JPH036535A - Wavelength selective optical switch - Google Patents

Abstract

PURPOSE:To enable low-voltage driving by controlling independently optical paths of light beams with different wavelengths LAMBDA and lambda which are multiplexed and inputted by controlling voltages applied to a 1st 45 deg. TN liquid crystal and 2nd - 4th TN liquid crystals respectively. CONSTITUTION:The voltages applied to the 45 deg. TN liquid crystals 9a - 9d are controlled properly to control and switch independently the light beams with the wavelengths LAMBDA and lambda as to whether an optical fiber 1a and an optical fiber 1b or the optical fiber 1a and an optical fiber 1c are coupled. Then the 45 deg. TN liquid crystals 9a - 9d control the rotation of the polarization azimuth of passing light with the applied voltage of several V. Consequently, the low- voltage driving is enabled as compared with a conventional wavelength selective optical switch while features of small size and low loss are maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a wavelength selective optical switch used in an optical fiber transmission system, and more particularly to a wavelength selective optical switch that is driven at a low voltage.

``Prior Art'' Optical switching technology is an important technology for diversifying and upgrading optical fiber transmission systems.

Therefore, many studies have been conducted regarding the configuration of optical switching networks and optical switches.

A conventional general optical switch receives input from a certain terminal,
The optical power output from another terminal was switched to be output from another terminal.

Furthermore, recently, wavelength selective optical switches that independently control the path of wavelength-multiplexed light for each wavelength have been studied.

Here, FIG. 3 is a diagram showing the configuration of such a wavelength selective optical switch (see Fujii, Minowa, "Optical Switch", Japanese Patent Application No. 63-154960). In this figure, 1 a,
1 b and 1 c are each optical fibers, and one surface of each is connected to one surface of lenses 2 a, 2 b, and 2 c. In this case, it is assumed that each of the optical fibers 1a=lc has its axis coincident with the optical axis of the lenses 2a to 2c. The other surface of the lens 2a is connected to the left surface (left surface) of the deflection beam splitter 3a in the drawing. A mirror 4a is connected to the lower side (lower surface) of the deflection beam splitter 3a in the drawing. Deflection beam splitter 3a
A variable retardation plate 6 and a retardation plate 5b are sequentially connected to the right side (right side) of each of the mirrors 4a and 4a in the drawing through a retardation plate 5a. Here, the phase difference plates 5a, 5b
each has an azimuth of 22.5 degrees, and its retardation is π for the wavelength and 2π for the wavelength λ. Further, the variable retardation plate 6 has an orientation of 0 degrees, and the retardation at the wavelength Δ is zero when no voltage is applied, and is π when the voltage V is applied.

As the variable retardation plate 6, a crystal exhibiting an electro-optic effect, such as lithium niobate or lithium tantalate, is used. Next, on the right side of the retardation plate 5b, a mirror 4b is arranged in order from the top.

A polarizing beam splitter 3b is connected, a lens 2b is connected to the right surface of the polarizing beam splitter 3b, and a lens 2c is connected to the lower surface.

In the wavelength selective optical switch configured in this way, wavelength multiplexed light (wavelength = 8 and λ
) is converted into a parallel beam by the lens 2a, and then separated by the polarization beam splitter 3a into linearly polarized beams with polarization directions of 0 degrees and 90 degrees. Here, since the separated light beam with a polarization direction of 0 degrees and the light beam with a polarization direction of 90 degrees are in the same state on their subsequent paths, the state of the light beam with a polarization direction of 0 degrees will be described below.

Now, the light having the wavelength λ of the light beam with a polarization direction of 0 degrees separated by the polarization beam splitter 3a is separated by the retardation plate 5a,
5b, the beam passes through without changing its deflection direction. Further, since the light enters the variable retardation plate 6 with its polarization direction parallel to the direction of the same retardation plate 6, the light passes through the variable retardation plate 6 without changing its polarization direction. That is, the light having the wavelength λ is coupled to the optical fiber lc regardless of the state of the variable retardation plate 6.

On the other hand, when no voltage is applied to the variable retardation plate 6, the light of the wavelength Δ of the light beam with the polarization direction of 90 degrees is
Since the polarity difference in the same retardation plate 6 is zero, this variable retardation plate 6 can be removed, and this is equivalent to passing through two half-wavelength plates in the same direction. Therefore, in this case as well, the polarization direction of the light to the wavelength is determined by the retardation plate 5.
a, remains unchanged even after passing through the variable retardation plate 6 and the retardation plate 5b, and is coupled to the optical fiber 1c.

