JP2994081B2 - Directional coupler type optical functional device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a directional coupler type optical functional device having a novel structure, and more particularly, to an optical switch, an optical polarization splitter, an optical modulator, an optical coupler, having an extremely high extinction ratio characteristic. The present invention relates to a directional coupler type optical functional element suitable for use in a wave device or the like.

[0002]

2. Description of the Related Art Recently, various optical functional devices having a waveguide type directional coupler structure have been developed, and optical switches, optical polarization splitters, optical modulators, optical multiplexers / demultiplexers, and the like using the optical functional devices have been proposed. Have been. FIG. 13 shows a plane pattern of an example of a conventional directional coupler type optical function element. The element shown in FIG. 13 is an element having two inputs and two outputs.

[0003] In FIG. 13, in parallel spaced G in proximity to the two optical waveguides A, B and these become evanescent possible linkages of equal path width W to each other, coupling portions C _o of the length L Is configured. Curved optical waveguides D ₁ , D ₂ , D ₃ , having a path width of W and a radius of curvature R, are provided at input ends A ₁ , B ₁ and output ends A _2, B ₂ of optical waveguides A, B, respectively.
D ₄ is incident side lead section C ₁ is optical, the emitting side lead section C ₂ is formed. Further, the curved optical waveguides D ₁ , D
Linear optical waveguides E ₁ , E ₂ , E ₃ , and E ₄ each having a path width of W are optically connected to ₂ , D ₃ , and D ₄ , respectively. Straight waveguide E _1, E ₂ Michihaba distance between the centers, and the linear optical waveguides E _3, the distance between the road width center in E ₄ are both turned G _F.

[0004] Then, the optical waveguide A at the junction C _0,
Electrodes F ₁ , F ₂ , F ₃ , F ₄ are loaded on B, from which electric signals can be introduced into each optical waveguide. The electrode F ₁ and electrode F _3, electrode spacing F ₂ and the electrode F ₄ is almost zero. Here, for example, a straight waveguide E ₁ and enters port, straight waveguide E _3, E ₄ each through port becomes the cross port. Further, when a straight waveguide E ₂ and enters port, straight waveguide E _3, E ₄ is a cross-port, respectively, the through port.

In the case of this optical functional device, the electrodes F ₁ , F ₂ ,
By providing an appropriate electric signal from F ₃ and F ₄ , a perfect cross state can be realized in theory. However, in the through state, complete through state by the binding of the incident-side lead section C ₁ and the output side lead section C ₂ can not be obtained, the extinction ratio in that case is about 15～30DB.

As described above, the conventional device has a low extinction ratio in either the through state or the cross state,
High extinction characteristics are not exhibited in both states. Since the extinction ratio characteristic of the optical functional element is defined by the lower extinction ratio of the extinction ratio in the through state or the cross state, the extinction ratio of the entire element is only a low value.

Note that the extinction ratio here means that when the output power of the through port is | r | ² and the output power of the cross port is | s | ² , the following equation: ₁₀ log ₁₀ (| r | ² / | S | ² ). Even in the optical function element having the above-described structure, those having relatively high extinction ratio characteristics include:
For example, Granestrand et al. Tech Dig. IGWO '8
6, an optical switch with an extinction ratio of about 27 dB,
M. An optical polarization splitter having an extinction ratio of about 28 dB, which was announced by Mak et al. At the Institute of Electronics, Information and Communication Engineers 1990 National Convention C-216, is known.

[0008] H. M. Mak et al., Electronic Information Communication
At the 1991 Spring National Convention C-224,
A device having the structure shown in FIG. This element is long
Connection part C of L₀And p₁, P_Two, P_ThreeIs p₁+ P_Two+
p_Three<1 (however, p₁Decimal or zero that satisfies ≠ 0)
And the length p₁× L front part connection part
C _Three, Length (1-p₁-P_Two-P_Three) × L / 2 previous stage power
Partial connection part C with pole_Four, Length p_Two× L central part joint
C_Five, The latter stage of the same length as
Partial connection part C with pole₆, Length p_Three× L Subsequent partial connection
C₇Are optically connected to each other.

In the case of this element, an extinction ratio of at least about 40 dB can be obtained in theory.

