Coupling apparatus and method, wavelength locking system and method, and phase unwrap system and method

Abstract

The present disclosure relates to coupling devices and methods, wavelength locking systems and methods, and phase-unwinding systems and methods. A configuration of an optical device for splitting and wavelength locking is disclosed. The optical device can be a 2x3 coupler in which a first waveguide is coupled to a second waveguide, and a third waveguide is coupled to the second waveguide. The first waveguide and the third waveguide can receive input light and optically couple light to the second waveguide. Output signals of the first waveguide, the second waveguide, and the third waveguide can have constant phase difference values from each other over a wideband wavelength range, which can allow for phase unwinding. By phase unwinding the output signals over an FSR and performing further phase unwinding over the wideband wavelength range, a continuous signal can be produced and used to sequentially lock each optical wavelength emitted by an optical source over the wideband wavelength range.

Description

[0001] Cross-reference to related applications

[0002] This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 236,567, filed August 24, 2021, pursuant to 35 U.S.SC §119(e), the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates generally to optical couplers. More specifically, embodiments thereof relate to an optical system having an optically coupled waveguide that outputs a signal that can be used for phase dewinding to wavelength-locked a 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 multiple different wavelengths of light simultaneously and / or sequentially. However, as the number of wavelengths monitored increases, so does the size and complexity of the system. Because the size of an optical system varies proportionally with 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 a 2×3 coupler for wavelength locking. Systems, apparatuses, methods, and devices relating to phase dewinding of all wavelengths in both the free spectral range and a broadband wavelength range are also described. The 2×3 coupler can generate an output signal with a sinusoidal wavelength response that has a constant phase difference from each other across the broadband wavelength range, which allows for phase dewinding across the broadband wavelength range. By phase dewinding the output signal in the free spectral range and performing further phase dewinding in the broadband wavelength range, a continuous signal can be generated and used to lock each wavelength across the broadband wavelength range. The continuous signal can establish a one-to-one relationship between each wavelength and the phase-dewinded signal.

[0007] In some examples, this disclosure describes an optical device. The optical device may include: a first waveguide configured to receive first light and output a first output signal having a first wavelength response with a first phase shift; a second waveguide optically coupled to the first waveguide and configured to output a second output signal having a second wavelength response with a second phase shift; and a third waveguide optically coupled to the second waveguide and configured to receive the second light and output a third output signal having a third wavelength response with a third phase shift, wherein the phase difference between the first phase shift, the second phase shift, and the third phase shift is constant.

[0008] In some examples, this disclosure describes an optical system for monitoring the wavelength of a light source. The optical system may include: a light source configured to generate light; a beam splitter configured to receive light received from the light source and split it into a first beam and a second beam; a phase shifter positioned to receive the first beam and perform a phase shift on it; and a 2×3 coupler configured to receive the first beam from the phase shifter, receive the second beam from the beam splitter, and output a first output signal, a second output signal, and a third output signal, each having a corresponding intensity based on a corresponding interference between the first and second beams. The optical system may also include: a controller configured to monitor the wavelength of the light received by the beam splitter using the intensities of the first, second, and third output signals.

[0009] In some examples, this disclosure describes a method for phase dewinding a signal. The method may include: generating a first output signal, a second output signal, and a third output signal, each having a wavelength response separated from each other by a constant phase difference; extracting the dewinding phase from the first, second, and third output signals across a wavelength range to generate a dewinding phase signal; differentiating the dewinding phase signal to generate a differential signal; generating a compensated differential signal by comparing the differential signal with a threshold voltage; and integrating the compensated differential signal to generate an integrated signal configured to generate a continuous signal for wavelength locking.

[0010] 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

[0011] Figure 1 This is a block diagram of an exemplary wavelength locking system.

[0012] Figure 2 This is a block diagram of an exemplary wavelength locking system including 2×3 couplers.

[0013] Figure 3A This is a cross-sectional view of a 2×3 coupler.

[0014] Figure 3B yes Figure 3A The image shows a cross-sectional view of an exemplary wavelength locking system with 2×3 couplers.

[0015] Figure 4A illustrates the effect from a wavelength locking system (such as...) Figure 2 The graph shows an exemplary output signal of the wavelength locking system.

[0016] Figure 4B is a graph illustrating an exemplary extraction phase from the exemplary output signal of Figure 4A.

[0017] Figure 5 This is a sampling circuit diagram of an exemplary circuit used for phase dewinding of the output signal.

[0018] Figures 6A to 6D Is Figure 5 The curves of the signals measured at each node of the circuit diagram.

[0019] Figure 7A This is a cross-sectional view of another variant of the 2×3 coupler. Figure 7B It is a combination Figure 7A A schematic diagram of a wavelength locking system with a 2×3 coupler.

[0020] 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.

[0021] 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

[0022] 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.

[0023] Two elements "coupled" to each other may be physically coupled to each other permanently or removably and / or operationally or functionally coupled. Generally, a physically coupled element refers to a physical connection between two or more elements that at least partially defines or restricts the relative positioning of the elements. Furthermore, two or more elements that are operationally or functionally coupled may influence each other, as the operation of the first element may directly or indirectly affect the operation of the second element. Additionally, two elements "optically coupled" to each other may allow light to pass from one element and / or couple to the other.

[0024] The accompanying drawings will be referenced in the following description of the examples, which illustrate specific examples that can be implemented by way of example. It should be understood that other examples may be used and structural changes may be made without departing from the scope of the individual examples.

[0025] This paper discloses an integrated photonic system employing one or more light sources that output multiple wavelengths, which can be combined using a 2×3 coupler with two inputs and three outputs. Specifically, the 2×3 coupler splits light received at each of its inputs among its three outputs. When light is received simultaneously at two inputs of the coupler, the three outputs will each output different combinations of the input light. The 2×3 coupler can be used to combine light across a wide wavelength range (simultaneously or sequentially) while maintaining a compact form factor. The output signal from the 2×3 coupler can be used by the integrated photonic system to control and stabilize the wavelength of light emitted by the integrated photonic system via wavelength locking.

[0026] The integrated photonic system may also include an on-chip wavelength locking system for locking the wavelength of a light source to a target wavelength. In some embodiments, the integrated photonic system includes a wavelength locking system having multiple light sources, and the wavelength locking system can sequentially lock each of the multiple light sources to a corresponding target wavelength. At least some of the multiple light sources may each emit light with different corresponding nominal wavelengths, which together span a wavelength range (as determined by the overall specifications of the integrated photonic system), so it may be desirable for the wavelength locking system to effectively perform wavelength locking across the entire wavelength range. Generally, the embodiments described herein are capable of locking wavelengths across a wide wavelength range (e.g., across a wavelength range of at least one micrometer). In other words, the wavelength locking system is capable of locking the wavelengths of two light sources, wherein the wavelengths emitted by each light source are spaced at least one micrometer apart.

[0027] An on-chip wavelength locking system can utilize a 2×3 coupler as described herein. Specifically, the 2×3 coupler can be configured to receive two input signals and output three output signals, and can be configured such that when the two inputs include phase-shifted light of a certain wavelength (collectively referred to as “input light”), each output signal has an intensity based on the corresponding interference between the input signals (as described in more detail herein). The intensity of each output signal is wavelength-dependent, such that the intensity of each output signal changes as the wavelength of the input light changes. Specifically, for each output, there is a sinusoidal wavelength relationship between the input light wavelength and the output intensity; in other words, the output intensity changes sinusoidally as a function of the input light wavelength. The 2×3 coupler can be configured such that the sinusoidal wavelength relationship of each output has a different phase, such that there is no simultaneous overlap between the maximum and minimum values ​​of the three output signals across the target wavelength range. This allows the output signals to be used to lock the wavelength of the input light, as described further herein.

[0028] A wavelength-locking system may include a 2×3 beam splitter coupler for splitting two optical inputs into three optical outputs. The wavelength-locking device can also be used to monitor the wavelength of a corresponding light source and lock its wavelength to a target wavelength. Generally, each light source can sequentially emit individual optical wavelengths to which it can be locked. The 2×3 coupler includes an intermediate waveguide located between the two outer arms of the device, thereby generating three output signals. As previously mentioned, the intensity of each output signal can be wavelength-dependent, such that the intensity of each output signal changes as the wavelength of the input light changes.

