Integrated Bias for Waveguide Amplitude Modulator

摘要

It is the general purpose and object of the present invention to provide an integral, interferometric, optical-waveguide, amplitude modulator having a linear response to small applied voltages. Still another object is to provide a reliable modulator which can be easily and inexpensively manufactured. These and other objects of the present invention are accomplished by increasing the physical length of a first waveguide arm relative to that of a second waveguide arm, the increase, delta, being defined by delta = pii/(2Kn), where K = 2 pi/lambda and K is the free-space wavevector, lambda is the free-space wavelength of the optical energy, and n is the index of refraction of the waveguide material. The increase, delta, provides an integral bias of pi/2 radians to the modulator for producing a linear modulation of signal amplitude in response to small applied voltages. The novel feature of the present invention is the difference in length of pi/(2Kn) between two parallel waveguide arms, that is, an unbalanced bridge for providing a built-in phase bias of pi/2 radians between two optical paths.