U.S. Philips Corporation

Bastiaan H Verbeek

Lukas Frederik Tiemeijer

Coen T Liedenbaum

John J Reid

Engelbertus C Pennings

Raymond Van Roijen

Wilma Van Es-Spiekman

Leonardus J Hendrix

The invention relates to an optical unit (17) for synchronizing clock signals. The unit (17) comprises at least two ring lasers (1', 1'), each ring laser (1', 1') generating a repetitive optical pattern at a different repetition frequency f.sub.i. The repetition frequency of at least one of the ring lasers (1', 1') is variable. The unit (17) comprises detection means (19) adapted to simultaneously receive the optical patterns from two ring lasers (1', 1') to be synchronized with each other and to compare these patterns. The ring laser, whose repetition frequency is variable, is controllable on the basis of a signal from the detection means, by which the optical path length of this laser is changed. The invention also relates to a high-frequency carrier transmission system comprising an optical unit as described hereinbefore.

Optical unit for synchronizing clock signals

An optical unit for multiplying the frequency of a clock signal includes at least two series-arranged ring lasers. Each ring laser has a different resonance frequency f.sub.i. The unit has an input for receiving a signal, for example, a low-frequency electric signal for modulating one of the ring lasers. The repetition frequency of at least one of the ring lasers is variable by adapting the optical path length of the resonator.

Optical unit for multiplying the frequency of a clock signal

An optical amplifier with a semiconductor body comprising a layer structure grown on a substrate 1 with an active layer 4 situated between two cladding layers (2, 3) with a strip-shaped amplification region bounded by two end surfaces (7, 8) which form the input and output surfaces of the radiation to be amplified. The active layer comprises a number of quantum well (QW) layers 4A with direct band transition, which are separated by barrier layers 4B of a different semiconductor material. The material, the number, and the thickness of the QW layers 4A and the barrier layers 4B in combination with the length 1 of the amplification region are chosen in such a way that two optical transitions can take place in the active layer 4, maximum amplification occurring at a certain current density through the PN junction for the radiation wavelengths corresponding to these optical transitions, while the end surfaces (7, 8) are provided with an anti-reflection layer 9 which has a reflection coefficient R of at most 0.5% for these two wavelengths. An anti-reflection layer made up of four layers of alternately titanium oxide and aluminum oxide is advantageously used.

Optical amplifier having gain at two separated wavelengths

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Eindhoven, Netherlands

Bastiaan H Verbeek