[0029] The wavelength-locking device can be symmetrical about a horizontal axis, and the light in one arm can have a phase shift relative to the light in the other arm (and / or the input light to the coupler), thereby outputting signals each having an amplitude (e.g., intensity) and a sinusoidal wavelength relationship with each other. The sinusoidal wavelength relationship ensures that the maximum and minimum values ​​of at least one of the output signals are not aligned with the maximum and minimum values ​​of the other output signals. A 2×3 coupler can have a relatively small footprint while outputting signals used to lock the output wavelength to the desired wavelength. In some embodiments, this wavelength locking is performed for light with a broadband wavelength range of approximately one micrometer.

[0030] By coupling light into an intermediate waveguide positioned between two external waveguides in a 2×3 coupler, the two external waveguides can generate an output signal with a sinusoidal wavelength relationship over a wide wavelength range. The output signal of the 2×3 coupler can be similar to the output signal of three Mach-Zehnder interferometers (“MZI”), but the 2×3 coupler can be smaller than such an MZI combination because the size and complexity of the locking technique increase with the wavelength range.

[0031] As described in this paper, a constant phase difference is a sinusoidal wavelength relationship of the output signals generated by a multimode 2×3 coupler, which may result in dead zones where the output signals are misaligned with each other. That is, each output signal may have an intensity based on the corresponding interference between the input signals and each other. The intensity of each output signal is wavelength-dependent, such that for each output, there is a sinusoidal wavelength relationship between the input light wavelength and the output intensity, and the output intensity changes sinusoidally as a function of the input light wavelength. The sinusoidal wavelength relationship of each output signal can have its own different phase and a constant phase difference between the sinusoidal wavelength relationships, so that the output signals do not overlap between the maximum and minimum values ​​of the three output signals across the target wavelength range; this allows the output signals to be used to sequentially lock the wavelength of the input light.

[0032] While systems available for wavelength locking exist, they may be limited to operating within narrow wavelength ranges (such as 50 nm), may introduce unconsidered phase shifts, may have high optical losses, or may be too large to integrate into electronic devices (such as mobile or wearable devices), among other things. Wavelength locking can be used in a variety of photonic applications, including but not limited to telecommunications, medical devices, and spectrometers. Maintaining wavelength accuracy in photonic applications can be critical for accurate data collection, and wavelength locking prevents undesirable deviations in the emitted light wavelength. References in this article... Figure 1 Wavelength locking and its implementation are described in further detail.

[0033] As used herein, the “working region” is the wavelength range of a single output signal, wherein the single output signal has a slope that is non-zero or substantially close to zero. Similarly, the “dead zone” is the wavelength range of a single output signal, wherein the single output signal has a slope that is zero or close to zero, such as at and around the peaks and troughs of the single output signal. In other words, the working region is any part of a single output signal that is not a dead zone. Therefore, points in the working region have a higher slope than points in the dead zone. In other embodiments having multiple output signals with a sinusoidal wavelength relationship to each other, the multiple output signals may each have a consistently different phase. 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 slope that is non-zero or not a “dead zone”.

[0034] As described herein, small wavelength variations may be difficult to discern within the dead zone of the output signal of other solutions, potentially limiting the accuracy of wavelength locking based on that output signal. In contrast, the wavelength locking device described herein operates more efficiently because at least one output signal lies within the corresponding operating zone for any given wavelength. Therefore, an output signal with a large slope and a large difference between the target wavelength and the measured wavelength can always be present.

[0035] Wavelength locking devices that sequentially generate multiple output signals with constant phase differences within a target wavelength range are typically small in size (at least compared to other existing devices performing wavelength locking), have lower complexity than other structures with similar functionality, and are capable of accurately determining 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 a sinusoidal output signal for wavelength locking is described in further detail.

[0036] 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. For example, "209" may refer to any one of optical paths 209 (e.g., optical path 209a or optical path 209b, etc.), or it may refer to both optical paths 209, depending on the context in which the optical path is used. The term optical path 209 may be used when discussing the general properties of optical paths.

[0037] 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.

[0038] The following text is for reference only. Figures 1 to 7B These and other implementation schemes are discussed. 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.

[0039] Wavelength locking system

[0040] Figure 1 A block diagram of an exemplary wavelength locking system 100 is shown, including a light source 113, a beam splitter 102, and a wavelength locking device 117. The light source 113 emits input light along an optical path 103 toward the beam splitter 102. Generally, the optical path 103 may represent a waveguide, optical fiber, free-space optics, or other element or medium through which light travels. Figure 1 In one implementation, optical path 103 is a waveguide, although alternative waveguides (e.g., light propagating through a medium such as air or polysilicon between devices) may be used in larger systems to couple light into wavelength-locked device 117.

[0041] The beam splitter splits the input light received from input optical path 103 and passes the split light to wavelength-locking device 117. Wavelength-locking device 117 typically includes three waveguides (e.g., in the form of 2×3 couplers) that receive light (directly or indirectly) from beam splitter 102. In some embodiments, wavelength-locking device 117 may include additional beam splitters that provide light to multiple waveguides optically coupled to each other. In other embodiments, wavelength-locking device 117 may include multiple waveguides and / or may not include additional beam splitters. For example, two optical inputs may be passed to wavelength-locking device 117 via two optical paths, rather than one optical input being split and passed to wavelength-locking device 117. Additionally, a phase shifter (not shown) may receive light from one output of beam splitter 102 to phase-shift the light passed to one of the waveguides. References below... Figures 2 to 7B These implementation schemes will be described in further detail.

[0042] In some implementations, wavelength-locking device 117 can generate output signals (e.g., output light) via optical paths 107a, 107b, and 107c for locking the optical wavelength of light source 113. The output signals can be generated via interference between phase-shifted light rays in one of the waveguides of the 2×3 coupler. Wavelength-locking device 117 can generate output signals, each with a sinusoidal relationship to the optical wavelength, and the output signals have a constant phase difference between the sinusoidal relationships. Therefore, the dead zone of the output signal may not be aligned for any wavelength within the wavelength range of the light input from light source 113.

[0043] By analyzing the output of wavelength-locking device 117, wavelength-locking system 100 can identify wavelength shifts in the light output from light source 113. Specifically, the intensity of each output will vary according to a sinusoidal wavelength relationship as the wavelength changes. A controller (not shown) can measure changes in one or more output signals and can use one or more of these changes (e.g., the output signal with the largest possible value change) as an indication of wavelength changes. The controller can use such changes as feedback on aspects of controlling the output of light source 113.

[0044] Optionally, the output signal can be transmitted to a phase unlocking device (which may be an integrated circuit, digital logic unit, etc., performing a specific function) that extracts the phase from the output signal. This extracted phase information can be used to determine the difference between the measured wavelength and the target wavelength, allowing the light source to be adjusted to emit the target wavelength. References herein... Figures 2 to 7B The wavelength locking system and the 2×3 coupler are described in further detail.

[0045] Figure 2A block diagram of an exemplary wavelength locking system 200 is shown, including a 2×3 coupler and a controller block (which may include a set of photodetectors). Wavelength locking system 200 can be used to lock a light source to any target wavelength selected from a wavelength range. In some cases, wavelength locking system 200 can be used to lock generated light to any of a plurality of different wavelengths within a wavelength range spanning one micrometer; however, it should be understood that the wavelength locking system described herein can be used with any suitable wavelength range (e.g., spanning less than 100 nm, spanning at least 100 nm, spanning at least 500 nm, or spanning at least 1300 nm). In practice, in some cases, the wavelength range is limited to the range of wavelengths that can be emitted by one or more light sources and the underlying material used to form the coupler itself (e.g., the wavelengths that light can be carried by a given waveguide material).

