Abstract: In known coherent optical receivers with two detectors, optical 90.degree. hydrids have a throughput .ltoreq.25%. Theoretical analysis shows that a higher throughput, up to a maximum of approximately 29.3%, is possible. The invention provides such a 90.degree. hybrid (30) of the polarisation type. In an optical hybrid (3) having a structure known per se, i.e. polarisation controllers (38, 39) at the inputs (40 and 41) of a power coupler (42), and polarisers (45, 46) at the outputs (43 and 44) thereof, the polarisation controllers and the polarisers are put into such positions, that the points on the Poincare sphere, which correspond to those positions, comply with two conditions which guarantee a 90.degree. phase difference and the higher throughput. For example, the positions correspond to points which represent positions in which the polarisation controllers produce mutually opposite elliptical polarisations at an angle .alpha. and the polarisers are placed linearly at angles .alpha. and -.alpha., and .

Abstract: System in which subscribers (2) are able to transmit, via the telephone network (1) and a processing system (7), selection codes to a TV or radio station (5) in response to a selection question presented in a TV or radio program using a code transmitter (6). The processing system is connected to different TV or radio stations which each transmit programs in which one or more selection questions are presented. Each of said selection questions is coded by the processing system to form a selection code which is part of a single, simple series of selection codes. Regardless of the TV station or the program, the questions can be answered by means of selection codes taken from the same series in all cases.

Abstract: An optical transmission system includes a number of transceivers which are mutually connected by means of a network and are provided with a transmitter, a receiver and a local oscillator. Connected to the local oscillator or a second oscillator is a frequency control device for mutually locking the frequency of the additional signal originating from the second oscillator and the frequency of the output signal of the local oscillator. The receiver is provided with an input for feeding at least a portion of the additional signal. At least one receiver is provided with a first mixing device to which the output signal of the local oscillator and at least a portion of the additional signal are fed. Connected to an input of a mixing and splitting device for obtaining mixed signals having mutually orthogonal polarisations is the output of the first mixing device. The received signal is fed to another input of the mixing and splitting device.

Abstract: An optical mixing device having intensity-noise suppression, for use in a heterodyne receiver, comprises a coupler (31) having two optical input ports (32, 33) for a received signal (E.sub.S) and a local oscillator signal (E.sub.L), respectively, and two optical output ports (34, 35). An optical path-length difference is created between light signals emerging from the two output ports (34, 35) and a photodetector (36), and the light signals are fed from the output ports (34, 35) to the photodetector (36) in separate beams. The mixing device has a simple optical fiber construction and does not require polarization-influence devices. A coherent heterodyne receiver is also provided which includes the optical mixing device.

Abstract: Optical circuit for a measuring system for measuring the reflection sensitivity of an optical transmission network, comprising a first and a second connection point (1, 4) for a first and a second optical signal source (S1, S2), respectively, a third connection point (2) for optical receiving means (R), optical reflection means (RF), and coupling means. The coupling means consist of a first waveguide junction (C2) via which the second connection point (4) is coupled in the forward signal direction to the reflection means, and a second waveguide junction (C1) via which the first connection point (1) is coupled in the forward signal direction to the third connection point. The two junctions are coupled in such a way that the reflection means are coupled in the forward signal direction to the third connection point via the first and second junctions.

Abstract: A method of optimally packing, either intermittently or continuously, a storage or transportation area or space with rectangular parallelepiped objects, e.g. parcels, comprises two main steps of complex calculations. A first main step implies the locating of one or more free subareas or free subspaces on the area or in the space available for packing by means of a matrix reduction procedure for a 2- or 3-dimensional matrix representing free and occupied parts of rectangular or rectangular parallelepiped form. In a second main step a score is established for each different combination of a free subarea or subspace and an object to be packed and a possible orientation of the object for fitting in the subarea or subspace. The score is established by assigning a score value to each combination by passing through a hierarchy of determinations, whereby a score is the more favorable if the score value is assigned at a higher level in the hierarchy.

