Patent Description:
Optical communications use modulated light beams to transmit information through optical fibers, free space, or waveguides. In advanced optical communication technologies, such as those based on silicon photonics, electronics and optical components can be integrated on the same circuit unit. The integration of components can lead to production of low-cost devices on silicon wafers through standard processes from the microelectronics industry. However, there remains some challenges in the integration in order to unlock the full potential of silicon photonics.

Document <CIT> refers to a high-power laser which comprises an edge-emitting laser chip (<NUM>) and a waveguide mode field converter. The edge-emitting laser chip (<NUM>) and the waveguide mode field converter are coupled by a silicon-based diffraction lens (<NUM>) fixed on a silicon-based optical substrate (<NUM>), an annular groove is etched in the working end surface of the silicon-based diffraction lens (<NUM>), the bottom surface of the groove is an inclined surface, the waveguide depth of the inclined surface of the groove is H (r, theta) = lambda phi f (r, theta)/2pai, r is polar coordinate distance on the working surface of the silicon-based diffraction lens (<NUM>), theta is polar coordinate azimuth angle on the working surface of the silicon-based diffraction lens (<NUM>), phi f (r, theta) is phase distribution of the silicon-based diffraction lens (<NUM>), and lambda is wavelength of incident light. The high-power laser solves the problems of mismatching of half width of a mode field and aberration of a coupling lens in coupling of the edge-emitting laser chip and the mode field converter by the aid of the diffractive lens, and coupling efficiency is improved. The high-power laser is beneficial to mass production.

Document <CIT> refers to optically aligning and connecting optical devices to optical grating couplers using a variety of bonding techniques, as a means of transferring optical signals to and from optoelectronic integrated circuits.

Document <CIT> refers to a waveguide (<NUM>) fabrication method that includes depositing a photodefinable copolymer material (<NUM>) comprising methyl methacrylate, tetrafluoropropyl methacrylate, and an epoxy monomer; fixing optical elements (<NUM>, <NUM>) relative to the copolymer material; sending light through at least one of the optical elements and copolymer material towards the other; volatilizing uncured monomer. Another waveguide (<NUM>) fabrication method includes: fixing optical elements (<NUM>, <NUM>) relative to each other, each having an optical surface (<NUM>, <NUM>); providing a copolymer blob (<NUM>) over the optical surfaces with sufficient surface tension to result in the copolymer blob having a curved surface (<NUM>); sending light through each of the optical elements towards the curved surface and the other; volatilizing uncured monomer.

Document <CIT> refers to an integrated optical assembly that includes an optics mount. The optics mount has disposed thereon a light source for providing a beam of light and a lens configured to focus the beam of light. The integrated optical assembly includes a photonic integrated circuit (PIC) mechanically coupled to the optics mount. The PIC has disposed thereon a grating coupler for receiving the beam of light and coupling the beam of light into a waveguide. The integrated optical assembly includes a microelectromechanical systems (MEMS) mirror configured to receive the beam of light from the lens and redirect it towards the grating coupler. A position of a reflective portion of the MEMS mirror is adjustable to affect an angle of incidence of the beam of light on the grating coupler.

Document <CIT> refers to a light source assembly supporting direct coupling to a photonically enabled complementary metal-oxide semiconductor (CMOS) chip are disclosed. The assembly may include a laser, a microlens, a turning mirror, reciprocal and/or non-reciprocal polarization rotators, and an optical bench. The laser may generate an optical signal that may be focused utilizing the microlens. The optical signal may be reflected at an angle defined by the turning mirror, and may be transmitted out of the light source assembly to one or more grating couplers in the chip. The laser may include a feedback insensitive laser. The light source assembly may include two electro-thermal interfaces between the optical bench, the laser, and a lid affixed to the optical bench. The turning mirror may be integrated in a lid affixed to the optical bench or may be integrated in the optical bench.

At least one aspect is directed to a photonic integrated circuit according to claim <NUM>.

