US20190310496A1

US20190310496A1 - Optoelectronic device and array thereof

Info

Publication number: US20190310496A1
Application number: US16/375,797
Authority: US
Inventors: Aaron John Zilkie; Andy McKee; Pradeep Srinivasan
Original assignee: Compound Semiconductor Technologies Global Ltd; Rockley Photonics Ltd
Current assignee: Compound Semiconductor Technologies Global Ltd; Rockley Photonics Ltd
Priority date: 2018-04-06
Filing date: 2019-04-04
Publication date: 2019-10-10
Also published as: US20210199995A1; US11681167B2; US20210080761A1; GB2572641A; US20210311333A1; US20200363663A1; GB201805782D0; US20230359069A1; GB2572641B; WO2019193111A1; CN210864104U; CN110346868A

Abstract

An optoelectronic device and an array comprising a plurality of the same. The device(s) comprising: an optically active region with an electrode arrangement for applying an electric field across the optically active region; a first curved waveguide, arranged to guide light into the optically active region; and a second curved waveguide, arranged to guide light out of the optically active region; wherein the first curved waveguide and the second curved waveguide are formed of a material having a different band-gap to a band-gap of the optically active region, and wherein the overall guided path formed by the first curved waveguide, the optically active region and the second curved waveguide is U-shaped.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to United Kingdom Patent Application No. GB 1805782.8, filed Apr. 6, 2018, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

Some embodiments of the present invention relate to a high speed optoelectronic device having curved waveguides which both curve in a same direction.

BACKGROUND

In conventional optoelectronic devices an input waveguide couples a facet on a first edge of the device to an optically active region. An output waveguide then couples the optically active region to a facet on a second edge of the device, generally opposite the first. This is because introducing curvatures into waveguides can substantially increase the signal loss incurred by transmission through the same.
However, such devices are more difficult to hybrid integrate into silicon and require longer driver interconnect lengths when in an array form as the active region cannot be located near the edge of the device.

