JP2009036902A - Method and device for electromagnetically induced transparency - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for electromagnetically induced transparency for short-pulse signal light, which suppress the degradation in the waveform of signal light. <P>SOLUTION: The method for electromagnetically induced transparency for short-pulse signal light, which has a center frequency fs and a broadening width Δfs (<Δfz) of the optical frequency, includes the following steps. In a step S501, first control light at an optical frequency fp from a first light source 406 is input to a glass medium 401 whose optical transition frequencies has a distribution width of ΔFO, assuming that a center frequency is FO, wherein the center frequency fs is set to be within the range of the distribution width ΔFO and the optical frequency fp is set to fs+fz. In a consecutive step S502, second control light at an optical frequency fh from a second light source 407 is input to the glass medium 401, wherein the optical frequency fh of the second control light is swept in a range from fs-Δfs/2 to fs+Δfs/2 so as to cover the entire range of the optical frequency spectrum of the short-pulse signal light. Finally in a step S503, the first control light and the short-pulse signal light are input to the glass medium 401. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electromagnetic wave induced transmission method and apparatus, and more particularly to an electromagnetic wave induced transmission method and apparatus for short pulse signal light.

  Electromagnetically Induced Transparency (EIT) technology allows control light to be incident so as to satisfy predetermined conditions for frequency and intensity even when signal light propagating in the substance interacts strongly with the substance. This makes it possible to simultaneously satisfy the contradicting requirements of strong interaction with matter and low-loss light propagation. EIT is not only interesting as a natural phenomenon, but also a number of technologies in the field of quantum electronics, such as the realization of strong interaction between light and light through materials, and efficient light amplification that does not require the formation of inversion distributions. Application is expected (see Non-Patent Document 1).

  Particularly in recent years, EIT has made use of the fact that significant modulation occurs near the resonance frequency of the dispersion characteristics of a substance, so that the speed of propagating light can be extremely slowed down, or the phase of the light can be set as the limit of zero speed. Experimental results have also been reported in which the substance is temporarily stored in the substance without being damaged, and is read later. This is highly anticipated as enabling the storage of the quantum mechanical state of light.

  Hereinafter, the physical principle of EIT will be briefly described. FIG. 1 shows the energy levels of electrons belonging to individual atoms or ions constituting a substance through which signal light propagates. Here, the position 1 and the position 2 are two different ground states, and the position 3 is an excited state. The position 1 and the position 3 and the position 2 and the position 3 are connected by optical transition, respectively. Since the energy difference between the position 1 and the position 2 is much smaller (100 MHz to several GHz) than the optical transition frequency (several hundreds of THz), the electrons are in the position 1 at a sufficiently low temperature (about several Kelvin). In addition, it is distributed with almost equal probability in the prone position 2 and never in the prone position 3. As for the position 1 and the position 2, one energy position is a hyperfine structure interaction (interaction between the electron and the electromagnetic moment of the nucleus) or a Zeeman effect (electron magnetic moment and external magnetic field). In many cases, it is used that is divided into a plurality of positions due to the interaction between the two.

  When the optical frequency fs of the signal light is set so as to resonate with the optical transition frequency F23 between the position 2 and the level 3, the electrons are placed between the position 2 and the position 3 by the interaction with the signal light. Periodic round trips. On average, the probability of finding an electron at position 3 increases, so that the signal light undergoes considerable absorption under resonance conditions.

In order to suppress such absorption of the signal light, the control light set so that the optical frequency fp resonates with the optical transition frequency F13 between the position 1 and the position 3 is incident. Here, the quantum states (wave functions) of the electrons at the position 1, the position 2, and the position 3 are represented as | 1>, | 2>, and | 3>, respectively, and photons having the optical frequency fp are included in the control light. The quantum state of light including N is represented by | N> _ph . Due to the interaction between the electrons and the control light, the system consisting of the substance and the control light reciprocates between two quantum states | 1> | N> _ph and | 3> | N-1> _ph . The latter is a state in which electrons have absorbed one photon and transitioned from the position 1 to the level 3. The energy of these two states is equal, but because they are coupled via photo-electron interaction, the quantum state of the system is
| A> = (| 1> | N> _ph + | 3> | N-1> _ph ) / √2,
| B> = (| 1> | N> _ph- | 3> | N-1> _ph ) / √2
Will be separated into two composite states (referred to as “dressed states”) each having different energy levels E _A and E _B (see Non-Patent Document 2). Dressed state, as shown in FIG. 2, also seen to做as separated equally slightly vertically E _A and E _B by the interaction energy凖位is a control light of凖位3.

  In this state, if the optical frequency fs of the signal light is set so as to resonate with the optical transition frequency F23, the absorption of the signal light disappears. This is because the probability amplitude of the optical transition from the state | 2> to the state | A> and the probability amplitude of the optical transition from the state | 2> to the state | B> are equal in magnitude and have opposite signs. This is to cancel each other. The probability of an optical transition between the recumbent position 2 and the recumbent position 1 is extremely small and can be ignored.

