JPH04225134A - Method and apparatus for measuring reflecting point of optical part - Google Patents

Abstract

PURPOSE:To measure the position of low reflectivity of -100dB or less in an optical part and the reflectivity. CONSTITUTION:The incoherent light from an incoherent light source 1 is split. One is cast on an optical part 19. The obtained reflected light is made to be the measuring light. The other is made to be the reference light. The length of the light path of at least one of the reference light and the measuring light is relatively changed, 2 and the reference light and the measuring light are made to interfere to each other. Thus, the two interference lights are obtained. The intensities of two interference lights are individually detected, and the difference between two detected outputs is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring reflection points of optical components used for measuring the positions and reflectances of reflection points in optical components for optical communications.

0002

2. Description of the Related Art An example of the configuration of a conventional optical component reflection point measuring device is shown in FIGS. 5 and 6.

In FIG. 5, 1 is an incoherent light source, 2 is a beam splitter, 11 is a movable plane mirror, and 13 is a movable plane mirror.
is a photodetector, 15 is an amplifier, 17 is a frequency filter, 1
8 is a photodetector output monitor, and 19 is an optical component.

[0004] The incoherent light source 1 is arranged on an extension line of the moving direction of the movable plane mirror 11, which is indicated by an arrow A in the figure. A beam splitter 2 is arranged between the incoherent light source 1 and the movable plane mirror 11. An optical component 19 to be measured and a photodetector 13 are placed facing each other with the beam splitter 2 in between. The detection output from this photodetector 13 is supplied to a frequency filter 17 via an amplifier 15, and the filter output is supplied to a photodetector output monitor 18.

The light emitted from the incoherent light source 1 with a center wavelength λ is split by a beam splitter 2, one of which is irradiated onto an optical component 19 as a measurement light, and the other is irradiated with a movable plane mirror 11 as a reference light. . The reflected light from the optical component 19 and the reference light are again combined by the above-mentioned beam splitter 2, the combined light intensity of this combined light is detected by the photodetector 13, and this detection signal is amplified by the amplifier 15. . The interference signal has a frequency f with respect to the movable mirror speed v.
=2v/λ AC signal.

Therefore, from the detection signal, the frequency filter 1
7 extracts the frequency f component, and the output monitor 18 measures the power or the square value of the voltage amplitude of the extracted signal. This measurement is proportional to the reflectance at a location in the optical component that is away from the bifurcation point by an optical distance equal to the optical distance from the bifurcation point to the movable mirror 11.

For example, when measuring an optical component 19 having a scattering point c in the optical waveguide shown in FIG.
(=mirror speed x time), and the output voltage V at that time is plotted on the vertical axis. As shown in Figure 7, the input end a
, a waveform vibrating at a frequency f is obtained at the emission end b and the scattering point c. The peak value Vmax of the output voltage V is determined by the complex amplitude Emi of the light incident on the movable mirror 5 and the optical component 19.
Using Esample and the reflection coefficient r of each point in the optical component 19, Vmax=c|Emirror・r
It is expressed as Esample* |. Here, c is a proportionality coefficient, and Esample* is the complex conjugate of Esample. Since the reflectance R at each point is proportional to r2, plot the output power value measured by a level measuring device or the squared value of the measured output voltage on the vertical axis and the position of the movable mirror on the horizontal axis. As a result, the results shown in FIG. 8 are obtained. Here, the vertical axis is expressed logarithmically, and the reflectance is calibrated from the measured value of a reflective object whose reflectance is known. The reflection point position and reflectance are measured from this waveform.

[0008]

[Problems to be Solved by the Invention] However, in the conventional optical component reflection point measuring device, the measurement limit of reflectance is -100 dB due to light intensity noise from the light source, which does not meet the required sensitivity for optical component diagnosis. It wasn't.

An object of the present invention is to solve the above-mentioned technical problems and to provide a highly sensitive optical component reflection point measuring device capable of measuring reflection points with a low reflectance of -100 dB or less in optical components. be.

0010

[Means for Solving the Problems] In order to achieve such an object, the present invention splits incoherent light from an incoherent light source, irradiates one of them onto an optical component, and measures the reflected light obtained. The other incoherent light is used as a reference light, and the reference light and the measurement light are made to interfere with each other while relatively changing the optical path length of at least one of the reference light and the measurement light. Obtain the interference light, and the 2
It is characterized in that the light intensities of the two interference lights are detected individually, and the difference between the two obtained detection outputs is determined.

The present invention also provides an incoherent light source, branching the incoherent light from the incoherent light source, irradiating one of the incoherent lights to an optical component, and using the reflected light as reflection point measuring light, The other incoherent light is used as a reference light, and the optical path length of at least one of the reference light and the reflection point measurement light can be relatively changed, so that the reference light and the reflection point measurement light interfere with each other. an interferometer that outputs two interference lights, a light intensity detection means for individually detecting the light intensities of the two interference lights, and a means for outputting a difference between the light intensity outputs obtained from the light intensity detection means. It is characterized by having the following.

