JPH06310790A - Optical chaos controller - Google Patents

Abstract

PURPOSE:To control the coupling efficiency of an outer resonator in a semiconductor laser with high reproducibility by stabilizing the time series of optical intensity from a chaos state to a periodic state. CONSTITUTION:A mirror 21 disposed on the optical axis of a semiconductor laser element 1 reflects laser light from the laser element 1 on the optical axis to cause optical resonance and constitutes a resonator together with the outlet end face of the semiconductor laser element 1. A coupling efficiency regulation system 22 disposed on the outlet side optical path of laser beam in an outer resonator 2 regulates the resonant state. A light receiver 3 detects the quantity of laser light transmitted through the mirror 21 and delivers a signal to a feedback control circuit 4. The feedback control circuit 4 delivers the detection output from the light receiver 3 to the coupling efficiency regulation system 22 in the outer resonator 2 and imparts perturbation to the coupling efficiency. This constitution allows to control the time series of optical intensity from chaos state to a desired and stabilized periodic state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical chaos control device for controlling chaotic state-metastable state in optical chaos.

[0002]

2. Description of the Related Art A complex phenomenon that changes stochastically while complying with the laws of dynamics is called chaos, and has recently attracted attention in various fields such as mathematics, physics, and biology.

By the way, chaos is a phenomenon that occurs non-linearly and cannot occur linearly.

On the other hand, in the field of physics, focusing on semiconductors, the semiconductor material itself has already been studied as a non-linear optical element and is the subject of chaos research. In a non-linear optical system, optical beams having a large number of degrees of freedom such as amplitude, phase, direction, and wavelength interact in a non-linear manner, and optical chaos with complex and multidimensional light pattern generation often appears. Therefore, it has the potential to be used for optical communication and optical signal processing.

The optical chaos described here is one of the phenomena utilizing the optical nonlinearity of a semiconductor laser. Optical chaos is originally derived from a dynamic system of laser operation such as that seen in unstable oscillation of a CO ₂ laser, and unstable oscillation seen in a passive resonator in which a nonlinear optical element is arranged in a ring resonator. Mainly studied.

On the other hand, in semiconductor lasers, the problem of return light noise has been known for a long time, and it is indispensable to suppress the return light noise and operate it stably in practical use. I spend a lot of time researching control technology for that purpose, but on the other hand, I am interested in the behavior of returning optical noise being chaotic.

FIG. 20 shows a schematic configuration diagram of a composite resonator, in which LD is a semiconductor laser element and M is a mirror. The mirror M is arranged on the optical axis of the semiconductor laser element LD, and reflects the laser light from the semiconductor laser element LD on the optical axis to cause optical resonance. r1 and r2 are end faces of the semiconductor laser device, and r3 is a reflecting face of the mirror M.

When the behavior of the composite resonator configured as shown in FIG. 20 is numerically solved by the generalized Van der Pol equation, the nonlinear polarization of the active layer of the semiconductor laser device (LD) and the third-order nonlinearity are obtained. The susceptibility is

[Equation 1] Here, g ₀ is a small signal gain, and α is a parameter peculiar to a semiconductor laser, and is a ratio of variation of the refractive index n of the active layer and the gain G with respect to the carrier density N.

[Equation 2] It is represented by. This is the non-linear source in semiconductor lasers.

Here, the phase condition of the two cavities is

[Equation 3] The natural oscillation frequency ω is the frequency that satisfies the above phase condition (1).
a _{s, (1) F (φ} 0) when the right-hand side was the F (φ ₀₎ =
The frequency that satisfies 0 is the amplified spontaneous emission frequency ω _a .

The mechanism for amplifying a frequency different from the natural oscillation frequency can be explained by parametric four-wave mixing in a Kerr medium, which is a medium having a non-linear refractive index (that is, the refractive index changes), but detailed description thereof is omitted here. The results are shown in FIG.

FIG. 21 shows changes in gain due to spontaneous emission and an increase in α parameter. In FIG. 21 (b),
The horizontal axis represents the oscillation frequency, which corresponds to the deviation from the natural frequency ωs. The vertical axis is the gain. In Fig. 21 (b), since there is a maximum value of gain at a position deviating from the natural frequency ωs, there is a spontaneous amplified emission (Amplified Spontaneous Emi).
ssion) occurs. The electric field at this time is Ea, and the frequency is ωa.

As the non-linearity parameter α increases, the gain at the frequency ωa increases. Considering the resonance of such naturally amplified light, if you make a rate equation for the composite resonator,

[Equation 4] Here, N is the carrier density, Sa is the number of photons of natural amplification, Esm is the electric field of the eigenmode, m = 1, 2, β is the spontaneous emission coefficient, τ _p is the photon lifetime, and κ is the image resolution coefficient (in the case of Fabry-Perot). , Κ = (1-r ₂ ) (r3 / r2) ^1/2 c / 2
n / L _ext , n; refractive index).

FIG. 22 shows the time evolution of the output power and the change of the power spectrum with the detuning of the electric field Ea of the naturally amplified light and the eigenmode Es2 as variables. It should be noted that the number in [] shown in FIG. 22 is a dimensionless number indicating the magnitude of frequency detuning of the frequency ωa of the spontaneously amplified emission light.

There is a branch from a quasi-periodic solution to a periodic solution and chaos. According to Equation 4, ω _a and ω _{s 2} are also functions of the coupling efficiency (function of reflectance and external cavity length) of the external resonator. Therefore, by controlling these state variables, fluctuations in the output light intensity are controlled. The state of can be changed.

[0015]

As described above, in a composite resonator type light generator using a semiconductor laser device, it is necessary to control the coupling efficiency (function of reflectance and external resonator length) of the external resonator. Can change the fluctuation state of the output light intensity.