  In this way, by causing the control light to enter and create a dressed state, it is possible to reduce or suppress the absorption of the signal light even under the resonance condition. In other words, when the control light and the signal light are simultaneously incident on the substance, the frequency fs of the signal light is set to the resonance frequency between the position 2 and the position 3, and the frequency fp of the control light and the frequency fs of the signal light are set. Is equal to the frequency difference F12 (= F13-F23) corresponding to the energy difference between the saddle position 1 and the saddle position 2 (the condition for developing EIT) It is called “EIT condition”). Note that the optical transition from the state | A> or | B> to | 1> is not forbidden.

  FIG. 3 shows the absorption / transmission characteristic α (imaginary part of complex refractive index) and dispersion characteristic Δn (real part of complex refractive index) of the signal light from the resonance frequency between the positions 2-3 of the optical frequency fs of the signal light. As a function of the deviation δfs. Under EIT conditions, the absorption rapidly becomes zero near the resonance frequency, and the frequency dependence of the refractive index becomes remarkable. Utilizing these characteristics, the signal light and the substance can be strongly interacted, such as controlling the propagation speed of light or enhancing the nonlinear interaction while suppressing loss (see Non-Patent Documents 3 and 4). .

  In order to actually realize EIT, as a substance for propagating signal light, a gas cell encapsulating alkali atoms, a cooled alkali atom group in which free movement is suppressed by laser cooling, or an ionic crystal doped with a large number of rare earth ions Often used. In particular, rare earth ion-doped crystals are often used recently because the spatial density of ions causing EIT is several orders of magnitude higher, the ions are spatially fixed and do not diffuse, and are solid and easy to handle. (See Non-Patent Documents 5 and 6).

S.E.Harris, “Electromagnetically induced transparency,” Physics Today, June, p.36, 1997 P. Meystre and M. Saegent III, “Elements of Quantum Optics,” Chapter 13, Springer-Verlag, 1991 S.E.Harris et al., “Nonlinear optical processes using electromagnetically induced transparency,” Physical Review Letters., 64, p.1107, 1990 L. Hau et al., “Light speed reduction to 17 meters per second in an ultracold atomic gas,” Nature, 397, p.594, 1999 Koichi Ichimura, “Electromagnetic wave induced transparency in solids”, Optics 29, 8, 2000 A.V. Turukhin et al., “Observation of Ultraslow and Stored Light Pulses in a Solid,” Physical Review Letters, 88, 023602, 2002 V.S.Zapasskii, “Optical detection of Spin-System Magnetization in Rare-Earth-Activated Crystals and Glasses,” chapter 12 in Spectroscopy of Solids Containing Rare Earth Ions edited by A.A. Kaplyanskii and R.M.Macfarlane, Elsevier Science Publishers B.V., 1987 Hiroyuki Suzuki, Masaharu Mitsunaga, "Ultra High Resolution Spectroscopy and its Applications-Spectral Hole Burning and Photon Echo", edited by IEICE, p.57, 1997

  However, when the signal light is not continuous light or pulse light with a relatively long time width but short pulse light, the conventional EIT technique cannot sufficiently realize low-loss light propagation. In order to process a large amount of information on the time axis and perform high-speed processing, it is desired to shorten the pulse time width of the signal light to at least about 1 ns, which corresponds to 1 GHz in the frequency bandwidth. In this case, in the optical spectrum, the signal light has “optical frequency spread” defined by the reciprocal of the pulse time width. Since EIT is a physical phenomenon that is sensitive to optical frequency, even if the EIT condition is satisfied at a certain optical frequency, absorption occurs at other optical frequencies included in the optical frequency spectrum, and the waveform of the signal light deteriorates.

  In the current method using an atomic gas cell, a laser cooled atom, a rare earth doped crystal, or the like, it is considered extremely difficult to widen the EIT circumference bandwidth so far. The frequency bandwidth at which EIT is possible is currently about several MHz at the maximum, which is about microseconds in terms of time width.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an electromagnetic wave induced transmission method and apparatus for short pulse signal light in which the waveform deterioration of the signal light is suppressed.

  In order to achieve such an object, the present invention described in claim 1 is an electromagnetic wave induced transmission method of short pulse signal light having a center frequency fs and an optical frequency spread Δfs, wherein a plurality of rare earth ions are doped. A cooling step of cooling a glass medium having an optical transition frequency of a center frequency FO and a distribution width ΔFO and having the center frequency fs within the range of the distribution width ΔFO to a temperature of several Kelvin, and the cooled glass Applying a magnetic field to the medium and applying a magnetic field to cause Zeeman splitting in which the average value is fz and the distribution width is Δfz greater than Δfs at the energy level of each of the plurality of rare earth ions in the 4f electron system And a first control step of inputting the first control light having the optical frequency fp to the glass medium from time T0 to T1, wherein the optical frequency fp is fs + a first control step of fz and a second control step of inputting the second control light of optical frequency fh to the glass medium from time T1 to T2, wherein the optical frequency fh is from time T1 to T2. Until the second control step swept over a range from fs−Δfs / 2 to fs + Δfs / 2, and the first control light and the short pulse signal light to the glass medium from time T2 to T3. And an electromagnetic wave induced transmission expression step that satisfies an EIT condition in the entire range of the optical frequency spectrum of the short pulse signal light.

