Abstract: An optical receiver is described. Using silicon-photonic components that support a single polarization, the output of an optical receiver is independent of the polarization of an optical signal. In particular, using a polarization-diversity technique, the two orthogonal polarizations in a single-mode optical fiber are split in two and processed independently. For example, the two optical signals may be provided by a polarization-splitting grating coupler. Subsequently, a redistribution element provides mixtures of the two optical signals. Next, a wavelength channel in the two mixed optical signals is selected using a wavelength-selective filter (for example, using ring-resonator drop filters or an echelle grating) and converted into an electrical signal at an optical detector (such as a photodetector) to achieve polarization-independent operation.

Abstract: A multi-chip module (MCM) is described. This MCM includes a driver integrated circuit that includes electrical circuits, a photonic chip, an interposer, and an optical gain chip. The photonic chip may be implemented using a silicon-on-insulator technology, and may include an optical waveguide that conveys an optical signal and traces that are electrically coupled to the driver integrated circuit. Moreover, the interposer may be electrically coupled to the traces. Furthermore, the optical gain chip may include a III/V compound semiconductor (and, more generally, a semiconductor other than silicon), and may include a second optical waveguide that conveys the optical signal and that is vertically aligned with the optical waveguide relative to a top surface of the interposer. Additionally, the optical gain chip may be electrically coupled to the interposer.

Abstract: A reflectivity test circuit is described. The reflectivity test circuit includes a symmetric structure that cancels errors in the reflectivity measurements. In particular, the reflectivity test circuit includes an optical waveguide that is optically coupled to two optical ports and two optical couplers. The optical couplers are optically coupled to adjacent optical waveguides, at least one of which is optically coupled to a third optical port and the mirror. Moreover, a length of the optical waveguide is chosen to match the round-trip optical path length in at least the one of the adjacent optical waveguides. During operation, control logic determines the reflectivity of the mirror based at least on a ratio of an optical power measured on one of the two optical ports to an input optical power on the third optical port.

Abstract: An integrated circuit is described. This integrated circuit includes an optical waveguide defined in a semiconductor layer, and a dielectric optical waveguide disposed on the semiconductor layer and that overlaps a region of the optical waveguide. Moreover, the dielectric optical waveguide includes an optical device (such as a mirror) on a facet separating a first portion of the dielectric optical waveguide and a second portion of the dielectric optical waveguide. The facet may be at an angle relative to a plane of the dielectric optical waveguide and may include a metal layer. During operation, an optical signal conveyed by the optical waveguide is evanescent coupled to the dielectric optical waveguide. Then, the optical signal may be reflected by the optical device. For example, the angle of the facet may be 45°, so that the optical signal is reflected normal to the plane of the dielectric optical waveguide.

Abstract: A multi-chip module (MCM) includes: an interposer, a photonic chip, an optical gain chip, and a waveguide-fiber connector. The photonic chip, which may be electrically coupled to the interposer, may be implemented using a silicon-on-insulator (SOI) technology, and may include an optical waveguide that conveys an optical signal. Moreover, the optical gain chip, which may be electrically coupled to the interposer, may include a III-V compound semiconductor, and may include a second optical waveguide that conveys the optical signal and that is vertically aligned with the optical waveguide relative to a top surface of the interposer. Furthermore, the waveguide-fiber connector may be mechanically coupled to the interposer, and remateably mechanically coupled to an optical fiber coupler that includes the optical fiber. The waveguide-fiber connector may convey the optical signal between the optical waveguide in the photonic chip and the optical fiber.

Abstract: A photonic integrated circuit (PIC) is described. This PIC includes an inverse facet mirror on a silicon optical waveguide for optical proximity coupling between two silicon-on-insulator (SOI) chips placed face to face. Accurate mirror facets may be fabricated in etch pits using a silicon micro-machining technique, with wet etching of the silicon <110> facet at an angle of 45° when etched through the <100> surface. Moreover, by filling the etch pit with polycrystalline silicon or another filling material that has an index of refraction similar to silicon (such as a silicon-germanium alloy), a reflecting mirror with an accurate angle can be formed at the end of the silicon optical waveguide using: a metal coating, a dielectric coating, thermal oxidation, or selective silicon dry etching removal of one side of the etch pit to define a cavity.

Abstract: A chip package includes an optical integrated circuit (such as a hybrid integrated circuit) and an integrated circuit that are proximate to each other in the chip package. The integrated circuit includes electrical circuits that modulate data, communicate data, and serialize/deserialize data, and the optical integrated circuit communicates optical signals with very high bandwidth. Moreover, a front surface of the integrated circuit is electrically coupled to a top surface of an interposer, and a top surface of the integrated circuit is electrically coupled to a front surface of the optical integrated circuit. Furthermore, a bottom surface of the optical integrated circuit faces the top surface of the interposer, and the front surface of the optical integrated circuit is optically coupled to an optical-fiber receptacle, which in turn is optically coupled to an optical-fiber connector.

