GB2121954A

GB2121954A - Optical fibre laser gyro

Info

Publication number: GB2121954A
Application number: GB08313022A
Authority: GB
Inventors: Hiroshi Kajioka
Original assignee: Hitachi Cable Ltd
Current assignee: Hitachi Cable Ltd
Priority date: 1982-05-12
Filing date: 1983-05-11
Publication date: 1984-01-04
Also published as: GB2121954B; JPS58196416A; FR2526938B1; JPH0247684B2; GB8313022D0; FR2526938A1

Abstract

Polarised light from a laser 11 is split at 15 into orthogonally polarised beams 15a and 15b incident on respective ends of a loop 16 of single polarisation optical fibre. After the transmitted beams have been recombined at 15, their relative phase is determined using a g DIVIDED 4 plate 17, analyser 18 and detector 19. Alternatively the recombined beams may be directed via a g DIVIDED 4 plate and a further polarising beam splitter to two photodetectors connected to the imputs of a differential amplifier, or the single detector 19 may be in a nulling loop where it controls a Pockels and Faraday element acting on the recombined beams. Polarising splitter 15 may be replaced by an ordinary splitter if one end of coil 16 is preceded by a 45 DEG rotation Faraday element. <IMAGE>

Description

SPECIFICATION Optical fiber laser gyro Background of the Invention The present invention relates to an optical fiber laser gyro utilizing single polarization optical fiber, and particularly to an optical fiber laser gyro by which rotational direction as well as minute rotational angular velocity of a rotating body can be detected.

Description of the Prior Art A conventional optical fiber laser gyro generally comprises an optical fiber having a length of about 1 km and being wound in loop-form, a beam splitter for separating laser light supplied from a laser light source into two components and inputting them through both ends of the optical fiber, and a light receiver for receiving light obtained by composing the light components left both the ends of the optical fiber which had entered the same and advanced the interior of the optical fiber.

In accordance with such type of optical fiber laser gyro as described above, when a rotating body rotates with angular velocity W, the light advances inside the optical fiber in the same direction as that of the rotation shifts in a longer distance than that in the case where the laser gyro is stationary, whilst the light which advances in the adverse direction to that of the rotation shifts in a shorter distance than that of the above case.

Accordingly, a phase difference A0 between lights leaving both ends of the optical fiber may be expressed by the following equation in response to rotational angular velocity W in accordance with Sagnac effect: 47r1 AO= .r.W c# where A is wavelength of light, c is velocity of light, I is length of the optical fiber, and r is radius of the optical fiber wound in loop-form. Output P of the light receiver which has received the composed light of the lights which has left both the ends of the optical fiber may be expressed on the basis of the above phase difference AS as follows: P=K(1 +cosh Rotational angular velocity W can be obtained from the output P, and when the rotational angular velocity W is integrated with respect to time, the position of a moving object can correctly be found.

In such conventional optical fiber laser gyro, however, since output P of the light receiver is computed on the basis of "cos A()", precision in the detection is unfavourable in the case where the phase difference AO is very small because of a small gradient in tangent line of "cos AS" curve.

Moreover, detection in its rotational direction is not possible because of a relationship "cos A6 cos (-A0)", besides there is such a disadvantage of occurence of mode conversion when bending, vibration or the like is applied to the optical fiber.

Summary of the Invention Accordingly, it is an object of the present invention to provide an optical fiber laser gyro which does not deteriorate precision in detection, even if whose phase difference AO is very small.

It is another object of the present invention to provide an optical fiber laser gyro which can detect rotational direction of a rotating body.

It is still another object of the present invention to provide an optical fiber laser gyro in which mode conversion is prevented to keep polarized condition of light in constant, whereby stabilization in measurement is intended.