  Further, the present invention according to claim 2 is an electromagnetic wave induced transmission method of short pulse signal light having a repetition period in which modulation frequency components are arranged at both sides centered on a carrier wave component fs at an interval of Δfm. A cooling step of cooling a glass medium doped with rare earth ions, having an optical transition frequency of a center frequency FO, a distribution width ΔFO and the carrier component fs within the distribution width ΔFO to a temperature of several Kelvin; A magnetic field applying step of applying a magnetic field to the cooled glass medium to cause Zeeman splitting in the energy level of each 4f electron system of the plurality of rare earth ions with an average value fz and a distribution width Δfz smaller than Δfm. And the first control light having a repetition period in which the modulation frequency components are arranged on both sides around the carrier wave component fp at an interval of Δfm. A first control step for inputting to the medium from time T0 to T1, wherein the carrier wave component fp is fs + fz, and modulation frequency components are arranged at both sides of the carrier wave component fs at intervals of Δfm. A second control step of inputting a second control light having a repetition period to the glass medium from time T1 to T2, and the first control light and the short pulse signal light to the glass medium from time T2. And an electromagnetic wave induced transmission expression step of inputting until T3 and satisfying the EIT condition in the entire range of the optical frequency spectrum of the short pulse signal light.

  According to a third aspect of the present invention, in the first or second aspect, the glass medium is an optical fiber.

  The present invention according to claim 4 is an electromagnetic wave induced transmission device for short pulse signal light having a center frequency fs and an optical frequency spread Δfs, wherein a plurality of rare earth ions are doped, and the optical transition frequency is the center frequency FO. A glass medium having a distribution width ΔFO, the center frequency fs being within the range of the distribution width ΔFO, a cooling device for cooling the glass medium to a temperature of several Kelvin, and a magnetic field applied to the glass medium. A magnetic field applying device that generates Zeeman splitting having an average value of fz and a distribution width of Δfz greater than Δfs at the energy level of each of the plurality of rare earth ions in the 4f electron system; a first light source that inputs first control light of fp to the glass medium, the first light source having an optical frequency fp of fs + fz, and a second light source of optical frequency fh. A second light source for inputting control light to the glass medium; an input port for inputting the short pulse signal light to the glass medium; an output port for outputting the short pulse signal light propagated through the glass medium; First control means for turning on the first light source from time T0 to T1, and second control means for turning on the second light source from time T1 to T2, wherein the optical frequency fh is set to time In synchronization with the input of the short pulse signal light, the second control means for sweeping over the range from fs−Δfs / 2 to fs + Δfs / 2 between T1 and T2, the first light source is turned on for a time T2. To T3, and electromagnetic wave induced transmission expression means for satisfying EIT conditions in the entire optical frequency spectrum of the short pulse signal light is provided.

  The present invention according to claim 5 is an electromagnetic wave induced transmission device for short pulse signal light having a repetition period in which modulation frequency components are arranged at both sides centered on a carrier wave component fs at an interval of Δfm. A glass medium doped with rare earth ions and having an optical transition frequency of a center frequency FO and a distribution width ΔFO, a carrier medium component fs being in the range of the distribution width ΔFO, and a temperature of several Kelvin. And a magnetic field is applied to the glass medium, and Zeeman splitting occurs in the energy level of each of the plurality of rare earth ions in the 4f electron system with an average value fz and a distribution width Δfz smaller than Δfm. And a first light source having a repetition period in which modulation frequency components are arranged on both sides around the carrier wave component fp at an interval of Δfm. Then, the first light source having the optical frequency fp of fs + fz and the second control light having a repetition period in which the modulation frequency components are arranged at both sides around the carrier wave component fs at the interval of Δfm are input to the glass medium. A second light source, an input port for inputting the short pulse signal light to the glass medium, an output port for outputting the short pulse signal light propagated through the glass medium, and the first light source from time T0 to T1 First control means for turning on the second light source, second control means for turning on the second light source from time T1 to T2, and the first light source in synchronization with the input of the short pulse signal light And an electromagnetic wave induced transmission expression unit that is turned on from time T2 to T3 and satisfies EIT conditions in the entire optical frequency spectrum of the short pulse signal light.

  According to a sixth aspect of the present invention, in the fourth or fifth aspect, the glass medium is an optical fiber.