In some implementations, the beam redirector is configured for longitudinal movement along the v-groove bench to set a focal point of the redirected light onto a surface plane of the grating coupler. In some implementations, the beam adjuster is configured for rotational movement within the v-groove bench to set an angle of incidence between the second direction and a direction normal to the surface plane of the grating coupler. In some implementations, the cylindrical portion has a diameter between about <NUM> to about <NUM>. In some implementations, the cylindrical portion has a diameter of about <NUM>. In some implementations, the longitudinal movement is limited to about <NUM>.

In some implementations, the reflector portion is a prism and the cylindrical portion is a glass. In some implementations, the reflector portion is a mirror and the cylindrical portion is a hollowed tube. The reflector portion and the cylindrical portion are bonded to one another. In some implementations, the reflector portion is positioned above the grating coupler. In some implementations, one of a half-wave plate or an isolator is attached to one of the beam redirector or the coupling lens system.

At least one aspect is directed to a method of manufacturing a photonic integrated circuit according to claim <NUM>.

In some implementations, the longitudinal movement of the beam director is along the v-groove bench to set a focal point of the redirected light on the surface plane of the grating coupler. In some implementations, the rotational movement of the beam director is within the v-groove bench to set an angle of incidence between the second direction of the redirected light and a direction normal to the surface plane of the grating coupler.

In some implementations, the method further includes measuring a light coupling efficiency as a function of the one of longitudinal movement or rotational movement of the beam director.

In some implementations, the method further includes bonding the optical system to the v-groove bench. In some implementations, the bonding occurs after the redirected light is set on the surface plane of the grating coupler at an optimum light coupling efficiency. At least one aspect is directed to the optical assembly according to claim <NUM>, wherein in.

The beam redirector includes a cylindrical portion and a reflector portion that are bonded to one another. In some implementations, the reflector portion is a prism and the cylindrical portion is a glass. In some implementations, the reflector portion is a mirror and the cylindrical portion is a hollowed tube. In some implementations, the reflector portion is positioned above the grating coupler. In some implementations, one of a half-wave plate or an isolator is attached to one of the beam redirector or the coupling lens system. In some implementations, the beam redirector is bonded in a position along the v-groove bench and in a rotational orientation that provides an optimum optical coupling of light emitted by the laser source into the grating coupler.

The disclosure as described herein offers a solution to some of the challenges to unlocking the potential of integrated silicon photonics. The disclosure generally relates to a method and device for coupling a light source to a photonic integrated circuit. The photonic integrated circuit as disclosed herein includes a grating coupler disposed on a substrate and an optical assembly for coupling a light signal to the grating coupler. The optical assembly includes an optical system disposed on a v-groove bench. The optical system includes a laser source for generating a light for the light signal and a coupling lens system for receiving the light from the laser source and for guiding the light to a beam redirector. The beam redirector redirects the light from the coupling lens system onto the grating coupler. The beam redirector includes a cylindrical portion and a reflector portion. The cylindrical portion and the reflector portion are bonded together. The photonic integrated circuit can also include other optical components, such as a beam splitter, a power splitter, a half-wave plate, a quarter-wave plate, isolator, a modulator, and a monitor photodiode.

The substrate used in silicon photonics is silicon. However, as an indirect bandgap semiconductor, silicon is a weak light emitter. In contrast, a direct bandgap semiconductor, such as, those based on III-V materials, offers a more suitable alternative. Since silicon photonics is an up and coming optical technology, there is a need for developing efficient and cost-effective ways to integrate and package a direct-gap III-V laser source with silicon photonics.

