Broadband electro-absorption optical modulator using on-chip RF input signal termination
An electro-absorption modulator (EAM) is configured to include an on-chip AC ground plane that is used to terminate the high frequency RF input signal within the chip itself. This on-chip ground termination of the modulation input signal improves the frequency response of the EAM, which is an important feature when the EAM needs to support data rates in excess of 50 Gbd. By virtue of using an on-chip ground for the very high frequency signal content, it is possible to use less expensive off-chip components to address the lower frequency range of the data signal (i.e., for frequencies less than about 1 GHz).
1. An electro-absorption optical modulator, comprising:
a substrate;
an electro-absorption modulating (EAM) device formed on the substrate, the EAM device having an optical input for receiving a continuous wave (CW) optical signal, an optical output for emitting a modulated optical output signal;
an RF input signal path coupled to the EAM device for providing a modulated electrical input signal to the EAM device;
an on-chip AC ground plane disposed on the substrate; and
a resistive RF signal termination path coupled between the on-chip AC ground plane and the RF input signal path, the on-chip AC ground plane terminating a high frequency portion of the modulated electrical input signal.
2. The electro-absorption optical modulator as defined in claim 1 , further comprising:
a dielectric layer disposed between the substrate and the on-chip AC ground plane, forming a distributed capacitance for minimizing the presence of parasitics within a frequency response of the EAM device.
3. The electro-absorption optical modulator as defined in claim 1 , further comprising
a termination resistor disposed along the resistive RF signal termination path, the termination resistor sized to provide impedance matching with a source of the electrical input modulating signal.
4. The electro-absorption optical modulator as defined in claim 3 , further comprising:
a wirebond disposed in series with the termination resistor, the wirebond having an inductance selected to provide enhancement of the modulator gain at the Nyquist frequency of the electrical input modulating signal.
5. The electro-absorption optical modulator as defined in claim 1 , further comprising:
a de-Q-ing resistor coupled between the conductive layer and an off-chip capacitor, minimizing creation of a resonant frequency within the RF signal termination path.
6. The electro-absorption optical modulator of claim 1 , further comprising:
a DC voltage source coupled to the on-chip AC ground plane, the DC voltage source providing a reverse bias DC voltage for operating the EAM device.
7. An electro-absorption modulated laser, comprising:
a laser diode source biased to emit a CW optical beam; and
a substrate;
an electro-absorption modulating (EAM) device formed on the substrate, the EAM device having an optical input for receiving the CW optical beam from the laser diode source, and an optical output for emitting a modulated optical output signal;
an RF input signal path coupled to the EAM device for providing a modulated electrical input signal to the EAM device;
an on-chip AC ground plane disposed on the substrate; and
a resistive RF signal termination path coupled between the on-chip AC ground plane and the RF input signal path, the on-chip AC ground plane terminating a high frequency portion of the modulated electrical input signal.
8. The electro-absorption modulated laser as defined in claim 7 , wherein the laser diode source is formed on the substrate in optical alignment with the EAM device.