JPH01231019A - Optical modulator - Google Patents

Abstract

PURPOSE:To widen a modulation frequency band with a low operating voltage by constituting the optical modulator in such a manner that N-pieces of progressive wave electrodes are driven by the microwave electric signals which are divided in power to N components hereby equalizing the progression speed of light and the progression speed of microwaves. CONSTITUTION:N-pieces (N>=2) of the progressive wave electrodes 14a-14d which are arranged in the progressing direction of the light waves in order to modulate the light waves to light signals of prescribed wavelengths and power dividing means 19a-19c which divide the powers of the microwave electric signals for modulation to the N-components as well as delay means 20a-20c which supply the divided powers successively to the progressive wave electrodes by delaying the same for the prescribed period of time are provided. The delay time of the power is thereby set at the optimum value, by which the equalizing of the progressive speeds of the light and the microwaves is enabled and the modulation band is widened while the increase of the operating voltage is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical modulator that modulates direct current light into an optical signal of a predetermined wavelength by supplying a microwave electric signal to a traveling wave electrode.

(Conventional technology) Conventionally, as a technology in this field, there is a technology described in "Optoelectronics" by Tadashi Sueda, first edition (April 15, 1985), published by Shokodo P.
, 182-185. below,
Its configuration will be explained using figures.

FIG. 2 is a diagram showing an example of the configuration of an optical modulator using a conventional traveling wave electrode.

This optical modulator is equipped with a crystal substrate 1 having an electro-optic effect such as a LiNbo3-z board, and each crystal substrate 1 is formed with an optical input port 2b and an optical signal output port 2b. 2 branched between output ports 2a and 2b
Two arms 3a.

A Matsuha-Zehnder type interferometer 3 having 3b is formed. These input/output ports 2a, 2b and the interferometer 3 are constituted by waveguides. A traveling wave electrode 4 and a ground electrode 5 are formed on both sides of the interferometer 3. Further, an input terminal 6 for inputting a microwave electric signal is connected 8' to one end of the traveling wave electrode 4 via the center conductor 7a of the coaxial cable 7, and the other end of the traveling wave electrode 4 is connected to the impedance matching terminal 6. It is connected to one end of a ground electrode 5 via a terminating resistor 8, and the other end of the ground electrode 5 is connected to the ground via an external conductor 7b of a coaxial cable 7.

In the above configuration, the microwave electric signal is input to the input terminal 6.
When DC light is supplied to the input port 2a, an electric field is generated between the traveling wave electrode 4 and the ground electrode 5, and this electric field causes a phase difference in the light waves traveling through the two arms 3a and 3b of the interferometer 3. The optical signal of a predetermined wavelength is transmitted from the output capacitors 1 to 2b.

In this type of optical modulator, light waves and microwaves propagate in the same direction, so the interferometer 3 becomes a kind of transmission line for the microwaves, and there is no bandwidth restriction due to electricity VIII as in the centralized type. This has the characteristic that the modulation band can be widened.

(Problems to be Solved by the Invention) However, the optical modulator having the above configuration has the following problems.

If the length of the traveling wave voltage 4 is the length of the element, and the voltage of the microwave electric signal to be supplied is Vio, then LXV, o=
In order to reduce the micro voltage Vjo to a constant value, it is necessary to increase the element length accordingly.

However, since the traveling speeds of light and microwaves are different, increasing the length of the element increases the speed difference between the two and lowers the modulation band, making it possible to obtain an optical modulator with a wide band at low voltage. It is always difficult to do this.

The present invention provides an optical modulator that solves the problem of the prior art, which is that it is difficult to obtain an optical modulator with a wide band at low voltage.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an optical modulator that modulates DC light into an optical signal of a predetermined wavelength by supplying a microwave electric signal to a traveling wave type 4~. , in order to modulate the light wave into an optical signal of a predetermined wavelength, N (however, Na3) traveling wave electrodes are arranged in the traveling direction of the light wave, and the power of the microwave electric signal for modulation is divided into N equal parts. power dividing means;
It is necessary to include a delay means for delaying the power divided into N equal parts by the power dividing means for a predetermined time and sequentially supplying the power to each of the traveling wave electrodes.

