Variable optical wavelength filter

Details Variable optical wavelength filter Variable optical wavelength filter

2001-08-14

2003-05-06

Chang, Audrey (Department: 2872)

Optical: systems and elements

Light interference

Electrically or mechanically variable

C359S589000, C359S199200, C359S199200, C359S199200, C372S038060, C385S024000, C385S037000

Reexamination Certificate

active

06560021

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable optical wavelength filter for selecting the wavelength of an optical output signal from the wavelength of an optical input signal and outputting the optical output signal.
2. Description of Related Art
Conventionally, dielectric multilayer filters are used in variable optical wavelength filters in the field of optical interconnections. The wavelength of the optical input signal input to this dielectric multilayer filter may vary because of temperature variations in the oscillator generating this optical input signal. It is normally necessary to substantially maximize the transmittance of the dielectric multilayer filter with respect to the optical output signal corresponding to this wavelength variation. For this reason, before now, the filter was controlled and caused to follow this wavelength variation, so that the dielectric multilayer filter comes to a position at which the maximum transmittance is substantially provided, with the axis of rotation being the center line of the dielectric multilayer filter, orthogonal to the crossover line of the incident plane at which the optical input signal is incident to the dielectric multilayer filter and the dielectric multilayer filter.
However, there are two problems with a variable optical wavelength filter having a conventional constitution. The first problem is that it becomes impossible to control the rotation of the dielectric multilayer filter in the event of a momentary interruption of the optical input signal (caused by a lightning strike, for example). The second problem is that it becomes impossible to control the rotation of the dielectric multilayer filter when the frequency of wavelength variation of the optical input signal discussed above becomes a specific frequency (detection frequency). The desired optical output signal cannot be branched or outputted from the dielectric multiplayer filter when it becomes impossible to control the rotation of the dielectric multilayer filter.
In order to resolve the first problem, it is desirable to develop a variable optical wavelength filter that can retain the position of the optical wavelength filter even in the event of a momentary interruption of the optical input signal.
In order to resolve the second problem, it is desirable to develop a variable optical wavelength filter with which the movement of the optical wavelength filter can be controlled regardless of a variations in intensity of the optical input signal.
SUMMARY OF THE INVENTION
In order to resolve the first problem, the variable optical wavelength filter according to a first aspect of the present invention is provided an optical wavelength filtering portion and optical wavelength filter control system, for a constitution for selecting the wavelength of the optical output signal from the wavelengths of the optical input signal and outputting or branching this optical output signal.
This optical wavelength filtering portion comprises an optical wavelength filter for selecting the specific wavelength for providing the maximum transmission peak to the optical output signal from the wavelengths of the optical input signal.
This optical wavelength filter control system outputs to the optical wavelength filtering portion a control signal comprising: a direct current movement signal for moving the wavelength filter to the position for selecting the specific wavelength of the optical output signal according to the wavelength variation of the optical input signal; and an alternating current detection signal for providing the amplitude frequency to the optical output signal by causing the optical wavelength filter to vibrate slightly at a fixed detection frequency.
Furthermore, this optical wavelength filter control system comprises an optical wavelength filter control portion including a direct current component forming portion for sustaining the output of the abovementioned direct current movement signal even in the event of a momentary loss of the optical input signal, and determining the size of the direct current movement signal based on the amplitude of the optical output signal; and an alternating current detection signal generator for outputting the abovementioned alternating current detection signal of the detection frequency.
With the abovementioned variable optical wavelength filter according to the present invention, this optical wavelength filter control portion can output the direct current movement signal for filtering the optical output signal to the optical wavelength filtering portion even in the event of a momentary loss of the optical input signal. Consequently, this optical wavelength filter control portion can maintain the position of the abovementioned optical wavelength filter when there is an optical input signal, of course, and in the same way when the optical input signal is lost.
For realizing the optical variable wavelength filter according to a first aspect of the present invention, the optical wavelength filter control system may preferably comprise a beam splitting portion for splitting the optical output signal into an optical monitoring signal and an optical main signal; and a photoelectric converting portion for converting this optical monitoring signal to an electric feedback monitoring signal and outputting this signal to the abovementioned optical wavelength filter control portion.
With the constitution as described above, the electric feedback monitoring signal having amplitude frequency can be output to the optical wavelength filter control portion.
For realizing the variable optical wavelength filter according to a first aspect of the present invention, the optical wavelength filter control system preferably comprises first and second beam splitting portions, first and second photoelectric converting portions, and a divider or dividing portion, in order to resolve the second problem discussed above.
The first beam splitting portion splits the optical input signal into a first optical monitoring signal and an optical input signal. Also, the second beam splitting portion splits the optical output signal into a second optical monitoring signal and an optical main signal. These first and second photoelectric converting portions convert the first and second optical monitoring signals to first and second electric monitoring signals respectively. Also, this divider divides the second electric monitoring signal by the first electric monitoring signal and outputs the result as the electric feedback monitoring signal to the abovementioned optical wavelength filter control portion.
With the constitution as discussed above, the amplitude of the optical output signal becomes the product of the amplitude of the optical input signal and the transmittance of the abovementioned wavelength filter which vibrates slightly at the detection frequency, in the case where the optical input signal is a single wavelength beam. The components of these optical input and output signals are equivalent respectively to the components of the first and second electric monitoring signals. Consequently, the amplitude of the second electric monitoring signal becomes the product of the amplitude of the first electric monitoring signal and the transmittance of the wavelength filter which vibrates slightly at the detection frequency. Accordingly, by dividing the second electric monitoring signal by the first electric monitoring signal, the divider or dividing portion discussed above can output to the abovementioned optical wavelength filter control portion an electric feedback monitoring signal that is a signal with the component of the first electric monitoring signal removed from the second electric monitoring signal. As discussed above, the component of the first electric monitoring signal is equivalent to the component of the optical input signal. As a result, the component of the optical input signal is not included in the electric feedback monitoring signal output to the optical wavelength filter control portion. Accordi

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