JPH03209106A - Rotary mirror type interferometer, interference measuring method, and optical waveguide circuit diagnostic device - Google Patents

Abstract

PURPOSE:To measure the distance to an measurement object in the direction perpendicular to the optical axis by providing the extent of frequency shift due to the Doppler effect to the reflected light on a reflection mirror, and measuring the intensity of light with respect to each frequency. CONSTITUTION:The incoherent light from a light source 1 is converted to a luminous flux of parallel rays and traverses the (y) axis in a linear part and is branched into two in the linear part on the reflection face of a half mirror 7. One branched luminous flux is thrown to a measurement object 21, and the vertical reflection light is made incident on the mirror 7 again as signal light. The other branched luminous flux is reflected when a total reflection mirror 8 is perpendicular to the optical axis, and the reflection light is made incident on the mirror 7 as reference light and is coupled with signal light. This coupled light traverses the (x) axis in the linear part and is condensed on a photodetector 17 by a lens 5. The light traversing the (y) axis at a point out of this light is branched into two at a point in the mirror 7, and one branched light is reflected at a point of the measurement object 21. The other branched light is reflected at a point of the mirror 8. Both reflected light interfer with each other in the position where they have the same optical path length when the mirror 8 is swept by a stage 14.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a rotating mirror interferometer, an interference measurement method using the rotating mirror interferometer, and an optical waveguide circuit diagnosis using the rotating mirror interferometer. It is related to the device.

[Conventional technology]

FIG. 7 shows the configuration of an example of a conventional Michelson interferometer.

In FIG. 7, l is an incoherent light source, 2 and 5 are lenses, 7 is a half mirror, 8 is a total reflection mirror, l4 is a stage movable in the direction of the optical axis indicated by the arrow, 17 is a photodetector, and 19 is a Waveform recorders 20 and 21 are objects to be measured as samples for shape measurement.

The incoherent light from the light source 1 is made into parallel light by the lens 2, and then split into two by the half mirror 7. One of the branched lights is irradiated onto the measurement object 20 as a signal light, and the reflected light is passed back to the half mirror. 7. Is the other branched light a total reflection mirror? The reference light and the signal light from the measurement object 20 are reflected by the half mirror 7.
and enters the photodetector 17 via the lens 5. When the total reflection mirror 8 is swept in the direction of the arrow by the stage 14, the signal light and the reference light whose propagation optical path lengths match each other interfere with each other, and the photodetector 17 detects an interference fringe. In the case of a step-shaped measurement object 20 having surfaces a, b, and c, fringes a', b", and c" are measured for the surfaces a, b, and c, as shown in FIG. The distance of the step is measured by However, like the width of surface b,
It was not possible to measure the distance in the direction perpendicular to the optical axis. Furthermore, it was not possible to measure objects with curved external shapes, such as object 2l. FIG. 9 shows the configuration of a conventional optical waveguide circuit diagnostic device using a Matsuha-Zehnder interferometer.

Here, l is an incoherent light source, 2, 3, 4.5 are lenses, 6 is an optical fiber, 7 is a half mirror, 8 is a total reflection mirror, 14 is a stage, l5 is a big tilt Tl, T
2, an optical fiber coupler having T3, T4 and an optical coupling part Ct, l7 a photodetector, l9 a waveform recorder, 22 optical waveguides G11, G12, G21, G22, G31, G
32 and 2×2 Bo} PI, P2 . P3, P
4 and two optical coupling parts Cl and C2.

The light emitted from the light source 1 enters the big tail T1 at one end of the optical fiber coupler 15 via the lens 2, and is split into two at the optical coupling portion Cf. One of the branched lights is sent to the optical waveguide circuit 22 via the big tail T3 of the optical fiber coupler l5.
from its boat P1, from the optical waveguides, i.e. paths Gll→G21→G31, and from Gll-G22→
The light propagated through G31 is emitted from the boat P3 with a delay depending on the respective optical path lengths. This emitted light is further converted into parallel light by a lens 3 via an optical fiber 6, and then enters a half mirror 7 as a signal light.

The other branched light is parallelized from the big tail T4 of the optical fiber coupler 15 via the lens 4, and enters the half mirror 7 as a reference light perpendicularly to the output light from the optical waveguide circuit 22, and the transmitted light is is reflected by the total reflection mirror 8,
Furthermore, it is combined with the signal light emitted from the optical waveguide circuit 22 by the half mirror 7 .