(Function) According to the present invention, since the optical modulator is configured as described above, the microwave electrical signal is divided into a plurality of powers by the power dividing means, and then each of these powers is sequentially delayed by the delay means. and is sequentially supplied to N traveling wave electrodes. Therefore, by setting the power delay time to an optimal value, it is possible to equalize the propagation speeds of light and microwaves, thereby expanding the modulation band while suppressing the increase in operating voltage. . Therefore, the above problem can be solved.

(Embodiment) FIG. 1 is a configuration diagram of an optical modulator showing a first embodiment of the present invention.

This optical modulator is equipped with a crystal substrate 11 having an electro-optic effect such as a LiNb03-Z board, and the crystal substrate 11 is formed with an optical input port 12a and an optical signal output port 12b. Between 12a and 12b,
A Matsuha-Zehnder type interferometer 13 having two branched arms 13a and 13b is formed. These input/output ports 12a, 12b and the interferometer 13 are constructed of waveguides. On both sides of the interferometer 13, there are N pieces (however,
Na3) traveling wave electrodes 14 to 14d and a ground electrode, 15
are formed, and each of the traveling wave electrodes '14a to 14d and the ground electrode 15 are connected by terminating resistors 16a to 16d for impedance matching of, for example, 50Ω.

In addition, an input terminal 1 for inputting a microwave electric signal is provided.
7 is connected to (N-
1) Single-powered two-output microwave power dividers 19a to 19o are connected, and the power divider vj unit 19a
The power of the input microwave is divided into N by 19o. One output side of the power divider 19a is connected to the traveling wave electrode 14a and the ground electrode 11 by a coaxial cable 18, and the other output side of the power divider 19a and the two output sides of the power divider 19b are connected to the coaxial cable. It is connected to each of the traveling wave electrodes 14b to 14d and the ground electrode 15 via microwave delay devices 18 and microwave delay devices 20° to 20o, respectively. The delay times of the delay devices 20a, 20b, and 20C are set to 20a x 20b x 20o.

Here, as the power dividers 19 to 19o, for example, product number 1 manufactured by Yokogawa Hewlett Packard Co., Ltd. (YHP) is used.
1667A, 11667B, etc. may be used. However, if the microwave strip line is simply branched, there are problems such as large reflection loss due to impedance mismatch at the branch, or a decrease in the magnitude of the electric field after the branch. ,I can not use it.

Next, the operation shown in FIG. 1 will be explained.

While supplying a microwave electric signal to the input terminal 17,
When direct current light is supplied to the input port 12a, the power of the microwave electric signal is divided into two by the power divider 19o, and the divided power is roughly divided into two by the power divider 19a, 1.
9b, one output of the power divider 19a is supplied between the traveling wave electrode 14a and the earth electrode 15, and an electric field is generated between the traveling wave electrode 14a and the earth electrode 15. The output from the other end of the power divider 19a is delayed by a delay device 19a for a certain period of time and is supplied between the traveling wave electrode 14b and the ground electrode 15, and the power divider 1a'J is supplied between the traveling wave electrode 14b and the ground electrode 15.
The output of the power divider 19b is further delayed by one output delay device 20b and supplied between the traveling wave electrode 14o and the ground electrode 15, and the other output of the power divider 19b is further delayed by the delay device 20o and supplied to the traveling wave electrode. 14d and earth electrode 15
will be supplied in the meantime. In this way, the delay devices 20a, 20b
.

The microwave power sequentially delayed at 20o is transmitted to the traveling wave electrode 14.
When they are sequentially supplied between b to 14d and the ground electrode 15, an electric field is generated between them. Correspondingly, the DC light supplied to the input port 12a is
Branching and proceeding through the two arms 13a and 13b of 3,
During that time, an optical signal of a predetermined wavelength is modulated and output to port 1.
It is output from 2b.

Here, the DC light input from the input port 12i1 is 2
Each traveling wave electrode 14. is divided into two arms 13a, 13b. The time Ta to reach ~14d and the input terminal 17
The time Tb for the microwaves inputted from the terminals to reach the respective advancing branch electrodes 14a to 14d after being delayed by the delay devices 20 to 20o is set to be the same. Therefore, the input DC light is transmitted to each of the traveling wave electrodes 148 to 1.
4d, two arms 13a of the interferometer 13;

