Repetition rate tunable optical pulse source chip

Abstract

This application provides a tunable optical pulse source chip, relating to the field of semiconductor optoelectronic integrated device technology. The optical pulse source chip includes: a gain region for generating and amplifying an optical signal; a pulse selection region for receiving an external periodic electrical signal to form a periodically switching switching window, through which the amplified optical signal passes or is blocked; and a saturable absorption region for nonlinearly absorbing the optical signal passing through the pulse selection region to achieve mode locking, thereby generating and outputting an optical pulse. The repetition frequency of the optical pulse is tunable by controlling the frequency of the periodic electrical signal. This application integrates the gain region, pulse selection region, and saturable absorption region monolithically, and uses a periodic electrical signal to control the switching window of the pulse selection region. The output optical pulse repetition frequency is independently controlled by the frequency of the external electrical signal, decoupling the repetition frequency from the cavity length, thus enabling a wide-range, continuously tunable pulse repetition frequency.

Description

Technical Field

[0001] This application relates to the field of semiconductor optoelectronic integrated device technology, and in particular to a light pulse source chip with tunable repetition frequency. Background Technology

[0002] Traditional two-stage semiconductor mode-locked lasers consist of a gain region and a saturable absorption region. Due to their ability to generate ultrashort pulses, they have wide applications in various fields. Pulse width, peak power, and repetition rate are the core performance parameters. High peak power applications require the laser to operate at a relatively low repetition rate. However, traditional semiconductor mode-locked lasers typically operate at repetition rates above 10 GHz, with output pulse widths ranging from hundreds of femtoseconds to several picoseconds, and duty cycles on the order of approximately 1%.

[0003] Achieving lower repetition rates and lower duty cycles in semiconductor mode-locked structures is mainly achieved through two methods: One method is to extend the cavity length to reduce the repetition rate. This requires a cavity length on the order of centimeters. Whether monolithically integrated on a III-V substrate or heterogeneously integrated on a III-V / Si substrate, the increased cavity length significantly affects pulse formation due to dispersion, and also results in larger device dimensions. The second method is to integrate a pulse selector outside the cavity to select pulses from a high-repetition-rate mode-locked pulse train. This method causes significant energy loss, utilizing only 1 / N of the pulse energy (where N is the subharmonic number of the fundamental frequency). Furthermore, the repetition rate of existing mode-locked lasers is inherently limited by the cavity length, preventing wide-range continuous arbitrary tuning. Summary of the Invention

[0004] In view of the above problems, this application provides a light pulse source chip with tunable repetition frequency.

[0005] A repetition frequency tunable optical pulse source chip according to an embodiment of this application includes: a gain region for generating and amplifying an optical signal; a pulse selection region for receiving an external periodic electrical signal to form a periodically switching switching window, through which the amplified optical signal is passed or blocked; and a saturable absorption region for nonlinearly absorbing the optical signal passing through the pulse selection region to achieve mode locking, thereby generating and outputting an optical pulse; wherein, the repetition frequency of the optical pulse is tunable by controlling the frequency of the periodic electrical signal.

[0006] According to embodiments of this application, the gain region, pulse selection region, and saturable absorption region are all integrated on the same substrate, and the substrate material includes semiconductor materials such as indium phosphide or gallium arsenide.

[0007] According to an embodiment of this application, the periodic electrical signal includes a high-level signal and a low-level signal; when the periodic electrical signal is a high-level signal, the pulse selection area forms an open switch window according to the high-level signal to allow the currently amplified optical signal to pass through according to the switch window; when the periodic electrical signal is a low-level signal, the pulse selection area forms a closed switch window according to the low-level signal to block the currently amplified optical signal according to the switch window.

[0008] According to an embodiment of this application, the saturable absorption region is configured to: upon receiving a reverse bias voltage, nonlinearly absorb the optical signal passing through the pulse selection region to achieve mode locking, thereby generating and outputting an optical pulse.

[0009] According to embodiments of this application, the length of the pulse selection region is 30 μm to 300 μm; the length of the saturable absorption region is 30 μm to 300 μm.

[0010] According to embodiments of this application, the gain region and the saturable absorption region adopt the same epitaxial structure; the structure of the pulse selection region includes one of the following: the pulse selection region adopts the same epitaxial structure as the gain region and the saturable absorption region; or the pulse selection region adopts a different epitaxial structure than the gain region and the saturable absorption region.

