Fibre optic gyroscope

Claim 2

A fibre optic gyro including a laser diode (LD), a light detector (DET 2 ), first (L 3 ) and second (L4) lenses arranged on opposite sides of a half mirror (HF) and a coiled optical fibre which is arranged so that the opposite ends of the optical fibre (FG) face the first (L 3 ) and second (L 4 ) lenses, respectively, the arrangement being such that a light beam from the laser diode (LD) is directed onto the half mirror (HF) through the first lens (L3), the light reflected from the half mirror (HF) is directed onto one end (F 3 ) of the coiled optical fibre (FC 1 ) through the first lens (L 3 ), the light transmitted through the half mirror (HF) is directed onto the other end of the coiled optical fibre (FC 1 ) through the second lens (L 4 ) so that the light beams are propagated through the coiled optical fibre (FC1) in opposite directions, after passage around the coiled optical fibre (FC 1 ) the light beams are synthesised and applied to the light detector (DET 2 ), the output of the light detector (DET 2 ) enabling the speed of rotation of the coiled optical fibre (FC 1 ) to be derived.

Claim 3

A fibre-optic gyro according to claim 1, wherein the lenses (L 3 , L 4 ) are formed from a monoaxial crystal.

Claim 4

A fibre-optic gyro according to claim 1 or 2, wherein a control portion (PC 2 ) for controlling the orientation of the polarisation plane of the light is provided on a part of the coiled optical fibre (FC 1 ).

Claim 5

A fibre-optic gyro according to any one of the preceding claims, wherein a control portion (PC 1 ) for controlling the orientation of the polarisation of the light is provided between the laser diode (LD) and the first lens (L3).

Claim 6

A fibre-optic gryo including a half mirror (HF2) having a dielectric multilayer film formed on one surface of an optical substrate, first (F 11 ) and second (F 12 ) optical fibres being aligned with their adjacent ends spaced from one another (F 11a , F 12a ) ' and a single-mode fibre (F 13 ) having a polarisation plane storing property and being coiled, the ends (F 13a , F 13b ) of the single-mode fibre being aligned, being spaced from one another and being parallel to the ends (F 11a , F 12a ) of the first (F 11 ) and second (F 12 ) fibres, the half mirror (HF 2 ) being interposed between the adjacent ends of the first (F 11 ) and second (F 12 ) fibres and between the ends of the single-mode fibre, end faces (F 11a ' F12a ) of the adjacent ends of the first (F 11 ) and second (F 12 ) fibres and end faces (F 13a ' F 13b ) of the single-mode fibre (F 13 ) being inclined with respect to the optical axes (OX 1 , OX 2 ) of the optical fibres (F 11 , F 12 , F 13 ) the arrangement being such that when a single-mode laser beam of predetermined polarisation orientation is carried by the first optical fibre (F 11 ), the laser beam emerging from the inclined end face of the first optical fibre (F 11 ) is divided into two beams by the half mirror (HF 2 ), and the two beams impinge on the end faces (F 13a , F 13b ) of the single-mode fibre (F 13 ), respectively, and propagate through the single-mode fibre in opposite directions, the light beams emerging from both the end faces (F 13a , F 13b ) of the single-mode fibre are synthesised and impinge on the inclined end face (F 12a ) of the second optical fibre (F 12 ) ' the gyro also including a light detector (DET) to detect a laser beam emerging from the other end of the second optical fibre ( F 12 ).

Claim 7

A fibre-optic gryo including a half mirror (HF2) having a dielectric multilayer film formed on one surface of an optical substrate, first (F 11 ) and second (F 12 ) optical fibres being aligned with their adjacent ends spaced from one another (F 11a , F 12a ) ' and a single-mode fibre (F 13 ) having a polarisation plane storing property and being coiled, the ends (F 13a , F 13b ) of the single-mode fibre being aligned, being spaced from one another and being parallel to the ends (F 11a , F 12a ) of the first (F 11 ) and second (F 12 ) fibres, the half mirror (HF 2 ) being interposed between the adjacent ends of the first (F 11 ) and second (F 12 ) fibres and between the ends of the single-mode fibre, end faces (F 11a ' F12a ) of the adjacent ends of the first (F 11 ) and second (F 12 ) fibres and end faces (F 13a ' F 13b ) of the single-mode fibre (F 13 ) being inclined with respect to the optical axes (OX 1 , OX 2 ) of the optical fibres (F 11 , F 12 , F 13 ) the arrangement being such that when a single-mode laser beam of predetermined polarisation orientation is carried by the first optical fibre (F 11 ), the laser beam emerging from the inclined end face of the first optical fibre (F 11 ) is divided into two beams by the half mirror (HF 2 ), and the two beams impinge on the end faces (F 13a , F 13b ) of the single-mode fibre (F 13 ), respectively, and propagate through the single-mode fibre in opposite directions, the light beams emerging from both the end faces (F 13a , F 13b ) of the single-mode fibre are synthesised and impinge on the inclined end face (F 12a ) of the second optical fibre (F 12 ) ' the gyro also including a light detector (DET) to detect a laser beam emerging from the other end of the second optical fibre ( F 12 ).

