An all-fiber Mach-Zehnder interferometer has a central fiber structure in which two single-mode fibers are placed to have a desired path difference and are stabilized in such position by bonding them in certain spots. A coupler is then made on each side of the central fiber structure to produce the Mach-Zehnder effect. The combination of the central fiber structure and of the couplers at each end is mounted on a substrate and packaged to produce the interferometer.

The present invention relates to an apparatus and method of making a Dense Wavelength-Division Multiplexer (DWDM) using a Fused-Biconical Taper ("FBT") technique. The DWDM according to the present invention comprises a multiple of Multi-window Wavelength-Division Multiplexers ("MWDMs") which cascade together in several stages, each stage has several MWDMs having an identical window spacing. For a N-channel DWDM, there are 2.sup.m-1 MWDMs cascaded in m-th stage, and the window spacing of the m-th stage MWDMs is 2.sup.m-1 .DELTA..lambda., where m is from 1 to (logN/log2), for example, the first stage(m=1) having 1 MWDM and the window spacing is .DELTA..lambda., the second stage(m=2) having 2 MWDMs and the window spacing is 2.DELTA..lambda., the third stage(m=3) having 4 MWDMs and the window spacing is 4.DELTA..lambda., etc., and the (logN/log2)-th stage has (N/2) MWDMs with a window spacing (N/2).DELTA..lambda.. The number N could be 2, 4, 8, 16 or more.

An interferometer employs liquid crystals to effect optical path length cges in a Michelson-type interferometer. A beam splitter divides a first optical signal into second and third optical signals. The second optical signal is directed through a first array of liquid crystals, and the third optical signal is directed through a second array of liquid crystals. Mirrors reflect the second and third optical signals back through the arrays to the beam splitter which combines them into a fourth optical signal having an interference pattern. A detector array transforms the fourth optical signal into an electrical signal. A processing circuit is used to modulate the indices of refraction of the liquid crystals to effectuate optical path length changes between the second and third optical signals. The data processor may also be employed to transform the electrical signal into digital data which may be analyzed to discern spectral characteristics of the first optical signal that are of interest.

The invention provides an all-fiber Mach-Zehnder interferometer in which the composition of one of the arms, which connect the couplers, or of a segment of such arm, is doped with dopants, such as GeO.sub.2, P.sub.2 O.sub.5, B.sub.2 O.sub.3 and F. The doping is adjusted to obtain a desired thermal dependence of the interferometer within a given temperature range. The segments can further be tapered with an adiabatic taper.

A waveguide optical device having a guide member for propagation of light in a longitudinal direction. The guide member has upper and lower boundaries. A mass of birefringent material is disposed proximal to the guide member. The birefringent material has molecular dipoles subject to alignment by an imposed electrical field. The birefringent mass is overlapped by the optical field of the propagated light. An upper electrode is disposed in spaced relation to the birefringent mass. A lower electrode is disposed in spaced relation to the guide member. The electrodes have the capability of imposing an alternating current voltage across the birefringent mass to rotate the molecular dipoles of the birefringent mass in a plane defined by the normal to the guide member and the propagation vector of the light. The boundaries and the electrodes define an upper isolation zone between the upper electrode and the upper boundary, a guide path between the boundaries, and a lower isolation zone between the lower boundary and the lower electrode. The guide path has an effective index of refraction greater than the effective indexes of refraction of the isolation zones.