Therefore, if the information (periodic state) inherent in the chaotic state can be taken out in the composite resonator type optical communication device using the semiconductor laser element, it can be used for transmission as a multilevel signal, which is useful. is there.

However, at present, there is no method for controlling the coupling efficiency of the external resonator in the semiconductor laser device with good reproducibility.

An object of the present invention is to provide an optical chaos control device capable of controlling the coupling efficiency of an external resonator in a semiconductor laser device with good reproducibility.

[0019]

In order to achieve the above object, the present invention is configured as follows.

That is, a laser resonator, an external resonator that optically resonates the light emitted from the laser resonator and makes the time series of the light intensity chaotic, and is arranged in the external resonator to transmit light. Based on the detection output of the light control means for controlling the optical resonance efficiency by giving a change corresponding to the control signal, the light emitted from the external resonator, and the detection output of this light detection means, the chaotic state is cycled. Control means for generating a control signal that gives a predetermined time-varying perturbation that stabilizes the normal state.

[0021]

In the present apparatus having such a structure, the emitted light from the laser resonator, which is the light source, is optically resonated by the external resonator and the time series of the light intensity is chaotic. A control signal is generated from the control means to give a predetermined time-varying perturbation corresponding to the detection output of the light detection means,
The control signal controls the light control means in the external resonator. The optical control means controls the optical resonance efficiency by giving a change corresponding to the control signal to the transmitted light, and the control signal controls the chaotic state so as to stabilize it in a periodic state. The efficiency of the external resonator is controlled to stabilize the chaotic state in a periodic state. Therefore, by providing a correspondence relationship between the time-varying perturbation and the periodic state to be stabilized, switching control can be performed so as to obtain a plurality of types of periodic states.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. First, the principle of the present invention will be described.

(Principle of the Present Invention) [Periodic State Inherent in Chaotic State] To use chaos for information transmission, each periodic orbit inherent in the chaotic state is used as one of different information. There are possible forms.

Therefore, the periodic state inherent in the chaotic state is observed, and it is confirmed that the mode close to the periodic orbit is inherent in the chaotic state. This can be done by examining the statistical properties of chaotic orbits, and it is possible to confirm that there is an inherent mode close to a periodic orbit in the chaotic state.

A general method for the analysis is that the time series is a discrete sequence S _i τ, S _{(i + 1) τ} , S of time intervals τ.
_{(I + 2) τ} . ． ． (FIG. 1 (a)), and then a vector Xn = (S _nτ , S _{(n + 1) τ} S having these as components
_{(N + 2) τ} ) and define a time series in the vector space (Fig. 1 (b)). Hereinafter, this is treated as a manifold. That is, a time series discretized at time intervals τ (see FIG.
From (a)), we construct a manifold as shown in Fig. 1 (b) in the state space.

Next, the statistical properties of a three-dimensional manifold composed of time series data showing chaotic behavior will be investigated. Figure 2 (a) shows a two-dimensional projection diagram of a three-dimensional manifold constructed by the method of Figure 1 from a time series of chaotic states.

In FIG. 2, (a) is a chaotic orbit,
(b) is a trajectory of the first period included in it, (c) is a trajectory of the second period included in the chaotic orbit, and (d) is a trajectory of the third period included in the chaotic orbit.

Here, starting from a point Xi which is an arbitrary point on the chaotic orbit of FIG.

[Equation 5] (However, k is an arbitrary number). k-i = m
(Where m is the regression interval), the point Xi that satisfies the above inequality is called the recursive point of (m, ε). Examining the distribution of the recursive points, the result is as shown in FIG. 3, and a periodic distribution is observed.

Assuming that the basic period is m = 125,
(b), (c), and (d) correspond to the trajectories from the recurrence points of the first, second, and third periods, respectively. That is, as is clear from FIG. 3, it can be seen that the chaotic orbit shown in FIG. 2 (a) includes a portion close to the periodic orbit.

It should be emphasized here that both ends of such an orbit do not coincide with each other and do not converge, but temporarily fall within the range of ε. Such end points are near the saddle point.

Next, the conversion between Xi and Xi + m is linearized.

[Equation 6] , And construct the tangent vector space of the manifold. Where A
Is a matrix having the same dimension as Xi, and b is a constant vector. Here, Xi is a three-dimensional vector and A is Jaco
Replacing with the bi (Jacobi) matrix,

[Equation 7] Here, F _(Xi) formally represents the mapping from Xi to Xi + m, and F ⁽¹⁾ , F ⁽²⁾ ... are the components X ⁽¹⁾ , X ⁽²⁾ ... of Xi.
Is a scalar function that converts the. Since F _(Xi) is not given now, it has to be statistically obtained from the relationship between Xi and Xi + m for various values of i. The actual method is to calculate the average value of the tangent vectors of points adjacent to a certain reference point Xγ, assuming that the direction of the tangent vector continuously changes at any point in the manifold as shown in Fig. 2 (a). Xr
Is taken as the measured value of the tangent vector of.

At this time, in the chaotic state, the eigenvalues of the Jacobi matrix have at least one positive value and at least one negative value. In order to explain this situation graphically by omitting the detailed mathematical description, the manifold composed of the time series as described above is cut along the cross section Fc as shown in FIG. Investigate the properties and behaviors in.

Now, let the points recursive on the diagram of the Fc cross section be Xs,
Xs + 1 ... And the mapping between two adjacent points is linearized in the same manner as before to obtain the tangent vector. FIG. 5 shows the state of the tangent vector near the saddle point on the Fc sectional view. Here, the tangent vectors VA to VD follow the flow indicated by the solid line in the figure. Considering the saddle point Ps as the center, the tangent vectors VA to VD at the respective positions are components v that approach the saddle point Ps.
It can be decomposed into a, va 'and distant components vb, vb'.

