JPS58189507A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To provide an optical fiber gyro which does not require adjustment for optical axis, is strong to oscillation, and has a small size, lightness and improved S/N by providing optical waveguides, a laser, a photodiode and a modulator monolithically on a substrate having an electrooptic effect. CONSTITUTION:The light of a laser diode 10 is divided to clockwise light (r) and counterclockwise light (l) by a grating 6. The light (r) receives amplitude modulation with a modulator 11, is made incident to an optical fiber 16, enters an optical waveguide 3, is bent by a grating 8 and arrives at a photodiode 14. The light (l) passes through an optical wavegide 2, turns the loop of the fiber 16 counterclockwise, enters the end of an optical waveguide 5, is bent by a grating 9 to an optical waveguide 4 and arrives at the diode 14. When the fiber loop rotates at an angle OMEGA, a phase difference DELTAtheta is produced between the light (l) and the light (r). The electric signal of the angular frequency equal to a modulation angular frequency is included in the output of the diode 14 and a phase difference DELTAtheta' is included in the amplitude. Therefore, if said amplitude is known, the phase difference DELTAtheta is determined.

Description

[Detailed description of the invention]

The present invention relates to an integrated optical fiber gyro that includes a modulator on a substrate. The fiber optic gyro for detecting rotational speed is Sa
It utilizes the gnac effect and is expected to have various benefits. It has no moving parts and is resistant to acceleration. High sensitivity. Good linearity. The structure is simple. Low power consumption. Although such advantages are expected, they have not yet become practical. FIG. 7 is a plan view showing the configuration of a known optical fiber gyro. The optical fiber 40 has a loop shape wound a plurality of times. The laser 41 is a He-Ne laser, and the laser beam is divided into two beams by a half mirror 42. The two light fluxes enter the two ends of the optical fiber 40 from lenses 43 and 44, and become clockwise light and counterclockwise light. The two beams that passed through the optical fiber loop are sent to the half mirror 4.
2, the photodetector 45 is superimposed on the same optical axis.
incident on the The lengths of the optical paths of the right-handed light and the left-handed light are exactly the same. If the entire gyro is rotating around the normal line of the fiber loop with an angular velocity Ω, then the two light beams are
Phase difference Δθ 80-4rr E-a Ω (1) Add 1 node to Cλ. Here, l- is the length of the optical fiber, a is the h diameter, n is the wavelength of the laser beam, and C is the speed of light. In the optical system shown in FIG. 7, the laser, photodetector, λ-7 mirror, etc. were comprised of ordinary optical parts. Since vibration resistance is strictly required, the optical components are fixed to a small, spacious surface plate using a magnetic stand or -C. It is not practical because it is large in size, heavy, and inconvenient to handle. There is also a problem with optical axis adjustment tC. Therefore, in order to make it lightweight and compact, as shown in FIG.
An optical fiber gyro of lJ has been proposed. Optical waveguides 47 and 47 are provided at -1- of the IC board 46 so as to be perpendicular to each other, and a grating 48 is formed at the intersection. A laser diode 49 and a photodiode 50 are bonded to the ends of the optical waveguides 47, 47. The loop end of the optical fiber 40 is an optical waveguide 47°4.
It is connected to the other end of 7. Since all optical elements are installed on the 7th part of the IC board, it is lightweight.
Can be made small. It also has excellent vibration resistance. Optical axis adjustment is not necessary. This type of method is called a homodyne method, but this method has the disadvantage of a low /N ratio.The present invention has the advantage of incorporating a modulation element in addition to a laser diode, photodiode, and grating on a single substrate. established,
The purpose is to provide an optical fiber gyro that modulates a single beam of light and improves the S/N ratio. There are three modulation styles. They are amplitude modulation, phase modulation, and frequency shift modulation. The present invention can use either modulation format. Hereinafter, the configuration, operation, and effects of the present invention will be explained with reference to drawings showing examples. FIG. 1 is a perspective view of a substrate portion of an optical fiber gyro according to an embodiment of the present invention. JIt, plate 1 has an electro-optic effect and is made of GaAs.
. InP, I, 1Nl) o3. L eyes 'ao3. R
i I 2S 102o, Bi 12Geo2o
. It is a crystal such as. J+ (4 optical waveguides 2゜3 perpendicular to 1- of plate 1
．． 4.5 is formed. At the orthogonal portions of the 9J84 wave paths 2.3.4.5, gratings 6.7 and 8.9, which function as half mirrors, are provided in the f direction of the -equisector line. Since crating is a large number of equally spaced parallel lines,
It can be used to diffract light of a certain wavelength. Here, the grating has the effect of bending light from a certain optical waveguide to a leading waveguide perpendicular to it. A chip-shaped laser diode 1 is installed at the starting end of the optical waveguide 5.
