JPH02262127A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To select a switching structure matching each polarized wave and to improve manufacture conditions by switching each polarized wave with a TE optical switch and a TM optical switch and joining respective polarized waves by a confluence part. CONSTITUTION:Electrodes 31 and 33 are respectively controlled to put a TE optical switch 30 in a bar state and a TM optical switch 32 in a cross state. In those states, a TE-mode polarized wave after passing through a waveguide 23 enters the TE optical switch 30 in the bar state and has no transition here to reach an exit terminal 36. A TM-mode polarized wave, on the other hand, enters the TM optical switch 32 in the cross state after passing through the waveguide 23 and has transition here to pass through a waveguide 26 and the polarized wave is joined with the TE-mode polarized wave at a confluence point 35 to reach the exit end 36. Consequently, the E optical switches 30 and TM signal switch 32 select switching structures matching the respective polarized waves and the manufacture conditions are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a waveguide type optical switch used for optical communication, optical measurement, etc.

[Conventional technology]

Currently, as a waveguide type optical switch, a directional coupler type optical switch based on Ti (titanium) diffused LiNbO3 and lithium oxide is well known. This type of optical switch is shown in FIG. 4(a).

As shown in (b), there are two leading waveguides (1) and (2).
are in close proximity to form an optical directional coupler section (3), and electrodes (4) are disposed above the leading waveguides (1) and (2) of this coupler section (3).

(5) is installed. When no voltage is applied, the light incident from the boat (6) of the leading waveguide (1) passes through another nearby optical waveguide (2) at the directional coupler section (3).
and is transferred to the output port (8) depending on the length of the coupler section (3). The state where the incident light from the boat (6) is completely transferred to the boat (8) is the ■ state (cross state).
(curve A in FIG. 4(b)), and the length of the coupler section (3) at this time is called the complete coupling length Lc.

On the other hand, when a voltage is applied to the electrodes (4) and (5), the waveguide (1) is formed due to the electro-optic effect (Pockels effect).

The refractive index of (2) changes, and a phase mismatch Δβ (Δβ is the difference in propagation constant) occurs between the two trees of leading wavepaths (1) and (2) in the coupler section (3), and the boat (8 ) is now emitted from the boat (7), and switching is performed. This state is called e state (bar state) (
Curve B in FIG. 4(b)).

[Part 1 to be solved by the invention Such a waveguide optical switch is used as a key device in optical exchanges, high-speed LAN nodes, optical measuring instruments, etc., but it is not suitable for systems using ordinary single mode fibers. An important issue is to eliminate the dependence on incident polarization, which is a constraint on the application of

As an attempt to make this polarization independent, in a cross state (that is, the voltage is 0), the complete coupling length Lc of the TE mode and TM mode is
It has been proposed to satisfy each of these conditions by adjusting the waveguide structure, coupling length, etc. so that the voltages at the time of the bar state are the same in both modes. Here T
The E mode is composed of an electric field component E and magnetic field components Hx and H, when the light propagation direction is the Z direction.
, E, and the magnetic field component H, refer to non-existent ones, and T
The M mode consists of an electric field component E,, E, and a magnetic field component H, where E,, H,,)l.

refers to something that does not exist.

However, since the waveguide in the polarization-independent optical switch described above has a weak light confinement effect, there is a problem that the waveguide propagation loss and the radiation loss at the waveguide milling part become large. In order to create a waveguide structure that satisfies each of the conditions, the manufacturing conditions are strict, making it difficult to manufacture.

In addition, as another attempt to make polarization independent, LiNb0°2
The axis is taken in the direction of light propagation (i.e. X cut)
), it has been proposed to match the electro-optic constants for TE mode and TM mode, but this
Since the available electro-optic constant is small in the cut type, the electro-optic effect is weak, and as a result, the problem is that the drive voltage required for light switching becomes large.

The present invention was made to solve such problems,
The purpose of this invention is to obtain a waveguide type optical switch that can improve manufacturing conditions.