[0011] According to an embodiment of this application, when the pulse selection region adopts the same epitaxial structure as the gain region and the saturable absorption region, the gain region, the pulse selection region and the saturable absorption region have the same structure, and the structure includes an N-type electrode layer, a substrate layer, a buffer layer, a lower confinement layer, an active layer, an upper confinement layer, an upper capping layer and an ohmic contact layer stacked sequentially from bottom to top.

[0012] According to the embodiments of this application, the top of the gain region, the pulse selection region, and the saturable absorption region are each provided with their respective corresponding P-type electrodes, and an electrical isolation trench is left between two adjacent P-type electrodes.

[0013] According to embodiments of this application, the active layer in the gain region and the active layer in the saturable absorption region are made of the same active material; the material of the active layer in the pulse selection region includes one of the following: the material of the active layer in the pulse selection region is the same as the material of the active layer in the gain region and the material of the active layer in the saturable absorption region; or the material of the active layer in the pulse selection region is different from the material of the active layer in the gain region and the material of the active layer in the saturable absorption region.

[0014] According to an embodiment of this application, a raised portion is provided in the upper cover layer along the propagation direction of the optical signal; an ohmic contact layer is disposed on the upper surface of the raised portion in the upper cover layer; and a P-type electrode covers a portion of the ohmic contact layer and the upper cover layer.

[0015] The optical pulse source chip with tunable repetition frequency provided in this application has at least the following technical effects:

[0016] 1. By monolithically integrating the gain region, pulse selection region, and saturable absorption region, and using an external periodic electrical signal to control the switching window of the pulse selection region, the repetition frequency of the output optical pulse is independently controlled by the frequency of the external electrical signal, thus decoupling the repetition frequency of the output optical pulse from the optical length of the resonant cavity. Compared with traditional mode-locking technology, this application is no longer limited by the cavity length constraint on the repetition frequency, thereby enabling a wide range of continuously adjustable pulse repetition frequencies.

[0017] 2. The pulse selection function is integrated into the chip resonant cavity, so that the gain of the resonant cavity is used only to amplify the selected target pulse. Compared with the scheme of pulse selection outside the cavity, this application avoids external cavity loss, can make fuller use of the internal cavity gain, and significantly improves the energy extraction efficiency of the system and the energy potential of the output pulse.

[0018] 3. The synergistic operation of the periodic switching window gating mechanism in the pulse selection region and the passive mode-locked pulse compression mechanism in the saturable absorption region enables the maintenance of ultrashort pulse widths in the femtosecond to picosecond range even at extremely low repetition frequencies, thereby achieving extremely low pulse duty cycles. With the average power remaining constant, the pulse peak power is inversely proportional to the duty cycle; the extremely low duty cycle translates into ultra-high peak power, providing ideal conditions for subsequent pulse amplification and facilitating the generation of optical pulses with ultra-high peak power. Attached Figure Description

[0019] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0020] Figure 1 The diagram schematically illustrates the structure of a repetition frequency tunable optical pulse source chip according to an embodiment of this application;

[0021] Figure 2 A top view of a repetition frequency tunable optical pulse source chip according to an embodiment of this application is schematically shown;

[0022] Figure 3 A cross-sectional view of a repetition frequency tunable optical pulse source chip according to an embodiment of this application is shown schematically.

[0023] Reference numerals: 1-Gain region; 2-Pulse selection region; 3-Saturable absorption region; 4-P-type electrode; 5-Electrically isolated trench; 11-N-type electrode layer; 21-Substrate layer; 31-Buffer layer; 41-Lower confinement layer; 51-Active layer; 61-Upper confinement layer; 71-Upper capping layer; 81-Ohmic contact layer. Detailed Implementation

[0024] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0026] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0027] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0028] Figure 1 A schematic diagram of a repetition frequency tunable optical pulse source chip according to an embodiment of this application is shown.

[0029] like Figure 1 As shown, this application embodiment provides a repetition frequency tunable optical pulse source chip, including: a gain region 1 for generating and amplifying an optical signal; a pulse selection region 2 for receiving an external periodic electrical signal to form a periodically switching switching window, through which the amplified optical signal is passed or blocked; and a saturable absorption region 3 for nonlinearly absorbing the optical signal passing through the pulse selection region 2 to achieve mode locking, thereby generating and outputting an optical pulse; wherein, the repetition frequency of the optical pulse is tunable by controlling the frequency of the periodic electrical signal.

