JPS59195220A - Optical detector - Google Patents

Abstract

PURPOSE:To obtain a small-sized optical detector which eliminates the need for alignment by providing four light guides on one substrate, and demultiplexing and multiplexing specific light among those light guides. CONSTITUTION:Incident light having intensity Iin=¦A¦<2> is incident to the 1st light guide 11, split equally at a coupling part 15 to light guides 12 and 13 to propagate therein, and modulated by DELTAphi and -DELTAphi by a modulator which includes an electrode 16 for phase modulation to travel with electric fields E1 and E2 of speific light. The light beams traveling in the light guides 112 and 13 pass through an optical fiber 3 with a radius R and reach the light guides 13 and 12. Those light beams are phase-modulated by an optical modulator (16) and the light beams e1 and e2 interfere with each other at the coupling part 15 to output light with specific intensity Iout from the 4th light guide 14. Thus, the small- sized optical detector which eliminates the need for alignment is obtained.

Description

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for detecting a signal from a sensor using light, such as an optical fiber gyro or a current sensor.

Conventionally, sensors using light have been constructed by combining individual optical components such as lenses and half mirrors in order to process optical signals. Therefore, it is important to downsize (
In addition, it requires precise axis alignment between each component, making assembly troublesome, and there are disadvantages such as the axis being misaligned due to changes in ambient humidity and temperature, resulting in inoperability.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compact optical detection device that does not require alignment.

The optical detection device according to the invention includes a first
, second, third and fourth single mode optical waveguides are integrally formed, and these optical waveguides are such that the laser beam propagating through the optical waveguide @l reaches the second and third optical waveguides for 0 minutes. 7;
The laser beam is propagated through the second and third optical waveguides in opposite directions, and then the laser beam is propagated through the fourth optical waveguide (combined with −11
The optical waveguide is configured such that the light is guided at a certain angle, and is characterized in that it is provided with means for imparting phase modulation to the light propagating through the second and third optical waveguides.

According to this emission Fy], the light 3j3 that performs the splitting and multiplexing 5-1 of the light changes into the 3 wave path and the light i1! ] is provided on the same substrate, making it possible to make the device smaller and eliminate adjustment.

DESCRIPTION OF EMBODIMENTS First, the operating principle when the present invention is applied to an angular velocity sensor, a so-called optical fiber gyro, will be explained.

As shown in Figure 1, the incident light of intensity = 1A12 enters the first optical waveguide (11), and the coupling part (
15) @2 and the third optical waveguide +12+' (13
The light is divided equally into +121 and +131 and propagates through these optical waveguides +121 and +131. Optical waveguide 121 f13i ) This provided phase shift m! These lights undergo phase modulation of Δφ and −Δφ in the modulation section including the d electrode (16). At this time, the electric fields E□ and E2 of light in each optical waveguide (121+13) are given by the following equation.

E1=r A *Oxp (,iΔφ) −+
1) E2-woA...p(=]Δφ)...(
2) Both ends of one optical fiber are connected to the exit of each leading waveguide f121 +131, and this optical fiber is wound into a coil with a radius R (indicated by (3)). The light (El) propagating through the optical fiber coil (3) passes through the optical fiber coil (3) and proceeds to the optical waveguide Q3i. optical waveguide f
l(.

The light (E2) of (13) travels through the optical fiber coil (3) to the optical waveguide (12).

Figure 1 [When the entire optical system shown in this figure is rotated in a predetermined direction,
When light propagates in the optical fiber coil (3), two lights traveling in opposite directions (as described above) produce a phase difference (Sakunatsu effect).This phase shift occurs.

Let be r. The two lights that have passed through the optical fiber coil (3) enter the optical waveguide (13i (12i +)).

When these lights travel in the opposite direction through the leading wavepath f131 (+2), the electric field C of the light after being modulated is
E and e2 are respectively expressed by the following equations.

c1! E2・Oλp(jΔψ)...
(3) a = E11 [IX]l (-, iΔψ)・
O Angular velocity of rotation of the entire system C1 Speed of light (2
'L in the air), and the difference r is based on one light.

These two lights (0), (C2) are the connecting part (15)
The output light intensity obtained by combining and interfering these lights is expressed by the following equation using equations 11 to 4j. .

I out -2101-ri 2 - 〇in J・(-, i(Δφ−Δψ month) 2
... (6) Assuming that a phase change yrrB is given in the form of a sine wave propagating through the optical waveguide f]21ll31,
Change GW JM 11J a, change ird ffl Il'
When the d wave number is ω, Δφ and Δψ are given by the following equations.

Δφ= a ++ sin ((II L )
River (71Δψ−a*5in(ω(L+t9))
e-*ts+ also 0-ll L/Cll
11- (9) 11: Since the phase of the refractive index modulated wave of the optical fiber with respect to the light wave is not intercondylar, the following replacement is performed.

ω1 −+−ω(t-to/z) ω(j+t.)→ω(v+to/2) As a result, Δφ−Δcp == −2a * 5in (ω is also 0/
2) @ 00B (ωt) so (IQ).

? J Substituting equation (10) into equation (6) yields the following equation.

I out = −[1− cos (r)” (J6Cα)+Σ(−1)+2.,
(α) cos(2 to ωt)) +1 ・'-(11) Here α-=-4am sin (cilto/2)
@1111 [121J1, (α): Heso cell numerical aperture.

1 (11+Equation) If we extract the lower-order frequency components among the included frequency components, we obtain the following equation.

