JP2006113490A - Wavelength conversion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength conversion apparatus wherein the output wavelength of outputted wavelength converted light is restored in a regulated range and the output wavelength is exact even when wavelength conversion is repeated a plurality of times. <P>SOLUTION: The wavelength conversion apparatus including a signal light input terminal (102), an optical nonlinear element (108) having one phase matching optical frequency of V<SB>m</SB>and having a secondary optical nonlinear susceptibility, a first excitation light source (104-1) outputting a first excited light beam having an optical frequency V<SB>1</SB>= 2V<SB>m</SB>-V<SB>s</SB>to a signal light beam having an optical frequency V<SB>s</SB>, a second excitation light source (104-2) outputting a second excited light beam having an optical frequency V<SB>2</SB>=2V<SB>m</SB>-V<SB>d</SB>to a desired wavelength converted light beam having an optical frequency V<SB>d</SB>and an optical multiplexing part (106) multiplexing the excited light beams and the signal light beam is provided with a branching part (110) branching a difference frequency light beam (light frequency:V<SB>1</SB>+V<SB>s</SB>-V<SB>2</SB>) of a sum frequency light beam (of the first excited light beam and the signal light beam) and the second excited light beam and a wavelength locker (130) inputting the difference frequency light beam and controlling the wavelength of the second excited light beam. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wavelength conversion device that can be mounted on an optical node such as an optical router or an optical cross-connect in an optical communication network.

  In order to cope with the rapid increase in traffic on the network and the diversification of protocols, construction of an optical communication network that does not depend on the bit rate or the protocol is in progress. In such an optical communication network, a wavelength path network characterized in that an output route is determined by using the wavelength of an incident optical signal as a label in an optical relay node that is a component of the optical communication network. In this wavelength path network, optical signals having the same wavelength emitted from different fibers may be destined for the same output fiber. In that case, by converting the wavelengths of the overlapping optical signals, the wavelengths can be made different from each other, and then wavelength-division multiplexed and accommodated in the same output fiber.

  For this wavelength conversion, conventionally, an OEO conversion method is known in which an input optical signal is once converted into an electrical signal, and is then transmitted again as an optical signal by an optical transmitter having a desired transmission wavelength. Since the configuration of the OEO converter using the conventional OEO conversion method depends on the modulation mode and modulation speed of the input optical signal, it is difficult to cope with switching of optical paths having various modulation / demodulation modes. .

  As a conventional wavelength conversion method, a parametric wavelength conversion method using a second-order optical nonlinear effect is known. Since the wavelength converter using the parametric wavelength conversion method using the second-order optical nonlinear effect can convert only the wavelength without depending on the modulation mode and modulation speed of the input signal light, or the number of wavelength multiplexing, the above-mentioned There is no problem. For this reason, the parametric wavelength conversion method using the second-order optical nonlinear effect is regarded as a promising wavelength conversion method for providing a flexible photonic network.

Parametric wavelength conversion is an optical nonlinear material having an optical nonlinear susceptibility, in which excitation light is incident together with signal light to be wavelength-converted, and a new wavelength is generated by optical nonlinear interaction between the excitation light and signal light in the optical nonlinear material. Light (light generated as a process for obtaining the target wavelength-converted light or the target wavelength-converted light) is generated and used. For example, the input signal light of the optical frequency v _s and optical frequency v _p optical frequency v _{s +} v sum frequency light of _p and optical frequency v _s -v difference frequency light of _p generated by the interaction between the excitation light Is used.

  The conversion efficiency from incident signal light to wavelength-converted light greatly depends on the phase matching condition between pump light or signal light and newly generated light. This phase matching condition depends on the material parameters of the optical nonlinear material, the wavelengths of the signal light and the excitation light, and the like. In particular, in order to increase the element length and satisfy the phase matching condition over the entire element, the optical axis of the optical nonlinear crystal is periodically inverted (periodic inversion structure) quasi phase matching (QPM: Quasi Phase Matching). In the element, high conversion efficiency can be obtained, but the phase matching range in which high conversion efficiency can be obtained becomes narrow. For example, the bandwidth of the phase matching wavelength of a quasi phase matching optical nonlinear element using a lithium niobate crystal waveguide having a length of about 5 centimeters is about 0.1 nm.

