JP4644180B2 - Optical variable delay unit and optical variable delay device - Google Patents

Description

  The present invention relates to an optical variable delay unit and an optical variable delay device. More specifically, the present invention relates to an optical variable delay unit that delays and outputs signal light that is input pulse light of a specific wavelength with control light, and an optical variable delay device using the optical variable delay unit.

  There is an optical delay device that converts the wavelength of input light using a control signal and delays and outputs the wavelength-converted light (for example, Patent Documents 1 to 3). For example, the optical delay devices of Patent Documents 1 and 2 take out signal light having the same frequency as the probe light from the coupler by inputting both probe light and clockwise signal light into the optical fiber loop. Further, the signal light is passed through a plurality of high-dispersion optical fibers having different lengths through a variable wavelength optical filter, thereby obtaining a different delay amount for each high-dispersion optical fiber.

In the optical delay device of Patent Document 3, signal light is input to a loop of an optical fiber in which an FBG is arranged, and then the wavelength of the signal light is shifted by an optical SSB modulator using an electric signal. When the wavelength of the signal light deviates to a wavelength that passes through the FBG, the signal light passes through the FBG and is output. At this time, since the signal light rotates in the loop, a different delay amount is obtained by controlling the amount by which the wavelength is shifted.
JP-A-8-146479 Japanese Patent Laid-Open No. 8-248452 JP 2003-207812 A

  However, all of the above-mentioned Patent Documents 1 to 3 have a problem that the apparatus is increased in size because an optical fiber loop is used. Further, according to the optical delay devices described in Patent Documents 1 and 2, since the wavelength is converted using the dispersion characteristics of the optical fiber loop, there is a problem that the conversion efficiency is not high. Further, according to the optical delay device described in Patent Document 3, since the control signal for shifting the wavelength is an electrical signal, it is difficult to control at high speed.

  In order to solve the above-described problem, in the first embodiment of the present invention, an optical variable delay unit that outputs a signal light that is a pulsed light having a specific wavelength and that is delayed by a control light is output. When input alone, the signal light of a specific wavelength is output as it is as non-converted light, and when the signal light and control light are superimposed in time, the specific wavelength corresponds to the wavelength of the control light. A wavelength conversion element having a periodically poled structure that outputs converted light obtained by converting the wavelength of the signal light to a different conversion wavelength, and a different path length depending on the wavelengths of the non-converted light and the converted light. Accordingly, a delay unit that outputs one of the non-converted light and the converted light while being delayed with respect to the other is provided.

  According to a second aspect of the present invention, there is provided an optical variable delay device that outputs a signal light that is a pulsed light having a specific wavelength by delaying the control light with a control light. When the control light source to be output and the signal light from the signal light source are input alone, the signal light of a specific wavelength is output as it is as non-converted light, and the signal light from the signal light source and the control light from the control light source are temporally Wavelength conversion with a periodic domain-inverted structure that outputs converted light in which the wavelength of the signal light is converted to a conversion wavelength different from the specific wavelength, corresponding to the wavelength of the control light A delay unit that delays one of the non-converted light and the converted light with respect to the other by passing through different path lengths according to the wavelengths of the element and the non-converted light and the converted light; Is provided.

  The above summary of the invention does not enumerate all the necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.

  It is possible to provide an optical variable delay device that is small and can vary the delay amount at high speed.

  Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the scope of claims, and all combinations of features described in the embodiments are included. It is not necessarily essential for the solution of the invention.

  FIG. 1 is a configuration diagram of an optical variable delay device 10 that delays and outputs input pulsed light of a specific wavelength. As shown in FIG. 1, the optical variable delay device 10 includes a signal light source 20, a control light source 30, a wavelength control signal generation unit 32, a wavelength conversion unit 100, and a delay unit 200.

