Semiconductor mode-locked laser and preparation method thereof

Abstract

This invention provides a semiconductor mode-locked laser and its fabrication method, relating to the field of optoelectronics. It addresses the problem in existing technologies where femtosecond pulses are difficult to output due to self-phase modulation and dispersion effects, thereby avoiding the use of external pulse compression technology and reducing production costs. The semiconductor mode-locked laser includes a mirror region, a gain region, and a saturable absorption region. The gain region is located between the mirror region and the saturable absorption region and is connected to both regions. The semiconductor mode-locked laser also includes a substrate, and a chirped grating layer and an active layer disposed on the same side of the substrate. The chirped grating layer is located in the mirror region and includes multiple gratings with a grating period linearly decreasing along the emission direction of the semiconductor mode-locked laser. The active layer is located in the gain region and the saturable absorption region, and the distance between the chirped grating layer and the substrate is greater than the distance between the active layer and the substrate.

Description

Technical Field

[0001] This invention relates to the field of optoelectronics technology, and in particular to a semiconductor mode-locked laser and its fabrication method. Background Technology

[0002] Since their emergence in the late 20th century, femtosecond pulses have experienced rapid development due to their superior characteristics, such as extremely short pulse widths (duration on the order of E-15s), extremely high peak power, and extremely wide spectral coverage. Femtosecond pulsed lasers, developed based on femtosecond pulses, have broad application prospects in microscopic ultrafast fields such as fundamental sciences (e.g., physics, chemistry).

[0003] Femtosecond pulse generation includes various structures, among which semiconductor mode-locked lasers have advantages such as small size, low power consumption, good stability, high repetition rate, and ease of mass production, making them the most advantageous among many structures.

[0004] However, traditional semiconductor mode-locked lasers are limited by the effects of self-phase modulation (SPM) and dispersion, making it difficult to achieve femtosecond pulses and prone to pulse splitting. External pulse compression technology is required to achieve femtosecond pulse output. Summary of the Invention

[0005] This invention provides a semiconductor mode-locked laser and its fabrication method, which solves the problem that femtosecond pulses are difficult to output due to self-phase modulation and dispersion effects in the prior art, thereby avoiding the use of external pulse compression technology and reducing production costs.

[0006] This invention provides a semiconductor mode-locked laser, comprising: a mirror region, a gain region, and a saturable absorption region; the gain region is disposed between the mirror region and the saturable absorption region, and is connected to both the mirror region and the saturable absorption region.

[0007] The semiconductor mode-locked laser further includes a substrate, and a chirped grating layer and an active layer disposed on the same side of the substrate; wherein, the chirped grating layer is disposed in the mirror region and includes a plurality of gratings with grating periods linearly decreasing along the emission direction of the semiconductor mode-locked laser, the active layer is disposed in the gain region and the saturable absorption region, and the distance between the chirped grating layer and the substrate is greater than the distance between the active layer and the substrate.

[0008] According to a semiconductor mode-locked laser provided by the present invention, the mirror region includes a first multilayer growth structure, and the gain region and the saturable absorption region each include a second multilayer growth structure;

[0009] The first multilayer growth structure and the second multilayer growth structure are integrated on the same side of the substrate.

[0010] According to a semiconductor mode-locked laser provided by the present invention, the first multilayer growth structure includes: a first buffer layer, a first confinement layer, a second confinement layer, a first waveguide layer and a first electrode layer sequentially stacked on the substrate; wherein the chirped grating layer is disposed on the side of the second confinement layer near the first waveguide layer;

[0011] The second multilayer growth structure includes: a second buffer layer, a third confinement layer, a fourth confinement layer, a second waveguide layer, and a second electrode layer sequentially stacked on the substrate; wherein the active layer is disposed on the side of the third confinement layer near the fourth confinement layer.

[0012] According to the present invention, a semiconductor mode-locked laser is provided in which growth structures having the same function and disposed in different regions, except for the first electrode layer and the second electrode layer, the first waveguide layer and the second waveguide layer, are integrally connected.

[0013] According to a semiconductor mode-locked laser provided by the present invention, in the reflector region, the first waveguide layer includes three first waveguide portions arranged parallel to each other along a preset direction, the preset direction being perpendicular to the emission direction of the semiconductor mode-locked laser; a first groove is provided between adjacent first waveguide portions to expose at least the second confinement layer; the chirped grating layer and the first waveguide portion located in the middle position at least partially overlap in a direction perpendicular to the substrate;

[0014] In the gain region and the saturation absorption region, the second waveguide layer includes three second waveguide portions arranged parallel to each other along the preset direction; a second groove is provided between adjacent second waveguide portions to expose the fourth confinement layer.

