JPH09230404A - Light frequency converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a large frequency conversion width with high accuracy by performing the frequency conversion of a light signal in the light frequency conversion width in terahertz units and converting the converted light frequency in the light frequency conversion in megahertz units. SOLUTION: A frequency converting part 1 performing the frequency conversion of the light signal in the light frequency conversion width in terahertz units and a wavelength plate rotary type frequency converter 2 converting the light frequency converted in the frequency converting part 1 in the light frequency conversion width in megahertz units are provided. Then, the light frequency conversion having the largeness (being >= several Å in a wavelength) of no less than several terahertz by inputting the light signal becoming the object of the light frequency modulation to the frequency converting part 1 of a four light mixing system or in which a wavelength converting laser is applied. Next, the signal subjected to the frequency conversion in the frequency converting part 1, etc., are inputted to the wavelength plate rotary system light frequency converter 2 applied with a wavelength plate rotary system. Thus, a frequency conversion whose conversion width are several terahertz is performed with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical frequency conversion device for converting and controlling the frequency of an optical signal, which is important in an optical frequency multiplex transmission technique and a measurement technique using light, and particularly to a large frequency conversion width. The present invention relates to an optical frequency conversion device suitable for obtaining with high accuracy.

[0002]

2. Description of the Related Art An optical frequency conversion device is for converting the frequency of a carrier wave for transmitting an optical signal without damaging the signal component. Conventionally, as the optical frequency conversion device, a four-wave mixing method described below, a method using a wavelength conversion laser, a wavelength plate rotation method, and OE / E
There is an O method.

The four-wave mixing method is a technique described on page 1106 of Vol. 2, Electronics Letters, and uses the non-linearity of a semiconductor optical amplifier to perform optical frequency conversion. FIG. 7 shows the apparatus configuration, and FIG. 8 shows the relationship of each signal spectrum. As shown in FIG. 7, the carrier frequency of the signal is fs, and the laser light from the pump lasers 26 and 27 which emits at frequencies fp and fc different from the carrier frequency is multiplexed into the signal. At this time, if the frequency difference between the frequency fs and the frequency fp is set to the relaxation oscillation frequency or less, the semiconductor optical amplifier 21
As shown in FIG. 8, beat components fs 'and fp' of the difference frequency between fs and fp are generated therein. This beat also generates sideband wave components fs "and fs'" of the signal of frequency fc due to the non-linear effect in the semiconductor optical amplifier 21. By filtering the component of the frequency fs "with the low-pass filter 22 shown in FIG. 7 or the like, the carrier frequency of the signal is converted from the frequency fs to fs" as shown in FIG.

In the method using a wavelength conversion laser, the frequency of a carrier wave is converted by a laser element to which a bistable laser is applied as described in "Eye Triple E" Journal of Quantum Electronics Vol. 24, page 2153, etc. It is a thing. Further, a wavelength plate rotation type optical frequency converter is disclosed in Japanese Patent Application No. 56-150724 and Japanese Patent Application No. 5-2.
As described in No. 40901 and the like, a technique that realizes a state equivalent to a half-wave plate that rotates in an optical path by utilizing the electro-optical effect. It is a device that can convert by the same size. In the OE / EO method, an optical signal is once converted into an electric signal level and then converted again into an optical signal having a different carrier frequency and then output.

[0005]

However, the conventional techniques have the following problems to be solved. The main function required for the optical conversion device is a large optical frequency conversion width and the stability of the conversion width. However, each of the conventional optical frequency conversion devices described above is insufficient in the performance of either one. As a result, it cannot be put to practical use. That is, when the optical frequency conversion device is used in an optical frequency multiplex transmission device or the like for practical application, stability of a frequency conversion width of about 1 THz (terahertz) and a frequency conversion width of several MHz (megahertz) or less is required. .

However, for example, in the conventional four-wave mixing method, lasers of two different frequencies are prepared independently of the signal light, and these frequencies are independently controlled to realize optical frequency conversion. , Optical frequency conversion width is about 1TH
It is possible to obtain z, but it is difficult to obtain the stability of the frequency conversion width of several MHz or less due to problems such as laser temperature control technology. Similarly, even in the technique using the wavelength conversion laser, the optical frequency conversion width can be obtained in the THz order, but it is difficult to stabilize the laser operation and it is difficult to obtain the stability of the frequency conversion width of several MHz or less.

