JP2921072B2 - Multi-channel integrated optical interferometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention uses position, displacement,
The present invention relates to an interferometer for measuring a speed or the like, and more particularly, to an integrated optical interferometer in which an interference optical system is configured using an optical waveguide.

[Prior Art] Conventionally, a heterodyne interferometer for measuring position, displacement and velocity with high accuracy is a light source He-dyne as shown in FIG.
Ne laser 71, half mirror 72, λ / 2 plate 74, mirror 75, Bragg cell 76, half mirror 77, polarization beam splitter 78, λ /
It is composed of four plates 79 and a photodetector 80. He-Ne laser
The light emitted from 71 is linearly polarized light polarized in a direction parallel to the plane of the paper, and is split by the half mirror 72 into two beams. The first beam of the two split beams is applied to the moving DUT 82 through the polarizing beam splitter 78 and the λ / 4 plate 79. The reflected light that is, the signal light received Doppler shift f _S by moving the measurement object 82, the polarization plane is rotated 90 ° by passing through the lambda / 4 plate 79 again,
The beam becomes a beam polarized in a direction perpendicular to the plane of the paper, and is reflected by the polarization beam splitter 78. On the other hand, the second beam of the two split beams is rotated by 90 ° by the λ / 2 plate 74 to be perpendicular to the plane of the paper, is reflected by the mirror 75, and enters the Bragg cell 76. The Bragg cell 76 is an optical modulator using an acousto-optic effect, and the primary light diffracted by the elastic wave of the frequency f _R excited by the driving circuit 84 is f _R
And the reference light is given. When heterodyne detection is performed by multiplexing and interfering the signal light and the reference light with the half mirror 77, a signal oscillating at the Doppler beat frequency f _R ± f _S is detected by the photodetector 80.
This signal is amplified by the amplifier 86, and the Doppler beat frequency f _R ± f _S is measured by the spectrum analyzer 88, whereby the moving speed of the device under test 82 can be measured simultaneously with the moving direction of the device under test 82. In addition, the displacement of the device under test 82 can be measured by integrating the speed with time. In the multi-channel type, N interferometers are arranged in parallel and measured.

[Problems to be Solved by the Invention] However, this multi-channel type heterodyne interference optical system is usually configured by arranging and fixing necessary optical components on a vibration isolating table such as an optical bench, and subtle interference between components. Optical axis adjustment is required, reliability and productivity are low, and
There is a problem that the optical system is large and heavy.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to integrate a main part of an interference optical system on a single substrate using a thin-film waveguide technique. Another object of the present invention is to provide a compact, stable, and highly reliable optical integrated interference system that does not require optical axis adjustment.

Means for Solving the Problems In order to achieve this object, a multi-channel optical integrated interferometer of the present invention comprises a light source, an optical waveguide for dividing light from the light source into N channels, A first, a second, and a third optical waveguide for demultiplexing the light demultiplexed into the channel into three, an optical frequency shifter for giving a constant frequency shift to the light guided to the second waveguide; Fourth and fifth optical waveguides for demultiplexing the frequency-shifted light into two light beams, and the light guided to the first waveguide is condensed and irradiated on the object to be measured, and the reflected light is converted to a sixth light beam. An optical means for guiding the light passing through the third optical waveguide, an optical waveguide for performing multiplex interference between light passing through the third optical waveguide and light passing through the fourth optical waveguide, and a first optical sensor detecting the interference signal. An optical waveguide for multiplexing interference between light passing through the fifth optical waveguide and light passing through the sixth optical waveguide; It is constructed by arranging light integrated heterodyne interference sensor and a second optical sensor for detecting the into N parallel.