[0015] According to a semiconductor mode-locked laser provided by the present invention, the first waveguide portion includes a first upper cover portion and a first contact portion, wherein the first contact portion is disposed on the side of the first upper cover portion away from the substrate;

[0016] The second waveguide portion includes a second upper cover portion and a second contact portion, wherein the second contact portion is disposed on the side of the second upper cover portion away from the substrate;

[0017] The first upper cover and the second upper cover are integrally connected, and the first contact portion and the second contact portion are independent of each other.

[0018] According to a semiconductor mode-locked laser provided by the present invention, the semiconductor mode-locked laser further includes a third electrode layer; the third electrode layer is disposed in the mirror region, the gain region and the saturation absorption region, and is located on the side of the substrate away from the first buffer layer and the second buffer layer.

[0019] According to a semiconductor mode-locked laser provided by the present invention, the length of the saturated absorption region along the emission direction of the semiconductor mode-locked laser is smaller than the lengths of the mirror region and the gain region along the emission direction of the semiconductor mode-locked laser.

[0020] According to the present invention, a semiconductor mode-locked laser further includes an emitting end face and a reflecting end face, wherein the emitting end face is disposed in the saturated absorption region and the reflecting end face is disposed in the reflecting mirror region;

[0021] The semiconductor mode-locked laser further includes: an anti-reflection coating disposed on the side of the reflective end face away from the emission end face;

[0022] And / or, an antireflective film disposed on the side of the emission end face away from the reflective end face.

[0023] The present invention also provides a method for fabricating any one of the above-mentioned semiconductor mode-locked lasers, comprising:

[0024] A mirror region, a gain region, and a saturable absorption region are formed; wherein the gain region is disposed between the mirror region and the saturable absorption region, and is connected to both the mirror region and the saturable absorption region respectively;

[0025] The formation of the mirror region, gain region, and saturable absorption region includes:

[0026] Provide substrate;

[0027] An active layer is formed on the substrate; wherein the active layer is disposed in the gain region and the saturation absorption region;

[0028] A chirped grating layer is formed using a docking growth process; wherein the chirped grating layer is disposed in the mirror region and includes a plurality of gratings with grating periods linearly decreasing along the emission direction of the semiconductor mode-locked laser, and the distance between the chirped grating layer and the substrate is greater than the distance between the active layer and the substrate.

[0029] This invention provides a semiconductor mode-locked laser and its fabrication method. The semiconductor mode-locked laser includes a mirror region, a gain region, and a saturable absorption region. The gain region is disposed between the mirror region and the saturable absorption region and is connected to both the mirror region and the saturable absorption region. The semiconductor mode-locked laser also includes a substrate, and a chirped grating layer and an active layer disposed on the same side of the substrate. The chirped grating layer is disposed in the mirror region and includes a plurality of gratings with a grating period that decreases linearly along the emission direction of the semiconductor mode-locked laser. The active layer is disposed in the gain region and the saturable absorption region. The distance between the chirped grating layer and the substrate is greater than the distance between the active layer and the substrate. The semiconductor mode-locked laser provided in this invention achieves dispersion compensation for each frequency component of the optical pulse at different positions of the grating by setting a chirped grating layer in the reflector region. This eliminates the constraint on pulse width caused by pulse self-phase modulation and dispersion effects, thereby shortening the pulse width and realizing femtosecond pulse output. This semiconductor mode-locked laser can achieve femtosecond pulse output without the need for external pulse compression technology, significantly reducing production costs. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the semiconductor mode-locked laser provided by the present invention;

[0032] Figure 2 yes Figure 1 A magnified schematic diagram of the intermediate chirped grating layer;

[0033] Figure 3 yes Figure 1 Top view of the chirped grating layer;

[0034] Figure 4 yes Figure 1 Top view of the first and second waveguide layers in the middle;

[0035] Figure 5 This is a schematic flowchart of the method for fabricating a semiconductor mode-locked laser provided by the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0037] In the embodiments of the present invention, the use of terms such as "first" and "second" to distinguish identical or similar items with essentially the same function and effect is only for the purpose of clearly describing the technical solutions of the embodiments of the present invention, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0038] In embodiments of the present invention, "multi-layer" means two or more layers, "at least one layer" means one or more layers, and "multiple" means two or more layers, unless otherwise explicitly defined.

