JPH04182630A - Optical functional element and driving method therefor - Google Patents

Abstract

PURPOSE:To realize monolithic integration with the other active element by disposing an electrode having the inversion DELTAB structure of an N stage at an integration part, forming a first and a second electrode by conducting one upstream side and the other downstream side of an optical waveguide and one downstream side and the other upstream side and changing the driving condition of both of them. CONSTITUTION:When light in which a TE mode and a TM mode coexist is mad incident on the incident end 11a of this optical functional element and the currents of 15mA from the first electrodes 13a, 13b and 13c are injected in the optical waveguide, all of the light is emitted from an emitting end 11b. When such an state is maintained and the reversed bias voltage of -16V is impressed on the second electrodes 14a, 14b and 14c, the light of the TE mode is emitted from an emitting end 12b and the light of the TM mode is emitted from the emitting end 11b. Then, both modes are separated and they function as a light mode splitter. Next, by changing the driving condition to a state that a current value is 33mA and a reversed voltage value is -18V from a state that the current value is 15mA and the reversed voltage value is -16V, the optical functional element acts as a polarized wave switch.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an optical functional element with a novel structure and a method for driving the same, and more specifically to an optical functional element useful as an optical polarization separator or an optical polarization switch. and its driving method.

(Prior Art) Recently, various waveguide type optical functional devices have been proposed. However, many of these devices only operate with light polarized in a particular direction. Therefore, in optical fiber communication, which is currently in the implementation stage, there is a problem that the above-mentioned device cannot be put to practical use unless the polarization of light is controlled in advance.

For this reason, research on polarization separators and polarization-independent optical switches is being actively conducted. Examples of these will be illustrated below with reference to the drawings.

Figure 11 is from Tadasu 5unada IEICE Transactions C-I (vol J 73-
C-I.

No9. It is a schematic perspective view of what was published in pp. 559-566 (September 1990).

This device consists of a TiN on a LiN b 03 substrate 1.
An asymmetrical X-branch optical waveguide 2 is formed with doped 5iCh, and three electrodes 3 are arranged at the positions shown in the figure so that a voltage can be applied between each electrode as shown in the figure. It can function as a dependent optical switch and a TE mode/TM mode separator.

Figure 12 shows the E COC9
This is a schematic plan view showing what was proposed in O-229 (1990).
An optical waveguide is formed using iO2, and electrodes (shaded areas) are arranged as shown in the figure, so that a voltage can be applied to each electrode as shown in the figure.

The device shown in FIG. 13 and FIG. 14, which is a cross-sectional view along line XIV-XIV in FIG.
Raka Photonic Switching pp38
40, 1990, a core 5 made of 8102 is embedded in a cladding 6 on a Si substrate 4 to form a directional coupler type optical waveguide 7, and one optical waveguide is placed at the position shown in the figure. A Cr thin film is attached as a current injection electrode 8,
An a-3i thin film 9 is loaded at the position shown in the figure on the other optical waveguide.

By the way, all parts of the above devices are not made of semiconductor materials, so for example, LD, LED,
It is impossible to use it in an optical integrated circuit device for a polarization diversity optical reception system, which is manufactured by integrating active elements such as PDs, which are mostly made of semiconductor materials, into a monolink.

In addition, these devices have large dimensions, significant characteristic deterioration due to temperature changes, slow response speed, and high power consumption, resulting in optical damage and DC
The problem is that it is susceptible to drift.

For monolink integration with the above-mentioned active elements, the entire device may be constructed of semiconductor material.

Such devices include, for example, M. Erma
An optical mode splinter as shown in Fig. 15 has been proposed by N et al. (15th, EC0C, ThB20
-1.1989).

This optical mode splitter has two waveguides 10a and 10b arranged in parallel to each other, forming a directional coupler type optical waveguide using a semiconductor material.
b) The metal layer 11 is simply coated on the upper surface.

In addition, in Japanese Patent Application Laid-Open No. 1-170103, the first
6 and 16, which is a sectional view taken along the line X■-X■
A device having a structure as shown in FIG. 7 is disclosed.

