Single-element interferometer

doi:10.1016/j.optcom.2007.07.038

Optics Communications

Volume 279, Issue 2, 15 November 2007, Pages 235-239

https://doi.org/10.1016/j.optcom.2007.07.038 Get rights and content

Abstract

A very simple and stable interferometer using a single optical element – a beam-splitter cube – is presented. The device resembles a two-arm interferometer in which the arms are together in one collimated beam, and the two beam halves interfere with the help of the beam-splitter cube. The proposed device produces simultaneously two interferograms with a relative phase-shift of π (rad). Since the period of straight interference fringes can be stably controlled, the device has potential application in spatial-carrier interferometry and for flexible writing of fiber Bragg gratings.

Introduction

Interferometers are phase-sensitive devices for testing optical elements [1]. Standard two-beam interferometers are difficult to implement in a vibration-insensitive apparatus as required by commercial applications. There are some alternative interferometers that are not sensitive to vibrations. One of these is the point-diffraction interferometer (see e.g. [2] and the references therein). The difficulty with point-diffraction interferometers is that the pinhole diameter and the transmission factor of the semitransparent coating must be chosen carefully to achieve good interferograms.

Another alternative device is the so-called one-beam interferometer proposed by the authors some years ago [3], [4]. The one-beam interferometer resembles a two-arm interferometer in which the arms are together in one collimated beam.

The purpose of this paper is to present a robust optical architecture that employs a single element (a beam-splitter cube) to produce the interference of the two halves of a collimated beam. The beam-splitter cube generates simultaneously two interferograms with a relative phase-shift of π (rad). The advantages of the proposed interferometric architecture – with respect to standard ones – are its stability and the possibility to generate controllable straight interference fringes.

In the literature, to the best of our knowledge, there are not references to a similar optical architecture. The only relevant references we found are the reversed-wavefront Young interferometer to measure the two-point correlation function of a partially coherent light field recently proposed by Santarsiero and Borghi [5], and the shearing stellar interferometer proposed by Ribak and Lipson [6]. (There are also references to shearing interferometers using beam-splitters in the paper by Gustafsson and Karawacki [7].)

The proposed interferometer is described in the next section, and some experimental results are presented in Section 3.

Section snippets

Basic setup

The proposed interferometer is shown in Fig. 1. A light wave traveling along the z-axis is incident on a beam-splitter cube (BS) with its central semi-reflecting layer placed along the propagation direction. The top half of the light beam (Path 1) acts as the reference arm of the interferometer, and the bottom half (Path 2) is the test arm, or vice versa.

Fig. 2 shows the ray trajectories in the beam-splitter cube. The lens that images the input (object) plane Σ_in on the image plane Σ_out is not

Experimental results

In our setup we used a polarized He–Ne laser beam (λ = 633 nm), which was filtered and expanded to a diameter of ∼20 mm with the help of standard optics. The beam-splitter was a casually available polarizing beam-splitter cube (15 mm lateral size). The best interference contrast was obtained with vertical polarization, i.e., orthogonal to the plane of Fig. 1. (We also made experiments with other – polarizing and non-polarizing – beam-splitter cubes. In each case, the interference contrast depends on

Discussion and conclusions

In this paper we have presented a novel interferometer that employs a single element – a beam-splitter cube – to produce the interference of the two halves of a collimated beam. The interferometer is robust and easy to adjust because it has only one degree of freedom – the angle of rotation around an axis orthogonal to the plane of Fig. 1.

When the coherence length of the light source is large (e.g., a laser), the relative misalignment of the prisms that form the beam-splitter cube [8], i.e.,

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Single-element interferometer

Abstract

Introduction

Section snippets

Basic setup

Experimental results

Discussion and conclusions

Opt. Commun.

J. Opt. Soc. Am. A

Opt. Lett.

Appl. Opt.