  According to the present invention, the EIT condition is applied to the entire optical frequency spectrum of the short pulse signal light by using semi-permanent hole burning by the first and second control lights for the glass medium doped with a plurality of rare earth ions. By satisfying the above, it is possible to provide an electromagnetic wave induced transmission method and apparatus for short pulse signal light, in which the waveform deterioration of the signal light is suppressed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the principle of the present invention will be described, and then Embodiments 1 and 2 will be described.
(Principle of the present invention)
In the present invention, a glass medium doped with rare earth ions is used as a substance for propagating short pulse signal light. When rare earth ions are doped in a solid, the energy splitting magnitude δEz due to the Zeeman effect differs for each rare earth ion due to subtle differences in the local local molecular electric field. Energy splitting due to the Zeeman effect is expressed as δEz = G · H where H is the strength of the applied magnetic field and G is the proportionality coefficient.
As shown, a distribution occurs in the proportionality constant G. When a rare earth ion is doped into a glass medium having a disordered structure of atoms and ions among solids, orbital angular momentum of 4f electrons and spin (or combined angular momentum combined with orbital angular momentum and spin) behave in the periphery. It is strongly influenced by the local molecular electric field. In this case, it has been experimentally known that the average frequency fz corresponding to the energy split δEz and the statistical distribution width Δfz have the same magnitude (see Non-Patent Document 7). The average value fz can be adjusted almost arbitrarily according to the strength of the magnetic field. As the average value fz changes, the distribution width Δfz also changes.

  As shown in FIG. 1, when two ground states splitted by Zeeman are used as the potential position 1 and the stress position 2, in a glass medium doped with rare earth ions, the energy difference between the levels 1-2 has a distribution width of Δfz. Have. Therefore, even if the optical frequency fp of the control light is fixed to a certain value, a width of ± Δfz / 2 is allowed for the optical frequency fs of the signal light that satisfies the EIT condition. Since the distribution width Δfz can be adjusted to about several GHz by the magnetic field strength H, the EIT condition is satisfied over the entire range of the optical frequency spectrum of the signal light even for a short pulse signal light having a frequency bandwidth of about 1 GHz. It becomes possible.

  In the case of a conventional substance rather than a glass medium doped with rare earth ions, the distribution width Δfz of the energy split δEz does not become as large as that of the glass medium, and satisfies the EIT condition over the entire optical frequency spectrum of the pulse signal light. Since this is not possible, the waveform of the signal light deteriorates.

(Embodiment 1)
FIG. 4 shows an apparatus for carrying out the electromagnetic wave induced transmission method according to the first embodiment. The apparatus 400 includes a glass medium 401 doped with a plurality of rare earth ions, a cooling apparatus 402 that cools the glass medium 401 to a temperature of several Kelvin, a magnetic field applying apparatus 403 that applies a magnetic field to the glass medium 401, and a center frequency fs. , An input port 404 for inputting a short pulse signal light having an optical frequency spread Δfs to the glass medium 401, an output port 405 for outputting the short pulse signal light propagated through the glass medium 401 to the outside, and a first optical frequency of fp. The first light source 406 that inputs the control light to the glass medium 401, the second light source 407 that inputs the second control light having an optical frequency of fh to the glass medium 401, the first light source 406 and the second light source 406 And a synchronization control unit 408 that controls the light source 407 in synchronization.

  The optical transition frequency of the glass medium 401 has a distribution width of ΔFO with the center frequency as FO. This is because the local environment is slightly different for each rare earth ion as in the distribution of Zeeman splitting described above. The center frequency FO is several hundred THz, and the distribution width ΔFO is several THz. When a magnetic field is applied, Zeeman splitting occurs for each guest ion in the glass medium 401, but the optical transition frequency distribution is hardly changed. The center frequency fs of the short pulse signal light is set so as to fall within the range of the distribution width ΔFO.

  The cooling device 402 can be a cryostat made of liquid helium, for example. The synchronization control unit 408 functions as means for executing the steps described below.

Hereinafter, the electromagnetic wave induced transmission method according to the present embodiment will be described with reference to FIGS.
First, a cooling step for cooling the glass medium 401 to a temperature of several Kelvin and a magnetic field application step for applying a magnetic field to the glass medium 401 are executed.

  Consider the ground state and excited state of the 4f electron system of rare earth ions doped in the glass medium 401 (hereinafter, the doped rare earth ions are referred to as “guest ions”). The ground state is Zeeman split into level 1 and level 2 by the magnetic field applied by the magnetic field application device 403. Excited position 3 is also split by the Zeeman effect, but only the lowest energy position is considered as position 3 for simplicity of explanation. As described in the principle of the present invention, the level 2 is distributed with the distribution width Δfz having the same size as the average value fz of the frequency corresponding to the energy difference between the levels 1-2 (FIG. 6). (A)). The magnitude H of the magnetic field is set so that the distribution width Δfz is larger than the optical frequency spread Δfs.

  In step S501 (corresponding to the first control step), first control light having an optical frequency of fp is input from the first light source 406 to the glass medium 401 from time T0 to time T1. The optical frequency fp is set to fs + fz. FIG. 6 shows the phenomenon that occurs during step S501.

