JPH05313082A - Polarization direction switching unit - Google Patents

Abstract

PURPOSE:To evaluate a polarization characteristic of a waveguide type optical part precisely over a wide range of light wave length by installing one fiber of two polarization maintaining optical fibers on the other fiber in a condition of being twisted by 90 degrees. CONSTITUTION:A polarization direction switching unit is composed of N (optional positive integer) X two optical space switches 3, a 2X2 polarization holding photocoupler 12 and two polarization maintaining optical fibers 1 to connect these to each other. One polarization maintaining optical fiber 1 is installed on the other polarization maintaining optical fiber 1 in a condition of being twisted by 90 degrees. Thereby, the polarization direction of light incident on the photocoupler 12 becomes different on condition that through which the light is propagated among the two polarization maintaining optical fibers 1. Thereby, the polarization direction of an output light of the 2X2 polarization maintaining photocoupler 12 can be rotated by 90 degrees by switching the N - two optical space switches 3 to/from each other. Since a twist of the polarization maintaining optical fibers 1 is used this polarization direction switching unit as a polarization rotating mechanism, the dependency on a wave length is not required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization direction switching device for switching the polarization direction required for measuring the polarization characteristics of a passive optical circuit component such as an optical waveguide circuit component. It is mainly used for evaluation of products in the manufacture of waveguide type optical components for optical communication or optical information processing.

[0002]

2. Description of the Related Art In a passive optical circuit component such as an optical waveguide circuit, it is a very important subject to eliminate the polarization dependence of the component.

For example, a silica-based optical waveguide circuit component manufactured by depositing silica-based glass on the surface of a Si substrate is a practical passive device because of its good compatibility with an optical fiber and its small optical loss. Practical application as an optical circuit component is expected. The most important issue of such passive optical circuit components is
"The characteristics should not change depending on the polarization state of the input light." This is because most of the optical fibers that have already been installed are single mode optical fibers, and the polarization state of the propagating light is not stable due to the disturbance of the optical fiber. Therefore, if the passive optical circuit component for branching the propagated light or processing the signal has polarization dependency, its function is also unstable depending on the polarization state of the input light.

However, in general, an optical waveguide formed on the surface of a substrate has a birefringence having a principal axis in a direction parallel to or perpendicular to the substrate surface due to the anisotropy of its structure. That is, there is polarization dependence between TE polarized light having an electric field component in the direction parallel to the substrate surface and TM polarized light having an electric field component in the direction perpendicular to the substrate surface. The biggest challenge in putting the waveguide type optical component to practical use is to eliminate this polarization dependence.

As a method of eliminating the polarization dependence of the waveguide type optical component, a method of laser-trimming the stress-imparting film, a method of loading a different kind of thin film and the like have been proposed. However, in order to eliminate the polarization dependency with high accuracy, a measurement device that accurately and easily evaluates the polarization dependency is required.

Conventionally, there have been the following two methods for evaluating the polarization characteristics of a waveguide type optical component.

(Prior Art 1) A method in which a polarization-maintaining optical fiber with a thin-film polarizer is used as an input fiber and is mechanically rotated to evaluate the polarization characteristics of a waveguide type optical component.

(Prior Art 2) A polarization-maintaining optical fiber is used as an input fiber, a half-wave plate is inserted therein, and the angle thereof is mechanically rotated, whereby the waveguide type optical component is polarized. Method to evaluate wave characteristics.

FIG. 1 shows a schematic configuration of a polarization characteristic measuring apparatus adopting the above-mentioned conventional polarization characteristic evaluation method 1. Here, 20 is a light source with a wavelength of 1.3 μm, and 21 is a wavelength of 1.5
A 5 μm light source, 43 and 44 are polarization-maintaining optical fibers, 3 is an optical channel selector, and 42 is a polarization-maintaining optical fiber with a thin-film polarizer having a thin-film polarizer commercially available under the name “Lamipol” (trademark). , And 41 are optical fiber rotating devices. Further, 25 is a waveguide type optical component as a sample to be measured, 45 is a single mode optical fiber, and 31 is an optical power meter for measuring the optical insertion loss of the sample to be measured. In this conventional device, the polarization-maintaining optical fiber 42 with a Lamipole thin film polarizer is used as the input fiber of the sample 25 to be measured. As a result, the input polarization state of the sample 25 to be measured can be defined as the direct polarization, and the characteristics of the sample 25 to be measured can be evaluated. further,
By rotating the input optical fiber 42 by the optical fiber rotating device 41, the dependency of the measured sample 25 on the input polarization can be evaluated.

