GB2492349A

GB2492349A - Photonic assembly

Info

Publication number: GB2492349A
Application number: GB1110977.4A
Authority: GB
Inventors: Adrian Perrin Janssen; Colin Smith
Original assignee: Oclaro Technology Ltd
Current assignee: Lumentum Technology UK Ltd
Priority date: 2011-06-28
Filing date: 2011-06-28
Publication date: 2013-01-02
Also published as: GB201110977D0

Abstract

A photonic assembly comprises a laser chip 302 having formed thereon a light emitting device. The chip is configured so that output light 310 is emitted from the device at an oblique angle relative to a nominal lasing axis of the chip. An optical unit for example, a spherical lens 311, is located adjacent the chip and configured to redirect (collimated beam 312) the output light to a direction generally parallel to the lasing axis of the chip. The chip (402, Figure 4) may have ten tunable lasers each emitting light (410, Figure 4) at an angle from the end of the chip. The light then enters a collimating lens array (411, Figure 4) which includes ten spherical lenses each of which collimates the output from an individual laser and redirect that light so that it travels as collimated beams (412, Figure 4) normal to window (414, Figure 4).

Description

PHOTONIC ASSEMBLY

Technical Field

The present invention relates to a photonic assembly. In particular, although not exclusively, the invention relates to an optoelectronic package including a light source such as a laser.

Backci round In this specification the term light" will be used in the sense that it is used in optical systems to mean not just visible light, but also electromagnetic radiation having a wavelength outside that of the visible range.

There is considerable and growing interest in high capacity optical interconnects.

Interconnects capable of data rates of 40 Gb/s or 100 Gb/s or more are commonly required in various implementations. Due, at least in part, to difficulties in implementing these data rates in a serial format, parallel multichannel single fibre interconnect implementations are finding favour.

Many conventional parallel multichannel array implementations utilise an array of fixed wavelength lasers or integrated laser modulators and operate at a given wavelength band (e.g. C-band or [-band) within an ITU grid. That is, each laser of an array may operate at a particular channel and corresponding frequency (wavelength) of an ITU grid. Grid alignment of each of the lasers in the array is accomplished by a specific grating pitch, built in the manufacturing process, combined with some thermal adjustment.

Other arrays use lasers which are either independently tunable or which have a predefined relationship to each other so that all of the lasers in the array can be tuned simultaneously. For example, a laser array chip may include multiple (n) tunable lasers. These may be configured to give n outputs, n/m outputs, or just one output, by combination on the chip.

In general, lasers in such arrays have in common that the output direction of light is at an angle compared to the edge of the chip. The reason for this can be understood with reference to Figure 1, which illustrates schematically a top view of the output of a laser 101 (which may be part of an array) on a chip 102. Light exits from the laser 101 along a waveguide 103 which has a curved portion 104 before it intersects output facet 105 at the edge of the chip 102. The waveguide curvature and oblique intersection significantly reduce the amount of light reflecting from the output facet 105 back into the laser 101.

In an optoelectronic package it is generally desirable for light to be transmitted parallel to the sides of the package. If the light is emitted from the laser chip at an angle, the laser chip generally needs to be positioned within the package at a complimentary angle to compensate, as can be seen from Figure 2, which shows light 210 emitted from an exemplary laser chip 202 at an oblique angle compared to a nominal lasing axis 216 of the chip. A collimating lens 211 ensures that the final output is a collimated beam 212 parallel to the edge 213 of the package 214 in which the chip is contained (or normal to the end 214 of the package 215).

Placing the chip at an angle is undesirable. A larger package is required than would be the case if the chip could be aligned with the package edge. The angled topology also places restrictions on electrical interconnects, especially any RF interconnects which can be become asymmetric. The problem becomes particularly acute when the chip comprises an array of lasers, since it then occupies a great deal of space, and the additional space required to accommodate the angled orientation becomes a significant issue.

It would therefore be desirable to provide a system which enables a light source or other optical component from which light is emitted to be aligned with the package in which it is contained.

Summary

In accordance with one aspect of the present invention there is provided a photonic assembly. The assembly comprises a chip having formed thereon a light emitting device. The chip is configured so that output light emitted from the device exits the chip at an oblique angle relative to a nominal lasing axis of the chip. An optical unit is located adjacent the chip and configured to redirect the output light to a direction geneially parallel to the lasing axis of the chip.

The optical unit may be configured to collimate the output light, and may comprise a lens, optionally a spherical lens. The chip may comprise an output facet through which the output light is transmitted, and the optical unit may be laterally offset from the output facet.

The light emitting device may comprise a laser or an optical amplifier In one embodiment the chip comprises an array of lasers arranged side by side, the output light from each laser exiting the chip at the oblique angle relative to the lasing axis of the chip. An array of optical units may be located and configured to redirect the output light from each of the lasers to a direction generally parallel to the lasing axis of the chip. Alternatively, an array of chips may be arranged side by side, with the array of optical units configured to rediiect the output light from each of the hips to a direction generally parallel to the lasing axis of the chips.