Further, in the wave plate rotation method, since the frequency conversion width is determined by the frequency of the input electric signal, it is possible to easily obtain the stability of the frequency conversion width of several MHz or less, but several GHz or more. The frequency conversion width of is difficult as long as an electric signal is used. Further, although it is technically possible to realize a stable and large frequency conversion width in the OE / EO conversion method, since the optical signal is once lowered to the electric signal level, a high-speed large-capacity signal flowing in the optical signal system is transmitted. When dealing with it, the scale and complexity of the conversion device itself cannot be avoided. Further, in order not to impair the high bandwidth of the optical signal, it is desirable to process the optical signal as light as possible. An object of the present invention is to solve these problems of the prior art and to provide an optical frequency conversion device capable of obtaining a large frequency conversion width with high accuracy.

[0008]

In order to achieve the above object, an optical frequency conversion device of the present invention is (1) an optical frequency conversion device for converting the frequency of an optical signal, wherein the optical frequency conversion device is a terahertz (THz) unit. First optical frequency conversion means (frequency conversion unit 1) for frequency converting an optical signal with a frequency conversion width
And a second optical frequency conversion means (wavelength plate rotary frequency conversion device 2) for converting the optical frequency converted by the first optical frequency conversion means with an optical frequency conversion width in the unit of megahertz (MHz). It is characterized by (2) In the optical frequency conversion device described in (1) above, the wavelength plate rotating optical frequency conversion device 2 is provided as the second optical frequency conversion means. (3) In the optical frequency conversion device according to (1) or (2) above, as the first optical frequency conversion means, at least an optical frequency conversion device using a four-wave mixing method (semiconductor) is used. It is characterized in that any one of the optical amplifier 21) and an optical frequency conversion device (wavelength conversion laser 31) using a wavelength conversion laser is provided. Further, (4) in the optical frequency conversion device according to any one of (1) to (3), means for detecting a difference frequency between the optical signal and the optical signal converted by the second optical frequency conversion means ( A difference frequency detector 3) and means for feedback-controlling the second optical frequency conversion means based on the difference frequency, and suppressing fluctuations in the conversion width of the optical frequency by the second optical frequency conversion means (control section 3a). ) And are provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a method such as a four-wave mixing method capable of realizing a frequency conversion width of several THz and a wavelength plate rotation type optical frequency converter having a conversion width stability of several MHz or less are provided. The optical frequency conversion units are configured by connecting them in tandem. As a result, frequency conversion width of several THz or more and several MH
The conversion width stability of z or less can be obtained together. That is, in the conventional optical frequency conversion device to which the four-wave mixing or wavelength conversion laser is applied, a large frequency conversion width can be obtained, while the conversion width fluctuates due to the influence of temperature fluctuations. In addition, in the wavelength plate rotation type optical frequency conversion, it is difficult to obtain a large optical frequency conversion width, but the frequency of the input electric signal is directly obtained as the optical frequency conversion width, so that highly accurate optical frequency conversion can be stably obtained. Therefore, in the present invention, by combining the two methods, it is possible to simultaneously satisfy a large conversion width and high accuracy required for optical frequency conversion for the first time.

Further, by observing the difference frequency between the optical frequency-converted signal and the input signal, feedback is given to the operation of the wavelength plate rotation type optical frequency converter so as to keep the difference frequency constant. A stabilizing operation of the converter can also be realized. In this combination, a waveplate rotary optical frequency converter is used as a means for adjusting the optical frequency conversion width.
Then, according to the difference frequency between the input and output signals, the wavelength plate rotation type optical frequency conversion device is feedback-controlled so as to suppress the fluctuation of the optical frequency width. Further, as a means for obtaining a large frequency conversion width, an optical frequency conversion device using a four-wave mixing method is cascaded in front of a wave plate rotation type optical frequency conversion device, and an optical frequency using a four-wave mixing method is used. The frequency conversion width of the signal light subjected to the optical frequency conversion by the conversion device is readjusted by the wavelength plate rotating optical frequency conversion device. This readjustment is performed by feedback-controlling the wavelength plate rotation type optical frequency converter so as to suppress the fluctuation of the optical frequency width according to the difference frequency between the input signals.

