JPS62251728A - Optical switch - Google Patents

Abstract

PURPOSE:To make switching of optical paths without relying on the property of polarization of light inputted fro an optical fiber, by switching the optical paths under the switching condition of TM waves. CONSTITUTION:The light from an optical fiber 17 is separated into TE waves 27 and TM waves 28 by means of a double-refracting material 19 after image transformation by a lens 18. The TE waves 27 are changed to TM waves by means of a 90 deg. optical rotator 21 and passed through the 1st optical switching element 13 and the TM waves 28 are passed through the 2nd optical switching element 14. At both optical switching elements 13 and 14 the optical paths are switched to waveguides 15c and 16c. The TM waves passed through the waveguide 15c and the TE waves which are changed from the TM waves by a 90 deg. optical rotator 26 after passing through the waveguide 16c are joined together at a double-refracting material 24 and coupled with the optical fiber 22 on the other side. Thus the optical paths of this optical switch 11 are switched to each other under the switching condition of the TM waves without relying the property of polarization of light inputted from the optical fiber on the input side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical switch inserted into an optical transmission line to switch optical paths, and more particularly to a waveguide-type optical switch using an electro-optic effect.

[Conventional technology]

A waveguide type optical switch using an electro-optic effect has high switching reliability because it does not have a moving part, and is capable of high-speed switching response. Furthermore, it has unique features such as being able to be formed on a conductive substrate or a semiconductor element substrate by applying conventional semiconductor photolithography technology and sales promotion technology, and being suitable for high integration.

In the conventional waveguide optical switch 1 shown in FIG.
1) Two waveguides 3.4 are formed on the 03 substrate (hereinafter referred to as the substrate) 2 by diffusing Ti. Waveguide 3.
An electrode 5 is formed on 4. The optical fiber 6 is connected to the input side of the waveguide 3 and the optical fiber 7.8 is connected to the output side of the waveguide 3.4. optical fiber 6
The optical path of the light is switched by applying a voltage to the electrode 5 and changing the refractive index of the waveguide by the electro-optic effect.

At present, optical fiber waveguide-optical fiber insertion loss of about 2 dB, crosstalk of 20-30 dB, switching voltage of about 5 cm, and switching speed of several ns or less have been achieved.

[Problem that the invention seeks to solve]

As mentioned above, conventional waveguide type optical switches have many features, but a major practical problem is that they are highly polarized-wave dependent. In other words, since the electro-optic effect (electromechanical coupling coefficient) is different for TE and TM polarized waves, when the switching conditions are satisfied with TM waves,
Even in waves, the switching conditions are not always satisfied.

As a result, although good characteristics are exhibited for a specific polarized wave, the characteristics are significantly degraded for the other polarized wave.

The characteristic example of the waveguide type optical switch l described above is a value for a TM wave.

Conventionally, to solve this problem, optical switches without polarization dependence have been proposed. For example, rL,
IAe Canghani LOI Loss
Polarijion-Independent
Electro optical 5w1tches
atλ=1.3 p m, Journal of L
i)<htwave Technolo.

VoL, Lt-2, Nol, Feb, 1984
, P51-55 J, etc.

In this optical switch, as shown in FIG.
To ensure that the waves have a common switching voltage a, Li
Nb0. The waveguide parameters of Ti diffused upward are controlled, but in TE and TM waves, the electrical material engagement coefficient essentially differs by about 3 times, so the switching voltage a at the time of switching becomes higher. There is a problem with this. For example, with TM waves alone, it is possible to switch a switch with a switching voltage of about 5V, but with the optical switch proposed above, the voltage is as high as about 70V. If this switching voltage is high, there are practical problems such as being susceptible to drift and complicating an optical switch drive circuit that responds at high speed.

[Means for solving problems]

In the optical switch of the present invention, first and second waveguide type optical switch elements are formed in parallel on a substrate made of a dielectric or semiconductor material having a large electro-optic effect so that switching conditions are satisfied using TM waves. , a first 90° optical rotator is disposed at the input side of the first waveguide type optical switch element, and a second 90° optical rotator is disposed at the output end of the second optical switch element.