[0010]

Although the device shown in FIG. 14 can indeed achieve a high extinction ratio theoretically, the dimensional parameters and the like of the respective partial coupling portions are substantially the same as the theoretical values. Only when it is.
However, when actually manufacturing an element, these partial joints and the like cannot always be manufactured with the dimensional accuracy according to the theoretical value, and may slightly deviate from the theoretical value.

When such a problem occurs, the actual coupling state between the optical waveguides at each partial coupling portion deviates from the theoretically calculated state, and the extinction ratio decreases in the cross state or the through state. Inevitable. The present invention
In the element shown in FIG. 14, the problem caused by the above-mentioned variation in the accuracy of the dimensional parameter at the time of manufacturing is solved, and the directional coupling of the novel structure having an extinction ratio characteristic of 30 dB or more in both the cross state and the through state. The purpose of the present invention is to provide an optical functional device having a rectangular shape.

[0012]

In order to achieve the above-mentioned object, in the present invention, an equal-width material made of a material exhibiting an electro-optic effect or a material having a structure capable of controlling the refractive index by introducing an electric signal. And a coupling portion having a length L in which the two optical waveguides are arranged in parallel, and the incident ends of the two optical waveguides of the coupling portion are optically connected to curved or linear optical waveguides, respectively, to form an incident-side lead portion. In the two-input / two-output directional coupler, the output ends of the two optical waveguides of the coupling portion are optically connected to a curved or straight optical waveguide to form an output-side lead. ₁ , p ₂ and p ₃ are p ₁ +
When a decimal number or zero satisfying p ₂ + p ₃ <1 (where p ₁ ≠ 0) is satisfied, the coupling portion has a length p ₁ × L on which control means for coupling coefficient or coupling state between the optical waveguides is loaded.
, Length (1−p ₁ −p ₂ −p ₃ ) × L
/ 2, a central coupling part having a length p ₂ × L loaded with control means for controlling the coupling coefficient or coupling state between the optical waveguides, and having the same length as the partial coupling part having the preceding electrode. The length p ₃ × loaded with the means for controlling the coupling coefficient or the coupling state between the partial coupling portion with the rear electrode and the optical waveguide.
L is connected optically in this order from the incident end, and a control means for controlling a coupling coefficient or a coupling state between the optical waveguides is loaded on each of the incident-side lead portion and the output-side lead portion. There is provided a directional coupler type optical functional device characterized in that:

FIG. 1 is a plan view showing the basic structure of the optical functional device of the present invention. As is clear from the drawing, the planar pattern of the optical functional device of the present invention has the same configuration as that of the optical coupling device except that the coupling portion C ₀ , the incident-side lead portion C _1, and the emission-side lead portion C ₂ have a configuration described later. The conventional 2 shown in FIG.
There is no difference from the input / two-output directional coupler type optical functional element.

First, the joint C₀In, equal width (road width
W), the two optical waveguides A and B are arranged in parallel at a minute interval G.
And the respective incident ends A of these optical waveguides A and B.₁, B
_TwoHas a radius of curvature R₁And a curved optical waveguide with a path width of W
D₁, D_TwoIs optically connected to the incident side lead portion C.₁Configure
Output ends A of the optical waveguides A and B_Two, B_Two
Has a radius of curvature R_TwoAnd the optical waveguide D having a path width W_Three, D_Four
Is optically connected to the output side lead portion C._TwoIs composed. Change
These curved optical waveguides D₁, D_TwoBetween the centers of the waveguides
Distance is G₁And a straight optical waveguide E having a path width W₁, E_TwoEach
Optically connected and curved optical waveguide D_Three, D_FourHas a waveguide
The distance between road centers is G₀, A linear optical waveguide E with a path width _Three, E_Four
Are optically connected. Here, the linear optical waveguide E
₁Is the incident port, the linear optical waveguide E_Three, E_FourHaso
It becomes a through port and a cross port, respectively.

In the present invention, the incident-side lead C
₁ and the exit-side lead section C ₂ is not limited to be constituted by curved waveguide such as shown, for example, entrance end A ₁ and straight waveguide E _1, incident end B ₁ and the straight waveguide E
_2, exit end A ₂ and straight waveguide E _3, between the exit end B ₂ and straight waveguide E _4, respectively, may be optically connected by straight waveguide made of small taper angle.