As a means for adjusting the optical frequency conversion width, an optical frequency conversion device using a wavelength conversion laser is used instead of the optical frequency conversion device using the four-wave mixing method, and this wavelength conversion laser is used. The frequency conversion width of the signal light that has been subjected to optical frequency conversion by the used optical frequency conversion device is readjusted by the wavelength plate rotation type optical frequency conversion device. This readjustment is also performed by feedback-controlling the wavelength plate rotating optical frequency converter so as to suppress the fluctuation of the optical frequency width according to the difference frequency between the input signals.

Hereinafter, specific examples of the embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of the configuration of the optical frequency conversion device of the present invention according to the present invention. In the figure, 1 is a frequency conversion unit as the first optical frequency conversion means of the present invention, and 2 is a wave plate rotary frequency conversion device as the second optical frequency conversion means of the present invention. The four-wave mixing method used in the frequency conversion unit 1 or the method using the wavelength conversion laser can obtain a conversion width of several THz or more, but the frequency conversion width fluctuates due to changes in temperature and other environments. To do. On the other hand, the wavelength plate rotating optical frequency conversion device 2 has a small optical frequency conversion width of several GHz at the maximum, but the conversion width can be controlled to a size of several kHz or less.

Therefore, in this embodiment, these two are combined to perform frequency conversion with a conversion width of several THz and an accuracy of the order of kHz. That is, the optical signal to be subjected to the optical frequency conversion is first input to the frequency conversion unit 1 applying a four-wave mixing method or a wavelength conversion laser, and an optical signal having a size of several THz or more (wavelength of several Å or more) is input. Perform frequency conversion. Then, next, the signal whose frequency has been converted by the frequency conversion unit 1 is input to the wave plate rotation type optical frequency conversion device 2 to which the wave plate rotation system of the latter stage is applied. As a result, frequency conversion with a conversion width of several THz can be performed with an accuracy of the order of kHz.

FIG. 2 is a block diagram showing a second embodiment of the configuration according to the present invention of the optical frequency conversion device of the present invention.
This example shows a configuration example in which the four-wave mixing method is used for the frequency conversion unit 1 in FIG. 1, and in this figure, 21 is a semiconductor optical amplifier as an optical frequency conversion device using the four-wave mixing method, 22 Is a low-pass filter that extracts only the output signal to be converted from the output of the semiconductor optical amplifier 21, 23 is a wavelength plate rotating optical frequency converter as a wavelength plate rotating optical frequency converter, and 24 and 25 are wavelength plate rotating optical frequencies. A polarization control device for controlling the polarization state of the input / output light of the conversion device 23, and 26 and 27 are pump light used for frequency conversion of the input signal and pump lasers for generating the converted light.

The carrier frequency of the input signal light is fs,
The frequencies of the pump light and the converted light from the pump lasers 26 and 27 are represented as fp and fc, respectively. Further, the frequency difference between fs and fp is set to be equal to or lower than the relaxation frequency of the semiconductor optical amplifier 21, and f
c is set to a frequency within the gain band of the semiconductor optical amplifier 21. At this time, the difference between fc and fs defines the optical frequency conversion width. After extracting only the output signal to be converted from the signal frequency-converted by the semiconductor optical amplifier 21 using the low-pass filter 22, the polarization state is controlled by the polarization controller 24,
Input to the wave plate rotation type optical frequency converter 23. The wavelength plate rotation type optical frequency conversion device 23 controls the polarization state of the input light to be circularly polarized in the wavelength plate rotation type optical frequency conversion element.

The wave plate rotating optical frequency converter 2
After conversion of the frequency by 3, the polarization controller 25
Output with arbitrarily polarized light. In the four-wave mixing method, that is, in the semiconductor optical amplifier 21, a frequency conversion of 10 nm (nanometer) or more (several THz in frequency) can be performed in terms of wavelength, but a frequency fluctuation of several hundred kHz occurs. The fluctuation is corrected by the wavelength plate rotating optical frequency converter 23. With this, the conversion width accuracy in units of several kHz,
Optical frequency conversion in units of several THz can be performed.

