JP3193427B2 - Optical switch and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch used for optical communication and the like and a method for manufacturing the optical switch. In particular, the present invention relates to a novel shape of an electrode of an optical switch using electric-field-induced refractive index fluctuation and a method for manufacturing an optical switch using the same.

[0002]

BACKGROUND OF THE INVENTION During the last decade, telecommunications has changed dramatically with the introduction of large-scale fiber optic communications. A huge communication bandwidth is available, which makes the network designer more limited by node (comprising switches, amplification factors, etc.) capability than link capability. Therefore, it is basically important to be able to handle and propagate high-speed communication information through an optical switch. In recent years, it has been proposed that the refractive index of a cross-type optical switch made of a semiconductor can be changed by adding an electric field. (H.Ymamot
o, M. Asada and Y. Suematsu, IEEE Journal of Lightwav
e Technology, vol.6, no.12, pp 1831-1840, "Theo
ry of refractive index variation in quantum well s
tructure and related intersectional optical switc
h ”and KGRavikumar, K.Shimomura, T.Kikugawa, AI
zumi, K.Matsubara, S.Arai, Y.Suematsu, "GaInAsP / In
P MQW intersectional optical switch / modulator usin
g field induced refractive index variation ”, Tran
sactions of the Institute of Electronics, Informati
on and Communication Engineers (IEICE), vol.E72, no.
4, pp 384-392, April 1989, and T. Kikugawa, K.
G.Ravikumar, K.Shimomura, A.Izumi, K.Matsubara, YM
iyamoto, S.Arai and Y.Suematsu, “Switching operati
on in OMVPE grown GaInAs / InP MQW intersectional op
tical switch structure ”, IEEE Photonic Technology
Letters, vol.1, no.6, pp 126-127, June 1988 and J. Nayyer, Y. Suematsu and K. Shimomura, "Analysis
of reflection type optical switches with intersect
ing waveguides ”, IEEE Journal of Lightwave Techno
logy, vol.6, no.6, pp 1146-1152, June 1988 and
K. Shimamura, Y. Suematsu and S. Arai, “Analysis of s
emicoduntor intersectinal waveguide optical switch
-modulator ”, IEEE Journal of Quantum Electronics, v
ol. 26, no.5 pp 883-892, May, 1990 and J. Nayyer
and Safavi-Naini, “Characteristics of reflection
type optical switches with intersecting waveguides
-Electrode length dependency- ”, Transactions of t
he Institute of Electronics, Information and Commu
nication Engineers (IEICE), vol.E73, no.2, pp 195-19
7, Feb. 1990 article: see) This crossed optical switch is
This is advantageous in that it can be monolithically integrated into a semiconductor laser. Based on the results of these experiments and theory, in order to improve the characteristics of the optical switch, the refractive index fluctuation is 1% or more and the value of α (the real value / imaginary value of the refractive index fluctuation) is ≧ 10.
Must.

[0003] This type of cross-type optical switch utilizes the refractive index fluctuation due to the electro-optic effect, so that good high-speed response characteristics can be expected. Further, in the above-mentioned switch, the refractive index fluctuation caused by the addition of an electric field is used in the structure of the quantum well, so that there is a strong possibility that the refractive index fluctuation of 1% or more can be obtained.

[0004] Such a cross-type optical switch can be miniaturized because a large refractive index fluctuation can be obtained. Therefore, there is a strong demand for an electro-optic effect that is substantially more efficient and for improving its switching characteristics.

In a cross-type optical switch, incident light is totally reflected within a critical angle range, but the critical angle should be as large as possible to be practical and capable of reducing insertion loss. It is.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an optical cross-type optical switch having a curved end face electrode having improved switching characteristics of the optical cross-type optical switch and having a high power reflectivity. The purpose is to do. Therefore,
SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical cross-type optical switch having a reduced electrode length and capable of realizing low insertion loss. Further, the present invention operates even when the refractive index difference is within 1% and the α value is within 10 (that is, the operating conditions are relaxed).
It is an object to provide an optical cross-type optical switch.

[0007]

According to the present invention, in order to solve the above-mentioned technical problems, the shape of an electrode end face for providing an electric field constituting an optical cross-type optical switch has a curvature of an exponential function. Provided is an optical cross-type optical switch having improved power reflectivity.

