Tunable laser device and wavelength locking method

Abstract

The present invention relates to the technical field of laser device wavelength locking, and particularly relates to a tunable laser device and a wavelength locking method. The tunable laser device comprises a laser device, a first etalon and a second etalon, wherein the first etalon and the second etalon have the same free spectral range (FSR); the peak value of the first etalon is aligned with an ITU wavelength; a wavelength aligned with the peak value of the second etalon has a preset wavelength interval from the ITU wavelength; and within a wavelength locking range of the laser device, the first etalon or the second etalon is alternately used to perform wavelength locking on a laser signal emitted by the laser device, so as to avoid peak value positions or valley value positions of a transmission spectrum of the etalon. Using a first etalon and a second etalon implements the locking of any wavelength of a laser device, thereby preventing the problem of it being impossible to lock a wavelength due to the fact that a wavelength to be locked falling into a region having a smaller etalon slope causes a circuit to be unable to be detected.

Description

A tunable laser and wavelength locking method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from the following patent applications:

[0003] (1) A Chinese patent application entitled “A tunable laser and wavelength locking method” was submitted to the China Patent Office on December 5, 2023, with application number 202311668166.6. Technical Field

[0004] The present invention relates to the technical field of laser wavelength locking, in particular to a tunable laser and a wavelength locking method. Background Art

[0005] The continuous development of high-speed services such as high-definition video, cloud storage, and interactive Internet Protocol Television (IPTV) has led to a rapid increase in Internet Protocol (IP) traffic. Currently, IP traffic accounts for 99% of total backbone network traffic, while peer-to-peer (P2P) traffic, represented by HD video, has exceeded 50%. The rapid development of these services has placed tremendous pressure on network bandwidth. To meet this demand, research on dense wavelength division multiplexing (DWDM), wavelength division multiplexing (WDM), and optical time division multiplexing (OTDM) systems has made rapid progress.

[0006] In DWDM systems, replacing multiple fixed-wavelength lasers with a single tunable laser can effectively reduce system complexity and simplify the system model. Software algorithms can be used to adjust the wavelength instead of hardware changes, making the network layout more flexible. In optical network systems, the wavelength tunability of tunable lasers allows for dynamic configuration of wavelengths on optical routes, which has important applications in dynamic reconfiguration. On the other hand, during the lifecycle of a laser, due to aging, the wavelength can drift by up to 0.15nm. This wavelength drift can cause crosstalk between adjacent channels and lead to system bit errors. It is necessary to find ways to eliminate this wavelength drift caused by laser aging. To eliminate wavelength drift, a solution can be adopted: recalibrating the laser wavelength: using a tunable laser to tune or lock the laser wavelength, so that the laser wavelength can be tuned to a specific wavelength. Tunable lasers generally use etalons or thin-film filters for wavelength calibration. However, the wavelength of etalons or thin-film filters is sensitive to temperature, so a semiconductor electric cooler (TEC) is generally required to control the temperature of the etalon or thin-film filter to achieve wavelength calibration stability.

[0007] In order to achieve more flexible wavelength selection, wavelength spacing channels or expand the application range of tunable lasers, it is necessary to achieve the locking of tunable lasers to arbitrary wavelengths. The traditional arbitrary wavelength locking solution uses dual TECs to control the temperature of the tunable laser and the etalon separately. When the wavelength to be locked falls into the area with a small slope of the etalon, the circuit end cannot detect the slope of the etalon, resulting in the inability to lock the wavelength. At this time, it is necessary to adjust the temperature of the etalon temperature control TEC to shift the peak transmission wavelength of the etalon as a whole, so that the wavelength to be locked falls into the area with a large slope of the etalon, in order to achieve wavelength locking. However, this solution requires a dual TEC control design. Corresponding to different wavelength locking, the etalon temperature control needs to be adjusted, and the control is more complicated. The change in TEC control temperature will affect the temperature field distribution at the laser end inside the device, thereby affecting the laser wavelength stability. The device design end needs to consider the temperature crosstalk problem of the dual TEC.

[0008] In view of this, overcoming the defects of the prior art is an urgent problem to be solved in this technical field.

[0009] Application Contents

[0010] The technical problem to be solved by the present invention is: how to achieve locking of any wavelength of a laser.

[0011] The present invention adopts the following technical solutions:

[0012] In a first aspect, a tunable laser is provided, comprising: a laser, a first etalon, and a second etalon;

[0013] The first etalon and the second etalon have the same transmittance period frequency interval (Free Spectral Range, abbreviated as FSR);

[0014] The peak of the first etalon is aligned with the ITU wavelength, and the wavelength to which the peak of the second etalon is aligned is separated from the ITU wavelength by a preset wavelength interval;

[0015] In the wavelength locking range of the laser, the first etalon or the second etalon is alternately used to perform wavelength locking on the laser signal emitted by the laser, so as to avoid the peak position or the valley position of the transmission spectrum of the etalon.

[0016] Preferably, the wavelength locking range of the laser is divided into a plurality of locking intervals using any intersection position of the first transmission spectrum of the first etalon and the second transmission spectrum of the second etalon as a dividing point and the transmittance period FSR as a dividing period;

[0017] The locking interval is divided into at least two locking areas according to the preset wavelength interval, and the first etalon or the second etalon is alternately used in the at least two locking areas to wavelength lock the laser signal emitted by the laser to avoid the peak position or the valley position of the transmission spectrum of the etalon.

[0018] Preferably, the wavelength to which the peak of the second etalon is aligned is ITU wavelength ± a*FSR.