There has been proposed a method of converting a wavelength from an arbitrary wavelength to an arbitrary wavelength while using such an optical nonlinear element having a phase matching condition with a strict wavelength range (see, for example, Patent Document 1). The proposed method uses two excitation lights. The arrangement of these optical frequencies will be described with reference to FIG. In optical nonlinear element having a phase matching optical frequency v _m, only the difference frequency light between the light of the sum frequency light or optical frequency 2v _m generated in the optical frequency 2v _m occurs at high efficiency. Therefore, first, for an input signal light of the optical frequency v _s, the optical frequency v ₁ prepares the first excitation light v _{1 =} 2v _m -v _s, the sum of the input signal light and the first excitation light generating a frequency light to the optical frequency 2v _m. Next, a second pumping light source having a target conversion destination optical frequency of v _d and an optical frequency v ₂ of v ₂ = 2v _m −v _d is prepared, and the previously generated sum frequency light and second Difference frequency light of excitation light is generated and output as wavelength converted light. That is, by adjusting the optical frequency v ₁ of the two excitation light and v _2, it is possible to convert a signal light having an arbitrary optical frequency (wavelength) to an arbitrary frequency (wavelength).

  On the other hand, in an optical communication network, an optical frequency grid such as an interval of 100 GHz or an interval of 200 GHz is determined, and an optical frequency to be used is used within a range defined around the grid. Usually, in a light source in an optical transmission device, a semiconductor laser module includes an oscillation wavelength control circuit called a wavelength locker. By utilizing the temperature dependence of the oscillation wavelength of the semiconductor laser, a part of the oscillation light is stabilized at the shoulder portion of the periodic wavelength-transmitted light power curve of the Fabry-Perot interferometer, and usually a sufficient grid interval of 1 A certain degree of wavelength accuracy is obtained. Even in the wavelength converter, the optical frequency after wavelength conversion must be within the range. In the OEO conversion method described above, this is realized by providing a wavelength locker in the optical transmitter of the OEO wavelength conversion device.

JP 2004-93583 A (41st to 58th paragraphs, FIGS. 1 and 3)

  However, in the parametric wavelength conversion method, even if the wavelength locker is used in the excitation light source used in the wavelength conversion device, the wavelength converted light does not always fall within the optical frequency grid. This is because the deviation accumulates every time it passes through the wavelength converter. That is, when the deviation from the grid center value of the oscillation frequency of each pumping light source is δ, even if δ is within the specified deviation, the worst case deviation becomes Nδ when wavelength conversion is repeated N times. There is.

  Therefore, there is a need for a wavelength control method in which the optical frequency of wavelength-converted light is within the range defined by the optical communication network even when wavelength conversion is repeated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an output in which the wavelength of the wavelength converted light to be output falls within a specified range even when wavelength conversion is repeated a plurality of times. An object of the present invention is to provide a wavelength converter having an accurate wavelength.

The present invention, in order to achieve the above object, an invention according to claim 1, light having the signal light input terminal, a second-order optical nonlinear susceptibility one is v _m of the phase matching optical frequency a nonlinear element, with respect to the signal light of the optical frequency v _s is inputted from the signal light input terminal, an optical frequency v ₁ is v _{1 =} 2v _m is -v _s first which outputs a first excitation light an excitation light source, with respect to the desired wavelength-converted light of the light frequency _{v d,} and a second excitation light source for outputting second pumping light optical frequency _{v 2} is _v 2 = _2v m -v _d, the excitation In a wavelength converter including an optical multiplexing unit that combines the excitation light and the signal light output from a light source and outputs the combined light to the optical nonlinear element, the first of the lights output from the optical nonlinear element A difference frequency light between the sum frequency light of the excitation light and the signal light and the second excitation light, and the light A bifurcation wavenumber branches the v _{1 +} v _s -v difference frequency light is _2, enter the difference frequency light, characterized in that a wavelength locker controls the wavelength of the second excitation light .

According to a second aspect of the invention, the signal light input terminal, an optical nonlinear element having a second-order optical nonlinear susceptibility one is v _m of the phase matching optical frequency, the light inputted from the optical signal input terminal with respect to the signal light of frequency _{v s,} the optical frequency _{v 1} is _v 1 = a first pumping light source that outputs a first excitation light is _2v m -v _s, desired wavelength converted light of the light frequency _{v d} On the other hand, the optical frequency v ₂ is v ₂ = 2v _m −v _d , and the second excitation light source that outputs the second excitation light within the range of the prescribed optical frequency grid, and the excitation light source In a wavelength converter including an optical multiplexing unit that combines the output excitation light and the signal light and outputs the combined light to the optical nonlinear element, the first excitation of the light output from the optical nonlinear element a sum frequency light between light and signal light, Wako frequency is v _{1 +} v ₂ A branch portion for branching the wave light, enter the sum frequency light, characterized in that a wavelength locker for controlling the wavelength of the first excitation light.

