Optical modulator

1. A method for operating an optical modulator that includes a modulator optical waveguide formed on a substrate, the method comprising:

(a) launching an continuous-wave input optical signal to propagate along the modulator optical waveguide, the input optical signal being characterized by an input optical power level; and

(b) applying an electrical modulation signal to a modulator electrode positioned over a semiconductor modulator active region of the modulator optical waveguide so as to modulate an optical transmission level of the input optical signal through the modulator resulting in a modulated output optical signal emitted from the modulator,

wherein:

(c) the optical modulator is characterized by a zero-current modulator optical transmission level that is less than 100% and occurs at a positive modulator bias voltage level that results in charge carriers being neither injected into nor extracted from the modulator active region;

(d) an electrical modulation signal level that causes charge carriers to be injected into the modulator active region results in a modulator optical transmission level higher than the zero-current modulator transmission level; and

(e) an electrical modulation signal level that causes charge carriers to be extracted from the modulator active region results in a modulator optical transmission level lower than the zero-current modulator transmission level.

2. The method of claim 1 wherein the zero-current modulator optical transmission level is dependent on the input optical power level.

3. The method of claim 1 wherein the electrical modulation signal comprises a sum of a substantially constant positive modulator bias voltage and an information-carrying RF modulation signal applied to the modulator electrode.

4. The method of claim 3 wherein the modulator bias voltage is greater than about 0.4 V.

5. The method of claim 3 wherein applying the modulator bias voltage and the RF modulation signal results in charge carriers being extracted from the modulator active region over a portion of a negative-current region of an I-V characteristic of the modulator active region.

6. The method of claim 5 wherein the charge carriers extracted from the modulator active region result in a negative current from about 0 mA to about 50 mA.

7. The method of claim 1 further comprising generating the continuous-wave input optical signal from a semiconductor laser by applying a substantially constant electrical laser bias voltage to a laser electrode positioned over a semiconductor laser active region of a laser optical waveguide formed on the substrate, wherein the laser and modulator waveguides are arranged so that at least a portion of optical output of the semiconductor laser is launched to propagate as the input optical signal along the modulator optical waveguide.

8. The method of claim 7 wherein the laser and modulator electrodes are electrically separated by a vertical gap formed in semiconductor material between the electrodes.

9. The method of claim 7 wherein the laser and modulator optical waveguides are distinct portions of a common optical waveguide formed on the substrate.

10. The method of claim 7 wherein the laser bias voltage is greater than the modulator bias voltage.

11. The method of claim 7 wherein the semiconductor laser includes InP.

12. The method of claim 7 wherein the laser optical waveguide includes a reflective first end region and a second end region adjacent the modulator optical waveguide.

13. The method of claim 7 wherein the input optical signal is characterized by a wavelength of about 1550 nm.

14. The method of claim 1 wherein the optical modulator includes InP.

15. The method of claim 1 wherein the input optical signal is characterized by a wavelength of about 1550 nm.