The total reflection mirror 8 is swept in the direction of the arrow by the stage l4 to cause the signal light and reference light propagating through each path to interfere with each other, and the intensity of the interference light and the amount of delay at the interference position are measured. Similarly, the paths Gll→G21→G32 and Gll→G2
2 → Regarding the signal light propagated through G32, port P4
The optical fiber 6 is coupled to the optical fiber 6, and the interference light intensity and the amount of delay at the interference position are similarly measured. Based on these results, the branching ratio of each optical branching unit CI and C2 and the paths G21 and G
22 can be determined. but,
It is necessary to perform measurements from ports P3 and P4 separately twice in total, which takes time, and when the number of ejection boats increases, there is a problem that the measurement time increases dramatically.

[Problems to be Solved by the Invention] As described above, the conventional interferometers have the drawback that they can only measure objects with a specific shape or specific parts of the objects. Further, the conventional optical waveguide circuit diagnostic apparatus using such a conventional interferometer has a drawback that it is not possible to simultaneously measure the optical signals output to each port of the optical waveguide circuit.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an interferometer and an interferometric measurement method that can perform measurements in a direction perpendicular to the optical axis using a rotating mirror. Another object of the present invention is to provide an optical waveguide circuit diagnostic device that can simultaneously measure optical signals output to each port of an optical waveguide circuit. [Means for Solving the Problems] In order to achieve such an object, the interference measurement method of the present invention splits incoherent light into two, and makes one of the branched lights incident on the object to be measured. The signal light and no,
and the other branched light is made incident on a reflective mirror that is movable in the optical axis direction, and the reflected light obtained is used as a reference light, and the interference measurement method involves interfering the signal light and the reference light,
The reflection mirror is rotated to give the reference light a frequency shift amount due to the Doppler effect according to the distance from the rotation center within the same wavefront when reflected by the reflection mirror, and the reference light is interfered with the signal light. The present invention is characterized in that the intensity of a beat signal in the generated light intensity is detected for each beat frequency, and the distance in the direction perpendicular to the optical axis of the object to be measured is measured in correspondence to the beat frequency.

The interferometer of the present invention includes an incoherent light source, a reflecting mirror movable in the optical axis direction, and an incoherent light beam from the incoherent light source that is split into two, and one of the branched lights is made to enter the object to be measured. an optical means for making the reflected light as a signal light, and making the reflected light obtained by making the other branched light incident on the reflecting mirror as a reference light, and causing interference between the signal light and the reference light, and the reflecting mirror; A reflecting mirror rotating means for rotating, and a detecting means for receiving interference signal light between the signal light and the reference light extracted from the optical means and detecting light intensity for each beat frequency from the interference signal light. It is characterized by:

The optical waveguide circuit diagnostic device of the present invention is an optical waveguide circuit diagnostic device that measures the branching ratio of optical branching parts of an optical waveguide circuit and/or the optical path length difference between the optical branching parts. a movable reflecting mirror, an interference means, and the incoherent light from the incoherent light source is split into two, and one of the branched lights is made to enter the optical waveguide circuit,
an optical fiber coupler type branching means for guiding the other branched light to the reflecting mirror; an optical means for simultaneously receiving a plurality of signal lights emitted from the optical waveguide circuit and guiding them to the interference means; and rotating the reflecting mirror. a reflecting mirror rotating means;
The reflected light from the reflecting mirror is made to enter the interference means as a reference light, and the interference means receives the interference signal light obtained by interfering the signal light and the reference light, and extracts beats from the interference signal light. The present invention is characterized by comprising a detection means for detecting light intensity according to frequency.

[Function] In the interferometer and interferometric measurement method of the present invention, a rotating beam mirror is used, and the amount of frequency shape shift due to the Doppler effect is given to the reflected light from the reflecting mirror according to the reflection position of 1, so that the light is divided by frequency. By measuring the intensity, there is an advantage that the distance in the direction perpendicular to the optical axis can be measured for objects having various two-dimensional shapes.

The optical waveguide circuit diagnostic device of the present invention uses the above-mentioned subsidence meter and mainly uses a cylindrical power lens, so that optical signals output to each boat can be transmitted to the optical waveguide circuit having a large number of output boats. 7 can be measured at the same time, making it possible to diagnose such a light wave circuit in a short time.