[0039] In the embodiments of the present invention, the terms "upper" and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0040] Femtosecond pulse generation includes the following structures: dye-mode-locked lasers, solid-state mode-locked lasers, gain fiber mode-locked lasers, and semiconductor mode-locked lasers. Dye-mode-locked lasers, the first generation to realize femtosecond pulses, use dye as the gain medium. However, due to the instability of the dye gain medium, their operating state also exhibits instability, thus limiting their practical application to the laboratory. Second-generation femtosecond lasers are solid-state mode-locked lasers, represented by Ti:sapphire mode-locked lasers. They can generate high peak power femtosecond pulses on the order of a few femtoseconds and have been widely used in various fields. However, their high cost, large system size, poor long-term stability, high power consumption, and complex debugging and maintenance make them unsuitable for large-scale production and application. Gain fiber mode-locked lasers use rare-earth-doped optical fibers as the gain medium. Together with other mature optical components, they have made further progress in miniaturization, low cost, and long-term stability. However, their discrete component structure results in a low laser output repetition rate, which still limits their application range. Semiconductor mode-locked lasers (SMLS) offer advantages such as small size, low power consumption, high stability, high repetition rate, and ease of mass production, making them a superior choice among various laser architectures. However, traditional SMLs are limited by self-phase modulation and dispersion effects, making it difficult to achieve femtosecond pulses and prone to pulse splitting. External pulse compression techniques are required to achieve femtosecond pulse output.

[0041] Based on the above, embodiments of the present invention provide a semiconductor mode-locked laser, with reference to... Figure 1 As shown, it includes: a mirror region A1, a gain region A2, and a saturation absorption region A3; the gain region A2 is located between the mirror region A1 and the saturation absorption region A3, and is connected to both the mirror region A1 and the saturation absorption region A3.

[0042] refer to Figure 1-3 As shown, the semiconductor mode-locked laser also includes a substrate 1, and a chirped grating layer 2 and an active layer 3 disposed on the same side of the substrate 1; wherein, the chirped grating layer 2 is disposed in the mirror region A1, and includes a grating period d along the emission direction of the semiconductor mode-locked laser. Figure 1 Multiple gratings 21 linearly decreasing in the OO1 direction shown, with an active layer 3 disposed in the gain region A2 and the saturation absorption region A3, and the distance L1 between the chirped grating layer 2 and the substrate 1 being greater than the distance L2 between the active layer 3 and the substrate 1.

[0043] The aforementioned gain region (also known as the Gain region) can be injected with current, its function being to provide gain to each mode of laser, i.e., to provide the energy required for lasing, thereby enabling the laser to las. The aforementioned saturable absorber (SA) includes a saturable absorber that, after reverse bias and modulation by an RF signal source, enters a hybrid mode-locked state. Its function is to saturately absorb each mode of laser, giving them a fixed phase difference. The aforementioned mirror region can employ a distributed Bragg reflection (DBR) structure, in which case the mirror region is also called the DBR region. The mirror region serves two purposes: firstly, to provide feedback to the semiconductor mode-locked laser; secondly, by setting a chirped grating layer, utilizing the characteristics of the chirped grating—that is, the grating period of the chirped grating varies with spatial position—it allows for feedback of different mode components at different grating positions, achieving dispersion compensation for different mode components at different grating locations.

[0044] The aforementioned reflector region can be located in the same cavity as the gain region and the saturable absorption region; or the reflector region can be located in one cavity, while the gain region and the saturable absorption region can be located in another cavity; of course, other structures are also possible, which are not limited here.

[0045] The aforementioned gain region and saturation absorption region can be fabricated using direct bandgap semiconductor material systems (e.g., GaAs-based and InP-based material systems), that is, integrated together on the same substrate using standard semiconductor processes to form a semiconductor femtosecond pulse mode-locked laser.

[0046] The active layer described above is located in the gain region and the saturation absorption region. Therefore, both the gain region and the saturation absorption region are active structures, while the mirror region is a passive structure. The specific structure of the active layer is not limited; for example, the active layer may include at least one quantum well layer.

