JPH02126240A - Optical kerr waveguide - Google Patents

Abstract

PURPOSE:To remove the influence of a nonlinear refractive index upon a nondiagonal component by forming optical waveguide of double refractivity materials where polarized wave dispersion caused by double refractivity is much larger than the wavelength dispersion between signal light and pump light. CONSTITUTION:When the polarized wave dispersion per unit length in the optical Kerr waveguide 1 is denoted as taup and the waveguide length L=l, the phase shift phix of signal light due to Kerr effect in a main-axial direction is equal phi0 in a section of 0<=L<=l, but the time width of the phase shift phiy perpendicular to the main axis is taupl. At this time, the saturation phase quantity of the phase shift phiy is phiy=phi0X(tau/taup) and the polarized wave dispersion taup is therefore set much larger than a group delay difference tau per unit length to obtain phiy<<phi0=phix and, therefore, phix-phiy=phix(1-phiy/phix)=phix, thereby removing the influence of the nondiagonal component.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is applied to an all-optical controlled ultra-high speed optical switch. In particular, the present invention relates to an optical Kerr waveguide that rotates the polarization direction of signal light using the optical Kerr effect. In the present invention, the optical Kerr waveguide is formed of a birefringent material whose polarization dispersion caused by birefringence is sufficiently larger than the wavelength dispersion between the signal light and the pump light. The object of the present invention is to provide an optical Kerr waveguide that eliminates the influence of components and allows good optical switching with low pump power.

[Conventional technology]

2. Description of the Related Art An optical Kerr shutter that uses the optical Kerr effect, which is a third-order nonlinear effect, has been known as an optical switch for all-light control, that is, a switch that controls light using light. The optical Kerr shutter uses a third-order nonlinear element, and receives a pump light pulse polarized in the direction of its principal axis and a signal light pulse polarized in a direction of 45 degrees with respect to the pump light pulse. At this time, the phase of the main axis direction component of the signal light pulse is changed by the pump light pulse, and the polarization direction of the signal light pulse is changed by 90 degrees.

Thereby, the signal light is switched.

However, in this case, the pump light polarized in the principal axis direction is
Not only does the diagonal component of the nonlinear constant change the phase of the signal light component in the principal axis direction, but the non-diagonal component also changes the phase in the direction perpendicular to the principal axis direction. In the case of an isotropic medium, the off-diagonal component 12il of this nonlinear constant (refractive index) 12B takes a value of 173 with respect to the diagonal component n2B.

FIG. 4 shows a conventional optical Kerr waveguide using an isotropic medium, and FIGS. 5 and 6 show each L in the optical Kerr waveguide.
-β, 2I! The phase modulation waveforms at two points are shown.

When the waveguide length L=l, the saturation value (ccn2Il,/τ) of the phase change φ8 of the signal light due to the pump light is φ.

Then, the phase change in the direction perpendicular to the principal axis (Y axis) is φ,
The saturation value of is φ. /3. Here, τ is the group delay difference per unit length between the pump light and the signal light, and this group delay difference is caused by chromatic dispersion and other factors. therefore,
The effective phase changes for the optical Kerr switch are φ, −φ, −2φ, /3.

When the group delay difference τl at the waveguide length L=A is sufficiently larger than the pulse width of the pump light, the time width of the force-modulation waveform becomes τβ. The waveguide length is 12I! , the phase changes φ8, φ9, φ8−φ.

is the same as when the waveguide length is 1β, but the time width of the Kerr modulation waveform is 2τ! becomes.

[Problem 3 to be solved by the invention: In the conventional optical Kerr waveguide using an isotropic medium, due to the influence of the non-diagonal component n2B with a nonlinear refractive index of 12B, compared to the case without the non-diagonal component, The Kerr modulation efficiency was reduced to 2/3, and large pump power was required. In addition, since φ is generally a function of wavelength dispersion and polarization dispersion, its waveform is complex, and φ8−φ is not a perfect rectangle.
There was a drawback that it caused crosstalk deterioration.

The present invention solves the above problems and provides a nonlinear refractive index n2B
The off-diagonal component n23. The purpose of this invention is to provide an optical Kerr waveguide that operates with less pump power by eliminating the influence of vertically polarized light components due to

[Means for solving problems]

In the optical Kerr waveguide of the present invention, the plurality of optical waveguides forming the optical Kerr waveguide are birefringent, and the polarization dispersion caused by the birefringence is compared to the wavelength dispersion between the signal light and the pump light. It is characterized by being sufficiently large.

[For production]

The polarization dispersion per unit length of the optical Kerr waveguide is τ.