Abstract: Method for the automatic generation, from a system or protocol specified as an FSM, of unique test sequences in order to establish whether or not the implementation is in a particular state. On the basis of the FSM a table comprising legal possibilities is generated for each state, as well as a series of tables comprising legal impossibilities for the remaining states. Unique test sequences are found by selecting those IO sequences which occur in the "possibilities table" and in all the "impossibilities tables". If required, the shortest UIO sequence can be selected therefrom.

Abstract: An encoder for coding a digital signal comprises an encoder input for receiving the digital signal; a first data processor, having an input which is coupled to the encoder input, for generating a first coded digital signal at a first output of the first data processor; a first reduction device coupled to the encoder input, for reducing the received digital signal; a second data processor, having an input which is coupled to the first reduction device, for generating a second coded digital signal at a first output of the second data processor; a first encoder memory having an input which is coupled to a second output of the first data processor, and having an output which is coupled to the input of the first data processor; a second encoder memory having an input which is coupled to a second output of the second data processor, and having an output which is coupled to the input of the second data processor; and a first encoder prediction device having a first side which is coupled to the second output of the s

Abstract: A method of managing, in a telecommunication network, user data of a user who may move from a base work area associated with a base exchange which comprises a base memory to another work area associated with another exchange which comprises another memory, independent of whether or not the user is communicating. The method comprises effecting a coupling between the base memory and the another memory when the user moves from the base work area to the another work area; copying a largest portion of the user data stored in the base memory and storing the copied data in the another memory via the coupling, the user data stored in the base memory remaining available for further copying, and changes to be made in the user data taking place both in the base memory and in the another memory.

Abstract: An integrated optical, polarization-manipulating device, comprises a first waveguiding section (A) with a first guide (21), a second waveguiding section (E) with a second and a third optically decoupled and physically separated guide (28, 29) and an intermediary waveguiding section (C) for an adiabatic coupling between the first and the second sections (A, E). The intermediary section (C) comprises a polarization-sensitive asymmetric Y-branching device, provided with two mutually diverging intermediary guides (25, 27) coupled to the guides (28, 29) of the second section. At least one of the two intermediary guides (25) has a channel structure fragmented in the longitudinal direction. Coupling sections (B, D) for adiabatic couplings between guides of successive sections are provided, on the respective coupling sides, with the fragmented waveguide of a corresponding fragmented structure.

Abstract: A composite signal which comprises a video signal situated in the base band and a frequency-modulated audio signal situated outside the base band is coded by an N-bit pulse code modulator or an N-bit noise-shaped pulse code modulator with inadequate quality for, for example, N<5 (in particular for N=1) because, after modulation, demodulation and decoding, the video signal is found to affect the audio signal if, as is usual, the amplitude of the video signal is, for example, ten times greater than the amplitude of the frequency-modulated audio signal. If the amplitude of the video signal is not more than five times greater (in the ideal case one and a half times greater) than the amplitude of the frequency-modulated audio signal, the effect mentioned is apparently considerably reduced.

Abstract: Known systems based on layered video coding and video decoding code with inadequate efficiency because a new high-resolution picture is predicted by means of switching means present in the system either on a basis of the preceding high-resolution picture or on the basis of an instantaneous low-resolution picture. According to the invention, designing the switching means for a adjustment of a ratio of the signal representing a preceding high-resolution picture and the signal representing the instantaneous low-resolution picture and for then adding both adjusted signals achieves a gain of 3 dB in the prediction with the correct ratio, thus resulting in an improvement in the coding efficiency.

Abstract: Known methods of transferring between centers the handling of an active connection between a user and a mobile terminal in a telecommunication system designed for mobile communication generally have the disadvantage that the routing obtained is inefficient. By investigating both a first route between a first switching center and the user and a second route between a second switching center and the user for common centers which are able to handle call control and connection control separately, of which the common center situated nearest the first switching center is designated as a central intelligence point or, if the latter is not found, by designating the center situated nearest the user as a central intelligence point and then setting up a connection between the central intelligence point found in this way and the second switching center, the most efficient routing is obtained.