0 or bonding. The light emitted from the laser diode 10 is rotated clockwise by the grating tincture.
Divides into counterclockwise light. A part of the optical waveguide 5 through which the right QpIj r propagates is branched, and constitutes a modulator 11 that modulates the amplitude of light. An enlarged plan view of the modulator is shown in FIG. Electrodes 12a and 12b are provided on the branched optical waveguides 5a and 5b by vapor deposition, printing, or other methods. A modulation signal generating tc13 is fixed on the substrate. This is the electrode 12a
, 12b is applied, and due to the electro-optic effect,
The refractive index of the branched optical waveguides 5a and 5b is changed. Since the speed of light in the optical waveguides 5a and 5b is inversely proportional to the refractive index, when different electric fields are applied to the branched optical waveguides 5a and 5b, the speed of light in both waveguides is different. The branched optical waveguides are integrated into one again, but since the light passing through each branch has a different phase, the amplitude of the integrated light cannot be calculated by simply adding the amplitude of the light passing through the two branches. No. In the ideal case, the integrated light amplitude would be a function containing the cosine of the phase difference φ. Therefore, by periodically varying the voltage applied to the two branched electrodes 12a and 12b and periodically changing the phase difference φ, the amplitude of the light exiting the branched optical waveguide will vary periodically. Become. The branch waveguides 5a and 5b are connected to the Matsuhatsu Enda interferometer on the right! The Iff light is thus subjected to amplitude modulation by the modulator 11. The structure of an optical element in which an alternating electric field is applied to a branch waveguide and whose amplitude is Jn+ is known. Light in the counterclockwise direction is not modulated. A photodiode 1-'14 is bonded to the extended end of the orthogonal part of the optical waveguide 4.3. The output of the photodiode 14 is amplified by a detection signal processing IC 5 and subjected to appropriate processing. The right-handed signal r follows the optical waveguide 5 and is modulated, and then enters the optical fiber 16 . The optical fiber 16 is in the form of a loop that has been passed around three times, but the loop portion is omitted here at -C. The clockwise light r passing through the optical fiber loop 16 is )+I
', enters the end of the waveguide 2, is bent by the grating 7, enters the optical waveguide 3, is further bent by the grating 8, and reaches the photodiode 14. The counterclockwise light l passes through the laser diode 10, the grating 6, and the optical waveguide 2, and enters the loop of the optical fiber 16. The counterclockwise light 1 that has passed counterclockwise within the loop enters the end of the optical waveguide 5, is bent by the grating 9 into the optical waveguide 4, and reaches the photodiode 14. The photodiode simultaneously receives clockwise light r and counterclockwise light l, but only two of them are amplitude-modulated. When the fiber loop rotates at an angular velocity Ω, a phase difference Δ0 occurs between the left-handed light and the right-handed light. There is a modulation angular frequency t! in the output of the photodiode. i
Either an electrical signal with an angular frequency equal to m is included, or the amplitude of this signal includes a phase difference Δθ'. Therefore, if this amplitude is known, the phase difference Δθ can be determined. Let me explain in more detail. Let the angular frequency of the laser beam be ω. When clockwise light and counterclockwise light exit from the optical waveguide 5.2, respectively (right) (1+as stone ωm

[)C10Jt (left)
It can be expressed by the formula l ml . ωm is the tuning angular frequency of the modulator 11. Turn the fiber loop clockwise, then left 1! ! Assume that when the light passes through the opposite direction, the light around A1° advances by Δ0/straddle phase, and the counterclockwise light lags behind Δ0/straddle phase. The phase difference Δ0 is (1)
It is related to the angular velocity Ω of the fiber loop. Therefore, when the right-handed light and left-handed light enter the photodiode, (right) ■, : , (1+, sin ,,, □
, ) , '('I'' + s o/2 ) (/
l, ) Et c I
(tl) [-Δ0/2) 0) Take the number of peaks. Since the photodiode performs square law detection, the square of the sum of the two,
Gives the strength of the electrical signal that is the output of the photodiode. 7H force electric signal-J l is t2Et2+Er2(1-1-25110m t)
+2ErElccsΔ0(l−1−atha+tTl