13b is accumulated. At this time, the microwave power is divided into 1/N equal parts by power dividers 19 to 19o and supplied to each traveling wave electrode 14a to 14d, but (electric field)
Since 2 is proportional to the microwave power, each traveling wave electrode 1
The electric field generated between 4a to 14d and the ground electrode 15 is 1
/(The phase difference required to switch the interferometer 13 is π.If the total length of the electrode 13, that is, the element length is L, then E= Constant x π/L. When divided into N, the required electric field E is Eo = constant x
πX ff/L. -On the other hand, the 3dB band suitable for evaluating the modulation frequency is proportional to N/L, so the 3dB band/Eo is f
It is proportional to l. Therefore, the larger the number of divisions N, the more accurately the light arrival time Ta and the microwave arrival time Tb can be matched, that is, the traveling speed of light and the traveling speed of microwaves can be matched with high precision. This allows wideband modulation at low voltages.

FIG. 3 is a block diagram of an optical modulator showing a second embodiment of the present invention, and the same elements as those in FIG. 1 are given the same reference numerals.

In this optical modulator, as in the first embodiment, a crystal substrate 1
1 on input port 12. and an output port 12b are formed, and a Matsuha-Zehnder type interferometer 13 having two branched arms 13a, 13b is formed between the input/output ports 12a, 12b. There are lengths on both sides of this interferometer 13. N traveling wave electrodes 24a to 24d,
Correspondingly, Ng ground electrodes 25a to 25d are formed, and between each of these traveling wave electrodes 24a to 24d and the ground electrodes 25 to 25d, a terminating resistor 26a to 26d of, for example, 50Ω for impedance matching is formed. Teledere is connected. As in the first embodiment, the input terminal 17 for inputting microwave electricity is connected to the coaxial cable 18 that covers the center conductor 18a and the outer conductor 18b (
N-1) One-power two-output type microwave power dividers 19a to 19o of f[I are connected, and the power divider 1
The power of the input microwave is divided into N by 9a to 9°.

In this embodiment, the delay devices 20a to 20o of the first embodiment are
Instead, (N-1>microwave delay lines 30 to 30o are formed on the crystal substrate 11, and these delay lines 30 to 30o are
The propagation distance is changed at 30 degrees, and the maximum delay is changed.

That is, the traveling wave electrode 24a and the ground electrode 25a on the input port 12 side are directly connected to one output side of the power divider 19 via the coaxial cable 18, and the traveling wave electrode 24b and the earth electrode 25b are connected directly to one output side of the power divider 19 via the coaxial cable 18. Delay line 3 of 艮zaL
0a and coaxial cable 1B to the other output side of the low power divider 19a.
4 and the ground electrode 25 are connected to the power divider 1 via the delay line 30b and the coaxial cable 18 with a length of 2Lm.
On one output side of the power divider 19b, the traveling wave electrode 24d and the ground electrode 25d on the output port 121° side are connected to the other output side of the power divider 19b via a delay line 30o having a length of 3L and the same sheath cable 18. , are connected to each other.

Lengths of delay lines 30a, 30b, 30o □.

21m, 31m and their arrangement angle θ shown in FIG. 3 may be determined as follows.

The length + of the delay line 30a is each divided traveling wave wave, 1
The length is 24a to 24d. , and the ratio of propagation speeds between light and microwaves. The speed of light is C1 the refractive index of light is n. 0, which corresponds to
No, the propagation speed of the microwave is assumed to be C/nll1. At the time when the light reaches the beginning of the Nth traveling wave electrode from the input port 12a. Similarly, the time τ for the microwave to reach the starting end of the Nth traveling wave electrode is, however, ζ□: Phase difference between the light and the microwave by d-3 at the time of input.

bawl. In Equation (2), since the input light to the input capos 1 to 12a is DC light, the phase difference ζ. =O can be set. Phase difference τ. =τ. In other words, (1), (2>
From the ceremony. It becomes no-LIIlnIIl.

Therefore Lllll-ri. rlo/nll.

For example, when a Li\bo3-z plate is used as the crystal substrate 11, normally the LiNbO3-7 plate has no/
r) lTl: 1/2, so Lm/L-8=1/2
Therefore, the arrangement angle θ in Fig. 3 is 30°.
Then, the same operation and effect as in the first embodiment will be 17.
It will be done.

FIG. 4 is a characteristic diagram showing the performance when a LiNbO3-Z plate is used as the crystal substrate 11 in FIGS. 1 and 3. Here, arm 13a.

