Photonic integrated circuit

Abstract

A photonic integrated circuit and a method for manufacturing is disclosed. The photonic integrated circuit comprises a semiconductor gain medium configured to generate laser radiation that is spatially separated from an output coupling region. The photonic integrated circuit further comprises a semiconductor optical waveguide that optically couples the semiconductor gain medium and output coupling region and defines a device plane of the photonic integrated circuit. The output coupling region comprises a photonic crystal which redirects the laser radiation out of the device plane to form an output field of the photonic integrated circuit. The characteristics of the photonic crystal can be used to manipulate the output field properties. Furthermore, the above photonic integrated circuit reduces the redirection of back-reflected light toward the semiconductor gain medium.

Description

[0001] Photonic Integrated Circuit

[0002] The present invention relates to the field of photonic integrated circuits. Specifically, the present invention relates to photonic integrated circuits comprising a semiconductor laser system and methods for manufacturing the same.

[0003] A photonic integrated circuit (PIC) is a chip that integrates two or more photonic components onto a single semiconductor chip. A PIC can manipulate and control light and enables compact, efficient, and cost-effective solutions for various applications including optical communication, sensing, and signal processing.

[0004] The typical photonic components forming the PIC usually include a light source and a waveguide. Other components found on the PIC may include optical modulators, detectors, power splitters, filters, and more. The waveguide is responsible for guiding and directing light to enable communication between different components on the chip.

[0005] Semiconductor laser devices commonly function as the light sources of the PIC. Semiconductor laser devices are those based on a semiconductor gain media, where optical amplification is usually achieved through stimulated recombination of charge carriers. Most semiconductor laser devices are laser diodes based on a semiconductor gain medium, which is pumped with an electrical current in a region where n-doped and p- doped semiconductor materials meet. As the photon energy of a laser diode is close to the bandgap energy, compositions with different bandgap energies allow for different emission wavelengths.

[0006] There is a great variety of semiconductor laser devices, spanning wide parameter regions and many different application areas. Fabry Perot (FP) lasers are the original, semiconductor laser device technology. In these devices the laser feedback and emission are both in-plane, and the feedback is produced by facet mirrors such that the generated output light comes out of an end of the laser. For this reason, FP lasers are often referred to as edge emitting lasers (EEL).

[0007] An alternative type of EEL laser is a Distributed Feedback Laser (DFB). DFB lasers also have in-plane feedback and emission, but in these devices the feedback is produced by the employment of a grating structure.

[0008] Another type of known semiconductor laser device technology are Vertical Cavity Surface Emitting Lasers (VCSELs). The laser resonator of a VSCEL consists of two distributed Bragg reflector (DBR) mirrors, with an active region arranged between the DBR mirrors. Within a VSCEL, both the laser feedback and emission are both out of plane, where the laser output light emits from a top or bottom surface of the laser.

[0009] Photonic crystal surface emitting lasers (PCSELs) are a newer class of semiconductor laser device. PCSELs have been found to have beneficial properties including coherent oscillation, and low divergences of emitted light. PCSELs are also the only semiconductor laser design that employs in-plane feedback and out of plane, surface emission.

[0010] PCSELs employ a photonic crystal structure to control the emission of light. The photonic crystal layer consists of a two-dimensional array of periodic dielectric or semiconductor material, which creates a photonic bandgap that affects the propagation of light within a semiconductor layer of the PCSEL. The periodic regions may be provided by air gaps or voids. Alternatively, the periodic regions may be filled by overgrowth with a suitable filler material having a second refractive index. While significant advancements have been made to enhance the performance and efficiency of photonic integrated circuits it is desirable to provide further improvements and alternative devices for the large range of commercial applications. In particular, improved output power efficiency, beam quality, beam control, increased wavelength range, single mode operation and multi-wavelength production are all desirable features. Such features require further development for both existing and potential future applications of photonic integrated circuits.

[0011] Summary of Invention

[0012] It is therefore an object of an embodiment of the present invention to provide an alternative photonic integrated circuit to those known in the art.

[0013] It is a further object of embodiment of the present invention to provide a photonic integrated circuit that obviates or mitigates one or more drawbacks or disadvantages of the prior art.

[0014] Further aims and objects of the invention will become apparent from reading the following description.

[0015] According to a first aspect of the present invention there is provided a photonic integrated circuit comprising: a semiconductor gain medium configured to generate laser radiation; a semiconductor optical waveguide defining a device plane of the photonic integrated circuit and optically coupled to the semiconductor gain medium; an output coupling region of the semiconductor optical waveguide spatially separated from the semiconductor gain medium; wherein the output coupling region comprises a photonic crystal comprising a periodic array of scattering centres arranged within a first semiconductor material and configured to redirect laser radiation optically coupled within the semiconductor optical waveguide out of the device plane to form an output field of photonic integrated circuit.

[0016] Laser radiation optically coupled within the semiconductor optical waveguide interacts with the photonic crystal which redirects the light out of the photonic integrated circuit due to the specific arrangement of the scattering centres within the photonic crystal. In particular, the properties of the photonic crystal may be used to select the precise output wavelength of the output field, in addition to shaping and guiding the incoming light.

[0017] The structure of the above-described photonic integrated circuit provides several advantages. These include the ability to select the output power level of the output field, determining the precise wavelength of the output field, and control over the beam quality and emission direction. Additionally, the photonic crystal helps reduce the amount of light reflected back towards the semiconductor gain medium. This reduction in the level of back reflected light reduces the need for further optical isolating components to be incorporated within the photonic integrated circuit.

[0018] Significantly the components of the photonic integrated circuit can all be processed from the same semiconductor material, the choice of which is dependent on the desired wavelength of the first output field. For example, the semiconductor material may comprise Indium Phosphide (InP), Gallium Arsenide (GaAs), Gallium Nitride (GaN) or Gallium Antimonide (GaSb). This allows for the photonic integrated circuit to be produced as an integrated structure based on a single semiconductor material.

[0019] Preferably the scattering centres comprise voids formed within the first semiconductor material. Most preferably the voids are infilled with a second semiconductor or dielectric material the second semiconductor or dielectric material having a different refractive index to the first semiconductor material.

[0020] Preferably the photonic crystal comprises a second order photonic crystal.

[0021] The photonic crystal is preferably arranged on the semiconductor optical waveguide, or partially or fully embedded in the semiconductor optical waveguide.

[0022] Preferably the photonic integrated circuit comprises a semiconductor laser within which the semiconductor gain medium is located. Preferably the semiconductor laser comprises an edge emitting laser.

[0023] The gain medium may comprise an active layer on opposite sides of which are located a first cladding layer and a second cladding layer. Preferably the active layer comprises a Multi-Quantum Well (MQW) active layer. Preferably the semiconductor laser further comprises a substrate upon which the layers of the semiconductor laser are formed.

