JP2994807B2 - Waveguide type optical switch - Google Patents

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 the middle of a core waveguide.

[0002]

2. Description of the Related Art As optical communication systems become more sophisticated,
There is an increasing need for a space division optical switch having low insertion loss and low crosstalk characteristics.

As a method of the above optical switch, the present inventor has previously proposed an optical switch shown in FIG.
No. 9489). As shown in FIG. 5 (a), this optical switch is provided at approximately 45 crossing points of the T-shaped core waveguide 4 at a right angle.
The core waveguide 4 is cut into a substantially L-shaped bent waveguide and a straight waveguide by providing a gap 17 having an angle of
The liquid 8 having a refractive index substantially equal to the refractive index of the core waveguide 4 is provided in the groove of the gap 17 as shown in FIG.
It has a special structure filled with. Then, an electric heating element (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.
The liquid 8 in the inside can be vaporized. That is, when the liquid 8 filled in the gap 17 is vaporized, the optical switch switches the core waveguide 4 inside the gap 17.
The switching is performed by utilizing the fact that the refractive index is lower than the refractive index of. In FIG. 5A,
When energization of the electric heating element 19 is turned on to evaporate and evaporate the liquid 8 in the gap 17, the light propagating in the core waveguide 4 from the direction of the arrow 12A to the direction of the arrow 12B in the core waveguide 4 until then becomes the core conduction of the gap 19. The light is reflected by the end face of the wave path, the optical path is switched to the orthogonal waveguide, and the light propagates in the direction of arrow 12C. If the power supply to the electric heating element 19 is turned off and heating is stopped, the area around the gap 17 is immediately cooled to the temperature before heating by the heat transfer, and the vaporized liquid 8 is condensed and injected into the gap 17. Again goes straight in the direction of arrow 12B. As described above, this optical switch has the gap 17
The switching operation is performed by achieving the operation of injecting and removing the liquid 8 into the inside by evaporating and condensing the liquid 8 by heating and cooling.

[0004]

In the optical switch shown in FIG. 5, the entire surface of the core waveguide 4 having a thickness of about 8 .mu.m formed on the substrate 1 with the low refractive index layer 2 interposed therebetween has a thickness of 20 to 30 μm.
It consists of a buried waveguide completely covered by a cladding 18 of μm. Therefore, the gap 17 is formed in the core waveguide 4.
Must be formed so as to reach the boundary surface between the core waveguide 4 and the lower refractive index layer 2 thereunder so as to completely cut off. That is, the groove depth of the gap 17 is 28
3838 μm. The gap 17 is formed by forming the clad 18 and then performing dry etching using a metal film (for example, a WSi film) as a mask and using a fluorine-based gas (for example, CHF ₃ ). here,
The upper limit of the thickness at which the metal film can be formed is 1 μm in consideration of the warpage of the substrate 1 due to the generation of stress, the generation of cracks, and the accuracy of the etching pattern. 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 having an etching selectivity of 28 or more must be used. However, at present, the etching selectivity is limited to about 20. For this purpose, a method of forming a metal film (for example, Cr and WSi film) of different materials in two layers to increase the etching selectivity has been studied. However, as the thickness of the metal film increases, the accuracy of the mask pattern deteriorates. , Desired gap shape (gap width 6 μm
, A length of 50 μm and a depth of 28 μm or more) cannot be formed accurately at the desired intersection of the core waveguide 4, and as a result, a low-loss optical switch is realized at the current technical level. Then it turned out to be difficult. When the deep gap 17 is formed as described above, the gap 17
As the depth of the gap becomes deeper, the gap width of the gap 17 increases more and more due to undercutting.
μm), and as a result, when the gap 17 is filled with the liquid 8, the arrow 12A
It has been found that the loss when the incident light propagating from the direction passes through the gap 17 and propagates in the direction of the arrow 12B increases. That is, the transmission loss Tt caused by light passing through the gap 17 is equal to the gap 1 as shown by the following equation.
7 increases as the clearance width S increases. This is a loss caused by the mismatch between the optical electric field distribution in the input waveguide and the optical electric field distribution in the output waveguide caused by the expansion of the input optical electric field distribution in the gap.

