. K. Hitzenberger, “Corneal birefringence compensation for polarization sensitive optical coherence tomography of the human retina,” J. Biomed. Opt. 12(4), 10 ( 2007). [CrossRef]

42.

R. W. Knighton and X. R. Huang, “Linear birefringence of the central human cornea,” Invest. Ophthalmol. Vis. Sci. 43(1), 82–86 ( 2002). [PubMed]

43.

E. Götzinger, M. Pircher, I. Dejaco-Ruhswurm, S. Kaminski, C. Skorpik, and C. K. Hitzenberger, “Imaging of birefringent properties of keratoconus corneas by polarization-sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. 48(8), 3551–3558 ( 2007). [CrossRef] [PubMed]

44.

B. Baumann, E. Götzinger, M. Pircher, and C. K. Hitzenberger, “Single camera based spectral domain polarization sensitive optical coherence tomography,” Opt. Express 15(3), 1054–1063 ( 2007). [CrossRef] [PubMed]

45.

B. Cense, M. Mujat, T. C. Chen, B. H. Park, and J. F. de Boer, “Polarization-sensitive spectral-domain optical coherence tomography using a single line scan camera,” Opt. Express 15(5), 2421–2431 ( 2007). [CrossRef] [PubMed]

46.

D. P. Davé, T. Akkin, and T. E. Milner, “Polarization-maintaining fiber-based optical low-coherence reflectometer for characterization and ranging of birefringence,” Opt. Lett. 28(19), 1775–1777 ( 2003). [CrossRef] [PubMed]

47.

C. Ahlers, E. Götzinger, M. Pircher, I. Golbaz, F. Prager, C. Schütze, B. Baumann, C. K. Hitzenbeger, and U. Schmidt-Erfurth, “Imaging of the retinal pigment epithelium in age-related macular degeneration using polarization sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. , doi:. [CrossRef] [PubMed]

OCIS Codes
(170.4470) Medical optics and biotechnology : Ophthalmology
(170.4500) Medical optics and biotechnology : Optical coherence tomography
(170.4580) Medical optics and biotechnology : Optical diagnostics for medicine
(230.5440) Optical devices : Polarization-selective devices

ToC Category:
Medical Optics and Biotechnology

History
Original Manuscript: October 23, 2009
Revised Manuscript: November 20, 2009
Manuscript Accepted: November 23, 2009
Published: November 25, 2009

Virtual Issues
Vol. 5, Iss. 1 Virtual Journal for Biomedical Optics

Citation
Erich Götzinger, Bernhard Baumann, Michael Pircher, and Christoph K. Hitzenberger, "Polarization maintaining fiber based ultra-high resolution spectral domain polarization sensitive optical coherence tomography," Opt. Express 17, 22704-22717 (2009)
http://www.opticsinfobase.org/vjbo/abstract.cfm?URI=oe-17-25-22704


