Semiconductor laser

Abstract

The invention provides a semiconductor laser. The semiconductor laser comprises an N-type electrode; a substrate, an N-type coating layer, an active region, a P-type coating layer, an ohmic contact layer and a P-type electrode are sequentially stacked on the N-type electrode; and the P-type coating layer, the ohmic contact layer and the P-type electrode form a ridge waveguide of the laser. The laser adopts a four-order collision mode-locking design, so that stable mode-locking occurrence rate, higher repetition frequency and narrower optical pulse width are realized. In addition, a quantum dot structure is adopted as a gain region, the gain spectrum is effectively broadened, the pulse width of the laser is further reduced, and the performance of the mode-locked laser is improved.

Description

Technical Field

[0001] The invention relates to the field of optoelectronic technology, and in particular to a semiconductor laser. Background Art

[0002] Semiconductor lasers are widely used in daily life due to their small size, high efficiency, low power consumption and long life. However, traditional continuous wave lasers can hardly meet the application requirements of high energy and short pulse lasers. Therefore, semiconductor short pulse lasers with high repetition rate and short pulse width came into being and became the research focus in the fields of high-speed optical communication systems, ultrafast data processing and optical computing.

[0003] Common semiconductor pulse laser generation methods include gain switching, Q modulation and mode locking technology. Among these technologies, mode locking technology can perform special modulation on the laser beam so that different longitudinal modes in the beam have a certain phase relationship, so that each mode can be coherently superimposed to obtain ultra-short pulses and high peak power. In the laser spectrum, this phenomenon is manifested as an optical frequency comb structure with a fixed wavelength interval. However, the currently used mode locking method has problems such as unstable pulse formation, long pulse width and large pulse noise. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the above shortcomings, the main purpose of the present invention is to provide a semiconductor laser, which achieves a stable mode-locking rate, a higher repetition frequency and a narrower optical pulse width by adopting a fourth-order collision mode-locking design. In addition, a quantum dot structure is used as a gain region to effectively broaden the gain spectrum, further reduce the pulse width of the laser, and improve the performance of the mode-locked laser.

[0006] (II) Technical solution

[0007] In order to achieve the above-mentioned object, the present invention provides a semiconductor laser, comprising: an N-type electrode; a substrate, an N-type cladding layer, an active region, a P-type cladding layer, an ohmic contact layer and a P-type electrode are sequentially stacked on the N-type electrode; the P-type cladding layer, the ohmic contact layer and the P-type electrode form a ridge waveguide of the laser.

[0008] In the above scheme, reflectors are arranged on the two end faces of the laser along the first direction to form a laser resonant cavity. The laser resonant cavity includes a saturated absorption region and a gain region along the propagation direction of the light field, wherein the light field is located in the active region.

[0009] In the above scheme, the saturated absorption region includes a first absorption sub-region, a second absorption sub-region and a third absorption sub-region, wherein the first absorption sub-region is located at 1 / 4 of the laser resonant cavity along the first direction, the second absorption sub-region is located at 1 / 2 of the laser resonant cavity along the first direction, and the third absorption sub-region is located at 3 / 4 of the laser resonant cavity along the first direction, and the first direction is parallel to the propagation direction of the light field.

[0010] In the above scheme, the distances between every two adjacent absorption sub-regions in the saturated absorption region are the same, and the first absorption sub-region, the second absorption sub-region and the third absorption sub-region divide the gain region of the laser resonant cavity into four gain sub-regions along the first direction.

[0011] In the above solution, each gain sub-region and each absorption sub-region are electrically connected via a P-type electrode.

[0012] In the above scheme, an isolation region is provided between the saturated absorption region and the gain region, and the isolation region includes an etched high-doping layer and H ions.

[0013] In the above scheme, the total length of the laser cavity along the first direction ranges from 500μm to 2000μm, the length of the saturated absorption region along the first direction accounts for 5% to 15% of the total length of the resonator, and the length of the isolation region ranges from 5μm to 20μm.