[0046] The wavelength locking system 200 includes a beam splitter 205, a phase shifter 210, a 2×3 coupler 260, and a controller 265. For example... Figure 2 As shown, beam splitter 205 is a 1×2 beam splitter; however, similar optical beam splitting functionality (e.g., 1×N beam splitters and N×M beam splitters) can be achieved using any suitable components or combinations of components to provide two inputs to 2×3 coupler 260. Beam splitter 205 is optically coupled to one or more light sources 213 and receives input light from one or more light sources 213 via optical path 203. Beam splitter 205 can split the light output of light source 213 between two output optical paths, and transmit the first split beam to 2×3 coupler 260 via optical path 209a and the second split beam to phase shifter 210 via optical path 209b. Phase shifter 210 can introduce a phase shift or delay into the light received via optical path 209b to create a phase difference between the light received via optical paths 290a and 290b. Although in Figure 2 The 2×3 coupler 260 is described in the context of wavelength-locked system 200, but the 2×3 coupler 260 can be used in any system that combines two optical inputs and outputs three signals. Controller 265 can receive a first optical output signal 230, a second optical output signal 235, and a third optical output signal 240 from the 2×3 coupler 260. Controller 265 can use the intensity of the first output signal 230, the second output signal 235, and the third output signal 240 to monitor the wavelength of the light received by beam splitter 205.

[0047] Light source 213 can emit light along optical path 203, which is received by beam splitter 205. Light source 213 can include a single light source or multiple light sources. In some examples, light source 213 can be any coherent or semi-coherent light source or any combination thereof. Each light source 213 can emit light of a single wavelength, or can be configured as a tunable light source capable of emitting light across, for example, a 15-nanometer wavelength range, but other tunable light sources may have different ranges that are greater than or less than 15 nanometers. Furthermore, any number of light sources can be used in wavelength locking system 200.

[0048] continue Figure 2 As described, beam splitter 205 transmits split light to 2×3 coupler 260 via optical paths 209a and 209b. 2×3 coupler 260 typically includes three waveguides. The first waveguide of 2×3 coupler 260 receives light via optical path 209a, and the third waveguide of 2×3 coupler 260 receives light via optical path 209b. The second waveguide may be an intermediate waveguide optically coupled to both the first and third waveguides and positioned between them. All three waveguides of 2×3 coupler 260 can output light via a single output optical path along the corresponding output of 2×3 coupler 260. See below for reference. Figure 3A and Figure 3B An example of the configuration and relative layout of a 2×3 coupler 260 is discussed below, with reference to... Figure 7A and Figure 7B Let's discuss another example. Light can be coupled from the first and third waveguides to the second intermediate waveguide, allowing the light between the waveguides to interfere with each other and generate three optical output signals 230, 235, and 240.

[0049] Specifically, some of the light received by the first waveguide will couple to the second waveguide, and from the second waveguide to the third waveguide. Similarly, some of the light received by the third waveguide will couple to the second waveguide, and from the second waveguide to the first waveguide. Therefore, each waveguide output includes components of light received from both the first and third waveguides. The first waveguide may generate a first output signal 230, the second waveguide may generate a second output signal 235, and the third waveguide may generate a third output signal 240. As previously described, each output signal may have an intensity based on the corresponding interference between the input signals. The intensity of each output signal is wavelength-dependent, such that for each output, there is a sinusoidal wavelength relationship between the input light wavelength and the output intensity, and the output intensity changes sinusoidally as a function of the input light wavelength (also referred to herein as the “wavelength response” of the output signal). (Refer to...) Figure 3A The configuration and function of the three waveguides are discussed in further detail in Figure 4B.

[0050] As previously described, controller 265 may receive a first output signal 230, a second output signal 235, and a third output signal 249 from 2×3 coupler 260. Controller 265 may include a set of detectors 270 that convert the first output signal 230, the second output signal 235, and the third output signal 240 into a first digital output signal, a second digital output signal, and a third digital output signal, respectively. In some embodiments, the first output signal 230, the second output signal 235, and the third output signal 240 may be light intensity, while the first digital output signal 245, the second digital output signal 250, and the third digital output signal 255 may be digital signal equivalents of these light-based output signals that can be converted by the set of detectors 270.

[0051] The controller 265 can generate a feedback signal 275 based on the first output signal 230, the second output signal 235, and the third output signal 240 to control the light source 213. When the wavelength of the light emitted by the light source 213 deviates from the target wavelength, the feedback signal 275 adjusts the operation of the light source to bring the wavelength of the light emitted by the light source 213 back to the target wavelength. For example, at a given wavelength, the first output signal 230, the second output signal 235, and the third output signal 240 will each have a corresponding target output value (e.g., a first output target, a second output target, and a third output target). Similarly, the first digital output signal 245, the second digital output signal 250, and the third digital output signal 255 will have corresponding target digital values.

[0052] The controller 265 can compare the first output signal 230, the second output signal 235, and the third output signal 240 with their corresponding target output values ​​(e.g., by comparing the first digital output signal 245, the second digital output signal 250, and the third digital output signal 255 with their corresponding digital target values), and can generate a feedback signal 275 as a function of the deviation from these target output values. The feedback signal 275 then controls the light source 213 to adjust one or more operating parameters that change the wavelength of the light source 213. Therefore, the controller 265 can provide closed-loop control of the light source 213 to maintain the wavelength at a target wavelength by holding the first output signal 230, the second output signal 235, and the third output signal 240 at their respective target output values.

[0053] As previously mentioned, many existing optical couplers are large and difficult to reduce in size. Compared to such existing couplers, a single 2×3 coupler 260 can be more compact and space-efficient. Furthermore, the wavelength-locked system 200 can be temperature-insensitive, while many other optical couplers change their output with temperature. Additionally, the output signal generated by the wavelength-locked system 200 may not have alignment dead zones (e.g., the dead zones of the output signals may be temporally offset), and therefore can reliably generate output light carrying information about any differences between the actual wavelength or wavelength range of the output light and the target wavelength or target wavelength range of the target light.

[0054] 2×3 Coupler

[0055] Figure 3A This is a cross-sectional view of a 2×3 coupler 301 that defines five regions. The first region (or "input region") is located between lines S0 and S1, and typically represents an input region where each waveguide is positioned sufficiently far from each other, where no coupling will occur between the waveguides. The second region (or "first S-curve region") is located between lines S1 and S2, representing a first S-curve region or point where the sidewalls of the output waveguide begin to bend and light can begin to couple from the first and third waveguides (e.g., the outer waveguide) to the second waveguide (e.g., the middle waveguide). The third region (or "center region") is located between S2 and S3, representing a primary coupling region where light can couple between the first and third waveguides (e.g., the outer waveguide) and the second waveguide (e.g., the middle waveguide). The fourth region (or "second S-shaped bend region") lies between S3 and S4, representing the second S-shaped bend region or point where the bend in the sidewalls of the first and third waveguides can terminate, and light can terminate coupling from the first and third waveguides (e.g., the outer waveguide) to the second waveguide (e.g., the middle waveguide). The fifth region (or "output region") lies between S4 and S5, representing the region where light can be output from the first, second, and third waveguides without further coupling between the waveguides. These regions and their characteristics will be discussed herein. The regions discussed herein are for illustrative purposes and do not depict discrete regions with different material compositions within the device.

[0056] Furthermore, the S-shaped bend region can be of different shapes (e.g., 90-degree angle, straight, 45-degree angle, etc.), the waveguide in the central region can be tapered or non-tapered, and the waveguide in the input region can be curved, S-shaped, or any other shape. In yet another embodiment, the first waveguide 315 and the third waveguide 325 can bend at different rates relative to each other, and the waveguides may not have any linear segments or S-bend shapes in the first region defined by lines S0 and S1 and the second region defined by lines S1 and S2.

[0057] As described below, the region can have any configuration in which the waveguides have various shapes, as long as the waveguide configuration causes light to interact in the respective region in a desired manner. In other words, the specific embodiments described herein are for illustrative and not limiting purposes only, as the waveguides can be straight or curved in various ways, as long as the desired optical coupling and wavelength response are produced. The desired optical coupling can include the spacing of the waveguides in the input region such that little coupling occurs between the waveguides in the input region (e.g., the region defined by lines S0 and S1). In the input region, the waveguides can be positioned closer to each other so that optical coupling can begin to occur between the waveguides, and in the central region, the waveguides can be positioned relative to each other so that more light couples between the waveguides. In the second S-shaped curved region, the waveguides can be spaced apart and separated from each other so that light no longer couples between the waveguides.

[0058] In some implementations, the first waveguide 315, the second waveguide 320, and the third waveguide 325 may be strip waveguides, but in some cases, ridge waveguides may be used for a ridge-to-strip waveguide conversion. Furthermore, although the first waveguide 315, the second waveguide 320, and the third waveguide 325 are depicted with similar crosshair patterns, they are independent waveguides (although they may be formed or constructed from similar or identical materials).