[0019] Preferably, the tunable laser further comprises: a spectrometer, a first detector, a second detector and a third detector;

[0020] The optical splitter is used to receive a first optical signal from a laser and split the first optical signal into a second optical signal, a third optical signal, a fourth optical signal and a fifth optical signal, wherein the second optical signal is used to be transmitted to an optical fiber;

[0021] The first etalon is used to calibrate the third optical signal and transmit it to the first detector, and the first detector is used to generate a first detection signal; the second etalon is used to calibrate the fourth optical signal and transmit it to the second detector, and the second detector is used to generate a second detection signal;

[0022] The third detector is used to receive the fifth optical signal and generate a third detection signal;

[0023] According to the wavelength of the laser signal emitted by the laser, the first detection signal and the third detection signal, or the second detection signal and the third detection signal are selected to lock the wavelength of the laser.

[0024] Preferably, the tunable laser further comprises a heat sink and a thermoelectric cooler, wherein the heat sink is arranged on the thermoelectric cooler;

[0025] The laser, the first etalon, and the second etalon are all disposed on the heat sink.

[0026] Preferably, the beam splitter comprises a first beam splitter and a second beam splitter;

[0027] The first beam splitter is used to receive the first optical signal and split the first optical signal into a second optical signal and a sixth optical signal;

[0028] The second beam splitter is used to receive the sixth optical signal and split the sixth optical signal into a third optical signal, a fourth optical signal and a fifth optical signal.

[0029] In a second aspect, a wavelength locking method for a tunable laser is provided, comprising:

[0030] aligning the peak of the first etalon with the ITU wavelength, and spacing the wavelength to which the peak of the second etalon is aligned with the ITU wavelength by a preset wavelength interval;

[0031] In the wavelength locking range of the laser, the first etalon or the second etalon is alternately used to perform wavelength locking on the laser signal emitted by the laser, so as to avoid the peak position or the valley position of the transmission spectrum of the etalon.

[0032] Preferably, within the wavelength locking range of the laser, alternately using the first etalon or the second etalon to wavelength lock the laser signal emitted by the laser to avoid a peak position or a valley position of a transmission spectrum of the etalon includes:

[0033] Using any intersection of the first transmission spectrum of the first etalon and the second transmission spectrum of the second etalon as a dividing point and the transmittance period FSR as a dividing period, the wavelength locking range of the laser is divided into a plurality of locking intervals;

[0034] The locking interval is divided into at least two locking areas according to the preset wavelength interval, and the first etalon or the second etalon is alternately used in the at least two locking areas to wavelength lock the laser signal emitted by the laser to avoid the peak position or the valley position of the transmission spectrum of the etalon.

[0035] Preferably, the tunable laser further includes a first detector, a second detector, and a third detector, and the wavelength locking method of the tunable laser further includes:

[0036] The first etalon calibrates the received third optical signal and transmits it to the first detector, and the first detector generates a first detection signal;

[0037] The second etalon calibrates the received fourth optical signal and transmits it to the second detector, and the second detector generates a second detection signal;

[0038] The third detector receives the fifth light signal and generates a third detection signal;

[0039] According to the wavelength of the laser signal emitted by the laser, the first detection signal and the third detection signal, or the second detection signal and the third detection signal are selected to lock the wavelength of the laser.

[0040] Preferably, the step of selecting the first detection signal and the third detection signal, or the second detection signal and the third detection signal to lock the wavelength of the laser according to the wavelength of the laser signal emitted by the laser specifically includes:

[0041] determining a locking region in which the wavelength of the laser signal emitted by the laser is located, and selecting to use the first etalon or the second etalon for wavelength locking according to the determined locking region;

[0042] If the determined locking region does not cover the peak position or the valley position of the first transmission spectrum of the first etalon, wavelength locking is performed using the first etalon; during the wavelength locking process, adjusting the current of the laser so that the ratio of the first detection signal to the third detection signal is a fixed value;

[0043] If the determined locking region does not cover the peak position or the valley position of the second transmission spectrum of the second etalon, the second etalon is used to perform wavelength locking. During the wavelength locking process, the current of the laser is adjusted so that the ratio of the second detection signal to the third detection signal is a fixed value.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention sets the first and second etalons to have the same transmittance period (FSR); aligns the peak of the first etalon with the ITU wavelength, and aligns the wavelength of the second etalon with a preset wavelength interval from the ITU wavelength. Within the wavelength locking range of the laser, the first etalon and the second etalon are alternately used to wavelength-lock the laser signal emitted by the laser, avoiding peaks or valleys in the etalon's transmission spectrum. Using the first and second etalons enables locking of the laser to any wavelength, avoiding the problem of the locked wavelength falling within the region of the etalon's low slope, which would render the circuit undetectable and prevent wavelength locking. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0047] FIG1 is a schematic structural diagram of a tunable laser provided by an embodiment of the present invention;

[0048] FIG2 is a schematic diagram of a dual-etalon transmission spectrum of a tunable laser provided by an embodiment of the present invention;

[0049] FIG3 is a schematic diagram of a specific structure of a tunable laser provided by an embodiment of the present invention;

[0050] FIG4 is a schematic diagram showing how the transmittance of an etalon varies with wavelength, provided by an embodiment of the present invention;

[0051] FIG5 is a schematic diagram showing changes in transmittance and slope of an etalon according to frequency provided by an embodiment of the present invention;

[0052] 6 is a schematic flow chart of a wavelength locking method for a tunable laser according to an embodiment of the present invention;

[0053] 7 is a schematic diagram of a dual-etalon transmission spectrum waveform of a wavelength locking method for a tunable laser provided by an embodiment of the present invention;

[0054] FIG8 is a schematic diagram of a specific flow chart of wavelength calibration of a wavelength locking method for a tunable laser provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0056] The terms "first," "second," etc., used in this disclosure are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referenced. Thus, a feature identified with "first," "second," etc., may explicitly or implicitly include one or more of such features. In the description of this disclosure, unless otherwise specified, "plurality" means two or more.