As shown by the reference numeral 53 in FIG. 2, the LAMIPOL (multilayer thin film polarizer) has a metal thin film and a dielectric thin film (S).
It is obtained by alternately stacking about 200 layers of 70 μm of iO ₂ ) and thinly cutting it out to a thickness of about 30 μm. When light passes through this thin film, light having an electric field component parallel to the metal thin film is absorbed, and light having an electric field component perpendicular to the metal thin film is transmitted. As a result, this thin film functions as a polarizer. The advantage of this thin film polarizer is that it is small and functions as a polarizer in a wide wavelength region ranging from 1.3 μm to 1.6 μm. As shown in FIG. 2, the metal film direction of the thin film polarizer 53 and the principal stress directions of the polarization maintaining optical fibers 51 and 52 are connected together so that a linear polarization is always generated from the output end face of the polarization maintaining optical fiber 52. Can output waves.

FIG. 3 shows a schematic configuration of a polarization characteristic measuring apparatus adopting the polarization characteristic evaluation method of the above-mentioned prior art 2. Here, 61 is a light source, 62 is a collimating lens, and 63 is 1 /
A two-wave plate, a condenser lens 64, and a polarization maintaining optical fiber 65. In this conventional device, the half-wave plate 63 is inserted into the input optical fiber 65 of the measured sample 25, and
By rotating the angle of the / 2 wavelength plate 63, the input polarization state of the measured sample 25 is changed, and its dependency is measured.

Therefore, first, a linearly polarized state is formed by the polarization maintaining optical fiber 42 with a thin film polarizer, the linearly polarized light is collimated by a collimating lens 62 into a parallel beam in the air, and then 1/2 is formed. The light passes through the wave plate 63, is focused by the condenser lens 64, and enters the polarization maintaining optical fiber 65. The polarization state at the output end of the polarization maintaining optical fiber 65 can be changed by rotating the ½ wavelength plate 63.

[0013]

The characteristic of the measuring device of the above-mentioned prior art 1 is that the polarization characteristic of the sample to be measured can be evaluated in a wide light wavelength range. However, in this measuring device, the input fiber 42 must be rotated in order to measure the polarization characteristic. There is a problem that it is difficult to precisely evaluate the polarization characteristics of the measured sample 25 due to the positional deviation of the input fiber 42 that is inevitably generated at this time.

Further, in the measuring device of the above-mentioned conventional technique 2, it is not necessary to move the input fiber 65 when switching the input polarization state to the measured sample 25. Therefore, since there is no change in the optical axis of the input light, if the optical loss when the half-wave plate 63 is rotated is measured beforehand, the measured sample 25
It is possible to precisely evaluate the polarization characteristics of. However,
Since this measuring device uses the wavelength plate 63, there is a problem that the wavelength of the light source that can be used is limited by the wavelength plate 63.

The object of the present invention is therefore to solve the problems of the prior arts 1 and 2.
By solving the problems in the conventional polarization characteristic evaluation method of the waveguide type optical component as shown in Fig. 4, the polarization characteristic of the waveguide type optical component can be set to a wide optical wavelength ranging from 1.3 μm to 1.6 μm. It is to provide a polarization direction switching device that can be evaluated accurately within a range.

[0016]

To achieve the above object, a polarization direction switching device of the present invention comprises an N × 2 optical space switch, a 2 × 2 polarization maintaining optical coupler, and two connecting them. And a polarization maintaining optical fiber of (1), and one of the two polarization maintaining optical fibers is attached by being twisted by 90 degrees with respect to the other fiber.