Further, a lens and a birefringent material for coupling the input waveguide and the optical fiber are arranged between the substrate and the input optical fiber, and between the substrate and the output optical fiber, A lens and a birefringent material for coupling the output side waveguide and the optical fiber are respectively arranged.

The optical switch of the present invention has no polarization dependence as follows. In other words, human-powered light from an optical fiber is converted into an image by a lens, and then subjected to TE by a birefringent material.

The TE wave is separated into TMI, and the polarization plane of the TE wave is rotated by 90° by the first 90° optical rotator and converted into a TM wave.
in the waveguide of the optical switching element, and the TM wave is in the second waveguide.
are respectively coupled to the waveguides of the optical switching elements. The TM wave passing through the first optical switching element has its plane of polarization rotated by 90° by the 90° optical rotator on the output side and becomes TE.
It is converted into a wave and enters the birefringent material.

The TE and TM waves exiting the 90° optical rotator on the output side are combined by a birefringent material and coupled to any optical fiber on the output side by double image conversion of the lens.

Switching of the optical path from the optical fiber on the input side to any one of the plurality of optical fibers on the output side is performed by controlling the first and second optical switching elements.

As described above, in the optical switch of the present invention, the optical path is switched under the switching conditions of the TM wave, and the optical path can be switched without depending on the polarization of the manually-powered light from the optical fiber.

〔Example〕

The present invention will be explained below with reference to an illustrated embodiment.

In FIG. 1, a substrate 12 of an optical switch 11 is made of a waveguide substrate or a semiconductor material substrate.

On this substrate 12, first and second waveguide type optical switching elements (hereinafter referred to as optical switching elements) 13 and 14 that satisfy switching conditions using TM waves are formed in parallel.

Each optical switching element 13.1 is provided on the input side of the substrate 12.
4, and on the output side, a plurality of output waveguides 15b, 15C and 16b respectively coupled to each optical switching element.
, 16c are formed, respectively.

A lens 18 and a first birefringent material 19 are provided between the input-side optical fiber 17 and the substrate 12, respectively, to couple the optical fiber 17 and the input-side waveguides 15a, 16a, respectively. A 90° optical rotator 21 is arranged between the birefringent material 19 and the waveguide 153 to rotate the plane of polarization of the TE wave by 90° to make it TMiJp.

Group (12 and Mi number of optical fibers on the output side 22.23
A second birefringent material 24 and a lens 25 for coupling the output side waveguides 151] and 16b and the optical fiber 23, and the waveguides 15C and 116C and the optical fiber 22 are disposed between them. ing.

A second 90' optical rotator 26 is provided between the output side waveguides 16b, 16c and the birefringent material 24, which rotates the plane of polarization of the TM wave by 90 degrees to make it a TEM.

Now, when no voltage is applied to both optical switching elements 13.14, both optical switching elements 13.14
It is assumed that the optical paths of are coupled to waveguides 15b and 16b, respectively.

In this state, the light from the optical fiber 17 on the input side undergoes image conversion by the lens 18 and then undergoes TE conversion by the birefringent material 19.
Separated into He27 and TMM2B5. After the separation, the T and E waves 27 have their polarization planes rotated by 90 degrees by the 90 degrees optical rotator 21 to become TM waves and pass through the first optical switching element 13 . Then, the TMM2B5 passes through the second optical switching element 14 as it is.

The TM wave passing through the first optical switching element enters the birefringent material 24 through the waveguide 15. The TM wave passing through the second optical switching element 14 passes through the waveguide 16b and enters the birefringent material 26, where the plane of polarization is rotated by 90 degrees and converted into a TE wave.

The TM wave from the waveguide 1.5b and the TE wave after converting the TM wave from the waveguide 16b are combined in the birefringent material 24 and then enter the optical fiber 23 on the chemical horn side.

Next, when a voltage is applied to both optical switching elements 13 and 14, due to the electro-photoelectric effect, both optical switching elements 13.
At 14, the optical path is switched to waveguides 15c, 1, and 6c.

