JPH0254929B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical switch that electrically deflects the traveling direction of light traveling through a waveguide.

[Conventional technology]

Light switching can be performed by arranging two waveguides in parallel and controlling the interaction between each waveguide.

In other words, when two parallel waveguides have exactly the same structure, light incident on the input port of one waveguide gradually moves to the other waveguide, and after propagating a certain distance, the light The light completely transfers to the other waveguide, but as it propagates further, it gradually transfers back to the original waveguide, and after propagating a certain distance, it completely transfers to the original waveguide. . In this way, light periodically moves between the two waveguides and returns with respect to the propagation distance.

When the structures of the two waveguides, that is, the refractive indexes, are sufficiently different, the light does not immediately transfer to another waveguide, but propagates through the waveguide into which it is incident.

FIG. 2 is a plan view showing a conventional directional coupler type optical switch that utilizes such a phenomenon. In the figure, 1 and 2 are waveguides having the same structure. These waveguides 1 and 2 are arranged in parallel, and the propagation lengths 1c and 2c between the respective input ports 1a and 2a and output ports 1b and 2b are formed to have a length L that allows the light to completely migrate. , control electrodes 3 and 4 are arranged on the propagation paths 1c and 2c, respectively.

In this configuration, when no voltage is applied to the electrodes 3 and 4, for example, light incident on the input port 1a of one waveguide 1 is emitted from the output port 2b of the other waveguide 2. In addition, when voltage is applied to the electrodes 3 and 4, the propagation path 1 of the waveguides 1 and 2
Since there is a difference in refractive index between c and 2c, the light incident on the input port 1a of one waveguide 1 does not transfer to the other waveguide 2, but continues along the propagation path 1c and exits the same waveguide. 1 output port 1b.

Although the conventional directional coupler type optical switch has been described above, this optical switch has the following problems.

[Problem that the invention seeks to solve]

In other words, in the optical switch described above, the propagation path must be manufactured accurately to the length L where light transfers, and the manufacturing conditions are strict and the error is 6.
Only about % is allowed. However, with the current technology, when manufacturing the propagation path, the length L tends to change depending on the process, so it is difficult to manufacture the length L accurately.

One way to solve this problem is to, for example,
It is conceivable to construct a Δβ directional coupler type optical switch that controls two sets of electrodes as described in ``S2-2'', but since the electrode structure would be complicated, the high-speed operation of the element would be required. However, this method has the problem of going against the simplification of the control system.

Further, even in this Δβ directional coupler type optical switch, parallelism and uniformity of the two waveguides are still required.

The present invention was made in order to solve these problems, and has realized a waveguide type optical switch that has easy manufacturing conditions and can perform optimal switch operation with simple control as long as the element length is longer than a certain value. The purpose is to

[Means for solving problems]

Therefore, in the present invention, one of the two waveguides arranged in parallel is formed so that its equivalent refractive index changes at a constant value with distance, and the two waveguides have an equivalent refractive index. It is designed to have equal parts. Parts with equal equivalent refractive index can be obtained by making the waveguide widths the same or by electrically controlling the refractive index.

[Effect]

According to the above-described means, a good light switching operation can be performed by adjusting the magnitude of the equivalent refractive index by the voltage applied to the electrodes provided on each waveguide.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of a waveguide type optical switch according to the present invention. In the figure, 1 and 2 are waveguides arranged parallel to each other, each consisting of input ports 1a and 2a, output ports 1b and 2b, and propagation ports 1c and 2c. In the embodiment, the width of the propagation path 2c of one waveguide 2 is changed from the input port 2a to the output port 2b.
By forming the refractive index so that it gradually becomes wider toward , the equivalent refractive index changes at a constant value with distance.

The equivalent refractive index of the propagation path 1c of the waveguide 1 is constant as in the conventional case.

3 and 4 are electrodes provided on the propagation paths 1c and 2c.

Fig. 3 is a diagram showing the operating characteristics of the optical switch with the above-mentioned configuration, and Fig. 4 is a diagram showing the equivalent refractive index when operating the optical switch. Explain the action.

First, cross state, that is, waveguide 1 (or 2)
The light incident from input port 1a (or 2a) of
(or 1b).

Here, the equivalent refractive index of the propagation paths 1c and 2c in the waveguides 1 and 2 shown in FIG.
It is assumed that the lines change as shown by straight lines 1c' and 2c' in the figure.

In this state, a voltage is applied to electrodes 3 and 4. For example, in the case of a LiNbO ₃ -C plate, if electrode 3 is set to positive and electrode 4 is set to negative, the equivalent refractive index changes by a constant value Δn' regardless of the distance, and the straight line 1c ″, 2c″.

In this case, the light incident from the input port 1a (or 2a) of the waveguide 1 (or 2) passes through the waveguide 2 (or 2) while propagating through the propagation path 1c (or 2c) as shown in FIG. 1) Propagation path 2c
(or 1c). and,
Since the position of the transition point changes by changing Δn′ depending on the voltage, light will always migrate from input port 1a to output port 2b, or from input port 2a to output port 1b, if certain conditions described below are met. It is possible to create a state.

Next, the bar state, that is, the light incident from the input port 1a (or 2a) of the waveguide 1 (or 2),
Consider a state in which light is emitted from the output port 1b (or 2b) of the same waveguide 1 (or 2).