Abstract: When an unsafe port with a loss of signal is detected, a transceiver may enable one laser in a group of lasers associated with the unsafe port and may disable the remaining lasers. Then, the transceiver may instruct a transmitter associated with the one laser to transmit an optical signal on the unsafe port using a reduced transmit power that is less than a threshold value associated with the Class 1 conditions and at a different time than enabled lasers in other groups of lasers. Alternatively, for a safe port on which valid communication is received, the transceiver may enable lasers in a group of lasers associated with the safe port. Then, the transceiver may instruct transmitters associated with the lasers in this group of lasers to transmit optical signals on the safe port using a normal transmit power for the lasers that is greater than the threshold value.

Abstract: A dual-ring-modulated laser includes a gain medium having a reflective end coupled to a gain-medium reflector and an output end coupled to a reflector circuit to form a lasing cavity. This reflector circuit comprises: a first ring modulator; a second ring modulator; and a shared waveguide that optically couples the first and second ring modulators. The first and second ring modulators have resonance peaks, which are tuned to have an alignment separation from each other. During operation, the first and second ring modulators are driven in opposing directions based on the same electrical input signal, so the resonance peaks of the first and second ring modulators shift wavelengths in the opposing directions during modulation. The modulation shift for each of the resonance peaks equals the alignment separation, so the resonance peaks interchange positions during modulation to cancel out reflectivity changes in the lasing cavity caused by the modulation.

Abstract: An optical source is described. This hybrid external cavity laser includes a semiconductor optical amplifier (with a semiconductor other than silicon) that provides an optical gain medium and that includes a reflector (such as a mirror). Moreover, the hybrid external cavity laser includes a photonic chip with: an optical waveguide that conveys an optical signal output by the semiconductor optical amplifier; and a ring resonator (as a wavelength-selective filter), having a resonance wavelength, which reflects at least a resonance wavelength in the optical signal. Furthermore, the photonic chip includes an interferometer that provides optical signals on arms of the interferometer. Control logic in the hybrid external cavity laser thermally tunes the resonance wavelength to match a cavity mode of the hybrid external cavity laser based on measurements of the optical signals from the interferometer.

Abstract: An integrated circuit includes an optical reflector with one or two bus optical waveguides and a one-dimensional, photonic crystal nanobeam cavity to provide single-mode reflection with a narrow bandwidth. In particular, the nanobeam cavity may be implemented on a nanobeam-cavity optical waveguide (such as a channel or ridge optical waveguide), which is optically coupled to the one or two bus optical waveguides. The nanobeam-cavity optical waveguide may include notches along a symmetry axis of the nanobeam-cavity optical waveguide that are partially etched from edges of the nanobeam-cavity optical waveguide toward a center of the nanobeam-cavity optical waveguide. Furthermore, a fill factor of the notches may vary as a function of location along the symmetry axis, while a pitch of the notches is unchanged, to define the nanobeam cavity.

Abstract: A hybrid optical source that provides an optical signal having a wavelength (or a narrow band of wavelengths) is described. This hybrid optical source includes an optical amplifier (such as a III-V semiconductor optical amplifier) that is butt-coupled or vertically coupled to a silicon-on-insulator (SOI) platform, and which outputs an optical signal. The SOI platform includes an optical waveguide that conveys the optical signal. A temperature-compensation element included in the optical waveguide compensates for temperature dependence of the indexes of refraction of the optical amplifier and the optical waveguide. In addition, a reflector, adjacent to the optical waveguide after the temperature-compensation element, reflects a portion of the optical signal and transmits another portion of the optical signal that has the wavelength.

Abstract: An optical modulator is described. This optical modulator may be implemented using silicon-on-insulator (SOI) technology. In particular, the optical modulator may include a carrier-accumulation-type micro-disk resonator fabricated using optical waveguides having a composite structure. Moreover, the composite structure may embed a metal-oxide semiconductor capacitor in the disk resonator. For example, the composite structure may include polysilicon disposed on an oxide layer, which is disposed on a silicon layer in an SOI platform. The optical modulator may have high modulation efficiency and high-speed operation. In addition, the optical modulator may have a compact footprint with low power consumption.

