JPH11249094A - Waveguide type optical modulator and optical modulating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the sufficient frequency interval of optical carriers even when a high frequency signal such as a millimeter wave band signal is transmitted and to obtain satisfactory transmission characteristics without generating a noise signal such as a beat signal even when wavelength dispersing or chirping occurs in a transmission line. SOLUTION: This waveguide type optical modulator is provided with an optical carrier generating part 111 for facilitating the modulation of an input optical signal by converting this input optical signal to two optical carriers having respectively different frequencies lower than that of the optical signal and a modulating signal impressing part 112 for impressing a modulating signal to the optical carriers. In this case, an optical waveguide 106 for introducing reference light, with which one of the optical carriers disappears because of a difference, into the modulating signal impressing part 112 is provided separately from an optical waveguide for transmitting the optical signal. Thus, only the other optical carrier is stayed behind and the modulating signal is impressed only to this optical carrier.

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 lower frequency than the input optical signal and having different frequencies.
The present invention relates to a waveguide type optical modulator including a modulation signal applying unit for applying a modulation signal to the optical carrier, and an optical modulation method using the waveguide type optical modulator having such a configuration. The present invention relates to a waveguide type optical modulator which can be suitably used for subcarrier optical modulation for transmitting a high frequency signal such as a band 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 converts an input optical signal into a signal having a lower frequency than the input optical signal in order to easily modulate the optical signal. In addition, the optical carrier generating unit converts the optical carrier into two optical carriers having different frequencies, and a modulation signal applying unit that applies 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 light modulation for transmitting a high-frequency signal such as a millimeter-wave band signal, the following problems occur. Had occurred.

Assuming that the frequency of the laser beam incident on the waveguide type optical modulator is ω ₀ as shown in FIG. 19, the optical carrier outputted after passing through the optical carrier generator is as shown in FIG. the combined light of the two optical carrier having a frequency of omega ₁ or omega _2. Furthermore, when the combined light passes through the modulated signal applying unit, respectively to the modulation signal omega _m of each frequency omega ₁ and omega ₂ are superimposed. As a result, as seen in FIG. 21, the optical signal obtained is a composite light of the frequency omega ₁ or omega ₂ of the two optical signals having Saidondo the upper sideband and the lower sideband of the frequency band.

However, when a high-frequency signal such as a millimeter-wave band signal as described above is transmitted, a sufficient frequency interval between ω ₁ and ω ₂ cannot be obtained at a conventional modulation speed of several tens of GHz. Further, since the sideband is generated and for applying a modulation signal each frequency band of the omega ₁ and omega ₂ as described above, each frequency band of the omega ₁ and omega ₂ are as exist in close proximity. In such a case, if chromatic dispersion and chirping occur in the transmission path, the traveling speed of light at each frequency of ω ₁ and ω ₂ is shifted, and as a result, the frequencies of these lights also become ω ₁ and ω _The interference deviates from ₂ , and a noise signal such as a beat signal is generated, thereby deteriorating the transmission characteristics.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been developed in consideration of the above-mentioned problems. It is an object of the present invention to provide a waveguide type optical modulator and an optical modulation method capable of preventing interference of light in two frequency bands and preventing generation of a noise signal such as a beat signal.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, have established an optical waveguide for introducing reference light into a modulation signal application section of a waveguide type optical modulator. An optical waveguide for transmitting an optical signal is provided separately, a reference light is introduced into the modulation signal application unit, and a difference between the reference light and the two optical carriers obtained by the optical carrier generation unit is calculated. It has been found that the above problem can be solved by eliminating the photocarriers, and the present invention has been made.

That is, the present invention converts an input optical signal into two optical carriers having lower frequencies than the input optical signal and having different frequencies, thereby facilitating the modulation of the optical signal. In a waveguide type optical modulator including an optical carrier generation unit and a modulation signal application unit for applying a modulation signal to the optical carrier, a reference light for eliminating one of the optical carriers by a difference is applied to the modulation signal application unit. An optical waveguide for introducing an optical waveguide is provided separately from an optical waveguide for transmitting an optical signal.

