JP3990935B2 - Optical delay device and optical delay method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical delay device and an optical delay method.
[0002]
[Prior art]
Conventionally, in the field of optical communication, various techniques have been proposed for delaying a signal by a desired time.
[0003]
For example, Japanese Patent Laid-Open No. 10-41951 proposes a method of preparing a plurality of optical fibers having different lengths and selecting an optical fiber that allows a signal to pass according to a desired delay time. In this document, by setting the length of each optical fiber to a constant multiple of a certain length, the delay time is selected from a constant multiple of a predetermined unit time.
[0004]
On the other hand, Japanese Patent Application Laid-Open No. 11-231142 proposes a method for realizing a desired delay time by preparing an optical fiber having a predetermined length and changing its effective optical path length. In this document, the delay time is adjusted by changing the effective optical path length by applying stress or heat to an optical fiber wound around a bobbin or the like and installed in a coil shape.
[0005]
However, in the former method, it is necessary to prepare the same number of optical fibers as the number of types of desired delay times, which causes a problem that the apparatus becomes large. There is also a problem that the delay time can be selected only from one of the predetermined types.
[0006]
In the latter method, when it is desired to increase the delay time, it is necessary to increase the length of the optical fiber, resulting in a problem that the apparatus becomes larger. In addition, there is a problem that the operation speed is slow.
[0007]
[Problems to be solved by the invention]
Therefore, in such an optical signal delay technology, a new technology that can cope with the above-described problem, in particular, a technology suitable for realizing an optical buffer function that can extract a delayed signal at a desired timing. Is always sought.
[0008]
The present invention has been made to solve the above-described problems, and an object thereof is to provide an optical delay device and an optical delay method.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the following invention is disclosed in accordance with the principle of the present invention.
[0010]
An optical delay device according to a first aspect of the present invention delays signal light with control light, includes an optical waveguide portion and a medium portion, and is configured as follows.
[0011]
That is, the optical waveguide unit receives the signal light and the control light.
[0012]
On the other hand, when the signal light is incident on the optical waveguide part, the medium part is disposed in a region where the evanescent mode exists, and the medium part has at least an intermediate level, a signal side level, There are three levels, the control side level.
[0013]
The frequency ω _p of the incident signal light is equal to the resonance frequency ω _a between the signal side level and the intermediate level.
[0014]
Further, the frequency ω _c of the incident control light is equal to the resonance frequency ω _b between the control side level and the intermediate level.
[0015]
The optical waveguide unit delays the optical pulse of the incident signal light when the control light is incident, and then stops the incident of the control light, or after a predetermined delay time has elapsed. The delayed light pulse is emitted.
[0016]
In the optical delay device of the present invention, the optical waveguide portion is a solid core portion of the optical fiber, and the medium portion is filled with the medium in a hollow portion arranged around the solid core portion of the optical fiber. Can be configured to be
[0017]
In the optical delay device of the present invention, the optical waveguide portion may be a core portion of an optical fiber, and the medium portion may be configured such that the periphery of the optical fiber is filled with the medium.
[0018]
In the optical delay device of the present invention, the core portion of the optical fiber can be configured so as to be displaced from the center of the optical fiber.
[0019]
In the optical delay device of the present invention, the optical delay device can be configured as a planar waveguide, and the medium portion can be configured such that the medium is filled around the planar waveguide. .
[0020]
In the optical delay device of the present invention, the medium is atomic vapor, molecular vapor, or liquid, and the optical delay device can be configured to fill the medium by placing the optical delay device in the medium atmosphere. .
[0021]
In the optical delay device of the present invention, the medium is an atomic vapor, a molecular vapor, a liquid, or an organic crystal, and can be configured to be sealed in the hollow portion.
[0022]
In the optical delay device of the present invention, at least one of the intermediate level, the signal side level, and the control side level can be configured to be degenerate in terms of energy.
[0023]
In the optical delay device of the present invention, at least one of the intermediate level, the signal side level, and the control side level can be configured to have a band structure.
[0024]
Further, the optical delay device of the present invention can be configured to change the predetermined delay time by adjusting the intensity of the incident control light.