Here, regarding the two curves L1 and L2 passing through the saddle point Ps, L1 corresponds to Re (λ) <0 when Re (λ) <0 when the eigenvalue of the Jacobi matrix is Exp (λ). (Λ is a Lyapunov exponent, which is an index of stability and instability), and is a curve formed by an eigenvector in a stable direction approaching the saddle point Ps, and L2 corresponds to Re (λ)> 0. , And a curve formed by an eigenvector in an unstable direction away from the saddle point Ps.

This is considered as follows. That is, if all the tangent vectors VA to VD are stable, the orbit will fall within a periodic orbit, and all the tangent vectors VA to VD.
If VD is unstable, the orbit diverges infinitely and the manifold does not fit in a finite space (definition of saddle point).

The chaos control described below can be performed by utilizing the property of the saddle point Ps.

[Chaos Control] Here, chaos control will be described geometrically. As shown in (a) of FIG. 6, when the nth data point ξn approaches the saddle point ξF (p),
As shown in (b), the perturbation amount p'is given to the control variable p, and the saddle point ξF is shifted by the perturbation amount p'to the adjusted point ξF (p + p '). In FIG. 6A, the connection vector es,
The direction of eu is the direction of the solid line, and moves along the dotted line without control. In (b) where the perturbation amount of p ′ is given, the data points ξn and ξF are related to the direction of eu.
Since the positional relationship of is reversed, the tangent vector of ξn is corrected to the lower left direction.

As a result, as shown in (c), the data points ξn
+1 is the eigenvector e formed by the original saddle point ξF (p)
ride on the curve formed by s. Thus, in order to fix ξn in the vicinity of the saddle point ξF, giving a minute perturbation to the control variable p is the main point of chaos control in the present invention.

Although such control is expressed in an algebraic form, in general, the two eigenvectors of the Jacobi matrix are not always orthogonal, so the reciprocal vector f as shown in FIG. 7 is used.
Substitute u and fs. In order to calculate the perturbation amount p ′ of the control parameter, in the present invention, the rate of change g of the saddle point with respect to the change in the perturbation amount of the control parameter is experimentally obtained in advance.

[0040]

[Equation 8] This experimentally obtained rate of change g of the saddle point and equation (8)
From the relation of

[Equation 9] Given in. Such a perturbation is a function of time, and it is always necessary to calculate the required perturbation amount at each time by the above method. FIG. 8 shows an example in which the orbit is fixed near the unstable periodic points (saddle points) of one cycle and two cycles by controlling the chaotic state using such a perturbation control method. In the figure, the horizontal axis indicates the number of times the three-dimensional manifold has passed through the cut surface,
The position is taken on the vertical axis. By controlling the chaotic state, a unique pattern as shown in FIG. 8 is obtained,
It can be seen that this can be used for transmission as information transmission content.

[Characteristics of chaos control of a system in which a dynamical system cannot be determined] Here, the main points described above are summarized as follows: 1) Whether or not the behavior is chaotic even in experimental data in which a dynamical system is not determined is investigated. be able to. 2) The control target point (saddle point) can be found by examining the statistical properties of the manifold composed of time series data. 3) By treating the time-series data as a manifold, the vector flow in the tangent space is investigated and the mapping (Jacobi matrix) that characterizes the dynamical system is obtained. 4) When the eigenvalues and eigenvectors of the Jacobi matrix and the control parameter dependence of the saddle point (Equation (8)) are obtained, the perturbation amount of the control parameter can be obtained. 5) The amount of perturbation is very small and is a time variable. That is the point.

The present invention is intended for application of information transmission by optical chaos based on nonlinear optics by applying such control in an experimental system of optical chaos based on optical nonlinearity of a semiconductor laser. An example will be described.

In the present invention, the optical output of the resonator is monitored, and the state of the resonator, that is, the natural oscillation frequency and the coupling efficiency of the external resonator are feedback-controlled to generate a metastable state from the chaotic state.

(First Embodiment) As a first embodiment, chaos control in a compound resonator of a semiconductor laser will be described.

As is apparent from the conventional example, in the composite resonator using the semiconductor laser, by giving a small perturbation to the coupling efficiency and the resonator length of the external resonator, the structure shown in FIG.
It is possible to control the chaotic state as shown in.

FIG. 9 conceptually shows a system for controlling the chaotic state by controlling the coupling efficiency and the resonator length of the external resonator by giving a slight perturbation. The following shows the method of optical chaos control based on this concept.

FIG. 9 is a schematic configuration diagram of a composite resonance type optical signal generator as a basic configuration according to the first embodiment. From the light intensity obtained by the photodetector to the state parameter of the external cavity. Is a semiconductor laser device, and 2 is an external resonator of the semiconductor laser device 1. Reference numeral 21 is a mirror forming the external resonator 2.

The mirror 21 is arranged on the optical axis of the semiconductor laser element 1, reflects the laser beam (laser beam) from the semiconductor laser element 1 on the optical axis to cause optical resonance, and at the same time, the semiconductor laser element 1 is produced. A resonator is formed between the laser light emitting end face and the. Reference numeral 22 denotes a coupling efficiency adjusting system for adjusting the resonance state, which is provided in the laser beam emitting side optical path in the external resonator 2. A half mirror is used as the mirror 21, and a part of the resonated laser light is transmitted through this mirror 21 and becomes an output laser beam to the outside.

Reference numeral 3 denotes a light receiving device including a light receiving element such as a photodiode, which detects the light amount of the laser beam emitted through the mirror 21 and is fed back to the feedback control circuit 4.
To give to. In addition, the feedback control circuit 4
Receives the detection output from the photodetector, calculates the perturbation amount for the state function of the external resonator, and gives the perturbation to the coupling efficiency adjusting system 22 of the external resonator to perform the perturbation on the coupling efficiency.