  When the first control light is input, a group of guest ions A in which the resonance frequency F13 of the optical transition between the positions 1-3 is coincident with the optical frequency fp is optically excited (FIG. 6A). When the input of the first control light is continued until time T1, electrons existing at level 1 of the guest ion group A pass through excitation to the subordinate position 3 and subsequent deexcitation, and from the prone position 1 to the subordinate position 2 (FIG. 6B). At the same time, in another group of guest ion groups C in which the resonance frequency F23 of the optical transition between the positions 2-3 matches the optical frequency fp, the electron distribution shifts from the position 2 to the level 1 (FIG. 6 (c)).

  When the transition of the electron distribution is completed in this way, there are no electrons that can absorb the light with the optical frequency fp under the resonance condition, and the glass medium 401 loses optical activity with respect to the light with the frequency fp. As described in the background art, the electronic states at the position 1 and the position 2 are stable at a temperature of several Kelvin, and this state is maintained for a while. The appropriate temperature depends on the glass medium used. Thus, the so-called “semi-permanent hole burning” means that a hole having zero absorption due to the disappearance of optical activity is vacated on the absorption spectrum and the hole lasts for a long time (see Non-Patent Document 8). For example, in the case of erbium (Er) ions doped in a glass medium, it is estimated that the stabilization time ranges from several tens of seconds to several minutes.

  Next, in step S502 (corresponding to the second control step), the second control light having the optical frequency fh is input from the second light source 407 to the glass medium 401 from time T1 to time T2. FIG. 7 shows the phenomenon that occurs during step S502.

  The optical frequency fh of the second control light is continuously swept within the range from the minimum value fs−Δfs / 2 to the maximum value fs + Δfs / 2 so as to cover the entire range of the optical frequency spectrum of the short pulse signal light ( FIG. 5). By this operation, in the group of guest ion groups B having the resonance optical frequency of the optical transition between the supine positions 2-3 in the range of fs−Δfs / 2 to fs + Δfs / 2, optical excitation to the supine position 3 and subsequent deexcitation are performed. After that, the electron distribution shifts from the position 2 to the position 1 (FIG. 7A). Similarly, in another group of guest ion groups D having the resonant optical frequency of the optical transition between the positions 1-3 in the above frequency range, the electron distribution shifts from the position 1 to the position 2 (FIG. 7). (B)). When the transition of the electron distribution is completed in this way, there are no electrons that can absorb light having an optical frequency of fs−Δfs / 2 to fs + Δfs / 2 under resonance conditions. Lose optical activity. Considering a group of guest ion groups AB that form a common subset of the guest ion group A and the guest ion group B, the electron distribution is shifted from the position 2 to the position 1 by irradiation of the second control light, and the optical frequency fp. The optical activity of the first control light is restored (FIG. 8). Although FIG. 5 shows that the sweep in step S502 is performed from fs + Δfs / 2 toward fs−Δfs / 2, it is not intended to limit to such a mode.

  Finally, in step S503 (corresponding to the electromagnetic wave induced transmission expression step), the first control light having the optical frequency fp and the short pulse signal light having the optical frequency spread Δfs are input to the glass medium 401 from time T2 to T3. To do. By the input of the first control light, the position 1 and the position 3 are combined only in the guest ion group AB to form a dressed state. Since the short pulse signal light satisfies the first control light and the EIT condition in the entire range of the optical frequency spectrum, it is possible to realize electromagnetic wave induced transmission of the short pulse signal light while suppressing the waveform deterioration of the signal light.

  On the other hand, other guest ion groups remain optically inactive not only for the first control light but also for the pulse signal light, and the interaction between the control light and electrons and the pulse signal light and electrons. Interaction with is turned off. Therefore, no extra light absorption occurs due to the guest ion group deviating from the EIT condition. In this way, an ideal situation for EIT expression is realized.

  The synchronization control unit 408 synchronously controls on / off of the first light source 406 and the second light source 407 in executing steps S501 and S502. In step S503, the first light source 406 is turned on / off in synchronization with the input of the short pulse signal light. The duration of the state of step S503 in which the ideal situation for EIT expression is realized is limited by the stable duration τ of the saddle position 1 and the saddle position 2 of the guest ion. It is assumed that the steps S501 to S503 are repeated periodically in a slightly short time.

  By using an optical fiber as the glass medium 401, it is possible to propagate a relatively long distance while satisfying the EIT condition, and to effectively enhance the effect of propagation delay and the nonlinear optical effect.

  In addition, there is an error in the setting accuracy of the optical frequency of the laser light, and it is generally difficult to satisfy the EIT condition with the conventional electromagnetic wave induced transmission method. However, according to the electromagnetic wave induced transmission method according to the present embodiment, By adjusting the magnitude H of the magnetic field to be generated, the optical frequency range (band) in which EIT occurs can be made sufficiently wide.

