JPH0553025A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To provide the waveguide type optical switch which can be manufactured at a low loss. CONSTITUTION:The optical switch is provided with a core waveguide 4 for propagating light, formed by providing an intersecting part on a low refractive index layer 2 on a substrate 1, a gap 5 formed in the core waveguide 4 so as to intersect its intersecting part 3, a clad layer 7 formed on the surface of the core waveguide so as to cover its gap face 6, a liquid 8 which is filled in the remaining gap formed between its clad layers 7, and whose refractive index is almost equal to that of the core waveguide 4, and a heater 9 provided in the vicinity of the gap 5 in order to heat the liquid 8, and constituted so as to control the propagation direction of light in the core waveguide by evaporating or condensing the liquid 8 in the gap 5 by a temperature operation of the heater 9 and varying the refractive index in the gap 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical switch for switching or interrupting an optical path by utilizing a phase change of a liquid in a gap provided in a core waveguide.

[0002]

2. Description of the Related Art As optical communication systems become more sophisticated,
There is a growing need for space division type optical switches with low insertion loss and low crosstalk characteristics.

As a method of the above optical switch, the present inventor previously proposed the optical switch shown in FIG. 5 (Japanese Patent Application No. 2-26).
9489). As shown in FIG. 5 (a), this optical switch is provided with a substantially 45-degree cross-section of the T-shaped core waveguide 4.
A gap 17 forming an angle of ° is provided, and the core waveguide 4 is cut into a substantially L-shaped bent waveguide and a linear waveguide.
In the groove of the gap 17, as shown in FIG. 5B, the liquid 8 having a refractive index almost equal to that of the core waveguide 4.
It has a special structure filled with. Then, an electric heating body (thin film heater) 19 formed on the upper surface of the clad 18 around the gap 17 is energized through the distribution line 20 to heat only the vicinity of the gap 17 and the gap 17
The liquid 8 in the inside can be vaporized. That is, in this optical switch, when the liquid 8 filled in the gap 17 is vaporized, the inside of the gap 17 becomes the core waveguide 4
The switching is performed by utilizing the fact that the refractive index is lower than the refractive index of. In FIG. 5 (a),
When the liquid 8 in the gap 17 is evaporated and vaporized by turning on the electricity to the electric heating element 19, the light propagating in the core waveguide 4 from the direction of the arrow 12A to the direction of the arrow 12B is guided to the core of the gap 19. The light is reflected by the end face of the waveguide, the optical path is switched to the orthogonal waveguide, and propagates in the direction of arrow 12C. If the power supply to the electric heating element 19 is turned off and the heating is stopped, the area around the gap 17 is immediately cooled to the temperature before the heating by the heat transfer, and the vaporized liquid 8 is condensed and injected into the gap 17. Goes straight again in the direction of arrow 12B. As described above, this optical switch has the gap 17
A switching operation is performed by achieving the operations of injecting and removing the liquid 8 into and from the inside by evaporating and condensing the liquid 8 by heating and cooling.

[0004]

