JP4494347B2 - Light modulator - Google Patents

Description

  The present invention relates to an optical modulation device, and more particularly to an optical modulation device capable of performing SSB modulation with high accuracy.

A modulation system that modulates an optical signal to generate a modulated wave corresponding to the modulation frequency and removes one sideband component is SSB (Single Side Band) modulation. Further, a system in which the carrier light (modulated light) is further suppressed and only a single sideband component is extracted is particularly called carrier-suppressed SSB modulation.
Depending on the application, optical SSB modulation uses a frequency converter that inputs signal light (carrier light) and outputs light of a different frequency (single sideband light), and digital transmission using the generated sideband signal. This is a technology that can be used in various forms such as a modulation device for performing optical signals, and is very effective in the fields of optical communication systems, optical fiber wireless systems, optical measurement, and the like (for example, see Non-Patent Document 1). ).

Here, a general optical SSB modulator will be described.
In the configuration diagram of FIG. 2, the optical SSB modulator 10 has a waveguide configuration in which the first and second sub Mach-Zehnder waveguides 102 and 103 are arranged in the respective arms of the main Mach-Zehnder waveguide 101. Further, on each of the main and sub Mach-Zehnder waveguides 101 to 103, an RF electrode 104 and DC electrodes 105 and 106 for changing the phase of propagating light by voltage application are loaded.

A main Mach-Zehnder waveguide 101, the light wave of the frequency f ₀ is input. This input light is introduced into the two sub Mach-Zehnder waveguides 102 and 103 after branching, undergoes a phase change, and is multiplexed again and output.

A DC voltage is applied to the DC electrodes 105a and 105b on the first and second sub Mach-Zehnder waveguides 102 and 103 so that the phase difference of the light wave propagating through each arm constituting the Mach-Zehnder waveguide is π. Apply. In addition, the RF electrode 104a on the first sub Mach-Zehnder waveguide 102, by applying a RF voltage of the modulation frequency _{f 1,} the RF electrode 104b on the second sub Mach-Zehnder waveguide 103, also the modulation frequency _{f 1} The RF voltage is applied so that the phase difference with respect to the RF electrode 104a is π / 2. Further, a DC voltage is applied to the DC electrode 106 on the main Mach-Zehnder waveguide 101 so that the phase difference between the two sub-Mach-Zehnder waveguides 102 and 103 is π / 2 or −π / 2.

  Then, the frequency spectrum and phase of the light wave at each point (points A to G in FIG. 2) of the waveguide in the optical SSB modulator 10 are as shown in FIG. However, the case where the phase difference provided by the DC electrode 106 is π / 2 is shown. An arrow on the frequency axis (horizontal axis) represents the spectrum of the frequency, and the direction of the arrow represents the phase. It is assumed that the phase value is 0 for the upward arrow, π / 2 for the right upward arrow, π for the downward arrow, and 3π / 2 for the left downward arrow.

In FIG. 3, the carrier lights (frequency f ₀ ) at points A and B have opposite phases (phase difference π) due to the voltage applied to the DC electrode 105a. Further, by giving phase modulation in RF voltage of frequency f _1, the high-frequency component is generated at a frequency f ₁ interval around the frequency f ₀ of the carrier beam. However, here, only the first-order components are considered, ignoring the second-order and higher-order components. At this time, the + 1st order modulated light (frequency f ₀ + f ₁ ) and the −1st order modulated light (frequency f ₀ −f ₁ ) have the same phase (phase difference 0) at points A and B, respectively. .

When propagating light having such a phase relationship at points A and B on each arm of the first sub Mach-Zehnder waveguide 102 is multiplexed at point E, carrier waves having opposite phases cancel each other and disappear. Only ± 1st order modulation components remain.
Further, the phase relationship of propagating light at points C and D on each arm of the second sub Mach-Zehnder waveguide 103 is the same as described above, and at the point F, only ± 1st order modulation components remain.

