System architecture for integrated photonic optical gyroscopes

Abstract

To increase a length of an optical path while avoiding increased losses caused by crossing waveguides in prior art designs.SOLUTION: Novel waveguide design on an integrated photonics chip, acting as a front-end chip, ensures precise detection of phase change in a fiber coil or a sensing chip having a waveguide coil or ring resonator, where the sending chip is coupled to the front-end chip. Strip waveguides are designed to primarily select TE mode and TM mode when laser light is coupled into the integrated photonics chip. A plurality of mode-selective filters, based on multi-mode interference (MMI) filter, a serpentine structure, or other types of waveguide-based mode-selective structure, are introduced in the system architecture. Additionally, implant regions are introduced around the waveguides and other optical components to block unwanted / stray light into the waveguides and an optical signal leaking out of the waveguide.SELECTED DRAWING: Figure 3A

Description

Technical Field

[0001] The present disclosure relates to system-level integration of integrated photonics-based optical gyroscopes.

Background Art

[0002] A gyroscope (sometimes also called a "gyro") is a device capable of sensing angular velocity. Gyroscopes can be mechanical or optical, with various accuracies, performances, costs, and sizes. Applications include, but are not limited to, military, aircraft navigation, robots, autonomous vehicles, virtual reality, augmented reality, games, and others. Optical gyroscopes typically have the highest performance and are based on interferometry and the Sagnac effect (a phenomenon that occurs due to interference caused by rotation). Since optical gyroscopes have no moving parts, they have an advantage over mechanical gyroscopes in that they can withstand the effects of shock, vibration, and temperature changes. The most common optical gyroscope is the fiber optic gyroscope (FOG). The configuration of a FOG typically includes a long loop (or a coil including multiple loops) of polarization-maintaining (PM) fiber. Laser light is irradiated at both ends of the PM fiber and travels in different directions. When the coil of the optical fiber is moving, the light beams produce different optical path lengths relative to each other. By installing an interferometer system, a small optical path length difference proportional to the area of the enclosed loop and the angular velocity of the rotating coil can be measured.

[0003] The phase signal of an optical gyroscope is given by the following equation: Δφ=(8πNA / λc)Ω As shown, it is proportional to the product of the Sagnac effect and the rotational angular velocity. Here, N = the number of turns of the gyroscope, A = the enclosed area Ω = the rotational angular velocity Δφ = the optical phase difference signal λ = the wavelength of light C information speed of light That is the case.

[0004] These fog gates (FOGs) can achieve extremely high precision, but are also large, very expensive, and difficult to assemble due to being built on individual optical components that require precise alignment. Often, manual alignment is required, making mass production difficult. [Overview of the Initiative]

[0005] This specification discloses system components and methods for manufacturing small-footprint integrated photonic optical gyroscopes. While integrated photonic optical gyroscopes, abbreviated as SiPhOG® (Silicon Photonics Optical Gyroscope), can be silicon photonics-based, compound semiconductor (III-V semiconductor) based integrated photonic optical gyroscopes are also within the scope of this disclosure. Furthermore, several embodiments of integrated photonic optical gyroscopes may have a combination of silicon photonics and III-V semiconductor-based photonic components. The inventors design integrated photonic chips with a high level of system architecture and key performance parameters, including, but not limited to, laser performance, tuning parameters, detector parameters, and packaging considerations.

[0006] The key to the performance of fiber-based optical gyroscopes lies in the length of the high-quality, low-loss optical fiber used to measure the Sagnac effect. The inventors recognize that the emergence of integrated photonics suitable for wafer-scale processing presents an opportunity to replace FOGs with smaller integrated photonic chip solutions without sacrificing performance. Photonic-based optical gyroscopes can not only reduce size, weight, power consumption, and cost, but also be mass-producible, vibration-free, and potentially offer performance comparable to FOGs.

[0007] A key element of this integrated photonics solution is the coupling of an integrated photonics chip, which has integrated photonics components, with a waveguide chip that replaces long polarization-maintaining (PM) optical fiber coils containing ultra-low-loss waveguides. Both the integrated photonics chip and the waveguide chip can be manufactured using wafer-scale processes.

[0008] The solutions disclosed herein include low-loss waveguide coils (patterned in a helical shape, but may be circular or any other geometry suitable for mass production) or rings. Any of these WG coil designs may be coplanar or distributed across multiple vertical planes to increase the optical path length while avoiding the increased losses caused by waveguide intersections in prior art designs. The waveguide design and manufacturing techniques are described in concurrently pending U.S. Provisional Application No. 62 / 858,588, filed June 7, 2019.

[0009] A laser source with an appropriate wavelength (which may deviate from 1550 nm for optical gyroscope applications to achieve optimal waveguide loss) can be fiber-coupled to an integrated photonics chip. The receiving end of the waveguide on the photonics chip can be tapered (i.e., widening outwards to fit the core size of a single-mode fiber (typically 8-10 μm)). The waveguide on the integrated photonics chip maintains polarization (e.g., TE polarization), which can be achieved through appropriate waveguide design. For example, a strip waveguide is designed to primarily select the TE mode over the TM mode when the laser light is coupled to the integrated photonics chip. Multiple mode-selective filters (which may be multimode interference (MMI) filters or meandering structures), or other integrated device structures (integrated metal lines, changes in waveguide dimensions, etc.) are introduced into the system architecture. Furthermore, implant regions are introduced around the waveguide and other optical components to block unwanted / stray light into the waveguide and leakage of optical signals outside the waveguide.