[0005]

(Equation 1)

[0006] Here λ is the wavelength, n _c is the refractive index of the cladding, omega basic mode - is a spot size of the de light.

Further, it has been found that when the depth of the gap 17 increases, there arises a problem that 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 is switched.
If the surface is rough, scattering loss occurs here. Further, when the perpendicularity of the inner wall surface of the gap is deteriorated, there is a loss due to a mismatch between the optical electric field after reflection and the optical electric field in the output waveguide.

As described above, at the current technical level, a technology for accurately forming a gap having a depth of 28 μm or more with respect to width, surface roughness, verticality, etc. has not been realized, and the loss of the optical switch has been 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 with low loss and easy manufacture.

[0010]

In order to achieve the above object, a waveguide type optical switch according to the present invention comprises a core waveguide having a crossing portion formed on a low refractive index layer on a substrate, through which light propagates. When a gap is formed so as to cross the intersection thereof only in the core waveguide, and a cladding layer formed so as to cover the core waveguide surface, is filled in its formic cap, the refractive index Liquid 8 substantially equal to that of the core waveguide
And a heater provided in the vicinity of the gap to heat the liquid 8, and by changing the refractive index in the gap by vaporizing or condensing the liquid 8 in the gap by operating the temperature of the heater. A waveguide type optical switch configured to control the propagation direction of light in the core waveguide.
, So as to cover the gap end face of the core waveguide.
In which a cladding layer is formed . The shape of the intersection includes various shapes such as a T-shape, a cross shape, and a strut shape.

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

Preferably, the heater is provided immediately below the gap.

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

[0014]

In the optical switch of the present invention configured as described above, the gap is formed at the same time when the core waveguide is formed using the dry etching process. Therefore, it is possible to form a gap with good dimensional accuracy, little roughness of the inner wall surface, and good verticality. Moreover the gap, even if the gap distance, such as by undercutting during dry etching spread than the design value, by adjusting the thickness of the subsequent cladding layer formed over the gap end faces, a gap interval small
Not only can the loss be reduced.
Ku, it is possible to realize an optical switch capable of compensating for the deviation from the design value of the to KOR intervals.

The thickness W of the cladding layer covering the end face of the gap
Is set to be thinner than half the gap width G of the gap. This is because a gap for filling the liquid 8 is left even after the cladding layer is formed covering both gap end faces. That is, assuming that the clearance width of the remaining gap (the remaining gap) is S, the thickness W of the cladding layer is W <(GS) / 2. On the other hand, as the thickness of the cladding layer covering the peripheral surface of the core waveguide is larger, the propagation loss of light propagating in the waveguide can be reduced. Therefore, the above-mentioned another cladding layer is formed on the upper surface of the core waveguide between the core waveguide and the cladding layer formed so as to also cover the gap end face, thereby suppressing the light propagation loss.

If the heater is provided immediately below the gap and the liquid 8 in the gap is heated from below, the liquid 8 in the gap is vaporized from the lower side and the remaining liquid 8 is heated.
Is quickly pushed out of the gap by being pushed up by the rise of 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 low refractive index layer can be substituted for the substrate. That is, in that case, the low refractive index layer becomes unnecessary.

[0018]

Next, an embodiment of the present invention will be described.

FIG. 1 shows an embodiment of a waveguide type optical switch according to the present invention. FIG. 3A is a plan view, and FIG.
It is -A sectional drawing. This optical switch has an optical fiber 11
A 1 × 2 optical switch configured to switch the optical path of an optical signal propagating in a as shown by the arrow 12A to either the optical fiber 11b or the optical fiber 11c and to propagate the signal in the direction of the arrow 12B or 12C. is there. The optical fibers 11a, 11b, 11c are respectively connected to different side walls of a rectangular package 13 accommodating the waveguide type optical switch element. The waveguide type optical switch element has a T-shaped core waveguide 4 formed on a substrate 1 with a low refractive index layer 2 interposed therebetween.
b and 11c are provided so that the core 14 is brought into close contact with the core waveguide end face of the waveguide type optical switch element. A gap 5 is formed at the T-shaped intersection 3 of the core waveguide 4 so as to cross the optical axis of the incident light from the direction of arrow 12A at an angle of approximately 45 degrees. A cladding 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 contained in the upper space of the package 18, and the remaining gap formed between the clad layers 7 is filled with the liquid 8. Substrate 1
Inside, a heater 9 for heating the liquid 8 is provided just below the gap 5. That is, by turning on / off the power supply to the heater 9, the optical switch can vaporize the liquid 8 filled in the gap 5 by heating the heater, or stop the heating of the vaporized liquid 8 to condense liquid by stopping the heating of the heater. The switching of the optical path is achieved by the change in the refractive index in the gap.