Hybrid integration of fully-processed laser sources (chips) allows for a high level of customizability, and can be implemented with silicon photonics via either an edge-coupling or grating-coupling scheme. In the edge-coupling configuration, light is transferred horizontally from an edge-emitting laser source to an edge coupler on the photonic integrated circuit waveguide, directly or through a coupling optics system. Due to the difficulty to achieve a large enough spot size at an edge coupler of a silicon chip, tight sub-micron alignment tolerance is typically required. This tight tolerance makes the III-V laser to photonic integrated circuit alignment difficult. In addition, edge coupling cannot be easily achieved at the wafer-level because it requires chip edge processing, which may lead to higher cost in manufacturing of a photonic integrated circuit based on this technique.

As for integration via the grating-coupling scheme, there are several benefits to using a grating coupler. For example, a grating coupler can allow vertical integration that is compatible with wafer-level testing on a silicon substrate, and offers relatively efficient coupling and relaxed alignment tolerances due to its larger mode field size. However, grating couplers are sensitive to the angle of incidence, wavelength, and state of polarization of the incoming light. Grating couplers include diffractive elements with a limited optical bandwidth over which they can efficiently couple light. Therefore, process variations in the fabrication of the grating coupler can result in variation of the center wavelength from one grating coupler to another. In addition, the angle of incidence of light impinging on the grating coupler also affects the center wavelength; e.g., a steeper angle of incidence may result in a shorter center wavelength. Process variations in the assembly can also affect the angle of incidence of light on the grating coupler. Such process variations can include, for example and without limitation, position of the light source, coupling lens, mirror, and grating coupler, etc..

<FIG> shows a perspective view of a grating coupler <NUM> in a <NUM>-D Cartesian coordinate system with axes of x, y, and z, according to an illustrative implementation. The grating coupler <NUM> is designed for use, for example, in the y/z plane. The incoming light is directed within the y/z plane, and has a vertical angle of incidence (AOI) θ with respect to the z axis, which is perpendicular to the surface of the grating coupler <NUM>.

<FIG> shows a chart <NUM> of typical coupling loss characteristics of a grating coupler with respect to wavelength at different angles of incidence. For a fixed laser wavelength, a change in angle of incidence can lead to an increase in coupling loss, i.e., a reduction in coupling efficiency. For example, at <NUM>, a change of angle of incidence from <NUM>° to <NUM>° causes about an extra <NUM> dB of coupling loss.

In addition, most grating coupler designs are not radially symmetrical. If the incidence beam has an angle with respect to the design principal plane (angle α with respect to the y/z plane as shown in <FIG>), excessive loss will incur. Additionally, <NUM>-D grating couplers are also polarization sensitive. If the state of polarization of the incoming light is not aligned with the grating polarization, the light of the orthogonal polarization does not couple efficiently into the grating coupler, i.e., the grating coupler acts as a polarizer. Therefore, the angle of incidence, the wavelength and state of polarization of the incoming light with respect to the orientation of the grating coupler requires careful alignment and placement. As a result, passive alignment or placement of coupling components with respect to the orientation of the grating coupler can lead to reduced coupling efficiency. Moreover, the penalty from poor alignment during the fabrication, the assembly, or the bonding of the coupling components may also reduce coupling efficiency. Therefore, active placement and controlled alignment of the coupling components are needed to ensure an optimum coupling efficiency in an integrated photonics circuit.

The systems described herein rely on active placement accuracy and controlled alignment to couple the laser light from a III-V laser source to a grating coupler. This can lead to a more efficient device with low coupling losses and improved polarization alignments. Specifically, the method and device disclosed herein benefit from an active fine-tuning of the incidence beam onto the grating coupler via adjustments in the incoming angle of incidence and modification of the laser path length using a single component, such as a beam redirector as described below. This allows for a simpler fabrication process that can reduce the overall cost in manufacturing of the photonic integrated circuit while offering wider tolerances for optimization in light coupling efficiency. Various implementations of integrated silicon photonic systems are described in further detail below.