[0030] Along the direction of optical signal propagation, pulse selection region 2 is located between gain region 1 and saturable absorption region 3.

[0031] In this process, by applying a forward bias current in gain region 1, electrons and holes are injected into the multiple quantum wells in the active region. When the injection current is strong enough, a population inversion state is formed. At this time, the spontaneous emission light generated by the random recombination of electron-hole pairs in the active region serves as seed light. When the seed light passes through the active region in the population inversion state, it induces more electron-hole pair recombination, generating a new photon identical to the incident photon. This stimulated emission process exponentially amplifies the light intensity. Simultaneously, the resonant cavity formed by the two end faces of the chip provides optical feedback, causing the light to reflect back and forth within the cavity and repeatedly pass through gain region 1, thereby achieving continuous amplification and stable output of the optical signal. At this time, the optical signal output from gain region 1 is amplified continuous light, which has not yet formed a pulse.

[0032] In the initial state, a reverse bias voltage of appropriate strength is applied to the pulse selection region 2 to put it in a high optical loss state, which is used to block the optical signal from passing through or suppress the optical signal intensity. In the initial state, a reverse bias voltage of appropriate strength is applied to the saturable absorption region 3 to put it in a high absorption state, with high absorption for weak light and low absorption for strong light, so as to allow the pulse spike to pass through, thereby initiating and establishing the passive mode-locking process.

[0033] A periodic electrical signal is applied to pulse selection region 2, causing it to periodically switch between high-loss and low-loss states, forming a switching window that allows or suppresses the amplified optical signal. The optical signal passing through pulse selection region 2 enters saturable absorption region 3, propagating back and forth within the resonant cavity. After passing through saturable absorption region 3, it enters a mode-locked state due to the saturable absorption effect, allowing the output of short pulses. Applying a switching signal (such as a square wave signal) of appropriate intensity, frequency, and duty cycle to pulse selection region 2 can control the repetition frequency of the output optical pulses.

[0034] Based on the tunable repetition frequency optical pulse source chip provided in this application embodiment, by monolithically integrating the gain region 1, pulse selection region 2, and saturable absorption region 3, and using an external periodic electrical signal to control the switching window of the pulse selection region 2, the repetition frequency of the output optical pulse is independently controlled by the frequency of the external electrical signal, decoupling the repetition frequency of the output optical pulse from the optical length of the resonant cavity. Compared with traditional mode-locking technology, this application is no longer limited by the cavity length constraint on the repetition frequency, thereby enabling a wide range of continuously tunable pulse repetition frequencies. Integrating the pulse selection function inside the chip's resonant cavity allows the cavity gain to be used only to amplify the selected target pulse. Compared with the scheme of pulse selection outside the cavity, this application avoids external cavity losses, can make fuller use of the internal cavity gain, and significantly improves the system's energy extraction efficiency and the energy potential of the output pulse.

[0035] The optical pulse source chip with tunable repetition frequency provided in this application embodiment has two working states, as detailed below.

[0036] In the first operating state, the reverse bias voltage applied to the saturable absorption region 3 and the pulse selection region 2 is relatively shallow (i.e., the absolute value of the reverse bias voltage is small). The pulse selection region 2 receives an external periodic switching signal (square wave signal), which has a high level "1" and a low level "0" or "-1": When the switching signal is high level "1", the pulse selection region 2 is in a low optical loss state (switching window open), and the chip normally outputs a stable optical pulse that travels back and forth multiple times in the resonant cavity. When the switching signal is low level "0" or "-1", the pulse selection region 2 is in a high optical loss state (switching window closed), and the loss in the cavity causes the stable mode-locked pulse in the resonant cavity to be moderately extinct (the pulse is weakened but still exists, not completely disappeared). In this state, the duration of the high level of the switching signal is equal to the round-trip time of the fundamental frequency mode-locked pulse, and the modulation signal must be synchronized with the fundamental frequency mode-locked pulse in time. The final generated optical pulse repetition frequency is 1 / N of the fundamental mode-locked frequency (N is the ratio of the number of low-level to high-level pulses of the switching signal), and it is an ultrashort pulse that propagates stably in the cavity.