[0014] In the above scheme, the active region includes multiple quantum dot active layers and spacer layers, wherein the height of each quantum dot active layer ranges from 2nm to 5nm, and the height of each spacer layer ranges from 6nm to 10nm.

[0015] In the above scheme, the multi-layer quantum dots in the active region can serve as the medium of the saturated absorption region and the gain region.

[0016] In the above solution, the length of the ridge waveguide along the second direction ranges from 1.5 μm to 2 μm, wherein the first direction is perpendicular to the second direction.

[0017] (III) Beneficial effects

[0018] The technical solution of the embodiment of the present invention has at least the following beneficial effects:

[0019] It adopts the fourth-order collision mode-locking mechanism, which is divided into three saturated absorption sub-regions and four gain sub-regions. Shorter pulses can be generated through multi-order interactions, and multiple saturated absorbers provide better pulse energy and time interval stability.

[0020] More effectively reduce pulse-to-pulse noise and instability, achieving high repetition rate, ultra-short pulse width and high peak power.

[0021] Using quantum dot structure as the gain region to improve the performance of mode-locked lasers. The introduction of quantum dot structure provides an ultra-wide gain spectrum, further shortening the pulse width of the laser, thereby expanding the performance boundary of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram shows a front view of the structure of a semiconductor laser according to an embodiment of the present invention;

[0023] Figure 2 A schematic top view of the structure of a semiconductor laser according to an embodiment of the present invention is shown;

[0024] Figure 3 A time-domain pulse waveform diagram of an output optical signal of a semiconductor laser according to an embodiment of the present invention is schematically shown;

[0025] Figure 4 A schematic diagram of a current-light output curve of a semiconductor laser according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0027] Figure 1 The figure schematically shows a front view of the structure of a semiconductor laser according to an embodiment of the present invention. Figure 2 The figure schematically shows a top view of the structure of a semiconductor laser according to an embodiment of the present invention.

[0028] Please refer to Figure 1 The semiconductor laser includes an N-type electrode 1, a substrate 2, an N-type cladding layer 3, an active region 4, a P-type cladding layer 5, an ohmic contact layer 6 and a P-type electrode 7 which are sequentially stacked on the N-type electrode 1.

[0029] Exemplarily, the substrate 2 may be an N-InP substrate, the N-type cladding layer 3 may be an N-InP cladding layer, the active region 4 may be an InAs / InGaAsP quantum dot active layer, the P-type cladding layer 5 may be a P-InP cladding layer, and the ohmic contact layer 6 may be a P-InGaAs ohmic contact layer.

[0030] like Figure 1 As shown, the P-type cladding layer 5, the ohmic contact layer 6 and the P-type electrode 7 form a ridge waveguide of the laser.

[0031] Specifically, the laser is a ridge waveguide structure, and the P-type cladding layer 5 and the ohmic contact layer 6 outside the ridge area are etched away by a wet etching process or a dry etching process, and then an insulating layer and a P-type electrode 7 are arranged above the ridge area on the upper surface of the laser to form a ridge waveguide of the laser. The length of the ridge waveguide along the second direction X2 ranges from 1.5μm to 2μm, wherein the first direction X1 is perpendicular to the second direction X2.

[0032] In an embodiment of the present invention, reflective mirrors are respectively arranged on two end surfaces of the laser along the first direction X1 to form a laser resonant cavity.

[0033] like Figure 1 and Figure 2 As shown, the laser resonant cavity includes a saturated absorption region and a gain region along the propagation direction of the light field, wherein the light field is located in the active region 4. An isolation region 9 is provided between the saturated absorption region and the gain region, and the isolation region 9 is an electrical isolation region 9.

[0034] In an embodiment of the present invention, the total length of the laser cavity along the first direction X1 ranges from 500 μm to 2000 μm, the length of the saturated absorption region along the first direction X1 accounts for 5% to 15% of the total length of the resonator, and the length of the isolation region 9 ranges from 5 μm to 20 μm.