  Although the electromagnetic wave induced transmission method according to the present embodiment has been described above, since the synchronization control unit 408 functions as a unit that executes steps S501 to S503, the synchronization control unit 408 functions as such in the present invention. It is intended to include an electromagnetically induced transmission device.

(Embodiment 2)
The electromagnetic wave induced transmission method according to the second embodiment is an electromagnetic wave induced transmission method of short pulse signal light having a repetition period.

  For example, when the repetition period T = 0.1 ns and the pulse time width ΔT = 10 ps, the optical frequency spectrum of this signal light is centered on the carrier component fs corresponding to the average value of the short pulse signal light intensity over the repetition period T. The modulation frequency components are arranged on both sides at intervals of Δfm. In this case, Δfm is about 1 / T = 10 GHz, and the optical frequency spread Δfs is about 1 / ΔT = 100 GHz. Such signal light can be regarded as a set of modulation frequency components, each of which can be regarded as a monochromatic spectrum (see FIG. 9A).

  In the electromagnetic wave induced transmission method according to the first embodiment, the optical frequency spread Δfs can be allowed to about several GHz by adjusting the strength H of the applied magnetic field as described above in the principle of the present invention. However, when the signal light repetition period T is less than 1 ns and Δfm is about 10 GHz or more, the EIT condition cannot be satisfied for two or more spectral components by adjusting the strength H of the magnetic field.

  Therefore, in the electromagnetic wave induced transmission method according to the present embodiment, the first control light and the second control light are used to satisfy the EIT condition for each optical frequency spectrum component (carrier wave component and modulation frequency component) of the short pulse signal light. As the light, a short pulse light having a spectrum shape similar to that of the signal light and having a repetition period is used.

  FIG. 9B shows an optical frequency spectrum of the first control light. The first control light is obtained by shifting the optical frequency spectrum of the short pulse signal light in the positive direction by fz, and the carrier wave component fp is fs + fz. The strength of the magnetic field is adjusted so that the values of fz and Δfz are smaller than the basic modulation frequency Δfm. If fz and Δfz exceed the frequency interval Δfm, hole burning for each modulated bundle band component of the signal light will not function effectively. This is because rare earth ions are prepared so that the transition between levels 2-3 resonates with fs + kΔfm (k is an integer) and the transition between levels 1-3 resonates with frequency fs + (k + 1) Δfm. is there. In this case, absorption for the modulated bundle wave component having the frequency fs + (k + 1) Δfm does not disappear. Since this applies to all values of k, the efficiency of hole burning for each modulation frequency component of the signal light is significantly reduced. It is sufficient to use the same second control light as the short pulse signal light.

  In this way, by making only the guest ion group that satisfies the EIT condition for each optical frequency spectrum component optically active, EIT for short pulse signal light having a repetition period becomes possible. This will be described in more detail below.

  FIG. 10 shows an apparatus for carrying out the electromagnetic wave induced transmission method according to the second embodiment. The apparatus 1000 includes a glass medium 401 doped with a plurality of rare earth ions, a cooling apparatus 402 that cools the glass medium 401 to a temperature of several Kelvin, a magnetic field applying apparatus 403 that applies a magnetic field to the glass medium 401, and a carrier wave component fs. And the input port 1004 for inputting a short pulse signal light having a repetition period to the glass medium 401 and the short pulse signal light propagating through the glass medium 401 are output to the outside. An output port 1005, a first light source 1006 for inputting a first control light having a repetition period, in which modulation frequency components are arranged at intervals of Δfm on both sides around the carrier wave component fp, and the carrier wave component fs are input to the glass medium 401. A second control light having a repetition period in which modulation frequency components are arranged at both sides as a center at an interval of Δfm. Comprising a second light source 1007 to be input to the lath medium 401, and a synchronization control unit 1008 for controlling synchronization of the first light source 1006 and the second light source 1007.

  The optical transition frequency of the glass medium 401 has a distribution width of ΔFO with the center frequency as FO. The center frequency FO is several hundred THz, and the distribution width ΔFO is several THz. When a magnetic field is applied, Zeeman splitting occurs for each guest ion in the glass medium 401, but the optical transition frequency distribution is hardly changed. The carrier component fs of the short pulse signal light is set so as to fall within the range of the distribution width ΔFO. Since the distribution width ΔFO is as large as several THz, many modulation frequency components can be included.

  The cooling device 402 can be a cryostat made of liquid helium, for example. The synchronization control unit 1008 functions as means for executing the steps described below.

  Hereinafter, the electromagnetic wave induced transmission method according to the present embodiment will be described with reference to FIGS.

