# US 2024/0204484 A1 · Multi-section high power semiconductor optical amplifier (soa) and fabrication method thereof

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- Number: US 2024/0204484 A1
- Document ID: US20240204484A1
- Status: Published application
- Kind: A1
- Application number: 18/084,896
- Filed: 2022-12-20
- Published: 2024-06-20
- Earliest claimed: 2022-12-20
- Assignees: Applied Optoelectronics, Inc.
- Applicants: Applied Optoelectronics, Inc.
- Inventors: Dapeng XU; Klaus Alexander ANSELM; Huanlin ZHANG
- Web page: https://patentgrep.com/patent/US20240204484A1

## CPC

- H01S 5/2054: {Methods of obtaining the confinement}
- H01S 5/0206: {Substrates, e.g. growth, shape, material, removal or bonding; (specific crystal orientation H01S5/3202)}
- H01S 5/0265: {Intensity modulators (intra-cavity modulators H01S5/0625)}
- H01S 5/1014: {Tapered waveguide, e.g. spotsize converter (H01S5/1064 takes precedence)}
- H01S 5/227: Buried mesa structure {; Striped active layer}
- H01S 5/2275: {mesa created by etching}
- H01S 5/34306: {emitting light at a wavelength longer than 1000nm, e.g. InP based 1300 and 1500nm lasers}
- H01S 5/50: Amplifier structures not provided for in groups H01S5/02 - H01S5/30
- H01S 5/5027: {Concatenated amplifiers, i.e. amplifiers in series or cascaded}
- H01S 5/34: comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers (H01S5/36 takes precedence)
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL

## Abstract

A multi-section semiconductor optical amplifier (SOA) includes at least two sections in series—an input section at an input side and an output section at an output side—with the input section having a higher optical confinement (also referred to as a high gamma) and the output section having a lower optical confinement (also referred to as a low gamma). The input section may also have a shorter length than the output section. The multi-section structure allows optimizing the input side and the output side design separately such that the input section provides a high gain section configured to quickly increase optical power and the output section provides a low differential gain section that improves saturation. As a result, the multi-section SOA can achieve higher output power with high gain and lower signal noise while demanding low input power.

## Claims

### Claim 1

A multi-section semiconductor optical amplifier (SOA), comprising:
an input section disposed at an input side of the semiconductor optical amplifier, the input section having a first optical confinement factor Γ1, and wherein the input section provides a first optical gain;
an output section disposed at an output side of the semiconductor optical amplifier, the output section having a second optical confinement factor Γ2, and wherein the output section provides a second optical gain; and
wherein the first optical confinement factor Γ1 is higher than the second optical confinement factor Γ2, and wherein the first optical gain is higher than the second optical gain.

### Claim 2 (depends on 1)

The multi-section semiconductor optical amplifier according to claim 1 wherein the first optical confinement factor 1 is in a range of 2% to 15% and the second optical confinement factor Γ2 is in a range of 1% to 9%.

### Claim 3 (depends on 1)

The multi-section semiconductor optical amplifier according to claim 1 wherein the input section has a first length L1, wherein the output section has a second length L2, and wherein the second length L2 is longer than the first length L1.

### Claim 4 (depends on 3)

The multi-section semiconductor optical amplifier according to claim 3 wherein the first length L1 is in a range of 100 μm to 1 mm and wherein the second length L2 is in a range of 1 mm to 4 mm.

### Claim 5 (depends on 1)

The multi-section semiconductor optical amplifier according to claim 1, wherein input section and the output section are formed by a same active region.

### Claim 6 (depends on 5)

The multi-section semiconductor optical amplifier according to claim 5, further including a substrate, a buffer layer on the substrate, the active region on the buffer layer, and at least one cladding layer on the active region, wherein the active region includes first bottom SCH layer extending only in the output section and a second bottom SCH layer extending across both the input section and the output section.

### Claim 7 (depends on 6)

The multi-section semiconductor optical amplifier according to claim 6, wherein the active region further includes a MQW layer on the second bottom SCH layer and a top SCH layer on the MQW layer.