Also, in order to facilitate the modulation of the optical signal, the optical carrier generating section of the waveguide type optical modulator converts the input optical signal to two optical carriers having a lower frequency than the input optical signal and having different frequencies. In the optical modulation method of converting and applying a modulation signal to the two optical carriers in the modulation signal applying unit of the waveguide type optical modulator, the modulation is performed by an optical waveguide separately provided for the optical waveguide transmitting the optical signal. An optical modulation method characterized by introducing a reference light into a signal applying unit and calculating a difference between the two optical carriers to eliminate one of the optical carriers.

The optical carrier generator of the waveguide type optical modulator is capable of efficiently converting a high-frequency optical signal, and prevents generation of higher-order optical carriers during the conversion. From the viewpoint that the optical waveguide can be used, one input optical waveguide, a pair of π / 2 phase shift optical waveguides composed of two optical waveguides branched from the input optical waveguide, and the π / 2
Two sets of π-phase shift optical waveguides, each of which is composed of two optical waveguides branched from the phase-shift optical waveguide, and two optical carrier generators, each of which is composed of two optical waveguides constituting the π-phase shift optical waveguide. Preferably, an output optical waveguide is provided, and an optical carrier generating electrode is provided for each of the two sets of the π phase shift optical waveguides.

The conversion of an input optical signal into two optical carriers in the above-mentioned optical modulation method is based on the same viewpoint as in the case of the optical carrier generating section of the above-mentioned waveguide type optical modulator, and is divided into two branched π. An input optical signal is split into two by a / 2 phase shift optical waveguide, and each of the split input optical signals is propagated in a π phase shift optical waveguide, and a modulation signal is applied during propagation of the π phase shift optical waveguide. It is preferred to be carried out by Further, from the viewpoint that conventional FM modulation and AM modulation techniques can be used, the modulation signal applied in the modulation signal application unit is:
It is preferably a phase modulation signal and an intensity modulation signal.

[0011]

DETAILED DESCRIPTION OF THE INVENTION As described above, the present invention converts an input optical signal into two optical carriers having frequencies lower than the input optical signal and having different frequencies, respectively.
An optical carrier generator for facilitating modulation of an optical signal;
A waveguide-type optical modulator including a modulation signal application unit that applies a modulation signal to the optical carrier, wherein a reference light for eliminating one of the optical carriers by a difference is introduced into the modulation signal application unit. A waveguide type optical modulator characterized in that an optical waveguide is separately provided for an optical waveguide for transmitting an optical signal.

Furthermore, in order to facilitate the modulation of the optical signal, the optical carrier generating section of the waveguide type optical modulator converts the input optical signal to a signal having a lower frequency than the input optical signal and having different frequencies. In the optical modulation method of converting into two optical carriers and applying a modulation signal to the two optical carriers in the modulation signal applying unit of the waveguide type optical modulator, an optical waveguide separately provided for the optical waveguide transmitting the optical signal is provided. An optical modulation method characterized by introducing a reference light into the modulation signal applying unit through a wave path and eliminating one of the optical carriers by taking a difference between the two optical carriers. Hereinafter, the present invention will be described in detail with reference to examples.

[0013]

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

The waveguide type optical modulator of this embodiment is manufactured as follows. The substrate is a Z-plate lithium niobate (LiNb
O ₃ : may be abbreviated as LN), a waveguide pattern is formed on the substrate by using a photoresist and an etching technique, and then titanium (Ti) is reduced to about 800 ° by a vacuum deposition method. By depositing and heating at 1000 ° C. for 20 hours, titanium was diffused into the LN substrate to form a 10 μm-wide optical waveguide for transmitting an optical signal and an optical waveguide for introducing a reference light.

The substrate to be used is not limited to the above-mentioned lithium niobate as long as it has an electro-optical effect. For example, lithium tantalate (LiTaO ₃ ) and lead lanthanum zirconate titanate (PLZT) may be used. Can be used. Further, in addition to the above-described vacuum deposition method, a method of depositing titanium forming an optical waveguide on a substrate, a sputtering method,
An ion plating method, a CVD method, or the like can be used. Further, in this embodiment, the optical waveguide is formed from titanium, but in addition, nickel (Ni), copper (Cu),
And chromium (Cr).

