A Mach-Zehnder interferometer having two optical couplers interconnected by two optical fibers at least one of which is temperature insensitive. In use, temperature induced changes in the geometrical length and refractive index of the temperature insensitive fibers offset each other so that the optical path length of the fiber is unaffected by the temperature change. Where two temperature insensitive fibers are included these may be of the same or of different lengths. The interferometer may be ...

A method of forming an interferometer film for an interferometer sensor comprises forming a parylene polymer layer (8) of substantially uniform thickness directly on an interferometer substrate (4;45), the layer forming the interferometer film. Since the interferometer film (8) formed directly onto the surface of the interferometer substrate, there is improved conformity between the two surfaces at the interface between the polymer layer and the substrate and improved uniformity in the thickness...

The signal-to-noise ratio of the correction signal used for second harmonic interferometry is improved in two ways. First, an optical amplifier, tuned to the second harmonic frequency, is positioned in the optical path. Second, a doubling stage is positioned internal to the correction laser.

Interferometers utilizing polarization preserving optical systems by plane polarized beams are deviated through preselected angles without changing their linear state of polarization. The interferometers utilizing such optical systems have a variety of applications and are particularly suitable for use in the field of distance measuring interferometry (DMI) to enhance measurement accuracy by reducing undesirable polarization effects that can introduce errors associated with an otherwise present ...

An apparatus for reducing the computational requirements for resolving ambiguity in interferometer measurements where the interferometer elements are arranged arbitrarily. Each of a plurality of interferometer elements each measures the phase of the incoming electromagnetic signal. The interferometer elements are each separated by lengths defined as baselines, which are sorted and processed in ascending order. Following initialization, for each baseline (92, 108), the phase measurements of the n...

Two common-path interferometers share a measuring cavity for measuring opposite sides of opaque test parts. Interference patterns are formed between one side of the test parts and the reference surface of a first of the two interferometers, between the other side of the test parts and the reference surface of a second of the two interferometers, and between the first and second reference surfaces. The latter measurement between the reference surfaces of the two interferometers enables the measur...

An interferometer system includes a rhomboid assembly having a first optical stack and a second optical stack mounted on the first stack. The first stack includes a first prism having an angled face mounted to an angled face of a second prism. The interface between these angled faces includes a first polarizing beam-splitter. The second stack includes a third prism having an angled face mounted to an angled face of the fourth prism. The interface between these angled faces includes a second pola...

In general, in one aspect, the invention features an interferometer assembly for use in a lithography tool used for fabricating integrated circuits on a wafer, wherein the lithography tool includes a support structure and a stage for positioning the wafer relative to the support structure, the interferometer assembly including an interferometer configured to direct a measurement beam between the stage and the support structure and combine the measurement beam with another beam to form an output ...

An interferometer structure is disclosed in which alignment problems are reduced by providing a special retaining structure for the transparent beamsplitter plates. In order to minimize distortion of the beamsplitter plates, the metal housing surfaces, against which they are held, are each coated with a material which has a very slippery and extremely flat surface engaging the surface of the respective beamsplitter plate. The preferred coating material is polytetrafluoroethylene. A glass tool (o...

An automatic gain control circuit for an interferometer or a phase sensitive detector reduces sensitivity to fluctuations in amplitude of input signals. A pair of currents from the phase sensitive detector that represents a detected phase difference are input to an automatic gain control ratio detector. The output of the automatic gain control ratio detector is a function of the ratio of the difference and sum of the phase sensitive detector currents that is substantially independent of intensit...