[0010] On-chip detectors on integrated photonics chips can be pin photodetectors or avalanche photodiodes (APDs) that convert light into electrical signals. These detectors are used for measuring, testing, and monitoring the Sagnac effect.

[0011] Various types of integrated photonic chips can be manufactured to test the performance of optical gyroscopes. Various designs can be modified by adding or removing additional components for testing purposes, such as packaging experiments, testing, or assembly. Multi-project wafers (MPWs) can accommodate a variety of designs.

[0012] Specifically, aspects of the present disclosure include an integrated photonics-based front-end chip for coupling light to or from an optical gyroscope component, comprising: a laser light source that generates light, including one or more semiconductor lasers; control electronics for the laser light source; an input coupler that couples light from the laser light source to an integrated photonic waveguide structure, wherein the integrated photonic waveguide structure propagates the coupled light toward the optical gyroscope component in the form of a guided light beam; a first optical mode selection filter integrated with the integrated photonic waveguide structure for selecting a preferred optical mode of the guided light beam; at least one optical splitter in the path of the guided light beam to generate a first and a second branch of the guided light beam; and the guided light beam The integrated photonics-based front-end chip includes a phase modulator that modulates the optical phases of a first branch and a second branch relative to each other; a first output coupler that couples the first branch of the guided light beam to a first end of a gyroscope waveguide structure on an optical gyroscope component; a second output coupler that couples the second branch of the guided light beam to a second end of a gyroscope waveguide structure on an optical gyroscope component; and a photodetector coupled to at least one optical splitter, wherein the photodetector receives an optical signal representing the optical phase difference in the return paths of the first and second branches of the guided light beam after it has traveled through the gyroscope waveguide structure on the optical gyroscope component and, after being coupled to return to the integrated photonics waveguide structure via the first and second output couplers.

[0013] This disclosure will be better understood from the detailed description provided below and the accompanying drawings of various implementations of this disclosure. Note that the dimensions shown in the drawings are for illustrative purposes only and are not drawn to scale. [Brief explanation of the drawing]

[0014] [Figure 1] This figure shows a high-level architecture of a typical fiber optic gyroscope based on the Sagnac effect. [Figure 2]This figure shows a high-level architecture of a fiber optic gyroscope in which at least some of the components in the front end have been replaced with integrated photonics chips. [Figure 3A] This is a schematic diagram of one embodiment of an integrated photonics-based front-end coupled to a SiN waveguide chip. [Figure 3B] This is a schematic diagram of an embodiment shown in Figure 3A, which includes additional on-chip electronic components. [Figure 3C] This is a schematic diagram of the embodiment shown in Figure 3A, which features deep implants around the main detector used to measure the Sagnac effect. [Figure 4] This is a schematic diagram of another embodiment of an integrated photonics chip equipped with an optional polarizer or optical mode selector filter. [Figure 5A] This is a schematic diagram of yet another embodiment of an integrated photonics chip coupled with a SiN waveguide chip, designed to facilitate packaging of the integrated photonics chip. [Figure 5B] This figure shows light leakage from the rib waveguide into the slab portion, which is more pronounced around bends, curves, joints, or boundary sections. [Figure 5C] This is a perspective view of a ribbed waveguide structure equipped with high-dose implants and absorbers to prevent light leakage. [Figure 5D] This is a schematic top view of the embodiment shown in Figure 5A, which has been modified by having implants all around the waveguide according to the scheme shown in Figure 5C. [Figure 5E] This is a schematic top view of another embodiment of the integrated photonics chip, modified to have implants all around the waveguide according to the scheme shown in Figure 5C. [Figure 6] This is a schematic diagram of a package that houses a laser, various control integrated circuits, integrated photonics chips, and a SiN waveguide-based gyro chip (sensing chip). [Figure 7] This is a schematic diagram of a configuration in which a laser is coupled to an integrated photonics chip, but is not part of the integrated photonics chip itself. [Figure 8] Schematic diagram of an alternative configuration in which a laser is integrated on an integrated photonics chip. [Figure 9] Plot showing wavelength-dependent loss in different SiN waveguide configurations where the SiN waveguide is a strip waveguide. [Figure 10] Schematic diagram of an integrated photonics chip where optical signals from two lasers are combined. [Figure 11] Schematic diagram of an integrated photonics chip where optical signals from more than two lasers are combined, and optionally a thermal sensor integrated on-chip. [Figure 12] Diagram showing a modified design of a waveguide on an integrated photonics chip. [Figure 13] Diagram showing some exemplary positions of a TM filter on an integrated photonics chip. [Figure 14] Diagram showing an embodiment similar to the embodiment of FIG. 13, where a thermal modulator is added in addition to a high-speed electrical modulator as an additional means for shifting the phase on two output waveguide branches. [Figure 15A] Diagram showing a serpentine structure that can be used as a TM filter. [Figure 15B] Diagram showing a serpentine structure that can be used as a TM filter. [Figure 16] Diagram showing an MMI filter that can be used as a TM filter. ? [Figure 17] Simulation of TE / TM power transmittance plots for different lengths of an MMI filter. [Figure 18] Diagram comparing TE / TM optical power transmittance simulations for MMI filters of optimal length and width for effectively filtering TM.

