JP2756154B2 - Light switch - Google Patents

Description

Description: BACKGROUND OF THE INVENTION (Field of Industrial Application) The present invention relates to optical switching made of a semiconductor, and more particularly, to an optical switch that can suppress deterioration of an extinction ratio and an increase in excess loss.

(Prior Art) A Y-branch optical waveguide type optical switch composed of a semiconductor material is, for example, a perspective view shown in FIG. 11 and an XII-XII shown in FIG.
The structure is as shown in FIG. 12, which is a cross-sectional view along the line.

That is, an n ⁺ -type semiconductor layer 2 and an n ⁺ -type semiconductor layer 3 are sequentially stacked on the lower electrode 1, and a lower cladding layer 4 of an n ⁺ -type semiconductor and a core of an n ⁻ -type semiconductor are further formed thereon. The layers 5 are sequentially stacked.

On the core layer 5, as shown in FIG. 12, p ⁺ -type upper cladding layer 6 made of a semiconductor is formed on a ridge shape to Y branch at an angle theta, on its upper surface p ⁺ -type semiconductor cap layer
19 are laminated, and the upper surface thereof is covered with the insulating thin film 7.

Here, the main optical waveguide B located on the optical path upstream side of the branch part A is a light wave incident port, and the two branch side optical waveguides C ₁ and C ₂ located on the optical path downstream side of the branch part A are either Are also light wave output ports.

On the downstream side of the optical path from the branch portion A in the branch side optical waveguides C ₁ and C ₂ , a part of the insulating thin film 7 is removed in a slit shape to form windows 7 a and 7 b. From these windows, a predetermined material is vapor-deposited on the cap layer 9 located on the upper surface of the upper cladding layer 6, for example, and upper electrodes 8a and 8b to be joined to the cap layer 9 are formed. Wave path C ₁ ,
Refractive index control unit D _1, D ₂ in C ₂ is formed.

In the case of an optical switch having this structure, for example, the upper electrode 8a is connected to _one branch-side optical waveguide (this is referred to as a branch-side optical waveguide C1).
When a predetermined value of current is injected or a predetermined value of voltage is applied from above, the refractive index of that portion is reduced and the propagation of the light wave is completely stopped. As a result, all the light wave incident from the optical main waveguide B is emitted from the other branch side waveguide C _2, the optical path switching, i.e. to realize the switching action.

(Object-action to be Solved by the Invention) However, when considering the switching of optical paths in the optical switch of this structure, for example, when actuated the refractive index control unit D _1, the light wave propagated through the main optical waveguide B it is preferable that propagates immediately changing the traveling direction to the branch optical wave guide C ₂ immediately after the branch portion a.

For this purpose, for example, as shown in the plan view of FIG. 13, the refractive index control unit D ₁ of the branch portion A branch point an end face of the side A ₁ -A ₃
It constituted by plane connecting and it is ideal for constituting the end faces of the branch portion A side of the refractive index control unit D ₂ a plane connecting the branch point A ₂ -A _3.

However, with such a shape, the refractive index control units D ₁ and D ₂
When forming, for example the refractive index control unit D ₁ and actuated performing refractive index control of the branch optical wave guide C _1, contact refractive index control section D ₂ is the refractive index control unit D ₁ at a branch point A ₃ So
Refractive index control unit D ₂ also would operate together. That is,
When a refractive index control unit considered to be ideal as shown in FIG. 13 is formed, each of the refractive index control units cannot be operated independently of each other, and eventually, it becomes impossible to switch the optical path. The problem is inevitable.

On the other hand, as shown in the plan view of FIG. 14, when the end surface of each of the refractive index controllers D ₁ and D ₂ on the side of the branch A is separated from the branch A and formed on the downstream side of the optical path, When the positions of the refractive index controllers D ₁ and D ₂ are on the downstream side, the problem as in the case of FIG. 13 does not occur.

However, in this case, the optical path that has propagated through the main optical waveguide B reaches the respective refractive index control sections D ₁ and D ₂ after being completely distributed to the respective branch side optical waveguides C ₁ and C ₂ at the branch section A. As a result, the radiation mode significantly increases and recombine with the waveguide mode, thereby deteriorating the extinction ratio and increasing the loss.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in the conventional Y-branch optical waveguide type optical switch and to provide an optical switch capable of suppressing both deterioration of the extinction ratio and increase of the loss.

(Means and Actions for Solving the Problems) In general, when the distance between the two refractive index control units is reduced in the branching section of the Y-branch optical waveguide type optical switch, the deterioration of the extinction ratio decreases accordingly. This is because the traveling direction of each light wave is controlled by the action of the refractive index control unit before the light wave propagating through the main optical waveguide is completely distributed to the two branch-side optical waveguides at the branch part. That is, the guided mode becomes difficult to couple with the radiation mode.

Therefore, the present inventors have proposed a method of changing the spot size of a light wave propagating in a branch-side optical waveguide, which has a spot size defined as described below, when the spot size is changed. Investigation was made on the relationship between the extinction ratio and the amount of increase in excess loss, and it was confirmed that the relationship shown in FIG. 1 was established between these factors. In the figure, the solid line represents a change in the extinction ratio, and the dotted line represents a change in the amount of increase in excess loss.