Each of these optical waveguides has an electro-optical effect.
By introducing materials and electrical signals that
It is composed of a material whose structure can control the refractive index of
ing. For example, semiconductors such as GaAs / AlGaAs
The body material can be formed by laminating multiple layers by MOCVD.
it can. Incident side lead C₁Optical waveguide D₁, D_TwoTo
Means for controlling coupling coefficient or coupling state between both optical waveguides
K₁, K₁Are respectively loaded, and the emission side lead portion C_Twoof
Optical waveguide D_Three, D_FourIs the coupling coefficient between the two optical waveguides or
Control means K for connection state_Five, K _FiveAre each loaded
You.

Further, the coupling portion C ₀ has its incident ends A ₁ , B
_{From 1} to the output ends A ₂ and B ₂ , the front waveguides A ₃ and C ₂ , respectively, are provided with control means K ₂ and K ₂ for coupling coefficients or coupling states in the optical waveguides A and B, respectively. electrodes F _1, F ₂ are front electrode with partial combining unit are loaded respectively C _4, the optical waveguide a, the central portion coupling portion control means K _3, K ₃ of the coupling coefficient or coupling condition B are loaded respectively C ₅ , a partial coupling portion C ₆ with a rear-stage electrode in which the optical waveguides A and B are loaded with rear-stage electrodes F ₃ and F ₄ , respectively, and a coupling coefficient or coupling state control means K ₄ in the optical waveguides A and B, K ₄ is configured by optical connecting subsequent portion coupling part C ₇ being loaded respectively in this order.

The length of each partial joint is now₀of
Let L be the total length and p₁, P_Two, P_ThreeTo the following equation:
p₁+ P_Two+ P_Three<1 (however, p₁Small that satisfies ≠ 0)
When the number is 0 or 0,_ThreeIs p₁×
L, partial coupling part C with pre-stage electrode _FourIs (1-p₁-P_Two−
p_Three) × L / 2, central partial joint C_FiveIs p_Two× L, latter stage
Partial joint C with electrode₆Is (1-p₁-P_Two-P_Three) ×
L / 2, post-stage partial joint C₇Is p_Three× L.

Electrodes F ₁ , F ₂ , F ₃ and F ₃ for controlling the propagation constants of the optical waveguides A and B at the partial coupling portions C ₄ and C _6
4 are loaded so as to have an inverted Δβ structure. If for example, the material of the optical waveguide is a semiconductor, as shown in FIG. 2, the optical waveguide A, the electrode F ₁ to F ₄ and loaded onto a B, electrode F ₁ and electrode F _4, and the electrode F ₂ The electrode F _{3 is connected} to the lead f ₁ ,
In f ₂ may be connected.

When the optical waveguide material is a dielectric, for example,
LiNbO_ThreeIs shown by the plane pattern of FIGS. 3 and 4.
Just load as you did. That is, FIG.
bO _ThreeShows the case where the crystal direction of the₁
~ F_FourThe optical waveguide so that the voltage can be applied as shown in the figure.
A and B may be loaded. In addition, LiNbO_ThreeHow to crystallize
When the direction is Y-cut, as shown in FIG.
The common electrode is arranged in the middle of the optical waveguides A and B,
Arrange the electrodes on both sides so that the voltage can be applied as shown in the figure.
Just do it.

The above-mentioned control means K _{1 to} K ₅ include an incident-side lead portion C ₁ , an emission-side lead portion C _2, and each partial coupling portion C.
_3, C _5, C _7, or loaded with the electrode on the light waveguide in the C _2, or an electrode disposed in the vicinity of the optical waveguide can be formed by introducing an electrical signal from the electrodes. For example, the optical waveguides A and B and the optical waveguides D _{1 to} D ₄
Is composed of a semiconductor, electrodes are loaded at the positions of the above-described partial coupling portions C ₃ , C ₅ , C ₇ , C ₂ , the incident-side lead portion C ₁ , and the exit-side lead portion C ₂ , respectively. May be connected to an electric signal introduction system (not shown).
Here, when an appropriate electric signal is introduced from each of the control means K _{1 to} K ₅ into the optical waveguide immediately below it, two optical waveguides A and B are introduced.
And the refractive indices of the optical waveguides D _{1 to} D ₄ can be increased or decreased by the same degree, and the coupling coefficient k can be changed between the optical waveguides without causing the propagation constant Δβ. Further, even when the control means (electrodes) are not connected to each other, the same effect as described above can be obtained as long as the electric signals introduced to each control means are the same.