Embodiments for Carrying Out the Invention

[0015] Aspects of this disclosure are directed toward integrating a compact, ultra-low-loss waveguide chip with other system-level integrated photonic components for optical gyroscope applications. System integration is carried out with large-scale manufacturing in mind to facilitate the mass production of integrated photonic optical gyroscopes.

[0016] Figure 1 shows a high-level architecture 100 of a typical fiber optic gyroscope based on the Sagnac effect. This architecture includes a laser light source 110 that sends an optical signal to a polarization-maintaining (PM) fiber coil 124 via intermediate system components. The intermediate system components include an optical isolator 112, a polarizer 118, and phase modulators 120, 122. The polarizer 118 and phase modulators 120, 122 can be part of a lithium niobate (LiNbO3) multifunction integrated optical chip (MIOC) 116. Also, although the fiber coil 124 is shown to have only one loop for simplicity, in a real device, there can be multiple turns depending on the length of fiber required to utilize the Sagnac effect. The phase modulators 120, 122 can be located along two branches of a 50 / 50 splitter in the MIOC 116. Light traveling in one direction exhibits different (shorter or longer) path lengths than light traveling in the opposite direction, resulting in a measurable phase shift due to the Sagnac effect. The phase modulator can be electrically driven by a function generator 126 (e.g., a sine wave or square wave generator).

[0017] The signal from the function generator 126 is sent to the lock-in amplifier 128, which in turn receives a signal from the photodetector 114, which receives a directional optical signal from the circulator 112. Output 130 represents the phase shift of the gyroscope due to the Sagnac effect caused by the difference in optical path length.

[0018] Figure 2 shows a high-level architecture 200 for a fiber optic gyroscope in which at least some components of the front end of a conventional architecture (e.g., shown in Figure 1) are replaced with integrated photonic components. Components 212, 214, 216, 218, 220, 222, 226, and 228 are functionally equivalent to the corresponding components 112, 114, 116, 118, 120, 122, 126, and 128 shown in Figure 1. However, many of the components in the modified front end 250 can be manufactured using standard semiconductor manufacturing methods. For example, the components on MIOC216 can have all the integrated photonic components. The laser light source 210 and fiber coil 224 may be located outside the modified front end 250, although further integration is possible as described later. The fiber coil 224 constitutes the sensing unit 255 of the architecture 200, but in embodiments described later, the fiber coil can be replaced with a waveguide chip that functions as the sensing unit 255. The output 230 is the measured phase shift due to the optical path length difference. Furthermore, the electronic equipment can be integrated on a chip, for example, as shown with respect to the exemplary embodiment in Figure 3B below.

[0019] Figure 3A is a schematic diagram of one embodiment 300 of an integrated photonics chip 350 coupled to a fiber coil, or a waveguide chip (not shown) that can replace the fiber coil in Figures 1 and 2. The integrated photonics chip of embodiment 300 coupled to the waveguide chip constitutes a gyroscope (e.g., SiPhOG when silicon photonics are used) which can be part of an inertial measurement unit (IMU) package. In addition to the integrated photonic optical gyroscope, the IMU may have other components such as an accelerometer. Therefore, by miniaturizing the integrated photonic optical gyroscope section, the overall size, weight, power, and cost of the IMU can be reduced. This weight reduction can be extremely important in certain applications, such as lightweight unmanned aerial vehicles. The IMU can be a necessary technological element for more established sensing technologies for autonomous vehicles, such as LiDAR (Light Detection and Ranging), radar, and cameras, which will be used in next-generation autonomous vehicles.

[0020] In waveguide chips (also called "gyro chips" or "sensing chips"), the low-loss waveguide core can be made from silicon nitride (Si3N4), and the waveguide cladding can be made from fused silica or oxide. This waveguide structure is also simply called a "SiN waveguide," and a chip containing a SiN waveguide is referred to as a "SiN waveguide chip" in the diagram.

[0021] Referring again to Figure 3A, a laser light source (not shown) is coupled to an integrated photonics chip 350 via a fiber which can be a single-mode (SM) fiber. The core size of the SM fiber is typically in the range of 8–10 μm. The input waveguide on the integrated photonics chip 350 may have to be designed with outward-spreading ends to efficiently couple with the SM fiber that transmits the optical signal from the laser light source to the integrated photonics chip. Instead of fiber coupling, the laser light can be butt-coupled to the integrated photonics chip. Element 302, labeled as a fiber coupler in the illustrative figure, is generally an input coupler as described in the claims. An optical tap (e.g., a tap from which 0.5–1% of the optical power can be extracted) can send a portion of the optical signal to a detector 340 to measure the coupling efficiency between the laser light source and the integrated photonics chip. Optionally, an optical phase modulator 304 can be inserted into the optical path which ultimately leads to an optical splitter (e.g., 2×2 optical splitters 306 and 308). It should be noted that some embodiments may have two 2x2 splitters, some other embodiments may have a Y splitter, and yet other embodiments may have a 2x2 splitter and a Y splitter. It should also be noted that the laser light source may be directly mounted on-chip as shown in Figure 10, or it may be grown on a front-end chip substrate using III-V junction, epitaxial growth, or quantum dot technology. The optical phase modulator 304 can broaden the linewidth of the laser light source, as will be further described below.