[0035] Preferably, for example, the total length of the resonant cavity may be 1500 μm, the saturated absorption region accounts for 10% of the total length of the resonator, and the length of the isolation region 9 is 15 μm.

[0036] Specifically, the saturated absorption region includes a first absorption sub-region 11, a second absorption sub-region 12 and a third absorption sub-region 13, wherein the first absorption sub-region 11 is located at 1 / 4 of the laser resonant cavity along the first direction X1, the second absorption sub-region 12 is located at 1 / 2 of the laser resonant cavity along the first direction X1, and the third absorption sub-region 13 is located at 3 / 4 of the laser resonant cavity along the first direction X1, and the first direction X1 is parallel to the light field propagation direction.

[0037] In an embodiment of the present invention, the active region 4 includes a multi-layer quantum dot active layer and a spacer layer, wherein the height of each quantum dot active layer ranges from 2nm to 5nm, and the height of each spacer layer ranges from 6nm to 10nm. The multi-layer quantum dots in the active region 4 can serve as media for the saturated absorption region and the gain region.

[0038] Specifically, for example, when the active region 4 is composed of seven layers of InAs / InGaAsP / InP quantum dots, the PL photoluminescence wavelength of the laser is between 1500-1600nm, and the quantum dot material serves as both a gain region material to provide an ultra-wide gain bandwidth and a saturable absorption material, thereby achieving mode-locked pulse output.

[0039] In an embodiment of the present invention, the isolation region 9 includes etching of a high-doped layer and H ions.

[0040] Preferably, the isolation region 9 is manufactured in two steps. The first step is to corrode the highly doped InGaAs and InGaAsP above the isolation region 9. The second step is to use ion implantation equipment to implant H ions into the isolation region 9. After the implantation, the ions will form complexes or covalent bonds with the ions or atoms in the material, thereby inactivating the holes or electrons that were originally free in the material, thereby turning the material into a high-resistance state, so that the gain region and the absorption region have a resistance of several thousand to several megohms.

[0041] Furthermore, the isolation region 9 is electrically isolated by 6 H ion implantations, with ion energies of 35 keV, 55 keV, 80 keV, 120 keV, 160 keV, and 200 keV, respectively, and implantation doses of 1*1014 ions / cm 2 、2*1013 ions / cm 2 、8*1013 ions / cm 2 、8*1013 ions / cm 2 、5*1013 ions / cm 2 、8*1013 ions / cm 2 , the injection angle is 7°.

[0042] Please continue reading Figure 1 and Figure 2 , the distances between every two adjacent absorption sub-regions in the saturated absorption region are the same, and the first absorption sub-region 11, the second absorption sub-region 12 and the third absorption sub-region 13 divide the gain region of the laser resonant cavity into four gain sub-regions 14 along the first direction X1. Each gain sub-region 14 is electrically connected through the P-type electrode 7, and each absorption sub-region is also electrically connected through the P-type electrode 7.

[0043] Specifically, the P-type electrode 7 is divided into two parts separated from each other, which respectively provide forward current and reverse bias voltage during operation. By adjusting and selecting appropriate current and voltage, the laser can achieve high output power and stable mode locking.

[0044] For example, Figure 2As shown, the P-type electrode 7 is divided into two parts separated from each other, the gain region electrode 8 and the absorption region electrode 10. Each gain sub-region 14 in the gain region provides current through the same gain region electrode 8 to provide gain for the laser. The saturated absorption region provides reverse bias through the same absorption region electrode 10. Within a certain voltage range, the transmittance of the saturated absorption region is related to the light intensity. When the light signal passes through the saturated absorption region, the weak signal suffers a large loss, while the loss of the strong peak signal is very small. As a result, the strong light pulse forms a stable oscillation, while the weak light signal attenuates and disappears.

[0045] In an embodiment of the present invention, the distance between two adjacent absorption sub-regions is strictly equal, and the pulses propagating in opposite directions will couple and coherently superpose in the saturated absorption region to produce a transient standing wave, thereby forming a spatial grating in the saturated absorption region to make the saturated absorption more effective, achieve a more stable mode locking process, and produce narrower ultrashort light pulses.

