Semiconductor optical amplifier performing polarization-independent operation

• US 6,545,801 B2
• Filed: 09/24/2001
• Issued: 04/08/2003
• Est. Priority Date: 12/01/2000
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Morito, Ken
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US09/960,400
• Publication Number:
  US 20020067541A1
• Time in Patent Office: 561 Days
• Field of Search: 359/344, 372/43, 372/44, 257/13, 257/18, 257/21, 257/432
• US Class Current: 359/344
• CPC Class Codes: H01S 5/1014 Tapered waveguide, e.g. spotsize converter H01S5/1064 takes precedence
• CPC Class Codes: H01S 5/1064 varying width along the optical axis
• CPC Class Codes: H01S 5/1085 Oblique facets
• CPC Class Codes: H01S 5/4043 with vertically stacked active layers
• CPC Class Codes: H01S 5/5009 the arrangement being polarisation-insensitive

Abstract

A semiconductor optical amplifier includes a plurality of active layers of bulk crystal with at least one intervening spacer for optical amplification, wherein each of the active layers accumulates a tensile strain therein.

Claims

1. A semiconductor optical amplifier, comprising:

a substrate extending from a first end surface to a second end surface;

a first cladding layer formed on said substrate with a first conductivity type;

a plurality of active layers formed on said first cladding layer each having a bandgap smaller than a bandgap of said first cladding layer;

at least one spacer layer interposed between said plurality of active layers and having a bandgap larger than said bandgap of said active layers;

a second cladding layer formed on said substrate so as to cover said plurality of active layers and said at least one spacer layer;

a first electrode injecting carriers to each of said plurality of active layers through said first cladding layer; and

a second electrode injecting carriers to each of said plurality of active layers through said second cladding layer;

each of said plurality of active layers accumulates a tensile strain therein.

2. A semiconductor optical amplifier as claimed in claim 1, wherein said plurality of active layers and said at least one spacer layer form an active layer structure, and wherein said active layer structure is sandwiched on said substrate by a pair of optical confinement layers having a bandgap lager than a bandgap of said active layers.

3. A semiconductor optical amplifier as claimed in claim 2, wherein said pair of optical confinement layers have a composition identical with said spacer layer.

4. A semiconductor optical amplifier as claimed in claim 1, wherein said spacer layer has a thickness of 100 nm or more.

5. A semiconductor optical amplifier as claimed in claim 1, wherein said spacer layer has a thickness of 200 nm or less.

6. A semiconductor optical amplifier as claimed in claim 1, wherein each of said plurality of active layers has a thickness exceeding 30 nm.

7. A semiconductor optical amplifier as claimed in claim 1, wherein each of said plurality of active layers has a thickness of 100 nm or less.

8. A semiconductor optical amplifier as claimed in claim 1, wherein each of said plurality of active layers has a thickness of about 40 nm.

9. A semiconductor optical amplifier as claimed in claim 1, wherein each of said plurality of active layers accumulates therein a tensile strain of 0.18% or less.

10. A semiconductor optical amplifier as claimed in claim 1, wherein each of said plurality of active layers has a width that decreases toward said first end surface and said second end surface.

11. A semiconductor optical amplifier as claimed in claim 1, wherein each of said plurality of active layers has a thickness that decreases toward said first end surface and said second end surface.

12. A semiconductor optical amplifier as claimed in claim 1, wherein each of said plurality of active layers form a stripe structure extending from said first end surface to said second end surface, said stripe structure crossing obliquely to each of said first and second end surfaces.

13. A semiconductor optical amplifier as claimed in claim 1, wherein each of said first and second end surfaces carries thereon an antireflection coating.

14. A wavelength-multiplexed optical telecommunication system comprising:

a plurality of optical sources having respective, mutually different wavelengths;

a first optical coupler coupling said plurality of optical sources to a single optical fiber;

a semiconductor optical amplifier provided in said optical fiber;

a second optical coupler dividing an optical signal amplified by said semiconductor optical amplifier to a plurality of output optical fibers; and

an optical detector coupled optically to each of said output optical fibers,

said semiconductor optical amplifier comprising;

a substrate extending from a first end surface to a second end surface;

a first cladding layer formed on said substrate with a first conductivity type;

a plurality of active layers formed on said first cladding layer each having a bandgap smaller than a bandgap of said first cladding layer;

at least one spacer layer interposed between said plurality of active layers and having a bandgap larger than said bandgap of said active layers;

a second cladding layer formed on said substrate so as to cover said plurality of active layers and said at least one spacer layer;

a first electrode injecting carriers to each of said plurality of active layers through said first cladding layer; and

a second electrode injecting carriers to each of said plurality of active layers through said second cladding layer;

each of said plurality of active layers accumulates a tensile strain therein,

an input end of said active layer being coupled optically to a first part of said single optical fiber,

an output end of said active layer being coupled optically to a second part of said single optical fiber.