Interferometric device for wavelength locking

Abstract

This invention discloses a configuration of a modal interferometer for wavelength locking. The modal interferometer can be an interferometer comprising an input waveguide, an interference waveguide, and an output waveguide. Light of a fundamental mode can be emitted into the input waveguide, and the interference waveguide receives the fundamental mode and generates light of a higher-order mode, wherein the two modes can be superimposed as they propagate through the interference waveguide. The two modes can be received at the output waveguide, which collapses the two modes into a single mode and generates an output signal corresponding to the interference between the two modes. This output signal can be used to lock a measured wavelength to a target wavelength. Multiple output waveguides can produce output signals with dead zones that are misaligned with each other for any wavelength within the wavelength range of interest.

Description

[0001] Cross-references to related applications

[0002] This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 248,195, filed September 24, 2021, pursuant to 35 USC § 119(e), the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates generally to wavelength-locking systems. More specifically, embodiments thereof relate to a wavelength-locking system having a waveguide that generates an output signal using modal interference for a wavelength-locked light source. Background Technology

[0004] Generally, optical systems employ multiple light sources to measure various types of information. In some examples, monitoring the optical properties of the light emitted by a light source can be useful. For instance, the optical properties of the light emitted by a light source can be measured and monitored to ensure that the light source has a certain degree of wavelength stability. Furthermore, wavelength locking can be achieved when dealing with a single wavelength or a small wavelength range, but it increases complexity when dealing with multiple wavelengths or wavelength ranges spanning a greater number of wavelengths.

[0005] Some of these optical systems can output light at multiple different wavelengths. However, as the number of wavelengths monitored increases, so does the size and complexity of the system. Because the size of an optical system changes proportionally to the number of wavelengths locked, optical systems used for monitoring light may be unsuitable for certain applications due to factors such as size and complexity. For example, such optical systems may occupy too much space to be reasonably integrated into compact electronic devices such as mobile phones, tablet computers, laptops, wearable devices, etc. Furthermore, existing optical systems for monitoring light may operate within a narrow wavelength range and may not be able to operate across different or wide wavelength ranges. Therefore, it may be desirable to have systems that lock light across a wide wavelength range while maintaining a compact form factor for integration into compact electronic devices. Summary of the Invention

[0006] Embodiments of the systems, apparatuses, methods, and devices described in this disclosure relate to an interferometric device for wavelength locking. Systems, apparatuses, methods, and devices also are described that involve using waveguide modes to generate output signals that can be used to wavelength-lock light over a wide range of wavelengths while simultaneously reducing the size and complexity of the interferometric device. An input waveguide can receive and output a single mode of light. An interferometric waveguide can receive the single mode of light and generate at least one higher-order mode of light. Multiple modes of light can be superimposed and propagated through the interferometric waveguide. The light can collapse back into a single mode to generate an output signal for locking a measured wavelength to a target wavelength of light. In some embodiments, multiple output signals can be generated among multiple modes of light, which can be used to wavelength-lock light over a wide range of wavelengths.

[0007] This disclosure describes a wavelength locking device. The wavelength locking device may include a planar waveguide defining: a first waveguide configured to receive light and support a first single-mode light; a second waveguide having a first end optically coupled to the first waveguide and configured to receive the first single-mode light from the first waveguide and support at least two different modes of light; and a third waveguide optically coupled to a second end of the second waveguide and configured to receive the at least two different modes of light from the second waveguide, support a second single-mode light, and output the second single-mode light to lock the measured wavelength of the light to a target wavelength. The first waveguide has a first width, a first central axis, and is offset from the central axis of the second waveguide, which has a second central axis and a second width different from the first width, and is a bimodal waveguide. The third waveguide has a third central axis, a third width different from the second width, and the third central axis is offset from the central axis of the second waveguide, thereby increasing the sensitivity to the selected mode of the light of at least two different modes. In some embodiments, the first mode size of at least the first single mode of light and the second mode size of the light of at least two different modes are constant across different wavelengths of light. In some embodiments, the first waveguide and the third waveguide are tapered waveguides. In some embodiments, the second waveguide is an interference waveguide, and the second waveguide generates TE00 mode light superimposed with TE01 mode light. In some embodiments, the first waveguide is positioned such that the central axis of the first end of the second waveguide is aligned with the central axis of the first waveguide, and the third waveguide is positioned such that the central axis of the second end of the second waveguide is aligned with the central axis of the third waveguide.

[0008] Additionally, the second waveguide is an interference waveguide, and the second waveguide generates TE00 mode light superimposed on TE02 mode light. In some embodiments, the second waveguide supports at least three different modes of light. In some embodiments, the second waveguide may include a first end of a mode expander section optically coupled to the second waveguide, and three output waveguides optically coupled to a second end of the mode expander section. In some embodiments, the mode expander section allows adiabatic expansion of the at least three different modes of light, which interfere to provide three output signals with wavelength relationships having phase shifts relative to each other, and two of the three output waveguides are asymmetrically positioned relative to the center of the second end of the second waveguide. In some embodiments, the at least three different modes of light are TE00 mode light, TE01 mode light, and TE02 mode light, and the first output waveguide of the three output waveguides is placed at the zero point of the TE02 mode light, and the first and third output waveguides are asymmetrically positioned relative to each other.

[0009] In some embodiments, a wavelength locking system may include: a first waveguide configured to receive light and support a first single mode of light; a second waveguide having a first end optically coupled to the first waveguide and configured to receive the first single mode of light from the first waveguide and support at least two different modes of light; a mode splitter optically coupled to a second end of the second waveguide and configured to separate the at least two different modes of light, output the first mode of light from the at least two different modes of light, and output the second mode of light from the at least two different modes of light; and a beam splitter configured to generate a plurality of output signals having a wavelength relationship with a phase shift relative to each other, wherein the plurality of output signals are used to lock the measured wavelength of light to a target wavelength. The first waveguide is positioned such that its central axis is offset relative to the central axis of a first end of the second waveguide, thereby generating at least two modes of light in the second waveguide and reducing insertion loss. The second waveguide receives the first mode of light and generates the second mode of light, outputting a combination of the first and second modes of light. The beam splitter has two waveguide inputs and three waveguide outputs. In some embodiments, the first waveguide is configured to receive the light of a fundamental mode, and the first waveguide is narrower than the second waveguide. Additionally, the beam splitter generates three output signals, each of which has a wavelength relationship with a unique phase shift depending on the wavelength of the corresponding output signal. Furthermore, the beam splitter may include a free-propagating region having output ends and a first output waveguide having a central axis, the first output waveguide being positioned such that the central axis of the output end of the free-propagating region is aligned with the central axis of the first output waveguide. Furthermore, the wavelength locking device may include a second output waveguide having a central axis and a third interference output waveguide having a central axis, the second output waveguide being symmetrically positioned at the output end relative to the central axis of the free propagation region, and the third interference output waveguide being symmetrically positioned at the output end relative to the central axis of the free propagation region.

[0010] Additionally, a method for wavelength locking may include: receiving light of a first mode by a first waveguide; receiving the light of the first mode by a second waveguide; generating light of a second mode by the second waveguide; generating an output signal corresponding to interference between the light of the first mode and the light of the second mode; and using the output signal to lock the measured wavelength of the light to a target wavelength. Generating the output signal may include: generating a first output signal corresponding to interference between light of TE00 mode and light of TE01 mode; generating a second output signal corresponding to interference between light of TE00 mode and light of TE02 mode; and generating a third output signal corresponding to interference between light of TE01 mode and light of TE02 mode. In some embodiments, the method may include collapsing the light of the first mode and the light of the second mode into a single mode of light by the third waveguide. In yet another embodiment, the method may include superimposing the light of the first mode and the light of the second mode by the second waveguide as the light of the first mode and the light of the second mode propagate through the second waveguide.

[0011] In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent from the accompanying drawings and by studying the following description. Attached Figure Description

[0012] Figure 1 A block diagram of an exemplary wavelength locking system is shown.

[0013] Figure 2A A block diagram of an exemplary wavelength locking system including multiple interferometers is shown.

[0014] Figure 2B It shows Figure 2A A block diagram of the beam splitter and multiple interferometers of a wavelength-locked system.

