JP2514488B2 - Optical gyroscope optical ring resonator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical ring resonator used in a ring resonance type optical gyroscope.

[0002]

2. Description of the Related Art An optical ring resonator has a structure in which an effective optical waveguide length for one round of a ring-shaped optical waveguide forming the optical ring resonator is an integral multiple of a wavelength of light circulating in the inside of the ring-shaped optical waveguide. The multiple interference light satisfies the resonance condition, becomes a bright state, and has large energy. As shown in FIG. 2, one substrate 1
A linear input / output optical waveguide 20 and a ring-shaped optical waveguide 11 are arranged on the optical axis 0, and both are optically coupled by an optical directional coupler (hereinafter referred to as an optical coupler) 13 to cause coherence from the light source 12. The light is introduced into the input / output optical waveguide 20 and circulated (clockwise in the figure), a part of the circulated light is guided out through the optical coupler 14, and the light intensity of the derived light is detected by the photodetector 15. Then, the detected intensity I is relative to the optical frequency f of the light source 12,
As shown by the curve 16, the characteristic becomes a sharp pulse at a frequency satisfying the resonance condition. At this time, it becomes a bright state.

On the other hand, also in the optical coupler 13 that introduces light into the ring-shaped optical waveguide 11, a part of the circulating light in the ring-shaped optical waveguide 11 is guided to the outside, and this guided light interferes with the incident light. When the intensity of the interference light is detected by the light receiver 17, the characteristic becomes as shown by the curve 18. That is, at the optical frequency f satisfying the resonance condition, the detection intensity I is reduced in a sharp pulse shape to become a dark state. The characteristic 16 obtained by the light receiver 15 may be called a transmission characteristic of the optical ring resonator, and the characteristic 18 obtained by the light receiver 17 may be called a reflection characteristic. Either of them may be used to configure an optical resonance angular velocity meter (optical gyro). it can. Usually, when the optical coupler 13 is added to the ring-shaped optical waveguide 11, the characteristics of the optical ring resonator are deteriorated, so that the reflection characteristics are often used. Therefore, an outline of a conventional optical gyro will be described below by taking an example using a reflection characteristic. The reflection characteristic 18 is expressed by the following equation.

P = Iν [1-α / (1 + βsin ² (fτ / 2))] P: output light intensity, I: incident light intensity, ν: optical coupler loss α, β: constants determined by the optical system, f : Optical frequency τ: Propagation time around the ring of the ring-shaped optical waveguide 11 The principle of the optical gyro depends on the Sagnac effect regardless of the method. The Sagnac effect means that when a ring-shaped optical waveguide that encloses a finite closed area makes angular velocity motion about the normal direction of the closed area, the phase with respect to the light circulating in the ring-shaped optical waveguide deviates by Δφ. It is represented by a formula.

Δφ = (8πS / Cλ) Ω S: closed area, C: speed of light, Ω: angular velocity, λ: wavelength of light source When the ring-shaped optical waveguide constitutes an optical ring resonator, the resonance condition of light fr = m / τ (fr: optical resonance frequency, m: integer) also causes a difference between the two-direction light due to the Sagnac effect, and the resonance frequency difference Δfr of the two-direction light is Δfr = (4S / λL) Ω λ: optical wavelength, L : It is the circumference of the ring-shaped optical waveguide. Therefore, if an optical ring resonator is prepared and coherent light is externally introduced into the optical ring resonator and the resonance frequency difference between the two-direction light is detected by some method, the angular velocity of light input to the optical ring resonator can be quantified. An angular velocity meter based on this principle is called a passive ring resonator type optical gyro.

Although not directly related to the gist of the present invention, an example of a conventional optical gyro will be described with reference to FIG. Light source 1
The light from 2 is split into two by an optical coupler 19, both of these lights are subjected to optical frequency modulation by optical frequency shifters 21 and 22, respectively, and both of these optical frequency-modulated lights are subjected to a glass or optical crystal by the optical coupler 13. The light beams are introduced into the ring-shaped optical waveguide 11 formed of the optical waveguides as light beams that are opposite to each other. The oscillation output of the oscillator 23 is usually a sine wave, and the sine wave signals are applied as control signals to variable frequency oscillators (hereinafter referred to as VCOs) 26 and 27 through addition circuits 24 and 25, respectively, and the oscillation frequencies of the VCOs 26 and 27 are changed. It is changed at the time of sine wave. The optical frequency shifters 21 and 22 are modulated and driven by the oscillation outputs of the VCOs 26 and 27, respectively.