[0057] In the present invention, unless otherwise specified or limited, the term "connection" should be understood broadly. For example, "connection" can mean fixed connection, detachable connection, or integration; it can mean direct connection or indirect connection through an intermediary. Furthermore, the technical features involved in the various embodiments of the present invention described below may be combined as long as they do not conflict with each other.

[0058] Example 1:

[0059] In this embodiment, a tunable laser is proposed, as shown in Figures 1 and 2, including: a laser, a first etalon, and a second etalon; the first etalon and the second etalon have the same transmittance period (FSR); the peak of the first etalon is aligned with the ITU wavelength, and the wavelength to which the peak of the second etalon is aligned is separated from the ITU wavelength by a preset wavelength interval; within the wavelength locking range of the laser, the first etalon or the second etalon is alternately used to wavelength lock the laser signal emitted by the laser to avoid the peak position or valley position of the transmission spectrum of the etalon.

[0060] The peak of the transmission spectrum of the first etalon is aligned with the ITU wavelength, which means that the peak of the first etalon is aligned with a certain ITU wavelength in the ITU wavelength standard. For example, one of the peaks of the transmission spectrum of the first etalon is aligned with the ITU wavelength corresponding to 193.4 THz.

[0061] In a preferred embodiment, the peak of the first etalon is aligned with the ITU wavelength, and the incident angle of the second etalon is adjusted so that the wavelength position at which the peak of the second etalon is aligned is separated from the ITU wavelength by a preset wavelength interval, which is defined as a*FSR. For example, a = 1 / 4 is used for illustration, but other values ​​can be set depending on the circuit detection capability. The first and second etalon have the same FSR and exhibit good repeatability at long, medium, and short wavelengths. A specific implementation method may be as follows: First, for the first etalon, the peak corresponding to the ITU wavelength position needs to be found in the transmission spectrum. This can be achieved using an optical spectrum analyzer or other appropriate measurement equipment. Once the peak corresponding to the ITU wavelength position is found, the position or parameters of the first etalon can be adjusted to align it with this peak. This can be achieved by fine-tuning the etalon position or using other calibration methods. Next, the angle at which the optical signal enters the second etalon needs to be adjusted so that the peak in the transmission spectrum of the second etalon is aligned with the wavelength position of ITU + a*FSR. This can be achieved by adjusting the position or parameters of the second etalon. By adjusting the angle, the peak in the transmission spectrum of the second etalon is aligned with the wavelength position of ITU + a*FSR. When adjusting the angle, a is a constant and FSR is the frequency spacing of the etalon. By selecting an appropriate value of a and adjusting the angle accordingly, the peak in the second etalon's transmission spectrum can be aligned to the wavelength position of ITU+a*FSR.

[0062] The peaks of the first and second etalon are offset to avoid peaks or valleys in the transmission spectra of the first and second etalons. Wavelength locking is then achieved by selecting the appropriate etalon based on the wavelength range. The specific method for wavelength locking using the first or second etalon is described below.

[0063] As shown in FIG2 , any intersection position of the first transmission spectrum of the first etalon (etalon 1) and the second transmission spectrum of the second etalon (etalon 2) is used as a dividing point, and the transmittance period FSR is used as a dividing period to divide the wavelength locking range of the laser into multiple locking intervals; the locking interval is divided into at least two locking regions according to the preset wavelength interval, and the first etalon or the second etalon is alternately used in the at least two locking regions to wavelength lock the laser signal emitted by the laser to avoid the peak position or the valley position of the transmission spectrum of the etalon.

[0064] Based on the aforementioned alignment of the peak of the first etalon's transmission spectrum with the ITU wavelength position A and the peak of the second etalon's transmission spectrum with the ITU+a*FSR wavelength position B, in Figure 2, the transmission spectrum curves of the first and second etalons intersect at point M. Using any of these intersections M as a dividing point and the transmittance period FSR as a dividing period, the wavelength locking range of the transmission spectrum is divided into multiple locking intervals. These locking intervals are divided into at least two locking regions by a preset wavelength interval a*FSR. Within these at least two locking regions, the first and second etalons are used alternately for wavelength locking: in one locking region, the first etalon is used to lock the laser wavelength, while in the next locking region, the second etalon is used for locking. This approach avoids peaks or valleys in the etalon's transmission spectrum, i.e., locations where the slope approaches zero. The relationship between the etalon's transmission spectrum and its slope will be explained below.

[0065] In a preferred embodiment, as shown in FIG1 , the tunable laser further comprises a spectrometer, a first detector, a second detector, and a third detector; the spectrometer is configured to receive a first optical signal from the laser and split the first optical signal into a second optical signal, a third optical signal, a fourth optical signal, and a fifth optical signal, wherein the second optical signal is configured to be transmitted to an optical fiber; the first etalon is configured to calibrate the third optical signal and transmit it to the first detector, wherein the first detector is configured to generate a first detection signal; the second etalon is configured to calibrate the fourth optical signal and transmit it to the second detector, wherein the second detector is configured to generate a second detection signal; the third detector is configured to receive the fifth optical signal and generate a third detection signal; and according to the wavelength of the laser signal emitted by the laser, the first detection signal and the third detection signal, or the second detection signal and the third detection signal, are selected to lock the wavelength of the laser.