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

The substrate 1 is made of glass (quartz glass, quartz glass containing an additive for controlling the refractive index, multi-component glass,
), Semiconductor (Si, GaAs, InP, etc.), electro-optic crystal (LiNbO ₃ , LiTaO ₃ , etc.), magnetic material (eg, Y ₃ Fe ₅ O ₁₂ ), polymer material (polyurethane, epoxy, polycarbonate, etc.) ) And sapphire can be used.

The above-mentioned glass, semiconductor, polymer material and the like can be used for the low refractive index layer 2, the core waveguide 4, and the cladding layer 7. 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 0.1. It is selected from the range of several% to 2%. Here, n _c and n _b are substantially equal, or n _c > n in order to reduce the loss due to the radiation mode to the substrate.
_b is preferred. As the thickness of the low-refractive-index layer 2 increases, the propagation loss can be reduced. However, there is usually no problem if the thickness is 5 μm or more. As the thickness of the cladding layer 7 increases, the propagation loss of light propagating in the core waveguide 4 can be reduced. In this case, if the cladding layer 7 is selected from the range of 2 to 5 μm, the Can be suppressed small. When a quartz glass substrate is used as the substrate 1, the entire substrate has a low refractive index, so that the low refractive index layer 2 need not be separately formed 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 into a gap shape with good dimensional accuracy, inner wall state, and verticality. The depth of the gap 5 is set to a depth reaching the low refractive index layer 2. The gap 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 the gap width S is calculated from the equation (1). As can be seen, the narrower is preferable. The gap 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 the undercutting in the dry etching, the thickness can be compensated to an appropriate width by the thickness of the clad layer 7 formed thereafter. 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 a silica-based glass doped with Ge is used for the core waveguide 4,
As liquid 8, fluorobenzene (C ₆ H ₅ F: temperature 20
(Refractive index at 1.6412 ° C., boiling point 84.9 ° C.) can be used.

The heater 9 is inserted into a hole 15 extending from the lower surface of the substrate 1 to the vicinity of the upper surface. Since the heater 9 is provided immediately below the gap 5, the liquid 8 in the gap 5 is heated from below and is vaporized from below. The remaining liquid 8 in the gap 5 is quickly discharged out of the gap 5 so as to be pushed up by the rise of the gas generated earlier. Therefore, high-speed and reliable switching can be performed.

Although not shown in FIG. 1, the package 13 is actually provided with an upper lid, and adopts a structure in which the liquid 8 does not leak outside the package. Therefore, the optical fibers 11a, 11b and 11c are also package 1
3 and hermetically connected.

FIG. 2 shows another embodiment of the optical switch according to the present invention. 3A is a plan view of the optical switch element, and FIG. 3B is a cross-sectional view taken along line AA ′ of FIG. 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, and further covers the first clad layer 10 and the gap end face 6. Second
(Corresponding to the cladding layer 7 in FIG. 1). The refractive index n _c ′ of the first cladding 10 is
Than or equal to the refractive index _{n c} of the cladding layer 16 is chosen to be low refractive index _(n c _{'<n c).} The first cladding layer 10 is provided to improve confinement of light in the core waveguide 4 and has a thickness of 1
５5 μm.

As described above, the waveguide type optical switch of the present invention can be easily manufactured by using the dry etching process established as the manufacturing technology of the semiconductor integrated circuit, and can be easily mass-produced, thereby reducing the cost. Can be expected.