By the way, in the optical switch of FIG. 5, the entire surface of the core waveguide 4 having a thickness of about 8 μm formed on the substrate 1 via the low refractive index layer 2 has a thickness of 20 to 30.
It is composed of an embedded waveguide completely covered with a μm cladding 18. Therefore, the gap 17 is defined by the core waveguide 4
Must be formed so as to reach the boundary surface between the core waveguide 4 and the low refractive index layer 2 below the core waveguide 4 so as to completely cut. That is, the groove depth of the gap 17 is 28
It becomes ~ 38μm. The gap 17 is formed by forming the clad 18 and then etching the metal film (eg, WSi film) as a mask by dry etching using a fluorine-based gas (eg, CHF ₃ ). here,
The upper limit of the thickness of the metal film that can be formed is 1 μm in consideration of warpage of the substrate 1 due to stress generation, crack generation, and etching pattern accuracy. Therefore, using a metal film of this thickness as a mask,
In order to etch the gap 17 having a depth of m 2, the ratio of the etching rate of the glass film composed of the cladding 18 and the core waveguide 4 to the etching rate of the metal film (that is,
An etching gas and a metal film with an etching selectivity ratio of 28 or more must be used. However, at present, the etching selection ratio is limited to about 20. Therefore, a method of forming two metal films of different materials (for example, Cr and WSi films) to increase the etching selection ratio was also studied, but the accuracy of the mask pattern deteriorates as the thickness of the metal film increases. , Desired gap shape (clearance width 6 μm
, A length of 50 μm and a depth of 28 μm or more) cannot be accurately formed at a desired intersection position of the core waveguide 4, resulting in the realization of a low loss optical switch. Then it turned out to be difficult. When the deep gap 17 is formed as described above, the gap 17
The gap width of the gap 17 expands more and more due to undercutting as the depth of the
There is a problem of deviation from the arrow 12A when this gap 17 is filled with the liquid 8.
It was found that the incident light propagating from the direction increases the loss when passing through the gap 17 and propagating in the direction of the arrow 12B. That is, the transmission loss Tt due to the light passing through the gap 17 is equal to the gap 1 as shown by the following equation.
It increases as the clearance width S of 7 increases. This is a loss due to the mismatch between the optical electric field distributions in the input waveguide and the output waveguide, which is caused by the spread of the input optical electric field distribution in the gap portion.

[0005]

[Equation 1]

Where λ is the wavelength, n _c is the refractive index of the cladding, and ω is the spot size of the light in the basic mode.

Further, it has been found that when the depth of the gap 17 increases, the surface roughness of the inner wall surface of the gap 17 increases and the perpendicularity of the inner wall surface deteriorates. That is, when the liquid 8 does not exist in the gap 17, the incident light is reflected by the inner wall surface of the gap 17 and switched,
This surface roughness causes scattering loss here. Further, when the verticality of the inner wall surface of the gap is deteriorated, a loss is caused due to a mismatch between the optical field after reflection and the optical field in the output waveguide.

As described above, at the current technical level, a technique for accurately forming a gap having a depth of 28 μm or more in terms of width, surface roughness, verticality, etc. has not been realized, and the loss of the optical switch is reduced. It is difficult.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a waveguide type optical switch having a structure which is low in loss and easy to manufacture.

[0010]

In order to achieve the above object, a waveguide type optical switch according to the present invention is a core waveguide for propagating light formed with an intersection on a low refractive index layer on a substrate. A gap formed in the core waveguide so as to cross the intersection, a clad layer formed on the surface of the core waveguide so as to cover the gap surface, and a remaining layer formed between the clad layers. A liquid 8 filled in the gap and having a refractive index substantially equal to that of the core waveguide, and a heater provided near the gap for heating the liquid 8.
Configured to control the propagation direction of light in the core waveguide by vaporizing or condensing the liquid 8 in the gap by changing the temperature of a heater to change the refractive index in the gap. Is. The shape of the intersecting portion includes various shapes such as a T shape, a cross shape, and a brace shape.

It is desirable that another clad layer having a refractive index equal to or lower than that of the clad layer be formed on the upper surface of the core waveguide between the core waveguide and the clad layer.

It is desirable that the heater be provided directly below the gap.

It is desirable to use a quartz glass substrate as the substrate.

[0014]

In the optical switch of the present invention constructed as described above, the gap is formed at the same time when the core waveguide is formed by the dry etching process. Therefore, it is possible to form a gap with good dimensional accuracy, less surface roughness on the inner wall surface, and good verticality. Moreover, even if the gap is wider than the design value due to undercutting during dry etching, the gap can be designed by adjusting the thickness of the clad layer that covers the end face of the gap. It is possible to realize a low-loss optical switch by compensating for deviation from the value.

Thickness W of the clad layer covering the end face of the gap
Is set to be thinner than half the gap width G of the gap. This is to leave a gap for filling the liquid 8 even after the cladding layers are formed so as to cover both gap end surfaces. That is, when the gap width of the gap left here (the remaining gap) is S, the thickness W of the cladding layer is W <(GS) / 2. On the other hand, the thicker the cladding layer that covers the peripheral surface of the core waveguide, the smaller the propagation loss of light propagating in the waveguide. Therefore, another clad layer is formed on the upper surface of the core waveguide between the core waveguide and the clad layer formed so as to also cover the end face of the gap to suppress the propagation loss of light.

