GB2058345A

GB2058345A - Ring Interferometer Rotation Sensors

Info

Publication number: GB2058345A
Application number: GB8028964A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1979-09-07
Filing date: 1980-09-08
Publication date: 1981-04-08
Also published as: JPS5646468A; FR2465200A1; GB2058345B; DE2936249A1

Abstract

Ring interferometer rotation sensors provided with means by which a periodically fluctuating, non- reciprocal phase shift is impressed onto a light beam component of the light conducted in a light waveguide 1 of the interferometer, and a sensor 17 provides a signal that is processed by means of a phase-sensitive rectifier 15 using as a reference signal a signal in synchronism with the periodically fluctuating phase shift. As illustrated, the periodically fluctuating phase shift is imposed by a Faraday coil 6 wound around at least a portion of the waveguide 1. Alternatively the Faraday coil 6 may surround a block of lead glass interposed in the light path. <IMAGE>

Description

SPECIFICATION Ring Interferometer Rotation Sensors The invention relates to a ring interferometer rotation sensor, the ring interferometer comprising a light waveguide with two coupling points via each of which light may be injected to emerge from the other, the light from the two coupling points being superimposed and directed to at least one light receiving surface to measure angular rotation, and thus identify rotations and measure the angular speed thereof. Such interferometers utilise the relativistic Sagnac effect, which produces non-reciprocal transit time differences that are proportional to the angular speed. The Sagnac effect functions in respect of all polarisation states of the light employed. A measurement is carried out of transit time differences, and thus of the angular speed, derived from the integral intensity incident on the light receiving surface.This integral intensity is a periodic function of the angular speed, and in fact is dependent upon the angular speed in accordance with a quadratic sine function. As a result, the normal measurement of the angular speed cannot clearly define the direction of rotation, i.e. the sign, of the angular speed within one period.

One object of the present invention is to provide an improved ring interferometer, by which it is readily possible to measure the direction of the rotation.

The invention consists in a ring interferometer rotation sensor, wherein a ring interferometer comprising a light waveguide with two coupling points via each of which light can be injected to propagate through said waveguide and emerge at the other coupling point, wherein light components output coupled from the two coupling points are superimposed, when operating, to be fed to at least one light receiving surface, whereby the integral light intensity of the superimposed light components incident on the light receiving surface is a measure of the angular speed, since the light intensity changes that result from non-reciprocal transit time differences in the light waveguide, and which are produced by the Sagnac effect, are dependant upon the angular speed, and wherein means are provided by which a periodically fluctuating, non-reciprocal phase shift is impressed upon a light component conducted through the light waveguide, when operating, the integral intensity on the light receiving surface converted into a corresponding electric signal being fed to an input of a phase sensitive rectifier to which is fed a periodically fluctuating signal in synchronism with the periodically fluctuating phase shift. With such an arrangement the signal emitted from the phase sensitive rectifier contains the required information concerning both the value of the angular speed and its sign.

Advantageously the periodically fluctuating, non-reciprocal phase shift is produced by utilising the Sagnac effect, by a corresponding periodic agitation of the light waveguide, or by utilising the Faraday effect, by a corresponding periodically fluctuating magnetic field.

Expediently, the ring interferometer comprises an electric coil surrounding a component in the path of the light passing through the light waveguide. Thus, the periodically fluctuating, non-reciprocal phase shift is produced by means of the Faraday effect.

The invention will now be described with reference to the drawings, in which: Figure 1 schematically illustrates one exemplary embodiment of a ring interferometer in accordance with the present invention; and Figure 2 schematically illustrates another exemplary embodiment of a ring interferometer constructed in accordance with the invention.

In both of the illustrated embodiments the ring interferometer comprises a laser light source 5, a partially transparent reflector 2, a linear polariser 61', two optical feed systems 7 and 7', a light waveguide 1 in the form of a monomode light conducting fibre composed of glass and wound into a coil, its ends 11 and 11' forming the coupling points of the light waveguide 1, and a light receiving surface 4, which is a light sensitive surface of a sensor 17.

The light source 5 transmits a beam 50 in the direction indicated by an R, to be incident upon the partially transparent reflector 2 which is inclined at an angle of 450 thereto in this example. This reflector 2 reflects a component of the beam as a subsidiary beam 51 in a direction at right angles to the direction indicated by the R, whereas the residual light beam energy passes through the reflector 2 and is propagated on in the same direction as a subsidiary beam 51'. The linear polariser 61' is arranged in one of the beam paths, in this example that of the beam 51'. The two optical feed systems 7 and 7' focus the respective beams 51 and 51' onto the associated ends, 11 and 11' respectively, of the light waveguide 1 to input couple the respective beams into the light waveguide 1.

The light which has been input coupled into the light waveguide via one end, 11 or 1 1', is propagated through said light waveguide to the other end, 11' or 11 respectively, from where it is output coupled and focused by the associated optical feed system, 7' or 7 respectively. Thus, a light beam 1 10' is output coupled from the end 11 and directed on a path fundamentally opposite to the input beam 51, and is incident on one side of the partially transparent reflector 2. Similarly, a light beam 110 is output coupled from the end 11' and is fed on a path fundamentally oppositely directed to the input 51' to be incident on the other side of the reflector 2.

