1. Field of the Invention
The present invention relates to micro electromechanical systems (MEMS) devices and, more particularly, to a MEMS apparatus that compensates for signal path delay in optical systems.
2. Description of the Related Art
Advanced optical (light wave) systems generally include some sort of compensation in the transmitting and/or receiving of information through optical lines. Some examples of this are compensation of polarization mode dispersion (PMD) and optical pulse timing in wavelength-division multiplexed and optically time-division multiplexed (OTDM) transmitters. In such applications, small adjustments (equivalent to several bit periods in PMD compensators and a single bit-period in OTDM transmitters) in the optical path lengths are needed in order to compensate for signal path delay. For example, in a 40 Gb/s data rate system, the 25 ps bit period has a corresponding free space bit length of cT=7.5 mm.
As the bit speeds at which data and information are transferred increases in optical systems such as these, so does the propagation delay. Even in systems having fixed delay elements, the path delay changes (in small amounts). This path delay can be caused, for example, by the effect of the coefficient of thermal expansion as the temperature of the respective optical transmission lines changes.
Conventional variable optical delay lines are comprised of a motor driven linear translation stage that moves a retroreflector to change the path length from the input to the output. Digitally settable optical fiber delay lines can be made using optical switches to select different sections of optical fiber. Equivalent functions can also be obtained in integrated optical devices. Some of the drawbacks of these delay compensation systems include high power requirements, high cost, large physical size and slow speed.
The use of micro-machines or micro electromechanical systems (MEMS) devices is becoming increasingly preferred in the optical transmission field. This preference is a result of several advantages that MEMS devices offer over the components of existing systems, including small size, fast response time and low power consumption. Thus, it would be particularly advantageous to implement a variable optical delay line using MEMS devices.
It is therefore an object of the present invention to provide a MEMS variable optical delay line that overcomes and eliminates all of the drawbacks of prior art systems.
In is another object of the present invention to provide a MEMS variable optical delay line that can function as a variable attenuator, tunable optical filter, and optical switch.
These and other objects are achieved in accordance with an embodiment of the invention wherein the micro electro-mechanical (MEMS) variable optical delay line includes an input for receiving a light wave signal and an output adapted to provide a delay path compensated light wave signal. A micro machine linear rack has a reflector spaced from the input and output at a predetermined distance to receive the input light wave signal and reflect it towards the output. The distance between the reflector and the input and/or output is selectively variable in accordance with the predetermined amount of delay path compensation that is required. A controller connected to the micro machine linear rack is adapted to selectively control the distance between the reflector and the input and/or output in accordance with the required predetermined amount of delay path compensation.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.