Bipolar junction transistor optical modulator
AssigneeMassachusetts Institute of Technology
InventorsRajeev J. Ram, Marc De Cea Falco, Jin Xue
Life of this patent
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Abstract
Semiconductor optical modulators are described that utilize bipolar junction transistor (BJT) structure within the optical modulator. The junctions within the BJT can be designed and biased to increase modulator efficiency and speed. An optical mode may be located in a selected region of the BJT structure to improve modulation efficiency. The BJT structure can be included in optical waveguides of interferometers and resonators to form optical modulators.
Claims20
An optical device to modulate an optical wave passing through the optical device, the optical device comprising:
- an optical waveguide;
- a first doped region in the optical waveguide forming an emitter of a bipolar junction transistor;
- a second doped region in the optical waveguide forming a base of the bipolar junction transistor;
- a third doped region forming a collector of the bipolar junction transistor, wherein a base-emitter junction between the base and the emitter is configured to operate in a forward-bias mode and a base-collector junction between the base and the collector is configured to operate in a reverse-bias mode to modulate the optical wave;
- and
- a selected region within the optical waveguide for the optical wave to pass through, the optical wave having a transverse optical mode profile when present in the optical waveguide, wherein
- the selected region is configured to contain the optical mode down to a 1/e intensity value relative to a peak intensity of the optical mode,
- a center of the selected region is located between the base-emitter junction and the base-collector junction, and
- the transverse optical mode profile above the 1/e intensity value is contained within a first portion of the emitter where a minority carrier concentration is greater than 20% of a peak value of the minority carrier concentration in the emitter and a second portion in the base where a minority carrier concentration in the base is greater than 20% of a peak value of the minority carrier concentration in the base.
A method of modulating an optical wave, the method comprising:
- passing the optical wave through an optical waveguide containing at least a portion of a bipolar junction transistor (BJT) structure, wherein a peak intensity of the optical wave passes within 300 nm of a peak change in an injected minority-carrier concentration within a base of the BJT structure, and wherein a transverse mode profile from the peak intensity down to a 1/e relative intensity level of the optical wave is contained within a first portion of an emitter of the BJT structure where a minority carrier concentration is greater than 20% of a peak value of the minority carrier concentration in the emitter and a second portion in a base of the BJT structure where a minority carrier concentration in the base is greater than 20% of a peak value of the minority carrier concentration in the base;
- electrically modulating, under forward-bias conditions, a base-emitter junction of the BJT structure to change the injected minority-carrier concentration;
- and
- reverse biasing a base-collector junction of the BJT structure to remove minority carriers from the base of the BJT structure.
Dependencies are inferred from the claim text.