[0015] Figure 3 A block diagram of an exemplary wavelength locking system including an interferometer is shown.

[0016] Figure 4A A cross-sectional top view of an exemplary interference device is shown.

[0017] Figure 4B It shows Figure 4A A cross-sectional side view of an example of the input waveguide of an interferometric device.

[0018] Figure 4C It shows in Figure 4A A cross-sectional side view of a single mode of light in the input waveguide of an interferometer device.

[0019] Figure 4D It shows in Figure 4AA cross-sectional side view of higher-order modes of light in the interference waveguide of an interference device.

[0020] Figure 5A A cross-sectional top view of an exemplary interference device is shown.

[0021] Figure 5B It shows in Figure 5A A cross-sectional side view of a single mode of light in the input waveguide of an interferometer device.

[0022] Figure 5C It shows in Figure 5A A cross-sectional side view of higher-order modes of light in the interference waveguide of an interference device.

[0023] Figure 6 A top view of another exemplary interference device is shown.

[0024] Figure 7 A top view of another exemplary interference device is shown.

[0025] Figure 8 A top view of an example of a hybrid interferometer device is shown.

[0026] The use of crosshairs or shading in the accompanying drawings is generally provided to clarify the boundaries between adjacent elements and also to improve the readability of the drawings. Therefore, the presence or absence of crosshairs or shading does not indicate or suggest any preference or requirement for a particular material, material properties, element proportions, element dimensions, commonalities of similar illustrated elements, or any other feature, property, or characteristic of any element shown in the accompanying drawings.

[0027] It should be understood that the proportions and dimensions (relative or absolute) of the various features and elements (as well as their sets and groups), and the boundaries, spacing and positional relationships therebetween, are provided in the accompanying drawings solely to facilitate understanding of the various embodiments described herein, and are therefore unnecessarily presented or shown to measure and not intended to indicate any preference or requirement for the illustrated embodiments, in order to exclude embodiments in conjunction with them. Detailed Implementation

[0028] Reference will now be made specifically to the representative embodiments shown in the accompanying drawings. It should be understood that the following description is not intended to limit the embodiments to a single preferred embodiment. Rather, it is intended to cover alternative forms, modifications, and equivalents that may be included within the substance and scope of the embodiments defined by the appended claims.

[0029] As used in this article, two elements that are “optically coupled” to each other allow light to pass from one element to the other.

[0030] The accompanying drawings are referenced in the following description of the examples, which illustrate specific examples that can be practiced by way of illustration. It should be understood that other examples can be used and structural changes can be made without departing from the scope of the individual examples.

[0031] This paper discloses an integrated photonic system comprising an on-chip wavelength-locking system operable to lock the wavelength of a light source (or multiple light sources) to a target wavelength or wavelength range. While systems available for wavelength locking exist, they may be limited to operating within narrow wavelength ranges (e.g., 50 nm), may introduce unconsidered phase shifts, may have high optical losses, or may be too large to integrate into electronic devices (e.g., mobile or wearable devices). Wavelength locking can be used in a variety of photonic applications, including but not limited to telecommunications, medical devices, spectrometers, etc. Maintaining wavelength accuracy in photonic applications can be critical for accurate data collection, and wavelength locking prevents undesirable deviations in the emitted light wavelength.

[0032] When a photonic system comprises multiple different light sources (at least some of which emit light at different wavelengths), it may be desirable to lock each light source to a corresponding wavelength. Various ways exist to design wavelength-locking systems, taking into account different factors such as the size of the components, the phase difference in the light introduced by the components of the wavelength-locking system, the wavelength range expected for the wavelength-locking system to operate, temperature sensitivity, and any combination of the foregoing.

[0033] Generally speaking, the wavelength-locking system described herein can receive a single-mode input light (e.g., generated by a light source) and modify that input light from a single-mode light into multiple-mode light. Modifying the light into multiple modes may cause modal interference to produce an output signal whose intensity can vary with wavelength. This wavelength-dependent intensity variation allows the wavelength-locking system to lock onto the wavelengths of a group of light sources (e.g., tunable light sources, multiple light sources, etc.) spanning a wide wavelength range.

[0034] To facilitate modal interferometry, the wavelength-locking system described herein comprises one or more interferometric waveguides that output signals exhibiting this wavelength relationship. These output signals can be used by the wavelength-locking system to monitor the wavelengths of one or more light sources and / or lock that wavelength to a target wavelength. Due to the interference of multiple spatial modes within the same interferometric waveguide, wavelength variations can be converted into intensity variations. References herein... Figure 1 Wavelength locking and its implementation are described in further detail.

[0035] A given output of an interferometric waveguide will have a wavelength-intensity relationship such that the intensity varies with wavelength. As used herein, the “working region” is the wavelength range of a single output signal from an interferometric waveguide, where the single output signal has a non-zero or substantially zero slope in the wavelength-intensity relationship. The working region typically includes the area surrounding the signal where the maximum slope value (positive and negative) of the output signal is found.

[0036] Furthermore, the "dead zone" is the wavelength range of a single output signal where the individual output signal has a zero or near-zero slope in its wavelength-intensity relationship, such as at and around the peaks and valleys of the wavelength relationship. In other words, the working region is any part of the single output signal that is not a dead zone. Therefore, points in the working region have a higher slope than points in the dead region. Thus, a given increment in wavelength variation will result in a larger intensity variation in the working region than in the dead region. When the output signal has a sinusoidal wavelength relationship (i.e., the intensity of the output signal varies sinusoidally with wavelength), the output signal can alternate between the dead zone (at the peaks and valleys) and the working region (between adjacent peaks and valleys) across a certain wavelength range. It should be understood that the exact cutoff value between the dead zone and the working region can depend on the overall system requirements.

[0037] As described in this article, in regions where the slope of the output signal is close to or zero, small changes in wavelength may be difficult to discern (because these small changes result in relatively small changes in the intensity of the output signal), which in turn limits the accuracy of wavelength locking based on the output signal. In contrast, wavelength locking devices can operate more efficiently in the operating range because the output signal has a large slope and the deviation between the target wavelength and the measured wavelength will result in a large intensity difference in the output signal difference (compared to similar deviations occurring in the dead zone).

[0038] To help mitigate this situation, the wavelength locking system described herein can use multiple output signals, each with a different wavelength relationship. For example, the output signals may each have a sinusoidal wavelength relationship, but each wavelength relationship may have a different phase (so that the intensity peaks and troughs are aligned with certain wavelengths). The relative phase difference between the wavelength relationships can be selected to minimize the overlap between the dead zones of the wavelength relationships of different outputs. Although each of the multiple output signals may have a slope of zero or near zero at some point, the dead zone of each output may fall at different points within the wavelength range, so at least one of the multiple output signals may have a non-zero slope (i.e., not in the "dead zone"). For example, in the case of three outputs, the three outputs can be designed with a 120-degree phase difference between the wavelength relationships of each output. With a 120-degree phase difference between each wavelength relationship, at least one output will be located in the middle of its operating region for each wavelength across a certain input wavelength range.

[0039] The wavelength-locking device described herein can generate multiple output signals with a constant phase difference within the wavelength range of interest. These signals can be relatively small and low in complexity, yet still accurately determine the difference between the measured wavelength of the signal and the target wavelength. This determined difference can be used for wavelength locking. (Refer to...) Figure 1 The use of the output signal for wavelength locking is described in further detail. Although the wavelength range is discussed herein as spanning one micrometer, this range can be smaller or larger (such as 100 nanometers, 500 nanometers, or 1.3 micrometers). The dead zones of the output signals can be aligned with each other within this one-micrometer wavelength range. In other words, wavelength locking can be achieved at any wavelength within this range, at least in part, due to the consistent or largely consistent phase difference between the wavelength relationships of the outputs of the interferometer.

[0040] As used throughout this specification, a reference numeral without the character α following it may refer to a corresponding reference, a group of all references, or one or more of some references within a group of references. For example, "645" may refer to any output of output 645 (e.g., output 645a, output 645b, etc.), may refer to all outputs 645, or may refer to some outputs within an output group (e.g., output 645a, output 645b), depending on the context in which it is used.