Further, when a phase difference is applied by the DC electrode 106, at points E and F, as shown in FIG. 3, the + 1st order modulated light has the same phase and the −1st order modulated light has the opposite phase. As a result, at the point G on the output side of the main Mach-Zehnder waveguide 101, the combined light wave has only a + 1st order modulation component. When the phase difference applied by the DC electrode 106 is −π / 2, what remains at the point G is a −1 order modulation component.
Thus, the output of the optical SSB modulator has a spectrum composed of a single sideband with the carrier light and one sideband suppressed.
Hashimoto et al. A study on RF channel switching in RoF link using millimeter-wave self-heterodyne / optical heterodyne transmission system, IEICE General Conference, 2004

However, in order to completely output a single sideband component as described above, the phase difference between the DC electrodes 105a and 105b is π, and the phase difference between the DC electrodes 106 is π / 2 (or −π / 2). The phase condition must be strictly satisfied. That is, if these phase differences do not take correct values, the carrier light and the phase of the modulation component of each order (see FIG. 3) are shifted, and as a result of combining them, the output light (point G ), Unwanted carrier light and other sideband components remain.
When this residual component is transmitted together with the original transmission signal and received at the receiving device side, it generates a spurious signal and lowers the demodulation accuracy, which is a serious problem in practical use of the optical SSB modulator. It was.

In order to solve this, it is necessary to individually monitor the output light (points E, F, and G in FIG. 3) of each Mach-Zehnder waveguide and perform feedback control of the voltage applied to the DC electrode. However, for this purpose, it is necessary to newly form a guide optical waveguide for extracting monitor light and to provide a PD (photodiode) for detecting the extracted monitor light, which complicates the structure of the modulator and the manufacturing and mounting method. There is a fault that becomes.
As another method, only the final output light (point G in FIG. 3) of the above-described optical SSB modulator is measured by an optical spectrum analyzer, and a human can apply a DC voltage while confirming each obtained spectral component. Although manual adjustment is possible, it is not practical in terms of adjustment accuracy and long-term operation.

  The present invention has been made in view of the above points, and its object is to easily perform DC voltage control for complete SSB modulation without changing the configuration of the optical SSB modulator itself. The object is to provide a possible light modulation device.

  The present invention has been made to solve the above-mentioned problems, and the invention according to claim 1 is an SSB modulation means for modulating a light wave input with a carrier signal having a frequency f1 to generate a sideband component. And a reference light generating means for generating reference light having a frequency different by f2 (f2 <f1) with respect to the light wave input to the SSB modulating means, and the output light from the SSB modulating means and the reference light are combined. Multiplexing means for wave, optical detection means for receiving the combined light and converting it into an electrical signal, and signals having frequencies of f1-f2, f2, and f1 + f2 from the electrical signal obtained by the optical detection means The signal extraction means for extracting the components, and the SSB modulation means based on the respective signal components are feedback-controlled so that the power of each of the signal components has the minimum value for the frequency f2 component and the frequency f1-f2 Other one is the minimum value of f1 + f2 component min is a light modulation device and a control means for adjusting to take maximum value, respectively.

  According to a second aspect of the present invention, in the optical modulation device according to the first aspect, the reference light generating means is arranged in front of the SSB modulating means, and splits the input light wave into two. An optical branching unit that introduces one of them into the path on the SSB modulation unit side, an optical frequency converting unit that is arranged at a subsequent stage of the optical branching unit and that converts the other of the branched lightwaves and converts the frequency of the lightwave And the frequency-converted light wave is used as the reference light.

  The invention according to claim 3 is the optical modulation device according to claim 1, wherein the reference light generation means is arranged in front of the SSB modulation means, and modulates the input light wave to modulate the upper side wave. DSB modulation means for generating a band and a lower sideband and suppressing carrier light, an optical circulator arranged between the DSB modulation means and the SSB modulation means and connecting the two, and the other of the optical circulators Light transmitted from the light selection means, which is arranged at a subsequent stage of the connection end, and is configured to transmit one of the input upper sideband and lower sideband and reflect the other. The optical circulator passes the light wave output from the DSB modulation means to the light selection means side, and passes the light wave reflected from the light selection means to the SSB modulation means side. And characterized in that.