The cross type optical switch of the present invention has a width "a".
And two single-mode waveguides having an intersection angle ".theta.". The electrodes used to activate the predetermined regions of changing the refractive index are of a curved shape, as shown in FIG. The electric field distribution of the guided basic mode is expanded into an infinite number of plane wave components, Snell's law is applied to the combined component, and the power reflectance of the guided mode incident toward the electrode is , The ratio of the reflected component to the entire spatial spectrum of the plane wave.

That is, each component of the spatial frequency of the guided mode is incident on a specific point of the electrode as shown in FIG. It has been found that by adjusting the curvature of the electrode curve 9 in order to increase the reflectivity, all components emitted from the light source point can be totally reflected.

According to the present invention, first, the shape of the electrodes for applying an electric field constituting the cross-type optical switch has a predetermined curvature. That is, all components are incident within the critical angle with respect to the waveguide mode, and are therefore totally reflected.
This is because the curved curvature is adjusted by the inherent critical angle defined for the refractive indexes n ₁ and n ₂ of the medium.
As shown in FIG. 2, since the incident angle β is smaller than the critical angle,
Total reflection is obtained.

The cross-type optical switch of the present invention can be realized, for example, by using an OMVPE growth method with a GaInAsP multilayer quantum well structure on an InP wafer (see the above-cited reference).

In order to form such an electrode, a well-known photolithography technique can be used.

Then, Snell's law is applied to each component,
The power reflectivity of the waveguide mode after entering the electrode is the ratio of the reflection component to the entire spatial spectrum of the plane wave.
The details of the analytical processing method and the description of the parameters are the same as those described in the aforementioned conventional publications.

Each component of the spatial frequency in the propagation mode is shown in FIG.
As shown in FIG. Then, in order to increase the reflectance, the electrode curvature can be adjusted, and the component emitted from the light source point is totally reflected. To obtain this total reflection, the following equation is needed. ρ ^* (φ) / ρ (φ) = − C (1) ρ (φ) indicates the electrode curvature in the curved coordinates, C is a constant, and ρ ^* is The derivative is shown with respect to φ. The solution is ρ (φ) = ρ ₀ exp (−Cφ) (2) The condition of total reflection requires the following inequality. α = tan ⁻¹ C ≧ θ _C (3) Here, θ _C indicates a critical angle determined from the refractive index variation △ _{eq in} the form of the following form. . θ _C = sin ⁻¹ (1-2 △ _eq ) ^1/2 (4) α = θ _C + θ _m in order to consider the light source point along the lateral direction of the waveguide. ......... (5) The electrode length is shown as being several hundred times longer than the width of the waveguide. Therefore, a small θ of about 1-2 degrees
_{At m} , a high reflectance is obtained.

In a cross-type optical switch having linear electrodes, a satisfactory high reflectance of the switch could not be obtained unless the change in the refractive index was at least 1%. In the optical switch of the present invention, a sufficiently high reflectance can be obtained even with a refractive index fluctuation of 1% or less.

Next, the present invention will be described specifically with reference to examples, but the present invention is not limited thereto.

[0017]

FIG. 1 is a plan view showing the structure of a cross-type optical switch according to the present invention, showing an incident light mode, a reflected light mode and a transmitted light mode. The electrode 2 for applying an electric field according to the present invention has a shape whose boundary has a curve 9 as shown in the figure. It has two single-mode waveguides 3, 4 of width "a" that intersect each other at an intersection angle θ. The electrode 2 is for activating a region where the refractive index varies, and has a slightly curved surface 9 as shown in the figure. This curve 9 forms an exponential function. Waveguide basic mode
The electric field distribution of the field expands to an infinite number of plane waves. The portion where the electrode 2 is formed is indicated by oblique lines, and in this portion, the refractive index changes when an electric field is applied.

The light field distribution of the incident mode is as shown in the figure, while the light field distribution of the transmission mode emitted from the port is also shown. The light field distribution of the outgoing reflection mode is also shown.