This device has orthogonal output side optical waveguides 12a.

A diffraction grating 14 is introduced into the orthogonal part 13 of the optical waveguide 12b, and a metal layer 15 is formed on a part of the upper surface of the - side output side optical waveguide 12a, thereby serving as an optical demultiplexer that separates the TE mode and the 1M mode. Function.

By the way, in the case of the optical mode splitter shown in Fig. 15, it will not function unless the length of the coupling part is equal to the complete coupling length for the TE mode, so in order to realize this function, the coupling part must be made with extremely high dimensional accuracy. It becomes necessary to form. However, because it is difficult to form the required high-precision bonding using current photolithography and etching techniques, the ones actually manufactured have poor mode separation efficiency and high quenching. The problem is that a ratio cannot be obtained.

Furthermore, in the case of the devices shown in FIGS. 16 and 17, the extinction ratio is not clear, but it is estimated to be about ten or more dB. Furthermore, mode separation is determined by the uniformity of the depth of the grooves of the diffraction grating 14 introduced into the orthogonal section 13, but it is extremely difficult to control the uniformity in manufacturing. , and output side optical waveguides 12a and 12b for both modes.
Since these elements are orthogonally arranged, problems may arise in connection with each other when integrating other elements.

The problem is that devices made of the two types of semiconductor materials described above cannot function as a polarization optical switch in either case.

(Problems to be Solved by the Invention) The present invention aims to provide an optical functional element with a novel structure and a method for driving the same, which can solve all of the problems already described regarding conventional optical functional elements at once. .

(Means for Solving the Problems) In order to achieve the above object, in the present invention, two optical waveguides made of a semiconductor material and having a pn junction structure are evanescently coupled to each other with a perfect coupling length L0 and arranged in parallel. The electrode has an inverted Δβ structure in a continuous direction in the longitudinal direction of the bond.
An optical functional element arranged in stages (where N represents an integer of 3 or more), the M-th stage and the M+1 stage (where M is l) of the electrodes arranged in the inverted Δβ structure. ≦M≦N
between the electrodes (representing an integer that satisfies the relationship -1), first electrodes are formed in the upstream portion of one optical waveguide and the downstream portion of the other optical waveguide so as to be electrically conductive with each other, Further, second electrodes are formed in the downstream portion of the one optical waveguide and the upstream portion of the other optical waveguide, respectively, so as to be electrically conductive to each other and not electrically conductive to the first electrode. There is provided an optical functional device characterized by the above-mentioned method, in which L/L o is set to an appropriate value at L and L0, and a predetermined value of current is injected into the optical waveguide from the first electrode to form the optical waveguide. A cross state or a through state is formed between the optical waveguides, and then, while maintaining the cross state or through state, a voltage of a predetermined value is applied to the second electrode to create a cross state or a through state of only TE mode between the optical waveguides. By forming the TE of the light incident on the optical waveguide,
A method for driving an optical functional element characterized by separating a mode and a 1M mode, and a method for driving an optical functional element to the predetermined value from the first electrode without changing the L/LO value. A current of a larger value is further injected into the optical waveguides to form a cross state or a through state between the optical waveguides, and then, while maintaining the cross state or through state, a voltage of a predetermined value is applied to the second electrode. Driving an optical functional element characterized by converting the output paths of the TE mode and the 1M mode, which are separated by the above-described driving method, by forming a through state or a cross state of only the TE mode between the optical waveguides. method provided.

Hereinafter, the optical functional device of the present invention will be manufactured by one person as shown in Fig. 1.
A detailed explanation will be given based on the case of the output (IX2) directional coupler.

In the case of this optical functional element, the joint portion C has a total length.
In this example, optical waveguides 11 and 12 made of a semiconductor material and having a pn junction structure are evanescently coupled with a perfect coupling length L0 and are arranged parallel to each other.

Here, one end 11a of the optical waveguide 11 is an input end, from which light in which the TE mode and 1M mode coexist is incident. The other end 11b of the optical waveguide 11 and the other end 12b of the optical waveguide 12 are respectively output ends.