[0037] In the second operating state, the reverse bias voltage applied to the saturable absorption region 3 and the pulse selection region 2 is applied at a deeper position (i.e., the absolute value of the reverse bias voltage is larger). The pulse selection region 2 receives an external periodic switching signal (square wave signal), which has a high level "1" and a low level "0" or "-1": When the switching signal is a low level "0" or "-1", the pulse selection region 2 is in a high optical loss state (switching window closed), the cavity loss is strong, and the propagation of the mode-locked optical pulse is completely suppressed. When the switching signal is a high level "1", the pulse selection region 2 is in a low optical loss state (switching window open), corresponding to lower cavity loss. The optical signal with multiple longitudinal modes generated in the gain region can achieve primary phase synchronization (forming a primary mode-locked pulse) in a single pass through the saturable absorption region. Subsequently, it is amplified by the gain region 1 to generate a short pulse in the cavity. In this state, the shortest duration of the high-level signal of the switching signal corresponds to the round-trip time of the fundamental frequency mode-locked pulse, but it does not need to be synchronized with the period of the fundamental frequency pulse. Because the period of the external switching signal can be arbitrarily tuned, the repetition frequency of the optical pulses generated in this mode can be arbitrarily tuned over a wide range. This mode no longer relies on the multiple round-trip processes of the resonant cavity in traditional mode-locking schemes, thus achieving decoupling between the output pulse repetition frequency and the resonant cavity parameters, making the short pulse output independent of the cavity repetition frequency. In this state, the output pulse is the primary pulse that travels back and forth once within the resonant cavity.

[0038] Figure 2 A top view of a repetition frequency tunable optical pulse source chip according to an embodiment of this application is shown schematically.

[0039] like Figure 2As shown, the top of the gain region 1, the pulse selection region 2 and the saturable absorption region 3 are each provided with their own corresponding P-type electrode 4, and an electrical isolation trench 5 is left between two adjacent P-type electrodes 4.

[0040] Among them, the P-type electrode 4 at the top of the gain region 1 is used to receive the forward bias current, so that the gain region 1 generates and amplifies the optical signal.

[0041] The P-type electrode 4 at the top of the pulse selection area 2 is used to receive external periodic electrical signals (such as square wave signals) and initial reverse bias voltage to form a periodically switching switching window.

[0042] The P-type electrode 4 at the top of the saturable absorption region 3 is used to receive the reverse bias voltage, so that the saturable absorption region 3 is in a saturable absorption state, and the optical signal is mode-locked and shaped.

[0043] For example, the electrical isolation trench 5 is formed by He ion implantation or etching, effectively preventing leakage of driving voltage or current between the gain region 1, the pulse selection region 2, and the saturable absorption region 3. The electrical isolation trench 5 can be filled with an insulating dielectric material (such as benzocyclobutene, polyimide, or silicon dioxide) to further improve electrical isolation performance and surface smoothness.

[0044] For example, P-type electrodes 4 include square electrodes, round electrodes, etc.

[0045] In the embodiments of this application, the gain region 1, the pulse selection region 2, and the saturable absorption region 3 adopt the same epitaxial structure.

[0046] The three functional regions can be prepared in one go through the same epitaxial growth process, eliminating the need for complex selective epitaxy or secondary epitaxy for different regions. This simplifies the manufacturing process, shortens the production cycle, and reduces the difficulty of process development.

[0047] Figure 3 A cross-sectional view of a repetition frequency tunable optical pulse source chip according to an embodiment of this application is shown schematically.

[0048] like Figure 3 As shown, when the pulse selection region 2 adopts the same epitaxial structure as the gain region 1 and the saturable absorption region 3, the gain region 1, the pulse selection region 2 and the saturable absorption region 3 have the same structure, and the structure includes an N-type electrode layer 11, a substrate layer 21, a buffer layer 31, a lower confinement layer 41, an active layer 51, an upper confinement layer 61, an upper cover layer 71 and an ohmic contact layer 81 stacked from bottom to top.