  According to a fourth aspect of the present invention, in the light modulation device according to any one of the first to third aspects of the present invention, the SSB modulation means splits the light wave with two Mach-Zehnder interference systems. A branching unit that distributes the signals to the two Mach-Zehnder interference systems, a multiplexing unit that combines the light waves output from the two Mach-Zehnder interference systems, and a modulation that has a phase difference of π / 2 between the Mach-Zehnder interference systems. The two Mach-Zehnder interferences that give a phase difference π to the light wave propagating through each arm constituting the Mach-Zehnder interference system, and a modulation signal input means for phase-modulating the light waves that pass through each of the signals. Two first phase difference providing means provided in each of the systems, and a first for giving a phase difference of π / 2 or −π / 2 to the light wave output from each Mach-Zehnder interference system. Of the phase difference providing means consist, said control means and performing independent feedback control for each of the first and second phase difference providing means.

  According to a fifth aspect of the present invention, in the optical modulation device according to any one of the first to fourth aspects, a part of the light wave input to the SSB modulation means is extracted by branching and input. Data modulation means for modulating the light wave with a data signal; and output means for outputting the combined light wave output from the SSB modulation means and the data modulation means as a transmission signal. To do.

  According to a sixth aspect of the present invention, in the optical modulation device according to the fifth aspect, the SSB modulation means and the data modulation means are formed by forming an optical waveguide on the same substrate.

According to the present invention, the optical signal is SSB modulated at the frequency f ₁ and the frequency of the carrier light is shifted by f ₂ , and these are combined and optically detected to thereby detect the carrier light and the ± first-order sideband light. Therefore, it is possible to realize complete SSB modulation that outputs only a single sideband by performing feedback control to the SSB modulation means. Further, since the SSB modulation means itself does not require a special configuration, it can be easily manufactured as an optical modulation device and has high practicality.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<< First Embodiment >>
FIG. 1 is a configuration diagram of an optical modulation device according to the first embodiment of the present invention. This optical modulation device 1 includes a branching unit 112 that branches light from a laser diode (LD) 3 provided outside, an optical SSB modulator 10 to which one of the branched lights is input, and the other branched light. An AO shifter 111 that converts the optical frequency when it is input, a multiplexing unit 13 that combines the SSB modulated light and the frequency-converted light, and a photodiode that receives the light and converts it into an electric signal by square detection (PD) 14, band pass filters (BPF) 15 a to 15 c that pass electrical signals in a desired frequency band, ratio calculation circuits 16 a and 16 b that output the ratio of the inputted electrical signals, and the optical SSB modulator 10 A bias controller 17 that calculates a DC control voltage to output an optimum voltage, a data modulator 18 that gives modulation to the signal light by data to be transmitted, and a main output of the controlled signal light To an output unit 19. for sending to the transmission line removed.

  The configuration of the optical SSB modulator 10 is the same as that of the optical SSB modulator shown in FIG. However, the DC voltage controlled by the bias controller 17 is supplied to the DC electrodes 105a, 105b, 106 provided in the Mach-Zehnder waveguides 101 to 103 constituting the modulator. The phase difference given to the propagating light is maintained at an appropriate value.

  A Y-shaped branch waveguide is disposed in front of the optical SSB modulator 10, and one of the two branch output ends is connected to the modulator 10 and the other is connected to the input end of the data modulator 18. Similarly, the output ends of the optical SSB modulator 10 and the data modulator 18 are respectively connected to branch input ends of another Y-shaped branch waveguide disposed in the subsequent stage thereof.

  The data modulator 18 is a phase modulator composed of an optical waveguide and an electrode. By applying a modulation voltage based on a data signal to the electrode and modulating the phase of a light wave propagating through the waveguide, data is placed on the signal light. Output.

The optical SSB modulator 10 and the data modulator 18 (and the Y-shaped branching waveguide) are formed on the same lithium niobate (LiNbO ₃ ; LN) substrate 20. The waveguide is produced by thermally diffusing titanium (Ti) into the substrate, and the electrode is produced by gold (Au) plating treatment on the substrate surface.

  The AO (Acousto-Optic) shifter 111 is a frequency conversion device using an acoustooptic effect, and has a configuration in which a piezo (piezoelectric) element is bonded to the surface of an LN substrate on which an optical waveguide is formed. When the piezo element is driven, a surface acoustic wave having a predetermined frequency is excited on the substrate, and the frequency of light propagating through the waveguide changes according to the frequency. Using this, the conversion of the frequency of the input light is realized.