In the longitudinal direction of the coupling portion C, N stages of electrodes are successively arranged so that each stage has a length of L/N and has an inverted Δβ structure. However, N is an integer of 3 or more, that is, the electrodes are formed in three or more stages. Therefore, if the first stage electrode is +Δβ type, if N is an odd number, the final stage electrode will be +Δβ type, and if N is even number, the final stage electrode will be −Δβ type.

Of these N stages of electrodes, the Mth stage and M+1 stage (however,
M is an integer of ■, 2.3,...N-1)
The state of the electrode arrangement in is as shown in FIG.

That is, on the upstream part 11c of one optical waveguide (indicated as optical waveguide 11 in the figure) and the downstream part 12d of the other optical waveguide (indicated as optical waveguide 12 in the figure), electrodes 13a and 13b are provided, respectively. are formed in a state where they are electrically connected to each other at the conducting portion 13e.

In addition, the downstream portion lid of the optical waveguide 11 and the optical waveguide 12
On the upstream portion 12c of the electrodes 14a,
The electrodes 14b are electrically connected to each other at the conductive portion 14e, but not electrically connected to the electrodes 13a and 13b.

Among these electrodes, the electrodes 13a and 13b form the first electrode in the present invention, and the electrodes 14a and 14b form the second electrode. All of these electrodes are capable of independently injecting current and applying voltage, for example, the first electrode 13a.

When the electrode 13b is used for current injection (or voltage application), the second electrodes 14a and 14b are used for voltage application (or current injection).

By arranging the electrodes in this way, the region where the M-th electrode (electrodes 13a, 14b) is located and the region M
The Δβ of the optical waveguide is reversed between the region where the +1st stage electrodes (electrodes 14 a, l 3 b) are located.

FIG. 3 is a schematic plan view showing a two-manpower two-output (2×2) directional coupler of the present invention, and in this case also, the coupling portion C
is formed in the same way as in FIGS. 1 and 2.

(effect) Next, the operation of the optical functional element of the present invention will be explained.

First, the optical functional element of the present invention is of a directional coupler type made of a semiconductor material, and the optical waveguide at the coupling part has a pn junction structure.

By the way, when a predetermined amount of current is injected into an optical waveguide having a pn junction structure, a plasma effect or a band filling effect occurs in the optical waveguide, and its refractive index decreases. The above effect is produced in both the TE mode and the 1M mode and is independent of polarization.

On the other hand, when a predetermined voltage is applied to an optical waveguide having a pn junction structure, an electro-optic effect occurs in the optical waveguide, and the refractive index increases. The above effect is a polarization-dependent characteristic that occurs only in the TE mode.

The optical functional device of the present invention is driven by utilizing the above-described effects.

First, a case where electrodes are arranged in three stages will be explained. In this case, the joining part C (complete joining length).

FIG. 4 shows the state of the electrode arrangement at the length of the joint. In this arrangement, electrodes 13a, 13b.

13c is the first electrode, and electrodes 14a, 14b, 14c are the second electrodes.
Use as an electrode.

The relationship between L/L and Δβ in this case of N=3 is:
This is a switching characteristic diagram that depicts a trajectory as shown in FIG. Note that Δβ changes depending on the injected current value and the applied voltage value.

For example, now consider the case where the value of L/Lo corresponds to A in FIG.

When a current of an appropriate value of 11A is injected from the first electrodes 13a, 13b, and 13c, a through state is formed between the optical waveguides of the coupling part C, so that the TE mode and the 1M mode coexist from the input end 11a in FIG. When the light is incident, it is emitted from the output end 11b.

While maintaining this state, the second electrodes 14a and 14b.

When a voltage of a predetermined value VIA is applied to 14c, a cross state for only the TE mode is formed, so that the input end 11
Of the TE mode and TM mode incident from a, the TE mode is coupled with the optical waveguide 12 and exits from the output end 12b, or the TM mode is exited from the output end 11b as is. That is, the TE mode and TM mode are separated, and this element functions as an optical mode splitter.