<FIG> is a cross-sectional view of a photonic integrated circuit <NUM>, according to an illustrative implementation. The photonic integrated circuit <NUM> includes a grating coupler <NUM> disposed on a substrate <NUM>. The photonic integrated circuit <NUM> also includes an optical assembly <NUM> for coupling a light signal <NUM> to the grating coupler <NUM>. The optical assembly <NUM> includes an optical system <NUM> disposed on a v-groove bench <NUM>. The optical system <NUM> includes a laser source <NUM> for generating a light for the light signal <NUM> and a coupling lens system <NUM> for receiving the light from the laser source <NUM>, and guiding and focusing the light in a first direction. The optical system <NUM> also includes a beam redirector <NUM> for redirecting the light from the coupling lens system <NUM> to a second direction towards the grating coupler <NUM>. The beam redirector <NUM> further includes a cylindrical portion <NUM> and a reflector portion <NUM>. The reflector portion <NUM> redirects the light in the second direction, which is about <NUM>° from the first direction.

In some implementations, the grating coupler <NUM> is disposed on the substrate <NUM>. In some implementations, the grating coupler <NUM> is embedded in the substrate <NUM>. In some implementations, the grating coupler <NUM> is fabricated within the substrate <NUM>. In some implementations, the grating coupler <NUM> has a leveled surface flushed with the surface of the substrate <NUM>. In some implementations, the substrate <NUM> can be a silicon substrate, silicon-on-insulator substrate, silicon nitride coated silicon substrate, silicon oxide coated silicon substrate. Similarly, the v-groove bench <NUM> can be silicon or any other suitable material.

In some implementations, the laser source <NUM> produces a continuous-wave beam of light for the light signal <NUM> with a narrow bandwidth. In some implementations, the laser source <NUM> can be a laser diode in die form. In some implementations, the diode die can be mounted p-side down. In some implementations, the diode die can be mounted p-side up. The laser source <NUM> can be soldered to electrical contacts or pads on the surface of the v-groove bench <NUM> or to a driver via wire bonds. In some implementations, the laser source <NUM> can be packaged in a standalone die form, which is then mounted adjacent to the v-groove bench <NUM>. In some implementations, the light from an independently mounted laser source <NUM> can be manipulated in order to properly guide the light from the laser source <NUM> to the coupling lens system <NUM>.

In some implementations, the coupling lens system <NUM> includes a lens or a lens assembly containing more than one optical element for focusing the light onto the grating coupler <NUM>, either directly or indirectly (via one or more reflections). In some implementations, the coupling lens system <NUM> is mounted in the v-groove bench <NUM>, and optionally bonded using a glue or an epoxy. In some implementations, the coupling lens system <NUM> is mounted on an optics mount via one or more brackets or mounts, and then the optics mount containing the coupling lens system <NUM> is disposed in the v-groove bench <NUM>.

The beam redirector <NUM> includes a cylindrical portion <NUM> and a reflector portion <NUM>. The beam redirector <NUM> is disposed in the v-groove bench <NUM>. In some implementations, the cylindrical portion <NUM> is disposed in the v-groove bench <NUM> while the reflector portion <NUM> is not disposed in the v-groove bench <NUM>.

In some implementations, the cylindrical portion <NUM> has a diameter between about <NUM> to about <NUM>, inclusive of any diameters therebetween. In some implementations, the cylindrical portion <NUM> has a diameter between about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>, inclusive of any diameter therebetween.

In some implementations, the cylindrical portion <NUM> has a diameter of about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, or about <NUM>.

In some implementations, the cylindrical portion <NUM> has a length between about <NUM> to about <NUM>, inclusive of any lengths therebetween. In some implementations, the cylindrical portion <NUM> has a length between about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>, inclusive of any length therebetween.

In some implementations, the cylindrical portion <NUM> has a length of about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, or about <NUM>.