When the optical waveguides A and B and the optical waveguides D _{1 to} D ₄ are dielectrics, for example, LiNbO ₃ whose crystal direction is Z-cut is used.
In this case, the control means K may be loaded as shown in FIGS. For example, as shown in FIG. 5, the optical waveguides A and B at the partial coupling portions C ₃ , C ₅ , C ₇ , and C ₂ ,
A control means (electrode) K is loaded on the optical waveguides D ₁ and D _{2 of the} incident-side lead portion C ₁ and the optical waveguides D ₃ and D ₄ of the emission-side lead portion C ₂ to apply a voltage as shown in the figure. By doing so, between the optical waveguides A and B, between the optical waveguides D ₁ and D ₂ ,
The coupling coefficient between the optical waveguides D ₃ and D ₄ can be reduced. Also, as shown in FIG. 6, the grounded common electrode K is disposed between the optical waveguides A and B, and the optical waveguides A and
By arranging electrodes on both sides of B so that a voltage can be applied as shown in the figure, the coupling coefficient between the optical waveguides A and B can be increased.

[0023] In this case, the combined incidence-side lead section C ₁ and the front portion connecting portion C ₃ moiety is newly equivalent incidence-side lead section (C ₁ + C _3), also the exit side lead section C ₂ a portion of the combined subsequent portion coupling portion C ₇ becomes newly the equivalent emission side lead section (C ₂ + C _7). Therefore, among the coefficients p ₁ , p ₂ , and p ₃ that define the length of each partial coupling portion, the coefficients p ₁ and p ₃ determine the coupling state in the equivalent incident side lead (C ₁ + C ₃ ). Matching the coupling state at the equivalent emission side lead portion (C ₂ + C ₇ ),
The equivalent coupling at the incident-side lead (C ₁ + C ₃ ) is canceled out, so that the element as a whole is equivalent to the element having a perfectly symmetrical entrance-side lead and exit-side lead. Selected as a value.

The coefficient p_TwoIs the central part joint C_FiveHead of
When measuring the extinction ratio in the through state by changing the
The length when the value shows the maximum value, that is, the incident
Side lead C₁, The front part connecting portion C_Three, Post-stage connecting part
C₇And emission side lead C_TwoAnd the sum of each connected state of
The coefficient is selected so as to obtain a new coupling state.
Note that the electrodes and control means loaded on each
The gap g with an appropriate width₁~ G₁₂Are each formed
It is preferred that This is because each electrode F ₁~ F_Four
And control means K₁~ K_FiveAdjacent by electric signal introduced to
Electrode F of the partial coupling part₁~ F_FourAnd control means K₁~ K_Five
This is to prevent that is affected.

[0025]

In the optical functional device of the present invention, firstly, the equivalent incidence-side lead section consisting of incidence-side lead section C ₁ and the front portion connecting portion C ₃ Prefecture (C ₁ + C _3), and exit-side lead section C _{The function of the} equivalent emission-side lead portion (C ₂ + C ₇ ) composed of ₂ and the subsequent partial coupling portion C ₇ cancels each coupling, so that the element as a whole is completely symmetrical. The light emitting device has the emission lead portion, and as a result, it is possible to eliminate the deterioration of the extinction ratio in the cross state.

Further, the length of the central portion coupling portion C ₅ has been designed for such a length extinction ratio in the through state is maximum, the extinction ratio in the through state, theoretically, 60d
B or more. Further, by operating the control means K ₁ and K ₁ loaded on the incident-side lead C ₁ and the control means K ₅ and K ₅ loaded on the emission-side lead C ₂ ,
It is possible to recover the element to a high extinction ratio state by adjusting a deviation between an actual coupling state and a theoretical coupling state of each partial coupling portion based on a variation in dimensional accuracy at the time of manufacturing the element.

Therefore, the extinction ratio of this optical functional element is greatly improved in both the cross state and the through state as compared with the conventional structure.

[0028]

EXAMPLE An optical functional device of the present invention shown in the plan view of FIG. 7 was manufactured. This optical functional device is obtained by setting p ₁ = p ₃ = 0 in the device shown in FIG. 1, that is, the respective output ends A ₁ and B ₁ and the respective output ends A ₂ and B _{2 of the} optical waveguides A and B.
Has a structure in which direct curved optical waveguides D ₁ , D ₂ , D ₃ , and D ₄ are optically connected to each other, and the former partial coupling part and the latter partial coupling part do not exist.

