JP3467549B2 - Waveguide type optical modulator and optical modulation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical carrier generator for converting an input optical signal into two optical carriers having a frequency lower than that of the input optical signal and having different frequencies, and modulating the optical carrier. The present invention relates to a waveguide type optical modulator having a modulation signal applying section for applying a signal, and an optical modulation method using the waveguide type optical modulator having such a configuration. More specifically, it relates to a high frequency such as a millimeter wave band signal. The present invention relates to a waveguide type optical modulator that can be suitably used for subcarrier optical modulation for transmitting a signal, and an optical modulation method using the waveguide type optical modulator having such a configuration.

[0002]

2. Description of the Related Art Conventionally, a waveguide type optical modulator used in an optical transmission line of an optical communication system or the like mainly inputs an input optical signal with a frequency lower than that of the input optical signal in order to facilitate modulation of the optical signal. In addition, it is composed of only two components, that is, an optical carrier generating section for converting into two optical carriers having different frequencies and a modulation signal applying section for applying a modulation signal to the optical carrier. Therefore, when such a waveguide type optical modulator is used as a waveguide type optical modulator for subcarrier optical modulation for transmitting a high frequency signal such as a millimeter wave band signal, the following problems occur. Was occurring.

Assuming that the frequency of the laser light incident on the waveguide type optical modulator is ω ₀ as shown in FIG. 17, the optical carrier output after passing through the optical carrier generating section is as shown in FIG. It becomes a combined light of two optical carriers having a frequency of ω ₁ or ω ₂ . Further, when the combined light passes through the modulation signal applying section, the modulation signal ω _m is superimposed on each of the frequencies ω ₁ and ω ₂ . As a result, as shown in FIG. 19, the obtained optical signal becomes a combined light of two optical signals of frequency ω ₁ or ω ₂ having sidebands in the upper sideband and the lower sideband of each frequency band. .

However, the millimeter wave band signal as described above is used.
When transmitting a high frequency signal such as a signal,
At the conventional modulation speed, ω₁And ω₂The frequency interval between
I couldn't get enough. Also, apply the modulation signal.
Then, as described above, ω₁And ω ₂Side to each frequency band
Because a band occurs, ω₁And ω₂Each frequency band of is extremely
And come closer to each other.

In such a case, if chromatic dispersion or chirping occurs in the transmission line, the traveling speed of light at each frequency of ω ₁ and ω ₂ is deviated, and as a result, the frequencies of these lights are also ω. ₁ and ω _{2 are} deviated from each other and interfere with each other, and a noise signal such as a beat signal is generated to deteriorate the transmission characteristics.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides modulation for transmitting a high frequency signal such as a millimeter waveband signal in an optical transmission line even when the above fiber dispersion occurs. The present invention provides a waveguide type optical modulator and an optical modulation method capable of preventing the interference of light in the two frequency bands and preventing the generation of a noise signal such as a beat signal.

[0007]

As a result of intensive studies to solve the above problems, the present inventors have found that the frequency obtained by converting the input optical signal in the optical carrier generating section of the waveguide type optical modulator. It was found that the above-mentioned problems can be solved by mode-separating two optical carriers different from each other and applying a modulation signal to only one of the optical carriers, and the present invention has been completed.

Namely, the present invention provides an input optical signal, the
Two optical keys with lower and higher frequencies than the input optical signal
In the waveguide type optical modulator, the optical carrier is provided with an optical carrier generating section for converting the optical signal into a carrier to facilitate modulation of the optical signal, and a modulation signal applying section for applying a modulation signal to the optical carrier. The present invention relates to a waveguide type optical modulator, characterized in that a mode separation element for separating each of the optical carriers is provided between the generation section and the modulation signal application section.

