JP2007226076A - Wavelength converting method and wavelength converting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength converting method and a wavelength converting device that can perform high-speed signal processing since a signal processing speed is not limited to an operation speed of an external device, and then can perform wide-band all-optical-signal processing. <P>SOLUTION: The wavelength converting method and wavelength converting device employ selective transmissivity of optical signals by a filter and route selectivity of light by interference effect of a Sagnac interference system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a wavelength conversion method and a wavelength conversion apparatus.

  With the increase in speed and capacity of optical communication, an all-optical signal processing technique that performs signal processing without converting an optical signal into an electrical signal is required.

  In recent years, wavelength division multiplexing (WDM) has been developed as one technology for realizing this high speed and large capacity, and in this WDM, all bands of silica optical fibers extending to several THz have been developed. It can be used up. However, as such broadband signal processing becomes possible, when using WDM that transmits different information for each wavelength of light and uses it between sub-networks, new methods such as wavelength collision and wavelength routing are used. Problems arise. Therefore, wavelength conversion is used to solve such problems, and wavelength conversion is an indispensable technique in all-optical signal processing.

  When wavelength conversion is applied to all-optical signal processing in this way, a non-linear medium (NLM) that can obtain a large non-linear optical effect, such as a semiconductor optical amplifier (SOA), is used. Thus, not only can the system be miniaturized, but also operation with low power consumption is possible. Therefore, application of such a nonlinear medium to all-optical signal processing has been actively studied.

  The all-optical wavelength conversion method using the SOA includes an optical switch type such as cross gain modulation (XGM) or cross phase modulation (XPM), and a difference frequency generation (DFG). ) Or four-wave mixing (FWM). This coherent wavelength conversion can be performed utilizing the ultra-high speed of the non-linear response. Further, since phase information is maintained even after conversion, it is also possible to cope with a modulation format such as differential phase shift keying (DPSK).

  By the way, wavelength conversion in which the input signal light and the wavelength converted light are output in the same direction is called traveling wave wavelength conversion, and is generally more efficient than other wavelength conversions such as the opposite type and the non-parallel traveling type. Is expensive. However, it is not practical that all the input signal light is converted into wavelength converted light. That is, the input signal light and the wavelength converted light are emitted simultaneously from the nonlinear medium. Therefore, when it is desired to extract only the wavelength-converted light, a means for selectively extracting the wavelength-converted light after exiting from the nonlinear medium is required.

  As means for selectively extracting the wavelength-converted light, a four-wave mixing generation circuit using a dispersive medium and a Sagnac interference system composed of an optical fiber and an optical coupler, and the four-wave mixing generation circuit are used. An optical circuit is disclosed (for example, see Patent Document 1 and Non-Patent Document 1).

  Further, as means for selectively extracting wavelength-converted light, an optical parametric circuit using dispersibility by a dispersive medium and the interference effect of a Mach-Zehnder interference system is disclosed (for example, see Patent Document 2).

  Here, the operation principle of the Sagnac interference system will be described with reference to FIGS.

  FIG. 1 shows an optical coupler 12 constituting a Sagnac interference system. This optical coupler 12 has a total of four ports with two inputs and two outputs. The operation principle of the optical coupler will be described by taking the case where light is incident on the port 1 as an example.

  When light enters the port 1 of the optical coupler 12, the light is branched into the port 3 and the port 4. At this time, the phase of the light 11 emitted to the port 4 is delayed by p / 2 with respect to the light 10 emitted to the port 3. This is because the optical coupler 12 has the property that the light branched in the diagonal direction by the optical coupler 12 is delayed in phase by p / 2 with respect to the light branched in the straight traveling direction.

  FIG. 2 shows a Sagnac interference system. The Sagnac interference system 20 includes an optical fiber 21, a 2-input 2-output optical coupler (3 dB) 22 having a branching ratio of 1: 1, and an optical fiber 23 connected to the ports 1 and 2 of the optical coupler 21. The Both ends of the optical fiber 21 are connected to ports 3 and 4 on one side of the optical coupler 22 to form a loop.

  When light is input to port 1 of the optical coupler 22, the light is branched into two lights having a phase difference of p / 2, which are emitted from port 3 and port 4, respectively. Here, the property of the loop mirror of the Sagnac interference system will be described using an example in which these two lights are transmitted through the loop-shaped optical fiber 21 shown in FIG.

  Light that has propagated from the port 3 of the optical coupler 22 through the loop-shaped optical fiber 21 to reach the port 4 is called clockwise 30, and propagates from the port 4 of the optical coupler 22 through the loop-shaped optical fiber 21 to port 3. The reached light will be called counterclockwise 30. Further, it is assumed that both lights are not affected by the phase due to linear or non-linear effects and disturbances during transmission through the optical fiber. That is, it is assumed that the phase difference between the clockwise light and the counterclockwise light during transmission through the optical fiber is always p / 2.