Brief Description of the Invention The optical fiber laser gyro according to the present invention comprises a prescribed length of a single polarization optical fiber having intrinsic axis of polarization and being wound in loop-form; a light separating and composing means for separating an entering linearly polarized light into components in two directions to supply them into both ends of the aforesaid single polarization optical fiber, then causing the aforesaid components to advance in clockwise and counterclockwise directions, respectively, and thereafter composing two linearly polarized lights which have left the opposite ends to the aforesaid both ends of the single polarization optical fiber, respectively; and a detecting means for detecting a phase difference between two linearly polarized lights which have been composed by means of the aforesaid light separating and composing means. In such optical fiber laser gyro, the composed two linearly polarized lights are controlled so as to have planes of polarization being perpendicular to one another, and then the aforesaid two linearly polarized lights enter the aforesaid detecting means, whereby rotational angular velocity of a rotating body is decided by the aforesaid detecting means on the basis of the above phase difference.

Brief Description of the Drawings Fig. 1 is a cross-sectional view showing a single polarization optical fiber utilized in each embodiment of the present invention; Fig. 2 is an explanatory view illustrating the first embodiment of the present invention; Fig. 3 is an explanatory view illustrating the second embodiment of this invention; Fig. 4 is an explanatory view illustrating the third embodiment of the invention; Fig. 5 is an explanatory view illustrating the fourth embodiment of the invention; Fig. 6 is an explanatory view illustrating the fifth embodiment of the invention; Fig. 7 is an explanatory view illustrating the sixth embodiment of the invention; Fig. 8 is an explanatory view illustrating the seventh embodiment of the invention; and Fig. 9 is an explanatory view illustrating the eighth embodiment of the invention.

Detailed Description of the Invention The present invention will specifically be described hereinbelow by referring to the accompanying drawings illustrating embodiments of the invention, Fig. 1 shows a single polarization optical fiber 10, in its cross-section, utilized in the respective embodiments of the present invention wherein reference numeral 1 designates a circular core preferably made of SiO2 + GeO2 glass or the like, 2 a cladding having a circular section and made of high purity SiO2 glass, 3 an elliptical jacket substantially composed of SiO2 + P20s + B203 glass, 4 a support containing SiO2, respectively.

Fig. 2 illustrates the first embodiment of the optical fiber laser gyro according to the present invention which comprises a laser light source 11 for supplying such laser light polarized elliptically being very similar to linearly polarized light (In this case, He-Ne laser light may be utilized, but it is to be noted that a collimator lens is used at the same time in the event that semiconductor laser is employed.Furthermore, laser irradiation of reflected light in the case where an isolator is used can be prevented), a polarizer 12 for converting the laser light supplied from the laser light source 11 into linearly polarized light, a 1/2 wave plate 13 for changing an azimuth of the incident, linearly polarized light by 20, when an angle of the wave plate 13 is changed by a value 0, a beam splitter 14 such as a half mirror for reflecting upwardly a portion of laser light the azimuth of the linearly polarized light of which has been controlled by means of the 1/2 wave plate 13 as monitor light, whilst causing the remaining portion of the light to pass through and go straight on and at the same time, reflecting downwardly a portion of incident light supplied from the opposite side thereof, a polarization beam splitter 1 5 for separating the laser light which has passed through the beam splitter 14 into two linearly polarized lights, that is, a parallelly polarized light 1 5a and a serially polarized light 1 sub which are perpendicularly intersecting, a single polarization optical fiber 1 6 wound in loop-form and having a prescribed length, besides both ends of which are disposed in such that they intersect perpendicularly in respect of whose optic axis, a 1/4 wave plate 17 for providing 90 phase difference between two perpendicularly intersecting, linearly polarized lights which are supplied from the optical fiber 1 6 through the polarization beam splitter 1 5 and reflected by the beam splitter 14, an analyzer 18 disposed by previously adjusting the same in such that extinction condition thereof can be attained in the case where the single polarization optical fiber 1 6 is stationary, in other words, when a phase difference AS between two perpendicularly intersecting, linearly polarized lights is zero, and a photoelectric converter 1 9 for outputting electrical signal in response to a signal level received.