Here, the spot size is defined as the following value.

First, the light intensity distribution in the optical path cross section of the light wave propagating through the branch-side optical waveguide is drawn with the horizontal axis representing the path width extending from the center of the optical path to the left and right, and the vertical axis representing the light intensity. As shown in FIG. 2, the light intensity distribution curve p symmetrical light intensity on the left and right of the road-width direction has a peak value p ₁ at the optical path center decays are obtained.

Two points p ₂ and p ₃ (p ₂ = p ₃ = p ₁ × 1 / e) where the light intensity is reduced to a value of p ₁ × 1 / e ² (where e represents the base of natural logarithm)
² ) is obtained on the curve p. At this time, these points p
_2, p ₃ width value of the light path is indicated when minus perpendicular to the horizontal axis from, that is, the distance l shown in Figure 2 is defined as twice value of spot size. That is, the spot size in the present invention is defined as l / 2.

Normally, the extinction ratio is required to be larger than 20 dB. For this purpose, as apparent from FIG. 1, the ratio between the interval between the refractive index control units and the spot size is set to 5 or less. Is required. That is, it is necessary that the interval between the refractive index control units is within 5 times the spot size.

Also, if the allowable limit of the amount of increase in overprinting is set to 1.5 dB, it is necessary to set the interval between the refractive index control units within twice the spot size, as is apparent from FIG. Become.

Therefore, in order to suppress both the deterioration of the extinction ratio and the increase amount of the excess loss with the above values, the interval between the refractive index control units should be set to within twice the spot size.

For this reason, the optical switch provided in the present invention includes a main optical waveguide and two branch-side optical waveguides branched from the branch portion thereof, respectively. In an optical switch in which a refractive index control unit is formed, each refractive index control unit extends to the branching unit, where the branching unit is closest to and parallel to the branching unit, and each other in the branching unit. When the distance between the refractive index control units is the distance between the closest points between the branch-side optical waveguides, when drawing a light intensity distribution curve in the optical path cross section of the branch-side optical waveguide, the light intensity has a peak value of 1 / e ² times value (although, e is the base of natural logarithms)
Of the width value indicated by the light intensity distribution curve at the reduced point
It is characterized in that the value is not more than twice the spot size defined as a 1/2 value.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a schematic plan view of the optical switch according to the embodiment, and FIG. 4 is a sectional view taken along the line IV-IV in FIG.

In the figure, an n ⁺ GaAs semiconductor layer 12, n
⁺ GaAs semiconductor layers 13 are sequentially stacked, and further thereon n
⁺ Al _0.1 Ga _0.9 As semiconductor lower cladding layer 14, n ^- GaAs
A core layer 15 made of a semiconductor layer and having a thickness of 1 μm is laminated in this order.

An upper cladding layer 16 made of a p ⁺ Al _0.1 Ga _0.9 As semiconductor is formed on the core layer 15, and its upper surface is covered with an insulating thin film 17.

A part of the upper cladding layer 16 is in the form of a ridge having a thickness of 1 μm, and a cap layer 19 made of p ⁺ GaAs semiconductor is laminated on the upper surface of the upper cladding layer 16 in the ridge. Constitute the main optical waveguide B and the branch-side optical waveguides C ₁ and C ₂ .

Here, the main optical waveguide B and the branch optical waveguides C ₁ and C ₂ each have a path width of 6 μm, and the branch angle θ between the branch optical waveguides C ₁ and C ₂ is 2 °.

A part of the insulating thin film 17 covering the branch side optical waveguides C ₁ and C ₂ is removed, and windows 17 a and 17 b having a planar shape as shown in FIG. 3 are formed in each of the optical waveguides C ₁ and C ₂ . The upper electrodes 18a and 18b bonded to the cap layer 19 are formed in each window by depositing an appropriate electrode material from above. For example, upper electrode 1
When a current is injected from 8a into the cap layer 19 or a voltage is applied between the cap layer 19 and the n ⁺ type semiconductor layer 12, the window 17
The refractive index of the portion of the branch-side optical waveguide located below a changes. That is, the portions of the branch-side optical waveguide corresponding to the shapes of the windows 17a and 17b function as refractive index controls D ₁ and D ₂ .

The location where the branch-side optical waveguides D ₁ and D ₂ are closest to each other, that is, the interval x between the refractive index controllers D ₁ and D ₂ in the branch portion A is 1
It is 0 μm.

In the optical switch having such a structure, the spot size of the light wave propagating in the branch-side optical waveguide is set to 5 μm.
Computer simulation of light wave propagation in each of the branch-side optical waveguides C ₁ and C ₂ was performed. In this case, the interval x between the refractive index control units is twice the spot size.

The results are shown in FIGS. 5 and 6. FIG.
In view showing a refractive index distribution in a state in which current injection only to the refractive index control unit D _1, the refractive index of the branch optical wave guide C ₁ immediately after substantially branch portion A indicates that the decrease. Figure 6 is in a state of the refractive index control unit D ₁ as of FIG. 5 is a diagram obtained by simulating the state of a light wave propagating in the branch side waveguide C _2. Sixth
As is clear from the figure, the propagation state of the light wave is good.
At this time, the extinction ratio was 20 dB or more, and the increase in excess loss was suppressed to about 1.5 dB.