  The clockwise 30 light reaching the port 4 is branched into the port 1 and the port 2 with a branching ratio of 1: 1. Here, the light branched to port 1 is called clockwise 31 and the light branched to port 2 is called clockwise 32. Due to the nature of the optical coupler, the clockwise light 31 is delayed in phase by p / 2 with respect to the clockwise 32 light.

  On the other hand, the counterclockwise 30 light reaching port 3 is also branched into port 1 and port 2 at a branching ratio of 1: 1. Here, the light that has reached port 1 is referred to as counterclockwise 31, and the light that has reached port 2 is referred to as counterclockwise 32. Due to the nature of the optical coupler, the counterclockwise 32 light is delayed in phase by p / 2 with respect to the counterclockwise 31 light.

  FIG. 3 shows the phase difference between the light initially input to the port 1 and the light of the clockwise 31, clockwise 32, counterclockwise 31, and counterclockwise 32. Then, attention is paid to the phase relationship between the clockwise 31 and the counterclockwise 31, and the clockwise 32 and the counterclockwise 32. Here, since the phase change in the loop optical fiber 21 is not taken into consideration, the phase difference between the clockwise 31 and the counterclockwise 31 is zero. More specifically, since the phase of both the clockwise 31 light and the counterclockwise 31 light is delayed by p / 2 with respect to the light incident from the port 1, the phase difference becomes zero. Accordingly, the port 1 emits light obtained by superimposing the clockwise light 31 and the counterclockwise light 31. On the other hand, the phase relationship between the clockwise 32 and the counterclockwise 32 is p. More specifically, the clockwise light 32 has the same phase with respect to the light incident from the port 1, and the counterclockwise light 32 is delayed in phase by p, so that the phase difference is p. Accordingly, the clockwise light 32 and the counterclockwise light 32 interfere so as to cancel each other, and no light is emitted from the port 2. As a result of such interference between optical signals, the Sagnac interference system has optical signal route selectivity. The light incident from the port 1 is not emitted to the port 2 but returned to the port 1 alone, so that the route selectivity property of the optical signal is also referred to as a loop mirror.

Here, the principle of wavelength conversion will be described using four-wave mixing as an example. This four-wave mixing generally uses a third-order nonlinear optical effect, and light of w ₄ satisfying, for example, w ₄ = w ₂ + w ₃ -w ₁ from light of frequencies w ₁ , w ₂ , and w _3. Can be generated. Here, the case of w ₂ ≠ w ₃ is called non-degenerate four-wave mixing, while the case of w ₂ = w ₃ is called degenerate four-wave mixing. In the degenerate four-wave mixing, the spectrum of w ₄ is an inversion of the spectrum of w ₁ , and w ₄ becomes the phase conjugate light of w ₁ . This four-wave mixing can be realized by using the above-mentioned SOA, optical nonlinear optical fiber, or the like (for example, see Non-Patent Document 2).

Further, consider a degenerate four-wave mixing, the phase conjugate beam is generated w _c by inputting the signal light w _s and pumping light w _p. The correspondence with the general theory of four-wave mixing described above is w ₁ = w _s and w ₂ = w ₃ = w _p , and each frequency component satisfies the frequency relationship of w _c = 2w _p −w _s. ing. Here, as the frequency of the signal light is swept while the frequency of the pump light is fixed, the frequency of the phase conjugate light changes while satisfying the frequency relationship. On the other hand, even if the frequency of the pump light is swept while the frequency of the signal light is fixed, the frequency of the phase conjugate light changes while satisfying the frequency relationship. In this manner, the frequency of the phase conjugate light can be varied by adjusting the frequency of the signal light and the pump light.

Even in the case of such degenerate four-wave mixing, as in the general theory of progressive wavelength conversion, means such as a filter for cutting signal light and pump light are required. In other words, when the frequency of the phase conjugate light is made variable, the signal light and the pump light that correspond to the frequency of the swept signal light and the pump light and the variable phase conjugate light are cut. Means such as a filter are required. As a means such as a filter, a voltage application type variable bandpass filter that changes a transmission frequency band by an electric means is known.
JP-A-9-33967 PR. JP 2002-182256 PR. K. Mori, T. Morita, and M. Saruwatari, “Optical parametric loop mirror,” Opt. Lett. , Vol. 20, no. 12, pp. 1424-1425 (1995) G. P. Agrawal, “Population pulsations and non-degenerative four-wave mixing in semiconductor lasers and amplifiers,” J. Am. Opt. Soc. Am. B, Vol. 5, no. 1, pp. 147-159 (1988)

  In the conventional all-optical signal processing using wavelength conversion as described above, when a desired optical signal is selectively extracted using a voltage-applied variable bandpass filter or the like, the signal processing is performed depending on the operation speed of the filter. There is a problem that the speed is limited, and when an optical signal is selectively extracted using a dispersive medium and an interference system, there is a problem that the frequency and its bandwidth are limited.