[Operation] In the multi-channel integrated optical interferometer of the present invention having the above-described configuration, light emitted from a laser as a light source is split into N channels, and the light split into the N channels is further divided into first channels. , And is split into three by the second and third optical waveguides. Second
The light guided to the waveguide is given a certain frequency shift by the optical frequency shifter, and the optical frequency is set to f ₀ + f _R. The light having undergone the frequency shift is further demultiplexed to the fourth and fifth optical waveguides. Light guided in the first waveguide are converging and irradiating the object to be measured, the reflected light subjected to Doppler shift f _S
The light becomes f ₀ + f _S and is guided to the sixth waveguide. Light passing through the third optical waveguide is caused to interfere with light and multiplexer through the fourth optical waveguide, the reference signal f _R is detected by the second light sensor. The measurement light having passed through the sixth optical waveguide is multiplexed and interfered with the shift reference light having passed through the fifth optical waveguide, and the measurement signal f _R + f _S is detected by the first optical sensor. And by comparing the reference signal and the measurement signal, the Doppler shift f _S is determined, it is the moving speed and moving direction of the object to be measured can be measured.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, for example, an integrated optical interferometer is a GGG (Gd ₃ Ga
₅ O ₁₂₎ formed on the substrate 11, such as a _{Bi: YIG (Bi x Y 3} -x Fe 5 O
_{12), Bi: GdIG (Bi} x Gd 3-x Fe 5 O 12) magnetic thin film 12 having a magneto-optical effect, such as, a semiconductor laser 13, an optical isolator 14, a focusing lens 15, an optical fiber N_17, such as Si photodiode It consists of photodetectors N_Si and N_S2. Here, N represents N channels, and hereinafter all are abbreviated as N_.

The magnetic thin film 12 is provided with a ridge portion 21 whose film thickness is larger than other portions, thereby forming a ridge waveguide. The laser light propagates along the ridge portion 21. The ridge portion 21 is manufactured using well-known photolithography. That is, a magnetic thin film 12 is formed on a substrate 11 by a thin film forming means such as a liquid phase growth method or a sputtering method, and a photoresist is applied thereon. Then, after patterning into a predetermined ridge waveguide shape, a portion other than the portion to be the ridge 21 is etched by a predetermined thickness by plasma etching, sputter etching, wet etching using hot phosphoric acid, or the like. Finally, the ridge portion 21 is formed by removing the photoresist.

Laser light emitted from the semiconductor laser 13 propagates through an optical isolator 14 that transmits light in only one direction, and a focusing lens 15.
And is incident on the ridge-type waveguide 21. At this time, the semiconductor laser 13 is mounted so that the laser light propagating through the ridge-type waveguide 21 becomes a TM mode in which the direction of the magnetic field oscillation is parallel to the thin film surface. The laser light that has propagated through the ridge waveguide 21 is extracted by the Y-branches N_Y1, N_Y2, and N_Y3, and propagates through the N_1, N_2, and N_3 waveguides, respectively.

On the branch waveguide N_2, a buffer layer N made of SiO ₂ etc.
_31 and an electrode N_32 made of a metal such as Al are provided,
The frequency shifter N_33 is configured. By flowing a current from the oscillator 34 to the electrode N_32, the branch waveguide N_2
A magnetic field perpendicular to the propagation direction of the laser light and parallel to the thin film surface is applied. This magnetic field magnetizes the branch waveguide N_2,
A phase shift due to the magneto-optical effect occurs in the TM mode. That is, the propagation constant of the TM mode when no magnetic field is applied is β ₀ , and the propagation constant when a magnetic field is applied is β
Then, β = β ₀ + γ (1) Here, γ is the amount of phase shift due to the magneto-optical effect. Z-axis in the propagation direction of light, taking the x-axis in the direction perpendicular to the thin film plane, gamma is given by _{γ = 2ω 0 ε 0 ∫Re [} ε xz e x * e z] dx (2). Where ω ₀ is the angular frequency of the laser beam, ε
₀ is the vacuum dielectric constant, one of the non-diagonal elements of e _x and e _z are the electric field of the x component and the z component of the TM mode, epsilon _xz dielectric constant tensor of the magnetic thin film 12, * the complex conjugate, Re Represents the real part of a complex number. ε _xz has a relationship of Faraday rotation coefficient θ _F and ε _xz = j (2n ₁ / k) θ _F (3). Where n ₁ is the refractive index of the magnetic thin film 12,
k is the wave number of the laser light in a vacuum, and the wavelength of the laser light is λ
Then, k = 2π / λ (4) is given. Further, in a range where the magnetization of the magnetic thin film 12 is not saturated, the magnetization of the magnetic thin film 12 is applied magnetic field H, that is,
Since it is proportional to the current I flowing through the electrode N_32, if this proportionality constant is V, then θ _F = VI (5).

(3) becomes (2) substituting for the γ = 2ω ₀ ε ₀ in equation _{(2n 1 / k) θ F} ∫Re [je x * e z] dx = Aθ F (6). Here, A is a constant.