Further, the present invention includes an incoherent light source, branching the incoherent light from the incoherent light source, irradiating one of the incoherent lights to an optical component, and using the reflected light as reflection point measuring light, An interferometer that irradiates the other incoherent light onto a movable mirror, uses the reflected light as a reference light, causes the reference light and the reflection point measurement light to interfere in a beam splitter, and outputs two interference lights from the beam splitter. It is characterized by comprising: a light intensity detecting means for individually detecting the light intensities of the two interference lights; and a means for outputting a difference between the light intensity outputs obtained from the light intensity detecting means.

[0013]

[Operation] In the present invention, the phase of the light is reversed by 180° between the two combined lights, that is, the interference lights, obtained by combining the reflected light from the optical component and the reference light, so that the interference signal obtained is While the phase is also reversed by 180°, the optical intensity noise is not reversed and remains in the same phase. Therefore, in the differential signal obtained from the optical intensities of two interference lights, the interference signal is doubled, but the optical intensity noise is almost eliminated, and the signal/noise ratio (S/N) is improved by about 20 dB. .

That is, according to the present invention, the light intensities of two combined lights obtained by combining the reflected light from the optical component and the reference light are detected, and the difference between these two detection outputs is output. , it is possible to emphasize the interference signal of opposite phase between the two detection outputs and remove the optical intensity noise component of the same phase. As a result, for reflection points with low reflectance such as -100 dB or less, It becomes possible to measure the position of the reflection point and the reflectance.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.

In FIG. 1, 1 is an incoherent light source, 2 and 4 are beam splitters, 5 is a movable wedge-shaped mirror, 6 is a fixed wedge-shaped mirror, 7 is a fixed plane mirror,
12 and 13 are photodetectors as light intensity detection means;
6 is a differential amplifier, 17 is a frequency filter, 18 is a photodetector output monitor, and 19 is an optical component. The monitor 18 can be configured, for example, by an oscilloscope or a combination of a computer, a digital oscilloscope, or an XY recorder. In this embodiment, the first beam splitter 2 and fixed plane mirror 7 described above constitute a first interferometer, and the second beam splitter 4, movable wedge-shaped mirror 5 and fixed wedge-shaped mirror 6 constitute a first interferometer. 2 interferometers are constructed.

In the optical component reflection point measuring device of this example,
The light emitted from the incoherent light source 1 described above is the first
The beam is split by the beam splitter 2 of the interferometer, one of which is irradiated onto the optical component 19, and the other is irradiated onto the fixed plane mirror 7. The reflected light from the optical component 19 (reflection point measurement light) and the reflected light from the fixed plane mirror 7 (reference light) are combined again by the beam splitter 2 described above. This combined light is split again by the beam splitter 4 of the second interferometer, and one is guided to a movable wedge-shaped mirror 5 and the other to a fixed wedge-shaped mirror 6, respectively. The respective reflected lights from both wedge-shaped mirrors 5 and 6 are combined at a position different from the above-mentioned branch point of the beam splitter 4.

Here, by moving the movable wedge-shaped mirror 5 along the direction of arrow B in FIG.
The propagation optical path lengths of the reflected light from the mirror 9 and the reflected light (reference light) from the fixed plane mirror 7 are adjusted to cause the reflected light from both to interfere at the above-mentioned coupling point.

At this coupling point, two combined lights, that is, interference lights, are obtained, and the light intensities of these two combined lights are detected by the first photodetector 12 and the second photodetector 13, respectively. The detection outputs from the photodetectors 12 and 13 are supplied to the differential amplifier 16, the difference between the two outputs is taken and amplified, and the amplified output is passed through the frequency filter 17 to the output monitor 1.
8, and here, by determining the square value of the voltage amplitude or the power for the frequency f component in the differential output of the two interference signals corresponding to the two interference lights, the position of the reflection point and the reflectance can be determined. Obtain measurement output. The output voltage waveform and reflectance measurement waveform obtained by measuring the optical component 19 shown in FIG. 6 using the measuring device shown in FIG. 1 are shown in (B) in FIG. 3 and (B) in FIG. 4, respectively. . Comparing with (A) in FIG. 3 and (A) in FIG. 4 showing the results obtained by the conventional device shown in FIG.
The output voltage is doubled, the power is quadrupled (6dB increase), and the optical intensity noise component is almost removed, reducing the noise level to 15dB.
It can be seen that the value has decreased. As a result, the S/N improves by about 20 dB.

Between the detection outputs of the photodetectors 12 and 13, the interference signals are in opposite phases and the optical intensity noise components are in the same phase. Therefore, it is necessary to emphasize the opposite phases and remove the same phases. As a result, the output of the differential amplifier 16 becomes a signal with a high S/N ratio. Thereby, detection sensitivity can be improved.

In the above embodiment, the optical path length of the reference beam is changed by moving the wedge-shaped mirror 5, but the wedge-shaped mirror 6 is moved as shown by the broken line arrow in FIG. The optical path length of both lights may be changed, or the wedge-shaped mirrors 5 and 6 may be moved together to relatively change the optical path lengths of both lights. In short, it is sufficient if both lights can be made to interfere with each other.

FIG. 2 shows another embodiment of the invention.