Abstract: An integrated circuit includes an optical reflector with one or two bus optical waveguides and a one-dimensional, photonic crystal nanobeam cavity to provide single-mode reflection with a narrow bandwidth. In particular, the nanobeam cavity may be implemented on a nanobeam-cavity optical waveguide (such as a channel or ridge optical waveguide), which is optically coupled to the one or two bus optical waveguides. The nanobeam-cavity optical waveguide may include notches along a symmetry axis of the nanobeam-cavity optical waveguide that are partially etched from edges of the nanobeam-cavity optical waveguide toward a center of the nanobeam-cavity optical waveguide. Furthermore, a fill factor of the notches may vary as a function of location along the symmetry axis, while a pitch of the notches is unchanged, to define the nanobeam cavity.

Abstract: A technique for fabricating a hybrid optical source is described. During this fabrication technique, a III-V compound-semiconductor active gain medium is integrated with a silicon-on-insulator (SOI) chip (or wafer) using edge coupling to form a co-planar hybrid optical source. Using a backside etch-assisted cleaving technique, and a temporary transparent substrate with alignment markers, a III-V compound-semiconductor chip with proper edge polish and coating can be integrated with a processed SOI chip (or wafer) with accurate alignment. This fabrication technique may significantly reduce the alignment complexity when fabricating the hybrid optical source, and may enable wafer-scale integration.

Abstract: An optical source includes a semiconductor optical amplifier that provides an optical signal, and a photonic chip with first and second ring resonators that operate as Vernier rings. When the optical source is operated below a lasing threshold, one or more thermal-tuning mechanisms, which may be thermally coupled to the first ring resonator and/or the second ring resonator, may be adjusted to align resonances of the first ring resonator and the second ring resonator based on measured optical power on a shared optical waveguide that is optically coupled to the first and second ring resonators. Then, when the optical source is operated above the lasing threshold, a common thermal-tuning mechanism may be adjusted to lock the aligned resonances with an optical cavity mode of the optical source based on a measured optical power on an optical waveguide that is optically coupled to the first ring resonator.

Abstract: An optical device includes an optical reflector based on a coupled-loopback optical waveguide. In particular, an input port, an output port and an optical loop in arms of the optical reflector are optically coupled to a directional coupler. The directional coupler evanescently couples an optical signal between the arms. For example, the directional coupler may include: a multimode interference coupler and/or a Mach-Zehnder Interferometer (MZI). Moreover, destructive interference during the evanescent coupling determines the reflection and transmission power coefficients of the optical reflector.

Abstract: A standard-CMOS-process-compatible optical mode converter transitions an optical mode size using a series of adjacent regions having different optical mode sizes. In particular, in a partial-slab-mode region, which is adjacent to an initial rib-optical-waveguide-mode region, a width of a slab portion of the rib-type optical waveguide decreases and a width of a rib portion of the rib-type optical waveguide decreases to a first minimum tip size. Then, in a slab-mode region, which is adjacent to the partial-slab-mode region, the width of the slab portion decreases to a second minimum tip size. In addition, a dielectric layer is disposed over the slab portion, the rib portion and the BOX layer in the partial-slab-mode region, the slab portion and the BOX layer in the slab-mode region, and the BOX layer in a released-mode region that is adjacent to the slab-mode region and that does not include the semiconductor layer.

Abstract: A standard-CMOS-process-compatible optical mode converter transitions an optical mode size using a series of adjacent regions having different optical mode sizes. In particular, in a partial-slab-mode region, which is adjacent to an initial rib-optical-waveguide-mode region, a width of a slab portion of the rib-type optical waveguide decreases and a width of a rib portion of the rib-type optical waveguide decreases to a first minimum tip size. Then, in a slab-mode region, which is adjacent to the partial-slab-mode region, the width of the slab portion decreases to a second minimum tip size. In addition, a dielectric layer is disposed over the slab portion, the rib portion and the BOX layer in the partial-slab-mode region, the slab portion and the BOX layer in the slab-mode region, and the BOX layer in a released-mode region that is adjacent to the slab-mode region and that does not include the semiconductor layer.

Abstract: An optical modulator is described. This optical modulator may be implemented using silicon-on-insulator (SOI) technology. In particular, a semiconductor layer in an SOI platform may include a photonic crystal having a group velocity of light that is less than that of the semiconductor layer. Moreover, an optical modulator (such as a Mach-Zehnder interferometer) may be implemented in the photonic crystal with a vertical junction in the semiconductor layer. During operation of the optical modulator, an input optical signal may be split into two different optical signals that feed two optical waveguides, and then subsequently combined into an output optical signal. Furthermore, during operation, time-varying bias voltages may be applied across the vertical junction in the optical modulator using contacts defined along a lateral direction of the optical modulator.