[0047] refer to Figure 3 As shown, the chirped grating layer includes a plurality of gratings 21 with grating periods linearly decreasing along the emission direction of the semiconductor mode-locked laser. The grating period refers to the length from one refractive index change point to an adjacent change point. (Refer to...) Figure 2 As shown, the grating period d is the sum of the width of grating 21 and the spacing d2 between adjacent gratings. It should be noted that, for clarity, Figure 2 yes Figure 1 A magnified schematic diagram of the intermediate chirped grating layer. (Reference) Figure 1As shown, the emission direction of the semiconductor mode-locked laser can be the OO1 direction, that is, the laser is emitted from one side of the saturable absorption region. The grating periods of multiple gratings decrease linearly along the emission direction of the semiconductor mode-locked laser. Here, the specific formula satisfied by the linear decrease is not limited. For example, the grating periods of the gratings G1 and G2 adjacent along the emission direction of the semiconductor mode-locked laser can satisfy the formula:

[0048] y = -kx

[0049] where x is the grating period of the grating G1, y is the grating period of the grating G2, k is the proportionality coefficient, and 0 < k < 1 is satisfied. Of course, y and x can also satisfy other formulas for linear decrease, which are not listed here.

[0050] The material of the above substrate can include semiconductor materials such as InP or GaAs, which is not limited here.

[0051] The semiconductor mode-locked laser provided by the embodiment of the present invention realizes dispersion compensation for each frequency component included in the optical pulse at different positions of the grating by arranging a chirped grating layer in the mirror region, thereby eliminating the restriction of the pulse width due to the self-phase modulation and dispersion effects of the pulse, and further shortening the pulse width to achieve femtosecond pulse output; this semiconductor mode-locked laser can avoid using external pulse compression technology, that is, it can achieve femtosecond pulse output, greatly reducing the production cost.

[0052] In one or more embodiments, in order to avoid the coupling loss between discrete devices and improve the stability of the product, optionally, referring to Figure 1 As shown, the mirror region A1 includes a first multi-layer growth structure M1, and the gain region A2 and the saturable absorption region A3 respectively include a second multi-layer growth structure M2; the first multi-layer growth structure M1 and the second multi-layer growth structure M2 are integrated on the same side of the substrate 1.

[0053] Since the mirror region adopts a passive structure and the gain region and the saturable absorption region adopt an active structure, the first multi-layer growth structure and the second multi-layer growth structure can be integrated on the same substrate by using the active and passive butt-joint regrowth technology (BJR) to form a monolithic integrated semiconductor mode-locked laser. This semiconductor mode-locked laser has the advantages of high stability, small size, low power consumption, and easy mass production.

[0054] In order to further simplify the structure and facilitate manufacturing, optionally, referring to Figure 1 As shown, the first multi-layer growth structure M1 includes: a first buffer layer 9, a first confinement layer 4, a second confinement layer 5, a first waveguide layer 6, and a first electrode layer 7 stacked in sequence on the substrate 1; among them, the chirped grating layer 2 is disposed on the side of the second confinement layer 5 close to the first waveguide layer 6.

[0055] The second multilayer growth structure M2 includes: a second buffer layer 8, a third confinement layer, a fourth confinement layer 10, a second waveguide layer 11, and a second electrode layer 12 sequentially stacked on a substrate 1; wherein, the active layer 3 is disposed on the side of the third confinement layer near the fourth confinement layer 10. For ease of explanation, Figure 1 In the middle, the third confinement layer set in the gain region A2 and the third confinement layer set in the saturation absorption region A3 are marked as 9b and 9a, respectively.

[0056] The materials used in the above-mentioned layer structures are not limited. For example, the InP material system is used as an example for illustration. The substrate material can include N-type InP, the first and second buffer layers can be made of N-type InP, the first and third confinement layers can be made of InGaAsP, the second and fourth confinement layers can be made of InGaAsP, the first and second electrode layers can be made of metals, such as Au, the first and second waveguide layers can be made of P-type InP and InGaAs, the chirped grating layer can be made of InGaAsP, and the active layer can be made of InGaAsP. Of course, other material systems can also be used to fabricate each film layer, which is not limited here.

[0057] The active layer mentioned above may include at least one quantum well layer. To improve device efficiency, multiple quantum well layers are generally used. The quantum well layer may include a pair of quantum wells. Specifically, a pair of quantum wells may include a first barrier layer, an intermediate layer, and a second barrier layer stacked together.

[0058] To further reduce fabrication difficulty, growth structures with identical functions, located in different regions, are integrally connected, except for the first and second electrode layers, the first waveguide layer, and the second waveguide layer. The first and third confinement layers will be used as an example for illustration. (Refer to...) Figure 1 As shown, the first confinement layer 4 in the reflector region A1, the third confinement layer 9b in the gain region A2, and the third confinement layer 9a in the saturated absorption region A3 are integrally connected, which can be formed in a single fabrication process, thereby further simplifying the manufacturing process.

