Wavelength controller and system for tunable laser

Abstract

The present invention relates to a wavelength controller (100) for a tunable laser (10). A wavelength controller (100) is configured to receive an input signal and, in response thereto, generate a control signal for tuning a wavelength of the laser. The wavelength controller (100) is configured to receive at least a portion of an output of the laser (10) as an input signal. The wavelength controller (100) includes an interferometer-based circuit (110) configured to generate a phase shifted intensity value based on an input signal. The wavelength controller (100) comprises a vector-based signal synthesizer (120) configured to generate a complex vector-based signal based on the phase-shifted intensity values and to calculate a quantity of at least one vector representation based on the complex vector-based signal. The quantity represented by the one or more vectors is substantially linearly correlated to the wavelength. The wavelength controller (100) includes a control signal generator (130) configured to generate a control signal based at least in part on a quantity represented by the at least one vector.

Description

Technical Field

[0001] This specification relates to wavelength controllers for tunable lasers, and laser systems that include wavelength controllers and tunable lasers. Background Technology

[0002] Wavelength controllers and wavelength lockouts (WLLs) are indispensable components in optical communications, especially in stabilizing the wavelength output of lasers. Essentially, wavelength lockouts are used to ensure the precision of optical communication systems and to guarantee the accuracy and consistency of laser performance, for example, enabling efficient communication systems.

[0003] Current optical transceivers, typically used in high-speed fiber optic communications such as telecommunications and data centers, integrate all necessary components onto a single chip. These components include lasers and modulators, amplifiers, and detectors. For telecommunications applications such as dense wavelength division multiplexing (DWDM), there are stringent requirements for laser wavelength / frequency stability to avoid inter-channel crosstalk. For example, coherent transmission in ITU G.698.2 requires laser frequency stability below 1.8 GHz.

[0004] In existing technologies, multimode interference (MMI) devices are used to separate and combine optical signals in configurations such as 1×2 MMI, 2×2 MMI, and 4×4 MMI. The input signal can be split into two output signals, for example, and phase-shifted by a 90° phase shifter. A photodiode (PD) is used to convert the optical signal into an electrical signal. Signal processing typically involves using the outputs individually and selectively, or determining the type of response by summing the output signals.

[0005] Optical transceivers have traditionally implemented laser wavelength locking off-chip, and while wavelength locking technology has advanced, the trend is toward on-chip wavelength locking for further monolithic integration. However, miniaturization does not allow for compromises in functionality or performance, necessitating new and improved wavelength lockers. Summary of the Invention

[0006] The overall objective is to provide an improved wavelength controller for tunable lasers, and a corresponding laser system incorporating such a wavelength controller.

[0007] Here, the wavelength controller is sometimes referred to as a wavelength lockout (WLL).

[0008] One specific object of this specification is to provide a WLL, preferably on-chip, for arbitrary wavelength locking, i.e., locking a laser to any desired wavelength with minimal recalibration effort, to provide improved operational flexibility.

[0009] Another specific objective is to provide a high-precision and wide-range WLL with an integrated laser, featuring a compact size and an easy assembly process achieved through wire bonding, which does not require optical alignment.

[0010] Another objective is to provide a resource-efficient wavelength controller designed to reduce the amount of resources required, such as the number of photodiodes, thereby contributing to cost-effectiveness and sustainability.

[0011] The invention as defined in the independent claims satisfies at least some of these and other objectives in at least part. Preferred exemplary embodiments are set forth in the dependent claims.

[0012] According to one aspect, a wavelength controller for a tunable laser is provided, wherein the wavelength controller is configured to receive an input signal and, in response thereto, generate a control signal for tuning the wavelength of the tunable laser, and wherein the wavelength controller comprises: a jammer-based circuit configured to generate a phase-shifted intensity value based on the input signal; a vector-based signal synthesizer configured to generate a complex vector-based signal based on the phase-shifted intensity value and to calculate at least one vector-represented quantity based on the complex vector-based signal, wherein the at least one vector-represented quantity is substantially linearly related to the wavelength; and a control signal generator configured to generate the control signal at least partially based on the at least one vector-represented quantity.

[0013] Therefore, high-performance wavelength controllers and / or laser systems are provided.

[0014] For example, improved wavelength control accuracy can be provided. In particular, the fundamentally linear correlation between the quantity and wavelength, as shown in at least one example, enables the wavelength controller to precisely lock the tunable laser for a wider range of wavelengths.

[0015] The increased precision of wavelength controllers leads to improved performance in optical or laser systems that use them (e.g., wavelength lockers). This results in clearer and more reliable signal transmission.

[0016] Furthermore, because wavelength controllers can accurately lock onto more wavelengths, they offer improved performance and / or capacity, allowing for the transmission of more data. This results in increased efficiency, meaning that systems or wavelength lockers incorporating wavelength controllers are more effective for high-speed data transmission applications.

[0017] Furthermore, precise wavelength locking helps reduce interference between different wavelengths. Therefore, signal degradation and information loss can be reduced, ensuring that transmitted data is received completely at the other end.

[0018] The wavelength controller is also capable of handling any phase shift in the intensity value. Specifically, the phase shift can be any non-zero angle that is strictly greater than -180 degrees and strictly less than +180 degrees. This provides greater flexibility in managing different signal conditions and enhanced robustness of the wavelength controller, such as for variations in signal properties.

[0019] Furthermore, it should be understood that a quantity represented by one or more vectors can be regarded as a characteristic defined by a vector.

[0020] In the context of this specification, the meaning of "substantially linearly related" to two variables or quantities can imply a high degree of linearity between said variables or quantities. However, it does not necessarily imply a perfect linear relationship. When data is plotted on a graph, there may be some deviation from a perfect straight line. The term "substantially" is used to describe these minor variations that do not substantially affect the overall linear correlation between the variables. Therefore, it should be understood that the term is clearly and explicitly defined in accordance with the specific context provided in the specification, claims, and drawings of the patent application.