Next, a nichrome layer is formed as a base layer on the substrate on which the optical waveguide is formed, and about 20 μm of gold (Au) is deposited by a vacuum deposition method and an electroplating method, thereby forming a modulation electrode and a signal. An application electrode is formed. As the electrode material, in addition to the above gold, silver (Ag), copper, and the like can also be used.

The optical waveguide device obtained in this way is fixed to a stainless steel case, an optical fiber is connected to the entrance and exit ports, and each electrode is wired to an electrical connector. You can get a bowl.

Next, a 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 through the input optical waveguide 101, reaches the branch point, and Π / 2 phase-shifted optical waveguides 102 and further propagate through the π / 2 phase-shifted optical waveguides 102. Reaching the branch point, each of the two π-phase shifted optical waveguides 10
3 and propagate through the π phase shift optical waveguide 103.

In this propagation process, one of the branched π phase shift optical waveguides 103
7, modulation signals of frequency ω _C / 2 are applied,
The input optical signal is converted to an optical carrier. The light propagating in each of the π phase shift optical waveguides 103 then merges and propagates in the optical carrier generator output optical waveguide 104,
By further merging, the light propagates through the output optical waveguide 105.

[0021] By propagating in the output optical waveguide 105, the light is shifted from the optical carrier generation section to the modulation signal applying section, a modulation signal of frequency omega _m from a modulation signal application electrode 108 is applied to the optical carrier A modulation signal is superimposed.

On the other hand, the reference light ω ₁ is externally introduced into the modulation signal applying unit through the reference light introducing optical waveguide 106. The reference light ω ₁ makes one optical carrier ω ₁ disappear by taking the difference from the optical carrier. Further, in order to eliminate the optical carrier, the frequency of the reference light and the frequency of the optical carrier to be eliminated need to be the same.

In the present invention, the π phase shift optical waveguide and the π / 2 phase shift optical waveguide are defined as two sets of branched π phase shift optical waveguides or π / 2 phase shift optical waveguides. In the case of branching and propagating, these optical waveguides collectively refer to optical waveguides which are output with the phases of these branched optical signals shifted from each other by π or π / 2.

As long as the phase of the branched optical signal can be shifted by π or π / 2, the means for phase shifting is not limited. In this embodiment, as shown in FIG. 1, a π / 2 phase shift optical waveguide 10 serving as a phase shift electrode is used.
The phase shift was performed by installing the 9 and π phase shift optical waveguides 110. In the optical signal transmission process described above, the input optical signal changes as shown in FIGS.

The input light of frequency ω ₀ having the spectrum as shown in FIG. 2 is input to the π phase shift optical waveguide 103 branched as described above by applying the modulation signal of frequency ω _C / 2. The lower frequencies of the light are converted to two different optical carriers, each frequency being different. The two optical carriers respectively propagate after passing through the π-phase shift optical waveguide 103 and then propagate through the optical carrier generating unit output optical waveguide 104, and further merge and propagate through the output optical waveguide 105.

The optical carrier before the modulation signal is applied from the modulation signal applying electrode 108 in the output optical waveguide 105 is:
As shown in FIG. 3, it has an optical spectrum at two different frequencies, ω ₁ and ω ₂ .

When a modulation signal is applied, a large number of higher-order optical carriers are generated. However, the phases are mutually transmitted by propagating through the branched π / 2 phase shift optical waveguide 102 and π phase shift optical waveguide 103. π / 2 and π shifts,
These higher-order optical carriers disappear by interfering with each other in a portion where the branched π / 2 phase shift optical waveguide 102 and the π phase shift optical waveguide 103 are coupled.

When the modulation signal ω _m is applied from the modulation signal applying electrode 108 to the two optical carriers shown in FIG. 3, the optical carrier has a spectrum on which the modulation signal ω _m is superimposed as shown in FIG. .

