We report on a novel scheme for extending the depth of focus (DOF) of ultrathin (125 μm diameter) fiber probes for optical coherence tomography (OCT) using a simple phase mask consisting of graded-index (GRIN) fiber. The technique is compatible with existing all-in-fiber probe fabrication techniques, and our simulations show that it can provide a DOF gain of at a modest reduction of peak sensitivity. In a prototype device using commercially available GRIN fiber, a DOF gain of 1.55 is obtained, validated by beam profiling and OCT imaging.
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Bachmann, A. H.
Brown, C. T. A.
Chow, T. H.
Feit, M. D.
Fleck, J. A.
Fujimoto, J. G.
Herrington, C. S.
Howe, W. C.
Kirk, R. W.
Lee, W. M.
Leitgeb, R. A.
McLaughlin, R. A.
Nelson, J. S.
Ng, B. K.
Quirk, B. C.
Reed, W. A.
Sampson, D. D.
Schnitzer, M. J.
Sheppard, C. J. R.
Tan, K. M.
Yan, M. F.
Appl. Opt. (1)
Opt. Express (1)
Opt. Lett. (6)
EDOF probe using a GRIN fiber lens and a GRIN fiber phase mask. (a) Schematic of the design: PM, phase mask. (b) Illustration of the index profiles of the GRIN lens (green; upper line) and the phase mask (blue; middle line) relative to the Gaussian beam intensity profile (red; bottom line):
EDOF probe using a refractive lens and a GRIN fiber phase mask. (a) Schematic of the design. (b) Simulated output beam intensity distribution in water. (c) Simulated FWHM diameter and normalized on-axis intensity of the output beam in water. The dotted lines show the values for an ideal Gaussian beam. The vertical green lines indicate the boundaries of the extended DOF.
Results for the fabricated EDOF probe. (a) Fiber probe before formation of the refractive lens. The red arrow indicates the splice between the NCF and GRIN phase mask. (b) After formation of the lens. (c) and (d) OCT images of lemon pulp, log scale with 35 dB dynamic range. (e) Measured and simulated beam profile in water. The horizontal axes of plots (c), (d), and (e) are identical. The vertical green lines indicate the boundaries of the DOF.
Results for the fabricated normal refractive-lens probe. (a) and (b) OCT images of lemon pulp, log scale with 35 dB dynamic range. (c) Measured and simulated beam profile in water. The horizontal axes of plots (a), (b), and (c) are identical. The vertical green lines indicate the boundaries of the DOF.