FIG. 3 is a block diagram showing a third embodiment of the configuration of the optical frequency converter of the present invention according to the present invention.
This example shows a configuration example in which a wavelength conversion laser is used for the frequency conversion unit 1 in FIG. 1, in which 31 is a wavelength conversion laser, 23 is a wavelength plate rotating optical frequency conversion device,
Reference numerals 24 and 25 are polarization control devices for controlling the polarization state of the input / output light of the wavelength plate rotation type optical frequency conversion device 23. The carrier frequency fs of the input signal (signal light) is converted by the wavelength conversion laser 31 and then input to the wavelength plate rotation type optical frequency conversion device 23. At this time, the polarization state of the signal light is controlled by the polarization control devices 24 and 25 so as to be a circular polarization state in the wavelength plate rotation type optical frequency conversion device 23, as in the example of FIG.

Also when this wavelength conversion laser 31 is used,
Similar to the four-wave mixing method in FIG. 2, frequency conversion of 10 nm (nanometer) or more (several THz in frequency) is possible in terms of wavelength, but the conversion width fluctuates due to fluctuations in environmental temperature such as air temperature. . For example, a temperature change of 1 ° C
Frequency fluctuations of about MHz occur. By correcting the variation by the wavelength plate rotation type optical frequency conversion device 23,
Optical frequency conversion with an accuracy of several kHz can be performed in the conversion width THz order.

FIG. 4 is a block diagram showing a fourth embodiment of the configuration according to the present invention of the optical frequency conversion device of the present invention.
In this example, the optical frequency conversion device shown in FIG. 1 has a device configuration for achieving both a large optical frequency conversion width and operational stability. That is, in this example, the input signal is first converted by the optical frequency conversion unit 1 having a large optical frequency conversion width (however, the stability of the conversion width is small) using the four-wave mixing method or the wavelength conversion laser, and then the wavelength is converted. Input to the plate rotation type wavelength plate rotation type optical frequency conversion device 2,
At this time, the output signal and the input signal from the wavelength plate rotary optical frequency conversion device 2 are input to the difference frequency detector 3 via the couplers 4 to 6, and the difference frequency detector 3 uses the wavelength plate rotary optical The difference frequency between the optical frequency of the output signal from the frequency conversion device 2 and the optical frequency of the input signal is observed, and based on this observation result, the controller 3a rotates the wave plate in the direction of suppressing the fluctuation of the frequency difference. The operation of the optical frequency conversion device 2 is feedback-controlled. This makes it possible to obtain a large conversion width and stable operation.

FIG. 5 is a block diagram showing a fifth embodiment of the configuration according to the present invention of the optical frequency conversion device of the present invention.
This example shows a device configuration in which the four-wave mixing method shown in FIG. 2, that is, the semiconductor optical amplifier 21 is applied as a frequency conversion unit in the former stage of the optical frequency conversion device of FIG.
The input signal is multiplexed with the pumping light and the converted light from the pumping lasers 25 and 26 via the couplers 51 and 52 and is input to the semiconductor optical amplifier 21, and is also demultiplexed by the coupler 4 immediately after the input to the device. It is input to the difference frequency detector 3.

The frequency-converted signal of the wavelength plate rotating optical frequency converter 2 is also combined and input to the difference frequency detector 3 via the couplers 5 and 6. Then, the difference frequency detector 3 detects the frequency difference between these signals, and the control unit 3a feeds back the control signal based on the detection result to the wavelength plate rotary optical frequency conversion device 2 to generate the semiconductor optical signal. Amplifier 21
The wavelength plate rotation type optical frequency converter 2 is readjusted so as to suppress the fluctuation of the frequency conversion width of the signal light whose optical frequency has been converted in (1).

FIG. 6 is a block diagram showing a sixth embodiment of the configuration according to the present invention of the optical frequency conversion device of the present invention.
In this example, frequency conversion is performed using the wavelength conversion laser 31 shown in FIG. 3, instead of the frequency conversion device to which the four-wave mixing method of FIG. 5 is applied. Also in this example, by the same operation as that of the frequency conversion device shown in FIG. 5, a large frequency conversion width of several THz or more of the wavelength conversion laser system and the advantages of both the wavelength plate rotating optical frequency conversion system are combined.
It is possible to perform optical frequency conversion with high accuracy and a large conversion width.