In some implementations the cylindrical portion <NUM> is an optically transparent tube, such as a glass. In some implementations, the cylindrical portion <NUM> is a hollowed tube and the reflector portion is a mirror. In some implementations, the reflector portion <NUM> is a prism. In some implementations, the cylindrical portion <NUM> and the reflector portion <NUM> are coupled to one another. In some implementations, the cylindrical portion <NUM> and the reflector portion <NUM> are bonded to one another using an epoxy or any other suitable bonding material. In some implementations, the cylindrical portion <NUM> and the reflector portion <NUM> are attached to one another via a mechanical fixture.

In the optical system <NUM>, the laser source <NUM> generates a light for the light signal <NUM>. The coupling lens system <NUM> receives the light from the laser source <NUM> and guides the light in a first direction. The beam redirector <NUM> redirects the light from the coupling lens system <NUM> to a second direction towards the grating coupler <NUM>. In some implementations, the reflector portion <NUM> redirects the light in the second direction, which is about <NUM>° from the first direction.

Although not explicitly shown in <FIG>, the photonic integrated circuit <NUM> may include other optical components, such as, but not limited to a beam splitter, a power splitter, a half-wave plate, a quarter-wave plate, an isolator, a modulator, a monitor photodiode, or any other suitable optical components. In some implementations, optical components, such as a wave plate that converts TM polarization to TE polarization, or vice versa, can be included the photonic integrated circuit <NUM>. In some implementations, one or more of these optical components may be placed anywhere along the path of the light signal <NUM> between the laser source <NUM> and the grating coupler <NUM>. In some implementations, one or more of these optical components can be attached to the laser source <NUM>. In some implementations, one or more of these optical components can be placed between the laser source <NUM> and the coupling lens system <NUM>. In some implementations, one or more of these optical components can be attached to the coupling lens system <NUM>. In some implementations, one or more of these optical components can be placed within the coupling lens system <NUM> if the coupling lens system <NUM> includes more than one lens or optical element. In some implementations, one or more of these optical components can be placed between the coupling lens system <NUM> and the beam redirector <NUM>. In some implementations, one or more of these optical components can be placed between the cylindrical portion <NUM> and the reflector portion <NUM> of the beam redirector <NUM>. In some implementations, one or more of these optical components can be attached to the cylindrical portion <NUM>. In some implementations, one or more of these optical components can be attached to the reflector portion <NUM>. In some implementations, one or more of these optical components can be placed between the beam redirector <NUM> and the grating coupler <NUM>. In some implementations, one or more of these optical components can be placed above the grating coupler <NUM>.

<FIG> is a perspective view of alternative embodiment of a photonic integrated circuit <NUM>, according to an illustrative implementation. The photonic integrated circuit <NUM> includes a grating coupler <NUM> fabricated within or coupled to a substrate <NUM>. The photonic integrated circuit <NUM> also includes an optical assembly <NUM> for coupling a light signal <NUM> to the grating coupler <NUM>. The optical assembly <NUM> includes an optical system <NUM> disposed on a v-groove bench <NUM>. The v-groove bench <NUM> is mounted on the substrate <NUM>. The optical system <NUM> includes a laser source <NUM>, a coupling lens system <NUM>, and a beam redirector <NUM>, each disposed on the v-groove bench <NUM>. The beam redirector <NUM> further includes a cylindrical portion <NUM> and a reflector portion <NUM>. In some implementations, the cylindrical portion <NUM> is made from a glass. In some implementations, the cylindrical portion <NUM> can be a hollow tube. In some implementations, the reflector portion <NUM> is a prism. As shown in Figure 2B, the cylindrical portion <NUM> and the reflector portion <NUM> are bonded to one another.

Within the optical system <NUM>, the laser source <NUM> generates a light for the light signal <NUM>. The coupling lens system <NUM> receives the light from the laser source <NUM> and guides the light in a first direction. The beam redirector <NUM> redirects the light from the coupling lens system <NUM> to a second direction towards the grating coupler <NUM>. In some implementations, the cylindrical portion <NUM> receives the light from the coupling lens system <NUM>, and the reflector portion <NUM> redirects the light in the second direction, which is about <NUM>° from the first direction.