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References

  1. D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography,” Science 254(5035), 1178–1181 (1991). [CrossRef] [PubMed]
  2. A. F. Fercher, W. Drexler, C. K. Hitzenberger, and T. Lasser, “Optical coherence tomography - principles and applications,” Rep. Prog. Phys. 66(2), 239–303 (2003). [CrossRef]
  3. A. F. Fercher, C. K. Hitzenberger, G. Kamp, and S. Y. Elzaiat, “Measurement of intraocular distances by backscattering spectral interferometry,” Opt. Commun. 117(1-2), 43–48 (1995). [CrossRef]
  4. G. Häusler and M. W. Lindner, “"Coherence radar” and “spectral radar” - New tools for dermatological diagnosis,” J. Biomed. Opt. 3(1), 21–31 (1998). [CrossRef]
  5. M. Wojtkowski, R. Leitgeb, A. Kowalczyk, T. Bajraszewski, and A. F. Fercher, “In vivo human retinal imaging by Fourier domain optical coherence tomography,” J. Biomed. Opt. 7(3), 457–463 (2002). [CrossRef] [PubMed]
  6. R. Leitgeb, C. K. Hitzenberger, and A. F. Fercher, “Performance of fourier domain vs. time domain optical coherence tomography,” Opt. Express 11(8), 889–894 (2003). [CrossRef] [PubMed]
  7. J. F. de Boer, B. Cense, B. H. Park, M. C. Pierce, G. J. Tearney, and B. E. Bouma, “Improved signal-to-noise ratio in spectral-domain compared with time-domain optical coherence tomography,” Opt. Lett. 28(21), 2067–2069 (2003). [CrossRef] [PubMed]
  8. M. A. Choma, M. V. Sarunic, C. H. Yang, and J. A. Izatt, “Sensitivity advantage of swept source and Fourier domain optical coherence tomography,” Opt. Express 11(18), 2183–2189 (2003). [CrossRef] [PubMed]
  9. T. C. Chen, B. Cense, M. C. Pierce, N. Nassif, B. H. Park, S. H. Yun, B. R. White, B. E. Bouma, G. J. Tearney, and J. F. de Boer, “Spectral domain optical coherence tomography: ultra-high speed, ultra-high resolution ophthalmic imaging,” Arch. Ophthalmol. 123(12), 1715–1720 (2005). [CrossRef] [PubMed]
  10. M. Wojtkowski, V. Srinivasan, J. G. Fujimoto, T. Ko, J. S. Schuman, A. Kowalczyk, and J. S. Duker, “Three-dimensional retinal imaging with high-speed ultrahigh-resolution optical coherence tomography,” Ophthalmology 112(10), 1734–1746 (2005). [CrossRef] [PubMed]
  11. B. Potsaid, I. Gorczynska, V. J. Srinivasan, Y. Chen, J. Jiang, A. Cable, and J. G. Fujimoto, “Ultrahigh speed Spectral / Fourier domain OCT ophthalmic imaging at 70,000 to 312,500 axial scans per second,” Opt. Express 16(19), 15149–15169 (2008). [CrossRef] [PubMed]
  12. M. R. Hee, D. Huang, E. A. Swanson, and J. G. Fujimoto, “Polarization-sensitive low-coherence reflectometer for birefringence characterization and ranging,” J. Opt. Soc. Am. B 9(6), 903–908 (1992). [CrossRef]
  13. J. F. de Boer, T. E. Milner, M. J. C. van Gemert, and J. S. Nelson, “Two-dimensional birefringence imaging in biological tissue by polarization-sensitive optical coherence tomography,” Opt. Lett. 22(12), 934–936 (1997). [CrossRef] [PubMed]
  14. J. F. de Boer, T. E. Milner, and J. S. Nelson, “Determination of the depth-resolved Stokes parameters of light backscattered from turbid media by use of polarization-sensitive optical coherence tomography,” Opt. Lett. 24(5), 300–302 (1999). [CrossRef] [PubMed]
  15. B. Cense, T. C. Chen, B. H. Park, M. C. Pierce, and J. F. de Boer, “Invivo depth-resolved birefringence measurements of the human retinal nerve fiber layer by polarization-sensitive optical coherence tomography,” Opt. Lett. 27(18), 1610–1612 (2002). [CrossRef] [PubMed]
  16. B. Cense, T. C. Chen, B. H. Park, M. C. Pierce, and J. F. de Boer, “Thickness and birefringence of healthy retinal nerve fiber layer tissue measured with polarization-sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. 45(8), 2606–2612 (2004). [CrossRef] [PubMed]
  17. M. Mujat, B. H. Park, B. Cense, T. C. Chen, and J. F. de Boer, “Autocalibration of spectral-domain optical coherence tomography spectrometers for in vivo quantitative retinal nerve fiber layer birefringence determination,” J. Biomed. Opt. 12(4), 04125 (2007). [CrossRef]