In the figure, the length of the joint C ₀ is 8.0 mm,
The distance G between the optical waveguides A and B is 3.5 μm, and the through port E ₃
And any spacing G ₁ distance G ₀ and input port E ₁ and input port E ₂ of the cross port E ₄ is 250 [mu] m, curved waveguide D _1, the curvature of the D ₂ radii R ₁ and curved waveguide D _3, D ₄ Have a radius of curvature R ₂ of 30 μm and a road width W
Is 7 μm.

[0030] The length of the middle portion coupling portion C _5: p ₂
× L is 540 μm (p ₂ = 0.0675), and the length of the partial coupling portion C ₄ with the front-stage electrode and the length of the partial coupling portion C ₆ with the rear-stage electrode are both 3.73 mm. The partial coupling portions C ₄ and C ₆ with front and rear electrodes, the central partial coupling portion C ₅ , and the input / output side lead portions C ₁ and C ₂ in the coupling portion C ₀ correspond to lines VIII-VIII in FIG. 8, I which are cross-sectional views along
The configuration is as shown in FIG. 9, which is a cross-sectional view along the line X-IX.

That is, the lower layer made of AuGeNi / Au
On the unit electrode 1, n is applied by MOCVD.⁺GaAs
Substrate 2, n consisting of⁺0.5 μm thick made of GaAlAs
m buffer layer 3, n⁺GaAlAs thickness 3.0
μm lower cladding layer 4, n ^-GaAs thickness 1.
The 0 μm core layers 5 are stacked in this order. More
On the core layer 5 of n^-Crack made of GaAlAs
Do 6a, p^-Cladding 6b, p made of GaAlAs⁺
Caps 6c made of GaAs are sequentially formed by MOCVD.
To form an upper cladding layer 6, the upper surface of which is SiO 2
_TwoBy being covered with an insulating film 7 such as a film,
Two optical waveguides A and B each having W (7.0 μm) and an optical waveguide
D₁, D_Two, Optical waveguide D_Three, D_FourAre formed in a ridge shape
ing.

The optical waveguides A, B, D ₁ , D ₂ , D ₃ ,
D ₄ is obtained by applying ordinary photolithography and etching to a laminate obtained by laminating the above-described layers,
It is formed as a ridge having a predetermined depth h and a predetermined path width W. The optical waveguides A, B, D thus formed
_{At 1} , D ₂ , D ₃ , and D ₄ , the interface between the clad 6a and the clad 6b is a pn junction interface 6d. Therefore, when a predetermined electric signal is introduced from the electrodes F _{1 to} F ₄ and the control means K ₁ , K ₃ , K ₅ , an electro-optic effect, a plasma effect, a band filling effect, and the like are generated at the pn junction interface of the optical waveguide immediately below. And the refractive index of the core layer 5 located immediately below the electrode changes, and the distance between the optical waveguides D ₁ and D ₂ is increased.
The light coupling state between the optical waveguides A and B and between the optical waveguides D ₃ and D ₄ changes.

The above setting values are all optimum values when the ridge depth h of each optical waveguide is set to 1.0 μm. As shown in FIG. 8, portions where the electrodes F ₁ , F ₂ , F ₃ , and F ₄ are loaded are formed by removing a part of the insulating film 7 into slits to form windows 7a and 7b. Electrodes F ₃ , F ₄ (F ₁ , F ₂ ) are formed by evaporating Ti / Pt / Au, for example, on the upper surface of the cap 6c. The electrode F ₃ is connected to the electrode F ₂ via the lead f ₁ , F ₄ forms a reversed Δβ structure is connected to the electrode F ₁ through the lead f ₂ (Figure 7).

Control means K ₁ , K ₁ , K ₃ , K ₃ and K
_As shown in FIG. 9, windows 5a and 7b are similarly formed in the insulating film 7, and Ti / Pt / Au is deposited on the portions where the control means K ₃ and K ₅ are loaded, as shown in FIG. K
₃ (K _1, K _1, K _5, K ₅₎ is formed, between each of the control means K _3, K ₃ is read f ₄ (control means K _1, while the K ₁ is read f _3, the control unit K _5, between the K ₅ is lead f ₅₎
(FIG. 7).