In operation, when the laser light polarized elliptically being very similar to linearly polarized light is supplied from the laser light source 11 , the laser light is converted into linearly polarized light by means of the polarizer 12, and then the linearly polarized light is controlled by the 1/2 wave plate 1 3 so as to be such linearly polarized light having 450 azimuth with respect to the polarization beam splitter 1 5. The linearly polarized light which has been subjected to 450 azimuth control advances in such that a portion of which is reflected upwardly by means of the beam splitter 14 as monitor light, while the remainder enters the polarization beam splitter 15 at 450 azimuth.The laser light which has entered the polarization beam splitter 1 5 is separated into the parallelly polarized light 1 spa and the serially polarized light 1 sub being perpendicularly intersecting, two linearly polarized lights, so that the parallelly polarized light 1 5a advances through the single polarization optical fiber 1 6 in clockwise direction, whilst the serially polarized light 1 5b advances therethrough in counterclockwise direction.The polarized lights 1 spa and 1 sub are composed in the polarization beam splitter 1 5 after leaving the both ends opposite to the entrance ends thereof, and then the thus composed polarized lights are reflected by the beam splitter 14 so that the reflected polarized lights enter the 1/4 wave plate 17.There is a phase difference AS in response to rotational angular velocity W of the single polarization optical fiber 1 6 between the perpendicularly intersecting, two linearly polarized lights entering the 1/4 wave plate 1 7, and 900 phase difference is added to the aforesaid two linearly polarized lights at the time when they leave the 1/4 wave plate 1 7. More specifically, the perpendicularly intersecting, two linearly polarized lights leave the 1/4 wave plate 17 with phase difference of (AS + 90 ). When the perpendicularly intersecting, two linearly polarized lights having the phase difference of (AO + 900) enter the analyzer 18, such analyzer is rotated so as to minimize electrical output of the photoelectric converter 19, in other words, in such that the lights to be left from the analyzer 1 8 become extinction condition. The aforementioned phase difference (AS + 900) can be known from rotational angle of the analyzer 18 so that a rotational angular velocity W can be obtained from the above equation as follows: 4 7rl cos(A0+900)= .r.W c,l 4 vrl sinAO= .r.W cA As a result, even if A 0 is a very small amount, the rotational angular velocity W can be detected with a high precision, because the above equation has been expressed in accordance with sine curve.

In addition, since there is such a relationship "sin A = -sin (- A 0)", the rotational direction can also be detected.

Fig. 3 illustrates the second embodiment of the optical fiber laser gyro according to the present invention which comprises a Faraday element 20 for controlling a phase difference between perpendicularly intersecting, two linearly polarized lights in response to current level supplied from the outside and the Faraday element being disposed in between the 1/4 wave plate 17 and the analyzer 18, and a current controlling circuit 21 for outputting current of such level providing extinction condition of the analyzer 18 based on electrical output of the photoelectric converter 19 in addition to the constructional elements of the laser gyro of the above first embodiment.

In operation, when such situation that output of the analyzer 18 is not extinct is detected by the current controlling circuit 21 on the basis of electrical output of the photoelectric converter 19, a current level to be applied to the Faraday element 20 is controlled and such current level increases until the analyzer 18 reaches its extinction condition. In this connection, the aforementioned phase difference (AO + 900) can be obtained from the current level at which the analyzer 18 reaches the extinction condition.

According to the second embodiment of the present invention, rotating operation of the analyzer 18 may be omitted so that the construction of the optical fiber laser gyro can be simplified.

Fig. 4 illustrates the third embodiment of the optical fiber laser gyro according to the present invention wherein the same parts as those of the first embodiment are shown by the same reference characters as those of the first embodiment so that the description to be repeated will be omitted.

In the laser gyro of the third embodiment, the polarizer 12 is involved in the laser light source 11, and both ends of the single polarization optical fiber 16 into one of which light enters, whilst from another of which light leaves are coupled with the polarization beam splitter 15 through micro-lenses 23 and 24, respectively. Furthermore, a polarization beam splitter 22 is provided in the stage following to the 1/4 wave plate 17.

Photoelectric converters 25 and 26 are disposed at the positions where perpendicularly intersecting, two linearly polarized lights separated by means of the polarization beam splitter 22 are received, and a differential amplifier 27 is connected with the outputs of the photoelectric converters 25 and 26. Besides, a single polarization optical fiber 28 may be provided as indicated by broken line in Fig. 4 to avoid influence of oscillation in the case where the medium is air.