Next, when the current value injected from the first electrodes 13a, 13b, and 13c is increased to I tA (12A>IIA), a cross state is formed between the optical waveguides at the coupling part C, so that the input from the input end 11a TE mode and TM
The mode is coupled with the optical waveguide 12 and exits from its output end 12b. If a suitable value V1/that voltage is applied to the second electrode while maintaining this state, it will switch to the through state of only the TE mode, so that the TE coupled to the optical waveguide 12
Among the modes and TM modes, only the TE mode is in the optical waveguide 1.
1, and the TM mode remains coupled to the optical waveguide 12, so the output end 12
It emits from b.

In this way, the TE mode and TM mode separated by the initial injection of IIA and application of VIA are converted at their respective emission ends. In other words, a polarization switching operation is realized.

If the L/Lo value corresponds to B in Figure 5, the first
When a current of an appropriate value 11B is injected from the electrodes 13a, 13b, and 13c, a cross state is formed between the optical waveguides of the coupling part C, so that light coexisting in TE mode and TM mode is transmitted from the input end 11a in FIG. When the light is incident, these modes are coupled to the optical waveguide 12 and both are emitted from the output end 12b.

While maintaining this state, the second electrodes 14a and 14b.

When a voltage of a predetermined value VIB is applied to 14c, a through state for only the TE mode is formed, so that the input end 11
Of the TE mode and TM mode that entered from a, the TE mode exits from the output end 11b as it is, but the TM mode
The mode is emitted from the emitting end 12b. That is, T
E mode and TM mode are separated.

Next, when the current value injected from the first electrodes 13a, 13b, and 13c is increased to I 2B (I2B> I +s), a through state is formed between the optical waveguides at the coupling part C, so that the input from the input end 11a TE mode and T
Both M modes are emitted from the output end 11b of the optical waveguide 11. While maintaining this state, set the appropriate value V to the second electrode.
When a voltage of 1.1 is applied, a cross state of only the TE mode is formed, so that
Among the modes and TM modes, only the TE mode is in the optical waveguide 1.
T
The M mode continues to be emitted from the emitting end 11b.

In this case as well, the separated TE mode and TM mode are converted at their respective emission ends. In other words, a polarization switching operation is realized.

Next, FIG. 6 shows an example in which electrodes are arranged in four stages. The relationship diagram between the L/LO value and Δβ in this case, that is, the switching characteristic diagram is as shown in FIG.

This optical functional element can also be operated as an optical mode splitter or a polarization optical switch by driving in the same manner as the elements shown in FIGS. 4 and 5.

(Embodiments of the Invention) Example 1 FIG. 8 is a schematic plan view showing a 1×2 directional genital type optical functional device of the present invention, and FIG. 9 is a cross-sectional view taken along the line IX-IX in FIG. 8. It is a diagram.

In the figure, the length of the joint C is 7.5M, and the electrode arrangement is 3
The L/LO value is approximately 2.8.

The cross-sectional structure of the coupling portion C of this optical functional element is as follows:
For example, on a lower electrode 21 made of AuGeNi/Au, a substrate 22 made of n"GaAs, the same<n"GaAs
A buffer layer 23 having a thickness of 0.5 μm is formed. Then, on this buffer layer 23, n”A
3.0μ thick made of l o, +Gao, llAs
m lower cladding layer 24. Thickness 1 consisting of n-GaAs
．． A core layer 25 with a thickness of 0 μm is sequentially formed, and further a core layer 25 is formed.
An upper cladding layer 26 is formed on top of the cladding layer 5 in a ridge shape. This upper cladding layer 26 has n-A 1 o,
Clat 26a and I) consisting of +Gao, sAs
It consists of a cladding layer 26b made of −A Iio, +Gao, sAs, and a cap layer 26c of p''A j!o, +Gao, oAs formed on this cladding 26b, The interface has a pn junction structure.