[0025]
An optical delay method according to another aspect of the present invention includes an optical waveguide part and a medium part, delays signal light by control light, and includes an incident process and a control process, as follows: Constitute.
[0026]
That is, in the incident step, the signal light is incident on the optical waveguide portion.
[0027]
On the other hand, in the control step, the control light is incident on the optical waveguide portion, and the optical pulse of the incident signal light is delayed.
[0028]
Further, when the signal light is incident on the optical waveguide portion, the medium portion is arranged in a region where the evanescent mode exists, and the medium portion has at least an intermediate level and a signal side level. And the control side level.
[0029]
The frequency ω _p of the incident signal light is equal to the resonance frequency ω _a between the signal side level and the intermediate level.
[0030]
Further, the frequency ω _c of the incident control light is equal to the resonance frequency ω _b between the control side level and the intermediate level.
[0031]
Further, when the control light is incident and the optical pulse of the incident signal light is delayed and then the control light is stopped, or when a predetermined delay time has elapsed, from the medium portion, The delayed light pulse is emitted.
[0032]
The optical delay method of the present invention further includes an adjustment step and can be configured as follows.
[0033]
That is, in the adjustment step, the predetermined delay time is changed by adjusting the intensity of the incident control light.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below. In addition, embodiment described below is for description and does not limit the scope of the present invention. Therefore, those skilled in the art can employ embodiments in which each or all of these elements are replaced with equivalent ones, and these embodiments are also included in the scope of the present invention.
[0035]
(First embodiment)
FIG. 1 is a schematic diagram showing a schematic configuration of a first embodiment of an optical delay device of the present invention. Hereinafter, a description will be given with reference to FIG.
[0036]
In the optical delay device 101 shown in this figure, a hollow fiber 102 is arranged in an atomic vapor atmosphere 103.
[0037]
The hollow fiber 102 is also called a photonic crystal fiber (see Japanese Patent Application Laid-Open No. 2002-55241), a holey fiber, or the like, and a hollow (hollow part) is provided in the core part. The hollow fiber 102 is used in the field of optical pulse compression because high nonlinearity can be obtained. FIG. 2 is a cross-sectional view of the hollow fiber 102. Hereinafter, a description will be given with reference to FIG.
[0038]
In the cross section of the hollow fiber 102, the core portion 201 is disposed at the center, and the cladding portion 202 covers the periphery thereof.
[0039]
In the center of the core portion 201, a plurality of cavities (hollow portions) 203 are disposed in a pipe shape in the longitudinal direction of the fiber, and an optical waveguide portion (solid portion) 204 is disposed so as to be surrounded by the cavities 203. Yes.
[0040]
In the drawing, the size of the core portion 201 is highlighted and various aspects can be arbitrarily adopted as the size and number of each portion.
[0041]
When the hollow fiber 102 is arranged in the atomic vapor atmosphere 103, the cavity 203 is filled with the atomic vapor.
[0042]
When the optical signal passes through the optical waveguide portion 204, a part of the energy appears as an evanescent mode so as to leak into the cavity 203. Accordingly, an EIT interaction between the evanescent mode and the atomic vapor occurs.
[0043]
One end of the hollow fiber 102 is provided with signal light 104 representing a signal to be transmitted as an optical pulse. Further, control light 105 for performing delay control of the signal is given from one end of the hollow fiber. On the other hand, the emitted light 106 corresponding to the signal light 104 is emitted from the other end different from the one end of the hollow fiber 102 to which the signal light 104 is given.
[0044]
This figure shows the case where the signal light 104 and the control light 105 are given from different ends.
[0045]
Considering the case where the signal light 104 is incident while the control light 105 is not incident at all, in this case, the optical waveguide portion 204 of the hollow fiber 102 passes the signal light 104 as it is and the signal light is transmitted from the other end. 104 is emitted. Therefore, the signal light 104 is delayed by the effective optical path length of the hollow fiber 102. This is the minimum delay time. That is, the output of the emitted light 106 is delayed by a minimum delay time with respect to the input of the signal light 104.
