Wavelength tunable filter device

Abstract

A wavelength tunable filter device has at least two optical fibers through which an optical signal is input or output; a wavelength selective element which the optical signal is input to and output from through a lens and which selects a wavelength; a mounting jig to which the wavelength selective element is fixedly secured; a rotating mechanism, having an ultrasonic motor and an encoder, for rotating the wavelength selective element; and a motor controller for controlling the ultrasonic motor for driving, wherein the mounting jig is rigidly mounted directly to a rotating shaft of the ultrasonic motor, and the amount of power that does not exceed the driving power necessary to cause the ultrasonic motor to start rotating from a stopped condition is intermittently applied to the motor controller.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a wavelength tunable filter for use in a wavelength division multiplexing transmission system and apparatus in optical communications, and also relates to a wavelength tunable filter device using the same.[0003] 2. Related Art of the Invention[0004] In optical communications, there has been known a technique of wavelength division multiplexing which transmits signals of multiple channels through a single optical fiber. In wavelength division multiplexing, signals of different channels are optically multiplexed at different wavelengths by using a optical multiplexer at the transmitting end, and the thus multiplexed signals are transmitted through a single fiber to the receiving end; at the receiving end, the multiplexed signals are separated according to their wavelengths by means of a wavelength filter, to recover the original signals. In particular, by using a wavelength tunable filter whose wavelength is capab...

AI Technical Summary

Problems solved by technology

In high density wavelength division multiplexing transmission where signals are transmitted at closely spaced wavelengths, enhancing the operational stability and the accuracy in setting the filter for the selected wavelength has been a major challenge in the design of the filter.

However, such a high resolution characteristic has been unachievable with a conventionally used stepping motor alone, and improvements in the rotating mechanism have been necessary.

Accordingly, the hysteresis that the reduction gear has in its rotational direction becomes a factor that limits the rotational angular resolution of the diffraction grating.

Furthermore, the rotational resolution of the stepping motor is greatly affected by the connecting condition of the joint between the reduction gear and the stepping motor.

Moreover, the use of the reduction gear increases not only the overall size but also the axial length of the rotating mechanism, as a result of which stability cannot be secured for the rotational operation of the mounting jig which has eccentricity as shown in FIG. 4(b).

Furthermore, since the rotation control is such that the rotational motion is stopped abruptly at the desired angular (wavelength) position, the absolute angular precision of the stopping motion may degrade.

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