Next, with regard to the operation of the optical modulation device 1, a case where data modulation is not performed by the data modulator 18 will be described first, and then a case where data modulation is performed will be described. In the case where data modulation is not performed, the light modulator can be configured by omitting the data modulator 18 in FIG. 1 (and FIG. 5 described later).
(1) laser diode 3 If no data modulation is outputting a single-mode light having a single spectral frequency f _0. The output light is introduced into the branching unit 112 and branched to the optical SSB modulator 10 side and the AO shifter 111 side.

The optical SSB modulator 10 performs SSB modulation with one of the branched light waves as an input. Here, in order to output the + 1st order sideband, the optical SSB modulator 10 is driven under the condition that the phase difference by the DC electrode 106 is π / 2. It shall be. If feedback control is not performed at this time, carrier light and a minus first-order component remain as described above. The signal light output from the optical SSB modulator 10 has a spectral shape as shown in FIG. 1 (point P ₂ ), and has a frequency f ₀ + f ₁ of a desired + _1st order sideband. In addition to the signal light, unnecessary components (spurious signals) having frequencies f ₀ and f ₀ -f ₁ are included. Setting the spurious signal to zero is the role of the control system of the optical modulation device 1 including the bias controller 17 and the like.

On the other hand, the other light wave branched from the branching unit 112 is input to the AO shifter 111 and converted into a light wave (frequency f ₀ + f ₂ ) shifted in frequency by + f ₂ .
In this embodiment, as described above, a part of the signal light having the frequency f ₀ input to the optical SSB modulator 10 is extracted by the branching unit 112, and frequency-converted by the AO shifter 111. ₀ + f ₂ light (reference light) is generated. That is, the AO shifter 111 and the branching unit 112 function as the reference light generation unit 11.

Output light from the optical SSB modulator 10 and the AO shifter 111 is multiplexed by the multiplexing unit 13 and then received by the photodiode 14. The photodiode 14 converts the received signal light into an electric signal by square detection.
In square detection, an electrical signal corresponding to the product (difference in frequency) of each spectral component included in the signal light is obtained as an output. Here, the spectrum of the light wave input to the photodiode 14 is composed of four frequency components as described above, and these are hereinafter referred to as E ₀ (frequency f ₀ ), E ₊₁ (frequency f ₀ + f ₁ ), E _{−. 1} (frequency f ₀ -f ₁ ) and E ₂ (frequency f ₀ + f ₂ ). Then, the frequency of each electric signal obtained by the square detection is as follows (right side of the arrow). However, the product is represented by “·”.
E ₀・ E ₊₁ → f ₁
E ₀・ E _-1 → f ₁
E ₀・ E ₂ → f _{2
E +1} · E _-1 → 2f ₁
E _{+ 1} · E ₂ → f ₁ −f ₂
E ₋₁ · E ₂ → f ₁ + f ₂

In the above correspondence relationship, the frequency component f ₂ included in the output signal after the square detection is generated from the signal lights E ₀ and E ₂ , and similarly, the f ₁ -f ₂ component is the signal light E ₊₁ and From E ₂ , f ₁ + f ₂ components are generated from the signal lights E ₋₁ and E ₂ , respectively. Therefore, changes in the signal lights E ₀ , E ₊₁ , E ₋₁ can be detected by the output signal components f ₂ , f ₁ -f ₂ , f ₁ + f ₂ from the photodiode 14. This detection is made possible by introducing the signal light E ₂ (reference light).

Each component has a power value proportional to the product of the signal light, but since E ₂ is common, the ratio is E ₀ : E ₊₁ : E ₋₁ . Therefore, by measuring the voltage ratio of the frequencies f ₂ , f ₁ -f ₂ , f ₁ + f ₂ in the electric signal obtained by the square detection, the signal light E ₀ , E ₊₁ , E ₋₁ , that is, the optical SSB The ratio of the magnitudes of the respective modulation components by the modulator 10 can be known.

This ratio is calculated using a band pass filter 15 and a ratio calculation circuit 16 provided in the subsequent stage of the photodiode 14. That is, the output signal from the photodiode 14 is distributed and inputted to the three band pass filters 15a, 15b, and 15c, and the frequencies of the respective pass bands (f ₁ + f ₂ , f ₁ -f ₂ , f _{2 in order} ). Only the components are output from each filter. The output of the band pass filter 15a and 15b is input to the ratio calculation circuit 16a, voltage ratio _{R 1} of _f 1 + _{f 2} with respect to the frequency components _f 1 -f ₂ is calculated. Similarly, the output of the band pass filter 15b and 15c is input to the ratio calculation circuit 16b, the voltage ratio _{R 2} of _{f 2} with respect to the frequency components _f 1 -f ₂ is calculated.

