JPH0225719A - Optical interference signal extractor - Google Patents

Abstract

PURPOSE:To eliminate noise based on an optical power fluctuation which a light beam to be measured by providing a second light receiving device for detecting optical power of the light beam to be measured in addition to a light receiving device for receiving an interference light, and dividing an optical interference signal by a photodetecting signal obtained by said second light receiving device. CONSTITUTION:The title device is provided with the second light receiving device for detecting optical power of a light beam to be measured 11. When a light source 10 is excited by a commercial power source, noise of 50 to 60Hz or 100 to 120Hz is mixed in. Also, in the case of DC lighting, it is accompanied by the optical power fluctuation of a low frequency generated by a power supply voltage fluctuation of a DC power source. This optical power fluctuation is fetched as a signal SB outputted from the second light receiving device 40. Subsequently, an optical interference signal SA outputted from a first light receiving device 30 and the detecting signal SB outputted from the second light receiving device 40 are applied to a divider 50, and an interference signal SC is outputted. As for this interference signal SC, its S/N is satisfactory, and a wavelength distribution of the light beam to be measured 11 can be derived exactly.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an optical interference signal extraction device used for measuring wavelength distribution of light to be measured.

"Prior Art" FIG. 4 shows a conventionally used optical interference signal extraction device. In the figure, reference numeral 10 indicates a light source that emits light to be measured, and reference numeral 20 indicates an optical interferometer capable of sweeping the optical path difference. Although a Michelson interferometer is shown in this example, a Fabry-Perot interferometer can also be used.

The Michelson interferometer 20 is composed of a half mirror 21 for performing demultiplexing and multiplexing operations, a fixed mirror 22 for forming a fixed optical path 24, and a movable mirror 23 for forming a variable optical path 25.

The light to be measured 11 emitted from the light source 10 is passed through the half mirror 2
1 into a fixed optical path 24 and a variable optical path 25,
The light passing through the fixed optical path 24 and the movable optical path 25 is combined again by the half mirror 21, and the combined light is converted into an electrical signal by the optical receiver 30.

Fixed optical path 24 when multiplexed in half mirror 21
The light passing through the variable optical path 25 and the light passing through the variable optical path 25 are given a phase difference due to the difference in optical path difference, and this difference in phase causes interference. Light interference occurs in synchronization with the movement of the movable mirror 23. Therefore, the light output from the optical interferometer 20 is interference light, and by converting this interference light into an electrical signal by the light receiver 30, an interference signal as shown in FIG. 5 can be obtained. By frequency-analyzing this interference signal, the spectrum of the light to be measured 11 can be drawn.

"Problem to be Solved by the Invention" The interference signal shown in FIG. 5 shows a waveform when the optical power of the light to be measured 11 is stable. In this way, the light to be measured 11
If the optical power is stable, an interference signal with a good S/N ratio can be obtained.

On the other hand, if the optical power of the light to be measured 11 fluctuates as shown in Fig. 6, the S/N ratio of the interference signal becomes poor, and therefore, when the spectrum is drawn by frequency analysis, the The fluctuation component of the optical power of the light to be measured 11 is also displayed as a spectrum, and the light to be measured 11
The disadvantage is that it is not possible to accurately measure the wavelength distribution of

An object of the present invention is to provide an optical interference extraction device that can remove noise based on optical power fluctuations of light to be measured.

"Means for Solving the Problem" In the present invention, a second light receiver that detects the optical power of the light to be measured is provided separately from the light receiver that receives the interference light, and the second light receiver that detects the optical power of the light to be measured is provided.
The configuration is such that the optical interference signal is divided by the light reception signal obtained by the light receiver.

According to the configuration of the present invention, the light reception signal received by the second light receiver can be treated as a fluctuation signal of the optical power of the light to be measured. Therefore, by dividing the optical interference signal by this received light signal, fluctuations in the optical power of the light to be measured can be removed from the optical interference signal.

Therefore, according to the optical interference signal extraction device of the present invention, it is possible to obtain an optical interference signal with a good signal-to-noise ratio, and it is possible to provide an optical spectrum analyzer that can accurately measure the wavelength distribution of light.

"Example" FIG. 1 shows an embodiment of the present invention.

In FIG. 1, parts corresponding to those in FIG. 4 are given the same reference numerals, and explanations of the overlapping parts are omitted. establish. In other words, the light source 1 that emits the light to be measured 11
0 and the optical interferometer 20, a part of the light given to the optical interferometer 20 is branched by the half mirror 12, and this branched light is received by the second light receiver 40. Shows the case where it is configured.

