Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-05-30
2001-04-10
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06215569
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an E/O switch controlling apparatus for controlling an E/O switch (electric field optical switch), and more particularly to an E/O switch controlling apparatus and a method for controlling the E/O switch for effectively employing the E/O switch using ferromagnetic crystal such as LiNbO
3
in a good polarized state.
One of previously known electro-optical switches is an E/O switch using ferromagnetic crystal such as LiNbO
3
crystal. The ferromagnetic crystal used in these E/O switches has a characteristic that refractive index changes according to an applied voltage. The E/O switch using such a characteristic has been employed.
The polarizing characteristic of the E/O switch incorporating the ferromagnetic crystal is improved when charges are accumulated in the ferromagnetic crystal. For this reason, when the E/O switch is used, a voltage for accumulating charges in the ferromagnetic crystal is applied to the ferromagnetic crystal, thereby charging the ferromagnetic crystal.
However, it is known that the polarizing characteristic of the E/O switch is abruptly deteriorated when it is used continuously used for a prescribed time or longer. This is because the charges accumulated in the ferromagnetic crystal exceeds a suitable value when charging for the ferromagnetic crystal is continued.
When the charges accumulated in the ferromagnetic crystal exceed a suitable value, the polarizing characteristic of light incident on the E/O switch is greatly deteriorated so that the insertion loss of the P-wave (parallel polarizing wave) and S-wave (vertical polarizing wave) is increased and crosstalk is increased. In this state, when the operation of the E/O switch is forcibly continued, as the case may be, “offset displacements” that an applied voltage exceeds a prescribed voltage occurred.
Conventionally, the characteristic of the E/O switch was recovered by properly discharging the excessive charges accumulated in the ferromagnetic crystal. Namely, when the E/O switch was continuously used, excess charging was prevented by making exchange between a charging operation of accumulating charges in the ferromagnetic crystal and a discharging operation of discharging the accumulated charges at regular intervals.
However, in the conventional method, alternate exchange between the charging operation and discharging operation requires a certain time while the E/O switch is not operated. This is inferior in time efficiency.
As described above, the ferromagnetic crystal, when charged, falls in a state with good polarizing characteristic. However, the characteristic thereof is greatly deteriorated while it is discharged. Therefore, it was very difficult to adapt the E/O switch to the characteristics of the ferromagnetic crystal during both its charging and discharging. Namely, the E/O switch could not used during the discharging operation.
In the conventional method, it was necessary to make exchange into the discharging operation before the ferromagnetic crystal within the E/O switch is excessively charged. For this purpose, the elapsed time during the charging operation was counted. Further, in order to use the E/O switch in a state with good polarizing characteristic, as the case may be, the discharging operation was made for a longer time than the charging operation. In this case, the using efficiency of the E/O switch was further attenuated.
In order to solve the above problem, the present invention intends to provide an E/O switch controlling apparatus which permits an E/O switch using ferromagnetic crystal to be used efficiently and continuously in a stable state.
SUMMARY OF THE INVENTION
In order to solve the above problem, the invention defined in aspect
1
is an E/O switch controlling apparatus for controlling an E/O switch incorporating ferromagnetic crystal, characterized by comprising
clock signal generating means generates a clock signal having a prescribed frequency, and
charging/discharging means (switch controlling apparatus
3
producing a charging/discharging controlling signal
33
) for making exchange between a charging operation of charging ferromagnetic crystal contained in the E/O switch and a discharging operation of discharging charges in the ferromagnetic crystal in synchronism with a clock signal at a prescribed frequency.
In accordance with the invention defined in aspect
1
, in an E/O switch controlling apparatus for controlling an E/O switch incorporating ferromagnetic crystal, the charging/discharging means makes exchange between a charging operation of charging ferromagnetic crystal contained in the E/O switch and a discharging operation of discharging charges in the ferromagnetic crystal in synchronism with a clock signal at a prescribed frequency.
The invention defined in aspect
5
is a method for controlling an E/O switch incorporating ferromagnetic crystal, characterized by comprising the steps of:
generating a clock signal having a prescribed frequency, and
making exchange between a charging operation of charging ferromagnetic crystal contained in the E/O switch and a discharging operation of discharging charges in the ferromagnetic crystal in synchronism with a clock signal (e.g. charging/discharging signal
33
) at a prescribed frequency.
The ferromagnetic crystal may be LiNbO
3
(lithium niobate) KTaO
3
(potassium tantalate), BaTiO
3
(barium titanate), etc. However, the ferromagnetic crystal is not limited as long as it can be applied to the E/O switch.
Thus, in a E/O switch incorporating ferromagnetic crystal, exchange is made between a charging operation of charging ferromagnetic crystal contained in the E/O switch and a discharging operation of discharging charges in the ferromagnetic crystal in synchronism with a clock signal at a prescribed frequency.
Therefore, the ferromagnetic crystal is not completely shifted into a state of the discharging operation so that the deterioration of the polarizing characteristic and increase in the crosstalk do not occur. Thus, the E/O switch can be used during both the charging operation and the discharging operation so that the E/O switch can be continuously operated.
The invention defined in aspect
2
is an E/O switch controlling apparatus for controlling an E/O switch according to aspect
1
, characterized by further comprising light transmission/interruption controlling means (switch controlling apparatus
3
producing a light transmission/interruption controlling signal
3
) for switching the light incident on the E/O switch between its transmission and its interruption, and in that the charging/discharging means does not make exchange between the charging operation and discharging operation for the ferromagnetic crystal while the light incident on the E/O switch is produced by controlling the light transmission/interruption controlling means.
In accordance with the invention defined in aspect
2
, in an E/O switch controlling apparatus for controlling an E/O switch according to aspect
1
, the light transmission/interruption controlling means switches the light incident on the E/O switch between its transmission and its transmission, and the charging/discharging means does not make exchange between the charging operation and discharging operation for the ferromagnetic crystal while the light incident on the E/O switch is produced by controlling the light transmission/interruption controlling means.
The invention defined in aspect
6
is a method for controlling an E/O switch according to aspect
5
, characterized by further comprising the step of switching the light incident on the E/O switch between its transmission and its interruption (e.g. operation of producing a light transmission/interruption controlling signal
32
by the switch controlling apparatus
3
) and in that exchange is not made between the charging operation and discharging operation for the ferromagnetic crystal while the light incident on the E/O switch is produced by controlling the light transmission/interruption controlling means.
Therefore, it is possible to prevent the lig
Ando Electric Co. Ltd.
Dang Hung Xuan
Fish & Richardson P.C.
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