[0021] Alternatively, the quantity represented by the at least one vector may be linearly related to the wavelength. Therefore, any change in the wavelength will cause a direct, proportional change in the quantity represented by the vector, without any deviation.

[0022] According to an exemplary embodiment, the quantity represented by the at least one vector may include the angle and / or amplitude of a signal based on a complex vector. The angle and amplitude may also be referred to as the phase and amplitude / intensity of the complex signal, respectively. In other words, in a wavelength controller, wavelength information can be converted into parameter values ​​such as intensity or angle.

[0023] According to another exemplary embodiment, the control signal generator can be configured to perform control signal calculations based on at least one vector-represented quantity. In other words, the control signal generator can be designed to perform calculations for generating control signals, where at least one quantity representing a vector is used in these calculations. Essentially, the control signal generator can calculate control signals using vector-represented quantities as input.

[0024] According to yet another exemplary embodiment, the circuitry based on the interference device may include a phase shifter for providing a phase shift when generating a phase-shifted intensity value. The phase shifter may be a thermal phase shifter, which can be configured to induce a thermal phase shift. A thermal phase shifter may, for example, be a heater-based unipolar-to-bipolar converter.

[0025] Including a phase shifter in a jammer-based circuit enhances control over the jamming pattern generated by the jammer. By adjusting the phase shift, the circuit can manipulate the resulting jamming pattern.

[0026] Therefore, by controlling the phase shift, digital locking to any wavelength can be provided. In other words, a wavelength controller can provide the ability to easily adjust and lock to any desired wavelength using a phase shifter through digital control (e.g., increasing the heat of a heater).

[0027] According to another exemplary embodiment, the circuit based on the jammer may include at least two different waveguides with different free spectral ranges (FSRs), including a first waveguide having a first FSR and a second waveguide having a second FSR, wherein the second FSR is greater than the first FSR, to achieve higher wavelength resolution for the signal passing through the first waveguide and a larger wavelength correction range for the signal passing through the second waveguide.

[0028] In other words, a jammer-based circuit can include at least two different waveguides, each with a different FSR. The difference in FSR allows for higher wavelength resolution of the signal passing through the first waveguide and a wider wavelength correction range for the signal passing through the second waveguide.

[0029] The combination of high resolution and a large correction range makes interference-based circuits more robust. For example, to improve accuracy (or wavelength resolution), a small FSR is needed. However, the wavelength correction range is within a period (2π), so when the wavelength shifts beyond the FSR, the calculated vector-based quantities may overlap, and these values ​​may become indistinguishable. Therefore, to achieve both high accuracy and a large range, two FSRs can be implemented (a small FSR for high accuracy and a larger FSR for a large locking range). In other words, by designing an integrated small and large FSR structure, the wavelength controller can simultaneously achieve high frequency accuracy / resolution and a large correction range.

[0030] According to yet another exemplary embodiment, the wavelength controller may further include an optical input switch for selectively feeding one of at least two different signals as an input signal to the wavelength controller.

[0031] Because a wavelength controller can act as a wavelength meter (capable of measuring a single wavelength at a time, typically with high precision), it can enable optical switching, allowing for efficient comparison of two wavelengths.

[0032] Optionally or additionally, the optical switch can be integrated into the jammer-based circuitry.

[0033] According to an exemplary embodiment, at least two different signals may include the emitted (Tx) laser signal and the received (Rx) laser signal.

[0034] Therefore, in conjunction with the optical switch, the optical switch can enable the selection of the Rx wavelength or Tx wavelength to be measured (where the typical suppression of the optical switch can be approximately -20 dB to -30 dB).

[0035] In one example, the control signal calculation (performed by the control signal generator) may include comparing the laser wavelength (Tx) with the wavelength from another (Rx) source. Wavelength switching can be implemented such that a vector representation of Rx can be measured first, then a vector representation of Tx can be measured, and finally compared, wherein, if necessary, the laser wavelength of Tx can be adjusted to match the wavelength of Rx.

[0036] According to another exemplary embodiment, the wavelength controller can be configured to provide time-interleaved tracking of the emitted (Tx) laser signal and the received (Rx) laser signal. In other words, if Tx and Rx are simultaneously fed into a single wavelength measurement structure, the wavelengths of Rx and Tx will be indistinguishable and cannot be measured; therefore, the wavelengths can instead be measured sequentially, i.e., time-interleaved.

[0037] Therefore, time-interleaved tracking of the emitted (Tx) and received (Rx) laser signals allows for the sharing of the same optical detection unit, thus reducing complexity and cost because separate detection units for the Tx and Rx signals are not required. For example, the total number of PDs and / or other components can be halved.

[0038] According to an exemplary embodiment, the wavelength controller can be configured to provide time-interleaved tracking, thereby enabling the reduction of the wavelength difference between the received (Rx) laser signal and the local oscillator signal (LO) and / or the maintenance of the emitted laser signal's stability.

[0039] In other words, the wavelength difference between the received laser signal (Rx) and the local oscillator signal (LO) can be reduced, and the transmitted signal (Tx) can remain stable. Therefore, a near-coherent receiver can be provided so that the Rx signal and the Tx local oscillator are at essentially the same wavelength, thereby coherently amplifying that wavelength.

[0040] Therefore, by reducing the wavelength difference between the received (Rx) and local oscillator (LO) signals, the wavelength controller can reduce potential interference and signal degradation, resulting in a clearer and more reliable signal. Furthermore, by maintaining the stability of the transmitted signal (Tx), the consistent performance of the wavelength controller can be ensured. This is particularly advantageous for applications requiring high precision and reliability, such as telecommunications or data centers. Additionally, time-interleaved tracking allows for more efficient use of available bandwidth, as the signal can be more accurately targeted at a specific wavelength.

