A fiber amplifier containing a waveguide activated with Er3+ ions was used for the first time to reduce the losses and thus improve the resolving power of a fiber Michelson interferometer. An interferometer with a path difference between the arms amounting to 5 km was constructed and the losses in this interferometer were fully compensated by the use of such an amplifier.

This paper discusses the use of single-mode fibre ring interferometers for injection laser line narrowing and for enhancement of optical emission power. The efficient launching into fibre ring interferometers of multi-frequency external cavity injection laser emission, in both the c.w. and mode-locking regime, has been achieved. Matching the optical lengths of the external cavity and fibre interferometer allowed the measurement of mode width of such a laser. A method is proposed for shaping optical pulses in fibre ring interferometers from constant intensity frequency modulated emission. The mode-locking regime of all-fibre external cavity injection lasers has been achieved.

A Mach-Zehnder fiber interferometer has been assembled on the basis of two X-shaped splitters. The directional couplers and the reference arm of the interferometer were manufactured from a waveguide with the known dispersion characteristic. The spectral dependence of the group delay in the waveguide under study was measured with the reproducibility of 0.01 ns/km. A comparison of the results obtained from the dispersion measurements with the use of the fiber interferometer and the Mach-Zehnder interferometer with the air reference arm has shown that they are in good agreement.

A study was made of the use of single-mode fiber ring interferometers in narrowing the emission lines of semiconductor lasers and increasing the optical radiation power. Efficient coupling of radiation, emitted by a multifrequency injection laser with an external resonator, into a fiber ring interferometer was achieved both under cw and mode-locking conditions. Matching of the optical lengths of the external resonator and the fiber interferometer made it possible to determine the mode width for this laser. A method for generation of optical pulses in a fiber ring interferometer from cw frequency modulated radiation was developed.

A report is given of the fabrication of the first semiconductor laser with an external dispersive resonator in which a loop fiber reflector with a selective fused single-mode coupler is employed as a frequency discriminator. Single-mode emission and tuning of the emission frequency are reported for this laser.

Linewidth reduction and frequency-hopping for a semiconductor laser due to Rayleigh backscattering from a fibre ring interferometer have been observed. The significant decrease of the frequency-hopping range caused by the resonant nature of such backscattering is shown.<>

A pair of coupled step-index waveguides is analyzed. Characteristic equations are obtained and used to evaluate the cutoff frequencies and coupling constants. Mode transformation at tapers is analyzed. The spectral properties of fused couplers and tapered filters for which cutoff frequencies of higher modes were observed are studied. A fiber polarization splitter is realized. A semiconductor laser...

A new design of Y-type directional couplers with end matching and utilizing single-mode fiberoptic waveguides is proposed. The optimal parameters required to attain losses of ~0.5–1 dB are determined. A method is described for making such couplers by welding single-mode waveguides with a partially retained cladding in an electric-arc apparatus. The additional losses of the couplers when used for splitting a signal between two channels are 1–3 dB, in good agreement with numerical calculations. The decoupling of the counterpropagating channels is better than 60 dB, indicating a high directivity. It was found experimentally that the polarization state of radiation propagating in these couplers is conserved.