To give a perturbation to the coupling efficiency of the external resonator 2, a method of controlling the propagation efficiency of light in the resonator and a method of controlling the reflectance of the external resonator 2 can be considered.

Therefore, as the first embodiment, the former method of controlling the propagation efficiency of light will be described.

In the case of controlling the propagation efficiency, as shown in FIG. 10, a half mirror 21a for the laser beam emission path BL1 and a reflection path B are used as the mirror 21 constituting the external resonator 2.
A total reflection mirror 21b for L2 is provided. Reflection path B
The total reflection mirror 21b for L2 has a laser beam emission path BL1.
Is a mirror for returning the laser light reflected by the half mirror 21a for laser light to the emission end face side of the semiconductor laser element 1.
The half mirror 21a partially transmits the laser light emitted from the emission end face side of the semiconductor laser element 1 along the laser light emission path BL1 and emits the laser light to the outside, and partially reflects it to distribute it to the total reflection mirror 21b. .

The coupling efficiency adjusting system 22 is arranged in the laser beam emitting path BL1 between the emitting end face side of the semiconductor laser device 1 and the half mirror 21a.
2 has the following configuration.

That is, the polarizer 22a, the EOM 22b, the 1/4 λ phase plate 22c, and the semiconductor laser device 1 are sequentially arranged from the semiconductor laser device 1 side.
A polarizer 22d is provided to control the light propagation efficiency. The polarizers 22a and 22d are for polarizing light, and the EOM 22b is an electro-optical modulator, which is an element whose refractive index is changed or light absorption is changed when an electric field is applied. In this embodiment, the feedback control circuit 4 controls the EOM 22b to control the light propagation efficiency.

The 1 / 4λ phase plate 22c is for shifting the phase of the laser light by 1/4 wavelength.
A phase difference is generated between the emitted laser light and the laser light that is reflected and returned, which causes an optical chaos phenomenon.

Reference numeral 5 denotes an isolator arranged in the reflection path BL2, which is for passing light in only one direction, and blocks backward light. Reference numeral 6 denotes a Y-shaped waveguide, which is arranged on the emission end face side of the semiconductor laser device 1 and optically couples the emission end face side of the semiconductor laser device 1 with the laser light emission path BL1 and the reflection path BL2. belongs to.

Since the external resonator 2 is a ring type, the propagation direction of light is limited by the isolator 5.

In such a structure, the laser light emitted from the emission end face side of the semiconductor laser device 1 is sent out to the laser light emitting path BL1 by the Y-shaped waveguide 6 and is polarized by the polarizer 22a. 1/4 via EOM22b
The λ phase plate 22c shifts and delays the phase by a quarter wavelength, and after being polarized again by the polarizer 22d, it reaches the half mirror 21b. The half mirror 21b partially transmits the reached laser light to the outside and partially reflects the laser light to the total reflection mirror 21b.

In the total reflection mirror 21b, the reflected laser light is returned to the reflection path BL2 and is made incident on the emission end face side of the semiconductor laser device 1 from the Y-shaped waveguide 6 via the isolator 5.

By following such a path, a part of the light emitted from the semiconductor laser device 1 is returned to cause an optical resonance phenomenon with the semiconductor laser device 1. Reflection path B
Since the laser light returned at L2 has a phase difference of 1/4 wavelength from the excitation laser light from the semiconductor laser element 1, this causes the laser light in the resonance state to exhibit a chaotic state.

On the other hand, the output laser light emitted from the half mirror 21b to the outside is detected and monitored by the light receiver 3. The detection output of the photodetector 3 is sent to the feedback control circuit 4, where a perturbation amount (corresponding to equation 9) that can obtain a desired trajectory is calculated from the value, and the obtained perturbation amount is obtained. The EOM 22b is generated with a control amount that provides a necessary voltage according to the voltage-refractive index (or voltage-light absorption) characteristics of the EOM 22b.

As a result, the EOM 22b is applied with a voltage corresponding to the control amount to control the transmitted light amount, and the polarizer 22
After passing through d, the half mirror 21b is reached. Then, a part of it returns to the emission end face side of the semiconductor laser device 1 along the reflection path BL2, and the coupling efficiency of the resonance system is adjusted. As a result, the required perturbation amount can be obtained.

As described above, the first embodiment of the composite resonance type optical signal generator according to the optical propagation efficiency control system shown in FIG.
A device that performs amplitude modulation with a first-order electro-optical effect element (EOM) is placed in the external resonator, the output light from the half mirror 21b is monitored, and the perturbation amount with respect to the voltage applied to the EOM 22c is monitored from that value. 8 (corresponding to equation 9) is calculated every hour, the amount of amplitude loss of the external resonator is changed with time, the coupling efficiency of the external resonator is controlled, and according to the algorithm of equations 7 to 9 described above, It is possible to control the chaotic state in the same manner as described above.

Therefore, since it is possible to control the trajectory from the chaotic state to a desired cycle, it can be applied to information transmission by chaos control.

In the above, by arranging the polarizer and the crystal having the first-order electro-optical effect in the external resonator, the reflection efficiency of the entire external resonator is electrically controlled and the time-varying perturbation is given. It is a thing. However, it is also possible to use a nonlinear optical crystal instead of the electro-optical crystal to optically control the efficiency of the external resonator so as to give a time-varying perturbation. This example will be described below.