[0041] The local oscillator can be tuned, meaning it can include a wavelength-tunable laser. Depending on the accuracy of the RX signal, the local oscillator (i.e., the Tx laser) may require tuning, for example, in the range of approximately tens to hundreds of GHz. This tuning can be accomplished, for example, through external cavity tuning, thermal tuning, and / or current injection tuning.

[0042] According to another exemplary embodiment, the interference-based circuit may include: a first signal distributor configured to split an input signal into two distinct signal paths, a first signal path and a second signal path; a second signal distributor in the first signal path configured to split the signal of the first signal path into two parts having the same phase; a third signal distributor in the second signal path configured to split the signal of the second signal path into two parts having different phases to provide a non-zero relative phase shift; two signal combiners, each configured to perform signal combining based on the output of the second signal distributor and the corresponding output of the third signal distributor to provide a combined signal respectively; and two detectors, each configured to detect the intensity value of the combined signal of the corresponding signal combiner, wherein the intensity values ​​of the two detectors are phase-shifted relative to each other and are provided as input to a vector-based signal synthesizer.

[0043] In other words, only two detectors (e.g., single-ended photodetectors) may be required. Therefore, fewer resources are needed, and a smaller footprint can be provided, which also reduces the technical difficulty.

[0044] According to a specific exemplary embodiment, the first signal distributor may be based on a 1×2 multimode jammer (MMI), the second signal distributor may be based on a 1×2 MMI, the third signal distributor may be based on a 2×2 MMI, and each signal combiner may be based on a 2×1 MMI, while each detection unit may be based on a photodetector.

[0045] MMIs such as 1×2 and 2×2 MMIs can be considered simple divergent elements and, compared to other MMIs, can have smaller size and smaller component phase errors, resulting in more compact and efficient designs. Furthermore, 1×2 and 2×2 MMIs can provide wider bandwidths than larger MMIs.

[0046] As described above, the wavelength controller is capable of handling any phase shift in intensity value. Specifically, the phase shift can be any non-zero angle that is strictly greater than -180 degrees and strictly less than +180 degrees. According to a particular exemplary embodiment, the relative phase shift can be between 60 degrees and 120 degrees. This provides good performance, for example, in terms of signal-to-noise ratio (SNR). The relative phase shift can be, for example, close to 90 degrees.

[0047] According to an exemplary embodiment, a phase-shift-based unipolar to bipolar converter can be incorporated into a first signal path or a second signal path to provide a thermal phase shift when generating a phase shift intensity value.

[0048] Thermal phase shifters (such as phase-shift-based unipolar to bipolar converters) can provide efficient phase transitions. Furthermore, they can offer a smaller on-chip size compared to other phase shifters (such as PN junctions).

[0049] According to an exemplary embodiment, the wavelength controller can be configured to tune the wavelength to a limited wavelength range.

[0050] According to an exemplary embodiment, the wavelength controller may be a wavelength lockout (WLL).

[0051] According to an exemplary embodiment, the wavelength controller can be integrated onto the same integrated circuit as the laser. This provides a reduced component size and ease of manufacture.

[0052] According to an exemplary embodiment, the wavelength controller can be configured to receive at least a portion of the output of the tunable laser as the input signal, or configured to receive at least a portion of the received laser signal as the input signal. Therefore, improved flexibility and capability for processing different types of input signals are provided.

[0053] The output portion of the tunable laser (or local oscillator) received by the wavelength controller can, for example, be between 0.1% and 10%. This flexibility in light output allows for adaptation to different electronics and photodiode sensitivities. For example, switching the LO light from 0.1% to 10% can result in a two-order-of-magnitude increase in the power measurement of the photodiode. At least a portion of this output can be, for example, on an order of magnitude, providing sufficient light for suitable measurements while preventing the photodiode from saturating due to excessive light.

[0054] According to another aspect, a laser system is provided, including a tunable laser and a wavelength controller according to any one of the preceding claims.

[0055] For example, a laser system can be viewed as a wavelength locker, especially when considered as a closed loop. In other words, a wavelength locker can include a tunable laser and a wavelength controller.

[0056] This aspect can usually present the same or corresponding advantages as the previous aspect. Attached Figure Description

[0057] The foregoing contents, additional objects, features, and advantages of this specification will be better understood through the following illustrative and non-limiting detailed description with reference to the accompanying drawings. Unless otherwise stated, the same reference numerals will be used for the same elements in the drawings.

[0058] Figure 1 This is a schematic diagram illustrating an overview of a laser system having a tunable laser and an associated wavelength controller according to one embodiment.

[0059] Figure 2 This is a schematic diagram illustrating an example of a jammer-based circuit according to one embodiment.

[0060] Figure 3 This is a schematic diagram illustrating another example of a jammer-based circuit according to one embodiment.

[0061] Figure 4 This is a schematic diagram illustrating a specific example of a jammer-based circuit according to one embodiment.

[0062] Figure 5 This is a schematic diagram illustrating an example of a wavelength controller according to one embodiment.

[0063] Figure 6 This is a schematic diagram illustrating an example of a laser system according to one embodiment.

[0064] Figure 7 This is a schematic diagram illustrating an example of a laser system according to one embodiment.

[0065] Figure 8A This is a schematic diagram illustrating an example of a jammer-based circuit according to one embodiment.

[0066] Figure 8B This is a schematic diagram illustrating an example of the angle-wavelength relationship between a waveguide with a smaller FSR and a waveguide with a relatively larger FSR.