The ring-shaped optical waveguide 11 is multi-circulated, and a part of the double-rotated light that has undergone multi-interference is partially coupled to the optical coupler 1.
3 is guided to the outside, and the guided light is guided to the optical coupler 1
3, the optical frequency shifter 21, which is incident on them,
The light from 22 interferes with the light, and the respective interference lights are converted into electric signals by the light receivers 31 and 32 via the optical couplers 28 and 29, respectively. The outputs of these light receivers 31 and 32 are respectively supplied to lock-in amplifiers 33 and 34,
Synchronous detection is performed by the output of the oscillator 23, and the detected outputs are added to the output of the oscillator 23 by the adder circuits 24 and 25, respectively, and supplied to the VCOs 26 and 27 as control signals.

The frequency f of the output light of one optical frequency shifter 21 is frequency-modulated by the sine wave output of the oscillator 23 as shown by the curve 35 in FIG. 4A, and the center frequency thereof is set to the reflection characteristic 18 in FIG. When the frequency at the minimum value of one dip is matched, the intensity I of the signal (output from the optical coupler 28) obtained from the photodetector 31 with respect to the one dip characteristic 36 is as shown in the curve 37. It fluctuates at a frequency twice the output frequency of 23. Therefore, the output of the lock-in amplifier 33, that is, the synchronous detection output becomes zero.

However, when the angular velocity around the axis of the ring-shaped optical waveguide 11 is input, the resonance frequency of the ring-shaped optical waveguide 11 shifts due to the Sagnac effect. For example, as shown in FIG. With respect to the center of the frequency of the output light, the frequency at which the minimum value of the drop characteristic 36 of the reflection characteristic is shifted, and as a result, the signal intensity obtained at the output of the photodetector 31 is as shown in the curve 37, the output frequency of the oscillator 23. Is the main component. Therefore, the output of the lock-in amplifier 33, that is, the synchronous detection output corresponds to the input angular velocity. The output of the lock-in amplifier 33 is negatively fed back to the VCO 26 through the adder circuit 24, and the center frequency of the optical frequency modulation by the optical frequency shifter 21 is shifted so that the deviation with respect to the frequency having the minimum value of the drop characteristic 36 of the reflection characteristic is returned. Be done.

Output from the other optical frequency shifter 22,
Regarding the light introduced into the ring-shaped optical waveguide 11, the light receiver 32, the lock-in amplifier 34, the adding circuit 25, the VCO
27 operates in the same manner. Therefore, the ring-shaped optical waveguide 1
The bidirectional light in 1 is controlled so that the center of each frequency always resonates in the ring-shaped optical waveguide 11.
The frequency difference between the outputs of the VCOs 26 and 27 is detected by the double balanced mixer 38 as the frequency difference between the two-direction light, and the difference frequency is a detection amount indicating the input angular velocity to the ring-shaped optical waveguide 11.

[0011]

The optical gyro described above has an advantage that the optical waveguide length can be shorter than that of the optical fiber gyroscope because the sensitivity can be improved by multiple interference. However, when the optical ring resonator as shown in FIG. 2 is configured, the optical waveguide length is extremely short, the diameter of the ring becomes, for example, about 20 mm, and the area S surrounded by this becomes extremely narrow, so the optical ring resonance There was a problem that the sensitivity as a container decreased. The present invention avoids the above-mentioned problems and improves the sensitivity of the optical ring resonator by using substrates of the same size.

[0012]

A light source 1 for introducing light at one end
2 is provided, a photodetector 17 for detecting the intensity of the emitted light is provided at the other end, and a light input / output optical waveguide 20 is provided on the substrate 10, and a plurality of optical waveguides 20 are provided on the substrate 10. In an optical ring resonator of an optical gyroscope having (n: positive integer) ring-shaped optical waveguides 11, an input / output optical waveguide 20 and an outermost first ring-shaped optical waveguide 11a are first optically coupled. Optical coupling by the optical coupler 13a, and thereafter, the first ring-shaped optical waveguide 11a and the second ring-shaped optical waveguide 11b inside thereof are optically coupled by the second optical coupler 13b. 11b and the third ring-shaped optical waveguide 11c inside thereof are optically coupled by the third optical coupler 13c, and similarly, the (n-1) th ring-shaped optical waveguide and the n-th ring-shaped optical waveguide inside thereof are formed. And are optically coupled by the nth optical coupler It was constructed an optical ring resonator optical gyroscope.

[0013]

FIG. 1 shows an embodiment of a ring resonance type optical gyroscope according to the present invention, and parts corresponding to those in FIG. 2 are designated by the same reference numerals. An input / output optical waveguide 20 and a plurality of (three in the illustrated example) first, second, and third ring-shaped optical waveguides 11a, 11b, and 11c are arranged on the substrate 10, and the input / output optical waveguide is provided. 20 and the first ring-shaped optical waveguide 11a are optically coupled by the first optical coupler 13a,
First ring-shaped optical waveguide 11a and second ring-shaped optical waveguide 1
1b is optically coupled with the second optical coupler 13b,
Ring-shaped optical waveguide 11b and third ring-shaped optical waveguide 11c
And are optically coupled by the third optical coupler 13c. The plurality of ring-shaped optical waveguides 11a, 11b, 11
c is arranged so as not to cross over the other ring-shaped optical waveguides.