[0024] Preferably the photonic integrated circuit further comprises a first and a second electrical contact located on opposite sides of the active layer, thus defining a laser region of the photonic integrated circuit.

[0025] Optionally, the semiconductor optical waveguide is provided by one or more of the layers that extend from the semiconductor laser into the output coupling region.

[0026] Preferably, one or more of the layers of the semiconductor laser extend into the optical waveguide.

[0027] Optionally, the photonic crystal may be located partially within one or more of the layers of the optical waveguide that extend into the output coupling region. Optionally, the photonic crystal may be located entirely within one or more of the layers of the optical waveguide that extend into the output coupling region.

[0028] Preferably, the semiconductor optical waveguide comprises a first tapered section wherein the first tapered section reduces in width in a direction from the semiconductor gain medium towards the output coupling region.

[0029] Preferably, the semiconductor optical waveguide comprises a second tapered section wherein the second tapered section increases in width in a direction from the semiconductor gain medium towards the output coupling region.

[0030] Preferably the semiconductor gain medium comprises a gain tapered section wherein the gain tapered section reduces in width in a direction from the semiconductor gain medium towards the output coupling region.

[0031] Most preferably the gain tapered section is located between first tapered section and the output coupling region.

[0032] Optionally, the photonic integrated circuit comprises a spacer semiconductor layer located between semiconductor gain medium and the semiconductor optical waveguide. Most preferably the spacer semiconductor layer comprises a tapered section that reduces in width in a direction from the semiconductor gain medium towards the output coupling region.

[0033] The tapered sections of the semiconductor optical waveguide, the semiconductor gain medium and the spacer semiconductor layer allow for the light to efficiently couple into the optical waveguide and determines the shape and size of the laser radiation within the waveguide.

[0034] Optionally, the semiconductor optical waveguide comprises a notch located between the semiconductor gain medium and the output coupling region.

[0035] The notch acts to reduce the amount of back reflected light that is directed towards the semiconductor gain medium. The notch therefore further reduces the need for optical isolating components to be incorporated within the photonic integrated circuit.

[0036] Preferably, the width of the notch is in the range of 10nm to 500nm. Alternatively, the width of the notch is in the range of 50nm to 150nm. Preferably the notch is rectangular in shape. The notch may comprise a tapered cross sectional profile.

[0037] Preferably the notch extends fully through the semiconductor optical waveguide. Optionally the notch extends partially through the semiconductor optical waveguide. Preferably the notch comprises an air gap in the semiconductor optical waveguide. Optionally the notch is filled with a semiconductor or dielectric material.

[0038] Optionally the semiconductor waveguide comprises an angled face on one end of the semiconductor optical waveguide. The angled face acts to reduce the amount of back reflected light that is directed towards the semiconductor gain medium. Most preferably the angled face is arranged on the opposite end of the semiconductor waveguide to the output coupling region.

[0039] Preferably the first output field is parallel to a normal of the output surface. Alternatively, the first output field is non parallel to the normal of the output surface.

[0040] Optionally, the photonic integrated circuit further comprises an output coupler. Optionally the output coupling region comprises an array of photonic crystals each of which generates an output field from the output surface of the photonic integrated circuit.

[0041] Most preferably the elements of the array of photonic crystals are arranged to be coplanar. The elements of the array of photonic crystals may be coplanar with a plane that is parallel to the device plane. Alternatively, or in addition, the elements of the array of photonic crystals may be coplanar with a plane that is perpendicular to the device plane.

[0042] Preferably the array of photonic crystals is a regular array, wherein a photonic crystal is located at each site of the array. Alternatively, the array of photonic crystals is an irregular array. The irregular array may comprise a regular array where there is no photonic crystal located at one or more of the array sites.

[0043] Optionally, the photonic integrated circuit generates two or more output fields. The two or more output fields may be at different wavelengths or the same wavelength.

[0044] Optionally the two or more output fields are directed into separate output couplers. Alternatively, the two or more output fields are directed into the same output coupler.

[0045] Optionally the photonic integrated circuit further comprises a second semiconductor gain medium configured to generate laser radiation.

[0046] Preferably the output coupling region is located between the first and second semiconductor gain media.

[0047] Preferably the output coupling region is spatially separated from, and optically coupled to, the second semiconductor gain medium by the semiconductor optical waveguide, and the output coupling region generates a second output field from the output surface of the photonic integrated circuit.

[0048] By providing the second semiconductor gain medium, more output power can be provided at the output surface of the photonic integrated circuit by operating the first and second semiconductor gain mediums simultaneously. Alternatively, the second semiconductor gain medium can help extend the lifetime of the photonic integrated circuit. The first and second semiconductor gain medium each have associated operational lifetime, where at the end of that lifetime they will no longer be able to generate laser radiation. Therefore, when the first semiconductor gain medium reaches the end of its lifetime, the second semiconductor gain medium can be activated to extend the lifetime of the photonic integrated circuit.

[0049] Optionally, one or more wavelength-selective reflectors may be placed around one or more sides of the semiconductor optical waveguide. The presence of the one or more reflectors act to reduce the effects of undesired light leakage from the photonic integrated circuit.

[0050] According to a second aspect of the present invention there is provided a method of manufacturing a photonic integrated circuit the method comprising: providing a semiconductor gain medium configured to generate laser radiation; providing a semiconductor optical waveguide defining a device plane of the photonic integrated circuit and optically coupled to the semiconductor gain medium; providing an output coupling region of the semiconductor optical waveguide that is spatially separated from the semiconductor gain medium, providing a photonic crystal comprising a periodic array of scattering centres arranged within a first semiconductor material within the output coupling region; and configuring the photonic crystal to redirect laser radiation optically coupled within the semiconductor optical waveguide out of the device plane to form an output field of photonic integrated circuit.

[0051] Preferably providing the photonic crystal comprises providing a second order photonic crystal.

[0052] Embodiments of the second aspect of the present invention may comprise features to implement the preferred or optional features of the first aspect of the present invention.

[0053] Brief Description of Drawings

[0054] There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which: Figure 1 presents (a) a cross sectional view and (b) a top view of a photonic integrated circuit (PIC) in accordance with an embodiment of the present invention;

[0055] Figures 2 (a) to (d) present theoretical modelling of the position and shape of the generated laser radiation at the different regions (A, B, C and D) of the photonic integrated circuit (PIC) of Figure 1 ;

[0056] Figure 3 presents (a) a cross sectional view and (b) a top view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0057] Figure 4 presents (a) a cross sectional view and (b) a top view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0058] Figure 5 presents (a) a cross sectional view and (b) a top view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0059] Figure 6 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0060] Figure 7 presents a top view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0061] Figure 8 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0062] Figure 9 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0063] Figure 10 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0064] Figure 11 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention; Figure 12 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0065] Figure 13 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0066] Figure 14 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0067] Figure 15 presents a top down view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention;

[0068] Figure 16 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention; and

[0069] Figure 17 presents a cross sectional view of a photonic integrated circuit (PIC) in accordance with an alternative embodiment of the present invention.