[0067] Figure 8C This is a schematic diagram illustrating an example of the wavelength correction range for a given FSR.

[0068] Figure 8D This is a schematic diagram illustrating an example of how to combine two different FSRs to provide a relatively large correction range (large FSR) while maintaining the desired accuracy (small FSR).

[0069] Figure 9 This is a schematic diagram illustrating another example of a jammer-based circuit according to one embodiment.

[0070] Figure 10 This is a schematic diagram illustrating yet another example of a jammer-based circuit according to one embodiment.

[0071] Figure 11AThis is a schematic diagram illustrating an example of the frequency response of the output of a photodetector based on a jammer circuit according to one embodiment.

[0072] Figure 11B It shows the corresponding Figure 11A A schematic diagram of the intensity-frequency curve of the photodetector.

[0073] Figure 11C This indicates that when vector composition has been performed, it corresponds to Figure 11B A schematic diagram of the basic linear angle-frequency curve.

[0074] Figure 12 This is a schematic diagram illustrating how an intensity-frequency curve of wavelength shift can be introduced by applying a specific voltage to a phase shifter. Detailed Implementation

[0075] The proposed technology will now be described with reference to various exemplary embodiments.

[0076] As previously mentioned, the proposed technology relates to wavelength controllers for tunable lasers and corresponding laser systems.

[0077] Figure 1 This is a schematic diagram illustrating an overview of a laser system 1000 having a tunable laser 10 and an associated wavelength controller 100 according to one embodiment.

[0078] Wavelength controller 100 is configured to receive an input signal and, in response, generate a control signal for tuning the wavelength of the tunable laser. In this particular example, wavelength controller 100 is configured to receive at least a portion of the output of laser 10 as an input signal.

[0079] Wavelength controller 100 includes interference-based circuitry 110 configured to generate phase shift intensity values ​​based on an input signal. Wavelength controller 100 also includes a vector-based signal synthesizer 120 configured to generate a complex vector-based signal based on the phase shift intensity values ​​and to calculate at least one vector-represented quantity based on the complex vector-based signal. The one or more vector-represented quantities are substantially linearly related to the wavelength. Wavelength controller 100 also includes a control signal generator 130 configured to generate a control signal at least partially based on the at least one vector-represented quantity.

[0080] Therefore, high-performance wavelength controllers and / or laser systems are provided. For example, compared to conventional solutions, improved laser stability control with high precision is achieved for all or at least a large range of wavelengths.

[0081] Specifically, the wavelength controller may include a wavelength-sensitive element that can convert the wavelength into, for example, a phase, and the phase information can be used for laser stability control, where it is understood that wavelength locking can be achieved without any active optical control mechanism, such as active optical phase shifting.

[0082] For example, the wavelength controller can be integrated onto the same integrated circuit as the laser, such as a photonic integrated circuit (PIC).

[0083] In other words, a wavelength controller suitable for integrated WLLs is provided, which can create linear wavelength feedback for laser stability control, where all wavelengths have the same high precision. Linear wavelength feedback can be created, for example, by constructing a complex vector-based signal (R+j*Q) using two (cost-effective and / or low-speed) photodiodes and associated photonic circuitry.

[0084] After initialization / calibration, the tunable laser can be locked to any position within a wide wavelength spectrum. The wide spectrum can include, but is not limited to, the C-band and L-band, where the C-band (conventional band) ranges from 1530 nm to 1565 nm, and the L-band (long wavelength band) ranges from 1565 nm to 1625 nm.

[0085] In this article, the term "lock-in" refers to the ability of a laser to maintain a stable output at a specific wavelength.

[0086] Furthermore, it should be understood that the quantities represented by the one or more vectors can be regarded as properties of the vector definition.

[0087] In the context of this specification, the meaning of "substantially linearly related" to two variables or quantities can imply a high degree of linearity between said variables or quantities. However, it does not necessarily imply a perfect linear relationship. When the data is plotted on a graph, it may deviate to some extent from a perfect straight line. The term "substantially" is used to account for these minor variations that do not substantially affect the overall linear correlation between the variables. Therefore, it should be understood that the term is clearly and explicitly defined in accordance with the specific context provided in the specification, claims, and drawings of the patent application.

[0088] Alternatively, at least one vector representation of a quantity can be linearly related to the wavelength. Therefore, any change in the wavelength will cause the quantity represented by the vector to change directly and proportionally, without any deviation.

[0089] According to an exemplary embodiment, at least one vector-represented quantity may include the angle and / or amplitude of a signal based on a complex vector. The angle and amplitude may also be referred to as the phase and amplitude / intensity of the complex signal, respectively. In other words, in a wavelength controller, wavelength information can be converted into parameter values ​​such as intensity or angle.

[0090] As described above, linear wavelength feedback can be created by constructing a complex vector-based signal (R+j*Q) (e.g., using two photodiodes and associated photonic circuitry). Therefore, for a given wavelength, the intensities of the two photodiodes can be used as parts of the real (Re) and imaginary (Im) parts of the complex vector-based signal, respectively. See also... Figure 11A -C, which will be described in more detail later. The synthesized complex value can be constructed as (Re–Calibration_average) + j*(Im–Calibration_average), where Calibration_average is the average value that can be calculated in WLL calibration. Therefore, two-signal vector synthesis can be used, meaning two signals can be combined to create a complex output. The angle of the complex vector-based signal can be calculated by iterating through different wavelengths, thus obtaining a linear angle-wavelength curve. Either the angle or the amplitude of the complex vector-based signal can be linearly related to the wavelength.