) (2) becomes. The output power electrical signal consists of a DC component, an orm component, and a 2ωm component. Generating an electrical signal with an angular frequency ωm as a reference signal,
In addition to the output electric signal l in equation (2), if synchronous detection is performed on the electric tf, the +m component in the output electric signal ■ can be obtained. The amplitude of the ωm component (Ma2Er a + 2
Since Er Ez a as Δθ, the phase difference Δ
Vehicle power 1 that knows θ can be done. It is also possible in the embodiment shown in FIG. 2 to amplitude modulate either the left-handed light or the right-handed light. A directional coupler type amplitude modulator 17 is used. The optical waveguide 5 is not continuous, and includes partial waveguides 5c,
It is divided into 5d. Partial waveguides 5c, 5a jj
, are close to each other in a part, and here (this electrode 18 (.18d) is provided. When two Nori wave paths are provided side by side close to each other on the order of the wavelength, the intermediate low J++ is folded. Two waveguides can be coupled by an evanescent wave extending in the area of the waveguide. This is called evanescent wave coupling, and when the optical phase constants of the two waveguides are equal, the coupling is maximum. Ideal In other words, all the energy in one waveguide is transferred to the other waveguide. (B) When the f-phase constant is set to W, the coupling becomes weaker and the transition of E and Lugi also decreases. Optical phase constant is proportional to the refractive index.The refractive index is jI'7
．． 7. If there is an electro-optic effect in one direction, it can be varied by the electric field. ], (A modulation voltage is applied to the electrodes 18C and 18d by the modulation signal generation IC 19 provided at the top of the plate 1. The amplitude of the light transmitted from the optical waveguide 5C to 5d is the change in the modulation angular frequency 01 m. In other words, in this example, the clockwise light has undergone amplitude modulation. In the embodiment of FIG. 2, the grating is not used. The optical waveguide 2.3.4.5 is In the vicinity of the intersection area, they are not orthogonal but are connected smoothly so that the directions of the center lines coincide.In the examples shown in Figures 1 and 2, the S/
This was an example in which the /N ratio could be reduced by -1. It is also possible to change the phase. A phase modulator 20 as shown in FIG. 5 is provided for either clockwise or counterclockwise light. Since there is an electro-optic effect in the waveguide, the refractive index changes depending on the electric field. When a voltage is applied to the electrodes 21 and 22, the refractive index of the waveguide in the portion sandwiched between the electrodes changes, and the speed of light changes. Therefore, phase modulation is possible. The magnitude of phase modulation is expressed as b 8 stones ω m [ . The left-handed light and the right-handed light can be expressed respectively as follows. Counterclockwise light Δθ! ((+) [+□) Right-handed light Δ0 i (m 17″b sin m m t ) and −; are calculated.) Then, when square detection is performed with a detector, the output signal phase is Jslbls
It contains a phase of inΔOsln tn m t. J+(b)
is the Bessel function, Ol m is the modulation 1, and '4 lIk number. Therefore, by electrically detecting the same signal using a reference signal having a frequency of l·+m, it is possible to extract sin Δ0. )'J, 1'' The method described is one in which either the left-handed light or the right-handed light is amplitude-modulated or phase-modulated. The optical heterodyne method using the frequency shift of W4 is also ul'
fit': is. FIG. 6 is a schematic diagram of a curved elastic wave generator for utilizing the unique frequency shifting method. A comb-shaped electrode 23 is provided on the side of the optical waveguide 5e.
An alternating current voltage of frequency or m is applied to the drive circuit 24 or the comb-shaped electrodes 23. The substrate 1 is required to have an acousto-optic effect. When an alternating current voltage is applied to the comb-shaped electrode 23, a surface acoustic wave is generated that travels in the direction of the broken line. Since the substrate 1 has an acousto-optic effect, there is a portion where the refractive index changes with the surface acoustic waves. This causes the surface acoustic waves and light to interact. Light is modulated so that the conservation laws regarding wave number and frequency of light and surface acoustic waves hold. The light along the waveguide 5e is directed to the waveguide 5f which is inclined to the waveguide 5e.