[0070] In the description which follows, like parts are marked throughout the specification and drawings with the same reference numerals. The drawings are not necessarily to scale, and the proportions of certain parts have been exaggerated to better illustrate details and features of embodiments of the invention.

[0071] Detailed Description

[0072] Figure 1 (a) and (b) present a cross sectional view and a top view, respectively, of a photonic integrated circuit (PIC), as generally depicted by reference numeral 1 , in accordance with an embodiment of the present invention. Axes are included for reference, where the width, length, and height of the photonic integrated circuit 1 are along the x, y and z axis, respectively.

[0073] The photonic integrated circuit 1 can be seen to comprise a semiconductor gain medium 2, located on a spacer semiconductor layer 3. The semiconductor gain medium 2 generates the laser radiation of the PIC 1 and defines a laser region 4. The PIC 1 also comprises an output coupling region 5, where the output coupling region 5 is spatially separated from the laser region 4 by a semiconductor optical waveguide 6. The semiconductor optical waveguide 6 acts to optically couple the semiconductor gain medium 2 and the output coupling region 5. In the presently described embodiment, the semiconductor optical waveguide 6 extends from the laser region 4 into the output coupling region 5. As will be appreciated by a person skilled in the art, the entire photonic integrated circuit 1 is located on a substrate layer, not explicitly shown in Figure 1 .

[0074] The semiconductor gain medium 2 of the PIC 1 may be provided by a semiconductor laser, for example an edge emitting laser. The edge emitting laser may be a Fabry Perot laser (FP), a distributed-feedback laser (DFB laser) or distributed Bragg reflector laser (DBR laser). Within each type of edge emitting laser various semiconductor layers are carefully engineered to create a functional laser device. These layers serve specific purposes in achieving optical gain and the controlled emission of laser light.

[0075] The spacer semiconductor layer 3 depicted in Figure 1 comprises a semiconductor material such as Indium Phosphide (InP). Each layer that is formed on the spacer semiconductor layer 3 is then generally made from different combinations of InP or other materials like Indium Gallium Arsenide (InGaAs) or Indium Gallium Phosphide (InGaP). Such materials generally result in a typical output wavelength of 1 .3 pm. This output wavelength is commonly used in fibre-optic communication systems for long-distance data transmission. However, it is known in the art to produce wavelengths in the range of 1 pm to 2.1 pm from Indium Phosphide (InP) based devices.

[0076] In the embodiment presented in Figure 1 , an Indium Phosphide (InP) layer provides the semiconductor optical waveguide 6 of the photonic integrated circuit 1 . The semiconductor optical waveguide 6 can be seen to comprise two distinct adiabatic tapered sections, where the first and second adiabatic tapered sections are denoted as 7a and 7b, respectively. The adiabatic tapered sections 7a and 7b efficiently couple light between different regions of the PIC 1. They provide a gradual change in the width and geometry of the semiconductor optical waveguide 6 within the device plane to match the mode profile of light between the different regions of the PIC 1 . The adiabatic tapered sections 7a and 7b are essentially employed as spot size converters, where gradually adjusting the optical waveguide 6 dimensions allows for the light to be effectively channelled with minimal dispersion and reduced optical loss. The first adiabatic tapered section 7a provides a gradual transition of the width of the semiconductor optical waveguide 6 and the spacer semiconductor layer 3 within the region of the PIC 1 comprising the semiconductor gain medium 2 i.e., at the output of the laser region 4. In particular, the first adiabatic tapered section 7a results in the semiconductor optical waveguide 6 and the spacer semiconductor layer 3 becoming narrower as it moves away from the laser region 4, following the direction of the y-axis, as illustrated in Figure 1 . The first adiabatic tapered section 7a aids in efficiently coupling generated laser radiation from the semiconductor gain medium 2 into the semiconductor optical waveguide 6, as the light travels from laser region 4 towards the output coupling region 5. The first adiabatic tapered section 7a of the optical waveguide 6 and the spacer semiconductor layer 3 facilitates efficient mode conversion during optical coupling into the semiconductor optical waveguide 6. Moreover, it reduces optical losses by gradually matching the optical mode to the required size of the semiconductor optical waveguide 6 i.e. the size at the end of the adiabatic taper section 7a.

[0077] In the region between the first 7a and second 7b adiabatic tapered sections the size of the semiconductor optical waveguide 6 does not change. Between the first 7a and second 7b adiabatic tapered sections the semiconductor optical waveguide 6 is passive, i.e. it does not actively manipulate the light passing through it. This part of the semiconductor optical waveguide 6 acts to guide the light to the output coupling region 5.

[0078] The second adiabatic tapered section 7b of the semiconductor optical waveguide 6 then gradually increases the width along the direction of the y-axis, as the semiconductor optical waveguide 6 enters the output coupling region 5. Therefore, the second adiabatic tapered section 7b of the semiconductor optical waveguide 6 ensures that the laser radiation is efficiently coupled into the output coupling region 5 of the PIC 1 .

[0079] It is noted that the semiconductor gain medium 2 also comprises an adiabatic tapered section 8. The adiabatic tapered section of the semiconductor gain medium 2 provides a gradual change in the size or shape of the optical mode for the generated laser radiation. In Figure 1 , the adiabatic tapered section 8 acts to reduce the spot size of the laser radiation. The adiabatic taper section 8 matches the mode of incoming light to the mode of the semiconductor optical waveguide 6, to further enhance the coupling efficiency. In the present embodiment, the adiabatic tapered section 8 of the semiconductor gain medium 2 follows directly after the first adiabatic tapered section 7a of the semiconductor optical waveguide 6 and the spacer semiconductor layer 3.

[0080] Figures 2 (a) through (d) present theoretical modelling depicting the position and shape of the generated laser radiation at various locations within the photonic integrated circuit (PIC) 1 of Figure 1 . More specifically, it shows the position and shape of the generated laser radiation at the locations A, B, C and D respectively,

[0081] In Figure 2 (a), the laser radiation is depicted within the laser region 4 of the PIC 1 (i.e. location A of Figure 1 ). The laser radiation is generated within the semiconductor gain medium 2 in the laser region 4. Therefore, in Figure 2 (a) the laser radiation is primarily within the semiconductor gain medium 2.

[0082] However, as the laser radiation emerges from the laser region 4, it passes through the first adiabatic tapered section 7a of the semiconductor optical waveguide 6 and the spacer semiconductor layer 3. Figure 2 (b) shows the position of the laser radiation directly after exiting the first adiabatic tapered section 7a, corresponding to location B of Figure 1 . The profile of the light is elongated along the vertical direction (i.e. along the z axis of Figure 1 ) indicating the initiation of coupling into the semiconductor optical waveguide 6.