[0066] The implementation of the beam splitter typically utilizes the principles of light refraction and reflection. A common implementation method is to use a prism or a half-reflecting mirror. The beam splitter splits the received laser beam into four parts and sends them to different locations. The specific splitting ratio and direction depend on the design and material of the beam splitter. In this embodiment, as shown in Figure 3, the beam splitter includes a first beam splitter and a second beam splitter. The first beam splitter is used to receive the first light signal and split it into a second light signal and a sixth light signal. The second beam splitter is used to receive the sixth light signal and split it into a third light signal, a fourth light signal, and a fifth light signal. The first beam splitter receives the first light signal from the laser. Then, by adjusting the angle and reflectivity of the first beam splitter, the first light signal is split into a second light signal and a sixth light signal. The second light signal is transmitted to an optical fiber, and the sixth light signal is transmitted to the second beam splitter for further splitting. The second beam splitter receives the sixth light signal from the first beam splitter. Then, by adjusting the angle and reflectivity of the second beam splitter, the sixth light signal is split into a third light signal, a fourth light signal, and a fifth light signal. These three optical signals are used for further processing and detection respectively.

[0067] The first and second etalons can be implemented in a variety of ways, depending on the parameter to be calibrated and the accuracy. For example, if the wavelength of an optical signal needs to be calibrated, the etalon can be a component with known spectral characteristics, such as a grating, spectral filter, or interferometer. These components can modify the wavelength distribution of the light passing through, thereby achieving the calibration function.

[0068] The implementation of the first, second, and third detectors typically relies on the photoelectric effect, which is the phenomenon whereby light energy is converted into electrical energy. Common photoelectric conversion elements include photodiodes, photomultiplier tubes, and charge-coupled devices. In this embodiment, the first and second detectors convert received light signals into electrical signals for subsequent processing and analysis.

[0069] The process of achieving laser wavelength locking typically involves a feedback control system. In this embodiment, a microprocessor or digital signal processor can be provided to receive and analyze the electrical signals generated by the first, second, and third detectors. By comparing these electrical signals with preset standard values, the processor can calculate the deviation of the laser's operating parameters (such as current and temperature), and then generate corresponding adjustment signals, which are sent to the laser's driver circuit to adjust the laser's operating state and achieve precise wavelength locking.

[0070] The present invention employs a method in which the first etalon and the second etalon have the same transmittance period (FSR); the peak of the first etalon is aligned with the ITU wavelength, and the wavelength to which the peak of the second etalon is aligned is spaced apart from the ITU wavelength by a predetermined wavelength interval; and within the wavelength locking range of the laser, the first etalon and the second etalon are alternately used to wavelength-lock the laser signal emitted by the laser, avoiding peaks or valleys in the transmission spectrum of the etalon. Using the first and second etalons, the laser can be locked to any wavelength, avoiding the problem of the locked wavelength falling within a region with a small etalon slope, which would render the circuit undetectable and prevent wavelength locking.

[0071] Other structures and specific implementation methods of the tunable laser will be described below.

[0072] In a preferred embodiment, as shown in FIG3 , the tunable laser further includes a heat sink and a thermoelectric cooler, wherein the heat sink is disposed on the thermoelectric cooler; and the laser, the first etalon, and the second etalon are all disposed on the heat sink.

[0073] A thermoelectric cooler is a device based on the Peltier effect. It controls temperature by creating a temperature difference between two different thermoelectric materials through the manipulation of electric current. In a tunable laser, the thermoelectric cooler is placed beneath the heat sink. It absorbs and transfers heat, thereby lowering the temperature of the laser and etalon. By adjusting the current in the thermoelectric cooler, the laser wavelength can be precisely controlled and locked.

[0074] Traditional arbitrary wavelength locking schemes use dual TECs to separately control the temperature of the tunable laser and etalon, locking the laser wavelength using the rising or falling edges of the etalon. However, when the desired wavelength falls within the region of the etalon's low slope, the circuit cannot detect the etalon's slope, preventing wavelength lock. In this case, the temperature of the etalon's temperature-controlling TEC must be adjusted to shift the etalon's FSR, shifting the desired wavelength into the region of the etalon's high slope. This approach requires a dual-TEC control design. In this embodiment, a single TEC is used to simultaneously control the temperature of the laser and the first and second etalons. Separate temperature adjustments are not required for the first and second etalons, simplifying device packaging and the module temperature control process. Compared to dual-TEC temperature control schemes, single-TEC packaging also reduces device power consumption. Furthermore, since both etalons are located on the same TEC, they maintain the same temperature and FSR, resulting in better repeatability in periodic calibration region selection.

[0075] The heat sink is a component designed to absorb and dissipate heat. In the tunable laser, the heat sink is positioned above the thermoelectric cooler. It effectively absorbs the heat generated by the laser and etalon and dissipates it into the surrounding environment. This helps maintain the operating temperature of the laser and etalon within a stable range. The laser, the first etalon, and the second etalon are typically mounted on the heat sink. The laser is the core component for generating the laser beam, while the first and second etalons are used to reference and calibrate the laser's wavelength. Their proximity to the heat sink ensures that their temperatures are stably controlled by the heat sink and the thermoelectric cooler, thereby maintaining wavelength stability and locking performance.

[0076] In a preferred embodiment, as shown in FIG3 , the tunable laser further includes a collimating lens and a first fixing groove, wherein the collimating lens is disposed in the first fixing groove; the first fixing groove is disposed on the heat sink, and the collimating lens is disposed behind the output end face of the laser for collimating the first optical signal to improve the focusing capability of the first optical signal; the first fixing groove is used to position the collimating lens so as to align the collimating lens with the optical path of the first optical signal transmission.

[0077] The collimating lens' primary function is to collimate the first optical signal to improve its focusing capability. When the optical signal passes through the collimating lens, it refracts and focuses it, allowing the light to propagate more directly. This enhances the focusing effect, making the beam more concentrated and focused, and improving the performance and accuracy of the tunable laser.