[Example 1 Hereinafter, the present invention will be explained in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a configuration diagram showing a Michelson interferometer type shape measuring device using a rotating mirror as a first embodiment of the present invention.

Here, 1 is an incoherent light source, 2 and 5 are lenses,
7 is a half mirror, 8 is a total reflection mirror 9 is a mirror holder that holds the total reflection mirror 8, 10 is a rotation axis that rotates the mirror holder 9, 11 is a rotation motor that rotates the rotation axis lO, and l4 is a rotation axis that is vertical. 17 is a photodetector, 18 is a spectrum analyzer, 19 is a waveform recorder, and 2l is a measurement object having a two-dimensional shape. . The total reflection mirror 8 has a rotating shaft 10 vertically protruding from the stage 14.
is attached to the mirror holder 9 via a mirror holder 9, and is rotated by a rotation motor 1l.

Hereinafter, the coordinate axes on the optical system in the first embodiment will be explained using the coordinates x-y shown in FIG. In the coordinate x-y, the X-axis and the y-axis are parallel to the light flux emitted from the light source 1 and the light flux incident on the photodetector l7, respectively,
The y-axis passes through the center of rotation of the rotating shaft 10, and the origin O is on the extension of the reflective surface of the half mirror 7.

The incoherent light from the light source 1 is turned into a parallel beam of diameter (L2-LL) by the lens 2, and the y-axis is aligned with a straight line (0,
Ll) − (0, L2>), the straight line (Ll, Ll) − (L2
, L2) is branched into two. One of the branched light beams is irradiated onto the measuring object 2l, and its vertically reflected light enters the half mirror 7 again as a signal light. The other branched light beam is reflected when the rotating total reflection mirror 8 becomes perpendicular to the optical axis.
The reference light enters the half mirror 7 and is combined with the signal light. The combined light has the X axis as a straight line (Ll, 0) −
It crosses at the (L2, O) portion and is focused by the lens 5 onto the photodetector l7.

Looking at the light that crosses the y-axis at the point (0, L), it is split into two at the point (L, L) in the half mirror 7, and one branched light is at the point (D, L) on the measurement object 21. reflected. The other branched light is reflected at the point (L, D') of the total reflection mirror 8. When the stage 14 sweeps the total reflection mirror 8, these two reflected lights interfere at a position where the optical path lengths match (D=D'). At this time, the reflected light undergoes a Doppler shift due to the rotational movement of the total reflection mirror 8 and the linear movement of the stage 14, and a beat of a frequency corresponding to the shift amount is generated in the interference light intensity.

The amount of frequency shift fdr caused by Doppler shift due to rotational motion is the total reflection mirror 8 when the rotational speed of the rotational axis is fm.
The speed Vr(L) of Vr(L) varies depending on the distance L from the center of rotation.
(L) = 2 7C fmL, so the frequency shift amount fdr (L) = 2Vr/circle = 4K f
It is mL/9 and depends on the distance L.

On the other hand, when the sweep speed of the stage in the optical axis direction is Vs, the frequency shift amount fds due to linear motion is independent of L.
ds = 2Vs/λ.

These two frequency shifts cause a beat of frequency fdr(L)±fds in the interference light intensity, but the sweep speed is low compared to the rotation speed of the total reflection mirror 8, for example, fm=10rps, Ll= = 1 am, L2=
2 cm, Vs=40μm/s. L=1.
When it is 3 μm, fdr(Ll) = I M
Hz. fdr(L2)=2MHz. fds=60
Hz, fdr ) fds. Therefore, considering the measurement performance of the spectrum analyzer 18,
The measured beat frequency can be regarded as fdr (L).

Therefore, while the stage 14 sweeps the total reflection mirror 8 in the direction of the optical axis indicated by the arrow, the spectrum analyzer 18
If the frequency is swept from fd(LL) to fd(L2) and the light intensity is measured, the two-dimensional shape of the measurement object 21 is determined by the waveform recorder 19 as shown in FIG. Can be measured with a sweep of

In addition, in FIG. 3, L2≦2×L1. fd(L2)≦2
×fd(Ll) so that the sum component of the two frequencies does not fall into the measurement frequency region. Furthermore, the measured intensity in the figure has been corrected for the reflectance due to the light intensity distribution of parallel light and the shape of the object to be measured.