In this device, the wavelength is set at the entrance port E ₁ .
FIG. 10 shows a theoretical characteristic diagram of switching characteristics in a case where 1.3 μm TE mode light is excited and a reverse bias voltage is applied to the electrodes so that only the electro-optical effect is exhibited. When this element is actually driven with a reverse bias voltage, the extinction ratio is 30 dB or more when the applied voltage in the cross state is -7 V, and the extinction ratio is -15 V in the through state due to the convenience of the measurement system. Again, it can be evaluated to be 30 dB or more.

Next, the variation of the extinction ratio when the length p ₂ × L of the central partial coupling portion C ₅ is changed by changing the coefficient p ₂ in this element is shown in FIG. 11 as a relationship with p ₂ . In the figure, a circle indicates a through state, and a black square indicates a cross state.
As is apparent from FIG. 11, a p ₂ .066 to .068
To form a central portion coupling portion C ₅ in the value, this device, through state, theoretically any case the cross state, it is possible to obtain a more extinction ratio 60 dB.

Further, it can be seen that the coefficients p ₁ , p ₂ , and p ₃ should be selected to have certain values in order for this element to exhibit the maximum extinction ratio. For example, G ₀ , G ₁ , G, R ₁ , R ₂ , W
Is set to the above value, unless the values of p ₁ = 0 and p ₃ = 0 are set, the deterioration of the extinction ratio in the cross state cannot be avoided, and if p ₂ deviates from 0.0675, 74. 2
The maximum extinction ratio in the through state of 9 dB cannot be obtained.

According to FIG. 11, when the value of p ₂ changes from at least 0.0675 to 0.062 or less, the extinction ratio of the device becomes 30 dB from the maximum extinction ratio.
It can be seen that it deteriorates as follows. That is, the length p ₂ × L
When the dimensional parameters of the central portion coupling portion C ₅ has occurred a diagram of 44μm from theoretical setting value when the depth h of the optical waveguide ridge and 1.0 .mu.m, the extinction ratio of the device Degrades to 30 dB or less.

Usually, as described above, the device is manufactured by combining photolithography and etching. In this case, the accuracy of the photomask is at least 1 μm.
Because they are managed in the following, the accuracy of the dimensional parameters on the length of the central portion coupling portion C _5, wherein the tolerance: 4
Control within the range of 4 μm is technically sufficiently possible.

However, the depth h of the ridge etched by the etching greatly affects the extinction ratio.
Here, in the element in which the ridge depth h was changed, 1.
The value of the 0-h (μm), that is, when the measured and etching remaining, the relationship between the coefficient p ₂ when the maximum extinction ratio can be obtained, both in a relationship as shown in Figure 12.

As is apparent from FIG. 12, when the ridge depth h is shifted from ± 1.0 μm, for example, from 1.0 μm, the central partial coupling portion C ₅ optimal for obtaining the maximum extinction ratio is obtained.
Is the above set value of 540 μm when h is 1.0 μm.
To 608 μm or 496 μm. For example, in the device shown in FIG. 7, although the target value of the ridge depth h is set to 1.0 μm and the dimensional parameters of the device are manufactured with the above values, the actual ridge depth h is obtained. Is about 0.95 μm, which is about 0.05 μm shallower than the set value. Since the overall symmetry is not broken in the cross state, the voltage applied to the electrodes F _{1 to} F ₄ also depends on the measurement system. In the case of −7 V, the extinction ratio of the element is 30 dB or more. However, in the through state, when the applied voltage is −15 V, the obtained maximum extinction ratio is about 25 dB, which is much lower than the theoretical value.

Therefore, the control means (electrodes) K ₁ , K _{1 of} the incident-side lead portion C ₁ , the control means (electrodes) K ₃ , K _{3 of} the central partial coupling portion C ₅ , and the control of the emission-side lead portion C ₂ applying means (electrode) K _5, a reverse voltage of about -16V to K _5, at the same time, the extinction ratio and applying a reverse voltage of -15V to the electrode F ₁ to F ₄ was obtained through state than 30 dB.
This incident side lead section C _1, the central portion coupling portion C _5, at the exit side lead section C _2, the refractive index increase in the optical waveguide and expressed electro-optical effect of the optical waveguide by the reverse voltage applied is caused As a result, the confinement of light is increased and the coupling coefficient between the two optical waveguides is reduced, and as a result, the length p ₂ × L of the central partial coupling portion C ₅ is 496 μm corresponding to h = 0.95 μm. From this, it is equivalently approached to the set value 540 μm corresponding to h = 1.0 μm.