Next, from the reference light introducing optical waveguide 106,
Same frequency ω as the frequency of the optical carrier ω ₁ in order to disappear
_{When the} reference light ω ₁ having ₁ is introduced and the difference between the reference light ω ₁ and the optical carrier is taken, the optical carrier has a spectrum as shown in FIG. The optical carrier shown in FIG. 5 is output as a final optical signal. For example, an optical signal having a frequency of 194 THz is used as the input light ω ₀ , and a frequency of 100 GHz is used as the modulation signal ω _C / 2 for generating an optical carrier.
When the millimeter wave is used, two optical carriers ω ₁ having a frequency of 193.9 THz and an optical carrier ω ₂ having a frequency of 194.1 THz are obtained.

The modulation signal ω _m has a frequency of 1 GHz.
Using microwaves of z, the optical carriers ω ₁ and ω ₂
On both sides of the spectrum with sidebands at intervals corresponding to the frequency 1GHz of the modulation signal omega _m are obtained. Introducing a reference beam having the same frequency (193.9THz) and the optical carrier omega _1, when a difference between the optical carrier omega _1, eventually it is possible to obtain an optical carrier of 200GHz corresponding to the frequency omega _C .

As is clear from the above, in this embodiment, one of the two optical carriers is eliminated by taking the difference from the reference light introduced from the outside, so that as shown in FIG. In addition, there is no possibility that two optical carriers exist in a frequency band close to each other. Therefore, even when a high-frequency signal such as a millimeter-wave band signal is transmitted, the optical carrier interval in each frequency band can be made sufficiently large, so that light interference due to chromatic dispersion and chirping in the transmission path, etc. Can be prevented, and as a result, good transmission characteristics can be obtained.

Embodiment 2 FIG. 6 is a schematic diagram showing another embodiment in which the waveguide type optical modulator of the present invention is used for a subcarrier optical modulator.
The waveguide type optical modulator of this embodiment was manufactured basically in the same manner as in the first embodiment, and the shapes and sizes of each optical waveguide and electrode structure were the same. However, in the present embodiment, as is apparent from FIG. 6, a structure is adopted in which the output optical waveguide 105 is further branched into an additional Mach-Zehnder type optical waveguide 213 in order to apply an intensity modulation signal in the modulation signal application section. ing.

The transmission process of the optical signal in FIG. 6, that is, the optical transmission of the so-called subcarrier system, is the same as that of the first embodiment up to the additional Mach-Zehnder optical waveguide 213. However, the transmission process after reaching the additional Mach-Zehnder optical waveguide 213 is different from that of the first embodiment as described below.

The optical carrier that has propagated through the output optical waveguide 205 reaches the branch point and propagates through the additional Mach-Zehnder optical waveguide 213. In this propagation process, the modulation signal ω _m is superimposed on one of the additional Mach-Zehnder optical waveguides 213 from the signal application electrode 208. After that, the light propagating through the additional Mach-Zehnder optical waveguide 213 joins the output optical waveguide 205. The merged light
Finally, it is extracted as an optical signal.

In this embodiment, an additional Mach-Zehnder optical waveguide 21 is added to the waveguide optical modulator of the first embodiment.
3 and an additional Mach-Zehnder optical waveguide 2
By applying a modulation signal to one of the optical waveguides 13, the intensity modulation signal is applied when the additional Mach-Zehnder optical waveguide 213 is viewed as a whole.

As in the first embodiment, when a modulation signal is applied, many 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.

Transmission process of the above optical signal in this embodiment
Of the input optical signal in FIG.
Is the same as That is, as is apparent from FIG.
Mach-Zehnder light added to the power waveguide 205
A waveguide 213 is provided and an additional Mach-Zehnder optical waveguide is provided.
The modulation signal ω is applied only to the optical carrier passing through one of the paths 213._mTo
Apply and add additional Mach-Zehnder optical waveguide 213
Ω₁And ω_TwoFrequency ω to the optical carrier of
_mAre superimposed.

[0038] However, when the spectral resolution of the intensity-modulated optical signal at optical frequencies, likewise, the frequency omega ₁ and omega ₂ sidebands of frequency interval omega _C to the upper sideband and the lower sideband of Example 1 A modulated signal with
As a result, the optical signal obtained in the output optical waveguide 205 becomes an optical signal having a frequency ω _C having a side band as shown in FIG. 5 due to a difference from the reference light.