[0059] The first electrode layer and the second electrode layer belonging to different regions are independently arranged to avoid mutual interference and achieve electrical isolation between the saturated absorption region, the gain region, and the reflector region. The first and second electrode layers can be fabricated using the same material through a selective wet etching process; for example, they can be made of metal. The patterns of the first electrode layer and the second electrode layers in each region can be the same or different; different patterns can be used for easy differentiation.

[0060] To facilitate the formation of a transverse laser light field for directional laser output, optionally, it can be combined with... Figure 1 and Figure 4 As shown, in the reflector region A1, the first waveguide layer 6 includes components along a predetermined direction ( Figure 4 The three first waveguide sections 60, arranged in parallel at intervals in the OO2 direction shown, have a preset direction ( Figure 4 The OO2 direction shown is different from the emission direction of the semiconductor mode-locked laser. Figure 4 The direction shown (OO1) is perpendicular; a first groove is provided between adjacent first waveguide portions 60 to expose at least the second confinement layer; the chirped grating layer and the first waveguide portion located in the middle position at least partially overlap in a direction perpendicular to the substrate.

[0061] In the gain region A2 and the saturation absorption region A3, the second waveguide layer 11 includes a waveguide layer along a predetermined direction ( Figure 4 Three second waveguide sections 110 are arranged in parallel at intervals in the OO2 direction shown; a second groove is provided between adjacent second waveguide sections 110 to expose the fourth confinement layer.

[0062] Figure 4 The first and second waveguide layers shown adopt a double-groove ridge waveguide structure. The thickness of the double-groove ridge waveguide is not limited. If the thickness is small, it can be called a shallow ridge waveguide structure. Of course, other waveguide structures can also be used according to design requirements.

[0063] The above three first waveguide sections, refer to Figure 4 As shown, the first waveguide section located in the middle position is along a preset direction ( Figure 4 The width W of the first waveguide section located on both sides along the preset direction (as shown in the OO2 direction) is smaller than that of the second waveguide section located on both sides along the preset direction (as shown in the OO2 direction). Figure 4 The widths W1 and W2 (in the OO2 direction shown) are designed to better prevent the occurrence of higher-order transverse modes, allowing the laser to operate in the fundamental transverse mode. The widths of the first waveguide sections located on both sides along the preset direction can be the same or different; this is not limited here. Figure 4 The illustration is given as an example where the width of the first waveguide sections located on both sides is the same along a preset direction. The arrangement of the three second waveguide sections is similar to that of the three first waveguide sections, and will not be described again here.

[0064] In the aforementioned reflector region, the chirped grating layer and the first waveguide portion located in the middle position at least partially overlap in a direction perpendicular to the substrate, meaning that: the chirped grating and the first waveguide portion located in the middle position overlap in a direction perpendicular to the substrate, and in this case, the orthographic projection of the first waveguide portion located in the middle position onto the substrate covers the orthographic projection of the chirped grating onto the substrate; or, the chirped grating and the first waveguide portion located in the middle position partially overlap in a direction perpendicular to the substrate, and in this case, the orthographic projection of the chirped grating onto the substrate partially overlaps with the orthographic projection of the first waveguide portion located in the middle position onto the substrate.

[0065] The operating current or voltage of the mirror region, gain region, and saturable absorption region are different. To facilitate individual power supply to different regions and avoid mutual interference, it is optional to combine... Figure 1 and Figure 4 As shown, the first waveguide portion 60 includes a first upper cover portion 61 and a first contact portion 62, with the first contact portion 62 disposed on the side of the first upper cover portion 61 away from the substrate 1; the second waveguide portion 110 includes a second upper cover portion 111 and a second contact portion 112, with the second contact portion 112 disposed on the side of the second upper cover portion 111 away from the substrate 1; wherein, the first upper cover portion 61 and the second upper cover portion 111 are integrally connected, and the first contact portion 62 and the second contact portion 112 are independent of each other.

[0066] When other layer structures use the InP material system, the materials of the first upper cover and the second upper cover may include P-type InP, and the materials of the first contact portion and the second contact portion may include P-type InGaAs.