SUMMARY

Some embodiments of the invention provide an optoelectronic device which utilizes curved waveguides formed of a material having a band-gap which is different from an optically active region. The optoelectronic device may have a high speed optoelectronic part and be connected by short traces to an electronic chip such as an ASIC. Shorter traces can advantageously lead to faster operation.
Accordingly, in a first aspect, some embodiments of the invention provide an optoelectronic device comprising: an optically active region with an electrode arrangement for applying an electric field across the optically active region; a first curved waveguide, arranged to guide light into the optically active region; and a second curved waveguide, arranged to guide light out of the optically active region; wherein the first curved waveguide and the second curved waveguide are formed of a material having a different band-gap to a band-gap of the optically active region, and wherein the overall guided path formed by the first curved waveguide, the optically active region and the second curved waveguide is U-shaped. That is to say, the first curved waveguide, second curved waveguide and the optically active material together form a waveguide U-bend. The optically active region and electrode arrangement together act as a high speed optoelectronic part fabricated in the active material of the optically active region, and located at the base of the “U”.
In this way, it allows the high speed optoelectronic part of the optically active region to be located near an edge of the optoelectronic device, but to retain a device large enough to facilitate flip-chip bonding. Furthermore, by de-coupling the optically active region from the curved waveguides (which may be passive), the performance of the optically active region can be optimized without requiring modification of the curved waveguides.
The first curved waveguide or the second curved waveguide may be formed as quantum well intermixed or epitaxially regrown waveguide(s).
The maximum distance between the first curved waveguide and the second curved waveguide may be no more than 250 μm for applications requiring high density integration of multiple optoelectronic devices in array such as co-packaging with ASICs. The maximum distance may also be between 100 μm and 160 μm, or greater than 250 μm in applications where high density integration is not needed.
A radius of curvature of the first curved waveguide or the second curved waveguide is less than 100 μm. The radius of curvature may be between 10 μm and 80 μm, for example between 30 um and 80 um.
The first curved waveguide and the second curved waveguide each curve through an angle of 90°.
The optoelectronic device may further comprise first and second electrodes, said electrodes being disposed on a first side of the optically active region and electrically connected thereto. The first electrode may be a signal electrode and the second electrode may be a ground electrode. The optoelectronic device may further comprise a third electrode which is a second ground electrode.
The first curved waveguide and the second curved waveguide may be low-loss passive waveguides. By low-loss, it may be meant that the first and second curved waveguides incur less attenuation of an optical signal than the optically active region at a wavelength of operation of the optically active region.
The first curved waveguide or the second curved waveguide may be deep-etched waveguides. By deep-etched, it may be meant that either the waveguides are slab waveguides (as opposed to rib waveguides) or that a sidewall etch step is deeper than the centre of the optical mode of the waveguides. The deep-etched waveguides may be formed of indium phosphide.
The optoelectronic device may further comprise a passive low-loss input waveguide coupled to or provided as a continuation of the first curved waveguide; and a passive low-loss output waveguide coupled to or provided as a continuation of the second curved waveguide; wherein each of the input waveguide and the output waveguide have an end adjacent to a first edge of the optoelectronic device, and the same band-gap as the first and second curved waveguides. The first and second electrodes described above may be disposed adjacent to an edge of the optoelectronic device which is different to the first edge.
The optoelectronic device may further comprise: a distributed feedback laser, coupled to the first curved waveguide; and an output waveguide, coupled to or provided as a continuation of the second curved waveguide; such that the optoelectronic device is an electro-absorption modulated laser. The distributed feedback laser may be formed of a material having a band-gap which is the same as the band-gap of the optically active region, or may have a third band-gap different from that of both the optically active region and the first and second curved waveguides.
The high speed optoelectronic part of the optically active region may be an electro-absorption modulator. When a distributed feedback laser is also included, the device may be an electro-absorption modulated laser (EML). The high speed optoelectronic part may also be inter alia a MOS-CAP Mach-Zehnder modulator or a ring resonator modulator.
The first curved waveguide and the second curved waveguide may be formed of a material having a band-gap which is lower in wavelength than a band-gap of the optically active region.
Each of the first and second curved waveguides may take the form of an Euler bend, examples of which can be found in U.S. Pat. No. 9,778,417 B1.
In a second aspect, some embodiments of the invention provide an array of optoelectronic devices disposed on a chip, wherein: each optoelectronic device is set out as described in relation to the first aspect; and a distance between optically active region of adjacent pairs of optoelectronic devices is no more than 250 μm.
Each optoelectronic device may have: an input waveguide coupled to or provided as a continuation of each first curved waveguide; and an output waveguide coupled to or provided as a continuation of each second curved waveguide; wherein each input waveguide and each output waveguide has a first end distal to its respective optically active region, and adjacent to a same side of the chip.
Each optoelectronic device may have: a distributed feedback laser, coupled to each first curved waveguide; and an output waveguide, coupled to or provided as a continuation of each second curved waveguide; such that the optoelectronic device is an electro-absorption modulated laser; wherein an end of each output waveguide distal to its respective optically active region is adjacent to a same side of the chip.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIGS. 1A-10 each show a variant of an optoelectronic device according to an embodiment of the invention;

FIG. 2 shows a further optoelectronic device, the device including a distributed feedback laser (DFB);

FIGS. 3A and 3B each show further optoelectronic devices according to embodiments of the present invention, the optoelectronic devices including a semiconductor optical amplifier (50A);

FIGS. 4A and 4B each show yet further optoelectronic devices according to embodiments of the present invention, where these devices also include a semiconductor optical amplifier.

FIG. 5 shows an array of optoelectronic devices according to an embodiment of the invention; and

FIG. 6 shows an array of optoelectronic devices according to an embodiment of the invention.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES

FIG. 1A shows an optoelectronic device 100. The device is formed on a III-V semiconductor chip or wafer 101 and is made with, for example, InGaAsP/InP or InAlGaAs/InP. The device generally comprises an optically active region 102, formed of a first material structure (for example InGaAsP or InAlGaAs multiple quantum well heterostructure, InGaAsP, or InAlGaAs bulk material) which has an associated band-gap. Adjacent to opposing ends of the optically active region are first 103 and second 104 curved waveguides. The first curved waveguide 103, the optically active region 102 and the second curved waveguide 104 together form a U-bend; a U-shaped guided optical path. The first and second curved waveguides are formed of or adjusted to have a material structure which has a different band-gap from that of the optically active region. The different bandgaps are achieved by either adjusting the atomic ratios of the elements in the InGaAsP or InAlGaAs quaternaries in certain layers, or changing the thicknesses or material interface profile of the quantum wells in the multiple quantum well heterostructures. The band-gap in the waveguides is typically made to be lower than that in the optically active region. The shift in band-gap wavelength may be 50-100 nm lower, and in some examples may be up to 200 nm lower. The first and second curved waveguides are passive devices in that they are not used to actively modulate optical signals being passed therethrough. In the example shown in this figure, the curved waveguides have an effective radius of curvature of 50 μm, or around 50 μm. The curved waveguides may be either quantum well intermixed or regrown so as to change the band-gap of the curved waveguides relative to the optically active region 102. The degree of curvature of the curved waveguides may be described as a tight bend or Euler bend. The degree of curvature in this example is 90°.
Quantum well intermixing is a process where the atoms from quantum wells and their corresponding barriers interdiffuse, or where an impurity material (e.g. zinc or copper or alloys thereof) are diffused into the active region by high temperature annealing. Interdiffusion can be achieved using laser irradiation to accomplish intermixing through photo-absorption induced disordering, or other methods such as implantation of elements which introduce point defects that induce interdiffusion, or the impurity-free-diffusion method (as disclosed in, for example, Helmy et al, IEEE Journal of Selected Topics in Quantum Electronics, Vol. 4, No. 4, July/August 1998, pp 653-660). Impurity diffusion may be done by patterning a surface of the device body with areas of the impurity material, which may be incorporated in a carrier material, and then raising the device body temperature for a controlled predetermined time (e.g. annealing) which may cause the impurity material to diffuse into the optically active region (e.g. quantum wells), and out-diffusion of existing ions or atoms from the optically active region (e.g. quantum wells) to the carrier or substrate material or spacer layers, as described for example in U.S. Pat. No. 6,719,884 B2. Regrowing is a process where a portion of the existing semiconductor optically active material is etched away, and then a second optically active material with a different band-gap wavelength (e.g. with different atomic ratios of elements, or different quantum well thicknesses) are re-grown into the region that was etched away. The regrowth may be epitaxial.
An input waveguide 105 couples an edge 109 of the chip 101 to one end of the first curved waveguide 103. Similarly, an output waveguide 106 couples the second curved waveguide 104 to the same edge 109 of the chip 101. The input and output waveguides are either distinct waveguides to the first and second curved waveguides or provided as continuations thereof, but have the same band-gap as the curved waveguides 103 and 104. The input and output waveguides may be coupled to tapers or mode converters near the edge 109 of the chip 101.
The device also includes a signal electrode 107 and ground electrode 108 to electrically drive the optically active region. In this example, both electrodes are disposed adjacent to a second edge 110 of the chip, which is on an opposite side to the edge 109 adjacent to the input and output waveguides. As both electrodes are on the same edge of the chip, this allows flip-chip bonding with short RF traces or wire bonding with short wire bond lengths to an off-chip driver chip. The distance between the input waveguide 105 and the output waveguide 106 in the device may be used to determine an overall ‘width’ of the optoelectronic device. This width may be less than 250 μm, and may be between 100 μm and 160 μm.
FIG. 1B shows a variant device which differs from the device of FIG. 1A in that an additional ground electrode 111 is disposed on an opposing side of the source or signal electrode 107 to the first ground electrode 108. Aside from this, the device is identical to that shown in FIG. 1A. Similarly, the device shown in FIG. 10 differs from that shown in FIG. 1A in that the ground electrode 108 and the source or signal electrode 107 have been swapped so that the ground electrode 108 is located proximate the first curved waveguide 103 and the source/signal electrode 107 is located proximate the second curved waveguide 104.