The invention according to claim 3 is the wavelength conversion device according to claim 1 or 2, wherein the optical nonlinear element is a quasi phase matching optical nonlinear element, and the quasi phase of the quasi phase matching optical nonlinear element. wherein the one alignment light frequency is v _m.

  As described above, according to the present invention, even when wavelength conversion is repeated in multiple stages, the optical frequency of the wavelength-converted light output from the apparatus can be kept within a specified range.

(First embodiment)
A first embodiment of a wavelength conversion device according to the present invention will be described with reference to FIG. FIG. 1 shows a basic configuration of the wavelength conversion device of the present embodiment. Wavelength converter (100) includes a signal light input terminal for inputting a signal light of the optical frequency _{v s} (102), the pumping light source for outputting pumping light 1 in the optical frequency _{v 1} 1 and (104-1), the optical frequency v an excitation light source 2 for outputting pumping light 2 ₂ (104-2), the signal light, optical multiplexer for multiplexing the excitation light 1 and the pump light 2 (106), combined signal light, the pumping light An optical nonlinear element (108) that inputs 1 and pumping light 2 and outputs wavelength-converted light, and an optical branching unit (110) that branches wavelength-converted light having an optical frequency v ₁ + v _s −v _{2 from} the wavelength-converted light , enter the split optical frequency _v 1 ₊ v s wavelength conversion light -v _2, a wavelength locker for controlling the pumping light 2 output from the pumping light source 2 (104-2) (130), split optical wavelength converted light output terminal for outputting the wavelength-converted light of frequency v _d and a (116) Obtain.

Next, the operation of this embodiment will be described. The wavelength converter (100) of this embodiment operates in the 1.5 micrometer band of the optical communication wavelength band. An excitation light source 1 (104-1) and 2 (104-2), respectively an optical frequency _{v 1} which is output from the _{v 2} of the excitation light 1 and 2, the optical frequency _{v s} is inputted from the signal light input terminal (102) The input signal light is multiplexed by the optical multiplexing unit (106). The optical multiplexing unit (106) can be realized by a wavelength multiplexing filter, an optical fiber coupler, or the like using a dielectric multilayer film or a fiber Bragg grating (FBG).

The combined pumping lights 1 and 2 and signal light are input to a quasi phase matching optical nonlinear element (108) having a phase matching optical frequency in the vicinity of the pumping light frequency. The optical nonlinear element has a second-order optical nonlinear susceptibility one phase matching optical frequency is v _m. For example, a quasi phase matching optical nonlinear element can be used as the optical nonlinear element (108). As a quasi-phase matching optical nonlinear element, an element in which an optical waveguide is formed by using a proton exchange method or the like on an element in which the optical axis of a lithium niobate crystal is periodically inverted at a period of several tens of micrometers has already been developed. This can be used. Quasi-phase matching optical frequency of the quasi-phase matching optical nonlinear element v _m, the optical parameters of the effective refractive index, etc. of the lithium niobate waveguide is determined by the inversion period.

In the present embodiment, as described in the background, the optical frequency of the pumping light 1 and 2, when the destination optical frequency to a target and v _d,
v ₁ = 2v _m −v _s , v ₂ = 2v _m −v _d
Is adjusted so as to be almost satisfied. However, the phase matching optical frequency only needs to be within the phase matching bandwidth. In the case of a quasi-phase matching optical nonlinear element having a length of several centimeters, a value of about the center phase matching optical frequency ± ten GHz is allowed. Therefore, the optical frequency of the pumping light is adjusted so that the optical frequency deviation of the wavelength-converted light is not more than a specified value within the range where the above equation is satisfied.

In this embodiment, the optical branching unit (110) extracts wavelength-converted light having the optical frequency v ₁ + v _s −v ₂ from the wavelength-converted light output from the nonlinear element (108). The branched light is input to the wavelength locker (130).