Again, it is assumed that the equivalent refractive indexes of the propagation paths 1c and 2c change with distance like the straight lines 1c' and 2c' shown in FIG. 4.

In this state, in the opposite direction to the cross state mentioned above,
For example, in the case of a LiNbO ₃ -C plate, by applying a negative voltage to electrode 3 and a positive voltage to electrode 4, the equivalent refractive index is changed by Δn″ to become straight lines 1c″ and 2c″. In this case, the equivalent refractive index The amount of change Δn″ is set to be greater than the amount of change Δn′ in the equivalent refractive index that creates a cross state.

Therefore, when light is made to enter from the input port 1a (or 2a), the power of the light propagates through the propagation path 1c (or 2c) while vibrating as shown in FIG. At this time, there is a point where the light power completely remains in the incident propagation path 1c (or 2c), but by changing the amount of change Δn'' in the equivalent refractive index, this light power completely remains. You can move the pointing point.

In this way, the light travels along the propagation path 1c (or 2c),
The light is emitted from the output port 1b (or 2b).

Next, the relationship between the required element length of the optical switch and the switch voltage will be explained.

In the cross state, the propagation path 1c (or 2c)
When light is incident on the propagation path 1c (or 2c)
The transition power at infinity when extended is P (1c → 1b) = 1-EXP {-π/(α/K ² )} where K is the coupling coefficient and α is the rate of change in the equivalent refractive index difference with respect to distance.
...It is expressed as (1). That is, the power of the light oscillates as shown in FIG. 3 and converges to the value determined by equation (1) above.

When the ratio of the power of the light incident on the propagation path 1c (or 2c) and the power of the light remaining on the propagation path 1c (or 2c) is 30 dB, α/K ² = 0.45,
At 20dB, α/K ² =1.47. That is, unless α/K ² is sufficiently small, the high extinction ratio characteristics shown in FIG. 3 cannot be obtained.

If the element length is 2l as shown in Figure 1, the normalized equivalent refractive index difference is Δn/K = αl/K, and the normalized element length is Kl, then α/K ² = (Δn/K) /(Kl), and the characteristics of the convergence of optical power are determined using this value as a parameter. This is stated in "Transactions of the Institute of Electronics and Communication Engineers J64-C [10] 666 ('81)".

However, the switch operation shall be performed under the condition of Δn′Δn.

The required length of the element is determined by the parameter αl ² , according to “J.Opt.Soc.America 65
[7] 804 ('75)". That is,
It can be expressed as αl ² = α/K ²・(Kl) ² = (Δn/K)・Kl. αl ²
determines how the optical power changes with respect to the propagation distance, especially the number of oscillations of the optical power.

A graph of Δn/K versus Kl with α/K ² and αl ² as parameters is shown in FIG. This determines the characteristics of the optical switch, αl ² needs to be approximately 10 or more,
α/ ^K2 must be 1.47 or less.

Since αl ² =(Δn/K)·Kl, a curve with αl ² = constant is represented by a hyperbola, and the value increases as it goes to the upper right. Also, since α/K ² = (Δn/K)/(Kl),
A line where α/K ² =constant is represented by a straight line, and the smaller αK ² is, the smaller the slope of the straight line is.

The black circle αl ² =5 in FIG. 5 indicates the operating point of a normal directional coupler. Moreover, the points , , , indicate the values of the element structure parameters in FIG. 3 , , , , . According to this, the points are α/K ² =1.47 or more and αl ² =10 or less, which is inappropriate as an element structure, and the characteristics are poor as shown in FIG.

〔Effect of the invention〕

As explained above, the present invention forms one of the two waveguides arranged in parallel by changing the width so that the equivalent refractive index changes at a constant value with distance, and Since the structure is such that electrodes are provided on the wavefront, the following effects can be obtained.

In other words, in the conventional directional coupler type optical switch, high precision was required for the parallelism and uniformity of the two waveguides, but in the optical switch according to the present invention, this is not necessary and If there is, a switch operation is possible, which greatly eases the manufacturing conditions.

Furthermore, the conventional Δβ directional coupler type optical switch uses four electrodes and performs switch operation based on the combination of voltages applied thereto, making high-speed operation difficult; however, in the present invention, the electrodes Since only two electrodes are required, ultrahigh-speed operation is possible by employing traveling wave electrodes.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an embodiment of the waveguide type optical switch according to the present invention, FIG. 2 is a plan view showing a conventional optical switch, and FIG. 3 is a diagram showing the operating characteristics of the embodiment of FIG. 1. , FIG. 4 is a diagram showing changes in the equivalent refractive index of the waveguide during operation of the embodiment of FIG. 1, and FIG.
The figure shows the characteristics of an optical switch element. 1, 2: Waveguide, 1a, 2a: Input port, 1
b, 2b: output port, 1c, 2c: propagation path,
3, 4: Electrode.

Claims (1)

[Claims] 1. In a waveguide type optical switch constructed by arranging two waveguides in parallel and providing an electrode on each waveguide, the equivalent refractive index of one waveguide is What is claimed is: 1. A waveguide type optical switch, characterized in that the two waveguides have portions having an equal equivalent refractive index; 2. The waveguide type optical switch according to claim 1, wherein said one waveguide changes the equivalent refractive index at a constant value with distance by changing the width.