  18. M. Yamanari, M. Miura, S. Makita, T. Yatagai, and Y. Yasuno, “Phase retardation measurement of retinal nerve fiber layer by polarization-sensitive spectral-domain optical coherence tomography and scanning laser polarimetry,” J. Biomed. Opt. 13(1), 014013 (2008). [CrossRef] [PubMed]
  19. E. Götzinger, M. Pircher, B. Baumann, C. Hirn, C. Vass, and C. K. Hitzenberger, “Retinal nerve fiber layer birefringence evaluated with polarization sensitive spectral domain OCT and scanning laser polarimetry: A comparison,” J.f Biophoton. 1(2), 129–139 (2008). [CrossRef]
  20. M. Pircher, E. Götzinger, R. Leitgeb, H. Sattmann, O. Findl, and C. K. Hitzenberger, “Imaging of polarization properties of human retina in vivo with phase resolved transversal PS-OCT,” Opt. Express 12(24), 5940–5951 (2004). [CrossRef] [PubMed]
  21. E. Götzinger, M. Pircher, and C. K. Hitzenberger, “High speed spectral domain polarization sensitive optical coherence tomography of the human retina,” Opt. Express 13(25), 10217–10229 (2005). [CrossRef] [PubMed]
  22. M. Pircher, E. Götzinger, O. Findl, S. Michels, W. Geitzenauer, C. Leydolt, U. Schmidt-Erfurth, and C. K. Hitzenberger, “Human macula investigated in vivo with polarization-sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. 47(12), 5487–5494 (2006). [CrossRef] [PubMed]
  23. E. Götzinger, M. Pircher, W. Geitzenauer, C. Ahlers, B. Baumann, S. Michels, U. Schmidt-Erfurth, and C. K. Hitzenberger, “Retinal pigment epithelium segmentation by polarization sensitive optical coherence tomography,” Opt. Express 16(21), 16410–16422 (2008). [CrossRef] [PubMed]
  24. M. Miura, M. Yamanari, T. Iwasaki, A. E. Elsner, S. Makita, T. Yatagai, and Y. Yasuno, “Imaging polarimetry in age-related macular degeneration,” Invest. Ophthalmol. Vis. Sci. 49(6), 2661–2667 (2008). [CrossRef] [PubMed]
  25. C. E. Saxer, J. F. de Boer, B. H. Park, Y. Zhao, Z. Chen, and J. S. Nelson, “High-speed fiber based polarization-sensitive optical coherence tomography of in vivo human skin,” Opt. Lett. 25(18), 1355–1357 (2000). [CrossRef] [PubMed]
  26. M. Yamanari, S. Makita, and Y. Yasuno, “Polarization-sensitive swept-source optical coherence tomography with continuous source polarization modulation,” Opt. Express 16(8), 5892–5906 (2008). [CrossRef] [PubMed]
  27. W. Y. Oh, S. H. Yun, B. J. Vakoc, M. Shishkov, A. E. Desjardins, B. H. Park, J. F. de Boer, G. J. Tearney, and B. E. Bouma, “High-speed polarization sensitive optical frequency domain imaging with frequency multiplexing,” Opt. Express 16(2), 1096–1103 (2008). [CrossRef] [PubMed]
  28. M. K. Al-Qaisi and T. Akkin, “Polarization-sensitive optical coherence tomography based on polarization-maintaining fibers and frequency multiplexing,” Opt. Express 16(17), 13032–13041 (2008). [CrossRef] [PubMed]
  29. W. Drexler, “Ultrahigh-resolution optical coherence tomography,” J. Biomed. Opt. 9(1), 47–74 (2004). [CrossRef] [PubMed]
  30. M. Wojtkowski, V. Srinivasan, J. G. Fujimoto, T. Ko, J. S. Schuman, A. Kowalczyk, and J. S. Duker, “Three-dimensional retinal imaging with high-speed ultrahigh-resolution optical coherence tomography,” Ophthalmology 112(10), 1734–1746 (2005). [CrossRef] [PubMed]
  31. U. Schmidt-Erfurth, R. A. Leitgeb, S. Michels, B. Povazay, S. Sacu, B. Hermann, C. Ahlers, H. Sattmann, C. Scholda, A. F. Fercher, and W. Drexler, “Three-dimensional ultrahigh-resolution optical coherence tomography of macular diseases,” Invest. Ophthalmol. Vis. Sci. 46(9), 3393–3402 (2005). [CrossRef] [PubMed]
  32. T. C. Chen, B. Cense, M. C. Pierce, N. Nassif, B. H. Park, S. H. Yun, B. R. White, B. E. Bouma, G. J. Tearney, and J. F. de Boer, “Spectral domain optical coherence tomography: ultra-high speed, ultra-high resolution ophthalmic imaging,” Arch. Ophthalmol. 123(12), 1715–1720 (2005). [CrossRef] [PubMed]