### Claim 8 (depends on 1)

The multi-section semiconductor optical amplifier according to claim 1, wherein the input section and the output section are formed by different active regions.

### Claim 9 (depends on 8)

The multi-section semiconductor optical amplifier according to claim 8, further including a substrate, a buffer layer on the substrate, first and second active regions on the buffer layer and in the input section and the output section, respectively, and at least one cladding layer on the active regions.

### Claim 10 (depends on 9)

The multi-section semiconductor optical amplifier according to claim 9, wherein the first active region includes a first bottom SCH layer and a first MQW layer on the first bottom SCH layer and a first top SCH layer on the first MQW layer and wherein the second active region includes a second bottom SCH layer and a second MQW layer on the second bottom SCH layer and a second top SCH layer on the second MQW layer, and wherein the first and second optical confinement factors Γ1, Γ2, are provided by different SCH thicknesses, different SCH compositions and/or different MQW layers.

### Claim 11

A method of fabricating a semiconductor optical amplifier (SOA), comprising:
providing a substrate;
depositing, on the substrate, a buffer layer, a first bottom SCH layer and a cap layer to form a starting structure;
depositing a patterning mask layer on a portion of the starting structure;
etching another portion of the starting structure layer to form a mesa structure and to expose a portion of the buffer layer;
depositing a side layer on the portion of the buffer layer on one side of the mesa structure;
removing the patterning mask layer; and
depositing, on the cap layer and the side layer, a second bottom SCH layer, a MQW layer, a top SCH layer and at least one top cladding layer, wherein the second bottom SCH layer, the MQW layer, and the top SCH layer form a portion of an active region extending across both an input section and an output section of the SOA, and wherein the first bottom SCH layer forms a portion of the active region extending only in the output section of the SOA.

### Claim 12 (depends on 11)

The method of claim 11 wherein the substrate is an InP substrate, the buffer layer is an InP buffer layer, the first and second bottom SCH layers are InGaAsP SCH layers, the top SCH layer is an InGaAsP SCH layer, and the at least one top cladding layer includes an InP layer and an InGaAs layer.

### Claim 13 (depends on 11)

The method of claim 11 wherein the input section has a first optical confinement factor and the output section has a second optical confinement factor, and wherein the first optical confinement factor is higher than the second optical confinement factor.

### Claim 14 (depends on 13)

The method of claim 13 wherein the input section has a first length and the output section has a second length, and wherein the first length is less than the second length.

### Claim 15

A method of fabricating a semiconductor optical amplifier (SOA), comprising:
providing a substrate;
depositing, on the substrate, a buffer layer, a first bottom layer, a first MQW layer, a first top SCH layer, and a first cap layer to form a first SOA active structure including a first active region;
depositing a patterning mask layer on a portion of the first SOA active structure;
etching another portion of the first SOA active structure to form a mesa structure and to expose a portion of the buffer layer;
depositing, on the portion of the buffer layer, a second bottom SCH layer, a second MQW layer, a second top SCH layer, and a second cap layer to form a second SOA active structure including a second active region;
removing the patterning mask layer;
depositing at least one top cladding layer on the cap layers, wherein the first active region is located in an input section and the second active region is located in an output section, and wherein different optical confinement factors are achieved in the first and second active regions by different SCH thicknesses, different SCH compositions and/or different MQW layers.

### Claim 16 (depends on 15)

The method of claim 15 wherein the substrate is an InP substrate, the buffer layer is an InP buffer layer, the first and second bottom SCH layers are InGaAsP SCH layers, the first and second top SCH layers are InGaAsP SCH layers, and the top cladding layers include an InP layer and an InGaAs layer.

### Claim 17 (depends on 15)

The method of claim 15 wherein the input section has a first optical confinement factor and the output section has a second optical confinement factor, and wherein the first optical confinement factor is higher than the second optical confinement factor.

### Claim 18 (depends on 17)

The method of claim 17 wherein the input section has a first length and the output section has a second length, and wherein the first length is less than the second length.