Half external cavity type tunable laser and cavity membrane locking method thereof

Abstract

The invention relates to the technical field of optical communication, in particular to a half external cavity type tunable laser and a cavity film locking method thereof, and the half external cavity type tunable laser comprises a control circuit, a first optical detector, a light splitting reflector, an etalon assembly, an inner cavity laser assembly, a light splitting sheet and a second optical detector; the control circuit is connected with the first optical detector, the second optical detector, the etalon assembly and the inner cavity laser assembly. The inner cavity laser assembly comprises a gain chip and an optical frequency locker; a very long resonant cavity is formed by the light splitting reflector, the etalon assembly, the gain chip and the optical frequency locker, and the half external cavity type tunable laser has the advantages of narrow line width and large tuning range of an external cavity type tunable laser, and also has the advantages of fast cavity mode locking, good stability, low cost and the like. And meanwhile, the defects that an external cavity type tunable laser is poor in stability and easy to be interfered by the outside world are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of optical communication, and particularly to a semi-external cavity tunable laser and a cavity film locking method thereof. Background Art

[0002] Tunable lasers have been widely used in the field of optical communication. Especially in recent years, with the development of high-speed optical communication network technology, the demand for narrow linewidth tunable lasers has been increasing continuously. Tunable lasers play an important role in future optical communication networks.

[0003] In terms of structure, tunable lasers can be divided into internal cavity (monolithic integrated) tunable lasers and external cavity tunable lasers. Internal cavity tunable lasers have the advantages of small volume and good stability. However, at present, their linewidth is wider than that of external cavity tunable lasers and they are not suitable for long-distance optical transmission communication. External cavity tunable lasers have the advantages of narrow linewidth and large tuning range. In the existing commercial optical network transmission systems, external cavity tunable lasers account for a large share. But compared with internal cavity tunable lasers, their stability is poor and they are easily interfered by various external factors, resulting in mode hopping, which in turn causes the degradation of the laser characteristics and affects the system transmission performance.

[0004] In view of this, overcoming the defects of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: how to overcome the technical defects that the internal cavity tunable laser has a wider linewidth and the external cavity tunable laser has poor stability and is easily interfered by various external factors.

[0006] The present invention adopts the following technical solutions:

[0007] In a first aspect, a semi-external cavity tunable laser is provided, including: a control circuit, a first photodetector, a beam splitting mirror, an etalon assembly, an internal cavity laser assembly, a beam splitter, and a second photodetector; the control circuit is respectively connected to the first photodetector, the second photodetector, the etalon assembly, and the internal cavity laser assembly; the internal cavity laser assembly includes a gain chip and an optical frequency locker.

[0008] The gain chip is used to emit a laser signal. After the laser signal passes through the etalon assembly, transmitted light and reflected light are obtained by the beam splitting mirror.

[0009] The first photodetector is used to detect the transmitted light to obtain a first detection result and transmit the first detection result to the control circuit; after the reflected light passes through the etalon assembly, the gain chip, the optical frequency locker, and the beam splitter in sequence, a part of the reflected light is transmitted to the optical fiber, and another part of the reflected light is transmitted to the second photodetector; the etalon assembly and the optical frequency locker are used to lock the frequency of the reflected light; the second photodetector is used to detect the reflected light transmitted from the beam splitter to obtain a second detection result and transmit the second detection result to the control circuit;

[0010] The control circuit is used to control the working currents of the etalon assembly and the optical frequency locker according to the first detection result to control the frequency of the reflected light; the control circuit is also used to control the working current of the gain chip according to the second detection result to control the power of the output light of the laser.

[0011] Preferably, an anti-reflection film is provided on one side of the beam splitter mirror close to the etalon assembly, and a reflection film is provided on the other side of the beam splitter mirror;

[0012] After the laser signal passes through the etalon assembly, it passes through the anti-reflection film, and a part of the light continues to transmit forward to obtain the transmitted light; another part of the light is reflected by the reflection film to obtain the reflected light.

[0013] After the laser signal passes through the etalon assembly, another part of the light in the laser signal is reflected by the reflection film to obtain the reflected light.

[0014] Preferably, the etalon assembly includes an etalon and a heating resistor; the optical frequency locker includes a phase region and a grating region; the etalon assembly, the phase region, and the grating region form a locking optical path;

[0015] The free spectral range (Free Spectral Range, abbreviated as FSR) of the etalon is FSR1, and the free spectral range of the grating region is FSR2, then the free spectral range JFSR of the locking optical path is obtained from Formula 1;

[0016] Formula 1 is: JFSR = (FSR1 * FSR2) / (FSR1 - FSR2);

[0017] The control circuit is used to change the current of the heating resistor to change the temperature of the etalon, thereby changing the free spectral range of the etalon to achieve wavelength locking.