[0067] In order to better supply power to the first contact portion located in the middle position, especially when the width of the first contact portion located in the middle position along the preset direction is small, optionally, in the first multilayer growth structure, the first electrode layer includes an electrically connected first electrode and a second electrode; the first electrode covers the first contact portion located in the middle position, and the second electrode covers a portion of either first contact portion located on both sides.

[0068] Similarly, in order to better supply power to the second contact portion located in the middle position, especially when the width of the second contact portion located in the middle position along the preset direction is small, optionally, in the second multilayer growth structure, the second electrode layer includes an electrically connected third electrode and a fourth electrode; the third electrode covers the second contact portion located in the middle position, and the fourth electrode covers a portion of either second contact portion located on the two sides.

[0069] The first, second, third, and fourth electrodes mentioned above can be made of the same material and fabricated using a selective wet etching process.

[0070] To ensure the electrical connection between the first and second electrodes, optionally, refer to... Figure 4 As shown, in the first multilayer growth structure, the first waveguide layer 6 may further include a first waveguide connection portion 63, which is connected to the adjacent first waveguide portion 60.

[0071] The first waveguide connection portion may further include a first upper cover connection portion and a first contact connection portion, with the first contact connection portion covering the first upper cover connection portion; the first electrode layer may further include a first connecting electrode, with the first connecting electrode covering the first contact connection portion and being connected to the first electrode and the second electrode respectively.

[0072] The first upper cover connecting part and the first upper cover part can be integrally formed, the first contact connecting part and the first contact part can be integrally formed, and the first connecting electrode, the first electrode and the second electrode can be integrally formed.

[0073] Similarly, to ensure the electrical connection between the third and fourth electrodes, optionally, refer to... Figure 4 As shown, in the second multilayer growth structure, the second waveguide layer 11 may further include a second waveguide connection portion 113, which is connected to the adjacent second waveguide portion 110.

[0074] The second waveguide connection portion may further include a second upper cover connection portion and a second contact connection portion, with the second contact connection portion covering the second upper cover connection portion; the second electrode layer may further include a second connecting electrode, with the second connecting electrode covering the second contact connection portion and connected to the third electrode and the fourth electrode respectively.

[0075] The second upper cover connecting part and the second upper cover part can be integrally formed, the second contact connecting part and the second contact part can be integrally formed, and the second connecting electrode, the third electrode and the fourth electrode can be integrally formed.

[0076] To further facilitate power supply to various areas, refer to Figure 1 As shown, the semiconductor mode-locked laser also includes a third electrode layer 13. The third electrode layer 13 is disposed in the mirror region A1, the gain region A2, and the saturable absorption region A3, and is located on the side of the substrate 1 away from the first buffer layer 9 and the second buffer layer 8. The third electrode layer can be disposed entirely on the side of the substrate away from the first and second buffer layers using standard semiconductor processes such as thinning, polishing, and evaporation; its material is not limited. The third electrode layer is generally used as a negative electrode layer, while the aforementioned first and second electrode layers are generally used as positive electrode layers.

[0077] It should be noted that when the materials of the first and second upper cover portions include P-type InP, the materials of the first and second contact portions include P-type InGaAs, the material of the substrate includes N-type InP, and the materials of the first and second buffer layers include N-type InP, the semiconductor mode-locked laser can apply an appropriate forward current (e.g., a current value of 500mA or more) to the second electrode layer of the gain region during operation. The gain region can then generate broadband gain light with a center wavelength around 1550nm, thereby enabling the semiconductor mode-locked laser to reach the lasing condition (i.e., optical gain greater than optical loss); it can also apply a forward current to the saturation absorption region. A reverse bias voltage (e.g., -2 to -1V) is applied to the second electrode layer. The material and structure of the saturation absorption region are the same as those of the gain region, thus absorbing light near 1550nm. Utilizing the saturation absorption characteristics of semiconductor materials, a fixed phase difference is achieved between the various modes in the laser, thereby realizing the active / passive mode-locking operation of the semiconductor mode-locked laser. When tuning is required, the first electrode layer of the mirror region can be energized; if tuning is not required, no energization is needed. Under the combined action of the three regions, this semiconductor mode-locked laser can operate near the 1550nm communication wavelength, with a pulse output of approximately 200–400 fs.