[0041] This section describes representative applications of the methods and apparatus according to this disclosure. These examples are provided only to add context and aid in understanding. Therefore, it will be apparent to those skilled in the art that the examples can be practiced without some or all of the specific details. Other applications are possible, such that the following examples should not be considered limiting.

[0042] The following text is for reference only. Figures 1 to 8 These and other implementation schemes will be discussed here. However, those skilled in the art will readily understand that the detailed descriptions given herein with respect to the accompanying drawings are for illustrative purposes only and should not be construed as limiting.

[0043] Figure 1 A block diagram of an exemplary wavelength locking system 100 is shown, including a light source 113, a beam splitter 102, an interferometer 105, a power monitor 108, and controllers 109a and 109b. The light source 113 emits input light along an optical path 103 toward the beam splitter 102. The beam splitter 102 splits the input light received on the input optical path 103 and transmits the split light to the interferometer 105 and the power monitor 108. Generally, the optical path can be a waveguide, optical fiber, free-space optics, or other light-transmitting components. Figure 1In one embodiment, optical path 103 is a waveguide, but alternative types of waveguides may be used in a larger system to couple light into the wavelength-locked system 100. In some embodiments, the wavelength-locked system 100 may include an additional beam splitter to provide light to an interferometer or other components. In other embodiments, the wavelength-locked system 100 may include an interferometer and / or may not include an additional beam splitter. Reference Figures 2A to 8 These implementation schemes will be described in further detail.

[0044] Generally, as described herein, a wavelength-locking system may include components for wavelength locking, including one or more of the following: one or more light sources, one or more wavelength-locking devices, one or more beam splitters, one or more interferometers, one or more photodiodes that convert optical output into electrical signals, one or more controllers, one or more power monitors, any combination thereof, etc. One or more wavelength-locking devices may include one or more of the following: one or more beam splitters, one or more interferometers, one or more photodiodes, one or more power monitors, one or more controllers, any combination thereof, etc. Additionally, one or more wavelength devices may receive light, split the light, and output one or more interference-based outputs, each interference-based output having an intensity with a different wavelength relationship (where one or more outputs may be generated by one or more interferometers). Furthermore, one or more interferometers may include a cladding layer or an interferometric waveguide, and may be capable of outputting one or more interference-based outputs. In other words, the interferometric waveguide may be a waveguide within the interferometer that may cause interference.

[0045] Additionally, the wavelength locking system 100 includes a power monitor 108, but the power monitor 108 (and consequently the beam splitter 102) may be optional and is not included in the wavelength locking system 100 in other embodiments. The power monitor 108 may receive light from the beam splitter 102 and transmit a power signal to a controller 109b. The controller 109b may determine whether the light source is outputting a predetermined power and transmit the signal back to the light source 113 to adjust the power as needed. Reference Figure 2A , Figure 2B and Figure 3 Describe the functions of power monitor 108 and controllers 209a and 209b.

[0046] In some implementations, the interference device 105 may be one or more devices (e.g., such as...). Figure 2A , Figure 2B and Figure 3The three interferometers discussed herein can generate output signals (e.g., output light) on optical paths 107a, 107b, and 107c. The output signals can be generated by the pattern of the interfering light propagating in the interferometric waveguides within the interferometers. The interferometric waveguides generate the output signals, each of which has a constant intensity at a fixed wavelength. As described above, this intensity is wavelength-dependent, such that each output signal will have a sinusoidal wavelength relationship as previously discussed, but with a different relative phase. In this way, dead zones may not be aligned with each other for any wavelength within the wavelength range of the light input from light source 113. The output signals can be transmitted to controller 109a, which measures the relative intensity of each output.

[0047] Specifically, the output signals can be used to measure any difference between the wavelength of the light (i.e., generated by the light source and received by the wavelength-locking system) and the target wavelength. Specifically, the target wavelength will have a desired intensity for each of the output signals. The difference between the measured intensity and these desired intensities indicates the difference between the measured wavelength and the target wavelength. Therefore, the measured intensity can be used to determine the wavelength of the measured light or a change in the wavelength of the measured light. Additionally or alternatively, these measured intensities can be used to generate a feedback signal for controlling the operation of the light source to change the wavelength of the generated light and thereby lock it to the target wavelength. In this way, the controller 109a can determine whether a given light source 113 is emitting light at the target wavelength and can pass a signal back to the light source 113 to adjust the emitted wavelength if necessary. In some variations of the wavelength-locking system described herein, the output signals can be used to measure and monitor the wavelength of the light generated by the light source and received by the wavelength-locking system without using this information as feedback to actively control the wavelength of the light source.

[0048] Figure 2A A block diagram of an exemplary wavelength-locking system including multiple interferometric devices is shown. Wavelength-locking system 200 typically includes a light source 213, a beam splitter 202, a wavelength-locking device 217, and a power monitor 208. Individual components of wavelength-locking system 200 may be the light source 213, beam splitters 202, 204a and 204b, interferometric devices 205a, 205b and 205c, power monitor 208, and controller 230. Interferometric devices 205a, 205b, 205c, beam splitters 202, 204a, 204b, and power monitor 208 may be included in wavelength-locking device 217. Figure 2A As shown, beam splitters 202, 204a, and 204b are 1×2 beam splitters; however, similar beam splitting functionality can be achieved using any suitable components or combinations thereof. Beam splitters 202, 204a, and 204b can split the received light between two output optical paths. Interference devices 205a, 205b, and 205c can be used with, for example... Figure 1The interference device 105 works similarly.

[0049] exist Figure 2A In this configuration, beam splitter 202 receives input light from one or more light sources 213 on optical path 203. Beam splitter 202 splits the input light and transmits the split light to beam splitters 204a and 204b on optical paths 209a and 209b, respectively. Beam splitters 204a and 204b both split the light and transmit it along optical paths 211a, 211b, and 211c to interferometers 205a, 205b, and 205c, respectively. That is, beam splitter 204a transmits light to interferometers 205a and 205b via optical paths 211a and 211b, while beam splitter 204b transmits light to interferometer 205c via optical path 211c. Additionally, beam splitter 204b can transmit light to power monitor 208 on optical path 211d.

[0050] Interferometers 205a, 205, and 205c can be configured to generate output signals, each having a sinusoidal wavelength relationship. It may be desirable that these wavelength relationships have different phases, such that the peaks and valleys of one wavelength relationship are not aligned with the peaks and valleys of other wavelength relationships. This results in at least one signal having a working region at each wavelength within the wavelength range. Therefore, the entire wavelength range can be the working region, where measurable information about the difference between the actual wavelength or wavelength range and the target wavelength or target wavelength range is available.

[0051] Light source 213 may be a single light source, or may include multiple individual light sources (whose outputs may be multiplexed or otherwise combined into optical path 203, which may then be received by beam splitter 202). Light source 213 may include any combination of coherent or semi-coherent light sources. Each light source 213 may emit light of a single wavelength (but may generate small offsets on the order of a few nanometers) or may be a tunable light source configured to emit light within a certain wavelength range. Additionally, even though a single light source 213 is shown, any number of light sources may be used in wavelength locking system 200.

[0052] As discussed, beam splitter 202 transmits the split light to beam splitters 204a and 204b, which further split the light and transmit it to interferometers 205a, 205b, and 205c. Interferometer 205a can receive light that can be in the basic mode TE00. For example, interferometer 205a can receive light on optical path 211a and can output light on optical path 215a. As light propagates through different waveguides of interferometer 205a, it can be converted from a single-mode light to two-mode light (i.e., having two different modes) and back to a single-mode light. Similarly, interferometers 205b and 205c can receive light on optical paths 211b and 211c, and can output light on optical paths 215b and 215c, respectively. These outputs on optical paths 215a to 215c can be connected to a controller (such as the previously discussed controller 109a), which can use the strength of these output signals to perform the previously discussed wavelength locking operation.