According to this structure, a part of the light emitted from the light source 12 and introduced into the input / output optical waveguide 20 is the first light.
The light is introduced into the first ring-shaped optical waveguide 11a by the optical coupler 13a, and the remainder goes directly to the light receiver 17 as the light detecting means. In this case, the first optical coupler 13 is adjusted so as to obtain an optimum resonance state in the first ring-shaped optical waveguide 11a, and for example, 10% of the light introduced from the light source 12 into the input / output optical waveguide 20 is the first 9 is introduced into the ring-shaped optical waveguide 11a,
It is adjusted so that 0% goes directly to the light receiver 17.

The light introduced into the first ring-shaped optical waveguide 11a circulates in the inside, and the circulated light is the second optical coupler 13.
By b, it is introduced into the second ring-shaped optical waveguide 11b and circulates around it, and this circulated light is further introduced into the third ring-shaped optical waveguide 11c by the third optical coupler 13c and circulates around it. The light circulating in the third ring-shaped optical waveguide 11c is the third light.
The second ring-shaped optical waveguide 11b is again provided by the optical coupler 13c.
The light introduced into the first optical coupler 11a is guided to the first ring-shaped optical waveguide 11a again by the second optical coupler 13b, and the light further circulating therein is input to the input / output optical waveguide 20 by the first optical coupler 13a. It is introduced, interferes with the light from the light source 12, and reaches the light receiver 17.

Here, the second and third optical couplers 13b and 13c
So that light is completely introduced into the next ring-shaped optical waveguide,
Its length and spacing are adjusted. This optical coupler 13
Directional optical couplers are used as b and 13c, and the first ring-shaped optical waveguide 11a to the second ring-shaped optical waveguide 11b are used.
When the movement of light to the first ring-shaped optical waveguide 11a is 100%, the opposite movement of the light to the first ring-shaped optical waveguide 11a is also 100%. By repeating such an operation, multiple interference light is obtained, and the light intensity of this interference light is detected by the light receiver 17.

[0017]

As described above, according to the present invention, the area S surrounding the ring-shaped optical waveguide forming the optical ring resonator can be made larger than that of the conventional optical gyroscope. There is an effect that the sensitivity of the optical ring resonator can be significantly improved. That is, first, second, third ring shaped optical waveguide 11a, 11b, if the area surrounded by the respective 11c and S _1, S _2, S ₃ respectively, ring-shaped optical waveguide of the optical resonator in this configuration Has a total area S of S = S ₁ + S ₂ + S ₃ , and when there are a large number n of ring-shaped optical waveguides, S = S ₁ + S ₂ + ...
・ It becomes + Sn. Therefore, the area S surrounding the ring-shaped optical waveguide
However, the value is larger than that in the case of one (conventional case), and the area S in the above-mentioned Δφ = (8πS / Cλ) Ω formula should be set to a larger value than that in the case shown in FIG. 2 of the related art. Therefore, the sensitivity can be greatly improved, for example, S / S ₁ as compared with the conventional optical gyroscope. Further, since the plurality of ring-shaped optical waveguides are arranged in the conventional ring 11 shown in FIG. 2, there is no increase in size.

[0018]

[Brief description of drawings]

FIG. 1 is a plan view showing an example of an optical ring resonator of a ring resonance type optical gyroscope according to the present invention.

FIG. 2 is a plan view for explaining an optical ring resonator.

FIG. 3 is a block diagram showing a conventional ring resonance type optical gyroscope.

FIG. 4 is a diagram showing the relationship between the optical frequency change and the derived light intensity in FIG.

Claims (1)

(57) [Claims] 1. A light input / output optical waveguide arranged on a substrate, wherein a light source for introducing light is provided at one end, and a photodetector for detecting the intensity of the emitted light is provided at the other end. In an optical ring resonator of an optical gyroscope having a plurality of n (n: positive integer) ring-shaped optical waveguides arranged above, an input / output optical waveguide and an outermost first ring-shaped optical waveguide are provided. Optically coupled by the first optical coupler, and hereinafter, the first ring-shaped optical waveguide and the second ring-shaped optical waveguide inside thereof are optically coupled by the second optical coupler, And the third ring-shaped optical waveguide inside thereof are optically coupled by a third optical coupler, and similarly, the (n-1) th ring-shaped optical waveguide and the n-th ring-shaped optical waveguide inside thereof are coupled to each other. Optical gyroscope characterized by being optically coupled by an n optical coupler Optical ring resonator.