JP6907917B2 - Wavelength converter - Google Patents

Description

The present invention relates to a wavelength conversion device using a second-order nonlinear optical element.

Wavelength conversion technology is used in various application fields such as optical signal wavelength conversion in optical communication, optical processing, medical treatment, and biotechnology. The wavelength range of light that is the target of wavelength conversion ranges from the ultraviolet region to the visible region, infrared region, and terahertz region, which cannot be directly output by a semiconductor laser. Further, the wavelength conversion technology is also used in applications where a semiconductor laser cannot obtain a sufficiently high output even if the wavelength range can be directly output by the semiconductor laser. Also in the optical communication system, for example, a wavelength conversion technique is used for a wavelength conversion operation by generating a difference frequency, which will be described later, or a wavelength conversion device that performs an amplification operation using a parametric effect. _{Focusing on the material used for wavelength conversion, a periodic polarization inversion optical waveguide using lithium niobate (LiNbO 3} ), which is a second-order nonlinear material and has a large nonlinear constant, is commercially available due to its high wavelength conversion efficiency. Widely used for light sources.

In the second-order nonlinear optical effect, a wavelength conversion mechanism is used in which _{light having a wavelength λ 1} and light having a wavelength λ ₂ are input to a second-order nonlinear medium _{to generate a new wavelength λ 3.} Wavelength conversion expressed by the following equation is called sum frequency generation.

1 / λ ₃ = 1 / λ ₁ + 1 / λ ₂ Equation (1)
Further, the wavelength conversion satisfying the following equation obtained by modifying the equation (1) with _{λ 1} = λ _{2 is called the second harmonic generation.}

λ ₃ = λ _1/2 Equation (2)
Further, wavelength conversion that satisfies the following equation is called differential frequency generation.

_{1 / λ 3 = 1 / λ} 1 -1 / λ 2 Equation (3)
_{The wavelength λ 1} used when generating the difference frequency according to the above equation (3) is called excitation light, λ ₂ is called signal light, and λ ₃ is called idler light. Further, it is also possible to construct an optical parametric oscillator in which a nonlinear medium is put in a resonator and _{only λ 1 is input to generate λ 2} and λ ₃ satisfying the equation (3).

In recent years, improvements in wavelength conversion efficiency (ratio of wavelength conversion light intensity to incident light intensity) have made it possible to perform optical amplification operation by a secondary nonlinear effect in the field of communication. This optical amplifier can be amplified without deteriorating the signal-to-noise ratio of the input light by performing a phase-sensitive operation, and is expected as an optical amplifier for long-distance transmission in place of the erbium-added fiber amplifier.

Two amplification operations are known for phase-sensitive amplifiers. One is an operation using reduced parametric amplification in which a signal light and an excitation light having a wavelength half the wavelength of the signal light are input to a secondary nonlinear medium to amplify the signal light (Non-Patent Document 1). The other is an operation using non-reduced parametric amplification in which a pair of signal light and idler light and an excitation light having a wavelength that is the sum frequency of the signal light and idler light are input to amplify the signal light and idler light. (Non-Patent Document 2). The signal light and idler light pairs are generated by the above-mentioned difference frequency generation mechanism.

When the wavelength conversion technique using the second-order nonlinear optical effect is used in the communication field, the difference frequency generation and the parametric amplification are mainly used in the mechanism by the second-order nonlinear effect described above. In the differential frequency generation and parametric amplification, since the signal light and the idler light are present in the communication wavelength band of the 1.55 μm band, the excitation light is the light of the 0.78 μm band. Although the required level of this excitation light is lower than before in order to improve the wavelength conversion efficiency in recent years, it is still required to be several hundred mW to several watts.

FIG. 1 is a diagram showing a configuration of a wavelength conversion device of the prior art. The wavelength conversion device 100 inputs signal light 101 in the 1.55 μm band from the 1.55 μm band optical fiber 105 on the left side of FIG. 1, and uses two lenses 109-1 and 109-2 to transmit a waveguide type wavelength conversion element. Photocoupled to 114. Further, the excitation light 102 is input from the 0.78 μm band optical fiber 105 and is photocoupled to the wavelength conversion element 114 by the two lenses 110 and 109-2. On the side close to the wavelength conversion element 114, the lens 109-2 common to the 1.55 μm band and the 0.78 μm band is used. Further, in order to combine 1.55 μm band light and 0.78 μm band light, a dichroic mirror 113 that transmits 1.55 μm light and reflects 0.78 μm light is provided.

