Integrated termination for EO modulator with RF signal monitoring functionality
View Patent ↗The invention relates to RF termination for reducing electrical signal reflections at the end of transmission line electrodes on an electro-optical (EO) optical modulator. The disclosed termination incorporates a RF tap which permits the monitoring of the RF power and reflection conditions at the EO modulator. The integrated termination/tap can also be integrated with detection circuitry, such as RF diodes and passive components, giving improved performance, lower cost manufacturability as well as a more compact and efficient package.
1. A RF termination for an optical modulator comprising:
a substrate chip having an input port for receiving a residual RF modulation signal from the optical modulator;
a ground connection on the substrate chip for providing an electrical DC and RF return path;
a resistive transmission line on the substrate chip having a width and a length extending from an input end to a grounded end for absorbing the residual RF modulation signal, wherein the input end is connected to the input port and the grounded end is connected to the ground connection; and
a RF tap output port on the substrate chip, connected to an edge of the resistive transmission line at an intermediate stage, for coupling out a RF monitoring signal at a split ratio of the residual RF modulation signal.
2. The RF termination of claim 1 , wherein the width of the resistive transmission line has a widening taper from the grounded end to the intermediate stage and narrowing taper from the intermediate stage to the RF input port.
3. The RF termination of claim 2 , wherein the widening taper or the narrowing taper follows a profile function which is one of linear, quadratic and exponential.
4. The RF termination of claim 2 , wherein the resistive transmission line comprises a resistive material selected from one of thin film and thick film.
5. The RF termination of claim 4 , wherein the resistive material comprises carbon-filled polymer.
6. The RF termination of claim 2 , wherein the widening taper or the narrowing taper is laser trimmed.
7. The RF termination of claim 2 , wherein the resistive transmission line is one of a coplanar waveguide and a microstrip line.
8. The RF termination of claim 2 , wherein the split ratio is in the range of about 6 dB to −20 dB.
9. The RF termination of claim 2 , wherein the RF tap output port has an impedance in the range of about 30 ohm to 75 ohm.
10. The RF termination of claim 2 , wherein the substrate chip comprises one of ceramic and semiconductor.
11. The RF termination of claim 2 , wherein the substrate chip is fabricated from hybrid printed circuit board technology.