[0018] Preferably, the intracavity laser assembly further includes a power amplifier, and the power amplifier is used to amplify the power of the output light from the optical frequency locker;

[0019] The control circuit includes a frequency modulation control circuit and a power control circuit; the frequency modulation control circuit is respectively connected to the heating resistor, the phase region and the grating region, and the frequency modulation control circuit is used to control the working current of the heating resistor, the phase region and the grating region to control the frequency of the output light of the laser;

[0020] The power control circuit is respectively connected to the gain chip and the power amplifier, and the power control circuit is used to control the working current of the gain chip and the power amplifier to control the power of the output light of the laser.

[0021] Preferably, the first photodetector is connected to the frequency modulation control circuit, and the second photodetector is connected to the power control circuit;

[0022] The first photodetector is connected to the frequency modulation control circuit, and the second photodetector is connected to the power control circuit; the frequency modulation control circuit is used to analyze the first detection result to adjust the output frequency of the laser;

[0023] The power control circuit is used to obtain power magnitude information according to the second detection result, and adjust the working current of the gain chip and the power amplifier according to the power magnitude information.

[0024] Preferably, the frequency modulation control circuit includes a demodulation circuit, an AC analysis circuit, a DC analysis circuit, a control center, an AC signal generation circuit, a first DC signal driving circuit, a second DC signal driving circuit, a third DC signal driving circuit and a signal synthesis circuit;

[0025] The demodulation circuit is used to demodulate the AC signal and DC signal in the first detection result. The AC signal passes through the AC analysis circuit, and the DC signal passes through the DC analysis circuit to obtain an analysis result;

[0026] The control center controls the AC signal generation circuit, the first DC signal driving circuit, the second DC signal driving circuit and the third DC signal driving circuit according to the analysis result to adjust the output of the driving current to lock the target frequency;

[0027] Wherein, the AC signal generation circuit and the first DC signal driving circuit are connected to the phase region after passing through the signal synthesis circuit; the second DC signal driving circuit is connected to the grating region, and the third DC signal driving circuit is connected to the etalon assembly.

[0028] Preferably, the semi-external cavity tunable laser further includes a thermoelectric cooler, the internal cavity laser assembly further includes a thermistor, and the control circuit further includes a temperature control circuit; the thermoelectric cooler is disposed at the bottom of other structures of the semi-external cavity tunable laser; the input end of the temperature control circuit is connected to the thermistor, and the output end of the temperature control circuit is connected to the thermoelectric cooler;

[0029] The temperature control circuit is configured to control the thermoelectric cooler according to the temperature fed back by the thermistor, so as to control the operating temperature of the semi-external cavity tunable laser.

[0030] Preferably, the semi-external cavity tunable laser further includes a first collimating lens, a second collimating lens, an optical isolator, and a focusing lens;

[0031] The first collimating lens is disposed between the internal cavity laser assembly and the etalon assembly, and the first collimating lens is configured to collimate the laser signal;

[0032] The second collimating lens is disposed between the internal cavity laser assembly and the beam splitter, and the second collimating lens is configured to collimate the reflected light;

[0033] The optical isolator is disposed between the second collimating lens and the beam splitter, and the optical isolator is configured to achieve unidirectional transmission of the reflected light;

[0034] The focusing lens is disposed between the beam splitter and the optical fiber, and the focusing lens is configured to focus the reflected light and transmit it to the optical fiber.

[0035] In a second aspect, a method for locking the cavity film of a semi-external cavity tunable laser is provided, including: the control circuit includes a frequency modulation control circuit and a power control circuit; the optical frequency locker includes a phase region and a grating region;

[0036] When the semi-external cavity tunable laser operates normally, the power control circuit controls the operating currents of the gain chip and the power amplifier in the internal cavity laser assembly; the frequency modulation control circuit controls the operating currents of the etalon assembly, the phase region, and the grating region;

[0037] When frequency switching is required, the control center in the frequency modulation control circuit respectively sets the operating currents of the etalon in the etalon assembly, the phase region, and the grating region according to the pre-calibrated operating currents;

[0038] Adjust the working current of the phase region to minimize the AC component of the first detection result; adjust the working current of the grating region to minimize the AC component of the first detection result, and further adjust the working current of the grating region to adjust the DC component of the first detection result to the maximum to lock the target frequency value.