[0083] Figure 2 (c) depicts location C of Figure 1 , showing the position of the laser radiation directly after travelling through the adiabatic tapered section 8 of the semiconductor gain medium 2. This adiabatic tapered section 8 acts to efficiently couple the generated laser radiation into the semiconductor optical waveguide 6. This is clear from Figure 2 (c), where the light is fully coupled into the semiconductor optical waveguide 6 leaving only a negligible amount of laser radiation within the semiconductor gain medium 2 of the PIC 1 .

[0084] Lastly, Figure 2 (d) shows the shape and position of the light within the semiconductor optical waveguide 6, before proceeding into the second adiabatic tapered section 7b of the semiconductor optical waveguide 6 and to the output coupling region 5 of the PIC 1 . More specifically, it illustrates the light within the passive area of the semiconductor optical waveguide 6 at location D of Figure 1 , where the light remains confined within the semiconductor optical waveguide 6. As seen in Figure 1 , the output coupling region 5 comprises a photonic crystal 9. The photonic crystal 9 is a patterned structure consisting of repeating features or elements arranged in a regular or irregular grid across two dimensions. The photonic crystal 9 is employed to manipulate the behaviour of light or other electromagnetic waves based on their interactions with the periodic structure. The properties of the photonic crystal 9 depend on the spacing, size, shape, and orientation of the repeating elements.

[0085] An example of a suitable photonic crystal 9 is a second-order photonic crystal the function of which is to redirect light optically coupled within the semiconductor optical waveguide 6 out of the device plane (the x-y plane) to form an output field 10 of the photonic integrated circuit 1 . A second-order photonic crystal structure comprises a semiconductor material, in the present example Indium Gallium Arsenide Phosphide (InGaAsP), comprising a two- dimensional period array of voids or scattering centres (e.g. Indium Phosphide (InP)) distributed in an array plane. The array of voids or scattering centres usually form a periodic lattice structure, where the refractive index of the void or scattering centres is different to the photonic crystal material. The lattice structure of the photonic crystal structure causes diffraction within the photonic crystal, which in turn causes light to resonate at a particular wavelength determined by the periodicity, or lattice constant, of the photonic crystal structure. The scattering centres of the photonic crystal structure may comprise regular or irregular geometric shapes (e.g. circular, triangular, oval, diamond, square or chevron shapes). The lattice constant (a) is set to match the desired wavelength (e.g. 1 .31 pm) of the output field 10. The lattice may comprise alternative regular or irregular lattice structures (e.g., triangular, hexagonal or Kagome) having different lattice constants (a).

[0086] As can be seen from Figure 1 , the photonic integrated circuit 1 may further comprise one or more reflectors 11 arranged around one or more sides of the semiconductor optical waveguide 6 within the output coupling region 5. The function of these reflectors 11 is to retain light optically coupled into the semiconductor optical waveguide 6 within the device plane (the x-y plane) of the photonic integrated circuit 1 . In the presently described embodiment the reflectors 11 comprise distributed Bragg reflectors (DBR). Each DBR 11 is configured to reflect light that is incident upon it and in particular light travelling out of the optical waveguide 6. The DBR’s 11 are specifically designed to reflect light at a selected wavelength i.e., the wavelength of the output field 10. Each DBR 11 may comprise alternative layers of semiconductor materials. In the present embodiment, the layers of the DBR 11 are again based on InP and may comprise InP, InGaAsP or InGaP.

[0087] During operation of the PIC 1 , the laser radiation generated within the semiconductor gain medium 2 in the laser region 4 is optically coupled into the semiconductor optical waveguide 6. The adiabatic tapered sections 7a, 7b and 8 of the semiconductor optical waveguide 6, the spacer semiconductor layer 3 and the semiconductor gain medium 2 ensure efficient coupling of the light. The semiconductor optical waveguide 6 then guides and confines the light and ensures that the laser radiation travels along the desired path to the output coupling region 5. Within the output coupling region 5 the photonic crystal 9 acts to diffract the incoming laser radiation, that travels from the semiconductor gain medium 2, towards the output surface 12, generating the output field 10.

[0088] The specific wavelength of the output field 10 is determined by the combined properties of the semiconductor materials from which the semiconductor gain medium 2 and the photonic crystal 9 are produced.

[0089] The process of creating the described photonic integrated circuit 1 with an optical waveguide 6 and a photonic crystal 9 involves using known growth and etching processes to selectively deposit different semiconductor layers onto a substrate, forming a single, Indium Phosphide (InP) based integrated structure. The use of masking techniques allows for controlled deposition of materials, creating distinct regions for the photonic integrated circuit 1 (e.g. the output coupling region 5 and the laser region 4).

[0090] The design of the photonic crystal 9 within the photonic integrated circuit 1 provides a means for selecting predetermined power levels, precise wavelengths and enhanced beam quality and control of the output field 10.

[0091] An additional advantage of design of the PIC 1 is that there is a reduction in the light levels back reflected towards the semiconductor gain medium 2. For example, the photonic crystal 9 may be designed to couple around 10% of the output power from semiconductor gain medium 2 into the output field 10. The output field 10 may then be coupled into an optical fibre, or other Silicon Photonics (SiP) system. Such optical systems are known to cause back reflections towards the photonic integrated circuit 1 . However, as will be appreciated by the skilled reader, the photonic crystal 9 will result in less than 10% of the back reflected light being redirected towards the semiconductor gain medium 2. This reduction in the level of back reflected light reduces the need for further optical isolating components to be incorporated within the photonic integrated circuit 1 .

[0092] It will be appreciated by the skilled reader that alternative semiconductor materials to Indium Phosphide (InP) may be employed to produce the photonic integrated circuit 1 of Figure 1 . These alternative semiconductor materials include Gallium Arsenide (GaAs), Gallium Nitride (GaN) or Gallium Antimonide (GaSb), which allow for output wavelengths from the ultra-violet range to the mid-infrared range of the electromagnetic spectrum to be produced within an integrated structure based on a single semiconductor material.

[0093] A photonic integrated circuit 13 in accordance with an alternative embodiment of the present invention is presented in Figures 3(a) and (b). While the photonic integrated circuit 13 has a similar structure to the PIC 1 of Figure 1 , Figure 3 introduces an angled face 14 situated at one end along the length of the semiconductor optical waveguide 6 (i.e. along the y-axis).

[0094] In particular, the angled face 14 is provided at the edge of the semiconductor optical waveguide 6 within the laser region 4 of the PIC 13. The angled face 14 extends along the width of the semiconductor optical waveguide 6 (i.e. along the x-axis). The angled face 14 is defined by an angle 9 ranging from 7 to 11 degrees, measured with respect to the x axis of the PIC 13.