[0022] In the embodiment shown in Figure 3A, the splitter and / or directional coupler is designed on-chip to emulate a circulator (as in Figures 1 and 2) for optimized light returning to detector 338 (sometimes referred to as the Sagnac detector, which is the primary detector in the integrated photonics chip 350) for phase measurement. Additionally, electrical (pn junction-based) or other types of phase modulators can be incorporated into one or both of the two branches of the waveguide, which lead to output couplers 332a and 332b optimized for coupling with the SiN waveguide chip. For example, a thermal phase modulator may have lower insertion loss compared to other types of phase shifters and is easier to integrate with the waveguide. The phase modulators can operate in a push-pull configuration to enhance the Sagnac effect. In push-pull operation, phase modulators are included in both output waveguide branches. However, in some embodiments, only one branch of the output waveguide has a phase modulator, i.e., one of the modulators 320 or 322 may be absent or not used. For example, Figure 5D shows that only one branch of the waveguide has a phase modulator. Figure 13 shows that the optical beam can only be modulated at one branch, even though a phase modulator 322 is included (dashed line) for optional use in push-pull mode. Also, the term “output” is used to describe the waveguide branch and output couplers 332a, 332b, but note that the same structure receives the returned optical beam as input from the SiN chip once the beam has passed through the transmitting coil or optical resonator within the SiN chip.

[0023] Non-limiting exemplary dimensions of a SiN waveguide within a gyro chip include a height (i.e., thickness of the patterned waveguide core layer) of 90 nm and a transverse width of 2.8 μm. Those skilled in the art will understand that these exemplary dimensional values ​​described herein do not limit the scope of this disclosure. To reduce waveguide loss, it may be advantageous to have symmetrical upper and lower cladding around the SiN core. This structure can be obtained by wafer bonding of a fused silica wafer or other suitable material such as oxide. Depending on the desired (preferred) optical mode, the thickness of the waveguide SiN layer can vary from 60 to 90 nm, and the width can vary from 2 to 5 μm. The design of the output couplers 332a and 332b varies based on the waveguide dimensions on the waveguide SiN chip. The output spacing and / or optimal placement of couplers 332a and 332b on the photonics chip can be determined using simulation before manufacturing the integrated photonics chip 350. SiN waveguides on a fused silica platform are described in concurrently pending U.S. provisional application 62 / 858,599, filed on June 7, 2019, under the title "Integrated Silicon Photonics Optical Gyroscope on Fused Silica Platform," and concurrently pending U.S. provisional application 62 / 896,365, filed on September 5, 2019, under the title "Single-layer and Multi-layer Structures for Integrated Silicon Photonics Optical Gyroscopes."

[0024] In addition to the Sagnac detector 338, additional detectors 333, 334, 336, and 337 can be incorporated to measure propagation and coupling losses at various locations along the integrated photonics chip (for testing and / or monitoring), as well as to measure the coupling efficiency between the integrated photonics chip and the SiN waveguide chip. For example, detectors 333 and 334 can be coupled to optical taps (e.g., 0.5–1% of the optical power is tapped) to measure the coupling efficiency at output couplers 332a and 332b. The detectors can be PIN photodetectors (PIN diodes) that convert light into electrical signals. The detectors can also be avalanche photodiodes (APDs). One advantage of using APDs is that the gain obtained by the detector reduces the need to increase the laser output. Note that not all of detectors 333, 334, 336, and 337 are necessarily used in all embodiments. Furthermore, some detectors on the test chip mask can be removed from the product mask once the chip design and performance are optimized, reducing the number of detectors required for monitoring.

[0025] Figure 3B shows various electronic components integrated on the integrated photonics chip 350. For example, an on-chip signal generator 305 can be coupled to a phase modulator 304. On-chip transimpedance amplifiers (TIAs) and / or other types of amplifiers for boosting the detected signal can also be integrated on-chip, as shown in components 341, 339, 342, 343, and 335 coupled to the corresponding detector. Furthermore, a phase modulator driver 321 can be integrated on-chip to provide a phase difference of light between two output waveguide branches. In some cases, integrating electronics with photonics provides improved performance, noise reduction, and feedback control. Although not shown in Figure 3B, a laser power monitoring detector and its corresponding electronics can also be part of the integrated photonics chip.

[0026] Figure 3C shows that deep implants (shown as thick rectangles) around the Sagnac detector 338 are key to preventing optical signals from leaking or scattering from the integrated photonics chip into the Sagnac phase difference signal being measured by the detector 338. Further details regarding the use of implants to prevent light leakage are explained with respect to Figures 5B-5E.

[0027] Figure 4 is a schematic diagram of an alternative embodiment 400 of an integrated photonics chip coupled to a SiN waveguide chip, where the optical path includes a polarizer 404 or an optical mode-selective filter. Other components of embodiment 400, such as 402, 406, 408, 420, 422, 432a, 432b, 436, 438, etc., are functionally equivalent to the corresponding components 302, 306, 308, 320, 322, 332a, 332b, 336, 338 shown and described with respect to Figure 3A.

[0028] Figure 5A is a schematic diagram of yet another embodiment 500 of an integrated photonics chip coupled to a SiN waveguide chip, the integrated photonics chip designed for easy packaging. In this design, a Y-splitter 542 is incorporated instead of a 2x2 splitter. Note that the Y-splitter should be as close to 50-50 as possible. The embodiment shown in Figure 5A can be used for customized test purposes.