[0078] The first fixing groove may be a V-shaped groove, which is used to position and secure the collimating lens so that it is aligned with the optical path of the first optical signal. By fixing the position of the collimating lens, the collimation and stability of the optical signal during transmission can be ensured. The first fixing groove is generally a fixed structure that firmly places the collimating lens in the correct position to ensure the correct positioning and transmission of the optical signal.

[0079] In a preferred embodiment, as shown in FIG3 , the tunable laser further includes an isolator, which is disposed between the first beam splitter and the collimating lens; the isolator is used to isolate the reflected light beam of the first beam splitter to ensure the stability of the tunable laser.

[0080] The isolator isolates the reflected beam from the first beam splitter to ensure the stability of the tunable laser. During wavelength locking, a portion of the first optical signal is split by the first beam splitter, while the remaining portion is reflected back to the laser. This reflected beam is called the reflected beam. To maintain the stability of the tunable laser, the reflected beam must be isolated to prevent it from interfering with the laser. The isolator isolates the reflected beam from other beams to prevent it from interfering with the normal operation of the tunable laser.

[0081] In a preferred embodiment, as shown in FIG3 , the tunable laser further includes a converging lens and a second fixing groove, wherein the second fixing groove is provided on the heat sink, and the converging lens is provided in the second fixing groove, and the converging lens is provided on the optical path for transmission of the second optical signal; the converging lens is used to focus the second optical signal and transmit the focused optical signal to the optical fiber; the second fixing groove is used to position the converging lens so that the converging lens is aligned with the optical path for transmission of the second optical signal.

[0082] The converging lens is positioned within a second fixing groove, typically a fixed structure that securely positions the converging lens to ensure accurate positioning and transmission of the optical signal. The second fixing groove can be a V-shaped groove. The converging lens focuses the second optical signal and transmits it to the optical fiber. The use of the converging lens further concentrates and focuses the energy of the second optical signal, improving the sensitivity and accuracy of the tunable laser.

[0083] Example 2:

[0084] A tunable laser is proposed in Example 1. In this example, a wavelength locking method for a tunable laser is proposed. The wavelength locking method is applicable to the tunable laser described in Example 1.

[0085] In this embodiment, the laser can be a laser based on the principle of digital super-mode distributed Bragg reflector (DS-DBR) or sample grating distributed Bragg reflector (SG-DBR), and the wavelength within the cycle can be locked and adjusted by changing the front mirror / rear mirror / phase current in real time. The laser combined with the standard tool can achieve the effect of locking or tuning the wavelength. Different wavelengths are aligned with different positions of the transmission spectrum, and the transmission spectrum of the standard tool changes periodically with the wavelength. The wave locking function of the laser can be achieved by keeping the transmission wavelength intensity of the standard tool at a certain value. P(λ)=1 / (1+F×sin(thita / 2)^2) Formula 1 F=4×R / (1-R)^2 Formula 2thita=4×pi×nt×d×cos(phi) / λ Formula 3

[0086] In Formulas 1 to 3, P(λ) is the transmission spectrum curve of the etalon, F is the finesse factor, thisa is the phase change of light after a single reflection in the etalon, phi is the reflection angle of light inside the etalon, and nt is the refractive index of the material.

[0087] According to the Sellmeier dispersion formula, the relationship between wavelength λ and refractive index n is as shown in Formula 4 (the angle of incidence etalon is 22 degrees): n=sqrt(A1×λ^2 / (λ^2-B1)+A2×λ^2 / (λ^2–B2)+A3×λ^2 / (λ^2–B3)+1) Formula 4

[0088] According to Corning, the relationship between refractive index change and temperature is as shown in Formula 5: dn=(C1+C2×λ^(-2)+C3×λ^(-4)+C4×λ^(-6))×dt Formula 5

[0089] In formula 5, dn represents the rate of change of refractive index when the temperature changes by dt (relative to 22 degrees), and C1, C2, C3 and C4 are known constants. nt=n+dn Formula 6

[0090] Equations 4, 5, and 6 can be used to calculate the transmittance at a specific wavelength and temperature, as shown in Figure 4. Figure 4 shows three different curves, representing the transmittance when the etalon's reflectivity is 0.3 and the temperature is 22°C; the transmittance when the etalon's reflectivity is 0.3 and the temperature is 32°C; and the transmittance when the etalon's reflectivity is 0.3 and the temperature is 22°C, with an incident angle of 0.5°.

[0091] Equations 1 through 6 provide the relationship between wavelength and transmittance. As shown in Figure 5, the transmittance exhibits a periodic variation, with the period being the FSR. The FSR is related to the material's refractive index and thickness. When the internal reflection angle phi of the etalon changes, or when the temperature fluctuates, the FSR shifts overall. Temperature fluctuations also cause changes in nt, resulting in smaller changes in the FSR.

[0092] As shown in FIG5 , when the transmittance of the etalon approaches the maximum or minimum position (i.e., corresponding to the peak position and valley position of the transmittance curve diagram in FIG5 ), the slope is close to 0. The slope is too small, resulting in the circuit end being unable to detect the slope of the etalon at this time, resulting in the inability to lock the wavelength.

[0093] This embodiment uses an etalon with FSR=50 GHz and reflectivity of 30% to illustrate an arbitrary wavelength locking scheme and implement an arbitrary wavelength locking method.

[0094] As shown in FIG6 , the wavelength locking method includes:

[0095] Step 101: Align the peak of the first etalon with the ITU wavelength, and space the wavelength to which the peak of the second etalon is aligned from the ITU wavelength by a preset wavelength interval.