[0095] The angled face 14 acts to further improve the operation of the photonic integrated circuit 13. In particular, the angled face 14 greatly reduces the likelihood of any back reflections travelling back into the semiconductor gain medium 2 and interfering with the generation of light within the semiconductor gain medium 2. Therefore, the angled face 14 further reduces any potential challenges associated with unwanted back reflections.

[0096] A photonic integrated circuit 15 in accordance with an alternative embodiment of the present invention is presented in Figures 4(a) and (b). In Figure 4 an angled face 16 is again present at one end along the length of the semiconductor optical waveguide 6. However, in Figure 4, the angled face 16 extends along the height of the semiconductor optical waveguide 6. The angled face 16 is defined by an angle 9 ranging from 7 to 11 degrees, measured with respect to the z axis of the PIC 15. Again, the angled face 16 acts to further improve the operation of the photonic integrated circuit 15 by greatly reducing the likelihood of any back reflections travelling back into the semiconductor gain medium 2 and interfering with the generation of light within the semiconductor gain medium 2.

[0097] As will be appreciated by a person skilled in the art, the angled faces 14 and 16 of the embodiments of Figures 3 and 4 may be combined within a single PIC.

[0098] A photonic integrated circuit 17 in accordance with an alternative embodiment of the present invention is presented in Figures 5(a) and (b). A notch 18 is provided within the semiconductor optical waveguide 6. The notch 18 is located between the semiconductor gain medium 2 and the output coupling region 5. In particular, the notch 18 is located within the region of the semiconductor optical waveguide 6 comprising the second tapered section 7b. However, as will be appreciated by a reader skilled in the art, the notch 18 may be provided in any other suitable location. For example, the notch 18 could instead be located between the first 7a and second 7b tapered sections of the semiconductor optical waveguide 6.

[0099] In the presently described embodiment, the notch 18 is rectangular in shape, but as will be appreciated by the skilled reader, the notch 18 could alternatively be any other suitable shape and or comprise a tapered cross section profile.

[0100] The notch 18 acts to improve the operation of the photonic integrated circuit 17 by again reducing the likelihood of any back reflections, travelling from the output coupling region 5, from reaching the semiconductor gain medium 2 located within the laser region 4 of the PIC 17.

[0101] In Figure 5, the width of the notch 18 is in the range of 50nm to 500nm, and it extends partially through the height of the semiconductor optical waveguide 6 (along the x axis). However, the notch 18 could alternatively extend fully through the semiconductor optical waveguide 6. The notch 18 of Figure 5 is an air-filled gap, however, as will be appreciated by the skilled reader, the notch 18 could alternatively be backfilled with a semiconductor or dielectric material. As will be appreciated the skilled reader, any combination of the embodiments described with reference to Figures 3, 4 and 5 can be used within a single PIC.

[0102] A photonic integrated circuit (PIC) 19 in accordance with an alternative embodiment of the present invention is presented in Figure 6. Within the photonic integrated circuit 19 of Figure 6 the output coupling region 5 comprises a first photonic crystal 9a and a second photonic crystal 9b. The photonic crystals 9a and 9b are spatially separated along the length of the waveguide 6, i.e. along the y-axis of the photonic integrated circuit 19.

[0103] When the semiconductor gain medium 2 generates laser radiation within the laser region 4, the generated laser radiation is optically coupled to the output coupling laser region 5 via the semiconductor optical waveguide 6. When the generated radiation enters the output coupling laser region 5 it interacts with both the first 9a and second 9b photonic crystals, creating a first 10a and a second 10b output field from the output surface 12.

[0104] The particular properties of the first 9a and second 9b photonic crystals may be chosen to provide output fields 10a and 10b which have the same wavelength. This allows for the output fields 10a and 10b to be either combined to provide higher output power, or to be used separately, as required. Alternatively, the properties of the first 9a and second 9b photonic crystals may be selected to provide different wavelengths (e.g. 1 ,310 nm and 1 ,315 nm) for the first 10a and second 10b output fields, providing a photonic integrated circuit 19 with multi-wavelength production. In general, the maximum difference between the produced wavelengths for the first 10a and second 10b output fields typically fall within a range of approximately 60nm to 100nm.

[0105] As will be appreciated by the skilled reader, further photonic crystal structures 9 may be arranged along length of the photonic integrated circuit 19 within the output coupling region 5. This allows for further output fields 10 with specific wavelengths, as determined by each associated photonic crystal 9, to be generated by the photonic integrated circuit 19.

[0106] A top view of a photonic integrated circuit (PIC) 20 in accordance with an alternative embodiment of the present invention is presented in Figure 7. The photonic integrated circuit 20 again comprises an integrated device based on Indium Phosphide (InP) having a semiconductor gain medium 2, a semiconductor optical waveguide 6 and an output coupling region 5. However, as can be seen from Figure 7, a three by three array of photonic crystals 9a to 9i are arranged within the output coupling region 5. Each of the photonic crystals 9a to 9i can create a separate output field 10 with a wavelength determined by the specific properties of each of the distinct photonic crystal 9a to 9i.

[0107] Similar to the previous embodiment presented in Figure 6, the photonic crystals 9a to 9i can each provide an identical wavelength, or different wavelengths or a combination thereof may be provided by some or all of the photonic crystals 9a to 9i. Note that a smaller or larger array of photonic crystals 9 could instead be arranged within the photonic integrated circuit 20 to provide less or more output fields as required for a particular application.

[0108] It will be appreciated by the skilled reader that the array of photonic crystals 9a to 9i within the photonic integrated circuit 20 can be arranged in any desired geometry. The array of photonic crystals 9a to 9i in Figure 7 comprises a regular two-dimensional array. However, an alternative arrangement, such as an irregular array of photonic crystals 9 e.g. where one or more of the array sites do not comprise a photonic crystal could instead be provided.

[0109] Figure 8 presents a cross sectional view of a photonic integrated circuit (PIC) 21 , in accordance with an alternative embodiment of the present invention.

[0110] The photonic integrated circuit 21 can be seen to comprise a number of layers. Firstly, the photonic integrated circuit 21 comprises a substrate layer 22 on which the other layers of the photonic integrated circuit 21 are formed or grown. The semiconductor gain medium 2 of the photonic integrated circuit 21 is provided by the active layer. The active layer 2 is arranged between a first cladding layer 23 and a second 24 cladding layer.

[0111] The active layer 2 generates laser radiation within the laser region 4. The purpose of the first 23 and second 24 cladding layers is to confine the light generated in the active layer 2. In particular, the active layer 2 generates the laser radiation when an electrical current is produced with the photonic integrated circuit 21 by employing a first 25 and a second 26 electrical contact. In this embodiment the electrical contacts 25 and 26 are located on opposite external surfaces of the photonic integrated circuit 21 and effectively define the location of the laser region 4.