When the depth h of the ridge becomes large, current is injected from each control means and a plasma effect in the optical waveguide immediately therebelow is used to exhibit the effect of increasing the refractive index of the optical waveguide. increases the coupling coefficient between the optical waveguides concomitant, the length of the portion coupling portion C ₅ may be so equivalently shortened.

[0044]

As is apparent from the above description, the present invention
The directional coupler-side optical functional element exhibits an electro-optic effect
A structure that can control the refractive index by introducing materials or electric signals.
Two equal-width optical waveguides made of structural material
A coupling portion having a length L disposed between the two light guides of the coupling portion.
The input ends of the waveguides are curved or straight optical waveguides and optical
Connected to form an incident-side lead, and the two
The output end of the optical waveguide is a curved or straight optical waveguide, respectively.
Input, 2 optically connected to form the output side lead
In the output directional coupler, p₁, P_Two, P_ThreeIs p₁
+ P_Two+ P_Three<1 (however, p₁ま 0)
Or zero, the coupling part is a coupling between the optical waveguides.
Length p loaded with control means for the coefficient or the coupling state₁×
L partial connection part, length (1-p₁-P_Two-P_Three) ×
L / 2 partial coupling portion with front-end electrode, coupling member between optical waveguides
Length p loaded with control means of number or coupling state_Two× L
The same as the partial joint with the preceding electrode
Length between the partial coupling with the rear electrode and the connection between the optical waveguides
Length p loaded with control means for joint coefficient or joint state _Three
× L optically connected in this order from the incident end
And the input side lead portion and the output side
Each side lead has a coupling coefficient or coupling between the optical waveguides.
Characterized in that the control means of the combined state is loaded
And the equivalent consisting of the input side lead and the pre-stage partial coupling
Connection state at the input side lead and partial connection at the subsequent stage
Emission-side lead composed of a part and an emission-side lead
By properly designing the connection condition at the
Input-side lead and output-side lead in a conventional directional coupler
Extinction ratio in the cross state based on the asymmetry of coupling at the gate
And variations in dimensional parameter accuracy during manufacturing
Eliminating extinction ratio degradation during cross state based on
Can be. In addition, the central partial joint is in the through state
Since it is formed with a length that maximizes the extinction ratio,
The extinction ratio in the through state can also be realized at a high level.
That is, the optical functional element of the present invention is in a through state, a cross state,
It shows a high extinction ratio in any of the states.

In the embodiment, the case where the optical function device is driven as an optical switch has been described. However, in the optical function device of the present invention, the TE mode light and the TM mode It can also be used as an optical polarization splitter for splitting light. Furthermore, when used as an optical modulator or an optical multiplexer / demultiplexer, a high extinction ratio characteristic can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view showing a basic structure of an optical functional device according to the present invention.

FIG. 2 is a plane pattern diagram showing a loaded state of electrodes.

FIG. 3 is a plan view showing another state of loading electrodes.

FIG. 4 is a plan view showing another loading state of electrodes.

FIG. 5 is a plan view showing a loading state of the control means.

FIG. 6 is a plan pattern diagram showing another loading state of the control means.

FIG. 7 is a plan pattern diagram showing an optical functional element of an example.

8 is a sectional view taken along the line VIII-VIII in FIG.

FIG. 9 is a sectional view taken along the line IX-IX of FIG. 7;

FIG. 10 is a theoretical characteristic diagram of switching characteristics of the element of Example.

FIG. 11 is a graph showing the relationship between the coefficient p ₂ and the extinction ratio when p ₁ = p ₃ = 0 in the example device.

FIG. 12 shows a coefficient p ₂ with respect to an etching depth of an optical waveguide.
6 is a graph showing a change in the graph.

FIG. 13 is a plan view showing a conventional example of a two-input / two-output directional coupler.

FIG. 14 is a plane pattern diagram showing another conventional example of a two-input / two-output directional coupler.