13b spacing 15 μm, optical wavelength 1.3 μm, impedance of each terminal resistor 16a to 16d, 26a to 26d 50
As Ω, a 3 dB band performance curve A when a 5 V microwave electric signal is supplied to the input terminal 17 and a performance curve B of the element length are shown.

For example, traveling wave electricity 114a-14. d, 24a-24d
The number of divisions N is 4. In this case, from curve A, the modifiable band of 3 dB band is O~140H2, and roughly from curve B, the total length of the traveling wave electrode, that is, the element length is 4 cm.

Further, when the number of divisions is N or 8, the modifiable band of the 3 dB band is O to 20 G, and the element length is 5.7 cm.

It can be seen that by increasing the Vj number N in this way, it is possible to expand the modulation band while maintaining the operating voltage at a low voltage, such as 5V.

FIG. 5 is a block diagram of an optical modulator showing a third embodiment of the present invention, and the same elements as those in FIG. 1 are given the same reference numerals.

In this optical modulator, a compound semiconductor substrate 41 is used, on which a multi-quasi-quasi-well (MQW) type or electroabsorption type optical waveguide 43 is formed. A port 43a and an output boat 43b are formed on the other end surface, respectively. N traveling wave electrodes/44a to 44d are formed on the optical waveguide 43, and a ground electrode 45 is formed on the bottom surface of the substrate 41, and each of these traveling wave electrodes 44a to 44d, the ground electrode 45, and a terminal resistor are formed. 16a to 16d are connected. The input terminal 17 for inputting the microwave electrical signal is connected to the coaxial cable 18 to receive the power component v, as in the first embodiment.
Each of the traveling wave electrodes 43a to 43d and the ground electrode 45 are connected to each other via delay units 19a to 19o and delay units 20a to 20o.

In the above configuration, if DC light is supplied to the input port 43a and a microwave electric signal is supplied to the input terminal 17, the traveling speed of the light passing through the optical waveguide 43 can be adjusted as in the first embodiment. The traveling speed of the microwaves supplied to Φ44a to 44d becomes equal, and an optical modulator with a wide band at low voltage can be obtained.

Note that the present invention is not limited to the illustrated embodiment; for example, the fifth embodiment
The delay devices 20a to 2oo in the figure are replaced by the delay lines 30a to 30 in FIG.
0o, or interferometer 13, optical waveguide 4
3. Traveling wave electrodes 14a-14d, 24a-2=1d, 4
4a to 44d1 power divider 19a to 19o, delay device 2
It is also possible to modify the delay elements 30a to 306, etc. to shapes and structures other than those shown in the drawings.

(Effects of the Invention) As explained in detail above, according to the present invention, the microwave electric signal whose power is divided into N equal parts v1 is used to generate N9i
Since the configuration is such that one traveling wave electrode is driven, it is possible to equalize the traveling speed of light and the traveling speed of microwaves, and thereby the modulation band can be expanded with a low operating voltage.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical modulator showing a first embodiment of the present invention, FIG. 2 is a block diagram of a conventional optical modulator, and FIG. 3 is a light modulation diagram showing a second embodiment of the present invention. FIG. 4 is a diagram showing the characteristics of FIGS. 1 and 3, and FIG. 5 is a diagram showing the configuration of an optical modulator according to a third embodiment of the present invention. 11...Crystal substrate, 12.43a...
Input port, 12b, 43b...output port,
13...Matsuha-Zehnder type interferometer, 14-1
4d. 24a to 24d, 44a to 44d... Traveling wave electrode, 15.25 to 25d, 45... Earth electrode, 17... Input terminal, 19 to 19...
...Power divider, 20a-20o...Delay device, 3oa-300...Delay line. Applicant's agent Kaki Mizu Kyo Sei 11゛ Aquarium Burglary J5: Earth tank 12a: Hekaboto 17: Input terminal 126゛ Output boat
19α~19c: Power divider +4Q~+4
d: 1tyaQ The first embodiment of the invention, the modulation device, Figure 1, the second embodiment of the invention, the modulation ticket, Figure 3

Claims (1)

[Claims] N (N≧2) traveling wave electrodes arranged in the traveling direction of the light wave in order to modulate the light wave into an optical signal of a predetermined wavelength, and a microwave electric signal for modulation. The power dividing means divides the power into N equal parts, and the delay means delays the power divided into N equal parts by the power dividing means by a predetermined time and sequentially supplies the power to each of the traveling wave electrodes. optical modulator.