  The structure of a typical wavelength locker and the operation principle when using a Fabry-Perot interferometer (etalon) are shown in FIGS. 4 and 5, respectively. The feedback signal is fed back to the excitation light source 2 so that the power of the light transmitted through the etalon (404) becomes a predetermined value, and the oscillation wavelength (optical frequency) of the excitation light source 2 is controlled. In the wavelength locker, the power fluctuation is canceled by using the photodiode PD1 (406) and the differential amplifier (410) in order to discriminate the fluctuation of the optical power and the wavelength fluctuation of the branched light.

  As a result, the optical frequency of the wavelength-converted light that is the output light is stabilized to the grid frequency with an accuracy determined by the wavelength locker.

Incidentally, in the wavelength converted light output terminal (116), to the optical frequency of the wavelength converted light output from the optical nonlinear element (108) to obtain the desired wavelength-converted light is v _d, the optical passband filter (Not shown) must be provided. For example, a dielectric multilayer filter, an acousto-optic filter, an array diffraction grating filter, or the like can be used as the light passband filter.

(Second Embodiment)
Next, a second embodiment of the wavelength conversion device according to the present invention will be described with reference to FIG. FIG. 2 shows a basic configuration of the wavelength conversion device of the present embodiment. Wavelength converter (200) includes a signal light input terminal for inputting a signal light of the optical frequency _{v s} (202), the pumping light source for outputting pumping light 1 in the optical frequency _{v 1} 1 and (204-1), the optical frequency v an excitation light source 2 for outputting pumping light 2 ₂ (204-2), the signal light, optical multiplexer for multiplexing the excitation light 1 and the pump light 2 (206), combined signal light, the pumping light An optical nonlinear element (208) that inputs 1 and pumping light 2 and outputs wavelength-converted light, and wavelength-converted light having an optical frequency v ₁ + v ₂ that is the sum frequency light from the wavelength-converted light to pumping light 1 and signal light And a wavelength locker (230) that controls the pumping light 2 output from the pumping light source 2 (204-2) by inputting the branched wavelength converted light having the optical frequency v ₁ + v _2. ) And the wavelength-converted light output for outputting the wavelength-converted light having the branched optical frequency v _d A terminal (216).

Next, the operation of this embodiment will be described. The wavelength converter (200) of this embodiment operates in the 1.5 micrometer band of the optical communication wavelength band. The pumping light 1 with the optical frequency v _{1 and} the pumping light ₂ with the optical frequency v 22 output from the pumping light sources 1 (204-1) and 2 (204-2), respectively, and input from the signal light input terminal (202). an input signal light of the optical frequency v _s to be are multiplexed by the optical multiplexing section (206). The optical multiplexing unit (206) can be realized by a wavelength multiplexing filter, an optical fiber coupler, or the like using a dielectric multilayer film or a fiber Bragg grating (FBG).

The combined pumping lights 1 and 2 and signal light are input to the quasi phase matching optical nonlinear element (208) having a phase matching optical frequency in the vicinity of the pumping light frequency. The optical nonlinear element has a second-order optical nonlinear susceptibility one phase matching optical frequency is v _m. As the optical nonlinear element (208), a quasi phase matching optical nonlinear element can be used. As a quasi-phase matching optical nonlinear element, an element in which the optical axis of a lithium niobate crystal is periodically inverted at a period of several tens of micrometers and an optical waveguide is formed using a proton exchange method has already been developed. This can be used. Quasi-phase matching optical frequency of the quasi-phase matching optical nonlinear element v _m, the optical parameters of the effective refractive index, etc. of the lithium niobate waveguide is determined by the inversion period.

In the present embodiment, as described in the background, the optical frequency of the pumping light 1 and 2, when the destination optical frequency to a target and v _d,
v ₁ = 2v _m −v _s , v ₂ = 2v _m −v _d
Is adjusted so as to be almost satisfied. However, the phase matching optical frequency only needs to be within the phase matching bandwidth. In the case of a quasi-phase matching optical nonlinear element having a length of several centimeters, a value of about the center phase matching optical frequency ± ten GHz is allowed. Therefore, the optical frequency of the pumping light is adjusted so that the optical frequency deviation of the wavelength-converted light is not more than a specified value within the range where the above equation is satisfied.

In this embodiment, the optical branching unit (210) does not extract the wavelength-converted light to be output, but branches the sum frequency light of the signal light and the first excitation light. Optical frequency v ₁ of the excitation light 1 according to the network control signal (usually the primary signal is being transferred by a separate line with) the input signal given from the light frequency v _s, approximately satisfies v 1 ₌ 2v _m -v _s To be controlled. Therefore, the sum frequency light of the excitation light 1 and the signal light is approximately 2v _m optical frequency (wavelength band 0.75 micrometers).

