Electro-absorption modulator and monolithic electro-photonic integrated circuit comprising an electro-absorption modulator and driver electronics

1 . An electro-photonic device comprising

a semi-insulating (SI) indium phosphide (InP) substrate;

an epitaxial layer stack formed on the SI InP substrate comprising a first plurality of semiconductor layers forming an electro-absorption modulator (EAM) driver and an overlying second plurality of semiconductor layers forming an EAM;

the EAM driver comprising one or more InP heterojunction bipolar transistors;

the EAM configured as a PIN waveguide and comprising an n-layer structure, a p-layer structure and an i-region between the n-layer structure and the p-layer structure;

the i-region comprising an optical material defining an operational wavelength range;

the n-layer structure and the p-layer structure configured to optically confine one or more modes of an optical signal to propagate through the i-region; and

at least one of the n-layer structure and the p-layer structure comprising a mode-extending layer.

2 . The electro-photonic device of claim 1 , wherein the mode-extending layer comprises a quaternary material and the epitaxial layer stack is fabricated with group III-V semiconductor materials, including an Indium Phosphide (InP)-based material system comprising binary, ternary, quaternary and other compositions of In, Ga, As, P, Al and Sb.

3 . The electro-photonic device of claim 1 , wherein the mode-extending layer comprises one of:

i) an n-type layer in the n-layer structure;

ii) a p-type layer in the p-layer structure; and

iii) a p-type layer in the p-layer structure and an n-type layer in the n-layer structure.

4 . The electro-photonic device of claim 1 , wherein the i-region comprises an absorption material.

5 . The electro-photonic device of claim 4 , wherein the i-region comprises InGaAs or a quaternary absorption material selected within an InP-based materials system.

6 . The electro-photonic device of claim 4 , wherein the absorption material comprises a Quantum Confined Stark Effect (QCSE) multi-quantum well (MQW) structure comprising N wells and N−1 barriers.

7 . The electro-photonic device of claim 6 , wherein the MQW structure comprises InGaAsAl or InGaAsP.

8 . The electro-photonic device of claim 6 , wherein N is between ≥8 and ≤24.

9 . The electro-photonic device of claim 6 , wherein a well thickness, a barrier thickness and N are selected to provide a thickness d of the i-region which is related to a transit time limit t tr of carriers in the i-region, where t tr =d/v, and v is a carrier velocity of the carrier.

10 . The electro-photonic device of claim 6 , wherein a ratio of barrier thickness to well thickness is one of:

i) ≤1:1

ii) 6:10.

11 . The electro-photonic device of claim 1 , wherein a required performance of the EAM is achieved by balancing one or more parameter comprising:

parameters of equations defined herein;

parameters of a compositions, size, materials or doping of the epitaxial layer stack;

an extinction ratio;

inclusion of one or more separate confinement heterostructure (SCH) layers;

defining a refractive index of each layer of the epitaxial layer stack

selecting processing from MBE, MOCVD, or any other process;

balancing fall-off of voltage and/or electric field profile over a length of the i-region;

balancing a width of the i-region relative to a width of the EAM;

a transit time of a carrier (holes or electrons as the case may be);

a difference between the transit times of holes and electrons;

balancing a thickness d of the i-region and the transit time,

grading of one or more layers of the epitaxial layer stack;

inclusion of multi-quantum well MQW material and where used, balancing a number of wells and barriers and a ratio of thicknesses of wells to barriers;

providing an undercut to the i-region for reducing the width of the i-region relative to a width of a ridge of the waveguide, to reduce capacitance;

balancing an absorption length of the i-region with a RC value thereof;

balancing one or more parameter to accommodate absorption of a single mode or multiple modes in the i-region;

balancing a waveguide width, waveguide length and thickness of the i-region to provide a quantum efficiency (QE) of ≥80% over a required operational wavelength range;

balancing a waveguide width, waveguide length and thickness of the i-region to provide a capacitance of ≤0.70 fF/μm of length; and

wherein the waveguide is a ridge waveguide having a ridge width and a ridge length, and the i-region has a width which is less than the ridge width.

12 . The electro-photonic device of claim 1 , wherein a width of the i-region is tapered, having a first width at an optical input and narrowing to a second width at a back facet of the EAM.

13 . The electro-photonic device of claim 1 , wherein the waveguide is made from waveguide materials and dimensions selected to provide one or more of the following:

a dynamic extinction ratio (ER) of ≥5 dB;

a device capacitance of one of:

i) ≤0.85 fF/μm; and

ii) ≤0.70 fF/μm.

14 . The electro-photonic device of claim 1 , wherein the electro-photonic device is configured as a transmitter.

15 . The electro-photonic device of claim 1 , wherein the EAM driver is electrically interconnected by conductive traces to contact layers of the EAM.