[0053] Figure 2B It shows Figure 2A A block diagram of the wavelength-locking device 217, comprising a beam splitter and multiple interferometers 205a, 205b, and 205c, is provided, and the interferometers 205a, 205b, and 205c will be described in further detail herein. The interferometers 205a, 205b, and 205c may be multimode waveguides (e.g., two-mode waveguides, three-mode waveguides, or any other number of modes such as n-mode waveguides) in which multiple modes of light are carried. Figure 2B In this paper, each of the interferometric devices 205a, 205b, and 205c includes components such as an input waveguide, an interferometric waveguide, and an output waveguide. Figures 4A to 8 The components of interferometers 205a, 205b, and 205c are described in further detail. (Although references are available...) Figure 2A and Figure 2B The implementation scheme discusses two modes of waveguides, but other interferometric waveguides (e.g., n The three-mode waveguide can be used with this embodiment or any other embodiment. For example, a three-mode waveguide can be used in the wavelength locking system 200; see reference. Figures 6 to 8 This type of waveguide is discussed. Other interferometric waveguides, such as four-mode waveguides and five-mode waveguides, can also be used in wavelength-locked systems.

[0054] In some implementations, light can be transmitted from an input waveguide to a dual-mode (i.e., two-mode) waveguide that supports two modes of light, such as TE00 and TE01. The two modes can be optically beat together, thereby generating an interference-based output signal similar to that from a Mach-Zehnder interferometer (MZI). The two modes can collapse into a single mode at the output. By using a dual-mode waveguide, the device size can be smaller and relatively insensitive to temperature compared to wavelength-locked systems that may include other interferometric devices, such as those employing one or more MZIs.

[0055] The wavelength relationship of the output signal generated by interferometer 205a may have a dead zone that is not aligned with the dead zones of the wavelength relationships of other output signals (e.g., from other interferometers 205b and 205c), and therefore, the interferometers together can reliably generate the output signal using information about the difference between the measured wavelength and the target wavelength, regardless of where the measured wavelength falls within the operating range of the wavelength locking system. That is, interferometer 205 can generate an output signal that, together, can be used to reliably wavelength lock onto any wavelength within the wavelength range of interest. The free spectral range of the output signal may depend at least in part on the length of the interferometric waveguide, the wavelength, and the mode of light propagating in the interferometric waveguide. The interferometric waveguide may be designed such that the output signal has misaligned peaks and valleys, thereby allowing the output signal to be used for wavelength locking. Interferometers 205b and 205c perform the same function and have the same or similar configuration as interferometer 205a.

[0056] In some variations, the wavelength locking system 200 optionally includes a power monitor 208. The power monitor 208 can receive light from the optical path 211d from the beam splitter 204b (but in variations excluding the power monitor 208, the wavelength locking system 200 may exclude the beam splitter 204b), and can compare the measured power of the light propagating along the output optical path with a target power. The power monitor 208, which may be an optical detector, can be configured to measure the power or signal strength of the light received from the optical path 211d, which may vary (or otherwise correspond to) the light input to each of the interferometers 205a, 205b, and 205c, as long as the light propagating along the optical path 211d outputs from the beam splitter 204b, which is the input to each of the interferometer waveguides. In some embodiments, the power monitor 208 can transmit a signal 219 corresponding to the received light to a controller 230, and the controller 230 can provide a feedback electrical signal to a current source on path 221. Figure 2A (Not shown in the image), the current source can be adjusted to tune the output light of the light source 213. Additionally, the controller 230 can provide a signal to the current source, which can adjust the optical power of the light provided by the light source 213.

[0057] Additionally or alternatively, the power measured by the power monitor can be used to assist the wavelength locking operation described herein. Although the interferometric devices described herein (such as interferometers 205a-205c) produce one (or more) output signals with a constant intensity for a given wavelength, this intensity may depend on the intensity of the light introduced into the interferometer. Therefore, the power measured by the power monitor 208 can be used to calculate the power received by the given interferometer. By knowing the power of the input light to the given interferometer, the wavelength locking system may be able to distinguish whether a change in the intensity of the given output signal results in a change in wavelength or a change in the power of the input light.

[0058] Figure 3 A block diagram of an exemplary wavelength-locked system including an interferometer that generates multiple output signals is shown. Wavelength-locked system 300 includes a beam splitter 302, an interferometer 305, a power monitor 308, and a controller 330, wherein the interferometer 305 and power monitor 308 may be part of wavelength-locked system 317. Although wavelength-locked system 300 includes beam splitter 302 and power monitor 308, in some embodiments these are optional components. Components of wavelength-locked system 300 can perform similar functions and, except for interferometer 305, can be configured similarly to components of wavelength-locked system 200. Interferometer 305 can receive a single optical input from beam splitter 302, and modes can interfere with each other to generate multiple output signals that can be output on a first optical path 315a, a second optical path 315b, and a third optical path 315c. In some embodiments, interferometer 305 may include three mode waveguides, which will be referenced... Figure 6 and Figure 8 The three waveguide modes are described in further detail. (Although reference...) Figure 3 The implementation scheme discusses three modes of waveguides, but other interferometric waveguides (e.g., n A mode waveguide (such as a waveguide) can be used with this embodiment or any other embodiment. Wavelength locking device 317 may also include interferometer 305. Wavelength locking device 317 can be used with... Figure 1 The interference device 105 functions similarly. Additionally, it should be understood that even though outputs 315a, 315b, and 315c terminate within the wavelength-locked device 317, outputs 315a, 315b, and 315c can also be used as outputs from the wavelength-locked device 317.

[0059] exist Figure 3In this system, light source 313 emits light, which propagates along optical path 303 and is received by beam splitter 302. Beam splitter 302 can split the light and output the split portion of the light along optical paths 310a and 310b. One optical path 310a transmits the first split portion of the light from beam splitter 302 to interferometer 305, while another optical path 310b transmits the second split portion of the light from beam splitter 302 to power monitor 308. The split portion of the light received by interferometer 305 can be a single-mode light (e.g., basic mode TE00). Interferometer 305 can be used to convert the single-mode light into two superimposed modes (e.g., TE00, TE01) and in some cases, three superimposed modes such as TE00, TE01, and TE02, which can be combined light modes. These superimposed modes can be extended within a portion of interferometer 305 and interfere with each other, such that the different outputs of interferometer 305 can have intensities with wavelength relationships that vary with phase.

[0060] In other words, the first optical path 315a can output light with a certain intensity that has a sinusoidal wavelength relationship with the first phase, the second optical path 315b can output light with a sinusoidal wavelength relationship with the second phase, and the third optical path 315c can output light with a sinusoidal wavelength relationship with the third phase, wherein all phases are offset from each other. Similar to Figure 2, Figure 3 The power monitor 308 transmits light along the optical path 319 to the controller 330. The power monitor 308 and controller 330 perform the same functions as the power monitor 208 and controller 230 described with reference to FIG2. For example, the controller 330 can adjust the output of the light source 313 by transmitting an electrical signal along path 321 to a current source.

[0061] Interferometer 305 typically outputs three signals exhibiting different interferences between different modes of light. The three modes of light can propagate at different group velocities within a portion of interferometer 305 (e.g., an interferometric waveguide), resulting in different interferences between modes TE00 and TE01, TE00 and TE02, and TE01 and TE02. Similar to interferometer 205 of Figure 2, interferometer 305 effectively generates output signals that can be used for wavelength-locked light sources because the multiple output signals generated by interferometer 305 can have wavelength relationships with dead zones that are misaligned with each other. Interferometer 305a can reliably generate output light using information about the difference between the measured wavelength and the target wavelength. That is, interferometer 305 can reliably wavelength-lock to any wavelength within the wavelength range of interest. In some embodiments, the wavelength range of interest may depend at least in part on the waveguide material and the design of the interferometer. References herein Figure 6 The implementation plan further discusses in detail the configuration and function of the interference device 305.