[0049] The N-type electrode layer 11 is used to form an N-type ohmic contact and provide a current loop; the substrate layer 21 is used for mechanical support and serves as an N-type current channel; the buffer layer 31 is used to block substrate defects and provide a high-quality epitaxial surface; the lower confinement layer 41 is used for vertical optical field confinement and for electron injection; the active layer 51 is used as the core region for optical gain / absorption; the upper confinement layer 61 is used for vertical optical field confinement and for hole injection; the upper capping layer 71 is used to etch the ridge waveguide structure; and the ohmic contact layer 81 is used to form a P-type ohmic contact and reduce contact resistance.

[0050] It is important to understand that the gain region 1, the pulse selection region 2, and the saturable absorption region 3 achieve functional differentiation through electrode partitioning and electrical isolation trenches 5. The three regions share the same epitaxial layer structure, and only by applying different bias conditions to the P-type electrodes 4 on their respective tops (forward current is applied to the gain region 1, reverse bias is applied to the saturable absorption region 3, and periodic electrical signals and reverse bias are applied to the pulse selection region 2) can the same epitaxial structure exhibit different optical characteristics in different regions.

[0051] For example, the substrate layer 21 is made of InP; the buffer layer 31 is made of InP; the lower confinement layer 41 is made of AlGaInAs; the active layer 51 is made of AlGaInAs; the upper confinement layer 61 is made of AlGaInAs; the upper capping layer 71 is made of InP; and the ohmic contact layer 81 is made of InGaAs.

[0052] In this embodiment, the active layer in gain region 1 and the active layer in saturable absorption region 3 are made of the same active material; the material of the active layer in pulse selection region 2 includes one of the following: the material of the active layer in pulse selection region 2 is the same as the material of the active layer in gain region 1 and the material of the active layer in saturable absorption region 3; or the material of the active layer in pulse selection region 2 is different from the material of the active layer in gain region 1 and the material of the active layer in saturable absorption region 3.

[0053] For example, the active layers of gain region 1, pulse-selective region 2, and saturable absorption region 3 use the exact same semiconductor material system. Specifically, taking the InP-based material system as an example, the active layers of all three regions adopt an InGaAsP / InP multi-quantum-well structure with the same well width, barrier width, and number of periods. Since the active layer materials of the three regions are exactly the same, chip manufacturing only requires one epitaxial growth to complete the epitaxial structure of all regions, eliminating the need for selective epitaxy or secondary epitaxy. When the optical signal propagates between the three regions, due to the identical active layer materials and consistent refractive index distribution, the optical field mode matching is excellent, and the coupling loss between regions is extremely low.

[0054] For example, the active layers of gain region 1 and saturable absorption region 3 use a first active material (such as InGaAsP / InP multiple quantum wells), while the active layer of pulse selection region 2 uses a second active material, which can be optimized for performance.

[0055] In this embodiment, the upper cover layer 71 has a protrusion along the direction of optical signal propagation; the ohmic contact layer 81 is disposed on the upper surface of the protrusion in the upper cover layer 71; and the P-type electrode 4 covers a portion of the ohmic contact layer 81 and the upper cover layer 71.

[0056] The raised portion of the upper cover layer 71 forms a ridge waveguide structure to confine the optical field in the horizontal direction. An ohmic contact layer 81 is disposed on the upper surface of the raised portion of the upper cover layer 71 to form a low-resistance ohmic contact.

[0057] For example, the P-type electrode 4 completely covers the ohmic contact layer 81 and extends to the flat areas on both sides of the protrusion, covering a portion of the upper cover layer 71 to reduce contact resistance and improve current injection uniformity.

[0058] In this embodiment, the gain region 1, the pulse selection region 2, and the saturable absorption region 3 are all integrated on the same substrate, and the substrate material includes III-V semiconductor materials such as indium phosphide or gallium arsenide.

[0059] In this embodiment, the periodic electrical signal includes a high-level signal and a low-level signal; when the periodic electrical signal is a high-level signal, the pulse selection area 2 forms an open switch window according to the high-level signal, so as to allow the currently amplified optical signal to pass through according to the switch window; when the periodic electrical signal is a low-level signal, the pulse selection area 2 forms a closed switch window according to the low-level signal, so as to block the currently amplified optical signal according to the switch window.

[0060] For example, a periodic electrical signal can be a square wave signal with high and low levels.