[0091] Therefore, due to the linear correlation between angle (and / or amplitude) and wavelength, a wavelength controller with the same resolution is provided for any wavelength of the tunable laser. Furthermore, linearity provides the ability to lock onto any wavelength within the operating range of the tunable laser without dead-locked ranges (i.e., no dead zones or ranges where the wavelength controller cannot lock onto a particular wavelength).

[0092] Compared to conventional circuit designs, the proposed circuit design discussed in this paper offers additional advantages such as smaller footprint, smaller component phase errors, simpler on-chip components, improved manufacturing tolerances, and easier phase error compensation.

[0093] According to another exemplary embodiment, the control signal generator can be configured to perform control signal calculations based on the at least one vector-represented quantity. In other words, the control signal generator can be designed to perform calculations for generating control signals, whereby at least one quantity representing a vector is used in these calculations. Essentially, the control signal generator can calculate control signals using the vector-represented quantity as input.

[0094] Control signal calculations can be incremental value calculations. For example, for a given wavelength, there may be a corresponding value (e.g., angle) for the quantity represented by the vector, and as the wavelength shifts, another value for the quantity represented by the vector can be obtained. Therefore, the calculated incremental value can be the difference (e.g., absolute difference) between the values ​​of the quantities represented by the vectors of two different wavelengths. In other words, if only the wavelength of the laser itself is measured, the incremental value can be calculated by comparing the quantity represented by the vector at the measured wavelength with the quantity represented by the vector at a previously measured wavelength.

[0095] This increment can also be used as feedback information to tune, control, and / or lock the wavelength of the laser. However, the increment can be further used, for example, to calculate an incremental signal that varies over time for further signal processing involving any widely accepted control program, such as proportional-integral-derivative (PID) regulation.

[0096] According to yet another exemplary embodiment, the circuitry based on the interference device may include a phase shifter for providing a phase shift when generating a phase-shifted intensity value. For example, the phase shifter may be a thermal phase shifter, which can be configured to induce a thermal phase shift. A thermal phase shifter may, for example, be a heater-based unipolar-to-bipolar converter.

[0097] Including a phase shifter in the jammer-based circuit enhances control over the jamming pattern generated by the jammer. By adjusting the phase shift, the circuit can manipulate the resulting jamming pattern.

[0098] Therefore, by controlling the phase shift, digital locking to any wavelength can be provided. In other words, a wavelength controller can provide the ability to easily adjust and lock to any desired wavelength using a phase shifter through digital control (e.g., increasing the heat of a heater).

[0099] In a thermal phase shifter, the metal (i.e., the heater) can be supplied with different voltages / currents, causing the metal to heat its waveguide to change the waveguide index and thus alter the phase of the light. See, for example... Figure 12 .

[0100] Figure 12 This is a schematic diagram of the intensity-frequency curve, illustrating how a wavelength shift can be introduced by applying a specific voltage to a phase shifter. Therefore, different wavelength shifts can be achieved by applying different voltages.

[0101] For example, during calibration, the maximum power can be retrieved via a tuning phase shifter. Figure 12A fixed laser (i.e., no wavelength variation) is obtained by measuring the peak power (peak power) and minimum power (peak-to-bottom power) of the sine wave. Furthermore, in operating mode, the average of the maximum and minimum power can be used to convert the unipolar photodiode current into a bipolar signal. Therefore, the average intensity of the maximum and minimum power detected for unipolar-to-bipolar conversion can be obtained.

[0102] Furthermore, thermal phase shifters (on-chip) can efficiently change the phase with low insertion loss, for example, tuning up to 22 kHz. However, for high-speed tuning (e.g., above 1 MHz), non-thermal phase shifters (e.g., stress optical phase shifters and / or electro-optic phase shifters) can be used to provide the phase shift.

[0103] Figure 2 This is a schematic diagram illustrating an example of a jammer-based circuit according to one embodiment.

[0104] exist Figure 2 In the example, the jammer-based circuitry includes a first signal distributor 112 configured to split an input signal into two distinct signal paths, a first signal path 115-1 and a second signal path 115-2; a second signal distributor 114 in the first signal path configured to split the signal of the first signal path into two parts having the same phase; a third signal distributor 116 in the second signal path configured to split the signal of the second signal path into two parts having different phases to provide a non-zero relative phase shift; two signal combiners 117-1 and 117-2, each configured to perform signal combining based on the output of the second signal distributor 114 and the corresponding output of the third signal distributor 116 to provide combined signals respectively; and two detectors 118-1 and 118-2, each configured to detect the intensity value of the combined signal from the corresponding signal combiner 117-1 and 117-2, wherein the intensity values ​​of the two detectors 118-1 and 118-2 have a phase shift relative to each other and are provided as input to a vector-based signal synthesizer. Figure 2 (Not shown in the image).

[0105] In other words, only two detectors (e.g., single-ended photodetectors) may be required. Therefore, fewer resources are needed, and a smaller footprint can be provided, which also reduces the technical difficulty.

[0106] Figure 3 This is a schematic diagram illustrating another example of a jammer-based circuit according to one embodiment.

[0107] Figure 3 Examples are similar to Figure 2The example includes a phase shifter 111 in the second signal path 115-2, which provides a phase shift when generating a phase shift intensity value. As previously mentioned, the phase shifter can be a thermal phase shifter, which can be configured to cause a thermal phase shift. A thermal phase shifter can, for example, be a heater-based unipolar-to-bipolar converter. It should be understood that the phase shifter can be incorporated into either the first signal path 115-1 or the second signal path 115-2 to provide a thermal phase shift when generating a phase shift intensity value.

[0108] Phase shifter 111 allows phase control by changing the optical path length. Interference occurs when light is recombined, such as in a combiner like 117-2. This interference depends on the extra time the light spends in the signal path, especially... Figure 3 The second signal path 115-2 in the diagram. The change in optical path length can be, for example, approximately 1 μm (or a maximum of 1 μm). Therefore, time shift can be equated to phase shift.

