Abstract: A bidirectional coherent optical transmission system comprises two stations (I and II) each having only a single laser (2, 9), part of the light signal generated by the laser being fed to a glass fibre T and another part of the light signal generated by the laser being used for mixing the received light signal down to an intermediate frequency by means of a photoelectric diode (4, 11). In contradistinction to the prior art transmission system, in the system according to the invention the light signal is modulated by applying a modulation signal to each of the lasers (2, 9).

Abstract: A ball lens connector part having low total reflections as well as a method of manufacturing such a ball lens connector part are described. The total reflections can be limited to less than -60 dB by means of the present ball lens connector part. The ball lens connector part comprises a fiber with an inclined fiber end in a tubular housing which housing further comprises a ball lens. If the ball lens comprises a flat surface, the total reflections can be lower than -80 dB. By subjecting the end of the housing to a machining treatment, the center line of the said end is moved in such a manner that it coincides with the optical axis of the emanating light beam.

Abstract: Apparatus for modulating the output signal of a converter for converting electric signals into other signals, for example optical signals. An analog signal is applied to a subtraction device (6) the output signal of which controls a limiter (7). The binary output signal thereof controls the semiconductor laser diode (1) which is coupled to a photo-sensitive detector (3) for producing a feedback signal. After being amplified in a broad-band amplifier (9) and integrated in an integrator (13), this feedback signal is applied to the subtraction device (6), so that the feedback signal is subtracted from the analog signal. Variations in the optical output signal due to a non-linear conversion characteristic of the laser diode (1) and due to an optical retroaction of the fibre (2) on the laser diode, as well as output noise and signal-dependent amplitude variations, are reduced by the negative feedback.

Abstract: A RF signal converter circuit for connection to the aerial input of an RF superheterodyne receiver. In order to avoid a separate remote control of the converter circuit use is made of the local oscillator radiation which is present at the aerial input of a RF-superheterodyne receiver as an indication of the tuning frequency selected by the user with tuning portion of the said RF superheterodyne receiver. The converter circuit comprises a frequency search circuit in which the frequency of the oscillator radiation is detected, an RF signal selector which is controlled by the frequency search circuit and by means of which the desired RF signal is selected from the RF signals applied to the converter circuit, furthermore comprising a modulator which is also controlled by the frequency search circuit and in which the selected RF signal is modulated on a carrier frequency which is determined by the tuning frequency and the intermediate frequency of the RF superheterodyne receiver.

Abstract: A wave guide to microstrip transition is disclosed in which the substrate of the microstrip line is arranged parallel to and in the longitudinal direction of the wave guide. The microstrip conductor is connected to the wave guide wall by a strip-shaped conductor provided on the substrate and the base plate has a first portion which extends to the opposite wall and a second portion which is located opposite the strip-shaped conductor. The edge of the second portion forms with an edge of the strip-shaped conductor a high impedance transmission line so that a low-loss asymmetrical conductor structure is obtained.