Then, the upper surface of the upper cladding layer 26 is covered with an insulating film 27 such as SiO2, and after a window 27a is formed on the upper part of the window 27a, for example, Ti/Pt/Au is deposited thereto to form electrodes 13a, 13b, 13c. , 14a.

14b and 14c are formed.

Light in which the TE mode and 1M mode coexist is incident on the incident end 1.1a of this optical functional element, and the first electrode 13a is connected to the first electrode 13a.

A current of 15 mA was injected into the optical waveguide from 13b and 13c. All the light was emitted from the output end 11b.

While maintaining this state, the second electrodes 14a and 14b.

When a reverse bias voltage of -16V was applied to 14c,
The TE mode was emitted from the emitting end 12b, and the 1M mode was emitted from the emitting end 11b, and both modes were separated and functioned as an optical mode splitter.

Next, when the current injected from the first electrode was increased to about 33 mA, all the light was emitted from the output end 12b. When this state was maintained and a reverse bias voltage of -18 V was applied to the second electrode, the TE mode was emitted from the emission end 11b, and the TM mode was emitted from the emission end 12b as it was.

That is, by changing the driving conditions from a current value of 15 mA and a reverse voltage value of -16 V to a current value of 33 mA and a reverse voltage value of -18 V, this optical functional element operated as a polarization switch.

Note that the extinction ratio of this optical functional element was about 30 dB.

Embodiment 2 FIG. 2 is a schematic plan view of a 2×2 directional genital type element in which four stages of inverted Δβ electrodes are arranged in a coupling portion C.

The length of the joint of this element is approximately 8.8 cm, and L/L is approximately 3
．． 3, and the cross-sectional structure at the joint C is the same as that in FIG.

Light in which the TE mode and 1M mode coexist is incident on the incident end 11a of this optical functional element, and the first electrode 13a is formed.

Approximately 11 mA from 13 b, 13 c, 13 d
current was injected into the optical waveguide. All light is at the output end 12b
It was emitted from

While maintaining this state, the second electrodes 14a and 14b.

When a reverse bias voltage of -17V was applied to 14c and 14d, the TE mode was emitted from the output end 11b, the 1M mode was emitted from the output end 12b, and both modes were separated.
It functioned as an optical mode splitter.

Next, when the current injected from the first electrode was increased to about 29 mA, all the light was emitted from the output end 11b. When this state was maintained and a reverse bias voltage of -15V was applied to the second electrode, the TE mode remained unchanged at the output end llb.
The 1M mode was emitted from the emitting end 12b.

Extinction ratio is approximately 30 dB0, that is, from a state of current value 11 mA and reverse voltage value -17V, current value 29 mA and reverse voltage value -15
By changing the driving conditions to V, this optical functional element operated as a polarization switch.

(Effects of the Invention) As is clear from the above explanation, the optical functional device of the present invention has the following features:
Since it is entirely made of semiconductor materials, monolink integration with active elements made of other semiconductor materials is possible. Moreover, the size and shape of the element can be reduced, and finally mode selection can be made by applying a voltage, resulting in high-speed operation.

Further, power consumption occurs only when the electrode is driven for current injection, and the pn junction structure enables low forward bias voltage driving, resulting in low power consumption. Furthermore,
Since it is made of a semiconductor material, it will not suffer from optical damage or DC drift, and will not suffer from characteristic deterioration due to temperature changes. And its extinction ratio is extremely high.

Therefore, the optical functional device of the present invention solves all the problems that could not be solved with conventional devices, and has extremely great industrial value.