[0078] In one or more embodiments, to ensure the laser's emission power, optionally, the length of the saturable absorption region along the emission direction of the semiconductor mode-locked laser is smaller than the lengths of the mirror region and the gain region along the emission direction of the semiconductor mode-locked laser. For example, the lengths of the saturable absorption region, mirror region, and gain region along the emission direction of the semiconductor mode-locked laser are 50 μm, 310 μm, and 320 μm, respectively. In the mirror region, the length of the chirped grating along the emission direction of the semiconductor mode-locked laser is 300 μm, and the grating period linearly decreases from 243 nm to 239.8 nm along the emission direction. Correspondingly, the Bragg wavelength reflected by gratings with different grating periods linearly changes from 1560 nm to 1540 nm. In the chirped grating, gratings at different positions satisfy Bragg reflection conditions for different wavelengths. Therefore, by changing the center wavelength of the grating, the transmission distance of short-wavelength mode components can be increased, thereby achieving dispersion compensation for the semiconductor mode-locked laser pulse and ultimately realizing the output of femtosecond-level ultrashort optical pulses.

[0079] In one or more embodiments, the semiconductor mode-locked laser further includes an emitting end face and a reflecting end face, wherein the emitting end face is disposed in the saturated absorption region and the reflecting end face is disposed in the mirror region; the emitting end face and the reflecting end face are natural cleavage surfaces, which together form the cavity surface of the semiconductor mode-locked laser.

[0080] refer to Figure 1As shown, the semiconductor mode-locked laser also includes: an anti-reflection coating (HR) 15 disposed on the side of the reflective end face away from the emitting end face; and / or, an anti-reflection coating (AR) 14 disposed on the side of the emitting end face away from the reflective end face.

[0081] The aforementioned semiconductor mode-locked laser further includes: an anti-reflection coating disposed on the side of the reflecting end face away from the emitting end face; and / or, an anti-reflection coating disposed on the side of the emitting end face away from the reflecting end face, comprising three structures:

[0082] The first type of semiconductor mode-locked laser also includes an anti-reflection coating disposed on the side of the reflective end face away from the output end face. This anti-reflection coating can be made of a high-reflectivity material to change the optical path of the laser beam directed toward the reflective end face, thereby increasing the power output value.

[0083] The second type of semiconductor mode-locked laser also includes an anti-reflection coating disposed on the side of the emission end face away from the reflection end face. This anti-reflection coating can improve the light transmittance, thereby increasing the power output value.

[0084] The third type of semiconductor mode-locked laser also includes: an anti-reflection coating disposed on the side of the reflecting end face away from the emitting end face, and an anti-reflection coating disposed on the side of the emitting end face away from the reflecting end face. The anti-reflection coating can be made of a high-reflectivity material to change the optical path of the laser beam directed toward the reflecting end face; at the same time, the anti-reflection coating can improve the light transmittance. By setting the anti-reflection coating and the anti-reflection coating, the power output value can be further improved.

[0085] Embodiments of the present invention also provide a method for fabricating a semiconductor mode-locked laser, comprising:

[0086] S01, forming a mirror region, a gain region, and a saturation absorption region; wherein, the gain region is located between the mirror region and the saturation absorption region, and is connected to both the mirror region and the saturation absorption region respectively.

[0087] It should be noted that the relevant descriptions of the mirror region, gain region, and saturable absorption region can be found in the aforementioned embodiments of the semiconductor mode-locked laser, and will not be repeated here.

[0088] refer to Figure 5 As shown, S01, the region forming the mirror region, the gain region, and the saturable absorption region includes:

[0089] S10, Provides a substrate.

[0090] S11. An active layer is formed on the substrate; wherein the active layer is disposed in the gain region and the saturation absorption region.

[0091] S12. A chirped grating layer is formed using a docking growth process; wherein the chirped grating layer is disposed in the mirror region and includes multiple gratings with grating periods linearly decreasing along the emission direction of the semiconductor mode-locked laser, and the distance between the chirped grating layer and the substrate is greater than the distance between the active layer and the substrate.

[0092] By executing steps S10-S12, a monolithically integrated semiconductor mode-locked laser can be formed. The fabrication method is simple and easy to implement. The semiconductor mode-locked laser formed by the above method has a chirped grating layer in the mirror region. This allows for dispersion compensation of each frequency component contained in the optical pulse at different positions of the grating, thereby eliminating the constraints on pulse width caused by pulse self-phase modulation and dispersion effects, thus shortening the pulse width and achieving femtosecond pulse output. This semiconductor mode-locked laser can achieve femtosecond pulse output without the need for external pulse compression technology, significantly reducing production costs.

[0093] The terms "an embodiment," "embodiment," or "one or more embodiments" as used herein mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the invention. Furthermore, please note that the examples of the phrase "in one embodiment" do not necessarily all refer to the same embodiment.