If a heater is provided directly below the gap and the liquid 8 in the gap is heated from below, the liquid 8 in the gap is vaporized from the bottom side first, and the remaining liquid 8 is evaporated.
Is quickly exhausted out of the gap by being pushed up by the rise of the generated gas.

The low refractive index layer is a guide layer provided to reduce the propagation loss of light propagating in the core waveguide. Therefore, when a quartz glass substrate having a low refractive index is used as the substrate, the substrate can be used as the low refractive index layer. That is, in that case, the low refractive index layer becomes unnecessary.

[0018]

EXAMPLES Next, examples of the present invention will be described.

FIG. 1 shows an embodiment of the waveguide type optical switch of the present invention. 6A is a plan view, and FIG. 6B is a sectional view taken along the line AA of FIG. In this optical switch, an optical signal propagating in the optical fiber 11a as indicated by an arrow 12A is sent to the optical fiber 1
It is a 1 × 2 optical switch configured to switch the optical path to either 1b or the optical fiber 11c and propagate it in the arrow 12B direction or the arrow 12C direction. The optical fibers 11a, 11b and 11c are respectively connected to different side walls of a rectangular package 18 containing a waveguide type optical switch element. The waveguide type optical switching element has a T-shaped core waveguide 4 formed on a substrate 1 via a low refractive index layer 2, and each of the optical fibers 11a, 11b, 11
The c is provided so that the core 14 is brought into close contact with the end face of the core waveguide of the waveguide type optical switch element. At the T-shaped intersection 3 of the core waveguide 4, a gap 5 is formed so as to cross the optical axis of incident light from the direction of arrow 12A at an angle of approximately 45 degrees. A clad layer 7 is formed on the surface of the core waveguide 4 so as to cover the gap end face 6 as well. The liquid 8 is stored in the upper space of the package 18, and the remaining gaps formed between the clad layers 7 are filled with the liquid 8. Inside the substrate 1, a heater 9 for heating the liquid 8 is provided directly below the gap 5. That is, in this optical switch, the liquid 8 filled in the gap 5 can be vaporized by heating the heater by turning on / off the power supply to the heater 9, or the vaporized liquid 8 can be stopped by heating the heater and condensed. The optical path is switched by changing the refractive index in the gap.

Each component of this optical switch will be described more specifically.

The substrate 1 is made of glass (quartz glass, quartz glass containing a refractive index controlling additive, multi-component glass,
Etc.), semiconductors (Si, GaAs, InP, etc.), electro-optic crystals (LiNbO ₃ , LiTaO ₃ , etc.), magnetic materials (eg Y ₃ Fe ₅ O ₁₂ ), polymer materials (polyurethane, epoxy, polycarbonate, etc.) ), Sapphire or the like can be used.

For the low refractive index layer 2, the core waveguide 4, and the clad layer 7, the above-mentioned glass, semiconductor, polymer material or the like can be used. However, the refractive index n _w of the core waveguide 4 has a refractive index n _c of the cladding 4, so that a higher value than the refractive index n _b of the low refractive index layer 2 is adjusted by the refractive index control additives. For example, when the waveguide is a single mode waveguide, the thickness and width of the core waveguide 4 are selected from the range of several μm to 15 μm, and the refractive index n _w of the core waveguide 4 and the refractive index n _{c of the} cladding layer 7 are selected. (Or the refractive index n _b of the low refractive index layer 2)
And the relative refractive index difference is 0. It is selected from the range of several% to 2%. Here, n _c and n _b are substantially equal values, or n _c > n in order to reduce the radiation mode loss to the substrate.
_b is preferred. The thicker the low refractive index layer 2 is, the more the propagation loss can be reduced, but if the thickness is 5 μm or more, there is no problem. The thicker the clad layer 7 is, the more the propagation loss of the light propagating in the core waveguide 4 can be reduced. In this case, if the clad layer 7 is thick enough, The increase in loss with respect to can be kept small. When a quartz glass substrate is used as the substrate 1, since the entire substrate has a low refractive index, it is not necessary to separately form the low refractive index layer 2 on the surface thereof. Therefore, the step of forming the low refractive index layer 2 can be omitted, and the manufacturing process of the optical switch can be simplified.