The signal light source 20 generates signal light 25 that is pulsed light having a specific wavelength λ ₁ with a constant pulse width and pulse interval. An example of the signal light source 20 is a pulse laser, but is not limited thereto, and may be a combination of a CW laser and a modulator. The wavelength control signal generator 32 outputs the wavelength control signal to the control light source 30. For example, a high-frequency electric signal generator provided with a variable-frequency high-frequency power source is used for the wavelength control signal generator 32. In this case, the wavelength control signal is a high-frequency electric signal. When the wavelength control signal output from the wavelength control signal generator 32 is input, the control light source 30 generates control light 35 that is pulsed light having a wavelength λ ₂ corresponding to the wavelength control signal. That is, the wavelength λ ₂ is not limited to a specific wavelength. For example, when a high-frequency electrical signal having a different frequency is output from the wavelength control signal generation unit 32 as a wavelength control signal and input to the control light source 30, the control light source 30 Then, the control light 35 having a different wavelength λ ₂ corresponding to the frequency of the high-frequency electric signal is generated. For example, a DFB laser is used as the control light source 30, but other light sources can be used as long as they can convert wavelengths.

  The wavelength conversion unit 100 includes an optical coupler 110 and a wavelength conversion element 120. The optical coupler 110 is connected to the signal light source 20 and the control light source 30 by optical fibers 71 and 72 on the input side, and is connected to the input side of the wavelength conversion element 120 on the output side. When the signal light 25 and the control light 35 are input from the signal light source 20 and the control light source 30, respectively, the optical coupler 110 multiplexes the input lights and outputs them to the wavelength conversion element 120.

FIG. 2 is a perspective view showing a structure of a PPLN (Periodically Poled LiNbO ₃ : periodic polarized lithium niobate) optical waveguide used for the wavelength conversion element 120. As shown in FIG. 2, the PPLN optical waveguide includes a LiNbO ₃ substrate 122 having a very short periodic polarization inversion structure, and an optical waveguide 124 formed on the LiNbO ₃ substrate 122 so as to cross the polarization distribution to be inverted. Have. In the wavelength conversion element 120 using such a PPLN optical waveguide, when two laser beams having different wavelengths are input with temporal overlap, the second harmonic light of one of the laser beams is generated. Further, a difference frequency light between the generated second harmonic and the other laser beam is output. The two laser beams input to the wavelength conversion element 120 are preferably TM mode linearly polarized light. For the wavelength conversion element 120, for example, LiB ₃ O ₅ , BaB ₂ O ₄ , KTiOPO ₄ , LiTaO ₃ or the like having a periodically poled structure can be used instead of such a PPLN optical waveguide.

FIG. 3 shows the respective pulses of the signal light 25 output from the signal light source 20 as pulsed light, the control light 35 output from the control light source 30 as pulsed light, and the converted signal light 45 output from the wavelength converter 100. It is a figure which compares a waveform and compares a mutual timing. As shown in FIG. 3, when the signal light 25 having the specific wavelength λ ₁ and the control light 35 having the specific wavelength λ ₂ are input to the wavelength conversion element 120, the control light among the pulse lights of the signal light 25 is input. The pulse light corresponding to each of the 35 pulse lights in time (having temporal overlap) is wavelength-converted to a wavelength λ ₃ different from the specific wavelength λ ₁ . Further, the wavelength conversion element 120 converts the pulsed light of the signal light 25 that does not temporally correspond to any of the pulsed light of the control light 35 (does not have temporal overlap) with the specific wavelength λ _1. Output as is.

Therefore, the wavelength conversion element 120 outputs the converted signal light 45 in which the pulse light having the wavelength λ ₁ that has not been wavelength-converted and the pulse light having the wavelength λ ₃ that has been wavelength-converted are mixed. Hereinafter, the pulsed light of wavelength λ ₁ that has not been wavelength-converted, that is, the signal light 25 that has been output without being wavelength-converted by the wavelength conversion element 120 is referred to as “non-converted light”. The pulsed light having the wavelength λ ₃ is referred to as “converted light”.