The beam redirector <NUM>, which includes the cylindrical portion <NUM> and the reflector portion <NUM> that are bonded together, is disposed in the v-groove bench <NUM>. The cylindrical portion <NUM> of the beam redirector <NUM> is in contact with the v-groove bench <NUM> in a tangent manner while the reflector portion <NUM> is suspended or floating beyond the edge of the v-groove bench <NUM> as shown in Figure 2B. One prism surface of the reflector portion <NUM> is attached to the cylindrical portion <NUM> and the other prism surface is directly above the grating coupler <NUM>.

In some implementations, the beam redirector <NUM> can be moved longitudinally (longitudinal movement) along the length of the v-groove bench <NUM>, i.e., in the direction <NUM>. In some implementations, the beam redirector <NUM> can be moved longitudinally between about <NUM> to about <NUM>, inclusive of any distance values therebetween. In some implementations, the beam redirector <NUM> can be moved longitudinally between about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>, inclusive of any distance values therebetween. In some implementations, the beam redirector <NUM> can be moved longitudinally about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, or about <NUM> or less.

In some implementations, the beam redirector <NUM> can be rotated axially in the direction <NUM> within the v-groove bench <NUM>. In some implementations, the beam redirector <NUM> can be rotated by about +/- <NUM>°, about +/- <NUM>°, about +/- <NUM>°, about +/- <NUM>°, or about +/- <NUM>°. Since the cylindrical portion <NUM> is attached to the reflector portion <NUM>, moving and/or rotating the cylindrical portion <NUM> in the v-groove bench <NUM> cause appropriate movements and/or rotations of the reflector portion <NUM>.

<FIG> illustrates an adjustment of a focal point of the light via a longitudinal movement of the beam redirector <NUM> in the optical system <NUM>, according to illustrative implementations. <FIG> shows the original position of the optical system <NUM>, which may have an out of focus beam of light <NUM> impinging on the grating coupler <NUM>. In order to properly focus the beam of light <NUM> onto the grating coupler <NUM> for improved, and in some cases, optimum coupling efficiency, the beam redirector <NUM> can be moved along the y-direction (direction <NUM>) towards or away from the coupling lens system <NUM>, as shown in <FIG>. Moving the beam director <NUM> by a "dy" amount in the y-direction results in the focal point of the beam of light <NUM> changing by an equal magnitude of a "dz" amount in the z-direction, i.e., towards the surface of the grating coupler <NUM>. Similarly, moving the beam director <NUM> by a "dy" amount in the negative y-direction (away from the coupling lens system <NUM>) would result in the focal point of the beam of light <NUM> changing by an equal magnitude of a "dz" amount in the negative z-direction, i.e., away from the surface of the grating coupler <NUM>.

<FIG> illustrates an adjustment of an angle of incidence of the light via a rotational movement of the beam redirector <NUM> in an optical system <NUM>, according to illustrative implementations. <FIG> shows the original position of the optical system <NUM> which may have the beam of light <NUM> impinging on the grating coupler <NUM> at an angle of incidence θ. In order to adjust the beam of light <NUM> onto the grating coupler <NUM> for an improved or optimum angle of incidence θ to achieve an improved or optimum coupling efficiency, the beam redirector <NUM> can be rotated in a direction <NUM> (clockwise around the y-axis) as shown in <FIG>. Rotating the beam redirector <NUM> by a "β" in the direction <NUM> results in the change in the angle of incidence θ by an equal magnitude of a "β", resulting in the final angle of incidence of (θ + β) on the surface of the grating coupler <NUM>. This is further explained below in mathematical equations. Similarly, rotating the beam redirector <NUM> counter-clockwise (i.e., β < <NUM>) results in an opposite change in the angle of incidence θ.

For the angle of incidence θ, the beam of light <NUM> to the grating coupler <NUM> is denoted as: <MAT> where <MAT> is a vector of the beam of light <NUM>. After rotation around the y-axis by an angle of β, the rotation matrix Ry is expressed as: <MAT> then the resultant chief ray <MAT> is: <MAT>.