The present invention also provides, as one form thereof, the above-mentioned 2
The × 2 polarization maintaining optical coupler is a waveguide type wavelength independent coupler having a structure of a Mach-Zehnder interferometer, and a thin film polarizer is inserted in each of the two polarization maintaining optical fibers. Is characterized by.

[0018]

As described above, the polarization direction switching device of the present invention includes the N (arbitrary positive integer) × 2 optical space switch, the 2 × 2 polarization maintaining optical coupler, and the two connecting cables. It is composed of a polarization maintaining optical fiber and one polarization maintaining optical fiber is twisted by 90 degrees with respect to the other polarization maintaining optical fiber. Therefore, the polarization direction incident on the optical coupler differs by 90 degrees depending on which of the two polarization-maintaining optical fibers has propagated. Therefore, the polarization direction of the output light of the 2 × 2 polarization maintaining optical coupler can be rotated by 90 degrees by switching the N × 2 optical space switch. Since this polarization direction switching device uses the twist of the polarization maintaining optical fiber as a polarization rotation mechanism, it has no wavelength dependence.

Therefore, in the polarization characteristic evaluation device using the polarization direction switching device according to the present invention, an optical component (sample to be measured) to be evaluated when switching the polarization direction of the input light.
Since there is no relative position change between the input optical fiber and the input optical fiber, it is possible to evaluate the precise polarization characteristics of the sample to be measured, and there is no wavelength dependence in switching the polarization direction. Polarization characteristics can be evaluated.

[0020]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 4 shows a schematic configuration of a polarization direction switching device according to an embodiment of the present invention. The polarization direction switch of this example is
Polarization-maintaining optical fiber with three Lamipole thin-film polarizers connected to a light source (not shown) 2, Optical channel selector 3 using reflection mirror as 3 × 2 optical space switch 3, 2 × 2 Polarization-maintaining optical coupler Waveguide type wavelength independent coupler 1
2, and two polarization-maintaining optical fibers 1 with a lamipole thin film polarizer that connect these 3 and 12. Since the configuration of the LAMIPOL (trademark) thin film polarizer 13 is the same as that shown by the reference numeral 53 in FIG. 2, its details are omitted.

The waveguide type wavelength independent coupler 12 is composed of:
The one manufactured so as to have a binding rate of approximately 50% over 2 μm to 1.6 μm is used. This coupler is already K.K. "Mach-Zehnde" by Jinguji et al.
r Interferometer Type Opt
ical Waveguide Coupler Wi
th Wavelength-flattened C
oupling Ratio. "(Mach-Zehnder interferometer type optical waveguide coupler with wavelength smoothing coupling ratio) E
electron Lett. vol. 26, No. 1
7, p. 1326, 1990, embedded single mode glass waveguides 4, 5, 6, 7, 8, 9 using flame deposition, photolithography and reactive ion etching on a silicon substrate. Was produced. At this time, the core glass of this waveguide is doped with germanium so that the refractive index thereof is 0.3% higher than that of the surrounding clad glass. The pattern is a Mach-Zehnder interferometer, which includes two directional couplers 10 and 11, two asymmetrical arm waveguides 6 and 7, and two input / output waveguides 4, 5, and 8. , 9
It consists of

The characteristics of the waveguide type wavelength independent coupler 12 of FIG. 4 are shown in FIG. From this figure, the waveguide-type wavelength-independent coupler 12 has a wide wavelength range of 1.3 μm to 1.6 μm.
You can see that the binding rate is%. Further, since the waveguide type wavelength independent coupler 12 has birefringence in the waveguide, there is no mode conversion between the TE polarized wave and the TM polarized wave.

In the polarization-maintaining optical fibers 1 and 2 with a lamipole thin film polarizer, only light having an electric field component in the principal stress direction of the polarization-maintaining optical fiber is transmitted. 2 connecting the channel selector 3 and the waveguide type wavelength independent coupler 12
In the polarization-maintaining optical fiber 1 with a lamipole thin film polarizer of the present invention, one fiber is attached in a state in which the fiber is twisted by 90 degrees as compared with the other fiber, as shown by reference characters A and B in FIG. There is.