Further, the waveguide-type optical modulator to facilitate the modulation of the optical signal at the optical carrier generator, an input optical signal, the
Two optical keys with lower and higher frequencies than the input optical signal
In the optical modulation method of converting a carrier into a carrier wave and applying a modulation signal to the two optical carriers in a modulation signal applying unit of a waveguide type optical modulator, the two optical carriers are mode-separated by a mode separation element, and one of the two optical carriers is separated. The present invention relates to an optical modulation method characterized in that a modulation signal is applied only to an optical carrier.

The optical carrier generator of the waveguide type optical modulator is capable of efficiently converting a high-frequency optical signal into an optical carrier, and generating a higher-order optical carrier during conversion. From the viewpoint of being able to prevent this, one set of π / 2 phase shift optical waveguides consisting of one input optical waveguide and two optical waveguides branched from this input optical waveguide, and this π / 2 phase shift Two sets of π phase shift optical waveguides, each of which is composed of two optical waveguides branched from the optical waveguide, and two output optical waveguides, which are formed by coupling two optical waveguides of the π phase shift optical waveguide, are provided. It is preferable to provide a so-called SSB modulation structure in which an optical carrier generating electrode is provided for each of the two sets of π phase shift optical waveguides.

Further, the conversion of the input optical signal into two optical carriers in the optical modulation method is divided into two π from the same viewpoint as in the case of the optical carrier generator of the above-mentioned waveguide type optical modulator. The input optical signal is divided into two by the / 2 phase shift optical waveguide, and each of the divided input optical signals is propagated through the π phase shift optical waveguide, and a modulation signal is applied during the propagation of the π phase shift optical waveguide. Is preferably carried out by

Further, from the viewpoint that the conventional FM modulation and AM modulation techniques can be used, it is preferable that the modulation signal applied in the modulation signal applying section is a phase modulation signal and an intensity modulation signal.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the present invention provides an input optical signal with a frequency lower than that of the input optical signal and higher than that of the input optical signal.
Waveguide optical modulator including an optical carrier generation unit for converting the optical signal into two optical carriers to facilitate the modulation of the optical signal, and a modulation signal application unit for applying the modulation signal to the optical carrier. 2. A waveguide type optical modulator, characterized in that a mode separation element for separating each of the optical carriers is provided between the optical carrier generation section and the modulation signal application section.

Further, in order to facilitate the modulation of the optical signal, the input optical signal is input to the optical carrier generating section of the waveguide type optical modulator.
There are two frequencies lower and higher than this input optical signal.
In the optical modulation method of converting into optical carriers and applying a modulation signal to the two optical carriers in a modulation signal applying section of a waveguide type optical modulator, the two optical carriers are mode-separated by a mode separation element, The present invention relates to an optical modulation method, characterized in that a modulation signal is applied only to the optical carrier. Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 1 is a schematic diagram showing an embodiment in which the waveguide type optical modulator of the present invention is used as a subcarrier optical modulator. FIG. 2 is a schematic view of an asymmetric crossed waveguide type mode separation element used in an embodiment of the present invention. The waveguide type optical modulator of the present embodiment is manufactured as follows.

The substrate is a Z-plate lithium niobate (LiNbO ₃ :
(Hereinafter, it may be abbreviated as LN), a photoresist pattern and a waveguide pattern are formed on this substrate, and then titanium (Ti) is deposited to about 800 Å by a vacuum deposition method. Titanium was diffused into the LN substrate by heating at 1000 ° C. for 20 hours to give a width of 10
An optical waveguide having a thickness of 12 μm and a mode separation element having a width of 12 μm and 8 μm were formed on the same substrate.

The substrate used is not limited to the above lithium niobate as long as it has an electro-optical effect, and lithium tantalate (LiTaO ₃ ) and lead lanthanum zirconate titanate (PLZT) are used. Can be used.

Regarding the method of depositing titanium for forming the optical waveguide and the mode separation element on the substrate, in addition to the above vacuum vapor deposition method, sputtering method, ion plating method,
And a CVD method etc. can be used.