(Example 2) FIG. 4 shows a total reflection mirror according to a second embodiment of the present invention in which the horizontal direction of the total reflection mirror rotation part of the Michelson interferometer type shape measuring device according to the first embodiment is changed. It is a partial block diagram.

In FIG. 4, 8 is a total reflection mirror, 9 is a mirror holder, 1O is a rotation axis, 12 is an electrostrictive vibrator, 13 is a spring, 14
is the stage. In the figure, the coordinate axis X is perpendicular to the optical axis, and the center of rotation is the origin O.

In this embodiment, instead of continuously rotating the total reflection mirror 8 about the rotation axis 10, the electrostrictive vibrator l2 and the spring l3 are rotated about the rotation axis 10 and a straight line perpendicular to the optical axis. By reciprocating the mirror 8, the total reflected light is given a frequency shift amount due to Doppler shift corresponding to the reflection position, and is used as a reference light. Then, as in the first embodiment, this reference light is caused to interfere with the signal light obtained by being reflected from the object 2l to measure the two-dimensional shape.

Here, when the electrostrictive vibrator l2 drives the total reflection mirror 8 in the portion of is fd (L) = 2vmL/L2/e. Here, for example, vm=1 mm/s. L1=l
cm, L2=2cm, L=1.3μm, f
d(Ll) = 0. 77k}Iz. fd(L2)=
It is 1.54kHz.

(Embodiment 3) FIG. 5 is a configuration diagram showing an optical waveguide circuit diagnostic apparatus of the present invention using a rotating mirror type interferometer as a third embodiment of the present invention. In this embodiment, a leading wave circuit diagnostic apparatus using an interferometer in the form of a Matsuha-Zehnder interferometer will be described.

In FIG. 5, 1 is an incoherent light source, 2, 4 .
5 is a lens, 7 is a half mirror, 8 is a total reflection mirror 9
1 is a mirror holder that holds the total reflection mirror 8, 10 is a rotation axis for rotating the mirror holder 9, and 14 is a stage with a rotation axis 10 vertically protruding, and the total reflection mirror 8 can be moved in the direction of the optical axis indicated by the arrow. , 15 is big tail Tl, T2, T3
, T4 and an optical fiber coupler having an optical coupling part Cf, l
6 is a cylindrical lens, 17 is a photodetector, l8 is a spectrum analyzer, l9 is a waveform recorder, 22 is a light guide path, that is, paths G11, G12, G21, G22.
, G31, G32 and 2×2 ports PI, P2 . P3
, P4, and two optical coupling parts CI and C2.

The light emitted from the light source 1 enters the big tail T1 at one end of the optical fiber coupler 15 via the lens 2, and is split into two at the optical coupling part Cf. On the other hand, the branched light is transmitted by the big-tilt T of the optical fiber coupler l5.
3 from the boat PI to the optical waveguide circuit 22 via the path Gll→G21-hG31. Gll-G22→G
31 from the boat P3 and from the path Gll
-G21→G32, Gll-G22→G32, the light is emitted from the boat P4 as a signal light with a delay according to each propagation optical path length, is made into parallel light by the cylindrical lens 16, and then is made into a parallel light by a half mirror. 7.

The other branched light is used as a reference light by an optical fiber power puller.
The light is parallelized from the big tail T4 of No. 5 through the lens 4, and then enters the half mirror 7 perpendicularly to the light emitted from the optical waveguide circuit 22. The transmitted light from the half mirror 7 is reflected by a rotary total reflection mirror 8 similar to that shown in Embodiment 1 or 2, becomes a reference light, returns to the half mirror 7, and receives the signal light emitted from the optical waveguide circuit k2. is combined with The combined light output is transmitted to the photodetector 1 via the lens 5.
Light is received at 7. By subjecting the photodetection output from the photodetector 17 to the same signal processing as in Example 1, measurement results as shown in FIG. 6 can be obtained.

In the measurement results shown in Figure 6, the path Gll→G21→G3
1. G11→G22→G31. Gll→G21-G3
2. The intensity of the propagating light from Gll→G22-G32 is A, B, C. Corresponds to D. According to this embodiment, these four measurements can be performed simultaneously with one mirror sweep.