  The present invention is a wavelength conversion method including a step of splitting light, comprising: an optical coupler; and a loop-shaped optical fiber having both ends connected to a first port and a second port of the optical coupler. The Sagnac interference system configured is a Sagnac interference system including a nonlinear medium and means for attenuating a predetermined frequency band in the loop of the loop-shaped optical fiber, and wavelength conversion is performed on a predetermined port of the optical coupler. A first step of inputting a first light group composed of pump light serving as a reference and signal light serving as a wavelength conversion signal; and the loop-shaped optical fiber from the first port. The first light group is branched into a first route propagating to a second port and a second route propagating the looped optical fiber from the second port to the first port. And the second step A third step in which a second light group is formed from the first light group propagating through the first route by the nonlinear medium and means for attenuating the predetermined frequency band; and the nonlinear medium And a means for attenuating the predetermined frequency band, a fourth step in which a third light group is formed from the first light group propagating through the second route, and the first of the optical coupler. The light constituting the second light group input to the second port interferes with the light constituting the third light group input to the first port of the optical coupler at the optical coupler. And a fifth step of branching to a predetermined port.

  In the present invention, since the signal processing speed is not limited by the operating speed of the external device, high-speed signal processing is possible. In addition, broadband all-optical signal processing is possible.

  The configuration of the first embodiment of the present invention will be described with reference to FIG. The configuration shown in FIG. 4 includes an optical fiber 41, a 2-input 2-output optical coupler (3 dB) 42 having a branching ratio of 1: 1, and an optical fiber 45 connected to ports 1 and 2 of the optical coupler 42. The Sagnac interference system 40 is a Sagnac interference system having a nonlinear medium 43 and means 44 for attenuating a predetermined frequency band, which are connected in a loop of the optical fiber 41.

  The arrangement of the non-linear medium 43 and the means 44 for attenuating the predetermined frequency band with respect to the Sagnac interference system 40 is not limited to FIG. 4, and the means 44 for attenuating the non-linear medium 43 and the predetermined frequency band is It only needs to be in the loop of the optical fiber 40.

  In the present invention, in addition to the Sagnac interference system, a Michelson interference system or a Mach-Zehnder interference system can be used. However, the Sagnac interference system is easier to adjust the phase difference than other interference systems. Therefore, a Sagnac interference system will be described as one of the configurations for carrying out the present invention.

The configuration of the first embodiment of the present invention and an example of the peripheral configuration will be described with reference to FIG. FIG. 5 shows a Sagnac interference system 50 including a polarization-maintaining directional coupler 52 and an optical fiber 51, which includes a SOA 54 and a filter 53 in a loop-shaped optical fiber 51. And a polarization controller 55, a simultaneous incidence directional coupler 56, and an optical circulator 57. Here, FIG. 5 will be described in detail based on the fact that the signal light w _s and the pump light w _p are incident on the optical signal input unit of the polarization controller 55.

First, in the polarization controller 55, the polarization states of the signal light w _s and the pump light w _p are matched. This polarization state affects the conversion efficiency of wavelength conversion. In some cases, the conversion efficiency is highest when the polarization states are the same, and in other cases, the conversion efficiency is highest when the polarization states are not the same. This is determined by the characteristics of the nonlinear medium used for wavelength conversion. Further, the output value of the wavelength converted light depends on the phase relationship between the signal light w _s and the pump light w _p for the nonlinear medium and the nonlinear optical effect. Therefore, the phase relationship between the input signal light w _s and the pump light w _p− is determined in accordance with the characteristics of the nonlinear medium and the nonlinear optical effect.

Next, the signal light w _s and the pump light w _p are combined in the directional coupler 56 for simultaneous incidence. This multiplexing is performed so that the signal light w _s and the pump light w _p are incident on the port 1 of the polarization maintaining directional coupler 52 constituting the Sagnac interference system 50.

Next, the combined signal light w _s and pump light w _p are passed to the optical circulator 57. The optical circulator 57 plays a role of preventing the light traveling in the direction of the optical circulator 57 from the port 1 of the polarization maintaining directional coupler 52 from traveling to the directional coupler 56 for simultaneous incidence. Thereby, it is possible to avoid the light incident on the Sagnac interference system and the light emitted from the Sagnac interference system from interfering with the directional coupler 56 for simultaneous incidence.

Next, the signal light w _s and the pump light w _p are input to the port 1 of the 2-input 2-output polarization-maintaining directional coupler 52 having a branching ratio of 1: 1 that constitutes the Sagnac interference system 50. The signal light w _s and the pump light w _p are branched into the ports 3 and 4 at a branching ratio of 1: 1.