  The delay unit 200 includes an optical delay line 210 and an optical circulator 220. The optical circulator 220 is connected to the output side of the wavelength conversion element 120 through an optical fiber 73, and is connected to the optical delay line 210 through an optical fiber 74. An optical fiber 75 is connected to the optical circulator 220. The optical circulator 220 inputs the converted signal light 45 output from the wavelength conversion element 120 to the optical delay line 210 and guides the delay portion output light 55 reflected by the optical delay line 210 to the optical fiber 75.

  The optical delay line 210 is an optical fiber that is continuously connected to the optical fiber 74. As shown in FIG. 1, an FBG (fiber Bragg grating) 212 and an FBG 214 whose refractive index is periodically changed in the axial direction are respectively provided in the core portion of the optical delay line 210. They are formed at different positions in the direction. These FBG 212 and FBG 214 are Bragg gratings, and are given by twice the product of the refractive index of the optical fiber of the optical delay line 210 and the interval of refractive index change in the FBG 212 and FBG 214 among the input light to the optical delay line 210. Only narrowband light centered around the wavelength (hereinafter referred to as the “Bragg wavelength”) is reflected.

Here, as shown in FIG. 1, the FBG 212 and the FBG 214 are formed on the optical delay line 210 in order from the side closer to the optical fiber 74. Further, the Bragg wavelength of FBG212 is lambda _1, the Bragg wavelength of FBG214 is lambda _3. Therefore, when the converted signal light 45 is input to the optical delay line 210, the non-converted light having the wavelength λ ₁ of the converted signal light 45 is reflected by the FBG 212, and the converted light having the wavelength λ ₃ is transmitted through the FBG 212 and reflected by the FBG 214. . At this time, the path length of the converted light reflected by the FBG 214 is longer than the path length of the non-converted light reflected by the FBG 212. In addition, since the optical delay line 210 is uniform in the length direction, the above-described difference in path length is equivalent to the difference in optical path length.

FIG. 4 is a diagram showing the respective pulse waveforms of the converted signal light 45 and the delay unit output light 55 by comparing the timings thereof. As shown in FIG. 4, in the delay portion output light 55 including the non-converted light having the wavelength λ ₁ reflected by the FBG 212 and the converted light having the wavelength λ ₃ reflected by the FBG 214, the converted light is timed by Δt with respect to the non-converted light. Delay. This is because the optical delay line 210 reflects the incident converted light and non-converted light with different optical path lengths as described above.

  Here, when the FBG 214 is formed on the side near the optical fiber 74 of the optical delay line 210 and the FBG 212 is formed on the side far from the optical fiber 74, the temporal conversion of the converted light and the non-converted light in the delay unit output light 55. The delay relationship is reversed. Further, by adjusting the pulse width and pulse interval of the control light 35 and changing the ratio of the converted light included in the converted signal light 45 output from the wavelength conversion element 120, the delay included in the delay unit output light 55 is changed. The ratio of the pulsed light can be set as desired. Furthermore, the delay time of the delayed pulse light (Δt in FIG. 4) can be set as desired by changing the formation interval of the FBG 212 and the FBG 214 in the axial direction of the optical delay line 210.

  As described above, the optical variable delay device 10 according to the present embodiment converts the converted light that has been wavelength-converted by the wavelength conversion element 120 and the non-converted light that has not been wavelength-converted into the FBG 212 and the FBG 214 that correspond to the respective wavelengths in the axial direction. By reflecting with the optical delay line 210 formed at different positions, the path length of the non-converted light and the path length of the converted light are made different from each other according to the wavelengths of the non-converted light and the converted light. Thereby, one of the non-converted light and the converted light can be delayed in time with respect to the other. Therefore, since the signal light 25 can be wavelength-converted for each pulse and delayed in time, a pulse signal at a desired timing can be generated. Further, since the delay unit 200 does not include an electrical element such as an electrical circuit, signal degradation associated with optical-electrical conversion does not occur. In addition, it is also possible to form the optical variable delay unit 15 by combining the wavelength conversion unit 100 and the optical delay unit 200 that are surrounded by a dotted line in FIG.