When the waveguide length L=f, the time width of the phase change φ in the direction perpendicular to the principal axis is τPβ. At this time, the saturation phase amount of the phase change φ, is φ,=φ from the law of conservation of energy. ×(τ/τP). Therefore, if the polarization dispersion r, is sufficiently larger than the group delay difference τ per unit length, φ, (φ.=φ8, and φ8−φ,=φ, (1−φ,/φN )αφ8.In other words, the influence of off-diagonal components can be removed.

〔Example〕

FIG. 1 shows a perspective view of an optical Kerr waveguide according to an embodiment of the present invention.

This optical Kerr waveguide includes a plurality of optical waveguides 1 formed of a medium exhibiting an optical Kerr effect, and these optical waveguides 1 are connected in cascade with respect to adjacent optical waveguides 1 with their fast axes substantially perpendicular to each other. Ru. In FIG. 1, two optical waveguides 1 are shown separated to show the structure, but in reality, these optical waveguides 1 are fused together. The reason why the fast axes are orthogonal is to compensate for polarization dispersion τ2. The optical waveguides 1 are formed of, for example, polarization-maintaining optical fibers with large birefringence, and each optical waveguide 1 has the same length.

Here, the feature of this embodiment is that the plurality of optical waveguides 1 are birefringent, and the polarization dispersion caused by the birefringence is sufficiently large compared to the wavelength dispersion between the signal light and the pump light. There is a particular thing.

FIGS. 2 and 3 show the L-
/! , 2β shows phase modulation waveforms at two points.

In the section where the waveguide length is 0≦L≦β, the phase change φ8 due to the Kerr effect in the principal axis direction of the signal light is φ0, as in the conventional example, as shown in FIG. 2(a). On the other hand, the phase change φ in the direction perpendicular to the principal axis.

As shown in FIG. 2(b), φ,=φ. ×(τ/τP). Here, since the polarization dispersion γ is sufficiently larger than the group delay difference τ per unit length, φ, (φ0=φ8, and as shown in Figure 2(C), φ8−φ,=φ A (l-φy/φi) 2φi.

In addition, in the section where the waveguide length is 0≦L≦2β, the signal light component in the direction perpendicular to the principal axis sweeps the pump light in the opposite direction to the section where O≦L≦β, so the pump light is directed to the coordinate origin of the signal light. Return to That is, as shown in Fig. 3 et al., the time width of the daily change φ remains unchanged at τP p, and the time width of the phase change φ8 becomes 2τβ, as shown in Fig. 3 et al. Therefore, as shown in FIG. 3(C), the time width of φ8-φ is 2πβ, which is the same as the phase change φ8, and the saturation amount is φ. becomes.

Therefore, the pump power is reduced to 2/3 compared to the conventional example.
However, the same light switching effect can be obtained. In other words, the same effect as if the value of the nonlinear refractive index were increased by 50% can be obtained.

In the above embodiments, a polarization-maintaining optical fiber is used as an optical waveguide, but the present invention can be similarly implemented using calcite or other materials with large birefringence.

〔Effect of the invention〕

As described above, the optical Kerr waveguide of the present invention can eliminate the influence of the signal light component in the direction orthogonal to the principal axis due to the off-diagonal component 12B of the nonlinear refractive index. Therefore, compared to the conventional method, there is an effect that the pump power can be reduced to 2/3 in the case of an isotropic medium. In addition, by removing the influence of phase change φ, which is a complex function of wavelength dispersion and polarization dispersion, a flat Kerr modulation waveform φ8−φ
, which has the effect of improving crosstalk characteristics.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an optical Kerr waveguide according to an embodiment of the present invention. FIG. 2 is a diagram showing a phase modulation waveform at a point L=f in the optical Kerr waveguide. FIG. 3 is a diagram showing a phase modulation waveform at a point L=2f in the optical Kerr waveguide. FIG. 4 is a diagram showing a conventional optical Kerr waveguide. FIG. 5 is a diagram showing a phase modulation waveform at the point β in the optical Kerr waveguide. FIG. 6 is a diagram showing a phase modulation waveform at a point L=2β in the optical Kerr waveguide. Patent Applicant Nippon Telegraph and Telephone Corporation Agent Patent Attorney Nao Takashi IdeExample Figure (a) (b) Figure (a) (b) Figure Figure Conventional Example Figure

Claims (1)

[Claims] 1. An optical system comprising a plurality of optical waveguides formed of a medium exhibiting the optical Kerr effect, the optical waveguides being connected in cascade with their fast axes substantially orthogonal to adjacent optical waveguides. In the Kerr waveguide, the plurality of optical waveguides are birefringent, and the polarization dispersion caused by the birefringence is sufficiently larger than the wavelength dispersion between the signal light and the pump light. waveguide.