[0059] The 2×3 coupler 301 includes an input region (in Figure 3A (defined by lines S0 and S1), this input region includes the corresponding input regions of the first waveguide 315 and the third waveguide 325, as well as the input region of the second waveguide 320 (in... Figure 3A (As shown in the embodiment). Specifically, when the 2×3 coupler 301 is incorporated into the optical system, the input regions of the first waveguide 315 and the third waveguide 325 can be optically connected to other components of the optical system to receive light from them. Conversely, the second waveguide 320 can be incorporated into the optical system such that it exists in the input region but does not receive light via the input region of the second waveguide 320. Therefore, in these cases, the second waveguide 320 can receive light only via coupling relative to the first waveguide 315 and the third waveguide 325. Although the second waveguide 320 is in Figure 3A The input region shown is located in the input region of the 2×3 coupler 301, but it may alternatively begin in a second region (i.e., defined by lines S1 and S2).

[0060] The second region (as shown, the first S-shaped bend region defined by S1 and S2) is the region in which the distance between the first waveguide 315, the second waveguide 320, and the third waveguide 325 decreases between the first and third regions to allow coupling between the waveguides in the third region. Therefore, one or more of the first waveguide 315, the second waveguide 320, and the third waveguide 325 include one or more bends or curves (such as S-shaped bends or C-shaped bends). The terms S-shaped bend and S-shape are used interchangeably herein to describe the shapes of the first waveguide 315 and the third waveguide 325, as... Figure 3A The first and second S-shaped bending regions are depicted. Each waveguide of the 2×3 coupler may have any suitable combination of bent and straight segments, and the bent segments may bend away from the trajectory of the preceding segment at any suitable angle (e.g., 90 degrees, 45 degrees, 30 degrees). As previously stated, although the second and fourth regions are referred to herein as the first and second S-shaped bending regions, this is for reference and illustration purposes only, and the waveguides defined by S1 and S2 are not limited to S-shaped bends.

[0061] exist Figure 3A In the illustrated variant, the first S-shaped bend region has S-shaped portions of the first waveguide 315 and the third waveguide 325, and also includes a straight accompanying portion of the second waveguide 320. In the first S-shaped bend region, a portion of the first waveguide 315 is bent and has an S-bend shape, positioning the outer arm of the 2×3 coupler closer to a portion of the second (e.g., middle) waveguide 320. Similarly, a portion of the third waveguide 325 has an S-bend shape, positioning the other outer arm of the 2×3 coupler closer to a middle portion of the second waveguide 320. The second waveguide 320 is shown as straight in the input region and the first S-shaped bend region, but in other embodiments, these portions of the second waveguide 320 may be bent. Generally, the shape of these portions of the second waveguide 320 depends primarily on the shape or configuration of the corresponding portions of the first waveguide 315 and the third waveguide 325 and the desired portion for optical coupling efficiency. For example, these portions of the second waveguide 320 can be S-shaped to optically couple more light from one waveguide (compared to light from the other waveguide).

[0062] Additionally, the third waveguide 325 is depicted as having a shape approximately symmetrical or mirror-image of the corresponding portion of the first waveguide 315 in five regions of the wavelength locking system 300. In other embodiments, the third waveguide 325 may be symmetrical to the corresponding portion of the first waveguide 315 in some regions but not others. As another option, a portion of the third waveguide 325 may not be symmetrical to the corresponding portion of the first waveguide 315 in any of the five regions. It will be understood that, as described herein, the first waveguide 315 is a single waveguide extending between lines S0 and S5, wherein the various portions of the waveguide are located in each of the regions indicated by adjacent lines (e.g., one portion is located in the region defined by S0 and S1, and another portion is located in the region defined by S1 and S2). Similar logic can be applied to the second waveguide 320 and the third waveguide 325.

[0063] The central region (e.g., extending from S2 to S3) is the area in which light is coupled between the first waveguide 315, the second waveguide 320, and the third waveguide 325. Specifically, a portion of the light traveling through the first waveguide 315 in the central region can be coupled into the second waveguide 320, and vice versa. Similarly, a portion of the light traveling through the third waveguide 325 in the central region can be coupled into the second waveguide 320, and vice versa. Thus, the central region of the 2×3 coupler 301 can be configured such that light received at the input region of the first waveguide 315 is at least partially coupled into the second waveguide 320, and at least a portion of that light is coupled from the second waveguide 320 into the third waveguide 325. Similarly, the central region of the 2×3 coupler 301 can be configured such that light received at the input region of the third waveguide 325 is at least partially coupled into the second waveguide 320, and at least a portion of that light is coupled from the second waveguide 320 into the first waveguide 315. Therefore, when the first input light and the second input light are simultaneously introduced into the input regions of the first waveguide 315 and the third waveguide 325 respectively, the first waveguide 315, the second waveguide 320 and the third waveguide 325 will each output a combination of the first input light and the second input light.

[0064] In some variations, the central region is configured such that portions of the first waveguide 315, the second waveguide 320, and the third waveguide 325 can vary in width and can be enlarged or reduced in size within the central region. For example, as... Figure 3AAs shown, the second waveguide 320 narrows from the second and fourth regions in the central region, while the first waveguide 315 and the third waveguide 325 each widen from the second to the fourth region in the central region. In some cases, the first waveguide 315, the second waveguide 320, and the third waveguide 325 are thermally tapered to provide thermally adiabatic optical coupling between the first waveguide 315 and the second waveguide 320, and between the second waveguide 320 and the third waveguide 325. In some embodiments, portions of the first waveguide 315 and the second waveguide 320 in the central region may still be thermally coupled and may not be tapered.

[0065] like Figure 3A As shown in the output region, the first waveguide 315 and the third waveguide 325 can taper across the output region. That is, the first waveguide 315 can be wider around S4 than at S5, and the third waveguide 325 can taper similarly. Additionally, the second waveguide 320 has a cross-section that expands in the output region and widens from S4 to S5. As shown, the second waveguide 320 can expand wider at different locations in the output region than at the locations where the first waveguide 315 and the third waveguide 325 begin to expand. In another embodiment, the narrowing locations of the first waveguide 315 and the third waveguide 325 and the location of the second waveguide 320 can be at different locations in the output region.

[0066] The first waveguide 315 and the third waveguide 325 can be thermally and optically coupled to the second waveguide 320 in the central region and in the first and second S-shaped bend regions. Figure 3A In this configuration, the second waveguide 320 can receive approximately equal amounts of light from both the first waveguide 315 and the third waveguide 325 because the first gap 322 (e.g., the distance between the first waveguide 315 and the second waveguide 320) is approximately or exactly the same as the second gap 323 (e.g., the distance between the second waveguide 320 and the third waveguide 325). As long as the first gap 322 and the second gap 323 are approximately equal, the optical coupling from the first waveguide 315 and the third waveguide 325 to the second waveguide 320 is approximately equal. For example, the width of the first gap 322 can be increased in the central region; as long as the width of the second gap 323 varies similarly, the optical coupling from the first waveguide 315 and the third waveguide 325 to the second waveguide 320 remains approximately the same.

[0067] like Figure 3A As shown, the first waveguide 315 and the third waveguide 325 widen along the central region, while the second waveguide 320 decreases in width. In other embodiments, the central region may be omitted, and therefore, the waveguide width may not change when transitioning from the first S-shaped bend region to the second S-shaped bend region. In such embodiments, the waveguides can be optically coupled in both the first and second S-shaped bend regions.

[0068] The fourth region (the second S-shaped bend region between S3 and S4) is the region where the distance between the first waveguide 315, the second waveguide 320, and the third waveguide 325 increases from the third region to the fifth region to terminate the coupling between these waveguides. Therefore, one or more of the first waveguide 315, the second waveguide 320, and the third waveguide 325 include one or more bends or curves (such as S-shaped bends or C-shaped bends). For example, in Figure 3A In the variant shown, the portions of the first waveguide 315 and the third waveguide 325 in the fourth region are S-shaped and approximately symmetrical as in the first S-shaped bend region, and the corresponding portion of the second waveguide 320 has a constant cross-section. As described in further detail herein, the S-shaped portions of the first waveguide 315 and the third waveguide 325 can enhance optical coupling in the first S-shaped bend region and reduce optical coupling between the first waveguide 315 and the second waveguide 320, and between the second waveguide 320 and the third waveguide 325, in the second S-shaped bend region.