[0046] Through the embodiments of the present invention, a fourth-order collision mode locking mechanism is adopted, which is divided into three saturated absorption zones and four gain zones, and multiple saturated absorbers are used to enhance the formation and stability of pulses. Specifically: through multi-order interactions, shorter pulses can be generated; multiple saturated absorbers provide better pulse energy and time interval stability, more effectively reduce noise and instability between pulses, and achieve high repetition frequency, ultra-short pulse width and high peak power. The introduction of the quantum dot structure provides an ultra-wide gain spectrum, further reducing the pulse width of the laser, thereby expanding the performance boundary of the laser.

[0047] Specifically, the semiconductor laser may be a high repetition rate, short pulse quantum dot mode-locked laser used in the C-band frequency range, which is described in detail below.

[0048] In the embodiment of the present invention, the laser can be divided into three absorption sub-regions and four gain sub-regions 14 along the propagation direction of the optical field. The absorption sub-regions are respectively located at 1 / 4, 1 / 2 and 3 / 4 of the laser resonant cavity, and the distances between the absorption sub-regions are strictly equal, dividing the entire resonant cavity into four gain sub-regions 14 on average.

[0049] Specifically, in a multi-order collision-locked laser, each saturated absorber can produce a nonlinear interaction when interacting with the saturated absorber, making the pulse sharper and affecting the formation and stability of the pulse. The pulses arrive at the saturated absorber precisely and synchronously, coherently superimpose, form a periodic light intensity distribution, and produce spatial modulation of the light intensity, making the saturated absorption more effective, thereby making the locking process more stable, and the pulse width generated is narrower, and correspondingly has a very high peak power. Figure 3 The time domain pulse waveform of the output optical signal of the semiconductor laser according to the embodiment of the present invention is schematically shown. Figure 3As shown, the time domain pulse waveform diagram of the output optical signal of the fourth-order quantum dot mode-locked laser of the present invention is obtained.

[0050] In the embodiment of the present invention, an isolation region 9 is provided between the saturated absorption region and the gain region to isolate the electrical injection of the absorption region and the gain region from each other; the isolation region 9 is formed by etching the highly doped InGaAs and InGaAsP layers above the isolation region 9 and performing H ion implantation. There is a resistance value of several thousand to several megohms between the gain region and the absorption region.

[0051] Specifically, a voltage is applied to the absorption region, and the absorption rate and saturation intensity of the absorber are adjusted by changing the electric field, thereby obtaining Figure 4 As shown, Figure 4 A schematic diagram of a current-light output curve of a semiconductor laser according to an embodiment of the present invention is shown.

[0052] Based on the structural description of the semiconductor laser described above, an embodiment of the present invention further provides a method for manufacturing the semiconductor laser, which is described in detail as follows.

[0053] MBE or MOCVD is used to grow epitaxial layers, and an N-type InP buffer layer is grown from bottom to top on an InP substrate; an InGaAsP lower separation confinement layer; a seven-layer InAs / InGaAsP quantum dot active layer; an InGaAsP upper separation confinement layer; a P-type InP layer, whose refractive index is gradient distributed and belongs to a separately confined heterostructure; and finally a heavily doped P-InGaAs ohmic contact layer is grown.

[0054] Through the above preparation method, the quantum dot active region provides higher electron and hole confinement, reducing the laser's turn-on current. Due to the discrete energy levels, quantum dots have better tolerance to temperature changes, and the three-dimensional confinement structure of quantum dots provides higher gain efficiency.