Bias controller 17, the DC electrodes 105a of the optical SSB modulator 10, the feedback control for the 105b, 106 performs as an input voltage ratio _{R 1} and _{R 2} above. In this control, the voltage ratios R ₁ and R ₂ are both minimum, that is, the frequency f ₁ −f ₂ component (corresponding to the signal light E _{+ 1} ) is maximum and the frequency f ₁ + f ₂ component (corresponding to the signal light E ₋₁ ). f ₂ component (corresponding to the signal light E ₀₎ on each of the DC voltage so as to minimize is adjusted. As a result, ideal SSB modulation in which only the signal light of the + 1st order sideband is generated from the optical SSB modulator 10 is realized.

(2) When Data Modulation When the data modulator 18 modulates the transmission data, the signal light obtained by combining the data-modulated light wave and the light wave SSB-modulated by the optical SSB modulator 10 is converted into an AO shifter. The output light from 111 is combined and received by the photodiode 14. The output unit 19 takes out the main output of the signal light and sends it to the transmission line. Hereinafter, a signal input to the photodiode 14 is referred to as a control signal, and a signal transmitted to the transmission path is referred to as a transmission signal.

FIG. 4 shows the optical spectrum of the transmission signal and the control signal and the electrical spectrum after square detection. FIG. 6A shows a transmission signal and FIG. 5B shows a control signal.
When the feedback control by the bias controller 17 is not performed, the transmission signal has carrier light E ₀ (frequency f ₀ ) as signal components by SSB modulation, and + 1st order and −1st order sideband lights E ₊₁ , E _{−. 1} (frequency f ₀ + f ₁ , f ₀ −f ₁ , respectively). That is, carrier light and one sideband component still remain. Further, when the maximum value of the modulation frequency of the transmission data and f _m, (and E ₃₎ phase-modulated component of the signal light band has a spread over a range of frequencies f ₀ ± f _m (FIGS. 4 (a) upper left ).

When the transmission signal of such an optical spectrum is square-detected (on the receiving side), the electric spectrum becomes a shape as shown in the upper right of FIG. Signal component extends from the frequency _f 1 -f _m to _f 1 + _{f m is} the original data signal generated by the _{E +1} and _{E 3.} The signal components generated from E ₀ and E ₃ overlap on the low frequency side of this signal, and this deteriorates reception characteristics as spurious. Further, also occurs spectral components of the original data signal and symmetrical about the frequency f ₁ from the E ₊₁ and E _3, the influence of the delay between each component of the component signal light due to dispersion of the transmission line It works as a factor of S / N ratio deterioration.

On the other hand, the optical spectrum of the control signal, the signal component E ₂ of the AO shifter 111 are summed with respect to that of the transmission signal (see FIG. 4 (b) left). When this is square-detected by the photodiode 14, the spectrum of electricity is as shown on the right in FIG. Here, E ₀ · E ₂ , E ₊₁ · E ₂ , and E _-1 · E ₂ are used for feedback control as in the case of (1) described above. These components are cut out by the band pass filters 15 a to 15 c, and appropriate DC voltages are calculated by the ratio calculation circuits 16 a and 16 b and the bias controller 17 to control each DC electrode of the optical SSB modulator 10.

  As a result, when the output from the optical SSB modulator 10 is only the + 1st order sideband component, the spectrum of the transmission signal is as shown in the lower left and lower right of FIG. Since the influence of spurious signals and transmission path dispersion is reduced, transmission characteristics are improved.

As described above, according to the present embodiment, an output signal from the optical SSB modulator 10 having a residual component composed of the carrier light and the −1st order sideband in addition to the desired + 1st order sideband component. The light is combined with the signal light obtained by frequency-converting the carrier light by the AO shifter 111 and then square-detected by the photodiode 14. Components of frequencies f ₂ , f ₁ -f ₂ , and f ₁ + f ₂ corresponding to the carrier light, the + 1st order and the −1st order sideband lights are extracted from the detected signal, and the ratio of these components is obtained. Based on this, the bias controller 17 feedback-controls the DC voltage of the optical SSB modulator 10.
As a result, the suppression ratio of the carrier light and the −1st order sideband component can be made sufficiently large, and complete SSB modulation is possible. Further, since the optical SSB modulator 10 itself does not have a special configuration, it can be easily put into practical use.