[0109] Figure 4 This is a schematic diagram illustrating a specific example of a jammer-based circuit according to one embodiment. In this example, a first signal distributor 112 is based on a 1×2 multimode jammer (MMI), a second signal distributor 114 is based on a 1×2 MMI, and a third signal distributor 116 is based on a 2×2 MMI, while each signal combiner 117-1, 117-2 is based on a 2×1 MMI, and each detection unit 118-1, 118-2 is based on a photodetector (PD).

[0110] also, Figure 4 A phase shifter 111 is optionally included in the second signal path 115-2.

[0111] Figure 5 This is a schematic diagram illustrating an example of a wavelength controller according to one embodiment.

[0112] In this example, the wavelength controller may further include an optical input switch 90 for selectively feeding one of at least two different signals as an input signal to the wavelength controller 100.

[0113] Because the wavelength controller can act as a wavelength meter (capable of measuring a single wavelength at a time, typically with high precision), the optical switch can be implemented, allowing for efficient comparison of two wavelengths.

[0114] Optionally or additionally, the optical switch can be integrated into the jammer-based circuitry, such as... Figure 5 The dashed line in the middle is used for illustration.

[0115] According to an exemplary embodiment, at least two different signals may include the emitted (Tx) laser signal and the received (Rx) laser signal.

[0116] Therefore, in conjunction with the optical switch, the optical switch can enable the selection of the Rx wavelength or Tx wavelength to be measured (where the typical suppression of the optical switch can be approximately -20 dB to -30 dB).

[0117] In one example, the control signal calculation (performed by the control signal generator) could involve comparing the laser wavelength (Tx) with the wavelength from another (Rx) source. Wavelength switching can be implemented such that a vector representation of Rx can be measured first, then a vector representation of Tx can be measured, and finally compared, where the laser wavelength of Tx can be adjusted to match the wavelength of Rx if needed.

[0118] According to another exemplary embodiment, the wavelength controller can be configured to provide time-interleaved tracking of the emitted (Tx) laser signal and the received (Rx) laser signal. In other words, if Tx and Rx are simultaneously fed into a single wavelength measurement structure, the wavelengths of Rx and Tx will be indistinguishable and cannot be measured; therefore, the wavelengths can instead be measured sequentially, i.e., time-interleaved.

[0119] Therefore, time-interleaved tracking of the emitted (Tx) and received (Rx) laser signals allows for the sharing of the same optical detection unit, thus reducing complexity and cost because separate detection units for the Tx and Rx signals are not required. For example, the total number of PDs and / or other components can be halved.

[0120] According to an exemplary embodiment, the wavelength controller can be configured to provide time-interleaved tracking, thereby enabling the reduction of the wavelength difference between the received (Rx) laser signal and the local oscillator signal (LO) and / or the maintenance of the emitted laser signal's stability.

[0121] In other words, the wavelength difference between the received laser signal (Rx) and the local oscillator signal (LO) can be reduced, and the transmitted signal (Tx) can remain stable. Therefore, a near-coherent receiver can be provided so that the Rx signal and the Tx local oscillator are at essentially the same wavelength, thereby coherently amplifying that wavelength.

[0122] Therefore, by reducing the wavelength difference between the received (Rx) and local oscillator (LO) signals, the wavelength controller can reduce potential interference and signal degradation, resulting in a clearer and more reliable signal. Furthermore, by maintaining the stability of the transmitted signal (Tx), the consistent performance of the wavelength controller can be ensured. This is particularly advantageous for applications requiring high precision and reliability, such as telecommunications or data centers. Additionally, time-interleaved tracking allows for more efficient use of available bandwidth, as the signal can be more accurately targeted at a specific wavelength.

[0123] The local oscillator can be tuned, meaning it can include a wavelength-tunable laser. Depending on the accuracy of the RX signal, the local oscillator (i.e., the Tx laser) may require tuning, for example, in the range of approximately tens to hundreds of GHz. This tuning can be accomplished, for example, through external cavity tuning, thermal tuning, and / or current injection tuning.

[0124] Figure 6 This is a schematic diagram illustrating an example of a laser system according to one embodiment. In this example, a laser is used as a local oscillator (LO) 70, and a splitter 80 is configured to divide a small portion of the laser output into separate branches for LO feedback into an optical input switch 90. This provides the possibility of matching the LO and RX, and the wavelength of the TX wavelength of the laser 70 can also be changed or adjusted.

[0125] Figure 7 This is a schematic diagram illustrating an example of a laser system according to one embodiment. In this example, two independent lasers can be used: a stable emission (Tx) laser 10 (without any feedback to / from the wavelength controller 100) and a local oscillator (LO) 70, which is essentially an independent laser that can be tuned using the wavelength controller 100. For example, it is possible to measure the output of the local oscillator 70 and adjust the LO wavelength to match (or at least be relatively close to) the Rx wavelength of the received signal.

[0126] According to another exemplary embodiment, the circuit based on the jammer may include at least two different waveguides with different free spectral ranges (FSRs), including a first waveguide having a first FSR and a second waveguide having a second FSR, wherein the second FSR is greater than the first FSR, to achieve higher wavelength resolution for the signal passing through the first waveguide and a larger wavelength correction range for the signal passing through the second waveguide.

[0127] In other words, a jammer-based circuit can include at least two different waveguides, each with a specific FSR. The difference in the FSRs allows for higher wavelength resolution of the signal passing through the first waveguide and a wider wavelength correction range for the signal passing through the second waveguide.