  In the implementation of the present invention, examples of the optical coupler that can be used other than the polarization-maintaining directional coupler 52 include a multimode interference coupler.

  Next, the optical signals emitted from the ports 3 and 4 are transmitted through the loop-shaped optical fiber. In the loop optical fiber, a filter 53 is connected as means for attenuating a predetermined frequency band, and an SOA 54 is connected as a nonlinear medium.

  FIG. 6 shows a module 60 in which a filter and SOA are modularized. In this module 60, the light that has entered the module 60 from the optical fiber 61 is converted into parallel light by the lens 62, passes through the filter 63, and is collected by the lens 64 onto the SOA 65. The light that has passed through the SOA 65 is converted into parallel light by the lens 66, and is condensed on the optical fiber 68 by the lens 67. Here, the connection surface is connected by fusion so that reflection does not occur at the connection surface between the optical fiber in the loop and the module.

  In the present invention, the configuration method of the means for attenuating a predetermined frequency band and the nonlinear medium is not limited to the configuration of FIG. 6, and for example, the filter 63 and the SOA 65 can be configured by separate modules.

Next, in the first embodiment of the present invention, consider wavelength conversion in which signal light w _{s of} 1555 nm and pump light w _{p of} 1551 nm are incident and phase conjugate light is obtained by degenerate four-wave mixing.

The filter 53 in the first embodiment will be described with reference to FIG. The vertical axis of the graph shown in FIG. 7 is the output value of the optical signal, and the horizontal axis is the frequency. This graph shows output values of the signal light w _s , the pump light w _p , and the wavelength converted light w _c . The frequency band indicated by the hatched portion 70 is the transmission frequency band of the filter 53. In practicing the present invention, the specification of the filter is a filter that transmits the pump light w _p and has a wavelength inclination width determined by the high transmission limit wavelength and the absorption limit wavelength as small as possible in the vicinity of the frequency of the pump light w _p. is there. When this filter is used, the band that can be used for wavelength conversion is widened. Specifically, in the first embodiment, the absorption limit wavelength defined as a transmittance of 5% or less is 1549.2 nm, and the high transmission limit wavelength defined as a transmittance of 72% or more is 1550 nm. The dielectric multilayer high-pass filter has a wavelength inclination width of 0.8 nm.

However, the specification of the filter when implementing the present invention is not limited to the dielectric multilayer high-pass filter. In addition, which frequency band the filter attenuates depends on the relationship between the frequency of the signal light w _s , the pump light w _p , and the wavelength-converted light w _c and the implementation method, which will be described with reference to FIGS. It depends on.

FIG. 8 shows a cross-sectional view of a quantum well SOA 80 using indium gallium arsenide (hereinafter referred to as InGaAs). The structure of the quantum well SOA 80 includes a structure in which an InGaAs quantum well 81 is sandwiched between indium gallium arsenide phosphorus (hereinafter referred to as InGaAsP) separate confinement hetero-structure (SCH) 82 and p-type indium gallium arsenide (SCH). p-InGaAs) 83, first p-type indium phosphide (p-InP) 84, second p-type indium phosphide (p-InP) 85, and first n-type indium phosphide (n-InP) 86 And a second n-type indium phosphide (n-InP) 87. Here, corresponding to the frequency band of the first embodiment, the quantum well layer 81 has a thickness of 5 nm, a strain amount of −0.70%, and a composition ratio of In _0.43 Ga _0.57. A barrier layer to be As and a well layer having a film thickness of 5 nm, a strain amount of + 0.50%, and a composition ratio of In _0.6 Ga _0.4 As are alternately laminated for six periods, A structure in which only one barrier layer having a thickness of 5 nm, a strain amount of −0.70%, and a composition ratio of In _0.43 Ga _0.57 As is stacked is used. The emission wavelength of InGaAsP in the SCH layer is 1.15 μm and the layer width is 50 nm. However, the configuration of the nonlinear medium corresponds to the frequency band of the first embodiment, and the present invention is not limited to this.

  In addition, the subscript shown together with In and Ga has shown the composition ratio of In and Ga. InGaAs is a semiconductor generally called a III-V group compound semiconductor. Here, In and Ga belong to Group III. On the other hand, As belongs to the V group. InGaAs is composed of a group III element, which is a combination of In and Ga, and a group V As in a composition ratio of 1: 1.

Note that, as a nonlinear medium that can be used in the present invention, oxide strong such as LiTaO ₃ , LiNbO ₃ , KLiOPO ₄ (KTP), KH ₂ PO ₄ (KDP), and KNbO ₃ that can use a second-order nonlinear optical effect. There are dielectrics. In addition, organic materials AANP crystal, MMA polymer, DAN crystal that can use the third-order nonlinear optical effect, semiconductor amplifiers such as GaN, ZnSSe, GaAs / GaAlAs quantum wells, AgGaSe ₂ and AgGaS, highly nonlinear optical fibers, etc. There is.