[0112] The active layer 2 of the photonic integrated circuit 21 may contain quantum wells and or quantum dots. For example, it may contain one or more of InGaAs / GaAs quantum wells, InAs / GaAs quantum dots, GaAs / AIGaAs quantum wells, InGaAsP quantum wells and AllnGaAsP quantum wells, although many other active layer designs are known to those in the art. As will be appreciated, the choice of the semiconductor materials for the active layer 2 will depend on the desired wavelength of the output field 10.

[0113] In Figure 8, the semiconductor layers of the laser region 4 extend into the output coupling region 5 of the photonic integrated circuit 21 and so provide the function of the optical waveguide 6. The output coupling region 5 of the PIC 21 further comprises a photonic crystal 9 that is located within the second cladding layer 24.

[0114] When light is generated within the active layer 2 of the laser region 4, it propagates through the optical waveguide 6 into the output coupling region 5. The active layer 2, first cladding layer 23 and second cladding layer 24 provide the semiconductor optical waveguide 6 from which the generated radiation propagates into the output coupling region 5. The presence of the photonic crystal 9 within the output coupling region 5 acts to diffract the incoming light towards the output surface 12, generating an output field 10.

[0115] As shown in Figure 8, the photonic integrated circuit 21 may also comprise an output coupler 27. The output coupler 27 directs the output field 10 to any desired location, such as a fibre. The location to which the output field 10 is directed depends on the requirements of the application.

[0116] As will be appreciated by the skilled reader, one or more intermediate layers may be arranged between the substrate layer 22 and the first cladding layer 23 of the photonic integrated circuit 21 . Furthermore, one or more intermediate layers can also be arranged between the second cladding layer 24 and the second electrical contact 26.

[0117] It will be noted that the output field 10 does not need to travel through any additional layers before exiting the photonic integrated circuit 21 through the output surface 12. This is beneficial as a higher output power can be supplied by the photonic integrated circuit 21 , as there is no optical loss or attenuation within further semiconductor layers before the output field 10 reaches the output surface 12.

[0118] A photonic integrated circuit (PIC) 28 in accordance with an alternative embodiment of the present invention is presented in Figure 9. The photonic integrated circuit 28 of Figure 9 is similar to that shown in Figure 8. However, in the presently described embodiment the photonic crystal 9 of the output coupling region 5 extends across two layers of the photonic integrated circuit 28, namely the second cladding layer 24 and the active layer 2.

[0119] As will be appreciated by the skilled reader, the photonic crystal 9 may alternatively be arranged within any suitable layer, or suitable combination of layers, of the photonic integrated circuit 28 provided a substantive part remains located within the output coupling region 5 and that light propagates via an optical waveguide 6 from the laser region 4 to the output coupling region 5. Additionally, if further intermediate layers are present, photonic crystal 9 may alternatively be present within any of or any combination of said intermediate layers.

[0120] By way of example, a further alternative embodiment of a photonic integrated circuit (PIC) 29 is presented in Figure 10. In Figure 10, the photonic integrated circuit 29 comprises a similar structure to those described with reference to Figures 8 and 9, however in the presently described embodiment a further intermediate layer 30 is arranged between the second cladding layer 24 and the second electrical contact 26. The photonic crystal 9 is located within the intermediate layer 30 of the output coupling region 5. Therefore, in this embodiment, the second cladding layer 24, the intermediate layer 30 and the active layer 2 may be considered as the semiconductor optical waveguide 6 from which the generated radiation propagates into the output coupling region 5 to interact with the photonic crystal 9.

[0121] A photonic integrated circuit (PIC) 31 in accordance with an alternative embodiment of the present invention is presented in Figure 11. In Figure 11 , the photonic crystal 9 is again located within the intermediate layer 30 of the photonic integrated circuit 31 . However in this embodiment, the substrate layer 22, first cladding layer 23 and active layer 2 do not extend into the output coupling region 5 and are only present within the laser region 4 of the PIC 31. The semiconductor optical waveguide 6 is therefore provided by the second cladding layer 24 and the intermediate layer 30.

[0122] The process of creating the described photonic integrated circuits 21 , 28, 29 and 31 involves using known growth and etching processes to selectively deposit different semiconductor layers onto a substrate, forming a single, Indium Phosphide (InP) based integrated structure. The use of masking techniques allows for controlled deposition of materials, creating distinct regions for the photonic integrated circuits 21 , 28, 29 and 31 (i.e., the laser region 4 and the output coupling region 5).

[0123] As will be appreciated by the skilled reader, common techniques in semiconductor laser fabrication allow for selectively depositing or etching materials in specific areas, allowing for precise control over the layer growth process. By using such techniques, it is possible to control the location of the different layers of the photonic integrated circuits 21 , 28, 29 and 31.

[0124] As will be further appreciated by the skilled reader, the structure of layers present within the laser region 4 and output coupling region 5 may be customised to any suitable configuration for the photonic integrated circuits 21 , 28, 29 and 31 of Figures 8 to 11 , provided that the laser radiation can still propagate to the output coupling region 5 and interact with the photonic crystal 9.

[0125] By way of example, a photonic integrated circuit (PIC) 32 in accordance with an alternative embodiment of the present invention is presented in Figure 12. The intermediate layer 30 of Figure 12, i.e. the layer closest to the output surface 12 of the of the photonic integrated circuit 32, does not extend into the output coupling region 5. However, the other layers, namely the substrate layer 22, the first cladding layer 23, the second cladding layer 24 and the active layer 2, each extend into the output coupling region 5. In this embodiment, the photonic crystal 9 is located in the output coupling region 5 within the second cladding layer 24.

[0126] As the intermediate layer 30 is absent from the output coupling region 5, the output field 10 does not need to travel through any additional layers before exiting the photonic integrated circuit 32 through the output surface 12. This again provides the benefit of higher output powers being supplied by the photonic integrated circuit 32, as there is no optical loss or attenuation within further semiconductor layers before the output field 10 reaches the output surface 12.

[0127] A photonic integrated circuit (PIC) 33 in accordance with an alternative embodiment of the present invention is presented in Figure 13. The photonic integrated circuit 33 comprises a first 2a and a second 2b semiconductor gain medium, defining first 4a and second 4b laser regions. The output coupling region 5 is located between the first 2a and the second 2b semiconductor gain mediums.

[0128] In Figure 13, the substrate layer 22, the first cladding layer 23 and the second cladding layer 24 each extend across into the output coupling region 5. However, the first 2a and second 2b semiconductor gain mediums are not provided as one continuous layer e.g. an active layer as for the embodiments of Figures 8 to 12. In particular, the first 2a and second 2b semiconductor gain mediums do not extend into the output coupling region 5. The structure of the presently described embodiment can be achieved through suitable control of the layer growth and etching processes during fabrication.

[0129] The first semiconductor gain medium 2a generates laser radiation when an electrical supply is provided to the photonic integrated circuit 33 by employing the first 25 and second 26 electrical contacts. Similarly, the second semiconductor gain medium 2b generates laser radiation when an electrical supply is provided to the photonic integrated circuit 33 by employing third 34 and fourth 35 electrical contacts which are located in the second laser region 4b. As with the previous embodiments, a photonic crystal 9 is located within the output coupling region 5.