In the above embodiment, the optical delay line 210 has the FBG 212 and the FBG 214 that reflect at two different wavelengths λ ₁ and λ ₃ arranged at different positions in the axial direction, but the configuration of the optical delay line 210 is not limited to this. Absent. As another optical delay line 210, a chirped FBG whose pitch continuously changes in the axial direction so as to reflect in a wavelength region including the wavelengths λ ₁ and λ ₃ may be used. In this case, the delay amount can be changed continuously by changing the wavelength of the converted light according to the wavelength of the control light.

  FIG. 5 is a diagram schematically showing the structure of an optical variable delay device 11 according to another embodiment. In the optical variable delay device 11, the same components as those of the optical variable delay device 10 described above are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 5, the delay unit 201 of the optical variable delay device 11 includes an AWG (arrayed waveguide grating) demultiplexer 250 and a delay line 270 coupled to the AWG demultiplexer 250. .

  The AWG duplexer 250 has a pair of slab waveguides 252 and 258 and a plurality of arrayed waveguides 254, 255, 256 and 257 arranged between them. This AWG demultiplexer 250 divides the non-converted light and the converted light included in the converted signal light 45 input from the wavelength conversion unit 100 via the optical fiber 73 according to the respective wavelengths, and slab waveguides in the subsequent stage At 258, output from a different waveguide.

  The delay line 270 includes a plurality of arrayed waveguides 274, 275, 276, 277, and a multiplexer 278. The plurality of arrayed waveguides 274, 275, 276, and 277 have different lengths. The delay line 270 inputs the respective lights output from the different waveguides of the AWG duplexer 250 to the corresponding plurality of arrayed waveguides 274, 275, 276, and 277. Output to the fiber 75. At this time, since the path length of the arrayed waveguide 274 is longer than that of the arrayed waveguide 275, for example, when converted light of the converted signal light 45 passes through the arrayed waveguide 274 and non-converted light passes through the arrayed waveguide 275, The converted light is delayed in time with respect to the non-converted light. Here, when the converted light passes through the arrayed waveguide 275 and the non-converted light passes through the arrayed waveguide 274, the temporal delay relationship between the converted light and the non-converted light in the delay unit output light 55 is reversed. As described above, the delay unit 201 of the optical variable delay device 11 can output one of the non-converted light and the converted light with a time delay with respect to the other. In addition, it is also possible to form the optical variable delay unit 16 by combining the wavelength conversion unit 100 and the optical delay unit 201 surrounded by a dotted line in FIG.

  FIG. 6 is a diagram schematically illustrating the structure of an optical variable delay device 12 according to still another embodiment. In the optical variable delay device 12, the same components as those of the optical variable delay devices 10 and 11 are given the same reference numerals, and the description thereof is omitted. As shown in FIG. 6, the delay unit 202 of the optical variable delay device 12 includes the AWG duplexer 250 shown in FIG. 6 and optical fibers 281, 282, 283, 284, connected to the AWG duplexer 250. And a multiplexer 278 connected to these optical fibers 281, 282, 283, 284. According to such a configuration, by adjusting the lengths of the optical fibers 281, 282, 283, and 284, the path length through which the non-converted light and the converted light separated by the spectroscopic unit 231 pass can be set as desired. Can do. Therefore, the optical variable delay device 12 can delay one of the non-converted light and the converted light included in the delay unit output light 55 with respect to the other by a larger time. In addition, it is also possible to form the optical variable delay unit 17 by combining the wavelength conversion unit 100 and the optical delay unit 202 that are surrounded by a dotted line in FIG.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