(Second Embodiment) The second embodiment has a structure as shown in FIG. 11 and has been described with reference to FIGS. 9 and 10 as a method of controlling the amplitude loss of the external resonator 2 to adjust the coupling efficiency. Instead of using an EOM or a polarizer as in the first embodiment, as shown in FIG. 11, a non-linear optical element (crystal having a non-linear optical effect) 11 whose amplitude transmission can be varied by voltage is arranged, A laser beam from the control laser element 12 is made incident on the nonlinear optical element 11 to control the transmittance.

As in the first embodiment, the feedback control circuit 4 calculates the required light intensity of the control laser element 12 from the detection output of the light receiver 3 to determine the amplitude transmittance of the nonlinear optical element 11. As a configuration for calculating the variable perturbation amount, obtaining the control amount, and controlling the transmittance of the nonlinear optical element 11 by controlling the output laser intensity of the controlling laser element 12, thereby controlling the coupling efficiency of the external resonator 2. There is.

This also makes it possible to control the chaotic state as described with reference to FIG.

In the above, the nonlinear optical crystal is arranged in the external resonator to optically control the efficiency of the external resonator and to give a time-varying perturbation.

It is possible to dispose a semiconductor laser device in the external resonator, electrically control the efficiency of the external resonator, and give a time-varying perturbation. An example thereof will be described below as a third embodiment.

(Third Embodiment) In this embodiment, a semiconductor laser element is arranged in an external resonator, and the injection current of the semiconductor laser element is controlled to amplitude-modulate the efficiency of the external resonator electrically. As shown in FIG. 12, another semiconductor laser element 13 is prepared separately from the semiconductor laser element 1, and the semiconductor laser element 13 is arranged in the external resonator 2. Then, the perturbation amount with respect to the injection current value of the semiconductor laser device 13 is calculated by the feedback control circuit 4 in the same manner as in the case of FIG. 10, and in order to obtain the required perturbation amount, the semiconductor laser device 13 The injection current is controlled by the feedback control circuit 4 so that the ratio of the amount of emitted light to the light incident on the semiconductor laser element 13 is temporally changed, and the coupling efficiency of the external resonator 2 is controlled.

This also makes it possible to control the chaotic state as described with reference to FIG.

(Fourth Embodiment) A fourth embodiment will be described below as a fourth embodiment in which the reflectance of the external resonator 2 is controlled to give a perturbation to the coupling efficiency of the external resonator 2.

In this example, a phase conjugate mirror (PCM) may be used as the reflecting mirror of the external resonator 2. Hereinafter, a phase conjugate mirror (PCM) is used as a reflecting mirror of the external resonator 2 to electrically or optically control the reflectivity to give a time-varying perturbation to the coupling efficiency of the external resonator as described above. A method for controlling output light in a chaotic state from a compound resonator is shown.

Here, the phase conjugate mirror is a phase conjugate wave (PC
W) is generated, and the phase conjugate wave is
It is a wave having the same wavefront as that of an incident wave and traveling in the opposite direction, that is, a time-reversed wave of the incident wave. Since it is a time-reversed wave of the incident wave, by giving the phase conjugate wave to the external resonator, it is possible to make it into a chaotic state, and by electrically or optically controlling the reflectance of the phase conjugate mirror, A time-varying perturbation can be given to the coupling efficiency of the external resonator.

The semiconductor laser device is known as a device which generates a phase conjugate wave, and is studied as a device which generates a phase conjugate wave by four-wave mixing. And
For example, the composite resonator 2 can be configured with an optical arrangement as shown in FIG.

That is, in FIG. 13, the semiconductor laser device LD-1 is the first laser device, and
It corresponds to the semiconductor laser device 1 in the embodiment. Further, M is a mirror, which uses a half mirror and is arranged on the emission optical path of the semiconductor laser element LD-1, and reflects a part thereof and allows a part thereof to pass therethrough. This mirror M corresponds to the mirror 21b in the previous embodiment.

The semiconductor laser element LD-2 is a laser element for a phase conjugate mirror, and is arranged with its own optical axis aligned with the reflection optical path of the mirror M. FP is a frequency discriminator using a Fabry-bellow etalon plate. The frequency discriminator FP discriminates the frequency of the laser light transmitted through the mirror M, and the photodetector 3 detects the frequency-discriminated laser light. , And outputs a detection signal corresponding to the light amount.

The feedback control circuit 4 uses the light receiver 3
The perturbation amount is calculated on the basis of the detection signal from, the injection current having the reflectance corresponding to the perturbation amount is calculated, and the current having the current value is given to the semiconductor laser element LD-2.

Here, the semiconductor laser devices LD-1 and P
The injection currents of the semiconductor laser element LD-2 for CM are made different, and the original oscillation laser beam from the semiconductor laser element LD-1 and the phase conjugate from the semiconductor laser element LD-2 for PCM are used. The oscillation wavelength is different from that of light. The two types of laser light having different oscillation wavelengths are Fabry-Peru etalon plates (plates formed by stacking media with different refractive indexes,
The wavelength can be separated by a frequency discriminator (such as acting as a spectroscope). Therefore, such a frequency discriminator DT
Is provided in front of the light receiver 3, and the semiconductor laser device LD-1
Only the output light from is detected.

By the way, a semiconductor laser device L for PCM
The phase conjugate wave generation rate of D-2 is determined by the semiconductor laser device L
FIG. 14 shows the dependency on the injection current of D-2. This figure shows the relationship between the injection current and the phase conjugate wave generation rate of the semiconductor laser element LD-2 used as the phase conjugate mirror, the vertical axis represents the phase conjugate light generation rate, and the horizontal axis represents the semiconductor laser. -Indicates the injection current of the element LD-2. Also,
A, B, and C have the power of the semiconductor laser element LD-1 as a parameter. The power of the semiconductor laser element LD-1 is increased in the order of A, B, and C.