Here, when a voltage is applied to the variable retardation plate 6, the orientation of each of the retardation plates 5a and 5b and the orientation of the variable retardation plate 6 located between them are different, so that the wavelength of light is is incident on both of the retardation plates 5a, 5b and the variable retardation plate 6 with a deflection direction that is not parallel to that direction. As a result, the light of wavelength A passes through the retardation plates 5a, 5b and the variable retardation plate 6, so that its deflection direction changes sequentially to 45 degrees, 45 degrees, and -90 (90) degrees. Therefore, light at the wavelength is coupled to the optical fiber 1b when a voltage is applied to the variable retardation plate 6.

In this way, in the conventional wavelength selective optical switch mentioned above,
Optical fiber by switching the voltage applied to the variable retardation plate 6! Separate the multi-wavelength lightning incident from a,
You can choose not to.

Note that if a 90 degree TN liquid crystal is inserted between the retardation plate 5b, the mirror 4b, and the deflection beam deflection beam splitter 3b, this 90 degree TN liquid crystal will change the polarization of the linearly polarized light that passes through it when a voltage is applied. Since the orientation is not rotated and the polarization orientation is rotated by 90 degrees when no voltage is applied, in the end, by controlling the voltage applied to the variable retardation plate 4 and the voltage applied to the 90 degree TN liquid crystal, it is possible to The output terminal for the light of wavelength λ can be independently selected as the optical fiber 1b or the optical fiber Ic.

"Problems to be Solved by the Invention" By the way, the above-mentioned conventional wavelength selective optical switch has the following problems. That is, the variable retardation plate 6
Crystals that exhibit an electro-optic effect, such as lithium niobate and lithium tantalate, which are used as crystals, have a considerably small electro-optic effect, so an applied voltage on the order of KV is required to operate the retardation plate 6. . For this reason, there was a problem that it was difficult to handle.

This invention was made in view of the above-mentioned circumstances, and an object of the invention is to provide a wavelength selective optical switch that can be driven at a low voltage.

``Means for Solving the Problems'' This invention provides an Ix2 wavelength selective optical switch in which light of λ is wavelength-multiplexed into different wavelengths and manually controlled, and these optical paths are independently controlled. A retardation plate whose orientation is α degrees and acts as a half-wave plate for light with wavelength Δ and as a single-wave plate for light with wavelength λ, and The direction of Tsumugi is α degree,
The first 45 degree TN liquid crystal whose direction is (α+45) degrees of the long axis or short direction of the molecule on the emission side, and the second 45 degree TN liquid crystal, and the direction of the long axis or short direction of the molecule on the light incident side. The direction is (α
+45) degrees, and the direction of the long axis or short pongee of the exit side molecule is α
The third 45 degree TN liquid crystal, the direction of the long axis or short pongee of the molecules on the light input side is (α + 45) degrees, and the direction of the long axis or short pongee of the molecules on the output side is (α + 90) degrees. Fourth 45 degree TN liquid crystal, light with polarization direction α degree and polarization direction (α+90)
and a polarizing beam splitter that separates the wavelength-multiplexed light into separate directions, and from the incident side of the wavelength-multiplexed light, the first 45-degree TN liquid crystal, the retardation plate, the second TN liquid crystal, and the polarizing beam splitter, and the second T
The third T is between the N liquid crystal and the polarizing beam splitter.
N liquid crystal and the fourth TN liquid crystal are arranged, and the first TN liquid crystal and the fourth TN liquid crystal are arranged.
By controlling the voltages applied to each of the 45 degree TN'/fL crystal, the second TN liquid crystal, the third TN liquid crystal, and the fourth TN liquid crystal, different wavelengths Δ that are multiplexed and manually input can be It is characterized by independently controlling the optical path of light of λ.

"Operation" The wavelength selective optical switch of the present invention can control the polarization direction in four ways.
The main feature is that it uses a 5 degree TN liquid crystal. This TN liquid crystal has a thickness of about 1 mm, and can control the rotation of the polarization direction of passing light with an applied voltage of about several volts.

Therefore, the present invention is completely different from conventional wavelength-selective optical switches in terms of the elements used and the configuration, and can be driven at low voltage, with low loss, and downsized at the same time.

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

FIG. 1 is a block diagram showing a first embodiment of the present invention. In this figure, parts common to those in FIG. 3 described above are designated by the same reference numerals, and their explanation will be omitted.