Further, although the optical waveguide and the mode separation element are formed of titanium in the present embodiment, nickel (Ni), copper (Cu), chromium (Cr) and the like can be used instead.

Next, a nichrome layer is formed as a base layer on the substrate on which the optical waveguide is formed, and gold (Au) is deposited to a thickness of about 20 μm by a vacuum vapor deposition method and an electroplating method. Signal application electrode, and π /
2. Form an electrode for π phase shift. In addition to the above gold, silver (Ag), copper, and the like can be used as the electrode material.

The optical waveguide device thus obtained is fixed to a stainless steel case, an optical fiber is connected to the entrance / exit port, and each electrode is wired to an electrical connector to finally obtain a waveguide-type optical modulation. You can get a vessel.

Next, the transmission process of an optical signal when the waveguide type optical modulator of the present invention is used as a subcarrier optical modulator as shown in FIG. 1, that is, a so-called subcarrier type optical transmission will be described.

Assuming that the frequency of the laser light which is the input optical signal to the waveguide type optical modulator shown in FIG. 1 is ω ₀ , this light propagates in the input optical waveguide 101, reaches the branch point, and reaches two branches. To the π / 2 phase shift optical waveguide 102 and further propagate in the π / 2 phase shift optical waveguide 102. The two π phase shift optical waveguides 10 each reaching the branch point again
3 and propagate in the π phase shift optical waveguide 103.

In this propagation process, the carrier generation electrode 10 is provided on one of the branched π phase shift optical waveguides 103.
The modulation signals of frequency ω _c / 2 are applied from 8 respectively,
The input optical signal is converted into an optical carrier.

The lights propagating in the respective π phase shift optical waveguides 103 are then merged, propagate in the optical carrier generating section output optical waveguides 104, and reach the mode separation element 105. In this mode separation element 105, optical carriers are separated into an even mode and an odd mode.

The optical carriers separated into the even mode and the odd mode respectively propagate in the mode separation optical waveguide 106.
In this propagation process, the modulation signal having the frequency ω _m is applied to one of the mode separation optical waveguides 106 from the signal application electrode 109, and the modulation signal is superimposed on one of the separated optical carriers.

After that, the lights propagating through the mode separation optical waveguides 106 merge and propagate through the output optical waveguide 107. Then, the propagated light is extracted as a final output optical signal.

In this embodiment, an asymmetrical crossed waveguide type mode separation element as shown in FIG. 2 is used, but the present invention is not limited to this, and a directional coupler type mode separation element is used. It can also be used.

The π phase shift optical waveguide and the π / 2 phase shift optical waveguide in the present invention mean that an optical signal is transmitted through a pair of two branched π phase shift optical waveguides or π / 2 phase shift optical waveguides. This is a generic term for optical waveguides in which, when branched and propagated, the phases of these branched optical signals are shifted from each other by π or π / 2.

The means for phase shifting is not limited as long as the phase of the branched optical signal can be shifted by π or π / 2. In this embodiment, as shown in FIG. 1, a π / 2 phase shift optical waveguide 11 which is an electrode for phase shift.
The phase shift was performed by installing the 0 and π phase shift optical waveguides 111. In the above-mentioned optical signal transmission process, the input optical signal changes as shown in FIGS.

Input light having a frequency ω ₀ having a spectrum as shown in FIG. 3 is input to the carrier generation electrode 108 in the π phase shift optical waveguide 103 branched as described above.
Is applied with a modulation signal of frequency ω _c / 2,
By being merged after propagating through the phase shift optical waveguide 103, they are converted into two optical carriers having a frequency lower than that of the input light and different in each frequency. These two optical carriers are the asymmetric crossed waveguide type mode separation element 1
To 05. The optical carrier immediately before entering the mode separation element 105 is composed of two optical spectra of frequencies ω ₁ and ω ₂ having a carrier spacing ω _c , as shown in FIG.