A component of the output coupled light beam 1 10' passes through the reflector 2 and is propagated on in the same direction, as part of a beam 111, whereas the remainder of the beam 11 0' is reflected. A component of the output coupled light beam 110 is reflected by the reflector 2 to be superimposed in the beam 111, the remainder of the beam 110 passing through the reflector 2 to be propagated on in the same direction. The light receiving surface 4 is arranged in the path of the light beam 111. Up to this point the description has referred to components of a known construction of ring interferometer, which can be operated as a rotation sensor.

In order to determine the direction of rotation, i.e. the sign of the rotation dependant output signal, a periodically fluctuating, non-reciprocal phase shift is impressed onto a light beam component that passes through the light waveguide 1 to the light receiving surface 4, and the electric signal which is produced by the light sensitive sensor 17, which is proportional to the integral intensity on the light receiving surface 4, is fed to an input 1 51 of a phase sensitive rectifier 15, which is synchronized with a periodically fluctuating signal which corresponds to the periodically fluctuating phase shift.

The periodically fluctuating phase shift can either be impressed by utilising the Sagnac effect, by a corresponding periodic agitation of the light waveguide, or by utilising the Faraday effect, employing a periodically fluctuating magnetic field. The Faraday effect has been utilised in the exemplary embodiments illustrated in Figures 1 and 2. For this purpose, in both exemplary embodiments, an electric coil 6 has been provided. In the exemplary embodiment illustrated in Figure 1 the turns of this coil 6 surround a section of the path of the wound light waveguide 1. In the exemplary embodiment illustrated in Figure 2 the turns of the coil 6 surround a lead glass component 60, which is arranged in the path of the oppositely directed beams 51' and 1 10.The coil 6 is linked to the output of an alternating current generator 13 which feeds a current iw=iwO-cos w1.t through the coil. An alternating voltage Uw=UWO-c S w1.t is tapped from the alternating current generator 13 and fed to the phase sensitive rectifier 1 5 as a reference signal. The signal obtained from a signal output 1 52 of the phase sensitive rectifier 1 5 is then integrated in an integrator circuit 1 6 and the signal emitted from the integrator circuit 16 contains the required information concerning the direction of rotation and the value of the angular speed.

As the Faraday effect only functions along the above lines when circularly polarised light is passing through the waveguide, the light energy which has impressed thereupon the periodically fluctuating, non-reciprocal phase shift must be polarised in circular fashion. In each of the two exemplary embodiments illustrated, circularly polarised light is produced by a A/4 plate 62', which is arranged between the linear polariser 61' and the optical feed system 7' in the path of the beam 51'. This plate 62' converts the linearly polarised light emanating from the linear polariser 61' into a beam of circularly polarised light. Other known means could also be used to produce the circularly polarised light.

A further linear polariser 61 and a further A/4 plate 62 may be arranged in the path of the other beam 51, as illustrated in Figure 1.

The or each linear polariser, 61 and 61', can be omitted if the light source 5 itself emits linearly polarised light, as is generally the case with a laser source.

Claims

1. A ring interferometer rotation sensor, wherein a ring interferometer comprising a light waveguide with two coupling points via each of which light can be injected to propagate through said waveguide and emerge at the other coupling point, wherein light components output coupled from the two coupling points are superimposed, when operating, to be fed to at least one light receiving surface, whereby the integral light intensity of the superimposed light components incident on the light receiving surface is a measure of the angular speed, since the light intensity changes that result from non-reciprocal transit time differences in the light waveguide, and which are produced by the Sagnac effect, are dependant upon the angular speed, and wherein means are provided by which a periodically fluctuating, non-reciprocal phase shift is impressed upon a light component conducted through the light waveguide, when operating, the integral intensity on the light receiving surface converted into a corresponding electric signal being fed to an input of a phase sensitive rectifier to which is fed a periodically fluctuating signal in synchronism with the periodically fluctuating phase shift.

2. A rotation sensor as claimed in Claim 1, in which said means by which the periodically fluctuating, non-reciprocal phase shift is impressed utilises the Sagnac effect by producing a periodic agitation of the light waveguide.

3. A rotation sensor as claimed in Claim 1, in which said means by which the periodically fluctuating non-reciprocal phase shift is impressed utilises the Faraday effect by using a periodically fluctuating magnetic field.

4. A rotation sensor as claimed in Claim 3, in which said means comprise an electric coil whose turn or turns surround the path of a light path component through which is conducted the light passing through the light waveguide, when operating, said light being circularly polarised, and said coil being connected to an alternating current generator.

5. A rotation sensor as claimed in Claim 4, in which said coil surrounds a section of the light waveguide.

6. A rotation sensor as claimed in Claim 5, in which said coil surrounds a glass component arranged in a path of the light between the light waveguide and the light receiving surface.

7. A rotation sensor as claimed in Claim 5, in which said glass component consists of lead glass.

8. A ring inteferometer rotation sensor substantially as described with reference to Figure 1 or Figure 2.