The 1.55 μm band light output from the output end of the wavelength conversion waveguide 115 is optically connected to the 1.55 μm band optical fiber 108 by the two lenses 111-2 and 111-1. The signal light 104 that has undergone the wavelength conversion operation (amplified) is output from the 1.55 μm band optical fiber 108. A second dichroic mirror 116 is provided in order to remove light in the 0.78 μm band from the output light of the wavelength conversion waveguide 115. In the conventional wavelength conversion device shown in FIG. 1, the 0.78 μm band light output from the wavelength conversion waveguide 115 is also optically connected to the 0.78 μm band optical fiber 107 using two lenses 111-2 and 112. Has been done. If 0.78 μm light can be separated from the output light subjected to the wavelength conversion operation by the dichroic mirror 116, it is not always necessary to connect to the optical fiber 107. As the wavelength conversion element 114, for example, a waveguide type element made of lithium niobate having a polarization inversion structure can be used.

As described above, when the wavelength conversion device of FIG. 1 is used as a phase-sensitive amplifier, the input intensity of the excitation light 102 in the 0.78 μm band of about several hundred mW to several W is required. On the other hand, the signal light 101 is usually attenuated in the transmission line at the stage of being input to the wavelength conversion device, and is input in a state where an amplification operation is required. Therefore, the light intensity of the signal light 101 is at a very small level of −10 dBm or less per wavelength. In the case of multi-wavelength input such as a wavelength division multiplexing signal, the level is the sum of the input lights for the number of wavelengths.

In the wavelength conversion device 100, excitation light in the 0.78 μm band is required in the wavelength conversion element 114 for the wavelength conversion operation, but it should not be output to the 1.55 μm band optical fiber 108 on the output side. This is because if the light in the 0.78 μm band has high light energy and high light intensity, the optical components on the rear side of the wavelength converter 100 are deteriorated. As the deterioration of the optical component, for example, the deterioration of the adhesive of the optical connector is known. Therefore, on the output side of the wavelength conversion device 100, it is necessary to block the excitation light with a second dichroic mirror 116 or the like. The wavelength converter 100 shown in FIG. 1 also has a structure in which the excitation light is guided to the 0.78 μm band optical fiber 107 at the output stage and the excitation light is blocked from the optical line of the 1.55 μm signal.

T. Umeki, O. Tadanaga, A. Takada, and M. Asobe, “Phase sensitive degenerate parametric amplification using directly-bonded PPLN ridge waveguides,” Optics Express Vol.19, No. 27, pp.6326-6332, 2011 T. Umeki, O. Tadanaga, M. Asobe, Y. Miyamoto, and H. Takenouchi, “First demonstration of high-order QAM signal amplification in PPLN-based phase sensitive amplifier,” Optics Express Vol.22, No. 3, pp.2473-2482, 2014

However, it has been confirmed that the wavelength conversion device shown in FIG. 1 still has a problem of deterioration of the optical component on the rear side of the device. The inventors noticed a phenomenon in which the optical component on the rear stage side deteriorated when using the wavelength conversion device having the configuration shown in FIG. 1, and investigated the cause. As a result, it was found that light having a wavelength of about 0.52 μm was mixed in the signal light line in the 1.55 μm band. Such light in the 0.52 μm band has a wavelength of two-thirds of the excitation light. That is, when degenerate parametric amplification is used and the signal light wavelength is λs, the excitation light wavelength is λs / 2. It was found that light having a wavelength of λs / 3, which is a sum frequency component of these two wavelengths, was emitted to a signal light line in the 1.55 μm band. Even when used for non-degenerate parametric amplification or normal differential frequency generation, the sum is centered on two-thirds of the wavelength of the excitation light due to the relationship between the signal light and idler light existing in the 1.55 μm band and the excitation light. Frequency light is generated.