It is a block diagram of the optical variable delay apparatus 10 which delays and outputs the input pulsed light of a specific wavelength. ₃ is a perspective view showing a structure of a PPLN (Periodically Poled LiNbO ₃ : Periodically Polarized Lithium Niobate) optical waveguide used for the wavelength conversion element 120. FIG. It is a figure which shows each pulse waveform of the signal light 25, the control light 35, and the conversion signal light 45 by comparing mutual timing. It is a figure which compares each pulse waveform of the conversion signal light 45 and the delay part output light 55, comparing a mutual timing. It is a figure which shows typically the structure of the optical variable delay apparatus 11 which concerns on other embodiment. It is a figure which shows typically the structure of the optical variable delay apparatus 12 which concerns on other embodiment.

Explanation of symbols

10, 11, 12 Optical variable delay device, 15, 16, 17 Optical variable delay unit, 20 Signal light source, 25 Signal light, 30 Control light source, 32 Wavelength control signal generator, 35 Control light, 45 Conversion signal light, 55 Delay Part output light, 71, 72, 73, 74, 75 optical fiber, 100 wavelength conversion part, 110 optical coupler, 120 wavelength conversion element, 122 LiNbO ₃ substrate, 124 optical waveguide, 200, 201, 202 delay part, 210 optical delay Line, 212, 214 FBG, 220 Optical circulator, 230 Substrate, 231 Spectrometer, 232, 234 Optical waveguide, 252, 254 Optical fiber

Claims (7)

An optical variable delay unit that delays and outputs signal light, which is input pulse light of a specific wavelength, with control light,
When the signal light is input alone, the signal light of the specific wavelength is output as it is as non-converted light, and when the signal light and control light are temporally superimposed and input, Corresponding to the wavelength, a wavelength conversion element having a periodic polarization inversion structure that outputs converted light obtained by converting the wavelength of the signal light to a conversion wavelength different from the specific wavelength;
A delay unit that outputs one of the non-converted light and the converted light with a time delay relative to the other by passing through different path lengths according to the wavelengths of the non-converted light and the converted light, respectively. An optical variable delay unit comprising:   The wavelength conversion element includes PPLN (periodically poled lithium niobate) that outputs the converted light having a difference frequency wavelength between the second harmonic light of one of the input signal light and the control light and the other. The optical variable delay unit according to claim 1.   The delay unit is a spectroscopic unit that splits the input non-converted light and the converted light into a plurality of paths, a plurality of optical waveguides connected to each of the plurality of paths and having different path lengths, and The optical variable delay unit according to claim 1, further comprising an output unit configured to output the non-converted light and the converted light from a plurality of optical waveguides on the same path.   The optical variable delay unit according to claim 3, wherein the spectroscopic unit includes an AWG demultiplexer.   The delay unit includes an optical fiber in which a plurality of FBGs (fiber Bragg gratings) that reflect the non-converted light and the converted light are formed side by side in a passing direction of the non-converted light and the converted light. 3. The optical variable delay unit according to 1 or 2.   3. The optical variable delay unit according to claim 1, wherein the delay unit includes an optical fiber in which a chirped FBG whose pitch continuously changes is formed in a passing direction of the non-converted light and the converted light. An optical variable delay device that delays and outputs signal light, which is pulse light of a specific wavelength, with control light,
A signal light source for outputting signal light;
A control light source that outputs control light;
When the signal light from the signal light source is input alone, the signal light of the specific wavelength is output as it is as non-converted light, and the signal light from the signal light source and the control light from the control light source are timed. A periodic polarization inversion structure that outputs converted light in which the wavelength of the signal light is converted to a conversion wavelength different from the specific wavelength corresponding to the wavelength of the control light when being input in a superimposed manner A wavelength conversion element having
A delay unit that outputs one of the non-converted light and the converted light with a time delay relative to the other by passing through different path lengths according to the wavelengths of the non-converted light and the converted light, respectively. An optical variable delay device comprising:

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