FIG. 2 shows a state in which a plane wave incident from the center of the waveguide 3 having a width a is totally reflected at a boundary surface 9 between the electrode 2 (see FIG. 1) and a portion whose refractive index is changed by the addition of an electric field. Is shown. The refractive index of the crystal in the portion where no electric field is applied is n ₁ , the refractive index of the portion where the electric field is added is n ₂ , the tangent 7 at the boundary 9 and the perpendicular 8, and the angle φ from the center of the waveguide 3. Incident on the boundary surface 9 with a function ρ (φ) and an angle of about β
Is reflected by

FIG. 3 is a graph in which the vertical axis represents the power reflectance R _Xr from the bent electrode 2 (see FIG. 1) to the port, and the normalized electrode length for various refractive index differences of the waveguide. The relationship l / a is shown on the horizontal axis. The electric field-induced refractive index variation, and △ _eq, if, △ _eq = 1% to. In addition, と し て_W is a normalized refractive index △ _w of the core and clad portions of the waveguide, and these are parameters in FIG.
Indicated. That is, a case having a bent electrode according to the present invention is indicated by a straight line, and a conventional straight electrode is indicated by a dotted line. △ _W is 0.05%, for the case of each of the 0.1% and 0.25%, respectively, normalized electrode length (l / a) and power - the relationship between the reflectance (R _Xr) (%) Is indicated by a solid line. The incident angle θ normalized by the critical angle θ _C is (θ _N = θ / 2θ _C ) θ _N
= 0.4.

In the case of a straight electrode, each result is shown by a broken line for comparison. The power reflectivity of the electrode according to the invention starts to saturate at a shorter distance than in the case of a straight electrode. This has the effect of reducing the insertion loss of the device and relaxes the condition that the ratio (α) between the real part and the imaginary part of the refractive index fluctuation due to the addition of an electric field must be greater than 10. Furthermore, in the case of a moderately standardized waveguide refractive index difference of 0.1% or more, it is impossible to achieve a sufficient power refractive index close to 100% with a linear electrode. However, in the electrode of the present invention,
Exponentially curved electrodes made this possible.

FIG. 4 shows that the intersection angle θ is 6.5 ° and C is 1
When it is 7.6, it indicates the curvature of each electrode with respect to the difference value of ρ ₀ [ρ ₀ / (a / 2) = C, 2C and 3C].
C must be increased in order to obtain a large power reflectivity as observed, i.e. to improve collimated incidence. Therefore, the absorption loss increases.

FIG. 5 shows the extinction ratio (dB) of the port and the port and the normalized crossing angle θ _N [= θ / (2
θ _C )]. The following can be seen from the results. That is, in order to obtain a large extinction ratio (for example, an excess of 30 dB) at the standardized crossing angle θ _N ０．４0.4, the extinction ratio of the port is increased as the standardized crossing angle increases. Increasing the component increases the component that receives total reflection due to the electrode of a fixed length.

That is, the guided mode of incidence is expanded into an infinite spectrum of plane waves, Snell's law is applied to each plane wave, and the reflected and transmitted powers used to calculate the extinction ratio can be calculated.

[0025]

As described above, the following remarkable technical effects were obtained by the optical switch and the method of manufacturing the same according to the present invention. First, depending on the electrode of the curve, the power
Reflectivity was improved. Second, the electrode length was shortened, and the absorption loss of the switch was reduced. Third, therefore, assuming that the refractive index variation due to the applied voltage is 1%,
The electrode shape (advantage of electrode curvature) according to the present invention provides a crossed optical switch in which this variation is further increased.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing the structure of a cross-type switch of the present invention.

FIG. 2 is a schematic explanatory view showing an optical configuration of a cross switch according to the present invention.

FIG. 3 is a graph showing the relationship between the power reflectance R _Xr and the normalized electrode length l / a by the crossed optical switch of the present invention.

FIG. 4 shows the cross angle θ in the cross optical switch of the present invention.
Is 6.5 ° and C is 17.6, ρ ₀ [ρ ₀ /
(A / 2) = C, 2C and 3C] showing the respective electrode curvatures with respect to the difference value.

FIG. 5 is a graph showing the relationship between the attenuation ratio of the cross switch according to the present invention and the normalized cross angle θ _N.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cross-type optical switch 2 Cross-type optical switch electrode, the area | region where a refractive index fluctuates 3 Incident light distribution, incident waveguide 5, 6 port and port 7 Tangent line 8 Normal line 9 Curve which forms an electrode

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor: Safabi Naini Saffieden, Iran, Tehran 14, Noskargarh Avenue, Tehran University, Department of Electrical Engineering (56) References JP-A-59-15225 (JP, A) Journal of Lightwave Technology, Vol. 6, No. 6 (June 1988) p.p. 1146-1152 (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/00-1/035 G02F 1/29-1/313 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. An optical cross-type optical switch characterized in that the shape of an electrode for applying an electric field constituting the optical cross-type optical switch has an exponential curvature, and the power reflectivity is improved.