<< Second Embodiment >>
FIG. 5 is a configuration diagram of an optical modulation device according to the second embodiment of the present invention. The optical modulation device 2 uses a DSB modulator 121, an optical circulator 122, and a fiber grating (FBG) 123 instead of the AO shifter 111 and the branching unit 112 in the first embodiment. is there.

DSB modulator 121, a signal light of a frequency f ₀ output from the laser diode 3 DSB (Double Side Band) is modulated, the upper sideband frequency difference is f ₂ and the lower sideband (frequency _{f 0 + f 2/2,} f 0 -f 2/2) to generate a DSB signal light suppressed carrier consisting respectively. The configuration includes a Mach-Zehnder waveguide 124, an RF electrode 125, and a DC electrode 126, as shown in FIG. The RF electrode 125 by applying a modulating voltage of frequency f _2/2, the DC electrode 126 phase difference between each arm of the Mach-Zehnder waveguide 124 applies a DC voltage so that the [pi. Then, the spectrum and phase of the light wave propagating in the modulator are in the same state as in the first sub Mach-Zehnder waveguide 102 in the optical SSB modulator 10 (points A, B, and E in FIG. 3). equivalent. However the frequency _{f 1} is replaced by a _f 2/2) become.

The signal light having the two spectral components generated as described above is input to the optical circulator 122 and introduced into the path on the fiber grating 123 side. Fiber gratings 123 has a very steep filter characteristic having a center frequency f ₀ -f _2/2, and reflected light waves of the frequency components of the two component input, the other frequency f _{0 +} f and it transmits the light wave of _2/2. The reflected wave returns to the optical circulator 122 and is input to the optical SSB modulator 10.
In this embodiment, the DSB modulator 121, the optical circulator 122, and the fiber grating 123 generate reference light having a frequency different from that of the input light to the optical SSB modulator 10, and these three components generate reference light. It functions as the means 12.

Optical SSB modulator 10 the input signal light to the (frequency _f 0 _-f 2/2), applying a SSB modulation by applying the same RF and DC voltages as in the first embodiment to each electrode. As shown in FIG. 5, the output light obtained as a result of this modulation includes residual components (carrier light and −1st order component) in addition to the desired + 1st order sideband component as in FIG. 1. Will have. However, the frequency of each of these components, the partial only difference between the frequencies of the input light (-f _2/2) is different from that of FIG.

Here, the transmitted light from the signal light and the fiber grating 123 having the above components by the SSB modulation, the difference between the relative frequency is in the f _2. Therefore, when these light waves are combined and square-detected by the photodiode 14, the spectrum after detection is exactly the same as that in the first embodiment. The band pass filter 15, the ratio calculation circuit 16, and the bias controller 17 perform the same operation as in the first embodiment, and perform feedback control on the optical SSB modulator 10. As a result, ideal SSB modulation in which only + 1st order sideband signal light is generated from the optical SSB modulator 10 is realized.

As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to
For example, as the reference light generating means, in addition to those described in the first and second embodiments, the DSB modulator described above, the branching section disposed in the subsequent stage, and the branching destination waveguide are provided. An optical filter (such as a fiber grating or a dielectric multilayer filter) that transmits only one of the upper and lower sidebands by DSB modulation can also be used. In this case, the output of one optical filter is used as an input to the optical SSB modulator, and the output and the output of the other optical filter are combined and detected by a photodiode.

Further, the data modulator 18 may be simply constituted by a straight waveguide and a modulation electrode, or may be the same as the optical SSB modulator 10.
In the above embodiment, the control for finally obtaining the + 1st order sideband component has been described. However, the device design can be changed so that the −1st order component can be obtained. is there.
The ratio calculation circuit 16 can also be configured by software. By doing so, the + 1st order and −1st order sideband signals can be arbitrarily selected in real time.
A frequency conversion device based on an existing technology other than the AO shifter 111 can also be applied.