In operation, two of the linearly polarized lights to which a phase difference of 900 is added by means of the 1/4 wave plate 17 are separated again by the polarization beam splitter 22 into P polarized light and S polarized light, and both the polarized lights enter the photoelectric converters 25 and 26, respectively.

In this case, assuming that the P polarized light and the S polarized light entering the 1/4 wave plate 17 have the following relationships: ep = A cos (c,)tA H) = = A cos wt where A is a constant, and w is circular frequency of light, the P polarized light and the S polarized light leaving the 1/4 wave plate 17 come to have the following relationships: ep = A cos (o)tAH90 ) = A sin (#t - #0) es = A cos #t.

Since light inputs p01 and p02 entering the photoelectric converters 25 and 26 are expressed as follows: p01 (t) = -- kA2 (sin (wt - A0) + cos wt} 2 p02 (t) = -- kA2 jsin (wt - A0) - cos #t}2, 2 where k is a constant, these expressions may be rearranged as follows: 1 T 1 p01=p01= -# p01(t)dt -kA(1 -sin##) TO 2 T P02 = P02 = - # p02(t)dt=-kA2(1 +sinA0).

TO 2 The light inputs or light signals are photoelectrically converted, and then, when they are inputted to the differential amplifier 27, such output "p02 - p01 = kA2 sin AH" can be obtained from the differential amplifier 27, whereby A() can be detected. As a result, rotational angular velocity of a rotating body can be known.

Fig. 5 illustrates the fourth embodiment of the optical fiber laser gyro according to the present invention wherein the same parts as those of the above first, second and third embodiments are shown by the same reference characters as those of these embodiments so that the description to be repeated will be omitted. The laser gyro of the fourth embodiment is provided with a Pockels element 28 from which linearly polarized lights leave after a phase difference ## is cancelled by applying a voltage corresponding to the phase difference A8 thereto when the linearly polarized lights having the phase difference A f) enter the Pockels element in response to a rotational angular velocity W.In the succeeding stage of the Pockels element 28, the analyzer 18 is disposed and adjusted in such that two linearly polarized lights become extinction condition when no phase difference arises. In addition to the above parts. a controlling part 30 for deciding a voltage level to be applied to the Pockels element 28 on the basis of output signal of the photoelectric converter 1 9 which detects extinction condition of the analyzer 1 8 is provided together with a power source 29 being controlled by the controlling part 30 to apply a prescribed voltage to the Pockels element 28.

In operation, linearly polarized lights having a phase difference AO are supplied from the beam splitter 14 to the Pockels element 28, and then when the lights left from the Pockels element 28 are received by the analyzer 1 8, extinction condition thereof disappears. When a level of electrical output of the photoelectric converter 1 9 increase in response to the disappearance of extinction condition, the controlling part 30 controls the power source 29 in response to the level whereby voltage applied to the Pockels element 28 is controlled.On the basis of the level of the voltage applied to the Pockels element 28, a phase difference AO between perpendicularly intersecting, two linearly polarized lights leaving the single polarization optical fiber 1 6 can be known, and furthermore rotational angular velocity W of a rotating body can also be obtained from such phase difference AO. On one hand, its rotating direction of the rotating body can also be found in accordance with such fact whether the voltage to be applied to the Pockels element 28 is positive or negative.

Fig. 6 illustrates the fifth embodiment of the optical fiber laser gyro according to the present invention the construction of which is similar to that of the second embodiment described above, but differs from one another in that the polarization beam splitter 15 is omitted in the fifth embodiment and the Faraday element 31 providing rotation of 450 polarization is disposed in the position of the polarization beam splitter omitted, besides the single polarization optical fiber 1 6 is arranged in such that their intrinsic polarization axes are shifted from one another with 450 angle at both ends of the optical fiber 16.

