WO1996009668B1

WO1996009668B1 - Optical device

Info

Publication number: WO1996009668B1
Application number: PCT/GB1995/002191
Authority: WO
Filing date: 1995-09-14
Publication date: 1996-05-23
Anticipated expiration: 1997-03-14

Abstract

An optical device for use as an amplifier or modulator comprises a semiconductor substrate (2) with an elongate waveguide region (1) with a light guiding boundary that extends between an input (3) and an output (4) for optical radiation. An optically active layer of material (6) produces amplification of light travelling inthe waveguide region (1). The width (w) of region (1) tapers outwardly from the input to allow amplification of input optical signals, and tapers towards the output (4) so as to concentrate the amplified light in a single mode to the output. The concentration of the amplified light in the active region may produce non-linear effects which are exploited in order to achieve data modulation or switching. In one embodiment, the waveguide region includes a first active region (30) to produce optical amplification, and a second passive region (31) for concentrating light to the output.

Claims

AMENDED CLAIMS

[received by the International Bureau on 5 March 1996 (05.03.96); original claims 1-32 replaced by amended claims 1-30 (5 pages)]

i 1. An optical device comprising an elongate waveguide region (1) having a boundary that extends along the length it) thereof to an optical output (4) at one end, an optical input (3) at the other end of the waveguide region for introducing optical radiation to be amplified therein, and active material (6, 15) for producing amplification of light travelling in the waveguide region, the to boundary being configured to concentrate the amplified light laterally within the waveguide region (1) towards the output (4).

2. A device as claimed in claim 1 wherein the waveguide region has a width (w) which tapers along the length (/) thereof towards the output (1).

;J

3. A device as claimed in claim 1 or 2 including means (10) for applying an electric current to the active material to produce optical amplification therein.

20 4. A device as claimed in claim 3 wherein the width (w) of the waveguide region progressively increases along the length (/) thereof from the input (3) to an intermediate region (5), from which the width of the waveguide region progressively decreases along the length thereof to the output (4).

2i 5. A device as claimed in claim 4 wherein the rate of increase and decrease of the width (w) of the waveguide region varies along the length (/) thereof.

6. A device as claimed in claim 4 or 5 wherein the boundary of the

30 waveguide region is parabolic in shape in regions (p) between the intermediate region (5) and the ends (3, 4) thereof, and conforms to portions of circular arcs (x, y, z) at the ends (3, 4) thereof and in the intermediate region (5). ^{O 96/09668} PCI7GB95/02191

20

7. A device as claimed in claim 5, 6 or 7 wherein the shape of the boundary is symmetrical on either side of the intermediate region (5).

8. A device as claimed in any preceding claim having a first source (22) of ; optical data pubes (K-) coupled to the input (3) of the waveguide region and a second source (23) of optical radiation (K-) coupled to the waveguide region.

9. A device as claimed in claim 8 wherein the radiation from the second source and the data pulses from the first source interact so as to produce gain to saturation in the active material, whereby the radiation from the second source is modulated by the data pulses.

10. A device as claimed in claim 9 wherein the data pulses comprise optical radiation at a first wavelength (λ,) and the radiation (K-) from the second a source comprises essentially continuous wave (ca;) optical radiation at a second different wavelength.

11. A device as claimed in claim 10 with a filter (25) coupled to the output of the waveguide region for preferentially passing the modulated radiation at

2o the second wavelength.

12. A device as claimed in claim 10 or 11 and coupling means (21) for coupling both the first source (22) and the second source (23) to the input (3) of the waveguide region (1).

25

13. A device as claimed in any one of claims 7 to 10 wherein the radiation from the sources interacts whereby the radiation from the first source is phase modulated by the data pulses from the second source.

30 14. A device as claimed in claim 13 with phase responsive means (27, 28) coupled to the output (4) of the waveguide region for comparing the phase modulated signals with the phase of signals from said output. 21

15. A device as claimed in any one of claims 7 to 14 wherein the radiation from the first and second sources interacts to produce radiation at the output (4) which is of a different wavelength from that of the radiation from the second source and the data pulses from the first source.

5

16. A device as claimed in claim 14 with filtering means (25) coupled to the output (4) of the waveguide region (1) and selectively responsive to said different wavelength at the output.

lo 17. A device as claimed in any preceding claim wherein the active material (6, 15) extends over the entire extent of the waveguide region (1).

18. A device according to any preceding claim including means (10a, 10b) for profiling the current density that in use passes through the aαive material

7 (6) for controlling optical gain saturation.

19. A device as claimed in claim 18 including a conduαive layer 10 for feeding an eleαric current through the aαive material (6), the conduαive layer being configured in first and second separate portions (10a, 10b) for applying 0 different values of current to different regions of the aαive material.

20. A device according to any one of claims 1 to 16, wherein the waveguide region (1) includes a first aαive portion (30) optically coupled to the aαive material (6) to produce the optical amplification, and a second

25 passive portion (31) which is not coupled to the aαive material and has its boundary configured to produce said concentration of the amplified light within the waveguide region towards the output.

21. A device as claimed in claim 20 wherein the passive portion has a 0 width (w) that tapers along the length (I) thereof towards the output.

22. A device as claimed in claim 20 or 21, wherein the aαive portion (30) 22

of the waveguide region has a width (w) which increases along the length (I) thereof in a direαion towards the output (4).

23. A device as claimed in claim 20, 21 or 22, wherein the waveguide J region (1) includes a passive optically transparent layer (32) extending through both of the aαive and passive portions, and a layer (6) of the aαive optical amplification, said layer (6) and the passive transparent layer (32) overlying one another in the aαive portion (30).

to 24. A device as claimed in any one of claims 20 to 22, wherein the waveguide region includes a heterolayer (6, 34) that comprises the aαive amplification material (6) in the aαive portion (30) and a passive transparent layer (34) in the passive portion (31).

is 25. A device as claimed in claim 24, wherein the heterolayer (6, 34) has been formed by seleαively removing a portion thereof and regrowing the layer (34) in the removed portion with different optical charaαeristics.

26. A device according to any precding claim including anti-refleαion 20 coatings on said input (3) and said output (4).

27. A device as claimed in any preceding claim wherein the aαive region comprises a buried heterostruαure (6) on a substrate (2).

25 28. A device as claimed in claim 27, wherein the aαive material (6) comprises a layer of InGaAsP disposed between a layer (7) of InP of a first conduαivity type and a region (9) of InP of a second conduαivity type.

29. A device as claimed in any one of claims 1 to 26 wherein the 30 waveguide region comprises a rib waveguide struαure (9, 10).

30. A device as claimed in claim 28 including a layer (14) of InP of a first 23

conduαivity type overlaid by a layer of i-InGaAsP (15) that comprises the aαive material, itself overlaid by a layer (16) of InGaAsP of a second conduαivity type, and an overlying strip (9) of InP having a configuration that defines the boundary of said waveguide region in said i-InGaAsP layer.