In the conventional wavelength conversion device shown in FIG. 1, the excitation light and the signal light are separated by the dichroic mirror 116. The dichroic mirror 116 is configured by forming a dielectric multilayer film on the surface of, for example, a transparent glass substrate in the wavelength band used. In the case of the wavelength conversion device of FIG. 1, a non-reflective film is formed on the dichroic mirror 116 with respect to the signal light so as to transmit the signal light propagating through the wavelength conversion waveguide 115. When producing a non-reflective film, for example, a plurality of dielectrics having different refractive indexes have a structure in which these dielectric layers are laminated so that their optical lengths are one-fourth of the target wavelength. The non-reflective film having such a laminated structure is simultaneously subject to non-reflective conditions even at a wavelength one-third of the target wavelength. That is, when viewed from a wavelength of one-third of the target wavelength, the thickness of each layer of the laminated structure of a plurality of dielectric films having different refractive indexes is three-quarters of the wavelength in optical length, which is higher order. Satisfies the non-reflective film condition. Therefore, if the dichroic mirror having a structure in which the dielectric layers are laminated is used to set the non-reflective condition in the 1.55 μm band, the non-reflective condition is also obtained in the 0.52 μm band at the same time.

FIG. 2 is a diagram showing a configuration of another wavelength conversion device of the prior art. The wavelength conversion device 200 of FIG. 2 has the positions of the signal light and the excitation light exchanged as compared with the wavelength conversion device 100 of FIG. That is, the dichroic mirror 213 is configured to reflect at the wavelength of the signal light 201 and transmit at the wavelength of the excitation light 202, and the conditions of reflection and transmission in the dichroic mirror 113 of FIG. 1 are reversed. The same applies to the second dichroic mirror 216 on the output side. Since the other configurations of the wavelength converter 200 are the same as those of the wavelength converter 100 of FIG. 1, the description thereof will be omitted.

Even in the case of the configuration of the wavelength conversion device of the prior art shown in FIG. 2, in order to produce a high reflectance film with the dichroic mirrors 213 and 216, a plurality of dielectrics having different refractive indexes are each divided into four parts of the target wavelength by the optical length. The thickness of 1 is set to a structure in which these dielectric layers are laminated. At this time as well, high reflection conditions are obtained at the same time even at a wavelength that is one-third of the target wavelength. Therefore, if the dichroic mirror having a structure in which the dielectric layers are laminated is used to set the reflection condition in the 1.55 μm band, the reflection condition is simultaneously set in the 0.52 μm band.

As described above, when a dichroic mirror is designed for 1.55 μm band light for use in a conventional wavelength converter, the reflection condition is satisfied even in the 0.52 μm band if the reflection condition is 1.55 μm band light. .. Similarly, if the non-reflective condition is set for 1.55 μm band light, the non-reflective condition is satisfied even for the 0.52 μm band. That is, since transmission or reflection is set in the 0.52 μm band under the same conditions as the desired 1.55 μm band signal light, the 0.52 μm band light, which is the sum frequency light, is the 1.55 μm band light in the subsequent stage. It was mixed in the fiber. As a result, there has been a problem of deteriorating the optical component on the rear side of the wavelength converter.

The present invention has been made in view of such a problem, and an object of the present invention is to prevent sum frequency light from being mixed into a 1.55 μm band output optical fiber in a wavelength converter.

In order to achieve such an object, the present invention according to claim 1 is that an excitation light and a signal light are input, and the input signal light is attenuated and parametrically amplified, or the input is input. In a wavelength conversion device provided with a secondary nonlinear optical element that generates a difference frequency from signal light and outputs signal light from the secondary nonlinear optical element to an optical fiber, between the secondary nonlinear optical element and the optical fiber. The wavelength conversion device is further provided with an optical element that transmits the output signal light and absorbs and removes light having a wavelength of two-thirds of the excitation light.