111 flow component So = ■ill (1-Jo(α) e cos
(r) '1 eat f131 fundamental wave component Sl = "i++" Jl(α) m 5in(
r) aha (141 second harmonic component S22l1nIIJ2(α)IIQθ8(γ)
...-t151 3rd harmonic component S321i, 1IIJ3 (α) @ sin (r)
"" f161 4th harmonic component C4 = -1in " +4 (") ・cosCr)
*・m (The following equation is obtained from the 171st equation (■4) to the (17i equation).

1 sin (γ) = -111111 ■in ” Jl (Le - (181α
S-8 also a IN (γ) = −・ □
... (1!] 14 82 Find the phase difference γ using the 8th equation of equations (18) to ρ0, and then obtain the angular velocity of rotation from equation (5). be able to.

FIG. 2 shows the specific configuration of the optical fiber gyro. The above-mentioned optical waveguides (11) to (14) are formed on the lithium niobate substrate (10) by diffusion of Ti and other oxygen. These optical waveguides (11) to (14) are all +41-mote-7 optical axis waveguides, and the leading waveguide (
11) +121 (+1j of 131 is set so that their phase constants are the same. The rlJ of only the optical waveguide 04 is narrow and its phase constant is set small.

The optical waveguides (11) to (14) are connected at a coupling part, but the angle between the leading waveguides (11) and (14) and the angle between the top of the optical waveguide (13) are both extremely small. It is small, for example, 1° or less.The detailed structure of such a leading waveguide and the Q-light propagation theory are described in Japanese Patent Application No. 1986-8617B as a waveguide beam splitter.

Such an optical waveguide (121 (131) is provided with a pair of phase modulation electrodes (16j or Si02 buffer layer if necessary). A voltage is applied.The reason why the guided light is subjected to phase modulation is to improve measurement accuracy in a region where the phase difference γ is small.

Laser light from a laser light source (1) is introduced into the optical waveguide (11). The laser light source (1) is, for example, a laser diode. Both ends of two optical fiber coils (3) are optically coupled to one end of the optical waveguides f121 to f13i.

This optical fiber coil (3)l thus leads to a leading waveguide of +1
Light from one of the optical waveguides 21 (13) is guided to the other. A photodetector (2) is provided at the light output end of the optical waveguide and converts the multiplexed and interfered optical signals into electrical signals. Photodetector (
The output signal of 2) is inputted to each narrow band pass filter (23) to (2[il i) through an amplifier (22).
1 to S4 are extracted. Filter (23) ~ (
26) is sent to the arithmetic circuit (27),
2nd to t2th [1j style performances are held. performance% circuit! 2
7) can be configured by a microprocessor (for example), but it can also be configured by a combination of adders, multipliers, dividers, etc.
2), filters (23) to (2G) and arithmetic circuit (2)
7) constitutes a processing device (20).

Now, the wavelength λ of the laser beam is 0.8 PITI, the length of the modulation electrode (16) measured in the optical waveguide direction is 15 cm, and the distance between a pair of 1 (L poles (16) is 12.M is 157 m). ], Summer 11,
Assuming that the radius R of the optical fiber (3) is 10 cm and the length L of the optical fiber is 1 km, the half wavelength 'l eave pressure V required for modulating the light.

Haha +, a1.2 v. At this time, t. -11
L/C (Equation (9))-5QpS. 43 for modulation
[1′d wave number r = ω/ 2π”−HI M
Hz, electric current [E (corresponding to a +) -=-1■ changes the frequency f by a factor of ±05 or changes the applied voltage, then σ-4Ht @Sil+ (ωto
/2) (Equation (12)) can be varied within a range of 6 or less in terms of absolute value.

The phase difference is γ-4πLRΩ/λC (formula (15))% formula%
) 8th place 411 When the difference γ (angular velocity Ω) is minute [In this case, if the modulation frequency f or the applied voltage is adjusted to α-514, the second harmonic component 52 of the frequency components of the output signal
-0, Equation (20) 4 % (21 Measurement of component S3 and Si (From this, the phase difference γ, that is, the angular velocity Ω can be measured).

When the phase difference γ is large (this is so that α is 3.83 (this 1.'il wave number 1 or applied voltage: n!) l1
When ff+, S becomes -O, and from equation (19), 1 = Lan' (0,958S3/S2)
``'' t221, and from this point γ and Ω can be measured.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the principle when the present invention is applied to an angular velocity sensor, that is, a so-called optical fiber gyro, and FIG. 2 is a block diagram showing an embodiment of the present invention. (10)...Substrate, (11)-t14)--Optical waveguide, (15)...Coupling portion, (16+...Modulation electrode.

Claims (1)

[Claims] (1) First, second, third, and fourth single-mode optical waveguides are integrally formed on one substrate, and these optical waveguides are connected to the leading waveguide of @1. The laser beam propagating through the second and third optical waveguides is split and propagated, and the laser beam propagating in the opposite direction through the second and third optical waveguides is combined and interfered with by the fourth leading waveguide. The light propagating through the second and third optical waveguides is configured such that the light propagates through the second and third optical waveguides (means for imparting this phase modulation is provided). The optical detection device according to claim (1), which is made narrower than a cow. (3) The phase modulation means allows the light propagating through the second optical waveguide and the third optical waveguide to propagate. The optical detection device according to claim (1), wherein phase modulation of equal magnitude and opposite sign is applied to the light emitted from the fourth optical waveguide. (4) Photoelectric conversion of the light emitted from the fourth optical waveguide. An optical detection device according to claim 1, comprising: a photodetector for detecting a photodetector; and a bandpass filter for passing a desired frequency component of a signal output from the photodetector.