Abstract: An optical fiber provided with a synthetic resin coating, comprising a glass fibre, a first enveloping layer of a synthetic rubber having a modulus of elasticity from 0.1 to 10 MPa and a subsequent enveloping layer of a synthetic resin having a larger modulus of elasticity than the first layer, obtains a large mechanical resistance and a high insensitivity to temperature variations within the range from -60.degree. C. to +80.degree. C., in that the thickness of the first layer is from 5 to 20 .mu.m and in that the modulus of elasticity of the second layer is more than 1000 MPa.

Abstract: A piezoelectric resonator having a rectangular resonator body cut from a piezoelectric crystal in accordance with a rotated X-cut. One of the end faces bounding the major surfaces is intended for mounting, whereas in the vicinity of the other end face an electrode array is arranged. The electrode array in conjunction with the crystal cut have been selected so that a combined resonant mode is generated, comprising an XY' thickness-shear vibration and a thickness vibration in the X or Y' direction.