[0029] Figure 5B(I) illustrates how light typically confined within the raised portions of the rib waveguide on the photonic chip 350 (shown in Figure 5B(II)) may leak into the slab portions of the rib waveguide. This leakage occurs in the straight portions of the waveguide as well, but is particularly pronounced near bends, curves, junctions, and / or junctions. Both Figures 5B(I) and (II) show simulated contours of optical modes within the rib waveguide. Leaked or scattered light can propagate and bounce throughout the integrated photonic chip 350, which can adversely affect the performance of detectors, including the main Sagnac detector 338, if the leaked light mixes with the optical signal from the waveguide gyrocoil. In one embodiment, the raised portion of the rib waveguide may have a height of 0.2–0.5 μm, the slab portion of the rib waveguide may have a height of 0.2–0.5 μm, and the total height of the rib waveguide will be in the range of 0.4–1.0 μm. Other dimensions may be used.

[0030] The inventors use the solution shown in Figure 5C to confine the light in the waveguide. A high dose implant (e.g., 1 cm) is placed throughout the slab around the waveguide. 3 10 19 The peak concentration of each dopant absorbs scattered light and prevents leakage to the detector or other components, including adjacent waveguides. As shown in the following figures, alternative waveguide designs are also introduced for confining specific modes within the waveguide. One alternative design is known as the strip waveguide, shown in Figure 12.

[0031] Figure 5D is a top view of a chip layout very similar to the one shown in Figure 5A, where implants (indicated by thick lines) are shown around the waveguide containing the Y junction to reduce crosstalk between the two branches of the Y splitter and to block scattered light that could reach the edge of the chip from an external source.

[0032] Figure 5E is a top view of another layout of an integrated photonic optical gyroscope front end, with implants (shown by thick lines) all around the waveguide of a 2x2 splitter (such as the splitter schematically shown in Figure 3A) and around the Sagnac photodetector (such as detector 338 schematically shown in Figure 3A). Figure 5E shows a polarizer (such as the polarizer shown in Figure 4) as an optional component. The need for a polarizer can be eliminated by a proper waveguide design (e.g., a TE polarizing waveguide) or by using a suitable mode-selective filter within the integrated chip.

[0033] Figure 6 is a schematic diagram of a package housing a laser, various integrated circuits for control, an integrated photonics chip, and a SiN waveguide chip. Package 600 includes an integrated photonics chip 650 (which may be the same as in the embodiments shown in Figures 3-5) and a SiN waveguide chip 624. The SiN waveguide chip 624 may have a waveguide spiral in one plane, as shown in Figure 6, where the input waveguide and output waveguide intersect, as the direction of light cannot be changed. Alternatively, to avoid waveguide intersection, a portion of the waveguide coil or ring may be dispersed between multiple vertical planes, as described in concurrently pending U.S. Provisional Application No. 62 / 858,588 filed June 7, 2019. The laser light source 610 is located outside the integrated photonics chip 650 and may be fiber-coupled or contact-coupled to the chip 650. The discrete control ICs 660, 662, and 664 for the laser 610 and / or chip 650 may be located inside the package 600, but are not integrated on the same wafer platform. Furthermore, as integration density increases, many of these discrete ICs may be monolithically integrated on chip 650.

[0034] Figure 7 is a schematic diagram of a configuration in which the laser chip 770 is mounted on the integrated photonics chip 750 but is not part of the integrated photonics chip, i.e., the laser is off-chip. Additional components such as an isolator 772 and a lens 774 (a ball lens or other suitable type of lens) may be hybridized on the laser chip 770. The components on chip 750 are similar to those shown and described with respect to Figure 3A, but those skilled in the art will readily see that other arrangements of system components (e.g., those shown in Figure 4 or 5A) are also fully feasible. Focusing the light emitted from the laser 710 using a lens may determine the design of the optical coupler 702 (at the input waveguide end) on chip 750.

[0035] Figure 8 is a schematic diagram of a configuration showing a higher level of on-chip integration, in which a laser 810, an isolator 872, and a lens 874 are integrated on an integrated photonics chip 850. Focusing the light from the laser 810 using the lens can determine the design of the optical coupler 802 (input waveguide end) on the chip 850. The other components in Figure 8 are the same as those in the embodiment of Figure 7. Furthermore, the laser can be bonded using III-V hybrid bonding or epitaxially grown on silicon.

[0036] Figure 9 is a plot showing wavelength-dependent losses in different waveguide configurations. It should be noted that in the overall design of an integrated photonic optical gyroscope, the laser source is designed with a wavelength optimized for waveguide loss. The laser source itself can be broadband and can be tuned to the desired wavelength using additional components. Waveguide attenuation is caused by loss of the optical signal due to absorption and scattering within the waveguide, as well as radiative loss due to the waveguide's geometric characteristics such as microbending and / or sidewall roughness. Scattering and absorption are wavelength-dependent. In silica waveguides containing hydroxide ion (OH-) impurities, the interaction between the oscillating silicon-hydroxyl ion (Si-OH) bond and the electromagnetic field of the optical signal promotes absorption at specific harmonic wavelengths. In long-distance optical fiber communication systems, 1550 nm is used as the optimal wavelength for single-mode optical fibers because it is well outside the absorption enhancement window and scattering loss is extremely small. However, for integrated photonic optical gyroscope applications, where long-distance optical communication is not anticipated, strict adherence to a 1550nm wavelength is not necessary. Rather, it is important to select a wavelength that corresponds to the lowest loss in a SiN waveguide.