In FIG. 2, 3 is a beam splitter, 8
, 9 and 10 are fixed plane mirrors, 14 is a balanced photodetector as a light intensity detection means, and 15 is an amplifier. In this embodiment, the beam splitters 2 and 3, the movable wedge mirror 5 and the fixed plane mirror 8 constitute one interferometer.

In the optical component reflection point measuring device of this example,
The emitted light from the above-described incoherent light source 1 is split by a beam splitter 2, one of which is further applied to an optical component 19 via a beam splitter 3, and the other is applied to a movable wedge-shaped mirror 5. The reflected light as reflection point measurement light from the optical component 19 is guided via the beam splitter 3 and the fixed plane mirror 8 to a position different from the above-mentioned branch point in the beam splitter 2, and at this position, the above-mentioned movable wedge-shaped mirror 5 It is combined with the reflected light as a reference light from.

Here, this movable wedge-shaped mirror 5 is shown in FIG.
By moving it along the direction of arrow B inside, the propagation optical path length of the reflected light from the optical component 19 and the reflected light from the movable wedge-shaped mirror 5 is adjusted, and both reflected lights are caused to interfere at the above-mentioned coupling point. .

At this coupling point, two coupled lights are obtained, and these two coupled lights are each coupled to a fixed plane mirror 9.
, 10 to one balanced photodetector 14, where the difference in light intensity between the two coupled lights is detected. This difference is amplified by an amplifier 15, passed through a frequency filter 17, and an output monitor 18 obtains a measurement output for the reflection point as the square value or power of the voltage amplitude of the interference signal.

In this embodiment as well, the interference signal is in opposite phase between the two detection outputs, and the optical intensity noise component is in the same phase. Therefore, by emphasizing the opposite phase and removing the same phase, a high A signal with an S/N ratio is obtained.

In the embodiment described above, the number of times the reference light passes through the beam splitter is one less than that of the first embodiment shown in FIG. 1, so the optical intensity of the detection signal is doubled. There is. Moreover, if the above-mentioned balanced photodetector 14 uses a photodetector with uniform photoelectric conversion efficiency,
Another advantage is that high noise removal characteristics can be expected.

[0030]

[Effects of the Invention] As explained above, according to the present invention,
The light intensity of the two combined lights obtained by combining the reflected light from the optical component and the reference light is detected, and the difference between these two detection outputs is output. It is possible to emphasize the phase interference signal and remove the optical intensity noise component of the same phase.This makes it possible to measure the position and reflectance of reflection points with low reflectance, such as -100 dB or less. becomes.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a first embodiment of an optical component reflection point measuring device of the present invention.

FIG. 2 is a diagram showing the configuration of a second embodiment of the optical component reflection point measuring device of the present invention.

FIG. 3 is a graph showing the waveform of the output voltage measured by the optical component reflection point measuring device.

FIG. 4 is a graph showing a waveform for measuring reflectance measured by an optical component reflection point measuring device.

FIG. 5 is a diagram showing an example of the configuration of a conventional optical component reflection point measuring device.

FIG. 6 is a diagram showing an example of the configuration of an optical component that is a target of reflection point measurement.

[Explanation of symbols]

1 Incoherent light source 2, 3, 4 Beam splitter 5. Movable wedge-shaped mirror 6 Fixed wedge mirror 7, 8, 9, 10 Fixed plane mirror 11 Movable plane mirror 12,13 Photodetector 14 Balanced photodetector 15 Amplifier 16 Differential amplifier 17 Frequency filter 18 Output monitor 19 Optical parts

Claims (3)

[Claims] 1. Incoherent light from an incoherent light source is split, one of which is irradiated onto an optical component, the resulting reflected light is used as measurement light, the other incoherent light is used as reference light, and the reference light and the While relatively changing the optical path length of at least one of the measurement lights, the reference light and the measurement light are caused to interfere with each other to obtain two interference lights, and the light intensities of the two interference lights are individually detected. A method for measuring a reflection point of an optical component, characterized in that the difference between the two obtained detection outputs is determined. 2. An incoherent light source; the incoherent light from the incoherent light source is branched, one incoherent light is irradiated onto an optical component, the reflected light is used as reflection point measurement light, and the other incoherent light is The light is used as a reference light, and the optical path length of at least one of the reference light and the reflection point measurement light can be relatively changed, and the reference light and the reflection point measurement light are made to interfere with each other to cause interference between the two. An interferometer that outputs light, a light intensity detection means that individually detects the light intensity of the two interference lights, and a means that outputs a difference between the light intensity outputs obtained from the light intensity detection means. An optical component reflection point measuring device characterized by: 3. An incoherent light source; the incoherent light from the incoherent light source is branched, one incoherent light is irradiated onto an optical component, the reflected light is used as reflection point measurement light, and the other incoherent light is an interferometer that irradiates a movable mirror with light, uses the reflected light as a reference light, causes the reference light and the reflection point measurement light to interfere in a beam splitter, and outputs two interference lights from the beam splitter; An optical component reflection point measuring device comprising a light intensity detection means for individually detecting the light intensity of two interference lights, and a means for outputting a difference between the light intensity outputs obtained from the light intensity detection means. .