JPH0760236B2 - Optical switch element - Google Patents

Description

TECHNICAL FIELD The present invention relates to the fields of optical communication, optical applied measurement, optical information processing, and the like.

2. Description of the Related Art In recent years, optical switch elements for switching optical paths have been researched and developed as important key devices in optical fiber communication measurement and the like. Among them, waveguide optical switching elements
It is of particular interest for its fast response above GHz. In particular, the waveguide optical switch called TIR (Total Internal Reflection) type is in the spotlight because it is said to have a small element and high speed.

FIG. 4 shows a conventional example. Input waveguides 24a, 24b and output waveguides connected to the ridge-shaped crossing waveguide 23 with a structure having a control electrode 25 installed on the crossing waveguide 23 provided on the substrate 21 via a buffer layer having a low refractive index. It consists of 24c and 24d. If no voltage 26 is applied between the electrodes 25, guided light 22a (or 22b) guided in the input waveguide 24a (or 24b)
Output to the output waveguide 24c (or 24d) via the cross waveguide 23. A voltage 26 is applied to cause total reflection at a portion directly below the gap of the electrode 25 in the crossed waveguide 23, and the guided light 22a (or 22
b) was switched to the output waveguide 24d (or 24c). (IEEE J. Lightwave Tech., Vol.LT-2, No. 5, 1984, P7
10) Problems to be Solved by the Invention Such a conventional optical switch element has a problem that crosstalk is deteriorated due to coupling between the waveguides at the crossed waveguide portions. In addition, since it has a thin-film waveguide garridge type cross-sectional shape, scattering loss at the waveguide side wall,
There is a scattering loss at the crossing portion of the crossing waveguide, which is a problem in the low loss optical switch.

Means for Solving the Problems In order to solve the above problems, the present invention provides an input / output optical waveguide by providing a transparent dielectric ribbon on a thin film having an electro-optical effect, and introduces a conductive dielectric between the input / output optical waveguides. To form a waveguide lens, a rotationally symmetric body having a circular bottom surface having a refractive index higher than that of the buffer layer is arranged so that the input / output optical waveguides have an image forming relationship, and the input / output optical waveguides are connected to each other to form a buffer. By providing a control electrode on the layer and applying a voltage to the control electrode, the light output is switched.

Action The present invention has the above-described configuration, and therefore the scattering on the side wall of the waveguide becomes the scattering on the side wall of the transparent dielectric thin body in the portion where the guided light is extruded, so that the scattering loss is much smaller than that of the conventional one, and the rotational symmetry is also present. Since the input and output waveguides are connected by the waveguide lens action of the body, there is no coupling between the input and output optical waveguides, crosstalk does not deteriorate, and light is scattered at the intersections. It is possible to realize an optical switch with low loss and low crosstalk.

Example FIG. 1 is a bird's-eye view showing an example of the optical switching element of the present invention. In FIG. 1, after a transparent thin film 2 having an electro-optical effect is formed on a substrate 1, a buffer layer 3 and a strip load 4 in which a transparent dielectric material having a refractive index higher than that of the buffer layer is formed into a ribbon shape are formed in a waveguide shape. And is surrounded by the buffer layer and the thin film 2. The effective refractive index of the thin film 2 immediately below the strip road 4 is increased, lateral confinement is performed, and the thin film 2 is guided along the strip road 4. The portion directly below the strip road 4 serves as an optical input and output waveguide. Here, for convenience of expression, the strip load will be simply referred to as an input and output waveguide.

In this embodiment, two optical waveguides are provided for both input and output. The two sets of input and output optical waveguides are arranged so as to be imaged in the in-plane direction via the lens load 5 whose bottom surface is a rotationally symmetrical body having a circular shape. Here, the lens load 5 is formed on the thin film 2, and the effective refractive index of the waveguide layer surrounded by the substrate 1 and the buffer layer 3 is set to be the film thickness and / or the refractive index of the lens load 5. By changing it, the effective refractive index of the central part is raised and the effective refractive index is lowered as it goes to the peripheral part, and the waveguide lens (Luneberg lens) is constructed as a whole. ing. An electrode 6 having a narrow electrode gap 7 is formed on the lens load 5 via the buffer layer 3. The gap 7 is arranged so that the thin film 2 immediately below is on the bisector of the intersection line connecting the ends of the two sets of input / output optical waveguides. When a voltage is applied to the electrode 6 from the power source 9, it switches.