[0037] Figure 9 shows three graphs plotting the measured loss (in dB / m) against wavelength for three different waveguide configurations: Graph 902 for a narrow waveguide, Graph 904 for a medium-width waveguide, and Graph 906 for a wide waveguide. As shown in Figure 9, in all three waveguide configurations, the loss in the 1550 nm wavelength range is significantly higher (around 0.7 dB / m) compared to the loss in the 1570-1580 nm wavelength range (where the loss is less than 0.35 dB / m). By focusing on improving the waveguide manufacturing process (including fine-tuning the annealing process to remove moisture from fused silica or oxide) and smoothing the sidewalls, it is possible to reduce the loss to less than 0.1 dB / m. By selecting an appropriate laser wavelength, signal optimization, reduction of laser power, and improvement of the overall performance of the integrated photonic optical gyroscope can be achieved. Note that even lower losses than those shown in Figure 9 have been measured when the waveguide design and dimensions have been changed.

[0038] Figure 10 shows embodiment 1000, in which many components are similar to the design shown in Figure 3A. However, the main difference from Figure 3A is the use of two lasers 1010a and 1010b to double the power and / or for redundancy in case one laser fails. Commonly available distributed feedback (DFB) or Fabry-Perot (FP) lasers may have low power output per laser (in the range of 25-50 mW). Therefore, combining lasers helps to utilize more power with low-cost, mass-produced lasers that are readily available on the market.

[0039] Furthermore, it is possible to use two or more lasers (instead of using one) to directly modulate the lasers, broaden the linewidth, and improve coherence. The modulator 1004 can smear these by introducing random phase noise to the combined beams from two or more lasers, addressing the coherence between the two lasers and producing an output beam equivalent to broadband light coming from a single source. Thus, by combining two or more lasers, the overall output can be greater than that of a single laser with high output. Additional detectors can be used to tap the optical signal and monitor the laser signal and power level.

[0040] Figure 11 is identical to Figure 10, except that instead of two lasers, there is a series of lasers (1, ..., N). Figure 11 also integrates additional components, such as a thermal sensor 1100, onto the integrated photonics chip to monitor whether the chip is operating within a desired temperature range to prevent degradation of laser performance.

[0041] Figure 12 shows a modified waveguide design on the integrated photonics chip 350. Since strip waveguides are better suited to confining transverse electron (TE) modes than transverse magnetic (TM) modes (i.e., the confined optical modes 1208 primarily have a TE component), a strip waveguide 1204 is introduced instead of the rib waveguide shown in Figure 5B. In one embodiment, the strip waveguide can have a height (h) of 0.2 μm and a width of 1-2 μm. A major difference between the rib waveguide and the strip waveguide is that the strip waveguide has no slab portion, and the waveguide is etched down to the substrate 1206 (e.g., an embedded oxide film on a silicon substrate). The implant region 1202 surrounds the strip waveguide and can prevent light leakage and / or block stray light from other components or the chip environment. For example, if TM or TE modes leak from the strip waveguide, they are absorbed in the implant region so as not to reach the detector or other optical components. In addition to designing the waveguide to be inherently TE mode selector, TM filters can be placed at various locations along the optical path on the integrated photonics chip. While rib waveguides can have low loss in both TE and / or TM modes, strip waveguides can be designed to have low loss in TE mode and high loss in TM mode. Furthermore, transitions from strip waveguides to rib waveguides and vice versa can be made across various optical device chips. For example, phase modulators are typically rib waveguide-based devices. It should be noted that SiN waveguides on gyro chips are already similar to strip waveguides because they lack a slab section.

[0042] Figure 13 shows several exemplary locations for TM filters. Since the input light from the fiber can have both TE mode and TM mode, a TM filter can be present between the input coupler 302 and the first 2x2 splitter 306. Each TM filter can constitute a TM filter bank with multiple individual filters in series. For example, in Figure 13, each stage 1360, 1362 of the TM filters can have 1, 2, 4, 6... multimode interference (MMI) filters. To improve performance, one or more TM filters 1366 may also be placed before the light reaches the key detector (i.e., the Sagnac detector 338 shown in the previous figure) or elsewhere in the integrated photonics chip, as needed. For example, a TM filter 1364 may be included to provide the function of the polarizer 404 shown in Figure 4 or the polarizer shown in Figure 5E. Note that, although not shown in Figure 13, the main detector 338 may be surrounded by an implant region. It should be noted that in some embodiments, only one branch of the waveguide has a (electrical and / or thermal) phase modulator. For example, phase modulator 322 (shown by a dashed line) may be completely absent or not actively used in certain operating modes, while phase modulator 320 can be actively used to introduce a phase difference between the optical beams at the two branches of the output waveguide.

[0043] Figure 14 shows an embodiment similar to the embodiment in Figure 13, but with the addition of thermal modulators (1421, 1423) in addition to the fast electrical modulators (1420, 1422) for phase shift at the two output waveguide branches. This system can have fast modulators only, thermal modulators only, or a combination of both on one arm or both arms.