[0039] Preferably, the cavity mode locking method of the semi-external cavity tunable laser further includes:

[0040] After locking the target frequency value, monitor whether the AC component of the first detection result is below a preset threshold range;

[0041] If the AC component of the first detection result is higher than the preset threshold, adjust the working currents of the phase region and the grating region to minimize the AC component of the first detection result; further adjust the working current of the grating region to adjust the DC component of the first detection result to the maximum to achieve real-time closed-loop control of the optical frequency.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] The present invention forms a very long resonant cavity through a beam splitter mirror, a Fabry-Perot etalon assembly, a gain chip, and an optical frequency locker. With a very long resonant cavity, the narrow linewidth characteristic of the laser is ensured. The control circuit controls the working currents of the Fabry-Perot etalon assembly and the optical frequency locker according to the first detection result to control the frequency of the reflected light; the control circuit also controls the working current of the gain chip according to the second detection result to control the power of the reflected light; through the control of the control circuit over the operation of the entire laser, it has the characteristics of fast frequency modulation and excellent frequency modulation; therefore, the semi-external cavity tunable laser proposed by the present invention has both the advantages of narrow linewidth and large tuning range of the external cavity tunable laser, and also has fast cavity mode locking and good stability, while overcoming the defects of poor stability and susceptibility to external interference of the external cavity tunable laser. Description of the Drawings

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0045] Figure 1 is a schematic structural diagram of a semi-external cavity tunable laser provided by an embodiment of the present invention;

[0046] Figure 2It is a schematic structural diagram of the locking optical path of a semi-external cavity tunable laser provided by an embodiment of the present invention;

[0047] Figure 3 It is a schematic structural diagram of the control circuit of a semi-external cavity tunable laser provided by an embodiment of the present invention;

[0048] Figure 4 It is a schematic diagram of the frequency locking principle of a semi-external cavity tunable laser provided by an embodiment of the present invention;

[0049] Figure 5 It is a schematic structural diagram of the frequency modulation control circuit of a semi-external cavity tunable laser provided by an embodiment of the present invention;

[0050] Figure 6 It is a schematic plan view of a semi-external cavity tunable laser provided by an embodiment of the present invention;

[0051] Figure 7 It is a specific schematic structural diagram of a semi-external cavity tunable laser provided by an embodiment of the present invention;

[0052] Figure 8 It is a schematic flow chart of the cavity film locking method of a semi-external cavity tunable laser provided by an embodiment of the present invention. Detailed implementation manners

[0053] In order to make the objectives, technical solutions and advantages of the present invention clearer, 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 used to limit the present invention.

[0054] In the present invention, terms such as "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0055] In the present invention, unless otherwise clearly defined and limited, the term "connection" should be understood in a broad sense. For example, "connection" may be a fixed connection, a detachable connection, or an integral body; it may be directly connected or indirectly connected through an intermediate medium. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0056] Embodiment 1:

[0057] In view of the technical defects that the line width of the intracavity tunable laser is relatively wide and the stability of the external cavity tunable laser is poor and it is easily interfered by various external factors, a semi-external cavity tunable laser is proposed, as Figure 1 shown, which includes: a control circuit, a first photodetector, a beam splitting reflector, an etalon assembly, an intracavity laser assembly, a beam splitter, and a second photodetector; the control circuit is respectively connected to the first photodetector, the second photodetector, the etalon assembly, and the intracavity laser assembly; the intracavity laser assembly includes a gain chip and an optical frequency locker; the gain chip is used to emit a laser signal, and after the laser signal passes through the etalon assembly, the transmitted light and the reflected light are obtained by the beam splitting reflector.

[0058] The first photodetector is used to detect the transmitted light to obtain a first detection result and transmit the first detection result to the control circuit; after the reflected light passes through the etalon assembly, the gain chip, the optical frequency locker, and the beam splitter in sequence, a part of the reflected light is transmitted to the optical fiber, and another part of the reflected light is transmitted to the second photodetector; the etalon assembly and the optical frequency locker are used to lock the frequency of the reflected light; the second photodetector is used to detect the reflected light transmitted from the beam splitter to obtain a second detection result and transmit the second detection result to the control circuit.

[0059] The control circuit is used to control the working current of the etalon assembly and the optical frequency locker according to the first detection result to control the frequency of the reflected light; the control circuit is also used to control the working current of the gain chip according to the second detection result to control the power of the output light of the laser.