As you can see in the diagram, 8 is a deflector, and the lens 2a is connected to the left side of the drawing (left side), and the 4 side is connected to the right side.
A 5 degree TN liquid crystal 9a is connected.

45 degree TN liquid crystals 9b to 9d are sequentially connected to the right side of this 45 degree TN liquid crystal 9a via a retardation plate 10. 4
A deflection beam splitter 3a is connected to the right side of the 5 degree TN liquid crystal 9d as shown in the figure.

A lens 2b is connected to the right surface of the deflection beam splitter 3a, and a lens 2c is connected to the bottom surface. Here, the coordinates x, y, and z shown in the figure are an orthogonal coordinate system temporarily determined in order to explain the operation of this first embodiment. In addition, the polarization direction, the direction of the polarizer 8, the 45 degree TN liquid crystal 9
a to 9d each molecule long axis (short axis) direction, retardation plate IO
The directions of the fast (slow) pongee are all expressed as angles with respect to the +X direction, and if the force is in the +y direction, it is positive, and if it is in the -y direction, it is negative. When you decide like this, (a)
The orientation of the polarizer 8 is 0 degrees, (o) 45 degrees TN liquid crystal 9a.

9b, when no voltage is applied, the direction of the molecule on the light incidence side is 0 degrees, the direction of the molecule on the outgoing side is 45 degrees, (c) the direction of the phase difference Ifi, to is 0 degree, (d) 45 degrees TN liquid crystal 9
When no voltage is applied, the direction of the molecule on the incident side of light is 45 degrees, the direction of the molecule on the outgoing side is 0 degrees, and (e) 45 degrees TN.
It is assumed that when no voltage is applied to the liquid crystal 9d, the orientation of molecules on the incident side of light is set to 45 degrees, and the orientation of molecules on the exit side is set to 90 degrees. Also, 45 degree TN liquid crystal 9a~
It is assumed that when a voltage is applied to each of the molecules 9d, the long axes of the molecules are oriented in two directions. Furthermore, the retardation plate IO
shall act as a half-wave plate for light of wavelength λ, and act as a one-wave plate for light of wavelength λ.

Next, the operation of the wavelength selective optical switch having the above configuration will be explained.

First, as the first switch state, the 45 degree TN liquid crystal 9a
Consider the case where voltage is applied to all of ~9d.

In this case, even if the light passes through each of the 45 degree TN liquid crystals 9a to 9d, the polarization direction does not change. That is, the optical fiber 1a
The wavelength multiplexed light (wavelength to λ) emitted from lens 2
It is converted into a parallel beam by a, passes through a polarizer 8, and becomes linearly polarized light with a polarization direction of 0 degrees. This wavelength multiplexed light enters the retardation plate 10 without changing its polarization direction, but since the direction of the retardation plate 10 is 0 degrees, the polarization direction of the light to the wavelength from which it is emitted is different from that of the light of wavelength λ. It remains at 60 degrees with the polarization direction. Further, even if the light passes through each of the 45-degree TN liquid crystals 9b to 9d, the polarization direction does not change, so that the light having a wavelength of λ enters the polarizing beam splitter 3b with a polarization direction of 0 degrees. Therefore, light of wavelength λ is transmitted through optical fiber t
Join to b.

Next, in the second switch state, the 45 degree TN liquid crystal 9 a
, 9c, a voltage is applied to each of the 45 degree TN liquid crystal 9
No voltage is applied to each of b and 9d. In this state, as in the first switch state, light of wavelengths Δ and λ with a polarization direction of 0 degrees enters the 45 degree TN liquid crystal 9b. In this case, the polarization direction of the incident light and the 45 degree TN liquid crystal 9b Since the orientations of the molecules on the light incident side are parallel, the 45-degree TN liquid crystal 9b operates in TN mode, and the light with wavelengths Δ and λ passes through the 46-degree TN liquid crystal 9b, so that its polarization direction becomes 45 degrees. . Next, the light passes through the TN liquid crystal 9c at 45 degrees, but the polarization direction remains unchanged. Therefore, the light having a wavelength of λ has a polarization direction of 45 degrees and is incident on the TN liquid crystal 9d at 45 degrees. In this case, since the polarization direction of the incident light and the direction of the molecules on the incident side of the light of the 45 degree TN liquid crystal 9d are parallel, the 45 degree TN liquid crystal 9d operates in the TN mode, and the light of wavelength λ is 45 degrees TN. By passing through the liquid crystal 9d, its polarization direction becomes 90 degrees. Eventually, the light of wavelength λ is reflected by the polarizing beam splitter 3b and coupled to the optical fiber lc.