Claim 8

A fibre-optic gyro according to any one of the preceding claims wherein the half mirror (HF 1 , HF 2 ) is- coupled to an electrostriction element (14, 28, 29) to shift the position of the half mirror (HF 1 , HF 2 ) to provide a phase difference between the light beams incident on the ends of the coiled optical fibre (FC 1 ) and when the light beams are synthesised and converted to an electrical signal, phase detection is carried out and the phase difference is measured.

Claim 9

A fibre-optic gyro system according to claim 6, wherein the coil delay time determined by the length L of the coiled optical fibre (FC) and the light propagation speed C of the coiled optical fibre (FC) is adjusted to T coil, and the light emission time interval D is adjusted so that the following relationship is established: D > T coil the light emission time interval D is made equal to a time interval D det for opening an electric gate in the light detector (DET) and the time deviation between the interval D and the interval D det is made equal to the delay time.

Claim 10

A fibre-optic gyro which includes a Rochon prism (41, Figure 20) having the same tilt angle α 1 on its incident (42) and emergent (43) end faces, an input optical fibre (47) having its optical axis parallel to the longitudinal mechanical axis (44) of the Rochon prism (41) and an end face inclined at an angle 8p to the normal, the optical axis of the input optical fibre (47) being separated by a distance h from the mechanical axis (44), a first lens (45) having a focal length F interposed between the input optical fibre (47) and the Rochon prism (41) and having a centre (O) lying on the mechanical axis (44) of the prism (41) and at a point separated by a distance ℓ1 from the incident end face (42) of the Rochon prism (41), opposite ends (48, 49) of an optical fibre coil are parallel to the mechanical axis (44) and arranged at points separated by a distance h from an axis parallel to the mechanical axis and passing through the equivalent light branching point of the Rochon prism (41), end faces of the ends (48, 49) being inclined to the normal by angles of θp and - 8p, and a second lens (46) having a focal length F interposed between the ends (48,49) of the optical fibre and the Rochon prism (41) and having its centre (O') on the axis parallel to the mechanical axis (44) and passing through the equivalent light branching point and separated by a distance ℓ1 from the equivalent light branching point, the tilt angle α 1 of the Rochon prism (41), the emergent angle 8 0 of light from the input optical fibre 47, the incident angle 8r of light into and out of the output optical fibre, and the focal distance F of both the lenses being determined by the following relationships:- and wherein n represents a refractive index of the Rochon prism (41) to the extraordinary light beam, n o represents a refractive index of the Rochon prism (41) to the ordinary light beam, δ stands for a separation angle in the Rochon prism (41) for the extraordinary and ordinary light beams, n c represents the refractive index of inlet and outlet optical fibre cores, and n a represents the refractive index of air.

Claim 11

A fibre-optic gyro which includes a Rochon prism (41, Figure 20) having the same tilt angle α 1 on its incident (42) and emergent (43) end faces, an input optical fibre (47) having its optical axis parallel to the longitudinal mechanical axis (44) of the Rochon prism (41) and an end face inclined at an angle 8p to the normal, the optical axis of the input optical fibre (47) being separated by a distance h from the mechanical axis (44), a first lens (45) having a focal length F interposed between the input optical fibre (47) and the Rochon prism (41) and having a centre (O) lying on the mechanical axis (44) of the prism (41) and at a point separated by a distance ℓ1 from the incident end face (42) of the Rochon prism (41), opposite ends (48, 49) of an optical fibre coil are parallel to the mechanical axis (44) and arranged at points separated by a distance h from an axis parallel to the mechanical axis and passing through the equivalent light branching point of the Rochon prism (41), end faces of the ends (48, 49) being inclined to the normal by angles of θp and - 8p, and a second lens (46) having a focal length F interposed between the ends (48,49) of the optical fibre and the Rochon prism (41) and having its centre (O') on the axis parallel to the mechanical axis (44) and passing through the equivalent light branching point and separated by a distance ℓ1 from the equivalent light branching point, the tilt angle α 1 of the Rochon prism (41), the emergent angle 8 0 of light from the input optical fibre 47, the incident angle 8r of light into and out of the output optical fibre, and the focal distance F of both the lenses being determined by the following relationships:- and wherein n represents a refractive index of the Rochon prism (41) to the extraordinary light beam, n o represents a refractive index of the Rochon prism (41) to the ordinary light beam, δ stands for a separation angle in the Rochon prism (41) for the extraordinary and ordinary light beams, n c represents the refractive index of inlet and outlet optical fibre cores, and n a represents the refractive index of air.