[0130] The photonic integrated circuit 33 of Figure 13 has two modes of operation. In the first mode of operation, both the first 4a and second 4b laser regions are operated simultaneously by generating laser radiation within both the first 2a and second 2b semiconductor gain mediums. This results in a higher output power for the photonic integrated circuit 33, as the generated laser radiation from both the first 4a and second 4b laser regions interact with the photonic crystal 9 to provide a combined higher output power for the output field 10.

[0131] In the second mode of operation the first 4a and second 4b laser regions are operated individually to extend the lifetime of the photonic integrated circuit 33. Both the first 4a and second 4b laser regions have an associated operational lifetime, where the laser region no longer produces a sufficient amount of laser radiation at the end of that lifetime. However, in the second mode of operation the user first activates the first laser region 4a by applying a voltage to the first 25 and second 26 electrical contacts, while no voltage is applied to the third 34 and fourth 35 electrical contacts. Once the first laser region 4a fails or reaches the end of its lifetime, the second laser region 4b can then be activated by applying a voltage to the third 34 and fourth 35 electrical contacts, while the voltage across the first 25 and second 26 electrical contacts may be switched off. In this way, an output field 10 is continuously provided at the output surface 12, and the overall lifetime of the photonic integrated circuit 33 is significantly increased.

[0132] A photonic integrated circuit (PIC) 36 in accordance with an alternative embodiment of the present invention is presented in Figure 14. The photonic integrated circuit 36 provides both a first photonic crystal 9a and second photonic crystal 9b within the output coupling region 5. Furthermore, in Figure 14 the optical waveguide 6 is provided by the active layer 2 and the first 23 and second 24 cladding layers.

[0133] The first 9a and second 9b photonic crystals are arranged within the second cladding layer 24 of the photonic integrated circuit 36.

[0134] The first 9a and second 9b photonic crystal structures are spatially separated, and in particular are located next to each other along the length (y axis) of the photonic integrated circuit 36. The generated radiation from the active layer 2 that enters the output coupling region 5 interacts with both the first 9a and second 9b photonic crystal structures, creating a first 10a and a second 10b output field at the output surface 12. The output fields 10a and 10b may each directed into separate output couplers 27a and 27b, respectively. However, as will be appreciated by the skilled reader, the output fields 10a and 10b could alternatively be directed into the same output coupler 27 using appropriate beam steering techniques.

[0135] The particular properties of the first 9a and second 9b photonic crystals may be chosen to provide output fields 10a and 10b which have the same wavelengths or different wavelengths. Further photonic crystals 9 may be arranged within the output coupling region 5 of the photonic integrated circuit 36. This allows for further output fields 10 with specific wavelengths, as determined by each associated photonic crystal 9, to be generated by the photonic integrated circuit 36.

[0136] A top view of a photonic integrated circuit (PIC) 37 in accordance with an alternative embodiment of the present invention is presented in Figure 15. In this embodiment, a three by three array of photonic crystals 9a to 9i is provided within the output coupling region 5. In the present embodiment, the second cladding layer 24 provides the semiconductor optical waveguide 6 and comprises a tapered section 7. As will be appreciated by the skilled reader, any suitable semiconductor layer, or combination of semiconductor layers, of the laser region 4 could alternatively provide the optical waveguide 6 of the photonic integrated circuit 37. The tapered section 7 acts to extend the size of the semiconductor optical waveguide 6 before the laser radiation enters the output coupling region 5.

[0137] Each photonic crystal 9a to 9i of Figure 15 creates a separate output field 10 with a wavelength determined by the specific properties of each of the photonic crystals 9a to 9i. The photonic crystals 9a to 9i can each provide an identical wavelength, or multiple different wavelengths may be provided by some or all of the photonic crystals 9a to 9i. Note that a smaller or larger array of photonic crystals 9 or an array of any desired geometry could instead be arranged within the output coupling region 5.

[0138] A photonic integrated circuit (PIC) 38 in accordance with an alternative embodiment of the present invention is presented in Figure 16. The photonic integrated circuit 38 of Figure 16 provides both a first photonic crystal 9a and a second photonic crystal 9b within the output coupling region 5. The photonic crystals 9a and 9b are stacked above one another along the z axis. Each photonic crystal 9a and 9b are within a separate layer of the photonic integrated circuit 38, namely the second cladding layer 24 and the intermediate layer 30, respectively.

[0139] It is noted that while the photonic crystals 9a and 9b are located in the same position along the length of the PIC 38 (the y axis of Figure 16), this is not a requirement, and the photonic crystals 9a and 9b could alternatively be offset from one another along the y axis. Furthermore, the photonic crystals 9a and 9b could be arranged within any alternative semiconductor layers that extend into the output coupling region 5.

[0140] When the light generated within the active layer 2 enters the output coupling region 5 it can interact with both the first 9a and second 9b photonic crystal, creating first 10a and second 10b output fields at the output surface 12. Note that while the output fields 10a and 10b are shown to be emitted from different locations on the output surface 12, depending on the location and properties of the photonic crystals 9a and 9b, the output fields 10a and 10b may directly coincide.

[0141] Similar to the previous embodiments, the wavelength of the output fields 10a and 10b may have identical or different wavelengths depending on the properties of the first 9a and second 9b photonic crystal. Additionally, the output fields 10a and 10b may be coupled into the same output coupler 27 as shown in Figure 16, or different output couplers 27, as required for the specific application.

[0142] A photonic integrated circuit (PIC) 39 in accordance with an alternative embodiment of the present invention is presented in Figure 17. The photonic integrated circuit 39 depicts a combination of the embodiments of Figure 14 and Figure 16. In particular, four photonic crystals structures 9a to 9d are present within the output coupling region 5, where the first 9a and second 9b photonic crystals are located adjacent to each other along the length (y axis) of the photonic integrated circuit 39 and the third 9c and fourth 9d photonic crystals are located above the first 9a and 9b photonic crystals respectively (i.e. stacked along z axis).

[0143] An output field 10a to 10d is diffracted by each photonic crystal structure 9a to 9d, where each output field 10a to 10d can be at the same or at different wavelengths as desired. It will be appreciated by the skilled reader that the array of photonic crystals 9a to 9d within the photonic integrated circuit 39 can be arranged in any alternative geometry. Furthermore, additional photonic crystal structures 9 can be included within the photonic integrated circuit 39 to provide further output fields 10.

[0144] In summary, the present invention provides an alternative photonic integrated circuit to those known in the art. The semiconductor materials used within the photonic integrated circuit are specifically chosen to provide the desired output wavelength for the output field 10 of the device. In particular, the different layers of the photonic integrated circuit may be fabricated using one type of semiconductor material to create a highly integrated structure.