[0060] The linewidth of a laser has a direct relationship with the length of its resonant cavity. The laser linewidth refers to the width of the laser frequency, which reflects the purity of the laser beam frequency. The length of the resonant cavity determines the spatial distribution and frequency interval of the fundamental mode, which is usually referred to as the mode interval or the free spectral range. A longer resonant cavity will result in a narrower mode interval, thus potentially reducing the linewidth of the laser. In a simple laser model, the physical length of the resonant cavity directly affects the coherence length and linewidth of the laser. Theoretically, a longer resonant cavity can produce a narrower linewidth because it provides a longer coherence length and more stringent mode selection. Among them, in this embodiment, the rear grating region inside the intracavity tunable laser chip is moved outside the chip and replaced with a more reliable and stable etalon component. In this way, the beam splitter mirror, the etalon component, the gain chip, and the optical frequency modulator form a very long resonant cavity. With a sufficiently long resonant cavity, the characteristic of the narrow linewidth of the laser is ensured, and the spectral range of the gain chip can cover the C-band, the L-band, and / or other specified optical communication bands. At the same time, the operation of the entire laser is controlled by a control circuit, which has the characteristics of fast frequency modulation and excellent frequency modulation.

[0061] Next, the structure of the semi-external cavity tunable laser will be specifically described.

[0062] In a preferred embodiment, an anti-reflection film is provided on one side of the beam splitter mirror close to the etalon component, and a reflection film is provided on the other side of the beam splitter mirror; after the laser signal passes through the etalon component, it passes through the anti-reflection film, and a part of the light continues to be transmitted forward to obtain the transmitted light; the other part of the light is reflected by the reflection film to obtain the reflected light.

[0063] Among them, the beam splitter mirror has the functions of beam splitting and reflection at the same time. When the laser signal reaches the anti-reflection film after passing through the etalon component, the laser signal will pass through the anti-reflection film, and a part of the laser signal will continue to be transmitted forward and is used to be detected by the first photodetector; while the other part of the light in the laser signal is reflected back by the reflection film to obtain the reflected light. In this way, the same laser signal is divided into two parts: one part continues to be transmitted forward and is detected by the first photodetector, and the other part is reflected by the reflection film to obtain the reflected light. The reflected light is used as the output light of the semi-external cavity tunable laser. After passing through other structures, the reflected light is transmitted to the optical fiber.

[0064] In a preferred embodiment, as Figure 2 shown, the etalon component includes an etalon and a heating resistor; the optical frequency locking device includes a phase region and a grating region; the etalon component, the phase region, and the grating region form a frequency locking optical path; the free spectral range of the etalon is FSR1, and the free spectral range of the grating region is FSR2, then the free spectral range JFSR of the frequency locking optical path is obtained from Equation 1.

[0065] Formula 1 is: JFSR = (FSR1 * FSR2) / (FSR1 - FSR2);

[0066] The control circuit is used to change the current of the heating resistor to change the temperature of the etalon, thereby changing the free spectral range of the etalon to achieve wavelength locking.

[0067] As a preferred embodiment of the present invention, the grating region may be a Bragg grating region. Wherein, the etalon assembly further includes a thermistor. In order to obtain higher frequency locking accuracy and improve frequency stability, a frequency locking optical path is formed by using the etalon assembly, the phase region and the grating region. The etalon assembly is the first optical frequency locker, and the grating region is the second optical frequency locker. Let the free spectral range of the first optical frequency locker be FSR1, and let the free spectral range of the second optical frequency locker be FSR2. Using the vernier effect, control that there is a slight difference between FSR1 and FSR2, then the combined free spectral range JFSR of the frequency locking optical path formed by their combination can be obtained from Formula 1. In this way, the combined free spectral range JFSR of the entire frequency locking optical path can be very large, ensuring that there is only a unique solution within the entire adjustable frequency range, improving the frequency locking accuracy and frequency stability, and excluding the possibility of optical mode hopping. Specifically, the etalon assembly is composed of an etalon, a heating resistor and a thermistor. By changing the current of the heating resistor, the temperature of the etalon can be changed, and the free spectral range of the etalon can be changed, thereby realizing fast wave locking.

[0068] In a preferred embodiment, as Figure 3 shown, the intracavity laser assembly further includes a power amplifier, and the power amplifier is used to amplify the power of the output light from the optical frequency locker; continue to refer to Figure 3 , the control circuit includes a frequency modulation control circuit and a power control circuit; the frequency modulation control circuit is respectively connected to the heating resistor, the phase region and the grating region, and the frequency modulation control circuit is used to control the working currents of the heating resistor, the phase region and the grating region to control the frequency of the output light of the laser; the power control circuit is respectively connected to the gain chip and the power amplifier, and the power control circuit is used to control the working currents of the gain chip and the power amplifier to control the power of the output light of the laser.

