We propose and demonstrate a novel method to enhance the visibility of an optical interferometer when measuring low reflective materials. Because of scattering from a rough surface or its own low reflectivity, the visibility of the obtained interference signal is seriously deteriorated. By amplifying the weak light coming from the sample based on an injection-locking technique, the visibility can be enhanced. As a feasibility test, even with a sample having a reflectivity of 0.6%, we obtained almost the same visibility as a metal coated mirror. The suggested visibility enhanced interferometer can be widely used for measuring low reflective materials.

© 2010 OSA

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Figures (3)

Fig. 1
Fig. 1

Optical layout of VEI (DFB laser: distributed feedback laser, CL: collimation lens, M: mirror, C: circulator, PD: photo detector, OSA: optical spectrum analyzer, ND filter: neutral density filter).

Fig. 2
Fig. 2

Spectrums of the master laser, the slave laser, and the injection-locked light. The intensity of the spectrum of the master laser was adjusted for easy comparison.

Fig. 3
Fig. 3

Interference signals obtained by VEI and a normal interferometer; (a) VEI without the ND filter (V=0.65), (b) VEI with the ND filter (V=0.65), (c) The normal interferometer without the ND filter (V=0.69), (d) The normal interferometer with the ND filter (V=0.06). Figures (a) and (c) were measured with two metal coated mirrors, and figures (b) and (d) were measured with the ND filter having a transmittance of 0.08. For clear recognition, the two-dimensional figures were generated numerically from the obtained interference signal profiles.

Equations (4)

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V = 2 I r I s I r + I s .
Δ φ = sin 1 ( Δ ν/ Δ ν L ) tan 1 α,
δΔφ = γ δI/Δν L ,
δΔφ = γ δI/Δν L 1 cos ( Δν/Δν L ) .