[0061] A reverse bias voltage is applied to pulse selection area 2 (switching window closed) to block or suppress the propagation of optical signal in the cavity. After receiving square wave signal, it periodically switches between high and low levels to adjust the repetition frequency.

[0062] Based on the tunable repetition frequency optical pulse source chip provided in this application embodiment, by changing the frequency of the square wave signal, the repetition frequency of the output pulse can be continuously adjusted from low to any desired frequency to the fundamental frequency mode-locked frequency, realizing wide-range and high-precision electronic control tuning.

[0063] In this embodiment, the saturable absorption region 3 is configured to: upon receiving a reverse bias voltage, nonlinearly absorb the optical signal passing through the pulse selection region 2 to achieve mode locking, thereby generating and outputting an optical pulse.

[0064] For example, a reverse bias voltage is input to the saturable absorption region 3 through the P-type electrode 4 at the top of the saturable absorption region 3. By adjusting the magnitude of the reverse bias voltage, the mode-locking performance of the saturable absorption region 3 can be optimized.

[0065] Under the influence of a reverse bias voltage, the saturable absorption region 3 achieves nonlinear modulation of the optical absorption coefficient through the saturable absorption effect: First, in response to weak light: when the incident light signal intensity is low, the saturable absorption region 3 is in an unsaturated state, exhibiting a high absorption coefficient, effectively absorbing and suppressing weak light components; Second, in response to strong light: when the incident light signal intensity is high (such as a pulse peak), a large number of photogenerated carriers generated by the strong light fill the conduction band energy states of the quantum well, leading to band-edge absorption saturation. The saturable absorption region 3 exhibits a low absorption coefficient, allowing the pulse peak to pass through with low loss. After the optical signal is selected by the pulse selection region 2 and enters the saturable absorption region 3, it undergoes the above-mentioned nonlinear absorption shaping each time it passes through the saturable absorption region 3 during its round-trip propagation within the cavity. Through round-trip accumulation, the optical signal is compressed into an ultrashort optical pulse. The compressed ultrashort optical pulse is output from the end face of the saturable absorption region 3 to the outside of the chip.

[0066] In the embodiments of this application, the length of the pulse selection region 2 is 30μm~300μm; the length of the saturable absorption region 3 is 30μm~300μm.

[0067] The tunable repetition frequency optical pulse source chip provided in this application embodiment can be used in common communication bands such as 1310nm and 1550nm or other energy-type laser bands.

[0068] For example, coatings are applied to both ends of a chip to improve its performance, such as depositing a 90% high-reflectivity film on the end face of gain region 1 and a 10% anti-reflection film on the end face of saturable absorption region 3.

[0069] In another embodiment, the pulse selection region 2 may employ a different epitaxial structure than the gain region 1 and the saturable absorption region 3. Because the pulse selection region is independently designed, its performance is superior.

[0070] For example, pulse selection region 2 employs an electroabsorption modulation epitaxial structure. This structure is specifically optimized for high-speed switching applications, offering faster switching speeds, narrower switching window widths, and higher extinction ratios, thus enabling shorter pulse switching windows. Through selective epitaxy or docking growth processes, pulse selection region 2 can be integrated with gain region 1 and saturable absorption region 3 onto the same chip, forming a monolithically integrated optical pulse source chip.

[0071] In another embodiment, the relative positions of the gain region 1, the pulse selection region 2, and the saturable absorption region 3 can be adjusted.

[0072] For example, along the direction of optical signal propagation, the saturable absorption region 3 is located between the gain region 1 and the pulse selection region 2.

[0073] Among them, the gain region 1 is located at one end of the chip and is used to receive the forward bias current to generate and continuously amplify the optical signal.

[0074] The saturable absorption region 3 is arranged adjacent to the gain region 1 to receive the reverse bias voltage. It establishes a passive mode-locked state through the saturable absorption effect, compressing the amplified continuous optical signal into an ultra-short pulse sequence.

[0075] Pulse selection region 2 and saturable absorption region 3 are located adjacent to each other at the chip's output terminal. They are used to receive external periodic square wave signals, forming a periodically switching switching window. When the square wave is high, the switching window is open (low optical loss state), allowing the mode-locked pulse to pass through and be output; when the square wave is low, the switching window is closed (high optical loss state), blocking the mode-locked pulse. By controlling the frequency of the square wave signal, a portion of the pulses can be selected for output from the mode-locked pulse sequence, achieving tunability of the output pulse repetition frequency.