When the length of the portion where the magnetic field is applied in the branch waveguide N_2 a 1, field of the TM mode which has received the phase _{shift, e x = E x sin [} ω 0 t + (β 0 + γ) 1] = E _x sin [ω ₀ t + Aθ _F 1 + β ₀ 1] (7) _{Here, θ F = ω R t /} (Al) (8) i.e., (5) from equation _{I = ω R t / (AlV} ) (9) and so as to when an electric current is applied to the electrode 32 e _x = E _x sin [(ω ₀ + ω _R ) t + β 1] (10), and the angular frequency of the laser beam is from ω ₀ = 2πf ₀ to ω ₀ ω
_R = 2π (f ₀ + f _R ), that is, the frequency of the laser light is
to shift from f ₀ only f _R, the f ₀ + f _R. However, the electrode N_
As shown in FIG. 2, the current of the reference signal flowing through 32 has an amplitude of 2π /
(AlV), similar frequency shift can be obtained as a sawtooth wave of period 2π / ω _R. The laser light having the frequency f ₀ as shown in FIG. 3A incident on the branch waveguide in this manner is shifted in frequency by f _R by the frequency shifter as shown in FIG. ₀ + f _R becomes the reference light.

On the other hand, the laser light that has propagated through the branch waveguide N_1 enters the optical fiber N_17, and further becomes parallel light by a Selfoc lens N_41 provided at the tip of the optical fiber N_17,
The moving object N_43 is irradiated. DUT N_43
The laser light reflected from the object undergoes a Doppler shift by a frequency f _S according to the speed of the object N_43, and the frequency becomes f ₀ + f _S as shown in FIG.
The light enters the optical fiber N_17 through N_41. Signal light received only the Doppler shift The f _S is propagated through the branching waveguides N_6 from the optical fiber N_17. Also, f
_The reference light having undergone the frequency shift by _R is split into two by the Y branch N_Y5, and propagates through the branch waveguides N_4 and N_5, respectively.
The reference light propagating through the branch waveguide N_5 and the branch waveguide N_6
Is multiplexed with the signal light that has propagated through Y branch N_Y6. The combined laser beam, the amplitude due to interference has vibrated in Doppler beat frequency f _R -f _S, which upon detection by the light detector N_S1, Doppler beat frequency as in the third diagram (d) A signal oscillating at f _R −f _S is obtained.

Further, the reference light that has propagated through the branch waveguide N_4 and the laser light that has not undergone the frequency shift that has propagated through the branch waveguide N_3 are multiplexed by the Y branch N_7. Amplitude of the multiplexed laser light is vibrated in its amplitude frequency f _R by interference, by this is detected by the photodetector N_S2, oscillates at a frequency f _R as FIG. 3 (d) A signal is obtained.

By determining the Doppler shift f _S by comparing the output signal of the photodetector N_S1 and N_S2, can simultaneously measure the speed and direction of movement measured object N_43. At this time, even if the frequency shift f _R of the reference light fluctuates due to fluctuations in the temperature of the frequency shifter N_33, the Doppler beat frequency f _R −f _S of the output of the photodetector N_S1, as shown in FIG. the difference f _S of the frequency f _R of the reference signal at the output of the photodetector N_S2 can be accurately obtained the Doppler shift f _S becomes constant. When the moving direction of the device under test N_43 is reversed, as shown in FIG. 3 (e), the frequency shift f _R of the reference light becomes f _R + f _S
Doppler beat occurs at the position. Furthermore, it is possible to measure also the displacement amount by integrating the velocity of the moving object N_43 determined from the Doppler shift f _S time. By the way, the laser light returning from the optical fiber N_17 to the branch waveguide N_1 propagates through the ridge portion 21, the focusing lens 15, and enters the optical isolator 14, but the optical isolator 14 is in the direction from the semiconductor laser 13 to the focusing lens 15. Since the light is transmitted only in one direction, the return light from the optical fiber N_17 cannot pass through and does not reach the semiconductor laser 13. Accordingly, in the semiconductor laser 13, since no noise is generated due to the return light, measurement with good S / N can be performed.

As described above, one embodiment of the present invention has been described in detail with reference to the drawings. However, the present invention is not limited to this embodiment, and various modifications can be made.

That is, the materials of the substrate, the magnetic thin film, the buffer layer, and the electrode are not particularly limited. For example, sapphire, glass, etc. are used for the substrate, rare-earth semiconductors such as CdMnTe, paramagnetic materials such as Faraday rotating glass, TAG (Tb ₃ Al ₅ O ₁₂ ), etc. Oxides and nitrides such as ZnO and AlN may be used for the layers, and gold or the like may be used for the electrodes.