[0069] The power amplifier is used to enhance the power of the reflected light from the optical frequency locker. This enables the laser to operate at a higher output power, expanding its application range, especially for scenarios that require high-power laser output. The frequency modulation control circuit is respectively connected to the heating resistor, the phase region, and the grating region. It is responsible for controlling the working current of these components to precisely adjust the frequency of the reflected light. By adjusting the heating resistor, the temperature of the etalon can be changed, thereby affecting its frequency. The adjustment of the phase region and the grating region directly affects the frequency characteristics of the reflected light. The power control circuit is responsible for controlling the working current of the gain chip and the power amplifier, thereby adjusting the power of the reflected light.

[0070] Among them, the specific structures of the frequency modulation control circuit and the power control circuit are not elaborated in detail in this embodiment.

[0071] The first photodetector is connected to the frequency modulation control circuit, and the second photodetector is connected to the power control circuit; the first photodetector is connected to the frequency modulation control circuit, and the second photodetector is connected to the power control circuit; the frequency modulation control circuit is used to analyze the first detection result to adjust the output frequency of the laser; the power control circuit is used to obtain power magnitude information based on the second detection result to adjust the working current of the gain chip and the power amplifier according to the power magnitude information.

[0072] As Figure 4 shown, it is the theoretical basis for frequency locking of a semi-external cavity tunable laser: when the peak values of the central wavelength of the grating region, the central wavelength of the etalon, and the cavity film center of the phase region are all aligned, the optical power of the laser output light is the maximum, and the AC component at this time is the minimum.

[0073] In a preferred embodiment, as Figure 5 shown, the frequency modulation control circuit includes a demodulation circuit, an AC analysis circuit, a DC analysis circuit, a control center, an AC signal generation circuit, a first DC signal drive circuit, a second DC signal drive circuit, a third DC signal drive circuit, and a signal synthesis circuit; the demodulation circuit is used to demodulate the AC signal and the DC signal in the first detection result, the AC signal passes through the AC analysis circuit, and the DC signal passes through the DC analysis circuit to obtain an analysis result; the control center controls the AC signal generation circuit, the first DC signal drive circuit, the second DC signal drive circuit, and the third DC signal drive circuit according to the analysis result to adjust the output of the drive current to lock the target frequency; among them, the AC signal generation circuit and the first DC signal drive circuit are connected to the phase region after passing through the signal synthesis circuit; the second DC signal drive circuit is connected to the grating region, and the third DC signal drive circuit is connected to the etalon assembly.

[0074] Among them, the frequency modulation control circuit is used to control the working currents of the etalon assembly, the phase region, and the grating region, so as to change the central wavelength of the filtering spectrum and the optical length of the resonant cavity of the semi-external cavity laser, thereby changing the output laser frequency, and at the same time providing an alternating current signal with a fixed frequency in the phase region for dynamic frequency adjustment. Refer to Figure 5 , the first detection result enters the demodulation circuit of the frequency modulation control circuit, and the demodulation circuit demodulates the alternating current signal and the direct current signal in the first detection result. Among them, the alternating current signal passes through the alternating current analysis circuit, and the direct current signal passes through the direct current analysis circuit. The results obtained after analysis are input to the control center. The control center can also control the alternating current signal generation circuit and the driving circuits of three direct current signals (the first direct current signal, the second direct current signal, and the third direct current signal) to adjust the output of the driving current to control and lock the target frequency.

[0075] The alternating current signal in the first detection result reflects that the cavity mode is aligned with the grating region and the combined filtering spectrum of the cavity film and the etalon; the direct current signal in the first detection result reflects that the grating region and the etalon are aligned; the photocurrent of the second photodetector feedbacks the output optical power, and the photocurrent of the first photodetector feedbacks the frequency deviation. This feedback information is provided to the frequency modulation control circuit for adjusting the output frequency of the laser. The photocurrent of the second photodetector feedbacks the magnitude of the optical power. This feedback information is provided to the power control circuit for automatically adjusting the currents of the gain chip and the power amplifier.

[0076] In a preferred embodiment, as Figure 6 and Figure 7 shown, the semi-external cavity tunable laser further includes a thermoelectric cooler, the internal cavity laser assembly further includes a thermistor, and the control circuit further includes a temperature control circuit; the thermoelectric cooler is disposed at the bottom of other structures of the semi-external cavity tunable laser; the input end of the temperature control circuit is connected to the thermistor, and the output end of the temperature control circuit is connected to the thermoelectric cooler; the temperature control circuit is used to control the thermoelectric cooler according to the temperature fed back by the thermistor to control the working temperature of the semi-external cavity tunable laser. By dynamically controlling the temperature through the thermoelectric cooler to stabilize the entire optical path, the response speed of frequency modulation and frequency locking is greatly improved, and the frequency switching time is reduced.

[0077] Among them, in this embodiment, except for the optical fiber, other components are fixed on the thermoelectric cooler, and the working temperature is controlled by the thermoelectric cooler, so that the entire semi-external cavity tunable laser is in a stable working state.