Although a large number of high-order optical carriers are generated when a modulation signal is applied, the phases are mutually propagated by propagating in the branched π / 2 phase shift optical waveguide 102 and π phase shift optical waveguide 103. π / 2 and π shift, so
These high-order optical carriers disappear by interfering with each other in the part where the branched π / 2 phase shift optical waveguide 102 and the π phase shift optical waveguide 103 are coupled.

Next, in the asymmetric cross waveguide type mode separation element 105 shown in FIG. 2 as described above, the frequency ω ₁
And the optical carriers of ω ₂ are mode-separated into an even mode and an odd mode. The mode-separated optical carriers of frequencies ω ₁ and ω ₂ propagate in the mode-separated optical waveguide 106, respectively. The optical carriers at this time have the spectra shown in FIGS. 5 and 6, respectively.

For the optical carrier ω ₁ passing through the mode separation optical waveguide 106 on the lower side of FIG.
When the modulation signal ω _m is applied from, the modulation signal ω _m is superimposed on the optical carrier ω ₁ . Finally, the output optical waveguide 10
The optical signal output through 7 is as shown in FIG.
A spectrum having sidebands on both sides of the optical carrier ω _{1 at} an interval ω _m is obtained.

For example, the input light ω ₀ has a frequency of 194T
Modulation signal ω for optical carrier generation using the optical signal of Hz
_When a millimeter wave having a frequency of 100 GHz is used as _c / 2, two optical carriers ω ₁ having a frequency of 193.9 THz and ω ₂ having a frequency of 194.1 THz are obtained.

Then, a frequency of 1 GHz is obtained as the modulation signal ω _m.
Using the microwave of z, the frequency is 193.9 THz
On both sides of the optical carrier omega _1, the frequency 1G of the modulation signal omega _m
A spectrum with sidebands at intervals corresponding to Hz is obtained.

As is apparent from the above, in the present embodiment, as shown in FIG. 7, the optical carrier generated by the conversion of the input optical signal in the optical carrier generating section is subjected to mode separation by the mode separation element. Since the modulation signal is applied only to one of the optical carriers, the sideband generated by superimposing the modulation signal does not occur on the side of the optical carrier to which the modulation signal is not applied.

Therefore, even when a high frequency signal such as a millimeter wave band signal is transmitted, it is possible to sufficiently widen the optical carrier spacing in each frequency band, resulting in chromatic dispersion and chirping in the transmission line. Light interference can be prevented, and as a result, good transmission characteristics can be obtained.

Embodiment 2 FIG. 8 is a schematic view showing another embodiment in which the waveguide type optical modulator of the present invention is used as a subcarrier optical modulator.

The waveguide type optical modulator of this example was manufactured basically in the same manner as in Example 1 described above, and the optical waveguides and the electrode structures had the same form and size. However, in this embodiment, as is apparent from FIG. 8, in order to apply the intensity modulation signal in the modulation signal applying section, an additional Mach-Zehnder type optical waveguide 214 is added to one mode separation optical waveguide 206, It has a branched structure.

The mode separation element 2 in this embodiment is also used.
Also in 05, as in Example 1, the asymmetric cross waveguide type mode separation element shown in FIG. 2 was used.

The optical signal transmission process in FIG. 8, that is, the so-called subcarrier type optical transmission is the same as that of the first embodiment up to the mode separation element 205. However, the transmission process after passing through the mode separation element 205 is
As shown below, it differs from the first embodiment.

The optical carriers separated into the even mode and the odd mode in the mode separation element 205 respectively propagate in the mode separation optical waveguide 206 of the modulation signal applying section 213.
The optical carriers propagating through one of the mode separation optical waveguides 206 reach the branch points of the additional Mach-Zehnder optical waveguides 214 and propagate in the additional Mach-Zehnder optical waveguides 214, respectively. In this propagation process, the modulation signal ω _m is superimposed on one of the additional Mach-Zehnder interferometer type optical waveguides 214 from the signal application electrode 209.