Since the gap 5 is formed at the same time when the core waveguide 4 is formed by using the dry etching process, the gap 5 is formed in a good shape with good dimensional accuracy, inner wall surface condition and verticality. The depth of the gap 5 is set to reach the low refractive index layer 2. The clearance width S of the remaining gap finally formed by covering the surface of the core waveguide 4 with the cladding layer 7 is selected from the range of 1 to 6 μm, and this clearance width S is calculated from the equation (1). As you can see, it is preferable to be narrow. This clearance width S can be easily controlled by adjusting the thickness of the cladding layer 7. Even if the gap width of the gap 5 becomes wider than the set value due to undercutting during dry etching, the thickness of the clad layer 7 to be formed thereafter can compensate for the proper width. This enables a low-loss optical switching operation.

As the liquid 8, a liquid having a refractive index equal to that of the core waveguide 4 is used. For example, when silica glass containing Ge is used for the core waveguide 4,
As liquid 8, fluorobenzene (C ₆ H ₅ F: temperature 20
A refractive index of 1.46412 at ℃, boiling point 84.9 ℃) can be used.

The heater 19 is inserted into the hole 15 formed by extending from the lower surface of the substrate 1 to the vicinity of the upper surface. Since the heater 19 is provided immediately below the gap 5, the liquid 8 in the gap 5 is heated from below and is vaporized first from below. The remaining liquid 8 in the gap 5 is pushed up by the rise of the previously generated gas and is quickly discharged to the outside of the gap 5. Therefore, switching can be performed at high speed and reliably.

Although not disclosed in FIG. 1, the package 18 is actually provided with an upper lid, and has a structure in which the liquid 8 does not leak to the outside of the package. Therefore, the optical fibers 11a, 11b, 11c are also package 1
8 is airtightly connected.

FIG. 2 shows another embodiment of the optical switch of the present invention. Figure (a) is a plan view of the optical switch element, and (b) is (a).
A-A 'sectional drawing of is shown. A first clad layer 10 is formed on the surface of the T-shaped core waveguide 4 so as to cover only the upper surface thereof, and further covers the first clad layer 10 and the gap surface 6 as well. The second clad layer 16 (corresponding to the clad layer 7 in FIG. 1) is formed. Refractive index n _c 'is the refractive index n _c equal to or lower refractive index than that of the second cladding layer 16 (n _c' of the first cladding 16 are chosen to be <n _c). The first cladding 10 is provided to improve the confinement of light in the core waveguide 4, and its thickness is 1 to 5 μm.
Selected from the range of.

As described above, the waveguide type optical switch of the present invention can be easily manufactured by using the dry etching process established as a manufacturing technique of semiconductor integrated circuits, and can be easily mass-produced, so that the cost is low. Can be expected.

As described above, the bending angle θ _I intersecting the T-shape (that is, the bending angle θ _I from one exit side core waveguide 4b coaxially provided with the entrance side core waveguide 4a to the other exit side core waveguide 4c Although the optical switch having the core waveguide 4 (set to θ _I = 90 °) has been described as an example, the bending angle θ _I may be in the range of θ _I = 40 ° to 90 °. However, when the bending angle θ _I is θ _I = 40 °, the gap angle θ _{II with} respect to the incident optical axis is θ _II = 20 °, and θ _I = 60.
The gap angle θ _II is also selected from the range of θ _II = 20 ° to 45 ° according to the bending angle θ _I , such as θ _II = 30 ° when the angle is °.