The TM wave passing through the waveguide 15c and the TM wave passing through the waveguide 16C 90
° A TE wave that is a TM wave converted into a TE wave by the optical rotator 24 is
After being merged at the birefringent material 24, it is coupled to the other optical fiber 22.

In this manner, the optical switch 11 can switch the optical path under the switching conditions of the TM wave, and can perform the switching without depending on the polarization of the manually-powered light from the input optical fiber. Furthermore, switching of the TM wave can be performed even with a low voltage, as shown in FIG.

FIG. 4 shows a concrete example of the above-mentioned optical switch 11, and the same functions are denoted by the same reference numerals and the explanation thereof will be omitted.

In Figure 2, on the L+NbO3 substrate, 250 μm
Ti diffusion waveguides 15a, 15b, 16a, 16b with a width of
are formed, and other waveguides 15c and 16C are formed to have a width of 8 μm in both optical switching elements 13 and 14 and 125 μm at the output end of the substrate.

As the 90° optical rotation photon 21.26, a crystal plate with a thickness of 140 μm is used, and as the birefringent material 19.24, a thickness of 2.5 mm is used.
Calcite is used, and the quartz plate 21.26 and each corresponding calcite 19.24 are bonded with an adhesive that also serves for refractive index matching. Note that, in order to fill the gap between the calcite 19.24 and the substrate 12, glass spacers 27.28 with a thickness of 140 μm are used.

The lens 18 is a focusing lens with a focal length of 3 mm, and the optical fibers 17, 22, and 23 have a core diameter of 10 μm and an outer diameter of 125
μm single mode optical fiber, both optical fibers 22
．． 23 are arranged at intervals of 125 μm.

The waveguide length of the optical switching portion of the optical switching elements 13 and 14 is 13 mm, and the electrodes have a β-inverted I configuration.

The prototype results according to this example show an insertion loss of 2.5 dB, a crosstalk of -25 dB, a switching voltage of 6 cm, and a switching time of 5 ns.
Hereinafter, the polarization dependence of insertion loss was 0.1 dB or less.

〔Effect of the invention〕

As explained above, in the optical switch of the present invention, two optical switching elements optimal for TM waves are formed in parallel on a substrate made of a dielectric or semiconductor material, and a 90° optical polarizer is connected to a waveguide. By providing each at the input and output ends, and further separating and combining the TE and TM waves using a birefringent material,
Switching of the optical switch is possible without polarization dependence and at low voltage, and a highly practical optical switch can be constructed.

[Brief explanation of drawings]

FIG. 1 is a plan view of an optical switch showing an embodiment of the present invention, FIG. 2 is a plan view showing a specific configuration of the optical switch,
FIG. 3 is a plan view showing an example of a conventional optical switch, and FIG. 4 is a diagram showing the relationship between applied voltage and optical output power of a conventional non-polarized optical switch. 11... Optical switch, 12... Board,
13...First optical switching element, 14...
...second optical switching element, 15a, 15b,
15 c, 16 aSl 6 b. 16C...Waveguide, 17...Input side optical fiber, 18.25...
... Lens, 19... First birefringent material, 21... First 90° optical rotator, 22.23.
...Output side optical fiber, 24...2nd
birefringent material, 26... second 90° optical rotator. Applicant: NEC Corporation Representative

Claims (1)

[Claims] A substrate made of a dielectric or semiconductor material and an optical signal from an input waveguide can be selectively switched to one of a plurality of output waveguides under switching conditions using TM waves. , first and second waveguide-shaped optical switching elements formed in parallel on the substrate, and a respective one between the optical fiber and the substrate so as to couple the optical fiber on the input side and the waveguide on the substrate. arranged lenses and TE,
a first birefringent material that separates both TM waves; a first 90° optical rotator disposed between the first birefringent material and the input waveguide of the first optical switching element; A second birefringent material and a lens that combine both TE and TM waves are respectively arranged between the substrate and the optical fiber so as to couple the output side waveguide on the substrate and the output side optical fiber. and a second 90° optical rotator disposed between the output side waveguide of the second optical switching element and the second birefringent material.