As a result, the angle of incidence of the beam of light <NUM> is changed from θ to (θ + β) after the rotation. The change in the angle of incidence is <NUM>:<NUM> proportional to the rotation angle β. This demonstrates the disclosed method is able to effectively tune the angle of incidence of the grating coupler <NUM>. It is noted that the beam of light <NUM> is still within the principal plane x/z after the beam redirector <NUM> is rotated. In addition, the rotation in the angle of incidence θ causes a change in the location of the focal point since the focal point is also slightly moved as the path of the beam of light <NUM> changes.

<FIG> is an illustration <NUM> that shows a change in a focal point of the light as a function of the rotational movement of the beam redirector <NUM>. The correlation between the movement of the focal point (dx and dz) and the rotation in the angle of incidence (θ to (θ + β)) can be expressed as: dx = h[tan( θ + β) - tanθ ] and dz = h[cosθ - cos( θ+ β)]. Using these relationships, dx and dz values can be determined from known θ, β, <MAT>, Ry, and <MAT>. <FIG> show some example values obtained via the aforementioned mathematical relationships.

<FIG> shows a chart <NUM> of a lateral offset as a function of a rotational angle of the beam redirector <NUM>. The calculated numerical values plotted in the chart <NUM> are verified via experimental measurements. For example, an angle of incidence change from <NUM>° to <NUM>°, i.e., for the β of <NUM>°, the lateral offset dx (i.e., focal point shift) is measured to be about <NUM>, and for β of <NUM>°, dx is about <NUM>.

<FIG> similarly shows a chart <NUM> of an axial offset as a function of a rotational angle of the beam redirector <NUM>. For example, for an angle of incidence change from <NUM>° to <NUM>°, i.e., for the β of <NUM>°, the axial offset dz is about <NUM>, and for β of <NUM>°, dz is about <NUM>. In some implementations, dx and dz values can be used to determine β and/or θ.

<FIG> is a flowchart of an example method <NUM> of manufacturing a photonic integrated circuit, according to an illustrative implementation. The method <NUM> includes providing a grating coupler disposed on a substrate (stage <NUM>). The method <NUM> also includes providing an optical assembly for coupling a light signal to the grating coupler (stage <NUM>). The method <NUM> further includes adjusting the light onto a surface plane of the grating coupler (stage <NUM>). In some implementations, the method <NUM> optionally includes measuring a light coupling efficiency of the grating coupler (stage <NUM>). In addition, the method <NUM> optionally includes bonding an optical system to a v-groove bench in the optical assembly (stage <NUM>). All the components described below in the method <NUM> are similar to those included in the photonic integrated circuits described with respect to <FIG> and <FIG>, and therefore, will not be provided in further detail.

The method <NUM> includes providing a grating coupler disposed on a substrate (stage <NUM>). The grating coupler can be similar to the grating couplers <NUM> or <NUM> as described with respect to <FIG> and <FIG>. The substrate can be similar to the substrate <NUM>, and therefore the substrate can be a silicon substrate, silicon-on-insulator substrate, silicon nitride coated silicon substrate, silicon oxide coated silicon substrate, or any other suitable substrate.

The method <NUM> also includes providing an optical assembly for coupling a light signal to the grating coupler (stage <NUM>). The optical assembly includes a v-groove bench and an optical system disposed on the v-groove bench. The optical system includes a laser source for generating a light for the light signal, a coupling lens system for receiving the light from the laser source and guiding the light in a first direction, and a beam redirector for redirecting the light to a second direction. The second direction of redirected light is about <NUM>° from the first direction. The beam redirector includes a cylindrical portion and a reflector portion. The cylindrical portion and the reflector portion can be coupled to one another. All the components described with respect to the optical assembly, the optical system and the v-groove bench in the method <NUM> are similar to those included in the photonic integrated circuits described with respect to <FIG> and <FIG>, and therefore, will not be provided in further detail.