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 sufficiently widened. For this reason, interference of optical signals can be prevented, and generation of noise signals such as beat signals can be prevented, and good transmission characteristics can be obtained.

Further, even if such an intensity modulation signal is applied in addition to the phase modulation signal shown in the first embodiment, the same optical signal can be obtained as shown in FIG.
As a modulation signal, not only an FM modulation signal but also an AM modulation signal can be used. Therefore, the present invention also has an advantage that the degree of freedom on the user side using the waveguide type optical modulator of the present invention is increased.

In this embodiment, as apparent from FIG. 6, the intensity modulation signal is applied by providing an additional Mach-Zehnder optical waveguide 213 in the modulation signal application section. Without providing an optical waveguide, an intensity modulation signal can be directly introduced from the outside in the same manner as in FIG.

Embodiment 3 FIG. 7 is a schematic diagram showing still another embodiment in which the waveguide type optical modulator of the present invention is used for a subcarrier optical modulator. The waveguide type optical modulator of the present embodiment was manufactured basically in the same manner as in the first embodiment, and the shapes and sizes of the respective optical waveguides and electrode structures were the same. However, as is apparent from FIG. 7, in the present embodiment, unlike the first embodiment, the reference light is introduced before applying the modulation signal from the modulation signal applying electrode 308.

The transmission process of the optical signal in FIG. 7, that is, the optical transmission of the so-called subcarrier system is basically the same as that of the first embodiment, but one optical carrier of frequency ω ₁ is calculated as a difference from the reference light. Thus, the difference is that the modulation signal is applied and the modulation signal application electrode 308 applies the modulation signal.
Therefore, the change of the optical signal in the transmission process of the optical signal according to the present embodiment is as follows.

As shown in FIG. 8, when the frequency of the input optical signal is ω _0, which is the same as that of the first embodiment, the signal propagates through the optical carrier generator 311 and the reference light introducing optical waveguide 306 is coupled to the output optical waveguide 305. Immediately after arriving at the portion, the optical carrier has the frequency ω as shown in FIG.
Composed of ₁ and omega ₂ of the two light spectrum.

[0045] In a portion where the reference light introducing optical waveguide 306 and the output optical waveguide 305 is attached, the optical carrier omega ₁ disappeared by the difference between the optical carrier and the reference light is taken, the modulated signal application electrode The spectrum of the optical carrier before reaching 308 is as shown in FIG.

Next, a modulation signal is applied to the optical carrier as shown in FIG. 10 from the modulation signal applying electrode 308, and the modulation signal is superimposed only on one of the remaining optical carriers. As a result, the final output signal has a spectrum as shown in FIG.

As is clear from the above, also in this embodiment, two optical carriers do not exist close to each other in frequency band as in the first embodiment. Therefore,
Even when transmitting high-frequency signals such as millimeter-wave signals,
Since the optical carrier interval of each frequency band can be made sufficiently wide, it is possible to prevent light interference due to chromatic dispersion and chirping in the transmission path, and as a result,
Good transmission characteristics can be obtained.

As is apparent from Examples 1 to 3,
One of the optical carriers can be completely eliminated by introducing the reference light before applying the modulation signal as well as introducing the reference light after applying the modulation signal. However, when the reference light is introduced into the optical carrier generation unit, higher-order optical carriers remain, and it becomes difficult to convert the input signal into two optical carriers. Therefore, the reference light may be introduced into the modulation signal application unit. is necessary.

In the first to third 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, a plurality of lights having different wavelengths are used as the input light. The waveguide type optical modulator of the present invention can also be used in a so-called wavelength multiplexing system using the method. Hereinafter, examples in which the waveguide type optical modulator of the present invention is used in a wavelength division multiplex system in Examples 4 and 5 will be described.