[0069] In addition to the thermally adiabatic optical coupling between waveguides in the central region, optical coupling can also occur in the first S-shaped bend region and the second S-shaped bend region. In these regions, the first waveguide 315 and the third waveguide 325 have S-shaped cross-sections and are symmetrical about the second waveguide. The S-shaped cross-section enables optical coupling between the first waveguide 315 and the second waveguide 320 because the gap width between these two waveguides decreases from the beginning to the end of the first S-shaped bend region, and the gap width between the third waveguide and the second waveguide is the same. That is, as the gap between the waveguides decreases, the optical coupling between the waveguides can increase. In other embodiments, optical coupling may not occur in these S-shaped bend regions.

[0070] In other embodiments, portions of the first waveguide 315 and the third waveguide 325 may be asymmetrical in shape. Additionally, in other embodiments, the second waveguide 320 may be curved (e.g., not straight). The widths of the first waveguide 315, the second waveguide 320, and the third waveguide 325 are shown as substantially the same, but may differ in some embodiments.

[0071] In the output region (e.g., shown between S4 and S5), the first, second, and third waveguides are sufficiently separated such that there is no coupling between them. Therefore, when light is introduced into the input region of the first waveguide 315 and / or the third waveguide 325, the first, second, and third waveguides will output a first output signal 330, a second output signal 335, and a third output signal 340, respectively. If first and second input light having the same wavelength but different phases are simultaneously introduced into the input regions of the first waveguide 315 and the third waveguide 325, respectively, the first waveguide 315 outputs a first output signal 330 with a first wavelength response having a first phase shift, the second waveguide 320 outputs a second output signal 335 with a second wavelength response having a second phase shift, and the third waveguide 325 outputs a third output signal 340 with a third wavelength response and a third phase shift. Therefore, the wavelength response of the first output signal 330, the second output signal 335, and the third output signal 340 causes each output signal to undergo a sinusoidal change as a function of the wavelengths of the first and second input light, but with a different phase compared to the other output signals (i.e., it can have three different phases). Referring to Figures 4A to... Figure 6D The output signal and its corresponding phase are described in further detail.

[0072] Figure 7A Another variant of the 2×3 coupler 700 as described herein is shown. The 2×3 coupler 700 includes a first waveguide 705, a second waveguide 710, and a third waveguide 715, wherein the second waveguide 710 is positioned between the first waveguide 705 and the third waveguide 715. Figure 3A Like the 2×3 coupler 301, the 2×3 coupler 700 includes a first region (extending upward to line S1), a second region (located between line S1 and line S2), a third region (located between line S2 and line S3), a fourth region (located between line S3 and line S4), and a fifth region (extending from line S4).

[0073] The first region acts as the third region, in which the first waveguide 705, the second waveguide 710, and the third waveguide 715 are not optically coupled to each other (and therefore no light is transmitted between these waveguides in the first region). Although Figure 7AThe embodiment of the 2×3 coupler 700 shown depicts a second waveguide 710 extending into the input region; however, in other variations, the second waveguide 710 alternatively begins in a second region (and therefore is not present in the first region). The second region acts as a first curved region in which the distance between the first, second, and third waveguides decreases such that light can couple between waveguides in the third region. It should be understood that some coupling can occur within the first curved region between the first waveguide 705 and the second waveguide 710 and / or between the second waveguide 710 and the third waveguide 715. To bring the waveguides closer together, some or all of the first waveguide 705, the second waveguide 710, and the third waveguide 715 include one or more curved segments. For example, in Figure 7A In the variant shown, the first waveguide 705 and the third waveguide 715 are each bent toward the second waveguide 710, and the second waveguide 710 is straight in the first bending region.

[0074] The third region serves as a coupling region where light is coupled between the first waveguide 705, the second waveguide 710, and the third waveguide 715. Specifically, a portion of the light traveling through the first waveguide 705 in the coupling region can be coupled into the second waveguide 710, and vice versa. Similarly, a portion of the light traveling through the third waveguide 715 in the central region can be coupled into the second waveguide 710, and vice versa. Thus, the central region of the 2×3 coupler 700 can be configured such that the first waveguide 705 is at least partially coupled into the second waveguide 710 in the input region, and at least a portion of that light is further coupled from the second waveguide 710 into the third waveguide 715. Similarly, the central region of the 2×3 coupler 700 can be configured such that light received by the third waveguide 715 in the input region is at least partially coupled into the second waveguide 710, and at least a portion of that light is further coupled from the second waveguide 710 into the first waveguide 705. Therefore, when the first input light and the second input light are simultaneously introduced into the first waveguide 705 and the third waveguide 715 in the input region, respectively, the first waveguide 705, the second waveguide 710 and the third waveguide 715 will each output a combination of the first input light and the second input light.

[0075] The fourth region acts as a second curved region in which the increased distance between the first, second, and third waveguides causes the first waveguide 705, second waveguide 710, and third waveguide 715 to no longer be optically coupled within the fifth region. For example, in Figure 7AIn the variant shown, the first waveguide 705 and the third waveguide 715 are each bent away from the second waveguide 710, and the second waveguide 710 is straight in the second bent region. It should be understood that some coupling can occur in the second bent region between the first waveguide 705 and the second waveguide 710 and / or between the second waveguide 710 and the third waveguide 715. The fifth region serves as an output region in which each of the first waveguide 705, the second waveguide 710, and the third waveguide 715 is optically decoupled from the remaining waveguides. The fifth region can be used to provide output to other parts of the optical system of the 2×3 coupler 700 (e.g., one output from each waveguide).

[0076] exist Figure 7A In the variant of the 2×3 coupler 700 shown, the width of each of the first waveguide 705, the second waveguide 710, and the third waveguide 715 can be constant in the coupling region. In some of these variants, the second waveguide 710 has a width greater than the widths of the first waveguide 705 and the third waveguide 715. In some of these variants, the width of the first waveguide 705 can be the same as the width of the third waveguide 715. When the 2×3 coupler 700 is configured as follows... Figure 7A As shown, when each waveguide in the third region has a constant width (where the second waveguide 710 is wider than the first waveguide 705 and the third waveguide 715 in this region), the relative widths of the waveguides (and the spacing between them) can be selected to achieve a target phase difference value between the output wavelength responses. In some variations of these variants, the first waveguide 705, the second waveguide 710, and the third waveguide 715 may have constant widths across some or all of other regions (e.g., the first region, the second region, the fourth region, and / or the fifth region). For example, in some variations, the first, second, and third waveguides have constant widths across the entire 2×3 coupler 700.

[0077] Specifically, the 2×3 coupler 700 is configured such that when the first waveguide 705 and the third waveguide 715 receive first and second input light having the same wavelength but different phases, respectively, the first, second, and third waveguides will each output light with corresponding intensities (having a sinusoidal wavelength relationship), as described above. In some cases, the waveguide dimensions and positions can be set to achieve a 120-degree phase difference between wavelength relationships for each output. In these cases, a 120-degree phase difference exists between the wavelength relationships of the output signals from the first waveguide 705 and the second waveguide 710, between the wavelength relationships of the output signals from the first waveguide 705 and the third waveguide 715, and between the wavelength relationships of the output signals from the second waveguide 710 and the third waveguide 715. With a 120-degree phase difference between each wavelength relationship, at least one output of the 2×3 coupler 700 will be located in the middle of its operating region for each wavelength within its input wavelength range.

[0078] The aforementioned 2×3 coupler is capable of operating across the input wavelength range, such that the first, second, and third output signals will each have their corresponding wavelength response across this range. Therefore, the 2×3 coupler can receive phase-shifted input light of any wavelength within this range, and wavelength shifts in the input light will cause a sinusoidal change in each output signal. Thus, when the 2×3 coupler is used in conjunction with a wavelength-locking system as discussed herein, these output signals can be used to lock the wavelength of the light source to any target wavelength within the wavelength range. As described above, the wavelengths of light received by the 2×3 coupler during operation of the optical system can span wavelength ranges of at least 50 nm, at least 100 nm, at least 400 nm, at least 1000 nm, at least 1500 nm, etc.