In this embodiment, the electro-optical material thin film 2 is PLZT (x / y /
z) thin film 0 ≦ x, y, z ≦ 100, y + z = 100] was used. Actually, a PLZT (28/0/100) composition target was used on the sapphire substrate 1 and PL was produced by the planar magnetron sputtering method.
The ZT thin film was grown as a single crystal. The film thickness was 3500Å.
Ta ₂ O ₅ was sputtered on the strip load 4 and formed into a 2 × 2 input / output waveguide with a width of 10 μm and a film thickness of 200Å crossing angle of 1 ° by the lift-off method. The total length was about 10 mm including the bent waveguide. There is no strip road at the intersection center diameter 2 mm.

Next, Ta ₂ O ₅ is sputtered in the center of the intersection using a circular opening mask with an inverse taper edge, and the center is about 400 Å
The dome-shaped disk-shaped lens load 5 was formed so as to be moderate. The diameter was about 2.2 mm. The peripheral portion of the disk was tapered, and the connection with the input / output waveguide portion was made without loss. The buffer layer 3 on top of which Ta with Al added
_{A 2} O ₅ film was formed by sputtering. The film thickness was about 1800Å. The refractive index of PLZT thin film is 2.6Ta ₂ O ₅ film is 2.08, Al ₂ O ₃
The membrane was 2.0. On top of that, gap 4μm, width 20μm,
Al was patterned by a lift-off method so that a parallel electrode having a length of 2 mm was located at the center of the intersection. A semiconductor laser beam of 1.3 μm is made incident from one end of the load 4 which becomes the input optical waveguide,
When the optical output from the output optical waveguide was measured, the insertion loss was almost the same as the propagation loss of the film of 5 dB / cm except for the coupling loss, and the coupling loss due to the lens aberration was about 0.5 dB, which was extremely small. In the conventional 1 ° crossing ridge waveguide, the loss at the crossing portion was ridge type, so a large value of about 1.5 dB was obtained, and the crosstalk was only 3 to 5 dB at 1 °. In the embodiment of the present invention, low crosstalk of 15 dB or more was realized. It is considered that this is because there is almost no coupling between the waveguides because the closest distances between the input and output waveguides are 25 μm.

Next, the principle of operation will be described based on examples. Second
FIG. 3 and FIG. 3 are schematic views of the top view of the optical switch of FIG. 1 of this embodiment. In the figure, the buffer layer is omitted for simplicity of explanation. 2 and 3 show the case where no voltage is applied to the electrode 7 of FIG. 1, respectively. In FIG. 2, the incident light 11 propagating through the input optical waveguide 4a spreads at the end portion, is condensed in the in-plane direction by the lens 5, enters the output optical waveguide 4c, and goes to the straight light output 13. The reflection loss at the input / output waveguide ends is extremely small because the effective refractive indices of the waveguides are almost the same. The loss depends on the aberration of the lens. In the case of this example, a small aberration loss of 0.5 dB was confirmed by the scattered light measurement method. In FIG. 1, when a voltage is applied to the electrode 6, the electric field is concentrated in the portion of the PLZT thin layer 2 immediately below the electrode gap 7 in FIG. 1, and in FIG. Is reduced. Due to the Kerr effect, the central portion of the region 8 has a particularly low refractive index. In FIG. 3, the light 11 propagating through the input optical waveguide 4a is condensed by the lens 5 after being emitted, but is totally reflected by the region 8 having a low refractive index and condensed on the output optical waveguide 4d. The reflected light output is 15. It was confirmed that the extinction ratio of 15 dB was obtained at a switch voltage of about 3 V, and the output was almost constant even when a higher voltage was applied, and the extinction ratio improved. In the conventional case, an extinction ratio of 10 dB was obtained at about 4 V, and a sinusoidal optical output variation with respect to the voltage was observed, but this was not observed at all in this example. This is because there is no optical coupling at the intersection (lens portion). The excess switch loss was about 0.5 dB. Conventionally, it was about 1 dB due to scattering at the intersection.