Next, the polarization direction switching operation in this embodiment shown in FIG. 4 will be described. Arbitrary light from a light source (not shown) passes through the polarization maintaining optical fiber 2 with a lamipole thin film polarizer and enters the optical channel selector 3 in a linearly polarized state. In the optical channel selector 3, the incident light can be output to either of the two output ports by moving the internal reflection mirror mechanically. At this time, the polarization mode in the waveguide type wavelength independent coupler 12 differs depending on which one of the polarization-maintaining optical fibers 1 with a lamipole thin film polarizer is output. However, since the coupling ratio of the waveguide type wavelength independent coupler 12 is always 50% regardless of the optical wavelength, the waveguide type wavelength independent coupler 12 can be used regardless of which LAMIPOL thin film polarizer-attached polarization maintaining optical fiber 1 is used. The output light intensity of the dependent coupler 12 is equal.

Therefore, the waveguide type wavelength independent coupler 12
With respect to the output light, the polarization direction can be switched without changing the light intensity by switching the optical channel selector 3. Moreover, since this polarization direction switching device does not use a wave plate or the like, it has a characteristic that it has no wavelength dependence. In reality, the coupling ratio of the waveguide type wavelength independent coupler 12 is slightly deviated from 50%. However, there is no problem because this can be corrected by taking a reference to be described later in advance.

FIG. 6 shows a schematic configuration of a polarization characteristic measuring apparatus according to the present invention, which incorporates the polarization direction switching device of FIG.
It is necessary to reduce the polarization dependence and wavelength dependence of passive optical circuit components as much as possible. For that purpose, a device that accurately measures the polarization characteristics in a wide wavelength range is required. FIG. 6 shows a measuring system according to the present invention for accurately measuring the polarization characteristics of a waveguide type optical component in a wide wavelength range.

The polarization characteristic measuring apparatus of this example has a wavelength of 1.3 μm.
m light source 20, a plurality of light sources including a light source 21 having a wavelength of 1.55 μm and a white light source 22, a polarization direction switching device 23 having the configuration of FIG. 4 according to the present invention, a sample to be measured (waveguide type optical component) 25, and input. A polarization maintaining optical fiber 26, an automatic centering device 24 for aligning the optical axes of the output single mode optical fiber 27, an optical power meter 30 for measuring the amount of reference light, and an optical insertion of the measured sample 25. An optical power meter 31 for measuring the loss, an optical spectrum analyzer 32 for measuring the spectrum of the transmitted light of the measured sample 25, a channel selector 33 for switching the optical path depending on which of 31 and 32 is to be measured, and It comprises a microcomputer 34 that manages these operations. 28 and 29 are single mode optical fibers.

Next, a specific measuring method in this example will be described step by step with reference to FIG.

First, a reference is taken. Therefore, the sample 25 to be measured is removed and the input / output fibers 26, 2
7 is directly applied and the difference between the outputs of the optical power meter 30 and the optical power meter 31 is measured using the microcomputer 34. This reference measurement is performed by using the input / output terminals of the 3 × 2 optical channel selector 3, I ₁ -O ₁ and I _{1-.
O 2, I 2 -O 1,} I 2 -O 2, I 3 -O 1, I 3 -O
_Repeat for each of the 6 states in which ₂ is tied. This is for compensating for the slight wavelength dependence and polarization dependence of the waveguide type wavelength independent coupler 12 and the optical channel selector 3.

Next, the sample 25 to be measured is adjusted by the automatic centering device 24.
It is set between the input / output fibers 26 and 27 of. At this time, the main stress of the input polarization-maintaining optical fiber 26 is set so as to be horizontal or vertical to the substrate surface of the measured sample 25. In this state, the self-centering device 24 is driven to align the three optical axes, and the optical axes of the input / output fibers 26 and 27 with respect to the measured sample 25 are fixed.

Next, light sources 20, 21, 2 are selected according to the purpose.
Select one from the two and select the two polarizations (TE polarization, TM
The characteristics with respect to the polarized wave) are respectively measured by selecting the output O ₁ or O ₂ of the optical channel selector 3. However, this measurement is to measure the difference between the optical power meter 30 and the optical power meter 31. By compensating this measurement result with the reference measured beforehand, the precise evaluation can be realized.

