The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Oct. 20, 1998
Filed:
Jan. 12, 1996
Alex Harwit, Palo Alto, CA (US);
Lockheed Missiles & Space Co., Sunnyvale, CA (US);
Abstract
An electro-optic modulator (300) comprises a multiple quantum well core layer (320) in which the band gap and refractive index are adjusted to make the core layer (320) transparent to light at a selected wavelength and a voltage tunable, multiple quantum well cladding layer (330) in which an exciton absorption provides the cladding layer (330) with a first refractive index that is less than the core refractive index when a first voltage is applied and a second refractive index that approaches or exceeds the core refractive index when a second voltage is applied. The exciton absorption also provides the voltage tunable cladding layer (330) with a substantially greater absorption coefficient at the selected wavelength than that of the core layer (320). The core and voltage tunable cladding layers (320, 330) are combined with a second cladding layer (310) to form a waveguide in which light is confined to the low loss core layer (320) in the first voltage state and diverted into the highly absorbing voltage tunable cladding layer (330) in the second voltage state. In a preferred embodiment of the modulator (300), the multiple quantum well core and cladding layers (320, 330) comprise GaAs quantum wells and AlGaAs barriers. The small effective absorption coefficient of the core layer (320) and the large difference between this absorption coefficient and that of the voltage tunable cladding layer (330) in the off state provide a modulator (300) characterized by a higher contrast ratio and, simultaneously, a lower insertion loss than are available from conventional electro-absorption or electro-refraction based modulators.