, and along with this, the angular frequency becomes (OJ + ω
m). When subjected to such a frequency shift, this light can be expressed as i(Cυ+ωm)t in the optical waveguide 5r. After passing through the optical fiber loop, each light becomes Δθ counterclockwise Etei (“′+T).The sum of these lights is ゛Since the photodiode performs square law detection, the output signal phase of the photodiode is EtF−rcos
(cl)mL−Δ0). This output is electrically compared with the reference signal CQS m m t to extract the phase difference ΔO. Although this method is a signal processing system, it is not easily affected by level drift because it uses the output of a photodetector or an alternating current signal (frequency ωm). Another feature is that the detection range of the phase difference Δ0 is arbitrary. Since the present invention is an optical fiber gyro in which a light guide, a laser diode, a photodiode, and a modulator are monolithically provided on a substrate 1 having an electro-optical effect, the present invention has the following effects. (1) The device is small, lightweight, and resistant to vibration. No optical axis adjustment required. This is because functional elements such as a laser diode, photodiode, guiding waveguide, and modulator are integrated on a single substrate. (2) It is possible to provide an optical fiber gyro with a high SΔ ratio. This is because a modulator such as an optical amplitude modulator, an optical phase modulator, or a frequency shifter is interposed in the optical path of either the right-handed light or the left-handed light. (3) GaAs as a substrate having an electro-optic effect. If a semiconductor such as InP is used, the modulation signal generation circuit and the detection signal electrical processing circuit can also be constructed monolithically.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a substrate portion of an optical fiber gyro according to an embodiment of the present invention. FIG. 2 is a perspective view of a substrate portion of an optical fiber gyro according to another embodiment of the present invention. 3 is an enlarged plan view of only a portion of the directional coupler type amplitude modulator in FIG. 2; FIG. FIG. 4 is an enlarged plan view of only the Matsuhatsu Enda interferometer type amplitude modulator portion in FIG. FIG. 5 is a) a schematic diagram showing an embodiment using a γ-phase modulator; FIG. 6 is a schematic cross-sectional view of a surface acoustic generator provided near the optical waveguide in order to shift the frequency. FIG. 7 is a cross-sectional view of the configuration of a known optical fiber gyro that combines individual optical devices. FIG. 8 is a perspective view of a known optical homodyne 11 type optical IC type optical fiber gyro. 1... Substrate 2.3, 4.5... Optical waveguide 6.7, 8.9, grating 10, laser diode 11... modulator 12... electrode 13, - IC for modulating signal generation 14 Photodiode 15... RC for detection signal processing 16... Optical fiber 17... Modulator 18... Electrode 19... IC for modulating signal generation 20...・Phase modulator 21, 22... Electrode 23... Comb-shaped electrode 24... Drive circuit inventor Yoshi 1) Ken -
Yasushi Yokohara, Kozo Ono, Yu Nishi, Yu Waki, Hiroshi Watsuno - Fig. 1 7' 6 Fig. 2 6 Fig. 3 Fig. 4 Fig. 5 Fig. 6 f Fig. 7 0 Fig. 8 6 Head - 27. 0

Claims (5)

[Claims] (1) An optical fiber wound many times in a loop,
A substrate on which an optical waveguide for right-handed light and an optical waveguide for left-handed light are formed at least partially separated; a right-handed light waveguide provided on the optical waveguide of the substrate; A laser diode for applying the same laser light to the optical waveguide for circular light; a light receiving element provided on the optical waveguide of the substrate for simultaneously receiving and detecting the counterclockwise light and the clockwise light that have passed through the optical fiber; An optical fiber gyro comprising: a modulator provided at -E for modulating either right-handed light or counter-clockwise light. (2) The substrate has an electro-optic effect, and a part of the optical waveguide is branched to form a Matsuhatsu Enda type interferometer. Electrodes are formed at the branched portions, and a modulation signal generation IC is mounted on the substrate. Claim (1) in which one of the lights is amplitude-modulated by applying an AC voltage for modulation to the branching part.
Optical fiber gyro as described in section. (3) The substrate has an electro-optic effect, and an optical directional coupler is formed in a part of the optical waveguide, and an alternating current electric field for modulation is applied to waveguide -F of the optical directional coupler to generate a modulation signal. IC for
The optical fiber gyro according to claim 1, wherein one of the lights is amplitude-modulated. (4) The substrate has an electro-optic effect, and an electrode is provided on the straight part of the optical waveguide, and an alternating current electric field for modulation is applied by an RC for generating a modulation signal to perform phase modulation. The optical fiber gyro described in (1). (5) The substrate has an acousto-optic effect, and a comb-shaped electrode and a drive circuit for generating surface acoustic waves are provided on the substrate, and a modulator for shifting the optical frequency is provided. Optical fiber gyro as described in section.