[0079] Wavelength locking device

[0080] The aforementioned 2×3 coupler can be incorporated into a wavelength-locking system to lock the wavelength of the light source to the target wavelength described above. For example, Figure 3B It shows the use of Figure 3AAn exemplary wavelength locking system 300 is described below, comprising a 2×3 coupler 301. The wavelength locking system 300 includes a beam splitter 305, a cladding layer 307, a phase shifter 310, and a 2×3 coupler 301 (which includes a first waveguide 315, a second waveguide 320, and a third waveguide 325 as described above). The cladding layer 307 may surround the components of the wavelength locking system 300 to reduce light loss and confine light to a propagation area, thereby defining the waveguides. The components of the wavelength locking system 300 have similar functions and may be similarly configured as corresponding components of the wavelength locking system 200. The wavelength locking system 300 is a structure that generates three output signals with wavelength responses having different phases. These three output signals may optionally be unwound as discussed below for wavelength locking purposes and to cover a wide wavelength range. Phase unwound is used to form a monotonic relationship between the extracted phase value and the wavelength, which may assist in wavelength tracking during wavelength shifts.

[0081] exist Figure 3B In embodiment 300, beam splitter 305 can receive input light and split it across two outputs. Beam splitter 305 can be a 1×2 beam splitter that splits the light between the two outputs (approximately or completely) equally. In other examples, beam splitter 305 can asymmetrically split the power, where 2×3 coupler 301 still outputs signals with different sinusoidal wavelength relationships. Any beam splitter or combination of beam splitters can be used, as long as the two outputs provide light to the corresponding inputs of 2×3 coupler 301, and the 1×2 beam splitter is for illustrative purposes only. The first output 304a of beam splitter 305 can be passed to the first input of 2×3 coupler 301, i.e., to the first waveguide 315 in the input region of 2×3 coupler 301. The second output 304b can be passed to the second input of 2×3 coupler 301 via phase shifter 310, which introduces a phase shift in the light of the second output relative to the light of the first output. Phase shifter 310 can be used as a delay line, similar to the delay introduced by different length arms of an MZI. In other words, the second output 304b can have a sufficiently different length from the first output 304a to introduce a phase delay. Alternatively, phase shifter 310 can be an active component (e.g., an electro-optic phase shifter, a thermo-optical phase shifter, or an optomechanical phase shifter) that is actively controlled to produce a phase shift. Light passes through phase shifter 310 to a third waveguide 325 in the input region of 2×3 coupler 301.

[0082] As previously described, the wavelength locking system 300 can be used to lock input light received by the wavelength locking system 300 to a target wavelength. For this purpose, input light to the beam splitter 305 can receive light of any wavelength from a wavelength range spanning a wide broadband wavelength range. In practice, at different times, the wavelength locking system 300 can lock input light to different wavelengths across a broad target wavelength range. In some examples, light of a first wavelength can be received as input light (and locked to a first target wavelength) at a first time, and light of a second wavelength can be received as input light (and locked to a second target wavelength) at a second time.

[0083] As described above, when the beam splitter 305 receives input light of a given wavelength, the 2×3 coupler 301 receives a first input light and a second input light at the first waveguide 315 and the third waveguide 325, where the first and second input lights have the same wavelength but different phases. The first and second input lights will couple between the first waveguide 315, the second waveguide 320, and the third waveguide 325 to generate three output signals. A portion of the first light in each waveguide will interfere with a portion of the second light in that waveguide, resulting in a constant intensity of the output signal. As described above, this intensity is wavelength-dependent, such that each output signal will have a sinusoidal wavelength relationship as discussed previously, but with different relative phases. That is, the three wavelength relationships can have relative delays to each other (e.g., they can have constant phase differences). This can result in dead zones shifting relative to each other with respect to the wavelength relationships, such that at any given wavelength, at least one output signal exists in its operating region (and therefore, in general, the overall wavelength locking system 300 effectively has no dead zones). This enables accurate locking to any target wavelength over a wide wavelength range. Additionally, phase decoupling of the output signal can be performed, allowing each wavelength to be locked. Refer to Figure 4A to... Figure 6D The phase unwinding is described in further detail.

[0084] Figure 4A is a graph showing the sample wavelength relationship of the output signal from the wavelength-locked system, while Figure 4B is a graph showing an example of the extracted phase of the output signal from Figure 4A. The output signal graph 400 includes the intensity of each of the first output signal 430, the second output signal 435, and the third output signal 440 as functions of wavelength. These output signals can correspond to the first, second, and third output signals of Figure 3. The output signal of Figure 4A can be generated in the same manner as discussed in Figure 3, relative to the outputs of the first output 330, the second output 335, and the third output 340 from the first waveguide 315, the second waveguide 320, and the third waveguide 325.

[0085] In the graph of Figure 4A, the horizontal axis represents the wavelength range spanned by the light, while the vertical axis represents the signal amplitude. The horizontal axis of the graph has arbitrarily assigned numbers 4 and 5, and it represents the wavelength range. (Figures 4A and 4B are also mentioned.) Figure 6A , Figure 6B , Figure 6C and Figure 6D The points 4 on each X-axis of these graphs are numbered consistently to represent the same wavelength within the wavelength range. As shown in Figure 4A, the phase difference of the wavelength responses of the output signals 430, 435, and 440 is consistent, as is the relative offset between the output signals. The wavelength responses of the output signals 430, 435, and 440 are typically sinusoidal signals.

[0086] 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 430, 435, and 440. 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. Additionally or alternatively, these measured intensities can be used to generate a feedback signal that controls the operation of the light source to change the wavelength of the generated light and thereby lock it to the target wavelength.

[0087] As mentioned above, when the output signal is in its dead zone, changes in wavelength will result in relatively small changes in the intensity of the output signal. Therefore, the effectiveness of a single output signal in determining wavelength changes is limited due to the dead zone of the output signal. However, in the wavelength-locked system described herein, multiple output signals can have a constant phase difference between their wavelength responses. This may result in the dead zone of each output signal not being aligned with the dead zones of other output signals. Therefore, usable information can be obtained from at least one output signal for all wavelengths across the wavelength range.

[0088] Specifically, each of the output signals 430, 435, and 440 has a varying slope and inflection point. When the slope is at its steepest or maximum (i.e., within the operating range), most of the information about the given output signal is available for the wavelength, resulting in the maximum change in signal strength as a function of wavelength. At each wavelength, at least one of the output signals 430, 435, and 440 has a non-zero slope (e.g., there is no simultaneous overlap between the maximum or minimum values ​​of all output signals), thus each of the output signals 430, 435, and 440 can have information available for wavelength locking at that particular wavelength. As described above, this can be advantageous for wavelength locking across a wide wavelength range (e.g., with a bandwidth of 1000 nm).

[0089] Figure 7B Another variant of the wavelength locking system 701 is shown, which includes Figure 7A The 2×3 beam splitter 700 is described in the figure. As shown, the wavelength locking system 701 includes a beam splitter 702 that receives input light (e.g., from a light source as described above) at input 755 and splits the input light between a first output 704a and a second output 704b. The second output 704b includes a phase shifter 706 that can introduce a phase shift relative to the first output 704a, as described above. Therefore, when light of a given wavelength is received at input 755 of the beam splitter 702, the first output 704a and the second output 704b of the beam splitter 702 will output light of that wavelength with two different phases.

[0090] The first output 704a and the second output 704b optically couple the beam splitter 702 to the 2×3 beam splitter 700 at line S0. Specifically, the first output 704a and the second output 704b are optically coupled to the first waveguide 705 and the third waveguide 715 of the 2×3 coupler 700, respectively, in the input region of the 2×3 coupler 700. Thus, when light of a given wavelength is introduced into the input 755 of the beam splitter 702, the first waveguide 705 receives the first input light having that wavelength and a first phase, and the third waveguide 715 receives the second input light having that wavelength and a second phase. When receiving these inputs, the first waveguide 705, the second waveguide 710, and the third waveguide 715 will output a first output signal 730, a second output signal 735, and a third output signal 740, respectively. These output signals will each have a constant intensity (i.e., due to the interference between the phase-shifted first input light and the second input light), which changes sinusoidally as a function of the wavelength of the input light.

