JPS6360432A - Waveguide light phase modulator - Google Patents

Abstract

PURPOSE:To execute an exact phase modulation being free form a malfunction by constituting the titled modulator of a push-pull type, and impressing a voltage by which phases of light in each linear waveguide part have the same magnitude each other and become each reverse code, and a voltage before and after a part where a composite phase of each phase is inverted, to an electrode part. CONSTITUTION:The titled modulator is provided with two pieces of linear waveguide parts 13, 14 having each equal length and width between two Y branch waveguide parts 11, 12, and constituted of a push-pull type in which electrodes 15, 16 have been placed on the linear waveguide parts 13, 14, respectively. In case a voltage has been impressed between the electrodes 15, 16, when electric fields whose directions are reverse to each other and whose magnitudes are equal are generated in the linear waveguide parts 13, 14, in accordance therewith, phases of light propagated in the linear waveguide parts 13, 14 also become each reverse code and the same magnitude. Therefore, a phase (namely, a phase of light which has been synthesized and outputted as a vector by the Y branch waveguide part 12) of an output light has only one state of (omicron) and (pi), and an incomplete phase state does not exist.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a push-pull type waveguide optical modulator that includes:
In order to enable accurate phase modulation without malfunction, a voltage is applied so that the phases of the light in each waveguide have the same magnitude and opposite signs, and the phase of the output light (synthesis of the above phases) is applied. By driving with voltages before and after the point where the phase) is reversed, the output light can be changed discontinuously between the two phase states, and the half-finished state in between can be removed. .

[Industrial application field]

The present invention relates to a waveguide optical phase modulator that performs phase modulation using a push-pull type waveguide optical modulator.

[Conventional technology]

The configuration of a conventional waveguide optical phase modulator is shown in FIG. This phase modulator has a configuration in which a pair of electrodes 2.3 are provided on both sides of the linear waveguide section 1. Phase modulation is performed using electrodes 2.3
This is done by applying a predetermined voltage between them to apply an electric field to the linear waveguide section 1, changing the refractive index by the electro-optic effect, and giving the output light a binary phase change of rOJ and "π". ing.

[Problem that the invention seeks to solve]

In the conventional phase modulator described above, the voltage required for the phase of the output light to be "0" and "π", respectively, is . (=0
), V le, as shown in Figure 4 (C1), the voltage is
. When the refractive index of the linear waveguide section l changes continuously according to the magnitude of the applied voltage, the phase of the output light also changes continuously from "O" to "π". It changes.

In other words, even though only rOJ and "π" are required as phase information, even intermediate phases between them are included. If the output light contains half-finished phase information in this way, errors will occur in the judgment when reading information, and incorrect information will be transmitted.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a waveguide optical phase modulator that eliminates half-finished phase states and enables accurate phase modulation without malfunction.

[Means for solving problems]

The waveguide optical phase modulator of the present invention is a push-pull type optical phase modulator having two straight waveguide sections between two Y-branch waveguide sections, and an electrode section provided for each of these straight waveguide sections. A waveguide optical modulator is used, and the voltage is such that the phases of the light in each of the linear waveguide sections have the same magnitude and opposite signs, and the combined phase of the above phases is It is characterized in that voltages before and after the point of inversion are applied to the electrode portion.

[For production]

In the push-pull waveguide optical modulator described above, when a voltage is applied to the electrode section, electric fields in opposite directions are generated within the two straight waveguide sections. In accordance with such changes in the electric field, the phases of the lights in the linear waveguide section also change in opposite directions.

Therefore, considering this point, if voltages are applied such that the phases of the above-mentioned lights have the same magnitude and opposite signs, the phase of the output light (the phase that is vectorially combined of the above-mentioned phases)
For example, only one of rOJ and "π" can exist. Furthermore, the phase of the output light is, for example, r
For example, if the applied voltage is set to a voltage before and after inversion between OJ and "π" (for example, Vo, Vc), then, for example, ■. to ■1 (or from Vc to V.)
Even when the applied voltage is continuously changed, the phase of the output light is discontinuously switched between, for example, rOJ and "π", and binarized phase information is reliably sent out.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

In this embodiment, two straight waveguide sections 13 having the same length and width are provided between two Y-branch waveguide sections 11 and 12.
．． 14, and these straight waveguide sections 13.
It has a push-pull configuration with electrodes 15 and 16 arranged on each of the electrodes 14 and 14, respectively. Furthermore, the Y-branch waveguide section 11.12 has cut regions 11a and 12a having a narrower width and lower refractive index than each waveguide, which extend gradually from near the center toward the branch side. It was established. Each of the waveguide sections 11 to 14 described above is made of an electro-optic crystal, for example.
iNb0. A substrate 10 made of a Z plate is formed by diffusing Ti or the like through a mask pattern.

In the push-pull configuration described above, when a voltage is applied between the electrodes 15.16, electric fields of equal magnitude and opposite directions are generated within the straight waveguide section 13.14. Accordingly, the phases of the lights propagating in the straight waveguide sections 13 and 14 also have opposite signs and the same magnitude.

Therefore, the phase of the output light (i.e., Y-branch waveguide section 1
2) is the phase of the light vectorially synthesized and outputted.
It has only one state, "O" or "π", and there is no intermediate phase state.

