Polymer phase modulator for fiber optic gyroscopes

Replacement of lithium niobate crystal with a polymer enables integration of all front-end components of an Interferometric Fiber Optic Gyroscope into a single transceiver module

Photonics Sensors

A cross-section of an etched rib polymer waveguide

The interferometric fiber optic gyroscope (IFOG) has rapidly gained acceptance as a lightweight, low power, and highly reliable device for high precision inertial navigation applications. Advances in IFOG technology have resulted in a plethora of individual optical fiber components including sources, detectors, modulators, and couplers used in transceivers which limit the potential to reduce size and cost as necessary for many applications.

Precision guidance in navigation systems requires highly accurate, compact, and low-cost inertial measurement units (IMUs). The key active guided-wave component of the IMU is the phase modulator. Phase modulators used in conventional IFOG systems are made of inorganic crystalline materials such as lithium niobate have low insertion loss, but they make integration a challenge, particularly if navigation grade performance is to be maintained. Furthermore, the common method to produce phase modulators is expensive.

While maintaining the necessary accuracy, Navy researchers have lowered the cost and decreased the size of the phase modulator with the use of polymer materials. The waveguides are constructed of an electro-optic core material in between two polymer cladding materials that have lower indices of refraction for the guided mode. This three-layer stack is coupled to a silicon substrate. The waveguide pattern includes a coupler that splits the light almost equally along two symmetric channels. Gold electrodes are also fabricated on one or both arms depending on the type of configuration. The light is coupled into and out of the modulator via PM fiber integrated with the waveguides.

When compared with the conventional gyroscopes based on lithium niobate, the use of polymer waveguides in the fabrication of IFOG components allows an efficient integration of subcomponents, hence reducing the cost of the devices using semiconductor wafer scale microfabrication processes.

This US patent 7,228,013 is related to US patents 7,228,022; 7,236,654; 7,302,119; 7,239,765; and 7,620,277.

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