As described above, the bending angle θ _I crossing the T-shape (that is, from one output-side core waveguide 4b provided coaxially with the input-side core waveguide 4a) to the other output-side core waveguide 4c is determined. Although the optical switch having the core waveguide 4 (set at 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, the bending angle theta gap angle theta _II with respect to the incident optical axis when the _I is theta _I = 40 ° is the theta _II = 20 °, also theta _I = 60
In the case of °, the gap angle θ _II is selected from the range of θ _II = 20 ° to 45 ° in accordance with the bending angle θ _I such as θ _II = 30 °.

The waveguide type optical switch according to the present invention is not limited to the 1 × 2 type optical switch described above, but may be an n × m type or m × m type optical switch (n × m type) as shown in FIGS.
≧ 1, m> 2). That is,
The optical switch of the present invention can be easily integrated and made multifunctional by utilizing a semiconductor integrated circuit manufacturing process. FIG. 3 shows an example of a 4 × 8 optical switch with 4 inputs and 8 outputs, and FIG. 4 shows 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. Arrow _A 1 to A ₄ in FIG. 3
Indicate the direction of the optical signal incident to the core waveguide 4a ~ 4d, 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 directions of incident optical signals, and arrows F _{1 to} F ₃ and G _{1 to} G ₃ indicate directions of output optical signals, respectively. . 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 obtained.

(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 necessary to form a gap having good dimensional accuracy, inner wall surface condition, and verticality. it can. Moreover, even if the gap width is widened due to undercutting during dry etching, the width can be compensated to an appropriate width by the thickness of the subsequently formed cladding layer. 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 gap end face, another refractive index equal to or lower than that of the clad layer is provided. By forming the cladding layer,
Light propagation loss can be reduced.

(3) By providing the heater immediately 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 low refractive index layer can be substituted for the substrate, so that the manufacturing process of the optical switch can be simplified.

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

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a waveguide type optical switch according to the present invention, wherein FIG. 1 (a) is a plan view and FIG. 1 (b) is a sectional view taken along line AA ′ of FIG.

FIGS. 2A and 2B are diagrams showing another embodiment of the waveguide type optical switch according to the present invention, wherein FIG. 2A is a plan view of the waveguide type optical switch element, and FIG. FIG.

FIG. 3 is a schematic diagram showing an embodiment 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.

FIG. 5 is a diagram showing a conventional example, where (a) is a plan view and (b)
FIG. 3 is a sectional view taken along line AA ′ of FIG.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Low refractive index layer 3 Intersection 4 Core waveguide 5 Gap 6 Gap surface 7 Cladding layer 8 Liquid 9 Heater 10 First cladding layer (another cladding layer)

Continuation of the front page (72) Inventor Katsuyuki Imoto 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki Hitachi Advanced Research Center, Ltd. (56) References JP-A-60-243642 (JP, A) JP-A-62- 119504 (JP, A) JP-A-62-119517 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B ⁶ /12-6/14 G02B 26/08

Claims (4)

(57) [Claims] 1. A core waveguide for light propagation formed with a cross section in the low refractive index layer on a substrate, of the core waveguide
A gap is formed so as to cross the intersection thereof to wear, and a cladding layer formed so as to cover the core waveguide table surface, is filled in the gap, the refractive index of the core waveguide therewith substantially Having an equal liquid and a heater provided near the gap to heat the liquid, and changing the refractive index in the gap by vaporizing or condensing the liquid in the gap by operating the temperature of the heater. In the waveguide type optical switch configured to control the propagation direction of light in the core waveguide,
A waveguide type optical switch , wherein a clad layer is formed so as to cover a gap end face . 2. A cladding layer having a refractive index equal to or lower than that of the cladding layer is formed on an upper surface of the core waveguide between the core waveguide and the cladding layer. Waveguide type optical switch. 3. The waveguide type optical switch according to claim 1, wherein said heater is provided immediately below said gap. 4. The waveguide type optical switch according to claim 1, wherein a quartz glass substrate is used as said substrate.