[0062] Figure 4A This shows what can be related to the above about Figure 2A and Figure 2B An exemplary interferometric device 400 used in the described system. For example, any or all of the interferometric devices 205a, 205b, and 205c of a wavelength-locked system can be configured as interferometric device 400. As shown, interferometric device 400 may include a first waveguide as an input waveguide 435, a second waveguide as an interference waveguide 440, and a third waveguide as an output waveguide 445. Figure 4A As shown, the interference waveguide 440 can be connected to the input waveguide 435 and the output waveguide 445. Although Figure 4A The diagram depicts an output waveguide 445, but the interferometer 400 may include multiple output waveguides 445. A cladding layer 420 may surround the input waveguide 435, the interferometer waveguide 440, and the output waveguide 445 to reduce optical loss and confine light to the propagation region, thereby defining the waveguides. The input waveguide 435 may be optically coupled to the interferometer waveguide 440 at a first end 441, and the output waveguide 445 may be optically coupled to the interferometer waveguide 440 at a second end 442. The positioning of the input waveguide 435 and the output waveguide 445 relative to the interferometer waveguide 440 and to each other may affect the power of each mode of light carried by the interferometer waveguide 440 and how much light is coupled back to a single mode of light in the output waveguide 445. The interferometer 400 may be designed such that each mode of light in the multiple modes has the same power as the others, but in other cases, the interferometer 400 is configured such that different modes of light in the multiple modes have different powers.

[0063] Input waveguide 435 receives light with a single mode and transmits it to interferometric waveguide 440. At the interface between input waveguide 435 and interferometric waveguide 440, a portion of the single-mode light can be converted into higher-order modes. The mode conversion depends at least in part on the configuration (e.g., relative size, location, and orientation) of input waveguide 435 and interferometric waveguide 440. For example, input waveguide 435 can be narrow and confine the light to a single mode, while interferometric waveguide 440 can be wider, thereby allowing higher-order modes of light to propagate in addition to the single-mode light.

[0064] Interferometric waveguide 440 can then transmit both single-mode and higher-order-mode light to output waveguide 445. At the interface between interferometric waveguide 440 and output waveguide 445, the higher-order-mode light can be converted back to single-mode light. Therefore, output waveguide 445 can receive single-mode and higher-order-mode light and output a second single-mode light. Similar to input waveguide 435, output waveguide 445 can be narrow and support light with a single mode. The output can be used to lock the measured wavelength of the light to a target wavelength, as described herein.

[0065] Specifically, different modes of light will interfere along the length of the interference waveguide 440. The amount of interference of light of a given wavelength varies spatially within the interference waveguide 440, and thus, the intensity of the light received by the output waveguide 445 has a constant intensity at a given wavelength. As previously mentioned, this intensity varies sinusoidally with wavelength. The relative size, location, and orientation of the input waveguide 435, the interference waveguide 440, and the output waveguide 445 will set the phase of this sinusoidal wavelength relationship. Therefore, when a wavelength-locked system (such as the wavelength-locked system 200 discussed earlier) uses multiple interferometers, multiple types of interference waveguides 440 can be designed to have wavelength relationships with different phases.

[0066] Each of the input waveguide 435, the interferometric waveguide 440, and the output waveguide 445 may have a first cladding layer, a propagation region, and a second cladding layer, which are respectively the structure of the waveguide: an upper cladding layer, a propagation region through which light propagates, and a lower cladding layer. Single-mode light and higher-order modes of light propagate in the propagation region of the waveguide, which will affect the propagation region. Figure 4B A further detailed description follows. Input waveguide 435 supports single-mode light and is optically coupled to a first end 441 of interferometric waveguide 440, allowing light to pass from input waveguide 435 to interferometric waveguide 440 with minimal optical loss. Interferometric waveguide 440 supports both single-mode and higher-order modes of light and receives the first single-mode light from input waveguide 435. Interferometric waveguide 440 transmits both single-mode and higher-order modes of light to output waveguide 445 with minimal optical loss. Output waveguide 445 supports a second single-mode of light and is optically coupled to a second end 442 of interferometric waveguide 440 to receive both single-mode and higher-order modes of light from interferometric waveguide 440. The output light from output waveguide 445 can be used to lock the measured wavelength of light to a target wavelength.

[0067] In some implementations, the widths of the input waveguide 435, the interference waveguide 440, and the output waveguide 445 at least partially determine the mode of light that can propagate through each of them. Figure 4A As shown, the input waveguide 435 may have a first width, the interfering waveguide 440 may have a second width, and the output waveguide 445 may have a third width, wherein each of the first, second, and third widths is constant. In other variations, one or more of the input waveguide 435, the interfering waveguide 440, and the output waveguide 445 may be tapered. Generally, the first width of the input waveguide 435 may differ from the second width of the interfering waveguide 440. Figure 4A As shown, the first width is narrower than the second width, but in some embodiments, the first width may be the same as the second width. The third width (e.g., output waveguide 445) may also be different from the second width (e.g., interference waveguide 440), and also as... Figure 4A As shown, the third width (e.g., output waveguide 445) may be narrower than the second width (e.g., interference waveguide 440). Additionally, in some embodiments, the first and third widths may be the same, but in other embodiments, they may be different from each other. The widths of the input waveguide 435, interference waveguide 440, and output waveguide 445 can be selected to reduce the optical loss of the interferometric device 400. For example, optical loss can be reduced by decreasing the widths of the input waveguide 435 and output waveguide 445 compared to the interference waveguide 440, and optical loss can also be reduced by offsetting the central axes of the input waveguide 435 and output waveguide 445 relative to the central axis of the interference waveguide 440. That is, the central axes of the input waveguide 435 and output waveguide 445 are offset from the central axis of the interference waveguide 440.

[0068] The central axis of the input waveguide 435 may be located offset from the central axis of the interferometer waveguide 440, and / or the central axis of the output waveguide 445 may be located offset from the central axis of the interferometer waveguide 440. The input waveguide 435 and output waveguide 445 may be positioned relative to the interferometer waveguide 440 to increase sensitivity to the selected mode of light. Figure 4A In this process, by shifting the central axes of both the input waveguide 435 and the output waveguide 445 away from the central axis of the interference waveguide 440, the interference waveguide can support the TE01 mode, which is the first higher mode of light. By controlling the displacement of the central axes of the input waveguide 435 and the output waveguide 445, optical power can be shunted between superimposed modes within the interference waveguide 440. Although the input waveguide 435 and the output waveguide 445 are... Figure 4A The input waveguide 435 is shown offset from the interferometric waveguide 440 in one direction, but this is only one example of the configuration of the interferometric device 400. Other configurations of the input waveguide 435, interferometric waveguide 440, and output waveguide 445 are possible and will be referenced. Figures 5A to 5C Describe several configurations.

[0069] Input waveguide 435, interferometer waveguide 440, and output waveguide 445 can be strip waveguides, but in some cases, input waveguide 435 and / or output waveguide 445 can be rib waveguides and can be used with strip-to-rib or rib-to-rib waveguide conversions. Although strip waveguides or rib waveguides can be used, strip waveguides have a larger refractive index change between optical modes, while rib waveguides have a smaller refractive index change between optical modes, and therefore, in some applications, only strip waveguides can be used. Higher-order modes may decay more rapidly in rib waveguides compared to strip waveguides. Additionally, when using rib waveguides, due to the reflection characteristics associated with higher refractive indices, the smaller refractive index change between layers in rib waveguides may not generate higher-order modes as rapidly as the larger refractive index change between layers in strip waveguides; therefore, input waveguide 435, interferometer waveguide 440, and output waveguide 445 may all be rib waveguides.

[0070] Figure 4B It shows along Figure 4A The image shows an example cross-section of a waveguide taken along line A-A'. Waveguide 401 illustrates a general structure through which light can propagate and is not drawn to scale. Waveguide 401 includes a silicon substrate 421, a first capping layer 420, a propagation layer 425, and a second capping layer 430. Figure 4B As shown, a first capping layer 420 is disposed on a silicon substrate 421, a propagation layer 425 (which may be a propagation region) is disposed on the first capping layer 420, and a second capping layer 430 is disposed on the propagation layer 425. Although Figure 4B A first capping layer 420 and a second capping layer 430 are depicted, but capping layers surrounding the sides of the waveguide, as well as capping layers above and below the capping layers, may be present. In this embodiment, light emitted by the light source propagates into or out of the plane shown in the figure, and specifically through the propagation region of the waveguide (which is the propagation layer 425). In some embodiments, the first capping layer 420 and the second capping layer 430 may be formed of oxides such as silicon dioxide or other suitable dielectric materials.