  First, a cooling step for cooling the glass medium 401 to a temperature of several Kelvin and a magnetic field application step for applying a magnetic field to the glass medium 401 are executed. The magnitude H of the magnetic field is set so that the average value fz of frequency corresponding to Zeeman splitting and the distribution width Δfz are smaller than the basic modulation frequency Δfm. If Δfm is too small, the proportion of rare earth ions that do not have a sufficient energy difference between levels 1-2 increases, and the effect of hole burning is expected to decrease. And

  In step S1101, (corresponding to the first control step), from time T0 to T1, modulation frequency components are arranged at intervals of Δfm from the first light source 1006 around the carrier wave component fp. 1 control light is input to the glass medium 401. The carrier wave component fp is set to fs + fz. When the first control light is input, hole burning occurs on the same principle as described in the first embodiment, and the glass medium 401 loses optical activity with respect to light having the optical frequency fp ± kΔfm (k is an integer). .

  Next, in step S1102 (corresponding to the second control step), from time T1 to T2, the second light source 1007 has a repetition period in which modulation frequency components are arranged at intervals of Δfm on both sides centering on the carrier wave component fs. The control light is input to the glass medium 401. When the second control light is input, hole burning occurs on the same principle as described in the first embodiment, and the glass medium 401 loses optical activity with respect to light having the optical frequency fs ± kΔfm (k is an integer). In step S1101, in the atomic group that has lost the optical activity between the levels 1-3, the optical activity with respect to the first control light is restored.

  Finally, in step S1103 (corresponding to the electromagnetic wave induced transmission expression step), the first control light and the short pulse signal light are input to the glass medium 401 from time T2 to T3. The dressed state is formed by the input of the first control light, and the short pulse signal light satisfies the first control light and the EIT condition in the entire range of the optical frequency spectrum. Therefore, it is possible to realize electromagnetic wave induced transmission of short pulse signal light while suppressing waveform deterioration of signal light.

  The synchronization control unit 1008 synchronously controls on / off of the first light source 1006 and the second light source 1007 in executing steps S1001 and S1002. In step S1003, the first light source 1006 is turned on / off in synchronization with the input of the short pulse signal light. The time for which the state of step S1003 in which an ideal situation for EIT expression is realized is limited by the stable duration τ of the position 1 and the position 2 of the guest ion. It is assumed to be used such that steps S1001 to S1003 are periodically repeated in a slightly short time.

  By using an optical fiber as the glass medium 401, it is possible to propagate a relatively long distance while satisfying the EIT condition, and to effectively enhance the effect of propagation delay and the nonlinear optical effect.

  Although the electromagnetic wave induced transmission method according to the present embodiment has been described above, the synchronization control unit 1008 functions as a unit that executes steps S1001 to S1003. Therefore, in the present invention, the synchronization control unit 1008 functions as such. It is intended to include an electromagnetically induced transmission device.

It is a figure which shows the energy level of the electron which belongs to each atom or ion which comprises the substance which signal light propagates. It is a figure for demonstrating a dressed state. It is a figure which shows the absorption transmission characteristic (alpha) and dispersion | distribution characteristic (DELTA) n of signal light as a function of the shift | offset | difference (delta) fs from the resonant frequency between the crest 2-3 of the optical frequency fs of signal light. It is a figure which shows the apparatus for implementing the electromagnetic wave induction transmission method which concerns on Embodiment 1. FIG. It is a figure for demonstrating the flow of the step of the electromagnetic wave induction transmission method which concerns on Embodiment 1. FIG. It is a figure for demonstrating a 1st control step. It is a figure for demonstrating a 2nd control step. It is a figure for demonstrating a 2nd control step. It is a figure for demonstrating the short pulse signal light which concerns on Embodiment 2, and 1st control light. It is a figure which shows the apparatus for enforcing the electromagnetic wave induction transmission method which concerns on Embodiment 2. FIG. It is a figure for demonstrating the flow of the step of the electromagnetic wave induction transmission method which concerns on Embodiment 2. FIG.

Explanation of symbols

400 Electromagnetic wave induced transmission device 401 Glass medium 402 Cooling device 403 Magnetic field applying device 404 Input port 405 Output port 406 First light source 407 Second light source 408 Synchronization control unit (first control means, second control means, and electromagnetic wave) Compatible with induced permeation means)
1000 Electromagnetic wave induced transmission device 1004 Input port 1005 Output port 1006 First light source 1007 Second light source 1008 Synchronization control unit (corresponding to first control means, second control means, and electromagnetic wave induced transmission expression means)

Claims (6)