It is a block diagram of the optical modulation apparatus by the 1st Embodiment of this invention. It is a block diagram of an optical SSB modulator. It is the figure which showed the frequency spectrum and phase behavior of the light wave in an optical SSB modulator. It is the figure which showed the spectrum of the transmission signal and the signal for control. It is a block diagram of the optical modulation apparatus by the 2nd Embodiment of this invention. It is a block diagram of a DSB modulator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Optical modulation apparatus 10 ... Optical SSB modulator 11, 12 ... Reference light production | generation means 13 ... Multiplexing part 14 ... Photodiode 15 ... Band pass filter 16 ... Ratio operation circuit 17 ... Bias controller 18 ... Data modulator 19 DESCRIPTION OF SYMBOLS ... Output part 20 ... LN substrate 101 ... Main Mach-Zehnder waveguide 102, 103 ... Sub Mach-Zehnder waveguide 104 ... RF electrode 105, 106 ... DC electrode 111 ... AO shifter 112 ... Branching part 121 ... DSB modulator 122 ... Optical circulator 123 ... Fiber grating 124 ... Mach-Zehnder waveguide 125 ... RF electrode 126 ... DC electrode

Claims (6)

SSB modulation means for modulating the input light wave with a carrier signal of frequency f1 to generate a sideband component;
Reference light generating means for generating reference light having a frequency different by f2 (f2 <f1) with respect to the light wave input to the SSB modulating means;
Multiplexing means for multiplexing the output light from the SSB modulation means and the reference light;
Optical detection means for receiving the combined light and converting it into an electrical signal;
Signal extracting means for extracting each signal component having a frequency of f1-f2, f2, and f1 + f2 from the electrical signal obtained by the optical detection means;
The SSB modulation means is feedback controlled based on each signal component, and the power of each signal component has a minimum value for the frequency f2 component, and one of the frequency f1-f2 component and the f1 + f2 component has the minimum value for the other. Control means for adjusting each to take a maximum value;
A light modulation device. The reference light generation means includes
An optical branching unit arranged in a preceding stage of the SSB modulation unit, for branching an input light wave into two and introducing one of them into the path on the SSB modulation unit side;
An optical frequency conversion means that is arranged at a subsequent stage of the optical branching means and receives the other of the branched light waves and converts the frequency of the light waves;
The light modulation device according to claim 1, wherein the reference light is a light wave that is configured by the frequency conversion and is frequency-converted. The reference light generation means includes
A DSB modulation unit disposed in a preceding stage of the SSB modulation unit to modulate an input light wave to generate an upper sideband and a lower sideband and to suppress carrier light;
An optical circulator disposed between the DSB modulation means and the SSB modulation means and connecting the two;
A light selection means disposed at a stage subsequent to the other connection end of the optical circulator, transmitting one of the input upper sideband and lower sideband and reflecting the other;
The transmitted light from the light selection means is configured as the reference light,
The optical circulator is
2. The light modulation according to claim 1, wherein a light wave output from the DSB modulation unit is passed to the light selection unit side, and a light wave reflected from the light selection unit is passed to the SSB modulation unit side. apparatus. The SSB modulation means includes
Two Mach-Zehnder interference systems,
A branching unit that splits a light wave and distributes it to the two Mach-Zehnder interference systems;
A multiplexing unit that combines the light waves output from the two Mach-Zehnder interference systems;
Modulation signal input means for phase-modulating light waves that pass through each of the Mach-Zehnder interference systems by inputting modulation signals having phases different from each other by π / 2;
Two first phase difference providing means provided in each of the two Mach-Zehnder interference systems for providing a phase difference π to the light wave propagating through each arm constituting the Mach-Zehnder interference system;
Second phase difference providing means for providing a phase difference π / 2 or −π / 2 to the light wave output from each Mach-Zehnder interference system;
Consists of
4. The optical modulation device according to claim 1, wherein the control unit performs feedback control independently for each of the first and second phase difference providing units. 5. . A part of the light wave input to the SSB modulation means is taken out and input by branching, and the data modulation means modulates the light wave with a data signal;
An output means for outputting the combined light wave output from the SSB modulation means and the data modulation means as a transmission signal;
The light modulation device according to claim 1, further comprising: 6. The optical modulation device according to claim 5, wherein the SSB modulation unit and the data modulation unit are formed by forming an optical waveguide on the same substrate.

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