In the present embodiment, after all, a crosstalk of 15 dB or more, a switch voltage of 3 V, an extinction ratio of 15 dB, an insertion loss of 5 dB, and a switch loss of 0.5 dB were obtained. Loss 1dB, Switch loss 0.5dB
Improved. Also, the switch voltage is 3 V, which is
It is 1V lower and the characteristics are stable. In the present invention, the switch voltage becomes smaller as the crossing angle of the input / output waveguides becomes smaller, and the crosstalk does not deteriorate. In the past, when the crossing angle became small, crosstalk increased, and it was not possible to stay below 2 °.

In this example, PLZT (28/0/10
Although the PLZT film obtained from the target composition of 0) was described, any composition having electro-optical characteristics can be used. Using Ta ₂ O ₅ in the strip loading and lens load, Ta ₂ O ₅ added with Al ₂ O ₃ in the buffer layer
However, without being limited to these, Nb ₂ O ₅ , Al
₂ O ₃ , yttrium oxide, titanium oxide, SiO _2, etc. may be any transparent film having a lower refractive index than the electro-optic thin film.

EFFECTS OF THE INVENTION According to the present invention, crosstalk is much smaller than that of the conventional one, and an improvement of 10 dB or more can be obtained at a crossing angle of 1 °. Crosstalk deterioration is not observed even if the crossing angle is further reduced. . In addition, the switch voltage can be reduced accordingly. Conventionally, when the crossing angle is made small, the voltage / light output characteristic is a wavy and difficult to use switch that does not have a large extinction ratio, and about 2 ° is a practical value. A low voltage (3V), high extinction ratio (15 dB or more) is obtained, and the crossing angle can be reduced without reducing the extinction ratio.

[Brief description of drawings]

FIG. 1 is a bird's-eye view showing an embodiment of the optical switching element of the present invention, FIGS. 2 and 3 are schematic views showing the upper surface of the element, and FIG. 2 is a diagram when no voltage is applied. The figure shows that when voltage is applied. FIG. 4 is a schematic plan view of a conventional optical switch element. 1 ... Substrate, 2 ... Electro-optical material thin film, 3 ... Buffer layer, 4,4a, 4b, 4c, 4d ... Strip load, 5 ... Lens load, 6 ... Electrode, 7 ... Electrode gap , 8 ……
Refractive index changing region, 11 …… incident light, 12,14 …… propagating light, 13
...... Straight light output, 15 …… Reflected light output, 22a, 22b, 22c, 22d
...... Input / output optical waveguide, 23 …… Cross waveguide.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Yamazaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-56-109306 (JP, A) (JP, U)

Claims (2)

[Claims] 1. An optical switch element using a thin film having an electro-optical effect formed on a substrate, wherein a buffer layer which is a transparent dielectric thin film and a buffer layer which is a transparent dielectric thin film are provided on the thin film having an electro-optical effect. A transparent dielectric ribbon for confining the guided light propagating in the thin film having a high refractive index and having the electro-optical effect in the lateral direction, and a lateral condensing of the guided light propagating in the thin film having the electro-optical effect. And a rotationally symmetric body having a circular bottom surface having a waveguide lens function for performing the above-mentioned operation, is formed between the thin film having the electro-optical effect and the buffer layer, and the transparent dielectric ribbon forms the rotationally symmetric body. One or more pairs of sandwiching transparent dielectric ribbons are arranged so that the ends of the transparent dielectric ribbons facing each other are in an imaging relationship, and a control electrode for switching an optical path having a gap is provided on the buffer layer. Control power By applying a voltage in between to lower the refractive index of the thin film having the electro-optical effect, the effective refractive index in the vicinity of the gap is lowered, and a total reflection region is formed in the rotationally symmetric body. Optical switch element. 2. The optical switch element according to claim 1, wherein the thin film having an electro-optical effect is a PLZT type thin film.