An electromagnetic wave induced transmission method of a short pulse signal light having a center frequency fs and an optical frequency spread Δfs,
Cooling for cooling a glass medium doped with a plurality of rare earth ions, having an optical transition frequency of a center frequency FO, a distribution width ΔFO, and the center frequency fs within the range of the distribution width ΔFO to a temperature of several Kelvin Steps,
A magnetic field is applied to the cooled glass medium, and the Zeeman splitting in which the average value is fz and the distribution width is Δfz larger than Δfs is applied to the energy level of each of the plurality of rare earth ions in the 4f electron system. Applying a magnetic field,
A first control step of inputting a first control light having an optical frequency fp to the glass medium from time T0 to T1, wherein the optical frequency fp is fs + fz;
In the second control step, the second control light having the optical frequency fh is input to the glass medium from the time T1 to T2, and the optical frequency fh is fs−Δfs / 2 between the times T1 and T2. And a second control step swept over a range from fs + Δfs / 2,
An electromagnetic wave induced transmission expression step of inputting the first control light and the short pulse signal light to the glass medium from time T2 to T3 and satisfying an EIT condition in the entire range of the optical frequency spectrum of the short pulse signal light; An electromagnetic wave induced transmission method comprising: An electromagnetic wave induced transmission method of a short pulse signal light having a repetition period in which modulation frequency components are arranged on both sides around a carrier wave component fs at intervals of Δfm,
Cooling for cooling a glass medium doped with a plurality of rare earth ions, having an optical transition frequency of a center frequency FO, a distribution width ΔFO, and a carrier component fs within the distribution width ΔFO to a temperature of several Kelvin Steps,
A magnetic field applying step of applying a magnetic field to the cooled glass medium to cause Zeeman splitting in the energy level of each 4f electron system of the plurality of rare earth ions with an average value fz and a distribution width Δfz smaller than Δfm. When,
A first control step of inputting, to the glass medium from time T0 to time T1, first control light having a repetition period in which modulation frequency components are arranged on both sides with a carrier wave component fp at the center at intervals of Δfm, A first control step in which the carrier wave component fp is fs + fz;
A second control step of inputting a second control light having a repetition period in which modulation frequency components are arranged on both sides around the carrier wave component fs into the glass medium from time T1 to time T2,
An electromagnetic wave induced transmission expression step of inputting the first control light and the short pulse signal light to the glass medium from time T2 to T3 and satisfying an EIT condition in the entire range of the optical frequency spectrum of the short pulse signal light; An electromagnetic wave induced transmission method comprising:   The electromagnetic wave induced transmission method according to claim 1, wherein the glass medium is an optical fiber. An electromagnetic wave induced transmission device for short pulse signal light having a center frequency fs and an optical frequency spread Δfs,
A glass medium doped with a plurality of rare earth ions and having an optical transition frequency of a center frequency FO and a distribution width ΔFO, and a center frequency fs within the range of the distribution width ΔFO;
A cooling device for cooling the glass medium to a temperature of several Kelvin;
Applying a magnetic field to the glass medium, a magnetic field that causes Zeeman splitting at an energy level of the 4f electron system of each of the plurality of rare earth ions having an average value of fz and a distribution width of Δfz greater than Δfs. An application device;
A first light source that inputs first control light having an optical frequency fp to the glass medium, wherein the optical frequency fp is fs + fz;
A second light source for inputting second control light having an optical frequency fh to the glass medium;
An input port for inputting the short pulse signal light to the glass medium;
An output port for outputting the short pulse signal light propagated through the glass medium;
First control means for turning on the first light source from time T0 to T1,
The second control means for turning on the second light source from time T1 to T2, wherein the optical frequency fh ranges from fs−Δfs / 2 to fs + Δfs / 2 between times T1 and T2. A second control means for sweeping over,
Synchronously with the input of the short pulse signal light, the first light source is turned on from time T2 to T3, and electromagnetic wave induced transmission expression means for satisfying EIT conditions in the entire optical frequency spectrum of the short pulse signal light is provided. An electromagnetic wave induced transmission device comprising: An electromagnetic wave induced transmission device for short pulse signal light having a repetition period in which modulation frequency components are arranged on both sides around a carrier wave component fs at intervals of Δfm,
A glass medium doped with a plurality of rare earth ions, having an optical transition frequency of a center frequency FO, a distribution width ΔFO, and a carrier wave component fs within the range of the distribution width ΔFO;
A cooling device for cooling the glass medium to a temperature of several Kelvin;
A magnetic field applying device that applies a magnetic field to the glass medium and causes Zeeman splitting in the energy level of each 4f electron system of the plurality of rare earth ions to have an average value fz and a distribution width Δfz smaller than Δfm;
A first light source having a repetition period in which modulation frequency components are arranged on both sides with a carrier wave component fp as a center, and the optical frequency fp is fs + fz;
A second light source for inputting a second control light having a repetition period to the glass medium, in which modulation frequency components are arranged at intervals of Δfm on both sides around the carrier wave component fs;
An input port for inputting the short pulse signal light to the glass medium;
An output port for outputting the short pulse signal light propagated through the glass medium;
First control means for turning on the first light source from time T0 to T1,
Second control means for turning on the second light source from time T1 to time T2,
Synchronously with the input of the short pulse signal light, the first light source is turned on from time T2 to T3, and electromagnetic wave induced transmission expression means for satisfying EIT conditions in the entire optical frequency spectrum of the short pulse signal light is provided. An electromagnetic wave induced transmission device comprising:   The electromagnetic wave induced transmission device according to claim 4, wherein the glass medium is an optical fiber.

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