Embodiment 4 FIG. 12 is a schematic diagram showing an embodiment in which the waveguide type optical modulator of the present invention is used for a wavelength division multiplexing type subcarrier optical modulator. In this embodiment, the same optical waveguide modulator as in Example 1 was used in two juxtaposed state, the input light using the frequency omega ₁₀ and omega ₂₀ laser beam. 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 the transmission process is basically the same as that of the first embodiment, and the input light having the frequencies ω ₁₀ and ω ₂₀ shown in FIG. Before reaching the modulation signal applying electrode 408 through the carrier generation modulation electrodes 407, as shown in FIG. 14, the carrier intervals ω _C and ω _C ′ depend on the frequency of the modulation signal applied from the carrier generation modulation electrode 407, respectively. Are converted to two optical carriers at frequencies ω ₁₁ and ω ₁₂ , and ω ₂₁ and ω ₂₂ . Here, the values of ω _C ′ and ω _C are, for example, the minimum bandwidth at which the channels do not interfere with each other is 1 GHz.
In the case of z, the magnitude is selected so that the magnitude of (ω _C ′ −ω _C ) is 1 GHz or more. Subsequently, when a modulation signal is applied to these two optical carriers from the modulation signal application electrode 408, the optical carriers have a spectrum as shown in FIG.

Next, by introducing the reference light from the reference light introducing optical waveguide 406 to eliminate the optical carriers ω ₁₁ and ω ₁₂ , the optical signal obtained as the output of each waveguide type optical modulator is shown in FIG. It becomes as shown in.

Assuming that the upper waveguide type optical modulator in FIG. 12 is channel 1 and the lower waveguide type optical modulator is channel 2, an optical signal finally obtained by combining these is shown in FIG.
The state shown in FIG. Therefore, similarly to the first embodiment, even when a high-frequency signal such as a millimeter-wave band signal is transmitted, the carrier interval of each frequency band can be sufficiently widened, and as a result, interference of optical signals can be prevented. Thus, it is possible to prevent noise signals such as beat signals from being generated, thereby obtaining good transmission characteristics.

In this embodiment, the multiplexing of only two wavelengths has been described. However, even in the case of further multiplexing using three or more wavelengths, the waveguide of the present invention may be used in accordance with the number of wavelengths. This can be easily achieved by providing a type light modulator. For example, in the case of wavelength division multiplexing transmission requiring a bandwidth of 1 GHz, as in the conventional case, a frequency of 10 GHz is used as input light.
When a microwave of about GHz was used, only a few channels could be secured.

On the other hand, as described in the first embodiment, using the waveguide type optical modulator and the optical modulation method of the present invention,
Further, when an optical signal of a THz band is used as input light and a millimeter wave of several hundred GHz is used as a modulation signal for generating an optical carrier, the frequency band of several hundred GHz can be used. , Several tens of channels can be secured.

Embodiment 5 FIG. 18 is a schematic diagram showing another embodiment in which the waveguide type optical modulator of the present invention is used for a wavelength division multiplexing type subcarrier optical modulator. In this embodiment, the same optical waveguide modulator as in Example 2 was used in the two parallel state, using a laser beam of Example 4 in the same manner as the frequency omega ₁₀ and omega ₂₀ as input light. The transmission process of the optical signal in each waveguide type optical modulator is as follows.
This is the same as the transmission process described in the second embodiment. Changes in the input light during the transmission process in each waveguide type optical modulator also
This is the same as the case of the second or third embodiment.

As described in the second embodiment,
Even when the output optical waveguide 505 is branched into an additional Mach-Zehnder type optical waveguide 513 and an intensity modulation signal is applied, the output optical waveguide 505 is spectrally decomposed at the optical frequency, and thus the output optical waveguide 505 is of the third embodiment. as with, the upper sideband and the lower sideband of the frequency omega _C and omega _C 'as shown in FIG. 16, it exhibits a spectrum sidebands are formed spacing omega _m.

Therefore, also in this embodiment, FIG.
Assuming that the upper waveguide-type optical modulator is channel 1 and the lower waveguide-type optical modulator is channel 2, the optical signal finally obtained by combining them has a spectrum as shown in FIG. Thus, the same effect as in the fourth embodiment can be obtained.