[0078] In a preferred embodiment, refer to Figure 7, the semi-external cavity tunable laser further includes a first collimating lens, a second collimating lens, an optical isolator, and a focusing lens; the first collimating lens is disposed between the internal cavity laser assembly and the etalon assembly, and the first collimating lens is used to collimate the laser signal; the second collimating lens is disposed between the internal cavity laser assembly and the beam splitter, and the second collimating lens is used to collimate the reflected light; the optical isolator is disposed between the second collimating lens and the beam splitter, and the optical isolator is used to achieve unidirectional transmission of the reflected light; the focusing lens is disposed between the beam splitter and the optical fiber, and the focusing lens is used to focus the reflected light and transmit it to the optical fiber.

[0079] Among them, the main function of the first collimating lens is to collimate the laser signal, that is, to convert the divergent beam of the laser signal emitted by the gain chip into an almost parallel beam, so as to ensure the effective transmission of the laser signal between other structures of the system; the second collimating lens collimates the reflected light, and the collimated reflected light is more easily and effectively processed by other optical elements in the system; the main function of the optical isolator is to ensure the unidirectional transmission of the reflected light and prevent the reverse beam from returning to the laser, so as to protect the laser from damage by the reflected light or scattered light; the function of the focusing lens is to focus the reflected light and transmit it to the optical fiber, ensuring that the reflected light can be effectively coupled into the optical fiber for easy transmission of the reflected light to the optical fiber.

[0080] In summary, these optical components together constitute a highly precise and adjustable semi-external cavity tunable laser system. Each component plays a key role in ensuring the quality, stability, and safety of the laser signal.

[0081] Embodiment 2:

[0082] In Embodiment 1, a semi-external cavity tunable laser is proposed. In this embodiment, a method for locking the cavity film of a semi-external cavity tunable laser will be proposed, as Figure 8 shown, including: the control circuit includes a frequency modulation control circuit and a power control circuit; the optical frequency locker includes a phase region and a grating region.

[0083] Step 101: When the semi-external cavity tunable laser is operating normally, the power control circuit controls the operating currents of the gain chip and the power amplifier in the internal cavity laser assembly; the frequency modulation control circuit controls the operating currents of the etalon assembly, the phase region, and the grating region.

[0084] Among them, when the semi-external cavity tunable laser is operating normally, the power control circuit and the frequency modulation control circuit are respectively responsible for controlling the following two key aspects:

[0085] 1. For the power control circuit:

[0086] Operating current of the gain chip: The gain chip is part of the intracavity laser assembly and is responsible for generating the laser signal. The power control circuit monitors and controls the operating current of the gain chip to adjust the output power of the laser. Precise control of the laser power can be achieved by adjusting the operating current of the gain chip.

[0087] Operating current of the power amplifier: The power control circuit is also responsible for controlling the operating current of the power amplifier. The power amplifier is used to enhance the intensity of the reflected light obtained from the laser signal, and the adjustment of its operating current can affect the amplification degree of the output power.

[0088] 2. For the frequency modulation control circuit:

[0089] Operating current of the etalon assembly: The frequency modulation control circuit adjusts the operating current of the etalon assembly to affect the output frequency of the laser. Tuning of the output wavelength of the laser can be achieved by changing the operating current of the etalon assembly.

[0090] Operating currents of the phase region and the grating region: The frequency modulation control circuit is responsible for adjusting the operating currents of the phase region and the grating region to achieve precise tuning of the laser frequency. During normal operation, these two control circuits work together in coordination to ensure that the power and frequency of the laser are adjusted and controlled according to the predetermined requirements.

[0091] Step 102: When frequency switching is required, the control center in the frequency modulation control circuit sets the operating currents of the etalon in the etalon assembly, the phase region, and the grating region respectively according to the pre-calibrated operating currents.

[0092] Among them, when the tunable laser needs to perform frequency switching, the control center of the frequency modulation control circuit will first set the current values of the etalon, the phase region, and the grating region according to the pre-calibrated operating currents.

[0093] In the control center, the operating currents of the etalon, the phase region, and the grating region in the corresponding collimator assembly are preset in advance according to the frequency. When the frequency is switched, the control center adjusts the operating current of the etalon assembly according to the preset etalon operating current value. The etalon assembly is used in a semi-external cavity tunable laser to achieve precise frequency tuning. By adjusting the operating current of the etalon, the output frequency of the laser can be changed; the frequency modulation control circuit adjusts the operating current of the phase region according to the preset operating current value of the phase region. The phase region is used to control the optical path difference when tuning the laser, thereby affecting the output frequency. By adjusting the operating current of the phase region, the frequency of the laser can be precisely adjusted; the grating region is used for frequency selection and tuning in the semi-external cavity tunable laser. The control center adjusts the operating current of the grating region according to the preset operating current value of the grating region. By changing the operating current of the grating region, the spectral characteristics of the laser output can be affected.