〔Effect of the invention〕

As is clear from the above, in the interferometer and interferometric measurement method of the present invention, a rotating reflecting mirror is used, and the amount of frequency shift due to the Doppler effect is given to the light reflected by the reflecting mirror according to the reflection position, so that the light can be divided by frequency. By measuring the intensity, there is an advantage that the distance in the direction perpendicular to the optical axis can be measured for objects having various two-dimensional shapes.

The optical waveguide circuit diagnostic device of the present invention uses the above-mentioned interferometer and a cylindrical power lens to simultaneously measure the optical signals output from each boat in an optical waveguide circuit having a large number of output boats. Therefore, such optical waveguide circuits can be diagnosed in a short time.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a Michelson interferometer type shape measuring device as a first embodiment of the present invention, FIG. 2 is an explanatory diagram of coordinate axes on the optical system in the first embodiment, and FIG. An explanatory diagram of the measurement results according to the first embodiment, FIG. 4 is a diagram showing a part of the rotating reflection mirror in the Michelson interferometric shape measuring device as the second embodiment, and FIG. 5 is a diagram showing the third embodiment. FIG. 6 is an explanatory diagram of measurement results according to the third embodiment; FIG. 7 is a diagram illustrating a conventional example of a Michelson interferometer; FIG. 8 7 is an explanatory diagram of the measurement results according to the conventional example shown in FIG. 7, and FIG. 9 is a diagram showing the structure of the conventional example of the light guide circuit diagnostic device. 1... Incoherent light source, 2.3, 4.5... Lens, 6... Optical fiber, 7... Half mirror 8... Total reflection mirror 9... Mirror holder, lO...・Rotating shaft, 11... Rotating motor, 12... Electrostrictive vibrator, 13... Spring, 14... Stage, ]5... Optical fiber coupler, 16... Cylindrical lens, l7. ...Photodetector, 18...Spectrum analyzer, l9...Waveform recorder, 20. 21... Sample for shape measurement, 22... Light guiding circuit having a 2×2 boat and two optical coupling parts.

Claims (1)

[Claims] 1) splitting the incoherent light into two, making one of the branched lights incident on the object to be measured, and using the reflected light obtained as the signal light;
and the other branched light are made incident on a reflective mirror that is movable in the optical axis direction, and the reflected light obtained is used as a reference light, and the signal light and the reference light interfere with each other.In the interference measurement method, the reflective mirror is rotated. and giving the reference light a frequency shift amount due to the Doppler effect according to the distance from the rotation center within the same wavefront when reflected by the reflection mirror, and the light intensity generated by interfering the reference light with the signal light. 1. An interference measurement method comprising: detecting the intensity of a beat signal in each beat frequency; and measuring a distance in a direction perpendicular to an optical axis of the object in correspondence with the beat frequency. 2) An incoherent light source, a reflecting mirror movable in the optical axis direction, and an incoherent light source from the incoherent light source.
the reflected light obtained by making one branched light incident on the object to be measured is used as a signal light, and the reflected light obtained by making the other branched light incident on the reflecting mirror is used as a reference light;
an optical means for causing interference between the signal light and the reference light; a reflecting mirror rotating means for rotating the reflecting mirror; and receiving an interference signal light between the signal light and the reference light extracted from the optical means; 1. An interferometer comprising: detection means for detecting light intensity for each beat frequency from the interference signal light. 3) In an optical waveguide circuit diagnostic device that measures the branching ratio of optical branching parts of an optical waveguide circuit and/or the optical path length difference between the optical branching parts, an incoherent light source, a reflective mirror movable in the optical axis direction, and an interference means, and incoherent light from the incoherent light source,
an optical fiber coupler type branching means that branches into two and makes one branched light enter the optical waveguide circuit and guide the other branched light to the reflection mirror; and a plurality of signal lights emitted from the optical waveguide circuit simultaneously. an optical means that receives light and guides it to the interference means; a reflection mirror rotation means that rotates the reflection mirror; a reflection light from the reflection mirror is made incident on the interference means as a reference beam, and the interference means converts the light into the signal light; An optical waveguide circuit diagnostic apparatus comprising: a detection means for receiving interference signal light obtained by interfering with the reference light and detecting light intensity for each beat frequency from the interference signal light.