In operation, the laser light reflected by the beam splitter 14 enters one end of the single polarization optical fiber 1 6 having an intrinsic polarization axis including 450 with respect to its horizontal plane, and the laser light advances in clockwise direction, whilst the laser light passed through the beam splitter 14 is rotated with 450 polarization by means of the Faraday element 31, then, enters the other end of the single polarization optical fiber 1 6 having horizontal intrinsic polarization axis as a linearly polarized light possessing horizontal polarization plane, and then advances in counterclockwise direction.The linearly polarized light which has advanced through the single polarization optical fiber 1 6 in clockwise direction and left the other end thereof comes to have a polarization plane shifting at an angle of 900 from that of the linearly polarized light which has advanced in counterclockwise direction because such light is rotated with 450 polarization by means of the Faraday element 31 and left another end of the single polarization optical fiber 1 6. Consequently, these two linearly polarized lights intersect perpendicularly to each other.When the perpendicularly intersecting, two linearly polarized lights enter the 1/4 wave plate 1 7, 900 phase difference is given to these lights in addition to a phase difference AO between them in response to rotational angular velocity W, and then these linearly polarized lights leave the 1/4 wave plate 1 7. The operation hereof is identical to that of the second embodiment, so that phase difference AO 8 can be detected from a current value of the current controlling circuit 21.

Fig. 7 illustrates the sixth embodiment of the optical fiber laser gyro according to the present invention which is obtained by combining a partial construction of the third embodiment with a partial construction of the fifth embodiment, and accordingly the description therefor will be omitted because it is self evident from the description described above.

Fig. 8 illustrates the seventh embodiment of the optical fiber laser gyro according to the present invention wherein the respective parts designated by reference numerals 11 through 27 are common to those mentioned in the above embodiments. In the seventh embodiment, a beam splitter 32 is especially disposed in between the beam splitter 14 and the 1/4 wave plate 17, and the linearly polarized light which passed through the beam splitter 32 enters the 1/4 wave plate 1 7.

Furthermore, the optical fiber laser gyro of the seventh embodiment comprises a polarization beam splitter 33 being placed so as to be 450 azimuth with respect to its polarization axis in such a position where the linearly polarized light reflected by the beam splitter 32 is received, photoelectric converters 33 and 34 to which perpendicularly intersecting, two linearly polarized lights separated by the polarization beam splitter 33 enter, a differential amplifier 36 to which electrical outputs of the photoelectric converters 33 and 34 are inputted, and a computing part 37 for computing a phase difference AO by inputting outputs of the differential amplifiers 27 and 36 thereto in addition to the above respective parts.

In operation, as described in the above third embodiment, output of the differential amplifier 27 becomes "2K sin AO" (where K is a constant) on the basis of the outputs "K(1 - sin AO)" and "K(1 + sin Ao)" of the photoelectric converters 25 and 26, whilst output of the differential amplifier 36 comes to be "2K cos AO" based on the outputs "K(1 - cos AO)" and "K(1 + cos Ao)" of the photoelectric converters 35 and 36. The computing part 37 computes a phase difference AO from the outputs of these differential amplifiers 27 and 36 so that the optical fiber laser gyro of this embodiment detects rotational angular velocity W. As an example of such computation, results of detection with high precision can be obtained even if phase difference AO is very small, besides rotating direction can also be known by such a manner that the aforesaid "sin AO" and "cos AH" are multiplied by "sin W" and "cos W" to obtain "2 cos AO cos W" and "2 sin AO sin W", respectively, from which "2 cos (W - A6)" is extracted, and then.a linear signal of "(W - AO)" is found by means of a phase detector.