Claim 12

A fibre-optic gyro including a source of circularly polarised light, a light branching and synthesising device (74, 81, 82) having four terminals and a half mirror (82), an optical fibre loop (75) composed of a polarisation plane storing fibre, and a light detector (77), wherein a circularly polarised wave light incident from the first terminal is separated by the half mirror (82) into two linearly polarised light beams having mutually perpendicular polarisation planes , the linearly polarised light beams emerge from the second and third terminals and enter the ends of the single polarisation maintaining single mode optical fibre loop (75), respectively, the beams propagate through the optical fibre loop (75) in opposite directions and then enter the third and second terminals and are synthesised by the half mirror (82) and emerge from the fourth terminal, light output froIDfhe fourth terminal being detected by the detector (77) through a Babinet compensator phase plate (76).

Claim 13

A fibre-optic gyro including a source of circularly polarised light, a light branching and synthesising device (74, 81, 82) having four terminals and a half mirror (82), an optical fibre loop (75) composed of a polarisation plane storing fibre, and a light detector (77), wherein a circularly polarised wave light incident from the first terminal is separated by the half mirror (82) into two linearly polarised light beams having mutually perpendicular polarisation planes , the linearly polarised light beams emerge from the second and third terminals and enter the ends of the single polarisation maintaining single mode optical fibre loop (75), respectively, the beams propagate through the optical fibre loop (75) in opposite directions and then enter the third and second terminals and are synthesised by the half mirror (82) and emerge from the fourth terminal, light output froIDfhe fourth terminal being detected by the detector (77) through a Babinet compensator phase plate (76).

Claim 14

A fibre-optic gyro according to claim 9, wherein the source of circularly polarised light comprises a laser oscillator (71), a prism (72) for converting a laser beam from the laser oscillator to a linearly polarised light beam and a phase plate (73) for converting the output from the prism (72) to a circularly polarised light beam.

Claim 15

A fibre-optic gyro according to claim 9, wherein the source of circularly polarised light comprises a laser oscillator (71), a prism (72) for converting a laser beam from the laser oscillator to a linearly polarised light beam, and a phase modulator (84) for phase-modulating the output from the prism (72) to a circularly polarised light beam.

Claim 16

A fibre optic gyro comprising a laser oscillator, a polarisation plane converting optical system for converting the output of the laser oscillator to linearly polarised wave light and then to circularly polarised wave light, a light branching and synthesising device having an optical fibre loop composed of a polarisation plane storing fibre, four terminals, and a half mirror, a phase modulator, a light detector, and a phase detector, wherein the laser oscillator is phase modulated by the phase modulator, the output of the polarisation plane converting optical system is put in the first terminal, separated into two linearly polarised wave lights crossing at right angles by the half mirror, and emerge from the second and third terminals connected to both the ends of the optical fibre loop, respectively, the lights propagated through the optical fibre loop in directions opposite to each other are synthesised by the half mirror and emerge from the fourth terminal, the output light from the fourth terminal is detected by the light detector, and the output of the light detector is put in the phase detector to effect the phase detection and detect the phase difference between the lights propagated through the optical fibre loop in directions opposite to each other.

Claim 17

A fibre optic gyro comprising a laser oscillator, a polarisation plane converting optical system for converting the output of the laser oscillator to linearly polarised wave light and then to circularly polarised wave light, a light branching and synthesising device having an optical fibre loop composed of a polarisation plane storing fibre, four terminals, and a half mirror, a phase modulator, a light detector, and a phase detector, wherein the laser oscillator is phase modulated by the phase modulator, the output of the polarisation plane converting optical system is put in the first terminal, separated into two linearly polarised wave lights crossing at right angles by the half mirror, and emerge from the second and third terminals connected to both the ends of the optical fibre loop, respectively, the lights propagated through the optical fibre loop in directions opposite to each other are synthesised by the half mirror and emerge from the fourth terminal, the output light from the fourth terminal is detected by the light detector, and the output of the light detector is put in the phase detector to effect the phase detection and detect the phase difference between the lights propagated through the optical fibre loop in directions opposite to each other.

Claim 18

A fibre-optic gyro according to any one of the preceding claims, wherein reflecting members (R 1 , R 2' M 1 , M 2' M 3 ) are arranged on opposite sides of the semiconductor laser diode (LD) so that an etalon is constructed.

Claim 19

A fibre optic gyro according to claim 13, wherein one of the reflecting members is a reflecting film (R 1 , R 2 ) formed on the end face of a single-mode fibre (SMF).

Claim 20

A fibre-optic gyro according to any one of the preceding claims, wherein the laser diode (LD) is provided with a narrow-band reflection filter (BRF 1 , BRF 2 ).

Claim 21

A fibre-optic gyroscope according to any one of the preceding claims, wherein the coiled optical fibre (FC) is a single-mode polarisation plane storing optical fibre comprising a fibre composed of quartz and having a triple structure (Figure 32A) including a core (101) a clad (102) and a jacket (103) in which the difference of the refractive index between the core (101) and the clad (102) is defined as in which nl represents the refractive index of the core (101) and n2 stands for the refractive index of the clad (102), is 0.13 ± 0.05, the fibre being wound on a drum.