[0091] These output signals can be used to determine the wavelength of the input light and / or as feedback to control the operation of the light source (e.g., to lock the input light to a target wavelength), as previously described. The wavelength responses of these output signals can be phase-shifted relative to each other, such that at least one output signal is always not in a dead zone within the wavelength range. These wavelength responses can be similar to the wavelength responses shown in Figure 4A, but with different relative phases between the wavelength responses of each output signal. For example, the 2×3 coupler 700 can be configured such that there is a 120-degree phase shift between the wavelength responses of each of the first output signal 730, the second output signal 735, and the third output signal 740.

[0092] Phase unwinding

[0093] As described above, the system described herein can optionally use phase decoupling techniques to perform wavelength locking. As shown in Figure 4B, the extracted phase profile 450 illustrates the decoupling phase of the free spectral range (“FSR”) within a portion of the wavelength range of the input light, denoted by arbitrarily assigned numbers 4 to 5. The free spectral range is the interval between the maximum or minimum optical intensity values ​​of two consecutive reflections or transmissions in a single output signal 430, 435, 440 (i.e., the free spectral range of output signal 440 is shown in Figure 4B). In other words, the free spectral range is the wavelength range between consecutive peaks or valleys of the output signal. By performing phase decoupling on the signal to reconstruct the initial phase of the signal, the difference between the measured wavelength (or wavelength range) of the ideal output signal and the target wavelength or target wavelength range is obtained.

[0094] Phase dewinding can be achieved by using a complex variable S to represent the operation of the 2×3 coupler. General formulas for the complex variable S may not be suitable because they are typically applicable to narrowband devices and do not extract the dewinding phase for broadband devices. A derived complex variable S for broadband devices can have an angle proportional to the phase shift between the first and third waveguides in Figure 3. The complex variable S can be expressed by the following formula:

[0095] S = x + jy,

[0096] in

[0097] x = x bar / k x And y = y bar / k y

[0098] and

[0099] x bar =I3 / |c2| 2 –((I1+I2) / (|a2| 2 +|b2| 2 And y bar =I1–I2

[0100] and

[0101] k x =1–((2|a2||b2|) / (|a2|) 2 +|b2| 2 )*cos(ΔΘ) and k y = -2*|a²||b²|*sin(ΔΘ)

[0102] Where |a2|, |b2|, and |c2| are the amplitudes of the scattering parameters used for the 2×3 coupler between the first input and the first output signal 430, the second output signal 435, and the third output signal 440. I1, I2, and I3 are the output signals 430, 435, and 440 corresponding to the FSR. Additionally, ΔΘ is the phase difference between output signals 430 and 440. Using these formulas to obtain data across a given wavelength range (e.g., a bandwidth of 1000 nm or other bandwidths as described above), the unwound phase can be extracted within the wavelength range received by the 2×3 coupler included in the wavelength-locked system 300 of FIG. 3 to generate an unwound phase signal.

[0103] Although the phase has been extracted from the FSR of the output signal 430 as shown in Figures 4A and 4B, the unwound phase signal still includes the zeros of the output signal. Similar to the output signal curve 400, at the peak or zero 452 of the extracted phase curve 450 (e.g., the vertical line in the extracted phase curve 450, also known as the "jump"), there is little information available for wavelength locking at the specific wavelength where the zero 452 occurs. Furthermore, and as previously described with reference to Figure 3, the phase can be shifted or delayed by a phase shifter. As the delay increases, the phase difference (e.g., the free spectral range) may decrease. Moreover, as the delay increases, the wavelength locking efficiency improves.

[0104] Figure 5 This is an exemplary circuit diagram for phase dewinding of the output signal, and Figures 6A to 6D A graph corresponding to the output signal at points along the circuit diagram is shown. The phase dewinding circuit 500 implements an algorithm for dewinding the phase of the output signal. The phase dewinding circuit 500 includes a 2×3 coupler 560, a photodetector 565, a phase extraction block 570, a differentiator 575, a negative transition comparator 580a, a positive transition comparator 580b, a first adder 585, an integrator 590, and a second adder 595. Points A, B, C, and D are shown on the phase dewinding circuit 500; Figure 6A , Figure 6B , Figure 6C and Figure 6D The graph shows the signals measured at each of these points.

[0105] Point A is measured at its location. Figure 6A The points on the graph show the signal points, located between phase extraction block 570 and differentiator 575. Point B is where the measurement is taken. Figure 6B The point C is the signal point shown on the graph, located between the first adder 585 and the integrator 590. Point C is where the measurement is taken. Figure 6CThe point D on the graph represents the signal and is located between integrator 590 and second adder 595, and point D is where the measurement is taken. Figure 6D The point on the graph shows the signal and is located after the second adder 595. The signal measured at point D is the output signal of the phase unwinding circuit 500.

[0106] A 2×3 coupler 560 outputs three signals to a photodetector 565. These three output signals can be optical output signals as described with reference to Figures 3 and 4A-4B. The photodetector 565 receives the optical output signals and converts them into output signals, as depicted in the output signal curve 400 of Figure 4A. The photodetector 565 can be part of an array or a single unit. Furthermore, the photodetector 565 can be any suitable optical detector. The output signals from the photodetector 565 can be transmitted to a phase extraction block 570.

[0107] Phase extraction block 570 performs the operation described with respect to FIG. 4B, namely, dewinding the phase of the output signal. Therefore, the phase extraction block can take the signal shown in the graph of FIG. 4A and use it as input to generate the signal shown in the graph of FIG. 4B. More specifically, phase extraction block 570 can extract the dewound phase from the output signal by implementing the formula described with reference to FIG. 4B (e.g., generating a signal corresponding to the dewound phase). Furthermore, the output of phase extraction block 570 can be measured at point A; this measurement is performed at... Figure 6A The curve in Figure 4B is shown. It should be understood that the curve in Figure 4B is... Figure 6A A segment of the curve, and specifically Figure 6A An expanded view between points 4 and 5 on the horizontal axis.

[0108] As discussed previously with reference to Figure 4B, Figure 6A The graph (showing the extracted phase) can still include the zeros of the output signal or have corresponding points. Figure 6A At the peaks or zeros of the extracted phase curve (e.g., the vertical lines in the extracted phase curve 450), there is little information available for wavelength locking for a specific wavelength, and therefore a continuous curve may be desired for wavelength locking because it produces a one-to-one relationship between the wavelength and the output signal.

[0109] Figure 6A The peak value in the graph indicates that the signal increases or "jumps" by two π. Typically, a phase jump occurs when the phase value exceeds the value of π or -π, causing the point to jump to the opposite value even if the phase can continuously increase or decrease. Detection and mitigation. Figure 6AOne way to identify sharp transitions or peaks in a graph is by differentiating the signal. When scanning the wavelength in the positive direction (e.g., a phase transition from π to -π), the output of the differentiating block is a negative peak. Conversely, when scanning the wavelength in the negative direction (e.g., a phase transition from -π to π), the output has a positive peak. Depending on whether the peak is detected in the positive or negative direction, two πs can be subtracted or added respectively until the phase is within -π to π.

[0110] return Figure 5 The phase extraction block 570 provides the extracted phase signal to the differentiator 575, which differentiates the signal received from the phase extraction block 570. The differentiator 575 can be used to detect peak values ​​in the signal (e.g., two π transitions) and transmit this information in the differentiated signal to negative transition comparators 580a and positive transition comparators 580b. The differentiated signal is the output of the differentiator 575 and has a negative peak value when the wavelength is scanned in the positive direction (e.g., a phase transition from π to -π). Furthermore, the output has a positive peak value when the wavelength is scanned in the negative direction (e.g., a phase transition from -π to π).

[0111] Negative transition comparator 580a and positive transition comparator 580b are used to add or subtract two π from the signal at the wavelength where the peak occurs. The signals from negative transition comparator 580a and positive transition comparator 580b can be added together by first adder 585. The signal output of first adder 585 is measured at point B, and... Figure 6B The curve is shown in the figure. Negative transition comparator 580a and positive transition comparator 580b compare the differential signal with a specific threshold voltage. Negative transition comparator 580a and positive transition comparator 580b can distinguish between two cases: a first case where the wavelength gradually increases; and a second case where the wavelength gradually decreases. The first case may result in a negative transition of the signal in Figure 4B, and therefore two πs can be added to the signal by negative transition comparator 580a. Conversely, the second case may result in a positive transition, and two πs can be subtracted by positive transition comparator 580b. Negative and positive transitions are determined by comparing the differential signal with the negative and positive values ​​of negative transition comparators 580a and positive transition comparators 580b, as well as the voltage threshold.