After that, the light propagating through each additional Mach-Zehnder type optical waveguide 214 joins the mode separation optical waveguide 206, and the light propagating through the two mode separation optical waveguides 206 is output to the output optical waveguide 207. Join. The combined light is finally extracted as an optical signal.

In the present embodiment, two additional Mach-Zehnder type optical waveguides 214 that are branched are provided in the waveguide type optical modulator of the above-described first example, and one additional Mach-Zehnder type optical waveguide 214 is provided. By applying the modulation signal, the intensity modulation signal is applied when the additional Mach-Zehnder optical waveguide 214 is viewed as a whole.

Also in this embodiment, as in the first embodiment, not only the asymmetric cross waveguide type mode separation element but also the
A directional coupler type mode separation element can be used.

As in the case of the first embodiment, when a modulation signal is applied, a large number of high-order optical carriers are generated.
By propagating through the two-phase shift optical waveguide 202 and the π phase-shift optical waveguide 203, higher-order optical carriers cancel each other and disappear.

Therefore, also in the above-mentioned optical signal transmission process in the present embodiment, the changes in the input optical signal are the same as those in the first embodiment shown in FIGS.

That is, as is apparent from FIG. 8, in the present embodiment, unlike the first embodiment, the Mach-Zehnder type optical waveguide 214 is provided with respect to the lower mode separation optical waveguide 206 through which the optical carrier of frequency ω ₁ passes. Is provided, the optical carrier is further branched into two, and the modulation signal ω _m is applied only to the optical carrier passing through one of the additional Mach-Zehnder optical waveguides 214, and when viewed as the entire Mach-Zehnder optical waveguide 214, The intensity modulated signal of frequency ω _m is superimposed on the optical carrier of ω ₁ .

However, when the intensity-modulated optical signal is spectrally decomposed at the optical frequency, the frequency interval ω is divided into the upper sideband and the lower sideband of the frequency ω ₁ as in the first embodiment.
modulated signal with a sideband of _m is obtained, as a result, an optical signal obtained at the output optical waveguide 207, as shown in FIG. 7, the frequency omega ₁ having a side band optical signal and the frequency omega ₂ of the light It becomes the synthetic light with the signal.

Therefore, similarly to the first embodiment, even when a high frequency signal such as a millimeter wave band signal is transmitted, the carrier interval in each frequency band can be made sufficiently wide. Therefore, it is possible to prevent interference of optical signals, prevent generation of noise signals such as beat signals, and obtain good transmission characteristics.

Further, not only the phase-modulated signal shown in the first embodiment, but the same optical signal as shown in FIG. 7 can be obtained by applying such an intensity-modulated signal.
As the modulation signal, not only the FM modulation signal but also the AM modulation signal can be used. Therefore, the present invention also has the advantage of increasing the degree of freedom on the side of the user who uses the waveguide type optical modulator of the present invention.

In this embodiment, as is clear from FIG. 8, the intensity modulation signal is applied by providing the Mach-Zehnder type optical waveguide 214 in the modulation signal applying section. It is also possible to directly introduce the intensity modulation signal from the outside in the same manner as in FIG.

As described above, in the first and second embodiments,
The case where a single light is used as the input light for the waveguide type optical modulator of the present invention has been described. However, even in the so-called wavelength multiplexing system in which a plurality of lights having different wavelengths are used as the input light, A waveguide type optical modulator can be used.

Examples in which the waveguide type optical modulator of the present invention is used in the wavelength multiplexing system will be described below in Examples 3 and 4.

Embodiment 3 FIG. 9 is a schematic view showing an embodiment in which the waveguide type optical modulator of the present invention is used in a wavelength division multiplexing subcarrier optical modulator.