[0071] Figure 4C It shows along Figure 4A The cross-section of an example waveguide is shown by line A-A', and a cross-section of waveguide 401 is shown, through which light 450 with a single mode propagates. As previously shown in Figure 4AAs discussed above, the input waveguide 435, interferometric waveguide 440, and output waveguide 445 can all support a single mode of light 450 (such as a fundamental mode of light (e.g., TE00)). Light with the fundamental mode can propagate through the input waveguide 435 and into the interferometric waveguide 440. Although the single-mode light 450 is described above as propagating through the interferometric waveguide 440, the interferometric waveguide 440 can support light beyond the fundamental mode. Additionally, the supported modes of light in the interferometric waveguide 440 can collapse into a single-mode light 450 in the output waveguide 445, which can output... Figure 4C The basic pattern of light 450 is shown.

[0072] Figure 4D It shows along Figure 4A An example cross-section of the waveguide cut by line B-B' is shown. Figure 4A The cross-section of higher-order modes of light in the interference waveguide of the interferometric device. Waveguide cross-section 403 includes... Figure 4C The waveguide cross-section is similar to that of a 401 element, the difference being... Figure 4D The aforementioned higher-order mode of light 455 is shown. The interferometric waveguide 440 can receive single-mode light 450 from the input waveguide 435 and convert a portion of the single-mode light 450 into higher-order mode light 455. For example, the interferometric waveguide 440 converts a portion of the single-mode light 450 into TE01 mode light 455. Although Figure 4D Only the higher-order modes of light 455 are shown, but the interferometric waveguide 440 also allows Figure 4C Single-mode light 450 and Figure 4D The higher-order mode of light 455 along the length of the interference waveguide L Propagation occurs at different group velocities and phase velocities (thus causing interference between modes as previously discussed). Furthermore, Figure 4A The interferometric waveguide 440 supports the propagation of combined light with two modes (e.g., TE00 and TE01) through the interferometric waveguide 440.

[0073] Figure 5A This shows what can be related to the above about Figure 2A and Figure 2B Another exemplary interferometer 500 used in conjunction with the system described above (e.g., some or all of the interferometers 205a to 205c that replace the wavelength locking system 200). Interferometer 500 includes... Figure 4A The device shows similar components and another configuration of components supporting different higher-order modes of light. The interferometer 500 includes an input waveguide 535, an interference waveguide 540, and an output waveguide 545. The input waveguide 535 and the output waveguide 545 may be physically similar to... Figure 4AThe input waveguide 435 and output waveguide 445 are similar in function, with the similarity being that the input waveguide 535 and output waveguide 545 support a single mode of light and each includes a first cladding layer, a second cladding layer, and a propagation layer. Figure 4A Similarly, the cladding layer 520 can surround the input waveguide 535, the interference waveguide 540, and the output waveguide 545 to reduce optical loss.

[0074] exist Figure 5A In this design, input waveguide 535 and output waveguide 545 are symmetrically positioned such that their central axes are aligned with the central axis of interference waveguide 540. This symmetrical positioning of the input and output waveguides 535 enables the generation of light in the first or even higher modes TE02 within the interference waveguide 540, while ensuring that the TE01 mode is not excited within it. Therefore, interference waveguide 540 is a dual-mode waveguide supporting both single-mode light and higher modes (such as the first or even higher modes TE02). The single-mode and higher-mode light superimpose on each other and propagate through interference waveguide 540.

[0075] Additionally, the interference waveguide 540 is comparable Figure 4A The equivalent waveguide width shown allows it to support higher-order modes, such as TE02. Generally, interferometric waveguides of varying widths can be used, as long as they support the appropriate modes used in the interferometric device. Furthermore, the sizes (e.g., width, length, and / or other dimensions) of the input, interferometric, and output waveguides can affect many different aspects of the waveguide device, such as optical power, the light of the supported modes, coupling efficiency between waveguides, interference between modes, and any combination thereof.

[0076] and Figure 4A Similarly, input waveguide 535 receives a single mode of light (e.g., TE00), which propagates through the propagation layer and is delivered to interference waveguide 540. Interference waveguide 540 generates a superposition of two modes, TE00 and TE02, propagating through it. As previously described, interference waveguide 540 can support modes with different refractive indices, and higher modal dispersion allows for a more compact device than MZI. The refractive index (e.g., modal refractive index) depends on various factors, including the wavelength and mode of the light. Interference waveguide 540 delivers both the single mode and even higher-order modes to output waveguide 545, which causes the modes to collapse back into the single mode of light. Output waveguide 545 outputs an output signal with a sinusoidal wavelength relationship similar to that from a single MZI. The phase of the sinusoidal wavelength relationship can be set by the relative size, position, and orientation of input waveguide 535, interference waveguide 540, and output waveguide 545, as previously described. The output signal allows for the measurement of information about the difference between the actual wavelength or wavelength range and the target wavelength or target wavelength range, as previously discussed.

[0077] Figure 5B It shows along Figure 5A An example cross-section of a waveguide cut by line C-C' is shown and illustrated along... Figure 4A An example cross-section of the waveguide taken by line B-B', and Figure 5C It shows along Figure 5A An example cross-section of a waveguide cut by line D-D' and similar to Figure 5B The cross-section differs in that it includes light of higher-order modes rather than light of the fundamental modes. Figure 5B Waveguide 501 and Figure 5C The waveguide 502 is similar to Figure 4C and Figure 4D The waveguides 501 and 502 both include a first cladding layer 520, a propagation layer 525, and a second cladding layer 530. Figure 5B Waveguide 501 shows a single mode of light TE00 propagating along it, while Figure 5C Waveguide 502 includes light 556 in which higher-order mode TE02 propagates.

[0078] Figure 6 Another exemplary interferometric device is shown, illustrating the use of light with additional modes that generate additional interference signals, particularly light with additional modes that can produce multiple output signals. Interferometric device 600 may include an input waveguide 635, an interference waveguide 640, a mode extension segment 670, and a first output waveguide 645a, a second output waveguide 645b, and a third output waveguide 645c. The input waveguide 635 and output waveguides 645a to 645c perform and reference... Figure 4A and Figure 5A The described input and output waveguides function similarly, in that they support a single mode of light. As described herein, the mode extension section 670 is used to extend the interference modes. Although Figure 6 The diagram shows three output waveguides 645a to 645c; however, it should be understood that the interferometer 600 can be configured to produce only two outputs and can be paired with additional interferometers (such as those mentioned above). Figure 4A and Figure 5A One of the interferometers discussed (an interferometer device) jointly generates three output signals.

[0079] and Figure 4A and Figure 5A similar, Figure 6The input waveguide 635 receives a single-mode light (e.g., TE00) as input light and transmits it to the interference waveguide 640. The interference waveguide 640 receives the single-mode input light and generates a superposition of three modes of light (e.g., TE00, TE01, and TE02 modes). The three modes of light can propagate along the length L of the interference waveguide 640 at different group velocities and (in the case where the interferometer 600 includes a mode extension section 670) are transmitted to the mode extension section 670. The mode extension section 670 allows the three modes of light to be extended via adiabatic extension or free diffraction (similar to diffraction in a planar waveguide). The mode extension section 670 effectively extends the width of the interference waveguide 640, which provides additional space to place the output waveguides 645a to 645c. In some embodiments, the mode extension section 670 can be optional, and the three modes can be transmitted directly from the interference waveguide 640 to the output waveguides 645a, 645b, and 645c.

[0080] Depending on the relative placement and dimensions of the input waveguide 635, the interference waveguide 640, and the output waveguides 645a to 645c, each of the output waveguides 645a to 645c will generate an output signal based on interference between some or all of the modes in the mode. The output signal of each of the output waveguides 645a to 645c will have a wavelength relationship such that the intensity of the output signal of a given output waveguide (e.g., the first output waveguide 645a) varies with the wavelength of the input light. This wavelength relationship may or may not be sinusoidal, depending on which mode is present at the beginning of a given output waveguide. For example, in some cases, the wavelength relationship may be a superposition of multiple sinusoidal waves with different frequencies. It is desirable to position the first output waveguide 645a, the second output waveguide 645b, and the third output waveguide 645c with different relative contributions of different modes, such that each of these output waveguides has a different wavelength relationship. This can thus facilitate wavelength locking using the interferometer 600 by reducing the alignment of the dead zone between the output signals of the first output waveguide 645a, the second output waveguide 645b, and the third output waveguide 645c.

