Electro-optic modulators

Details Electro-optic modulators Electro-optic modulators

1999-06-04

2001-01-09

Mai, Huy (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S245000, C385S003000

Reexamination Certificate

active

06172791

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to electro-optic modulators and to methods for their manufacture.
BACKGROUND OF THE INVENTION
Electro-optic modulators, typically lithium niobate modulators, are essential components of most lightwave systems. In state of the art commercial systems, these devices are digital and operate with data transmission rates up to 10 Gbits. Systems under development are expected to reach data rates of 40 Gbits or more. However, as bit rates increase, drive voltages increase as well. Excessive drive voltages currently limit practical implementation of ultra high bit rate modulators. New device designs, with reduced drive voltages, are critical to the development and large-scale commercial application of these modulators.
Among proposals for achieving lower drive voltages in Mach-Zehnder electro-optic modulators is the optimization of the region of interaction between the optic and electric fields. A technique that has had limited success is the etching of ridges into the lithium niobate crystal so the waveguide is located in a rdige of electro-optic material. This improves the field penetration and allows the drive voltage to be reduced. This structure also reduces the RF line capacitance in the interaction region. However, the profiles of the optical and electric fields in this device structure remain quite different, which prevents optimal interaction over the available interaction region.
STATEMENT OF THE INVENTION
We have designed a lithium niobate electro-optic modulator in which the profile of the electric field more closely matches the profile of the optic field where the two fields are at maximum. This result is achieved by shaping the geometry of the ridge in a ridge modulator structure which in turn shapes the electric field profile. Shaping essentially involves producing a ridge for the waveguide with a re-entrant sidewall. Using this expedient, the maximum in the electric field profile can be made to occur below the surface of the ridge, at a position closer to the maximum of the optic field. By matching the maxima in the profiles, the RF/optic overlap in the device can be enhanced substantially, thereby reducing the necessary drive voltage.


REFERENCES:
patent: 5091980 (1992-02-01), Ogawa et al.
patent: 5347601 (1994-09-01), Ade et al.
patent: 5561549 (1996-10-01), Hatori et al.
patent: 5781327 (1998-07-01), Brock et al.

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