[0044] As described above, the TM filter can be based on a meandering structure (S-bend shown in Figures 15A-B) or on an MMI filter. Figures 15A and 15B show meandering structures that can be used as TM filters. Figure 15A shows the simulated leakage of TE light around the bend of the meandering structure, and Figure 15B shows the simulated leakage of TM light around the bend of the meandering structure. Since the TM leakage is extremely significant, the output of the meandering structure is almost entirely TE light, and the TM light is filtered out.

[0045] Figure 16 shows an MMI filter that can be used as a TM filter. By designing the appropriate length and width of the MMI portion, most TM modes can be filtered.

[0046] Figure 17 shows simulated plots of TE / TM optical power transmittance for MMI filters of different lengths. Plot 1702 shows the TE power transmittance, and plot 1704 shows the TM power transmittance. For example, at a design length of 43.35 μm, the transmittance for the TE mode is 97.42% and the transmittance for the TM mode is 37.53% for each MMI filter. This corresponds to a TE mode loss (LTE) of -0.1132 dB per MMI filter and a TM mode loss (LTM) of -4.2560 dB per MMI filter. The extinction ratio (ER) is 4.1425 dB per MMI filter. By using multiple MMI filters in series, the effect of filtering TM can be achieved (e.g., 2, 4, or more MMI filters).

[0047] Figure 18 shows a simulation of TE / TM optical power transmittance for an MMI filter 1830 with optimal length and width for effectively filtering TM. Figure 1810 above shows TE signal transmission, and Figure 1820 below shows TM signal transmission. Most of the TE light 1832 coupled at the input end is transmitted through the MMI filter at the output end, while the TM light 1836 coupled at the input end is partially scattered by the substrate. Therefore, there is a need for implants to absorb the scattered light (i.e., as shown in Figures 5C and 12). Figure 18 clearly shows that the transmitted TE light 1834 at the output end is significantly more pronounced than the transmitted TM light 1838.

[0048] In the aforementioned specification, the embodiments of the Disclosure have been described with reference to specific exemplary embodiments. It will be apparent that various modifications can be made without departing from the broader spirit and scope of the embodiments of the Disclosure, as described in the following claims. Accordingly, this specification and drawings should be considered illustrative, not restrictive. Furthermore, terms such as “up,” “down,” and other directional terms do not limit the scope of the Disclosure to any fixed direction, but rather encompass various directional rearrangements and combinations. [Explanation of Symbols]

[0049] 302 Fiber Coupler 304 Modulator 340 Tap for joining 338 detectors 306, 308 2x2 Splitter 320, 322 Phase modulators 333, 334 connecting taps

Claims

1. A photonics-based integrated front-end chip for coupling light to or from an optical waveguide chip, A light source including one or more semiconductor lasers, Control electronic equipment for the light source, An input coupler that couples light from the light source to an integrated photonic waveguide structure on the front-end chip, wherein the integrated photonic waveguide structure propagates the coupled light toward the optical waveguide chip in the form of a guided light beam; One or more optical mode selection filters, which are integrated with the aforementioned integrated photonic waveguide structure and select the preferred optical mode of the guided optical beam, To generate the first and second branches of the waveguided light beam, at least one optical splitter is located in the path of the waveguided light beam, A phase modulator that modulates the optical phases of the first and second branches of the waveguide beam relative to each other, A first output coupler connects the first branch of the waveguided light beam to the first end of the silicon nitride waveguide on the optical waveguide chip, A second output coupler connects the second branch of the waveguided light beam to the second end of the silicon nitride waveguide on the optical waveguide chip, A photodetector coupled to at least one of the aforementioned optical splitters, Equipped with, The photodetector receives an optical signal representing the optical phase difference in the return paths of the first and second branches of the guided light beam after it has moved through the silicon nitride waveguide on the optical waveguide chip and been coupled back to the integrated photonic waveguide structure on the front-end chip via the first and second output couplers. At least a portion of the integrated photonic waveguide structure is surrounded by implant regions positioned laterally apart from the photonic waveguide structure to prevent lateral leakage of the waveguided light beam in modes that propagate in the planar direction. The integrated photonic waveguide structure on the front-end chip includes a rib waveguide, the rib waveguide having an upper raised portion and a lower slab portion adjacent to the oxide layer on the silicon substrate, The implant region is provided in the slab portion of the rib waveguide. Photonics-based integrated front-end chip.

2. A photonics-based integrated front-end chip for coupling light to or from an optical waveguide chip, A light source including one or more semiconductor lasers, Control electronic equipment for the light source, An input coupler that couples light from the light source to an integrated photonic waveguide structure on the front-end chip, wherein the integrated photonic waveguide structure propagates the coupled light toward the optical waveguide chip in the form of a guided light beam; One or more optical mode selection filters, which are integrated with the aforementioned integrated photonic waveguide structure and select the preferred optical mode of the guided optical beam, To generate the first and second branches of the waveguided light beam, at least one optical splitter is located in the path of the waveguided light beam, A phase modulator that modulates the optical phases of the first and second branches of the waveguide beam relative to each other, A first output coupler connects the first branch of the waveguided light beam to the first end of the silicon nitride waveguide on the optical waveguide chip, A second output coupler connects the second branch of the waveguided light beam to the second end of the silicon nitride waveguide on the optical waveguide chip, A photodetector coupled to at least one of the aforementioned optical splitters, Equipped with, The photodetector receives an optical signal representing the optical phase difference in the return paths of the first and second branches of the guided light beam after it has moved through the silicon nitride waveguide on the optical waveguide chip and been coupled back to the integrated photonic waveguide structure on the front-end chip via the first and second output couplers. At least a portion of the integrated photonic waveguide structure is surrounded by implant regions positioned laterally apart from the photonic waveguide structure to prevent lateral leakage of the waveguided light beam in modes that propagate in the planar direction. The integrated photonic waveguide structure on the front-end chip includes a strip waveguide, the strip waveguide having a rectangular cross-section etched down to the oxide layer on the substrate, The implant region is adjacent to the substrate and is provided on both sides of the strip waveguide on the same plane as the strip waveguide. Photonics-based integrated front-end chip.