In the present invention, nonlinear optical effects such as four-wave mixing, difference frequency generation, and cascaded second-order nonlinear optical effects can be used in accordance with the characteristics of the nonlinear medium.
Next, four embodiments (a), (b), which have different operating principles in the first embodiment, depending on the magnitude relationship between the frequencies of the signal light and the pump light and the combination of filter types corresponding to the magnitude relationship. (C) and (d) will be described.
FIG. 9 summarizes the magnitude relationship of the frequencies in each embodiment and the specifications of the means for attenuating the predetermined frequency band to be used.
The embodiment (a) will be described with reference to FIGS.
In the embodiment (a), the frequency of the signal light w _s is larger than the frequency of the pump light w _p . Further, as a means for attenuating a predetermined frequency band, a high-pass filter 102 that transmits at least a frequency band equal to or higher than the frequency of the pump light w _p is used. In FIG. 10, a nonlinear medium 101 connected to a loop-shaped optical fiber, a high-pass filter 102, a Sagnac interference system 100 including this loop-shaped optical fiber and an optical coupler having a branching ratio of 1: 1, a signal _Illustrated are light w _s , pump light w _p , wavelength converted light w _c, and arrows indicating the propagation of light of each frequency component. In addition, the vertical axis of the graph shown in accordance with the high-pass filter 102 is the output value of the optical signal, and the horizontal axis is the frequency. This graph shows output values of the signal light w _s , the pump light w _p , and the wavelength converted light w _c . Further, the hatched portion of this graph is the transmission frequency band of the high-pass filter 102.

The embodiment (a) will be described separately in steps with reference to FIGS. 10 and 11. FIG. 11 shows the state of the signal light w _s , the pump light w _p , and the wavelength-converted light w _c that propagates clockwise and counterclockwise through the optical fiber on the loop of the Sagnac interference system 100.

The signal light w _s and the pump light w _p are input to port 1 of the optical coupler and branched to ports 3 and 4. The signal light w _s and the pump light w _p emitted from the port 3 pass through the high-pass filter 102 and enter the nonlinear medium 101, and reach the port 4 together with the generated wavelength converted light w _c . On the other hand, the signal light w _s and the pump light w _p output from the port 4 are incident on the nonlinear medium 101 and are incident on the high-pass filter 102 together with the generated wavelength converted light w _c . At this time, the wavelength-converted light w _c is cut by the high-pass filter 102, and the signal light w _s and the pump light w _p that have passed through the high-pass filter 102 reach the port 3. The light propagating clockwise and counterclockwise through the loop-shaped optical fiber is incident on the port 3 or port 4 of the optical coupler. At this time, the signal light w _s and the pump light w _p incident on the port 3 and the port 4 of the optical coupler become a loop mirror and are emitted from the port 1. On the other hand, the wavelength-converted light w _c is incident on the optical coupler only from the port 4 and thus is branched into the port 1 and the port 2. That is, only the wavelength converted light w _c is emitted from the port 2.

Note that the specifications required for the means 102 for attenuating the predetermined frequency band used in the embodiment (a) are referred to from the point of the optical signal, and the wavelength conversion is performed by transmitting the signal light w _s and the pump light w _p. The specification is that the light w _c is attenuated. Furthermore, in the case of the wavelength-converted light w _c is variable by sweeping the frequency of the signal light w _s or pump light w _p is by transmitting a frequency band of the signal light w _s or sweeping the pump light w _p sweeps In this specification, the frequency band of the variable wavelength converted light w _c is attenuated.

The embodiment (b) will be described with reference to FIG. The basic configuration is the same as in the embodiment (a), and here, the frequency of the signal light w _s is larger than the frequency of the pump light w _p . However, as means for attenuating a predetermined frequency band, a low-pass filter 122 that transmits at least a frequency band equal to or lower than the frequency of the pump light w _p is used. In FIG. 12, a non-linear medium 121 connected to a loop-shaped optical fiber, a low-pass filter 122, a Sagnac interference system 120 including this loop-shaped optical fiber and an optical coupler having a branching ratio of 1: 1, a signal _Illustrated are light w _s , pump light w _p , wavelength converted light w _c, and arrows indicating the propagation of light of each frequency component. In addition, the vertical axis of the graph shown in the figure according to the low-pass filter 122 is the output value of the optical signal, and the horizontal axis is the frequency. This graph shows output values of the signal light w _s , the pump light w _p , and the wavelength converted light w _c . Further, the hatched portion of this graph is the transmission frequency band of the low filter 122.