Pin is the incident light intensity on the semiconductor laser element LD-2, Pc is the phase conjugate light intensity, I is the injection current of the semiconductor laser element LD-2, and Ith-1 is the semiconductor laser. −
It is the oscillation threshold of the element LD-2.

In the complex resonator using the semiconductor laser element as the external mirror, the reflectance of the external mirror can be changed at high speed, and therefore the state of the external resonator can be time-varying perturbed at high speed. . Here, the reflectance of the phase conjugate light is R
_The coupling coefficient κ as the _pcm and the round-trip time τ of the external resonator are

[Equation 10] FIG. 15 shows the dependence of the output light intensity fluctuation on the parameter Cf when the parameter Cf is defined as Cf = k [tau] (1+ [alpha] ² ) ^1/2 (11). From these results,
In the composite resonator using the semiconductor laser element as the phase conjugate mirror, the coupling efficiency of the external resonator can be electrically controlled. Therefore, when the reflectance of the external resonator is feedback-controlled by the same algorithm as the equations 7 to 9 in the configuration shown in FIG. 13, the optical chaos can be controlled.

In the above description, a semiconductor laser is used as a reflecting mirror instead of the non-linear optical element, and the reflectance is electrically controlled to give a time-varying perturbation to the state of the resonator. It is also possible to control the reflectance by using it. For example, using a device (phase conjugate mirror) that generates a phase conjugate wave (PCW) by four-wave mixing by using a nonlinear medium having a Kerr effect whose refractive index changes as a phase conjugate mirror (PCM), To control.

(Fifth Embodiment) An example will be described as a fifth embodiment. As shown in FIG. 16, a semiconductor laser device LD
It is made incident on the Kerr medium Md via the mirror M on the optical axis of −1, and the Kerr medium Md is provided with respective outgoing lights as pump lights from the pump light laser elements LD-P1 and LD-P2. The pump light laser elements LD-P1 and LD-P2 have the same wavelength as the semiconductor laser element LD-1, and the pump light laser element LD-P1 is controlled to a constant value.
In the pump light laser element LD-P2, the injection current is controlled by the feedback control circuit 4.

The laser element LD is arranged in the arrangement shown in FIG.
Pump light is incident on the Kerr medium Md from -P1 and LD-P2 to generate a phase conjugate wave (PCW) of the emitted light of the semiconductor laser element LD-1. Laser element LD for pump light
The reflectance of the phase conjugate mirror (PCM) with respect to the output aw of the pump light laser element LD-P2 when the output of -P1 is constant is as shown in FIG. Therefore, by controlling the reflectance of the external resonator from the light intensity received by the light receiver 3 according to the same algorithm as described above, the same result as in FIG. 15 can be obtained and the optical chaos can be controlled.

As described above, in the fifth embodiment, the phase conjugate mirror having the nonlinear optical element is used as the reflecting mirror of the external resonator, and the reflectance is 4%.
It is controlled by light wave mixing to give a time-varying perturbation to the state of the resonator. Next, consider the application.

(Sixth Embodiment) As a modification of the configuration shown in FIG. 13, consider application to optical communication.

This embodiment uses a resonator coupled by a fiber waveguide, and two semiconductor laser elements LD1, LD2 coupled by a fiber waveguide W as shown in FIG.
Consider bidirectional optical communication with a resonator consisting of. Two
Of the semiconductor laser elements LD1 and LD2, if LD1 is the transmitting side and LD2 is the receiving side, the semiconductor laser element LD2 on the receiving side is also used as a phase conjugate mirror (PCM). A chaotic state is obtained by resonating with a resonator composed of two semiconductor laser elements LD1 and LD2 coupled by a fiber waveguide W to generate phase conjugate light (PCW).

In the initial state, the natural oscillation frequency of the semiconductor laser element LD1 on the transmission side and the reflectance (Rpcm) of the semiconductor laser element LD2 on the phase conjugate mirror side are set so that the time series of the resonance light intensity is in a chaotic state. Keep it.

Here, for convenience, it is assumed that the semiconductor laser device LD1 is on the sender side and the phase conjugate mirror semiconductor laser device LD is on the receiver side. In brief, the above-mentioned chaotic control calculates a minute time-varying perturbation amount to the control parameter from the relative positional relationship between the time series data of the chaotic state and the unstable periodic point (saddle point) of the chaotic trajectory, To fix the orbit near the saddle point.

For example, the intensity of light resonating on the sender side is monitored, and feedback control is performed to obtain the perturbation amount of the injection current at each time in accordance with the above-described chaos control method, and fixed to a specific state. (Switching) is possible (Fig. 19 (a); sender-initiated system), and on the other hand, the receiver side can monitor the light intensity while controlling the reflectance with a similar mechanism. It is possible (Fig. 19 (b); recipient-initiated system).

From a different point of view, such chaotic control is an associative switch that recalls a specific state from the chaotic state.

In the case of the configuration of FIG. 18, the fiber waveguide W
The sender-receiver coupled in shows an example where a periodic state can be selected from unstable resonances of chaotic states. In particular, it is interesting to observe the chaotic state on the receiver side and switch to the proper mode by control.

This is a communication system designed to recall the information desired by the receiver from the multiple information contained in the transmitted chaotic signal.

In the case of utilizing chaos, first, the optical signal sent to the communication path is placed in a chaotic state, and then a minute perturbation is given to obtain a periodic state, and this periodic state is used as meaningful information. use. When optical chaos is used, the information generated differs depending on the situation, so it is also useful for confidentiality of communication.

In the application example shown here, communication of one-dimensional time-series information is described, but as an extension thereof, optical communication of dynamic information that changes in two dimensions with time is possible.