In this embodiment, two waveguide type optical modulators, which are the same as those in the first embodiment, are used in parallel, and two laser lights having frequencies ω ₁₀ and ω ₂₀ are used as input lights.

The transmission process of the optical signal in each waveguide type optical modulator is the same as the transmission process described in the first embodiment.

The change of the input light in this transmission process is also the same as that of the first embodiment, and the input lights of the frequencies ω ₁₀ and ω ₂₀ as shown in FIG. 11 are frequencies ω ₁₁ and ω ₁₂ having carrier intervals ω _c , and ω ₂₁ as shown in FIG.
And two optical carriers of ω ₂₂ .

After passing through the mode separation element 305,
As shown in 12 and 13, the frequency ω ₁₂And ω_{twenty two}, And
ω₁₁And ω_{twenty one}Mode separated into the output optical waveguide 307
The modulation signal ω_mBy superposing
Frequency ω as shown in₁₁And ω_{twenty one}Upper sideband and below
A sideband is formed in the sideband.

When the upper waveguide type optical modulator of FIG. 9 is channel 1 and the lower waveguide type optical modulator is channel 2, the optical signal finally obtained by combining these is shown in FIG.
As shown in FIG. 5, a spectrum having sidebands with an interval ω _m on both sides of the optical carriers ω ₁₁ and ω ₂₁ is exhibited.

Therefore, as in the first embodiment, even when a high frequency signal such as a millimeter wave band signal is transmitted, the carrier interval in each frequency band can be made sufficiently wide, and as a result, the interference of the optical signal can be prevented. It is possible to prevent the generation of a noise signal such as a beat signal and obtain good transmission characteristics.

Further, in the present embodiment, the description has been made about the multiplexing of only two wavelengths, but even when the multiplexing is further performed by using three or more wavelengths, the waveguide of the present invention is selected according to the number of wavelengths. This can be easily achieved by providing a type optical modulator.

For example, in the case of wavelength division multiplex transmission requiring a bandwidth of 1 GHz, the frequency of 10
When a microwave of about GHz was used, only a few channels could be secured.

On the other hand, by using the waveguide type optical modulator and the optical modulation method of the present invention, an optical signal having a frequency of about 194 THz can be used as the input light in the present invention, so that tens of thousands of channels are secured. can do.

Embodiment 4 FIG. 16 is a schematic diagram showing another embodiment in which the waveguide type optical modulator of the present invention is used in a wavelength division multiplexing subcarrier optical modulator.

In the present embodiment, two waveguide type optical modulators used in the second embodiment are used in a parallel state, and two laser lights having frequencies ω ₁₀ and ω ₂₀ are used as input light as in the third embodiment. did.

The transmission process of the optical signal in each waveguide type optical modulator is the same as the transmission process described in the second embodiment.
The change of the input light in the transmission process is also the same as in the second or third embodiment.

Further, as described in the second embodiment,
Even in the case where one of the mode separation optical waveguides 406 is branched to the additional Mach-Zehnder optical waveguide 414 and the intensity modulation signal is applied, the output optical waveguide 407 can be applied to the embodiment by performing spectrum decomposition at the optical frequency. Three
Similar to the above case, the spectrum has sidebands formed in the upper and lower sidebands of the frequencies ω ₁₁ and ω ₂₁ , as shown in FIG.

Therefore, also in this embodiment, FIG.
In FIG. 15, the upper optical waveguide type optical modulator in Channel 1 is the channel 1, and the lower optical waveguide type optical modulator is in the channel 2. The optical signal finally obtained by combining these is a spectrum as shown in FIG. The same effect as the case of Example 3 is exhibited.

Also in this embodiment, as described in the third embodiment, by providing the waveguide type optical modulator of the present invention according to the number of wavelengths, multiplexing of three or more wavelengths can be easily achieved. be able to.

Furthermore, regarding the application of the intensity modulation signal,
As in the second embodiment, the modulation signal applying section can directly apply the modulation signal from the outside.