[0046]
On the other hand, when the incidence of the control light 105 is started while the signal light 104 is incident, the group velocity of the signal light 104 propagating through the optical waveguide portion 204 is reduced by EIT. For example, even when the signal light 104 and the control light 105 face each other, the control light 105 is already incident when a certain optical pulse expressed by the signal light 104 passes through one end of the optical waveguide unit 204. If the optical waveguide 204 exists throughout the optical waveguide 204, the group velocity of the optical pulse is reduced.
[0047]
Therefore, if the incidence of the control light 105 is continued as it is, the signal light 104 is delayed by the time obtained by dividing the effective optical path length of the hollow fiber 102 at the reduced group velocity. This is the maximum delay time. That is, in this case, the output of the outgoing light 106 is delayed by the maximum delay time with respect to the input of the signal light 104.
[0048]
If the incidence of the control light 105 is stopped before the maximum delay time elapses, then the signal light 104 passes through the optical waveguide portion 204 at a normal group velocity. Therefore, by changing the timing at which the incidence of the control light 105 is stopped, the outgoing light 106 in which the delay time of the signal light 104 is freely and continuously changed from the minimum delay time to the maximum delay time is changed. Obtainable. Also, the quick response to the change of the delay time is good.
[0049]
Note that the light group velocity can be reduced to 17 m / s by using the specifications shown in the literature described later. When the maximum delay time is 500 ns, the length of the hollow fiber 102 is 8.5 μm, and the apparatus can be downsized. Further, by using an optical fiber, the optical field strength can be increased and the rabbi frequency can be increased, so that it is possible to control the delay of transmission of a short pulse signal having a wide spectral width.
[0050]
In the above embodiment, the hollow fiber 102 is disposed in the atomic vapor atmosphere 103 to fill the cavity 203 with the atomic vapor. However, a molecular vapor atmosphere that generates EIT is used, or EIT is generated. The same effect can be obtained by immersing the hollow fiber in the liquid and filling the cavity 203 with these media.
[0051]
Further, without using the atomic vapor atmosphere 103 or the molecular vapor atmosphere, an atomic vapor, molecular vapor, liquid, or organic crystal that generates EIT in the cavity 203 may be filled and sealed in advance. In this case, it can be handled in the same way as a normal optical fiber, and portability and workability can be improved.
[0052]
It is not necessary for the signal light 104 and the control light 105 to enter the optical waveguide portion 204 in the same direction. Rather, it is preferable that the signal light 104 and the control light 105 are incident in opposite directions from different ends of the optical waveguide portion 204. Further, the control light 105 may be incident / stopped from the direction orthogonal to the direction in which the signal light 104 is incident. In these cases, it is not necessary to remove the control light 105 component from the output.
[0053]
Further, the maximum delay time can be changed by adjusting the intensity of the control light 105. Therefore, errors due to manufacturing can be calibrated and compensated by adjusting the intensity of the control light 105.
[0054]
(Other embodiments)
In the above embodiment, the optical delay is controlled by filling a medium that causes EIT in the cavity 203 of the hollow fiber 102. In the present embodiment, the same effect is obtained in an eccentric fiber or a planar waveguide (planar waveguide) by appropriately arranging the optical waveguide portion.
[0055]
FIG. 3 is a cross-sectional view of an embodiment of an optical delay circuit using an eccentric fiber. Hereinafter, a description will be given with reference to FIG.
[0056]
The optical waveguide portion 302 of the eccentric fiber 301 is arranged eccentric from the center. Therefore, when an optical signal passes through the optical waveguide section 302, a region 304 (enclosed by a dotted line in the figure) in which an evanescent mode is generated further outside the cladding section 303 around the optical waveguide section 302 (outside the eccentric fiber 301). Area) will ooze out.
[0057]
Therefore, by arranging the eccentric fiber 301 in the atomic vapor atmosphere 305 that generates EIT, an optical delay can be generated as in the above embodiment.
[0058]
FIG. 4 is a cross-sectional view of an embodiment of an optical delay circuit using a planar waveguide. Hereinafter, a description will be given with reference to FIG.
[0059]
When an optical signal passes through the optical waveguide portion 402 of the planar waveguide 401, a region 404 (region surrounded by a dotted line in the drawing) where the evanescent mode oozes is outside the cladding portion 403 of the planar waveguide 401. The planar waveguide 401 is configured so as to be present (outside the planar waveguide 401). As in the case of the eccentric fiber 301, by arranging the planar waveguide 401 in an atomic vapor atmosphere 405 that generates EIT, an optical delay can be generated as in the above embodiment.
