Strong continuous three-wave mixing of 514.5-nm argon laser light in a single-mode fiber is reported. The effect, due to the third-order nonlinearity of silica, has been observed for light whose frequency spectrum consists of either a few discrete monochromatic frequency components separated by ∼1 GHz or a quasicontinuous distribution of frequencies having a spectral envelope ∼4 GHz wide. We show that the effect provides a simple and effective method for measuring the nonlinearity of silica. In the first manifestation of the effect, the nonlinearity mixes the frequency components to produce new frequencies. In the second, multiple mixing occurs that broadens the quasicontinuous spectrum. This manifestation of the effect is large; broadening by a factor of 4 has been observed with lower intensity levels than are required to produce stimulated Brillouin scattering in the same fiber. A theoretical model is presented to describe spectral broadening by three-wave mixing for the case of small broadening. The effect of three-wave mixing on the operation of continuous stimulated Brillouin and Raman oscillators is also discussed. Finally, it is noted that the presence of this effect may constrain the design of long-haul single-mode fiber optical communication trunks.

Novel designs for phased-array wavelength-division multiplexers based on self-imaging properties of multimode interference (MMI) couplers are presented. These devices, which operate on N equally spaced wavelength channels, consist of two MMI couplers connected by an array of N monomode waveguides. The MMI couplers function as power splitters/combiners, and the waveguide array is the dispersive element. The excellent characteristics of MMI couplers offer the possibility of designing small-size devices with low loss and with high uniformity among different channels. A general theoretical formulation for an N-channel multiplexer is presented, and a simple procedure for finding an optimum set of lengths for the array guides is given. We show that these multiplexers can function as N x N wavelength-selective interconnecting components. The simulated performance of three variations of a five-channel device, designed in a rib waveguide system, is given. It is demonstrated that sidelobes in the multiplexer spectral response can be suppressed by weighting the power samples in the array waveguides through appropriate design of a nonuniform MMI power splitter.

A correlation reflectometer operating in the frequency domain is described. It is shown that such an instrument is well adapted to detecting weak discrete reflections. The detection of end reflections in a 2.2-km length of fiber whose end is index matched is demonstrated. A round-trip range of over 70 dB is obtained with a 1-mW optical source power. The method shows promise for characterizing the reflective properties of optical fiber elements, such as tapers, microbends, and splices, and may be useful in fault location.

produce Selectively complemented data blocks. A cumula s 1 as a 1 s a 1-2 a Y-s s s tive disparity is then determined between the logical values of different twpe included within ones of the selectivel 56) References Cited of Nat blocks previously encoded into E.

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