  33. R. Leitgeb, W. Drexler, A. Unterhuber, B. Hermann, T. Bajraszewski, T. Le, A. Stingl, and A. Fercher, “Ultrahigh resolution Fourier domain optical coherence tomography,” Opt. Express 12(10), 2156–2165 (2004). [CrossRef] [PubMed]
  34. M. Pircher, E. Götzinger, R. Leitgeb, H. Sattmann, and C. K. Hitzenberger, “Ultrahigh resolution polarization sensitive optical coherence tomography,” Proc. SPIE 5690, 257–262 (2005). [CrossRef]
  35. K. Wiesauer, M. Pircher, E. Goetzinger, C. K. Hitzenberger, R. Engelke, G. Ahrens, G. Gruetzner, and D. Stifter, “Transversal ultrahigh-resolution polarizationsensitive optical coherence tomography for strain mapping in materials,” Opt. Express 14(13), 5945–5953 (2006). [CrossRef] [PubMed]
  36. J. Moreau, V. Loriette, and A. C. Bocarra, “Full-Field Birefringence Imaging by Thermal-Light Polarization-Sensitive Optical Coherence Tomography. II. Instrument and Results,” Appl. Opt. 42(19), 3811–3818 (2003). [CrossRef] [PubMed]
  37. C. K. Hitzenberger, E. Goetzinger, M. Sticker, M. Pircher, and A. F. Fercher, “Measurement and imaging of birefringence and optic axis orientation by phase resolved polarization sensitive optical coherence tomography,” Opt. Express 9(13), 780–790 (2001). [CrossRef] [PubMed]
  38. M. Wojtkowski, V. Srinivasan, T. Ko, J. Fujimoto, A. Kowalczyk, and J. Duker, “Ultrahigh-resolution, high-speed, Fourier domain optical coherence tomography and methods for dispersion compensation,” Opt. Express 12(11), 2404–2422 (2004). [CrossRef] [PubMed]
  39. B. Cense, E. Koperda, J. M. Brown, O. P. Kocaoglu, W. Gao, R. S. Jonnal, and D. T. Miller, “Volumetric retinal imaging with ultrahigh-resolution spectral-domain optical coherence tomography and adaptive optics using two broadband light sources,” Opt. Express 17(5), 4095–4111 (2009). [CrossRef] [PubMed]
  40. R. J. Zawadzki, B. Cense, Y. Zhang, S. S. Choi, D. T. Miller, and J. S. Werner, “Ultrahigh-resolution optical coherence tomography with monochromatic and chromatic aberration correction,” Opt. Express 16(11), 8126–8143 (2008). [CrossRef] [PubMed]
  41. M. Pircher, E. Götzinger, B. Baumann, and C. K. Hitzenberger, “Corneal birefringence compensation for polarization sensitive optical coherence tomography of the human retina,” J. Biomed. Opt. 12(4), 10 (2007). [CrossRef]
  42. R. W. Knighton and X. R. Huang, “Linear birefringence of the central human cornea,” Invest. Ophthalmol. Vis. Sci. 43(1), 82–86 (2002). [PubMed]
  43. E. Götzinger, M. Pircher, I. Dejaco-Ruhswurm, S. Kaminski, C. Skorpik, and C. K. Hitzenberger, “Imaging of birefringent properties of keratoconus corneas by polarization-sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. 48(8), 3551–3558 (2007). [CrossRef] [PubMed]
  44. B. Baumann, E. Götzinger, M. Pircher, and C. K. Hitzenberger, “Single camera based spectral domain polarization sensitive optical coherence tomography,” Opt. Express 15(3), 1054–1063 (2007). [CrossRef] [PubMed]
  45. B. Cense, M. Mujat, T. C. Chen, B. H. Park, and J. F. de Boer, “Polarization-sensitive spectral-domain optical coherence tomography using a single line scan camera,” Opt. Express 15(5), 2421–2431 (2007). [CrossRef] [PubMed]
  46. D. P. Davé, T. Akkin, and T. E. Milner, “Polarization-maintaining fiber-based optical low-coherence reflectometer for characterization and ranging of birefringence,” Opt. Lett. 28(19), 1775–1777 (2003). [CrossRef] [PubMed]
  47. C. Ahlers, E. Götzinger, M. Pircher, I. Golbaz, F. Prager, C. Schütze, B. Baumann, C. K. Hitzenbeger, and U. Schmidt-Erfurth, “Imaging of the retinal pigment epithelium in age-related macular degeneration using polarization sensitive optical coherence tomography,” Invest. Ophthalmol. Vis. Sci. , doi:. [CrossRef] [PubMed]

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