FIG. 2 shows an alternative device 200, which shares a number of features with the device 100 discussed above. Like features are indicated by like reference numerals. The device 200 in FIG. 2 however contains a distributed feedback laser 201 instead of the input waveguide 105 (as discussed above). The laser is coupled to the first curved waveguide 103, so as to provide laser light to the optically active region 102. The distributed feedback laser 201 may be formed of a material having a band-gap which is the same (or substantially the same) as the optically active region. Alternatively, it can formed of a material having a band-gap which is different from both the optically active region and the passive waveguide regions. Whilst not shown, the electrodes 107 and 108 in the device 200 can have any of the configurations described above in FIGS. 1A-10.
FIG. 3A shows an alternative device 300A, which shares a number of features with the device 100 discussed above. Like features are indicated by like reference numerals. The optically active region 102 forms a high speed optoelectronic device such as an electro-absorption modulator EAM. The device 300A differs from the device 100 shown in FIG. 10 in that it further comprises a semiconductor optical amplifier (SOA), the SOA including a further optically active region 112, a further ground electrode 118, and a further source electrode 117. The EAM and SOA are typically formed of the same semiconductor materials but may be different on structure and/or compositions. The EAM and SOA are both located at the base of the U-bend, in-between the first curved waveguide 103 and the second curved waveguide 104.
FIG. 3B shows an alternative device 300B, which shares a number of features with the device 300A discussed above in relation to FIG. 3A. Again, like features are indicated by like reference numerals. The device differs from that of FIG. 3A in that it includes a distributed feedback laser 201 coupled to the first curved waveguide 103. The device differs from that of FIG. 2 in that it comprises a SOA region located at the base of the U-bend, adjacent the optically active region 102 of the EAM.
FIGS. 4A and 4B show alternative devices which differ from the devices of FIGS. 3A and 3B respectively in that rather than being located at the base of the U-bend, the SOA is located at the other side of the second curved waveguide 104 to the first optically active region 102 of the EAM. In other words, the SOA is located on the leg of the U-bend, along the output waveguide 106.
In each of the embodiments described above in relation to FIGS. 3A, 3B, 4A and 4B, the electrode pads 107, 108, 117, 118, could be positioned in other locations and in other configurations. The DFB and SOA pads are DC pads and so may be positioned away from the edge of the die. However, the EAM pads are RF pads and should therefore be located close to the edge of the die.
FIGS. 3A and 3B show the SOA also at the edge and close to the EAM. Thus there could be a single driver chip (DC and RF), but it is noted that the spacing of the waveguides is quite large. To reduce the spacing, an arrangement such as FIGS. 4A and 4B can be used but here the EAM is distance from the SOA and so the RF (high speed) driver may be a separate chip from the DC driver/source.
In any one of the embodiments described above, the DFB and SOA are forward biased whilst the EAM is reverse biased.
FIG. 5 shows an array 500 of high speed optoelectronic devices 100 a-100 n disposed on a single wafer or chip. As can be seen, all of the input and output waveguides are coupled to the same edge of the chip which can facilitate flip-chipping to a host PIC with only one side of the chip requiring precise alignment to the host PIC waveguides, or fiber attachment to only one side of the chip, and installation in an optical network. Of note is the pitch 501 between devices i.e. the distance between like features in adjacent optoelectronic devices 100 a-100 n. For example, the distance between the input waveguide in optoelectronic device 100 a and the respective input waveguide in the optoelectronic device 100 b may be referred to as the pitch. The pitch is generally less than 250 μm.
FIG. 6 shows an alternative array 600 of high speed optoelectronic devices 200 a-200 n disposed on a single wafer or chip. As can be seen, all of the output waveguides are coupled to the same edge of the chip which can facilitate flip-chipping to a host PIC with only one side of the chip requiring precise alignment to the host PIC waveguides, or fiber attachment to only one side of the chip, and installation in an optical network. Of note is the pitch 601 between devices i.e. the distance between like features in adjacent optoelectronic devices 200 a-200 n. For example, the distance between the output waveguide in optoelectronic device 200 a and the respective output waveguide in the optoelectronic device 200 b may be referred to as the pitch. The pitch is generally less than 250 μm.
Whilst not shown, an array of optoelectronic devices as described above may include at least one optoelectronic device according to FIGS. 1A-10 and at least one optoelectronic device according to FIG. 2.
While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. As used herein, the word “or” is inclusive, so that, for example, “A or B” means any one of (i) A, (ii) B, and (iii) A and B.
All references referred to above are hereby incorporated by reference.