3. The front-end chip according to claim 1 or 2, wherein the light source includes one or more semiconductor lasers or broadband light sources.

4. The front-end chip according to claim 1 or 2, wherein the wavelength of the waveguided light beam is in the infrared region.

5. The front-end chip according to claim 3, wherein the control electronic equipment for the light source includes an additional phase modulator.

6. The front-end chip according to claim 1 or 2, wherein an additional optical phase modulator is inserted before the at least one optical splitter in the path of the waveguided light beam, and the additional optical phase modulator broadens the linewidth of the light source.

7. The front-end chip according to claim 1 or 2, wherein the control electronic equipment includes a direct frequency modulation circuit for the light source.

8. The implant region blocks external light, as described in claim 1 or 2.

9. The front-end chip according to claim 8, further comprising a coupler for coupling the at least one optical splitter and the photodetector, wherein the coupler is part of the integrated photonic waveguide structure on the front-end chip.

10. The front-end chip according to claim 8, wherein the photodetector is completely surrounded by the implant region.

11. The front-end chip according to claim 1 or 2, wherein the photodetector includes a p-i-n photodetector or an avalanche photodiode (APD).

12. The front-end chip according to claim 1 or 2, wherein at least one of the optical mode selection filters includes a structure obtained by locally modifying the integrated photonic waveguide structure on the front-end chip.

13. The front-end chip according to claim 12, wherein at least one of the optical mode selection filters includes a multimode interference (MMI) filter.

14. The front-end chip according to claim 12, wherein at least one of the optical mode selection filters includes one or more individual MMI filters connected in series.

15. The front-end chip according to claim 1 or 2, wherein at least one of the optical mode selection filters includes a meandering structure having one or more bends that substantially allow non-priority modes to leak while the preferred mode propagates.

16. The front-end chip according to claim 1 or 2, wherein the phase modulator includes a thermal phase modulator or an electrical phase modulator.

17. The front-end chip according to claim 1 or 2, wherein the phase modulator includes both a thermal phase modulator and an electrical phase modulator.

18. The front-end chip according to claim 1 or 2, wherein the phase modulator includes a first stage of electrical phase modulation followed by a second stage of thermal phase modulation.

19. The front-end chip according to claim 1 or 2, wherein the phase modulator includes a first stage of thermal phase modulation followed by a second stage of electrical phase modulation.

20. The front-end chip according to claim 1 or 2, wherein the phase modulator modulates the optical phase of one or both of the first and second branches of the waveguided light beam.

21. The optical waveguide chip includes a rotation detection element for a gyroscope, according to claim 1 or 2.

22. A photonics-based integrated front-end chip for coupling light to and from an optical gyroscope component, A laser light source that generates light, including one or more semiconductor lasers, Control electronic equipment for the laser light source, An input coupler that couples light from the laser light source to an integrated photonic waveguide structure, wherein the integrated photonic waveguide structure propagates the coupled light toward the optical gyroscope component in the form of a guided light beam; One or more optical mode selection filters integrated with the integrated photonic waveguide structure for selecting the preferred optical mode of the guided optical beam, the optical mode selection filters include a multimode interference (MMI) filter or a meandering structure having one or more bends that substantially leak non-preferential modes while the preferred mode propagates, To generate the first and second branches of the waveguided light beam, at least one optical splitter is located in the path of the waveguided light beam, A phase modulator that modulates the optical phases of the first and second branches of the waveguide beam relative to each other, A first output coupler connects the first branch of the waveguide light beam to the first end of the gyroscope waveguide structure on the optical gyroscope component, A second output coupler connects the second branch of the waveguide beam to the second end of the gyroscope waveguide structure on the optical gyroscope component, A photodetector coupled to at least one of the aforementioned optical splitters, Equipped with, The photodetector receives an optical signal representing the optical phase difference in the return paths of the first and second branches of the guided light beam after it has moved within the gyroscope waveguide structure on the optical gyroscope component and has been coupled back to the integrated photonics waveguide structure via the first and second output couplers. At least a portion of the integrated photonic waveguide structure is surrounded by implant regions positioned laterally apart from the photonic waveguide structure to prevent lateral leakage of the waveguided light beam in modes that propagate in the planar direction. The integrated photonic waveguide structure on the front-end chip includes a rib waveguide, the rib waveguide having an upper raised portion and a lower slab portion adjacent to the oxide layer on the silicon substrate, The implant region is provided in the slab portion of the rib waveguide. Photonics-based integrated front-end chip.

Images