JPH07128008A - Interferometer - Google Patents

Abstract

PURPOSE:To achieve use over wide wavelength range with a simple and inexpensive structure by serially connecting two optical couplers without any wavelength dependency of a specific branch ratio. CONSTITUTION:For example. two single modes 1313-1550WIC 21 and 22 are serially connected as an optical fiber coupler (WIC) with a branch ratio of 50%, without any wavelength dependency at a wavelength region of 1.3-1.55mum and then a light path difference DELTAL is created at a light side, where the light path length changes according to the physical quantity such as stress given to a sensor. Then. for example, the light path difference DELTAL is set to 1.38mm. light with a wavelength of 1.3-1.55mum is applied. and then output p1 and P2 applied from the WIC 21 and 22 are measured by light reception elements 17 and 18, thus measuring the physical quantity such as stress given to the sensor. As a result. the title interferometer operates as the interferometer in a wide range with a wavelength of 1.3-1.55mum and can be used as a light branching wave synthesizer with an extremely small wavelength difference of DELTAL.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer, and more particularly to a Mach-Zehnder type interferometer using an optical fiber coupler.

[0002]

2. Description of the Related Art Conventionally, known Mach-Zehnder type interferometers are those using optical components such as a beam splitter and a Hafmylar, and those using a so-called 3 dB optical coupler having a branching ratio of 50%. Has been.

The former, as shown in FIG. 6, divides a light 1 indicated by an arrow into two lights 3 and 4 by a beam splitter-2,
The respective lights are reflected by the mirrors 5 and 6, and the half mirror
7, the interference light of the reflected light 3B of the light 3 and the transmitted light 4A of the light 4 goes to the light receiving element 8, and the interference light of the transmitted light 3A of the light 3 and the reflected light 4B of the light 4 goes to the light receiving element 9. When the sensor 10 changes the optical path length of the light 4 to enter a physical quantity such as a stress applied to the sensor 10 placed on the optical path of the light 4, the light 3
It is measured by interference with.

However, in such an interferometer, it is necessary to dispose optical components such as a beam splitter and a half mirror with high precision, which is complicated and expensive.

On the other hand, the latter has a branching ratio of 5 as shown in FIG.
The 0% so-called 3 dB optical fiber couplers 11 and 12 are connected in series, and the light 13 incident at the output of P ₀ is 3 dB.
The optical fiber coupler 11 splits the light into 14 and 15,
Reference numeral 4 indicates the outputs P ₁ and P emitted from the 3 dB optical fiber coupler 12 according to the interference conditions after the optical path length changes due to the physical quantity such as stress applied to the sensor 16 and then enters the 3 dB optical fiber coupler 12. ₂ is the light receiving element 17, 1
8, the physical quantity such as the stress applied to the sensor 15 is measured.

However, such an interferometer has a problem that the wavelength range in which the 3 dB optical fiber coupler exhibits a branching ratio of 50% is narrow.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an interferometer having a wide usable wavelength range and a simple structure.

[0008]

DISCLOSURE OF THE INVENTION As a result of earnest studies on widening the wavelength range used, the present inventor has replaced an interferometer using a 3 dB optical coupler with a light having no wavelength dependence in place of the 3 dB optical coupler. Coupler (WIC = Wavelength Indep
The present invention has been accomplished on the assumption that the use wavelength region can be widened by using an endent coupler.

That is, the present invention provides an interferometer characterized in that two optical couplers having a branching ratio of 50% and having no wavelength dependence are connected in series.

The structure of the interferometer of the present invention is shown in FIG. Figure 6
Compared with the interferometer shown by, the 3 dB optical fiber coupler 11,
12 is replaced by an optical coupler without wavelength dependence (WIC = Wa
velength Independent Couplers) 21 and 22 are used, and the same numbers are used in the figure as those in FIG.

In the interferometer of the present invention, for example, 1.3-1.
Branching ratio 5 with no wavelength dependence in the wavelength region of 55 μm
By using 0% of the optical couplers 21 and 22, 1.
It can be used as an interferometer in the wavelength range of 3 to 1.55 μm.

Further, the interferometer of the present invention is an optical demultiplexer-multiplexer (WDM = Wavelength division) having a very small wavelength difference.
It can also be used as a multiplexer / demultiplexer), for example, it can demultiplex and combine lights of 1.550 μm and 1.551 μm, and simultaneously can demultiplex and combine lights of 1.300 μm and 1.301 μm.

[0013]

EXAMPLE Single mode 13 manufactured by Nikko Kyokushi Co., Ltd., which is commercially available as an optical fiber coupler having a branching ratio of 50% and having no wavelength dependence in the wavelength region of 1.3 to 1.55 μm.
As shown in FIG. 2, using a 13-1550 WIC, light 1
The optical path difference of ΔL is provided on the fourth side. First, with ΔL set to 1.38 mm, light having a wavelength of 1.3 to 1.55 μm was introduced, and the outputs of P ₁ and P ₂ were measured. The result is the wavelength splitting ratio (Splitting Ratio) = 20log (P
₁ / P ₂ ) is shown in FIGS.

Further, the same measurement was performed with ΔL set to 1 mm and 10 mm. Table 1 shows a summary of the above measurement results by the wavelength difference (channel spacing) ΔΛ between peaks and valleys in FIGS.

[Table 1]

From the above results, the interferometer of the present invention operates as an interferometer in a wide wavelength range of 1.3 to 1.55 μm, and the optical demultiplexer-multiplexer (WDM) having a very small wavelength difference.
= Wavelength division multiplexer / demultiplexer)
Can also be used as, for example, 1.550 μm and 1.551
At the same time that the light of μm can be demultiplexed and combined,
It can be seen that the light of 1.301 μm can be demultiplexed and combined.

[0016]

As described above, according to the present invention,
An interferometer that can be used in a wide wavelength range is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an interferometer of the present invention.

FIG. 2 is a diagram showing an example of the present invention.

FIG. 3 is a diagram showing wavelength separation in the vicinity of 1.5 μm by the interferometer of the present invention.

FIG. 4 is a diagram showing wavelength separation in the vicinity of 1.4 μm by the interferometer of the present invention.

FIG. 5 is a diagram showing wavelength separation in the vicinity of 1.3 μm by the interferometer of the present invention.

FIG. 6 is a diagram showing an outline of an interferometer using a conventional optical component.

FIG. 7 is a diagram showing an outline of an interferometer using a conventional 3 dB optical fiber coupler.

Claims (1)

[Claims] 1. An interferometer characterized in that two optical couplers having a branching ratio of 50% and having no wavelength dependence are connected in series.