Next, in the third switch state, the 45 degree TN liquid crystal 9 b
, 9d, a voltage is applied to each of the 45 degree TN liquid crystal 9a.
, 9c, no voltage is applied. In this state, the light of wavelength λ, which has become linearly polarized light with a polarization direction of 0 degrees by the polarizer 8, passes through the TN liquid crystal 9a at 45 degrees, so that the polarization direction becomes 45 degrees. Input to IO. In this case, unlike the first and second switch states described above, the polarization direction of the incident light and the axial direction of the retardation plate IO are not parallel, so the light of wavelength A passes through the retardation plate 10. Therefore, its polarization direction is 145 degrees. On the other hand, even if the light having the wavelength λ passes through the retardation plate IO, its polarization direction remains at 45 degrees. Since a voltage is applied to the 45-degree TN liquid crystal 9b, the polarization direction does not change even if the light passes through the 45-degree TN liquid crystal 9b, and the light of wavelength Δ enters at the point of incidence on the 45-degree TN liquid crystal 9c. The polarization direction of is 145 degrees, and the polarization direction of light with wavelength λ is 45 degrees. Therefore, 45 degree TN liquid crystal 9c
operates in TN mode, and the polarization direction of the light to the wavelength emitted from this 45 degree TN liquid crystal 9C is 90 (-90) degrees,
The polarization direction of light with wavelength λ is 0 degrees.

Even if these lights pass through the TN liquid crystal 9c at 45 degrees, the polarization direction does not change, so the light with the wavelength Δ is eventually coupled to the optical fiber 1c, and the light with the wavelength λ is coupled to the optical fiber Ib.

Finally, in the fourth switch state, the 45 degree TN liquid crystal 9
Apply a voltage to each of b and 9 c, and the 45 degree TN liquid crystal 9
No voltage is applied to each of a and 9d. In this state, as in the third switch state described above, the polarization direction of the light with the wavelength Δ emitted from the 45° TN liquid crystal 9b is 145 degrees, and the polarization direction of the light with the wavelength λ is 45 degrees. 45 degree TN
Since no voltage is applied to the liquid crystal 9c, the wavelengths Δ and λ
The light enters the 45 degree TN liquid crystal 9d with the above polarization direction unchanged. When light with wavelengths A and λ passes through the TN liquid crystal 9d at 45 degrees, both polarization directions are rotated by 45 degrees.
The polarization direction of the light having the wavelength that has passed through the N liquid crystal 9d is 0 degrees, and the polarization direction of the light having the wavelength λ is 90 degrees. Therefore, light with wavelength Δ is connected to optical fiber lb, and light with wavelength λ is connected to optical fiber 1.
Combines with c.

In this way, in the wavelength selective optical switch according to the first embodiment, by appropriately controlling the voltages applied to each of the 45 degree TN liquid crystals 9a to 9d, the wavelength of light of λ can be adjusted. , it is possible to achieve the function of a wavelength-selective optical switch that independently (two-controls and switches) whether to couple optical fiber Ia and optical fiber lb, or to couple optical fiber la and optical fiber lc. LCD 9a
~9d each has a thickness of about 1 mm, and the rotation of the polarization direction of the passing light can be controlled with an applied voltage of about several volts, so it maintains the characteristics of small size and low loss compared to conventional wavelength selective optical switches. At the same time, low voltage driving becomes possible.

Next, FIG. 2 is a diagram showing the configuration of a second embodiment of the present invention. In addition, in this figure, the above-mentioned figures 1 and 3
Portions common to each figure are given the same reference numerals and their explanations will be omitted.

In the first embodiment described above, if the light emitted from the optical fiber 1a is not linearly polarized light with a polarization direction that matches the direction of the polarizer 8, loss occurs due to the light passing through the polarizer 8. The second embodiment solves this problem.

In this figure, Ila is a right angle prism, and as shown, its upper surface is connected to the lower surface of the polarizing beam splitter 3a. On the right side of each of the polarizing beam splitter 3a and the right angle prism lla, 45
TN liquid crystals 9a to 9d are connected in sequence. 45 degree T
The left surface of the right-angle prism llb is connected to the upper right surface of the N liquid crystal 9d.