(Means for Solving the Problems) A waveguide type optical switch according to the present invention includes a mode splitter that separates unpolarized incident light into TE mode polarization and TM mode polarization, and a mode splitter that separates unpolarized incident light into TE mode polarization and TM mode polarization, and a switching method for the TE mode polarization. a TE optical switch for switching the TM mode polarized waves, a merging section for merging the respective polarized waves output from each of the optical switches, and a TE optical switch for switching the TM mode polarized waves; It is equipped with an attached board.

(Function) In the present invention, in order to switch TE mode polarization and TM mode polarization independently, the TE optical switch and the TM mode polarization are switched independently.
For the M optical switch, a switch structure suitable for each polarization can be selected.

(Example) An example of the present invention will be described below based on FIGS. 1 to 3. FIG. 1 is an external view of a waveguide type optical switch, and light moves from left to right in the figure. In FIG. 1, (21) is a substrate made of a material having an electro-optic effect, such as Li.
NbO3 crystal, LITa03 crystal, BaTi0. Crystals or GaAs crystals can be used, but Z-cut LiNb
0. Most preferably, crystals are used.

(22) to (26) are waveguides formed on the substrate (21) by the Ti diffusion method, and (27) is a single inlet side connected to the waveguide (22) and into which unpolarized incident light (28) enters. The mode fiber (29) separates the unpolarized incident light (28) entering from the waveguide (22) into TE mode polarization and TM mode polarization, and the TE mode polarization is transmitted through the waveguide (23).
A mode splitter outputs the TM mode polarized wave to the waveguide (24).

(30) performs switching of the TE mode polarized wave incident from the waveguide (23), and the waveguide (23) or (25)
), and this TE optical switch (30) has two leading waveguides (23) and (25) in close proximity to form an optical directional coupler section. An electrode (31) for applying a voltage V is installed above the leading waveguides (23) and (25). In this TE optical switch (30), a voltage V is applied to the electrode (31). is not applied, it becomes a cross state, and the waveguide (23
) is emitted only to the waveguide (25), but when voltage v0 is applied, it becomes a bar state, and the TE mode polarized wave is emitted only to the waveguide (23).

(32) performs switching of the TM mode polarized wave incident from the waveguide (24), and the waveguide (24) or (26)
This TM optical switch (32) has two leading waveguides (24), (H) in close proximity to form an optical directional coupler section, and the leading waveguide of this coupler section An electrode (33) for applying voltage v0 is installed above the wave paths (24) and (26). In this TM optical switch (32), when no voltage is applied to the electrode (33), it is in a cross state, and the TM mode polarized wave incident from the waveguide (24) is emitted only to the waveguide (26). Voltage V. In the state where is applied, the state becomes a bar state and the TM mode polarized wave is emitted only to the waveguide (24).

(34) is a merging section for merging the respective polarized waves output from the optical switches (30) and (32), and a waveguide (2
3).

The light from (26) merges at the confluence point (35), passes through the waveguide (23), and is emitted from the exit end (36).
The light from the waveguides (24) and (25) meet at the confluence point (37)
After merging at the waveguide (24), the light is emitted from the exit end (38). In addition, the waveguide exit end (
Exit side single mode fibers (39) and (40) are connected to 36 and 38, respectively.

The mode splitter (29) and the optical switch (30).

(32), the confluence part (34) is attached to the substrate (21), and especially in the optical switch (30), (32), the waveguides (23), (25) and the waveguide (24) are attached to the substrate (21).
), (2B) is formed by Ti diffusion method etc.,
A buffer layer such as 5in2 is coated, and an electrode pattern is finally provided.

By the way, there are several variations in the structure of the optical switches (30) and (32), but for example, if both the optical switches (30) and (32) are made uniform Δβ, both switches (30) , (32)
Therefore, in order to perform switching as a whole of the waveguide type optical switch, each switch (
30) and (32) each require a driving electric circuit. On the other hand, the TM optical switch (32) -
When the TE optical switch (30) has a reverse Δβ switch structure, when the electrodes (31) and (33) are in no electric field, the TM optical switch (32) is in the crossed state, and the T
When the E optical switch (30) is in the bar state and an electric field is applied to the electrodes (31) and (33), the TM
The optical switch (32) is in the bar state, and the TE optical switch (3
0) can be placed in a crossed state, which is preferable because it allows driving to be performed all at once. In any case, the driving voltage is both switches (30), (32)
It is desirable to adjust the bond length so that both are the same.