[0060]
The same effect can be obtained by immersing the eccentric fiber 301 or the planar waveguide 401 in a liquid that generates EIT or disposing it in an organic crystal.
[0061]
(Embodiment of Optical Buffer Device)
5 and 6 are schematic views showing a schematic configuration of an optical buffer device using an optical delay device. Hereinafter, a description will be given with reference to FIG.
[0062]
The optical buffer device 501 includes a schedule unit 502, a plurality of port units 503, and a sending unit 504.
[0063]
The scheduling unit 502 accepts optical signals such as optical packets, but schedules optical packets that may collide with each other.
[0064]
When buffering is necessary, the optical signal 505 and the delay time information 506 are sent to the free port unit 503.
[0065]
The port unit 503 receives the optical signal 505 and the delay time information 506. The optical signal 505 is supplied to the optical delay device 101 described above.
[0066]
The delay time information 506 is given to the drive unit 509 of the control light source 508, and the light emitted from the control light source 508 is given to the optical delay device 101 via the optical circulator 507.
[0067]
Further, the optical signal emitted from the optical delay device 101 becomes an output of the port unit 503 via the optical circulator 507.
[0068]
When the control light source 508 is not driven, a transit time is required for the minimum delay time of the optical delay device 101. On the other hand, when the control light source 508 is driven at an appropriate timing, the passage time can be increased. On the other hand, if the drive of the control light source 508 is stopped, the group velocity delay effect disappears and an optical signal is immediately emitted.
[0069]
Therefore, the optical signal can be buffered by the drive unit 509 controlling the control light source 508 so that the optical signal is emitted from the optical delay device 101 after a desired delay time has elapsed.
[0070]
The optical signal emitted from the optical delay device 101 becomes the output of the port unit 503, which is given to the sending unit 504, and the buffered optical signal is outputted from the sending unit 504.
[0071]
(Theoretical background)
The present invention realizes optical delay by utilizing the fact that the energy of an optical signal transmitted through an optical waveguide such as an optical fiber interacts with a medium by EIT (Electromagnetic Induced Transparency). Regarding EIT, documents LVHau, SEHarris, X. Dutten and C. Behroozi “Nature (London)” No. 397, pp. 594 (1999), PRHemmer, KZ Cheng and J. Kierstead “Optic Letters” Vol. 19, No.4, pp.296-298 (1994) etc. have been experimentally reported.
[0072]
FIG. 7 is an explanatory diagram illustrating conditions that cause EIT. Hereinafter, a description will be given with reference to FIG.
[0073]
A medium such as an atomic vapor, a molecular vapor, a liquid, or an organic crystal has three levels of an intermediate level 601, a signal side level 602, and a control side level 603. In order to generate EIT, the following two conditions may be satisfied.
(1) The frequency ω _{p of the} signal light is equal to the resonance frequency ω _a between the signal side level 602 and the intermediate level 601.
(2) The frequency ω _{c of the} control light is equal to the resonance frequency ω _b between the control side level 603 and the intermediate level 601.
[0074]
Note that the intermediate level 601, the signal side level 602, and the control side level 603 may or may not be degenerate in terms of energy. In addition, any of these may or may not have a band structure. Further, any of the upper and lower energy relationships of the intermediate level 601, the signal side level 602, and the control side level 603 may be higher.
[0075]
Although what is shown in FIG. 7 is called a [Lambda] -type level, even if the relationship between levels shown in FIG. 8 and FIG. Will occur.
[0076]
By satisfying such a condition, when EIT occurs, the optical delay of the present invention can be realized.
[0077]
【The invention's effect】
As described above, according to the present invention, an optical delay device and an optical delay method can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of a first embodiment of an optical delay device of the present invention.
FIG. 2 is a cross-sectional view of a hollow fiber.
FIG. 3 is a cross-sectional view of an embodiment of an optical delay circuit using an eccentric fiber.
FIG. 4 is a cross-sectional view of an embodiment of an optical delay circuit using a planar waveguide.
FIG. 5 is a schematic diagram showing a schematic configuration of an embodiment of an optical buffer device.