[0145] The output coupling region 5 is spatially separated from the semiconductor gain medium 2 of the PIC. A photonic crystal 9 is located within the output coupling region 5 to generate the output field 10 of the PIC. The properties of the photonic crystal 9, are purposely selected to provide a particular output wavelength. The choice of the materials used within the PIC, coupled with the properties of the photonic crystal 9, determine the output power and wavelength of the output field. In addition, the properties of the photonic crystal 9, provide a means to manipulate the output beam characteristics, beam quality and to control the direction of emission. An additional advantage of the above-described PIC is that the structure of the device results in a reduction in the light levels reflected back towards the semiconductor gain medium 2, reducing the need for additional optical isolating components.

[0146] A photonic integrated circuit and a method for manufacturing is disclosed. The photonic integrated circuit comprises a semiconductor gain medium configured to generate laser radiation that is spatially separated from an output coupling region. The photonic integrated circuit further comprises a semiconductor optical waveguide that optically couples the semiconductor gain medium and output coupling region and defines a device plane of the photonic integrated circuit. The output coupling region comprises a photonic crystal which redirects the laser radiation out of the device plane to form an output field of the photonic integrated circuit. The characteristics of the photonic crystal can be used to manipulate the output field properties. Furthermore, the above photonic integrated circuit reduces the redirection of back- reflected light toward the semiconductor gain medium.

[0147] Throughout the specification, unless the context demands otherwise, the term “comprise” or “include”, or variations such as “comprises” or “comprising”, “includes” or “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0148] Furthermore, reference to any prior art in the description should not be taken as an indication that the prior art forms part of the common general knowledge.

[0149] The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.

Claims

Claims1 . A photonic integrated circuit comprising: a semiconductor gain medium configured to generate laser radiation; a semiconductor optical waveguide defining a device plane of the photonic integrated circuit and optically coupled to the semiconductor gain medium; an output coupling region of the semiconductor optical waveguide spatially separated from the semiconductor gain medium; wherein the output coupling region comprises a photonic crystal comprising a periodic array of scattering centres arranged within a first semiconductor material and configured to redirect laser radiation optically coupled within the semiconductor optical waveguide out of the device plane to form an output field of photonic integrated circuit.

2. A photonic integrated circuit as claimed in claim 1 wherein the photonic crystal comprises a second order photonic crystal.

3. A photonic integrated circuit as claimed in claim 1 or claim 2, where the photonic crystal is arranged on the semiconductor optical waveguide, or the photonic crystal is partially or fully embedded in the semiconductor optical waveguide.

4. A photonic integrated circuit as claimed in any of the preceding claims wherein the photonic integrated circuit comprises a semiconductor laser comprising two or more layers of semiconductor material.

5. A photonic integrated circuit as claimed in claim 4, wherein one or more of the layers of the semiconductor laser extend into the optical waveguide.

6. A photonic integrated circuit as claimed in any of the preceding claims wherein, the semiconductor optical waveguide comprises a first tapered section, the first tapered section reducing in width in a direction from the semiconductor gain medium towards the output coupling region.

7. A photonic integrated circuit as claimed in any of the preceding claims wherein, the semiconductor optical waveguide comprises a second tapered section, the secondtapered section increasing in width in a direction from the semiconductor gain medium towards the output coupling region.

8. A photonic integrated circuit as claimed in any of the preceding claims wherein the semiconductor gain medium comprises a gain tapered section, the gain tapered section reducing in width in a direction from the semiconductor gain medium towards the output coupling region.

9. A photonic integrated circuit as claimed in claim 8, wherein the gain tapered section is located between first tapered section and the output coupling region.

10. A photonic integrated circuit as claimed in any of the preceding claims wherein the photonic integrated circuit comprises a spacer semiconductor layer located between semiconductor gain medium and the semiconductor optical waveguide.

11. A photonic integrated circuit as claimed in claim 10, wherein the spacer semiconductor layer comprises a tapered section that reduces in width in a direction from the semiconductor gain medium towards the output coupling region.

12. A photonic integrated circuit as claimed in any of the preceding claims wherein the semiconductor optical waveguide comprises a notch located between the semiconductor gain medium and the output coupling region.

13. A photonic integrated circuit as claimed in claim 12 wherein the width of the notch is in the range of 10 nm to 500 nm or wherein the width of the notch is in the range of 50 nm to 150 nm.

14. A photonic integrated circuit as claimed in either of claims 12 or 13 wherein the notch comprises an air gap in the semiconductor optical waveguide, or wherein the notch is filled with a semiconductor or dielectric material.

15. A photonic integrated circuit as claimed in any of the preceding claims wherein the semiconductor optical waveguide comprises an angled face on one end.

16. A photonic integrated circuit as claimed in any of the preceding claims wherein the output coupling region comprises an array of photonic crystals each of which generates an output field from the output surface of the photonic integrated circuit.

17. A photonic integrated circuit as claimed in claim 16 wherein the elements of the array of photonic crystals are coplanar with a plane that is parallel to the device plane and or the elements of the array of photonic crystals are coplanar with a plane that is perpendicular to the device plane.

18. A photonic integrated circuit as claimed in claim 16 or claim 17 wherein the two or more output fields are at different wavelengths.

19. A photonic integrated circuit as claimed in any of claims 16 to 18 wherein the photonic integrated circuit comprises two or more output couplers and the two or more output fields are directed into separate output couplers.

20. A photonic integrated circuit as claimed in any of the preceding claims wherein the photonic integrated circuit further comprises a second semiconductor gain medium configured to generate laser radiation.21 . A photonic integrated circuit as claimed in claim 20 wherein the output coupling region is located between the first and second semiconductor gain medium.

22. A photonic integrated circuit as claimed in claim 20 or claim 21 wherein the output coupling region is spatially separated from, and optically coupled to, the second semiconductor gain medium by the semiconductor optical waveguide, and the output coupling region generates a second output field from the output surface of the photonic integrated circuit.

23. A photonic integrated circuit as claimed in any of the preceding claims wherein one or more wavelength-selective reflectors are located around one or more sides of the semiconductor optical waveguide.

24. A method of manufacturing a photonic integrated circuit the method comprising: providing a semiconductor gain medium configured to generate laser radiation;providing a semiconductor optical waveguide defining a device plane of the photonic integrated circuit and optically coupled to the semiconductor gain medium; providing an output coupling region of the semiconductor optical waveguide that is spatially separated from the semiconductor gain medium, providing a photonic crystal comprising a periodic array of scattering centres arranged within a first semiconductor material within the output coupling region; and configuring the photonic crystal to redirect laser radiation optically coupled within the semiconductor optical waveguide out of the device plane to form an output field of photonic integrated circuit.25) A method of manufacturing a photonic integrated circuit as claimed in claim 24 wherein providing the photonic crystal comprises providing a second order photonic crystal.

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