Next, the operation will be explained with reference to FIGS. 2 and 3. First, to explain the case where light is emitted from the exit end (36) as shown in FIG.
), and is separated into TE mode polarization and TM mode polarization by a mode splitter (29).

The mode splitter (29) includes an optical switch (30),
Since a constant electric field is always applied regardless of the cross state or bar state of (32), the incident light (28) is always separated into TE mode polarization and TM mode polarization.

In addition, the optical switches (30) and (32) control the electrodes (31) and (33), respectively, so that the TE optical switch (30) is in the bar state and the TM optical switch (32) is in the cross state. . In such a state, the TE mode polarized wave passes through the waveguide (23) and then becomes a bar-state TE.
It enters the optical switch (30), does not migrate here, and passes through the waveguide (
23) to reach the outlet end (36). On the other hand, after passing through the waveguide (24), the TM mode polarized wave enters the TM optical switch (32) in a crossed state, where it undergoes a transition, passes through the waveguide (26), and enters the TE mode at the confluence (35). After merging with the polarized wave, it reaches the exit end (36). This allows the outlet end (36
), TE mode polarized waves and TM mode polarized waves are emitted, and the output from the exit end (38) becomes zero.

Next, the case where light is emitted from the exit end (38) as shown in FIG. 3 will be described. The incident light (28) is separated into TE mode polarization and TM mode polarization by the mode splitter (29) as shown in Fig. 2, but in this case, the TE optical switch (30) is in the crossed state. and leave the TM optical switch (32) in the bar state. In this state, the TE mode polarized wave passes through the waveguide (23) and then enters the cross-state TE optical switch (30), where the transition occurs and passes through the waveguide (25) to the confluence (37). to the outlet end (38). On the other hand, the TM mode polarized wave passes through the waveguide (24) and then passes through the bar-state TM optical switch (3).
2), passes through the waveguide (24) without transitioning here,
After merging with the TE mode polarized wave at the confluence point (37), the exit end (
38). As a result, TE mode polarization and TM mode polarization are emitted from the exit end (38), and the exit end (36)
) is zero.

Therefore, in this embodiment, polarization independence can be achieved, and since a two-cut substrate (21) is used, a high electro-optical constant can be utilized. In addition, since TE mode polarization and TM mode polarization are switched independently, the optical switches (30) and (32) can be configured to suit each polarization, and the coupling length for both modes can be adjusted individually. can be selected, a waveguide structure suitable for each polarization state can be used, tolerance is improved, and as a result, propagation loss isolation can be improved.

Also, mode splitter (29), optical switch (30)
(32) etc. are integrally integrated on the substrate (21), making it easy to manufacture and handle, and downsizing can be achieved.

In addition to the switching that distributes the incident light (28) to the exit end (36) or (38), the present invention provides, for example, a TE mode polarized wave to be sent to the exit end (36) and a
38), TM mode polarization can be sent, or vice versa, allowing variations in modulation.

〔Effect of the invention〕

As explained above, the present invention employs a configuration in which switching of each polarized wave is performed by a TE optical switch and a TM optical switch, and each polarized wave is merged at a merging section, so that a switch structure suitable for each polarized wave is adopted. This will allow us to select the desired value and improve the manufacturing conditions.

[Brief explanation of drawings]

1 to 3 are diagrams showing one embodiment of the present invention, in which FIG. 1 is an external view of a waveguide type optical switch, FIGS. 2 and 3 are explanatory diagrams showing the operation, and FIG. 4(b) is a graph showing the operation of FIG. 4(a). (21)... Substrate, (28)... Incident light, (29)... Mode splitter, (30)... TE optical switch, (32)... TM optical switch, (34)...・Confluence section. Note that the same reference numerals in each figure indicate the same or corresponding parts. Patent applicant: Shimadzu Corporation

Claims (1)

[Claims] a mode splitter that separates unpolarized incident light into TE mode polarization and TM mode polarization; a TE optical switch that switches the TE mode polarization; and a TM optical switch that switches the TM mode polarization. A waveguide type optical switch comprising: a merging section for merging the respective polarized waves output from each of the optical switches; and a substrate to which the mode splitter, each optical switch, and the merging section are attached.