In the wavelength selective optical switch according to the second embodiment configured as described above, the wavelength-multiplexed light (wavelength: λ) emitted from the optical fiber la is converted into a parallel beam by the lens 2a, and sent to the polarizing beam splitter 3a. incident. The polarizing beam splitter 3a separates the wavelength multiplexed light into two linearly polarized light beams A and B. Of these, light beam A
enters the TN liquid crystal 9a at 45 degrees from point a with a polarization direction of 0 degrees, and exits from point C of the 45 degree TN liquid crystal 9d. On the other hand, since the light beam B is focused at a polarization direction of 90 degrees, the 45 degree TN liquid crystal 9a
The light enters at point d and exits from point d of the 45 degree TN liquid crystal 9d. It is obvious that the operation of the light beam A for the four switch states from point a to point C is exactly the same as that shown in the first embodiment described above. Furthermore, the operation of the light beam B for the four switch states from point 2 to point d can be easily understood since the polarization direction of the light beam A only needs to be rotated by 90 degrees. Therefore, in this second embodiment, the light emitted from the optical fiber 1a is transmitted to the optical fiber 1b or the optical fiber 1a without loss in principle, regardless of its polarization state, depending on the switch state. Combines with 1c. That is, in the first switch state, the wavelength λ
In the second switch state, light with wavelength λ is coupled into optical fiber tb, and in the third switch state, light with wavelength Δ is coupled into optical fiber Ic, with wavelength λ
The light of wavelength λ is coupled to optical fiber 1b, and in the fourth switch state, the light of wavelength λ is coupled to optical fiber lb, and the light of wavelength λ is coupled to optical fiber lc.

In this way, in this second embodiment, as in the first embodiment shown in FIG. In contrast, it is possible to achieve the function of a wavelength selective optical switch that independently controls and switches whether to couple the optical fibers 1a and 1b or the optical fibers Ic. As a result, it is possible to drive at a low voltage while maintaining the characteristics of small size and low loss.

"Effects of the Invention" As explained above, the main feature of the wavelength selective optical switch of this invention is that a 45 degree TN liquid crystal is used as an element for controlling the polarization direction of light of wavelength λ. Since this 45 degree TN liquid crystal has a thickness of about 1 mm, rotation of the polarization direction of the passing light can be controlled with an applied voltage of about several volts. Therefore, there is an effect that low voltage driving can be achieved while maintaining the small size and low loss characteristics of the conventional wavelength selective optical switch.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a wavelength selective optical switch which is a first embodiment of the present invention, Fig. 2 is a block diagram of a wavelength selective optical switch which is a second embodiment of this invention, and Fig. 3 is a diagram of a conventional wavelength selective optical switch. FIG. 2 is a configuration diagram of an optical switch. 1a=1c...Optical fiber, 2a-2C...
...Lens, 3a, 3b...Polarizing beam splitter, 8.12...Polarizer, 9a to 9d...45 degree TN liquid crystal, 10...
...Retardation plate, 11a, 11b...Right angle prism.

Claims (1)

[Claims] In a 1×2 wavelength selective optical switch in which lights of different wavelengths Λ and λ are wavelength-multiplexed and input and these optical paths are independently controlled, the direction of the fast axis or slow axis is α degree. , acts as a half-wave plate for light of wavelength Λ, and acts as a half-wave plate for light of wavelength λ.
A retardation plate that acts as a wave plate, and a first plate whose long axis or short axis of the molecule on the light incident side is oriented at α degrees and whose azimuth of the long axis or short axis of the molecule on the outgoing side are (α + 45) degrees. The orientation of the long axis or short axis of the molecules on the light incident side of the 45 degree TN liquid crystal and the second 45 degree TN liquid crystal is (α+45
) degree, and the third 45 degree TN liquid crystal whose major axis or short axis of the molecule on the emission side is oriented at α degrees, and the direction of the long axis or short axis of the molecule on the light incident side is (α+45 degrees).
) degree, and the direction of the long or short axis of the molecule on the exit side is (α+
90) degrees, and a polarizing beam splitter that separates light with a polarization direction of α degrees and light with a polarization direction of (α+90) degrees into separate directions, from the input side of the wavelength multiplexed light. , the first 45 degree TN liquid crystal;
The retardation plate, the second TN liquid crystal, and the polarizing beam splitter are arranged in this order, and the third TN liquid crystal and the fourth TN liquid crystal are arranged between the second TN liquid crystal and the polarizing beam splitter. liquid crystals are arranged, and are multiplexed by controlling voltages applied to each of the first 45 degree TN liquid crystal, the second TN liquid crystal, the third TN liquid crystal, and the fourth TN liquid crystal. A wavelength selective optical switch that independently controls the optical path of input light of different wavelengths Λ and λ.