According to the second aspect of the present invention, light having a wavelength twice that of the required excitation light and signal light are input, and a second harmonic is generated from the light having twice the wavelength to generate the excitation light. the input signal light degenerate parametric amplification, or a secondary non-linear optical element for generating a difference frequency from the input signal light, and outputs the output signal light from the second order nonlinear optical element to the optical fiber In the wavelength conversion device, an optical element that transmits the output signal light and absorbs and removes light having a wavelength of two-thirds of the excitation light is further provided between the secondary nonlinear optical element and the optical fiber. It is a wavelength conversion device characterized by being equipped.

The invention according to claim 3 is the wavelength conversion device according to claim 1 or 2 , wherein the optical element has a film on a silicon substrate that is non-reflective in the wavelength band of the signal light, and is absorbed. It is characterized by operating to remove light having a wavelength of two-thirds of the excitation light.

Preferably, the second-order nonlinear optical element is one of LiNbO ₃ , LiTaO ₃ or LiNb _(x) Ta _(1-x) O ₃ (0 ≦ x ≦ 1), or Mg, Zn, Sc, to these. It can be said that at least one selected from the group consisting of In is contained as an additive.

Preferably, the second-order nonlinear optical element can be a waveguide type and the polarization can be periodically inverted.

As described above, according to the present invention, unnecessary sum frequency light is not mixed into the signal optical fiber on the output side of the wavelength converter and the optical components in the subsequent stage are not deteriorated, so that the transmission line can be operated stably.

FIG. 1 is a diagram showing a configuration of a wavelength conversion device of the prior art. FIG. 2 is a diagram showing a configuration of another wavelength conversion device of the prior art. FIG. 3 is a diagram showing a configuration of a wavelength conversion device according to the first embodiment of the present invention. FIG. 4 is a diagram showing a configuration of a wavelength conversion device according to a second embodiment of the present invention. FIG. 5 is a diagram showing a configuration of a wavelength conversion device according to a third embodiment of the present invention. FIG. 6 is a diagram showing a configuration of a wavelength conversion device according to a fourth embodiment of the present invention.

The wavelength conversion device of the present invention includes an optical element (absorber) whose output stage transmits signal light and removes light having a wavelength of two-thirds of the excitation light. Since unnecessary sum frequency light (0.52 μm band light) is not mixed into the signal optical fiber on the output side of the wavelength conversion device, it is possible to prevent the optical components on the rear side of the wavelength conversion device from deteriorating. It is possible to operate a transmission line using a wavelength converter that is stable for a long period of time. More specifically, in the wavelength converter of the present invention, the excitation light and the signal light are input, and the input signal light is photosensitized and amplified, or a secondary frequency is generated from the input signal light. It is equipped with a nonlinear optical element and outputs the output signal light from the second-order nonlinear optical element to the optical fiber. An optical element that transmits output signal light and removes light having a wavelength of two-thirds of the excitation light is further provided between the second-order nonlinear optical element and the output optical fiber. The wavelength converter can also operate as a light sensitive amplifier. Hereinafter, the configuration and operation of the wavelength conversion device will be described in detail together with various embodiments of the wavelength conversion device of the present invention.

[First Embodiment]
FIG. 3 is a diagram showing a configuration of a wavelength conversion device according to the first embodiment of the present invention. The configuration of the wavelength conversion device 300 is the same as that of the conventional wavelength conversion device 100 shown in FIG. 1, except for the optical element 317 described later. That is, the first dichroic mirror 313 is configured to transmit the signal light 301 in the 1.55 μm band and reflect the excitation light 302 in the 0.78 μm band. The same applies to the second dichroic mirror 316. Therefore, the dichroic mirrors 313 and 316 function as selective transmission and reflection means that reflect the excitation light and transmit the output signal light between the second-order nonlinear optical element and the optical fiber. More specifically, a 45-degree mirror can be used as the dichroic mirror. Since the other components of the wavelength converter 300 are the same as those in FIG. 1, the description thereof will be omitted.

The wavelength conversion device 300 of the present invention includes an optical element 317 between a second dichroic mirror 316 on the output side of the wavelength conversion element 314 and a lens 311-1 coupled to a 1.55 μm band optical fiber 308. The optical element 317 operates so as to transmit 1.55 μm band light but block 0.52 μm band light by absorption. The optical element 317 is a light absorber in the 0.52 μm band, which is the sum frequency light of the signal light and the excitation light. Specifically, the optical element 317 is non-reflective in the 1.55 μm band with respect to a plate made of silicon. A film is applied to both sides of the board. By providing the optical element 317, the 0.52 μm band light, which is the sum frequency light of the signal light and the excitation light, is blocked on the 1.55 μm band optical fiber 308 on the output side.