[0076] Those skilled in the art will understand that the features described in the various embodiments of this application can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this application. In particular, the features described in the various embodiments of this application can be combined or combined in various ways without departing from the spirit and teachings of this application. All such combinations or combinations fall within the scope of this application.

[0077] The embodiments of this application have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of this application. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Without departing from the scope of this application, those skilled in the art can make various substitutions and modifications, all of which should fall within the scope of this application.

Claims

1. A tunable repetition frequency optical pulse source chip, characterized in that, include: Gain region (1) is used to generate optical signals and amplify the optical signals; The pulse selection area (2) is used to receive external periodic electrical signals to form a periodically switching switching window, through which the amplified optical signal is passed or blocked; The saturable absorption region (3) is used to nonlinearly absorb the optical signal passing through the pulse selection region (2) to achieve mode locking, thereby generating an optical pulse and outputting it; The repetition frequency of the optical pulses can be tuned by controlling the frequency of the periodic electrical signal.

2. The optical pulse source chip according to claim 1, characterized in that, The gain region (1), the pulse selection region (2), and the saturable absorption region (3) are all integrated on the same substrate, and the substrate material includes semiconductor materials such as indium phosphide or gallium arsenide.

3. The optical pulse source chip according to claim 1, characterized in that, The periodic electrical signal includes a high-level signal and a low-level signal; When the periodic electrical signal is a high-level signal, the pulse selection area (2) forms an open switch window according to the high-level signal, so as to allow the currently amplified optical signal to pass through according to the switch window; When the periodic electrical signal is a low-level signal, the pulse selection area (2) forms a switch window in a closed state according to the low-level signal, so as to block the currently amplified optical signal according to the switch window.

4. The optical pulse source chip according to claim 1, characterized in that, The saturable absorption region (3) is configured to nonlinearly absorb the optical signal passing through the pulse selection region (2) when a reverse bias voltage is received to achieve mode locking, thereby generating an optical pulse and outputting it.

5. The optical pulse source chip according to claim 1, characterized in that, The length of the pulse selection region (2) is 30μm~300μm; The length of the saturable absorption region (3) is 30 μm to 300 μm.

6. The optical pulse source chip according to claim 1, characterized in that, The gain region (1) and the saturable absorption region (3) adopt the same epitaxial structure; The structure of the pulse selection region (2) includes one of the following: The pulse selection region (2) adopts the same epitaxial structure as the gain region (1) and the saturable absorption region (3); or The pulse selection region (2) adopts an epitaxial structure different from that of the gain region (1) and the saturable absorption region (3).

7. The optical pulse source chip according to claim 1, characterized in that, When the pulse selection region (2) adopts the same epitaxial structure as the gain region (1) and the saturable absorption region (3), the gain region (1), the pulse selection region (2) and the saturable absorption region (3) have the same structure, and the structure includes an N-type electrode layer (11), a substrate layer (21), a buffer layer (31), a lower confinement layer (41), an active layer (51), an upper confinement layer (61), an upper capping layer (71) and an ohmic contact layer (81) stacked from bottom to top.

8. The optical pulse source chip according to claim 7, characterized in that, The top of the gain region (1), the pulse selection region (2) and the saturable absorption region (3) are each provided with a corresponding P-type electrode (4), and an electrical isolation trench (5) is left between two adjacent P-type electrodes (4).

9. The optical pulse source chip according to claim 8, characterized in that, The active layer in the gain region (1) and the active layer in the saturable absorption region (3) use the same active material; The active layer material in the pulse selection region (2) includes one of the following: The active layer in the pulse selection region (2) is made of the same material as the active layer in the gain region (1) and the active layer in the saturable absorption region (3); or The material of the active layer in the pulse selection region (2) is different from the material of the active layer in the gain region (1) and the material of the active layer in the saturable absorption region (3).

10. The optical pulse source chip according to claim 8, characterized in that, The upper cover layer (71) has a protruding portion along the propagation direction of the optical signal; The ohmic contact layer (81) is disposed on the upper surface of the protruding portion in the upper cover layer; The P-type electrode (4) covers a portion of the ohmic contact layer (81) and the upper cover layer (71).

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