[0094] Step 103: Adjust the operating current of the phase region to minimize the AC component of the first detection result, and record the DC component of the first detection result; adjust the operating current of the grating region to minimize the AC component of the first detection result; further adjust the operating current of the grating region to adjust the DC component of the first detection result to the maximum to lock the target frequency value.

[0095] Among them, by slightly adjusting the operating current of the etalon, the resistance value R of the thermistor in the etalon assembly reaches the preset calibrated resistance value. Then, slightly adjust the operating current of the phase region to minimize the AC component of the first detection result, and record the DC component of the first detection result; then, slightly adjust the operating current of the grating region, and repeat the above process. Finally, on the premise of ensuring that the AC component of the first detection result is minimized, adjust the DC component to the maximum. At this time, the target frequency value is basically locked.

[0096] In a preferred embodiment, after locking the target frequency value, monitor whether the AC component of the first detection result is below the preset threshold range; if the AC component of the first detection result is higher than the preset threshold, adjust the operating currents of the phase region and the grating region to minimize the AC component of the first detection result; further adjust the operating current of the grating region to adjust the DC component of the first detection result to the maximum to achieve real-time closed-loop control of the optical frequency.

[0097] First, a reasonable threshold for the AC component of the first detection result needs to be set. After locking to the target frequency value, it is also necessary to monitor in real time whether the AC component of the first detection result is below the range of the reasonable threshold. If it is higher than this threshold, the working currents of the phase region and the grating region need to be adjusted accordingly, so that on the premise that the AC component of the first detection result is minimized, the DC component of the first detection result is adjusted to the maximum. By repeating this cycle, real-time closed-loop control of the optical frequency is achieved.

[0098] For the specific structure of the semi-external cavity tunable laser, refer to Embodiment 1, which will not be elaborated herein.

[0099] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A semi-external cavity tunable laser, characterized in that, Comprising: A control circuit, a first optical detector, a beam splitting mirror, an etalon assembly, an intracavity laser assembly, a beam splitting plate, and a second optical detector; the control circuit is respectively connected to the first optical detector, the second optical detector, the etalon assembly, and the intracavity laser assembly; the intracavity laser assembly includes a gain chip and an optical frequency locking device; The gain chip is used to emit a laser signal, and after the laser signal passes through the etalon assembly, a transmitted light and a reflected light are obtained by the beam splitting mirror; The first optical detector is used to detect the transmitted light to obtain a first detection result and transmit the first detection result to the control circuit; After the reflected light passes through the etalon assembly, the gain chip, the optical frequency locking device, and the beam splitting plate in sequence, a part of the reflected light is transmitted to an optical fiber, and another part of the reflected light is transmitted to the second optical detector; the etalon assembly and the optical frequency locking device are used to lock the frequency of the reflected light; the second optical detector is used to detect the reflected light transmitted from the beam splitting plate to obtain a second detection result and transmit the second detection result to the control circuit; The control circuit is used to control the working current of the etalon assembly and the optical frequency locking device according to the first detection result to control the frequency of the reflected light; the control circuit is also used to control the working current of the gain chip according to the second detection result to control the power of the output light of the laser.

2. The semi-external cavity type tunable laser according to claim 1, characterized in that, The beam splitting mirror is provided with an anti-reflection film on the side close to the etalon assembly and a reflection film on the other side of the beam splitting mirror; After the laser signal passes through the etalon assembly, it passes through the anti-reflection film, and a part of the light continues to transmit forward to obtain the transmitted light; another part of the light is reflected by the reflection film to obtain the reflected light.

3. The semi-external cavity tunable laser according to claim 1, wherein, The etalon assembly includes an etalon and a heating resistor; the optical frequency locking device includes a phase region and a grating region; the etalon assembly, the phase region, and the grating region form a frequency locking optical path; The free spectral range of the etalon is FSR1, and the free spectral range of the grating region is FSR2, then the free spectral range JFSR of the frequency locking optical path is obtained by formula one; Formula one is: JFSR = (FSR1 * FSR2) / (FSR1 - FSR2); The control circuit is used to change the current of the heating resistor to change the temperature of the etalon, thereby changing the free spectral range of the etalon to achieve wavelength locking.