[0055] Through the embodiment of the present invention, a fourth-order collision mode-locking structure is adopted, and the repetition frequency of the pulse generated by the laser resonant cavity is 4 times that of the two-stage passive mode-locking laser with the same cavity length. By designing the resonator length, the length of the isolation zone 9, and the position of the isolation zone 9, in the multi-order collision mode-locking laser, each saturated absorber can produce a nonlinear interaction when interacting with the saturated absorber, and the pulse becomes sharper, affecting the formation and stability of the pulse. The pulses arrive at the saturated absorber precisely and synchronously, and coherently superimpose to form a periodic light intensity distribution, and generate spatial modulation of the light intensity. The pulses transmitted in the laser resonant cavity will collide in the absorption zone, forming a spatial grating to make the saturated absorption more effective, thereby making the mode-locking process more stable, and the pulse width generated is narrower, and correspondingly has a very high peak power. In addition, the laser gain region of the present invention adopts the design of quantum dots, which has a wider lasing spectrum compared with the quantum well laser, and thus has a narrower light pulse width.

[0056] It will be appreciated by those skilled in the art that, although the present invention has been shown and described with reference to specific exemplary embodiments of the present invention, it will be appreciated by those skilled in the art that, without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents, various changes in form and detail may be made to the present invention. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be determined not only by the appended claims, but also by the equivalents of the appended claims.

[0057] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A semiconductor laser, It is characterized in that include: N-type electrode (1); A substrate (2), an N-type cladding layer (3), an active region (4), a P-type cladding layer (5), an ohmic contact layer (6) and a P-type electrode (7) are sequentially stacked on the N-type electrode (1); The P-type cladding layer (5), the ohmic contact layer (6) and the P-type electrode (7) form a ridge waveguide of the laser.

2. The semiconductor laser according to claim 1, It is characterized in that Reflecting mirrors are arranged on two end faces of the laser along a first direction to form a laser resonant cavity, wherein the laser resonant cavity comprises a saturated absorption region and a gain region along the propagation direction of the light field, wherein the light field is located in the active region (4).

3. The semiconductor laser according to claim 1 or 2, It is characterized in that The saturated absorption region comprises a first absorption sub-region (11), a second absorption sub-region (12) and a third absorption sub-region (13), wherein: The first absorption sub-region (11) is located at a 1 / 4 position of the laser resonant cavity along a first direction, the second absorption sub-region (12) is located at a 1 / 2 position of the laser resonant cavity along the first direction, and the third absorption sub-region (13) is located at a 3 / 4 position of the laser resonant cavity along the first direction, and the first direction is parallel to the propagation direction of the light field.

4. The semiconductor laser according to claim 3, It is characterized in that The distances between every two adjacent absorption sub-regions in the saturated absorption region are the same, and the first absorption sub-region (11), the second absorption sub-region (12) and the third absorption sub-region (13) divide the gain region of the laser resonant cavity into four gain sub-regions (14) along a first direction.

5. The semiconductor laser according to claim 4, It is characterized in that Each gain sub-region (14) and each absorption sub-region are electrically connected via a P-type electrode (7).

6. The semiconductor laser according to claim 2, It is characterized in that An isolation region (9) is provided between the saturated absorption region and the gain region, and the isolation region (9) comprises a corroded high-doping layer and H ions.

7. The semiconductor laser according to claim 6, It is characterized in that The total length of the laser resonant cavity along the first direction ranges from 500 μm to 2000 μm, the length of the saturated absorption region along the first direction accounts for 5% to 15% of the total length of the resonator, and the length of the isolation region (9) ranges from 5 μm to 20 μm.

8. The semiconductor laser according to claim 1, It is characterized in that The active region (4) comprises multiple layers of quantum dot active layers and spacer layers, wherein the height of each quantum dot active layer ranges from 2 nm to 5 nm, and the height of each spacer layer ranges from 6 nm to 10 nm.

9. The semiconductor laser according to claim 8, It is characterized in that The multilayer quantum dots in the active region (4) can both serve as media for the saturation absorption region and the gain region.

10. The semiconductor laser according to claim 1 or 2, It is characterized in that A length of the ridge waveguide along the second direction ranges from 1.5 μm to 2 μm, wherein the first direction is perpendicular to the second direction.

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