Also in this embodiment, as described in the fourth embodiment, multiplexing of three or more wavelengths can be easily achieved by providing the waveguide type optical modulator according to the present invention in accordance with the number of wavelengths. be able to. Further, as for the application of the intensity modulation signal, similarly to the second embodiment, the modulation signal application unit can directly apply the modulation signal from outside.

In the fourth and fifth embodiments, the reference light introducing optical waveguide 6 and the output optical waveguide 5 are provided after the modulation signal applying electrode 8.
And one of the optical carriers is eliminated by introducing the reference light after applying the modulation signal.
Similarly to the above, the reference light introducing optical waveguide 6 and the output optical waveguide 5 may be coupled in front of the modulation signal applying electrode 8, and the reference light may be introduced before applying the modulation signal to cause one of the optical carriers to disappear. it can.

[0061]

According to the present invention, the input optical signal is converted into two optical carriers having a lower frequency than the input optical signal and having different frequencies, thereby facilitating the modulation of the optical signal. In a waveguide type optical modulator comprising an optical carrier generating unit and a modulation signal applying unit for applying a modulation signal to the optical carrier, a reference light for causing one of the optical carriers to disappear by a difference is applied to the modulation signal. Since the optical waveguide for introducing into the part is provided separately from the optical waveguide for transmitting the optical signal, the modulation signal can be superimposed only on one of the remaining optical carriers without being lost. .

Therefore, it is possible to avoid a phenomenon in which a side band is generated for each frequency band of each optical carrier. Even when a high-frequency signal such as a millimeter-wave band signal is transmitted, the frequency interval between the optical carriers is sufficiently reduced. Even when chromatic dispersion and chirping occur in the transmission path, good transmission characteristics can be obtained without generating noise signals such as beat signals.

The waveguide type optical modulator and optical modulation method of the present invention can use such THz band light and appropriately select the frequency of a modulation signal for generating an optical carrier. Thus, unlike the conventional wavelength multiplexing method in which only about several channels can be secured, tens or more channels can be secured. Furthermore, by using a so-called SSB modulator structure for the optical carrier generation section of the waveguide type optical modulator of the present invention, it is possible to efficiently modulate a high frequency optical signal in particular.

In both cases where a phase modulation signal or an intensity modulation signal is applied as the modulation signal, accurate modulation of the optical signal is possible. Therefore, 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 an advantage that the degree of freedom on the user side using the waveguide type optical modulator of the present invention is increased. 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 a wavelength multiplexing system, and an optical communication system in a very wide range You can see that it can be applied.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram illustrating a spectrum of an optical carrier before a modulation signal is applied in Examples 1 and 2.

FIG. 4 is a diagram illustrating a spectrum of an optical carrier after a modulation signal is applied in Examples 1 and 2.

FIG. 5 is a diagram illustrating an optical spectrum after one of optical carriers is lost by reference light in Examples 1 and 2.

FIG. 6 is a schematic diagram showing another embodiment in which the waveguide type optical modulator of the present invention is used for a subcarrier optical modulator.

FIG. 7 is a schematic diagram showing still another embodiment when the waveguide type optical modulator of the present invention is used for a subcarrier optical modulator.

FIG. 8 is a diagram illustrating a spectrum of input light in a third embodiment.

FIG. 9 is a diagram illustrating a spectrum of an optical carrier before a modulation signal is applied in a third embodiment.

FIG. 10 is a diagram illustrating an optical spectrum after one of optical carriers is lost by reference light according to a third embodiment.

FIG. 11 is a diagram illustrating a spectrum of an optical carrier after a modulation signal is applied in a third embodiment.

FIG. 12 is a schematic diagram showing an embodiment in which the waveguide type optical modulator of the present invention is used for a wavelength division multiplexing type subcarrier optical modulator.

FIG. 13 is a diagram illustrating a spectrum of input light in Examples 4 and 5.

FIG. 14 is a diagram illustrating a spectrum of an optical carrier before a modulation signal is applied in Examples 4 and 5.

FIG. 15 is a diagram illustrating a spectrum of an optical carrier after a modulation signal is applied in Examples 4 and 5.

FIG. 16 is a diagram illustrating an optical spectrum after one of optical carriers is lost by reference light in Examples 4 and 5.