Therefore, in the wavelength conversion device of the present invention, the excitation light 302 and the signal light 301 are input, and the input signal light is photosensitized and amplified, or the second-order nonlinear optics that generates a difference frequency from the input signal light. In a wavelength conversion device including the element 314 and outputting the output signal light 304 from the secondary nonlinear optical element to the optical fiber 308, the output signal light is transmitted between the secondary nonlinear optical element and the optical fiber. , It can be implemented as further provided with an optical element 317 that removes light having a wavelength of two-thirds of the excitation light.

When the output light of the 1.55 μm band optical fiber 308 on the output side was inspected, only the intensity of μW level was observed for the light in the 0.52 μm band. It was confirmed that there is no unnecessary sum frequency light that destroys the optical element in the stage after the wavelength converter 300.

[Second Embodiment]
FIG. 4 is a diagram showing a configuration of a wavelength conversion device according to a second embodiment of the present invention. The configuration of the wavelength conversion device 400 of the present embodiment is the same as that of the conventional wavelength conversion device 200 shown in FIG. 2, except for the optical element 417 described later. That is, the first dichroic mirror 413 is configured to reflect the signal light 401 in the 1.55 μm band and transmit the excitation light 402 in the 0.78 μm band. The same applies to the second dichroic mirror 416. Therefore, the dichroic mirrors 413 and 416 function as selective transmission and reflection means that transmit the excitation light and reflect the output signal light between the second-order nonlinear optical element and the optical fiber. More specifically, a 45-degree mirror can be used as the dichroic mirror. Since the other components of the wavelength converter 400 are the same as those in FIG. 2, the description thereof will be omitted.

The wavelength conversion device 400 of the present invention includes an optical element 417 between a second dichroic mirror 416 on the output side of the wavelength conversion element 414 and a lens 411-1 coupled to a 1.55 μm band optical fiber 408. The optical element 417 operates so as to transmit 1.55 μm band light but block 0.52 μm band light by absorption. The optical element 417 is an absorber of light in the 0.52 μm band, which is the sum frequency light of the signal light and the excitation light, and is specifically non-reflective in the 1.55 μm band with respect to a plate made of silicon. Films are applied to both sides of the board. By providing the optical element 417, the 0.52 μm band light, which is the sum frequency light of the signal light and the excitation light, is blocked on the 1.55 μm band optical fiber 408 on the output side. When the output light of the 1.55 μm band optical fiber 408 on the output side was inspected, only the intensity of μW level was observed for the light in the 0.52 μm band. It was confirmed that there was no unnecessary sum frequency light that would destroy the optical element on the rear side of the wavelength converter 400.

[Third Embodiment]
FIG. 5 is a diagram showing a configuration of a wavelength conversion device according to a third embodiment of the present invention. The wavelength conversion device 500 of the present embodiment is a modification of the wavelength conversion device 200 of the prior art of FIG. 2 or the wavelength conversion device 400 of the second embodiment of FIG. That is, the input directions of the signal lights 205 and 405 and the output directions of the signal lights 208 and 408 in FIGS. 2 and 4 are rotated by 90 degrees, respectively, and the input direction of the signal light 501 and the output direction of the signal light 504 are The configuration differs from that of FIGS. 2 and 4 in that it is parallel to the input direction of the excitation light 502 and the output direction of the excitation light 503, respectively. Specifically, mirrors 514 and 516 are installed between the 1.55 μm band fiber 506 and the wavelength conversion element 517, and between the 1.55 μm band fiber 507 and the wavelength conversion element 517, respectively, to return the signal light. The 1.55 μm band fibers 506 and 507 are also photocoupled in the same direction as the 0.78 μm band fibers 505 and 508. An optical element 519 is provided between the mirror 514 on the input side of the wavelength conversion element 517 and the lens 5091 coupled to the 1.55 μm band optical fiber 506. Similarly, a second optical element 520 is provided between the mirror 516 on the output side of the wavelength conversion element 517 and the lens 511-1 coupled to the 1.55 μm band optical fiber 507. The optical elements 519 and 520 are all configured to transmit signal light in the 1.55 μm band, but block light in the 0.52 μm band by absorption. Specifically, these optical elements 519 and 520 are provided with films on both sides of the plate made of silicon so as to be non-reflective in the 1.55 μm band.