[0096] The peak value in the transmission spectrum of the first etalon is aligned with the ITU wavelength position; and the angle at which the fourth optical signal enters the second etalon is modulated so that the peak value in the transmission spectrum of the second etalon is aligned with the ITU+a*FSR wavelength position, where a is a constant and FSR is the frequency standard of the etalon.

[0097] As shown in Figure 7, the peak of the first etalon is aligned with the ITU wavelength, and the second etalon is modulated at a certain angle to align the peak of the second etalon with the wavelength of ITU + a*FSR (FSR = 50 GHz in this embodiment). For illustration, a = 1 / 4 is used; of course, other values ​​can be set depending on the circuit's detection capabilities. The first and second etalon have the same FSR and are located on the same TEC at the same temperature, resulting in good repeatability at long, medium, and short wavelengths. A specific implementation method can be as follows: First, for the first etalon, the peak corresponding to the ITU wavelength in the transmission spectrum needs to be found. This can be achieved using an optical spectrum analyzer or other appropriate measurement equipment. Once the peak corresponding to the ITU wavelength is found, the position or parameters of the first etalon can be adjusted to align it with that peak. This can be achieved by fine-tuning the etalon's position or using other calibration methods. Next, the angle at which the fourth optical signal enters the second etalon needs to be adjusted to align the peak in the second etalon's transmission spectrum with the wavelength of ITU + a*FSR. This can be achieved by adjusting the position or parameters of the second etalon. By adjusting the angle, the operating frequency of the second etalon is changed, so that the peak in its transmission spectrum aligns with the wavelength of ITU + a*FSR. When adjusting the angle, a is a constant and FSR is the frequency standard of the etalon. By selecting an appropriate value of a and adjusting the angle accordingly, the peak in the transmission spectrum of the second etalon can be aligned with the wavelength position of ITU+a*FSR.

[0098] The wavelength is locked by staggering the peak of the first etalon and the peak of the second etalon and selecting the corresponding etalon according to the wavelength range.

[0099] Step 102: within the wavelength locking range of the laser, alternately use the first etalon or the second etalon to wavelength lock the laser signal emitted by the laser, so as to avoid the peak position or the valley position of the transmission spectrum of the etalon.

[0100] Since wavelength locking is achieved using two etalons in this embodiment, the wavelength locking method for a single etalon will be described first. The laser wavelength locking scheme for a single etalon is as follows: Assume that the third detector receives current P3, which is a constant value and does not change with the tunable laser wavelength. Assume that the first detector receives current P1, which varies with wavelength. When the laser wavelength is stable, P1 / P3 = D(λ), a constant value. When the laser wavelength changes, the current P1 decreases by ΔP. The magnitude of the change in ΔP / P1 depends on the etalon design and the wavelength alignment etalon position. At this point, the circuit detects that (P1-ΔP) / P3 ≠ D(λ), and the current ratio changes, indicating a change in the laser wavelength. In this case, the laser front mirror, rear mirror, and phase currents are readjusted to restore P1 / P3 = D(λ), achieving laser wavelength locking. The detection principle is that when the laser frequency changes, the transmittance of the etalon changes, realizing frequency detection. Each specific frequency of the laser corresponds to a specific P1 / P3 ratio of the etalon. Locking the P1 / P3 ratio means locking the laser wavelength. For a single etalon spectrum, its slope (% / GHz) represents the change in transmittance for every 1GHz change in frequency. The slope varies at different positions. At the peak and valley values, the slope is 0. This interval indicates that the transmission frequency of the etalon has changed, and the MPD current at its rear end remains basically unchanged. When the laser locking frequency is near the interval with a slope of 0, the MPD change △P detected when the laser frequency changes is less than the circuit detection capability, that is, P1 / P3 at the circuit detection end remains a certain value, and the laser frequency cannot be locked at this time. The size of the interval is related to the slope of the etalon and the minimum current detection capability of the circuit.

[0101] As shown in FIG8 , step 102 mainly includes:

[0102] Step 1021: The first etalon calibrates the received third optical signal and transmits the calibrated signal to the first detector, and the first detector generates a first detection signal.

[0103] When the third optical signal passes through the first etalon, it is calibrated and converted into a precise optical signal. The calibrated signal is transmitted to the first detector. The first detector is a photoelectric converter that converts optical signals into electrical signals. It receives the calibrated signal, converts it into a corresponding electrical signal, and outputs it as a first detection signal. The first detection signal can be a voltage, current, or other form of electrical signal for further analysis and processing.

[0104] Step 1022: The second etalon calibrates the received fourth optical signal and transmits it to the second detector, and the second detector generates a second detection signal.

[0105] When the fourth optical signal passes through the second etalon, it is calibrated and converted into an accurate optical signal. The calibrated signal is transmitted to the second detector. The second detector is a photoelectric converter that converts optical signals into electrical signals. It receives the calibrated signal, converts it into a corresponding electrical signal, and outputs it as a second detection signal. The second detection signal can be a voltage, current, or other form of electrical signal for further analysis and processing.

[0106] Step 1023: The third detector receives the fifth optical signal and generates a third detection signal.

[0107] The third detector converts the fifth optical signal into a corresponding electrical signal, which is the third detection signal. This third detection signal can be used as a standard signal for calibrating, comparing, or referencing other optical signals. It can be used to verify the accuracy of the tunable laser and make appropriate adjustments or corrections. By comparing it with a known standard signal, the performance and accuracy of the tunable laser can be evaluated and necessary corrections can be made.

[0108] Step 1024: Select the first detection signal and the third detection signal, or the second detection signal and the third detection signal to lock the wavelength of the laser according to the wavelength of the laser signal emitted by the laser.