[0081] In some cases, it may be desirable to center one or more of the output waveguides 645a to 645c around the zero point of one of the modes of light. When the output waveguide is centered around the zero point of a given mode, the output signal is based solely on the interference between the remaining two modes. For example, an output waveguide centered around the zero point of the TE02 mode will generate an output signal based on the interference between the TE00 and TE01 modes. An output waveguide centered around the zero point of the TE01 mode will generate an output signal based on the interference between the TE00 and TE02 modes, and an output waveguide centered around the zero point of the TE00 mode will generate an output signal based on the interference between the TE01 and TE02 modes. The output signal of an output waveguide centered around the zero point of a mode will have an intensity with a sinusoidal wavelength relationship.

[0082] In some variations, the output waveguides 645a to 645c are centered at different zero points, such that each output waveguide generates an output signal based on the interference of a different pair of modes. For example, one output waveguide will generate an output signal based on the interference between the TE00 mode and the TE01 mode, a second output waveguide will generate an output signal based on the interference between the TE01 mode and the TE02 mode, and a third output waveguide will generate an output signal based on the interference between the TE00 mode and the TE02 mode.

[0083] exist Figure 6 In the variant shown, the second waveguide 645b is centered on the zero point of the first mode (e.g., the TE00 mode). In some cases, the second waveguide 645b is also located at the center of the mode extension segment 670. It is desirable that the first output waveguide 645a, the second output waveguide 645b, and the third output waveguide 645c be positioned asymmetrically relative to the mode extension segment 670. Therefore, in the case where the second output waveguide 645b is centered on the central axis of the mode extension segment 670, the first output waveguide 645a and the third output waveguide 645c can be positioned asymmetrically relative to the mode extension segment 670.

[0084] In these cases, the first output waveguide 645a is positioned at a first distance from the second output waveguide 645b, and the third output waveguide 645c is positioned at a second distance from the second output waveguide 645b (different from the first distance). This asymmetric positioning allows the first output waveguide 645a and the third output waveguide 645c to experience different relative contributions (i.e., different "views") of the three modes. In some of these variations, the first output waveguide 645a or the third output waveguide 645c can be centered at the zero point of the second mode (e.g., the TE02 mode). In other cases (as described below)... Figure 7 Under the aforementioned conditions, it is desirable to have two waveguides positioned symmetrically relative to the mode extension portion 670.

[0085] The input waveguide 635 can have any suitable orientation relative to the interfering waveguide 640, which facilitates the generation of two additional modes, allowing the interfering waveguide 640 to carry light with three modes, as discussed above. Figure 6 In the variant shown, the position of the central axis of the input waveguide 635 can be offset from the central axis of the interferometric waveguide. The asymmetric displacement at startup can generate additional modes, and depending on its placement, allows for similar power generation for all three modes in the interferometric waveguide 640. In some embodiments, the input waveguide 635 can be tilted to achieve similar or identical results.

[0086] In some cases, the interferometer can be configured to generate multiple outputs that can be used to measure the power level of the light received by the interferometer. In these cases, the interferometer can be used as a power monitor, as previously described. These output signals can also be used to perform wavelength locking as described above, which allows a single component to provide all the signals required to perform power monitoring and wavelength locking operations.

[0087] Figure 7 Another exemplary interferometer 700 is shown, which provides a set of output signals that can be used to measure the power level of light and lock the wavelength of light. Interferometer 700 includes an input waveguide 735 and a length... L The interferometric waveguide 740, the optional mode extension section 770, and four output waveguides (including the first output waveguide 745a, the second output waveguide 745b, the third output waveguide 745c, and the fourth output waveguide 745d). Interferometer 700 and reference. Figure 6 The described interferometer device 600 works similarly, except for the number and placement of the output waveguides.

[0088] Specifically, two output waveguides (e.g., the second output waveguide 745b and the fourth output waveguide 745d) are centered at the zero point of the first mode (e.g., the TE02 mode). The output signals generated by the second output waveguide 745b and the fourth output waveguide 745d each have an intensity with a sinusoidal wavelength relationship. For example, when the second output waveguide 745b and the fourth output waveguide 745d are each positioned at the corresponding zero point of TE02, they will each generate an output signal with a sinusoidal wavelength relationship that varies based on the interference between the TE00 and TE01 modes. The second output waveguide 745b and the fourth output waveguide 745d can be positioned such that these wavelength relationships are 180 degrees out of phase. Therefore, the sum of the output signals will be independent of the wavelength of the input light, but will be proportional to the power of the input light received by the input waveguide 735. Therefore, the output signals of the second waveguide 745b and the fourth waveguide 745d can be used to calculate the power of the input light received by the interferometer 700.

[0089] Additionally, the first output waveguide 745a and the third output waveguide 745c can be positioned to generate output signals with different wavelength relationships. For example, one of the output waveguides, namely the third output waveguide 745c, can be centered at the zero point of the second mode. Figure 7 In the illustrated variant, the third output waveguide 745c is centered on the zero point of the TE00 mode and generates an output signal with a sinusoidal wavelength relationship based on the interference between the TE01 and TE02 modes. As shown, the third output waveguide 745c is centered on the mode extension section 770 (e.g., the central axis of the third output waveguide 745c is located on the central axis of the mode extension section 770). In these variants, the second output waveguide 745b and the fourth output waveguide 745d can be symmetrically positioned relative to the mode extension section 770, such that the second output waveguide 745b is separated from the third output waveguide 745c by a first distance, and the fourth output waveguide 74db is separated from the third output waveguide 745c by the same first distance.

[0090] Additionally, one waveguide in the waveguide can be positioned such that its output signal is based on interference between all three modes (e.g., interference between TE00 and TE01 modes, interference between TE01 and TE02 modes, and interference between TE00 and TE02 modes). For example, in Figure 7 In the variants shown, the first output waveguide 745a is positioned such that its output signal is based on interference between all three modes. In some of these variants, the first output waveguide 745a is centered on the peak of the first mode. For example, in some variants where the second output waveguide 745b and the fourth output waveguide 745d are centered on the corresponding zero point of the TE02 mode, the first output waveguide 745a may be centered on the peak of TE02.

[0091] Therefore, the output signals generated by the second output waveguide 745b and the fourth output waveguide 745d can be used to measure the power of the input light, and one or both of these output signals can be used in conjunction with the output signals of the first output waveguide 745a and the third output waveguide 745c to perform wavelength locking operations as discussed herein.

[0092] Figure 8 An example of a hybrid interferometer device is shown. Figure 8 An alternative method for achieving dead zones of misaligned output signals is illustrated by using an interferometer to interfere with optical modes, separating the modes into TE00 and TE01 modes, and then generating output signals, each signal having a wavelength relationship with a unique phase shift. The hybrid interferometer 800 includes an input waveguide 835, with a length... LThe interference waveguide 840, mode separator 875, beam splitter 860, and output waveguides 845a, 845b, and 845c.

[0093] Similar to some of the interferometric devices previously described, input waveguide 835 can receive input light with a single mode. When input waveguide 835 transforms into interferometric waveguide 840 (e.g., at the interface between the two waveguides), some of the input light is converted to higher-order modes, causing interferometric waveguide 840 to carry both modes of light. For example, if input waveguide 835 receives input light with a TE00 mode, the transformation to interferometric waveguide 840 can convert some of the input light to a TE01 mode, causing interferometric waveguide 840 to carry both TE00 and TE01 modes of light. In other cases, the input light generated in interferometric waveguide 840 can be TE00 and TE02 light. The generation of higher-order modes of light can be based on the relative size, position, and orientation between input waveguide 835 and interferometric waveguide 840, as previously discussed.