FIG. 6 is a schematic diagram showing details of a schematic configuration of an embodiment of an optical buffer device.
FIG. 7 is an explanatory diagram for explaining conditions that cause EIT;
FIG. 8 is an explanatory diagram for explaining conditions that cause EIT;
FIG. 9 is an explanatory diagram for explaining conditions that cause EIT.
[Explanation of symbols]
101 Optical delay circuit 102 Hollow fiber 103 Atomic vapor atmosphere 104 Signal light 105 Control light 106 Emission light 201 Core part 202 Cladding part 203 Cavity 204 Optical waveguide part 301 Eccentric fiber 302 Optical waveguide part 303 Cladding part 304 Evanescent mode region 305 Atom Steam atmosphere 401 Planar type waveguide 402 Optical waveguide section 403 Cladding section 404 Evanescent mode region 405 Atomic vapor atmosphere 501 Optical buffer device 502 Schedule section 503 Port section 504 Sending section 505 Optical signal 506 Delay time information 507 Optical circulator 508 Control light source 509 Drive unit 601 Intermediate level 602 Signal side level 603 Control side level

Claims (12)

An optical delay device that delays signal light with control light, comprising an optical waveguide portion and a medium portion,
The optical waveguide part receives the incident of the signal light and the control light,
When the signal light is incident on the optical waveguide part, the medium part is disposed in a region where the evanescent mode exists, and the medium part has at least an intermediate level, a signal side level, It has three levels of control side and
The frequency ω _p of the incident signal light is equal to the resonance frequency ω _a between the signal side level and the intermediate level,
The frequency ω _c of the incident control light is equal to the resonance frequency ω _b between the control side level and the intermediate level,
When the control light is incident, the optical waveguide part delays the optical pulse of the incident signal light, and then stops the incidence of the control light, or after a predetermined delay time has elapsed, It emits the delayed light pulse. The optical delay device according to claim 1,
The optical waveguide portion is a solid core portion of an optical fiber,
The medium portion is characterized in that a hollow portion disposed around a solid core portion of the optical fiber is filled with the medium. The optical delay device according to claim 1,
The optical waveguide portion is a core portion of an optical fiber,
The medium portion is characterized in that the medium is filled around the optical fiber. The optical delay device according to claim 3,
The core portion of the optical fiber is arranged to be shifted from the center of the optical fiber. The optical delay device according to claim 1,
The optical delay device is configured in a planar waveguide,
The medium section is characterized in that the medium is filled around the planar waveguide. The optical delay device according to any one of claims 2 to 5,
The medium is atomic vapor, molecular vapor or liquid,
The optical delay device is placed in the medium atmosphere to fill the medium. The optical delay device according to claim 2,
The medium is atomic vapor, molecular vapor, liquid, or organic crystal, and is sealed in the hollow portion. The optical delay device according to any one of claims 1 to 7,
At least one of the intermediate level, the signal side level, and the control side level is energetically degenerate. The optical delay device according to any one of claims 1 to 7,
At least one of the intermediate level, the signal side level, and the control side level has a band structure. The optical delay device according to any one of claims 1 to 7,
The intensity of the incident control light is adjusted to change the predetermined delay time. An optical delay method for delaying signal light by control light using an optical waveguide part and a medium part,
An incident step of entering the signal light into the optical waveguide portion;
A control step of causing the control light to enter the optical waveguide portion and delaying the optical pulse of the incident signal light;
With
When the signal light is incident on the optical waveguide part, the medium part is arranged in a region where the evanescent mode exists, and the medium part has at least an intermediate level, a signal side level, It has three levels of control side and
The frequency ω _p of the incident signal light is equal to the resonance frequency ω _a between the signal side level and the intermediate level,
The frequency ω _c of the incident control light is equal to the resonance frequency ω _b between the control side level and the intermediate level,
When the control light is incident and the optical pulse of the incident signal light is delayed, and then the control light is stopped, or when a predetermined delay time has elapsed, the delay from the medium portion Characterized in that a light pulse is emitted. The optical delay method according to claim 11, comprising:
A method further comprising an adjusting step of adjusting the intensity of the incident control light to change the predetermined delay time.

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