The signal light w _s and the pump light w _p are input to port 1 of the optical coupler and branched to ports 3 and 4. The signal light w _s and pumping light w _p exiting from port 3, the signal light w _s is cut by the low pass filter 122, only the pump light w _p passes through the nonlinear medium 121, to reach the port 4. On the other hand, the signal light w _s exiting from port 4 and the pump light w _p is incident to the nonlinear medium 121, and enters the low pass filter 122 together with the generated wavelength converted light w _c. At this time, the signal light w _s is cut by the low-pass filter 122, and the pump light w _p and the wavelength-converted light w _c that have passed through the low-pass filter 122 reach the port 3. The light propagating clockwise and counterclockwise through the loop-shaped optical fiber is incident on the port 3 or port 4 of the optical coupler. At this time, the pump light w _p incident on the ports 3 and 4 of the optical coupler becomes a loop mirror and is emitted from the port 1. On the other hand, the wavelength-converted light w _c is incident only from the port 3 and is branched to the port 1 and the port 2 of the optical coupler. That is, only the wavelength converted light w _c is emitted from the port 2.

Note that the specifications required for the means 122 for attenuating the predetermined frequency band used in the embodiment (b) are referred to from the point of the optical signal, and the signal is transmitted through the wavelength converted light w _c and the pump light w _p. The specification is to attenuate the light w _s . Further, when the wavelength converted light w _c is made variable by sweeping the frequency of the signal light w _s or the pump light w _p , the frequency band of the swept pump light w _p or the variable wavelength converted light w _c is transmitted. by a specification that attenuates the frequency band of the pump light w _s sweeping.

Example (c) will be described with reference to FIG. The basic configuration is the same as that of the embodiment (a), but here, the frequency of the signal light w _s is smaller than the frequency of the pump light w _p . As a means for attenuating a predetermined frequency band, a high-pass filter 132 that transmits at least a frequency band equal to or higher than the frequency of the pump light w _p is used. FIG. 13 shows a nonlinear medium 131 connected to a loop-shaped optical fiber, a high-pass filter 132, a Sagnac interference system 130 composed of the loop-shaped optical fiber and an optical coupler having a branching ratio of 1: 1, and signal light. The w _s , the pump light w _p , the wavelength-converted light w _c, and the arrows indicating the state of propagation of the light of each frequency component are illustrated. In addition, the vertical axis of the graph shown in the figure according to the high-pass filter 132 is the output value of the optical signal, and the horizontal axis is the frequency. This graph shows output values of the signal light w _s , the pump light w _p , and the wavelength converted light w _c . Further, the hatched portion of this graph is the transmission frequency band of the high pass filter 132.

The signal light w _s and the pump light w _p are input to port 1 of the optical coupler and branched to ports 3 and 4. The signal light w _s and pumping light w _p exiting from port 3, the signal light w _s is cut by the high-pass filter 132, only the pump light w _p passes through the nonlinear medium 131, to reach the port 4. On the other hand, the signal light w _s and the pump light w _p emitted from the port 4 are incident on the nonlinear medium 131 and are incident on the high pass filter 132 together with the generated wavelength converted light w _c . At this time, the signal light w _s is cut by the high pass filter 132, and the pump light w _p and the wavelength converted light w _c that have passed through the high pass filter 132 reach the port 3. The light propagating clockwise or counterclockwise through the loop-shaped optical fiber is incident from the port 3 or the port 4 of the optical coupler. At this time, the pump light w _p incident on the port 3 and the port 4 of the optical coupler becomes a loop mirror and is emitted to the port 1. On the other hand, the wavelength-converted light w _c is incident only from the port 3 of the optical coupler, so that it is branched to the port 1 and the port 2 of the optical coupler. That is, only the wavelength converted light w _c is emitted from the port 2.

In addition, if the specification required for the means 132 for attenuating the predetermined frequency band used in the embodiment (c) is mentioned in terms of the optical signal, the signal light is transmitted through the pump light w _p and the wavelength converted light w _c. The specification is to attenuate w _s . Further, when the wavelength converted light w _c is made variable by sweeping the frequency of the signal light w _s or the pump light w _p , the frequency band between the swept pump light w _p and the variable wavelength converted light w _c is changed. The specification is such that the frequency band of the signal light w _s that is transmitted and attenuated is attenuated.

Embodiment (d) will be described with reference to FIG. The basic configuration is the same as that of the embodiment (c), and here, the frequency of the signal light w _s is smaller than the frequency of the pump light w _p . However, as means for attenuating a predetermined frequency band, a low-pass filter 142 that transmits at least a frequency band equal to or lower than the frequency of the pump light w _p is used. FIG. 14 shows a non-linear medium 141 connected to a loop-shaped optical fiber, a low-pass filter 142, a Sagnac interference system 140 composed of this loop-shaped optical fiber and an optical coupler having a branching ratio of 1: 1, and signal light. The w _s , the pump light w _p , the wavelength-converted light w _c, and the arrows indicating the state of propagation of the light of each frequency component are illustrated. In addition, the vertical axis of the graph shown in the figure according to the low-pass filter 142 is the output value of the optical signal, and the horizontal axis is the frequency. This graph shows output values of the signal light w _s , the pump light w _p , and the wavelength converted light w _c . Further, the hatched portion of this graph is the transmission frequency band of the low-pass filter 142.