FIG. 17 is a diagram illustrating a combined light spectrum of a wavelength multiplexing method in Examples 4 and 5.

FIG. 18 is a schematic diagram showing another embodiment when the waveguide type optical modulator of the present invention is used for a wavelength division multiplexing type subcarrier optical modulator.

FIG. 19 is a diagram illustrating a spectrum of input light in a conventional example.

FIG. 20 is a diagram illustrating a spectrum of an optical carrier in a conventional example.

FIG. 21 is a diagram illustrating a spectrum of an output optical signal in a conventional example.

[Explanation of symbols]

101, 201, 301, 401, 501 Input optical waveguides 102, 202, 302, 402, 502 π / 2 phase shift optical waveguides 103, 203, 303, 403, 503 π phase shift optical waveguides 104, 204, 304, 404, 504 Optical carrier generating section output optical waveguide 105, 205, 305, 405, 505 Output optical waveguide 106, 206, 306, 406, 506 Reference light introducing optical waveguide 107, 207, 307, 407, 507 Optical carrier generating electrode 108 , 208, 308, 408, 508 Modulation signal application electrode 109, 209, 309, 409, 509 π / 2 phase shift electrode 110, 210, 310, 410, 510 π phase shift electrode 111, 211, 311, 411 , 511 Optical carrier generator 112, 212, 312, 4 2,512 modulated signal applying unit 213,513 additional Mach-Zehnder type optical waveguide

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shoichi Shimotsu 585 Tomimachi, Funabashi-shi, Chiba Sumitomo Osaka Cement Co., Ltd. Cement Corporation New Technology Laboratory

Claims (8)

[Claims] 1. An optical carrier generator for converting an input optical signal into two optical carriers having a lower frequency than the input optical signal and having different frequencies, thereby facilitating the modulation of the optical signal. And a modulation signal applying section for applying a modulation signal to the optical carrier, wherein a reference light for eliminating one of the optical carriers by a difference is introduced into the modulation signal applying section. The optical waveguide for transmitting an optical signal is provided separately from the optical waveguide for transmitting the optical signal. 2. The optical carrier generating section comprises: a single input optical waveguide; a pair of π / 2 phase shift optical waveguides including two optical waveguides branched from the input optical waveguide;
The two sets of π-phase-shifted optical waveguides, each of which is composed of two optical waveguides branched from the / 2-phase-shifted optical waveguide, and two optical waveguides constituting the π-phase-shifted optical waveguide are combined.
2. The waveguide type light according to claim 1, further comprising: a plurality of optical carrier generating section output optical waveguides; and an optical carrier generating electrode provided for each of the two sets of the π phase shift optical waveguides. Modulator. 3. The modulation signal applying unit according to claim 1, wherein a phase modulation signal is applied to two optical carriers generated by the optical carrier generation unit. A waveguide optical modulator according to claim 1. 4. The apparatus according to claim 1, wherein the modulation signal application section applies an intensity modulation signal to two optical carriers generated by the optical carrier generation section. A waveguide optical modulator according to claim 1. 5. An optical carrier generation section of a waveguide type optical modulator for facilitating modulation of an optical signal, wherein an input optical signal is divided into two lower frequencies than the input optical signal, each having a different frequency. In an optical modulation method of converting a light signal into an optical carrier and applying a modulation signal to the two optical carriers in a modulation signal application unit of the waveguide type optical modulator, an optical waveguide separately provided for the optical waveguide transmitting the optical signal A reference light is introduced into the modulation signal application section, and one of the optical carriers is eliminated by calculating a difference between the two optical carriers. 6. The conversion of the input optical signal into two optical carriers, the input optical signal is divided into two by a π / 2 phase shift optical waveguide branched into two, and each of the divided input optical signals is divided. 6. The method according to claim 5, wherein the transmission is performed by propagating through the π-phase shift optical waveguide and applying a modulation signal during the propagation of the π-phase shift optical waveguide.
3. The light modulation method according to 1. 7. The optical modulation method according to claim 5, wherein the modulation signal applied in the modulation signal application section 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 in the modulation signal application section of the waveguide type optical modulator is an intensity modulation signal.