The signal SB output from the second light receiver 40 is the light 11 to be measured.
This is a signal representing the optical power fluctuation of . In other words, the light source 10
50 to 60Hz when excited by commercial power
Alternatively, noise of 100 to 120 Hz is mixed. Also,
In the case of DC lighting, low frequency optical power fluctuations occur due to fluctuations in the power supply voltage of the DC power supply. This optical power fluctuation is extracted as a signal SB output from the second light receiver 40.

The optical interference signal SA output from the first optical receiver 30 and the second
The detection signal SB output from the light receiver 40 is applied to a divider 50, and the divider 50 calculates SA/SB.

Since the optical interference signal SA shown in FIG. 2A includes the fluctuation component SB of the measured light 11 shown in FIG. 2B, the divider 5
The interference signal SC shown in FIG. 2C from which the fluctuation component SB has been removed is output as the output of 0.

This interference signal SC has a good signal-to-noise ratio, and the wavelength distribution of the light to be measured 11 can be accurately determined.

FIG. 3 shows another embodiment of the invention. In this embodiment, in addition to the light to be measured 11, a reference light 61 is provided from a reference source 60. The reference light source 60 uses light having narrow spectrum characteristics, such as a helium-neon laser. Reference light 6
1 also has a fixed optical path 24 and a variable optical path 2 inside the optical interferometer 20.
5, is combined by a nof mirror 21, extracted as interference light, and received by a light receiver 62.

By using a light source that emits light with narrow spectrum characteristics as the reference light source 60, it is possible to obtain a signal whose amplitude value does not vary greatly with the movement of the movable mirror 23 in the optical interference signal SD output from the light receiver 61. This reference optical interference signal is applied to the N multiplier 62, the signal multiplied by N is taken out as a sampling clock, and this sampling clock is applied to the AD converters 31 and 41,
The interference light and the detection signal of the optical power fluctuation of the light to be measured 11 are given to the AD converter 41, and the digital data SA and SB which are AD-converted by these AD converters 31 and 41 are sent to the divider 50.
and calculate SA/SB.

Note that this example shows a case where the optical interference signal SA is multiplied by a coefficient bo. This coefficient bo is, for example, the value of the optical power of the measured light 11 in the vicinity of zero optical path difference between the fixed optical path 24 and the variable optical path 25 in the optical interferometer 20, or the value of the optical power of the measured light 11 in the vicinity of the optical path difference between the fixed optical path 24 and the variable optical path 25, or the area before and after the point where the optical path difference is zero. It can be an average value of optical power.

As a result, in this example, this is equivalent to multiplying the optical interference signal SA by the ratio of the noise component SB, which changes every moment with the passage of time, and the optical power 1)++ near the zero optical path difference point.

Even if a division operation is performed after AD conversion in this manner, the fluctuation component can be removed.

In this embodiment, the signal sC output from the division circuit 50 is applied to the frequency analyzer 51 and the envelope detector 52,
The output of the frequency analyzer 51 causes the optical spectrum of the light to be measured 11 to be displayed on the display 53, and the envelope detector 5
A case is shown in which a configuration is added to display the presence or absence of coherence on the display 54 based on the output of step 2.

In addition, the AD conversion output of the A and D converters 4J is displayed on the display 55.
It is possible to observe the amplitude fluctuation of the light to be measured 11 by displaying the .

"Effects of the Invention" As described above, according to the present invention, even if the optical power of the light to be measured 11 fluctuates, the optical spectrum can be measured by removing the fluctuation component.

Therefore, it is possible to display an optical spectrum that is not mixed with optical power fluctuations of the light to be measured, so that accurate optical spectrum measurements can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the invention in detail,
FIG. 3 is a block diagram for explaining a modified embodiment of the present invention, FIG. 4 is a block diagram for explaining the conventional technique, and FIGS. 5 and 6 are for explaining the waveform of an optical interference signal. FIG. IO=light source to be measured, 11; light to be measured, 20: optical interferometer,
21: Half mirror 22: Fixed mirror 23; Movable mirror
24: fixed optical path, 25: variable optical path, 30: first light receiver,
40: second light receiver, 50: divider. Crucible 1 hard

Claims (1)

[Claims] (1) A. An optical interferometer capable of sweeping the optical path difference; B. A first light receiver that converts the output light of this optical interferometer into an electrical signal; C. Measured light input to the optical interferometer. An optical interference extraction device comprising: a second light receiver that converts the amount of light of the first light receiver into an electrical signal; D. a divider that divides the output signal of the first light receiver by the output signal of the second light receiver.