The signal light w _s and the pump light w _p are input to port 1 of the optical coupler and branched to ports 3 and 4. The signal light w _s and the pump light w _p emitted from the port 3 pass through the low-pass filter 142 and enter the nonlinear medium 141 and reach the port 4 together with the generated wavelength converted light w _c . On the other hand, the signal light w _s and the pump light w _p emitted from the port 4 are incident on the nonlinear medium 141 and are incident on the low-pass filter 142 together with the generated wavelength converted light w _c . At this time, the wavelength converted light w _c is cut by the low-pass filter 142, and the signal light w _s and the pump light w _p that have passed through the low-pass filter 142 reach the port 3. The light propagating clockwise or counterclockwise through the loop-shaped optical fiber is incident from the port 3 or the port 4. At this time becomes a loop mirror the signal light w _s and pumping light w _p incident from the ports 3 and 4 which of the optical coupler, is emitted to the port 1 of the optical coupler. On the other hand, the wavelength-converted light is incident only from the port 4 and is branched to the port 1 and the port 2 of the optical coupler. That is, only the wavelength converted light is emitted from the port 2.

In addition, if the specification required for the means 142 for attenuating the predetermined frequency band used in the embodiment (d) is mentioned in terms of the optical signal, the wavelength conversion is performed by transmitting the signal light w _s and the pump light w _p. The specification is that the light w _c is attenuated. Furthermore, when the wavelength converted light w _c is made variable by sweeping the frequency of the signal light w _s or the pump light w _p , the frequency band of the pump light w _{s to be} swept or the pump light w _{p to be} swept is transmitted. In this specification, the frequency band of the variable wavelength converted light w _c is attenuated.

  The above is description of Example (a), (b), (c), (d).

According to the present invention, in the all-optical signal processing using wavelength conversion, the signal processing speed is not limited by the operation speed of the external apparatus such as the sweep speed of the filter. In the Sagnac interference system, the signal light w _s and the pump light w _p become the loop mirror, and the band of the wavelength converted light is determined by the transmission frequency band of the high-pass filter or low-pass filter and the characteristics of the nonlinear medium . Therefore, wideband wavelength conversion is possible.

  The present invention is applicable to an optical signal processing technique using wavelength conversion.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

(Supplementary note 1) A wavelength conversion method including a step of splitting light,
A Sagnac interference system composed of an optical coupler and a loop-shaped optical fiber having both ends connected to the first port and the second port of the optical coupler is in the loop of the loop-shaped optical fiber, A Sagnac interference system including a non-linear medium and means for attenuating a predetermined frequency band, and configured by a predetermined port of the optical coupler including pump light serving as a wavelength conversion reference and signal light serving as a wavelength conversion signal. A first step in which the first light group is input;
A first route for propagating the looped optical fiber from the first port to the second port; and a second route for propagating the looped optical fiber from the second port to the first port. A second step in which the first light group is branched to the root of
A third step in which a second light group is configured from the first light group propagating through the first route by the nonlinear medium and means for attenuating the predetermined frequency band;
A fourth step in which a third light group is constructed from the first light group propagating through the second route by the nonlinear medium and means for attenuating the predetermined frequency band;
Light constituting the second light group input to the second port of the optical coupler and light constituting the third light group input to the first port of the optical coupler And a fifth step of branching to a predetermined port by interference with the optical coupler. (1)
(Supplementary note 2) The wavelength conversion method according to supplementary note 1, wherein
The wavelength conversion method, wherein the predetermined frequency band is a frequency band larger than the frequency of the pump light. (2)
(Supplementary note 3) The wavelength conversion method according to supplementary note 1, wherein
The wavelength conversion method, wherein the predetermined frequency band is a frequency band smaller than the frequency of the pump light. (3)
(Supplementary note 4) The wavelength conversion method according to supplementary note 1, wherein
A wavelength conversion method using four-wave mixing in the nonlinear medium. (4)
(Additional remark 5) It is the wavelength conversion method of Additional remark 1, Comprising:
A wavelength conversion method, wherein the nonlinear medium is a semiconductor optical amplifier.
(Appendix 6) A Sagnac interference system including an optical coupler and a loop-shaped optical fiber having both ends connected to the first port and the second port of the optical coupler,
A wavelength conversion device characterized in that means for attenuating a predetermined frequency band and a nonlinear medium are arranged in a loop of the loop-shaped optical fiber. (5)
(Supplementary note 7) The wavelength converter according to supplementary note 6,
The wavelength converter according to claim 1, wherein the predetermined frequency band is a frequency band larger than a frequency of the pump light.