Fig. 9 illustrates the eighth embodiment of the optical fiber laser gyro according to the present invention which comprises a light source 11 supplying monochromatic light, a polarization beam splitter 1 5 for separating the entering monochromatic light into two polarized lights which are perpendicular to each other and for reversibly composing the lights separated, collimator lenses 38 and 39 for conducting the two polarized lights to both ends of a single polarization optical fiber 1 6 wound in loop-form wherein intrinsic polarization axes in both the ends intersect perpendicularly to each other and each axis has an inclination of 450 with respect to its horizontal plane as well as for conducting the linearly polarized lights leaving both the ends to a beam splitter 15, a polarization beam splitter 40 for separating again the linearly polarized light composed by means of the polarization beam splitter 1 5 into two polarized lights, collimator lenses 41 and 42 for conducting the polarized lights to entrance ends of single polarization optical fibers 43 and 44 intrinsic axes of polarization of which are placed so as to intersect perpendicularly to one another, a single polarization optical fiber 45, which has an intrinsic axis of polarization of 450 inclination with respect to those of the aforesaid optical fibers 43 and 44, for composing the linearly polarized lights supplied from both the optical fibers 43 and 44 to propagate the light composed, and a light receiver 46 disposed at the exit end of the single polarization optical fiber 45.

In operation, the monochromatic light supplied from the light source 11 is separated into two polarized lights by means of the polarization beam splitter 15, and these lights enter the single polarization optical fiber 1 6 through the collimator lenses 38 and 39, respectively.The one polarized light advances through the single polarization optical fiber 1 6 in counterclockwise direction, while the other polarization light advances through the optical fiber in clockwise direction, and then these polarized lights leave the both ends of the single polarization optical fiber 1 6 to be composed as the polarized light again by means of the polarization beam splitter 1 5. The composed light which has left the polarization beam splitter 1 5 is separated into two polarized lights by means of the polarization beam splitter 40, the one resulting polarized light enters the single polarization optical fiber 43 through the collimator lens 41 and advances thereinto, whilst the other resulting polarized light enters the single polarization optical fiber 44 through the collimator lens 44 and advances thereinto, thereafter both the polarized lights enter the single polarization optical fiber 45.

In this case, if a length of the synthesizing single polarization optical fiber 45 and propagation constants in two perpendicularly intersecting planes are represented by I as well as px and ssyt its propagation constant difference A may be expressed by such equation: Ap xpY | and there arises a phase difference of Apl between two linearly polarized lights at exit ends of the aforesaid optical fiber 45. Furthermore, supposing that a coupled length of the optical fiber 45 is L, a phase bias of 27r -I L is given, since 2# L.

When op,tical-path difference between two linearly polarized lights conducted from the polarization beam splitter 40 to the composing single polarization optical fiber 45 is corrected by changing the length I of the optical fiber 45 and in this case, if a phase difference in accordance with rotational direction of a rotating body is expressed by AO, intensity of the interfered light proportional to "sin AO" is obtained.

In order to attain such constructional condition ,as mentioned above, length I of the composing single polarization optical fiber 45 is successively changed to rotate a rotating body in counterclockwise or clockwise direction while monitoring output of the light receiver 46. In this case, it is sufficient to arrange the situation in such that change of the output light turns to positive or negative state with respect to stationary state.

In accordance with the optical fiber laser gyro of the present invention as described above, the following outstanding advantages can be obtained.

(1) Since a signal proportional to "sin AO" can be detected, rotational direction can be detected, besides sensitivity at a minute rotational angle (phase difference) is satisfactory.

(2) Since single polarization optical fiber is utilized, its plane of polarization is stable.

(3) Since disturbance of plane of polarization in light (extinction ratio of polarization) in the process for propagation of an optical fiber does not appear on its output part, there is not such a case wherein S/N ratio becomes worse.

(4) Since particular devices or equipments such as phase shifting equipment, frequency converter and the like are not required, the optical fiber laser gyro manufactured is inexpensive and highly reliable.

(5) Since null method can be applied in cases of the second, the fourth and the sixth embodiments, a range for scope of detection can be expanded.

Although the present invention has been described with reference to preferred embodiments thereof, many modification and alternation may be made within the spirit and scope of the present invention.