4. The semi-external cavity tunable laser according to claim 3, wherein, The intracavity laser assembly further includes a power amplifier, and the power amplifier is used to amplify the power of the output light from the optical frequency locking device; The control circuit includes a frequency modulation control circuit and a power control circuit; the frequency modulation control circuit is respectively connected to the heating resistor, the phase region, and the grating region, and the frequency modulation control circuit is used to control the working current of the heating resistor, the phase region, and the grating region to control the frequency of the output light of the laser; The power control circuit is respectively connected to the gain chip and the power amplifier. The power control circuit is used to control the operating currents of the gain chip and the power amplifier to control the power of the output light of the laser.

5. The semi-external cavity tunable laser according to claim 4, characterized in that, The first photodetector is connected to the frequency modulation control circuit, and the second photodetector is connected to the power control circuit; the frequency modulation control circuit is used to analyze the first detection result to adjust the output frequency of the laser; The power control circuit is used to obtain power magnitude information according to the second detection result, and adjust the operating currents of the gain chip and the power amplifier according to the power magnitude information.

6. The semi-external cavity type tunable laser according to claim 5, characterized in that, The frequency modulation control circuit includes a demodulation circuit, an AC analysis circuit, a DC analysis circuit, a control center, an AC signal generation circuit, a first DC signal drive circuit, a second DC signal drive circuit, a third DC signal drive circuit, and a signal synthesis circuit; The demodulation circuit is used to demodulate the AC signal and DC signal in the first detection result. The AC signal passes through the AC analysis circuit, and the DC signal passes through the DC analysis circuit to obtain an analysis result; The control center controls the AC signal generation circuit, the first DC signal drive circuit, the second DC signal drive circuit, and the third DC signal drive circuit according to the analysis result to adjust the output of the drive current to lock the target frequency; Among them, the AC signal generation circuit and the first DC signal drive circuit are connected to the phase region after passing through the signal synthesis circuit; the second DC signal drive circuit is connected to the grating region, and the third DC signal drive circuit is connected to the etalon assembly.

7. The semi-external cavity tunable laser according to claim 4, characterized in that, The semi-external cavity tunable laser further includes a thermoelectric cooler, the internal cavity laser assembly further includes a thermistor, and the control circuit further includes a temperature control circuit; the thermoelectric cooler is arranged at the bottom of other structures of the semi-external cavity tunable laser; the input end of the temperature control circuit is connected to the thermistor, and the output end of the temperature control circuit is connected to the thermoelectric cooler; The temperature control circuit is used to control the thermoelectric cooler according to the temperature fed back by the thermistor to control the operating temperature of the semi-external cavity tunable laser.

8. The semi-external cavity tunable laser according to claim 1, wherein The semi-external cavity tunable laser further includes a first collimating lens, a second collimating lens, an optical isolator, and a focusing lens; The first collimating lens is arranged between the internal cavity laser assembly and the etalon assembly, and the first collimating lens is used to collimate the laser signal; The second collimating lens is arranged between the internal cavity laser assembly and the beam splitter, and the second collimating lens is used to collimate the reflected light; The optical isolator is arranged between the second collimating lens and the beam splitter, and the optical isolator is used to achieve unidirectional transmission of the reflected light; The focusing lens is arranged between the beam splitter and the optical fiber, and the focusing lens is used to focus the reflected light and transmit it to the optical fiber.

9. A cavity film locking method for a semi-external cavity tunable laser, characterized in that, The method is implemented in a semi-external cavity tunable laser as described in any one of claims 1-8, and includes: the control circuit includes a frequency modulation control circuit and a power control circuit; the optical frequency locker includes a phase region and a grating region; When the semi-external cavity tunable laser operates normally, the power control circuit controls the operating current of the gain chip and the power amplifier in the internal cavity laser assembly; the frequency modulation control circuit controls the operating current of the etalon assembly, the phase region, and the grating region; When frequency switching is required, the control center in the frequency modulation control circuit sets the operating current of the etalon in the etalon assembly, the phase region, and the grating region respectively according to the pre-set and calibrated operating current; Adjust the operating current of the phase region to minimize the AC component of the first detection result; adjust the operating current of the grating region to minimize the AC component of the first detection result, and further adjust the operating current of the grating region to adjust the DC component of the first detection result to the maximum to lock the target frequency value.

10. The cavity film locking method of the semi-external cavity type tunable laser according to claim 9, characterized in that, The cavity film locking method of the semi-external cavity tunable laser further includes: After locking the target frequency value, monitor whether the AC component of the first detection result is below a preset threshold range; If the AC component of the first detection result is higher than the preset threshold, adjust the operating current of the phase region and the grating region to minimize the AC component of the first detection result; further adjust the operating current of the grating region to adjust the DC component of the first detection result to the maximum to achieve real-time closed-loop control of the optical frequency.

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