[0128] The combination of high resolution and a large correction range makes interference-based circuits more robust. For example, to improve accuracy (or wavelength resolution), a small FSR is needed. However, the wavelength correction range is typically within a period (2π), so when the wavelength shifts beyond the FSR, the calculated vector-based quantities may overlap, and these values ​​may become indistinguishable. Therefore, to achieve both high accuracy and a large range, two FSRs can be implemented (a small FSR for high accuracy and a larger FSR for a large locking range). In other words, by designing an integrated small and large FSR structure, the wavelength controller can achieve high frequency accuracy / resolution and a large correction range.

[0129] Figure 8A This is a schematic diagram illustrating an example of a jammer-based circuit according to one embodiment. Figure 8A In the example, Figure 2-4 A portion of the basic jamming circuit was copied and integrated for use with different waveguides. From Figure 8A As can be seen in the example, the jammer-based circuit 110 also includes two additional signal distributors 113-1, 113-2, another signal distributor 114-2 and another signal distributor 116-2, as well as two additional signal combiners 117-3, 117-4 and two additional detectors 118-3, 118-4.

[0130] Basically, the second signal path 115-2 includes an additional distributor 113-2 arranged upstream of the signal distributors 116-1 and 116-2 for splitting the signal of the second signal path 115-2 into a first waveguide 119-1 (corresponding to signal path 115-2A) having a first FSR and a second waveguide 119-2 (corresponding to signal path 115-2B) having a second FSR, wherein the second FSR is greater than the first FSR, to achieve higher wavelength resolution for the signal passing through the first waveguide 119-1 and a larger wavelength correction range for the signal passing through the second waveguide 119-2. Alternatively, the FSR of the first waveguide 119-1 may be greater than the FSR of the second waveguide 119-2.

[0131] However, in Figure 8, the second waveguide 119-2, with a large FSR, is designed to coarsely measure the wavelength, while the first waveguide 119-1, with a small FSR, is responsible for measuring the wavelength with high precision. However, the small FSR does not have a wide range, which means that the absolute wavelength may be unknown.

[0132] For example, in a specific scenario, if the wavelength to be measured is exactly 1550 nm, two interference meters are used: one with a 100 nm FSR and the other with a 1 nm FSR. The interference meter with the 100 nm FSR provides a rough estimate of the wavelength within 1550 ± 0.5 nm. The second interference meter can then precisely determine whether the wavelength falls within the 1550 ± 0.5 nm range, for example, identifying the wavelength as 1550.03 nm. Conversely, if only the second interference meter with the 1 nm FSR is used, it may be impossible to distinguish wavelengths such as 1550.03 nm, 1551.03 nm, and 1552.03 nm. Therefore, by measuring a coarse range, the wavelength can be precisely located. Thus, both coarse and precise wavelength control are provided simultaneously.

[0133] Figure 8B This is a schematic diagram illustrating an example of the angle-wavelength relationship between a waveguide with a smaller FSR and a waveguide with a relatively larger FSR.

[0134] Figure 8C This is a schematic diagram illustrating an example of the wavelength correction range for a given FSR.

[0135] Figure 8D This is a diagram that schematically illustrates an example of how to combine two different FSRs to provide a relatively large correction range (large FSR) while maintaining the desired accuracy (small FSR).

[0136] Figure 9 This is a schematic diagram illustrating another example of a jammer-based circuit according to one embodiment.

[0137] Figure 9 Similar to Figure 8, except that it exists Figure 9 The circuit solution shown includes an additional input switch. To address coherent applications, an alternative design is proposed by introducing an additional optical switch, which allows either the Tx or Rx signal to be fed into the WLL in a time-division multiplexed mode, as previously described. This means that Tx and Rx can share the same WLL structure, and switch 90 can be used to create separate feedback loops to maintain the stability of the Tx laser and maintain a small Rx-LO frequency, respectively. For example, switch 90 could be a Mach-Zehnder (MZ) based switch with an optional internal phase shifter 111 integrated within it.

[0138] Figure 10This is a schematic diagram illustrating yet another example of a jammer-based circuit according to one embodiment. This represents an alternative embodiment that uses an optical switch 80 to implement different waveguides. In this example, the second signal path 115-2 includes an optical switch 80 arranged upstream of the signal distributor 116 for switching between a first waveguide 119-1 having a first free spectral range (FSR) and a second waveguide 119-2 having a second FSR, wherein the second FSR is greater than the first FSR, to achieve higher wavelength resolution of the signal through the first waveguide 119-1 and a larger wavelength correction range of the signal through the second waveguide 119-2. For example, the switch 80 could be an MZ-based switch in which an optional internal phase shifter 111 is integrated.

[0139] Figure 11A This is a schematic diagram illustrating an example of the frequency response of the output of a photodetector based on a jammer circuit according to one embodiment.

[0140] Figure 11B It shows the corresponding Figure 11A A schematic diagram of the intensity-frequency curve of the photodetector.

[0141] Figure 11C This indicates that when vector composition has been performed, it corresponds to Figure 11B A schematic diagram of the basic linear angle-frequency curve.

[0142] For example, for a given wavelength, the intensity value of the photodetector can be determined and used as part of the real (Re) and imaginary (Im) components of the newly constructed complex signal, respectively. This is the composite complex value of (Re-CAL_aver) + j*Im-CAL_aver). Here, CAL_aver is the average value that can be calculated in WLL calibration. The angle of the complex signal is calculated using a frequency sweep / wavelength, such as... Figure 11C As shown, a linear angle-frequency / wavelength curve can be obtained.

[0143] Therefore, two-signal vector synthesis can be used, where two signals can be combined to create a complex output. The angle of the complex vector-based signal can be calculated by iterating through different wavelengths, thus obtaining a linear angle-wavelength curve. Either the angle or the amplitude of the complex vector-based signal can be linearly related to the wavelength.