Abstract: Known optical noise sources are equipped with a light source and an interference filter, optically coupled thereto and based on path length difference, for generating an optical composition signal. If the spectrum of a photodiode to be illuminated with the optical composition signal is to be as flat as possible, said path length difference must be considerably greater than the coherence length of the light source which in present practice leads to disadvantageously large path length differences. By feeding, according to the invention, a noise signal to the light source, the coherence length of the light source decreases, as a result of which it is sufficient to use considerably smaller path length differences.

Abstract: Method of transmitting information having different priorities in accordance with the DQDB protocol, in which a head station (4.sub.1, 4.sub.2) of a transmission channel (1, 2) always assigns to every time slot a priority by means of a code in the access field and an end station (5.sub.1, 5.sub.2) of each transmission channel always stores periodically the number of access units (3.sub.1, 3.sub.2, 3.sub.3) which transmit information having different priorities in time slots having a corresponding priority, and in which the ratio of the numbers of time slots which have different priorities and which are emitted by the head station is adjusted accordingly. Two different ways of storing the number of access units having different priorities are discussed. According to a first way, all the active access units report their priority periodically and according to a second way, all the nonactive access units report and access units having a higher priority which become active/inactive send start/stop codes.

Abstract: The invention relates to a method for switching packets, which are transferrable by transmission cells and comprise a control code, in a switching system having a number of inputs and a number of outputs, from the input at which the packet appears to a specific output derived from the control code of the packet. The invention provides that the packets appearing at the inputs are fed, via a number of first transmission channels containing first transmission cells, to a number of second transmission channels, containing second transmission cells, leading to the outputs of the switching system, a packet of this type transferred by a first transmission cell always being transmitted to the next sequential transmission cell, which is not already occupied by another packet, of that second transmission channel which leads to the specific output derived from the control code.

Abstract: An integrated optical, polarization-manipulating device, comprises a first waveguiding section (A) with a first guide (21), a second waveguiding section (E) with a second and a third optically decoupled and physically separated guide (26, 27) and an intermediary waveguiding section (C) for an adiabatic coupling between the first and the second sections (A, B). The intermediary section (C) comprises a polarization-sensitive asymmetric Y-branching device, provided with two mutually diverging intermediary guides (24, 25), a monomodal (24) and a bimodal (25), coupled to the guides (26, 27), respectively, of the second section. The guides (21, 27) form, with dummy guides (22, 28), respectively, polarization-insensitive asymmetric Y-junctions which function as mode converters between zeroth- and first-order guided modes. Bimodal coupling sections (B, D) provide for adiabatic couplings between asymmetric Y-junctions and the intermediary section (C).

Abstract: Known methods of detecting routing loops in telecommunication networks are cumbersome and time-consuming. In addition, the probability that an existing routing loop is even actually detected is too low. In a method of detecting a routing loop according to the invention, paths whose lengths are stored are assembled. As soon as the length of a (partly assembled) path exceeds a predetermined value which is greater than, or equal to, the largest existing path length in the telecommunication network, this indicates the existence of a routing loop.

Abstract: To manufacture a channel-type waveguide pattern (1.1) having Y-shaped branches and a sharp vertex (V) on or in a substrate (1), masks (6 and 7) which partially overlap one another are used for two different etching steps, which successively define a part of the Y-shaped pattern. In this process, use is made of only one auxiliary mask layer (2) made of suitably chosen material which can be etched in the first etching step but is resistant in a second etching step involving dry etching.

Abstract: Method of transferring, via a transmission medium comprising asynchronously time-division-multiplexed transmission channels, a data stream comprised of data cells. A monitoring apparatus at the beginning of the transmission medium stores, for each transmission channel, a counter position (variable) which, when a data cell arrives at the monitoring apparatus, is amended as a function of time which has elapsed from a reference time instant. Depending on the amended counter position and a threshold value, the data cell is granted or refused access to the downstream transmission medium. The reference time instant is determined by the monitoring apparatus completely or at least partly, independent of the time instant of the appearance of the data cells. A first option provides for the monitoring apparatus to shift the reference time instant in time in accordance with a fixed sequence schedule. According to a second option, the reference time instant is shifted in time in accordance with a fixed time schedule.