The wavelength conversion device 500 of the present embodiment includes optical elements 519 and 520 that absorb unnecessary sum frequency light on both sides of the wavelength conversion element 517, but the optical element 519 on the input side is not essential. However, by making the input side and the output side of the wavelength converter 500 equivalently, the input end and the output end can be interchanged and used. Also in this embodiment, when the output light of the 1.55 μm band optical fiber 507 on the output side was inspected, only the intensity of μW level was observed for the light in the 0.52 μm band. It was confirmed that there was no unnecessary sum frequency light that would destroy the optical element on the rear side of the wavelength converter 500.

[Fourth Embodiment]
FIG. 6 is a diagram showing a configuration of a wavelength conversion device according to a fourth embodiment of the present invention. The wavelength conversion device 600 is different from the wavelength conversion devices of the respective embodiments of FIGS. 3 to 5, and the wavelength conversion element 607 does not input the excitation light of the 0.78 μm band separately from the signal light of the 1.55 μm band. The second harmonic is generated inside. In the wavelength conversion element 607, the excitation light of the 0.78 μm band is obtained from the light of the 1.55 μm band by using the second harmonic generation mechanism, and the wavelength conversion operation or the amplification operation is performed. Therefore, the wavelength converter 600 does not have an input and an output dedicated to the excitation light. The 1.55 μm band optical fiber 603 that inputs the signal light 601 from the left side of the figure is photocoupled to the wavelength conversion waveguide 608 of the wavelength conversion element 607 of the waveguide type by two lenses 605-1 and 605-2. There is. The same 1.55 μm band light as the signal light is input to the 1.55 μm band optical fiber 603 to be input. The wavelength of this light in the 1.55 μm band may be exactly the same wavelength (frequency) as the signal light 601 or may have a slightly different wavelength depending on the function of the wavelength converter 600.

The signal light of the 1.55 μm band output from the output end of the wavelength conversion waveguide 608 is optically connected to the 1.55 μm band optical fiber 604 by two lenses 606-2 and 606-1. Between the two lenses 606-2 and 606-1 at the output end, a dichroic mirror 609 that transmits signal light in the 1.55 μm band and reflects excitation light in the 0.78 μm band and a dichroic mirror 609 reflect it. An optical element 610 that absorbs the excited light is installed. Further, an optical element 611 is provided between the dichroic mirror 609 and the lens 606-2 optically coupled to the output fiber 64. The optical element 611 transmits signal light in the 1.55 μm band, but operates so as to block light in the 0.52 μm band, which is unnecessary sum frequency light, by absorption. As described above, the optical element 611 is an absorber of light in the 0.52 μm band, which is the sum frequency light of the signal light and the excitation light, and is non-reflective in the 1.55 μm band with respect to the plate made of silicon. The film may be applied to both sides of the board.

Therefore, in the wavelength conversion device of the present invention, light having a wavelength twice the required excitation light and signal light 601 are input, and a second harmonic is generated from the light having the twice the wavelength to generate the excitation light. A secondary nonlinear optical element 607 that photosensitizes and amplifies the input signal light or generates a difference frequency from the input signal light is provided, and the output signal light 602 from the secondary nonlinear optical element is provided. In the wavelength converter 600 that outputs to the optical fiber 604, the optical that transmits the output signal light between the secondary nonlinear optical element and the optical fiber and removes light having a wavelength of two-thirds of the excitation light. It can be carried out as if the element 611 is further provided.