As described above with reference to FIGS. 1 to 6, in the optical frequency conversion device of this embodiment, a large frequency conversion device such as an optical frequency conversion device using a conventional four-wave mixing or wavelength conversion laser is applied. A device in which the conversion width fluctuates due to the influence of temperature fluctuations, etc., and it is difficult to obtain such a large optical frequency conversion width, but the frequency of the input electric signal is directly obtained as the optical frequency conversion width. Combined with the optical frequency converter of the formula. This allows
It becomes possible to convert the frequency of the optical signal as it is, and to achieve both the frequency conversion width of about 1 THz and the conversion width stability of several MHz or less, and achieve the large conversion width and high accuracy required for the optical frequency conversion. Can meet together. Also, by observing the difference frequency between the optical frequency converted signal and the input signal, by feeding back to the operation of the wavelength plate rotation type optical frequency converter so as to keep the difference frequency constant, the optical frequency converter Stabilization operation can also be realized.

The present invention is not limited to the embodiment described with reference to FIGS. 1 to 6, and various modifications can be made without departing from the scope of the invention. For example, in the embodiment, the apparatus is combined with the wavelength plate rotation type optical frequency conversion apparatus, and the optical frequency conversion apparatus to which the four-wave mixing or wavelength conversion laser is applied is described as an example, but other large frequency conversion width can be obtained. The optical frequency conversion device may be used.

[0025]

According to the present invention, a large frequency conversion width can be obtained with high accuracy in optical frequency conversion.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the configuration of the optical frequency conversion device of the present invention according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the configuration of the optical frequency conversion device of the present invention according to the present invention.

FIG. 3 is a block diagram showing a third embodiment of the configuration of the optical frequency conversion device of the present invention according to the present invention.

FIG. 4 is a block diagram showing a fourth embodiment of the configuration of the optical frequency conversion device of the present invention according to the present invention.

FIG. 5 is a block diagram showing a fifth embodiment of the configuration of the optical frequency conversion device of the present invention according to the present invention.

FIG. 6 is a block diagram showing a sixth embodiment of the configuration of the optical frequency conversion device of the present invention according to the present invention.

FIG. 7 is a block diagram showing a configuration example of a conventional four-wave mixing frequency converter.

8 is an explanatory diagram showing a relationship between respective signal spectra of the four-wave mixing type frequency conversion device in FIG. 7. FIG.

[Explanation of symbols]

1: frequency converter, 2: wave plate rotating frequency converter,
3: difference frequency detector, 3a: control unit, 4 to 6: coupler,
21: semiconductor optical amplifier, 22: low-pass filter, 2
3: Wave plate rotation type optical frequency converter, 24, 25: polarization controller, 26, 27: pump laser, 31: wavelength conversion laser, 51, 52: coupler.

Claims (4)

[Claims] 1. An optical frequency conversion device for converting the frequency of an optical signal, comprising: first optical frequency conversion means for performing frequency conversion of the optical signal within an optical frequency conversion width of a terahertz unit; and the first light. The optical frequency converted by the frequency conversion means,
An optical frequency conversion device comprising: a second optical frequency conversion means for converting with an optical frequency conversion width in the unit of megahertz. 2. The optical frequency conversion device according to claim 1, wherein a wavelength plate rotating optical frequency conversion device is provided as the second optical frequency conversion means. 3. The optical frequency conversion device according to claim 1 or 2, wherein the first optical frequency conversion means uses at least an optical frequency conversion device using a four-wave mixing method, and a wavelength. An optical frequency conversion device comprising any one of optical frequency conversion devices using a conversion laser. 4. The optical frequency conversion device according to claim 1, further comprising means for detecting a difference frequency between the optical signal and the optical signal converted by the second optical frequency conversion means. And a means for feedback-controlling the second optical frequency conversion means based on the difference frequency to suppress fluctuations in the conversion width of the optical frequency by the second optical frequency conversion means. Frequency converter.