In addition to the 1 × 2 type optical switch described so far, the waveguide type optical switch of the present invention has n × m type and m × m type optical switches (n
It can also be applied to ≧ 1, m> 2). That is,
The optical switch of the present invention can be easily integrated and multi-functionalized by utilizing the manufacturing process of the semiconductor integrated circuit. FIG. 3 is an example of a 4 × 8 optical switch with 4 inputs and 8 outputs, and FIG. 4 is an example of a 6 × 6 optical switch with 6 inputs and 6 outputs. A gap and a heater are formed at each lattice point position of the core waveguide 4 formed in a lattice shape so that switching can be performed at each lattice point of the core waveguide 4. In FIG. 3, arrows A _{1 to} A ₄
Indicate the direction of the optical signal incident to the core waveguide 41 a to 41 d, an arrow _{B 1 ~B 4, C 1 ~C} 4 indicates the direction of the optical signal emitted from the core waveguide. Similarly, in FIG. 4, arrows D _{1 to} D ₃ and E _{1 to} E ₃ indicate the directions of incident optical signals, and arrows F _{1 to} F ₃ and G _{1 to} G ₃ indicate the directions of outgoing optical signals. .. Here, core waveguide mutual distance a ₁ ~a ₃ adjacent, b ₁ ~b ₃ may have equally well be, or different from each other.

[0031]

In summary, according to the present invention, the following excellent effects can be exhibited.

(1) Since the gap can be formed at the same time when the core waveguide is formed by using the dry etching process, it is possible to form the gap shape with good dimensional accuracy, inner wall surface condition, and verticality. it can. Moreover, even if the gap width of the gap widens due to undercutting during dry etching, it is possible to compensate for the appropriate width by the thickness of the clad layer formed thereafter. Therefore, a low-loss optical switch can be realized.

(2) On the upper surface of the core waveguide between the core waveguide and the clad layer formed so as to cover the end face of the gap as well, another refractive index equal to or lower than that of the above clad layer is provided. By forming the clad layer,
The propagation loss of light can be reduced.

(3) By providing the heater just below the gap, the switching speed can be increased.

(4) If a quartz glass substrate having a low refractive index is used as the substrate, the substrate can be substituted for the low refractive index layer, so that the manufacturing process of the optical switch can be simplified.

Since it has a simple structure and can be easily manufactured, (5) it can be easily manufactured by utilizing the manufacturing process of a semiconductor integrated circuit, and the mass production is easy, so that cost reduction can be expected.

[Brief description of drawings]

1A and 1B are diagrams showing an embodiment of a waveguide type optical switch of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a sectional view taken along the line AA ′ in FIG.

2A and 2B are views showing another embodiment of the waveguide type optical switch of the present invention, wherein FIG. 2A is a plan view of the waveguide type optical switch element, and FIG. 2B is a sectional view taken along line AA ′ of FIG. 2A. It is a figure.

FIG. 3 is a schematic view showing an example in which the waveguide type optical switch of the present invention is applied to an n × m type optical switch.

FIG. 4 is a schematic view showing an embodiment in which the waveguide type optical switch of the present invention is applied to an m × m type optical switch.

5A and 5B are views showing a conventional example, in which FIG. 5A is a plan view and FIG.
FIG. 7A is a sectional view taken along the line AA ′ in (a).

[Explanation of sign]

 1 Substrate 2 Low Refractive Index Layer 3 Intersection 4 Core Waveguide 5 Gap 6 Gap Face 7 Cladding Layer 8 Liquid 9 Heater 10 First Cladding Layer (Another Cladding Layer)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuyuki Imoto 3550 Kidayomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable Ltd. Advanced Research Center

Claims (4)

[Claims] 1. A core waveguide through which light propagates and which is formed on a low refractive index layer on a substrate so as to have an intersection, and a gap formed in the core waveguide so as to cross the intersection. ,
A clad layer formed on the surface of the core waveguide so as to cover the gap surface, and the remaining gap formed between the gap surfaces of the clad layer are filled with a refractive index substantially equal to that of the core waveguide. A liquid and a heater provided in the vicinity of the gap for heating the liquid are provided, and the liquid in the gap is vaporized or condensed by operating the temperature of the heater to change the refractive index in the gap. Thus, the waveguide type optical switch is configured so as to control the propagation direction of the light in the core waveguide. 2. A clad layer having a refractive index equal to or lower than that of the clad layer is formed on an upper surface of the core waveguide between the core waveguide and the clad layer. Waveguide type optical switch. 3. The waveguide type optical switch according to claim 1, wherein the heater is provided immediately below the gap. 4. The waveguide type optical switch according to claim 1, wherein a quartz glass substrate is used as the substrate.