In the wavelength conversion device 600 of the present embodiment, 1.55 μm band light having a wavelength twice that of the excitation light is incident on the 1.55 μm band optical fiber 603 on the input side with high light intensity, and the light intensity is high. Excitation light in the 0.78 μm band is obtained in the wavelength conversion element 607 by the dual harmonic generation mechanism. A wavelength conversion operation or an amplification operation can be performed by using the second harmonic generation mechanism. Also in the wavelength conversion device of the present embodiment, when the output light of the 1.55 μm band optical fiber 604 on the output side was inspected, only the intensity of μW level was observed for the light in the 0.52 μm band. It was confirmed that there was no unnecessary sum frequency light that would destroy the optical element on the rear side of the wavelength converter 600.

In the third embodiment described above, the entire device has a symmetrical configuration, and an optical element that absorbs light in the 0.52 μm band, which is unnecessary sum frequency light, is inserted on both the input side and the output side. However, also in other embodiments, an optical element that absorbs 0.52 μm band light can be similarly adopted on both the input side and the output side.

Further, in each of the above-described embodiments, a waveguide type polarized lithium niobate is used as the wavelength conversion element, but the material is not limited to this as long as it exhibits a second-order nonlinear effect. Preferably, among Lithium niobate LiNbO ₃ or lithium tantalate LiTaO ₃ , their mixed crystal LiNb _(x) Ta _(1-x) O ₃ (0 ≦ x ≦ 1), or Mg, Zn, Sc, In. The selected element may be added.

As described in detail above, according to the present invention, unnecessary sum frequency light is not mixed into the signal optical fiber on the output side of the wavelength conversion device, and the optical components on the subsequent stage side of the wavelength conversion device are not deteriorated. , The transmission line can be operated stably.

The present invention can generally be used in communication systems. In particular, it can be used for an optical communication device of an optical communication system.

100, 200, 300, 400, 500, 600 Wavelength converter 101, 104, 201, 203, 301, 304, 401, 403, 501, 504, 601, 602 Signal light 102, 103, 202, 204, 302, 303 , 402, 404, 502, 503 Excitation light 105, 108, 205, 208, 305, 308, 405, 408, 506, 507, 603, 604 1.55 band optical fiber 106, 107, 206, 207, 306, 307 , 406, 407, 505, 508 0.78 band optical fiber 114, 214, 314, 414, 517, 607 Wavelength conversion element 113, 116, 213, 216, 313, 316, 413, 416, 513 to 516, 609 Dichroic Mirror 317, 417, 519, 520, 610, 611 Optical element (absorber)

Claims (5)

An excitation light and a signal light are input, and the input signal light is attenuated and parametrically amplified, or a second-order nonlinear optical element that generates a difference frequency from the input signal light is provided, and the second-order nonlinear optical element is provided. In a wavelength converter that outputs the output signal light of
A feature is that an optical element that transmits the output signal light and absorbs and removes light having a wavelength of two-thirds of the excitation light is further provided between the secondary nonlinear optical element and the optical fiber. Wavelength converter. Light having a wavelength twice that of the required excitation light and signal light are input, and a second harmonic is generated from the light having twice the wavelength to generate the excitation light, and the input signal light is reduced parametric. In a wavelength conversion device provided with a secondary nonlinear optical element that amplifies or generates a difference frequency from the input signal light, and outputs the output signal light from the secondary nonlinear optical element to an optical fiber.
A feature is that an optical element that transmits the output signal light and absorbs and removes light having a wavelength of two-thirds of the excitation light is further provided between the secondary nonlinear optical element and the optical fiber. Wavelength converter. The optical element is characterized in that a film that is non-reflective in the wavelength band of the signal light is formed on a silicon substrate, and operates so as to remove light having a wavelength of two-thirds of the excitation light by absorption. The wavelength conversion device according to claim 1 or 2. The second-order nonlinear optical element is _{either LiNbO 3} , LiTaO ₃ or LiNb _(x) Ta _(1-x) O ₃ (0 ≦ x ≦ 1), or is composed of Mg, Zn, Sc, and In. The wavelength conversion apparatus according to any one of claims 1 to 3, wherein at least one selected from the group is contained as an additive. The wavelength conversion device according to any one of claims 1 to 4, wherein the second-order nonlinear optical element is a waveguide type, and the polarization is periodically inverted.

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