[Brief explanation of drawings]

Fig. 1 is a schematic plan view showing an lX2 directional coupler type optical functional element, Fig. 2 is a schematic plan view showing an example of electrode arrangement in the M-th stage and M+1-th stage, and Fig. 3 is a schematic plan view showing an example of electrode arrangement in the M-th stage and M+1-th stage. A schematic plan view of a genital-shaped optical functional element. Fig. 4 is a schematic plan view showing an example in which electrodes are arranged in three stages with an inverted Δβ structure. Fig. 5 shows L / L O and Δβ in the case of a three-stage electrode arrangement. Fig. 6 is a schematic plan view showing an example of an inverted Δβ structure in which electrodes are arranged in four stages, Fig. 7 is a switching characteristic diagram of an optical functional element with a four-stage electrode arrangement, and Fig. 8 is a switching characteristic diagram showing the relationship between A schematic plan view of the optical functional device of the example, FIG. 9 is IX-I in FIG.
10 is a schematic plan view of another embodiment, FIG. 11 is a schematic perspective view of a conventional example, FIG. 12 is a schematic plan view of another conventional example, and FIG. 13 is a schematic plan view of another example. A schematic plan view of the conventional example,
Figure 14 is a sectional view taken along the line XIV-XI in Figure 13;
FIG. 15 is a schematic perspective view of yet another conventional example, FIG. 16 is a schematic plan view of another conventional example, and FIG. 17 is X-X in FIG. 16.
■It is a sectional view along the line. 11... Optical waveguide, lla... Input end, 1.1 b
...Outgoing end, tic...Upstream side portion of optical waveguide 11, lid...Downstream side portion of optical waveguide 11, 12...
Optical waveguide, 12a...input end, 12b...output end,
12c... Upstream portion of the optical waveguide 12, 12d...
downstream portions of the optical waveguide 12, 13a, 13b, 13c,
13d=-first electrode, 1.3e... conductive part between first electrodes, 14a. 14b, 14c, 1.4d--second electrode, 14e
- Conductive part between second electrodes, C... coupling part, 21... lower electrode, 22... substrate, 23... puff layer, 24
... lower cladding layer, 25 ... core layer, 26 ...
Upper cladding layer, 26a...n-type cladding, 26b...
...p-type cladding, 26c...cap layer, 27...
- Insulating film, 27a...window.

Claims (3)

[Claims] (1) Two optical waveguides made of a semiconductor material and having a pn junction structure have a coupling portion with a coupling length L in which they are evanescently coupled to each other with a perfect coupling length L_0 and are arranged in parallel, and the longitudinal direction of the coupling portion is An optical functional element in which N stages (N represents an integer of 3 or more) of electrodes having an inverted Δβ structure are continuously arranged in the direction, and the electrodes are arranged in the inverted Δβ structure. Between the electrodes of the M-th stage and the M+1-th stage (where M represents an integer satisfying the relationship 1≦M≦N-1), the upstream part of one optical waveguide and the downstream part of the other optical waveguide A first electrode is formed in each of the side portions so as to be electrically conductive with each other, and a downstream portion of the one optical waveguide and an upstream portion of the other optical waveguide are electrically conductive with each other, An optical functional element characterized in that each second electrode is formed without being electrically connected to the first electrode. (2) L/L_0 is set to an appropriate value in L and L_0 of claim 1, and a predetermined value of current is injected into the optical waveguide from the first electrode of claim 1 to create a cross state or a through state between the optical waveguides. and then, while maintaining the cross state or through state, apply a voltage of a predetermined value to the second electrode of claim 1 to form a cross state or through state of only the TE mode between the optical waveguides. 2. The method of driving an optical functional element according to claim 1, further comprising separating the TE mode and TM mode of the light incident on the optical waveguide. (3) L/L_0 is set to an appropriate value in L and L_0 of claim 1, and a predetermined value of current is injected into the optical waveguide from the first electrode of claim 1 to create a cross state or a through state between the optical waveguides. and then, while maintaining the cross state or through state, apply a voltage of a predetermined value to the second electrode of claim 1 to form a cross state or through state of only the TE mode between the optical waveguides. , separates the TE mode and TM mode of the light incident on the optical waveguide, and then,
A current larger than the predetermined value is further injected from the first electrode into the optical waveguide to form a cross state or a through state between the optical waveguides, and then, while maintaining the cross state or through state, the second electrode A claim characterized in that the output paths of the separated TE mode and TM mode are converted by applying a voltage of a predetermined value to form a through state or a cross state of only the TE mode between the optical waveguides. 1. Driving method of optical functional element.