[0094] Interferometric waveguide 840 is optically coupled to mode separator 875, which separates the two modes carried by interferometric waveguide 840 into separate waveguides. For example, in a variation where interferometric waveguide 840 carries light in TE00 and TE01 modes, a first waveguide may receive the TE00 mode, while a second waveguide may receive the TE01 mode. Mode separator 875 has a first segment 875a and a second segment 875b. The first segment 875a may be a first waveguide directly connected to interferometric waveguide 840 (i.e., the first segment 875a and interferometric waveguide 840 represent different parts of a common waveguide), while the second segment 875b is a second waveguide positioned sufficiently close to the first segment 875a to allow optical coupling between the two.

[0095] Specifically, each of the first segment 875a and the second segment 875b includes a corresponding cone that is thermally adiabatic and optically coupled to each other. The cone of the first segment 875a is directly connected to the interference waveguide 840. The first segment 875a initially receives light of two modes from the interference waveguide 840 (i.e., at the cone of the first segment 875a). The cones of the first segment 875a and the second segment 875b are configured such that, within the cone of the first segment 875a, light of one mode can be coupled into the second segment 875b of the mode separator 875 (i.e., into the cone of the second segment 875b). For example, in some cases, a higher-order mode (e.g., TE01 or TE02) can be coupled into the second segment 875b, while the original mode (e.g., TE00) remains in the first segment 875a and continues to propagate through the first segment 875a of the mode separator 875. In these cases, the second segment 875b can be configured to constrain higher-order mode light and convert the higher-order mode back to the original mode of the input light (e.g., converting TE01 or TE02 light to TE00 light). In this way, the first segment 875a and the second segment 875b can each output light having the same mode as the input light.

[0096] First segment 875a and second segment 875b can serve as input waveguides for beam splitter 860. Therefore, first segment 875a transmits a first amount of light to the first input of beam splitter 860, while second segment 875b transmits a second amount of light to the second input of beam splitter 860. The relative amounts of light in first segment 875a and second segment 875b (i.e., the first amount of light and the second amount of light) depend on the interference between the two modes at the transition between interference waveguide 840 and mode separator 875. Because this interference is wavelength dependent, the relative amounts of light in first segment 875a and second segment 875b (and thus the relative amounts of light received by beam splitter 860) will vary with the wavelength of the input light.

[0097] Beam splitter 860 is a two-to-three beam splitter with two input waveguides and three output waveguides. First segment 875a and second segment 875b serve as the two input waveguides. In some cases, it may be desirable to taper the widths of the first segment 875a and second segment 875b to the narrow width of the input of beam splitter 860. This can be used to improve the wavelength independence of beam splitter 860 by reducing insertion loss as a function of wavelength when light enters beam splitter 860. First output waveguide 845a, second output waveguide 845b, and third output waveguide 845c serve as the output waveguides of beam splitter 860.

[0098] A 2x3 beam splitter splits light received at each of its input waveguides among its three output waveguides. When light is received simultaneously at two input waveguides of the 2x3 beam splitter, the three output waveguides will each output different combinations of the input light. Because the relative amount of light received by each input waveguide (e.g., the first and second amounts described previously) changes, the relative intensity of the light output at each of the three output waveguides will also change. Since the relative amount of light received by each input waveguide varies with wavelength, the intensity of the output signals provided by the first output waveguide 845a, the second output waveguide 845b, and the third output waveguide 845c will also vary with wavelength. The positioning of the first output waveguide 845a, the second output waveguide 845b, and the third output waveguide 845c can be selected such that the output waveguides 845a to 845c have wavelength relationships with different phases relative to each other (e.g., 120-degree phase between each wavelength relationship). These output signals can be used for wavelength locking, as described in more detail above.

[0099] The function of beam splitter 860 can be performed by any suitable two-to-three beam splitter. Examples include two-to-three multi-mode interferometers (e.g., where light at each input waveguide is converted from a single mode to multiple modes within the interferometric waveguide), two-to-three-mode couplers (e.g., where the input and output waveguides are each connected to a free propagation region), etc. For example, in a two-to-three-mode coupler, beam splitter 860 includes a free propagation region connecting the input waveguide to the output waveguide. Light received by the first segment 875a and the second segment 875b of mode separator 875 is input into the free propagation region. In the free propagation region, light can diffract in the plane of the waveguide and can spread in a Gaussian profile, such that light from both inputs can be received by all three output waveguides 845a, 845b, 845c.

[0100] The relative positioning between the input waveguide and output waveguides 845a to 845c of the 2x3 triplet coupler provides the desired phase separation for the light received by each of the output waveguides 845a to 845c. For example, for a given wavelength, the first output waveguide 845a may receive light from the first input waveguide having a first phase separation (e.g., -60 degrees) from the light received by the first output waveguide from the second input waveguide. Similarly, the second output waveguide 845b may receive light from the first input waveguide having a second phase separation (e.g., 0 degrees) from the light received by the second output waveguide from the second input waveguide. The third output waveguide 845c may receive light from the first input waveguide having a third phase separation (e.g., 60 degrees) from the light received by the third output waveguide from the second input waveguide. In some implementations, for a given wavelength, the phase separation for the first output waveguide 845a, the second output waveguide 845b, and the third output waveguide 845c can be -60 degrees, zero degrees, and 60 degrees phase separation, but it should be understood that these phase separations can vary with wavelength.

[0101] In some variations, such as Figure 8 As shown, the central axes of the first output waveguide 845a and the third output waveguide 845 can be offset symmetrically relative to the central axis of the free propagation region, and the central axis of the second output waveguide 845b can be centered relative to the central axis of the free propagation region.

[0102] Furthermore, although process or method steps may be described in a sequential order, such processes and methods can be configured to operate in any suitable order. In other words, any sequence or order of steps described in this disclosure does not itself indicate that the steps must be performed in that order. Moreover, although described or implied to occur non-simultaneously (e.g., because a step is described after other steps), some steps may be performed concurrently. Furthermore, the illustration of the process in the accompanying drawings does not imply that the illustrated process excludes other variations and modifications thereof, does not imply that any step of the illustrated process or its steps must be one or more examples of the examples, and does not imply that the illustrated process is preferred.

[0103] This section describes representative applications of the methods and apparatus according to this disclosure. These examples are provided only to add context and aid in understanding. Therefore, it will be apparent to those skilled in the art that the examples can be practiced without some or all of the specific details. Other applications are possible, such that the following examples should not be considered limiting.

[0104] While the disclosed examples have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art. It should be understood that such changes and modifications are considered to be included within the scope of the disclosed examples as defined by the appended claims.

Claims

1. A wavelength locking device, the wavelength locking device comprising: An input waveguide configured to support a first single mode of light; An interferometric waveguide having a first end optically coupled to the input waveguide and configured as follows: Receive the first single-mode light from the input waveguide; as well as Converting the first single-mode light into at least three different modes of light; and A first output waveguide, a second output waveguide, and a third output waveguide, each output waveguide being optically coupled to a second end of the interference waveguide, and configured as follows: The at least three different modes of light are received from the interference waveguide; Supports a second single mode of light; and The second single-mode light is output to lock the measured wavelength of the light to the target wavelength.

2. The wavelength locking device according to claim 1, wherein: Light propagating from the input waveguide to the interference waveguide is converted into TE00 mode light, TE01 mode light, and TE02 mode light; and The light in TE00 mode, the light in TE01 mode, and the light in TE02 mode are superimposed within the interference waveguide.

3. The wavelength locking device according to claim 1, wherein: The input waveguide is positioned such that the central axis of the first end of the interference waveguide is offset from the central axis of the input waveguide.

4. The wavelength locking device according to claim 1, wherein the fourth output waveguide is optically coupled to the interference waveguide.

5. The wavelength locking device according to claim 4, wherein the second output waveguide and the fourth output waveguide are respectively positioned at the corresponding zero point of the first mode of light of the at least three different modes of light.

6. The wavelength locking device according to claim 1, wherein: Two of the first, second, and third output waveguides are positioned asymmetrically relative to the center of the second end of the interference waveguide.

7. The wavelength locking device according to claim 6, wherein: The at least three different modes of light are TE00 mode light, TE01 mode light and TE02 mode light; The first output waveguide is positioned at the zero point of the light in the TE02 mode; and The first output waveguide and the third output waveguide are positioned asymmetrically relative to each other.

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