In the above, an example in which the waveguide type wavelength independent coupler 12 is used as the polarization maintaining optical coupler has been described. However, instead of this, a polarization maintaining optical fiber obtained by fusing two polarization maintaining optical fibers. It should be noted that a coupler can be used instead.

Further, as the polarization-maintaining optical coupler 12, it is possible to substitute a 2 × 2 optical space switch capable of switching the optical path while maintaining the polarization, for example, an optical channel selector using a reflecting mirror. Please note that.

[0035]

As described above, according to the present invention,
As a polarization rotation mechanism, a 90-degree twist of a polarization-maintaining optical fiber is used, so that there is no wavelength dependence, that is, a polarization direction switch that can switch the polarization direction without being present in the optical wavelength. can get.

Therefore, by using the polarization characteristic measuring device using the polarization direction switching device according to the present invention,
It is possible to manufacture waveguide type optical components used in a wide optical wavelength range from 1.3 μm to 1.6 μm and to precisely evaluate polarization characteristics. Furthermore, by this evaluation, it is possible to manufacture an optical waveguide circuit component whose polarization characteristics are strictly suppressed.

In other words, in the polarization characteristic evaluation apparatus using the polarization direction switching device according to the present invention, when switching the polarization direction of the input light, the optical component (measurement sample) to be evaluated and the input light are evaluated. Since there is no relative position change with the fiber, it is possible to evaluate the precise polarization characteristics of the DUT, and there is no wavelength dependence in switching the polarization direction. Sex can be evaluated.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a polarization characteristic device of a waveguide type optical component of prior art 1.

FIG. 2 is a perspective view showing a configuration of a polarization-maintaining optical fiber with a lamipole thin film polarizer shown in FIG.

FIG. 3 is a schematic configuration diagram showing a polarization characteristic device of a waveguide type optical component of prior art 2.

FIG. 4 is a schematic configuration diagram showing a polarization direction switcher according to an embodiment of the present invention.

5 is a characteristic diagram showing a wavelength characteristic of a coupling rate of the waveguide type wavelength independent coupler of FIG.

FIG. 6 is a schematic configuration diagram showing a configuration of a polarization characteristic measuring device in a wide wavelength region using the polarization direction switching device of FIG.

[Explanation of symbols]

1 Polarization-maintaining optical fiber with lamipole thin-film polarizer 2 Polarization-maintaining optical fiber with lamipole thin-film polarizer 3 Optical channel selector (3 × 2 optical space switch) 4, 5, 8, 9 Waveguide-type wavelength-independent coupler input Output waveguide 6,7 Waveguide-type wavelength-independent coupler arm waveguide 10,11 Waveguide-type wavelength-independent coupler 3 dB directional coupler 12 Waveguide-type wavelength-independent coupler (2 × 2 polarization-maintaining optical coupling 13,53 Lamipole thin film polarizer 20 Light source with wavelength 1.3 μm 21 Light source with wavelength 1.55 μm 22 White light source 23 Polarization direction switcher 24 of the present invention 24 Positioning of waveguide type optical component and input / output fiber Self-aligning device for performing 25 Waveguide type optical component as sample to be measured 26 Polarization maintaining optical fiber 27, 28, 29 Single mode optical fiber 30 Reference light An optical power meter 32 the optical spectrum analyzer 33 channel selector 34 microcomputer for measuring the optical insertion loss of the optical power meter 31 the measurement sample for measuring the

Claims (2)

[Claims] 1. An N × 2 optical space switch, a 2 × 2 polarization-maintaining optical coupler, and two polarization-maintaining optical fibers connecting them, and the two polarization-maintaining optical fibers. A polarization direction switching device, characterized in that one fiber is attached by being twisted by 90 degrees with respect to the other fiber. 2. The 2 × 2 polarization maintaining optical coupler is a waveguide type wavelength independent coupler having a structure of a Mach-Zehnder interferometer, wherein thin film polarization is provided in each of the two polarization maintaining optical fibers. The polarization direction switching device according to claim 1, wherein a child is inserted.