LIST OF FEATURES

100, 200 Optoelectronic device
101 Wafer/chip
102 optically active region
103 First curved waveguide
104 Second curved waveguide
105 Input waveguide
106 Output waveguide
107, 117 Source/signal electrode
108, 118 Ground electrode
109 First edge of chip
110 Second edge of chip
111 Additional ground electrode
201 Distributed feedback laser (DFB)
300, 400 Array
301, 401 Pitch

Claims

1. An optoelectronic device comprising:

an optically active region with an electrode arrangement for applying an electric field across the optically active region;

a first curved waveguide, arranged to guide light into the optically active region; and

a second curved waveguide, arranged to guide light out of the optically active region;

wherein the first curved waveguide and the second curved waveguide are formed of a material having a different band-gap to a band-gap of the optically active region, and wherein the overall guided path formed by the first curved waveguide, the optically active region and the second curved waveguide is U-shaped.

2. The optoelectronic device of claim 1, wherein the first curved waveguide or the second curved waveguide are formed as quantum well intermixed or regrown waveguide(s).

3. The optoelectronic device of claim 1,

wherein a maximum distance between the first curved waveguide and second curved waveguide is no more than 250 μm, or,

a radius of curvature of the first curved waveguide, or,

the second curved waveguide is less than 100 μm, or,

the first curved waveguide and the second curved waveguide each curve through an angle of 90°.

4. The optoelectronic device of claim 1, wherein the electrode arrangement further comprises first and second electrodes, said electrodes being disposed on a first side of the optically active region and electrically connected thereto.

5. The optoelectronic device of claim 4, wherein the first electrode is a signal electrode and the second electrode is a ground electrode.

6. The optoelectronic device of claim 5, further comprising a third electrode which is a second ground electrode.

7. The optoelectronic device of claim 4, configured to operate as an electro-absorption modulator.

8. The optoelectronic device of claim 1, wherein the first curved waveguide and the second curved waveguide are low-loss passive waveguides.

9. The optoelectronic device of claim 1, wherein the first curved waveguide or the second curved waveguide are deep-etched waveguides.

10. The optoelectronic device of claim 9, wherein the deep-etched waveguides are formed of indium phosphide.

11. The optoelectronic device of claim 1, further comprising:

an input waveguide coupled to or provided as a continuation of the first curved waveguide; and

an output waveguide coupled to or provided as a continuation of the second curved waveguide;

wherein each of the input waveguide and the output waveguide have an end adjacent to a first edge of the optoelectronic device.

12. The optoelectronic device of claim 11, wherein the electrode arrangement further comprises first and second electrodes, said electrodes being disposed on a first side of the optically active region and electrically connected thereto, and the first and second electrodes are disposed adjacent to an edge of the optoelectronic device which is different to the first edge.

13. The optoelectronic device of claim 1, further comprising:

a distributed feedback laser, coupled to the first curved waveguide; and

an output waveguide, coupled to or provided as a continuation of the second curved waveguide;

such that the optoelectronic device is an electro-absorption modulated laser.

14. The optoelectronic device of claim 13,

wherein the distributed feedback laser is formed of a material having a band-gap which is the same as the band-gap of the optically active region, or,

wherein the distributed feedback laser is formed from material having a band-gap which is different from the band-gap of the optically active region and different from the band-gap of the first and second curved waveguides.

15. The optoelectronic device of claim 1,

wherein the optically active region is an electro-absorption modulator, or,

wherein the first curved waveguide and the second curved waveguide are formed of a material having a band-gap which is lower in wavelength than a band-gap of the optically active region.

16. The optoelectronic device of claim 7, further comprising a semiconductor optical amplifier (SOA).

17. The optoelectronic device of claim 16,

wherein the SOA is located between the first curved waveguide and the second curved waveguide, or,

wherein the optoelectronic device includes an output waveguide coupled to or provided as a continuation of the second curved waveguide; and wherein the SOA is located at the output waveguide.

18. An array of optoelectronic devices disposed on a chip, wherein:

each optoelectronic device is as set out in claim 1; and

a distance between optically active regions of adjacent pairs of optoelectronic devices is no more than 250 μm.

19. The array of claim 18, wherein each optoelectronic device has:

an input waveguide coupled to or provided as a continuation of each first curved waveguide; and

an output waveguide coupled to or provided as a continuation of each second curved waveguide;

wherein each input waveguide and each output waveguide has a first end distal to its respective optically active region, and adjacent to a same side of the chip.

20. The array of claim 18, wherein each optoelectronic device has:

a distributed feedback laser, coupled to each first curved waveguide; and

an output waveguide, coupled to or provided as a continuation of each second curved waveguide;

such that the optoelectronic device is an electro-absorption modulated laser;

wherein an end of each output waveguide distal to its respective optically active region is adjacent to a same side of the chip.