The optical waveguide does not need to be of the ridge type, and may be, for example, a rectangular waveguide as shown in FIG. 4 (a), an embedded waveguide as shown in FIG. 4 (b), a dielectric loaded waveguide, or the like. The shape may not be particularly limited as long as the light can be confined not only in the thickness direction but also in the lateral direction.

Alternatively, a magnetic thin film may be used only for the frequency shifter portion, and a dielectric material having no magneto-optical effect may be used for other portions. Further, the shape of the electrode for applying a magnetic field to the frequency shifter is not limited. Further, a magnetic field may be applied by providing an external electromagnet, a coil, or the like.

Further, instead of the Y-branch waveguide, the light may be demultiplexed by the directional couplers 52 and 53 in which two optical waveguides are formed in parallel as shown in the top view of FIG. At this time, 2
By adjusting the length of the parallel part of the two optical waveguides,
The splitting ratio can be changed. Although various other modifications are conceivable, those skilled in the art can implement the present invention in various modes without departing from the gist of the present invention.

[Effects of the Invention] As is apparent from the above description, according to the present invention, the main components of the interference optical system such as a laser beam splitter, a multiplexer, and a frequency shifter using the thin-film waveguide technology. Since the units are integrated on one substrate, the optical axis adjustment is unnecessary, and a small, stable, and highly reliable optical integrated interferometer can be manufactured with high productivity. In addition, since not only the Doppler beat frequency but also the frequency shift of the reference light are detected at the same time, stable and accurate multi-channel measurement that is not affected by fluctuations in the frequency shift of the reference light due to changes in temperature or the like must be performed. Can be.

[Brief description of the drawings]

FIGS. 1 to 5 show an embodiment embodying the present invention. FIG. 1 is a block diagram of a multi-channel optical integrated interferometer according to an embodiment of the present invention. FIG. 3 is a diagram showing a waveform of a current applied to an electrode of a frequency shifter. FIG. 3 is an explanatory diagram showing a relationship between laser light frequencies in an integrated optical interferometer according to one embodiment of the present invention. FIG. 4 is a partial view showing another embodiment of the optical waveguide, FIG. 5 is a top view showing another embodiment of the duplexer in the optical integrated interferometer, and FIG. 1 is a configuration diagram illustrating an optical system of a heterodyne interferometer of FIG. 11: Substrate 12: Magnetic thin film 13: Semiconductor laser 14: Optical isolator 15: Focusing lens 21: Ridge part 34: Oscillator 46: Y branch 47: Branch waveguide 48: Branch waveguide 49: Y branch 50: Y branch 52: Directional coupler 53: Directional coupler 61: Buffer layer 71: He-Ne laser 72: Half mirror 74: λ / 4 plate 75: Mirror 76: Bragg cell 77: Half mirror 78: Polarizing beam splitter 79: λ / 4 Plate 80: Photodetector 82: DUT 84: Drive circuit 86: Amplifier 88: Spectrum analyzer N_17: Optical fiber N_S1: Photodetector N_S2: Photodetector N_Y1, N_Y2, N_Y3: Y branch N_Y4, N_Y5, N_Y6 Y Branch N_1, N_2, N_3: Branch waveguide N_4, N_5, N_6: Branch waveguide N_31: Buffer layer N_32: Electrode N_33: Frequency shifter N_41: Selfoc lens N_43: DUT

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-296102 (JP, A) JP-A-64-43704 (JP, A) JP-A-64-12204 (JP, A) JP-A-63-63 47602 (JP, A) JP-A-60-85312 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 9/00-9/10 G01B 11/00-11/30 102

Claims (1)

(57) [Claims] 1. A light source, an optical waveguide for splitting light from the light source into N channels, and first, second, and third light sources for further splitting the light split into the N channels into three light beams. An optical waveguide, an optical frequency shifter for giving a constant frequency shift to the light guided to the second waveguide, and fourth and fifth optical waveguides for further splitting the frequency-shifted light into two. Optical means for condensing and irradiating the light guided to the first waveguide to the object to be measured and guiding the reflected light to the sixth waveguide; light passing through the third optical waveguide and a fourth optical waveguide An optical waveguide for multiplexing interference with light passing therethrough, a first optical sensor for detecting the interference signal, and multiplexing light passing through the fifth optical waveguide and light passing through the sixth optical waveguide. An optical integrated heterodyne interference sensor comprising an optical waveguide for causing interference, and a second optical sensor for detecting the interference signal; Multichannel optical integrated interferometer, characterized in that by arranging the sensor into N parallel.