Terminating impedance circuit for an electroabsorption modulator

Patent metadata

Field	Value
Publication number	US-2016202501-A1
Application number	US-201615074737-A
Country	US
Kind code	A1
Filing date	Mar 18, 2016
Priority date	Sep 19, 2013
Publication date	Jul 14, 2016
Grant date	—

Abstract

A terminating impedance circuit, which is thermally decoupled from a substrate, for an electroabsorption modulator, having a modulator capacitance includes a series resistance-emphasized RF delay line exhibiting an impedance distributed over its length, wherein the spatially distributed impedance has at least a predominant resistance per unit length, an inductance per unit length tuned to the modulator capacitance, and a parasitic capacitance per unit length, wherein the resistance per unit length takes the function of a terminating resistor, wherein furthermore the inductance per unit length, together with the modulator capacitance, forms a strongly damped resonant circuit which provides, together with the terminating impedance circuit, for a controlled increase in the frequency response of the electroabsorption modulator within an operating frequency range, and wherein, at least for radio-frequency signals, the parasitic capacitance per unit length is negligible relative to the modulator capacitance.

First claim

1 . A device comprising:
an electroabsorption modulator comprising a modulator capacitance, and a terminating impedance circuit connected in parallel to the electroabsorption modulator; wherein the terminating impedance circuit comprises an RF delay line comprising an impedance distributed over its length, wherein the spatially distributed impedance comprises a resistance per unit length, an inductance per unit length, and a parasitic capacitance per unit length, wherein the resistance per unit length and the line length of the RF delay line define a desired terminating impedance for the electroabsorption modulator, wherein the inductance per unit length and the line length of the RF delay line are selected to define, together with the modulator capacitance of the electroabsorption modulator, a damped resonant circuit system comprising a resonance frequency at a predefined value below an upper operating frequency limit of the electroabsorption modulator, thereby causing a controlled increase in the frequency response of the electroabsorption modulator within an operative frequency range, wherein the RF delay line is implemented to be a strip line, and wherein the RF delay line exhibits the following parameters:
resistance per unit length between 20 kohm/m and 200 kohm/m,
inductance per unit length between 100 nH/m and 1000 nHm,
leakage per unit length smaller than 20 mS/mm, and
capacitance per unit length between 10 pF/m and 200 pF/m.

2 . The device in accordance with claim 1 , comprising a dielectric for insulating the RF delay line both electrically and thermally from the electroabsorption modulator and/or a feeding laser source.

3 . The device in accordance with claim 1 , wherein the RF delay line comprises an input terminal which is connected to the electroabsorption modulator, and comprises an output-side short-circuit.

4 . The device in accordance with claim 3 , wherein the RF delay line and the output-side short-circuit are integrated monolithically or implemented together as a monolithic microwave circuit.

5 . The device in accordance with claim 3 , wherein the output-side short-circuit comprises an advantageously integrated capacitor or several parallel capacitors.

6 . The device in accordance with claim 1 , wherein the electroabsorption modulator and the terminating impedance circuit are integrated monolithically or implemented together as a monolithic microwave circuit.

7 . The device in accordance with claim 1 , wherein the strip line comprises a dielectric of a thickness between 0.1 μm and 10 μm and a relative permittivity ε r between 1.8 and 13.

8 . The device in accordance with claim 1 , wherein the RF delay line is of a meandering, serpentine or spiral implementation.

9 . The device in accordance with claim 1 , wherein the RF delay line comprises a broadening or tapering cross-section or width or comprises a stepped line tapering.

10 . The device in accordance with claim 1 , wherein the RF delay line comprises a length of at least 1/10 of the wavelength at the upper operating frequency limit of the electroabsorption modulator.

11 . The device in accordance with claim 1 , wherein the RF delay line comprises at least one of the following materials: gold, titanium, platinum, silver, nickel, chromium, tungsten.

12 . The device in accordance with claim 1 , wherein the RF delay line is realized alternatingly in sections over its length on a dielectric and in the form of airbridges.

13 . The device in accordance with claim 1 , wherein the parameters of the RF delay line are selected such that a resonance-distributed system, which comprises the electroabsorption modulator and the RF delay line, comprises a quality factor Q<1.

Assignees

• Fraunhofer Ges Forschung

Inventors

• Bach Heinz-Gunter
• Moehrle Martin
• Przyrembel Georges

Classifications

• G02F2001/0155

  Physics · mapped topic

• G02F1/015 Primary

  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction (G02F1/03 takes precedence) · CPC title

• G02F1/0155

  modulating the optical absorption · CPC title