[0073]

According to the present invention, an optical carrier for converting an input optical signal into two optical carriers having a lower frequency than the input optical signal and having different frequencies to facilitate the modulation of the optical signal. In a waveguide type optical modulator including a generator and a modulation signal applying unit that applies a modulation signal to the optical carrier, a mode separation element is provided between the optical carrier generating unit and the modulation signal applying unit. Therefore, the modulation signal can be applied only to the optical carrier of one mode that has been mode-separated.

Therefore, it is possible to avoid the phenomenon that a sub-band is generated in each frequency band of each optical carrier, and even when a high frequency signal such as a millimeter wave band signal is transmitted, the frequency interval of the optical carriers is sufficient. Therefore, even if chromatic dispersion and chirping occur in the transmission line, good transmission characteristics can be obtained without generating a noise signal such as a beat signal.

Further, since the waveguide type optical modulator and the optical modulation method of the present invention can use the light of the THz band as the input light, the light of the microwave band is used as the optical signal, Unlike the conventional wavelength multiplexing system, which can secure only about channels, tens of thousands of channels can be secured.

Furthermore, by making the optical carrier generating portion of the waveguide type optical modulator of the present invention a so-called SSB modulator structure, particularly a high frequency optical signal can be efficiently modulated.

Regardless of whether the phase modulation signal or the intensity modulation signal is applied as the modulation signal, since an accurate optical signal can be modulated, both the FM modulation signal and the AM modulation signal are used as the modulation signal. be able to. As a result, the waveguide type optical modulator of the present invention also has the advantage that the degree of freedom on the side of the user who uses the waveguide type optical modulator of the present invention increases.

Further, by installing the waveguide type optical modulator of the present invention for each wavelength according to the number of wavelengths to be used, the above effect can be obtained even in the wavelength division multiplexing system, and the light in a very wide range can be obtained. It can be seen that it can be applied to communication systems.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment in which a waveguide type optical modulator of the present invention is used as a subcarrier optical modulator.

FIG. 2 is a schematic view of an asymmetric crossed waveguide type mode separation element used in an embodiment of the present invention.

FIG. 3 is a diagram showing a spectrum of input light in Examples 1 and 2.

FIG. 4 is a diagram showing an optical spectrum immediately before entering a mode separation element in Examples 1 and 2.

5 is a diagram showing an optical spectrum in an upper mode-separating optical waveguide after mode separation in Examples 1 and 2. FIG.

FIG. 6 is a diagram showing an optical spectrum in a lower mode-separating optical waveguide after mode separation in Examples 1 and 2;

FIG. 7 is a diagram showing spectra of output optical signals in Examples 1 and 2.

FIG. 8 is a schematic view showing another embodiment in which the waveguide type optical modulator of the present invention is used as a subcarrier optical modulator.

FIG. 9 is a schematic diagram showing an embodiment in which the waveguide type optical modulator of the present invention is used in a wavelength division multiplexing subcarrier optical modulator.

FIG. 10 is a diagram showing spectra of input light in Examples 3 and 4.

FIG. 11 is a diagram showing an optical spectrum immediately before entering a mode separation element in Examples 3 and 4.

FIG. 12 is a diagram showing an optical spectrum in an upper mode-separating optical waveguide after mode separation in Examples 3 and 4.

FIG. 13 is a diagram showing an optical spectrum in a lower mode separation optical waveguide after mode separation in Examples 3 and 4.

FIG. 14 is a diagram illustrating spectra of output optical signals in Examples 3 and 4.

FIG. 15 is a diagram showing a synthesized optical spectrum of a wavelength division multiplexing system in Examples 3 and 4.

FIG. 16 is a schematic diagram showing another embodiment in which the waveguide type optical modulator of the present invention is used in a wavelength division multiplexing subcarrier optical modulator.

FIG. 17 is a diagram showing a spectrum of input light in a conventional example.