[0109] Wherein, a locking region in which the wavelength of the laser signal emitted by the laser is located is determined, and the first etalon or the second etalon is selected for wavelength locking according to the determined locking region; if the determined locking region does not cover the peak position or the valley position of the first transmission spectrum of the first etalon, the first etalon is used for wavelength locking; during the wavelength locking process, the current of the laser is adjusted so that the ratio of the first detection signal to the third detection signal is a fixed value; if the determined locking region does not cover the peak position or the valley position of the second transmission spectrum of the second etalon, the second etalon is used for wavelength locking; during the wavelength locking process, the current of the laser is adjusted so that the ratio of the second detection signal to the third detection signal is a fixed value.

[0110] The method of achieving wavelength locking by the first etalon or the second etalon is as follows:

[0111] In the locking area, according to PD1 / PD3=D(λ) or PD2 / PD3=C(λ), where PD1 is the first detection signal, PD2 is the first detection signal, PD3 is the third detection signal, and D(λ) and C(λ) are fixed values; when the wavelength of the laser changes, the first detection signal increases or decreases by ΔP, that is, (PD1±ΔP) / PD3≠D(λ) or (PD2±ΔP) / PD3≠C(λ), and the current of the laser is readjusted so that PD1 / PD3=D(λ) or PD2 / PD3=C(λ) is re-established, thereby achieving locking of the laser wavelength.

[0112] This method can lock the wavelength of a tunable laser to ensure wavelength stability and accuracy. By continuously monitoring the signals of PD1, PD2, and PD3 and adjusting the current accordingly, the laser wavelength can be precisely controlled and locked. At the same time, the dual-etalon locking scheme avoids the region where the etalon slope approaches zero, resulting in a larger slope for the wavelength lock D(λ), making the circuit easier to detect and achieving high-precision wavelength locking.

[0113] The specific structure of the tunable laser is shown in Example 1 and will not be described in detail in this embodiment.

[0114] Example 3:

[0115] In Example 1, a tunable laser is proposed. In Example 2, a wavelength locking method for a tunable laser is proposed. This embodiment will give examples to further illustrate the present invention.

[0116] As shown in FIG7 , the first etalon and the second etalon intersect at + / -12.5 GHz on the transmission spectrum. Based on the FSR=50 GHz period, one period is divided into four equal regions:

[0117] Region 1: T0 to T0+12.5G; Region 2: T0+12.5G to T0+25G; Region 3: T0+25G to T0+37.5G; Region 4: T0+37.5G to T0+50G.

[0118] The first etalon transmission spectrum is used for wavelength locking in the frequency range of region 1, the second etalon in region 2, the first etalon in region 3, and the second etalon in region 4. Alternating between different etalons avoids peaks or valleys in an etalon and areas where the slope approaches zero, thus preventing the laser wavelength from being locked when the circuit cannot detect it.

[0119] Region 1 wavelength locking: T0 to T0+12.5G, using PD1(λ) / PD3(λ)=D(λ);

[0120] Region 2 wavelength locking: T0+12.5G to T0+25G, using PD2(λ) / PD3(λ)=D(λ);

[0121] Region 3 wavelength locking: T0+25G to T0+37.5G, using PD1(λ) / PD3(λ)=D(λ);

[0122] Region 4 range wavelength locking: T0+37.5G to T0+50G, using PD2(λ) / PD3(λ)=D(λ).

[0123] Since the etalon has a 50 GHz FSR and 50 GHz periodic repeatability, the same alternating use of the first and second etalons for frequency calibration during the next cycle allows for locking to any frequency within the entire wavelength range. The dual-etalon locking scheme avoids regions where the etalon slope approaches zero, resulting in a larger wavelength lock D(λ), making the circuit easier to test and achieving high-precision wavelength locking. The starting point T0 for region selection can be flexibly chosen based on the test accuracy of the supporting circuit, ensuring that the four regions selected avoid regions with zero slope while still meeting the circuit test requirements.

[0124] The specific structure of the tunable laser is shown in Example 1 and will not be described in detail in this embodiment.

[0125] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A tunable laser, characterized in that: include: A laser, a first etalon, and a second etalon; The first etalon and the second etalon have the same transmittance period FSR; The peak of the first etalon is aligned with the ITU wavelength, and the wavelength to which the peak of the second etalon is aligned has a preset wavelength interval with the ITU wavelength; In the wavelength locking range of the laser, the first etalon or the second etalon is used alternately to perform wavelength locking on the laser signal emitted by the laser to avoid the peak position or valley position of the transmission spectrum of the etalon.

2. The tunable laser according to claim 1, characterized in that: Using any intersection position of the first transmission spectrum of the first etalon and the second transmission spectrum of the second etalon as a division point and the transmittance period FSR as a division period, the wavelength locking range of the laser is divided into a plurality of locking intervals; The locking interval is divided into at least two locking areas according to the preset wavelength interval, and the first etalon or the second etalon is alternately used in the at least two locking areas to perform wavelength locking on the laser signal emitted by the laser to avoid the peak position or valley position of the transmission spectrum of the etalon.

3. The tunable laser according to claim 1, characterized in that: The wavelength to which the peak of the second etalon is aligned is ITU wavelength±a*FSR, where a is a constant.

4. The tunable laser according to claim 1, characterized in that: The tunable laser further comprises: a spectrometer, a first detector, a second detector and a third detector; The optical splitter is used to receive a first optical signal from a laser, and split the first optical signal into a second optical signal, a third optical signal, a fourth optical signal and a fifth optical signal, wherein the second optical signal is used to be transmitted to an optical fiber; The first etalon is used to calibrate the third optical signal and transmit it to the first detector, and the first detector is used to generate a first detection signal; the second etalon is used to calibrate the fourth optical signal and transmit it to the second detector, and the second detector is used to generate a second detection signal; The third detector is used to receive the fifth optical signal and generate a third detection signal; According to the wavelength of the laser signal emitted by the laser, the first detection signal and the third detection signal, or the second detection signal and the third detection signal are selected to lock the wavelength of the laser.