The invention also provides an optical package complising the photonic assembly described above, where the chip is located within the package with its lasing axis parallel to an edge of the package.

In accordance with another aspect of the present invention there is provided an optical package, comprising a housing and a chip located within the housing. The chip is generally parallel to an edge of the housing and has formed thereon a light emitting device. The chip is configured so that output light emitted from the device exits the chip at an oblique angle to the edge of the housing. An optical unit is located adjacent the chip and configured to collimate and redirect the output light to a direction geneially parallel to the edge of the housing.

Brief Description of the Drawings

Some preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a schematic top view of the output facet of a laser; Figure 2 is a schematic top view of a laser package; Figure 3 is a schematic top view of a laser package with the laser chip aligned parallel to the package edge; and Figure 4 is a schematic top view of a laser chip array and collimating optics.

Detailed Description

Figure 3 is a schematic top view of a laser chip 302 similar to the chip 202 shown in Figure 2. The chip is placed in a package 315 to that it is parallel to the package edge 313. Light 310 is emitted at an angle relative to the chip. A spherical lens 311 is located so as to redirect and collimate the light 310 into a collimated beam 312 which is parallel to a nominal lasing axis of the chip 316 (and thus also parallel to the package edge 313 and normal to the package end 314). This enables the use of a laser which emits light at an angle to the output facet to be located parallel to the package edge. It is immediately apparent that the package itself can thus be made significantly smaller compared to the situation shown in Figure 2.

Figure 4 is a schematic top view of a multiple output chip 402 having ten tunable lasers included therein, each emitting light 410 at an angle from the end of the chip. The light 410 enters a collimating lens array 411, which includes ten spherical lenses, each located and shaped to collimate the output from an individual laser, and redirect that light so that it travels as collimated beams 412 normal to a window 414 in an output edge 413 of the package. The beams 412 can then be coupled to a lens array 415 of a further component, or individual ferrules or optical fibres as desired.

In one example of a chip array the lasers are laterally spaced by approximately 250 pm. In this case the distance from the chip to the lens array may be approximately 25-pm.

It will be noted that this has the additional advantage that the pitch of all the optical component arrays can be the same, and furthermore removes the need for any complex stepped approach which would be required if the chip were angled 402 relative to the package, allowing the use of a simple piano-convex lens array 411.

It will be appreciated that variations from the above described embodiments may still fall within the scope of the invention. For example, the examples above have been described with reference to a laser or laser array formed on a chip, but the same principles can be applied to an optical amplifier or amplifier array in place of a laser.

Furthermore, it will be appreciated that an array of chips may also be used in place of an array of lasers on one chip. A collimating lens array may still be employed in this situation to redirect the light from each chip so that it is propagated parallel to the edge of the package.

Claims

<claim-text>CLAIMS: 1. A photonic assembly, comprising: a chip having formed thereon a light emitting device, the chip configured so that output light emitted from the device exits the chip at an oblique angle relative to a lasing axis of the chip; and an optical unit located adjacent the chip and configured to redirect the output light to a direction generally parallel to the lasing axis of the chip.</claim-text> <claim-text>2. The assembly of claim 1, wherein the optical unit is further configured to collimate the output light.</claim-text> <claim-text>3. The assembly of claim 1 or 2, wherein the optical unit comprises a lens.</claim-text> <claim-text>4. The assembly of claim 3, wherein the lens is a spherical or aspheric lens.</claim-text> <claim-text>5. The assembly of any preceding claim, wherein the light emitting device comprises a laser.</claim-text> <claim-text>6. The assembly of any preceding claim, wherein the light emitting device comprises an optical amplifier.</claim-text> <claim-text>7. The assembly of any preceding claim, wherein the chip comprises an output facet through which the output light is transmitted.</claim-text> <claim-text>8. The assembly of claim 7, wherein the optical unit is laterally offset from the output facet.</claim-text> <claim-text>9. The assembly of any preceding claim, wherein: the chip comprises an array of lasers arranged side by side, the output light from each laser exiting the chip at the oblique angle relative to the lasing axis of the chip; and an array of optical units is located and configured to redirect the output light from all of the lasers to a direction gene parallel to the lasing axis of the chip.</claim-text> <claim-text>10. The assembly of any of claims ito 8, further comprising: an array of laser chips arranged side by side, the output light from each laser exiting its chip at the oblique angle relative to the lasing axis of the chip; and an array of optical units is located and configured to redirect the output light from all of the chips to a direction generally parallel to the lasing axis of the chips.ii. An optical package comprising the photonic assembly of any preceding claim, wherein the chip is located within the package with its lasing axis parallel to an edge of the package.12. An optical package, comprising: a housing; a chip located within the housing and generally parallel to an edge thereof, the chip having formed thereon a light emitting device, the chip being configured so that output light emitted from the device exits the chip at an oblique angle to the edge of the housing; and an optical unit located adjacent the chip and configured to collimate and redirect the output light to a direction generally parallel to the edge of the housing.13. A photonic assembly as herein described with reference to the accompanying drawings.</claim-text>