  The wavelength locker (230) controls the oscillation light frequency of the excitation light source 1 (204-1) so that the sum frequency light has a certain value of transmitted light power. In this case, regardless of the optical frequency of the input signal light, the sum frequency light with the pumping light 1 is generated at a certain optical frequency in the vicinity of the quasi-phase matching optical frequency, so that unlike the case of the first embodiment, The wavelength locker need not have periodic wavelength-transmission characteristics.

  The excitation light source 2 (204-2) is a light source provided with a normal wavelength locker (wavelength locker 2) inside. The maximum deviation of the wavelength-converted light that is output is the sum of the accuracy of the wavelength locker 1 and the accuracy of the wavelength locker 2. Therefore, each accuracy may be set to be less than half of the allowable deviation from the grid defined by the communication network.

Incidentally, in the wavelength converted light output terminal (216), to the optical frequency of the wavelength converted light output from the optical nonlinear element (208) to obtain the desired wavelength-converted light is v _d, the optical passband filter (Not shown) must be provided. For example, a dielectric multilayer filter, an acousto-optic filter, an array diffraction grating filter, or the like can be used as the light passband filter.

It is a block diagram of 1st Embodiment of the wavelength converter which concerns on this invention. It is a block diagram of 2nd Embodiment of the wavelength converter which concerns on this invention. It is the figure which showed the wavelength relationship in the arbitrary wavelength converter structure which this invention assumes. 1 is a block diagram of a typical wavelength locker that can be used to implement the present invention. It is a figure for demonstrating the principle of the typical wavelength locker which can be used for implementation of this invention.

Explanation of symbols

100, 200 Wavelength converters 102, 202 Signal light input terminals 104-1, 104-2, 204-1, 204-2 Excitation light source 106, 206 Optical multiplexing unit 108, 208 Optical nonlinear element 110, 210 Optical branching unit 116, 216 Wavelength conversion light output terminals 130 and 230 Wavelength locker 400 Wavelength rocker 402 Splitter 404 Etalon 406 and 408 Photodiode (PD)
410 Differential Amplifier

Claims (3)

A signal light input terminal;
An optical nonlinear element having a second-order optical nonlinear susceptibility one phase matching optical frequency is v _m,
For the signal light of the optical frequency v _s is inputted from the signal light input terminal, a first pumping light source that outputs a first excitation light optical frequency v ₁ is v _{1 =} 2v _m -v _s,
For the desired wavelength-converted light of the light frequency _{v d,} and a second excitation light source for outputting second pumping light optical frequency _{v 2} is _v 2 = _2v m -v _d,
In the wavelength converter including the optical multiplexing unit that multiplexes the excitation light and the signal light output from the excitation light source and outputs them to the optical nonlinear element,
Of the light output from the optical nonlinear element, it is a difference frequency light between the sum frequency light of the first excitation light and the signal light and the second excitation light, and the optical frequency is v ₁ + v _s −v. A branching section that branches the difference frequency light that is ₂ ;
A wavelength conversion device comprising: a wavelength locker that inputs the difference frequency light and controls the wavelength of the second excitation light. A signal light input terminal;
An optical nonlinear element having a second-order optical nonlinear susceptibility one phase matching optical frequency is v _m,
For the signal light of the optical frequency v _s is inputted from the signal light input terminal, a first pumping light source that outputs a first excitation light optical frequency v ₁ is v _{1 =} 2v _m -v _s,
For the desired wavelength-converted light of the light frequency v _d, an optical frequency v ₂ is v _{2 =} 2v _m -v _d, the outputs of the second excitation light is within the defined optical frequency grid Two excitation light sources;
In the wavelength conversion device, comprising: an optical multiplexing unit that multiplexes the excitation light output from the excitation light source and the signal light and outputs to the optical nonlinear element,
Of the light output from the optical nonlinear element, a branching unit for branching the sum frequency light of the first pumping light and the signal light and having an optical frequency of v ₁ + v ₂ ;
A wavelength conversion device comprising: a wavelength locker that inputs the sum frequency light and controls the wavelength of the first excitation light. The optical nonlinear element is a quasi-phase matching optical nonlinear element, the wavelength according to claim 1 or 2 one quasi-phase matching optical frequency of the quasi-phase matching optical nonlinear element is characterized in that the v _m Conversion device.

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