Alcatel N.v.

International Standard Electric Corporation

Standard Elektrik Lorenz Ag

Friedemann Mohr

Manfred Kaiser

Horst Ohnsorge

Wilfried Auch

Eberhard Schlemper

Klaus Herse

Kate Hiepe-Wohlleben

Walter Steudle

Werner Hofmann

Rolf Robberg

Leo Brautigam

Dieter Kuppers

Heinz Mieskes

The method consists of first splicing (FIG. 2) one short length of a single-mode fiber (3, 4) into each of the optical fibers (1, 2) of fibers lying parallel to each other (FIG. 1), then fusing the two spliced-in single-mode fibers (3, 4) together (FIG. 3) and pulling them to form a coupler (6) (FIG. 4), and then embedding the coupler (6) in a protective housing (7) up to points beyond the splices (5).

Method of manufacturing a fused-fiber optical coupler

For short-distance communication systems, particularly for optical-waveguide links in the subscriber area, it is proposed to operate the standard single-mode optical waveguide for long-distance applications, which is optimized for the wavelength range from 1300 nm to 1600 nm, with optical transmitters and optical receivers whose operating wavelengths lie clearly below the cutoff wavelength of the optical waveguide. By means of a suitable stable laser-waveguide coupling, it is ensured that single-mode operation is achieved, which is necessary to transmit digital signals at high bit rates. The increased loss of the optical waveguide at 800 nm can be accepted because of the relatively short length of subscriber lines. Both unidirectional and bidirectional transmission over a single optical waveguide using wavelength-division or modal multiplexing is possible.

Broadband optical communication system, particularly in the subscriber

Optical heterodyne receivers for ASK-, PSK-, FSK-, and DPSK-modulated signals are disclosed which contain a polarization controller. The receiver contains a unit (Q, Q') which works on the difference-detector principle to eliminate the shot noise of the local oscillator (LO), which emits circularly polarized light. It further includes a quadrature demodulator (D, D', D') which, besides delivering the useful signal (N), provides polarization control signals (S.sub.E, S.sub.W) with which the ellipticity and the polarization angle of the received light (E.sub.S) are adjusted in such a way that the received light (E.sub.S) is linearly polarized at an angle of 45.degree. or 135.degree..

Optical heterodyne receiver

An optical receiver is disclosed in which a portion of the electric signal produced by optical-to-electric conversion is coupled out and fed to an automatic control system (4, 5, 8, 9, 12-17). The automatic control system contains polarization control elements (4, 5) which control the polarization of the received light beam relative to that produced by the local oscillator so that the electric output signal is maximized. There is no requirement for either light beam to be polarized in a particular direction in order to have optimum matching.

Optical receiver with automatic polarization matching

Optical-waveguide coils are used in rotation rate measuring instruments. To protect the optical-waveguide coil (1) from external influences, such as sound waves, pressure, and temperature changes, which may result in measurement errors, it is wound on a coil form (2) of soft elastomer under low tension. The coil unit so formed (1/2) is then placed in the annular groove (4) of a housing (3/5). Spacers at the coil form (2) position the coil unit (1/2) in the annular groove in such a way that the coil (1) is exactly in the middle of the annular groove (4). The remaining free space of the annular groove (4) is then filled with a sealing compound (6) in a vacuum. The sealing compound also spreads between the windings of the coil (1). It is preferably the same material as that from which the coil form (2) is made.

Optical-waveguide coil and method of making same

A fiber-optic distribution system is disclosed which distributes broadband signals received by a network termination circuit from a broadband communications network (B-ISDN or cable-television network) among a plurality of subscriber terminals. The network termination circuit (4) contains devices for separating a forward channel and a backward channel. It also includes electric-to-optical and optical-to-electric transducers (5,6). The distribution system contains a fiber-optic multi-port coupler (10) which is made by the fusion technique and interconnects a plurality of optical fibers (12, 13, 14). On the subscriber's side, each of these optical fibers forms the forward channel and the backward channel for one of the terminals (32). On the network side, one of these optical fibers (16) forms the forward channel for the broadband signals, and all other optical fibers (17, 18) are combined to form the narrow-band backward channel. They are connected to a common large-area photodiode (6). As the backward channel is a narrow-band channel, the fact that large-area photodiodes, such as PIN diodes, are relatively slow does not cause any bandwidth problems.

Fiber-optic distribution system for broadband signals

In the rotation rate measuring instrument, two light beams traverse a coiled optical fiber (1) in opposite directions. The two beams emerging from the optical fiber are combined, and the rotation rate is determined from the Sagnac phase difference between the two beams. The optical fiber (1), which may be embedded in a sealing compound (4), is contained in a double-walled housing (8, 9) having its two walls linked by heat bridges (10, 10'). The material of the housing is a good thermal conductor. The heat bridges between the two walls are located so that external heat will act on the coiled optical fiber (1) at predetermined points.

Rotation rate measuring instrument

An optical fiber is coiled in an instrument in such a way that its beginning and its end belong to the same layer or to adjacent layers and are close together.

Optical fiber coil having juxtaposed ends in same or adjacent layers for

In the rotation rate measuring instrument, two component beams derived from a light beam produced by a laser circulate around a coiled optical waveguide (radius R, length L) in opposite directions. From the phase difference between the two component beams due to the Sagnac effect, the rotation rate is determined. Before entering the optical waveguide, each of the two component beams is modulated in a modulator (5, 6) such that the phase differences (2.nu.+1).pi./2, (2.nu.+5).pi./2, and (2.nu.+3).pi./2 (where .nu. is an arbitrary integer) exist periodically between the two component beams emerging from the optical waveguide. The drive signals for the two modulators, which exhibit periodic frequency changes of 2F, are varied in such a way that the output of an optical-to-electrical transducer (2) to which the two component beams are directed after travelling around the optical waveguide provides a constant signal. To compensate for the Sagnac phase difference, an additional frequency difference of .DELTA.f is required between the two drive signals. The rotation rate .OMEGA. is determined by the equation ##EQU1## where .lambda.=vacuum wavelength of the light, and C=velocity of light in vacuo.

In the measuring instrument, a light beam generated by a laser (1) is split into two component beams (L(CW), L(CCW)) which travel along a coiled optical waveguide (7) in opposite directions. After traversing the optical waveguide, the two component beams are superimposed on each other (5) and directed to an optical/electrical transducer (8). One of the two component beams (L(CW)) is frequency-modulated in a Bragg cell (6) before entering the optical waveguide (7), switchover being effected between two modulation frequencies (f1, f2) at a given frequency (F.sub.S). The modulation frequencies are chosen so that, after traversal of the optical waveguide (7), the phase differences (.phi..sub.B1, .phi..sub.B2) between the two component beams (if the rotation rate .OMEGA.=0) are .pi./2 and 3.pi./2 or even integral multiples thereof. In case of rotation, the phase difference (.phi..sub.S) caused by the Sagnac effect is superimposed on these phase differences. The output signal of the optical/electrcal transducer (8) is passed through a band-pass filter (10) whose midfrequency is equal to the frequency at which switching takes place between the two modulating signals. The amplitude of the band-pass output signal is directly proportional to the rotation rate (.OMEGA.). From this signal, a control signal can be derived which can be used to compensate for the phase difference (.phi..sub.S) caused by the Sagnac effect.

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Renningen, Germany

Friedemann Mohr