7 and 8 show the state of the refractive index distribution when the refractive index controllers D ₁ and D ₂ are not operated (FIG. 7), and the propagation state of the light wave in each branch-side optical waveguide at this time. (Eighth
Figure).

FIG. 9 shows that the formation positions of the refractive index controllers D ₁ and D ₂ are retreated to the downstream side, except that the distance x between the closest parts between the refractive index controllers D ₁ and D ₂ is 25 μm. FIG. 4 is a plan view of a comparative optical switch having the same structure as the optical switch of the embodiment. In this optical switch, the interval between the refractive index controllers is five times the spot size.

The extinction ratio of this optical switch is lower than that of the optical switch of the embodiment, but is about 20 dB. But,
The excess loss increases by about 3 dB, resulting in a loss of half of the incident power.

FIG. 10 shows that the formation positions of the refractive index controllers D ₁ and D ₂ are further retreated further downstream, and the distance x between the closest parts between the refractive index controllers D ₁ and D _{2 is set} to 50 μm. FIG. 11 is a plan view of a second comparative example optical switch having the same structure as the optical switch of the example except for the above. In this optical switch, the interval between the refractive index controllers is 10 times the spot size.

In the case of this optical switch, the traveling direction of the light wave is suppressed by the refractive index controllers D ₁ and D ₂ after the light wave incident at the branch part A is completely distributed to the branch side optical waveguides C ₁ and C ₂ . Therefore, the extinction ratio is less than 20 dB, which is not practical.

(Effects of the Invention) As is clear from the above description, in the optical switch of the present invention, the refractive index control portion extends to the branch portion, and the branch portion has the closest parallel relationship, and Since the interval between the refractive index control sections in the branch section is set to be equal to or less than twice the spot size of the light wave propagating through the branch-side optical waveguide, the number of waveguide modes coupled to the radiation mode decreases, and extinction occurs. The ratio can be suppressed to 20 dB or more, and the excess loss can be suppressed to within 1.5 dB.

[Brief description of the drawings]

FIG. 1 is a graph showing the correlation between the distance between the refractive index control units, the spot size of the light wave, the extinction ratio, and the amount of increase in excess loss. FIG. 2 is an explanatory diagram for defining the light wave spot size. FIG. 4 is a plan view of an optical switch according to an embodiment of the present invention, FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 3, and FIG. FIG. 6 is a computer simulation diagram showing a light wave propagation state under the state of FIG. 5, and FIG. 7 is a refractive index distribution when the refractive index control unit is not operated. FIG. 8, FIG. 8 is a computer simulation diagram showing a light wave propagation state in the state of FIG. 7, FIG. 9 is a plan view of a comparative example optical switch, FIG.
FIG. 11 is a plan view of another comparative example switch, FIG. 11 is a perspective view of an example of a Y-branch optical waveguide type optical switch, and FIG. 12 is XII-X of FIG.
13 is a cross-sectional view taken along the line II, FIG. 13 is a plan view showing an example of forming a refractive index control section, and FIG. 14 is a plan view showing another example of forming. 11 ... lower electrode, 12 ... n ⁺ type semiconductor layer, 13 ... n ⁺ type semiconductor layer, 14 ... lower cladding layer (n ⁺ type semiconductor layer), 15 ...
Core layer (n ^- type semiconductor layer), 16: Upper cladding layer (p ⁺ type semiconductor layer), 17: Thin insulating film, 17a, 17b ... Window, 18a, 18b
... top electrode, 19 ... cap layer (p ⁺ type semiconductor layer), A
…… Branch part, A ₁ , A ₂ , A ₃ … Branch point, B …… Main optical waveguide,
C ₁ , C ₂ … branch-side optical waveguide, D ₁ , D ₂ … refractive index controller, w
..., Path width, x... Distance of the closest point between the refractive index control units, θ...

Continuation of front page (56) References JP-A-1-128046 (JP, A) JP-A-61-73931 (JP, A) JP-A-59-214020 (JP, A) JP-A-57-200016 (JP, A) JP-A-63-314518 (JP, A) IEICE Technical Report OQE84-105 PP. 67-74 IEICE Technical Report OQE83-87 PP. 1-6

Claims (1)

(57) [Claims] 1. An optical switch in which a refractive index control section is formed in each of the branch-side optical waveguides of a Y-branch optical waveguide composed of a main optical waveguide and two branch-side optical waveguides branched from each other. In each of the above, the respective refractive index control units extend to the branch portion, at which the refractive index control portions are closest to each other and form a parallel relationship, and the interval between the refractive index control portions in the branch portion is equal to the branch value. When the light intensity distribution curve in the optical path cross section of the side optical waveguide is drawn, the light intensity distribution at the point where the light intensity decreases to 1 / e ² times the peak value (where e represents the base of natural logarithm) An optical switch characterized in that it has a value equal to or less than twice the spot size defined as a half value of the width value indicated by the curve.