Avanex Corporation

Oclaro (north America Inc.)

Simone M Pensa

Paolo Milanese

Giovanni Gilardi

Luigi Gobbi

Mario Bonazzoli

Antonino Nespola

An optical modulator comprises a Z-cut lithium niobate substrate on which is formed a Mach-Zehnder interferometer having two generally parallel waveguides lying beneath a buffer layer of dielectric material. First and second ground electrodes and a hot electrode are disposed on the buffer layer, the first and second ground electrodes being spaced either side of the hot electrode, the hot electrode and the first ground electrode being proximate to at least apart of the respective waveguides. The electrode structure is unsymmetrical in that (a) the hot electrode and the first ground electrode each have a width substantially less than that of the second ground electrode and or (b) the spacing between the first ground and hot electrodes is different from the spacing between the second ground and hot electrodes. whereby a range of chirp values can be obtained. When the spacing between the first ground and hot electrodes is smaller than the spacing between the second ground and hot electrodes, and preferably the hot and first ground electrodes have a width not exceeding 15 .&#x3bc;m, the modulator is capable of operation at frequencies above 10 GHz, possibly up to around 40 GHz.

Lithium niobate optical modulator

An optical modulator comprises a Z-cut lithium niobate substrate () on which is formed a Mach-Zehnder interferometer having two generally parallel waveguides () lying beneath a buffer layer of dielectric material (). First and second ground electrodes () and a hot electrode () are disposed on the buffer layer (), the first and second ground electrodes () being spaced either side of the hot electrode (), the hot electrode () and the first ground electrode () being proximate to at least apart of the respective waveguides (). The electrode structure is unsymmetrical in that (a) the hot electrode and the first ground electrode each have a width substantially less than that of the second ground electrode and or (b) the spacing between the first ground and hot electrodes is different from the spacing between the second ground and hot electrodes. whereby a range of chirp values can be obtained. When the spacing (G) between the first ground and hot electrodes () is smaller than the spacing (G) between the second ground and hot electrodes (), and preferably the hot and first ground electrodes have a width not exceeding 15 &#x3bc;m, the modulator is capable of operation at frequencies above 10 GHz, possibly up to around 40 GHz.

An electro-optical modulator is disclosed that has a microwave input, chip with a thin film resistor or a lumped resistor located between an input RF connector and an RF electrode on a Lithium Niobate chip. The accessory connection chip has a broadband attenuator like a thin film resistor which is placed in a microstrip line for effecting the electrical transmission to Lithium Niobate chip. The insertion of the thin film resistor before the RF electrode lowers the electrical return loss value as a function of frequency, allowing a lower driving voltage design or a reduced chip length without degrading the performances.

System for reducing the electrical return loss of a lithium niobate traveling wave optical modulator with low characteristic impedance

A high-speed external optical modulator formed on a lithium niobate substrate has a diffused optical waveguide, a surface buffer layer, and electrodes for applying modulating RF energy. The electrodes are electroplated in at least two steps, resulting in a top co-planar waveguide structure lying on a second one. Low driving voltage is achieved through selection of the width, position, and dimension of the lower hot and ground electrodes. The upper ground electrodes and, preferably, also the upper hot electrode, are narrower in width than the corresponding lower electrodes, which helps to provide good velocity matching, good impedance values, and low electrical losses.

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Albano Vercellese, Italy

Simone M Pensa