(Appendix 8) The wavelength converter according to appendix 6,
The wavelength converter according to claim 1, wherein the predetermined frequency band is a frequency band smaller than the frequency of the pump light.

(Supplementary note 9) The wavelength converter according to supplementary note 6,
A wavelength converter characterized by being a semiconductor amplifier for a wavelength converter characterized by using four-wave mixing in the nonlinear medium.

(Appendix 10) The wavelength converter according to appendix 6,
The wavelength conversion device, wherein the nonlinear medium is a semiconductor amplifier.

It is a figure which shows the principle of an optical coupler. It is a figure which shows a Sagnac interference system. It is a figure which shows the principle of a Sagnac interference system. It is a figure which shows the 1st Example of this invention. It is a figure which shows the 1st Example and peripheral part of this invention. It is a figure which shows the module of the filter and SOA which are used in the 1st Example of this invention. It is a figure which shows the specification of the filter used in the 1st Example of this invention. It is a figure which shows quantum well SOA used in the 1st Example of this invention. It is a figure which shows the specification of Example (a) of this invention, (b), (c), (d). It is a figure which shows the Example (a) of this invention. It is a figure which shows the operation | movement step of Example (a) of this invention. It is a figure which shows the Example (b) of this invention. It is a figure which shows the Example (c) of this invention. It is a figure which shows Example (d) of this invention.

Explanation of symbols

10: First route in optical coupler 11: Second route in optical coupler 12: Optical coupler 20: Sagnac interference system 21, 23: Optical fiber 22: Optical couplers 40, 50, 100, 120, 130, 140 : Sagnac interference systems 41, 45, 51, 55: Optical fiber 42: Optical coupler 43: Non-linear medium 44: Means for attenuating a predetermined frequency band 52: Polarization maintaining directional coupler 53: SOA
54: Filter 56: Polarization controller 57: Simultaneous incidence directional coupler 58: Optical circulator
60: Module 61 composed of filter and SOA, 68: Optical fibers 62, 64, 66, 67: Lens 63: Filter 65: Non-linear medium 70: Transmission frequency region of filter (shaded portion)
80: Quantum well SOA
81: Quantum well layer 82: SCH layer 83: p-InGaAs

84: First p-InP
85: Second p-InP
86: First n-InP
87: Second n-InP
100, 120, 130, 140: Sagnac interference systems 101, 121, 131, 141: Nonlinear medium 102: Filter used in Example (a) and transmission frequency band of the filter (shaded portion)
122: Filter used in Example (b) and transmission frequency band of the filter (shaded portion)
132: Filter used in Example (c) and transmission frequency band of the filter (shaded portion)
142: Filter used in Example (d) and transmission frequency band of the filter (shaded portion)

Claims (5)

A wavelength conversion method including a step of splitting light,
A Sagnac interference system composed of an optical coupler and a loop-shaped optical fiber having both ends connected to the first port and the second port of the optical coupler is in the loop of the loop-shaped optical fiber, A Sagnac interference system including a non-linear medium and means for attenuating a predetermined frequency band, and configured by a predetermined port of the optical coupler including pump light serving as a wavelength conversion reference and signal light serving as a wavelength conversion signal. A first step in which the first light group is input;
A first route for propagating the looped optical fiber from the first port to the second port; and a second route for propagating the looped optical fiber from the second port to the first port. A second step in which the first light group is branched to the root of
A third step in which a second light group is configured from the first light group propagating through the first route by the nonlinear medium and means for attenuating the predetermined frequency band;
A fourth step in which a third light group is constructed from the first light group propagating through the second route by the nonlinear medium and means for attenuating the predetermined frequency band;
Light constituting the second light group input to the second port of the optical coupler and light constituting the third light group input to the first port of the optical coupler And a fifth step of branching to a predetermined port by interference with the optical coupler. The wavelength conversion method according to claim 1,
The wavelength conversion method, wherein the predetermined frequency band is a frequency band larger than the frequency of the pump light. The wavelength conversion method according to claim 1,
The wavelength conversion method, wherein the predetermined frequency band is a frequency band smaller than the frequency of the pump light. The wavelength conversion method according to claim 1,
A wavelength conversion method using four-wave mixing in the nonlinear medium. A Sagnac interference system including an optical coupler and a loop-shaped optical fiber having both ends connected to the first port and the second port of the optical coupler;
A wavelength conversion device characterized in that means for attenuating a predetermined frequency band and a nonlinear medium are arranged in a loop of the loop-shaped optical fiber.

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