[Explanation of symbols]

1 the lower electrode 2 substrate 3 buffer layer 4 lower cladding layer 5 the core layer 6 upper cladding layer 6a, 6b clad 6c cap 6d pn junction interface 7 insulating film 7a, 7b window A waveguide A ₁ optical waveguide A entrance end A ₂ optical of exit end D ₁ of the incident end B ₂ optical waveguide B exit end B waveguide B ₁ optical waveguide B of waveguides _{a, D 2, D 3,} D 4 curved waveguide E _1, E ₂ straight waveguide (input port) E ₃ linear optical waveguide (through port) E ₄ linear optical waveguide (cross port) C ₀ coupling section C ₁ incident side lead section C ₂ exit side lead section C ₃ front partial coupling section C ₄ partial coupling section with front electrode C ₅ with the central portion coupling portion C ₆ subsequent electrode portion coupling unit C ₇ subsequent portion coupling portion _{f 1, f 2, f 3} , f 4, f 5 lead _{F 1, F 2, F 3} , F 4 electrodes K _1, K _{2 , K 3, K 4, K} 5 control means L of the coupling coefficient or the bonding state between the optical waveguides Length h waveguide A merging unit C _0, the etching depth g ₁ of _{B, g 2, g 3,} g 4, g 5, g 6, g 7, g 8, g 9, g 10, g 11, g
₁₂ gap _{p 1, p 2, p 3} , p 1 + p 2 + p 3 <1 ( where p ₁ ≠
Path width of fractional or zero W optical waveguide satisfying 0) G optical waveguide A, the distance G ₁ straight waveguide E ₁ between Michihaba center distance G ₀ straight waveguide E _3, E ₄ of _B, the E ₂ the distance between Michihaba central R ₁ curved waveguide D _1, D ₂ of a radius of curvature R ₂ curved waveguide D _3, the radius of curvature of D ₄

Continuation of the front page (56) References JP-A-2-235030 (JP, A) JP-A-63-142333 (JP, A) JP-A-2-308125 (JP, A) JP-A-57-200016 (JP) JP-A-4-238326 (JP, A) JP-A-62-59933 (JP, A) JP-A-3-13906 (JP, A) JP-A-60-217346 (JP, A) JP-A-60-217346 59-93428 (JP, A) 1990 IEICE Autumn National Convention Lecture Paper [Vol.4] Communications and Electronics p. 4-258 Mutsu Hanmei et. a l. , “C-216 Semiconductor Directional Coupler Optical Mode Splitter,” 1991 IEICE Spring National Convention Proceedings [Part 4] Communications and Electronics p. 4-241 Mutsu Hanmei et. a l. , “C-224 High extinction ratio directional coupling type optical functional device” (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/00-1/035 G02F 1/29-1/313 G02B 6 / 12-6/14

Claims (1)

(57) [Claims] 1. A coupling part having a length L in which two equal-width optical waveguides made of a material exhibiting an electro-optic effect or a material having a structure capable of controlling a refractive index by introducing an electric signal is provided. The incident ends of the two optical waveguides of the coupling portion are optically connected to curved or straight optical waveguides, respectively, to form incident side leads, and the emission ends of the two optical waveguides of the coupling portion are curved. Alternatively, in a two-input / two-output directional coupler optically connected to a linear optical waveguide to form an emission-side lead, p ₁ , p ₂ , and p ₃ are p ₁ + p ₂ + p ₃ <
When a decimal number or zero satisfying 1 (where p ₁ ≠ 0) is satisfied, the coupling section is a pre-partial coupling section of length p ₁ × L loaded with a coupling coefficient or coupling state control means between the optical waveguides. , Length (1−p ₁ −p ₂ −p ₃ ) × L / 2, a partial coupling portion with a pre-electrode, a coupling coefficient between optical waveguides or a length p ₂ × L loaded with control means for a coupling state. A central partial coupling portion, a partial coupling portion with a rear electrode having the same length as the partial coupling portion with a preceding electrode, and a posterior portion of a length p ₃ × L loaded with a coupling coefficient or coupling state control means between the optical waveguides. The coupling section is optically connected from the incident end in this order, and the entrance side lead section and the exit side lead section are each loaded with a coupling coefficient or coupling state control means between the optical waveguides. A directional coupler-type optical functional device, characterized by the following.