The method <NUM> further includes adjusting or guiding the redirected light onto a surface plane of the grating coupler (stage <NUM>). The adjusting or guiding the redirected light onto the surface plane of the grating coupler can be done via one of longitudinal movement or rotational movement of the beam director. The longitudinal movement of the beam director is along the v-groove bench to set a focal point of the redirected light on the surface plane of the grating coupler. In some implementations, the beam redirector can be moved longitudinally (longitudinal movement) in the v-groove bench. In some implementations, the beam redirector can be moved longitudinally a distance between about <NUM> to about <NUM>, inclusive of any distance values therebetween. In some implementations, the beam redirector <NUM> can be moved longitudinally between about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>, inclusive of any distance values therebetween.

The rotational movement of the beam director is within the v-groove bench to set an angle of incidence between the second direction of the redirected light and a direction normal to the surface plane of the grating coupler. In some implementations, the beam redirector can be rotated axially within the v-groove bench along its axis of the cylindrical portion. In some implementations, the beam redirector can be rotated by about +/- <NUM>°, about +/- <NUM>°, about +/- <NUM>°, about +/- <NUM>°, or about +/- <NUM>° or any degree of rotation included within any of the above ranges.

In some implementations, the longitudinal movement and/or rotational movement of the beam director can be facilitated mechanically via manual stages or a robotic arm, or electromechanically via an electromechanically-actuated robotic arm.

The method <NUM> optionally includes measuring a light coupling efficiency as a function of one of longitudinal movement or rotational movement of the beam director (stage <NUM>). The light coupling efficiency measurements obtained in stage <NUM> can help determine the optimum angle of incidence of the redirected light with respect to the normal axis of the surface of the grating coupler. Note that the measurement results for the optimum angle of incidence can depend on the wavelength of light. In other words, the optimum angle of incidence can vary as with the wavelength of the light being used in the integrated photonic system.

The method <NUM> also optionally includes bonding the optical system to the v-groove bench after the redirected light is set on the surface plane of the grating coupler at an optimum light coupling efficiency (stage <NUM>). Once the optimum angle of incidence is determined via measurements in stage <NUM>, the components in the optical assembly can be bonded to the v-groove bench in the determined position and orientation. The bonding can be done using an epoxy or any other suitable bonding material.

While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular inventions.

References to "or" may be construed as inclusive so that any terms described using "or" may indicate any of a single, more than one, and all of the described terms. The labels "first," "second," "third," and so forth are not necessarily meant to indicate an ordering and are generally used merely to distinguish between like or similar items or elements.

Claim 1:
An optical assembly (<NUM>) for coupling a light signal to a grating coupler (<NUM>), the optical assembly comprising:
a v-groove bench (<NUM>) bonded to a substrate (<NUM>), wherein the v-groove bench comprises a v-groove,
a grating coupler (<NUM>) disposed adjacent to the v-groove bench, and
an optical system (<NUM>) disposed on the v-groove bench, the optical system comprising:
a laser source (<NUM>) for generating a beam of light,
a coupling lens system (<NUM>) for receiving the beam of light from the laser source and guiding the beam of light in a first direction, and
a beam redirector (<NUM>) for redirecting the beam of light to a second direction, the second direction of redirected light being about <NUM>° from the first direction,
wherein the beam redirector comprises a cylindrical portion (<NUM>) and a reflector portion (<NUM>) that are bonded to one another, and wherein the reflector portion (<NUM>) is suspended beyond an edge of the v-groove bench (<NUM>);
wherein the coupling lens system and the beam redirector are bonded to the v-groove bench,
wherein the beam redirector sets a focal point of the redirected light onto a surface plane of the grating coupler, and
wherein the beam redirector sets an angle of incidence between the second direction of the redirected light and a direction normal to the surface plane of the grating coupler.