Claims

1. An optical fiber laser gyro comprising: a prescribed length of a single polarization optical fiber having intrinsic axis of polarization and being wound in loop-form; a light separating and composing means for separating an entering linearly polarized light into components in two directions to supply them into both ends of said single polarization optical fiber, then propagating said components in clockwise and counterclockwise directions, respectively, and thereafter composing two linearly polarized lights which have left the ends opposite to said both ends of the single polarization optical fiber, respectively, and a detecting means for detecting a phase difference between two linearly polarized lights which have been composed by means of said light separating and composing means;; said composed two linearly polarized lights being controlled so as to have planes of polarization being perpendicular to one another, and then said two linearly polarized lights entering said detecting means, whereby rotational angular velocity of a rotating body is decided by said detecting means on the basis of said phase difference.

2. An optical fiber laser gyro as claimed in claim 1, wherein said single polarization optical fiber is arranged in such that both the ends thereof intersect perpendicularly to one another with respect to its intrinsic axis of polarization, and said light separating and composing means is a polarization beam splitter providing intersecting perpendicular planes of polarization to two linearly polarized lights which are separated into two components to propagate through said single polarization optical fiber in clockwise and counterclockwise directions, respectively, and thereafter composed.

3. An optical fiber laser gyro comprising: a prescribed length of a single polarization optical fiber having intrinsic axis of polarization and being wound in loop-form; a light separating and composing means for separating an entering linearly polarized light into components in two directions to supply them into both ends of said single polarization optical fiber, then propagating said components in clockwise and counterclockwise directions, respectively, and thereafter composing two linearly polarized lights which have left the ends opposite to said both ends of the single polarization optical fiber, respectively; a phase difference adding means for adding 900 phase difference to a phase difference between two linearly polarized lights which have been composed by means of said light separating and composing means; and a detecting means for detecting the resultant phase difference between two linearly polarized lights to which said 900 phase difference has been added by said phase difference adding means, said composed two linearly polarized lights being controlled so as to have planes of polarization being perpendicular to one another, and then said two linearly polarized lights entering said detecting means, whereby rotational angular velocity of a rotating body is decided by said detecting means on the basis of said phase difference.

4. An optical fiber laser gyro as claimed in claim 3, wherein said single polarization optical fiber is arranged in such that both the ends thereof intersect perpendicularly to one another with respect to its intrinsic axis of polarization, and said light separating and composing means is a polarization beam splitter providing intersecting perpendicular planes of polarization to two linearly polarized lights which are separated into two components to propagate through said single polarization optical fiber in clockwise and counterclockwise directions, respectively, and thereafter composed.

5. An optical fiber laser gyro as claimed in claim 3, wherein said detecting means comprises an analyzer for receiving said composed two linearly polarized lights to provide extinction condition by means of rotating operation, and a photoelectric converter for detecting said extinction condition, whereby said phase difference is detected from a rotational angle of said analyzer.

6. An optical fiber laser gyro as claimed in claim 3, wherein said detecting means comprises a Faraday element for controlling said phase difference in accordance with a current level which is given by receiving said composed two linearly polarized lights, an analyzer for providing extinction condition at a predetermined, rotating position, and a photoelectric converter for detecting the extinction condition of said analyzer, whereby said phase difference is detected from said current level when said extinction condition is obtained.

7. An optical fiber laser gyro as claimed in claim 3, wherein said detecting means comprises a separating means for receiving said composed two linearly polarized lights to separate the same into two components, and a means for outputing two electrical signals in response to said two components separated, whereby said phase difference is detected from a level difference between said two electrical signals.

8. An optical fiber laser gyro as claimed in claim 3, wherein said detecting means comprises a Pockels element for receiving said composed two linearly polarized lights to control said phase difference on the basis of the current level applied, an analyzerforproviding extinction condition at predetermined, rotating position, and a photoelectric converter for detecting the extinction condition of said analyzer, whereby said phase difference is detected from said current level when said extinction condition is obtained.

9. An optical fiber laser gyro as claimed in claim 3, wherein said single polarization optical fiber is arranged in such that both the ends thereof have 450 azimuth with respect to its intrinsic axis of polarization, and said light separating and composing means comprises a beam splitter for separating linearly polarized light into two components and composing such two components to obtain linearly polarized light, and a Faraday element for affording 450 polarization one of said components.

10. An optical fiber laser gyro substantially as hereinbefore described with reference to Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8 or Figure 9 of the accompanying drawings.