16 . The electro-photonic device of claim 1 , comprising a spacer comprising one or more intermediate layers between the EAM driver and the EAM.

17 . The electro-photonic device of claim 16 , wherein the spacer comprises a semi-insulating layer.

18 . The electro-photonic device of claim 1 , wherein the EAM driver is formed on a first area of the substrate, and the EAM is provided on an adjacent area, and comprising an isolation region electrically isolating the first plurality of semiconductor layers of the first area from the first plurality of semiconductor layers of the adjacent area.

19 . An optical system comprising an electro-photonic device of claim 1 .

20 . The optical system of claim 19 , comprising two or more electro-photonic devices.

21 . The optical system of claim 19 , comprising one or more electro-photonic device operating as a transmitter and one or more electro-photonic devices operating as a receiver.

22 . The electro-photonic device of claim 1 , wherein the EAM is a ridge EAM having a ridge width in a range of 2 μm to 3 μm and wherein parameters of the i-region of the EAM are balanced to provide a required performance of the EAM by having at least one of:

i) a length of the i-region <100 μm

ii) a width of the i-region is less than the ridge width

iii) a thickness of the i-region <0.4 μm.

23 . A method of fabricating an electro-photonic device according to claim 1 , the method comprising

forming a semi-insulating (SI) indium phosphide (InP) substrate;

forming an epitaxial layer stack on the SI InP substrate comprising a first plurality of semiconductor layers forming an electro-absorption modulator (EAM) driver and an overlying second plurality of semiconductor layers forming an EAM;

configuring the EAM driver to comprise one or more InP heterojunction bipolar transistors;

configuring the EAM as a PIN waveguide, the PIN waveguide comprising:

an n-layer structure;

a p-layer structure; and

an i-region, between the n-layer structure and the p-layer structure, and comprising an optical material defining an operational wavelength range;

wherein the n-layer structure and the p-layer structure are configured to optically confine one or more modes of an optical signal to propagate through the i-region; and

wherein at least one of the n-layer structure and the p-layer structure comprising a mode-extending layer.

24 . The method of claim 23 , further comprising electrically interconnecting the EAM driver by conductive traces to contact layers of the EAM.

25 . The method of claim 23 , further comprising forming a spacer comprising one or more intermediate layers between the first plurality of semiconductor layers and the second plurality of semiconductor layers.

26 . The method of claim 25 , further comprising forming the spacer comprising a semi-insulating layer.

27 . The method of claim 23 , further comprising forming the EAM driver on a first area of the substrate, and forming the EAM on an adjacent area, and forming an isolation region electrically isolating the first plurality of semiconductor layers of the first area from the first plurality of semiconductor layers of the adjacent area.

28 . An optical device comprising:

an electro-absorption modulator (EAM); and

an integrated EAM driver circuit;

the EAM further comprising:

a semi-insulating (SI) indium phosphide (InP) substrate;

an epitaxial layer stack formed on the SI:InP substrate comprising a plurality of semiconductor layers structured to form the EAM, the epitaxial layer stack comprising:

an n-layer structure and a p-layer structure;

an i-region comprising optical material located between the n-layer structure and the p-layer structure, the i-region defining an operational wavelength range;

the n-layer structure and the p-layer structure configured to optically confine one or more modes of an optical signal configured to propagate through the i-region; and

one or more heterojunction bipolar transistors (HBTs) of the EAM driver circuit formed from another plurality of semiconductor layers of the epitaxial layer stack different from the plurality of semiconductor layers forming the EAM;

wherein at least one of the n-layer structure and the p-layer structure comprising a mode-extending layer.

29 . A waveguide (WG)-device configured to modulate light and comprising a p type material, an i-type material and an n-type materials (a PIN waveguide), the waveguide-device comprising:

a semi-insulating (SI) indium phosphide (InP) substrate;

an epitaxial layer stack formed on the SI:InP substrate comprising a plurality of semiconductor layers structured to form the WG device, the epitaxial layer stack comprising an n-layer structure and a p-layer structure and an i-region between the n-layer structure and the p-layer structure;

the i-region comprising optical material defining an operational wavelength range located and having a selected thickness d;

the n-layer structure and the p-layer structure configured to optically confine one or more modes of an optical signal configured to propagate through the i-region; and

wherein the selected thickness d of the i-region is related to a transit time t tr of carriers in the i-region to balance: one or more of:

i) a capacitance of the i-region;

ii) a required dynamic extinction ratio; and

iii) optical confinement of the one or more modes of the optical signal through the i-region for absorption;

where t tr =d/v, and v is a carrier velocity of the carrier.

30 . The waveguide (WG)-device of claim 29 , wherein the optical confinement of the one or more modes of the optical signal through the i-region is further provided by at least one mode-extending layer located in at least one of the n-layer structure and the p-layer structure.