FIG. 18 is a diagram showing a spectrum of an optical carrier in a conventional example.

FIG. 19 is a diagram showing a spectrum of an output optical signal in a conventional example.

[Explanation of symbols]

101, 201, 301, 401 Input optical waveguides 102, 202, 302, 402 π / 2 phase shift optical waveguides 103, 203, 303, 403 π phase shift optical waveguides 104, 204, 304, 404 Optical carrier generator output optical waveguides 105, 205, 305, 405 Mode separation element 106, 206, 306, 406 Mode separation optical waveguide 107, 207, 307, 407 Output optical waveguide 108, 208, 308, 408 Photocarrier generation electrode 109, 209, 309, 409 Modulation signal application electrodes 110, 210, 310, 410 π / 2 phase shift electrodes 111, 211, 311, 411 π phase shift electrodes 112, 212, 312, 412 Optical carrier generation unit 113, 213, 313, 413 Modulation Mach-Zehnder with additional signal application units 214 and 414 -Type optical waveguide

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Oikawa 585 Tomimachi, Funabashi, Chiba Sumitomo Osaka Cement Co., Ltd. New Technology Research Laboratory (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1 / 00-1/29 G02F 2/02

Claims (8)

(57) [Claims] 1. An input optical signal is lower than the input optical signal.
Convert to two optical carriers of high frequency and high frequency,
An optical carrier generator for facilitating the modulation of the optical signal,
In a waveguide type optical modulator comprising a modulation signal applying section for applying a modulation signal to the optical carrier, for separating each of the optical carriers between the optical carrier generating section and the modulation signal applying section. 1. A waveguide type optical modulator, characterized in that the mode separation element of (1) is provided. 2. The optical carrier generation section includes one input optical waveguide, and a pair of π / 2 phase shift optical waveguides composed of two optical waveguides branched from the input optical waveguide, and the π / 2 phase shift optical waveguide.
2 of two sets of π phase shift optical waveguides formed of two optical waveguides branched from the / 2 phase shift optical waveguide, and two optical waveguides constituting the π phase shift optical waveguide
2. The waveguide type according to claim 1, further comprising: a plurality of output optical waveguides for the optical carrier generating section, and an optical carrier generating electrode is provided for each of the two sets of π phase shift optical waveguides. Light modulator. 3. The modulation signal applying section applies the phase modulation signal only to one of the two optical carriers generated in the optical carrier generating section, which has been mode-separated. The waveguide type optical modulator according to claim 1 or 2. 4. The intensity modulation signal is applied to only one of the two optical carriers generated by the optical carrier generation unit, the optical carrier being mode-separated, among the two optical carriers generated by the optical carrier generation unit. The waveguide type optical modulator according to claim 1 or 2. In optical carrier generation section of 5. A waveguide-type optical modulator to facilitate the modulation of the optical signal, the input optical signal, the input
Two optical carriers with lower and higher frequencies than the optical signal
In the optical modulation method in which the optical signal is converted into the optical signal and the modulated signal application unit of the waveguide optical modulator applies the modulated signal to the two optical carriers, the two optical carriers are mode-separated by the mode separation element, An optical modulation method, wherein a modulation signal is applied only to an optical carrier. 6. The conversion of the input optical signal into two optical carriers is performed by dividing the input optical signal into two by a π / 2 phase shift optical waveguide branched into two, and dividing each of the divided input optical signals. The optical modulation method according to claim 5, wherein the optical modulation method is performed by propagating through the π phase shift optical waveguide and applying a modulation signal during propagation of the π phase shift optical waveguide. 7. The optical modulation method according to claim 5, wherein the modulation signal applied by the modulation signal application unit of the waveguide type optical modulator is a phase modulation signal. 8. The optical modulation method according to claim 5, wherein the modulation signal applied by the modulation signal application section of the waveguide type optical modulator is an intensity modulation signal.