Further, the perturbation amount of the state and the parameter before taking out the information is strictly limited by the distance between the two communicating parties, and even if the state is slightly different, the same information (periodic state) cannot be taken out. Therefore, when the communication type optical computer is realized by this embodiment, confidentiality of information can be secured.

The present invention is not limited to the above-mentioned embodiments, but can be carried out by appropriately modifying it without departing from the scope of the invention.

The various embodiments have been described above.
In short, the present invention provides an external resonator that optically resonates the light emitted from the laser resonator that is a light source and makes the time series of the light intensity chaotic, and that is arranged in the external resonator and that controls the transmitted light with a control signal. Of the chaotic state based on the detection output of the optical control means for controlling the optical resonance efficiency by giving the change of The output light from the laser resonator is optically resonated by the external resonator, and the time series of the light intensity is chaotic. Further, the efficiency is changed by controlling the optical control means in the external resonator by a control signal which gives a predetermined time-varying perturbation corresponding to the detection output of the optical detection means to the external resonator. .

The optical control means controls the optical resonance efficiency by giving a change corresponding to the control signal to the transmitted light, and the control signal controls so as to stabilize the chaotic state in a periodic state. Therefore, the chaotic state can be stabilized to a periodic state by the efficiency control of the external resonator. Therefore, by providing a correspondence relationship between the time-varying perturbation and the periodic state to be stabilized, switching control can be performed so as to obtain a plurality of types of periodic states.

[0102]

As described in detail above, according to the present invention, it becomes possible to control the coupling efficiency of the external resonator in the semiconductor laser device with good reproducibility. Since it becomes possible to control from the chaotic state to the desired periodic stabilization state, it becomes possible to extract the information (periodic state) that is inherent in the chaotic state, and it is used as a new technology for information transmission. It will be possible.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of the present invention, showing a time series discretized at time intervals τ and a manifold formed from the time series in a state space.

FIG. 2 is a diagram showing a chaotic state and trajectories from recursion points of the first, second, and third periods.

FIG. 3 is a diagram showing a distribution of recursive points.

FIG. 4 is a diagram for explaining a method of obtaining a tangent vector from a passage point Xs, Xs + 1-position permutation system on a cut surface of a manifold configured from time series.

FIG. 5 is a diagram showing a flow of a tangent vector at a saddle point on a cut surface and its vicinity.

FIG. 6 is a diagram for explaining a geometrical interpretation (geometrical image) of chaos control.

FIG. 7 is a diagram showing reciprocal vectors.

FIG. 8 is a diagram for explaining the principle of the present invention, in which a chaotic state is controlled by using a control perturbation amount control method, and the unstable periodic points (saddle points) of one cycle and two cycles are generated in the vicinity thereof. The figure which shows the example which fixed the orbit.

FIG. 9 is a conceptual diagram of a chaotic state control system according to the present invention.

FIG. 10 is a diagram for explaining the first embodiment of the present invention, showing a structural example in which a chaotic state is controlled by giving a small perturbation to the coupling efficiency and the resonator length of an external resonator. Fig.

FIG. 11 is a diagram for explaining the second embodiment of the present invention, which is a configuration example in which a nonlinear optical crystal is used to optically control the efficiency of an external resonator and to give a time-varying perturbation. FIG.

FIG. 12 is a view for explaining the third embodiment of the present invention, in which a semiconductor laser device is arranged in an external resonator, the efficiency of the external resonator is electrically controlled, and a time-varying perturbation is given. FIG.

FIG. 13 is a diagram for explaining the fourth embodiment of the present invention, showing a structural example in which the coupling efficiency of the external resonator is perturbed by controlling the reflectance of the external resonator. Fig.

FIG. 14 is a semiconductor laser device L used as a phase conjugate mirror.
The figure which shows the relationship of the injection current of D-2, and a phase conjugate wave generation rate.

FIG. 15 is a diagram showing the relationship between the reflection efficiency function Cf of PCM and the fluctuation of output light intensity.

FIG. 16 is a diagram showing an example of the configuration of the fifth embodiment of the present invention, in which the phase conjugate wave generation rate by four-wave mixing is controlled to give a time-varying perturbation to the efficiency of the external resonator.

FIG. 17 is a diagram showing the relationship between the output and the reflectance of the pump light laser element LD-P2 in the fifth embodiment of the present invention.

FIG. 18 is a conceptual diagram of a fiber waveguide type composite resonator using a semiconductor laser element as a phase conjugate mirror as an external mirror, which is a sixth embodiment of the present invention.

FIG. 19 is a conceptual diagram of a communication system using optical chaos control according to a sixth embodiment of the present invention, showing a sender-initiated system and a receiver-initiated system.

FIG. 20 is a diagram for explaining a conventional example and is a diagram showing an example of a composite resonator.

FIG. 21 is a diagram showing the relationship between spontaneous emission and a change in gain due to an increase in α parameter.

FIG. 22 is a diagram showing a change in fluctuation of the oscillation output light intensity with respect to the frequency detuning of the natural oscillation frequency ωs of the composite resonator and the frequency ωa of the spontaneously amplified emission light, and the corresponding power spectrum.

[Explanation of symbols]

1, 13 ... Semiconductor laser element 2 ... External resonator 3 ... Photodetector 4 ... Feedback control circuit 5 ... Isolator 6 ... Y-shaped waveguide 11 ... Nonlinear optical element 12 ... Control laser element 21, M ... Mirror 21a ... Half Mirror 21b ... Total reflection mirror 22 ... Coupling efficiency adjustment system 22a, 22d ... Polarizer 22b ... EOM
(Electro-optic modulator) 22c ... 1/4 lambda phase plate FP ... Fabry-bellow etalon plate BL1 ... Laser light emission path BL2 ... Reflection path LD1, LD-1 ... Semiconductor laser device LD2, LD-2 ... Phase conjugate mirror (PCM) ) Semiconductor laser element W ... Fiber waveguide Md ... Kerr medium LD-P1, LD-P2 ... Laser element for pump light.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 26, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

By the way, chaos is a phenomenon that occurs in a nonlinear system and cannot occur in a linear system .