In this embodiment, taking these points into consideration, as shown in FIG. Two voltages ■ that provide the maximum light output. (
=O), set Vx, and these two voltages■. ,VTt
By appropriately selecting one of these and applying it between the electrodes 15 and 16, binary phase information of "O" and "π" is sent out.

■ Such voltage. By modulating the voltage using
Even if the phase of the output light is changed continuously (up to o), the phase of the output light does not include any intermediate states other than roJ and "π" as described above, and it is discontinuous between "O" and "π". The phase can be switched.

Furthermore, the optical output becomes zero where the phase is reversed (that is, where the voltage becomes 3), which is advantageous for the negative layer.

Furthermore, in this embodiment, as shown in FIG. 1, cut regions 11a and 12a are provided in the Y-branch waveguide portions 11 and 12, thereby making it possible to reduce the loss. In conventional Y-branch waveguides, in order to reduce loss during branching, ideally the branching angle is very small, as shown by the dotted line in Figure 5.
(1° or less), but because it is difficult to form an extremely thin mask pattern for manufacturing, in practice the shape ends up with rounded corners, as shown by the solid line in the figure. , low loss had not been achieved. Therefore, by providing the cut regions 11a and 12a as in this embodiment, it is possible to create a Y-branch as designed without requiring an extremely thin mask pattern as in the conventional method. Therefore, the branching of the light is caused by the above cut area 1.
1a and 12a, thereby making it possible to reduce the loss at the time of branching. A phase modulator that has achieved low loss in this way can also be used for coherent optical communications.

Next, FIG. 2 is a block diagram showing another embodiment of the present invention.

In this embodiment, straight waveguide sections 23.24 of mutually different lengths are provided in place of the straight waveguide sections 13.14 of mutually equal length in FIG. By changing the lengths of each other in this way, an optical bias is applied, resulting in a voltage of 2 as shown in FIG. 4(b). (≠O), V=
It can be driven by c. In this embodiment, as in the above embodiment, it is possible to send out binarized phase information of "o" and "π", and it is possible to remove half-finished phases. It also becomes possible to reduce loss. Note that instead of changing the lengths of each of the linear waveguide sections 23 and 24, the optical bias may be applied by changing their widths.

FIG. 3 is a configuration diagram showing still another embodiment of the present invention. In this embodiment, the substrate 10' consists of an X plate or a Y plate of LtN box, and instead of the electrodes 15 and 16 in FIG. 25b; 26a and 26b are provided to form a push-pull configuration. In such an electrode configuration, voltages of equal magnitude and in opposite directions are applied between one electrode 25a and 25b and the other electrode 26a and 26b, and the output light is divided into "O" and "π". 2
It is sufficient to apply a voltage capable of switching between two phase states and drive in the same manner as in each of the above embodiments. In this case, a pair of electrodes 25
Since each distance between a and 25b and between 26a and 26b can be made smaller than the distance between the electrodes 15 and 16 described above, driving with a lower voltage is possible.

〔Effect of the invention〕

According to the waveguide optical phase modulator of the present invention, it is possible to reliably send out binarized phase information that does not include any half-finished phase states, so errors in judgment when reading information can be avoided. Therefore, very accurate phase modulation can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, FIG. 3 is a block diagram showing still another embodiment of the present invention, and FIG. Figure (at, (b), (
c) is a diagram showing the phase modulation output in one embodiment of the present invention, another embodiment, and a conventional example, respectively. FIG. 5 is a configuration diagram showing a conventional Y-branch waveguide, and FIG. 6 is a diagram showing a conventional waveguide. FIG. 2 is a configuration diagram showing an optical phase modulator. 11.12...Y branch waveguide section, 11a, 12a...notch region, 13.14...straight waveguide section, 15.16...electrode, 23.24...straight waveguide section , 25a, 25bH26a, 26b-=electrode. Comfort tP me [use shi fsu (b) (C) I stand A 1 bow redemption - key is 1 force 4 figure busy LylY bone this stick kan straddle figure 5 A [-Rimi/l * 3 B ξ J Figure 6

Claims (1)

[Claims] 1) Two straight waveguide parts (13, 14; 23, 24) are provided between two Y-branch waveguide parts (11, 12), and the two straight waveguide parts For each electrode part (15, 16
; 25a, 25b, 26a, 26b), the voltage is such that the phases of the light in each of the linear waveguides have the same magnitude and opposite signs; . A waveguide optical phase modulator, characterized in that voltages before and after the point where the combined phase of the respective phases is reversed are applied to the electrode portion. 2) A patent claim characterized in that the Y-branch waveguide section has a cut region (11a, 12a) having a narrower width and lower refractive index than each waveguide section, extending from the vicinity of the center toward the branch side. The waveguide optical phase modulator according to item 1. 3) The waveguide optical phase modulator according to claim 2, wherein the width of the cut region gradually increases toward the branching side. 4) According to any one of claims 1 to 3, wherein the electrode part consists of one electrode (15, 16) arranged on each of the straight waveguide parts. The described waveguide optical phase modulator. 5) The electrode portions each include a pair of electrodes (25a, 25b;
26a, 26b), the waveguide optical phase modulator according to any one of claims 1 to 3. 6) The waveguide optical phase modulator according to any one of claims 1 to 5, wherein the combined phases are mutually inverted between 0 and π. 7) The waveguide optical phase modulator according to any one of claims 1 to 6, wherein the optical output is minimized at a voltage at which the combined phase is inverted.