5. The tunable laser according to claim 4, characterized in that: The tunable laser further comprises a heat sink and a thermoelectric cooler, wherein the heat sink is arranged on the thermoelectric cooler; The laser, the first etalon and the second etalon are all disposed on the heat sink.

6. The tunable laser according to claim 5, characterized in that: The tunable laser further comprises a collimating lens and a first fixing groove, wherein the collimating lens is arranged in the first fixing groove; The first fixing groove is arranged on the heat sink, and the collimating lens is arranged behind the output end face of the laser, and is used to collimate the first optical signal to improve the focusing ability of the first optical signal; The first fixing groove is used for positioning the collimating lens so that the collimating lens is aligned with the optical path of the first optical signal transmission.

7. The tunable laser according to claim 6, characterized in that: The spectrometer includes a first spectrometer and a second spectrometer; the first spectrometer is used to receive the first optical signal and split the first optical signal into a second optical signal and a sixth optical signal; the second spectrometer is used to receive the sixth optical signal and split the sixth optical signal into a third optical signal, a fourth optical signal and a fifth optical signal.

8. The tunable laser according to claim 7, characterized in that: The tunable laser further comprises an isolator, which is arranged between the first beam splitter and the collimating lens; the isolator is used to isolate the reflected light beam of the first beam splitter to ensure the stability of the tunable laser.

9. The tunable laser according to claim 5, characterized in that: The tunable laser also includes a converging lens and a second fixing groove, wherein the second fixing groove is arranged on the heat sink, the converging lens is arranged in the second fixing groove, and the converging lens is arranged on the optical path of the second optical signal transmission; the converging lens is used to focus the second optical signal and transmit the focused optical signal to the optical fiber; the second fixing groove is used to position the converging lens so that the converging lens is aligned with the optical path of the second optical signal transmission.

10. A wavelength locking method for a tunable laser, characterized in that: The wavelength locking method of the tunable laser is applicable to the tunable laser according to any one of claims 1 to 9, comprising: Aligning the peak of the first etalon with the ITU wavelength, and spacing the wavelength to which the peak of the second etalon is aligned with the ITU wavelength by a preset wavelength interval; In the wavelength locking range of the laser, the first etalon or the second etalon is used alternately to perform wavelength locking on the laser signal emitted by the laser to avoid the peak position or valley position of the transmission spectrum of the etalon.

11. The wavelength locking method of a tunable laser according to claim 10, characterized in that: The step of alternately using the first etalon or the second etalon to perform wavelength locking on the laser signal emitted by the laser within the wavelength locking range of the laser to avoid the peak position or valley position of the transmission spectrum of the etalon comprises: Using any intersection position of the first transmission spectrum of the first etalon and the second transmission spectrum of the second etalon as a division point and the transmittance period FSR as a division period, the wavelength locking range of the laser is divided into a plurality of locking intervals; The locking interval is divided into at least two locking areas according to the preset wavelength interval, and the first etalon or the second etalon is alternately used in the at least two locking areas to perform wavelength locking on the laser signal emitted by the laser, To avoid the peak position or valley position of the transmission spectrum of the etalon.

12. The wavelength locking method of a tunable laser according to claim 11, characterized in that: The tunable laser further includes a first detector, a second detector and a third detector, and the wavelength locking method of the tunable laser further includes: The first etalon calibrates the received third optical signal and transmits it to the first detector, and the first detector generates a first detection signal; The second etalon calibrates the received fourth optical signal and transmits it to the second detector, and the second detector generates a second detection signal; The third detector receives the fifth light signal and generates a third detection signal; According to the wavelength of the laser signal emitted by the laser, the first detection signal and the third detection signal, or the second detection signal and the third detection signal are selected to lock the wavelength of the laser.

13. The wavelength locking method of a tunable laser according to claim 12, characterized in that: The method of achieving wavelength locking by the first etalon or the second etalon is as follows: In the locking area, according to PD1 / PD3=D(λ) or PD2 / PD3=C(λ), wherein PD1 is the first detection signal, PD2 is the first detection signal, PD3 is the third detection signal, and D(λ) and C(λ) are fixed values; When the wavelength of the laser changes, the first detection signal increases or decreases by ΔP, that is, (PD1±ΔP) / PD3≠D(λ) or (PD2±ΔP) / PD3≠C(λ), and the current of the laser is readjusted so that PD1 / PD3=D(λ) or PD2 / PD3=C(λ) is established again, thereby achieving locking of the laser wavelength.

14. The wavelength locking method of a tunable laser according to claim 12, characterized in that: The step of selecting the first detection signal and the third detection signal, or the second detection signal and the third detection signal to lock the wavelength of the laser according to the wavelength of the laser signal emitted by the laser specifically includes: Determine a locking region where the wavelength of the laser signal emitted by the laser is located, and select to use the first etalon or the second etalon for wavelength locking according to the determined locking region; If the determined locking region does not cover the peak position or the valley position of the first transmission spectrum of the first etalon, the first etalon is used to perform wavelength locking; during the wavelength locking process, the current of the laser is adjusted so that the ratio of the first detection signal to the third detection signal is a fixed value; If the determined locking area does not cover the peak position or valley position of the second transmission spectrum of the second etalon, the second etalon is used to perform wavelength locking; during the wavelength locking process, the current of the laser is adjusted so that the ratio of the second detection signal to the third detection signal is a fixed value.

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