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

On the other hand, in the field of physics, focusing on semiconductors, the semiconductor material itself has already been studied as a non-linear optical element and is the subject of chaos research. In the non-linear optical system, an amplitude, phase, direction,
Since optical beams with a large number of degrees of freedom such as wavelength interact non-linearly and complex and multidimensional optical pattern generation often appears, this can be used for optical communication and optical signal processing. Has sex.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

As the non-linearity parameter α increases, the gain at the frequency ωa increases. Considering the resonance of such naturally amplified light, if you make a rate equation for the composite resonator,

[Equation 4] Here, N is the carrier density, Sa is the number of photons for spontaneous amplification, Esm is the eigenmode electric field, (m = 1, 2), β is the spontaneous emission coefficient, τ _p is the photon lifetime, and κ is the image resolution coefficient (Fabry-Perot). In the case of κ = (1-r2) (r3 / r2) ^1/2 c
/ 2n / L _ext , where n is the refractive index).

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

According to the equation ( 4), ωa and ωs2 are also functions of the coupling efficiency (function of reflectance and external cavity length) of the external resonator. Therefore, by controlling these state variables, fluctuations in the output light intensity are obtained. Quasi-periodic solution of the state of
There is a branch to chaos.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

However, in the above case, the connection of the optical resonator is
How much the combination efficiency is changed will result in the output light.
How much does the fluctuation of intensity change?
Since there is no general rule, it has not been possible at present to control the coupling efficiency of the external resonator in the semiconductor laser device to a desired state .

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

[0018] Therefore it is an object of the present invention, the coupling efficiency of the external cavity in the semiconductor laser device, results
Another object of the present invention is to provide an optical chaos control device capable of controlling as much as a desired output can be obtained .

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

That is, the laser resonator and the light emitted from the laser resonator are optically resonated and the time series of the light intensity is obtained.
An external resonator to chaotic state, the disposed outside resonator, laser co giving change in the control signal corresponding to the transmitted light
A light control means for controlling the coupling efficiency to the resonator, a light detection means for detecting the light emitted from the external resonator, and a stable output of the chaotic state based on the detection output of the light detection means. And a control means for generating a control signal that gives a predetermined time-varying perturbation.

[Procedure Amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0056

[Correction method] Change

[Correction content]

Reference numeral 5 denotes an isolator arranged in the reflection path BL2, which is for passing light in only one direction, and blocks backward light. Reference numeral 6 denotes a Y-shaped waveguide, which is arranged on the emission end face side of the semiconductor laser device 1 and optically couples the emission end face side of the semiconductor laser device 1 with the laser light emission path BL1 and the reflection path BL2. belongs to. The Y-shaped waveguide 6 may be composed of a half mirror or the like.

[Procedure Amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0060

[Correction method] Change

[Correction content]

By following such a path, a part of the light emitted from the semiconductor laser device 1 is returned and a nonlinear interaction occurs in the semiconductor laser device 1. By this
As a result, the laser light in the resonance state exhibits a chaotic state.

[Procedure Amendment 11]

[Document name to be amended] Statement

[Name of item to be corrected] 0070

[Correction method] Change

[Correction content]

[0070] Instead of the electro-optic crystal, the semiconductor laser element is placed in the external resonator and by electrically controlling the efficiency of the external resonator, it is possible to provide a varying perturbation time. An example thereof will be described below as a third embodiment.

[Procedure Amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0091

[Correction method] Change

[Correction content]

Here, for convenience, it is assumed that the semiconductor laser device LD1 is on the sender side and the phase conjugate mirror semiconductor laser device LD is on the receiver side. In brief, the above-mentioned chaotic control is a minute time-varying perturbation from the relative positional relationship between the time series data of the chaotic state in the state space and the unstable periodic point (saddle point) of the chaotic trajectory to the control parameter. To calculate the quantity and fix the orbit around the saddle point.

[Procedure Amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0096

[Correction method] Change

[Correction content]

In the case of utilizing chaos, first, the optical signal sent to the communication path is placed in a chaotic state, and then a minute perturbation is given to obtain a periodic state, and this periodic state is used as meaningful information. use.

[Procedure Amendment 14]

[Document name to be amended] Statement

[Correction target item name] 0100

[Correction method] Change

[Correction content]

The various embodiments have been described above.
In short, the present invention provides an external resonator that optically resonates the light emitted from the laser resonator that is the light source and sets the time series of the light intensity to a chaotic state, and that is arranged in the external resonator and that controls the transmitted light by a control signal. and light control means for controlling the optical resonant efficiency giving a change in a light detecting means for detecting the emitted light of the external cavity, based on the detection output of the light detecting means, various periodic the chaos The laser light emitted from the laser resonator is optically resonated by the external resonator, and the time series of the light intensity is in a chaotic state. A control signal that gives a predetermined time-varying perturbation corresponding to the detection output of the photodetecting means to the external resonator made to change the efficiency by controlling the optical controlling means in the external resonator. Is.

Claims (1)

[Claims] 1. A laser resonator, an external resonator that optically resonates the light emitted from the laser resonator and makes the time series of the light intensity chaotic, and is disposed in the external resonator to transmit light. A light control means for controlling the optical resonance efficiency by giving a change corresponding to the control signal, a light detection means for detecting the light emitted from the external resonator, and a cycle of the chaotic state based on the detection output of the light detection means. And a control means for generating a control signal that gives a predetermined time-varying perturbation that stabilizes the optical chaos.