[0144] Therefore, due to the linear correlation between angle (and / or amplitude) and wavelength, a wavelength controller with the same resolution is provided for any wavelength of the tunable laser. Furthermore, linearity provides the ability to lock onto any wavelength within the operating range of the tunable laser without dead-locked ranges (i.e., no dead zones or ranges where the wavelength controller cannot lock onto a particular wavelength).

[0145] In the foregoing, the inventive concept has been described primarily with reference to a limited number of examples. However, as will be readily understood by those skilled in the art, other examples besides those disclosed above are equally possible within the scope of the inventive concept as defined by the appended claims.

Claims

1. A wavelength controller (100) for a tunable laser (10), in, The wavelength controller (100) is configured to receive an input signal and, in response thereto, generate a control signal for tuning the wavelength of the tunable laser (10), and wherein the wavelength controller (100) includes: The jammer-based circuit (110) is configured to generate a phase shift intensity value based on the input signal; A vector-based signal synthesizer (120) configured to generate a complex vector-based signal based on the phase shift intensity value, and to calculate at least one vector-represented quantity based on the complex vector-based signal, wherein the at least one vector-represented quantity is substantially linearly related to the wavelength; and A control signal generator (130) is configured to generate the control signal at least in part based on the at least one vector representation of the quantity.

2. The wavelength controller (100) according to claim 1, characterized in that, The quantity represented by the at least one vector includes the angle and / or amplitude of the complex vector-based signal.

3. The wavelength controller (100) according to claim 1 or 2, characterized in that, The control signal generator (130) is configured to perform control signal calculations based on the at least one vector representation of the quantity.

4. The wavelength controller (100) according to any one of the preceding claims, characterized in that, The interference-based circuit (110) includes a phase shifter (111) for providing a phase shift when generating the phase shift intensity value.

5. The wavelength controller (100) according to any one of the preceding claims, characterized in that, The interference-based circuit (110) includes at least two different waveguides (119-1, 119-2) with different free spectral ranges (FSRs), including a first waveguide (119-1) with a first FSR and a second waveguide (119-2) with a second FSR, wherein the second FSR is greater than the first FSR, to achieve higher wavelength resolution of the signal passing through the first waveguide (119-1) and a larger wavelength correction range of the signal passing through the second waveguide (119-1).

6. The wavelength controller (100) according to any one of the preceding claims, characterized in that, It also includes an optical input switch (90) for selectively feeding one of at least two different signals as the input signal of the wavelength controller (100).

7. The wavelength controller (100) according to claim 6, characterized in that, The at least two distinct signals include the emitted (Tx) laser signal and the received (Rx) laser signal.

8. The wavelength controller (100) according to claim 7, characterized in that, The wavelength controller (100) is configured to provide time-interleaved tracking of the emitted (Tx) laser signal and the received (Rx) laser signal.

9. The wavelength controller (100) according to claim 8, characterized in that, The wavelength controller (100) is configured to provide the time-interleaved tracking, thereby enabling the reduction of the wavelength difference between the received (Rx) laser signal and the signal of the local oscillator (70) and / or the maintenance of the emitted laser signal's emitted laser stability.

10. The wavelength controller (100) according to any of the preceding claims, characterized in that, The jammer-based circuit (110) includes: A first signal distributor (112) is configured to split the input signal into two different signal paths (115-1, 115-2), a first signal path (115-1) and a second signal path (115-2); In the first signal path (115-1), the second signal distributor (114) is configured to split the signal of the first signal path (115-1) into two parts with the same phase. In the second signal path (115-2), a third signal distributor (116) is configured to split the signal of the second signal path (115-2) into two parts with different phases to provide a non-zero relative phase shift; Two signal combiners (117-1, 117-2), each configured to perform signal combining based on the output of the second signal distributor (114) and the corresponding output of the third signal distributor (116), to provide combined signals respectively; and Two detectors (118-1, 118-2), each detector (118-1, 118-2) is configured to detect the intensity value of the combined signal of the corresponding signal combiner (117-1, 117-2), wherein the intensity values ​​of the two detectors (118-1, 118-2) are phase-shifted relative to each other and are provided as input to the vector-based signal synthesizer (120).

11. The wavelength controller (100) according to claim 10, characterized in that, The first signal distributor (112) is based on a 1×2 multimode jammer (MMI), the second signal distributor (114) is based on a 1×2 MMI, the third signal distributor (116) is based on a 2×2 MMI, each signal combiner (117-1, 117-2) is based on a 2×1 MMI, and each detection unit (118-1, 118-2) is based on a photodetector.

12. The wavelength controller (100) according to claim 10 or 11, characterized in that, The relative phase shift is between 60 and 120 degrees.

13. The wavelength controller (100) according to any one of claims 10 to 12, characterized in that, A phase-shift-based unipolar to bipolar converter (111) is integrated in the first signal path (115-1) or the second signal path (115-2) to provide a thermal phase shift when generating the phase shift intensity value.

14. The wavelength controller (100) according to any one of the preceding claims, characterized in that, The wavelength controller (100) is configured to tune the wavelength to a limited wavelength range.

15. The wavelength controller (100) according to any of the preceding claims, characterized in that, The wavelength controller (100) is a wavelength lockout (WLL).

16. The wavelength controller (100) according to any one of the preceding claims, characterized in that, The wavelength controller (100) and the laser (10) are integrated on the same integrated circuit.

17. The wavelength controller (100) according to any one of the preceding claims, characterized in that, The wavelength controller (100) is configured to receive at least a portion of the output of the tunable laser (10) as the input signal, or is configured to receive at least a portion of the received laser signal as the input signal.

18. A laser system (1000) comprising a tunable laser (10) and a wavelength controller (100) according to any one of the preceding claims.

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