[0094] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A semiconductor mode-locked laser, characterized in that, include: The system comprises a mirror region, a gain region, and a saturable absorption region; the gain region is disposed between the mirror region and the saturable absorption region, and is connected to both the mirror region and the saturable absorption region. The semiconductor mode-locked laser further includes a substrate, and a chirped grating layer and an active layer disposed on the same side of the substrate; wherein, the chirped grating layer is disposed in the mirror region and includes a plurality of gratings with grating periods linearly decreasing along the emission direction of the semiconductor mode-locked laser, the active layer is disposed in the gain region and the saturable absorption region, and the distance between the chirped grating layer and the substrate is greater than the distance between the active layer and the substrate; The mirror region includes a first multilayer growth structure, and the gain region and the saturation absorption region each include a second multilayer growth structure. The first multilayer growth structure and the second multilayer growth structure are integrated on the same side of the substrate; The first multilayer growth structure includes: a first buffer layer, a first confinement layer, a second confinement layer, a first waveguide layer, and a first electrode layer sequentially stacked on the substrate; wherein the chirped grating layer is disposed on the side of the second confinement layer near the first waveguide layer; The second multilayer growth structure includes: a second buffer layer, a third confinement layer, a fourth confinement layer, a second waveguide layer, and a second electrode layer sequentially stacked on the substrate; wherein the active layer is disposed on the side of the third confinement layer near the fourth confinement layer; In the reflector region, the first waveguide layer includes three first waveguide portions arranged parallel to each other along a preset direction, the preset direction being perpendicular to the emission direction of the semiconductor mode-locked laser; a first groove is provided between adjacent first waveguide portions to expose at least the second confinement layer; the orthographic projection of the chirped grating on the substrate overlaps with the orthographic projection of the first waveguide portion located in the middle on the substrate; In the gain region and the saturation absorption region, the second waveguide layer includes three second waveguide portions arranged parallel to each other along the preset direction; a second groove is provided between adjacent second waveguide portions to expose the fourth confinement layer; The first waveguide portion includes a first upper cover portion and a first contact portion, wherein the first contact portion is disposed on the side of the first upper cover portion away from the substrate; The second waveguide portion includes a second upper cover portion and a second contact portion, wherein the second contact portion is disposed on the side of the second upper cover portion away from the substrate; The first upper cover and the second upper cover are integrally connected, and the first contact portion and the second contact portion are independent of each other.

2. The semiconductor mode-locked laser according to claim 1, characterized in that, Except for the first electrode layer and the second electrode layer, the first waveguide layer and the second waveguide layer, the growth structure of the other layers is integrally connected.

3. The semiconductor mode-locked laser according to claim 1, characterized in that, The semiconductor mode-locked laser further includes a third electrode layer; the third electrode layer is disposed in the mirror region, the gain region and the saturable absorption region, and is located on the side of the substrate away from the first buffer layer and the second buffer layer.

4. The semiconductor mode-locked laser according to claim 1, characterized in that, The length of the saturated absorption region along the emission direction of the semiconductor mode-locked laser is less than the lengths of the mirror region and the gain region along the emission direction of the semiconductor mode-locked laser, respectively.

5. The semiconductor mode-locked laser according to claim 1, characterized in that, The semiconductor mode-locked laser also includes an output end face and a reflection end face, the output end face being disposed in the saturated absorption region, and the reflection end face being disposed in the mirror region; The semiconductor mode-locked laser further includes: an anti-reflection coating disposed on the side of the reflective end face away from the emission end face; And / or, an antireflective film disposed on the side of the emission end face away from the reflective end face.

6. A method for fabricating a semiconductor mode-locked laser as described in any one of claims 1-5, characterized in that, include: A mirror region, a gain region, and a saturation absorption region are formed; wherein, the gain region is disposed between the mirror region and the saturation absorption region, and is connected to both the mirror region and the saturation absorption region respectively; The formation of the mirror region, gain region, and saturable absorption region includes: Provide substrate; An active layer is formed on the substrate; wherein the active layer is disposed in the gain region and the saturation absorption region; A chirped grating layer is formed using a docking growth process; wherein the chirped grating layer is disposed in the mirror region and includes a plurality of gratings with grating periods linearly decreasing along the emission direction of the semiconductor mode-locked laser, and the distance between the chirped grating layer and the substrate is greater than the distance between the active layer and the substrate.

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