[0112] The output of the first adder 585 can be passed to the integrator 590, which integrates the two π-pair signals to generate a stepped signal, which corresponds to... Figure 6C Point C on the graph shown. The stepped signal generated from integrator 590 is a correction value for producing a perfectly linear and continuous signal. Because a continuous signal establishes a one-to-one relationship between wavelength and signal and is desirable, it can be used to... Figure 5 Point C and Figure 6CThe stepped signal from the curve in the graph is summed with the signal from differentiator 575 at the second adder 595 to produce a perfectly linear signal. This linear and continuous signal is Figure 6D The graph shown provides a one-to-one relationship between wavelength and signal. The output of point D or adder 595 provides the per-wavelength phase shift required for wavelength locking of the corresponding wavelength.

[0113] In practice, optical devices can include multiple (N) lasers operating at different wavelengths in a wavelength range between 1.4 and 2.4 μm. The optical devices can include driving electronics that time-multiplex the lasers, allowing each laser to emit light at a specific time. The driving electronics can also include a feedback loop that uses a controller to control the laser frequency. The input to the controller can be an output from a phase unwinding signal (response signal), which the controller compares to a desired target value (e.g., a predetermined value determined during the calibration steps described below). Due to environmental variations (e.g., temperature or other noise sources), changes in the laser frequency may affect the error signal (e.g., the difference between the setpoint and the response signal). The error signal can be used to change the value of the laser drive current (e.g., a control signal) to set the laser wavelength to the desired operating value.

[0114] In some implementations, a calibration step can be performed before operating in a closed-loop configuration to determine a setpoint equivalent to the target wavelength. The calibration step can be performed in an open-loop configuration, where the response signal can be measured along with the laser wavelength while scanning the drive current. Because a laser emits light only once, it may not be possible to lock more than one laser simultaneously. However, in some implementations, using a single circuit for wavelength locking may be more efficient, thus allowing for reductions in at least one, more than one, or all of weight, size, and power. Therefore, a calibration step can be performed individually for each laser.

[0115] Although process or method steps may be described in a sequential order, such processes and methods may 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. Furthermore, although described or implied to occur non-simultaneously (e.g., because a step is described after other steps), some steps may be performed concurrently. Moreover, the illustration of the process in the accompanying drawings does not imply that the process shown excludes other variations and modifications thereof, does not imply that any step of the process shown must be one or more of the examples, and does not imply that the process shown is preferred.

[0116] 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.

[0117] 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. An optical device, the optical device comprising: A light source configured to generate light; A beam splitter is used to receive light received from the light source and split it into a first beam along a first optical path and a second beam along a second optical path; A phase shifter, the phase shifter being positioned to receive the first beam splitting along the first optical path and to phase-shift the first beam splitting relative to the second beam splitting; A 2×3 coupler, the 2×3 coupler comprising: The first waveguide is configured as follows: Receive the first beam splitting along the first optical path; and The output signal has a first wavelength response and a first phase shift; A second waveguide, optically coupled to the first waveguide and configured to output a second output signal having a second wavelength response and a second phase shift; and A third waveguide, optically coupled to the second waveguide and configured as follows: Receive the second beam splitter along the second optical path; and The output signal has a third wavelength response and a third phase shift: A set of photodetectors, the set of photodetectors being positioned to receive the first output signal, the second output signal, and the third output signal, wherein: The first phase shift and the second phase shift are offset by the first phase difference value; The second phase shift and the third phase shift are offset by the second phase difference value; The first phase shift and the third phase shift are offset by the third phase difference value; The first phase difference, the second phase difference, and the third phase difference are constant; The first waveguide, the second waveguide, and the third waveguide have constant widths in the coupling region; and In the coupling region, the second waveguide is wider than the first waveguide and the third waveguide.

2. The optical device according to claim 1, further comprising a phase shifter operable to phase shift the second light; wherein: The phase shift of the second light controls the wavelength locking efficiency of the first, second, and third output signals; and The first phase shift, the second phase shift, and the third phase shift are constant within a wavelength range of approximately one micrometer.

3. The optical device according to claim 1, wherein the first waveguide and the third waveguide are symmetrical about the second waveguide.

4. The optical device according to claim 1, wherein the first waveguide, the second waveguide and the third waveguide have constant widths.

5. An optical system for monitoring the wavelength of a light source, the optical system comprising: A light source configured to generate light; A beam splitter is used to receive light received from the light source and split it into a first beam along a first optical path and a second beam along a second optical path; A phase shifter, the phase shifter being positioned to receive the first beam splitting along the first optical path and to phase-shift the first beam splitting relative to the second beam splitting; A 2×3 coupler, comprising a first waveguide, a second waveguide, and a third waveguide, and configured as follows: The first beam splitting is received from the phase shifter at the first waveguide along the first optical path; The second beam splitting is received from the beam splitter along the second optical path at the third waveguide; as well as A first output signal is output from the first waveguide, a second output signal is output from the second waveguide, and a third output signal is output from the third waveguide, each of which has a corresponding intensity based on the corresponding interference between the first beam splitter and the second beam splitter; A set of photodetectors, the set of photodetectors being positioned to receive the first output signal, the second output signal and the third output signal; and A controller configured to monitor the wavelength of the light received by the beam splitter using the intensities of the first output signal, the second output signal, and the third output signal, wherein: The first waveguide, the second waveguide, and the third waveguide have constant widths in the coupling region; and In the coupling region, the second waveguide is wider than the first waveguide and the third waveguide.

6. The optical system according to claim 5, wherein: The controller includes the set of photodetectors; The set of photodetectors converts the first output signal, the second output signal, and the third output signal into a first digital output signal, a second digital output signal, and a third digital output signal; The controller compares the first digital output signal, the second digital output signal, and the third digital output signal with the first target digital value, the second target digital value, and the third target digital value; and The controller sends a feedback signal to the light source to control the first output signal, the second output signal, and the third output signal to be at the first target digital value, the second target digital value, and the third target digital value, respectively.

7. The optical system according to claim 5, further comprising: A phase extraction block receives the first output signal, the second output signal, and the third output signal and extracts the unwound phase signal; Differentiator, the differentiator receiving the unwound phase signal and configured to: Detect the zero point in the unwound phase signal; as well as Generate a differential signal indicating the detected zero point; A set of comparators, the set of comparators being configured to adjust the zero point; and An integrator configured to generate an integrated signal for producing a continuous signal for wavelength locking; A set of photodetectors, the set of photodetectors being operable to: Receive the first output signal, the second output signal, and the third output signal; as well as The corresponding sinusoidal signal of each of the first output signal, the second output signal, and the third output signal is transmitted to the phase extraction block; A first adder is used to sum the first output signal, the second output signal, and the third output signal from the set of comparators; and A second adder is used to sum the integral signal and the differential signal to generate a sum signal, which is used to determine the per-wavelength phase shift used to lock the measured light wavelength to the corresponding target light wavelength.

8. The optical system of claim 7, wherein the integral signal is a correction value used to generate a one-to-one relationship between a specific wavelength of the first and second beams and the sum signal.

9. The optical system according to claim 7, wherein: The set of comparators includes: Negative transition comparator; and Positive transition comparator; The negative jump comparator adds two πs to the differential signal; The positive jump comparator subtracts two πs from the differential signal; and The optical system further includes a second adder configured to sum the integral signal and the differential signal to generate a sum signal containing information for sequentially locking each measured light wavelength across a wavelength range of approximately one micrometer.

10. The optical system according to claim 5, wherein: The first output signal has a first sinusoidal wavelength response with a first phase shift; The second output signal has a second sinusoidal wavelength response with a second phase shift; The third output signal has a third sinusoidal wavelength response with a third phase shift; and The first phase shift, the second phase shift, and the third phase shift are constant within a wavelength range of approximately one micrometer.

11. The optical system of claim 5, wherein the first output signal, the second output signal, and the third output signal are offset from each other by the same phase difference.

12. The optical system of claim 5, wherein the phase shifts of the first output signal, the second output signal, and the third output signal are constant over a wavelength range of approximately one micrometer.

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